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

A relation was obtained between electro-chemical properties of alkali, alka li-earth and aluminium-chlorides (LiCl, NaCl, KCI, RbCl, CsCl, MgCl2, CaCl2 , AlCl3) and the distribution coefficient K and the overall diffusion coeff icients D in symmetrical cellulose acetate membranes. Symmetrical cellulose acetate membranes was cast to have a wider range of water content, 15-30%. K and D were measured by the unsteady- and steady-state dialysis method. T he K values increase with the increase of water content and in the increasi ng order of CaCl2, MgCl2, AlCl3, LiCl, KCl, NaCl, RbCl and CsCl, and are in the range of 10(-2) for alkali chlorides, 10(-5)-10(-4) for alkali earth c hlorides, and 10(-4) for AlCl3. D was found to increase with the increase o f the solute concentration and the extrapolated values of D to zero concent ration D-(0) were obtained as 0.01-0.1 mum(2)/s for membranes cast from a d ense dope solution and 0.1-0.4 mum(2)/s for membranes from a thin one. D-(0 ) increases with the increase of water content in the membrane and in the o rder of NaCl, LiCl, MgCl2, RbCl, CaCl2, CsCl, KCl and AlCl3 for membranes f rom dense and NaCl, RbCl,CsCl, KCl and LiCl for membranes from thin. D can be divided into the concentration independent diffusion coefficients in the dense part D-d and in the porous D-p applying a two-part (perfect or dense and imperfect or porous) model of the membrane. D-d does not depend on the water content in the membrane W-w, but on dope composition. Contrary to D- d, D-p increases with the increase of W-w and can be correlated as D-p,D-o= (D) over bar (d) exp (gamma x W-w). It is shown that the averaged D-d, (D) over bar (d) increases almost linearly with the increase of the product of valence times ionic mobility u(o) of the solutes at infinite dilution, and that the parameter gamma increases with the increase of Stokes radius of i on r(Stokes). The value of K increases slightly with the increase of water content and decreases with the increase of the Flory-Huggins parameter chi. The Flory-Huggins parameter chi is calculated from the measured values of distribution coefficients and data offered from literatures. It was found t hat the gradient of linear decrease of chi (lambda (cat)) and of linear inc rease of chi (lambda (an)) depends on equivalent ionic conductivity of anio n and cation of salt, lambda (an) and lambda (cat), respectively. It seems possible to predict permeability for some specific solute through a membran e from measured diffusional values such as D-(0) and K for NaCl or some sta ndard solute.