Abstract
This study explores the applicability of the adsorption‐diffusion mechanism to describe the transport of binary “methanol‐water” and “ethanol‐water” mixtures in pervaporation through a commercial microporous silica membrane. Two different adsorption‐diffusion models are considered: one based on Fick's diffusion equation and another based on the Maxwell‐Stefan formulation. Basic models (Fick) assume concentration independent parameters; more complex models (Maxwell‐Stefan) incorporate flux coupling and other non‐idealities. The influence of feed temperature (40°C–90°C) on permeation flux was analysed in terms of activation energy for flux, permeability and diffusion, and heat of adsorption and vaporization. Also the occurrence of coupling effects was studied by determining the effect of feed composition (entire composition range) on permeation flux, permeability and selectivity. Adsorption‐diffusion models based on Fick's diffusion equation can be used to describe coupling effects if they are modified with concentration dependent diffusion and/or sorption coefficients. They are incapable of describing drag effects by water on alcohols. These drag effects should be modeled through models based on the Maxwell‐Stefan theory.
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