Mathematical model of supercritical CO2 adsorption on activated carbon: Effect of operating conditions and adsorption scale-up

A general mathematical model for supercritical CO2 adsorption on activated carbon has been developed. Adsorption curves obtained with a laboratory plant (adsorber of 10 ml) have been fitted by with this model and the results have been extrapolated to adjust the breakthrough curves obtained with a pilot plant (adsorber of 1 l). Moreover a wide range of operating conditions has been covered, extraction pressures from 14.7 to 20.0 MPa, temperatures between 30 and 50 °C and CO2 flow-rates ranging between 0.12 and 0.36 kg/h. oposed model takes into account equilibrium (adsorption isotherm), diffusion in the solid (effective diffusion coefficient, De), mass-transfer from the bulk of the fluid phase to the surface of the solid (mass-transfer coefficient related to the supercritical solvent, kf), axial dispersion (effective dispersion coefficient, Daz) and a first order reversible adsorption/desorption reaction at the solid surface site (adsorption and desorption kinetic constants, ka and kd). er to get a suitable adjust, the experimental adsorption curves have been represented by this model by fitting the kinetic coefficients (ka, De and Daz) to the experimental curves, obtained from the laboratory installation. The parameters kf and kd are calculated, kf by well-known correlation and kd by the determination of adsorption isotherm. A fair good fitting of all the available experimental laboratory results has been obtained using De values ranging between 2.4 and 4.8×10−9 m2/s, Daz values of 1.2–3.2 m2/s and ka values of 1.4–1.5 m3/kg s. With these optimised parameters it is possible to model the adsorption curves obtained with the pilot plant with reasonable accuracy (standard deviation, 7–11%).