Adsorption of water and methanol on micro- and mesoporous wood-based activated carbons

Sorption of water and methanol on two carbons of wood origin and their oxid ized counterparts was studied. The isotherms were measured at low relative pressure (p/p(0) < 0.3) at temperatures close to ambient. Before the experi ments, the detailed structural and chemical features of the carbon surfaces were determined by applying various physical and chemical methods. From th e isotherms, the heats of adsorption were calculated using the virial equat ion. The results showed the differences in the uptakes of water and methano l at a low relative pressure related to different mechanisms of the adsorpt ion processes. It was demonstrated that the effect of pore sizes and pore v olume on sorption uptake is more pronounced in the case of methanol, wherea s water sorption is governed mainly by surface chemistry. For both sorbates , the isosteric heats of adsorption were affected by the surface chemical h eterogeneity only at low surface coverage. At higher surface coverage, in t he case of water the highest heats of adsorption were equal to the heat of condensation, whereas in the case of methanol Q(st) was higher than the hea t of condensation.