络合浸渍氧化镁改性MCM-22催化甲苯烷基化反应的研究

以硝酸镁为前驱体,乙酰乙酸乙酯为络合剂,通过络合浸渍的方法制备不同负载量的MgO/MCM-22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)烷基化合成对二甲苯的过程进行了研究。采用X射线衍射、N2吸附-脱附、NH3程序升温脱附和吡啶吸附红外光谱等手段对催化剂进行了表征。结果表明,采用乙酰乙酸乙酯为络合剂,可以有效的覆盖分子筛外表面的酸性,避免其孔内酸性受到影响,催化剂能在保持较高甲苯转化率的同时显著提高对二甲苯选择性。在反应温度380℃、n(甲苯)∶n(DMC)=4∶1、空速1h-1条件下,当MgO负载量达到15%时,对二甲苯选择性和甲苯转化率分别为54.0%和34.3%。

STUDIES ON ALKYLATION OF TOLUENE OVER MGO MODIFIED MCM-22 PREPARED BY COMPLEXATION IMPREGNATION

A series of MgO/MCM-22 catalysts were prepared by a complexation-impregnation method with acetoacetate as complexing agent.Selective synthesis of p-xylene by alkylation of toluene with dimethyl carbonate(DMC) was carried out in a continuous flow fixed-bed reactor over MgO/MCM-22 catalysts.Several techniques such as X-ray diffraction,N2 adsorption-desorption,NH3-TPD and pyridine-IR were applied to characterize the structure and acidic properties of the catalysts.Results indicated that the acetoacetate as complexing agent can not only effectively cover the external surface acidic sites of zeolite,but also avoid the acid sites in the pores being affected.Therefore,high toluene conversion can be achieved along with an marked increase in the selectivity for p-xylene over the catalysts.Under the optimal conditions,i.e.reaction temperature of 380 ℃,n(toluene)∶n(DMC) of 4 and WHSV of 1 h-1,with 15% MgO,the selectivity to p-xylene and the conversion of toluene were 54.0% and 34.3%,respectively.