Deactivation by coke of a catalyst based on a SAPO-34 in the transformation of methanol into olefins

When methanol is converted to olefins on a SAPO-34 catalyst between 350 and 425°C, there is a rapid initial formation of coke, followed by a slower rate of coke deposition. The rate of coke formation decreases with increasing temperature, and with progression through the catalyst bed. The coke completely blocks the internal channels of the SAPO-34 crystals and subsequently blocks the mesopores (intercrystalline and those of the bentonite). Coke deposition mainly blocks sites of acidic strength above 175 kJ mol−1. The presence of water in the feed lessens coke formation, either by converting Lewis to Brønsted sites or by competing for surface sites with coke precursors.