Methanol conversion on SAPO-34: reaction condition for fixed-bed reactor

Abstract

Reaction temperature and space velocity for methanol conversion to light olefins over SAPO-34 catalyst were experimentally studied in a bench-scale fixed-bed reactor. Temperature was found to be the strongest factor that affects product C 2 :C 3  ratio. Different C 2 :C 3  ratios can be obtained by adjusting reaction temperature or controlling the deactivation state of the catalyst. Higher temperature or partially deactivated catalyst produced higher C 2 :C 3  ratios. Over SAPO-34, when the feed was composed of 20 mol% methanol and 80 mol% water the optimum reaction temperature in terms of methanol conversion, selectivity to C 2 –C 4  and catalyst deactivation rate was approximately 400 °C. Higher temperatures led to faster catalyst deactivation due to coke formation and lower selectivities to propylene and butenes; while lower temperatures led to higher selectivities to CO+CO 2 and CH 4, lower methanol conversion, and faster catalyst deactivation due to oligomer blockage of SAPO-34 pores. For the above feed, the optimum methanol weight hourly space velocity in terms of methanol conversion, selectivity to C 2 –C 4  and catalyst deactivation rate, was in the range of 2.6–3.6 h −1. Lower methanol space velocities led to lower selectivity to C 2 –C 4  and faster catalyst deactivation; while higher methanol space velocities led to lower methanol conversion. At the optimum reaction condition, approximately 20 g of methanol can be processed on 1 g of the catalyst with C 2 –C 4  selectivity of about 90% before methanol conversion drops below 100%. By-products, CO, CO 2, and CH 4, were produced from the decomposition of methanol and DME. This decomposition could be catalyzed on basic sites on SAPO-34. The formation of the by-products depends on the competition between the basic sites (on which methanol and DME decompose to carbon oxides and methane) and acidic sites (on which methanol and DME convert into hydrocarbons).