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

WANG Yongfei,XUE Bing,XU Jie,LI Yongxin   

  1. School of Petrochemical Technology,Changzhou University,Changzhou 213164,Jiangsu,China
  • Online:2011-07-05 Published:2011-07-05

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

王永飞,薛 冰,许 杰,李永昕   

  1. 常州大学石油化工学院,江苏 常州 213164

Abstract:

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 carbonateDMCwas 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 XRDNH3-TPD2,4-dimethylquinoline-IR and pyridine-IR.The results of experiments indicated that alkylation of toluene with DMC occurred mainly on Brønsted acid sites. With increasing MgO contentthere 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 contentthe amount of Brønsted acid sites decreased. When the amount of MgO was >9%Brønsted acid sites on the external surface almost disappeared.

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XRDNH3-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。

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