粗蓖麻油合成生物柴油反应热力学分析

目的]研究粗蓖麻油(含水、游离脂肪酸)与甲醇为原料的生物柴油合成体系的反应热力学特性。方法]采用Yoneda基团贡献法和其他经验公式计算了组成蓖麻油的5种脂肪酸甘油三酸酯(TG)、甘油二酸酯(DG)、甘油单酸酯(MG)、脂肪酸甲酯(ME)及游离脂肪酸(FFA)的焓、熵及热容等基础热力学数据;对生物柴油合成体系,反应涉及酯交换、酯化及水解共3类7个反应进行了热力学分析。结果]蓖麻油与甲醇的第1步和第3步酯交换反应的吉布斯自由能变化(△rG0)均小于0,第二步酯交换反应的△rG0大于0,游离脂肪酸与甲醇的酯化反应的△rG0小于0,蓖麻油与水的3步水解反应的△rG0均大于0。结论]蓖麻油中游离脂肪酸的存在比水的存在对蓖麻油的酯交换反应影响更大。

Thermodynamic Analysis of Biodiesel Synthesis from Rude Castor Oil

Obiective]The thermodynamics characters of biodiesel synthesis from rude castor oil(with water and free fatty acid) and methanol were studied.Method]Yoneda group contribution method and other empirical formulas were applied to calculate the enthalpy,entropy and heat capacity of triglycerides(TG),diacylglycerol(DG),monoglyceride(MG),methyl(ME) and free fatty acids(FFA) of five fatty acids in the system.The thermodynamic analysis of biodiesel synthesis system which involves transesterification,esterification and hydrolysis reaction was carried out.Result]The calculated results showed,Gibbs free energy change(△rG0) in the first and the third steps of transesterification were all less than zero,△rG0 of the second step of transesterification was greater than zero.△rG0 of the esterification(FFA and methanol) was less than zero △rG0 of the three steps of hydrolysis were greater than zero.Conclusion] The presence of FFA had more influence on the transesterification than the presence of water.