(152ab) Techno-Economic Analysis of Membrane-Adsorption Hybrid Process for Direct Air Capture

Direct air capture (DAC) technologies that extract CO₂ directly from ambient air could mitigate CO₂ emissions from non-stationary sources. However, the level of atmospheric CO₂ is only about 418 ppm, which imposes challenges for DAC if a high CO₂ purity is required. Recently, amine-containing polymeric membranes with exceptional CO₂/N₂ selectivity have been developed for CO₂ capture. Nevertheless, a high degree of air compression is needed to provide the transmembrane driving force, which makes the application prohibitive. Another approach for DAC is to employ solid sorbents with high CO₂ capacity, but the limited stability of the sorbent and the high regeneration energy usually lead to a high capture cost. In this work, we propose a membrane-adsorption hybrid process for DAC, where a less CO₂-selective yet robust physisorbent is used to enrich the CO₂ to 50%. This desorbed CO₂ is then further purified by a highly CO₂-selective membrane, where the higher feed CO₂ concentration relaxes the compression requirement. Next, techno-economic analyses of the hybrid process are carried out to evaluate the feasibility of the hybrid process for DAC. Owing to the enriched CO₂ feed gas, a single-stage membrane system with the CO₂ permeance of 1100 GPU (1 GPU = 10^–6 cm³(STP) cm^–2 s^–1 cmHg^–1) and the CO₂/N₂ selectivity of 100 was able to achieve the 95% CO₂ purity with 50% CO₂ recovery (overall process).