Study On Synthesis Of Trimethylolpropane Triesters Of Fatty Acid

With the increasing awareness of environment protection and highly variable price of crude petroleum, lubricants made or derived from vegetable oil have attracted more and more attention due to their excellent biodegradability, However, to compete with traditional petroleum-based lubricants, vegetable oil based lubricants have inade- quate oxidative and thermal stability, vegetable oil have unsaturated molecules, which makes them sensitive to oxidation, and thermal elimination may occur owing to the presence of aβ-hydrogen to the hydroxyl group. However, trimethylolpropane (TMP) do not possess it, only radical decomposition can occur, which requires more ener- gy, giving rise to higher decomposition temperatures. In addition to good thermal and oxidative stability, trimethylolpropane esters (TMPE) have many other advantages, such as good viscosity-temperature behavior, low pour point, low volatility and biodegradability.Six kinds of ionic liquids(IL) applied to catalize trimethylolpropane triesters were synth- esized by using inexpensive chemicals, including N-(3-sulfonic acid) propyl–triethylammo- nium hydrogen sulfate(IL1), N-(3-sulfonic acid) propyl-pyridine hydrogen sulfate(IL2), N-(3-sulfonic acid)propyl-3-methylimidazolium hydrogen sulfate(IL3), l-methylimidazolium hydrogen sulfate(IL4), l-methyl-2-pyrmlidonium- hydrogen sulfate(IL5), Caprolactam hydrogen sulfate(IL6). Their structures were characterized by NMR, and the results are in good agreement with those expected. Thermal stabilities and acidity of the ionic liquids were examined by UV-vis and TG-DSC respectively. ionic liquids have good stability at high temperature, and especially containing 1-methylimidazole in the cation, which thermal decomposition points were between 365～378℃. Sulfonic acid group functionalized ionic liquids have display higher acidity than others. These properties suggest applications as an efficient catalyst in the field of synthesis.The catalytic activity of the acidic ionic liquids for the esterification of TMP tricaprylate was studied, The catalytic activity order obtained in this work can be explained by the acidity order of these ionic liquids, because the esterification reaction is an acid catalyzed reaction, and catalysts IL1,IL2 and IL3 have a sulfonic group, which gives the strongest acidity among these ionic liquids. The optimum reaction conditions of using hydrogen sulfate ionic liquids were determined by single factor experiments, and various reaction system were discussed and compared in this work. The performance of IL2 catalyzing the esterification of n-heptanoic acid and TMP was checked with using water separator, when the mole ratio of acid/alcohol was 4.2:1, catalyst amount was 9%, and reaction temperature and time were 140℃and 2h, respectively, yield of trimethylolpropane tricaprylate (98.4%) were obtained. while catalyst amount was 20% without removal of the water during the reaction, yield of tricaprylate could reach 95.2%, to compete with catalytic system using water separator, the later yield of tricaprylate decreased, the results shows that removal water of reaction improve the catalytic activity of IL2. The IL2 was reused six times with the yield of tricaprylate decreasing slightly from 98.4% to 97.1%, showing good recycling performance of IL2. The composed catalyst systems were studied, and the results showed that the catalysts from IL5 and IL1 could improve catalytic performance of IL5 obviously. Other trimethylolpropane triesters were prepared by esterification under the optimal reaction conditions.The conversion of fatty acid was analyzed by test of oil acid value in the reaction mixture. The composition of the reaction mixture in fatty acid, monoesters, diesters and triesters was monitored by HPLC. The pure triesters purified by vacuum rectification and column chromatography, were subjected by FTIR, NMR and TGA respectively.