乙酸镁改性ZSM-5分子筛上甲苯与碳酸二甲酯的择形烷基化  

Selective synthesis of p-xylene by alkylation of toluene with dimethyl carbonate over magnesium acetate-modified ZSM-5

作　　者：王永飞[1] 薛冰[1] 许杰[1] 李永昕[1] 

机构地区：[1]常州大学石油化工学院,江苏常州213164

出　　处：《化工进展》2011年第7期1498-1502,共5页Chemical Industry and Engineering Progress

基　　金：江苏省高技术研究项目(BG2006015);江苏省高校重大基础研究项目(06KJA5013)

摘　　要：以乙酸镁为前体,采用等体积浸渍法制备不同负载量的MgO/ZSM-5催化剂,在气相连续流动固定床反应器上对甲苯与碳酸二甲酯(DMC)择形烷基化合成对二甲苯进行了研究。采用XRD、NH3-TPD、吡啶吸附红外和2,4-二甲基喹啉吸附红外等手段对催化剂进行了表征。结果表明:B酸中心是甲苯与DMC烷基化反应的活性中心;随着MgO负载量的增加,甲苯转化率下降,对二甲苯的选择性上升;当MgO负载量大于9%时,甲苯转化率和对二甲苯选择性基本保持不变。2,4-二甲基喹啉吸附红外表征结果表明,乙酸镁在改性过程中未进入ZSM-5孔道内,焙烧分解生成的MgO主要分布在分子筛的外表面,分子筛孔内酸位并未受到影响。随着MgO负载量的增加,催化剂外表面的B酸位数量下降,当负载量大于9%时,外表面的B酸位基本消失。MgO-modified ZSM-5 was prepared by impregnation of ZSM-5 with an aqueous solution of magnesium nitrate.Selective synthesis of p-xylene by alkylation of toluene with dimethyl carbonate（DMC）was carried out in a continuous flow fixed-bed rector over MgO-modified ZSM-5 zeolite.Physico-chemical properties of MgO/ZSM-5 catalysts were characterized by means of XRD,NH3-TPD,2,4-dimethylquinoline-IR and pyridine-IR.The results of experiments indicated that alkylation of toluene with DMC occurred mainly on Br？nsted acid sites.With increasing MgO content,there was a decrease in toluene conversion and increase in selectivity for p-xylene.With further increase in MgO content from 9% to 12%,no significant change in toluene conversion and selectivity for p-xylene was observed.The results of FT-IR characterization with 2,4-dimethylquinoline adsorption indicated that the MgO was only dispersed over the external surface of ZSM-5 zeolite.With increasing MgO content,the amount of Br？nsted acid sites decreased.When the amount of MgO was 9%,Br？nsted acid sites on the external surface almost disappeared.

关 键 词：ZSM-5分子筛 MgO氧化镁 碳酸二甲酯 烷基化 对二甲苯 

分 类 号：TQ243.1[化学工程—有机化工]