Preparation Of Immobilized Ionic Liquids Catalysts And Their Application For Conversion Of CO₂

The cycloaddition reaction of carbon dioxide?CO₂?and epoxide to synthesis cyclic carbonate conforms to the principle of green sustainable development.It is not only an effective way to achieve energy saving and low carbon economic development,but also opens a new route about non petroleum raw materials.And it is important for the production of cyclic carbonate to be used in the field of chemical engineering.However,the chemical properties of CO₂ are extremely inactive.In the relatively mild conditions,the choice of catalyst is the key element for the chemical fixation and resource conversion of CO₂.Ionic liquids?ILs?are widely made use of the cycloaddition reaction of CO₂ with its excellent catalytic performance,however,the phase state of ILs restrict the continuous conversion of CO₂,therefore,more and more supporters have been developed to immobilize ILs to achieve heterogeneous catalysis with immobilized ILs.This paper is focused on the preparation of high performance immobilized ILs catalysts based on these characteristics of different supporters and ILs,after that,the primarily utilization of them are about the cycloaddition reaction in batch reactor and fixed bed reactor.It is expected to provide new ways and new technologies for the continuous conversion of CO₂ in industrial production.A series of different side chain length imidazole ILs immobilized on silica gel catalysts were firstly synthesized as catalytic system,and they were applied to the cycloaddition reaction of propylene oxide?PO?and CO₂ to synthesize propylene carbonate?PC?in batch reactor.The experimental data showed that this catalytic system had great catalytic activity,the length of alkyl side chain of ILs had an important effect on the catalytic system compared with pure ILs,the longer side chain length of ILs,the better catalytic properties.SiO₂/[C₁₈MIM][Zn₂Br₅]owned the best catalytic performance,the conversion of PO was99.7%and the selection of PC was 96.3%with the optimal reaction temperature,pressure,time and the dosage of catalyst,besides that,this catalyst existed great catalytic activity when it was used first time,but the activity of this catalyst reduced gradually after many recycles.The second type of catalysts were functionalized ILs with molecular sieve MCM-X as supporter.Among them,the optimal catalyst was MCM-X-[CeMIM]Cl/?ZnBr₂?₂ when catalyzed the cycloaddition reaction of PO and CO₂ in batch reactor.It displayed that the degree acidity of the catalyst had great influence on this cycloaddition reaction,the higher acidity of catalyst,the more efficient catalytic performance.When the catalytic temperature was 120?,the pressure was 2.5 MPa and the dosage of catalyst was 2.0%,the conversion was 100%and yield was 97.4%.Under these conditions,the catalytic activity of the catalyst was still high after 8 cycles,but this catalyst also existed the phenomenon that the loss of active component IL.In the end,the catalytic mechanism of this catalyst was inferred in cycloaddition reaction.The third kind of catalysts were prepared by 3-chloropropyl triethoxysilane?CPTES?as coupling agent,molecular sieve MCM-X and SBA-15 as supporter to obtain immobilized functionalized ILs catalysts.This catalytic system completed the high energy chemical bonding among the silane coupling agent,molecular sieves and ILs,at the same time,which realized the continuous catalytic conversion of CO₂ in the fixed bed reactor.The experimental result manifested that MCM-X-CPTES-[AeMIM][Zn₂Br₅]exhibited good catalytic activity and service life in continuous catalytic reaction.The yield of PC stabilized at 61.6%after 50h successive reaction when 130? with CO₂ pressure?2.0 MPa?in the present of LHSV was 0.75 h^-1 and the molar ratio of CO₂/PO was 3:1.Under the same reaction conditions,molecular sieve SBA-15 immobilized amino functionalized IL catalyst SBA-15-CPTES-[AeMIM][Zn₂Br₅]possessed more effective catalytic properties,the yield of PC remained above 70%when the cycloaddition reaction was carried for 200h continuously.