High-pressure carbon dioxide adsorption kinetics of potassium-modified hydrotalcite at elevated temperature

A method for characterizing the high-pressure CO2 adsorption kinetics of potassium-modified hydrotalcite at elevated temperatures based on a modified static bed is proposed. The pressure drop of the adsorption tube with time was measured by a series of high-sensitivity pressure sensors to calculate the CO2 adsorption curves of the adsorbent. The concept of a hot/cold spot is introduced to eliminate the temperature deviation caused by the dead volume of the pipelines and the temperature disproportion in the tubes. As compared to conventional characterization methods such as thermal gravimetric analysis and fixed bed testing, the proposed method avoids the displacement effect, making it possible to obtain actual adsorption curves above atmospheric pressure. The effect of adsorption temperature (300-450 °C) and CO2 partial pressure (0.1-2 MPa) and a reversible adsorption isotherm with 30 min adsorption/30 min desorption, as well as desorption performance under vacuum, were investigated. The adsorption/desorption curves of hydrotalcite increased linearly with the logarithm of the adsorption time in almost all tested conditions. The CO2 uptake reached approximately 0.7 of the total adsorption capacity in less than 0.1 min of adsorption time and exceeded 0.9 after 5 min. A simple one-step kinetic model based on Elovich-type equations is built to describe the adsorption behavior of hydrotalcite at CO2 partial pressures above atmospheric pressure.