LIGHT ALKENES FROM SYNGAS VIA DIMETHYL ETHER

A new route, named the SDTO method, for the synthesis of light alkenes from syngas is proposed. The method consists of the conversion of syngas to dimethyl ether, followed by the conversion of dimethyl ether to light alkenes. Catalysts for the two reactions have been developed. For the first reaction, the catalyst was synthesized by combining a methanol synthesis catalyst with gamma-Al2O3 or zeolites, which possess both metallic and acidic functions. The conversion of the reaction is much higher than that of the methanol synthesis reaction. Suitable reaction conditions are: 210-280 degrees C; P>3.0 MPa and gas hourly space velocity (GHSV) <1500 h(-1). The catalyst for the second reaction was a modified SAPO-34 molecular sieve. The effects of the modification on the catalyst and the factors influencing the reaction have been investigated. A fluid bed reactor is considered to be a suitable reactor type for these catalysts. Under the reaction conditions of 550 degrees C and weight hourly space velocity (WHSV MeOH) >6 h(-1) or line velocity of MeOH>15, the selectivity for ethylene and total light alkenes are ca. 60 and ca. 90, respectively (conversion = 100%). The stability of the modified SAPO-34 catalyst has been tested under severe conditions. The results from the serial connection of the two conversion steps without any separation show that the yield of C-2(=)-C-4(=) alkenes could be >100 g/(m(3) syngas).