Chemisorption of carbon dioxide on sodium oxide promoted alumina



New equilibrium and column dynamic data for chemisorption of carbon dioxide from inert nitrogen at 250, 350, and 450°C were measured on a sample of sodium oxide promoted alumina, which was found to be a reversible chemisorbent for CO2. The equilibrium chemisorption isotherms were Langmuirian in the low pressure region (pmath image <2.0 kPa) with a large gas–solid interaction parameter. The isotherms deviated from the Langmuirian behavior in the higher pressure region. A new analytical model which simultaneously accounted for Langmuirian chemisorption of CO2 on the adsorbent surface and additional reaction between the gaseous and sorbed CO2 molecules was used to describe the measured equilibrium data. The heats of CO2 chemisorption and the additional surface reaction were, respectively, 64.9 and 37.5 kJ/mol. The column breakthrough curves for CO2 sorption from inert N2 on the chemisorbent as well as the desorption of CO2 from the chemisorbent by N2 purge at 350°C could be described by the linear driving force (LDF) model in conjunction with the new sorption isotherm. The same LDF mass transfer coefficients can be used to describe both sorption and desorption processes. 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 small due to highly favorable CO2 sorption equilibrium. Several sequential cyclic CO2 sorption–desorption column dynamic tests were conducted to demonstrate the apparent stability of the material. © 2007 American Institute of Chemical Engineers AIChE J, 2007