表面富硅型ZSM-5分子筛的甲醇制对二甲苯联产低碳烯烃催化性能

Catalytic performance of surface silicon-rich ZSM-5 zeolites in the co-production of lower olefins and p-xylene from methanol

  • 摘要: 通过表面化学改性制备表面富硅型ZSM-5分子筛,采用XRD、N2等温吸附-脱附、TEM、NH3-TPD和Py-FTIR等手段对其孔结构和酸性质进行了表征,考察其甲醇制对二甲苯联产低碳烯烃反应的催化性能。结果表明,引入Zn使催化剂中一部分强酸转变为中强酸,并增加了具有脱氢作用的Zn-L酸中心,提高乙烯和丙烯的选择性;Mg改性不仅可以调节孔道的择形性,而且增加了L酸中心的数量,有利于PX的生成;不同硅源的多次硅沉积使得SiO2可以更均匀地沉积在外表面,调变催化剂的酸性质和孔结构,从而进一步提高对二甲苯及乙烯和丙烯的选择性。最终,二甲苯中对位选择性可达到87.1%,二甲苯及乙烯和丙烯的选择性达到61%,乙烯在C2烃类的选择性高达97.8%,丙烯在C3烃类中选择性高达90.6%。

     

    Abstract: Surface silicon-rich ZSM-5 zeolites were prepared by surface chemical modification; their pore structure and acid properties were characterized by XRD, nitrogen sorption, TEM, NH3-TPD and Py-FTIR spectroscopy. The catalytic performance of modified ZSM-5 zeolites in the conversion of methanol to p-xylene and lower olefins was investigated. The results show that the introduction of Zn in ZSM-5 can change part of the strong acid sites into the medium ones and increase the Zn-Lewis acid sites with dehydrogenation capacity, which can enhance the selectivity to ethene and propene. The modification with Mg can not only adjust the pore shape selectivity, but also increase the amount of Lewis acid sites, which is beneficial to the formation of p-xylene. Through multiple silicon depositions from different silicon sources, SiO2 is uniformly deposited on the outer surface of modified ZSM-5 catalysts, which can modulate the acid properties and pore structure and thereby further improve the selectivity to p-xylene and ethene and propene. By using these modification approaches, the selectivity to p-xylene and ethene and propene reaches 61%, with 87.1% of p-xylene in the xylenes product, 97.8% of ethene in C2 hydrocarbons, and 90.6% of propene in C3 hydrocarbons.

     

/

返回文章
返回