Immobilization Of Ionic Liquids As Catalyst For Synthesis Of Cyclic Carbonates

In order to solve the greenhouse effect caused by excessive CO₂ emissions,chemical fixation of CO₂ into high value-added basic chemical products has attracted the attention of researchers.Epoxides and CO₂ generate cyclic carbonates,which not only solve the problem of excessive CO₂ content in the atmosphere,but the reaction also meets the concept of green chemistry with an atomic utilization rate of 100%.However,CO₂ is extremely inert and requires a catalyst to facilitate the reaction.At present,catalysts generally have low activity,require auxiliary catalysts,are unsuitable for separation,and have harsh reaction conditions.In this paper,number of effective functional groups?the effective functional group activity and the specific surface area and morphology structure of the carrier are proposed to improve the catalytic activity and improve the catalytic performance.First,from the perspective of increasing the degree of aggregation of effective functional groups per unit area,a heterogeneous polynuclear ionic liquid catalyst was prepared.An ionic liquid having a 4 times functional group number at a single site was prepared by the reaction of triethylenediamine and 1,4-dibromobutane,and then fixed onto polystyrene microspheres.The reaction yield increased with increasing temperature,time,initial pressure and amount,under optimal conditions?150°C,initial pressure of CO₂ 1.4 MPa,reaction 3 h and use of catalyst[PS-BiDABCO-OH]Br₄ 0.31 g?The yield of synthesized cyclic carbonate was 95.8%and the selectivity was 98.2%.In order to increase the activity of effective functional groups,a large sterically hindered dicyclohexylamine was grafted onto chloromethylated polystyrene microspheres.The steric hindrance and electron donating property of cyclohexane weakened the interaction between anion and cation bonds.The results showed that the large hindered[PS-MCH]Br increased the catalytic yield by 20%compared to[PS-DMEA]Br.The optimal conditions for the catalytic cycloaddition reaction were systematically studied.Temperature was an important factor affecting the catalytic efficiency.When the reaction temperature was raised from 110°C to 135°C,the yield of PC increased from 73.8%to 98.8%.at 135°C,CO₂initial pressure 1.0 MPa,reaction 3 h and the amount of catalyst 1.0 mol%,the highest yield of PC is 98.8%.The catalyst maintains a large catalytic efficiency at low temperatures and pressures.After a reaction cycle of 5 cycles at 96°C,initial CO₂ pressure of 0.5 MPa,11 h,and 1.0 mol%,the PC yield is?75%and the selectivity is?98%.To optimize the specific surface area and morphology of the support.Through the emulsion polymerization method,mesoporous divinylbenzene-polystyrene microspheres with different specific surface areas were prepared,and different ionic liquids were grafted after chloromethylation.The relationship between the specific surface area of the catalyst and the pore volume was investigated.The catalytic performance of different ionic liquids was compared.[PS-DMEA-OH]Br had the highest catalytic performance,130°C,initial pressure of CO₂ 1.2 MPa,time 2.5 h and catalyst dosage 0.45 mol%,catalytic cycloaddition yield 94.0%.The effect of temperature and pressure on the activity of the catalyst was tested.Under the optimum conditions?150°C,initial pressure of CO₂ 1.2 MPa,time 2.5 h and catalyst consumption 0.45 mol%?,the catalyst yield was 99.5%and selectivity was 99.6%.