This example demonstrates the continuous mode of operation for a bipolar membrane cell and supports the conclusion expressed in Example 3 that concentrations of hypophosphorous acid significantly higher than 1N are possible at a given current efficiency during the electrodialytic splitting of sodium hypophosphite salt into its acid and base components using a three-compartment cell equipped with anion, cation, and bipolar membranes. (7) means of circulating aqueous electrode rinse solutions through said electrode rinse compartments; (A) adding water to said acid and base compartments; (B) adding an aqueous solution of about 5 to about saturation of sodium hypophosphite to said salt compartments; (C) maintaining the temperature in said series of units at about 10° to about 45° C.; (D) passing direct current through said series of units at a density of about 50 to about 155 mA/cm. Also, if the acid content of the spent salt solution is to be used for pH control in the existing process for producing sodium hypophosphite, the concentration of acid and base in the acid compartment and base compartment, respectively, can be controlled so that the acid content of the spent salt solution is appropriate for that purpose (i.e., so that at least no additional acid is needed in the sodium hypophosphite process to adjust the pH). Similarly, fluid in salt compartments 1S, 2S, 3S, and 4S is recirculated through lines 13 and 14 and storage tank 15 by means of pump 16. The two electrode rinse membranes, ER+, separate the beginning and ending of the unit cells from the electrode compartments and generally consist of commercially available Nafion® type membranes. 3 the ordinate is current efficiency and the abscissa is normality (Eq/L). The sodium carbonate entering through line 51 can then be reduced nearly stoichiometrically. Hypophosphorous acid, which is typically about 10 to about 50 wt. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). A method according to claim 4 wherein the current density in said cell is about 50 to about 155 mA/cm. The sodium hypophosphite used in the hypophosphorous acid process can be obtained from various locations in the sodium hypophosphite process. A method according to claim 4 including the additional last step of using at least a portion of said sodium hypophosphite and hypophosphorous acid solution to adjust the pH of a second aqueous sodium hypophosphite solution prior to the evaporation and crystallization of said second aqueous sodium hypophosphite solution. They are combined with mother liquor from solid/liquid separator 45 from line 46 and are fed to solid/liquid separator 47, where the precipitated calcium phosphite is removed through line 48. 2H 2 O. The use of acids other than hypophosphorous acid in the existing sodium hypophosphite process to adjust the pH is eliminated, and therefore the sodium hypophosphite product will contain hypophosphite instead of foreign anions and be purer. This invention relates to a method of making hypophosphorous acid (HPA) using electrodialytic water splitting. %), but it is preferably about 5 to about 30 wt. The salt loop was operated to maintain a conductivity of 70 ms/cm through the continuous addition of the 25 wt. If crystalline sodium hypophosphite is used in the hypophosphorous acid process, it is dissolved in tank 63, then passed through line 64 to cation exchange material 65, which removes any divalent (e.g., calcium and magnesium) ions that may be present as these may damage the ion-exchange membranes. Depleted salt solution is removed through line 17 and additional fresh salt solution is added through line 18. FIG. 3 indicates, this CE is lower than the cumulative efficiency since the early part of the batch cycle operates at high current efficiency when the hypophosphorous acid concentration is relatively low. ADVANCED SEARCH. A comparison of Example 4 with Example 5 shows that the concentration and current efficiency results are reproducible. ACS reagent (1) BioChemika (1) BioUltra (1) Halal (1) ... Hypophosphorous acid-d 3 solution. Phosphine and hydrogen gases are removed from reactor 39 through line 43. 6. It has a melting point that varies between 17.4 and 26.5 degrees Celsius. A method according to claim 4 wherein a portion of said hypophosphorous acid and sodium hydroxide solutions is continuously drawn off and replaced with water and a portion of said sodium hypophosphite and hypophosphorous acid solution is continuously drawn off and replaced with fresh sodium hypophosphite solution. 18. The liquor of sodium hypophosphite passes through line 56 where, in the existing process, an acid is added through line 57 to lower the pH and precipitate sodium hypophosphite in evaporator/crystallizer 58. Browse other articles of this reference work: The full text of this article hosted at iucr.org is unavailable due to technical difficulties. The dilute caustic can also be used to generate calcium hydroxide from lime needed in the sodium hypophosphite process. As the FIG. This experiment operated for a total of about 450 minutes. A process for producing hypophosphorous acid (H 3 PO 2 ) by reacting, in the absence of a catalyst and under an acidic condition, phosphine with an aqueous solution of hydrogen peroxide to produce an acid solution. 3,052,519; 2,976,117; 4,521,391; 4,380,531; and EP 459751A1, herein incorporated by reference. This reaction, typically conducted in acidic medium, involves the preliminary formation of iminium ions from the carbonyl compound and the amine; the attack of the iminium ion to the hypophosphorous acid, which can be reiterated, afford α-aminoalkylphosphinic or bis(α-aminoalkyl)phosphinic acids, respectively. Our hypophosphorous acid is recognized for its quality, stability and ease of use. The appearance of the compound in the liquid state is shown in figure 2. Hypophosphorous acid is a strong reducing agent and further has applications as a neutralising agent, discolouring agent, and as a catalyst. Product was periodically removed from the acid recirculation loop to reduce the product liquor inventory. %). This allowed each cell stream to be operated independently in one of two different modes--batch/semi-batch and continuous. These two drastically different hypophosphorous acid concentrations at about equivalent current efficiencies provide additional support to the conclusion that acid concentrations significantly higher than those reported in the open literature for strong acids are possible during the bipolar membrane electrodialyses of sodium hypophosphite into hypophosphorous acid and sodium hydroxide. A method according to claim 14 wherein the concentration of said hypophosphorous acid in said hypophosphorous acid solution and the concentration of said sodium hydroxide in said sodium hydroxide solution are controlled so that the acid content of said sodium hypophosphite and hypophosphorous acid solution is the content needed to reduce the pH of said second aqueous sodium hypophosphite solution to the desired pH.
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