Kinetic Modeling of the Methanol-to-Olefins Process on a Silicoaluminophosphate (SAPO-18) Catalyst by Considering Deactivation and the Formation of Individual Olefins

A kinetic model for the formation of individual olefins (ethylene, propylene, and C 4+ olefins) from methanol over a SAPO-18 catalyst in a wide range of operating conditions has been proposed. The kinetic model takes into account three steps that evolve with time on stream: initiation period (where active intermediate compounds are formed), olefin production, and deactivation (by degradation of intermediate compounds to coke). This kinetic model predicts the experimental evolution of olefin production with time on stream, which initially increases, subsequently passes through a maximum (corresponding to the time on stream at which the maximum concentration of active intermediates is reached), and finally decreases (when deactivation by degeneration of intermediates to coke is faster than their formation). Different kinetic schemes for the formation of each individual olefin have been tested. Models that consider interconversion between olefins do not provide significant improvement over the model that quantifies formation of individual olefin only by direct reaction of oxygenates (methanol/DME) with intermediate compounds. The attenuating effect of water on each step of the kinetic scheme and on deactivation has been taken into account.