Direct synthesis of dimethyl ether from (H2+CO) and (H2+CO2) feeds.: Effect of feed composition

The effects of feed composition on the conversion of CO and CO2, selectivity to DME, yield of DME and product distribution are studied in the synthesis of DME from syngas and from (H2+CO2) in a single reaction step using the bifunctional catalysts CuO-ZnO-Al2O3/gamma-Al2O3 and CuO-ZnO-Al2O3/NaHZSM-5. For feeds made up of H2 and CO, the maximum conversion levels of CO, yield of DME and selectivity to DME obtained with both catalysts are very similar, close to 95 %, 75 % and 80 %, respectively, although the catalyst CuO-ZnO-Al2O3/gamma-Al2O3 requires a higher H2/CO ratio. For the feeds made up of H2 and CO2, the catalyst based on NaHZSM-5 zeolite (moderately acid function) performs better due to the fact that higher water content in the reaction medium leads to its adsorption on the Lewis acid sites of gamma-Al2O3 and limits the transformation capacity of methanol to DME.