AROMATIZATION OF ETHANE OVER GALLIUM-PROMOTED H-ZSM-5 CATALYSTS

Ethane was partly converted to aromatics over gallium-promoted H-ZSM-5 catalysts having different Si/Al ratios (15, 25, 34, 50, 75 and 95) and gallium contents ranging from 1.5 to 6 wt.-%. Temperatures varied between 823 and 973 K; the ethane partial pressure was 80 kPa. A maximum aromatics selectivity of 57% was obtained for a gallium (3.1 wt.-%) /ZSM 5 (Si/Al = 15) catalyst at 873 K (ethane conversion: 28.2%; W/F = 19.2 g h mol-1). The method of catalyst preparation (incipient wetness impregnation or ion exchange) had no influence on catalyst activity and selectivity. Kinetic measurements indicated that ethane is dehydrogenated by both Ga2O3 at the outside surface of the zeolite and by the acid centres of the H-ZSM-5 catalysts to ethylene; in a subsequent step the ethylene is oligomerized and cyclized in the channels of the zeolite. Aromatic hydrocarbons are formed after further dehydrogenation. Mainly benzene, toluene and xylenes were obtained.