晶化温度对ZSM-5铝分布的影响及其在苯-稀乙烯烷基化中的应用

Effect of Crystallization Temperature on Aluminum Distribution in ZSM-5 and Its Application in Alkylation of Benzene With Diluted Ethylene

采用晶种导向的方法,在不同晶化温度(80~170℃)下水热合成了b轴厚度为50 nm的ZSM-5分子筛;采用XRD、SEM、NH_(3)-TPD、Py-IR、XPS、ICP-AES、^(27)Al MAS NMR和UV-vis-DRS等手段对ZSM-5分子筛进行表征,研究了晶化温度对ZSM-5分子筛晶体生长和铝分布的影响,并考察了不同晶化温度制备的ZSM-5分子筛催化剂在苯-稀乙烯烷基化反应中的催化性能。结果表明:晶化温度改变了ZSM-5分子筛的铝分布,从而影响分子筛的酸性质和烷基化反应性能;低晶化温度80℃下制备的ZSM-5分子筛具有酸性弱,总酸量少、Lewis酸以及外表面酸中心少,骨架铝(Al_(F))主要分布在直孔道和交叉孔道处;在反应温度360℃、压力1.4 MPa、苯/稀乙烯摩尔比1、稀乙烯质量空速1.5 h^(-1)、反应时间35 h的条件下,H-ZSM-5-80分子筛催化苯-稀乙烯烷基化反应,乙基选择性最高为95.4%,副产物二甲苯选择性最低为0.09%。

ZSM-5 molecular sieve with b-axis thickness of 50 nm was synthesized by seed crystal orientation method at different crystallization temperatures(80—170℃),and the ZSM-5 zeolite was characterized by XRD,SEM,NH_(3)-TPD,Py-IR,XPS,ICP-AES,^(27)Al MAS NMR and UV-vis-DRS.The effects of crystallization temperature on the crystal growth and aluminum distribution of ZSM-5 zeolite are researched,and the catalytic performances of ZSM-5 zeolite catalysts prepared at different crystallization temperatures in the alkylation of benzene with dilute ethylene are investigates.The results show that the crystallization temperature has changed the aluminum distribution of ZSM-5 zeolite,thus affecting its acidity and alkylation reaction performance.The ZSM-5 zeolite prepared at a low crystallization temperature of 80℃has the characteristics of weak acidity,less total acid amount,less Lewis-acid and less surface acid centers,and framework aluminum(Al_(F))is mainly distributed in straight and cross channels.At the reaction temperature of 360℃,pressure of 1.4 MPa,molar ratio of benzene to dilute ethylene of 1,mass space velocity of dilute ethylene of 1.5 h^(-1),and reaction time of 35 h,the alkylation of benzene with dilute ethylene was catalyzed by H-ZSM-5-80 molecular sieve.The highest ethyl selectivity was 95.4%,and the minimum selectivity for by-product xylene was 0.09%.