Kinetics of water and alcohol vapors adsorption on natural zeolite

Alcohols are important high volatility industrial chemicals, and when present in low concentrations require highly selective separation techniques. This paper investigates the kinetics of the adsorption of water, methanol, and butanol vapors on natural clinoptilolite based on experimental data obtained from laboratory-scale equipment under constant saturated vapor pressure conditions at ambient temperature. In order to determine the corresponding mass transfer and diffusion coefficients of the adsorbed components in the zeolite particles, the kinetic curves have been investigated using two simple models - the linear driving force model (LDFM) as well as the particle diffusion model. The equilibrium and the kinetic parameters can also be determined from the experimental values of the statistical moments of the kinetic curves. Two main results have been obtained from this study. At the experimental conditions, the overall rates of adsorption of both methanol and water vapors are nearly equal, and they are of the same order of magnitude to the macro-(meso)-pore and intracrystalline diffusion rates predicted for the biporous clinoptilolite structure. In contrast, the diffusion of butanol vapors is much slower in the zeolite particles and particle crystals, where the intracrystalline mass transfer resistance plays a dominant role, even for the largest particles studied. The simple LDFM predictions exhibit very good correlation to the experimental data for all adsorptive components and particle sizes, despite the biporous zeolite structure. This model can be used to provide an acceptable and quick interpretation of adsorption rate curves, even at nonlinear equilibrium conditions. (C) 2009 Curtin University of Technology and John Wiley & Sons, Ltd.