Preparation And Application Of Ionic Liquids Catalysts Immobilized By Modified SBA-15

The massive emission of greenhouse gas carbon dioxide has brought serious harm to the ecological environment,so the conversion of carbon dioxide resources into high value-added chemical products has become a global research hotspot.Studies have shown that the carbonylation reaction of carbon dioxide and epoxy compounds is a green and environmentally friendly atomic economic reaction.And the product cyclic carbonate is widely used in various fields,but the performance of carbon dioxide is stable,and the selection of catalysts is the key in resource conversion.Ionic liquids have unique advantages in the conversion of carbon dioxide,but their liquid phase and high viscosity bring inconvenience to the separation and purification of products and catalysts.The ionic liquids are immobilized and their phase changes can not only solve the problem of energy consumption caused by separation and purification but also achieve efficient and continuous conversion of carbon dioxide.In this paper,modified molecular sieves Al/SBA-15 and Al-SBA-15 were prepared using molecular sieve SBA-15 as a carrier,and metal aluminum was grafted onto the SBA-15framework through post-graft and in-situ modification methods,in order to enhance the acidity of molecular sieves and improve their synergistic catalysis.The two modified molecular sieves were then immobilized with two composite ionic liquids[BMIM][Zn₂Br₅]and[HeMIM]Cl/?ZnBr₂?₂ to prepare four immobilized ionic liquid catalysts Al/SBA-15-[BMIM][Zn₂Br₅],Al/SBA-15-[HeMIM]Cl/?ZnBr₂?₂,Al-SBA-15-[BMIM][Zn₂Br₅],and Al-SBA-15-[HeMIM]Cl/?ZnBr₂?₂.They were used to catalyze the synthesis of cyclic carbonate from carbon dioxide and epoxy compounds in a kettle reaction.The effects of ionic liquids and epoxy compounds on catalytic performance were investigated.The results showed that the catalytic performance of the catalysts obtained by the post-grafting method and the in-situ modification method is very small,but the performance of the modified molecular sieve immobilized ionic liquid[BMIM][Zn₂Br₅]is slightly higher than that of[He MIM]Cl/?ZnBr₂?₂.In the process of catalyzing the synthesis of cyclic carbonate from carbon dioxide and epoxy compounds,the catalytic activity of ethylene oxide is the highest,and the catalytic activity of epoxycyclohexane is the lowest.However,during the recycling process,the active components of the immobilized catalyst gradually lost,and the phenomenon of unloading appeared.In order to further increase the chemical bonding strength of the molecular sieve-immobilized ionic liquid and reduce the loss rate of catalytically active components,the modified molecular sieve Al-SBA-15 prepared by the in-situ modification method,was immobilized by silane with composite ionic liquid to prepare the immobilized ionic liquid catalyst Al-SBA-15-CPTES-[BMIM][Zn₂Br₅],and its chemical structure,thermal stability and apparent morphology were measured.The catalyst was used to catalyze the synthesis of propylene carbonate from propylene oxide and carbon dioxide in a fixed bed.The effects of temperature,pressure,space velocity and reaction time on the catalytic performance were investigated.The results showed that under the conditions of the temperature of 130°C,pressure of 2.5 MPa,the LHSV of 0.75 h^-1,and the molar ratio of carbon dioxide to propylene oxide of 100:1,the immobilized catalyst Al-SBA-15-CPTES-[BMIM][Zn₂Br₅]exhibits good catalytic performance.For 50 hours of continuous catalysis,the yield of propylene carbonate changes little,which indicates that the silane strengthens the chemical bonding strength between the molecular sieve and the ionic liquid,and reduces the offloading rate to a certain extent.It solves the problem of the loss of active components when the ionic liquid catalyst is immobilized,and has a good catalytic service life.