Study On Synthesis Of Glycerol Carbonate Catalyzed By Complex Solid Base

Catalysts played a key role in the transesterification of glycerol to GC.The reported catalysts included homogeneous catalysts,biocatalysts and heterogeneous catalysts.Among homogeneous catalysts,ionic liquids had the best catalytic performance but high cost.Enzyme catalysts in biocatalysts were highly selective and environmentally sensitive.In heterogeneous catalysts,single component metal oxide catalysts had high activity but poor reusability.The supported catalysts and composite solid base catalysts could solve this problem very well.The preparation process of composite solid base catalysts was simple,and it is a good choice for the transesterification of glycerol to GC.In this paper,high-performance solid base catalysts was prepared and used to study the effect of the catalyst preparation conditions,reaction conditions on glycerol conversion and GC yield.Through structure characterization,the relationship between the structure and performance of the catalyst could be revealed.The main contents of this paper were as follows:Benson group contribution method,Trouton rule and the basic thermodynamic formulas were used to analyze the feasibility of GC synthesis.It was showed that the enthalpy change and the Gibbs free energy change of this reaction was respectively 10.42 k J/mol and-26.85k J/mol under the standard state,which indicated that the transesterification of glycerol was endothermic and spontaneous under the standard state.The relationship of enthalpy change,Gibbs free energy change and equilibrium constant with temperature was further studied and showed that the enthalpy change of the reaction decreased with the increasing of temperature and was above zero at the temperature range from 300 K to 390 K.It was induced that increasing temperature was favored for the reaction.Compared,Aspen plus software was also used to analyst the feasibility of the reaction.Under the conditions of 298.15 K and 101.325 kpa,the enthalpy change and the Gibbs free energy change of the reaction was 13.72 k J·mol^-1 and-30.52 k J·mol^-1,respectively,which were in good agreement with the Benson group contribution method.n?Li?:n?Mg?composite solid base catalysts with high activity were synthesized by co-precipitation method and then used to the synthesis of GC from glycerol and DMC.The effects of catalyst preparation conditions and reaction conditions on the glycerol conversion and the GC yield were studied by single factor experiments.The results showed that the optimum catalyst preparation conditions were n?Li?:n?Mg?=4:1.The optimum reaction conditions were n?glycerol?:n?DMC?=1:3,reaction temperature 80 ^oC,reaction time 2.0 h and 4.wt.%of the catalyst amount.It was found that the main active components of the catalyst were Li₂CO₃by the XRD and FT-IT characterization.The CO₂-TPD characterization and the performance of catalyst revealed that the strong base component not only favored the glycerol conversion but also promoted the decomposition of GC.The results of the repeated experiments and elemental analysis showed that the leaking of Li⁺resulted in the decrease of catalyst activity.Based on the catalyst prepared above,the modification was carried out by calcination method.It was reported that the modified catalyst reached 97.6%of glycerol conversion and95.5%of GC yield at the optimum conditions.Up to 92%GC yield after four times reusability indicated that had a good stability.Combined with XRD?FT-IR and CO₂-TPD characterization,the high activity and stability of the modified catalyst was attributed to the inversion of the weak and media basic components to strong basic components by calcination.The probably reaction mechanism was discussed.