The Technology And Thermodynamic Study On Using Quaternary Ammonium Ionic Liquids As Transesterification Catalyst For The Synthesis Of Biodiesel With Rice Bran Oil

Energy is important material resource to human survival and development. Theshortage of fossil energy makes the focus of world to find energy shift on torenewable energy. As an emerging renewable energy, biodiesel has been widespreadconcerned and rapidly developed.Biodiesel urgently needs for an efficient, safe and environment-friendly productionline. As green catalyst and solvent, especially SO₃H-functionalized ionic liquids areacidic strongest Bronsted acid ionic liquids used in the transesterification synthesis ofbiodiesel that can solve the environmental pollution, corrosion of productionequipment and the cost of the problem, which showed a good catalytic effect withgood industrial prospects.Rice bran oil raw materials are rich sources for biodiesel oil in China’s nationalconditions, this raw material preparation to biodiesel and has broad prospects, and thepresent reports on the refining of rice bran oil as raw materials to biodiesel is notmuch, and ionic liquid as a catalyst used in rice bran oil to biodiesel production hasn’tbeen reported.In this paper, one-step and two-step methods to synthesize a variety of quaternaryammonium ionic liquids were used, their structures were characterized by IRspectroscopy and NMR spectroscopy and their thermal stability were examined byTG-DTA analysis. Results showed that the structures of ionic liquids are targetstructures. With good thermal stability, their decomposition temperatures are above200℃, which can be used as transesterification catalyst.Compared to rice bran crude oil, refined rice bran oil has higher stability. Asystematic physical and chemical properties analysis of the rice oil were carried out.The results are: low water content of raw rice oil, only0.42%; content0.45%, barelynot free fatty acids are obtain, contaians a high level of C16and C18fatty acidglyceride, not branched-chain structures are presenced, which showed an ideal dieselsubstitute.The highest catalytic activity of [（C₄H₉）₃N（CH₂）₃SO₃H][C₇H₇O₃S] ionic liquid wasselected as the catalyst to optimized the biodiesel preparation process of rice oil transesterification reaction. The results showed that: under the conditions of reactiontime24h, the reaction temperature70℃, ionic liquids: oil: alcohol molar ratio of1:10:90, to obtain a best technology, with a yield of84.36%.[（C₄H₉）₃N（CH₂）₃SO₃H][C₇H₇O₃S] ionic liquid catalyst was used firstly at hightemperature and under high pressure to catalyze transesterification reaction of thebiodiesel, and the influences of reaction temperature and time on the yield wereinvestigated to optimize transesterification reaction in high temperature and pressureconditions. The results showed that: transesterification reaction at373K and reactiontime120min, obtain the highest yield of92.29%.Estimation methods were used to estimate the formation enthalpy and entropy ofeach component, and combined with existing literature datum, the equilibriumthermodynamic analysis of triolein and methanol transesterification reaction to thesynthesis of biodiesel was performed. The results show that: the thermal effects ofeach step of triolein with methanol transesterification reactions and the overallreaction are all not significant. The first step shows a slight endothermic reaction,while the other two steps and the overall reaction show slight exothermic reactions.There are no significant changes of enthalpy values in the second and third stepreactions as the temperature change, while in the first and overall reactions the valuesincrease as temperature increasing. Gibbs energy change of three steps and overallreactions are all positive, which indicate that reactions can not occur spontaneouslyunder standard state. Gibbs energy changes of three steps and overall reactionincrease when temperature increasing. From298.15K to428.15K, the equilibriumconstants of three steps and the overall reaction are all less than1, which is0.1to0.2,0.4to0.6and4to10×10^-4for each step,3to7×10^-5for overall reaction, respectively.The equilibrium constant of the first step slightly increases as temperature increasing,while the other two steps and overall reaction slightly decrease, which demonstratethat in order to make the reaction spontaneous, the concentration of the methanolreactant should be increased, or the concentration of the product in the reactionsystem should be reduced.