Equilibrium and Kinetic Behaviour of CO2 Adsorption onto Zeolites, Carbon Molecular Sieve and Activated Carbons

This study was carried out to characterize CO2 adsorption equilibrium and kinetics of commercial adsorbents that have potential for use in the pressure swing adsorption (PSA) process and also to provide a better understanding of CO2 adsorption behaviour under wide ranges of operating conditions. A comprehensive set of data and the analysis for CO2 adsorption equilibrium and kinetics are presented for six commercial adsorbents, i.e. zeolite 13x, zeolite 5A, zeolite 4A, carbon molecular sieve (MSC-3R), and activated carbons (GCA-830 and GCA-1240). The adsorption equilibrium and the kinetic data were taken at a temperature range of 293-333 K and pressure up to 35 atm. The CO2 adsorption isotherm was found to follow typical a type-I isotherm classification according to IUPAC, representing a monolayer adsorption mechanism. Among the six commercial adsorbents tested, activated carbon GCA-1240 offered the highest adsorption capacity, and zeolite 4A provided the lowest capacity. The obtained isotherm data were correlated as a function of temperature and pressure to fit with different model equations (i.e. Langmuir, Toth, Sips, and Prausnitz). The Sips model showed the best fit with the equilibrium data for zeolite 13X, zeolte 5A, zeolite 4A, and carbon molecular sieve (MSC-3R) while the Prausnitz model provided an excellent fit with the data for activated carbons (GCA-830 and GCA-1240). The isosteric heat of CO2 adsorption was also estimated for individual adsorbents according to the Clausius-Clapeyron equation. The CO2 adsorption kinetic, presented in terms of mass transfer coefficients (k), were analyzed from the plots of CO2 uptake rate using the well-recognized linear driving force (LDF) model. The k values were correlated by non-linear regression to reveal effects of adsorption temperature and pressure. Activation energies of CO2 adsorption on the individual adsorbents were also calculated and correlated according to the Arrhenius equation.