Determination of the electrolyte and osmotic permeability coefficients by conductometric and emf methods

The emf method has been compared with the conductometric one in determining the apparent electrolyte permeability of membrane ( ). It has been found that this method is limited to the membranes of low permeability ( of the order 10!7 m/s). In order to obtain the real permeability coefficient (Ps), the conductometric method of determining osmotic flow has been proposed. The influence of concentration polarisation on Ps has been estimated. The extended expression for the polarisation correction factor has been derived. The thickness of the polarisation layer has been calculated from the limiting current density, determined using the Nafion 117 membrane.

1. Regarding the electrolyte permeability coefficient, , the emf method yields similar results as the conductometric one only in the case of dense membranes of low permeability. It is not an appropriate method for membranes of high permeability. 2. The determination of the volume permeability coefficient from the changes of concentrations of solutions on both sides of a membrane is possible; however, a high degree of accuracy of measurements is required. 3. When calculating the correction for polarisation layers, Eq. (13), not Eq. (14), should be used. 4. When determining the thickness of the polarisation layer, lp, from the limiting current density using the Nafion 117 membrane, the corrections for the diffusion of electrolytes and volume osmotic flux through that membrane can be omitted; both Eqs. (15) and (20) yield practically the same values of lp.