Activity of Calcium Methoxide Catalyst for Synthesis of High Oleic Palm Oil Based Trimethylolpropane Triesters as Lubricant Base Stock Teck-Sin Chang, †,‡ Hassan Masood, † Robiah Yunus,* ,†,§ Umer Rashid, § Thomas S. Y. Choong, † and Dayang Radiah Awang Biak † † Department of Chemical and Environmental Engineering, Faculty of Engineering, and § Institute of Advanced Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia ‡ Solution Engineering Sdn. Bhd., No. 3, Jalan TPK 2/4, Taman Perindustrian Kinrara, 47100 Puchong, Selangor, Malaysia ABSTRACT: High oleic palm oil based trimethylolpropane triesters (TMPTE) are potential biodegradable base stocks for lubricant production. Calcium methoxide was used as a catalyst for the synthesis of TMPTE through chemical transesterification of high oleic palm oil methyl esters (POME) with trimethylolpropane (TMP). The effects of the main operating variables, i.e., temperature, pressure, molar ratio of TMP to POME, and the catalyst amount, on the yield of TMPTE were appraised. The amount of soap produced under these conditions was examined. The optimum conditions for the reaction were the reaction temperature set at 170 °C, molar ratio of TMP:POME set at 1:6, pressure of the system maintained at 50 mbar, and mass ratio of calcium methoxide set at 0.3% per weight of reaction mixture. Trimethylolpropane esters containing 98% w/w triesters were successfully synthesized under these conditions within 8 h reaction time. Saponification occurred under these conditions; however, the soap formation was less than that produced when homogeneous catalyst was used. 1. INTRODUCTION Vegetable oils are becoming an integral part of lubricant products due to their environmentally friendly nature. Lubricants based on vegetable oils are rapidly and completely biodegradable, and they have low ecotoxicity compared to mineral oil based lubricants. 1 However, there are some performance limitations associated with them, e.g., thermal, oxidative, and hydrolytic stability, and inadequate low temper- ature fluidity due to high pour points. 2 These limitations can be minimized by means of chemical modification through transesterification of vegetable oils with polyhydric alcohols or polyols. 3 This process causes the elimination of a hydrogen atom from the β-carbon of the vegetable oil structure and provides esters with a high degree of oxidative and thermal stability which is seldom found in vegetable oils. 4 Several studies have evidenced the improvement in performance of vegetable oils through their structural modification. 5-9 In a similar manner, trimethylolpropane triesters (TMPTE) had been synthesized as base oils for various types of lubricating oils by using trimethylolpropane (TMP) and vegetable oil methyl esters as starting materials. 10-13 The transesterification reaction involves three consecutive mechanisms with the presence of catalyst. Trimethylolpropane monoesters (TMPME) and trimethylolpropane diesters (TMPDE) are formed as the intermediate products toward the completion of the reaction producing TMPTE. The overall reaction stoichiometry requires 1 mol of trimethylolpropane (TMP) and 3 mol of methyl esters (ME). The reaction scheme is shown below: + ⇌ + TMP ME TMPME CH OH 3 (1) + ⇌ + TMPME ME TMPDE CH OH 3 (2) + ⇌ + TMPDE ME TMPTE CH OH 3 (3) The overall reaction is as follows: + ⇌ + TMP 3ME TMPTE 3CH OH 3 (4) Catalyst generally plays a crucial role in the production of TMPTE for obtaining better yield in less time. Uosukainen et al. 14 achieved 99% conversion to triesters in 10 h while using homogeneous sodium methoxide, 64% in 24 h with Candida rugosa lipase and 90% in 66 h by employing immobilized Rhizomucor miehei, for production of TMPTE from rapeseed oil methyl esters. Moreover, Gryglewicz et al. 15 obtained a yield of 85-90% after a reaction time of 20 h for the transesterification of TMP with methyl esters of animal fat in the presence of calcium methoxide as heterogeneous catalyst. It is probable that the steric hindrance of components is responsible for the slow reaction rate in these studies. Yunus et al. did the transesterification of TMP with palm oil methyl esters (POME) in a batch reactor utilizing sodium methoxide as homogeneous catalyst and managed to obtain trimethylolpropane esters containing 98% w/w triesters in less than 1 h. 16 However, the presence of alkali metal catalyst contributed to saponification due to the formation of free fatty acids along the reaction. The fatty soaps formed were in colloidal form partially soluble in the reaction products, and hence were required to be separated from the final product through several complicated filtration and separation processes. Furthermore, it was essential to maintain the anhydrous conditions in the system as the presence of alkaline catalyst can lead to irreversible hydrolysis of methyl esters to fatty acids. This has restricted the use of a higher percentage of catalyst. In Received: December 4, 2011 Revised: March 22, 2012 Accepted: March 25, 2012 Published: March 25, 2012 Article pubs.acs.org/IECR © 2012 American Chemical Society 5438 dx.doi.org/10.1021/ie2028365 | Ind. Eng. Chem. Res. 2012, 51, 5438-5442