Hybrid membrane–absorption direct air capture of CO2

[Geoengineering News]

https://www.sciencedirect.com/science/article/abs/pii/S1383586626029515

Authors: Anshika, Raghavendra Ragipani

18 August 2026

https://doi.org/10.1016/j.seppur.2026.139685

Highlights

•A systematic design of hybrid DAC using Aspen Plus® and Aspen Custom Modeler®.

•Sensitivity analysis for membrane selection with permeability–selectivity trade-off.

•Three-stage membrane cascade with retentate recycling enriches atmospheric CO2 from 400 ppm up to 50 vol%.

•Techno-economic analysis presented for hybrid DAC, membrane DAC, and absorber DAC.

Abstract

Atmospheric carbon dioxide removal via direct air capture (DAC) has attracted significant interest, with several separation technologies aiming to remove CO2 from air. Existing DAC approaches include adsorption, absorption, and vacuum-driven membrane separation. Besides economic viability concerns, each standalone DAC technology faces multiple challenges. Hybrid DAC units that synergistically integrate multiple separation technologies could therefore make DAC more attractive. In this work, a hybrid membrane-absorber DAC was considered to address two key challenges: the high cost of membrane-DAC and the evaporative water losses of absorber-DAC. A multi-stage membrane cascade and a rate-based absorber were rigorously simulated and cost-optimized using Aspen Plus® and Aspen Custom Modeler®. Using Robeson’s upper bound membrane selectivity–permeability trade-off constraint, the optimal CO2 enrichment for a membrane preconcentrator at a pressure ratio of 55 was 0.86 vol%, using a membrane with moderate CO2-N2 selectivity of 40 and a permeance of 7314 GPU. Within the system boundaries considered, the levelized cost of membrane-DAC and absorber-DAC was estimated at $900 and $141/tCO2, respectively. As expected, hybrid membrane-absorber DAC, at an estimated cost of $667/tCO2, was cheaper than membrane-DAC. Furthermore, the hybrid DAC reduced evaporative water losses by as much as 99.4% relative to the absorber-DAC. Although hybrid DAC remained expensive compared with the targeted $100/tCO2, several opportunities for improvement and further development exist, including the use of ultrahigh permeance membranes beyond Robeson’s upper bound, heat recovery from membrane-cascade compressors, and CO2 recycling from the absorber gas outlet.

Source: ScienceDirect