Effect of the Operating Conditions in the Transformation of DME to olefins over a HZSM‑5 Zeolite Catalyst

The effect of the operating conditions (cofeeding methanol and water, temperature, space time, and feed concentration) on the reaction indices of the transformation of dimethyl ether (DME) to light olefins has been studied, using a HZSM-5 zeolite catalyst (SiO2/Al2O3 molar ratio of 280) agglomerated with boehmite and alumina. The experiments have been carried out in an isothermal fixed bed reactor under the following conditions: 300–400 °C, space time, 0.2–6 gcat h molC –1; feed, pure DME, and diluted in He (25–90% of DME); time on stream, 18 h. The studied reaction indices are DME conversion, yields, and selectivities of the individual olefins and byproduct fractions (C2C4 paraffins, C5 + aliphatic, and BTX aromatics) and the catalyst stability. The reaction scheme is similar to that of the methanol transformation, although the reaction advance and deactivation by coke are higher in the transformation of DME, due to mainly the lower water concentration in the reaction medium. The suitable conditions to reach an olefin yield above 45% in the transformation of pure DME are (i) 375 °C and space time of 3–4 gcat h molC –1, and (ii) 400 °C and 1–2 gcat h molC –1. The catalyst deactivation by coke is favored by increasing the DME concentration in the feed and is attenuated by the formation of water in the reaction medium (as a consequence of the increased temperature and/or space time).