Effect of electro-chemical properties of sodium salts of various anions on their diffusional parameters in symmetrical cellulose acetate membranes

Abstract

A relation was obtained between electro-chemical properties of sodium salts (NaCl, NaBr, and Na 2SO 4), and the thermodynamic property of permeability in symmetrical cellulose acetate membranes, the distribution coefficient K and the kinetic property, the overall diffusion coefficients D. K and D were obtained by the method we proposed using measured unsteady- and steady-state dialysis data. The K values increase with the increase of water content and are in the range of 10 −2 for sodium halides and 10 −3 for Na 2SO 4. D is found to increase with the increase of the solute concentration, and the extrapolated values of D to zero concentration D (0) are obtained as 0.015–0.03 μm 2/s and increase with the increase of water content in the membrane. D can be divided into the concentration independent diffusion coefficients in the dense part of the membrane D d and in the porous D p , applying a two-part (perfect or dense and imperfect or porous) model of the membrane. Contrary to D d , D p increases with the increase of W w and can be correlated as D p,c = D d exp (γ × W w ). It is shown that the averaged D d , D D increases with the increase of the quantity of the ionic mobility u∘ of the solutes at infinite dilution divided by valence, and that the parameter γ increases with the increase of the ionic mobility u∘. The value of K increases slightly with the increase of water content and decreases with the increase of the Flory—Huggins parameter χ. The Flory—Huggins parameter χ is calculated from the measured values of distribution coefficients and data obtained from the literature. And it was found that the gradient of linear decrease of χ (λ cation) depends on equivalent ionic conductivity of anion of salt, λ an.