Work

Water-induced CO2 roll-up and regeneration complexity in zeolite 13× during humid direct air capture: Breakthrough, ex situ FTIR, and reduced-order modeling

Year: 2026

Type: article

Abstract: Commercial zeolite 13× is a benchmark hydrophilic FAU adsorbent with high dry-CO 2 capacity, but its application in humid direct air capture (DAC) is strongly limited by water competition. Here, 13× is used not as a new sorbent candidate, but as a model material to link bed-scale breakthrough, ex situ FTIR signatures, regeneration behavior, and reduced-order modeling during humid-air exposure. N 2 physisorption, mercury porosimetry, XRD, and FTIR confirmed a predominantly microporous FAU-type zeolite with a BET surface area of 710.1 m 2 ·g −1 and a micropore volume of 0.253 cm 3 ·g −1 . Under humid DAC conditions, the bed initially retained CO 2 , but the CO 2 breakthrough curve subsequently exhibited roll-up above unity, evidencing displacement of previously adsorbed CO₂ by the advancing water front. The maximum transient CO 2 uptake was only 0.0909 mmol·g −1 , whereas the final H₂O loading reached 13.38 mmol·g −1 and accounted for 96.4% of the measured bed mass increase. Staged ex situ FTIR supported this interpretation by showing early growth and later collapse of the molecular CO 2 band, together with progressive strengthening of H 2 O and carbonate−/bicarbonate-like regions. Dry pure- CO 2 adsorption was used as an upper-bound reference for intrinsic CO 2 affinity. Under this dry condition, the retained CO 2 loading reached 3.19 mmol·g −1 and breakthrough was monotonic, confirming that poor humid-DAC performance arises from competitive water adsorption. Thermal regeneration and reduced-order modeling further supported a water-driven CO 2 displacement mechanism, highlighting the need for humidity management, regeneration control, or sorbent modification in practical DAC processes.

Source: Chemical Engineering Journal

DOI: 10.1016/j.cej.2026.178718