A simple isotherm model has been developed for the type-5 equilibrium
adsorption systems by considering the effects of both primary and seco
ndary adsorptive sites. The model was applied to interpret experimenta
l data describing water vapor adsorption capacities of four activated
carbon adsorbents for relative vapor pressures from 0.0 to 0.95 and te
mperatures between 288 and 308 K. Good agreement was observed between
the model and experimental results. The isotherm parameters were found
to either correlate well to the Brunauer, Emmett, and Teller specific
surface area or have limited effect on describing the adsorption onto
adsorbents made from the same precursor but activated with different
degrees of burnout. The limiting pore volumes of the adsorbents obtain
ed from the model based on water vapor adsorption compared favorably w
ith those measured using volatile organic compounds.