(703e) Amine-Impregnated Al2O3 Materials for the Direct Air Capture of CO2 Under Sub-Ambient Conditions

Rising CO₂ emissions due to anthropogenic activities are largely responsible for increasing global temperatures leading to climate change. Capture of CO₂ from air (called direct air capture (DAC)) and its subsequent geological sequestration can be a potential solution to combat the devastating effects of climate change. While significant efforts have been made to develop materials to adsorb CO₂ from air, most of the studies have conducted experiments at ambient temperatures (25 °C) or higher under dry conditions. A significant portion of the natural environment where direct air capture plants can be deployed experience temperatures below 25 °C. In this study, we show the CO₂ adsorption behavior of amine impregnated alumina materials, which are leading materials for possible DAC deployment at warm temperatures, at sub-ambient temperatures.

CO₂ adsorption capacities at 25 ^oC and 400 ppm were highest for TEPA impregnated alumina samples (2.1 mmol/g), and moderate for PEI-alumina (0.9 mmol/g). The CO₂ capacities for both PEI-, and TEPA-alumina samples decreased at -20 ^oC (0.45 mmol/g, and 1.1 mmol/g, respectively). The loss of CO₂ uptake at low temperatures was primarily due to the freezing of the chains and their subsequent lower mobility that limits the diffusion of CO₂. TEPA impregnated alumina samples showed a promising working capacity of 0.8 mmol/g after 8 cycles of adsorption-desorption (adsorption at -20 ^oC and desorption conducted at 60 ^oC). For both PEI and TEPA samples, the CO₂ was strongly adsorbed at both 25 °C and -20 °C. Introducing moisture (70% RH at -20 °C) improved the CO₂ capacity of PEI impregnated alumina to ~0.8 mmol/g. Reducing the amine content from 40% to 20% decreased the CO₂ capacities at 25 °C as expected (0.6 mmol/g for PEI and 1.6 mmol/g for TEPA). While the CO₂ capacities at -20 °C decreased for both samples (0.43 mmol/g for PEI and 1.1 mmol/g for TEPA), these values are equal to those observed at -20 ^oC for the 40% amine samples, indicating that there is better amine utilization at slightly lower loadings due to better diffusion of CO₂ along the pores, which may arise due to greater volume available for CO₂ diffusion at low temperatures. These results indicate that alumina impregnated with amines are a potentially promising class of materials for direct air capture at sub-ambient conditions, opening up a variety of opportunities to optimize these materials for the scalable deployment of DAC plants at different environmental conditions.