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The potential of castor, palm kernel, and coconut oils as biolubricant base oil via chemical modification and formulation
Journal Pre-proofs The potential of castor, palm kernel, and coconut oils as biolubricant base oil via chemical modification and formulation Samuel Kofi Tulashie, Francis Kotoka PII: DOI: Reference:
S2451-9049(18)30577-8 https://doi.org/10.1016/j.tsep.2020.100480 TSEP 100480
To appear in:
Thermal Science and Engineering Progress
Received Date: Revised Date: Accepted Date:
8 October 2018 14 November 2019 13 January 2020
Please cite this article as: S. Kofi Tulashie, F. Kotoka, The potential of castor, palm kernel, and coconut oils as biolubricant base oil via chemical modification and formulation, Thermal Science and Engineering Progress (2020), doi: https://doi.org/10.1016/j.tsep.2020.100480
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Title: The potential of castor, palm kernel, and coconut oils as biolubricant base oil via chemical modification and formulation. Author’s full names and address: Samuel Kofi Tulashie*1 and Francis Kotoka1 1 University
of Cape Coast, School of Physical Sciences, Department of Chemistry, Industrial
Chemistry Section, Cape Coast, Ghana. Email:[email protected]
ABSTRACT This study focused on the chemical modification and the formulation of bio-based lubricants from castor, palm kernel, and coconut oils via transesterification and special additives addition. The bio-based lubricants physical-chemical properties were investigated and compared to SAE 40. At 40℃ and 100℃, the kinematic viscosities of the modified castor, palm kernel, coconut oils bio-based lubricants, and the SAE 40 were (208.39 cSt, 16.47 cSt), (58.49 cSt, 11.00 cSt), (42.43 cSt, 10.11 cSt) and (170.45 cSt, 15.60 cSt) respectively. The bio-based lubricants properties suggest that the base oils are comparatively good candidate for motor engines bio-based lubricants if properly modified. Keywords: Biolubricants; Biodegradability; Transesterification; Biodiesel; Fat and oils.
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1.0 INTRODUCTION In recent years, mineral oils and synthetic fluids have been largely used as base oils for lubricants and these oils have posed some serious environmental issues due to their nonbiodegradability [1]. Maintaining an eco-friendly environment has focused attention on environmental regulations and the use of environmentally friendly lubricants in the automobile industries in many countries. Vegetable oils (VO) are the potential candidates gaining popularity due to their excellent properties. Vegetable oils are natural oils that mainly contain a mixture of triacylglycerols [2]. Today, vegetable oils are gaining utmost attention because of increased environmental awareness and their significant environmental advantages [3]. Some of these advantages are their renewable sources and nontoxicity, biodegradability and adequate performance in a variety of applications [4], excellent lubricity due to their higher affinity to metal surfaces resulting in enhanced thin film strength as depicted in Figure 1, high viscosity indices, high flash point, and low evaporative loss [5]. Economically and sustainably, bio-based lubricants have greater advantage over mineral oils lubricants from petrochemical industries because vegetable oils are abundant whilst mineral oils depend only on the finite petroleum resources [6].
Figure 1. A comparison between the high affinity of bio-based lubricants to metals and the low affinity of petroleum-based fluids to metals [7]. The application of vegetable oils as lubricants has been known since ancient times. For example, olive oil was used as lubricant in 1650BC [4]. Recently, in another study, bio-based lubricant was formulated from soybean base oil, which yielded similar properties compared to commercial lubricant ISO VG 68 [8]. Also, the pour points, flash points, viscosities at 40℃ 2
and at 100 ℃, and the viscosity indices of bio-based lubricants from Jatropha curcas seed oil, and neem oil has been reported to be comparable to ISO VG-46 for commercial standards for light and industrial gears application [9], and commercial standards for engen super 20w/50 lubricant, respectively [10]. However, vegetable oils in nature have their associated drawbacks which have to be overcome [11, 12] usually through modification. A few solutions to some of these drawbacks include interesterification [13], blending with synthetic esters [14], blending with additives [15], transesterification with various polyols, acetylation across double bond [16],enzymatic synthesis [17,18], and blending with other oils to improve the antioxidative and other properties of the oils [4]. In view of that, other studies have considered transesterification with diols, and polyols such as ethylene glycol, and trimethylolpropane to enhance the thermal and oxidative stability of the resulting bio-based lubricant [19, 20]. However, these alcohols have been reported to be very toxic to humans, domestic pets and other animals. Thus, the oral lethal doses (LD 50) of ethylene glycol, and trimethyolpropane have been reported to be 1.4 mL/kg (1400-1600mg/kg in humans), and 13700-14100 mg/kg (in mouse, and rat), respectively [21, 22]. Meanwhile, the oil can be transesterified using KOH/CH3OH as catalyst, after which other less toxic compounds may be used to improve the physicalchemical properties of the vegetable oil into bio-based lubricants. This present study focused on the potential of castor, palm kernel, and coconut oils as biolubricant base oils via chemical modification and formulation. The oils were first transesterified followed by the addition of special additives (pour point depressant, viscosity modifier, and antioxidant) to formulate the lubricants. The viscosity indices (VI), total base numbers (TBN), flash points (FP), pour points (PP), elemental compositions of the oils and their respective modified bio-based lubricants were also investigated and compared with the commercial engine oil SAE 40.
2.0 MATERIALS AND METHODS The castor oil, coconut oil, and palm kernel oils were chosen based on their abundance, and higher lubricating potentials. The castor oil was obtained from ADM Packaged oils (Ghana) whereas the coconut oil and palm kernel oil were obtained from Mansuki Ghana Limited. 2.1 Materials and equipment 3
The glacial acetic acid, Iso-octane, iodine, and perchloric acid were obtained from SigmaAldrich Chemical Co.-Denmark, whereas the pour point depressant (copolymer of polymethacrylates),
viscosity
modifier
(Polymethacrylates),
and
antioxidant
(Zinc
dialkylthiophosphate, ZDDP) were obtained from Shenyang Hualun Lubricant Additive Co., Ltd.-Liaoning China. 2.2 Characterization of the oil samples and their respective modified bio-based lubricants 2.2.1 Viscosity and viscosity index determination The viscosity of oil is the measure of its resistance to gradual deformation by shear stress or tensile stress. The kinematic viscosity and viscosity indices of the vegetable oils and their respective formulated bio-based lubricants were determined and calculated by the ASTM D 445-97 [23] and ASTM methods D2270-93b [24] respectively. Multi-range viscometer tubes (HV M472) were used to measure the viscosity. Each vegetable oil sample was suctioned into the viscometer tubes with known constants. The viscometer tubes were then placed in the Koehler Scientific Viscometer baths one set at 100 ℃ and the other at 40 ℃. The oil in the viscometer tubes fell under gravity from a start point to the end point, after 15 minutes of subjection to the viscometer baths. The time taken for the oil to fall from the start point to the end point was then recorded. The kinematic viscosity of each oil sample was calculated from Equation (1). 𝑣 = 𝑘 × 𝑡……………………………………………………………………………………(1) where v is the kinematic viscosity of the oil, measured in centistokes cSt, k is the tube constant determined experimentally using a known fluid (distilled water) of known viscosity at specific temperature, and t is the time taken for the oil to fall under gravity within the viscometer tube. 2.2.2 Total base number determination Total base number (TBN) is a measure of a lubricant’s alkaline reserve in the sample. This parameter is of interest in order to determine the potential of each of the samples to neutralize combustion acidic products. TBN solvent was prepared by mixing glacial acetic acid and Iso-octane in the volumetric ratio of 1:3. The total base number was determined by ASTM D2896-11 [25].
4
50 ml of TBN solvent was added to 2.0 g of each of the oil samples in Erlenmeyer flasks. Two drops of iodine solution were added to the resulting mixture while stirring. 1.0 M perchloric acid in a burette was titrated against the resulting solution in the flask. The endpoint was then read and recorded. The average titre value was determined from duplicate endpoints. The total base number was calculated from the equation (2). 𝑔
𝑇𝐵𝑁 =
𝑒𝑞
𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑡𝑖𝑡𝑟𝑒(𝑚𝐿) × 𝑀𝐾𝑂𝐻(𝑚𝑜𝑙) × 𝐶( 𝐿 ) 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒 (𝑔)
…………………………………………………(2)
where 𝑀𝐾𝑂𝐻= Molar mass of potassium hydroxide and C is the concentration of the KOH. 2.2.3 Pour point determination Pour point of a lubricant is defined as the minimum temperature (℃) at which the sample still pours when the jar is tilted. The pour point temperature of the vegetable oils was measured by following ASTM D97-12 [26]. 50 ml of each of the oil samples were separately placed in stoppered test jars, which had a thermometer reading from +20 ℃ to -80 ℃. The test jars were placed in a digital pour point bath, after which the temperature was decreased at an interval of 3 ℃ until the sample stopped pouring. Below the pour point, the oil ceased to flow. 2.2.4 Flashpoint determination The flashpoint is one of the properties considered in assessing the flammability hazard of a lubricant. It can indicate the presence of highly volatile and flammable materials. The flashpoint (℃) of each oil sample was determined by applying the ASTM D92-12b, by the Cleveland open cup COC method [27]. 70 ml of each oil sample was poured into an open test cup, which was placed on a regulatory hotplate. A thermometer was immersed gently into each of the oil samples while gradually regulating the heat from the hotplate. A test flame was passed across the open cup containing the samples at regular interval. A blue flame ignition with the vapor of the oil sample indicated the flashpoint of that sample under test. The flashpoint of each of the oil samples was read and recorded. 2.2.5 Elemental analysis
5
The elemental analysis was used to characterize the chemical composition of the vegetable oils and their corresponding bio-based lubricants. Cannon S2 RANGER X-RAY fluorescence instrument was used in the determination of the elemental compositions of each oil sample and their respective bio-based lubricants. 7.0 g of each oil sample was weighed into a plastic cup, covered underneath with transparent polyethene. The samples were left on a plain white sheet of paper for 2 minutes to check for leakages. Each of the oil samples was then placed into the S2 RANGER X-ray fluorescence instrument for analysis. The percentage compositions by weight of element present in the oil samples were then read and recorded.
2.1.6 Chemical modification of vegetable oils via base catalyzed transesterfication The direct use of vegetable oil at high temperature regime can be problematic. For example, a highly toxic acrolein is formed through thermal decomposition of glycerol [28,29]. Therefore, the transesterification was performed to remove the glycerol from the vegetable oils to produce a biodiesel, which was further modified into the bio-based lubricants that would be environmentally friendly in its operations. Besides, according to Kleinaite et. al (2014), biodiesel is efficient starting material for biolubricant production [17]. Transesterification of vegetable oil is known to enhance lubricity, hence, reducing wear on the surface of metal [30, 31] where the lubricant is applied. This process (Scheme 1) involved two basic steps, namely, catalyst preparation (potassium methoxide solution), and transesterification. To determine the desired conditions, the amount of KOH catalyst, methanol, and oil required were investigated and determined prior to the reaction. In view of that, 1 g of KOH was completely dissolved in 5 g of methanol to get potassium methoxide solution (CH3OK). Each of the vegetable oils was preheated in a water bath to 60 ℃ to largely reduce the water content of the oil. To transesterify the oil, the potassium methoxide solution was gently added to 100 g of vegetable oil in an Erlenmeyer flask at 60 ℃, and stirred at 120 rpm for 2 hrs. The resulting mixture was gently transferred into a separating funnel, and allowed to settle overnight, after which the glycerol was drained off. With distilled water at 70 ℃, the biodiesel produced was washed severally, after which 1 g of sodium sulphate was added, vacuum filtered and stored for further modification.
6
O O O O
CH3OH
O
Tranesterification
O O H3CO
OH
H3CO
OH O
OH Glycerol
O H3CO Biodiesel
Scheme 1: Chemical equation depicting transesterification of vegetable oil.
2.2.7 Formulation of bio-based lubricant via special additive addition The following amounts of special additives were added to 94.72 wt.% of each vegetable oil biodiesel (VOB) to formulate the bio-based lubricant: 0.20 wt.% of the pour point depressant, PPD (copolymer of polymethacrylates); 5.0 wt.% of a viscosity modifier, VM (Polymethacrylates) 0.08 wt.% of antioxidant, AO (Zinc dialkylthiophosphate, ZDDP) (Figure 2) [32-34]. These are known for improving the pour point, viscosity and antioxidant capacities of lubricants. The resulting mixtures of each of the oil samples in each beaker were stirred for 15 minutes using magnetic stirrers at a constant velocity of 200 rpm to enhance effective mixing. The bio-based lubricant was clear and well mixed. Each formulated biobased lubricant was allowed to cool for 30 minutes, before running the tests for the various characteristic properties (Viscosity, TBN, Flashpoint, Pour point, and Elemental analysis) as described above. All reproducible methods were duplicated, and all statistical methods and analysis were done using Microsoft Excel 2010.
7
0.2
0.08 5
VOB AO/ZDDP VM PPD
94.72
Figure 2. The amount of vegetable oil biodiesel and additives (wt. %) used to formulate the bio-based lubricants. 3.0 RESULTS AND DISCUSSION 3.1 Viscosity and viscosity index determination Table 1 depicts the average kinematic viscosities and viscosity indices of the vegetable oils and their respective bio-based lubricants at 40 ℃ and 100 ℃. The castor oil lube had the highest viscosities (208.39 cSt, 16.47 cSt), followed by the commercial engine oil lube, palm kernel oil lube, and coconut oil lube. The higher castor oil lube viscosity may be attributed to the higher amount of ricin oleic acids (90%) in the castor oil [35]. Table 1: The Viscosity and viscosity index of the vegetable oils and their respective biobased lubricants. Oil Viscosity@40℃ Viscosity@100℃ Viscosity Index /cSt /cSt Castor oil 250.24 19.45 88 Castor oil lube 208.39 16.47 79 Coconut oil 26.58 5.83 172 Coconut oil lube 42.43 10.11 237 Palm kernel oil 29.46 6.30 173 Palm kernel oil lube 58.49 11.00 217 Com. engine oil lube (SAE 170.45 15.60 98 Crankcase 40 ) The viscosities of the castor oil lube was comparable to SAE Crankcase 50 whilst that of the palm kernel oil lube, and the coconut oil bio-based lube were comparable to SAE Crankcase 20 [36]. This indicates that at 40℃, and 100℃ operating temperatures, the 8
modified castor oil lube may provide better film thickness between gliding surfaces than the commercial engine oil lube SAE Crankcase 40. This result is consistent with other literature, which reported that bio-based lubricants provided better lubricity and viscosity than their corresponding commercial engine oil lubricants [5]. Conversely, the coconut oil lube and palm kernel oil lube had an appreciable increment in their viscosity indices from 172 to 237, and 173 to 217 (Figure 3), indicating 37.8%, and 25.4% improvement, respectively. These viscosity indices were far greater than the compared commercial lubricant, which had viscosity index of 98. Based on the viscosity indices, it may be implied that the coconut oil lube, and palm kernel oil lube have greater resistance to viscosity change than the commercial engine oil when exposed to varying temperatures [37].
Com. engine oil Lube(SAE 40) Palm kernel oil lube Palm kernel Oil Coconut oil lube
Viscosity Index
Coconut Oil Castor oil lube Castor Oil 0
50 100 150 200 250
Figure 3. Viscosity indices of the various oils and their respective bio-based lubricants. This excellent property exhibited may be implied that the molecular weight of the coconut oil, and palm kernel oil are more stable at varying stress temperatures than that of the commercial engine oil lube[38]. This agrees with Bhutada et. al, who reported the thermal stability of Moringa oil to be < 425-450℃. They indicated that the oil degraded only at 425450℃, implying that some oils from plants can be stable at higher temperatures[39].
9
3.2 Total base number determination Additives play a vital role in improving the alkaline reserves in oil. This is evident from the results of the raw vegetable oils, which had less than 1.0 mgKOH/g. Figure 4 shows that after modifying the oils, the alkaline reserve of the bio-based lubricants improved. The castor oil TBN elevated from 0.17 mgKOH/g to 1.37 mgKOH/g when modified. The 0.16 mgKOH/g of the coconut oil appreciated to 1.52 mgKOH/g after formulation, whereas the palm kernel oil displayed the highest TBN in its bio-based lubricant (8.94mgKOH/g). The experiment was repeated to confirm this extreme elevation and the result was similar.
Com. engine oil lubricant.
Modified biolubricant
Palm kernel oil
Raw
Coconut oil
Castor oil 0
2
4
6
8
Total base number mgKOH/g
10
Figure 4. Total base number of various oils and their respective bio-based lubricants. The TBN of the palm kernel oil lubricant was greater than the commercial engine oil lubricant (3.54 mgKOH/g). Unlike the castor oil bio-based lubricant, coconut oil bio-based lubricant, and the compared commercial engine oil lubricant which had TBN below the range for Major Brands of Passenger Car Engine Oil API SM 5-W-30-a, and monograde oil for petrol and diesel engine SAE 40, the TBN of the palm kernel oil bio-based lubricant potentially renders it suitable to be applied in petrol, diesel, and gas engines, since it is in the range of 7 to 10 for petrol, diesel, gas engines [40, 41]. 10
This implies that the palm kernel oil bio-based lubricant will have sufficient alkaline reserve to neutralize any acidic product yielded during use in internal combustion engines than that of the compared commercial engine oil lube. 3.3 Flashpoint determination In Figure 5, castor oil had a flashpoint of 240 ℃, which increased to 251 ℃ when modified. The coconut oil and palm kernel oil exhibited the same flashpoint from 224 ℃ to 245 ℃ before and after blend. The flashpoints of the vegetable oils and their bio-based lubricants were better than the compared commercial engine oil lubricant (175 ℃), and other commercial engine oils on the market [41, 42].
Com. engine oil lubricant Biolubricant
Palm kernel oil
Raw
Coconut oil Castor oil 0
100
200
300
Figure 5. Flashpoint of various oils and their respective bio-based lubricants The increment in the flashpoints of the bio-based lubricants may be due to the presence of the antioxidant (ZDDP) since oxidants are known to increase flammability. The results indicate that castor oil lubes, coconut oil lubes, and palm kernel oil lubes are safer to transport [8] than the compared commercial engine oil lube. 3.4 Pour point determination Pour point depressants in bio-based lubricants enable them to continually flow until the crystallization temperature. The pour points of the castor oil, coconut oil, and palm kernel oil improved by 66.7%, 181.3% and 179.6%, respectively, formulated into bio-based lubricants
11
(Figure 6). The pour points of all the oils and their respective bio-based lubricants were lower than the compared commercial engine oil lubricant, which had pour point of -62 ℃.
Caster oil
Coconut Palm kernel oil oil
Com. engine oil lubricnant
0
Pour point (℃)
-10 -20 -30
Raw
-40
Blend/biolubric ant
-50 -60 -70
Figure 6. Pour point of the various oils and their respective bio-based lubricants This indicates that the raw vegetable oils perform poorly in cold temperatures. However, the pour points were even better than similar engine oils of the same SAE grades ( SAE 20, and 50) on the market with pour points specifications -26 ℃ and -20 ℃ respectively [43]. The results imply that the bio-based lubricants can still be used in petrol and diesel engines in environments where the temperature does not go below the pour points of bio-based lubricants. 3.5 Elemental analysis The presence of metals and other elements have effects on the performance of a lubricant. The CH2 composition, which usually originates from the triglycerides in the oils, was in the range 99.0-99.9 wt. % (Table 2) in both the raw oil and lubricants. The other elements such as Phosphorus, Calcium, and Sulphur were in the range 0.01-0.08 wt. %, 0.02-0.41 wt. %, and 0.01-0.08 wt. % respectively.
12
Table 2. The Elemental composition of the various oils and their respective bio-based lubricants Element Percentage Composition (wt. %) Castor oil CH2 P S Ca Zn CH2 P S Ca Zn
Coconut oil
Palm kernel oil 99.93 99.89 99.85 0.0480 0.0100 0.0470 0.0100 0.0200 0.0900 0.0170 0.0800 0.0170 0.0000 0.0000 0.0000 Castor oil Coconut oil Palm kernel lube lube oil lube 99.36 99.52 99.50 0.0812 0.0764 0.0742 0.0708 0.0776 0.0796 0.4082 0.2431 0.262 0.0801 0.0771 0.0799
Commercial Engine oil SAE 40 Commercial engine oil SAE 40 99.25 0.1540 0.2610 0.2239 0.1135
The deficiency of antioxidant such as Zinc in vegetable oil may be the reason most vegetable oils such as castor oil, coconut oil, and palm kernel oil are susceptible to oxidation when used as lubricants. The zinc composition in the raw oil was 0wt%, however, it increased to an average of 0.08wt% in the bio-based lubricants. This increment may be as a result of the addition of the ZDDP. The elemental concentrations of the bio-based lubricants were generally lower than that of the compared engine oil, but were similar to other studies on similar engine oils [44, 45]. The appreciable Zn concentration obtained indicates that the modified bio-based lubricants have the potential to induce antioxidizing effects when used. 4.0 CONCLUSIONS This present study focused on the potential of castor, palm kernel, and coconut oils as biolubricant base oil via chemical modification and formulation. At 40℃ and 100℃, the castor oil bio-based lubricant had higher viscosity than the commercial engine oil, and the other bio-based lubricants. The viscosities of the castor oil, palm kernel oil, and the coconut oil bio-based lubricants were found to be comparable to SAE Crankcase 50, 20, and 20, respectively. The coconut oil and palm kernel oil bio-based lubricants obtained higher viscosity indices of 237 and 217, respectively, indicating their potential resistance to viscosity change at varying temperatures. Conversely, the bio-based lubricants showed higher flash points (245-251℃), rendering them thermally safer than the compared SAE 40. Though the pour points of the bio-based lubricants were not as good as the SAE 40, they were better than 13
similar grades SAE 50 and SAE 20 in the market, thereby, making them potentially and comparatively suitable for use. The palm kernel oil bio-based lubricants had the highest TBN (8.94mgKOH/g) indicating its potential to neutralize more acidic products produced from internal combustion engines. The elemental analysis showed that the CH2, Zn, S, P, and Ca concentrations of the bio-based lubricants were lower than the SAE 40, but similar to others reported in literature. The average Zn concentration (0.0797wt %) in the bio-based biolubricants reflects their potential to induce antioxidizing effects. The results of the study suggest that castor oil, coconut oil, and palm kernel oil can be comparatively good base oils for formulating motor engine bio-based lubricants if they are properly modified. Acknowledgements We are grateful to the University of Cape Coast-Ghana and Dr. Pranjal Kalita for their supports and advice. The authors also thank Charles Adjaku, Richard Acquah and Bright Dzah for their support during the laboratory experiment. Conflict of interests The authors have no conflict of interests with respect to the publication of this paper. 5.0 REFRENCES 1. Bartz WJ (1998) Lubricants and the environment. Tribol Int. 31: 35-47 2. Biermann U, Metzger JO (2008) Synthesis of alkyl-branched fatty acids: A review. Eur. F. Lipid Sci. Technol. 110:805-811 3. Sharma BK; Adhvaryu A; Pérez JM, Erhan SZ (2005) Soybean oil based greases: influence of composition on thermo-oxidative and tribochemical behavior. J. Agric Food Chem. 53:2961-2968 4. Gawrilow L (2003) Palm oil usage in lubricants. 3rd Global Oil and Fats business Forum
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33. Morina A, Neville A (2007) Understanding the composition and low friction tribofilm formation/removal in boundary lubrication. Tribology International 10:1696-1704. Doi: 10.1016/j.triboint.2007.02.001 34. ZDDP and Older Automobile Engines. http://www.nonlintec.com/sprite/oils_and_zddp.pdf . Accessed 28 07 2017 35. Silva JAC, Habert AC, Freire DMG (2013) A potential biodegradable lubricant from castor biodiesel esters. Lubrication Science 1:53-61 36. Bongfa B, Atabor PA, Barnabas A, Adeotic MO (2015) Comparison of lubricant properties of castor oil and commercial engine oil, Jurnal Tribologi 5:1-10 37. ISO-AGMA-SAE_Widman International. Comparison of ISO, AGMA, and SAE viscosities. http://www.widman.biz/English/Tables/ISO-SAE.html. Accessed 27 07 2017 38. Stambaugh RL, Kinker BG (2010) Viscosity index improvers and thickeners. In Chemistry and technology of lubricants. Doi 10.1007/978-1-4615-3272-9_5 39. Bhutada PR, Jadhav AJ, Pinjari, DV, Nemade PR, Jain RD (2016). Solvent assisted extraction of oil from Moringa oleifera Lam. Seeds. Industrial Crops and Products 82:74-80 https://doi.org/10.1016/j.indcrop.2015.12.004 40. Asadauskas S, Perez JH, Duda JL (1997) Lubrication properties of castor oilpotential base stock for biodegradable. Lubrication Engineering 53:35–40 41. Total Base Number (TBN): ASTM D2896 - 07a Standard Test Method for Base Number of Petroleum Products by Potentiometric Perchloric Acid Titration. http://pqiamerica.com/TBN.htm. Accessed 10 June 2017 42. Total, MOTOR OIL SAE 40. Monograde oil for Petrol & Diesel engine oil. http://4.total.fr/AMO/Liban/PDF/MOTOR%20OIL%20SAE%2040%20ENG.pdf . Accessed 20 July 2017 43. Aegis
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Dear Editor
Conflict of Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Thank you.
Yours faithfully,
Dr.-Ing. Samuel Kofi Tulashie Mr. Francis Kotoka
46.
Vegetable oils are promising commodities that can be used as eco-friendly biobased lubricants. The modified castor oil biobased lubricant had higher viscosities than the compared commercial engine oil lubricant. The viscosities of the castor oil, palm kernel oil, and the coconut oil biobased lubricants were found to be comparable to SAE Crankcase 50, and 20 respectively. Castor oil, coconut oil, and palm kernel oil are comparatively good candidate base oils for making commercial biobased lubricants.
47. 48.
18
S2451-9049(18)30577-8 https://doi.org/10.1016/j.tsep.2020.100480 TSEP 100480
To appear in:
Thermal Science and Engineering Progress
Received Date: Revised Date: Accepted Date:
8 October 2018 14 November 2019 13 January 2020
Please cite this article as: S. Kofi Tulashie, F. Kotoka, The potential of castor, palm kernel, and coconut oils as biolubricant base oil via chemical modification and formulation, Thermal Science and Engineering Progress (2020), doi: https://doi.org/10.1016/j.tsep.2020.100480
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Title: The potential of castor, palm kernel, and coconut oils as biolubricant base oil via chemical modification and formulation. Author’s full names and address: Samuel Kofi Tulashie*1 and Francis Kotoka1 1 University
of Cape Coast, School of Physical Sciences, Department of Chemistry, Industrial
Chemistry Section, Cape Coast, Ghana. Email:[email protected]
ABSTRACT This study focused on the chemical modification and the formulation of bio-based lubricants from castor, palm kernel, and coconut oils via transesterification and special additives addition. The bio-based lubricants physical-chemical properties were investigated and compared to SAE 40. At 40℃ and 100℃, the kinematic viscosities of the modified castor, palm kernel, coconut oils bio-based lubricants, and the SAE 40 were (208.39 cSt, 16.47 cSt), (58.49 cSt, 11.00 cSt), (42.43 cSt, 10.11 cSt) and (170.45 cSt, 15.60 cSt) respectively. The bio-based lubricants properties suggest that the base oils are comparatively good candidate for motor engines bio-based lubricants if properly modified. Keywords: Biolubricants; Biodegradability; Transesterification; Biodiesel; Fat and oils.
1
1.0 INTRODUCTION In recent years, mineral oils and synthetic fluids have been largely used as base oils for lubricants and these oils have posed some serious environmental issues due to their nonbiodegradability [1]. Maintaining an eco-friendly environment has focused attention on environmental regulations and the use of environmentally friendly lubricants in the automobile industries in many countries. Vegetable oils (VO) are the potential candidates gaining popularity due to their excellent properties. Vegetable oils are natural oils that mainly contain a mixture of triacylglycerols [2]. Today, vegetable oils are gaining utmost attention because of increased environmental awareness and their significant environmental advantages [3]. Some of these advantages are their renewable sources and nontoxicity, biodegradability and adequate performance in a variety of applications [4], excellent lubricity due to their higher affinity to metal surfaces resulting in enhanced thin film strength as depicted in Figure 1, high viscosity indices, high flash point, and low evaporative loss [5]. Economically and sustainably, bio-based lubricants have greater advantage over mineral oils lubricants from petrochemical industries because vegetable oils are abundant whilst mineral oils depend only on the finite petroleum resources [6].
Figure 1. A comparison between the high affinity of bio-based lubricants to metals and the low affinity of petroleum-based fluids to metals [7]. The application of vegetable oils as lubricants has been known since ancient times. For example, olive oil was used as lubricant in 1650BC [4]. Recently, in another study, bio-based lubricant was formulated from soybean base oil, which yielded similar properties compared to commercial lubricant ISO VG 68 [8]. Also, the pour points, flash points, viscosities at 40℃ 2
and at 100 ℃, and the viscosity indices of bio-based lubricants from Jatropha curcas seed oil, and neem oil has been reported to be comparable to ISO VG-46 for commercial standards for light and industrial gears application [9], and commercial standards for engen super 20w/50 lubricant, respectively [10]. However, vegetable oils in nature have their associated drawbacks which have to be overcome [11, 12] usually through modification. A few solutions to some of these drawbacks include interesterification [13], blending with synthetic esters [14], blending with additives [15], transesterification with various polyols, acetylation across double bond [16],enzymatic synthesis [17,18], and blending with other oils to improve the antioxidative and other properties of the oils [4]. In view of that, other studies have considered transesterification with diols, and polyols such as ethylene glycol, and trimethylolpropane to enhance the thermal and oxidative stability of the resulting bio-based lubricant [19, 20]. However, these alcohols have been reported to be very toxic to humans, domestic pets and other animals. Thus, the oral lethal doses (LD 50) of ethylene glycol, and trimethyolpropane have been reported to be 1.4 mL/kg (1400-1600mg/kg in humans), and 13700-14100 mg/kg (in mouse, and rat), respectively [21, 22]. Meanwhile, the oil can be transesterified using KOH/CH3OH as catalyst, after which other less toxic compounds may be used to improve the physicalchemical properties of the vegetable oil into bio-based lubricants. This present study focused on the potential of castor, palm kernel, and coconut oils as biolubricant base oils via chemical modification and formulation. The oils were first transesterified followed by the addition of special additives (pour point depressant, viscosity modifier, and antioxidant) to formulate the lubricants. The viscosity indices (VI), total base numbers (TBN), flash points (FP), pour points (PP), elemental compositions of the oils and their respective modified bio-based lubricants were also investigated and compared with the commercial engine oil SAE 40.
2.0 MATERIALS AND METHODS The castor oil, coconut oil, and palm kernel oils were chosen based on their abundance, and higher lubricating potentials. The castor oil was obtained from ADM Packaged oils (Ghana) whereas the coconut oil and palm kernel oil were obtained from Mansuki Ghana Limited. 2.1 Materials and equipment 3
The glacial acetic acid, Iso-octane, iodine, and perchloric acid were obtained from SigmaAldrich Chemical Co.-Denmark, whereas the pour point depressant (copolymer of polymethacrylates),
viscosity
modifier
(Polymethacrylates),
and
antioxidant
(Zinc
dialkylthiophosphate, ZDDP) were obtained from Shenyang Hualun Lubricant Additive Co., Ltd.-Liaoning China. 2.2 Characterization of the oil samples and their respective modified bio-based lubricants 2.2.1 Viscosity and viscosity index determination The viscosity of oil is the measure of its resistance to gradual deformation by shear stress or tensile stress. The kinematic viscosity and viscosity indices of the vegetable oils and their respective formulated bio-based lubricants were determined and calculated by the ASTM D 445-97 [23] and ASTM methods D2270-93b [24] respectively. Multi-range viscometer tubes (HV M472) were used to measure the viscosity. Each vegetable oil sample was suctioned into the viscometer tubes with known constants. The viscometer tubes were then placed in the Koehler Scientific Viscometer baths one set at 100 ℃ and the other at 40 ℃. The oil in the viscometer tubes fell under gravity from a start point to the end point, after 15 minutes of subjection to the viscometer baths. The time taken for the oil to fall from the start point to the end point was then recorded. The kinematic viscosity of each oil sample was calculated from Equation (1). 𝑣 = 𝑘 × 𝑡……………………………………………………………………………………(1) where v is the kinematic viscosity of the oil, measured in centistokes cSt, k is the tube constant determined experimentally using a known fluid (distilled water) of known viscosity at specific temperature, and t is the time taken for the oil to fall under gravity within the viscometer tube. 2.2.2 Total base number determination Total base number (TBN) is a measure of a lubricant’s alkaline reserve in the sample. This parameter is of interest in order to determine the potential of each of the samples to neutralize combustion acidic products. TBN solvent was prepared by mixing glacial acetic acid and Iso-octane in the volumetric ratio of 1:3. The total base number was determined by ASTM D2896-11 [25].
4
50 ml of TBN solvent was added to 2.0 g of each of the oil samples in Erlenmeyer flasks. Two drops of iodine solution were added to the resulting mixture while stirring. 1.0 M perchloric acid in a burette was titrated against the resulting solution in the flask. The endpoint was then read and recorded. The average titre value was determined from duplicate endpoints. The total base number was calculated from the equation (2). 𝑔
𝑇𝐵𝑁 =
𝑒𝑞
𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑡𝑖𝑡𝑟𝑒(𝑚𝐿) × 𝑀𝐾𝑂𝐻(𝑚𝑜𝑙) × 𝐶( 𝐿 ) 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒 (𝑔)
…………………………………………………(2)
where 𝑀𝐾𝑂𝐻= Molar mass of potassium hydroxide and C is the concentration of the KOH. 2.2.3 Pour point determination Pour point of a lubricant is defined as the minimum temperature (℃) at which the sample still pours when the jar is tilted. The pour point temperature of the vegetable oils was measured by following ASTM D97-12 [26]. 50 ml of each of the oil samples were separately placed in stoppered test jars, which had a thermometer reading from +20 ℃ to -80 ℃. The test jars were placed in a digital pour point bath, after which the temperature was decreased at an interval of 3 ℃ until the sample stopped pouring. Below the pour point, the oil ceased to flow. 2.2.4 Flashpoint determination The flashpoint is one of the properties considered in assessing the flammability hazard of a lubricant. It can indicate the presence of highly volatile and flammable materials. The flashpoint (℃) of each oil sample was determined by applying the ASTM D92-12b, by the Cleveland open cup COC method [27]. 70 ml of each oil sample was poured into an open test cup, which was placed on a regulatory hotplate. A thermometer was immersed gently into each of the oil samples while gradually regulating the heat from the hotplate. A test flame was passed across the open cup containing the samples at regular interval. A blue flame ignition with the vapor of the oil sample indicated the flashpoint of that sample under test. The flashpoint of each of the oil samples was read and recorded. 2.2.5 Elemental analysis
5
The elemental analysis was used to characterize the chemical composition of the vegetable oils and their corresponding bio-based lubricants. Cannon S2 RANGER X-RAY fluorescence instrument was used in the determination of the elemental compositions of each oil sample and their respective bio-based lubricants. 7.0 g of each oil sample was weighed into a plastic cup, covered underneath with transparent polyethene. The samples were left on a plain white sheet of paper for 2 minutes to check for leakages. Each of the oil samples was then placed into the S2 RANGER X-ray fluorescence instrument for analysis. The percentage compositions by weight of element present in the oil samples were then read and recorded.
2.1.6 Chemical modification of vegetable oils via base catalyzed transesterfication The direct use of vegetable oil at high temperature regime can be problematic. For example, a highly toxic acrolein is formed through thermal decomposition of glycerol [28,29]. Therefore, the transesterification was performed to remove the glycerol from the vegetable oils to produce a biodiesel, which was further modified into the bio-based lubricants that would be environmentally friendly in its operations. Besides, according to Kleinaite et. al (2014), biodiesel is efficient starting material for biolubricant production [17]. Transesterification of vegetable oil is known to enhance lubricity, hence, reducing wear on the surface of metal [30, 31] where the lubricant is applied. This process (Scheme 1) involved two basic steps, namely, catalyst preparation (potassium methoxide solution), and transesterification. To determine the desired conditions, the amount of KOH catalyst, methanol, and oil required were investigated and determined prior to the reaction. In view of that, 1 g of KOH was completely dissolved in 5 g of methanol to get potassium methoxide solution (CH3OK). Each of the vegetable oils was preheated in a water bath to 60 ℃ to largely reduce the water content of the oil. To transesterify the oil, the potassium methoxide solution was gently added to 100 g of vegetable oil in an Erlenmeyer flask at 60 ℃, and stirred at 120 rpm for 2 hrs. The resulting mixture was gently transferred into a separating funnel, and allowed to settle overnight, after which the glycerol was drained off. With distilled water at 70 ℃, the biodiesel produced was washed severally, after which 1 g of sodium sulphate was added, vacuum filtered and stored for further modification.
6
O O O O
CH3OH
O
Tranesterification
O O H3CO
OH
H3CO
OH O
OH Glycerol
O H3CO Biodiesel
Scheme 1: Chemical equation depicting transesterification of vegetable oil.
2.2.7 Formulation of bio-based lubricant via special additive addition The following amounts of special additives were added to 94.72 wt.% of each vegetable oil biodiesel (VOB) to formulate the bio-based lubricant: 0.20 wt.% of the pour point depressant, PPD (copolymer of polymethacrylates); 5.0 wt.% of a viscosity modifier, VM (Polymethacrylates) 0.08 wt.% of antioxidant, AO (Zinc dialkylthiophosphate, ZDDP) (Figure 2) [32-34]. These are known for improving the pour point, viscosity and antioxidant capacities of lubricants. The resulting mixtures of each of the oil samples in each beaker were stirred for 15 minutes using magnetic stirrers at a constant velocity of 200 rpm to enhance effective mixing. The bio-based lubricant was clear and well mixed. Each formulated biobased lubricant was allowed to cool for 30 minutes, before running the tests for the various characteristic properties (Viscosity, TBN, Flashpoint, Pour point, and Elemental analysis) as described above. All reproducible methods were duplicated, and all statistical methods and analysis were done using Microsoft Excel 2010.
7
0.2
0.08 5
VOB AO/ZDDP VM PPD
94.72
Figure 2. The amount of vegetable oil biodiesel and additives (wt. %) used to formulate the bio-based lubricants. 3.0 RESULTS AND DISCUSSION 3.1 Viscosity and viscosity index determination Table 1 depicts the average kinematic viscosities and viscosity indices of the vegetable oils and their respective bio-based lubricants at 40 ℃ and 100 ℃. The castor oil lube had the highest viscosities (208.39 cSt, 16.47 cSt), followed by the commercial engine oil lube, palm kernel oil lube, and coconut oil lube. The higher castor oil lube viscosity may be attributed to the higher amount of ricin oleic acids (90%) in the castor oil [35]. Table 1: The Viscosity and viscosity index of the vegetable oils and their respective biobased lubricants. Oil Viscosity@40℃ Viscosity@100℃ Viscosity Index /cSt /cSt Castor oil 250.24 19.45 88 Castor oil lube 208.39 16.47 79 Coconut oil 26.58 5.83 172 Coconut oil lube 42.43 10.11 237 Palm kernel oil 29.46 6.30 173 Palm kernel oil lube 58.49 11.00 217 Com. engine oil lube (SAE 170.45 15.60 98 Crankcase 40 ) The viscosities of the castor oil lube was comparable to SAE Crankcase 50 whilst that of the palm kernel oil lube, and the coconut oil bio-based lube were comparable to SAE Crankcase 20 [36]. This indicates that at 40℃, and 100℃ operating temperatures, the 8
modified castor oil lube may provide better film thickness between gliding surfaces than the commercial engine oil lube SAE Crankcase 40. This result is consistent with other literature, which reported that bio-based lubricants provided better lubricity and viscosity than their corresponding commercial engine oil lubricants [5]. Conversely, the coconut oil lube and palm kernel oil lube had an appreciable increment in their viscosity indices from 172 to 237, and 173 to 217 (Figure 3), indicating 37.8%, and 25.4% improvement, respectively. These viscosity indices were far greater than the compared commercial lubricant, which had viscosity index of 98. Based on the viscosity indices, it may be implied that the coconut oil lube, and palm kernel oil lube have greater resistance to viscosity change than the commercial engine oil when exposed to varying temperatures [37].
Com. engine oil Lube(SAE 40) Palm kernel oil lube Palm kernel Oil Coconut oil lube
Viscosity Index
Coconut Oil Castor oil lube Castor Oil 0
50 100 150 200 250
Figure 3. Viscosity indices of the various oils and their respective bio-based lubricants. This excellent property exhibited may be implied that the molecular weight of the coconut oil, and palm kernel oil are more stable at varying stress temperatures than that of the commercial engine oil lube[38]. This agrees with Bhutada et. al, who reported the thermal stability of Moringa oil to be < 425-450℃. They indicated that the oil degraded only at 425450℃, implying that some oils from plants can be stable at higher temperatures[39].
9
3.2 Total base number determination Additives play a vital role in improving the alkaline reserves in oil. This is evident from the results of the raw vegetable oils, which had less than 1.0 mgKOH/g. Figure 4 shows that after modifying the oils, the alkaline reserve of the bio-based lubricants improved. The castor oil TBN elevated from 0.17 mgKOH/g to 1.37 mgKOH/g when modified. The 0.16 mgKOH/g of the coconut oil appreciated to 1.52 mgKOH/g after formulation, whereas the palm kernel oil displayed the highest TBN in its bio-based lubricant (8.94mgKOH/g). The experiment was repeated to confirm this extreme elevation and the result was similar.
Com. engine oil lubricant.
Modified biolubricant
Palm kernel oil
Raw
Coconut oil
Castor oil 0
2
4
6
8
Total base number mgKOH/g
10
Figure 4. Total base number of various oils and their respective bio-based lubricants. The TBN of the palm kernel oil lubricant was greater than the commercial engine oil lubricant (3.54 mgKOH/g). Unlike the castor oil bio-based lubricant, coconut oil bio-based lubricant, and the compared commercial engine oil lubricant which had TBN below the range for Major Brands of Passenger Car Engine Oil API SM 5-W-30-a, and monograde oil for petrol and diesel engine SAE 40, the TBN of the palm kernel oil bio-based lubricant potentially renders it suitable to be applied in petrol, diesel, and gas engines, since it is in the range of 7 to 10 for petrol, diesel, gas engines [40, 41]. 10
This implies that the palm kernel oil bio-based lubricant will have sufficient alkaline reserve to neutralize any acidic product yielded during use in internal combustion engines than that of the compared commercial engine oil lube. 3.3 Flashpoint determination In Figure 5, castor oil had a flashpoint of 240 ℃, which increased to 251 ℃ when modified. The coconut oil and palm kernel oil exhibited the same flashpoint from 224 ℃ to 245 ℃ before and after blend. The flashpoints of the vegetable oils and their bio-based lubricants were better than the compared commercial engine oil lubricant (175 ℃), and other commercial engine oils on the market [41, 42].
Com. engine oil lubricant Biolubricant
Palm kernel oil
Raw
Coconut oil Castor oil 0
100
200
300
Figure 5. Flashpoint of various oils and their respective bio-based lubricants The increment in the flashpoints of the bio-based lubricants may be due to the presence of the antioxidant (ZDDP) since oxidants are known to increase flammability. The results indicate that castor oil lubes, coconut oil lubes, and palm kernel oil lubes are safer to transport [8] than the compared commercial engine oil lube. 3.4 Pour point determination Pour point depressants in bio-based lubricants enable them to continually flow until the crystallization temperature. The pour points of the castor oil, coconut oil, and palm kernel oil improved by 66.7%, 181.3% and 179.6%, respectively, formulated into bio-based lubricants
11
(Figure 6). The pour points of all the oils and their respective bio-based lubricants were lower than the compared commercial engine oil lubricant, which had pour point of -62 ℃.
Caster oil
Coconut Palm kernel oil oil
Com. engine oil lubricnant
0
Pour point (℃)
-10 -20 -30
Raw
-40
Blend/biolubric ant
-50 -60 -70
Figure 6. Pour point of the various oils and their respective bio-based lubricants This indicates that the raw vegetable oils perform poorly in cold temperatures. However, the pour points were even better than similar engine oils of the same SAE grades ( SAE 20, and 50) on the market with pour points specifications -26 ℃ and -20 ℃ respectively [43]. The results imply that the bio-based lubricants can still be used in petrol and diesel engines in environments where the temperature does not go below the pour points of bio-based lubricants. 3.5 Elemental analysis The presence of metals and other elements have effects on the performance of a lubricant. The CH2 composition, which usually originates from the triglycerides in the oils, was in the range 99.0-99.9 wt. % (Table 2) in both the raw oil and lubricants. The other elements such as Phosphorus, Calcium, and Sulphur were in the range 0.01-0.08 wt. %, 0.02-0.41 wt. %, and 0.01-0.08 wt. % respectively.
12
Table 2. The Elemental composition of the various oils and their respective bio-based lubricants Element Percentage Composition (wt. %) Castor oil CH2 P S Ca Zn CH2 P S Ca Zn
Coconut oil
Palm kernel oil 99.93 99.89 99.85 0.0480 0.0100 0.0470 0.0100 0.0200 0.0900 0.0170 0.0800 0.0170 0.0000 0.0000 0.0000 Castor oil Coconut oil Palm kernel lube lube oil lube 99.36 99.52 99.50 0.0812 0.0764 0.0742 0.0708 0.0776 0.0796 0.4082 0.2431 0.262 0.0801 0.0771 0.0799
Commercial Engine oil SAE 40 Commercial engine oil SAE 40 99.25 0.1540 0.2610 0.2239 0.1135
The deficiency of antioxidant such as Zinc in vegetable oil may be the reason most vegetable oils such as castor oil, coconut oil, and palm kernel oil are susceptible to oxidation when used as lubricants. The zinc composition in the raw oil was 0wt%, however, it increased to an average of 0.08wt% in the bio-based lubricants. This increment may be as a result of the addition of the ZDDP. The elemental concentrations of the bio-based lubricants were generally lower than that of the compared engine oil, but were similar to other studies on similar engine oils [44, 45]. The appreciable Zn concentration obtained indicates that the modified bio-based lubricants have the potential to induce antioxidizing effects when used. 4.0 CONCLUSIONS This present study focused on the potential of castor, palm kernel, and coconut oils as biolubricant base oil via chemical modification and formulation. At 40℃ and 100℃, the castor oil bio-based lubricant had higher viscosity than the commercial engine oil, and the other bio-based lubricants. The viscosities of the castor oil, palm kernel oil, and the coconut oil bio-based lubricants were found to be comparable to SAE Crankcase 50, 20, and 20, respectively. The coconut oil and palm kernel oil bio-based lubricants obtained higher viscosity indices of 237 and 217, respectively, indicating their potential resistance to viscosity change at varying temperatures. Conversely, the bio-based lubricants showed higher flash points (245-251℃), rendering them thermally safer than the compared SAE 40. Though the pour points of the bio-based lubricants were not as good as the SAE 40, they were better than 13
similar grades SAE 50 and SAE 20 in the market, thereby, making them potentially and comparatively suitable for use. The palm kernel oil bio-based lubricants had the highest TBN (8.94mgKOH/g) indicating its potential to neutralize more acidic products produced from internal combustion engines. The elemental analysis showed that the CH2, Zn, S, P, and Ca concentrations of the bio-based lubricants were lower than the SAE 40, but similar to others reported in literature. The average Zn concentration (0.0797wt %) in the bio-based biolubricants reflects their potential to induce antioxidizing effects. The results of the study suggest that castor oil, coconut oil, and palm kernel oil can be comparatively good base oils for formulating motor engine bio-based lubricants if they are properly modified. Acknowledgements We are grateful to the University of Cape Coast-Ghana and Dr. Pranjal Kalita for their supports and advice. The authors also thank Charles Adjaku, Richard Acquah and Bright Dzah for their support during the laboratory experiment. Conflict of interests The authors have no conflict of interests with respect to the publication of this paper. 5.0 REFRENCES 1. Bartz WJ (1998) Lubricants and the environment. Tribol Int. 31: 35-47 2. Biermann U, Metzger JO (2008) Synthesis of alkyl-branched fatty acids: A review. Eur. F. Lipid Sci. Technol. 110:805-811 3. Sharma BK; Adhvaryu A; Pérez JM, Erhan SZ (2005) Soybean oil based greases: influence of composition on thermo-oxidative and tribochemical behavior. J. Agric Food Chem. 53:2961-2968 4. Gawrilow L (2003) Palm oil usage in lubricants. 3rd Global Oil and Fats business Forum
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Dear Editor
Conflict of Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Thank you.
Yours faithfully,
Dr.-Ing. Samuel Kofi Tulashie Mr. Francis Kotoka
46.
Vegetable oils are promising commodities that can be used as eco-friendly biobased lubricants. The modified castor oil biobased lubricant had higher viscosities than the compared commercial engine oil lubricant. The viscosities of the castor oil, palm kernel oil, and the coconut oil biobased lubricants were found to be comparable to SAE Crankcase 50, and 20 respectively. Castor oil, coconut oil, and palm kernel oil are comparatively good candidate base oils for making commercial biobased lubricants.
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