Ind. Eng. Chem. Fundam. 1981, 20, 89-94
Diffusivities of Gases in Aqueous Electrolyte Solutions Kiyomi Akita Department of Chemical Engineering, Tokushima University, Tokushima, 770, Japan
Diffusivities of oxygen in aqueous electrolyte solutions were measured, using 18 species of cations, 13 species of anions, and combinations thereof. Electrolyte concentrations were varied to near saturation and temperatures were set at 10, 20, and 40 O C . The results were correlated on the basis of the Eyring theory of rate processes. The free energy of activation of oxygen in a solution is assumed to consist of the sum of contributions due to various chemical species in the solution. The variations of the free energy with temperature for different diffusing solutes are discussed. With the results of this work, prediction of the diffusivities of gases in aqueous electrolyte solutions is possible, if gas diffusivities in pure water and the densities of the solutions are available.
Introduction Diffusivities of gases dissolved in aqueous electrolyte solutions are necessary for the chemical engineer in the design and the analysis of gas absorption equipment using electrolyte solutions. Podolsky (1958) proposed a perturbation model and applied it to diffusion processes in electrolyte solutions. He assumed that in such solutions the free energy of activation for one mole of diffusing particles in pure water, AGw*,was perturbed by the amount Gi, when a water molecule adjoining a diffusing particle was replaced by a single ith ion. In a solution in which the mole fraction of the ith ion is x i , AGw* is perturbed on the average by the amount Ginxi due to the ith ion alone so that the total contribution by all the ions is ZGinxi, where n is the number of solvent molecules surrounding a diffusing particle. Therefore, the free energy of activation for one mole of diffusing particles in the solution is given by AG* = AGw*
+ nZGixi
(1)
According to Podolsky, 6i is proportional to the viscosity B coefficient of Jones and Dole (1929). Ratcliff and Holdcroft (1963) determined diffusivities of carbon dioxide in various liquids at 25 "C by measuring absorption rates of the gas into liquids flowing over spheres. Six species of electrolyte involving Na+, Mg2+, C1-, NO
