Comparative Tribological Evaluation of Trimethylolpropane-based Biolubricants derived from Methyl Oleate and Canola Biodiesel

Non-edible grade canola oil produced from green canola seeds has great potential for the production of oleo-chemicals which have extensive applications in various fields. It is proposed to develop a class of industrial-grade natural-synthetic lubricants from mixed canola fatty acid methyl esters (canola biodiesel) by transesterification with trimethylolpropane. First, methyl oleate was synthesized by esterification. The range of operating variables was: temperature (80-140ºC), methanol-to-oleic acid molar-ratio (3.0-12.0) and catalyst loading (2-8 vol %). It was found that temperature and catalyst loading had significant effects on methyl oleate yield. The optimum synthesis conditions for obtaining a methyl oleate yield of 99.4 wt % were temperature of 120ºC, methanol-to-oleic acid molar ratio of 9.0 and concentrated sulfuric acid loading of 4 vol %. Physicochemical characterization of methyl oleate yielded the following properties of the product: moisture content of 0.04 vol %, kinematic viscosity of 4.3 cSt at 40ºC, cloud point of -3ºC, pour point of -15ºC and oxidative induction time of 1.14 h. Model transesterification reactions were performed with methyl oleate using trimethylolpropane. The optimum synthesis conditions developed were obtained as temperature of 139ºC, molar-ratio of methyl oleate-to-trimethylolpropane of 4.9 and catalyst loading of 1.4 wt %. Under these conditions, a 91.2 wt % triester yield was obtained after 5 h of reaction time. Response surface measurement studies were made by drawing 2D surface and 3D contour plots. A model equation was developed for predicting the final triester yield in terms of the actual reaction parameters. The fit of the model was confirmed by comparing the absolute error between modeled and actual values, which was within 5%. The observed difference between final triester yields from six replicate experiments at center point was within 2 wt %, while the standard deviation between them was less than 0.75%. Transesterification of canola biodiesel with trimethylolpropane was performed under optimum reaction conditions developed earlier for transesterification of methyl oleate and resulted in 90.9 wt % yield of triester. The physicochemical properties of methyl oleate-derived biolubricant and canola biodiesel-derived biolubricant were obtained in accordance with established ASTM, AOCS and EN standards in order to determine their suitability for lubricant applications. Methyl oleate-derived biolubricant was found to have the following tribological properties: viscosities of 48.9 and 9.3 cSt at 40 and 100ºC, respectively; viscosity index of 191, cloud and pour points of -21 and -51ºC, respectively; oxidative induction time of 2.08 h and wear scar diameter of 242 µm. Canola biodiesel-derived biolubricant had the following lubrication properties: viscosities of 40.5 and 7.8 cSt at 40 and 100ºC, respectively; viscosity index of 204, cloud and pour points of -27 and -66ºC, respectively; oxidative induction time of 0.74 h and wear scar diameter of 223 µm. Both biolubricants complied with ISO VG 46 standards and are ideally suitable for use in automobiles with minor modifications