Adsorption Equilibria of Water Vapor on Surface-Modified Activated Carbons and Alumina

The adsorption equilibria of water vapor on surface-modified activated carbons (ACs) and activated alumina (AA) were measured at 283.15, 293.15, and 303.15 K at relative pressures of up to 0.9. The surface of commercial activated carbon was modified by acid treatment, thermal treatment, and KOH treatment. The adsorption isotherm was highly affected by the textual properties of the ACs. The isotherms and hysteresis of the thermally treated AC were similar to those of raw AC, whereas significant shifts were observed for the acid- and KOH-treated ACs. The amounts of water adsorbed by the thermally treated and KOH-treated ACs were relatively low compared to that of the raw AC in the very low concentration region. However, the adsorption amounts increased with increasing water vapor concentration. The adsorption isotherms of AC and AA were crossed over at a certain pressure, but the crossover point was shifted markedly to lower pressure for acid-treated AC. The modified cluster-formation-induced micropore-filling (CIMF) model was applied to the experimental isotherm data.