Equilibrium and kinetics of CO2 adsorption onto activated carbon

Knowledge of adsorption characteristics of adsorbent-adsorbate pairs is essential for designing adsorption beds for adsorption cooling and adsorptive gas capturing applications. We investigated the adsorption isotherms and the adsorption kinetics of CO2 onto microporous activated carbon powder of type Maxsorb III. Measurements were performed with gravimetric apparatus for temperatures from 30 to 70 °C and pressures up to 7 MPa for adsorption isotherms and up to 4 MPa for adsorption kinetics. The gravimetric adsorption data obtained were consistent with previously measured isotherms with volumetric apparatus. Both absolute and excess adsorption data have been fitted precisely with Tóth and Dubinin-Astakhov isotherm equations. The classical linear driving force (LDF) model with a constant mass transfer coefficient failed to correlate the experimental adsorption kinetics data. To overcome this problem, the authors presented a modified LDF equation with a variable mass transfer coefficient which is a function of the equilibrium and instantaneous uptakes. This modified LDF equation led to a better fitting and could be implemented easily in simulation of pressure swing adsorption (PSA), temperature swing adsorption (TSA) and adsorption chiller applications.