British Journal of Applied Science & Technology
9(1): XX-XX, 2015, Article no.BJAST.2015.247
ISSN: 2231-0843
SCIENCEDOMAIN international
www.sciencedomain.org
Effects of Process Variables and a Comparative
Study of Methods for Transfer Oil Production from
Spent Engine Oil
I. J. Ani1, J. O. Okafor1, M. A. Olutoye1 and U. G. Akpan1*
1
Department of Chemical Engineering, Federal University of Technology, Minna, Nigeria.
Authors’ contributions
This work was carried out in collaboration between all authors. Author IJA wrote the first draft of the
manuscript. Author JOO provided the initial topic which was eventually modified. Author MAO made
useful suggestions that added value to the study, while author UGA designed and guided the study at
every point to the production of the manuscript. All authors read and approved the final manuscript.
Article Information
DOI: 10.9734/BJAST/2015/17578
Editor(s):
(1)
(2)
Reviewers:
(1)
(2)
Complete Peer review History:
th
Review Article
Received 19 March 2015
Accepted 27th April 2015
th
Published 11 May 2015
ABSTRACT
The influence of process variables on the production of transfer oil from spent engine oil (SEO) is
presented in this paper. Various methods for SEO treatment are also highlighted. Process
parameters like solvent type, solvent to oil ratio, extraction temperature, adsorbent to oil ratio,
adsorption time (contact time), adsorption temperature and base oil to chemical additive ratio
greatly influenced regeneration of base oil from SEO using solvent extraction-adsorption method
which has also been established to be more advantageous over previous methods used in this
process.
Keywords: Spent engine oil (SEO); regeneration; transfer oil; process parameters; methods of
treatment of SEO.
_____________________________________________________________________________________________________
*Corresponding author: E-mail: ugaekon@yahoo.co.uk;
Ani et al.; BJAST, 9(1): xxx-xxx, 2015; Article no.BJAST.2015.247
1. INTRODUCTION
which can permit the re-used of the treated oil
[16]. However, not all of these methods are
economically viable, mainly due to the high
energy consumption along the recovery process,
together with the treatment of the produced
residue [17]. Acid treatments have been used for
SEO treatment by different authors for deasphalting and settling of acid sludge [10,14,18].
Udonne [19] reported that Acid/Clay treatment
proves to be the best option among
Distillation/Clay, Activated charcoal/Activated
clay and Acid treatment methods with optimum
yield of 80% (compare with that of crude oil
which is 5 to 10%), 89.1 cSt compare with the
92.8cst for the fresh lube oil and other improved
properties of the SEO. It was also observed that
acid/clay treatment is a good method for heavy
metal removal. Catalytic cracking (zoelite as
catalyst) and acid/clay treatment was used by
Rahman et al. [14], and Hani and Al-Wedyan [20]
with oil recovery between 62% and 66%. The
zeolite was used mainly for the removal of
carbon particles. It has been reported that the
clay was used to neutralize the acid of the
treated oil and for removal of colour [20]. The
method was used to produce brighter oil instead
of quality oil. 70% concentration of sulphuric acid
and activated carbon was the technical principle
used by Ogbeide [16] and it was discovered that
25 L of SEO yield 10 L of lubricating oil after
proper treatment and 50 L of SEO yield 20 L
whereas 220 L of crude oil would be required to
yield the same 10 L and 440 L of crude oil will be
required to produce 20 L of lubricating oil. Also,
acid treatment was used by Olutoye [13], but the
excess acid in the sludge was neutralized and
the sludge was further processed for the
production of ink. Emam and Shoaib [10] showed
that acid/clay treatment gave a better quality than
solvent/clay treatment but the later gave a higher
yield of 83%. A modified aluminium sulphatesodium silicate-acid-base method employing a
small quantity of acid and giving a high yield
(approximately 60%) was proposed [21] to
improve the conventional process of treating
SEO that yields approximately 50% which is
thought
to
be
time
consuming
and
environmentally perilous because of the acid
sludge. Acid to oil ratio and adsorbent to oil ratio
affected the regeneration of base oil from waste
lubricating oil. The efficiency of the operation
increases with increase in the ratios. Thus,
desludging ratio of 20:1 and that of adsorption of
10:1 gave the best yield of 82.9% [22]. Bridjanian
and Sattrin [23] reported that in this early
century, the most common technologies used are
sulphuric acid/bleaching earth and propane
The importance of environmental cleanliness to
the general wellbeing of man and his environ
cannot be overemphasized. This common factor
has driven researchers to finding solution to
environmental pollution; whether gaseous, liquid
or solid [1-3]. The discharge of spent engine oil
on the soil is an environmental pollution problem
which must be handled with seriousness. It has
been noted that there is a global increase in the
use of vehicles leading to increase in the
consumption of engine oil which is later
discarded after use [4]. This cycle of events
leads to the increase in the level of pollution by
spent engine oil (SEO). The used oil contains a
lot of contaminants like salt, broken down
additives, varnish, gum, hydrocarbons, heavy
metals, PCBs (polychlorinated biphenyls),
halogen compounds etc [4-6] that are poisonous
to aquatic life, human being and its environs.
SEO may contain hazardous components like
polycyclic aromatic hydrocarbons (PAHs) and
aliphatic hydrocarbons which have the ability to
cause skin cancer [7] and fuel, which may reduce
the flash point and make the material flammable
[6]. Also, most heavy metals such as V, Pb, Cr,
Cu, Si, Al, Mg, Zn, Ca, Ba, Mn, Ni and Fe which
are not easily detected in unused lubricating oil
have been noted in previous research [8-10] to
give high content in used oil. According to Yong
et al. [11], these heavy metals may be absorbed
in the soil in the form of exchangeable cations
and/or can also bound to organic matter in soils
though it depends on the local environmental
conditions and the type of constituent present in
the soil–water system. Zenon et al. [12] noted
that SEO is not safe ecologically but its technical
and physical properties go alongside with the
requirements of beneficial re-use and it allows
the recovery of mineral base oil used to create
new lubricants as a clean fuel. The sludge being
a by-product from recycled used lubricating oils
can be used for other purposes such as
production of ink [13], modifier for bituminous
materials for road, due to its richness in carbon, it
can be used for the generation of carbon bar, it
can be combustible which is capable of
generating a net heating value of 4,000 kcal/kg
[14,15] used in cement kilns for incineration.
Considering these points, re-refining SEO (for
environmental safety) is of a great interest due to
several benefits accrue to it.
Several methods have been used for the
treatment of SEO and the level of contaminants
removal depends on the type of method used
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Ani et al.; BJAST, 9(1): xxx-xxx, 2015; Article no.BJAST.2015.247
extraction/sulphuric acid/bleaching earth (clay)
treatment methods which generate acid sludge
(acid tar), filter cake from bleaching earth and
waste water which contains high concentration of
heavy metals or sulphuric acid (in the range of
17%w/w). They implied that using the first
method, about 200 tons of environmentally
harmful by-products is generated from each 1000
tons of used oil processed. Modern processes
like vacuum distillation and hydro-treatment
substitute sulphuric acid/bleaching earth and
propane extraction/sulphuric acid/bleaching earth
(clay) treatment methods; which gives a high
viscosity index lube oil with a good and stable
colour and oxidation resistance, yet having low
or no discards. This method (that is vacuum
distillation and hydro-treatment) has been used
by several authors [10,23,24] which is similarly
used in petroleum refining for the removal of
H2S, NH3, H2O and metals in two stages which
are: mixing the used oil with solid catalysts (CoMo with Alumina) in the presence of hydrogen
and removal of sulphur and nitrogen compounds
in used lubricants by alumina and Ni-Mo catalyst
in spherical or extruded shape [25].
94% yield. Composite solvent (25% 2-propanol,
37% 1-butanol and 38% butanone) of solvent to
oil ratio of 6:1 at vacuum pressure 600 mmHg
and distillation temperature of 250°C was used
by Durrani et al. [26] to treat used engine oil
followed by clay (fuller’s earth) which gave an
optimum yield of 68% base oil. The performance
was investigated on percentage sludge removal
and percentage oil loss. Hamad et al. [18] used
solvent extraction to treat used lubricating oils
and the solvent used are liquified petroleum gas
(LPG) condensate and stabilized condenser with
overall yield of oils as 79%. Activated clay
(fuller’s earth) was used but the major challenge
encountered with this method is the high
temperature of the solvent for its recovery. An
investigation was carried out on adsorption for
the elimination of a potentially carcinogenic
substances from waste lubricating oils such as
polycyclic aromatic hydrocarbons (PAHs) by
Moura et al. [17] with activated carbon as the
most efficient adsorbent in the removal of PAHs
and at the end of the process the technical
principle proposed for the recovery of base oil
from waste lube oil comprises of solvent
extraction, adsorption and solvent distillation
(recovery). They used the following solvents to
study the solubility of base oil in the waste
lubricating oils; n-pentane, n-hexane, toluene,
ethanol, propan-2-ol, 1-butanol and tert-butanol.
1-butanol presented better efficiency as
extraction agent of base oils followed by 2propanol and ethanol. The adsorption isotherm
indicated that activated carbon has a great
potential for concentrated PAHs molecules on its
surface. Waste lubricating oil was treated with a
stabilized condensate (solvent) [29] with few
drops of demulsifier followed by a fixed amount
of different adsorbents to study their activity on
the solvent treated waste oil. They reported that
out of the following adsorbents; activated
bentonite, bentonite, egg shale powder, date
palm kernel powder, and acid activated date
palm kernel, activated bentonite gave the best
physical properties followed by the date palm
kernel but the later with contact time of 4 h gave
the best conditions for treating the waste oil. The
whole process was carried out in ambient
temperature.
Lately, extraction process followed by adsorption
has become the most attractive and competitive
method for the treatment of SEO. The solvent
chosen must have high solubility parameters for
the base oil recovery [4,26,27] and less soluble
in additives and carbonaceous compounds [27].
Sterpu et al. [6] investigated the use of solvent
extraction followed by vacuum distillation for the
treatment of SEO. The solvent used are alcoholketone composite (25% 2-propanol, 50% 1butanol, 25% butanone also known as methyl
ethyl ketone (MEK) with an optimum yield of 92%
using solvent to oil ratio of 4:1. The optimum
was based on its high removal of ash content
(about 49%). Emam and Shoaib [27] used MEK
as the solvent for the oil recovery followed by
clay treatment which gave 83%. The activities of
three solvents (1-butanol, MEK and 2-propanol)
based on variation of parameters like solvent to
oil ratio and extraction temperature were studied
by Durrani et al [28] and it was discovered that
MEK gave the best performance and the result
was based on lowest oil percentage losses and
1-butanol being highest in sludge removal both at
50ºC. Kamal and Khan [4] studied the solvency
(for sludge formation) of the following solvent on
used lubricating oil: 1-butanol, MEK, 1-hexanol
and 2-butanol. 1-butanol gave the maximum
sludge formation followed by MEK with a slight
difference of 0.3%. MEK was preferred because
of its low boiling point (for easy recovery) with
These are the most common technical principles
used for the treatment of SEO globally but each
of them has different constraints environmentally
or economically. The acid- clay treatment which
is the conventional method generates acid
sludge, acid water, and low yield [14]. The byproducts from this process requires further
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Ani et al.; BJAST, 9(1): xxx-xxx, 2015; Article no.BJAST.2015.247
treatment
to
avoid
its
environmental
contamination by it thus making the process less
cost-effectively feasible, but it has great effect
on the quality of the produced base oil especially
in the removal of heavy metals [10,19]. In the
hydrogenation-distillation method, the challenge
is at the hydrogenation stage whereby the nature
of the heteroatom (S, O, N) can form gaseous
compounds and stable ones that can remain in
the solution and they are potentially pollutant
depending on the level of contaminants/
deterioration of the oil, temperature and catalyst
[30]. Solvent extraction is economically and
ecologically viable [30,31] but the product is not
commercially desirable because oxidation
product remain solubilised in the oil. Due to these
challenges, a lot of authors have worked on the
use of adsorbent for the treatment of SEO which
have appeared to improve the quality of the
solvent treated product [4,26,29,30] with a
reasonable yield. Thus solvent extractionadsorption process appears to be the best
method for SEO treatment.
As reported by Richardson et al. [32], one of its
important applications is in the separation of
aromatics from paraffin and naphthenic
compounds to improve the temperature-viscosity
characteristics of lubricating oils. Thus the
process is of great influence in the treatment of
spent engine oil. The major impact of this
technical principle is on the recuperation of the
base oil and formation of sludge. This is subject
to the type of solvent and other parameters used
based on previous findings [4,17,26,31].
1.2 Adsorption Process
Adsorption has to do with adherence of
molecules or particles on a solid surface by a
weak bond though the binding can be reversible
[34]. It is a physicochemical process.
Compounds with colour and those that have
taste or odour tend to bind stronger than any
other. Thus, the process aids in the removal of
colour and odour and some other impurities in
used oils with activated clay [29]. Impurities
accumulated in oils or used oil can be reduced
by bleaching via adsorption process that makes
use of clay [35], activated alumina, activated
clay, carbon and silica gel [36]. According to
Ajemba and Onukwuli [37], bleaching by
adsorption involves the elimination of impurities
like fatty acids, gums, trace metals, phosphatides
followed by decolourization. The adsorbent to be
used should have the ability to change the colour
of the oil without altering the chemical properties
of the oil [36] and with negligible loss of other
materials. Many studies have been carried out on
the use of adsorbents in form of activated carbon
or activated clay for the treatment of SEO to
regenerate lubricating base oil [4,14,16,19,
22,26,38] and their results showed a strong
improvement in the quality of the oil that have
either been acid-treated or solvent-treated. The
activation of the adsorbent (physical or chemical
treatment) such as acid, alkaline and ionexchange treatment are often necessary for most
adsorbent to modify their structure for higher
activity. A good adsorbent must encompass
carbonates compounds (carbonaceous material)
and much of the substances volatilizes on
heating, leaving behind a porous structure of
carbon that usually contains some hydrogen
(carbonization). This may then be activated to
The treatment of SEO regenerates base oil by
removing contaminants which may include
unused chemical additives [9,10].
1.1 Solvent Extraction Process
Extraction is the drawing or pulling out of
something from something else. In terms of
solvent extraction (liquid-liquid extraction) it is the
separation of components of a liquid mixture by
treatment with a solvent in which the desired
component (solute) is soluble preferentially [32].
The mechanism of this process begins with
vigorous agitation causing one phase to disperse
in the other. Small droplet creates high interfacial
area for interphase mass transfer, but care must
be taken to ensure that the droplets are not so
small that a diffuse layer appears in the region of
the interface because this can remain in a semistable state over a long period of time and
prevent effective separation from taking place
[33]. A sequential approach is given below
describing effective solvent extraction:
the molecules to reach the other solvent
and migrate into it.
The shorter the distance travelled by the
molecules, the more rapid the extraction
process.
As a result of vigorous agitation, the
dispersal is in the form of droplets.
More vigorous agitation gives rise to
smaller droplets.
The smaller the droplets the more surface
area between the two solvents
More surface area between the solvents
leads to smaller linear distance travelled by
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Ani et al.; BJAST, 9(1): xxx-xxx, 2015; Article no.BJAST.2015.247
further open up the pores and increase total
surface area [36] thus increasing the number of
active sites. In clay activation, the mechanism
involves the replacement of the structural cations
(Al2+, Mg2+, Fe3+) by protons H+ which leads to
high capacity of adsorption (leaching of
impurities)
[34].
Activated
carbons
are
distinguishable by their conditions of preparation,
consequent characteristics [39] and the kind of
precursor used for its production. It is of an
importance that each adsorbate must be weakly
adhered (physisorbed) to the active site of the
adsorbent for easy recycling and the adsorbent
must be inert to the base fluid and should not
irreversibly react (chemisorbs) with the
adsorbate(s) [40].
solubility parameters [26]. Components exhibits
better solubility if their solubility parameters are
very close and have to do with molecular weight.
Thus, since oil is a mixture of high molecular
weight components, it is necessary to use a
solvent with a high molecular weight compounds
that constitute the solvent [18]. This is one of the
most important bases for solvent selection
because from Reis and Jeronimo [41]
investigation, it was observed that when low
molecular weight hydrocarbons were used there
was no segregation of the sludge even after
many days settling by gravity. For solvent
selection, some important factors must be placed
into consideration: molecular weight, boiling point
for easy recovery, availability and cost. Table 1
shows that the solvent with molecular weight
closer to that of the treated oil gave better results
especially in terms of flocculation.
The produced lubricating base oil via the above
described technical principles can be used for
the production of transfer oil by "Blenders and
Compounders" to enhance the performance of
the base oil at required temperature (for viscosity
control) for long-time usage. Transfer oil in this
study refers to a low viscous hydraulic fluid which
can be obtained by blending the regenerated
base oil from SEO with chemical additives to
enhance the efficiency of the lubricant. The
foregone deliberation actually pointed out that
there are various parameters which greatly
influence the production of transfer oil. The
present study was therefore aimed at reviewing
these parameters and providing a new direction
on the production of transfer oil from SEO using
solvent extraction-adsorption method.
2.2 Effects of Solvent to Oil Ratio in
Treatment of SEO
Solvent to oil ratio has great influence on oil
recovery especially in terms of the quality of the
oil and percentage recovery. Durrani et al. [26]
showed that solvent to oil ratio higher than 6:1
reduces the solvency power and does not
improve the properties of the regenerated oil due
to ash content present in the oil. Thus, the higher
the solvent to oil ratio the greater the dissolution
of some contaminants in the surfactant phase
especially the ash forming materials which is not
wanted [6,26]. The effectiveness in the ash
content reduction increases and showed that the
maximum ash reduction is achieved at the ratio
of 4:1 (49% reduction) and declined from the
ratio of 5:1 [6]. But it also indicates that increase
in the amount of solvent used increased the oil
recovery (it improves the solvency power). Kamal
and Khan [4] showed that lower solvent to oil
ratio can lead to the saturation of base oil in the
extract phase which results to low oil recovery
and at higher ratio, maximum oil recovery can be
achieved with oil free sludge. In their study,
sludge formation remained constant at solvent to
oil ratio greater than 3:1 with increasing
temperature. Solvent to oil ratio can also affect
the percent oil losses in the sense that increase
in the ratio leads to decrease in percentage oil
losses. Katiyar and Husain [31] reported that
MEK (Methyl Ethyl Ketone) gave the lowest
percent oil losses followed by 1-butanol, 2propanol and MIBK (Methyl isobutyl Ketone)
respectively. Higher yield is attainable with
increase in the ratio but its affects the quality of
the oil because it decreases the settable matter
2. PROCESS VARIABLES AND THEIR
EFFECTS IN SOLVENT EXTRACTIONADSORPTION PROCESSES
In solvent extraction-adsorption process for the
production of transfer oil through regeneration of
spent engine oil, the following are the operating
parameters that have major effects on the
process: solvent type, solvent to oil ratio,
extraction temperature, adsorbent to oil ratio,
adsorption time (contact time), adsorption
temperature and base oil to chemical additive
ratio. The effects of these variables will be
discussed accordingly.
2.1 Solvent Types
The kind of solvent used is of great influence
especially in terms of its solubility (solvency)
sludge formation and easy recovery. The
efficiency of a polar solvent to flocculate
contaminants (sludge) from SEO depends on the
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Ani et al.; BJAST, 9(1): xxx-xxx, 2015; Article no.BJAST.2015.247
treatment
method.
For
instance,
iron
contamination decreased from 50 ppm to 13 ppm
for composite solvent, for single solvent, it
decreased to 30 ppm and acid treatment gave 15
ppm. The optimal ratio depends on the nature of
the SEO thus optimization is required to know
the optimum ratio for the regeneration of base oil
from spent engine oil. In Table 2, it is observed
that the quality of the treated oil improves up to a
particular solvent to oil ratio and then, begins to
decline.
concentration resulting in slower flocculation and
decrease in the speed of the settling process.
The kind of solvent or solvent composition and
the quantity used, have great effect in used oil
treatment. For instance, Abro et al. [43] carried
out the comparative study of treatment of SEO
by using composite solvent (butanol, propane
and butanone), single solvent (propane) and acid
treatment methods. Their best results based on
the different properties analysed were obtained
with the composite solvent followed by the acid
Table 1. Influence of solvent type in SEO treatment
S/N
1
2
3
Types of
solvent
1-butanol
Molecular
weight (g/mol)
74.12
2-propanol
60.1
MEK
72.11
MIBK
100.16
MEK
72.11
1-butanol
74.12
2-propanol
60.10
1-butanol
2-propanol
MEK
4
5
1-butanol
Tert-butanol
2-propanol
Ethanol
Liquefied
petroleum gas
condensate
(LPG) with
demulsifer
Stabilized
condensate with
74.12
60.10
46.04
Influence in SEO treat
Yield (%)
Ref.
Best in sludge removal
followed by MEK, MIBK and
2-propanl
Following MEK in low
percent oil losses but the
least in sludge removal
Best performance with
lowest percent oil losses
followed by 2-propanol,1butanol and MIBK
The least in terms of lowest
percent oil losses
Best performance with
lowest percent oil losses
followed by 2-propanol and
1-butanol
Best in sludge removal
followed by 2-propanol and
MEK
Following 1-butanol in
percent sludge formation
and MEK in percent oil
losses
1-butanol gave best
performance in sludge
removal followed by 2propanol
Followed MEK in best
performance for oil losses
Best performance with
regards to oil losses
In PAHs removal, 1-butanol
gave the best performance
followed by tert-butanol,2propanol and ethanol
Not indicated
Katiyar and
Husain [31]
Stabilized condensate gave
a better result in the purity
of the used oil
Not indicated
Not indicated
Not indicated
Not indicated
Not indicated
Not indicated
Nimir et al.
[42]
-
Not indicated
79
70
Durrani et al.
[28]
Moura et al.
[17]
Hamad et al.
[18]
Ani et al.; BJAST, 9(1): xxx-xxx, 2015; Article no.BJAST.2015.247
S/N
6
Types of
solvent
demulsifier
n-heptane
n-hexane
MIBK
MEK
Molecular
weight (g/mol)
1-butanol
2-butanol
Benzene
1-hexanol
Influence in SEO treat
Yield (%)
Ref.
No sludge formation
No sludge formation
No sludge formation
Best due to 0.3% difference
in sludge formation over 1butanol, low cost and low
boiling point.
1-batanol gave highest
sludge removal followed by
MEK,1-hexanol and 2butanol
-
97.6
Kamal and
Khan [4]
97.3
Not indicated
98.4
Table 2. Solvent to oil ratio influence on regeneration of base oil from spent engine oil for the
production of transfer oil
Type of SEO
Type of solvent
Ratio range tested
Mixed SEO
25% 2-propanaol,
37% 1-butanol and
38% butanone
Liquefied petroleum
gas condensate and
stabilized
condensate
25% 2propanaol,50% 1butanol and 25%
butanone
2:1-8:1
Not specified
15W40
Optimal solvent
to oil ratio
based on
quality
6:1
Durrani et al. [26]
1:4,1:2,1:1,2:1,3:1,4:1 and
5:1
4:1
Hamad et al. [18]
2:1-6:1
4:1
Sterpu et al. [6]
2.3 Influence of Extraction Temperature
Ref.
the results of previous studies [4,6,18,26,29,31]
considering the cost effectiveness of the process
and good quantity base oil obtained.
Temperature has a great effect on the extraction
process base on some studies that have been
conducted. Mostly temperature, greater than
40ºC do not have any significant change in the
process rather it may lead to poor quality oil. For
instant, Katiyar and Husain [31] investigated on
this effect and discovered that increase in
temperature leads to decrease in percent sludge
removal and reduces percent oil losses. This is
because with increase in temperature there is
always an increase in oil yield and at the same
time an increase in solubility of sludge in solvent
which results in poor quality oil and reduction in
sludge formation [4]. It can also be observed
from studies that increase in temperature up to
50°C reduces percent oil losses especially for
MEK and increased percent sludge removal
especially for 1-butanol. Thus, most treatments
of SEO using solvent extraction [28] are best
done at ambient temperature which is in line with
2.4 Influence of Adsorbent to Oil Ratio in
SEO Treatment
Adsorbent to oil ratio is an important variable to
be considered in SEO treatment because the
quantity of sorbent used with respect to that of oil
has its own maximum adsorbency which mostly
depend on some factors like the kind of
adsorbent, the activation method/conditions of
the adsorbent and the size of the adsorbent. For
instance, from the works of Ajemba and
Onukwuli [37] the optimum decolouration of
activated Ukpor clay for a given set of activation
condition may or may not coincide with its
maximum value of the surface area attained
under those conditions. This statement is in
agreement with their work whereby Ukpor clay,
activated with 5 M of H2SO4, gave the highest
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surface area of 239 m2/g than that of 4 M which
2
gave 226 m /g but the clay activated with 4 M of
sulphuric acid gave the highest bleaching
efficiency of 79.5% for the treatment of palm oil
in the ratio of 1:25 (adsorbent/oil in g/g). A study
carried out on Nteje activated clay showed that
with adsorbent dosage varied from 0.5-4 g, the
bleaching efficiency increased to an optimum
value of 1g and there was no significant effect on
the oil with increase in adsorbent dosage as a
result of equilibrium attainment at 1 g of clay
activated with 3 M HCl [43]. Durrani et al. [26]
varied adsorbent to oil ratio of 3-4 wt%/vol% and
they obtained their optimal value at 4 wt/vol%
(Table 3). Oil to adsorbent ratio of 1:3, 1:5, and
1:10 which gave percentage yield of 63, 74.8 and
82.9, respectively was studied [22]. The results
were simply attributed to the fact that the yield
depended on the amount of clay used. High
amount of clay and fine particles sizes of clay
used can lead to high retention of the oil. Thus,
the optimal yield should be determined by the
quality of the oil. Snail shell was used as a
precursor for activated carbon production with
85% H3PO4 by Kamalu et al. [36] and it was
used to study the bleaching efficiency of palm
kernel oil in which adsorbent dosage was varied
(1, 2 and 3 g). It was observed that for 20 mL
crude sample used, 2 g of the activated carbon
gave the decolourisation with 99.24% colour
reduction. 3 g gave no significant difference in
colour reduction over 2 g. Thus variation of
sorbent dosage is necessary for SEO treatment
to determine the optimal dosage for the process.
2.5 Influence of Adsorption Temperature
Metal uptake and efficiency in its removal is
always dependent on temperature. Therefore,
increase in temperature could enhance the
uptake in adsorption process which results to
increase in average kinetic energy of the metal
ions or colour pigment in solutions containing the
adsorbent. This effect increases the number of
metal ions or colour pigment adhering with the
adsorbent surface by increasing the rate at which
they hit the binding sites at the surface of the
adsorbent thus increasing the adsorption
capacities [44,48]. Increase in temperature can
also retard the rate at which metal ions hit the
active sites of the adsorbents. Oladunni et al.
[48] observed that with increase in temperature
from 30 to 60°C, there was no significant
influence in the adsorption of cadmium ions
using 1 M phosphoric acid activated locust bean
husk as an adsorbent. Also Olayinka et al. [49]
reported that there was no significant positive
effect on adsorption capacity on chromium and
nickel with increase in temperature using both
modified and unmodified coconut husk except for
nickel ions that showed an improvement at 50°C
with HCl modified coconut husk and unmodified
coconut husk after which it retarded at
temperature above 50°C. Their study was carried
out at temperature range of 40-60°C. Earlier
study on the removal of heavy metals from spent
engine oil using chitosan [47] observed that in
the interactive effect study, heavy metals
removals greatly depend on temperature and the
Table 3. Comparison of absorbent to oil ratio from past studies
Adsorbent Precursor
type
Activation
method/
condition
Adsorbent/ Optimal
oil ratio
ratio
Fuller’s
Clay
earth (clay)
Natural
clay
-
3-4 wt%/vol
-
20%wt/wt
SM-400
Activated
clay
C3445
Activated
carbon
Activated
carbon
Chitosan
-
Commercial
1-3wt%/vol
3 wt%/
vol
-
Commercial
0-10% wt
5%wt
Date palm
kernel
Chitosan
Thermal/
carbonized
-
0-10%wt
0.5g and
2.5g
4 wt%/
vol%
-
Optimal quality
Reference
Pour
Ash
Sulphur
point content content
(ºC)
(wt %)
-14
0.021
Durrani et al.
[26]
-6
0.17
0.81%
Emam and
Shoaib [27]
-
-
Shivankar [45]
-
-
38.78%
Al-Zubaidy et
al. [46]
6%wt
-
-
34.15%
0.5 g
-
-
-
Al-Zubaidy et
al. [46]
Jumil et al. [47]
72
2
Ani et al.; BJAST, 9(1): xxx-xxx, 2015; Article no.BJAST.2015.247
chitosan dosage. The temperatures that were
studied are 30°C and 70°C. From the works of
Ajemba and Onukwuli [44], temperature had
great effect on bleaching efficiency of palm oil
using acid activated Nteje clay. They observed
that bleaching efficiency was not favoured by low
temperature. But as temperature increased from
30°C to 120°C, there was an increase in
bleaching efficiency especially at 120°C with
optimum time of 60 min. According to Kamalu et
al. [36] findings, with temperature of 100-200°C,
200°C gave the best bleaching efficiency of
99.24% on palm oil with 2 g of activated snail
shell which did not give a significant difference at
180°C that gave 99.23% for 30 min. Aziz et al.
[38] worked on automobile used oil with
temperature of 150-450°C to determine the
bleaching capacity of local clays and from their
observations, 400°C gave the optimum
temperature with optimum contact time of 4 h
using bleaching efficiency to determine the
optimum condition. With these effects, there is
need to determine the optimum temperature for
an adsorption process based on the nature of the
oil and its contaminants, nature of the adsorbent,
contact time, adsorbent dosage and the size of
the adsorbent.
the kind of base oil and their blends most match
the requirements of the machinery and operating
conditions to which they can be subjected [51].
Lately, all types of lubricating oil contain at least
one chemical additive, and some contain
chemical additives of several different types with
their respective functions. The amount of additive
used varies from a few hundredths of a percent
to 30% or more and this amount varies
depending on the kind of additives in use and the
end use of the lubricant [51]. For instance, for
premium ashless anti-wear hydraulic fluids, TE5064 is always recommended at 0.9%wt-1.0%wt
with maximum handling temperature of 60°C
[52]. Also for anti-friction hydraulic oil, V3268 is
used as an additive which can also be used in
some kind of hydraulic oil and the percentage
recommendation for high level hydraulic oil is
0.85% with highest blending temperature of 66°C
[53]. For HitEC 317 industrial gear oil additive
package, 1.3% wt - 2.0% wt is always
recommended for conventional mineral oils with
maximum handling temperature of 60°C [54].
The additive dosage may be effective at low
dosages and the effectiveness can decrease as
the dosage increases. Thus, the additive may
need to attain a specific dosage before it
becomes active. That means, it performance
increases till a specific dosage and then begins
to decline. Thus optimization of the blending
process variables like base oil to additive ratio
and blending temperature is necessary to
determine the ideal treatment rate for the
production of a lubricant which may be different
for different systems [55].
2.6 Influence of Adsorption/Contact Time
There is need to study the optimum contact time
for an adsorption process because from most
studies reported, it was observed that there is
always an optimum time at which the adsorbent
attains its equilibrium and after that, increase in
the adsorbent dosage or the contact time will be
insignificant. Also in some cases, it can retard
the adsorption process. These effects are in
consonance with previous studies [22,29,36,
38,44,48,49].
3. CONCLUSION
Different process parameters influence the
regeneration of base oil from spent engine oil for
the production of transfer oil (low viscous
hydraulics). The effects of the parameters
depend on the nature of the oil and the level of
contaminants. Thus, variation of the parameters
helps to determine the best parameters for the
SEO treatment to regenerate base oil. Some
solvents are more effective at high temperature
while most of them are not. But considering cost
effectiveness, it is preferable to work with
ambient temperature. Also the dosage of
chemical additives in addition with the produced
base oil is highly influential because the chemical
additive only becomes active at a particular
dosage. The nature of an adsorbent greatly
affects the treatment of SEO along side with its
dosage to oil ratio, adsorption temperature and
the contact time. Several methods have been
2.7 Influence of Base Oil to Chemical
Additives Ratio
Engine oil originally contains base oil and
chemical additive. Engine oil is basically
condemned in a car engine as a result of
degradation of its chemical additives due to its
usage not the base oil. Thus, treatments of SEO
lead to regeneration of base oil only and leaching
of the condemned additives and other impurities.
Base oils are normally of mineral (petroleum) or
synthetic origin, although vegetable oils may be
used for specialized application [50]. The
performance of an additive is always influence by
73
Ani et al.; BJAST, 9(1): xxx-xxx, 2015; Article no.BJAST.2015.247
used for SEO treatment but lately, solvent
extraction-adsorption method is mostly adopted
because of it advantages over other methods;
such as no generation of acid sludge, solvent
recovery, ease of regeneration of spent
adsorbent, high yield of base oil and the
compatibility of the regenerated base with
standards or commercial products; thus it is cost
effective. The paper also revealed that composite
solvent gives better results in terms of both
quality and quantity of the base oil regenerated
than single solvents as a result of the interaction
between the solvents. Acid/clay treatment
method which is the conventional method gives
good quality base oil but produces lots of acid
sludge which requires further treatment; it is
therefore less cost effective and environmentally
unfriendly. Solvent extraction-adsorption process
is recommended for further studies.
8.
9.
10.
11.
COMPETING INTERESTS
Authors have
interests exist.
declared
that
no
competing
12.
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