Understanding the performance of membrane for direct air capture of CO2

Direct air capture (DAC) of CO₂ is becoming increasingly important for reducing greenhouse gas concentrations in the atmosphere. However, the cost and energy requirements associated with DAC make it less economically feasible than carbon capture from flue gases. While various methods like solid sorbents and gas–liquid absorption have been explored for DAC, membrane processes have only recently been investigated. The objective of this study is to examine the separation performance of a membrane unit for capturing CO₂ from ambient air. The performance of a membrane depends on several factors, including the composition of the feed gas, pressure ratio, material selectivity, and membrane area. The single-stage separation process with the co-current flow and constant permeability flux model is evaluated using a commercial module integrated with a process simulator to separate a binary mixture of carbon dioxide and nitrogen to assess the sensitivity of selectivity on purity and recovery of CO₂ in permeate, and power requirement. Additionally, three levels of CO₂ reduction from the feed stream to the retentate stream (25%, 50%, and 75%) are studied. A trade-off between purity and recovery factor is observed, and achieving high purity in permeate requires high concentration in the retentate.