3E analysis of a sub-ambient hybrid design for low-energy membrane CO2 capture

Climate change mitigation has intensified the development of efficient carbon capture technologies for industrial sources. A hybrid sub-ambient membrane-cryogenic process was investigated for post-combustion CO2 capture to minimize energy consumption and operating costs. The proposed configuration combined a counter-current polymeric membrane operated from −30 °C to 10 °C with a cryogenic distillation unit incorporating Joule-Thomson expansion for in situ cold generation, eliminating external refrigeration while enabling high-purity CO2 production. A key novelty is the explicit incorporation of temperature-dependent gas transport properties into the optimization framework, enabling rigorous quantification of the effect of sub-ambient operation on membrane performance. Process simulations were performed using Aspen Plus and Aspen Custom Modeler, and multi-objective optimization was conducted using the NSGA-III algorithm. Membrane properties were described by Arrhenius-type correlations accounting for the effects of temperature on permeability and selectivity. The optimization consistently identified the lowest investigated temperature as optimal, highlighting the enhancement of CO2/N2 selectivity under sub-ambient operation. At 95% CO2 recovery, specific electrical consumption decreased from approximately 914 kWh/tCO2 for flue gas containing 5.0 mol% CO2 to 305 kWh/tCO2 for flue gas containing 20.0 mol% CO2. Correspondingly, capture costs decreased from 270 to 70 €/tCO2 at an electricity price of 100 €/MWh. Overall, the results show that sub-ambient membrane systems coupled with cryogenic separation can provide a competitive and energy-efficient carbon capture solution, particularly for industrial flue gases containing more than 15 mol% CO2 and when powered by low-carbon or renewable electricity.