Enhancing methanol synthesis from CO2: A comparison of interstage product separation via condensation and membranes

Interstage product separation is a practical strategy to address challenges related to the equilibrium limitation in CO 2 -based methanol synthesis. While many studies assess intensification strategies at the reactor level, this work examines the process-wide implications of interstage condensation and membrane separation units in comparison to the performance of a single-stage condensation reference. Interstage condensation increases carbon efficiency by 3 to 12 percentage points over the reference without increasing power demand. Gains are most pronounced for the first additional stage at low pressures and diminish with both increasing stages and pressure. The required cooling and reheating before and after the condensation steps increases total heat transfer demand by 13 to 83 % over the single-stage reference, concentrated close to the reaction stages. Membrane-based interstage separation operates at elevated temperatures compatible with low-cost polymer membranes, avoiding this thermal burden near the reaction stages. Under more aggressive separation conditions, carbon efficiency can exceed the condensation process (e.g. 98.9% vs. 98.5% at 80 bar process pressure and three stages), but sweep handling increases total heat duty ( + 38 % ) and compressor power demand ( + 11 % ). Under milder separation conditions, compressor power demand approaches the condensation case ( + 2 % ) and total heat duty is reduced ( − 8 % ), but carbon efficiency drops to 98.3%. Interstage condensation emerges as the more robust and conceptually simpler option, although its operational advantages over the single-stage reference must be weighed against additional investment and equipment-related complexity.