Comparison of anionic membranes used to concentrate nitric acid to beyond the azeotropic mixture

Abstract

The electrolysis of concentrated nitric acid solutions was carried out in an electrochemical cell with parallel plates (FM01-LC ICI). An anionic membrane that permits the migration of nitrate ions under the influence of an electrical field separated the anodic and cathodic compartments. The current efficiency for the transported nitrate ions was evaluated for several membranes, at a constant current. All the membranes allowed the transport of nitrate ions at different current efficiencies, following the increase in acid concentration in the anodic compartment. This electroseparation membrane process concentrated nitric acid from 25% up to 90% in successive stages. A special case to be noted was when the acid concentration was near the azeotropic value. In this case, the acid concentration in the anodic compartment rose above the azeotropic value of 68.5%, thus breaking the azeotrope mixture. It is expected that, for some niche applications, this process could be competitive with extractive distillation