Role of acidity and microporous structure in alternative catalysts for the transformation of methanol into olefins

The transformation of methanol into light olefins (C2-C4) has been studied on several acid catalysts prepared by agglomerating different microporous acid phases (SAPO-11, SAPO-18, SAPO-34 and beta-zeolites) with bentonite and inert alumina. SAPO-11s and beta-zeolites have been prepared under different conditions and, consequently, they have different porous structure, total acidity and site acid strength. An analysis is made of the influence of their properties (micropore diameter, total acidity, acid strength and site density on their surface) on the kinetic behaviour of the catalysts (initial conversion and selectivity to olefins and deactivation rate). The catalyst SAPO-18 has a lower deactivation rate than the SAPO-34 due to a slightly lower acid strength and to a lower density of strong acid sites on the surface. This behaviour and the lower preparation cost make SAPO-18 an interesting alternative to SAPO-34, which is the one used in industry in the MTO process.