Influence of Precursors on the Induction Period and Transition Regime of Dimethyl Ether Conversion to Hydrocarbons over ZSM-5 Catalysts

Abstract

ZSM-5 catalysts were subjected to step response cycles of dimethyl ether (DME) at 300 °C in a temporal analysis of product (TAP) reactor. Propylene is the major olefin and displays an S-shaped profile. A 44 min induction period occurs before primary propylene formation and is reduced upon subsequent step response cycles. The S-shaped profile was interpreted according to induction, transition-regime, and steady-state stages to investigate hydrocarbon formation from DME. The influence of precursors (carbon monoxide, hydrogen, dimethoxymethane, and 1,5-hexadiene) was studied using a novel consecutive step response methodology in the TAP reactor. The addition of dimethoxymethane, carbon monoxide, hydrogen, or 1,5-hexadiene reduces the induction period of primary olefin formation. However, while dimethoxymethane, carbon monoxide, and hydrogen accelerate the transition regime toward hydrocarbon pool formation, 1,5-hexadiene attenuates it. Heavier hydrocarbons obtained from 1,5-hexadiene compete for active sites during secondary olefin formation. A phenomenological evaluation of multiple parameters is presented.