Understanding the Adsorption and Desorption Behavior of CO₂ on a K-Promoted Hydrotalcite-like Compound (HTlc) through Nonequilibrium Dynamic Isotherms

Abstract

A K-promoted hydrotalcite-like compound (HTlc) was synthesized and tested for its reversible CO2 capacity between 250 °C and 500 °C. Nonequilibrium dynamic adsorption and desorption isotherms were measured between 65 Torr and 980 Torr, using steps of 20 or 50 Torr and a 45-min duration between steps. The absolute CO2 capacity on K-promoted HTlc increased as the temperature decreased, with CO2 loadings of 2.25 and 1.02 mol/kg, respectively, at 250 and 500 °C and 980 Torr. The CO2 working capacity, which is defined as the change in CO2 loading between 65 Torr and 980 Torr, exhibited a maximum at 450 °C, with a value of 0.55 mol/kg, compared to values of 0.11 and 0.46 mol/kg, which were observed at 250 and 500 °C, respectively. It was surmised that three temperature-dependent, highly coupled, completely reversible, equilibrium-driven but kinetically limited, reactions were taking place, with the first one being a rapid and reversible chemisorption of CO2 that initiated and participated in the entire process.