ZnZSM-5沸石上某些环烷烃芳构化性能的研究

用脉冲微反技术研究了环己烷、甲基环己烷和甲基环戊烷在ZnZSM-5和HZSM-5上反应的产物分布和动力学、发现在ZnZSM-5上, 环己烷和甲基环戊烷以高选择性转化成苯, 甲基环己烷以高选择性转变为甲苯; 在HZSM-5上它们反应的芳烃选择性均很低且都得到以甲苯为主的BTX混合物。证明了这些反应都为动力学一级反应,求出了370 ℃—450 ℃间反应的速度常数和活化能。还发现环己烷反应的苯选择性与催化剂中的Zn含量有一致的对应关系。提出了ZnZSM-5上环烷烃反应的过程图式, 认为芳构化过程的控制步骤是环状碳离子的形成, 反应中非预计芳烃组分的产生与中间体环状碳离子的低温烷基化和高温脱烷基以及裂解所产生的小分子的再芳构化有关。

STUDY ON THE AROMATIZATION OF SEVERAL CYCLOALKANES OVER ZnZSM-5

The product distribution and the rate constants of the transformation of cyclohexane, methylcyclohexane and methylcyclopentane over ZnZSM-5 and HZSM-5 have been studied by the pulse microreactor technigue. It is found that the aromatic distribution produced over these two catalysts are completely different. Over ZnZSM-5, the cyclohexane and methyleyclopentane are mainly converted to benzene, methylcyclohexane to toluene, showing a nearly complete dehydrogenation behavior, while the transformation of these cycloalkanes over HZSM-5 leads to yield a BTX mixture, indicating a typical consecutive reaction scheme, catalyzed by a monofunctional acid catalyst. These reactions are proved to be of the first order. Their apparent rate constants and activation energies were measured in the temperature range of 370~450 ℃.For the aromatization of the methylcyclopentane, the transformation appears to proceed by methylcyclopentane isomerization to cyclohexane, followed by dehydrogenation. The kinetic data shows that the first step, i.e. isomerization, is much faster than the cyclohexane dehydrogenation.The relative reaction rates over...