Effect of some parameters on the improvement of the bipolar membrane electrodialysis process

A study of electrodialysis with biploar membranes of NaNO3 solutions to produce nitric acid and soda wasperformed with the object of stressing the role of the auxiliary ion-exchange membranes used to equip the bipolarmembrane electrodialysis cell. Efficiencies of the recovery of acid largely depend on the anion-exchange membraneproperties. In relation to such effects, characterization of several industrial anion-exchange membranes wasperformed. Our results of BPM electrodialysis led to select the AD-Solvay membrane. A stack of cells equipped withthis membrane was used to study the efficiency of HNO3 and NaOH production under the influence of theconcentrations of the solutions that were flowing across the cell compartments. Measurements were performedseparately for the effects of salt, acid and base solutions. It is shown that with increasing salt concentration the faradicyields of both acid and base increase and tend towards limiting values. The increase of initial acid and baseconcentration reduces the faradic yields as well as the ratio of the final to the initial acid and base concentration. Asimilar investigation was made by changing the volume of the NaNO3 solution that circulates across the saltcompartment. With increasing volumes of salt solutions, concentrations vary from an initial value of 0.1M to 3.9 Nfor acid and 4.5 N for base. Some measurements of acid production were made in the case of bipolar membraneelectrodialysis of a mixed NaNO3–NaCl salt solution.