Synthesis Of Trimethylolpropane Triesters As Biolubricant Base Stock From Bulk Oil

The objective of this study is to produce trimethylolpropane fatty acid triester(TFATE) as biolubricant base from bulk oil. There were two steps in the process. Inthe first step, fatty acid methyl ester (FAME) was produced by transesterification oftriacylglycerol (TG) with methanol. In the second step, TFATEs was synthsized bytransesterification of FAMEs with trimethylolpropane (TMP).A high temperature gas chromatography method was developed for analyzingTFATE by using a gas chromatography (GC) equipped with a capillary columnDB-1ht（15m×250μm×0.1μm). The oven temperature was set initially at50oC,increased by50oC/min to220oC, and then increased by30oC/min to290oC, increasedby40oC/min to330oC, held for2min, then increased by30oC/min to370oC, and heldfor another3min. Nitrogen was used as the carrier gas. Temperatrue for the injectorand detector were at380oC and400oC, respectively, with split ratio of20:1andinjection volume of1μL. This method showed good precision and reproducibility forTFATE analysis.Palm based TFATE was synthesized by transesterification reaction of palmbased FAME and TMP. Results showed that trimethylolpropane mono potassium salt(TMP-K) had the best performance for the reaction, under the optimal reactionparameters: mole ratio of TMP-K to TMP0.02:1, mole ratio of FAME to TMP4:1,reaction pressure300Pa, reaction temperature128℃and reaction time1h. Underthese conditions, the transestrification product contained90.11(w/w) TFATE and theconversion efficiency of FAME reached91.78%. After removal of trimethylolpropanefatty acid monoester (TFAME) and unreacted FAME by molecular distillation（MD）,the content of TFATE in the final product was97.02(w/w).Waste cooking oil (WCO) based TFATE was synthesized by transesterificationof WCO based FAME with TMP. The reaction parameters and oxidative stability ofTMPFATE were studied. Under selected conditions (potassium hydroxide as the catalyst, a mole ratio of catalyst to trimethylolpropane of0.25, a mole ratio of FAMEto trimethylolpropane of4:1, pressure at200Pa, reaction temperature at118oC, andthe reaction time at1.5h) a high selectivity for TFATE (85.71wt%) was obtained.After purification by MD at120oC, the content of TFATE in the product was99.59(w/w). The addition of α-tocopherol, BHA, TBHQ enhanced oxidative stability, whileDTBHQ and rosemary extract R40did not improve oxidative stability. The bestsynergism of antioxidants was found at a3:1ratio of α-T to BHA.The synthesis of TFATE was scale up by using canola oil as raw material,results in83.79%yield of TFATE catalysed by potassium carbonate under thecondition of reaction time3h, temperature130℃, molar ratio of FAME to TMP4:1,and molar ratio of potassium carbonate to TMP0.1:1. After purification by MD, thecontent of TFATE in the final product was99.3wt%.To overcome the drawbacks of TMPFATEs, such as relatively high viscositiescaused by high molecular weight, corn based TMPFATE was interesterified withglyceryl triacetate (GTA) to produce trimethylolpropane fatty aciddiester-monoacetate (TMP-DE-MA) with lower molecular weight.Trimethylolpropane mono potassium salt (TMP-K) was used as a catalyst, under theoptimal reaction conditions (reaction time3h, temperature190℃, molar ratio ofTMPFATE to GTA1:1.25, and the catalyst loading6%w/w),52.56%product yieldwas obtained under reaction pressure of800Pa. TMP-DE-MA with averagemolecular weight of690.8Da was obtained with yield of52.56%.