Taking action against the climate crisis is of vital importance to pursue a sustainable development. A crucial objective in this sense is the reduction of the CO2 emissions connected to the energy production and to the industrial sector. This work focuses on the capture of CO2 from the flue gas produced by power plants (XCO2 = 13.5%) and by cement and steel plants (XCO2 = 25%) via multi-stage membrane processes based on nanoporous single-layer graphene (NSLG) membranes. NSLG membranes have shown an exceptional CO2 permeance (i.e., 10000 GPU), combined with attractive CO2/N2 selectivity (i.e., 30). To assess the feasibility of using such membranes at the large scale in the next generation of sustainable plants, we performed techno-economic analyses of NSLG membrane-based capture process. In both cases, we found that using vacuum in the permeate of a double-stage process is the most suitable strategy to reduce capture penalty, since the energy consumption is lower than when feed is compressed and the membrane area is still limited thanks to the high membrane permeance. Optimizing the double-stage process configuration for carbon capture in power plants, we found a minimum capture penalty of 36.8 $/ton with permeate pressures of 0.05 and 0.1 bar in the first and in the second stage, with membrane module cost of 500 $/m2. The electricity cost is 0.05 $/kWh, assuming that the electricity produced by the power plant itself can be used for the capture process. The optimum permeate pressures come from tradeoffs between power consumption and membrane area and between different terms of power consumption. The capture from flue gas in cement and steel plants is favored by the higher CO2 concentration in the feed but the electricity cost is typically higher (0.1 – 0.2 $/kWh). The optimal permeate pressures vary with the cost of electricity, since a higher permeate pressure corresponds to a lower energy requirement but also to a larger membrane area. The minimum capture penalty ranges from 28 to 46 $/ton with optimal permeate pressures of 0.06 bar in the first stage and between 0.3 (with electricity cost of 0.1 $/kWh) and 0.4 bar (with electricity cost of 0.2 $/kWh) in the second stage. Overall, for both case studies, we found that NSLG membrane-based CO2 capture is competitive with the optimized polymeric membrane-based systems (capture penalty between 25 and 55 $/ton) and with the state-of-art absorption process (capture penalty between 50 and 110 $/ton).

Post-combustion carbon capture in power plants and cement plants via nanoporous single-layer graphene membranes: a techno-economic feasibility assessment

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