Comparison of Single-Stage and Two-Stage CO₂ Hydrogenation for Methanol Synthesis Gain and Phase Margins

Abstract

A two-stage CO₂ hydrogenation reaction was conducted to increase methanol yield. At the first-stage, CO₂ was converted to CO by the reverse water-gas shift reaction with Cu/ZnO/Al₂O₃, Fe₂O₃/Cr₂O₃, or MoS₂/TiO₂ catalyst, and then at the second-stage, methanol was synthesized from the effluents of the first-stage with a commercial methanol synthesis catalyst, Cu/ZnO/Al₂O₃. In the case of the two-stage CO₂ hydrogenation reaction, CO that was produced by the first-stage reverse water-gas shift reaction contributed to the methanol synthesis, increasing the methanol yield. Especially, with the two-stage CO₂ hydrogenation reaction, methanol yield obtained was two or three times higher than that of the single-stage one. It was found that to increase the methanol yield in the two-stage hydrogenation reaction, more CO₂ should be converted to CO at the first-stage. The XRD patterns of the Cu/ZnO/Al₂O₃ catalyst before and after reaction showed the presence of metallic bulk Cu and the absence of other bulk Cu species.