Actual Concentration Profiles in Membrane Permeation

Abstract

Abstract The concentration profiles and the concentration dependent diffusion coefficient, at steady-state liquid permeation, were investigated in plastic films by directly measuring the concentration profile. A stacked film packet was developed which permitted peeling of film sections and measuring incremental concentration of permeate. The membrane-permeate systems studied were: nylon 6-water, nylon 6-dioxane, cellulose acetate-water, and polyethylene-dioxane. Membrane thickness was varied from 2 to 53 mil and temperature from 35 to 75°C. Also, poylethylene-benzene and polyethylene–n.-hexane systems were studied at 17 mil and 35°C only. The analysis of the experimental data showed that the exponential model, D = 0 e α C , represented the directly measured concentration profiles to a satisfactory degree. The use of this exponential model leads to a linear variation of the diffusion coefficient with distance within the membrane, but nonlinear as a function of concentration.