Catalytic conversion of ethanol over ZSM-11 based catalysts

Abstract

The catalytic performance of ZSM-11 zeolites was studied in ethanol conversion to produce light olefins and BTX. Compared to HZSM-5 with same SiO2/Al2O3 ratio, it was found that HZSM-11 possesses significant advantages, resulting in higher stability and lower selectivity to light paraffins. The superior catalytic performance was attributed to the larger size of the intersections and the milder acid strength. Higher SiO2/Al2O3 ratio of HZSM-11 led to lighter and more olefinic products, with less formation of aromatics. Higher (para+meta)/ortho-xylenes ratios were obtained over HZSM-11 with higher SiO2/Al2O3 ratio, while the ratio of toluene/xylenes decreased. The yield of trimethylbenzenes (TMBs) was slightly enhanced over HZSM-11 catalysts with weaker acidity and well correlated with catalyst deactivation. Weak acidity led to faster deactivation and selectivity decay, and the growth of coke precursors inside the intersections was suggested as the main deactivation mechanism. A significant change of the hydrocarbon distribution can be obtained by modifying HZSM-11 with Fe and Ga oxides. Fe doping resulted in an increased selectivity to light olefins and C4+ hydrocarbons; while Ga modification of HZSM-11 showed slightly higher selectivity toward aromatics. The stability of HZSM-11 can be significantly improved by Ga doping.