Catalyst development for methanol and dimethyl ether production from blast furnace off gas

For Cu-ZnO-Al₂O₃ catalyst, compositional research was on two parameters, namely Cu/ZnO ratio (3/7∼5/5) and content of Al₂O₃ (0∼33.0 mol%). The influence of each parameter was estimated by DME and MeOH yields for the same catalyst mass. Some Cu-ZnO-Al₂O₃ catalysts synthesized DME more than MeOH, in which the DME activity was related to specific surface area and existence of broadened ZnO peaks in XRD patterns. In contrast, three other Cu-ZnO catalysts including another oxide (Cr₂O₃, ZrO₂ or Ga₂O₃) synthesized only MeOH without DME. Content of Al₂O₃ was more influential on DME synthesis than Cu/ZnO ratio. Physically-admixed (hybrid) catalysts of Cu-ZnO-Ga₂O₃ for CH₃OH synthesis and γ-Al₂O₃ for its dehydration were experimentally studied, in which the influence of mixing ratio of the two catalysts on both yield and selectivity of DME was mainly examined for the same catalyst mass. The results showed that the developed hybrid catalyst is very effective in producing DME directly from BFG without equilibrium limit of methanol. Interestingly, the yield of DME had a significant dependence of mixing ratio, and the hybrid catalyst with only 5 mass% γ-Al₂O₃ showed the highest yield with 99.3% selectivity of DME + methanol. This implies that methanol formation governs the rate of this series reaction (BFG→CH₃OH→DME) due to fast dehydration of methanol to DME. In conclusion, the most active composition of Cu-ZnO-Al₂O₃ catalyst for DME synthesis was Cu/ZnO=4/6 with 14.3mol% Al₂O₃. However catalysts mixture of Cu-ZnO-Ga₂O₃ (95%) and γ-Al₂O₃ (5%) showed higher activity.