二甲苯异构化反应机理研究及催化剂的改进

通过探针分子实验,验证了以Wheland中间体为核心的反应网络,对比了异构化/歧化反应路径的差别,分析了不同尺寸的芳烃在ZSM-5分子筛上的扩散-反应特征,建立了二甲苯异构化体系的反应过程模型。分子尺寸至少在一个方向上不超过苯环的烷基芳烃才能扩散进入孔道,对于贫对二甲苯(PX)的二甲苯原料,异构化反应主要在分子筛的外表面完成,产物PX进入孔道内,脱烷基生成甲苯等副产物。以此为理论基础,合成出晶粒尺寸更小、外表面更大的改进型分子筛,用于制备了SKI-210脱乙基型二甲苯异构化催化剂,取得了较好的工业应用效果。

STUDY ON XYLENE ISOMERIZATION MECHANISMS AND CATALYST IMPROVEMENT

By a series of probe molecule experiments, the aromatics reaction network was studied, the differences between the isomerization/disproportionation reaction path were compared，and the diffusion-reaction characteristics of aromatics with different sizes in ZSM-5 zeolite were analyzed. A model of xylene isomerization reaction was established. It is proves that only the aromatics with the size not larger than the benzene ring at least in one direction can diffuse into the ZSM-5 channel; the isomerization of lean PX feed occurs predominantly on the outside surface of the zeolite, the resulting PX diffuses into the channels, which then forms toluene through dealkylation. Based on this theory, a deethylation catalyst SKI-210 using the new molecular sieve with smaller size and larger surface was produced in industrial scale and applied in commercial units with good results.