酯交换制油酸甲酯的基团贡献法热力学分析

Thermodynamic analysis on preparation of methyl oleate via transesterification by group-contribution method

采用基团贡献法和赵氏经验公式(ΔSv=AslgTb+Bs)计算了三油酸甘油酯与甲醇之间发生的三步连续可逆酯交换反应的标准摩尔反应焓、标准摩尔熵、标准摩尔反应Gibbs函数和标准平衡常数,并分析了酯交换反应转化率的影响因素。结果表明,酯交换反应是放热反应,低温和高压有利于反应的进行。酯交换反应的转化率在甲醇液相时受温度和压力的影响较小,醇油比增大可以提高反应的转化率,当醇油比为20∶1时转化率达到98.8%。酯交换反应的转化率在甲醇气相时,随着压力的增大而增大,随着温度的增大而减小。通过计算结果与实验数据进行比较,表明本文提出的分析方法是可行的。

Biodiesel（FAME）is a biodegradable clean energy resource comprised of monoalkyl esters of long chain fatty acids that can be obtained from a wide variety of raw materials.The thermodynamics of transesterification reaction of triglyceride for production of biodiesel is evaluated using Gibbs energy method.The thermodynamic calculation for the three consecutive reversible transesterification reactions of triolein with methanol was carried out by means of group-contribution methods and Zhao＇s empirical formula,ΔSv○=AslgTb＋Bs.Factors affecting the conversion rate in transesterification of triolein and methanol are examined.From this analysis,it is concluded that the reaction enthalpy is-10.742 kJ·mol-1 at 298 K,showing a slightly exothermic reaction.The reactions occur more easily at lower temperatures and higher pressures.The conversion rate of triolein in liquid methanol changes little with temperature and pressure.Increase in molar ratio of methanol to triolein enhances the conversion of triolein.The equilibrium conversion of triolein reaches 98.8% at molar ratio of 20∶1,methanol to triolein.Increase in pressure of methanol vapor enhances the triolein conversion,while an increase in temperature of methanol vapor decreases the triolein conversion.Compared with experimental data in literature,the group-contribution analysis method is feasible.