Calorimetric study and simulation of the adsorption of methanol and propanol onto activated carbon fibers

Adsorption isotherms and differential heats of adsorption of methanol, ethanol, 1- and 2-propanol, and 1- and 2-butanol onto two types of activated carbon fiber (ACF) were measured at 298.0 K to investigate the mechanism for the adsorption of lower alcohols onto ACFs. The dependence of the differential heat at the initial stage of adsorption on the type of alcohol can be quantitatively explained by a dispersion pore potential. However, it is necessary to take into account the effect of surface functional groups on the total amount of differential heat. Therefore, a grand canonical Monte Carlo (GCMC) simulation was applied to the adsorption of methanol and propanol onto ACF using simple slit pore models with and without carbonyl functional groups. Large differences in the amount of alcohol adsorbed and the differential heat were observed for different carbonyl configurations. A comparison of the experimental and simulated isotherms and differential heats revealed that a surface without functional groups does not reproduce the experimental isotherm and differential heat. The positioning of five carbonyls close together on the carbon surface makes a very active site that provides similar features to those obtained experimentally. For the pore model with active sites, 1-propanol molecules form a bilayer structure similar to methanol molecules, whereas 2-propanol molecules do not form such a definite layer structure. This is a typical isomer effect that originates from the steric hindrance of the alkyl group on 2-propanol.