Study On Transesterification In The Present Of Br(?)nsted Ionic Liquids

Transesterification is one of the most common reactions in organic chemistry.Many esters and environmental biofuel, which are of wide application in fine chemistry and fossil energy, are prepared throught the transesterification in the present of traditional catalysts.However, these catalysts have many disadvantages such as equipment corrosion, more byproducts, and difficult separation from the products. Although solid acid catalysts may overcome some disadvantages of mineral acid catalysts, some disadvantages such as easy deactivation and short lifetime are the major limits for further application in green chemistry. Br(O|¨)nsted ionic liquid is an acid catalyst, the catalytic activity of which can be promonted by grafting the specific functional group into the molecular structure. They are stable in water and air, exhibit negligible vapor pressure, as well as high catalytic acitivity and offer the potential for recyclability. According to the detrimental effect of these catalysts in the transesterification, two main reactions including triglycerides transesterification and trimethylolpropane transesterification, which are catalyzed by Br(O|¨)nsted ionic liquids, are investigated.Transesterification of triglycerides catalyzed by sulfonate functionalized ionic liquid was first studied. The reaction mechanism and kinetics were also investigated. The effect of temperature, reaction time, catalyst dosage, molar ratio of reactants and the free fatty acid (FFA) content on the transesterification was carefully examined. The results of orthogonal experiment showed the primary and secondary factors in the transesterification of triglycerides for biodiesel production: temperature > catalyst dosage > molar ratio of reatants > reaction time. The yield of esters and the conversion of triglycerides reached 92.0% and 99.1% respectively when the reaction was carried out under the following conditions: molar ratio of oil/alcohol/catalyst 1:10:0.12, temperature 100?, time 5h. The content of FFA has a catalytic effect on the reaction. The catalyst exhibited constant activity for seven successive cycles after being recycled. The good reusability of this catalyst may be due to its molecular structure and the electrostatic force between the cation and anion of ionic liquid. The bond length, activation energies of elemental reactions, charge distribution and electrostatic potential (ESP) distribution were calculated by Guassian 04 HF method. The pathway in the transesterification of triglycerides catalyzed by Br(O|¨)nsted ionic liquid was deduced according to the above results calculated by computer simulation. Based on the deduced pathway, the kinetics of transesterification with three steps was analyzed. Meanwhile, three kinetic equations in the corresponding step-reaction of Jatropha oil transesterification and Soybean oil transesterification were deduced.The kinetic constants at 70?-100?, energies of activation and preexponential factors were obtained by the kinetic calculation. The experimental data suggested that the second step has the largest activation energy. The scope of application of these kinetic equations was analyzed by variance analysis to prove the reliability of the kinetic models.The transesterification of trimethylolpropane was also studied. A series of Keggin heteropolyacid (HPA) salts as catalysts were prepared and used in the reaction. The progression from a monophase catalysis to a biphase separation was observed in the process. The mechanism and kinetics were investigated. The pyridinium with PW12O403- as the anion ([PyBS]₃ PW₁₂O₄₀) showed the best catalytic performance among the HPA salts.The relation between molecular structure of ionic liquid and acidity and catalytic activity was also investigated. The effect of temperature, reaction time, catalyst dosage and molar ratio of reactants on the transesterification was carefully examined. The results of orthogonal experiment showed the primary and secondary factors in the transesterification of triglycerides for biolubricant production: temperature > catalyst dosage > molar ratio of reatants > reaction time. The yield of triesters and the conversion of trimethylolpropane reached 92.5% and 99.1% respectively when the reaction was carried out under the following conditions: molar ratio of trimethylolpropane/fatty acid methyl ester /catalyst 1:3.7:0.016, temperature 120?, time 3h. The fatty acid methyl esters with different alkyl chains were found to have an effect on the transesterification of trimethylolpropane. The reaction time varies depending upon the nature of the substrate. The recycling results of the catalysts showed that the HPA salts present a self-separation performance after reaction. They are easily recovered and quite steadily reused as demonstrated by an eight-run recycling test. The bond length, energies of activation in elemental reactions, charge distribution and ESP were calculated by Guassian 04 HF method. The mechanism in the transesterification of trimethylolpropane catalyzed by HPA salts was deduced according to the above results calculated by computer simulation. The simulated results showed that the fourth step-reaction with the largest activation energy is the rate determining-step and controls the rate of transesterification of trimethylolpropane. The ESP of reactants and tetrahedral intermediates were calculated by the method of HF and base term of Sto-3g. The calculation further proved the pathway deduced above. Based on the deduced mechanism, the kinetics of transesterification of trimethylolpropane with three steps was analyzed. Meanwhile, three kinetic equations in the corresponding step-reactions of trimethylolpropane transesterification were deduced. The kinetic constants at 100?-150?, energies of activation and preexponential factors were obtained by the kinetic calculation. The experimental data suggested that the third step has the largest activation energy. The scope of application of these kinetic equations was determined by variance analysis between the simulation data and the experimental data to prove the reliability of the kinetic models.