Direct Synthesis Of Cyclic Carbonates From Olefins And CO₂ Based On Ionic Liquid Catalysi

Carbon dioxide（CO₂）is not only one of the major greenhouse gases,but also a cheap,green,and renewable C1 resource.The chemical fixation of CO₂ into cyclic carbonate is one of the important ways of CO₂ chemical conversion.Currently,the classical method for the preparation of cyclic carbonates is the cycloaddition reaction between epoxides and CO₂.However,epoxides are expensive,high toxicity,and explosive,which have certain safety hazards.In this thesis,we use inexpensive and accessible olefins as the starting material to synthesize cyclic carbonates by direct oxidative carboxylation of olefins with CO₂.It can effectively avoid the preliminary synthesis and purification of epoxide,and is a CO₂conversion route with high economic value and market application prospects.The main research idea is to design an inexpensive,simple,and efficient two-component catalyst system to achieve highly selective conversion of various olefins to cyclic carbonates under mild conditions.However,the two-component catalyst system has problems such as difficult product separation and catalyst recovery.Based on this,this thesis prepared a series of supported ionic liquids（SILs）with different anions by green solvent-free mechanochemical grafting method.The SILs were used as catalysts for the synthesis of cyclic carbonates from olefins and CO₂,which aimed to establish a green and efficient catalytic system with easy catalyst recovery and product separation.The main studies are as follows:（1）Currently,multi-component catalyst systems are often constructed to catalyze the synthesis of cyclic carbonates from olefins with CO₂,but most epoxidation catalysts suffer from complex synthesis or high cost.Based on this,we first used a binary catalyst system consisting of KHCO₃ and N₄₄₄₄Br for the oxidative carboxylation reaction of olefins with CO₂,where KHCO₃ was the epoxidation catalyst and N₄₄₄₄Br was the cycloaddition catalyst to successfully achieve the oxidative carboxylation reaction of styrene.The effects of reaction solvent,CO₂ pressure,temperature and time on the reaction were investigated separately.Under optimum reaction conditions（5 bar CO₂,80^oC,28 h）,highly selective conversion of various olefins to cyclic carbonates was achieved,with the yield of styrene carbonate up to 86%.Furthermore,the KHCO₃/N₄₄₄₄Br system can be recycled for five times without any significant decrease in catalytic activity,which indicates that the binary catalytic system has excellent recovery performance.Based on the kinetic study and experimental results,the catalytic mechanism of KHCO₃/N₄₄₄₄Br synergistically catalyzed oxidative carboxylation of olefins with CO₂ was proposed.（2）Although the KHCO₃/N₄₄₄₄Br binary catalytic system showed excellent catalytic activity for the oxidative carboxylation of olefins with CO₂,the catalytic components were complex and the catalyst recovery was difficult.Based on this,we prepared amino-functionalized ILs@SBA-15 catalysts by solvent-free mechanochemical grafting strategy and used it for the oxidative carboxylation reaction of olefins with CO₂.This strategy effectively avoids the harsh conditions such as organic solvent use and high temperatures associated with traditional synthesis methods for supported ionic liquid catalysts（SILs）.The experimental results showed that the mechanochemical method can uniformly load ionic liquids onto SBA-15 and maintain the rich mesoporous structure of the carrier SBA-15.The styrene was chosen as the reaction substrate and 79%yield of styrene cyclic carbonate was obtained.Compared with the reported two-component catalyst systems or single catalyst systems,the ILs@SBA-15 catalyst has almost equal or superior catalytic activity,especially the ILs@SBA-15 catalysts can be easily recovered by centrifugal filtration.Based on the experimental results,the reaction mechanism of oxidative carboxylation of olefins with CO₂catalyzed by ILs@SBA-15 was proposed.（3）Halogen-containing catalysts are usually highly corrosive to reaction equipment.Based on this,we prepared a metal-and halogen-free C_nC_mIm HCO₃@SBA-15 bifunctional catalyst by ion exchange method and mechanochemical grafting,and successfully used it to catalyze the synthesis of cyclic carbonate from olefins with CO₂.The experimental results showed that the prepared C_nC_mIm HCO₃@SBA-15 catalyst exhibited excellent catalytic performance for the one-pot conversion of olefins to cyclic carbonates under metal-free and co-catalyst-free conditions,with the highest yield of cyclic carbonates up to 86%.Compared with catalysts containing halogen anions or most metal catalyst systems,C_nC_mIm HCO₃@SBA-15 not only has higher catalytic activity,but also possesses excellent cycling performance and excellent substrate versatility.