Experimental demonstration of an air contactor to capture CO2 from the atmosphere using Ca(OH)2 solid forms

This study demonstrates a proof-of-concept for a direct air capture system using a Ca(OH) 2 -based contactor. A laboratory-scale setup featuring air channels between 2 and 10 m in length was used, with airflow velocities ranging from 0.5 to 5 m/s. The carbonation reaction was evaluated on one wall of the channel, which was constructed using dry porous Ca(OH) 2 solid forms. The progression of CO₂ capture efficiency within the air channel, along with the extent of Ca(OH) 2 conversion to CaCO 3 in the solid phase, was assessed under various operating conditions and gas-solid contact configurations. Ca(OH)₂ layers approximately 3.5 mm thick, with porosities ranging from 0.45 to 0.55, reached carbonation conversions of 0.7 to 0.9 over a period of 8 to 10 days. Semi-continuous counter-current experiments achieved average CO 2 capture efficiencies between 40 % and 60 %, with capture rates at least 20 % greater than those observed in batch mode under similar conditions. Simplified kinetic and contactor models were developed to fit the CO 2 concentration profiles and depth of the carbonated layer in the solids, and were validated to support future scale-up efforts. • Proof-of-concept for a DAC system utilizing air channels lined with solid Ca(OH)₂. • CO₂ capture efficiencies of 40–60 % are achievable with air channel lengths of 5–8 m. • Counter-current air-solid contact reduces the contactor footprint by at least 20 %. • Experimental results align well with a plug flow model of the air contactor.