Methanol conversion over acid solid catalysts

A molecular sieve SAPO-34 with high density of strong acid sites was synthesized and its performance in methanol conversion was compared with the performances of ZSM-5, mordenite and beta commercial zeolites. Each catalyst was characterized by X-ray diffraction, X-ray fluorescence, textural analysis (BET method), and temperature programmed desorption of ammonia. The effects of temperature and time of reaction on methanol conversion were evaluated. Among the studied catalysts, SAPO-34 showed the highest initial selectivity to C2 and C3 compounds at 450 °C; however, it seems that the high density of strong acid sites of SAPO-34 resulted in an extremely fast deactivation of these sites, giving insignificant light olefins production after 1.5 h of reaction and turning the catalyst highly selective to dimethyl ether. Mordenite showed high selectivity towards C2 and C3 compounds at low temperatures, but underwent fast deactivation of its strong acid sites at high temperatures. ZSM-5 and beta zeolites were much more stable and also selective towards C2 and C3 compounds, proportionally to their densities of strong acid sites.