乙醛缩合反应体系热力学计算和分析

Thermodynamics of Aldol Condensation of Acetaldehyde

摘要:

采用Yoneda基团贡献法估算了乙醛羟醛缩合反应体系中各物质的标准生成焓、标准熵和等压热容,与部分文献值的比较表明估算较为准确.在此基础上计算了278~368 K液相反应和600 K气相反应时主、副反应的反应焓变、反应吉布斯自由能变和反应平衡常数.结果表明温度对主反应影响较大,低温液相反应对主反应有利,高温气相反应选择性低,主要副产物为2,4己二烯醛.热力学分析与实验结果一致,乙醛缩合反应不宜采用高温气固相反应.因此实际生产中需对反应温度进行合理控制或对反应产物和原料及时分离,以提高反应转化率和选择性.

Abstract:

The standard enthalpies of formation,the standard Gibbs free energy of formation and the heat capacity of each compound in acetaldehyde condensation reaction system were calculated with the application of Yoneda group contribution method.Comparison of the calculated results with some literature values show that the calculation results are reliable.Then the reaction enthalpies,reaction Gibbs free energy changes and equilibrium constants of relevant reactions in this system from 278 K to 368 K in liquid phase and 600 K in vapor phase were calculated and analyzed.The results show that the temperature has important influence on the main reaction.Conducting the reactions in liquid phase at low temperature benefited the main reaction,while high temperature led to low conversion and selectivity.2,4hexadienoic aldehyde was the main by-product.The thermodynamic analysis agreed well with experimental results.Acetaldehyde condensation is not recommended to proceed at high temperature.To improve the conversion and selectivity of practical reaction,the temperature is proposed be controlled reasonably or the main product needs to be separated from the reactant in time.