分子筛改性对一步法合成二甲醚的影响

采用浸渍法制备了MgO、CaO、ZnO改性的HZSM 5分子筛，并以改性HZSM 5为脱水剂与JC207甲醇合成催化剂组成双功能催化剂，在固定床反应器上考察了其对一步法合成二甲醚影响。结果表明，适量碱性氧化物的引入，引起分子筛表面的B酸中心（强酸中心）向L酸中心（弱酸中心）转变，而弱酸和中强酸中心是甲醇脱水生成二甲醚的活性中心，强酸中心会造成二甲醚进一步脱水生成烃类副产品，所以改性后产物中二氧化碳和烃类的选择性下降，二甲醚选择性升高。这种趋势在CaO/HZSM 5脱水剂上表现的更为明显。

Effect of the modified zeolite on one-step dimethyl ether synthesis

The bifunctional catalysts for one step DME synthesis were prepared by mixing JC207 catalyst and HZSM 5 zeolites modified by MgO、CaO、ZnO,respectively. The evaluation of catalytic activity was conducted in a fixed bed reactor. Results show that Brostead acid site(strong acid sites) shifted to Lewis acid site (Weak acid sites) when the proper basic oxide was used to modify zeolite. Weak and less strong acid sites on the HZSM 5 zeolite were activitive sites for the formation of DME whereas strong acid sites for by products such as hydrocarbons. Consequently, the selectivity of CO2 and hydrocarbons decreased over modified HZSM 5 zeolite, especially over the zeolite modified by CaO.