芳构化法制2,5-二羟基对苯二甲酸热力学分析及反应特性研究

Thermodynamic analysis and reaction characteristics for synthesis of 2,5-dihydroxyterephthalic acid by aromatization

对由1,4-环己二酮-2,5-二甲酸二甲酯(DMSS)经芳构化法制备2,5-二羟基对苯二甲酸(DHTA)过程中涉及到的两步反应:DMSS与双氧水反应生成2,5-二羟基对苯二甲酸二甲酯(DMDHT)(反应Ⅰ)和DMDHT水解生成DHTA(反应Ⅱ)进行了热力学分析。采用Constantinou-Gani和Rozicka-Domalski基团贡献法计算了芳构化法合成DHTA过程中涉及到的主要化合物的热力学参数,并计算得到了两步反应的焓变、Gibbs自由能变以及平衡常数随温度的变化情况。结果表明,反应Ⅰ是放热反应,吉布斯自由能变均小于0且平衡常数非常大,该反应可以自发进行且反应完全;反应Ⅱ是吸热反应,吉布斯自由能变大于0且平衡常数较小,反应无法自发进行。基于热力学计算的结果,进一步考察了工艺参数对芳构化法合成DHTA反应特性的影响,得到了较优的工艺条件:反应Ⅰ温度为105℃,反应时间为55 min,H_(2)O_(2)滴加速率为18 mL/h;反应Ⅱ温度98℃,反应时间50 min。

Thermodynamic analysis was carried out on the two reactions involved in the preparation of 2,5-dihydroxyterephthalic acid(DHTA)from 1,4-cyclohexanedione-2,5-dimethyl dicarboxylate(DMSS)by aromatization,which are the reaction of DMSS with hydrogen peroxide to produce dimethyl 2,5-dihydroxyterephthalate(DMDHT)(reactionⅠ)and the hydrolysis of DMDHT to produce DHTA(reactionⅡ).The thermodynamic parameters of the main compounds involved in the two reactions were calculated by the Constantinou-Gani and Rozicka-Domalski group contribution methods,and thus the enthalpy changes,Gibbs free energy changes and equilibrium constants at various temperatures were calculated.The results show that reactionⅠis an exothermic reaction with the Gibbs free energy changes less than zero and very large equilibrium constants,suggesting that the reaction can proceed spontaneously and completely.ReactionⅡis an endothermic reaction with the Gibbs free energy changes greater than zero and small equilibrium constants,meaning that the reaction cannot proceed spontaneously.Moreover,the effects of process parameters on the reaction characteristics were investigated,and the optimal operating conditions were obtained:For reactionⅠ,the temperature and reaction time were 105℃ and 55 min,respectively,and the feeding rate of H_(2)O_(2) was 18 mL/h,while for reactionⅡ,the temperature and reaction time were 98℃ and 50 min,respectively.