甲醛和异丁醛羟醛缩合反应体系热力学分析

Thermodynamic Analysis of Aldol Condensation of Formaldehyde and Isobutyraldehyde

摘要:

采用Joback和Yoneda基团贡献法及其他经验公式估算了甲醛(HCHO)和异丁醛（IBD）羟醛缩合体系中主产物2,2二甲基3羟基丙醛（HPA），副产物新戊二醇（NPG），2,2二甲基1,3丙二醇羟基特戊酸单酯（1115酯），异丁酸异丁酯等物质的生成焓、生成熵及摩尔定压热容等基础热力学数据，部分估算数据与文献值进行了对比，结果较为一致，说明估算方法可靠.计算了缩合体系中主、副反应在283~373 K反应焓变、熵变、摩尔吉布斯自由能变和平衡常数，结果表明，主、副反应均为放热反应，各反应均能自发进行，由于主反应放热量相对较少，低温对主反应有利，1115酯、新戊二醇、异丁酸异丁酯是体系的主要副产物.异丁醛的转化率随温度和n(IBD)∶n(HCHO)的升高而降低， n(IBD)∶n(HCHO)=0.90时IBD转化率达到99%.计算值与实验值接近，表明本文的分析方法可行，可为甲醛和异丁醛缩合反应合成HPA的工艺条件优化提供依据.

关键词:异丁醛; 甲醛; 羟醛缩合; 基团贡献法; 热力学

Abstract:

Thermodynamics of aldol condensation of formaldehyde and isobutyraldehyde (IBD) were studied. With the application of Joback and Yoneda (ABWY) group contribution methods and some other empirical formulas, the basic thermodynamic properties such as Hg,298, Sg,298, Cp of the main product of 2,2dimethyl3  hydroxypropionaldehyde (HPA), the byproducts of neopentylglycol (NPG), hydroxypivalaldehyde (1115 acetate), isobutyl isobutyrate and other substances were calculated. Then, the Hr,Gr, Kp of the main and side reactions were derived. The calculated thermodynamic properties agree well with available literature values, which means that the estimation is reliable. The calculated results show that the main and side reactions are exothermic and can happen spontaneously. Relative low temperature is good for the main reaction, because the absolute enthalpy of this main reaction is lower than that of the side reactions. NPG, 1115 ester, and isobutyl isobutyrate are the main byproducts. The conversion rate of IBD would decrease with the increase of temperature and n(IBD)∶n(HCHO). When the ratio of n(IBD) to n(HCHO) is 0.9, IBD conversion rate can reach 99%. The calculated conversion rates at different ratios of n(IBD) to n(HCHO) agree well with experimental data. The thermodynamic analysis would provide basis for the optimization of industrial HPA preparation.

Key words:isobutyraldehyde; formaldehyde; aldol condensation; group contribution method; thermodynamics