MgO改性MCM-22分子筛催化苯与碳酸二乙酯的烷基化反应

Alkylation of Benzene with Diethyl Carbonate over MgO-Modified MCM-22 Molecular Sieves

以Mg(NO3)2为前体,在MCM-22分子筛上负载不同量的MgO,制备了MgO改性的MCM-22分子筛(MgO/MCM-22)催化剂;在固定床连续微反装置上,考察了MCM-22分子筛原粉和MgO/MCM-22催化剂对苯与碳酸二乙酯进行烷基化反应合成乙苯的催化性能;采用XRD、BET、NH3-TPD和吡啶吸附红外光谱等手段对催化剂进行了表征。实验结果表明,随MgO负载量的增加,苯的转化率逐渐降低,而乙苯的选择性逐渐升高。表征结果显示,随MgO负载量的增加,催化剂的酸强度减弱,酸量减少;催化剂的比表面积和孔体积也随MgO负载量的增加而减小,从而导致苯的转化率随MgO负载量的增加而逐渐降低;而减少的酸中心抑制了副反应的发生,因此乙苯的选择性随MgO负载量的增加而增大。适宜的MgO负载量(质量分数)为3%。

MgO-modified MCM-22 molecular sieves （MgO/MCM-22） catalysts with different MgO loadings were prepared through impregnation with Mg （NO3 ）2 as precursor. Alkylation of diethyl carbonate with benzene was studied over parent MCM-22 molecular sieves and the prepared MgO/ MCM-22 catalysts separately in a continuous flow fixed-bed reactor. The MCM-22 molecular sieves and the catalysts were characterized by means of XRD, BET, NH3-TPD and pyridine-IR. The alkylation results showed that with increasing of MgO loading, conversion of benzene reduced, while selectivity to ethylbenzene rose. The characterization results showed that with increasing of MgO loading, acid strengths of the catalysts weakened and their acid quantities reduced, and both specific surface areas and pore volumes of the catalysts also decreased. Therefore, conversion of benzene lowered with increasing of MgO loading. Less acid sites suppressed further alkylation of ethylbenzene, so selectivity to ethylbenzene increased. 3%（w） MgO loading was considered appropriate for the alkylation catalyst.