DIFFUSION-BARRIERS IN THE KINETICS OF WATER-VAPOR ADSORPTION DESORPTION ON ACTIVATED CARBONS/

The adsorption of water vapor on a highly microporous coconut-shell-de rived carbon and a mesoporous wood-derived carbon was studied. These c arbons were chosen as they had markedly different porous structures. T he adsorption and desorption characteristics of water vapor on the act ivated carbons were investigated over the relative pressure range p/p( o) = 0-0.9 for temperatures in the range 285-313 K in a static water v apor system. The adsorption isotherms were analyzed using the Dubinin- Serpinski equation, and this provided an assessment of the polarity of the carbons. The kinetics of water vapor adsorption and desorption we re studied with different amounts of preadsorbed water for set changes in pressure relative to the saturated vapor pressure (p/p(o)). The ad sorption kinetics for each relative pressure step were compared and us ed to calculate the activation energies for the vapor pressure increme nts. The kinetic results are discussed in relation to their relative p osition on the equilibrium isotherm and the adsorption mechanism of wa ter vapor on activated carbons.