失水山梨醇油酸酯(Span 80)的合成热力学计算和分析

THERMODYNAMIC CALCULATION AND ANALYSIS FOR THE SYNTHESIS OF SORBITANOLEATE(SPAN 80)

以1,4-失水山梨醇和油酸连续酯化反应为模型,采用Benson基团贡献法、Myrdal-Krzyzaniak-Yalkowsky法、Marrero-Pardillo键贡献法和Somayajulu法估算了失水山梨醇油酸酯合成反应中相关物质的热力学参数,计算了各反应的标准摩尔反应焓、标准摩尔反应Gibbs自由能变和平衡常数。计算结果表明:在温度403.15～533.15 K内,单酯、双酯和三酯的生成反应均为吸热反应,升温有利于反应正向进行,标准摩尔反应Gibbs自由能变均小于0,说明反应为自发过程,反应能正向完全进行。基于以上数据计算了反应体系达到平衡时各个组分的浓度和质量分数,结果表明:随着温度升高,体系中单酯的浓度和质量分数稍有下降,而双酯和三酯无明显变化。利用高效液相色谱(HPLC)分析了平衡时各组分含量,实验结果表明:热力学计算的平均相对误差为4.05%,此方法可用于计算复杂反应体系的平衡组成。

The continuous esterification of 1, 4-sorbitan and oleic acid was taken as a model, the thermodynamic parameters of the related substances in the synthetic process were estimated based on Benson group contribution method, Myrdal-Krzyzaniak-Yalkowsky method, Marrero-Pardillo bond contribution method and Somayajulu method. The standard molar enthalpy, the Gibbs free energy change and the equilibrium constant of each reaction were calculated according to the principles of chemical thermodynamics at different temperatures. The results showed that the formation of monoester, diesterand triester were endothermic reactions as the temperature ranged from 403.15 K to 533.15 K, and the increase of temperature was beneficial for the reactions. Simultaneously, the Gibbs free energy change of all the reactions were less than zero, indicated that they were spontaneous processes, and the forward reactions could be carried out completely. The concentration and mass fraction of each component were discussed when the reaction system reached equilibrium based on the above data. The results indicated that as the temperature rised, the concentration and mass fraction of the monoester slightly decreased, that of the diesterand triester were no significant change. High performance liquid chromatography(HPLC) was used to analyze the content of each component in chemical equilibrium and the result showed that the average relative error of thermodynamic calculation was 4.05%. Therefore, this method can be used to calculate the equilibrium composition of complex reaction system.