Research On Green Conversion Of CO₂ Based On Carboxyl-imidazolium Salt Compounds

Due to the extensive use of fossil energy for human development,the amount of CO₂,which is one of the greenhouse gases,continues to increase,seriously harming the natural environment.However,CO₂ is a non-toxic,cheap,abundant and renewable C1 resource.Converting CO₂ into other useful compounds is considered to be one of the most promising strategies for fixing CO₂.The cycloaddition reaction of CO₂ and epoxide to synthesize cyclic carbonate or polycarbonate is considered as a promising reaction.The products cyclic carbonate and polycarbonate are widely used.Cyclic carbonate can be used as electrolytes,solvents,fine chemicals,etc.,and polycarbonate can be used as engineering plastics.However,due to the inert kinetics of CO₂,it is extremely necessary to develop corresponding efficient catalysts.Many catalytic systems have been developed for CO₂cycloaddition reactions.Although researchers have conducted a lot of research on the synthesis of highly efficient catalysts and have made some important progress,the catalysts also have disadvantages such as poor stability and difficulty in separation.In this paper,three types of carboxyl-imidazolium salt catalysts are designed and synthesized.The molecular structure of the catalyst is determined by infrared spectroscopy and nuclear magnetic resonance analysis.Applying the CO₂ cycloaddition reaction to the catalyst,it was found that these three types of catalysts can exhibit high-efficiency catalytic performance under mild conditions.The first type is succinic acid alkyl ester bis-imidazolium catalyst.In this paper,five succinic acid alkyl ester imidazolium catalysts were synthesized,and the effect of catalyst structure on catalyst performance was systematically studied.The reaction conditions of the catalyst were optimized through orthogonal experiments.In the absence of co-catalysts and solvents,the amount of catalyst was found to be 1.0 mol%.At 90?and 0.1 MPa,the conversion rate could reach 88%in 10 hours of reaction.In addition,the cycle stability and possible mechanism of the catalyst are also discussed.The second category is bis-succinic acid mono-alkyl ester imidazolium catalysts.In this paper,five bis-succinic acid mono-alkyl ester imidazolium catalysts were designed and synthesized,and the effects of carboxyl group and imidazole ring on the catalytic performance were studied.The reaction conditions of the catalyst were optimized through orthogonal experiments.In the absence of cocatalyst and solvent,the amount of catalyst was found to be 1.0 mol%,and the conversion rate could reach 89%at 80?and 0.1 MPa for 8 h.In addition,the mechanism and cycle stability of the catalyst were further explored.The third category is zinc catalysts supported by carboxylic acid ionic liquids in imidazolium.In this paper,the reaction of imidazolium succinic acid mono-alkyl ester with zinc bromide was used to synthesize a zinc catalyst supported by carboxylic acid ionic liquid in imidazolium.The catalyst was used to catalyze the CO₂ cycloaddition reaction.The reaction temperature was 90?,the amount of the catalyst was 1.5 mol%and the pressure was 0.1 MPa for 8 h,and the conversion rate was 89%.Since the ionic liquid and the metal are connected in the form of a chemical bond,the catalytic center is changed,and at the same time,the bromine ion and the carboxyl group synergistically improve the catalytic performance.In addition,the corresponding mechanism of the catalyst is also discussed.