An apparatus for removing arsenic from water by using sodium hypophosphite

Abstract

The application discloses a device for preparing electronic-grade sodium hypophosphite dearsenicated salt sodium salt, and belongs to the technical field of electronic chemical preparation. The device realizes the efficient dispersion of phosphine gas into micron-sized bubbles through a membrane dispersion reaction system, realizes the full and stable reaction of the phosphine gas with sodium hypochlorite solution, guarantees the high efficiency and uniformity of the main synthesis reaction from the source, and provides a composition-stable crude product liquid for subsequent continuous purification. Through a bypass arsenic removal unit integrated in a buffer adjustment system, the on-line circulation oxidation-precipitation-separation of arsenic impurities is realized without interrupting the main synthesis process, and the problem of the interruption of the synthesis route caused by the intermittent arsenic removal in the traditional process is solved. By arranging yellow phosphorus storage tanks in parallel and alternately working, the continuous and stable supply of the raw material yellow phosphorus to the phosphine reaction kettle is realized. The device ensures the long-term continuous and stable operation of the synthesis route and the high consistency of product batches, and is particularly suitable for the large-scale continuous production of electronic-grade sodium hypophosphite.

Description

Technical Field

[0001] This invention relates to the field of high-purity inorganic chemical preparation technology, specifically to an integrated device for the continuous and stable production of electronic-grade high-purity sodium hypophosphite, and for the deep removal of arsenic and sodium salt impurities therein. Background Technology

[0002] With the rapid development of high-tech industries such as semiconductors, flat panel displays, and solar cells, the application scale of wet electronics processes is increasing daily, placing unprecedentedly stringent requirements on the purity and impurity control of key electronic chemicals. Sodium hypophosphite (NaH2PO2), as an indispensable key raw material, is widely used in core processes such as electroless plating, cleaning, etching, and doping. Its purity directly determines the performance, yield, and reliability of the final electronic devices. Currently, electronic-grade sodium hypophosphite not only needs to achieve a main purity of over 99.99% (4N), but also requires strict control over chloride ions, sodium salts, and trace metal impurities such as arsenic (As). The content limits often need to meet ppb or even ppt levels, as any trace impurity can cause device failure or performance degradation. This makes the development of production technologies that combine efficient synthesis and deep purification capabilities a core requirement for industrial upgrading.

[0003] Currently, the mainstream industrial process for producing sodium hypophosphite is still the yellow phosphorus method, which involves reacting yellow phosphorus with sodium hydroxide to produce phosphine (PH3), which then reacts with sodium hypochlorite (NaClO) solution to synthesize sodium hypophosphite. However, this traditional process suffers from a series of long-standing and unresolved defects, the core of which lies in the inherent instability of the synthesis route, severely restricting continuous and high-quality production: First, poor synthesis efficiency and stability: the gas-liquid reaction between phosphine and sodium hypochlorite has low mass transfer efficiency, resulting in incomplete reactions and numerous byproducts, leading to large fluctuations in reaction yield and low and unstable primary purity of the crude product, placing a heavy and variable burden on subsequent purification. Second, the removal of key impurities disrupts production continuity: arsenic impurities associated with the raw material yellow phosphorus are difficult to remove deeply, and traditional intermittent arsenic removal operations must interrupt the main process, making continuous production impossible; simultaneously, the large amount of byproduct salts such as sodium chloride produced in the reaction also relies on intermittent separation, becoming a problematic link in the production process. Finally, the system lacks material balance and circulation design. The separation of synthesis and purification processes, and the failure to effectively reuse by-products such as salt, arsenic-containing waste, and crystallization mother liquor, not only leads to high material consumption and large emissions of waste, but also makes it difficult to maintain a constant material composition (such as electrolyte concentration) in the synthesis system, further affecting the long-term operational stability of upstream processes such as electrolysis and synthesis.

[0004] Therefore, developing a continuous production device that can achieve efficient and stable core gas-liquid reactions, remove impurities online without interrupting the synthesis process, and simultaneously realize the internal circulation of key materials is the key to solving the problem of unstable synthesis routes in existing technologies that cannot meet the requirements for continuous and stable production of electronic-grade products. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing sodium hypophosphite synthesis routes, which suffer from low reaction efficiency, production interruptions during purification operations, and system material imbalances, preventing long-term continuous and stable operation. This invention provides a highly integrated device with built-in circulation, enabling continuous and stable production throughout the entire process. It transforms the unstable factors and process interruptions in traditional processes into a continuous flow that can be processed online, thereby ensuring the continuity and operational stability of the entire synthesis route.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] An apparatus for the dearsenic removal of sodium hypophosphite from electronic-grade sodium hypophosphite includes an electrolysis system, a phosphine generation system, a membrane dispersion reaction system, a purification system, an evaporation crystallization system, and a drying system.

[0008] The electrolysis system is used to electrolyze sodium chloride solution to produce high-purity chlorine gas and sodium hydroxide solution, controlling the purity of raw materials from the source, and providing the required oxidant (chlorine gas) and pH adjuster (sodium hydroxide) for the subsequent online arsenic removal process.

[0009] The phosphine generation system is used to gently react yellow phosphorus with a portion of sodium hydroxide under nitrogen protection to generate phosphine gas, which is then purified by distillation. To achieve a continuous and stable supply of yellow phosphorus feedstock and avoid the impact of intermittent feeding on the synthesis process, the system is specially equipped with a continuous yellow phosphorus supply unit consisting of at least two parallel yellow phosphorus storage tanks, which achieves alternating charging and feeding through liquid level interlock control.

[0010] The membrane dispersion reaction system includes a membrane dispersion reaction tower equipped with a microporous distributor. This distributor disperses phosphine gas into microbubbles of 5-30 μm, significantly improving gas-liquid mass transfer efficiency and enabling the main reaction to proceed rapidly, completely, and stably, providing downstream processes with a stable crude product liquid.

[0011] The purification system includes a buffer tank and an integrated bypass arsenic removal unit, which can continuously perform "oxidation-precipitation-filtration" cycle treatment on a portion of the solution without stopping the main process, thereby achieving online removal of arsenic impurities.

[0012] The purification system also includes an electrodialysis desalination unit, which is used to efficiently remove chloride ions and excess sodium ions from the solution. The electrodialysis desalination unit is equipped with a reflux pipeline, which can return the concentrated brine to the electrolysis system for reuse as raw material, forming an internal material circulation system.

[0013] The evaporation crystallization system combines vacuum evaporation concentration with a three-stage temperature-controlled evaporation crystallization system to gradually separate and purify sodium hypophosphite crystals, while simultaneously achieving effective reuse of the mother liquor.

[0014] Furthermore, to achieve the separation and resource utilization of by-product salt, the device is also equipped with a circulating filtration unit. Continuous filtration and backwashing are achieved through valve switching, separating the by-product sodium chloride generated during sodium hypochlorite preparation and returning it to the electrolytic cell for recycling, ensuring the continuity of the sodium hypochlorite preparation process. A device for removing arsenic from electronic-grade sodium hypophosphite can achieve the following beneficial effects: 1. The entire process is continuous and online, fundamentally improving operational stability. By innovatively transforming all traditional intermittent or waste-producing stages, such as arsenic removal, by-product salt separation, electrolyte reuse, and mother liquor recovery, into online processing or closed-loop circulation modes, the equipment has completely eliminated production bottlenecks and achieved truly continuous and stable operation from raw materials to products, minimizing fluctuations in production capacity and product quality.

[0015] 2. The core synthesis reaction is highly efficient and stable, creating constant feed conditions for downstream processes. Membrane-dispersed microbubble technology ensures the high efficiency and stability of the phosphine conversion reaction. The composition and impurity content of the crude product liquid are uniform and controllable, significantly reducing the fluctuating load on subsequent purification stages, which is a prerequisite for the stable operation of the entire route.

[0016] 3. The system has extremely strong internal material circulation and self-balancing capabilities. Byproducts include salt and electrolytes (Na₂O₃). + Cl - The reaction alkali and even the crystallization mother liquor are all efficiently recycled within the system, significantly reducing the consumption of fresh raw materials and the emission of waste. This inherent material circulation and balance mechanism greatly reduces the plant's dependence on external material supply and waste disposal, enhances its anti-interference capabilities, and makes it particularly suitable for long-cycle, large-scale, stable production.

[0017] 4. The product has extremely high purity and excellent batch-to-batch consistency. Thanks to stable front-end synthesis and step-by-step, online deep purification (continuous arsenic removal, electrodialysis desalination, and stepwise crystallization), key impurities such as arsenic, chlorine, and sodium are systematically and deeply removed from the product. The product purity can be stably maintained at over 99.995%, and the content of key impurities is consistently below 1 ppm (As < 0.1 ppm). Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 A schematic diagram of the electronic-grade sodium hypophosphite production apparatus provided in an embodiment of the present invention.

[0019] In the diagram: 1-External sodium chloride solution; 2-First flow control valve; 3-First flow meter; 4-Electrolytic cell; 5-First gas phase valve; 6-Dehydrogenation drying tower; 7-First distillation tower; 8-First heat exchanger; 9-Second gas phase valve; 10-First liquid phase valve; 11-Second flow meter; 12-Second liquid phase valve; 13-Third flow meter; 14-Sodium hypochlorite reactor; 15-Third liquid phase valve; 16-Premixing tank; 17-First temperature detector; 18-Third liquid phase valve; 19-Fourth flow meter; 20-Nitrogen valve; 21-External yellow phosphorus; 22-Fourth liquid phase valve; 23-Fifth flow meter; 2 4-Phosphine reactor; 25-Third gas phase valve; 26-Gas phase feed pump; 27-Second distillation column; 28-Second heat exchanger; 29-Fourth gas phase valve; 30-Membrane dispersion reactor; 31-Microporous distributor; 32-Fifth liquid phase valve; 33-Sixth flow meter; 34-Buffer tank; 35-Liquid phase feed pump; 36-Sixth liquid phase valve; 37-Seventh flow meter; 38-Fifth gas phase valve; 39-pH meter; 40-Conductivity meter; 41-Seventh liquid phase valve; 42-First material pump; 43-Eighth liquid phase valve; 44-Eighth flow meter; 45-Electrodialysis desalination unit; 46-Ninth liquid phase Valves; 47-Second material pump; 48-Vacuum evaporator concentrator; 49-Tenth liquid phase valve; 50-Third material pump; 51-Eleventh liquid phase valve; 52-Fourteenth liquid phase valve; 53-Second and fourth temperature gauges; 54-Twelfth liquid phase valve; 55-Fifteenth liquid phase valve; 56-Third and fourth temperature gauges; 57-Thirteenth liquid phase valve; 58-Sixteenth liquid phase valve; 59-Fourth temperature gauge; 60-Fluidized bed dryer; 61-Sixth gas phase valve; 62-Fifth temperature gauge; 63-Sodium hypophosphatemia storage tank; 64-Fourth material pump; 65-Seventeenth liquid phase valve; 66-Chlorine gas diversion valve; 67 - Buffer tank to oxidation mixer valve, 68-Oxidation mixer, 69-Precipitator dosing valve, 70-Oxidation mixer to tubular reactor valve, 71-Tube reactor, 72-Tube reactor to filter valve, 73-Filter; 74-Filter to buffer tank valve, 75-Yellow phosphorus feed liquid phase pump one, 76-Yellow phosphorus storage tank nitrogen valve one, 77-Yellow phosphorus storage tank discharge liquid phase valve one, 78-Yellow phosphorus feed liquid phase pump two, 79-Yellow phosphorus storage tank nitrogen valve two, 80-Yellow phosphorus storage tank discharge liquid phase valve two; a-Filter one, b-Filter two, c-Filter three, d-Filter four, crystallizer A, crystallizer B and crystallizer C. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but it should not be construed as limiting the scope of protection of the present invention.

[0021] Example 1 like Figure 1 As shown, the present invention provides an apparatus for the dearsenic removal of sodium hypophosphite, comprising an electrolysis system, a phosphine generation system, a membrane dispersion reaction system, a purification system, an evaporation crystallization system, and a drying system. The phosphine generation system includes a yellow phosphorus continuous supply unit, which includes at least two yellow phosphorus storage tanks arranged in parallel. The outlet of each yellow phosphorus storage tank is connected to the phosphine reactor 24 through an independent outlet pipeline and outlet valve. The membrane dispersion reaction system includes a membrane dispersion reaction tower 30, which is equipped with a microporous distributor 31 to disperse phosphine gas into micron-sized bubbles so that it can react with sodium hypochlorite solution to generate crude sodium hypophosphite product liquid. The purification system includes a buffer tank 34 and a bypass arsenic removal unit integrated thereon. The bypass arsenic removal unit includes an oxidation mixer 68, a tubular reactor 71 and a filter 73 connected in sequence, forming a circulating purification branch in parallel with the buffer tank 34, which is used to oxidize-precipitate-filter part of the mixed solution to remove arsenic impurities online. The purified liquid is returned to the buffer tank 34. The purification system also includes an electrodialysis desalination unit for desalting the solution from the buffer tank 34, and is equipped with a reflux pipeline for returning the concentrated brine generated during the electrodialysis process to the electrolysis system for recycling.

[0022] The electrolysis system includes an electrolytic cell 4, the anode outlet of which is sequentially connected to a dehydrogenation drying tower 6 and a first distillation tower 7, and the first distillation tower 7 is connected to a first heat exchanger 8. The cathode outlet of the electrolytic cell 4 is divided into three paths: the first path is connected to the sodium hypochlorite reactor 14, the second path is connected to the premixing tank 16, and the third path is connected to the phosphine reactor 24 in the phosphine generation system. The outlet of the first distillation column 7 is provided with a chlorine gas diversion pipeline, which is connected to the oxidation mixer 68 in the bypass arsenic removal unit through a chlorine gas diversion valve 66.

[0023] Each of the yellow phosphorus storage tanks is equipped with a liquid level detector, which is configured to control each yellow phosphorus storage tank to alternately perform filling and feeding operations. The phosphine generation system further includes a second distillation column 27 and a second heat exchanger 28; the gas phase outlet of the phosphine reactor 24 is sequentially connected to the second distillation column 27 and the membrane dispersion reactor 30; the second distillation column 27 is connected to the second heat exchanger 28.

[0024] The sodium hypochlorite reactor 14 is equipped with a first filter group and a second filter group connected in parallel. The bottom outlet of the sodium hypochlorite reactor 14 is connected in parallel with the inlet of the first filter group and the second filter group through a liquid phase feed pump 35 to form a circulating filtration pipeline. The first filter group includes filter a and filter b connected in series, and the second filter group includes filter c and filter d connected in series; The bottoms of filters 2b and 4d are connected in parallel and then connected to the lower inlet of the electrolytic cell 4 to return the by-product sodium chloride solution separated by the circulating filtration pipeline to the electrolytic cell; The sodium hypochlorite reactor 14 is connected to the premixing tank 16.

[0025] The buffer regulation system includes a buffer tank 34 and a bypass arsenic removal unit, wherein: The buffer tank 34 is provided with a first inlet and a second inlet, which are used to receive liquid phase from the membrane dispersion reaction tower 30 and the phosphine reaction vessel 24, respectively. The bypass arsenic removal unit includes an oxidation mixer 68, a tubular reactor 71, and a filter 73; The bottom of the buffer tank 34 is connected to the inlet of the oxidation mixer 68.

[0026] The oxidation mixer 68 is provided with a chlorine inlet and a precipitant inlet. The chlorine inlet is connected to the chlorine distribution pipeline of the electrolysis system through a valve. The outlet of the oxidation mixer 68 is connected to the inlet of the tubular reactor 71; The outlet of the tubular reactor 71 is connected to the inlet of the filter 73; The clear liquid outlet of the filter 73 is connected to the upper part of the buffer tank 34; The filter 73 is provided with a slag discharge port at the bottom, which is connected to a drain pipe. The drain pipe is equipped with a seventh liquid phase valve 41 and a first material pump 42.

[0027] The liquid phase outlet of the membrane dispersion reaction tower 30 is connected in sequence via pipeline to the buffer tank 34 of the buffer regulation system, the electrodialysis desalination unit 45, the vacuum evaporation concentrator 48, the evaporation crystallization system, and the fluidized bed dryer 60.

[0028] The evaporation crystallization system includes crystallizers A, B, and C connected in series. Each crystallizer is equipped with an independent temperature sensor and discharge valve, namely, eleventh liquid phase valve 51, second and fourth temperature sensor 53, twelfth liquid phase valve 54, third and fourth temperature sensor 56, thirteenth liquid phase valve 57, and fourth temperature sensor 59.

[0029] The fluidized bed dryer 60 is equipped with a nitrogen inlet (a sixth gas phase valve 61 is installed on the nitrogen inlet pipe) and a fifth temperature sensor 62, and its outlet is connected to a sodium hypophosphite storage tank 63.

[0030] The outlet of the vacuum evaporator 48 is connected to the inlet of crystallizers A, B and C connected in series; the electrodialysis desalination unit 45 is also provided with a reflux pipeline, which is connected to the lower inlet of the electrolytic cell 4 through the ninth liquid phase valve 46 and the second material pump 47.

[0031] Its workflow is as follows: The refined sodium chloride solution, after being metered by the first flow control valve 2 and the first flow meter 3, enters the electrolytic cell 4 for electrolysis (corresponding to the rated current density of the electrolytic cell 4 being 2000-4000 A / m³). 2 The electrolysis conditions are: temperature 60-80℃, cell voltage 3-4 V. Chlorine gas is generated at the anode and sequentially passes through a dehydrogenation drying tower 6 to remove impurities, and then through a first distillation tower 7 (equipped with a first heat exchanger 8) for further purification, yielding electronic-grade chlorine gas (purity ≥99.99%). One stream of chlorine gas is diverted through a chlorine gas diversion valve 66 for subsequent arsenic removal oxidation. A sodium hydroxide solution (concentration approximately 28-32 wt%) is generated at the cathode and is divided into three parts.

[0032] The first portion of the sodium hydroxide solution (accounting for 15-25% of the total cathode liquid flow) enters the sodium hypochlorite reactor 14. Simultaneously, electronic-grade chlorine gas is introduced at a molar ratio of 1:1 to 1.2:1 with sodium hydroxide, reacting at a temperature <40℃ to generate a mixture of sodium hypochlorite and sodium chloride. This mixture is distributed as a product liquid into a premixing tank 16; another stream enters a circulating filtration unit consisting of parallel filter groups (a / b, c / d). Continuous filtration and backwashing are achieved through a liquid-phase feed pump 35 and valve switching, separating the by-product sodium chloride solution online and returning it to the lower inlet of the electrolytic cell 4 for recycling. This design ensures the continuity of sodium hypochlorite production and avoids production interruptions caused by intermittent salt removal operations.

[0033] The second portion of the sodium hydroxide solution (accounting for 30-40% of the total cathode solution) enters the premixing tank 16 and is mixed with the sodium hypochlorite product solution. The concentration of available chlorine (calculated as NaClO) in the mixed alkaline solution is controlled at 8-12 wt%, with an excess of sodium hydroxide of 5-15% (molar ratio), to obtain the mixed alkaline solution required for the reaction. The temperature of the premixing tank 16 is controlled at 10-25℃.

[0034] The third part, sodium hydroxide solution, enters the phosphine reactor 24 at a flow rate of 40-50% of the total catholy liquid.

[0035] To achieve a continuous and stable supply of yellow phosphorus, the device is equipped with two parallel yellow phosphorus buffer feeding units (yellow phosphorus storage tank I and yellow phosphorus storage tank II; only one tank is shown in the figure, but those skilled in the art will understand that multiple tanks are used). Initially, yellow phosphorus storage tank I is filled: yellow phosphorus from the yellow phosphorus storage tank enters yellow phosphorus storage tank I through yellow phosphorus feed liquid phase pump 75, and nitrogen gas is introduced into its top (controlled by yellow phosphorus storage tank nitrogen valve 76) to maintain an inert atmosphere and balance the pressure. When the liquid level in yellow phosphorus storage tank I reaches the preset high-high liquid level, the high liquid level gauge sends a signal to close the yellow phosphorus feed liquid phase pump 75 and the valve, completing the filling. At this time, the yellow phosphorus storage tank discharge liquid phase valve 77 of yellow phosphorus storage tank I is opened, and the yellow phosphorus in the tank, under the action of gravity and nitrogen pressure, continuously enters the phosphine reactor 24 through the yellow phosphorus storage tank discharge liquid phase valve 77 and the fifth flow meter 23. When the liquid level in yellow phosphorus storage tank I drops to the preset low level, the low-low level gauge sends a signal to close the yellow phosphorus storage tank discharge liquid phase valve 77, stopping the supply of material to the reactor. Subsequently, the supply switches to yellow phosphorus storage tank II (its operating logic is exactly the same as tank I, controlled by yellow phosphorus feed liquid phase pump 78, yellow phosphorus storage tank nitrogen valve 79, yellow phosphorus storage tank discharge liquid phase valve 80, and the level gauge), while yellow phosphorus storage tank I can begin filling preparations again. This cycle repeats, ensuring that one tank continuously supplies yellow phosphorus to the phosphine reactor 24, completely avoiding process interruptions or fluctuations caused by yellow phosphorus feeding operations.

[0036] Yellow phosphorus and sodium hydroxide (part 3) are reacted in a phosphine reactor 24 at a controlled molar ratio of 1:3.0 to 1:3.5 under nitrogen protection (introduced through nitrogen valve 20) at 80-90℃ and 0.1-0.5MPa, producing phosphine gas and sodium hypophosphite solution. After purification, the phosphine gas is introduced into a membrane dispersion reactor 30 at a molar ratio of 1:1 to 1:1.05 with the available chlorine in the mixed alkaline solution. A microporous distributor 31 inside the reactor disperses the gas into microbubbles with a diameter of 5-30μm. The mixed alkaline solution enters from the side of the top of the reactor and reacts fully with the microbubbles at 25-35℃ to produce a crude sodium hypophosphite solution. The smaller the bubble diameter, the larger the specific surface area, and the faster the gas-liquid mass transfer rate. When the bubble diameter is reduced to 5-30 μm, its specific surface area can reach more than 100 times that of conventional millimeter-sized bubbles, enabling the reaction between phosphine and sodium hypochlorite to be completed in a very short time, effectively suppressing side reactions, and thus significantly improving the selectivity and yield of sodium hypophosphite. If the bubbles are too small (<5 μm), their rising speed in the liquid phase is extremely slow, easily forming "flooding" or local accumulation in the column, which reduces the effective contact efficiency; if the bubbles are too large (>30 μm), the mass transfer area is insufficient, and the reaction is incomplete. Microbubbles of 5-30 μm can maintain a high rising speed to form continuous flow and have a sufficiently large specific surface area, achieving a unity of "highly efficient mass transfer" and "stable flow". This microbubble technology greatly enhances gas-liquid mass transfer, ensuring extremely high reaction rate and stable high conversion rate, producing a stable crude sodium hypophosphite solution, laying a solid foundation for subsequent continuous processing.

[0037] The crude sodium hypophosphite solution after the reaction is discharged from the bottom of the membrane dispersion reactor 30 and enters the buffer tank 34. Simultaneously, the byproduct liquid phase generated in the phosphine reactor 24 also enters the buffer tank 34. The mass ratio of the crude solution from the membrane dispersion reactor to the byproduct liquid from the phosphine reactor is approximately 1:8 to 1:12. The buffer tank 34 is equipped with a pH meter 39 and a conductivity meter 40, and can be protected by nitrogen gas and have its pH fine-tuned to 5.0-5.5.

[0038] The arsenic removal process is carried out continuously in the bypass arsenic removal unit integrated into the buffer tank 34: the solution at the bottom of the buffer tank 34 is drawn out through the buffer tank to the oxidation mixer valve 67 at a flow rate of 5-15% of the total circulation volume and enters the oxidation mixer 68. Simultaneously, chlorine gas (1.5-2.5 times the theoretical value for oxidizing trivalent arsenic) from the chlorine gas diversion valve 66 is introduced for oxidation. The oxidized liquid is mixed with a precipitant (such as a 10 wt% calcium chloride solution, added in an amount 100 times the molar amount of arsenic) in the tubular reactor 71, the pH is adjusted to 9-11 to form a co-precipitate, and finally separated by the filter 73. The purified liquid returns to the upper part of the buffer tank, and the arsenic-containing filter cake is discharged offline.

[0039] The purified solution in buffer tank 34 enters electrodialysis desalination unit 45 for further removal of Cl.- Excess Na + Impurity ions. The concentrated brine (rich in NaCl and NaOH) produced by electrodialysis is returned to the electrolytic cell 4 for recycling through the ninth liquid phase valve 46 and the second material pump 47, forming an electrolyte closed loop with sodium chloride as the main component, dynamically maintaining the system's material balance and operational stability.

[0040] After continuous purification through the aforementioned bypass circulation, the arsenic content in the solution in buffer tank 34 is reduced to an extremely low level. This solution is then transported to the electrodialysis desalination unit 45 via the eighth liquid phase valve 43 and the eighth flow meter 44. In this unit, the concentrated brine (rich in NaCl and NaOH) produced by electrodialysis is returned to the electrolytic cell 4 for recycling via the ninth liquid phase valve 46 and the second material pump 47, forming an electrolyte closed loop dominated by sodium chloride, dynamically maintaining the system's material balance and operational stability.

[0041] The deeply desalinated solution from the electrodialysis desalination unit 45 is concentrated in a vacuum evaporator 48 at 50-65℃ and a vacuum of -0.08 to -0.095 MPa. The concentrate is then sequentially crystallized in a three-stage temperature-controlled crystallizer (crystallizer A: 45-50℃, crystallizer B: 35-40℃, crystallizer C: 25-30℃). The mother liquor from crystallization can be returned to the concentrator for recycling. The wet crystals are dried in a fluidized bed dryer 60 at 60-90℃ under a nitrogen flow for 20-40 minutes to obtain the final electronic-grade sodium hypophosphite product.

[0042] In Example 1, under this continuous and stable operating mode, the device achieved a long-term operation cycle of over 500 hours. During this period, all system parameters remained stable, and there was no need to shut down the system for operations such as arsenic removal and desalination. The purity of the final product remained consistently between 99.998% and 99.999%, with chloride ion content consistently <0.1 ppm, arsenic content consistently <0.01 ppm, and other cations such as Mg... 2+ Al 3+ K + Ca 2+ Cr 3+ Mn 6+ Co 2+ Fe 3+ Ni 2+ Cu 2+ Zn 2+ Ti 4+ Pb 2+ All were controlled below 20 ppb; other anions such as SO42- 2- COO - NO3 - PO4 3-All values ​​were controlled below 20 ppb. This fully demonstrates that the integrated synthesis and purification route constructed by the device of this invention has excellent long-term operational stability, outstanding product consistency, and significant resource and environmental benefits, fully meeting the requirements for large-scale industrial production of high-end electronic chemicals.

Claims

1. An apparatus for removing arsenic salts from electronic-grade sodium hypophosphite, characterized in that, It includes an electrolysis system, a phosphine generation system, a membrane dispersion reaction system, a purification system, an evaporation crystallization system, and a drying system. The electrolysis system includes an electrolytic cell, the cathode outlet of which is divided into three paths: the first path is connected to the sodium hypochlorite reactor, the second path is connected to the premixing tank, and the third path is connected to the phosphine reactor in the phosphine generation system. The phosphine generation system includes a yellow phosphorus continuous supply unit, which includes at least two yellow phosphorus storage tanks connected in parallel. The outlet of each yellow phosphorus storage tank is connected to the phosphine reactor through an independent outlet pipeline and outlet valve. The gas phase outlet of the phosphine reactor is connected in sequence to a second distillation column and a membrane dispersion reaction column. The membrane dispersion reaction system includes a membrane dispersion reaction tower, which is equipped with a microporous distributor to disperse phosphine gas into micron-sized bubbles so that it can react with sodium hypochlorite solution to produce crude sodium hypophosphite product liquid. The purification system includes a buffer tank and an integrated bypass arsenic removal unit. The buffer tank is provided with a first inlet and a second inlet, which are respectively connected to the outlets of the membrane dispersion reaction tower and the phosphine reactor, and are used to receive the liquid phase from the membrane dispersion reaction tower and the phosphine reactor, respectively. The bypass arsenic removal unit includes an oxidation mixer, a tubular reactor, and a filter connected in sequence, forming a circulating purification branch in parallel with the buffer tank. It is used to oxidize, precipitate, and filter part of the mixed solution to remove arsenic impurities online, and the purified liquid is returned to the buffer tank. The liquid phase outlet of the buffer tank is connected in sequence to the electrodialysis desalination unit, the vacuum evaporator, the evaporation crystallization system, and the drying system via pipelines; The purification system includes an electrodialysis desalination unit for desalting the solution from the buffer tank, and is equipped with a reflux line for returning the concentrated brine generated during the electrodialysis process to the electrolysis system for recycling. The evaporation crystallization system includes crystallizer A, crystallizer B and crystallizer C connected in series. Each crystallizer is equipped with an independent temperature sensor and a discharge valve. The drying system includes a fluidized bed dryer, which is equipped with a nitrogen inlet and a temperature detector, and its outlet is connected to a sodium hypophosphite storage tank.

2. The apparatus according to claim 1, characterized in that: The anode outlet of the electrolytic cell is sequentially connected to a dehydrogenation drying tower and a first distillation tower, and the first distillation tower is connected to a first heat exchanger; the outlet of the first distillation tower is provided with a chlorine gas split pipeline, which is connected to the oxidation mixer in the bypass arsenic removal unit through a valve.

3. The apparatus according to claim 1, characterized in that: All yellow phosphorus storage tanks are equipped with level detectors, which are configured to control the alternating filling and feeding operations of each yellow phosphorus storage tank. The phosphine generation system also includes a second distillation column and a second heat exchanger; the second distillation column is connected to the second heat exchanger.

4. The apparatus according to claim 2, characterized in that: The sodium hypochlorite reactor is equipped with a first filter group and a second filter group connected in parallel. The bottom outlet of the sodium hypochlorite reactor is connected in parallel with the inlet of the first and second filter groups via a liquid phase feed pump to form a circulating filtration pipeline. The first filter group includes filter a and filter b connected in series; the second filter group includes filter c and filter d connected in series. The bottoms of filters 2b and 4d are connected in parallel and then connected to the lower inlet of the electrolytic cell to return the by-product sodium chloride solution separated by the circulating filtration pipeline to the electrolytic cell; The sodium hypochlorite reactor is connected to the premixing tank.

5. The apparatus according to claim 1, characterized in that: The bottom of the buffer tank is connected to the inlet of the oxidation mixer.

6. The apparatus according to claim 5, characterized in that: The oxidation mixer is equipped with a chlorine inlet and a precipitant inlet, and the chlorine inlet is connected to the chlorine distribution pipeline of the electrolysis system through a valve; The outlet of the oxidation mixer is connected to the inlet of the tubular reactor; The outlet of the tubular reactor is connected to the inlet of the filter; The filter's clear liquid outlet is connected to the top of the buffer tank; The filter is provided with a slag discharge port at the bottom, which is connected to a drain pipe. The drain pipe is equipped with a seventh liquid phase valve and a first material pump.

7. The apparatus according to claim 1, characterized in that: The outlet of the vacuum evaporator is connected to the inlet of crystallizers A, B and C connected in series; the electrodialysis desalination unit is also equipped with a reflux pipeline, which is connected to the lower inlet of the electrolytic cell through valves and a material pump.

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