Research On Synthesis Of Pentaerythritol Oleate

Because of its environmental acceptablity and renewablity, polyol esters are gaining increasing popularity as bio-lubricants to substitute mineral oil based lubricants. However, such problems as low yields, expensive catalysts, rigorous synthesizing conditions and environmental pollution are frequently involved in the synthesis of polyol esters. A high efficiency, reusable catalyst is considered key to solve these problems. In the present work, pentaerythritol oleate was synthesized from oleic acid and pentaerythritol by homogeneous and heterogeneous esterifications. The reaction conditions, catalyst and the product were studied.The parameters of synthesizing pentaerythritol oleate by homogeneous esterification were studied. The effect of reaction time, temperature, oleic acid/pentaerythritol ratio, amount of toluene, and amount of catalyst (p-toluenesulphonic acid) on the synthesis was studied and the optimum conditions were obtained by orthogonal experiment: reaction time 3h, temperature 160℃, oleic acid/pentaerythritol ratio 4.4:1, amount of p-toluenesulphonic acid 0.8%. An optimum conversion rate above 96% was reached.Active carbon, which is a cheap and abundant resource, was selected as catalyst carrier after literature survey and through comparative experiments. Active carbon supported p-toluenesulphonic acid (ACSpTA) at different p-toluenesulphonic acid loadings was prepared by impregnation method. Free p-toluenesulphonic acid and ACSpTA were compared in regard to their catalysis activity to the esterification rate, and the effect of amount of ACSpTA on esterification rate was also studied. Both Free p-toluenesulphonic acid and ACSpTA showed similar catalysis activity. And the suitable loading of p-toluenesulphonic acid on active carbon was determined at 45%. The fact that the p-toluenesulphonic acid had been supported on activated carbon was confirmed by thermal gravimetric analysis and infrared analysis.The parameters of synthesizing pentaerythritol oleate by heterogeneous esterification were studied. The effect of reaction time, temperature, oleic acid/pentaerythritol ratio, amount of the catalyst on the synthesis was studied and optimized by the response surface methodology (RSM): reaction time 2.7h, temperature 160℃, oleic acid/pentaerythritol ratio 4.16:1, amount of ACSpTA 2.51%. An optimum conversion rate above 95% was reached. Both homogeneous and heterogeneous esterification approaches showed similar results, except that the latter is featured by catalyst reuses for 5 times.Pentaerythritol oleate was purified by molecular distillation from the crude product obtained above showing a yield of ~80%, and then characterized by FT-IR spectrum. The basic physical and chemical indexes of the purified pentaerythritol oleate are comparable with commercial samples of the same kind.