Membrane Gas Separation Processes from Wet Postcombustion Flue Gases for Carbon Capture and Use: A Critical Reassessment

Membrane processes have been shown to offer interesting separation performances for postcombustion carbon capture and storage (CCS) from coal power plant flue gases. A 90% CO2 purity and recovery is typically required for that application. This set of constraints does not apply within a carbon capture and use (CCU) scenario, because the objective is to ensure carbon dioxide transformation at minimal cost. In this study, a dense polymeric glassy membrane (Matrimid) and a chemically reacting fixed site carrier membrane (FSCM) are investigated in order to achieve a partial carbon dioxide capture and concentration, which could be of interest in order to intensify the carbon dioxide transformation step. The importance of humidity in the carbon capture performance with solution-diffusion membranes is highlighted: flue gas compression significantly changes the inlet water content of the membrane module, and water decreases the membrane separation performances, increases the specific energy requirement, and decreases the membrane surface area because of an internal sweep effect. On the basis of a case study, the performance of a FSCM is shown to be close to the solution-diffusion membrane performance in terms of surface area and energy requirement. However, the FSCM offers two major advantages compared to the solutiondiffusion membrane: compatibility to wet flue gases and high CO2 purity. A FSCM single-stage module, operated with a 50% CO2 capture ratio, is suggested to offer the best trade-off for CCU applications with a high carbon dioxide purity (95%) and a low specific surface area and energy requirement.