INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,
MANAGEMENT & APPLIED SCIENCE (IJLTEMAS)
ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XIII, Issue IX, September 2024
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Analysis of Acid Options in the Purification of Spent Motor Engine
Oil Using Acidified Clay
A. A Aboje
1
, A. A Jibril
2
, H. Uthman
3
and N. Bello
4
1,2,3
Department of Chemical Engineering, Federal University of Technology, PMB 65 Minna, Niger State, Nigeria.
4
Department of Chemistry, Sokoto State University, Sokoto, Northwestern Nigeria.
DOI : https://doi.org/10.51583/IJLTEMAS.2024.130912
Received: 21 September 2024; Accepted: 04 October 2024; Published: 16 October 2024
Abstract: This research is centered on the purification of Spent Shell Helix (HX3 20W-50) lubricating oil using acidified clay
treatment with three acids options: mineral sulfuric acid (H
2
SO
4
), organic acetic acid (CH
3
COOH), and organic citric acid
(C
6
H
8
O
7
), (a novel washing agent). The clay mineral, spent, purified, and fresh lubrication oil samples were characterized to
determine their physicochemical properties. The clay mineral was characterized using Energy-Dispersive X-Ray Fluorescence
(EDXRF). The result indicated that the clay was bentonite clay and it was successfully acidified. The result also indicated that
properties of the spent lubricating oil such as Kinematic viscosities at 40
o
C and 100
o
C increased from 118.9 cSt and 13.9 cSt for
the spent oil to 169.7 cSt and 15.2 cSt, 178.2 cSt and 16.3 cSt, 183.4 cSt and 16.8 cSt for the oil samples purified with C
6
H
8
O
7
,
CH
3
COOH and H
2
SO
4
respectively Also, the flash point increased from 106
o
C for the spent oil to 133
o
C, 180
o
C, 189
o
C for the
oil samples purified with C
6
H
8
O
7
, CH
3
COOH and H
2
SO
4
respectively. The FTIR analysis of the spent oil revealed the presence of
primary oxidized products, absent in spent engine oil purified with mineral sulphuric acid (H
2
SO
4
), organic acetic acid
(CH
3
COOH), and fresh oil. Acidified clay effectively purified the spent engine oil, bringing its physicochemical properties closer
to those of fresh oil. However, the effectiveness of the treatment varied depending on the specific acid used.
Keywords: Spent oil, purification, shell helix, acidified clay, viscosity
I. Introduction
Lubricating oils, its derivatives, and lubricants exhibit significant chemical complexity [1]. Lubricating oil is essential for various
internal combustion engines, it goes beyond simply smoothing friction between moving parts. It also cleanses components, guards
against corrosion, enhances sealing, and cools the engine by transporting heat away. Due to its widespread use in a diverse range
of machinery, from cars and trucks to airplanes and industrial equipment, lubricating oil stands as one of the most crucial
products derived from crude oil [2]. Lubricating oils are viscous liquids that are used to minimize friction and wear between parts
rubbing together in a variety of combustion engines, automobiles, and machines [3].
Used lubricating oil includes engine oil, transmission oil, hydraulic oil, and cutting oil that have been used for a period of time.
Over time, the original oil components degrade and mix with contaminants like metals, ash, carbonaceous residue, water, varnish,
gums, and asphaltic substances from the engine's wear. This contamination makes the oil less effective, so it must be regularly
changed and removed from vehicles, machinery, and equipment to prevent damage [4].In 2008, The United States Environmental
Protection Agencies (EPA) set a standard for used oil, defining it through a three-part approval process.
Firstly, the oil must be derived from either Petroleum-based sources or synthetically derived materials, excluding animal and
vegetable oils. Secondly, the oil must have been used for lubrication, hydraulics, heat energy transfer, or similar purposes.
Unused oils, such as those from tank cleanouts or spills, are excluded. Additionally, products like antifreeze, kerosene, and those
used solely for cleaning or solvent purposes are not considered used oil. Finally, as a result of being used, oil inevitably becomes
contaminated with various physical and chemical impurities. These contaminants, generated from handling, storing, and
processing the oil, can include physical materials like metal shavings, sawdust, or dirt, as well as chemical substances such as
solvents, halogens, or saltwater [5].
Improper disposal of used lubricating oil can pose significant threats jeopardizing environmental sustainability and economic
stability. Discharging it onto land, water, or even burning it as fuel leads to serious pollution. These practices pollute the
environment with harmful metals and other contaminants [6]. Generally, Engine oil wears out for two key reasons:
i. Accumulation of impurities in the oil
ii. Oil chemical alterations.
These effects compromise the oil's critical properties, hindering its effectiveness in use [7].
To combat this issue, we must prioritize sustainable alternatives like recycling, which is currently considered the most effective
approach to addressing the detrimental effects of improper used oil disposal [8]. Beyond environmental benefits, re-refining used
lubricating oil offers a more sustainable approach to producing base oil compared to using crude oil. This process requires
significantly less raw material and utilizes up to 90% less energy, minimizing environmental impact [9].
INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,
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Certain large-scale industrial users of lubricants around the world have adopted on-site oil regeneration. This process utilizes
physicochemical methods to clean used oil, effectively removing contaminants. The regenerated oil is then either blended with
virgin oil for use in internal combustion engines (ICEs) or directly repurposed for industrial applications like gear lubrication,
cutting oils, and lubricants for metal rolling [10].
Despite a depth of comprehensive research, several studies have explored the potential of acidified clay for purifying used engine
oil. The Table 1 summarizes some of these investigations.
Table 1: Application of Acidified Clay technique in the purification of Used Engine Oil
S/N
Author
Sources
Of UEO
Acidification
Method
Purification
Parameters
Application
1.
Ugwele and
Chime,
2019
Used Mobil
oil
Acid/clay, acid/charcoal and
acid/clay/charcoal method
using sulfuric acid, acetic acid
and hydrochloric acid
Acid Concentration = 30ml
Bleaching Temp = 110
0
C for 10
minutes
To be used in combustion
engines of cars, industries and
factories
2.
Afolabi
et al., 2016
Used Total
Quartz
5000 20W-
50
Acid/clay method using H
2
S0
4
Acid Concentration = Varied
Conc Bleaching Temp =
Preheated for 10 minutes
To be used in combustion
engines of cars, industries and
factories
3.
Shabanzade
et al., 2018
Waste
Engine
Oil
Acid/clay method using H
2
SO
4
,
HCl and CH
3
COOH
Acid Concentration = Varied
Conc Bleaching Temp = 100
0
C
for 1hour
To be used in combustion
engines of cars, industries and
factories
4.
Mintesinot,
2021
Used
Engine
Oil
Acid/clay method using
Hydrochloric acid and Acetic
acid
Acid Concentration = 10 ml
Bleaching Temp = 250
0
C
To be used in combustion
engines of cars, industries and
factories
[3,8,15,17]
II. Materials and Methods
Materials
This research exclusively relied on locally sourced materials, they include the used (Shell Helix HX3 20W-50) Crankcase oil
from Honda civic 2008 model, Clay from the back of talba market in Minna Niger State, at a depth of about 30 cm, Conventional
laboratory reagents from Panlac Chemicals along Keteren Gwari Road, Minna Niger State. Apparatus and Equipment from
National Board for Technology Incubation David Mark Road, Minna Niger State.
Methods
A 1000 cm³ round-bottom flask was used to mix thoroughly 200 g of clay particles with a size of 74 μm with 400 cm
3
of 1M
H
2
SO
4
. The mixture was subjected to heating at 200 °C using a magnetically stirred hot plate for a duration of 3 hours [11].
Afterwards, the clay was subjected to washing with distilled water to eliminate remaining precipitates, stones, and impurities until
a neutral pH was reached as indicated by a pH indicator. The clay was then filtered and baked for about 6 hours at 200
o
C to
remove water and stored in dry place to be used later in the purification process. The obtained dry and clean clay is called
activated clay because it is active chemically and electrostatically as reported by [12].
To eliminate contaminants like micro impurities, metal chips and sand from used lubricating oil, a filtration process was carried
out. The filtration process involved the use of a buchner funnel and filter paper. The filter paper was fitted into the buchner funnel
and the used oil was then filtered by passing it through the set-up. Following a 24-hour settling period, the oil underwent
preheating at 45 °C for 30 minutes. This preheating step promotes the degradation of specific additives, reducing the workload of
the acid [13].
Three separate beakers were then used to accurately measure three samples of pre-treated engine oil each measuring 300 cm
3
.
Then Separate aliquots of each acid (30 cm³ each) were individually transferred into 50 cm³ beakers. To prepare for the reaction,
the regulated hot plate was activated, and the beaker containing 300 cm³ of used engine oil was placed on the hot plate. The oil
was heated for approximately 5 minutes until it reached a temperature of 45 °C. Following this heating step, each acid was
carefully added to its respective beaker containing the preheated oil. The first beaker 1M H
2
SO
4,
Second beaker 1M CH
3
COOH
and third beaker 1M C
6
H
8
O
7
. The whole mixture was then stirred consistently for 10 minutes. Following the acid treatment, the
acid-treated oils were left undisturbed for 24 hours. This allowed sedimentation of insoluble materials, forming a residue (acidic
sludge) at the bottom of the beakers. Subsequently, the acidic mixtures were carefully decanted using mesh filters into separate
500 mL beakers. This process effectively separated the treated oil from the settled sludge, which was then discarded properly [3].
The Acidified clay (30 g), grounded to a particle size of 74 μm, was packed into a Buchner funnel equipped with filter paper. This
setup was then connected to a vacuum pump. Subsequently, the sulfuric acid-treated oil was passed through the clay bed using the
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vacuum. This filtration process effectively removes impurities from the oil and was repeated for each of the acid-treated oil
samples [14].
To neutralize the acid in the three oil samples, 100 cm³ of 10 % sodium hydroxide (NaOH) solution was added to each oil sample.
The mixture was then left undisturbed for 24 hours to allow for phase separation between the oil and the aqueous layer. Following
this settling period, the oil layer was carefully decanted into a clean beaker, and the remaining residue at the bottom was
discarded appropriately. Finally, the pH of the decanted oil was measured and recorded to verify the effectiveness of the
neutralization process [3]. Finally, the resulting purified lubricating oil was obtained and ready for analysis as reported by [11].
III. Results and Discussion
The characterization of the clay sample was carried out using EDXRF analysis so as to determine the soil composition and type of
clay sample used for the experiment, Afterwhich the spent, purified and fresh engine oil samples (Shell Helix HX3 20W-50) were
characterized.
Characterization of Clay Sample using Energy-Dispersive X-Ray Fluorescence Spectroscopy (EDXRF) Analysis
Table 2: Result of Characterization of Clay Sample using Energy-Dispersive X-Ray Fluorescence spectroscopy (EDXRF)
Analysis
S/N
Element
Weight % (Concentration)
1.
Fe
2
O
3
7.399
2.
MgO
2.350
3.
Al
2
O
3
24.460
4.
SiO
2
49.819
5.
K
2
O
1.215
6.
TiO
2
0.927
7.
CaO
0.742
8.
BaO
O.512
9.
SrO
0.730
10.
L.O.I
11.846
L.O.I = Lost on Ignition
The result obtained in the analysis of the clay sample in Table 1 indicates that the sample is primarily composed of Alumina
(Al
2
O
3
) and silica (SiO
2
) as the two main constituents. It also contains Iron (III)oxide (Fe
2
O
3
) in large proportions while other
constituents such as Magnesium oxide (MgO), Barium oxide (BaO), Titanium oxide (TiO
2
), Calcium Oxide (CaO), Potassium
oxide (K
2
O), and Strontium oxide (SrO) are present in noticeable contents.
The result in Table 1 above indicates that the percentage ratio of Alumina (Al
2
O
3
) to Silica (SiO
2
) is approximately 0.5 which can
be compared to the basic composition of bentonite clay which is > 0.3 [15].
Characterization of Spent, Purified and Fresh Engine Oil Samples Using Quality Test Procedures Kinematic Viscosity:-
Figure 1: Effect of Kinematic Viscosities of Engine oil Samples at 40
O
C and 100
O
C
0
50
100
150
200
250
Spent oil
sample
Spent oil +
C6H8O7
Spent oil +
CH3COOH
Spent oil +
H2SO4
Fresh oil
sample
Kinematic viscosities at 40 degres celcius (cSt)
Kinematic viscosities at 100 degres celcius (cSt)
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Several factors contribute to an increase in engine oil's viscosity, making it flow less easily, factors such as dirt, glycol and soot
while fuel dilution and the breakdown of special molecules in some oils can make it thinner [16]. The thicker the oil (higher
viscosity), the stronger the protective film it forms on engine parts [3]. Figure 1 above indicates that the viscosity is greatly
influenced by the type of acids and clay spent for the purification of the used engine oil. The kinematic viscosity of the spent oil
was obtained as 118.9 cSt and 13.9 cSt which is in agreement with the work reported by [17]. While the kinematic viscosities of
the purified lubricating oil samples were much higher than that of the spent engine oil and comparable to that of the fresh oil. The
kinematic viscosity obtained for the fresh oil sample is in agreement with 192 cSt and 18.3 cSt reported by [18]. While used
engine oil is typically thinner due to impurities, the purification process using acids can convert and remove these contaminants,
resulting in thicker, higher viscosity oil after filtration. [19]. The result from figure 1 above indicates that the spent oil samples
purified with Organic acetic acid (CH
3
COOH) and Mineral sulphuric acid (H
2
SO
4
) solutions gives kinematic viscosities that are
very close and comparable to that of the fresh oil sample which means that the purification of spent engine oil using this two acids
with acidified clay is very effective in removing contaminants however purified engine oil using acidified clay method with
sulphuric acid as a purifying agent has advantage over other techniques [3].
Specific Gravity:-
Figure 2: Effect of Specific Gravity on Engine oil Samples
Specific gravity compares how tightly packed a substance is (its density) to a standard, often water and the more solid particles
there are in the used oil, the higher its specific gravity gets [20]. Figure 2 shows the effects of the specific gravity obtained for the
spent, purified and fresh engine oil samples using the acidified clay treatment procedure. The result for the spent engine oil is in-
line with 0.902 reported by [15], 0.900 obtained for used mobile oil reported by [3] and 0.91 reported by [21]. While the results of
the regenerated oil samples are less than that of the spent engine oil and in agreement with 0.8759 reported by [22] and 0.849 to
0.898 reported [23]. [24] reported that used engine oils thickens (higher specific gravity) with use due to the buildup of impurities
like worn metals and degraded oil components during operation. From the result obtained, The acidified clay purification method
using mineral sulphuric acid improved the specific gravity of the engine oil and gives values that are equivalent to that of the
fresh engine oil.
Sulphur Content:
Figure 3: Effect of Sulphur Content on Engine oil Samples
Spent oil sample Spent oil +
C6H8O7
Spent oil +
CH3COOH
Spent oil +
H2SO4
Fresh oil sample
0.82
0.84
0.86
0.88
0.9
0.92
Specific gravity (kg/cm
3
) of Engine oil samples
Specific gravity (kg/cm3) of Engine oil samples
0
0.2
0.4
0.6
0.8
Spent oil sample Spent oil +
C6H8O7
Spent oil +
CH3COOH
Spent oil +
H2SO4
Fresh oil sample
Sulphur Content (wt %) of Engine Oil Samples
Sulphur Content (wt %) of Engine Oil Samples
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High sulfur content in used oil indicates potential engine wear. As engine parts rub against each other, tiny metal particles
contaminate the oil. Sulfur in the oil reacts with these metal fragments, forming compounds with low melting points.
Furthermore, in engines using refined oils, leftover sulfur from fuel can oxidize (break down) into acidic compounds that
contribute to engine corrosion [14]. Figure 3 indicates that the spent engine oil has a high sulphur content as compared to the
purified engine oil samples which shows low values of sulphur content, the fresh engine oil shows a total absence of sulphur
content indicating that sulphur was introduced into the spent engine oil due to engine parts rubbing against each other [24]. The
result obtained is in agreement with the results reported by [3,11 ,14]. The result shows that the spent engine oil sample purified
with organic acetic acid gives the lowest sulphur content of 0.038 (wt%) which is comparable to the sulphur content of the fresh
engine oil sample.
Flash Point:
Figure 4: Effect of Flash point on Engine oil Samples
Engine oil's flash point indicates the minimum temperature at which its vapors become flammable, highlighting the importance of
using oil with a higher flash point as it signifies the lighter, more volatile components have evaporated, reducing fire risk [25]. A
significantly low flash point in engine oil warns of potential contamination with volatile substances like gasoline [19]. From
figure 4 the result obtained for the flash points of the purified engine oil and fresh engine oil samples are higher than that of the
spent engine oil and are in agreement with the results of the research work reported by [17,13,6]. Also, the results obtained for the
purified engine oil samples are higher than 130
o
C which is the minimum ASTM limit (ASTM D93) for the regeneration of spent
engine oil [26].
The flash point obtained from the purification process using Mineral sulphuric acid (H
2
SO
4
) is close to and comparable to that of
the fresh engine oil.
Pour Point:
Figure 5: Effect of Pour point on Engine oil Samples
0
50
100
150
200
250
Spent oil sample Spent oil +
C6H8O7
Spent oil +
CH3COOH
Spent oil +
H2SO4
Fresh oil sample
Flash point (
0
C) of Engine oil samples
Flash point (0C) of Engine oil samples
-16
-14
-12
-10
-8
-6
-4
-2
0
Spent oil
sample
Spent oil +
C6H8O7
Spent oil +
CH3COOH
Spent oil +
H2SO4
Fresh oil
sample
Pour point (
0
C) of Engine oil samples
Pour point (0C) of Engine oil samples
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Engine oil's pour point indicates the temperature at which it becomes too stiff to flow freely. This matters most in cold weather.
When the oil is too stiff due to a high pour point, it struggles to reach engine parts during startup [23]. Figure 5 shows the result
acquired for pour point of the spent engine oil, purified engine oil samples and the fresh engine oil. The values obtained for the
purified oil samples are within the range of -11
o
C to -9
o
C and are higher than that of the spent engine oil which is -15
o
C. This
result is in-line with the research work reported by [23, 24]. The acidified clay treatment using Organic Acetic acid (CH
3
COOH)
and Mineral Sulphuric acid (H
2
SO
4
) as washing agents gives pour point values that are very close and comparable to that of the
fresh engine oil, which indicates that they are very effective in the purification of spent/contaminated engine oil.
Characterization of Engine oil Samples using Fourier-Transformed Infrared Spectroscopy (FTIR) Analysis
Figure 6: FTIR Analysis of Spent Engine Oil Sample
Figure 7: FTIR Analysis of Spent Engine Oil Purified with Organic Citric Acid
Figure 8: FTIR Analysis of Spent Engine Oil Purified with Organic Acetic Acid
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Figure 9: FTIR Analysis of Spent Engine Oil Purified with Mineral Sulphuric Acid
Figure 10: FTIR Analysis of Fresh Engine Oil Sample
FTIR analysis is a technique used to identify the presence of contaminant-attracting molecules, like carboxyl and hydroxyl
groups, within a substance [8]. FTIR analysis is a versatile technique capable of examining various sample types, including
liquids, solutions, pastes, powders, films, fibers, and gases. It can even analyze materials present on the surfaces of other objects
[27]. FTIR spectrometers act as powerful, multi-purpose tools for monitoring oil health. Their ability to create a unique
"fingerprint" of the oil's molecules allows for comprehensive analysis of its condition [19]. The FTIR spectra of the spent,
purified and fresh oil samples are presented in Figures 6 to 10 respectively. Figure 6 represents the spectra of the spent engine oil.
The spectra points at 1230.0 cm
-1
, 1155.5 cm
-1
and 1036.2 cm
-1
shows the presence of primary oxidized products at high
temperatures with c-o stretch [27]. They indicate the presence of carboxylic acids. The strong band at 1606 cm
-1
indicates the
presence of nitration products [15] because it falls within the range of 1600-1650 cm
-1
.
Figure 7 represents the spectra of the
purified engine oil using acidified clay with organic citric acid (C
6
H
8
O
7
). The stretching bands at 1155.5 cm-1 and 1080.9 cm
-1
shows the presence of primary oxidized products at high temperatures. The presence of nitration products was also noticed at
spectra peak of 1651 cm
-1
. There is also a broad stretching band at 3410.5 cm
-1
suggest the presence of water, glycol
contamination and antioxidant additives because it fell within the absorbance region of 3600-3400 cm
-1
reported by [11]. Figure 8
represents the spectra of the purified engine oil using acidified clay with organic acetic acid. The spectra peak at 1651.2 cm
-1
indicate the presence of nitration products as reported by [11] because it falls within the range of 1650-1600 cm
-1
. Also, a broad
spectrum was observed at 3421.7 cm
-1
which may indicate the presence of antioxidant additives or water. The spectra peak
noticed at 723.1 is related to aromatic compounds because it falls within the region of 570-800 cm
-1
[28]. This method proved to
be very effective because it those not show the presence of carboxylic acid and aldehyde at 2359.56 cm
-1
[6]. Figure 9 represents
the spectra of the purified engine oil using acidified clay with mineral sulphuric acid (H
2
SO
4
). The spectra band at 1647.5 cm
-1
indicates the presence of nitration products, a broad stretching spectra was also observed at 3414.2 cm
-1
which suggest the
presence of antioxidants additives or water. The acidified clay mineral sulphuric acid treatment indicates the absence of carbonyl
compound, aldehyde, primary oxidized products at high temperatures and fuel residue in the spectra and it shows peaks which are
equivalent to the peaks of the fresh lubricating oil. This is in line with the result reported by [11] which proved its effectiveness in
the purification process.
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IV. Conclusions
The potential of acidified clay with 1M concentration of different acid options was investigated to determine its effectiveness in
the purification of spent engine oil. The acid options used were mineral sulphuric acid (H
2
SO
4
), organic acetic acid (CH
3
COOH)
and organic citric acid (C
6
H
8
O
7
) as a novel washing agent, The effectiveness of these acids in the purification process was
determined using different characterization techniques such as Specific gravity, Kinematic viscosities at 40
o
C and 100
o
C, Pour
point, Flash point, Sulphur content and FTIR analysis to determine the functional groups present in the oil samples. The clay
sample used for the purification process was also characterized using EDXRF to determine the type and group of clay used.
Based on the analysis carried out, the following conclusions were arrived at;
i. The clay soil was analysed and found to be bentonite clay which belongs to Smectite group of clay. Therefore, bentonite clay
can be said to be an effective adsorbent for the acidified clay purification technique using mineral sulphuric and organic acetic
acids. This is because they give results which are equivalent to that of the fresh lubricating oil in the purification process.
ii. The different characterizations carried out on the spent, purified and fresh engine oil samples indicates that the use of acidified
clay treatment with mineral sulphuric and organic acetic acids are very effective for the purification process as compared to the
use of acidified clay with organic citric acid. This is observed in the results obtained for the specific gravity, kinematic viscosities
at 40
o
C and 100
o
C,sulphur content, flash point and pour point. The result showed a substantial improvement in the quality of the
spent lubricating oil after going through the purification technique.
iii. The FTIR analysis carried out indicated the absence of contaminants such as carbonyl group in the spectra of the purified
engine oil using mineral sulphuric acid (H
2
SO
4
) and organic acetic acids (CH
3
COOH), only nitration products were noticed in
their spectra. The FTIR spectra of the spent and purified engine oil using acidified clay with organic citric acid showed the
presence of carboxylic acid and nitration product.
iv. From the points ii and iii above it can be concluded that the purification of used engine oil using mineral sulfuric acid (H
2
SO
4
)
and organic acetic acid (CH
3
COOH) appears to be more effective than using organic citric acid (C
6
H
8
O
7
). Additionally, mineral
sulfuric acid (H
2
SO
4
) demonstrated a slight advantage over organic acetic acid in terms of purification efficacy, effectively
treating spent engine oil and producing a comparable quality to fresh engine oil suitable for reuse in combustion engines for
lubrication purposes.
Acknowledgements
I extend my deepest appreciation to my esteemed Supervisors, Dr. A. A. Aboje, Dr. H. Uthman and N. Bello for their unwavering
patience, encouragement, and guidance throughout this research journey. May Almighty Allah (SWT) shower them with His
blessings, reward their families, and guide them in all their endeavors. Ameen.
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