Preparation Of H₃PO₂ By Bipolar Membrane Electrodialysis Dissociation Of NaH₂PO₂

Hypophosphorous acid?H₃PO₂?is an important fine chemical raw material,which is mainly used as a catalyst for preventing discoloration of a phosphorus resin,an esterification reaction,and a refrigerant.High-purity H₃PO₂is also used in a large number of electroless plating processes for precision electronic components.Industrially,methods for preparing H₃PO₂include yellow phosphorus synthesis decomposition method,phosphorus high temperature method,ion exchange method and electrodialysis method.The yellow phosphorus synthesis method and the phosphorus high temperature method are currently rarely used because of complicated processes and complicated chemical reactions.The ion exchange method is mostly used for the production of H₃PO₂by virtue of its technical maturity,but in the process of resin regeneration,the consumption of acid and alkali and a large amount of regenerated wastewater bring about huge environmental pollution.The disadvantage of electrodialysis is that it has low acid production efficiency,high energy consumption and high cost.In addition,H₂and O₂generated by the plates also have a large safety risk.Bipolar membrane electrodialysis?BMED?is a new type of membrane separation technology that combines traditional dialysis technology?ED?with bipolar membrane?BPM?.In recent years,it has been able to use salt.Many advantages such as simultaneous conversion to acid and alkali,no wastewater and low energy consumption are widely used in acid and alkali production,biomedicine,food engineering,high salt wastewater treatment,heavy metal recovery and other fields.If the bipolar membrane electrodialysis is used for the preparation of H₃PO₂,the production of acid-base wastewater in the production process will be greatly reduced,which is conducive to the realization of high-quality H₃PO₂clean energy-saving production.In this paper,we attempted to prepare H₃PO₂by three-compartment configuration BMED cleaning,optimized the experimental conditions of BMED to prepare H₃PO₂,and studied the production of Na⁺and H₃PO₃which affect the purity of H₃PO₂,and carried out resin adsorption and nitrogen replacement.The specific conclusions are as follows:?1?In this study,a BMED device with three-compartment configuration was used to treat Na H₂PO₂solution and prepare H₃PO₂.The effects of the current density,concentration of Na H₂PO₂and initial concentration of Na OH on the H₃PO₂production efficiency in terms of the voltage drop,current efficiency,energy consumption and sodium ion content in the acid chamber were investigated.Under the optimal operating conditions,the generation of H₃PO₃was minimized by applying different strategies to decrease the DO content in the solution.Under the optimum conditions,such a BMED system obtained a high concentration of H₃PO₂,a low Na⁺content and a low energy consumption,equal to 1.03 mol/L,670 ppm,and 1.18 k Wh/kg,respectively.To minimize the amount of phosphorous acid?H₃PO₃?generated from H₃PO₂oxidation during the BMED process,a nitrogen aeration operation was applied in both the acid and salt chambers,decreasing the HPO₃^2-content to 251 ppm,which was 44.1%lower than that without a dissolved oxygen?DO?content control strategy.The newly produced H₃PO₃during 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 H₃PO₂from Na H₂PO₂in industry.?2?In order to further reduce the content of impurity Na⁺in H₃PO₂produced by BMED to improve the quality and economic value of H₃PO₂,the resin adsorption treatment of H₃PO₂prepared by BMED system is firstly carried out,firstly,five strong acids of S108,001x7,42H,52H and 62MP are used.The type cation resin was statically adsorbed on Na⁺for 24 hours.Considering the adsorption and desorption properties and price of Na⁺in the H₃PO₂system of several resins,the dynamic adsorption of BMED acid was studied in the subsequent experiments using 42H resin.The Na⁺content of impurities in the secondary H₃PO₂produced is reduced to below100 ppm by coupling the BMED technology with the resin.And this coupling process is compared with direct production of H₃PO₂by ion exchange method,showing the quality of H₃PO₂production,acid production rate,unit acid production resin consumption,unit acid production wastewater discharge,unit acid production regeneration liquid consumption,etc.The coupling process between BMED and resin has great advantages and potential to replace traditional methods in green production of high quality H₃PO₂.