Two-stage membrane-based process utilizing highly CO₂-selective membranes for cost and energy efficient carbon capture from coal flue gas: A process simulation study

Membrane technology for CO₂ capture has become an attractive strategy due to its cost and energy efficiency and low materials costs. In the past decade, membrane-based process designs for post-combustion power plant CO₂ capture have been developed, utilizing existing highly CO₂-permeable membranes with relatively low CO₂/N₂ selectivity (<50), and have obtained reasonably economic carbon capture. However, few membrane-based process designs were proposed for moderate to highly CO₂-selective membranes (CO₂/N₂ selectivity of 50–300, and >300, respectively), which have vastly emerged in recent years, such as various facilitated transport membranes (FTMs). Herein, we proposed a two-stage membrane-base process design targeting economic carbon capture from coal-fired flue gas. This process design features the utilization of highly CO₂-selective membranes for one-stage CO₂ enrichment to 95% dry-base purity in the first stage and recycle of the remaining CO₂ by a highly CO₂-permeable membrane in the second stage, in order to achieve economic CO₂ capture with 90% capture rate and >95% CO₂ product purity. Through an integration-iteration membrane model and the Aspen Plus process simulation, a sensitivity study of operating pressures (feed and permeate pressures) and membrane properties (CO₂ permeance and CO₂/N₂ selectivity) was conducted. Critical CO₂/N₂ selectivity of 300–400 was found for the highly CO₂-selctive membranes to meet the demand for cost and energy efficient results. The lowest possible membrane area of 4.8 × 10⁵ m² and fractional energy of 19.3% were obtained, which is comparable to or even more attractive than reported membrane-based process designs. This work provides a new membrane process design option for highly CO₂-selective membranes and gives insights on the influence of membrane performance and operation condition.