Preparation Of Metal Based Ionic Liquid Catalyst For Synthesis Of Diphenyl Carbonate

Diphenyl carbonate is one of the important raw materials for the synthesis of polycarbonate.The traditional phosgene synthesis methods are highly toxic,flammable and explosive,corroding equipment and polluting the environment.Using the transesterification method of dimethyl carbonate and phenol instead of the traditional phosgene method to synthesize diphenyl carbonate has the advantages of simple process,safety and environmental protection,but the steric effect of dimethyl carbonate is greater and the reaction is limited in thermodynamics.Traditional tin catalysts have certain catalytic performance for the synthesis of diphenyl carbonate by transesterification,but the conversion and selectivity of phenol need to be further improved.Based on the research basis reported in the literature and combined with the characteristics of transesterification reaction,a variety of metal based ionic liquid catalysts were designed and prepared in this paper.Their catalytic performance was evaluated by reactive distillation unit,in order to obtain a new catalyst preparation method and action mechanism for the synthesis of diphenyl carbonate by efficient transesterification reaction.The main research contents are as follows.Firstly,with Fe、Cu、Zn、Ti、Al、Ni and Sn as the main active sites and strong proton donor sulfonic groups to enhance the lack of electricity of metal active sites,seven kinds of double acidic metal ionic liquids were designed and prepared to catalyze the transesterification of dimethyl carbonate and phenol to synthesize diphenyl carbonate.The results showed that the prepared seven kinds of double acidic ionic liquids were the target products and had certain catalytic performance.Among them,the catalytic effect of titanium catalyst[HO₃H-（CH₂）₃-mim]Cl-Ti Cl₄was the best.When the reaction temperature was160℃,the reaction time was 6h,and the amount of catalyst was 1%of the total mass of reactants,the conversion of phenol was 40.72%,the selectivity was 99.99%,and almost no by-product anisole was produced.In order to explore the synergistic catalysis of acid-base catalysts,alkaline metal oxides were selected as cocatalysts to form a composite system with double acidic ionic liquid catalysts,and the effects of different types of cocatalysts and the amount of cocatalysts on the catalytic effect were studied.The results showed that the addition of cocatalysts did not further improve the catalytic effect,but promoted the production of free phenoxy negative ions,resulting in a significant decrease in the selectivity of the catalyst.Secondly,in order to explore the influence of the acidity and alkalinity of ionic liquids on the catalytic performance,five functional complex salt ionic liquid catalysts with different acidity and alkalinity were prepared with chlorotitanate as the active site and imidazole ionic liquids with different acidity and alkalinity as the precursor.It is expected that the acid-base synergistic catalysis is better than the catalytic performance of double acid ionic liquids.The results show that under the same reaction conditions,with the gradual decline of the acidity of Br?nsted catalyst,the catalytic performance also decreases,while the acid-base synergistic catalytic effect of alkaline ionic liquid and chlorotitanate is not ideal.Therefore,the catalyst with the best catalytic performance is still the titanium double acidic ionic liquid catalyst with the strongest acidity.By optimizing the process conditions of gas catalysis,it is known that the best process conditions of the catalyst are that the reaction temperature is 160℃,the reaction time is 6h,and the amount of catalyst is 1,5%of the total mass of reactants.Under this condition,the conversion rate of phenol is 41.87%and the selectivity is 99.99%,but the recycling performance of the catalyst is poor.The reason should be that the catalyst belongs to homogeneous reaction and needs high-temperature distillation in the process of separation and recovery,which may lead to the decomposition of the catalyst.Finally,in view of the shortcomings of double acid metal ionic liquid catalysts,based on the above research,six kinds of titanium heteropoly acid ionic liquids coordinated with different metals were prepared by modifying and assembling heteropoly acids with ionic liquids,and their chemical structure,crystal structure,thermal stability and apparent morphology were tested and analyzed to study the catalytic performance of heteropoly acid ionic liquids for transesterification.The results show that the heteropoly acid ionic liquid has good thermal stability and can realize heterogeneous catalysis.The catalyst with the best catalytic performance is Bmim₄[Ti（H₂O）Ti Mo₁₁O₃₉].The optimum reaction conditions of the catalyst are that the reaction temperature is 180℃,the reaction time is 8h,the amount of catalyst is 1.5%of the total mass of reactants,the conversion of phenol is 46.17%,the selectivity of product is 98.89%,and the recycling performance is good.It is recycled for 3times,The conversion of phenol is 44.53%and the selectivity of the product is 95.16%,which shows that the heteropoly acid ionic liquid catalyst has better catalytic performance and is expected to realize the continuous catalytic synthesis of diphenyl carbonate in fixed bed.