Transport of nitric acid through the anion-exchange membrane NEOSEPTA-AFN

The paper presents the determination of mobility of H3O+ and NO3- ions and diffusivity of the non-dissociated form of acid on the basis of experiments with nitric acid carried out in a batch mixed cell with an anion-exchange membrane NEOSEPTA-AFN, which have been completed by measurements of membrane conductivity. The dependencies of mobility of H3O+ and NO3- ions upon the acid concentration in the membrane were approximated by the second degree polynomial, whose coefficients were determined by the numerical integration of the differential equation describing the time dependence of nitric acid in the cell followed by an optimizing procedure. Diffusivity of the non-dissociated form was calculated from mobilities of H3O+ and NO3- ions. The model used is based on the Nernst-Planck electro-diffusion equation and takes into account ionic equilibrium between the species. Using all the experimental data obtained at various acid concentrations and rotational speeds of the stirrers, it was found that the transport characteristics mentioned above (except for mobility of H3O+ ions) were affected by the nitric acid concentration in the membrane.