Research On Coupling Reaction Of Carbon Dioxide And Propylene Oxide By Ionic Liquid Catalyst

Owing to increasing awareness of energy,environment and sustainable development,fixation and utilization of carbon dioxide?CO₂?has increasingly becoming a worldwide topic.Polycarbonates and cyclic carbonates can be synthesized by the copolymerization and cycloaddition of CO₂ and strained heterocyclic molecules and cyclic carbonate with the presence of catalysts.Among the developed catalyst systems,double metal cyanide?DMC?complexes and ionic liquid?IL?are well-known effective catalysts for the effective utilization of CO₂.However,tedious procedures of DMC and IL preparation in conventional solvent-based methods are time-,energy-and materials-consuming.With an objective of simplifying the preparation and improving the selectivity,the work employed mechanochemistry,which is regard as bearing the concept “green chemistry”,to synthesize DMC and IL catalysts.The work greatly simplified the preparation processes,and presented a novel method for catalysts syntheses.In this work,Zn-Fe DMC catalysts were successfully synthesized with Zn Cl2 and K₃Fe?CN?₆ via clean and efficient ball milling.Imidazolium-based ionic liquids as cocatalysts were incorporated into the structure of the DMC catalysts during the grinding process.The modified Zn-Fe DMC catalysts were proven to be effective for alternating copolymerization of CO₂ and propylene oxide?PO?under controlled reaction conditions.The properties and structures of the Zn-Fe DMC catalysts and the resulting polymers were characterized by fourier transform infrared spectroscopy?FTIR?,scanning electron microscope?SEM?,X-ray diffraction?XRD?,gel permeation chromatography?GPC?,1H and ¹³C nuclear magnetic resonance?NMR?spectroscopy,and thermogravimetric analysis?TG?.The results indicate that the Zn-Fe DMC catalysts exhibit higher thermal stability compared with the DMC catalysts without imidazolium-based ionic liquids.It was also found that the introduction of a small amount of imidazolium-based ionic liquids can increase the carbonate content in the poly?propylene carbonate?copolymer with the range of 18.48²9.00%,and the turnover numbers of the poly?propylene carbonate?were close to 4.40 and number-average relative molecular mass?Mn?was up to 2.96⁴.98×10³.The terpolymer of carbon dioxide,propylene oxide and tetrachlorophthalic anhydride of poly?propylene carbonate tetrachlorophthalic phthalate??PPCPA?were synthesized by Zn-Co DMC catalysts successfully prepared using Zn Cl2,K3Co?CN?6 and imidazolium ionic liquids by ball milling.The results showed that turnover number of Zn-Co DMC catalysts was up to 25.67¹41.80 for the reaction,and the number-average relative molecular mass of the terpolymer PPCPA was up to 2.21³.15×10³.Zn-Fe DMC catalysts were successfully synthesized by ball milling using ZnBr₂ and K₃Fe?CN?₆.The cyclic carbonates?PC?of CO₂ and PO were synthesized by using this catalyst with assistance of imidazole ionic liquids.The results showed that the catalytic activity of cycloaddition reaction of CO₂ and PO could be improved by adding imidazole ionic liquids,and turnover number?TON?of Zn-Fe DMC catalysts was up to 2.33-182.67 for the reaction,and yield was up to 0.96⁷5.41%.Choline chloride?CHCl?was mixed with malonic acid?PA?,ethylene glycol?EG?,and urea?Urea?respectively.A series of new ionic liquid catalysts were prepared by ball milling.The cyclic carbonates?PC?of CO₂ and PO were synthesized by using this catalyst.The influence of reaction time,pressure,reaction temperature,the amount of catalyst,milling time and raw material ratio for reaction was investigated.The results show that the ionic liquid has high catalytic activity for cycloaddition reaction,the CHCl and PA prepared by ball milling for 5 min uses 2 m L,and the reaction is carried out at 80°C and 4 MPa for 24 h.The highest TON was 14.84 and yield was 90.93.