碳酸二甲酯和碳酸二乙酯合成碳酸甲乙酯的热力学分析

为了得到碳酸二甲酯(DMC)和碳酸二乙酯(DEC)酯交换合成碳酸甲乙酯(EMC)反应的热力学数据,用Benson基团贡献法计算了相关物质的标准摩尔生成焓、吉布斯自由能和摩尔定压热容.计算了300～1 000 K温度范围内,该反应的焓变、自由能变、平衡常数和平衡转化率.结果表明:由DMC和DEC酯交换合成EMC的反应的自由能变在300～1 000 K范围内均为负值,因此是热力学上可自发进行的反应.随着温度的升高,反应的自由能变逐渐减小,因此高温有利于反应的进行.但即使在1 000 K时,反应的平衡常数也仅为33.20,这说明该反应自发进行的程度不高.

Thermodynamic Analysis for Synthesis of Ethyl Methyl Carbonate from Dimethyl Carbonate and Diethyl Carbonate

In order to obtain the thermodynamic data of the synthesis of ethyl methyl carbonate (EMC) from dimethyl carbonate (DMC) and diethyl carbonate (DEC), the standard molar enthalpies of formation, Gibbs free energy and molar heat capacity under constant pressure are calculated by the method of Benson group contributions. The enthalpy change, free energy change, equilibrium constant and equilibrium conversion rate of the reaction are calculated and discussed according to the principles of chemical thermodynamics under 300～1 000 K. The results show that the free energy change in the synthesis of EMC by transesterification of DMC with DEC is negative and the reaction is thermodynamically feasible. The free energy change decreases with the increase in the temperature, and higher temperature is in favor of the reaction. The equilibrium constant of the reaction is only 33.20 even at 1 000 K and the spontaneous degree of the reaction is low.