几种分子筛转晶和混晶的控制及单一晶体的优化合成

Abstract

The influence of reaction temperature and reaction time on the crystallization of zeolites MCM-22, ZSM-5, ZSM-35 and mordenite was studied under the moderate ratio of silicon to aluminum using hexamethyleneimide as a template. MCM-22 was found to be an easily formed phase in this synthetic system because it appeared in the early stage of the crystallization process at both higher temperature and lower temperature. Whereas MCM-22 zeolite partially transformed to ZSM-5 and ZSM-35 with prolonging the reaction time at higher temperature, and finally transformed to ZSM-35. With this rule, the co-crystalline zeolite of MCM-22 and ZSM-35 was easily produced. The similar results of ZSM-5 and ZSM-35 mixed crystals could be achieved by varying reaction time at appropriate temperature. Upon analyzing the crystallization area of zeolites MCM-22, ZSM-5, ZSM-35 and mordenite, it is reasonable that the crystal transformations between these zeolites are prone to happen in this synthetic system, because all the zeolites have the same 5-ring sub-units, which bring little resistance to the reconstruction of frameworks, and the stability changing of the channel systems propels the occurrence of alternation of the linking modes of 5-ring units, leading to the formation of other type zeolites