Chapman (2008) - Membranes For The Dehydration of Solvents by Pervaporation

Journal of Membrane Science 318 (2008) 5–37
Contents lists available at ScienceDirect
Journal of Membrane Science

journal homepage: www.elsevier.com/locate/memsci
Review
Membranes for the dehydration of solvents by pervaporation

Peter D. Chapman a , Teresa Oliveira b , Andrew G. Livingston a , K. Li a,∗
a
Department of Chemical Engineering, Imperial College London, University of London, South Kensington, London SW7 2AZ, UK
b
GlaxoSmithKline, Stevenage, Hertfordshire SG1 2NY, UK
a r t i c l e i n f o a b s t r a c t
Article history: This review aims at summarizing the main research carried out up to 2007 in hydrophilic pervaporation.
Received 10 November 2007 Both polymeric and inorganic membranes are examined and the dehydration of alcohols such as ethanol
Received in revised form 17 February 2008 and isopropyl alcohol covered in depth. When considering polymeric membranes, the research has been
Accepted 25 February 2008
categorised into sections based upon the main polymer type used to achieve the separation. In the case
Available online 7 March 2008
of polymer blends, judgement has been used to group this accordingly. Inorganic membranes have been
classified into two categories: inorganic, covering a broad range of inorganic materials and zeolitic, cov-
Keywords:
ering any inorganic membranes containing zeolitic material. The amalgamation of organic and inorganic
Pervaporation
Dehydration
material in the production of hybrid membranes is also reported.
Solvent Research performed in developing pervaporation membranes for the dehydration of other commonly
Polymeric used organics; acetic acid, tetrahydrofuran and acetone is then detailed and a summary of the current
Inorganic state of hydrophilic pervaporation is finally made.
© 2008 Elsevier B.V. All rights reserved.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1. Pervaporation processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1.1. Operational characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2. Today’s pervaporation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2. Dehydration of alcohols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Alcohol dehydration using polymeric membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.1. Poly(vinyl alcohol) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.2. Chitosan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.1.3. Alginate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.1.4. Polysulfone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.5. Polyimides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.1.6. Polyamides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1.7. Polyelectrolyte membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.1.8. Polyaniline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.1.9. Other polymeric membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2. Alcohol dehydration using inorganic membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.1. Ceramics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.2. Zeolites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.3. Alcohol dehydration using mixed matrix membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3. Dehydration of acetic acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.1. Acetic acid dehydration using polymeric membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.2. Acetic acid dehydration using inorganic membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4. Dehydration of tetrahydrofuran . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.1. THF dehydration using polymeric membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2. THF dehydration using inorganic membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
∗ Corresponding author. Tel.: +44 207 5945676; fax: +44 207 5945629.
E-mail address: Kang.Li@imperial.ac.uk (K. Li).
0376-7388/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.memsci.2008.02.061
6 P.D. Chapman et al. / Journal of Membrane Science 318 (2008) 5–37
5. Dehydration of acetone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.1. Acetone dehydration using polymeric membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.2. Acetone dehydration using inorganic membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
6. Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction
Industry today has to constantly review its production methods

in order to remain competitive in the marketplace. This contin-
uous improvement has led companies to invest in research into
new technology to improve its production performance and reduce
costs. Membrane separation processes have been seen to offer
many advantages over existing separation processes such as “higher
selectivity, lower energy consumption, moderate cost to perfor- Fig. 1. Pervaporation membrane cell operation.
mance ratio and compact and modular design” [1]. The Membrane
Handbook [2] offers a good overview of the most commonly used They also reported on the fundamentals of pervaporation trans-
membrane processes in industry today. port in detail discussing modifications made to solution diffusion
Pervaporation is one such type of membrane separation process theory and discussion the importance of solvent coupling in dif-
with a wide range of uses such as solvent dehydration and separa- fusive transport and how this coupling can be accounted for. This
tion of organic mixtures. It has significant advantages in azeotropic review aims to complement the work of Shao and Huang taking a
systems where traditional distillation is only able to recover pure detailed look at hydrophilic pervaporation, identifying some of the
solvents with the use of entrainers, which then must be removed key work performed with the various polymers and ceramics that
using an additional separation step. Pervaporation can be used to have been used in developing pervaporation membranes for the
break this azeotrope, as its mechanism of separation is very dif- dehydration of alcohols and other key organics. Table 1 contains
ferent to that of distillation. The Basic Principles of Membrane some key data on the solvents covered in this review together with
Technology [3] contains information on different membrane mate- any binary azeotrope formed with water.
rials, fabrication techniques, module design and transport models
for pervaporation and other membrane processes. In theory perva- 1.1. Pervaporation processes
poration can be used to separate any liquid mixtures but in practice,
pervaporation tends to be used to separate azeotropic mixtures, 1.1.1. Operational characteristics
close boiling-point mixtures, for the recovery of small quantities of In pervaporation a liquid feed is passed over the membrane sur-
impurities and for the enhancement of equilibrium reactions. face and one component is able to pass through the membrane
Pervaporation is seldom used by itself as a single process as preferentially. The feed to the membrane is usually at a temperature
it has to compete with reliable and better-understood processes close to that of its saturation temperature and this combined with
such as distillation, liquid–liquid extraction, adsorption and strip- the underside of the membrane being held under vacuum causes
ping with existing infra-structure for such technologies available on the liquid passing across the membrane to vaporise. The vapour
many existing sites. However hybrid processes, combining perva- produced has a very different composition to that produced by
poration with one of these traditional separation techniques or with simple distillation. The fraction of the feed that diffuses across the
a chemical reactor are becoming increasingly common in industry membrane is defined as the permeate, and the fraction that fails to
where traditional techniques are insufficient and adding pervapo- pass through, the retentate. The permeate is then condensed which
ration allows performance targets to be met, superior performance maintains the vapour concentration at the underside of the mem-
and/or process optimisation. brane low whilst the retentate is often recycled around to the feed
A comprehensive review of polymeric membranes for pervapo- tank to allow further separation to occur. It is often run as a batch
ration was recently made and published by Shao and Huang [4]. operation with the run terminated once the required composition
They investigated the potential pervaporation had for separating in the retentate has been achieved. This is illustrated in Fig. 1.
liquid mixtures in the areas of alcohol and solvent dehydration, When selecting a membrane for a specific mixture there are
organic(s) removal from water and organic/organic separations. two main parameters that need to be considered: first the mass
Table 1
Chemical properties and azeotropes with water of the solvents detailed in this review
Chemical name Formula Molecular weight (g mol−1 ) Density (g cm−3 ) Boiling point (◦ C) Vapour pressure @ 20 ◦ C (hPa) Azeotrope with water (wt% water)
Ethanol C2 H5 OH 46.1 0.79 78 59.5 4

Isopropanol C3 H7 OH 60.1 0.78 82 43.2 12.6
n-Propanol C3 H7 OH 60.1 0.80 97 19.9 28.3
2-Butanol C4 H9 OH 74.1 0.81 98 16.7 26.8
n-Butanol C4 H9 OH 74.1 0.81 118 5.3 42.5
t-Butanol C4 H9 OH 74.1 0.78 82 41 11.76
Acetic acid C2 H4 O2 60.1 1.05 117 15.2 Non-azeotrope
Tetrahydrofuran C4 H8 O 72.1 0.89 66 190.7 5.3
Acetone C3 H6 O 58.1 0.79 56 245.3 Non-azeotrope
Chemical properties obtained from Sigma–Aldrich online MSDS sheets. Azeotropic data based on Azeotropic Data-III, in the Advances in Chemistry Series, American Chemical
Society.
P.D. Chapman et al. / Journal of Membrane Science 318 (2008) 5–37 7
flux across the membrane, J (kg m−2 h−1 ), Secondly the membrane costs of running a traditional style separation process are extremely
separation factor which is a measure of the quality of separation high.
that the membrane provides [5]: There are a large number of different types of membranes avail-
able today which can be used in a wide range of applications
yA /yB
˛= (1) depending on the individual characteristics of the membrane. In
xA /xB
the case of solvent dehydration where there is a low concentra-
The higher the value of ˛, the greater degree of separation tion of water that needs to be separated from a solvent, hydrophilic
offered by the membrane. As ˛ → ∞, the membrane tends towards membranes are often used as they preferentially allow water to
being superselective. permeate through, producing a permeate with a high-water con-
When looking at membranes to enhance performance, there tent and dehydrating the solvent in the retentate. Hydrophilic
is often a trade-off between separation factor and flux, perform- membranes are designed to incorporate attractive interactions
ing a modification that increases one leads to a decrease in the between water and the membrane material such as dipole-dipole
other. As an attempt to define the separation ability of a membrane, interactions, hydrogen bonding and ion-dipole interactions [6].
some researchers use an index called the pervaporation separation Conversely, when a small amount of solvent is required to be
index (PSI, kg m−2 h−1 ), defined as J × ˛. This factor can be useful in removed from a stream comprising mostly of water, hydrophobic
comparing similar membranes, however it fails to distinguish the membranes can be used that will leave water in the retentate whilst
overall performance of the membrane since a membrane with a allowing the solvents to pass across.
low-separation factor and high flux can have the same PSI as one
with a high-separation factor and a low flux. The particular sepa- 2. Dehydration of alcohols
ration requirements for an individual process need to be assessed
and an appropriate membrane selected, just selecting the mem- Ethanol and water form an azeotrope at approximately 4 wt%
brane with the highest PSI may not always be the optimum choice water [7] and isopropanol (IPA) and water form an azeotrope at
for a process. around 12 wt% water [8]. Traditionally the way to break these
Another characteristic that is often used to rate the hydrophilic- azeotropes and allow them to be completely dehydrated is to
ity of a membrane is the measurement of the contact angle between add an additional chemical such as cyclohexane to the mix-
a drop of water and the membrane. If a drop of water is placed on ture before distillation. However the use of cyclohexane as an
a non-porous membrane, then the angle it forms is an indication entrainer in turn adds another impurity to the alcohol which can
of the materials affinity for water. The higher the affinity, the more never entirely be removed thus rendering the alcohol product
the drop spreads out into a film rather than staying in a drop shape unsuitable for some processes requiring an extremely high-purity
and the lower the contact angle is. This is shown in Fig. 2 and is the alcohol such as in the pharmaceutical industry. Thus, pervapo-
wettability of the material with respect to water. This measurement ration has been turned to as an alternative method of alcohol
can also be made with respect to any solvent to be dehydrated to dehydration that does not rely on the liquids present reaching
assess the material compatibility. equilibrium with each other and so can break these azeotropes
If however the material is porous, then the liquid will enter the without the need for additional chemicals. A large amount of
pores if the contact angle is less than 90◦ whilst if it is greater it will work has been carried out on the dehydration of alcohols, mostly
require pressure to force it into the pores. The bubble point pro- concentrating on ethanol/water and IPA/water systems and some
cedure is a commonly used test method to characterise a porous work done on the dehydration of solvents. This review will first
membrane. The bubble point itself is a determination of the mini- look at alcohol dehydration before also considering the research
mum pressure (bubble point) at which a wetting liquid is pressed performed investigating the design and use of membranes to
out of the pores of a membrane while forming a steady flow of bub- dehydrate three other organics: acetic acid, tetrahydrofuran and
bles. This procedure can also be used to determine the maximum acetone.
pore size in a membrane by using the Laplace equation (Eq. (2)) There are two main classes into which most pervaporation
where r is the pore size, is the contact angle and is the surface membranes can be placed. Polymeric membranes which are based
tension: on organic polymer chains that are cross-linked together and form
2 tiny pores through which molecule can diffuse. More recently how-
r= cos (2) ever, inorganic membranes, fabricated from ceramics or zeolites,
P
have increasingly become a focus of research. Although these are
1.2. Today’s pervaporation more difficult to produce on a large-scale industrially and often
expensive, they may offer a number of advantages over polymeric
Pervaporation is often used when the molecule sizes that need membranes such as solvent resistance and the ability to operate
to be separated are relatively small such as between low-molecular at higher temperatures. A third class of membranes can also be
weight solvents and water, where traditional separation processes defined comprising of composite membranes that are based on
such as distillation are not effective due to azeotropy or the energy an organic polymeric membrane but have inorganic particles dis-
Fig. 2. Contact angle measurement on a non-porous surface.

persed throughout the polymeric structure, these are commonly

termed mixed matrix membranes.
2.1. Alcohol dehydration using polymeric membranes
Polymeric membranes are widely used today in solvent dehy-

dration. The material and structure of the membrane and its
support determine the performance of the membrane. They incor-
porate high-selective sorption and high-selective diffusion, which
are dependent on the inter- and intra-molecular structure. They are
often made of rigid chain polymers that are capable of ion–dipole
interactions or hydrogen bonding with water. Hydrophilic poly-
meric membranes act as molecular sieves that are durable to water
and preferentially sorb the water molecules over other molecules
in the process stream. Semenova et al. [6] stated that a good
polymer for the selective permeation of water needs to have high-
sorption centers. These should interact with water by dipole–dipole
actions, ion–dipole actions (In the case of a polyelectrolyte) and/or
hydrogen bonding. Thus selecting a membrane that has one of
Fig. 3. Graphical representation of membrane performance data presented in
these features incorporated in the polymer chain or modifying Table 2.
an existing membrane to include such features is often desir-
able.
A high-water perm-selectivity in a membrane can be achieved mechanical characteristics of a polymer so they are more suitable
in two ways, either by increasing the diffusion ratio of water to the for a particular process.
organic solvent or by increasing the sorption ratio of water to the Today work has progressed from initial studies with homoge-
organic solvent. The amount a membrane is able to swell during neous polymers by modifying the polymer properties in various
operation affects the overall performance of the membrane. When ways to attempt to increase the separation performance. By increas-
the membrane swells, the polymer chains are stretched and the ing the degree of cross-linking or increasing or decreasing the
pore size, in the space between them, increases. This has the effect hydrophilicity of the chosen polymer, the characteristics of its sep-
of increasing the flux through the pores but due to their increase in aration performance can be altered and so a number of different
size, decreases the membranes selectivity as the larger molecules experiments have to be performed in order to find a membrane
find it easier to pass through. that offers a suitable flux and separation factor for a given process.
By reducing the ratio of hydrophilic to hydrophobic moieties in Asymmetric membranes offer the advantage of a thin skin layer
a membrane, the degree to which a membrane can swell can be with a more porous underside and so offer higher fluxes than dense
reduced thus increasing the separation factor and decreasing the homogeneous membranes whilst composite membranes compris-
flux. The reverse is also true and so by manipulating this ratio the ing of a thin active layer on a different polymeric support also allow
properties of a membrane can be influenced. The degree of cross- high fluxes to be achieved whilst maintaining a high selectivity
linking also affects the membranes selectivity, the higher the level towards the desired permeate.
of cross-linking between the polymer chains, the more compact the
network structure becomes. This strengthens the membrane form- 2.1.1. Poly(vinyl alcohol)
ing a rigid, stable membrane structure and reduces the degree that Poly(vinyl alcohol) (PVA) films exhibit high-abrasion resistance,
membrane is able to swell when it is in operation. The glass transi- elongation, tensile strength, and flexibility. It is a hydrophilic poly-
tion temperature (Tg , below which a polymer is hard and brittle) of mer with excellent water perm-selective properties and is used in
a polymer is also important to consider when selecting a polymer a number of commercial membranes such as those developed by
for use, as the properties of the polymer material are quite different Sulzer Chemtech [9] and prior to that GFT before they were acquired
above and below this temperature. Modifying the glass transition by Sulzer in 1997. The pervaporation performance in alcohol dehy-
temperature of a material by blending is often used to improve the dration of the PVA-based membranes reviewed in this section can
Table 2
Dehydration of alcohols using PVA-based membranes
Binary mixture (mass Membrane support Separation layer Cross-linker/modification Separation factor Flux (kg m−2 h−1 ) Temperature Reference
ratio) (◦ C)
EtOH/H2 O (50:50) PVA PVA Amic acid 100 0.25 45 [10]

EtOH/H2 O (95:5) PVA, PAAM PVA, PAAM – 45–4100 0.1–0.06 75 [14]
EtOH/H2 O (95:5) PESF PVA, PAAM – Lower than [14] Up to 3.8 75 [15]
EtOH/H2 O (95:5) PAA, PVA PAA, PVA – 50 0.26 50 [16]
EtOH/H2 O (50:50) PVA, CD PVA, CD Glutaraldehyde Similar to [10] Similar to [10] – [17]
EtOH/H2 O (Azeotrope) PVA, PSStSA-co-MA PVA, PSStSA-co-MA Heat treated 190 0.43 30 [18]
EtOH/H2 O (Azeotrope) PVA PVA – Around 10 0.12 60 [20]
EtOH/H2 O (Azeotrope) PVA Allyl alcohol Plasma grafted 110 0.04 60 [20]
EtOH/H2 O (Azeotrope) PVA Acrylic acid Plasma grafted ≈10 >0.12 60 [20]
EtOH/H2 O (90:10) Sericin Sericin Dimethylolurea cross-linked ≈90 ≈0.07 60 [21]
EtOH/H2 O (90:10) PVA PVA Dimethylolurea cross-linked ≈115 ≈0.12 60 [21]
EtOH/H2 O (90:10) Sericin/PVA (50:50) Sericin/PVA (50:50) Thermally annealed ≈90 ≈0.12 60 [21]
EtOH/H2 O (90:10) Sericin/PVA (50:50) Sericin/PVA (50:50) Dimethylolurea cross-linked ≈105 ≈0.10 60 [21]
EtOH/H2 O (90:10) Sericin/PVA (50:50) Sericin/PVA (50:50) Dimethylolurea highly ≈130 ≈0.07 60 [21]
cross-linked
be found in Table 2 and the tabulated performance data shown 0.06–0.1 kg m−2 h−1 for pervaporation of ethanol containing 5 wt%
graphically in the logarithmic plot in Fig. 3. water at 75 ◦ C. Rukenstein and Liang [15] then continued trying
Huang [10] was one of the first to study PVA membranes for to improve the performance of these membranes by supporting
pervaporation and investigated the effect of the degree of cross- them on polyethersulfone (PESf) and demonstrated that by sup-
linking on the performance of PVA membranes. A separation factor porting them they could use much thinner films of around 4 ␮m
of around 100 with a flux of 0.25 kg m−2 h−1 was achieved at the compared to the self-supported membranes which were 30–40 ␮m
operating temperature of 45 ◦ C using a 50% ethanol feed mixture thick. These thin film composite membranes and thus could achieve
and a PVA membrane cross-linked with amic acid. PVA was shown a greater flux (up to 3.8 kg m−2 h−1 ) with some trade off in a lower
to be a successful membrane for alcohol dehydration in initial work separation factor. Experimental runs were performed for up to 6
such as this and thus lead numerous other researchers to investigate days but some longer term experiments would be interesting to
PVA-based membranes for pervaporation. test long-term membrane stability.
Praptowidodo [11] also studied how the degree of cross-linking Rukenstein and Liang [16] also worked with poly(acrylic acid)-
in the PVA membrane affected performance. Glutaraldehyde was poly(vinyl alcohol) PAA-PVA IPN and semi-IPN (SIPN) membranes
utilised as the cross-linking agent and copolymer membranes of where either PVA or both PVA and PAA were cross-linked. For
polyvinyl alcohol-co-itaconic acid (PVA-It) and polyvinyl alcohol- a 95 wt% ethanol feed at 50 ◦ C the IPN membrane was found to
co-N-3-trimethyl-ammonio-propyl-acrylamide-chloride (PVA-N) have a flux of 0.26 kg m−2 h−1 and separation factor of 50. Unfortu-
were also fabricated. The swelling of the membranes was stud- nately the SIPN membranes were only utilized for the separation
ied and found to be reduced in membranes that were more highly of ethanol–benzene mixtures so no direct comparison is possible.
cross-linked and with co-polymer membranes with a charged Cyclodextrin and PVA were used to produce a composite mem-
species present compared to PVA alone. Increased cross-linking and brane by Yamasaki et al. [17] by cross-linking the cyclodextrin
reduced swelling in pure PVA membrane led to a reduction in flux (CD) oligomer with PVA using glutaraldehyde to form a 2:1 by
and an increase in separation factor as would be expected from the- weight PVA/CD membrane. The cyclodextrin molecule contains a
ory by reducing the free volume available for transport. PVA-It and hydrophobic cavity which could influence the selectivity of the
PVA-N both possessed lower fluxes than PVA but increased separa- membrane by forming inclusion compounds. Their results showed
tion factors. The charged nature of the groups present in both these water selectivity over PVA alone for lower (0–40%) and higher
membranes is seen as the reason behind the improvement in water (>90%) ethanol concentrations in the feed but were not drastically
selectivity. different from pure PVA. The cyclodextrin oligomers effectively
Lee and Wong [12] showed that the degree of PVA hydroly- reduced the free volume for flow through the membrane and thus
sis was important in membrane performance as this determined smaller water molecules were able to diffuse more freely than the
properties such as the polymer crystallinity and polarity. It was larger ethanol molecules and thus improved the membrane sep-
shown that the flux through the membrane was inversely propor- aration factor. Cyclodextrin is a hydrophobic compound and thus
tional to the degree of hydrolysis whilst the separation factor was would have a greater affinity with ethanol than water. It would
directly proportional. They described how crystallinity reduced flux be interesting to also investigate a membrane filled with a more
by hindering solvent transport through the membrane however in hydrophilic compound.
the case of PVA, increased hydrolysis also increase the number of Chiang and Lin [18] worked on increasing the flux and separa-
hydroxyl groups and therefore this favours the transport of water tion factor of a PVA membrane by grafting hydrophilic copolymers
thus increasing the separation factor by preferentially transport- onto the PVA chains during cross-linking. Poly(sodium salt styrene
ing water. It would also be interesting to examine a case where the sulfonic acid-co-maleic acid) (PSStSA-co-MA) was selected as a
only effect was changing degree of crystallinity without also having cross-linker and added into the PVA solution before casting. Heat
the effect of changing functional groups so the transport hindrance treatment was then performed to cross-link the polymer chains
due to crystallinity could be evaluated with the influence of other and to react the hydroxyl groups of PVA with the carboxylic groups
factors. of the copolymer. They unfortunately did not fabricate any pure
Kang et al. [13] modified the surface of PVA by reacting it with PVA membrane to contrast performance to, instead compared their
monochloroacetic acid. This introduced carboxylic acid groups on results to those obtained by other researchers. It would have been
to the surface of the membrane and thus increased the membrane more useful to make a direct comparison but they concluded
hydrophilicity. The perm-selectivity of the surface-modified mem- the membranes fabricated maintained a reasonable flux with an
brane was almost doubled compared to the cross-linked PVA and improved separation factor.
the modification also caused a slight increase in flux. Experiments Sun and Huang [19] worked on developing a novel temperature-
were also performed with the membrane orientated both up and sensitive membrane by grafting poly(N-N-isopropylacrylamide)
down to help determine how the membrane surface and support PNIPAAm onto PVA forming PVA-g-NIPAAm. Cross-linked PNI-
layer both affect the separation. This is an interesting approach to PAAm gels shrink abruptly in water at approximately 32 ◦ C, a
studying transport across the membrane but they failed to make temperature close to the lower critical solution temperature (LCST)
any great distinctions on how each layer contributed towards the of the linear PNIPAAm in water. This is due to extensive hydrogen
overall separation, they simply concluded that both layers played a bonding that occurs at low temperatures and suddenly collapses
major role. above the LCST. The membranes exhibit the maximum flux and
A number of composite PVA membranes have been developed separation factor around this temperature but they found the sensi-
to enhance the performance attained with a simple PVA mem- tivity to temperature of the membrane was also affected by ethanol
brane. Liang and Ruckenstein [14] synthesised interpenetrating concentration in the feed. This is an interesting feature but in gen-
polymer networks (IPN’s) of PVA and polyacrylamide (PVA-PAAM eral, higher operating temperatures are often sought to improve
IPN). PAAM is a brittle material but sorbs a larger amount of water membrane flux. Due to the reduction in membrane separation fac-
than PVA and has a higher separation factor with respect to water as tor to roughly half of its maximum value attained around 32 ◦ C
well as a higher thermo-stability. The aim was to form an improved when operating at higher temperatures, the usefulness of this
material by combining the two polymers with PVA, improving membrane in daily operation is questionable.
the mechanical properties of PAAM. The membranes produced Plasma modification of PVA was investigated by Rafik et al. [20]
shows separation factors ranging from 45 to 4100 and fluxes of who showed that the hydrophilicity of non-porous PVA membranes
was enhanced by the deposition of a plasma layer on the surface of

the membrane. The PVA membranes were covered with a plasma-
polymerised layer of either acrylic acid or allyl alcohol and then
studied the pervaporation properties of these membranes at the
azeotropic feed concentration of 95.6 wt% ethanol. They found that
the allyl alcohol grafted membranes were not stable with time as
those stored for a 30-day period performed less well than freshly
produced membranes showing problems with stability. The acrylic
acid grafted PVA did not share this problem however the layer had
the tendency to form cracks. The membranes fabricated were dense
films and thus the fluxes obtained were low, fabrication of asym-
metric PVA membranes followed by plasma modification would
possibly have yielded membranes with better separation charac-
teristics. The flux for the acrylic acid treated membrane was slightly
higher than PVA and the separation factors were similar.
Recently, Gimines et al. [21] blended sericin and PVA together
and compared the performance with sericin and PVA membranes.
Sericin is a macromolecular protein consisting of amino acids con-
taining a large number of polar side-groups that cause the protein Fig. 4. Graphical representation of membrane performance data presented in
to be highly hydrophilic. They selected it as a suitable candidate Table 3.
to improve membrane performance to increase hydrophilicity but
also as it is available as a waste product from the manufacture of performance in alcohol dehydration of the chitosan-based mem-
silk and thus would be a cheap and environmentally available mate- branes reviewed in this section can be found in Table 3 and the
rial. Cross-linking chemically using dimethylolurea was compared tabulated performance data shown graphically in the logarithmic
to thermal cross-linking and they selected chemical cross-linking plot in Fig. 4.
as the most suitable technique. Blending PVA with sericin was seen Ge et al. [22] observed that the temperature at which a polymeric
to improve the separation factor but reduced the flux over utilising chitosan membrane is prepared at was the most important factor
PVA alone but did not significantly improve performance. in affecting its separation characteristics with the flux decreasing
as the heating temperature is increased and achieving the highest
2.1.2. Chitosan separation factor at a heating temperature of 373 K. They attributed
Chitosan (beta-(1,4)-2-amino-2-deoxy-d-glucose) is the deacy- this to the fact that the densest packing of crystals occurs when
lated form of chitin, a compound which is mostly obtained from the the membrane is prepared at this temperature. Also by using dif-
cuticle of a marine crustacean. It contains both hydroxyl and amino ferent concentrations of H2 SO4 for cross-linking they showed that
groups and thus makes it easily modifiable. This makes it a good the more highly cross-linked the membrane, the higher the sep-
starting point for pervaporation experiments. The pervaporation aration factor but the lower the flux attributed to the membrane
Table 3
Dehydration of alcohols using chitosan-based membranes
Binary mixture (mass Membrane support Separation layer Cross-linker/modification Separation Flux Temperature Reference
ratio) factor (kg m−2 h−1 ) (◦ C)
EtOH/H2 O (90:10) Chitosan Chitosan H2 SO4 1791 0.472 60 [22]

EtOH/H2 O (90:10) Chitosan Chitosan Glutaraldehyde 127 0.201 50 [23]
EtOH/H2 O (90:10) Chitosan Chitosan, carboxyl Glutaraldehyde, maleic anhydride 991 0.238 50 [23]
modified
EtOH/H2 O (90:10) Chitosan Chitosan Glutaraldehyde 105 0.250 60 [23]
EtOH/H2 O (90:10) Chitosan Chitosan, carboxyl Glutaraldehyde, maleic anhydride 634 0.300 60 [23]
modified
IPA/H2 O (90:10) Chitosan Chitosan Glutaraldehyde 337 0.169 50 [23]
IPA/H2 O (90:10) Chitosan Chitosan, carboxyl Glutaraldehyde, maleic anhydride 491 0.178 50 [23]
modified
IPA/H2 O (90:10) Chitosan Chitosan Glutaraldehyde 196 0.197 60 [23]
IPA/H2 O (90:10) Chitosan Chitosan, carboxyl Glutaraldehyde, maleic anhydride 366 0.211 60 [23]
modified
EtOH/H2 O (90:10) Chitosan/HEC Chitosan/HEC – 10,490 0.112 60 [24]
EtOH/H2 O (90:10) Cellulose acetate Chitosan/HEC – 5469 0.424 60 [25,26]
EtOH/H2 O (Azeotrope) Chitosan/PAA Chitosan/PAA Heat treated 2216 0.033 30 [27]
EtOH/H2 O (Azeotrope) PSF Chitosan/PAA Heat treated 1008 0.132 30 [27]
EtOH/H2 O (95:5) Chitosan/PAA Chitosan/PAA – Up to 19,000 ≈0.001 Various [28]
EtOH/H2 O (95:5) PESF Chitosan 80 min sulphuric acid cross-linked ≈350 ≈0.65 80 [29]
IPA/H2 O (85:15) PESF Chitosan 60 min sulphuric acid cross-linked ≈200 ≈1.6 80 [29]
IPA/H2 O (95:5) PSF Chitosan Binded with PVA ≈400 0.4–0.8 50 [30]
IPA/H2 O (90:10) PVA/chitosan 20:80 PVA/chitosan 20:80 Glutaraldehyde + thermal cross-link >900,000 0.644 60 [31]
IPA/H2 O (90:10) PVA PVA UFS solution to cross-link 77 0.095 30 [32]
IPA/H2 O (90:10) Chitosan Chitosan UFS solution to cross-link 5134 0.087 30 [32]
IPA/H2 O (90:10) PVA/chitosan 20:80 PVA/chitosan 20:80 UFS solution to cross-link 17,991 0.113 30 [32]
IPA/H2 O (90:10) PVA/chitosan 40:60 PVA/chitosan 40:60 UFS solution to cross-link 8562 0.149 30 [32]
IPA/H2 O (90:10) PVA/chitosan 60:40 PVA/chitosan 60:40 UFS solution to cross-link 6419 0.214 30 [32]
IPA/H2 O (90:10) PTFE PSSA-g- GPTMS cross-linker 1490 0.409 25 [33]
PTFE/chitosan
swelling being less when more highly cross-linked. The structural as a cationic polyelectrolyte and PAA acting as an anionic. The
analysis performed showed an interesting trend that more crys- blends were cast and then dried at 30 ◦ C in a conventional oven
talline chitosan and membranes with larger crystals appeared to for 24 h. Testing showed that the membrane may well be stable up
possess better separation characteristics. Chitosan was also used to almost 200 ◦ C allowing for higher temperature operation. The
by Zhang et al. [23] who selected glutaraldehyde to cross-link the ionic cross-linking between the polymers increased the rigidity of
dense membranes they produced via solvent evaporation. They the membrane over that of chitosan or PAA. The resultant mem-
formed carboxyl groups on the surface by treating the cross-linked branes showed high-separation factors of up to 19,000. However
membranes with maleic anhydride and showed this improved both since they were dense membranes, the fluxes were very low of the
flux and separation factor when dehydrating ethanol and IPA over order of 0.001 kg m−2 h−1 . Lee et al. [29] did attempt to produce
a range of temperatures. composite membranes with chitosan by casting a thin layer on to a
Chanachai et al. [24] produced a blended membrane from PESf ultrafiltration membrane as a support. This however was less
chitosan/hydroxyethylcellulose (CS/HEC) in ratios of 3:1 and 9:1. successful than the composite membranes that Shieh and Huang
They found that with increasing HEC content, the polymer net- produced as although the flux was significantly higher, the separa-
work flexibility is increased thus increasing the flux across the tion factor was greatly reduced. When separating ethanol and water
membrane. Increasing the HEC content improved the hydrophilic- they found that the separation factor increased up to a cross-linking
ity of the membrane but the increased free volume at higher time of 100 min whilst the maximum flux was achieved after cross-
HEC contents caused a reduction in selectivity as the membrane linking for 70 min. Membranes could be easily tailored to different
became less dense. The PSI was found to drop sharply for HEC separation requirements by varying this cross-linking time.
contents greater than 25 wt% at which the maximum flux was Huang et al. [30] worked with a composite chitosan/polysulfone
achieved with little variation in the separation factor with increas- (PSF) membrane. They found it was beneficial to first immerse the
ing HEC content. They concluded the optimum ratio was dependent PSF porous membrane into a hydrophilic binding polymer solu-
on the nature and composition of the mixture to be separated. tion before casting the chitosan layer on top to increase the affinity
Jiraratananon et al. [25,26] continued on with this work pro- between the two layers. This also increased the hydrophilicity of the
ducing a composite membrane using a cellulose acetate porous PSF layer. They performed some interesting analyses into the effects
support which they produced by phase inversion on which a of cross-linking and comparing dense membrane performance to
3:1 chitosan/hydroxyethylcellulose (CS/HEC) solution was cast and that of composite membranes. They failed however to look at long-
cross-linked with urea–formaldehyde–sulphuric acid mixture. The term performance of membranes produced using binding polymers
PSI of the composite membrane was found to be higher than that of to identify what improvements were offered in membrane stability
the blended membrane as the overall flux showed an almost four- over time by using this technique.
fold increase whilst the separation factor halved. The wide range of Two common materials used in the fabrication of hydrophilic
different approaches used over the course of these studies gave a membranes, chitosan and PVA were blended by Svang-Ariyaskul et
good basis for comparing the effects of varying various parameters al. [31] to produce dense membranes for IPA dehydration. Mem-
on the separation characteristics of the resultant membranes with branes were thermally cross-linked at 150 ◦ C and then chemically
comparisons easily drawn between composite and blend mem- cross-linked using glutaraldehyde and sulphuric acid. Blends of 3:1,
branes, varying HEC contents and skin layer thicknesses and also 1:1 and 1:3 were produced as well as PVA and chitosan mem-
the effects of varying operating parameters. branes for comparison. They reported the membrane containing
Blend membranes of chitosan and PAA were produced by Shieh 3:1 chitosan to PVA offered the best separation characteristics with
and Huang [27]. Two homogeneous CS/PAA membranes, one cast a permeate consisting of close to 100 wt% water. Chitosan and
and washed with water for 24 h to form a complex structure PVA were also used by Rao et al. [32] who produced blends con-
between CS and PAA (polyelectrolyte complex form) and one cast, taining 20, 40 and 60 wt% of PVA. Membranes were produced by
washed and then heated in an oven for a hour to induce a reac- solvent evaporation and cross-linked using a urea formaldehyde
tion between the amino group of CS and carboxyl group of PAA and sulphuric acid (UFS) mixture. The blends were found to per-
(cross-linked). A third composite membrane with a porous PSF form significantly better than either of the polymeric materials
support was also fabricated. The blend membranes were found alone and the cross-linking mixture was also deemed to provide
to be highly water selective with the second type (polyelectrolyte both mechanical strength and improve separation performance.
complex form) offering the best performance of the three mem- The blend containing 60 wt% PVA was found to offer the highest
branes at high-ethanol contents. The flux across the composite permeation whilst the blend containing 20 wt% achieved the high-
membrane was consistently higher over the entire ethanol concen- est separation factor whilst dehydrating IPA, the same conclusion
tration range than the homogeneous blend membranes. This is due reached by Svang-Ariyaskul et al. [31]. Overall, the performance
to the active layer being much thinner in the composite membrane. of the membranes produced by Svang-Ariyaskul seemed to out-
At ethanol concentrations >80 wt% the PSI of the composite mem- perform that of the membranes produced by Rao et al. which could
brane was greater than that of the homogeneous one suggesting be due to the effect of the thermal annealing.
that unless an extremely high-separation factor is desired, the com- Chitosan and poly(tetrafluroethylene) (PTFE) were used by Liu
posite membrane would be more suitable for high-initial ethanol et al. [33] to produce an effective membrane for IPA dehydra-
concentration dehydrations. Interestingly they found that mem- tion. PTFE was incompatible with chitosan since it was particularly
branes fabricated from higher molecular weight chitosan produced hydrophobic whilst chitosan was hydrophilic. Thus, before chitosan
membranes with lower permeances but improved separation per- could be cast on to the PTFE surface, the PTFE was modified using
formance. They attributed this to the reduced free volume and poly(styrene sulphuric acid) (PSSA) via plasma grafting. After graft-
therefore more dense structure formed in the skin layer with a ing this acidic polymer to the surface of the membrane, a layer
higher molecular weight polymer. It would however, be interest- of chitosan and ␥-(glycidyloxypropyl)trimethoxysilane (GPTMS), to
ing to compare the effect on the overall thickness of the skin layer act as a cross-linker, could then be cast and adhered to the surface.
instead of simply concluding it was due to skin layer densification. This grafting technique, coupled with the application of a dilute
Nam and Lee [28] also worked with chitosan and PAA to produce layer of chitosan casting solution allowed, upon solvent evapo-
a polyelectrolyte complex membrane. Its polyelectrolyte nature ration, an extremely thin chitosan separation layer to be formed
results from an electrostatic interaction between chitosan, acting on the PTFE support. The resultant membrane was also shown to
tially, the work focused onto stabilising the water-soluble polymer

and improving the mechanical strength of the material by work-
ing with blends. They also identified issues relating to operating
at elevated temperatures and poor long-term performance with
flux decline when working at 40 ◦ C. Upon cooling the membrane
and performing the test again, they found the flux had improved
somewhat before once again deteriorating. This was attributed to
the relaxation of the polymer chains upon heating causing the
membrane structure to densify which was then partially reversed
upon cooling. Cross-linking with glutaraldehyde reduced mem-
brane swelling, but worsened with the flux decline due to the
polymer relaxation effect. The flux and membrane selectivity also
decreased due to the reduced free volume for transport and the
hydrophobic nature of the cross-links promoting alcohol transport.
They overcame the relaxation issue by blending with PVA which
produced a stable membrane and also tested cross-linking with
glutaraldehyde.
Huang and Moon [39] looked at Na-Alg membranes for the dehy-
Fig. 5. Graphical representation of membrane performance data presented in dration of ethanol–water and IPA–water mixtures. They found the
Table 4. membrane to be mechanically weak but offered promising perva-
poration performance. The problem of the solubility of Na-Alg in
be particularly effective at dehydrating dimethylformamide and water was overcome by cross-linking the membrane ionically. Of
tetrafluropropanol. No adverse effect on the membrane perfor- all the ions they tried (Na+ , Ca2+ , Zn2+ , Mn2+ , Co2+ , Fe2+ , Al3+ ), Ca2+
mance was shown after immersion in IPA for 45 days, indicating was found to offer the highest PSI for pervaporation of a 90 wt%
that the membranes were relatively solvent stable. ethanol feed at 50 ◦ C. They also showed that the relaxation effect
observed by Yeom et al. [34] was greatly reduced by the presence of
2.1.3. Alginate the calcium counter ion. Huang and Moon [40] then went on to pro-
Alginate is a block ploymer consisting of two acid residues, duce a composite membrane consisting of an active alginate layer
␣-(1 → 4)-linked l-guluronic acid and ␤-(1 → 4)-linked d- with a supporting chitosan layer on top of poly(vinylidine fluoride),
mannuronic acid. ␤-(1 → 4)-linked d-mannuronic acid. It is PVDF. They found that modifying the surface properties of PVDF by
used widely in the food industry as a thickner and gelling agent blending it with 1% of the more hydrophilic polymethyl methacry-
and even has been used in medical applications as an immboliza- late (PMMA) was useful to give better adhesion to the alginate and
tion material for cell cultures and as dressings for surgical wounds. chitosan top layers. They modified the top Na-Alg layer producing
The hydrophilic nature of the polymer has led it being tested in membranes with alginic acid and cobalt cross-linked alginate top
the fabrication of a variety of different pervaporation membranes layers and tested the three different membranes. Although the per-
for the dehydration of alcohols. The pervaporation performance in formance of the alginic acid membrane showed a lower separation
alcohol dehydration of the alginate-based membranes reviewed in factor than that of the Na-Alg membrane, it had a higher overall flux
this section can be found in Table 4 and the tabulated performance and possessed better mechanical strength and long-term stability.
data shown graphically in the logarithmic plot in Fig. 5. The effect of blending Na-Alg and PVA was also tested by Kurkuri
Sodium alginate (Na-Alg) was first extensively studied for use in et al. [41] in order to improve on the flexibility of Na-Alg and the
alcohol dehydration by pervaporation by Yeom et al. [34–38]. Ini- performance of either of the polymers alone. This was an interest-
Table 4
Dehydration of alcohols using alginate-based membranes
EtOH/H2 O (90:10) Na-Alg Na-Alg – 10,000 > non- 0.290 50 [34]

stable non-stable
EtOH/H2 O (90:10) Na-Alg/PVA Na-Alg/PVA – ≈30,000 ≈0.12 50 [37]
EtOH/H2 O (90:10) Na-Alg/PVA Na-Alg/PVA HCl and 10 vol% glutaraldehyde ≈3000 ≈0.04 50 [37]
EtOH/H2 O (90:10) Na-Alg Na-Alg HCl and 10 vol% glutaraldehyde ≈500 ≈0.1 50 [38]
EtOH/H2 O (90:10) Alginate based Alginate based Ionically cross-linked, Ca2+ 300 0.230 50 [39]
EtOH/H2 O (Azeotrope) PVDF, chitosan Alginate – 202 0.095 50 [40]
EtOH/H2 O (Azeotrope) PVDF, chitosan Alginate Alginic acid 90 0.172 50 [40]
EtOH/H2 O (Azeotrope) PVDF, chitosan Alginate Cobalt alginate 99 0.046 50 [40]
IPA/H2 O (90:10) Na-Alg Na-Alg Glutaraldehyde followed by HCl 356 0.012 30 [41]
IPA/H2 O (90:10) Na-Alg/PVA 25/75 Na-Alg/PVA 25/75 Glutaraldehyde followed by HCl 195.5 0.024 30 [41]
IPA/H2 O (90:10) Na-Alg/PVA 75/25 Na-Alg/PVA 75/25 Glutaraldehyde followed by HCl 91 0.039 30 [41]
IPA/H2 O (90:10) PVA PVA Glutaraldehyde followed by HCl 21 0.041 30 [41]
IPA/H2 O (90:10) Na-Alg Na-Alg Glutaraldehyde followed by HCl 81.1 0.021 50 [41]
IPA/H2 O (90:10) PVA PVA Glutaraldehyde followed by HCl 16.7 0.095 50 [41]
IPA/H2 O (90:10) PSF PVA/Na-Alg (80:20) Maleic anhydride 1727 0.414 45 [42]
EtOH/H2 O (90:10) PSF PVA/Na-Alg (80:20) Maleic anhydride 384 0.384 45 [42]
EtOH/H2 O (95.4:4.6) Na-Alg/PVP (3:1) Na-Alg/PVP (3:1) Phosphoric acid 364 0.09 30 [43]
Table 5
Dehydration of alcohols using PSF-based membranes
EtOH/H2 O (90:10) PSF/PEG (5 wt% PEG) PSF/PEG (5 wt% PEG) – ≈325 ≈0.6 25 [44]
EtOH/H2 O (90:10) PSF PSF Sulfonation 600 0.7–0.9 25 [47]
EtOH/H2 O (90:10) Sodium sulfonate PSF Sodium sulfonate PSF Chlorosulfonic acid ≈1900 ≈0.75 25 [48]
EtOH/H2 O (90:10) Sodium sulfonate PSF Sodium sulfonate PSF Chlorosulfonic acid ≈1300 ≈0.88 45 [48]
EtOH/H2 O (90:10) 12.5% TGN, 87.5% PSF 12.5% TGN, 87.5% PSF TGN plasticiser ≈680 ≈0.44 25 [49]
EtOH/H2 O (90:10) PSF hollow fibre PSF – 23.9 0.173 25 [50]
EtOH/H2 O (90:10) PSF Poly(amic methyl ester) Interfacial polymerisation 240 1.7 40 [51]
ing study as they produced membranes in the ratios 3:1, 1:1 and bonate. PSF’s mechanical properties also remain relatively constant
1:3 PVA/Na-Alg but also fabricated pure PVA and pure Na-Alg mem- over a broad temperature range up to 140 ◦ C. The pervaporation
branes to allow the performance of the blends to be compared to the performance in alcohol dehydration of the PSF-based membranes
base performance of membranes fabricated from either polymer. As reviewed in this section can be found in Table 5 and the tabu-
with Yeom et al., they also used glutaraldehyde as a cross-linking lated performance data shown graphically in the logarithmic plot
agent. They showed that flux increased with increasing PVA content in Fig. 6.
with the opposite trend for separation factor. The separation per- Hsu et al. [44] found, for a polysulfone-poly(ethylene glycol)
formance they achieved was not as great as that reported by Yeom (PSF-PEG) membrane, that by increasing the PEG content, i.e.
and Lee [36]. Recently Dong et al. [42] blended PVA and Na-Alg and improving the polymer chain flexibility, the separation perfor-
produced membranes by coating the blend on PSF ultrafiltration mance of the membrane can be enhanced over PSF alone. For
supports with maleic acid utilised as a cross-linker. A 4:1 PVA to Na- an ethanol–water system, both the separation factor and the flux
Alg ratio was found to produce optimal membrane performance. across the membrane increased up to 2.5 wt% PEG in PSF after which
The thin defect free layers of PVA-Na-Alg they managed to produce the separation factor decreased with increasing PEG content and
allowed for a high flux whilst maintaining a high-separation factor the flux continued to increase. Although they claimed to carry out
when they dehydrated a range of alcohols although the compatibil- an aging experiment, they only tested a membrane for 8 h before
ity between the support and coatings was not fully discussed and concluding that there was no problem with PEG washout and the
long-term membrane stability was not assessed. membrane was stable with time. In reality, a much longer period
Na-Alg and poly(vinyl pyrrolidone) (PVP) were blended by of testing would be necessary to give a greater degree of certainty
Kalyani et al. [43] in different ratios and cross-linked with phos- in the long-term stability of the membrane.
phoric acid to form a covalent bond between the acetate group Kim et al. [45] used oxygen plasma treatment to convert the
of Na-Alg and the alkyl group of PVP. The blend ratios typically hydrophobic membrane surface to a more hydrophilic one whilst
produced brittle membranes unsuitable for use, the only ratio for Steen et al. [46] used low-temperature plasma treatment on asym-
which brittleness was not an issue was a 3:1 Na-Alg to PVP blend metric PSF membranes where the plasma penetrates the entire
so this was selected for pervaporation testing. Membrane selec- thickness of the membrane hydrophilically modifying the entire
tivity improves with increasing membrane thickness whilst flux membrane cross-section. They found a 2 min treatment with a
decreases and maintaining a low-permeate pressure was identified 25 W water vapour plasma was sufficient to hydrophilize the mem-
as an extremely important factor in achieving a good separation. brane whilst increasing the time or using a more highly powered
treatment caused visible structural damage to the membrane. The
2.1.4. Polysulfone treatment allowed the membrane to remain wettable for over 16
Polysulfone (PSF), a hydrophobic polymer, is an amorphous months after the treatment and that the plasma penetrated the
high-performance thermoplastic offering excellent mechanical, membrane since the effects of the modification were seen on both
electrical, and improved chemical resistance relative to polycar- surfaces. Neither of these studies tested these membranes for per-
vaporation use but the techniques could easily be applied to more
dense PSF membranes and tested for pervaporation.
Chen et al. [47] sulfonated PSF membranes to increase their
hydrophilicity. They found that the flux and separation factor
increased up to a substitution of 2.0 and that the dominant fac-
tor for separation was the diffusive difference between ethanol
and water in the membrane, not their difference in solubility in
the membrane. The glass transition temperature of the membrane
decreased with increasing substitution and the membranes swelled
to a greater extent, increasing the membrane free volume. They
found that the flux stayed relatively constant with temperature
whilst the separation factor decreased rapidly with increase in tem-
perature favouring membrane operation at low-feed temperatures.
Hung et al. [48] tested a sodium sulfonate PSF membrane and
found that the membranes perm-selectivity was strongly linked
to the membrane’s sodium content. They sulfonated the PSF using
chlorosulfonic acid before casting the membrane. A sodium sul-
fonate membrane was prepared by immersing this sulfonated
membrane in sodium hydroxide for 12 h. They found that the chain
flexibility increased with increasing degree of sodium substitution
Table 5. and both the flux and separation factor increased up to a substitu-
tion ratio of 0.9 after which the separation factor began to decrease
whilst the flux continued to increase due to the membranes increas-
ing ability to swell. They also concluded that although the flux
did not vary much with temperature, the separation factor did
decrease with increasing temperature (2000 at 15 ◦ C dropping to
around 1300 at 45 ◦ C) in agreement with the conclusion of Chen
et al. [47]. Thus, membrane performance was optimal at lower
operating temperatures. Hung et al. [49] again used PSF but with
a plasticizer, Ultramoll TGN, available from Merck Chemical Com-
pany. They showed that permeation flux was almost independent
of TGN content whilst separation factor increased with increas-
ing TGN content up to 6.25 wt% of TGN after which it was shown
to decrease again. This suggests an optimum plasticizer content
of around this value to maximise the membranes separation fac-
tor. These membranes performed less well than those produced by
sodium sulfonate substitution.
Hollow fibre PSF membranes were produced by Tsai et al. [50]
via a wet spinning phase inversion process. They investigated the
effect of the co-solvent (diethylene glycol dimethyl ether, DGDE)
present in the polymer solution on the morphology of the pro- Fig. 7. Graphical representation of membrane performance data presented in
Table 6.
duced membrane. By increasing the concentration of the co-solvent
they could reduce the speed of mixing, reducing the formation
of macrovoids. The performance of the resultant membranes was, pled with their reasonable solvent resistance make them a very
however, much below the fluxes and separation factors reported by stable polymer. The pervaporation performance in alcohol dehy-
other researchers and thus it would be interesting to compare the dration of the polyimide-based membranes reviewed in this section
performance of sulfonated PSF hollow fibres to identify whether can be found in Table 6 and the tabulated performance data shown
using DGDE as a co-solvent reduces the performance of the mem- graphically in the logarithmic plot in Fig. 7.
brane or whether the reduction in performance was related to the Kim et al. [51] prepared polyimide composite membranes using
morphology and nature of the membrane they produced. PSF as a support. They built up layers of poly(amic methyl ester)
on top of the support by interfacial polymerization of a range
2.1.5. Polyimides of different diamines with the organic solvent (toluene)-soluble
Polyimides are a group of very strong and also highly heat and diacyl chloride–diester—2,5-bis(methoxycarbonyl) terephthaloyl
chemical resistant polymers. They offer good resistance to wear chloride (BMTC). These were then converted to polyimides by heat-
and have excellent mechanical properties. These properties cou- ing in a vacuum to undergo thermal imidization. They showed this
Table 6
Dehydration of alcohols using polyimide-based membranes
Binary mixture (mass Membrane Separation layer Cross-linker/modification Separation Flux Temperature Reference
ratio) support factor (kg m−2 h−1 ) (◦ C)
EtOH/H2 O (95:5) PI-2080 aromatic PI-2080 aromatic – 900 1.0 60 [53]

polyimide polyimide
IPA/H2 O (85:15) P84 P84 Acetone additive, thermal 3508 0.432 60 [55]
treatment
IPA/H2 O (85:15) P84 P84 – 5 2.578 60 [56]
IPA/H2 O (85:15) P84 P84 p-Xylenediamine 1 h 59 1.599 60 [56]
IPA/H2 O (85:15) P84 P84 EDA 1 h 167 1.012 60 [56]
IPA/H2 O (85:15) P84 P84 EDA 2 h 206 0.534 60 [56]
IPA/H2 O (85:15) P84 P84 EDA 4 h 134 0.911 60 [56]
IPA/H2 O (85:15) P84 P84 EDA 6 h 83 1.104 60 [56]
IPA/H2 O (85:15) P84 P84 p-Xylenediamine 2 h, 335 1.105 60 [56]
100 ◦ C
IPA/H2 O (85:15) P84 P84 p-Xylenediamine 2 h, 592 0.335 60 [56]
200 ◦ C
EtOH/H2 O (90:10) BAPP BAPP – 22 0.27 25 [57]
EtOH/H2 O (88.9:11.1) PMDA-ODA PMDA-ODA Thermal treatment 346 0.014 45 [58]
EtOH/H2 O (88.9:11.1) PMDA-ODA PMDA-ODA Thermal treatment 445 0.043 75 [58]
EtOH/H2 O (88.9:11.1) PMDA-MDA PMDA-MDA Thermal treatment 47 0.023 45 [58]
EtOH/H2 O (88.9:11.1) PMDA-MDA PMDA-MDA Thermal treatment 19 0.130 75 [58]
EtOH/H2 O (88.9:11.1) BTDA-PDA BTDA-PDA Thermal treatment 1386 0.003 45 [58]
EtOH/H2 O (88.9:11.1) BTDA-PDA BTDA-PDA Thermal treatment 1594 0.005 75 [58]
EtOH/H2 O (88.9:11.1) BTDA-ODA BTDA-ODA Thermal treatment 395 0.011 75 [58]
EtOH/H2 O (88.9:11.1) BTDA-ODA BTDA-ODA Thermal treatment 562 0.022 45 [58]
EtOH/H2 O (88.9:11.1) BTDA-MDA BTDA-MDA Thermal treatment 237 0.015 75 [58]
EtOH/H2 O (88.9:11.1) BTDA-MDA BTDA-MDA Thermal treatment 478 0.035 45 [58]
EtOH/H2 O (90:10) BHTDA-BATB BHTDA-BATB – 27 0.282 35 [59]
EtOH/H2 O (90:10) BHTDA-BADTB BHTDA-BADTB – 15 0.325 35 [59]
EtOH/H2 O (90:10) BHTDA-DBAPB BHTDA-DBAPB – 141 0.255 35 [59]
was a good system for producing ultra-thin layers and that imidiza- tetracarboxylic dianhydride polyimide membrane at 25 ◦ C, how-
tion at 180 ◦ C for 3 h was sufficient for two diamines to produce ever the reported separation factor was rather low at only 22.
a viable pervaporation membrane. They noted however that crack Five different polyimides, synthesized from two dianhydrides
formation was a problem with the differential expansion/shrinkage (pyromellitic dianhydride (PMDA) and 3,3 4,4 -benzophenonete-
of the diamine layer during imidization compared to that of the PSF tracarboxylic dianhydride (BTDA)) and three diamines (4,4 -
support. They also showed that membranes could be run continu- diaminodiphenylether (ODA), 4,4 -diaminodiphenylmethane
ously for up to 6 days with no degradation in performance. (MDA) and phenylenediamine (PDA)) were tested by Xu et al.
Okamoto et al. [52] studied both vapour permeation and perva- [58] in membrane fabrication for the dehydration of ethanol.
poration of ethanol–water using polyimide membranes prepared Polyamic acid precursors of the polyimides were synthesised
by solution condensation of 3,3 ,4,4 -biphenyltetracarboxylic dian- and dense membranes cast from DMF solution via solvent
hydride (BPDA) with different aromatic diamines in p-chlorophenol evaporation, converted to the polyimide form by heat treat-
followed by thermal imidization. They calculated the permeability ments at high temperature. They found the flux was higher
coefficients for water and ethanol for the two separation systems for all the MDA-based membranes than analogous PDA mem-
and various membranes tested and found that vapour permeation branes with the same dianhydride whilst the separation factors
was much more sensitive to feed concentration whilst the excessive showed the reverse trend. They were however, unable to find
swelling during pervaporation with some of the membranes tested any correlation between estimated fractional free volumes in the
lead to a loss of performance by causing the separation factor to membranes and the resultant performance. Li and Lee [59] also
decrease much below that attainable using the same membrane for looked at different polyimides formed from one dianhydride and
vapour permeation. They did not report any flux data, instead focus- various diamines. The dianhydride they selected was 3,3 ,4,4 -
ing on permeance which complicates comparison with other work. benzhydrol tetracarboxylic dianhydride (BHTDA) and three
Yanagishita et al. [53] used phase inversion to produce asym- diamines, 1,4-bis(4-aminophenoxy)-2-tert-butylbenzene (BATB),
metric polyimide membranes. After testing they determined that 1,4-bis(4-aminophenoxy)-2,5-di-tert-butylbenzene (BADTB), and
the optimal time and conditions for annealing was 3 h at 300 ◦ C. 2,2 -dimethyl-4,4 -bis(4-aminophenoxy)biphenyl (DBAPB). They
Annealing at higher temperatures was found to damage the poly- reported the optimum membrane performance was achieved with
imide structure. They concluded that the best composition for a BHTDA-DBAPB polyimide-based membrane and in general the
membrane formation was a solution comprising of 25 wt% poly- fluxes were much greater than achieved by Xu et al. but separation
imide, 37.5 wt% dimethylformamide (DMF) and 37.5 wt% dioxane factors were lower.
to produce a membrane with good separation factor and high flux.
Both the flux and separation factor were found to increase with 2.1.6. Polyamides
increasing operating temperature. Polyamides are another range of relatively heat resistant poly-
Qiao et al. used the commercially available P84 co-polyimide mers, the most commonly known of which is Nylon which itself
(BTDA-TDI/MDI, copolyimide of 3,3 4,4 -benzophenone tetracar- has a number of forms depending on the exact monomers used
boxylic dianhydride and 80% methylphenylene-diamine + 20% in the polymerization. Since its initial discovery, a whole range of
methylene diamine) (HP Polymer GmbH, Austria) for a range of polymeric amides with numerous different properties have been
work in the pervaporative dehydration of alcohols. Initial work discovered. The pervaporation performance in alcohol dehydration
[54,55] utilised P84 in IPA dehydration as they identified ethanol of the polyamide-based membranes reviewed in this section can
caused excessive swelling. They found thermal annealing of the be found in Table 7. The tabulated performance data is also shown
membranes improved performance by reducing a number of graphically in the logarithmic plot in Fig. 8.
defects in the membrane skin layer thus vastly improving the sep- Nylon-4 was used by Lee et al. [60] onto which they tried
aration factor. They then went on to look at modifying P84 using plasma-grafting PVA to improve the membrane’s hydrophilicity.
diamine cross-linking with two diamines, p-xylenediamine and They demonstrated that plasma grafting did indeed improve mem-
ethylenediamine (EDA) [56] and showed low-cross-linking time brane performance, increasing both the flux and the separation
increased the separation factor, after which, increased swelling factor. A plasma power of 10 W and operating time of 10 min was
from the amide groups formed, decreased the separation factor found to densify the membrane top layer however, further increase
again. Low-temperature thermal treatments were found to pro-
duce membranes with a high flux and moderate separation factor
whilst high-temperature treatments produced membranes with
high-separation factors but lowered the fluxes attained.
Recently, Wang et al. [57] produced polyimide membranes
based on 3,3-bis[4-(4-aminophenoxy)phenyl] phthalide (BAPP).
They produced membranes by first reacting BAPP with a dianhy-
dride in a polycondensation reaction in N,N-dimethylacetamide.
The resultant polyimide was dissolved in N-methylpyrrolidinone
(NMP) to form a 10 wt% polymer solution, cast onto a glass plate
using a Gardener knife before being placed into an oven for 3 h
at 80 ◦ C to evaporate off the NMP. The membrane was taken and
placed under vacuum for a further 48-h to remove all traces of sol-
vent. They found that permeation rate increased with the addition
of bulky groups to the polymer backbone. Solubility parameters
suggested that the polyimide membranes would show a higher
affinity for alcohols over water due to the presence of all the
hydrophobic groups on the polymer backbone. The diffusivity of
water across the membrane however was much greater than that
of ethanol and thus the membranes were water selective. The Fig. 8. Graphical representation of membrane performance data presented in
best membrane performance was seen using a 3,3 ,4,4 -biphenyl Tables 7 and 8.
Table 7
Dehydration of alcohols using polyamide-based membranes
Binary mixture (mass ratio) Membrane support Separation layer Cross-linker/modification Separation factor Flux (kg m−2 h−1 ) Temperature (◦ C) Reference
EtOH/H2 O (90:10) Nylon-4 Nylon-4 – ≈4.5 ≈0.35 25 [60]

EtOH/H2 O (90:10) Nylon-4 Nylon-4/PVAc PVA grafted, NaOH hydrolysis ≈13 ≈0.40 25 [60]
EtOH/H2 O (90:10) Nylon-4 Nylon-4/PVA PVA grafted 13.5 0.42 25 [60]
EtOH/H2 O (90:10) PASA PASA – 1984 0.007–0.034 20 [62]
in power caused cracks to appear on the surface, resulting in the ically charged groups and the nature of the counter ion attracted
flux increasing but the separation factor being reduced. NaOH was to them. Negatively charged polyelectrolytes are cation-exchange
used to hydrolyze the polyvinyl acetate (PVAc) which they showed membranes and are capable of exchanging positively charged ions
marginally decreased the overall performance. The separation fac- such as metal ions. Positively charged polyelectrolytes are anion-
tor achieved with these modifications was low at 13.5 and thus the exchange membranes. These membranes are often referred to as
separation potential of the resultant membrane was not great. ion-exchange membranes and the nature of the counter ions bal-
Chitosan was used together with N-methylol Nylon-6 by Shieh ancing the charge on the polymer can influence the behaviour of
and Huang [61] produced blend membranes using solutions of the the material, a useful technique for modifying the characteristics of
two polymers. By varying the composition of the blend they adjust a membrane. The pervaporation performance in alcohol dehydra-
the hydrophilicity of the membrane. They also used a sulphuric tion of the polyelectrolyte membranes reviewed in this section can
acid treatment on the cast membranes to produce ionic cross- be found in Table 8. The tabulated performance data is also shown
linking in the chitosan which they found significantly improving the graphically in the logarithmic plot in Fig. 8.
overall performance. The separation factor increased with increas- Ihm and Ihm [63] prepared membranes by the plasma grafting
ing chitosan content in the membrane whilst the permeability of of styrene onto the surface of PVDF, then modified them by sul-
water decreased up to 40 wt% chitosan content and then remained fonation and then ionization and looked at the performance of the
constant whilst ethanol permeability continued to decrease. The different membranes. They found that with each modification, the
membranes produced were 20–40 ␮m thick, however since all permeation rate increased whilst the separation factors of the dif-
data reported was in terms of permeabilities, the actual achievable ferent membranes did not vary much with the grafted, sulfonated,
fluxes may only be estimated based on this thickness range. and then ionized Na+ membrane. This comparison of performance
Chan et al. [62] carried out pervaporation experiments through with each subsequent modification is a useful indication of the
membranes comprising of different poly(amide-sulfonamides) performance gains vs a more complicated membrane prepara-
(PASA’s). They found that the best separation factor was achieved tion procedure, however the feed compositions they worked at
with a membrane based on N,N ,-bis(4-aminophenylsulfonyl)-1,3- contained high-starting water concentrations of 20 or 65 wt%.
diaminopropane and isophtthaloyl chloride. However since they Attempting to dehydrate feeds of a higher ethanol concentration
produced dense membranes by solvent evaporation the fluxes for would have allowed their data to be better compared to other
all of the membranes prepared were very low in the region of research. In another study, using metal-ion-exchanged membranes,
0.007–0.034 kg m−2 h−1 . It would be interesting if they had tested Rhim et al. [64] worked with poly(vinyl alcohol)/sulfosuccinic acid
immersion precipitation as an alternative to solvent evaporation (PVA/SSA) membranes in which they converted the hydrogen form
to investigate if they could improve the membrane flux without to monovalent Li+ , Na+ and K+ forms and tested the different mem-
sacrificing the separation factor. branes for pervaporation of a 10/90 water/ethanol mixture at 30,
40 and 50 ◦ C. They found that the Li+ membranes swelled most
2.1.7. Polyelectrolyte membranes and the K+ least and that the Na+ gave the lowest flux and highest
These membranes contain an electrolyte group which disasso- separation factor.
ciates when dissolved forming a charged polymer. The property of Nafion hollow fibres were loaded with various cations and used
the polyelectrolyte material depends on the presence of these ion- for pervaporation experiments by Cabasso and Liu [65]. They found
Table 8
Dehydration of alcohols using polyelectrolyte membranes
EtOH/H2 O (80:20) PVDF g-PSS-Na+ Plasma grafting 35 3.1 50 [63]

EtOH/H2 O (90:10) PVA/SSA PVA/SSA-Na+ Aqueous solution containing Na+ 44 0.06 50 [64]
EtOH/H2 O (90:10) PVA/SSA PVA/SSA-Li+ Aqueous solution containing Li+ 39 0.07 50 [64]
EtOH/H2 O (90:10) PVA/SSA PVA/SSA-K+ Aqueous solution containing K+ 42 0.06 50 [64]
EtOH/H2 O (94.8:5.2) Nafion 811-Li+ Nafion 811-Li+ Aqueous solution containing Li+ 11.4 1.644 29 [65]
EtOH/H2 O (94.8:5.2) Nafion 811-H+ Nafion 811-H+ Aqueous solution containing H+ 11.6 1.437 29 [65]
EtOH/H2 O (94.8:5.2) Nafion 811-Na+ Nafion 811-Na+ Aqueous solution containing Na+ 14.8 1.257 29 [65]
EtOH/H2 O (94.8:5.2) Nafion 811-K+ Nafion 811-K+ Aqueous solution containing K+ 36.5 0.997 29 [65]
EtOH/H2 O (94.8:5.2) Nafion 811-Ca2+ Nafion 811-Ca2+ Aqueous solution containing Ca2+ 19.5 1.041 29 [65]
EtOH/H2 O (94.8:5.2) Nafion 811-Al3+ Nafion 811-Al3+ Aqueous solution containing Al3+ 3.6 0.317 29 [65]
EtOH/H2 O (90:10) Polypropylene PAA Plasma grafted ≈4.9 ≈0.175 24 [66]
EtOH/H2 O (90:10) Polypropylene PAA (Li+ counter ion) Plasma grafted, ion exchanged ≈8.0 ≈0.160 24 [66]
EtOH/H2 O (90:10) Polypropylene PAA (Na+ counter ion) Plasma grafted, ion exchanged ≈6.3 ≈0.215 24 [66]
EtOH/H2 O (90:10) Polypropylene PAA (K+ counter ion) Plasma grafted, ion exchanged ≈5.6 ≈0.380 24 [66]
EtOH/H2 O (90:10) Polypropylene PAA (Ca2+ counter ion) Plasma grafted, ion exchanged ≈5.5 ≈0.220 24 [66]
EtOH/H2 O (90:10) Polypropylene PAA (Al3+ counter ion) Plasma grafted, ion exchanged ≈5.0 ≈1.010 24 [66]
EtOH/H2 O (95:5) PAN hydrolysed PEI/PAA Layer-by-layer deposition 604 0.314 70 [68]
with NaOH
EtOH/H2 O (95:5) PESF PEI/PAA Layer-by-layer deposition 1207 0.140 40 [69]
that mass transfer properties of the membrane could be altered at

any point in the membranes life by loading it with different cations
and that the flux decreased in the following order H > Li > Na > K > Cs
with the reverse true for the separation factor. This technique
is interesting since it allows post-modification after the mem-
brane has been cast to tailor the separation characteristics to those
required in a specific application simply by charging the membrane
with a selected cation. It would be interesting to investigate if per-
formance was maintained after cycling through various cations as
an indication of the membrane stability.
Xu et al. [66] used poly(acrylic acid) grafted polypropylene hol-
low fibre membranes for the pervaporation of ethanol/water. They
found that the separation factor increased with the increasing graft-
ing degree of PAA and the nature of the counter ion also affected the
flux and separation factor decreasing from Li+ > Na+ > Ca+ > K+ >Al3+
with the true opposite sequence for decreasing flux. Cross-linking
was used to increase the packing density of the selective layer in
order to enhance the separation factor, however the separation fac-
tors achieved were still low. When dehydrating a 90 wt% ethanol
feed at 24 ◦ C with a PAA cross-linked membrane with Al3+ as the Table 9.
counter ion, the separation factor was around 5 whilst the flux was
over 1 kg m−2 h−1 , a slightly lower separation factor than the maxi-
mum value of 8 attained from the Li+ membrane but with an order had previously [69] attempted to produce membranes using a PESF
of magnitude higher flux. support structure and reached a similar results, however the lack
Semenova et al. [6] noted that a key disadvantage of using of any surface groups on PESF did not allow good adhesion so they
mobile counter ions is that they wash out of the membrane being believed PAN overall was more suitable.
replaced by the H+ form and therefore altering the membranes
performance with time. This may, however, be overcome by immo- 2.1.8. Polyaniline
bilising the counter ion containing species by grafting them onto Polyaniline (PAni) is a part of a special group of polymers called
the base polymer. Zhu et al. [67] used a recently developed layer- ICP’s, intrinsic conducting polymers that have a range of interesting
by-layer self-assembly technique to produce polyethyleneimine properties. PAni specifically has received a lot of attention since it
(PEI)/polyacrylic acid (PAA) membranes and chitosan/PAA mem- is environmentally stable and has exciting electrochemical, optical
branes on top of a PAN support. Application of polyanion, washing and electrical properties. It is thermally extremely stable and shows
with water, application of a polycation, washing with water and excellent chemical stability. The emeraldine base (EB) form of PAni
repetition of this process allowed the membrane to be assembled. may be protonated with acidic species to form the emeraldine
The use of polymeric anions and cations ensured leaching was not salt (ES) form thus opening up a range of modifications utilising
an issue and they found that if fabrication conditions were well different species to tailor the material to different separation appli-
controlled, only a few applications of the polyanion and polycation cations. The pervaporation performance in alcohol dehydration of
were required. the polyaniline membranes reviewed in this section can be found in
Zhang et al. [68] also prepared polyelectrolyte membranes by Table 9. The tabulated performance data is also shown graphically
a layer-by-layer deposition technique using a PAN support and PEI in the logarithmic plot in Fig. 9.
and PAA. They found that the solvents used during the fabrication The diffusion of alcohol was studied by Ball et al. [70] for acid
process had a significant effect on the performance of the resultant doped PAni membranes and blend membranes with acidic poly-
membrane and that membranes fabricated using PEI dissolved in mers. They showed that the selectivity of the membrane towards
ethanol exhibited a better flux and separation factor than those water was much greater with undoped PAni although the perme-
fabricated with aqueous PEI solutions. The lower swelling caused ability was greatly increased when dopants were used. They then
by ethanol on the PAA layer allowed a thinner and more uniform demonstrated that the properties of doped PAni were not constant
membrane to be formed. They also found the degree of hydrolysis with time since the dopants were prone to leeching out of the mem-
of the PAN support had a large effect on the performance of the final brane during use. Instead, blending PAni with acidic polymers such
membranes when the PEI and PAA layers assembled on top of the as polyamic acid or PAA prevented the leeching out effect although
support were very thin. Potassium hydroxide was found to produce these did not allow such full doping as with low-molecular weight
the most beneficial effect on the results of the final membrane. They dopants and thus the blended membranes possessed performances
Table 9
Dehydration of alcohols using other polymeric materials
EtOH/H2 O (50:50) Polyaniline Polyaniline – >10,000 0.0013 – [71]

EtOH/H2 O (50:50) Polyaniline Polyaniline HCl doped 17 maximum >0.0013 – [71]
IPA/H2 O (90:10) Polyaniline/PAA Polyaniline/PAA – >10,000 0.3 80 [72]
EtOH/H2 O (90:10) PVA PVA Glutaraldehyde, HCl catalysed 77.3 0.095 30 [73]
EtOH/H2 O (90:10) PVA/PAni 0.78:0.22 PVA/PAni 0.78:0.22 Glutaraldehyde, HCl catalysed 18.6 0.035 30 [73]
EtOH/H2 O (50:50) PAN, SStSA, HEMA PAN, SStSA, HEMA Copolymerised 212 0.65 30 [74]
EtOH/H2 O (95:5) Cellulose Octamethyltrisiloxane Plasma grafted 5.1 6.2 25 [75]
in-between those of undoped PAni and doped PAni but exhibited maximum separation factor achieved however was low at 5.1 and
stable performance. Unfortunately some of the work is unclear and occurred at a W/FM where the C:Si ratio was minimum. They con-
statements contradict each other reporting no permeation of one cluded that this plasma parameter was a useful tool to correlate
component and then referring to separation factors of 200 which membrane performance against and thus it would be interesting
clearly implies permeation of both species and thus it is difficult to see this comparison performed in other membrane formation
to understand what can be drawn from the results in the article, utilising plasma grafting where often only the power is varied.
apart from trends. In a previous short communication Ball et al.
[71] had produced on very similar work with similar conclusions, 2.2. Alcohol dehydration using inorganic membranes
they quoted performance data which is detailed in Table 9.
Lee et al. [72] used PAni doped with PAA to cast composite mem- Inorganic materials offer some significant advantages over poly-
branes to use for the dehydration of IPA. The doping with PAA meric ones such as higher chemical and thermal stability than most
increased PAni’s hydrophilicity so that it showed a higher affin- polymeric materials. Thus membranes made from ceramic mate-
ity for water over IPA and thus a high-water selectivity. When a rials can be operated at higher temperatures and in the presence
blend membrane was fabricated containing over 30 wt% PAA, the of solvents that would cause polymeric membranes to fail. They
water content in the permeate was around 100 wt% with an associ- offer a much better mechanical stability and do not swell and thus
ated flux of 0.3 kg m−2 h−1 when dehydrating a 90 wt% ethanol feed achieve a more constant performance with varying feed concen-
at 80 ◦ C. Even at low-water contents, the permeate flux still main- tration. Their ability to operate at higher temperatures with higher
tained a water content over 85 wt%. This indicated PAni as a good fluxes also reduces the required membrane area for operation
stable material for membrane fabrication with the hydrophilic and much below that required for a polymeric membrane. Inorganic
dopant qualities of PAA providing excellent separation potential. supported membranes are much harder than the thin polymer
Naidu et al. [73] used PAni to enhance PVA by dispersing PAni structure of the polymeric membranes; this can cause problems
particles within a PVA network. PAni was synthesised in a dilute with brittleness in some cases. Inorganic materials offer advantages
aqueous PVA solution with various aniline contents to produce such as being chemically inert and therefore better at operating
varying amounts of PAni in the resultant casting solution and with highly reactive compounds present and in harsh solvent envi-
final membrane. Glutaraldehyde was then used to cross-link the ronments.
membranes with HCl catalysing the process. Low-aniline contents
resulted in spherical PAni particles formed in the PVA film, higher
2.2.1. Ceramics
concentrations yielded PAni agglomerates. The free volume in the
Ceramics are very thermally and chemically stable materials
membranes was found to increase with increasing PAni content
with melting points of over 1000 ◦ C and able to operate at a wide pH
with a pure PVA membrane found to have the lowest free vol-
range and in any organic solvent. They are also very hard materials
ume. The PAni present was in the salt from, doped with the acid
offering good mechanical stability. Ceramic membranes often com-
present during synthesis and the increased flux in their presence
prise of multiple layers in a similar way to a composite polymeric
was attributed to the increase in hydrophilicity in the PVA mem-
membrane with a macroporous ceramic support coated with a thin
brane. The performance of the membrane however was likely to be
layer of ceramic powder dispersed solution or sol and are formed
affected over time as leaching out of the HCl dopant changed the
and stabilised by sintering. The pervaporation performance in alco-
hydrophilicity of PAni and thus long-term stability of membrane
hol dehydration of the ceramic-based membranes reviewed in this
performance is questionable.
section can be found in Table 10 and the tabulated performance
data shown graphically in the logarithmic plot in Fig. 10.
2.1.9. Other polymeric membranes
Song and Hong [76] studied the pervaporation of ethanol–water
Chiang and Lin [74] used polyacrylonitrile (PAN) and mod-
mixtures using tubular type ceramic-based membranes with cellu-
ified it by copolymerisation with sodium salt styrene sulfonic
lose acetate (CA) deposited on either the inner or outer side of the
acid (SStSA) and hydroxyethyl methacrylate (HEMA). They found
membrane. SEM photography showed a non-porous active layer
that the copolymerization improved the hydrophilic properties
and an intermediate layer on top of the porous ceramic support.
of PAN and increasing the molar percentages of the SStSA and
HEMA in the polymer synthesis lead to an increase in flux through
the membrane produced from the resultant copolymer but a
decrease in selectivity. They concluded that a polymer solution
with composition of 92.5/3.75/3.75 mol% PAN/SStSA/HEMA pro-
duced a polymer that, once used to fabricate a membrane, offered
the best pervaporation performance as a balance of flux and sepa-
ration factor. The performance of the membranes reviewed in this
section are also detailed in Table 9 and Fig. 9, together with the
polyaniline membrane performance data described in the previous
section.
Matsuyama et al. [75] produced a composite plasma poly-
merized membrane from octamethyltrisiloxane (C8 H24 O2 Si3 )
deposited on cellulose. They used a plasma parameter W/FM
where W was the power input in Watts, F the monomer flow
rate (g m−2 min−1 ) and M the monomer molecular weight which
the deposition rate was directly proportional to. They showed
that increasing this parameter increased both the degree of cross-
linking and the amount of oxygen incorporated into the polymer.
They also correlated this parameter to the membranes perfor-
mance with increase in W/FM decreasing the permeation rate as Fig. 10. Graphical representation of membrane performance data presented in
would be expected with increasingly cross-linked membranes. The Table 10.
Table 10
Dehydration of alcohols using ceramic membranes
Binary mixture (mass Membrane support Separation layer Separation factor Flux (kg m−2 h−1 ) Temperature (◦ C) Reference
ratio)
EtOH/H2 O (96:4) Ceramic tubular support Cellulose acetate 4–11 – 25–65 [76]
IPA/H2 O (95.6:5.4) Ceramic tubular support Cellulose acetate 8–240 – 25–65 [76]
IPA/H2 O (95:5) ␥-Alumina Silica 100 1.0 70 [77]
n-Butanol/H2 O (95:5) ␥-Alumina Silica 250 3.0 75 [77]
MeOH/H2 O (91:9) ␥-Alumina Silica 10–15 0.2 60 [78]
MeOH/H2 O (98:2) ␥-Alumina Silica 200 0.06 60 [78]
EtOH/H2 O (91:9) ␥-Alumina Silica 50 0.35 70 [78]
EtOH/H2 O (98:2) ␥-Alumina Silica 160 0.15 70 [78]
IPA/H2 O (95:5) ␥-Alumina Silica 500 0.25 70 [78]
IPA/H2 O (90:10) ␣-Alumina Silica 73 0.65 80 [79]
IPA/H2 O (90:10) ␣-Alumina Silica/zirconium 10 mol% 300 0.86 80 [79]
IPA/H2 O (90:10) ␣-Alumina Silica/zirconium 30 mol% 27 0.67 80 [79]
IPA/H2 O (90:10) ␣-Alumina Silica/titanium 10 mol% 400 0.78 80 [79]
IPA/H2 O (90:10) ␣-Alumina Silica/aluminium 10 mol% 210 0.08 80 [79]
IPA/H2 O (90:10) ␣-Alumina Silica/aluminium, 90 0.31 80 [79]
magnesium 10 mol%
2-Butanol/H2 O (95:5) ␣-Alumina Silica 360 0.76 80 [79]
2-Butanol/H2 O (95:5) ␣-Alumina Silica/zirconium 10 mol% 360 0.61 80 [79]
2-Butanol/H2 O (95:5) ␣-Alumina Silica/titanium 10 mol% 190 1.16 80 [79]
n-Butanol/H2 O (95:5) Ceramic and ␥-alumina Silica 1200 2.9 80 [81]
t-Butanol/H2 O Pervap SMS Pervap SMS 144 3.5 60 [82]
(90:10)
t-Butanol/H2 O SMART NaA SMART NaA 16,000 1.5 60 [82]
(90:10)
IPA/H2 O (91.8:8.2) Pervap SMS Pervap SMS 53 1.9 70 [83]
IPA/H2 O (90:10) ␣-Alumina and ␥-alumina Silica 1800 1.7 60 [85]
(ECN)
EtOH/H2 O (96.4:3.6) ECN silica membrane ECN silica membrane 350 ≈1.6 70 [86]
EtOH/H2 O (95.5:4.5) ECN silica membrane ECN silica membrane 208 ≈1.3 71 [86]
IPA/H2 O (95.5:4.5) ECN silica membrane ECN silica membrane 1150 ≈1.9 80 [86]
EtOH/H2 O (89.7:10.3) Mitsui (A-type zeolite) Mitsui (A-type zeolite) 18,000 1.12 70 [87]
IPA/H2 O (89.6:10.4) Mitsui (A-type zeolite) Mitsui (A-type zeolite) 30,000 1.58 75 [87]
EtOH/H2 O (89.9:10.1) Mitsui (T-type zeolite) Mitsui (T-type zeolite) 1000 0.91 70 [87]
IPA/H2 O (89.8:10.2) Mitsui (T-type zeolite) Mitsui (T-type zeolite) 9000 2.10 75 [87]
EtOH/H2 O (89.7:10.3) ECN silica membrane ECN silica membrane 60 2.33 70 [87]
IPA/H2 O (89.8:10.2) ECN silica membrane ECN silica membrane 90 2.76 75 [87]
EtOH/H2 O (89.0:11.0) Pervatech amorphous Pervatech amorphous silica 160 2.00 70 [87]
silica
IPA/H2 O (90.2:9.8) Pervatech amorphous Pervatech amorphous silica 190 2.55 75 [87]
silica
IPA/H2 O (90:10) Pervatech ‘PVP’ silica Pervatech ‘PVP’ silica Not reported 1.3 40 [88]
membrane membrane
membrane membrane
membrane membrane
EtOH/H2 O (90:10) ␣-Alumina PVA ≈56 ≈0.33 50 [90]
They reported that the flux increased with temperature but found a 3-month period. However, all testing was performed using one
when using membranes with CA deposited on the inner surface, membrane and therefore it is difficult to identify how reproducible
the separation factor was also found to increase with tempera- the membrane preparation process was to obtain similar perfor-
ture with the pure water flux increasing more than the alcohol mance in subsequent membranes.
flux with increasing temperature. They did not clearly state flux Sekulić et al. [79] attempted to improve existing microporous
data for dehydrating solvent mixtures and separation factors were silica membranes to produce a membrane with enhanced thermal
low for ceramic-based membranes at a maximum of 12. They con- and separation capabilities to increase the number of applications
cluded that operation at high temperature was therefore advisable which the membrane may be used for in industry. They aimed
to optimize performance and minimize membrane costs. to increase the operating range at high pH and high tempera-
Cuperus and van Gemert [77,78] produced tubular ceramic silica ture by replacing the ␥-alumina layer with mesoporous titania.
membranes and performed the dehydration of a number of differ- They also looked at improving the chemical stability of microp-
ent mixtures including IPA, butanol and acetic acid. They concluded orous silica by the addition on Al2 O3 , TiO2 or ZrO2 . They found that
that ceramics were suitable for the dehydration of all the mixtures doping with these oxides slightly improved chemical stability. The
tested and that operation with a sufficient Reynolds number so flux was greatly reduced when Al was present, but the rest were
that the feed was turbulent provided optimum separation condi- similar to silica. They concluded that further investigation was nec-
tions. This was attributed to the turbulent flow reducing the effect essary to understand how doping affects the microstructure of the
of concentration polarization. They found the ceramic membranes membranes. However the separation performances achieved were
to be quite stable and no noticeable decrease in performance over encouraging. Sekulić et al. [80] then used titania sols, deposited
on flat ␥-alumina mesoporous ␣-alumina discs to produce micro- study in-terms of comparing the ceramic and zeolitic membranes.
porous titania membranes with a pore size of around 0.9 nm for The results for the membranes tested in dehydrating ethanol and
pervaporation and nanofiltration. They did not perform much test- IPA can be found in Table 10 but data for additional solvents can be
ing on the membranes for pervaporation but did conclude that found in the original journal.
they were water selective and therefore suitable for dehydrating A microporous silica membrane from Pervatech was also tested
organics. for the dehydration of isopropanol by Casado et al. [88]. They
Silica based ceramic hollow fiber membranes were produced detailed an exponential dependency between the water flux and
by Peters et al. [81] who tested them for the dehydration of n- the activity of the water in the feed and hence that operation at
butanol. The membrane was prepared by coating am ␥-Al2 O3 layer higher temperatures showed a markedly improved flux with only a
on ceramic hollow fiber supports as an intermediate layer on which slight reduction in the overall water content in the permeate which
a silica separation layer was then coated by dip coating in a poly- still remained around 99.5 wt%. They used the data collected to
meric silica sol. They found that the membranes have a high flux develop a model which could be used to aid the design of a larger
when dehydrating an n-butanol mixture but also noted that the industrial-scale dehydration plant using the Pervatech membranes.
flux and separation factor of the membrane decreased somewhat Urtiaga et al. [89] then went on to develop their own perva-
over time but since overnight running of the apparatus was not poration membranes prepared by a sol–gel hot-coating method.
possible this complicated long-term testing with constant starting Several solutions were produced containing tetra-ethoxy silane and
and stopping during operation and thus made it hard to analyze the zirconium tetra-ethoxy silane and zirconium tetra-n-butoxide as
significance of this reduction. They also tested the membranes for pre-cursors to produce SiO2 –ZiO2 -50% membranes. A cloth soaked
the dehydration of DMF with similar results. with a diluted solution of one colloidal sols was then allowed to con-
Gallego-Lizon et al. [82,83] looked at a range of commercially tact the substrate which was heated to a temperature of 160–180 ◦ C
available polymeric and inorganic membranes and tested them for causing a very thin layer to be applied each time with simultaneous
t-butanol and IPA dehydration. They tested the microporous silica coating and drying and then being heated at 450 ◦ C in a furnace for
Pervap SMS membrane from Sulzer Chemtech and the Zeolite NaA 10–20 min. This was then repeated several times for each colloidal
membrane from the SMART Chemical Company as well as two poly- sol solution in succession. They then compared the results to those
meric membranes available from Sulzer Chemtech. They studied attained when using commercially attained samples of silica-based
the effect of temperature and found, as expected, larger fluxes for membranes from Pervatech and Sulzer. There was some variation
all the membranes tested. These are useful studies as they showed in membrane performance from one membrane to another how-
the performance of what purported to be industrially available ever all the membranes tested produced permeates with a water
ceramic membranes thus allowing a reader to get an understanding content of 95 wt% water or greater over the range of water con-
of the real-world performance. These membranes, however, have centrations and temperatures studied, indicating good membrane
not reached the market due to production problems from Sulzer performance is achievable. They reported higher water fluxes than
Chemtech and the SMART chemical company have since ceased in either of the commercial membranes however there were some dif-
trading. ferences in the experimental test conditions thus the Pervatch and
Verkerk et al. [84,85] tested a commercially available membrane Sulzer membranes should be re-tested under identical conditions
from ECN for the dehydration of IPA and n-butanol. They found to allow a fairer comparison.
the fluxes to be generally much higher than those attainable with An inorganic substrate of ␣-alumina was used by Peters et al.
polymeric membranes (0.4–2.8 kg m−2 h−1 ) and separation factors [90] on which they then built up layers of ␥-alumina to produce a
ranged from 300 to 1800 when dehydrating various alcohols. Van smooth surface on which they could then deposit an extremely thin
Veen et al. [86] also tested the same membrane finding it to offer layer of PVA, only 0.5–0.8 ␮m thick. The hybrid organic/inorganic
many advantages over polymeric membranes giving an extremely membrane achieved good separation performance when dehydrat-
constant operation over several weeks and allowing operation at ing a range of different alcohols, unlike PVA alone, swelling did not
much higher temperatures than polymeric membranes can be used become an issue which they believed could be due to the interac-
at (up to 300 ◦ C) giving much higher fluxes whilst retaining a high- tions of the thin layer with the inorganic substrate, mechanically
separation factor. This in turn means that the required membrane preventing swelling from occurring. It would be interesting to take
area can be vastly reduced. They look at a case study of dewatering other polymeric materials and blends that have shown encourag-
a 30,000 l/day stream of 95% ethanol to 99.9% ethanol and calcu- ing performance when tested as dense membranes but low fluxes
lated that around 1000 m2 of polymeric membranes at 80 ◦ C would and identify if a much thinner layer could possibly form a more
be required to perform the task whilst only 100 m2 of ceramic balanced membrane.
membranes would be required at the same temperature with this
required area dropping down to a few m2 when the temperature is 2.2.2. Zeolites
increased by 100 ◦ C. Obviously, this temperature rise has associated Zeolites (aluminasilicates) offer a good basis for a separation
costs but would be offset by a large reduction in capital costs for material due to their highly ordered well-defined structures. Their
purchasing the membrane and the ceramic membranes also have structure leaves micropores which can vary in size depending on
longer operating lives than polymeric membranes. the exact type of zeolite with their framework containing alu-
Ceramic and zeolite membranes were compared by Sommer minium, oxygen and silicon. A wide number of different zeolite
and Melin [87]. They tested five different types of commercially structures exist with different aluminium to silica ratios and with
available inorganic membrane which included A and T type zeo- pore sizes ranging from about 3–8 Angstroms. Type A Zeolites
lite membranes from Mitsui and microporous silica from ECN and form a 3D structure and contain cations thus making them very
Pervatech. They tested all four membranes for over 30 solvent dehy- hydrophilic. As with polyelectrolytes, the cation present is respon-
drations and came up with the general conclusion that the ranking sible for the properties of the material. A potassium (K+ ) ion
of the membranes in terms of separation factor decreased from containing zeolite is 3A, Na+ type 4A and Ca2+ type 5A. Other types
Zeolite A > Zeolite T > Pervatech silica > ECN silica across all solvents of zeolites have a 2D structure such as ZSM-5 and silicalite is entirely
tested. However in the ranking in terms of the flux, the order was made from silica and oxygen with no aluminium present. The per-
reversed. They found the chemical stability of all the tested mem- vaporation performance in alcohol dehydration of the zeolite-based
branes in aprotic solvents to be excellent and was an interesting membranes reviewed in this section can be found in Table 11 and
Table 11
Dehydration of alcohols using zeolite-based membranes
Binary mixture (mass ratio) Membrane support Separation layer Separation factor Flux (kg m−2 h−1 ) Temperature Reference
(◦ C)
EtOH/H2 O (95:5) UV-irradiated TiO2 Zeolite A Up to 54,000 0.86 45 [92]

coated metal
EtOH/H2 O (90:10) ␣-Alumina Zeolite A 10,000 2.15 75 [93]
EtOH/H2 O (90:10) ␣-Alumina Zeolite X 360 0.89 75 [93]
EtOH/H2 O (90:10) ␣-Alumina Zeolite Y 130 1.59 75 [93]
EtOH/H2 O (90:10) ␣-Alumina Zeolite T 830, 4400 0.81, 0.60 75 [93]
EtOH/H2 O (95:5) Mullite, Al2 O3 , NaA Zeolite >5000 2.35 95 [94,95]
cristobalite
EtOH/H2 O (90:10) ␣-Alumina Al2 O3 :SiO2 :Na2 O:H2 O 1:2:2:120, zeolite NaA 10,000 2.15 75 [96]
EtOH/H2 O (95:5) ␣-Alumina Al2 O3 :SiO2 :Na2 O:H2 O 1:2:2:120, zeolite NaA 16,000 1.10 75 [96]
MeOH/H2 O (90:10) ␣-Alumina Al2 O3 :SiO2 :Na2 O:H2 O 1:2:2:120, zeolite NaA 2100 0.57 50 [96]
MeOH/H2 O (95:5) ␣-Alumina Al2 O3 :SiO2 :Na2 O:H2 O 1:2:2:120, zeolite NaA 2500 0.23 50 [96]
n-Propanol/H2 O (95:5) ␣-Alumina Al2 O3 :SiO2 :Na2 O:H2 O 1:2:2:120, zeolite NaA 18,000 1.91 75 [96]
IPA/H2 O (95:5) ␣-Alumina Al2 O3 :SiO2 :Na2 O:H2 O 1:2:2:120, zeolite NaA 10,000 1.76 75 [96]
the tabulated performance data shown graphically in the logarith- ingly full of ethanol, allowing an increase in the ethanol permeation
mic plot in Fig. 11. across the membrane.
Chau et al. [91] studied the importance of the preparation of the Tanaka et al. [93] used Zeolite T membranes hydrothermally
support before trying to grow zeolites showing that the presence of synthesized on an ␣-alumina support to enhance an esterification
carbon deposit or other surface contaminants have a detrimental reaction between ethanol and acetic acid. They tested A, X, Y and T
effect on zeolite nucleation. Seeding reduces the effect of surface type zeolites for ethanol dehydration as part of their research build-
chemistry on zeolite formation allowing immediate zeolite growth ing towards investigating the enhancement of the esterification of
and also allows the deposition of zeolites onto a wider range of sup- acetic acid. Their studies indicated that type T zeolite membranes
port materials. They found that by surface coating the support with not only offered desirable separation properties for the dehydration
a thin metal or metal oxide layer, they could control the number and of alcohols but were also stable in acetic acid and could be used in
type of nucleation sites available on the support surface and this reaction enhancement, driving water forming reversible reactions
allowed for better reproducibility. Such a technique was employed such as esterifications.
by van den Berg et al. [92] where Zeolite A membranes were synthe- Kondo et al. [94] prepared tubular NaA Zeolite membranes by
sized on a UV-irradiated TiO2 coated metal support. Zeolite A was growing them hydrothermally on a tubular support. They tested
chosen as it is a very hydrophilic material since it has a low-Si/Al various different tubular supports to determine which produced
ratio. The increase in Ti-OH groups caused by the UV irradiation the best membrane performance. A gel was prepared consisting
improved the hydrophilicity of the support and so improved the of sodium silicate, aluminum hydroxide, sodium hydroxide and
interaction between the Zeolite A providing better attachment to deionised water. The tubular supports on which the zeolites were to
the support. They did however have problems with reproducibility be grown were polished using SiC paper and coated with the zeolitic
between different batches of membranes which they attributed to seed crystals. The support was then placed in the prepared gel and
flaws in the support structure. They calculated that for small defect hydrothermal treatment performed for 3.5 h at 100 ◦ C, removed and
sizes in the support (<1.6 nm) only water would be present inside dried. The permeability was found to increase with an increase in
the defect but for larger defect pore sizes, ethanol may also enter the alumina content in the support material and reached a constant
the pore. They thus explained that at lower water concentrations, at around 70 wt% Al2 O3 . They showed that high-separation factors
the selectivity decreased as these larger pores that were filled with were achievable when the water content was 5–10 wt% however
water when operating at a high-water content became increas- these dropped considerably when reaching 1 wt%. They do not offer
any real explanation for the large decrease at lower water concen-
trations although this agrees with the observations of van den Berg
et al. [92]
The first industrial use of zeolite membranes in industry was
reported by Morigami et al. [95] in a pervaporation plant producing
420 kg h−1 of 99.8 wt% ethanol. The plant reduces the water content
down from 10 to 0.2 wt%, operating at 120 ◦ C and consists of 16
modules each containing 125 lengths of zeolite membrane each
with an effective surface area of approximately 0.003 m2 giving a
total membrane area of about 5.8 m2 . The membrane was produced
in the same way as Kondo et al. [94] by growing the NaA zeolite
hydrothermally on the surface of a porous support which was then
removed after 3–4 h of treatment. The plant performed to or above
design specifications and the performance of the membranes was
tested over 400 h for ethanol dehydration and appeared constant
showing no signs of flux decrease. This is a good indication that
the method used by Kondo et al. is reproducible since they have
been able to synthesize enough tubes for industrial use and this
membrane system may be viable industrially.
Fig. 11. Graphical representation of membrane performance data presented in Okamoto et al. [96] worked with Zeolite NaA membranes on an
Table 11. ␣-alumina support and assessed the membranes performance in
dehydrating ethanol, methanol and dioxane. They proposed that Poly(dimethyl siloxane) (PDMS) was used by Jia et al. [99] to
water passed through the membrane by capillary condensation prepare zeolite filled membranes using zeolite silicalite-1 and pro-
through both zeolitic and non-zeolitic pores. This shows that defect duced both a thick film type and a composite type by dip coating
formation during membrane formation was unavoidable, however a thin active layer on top of a polyetherimide membrane support.
the presence of these defects only became noticeable in membrane They had problems of trying to disperse and keep stable zeolite
performance at low-water contents and they again explained this crystals in the polymer solution which was necessary to produce
by the same rational used by van den Berg et al. [92]. The sep- an effective membrane. They found that to achieve this it was nec-
aration factors achieved were not as great as those achieved by essary to use ultrafine silicalite crystals (<0.5 ␮m) and to slightly
other researchers using type T zeolites but the overall fluxes were pre-polymerize the PDMS solution to increase the solution viscos-
greater which follows the trend reported by Sommer and Melin ity. The resultant membrane however did not have a particularly
[87]. high flux or separation factor compared to membranes produced
Recently the application of zeolite membranes in pervaporation more recently.
was studied in detail in a review by Bowen et al. [97]. They looked at Kittur et al. [100] also used PVA but utilizing the hydrophobic
the characterization and synthesis of different zeolite membranes ZSM-5 zeolite. They found that 6 wt% zeolite gave the greatest sep-
including the hydrophilicity and hydrophobicity of different zeo- aration factor and attributed this to the reduction in free volume
lites and their suitability for different applications. They also looked available for diffusive transport. They also found that the degree
at different methods of measurement of adsorption and diffusion of swelling decreased with increasing zeolite loading and thus flux
through the membranes. They reviewed the various different areas is decreased, however overall the PSI increased with ZSM-5 load-
in pervaporation using zeolites that have successfully been applied ing up to 6 wt%. Increasing the feed temperature, as commonly is
to and studied examples of each before concluding by looking at observed, increased the trans-membrane flux but caused a decrease
the future challenges and advancements in this research area. in separation factor. More recently, Kittur et al. [101] used chi-
tosan together with NaY type zeolite to produce another mixed
2.3. Alcohol dehydration using mixed matrix membranes matrix membrane. They found that both flux and separation fac-
tor increased simultaneously with increasing NaY content. They
Mixed matrix membranes consist of a polymeric base mem- attributed this to the increase in hydrophilicity achieved due to
brane through which an inorganic material is dispersed and locked the presence of the hydrophilic zeolite improving the flux and the
into the polymer matrix. The addition of the inorganic material can molecular sieving qualities of the zeolite, inhibiting solvent trans-
help strengthen the mechanical properties of the membrane and port, improving the separation factor. Of the membranes tested, the
reduce the free volume through which molecules may diffuse. A chitosan membrane containing 40 wt% zeolite offered the best per-
summary of the performance data of the membranes described in formance when dehydrating IPA containing 5 wt% water at 30 ◦ C
this section can be found in Table 12 and the tabulated performance although operating at higher temperatures lead to a decrease in
data shown graphically in the logarithmic plot in Fig. 12. separation factor as increased plasticization of the chitosan allowed
Yeh et al. [98] prepared a nanocomposite membrane consist- the alcohol molecules to permeate more easily.
ing of PVA and clay (Na+ type montmorillonite). The introduction Gao et al. [102] used PVA as the base membrane to prepare
of the clay was hoped to improve the mechanical structure of the mixed matrix membranes filled with KA, NaA, CaA and NaX zeo-
membrane. They found that permeation rate decreased and the lites. They reported that the addition of type A zeolites helped to
separation factor increased with increasing clay content up to 5 wt% facilitate the transfer of water molecules due to their smaller size
clay after which the separation factor drops sharply. They also found compared to ethanol and higher molecular weight alcohols. They
that the heat stability of the composite membrane was greater than noted that flux increased with increasing zeolite loading in the
of PVA. They however only tested their membranes for vapour per- membrane whilst separation factor remained constant up to just
meation and not for pervaporation as well and failed to clearly state over 11 wt% zeolite at which point the separation factor started to
at which temperature(s) they were operating at which reduced the decrease with higher zeolite composition however the separation
value of this research. factors achieved when dehydrating IPA and ethanol were low. Oku-
mus et al. [103] also tested different zeolites only they selected to
use PAN as the base polymer to produce mixed matrix membranes.
They used three different types of zeolite, 3A, 4A and 13X which
were pretreated and added into the PAN casting solution. The mem-
branes synthesized were seen to have three distinct layers, a zeolite
free polymer layer, a zeolite full polymer layer and a skin layer. This
was particularly interesting as they identified the rate-controlling
step during permeation for membranes containing different zeolite
loadings. From 0 to 30 wt% zeolite content they found the perme-
ation rate to be controlled by the zeolite free polymer layer, from 30
to 35 wt% controlled by the hydrophilic corridors of zeolite parti-
cles but above this composition it weakens the membrane structure
resulting in a lack of selectivity. They found membranes contain-
ing 13X offered the highest separation factor, at a zeolite content
of around 32 wt% they found the flux to be around seven times
greater than that achievable with a homogeneous PAN membrane.
They concluded that annealing the membranes at 82 ◦ C optimized
their performance.
PSF was used by Fu et al. [104] for the dehydration of ethanol
and filled with Zeolite 4A and Zeolite 13X. To improve the com-
Fig. 12. Graphical representation of membrane performance data presented in patibility between the organic and inorganic material, they used
Table 12. 3-aminopropyltrimethoxysilane (APTMS) to help eliminate the
Table 12
Dehydration of alcohols using mixed matrix membranes
EtOH/H2 O (95:5) PVA/clay PVA/clay – 58 0.057 Not given [98]

EtOH/H2 O (95:5) PVA/clay PVA/clay – 112 0.039 Not given [98]
EtOH/H2 O (70:30) PDMS/silicalite-1 PDMS/silicalite-1 – 43.6 0.513 22 [99]
EtOH/H2 O (70:30) Polyetherimide PDMS/silicalite-1 – 13.6 0.527 22 [99]
EtOH/H2 O (65:35) Polyetherimide PDMS/silicalite-1 – 16 0.145 22 [99]
EtOH/H2 O (51:49) Polyetherimide PDMS/silicalite-1 – 33.5 0.150 22 [99]
IPA/H2 O (90:10) PVA–2 mass% ZSM-5 PVA–2 mass% ZSM-5 Cross-linked with glutaraldehyde 91.1 0.005 30 [100]
P.D. Chapman et al. / Journal of Membrane Science 318 (2008) 5–37

IPA/H2 O (95:5) Chitosan Chitosan – 422 0.032 30 [101]
IPA/H2 O (95:5) Chitosan with 10 wt% NaY Chitosan with 10 wt% NaY – 729 0.048 30 [101]
IPA/H2 O (90:10) Chitosan Chitosan – 171 0.048 30 [101]
IPA/H2 O (90:10) Chitosan with 10 wt% NaY Chitosan with 10 wt% NaY – 254.9 0.062 30 [101]
EtOH/H2 O (80:20) PVA PVA Thermally cross-linked 15.5 0.183 50 [102]
EtOH/H2 O (80:20) PVA with 11 wt% KA zeolite PVA with 11 wt% KA zeolite Thermally cross-linked 15.5 0.235 50 [102]
EtOH/H2 O (80:20) PVA with 11 wt% NaA zeolite PVA with 11 wt% NaA zeolite Thermally cross-linked 13.8 0.258 50 [102]
EtOH/H2 O (80:20) PVA with 11 wt% CaA zeolite PVA with 11 wt% CaA zeolite Thermally cross-linked 10.4 0.323 50 [102]
EtOH/H2 O (80:20) PVA with 11 wt% NaX zeolite PVA with 11 wt% NaX zeolite Thermally cross-linked 8.5 0.376 50 [102]
IPA/H2 O (80:20) PVA PVA Thermally cross-linked 40 0.140 50 [102]
IPA/H2 O (80:20) PVA with 11 wt% KA zeolite PVA with 11 wt% KA zeolite Thermally cross-linked 40 0.164 50 [102]
IPA/H2 O (80:20) PVA with 11 wt% NaA zeolite PVA with 11 wt% NaA zeolite Thermally cross-linked 36.6 0.172 50 [102]
IPA/H2 O (80:20) PVA with 11 wt% CaA zeolite PVA with 11 wt% CaA zeolite Thermally cross-linked 22.3 0.194 50 [102]
IPA/H2 O (80:20) PVA with 11 wt% NaX zeolite PVA with 11 wt% NaX zeolite Thermally cross-linked 19.4 0.214 50 [102]
EtOH/H2 O (92:8) PAN PAN Thermal annealed 281 0.007 50 [103]
EtOH/H2 O (91.3:8.7) PAN with 25 wt% zeolite X PAN with 25 wt% zeolite X Thermal annealed 35.9 0.054 50 [103]
EtOH/H2 O (91:9) PAN with 32 wt% zeolite X PAN with 32 wt% zeolite X Thermal annealed 51.9 0.088 50 [103]
EtOH/H2 O (93:7) PAN with 40 wt% zeolite X PAN with 40 wt% zeolite X Thermal annealed 3.2 0.369 50 [103]
EtOH/H2 O (91.5:8.5) PAN with 50 wt% zeolite X PAN with 50 wt% zeolite X Thermal annealed 7.1 0.277 50 [103]
EtOH/H2 O (90:10) Polyamide Polyamide – ≈26 ≈0.380 25 [105]
EtOH/H2 O (90:10) Polyamide/SDS-clay Polyamide/SDS-clay – ≈12 ≈0.280 25 [105]
EtOH/H2 O (85:15) 9:1 PVA:PEG, 10 wt% TEOS 9:1 PVA:PEG, 10 wt% TEOS Thermal annealed 12 h, 100 ◦ C ≈46 ≈0.2 50 [106]
EtOH/H2 O (96.5:3.5) q-Chitosan q-Chitosan HCl catalyst to homogenise 726 ≈1.3 × 10−6 40 [107]
EtOH/H2 O (96.5:3.5) q-Chitosan/10 mol% TEOS q-Chitosan/10 mol% TEOS HCl catalyst to homogenise 3098 ≈1.1 × 10−6 40 [107]
EtOH/H2 O (96.5:3.5) q-Chitosan/20 mol% TEOS q-Chitosan/20 mol% TEOS HCl catalyst to homogenise >35,500 7 × 10−7 40 [107]
EtOH/H2 O (96.5:3.5) q-Chitosan/20 mol% TEOS q-Chitosan/20 mol% TEOS HCl catalyst to homogenise 35,480 8 × 10−7 40 [107]
EtOH/H2 O (96.5:3.5) q-Chitosan/20 mol% TEOS q-Chitosan/20 mol% TEOS HCl catalyst to homogenise 30 ≈1.8 × 10−6 40 [107]
EtOH/H2 O (90:10) PVA with 5 wt% APTEOS PVA with 5 wt% APTEOS HCl catalyst to homogenise 1580 0.0265 30 [109]
23
interfacial voids often formed between the two materials and help ducing a viable membrane with fluxes much greater than attained
channel permeation through the zeolitic material rather than pass- previously.
ing though these voids. The permeation rate increased with zeolite
loading and separation factor decreased for both types of zeolites. 3. Dehydration of acetic acid
They found that by using APTMS they could improve membrane
separation, substantially reducing the amount of solvent present Acetic acid is an important compound frequently used in the
in the permeate and hence better utilizing the molecular sieving chemical industry. It has an extremely wide range of uses and is
and hydrophilic qualities of the zeolites. Thus they could improve also formed as an aqueous bi-product in a number of processes
flux and separation factor using PSF filled with zeolite and APTMS such as the production of aspirin. The production of acetic acid
over PSF alone. itself yields water as a bi-product in a number of production pro-
A mixed matrix nanocomposite polyamide and organo-clay (SDS cesses, requiring removal to purify the acetic acid before it can be
clay) membrane was fabricated by Wang et al. [105] who sought used. The relative volatility of acetic acid to water is very close to
to improve the thermal and mechanical properties of a straight unity and thus although it does not form an azeotrope with water,
polyamide membrane. The resultant membranes did attain higher it has traditionally been difficult to separate this mixture. Distilla-
thermal stability and mechanical strength up to 5 wt% SDS clay con- tion occurs with water being taken off as the distillate, this requires
tent and showed a higher separation factor than the pure polyamide a tremendous amount of energy and also requires a large number
membranes when dehydrating a 90 wt% ethanol solution with a of plates and thus a large column if a high-purity acetic acid prod-
slight decrease in the overall permeability. It would be interesting uct (>95 wt%) is required. Azeotropic distillation can still be used
if they had tested the clay with other polymers to show if this was as an alternative to allow an easier separation of the two compo-
effective for modifying the behaviours of other polymers. nents however this leads to impurities and is still an expensive and
Tetrahydroxysilane (TEOS) and poly(ethyleneglycol) (PEG) were energy intensive process. Thus simple distillation to a point where
used by Ye et al. [106] to modify PVA. A PVA:PEG ratio of 4:1 was the water content is around 10 wt% followed by an additional per-
found to produce phase separation in the resultant membranes, a vaporation separation stage is now being considered as a viable
ratio of 9:1 was used to produce a sol with TEOS. TEOS content alternative, capable of offering significant energy savings.
over 15 wt% was found to cause phase separation in the mem- The dehydration of acetic acid however is more difficult than the
branes and 10 wt% was found to optimize water pemselectivity. dehydration of alcohols due to the acidic nature of the compound.
They also investigated the effect of annealing time and tempera- This acidity prevents the use of membranes that have a low resis-
ture and showed that increasing temperature caused a reduction tance to acid such as NaA zeolites and can also damage polymeric
of flux, thus a moderate annealing temperature of 100 ◦ C was membranes over time requiring a more chemically inert material
selected. although the flux declined with annealing time, the sep- to be used for this kind of dehydration. Sulzer Chemtech produce a
aration factor increased rapidly and so 12 h was selected to offer polymeric membrane, Pervap 2205 which they claim is suitable for
a great improvement in membrane selectivity with sacrificing a dehydration of organic acids such as acetic acid with no limitation
great deal of the overall flux. Uragami et al. [107] produced mixed of acetic acid concentration and capable of dehydrating mixtures
matrix membranes of q-chitosan and also used TEOS to reduce initially containing up to 80 wt% water. Sulzer Pervap 2201 was
the degree of swelling. Quaternized chitosan (q-chitosan) shows tested for the dehydration of methanol, ethanol, isopropyl alcohol
a high selectivity to water over ethanol, but as the degree of (IPA) and acetic acid by Van Baelen et al. [110]. They found that the
quaternization is increased, so does the hydrophilicity and thus behaviour of the acetic acid during dehydration resembled that of
also the degree to which the membrane swells during opera- methanol dehydration more closely than IPA despite IPA and acetic
tion. They found that membranes containing a TEOS content of acid possessing similar molecular weights so concluded that the
up to 45 wt% showed an improved selectivity over membranes polarity and functional groups of the species were more important
fabricated from q-chitosan alone, however above this content the than molecular size in determining the separation characteristics.
mixed matrix membranes were found to show a higher degree Aminhabhavi and Toti [111] recently reviewed polymeric mem-
of swelling. The membranes they produced were formed by the branes for acetic acid dehydration summarizing the important
sol gel technique and were dense membranes, they possessed published works from 1990 to 2003. A summary of the performance
extremely high-separation factors tending towards infinity, but had data of the membranes described in this section can be found in
low-permeation fluxes in the region of 0.01 kg m−2 h−1 . It would be Table 13. The performances of the polymeric and inorganic-based
interesting to assess the performance of asymmetric membranes of membranes described in this section are depicted graphically in the
a similar composition to evaluate whether these membranes would logarithmic plot shown in Figs. 13 and 14, respectively.
have achieved higher fluxes whilst retaining a high-separation fac-
tor. 3.1. Acetic acid dehydration using polymeric membranes
Uragami et al. [108] went on to test PVA with oligosilane, a
chain shaped inorganic material in order to reduce the swelling Durmaz-Hilmioglu et al. [112] studied PVA modified with glu-
that occurred when working with pure PVA membranes. They were taldehyde and formaldehyde and its pervaporation performance.
again produced by the sol–gel technique and they found annealing Their article is rather short and lacking in detail but they concluded
at 100 ◦ C under nitrogen was necessary to produce good separa- that cross-linking with glutaldehyde gave a higher separation fac-
tion performance and flux was found to increase whilst membrane tor and lower flux than cross-linking with formaldehyde. However,
selectivity decreased with increasing organosilane content. The they failed to analyse the membranes properly to physically look at
sol–gel process was also applied by Zhang et al. [109] to from mixed the effect the two types of cross-linking on the membrane structure.
matrix membranes based on PVA. They selected ␥-aminopropyl- Kusumocahyo et al. [113] used cross-linked PVA membranes to
triethoxysilane (APTEOS) as an inorganic filler to control swelling dehydrate acetic acid over a range of different feed concentrations.
by bonding with the polymeric material. They then tested the They cast a 10 wt% PVA solution onto glass and left it to dry for 24 h
membranes in the dehydration of IPA and found the optimum before cross-linking. They found that increasing the amount of time
performance occurred at a 5 wt% content of APTEOS which also cor- taken in cross-linking the membrane using a glutaraldehyde/acid
responded to the point the hybrid material was found to be most solution decreased the overall membrane flux whilst the separa-
hydrophilic. The results they attained were much closer to pro- tion factor is increased. They attributed this to the cross-linking
Table 13
Dehydration of acetic acid
Acetic acid/H2 O (90:10) PVA PVA Formaldehyde 5.3 0.145 30 [112]

Acetic acid/H2 O (90:10) PVA PVA Glutaraldehyde 9 0.1 30 [112]
Acetic acid/H2 O (90:10) Nafion (C8 H17 )4 N+ Nafion (C8 H17 )4 N+ Charged membranes 243 0.18 30 [114]
Acetic acid/H2 O (90:10) PVA PVA – 11.61 0.0371 45 [115]
Acetic acid/H2 O (90:10) PVA PVA, polyacrylamide (48% grafted) – 6.17 0.0668 45 [115]

Acetic acid/H2 O (90:10) PVA PVA, polyacrylamide (93% grafted) – 5.63 0.0980 45 [115]
Acetic acid/H2 O (90:10) PVA/PAA PVA/PAA Heat treated 291 0.2 40 [116]
Acetic acid/H2 O (86:14) 4-Vinylpyridine, acrylonitrile 4-Vinylpyridine, acrylonitrile Copolymerised 496.2–58 0.027–0.874 20–70 [117]
Acetic acid/H2 O (90:10) Low-viscosity Na-Alg Low-viscosity Na-Alg – 15.7 0.022 30 [118]
Acetic acid/H2 O (90:10) Low-viscosity Na-Alg Low-viscosity Na-Alg 10 wt% PEG, 5 wt% PVA 40.3 0.0239 30 [118]
Acetic acid/H2 O (90:10) Low-viscosity Na-Alg Low-viscosity Na-Alg 10 wt% PEG, 10 wt% PVA 21 0.0425 30 [118]
Acetic acid/H2 O (90:10) Low-viscosity Na-Alg Low-viscosity Na-Alg 10 wt% PEG, 20 wt% PVA 10.6 0.0739 30 [118]
Acetic acid/H2 O (85:15) PAN Na-Alg, HDM Cross-linked with HDM 161 0.262 70 [119]
Acetic acid/H2 O (85:15) PAN Na-Alg, PVA Cross-linked with PVA 46 0.068 60 [119]
Acetic acid/H2 O (90:10) Na-Alg Na-Alg Glutaraldehyde 15 0.154 40 [120]
Acetic acid/H2 O (90:10) Na-Alg Na-Alg Glutaraldehyde 9 0.269 70 [120]
Acetic acid/H2 O (90:10) Na-Alg, 1 wt% STA Na-Alg, 1 wt% STA Glutaraldehyde ∞ 0.165 40 [120]
Acetic acid/H2 O (90:10) Na-Alg, 1 wt% STA Na-Alg, 1 wt% STA Glutaraldehyde 817 0.349 70 [120]
Acetic acid/H2 O (97:3) Polycarbonate Polycarbonate – Approaching ∞ 0.040 25 [121]
Acetic acid/H2 O (97:3) Polycarbonate Polycarbonate n-Butanol additive Approaching ∞ 0.0855 25 [121]
Acetic acid/H2 O (97:3) Polycarbonate Polycarbonate n-Hexanol additive Approaching ∞ 0.0902 25 [121]
Acetic acid/H2 O (97:3) Polycarbonate Polycarbonate n-Octanol additive 4.2 0.237 25 [121]
Acetic acid/H2 O (97:3) Polycarbonate Polycarbonate n-Decanol additive 1.1 0.385 25 [121]
Acetic acid/H2 O (80:20) TPX TPX – 79 0.088 25 [122]
Acetic acid/H2 O (80:20) TPX/5 wt% Co(acac)3 TPX/5 wt% Co(acac)3 – 114 0.012 25 [122]
Acetic acid/H2 O (97:3) TPX TPX Symmetric 6 0.105 25 [123]
Acetic acid/H2 O (97:3) TPX TPX Asymmetric 5 0.511 25 [123]
25
26
Table 13 (Continued )
Acetic acid/H2 O (97:3) TPX TPX As previous entry with n-butanol additive 2 3.425 25 [123]
Acetic acid/H2 O (97:3) TPX PAA/PEG As previous entry with PAA plasma grafted Approaching ∞ 0.960 25 [123]
Acetic acid/H2 O (90:10) Acrylonitrile-maleic anhydride Acrylonitrile-maleic anhydride – 3.9 0.26 30 [124]
Acetic acid/H2 O (90:10) PVA PVA Cross-linked with malic acid 670 0.048 40 [125]
Acetic acid/H2 O (90:10) PVA/TEOS 2:1 (mass ratio) PVA/TEOS 2:1 (mass ratio) – 36 0.113 30 [126]

Acetic acid/H2 O (90:10) PVA/TEOS PVA/TEOS – 1102 0.025 30 [127]
Acetic acid/H2 O (90:10) PVA/TEOS, 5 wt% NaY zeolite PVA/TEOS, 5 wt% NaY zeolite – 1277 0.041 30 [127]
Acetic acid/H2 O (95:5) Na-Alg Na-Alg – 28.5 0.022 30 [128]
Acetic acid/H2 O (95:5) Na-Alg–5 mass% NaY Na-Alg–5 mass% NaY – 31.0 0.029 30 [128]
Acetic acid/H2 O (90:10) Na-Alg Na-Alg – 16.7 0.034 30 [128]
Acetic acid/H2 O (90:10) Pervap 2205 Pervap 2205 – ≈61 ≈0.33 30 [129]
Acetic acid/H2 O (90:10) PVA/Na-Alg PVA/Na-Alg Glutaraldehyde cross-linked ≈22 ≈0.26 30 [129]
Acetic acid/H2 O (90:10) Pervap 1005 (Sulzer Chemtech) Pervap 1005 (Sulzer Chemtech) Cross-linked 48 0.88 80 [130]
Acetic acid/H2 O (90:10) CMC CF23 (CM Celfa) CMC CF23 (CM Celfa) – 61 16. 80 [130]
Acetic acid/H2 O (90:10) CMC VP43 (CM Celfa) CMC VP43 (CM Celfa) – 43 1.9 80 [130]
Acetic acid/H2 O (90:10) Symplex (GKSS) Symplex (GKSS) – 105 2.1 80 [130]
Acetic acid/H2 O (50:50) ␣-Alumina ZSM-5 – 5 0.084 70 [131]
Acetic acid/H2 O (50:50) ␣-Alumina ZSM-5 NaOH treated 14 0.284 70 [131]
Acetic acid/H2 O (50:50) ␣-Alumina Mordenite – 299 0.614 80 [132]
Acetic acid/H2 O (90:10) ␣-Alumina Mordenite – 50 <0.05 80 [132]
Acetic acid/H2 O (98:2) ␣-Alumina Silicalite-1 (altered to be hydrophilic) Liquid phase oxidation ∞ 0.0002 80 [133]
Acetic acid/H2 O (95:5) Stainless steel (0.5 ␮m pores) Ge-ZSM5 (2-layers) Calcination up to 480 ◦ C 133 0.075 30 [134]
Acetic acid/H2 O (50:50) ␣-Alumina Zeolite T Hydrothermal sythesis 37–86 ≈1.8 75 [93]
Acetic acid/H2 O (90:10) ␣-Alumina Silica – 525 5.9 100 [136]
Acetic acid/H2 O (90:10) ␣-Alumina Silica-zirconia Not stable – – 100 [136]
Acetic acid/H2 O (90:10) ␣-Alumina Silica-titania – ≈2050 2.16 100 [136]
PSI since it reduces the separation factor by the same factor as it

increases the flux, it is however an interesting technique for the
modification of the separation characteristics existing membranes.
Asman et al. [116] looked at using PVA modified with PAA to pre-
pare a flat sheet membrane suitable for the dehydration of acetic
acid by pervaporation. They studied a number of different param-
eters including membrane thickness, operational temperature and
feed composition on the membranes performance characteristics.
They identified that increasing the membrane thickness decreased
the overall flux and more greatly reduced the permeation rate of
acetic acid than that of water, thus improving the separation fac-
tor. They found that increasing the temperature caused an increase
in flux and decrease in separation factor and selected 40 ◦ C as
the optimal operating temperature whilst dehydrating the acetic
acid/water azeotrope. This however is inaccurate as there is no
actual azeotrope. The separation factor decreased with increasing
acetic acid concentration and indicated the membrane perfor-
mance was optimal at low-water concentration. However, the
membrane swelling was also lower in this region. They concluded
Fig. 13. Graphical representation of membrane performance data for polymeric
membranes presented in Table 13. that the optimum ratio of PVA/PAA was 75/25 by volume as this
offered a significantly higher separation factor with only a moder-
ate reduction in flux.
forming a more dense and rigid structure and examined perfor- A copolymer of 4-vinylpyridine and acrylonitrile was synthe-
mance from the azeotropic point up to high-water concentrations. sised by Lee and Oh [117] to prepare a dehydration membrane stable
Kusumocahyo et al. [114] had previously attempted to perform this for use with acetic acid. They believed the 4-vinyl pyridine would
separation with charged Nafion membranes. Here they found that form a complex with acetic acid, providing a catalytic transport
the selectivity of Nafion membranes was improved by charging mechanism so that water molecules are transported preferentially
the membrane with long-chained counter ions. They found this through the complex due to the action of ion-dipole moments. The
also had the effect of reducing the flux across the membrane as pyridine concentration in the polymer and resultant membrane
it reduced the average pore diameter in the membrane and hence was just 1.7 mol% and they achieved a good separation. However
decreased diffusivity in the membrane. Nafion (C8 H17 )4 N+ was they did not attempt to synthesize a pure PAN membrane in an
found to offer the best separation characteristics when dehydrating analogous way or compare directly to previous work using PAN to
a 90 wt% acetic acid mixture at 30 ◦ C. dehydrate acetic acid to attempt to elucidate the improvement in
PVA was grafted with polyacrylamide before being tested for separation offered by using the copolymer over that of the more
acetic acid dehydration by Aminabhavi and Naik [115]. They worked available PAN.
over the entire concentration range of acetic acid and water at 25, 35 Toti et al. [118] used Na-Alg membranes to look at the dehydra-
and 45 ◦ C. They found that increasing the amount of polyacrylamide tion of acetic acid and IPA. They first examined how the viscosity of
grafted onto the membrane increased the flux across the mem- the Na-Alg casting solution affected performance and determined
brane whilst the separation factor is decreased. They attributed this that the low-viscosity blend produced a membrane with the high-
to the interaction between acetic acid and polyacrylamide being est selectivity, probably due to the tighter packing of the polymer
greater than that of acetic acid with PVA and thus causing a rise in chains. They went on to show that by adding PEG with varying
acetic acid in the permeate. Thus although polyacrylamide graft- amounts of PVA, they could enhance the pervaporation characteris-
ing changes the polymers performance, it does not improve the tics of the membrane, increasing the membrane selectivity without
a significant reduction of the flux. A Na-Alg membrane modified
with 10 mass% PEG and 5 mass% PVA achieved the highest separa-
tion factor, although the flux levels achieved with the dense mem-
branes synthesized were all quite low, testing asymmetric mem-
branes of a similar nature would be interesting to identify if the flux
could be improved without significantly reducing the selectivity.
Wang [119] also investigated modified alginate membranes, by
producing composite membranes with 1,6-hexanediamine (HDM)
or PVA and cast onto a PAN support layer. Investigation on the
influence of the counter ion on the separation parameters was also
performed. It was identified that the HDM is the better cross-linker,
offering better separation performance. When looking at counter
cations, K+ was found to give a higher flux, but Na+ a higher sepa-
ration factor. Hydrolysis of the PAN support and increase in HDM
content both showed improvement in both separation factor and
membrane flux.
The use of the inorganic super acid, silicotungstic acid, STA
(H4 SiW12 O40 ) in enhancing the performance of Na-Alg in dehydrat-
ing acetic acid was studied by Teli et al. [120]. Dense membranes
containing the filler were cross-linked using glutaraldehyde with
Fig. 14. Graphical representation of membrane performance data for inorganic- a HCl catalyst prior to testing. The membrane selectivity was
based membranes presented in Table 13. enhanced substantially over pure Na-Alg by the use of the acid with
a low-1 wt% STA content exhibiting excellent separation approach- Isiklan and Sanli [125] used PVA membranes cross-linked with
ing an infinite selectivity whilst maintaining a reasonable flux and malic acid for acetic acid dehydration. They used a 5 wt% solution of
higher STA contents increasing flux whilst lowering the overall PVA and malic acid in water and blended them in different propor-
selectivity. This work was extremely promising showing an excel- tions, allowed the water to evaporate and then used thermosetting
lent separation of acetic acid with relatively high fluxes, it would be at 150 ◦ C to stabilise the membranes. They stated that the mem-
interesting to assess the performance in the dehydration of other branes could be re-used at least 10 times without any problems
organics and whether STA might also work to enhance the perfor- with deformation and no chemical changes visible on successive
mance in other materials. chemical analysis by FTIR. They identified a temperature of 40 ◦ C as
Polycarbonate was used to produce membranes by Huang et giving optimum separation performance and a malic acid concen-
al. [121] who investigated the effect of the additive used during tration of 15 wt% when dehydrating acetic acid containing 10 wt%
casting on the resultant structure and dehydration performance of water. The cross-linking density increased with increasing malic
the polycarbonate membrane. As additives in the casting solution acid content increasing the separation factor with an associated
they used n-butanol, n-hexanol, n-octanol and n-decanol as well as decrease in flux. They also reported data around the azeotropic
fabricating membranes with no additive for comparison. The mem- point for water and acetic acid which is inaccurate since no such
branes cast without an additive present and those with n-butanol azeotrope exists.
and n-hexanol all showed no sign of acetic acid in the permeate Mixed matrix membranes were prepared using PVA and
with fluxes less than 0.1 kg m−2 h−1 . Each of the membranes was tetraethylorthosilicate (TEOS) by Kariduraganavar et al. [126] and
tested dehydrating acetic acid containing 3 wt% water at 25 ◦ C. The used for the dehydration of acetic acid. They utilised the sol–gel pro-
membranes using n-octanol and n-decanol as additives possessed cess to produce a pseudo-homogeneous organic/inorganic solution
higher fluxes but their separation factors were both less than 5. which could then be used to produce membranes by solvent evap-
They tested the durability of the membrane cast using n-hexanol oration. They produced a pure PVA membrane as a control and then
as an additive by pervaporation for 2 months and reported it to be membranes with differing PVA:TEOS ratios. They found the mem-
stable. No acetic acid was detectable in the permeate however the brane swelling decreased with increasing TEOS content and that
flux appeared to be decreasing with time thus bringing long-term optimum performance was obtained when using a membrane com-
stability into question. prising of 1:2 mass ratio of PVA and TEOS and that all membranes
Lee and Wang [122] produced a blend membrane of poly(4- with a ratio greater than 2:1 showed good selectivity towards water.
methyl-1-pentene)/Co(III) (acetylacetonate), TPX/Co(acac)3 . They PVA and TEOS were used by Kulkarni et al. [127] however they
intended to use a glassy type and use the metal salt in order to also assessed the effect of adding NaY zeolite into the sol–gel mix-
promote the transport of water across the membrane. 10 wt% was ture and compared the performance of membranes with those only
found to offer the highest separation factor and it was not found to containing TEOS. They found membrane swelling increased with
dissolve in the acetic acid solution and leach out, thus should be rel- increasing zeolite content however this did not adversely affect
atively stable over time. The main disadvantage of this technique membrane selectivity as this was seen to increase over the whole
is the mobile nature of the salt used, any variation in the feed to water concentration range for increasing zeolite content. Since flux
the membrane could possibly destabilise the salt and reduce mem- also increased with increasing zeolite loading, the membrane with
brane performance over time. Wang et al. [123] continued to use the highest loading rate of 15 wt% zeolite showed the optimum per-
TPX producing asymmetric membranes by immersion precipitation vaporation performance although fluxes attained were still quite
phase inversion. They also investigated the effect of a non-solvent low compared to those achieved by other researchers.
used in casting and found n-butanol to be most effective. The TPX Kittur et al. [128] also used mixed matrix membranes to dehy-
membranes showed high fluxes but poor separation factors. Plasma drate acetic acid selecting to use Na-Alg filled with NaY type zeolite
grafting was subsequently used to add a selective layer of PAA with and investigating how the zeolite concentration in the casting solu-
PEG as a cross-linker onto the surface of the TPX and was then tion affected the properties of the fabricated membrane compared
thermally treated for stabilization. They found that the plasma to Na-Alg alone when dehydrating acetic acid containing various
treatment rendered the membrane hydrophilic and plasma pre- concentrations of water at 30 ◦ C. Both separation factor and flux
treatment of the TPX support helped to hydrophilically alter the increased with zeolite content up to 30 wt% zeolite which they
surface so the PAA was securely grafted onto the surface and did not attributed to the increase in hydrophilicity coupled with the molec-
peel away. The resultant membrane had a water content in the per- ular sieving properties of the NaY zeolite. They did not state why
meate approaching 100 wt% and thus a very high-separation factor they stopped at a zeolite loading of 30 wt% when both the sepa-
whilst marinating a high flux when dehydrating acetic acid con- ration factor and flux still appeared to be increasing and it would
taining 3 wt% water at 25 ◦ C. The grafting completely changed the be interesting to see if further improvement could be made or if
membrane performance, increasing the separation factors by 2–3 above this level, the mechanical strength of the membrane could
orders of magnitude demonstrating that a stable polymeric base be affected.
offering a high flux can make an excellent base from which to then Na-Alg was also used by Rao et al. [129] producing homogeneous
attempt to improve membrane selectivity. blend membranes with PVA, cross-linked with glutaraldehyde.
An acrylonitrile-maleic anhydride co-polymer membrane was They demonstrated that blending Na-Alg with PVA lowered the
fabricated by Ray and Ray [124], PAN was seen to offer good sepa- porosity of the membrane and membrane selectivity was seen to
ration performance but poor mechanical strength, so the synthesis increase however at low-water concentrations, their membrane
of a copolymer with maleic anhydride was intended to improve the showed both a lower flux and separation factor than the commer-
mechanical strength so as to fabricate a viable membrane whilst cially available Pervap 2205 although was capable of dehydrating
retaining the desirable performance of PAN. The resultant mem- acetic acid to greater than 99 wt% purity.
branes fabricated from the copolymer were indeed suitable for the Gorri et al. [130] tested four commercially available membranes
dehydration of acetic acid, as well as a number of alcohols and for the dehydration and subsequent recovery of acetic acid from
acetone and therefore could be useful in situations such as batch industrial effluent from and acylation process where it is pro-
plants where the solvent to be dehydrated may vary and thus one duced as a side product from acetic anhydride. They tested a
membrane capable of dehydrating the whole range of solvents used Symplex membrane from GKSS consisting of a polyelectorolyte on
would be desirable. a PVDF support; Pervap 1005 consisting of specially cross-linked
PVA to be acetic acid stable (Sulzer Chemtech, Germany); two ity to water. Unfortunately the flux of water across the membrane
more polymeric membranes CMC-VP43 and CMC-CF23 (CM Celfa, was too low to be commercially viable.
Switzerland). They demonstrated that all the membranes were Bowen et al. [134,135] investigated the pervaporation of acetic
water selective but the Symplex membrane showed the optimal acid and a range of other organic liquids from water for a germa-
separation characteristics when dehydrating acetic acid at 80 ◦ C nium substituted ZSM-5 membrane. They fabricated the membrane
with a higher water flux and separation factor over the entire range using crystallization from a synthesis gel of Ge(C2 H5 O)4 , SiO2 , tetra-
of study (up to 25 wt% water). Since this membrane was not avail- propyl ammonium hydroxide and a silica sol using 2-propanol as
able for commercial use, only as samples for testing, they selected a solvent onto a stainless steel support with 0.5 ␮m pores. They
the commercially available CMC-CF23 for extended testing and pro- attempted to explain differences in separation behaviour of the var-
duced a mathematical model they indicated to be suitable for the ious organic/water systems tested in terms of the fugacities of the
design of a waste acetic acid dehydration facility using the Celfa organic components finding these to be important in describing
CMC-CF23 membrane. the differences between separations of different types of organics.
When it came to the variation in performance within one organic
3.2. Acetic acid dehydration using inorganic membranes group such as alcohols or ketones, they found considerations such
as specific interactions of molecules with the membrane material
A number of inorganic membranes have been tested for acetic and molecular size were more important.
acid dehydration. However, zeolites are often affected by highly Zeolite T membranes were fabricated by hydrothermal synthesis
acidic or alkaline conditions requiring care in selecting a material onto an ␣-alumina support and tested for acetic acid dehydration
that will not degrade when working with high concentrations of the by Tanaka et al. [93] having been selected from testing a wide
acid. A summary of the performance data of the inorganic mem- range of zeolite membranes for IPA dehydration as reported earlier.
branes described in this section can be also found together with The resultant membranes were tested for dehydration of a 50:50
the polymeric membrane data in Table 13. The performance of the acetic acid–water mixture and for an esterification reaction. They
inorganic-based membranes described in this section is depicted found a variation in performance of the membrane depending on
graphically in the logarithmic plot shown in Fig. 14. how long it was immersed in acetic acid and water before it was
ZSM-5 zeolite membranes were prepared by Li et al. [131] who used for pervaporation with the separation factor decreasing and
used a porous asymmetric ␣-alumina tube as a support for the although immersing the membrane in alkali solution restored the
membrane. The ZSM-5 crystals were seeded onto the tube before performance, this led them to conclude further testing would be
being placed in an autoclave filled with a gel of molar composi- required in order to assess the long-term stability of the mem-
tion 26.75Na2 O:Al2 O3 :100SiO2 :4600H2 O and placed in an oven to brane.
undergo hydrothermal treatment for a number of hours. The flux Aseada et al. [136] also used porous silica, silica-zirconia and
of the resultant membrane for acetic acid dehydration was low silica-titania membranes to dehydrate acetic acid and propionic
very low compared to the pure water flux, they thus tried treat- acid mixtures. They found that silica and silica-titania membranes
ing the membranes with an alkali after production to remove some were stable at high-acetic acid concentrations whilst silica-zirconia
of the Si molecules and increase the free volume. When treated ones were not. Their long-term testing, up to 50 days operation
by 0.1 mol dm−3 NaOH for 2 h, the flux increased as did the sep- was performed with 20–30 wt% solutions of acetic acid, it would
aration factor. They found that the permeability coefficients of be interesting to have seen this also reported for a 90 wt% acetic
both water and acetic acid decreased with increasing tempera- acid solution. The silica membranes exhibited the highest fluxes in
ture, although the pervaporation fluxes of both water and acetic testing however the silica-titania membranes overall had a higher
acid were increased. They attributed this to an increase in trans- PSI as their less porous and more tightly packed structure restricted
membrane partial vapour pressure difference, thus increasing the the overall permeation but the reduction in permeation was much
driving force. Excessive alkali treatment however was found to greater for acetic acid than for water thus improving the separation
remove too much of the Si molecules, causing pinholes in the factor.
membrane and reducing performance. Li et al. [132] also pre-
pared mordenite membranes on the outer surface of a porous 4. Dehydration of tetrahydrofuran
␣-alumina tube by dip-coating. They selected mordenite for its
strong hydrophilicity, resistance in acidic media and also due to Tetrahydrofuran (THF) is frequently utilized as a solvent in many
its catalytic properties. They aimed to produce a membrane that pharmaceutical synthetic procedures because of its broad solvency
would act as a catalytic membrane reactor viable for use enhanc- for polar and non-polar compounds. THF is particularly capable
ing esterification reactions. They found the silica substrate used of dissolving many ionic species and organometallics which are
in forming the mordenite layers had a considerable effect on the commonly used in specialty syntheses. In many cases, THF makes
microstructure of the membrane and although the separation fac- higher yields and faster reaction rates possible. In addition, THF’s
tors achieved were far lower than those when dehydrating IPA, high volatility and very high purity facilitate solvent removal and
the mordenite membranes produced were effective at removing recovery without leaving residues in the desired product. Thus
low-water concentrations from acetic acid. companies are often left with a THF waste stream which they would
An acid-proof silicalite-1 zeolite membrane was prepared by like to reuse, if it was dehydrated. Again however the problem arises
Masuda et al. [133]. They repeatedly used hydrothermal synthe- from the fact that THF forms an azeotrope with water at 94.7 wt%
sis to build up a layer of silicalite-1 on top of ␣-alumina ceramic [137] thus ruling out simple distillation. BASF detail a system for
filter. They then used H2 O2 by liquid phase oxidation to remove the recovering THF by multistage distillation [138] using a first column
template molecules of tetra-n-propyl ammonium bromide (TPABr) to reach the azeotrope, then drying using solid potassium hydrox-
that were left in the membrane. The silanol groups present in the ide, then another distillation stage to produce pure THF. The use of
silicalite-1 crystals and in the apertures among the crystals hydro- pervaporation could cut this lengthy, complicated and costly pro-
gen bond to water molecules forming networks of water molecules. cess down to two stages. A summary of the performance data of the
The presence of these networks prevented other molecules from membranes described in this section can be found in Table 14 and
diffusing through the membrane and thus only allowed water to the tabulated performance data shown graphically in the logarith-
permeate across the membrane resulting in near infinite selectiv- mic plot in Fig. 15.
30
Table 14
Dehydration of THF
THF/H2 O (95:5) Cellulose acetate PVP Glutaraldehyde, DAS Not stated 0.34 40 [139]
THF/H2 O (95:5) Cellulose acetate PVA/PVP (50:50) Glutaraldehyde, DAS Not stated 0.18 40 [139]
THF/H2 O (95:5) Cellulose acetate PVA Glutaraldehyde, DAS Not stated 0.033 40 [139]

THF/H2 O (90:10) Na-Alg, PVA, PEG Na-Alg, PVA, PEG Glutaraldehyde 591 0.091 30 [141]
THF/H2 O (90:10) 46% PAA grafted Na-Alg, PVA, PEG 46% PAA grafted Na-Alg, PVA, PEG Glutaraldehyde 303 0.094 30 [141]
THF/H2 O (90:10) 93% PAA grafted Na-Alg, PVA, PEG 93% PAA grafted Na-Alg, PVA, PEG Glutaraldehyde 216 0.131 30 [141]
THF/H2 O (90:10) Na-Alg Na-Alg Glutaraldehyde 304 0.178 30 [142]
THF/H2 O (90:10) Na-Alg and 5 wt% HEC Na-Alg and 5 wt% HEC Glutaraldehyde and urea formaldehyde 543 0.161 30 [142]
THF/H2 O (96:4) PANHEMA PANHEMA AN:HEMA 0.971:0.029 160 0.145 30 [144]
THF/H2 O (93:7) Celfa CMC-CF-23 Celfa CMC-CF-23 – 595 0.752 55 [145]
THF/H2 O (93:7) SMART NaA zeolite SMART NaA zeolite – 1150 0.63 45 [145]
THF/H2 O (96:4) PVA/PEI PVA/PEI – 156 1.07 30 [146]
THF/H2 O (96:4) PVA/PEI PVA/PEI Glutaraldehyde and HCl 579 0.376 30 [146]
THF/H2 O (95:5) PVA PVA UFS solution to cross-link 210 0.210 30 [32]
THF/H2 O (95:5) Chitosan Chitosan UFS solution to cross-link 1940 0.083 30 [32]
THF/H2 O (95:5) PVA/chitosan 20:80 PVA/chitosan 20:80 UFS solution to cross-link 4203 0.098 30 [32]
THF/H2 O (95:5) SMART NaA zeolite SMART NaA zeolite – ≈2000 ≈0.8 55 [148]
THF/H2 O (97:3) SMART NaA zeolite SMART NaA zeolite – ≈1500 ≈0.9 55 [148]
THF/H2 O (90:10) ␣-Alumina Silica-zirconia Novel hot-coating process ≈3800 ≈7.2 50 [149]
THF/H2 O (95:5) Microporous silica (ECN) Microporous silica (ECN) – 147 5.82 60 [86]
tion containing glutaraldehyde. The membranes produced from the

grafted Na-Alg showed an improved flux but a reduction in separa-
tion factor with increased grafting %. Although the fluxes here were
quite low, they indicated their intension to develop thin film ver-
sions of the membranes to investigate if the flux could be increased
without a reduction in membrane selectivity. The authors of this
review however were unable to find any work yet published in
the literature to this effect. Naidu et al. [142] also investigated THF
dehydration using Na-Alg. They selected to blend the polymer with
hydroxyethylcellulose (HEC) to improve the pervaporation perfor-
mance over that of pure sodium alginate. They added increasing
amounts of HEC into the blend and cast dense membranes via
solvent evaporation and then cross-linked the membranes in two
steps, firstly using glutaraldehyde and HCl before being washed and
cross-linked in a second solution containing urea, formaldehyde
and sulphuric acid. The second cross-linking step was necessary
to effectively cross-link the HEC within the blend with the glu-
taraldehyde failing to stabilise the membrane. The water content
Fig. 15. Graphical representation of membrane performance data presented in in the permeate was found to increase with increasing HEC content
Table 14. and the membrane separation factor was found to reach a maxi-
mum with a Na-Alg membrane containing 10 wt% HEC. Raising the
operating temperature reduced the separation factor considerably
4.1. THF dehydration using polymeric membranes whilst only offering slight increases in flux therefore favouring the
operation of these membranes at low temperatures. There was no
One of the major drawbacks of polymeric membranes is there indication of how long-term stable the prepared membranes were
limited solvent stability. Some membranes are actually produced in THF, which would have been a good indication that the two step
using THF as a solvent and thus dehydrating this solvent becomes cross-linking was producing a stable membrane.
problematic with membranes fabricated from THF soluble poly- Hicke et al. [143] prepared a novel membrane from
mers with the membranes subject to re-dissolving or swelling poly(acrylonitrile-co-glycidyl methacrylate) (PANGMA) by immer-
excessively when coming into contact with the solvent. sion precipitation followed by ammonolysis. This resulted in
Lu et al. [139] developed a polymeric-based membrane extraordinarily solvent resistant membranes when the glycidyl
capable of dehydrating THF. It was produced from poly(vinyl methacrylate (GMA) content was above 7 mol% and it had under-
alcohol)/poly(vinyl pyrrolidone) (PVA/PVP) blends of different gone ammonolysis for at least 3 h at 50 ◦ C. The membrane was
compositions and PVA, chemically cross-linked with glutaralde- found to be completely insoluble in THF, acetone, acetonitrile,
hyde and PVP photochemically with a 4 wt% aqueous solution of DMSO, DMF, N-methyl pyrrolidone, hexafluoroisopropanol and
4,4 -diazolstilbene-2,2 -disulfonic acid disodium salt (DAS). DAS hexamethylphosphoric acid triamide. The resultant membranes
was used as it is able to substitute a hydrogen on the substituted showed similar performance to PAN membranes with alcohol
carbon of the polymer backbone and link with it. The solution was dehydrations but have the advantage of also being able to work
cast onto a cellulose acetate support and then heated in an oven at with these stronger solvents. Excess addition of GMA was seen
40 ◦ C for drying. The dried membranes were next irradiated with a to cause brittleness in the membrane and so they concentrated
UV lamp for cross-linking the PVP followed by heating in an oven to their work on PANGMA with 7 mol% GMA. The membranes were
cross-link the PVA. They found that permeation flux increase with designed for ultrafiltration applications but they also believed
increasing PVP content without a loss of selectivity and that a PVP that the membranes would act as a good solvent resistant support
content of 80 wt% was optimal for the process with far less fragile for nanofiltration and pervaporation membranes. Ray and Ray
than a pure PVP membrane, when operating at low-water concen- [144] investigated the copolymerisation of PAN with hydroxyethyl
trations at 40 ◦ C with close to 100 wt% water in the permeate. Lu et methacrylate (HEMA), producing PANHEMA membranes with
al. [140] also showed that based on a sorption-desorption process increasing HEMA contents. They produced dense films about
the presence of a hydration layer due to water hydrogen bonding 30 ␮m thick and annealed the films at 80 ◦ C for 6 h. The separation
with the carbonyl groups of PVP when water is present down to factor decreased with HEMA content and flux increased with
levels of about 1 wt% effectively excluded the THF molecules from membranes successfully dehydrating THF to a low level, however
entering the membrane. However as water content decreased fur- they did not report on the long-term stability of the material in
ther below this level, this layer was depleted and the separation THF.
factor decreased substantially as THF was no longer blocked from Ortiz et al. [145] investigated the dehydration of THF using
entering the membrane. the commercially available polymeric membrane CMC-CF-23 (CM
Kurkuri et al. [141] used Na-Alg-based membranes in order to Celfa) and also tested an inorganic NaA membrane, previously avail-
separate THF/water mixtures. They produced three different types able from the now defunct SMART chemical company. They showed
of membranes for testing: (1) neat Na-Alg with 10 mass% of PEG that both membranes appeared short-term stable in the solvents
and 5 mass% of PVA, (2) 46% grafted PAAm-g-Na-Alg membrane and were successful at dehydrating THF from 8 wt% water down to
containing 10 wt% of PEG and 5 wt% of PVA, and (3) 93% grafted a level of less than 1 wt% water. They did not attempt to directly
PAAm-g-Na-Alg membrane containing 10 wt% of PEG and 5 wt% compare the performance of the two membranes, instead focusing
of ‘PVA’. They grafted Na-Alg with polyacrylamide prior to use on assessing the suitability of models for the two different sys-
in preparing a casting solution and compared the performance of tems. Overall however, the zeolite membrane was more effective
membranes fabricated from these grafted polymers with those pro- with both a higher flux and separation factor when operating at
duced using neat Na-Alg. After the dense films had been formed by 55 ◦ C and was also able to dehydrate THF to a lower level than the
solvent evaporation, they were also cross-linked in an acetone solu- polymeric membrane.
Rao et al. [146] used a blend of PVA and poly(ethyleneimine) novel fabrication system reduced defect formation so that high-
(PEI) to produce hydrophilic, THF stable membranes. They selected separation factors were maintained.
a PVA:PEI ratio of 1:3 although did not specify exactly how this ratio In addition to the case study on ethanol Van Veen et al. [86]
was selected and produced dense membranes via solvent evapora- performed using a microporous silica membrane produced by the
tion. Cross-linking using glutaraldehyde and an HCl catalyst was Energy Centre of the Netherlands (ECN) to dehydrate a number
tested on the dried membranes to identify if this could enhance of additional solvents, including THF and acetone. Although, com-
the overall membrane performance and was shown to reduce the pared to ethanol dehydration, the separation factor was lower, the
overall flux but significantly raise the separation factor. Thus cross- flux was over three times that of when operating at comparable
linked PVA/PEI was reported to be an interesting membrane which temperature with ethanol. Thus this appears to be a particularly
they believed could be coupled with distillation as a final stage for suitable membrane for the dehydration of THF.
water removal in THF purification. More recently, the blend mem-
branes that Rao et al. [32] produced from PVA and chitosan using 5. Dehydration of acetone
a cross-linking mixture of urea, formaldehyde and sulphuric acid
were also shown to possess high-separation factors when dehy- Acetone (also known as dimethyl ketone, propan-2-one and 2-
drating THF containing 5–15 wt% water. Long-term pervaporation propanone) is another widely used chemical that is commonly used
experiments would be useful to identify if this performance was in the production of plastics and chemicals as well as a solvent in
sustainable for operating times longer than 6 h. the pharmaceutical industry. Acetone does not form an azeotrope
The commercially available Pervap 2210 was applied by Koczka with water [150] but a large reflux is required when attempting
et al. [147] to an industrial application where water was required to distil a solution necessitating a large column and high-energy
to be removed to a level of 0.05 wt%. The current process was utilis- costs. Therefore pervaporation is a good alternative to be used for
ing sodium hydroxide and potassium hydroxide to hygroscopically the final dehydration of acetone already brought to a low-water
remove water from a level of 7.1 to 0.5 wt%. Batch distillation was concentration by distillation. A summary of the performance data
then used to produce the final required THF with a water content of of the membranes described in this section can be found in Table 15
0.05 wt%. This process was both chemically poor with the require- and the tabulated performance data shown graphically in the log-
ment of large amounts of sodium and potassium hydroxide and also arithmic plot in Fig. 16.
highly wasteful. They investigated the replacement of the hygro-
scopic water removal by pervaporation and reported that doing 5.1. Acetone dehydration using polymeric membranes
this would reduce the utility costs by 84% and total annual cost by
83%, proving the viability of the use of pervaporation technology in Sridhar et al. [151] used deacylated chitosan to produce a sta-
industrial processes involving the recycle of THF. ble polymeric membrane suitable for dehydrating acetone. They
worked at a water content of 12 wt% and performed a fairly standard
4.2. THF dehydration using inorganic membranes range of tests to identify membrane transport phenomena. Separa-
tions yielded an acetone purity of greater than 99 wt% indicating
Ceramic membranes have been used to dehydrate THF as they a good degree of separation and although the authors contin-
are non-soluble in THF and so are not subject to a lot of the problems ued to refer to a water/acetone azeotrope, which in reality is just
that polymeric materials are shown. Urtiaga et al. [148] had looked the presence of a near unity point of the relative volatility, per-
at dehydrating THF using the same NaA zeolite-based membrane vaporation utilising this membrane was found to be a suitable
that had been tested by Ortiz et al. [145]. They demonstrated that technique for this separation. Zhang et al. [23] also used chitosan
dehydration was possible down to a level of 0.1 wt% water with a which they cross-linked with glutaraldehyde and then modified
maximum separation factor of 20,000 recorded at a water level of the membrane’s surface properties using maleic anhydride to form
0.8 wt% and water rich permeate was obtained down to a water level carboxyl groups on the chitosan surface, improving hydrophilicity.
of 0.15 wt% when operating at 45 ◦ C. Interestingly, at 7 wt% water, For acetone dehydration, this surface modification increased both
increasing the temperature by 10 ◦ C more than doubled the flux but the membrane flux and separation factor.
left the separation factor unchanged, temperature only seemed to
have any noticeable influence on the separation factor when oper-
ating around 1 wt% water. Unfortunately, since these membranes
are no longer available, this is only indicative of the possible perfor-
mance that might be attained when fabricating an NaA membrane
since the preparation technique for the membrane is unavailable.
Asaeda et al. [149] tested silica-zirconia membranes for the
dehydration of THF. They fabricated a membrane which they
reported to have pore sizes less than 1 nm via the sol–gel process.
They produced various silica-zirconia colloidal sols of 2, 1.5, 0.8
and 0.5 wt%, respectively and applied the several layers of each sol
before moving to the next, lower concentration sol using a hot-
coating method. The method consisted of using a cloth soaked with
a diluted solution of one colloidal sol and allowing it to contact the
substrate which was heated to a temperature of 160–180 ◦ C allow-
ing a very thin layer to be applied each time with simultaneous
coating and drying and then being heated at 450 ◦ C in a furnace for
10–15 min. This was then repeated several times for each colloidal
sol in succession. They claimed the thin active layer was around
0.3 ␮m and that their repetition of each coating prevented the for-
mation of pinholes. The trans-membrane flux of the membranes Fig. 16. Graphical representation of membrane performance data presented in
was relatively high due to the thin separation layer however the Table 15.
Reference
The acrylonitrile-maleic anhydride co-polymer membrane used
by Ray and Ray [124] successively in acetic acid dehydration, was
[149]
[148]
[148]
[124]
[154]
[154]
[152]
[152]
[152]
[152]
[152]
[153]
[155]
[151]
[23]
[23]
[95]
[86]
[88]
[88]
also applied to the dehydration of acetone. The separation factor
achieved in the dehydration was not particularly high at lower
water concentrations, with the maximum value achieved at 25 wt%
Temperature (◦ C)
water.
PVA was used by Burshe et al. [152] with different cross-linking
agents; citric acid, adipic acid, maleic acid, glutaraldehyde, and
glyoxal, to produce membranes suitable for acetone dehydration.
40
30
40
40
40
48
30
30
30
30
30
50
70
70
50
55
50
50
40
70
They showed that the selection of cross-linker affected the mor-
phology and separation characteristics of the final membrane and
Flux (kg m−2 h−1 )
concluded that for acetone dehydration, cross-linking with maleic

acid produced the best separation characteristics in the resultant
membrane. However, the tri-functional citric acid cross-linker pro-
≈0.098
0.084
≈0.936
0.752
≈0.372
≈0.813
≈0.180
0.314
0.117
0.44
0.34
0.22
0.24
0.91
0.13
duced the membrane with the highest separation factor but the
≈4.2
≈1.1
≈6.4
≈5.6
2.7
extensive cross-linking caused by the presence of the triester sig-
nificantly reduced the overall flux which was found to vary up to a
Separation factor
factor of 10 depending on the cross-linker used.

Polotskaya et al. [153] used membranes fabricated from a
structural support layer of poly(2,6-dimethyl-1,4-phenylene oxide)
5.4
2.4
(PPO) on which they cast an active layer of different imide con-

1276
57
208
1791
192
153
118
95
≈100
≈800
50
50
≈220
≈135
5600
33
≈1800
≈1800
taining poly(amic acids) (PI-PAA). They also fabricated and tested

homogeneous membranes of both PI-PAA and PPO. Unfortunately,
they did not attempt the dehydration of acetone containing a low
Glutaldehyde and maleic anhydride
concentration of water so it is hard to compare this data to other

work although the membrane was shown to be selective towards
Cross-linked glutaraldehyde
water.
Novel hot-coating process
Cross-linker/modification
Cross-linked maleic acid

Cross-linked adipic acid
Cross-linked citric acid
One commercially obtainable polymeric and one commer-

Cross-linked glyoxal
Hot-coating process
cially obtainable inorganic membrane were selected and tested

by Urtiaga et al. [154] for the dehydration of industrial ketonic
Glutaldehyde
effluent streams that comprised mainly of acetone containing

Heat treated
25–30 wt% water. The two commercial membranes tested were a

Symplex membrane from GKSS (Geesthacht, Germany) consisting
of polyelectrolytes on a microporous PVDF support and the ceramic
–
–
–
–
–
–
–
–
–
–
Pervap SMS membrane from Sulzer Chemtech. When comparing

the performance of both membranes at 70 ◦ C dehydrating acetone
Pervatech ‘PVP’ silica membrane
Acrylonitrile-maleic anhydride
Pervap SMS (Sulzer Chemtech)
containing a fixed water content of 20 wt%, the polelectolyte mem-

Chitosan, carboxyl modified
brane was demonstrated to have a water flux 3.7 times that of the
Microporous silica (ECN)
ceramic membrane. The selectivity of the Pervap SMS membrane

Deacetylated chitosan
SMART NaA zeolite

SMART NaA zeolite
was almost constant with water concentration with the permeate

Separation layer
Symplex (GKSS)
containing around 99.5 wt% water. The Symplex membrane pos-

Silica-zirconia
Silica-zirconia
sessed a similar selectivity to the inorganic membrane at water

NaA zeolite
Chitosan
contents below 9 wt%, whilst above this, the permeate linearly

PI-PAA
drops to contain around 93 wt% water at a water content of 25 wt%.

PVA
PVA
PVA
PVA
PVA
They concluded that the Symplex membrane was the most efficient
for dehydration as the much higher flux resulted in a faster dehy-
dration. If however, acetone concentration in the permeate was a

Acrylonitrile-maleic anhydride
Pervap SMS (Sulzer Chemtech)
more important consideration, the inorganic membrane may be a

Mullite, Al2 O3 , Cristobalite
more suitable option.

Microporous silica (ECN)
Deacetylated chitosan
This was an interesting study as the conclusion was that by

Membrane support
SMART NaA zeolite

SMART NaA zeolite
dehydrating the mixture adequately, it could then be incinerated

Symplex (GKSS)
without additional fuel being required to offset the high-water

content originally present. Much work goes into the recycle of sol-
␣-Alumina
␣-Alumina
Chitosan
Chitosan
vents, however industrially, where there may often be a number

of other impurities preventing simple recovery, ensuring the waste
PVA
PVA
PVA
PVA
PVA
PPO
can be disposed of with as little environmental impact as possi-

ble is important and hence negating the requirement of extra fuel
Binary mixture (mass ratio)
addition during disposal is highly advantageous.

Dehydration of acetone
Acetone/H2 O (80:20)
Acetone/H2 O (95:5)
Acetone/H2 O (95:5)
Acetone/H2 O (95:5)
Acetone/H2 O (95:5)
Acetone/H2 O (95:5)
Acetone/H2 O (97:3)
Acetone/H2 O (97:3)
5.2. Acetone dehydration using inorganic membranes
Inorganic membranes have also been applied to the dehydration

of acetone. Asaeda et al. [149] used the silica-zirconia membranes
Table 15
they fabricated and tested for their novel hot-coating process

to dehydrate acetone. Details of the formation process are given
previously. Yang et al. [155] also used the sol–gel technique and hot- fluxes were lower, the water content in the permeate was much
coating system developed by Asaeda et al. to produce SiO2 –ZrO2 higher for the commercially tested membranes.
membranes which they applied to the dehydration of acetone. The
varied the pore sizes of the resultant membranes by varying the par- 6. Perspectives
ticle sizes used in the sols and the coating times. They showed that
a small variation in pore size had a large effect on the separation The future of hydrophilic pervaporation lies in broadening the
performance of the membrane with separation factors decreasing current range of feasible applications, the utilisation of new mate-
by over a factor of 7 when pore size increased from around 0.5 ␮m rials and fabrication techniques in membrane production.
to around 0.57 ␮m whilst flux almost tripled. They concluded that Dehydration of alcohols has received a great deal of attention
a membrane with sufficiently small pores would effectively act as over the past few decades and is now a relatively well under-
a molecular sieve, preventing solvent transport however the flux stood area of membrane separations. A number of companies
may be too low at this point as to be practicable. produce commercial products which are highly suitable for this
Urtiaga et al. [148] used a commercially available inorganic zeo- type of application and these have been successfully utilised at
lite NaA membrane, obtained from the SMART chemical company. both the pilot plant and full-industrial scales. There are how-
They studied the dehydration of acetone down to water content ever many more organic solvents from which water removal
below 0.2 wt%. By increasing the temperature from 40 to 48 ◦ C, would be highly advantageous and in which many of the com-
the flux was more than doubled when dehydrating acetone con- mercially available polymeric membranes are unstable. Inorganic
taining 3 wt% water. Use of membrane for dehydrating acetone is membranes can be used in many of these cases but generally
therefore preferable at a high-operating temperature. NaA zeolite inorganic membranes are economically less viable than their
membranes were also tested in a full-scale pervaporation plant by polymeric counterparts. There have been a number of problems
Morigami et al. [95] who used tubular type membranes built into in the development of commercially available inorganic mem-
modules. They produced a full-scale system of 16 modules, each branes with a number of the supposedly commercially viable
with an outer membrane area of 0.36 m2 to dehydrate 530 l h−1 membranes tested, but failing to actually make them into the mar-
of solvent from 10 wt% water to 0.2 wt% water at 120 ◦ C. The full- ket.
scale plant was only tested for alcohol dehydration. However, the Further research is required into both the fabrication of poly-
successful operation of the large-scale plant in ethanol dehydra- meric membranes that are suitable in harsher environments and
tion and comparison with those attained dehydrating ethanol on a also, into simplifying and improving inorganic membrane man-
small-scale indicated the feasibility of acetone dehydration at this ufacture so these technologies can more easily be applied. The
larger scale. continued development of new materials and fabrication tech-
When dehydrating acetone at 50 ◦ C Van Veen et al. [86] using niques will provide new opportunities for membrane production
the same silica membranes they used for THF dehydration achieved both in lab scale research and the realisation of successful research
a flux of 0.752 kg m−2 h−1 and a separation factor of 33. This per- into commercial products.
formance was poor compared to the fluxes and separation factors
achieved when working with ethanol or THF. However, perfor-
Acknowledgements
mance at higher temperatures was not evaluated and raising the
operating temperature was seen to enhance ethanol dehydration
A CASE studentship provided by EPSRC and GSK to one of the
performance so this may also improve the characteristics of acetone
authors, Peter Chapman, is gratefully acknowledged.
dehydration.
Casado et al. [88] also tested the silica based commercial mem-
brane they had obtained from Pervatech for acetone dehydration. References
They investigated the influence of temperature and feed com- [1] F. Lipnizki, R.W. Field, P.-K. Ten, Pervaporation-based hybrid process: a review
position on the membrane performance and compared them to of process design, applications and economics, J. Membr. Sci. 153 (1999)
published data available for the silica Pervap SMS membrane. They 183.
[2] W.S. Winston, H. Kamalesh, K. Sirkar, Membrane Handbook, Chapman & Hall,
showed that fluxes across the silica membrane from Pervatech
1992.
were substantially higher than those that had been attained using [3] M. Mulder, Basic Principals of Membrane Technology, Kluwer Academic Press,
the Sulzer membrane although both membranes produced a per- AA Dordrecht, 1996.
meate with a water content of 99.5 wt% or greater and hence [4] P. Shao, R.Y.M. Huang, Polymeric membrane pervaporation, J. Membr. Sci. 287
(2007) 162.
showed excellent water selectivity. Data from both manufactur- [5] D. Hofmann, L. Fritz, D. Paul, Molecular modelling of pervaporation separation
ers indicated this was likely to be due to the selective layer of the of binary mixtures with polymeric membranes, J. Membr. Sci. 144 (1998) 145.
Pervatech membrane being almost 1/10th of the thickness of that [6] S.I. Semenova, H. Ohya, K. Soontarapa, Hydrophilic membranes for pervapo-
ration: an analytical review, Desalination 110 (1997) 251.
of the Sulzer membrane. They concluded that flux decreased with [7] L.H. Horsley, Azeotropic Data-III, in: R.F. Gould (Ed.), Advances in Chemistry
decreasing feed water content however the selectivity remained Series 116, American Chemical Society, Washington, D.C., 1973, p. 15.
almost unchanged over the entire water content range, increasing [8] L.H. Horsley, Azeotropic Data-III, in: R.F. Gould (Ed.), Advances in Chemistry
Series 116, American Chemical Society, Washington, D.C., 1973, p. 18.
the feed temperature did somewhat decrease the overall selectivity [9] S. Chemtech, Pervaporation Membranes for Organic Separation Instructions
whilst increased the trans-membrane flux. This membrane appears for Storage, Handling and Commissioning, Sulzer Chemtech GmbH.
to exhibit excellent characteristics in the dehydration of acetone [10] R.Y.M. Huang, Pervaporation Membrane Separation Processes, Membrane Sci-
ence and Technology Series 1, Elsevier, Amsterdam, 1991.
and it would be interesting to see a similar type of analysis for the
[11] V.S. Praptowidodo, Influence of swelling on water transport through PVA-
dehydration of a wide range of organics and calculation of the sep- based membrane, J. Mol. Struct. 739 (2005) 207.
aration factor to ease comparison to other research. Urtiaga et al. [12] C.H. Lee, W.H. Hong, Influence of different degrees of hydrolysis of poly(vinyl
alcohol) membrane on transport properties in pervaporation of IPA/water
[89] tested the SiO2 –ZiO2 -50% membranes they produced using a
mixture, J. Membr. Sci. 135 (1997) 187.
modified sol–gel process, as detailed earlier, for acetone dehydra- [13] Y.S. Kang, S.W. Lee, U.Y. Kim, Y.S. Shim, Pervaporation of water–ethanol
tion. They demonstrated that the membranes were indeed capable mixtures through crosslinked and surface-modified poly(vinyl alcohol) mem-
of acetone dehydration, however they concluded the commercially brane, J. Membr. Sci. 51 (1990) 215.
[14] L. Liang, E. Ruckenstein, Polyvinyl alcohol-polyacrylamide interpemetrating
available SiO2 -based membranes from Pervatech and Sulzer both polymer network membranes and their pervaporation characteristics for
exhibited a more efficient overall performance as although the ethanol–water mixtures, J. Membr. Sci. 106 (1995) 167.
[15] E. Ruckenstein, L. Liang, Pervaporation of ethanol–water mixtures through [41] M.D. Kurkuri, U.S. Toti, T.M. Aminabhavi, Syntheses and characterization of
polyvinyl alcohol-polyacrylamide interpenetrating polymer network mem- blend membranes of sodium alginate and poly(vinyl alcohol) for the perva-
branes unsupported and supported on polyethersulfone ultrafiltration poration separation of water + isopropanol mixtures, J. Appl. Polym. Sci. 86
membranes: a comparison, J. Membr. Sci. 110 (1996) 99. (2002) 3642.
[16] E. Ruckenstein, L. Liang, Poly(acrylic acid)-poly(vinyl alcohol) semi- and inter- [42] Y.Q. Dong, L. Zhang, J.N. Shen, M.Y. Song, H.L. Chen, Preparation of poly(vinyl
penetrating polymer network pervaporation membranes, J. Appl. Polym. Sci. alcohol)-sodium alginate hollow-fiber composite membranes and pervapora-
62 (1996) 973. tion dehydration characterization of aqueous alcohol mixtures, Desalination
[17] A. Yamasaki, T. Iwatsubo, T. Masuoka, K. Mizoguchi, Pervaporation of 193 (2006) 202.
ethanol/water through a poly(vinyl alcohol)/cyclodextrin (PVA/CD) mem- [43] S. Kalyani, B. Smitha, S. Sridhar, A. Krishnaiah, Separation of ethanol–water
brane, J. Membr. Sci. 89 (1994) 111. mixtures by pervaporation using sodium alginate/poly(vinyl pyrrolidone)
[18] W.-Y. Chiang, Y.-H. Lin, Properties of modified poly(vinyl alcohol) membranes blend membrane crosslinked with phosphoric acid, Ind. Eng. Chem. Res. 45
prepared by the grafting of new polyelectrolyte copolymers for water–ethanol (2006) 9088.
mixture separation, J. Appl. Polym. Sci. 86 (2002) 2854. [44] C.-S. Hsu, R.M. Liou, S.-H. Chen, M.-Y. Hung, H.-A. Tsia, J.-Y. Lai, Pervaporation
[19] Y.-M. Sun, T.-L. Huang, Pervaporation of ethanol–water mixtures through separation of a water–ethanol mixture by PSF-PEG membrane, J. Appl. Polym.
temperature-sensitive poly(vinyl alcohol-g-N-isopropyacrylamide) mem- Sci. 87 (2003) 2158.
branes, J. Membr. Sci. 110 (1996) 211. [45] K.S. Kim, K.H. Lee, K. Cho, C.E. Park, Surface modification of polysulfone ultra-
[20] M. Rafik, A. Mas, M.-F. Guimon, C. Guimon, A. Elharfi, F. Schulé, Plasma- filtration membrane by oxygen plasma treatment, J. Membr. Sci. 199 (2002)
modified poly(vinyl alcohol) membranes for the dehydration of ethanol, 135.
Polym. Int. 52 (2003) 1222. [46] M.L. Steen, L. Hymas, E.D. Havey, N.E. Capps, D.G. Castner, E.R. Fisher, Low
[21] M.L. Gimenes, L. Liu, X.S. Feng, Sericin/poly(vinyl alcohol) blend membranes temperature plasma treatment of asymmetric polysulfone membranes for
for pervaporation separation of ethanol/water mixtures, J. Membr. Sci. 295 permanent hydrophilic surface modification, J. Membr. Sci. 188 (2001) 97.
(2007) 71. [47] S.-H. Chen, K.-C. Yu, S.-S. Lin, D.-J. Chang, R.M. Liou, Pervaporation separation
[22] J. Ge, Y. Cui, Y. Yan, W. Jiang, The effect of structure on pervaporation of chitosan of water/ethanol mixture by sulfonated polysulfone membrane, J. Membr. Sci.
membrane, J. Membr. Sci. 165 (2000) 75. 183 (2001) 29.
[23] W. Zhang, G.W. Li, Y.J. Fang, X.P. Wang, Maleic anhydride surface-modification [48] M.-Y. Hung, S.-H. Chen, R.-M. Liou, C.-S. Hsu, J.-Y. Lai, Pervaporation separation
of crosslinked chitosan membrane and its pervaporation performance, J. of a water/ethanol mixture by a sodium sulfonate polysulfone membrane, J.
Membr. Sci. 295 (2007) 130. Appl. Polym. Sci. 90 (2003) 3374.
[24] A. Chanachai, R. Jiraratananon, D. Uttapap, G.Y. Moon, W.A. Anderson, R.Y.M. [49] M.Y. Hung, S.H. Chen, R.M. Liou, C.S. Hsu, H.A. Tsia, J.Y. Lai, Pervaporation sepa-
Huang, Pervaporation with chitosan/hydroxyethylcellulose (CS/HEC) blended ration of water/ethanol mixture by TGN/PSF blending membrane, Eur. Polym.
membranes, J. Membr. Sci. 166 (2000) 271. J. 39 (2003) 2367.
[25] R. Jiraratananon, A. Chanachai, R.Y.M. Huang, D. Uttapap, Pervaporation [50] H.A. Tsai, M.J. Hong, G.S. Huang, Y.C. Wang, C.L. Li, K.R. Lee, J.Y. Lai, Effect
dehydration of ethanol–water mixtures with chitosan/hydroxyethylcellulose of DGDE additive on the morphology and pervaporation performances of
(CS/HEC) composite membranes. 1. Effect of operating conditions, J. Membr. assymetric PSf hollow fiber membranes, J. Membr. Sci. 208 (2002) 233.
Sci. 195 (2002) 143. [51] J.-H. Kim, K.-H. Lee, S.Y. Kim, Pervaporation separation of water from ethanol
[26] R. Jiraratananon, A. Chanachai, R.Y.M. Huang, Pervaporation dehydration of through polyimide composite membranes, J. Membr. Sci. 169 (2000) 81.
ethanol–water mixtures with chitosan/hydroxyethylcellulose (CS/HEC) com- [52] K. Okamoto, N. Tanihara, H. Watanabe, K. Tanaka, H. Kita, A. Nakamura, Y.
posite membranes. 2. Analysis of mass transport, J. Membr. Sci. 199 (2002) Kusuki, K. Nakagawa, Vapor Permeation and pervaporation separation of
211. water–ethanol mixtures through polyimide membranes, J. Membr. Sci. 68
[27] J.-J. Shieh, R.Y.M. Huang, Pervaporation with chitosan membranes. 2. Blend (1992) 53.
membranes of chitosan and polyacrylic acid and comparison of homogeneous [53] H. Yanagishita, C. Maejima, D. Kitamoto, T. Nakane, Preparation of asymmetric
and composite membrane based on olyelectrolyte complexes of chitosan and polyimide membrane for water/ethanol separation in pervaporation by the
polyacrylic acid for the separation of ethanol–water mixtures, J. Membr. Sci. phase inversion process, J. Membr. Sci. 86 (1994) 231.
127 (1997) 185. [54] X.Y. Qiao, T.S. Chung, Fundamental characteristics of sorption, swelling, and
[28] S.Y. Nam, Y.M. Lee, Pervaporation and properties of chitosan-poly(acrylic acid) permeation of P84 co-polyimide membranes for pervaporation dehydration
complex membranes, J. Membr. Sci. 135 (1997) 161. of alcohols, Ind. Eng. Chem. Res. 44 (2005) 8938.
[29] Y.M. Lee, S.Y. Nam, D.J. Woo, Pervaporation of ionically surface crosslinked [55] X.Y. Qiao, T.S. Chung, K.P. Pramoda, Fabrication and characterization of BTDA-
chitosan composite membranes for water–alcohol mixtures, J. Membr. Sci. TDI/MDI (P84) co-polyimide membranes for the pervaporation dehydration
133 (1997) 103. of isopropanol, J. Membr. Sci. 264 (2005) 176.
[30] R.Y.M. Huang, R. Pal, G.Y. Moon, Crosslinked chitosan composite membrane [56] X.Y. Qiao, T.S. Chung, Diamine modification of P84 polyimide membranes for
for the pervaporation dehydration of alcohol mixtures and enhancement of pervaporation dehydration of isopropanol, AIChE J. 52 (2006) 3462.
structural stability of chitosan/polysulfone composite membranes, J. Membr. [57] Y.C. Wang, Y.S. Tsai, K.R. Lee, J.Y. Lai, Preparation and pervaporation per-
Sci. 160 (1999) 17. formance of 3,3-bis 4-(4-aminophenoxy)phenyl phthalide based polyimide
[31] A. Svang-Ariyaskul, R.Y.M. Huang, P.L. Douglas, R. Pal, X. Feng, P. Chen, L. Liu, membranes, J. Appl. Polym. Sci. 96 (2005) 2046.
Blended chitosan and polyvinyl alcohol membranes for the pervaporation [58] Y.X. Xu, C.X. Chen, J.D. Li, Experimental study on physical properties and per-
dehydration of isopropanol, J. Membr. Sci. 280 (2006) 815. vaporation performances of polyimide membranes, Chem. Eng. Sci. 62 (2007)
[32] K. Rao, M.C.S. Subha, M. Sairam, N.N. Mallikarjuna, T.M. Aminabhavi, Blend 2466.
membranes of chitosan and poly(vinyl alcohol) in pervaporation dehydra- [59] C.L. Li, K.R. Lee, Dehydration of ethanol/water mixtures by pervaporation using
tion of isopropanol and tetrahydrofuran, J. Appl. Polym. Sci. 103 (2007) soluble polyimide membranes, Polym. Int. 55 (2006) 505.
1918. [60] K.-R. Lee, R.-Y. Chen, J.-Y. Lai, Plasma deposition of vinyl acetate onto Nylon-4
[33] Y.L. Liu, C.H. Yu, K.R. Lee, J.Y. Lai, Chitosan/poly(tetrafluoroethylene) composite membrane for pervaporation and evapomeation separation of aqueous alco-
membranes using in pervaporation dehydration processes, J. Membr. Sci. 287 hol mixtures, J. Membr. Sci. 75 (1992) 171.
(2007) 230. [61] J.-J. Shieh, R.Y.M. Huang, Chitosan/N-methylol Nylon-6 blend membranes for
[34] C.K. Yeom, J.G. Jegal, K.H. Lee, Characterization of relaxation phenomena and the pervaporation separation of ethanol–water mixtures, J. Membr. Sci. 148
permeation behaviors in sodium alginate membrane during pervaporation (1998) 243.
separation of ethanol–water mixture, J. Appl. Polym. Sci. 62 (1996) 1561. [62] W.-H. Chan, C.-F. Ng, S.-Y. Lam-Leung, X. He, O.-C. Cheung, Water–alcohol
[35] C.K. Yeom, K.-H. Lee, Vapour permaeation of ethanol–water mixtures using separation by pervaporation through poly(amide-sulfonamide)s (PASAs)
sodium alginate membranes with crosslinking gradient structure, J. Membr. membranes, J. Appl. Polym. Sci. 65 (1997) 1113.
Sci. 135 (1997) 225. [63] C.-D. Ihm, S.-K. Ihm, Pervaporation of water–ethanol mixtures through sul-
[36] C.K. Yeom, K.H. Lee, Characterization of permeation behaviors of fonated polystyrene membranes prepared by plasma graft-polymerization, J.
ethanol–water mixtures through sodium alginate membrane with crosslink- Membr. Sci. 98 (1995) 89.
ing gradient during pervaporation separation, J. Appl. Polym. Sci. 69 (1998) [64] J.-W. Rhim, S.-W. Lee, Y.-K. Kim, Pervaporation separation of water-ethanol
1607. mixtures using metal-ion-exchanged poly(vinyl-alcohol) (PVA)/sulfosuccinic
[37] C.K. Yeom, K.H. Lee, Characterization of sodium alginate and poly(vinyl alco- acid (SSA) membranes, J. Appl. Polym. Sci. 85 (2002) 1867.
hol) blend membranes in pervaporation separation, J. Appl. Polym. Sci. 67 [65] I. Cabasso, Z.-Z. Liu, The permaselectivity of ion-exchange membranes for
(1998) 949. non-electrolyte liquid mixtures. 1. Separation of alcohol/water mixtures with
[38] C.K. Yeom, K.H. Lee, Characterization of sodium alginate membrane Nafion hollow fibers, J. Membr. Sci. 24 (1985) 101.
crosslinked with glutaraldehyde in pervaporation separation, J. Appl. Polym. [66] Z.-K. Xu, Q.-W. Dai, Z.-M. Liu, R.-Q. Kou, Y.-Y. Xu, Microporous polypropylene
Sci. 67 (1998) 209. hollow fiber membrane. Part 2. Pervaporation separation of water/ethanol
[39] R.Y.M. Huang, R. Pal, G.Y. Moon, Characteristics of sodium alginate membranes mixtures by the poly(acylic acid) grafted membranes, J. Membr. Sci. 214 (2003)
for the pervaporation dehydration of ethanol–water and isopropanol–water 71.
mixtures, J. Membr. Sci. 160 (1999) 101. [67] Z.Q. Zhu, X.S. Feng, A. Penlidis, Layer-by-layer self-assembled polyelectrolyte
[40] R.Y.M. Huang, R. Pal, G.Y. Moon, Pervaporation dehydration of aqueous ethanol membranes for solvent dehydration by pervaporation, Mater. Sci. Eng. C:
and isopropanol mixtures through alginate/chitosan two ply composite mem- Biomimetic Supramol. Syst. 27 (2007) 612.
branes supported by poly(vinylidene fluoride) porous membrane, J. Membr. [68] G.J. Zhang, H.H. Yan, S.L. Ji, Z.Z. Liu, Self-assembly of polyelectrolyte multi-
Sci. 167 (2000) 275. layer pervaporation membranes by a dynamic layer-by-layer technique on
a hydrolyzed polyacrylonitrile ultrafiltration membrane, J. Membr. Sci. 292 [97] T.C. Bowen, R.D. Noble, J.L. Falconer, Fundamentals and applications of perva-
(2007) 1. poration through zeolite membranes, J. Membr. Sci. 245 (2004) 1.
[69] G.J. Zhang, W.L. Gu, S.L. Ji, Z.Z. Liu, Y.L. Peng, Z. Wang, Preparation of poly- [98] J.-M. Yeh, M.-Y. Yu, S.-J. Liou, Dehydration of water–alcohol mixtures by vapor
electrolyte multilayer membranes by dynamic layer-by-layer process for permeation through PVA/clay nanocomposite membrane, J. Appl. Polym. Sci.
pervaporation separation of alcohol/water mixtures, J. Membr. Sci. 280 (2006) 89 (2003) 3632.
727. [99] M.-D. Jia, K.-V. Peinemann, R.-D. Behling, Preparation and characterization of
[70] I.J. Ball, S.-C. Huang, R.A. Wolf, J.Y. Shimano, R.B. Kaner, Pervaporation studies thin-film zeolite-PDMS composite membranes, J. Membr. Sci. 73 (1992) 119.
with polyaniline membranes and blends, J. Membr. Sci. 174 (2000) 161. [100] A.A. Kittur, M.Y. Kariduraganavar, U.S. Toti, K. Ramesh, T.M. Aminabhavi, Per-
[71] I.J. Ball, S.-C. Huang, K.J. Miller, R.A. Wolf, J.Y. Shimano, R.B. Kaner, The pervaporation separation of water–isopropanol mixtures using ZSM-5 zeolite
vaporation of ethanol/water feeds with polyaniline membranes and blends, incorporated poly(vinyl alcohol) membranes, J. Appl. Polym. Sci. 90 (2003)
Synth. Met. 102 (1999) 1311. 2441.
[72] Y. Moo Lee, S. Yong Nam, S. Yong Ha, Pervaporation of water/isopropanol mix- [101] A.A. Kittur, S.S. Kulkarni, M.I. Aralaguppi, M.Y. Kariduraganavar, Preparation
tures through polyaniline membranes doped with poly(acrylic acid), J. Membr. and characterization of novel pervaporation membranes for the separation
Sci. 159 (1999) 41. of water–isopropanol mixtures using chitosan and NaY zeolite, J. Membr. Sci.
[73] B.V.K. Naidu, M. Sairam, K. Raju, T.M. Aminabhavi, Pervaporation separation 247 (2005) 75.
of water plus isopropanol mixtures using novel nanocomposite mem- [102] Z. Gao, Y. Yue, W. Li, Application of zeolite-filled pervaporation membrane,
branes of poly(vinyl alcohol) and polyaniline, J. Membr. Sci. 260 (2005) Zeolites 16 (1996) 70.
42. [103] E. Okumus, T. Gürkan, L. Yilmaz, Effect of fabrication and process paprameters
[74] W.-Y. Chiang, Y.-H. Lin, Properties of modified polyacrylonitrile membranes on the morphology and performance of a PAN-based zeolite-filled pervapo-
prepared by copolymerization with hydrophilic monomers for water–ethanol ration membrane, J. Membr. Sci. 223 (2003) 23.
mixture separation, J. Appl. Polym. Sci. 90 (2003) 244. [104] Y.J. Fu, C.C. Hu, K.R. Lee, J.Y. Lai, Separation of ethanol/water mixtures by
[75] H. Matsuyama, A. Kariya, M. Teramoto, Characteristics of plasma polymerized pervaporation through zeolite-filled polysulfone membrane containing 3-
membrane from octamethyltrisiloxane and its application to the pervapora- aminopropyltrimethoxysilane, Desalination 193 (2006) 119.
tion of ethanol–water mixture, J. Membr. Sci. 88 (1994) 85. [105] Y.-C. Wang, S.-C. Fan, K.-R. Lee, C.-L. Li, S.-H. Huang, H.-A. Tsai, J.-Y.
[76] K.M. Song, W.H. Hong, Dehydration of ethanol and isopropanol using tubu- Lai, Polyamide/SDS-clay hybrid nanocomposite membrane application to
lar type cellulose acetate membrane with ceramic support in pervaporation water–ethanol mixture pervaporation separation, J. Membr. Sci. 239 (2004)
process, J. Membr. Sci. 123 (1997) 27. 219.
[77] F. Petrus Cuperus, Robert W. van Gemert, Dehydration using ceramic silica [106] L.Y. Ye, Q.L. Liu, Q.G. Zhang, A.M. Zhu, G.B. Zhou, Pervaporation characteristics
pervaporation membranes—the influence of hydrodynamic conditions, Sep. and structure of poly(vinyl alcohol)/poly(ethylene glycol)/tetraethoxysilane
Purif. Technol. 27 (2002) 225. hybrid membranes, J. Appl. Polym. Sci. 105 (2007) 3640.
[78] Robert W. van Gemert, F. Petrus Cuperus, Newly developed ceramic mem- [107] T. Uragami, T. Katayama, T. Miyata, H. Tamura, T. Shiraiwa, A. Higuchi, Dehy-
branes for dehydration and separation of organic mixtures by pervaporation, dration of an ethanol/water azeotrope by novel organic–inorganic hybrid
J. Membr. Sci. 105 (1995) 287. membranes based on quaternized chitosan and tetraethoxysilane, Biomacro-
[79] J. Sekuli, M.W.J. Luiten, J.E. ten Elshof, N.E. Benes, K. Keizer, Microporous sil- molecules 59 (2004) 1567.
ica and doped silica membrane for alcohol dehydration by pervaporation, [108] T. Uragami, S. Yanagisawa, T. Miyata, Water/ethanol selectivity of new
Desalination 148 (2002) 19. organic–inorganic hybrid membranes fabricated from poly(vinyl alcohol) and
[80] J. Sekulić, J.E. ten Elshof, D.H.A. Blank, A microporous titania membrane for an oligosilane, Macromol. Chem. Phys. 208 (2007) 756.
nanofiltration and pervaporation, Adv. Mater. 16 (2004) 1546. [109] Q.G. Zhang, Q.L. Liu, Y. Chen, J.H. Chen, Dehydration of isopropanol by novel
[81] T.A. Peters, J. Fontalvo, M.A.G. Vorstman, N.E. Benes, R.A. van Dam, Z. Vroon, poly(vinyl alcohol)-silicone hybrid membranes, Ind. Eng. Chem. Res. 46 (2007)
E.L.J. van Soest-Vercammen, J.T.F. Keurentjes, Hollow fibre microporous silica 913.
membranes for gas separation and pervaporation—synthesis, performance [110] D. Van Baelen, B. Van der Bruggen, K. Van den Dungen, J. Degreve, C. Van-
and stability, J. Membr. Sci. 248 (2005) 73. decasteele, Pervaporation of water–alcohol mixtures and acetic acid–water
[82] T. Gallego-Lizon, E. Edwards, G. Lobiundo, L.F.d. Santos, Dehydration of mixtures, Chem. Eng. Sci. 60 (2005) 1583.
water/t-butanol mixtures by pervaporation: comparative study of commer- [111] T.M. Aminabhavi, U.S. Toti, Pervaporation separation of water–acetic acid mix-
cially available polymeric, microporous silica and zeolite membranes, J. tures using polymeric membranes, Des. Monomers Polym. 6 (2003) 211.
Membr. Sci. 197 (2002) 309. [112] N. Durmaz-Hilmioglu, A.E. Yildirim, A.S. Sakaoglu, S. Tulbentci, Acetic acid
[83] T. Gallego-Lizon, Y.S. Ho, L.F.d. Santos, Comparative study of commercially dehydration by pervaporation, Chem. Eng. Process. 40 (2001) 263.
available polymeric and microporous silica membranes for the dehydration [113] S.P. Kusumocahyo, K. Sano, M. Sudoh, M. Kensaka, Water permselectivity in
of IPA/water mixtures by pervaporation/vapour permeation, Desalination 149 the pervaporation of acetic acid–water mixture using crosslinked poly(vinyl
(2002) 3. alcohol) membranes, Sep. Purif. Technol. 18 (2000) 141.
[84] A.W. Verkerk, P. van Male, M.A.G. Vorstman, J.T.F. Keurentjes, Properties of [114] S.P. Kusumocahyo, M. Sudoh, Dehydration of acetic acid by pervaporation with
high flux ceramic pervaporation membranes for dehydration of alcohol/water charged membranes, J. Membr. Sci. 161 (1999) 77.
mixtures, Sep. Purif. Technol. 22–23 (2001) 689. [115] T.M. Aminabhavi, H.G. Naik, Synthesis of graft copolymeric membranes of
[85] A.W. Verkerk, P. van Male, M.A.G. Vorstman, J.T.F. Keurentjes, Description of poly(vinyl alcohol) and polyacrylamide for the pervaporation separation of
dehydration performance of amorphous silica pervaporation membranes, J. water/acetic acid mixtures, J. Appl. Polym. Sci. 83 (2003) 244.
Membr. Sci. 193 (2001) 227. [116] G. Asman, O. Sanli, Characteristics of permeation and separation for acetic
[86] H.M. van Veen, Y.C. van Delft, C.W.R. Engelen, P.P.A.C. Pex, Dewatering of organ- acid–water mixtures through poly(vinyl alcohol) membranes modified with
ics by pervaporation with silica membranes, Sep. Purif. Technol. 22–23 (2001) poly(acrylic acid), Sep. Sci. Technol. 38 (2003) 1963.
361. [117] Y.M. Lee, B.K. Oh, Pervaporation of water–acetic acid mixture through poly(4-
[87] S. Sommer, T. Melin, Performance evaluation of microporous inorganic mem- vinylpyridine-co-acrylonitrile) membrane, J. Membr. Sci. 85 (1993) 13.
branes in the dehydration of industrial solvents, Chem. Eng. Process. 44 (2005) [118] U.S. Toti, T.M. Aminabhavi, Different viscosity grade sodium alginate and mod-
1138. ified sodium alginate membranes in pervaporation separation of water plus
[88] C. Casado, A. Urtiaga, D. Gorri, I. Ortiz, Pervaporative dehydration of organic acetic acid and water plus isopropanol mixtures, J. Membr. Sci. 228 (2004)
mixtures using a commercial silica membrane: determination of kinetic 199.
parameters, Sep. Purif. Technol. 42 (2005) 39. [119] X.P. Wang, Modified alginate composite membranes for the dehydration of
[89] A. Urtiaga, C. Casado, M. Asaeda, I. Ortiz, Comparison of SiO2 –ZrO2 -50% and acetic acid, J. Membr. Sci. 170 (2000) 71.
commercial SiO2 membranes on the pervaporative dehydration of organic [120] S.B. Teli, G.S. Gokavi, M. Sairam, T.M. Aminabhavi, Highly water selective
solvents, Desalination 193 (2006) 97. silicotungstic acid (H4 SiW12 O40 ) incorporated novel sodium alginate hybrid
[90] T. Peters, N. Benes, H. Buijs, F. Vercauteren, J. Keurentjes, Thin high flux composite membranes for pervaporation dehydration of acetic acid, Sep. Purif.
ceramic-supported PVA membranes, Desalination 200 (2006) 37. Technol. 54 (2007) 178.
[91] J.L.H. Chau, C. Tellez, K.L. Yeung, K. Ho, The role of surface chemistry in zeolite [121] J. Huang, M.L. Tu, Y.C. Wang, C.L. Li, K.R. Lee, J.Y. Lai, Dehydration of acetic
membrane formation, J. Membr. Sci. 164 (2000) 257. acid by pervaporation through an asymmetric polycarbonate membrane, Eur.
[92] A.W.C. van den Berg, L. Gora, J.C. Jansen, M. Makkee, Th. Maschmeyer, Zeolite Polym. J. 37 (2001) 527.
A membranes synthesized on a UV-irradiated TiO2 coated metal support: the [122] Y.C. Wang, J.F. Lee, Dehydration of acetic acid/water mixtures by pervaporation
high pervaporation performance, J. Membr. Sci. 224 (2003) 29. with a poly(4-methyl-1-pentane)/Co(III) (acetylacetonate) blend membrane,
[93] K. Tanaka, R. Yoshikawa, C. Ying, H. Kita, K.-i. Okamoto, Application of zeolite Water Sci. Technol. 38 (1998) 463.
membranes to esterification reactions, Catal. Today 67 (2001) 121. [123] D.M. Wang, F.C. Lin, T.T. Wu, J.Y. Lai, Pervaporation of water–ethanol mix-
[94] M. Kondo, M. Komori, H. Kita, K.-I. Okamoto, Tubular-type pervaporation mod- tures through symmetric and asymmetric TPX membranes, J. Membr. Sci. 123
ule with zeolite NaA membrane, J. Membr. Sci. 133 (1997) 133. (1997) 35.
[95] Y. Morigami, M. Kondo, J. Abe, H. Kita, K. Okamoto, The first large-scale perva- [124] S. Ray, S.K. Ray, Dehydration of acetic acid, alcohols, and acetone by pervapo-
poration plant using tubular-type module with zeolite NaA membrane, Sep. ration using acrylonitrile-maleic anhydride copolymer membrane, Sep. Sci.
Purif. Technol. 25 (2001) 251. Technol. 40 (2005) 1583.
[96] K.-i. Okamoto, H. Kita, K. Horii, K. Tanaka, Zeolite NaA membrane: prepa- [125] N. Isiklan, O. Sanli, Separation characteristics of acetic acid–water mixtures
ration, single-gas permeation, and pervaporation and vapor permeation of by pervaporation using poly(vinyl alcohol) membranes modified with malic
water/organic liquid mixtures, Ind. Eng. Chem. Res. 40 (2001) 163. acid, Chem. Eng. Process. 44 (2005) 1019.
[126] M.Y. Kariduraganavar, S.S. Kulkarni, A.A. Kittur, Pervaporation separation of [141] M.D. Kurkuri, S.G. Kumbar, T.M. Aminabhavi, Synthesis and characterization of
water–acetic acid mixtures through poly(vinyl alcohol)-silicone based hybrid polyacrylamide-grafted sodium alginate copolymeric membranes and their
membranes, J. Membr. Sci. 246 (2005) 83. use in pervaporation separation of water and tetrahydrofuran mixtures, J.
[127] S.S. Kulkarni, S.M. Tambe, A.A. Kittur, M.Y. Kariduraganavar, Preparation of Appl. Polym. Sci. 86 (2002) 272.
novel composite membranes for the pervaporation separation of water–acetic [142] B.V.K. Naidu, K. Rao, T.M. Aminabhavi, Pervaporation separation of water + 1,4-
acid mixtures, J. Membr. Sci. 285 (2006) 420. dioxane and water plus tetrahydrofuran mixtures using sodium alginate and
[128] A.A. Kittur, S.M. Tambe, S.S. Kulkarni, M.Y. Kariduraganavar, Pervaporation its blend membranes with hydroxyethylcellulose—a comparative study, J.
separation of water–acetic acid mixtures through NaY zeolite-incorporated Membr. Sci. 260 (2005) 131.
sodium alginate membranes, J. Appl. Polym. Sci. 94 (2004) 2101. [143] H.-G. Hicke, I. Lehmann, G. Malsch, M. Ulbricht, M. Becker, Preparation and
[129] P.S. Rao, A. Krishnaiah, B. Smitha, S. Sridhar, Separation of acetic acid/water characterization of a novel solvent-resistant and autoclavable polymer mem-
mixtures by pervaporation through poly(vinyl alcohol)-sodium alginate blend brane, J. Membr. Sci. 198 (2002) 187.
membranes, Sep. Sci. Technol. 41 (2006) 979. [144] S. Ray, S.K. Ray, Synthesis of Highly Selective Copolymer Membranes and Their
[130] D. Gorri, A. Urtiaga, I. Ortiz, Pervaporative recovery of acetic acid from an Application for the Dehydration of Tetrahydrofuran by Pervaporation, 2007,
acetylation industrial effluent using commercial membranes, Ind. Eng. Chem. p. 728.
Res. 44 (2005) 977. [145] I. Ortiz, D. Gorri, C. Casado, A. Urtiaga, Modelling of the pervaporative flux
[131] G. Li, E. Kikuchi, M. Matsukata, A study on the pervaporation of water–acetic through hydrophilic membranes, J. Chem. Technol. Biotechnol. 80 (2005) 397.
acid mixtures through ZSM-5 zeolite membranes, J. Membr. Sci. 218 (2003) [146] P.S. Rao, S. Sridhar, A. Krishnaiah, Dehydration of tetrahydrofuran by perva-
185. poration using crosslinked PVA/PEI blend membranes, J. Appl. Polym. Sci. 102
[132] G. Li, E. Kikuchi, M. Matsukaka, Separation of water–acetic acid mixtures (2006) 1152.
by pervaporation using a thin mordenite membrane, Sep. Purif. Technol. 32 [147] K. Koczka, J. Manczinger, P. Mizsey, Z. Fonyo, Novel hybrid separation processes
(2003) 199. based on pervaporation for THF recovery, Chem. Eng. Process. 46 (2007) 239.
[133] T. Masuda, S. Otani, T. Tsuji, M. Kitamura, S.R. Mukai, Preparation of hydrophilic [148] A. Urtiaga, E.D. Gorri, C. Casado, I. Ortiz, Pervaporative dehydration of indus-
and acid-proof silicalite-1 zeolite membrane and its application to selective trial solvents using a zeolite NaA commercial membrane, Sep. Purif. Technol.
separation of water from water solutions of concentrated acetic acid by per- 32 (2003) 207.
vaporation, Sep. Purif. Technol. 32 (2003) 181. [149] M. Asaeda, M. Ishida, Y. Tasaka, Pervaporation characteristics of silica-zirconia
[134] T.C. Bowen, H. Kalipcilar, J.L. Falconer, R.D. Noble, Pervaporation of membranes for separation of aqueous organic solutions, Sep. Sci. Technol. 40
organic/water mixtures through B-ZSM-5 zeolite membranes on monolith (2005) 239.
supports, J. Membr. Sci. 215 (2003) 235. [150] L.H. Horsley, Azeotropic Data-III, in: R.F. Gould (Ed.), Advances in Chemistry
[135] T.C. Bowen, S.G. Li, R.D. Noble, J.L. Falconer, Driving force for pervaporation Series 116, American Chemical Society, Washington, D.C., 1973, p. 16.
through zeolite membranes, J. Membr. Sci. 255 (2003) 165. [151] S. Sridhar, G. Susheela, G.S. Murthy, G. Veeraiah, M. Ramakrishna, Pervapora-
[136] M. Asaeda, M. Ishida, T. Waki, Pervaporation of aqueous organic acid tion performance of deacetylated chitosan membrane in the dehydration of
solutions by porous ceramic membranes, J. Chem. Eng. Jpn. 38 (2005) acetone, J. Polym. Mater. 20 (2003) 9.
336. [152] M.C. Burshe, S.A. Netke, S.B. Sawant, J.B. Joshi, V.G. Pangarkar, Pervaporative
[137] L.H. Horsley, Azeotropic Data-III, in: R.F. Gould (Ed.), Advances in Chemistry dehydration of organic solvents, Sep. Sci. Technol. 32 (1997) 1335.
Series 116, American Chemical Society, Washington, D.C., 1973, p. 21. [153] G.A. Polotskaya, Y.P. Kuznetsov, M.Y. Goikhman, I.V. Podeshvo, T.A. Maricheva,
[138] BASF, Tetrahydrofuran (THF) Storage and Handling, http://www.basf.com/ V.V. Kudryavtsev, Pervaporation membranes based on imide-containing
businesses/chemicals/diols/pdfs/thf brochure.pdf. poly(amic acid) and poly(phenylene oxide), J. Appl. Polym. Sci. 89 (2003) 2361.
[139] J. Lu, Q. Nguyen, J. Zhou, Z.-H. Ping, Poly(vinyl alcohol)/poly(vinyl pyrrolidone) [154] A.M. Urtiaga, C. Casado, C. Aragoza, I. Ortiz, Dehydration of industrial ketonic
interpenetrating polymer network: synthesis and pervaporation properties, effluents by pervaporation. Comparative behavior of ceramic and polymeric
J. Appl. Polym. Sci. 89 (2003) 2808. membranes, Sep. Sci. Technol. 38 (2003) 3473.
[140] J. Lu, Q. Nguyen, L. Zhou, B. Xu, Z. Ping, Study of the role of water in the transport [155] J. Yang, T. Yoshioka, T. Tsuru, M. Asaeda, Pervaporation characteristics of
of water and THF through hydrophilic membranes by pervaporation, J. Membr. aqueous-organic solutions with microporous SiO2 –ZrO2 membranes: exper-
Sci. 226 (2003) 135. imental study on separation mechanism, J. Membr. Sci. 284 (2006) 205.

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Journal of Membrane Science 318 (2008) 5–37

Contents lists available at ScienceDirect

Journal of Membrane Science

Membranes for the dehydration of solvents by pervaporation

Industry today has to constantly review its production methods

Ethanol C2 H5 OH 46.1 0.79 78 59.5 4

Fig. 2. Contact angle measurement on a non-porous surface.

persed throughout the polymeric structure, these are commonly

2.1. Alcohol dehydration using polymeric membranes

Polymeric membranes are widely used today in solvent dehy-

EtOH/H2 O (50:50) PVA PVA Amic acid 100 0.25 45 [10]

was enhanced by the deposition of a plasma layer on the surface of

EtOH/H2 O (90:10) Chitosan Chitosan H2 SO4 1791 0.472 60 [22]

tially, the work focused onto stabilising the water-soluble polymer

EtOH/H2 O (90:10) Na-Alg Na-Alg – 10,000 > non- 0.290 50 [34]

EtOH/H2 O (95:5) PI-2080 aromatic PI-2080 aromatic – 900 1.0 60 [53]

EtOH/H2 O (90:10) Nylon-4 Nylon-4 – ≈4.5 ≈0.35 25 [60]

EtOH/H2 O (80:20) PVDF g-PSS-Na+ Plasma grafting 35 3.1 50 [63]

that mass transfer properties of the membrane could be altered at

EtOH/H2 O (50:50) Polyaniline Polyaniline – >10,000 0.0013 – [71]

EtOH/H2 O (95:5) UV-irradiated TiO2 Zeolite A Up to 54,000 0.86 45 [92]

EtOH/H2 O (95:5) PVA/clay PVA/clay – 58 0.057 Not given [98]

P.D. Chapman et al. / Journal of Membrane Science 318 (2008) 5–37

Acetic acid/H2 O (90:10) PVA PVA Formaldehyde 5.3 0.145 30 [112]

P.D. Chapman et al. / Journal of Membrane Science 318 (2008) 5–37

P.D. Chapman et al. / Journal of Membrane Science 318 (2008) 5–37

PSI since it reduces the separation factor by the same factor as it

P.D. Chapman et al. / Journal of Membrane Science 318 (2008) 5–37

tion containing glutaraldehyde. The membranes produced from the

concluded that for acetone dehydration, cross-linking with maleic

factor of 10 depending on the cross-linker used.

(PPO) on which they cast an active layer of different imide con-

taining poly(amic acids) (PI-PAA). They also fabricated and tested

concentration of water so it is hard to compare this data to other

Cross-linked maleic acid

One commercially obtainable polymeric and one commer-

cially obtainable inorganic membrane were selected and tested

efﬂuent streams that comprised mainly of acetone containing

25–30 wt% water. The two commercial membranes tested were a

Pervap SMS membrane from Sulzer Chemtech. When comparing

Pervap SMS (Sulzer Chemtech)

containing a ﬁxed water content of 20 wt%, the polelectolyte mem-

ceramic membrane. The selectivity of the Pervap SMS membrane

SMART NaA zeolite

was almost constant with water concentration with the permeate

containing around 99.5 wt% water. The Symplex membrane pos-

sessed a similar selectivity to the inorganic membrane at water

contents below 9 wt%, whilst above this, the permeate linearly

drops to contain around 93 wt% water at a water content of 25 wt%.

dration. If however, acetone concentration in the permeate was a

Pervap SMS (Sulzer Chemtech)

more important consideration, the inorganic membrane may be a

more suitable option.

This was an interesting study as the conclusion was that by

SMART NaA zeolite

dehydrating the mixture adequately, it could then be incinerated

without additional fuel being required to offset the high-water

vents, however industrially, where there may often be a number

can be disposed of with as little environmental impact as possi-