The Technology Research Of Carbonate Synthesis By Transesterification Catalyzed Ionic Liquid

Over the past few centuries,People’s Daily needs for fuel,chemicals and electricity have come from carbon-rich fossil fuels,natural gas,oil and coal.Global warming is the result of excessive consumption of these resources.Reducing the concentration of CO₂to form high value-added fine chemicals through chemical conversion is a major issue of sustainable development,and is also the direction of common efforts in the chemical industry.The chemical products of carbonic acid esters are one of the fine chemicals with high added value.The conversion of CO₂to dimethyl carbonate through transesterification is currently considered promising in both academic and industrial fields.This synthetic route is favored by many researchers because of its high atomic efficiency and low environmental impact.But there are two big problems with carbonates.One is the transesterification method of the traditional sodium methoxide catalyst there are problems,because the catalyst sodium methoxide solubility is low,easy to precipitate into solid in the system,blocking the tray sieve.Another problem is the separation of methanol and dimethyl carbonate azeotrope.Ionic liquid,as a dominant substance,has the advantages of high solubility,recyclable,pollution-free and so on,both in catalytic effect and separation.Therefore,this topic has done the following work:（1）An ionic liquid was prepared as a novel catalyst for the synthesis of carbonate and used for transesterification reaction.Its chemical structure was characterized.The reaction mechanism of ionic liquid A to transesterification is deduced.（2）A new process of synthesis of mixed carbonate by"one pot method"was adopted.The catalytic activity of vinyl carbonate,methanol and ethanol catalyzed by ionic liquid A was evaluated by the new process of one pot method.The reaction time is 1h,the amount of catalyst is 0.1%of the total raw material,and the optimum reaction condition is that the yield of total carbonate is 92%when the ratio of vinyl carbonate,methanol and ethanol is1:3:3.Among them,the yield of dimethyl carbonate is 11%,the yield of methyl carbonate is60%,and the yield of diethyl carbonate is 21%.In the comparison of orthogonal experiment,ethanol has the greatest influence on the yield of dimethyl carbonate and diethyl carbonate in the mixed system of vinyl carbonate,methanol and ethanol.（3）Methanol and dimethyl carbonate were separated by freezing crystallization method,metal salt absorption method and extractive distillation method respectively,and the extractive distillation process was perfected by Aspen Plus.The azeotrope of this topic is methanol-DMC.Freezing crystallization separation method mainly from the raw material dimethyl carbonate content,stirring speed,cooling speed,as well as the seed amount of the impact on the separation effect.The effect of absorption temperature and particle size of metal salt on the separation effect is investigated by metal salt absorption method.Two ionic liquids[Hmim]Oac and[Omim]Oac were synthesized by extractive distillation and their chemical structures were characterized.In the actual test process,the content of dimethyl carbonate at the top of the tower never exceeded 81%,so the influence of a series of factors on the separation effect of methanol and dimethyl carbonate was explored with the help of the simulation tool Aspen Plus.The process was optimized.The results show that ionic liquids[Hmim]Oac and[Omim]Oac have good effects on extractive distillation separation.