Temperature-dependent co-adsorption of H2O and CO2 by aminated porous solid adsorbers for direct air capture

In our hypothesis, dynamic aspects of the chemisorption of CO 2 and co-adsorption of H 2 O on aminated adsorbents are highly important when used in direct air capture (DAC) technologies. In DAC, a key challenge is to selectively capture CO 2 from ambient air at a concentration of 0.04 % CO 2 in the presence of competing gases. Two aminated porous adsorbents, namely porous poly(ionic liquid) networks (termed “Polymer 3.0”) and three aminated (mono-, di-, and triamine-functionalized) porous silica-based sorbents, were tested and compared with the commercially available CO 2 adsorbent Lewatit VP OC 1065. Both static and dynamic adsorption experiments were performed, in addition to textural and elemental analysis of the adsorbents. The CO 2 adsorption and co-adsorption of H 2 O, and their temperature-dependence were studied in detail by dynamic adsorption experiments. A strong correlation was identified between CO₂ adsorption and two key factors: the number of amino groups and the specific surface area of the adsorbents. The latter alone was not always sufficient for determination of the CO 2 adsorption capacities. A positive correlation between the adsorption of CO 2 and H 2 O was observed for all the sorbents, which is in turn related to either the specific surface area or the number of accessible amino groups. Our results show that in comparison to pure CO 2 , the co-adsorption of CO 2 and H 2 O increased the CO 2 uptake, and that the CO 2 capacity decreased at higher temperatures as expected from the exothermic nature of adsorption. Comparative results from static and dynamic adsorption analyses demonstrated that both static and dynamic adsorption analyses are important for the characterization and evaluation of CO 2 adsorbents.