Ultrafiltration Membrane Dry Degumming
Ultrafiltration Membrane Dry Degumming
Ultrafiltration Membrane Dry Degumming
Ultrafiltration Membrane
for Degumming of Crude This work is licensed under a
Creative Commons Attribution 4.0
doi: 10.15255/CABEQ.2017.1244
N. Aryanti, D. Hesti Wardhani, and A. Nafiunisa
a,b,* a a
Original scientific paper
a
Department of Chemical Engineering, Diponegoro University Received: October 24, 2017
b
Membrane Research Centre (MeR-C), Diponegoro University Accepted: August 1, 2018
Ultrafiltration (UF) is a membrane technology that has been applied for crude palm
oil (CPO) degumming. It is considered as an alternative for the conventional CPO de-
gumming technology because of its lower energy consumption, no need for the addition
of chemicals, and almost no loss of natural oil. In this research, we separated a CPO-iso-
propanol mixture via laboratory-made flat-sheet polyethersulfone (PES) UF. Flux pro-
files confirmed that the increase in the CPO concentration resulted in lower fluxes. How-
ever, increasing the temperature from 30 °C to 45 °C initially raised the flux, but it was
further decreased when the feed temperature was raised from 40 °C to 45 °C. Using UF
of the CPO-isopropanol mixture at crude oil concentrations of 30 % and 40 %, we were
able to reject more than 99 % phospholipids and nearly 93 % phospholipids, respectively.
However, the separation of free fatty acids using this process was ineffective due to the
small size of free fatty acids. Through the evaluation of the blocking mechanism in the
Hermia model, it was proposed that the standard and intermediate blocking were the
dominant mechanisms of filtration of CPO at a concentration of 30 and 40 %, and 50 and
60 %, respectively.
Keywords:
crude palm oil, ultrafiltration, degumming
ols, and major fatty acids. Ong et al.13 studied ultra- Materials and methods
filtration (UF) of CPO degumming for the removal
of phospholipids, carotenes, Lovibond color, FFAs, Materials
and volatile matter. Lai et al.14 performed research
on the deacidification of a model fatty system of The main raw materials used in this experiment
CPO using various solvents and nanofiltration. On were CPO (Kalimantan, Indonesia) and isopropanol
the other hand, polyvinylidene fluoride (PVDF) has (Merck) as a solvent. The UF membrane was a lab-
been modified with polyvinyl alcohol (PVA) cross- oratory-made polyethersulfone (PES) flat-sheet
linked as a UF membrane in the deacidification of membrane. The PES material was Veradel PESU
CPO15. Deacidification of CPO using an aqueous 3100P (Solvay, Singapore). The membrane was pre-
NaOH solution in a hollow fiber membrane contac- pared via a non-solvent-induced phase separation
tor was carried out by Purwasasmita et al.16 Further- method with PEG as the additive and N-meth-
more, a hexane solvent combined with a UF mem- yl-2-pyrrolidone (NMP) as the solvent28.
brane has been applied to remove phospholipids
from residual palm oil fibers17. Membrane characterization
Similar molecular weights of TAGs and phos- The membrane was characterized for its molec-
pholipids (about 900 and 700 Da, respectively) can ular weight cut-off (MWCO), contact angle, perme-
interfere with their separation process using mem- ability, surface structure, and specific functional
brane technology. Phospholipids tend to form re- groups. The MWCO of the membrane represents
verse micelles in nonpolar media like hexane or the lowest molecular weight of solute (in Daltons),
crude oil because of their amphiphilic properties18,19. in which 90 % of the solute is rejected by the mem-
This unique feature of phospholipid micelles in- brane. The MWCO value is evaluated to describe
creases their average molecular weight from 700 Da the pore size distribution and retention capabilities
to around 20 kDa or even more12, which is signifi- of membranes. In this work, solute rejection exper-
cantly different from TAGs. As a result, the UF iments were performed using PEG (from Sigma-
membrane is able to separate the micelles from the Aldrich) as polymer solute with various molecular
solvent–oil mixture, and the phospholipids are re- weights (MWs) of 2, 6, 12, 20 and 35 kDa. The
tained by the UF membrane20. However, the prima-
PEG solution was prepared in 1 wt.% concentration
ry challenge in the use of membranes, especially
and then filtrated in a dead-end filtration cell. The
UF, is the existence of a phenomenon called foul-
permeate samples were analyzed using a digital
ing. Fouling is an irreversible membrane change
handheld refractometer (PAL-91S, ATAGO, Japan).
that is caused by specific physical and chemical in-
Plots of MW versus solute rejection were created,
teractions between the membrane and the various
and then the MW corresponding to 90 % rejection
components present in the process flow. Membrane
was estimated as MWCO of the membrane. The
fouling is represented by a decrease in the permeate
flux due to the effect of blocking on the surface as hydrophobic/hydrophilic character of the membrane
well as inside the membrane pores21,22. As it is es- was determined by measuring the water-membrane
sential to have a detailed investigation on fouling contact angle (θ). The water-membrane contact
and there is no research investigating membrane angle values of the prepared membrane were mea-
fouling in the degumming of crude palm oil, this sured using water contact angle meter (RACE con-
research is focused primarily on studying the flux tact angle meter, Japan) using deionized water as a
decline as well as the fouling mechanism in the de- probe liquid.
gumming of CPO by UF. Membrane permeability was evaluated by de-
Fundamental studies on fouling mechanisms on termining the membrane flux of distilled water or
UF membranes have been performed for coconut isopropanol in the membrane module at various op-
cream23, organic compounds24, whey models25, and erating pressures (1–3 bar). The fluxes were calcu-
polyethylene glycol (PEG)26. In more detail, the lated according to the sample volume (V), the sam-
fundamental studies focusing on the fouling mecha- pling time (t), and the membrane surface area (A).
nism in UF for oil degumming or separation of oil The volumetric permeate flow rate (Q) was calcu-
components are limited only for degumming corn lated by
oil18–27, crude sunflower oil, and soybean oil14. This V
study placed emphasis on the fundamental and Q= (1)
t
comprehensive analysis of the influence of oil sol-
vents and micelles on fouling mechanism models. Further, the flux (J) was determined by:
Specifically, this study addressed a novelty finding
in the analysis of the fouling model and fouling 1
J = ·Q (2)
mechanism in UF for degumming CPO. A
N. Aryanti et al., Ultrafiltration Membrane for Degumming…, Chem. Biochem. Eng. Q., 32 (3) 325–334 (2018) 327
The membrane’s surface and the cross-section- permeate flux and phospholipid/FFA rejection. Per-
al structure were characterized using scanning elec- meate fluxes (J) were determined by weighing the
tron microscopy (SEM, FEI Type Inspect-S50). The volume of the permeate collected at 5-min intervals
specific functional groups of the membrane were for 120 min and calculated using
determined using FTIR Spectroscopy (Prestige-21,
Shimadzu, Japan). W
J= (3)
A ·t
Evaluation of UF membrane performance for
degumming of the CPO-isopropanol mixture Where W represents the total weight of the per-
meate, A is the membrane area, and t is the time
The UF performance was examined using labo- interval.
ratory-made cell filtration based on the total recycle Rejection of phospholipids and FFAs was de-
model as illustrated in Fig. 1. termined on the basis of the concentration of phos-
The cell filtration was equipped with a centrif- pholipids/FFAs in the feed (Cf) and in the permeate
ugal pump (Kemflow, with nominal flow rate 1.0 (Cp). Rejection is calculated according to
LPM, maximum pump output of 7.58 bar, maxi-
mum inlet pressure of 4.14 bar) as the feed pump, C f − Cp
R= (4)
gate valves, pressure gauge (JAKO, with maximum Cf
pressure of 10.34 bar) and a stainless steel ultrafil-
tration housing. The total recycle model involved Characterization of CPO and permeate
returning the permeate and retentate flow back to
the feed tank to maintain equivalent concentration The specific characteristics of CPO and perme-
during the process. All experimental runs were con- ate included the phospholipid and FFA content.
ducted at room temperature (29 ± 2 °C). Before Phospholipids were expressed as total phosphorus
starting the experiments, membranes were first and analyzed according to the AOAC Ca 12–55
compacted by filtering water through the membrane method. Determination of FFA was performed via
at a pressure of 1 bar for 60 min. For each run, a the acid-base titration method14.
new circular membrane sheet with an effective area
of 13.85 cm2 was used. Blocking mechanism
A micellar solution was prepared by mixing The blocking mechanism of CPO-isopropanol
CPO with isopropanol with ratios of CPO of 30 %, UF was studied according to Hermia’s model. This
40 %, 50 %, and 60 % weight of the solution. The model has been previously applied for the evalua-
filtration cell was operated at 1 bar for 120 min, and tion of the fouling mechanism of dye solution UF28,
before returning it back to the feed tank, the perme- konjac glucomannan separation29, and UF of model
ate was collected every 5 min to determine the flux dye wastewater30. Hermia’s model describes the
and concentration of phospholipids/fatty acids. The mechanism of membrane fouling on the basis of the
feed temperature was varied –30 °C, 35 °C, 40 °C, blocking filtration law, consisting of complete pore
and 45 °C – in order to investigate the effect of tem- blocking, standard pore blocking, and intermediate
perature on UF performance. The feed tank was pore blocking and cake filtration. The blocking law
equipped with a temperature regulator and a mag- filtration is expressed in terms of permeation time
netic stirrer for homogenization of oil micelles. and filtration time, and was developed for dead-end
Membrane performance was evaluated in terms of filtration as shown in31:
n
d 2t dt
2
= k (5)
dV dV
where t is the filtration time, V is the permeate vol-
ume, k is a constant, and n is a value illustrating the
different fouling mechanisms.
The values of n are described as follows: com-
plete blocking with n = 2, intermediate blocking
with n = 1, standard blocking with n = 1.5, and cake
layer formation with n = 0. In the complete block-
ing model, it is assumed that each solute participat-
ed in blocking the entrance of the membrane pores
F i g . 1 – Schematic of ultrafiltration cell with total recycle completely. In intermediate blocking, it is assumed
operation that every solute stays on the previously deposited
328 N. Aryanti et al., Ultrafiltration Membrane for Degumming…, Chem. Biochem. Eng. Q., 32 (3) 325–334 (2018)
(1a) (2a)
(1b) (2b)
F i g . 5 – SEM images at magnification of 10,000x: Clean membranes (1a- Surface), (2a- Cross-sectional structure) and fouled
membrane after ultrafiltration of 30 % CPO-solvent mixture (1b-Surface), (2b-Cross-sectional structure)
meation through the UF membrane using sunflower obtained since the permeability is influenced by the
oil39 as well as coconut oil, groundnut oil, mustard viscosity35. In addition, a lower flux is obtained as a
oil, sunflower oil, and rice bran oil 36–40. In addition, result of polarized/gel layer formation. When the oil
it was reported that the flux reduction at the begin- concentration is higher, the layer becomes larger
ning of the sunflower oil–n-hexane filtration was and generates larger resistance to the flux perme-
type of concentration polarization phenomenon and ation33,36,41. As elucidated by Kim et al.41, convective
gel layer formation on the membrane surface39. solute transport to the membrane produces a sharp
Moreover, the flux drop at the end of the filtration gradient of concentration inside the boundary layer.
was due to the deposition of a gel on the membrane Because of diffusion, solute back-transport into the
surface38,41,42. The deposited layer is formed because bulk takes place, and a close-packed arrangement of
of the phospholipids retained on the membrane sur- the solute is formed. As a consequence, no more
face and pores plugging14,43. solute can be accommodated, and the mobility of
Fig. 4 also confirms that the increase in oil con- solutes is restricted.
centration leads to a higher reduction in flux. This Scanning electron microscopy images of the
decrease takes place due to an increase in oil con- fouled membrane, as displayed in Fig. 5, confirm
centration, resulting in the increase insolution vis- that a foulant layer on the membrane’s surface is
cosity. With the rise of viscosity, a smaller flux is present.
N. Aryanti et al., Ultrafiltration Membrane for Degumming…, Chem. Biochem. Eng. Q., 32 (3) 325–334 (2018) 331
Ta b l e 3 – Rejection of phospholipid and fatty acids at vari-
ous CPO concentrations at a pressure of 1 bar and feed tem-
perature of 30 oC
Phospholipid Free fatty acid
CPO concentration
rejection (%) rejection (%)
30 % >99.21 16.13
40 % 92.93 12.93
50 % 37.52 9.09
(a) (b)
(c) (d)
F i g . 7 – Fitting of experimental data (feed temperature: 30 °C, pressure: 1 bar) to Hermia’s model: (a) complete blocking, (b)
standard blocking, (c) intermediate blocking, and (d) cake/gel layer formation
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