THE DIRECT SYNTHESIS OF DIMETHYL ETHER FROM SYNGAS OVER THE HYBRID CATALYST WITH ANTIMONY MODIFIED HZSM-5 ZEOLITE AS ACID COMPONENT

A series of HZSM-5 zeolites modified with various mass fractions of antimony oxide Sb2O3(0-30%) were prepared by solid state ion exchange method,and then physically mixed with an industrial methanol synthesis catalyst(XNC-98) to form a series of hybrid catalysts CuO-ZnO-Al2O3+Sb2O3/HZSM-5.The direct synthesis of dimethyl ether(DME) from syngas was carried out over the prepared hybrid catalysts under pressurized fixed-bed continuous flow conditions.The results indicated that over the CuO-ZnO-Al2O3+Sb2O3/HZSM-5 hybrid catalysts with suitable amount of Sb2O3 the selectivities of undesired byproducts hydrocarbons and CO2 were significantly decreased from 9.3% and 32.4% to less than 1% and 28%,respectively,and the selectivity for DME was enhanced greatly from 55% to 69% under temperature of 260℃,pressure of 4 MPa and gas hourly space velocity of 1500 ml/(g·h),compared with that over the unmodified HZSM-5 hybrid catalysts.It was clear from the results of NH3-TPD characterization that the decrease in the formation of hydrocarbons and CO2 could be attributed to the significant decline in the amount of strong acid sites induced by Sb2O3 modification.In addition,the influences of the operating parameters,including the reaction temperature,pressure and space velocity of feed on the catalytic performance of the hybrid catalysts were also investigated.It was shown that at high reaction temperature and high gas hourly space velocity both lower CO conversion and lower DME selectivity were obtained,the suitable reaction temperature and gas hourly space velocity would be less than 280℃ and 3000 ml/(g·h),respectively.