Treatment process of by-product sodium hypophosphite in phosphorane preparation process

Abstract

The invention provides a treatment process of a byproduct sodium hypophosphite in a phosphorane preparation process, and aims to efficiently remove impurities and prepare a high-purity hypophosphorous acid product. The process comprises the following steps: carrying out small-volume sampling on reaction mother liquor, introducing carbon dioxide gas, and drawing an acidification curve of pH and conductivity; according to the plateau phase of an acidification curve, the CO2 flow rate and the pH value are controlled, step-by-step selective precipitation of impurities such as PO4 < 3->, HPO4 < 2->, Fe < 3 + >, AsO4 < 3-> and S < 2-> is achieved, and loss of a target component H2PO4 < 2-> is avoided; calcium hydroxide turbid liquid is introduced at a proper time to supplement Ca < 2 + > and promote efficient removal of phosphorus, arsenic and sulfur impurities; and subsequently removing excessive Na < + > and Ca < 2 + > through cation exchange, and concentrating to obtain a hypophosphorous acid product with the purity of more than or equal to 99.5%. The method is accurate in process control, thorough in impurity removal and good in repeatability and industrial adaptability, and the resource utilization efficiency of by-products and the added value of products are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hypophosphorous acid preparation, and particularly relates to a treatment process of by-product sodium hypophosphite in phosphine preparation process. BACKGROUND

[0002] Hypophosphorous acid has a wide range of applications and excellent reducing property, and is widely used in chemical electroplating, pharmaceutical and chemical industry, resin coating, ink, water treatment and other fields, and can be used as a reducing agent, an anti-oxidation color reducing agent, an anti-ultraviolet additive and the like; in addition, it can also be used as an intermediate to prepare hypophosphite compounds such as calcium hypophosphite, magnesium hypophosphite, aluminum hypophosphite, ammonium hypophosphite, nickel hypophosphite and the like; and has important value in the agricultural, pharmaceutical and electronic industries.

[0003] In the process of preparing phosphine (PH3) by using white phosphorus and strong alkali as raw materials, sodium hypophosphite (NaH3PO2) is often produced as a by-product in the reaction system, and may be mixed with unreacted NaOH, sodium phosphite (Na2HPO3), sodium phosphate (Na3PO4), metal ion impurities (such as Ca 2+ , Fe 3+ ), and sulfide, arsenate and other impurities. In the prior art, barium hypophosphite is usually added to the by-product solution to remove sodium phosphite, but the impurities caused by other side reactions, raw material impurities and environmental oxidation during the reaction are not considered, resulting in too low purity of the intermediate product sodium hypophosphite, and further limiting the resource recycling rate of the by-product sodium hypophosphite.

[0004] At present, there is still a lack of quantitative and accurate removal means for these impurities, which limits the purification and recycling of the by-product sodium hypophosphite in the preparation of phosphine, and it is urgent to develop an efficient treatment process to improve the resource utilization rate and product purity. SUMMARY

[0005] The present application aims to provide a treatment process for the by-product sodium hypophosphite in the preparation of phosphine, to at least solve the problem of how to quantitatively, efficiently and accurately remove impurities from the by-product sodium hypophosphite solution in the preparation of phosphine, maximize the retention of the target product sodium hypophosphite, realize resource utilization and ensure product purity.

[0006] The present application provides a treatment process for the by-product sodium hypophosphite in the preparation of phosphine, which comprises the following steps: S100. Taking the reaction mother liquor as a sample, carbon dioxide gas is introduced into the sample, and an acidification curve of pH and conductivity is drawn; S200. An acidification process is formulated according to the acidification curve, the pH of the reaction mother liquor is adjusted, and a high-purity sodium hypophosphite solution is prepared; S300. The high-purity sodium hypophosphite solution is subjected to ion exchange through a resin tower, and a dilute hypophosphorous acid solution is prepared; S400. The dilute hypophosphorous acid is concentrated to obtain a hypophosphorous acid product; The reaction mother liquor is a by-product solution containing sodium hypophosphite and impurity components generated during the preparation of phosphine using phosphorus element and strong base as raw materials.

[0007] Preferably, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau 1, wherein the pH value of plateau 1 is 10.2-11.1 and the conductivity value is 20.5-21.5 mS / cm; and no obvious precipitation is generated in plateau 1.

[0008] Preferably, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau 2, wherein the pH value of plateau 2 is 9.6-10.1 and the conductivity value is 19.8-20.5 mS / cm; CaS and CaCO3 are precipitated in plateau 2.

[0009] Preferably, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau 3, wherein the pH value of plateau 3 is 8.5-9.5 and the conductivity value is 17.5-19.5 mS / cm; the main precipitates of plateau 3 are Ca3(PO4)2 and CaCO3.

[0010] Preferably, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau 4, wherein the pH value of plateau 4 is 5.2-6.9 and the conductivity value is 15.8-17.5 mS / cm; the main precipitate of plateau 4 is CaHPO3.

[0011] Preferably, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau 5, wherein the pH value of plateau 5 is 4.0-4.5 and the conductivity value is 13.8-15.2 mS / cm; the main precipitate of plateau 5 is FeAsO4.

[0012] Preferably, calcium hydroxide suspension is added to the reaction system.

[0013] Preferably, after the pH reaches a plateau of 5, the introduction of CO2 is stopped, and a Ca(OH)2 suspension is added dropwise to the system until no precipitation is produced in the reaction system.

[0014] Preferably, the flow rate of CO2 is 0.04-0.20 L / min.

[0015] Preferably, the resin tower is filled with macroporous strongly acidic cation exchange resin, the resin functional group is sulfonic acid group, the resin type is sodium type or hydrogen type, and the operating flow rate is controlled at 6-9m / h.

[0016] Beneficial effects: The present invention provides a treatment process for sodium hypophosphite, a by-product produced during the preparation of phosphine. The present invention involves sampling a small volume of the reaction mother liquor before large-volume treatment, introducing CO2 to perform an acidification test, monitoring pH, conductivity, and precipitation in real time, drawing an acidification curve, and determining an optimal control window based on precipitation characteristics of each plateau. This provides a scientific basis and precise control parameters for the acidification treatment of large-volume reaction mother liquor, thereby significantly improving the selectivity and repeatability of impurity removal.

[0017] The present invention introduces CO2 gas for acidification, which can accurately control the precipitation window of various impurity ions at different pH plateaus and selectively remove PO4 in the solution. 3- 、HPO3 2- 、Fe 3+ 、AsO4 3- 、S 2- Plasma impurities while ensuring the target component H2PO2 - It exists stably throughout the entire process and does not participate in precipitation, oxidation, or decomposition reactions; combined with calcium hydroxide suspension as a calcium source, it can provide Ca without significantly increasing pH. 2+ , promote the directional precipitation of phosphorus, arsenic and sulfur impurities, and further combine cation exchange to remove excess Ca 2+ , and Na + Dilute hypophosphorous acid is prepared, and finally after a reduced pressure concentration step, the purity of the obtained hypophosphorous acid product can reach more than 99.5%, which significantly improves the resource utilization efficiency and product added value of the by-product and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 is the acidification curve of Example 1; Figure 2 is the acidification curve of Example 2; Figure 3 is the acidification curve of Example 3; Figure 4 This is a process flow chart for treating sodium hypophosphite, a by-product in the preparation of phosphine. DETAILED DESCRIPTION

[0020] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not considered critical for the purposes of the application. Any numerical range recited herein is intended to include all sub-ranges of the same numbers (i.e., every subset of numbers within the indicated range). For numerical ranges expressed in lower and upper limits, any numerical value falling within these limits is specifically contemplated as the maximum and minimum values.

[0021] The application will be further described with reference to the drawings and examples, but the scope of the application is not limited to the content.

[0022] The application provides a treatment process of sodium hypophosphite, a by-product in a phosphine preparation process, comprising the following steps: S100. Taking the reaction mother liquor, measuring the initial pH and conductivity; S101. Passing carbon dioxide gas into the reaction mother liquor to adjust the pH of the solution, and measuring the pH and conductivity of the solution in real time; and drawing an acidification curve according to the pH and conductivity; S200. Formulating an acidification process according to the acidification curve, adjusting the pH of the reaction mother liquor, and obtaining a high-purity sodium hypophosphite solution after filtration; S300. The high-purity sodium hypophosphite solution is subjected to ion exchange through a resin tower to prepare a dilute hypophosphorous acid solution; S400. The dilute hypophosphorous acid is concentrated to prepare a hypophosphorous acid product; The reaction mother liquor is a by-product solution containing sodium hypophosphite and impurities generated in the process of preparing phosphine from elemental phosphorus and a strong base.

[0023] In some preferred embodiments, carbon dioxide gas is continuously passed into the sample, the pH reaches a plateau 1, the pH value of the plateau 1 is 10.2-11.1, and the conductivity value is 20.5-21.5 mS / cm; no obvious precipitate is generated in the plateau 1. The pH value of the plateau 1 can be 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11.0, or 11.1.

[0024] In some preferred embodiments, carbon dioxide gas is continuously passed into the sample, the pH reaches a plateau 2, the pH value of the plateau 2 is 9.6-10.1, and the conductivity value is 19.8-20.5 mS / cm; CaS and CaCO3 precipitates are generated in the plateau 2. The pH value of the plateau 2 can be 9.6, 9.7, 9.8, 9.9, 10.0, or 10.1.

[0025] In some preferred embodiments, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau 3, wherein the pH value of plateau 3 is 8.5-9.5 and the conductivity value is 17.5-19.5 mS / cm; the main precipitates of plateau 3 are Ca3(PO4)2 and CaCO3. The pH value of plateau 3 can be 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, or 9.5.

[0026] In some preferred embodiments, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau 4, wherein the pH value of plateau 4 is 5.2-6.9, and the conductivity value is 15.8-17.5 mS / cm; the main precipitate of plateau 4 is CaHPO3. The pH value of plateau 4 can be 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, or 6.9.

[0027] In some preferred embodiments, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau 5, wherein the pH value of plateau 5 is 4.0-4.5 and the conductivity value is 13.8-15.2 mS / cm; the main precipitate of plateau 5 is FeAsO4. The pH value of plateau 5 can be 4.0, 4.1, 4.2, 4.3, 4.4, or 4.5.

[0028] In the present invention, the reaction mother liquor is derived from the reaction system of preparing phosphine with white phosphorus and strong base as raw materials. It is a by-product solution produced in the reaction process, mainly containing sodium hypophosphite and a certain amount of impurity components, including unreacted NaOH, sodium phosphite (Na2HPO3), sodium phosphate (Na3PO4), metal ion impurities (such as Ca 2+ 、Fe 3+ ) and impurities such as sulfide and arsenate. Treating the reaction mother liquor involved in the present invention can reduce the waste liquid discharge in the phosphine preparation process and greatly improve the resource utilization rate. In addition, the reaction mother liquor is formed under the reaction conditions of phosphine, so the components of the mixed solution are clear and the by-products are controllable. Compared with the conventional phosphate mixed solution, its composition has a higher concentration of sodium hypophosphite, and the types of impurities are relatively fixed and show a certain regularity. There is no interference from other complex components, and they can be removed in a targeted manner. This is also the basic condition of the by-product sodium hypophosphite treatment process system involved in the present invention. At the same time, the chemical environment formed in the phosphine preparation reaction process is conducive to subsequent acidification, ion exchange and concentration treatment processes.

[0029] The present invention samples and tests the reaction mother liquor, draws a pH-conductivity acidification curve, and then formulates a targeted acidification process based on the acidification curve, thereby achieving efficient separation and control of impurity ions in a large volume of mother liquor. Unlike the traditional method of removing impurities by relying on experience to set a fixed pH point or the amount of acid drop, the present invention is based on the specific physical and chemical properties of any batch of reaction mother liquor, and reflects the reaction process and solubility changes of various components in the system by detecting the changing trends of pH and conductivity, thereby obtaining the conditions for precipitation of impurities. During the acidification process, as the pH gradually decreases, impurities precipitate in a specific pH range. The degree of impurity removal can be determined based on the changes in pH and conductivity. The treatment process adopted by the present invention reduces acid loss and treatment load by targetedly controlling the acidification path, and also avoids the waste of subsequent ion exchange resin adsorption capacity and the risk of poisoning. The present invention is suitable for the treatment of by-product solutions with strong batch variability and complex components.

[0030] The present invention selectively removes impurities and phosphorus by-products by acidifying the reaction mother liquor, thereby significantly improving the chemical purity of the raw material. The sodium hypophosphite solution after the impurities are removed has high purity, which can effectively reduce the probability of side reactions in subsequent reactions, thereby further improving the purity of hypophosphorous acid.

[0031] In addition, during the acidification process, the temperature is maintained at 0-25°C throughout the process to ensure that the precipitate can be precipitated. At the same time, sodium hypophosphite can exist stably under low temperature conditions.

[0032] In the present invention, an acidification process for treating large volumes of mother liquor is developed based on the acidification curve obtained from the acidification test. The high-purity sodium hypophosphite solution obtained after solid-liquid separation is further treated in a resin tower, and finally the hypophosphorous acid product is produced through vacuum concentration technology. The processing pathway provided by the present invention is clear and resource-efficient, resolving the technical difficulties of traditional byproduct solutions with complex impurities and difficult processing. This allows the previously complex byproduct solution to be converted into a high-value-added raw material, achieving the recycling of sodium hypophosphite resources.

[0033] In some preferred embodiments, the treatment process of sodium hypophosphite, a by-product in the phosphine preparation process, further comprises a washing liquid recovery process, which specifically comprises: S301 After the ion exchange is completed, the resin in the resin tower is cleaned using a primary wash solution, a secondary wash solution and pure water. in: The first-stage washing liquid is pumped to the resin tower to clean the resin, and the washing liquid is collected in the recovery tank; The washing liquid after cleaning with the secondary washing liquid flows back to the primary washing liquid tank for recycling; After the pure water is washed until the pH value of the liquid is neutral, the washing liquid is returned to the secondary washing liquid tank and used as the subsequent secondary washing liquid.

[0034] Specifically, the primary and secondary washes consist of sodium hypophosphite solutions. After the resin tower completes ion exchange, the primary wash is graded and reused, allowing for recycling and resource utilization of the eluent. Specifically, after ion exchange in the resin tower, the resin in the tower is sequentially cleaned with the primary, secondary, and pure water washes. This wash recovery process effectively removes residual sodium hypophosphite and impurities from the resin. The primary wash, which has a higher sodium hypophosphite concentration, is used for initial cleaning of the resin. The resulting wash is collected in a sodium hypophosphite recovery tank and used to prepare the sodium hypophosphite solution. The secondary wash is primarily used to further elute residual components. The wash is then returned to the primary wash storage tank for the next cycle of the primary wash, maximizing the recovery of any remaining target components. A final rinse step, using pure water, is performed until the effluent pH approaches neutral. The resulting wash is then returned to the secondary wash tank and used as the secondary wash for subsequent steps.

[0035] The washing liquid recovery process adopted by the present invention effectively improves the cleaning efficiency of the resin and realizes the recovery and utilization of sodium hypophosphite through the graded recycling of the washing liquid. Compared with the traditional treatment method of single washing or direct disposal of the washing liquid, the washing liquid recovery process of the present invention reduces the consumption of fresh sodium hypophosphite solution and pure water, and reduces waste liquid discharge.

[0036] In some preferred embodiments, in the treatment process of the present invention, the resin tower is filled with macroporous strongly acidic cation exchange resin, the resin functional group is sulfonic acid group, the resin type is sodium type or hydrogen type, and the operating flow rate is controlled at 6-9m / h.

[0037] Specifically, macroporous resins offer advantages such as large surface area and excellent permeability, providing excellent mass transfer rates and ion exchange efficiency when treating high-concentration, complex ion systems. Sulfonic acid groups are strong acidic cation exchange groups with strong affinity and stability, enabling stable operation over a wide pH range, effectively adsorbing sodium ions from the solution, and ensuring excellent effluent quality. Operating flow rates within the range of 6-9 m / h ensure sufficient contact and reaction time between the resin and the solution, allowing for sufficient ion exchange. Furthermore, a moderate flow rate helps maintain the uniformity and stability of the resin bed, avoiding resin loss, compaction, or bed disturbances caused by excessive flow rates, thereby extending the equipment's operating cycle and reducing maintenance frequency. If the flow rate is too low, the processing capacity per unit time will decrease, affecting output. If the flow rate is too high, the contact time between ions and the resin will decrease, resulting in poor resin exchange efficiency and wasted resources. Therefore, a flow rate within the range of 6-9 m / h is the optimal choice.

[0038] Example 1 A process for treating sodium hypophosphite, a by-product in a phosphine preparation process, comprises the following steps: S100. Take 500 mL of the reaction mother liquor sample and measure the initial pH to be 11.8 and the initial conductivity to be 21.0 mS / cm. S101. Carbon dioxide gas was introduced into the reaction mother liquor at a flow rate of 0.05-0.12 L / min while stirring and monitoring the changes in pH and conductivity in real time while observing whether a precipitate was generated; Key point data during acidification process:

[0039] Plateau 1 corresponds to the initial stage of acidification. At this time, the pH of the reaction mother liquor is relatively high. This is due to the presence of strong alkaline components such as excess NaOH, and the system is in an alkaline environment. The initial pH is usually between 10.2-11.9. The solution contains OH. - with Na + ions, and the conductivity was maintained at a high level (21.0 mS / cm). In this stage, CO2 gas was continuously introduced at a low flow rate (0.05 L / min). CO2 first reacted with water to produce H2CO3, which was partially ionized to produce H + and reacts with OH⁻ in the solution to produce water and HCO3 - , thereby gradually weakening the alkalinity and lowering the pH. + The addition of 2HCO3 caused the pH to drop slightly to about 10.9, but due to the HCO3 generated in the reaction - As well as the original Na + The continuous presence of CO2 in the system increases the total ion concentration of the solution, causing the conductivity to rise slightly from 21.0 mS / cm to 21.5 mS / cm. As CO2 continues to be introduced, a HCO3 - The weak acid buffer system mainly composed of HCO3 - / CO2 buffer pair, effectively suppressing the large fluctuation of pH. - / CO3 2- The ratio is still significantly biased towards HCO3 - , and CO3 2- The concentration did not reach the solubility product threshold for CaCO3 precipitation (Ksp ≈2.8 × 10 -9 ), even if there is a trace amount of Ca in the system 2+ , and no obvious calcium salt precipitation will be formed, so the system remains clear and no obvious precipitation is generated.

[0040] Plateau 2: The pH value of this stage gradually decreases from about 10.1 to 9.9, and calcium salt impurities gradually begin to precipitate. As the amount of CO2 introduced continues to increase, the degree of ionization of the carbonic acid system in the system further deepens, and H2CO3 continuously ionizes to generate HCO3 - , and further generate CO3 under higher pH conditions 2- When the pH drops to between 9.6–10.1, CO3 2- The concentration reaches the same as Ca 2+ The minimum solubility product threshold for the formation of calcium carbonate precipitation is the Ca 2+ Start with CO3 2- At the same time, within this pH range, the soluble sulfide in the system also begins to react with CaCO3 to form a flocculent precipitate. 2+ The reaction generates CaS precipitate. 2+ 、CO3 2- 、S 2- The conductive ions are continuously converted into precipitates, resulting in a gradual decrease in the free ion concentration in the system, a decrease in ion mobility, and a decrease in conductivity from 21.5 mS / cm to approximately 19.9 mS / cm.

[0041] Plateau 3 is the key window for deep ionization of phosphate and efficient precipitation removal. In this pH range, the ionization equilibrium of phosphate tends to be high-charged, especially when pH>8.5. 3- Gradually becomes the dominant ion of phosphorus in the system, while H2PO4 - and HPO4 2- The proportion of low-charge forms decreases rapidly. This change in ionization form greatly improves the 2+ The solubility product of Ca3(PO4)2 is low (Ksp ≈ 1×10 -28 ), the precipitation tendency is very strong in the alkaline to neutral region. In this system, due to the presence of the carbonate buffer system, the pH drops relatively slowly, which is conducive to the crystal development and particle size growth of the precipitated particles, forming Ca3(PO4)2 crystals with stable precipitation structure. In order to further enhance the precipitation efficiency of phosphate, the CO2 ventilation rate is moderately increased to 0.08-0.12 L / min in the third stage of the plateau phase, which accelerates the generation of H2CO3 and releases H + Promote the ionization of phosphoric acid and further promote HPO4 2- To PO4 3- On the other hand, the conversion of Ca 2+ With PO4 3- collision, thereby increasing the precipitation rate and achieving complete precipitation.

[0042] In addition, as CO2 is introduced and pH continues to decrease, the CO3 2- The concentration is still maintained in the precipitation range, so while Ca3(PO4)2 is generated, Ca 2+ Continue with CO3 2- The reaction forms CaCO3 precipitate. The formation of two types of precipitates makes the Ca 2+ and PO4 3- 、CO3 2- The plasma concentration decreased significantly, resulting in a significant decrease in conductivity, from approximately 19.9 mS / cm in plateau 2 to 18.3 mS / cm at the end of plateau 3.

[0043] At plateau stage 4, 50 mL of Ca(OH)2 suspension was added to the reaction to introduce slow-release Ca 2+ This stage is the combination of phosphite and Ca 2+ The key window for the formation of CaHPO3 precipitation is to continue to introduce carbon dioxide and the pH gradually decreases. 2- The concentration increased significantly, and its pK a2 ≈6.7, with slow release of Ca 2+ CaHPO3 precipitate is formed. The reaction is fast in this stage, the precipitate particles gradually become dense, and the conductivity drops rapidly.

[0044] Before this stage, calcium hydroxide suspension is added as a calcium source in order to introduce a slowly released Ca 2+ This is to encourage the unreacted phosphate, phosphite and other anions to form insoluble precipitates. Calcium hydroxide suspension is selected as the calcium source because of its low solubility and ability to slowly release Ca in an acidified environment. 2+ This can avoid local oversaturation or non-selective precipitation caused by instantaneous excessive release. At the same time, the system establishes a stable H2CO3 / HCO3 due to the continuous introduction of CO2. - The buffer system has good pH adjustment ability. When alkaline calcium hydroxide is added, the OH - Although it can partially neutralize H + , but the system will compensate for H by releasing more CO2 to form new H2CO3 + , thereby maintaining the buffer balance and preventing a sharp rise in pH. The synergistic effect of the buffering effect of the carbonate system and the selective supplementation of calcium sources can not only effectively remove phosphorus impurities, but also avoid H2PO2 - Non-selective coprecipitation or oxidation occurs under low pH conditions, which maximizes the retention of the target product.

[0045] Plateau 5, this plateau is mainly used for AsO4 3- At pH = 4.2, Fe 3+ With AsO43- The reaction generates FeAsO4 precipitation. At this time, the CO2 ventilation rate is gradually reduced to 0.03-0.06 L / min, and the pH is controlled to drop steadily to prevent excessive acidity from causing the target product hypophosphorous acid to decompose or oxidize. 3- After the precipitation of ions, the conductivity of the system finally stabilized at 14.5 mS / cm.

[0046] After the pH reaches the plateau 5, stop the CO2 injection to avoid the pH rising too fast, and add Ca(OH)2 suspension to the system until no precipitation is produced. At this time, the residual CO3 in the system 2- or incompletely reacted HCO3 - is completely removed, and the remaining carbonate ions in the system are quickly 2+ Combined, a final round of CaCO3 precipitation is generated.

[0047] In the present invention, the reason for selecting CO2 as a pH regulator is that the carbonate buffer system is controllable and mild, CO2 gradually dissolves in water, and establishes the following equilibrium system:

[0048] When CO2 is continuously introduced, the equilibrium gradually shifts to the right, and the generated H2CO3 slowly releases H + , thereby achieving mild acidification of the alkaline system. Compared with strong acid, this process will not cause pH mutation, and can protect the hypophosphite in the system to prevent it from being oxidized or co-precipitated under low pH conditions. + After the release of NaOH and the neutralization of alkaline components, the pH of the system gradually decreases and enters the appropriate window for the selective precipitation of impurities such as phosphate, phosphite, and arsenate.

[0049] In order to achieve the selective precipitation of impurities, it is necessary to control the Ca 2+ With CO3 2- The concentration ratio is to prevent the generation of large amounts of CaCO3 precipitation after the introduction of CO2 and the premature consumption of calcium source. To this end, the strategy of CO2 introduction and the addition of Ca(OH)2 suspension solution needs to be strictly coordinated and regulated. During the CO2 introduction process, the flow rate of CO2 is controlled to control the H2CO3 and CO3 2- The generation rate of CO3 in the system 2- The concentration is always within a controllable range; at the same time, Ca(OH)2 is added in the form of a low-solubility suspension, which slowly releases Ca 2+ , avoid Ca 2+ The instantaneous excess leads to the violent precipitation of calcium carbonate, thus achieving Ca 2+ The gradual release of arsenic and its selective participation in the subsequent precipitation reactions of phosphorus and arsenic.

[0050] In addition, the carbonate system itself has acid-base buffering properties. When weak alkaline Ca(OH)2 is added, the released OH - First, it is neutralized by H2CO3 to generate HCO3 - , maintaining the pH in a slowly changing range; this prevents the pH of the system from rising significantly during calcium supplementation, thereby avoiding premature coprecipitation of phosphate or H2PO2 - The carbonate buffer acidification and timely calcium source supplementation strategy of the present invention can maintain a stable reaction environment and ensure that Ca 2+ Mainly used with PO4 3- 、HPO3 2- 、AsO4 3- It reacts with impurities such as FePO4, Ca3(PO4)2, FeAsO4, and CaHPO3 to form insoluble precipitates.

[0051] The reaction mother liquor sample after impurities removal is filtered to obtain a high-purity sodium hypophosphite solution.

[0052] According to pH and conductivity, the Figure 1 Acidification curve; S200: Develop an acidification process to adjust the pH of the reaction mother liquor for selective impurity removal. Figure 1 The acidification curve determines the CO2 injection rate and reaction control parameters corresponding to each key pH plateau. Following this process, the pH of the large-volume reaction mother liquor is adjusted, CO2 is introduced in stages, and Ca(OH)2 suspension is added at different pH points to replenish calcium and remove impurities.

[0053] After the acidification is completed, solid-liquid separation is performed, and the precipitate is filtered out to obtain a clear and transparent high-purity sodium hypophosphite solution.

[0054] S300: The high-purity sodium hypophosphite solution in the sodium hypophosphite tank V101 is fed into four-stage series-connected resin towers A, B, C, and D using a sodium hypophosphite feed pump P101. The hypophosphorous acid solution after ion exchange is placed into a dilute hypophosphorous acid tank V102 and then fed to a concentration process via a dilute hypophosphorous acid pump P102 to obtain a finished hypophosphorous acid product.

[0055] S400: Concentrating the diluted hypophosphorous acid to obtain a hypophosphorous acid product.

[0056] Example 2 The steps are the same as in Example 1, except that the acidification curve is different; The initial pH was measured to be 11.6, and the initial conductivity was 20.9 mS / cm; Key point data during acidification process:

[0057] According to pH and conductivity, the Figure 2Acidification curve; Example 3 The steps are the same as in Example 1, except that the acidification curve is different; The initial pH was measured to be 11.9, and the initial conductivity was 21.1 mS / cm; Key point data during acidification process:

[0058] According to pH and conductivity, the Figure 3 Acidification curve; In Example 1-3, the analysis results of the filtrate after sampling and acidification are: PO4 3- 、HPO3 2- 、Fe 3+ 、AsO4 3- 、S 2- The ion concentrations of all impurities were reduced to below the detection limit; total inorganic carbon: <10 mg / L, indicating that the impurity ions had been basically completely precipitated and removed; after ion exchange, the purity of hypophosphorous acid reached ≥99.5 wt%.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for treating sodium hypophosphite, a by-product in the preparation of phosphine, characterized in that: The treatment process comprises the following steps: S100. Take the reaction mother liquor as a sample, introduce carbon dioxide gas into the sample, and draw the acidification curve of pH and conductivity; S200. Formulate an acidification process according to the acidification curve, adjust the pH of the reaction mother liquor to obtain a high-purity sodium hypophosphite solution; S300. The high-purity sodium hypophosphite solution is subjected to ion exchange by a resin tower to obtain a dilute hypophosphorous acid solution; S400. The dilute hypophosphorous acid is concentrated to obtain a hypophosphorous acid product; The reaction mother liquor is a by-product solution containing sodium hypophosphite and impurity components generated during the preparation of phosphine using phosphorus element and strong base as raw materials.

2. The treatment process according to claim 1, characterized in that Carbon dioxide gas was continuously introduced into the sample, and the pH value reached plateau 1. The pH value of plateau 1 was 10.2-11.1, and the conductivity value was 20.5-21.5 mS / cm. No obvious precipitation was generated in plateau 1.

3. The treatment process according to claim 1, characterized in that: Carbon dioxide gas was continuously introduced into the sample until the pH reached plateau 2, wherein the pH value of plateau 2 was 9.6-10.1 and the conductivity value was 19.8-20.5 mS / cm; CaS and CaCO3 were precipitated in plateau 2.

4. The treatment process according to claim 1, characterized in that Carbon dioxide gas was continuously introduced into the sample until the pH reached plateau 3, wherein the pH value of plateau 3 was 8.5-9.5 and the conductivity value was 17.5-19.5 mS / cm; the main precipitates in plateau 3 were Ca3(PO4)2 and CaCO3.

5. The treatment process according to claim 1, characterized in that: Carbon dioxide gas was continuously introduced into the sample, and the pH value reached plateau 4. The pH value of plateau 4 was 5.2-6.9, and the conductivity value was 15.8-17.5 mS / cm. The main precipitate in plateau 4 was CaHPO 3 .

6. The treatment process according to claim 1, characterized in that: Carbon dioxide gas was continuously introduced into the sample, and the pH value reached plateau 5, wherein the pH value of plateau 5 was 4.0-4.5, and the conductivity value was 13.8-15.2 mS / cm; the main precipitate in plateau 5 was FeAsO 4 .

7. The treatment process according to claim 6, characterized in that: After the pH reaches the plateau of 5, the introduction of CO2 is stopped, and a Ca(OH)2 suspension is added dropwise to the system until no precipitation is produced in the reaction system.

8. The treatment process according to any one of claims 1 to 7, characterized in that: Calcium hydroxide suspension was added to the reaction system.

9. The treatment process according to any one of claims 1 to 7, characterized in that: The flow rate of CO2 is 0.04-0.20L / min.

10. The treatment process according to claim 1, characterized in that: The resin tower is filled with macroporous strongly acidic cation exchange resin, the functional group of the resin is sulfonic acid group, the resin type is sodium type or hydrogen type, and the operating flow rate is controlled at 6-9m / h.

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