Synthesis Of Ionic Liquid Catalysts And Their Application In CO₂ Cycloaddition Reaction

Because the burning of fossil fuels will produce a large amount of carbon dioxide,which leads to environmental problems such as global warming and ocean acidification,so the chemical fixation of carbon dioxide has been widely concerned.Because carbon dioxide has the advantages of non-toxic,non-flammable and low cost,it can be used as C1 feedstock to produce valuable chemicals such as methanol,formic acid,urea,carbyl formates,polycarbonate and cyclic carbonate.One of them,the direct synthesis of carbon dioxide and epoxy compound cyclic carbonate can reach 100%atomic utilization rate,so this efficient and economical synthesis route has attracted wide attention.However,the thermodynamic stability and kinetic inertness of carbon dioxide make it difficult to be activated,which poses a great challenge to the fixation of carbon dioxide.In order to overcome this problem,the researchers have developed a large number of catalysts to promote the cycloaddition reaction of carbon dioxide and epoxy compounds.Ionic liquids have the advantages of good thermal stability,low vapor pressure,non-flammable and non-volatile,and can be used as"green"catalysts in the cycloaddition reaction of carbon dioxide.The main contents of the paper are as follows:3,3-methylene divinylimidazole dibromide（[C₁DVIM]Br₂）was synthesized on the basis of previous studies,and then[C₁DVIM]Br₂ and ethylene glycol dimethacrylate（EGDMA）crosslinking agent were copolymerized by one-step synthesis to obtain an ionic liquid crosslinked polymer（PIL）.Three kinds of cross-linked polymers PIL-1,PIL-2 and PIL-3 based on imidazole salt ionic liquids were synthesized by changing the molar ratio between[C₁DVIM]Br₂ and EGDMA.The structure,properties and morphology of the prepared polyionic liquid were characterized by a series of analytical instruments.Epichlorohydrin was selected as the catalyst substrate,and the influence of reaction temperature,reaction time,reaction pressure and catalyst dosage on carbon dioxide cycloaddition reaction was investigated through a series of factor experiments.Subsequently,the general applicability of catalysts to various end-epoxides was investigated,and the possible catalytic reaction mechanism was proposed.The results show that the ionic liquid crosslinked polymer can catalyzed cycloaddition reaction of carbon dioxide and epoxide compound without solvent and catalyst.Under the condition of 100℃,0.7 MPa,8 h,catalyst dosage0.1 g,the yield of propylene chloride reached 98.9%.In addition,the catalyst has good stability and recycling performance in the cycloaddition reaction,can be reused five times,and the catalytic activity is not significantly reduced.A series of hydroxyl functionalized imidazole ionic liquid catalysts were synthesized,namely 3-hydroxyethyl-1-vinylimidazole p-hydroxybenzoic acid ionic liquid,3-hydroxyethyl-1-vinylimidazole aspartic acid ionic liquid,3-hydroxyethyl-1-vinylimidazole glutamic acid ionic liquid,3-hydroxyethyl-1-vinylimidazole acetic acid ionic liquid and 3-hydroxyethyl-1-vinylimidazole salicylic acid ionic liquid.The structures of the synthesized functional ionic liquid catalysts were characterized by ¹H NMR and FT-IR.The effects of reaction temperature,reaction time,reaction pressure and catalyst dosage on the cycloaddition of carbon dioxide were investigated through a series of factor experiments.Subsequently,the general applicability of catalysts to various end-epoxides was investigated,and the possible catalytic reaction mechanism was proposed.The experimental results show that the ionic liquid catalyst can catalyse cycloaddition reaction of carbon dioxide and epoxide compound without halogen and solvent.The yield of propylene chloride is 97.1%under 75℃,0.5 MPa,12 h,catalyst dosage 0.8 mol%.