Study On The Kinetics For Reaction Of Glycerol And Dimethyl Carbonate Using Eutectic Solvent As Catalyst And Reaction Mechanism By Density Functional Theory

The industrialization of biodiesel produces a lot of by-product glycerol.So it is important to convert glycerol into high value-added chemicals to promote the sustainable development of biodiesel industry.Glycidol and glycerol carbonate are important derivative of glycerol,which is widely used in many chemical fields.Using the one pot reaction to synthesize glycidol through glycerol and dimethyl carbonate has some advantages,such as mild reaction conditions and high yield,which is the most promising route for industrialization.However,the catalysts used at present have some problems,such as complex preparation,easy deactivation and so on.Deep eutectic solvents（DESs）are a kind of low melting mixture composed of hydrogen bond donor and hydrogen bond receptor.DESs have some advantages,such as easy to synthesize,high atom utilization,strong structure adjustability and high catalytic activity.Therefore,DESs were used to catalyze the reaction of glycerol and dimethyl carbonate to synthesize glycidol.Besides,the preparation of the catalyst,performance characterization,reaction kinetics and theoretical research of reaction mechanism are further disscussed.（1）In this paper,DESs were prepared with inorganic alkali potassium hydroxide as hydrogen bond acceptor,organic alkali ethanolamine and polyethylene glycol as hydrogen bond donors by oil bath magnetic stirring method.Then,DESs were used to catalyze glycerol and dimethyl carbonate to synthesize glycidol.The results showed that KOH/ethanolamine（1:2）had the best catalytic effect.Under the optimized conditions,KOH/ethanolamine（1:2）exhibited 98.56%of glycerol conversion,80.63%of glycidol yield and 83.38%of glycidol selectivity.Besides,the characterization results indicated that there is an intermolecular force similar to hydrogen bonding between potassium hydroxide and ethanolamine.Moreover,the effects of reaction temperature,reaction time,amount of catalyst and material ratio on the reaction were discussed to get the kinetic model.Furthermore,the MATLAB software was used to simulate the kinetic model to get the rate constant and activation energy of each reaction.The result indicated that the predicted value of the model was consistent with the experimental value.（2）In the current work,the mechanism of the reaction between glycerol and dimethyl carbonate catalyzed by ionic liquids is lack of theoretical support.In order to solve the problem,the reaction mechanism of glycerol and dimethyl carbonate to produce glycerol carbonate catalyzed by[TMHEA]OH（trimethyl hydroxyethyl ammonium hydroxide）was proposed.At the same time,theoretical calculations are carried out by using density functional theory at the level of M06-2X/6-311++G（d,p）.The results showed that the whole reaction was divided into two steps.In the absence of catalyst,the first step is the speed determination step of the whole reaction.Besides,the energy barrier reached 237.11 k J/mol.In the presence of[TMHEA]OH,the anionic HO^-of ionic liquid captures the H₅ of glycerol molecule to form glycerol carboanion-H₂O species,which enhances the nucleophilic ability of glycerol carboanion.The cation forms hydrogen bond with dimethyl carbonate,which enhances the electrophilic ability of carbonyl carbon C₁.The coordination of cation and anion makes the reaction easier.In the first step,the energy barriers of the two transition states were reduced to 40.85k J/mol and 70.29 k J/mol respectively.The result indicates that the ionic liquid has a good catalytic effect,which is consistent with the experimental results.