Chemisorption of carbon dioxide on potassium-carbonate-promoted hydrotalcite

Abstract

New equilibrium and column dynamic data for chemisorption of carbon dioxide from inert nitrogen at 400 and 520 °C were measured on a sample of potassium-carbonate-promoted hydrotalcite, which was a reversible chemisorbent for CO 2. The equilibrium chemisorption isotherms were Langmuirian in the low-pressure region ( p CO 2 < 0.2 atm ) with a large gas–solid interaction parameter. The isotherms deviated from Langmuirian behavior in the higher pressure region. A new analytical model that simultaneously accounted for Langmuirian chemisorption of CO 2 on the adsorbent surface and additional reaction between the gaseous and sorbed CO 2 molecules was proposed to describe the measured equilibrium data. The model was also capable of describing the unique loading dependence of the isosteric heat of chemisorption of CO 2 reported in the literature. The column breakthrough curves for CO 2 sorption from inert N 2 on the chemisorbent could be described by the linear driving force (LDF) model in conjunction with the new sorption isotherm. The CO 2 mass-transfer coefficients were (i) independent of feed gas CO 2 concentration in the range of the data at a given temperature and (ii) a weak function of temperature. The ratio of the mass-transfer zone length to the column length was very low due to highly favorable CO 2 sorption equilibrium.