Direct air capture of CO2 by amine-impregnated resin: The effect of resin pore structure and humid conditions

Direct air capture (DAC) by solid amine adsorbents is a promising technology to curb the increasing atmospheric CO2 level. Despite extensive efforts, there are still limited improvements for this type of materials in their CO2 uptake and adsorption kinetics under ultra-dilute conditions. And most current research focuses on powdered adsorbents, which need to be granulated or fabricated into devices for DAC application, resulting in a further decline in CO2 uptake. Herein, a series of commercial resin particles (1.0 mm) were used as supports, and it was found that X5 exhibited favorable support characteristics in the preparation of solid amine adsorbents. Notably, X5 possessed a large pore volume of 1.90 cm3/g and featured a hierarchical bimodal porous network comprising mesopores and macropores. The prepared adsorbents (PEI@X5) had considerable polyethyleneimine (PEI) dispersion even at PEI content up to 50 %, and thus demonstrated excellent CO2 adsorption performances with high CO2 uptakes of 118 or 108 mg/g in TGA or fixed bed under simulated ambient air conditions (25 °C, 400 ppm CO2). Additionally, the adsorbents exhibited superb cyclic stability with no decay observed over 10 adsorption-regeneration cycles. The introduction of 25 % relative humidity (RH) of water vapor significantly improved the CO2 uptake of the adsorbent to 130 mg/g, with a lifting efficiency of 20.4 %. However, further increases in RH reduced the CO2 uptake and adsorption rate due to the excessive adsorption water, which leached part of PEI from the pores of 50 %PEI@X5. Considering the commercial production of raw materials, the facile synthesis of 50 %PEI@X5, and its superior CO2 capture efficiency, these findings open up new avenues for DAC technology.