Experimental measurement and molecular modeling studies were made of the adsorption of water, methanol and ethanol on hydrophobic all-silica decadodecasil 3R (DD3R) zeolite. The simulation data were compared with permeation data on these components, measured using a DD3R membrane under pervaporation conditions. The pure-component isotherms were measured by vapor-phase adsorption and were calculated by using grand canonical Monte Carlo simulations. The latter results were in fair agreement with the experimental adsorption data. Computed mixture adsorption isotherms showed that the water loading was significantly increased as compared with pure-component adsorption. The shape of the computed water isotherm changed from type II to type I when alcohol was present. The loading of both methanol and ethanol at low fugacities was slightly enhanced by the presence of water. The self-diffusivites were calculated using molecular dynamics simulations. The self-diffusivity of water in DD3R was substantially larger than the diffusivities of either alcohol, but was decreased in the presence of methanol or ethanol. The ethanol diffusivity was too low to be determined using conventional molecular dynamics simulations. The flux deduced from the molecular dynamics and grand canonical Monte Carlo results over-estimated the experimental values, but the predicted membrane selectivity corresponded well to the experimental data. The separation mechanism in the de-watering of alcohols, using a hydrophobic DD3R membrane, was based upon the high diffusivity of water as compared to that of the alcohols. Ethanol in particular suffered from diffusion limitations.

Adsorption and Diffusion of Water, Methanol, and Ethanol in All-Silica DD3R: Experiments and Simulation. J.Kuhn, J.M.Castillo-Sanchez, J.Gascon, S.Calero, D.Dubbeldam, T.J.H.Vlugt, F.Kapteijn, J.Gross: Journal of Physical Chemistry C, 2009, 113[32], 14290-301