Potassium incorporated alumina based CO2 capture sorbents: Comparison with supported amine sorbents under ultra-dilute capture conditions

Amines supported on silica or alumina supports are among the most well-studied sorbents for CO2 capture from ultra-dilute sources, such as ambient air. Another class of sorbents that may also bind CO2 strongly enough to function well under ultra-dilute conditions are supported alkali metal based compositions. In this work, the synthesis of alumina-supported potassium (AlK) via calcination of impregnated potassium acetate is described and the resulting materials are evaluated for CO2 capture under ultra-dilute conditions (1% CO2), including under simulated air capture conditions (400 ppm CO2). The sorbents are evaluated at different adsorption and regeneration temperatures alongside two benchmark alumina-supported amine sorbents. The potassium-alumina sorbents are found to adsorb more CO2 than the amine benchmark sorbent at the tested 1% CO2 conditions, whereas the amine sorbent yielded a higher uptake under simulated air capture conditions of 400 ppm. Abbreviated adsorption isotherms are measured for the potassium-alumina sorbents at three temperatures, the isotherms are fit to a single site Toth adsorption model, and the assembled data are utilized to estimate the heat of adsorption using the Clausius-Clapeyron equation. The isosteric heat of adsorption for the potassium based sorbent is higher than those estimated and measured for amine based sorbents, which is consistent with the higher regeneration temperature required by the potassium based sorbents. Potassium-alumina sorbents may be useful adsorbents for ultra-dilute conditions due to their stability in oxygen relative to amine sorbents if plentiful heat is available for the significant temperature swings needed to effectively cycle the sorbents. (C) 2015 Elsevier B.V. All rights reserved.