Synthesis Of Novel Bifunctional Ionic Liquid For Catalytic Conversion Of CO₂ Into Cyclic Carbonate

CO₂ is not only the main greenhouse gas,but also a rich,cheap,non-toxic and renewable C1 resource.It is of great significance that using CO₂ as a raw material to synthesize high value-added chemicals.It can not only reduce the concentration of CO₂ in the atmosphere,but also cut down the consumption of non-renewable energy sources such as coal and petroleum.Catalytic conversion of CO₂ to cyclic carbonates has aroused widespread concern among many CO₂ resource utilization strategies.The reaction has atomic economy and can replace the traditional toxic phosgene process,which meets the requirements of green chemistry and environmental protection.And the synthesized cyclic carbonate has a wide range of uses in the fields of chemical engineering,medicine,energy and polymers.It is key that designing efficient catalysts to achieve CO₂ activation and catalytic conversion,due to CO₂ itself has thermodynamic stability and kinetic inertia.Based on CO₂ activation and catalytic conversion mechanism,using triethylamine?TEA?,triethanolamine?TEOA?,bromoaceticacid,1,8-diazabicycloundec-7-ene?DBU?,tetramethylguanidine?TMG?as raw materials,synthesing of series of quaternary ammonium salt double ion type ionic liquids.The application was studied about the catalytic conversion of CO₂ to cyclic carbonate.By examining the effect of different ionic liquid structures on the catalytic performance,the catalyst[^-O₂TEA⁺][Br^-][DBUH⁺]with better performance.The effects of different reaction temperature,catalyst dosage,CO₂ pressure and reaction time on the CO₂ cycloaddition reaction were systematically studied.The product yield was found to be 95%form the reaction condition of 30?,1.5 Mpa,15 h.At the same time,the universality and recycling performance of the catalyst were investigated.The catalyst has a certain catalytic activity for epoxides with different substituents,which can be recycled for 5 times without significantly reducing the activity.Combined with the experimental results,it was proposed the possible catalytic mechanism of the quaternary ammonium salt double-ionic ionic liquids for the CO₂ cycloaddition reaction.A series of aminophenol type eutectic ionic liquids were synthesized by a simple one-step method,and their catalytic performance in homogeneous catalytic CO₂cycloaddition reaction was studied.The effects of different catalyst structures and catalytic reaction conditions on the CO₂ cycloaddition reaction were investigated respectively.The study found that when using tetrabutylphosphonium bromide/3-aminophenol?TBPB/3-AP?as the catalyst,the activity is the highest,mainly due to the synergistic activation ability of the halogen ion in TBPB and the hydroxyl and amino groups in 3-AP.Halogen ions nucleophilically attack the less hindered carbon atoms in the epoxide,and the hydroxyl and amino groups form hydrogen bonds with the oxygen atoms in the epoxide,thereby promoting the ring opening of the epoxide.Using TBPB/3-AP as the catalyst,the reaction yield was96%and the selectivity was 99%under the reaction temperature of 80 ^oC and the reaction time for 1.0 h.By examining the effect of the catalyst on the catalytic activity of different epoxides,it was found that as the steric hindrance of the epoxide increases,the reactivity decreases.In addition,through the investigation of the recycling performance of the catalyst TBPB/3-AP,it was found that the catalyst was recycled for 5 times,the activity was not significantly decreased,and it showed good structural stability and recycling performance.Based on the experimental results,the mechanism was speculated of TBPB/3-AP catalytic CO₂ cycloaddition reaction.In order to further reduce the energy consumption of the CO₂ cycloaddition reaction,and at the same time be able to show the catalytic activity for different epoxides,synthesis of a series of choline-succinimide eutectic ionic liquids using a one-step method.It was compared that the effects of different choline anions on the CO₂ cycloaddition reaction and found that the eutectic ionic liquid choline iodide/hydroxysuccinimide?CHI/NHS?was the better catalyst.The best reaction conditions were reaction temperature 30 o C,reaction time 10.0 h,catalyst dosage 6mol%and were obtained by examining the reaction time,reaction temperature,catalyst dosage and CO₂ pressure.Under this condition,propylene oxide can be completely converted,and the yield of the product propylene carbonate is over 96%.Using CHI/NHS as a catalyst,the catalytic activity of the cyclic addition reaction of CO₂ with different substituent epoxides was investigated,and satisfactory product yields and selectivities were obtained;By examining the CHI/NHS recycling performance,It shows that the ionic liquid can be recycled for 5 times,and the catalytic activity remains stable.Finally,the reaction mechanism of CHI/NHS catalyzed CO₂ coupling epoxide to cyclic carbonate was explored.In summary,the above three new types of ionic liquids exhibit good catalytic activity under normal temperature,solvent-free,and co-catalyst-free conditions,which solves the problems of low catalytic activity,harsh reaction conditions,and difficulty in separation.