MgO/HZSM-5上甲苯与碳酸二甲酯择形烷基化反应性能的研究

STUDIES ON SHAPE-SELECTIVITY OF ALKYLATION OF TOLUENE WITH DIMETHYL CARBONATE OVER MgO/HZSM-5 CATALYSTS

实验以MgO/HZSM-5为催化剂,在气相连续流动固定床反应器上进行甲苯与碳酸二甲酯(DMC)择形烷基化反应的研究。采用等体积浸渍法制备了一系列MgO/HZSM-5催化剂,并采用XRD、NH_3-TPD、吡啶吸附IR、N_2吸附-脱附等手段对催化剂进行表征。考察了MgO负载量及反应条件对催化性能的影响。结果表明,B酸中心是MgO/HZSM-5催化甲苯与DMC烷基化反应的主要活性中心;HZSM-5负载MgO后,导致甲苯的转化率下降,对二甲苯的选择性明显提高,这主要是由于负载MgO后催化剂的B酸中心数量减少。以9%MgO/HZSM-5为催化剂,在反应温度380℃,空速1h^(-1),n(甲苯):n(DMC)=4:1,对二甲苯选择性高达51.2%。

MgO/HZSM-5 catalysts prepared by an incipient wet impregnation method have been tested for the synthesis of p-xylene by alkylation of toluene with dimethyl carbonate （DMC） using a fix＊bed reactor. Several techniques such as XRD, N2 adsorption-desorption, NH3-TPD, pyridine-IR, etc were applied to characterize the structure and acidic properties of the catalysts. The characterization results showed that the alkylation of toluene with DMC occurred mainly on Bronsted acid sites. The effects of MgO loading amounts and reaction conditions on the catalytic performance have also been investigated. Catalytic tests indicated that, with the increase of the loading amounts of MgO, the conversion of toluene decreased while the selectivity to p-xylene increased dramatically. The best catalytic perform ance was obtained over the 9%MgO/HZSM-5 catalyst at 380℃ with a ratio of toluene to DMC of 4 ： 1, affording a remarkable β-xylene selectivity of 51.2%.