Method for preparing high-purity hypophosphorous acid based on sodium hypophosphite

Abstract

This invention provides a method for preparing high-purity hypophosphite based on sodium hypophosphite. The method utilizes a multi-chamber concentric electrodialysis tank to perform an electrodialysis reaction on a sodium hypophosphite solution. The reacted solution is passed sequentially through at least two parallel glass columns filled with H-type modified resin at a set flow rate to achieve an ion exchange reaction. The liquid flowing out after ion exchange is evaporated, concentrated, and crystallized. In a sealed environment, the crystalline solid is stirred and mixed with diethyl ether. After solid-liquid separation, the liquid is repeatedly washed and the diethyl ether is removed by vacuum distillation. The resulting high-purity hypophosphite is obtained by evaporation and concentration. The multi-chamber concentric electrodialysis tank has a central cylinder as the raw material chamber, and at least two sets of acid-grade buffer chambers and one set of alkali-grade buffer chambers are located around it. The H-type modified resin is prepared by activating an H-type cation exchange resin with a hypophosphite solution. This invention uses a multi-chamber concentric electrodialysis tank combined with modified H-type cation exchange resin and supplemented with diethyl ether for impurity removal to obtain high-purity hypophosphite.

Description

Technical Field

[0001] This invention belongs to the technical field of hypophosphorous acid preparation, and specifically relates to a method for preparing high-purity hypophosphorous acid based on sodium hypophosphorus. Background Technology

[0002] Hypophosphoric acid has a wide range of applications and strong reducing properties. It is widely used as a reducing agent in industries such as chemical electroplating, pharmaceuticals, chemicals, resin coatings, inks, and water treatment. It is also used as an antioxidant and color-reducing agent in the preparation of alkyd resins, or as an anti-ultraviolet additive in the textile industry. It can also be used as an intermediate to prepare various high-quality hypophosphite products, such as calcium hypophosphite, magnesium hypophosphite, aluminum hypophosphite, ammonium hypophosphite, and nickel hypophosphite. In addition, it can be used as an additive in the electrolyte of aluminum electrolytic capacitors to effectively improve the oxidation efficiency of the electrolyte.

[0003] The purity of hypophosphite sold on the market is usually around 50%. Its mainstream synthesis process is as follows: (1) Ion exchange method, in which sodium hypophosphite solution is passed through a cation exchange resin (H type), and the Na in the solution... + Ions exchange H groups on the resin + (1) Hypophosphoric acid is obtained by ion exchange, and the resin is converted to the Na form. The purity of hypophosphoric acid prepared by resin exchange is generally about 51%. (2) Electrodialysis method: The positive and negative electrode chambers are separated by anion membrane and cation membrane. The anion membrane only allows negative ions to pass through, and the cation membrane only allows positive ions to pass through. When electricity is passed through the electrolytic cell, hydrogen ions are generated by electrolysis of water at the anode and hydroxide ions are generated by electrolysis of water at the cathode. Under the blockage of the cation / anion membrane, hydrogen ions combine with hypophosphoric acid to form hypophosphoric acid. The purity of hypophosphoric acid prepared by electrodialysis method is generally about 50-55%.

[0004] The two methods mentioned above have advantages over conventional chemical synthesis methods, such as simpler processes and less hazardous waste. However, they also have many drawbacks. For example, the product contains a high level of sodium hypophosphite impurities, and product purification is very difficult. The main reason is that when ion exchange or electrodialysis reaches a certain stage, the pH of the solution environment changes drastically, leading to a decrease in the selectivity of the resin and membrane, which in turn affects the purity of the product. This makes it difficult for the quality of hypophosphite to meet industrial needs (such as capacitor production). Summary of the Invention

[0005] Therefore, the present invention aims to provide a method for preparing high-purity hypophosphite based on sodium hypophosphite, in order to solve at least one technical problem in the background art.

[0006] This invention is implemented as follows:

[0007] A method for preparing high-purity hypophosphite based on sodium hypophosphite includes the following steps:

[0008] The sodium hypophosphite solution was subjected to electrodialysis reaction based on a multi-chamber concentric electrodialysis cell, in which hypophosphite ions and hydrogen ions synthesized hypophosphite.

[0009] The solution after the electrodialysis reaction is passed sequentially through at least two parallel glass columns at a set flow rate. The glass columns are filled with H-type modified resin to achieve the ion exchange reaction.

[0010] The liquid that flows out after ion exchange is evaporated, concentrated, and crystallized.

[0011] In a sealed environment, the crystalline solid is stirred and mixed with diethyl ether. After physical separation, the hypophosphorous acid-diethyl ether liquid is repeatedly washed and the diethyl ether is removed by vacuum distillation. Finally, it is evaporated and concentrated to obtain high-purity hypophosphorous acid.

[0012] Among them, the multi-chamber concentric circle electrodialysis cell has a central cylinder as the raw material chamber, and the outer perimeter includes at least two sets of acid-grade buffer chambers and one set of alkali-grade buffer chambers;

[0013] H-type modified resin is prepared by activating H-type cation exchange resin with hypophosphite solution.

[0014] Furthermore, the electrodialysis cell includes a raw material chamber located at the center, functional chambers distributed circumferentially along the outside of the raw material chamber, the functional chambers including an anode chamber with a built-in anode electrode, a cathode chamber with a built-in cathode electrode, and a product chamber, an acid grade buffer chamber, and an alkali grade buffer chamber arranged sequentially around the anode chamber and the cathode chamber.

[0015] In this process, the anode chamber electrolyzes water to produce hydrogen ions and oxygen. Hydrogen ions (H+) + It enters the product chamber through a cation exchange membrane;

[0016] The cathode chamber electrolyzes water to produce hydroxide ions (OH-). - and hydrogen;

[0017] The sodium hypophosphite solution located in the raw material chamber achieves separation of anions and cations through the action of anion exchange membranes and cation exchange membranes, wherein the hypophosphite ion (H₂PO₂) is separated. - The product chamber is formed by sequentially passing through at least two acid-grade buffer chambers via an anion exchange membrane and reacting with hydrogen ions to synthesize hypophosphoric acid; sodium ions (Na+) + The cation exchanger flows through the alkali buffer chamber into the cathode chamber, where it reacts with hydroxide ions to form sodium hydroxide.

[0018] Furthermore, the anode chamber and the cathode chamber are physically separated by a partition; the raw material chamber is separated from a set of acid-grade buffer chambers and a set of alkali-grade buffer chambers by arc-shaped anion exchange membranes and arc-shaped cation exchange membranes, respectively; the raw material chamber is physically separated from other functional chambers by partitions; adjacent acid-grade buffer chambers and alkali-grade buffer chambers are physically separated by partitions.

[0019] Furthermore, the anode chamber and the product chamber, as well as the cathode chamber and the alkali buffer chamber, are separated by cation exchange membranes; and the acid buffer chambers and the product chamber are separated by anion exchange membranes.

[0020] Furthermore, the anion exchange membrane and the cation exchange membrane adopt an arc-shaped or wavy structure.

[0021] Furthermore, the activation step of the H-type modified resin includes: immersing the H-type cation exchange resin in a hypophosphorous acid solution for 1-3 hours, and then washing and drying to obtain the H-type modified resin.

[0022] Furthermore, microwave processing is coupled during the activation step, and the activation environment is sealed.

[0023] Furthermore, the activation temperature is 80–120°C.

[0024] Furthermore, the ion exchange reaction temperature was set to 35–45 °C; the total hydraulic residence time of the solution in the H-type modified resin was 2–4 h.

[0025] Furthermore, before mixing the crystalline solid with the ether, the ether is dried to remove moisture.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. This invention uses a multi-chamber concentric electrodialysis cell combined with modified H-type cation exchange resin, and supplemented with diethyl ether to remove impurities, thereby obtaining high-purity hypophosphoric acid.

[0028] 2. This invention improves upon conventional electrodialysis cells by adding acid-grade and alkali-grade buffer chambers to ensure higher preparation efficiency. At the same time, it integrates the raw material chamber and functional chamber into a concentric circle structure, making the equipment more compact and beneficial for industrial production.

[0029] 3. In this invention, H-type cation exchange resin is activated by impregnation with hypophosphoric acid and coupled with microwave heating, thereby enhancing the H-type ion exchange resin's ability to exchange for H+. + It has a high affinity for sodium ions, which improves the replacement efficiency of sodium ions during subsequent ion exchange and helps to improve the purity of the resin itself, replacing the metal ions carried by the H-type ion exchange resin and removing metal impurities. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of the present invention;

[0031] Figure 2 This is a top view of the electrodialysis cell of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] like Figure 1 As shown, a method for preparing high-purity hypophosphite based on sodium hypophosphite includes the following steps:

[0034] S1. Based on a multi-chamber concentric electrodialysis cell, sodium hypophosphite solution is subjected to electrodialysis reaction, and hypophosphite ions and hydrogen ions are synthesized into hypophosphite.

[0035] Electrolysis of water in the anode chamber produces hydrogen ions and oxygen. Hydrogen ions (H+) + Water enters the product chamber through the cation exchange membrane; in the cathode chamber, water is electrolyzed to produce hydroxide ions (OH-). - And hydrogen gas; under the action of an electric field, the sodium hypophosphite solution located in the raw material chamber achieves the separation and migration of anions and cations under the action of anion exchange membranes and cation exchange membranes, wherein sodium ions Na + The cation exchanger flows through the alkaline buffer chamber into the cathode chamber, where it reacts with hydroxide ions to form sodium hydroxide; hypophosphite ions (H₂PO₂) are also produced. - It flows sequentially through at least two sets of acid-grade buffer chambers via anion exchange membrane into the product chamber, where it combines with hydrogen ions to synthesize hypophosphoric acid.

[0036] S2. The solution after the electrodialysis reaction is passed sequentially through at least two parallel glass columns at a set flow rate. The glass columns are filled with H-type modified resin to achieve the ion exchange reaction.

[0037] Specifically, the activation steps of the H-type modified resin include: immersing the H-type cation exchange resin in a hypophosphorous acid solution for 1-3 hours, and then washing and drying to obtain the H-type modified resin; in some preferred embodiments, microwave treatment is coupled in the activation step, and the activation temperature is set to 100-130°C; the ion exchange reaction temperature is set to 35-45°C; and the total hydraulic residence time of the solution in the H-type modified resin is 2-4 hours.

[0038] S3. The liquid that flows out after ion exchange is evaporated, concentrated and crystallized. The solid obtained after crystallization is a mixture of hypophosphorous acid and sodium hypophosphorous acid.

[0039] S4. The solid crystals are stirred and mixed with diethyl ether. After physical separation, the hypophosphorous acid-diethyl ether liquid is repeatedly washed and the diethyl ether is removed by vacuum distillation. Finally, the liquid is evaporated and concentrated to obtain high-purity hypophosphorous acid. Before mixing the crystalline solid with the diethyl ether, the diethyl ether is dried to remove moisture.

[0040] like Figure 2As shown, the multi-chamber concentric circle electrodialysis cell adopts a cylindrical structure. It is a seven-chamber electrodialysis cell, including a raw material chamber 1 located at the center, and functional chambers located around the raw material chamber 1 and distributed circumferentially. The functional chambers include an anode chamber 2, a cathode chamber 3, an alkali buffer chamber 4, a first acid buffer chamber 5, a second acid buffer chamber 6, and a product chamber 7, which are distributed around each other. The various sections of the functional chambers form a closed loop.

[0041] The anode chamber 2 contains the anode electrode, and the cathode chamber 3 contains the cathode electrode. Both the anode and cathode electrodes are connected to an external power source. In the anode chamber 2, the water electrolysis reaction 2H₂O = 4H₂O occurs. + +O2+4e; In cathode chamber 3, the electrolysis of water reaction 2H2O+2e=4OH- - +H2.

[0042] The anode chamber 2 and cathode chamber 3, as well as the alkali buffer chamber 4 and the first acid buffer chamber 5, are separated by partitions 10, thus isolating adjacent chambers. The raw material chamber 1 is physically separated from the anode chamber 2, cathode chamber 3, second acid buffer chamber 6, and product chamber 7 by solid partitions; within the raw material chamber 1, NaH₂PO₂ = H₂PO₂. - +Na + .

[0043] The cathode chamber 3 and the alkali buffer chamber 4 are separated by a first cation exchange membrane 8, and the raw material chamber 1 and the alkali buffer chamber 4 are separated by a second cation exchange membrane 9, i.e., the sodium hypophosphite cation Na in the raw material chamber 1... + The ions pass sequentially through the first cation exchange membrane 8 and the second cation exchange membrane 9 into the cathode chamber 3, while the anions H2PO2... - Because the cation membrane prevents passage, Na₂O₃ will then pass through the cathode chamber 3. + +OH - =NaOH.

[0044] The raw material chamber 1 is separated from the first acid-grade buffer chamber 5 by a first anion exchange membrane 11; the first acid-grade buffer chamber 5 is separated from the second acid-grade buffer chamber 6 by a second anion exchange membrane 12; the second acid-grade buffer chamber 6 is separated from the product chamber 7 by a third anion exchange membrane 13; and the anode chamber 2 is separated from the product chamber 7 by a third cation exchange membrane 14. The H₂ produced by electrolysis in the anode chamber 2... + The product enters through the third cation membrane 14, while the anion H2PO2 enters through the third cation membrane 14. - Since H enters the product chamber 7 sequentially through the first anion exchange membrane 11 and the second anion exchange membrane 12, + +H2PO2 - =H3PO2. Na + Because the anion exchange membrane prevents oxygen from entering the product chamber 7, and the cation exchange membrane also prevents oxygen generated during electrolysis in the anode chamber 2 from entering the product chamber 7, the oxidation of hypophosphoric acid is thus avoided.

[0045] In specific implementation, both cation and anion membranes can be fixed and erected in a set position by means of equipment such as a grid frame. The anion and cation membranes adopt an arc or wave-shaped structure to form a larger specific surface area, which is conducive to maximizing the utilization of the membrane's selective permeability. This invention integrates the electrodialysis tank into a functional chamber with a sodium hypophosphite raw material area in the center and a circumferential area around it. The distribution is dense, smooth and efficient. At the same time, three sets of buffer chambers are added between the anode chamber, product chamber and cathode chamber. Their functions include two aspects: (1) The buffer chamber can avoid the accumulation of hydrogen ions and hydroxide ions in the anode chamber and cathode chamber. If hydrogen ions and hydroxide ions accumulate to a certain value, the pH of the corresponding area will change significantly as electrolysis proceeds, affecting the electrolysis efficiency. At the same time, it will reduce the selective permeability of the membrane, causing hydrogen ions and hydroxide ions to enter the raw material chamber in the opposite direction, resulting in a decrease in current efficiency and loss; (2) Adding a buffer chamber can improve the purity of the product hypophosphite. Since the membrane permeability is not 100%, some sodium ions will enter the product chamber. Adding a buffer chamber will increase the corresponding ion membrane and reduce the probability of sodium ions entering the product chamber. (3) The functional chambers distributed around the perimeter, compared with the conventional parallel distribution, can promote the reverse migration of corresponding ions to the corresponding electric field and reduce the permeation of opposite ions through the exchange membrane.

[0046] The present invention uses two sets of acid-grade buffer chambers and one set of alkali-grade buffer chambers to ensure high preparation efficiency. In fact, more buffer chambers can be added, but this would significantly increase the cost of land and membranes, and have limited effect on improving the efficiency of electrodialysis.

[0047] In practical implementation, the anode and cathode electrodes adopt electrode materials and structures permitted in the art. Except for the solution used in the sodium hypophosphite electrodialysis functional chamber, which uses a conventional solvent in the art, the anion and cation membranes in the electrodialysis tank are also sampled from any material permitted in the art. The materials, structures, and compositions of the above units are not described in detail here. The DC voltage and current for electrodialysis can be set conventionally; for example, the voltage can be set to 10–24V, and the current to 1–5A. These can also be adjusted according to actual conditions, and no specific limitations are made here.

[0048] This invention employs hypophosphite impregnation of H-type ion exchange resin, coupled with microwave treatment. This process, on the one hand, further enhances the H-type ion exchange resin's ability to process H+ after activation by hypophosphite impregnation. + The affinity of hypophosphite for sodium ions is enhanced, improving the replacement efficiency of sodium ions during subsequent ion exchange and further optimizing the purity of the hypophosphite product. On the other hand, activation through hypophosphite impregnation helps improve the purity of the resin itself, replacing metal ions carried by the H-type ion exchange resin and removing metal impurities. Furthermore, synergistic activation via microwave treatment allows the impregnated hypophosphite to form a gas-liquid mixture in a sealed environment, improving activation efficiency and increasing the resin's affinity for sodium ions. +The optimal temperature range for the resin is 80–120°C, as this range is crucial for both vapor formation and environmental safety. The waste acid solution after resin activation is primarily hypophosphoric acid, which, after collection and filtration, can be used as a dissolving liquid for preparing sodium hypophosphorus solution.

[0049] After ion exchange, the liquid is evaporated, concentrated, crystallized, and then condensed and recovered. The liquid is a mixture of hypophosphite and sodium hypophosphite. It can also be recycled and treated to be used as a liquid for preparing sodium hypophosphite solution.

[0050] Studies have found that heating the system to 35–45°C during ion exchange can improve ion exchange efficiency without damaging the resin. Limiting the hydraulic residence time reduces time costs while maintaining ion exchange efficiency. This residence time in the resin is generally controlled by the liquid flow rate, which can be kept below 20 m / h in time-based applications. Multi-stage parallel ion exchange resin glass columns are more efficient than single-stage columns and require less energy from auxiliary equipment such as pumps. Generally, 2–4 stages in parallel are preferred; further increasing the number of stages does not significantly improve ion exchange efficiency but instead increases costs.

[0051] Hypophosphoric acid with a purity of over 90% was obtained using the electrodialysis and ion exchange method of this invention. The main impurity was sodium hypophosphite. To purify the product, diethyl ether was used for impurity removal. Studies have shown that hypophosphoric acid is soluble in diethyl ether, but sodium hypophosphite is completely insoluble in diethyl ether. Using diethyl ether as a dissolving agent can remove sodium hypophosphite, and the evaporation of diethyl ether can be avoided in a closed environment. Since commercially available diethyl ether has a certain water content, and both hypophosphoric acid and sodium hypophosphite are soluble in water, the diethyl ether needs to be dried in the preceding steps to avoid interference from free water in the impurity removal process. Generally, desiccants such as metallic sodium, anhydrous magnesium sulfate, or anhydrous sodium sulfate are used to dry the ether to prepare anhydrous diethyl ether. Diethyl ether has a very low boiling point (34.6℃) and is a volatile liquid, so distillation can remove it in subsequent steps. A condenser can be used to recover and reuse the diethyl ether.

[0052] Example 1

[0053] A method for preparing high-purity hypophosphite based on sodium hypophosphite includes the following steps:

[0054] S1, Electrodialysis reaction

[0055] Prepare a sodium hypophosphite solution. Use industrial-grade sodium hypophosphite, which generally has a purity of around 99%. The mass concentration of the prepared sodium hypophosphite solution is 20%.

[0056] Sodium hypophosphite solution was pumped into the raw material chamber of a seven-chamber concentric electrodialysis tank, while pure water was added to the other functional chambers. A titanium-coated ruthenium electrode plate was used as the anode electrode, and a stainless steel electrode plate as the cathode electrode. The anode and cathode electrodes were connected to a DC power supply with a voltage of 15V and a current of 3A. After energization, hydrogen ions and oxygen were generated by electrolysis of water in the anode chamber, and hydroxide ions (OH-) were generated by electrolysis of water in the cathode chamber. - And hydrogen gas, hydrogen ions H + It enters the product chamber through a cation exchange membrane;

[0057] Sodium ion Na + The cation exchanger flows through the alkali buffer chamber and migrates into the cathode chamber, where it reacts with hydroxide ions (OH-). - Sodium hydroxide is produced; hypophosphatemoid H2PO2 is produced. - The product chamber is formed by the flow of the anion exchange membrane through the first and second acid level buffer chambers and then into the product chamber, where it is synthesized with hydrogen ions to form hypophosphoric acid.

[0058] Conductivity is set in the product chamber, anode chamber, and cathode chamber. The progress of the electrodialysis reaction is judged by the changes in conductivity. When the conductivity in the product chamber reaches its upper limit and does not change significantly within a certain time (e.g., ten minutes), the reaction liquid in the product chamber can be extracted for subsequent ion exchange reactions. The alkaline solution in the cathode chamber is discharged, and sodium hypophosphite solution is added to the raw material chamber, while pure water is added to the other functional chambers. In addition, the electrodialysis tank is equipped with conventional structures such as pumps and valves, which will not be described in detail here.

[0059] S2, ion exchange reaction

[0060] H-type cation exchange resin was impregnated in a 0.5 mol / L hypophosphite solution for 3 hours, and then washed and dried to obtain H-type modified resin.

[0061] Three sets of glass columns were set up side by side, and each glass column was filled with H-type modified resin;

[0062] The internal temperature of the three glass columns was heated to 40°C. The reaction solution after electrodialysis was slowly passed through the first glass column from the bottom at a flow rate of 10 m / h. The liquid flowing out from the top of the first glass column was then slowly pumped into the second glass column from the bottom at a flow rate of 10 m / h, and then the process was repeated in the third glass column. The total hydraulic residence time of the reaction solution in the glass column was 3 hours.

[0063] S3. The liquid that flows out after ion exchange is evaporated, concentrated and crystallized. The solid obtained after crystallization is a mixture of hypophosphorous acid and sodium hypophosphorous acid.

[0064] S4, Impurity Removal

[0065] Anhydrous diethyl ether is prepared by slowly adding metallic sodium to industrial diethyl ether under low-temperature conditions and then drying the ether.

[0066] Anhydrous diethyl ether is added to the solid crystals and the two are stirred and mixed until no solid increases, forming a hypophosphite-diethyl ether solution and a precipitate. The precipitate is removed by filtration.

[0067] The hypophosphoric acid-ethyl ether solution was repeatedly washed and the ether was removed by vacuum distillation. Finally, the solution was evaporated and concentrated to obtain high-purity hypophosphoric acid.

[0068] The products of each step can be sampled and the hypophosphite content can be determined using an automatic potentiometer. The results are shown in Table 1.

[0069] Example 2

[0070] This embodiment is based on the preparation of high-purity hypophosphite from sodium hypophosphite. The difference between this embodiment and the method in Example 1 is that the resin is activated in the S2 ion exchange reaction. The resin activation step in this embodiment is as follows: H-type cation exchange resin is immersed in 0.5 mol / L hypophosphite solution, the container is sealed, and microwave heated to 80°C for 3 hours. After cleaning and drying, H-type modified resin is obtained.

[0071] The remaining steps and parameters are the same as in Example 1. Samples of the products from each step were taken, and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0072] Example 3

[0073] This embodiment is based on the preparation of high-purity hypophosphite using sodium hypophosphite. The difference between this embodiment and Example 2 lies in the resin activation in the S2 ion exchange reaction. In this embodiment, the resin activation step is as follows: H-type cation exchange resin is immersed in a 0.5 mol / L hypophosphite solution, the container is sealed, and microwave-heated to 100°C for 1.7 h. After cleaning and drying, H-type modified resin is obtained.

[0074] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0075] Example 4

[0076] This embodiment is based on the preparation of high-purity hypophosphite using sodium hypophosphite. The difference between this embodiment and Example 2 lies in the resin activation in the S2 ion exchange reaction. In this embodiment, the resin activation step is as follows: H-type cation exchange resin is immersed in a 0.5 mol / L hypophosphite solution, the container is sealed, and microwave-heated to 120°C for 1 hour. After cleaning and drying, H-type modified resin is obtained.

[0077] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0078] Example 5

[0079] This embodiment is based on the preparation of high-purity hypophosphite from sodium hypophosphite. The difference between this embodiment and the method steps in Embodiment 2 is the S2 ion exchange reaction. In this embodiment, the resin activation step is as follows: two sets of parallel glass columns are set up, and both glass columns are filled with H-type modified resin.

[0080] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0081] Example 6

[0082] This embodiment is based on the preparation of high-purity hypophosphite from sodium hypophosphite. The difference between this embodiment and the method in Example 2 is the S2 ion exchange reaction. In this embodiment, four sets of parallel glass columns are set up, and all glass columns are filled with H-type modified resin.

[0083] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0084] Example 7

[0085] This embodiment is based on the preparation of high-purity hypophosphite from sodium hypophosphite. The difference between this embodiment and the method in Example 2 is the S2 ion exchange reaction. In this embodiment, the flow rate of the reaction solution through the resin is increased so that the total hydraulic residence time is 2 hours.

[0086] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0087] Example 8

[0088] This embodiment is based on the preparation of high-purity hypophosphite from sodium hypophosphite. The difference between this embodiment and the method steps in Example 2 is the S2 ion exchange reaction. In this embodiment, the flow rate of the reaction solution through the resin is reduced so that the total hydraulic residence time is 4 hours.

[0089] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0090] Example 9

[0091] This embodiment is based on the preparation of high-purity hypophosphite from sodium hypophosphite. The difference between this embodiment and Example 2 lies in the S2 ion exchange reaction. In this embodiment, the temperature of the ion exchange reaction is set to 35°C.

[0092] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0093] Example 10

[0094] This embodiment is based on the preparation of high-purity hypophosphite from sodium hypophosphite. The difference between this embodiment and Example 2 lies in the S2 ion exchange reaction. In this embodiment, the temperature of the ion exchange reaction is set to 45°C.

[0095] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0096] Comparative Example 1

[0097] This comparative example is based on the preparation of high-purity hypophosphite using sodium hypophosphite. The difference between this method and Example 1 is that the resin activation occurs during the S2 ion exchange reaction. In this comparative example, the resin activation step is as follows: H-type cation exchange resin is immersed in a 0.5 mol / L hypophosphite solution, the container is sealed, and microwave-heated to 75°C for 3 hours. After cleaning and drying, H-type modified resin is obtained.

[0098] The remaining steps and parameters are the same as in Example 1. Samples of the products from each step were taken, and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0099] Comparative Example 2

[0100] This comparative example is based on the preparation of high-purity hypophosphite using sodium hypophosphite. The method and steps differ from those in Example 2 in that the S2 ion exchange reaction is used. In this comparative example, a set of parallel glass columns are set up, and all glass columns are filled with H-type modified resin. The total amount of resin used in this comparative example is the same as that in Example 2.

[0101] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0102] Comparative Example 3

[0103] This comparative example is based on the preparation of high-purity hypophosphite from sodium hypophosphite. The method and steps differ from those in Example 2 in that the S2 ion exchange reaction is used. In this comparative example, five sets of glass columns are set up in parallel, and all glass columns are filled with H-type modified resin. The total amount of resin filled in this comparative example is the same as that in Example 2.

[0104] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0105] Comparative Example 4

[0106] This comparative example is based on the preparation of high-purity hypophosphite using sodium hypophosphite. The difference between this method and Example 2 lies in the S2 electrodialysis reaction. In this comparative example, a conventional seven-chamber electrodialysis cell is set up. The cells are arranged in the following order from left to right: anode chamber, cation membrane, product chamber, anion membrane, buffer chamber, anion membrane, buffer chamber, anion membrane, raw material chamber, cation membrane, buffer chamber, cation membrane, and cathode chamber.

[0107] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0108] Comparative Example 5

[0109] This comparative example is based on the preparation of high-purity hypophosphite from sodium hypophosphite. The difference between this method and Example 2 is the S2 ion exchange reaction, in which the ion exchange reaction temperature is set to 30°C.

[0110] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0111] Comparative Example 6

[0112] This comparative example is based on the preparation of high-purity hypophosphite from sodium hypophosphite. The difference between this method and Example 2 is the S2 ion exchange reaction, in which the ion exchange reaction temperature is set to 50°C.

[0113] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0114] Comparative Example 7

[0115] This comparative example is based on the preparation of high-purity hypophosphite from sodium hypophosphite. The difference between this method and Example 2 is the S2 ion exchange reaction. In this comparative example, the flow rate of the reaction solution through the resin is increased so that the total hydraulic residence time is 1.5 h.

[0116] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0117] Comparative Example 8

[0118] This comparative example is based on the preparation of high-purity hypophosphite from sodium hypophosphite. The difference between this method and Example 2 is the S2 ion exchange reaction. In this comparative example, the flow rate of the reaction solution through the resin is reduced so that the total hydraulic residence time is 4.5 h.

[0119] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0120] Comparative Example 9

[0121] This comparative example is based on the preparation of high-purity hypophosphite from sodium hypophosphite. The difference between this method and Example 1 is that the S2 ion exchange reaction is used in this comparative example, and an unactivated H-type cation exchange resin is used.

[0122] The remaining steps and parameters are the same as in Example 1. Samples of the products from each step were taken, and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0123] Comparative Example 10

[0124] This comparative example is based on the preparation of high-purity hypophosphite using sodium hypophosphite. The difference between this method and Example 2 is that the electrodialysis reaction step is omitted, and the ion exchange reaction is used directly.

[0125] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0126] Comparative Example 11

[0127] This comparative example is based on the preparation of high-purity hypophosphite using sodium hypophosphite, with steps S1 and S2 interchanged.

[0128] The remaining steps and parameters are the same as in Example 2. Samples of the products from each step were taken and the hypophosphite content was determined using an automatic potentiometer. The results are shown in Table 1.

[0129] The hypophosphite content in the products of different reaction stages in each embodiment and comparative example was measured. The product refers to the solid after concentration and crystallization.

[0130] Specifically, the hypophosphite content of the sample was determined using the DW-100J fully automated potentiometric titration method, and the steps are as follows:

[0131] (1) Use a 100ml beaker, add a magnetic stir bar, accurately weigh the sample M1, add 60ml of water, place it on the stir bar and stir evenly. Set the stir bar speed to 500r / min to form the test solution; M1 is generally selected to be 0.3-0.8g.

[0132] (2) Select the pH composite electrode as the measuring electrode. No reference electrode is needed. Clean the pH composite electrode with a wash bottle, dry it with filter paper, put the pH composite electrode and burette into the solution to be tested, tighten the electrode holder screws, and fix the electrode and burette.

[0133] (3) The concentration of the sodium hydroxide standard titration solution is C2 mol / L. The titration parameter is set to automatic endpoint potentiometric titration. The method constant is set to the coefficient of molar mass correlation of hypophosphite, which is 65.99. The sample concentration unit is set to percentage concentration.

[0134] (4) Set the initial volume to 8 ml, the interval volume to 0.001 ml, enter the sample weight, click confirm, and start titration.

[0135] (5) Based on the potential jump point, the instrument automatically determines the titration endpoint, automatically reads the titration volume V2 (ml), and automatically calculates the hypophosphite content in the test sample as 50.12532%.

[0136] During the titration process, hypophosphoric acid reacts with sodium hydroxide: H3PO2 + NaOH = NaH2PO2 + H2O. Therefore, the hypophosphoric acid content in the sample, M (g), is calculated as C2 * V2 * 65.99 / 1000, and the hypophosphoric acid purity, K (%), is calculated as 100 * M / M1.

[0137] Table 1

[0138]

[0139] Note: Product yield is calculated based on the molar amount of sodium hypophosphite.

[0140] As shown in Table 1, the purity of hypophosphite after purification of the products in each example and comparative example can be seen from the results. It can be seen that by using diethyl ether as a solvent, hypophosphite and sodium hypophosphite can be separated to obtain high-purity hypophosphite. However, the yield of the products varies greatly because the yield of hypophosphite obtained by electrodialysis and ion exchange in the preceding steps is different.

[0141] A comparison of Examples 1 and 2 shows that the modified resin prepared by synergistic microwave treatment during the activation of the H-type cation exchange resin has a higher ion exchange efficiency than the resin without synergistic microwave treatment. A comparison between Example 1 and Comparative Example 9 shows that the ion exchange efficiency of the H-type cation exchange resin after activation with hypophosphorous acid is significantly better than that of the unactivated resin.

[0142] As can be seen from Examples 2 to 4, within the microwave activation temperature range of 80–120°C, the resin's exchange efficiency for sodium ions increases with increasing temperature, thus enhancing the H-type ion exchange resin's ability to exchange sodium ions for H+. +The affinity of the resin increases the purity of hypophosphoric acid obtained after the ion exchange reaction. When the temperature exceeds 120°C, its modification effect on the resin is not significant, and when the temperature exceeds 130°C, hypophosphoric acid will undergo a disproportionation reaction. Comparing Comparative Example 1 and Example 2, it can be seen that at a microwave activation temperature below 80°C, its effect is not much different from the activation effect of Example 1 without microwave. Therefore, the microwave temperature of 80-120°C is the most suitable.

[0143] A comparison of Examples 1, 5-6, and Comparative Examples 2-3 shows that when using ion exchange resin glass columns arranged in parallel with 2 to 4 stages, the ion exchange efficiency increases with the increase of the number of stages, and the purity of the obtained hypophosphoric acid increases. Comparative Example 2, which uses a single ion exchange resin, has a much lower efficiency than the multi-stage parallel arrangement. When the number of stages increases to 5, it can be seen that the synergistic effect is not obvious.

[0144] As can be seen from Example 2 and Comparative Example 4, the hypophosphite produced by the seven-chamber concentric circle electrodialysis cell of the present invention is superior to that of the conventional square-distributed seven-chamber electrodialysis cell, and it occupies a smaller area.

[0145] A comparison of Examples 2, 9-10, and Comparative Examples 5-6 shows that the ion exchange temperature has a certain impact on the sodium ion replacement efficiency. Increased temperature is beneficial for the resin's replacement of sodium and hydrogen ions. Higher temperatures intensify ion migration in the solution phase, reduce water viscosity and the thickness of the liquid retention layer around the resin, decrease mass transfer resistance at the resin boundary layer, and increase the rate of ion diffusion. However, when the temperature rises above 45°C, the sodium ion replacement efficiency decreases. This is because the replacement in ion exchange resins is a reversible reaction; at excessively high temperatures, some sodium ions may undergo reverse replacement, leading to a slight decrease in the purity of the final hypophosphoric acid.

[0146] A comparison of Examples 2, 7-8, and Comparative Examples 7-8 shows that in the ion exchange reaction, the efficiency of sodium ion replacement increases with the increase of hydraulic residence time, but the increase is not significant after 4 hours.

[0147] As can be seen from the comparison between Example 2 and Comparative Example 10, the yield of hypophosphoric acid prepared by ion exchange reaction is relatively low, but it is better than conventional ion exchange reaction. The replacement efficiency of existing H-type ion exchange resin is about 50%.

[0148] A comparison of Example 2 and Comparative Example 11 shows that the yield of hypophosphite prepared by first undergoing ion exchange followed by electrodialysis is lower than that prepared by first undergoing electrodialysis followed by ion exchange. This is because the ion exchange reaction converts a portion of the sodium hypophosphite into hypophosphite, resulting in a decrease in the pH of the raw material, making it moderately acidic. In this state, electrodialysis reduces the selective permeability of the ion exchange membrane, thereby decreasing the yield of hypophosphite.

[0149] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing high-purity hypophosphite based on sodium hypophosphite, characterized in that, The method includes the following steps: The sodium hypophosphite solution was subjected to electrodialysis reaction based on a multi-chamber concentric electrodialysis cell, in which hypophosphite ions and hydrogen ions synthesized hypophosphite. The solution after electrodialysis is passed sequentially through at least two parallel glass columns at a set flow rate. The glass columns are filled with H-type modified resin to achieve ion exchange reaction. The ion exchange reaction temperature is set to 35~45℃. The total hydraulic residence time of the solution in the H-type modified resin is 2~4h. The liquid that flows out after ion exchange is evaporated, concentrated, and crystallized. In a sealed environment, the crystalline solid is stirred and mixed with diethyl ether. After physical separation, the hypophosphorous acid-diethyl ether liquid is repeatedly washed and the diethyl ether is removed by vacuum distillation. Finally, it is evaporated and concentrated to obtain high-purity hypophosphorous acid. The multi-chamber concentric circle electrodialysis cell has a central cylinder as the raw material chamber, and at least two sets of acid-grade buffer chambers and one set of alkali-grade buffer chambers on the periphery. The electrodialysis cell includes a central raw material chamber, functional chambers distributed circumferentially along the outer edge of the raw material chamber, and functional chambers including an anode chamber with an internal anode electrode, a cathode chamber with an internal cathode electrode, and a product chamber, acid-grade buffer chamber, and alkali-grade buffer chamber arranged sequentially around the anode and cathode chambers. The anode chamber electrolyzes water to produce hydrogen ions and oxygen. Hydrogen ions (H+)... + Water enters the product chamber through the cation exchange membrane; in the cathode chamber, water is electrolyzed to produce hydroxide ions (OH-). - And hydrogen gas; the sodium hypophosphite solution located in the raw material chamber achieves the separation and migration of anions and cations under the action of anion exchange membranes and cation exchange membranes, wherein hypophosphite (H2PO2) is separated. - The product chamber is formed by sequentially passing through at least two acid-grade buffer chambers via an anion exchange membrane and reacting with hydrogen ions to synthesize hypophosphoric acid; sodium ions (Na+) + The material flows through the cation exchange membrane into the alkali buffer chamber and then into the cathode chamber, where it reacts with hydroxide ions to form sodium hydroxide. The anode chamber and cathode chamber are physically separated by a partition. The raw material chamber is separated from a set of acid buffer chambers and a set of alkali buffer chambers by anion exchange membranes and cation exchange membranes, respectively. The raw material chamber is physically separated from other functional chambers by partitions. Adjacent acid buffer chambers and alkali buffer chambers are physically separated by partitions. The anode chamber and product chamber, and the cathode chamber and alkali buffer chamber are separated by cation exchange membranes. The two sets of acid buffer chambers and the product chamber and acid buffer chamber are separated by anion exchange membranes. H-type modified resin is prepared by activating H-type cation exchange resin with hypophosphite solution.

2. The method for preparing high-purity hypophosphite based on sodium hypophosphite according to claim 1, characterized in that, The anion exchange membrane and cation exchange membrane adopt an arc-shaped or wavy structure.

3. The method for preparing high-purity hypophosphite based on sodium hypophosphite according to claim 1, characterized in that, The activation step of the H-type modified resin includes: immersing the H-type cation exchange resin in a hypophosphorous acid solution for 1-3 hours, and then washing and drying to obtain the H-type modified resin.

4. The method for preparing high-purity hypophosphite based on sodium hypophosphite according to claim 3, characterized in that, The activation step involves coupled microwave processing, and the activation environment is sealed.

5. A method for preparing high-purity hypophosphite based on sodium hypophosphite according to claim 3 or 4, characterized in that, The activation temperature is 80~120℃.

6. The method for preparing high-purity hypophosphite based on sodium hypophosphite according to claim 1, characterized in that, Before mixing the crystalline solid with diethyl ether, the diethyl ether is dried to remove moisture.

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