Preparation Of Polyether Ionic Liquid Catalysts Immobilized On Zeolite And Their Conversion Performance Of CO₂

CO₂ as a greenhouse gas,meanwhile,is also a rich C1 resource.Converting CO₂ into chemical products,which could turn waste into treasure and provide a way for the treatment of greenhouse gases.The chemical property of CO₂ is stable,so the selection of catalyst is the key to achieve the conversion.Ionic liquids?ILs?have been widely used for their excellent catalytic properties which also showed excellent catalytic performance in the cycloaddition reaction of CO₂ and epoxy alkanes to cyclic carbonates.However,due to their high viscous liquid state,traditional ionic liquid?IL?catalysts have some difficulties in industrialized application,such as product separation,catalyst reuse and restriction of intermittent batch reactor.Grafting ILs onto the carrier to realize the immobilization is expected to be a relatively effective solution to these problems.In this dissertation,polyether ionic liquids?PILs?were synthesized,and composite PILs were synthesized using PILs and ZnBr₂ as reactant.Then immobilized composite PILs on zeolite and silane zeolite to synthesize immobilized PILs catalysts.The catalysts were used to catalyze the cycloaddition of CO₂ with propylene oxide?PO?to propylene carbonate?PC?in batch and fixed-bed reactor.Three PILs HO-[PECH-MIM]Cl,HOOC-[PECH-MIM]Cl and H₂N-[PECH-MIM]Cl were synthesized and their catalytic properties in the batch reaction of CO₂ with PO were studied.The results show that all PILs have good catalytic activity.HOOC-[PECH-MIM]Cl had the highest conversion of 95.1%and selectivity of 96.8%under the condition:catalyst dosage of 2.5%,temperature of 120°C,pressure of 2.5MPa,reaction time of 1h.To improve the catalytic performance and increase the concentration of active component,three composite PILs HO-[PECH-MIM]Cl/[ZnBr₂],HOOC-[PECH-MIM]Cl/[ZnBr₂]and H₂N-[PECH-MIM]Cl/[ZnBr₂]were prepared by compounding PILs with Lewis acid ZnBr₂.Their catalytic properties were tested by batch catalysis.Results showed that conversion and selectivity of HOOC-[PECH-MIM]Cl/[ZnBr₂]were up to 100%and 98.9%respectively.In order to achieve immobilizations,three PILs were immobilized on three zeolites ZSM-5,MCM-X and SBA-15,the obtained catalysts were used to catalyze the synthesis of PC from CO₂ and PO.The optimum reaction conditions were investigated.Under the optimum condition:catalyst dosage of 2.5%,temperatureof130°C,pressureof2.5MPa,reactiontimeof0.75h,ZSM-5-HOOC-[PECH-MIM]Cl/[ZnBr₂]has the best catalytic performance with conversion of96.3%,selectivity of 96.8%.The conversion and selectivity have dropped to 86.7%and 77.9%respectively after 8 cycles since a certain amount of composite PILs lost during the cyclic use of ZSM-5-HOOC-[PECH-MIM]Cl/[ZnBr₂]and the mechanical strength of the catalyst spline is poor,so it is difficult to be applied in fixed-bed continuous reactor.Silane coupling agent 3-chloropropyl triethoxysilane?CPTES?,which was used to enhance the connection between PILs and supporters MCM-X and SBA-15 to obtain silane molecular sieves MCM-X-CPTES,SBA-15-CPTES and catalysts,also improved the mechanical strength of the prepared catalyst.This method is hopeful to realize continuous catalysis in fixed-bed.Synthesized catalysts,using silane molecular sieves as supporters,composite PILs as catalytic components was applied to the cycloaddition in the fixed bed reactor,and the optimum reaction condition was also investigated.The results showed that under the optimum condition,reaction temperature of 120°C,pressure 3.0MPa,time of 5.0h and liquid hourly space velocity of 0.50h^-1,the catalyst SBA-15-CPTES-HOOC-[PECH-MIM]Cl/[ZnBr₂]had the best catalytic performance,the conversion rate was 95.3%and the selectivity was 85.8%.After continuous reaction for 50h,only a small amount of PILs lost,the catalyst spline comminution phenomenon decreased owing to the enhancement of mechanical strength.Although the catalytic performance of the catalyst used at the first time is slightly lower than that of the catalyst prepared by directly supporting on molecular sieve,the immobilization and performance are more stable.The obtained catalysts with a good service life can effectively decrease the loss of active components and unloading,and can be continuously applied in the fixed-bed reactor.