Ainhoa Alonso

Development of Alternative Catalysts Based on HZSM-5 Zeolite for the BTO Process

The catalytic behaviour of a commercial HZSM-5 zeolite (Si/Al=30) for the selective transformation of bio-ethanol into olefins (BTO process) has been improved by two alternative methods: a) treatment with 0.2M alkali solution for a short time; and b) impregnation with Ni. By means of experimentation in an isothermal fixed bed reactor connected on-line to a GC for the analysis of the reaction products, it has been proven that moderate alkali treatment (10 min) slightly modifies the superficial structure and acidity of the HZSM-5 zeolite, which provokes a significant increase in the concentration of C2-C4 olefins, whereas deactivation rate and hydrothermal stability are similar. Moreover, 1 wt% nickel content in the catalyst is the optimum in order to obtain the better compromise concerning hydrothermal stability of the catalyst, coke deactivation, total yield of olefins and selectivity to C3-C4 olefins in the 400-500 °C range. In fact, the average production rate of C3-C4 olefins is twice as high as that of the parent zeolite in 8 h time on-stream experiments at 450 °C and 75wt% water content in the feed. Both methods are highly interesting because of the simplicity and reproducibility for obtaining economic and selective catalysts for the BTO process at moderate temperatures (catalysts modified by alkali treatment) and high temperatures (nickel based catalysts).