CONTINUOUS-FLOW TOLUENE METHYLATION OVER ALPO4 AND ALPO4-AL2O3 CATALYSTS

Toluene methylation with methanol over AlPO4 (AP) and AlPO4-Al2O3 (APA l) catalysts, obtained through different methods, was carried out in a continuous down-flow fixed bed reactor. The main products were xylene s (XYL), although trimethylbenzenes (TMB) were also found over APAl ca talysts. The benzene and ethylbenzene selectivities increased slightly with time on stream at the expense of XYL and TMB selectivities. Isom er distribution was approximately 50, 24 and 26 mol% for o-, m- and p- XYL, and 72, 27 and 0 mol% for 1,2,3-, 1,2,4- and 1,3,5-TMB. The initi al reaction rate constants were higher on APAl catalysts and, furtherm ore, APAl catalysts exhibited similar catalytic activities, although t hose obtained in ethylene or propylene oxide are the most active ones. The same occurs on AP catalysts. Moreover, the changes in catalytic a ctivity are similar to the changes in the acidic characteristics measu red, in gas phase, versus pyridine. Furthermore, the activity decrease d with time on stream due to coke deposition according to the expressi on k = k0 exp(-betat). The rate of deactivation, evaluated from the de activation coefficients (beta), was greater for APAl than for AP catal ysts.