Water vapor adsorption on activated alumina has been determined by a flow method for three temperatures ranging from 22.5°C to 60°C. Dissociative chemisorption occurs on dehydroxylated surface of alumina followed by strong molecular adsorption, multilayer edification and capillary condensation. The determination of the quantity of water vapor adsorbed indicates that a molecule of water is physically linked on two adjacent hydroxyl groups. In the first molecular layer, the high initial heat of adsorption is attributed to the formation of a hydrogen-bond and the polarity of the adsorbent. In the multilayers and the capillary condensation ranges, the heat of adsorption is constant and equal to the condensation heat. Three models are used to fit the adsorption isotherms data. In particular, BET equation with finite molecular layers provides a number of molecular layers n similar to that calculated from the mean pore size of the adsorbent and the thickness of the adsorbed film.
M. Baguenne, A. Bellagi