Chemisorption of carbon dioxide on potassium-carbonate-promoted hydrotalcite

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 CO2. The equilibrium chemisorption isotherms were Langmuirian in the low-pressure region (pCO2<0.2 atm)(pCO2<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 CO2 on the adsorbent surface and additional reaction between the gaseous and sorbed CO2 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 CO2 reported in the literature. The column breakthrough curves for CO2 sorption from inert N2 on the chemisorbent could be described by the linear driving force (LDF) model in conjunction with the new sorption isotherm. The CO2 mass-transfer coefficients were (i) independent of feed gas CO2 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 CO2 sorption equilibrium.

The chemisorption isotherm of CO2 on K2CO3-promoted hydrotalcite at 400 °C can be described by the Langmuir model only in the low-pressure region. A novel chemisorption–surface reaction model is developed to describe the isotherm in the high-pressure region.Figure optionsDownload as PowerPoint slide