Steady-state concentration and composition gradients of pervaporating liquids inside the membranes were measured using stacks of membranes. The experimental results on pure components agree well with a simple mechanism of diffusion down a chemical potential gradient in a nonporous membrane. For mixtures, concentration gradients are similar to those obtained for pure liquids, and composition distribution shows that the selection between the two species does not take place at a given interface in the membrane but is progressive along the diffusional paths through the membrane. Data are also listed to show that solubility and diffusivity enhancements occur for components which are hydrogen bonded with the basic groups of the membrance.
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Aptel et al. (1974) studied this question.