Study On Synthesis Of Glycerol Carbonate Through Coupling Reaction Of Glycerol And CO₂ Catalyzed By Functional Quaternary Ammonium Ionic Liquids

The rapid development of the biodiesel industry has led to a significant increase in global glycerol production.The conversion of glycerol into a high value-added chemical product,glycerol carbonate?GLC?,can promote the high value-added use of glycerol,thereby promoting the industrialization of biodiesel.There are many ways to synthesize glycerol carbonate from glycerol,such as oxidative carbonylation of glycerol with CO,alcoholysis of glycerol with urea,transesterification of glycerol with carbonate,and reaction of glycerol with CO₂.Among these methods,reaction between glycerol and CO₂ is the most promising one,because of its high atomic utilization and the use of greenhouse gas CO₂,.However,stable nature of CO₂ makes the reaction difficult to process directly,hence leads to low reaction equilibrium constant and low product yield.To solve this problem,this thesis proposes to add propylene oxide as a coupling reactant in the reaction system to increase the equilibrium constant of the reaction and promote the conversion of glycerol and CO₂.According to literature surveys,ionic liquids have the advantages of modulating structure easily,loading easily,and high activity,and have excellent catalytic activity upon the step-by-step reaction of the coupling reaction,so we propose functional quaternary salt ionic liquids as catalysts of the coupling reaction of glycerol,CO₂ and propylene oxide.Firstly,we synthesized a variety of ionic liquids using inexpensive triethylamine.The ionic liquids' cations include hydroxyl,carboxyl,amino-functionalized quaternary ammonium cations and triethylammonium cations.Anions include OH^-,Cl^-,Br^-,I^-.And using FT-IR,¹HNMR and ESI-MS methods characterized the synthesized ionic liquids.The results showed that the synthesized ionic liquids were of correct structure and high purity.Then,we systematically investigated the catalytic effect of ionic liquids on the coupling reaction.By changing the functional groups on the cations and anionic species of ILs,we investigated their effect on the ionic liquids' catalytic activity.The results indicate that the cations containing amino-functional groups has the best effect,the I^-containing ionic liquids had the best catalytic performance.Then,we using the amino-functionalized iodonium ionic liquid as a catalyst,optimized the reaction conditions.The results show that the increase of temperature can promote the reaction but too high temperature decreases the product's selectivity;increasing the CO₂ pressure can promote the conversion of glycerol,but too high CO₂ pressure will also dilute reaction solution and slow down the reaction;increasing the added amount of propylene oxide can promote the conversion of glycerol and the formation of the product.At 110°C,6 of the propylene oxide/glycerol molar ratio,and the 2 MPa of CO₂ pressure,the amino-functionalized ionic liquid catalyzing the reaction for 3h get the best result that the glycerol conversion rate was 92.2%,the GLC yield was 87.6%,and GLC selectivity was 95.0%.In this paper,the synthesized ionic liquids are also used to catalyze the stepwise reaction of coupling reaction of glycerol with CO₂,that is,the cycloaddition reaction of propylene oxide with CO₂ and the transesterification reaction of propylene carbonate with glycerol.And the reaction results of coupling reactions and step-by-step reactions are compared.The results show that the cycloaddition reaction is a decisive step reaction of the coupling reaction,and the presence of hydroxyl groups can effectively promote cycloaddition reaction.The two step reactions may have mutual promotion effect on each other.