Adsorption of water vapor on active carbons: Estimation of pore width

Transport and sorption of volatile organic compounds and water vapor in porous media

“…Instead, the diffusion models incorporate isotherm nonlinearity to account for sorption rate asymmetry. Model results indicate that convex nonlinear isotherms (i.e., diminishing rate of increase in sorption capacity with increasing fluid-phase concentration) would accelerate the rate of uptake by sorption slightly, but would decelerate the rate of desorption more strongly , 1990. Asymmetric sorption rates, although observed in many environmental applications, have only been studied systematically in a few cases, such as for hydrocarbons in zeolite and sulfur dioxide in activated carbon.…”

“…Experimental studies of sorption kinetics have revealed slow and asymmetric sorption-desorption rates for some porous sorbent systems, including zeolite and activated carbon , 1990. Two classes of mechanisms could control the slow and asymmetric sorption kinetics: reaction rates and mass transfer processes (Weber et al, 1991).…”

“…Depending on the properties of zeolite, either macropore or micropore diffbsion or both could be the rate-controlling mechanism. Using a similar idea, , 1990 developed models to describe sorption of sulfur dioxide and carbon dioxide onto activated carbon, accounting for gasphase diffusion through macropores and micropores simultaneously, or else treating gasphase macropore diffusion and surface diffusion together. However, often a model of macropore diffusion alone can produce a similar quality of predictions to the macropore and micropore diffusion model for activated carbon systems.…”

“…The intraparticle diffusion models have been applied to many commercial sorbent systems, including zedite , activated carbon , 1990 and activated alumina (Desai et al, 1992). Based on the unique pore structure of zeolite, Ruthven and co-workers developed a model to describe the sorption and diffusion of light-weight hydrocarbons in the macropores of the zeolite pellets and in the micropores of crystals within the pellet.…”

“…Many investigations have addressed the relationship between sorption kinetics and equilibrium for different sorbentlsorbate combinations Garg and Ruthtren, 1972;, 1990Desai et al, 1992; Chapter 11 of this dissertation). These studies have revealed that adsorption rates are faster than desorption rates whenever the sorption isotherms are convex (diminishing slope with increasing gas-phase concentration).…”