Synthesis method of high-purity electronic-grade sodium hypophosphite

Abstract

The application discloses a kind of synthesis methods of high-purity electronic grade sodium hypophosphite, dilute phosphine gas is passed into to the mixed solution of sodium hypochlorite and sodium hydroxide that has been pre-cooled with sufficient stirring, and sodium hydroxide is added to carry out reaction;After reaction is completed, filtration, concentration, crystallization, separation are carried out, and the obtained product is purified by resin to obtain high-purity electronic grade sodium hypophosphite product.Compared with the traditional "yellow phosphorus-lime-soda" oxidation-reduction method for preparing industrial grade product and then preparing high-purity electronic grade sodium hypophosphite, the product purification difficulty of the application is low, by using 7N grade ultra-high purity phosphine without any metal impurities, the problem that arsenic, silicon, germanium, nickel, chromium and other metal impurities cannot be completely removed by traditional process can be effectively solved.In addition, the application also has the advantages of effectively solving the problem of three wastes, high recycling rate of by-products, high economy and the like.

Description

Technical Field

[0001] This invention relates to a method for synthesizing sodium hypophosphite, which employs a microchannel reactor to achieve slow and sufficient contact of the reaction raw materials and precisely control the reaction temperature. Specifically, it involves a method for preparing high-purity electronic-grade sodium hypophosphite using high-purity electronic-grade sodium hypochlorite, ultra-high-purity phosphine, and high-purity electronic-grade sodium hydroxide as raw materials. Background Technology

[0002] With the rapid development of semiconductor technology, electroless plating has become a key step in its manufacturing process. It is mainly used to deposit critical metals such as nickel, palladium, gold, and silver to precisely control the electrical properties and microstructure of wafers, meeting the ever-growing demands of information technology. In this process, high-purity sodium hypophosphite plays a crucial auxiliary role, primarily acting as a core reducing agent in electroless plating (especially for nickel, palladium, gold, and silver) to deposit precise, non-magnetic nickel-phosphorus alloy conductive films on chip substrates and other components. Secondly, it acts as a chelating agent and stabilizer in post-wafer cleaning (especially cleaning after chemical mechanical polishing), effectively removing metal contaminants with extremely low corrosiveness.

[0003] Currently, high-purity electronic-grade sodium hypophosphite is mainly obtained by purifying industrial-grade sodium hypophosphite. However, the raw material—industrial-grade sodium hypophosphite prepared using the traditional "yellow phosphorus-lime-soda ash" oxidation-reduction method—inevitably introduces associated metal impurities such as arsenic, silicon, germanium, nickel, and chromium, posing a continuous technical challenge to subsequent purification. Although this industrial preparation process is mature, the resulting product contains a wide variety and high concentration of impurities, making it difficult to directly meet the stringent requirements of the semiconductor industry. Therefore, developing an efficient and stable green production process for high-purity electronic-grade sodium hypophosphite has become a key issue for technological upgrading in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a new method for synthesizing high-purity electronic-grade sodium hypophosphite to solve the problems mentioned in the background above.

[0005] The technical solution of this invention is: a method for synthesizing high-purity electronic-grade sodium hypophosphite, which uses a microchannel reactor to achieve slow and sufficient contact of the reaction raw materials and precisely controls the reaction temperature, including the following steps:

[0006] Diluted phosphine gas and a pre-cooled mixed solution of sodium hypochlorite and sodium hydroxide are continuously fed into a microchannel reactor via a mass flow controller and a precision metering pump, respectively, where a gas-liquid two-phase reaction takes place. After the reaction, the effluent is filtered, concentrated, crystallized, and separated. The resulting product is then purified by resin to obtain high-purity electronic-grade sodium hypophosphite. The process includes the following steps: (1) Raw material pretreatment: Ultra-high purity phosphine gas is diluted with high purity nitrogen to obtain phosphine mixed gas; sodium hypochlorite solution and sodium hydroxide solution are diluted and mixed, and pre-cooled to obtain pre-cooled mixed liquid; (2) Microchannel reaction: The phosphine mixture and the pre-cooled mixture from step (1) are fed into a microchannel reactor for continuous gas-liquid two-phase reaction. The reaction temperature is controlled at -5~0℃ and the pH of the reaction system is maintained at 11-14. (3) Preparation of crude product: After filtering the reaction effluent from step (2), the crude sodium hypophosphite is obtained by concentration, crystallization and separation; (4) Purification: The crude sodium hypophosphite from step (3) is purified by resin and separated by membrane, then recrystallized and dried to obtain high-purity electronic-grade sodium hypophosphite.

[0007] In this process, ultra-high purity phosphine, high purity electronic-grade sodium hypochlorite, and high purity electronic-grade sodium hydroxide react to synthesize sodium hypophosphite, and the purification of the product sodium hypophosphite is carried out. The process route is as follows: PH3+ 2NaClO + NaOH → NaH2PO2+ 2NaCl + H2O.

[0008] The key technology lies in replacing the traditional batch reactor with a microchannel reactor continuous flow reaction system. The microchannel reactor is made of corrosion-resistant Hastelloy, with internal channels having hydraulic diameters in the micrometer range, providing an extremely large specific surface area for efficient heat and mass transfer. Reactants are fed in via precision control equipment: phosphine gas (diluted with high-purity electronic-grade nitrogen) enters at a slow flow rate via a mass flow controller; a mixed solution of sodium hypochlorite and sodium hydroxide, pre-cooled to -5 to 0°C by a cryogenic heat exchanger, is then fed into the microchannel reactor at a corresponding flow rate (adjusted according to the stoichiometric ratio) via a precision metering pump. The two materials are microscopically mixed within the microchannels through a specially designed mixing structure (Y-shaped inlet, internal baffle structure), forming a stable gas-liquid slug flow or annular flow. This significantly increases the gas-liquid contact area, ensuring slow and thorough contact of the reactants and avoiding excessively high local concentrations and violent exothermic reactions.

[0009] The reaction temperature is precisely controlled between -5°C and 0°C by immersing the entire microchannel reactor in a low-temperature constant-temperature circulating bath. Due to the small size and extremely high heat exchange efficiency of the microchannels, the heat of reaction can be rapidly removed, ensuring the reaction proceeds under constant temperature conditions and effectively suppressing side reactions. The reaction residence time is controlled by adjusting the feed flow rate and the microchannel length, allowing the reaction to proceed slowly until completion. The pH of the reaction system must be maintained between 11 and 14, achieved by controlling the excess of sodium hydroxide.

[0010] The reaction effluent is continuously collected and enters subsequent processing steps: it is filtered through a primary filter, concentrated under reduced pressure, cooled and crystallized, and centrifuged to obtain crude sodium hypophosphite. Then, it is passed through an ultra-high purity cation exchange resin to remove metal ions, and an ultra-high purity anion exchange resin to remove chloride ions, hypochlorite ions, and other anions. Reverse osmosis membrane separation technology is then used for further desalination and removal of nanoscale particles. Finally, recrystallization and product packaging are carried out in a Class 100 cleanroom to obtain high-purity electronic-grade sodium hypophosphite.

[0011] Furthermore, the microchannel reactor is made of corrosion-resistant Hastelloy material, with an internal channel hydraulic diameter of 300-500 micrometers, and has a very large specific surface area.

[0012] Furthermore, the molar ratio of the reaction raw materials is PH3: NaClO: NaOH = 1.0-1.2:2.0:1.0-1.2.

[0013] Furthermore, the reaction temperature is controlled at -5 to 0 ℃.

[0014] Furthermore, the ultra-high purity phosphine gas is diluted to 5-10% using high-purity electronic-grade nitrogen; sodium hypochlorite is diluted to an effective chlorine content of 5-10%; sodium hydroxide concentration is diluted to 5-12%; and the molar ratio of sodium hypochlorite to sodium hydroxide is 2:(1.0-1.2).

[0015] Furthermore, the ultra-high purity phosphine gas used has a purity of 7N or higher and contains no metal impurities; the high purity electronic-grade nitrogen gas used has a purity of 5N or higher; and the volume fraction of phosphine in the phosphine mixture is 5-10%.

[0016] Furthermore, before the reaction, the mixed solution of sodium hypochlorite and sodium hydroxide is pre-cooled to a reaction temperature of -5 to 0 °C using a low-temperature heat exchanger.

[0017] Furthermore, the reaction system needs to maintain pH = 11-14, and the reaction should be carried out at -5~0 °C.

[0018] Furthermore, the phosphine mixture is controlled by a mass flow controller to slowly enter the reactor at a flow rate of 300-500 sccm.

[0019] Furthermore, the reduced pressure concentration temperature during the product purification process is controlled at 40-50 ℃.

[0020] Furthermore, the container material used for the product packaging is PFA.

[0021] In step (4), the resin purification process sequentially uses ultra-high purity cation exchange resin and ultra-high purity anion exchange resin. The cation exchange resin removes metal ions, and the anion exchange resin removes chloride ions and hypochlorite anions.

[0022] The ultra-high purity cation exchange resin is a resin with a polymer backbone linked to sulfonic acid groups, and the ultra-high purity anion exchange resin is a resin with a polymer backbone linked to quaternary ammonium groups.

[0023] The membrane separation in step (4) is reverse osmosis membrane separation, which is used for further desalination and removal of nanoscale particles; the recrystallization is carried out in a Class 100 cleanroom using ultrapure water, and the drying is vacuum drying.

[0024] Compared with existing technologies, the microchannel reactor used in this invention has the following advantages: (1) The reactants are mixed at the molecular level in the microchannel, with sufficient and slow contact, and the reaction is stable and controllable, avoiding the risks of uneven gas bubbling, local overheating and by-product generation in traditional batch reaction; (2) Continuous flow operation improves production efficiency and safety, and is especially suitable for the treatment of highly toxic phosphine gas, reducing the amount of hazardous materials in the reactor; (3) Precise temperature control and residence time control help improve product purity and simplify subsequent purification processes when combined with high-purity raw materials. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process flow for synthesizing high-purity electronic-grade sodium hypophosphite as described in this invention. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. The scope of protection of this invention is not limited to the following embodiments. Variations and advantages that can be conceived by those skilled in the art without departing from the spirit and scope of the inventive concept are included in this invention and are protected by the appended claims. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0028] The following description of the embodiments is merely illustrative and is in no way intended to limit the invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0029] Example 1 High-purity electronic-grade sodium hypochlorite (6N grade) is diluted to an effective chlorine content of 8%, and high-purity electronic-grade sodium hydroxide (6N grade) is diluted to a concentration of 9%. The two are mixed uniformly in a molar ratio of NaClO:NaOH = 2:1.05 via a precision metering pump in a premixer. After being precooled to 0 °C by a low-temperature heat exchanger, the mixture is continuously fed into the liquid inlet of the microchannel reactor as a liquid-phase reactant. 7N grade ultra-high-purity phosphine gas, free of metallic impurities, is mixed with 5N grade high-purity electronic-grade nitrogen in a buffer to dilute the phosphine concentration to 8%. The mixed gas is then precooled to 0 °C by a mass flow controller and a gas precooler before being continuously fed into the gas inlet of the microchannel reactor.

[0030] The microchannel reactor is made of Hastelloy alloy and consists of rectangular microchannels with an equivalent diameter of 500 μm and a total length of 10 m. It is designed with a multi-layered parallel structure to increase throughput. The entire reactor is immersed in a low-temperature constant-temperature circulating bath, with the temperature precisely controlled at 0 °C. The total liquid feed flow rate is set to 20 mL / min, and the gas feed flow rate (diluted mixed gas) is set to 50 mL / min (standard conditions) via a mass flow controller. The phosphine flow rate is 4 mL / min, corresponding to a molar ratio of approximately 1.05:2 between phosphine and sodium hypochlorite (accurate metering achieved after flow calibration). The two phases are micro-mixed at the microchannel inlet using a Y-type mixer, forming a stable gas-liquid slug flow with a gas-liquid contact surface area as high as 20,000 m². 2 / m 3 The above ensures that the phosphine gas and sodium hypochlorite solution react slowly and completely at low temperature. The reaction residence time is controlled at approximately 2 minutes by adjusting the channel length and total flow rate to ensure complete reaction. During the reaction, due to the extremely small size and high heat exchange efficiency of the microchannels, the heat of reaction is rapidly removed, and the temperature fluctuation of the entire reaction system is less than ±0.5 ℃, while the pH is maintained at 12-13.

[0031] After the reaction is complete, the effluent is continuously collected in a buffer tank, where residual trace amounts of phosphine are removed by nitrogen purging. Then, insoluble particles are removed through a primary filter, followed by vacuum concentration (50 °C), cooling crystallization, and centrifugation to separate sodium hypophosphite from sodium chloride and water. The separated sodium chloride is then resaturated and adjusted to neutral pH before being recycled in the chlor-alkali industry. The separated crude sodium hypophosphite is fed into a multi-effect ion exchange column, where it is passed sequentially through an ultra-high purity cation exchange resin (consisting of microparticles with a polymer backbone linked to sulfonic acid groups, i.e., ultra-high purity gel-type styrene-divinylbenzene sulfonic acid cation exchange resin (H type)) to remove metal ions, and an ultra-high purity anion exchange resin (consisting of microparticles with a polymer backbone linked to quaternary ammonium groups, i.e., ultra-high purity gel-type styrene-divinylbenzene quaternary ammonium type I strong base anion exchange resin (OH type)) to remove chloride ions, hypochlorite, and other anions. Further desalination and removal of nanoscale particles are then performed using reverse osmosis membrane separation technology. Finally, the product is recrystallized with ultrapure water in a Class 100 cleanroom, centrifuged, and vacuum dried to obtain a high-purity electronic-grade sodium hypophosphite product (yield 92%), which is packaged and stored in PFA bottles. The total cation content in the product is less than 20 ppb, and the anion content is less than 20 ppb, including Mg2+ ions. 2+ Al 3+ K + Ca 2+ Cr 3+ Mn 6+ Co 2+ Fe 3+ As 3+ Ni 2+ Cu 2+ Zn 2+ Ti 4+ Pb 2+ Anions include SO42-. 2- Cl - COO - NO3 - PO4 3- .

[0032] Example 2 Using the scheme of Example 1, if the raw materials are not pre-cooled and are directly fed into a microchannel reactor at 0 °C for reaction, the yield of high-purity electronic-grade sodium hypophosphite is 83%. The main reason for the decrease in yield is that the temperature rise causes side reactions, and sodium hypophosphite is further oxidized to generate sodium phosphite as a byproduct. At the same time, sodium hypochlorite undergoes a disproportionation reaction, consuming the reaction raw materials.

[0033] Example 3 The reaction was carried out in a batch reactor. High-purity electronic-grade sodium hypochlorite (6N grade) was diluted to an effective chlorine content of 8%, and the resulting high-purity electronic-grade sodium hydroxide was diluted to a concentration of 9%. Both were mixed thoroughly in a premixer and pre-cooled to 0 °C before being fed into the synthesis reactor (the molar ratio of sodium hypochlorite to sodium hydroxide entering the premixer was controlled by a flow meter at 2:1.05). The reactor temperature was maintained at 0 °C. 7N grade ultra-high-purity phosphine gas, free of metallic impurities, was mixed with 5N grade high-purity electronic-grade nitrogen in a buffer. The phosphine concentration was diluted to 8%, and the gas was pre-cooled to 0 °C. The mixed gas was then bubbled into the solution in the reactor using a gas redistributor, with the bubbling speed controlled by a flow meter at 500 sccm. The reaction was stopped when the molar ratio of phosphine to sodium hypochlorite entering the reactor reached 1.05:2.

[0034] The post-processing adopts the same processing method as in Example 1.

[0035] The yield of high-purity electronic-grade sodium hypochlorite decreased to 75%. The main reason for the decrease in yield was that phosphine did not fully contact and react with the mixed solution of sodium hypochlorite and sodium chloride, and some of the phosphine was discharged without fully reacting.

[0036] In summary, this invention yields a high-purity electronic-grade sodium hypophosphite product. The key technical points are: 1) The use of a microchannel reactor enables molecular-level mixing of the gas and liquid phases within a micron-scale channel, ensuring sufficient and uniform contact of reactants and avoiding local over-concentration and side reactions caused by uneven gas bubbling in traditional batch reactors. 2) By precisely controlling the feed flow rate of the reactants through a mass flow controller and a precision metering pump, continuous and slow feeding is achieved, allowing the reaction to proceed smoothly within a controllable residence time; 3) The high heat exchange capacity of the microchannel reactor, combined with the low-temperature constant-temperature circulating bath, precisely maintains the reaction temperature at 0℃, effectively suppressing exothermic side reactions and improving product purity. These measures ensure the safe, stable, and efficient conduct of the reaction, significantly improving product quality and production efficiency.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A method for synthesizing high-purity electronic-grade sodium hypophosphite, characterized in that, Includes the following steps: (1) Raw material pretreatment: Ultra-high purity phosphine gas is diluted with high purity nitrogen to obtain phosphine mixed gas; sodium hypochlorite solution and sodium hydroxide solution are diluted and mixed, and pre-cooled to obtain pre-cooled mixed liquid; (2) Microchannel reaction: The phosphine mixture and the pre-cooled mixture from step (1) are fed into a microchannel reactor for continuous gas-liquid two-phase reaction. The reaction temperature is controlled at -5~0℃ and the pH of the reaction system is maintained at 11-14. (3) Preparation of crude product: After filtering the reaction effluent from step (2), the crude sodium hypophosphite is obtained by concentration, crystallization and separation; (4) Purification: The crude sodium hypophosphite from step (3) is purified by resin and separated by membrane, then recrystallized and dried to obtain high-purity electronic-grade sodium hypophosphite.

2. The method for synthesizing high-purity electronic-grade sodium hypophosphite according to claim 1, characterized in that: The purity of the ultra-high purity phosphine gas mentioned in step (1) is above 7N, and the purity of the high purity nitrogen gas is above 5N; the volume fraction of phosphine in the phosphine mixture is 5-10%.

3. The method for synthesizing high-purity electronic-grade sodium hypophosphite according to claim 1, characterized in that: The sodium hypochlorite solution in step (1) is diluted to an effective chlorine content of 5-10%, and the sodium hydroxide solution is diluted to a mass concentration of 5-12%; the molar ratio of sodium hypochlorite to sodium hydroxide is 2:(1.0-1.2).

4. The method for synthesizing high-purity electronic-grade sodium hypophosphite according to claim 1, characterized in that: In step (1), the pre-cooling temperature of the pre-cooled mixture is -5~0℃, and the pre-cooling method is low-temperature heat exchanger heat exchange.

5. The method for synthesizing high-purity electronic-grade sodium hypophosphite according to claim 1, characterized in that: In step (1), during the preparation of the phosphine mixture, the phosphine gas is mixed with high-purity nitrogen gas through a buffer, and the mixture is sent into the microchannel reactor after pre-cooling.

6. The method for synthesizing high-purity electronic-grade sodium hypophosphite according to claim 1, characterized in that: In step (2), the feed flow rate of the phosphine mixture is 300-500 sccm; the molar ratio of phosphine, sodium hypochlorite and sodium hydroxide is (1.0-1.2):2.0:(1.0-1.2).

7. The method for synthesizing high-purity electronic-grade sodium hypophosphite according to claim 1, characterized in that: The microchannel reactor described in step (2) is made of corrosion-resistant alloy material, and the hydraulic diameter of the internal channels is 300-500 micrometers; the temperature control method of the microchannel reactor is to immerse it entirely in a low-temperature constant-temperature circulating bath. The corrosion-resistant alloy is Hastelloy, and the microchannel reactor has a multi-layer parallel structure with a Y-shaped inlet and a baffle mixing structure inside. Phosphine gas mixture and pre-cooled liquid mixture form a gas-liquid slug flow or annular flow in a microchannel reactor. The reaction residence time is controlled by adjusting the reactor channel length and the material feed rate.

8. The method for synthesizing high-purity electronic-grade sodium hypophosphite according to claim 1, characterized in that: In step (4), the resin purification process sequentially employs ultra-high purity cation exchange resin and ultra-high purity anion exchange resin. The cation exchange resin removes metal ions, while the anion exchange resin removes chloride ions and hypochlorite anions.

9. The method for synthesizing high-purity electronic-grade sodium hypophosphite according to claim 8, characterized in that: The ultra-high purity cation exchange resin is a resin with a polymer backbone linked to sulfonic acid groups, and the ultra-high purity anion exchange resin is a resin with a polymer backbone linked to quaternary ammonium groups.

10. The method for synthesizing high-purity electronic-grade sodium hypophosphite according to claim 1, characterized in that: The membrane separation in step (4) is reverse osmosis membrane separation, which is used for further desalination and removal of nanoscale particles; the recrystallization is carried out in a Class 100 cleanroom using ultrapure water, and the drying is vacuum drying.

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