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Alternative Source of Propylene

Synthesis gas derived from natural gas, coal, biomass or any other hydrocarbon source can be advantageously utilized to produce propylene. The approach adopted by the current investigation carries out the conversion of syngas in two stages: single-stage dimethyl ether (DME) synthesis followed by dimethyl ether conversion. Single-stage DME synthesis is carried out in the liquid phase utilizing the synergistic effect of dual catalysts, Cu/ZnO/Al 2 O 3 and γ-alumina. Dimethyl ether produced by this process is then converted to propylene using a shape-selective H-ZSM-5 catalyst. Very high selectivity towards propylene (as high as 68 wt%, the rest being ethylene and butenes) can be achieved by using this catalyst at appropriate reaction and feed conditions. In general, higher temperatures, low partial pressures of DME in the feed, and short contact times used over a H-ZSM-5 catalyst with low acidity increase the selectivity of DME conversion to propylene by inhibiting competing as well as successive reactions which would otherwise form other olefins, paraffins and aromatics. This article describes at length the second stage of the overall syngas-to-propylene process, focusing on the conversion of dimethyl ether to propylene over a wide range of reaction and feed conditions.