Direct Air Capture of CO2 Using Amine/Alumina Sorbents at Cold Temperature

Rising CO2 emissions are responsible for increasingglobal temperatures causing climate change. Significant efforts areunderway to develop amine-based sorbents to directly capture CO2 from air (called direct air capture (DAC)) to combat theeffects of climate change. However, the sorbents' performanceshave usually been evaluated at ambient temperatures (25 & DEG;C) orhigher, most often under dry conditions. A significant portion ofthe natural environment where DAC plants can be deployed experiencestemperatures below 25 & DEG;C, and ambient air always contains somehumidity. In this study, we assess the CO2 adsorption behaviorof amine (poly(ethyleneimine) (PEI) and tetraethylenepentamine (TEPA))impregnated into porous alumina at ambient (25 & DEG;C) and cold temperatures(-20 & DEG;C) under dry and humid conditions. CO2 adsorption capacities at 25 & DEG;C and 400 ppm CO2 arehighest for 40 wt% TEPA-incorporated & gamma;-Al2O3 samples (1.8 mmol CO2/g sorbent), while 40 wt % PEI-impregnated & gamma;-Al2O3 samples exhibit moderate uptakes(0.9 mmol g(-1)). CO2 capacities for bothPEI- and TEPA-incorporated & gamma;-Al2O3 samplesdecrease with decreasing amine content and temperatures. The 40 and20 wt % TEPA sorbents show the best performance at -20 & DEG;Cunder dry conditions (1.6 and 1.1 mmol g(-1), respectively).Both the TEPA samples also exhibit stable and high working capacities(0.9 and 1.2 mmol g(-1)) across 10 cycles of adsorption-desorption(adsorption at -20 & DEG;C and desorption conducted at 60 & DEG;C).Introducing moisture (70% RH at -20 and 25 & DEG;C) improvesthe CO2 capacity of the amine-impregnated sorbents at bothtemperatures. The 40 wt% PEI, 40 wt % TEPA, and 20 wt% TEPA samplesshow good CO2 uptakes at both temperatures. The resultspresented here indicate that & gamma;-Al2O3 impregnatedwith PEI and TEPA are potential materials for DAC at ambient and coldconditions, with further opportunities to optimize these materialsfor the scalable deployment of DAC plants at different environmentalconditions.