Preparation of Hypophosphorous Acid by Bipolar Membrane Electrodialysis: Process Optimization and Phosphorous Acid Minimization

Hypophosphorous acid (H₃PO₂) is an important chemical product with wide applications in pharmaceuticals and electroless plating. In this study, bipolar membrane electrodialysis (BMED) was used to produce H₃PO₂ from sodium hypophosphite salt (NaH₂PO₂) to replace the traditional preparation methods. The BMED process was optimized in terms of current density, NaH₂PO₂ salt concentration, and initial NaOH concentration of the base solution. The results indicated that low Na⁺ leakage occurred at lower salt concentrations. Under the optimum conditions, such a BMED system obtained a high concentration of H₃PO₂, a low Na⁺ content, and a low energy consumption, equaling to 1.03 mol/L, 670 ppm, and 1.18 kW h/kg, respectively. To minimize the amount of phosphorous acid (H₃PO₃) generated from H₃PO₂ oxidation during the BMED process, a nitrogen aeration operation was applied in both the acid and salt chambers, decreasing the HPO₃²– content to 251 ppm, which was 44.1% lower than that without a dissolved oxygen content control strategy. The newly produced H₃PO₃ during the BMED process was reduced by 96.5%. The obtained results indicated that the BMED process has great potential for application in the production of high-quality H₃PO₂ from NaH₂PO₂ in industry.