Adsorption of Water and Methanol on Micro- and Mesoporous Wood-Based Activated Carbons

Abstract

Sorption of water and methanol on two carbons of wood origin and their oxidized counterparts was studied. The isotherms were measured at low relative pressure (p/p0 < 0.3) at temperatures close to ambient. Before the experiments, the detailed structural and chemical features of the carbon surfaces were determined by applying various physical and chemical methods. From the isotherms, the heats of adsorption were calculated using the virial equation. The results showed the differences in the uptakes of water and methanol at a low relative pressure related to different mechanisms of the adsorption processes. It was demonstrated that the effect of pore sizes and pore volume on sorption uptake is more pronounced in the case of methanol, whereas water sorption is governed mainly by surface chemistry. For both sorbates, the isosteric heats of adsorption were affected by the surface chemical heterogeneity only at low surface coverage. At higher surface coverage, in the case of water the highest heats of adsorption were equal to the heat of condensation, whereas in the case of methanol Qst was higher than the heat of condensation.