Adsorption equilibria and kinetics of CO2, CO, and N2 on carbon molecular sieve

Abstract

Abstract Adsorption equilibria and kinetics of CO2, CO, and N2 on carbon molecular sieves (CMSs) were measured by a gravimetric method at temperatures of 298, 308, and 318\u202fK and pressures up to 10\u202fbar. The validity of the experimental isotherms and kinetics was confirmed by comparing with experimental results from an additional volumetric method. Experimental adsorption isotherms were well correlated with a temperature-dependent Sips model and the results were compared with the Langmuir and Sips models. The order of the adsorbed amounts and isosteric heats of adsorption were CO2\u202f>\u202fCO\u202f≥\u202fN2 and their heats of adsorption changed from vertical interactions to lateral interactions with an increase in loading amount. The adsorbed amounts and heats of adsorption were lower for the CMSs than those of activated carbon, which has higher surface area and pore size. The microporous diffusional time constants (Dμ/r2) of CO and N2 could be obtained from an isothermal kinetic model, while a non-isothermal kinetic model was required for CO2 due to its higher heat of adsorption and adsorption rate. In addition, the variation in Dμ/r2 with surface coverage were well correlated by the Darken relation combined with Sips isotherm model, and a steep variation was observed from a surface coverage of 0.2 in all the components. The adsorption rate was highly affected by the electrical properties of the adsorbate rather than kinetic diameters. The order of adsorption rate was CO2\u202f≫\u202fCO\u202f>\u202fN2, while the order of the activation energies in the Arrhenius equation was opposite. The validity of obtained equilibria and kinetics results was confirmed by comparing the experimental breakthrough curves and dynamic simulation results in a CMS bed.