烃类在HZSM－5和ZnHZSM－5上芳构化反应和动力学考察

研究了链烷烃、烯烃及环烷烃在ＨＺＳＭ－５和ＺｎＨＺＳＭ－５佛石催化剂上的转化反应特征，考察了ＺｎＨＺＳＭ－５沸石的改性Ｚｎ含量与ＺｎＯ对转化反应和产物分布的影响。结果表明，在低温条件下（＜４５０℃），链烷烃在ＺｎＨＺＳＭ－５沸石的直接脱氢芳构化活性中心上不易发生裂解，反应进行的第一步─表面正碳离子形成，其活性随Ｚｎ含量增加而降低。环烷烃在ＺｎＨＺＳＭ－５上转化动力学为非一级。在高温下，转化反应与芳构化活性则随Ｚｎ含量增加而提高，由于烯烃较活泼，在反应条件下首先产生部分热裂解，在ＺｎＨＺＳＭ－５上的芳构化反应为动力学一级。环己烷和甲基环己烷在ＺｎＨＺＳＭ－５上转化活性均低于ＨＺＳＭ－５上的转化活性，但它们在ＺｎＨＺＳＭ－５上直接脱氢芳构化生成相应本和甲苯。实验表明，环己烷和甲基环己烷在ＺｎＯ上于３５０～５５０℃范围内存在直接脱氢生成苯和甲苯的催化活性。作者利用脉冲反应技术测定不同反应物在ＺｎＨＺＳＭ－５沸石上转化和芳构化反应活化能，并探讨了烃类在ＺｎＨＺＳＭ－５上转化可能的反应历程。

Investigation on aromatization of hydrocarbons over HZSM-5 and ZnHZSM-5 and its kinetics

haracteristtics of conversion reaction of paraffins, olefins and cycloparaffins over HZSM-5 and ZnHZSM-5 zeolites have been studied and effects of the modified Zn contents and ZnO of ZnHZSM-5 on conversion reaction and product distribution have also been investigated.The results showed that under lower temperatures (below 450℃), it was not easy for paraffins to cleave on the active sites for direct dehydrogenation aromatization over ZnHZSM-5.In the first step of the reaction to form surface carbonium ions, its activity decreased with the increase of Zn content. The conversion of cycloparaffins over ZnHZSM-5 was non-first order on kinetics. Under higher temperatures, the activities for conversion and aronatization raised with the increase of Zn contern. As olefins were more active,the partial thermlal cracking took place first under reaction conditions. The aromatization of olefins over ZnHZSM-5 was the first order on kinetics.The activities for conversion of cyclohexane and methylcyclohexane over ZnHZSM-5 were lower than those over HZSM-5. However,their direct dehydrogenation over Zn-HZSM-5 yielded corresponding benzene and xylene. The experiment indicated that in the range of 350-550℃ ZnO possessed the catalytic activity for direct dehydrogenation of cyclohexane and methylcyclohexane to benzene and xylene.In the paper, the activation energies for conversion and aronatization of various reactants over ZnHZSM-5 are determinde by using pulse reaction technique and the possible reaction mechanism for conversion of hydrocarbons over ZnHZSM-5 are discussed.