A method and system for co-production of potassium phosphite and potassium hypophosphite

Abstract

The present application relates to the field of potassium hypophosphite production, and particularly relates to a method and system for co-producing potassium hypophosphite and potassium phosphite, which comprises: replacing all the reaction kettles and pipelines with nitrogen to maintain a slight positive pressure in the system; continuously feeding potassium hydroxide aqueous solution and molten yellow phosphorus into the first-stage reaction kettle to generate potassium hypophosphite and phosphine through disproportionation reaction; feeding the reaction liquid into the second-stage reaction kettle to gradually increase the alkali concentration, and convert part of the potassium hypophosphite into potassium phosphite; feeding the reaction liquid into the third-stage reaction kettle to maintain the alkali concentration at a certain level, and convert part of the potassium hypophosphite into potassium phosphite and release hydrogen; feeding the reaction liquid into the fourth-stage reaction kettle to maintain the alkali concentration at a certain level, and continuously discharge the product containing the mixture of potassium phosphite and potassium hypophosphite from the fourth-stage reaction kettle after the reaction approaches equilibrium, thereby improving the production efficiency, reducing the raw material cost, improving the process safety, thermal energy utilization efficiency and product quality, and realizing the comprehensive utilization of the gas byproducts.

Description

Technical Field

[0001] This invention relates to the field of potassium hypophosphite production, and in particular to a method and system for the co-production of potassium hypophosphite from potassium phosphite. Background Technology

[0002] Potassium phosphite (K₂HPO₃) is a special phosphorus and potassium fertilizer containing trivalent phosphorus, possessing the dual functions of phosphorus nutrient supply and disease suppression. Unlike traditional orthophosphate (pentavalent phosphorus), phosphite ions can be transported bidirectionally within the plant through both the phloem and xylem. This phosphorus transport efficiency is significantly higher than that of orthophosphate ions, which can only be transported upwards through the xylem. Therefore, by partially replacing orthophosphate during the crop's growth period, it not only meets the plant's phosphorus nutrient requirements but also suppresses diseases. Simultaneously, as a systemic fungicide, potassium phosphite exhibits excellent control effects against fungal diseases such as downy mildew, late blight, and root rot, and repeated use does not lead to resistance. It has been widely applied in agricultural production.

[0003] Potassium hypophosphite (KH₂PO₂) is a compound containing +1 valent phosphorus and possesses strong reducing properties. Industrially, it is commonly used as a reducing agent in electroless nickel plating, a heat stabilizer for polymer materials, and a raw material for the synthesis of certain pharmaceutical intermediates. In agriculture, potassium hypophosphite can be used as a slow-release phosphorus fertilizer, as its +1 valent phosphorus can be slowly oxidized to +3 or +5 valent phosphorus in the soil, ensuring a long-term supply of phosphorus. Furthermore, potassium hypophosphite also has a certain inhibitory effect on some soil-borne diseases. Currently, industrially, potassium hypophosphite is mainly produced by reacting yellow phosphorus with alkali metal hydroxides or carbonates under strictly controlled temperature conditions, or by neutralizing hypophosphite with potassium hydroxide. However, its production process is mostly batch-operated single-reactor operation, suffering from low efficiency and high cost similar to potassium phosphite production.

[0004] Regarding relevant product standards, my country has issued the group standard T / HNFLXH 001-2024 "Agricultural Potassium Phosphite", which applies to liquid fertilizers produced using phosphorous acid, potassium hydroxide, and other raw materials as main raw materials. It specifies limits on phosphorus content, potassium content, water-insoluble matter, pH, and toxic and harmful substances. For potassium hypophosphite products, there are currently no unified national or chemical industry standards; industrial-grade products can refer to HG / T 3253-2023 "Industrial Sodium Hypophosphite".

[0005] From the perspective of production process routes, the current domestic and international production methods of potassium phosphite can be roughly divided into three technical routes based on phosphorus source and process type: phosphorous acid-alkali neutralization route, yellow phosphorus direct oxidation-neutralization two-step route, and phosphorus-containing waste liquid resource utilization route. Among them, the phosphorous acid-alkali neutralization route and the yellow phosphorus direct oxidation-neutralization two-step route are the most common. The former uses phosphorous acid and potassium hydroxide (or potassium carbonate) as the main raw materials, which are stirred and mixed in a reactor, neutralized with acid and alkali, and then filtered to obtain the product; the latter uses yellow phosphorus as raw material, which is catalytically oxidized to prepare phosphorous acid solution, and then neutralized with potassium hydroxide to obtain potassium phosphite. Both adopt a batch single-reactor operation mode.

[0006] For the production of potassium hypophosphite, existing technologies mainly include two routes: one is to react yellow phosphorus with potassium hydroxide or calcium hydroxide under strictly controlled temperature (usually below 50°C) to produce hypophosphite, which is then subjected to metathesis or neutralization reactions to obtain potassium hypophosphite; the other is to directly neutralize hypophosphite (H3PO2) with potassium hydroxide. Existing technologies are also mainly based on batch single-reactor operation, and there are no reported technical solutions for the co-production of potassium phosphite and potassium hypophosphite in the same continuous process.

[0007] The disadvantages of the above-mentioned existing technologies are as follows: (1) Intermittent operation, resulting in low production efficiency.

[0008] (2) The phosphite neutralization route is subject to the supply of upstream raw materials and has high costs.

[0009] (3) There are safety hazards in the direct oxidation route of yellow phosphorus.

[0010] (4) Lack of comprehensive utilization methods for by-products.

[0011] (5) Low thermal energy utilization efficiency.

[0012] (6) Product quality needs to be improved. Summary of the Invention

[0013] The purpose of this invention is to provide a method and system for the co-production of potassium hypophosphite from potassium phosphite, achieving continuous production and improving production efficiency; directly using yellow phosphorus as raw material, reducing raw material costs; improving process safety; realizing comprehensive utilization of gaseous byproducts; improving thermal energy utilization efficiency; and improving product quality. The specific technical solution of this invention is as follows: In a first aspect, the present invention provides a method for the co-production of potassium hypophosphite from potassium phosphite, specifically comprising the following steps: Step (1) Replace all reactors and pipelines with nitrogen to maintain a slight positive pressure in the system; Step (2) The potassium hydroxide aqueous solution and molten yellow phosphorus are continuously fed into the first-stage reactor to undergo a disproportionation reaction, generating potassium hypophosphite and phosphine; Step (3) The reaction solution from step (2) enters the second-stage reactor, and the alkali concentration gradually increases, with some potassium hypophosphite beginning to be converted into potassium phosphite; Step (4) The reaction solution from step (3) enters the third-stage reactor, where the alkali concentration is maintained at a certain level. Potassium hypophosphite is partially converted into potassium phosphite and hydrogen gas is released. Step (5) The reaction solution from step (4) enters the fourth stage reactor. The alkali concentration is maintained at a certain level. After the reaction approaches equilibrium, the product is continuously discharged from the fourth stage reactor to obtain a mixed solution product containing potassium phosphite and potassium hypophosphite.

[0014] As a preferred option, in step (2), the concentration of potassium hydroxide aqueous solution is 12-16wt%, the reaction temperature is controlled at 55-65°C, the stirring speed is 80-120 rpm, the molar ratio of yellow phosphorus to KOH is 1:3-3.5, and the residence time is 21.3-24.8 min.

[0015] As a preferred option, in step (3), the reaction temperature is controlled at 65-75°C, the stirring speed is 80-120 rpm, the alkali concentration is gradually increased to 16-19 wt%, and the residence time is 27-29.2 min.

[0016] As a preferred option, in step (4), the reaction temperature is controlled at 75-95°C, the stirring speed is 100-150 rpm, the alkali concentration is maintained at 19-22 wt%, potassium hypophosphite is partially converted into potassium phosphite and hydrogen is released, and the residence time is 29.5-32.5 min.

[0017] As a preferred option, in step (5), the reaction temperature is controlled at 80-95°C, the stirring speed is 80-120 rpm, the alkali concentration is maintained at 19-22 wt%, and the residence time is 33.7-35.8 min.

[0018] As a preferred option, in steps (3) and (4), the alkali concentration in the reaction solution is monitored in real time, and potassium hydroxide is automatically added when the alkali concentration is lower than the lower limit of the target range; the potassium hydroxide added in steps (3) and (4) is added in solid form or in the form of a concentrated solution with a concentration of ≥30 wt%.

[0019] As a preferred embodiment, the conversion depth of potassium hypophosphite to potassium phosphite is controlled by adjusting the reaction temperature and / or alkali concentration and / or material residence time in the third-stage and fourth-stage reactors, so that the mass ratio of potassium phosphite to potassium hypophosphite in the product is continuously adjustable within the range of 1:3 to 10:1.

[0020] As a preferred embodiment, step (6) is also included, in which all gaseous products are collected from the top of each vessel and then subjected to combustion absorption treatment. The gaseous products include phosphine and hydrogen. The specific method of combustion absorption treatment is as follows: The mixed gas collected in the gas tank is sent into the combustion chamber for controlled combustion, and the P4O generated by the combustion of phosphine is produced. 10 Phosphoric acid solution is obtained through water absorption. Hydrogen is burned to generate water vapor and recover heat. The residual tail gas is washed with alkaline solution and discharged in compliance with standards. The heat generated by combustion is recovered as by-product low-pressure steam through a waste heat boiler. The phosphoric acid solution obtained through water absorption is further reacted with potassium hydroxide to produce potassium dihydrogen phosphate fertilizer.

[0021] In a second aspect, the present invention provides a system for the co-production of potassium hypophosphite from potassium phosphite, comprising: Four-stage reactors, with decreasing height, and adjacent reactors connected by overflow pipes; A yellow phosphorus feed metering pump and a KOH solution feed metering pump are connected to the primary reactor; A continuous discharge metering valve connected to the bottom of the four-stage reactor; Gas outlet pipes installed at the top of each reactor collect gas into a gas collection tank. The online monitoring system adjusts the temperature, alkali concentration, and feed rate of each reactor in real time. Aqueous potassium hydroxide solution and molten yellow phosphorus are continuously fed into the first-stage reactor, where a disproportionation reaction occurs to produce potassium hypophosphite and phosphine. The reaction solution enters the second-stage reactor, where the alkali concentration gradually increases, and some potassium hypophosphite begins to be converted into potassium phosphite. Then, the reaction solution enters the third-stage reaction vessel, where the alkali concentration is maintained at a certain level, and potassium hypophosphite is partially converted into potassium phosphite and hydrogen gas is released. Then, the reaction solution enters the fourth-stage reactor, the alkali concentration is maintained at a certain concentration, and after the reaction approaches equilibrium, the product is continuously discharged from the fourth-stage reactor to obtain a mixed solution product containing potassium phosphite and potassium hypophosphite. The four glass-jacketed reactors have decreasing heights and are connected to each other. The reaction liquid flows automatically in stages by relying on the gravity difference.

[0022] As a preferred embodiment, it also includes: a gas outlet pipe located at the top of each reactor, which is connected to a gas main pipe; and a gas collection tank connected to the gas main pipe. Combustion chamber and waste heat boiler; Phosphoric acid absorption tower and alkaline scrubbing tower; A heat transfer oil heating / cooling system connected to the jackets of each reactor; The mixed gas collected in the gas tank is sent into the combustion chamber for controlled combustion, and the P4O generated by the combustion of phosphine is produced. 10Phosphoric acid solution is obtained through water absorption. Hydrogen is burned to generate water vapor and recover heat. The residual tail gas is washed with alkaline solution and discharged in compliance with standards. The heat generated by combustion is recovered as by-product low-pressure steam through a waste heat boiler and reused for preheating and heating of the reaction vessel. The phosphoric acid solution obtained through water absorption is further reacted with potassium hydroxide to produce potassium dihydrogen phosphate fertilizer.

[0023] The beneficial effects of this invention are as follows: (1) Achieve continuous production and improve production efficiency. Transform the existing intermittent single-reactor operation into a continuous multi-reactor series operation, shorten the reaction time, eliminate the auxiliary time loss between batches, realize the continuous discharge of potassium phosphite and potassium hypophosphite co-production products, and significantly improve equipment utilization and capacity.

[0024] (2) Use yellow phosphorus directly as raw material to reduce raw material costs. Abandon the route that uses phosphorous acid as an intermediate and use yellow phosphorus and potassium hydroxide directly as starting materials to avoid the cost accumulation caused by multiple upstream processes of phosphorous acid and improve economic efficiency.

[0025] (3) Improve process safety. The disproportionation reaction route does not introduce external oxidants (such as oxygen) and is carried out in a closed system under nitrogen protection, which fundamentally avoids the risk of spontaneous combustion of yellow phosphorus and explosion of phosphine combustion.

[0026] (4) Achieve comprehensive utilization of gaseous byproducts. Phosphine (PH3) and hydrogen (H2) generated during the reaction are collected and absorbed by combustion. Phosphine is burned to produce phosphoric acid, which can be recycled for the production of phosphorus-containing byproducts or used as raw material for phosphate fertilizer, thus realizing resource utilization and relieving the environmental pressure of tail gas emissions.

[0027] (5) Improve thermal energy utilization efficiency. By utilizing the self-exothermic characteristics of the disproportionation reaction and the temperature gradient design of multiple reactors in series, the dependence on external heat source input is reduced, and the repeated process of heating, cooling and reheating is avoided, so as to realize the cascade utilization of energy.

[0028] (6) Improve product quality. By independently and precisely controlling the reaction conditions of each reactor under multi-reactor series conditions, deep oxidation side reactions are effectively suppressed. A mixed product of potassium phosphite and potassium hypophosphite can be obtained simultaneously in the same continuous process. Furthermore, the ratio of the two components can be flexibly adjusted according to market demand by regulating the reaction conditions (temperature, alkali concentration, feed rate), thereby improving the market adaptability and economy of the product. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the system structure according to one embodiment of the present invention; Figure 2 This is a schematic diagram of the gas comprehensive utilization and exhaust gas treatment section of one embodiment of the system of the present invention; wherein: 1-First-stage reactor (Reactor I), 2-Second-stage reactor (Reactor II), 3-Third-stage reactor (Reactor III), 4-Fourth-stage reactor (Reactor IV), 5-Overflow pipe, 6-Jacketed heat transfer oil inlet, 7-Jacketed heat transfer oil outlet, 8-Stirring motor, 9-Stirring paddle, 10-Gas outlet pipe, 11-Gas main pipe, 12-Yellow phosphorus feed metering pump, 13-KOH solution feed metering pump, 14-KOH supplementary feed port, 15-Continuous discharge metering valve, 16-Nitrogen inlet pipe, 17-Temperature sensor, 18-pH / alkali concentration online monitoring probe, 19-KOH supplementary metering pump, 20-KOH storage tank, 21-Gas collection tank, 22-Flame arrestor, 23-Combustion chamber, 24-Waste heat boiler, 25-Phosphoric acid absorption tower, 26-Alkali washing tower, 27-Fan, 28-Chimney, 29-Phosphoric acid solution storage tank. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased.

[0031] Unless otherwise stated, all percentages in this invention represent mass fractions. Ratios are mass percentages, and concentrations are mass concentrations.

[0032] Unless otherwise specified, all materials, instruments, and equipment used below are conventional materials, instruments, and equipment or obtained through commercial channels; all testing methods used are existing methods unless otherwise specified.

[0033] From the perspective of preparation process routes, the current domestic and international production methods of potassium phosphite can be roughly divided into the following three technical routes according to phosphorus source and process type: (I) Phosphorous acid-base neutralization route: Potassium phosphite is produced by acid-base neutralization reaction of phosphorous acid (H3PO3) with potassium hydroxide or potassium carbonate aqueous solution as the phosphorus source. This method is simple and safe to operate (it does not involve toxic gases such as phosphine), but the route is subject to the supply of upstream phosphorous acid. Furthermore, phosphorous acid itself is usually produced by the hydrolysis of phosphorus trichloride or the oxidation of yellow phosphorus. The phosphorus trichloride route involves the use of chlorine, which poses risks of equipment corrosion and environmental pressure; while the yellow phosphorus oxidation route has problems such as difficulty in reaction control and low phosphorus utilization.

[0034] (II) Two-step route of direct oxidation-neutralization of yellow phosphorus. Using yellow phosphorus (P4) as the starting phosphorus source, it is first catalytically oxidized to obtain a phosphorous acid solution, which is then neutralized with potassium hydroxide to obtain potassium phosphite. For example: water is first added to the reactor, and after heating, solid yellow phosphorus is added and stirred at low speed until the yellow phosphorus is completely melted. Then, a catalyst is added and ultrasound is started, and an oxidant is slowly added dropwise. The reaction is carried out at 45-75℃ for 2-3 hours to obtain a phosphorous acid solution. After cooling to room temperature, solid potassium hydroxide is added for neutralization, and the solution is concentrated to obtain a liquid potassium phosphite product. This route uses a one-step catalytic oxidation method for yellow phosphorus, which has a relatively short process, mild reaction conditions, no chlorine production, and is environmentally friendly. The raw material, yellow phosphorus, is more readily available and cheaper than phosphorous acid. However, this route is essentially still a batch operation, with a long single-batch reaction time (2-3 hours for the oxidation stage), limiting production efficiency; the oxidation reaction requires precise control of oxygen levels, necessitating high operational safety; and cooling and alkali neutralization are required between the two steps, resulting in low thermal energy utilization, making it unsuitable for large-scale continuous industrial production.

[0035] (III) Resource Utilization Route for Phosphorus-Containing Wastewater. Using crude phosphorous acid wastewater, a byproduct of the reaction between phosphorus trichloride (PCl3) and carboxylic acids, as raw material, potassium phosphite is prepared by reacting it with potassium hydroxide, potassium bicarbonate, or potassium carbonate after separation and purification. This is mainly used for the resource utilization of crude phosphorous acid wastewater in acyl chloride production and is an important direction for industrial-grade potassium phosphite production abroad. For example, in a continuous reactor, a method is used to prepare potassium salt compositions by reacting a mixture of phosphorous acid and phosphoric acid with potassium hydroxide solution at 65-260℃. The product is a mixture of phosphate, phosphite, and copolymers, which has both bactericidal and plant nutrient functions. This route achieves the resource utilization of organic wastewater, and some processes have continuous characteristics. However, the process flow is long, involves many pieces of equipment, and is affected by fluctuations in the composition of upstream wastewater, resulting in a complex product composition that makes it difficult to directly obtain high-purity potassium phosphite as a single product. Furthermore, the storage, transportation, and treatment of phosphorous acid wastewater involve additional safety and environmental management costs.

[0036] Of the three routes mentioned above, the two-step route of neutralization of phosphorous acid and direct oxidation of yellow phosphorus is the most common, both of which adopt a batch single-reactor operation mode.

[0037] For the production of potassium hypophosphite, existing technologies mainly include two routes: one is the reaction of yellow phosphorus with potassium hydroxide or calcium hydroxide under strictly controlled temperature (usually below 50°C) to produce hypophosphite, which is then subjected to metathesis or neutralization reactions to obtain potassium hypophosphite; the other is the direct neutralization of hypophosphite (H3PO2) with potassium hydroxide. Both routes are mainly batch single-reactor operations, and suffer from problems similar to potassium phosphite production, such as low efficiency, high energy consumption, and high cost. In particular, although the route for the direct preparation of hypophosphite from yellow phosphorus also produces phosphine gas as a byproduct, existing technologies also lack effective means to recover and utilize this toxic gas. Furthermore, existing technologies are also mainly batch single-reactor operations, and there are no reported technical solutions for the co-production of potassium phosphite and potassium hypophosphite in the same continuous process.

[0038] In summary, the existing technology has the following drawbacks: (1) Intermittent operation, resulting in low production efficiency. Existing technologies generally adopt single-reactor intermittent operation. The yellow phosphorus catalytic oxidation route takes more than 2-3 hours per batch, and the phosphorous acid neutralization route also requires batch feeding and auxiliary operations such as unloading and cleaning after the reaction, making continuous production impossible. Equipment utilization is low, and the production capacity is constrained by the high proportion of auxiliary time in intermittent operation, and batch-to-batch product quality fluctuations are difficult to avoid. Potassium hypophosphite production also faces the efficiency bottleneck of intermittent operation.

[0039] (2) The alkaline neutralization route of phosphorous acid is constrained by the supply of upstream raw materials and has high costs. The production method using phosphorous acid as the phosphorus source requires phosphorous acid itself to be a deep-processed product. It needs to be produced by multiple processes such as phosphorus trichloride hydrolysis or yellow phosphorus oxidation. The raw material cost is high and the supply is greatly affected by market fluctuations, resulting in poor economic efficiency.

[0040] (3) The direct oxidation route of yellow phosphorus poses safety hazards. The direct oxidation route of yellow phosphorus requires the introduction of oxygen or oxidant into the reactor. Yellow phosphorus is flammable in an oxidizing atmosphere, and the operation and control requirements are strict, posing a risk of fire and explosion. The safety of the reaction process restricts industrial production.

[0041] (4) Lack of comprehensive utilization methods for by-products. In the reaction of yellow phosphorus with potassium hydroxide aqueous solution, in addition to the main product, phosphine (PH3) and hydrogen (H2) are also generated. If the target product is potassium phosphite, the existing technology often further converts the intermediate potassium hypophosphite; if the target product is potassium hypophosphite, the conversion conditions need to be strictly controlled to avoid further reaction. Most existing technologies only focus on the preparation of a single target product and lack a co-production scheme to obtain two valuable products, potassium phosphite and potassium hypophosphite, in the same process. They also do not effectively recover and utilize phosphine and hydrogen, resulting in resource waste and increasing the environmental pressure of tail gas treatment.

[0042] (5) Low thermal energy utilization efficiency. The two-step oxidation and neutralization method of yellow phosphorus requires heating to oxidize, then cooling to neutralize, and finally concentrating. The reaction system goes through a process of heating, cooling, and heating again, resulting in large heat loss and unreasonable energy utilization. The traditional preparation process of potassium hypophosphate also has the problem of low thermal energy utilization efficiency.

[0043] (6) Product quality needs to be improved. The existing batch single-reactor reaction conditions are not easy to control precisely, resulting in high content of impurities such as phosphate in the product. For potassium phosphite, the proportion of +3 valent phosphorus decreases; for potassium hypophosphite, the proportion of +1 valent phosphorus decreases, affecting the application effect of the product.

[0044] Furthermore, in a first aspect, the present invention proposes a method for the co-production of potassium hypophosphite from potassium phosphite, specifically comprising the following steps: Step (1) Replace all reactors and pipelines with nitrogen to maintain a slight positive pressure in the system; Step (2) The potassium hydroxide aqueous solution and molten yellow phosphorus are continuously fed into the first-stage reactor to undergo a disproportionation reaction, generating potassium hypophosphite and phosphine; Step (3) The reaction solution from step (2) enters the second-stage reactor, and the alkali concentration gradually increases, with some potassium hypophosphite beginning to be converted into potassium phosphite; Step (4) The reaction solution from step (3) enters the third-stage reactor, where the alkali concentration is maintained at a certain level. Potassium hypophosphite is partially converted into potassium phosphite and hydrogen gas is released. Step (5) The reaction solution from step (4) enters the fourth stage reactor. The alkali concentration is maintained at a certain level. After the reaction approaches equilibrium, the product is continuously discharged from the fourth stage reactor to obtain a mixed solution product containing potassium phosphite and potassium hypophosphite.

[0045] This invention proposes a method for the continuous production of potassium phosphite and the concurrent production of potassium hypophosphite through the disproportionation reaction of yellow phosphorus (white phosphorus, P4) and potassium hydroxide (KOH) aqueous solution under nitrogen protection, using four reactors connected in series. The method also includes centralized recovery and comprehensive utilization of the gaseous products (phosphine and hydrogen) generated during the reaction. The reactors can be glass-jacketed reactors. The entire reaction is carried out under positive pressure with nitrogen protection, ensuring controlled oxygen content and effectively preventing the risk of spontaneous combustion of yellow phosphorus and explosion of phosphine, thus improving the inherent safety of the process.

[0046] The core technical concept of this invention is based on the unique reaction kinetic differences in the reaction between yellow phosphorus and potassium hydroxide aqueous solution.

[0047] The reaction of yellow phosphorus (white phosphorus, P4) with potassium hydroxide (KOH) aqueous solution is a typical alkaline disproportionation reaction. This reaction needs to be carried out under heating and air-free conditions. The main products are phosphine and potassium hypophosphite, while various side reactions produce byproducts such as biphosphine, phosphite, and phosphate.

[0048] The disproportionation reaction of yellow phosphorus proceeds stepwise and continuously under hot alkaline conditions: (1) First step: Main reaction (potassium hypophosphite formation, low temperature is dominant): P4+3KOH+3H2O ═══3KH2PO2+PH3↑ This potassium phosphate formation reaction is a first-order reaction with respect to P4 and with respect to OH. - It is a first-order reaction, and the overall reaction order of the main reaction is second-order. The activation energy Ea ≈ 40 kJ / mol, which is an exothermic reaction.

[0049] Lower temperature conditions are more favorable, at which point potassium hypophosphite and a small amount of phosphine are mainly produced.

[0050] Reaction mechanism: disproportionation reaction (phosphorus is simultaneously oxidized and reduced). Reduction: 1 mol of P in 1 mol of P4 decreases from 0 to -3, producing phosphine (PH3). Oxidation: 3 mol of P increases from 0 to +1 oxidation state, producing potassium hypophosphite (KH2PO2). Redox ratio: The molar ratio of oxidized phosphorus (KH2PO2) to reduced phosphorus (PH3) is 3:1.

[0051] (2) Second step: side reaction 2.1 Further disproportionation of hypophosphate, formation of potassium phosphite, dominated by high temperature and high alkali: KH2PO2 + KOH ═══ K2HPO3 + H2↑ The main product, potassium hypophosphite, is unstable in hot alkaline conditions and will undergo further disproportionation to produce potassium phosphite and hydrogen gas. This potassium phosphite formation reaction is a first-order reaction with respect to P4 and an even-order reaction with respect to OH-. - This is a second-order reaction, with an overall reaction order of three. The rate is proportional to the square of the base concentration, which is the core difference between the side reaction and the main reaction. Under conditions of high temperature (80-95°C) and high base concentration (KOH content ≥20wt%), the rate constant of this side reaction will increase significantly and exceed that of the main reaction, becoming the dominant reaction. The activation energy of this reaction is Ea≈50-60kJ / mol, which is also exothermic, and the degree of exothermic reaction is much higher than that of the main reaction.

[0052] Based on the reaction kinetic differences between the main reaction (favorable at low temperatures, Ea ≈ 40 kJ / mol) and the main side reaction (favorable at high temperatures, Ea ≈ 50-60 kJ / mol, promoted by high alkali concentration), this invention achieves continuous synthesis of potassium hypophosphite co-produced from potassium phosphite by physically separating the two-step reaction in space and time through a stepped temperature control and stirring strategy using a four-stage series reactor.

[0053] 2.2 Deep oxidation (to produce phosphates) In the presence of trace amounts of oxygen or under high temperature conditions in the reaction system, some phosphorus will be deeply oxidized to phosphate (PO4). 3- ).

[0054] 2.3 Direct reaction of yellow phosphorus with water (high temperature) Yellow phosphorus can react directly with water under high temperature and strong alkaline conditions. This side reaction will reduce the amount of yellow phosphorus as a reactant, so high temperatures (>100°C) should be avoided. o C) and the reaction environment of strong bases.

[0055] Therefore, since the activation energies of the main reaction (Ea≈40kJ / mol) and the main side reaction (Ea≈50-60kJ / mol) are relatively close, and the exothermic degree of the main side reaction is much higher than that of the main reaction, and the chemical reaction rate of the main side reaction is proportional to the square of the base (KOH) concentration, the design concept of this invention is to: appropriately increase the reaction temperature (slightly higher than the main reaction temperature), but not significantly increase the temperature to the point of creating a high-temperature environment (>100°C); and increase the base (KOH) concentration to increase the chemical reaction rate constant of the main side reaction (forming potassium phosphite); allowing the potassium hypophosphite generated in the main reaction to continuously undergo partial deep disproportionation reaction in this reaction system to form potassium phosphite. Furthermore, it is essential to isolate the reaction from air (N2 protection) to prevent spontaneous combustion of P4, explosion of PH3, and the formation of phosphates in the direction of deep oxidation.

[0056] This invention achieves continuous synthesis of potassium phosphite and potassium hypophosphite by using a four-stage series reactor with tiered temperature control and alkali concentration management, thereby physically separating the main reaction (low-temperature disproportionation to generate potassium hypophosphite) from the main side reaction (deep conversion to generate potassium phosphite under high-temperature and high-alkali conditions) in time and space, thus realizing continuous synthesis of potassium phosphite and potassium hypophosphite co-production.

[0057] It is important to note that in the actual reaction process, the potassium hypophosphite generated in the first main reaction cannot be completely converted under the conditions of the second main side reaction. The process parameters such as the temperature and alkali concentration of the reaction system control the degree of conversion. Therefore, the final product continuously discharged from the fourth-stage reactor is a mixed solution of potassium phosphite and incompletely converted potassium hypophosphite.

[0058] In one embodiment, in step (2), the concentration of potassium hydroxide aqueous solution is 12-16 wt%, the reaction temperature is controlled at 55-65°C, the stirring speed is 80-120 rpm, and the residence time is 21.3-24.8 min. The molar ratio of yellow phosphorus to KOH is 1:3-3.5. Yellow phosphorus undergoes the main reaction with water and KOH, potassium hypophosphite accumulates in large quantities, and some phosphine gas is released.

[0059] In one embodiment, in step (3), the reaction temperature is controlled at 65-75°C, the stirring speed is 80-120 rpm, the alkali concentration is gradually increased to 16-19 wt%, potassium hypophosphite begins to convert to potassium phosphite, and the residence time is 27-29.2 min.

[0060] In one implementation method, in step (4), the reaction temperature is controlled at 75-95°C, the stirring speed is 100-150 rpm, the alkali concentration is maintained at 19-22 wt%, and the residence time is 29.5-32.5 min. Potassium hypophosphite is partially and deeply converted into potassium phosphite and releases hydrogen gas. The increase in alkali concentration and the increase in temperature synergistically promote the side reaction of potassium phosphite formation, making it the dominant reaction; potassium hypophosphite is partially and deeply converted into potassium phosphite, while releasing hydrogen gas.

[0061] This invention utilizes a stepwise temperature control and alkali concentration regulation strategy based on the differences in reaction kinetics. It fully leverages the kinetic differences between the main reaction (potassium hypophosphite formation, activation energy ≈40 kJ / mol) and the side reaction (potassium phosphite formation, activation energy ≈50-60 kJ / mol) in the yellow phosphorus disproportionation reaction. The main reaction is completed under low-temperature and low-alkali conditions in the first-stage reactor, while the side reaction is driven to become dominant under high-temperature and high-alkali conditions in the third-stage reactor, achieving the co-production synthesis of potassium phosphite and potassium hypophosphite with an adjustable ratio.

[0062] In one implementation method, in step (5), the reaction temperature is controlled at 80-95°C, the stirring speed is 80-120 rpm, the alkali concentration is maintained at 19-22 wt%, and the residence time is 33.7-35.8 min. The reaction proceeds further and reaches equilibrium, so that the mixed solution containing potassium phosphite and potassium hypophosphite is continuously discharged to the post-processing section.

[0063] In one implementation method, in steps (3) and (4), the alkali concentration in the reaction solution is monitored in real time, and potassium hydroxide is automatically added when the alkali concentration is lower than the target range lower limit. The potassium hydroxide added in steps (3) and (4) is added in solid form or as a concentrated solution with a concentration ≥30 wt%. The addition of potassium hydroxide in the second and third reactors is to increase the alkali concentration in the second and third reactors so that the conversion of potassium hypophosphite to potassium phosphite is basically completed in the second and third reactors. The fourth reactor cannot be replenished, as the unreacted potassium hydroxide is discharged with the fourth reactor, further increasing the difficulty of separation. The fourth reactor is equivalent to a further maturation process of the second and third reactors, ensuring that when the fourth reactor is discharged, potassium hypophosphite is basically converted into potassium phosphite (with a higher potassium phosphite content), making the subsequent separation of the fourth reactor easier and reducing energy consumption costs. The first reactor cannot be replenished because yellow phosphorus only generates the main product potassium hypophosphite under low alkali concentration.

[0064] This invention addresses the side reaction of deep oxidation by preventing trace amounts of oxygen from entering the system through positive pressure operation under N2 protection throughout the process; it also addresses the side reaction of yellow phosphorus reacting directly with water at high temperatures by strictly controlling the temperature of each reactor to not exceed 95°C; and it addresses the potential risk of incomplete conversion due to low alkali concentration during the IV ripening stage of the reactor by maintaining the optimal alkali concentration range through online monitoring and automatic alkali replenishment.

[0065] In one implementation method, the conversion depth of potassium hypophosphite to potassium phosphite is controlled by adjusting the reaction temperature and / or alkali concentration and / or material residence time in the third-stage and fourth-stage reactors, so that the mass ratio of potassium phosphite to potassium hypophosphite in the product is continuously adjustable within the range of 1:3 to 10:1.

[0066] By adjusting the reaction temperature (75-95°C range), alkali concentration (19-22 wt%), and average residence time of the material in the high-temperature section of the third and fourth stage reactors, the conversion depth of potassium hypophosphite to potassium phosphite can be flexibly controlled. The residence time is used to control the degree of reaction, so that the mass ratio of potassium phosphite to potassium hypophosphite in the product can be continuously adjusted within the range of 1:3 to 10:1 to meet the needs of different downstream application scenarios.

[0067] This invention, by controlling the stage conditions of a four-stage reactor, enables the adjustment of the ratio of potassium phosphite to potassium hypophosphite, thus forming a technical solution for the co-production of potassium hypophosphite from potassium phosphite. Compared to processes that solely pursue high yields of potassium phosphite, this co-production model offers higher raw material utilization efficiency and stronger market adaptability. When market demand for potassium hypophosphite is high, the temperature and alkali concentration of the third and fourth stage reactors can be appropriately reduced to retain more potassium hypophosphite product.

[0068] As one implementation method, it also includes step (6), in which all gaseous products are collected from the top of each vessel and then subjected to combustion absorption treatment. The gaseous products include phosphine and hydrogen. The specific method of combustion absorption treatment is as follows: The mixed gas collected in the gas tank is sent into the combustion chamber for controlled combustion, and the P4O generated by the combustion of phosphine is produced. 10 Phosphoric acid solution is obtained through water absorption. Hydrogen is burned to generate water vapor and recover heat. The residual tail gas is washed with alkaline solution and discharged in compliance with standards. The heat generated by combustion is recovered as by-product low-pressure steam through a waste heat boiler and reused for preheating and heating of the reaction vessel. The phosphoric acid solution obtained through water absorption is further reacted with potassium hydroxide to produce potassium dihydrogen phosphate fertilizer.

[0069] This invention not only yields a mixed liquid product of potassium phosphite and potassium hypophosphite, but also collects phosphine and hydrogen gas and converts them into phosphoric acid byproducts through combustion absorption, achieving almost complete recovery of phosphoric acid. At the same time, the heat released by combustion is recycled to the process heating stage through byproduct steam from a waste heat boiler, realizing the dual comprehensive utilization of energy and materials of gaseous products, reducing waste gas emissions, and lowering environmental treatment costs.

[0070] Secondly, embodiments of the present invention provide a system for the co-production of potassium hypophosphite from potassium phosphite, comprising: Four-stage reactors, with decreasing height, and adjacent reactors connected by overflow pipes; A yellow phosphorus feed metering pump and a KOH solution feed metering pump are connected to the primary reactor; A continuous discharge metering valve connected to the bottom of the four-stage reactor; Gas outlet pipes installed at the top of each reactor collect gas into a gas collection tank. The online monitoring system adjusts the temperature, alkali concentration, and feed rate of each reactor in real time. Aqueous potassium hydroxide solution and molten yellow phosphorus are continuously fed into the first-stage reactor, where a disproportionation reaction occurs to produce potassium hypophosphite and phosphine. The reaction solution enters the second-stage reactor, where the alkali concentration gradually increases, and some potassium hypophosphite begins to be converted into potassium phosphite. Then, the reaction solution enters the third-stage reaction vessel, where the alkali concentration is maintained at a certain level, and potassium hypophosphite is partially converted into potassium phosphite and hydrogen gas is released. Then, the reaction solution enters the fourth-stage reactor, the alkali concentration is maintained at a certain concentration, and after the reaction approaches equilibrium, the product is continuously discharged from the fourth-stage reactor to obtain a mixed solution product containing potassium phosphite and potassium hypophosphite. The four glass-jacketed reactors have decreasing heights and are connected to each other. The reaction liquid flows automatically in stages by relying on the gravity difference.

[0071] This invention employs four reactors connected in series via overflow pipes, relying on height differences to achieve automatic, stepwise material flow. Each reactor independently controls its temperature and stirring conditions, realizing a rational allocation of the main and side reactions in time and space during the yellow phosphorus disproportionation reaction, thus completing the continuous production from yellow phosphorus to potassium phosphite and potassium hypophosphite.

[0072] This invention achieves continuous product discharge through a metering discharge valve at the bottom of the fourth-stage reactor, and is equipped with an online monitoring system to adjust the temperature, alkali concentration and feed rate of each reactor in real time, ensuring the stability and uniformity of product quality.

[0073] As one embodiment, it also includes: a gas outlet pipe disposed on the top of each reactor and collected into a gas main pipe; and a gas collection tank connected to the gas main pipe; Combustion chamber and waste heat boiler; Phosphoric acid absorption tower and alkaline scrubbing tower; A heat transfer oil heating / cooling system connected to the jackets of each reactor; The mixed gas collected in the gas tank is sent into the combustion chamber for controlled combustion, and the P4O generated by the combustion of phosphine is produced. 10 Phosphoric acid solution is obtained through water absorption. Hydrogen is burned to generate water vapor and recover heat. The residual tail gas is washed with alkaline solution and discharged in compliance with standards. The heat generated by combustion is recovered as by-product low-pressure steam through a waste heat boiler. The phosphoric acid solution obtained through water absorption is further reacted with potassium hydroxide to produce potassium dihydrogen phosphate fertilizer.

[0074] The materials in each reactor are connected in series via overflow pipes, and the reaction liquid automatically flows into the next stage by gravity due to the height difference between the reactors. All gaseous products (phosphine and hydrogen) are collected in a gas tank and then sent to a combustion absorption device for treatment. Phosphoric acid generated from the combustion of phosphine is recovered in the form of phosphoric acid solution, and the combustion flue gas is discharged after being scrubbed with alkaline solution to meet emission standards.

[0075] Potassium hypophosphite, as one of the co-products of this invention, has broad application prospects. In the industrial field, potassium hypophosphite can be used as a reducing agent in electroless nickel plating and a heat stabilizer for polymer materials; in the agricultural field, potassium hypophosphite can be used as a slow-release phosphorus fertilizer, where its +1 valent phosphorus is slowly oxidized in the soil, ensuring a long-term supply of phosphorus. The potassium phosphite-potassium hypophosphite mixed solution prepared by this invention can be sold directly according to end-use requirements, or further separated into single-component products through stepwise crystallization, membrane separation, and other technologies.

[0076] In the embodiments of this invention, the potassium phosphite component and the potassium hypophosphite component can be further separated by stepwise crystallization or membrane separation to obtain single potassium phosphite products and single potassium hypophosphite products, respectively. The single potassium phosphite product meets the requirements of T / HNFLXH 001-2024 "Agricultural Potassium Phosphite" standard, and the single potassium hypophosphite product complies with the requirements of HG / T 3253-2023 "Industrial Sodium Hypophosphite" standard.

[0077] The product of this invention is a mixed aqueous solution or mixed solid of potassium phosphite and potassium hypophosphite, wherein the mass ratio of potassium phosphite to potassium hypophosphite is 1:3 to 10:1, the total phosphorus (as P2O5) content is ≥240.0 g / L, the potassium (K2O) content is ≥320.0 g / L, the water-insoluble matter is ≤10.0 g / L, the pH (1% aqueous solution) is 3.0-9.0, and the harmful impurities meet the requirements of GB38400-2019 "Limits of Toxic and Hazardous Substances in Fertilizers".

[0078] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a method and system for the co-production of potassium hypophosphite from potassium phosphite provided by the present invention.

[0079] The main experimental materials used in this invention are shown in Table 1 below: Table 1

[0080] like Figure 1 , 2 As shown, the system of the embodiment includes: four-stage reaction vessels with decreasing height, adjacent vessels are connected by overflow pipes 5, valves are provided on the overflow pipes 5, the outlet of the overflow pipes 5 can be located at about 2 / 3 of the vessel height, which can be adjusted according to the size of the vessel. The inlet of the overflow pipe 5 of the next stage reaction vessel is at the bottom of the vessel. When the liquid reaches the height of the overflow pipe 5, the reaction liquid automatically flows into the next stage by gravity due to the height difference between the vessels.

[0081] Yellow phosphorus feed metering pump 12 and KOH solution feed metering pump 13 are connected to the first-stage reactor 1, and valves are provided on the pipeline between the metering pumps and the first-stage reactor 1.

[0082] Each reactor's glass jacket is equipped with a jacketed heat transfer oil inlet 6 and a jacketed heat transfer oil outlet 7, with the inlet 6 located at the bottom and the outlet 7 at the top. Each reactor also contains a stirring paddle 9 connected to a stirring motor 8. A gas outlet pipe 10 is located at the top of the reactor body, connected to a main gas pipe 11. A nitrogen inlet pipe 16 is also located on one side of the reactor body. A temperature sensor 17 and a pH / alkali concentration online monitoring probe 18 are installed inside the reactor. The second-stage reactor 2, third-stage reactor 3, and fourth-stage reactor 4 are also equipped with KOH storage tanks 20, connected to the reactor body via a KOH metering pump 19.

[0083] A continuous discharge metering pump 15 is connected to the discharge pipe at the bottom of the fourth-stage reactor 4 to transport the final product to the filtration section. The bottom of the first-stage reactor 1 may also be equipped with a pipe connecting to the filtration section, and a metering pump is also installed thereto. When necessary, the reaction material in the first-stage reactor 1 that has reached the required level can be filtered.

[0084] The system also includes an online monitoring system connected to the stirring motors 8, temperature sensors 17, pH / alkali concentration online monitoring probes 18, valves on the pipelines, and metering pumps in each reactor. The online monitoring system collects the temperature and alkali concentration of each reactor in real time. It can adjust the temperature, alkali concentration, stirring rate, and feed rate of each reactor according to the product situation, and open and close valves. When needed, KOH can be supplemented through the KOH supplement metering pump 19.

[0085] The generated gases are collected from the gas outlet pipes 10 at the top of each reactor to the gas main pipe 11, which is connected to the gas collection tank 21. The gas collection tank 21 is connected to the combustion chamber 23 via a blower 27, and a flame arrester 22 is located near the ignition source (such as a burner or flare) in the combustion chamber 23. A chimney 28 is provided on the combustion chamber 23, and the upper end of the combustion chamber 23 is connected to the phosphoric acid absorption tower 25 via a blower. The upper end of the combustion chamber 23 is also connected to the waste heat boiler 24. The phosphoric acid absorption tower 25 is connected to the phosphoric acid solution storage tank 29 and the alkaline scrubbing tower 26.

[0086] The mixed gas from gas collection tank 21 is sent into combustion chamber 23 for controlled combustion, and the P4O generated by the combustion of phosphine is produced. 10 Phosphoric acid solution is obtained through water absorption. Hydrogen is burned to generate water vapor and recover heat. The residual tail gas is washed with alkaline solution and discharged in compliance with standards. The heat generated by combustion is recovered as by-product low-pressure steam through a waste heat boiler. The phosphoric acid solution obtained through water absorption is further reacted with potassium hydroxide to produce potassium dihydrogen phosphate fertilizer.

[0087] All gaseous products (phosphine and hydrogen) are collected in a gas tank and then sent to a combustion absorption device for treatment. Phosphoric acid generated from the combustion of phosphine is recovered in the form of phosphoric acid solution, and the combustion flue gas is discharged in compliance with standards after being washed with alkaline solution.

[0088] Based on the above system, the method steps of the embodiment are as follows: Step 1: Nitrogen Replacement and Anaerobic Environment Protection All four glass-jacketed reactors and their connecting pipelines were purged with nitrogen to replace the existing air inside the reactors, reducing the oxygen content of the system to below 0.5% (v / v). Throughout the reaction, a small amount of nitrogen was continuously introduced to maintain a slight positive pressure of 0.02-0.05 MPa to prevent backflow of external air.

[0089] Step 2: Preparation of alkali solution and initial feeding In the mixing tank, potassium hydroxide and deionized water are mixed to prepare a KOH aqueous solution with a concentration of 12-16 wt%; yellow phosphorus is melted with hot water and then fed into reactor I through its respective metering pump.

[0090] Step 3: Low-temperature disproportionation reaction occurs in reactor I (main reaction dominant stage). The KOH solution (12-16 wt%) prepared in step two is continuously fed into reactor I via a metering pump, while molten yellow phosphorus is simultaneously pumped into reactor I at a set flow rate. The jacket of reactor I is heated with heat transfer oil, maintaining the internal temperature at 55-65°C. The mechanical stirring speed is 80-120 rpm, and the residence time is 21.3-24.8 min. The molar ratio of yellow phosphorus to KOH is controlled at 1:3.

[0091] Under these low-temperature and low-alkali concentration conditions, yellow phosphorus reacts primarily with KOH in the main reaction (activation energy ≈ 40 kJ / mol, reaction order second), producing potassium hypophosphite (KH₂PO₂) and releasing phosphine gas (PH₃). The phosphine gas is drawn from the top of reactor I and collected in the gas main pipe 11.

[0092] Step 4: A medium-temperature transition reaction occurs in reactor II. The reaction solution in reactor I flows into reactor II via overflow pipe 5 due to gravity. The temperature inside reactor II is controlled at 65-75°C by jacket heating, the stirring speed is 80-120 rpm, and the residence time is 27-29.2 min. The alkali concentration is gradually increased to 16-19 wt%. KOH is added as needed to gradually increase the alkali concentration of the system.

[0093] At moderate temperatures and gradually increasing alkali concentrations, some potassium hypophosphite begins to convert to potassium phosphite, releasing hydrogen gas (H2) in the process. The gaseous products are drawn from the top of reactor II and collected in the gas main duct 11.

[0094] Step 5: High-temperature, high-alkali deep conversion reaction occurs in reactor III (mainly dominated by side reactions) The reaction solution in reactor II enters reactor III through overflow pipe 5. The temperature inside reactor III is controlled by jacket heating at 75-95°C, the stirring speed is 100-150 rpm, the alkali concentration is maintained at 19-22 wt%, and the residence time is 29.5-32.5 min.

[0095] Under the high temperature and high alkalinity conditions at this stage, the rate of the side reaction that generates potassium phosphite (activation energy ≈ 50-60 kJ / mol, NaOH concentration square-dependent reaction rate) significantly increases and becomes the dominant reaction. Potassium hypophosphite is partially and deeply converted into potassium phosphite, accompanied by the release of hydrogen gas. The gaseous products are drawn from the top of reactor III and collected in the gas main pipe 11.

[0096] Step Six: High-temperature curing and continuous discharge occur in reactor IV. The reaction solution in reactor III flows into reactor IV through an overflow pipe. Reactor IV is heated by a jacket to maintain the internal temperature at 80-95°C, the stirring speed at 80-120 rpm, the alkali concentration at 19-22 wt%, and the residence time at 33.7-35.8 min. The reaction continues until it approaches equilibrium.

[0097] The mixed solution containing potassium phosphite and unconverted potassium hypophosphite after the reaction is completed is continuously discharged from the bottom of reactor IV through a metering discharge valve to the filtration section. After filtration or separation and purification, and drying (if necessary, if a solid product needs to be prepared), a co-produced solid product of potassium phosphite and potassium hypophosphite is obtained, or a mixed liquid product is obtained directly.

[0098] Alternatively, the potassium hypophosphite solution (containing a small amount of potassium phosphite) after the reaction is completed is continuously discharged from the bottom of reactor I through a metering discharge valve to the filtration section. After filtration or separation and purification, and drying (if necessary, if a solid product needs to be prepared), a solid product with high potassium hypophosphite content is obtained, or a mixed liquid product with high potassium hypophosphite content is obtained directly.

[0099] Based on market demand, the co-produced products can be post-processed using the following existing methods: (1) If a single product of potassium phosphite is required, the difference in solubility of potassium phosphite and potassium hypophosphite in water can be utilized by stepwise crystallization (potassium hypophosphite usually has higher solubility). Potassium phosphite crystals are preferentially precipitated under low temperature conditions. After filtration and separation, high-purity potassium phosphite is obtained, and the mother liquor is potassium hypophosphite enrichment solution.

[0100] (2) If a single product of potassium hypophosphate is required, membrane separation technology (such as nanofiltration membrane) can be used to separate the two ions based on the difference in their hydration radii, or selective adsorption separation can be performed using ion exchange resin.

[0101] (3) If the mixed product can directly meet the end-use requirements (such as as a compound phosphorus source fertilizer or a chemical nickel plating reducing agent), then there is no need to separate it and it can be packaged and sold directly.

[0102] Step 7: Gaseous Product Collection and Tail Gas Treatment All gaseous products (phosphine PH3 and hydrogen H2) converge into the gas main 11 through the exhaust pipes at the top of each vessel, and are then collected in the gas collection tank 21. The gas collection tank 21 is filled with nitrogen to dilute and maintain the PH3 concentration below 25% of the lower limit of auto-ignition explosion. The mixed gas in the tank is periodically introduced into the combustion chamber 23 through a flame arrester 22 for controlled combustion under excess O2 conditions. PH3 is converted to P4O by combustion. 10 (It absorbs water to form a phosphoric acid solution), and H2 burns to produce water vapor.

[0103] The heat generated by combustion is recovered through waste heat boiler 24. The phosphorus-containing flue gas after combustion is absorbed by water in phosphoric acid absorption tower 25 to obtain the by-product phosphoric acid solution (concentration 35-50%); the residual tail gas is then treated by alkaline solution (NaOH) scrubbing tower 26 before being discharged in compliance with standards.

[0104] The phosphoric acid solution obtained in step seven can be sold as an industrial phosphoric acid product; it can also be further used in other processes within the factory to react with potassium hydroxide to produce orthophosphate products such as potassium dihydrogen phosphate (KH2PO4), thus realizing the closed-loop comprehensive utilization of phosphorus resources.

[0105] Example 1 (Standard Co-production Process) The method for co-producing potassium hypophosphite from potassium phosphite in this embodiment: Yellow phosphorus (purity ≥99.5%), potassium hydroxide (purity ≥90%), and deionized water were fed into a four-stage series glass-jacketed reactor assembly. Under nitrogen protection and positive pressure (0.04 MPa), the initial concentration of KOH was 14 wt%. The molar ratio of yellow phosphorus to KOH was controlled at 1:3. The reaction is carried out continuously according to the above process steps.

[0106] The process parameters for each reactor are set as follows: Reactor I: Temperature 60°C, KOH concentration 14 wt%, stirring speed 100 rpm, residence time 21.5 min.

[0107] Reactor II: Temperature 70°C, KOH concentration 18 wt%, stirring speed 100 rpm, residence time 28.1 min.

[0108] Reactor III: Temperature 85°C, KOH concentration 21 wt%, stirring speed 130 rpm, residence time 31 min.

[0109] Reactor IV: Temperature 90°C, KOH concentration 21 wt%, stirring speed 100 rpm, residence time 34.3 min.

[0110] Through continuous steady-state sampling and analysis, the average phosphorus (P2O5) content, average potassium (K2O) content, average water-insoluble matter content, and average pH (1% aqueous solution) of the potassium phosphite and potassium hypophosphite co-produced in Example 1 were 245 g / L, 330 g / L, 6.8 g / L, and 6.8, respectively. The mass ratio of potassium phosphite to potassium hypophosphite was approximately 5:1. The remaining harmful impurities met the limit requirements for toxic and harmful substances in fertilizers (GB38400-2019).

[0111] In Example 1, some of the controls are shown in Table 2 below: Table 2

[0112] Example 2 (Potassium hypophosphate co-production process) The method for co-producing potassium hypophosphite from potassium phosphite in this embodiment: When market demand is primarily for potassium hypophosphite, the process parameters should be adjusted as follows: Reactor I: Temperature 60°C, KOH concentration 14 wt%, stirring speed 100 rpm, residence time 21.3 min.

[0113] Reactor II: Temperature 65°C, KOH concentration 16 wt%, stirring speed 100 rpm, residence time 27 min.

[0114] Reactor III: Temperature 75°C, KOH concentration 19 wt%, stirring speed 120 rpm, residence time 29.5 min.

[0115] Reactor IV: Temperature 80°C, KOH concentration 19 wt%, stirring speed 100 rpm, residence time 33.7 min.

[0116] Continuous steady-state sampling and analysis revealed that the mass ratio of potassium phosphite to potassium hypophosphite in the product was approximately 1:2 (i.e., potassium hypophosphite was the main product), the total phosphorus (P₂O₅) content was 238 g / L, and the total potassium (K₂O) content was 325 g / L. This product can be directly used in industrial applications requiring strong reducing properties (such as electroless nickel plating), or potassium hypophosphite crystals can be preferentially separated using a stepwise crystallization method. The rest is the same as in Example 1.

[0117] Example 3 (High Potassium Phosphite Ratio Co-production Process) The method for co-producing potassium hypophosphite from potassium phosphite in this embodiment: When market demand is primarily for potassium phosphite, the process parameters should be adjusted as follows: Reactor I: Temperature 60°C, KOH concentration 16 wt%, stirring speed 100 rpm, residence time 21.3 min.

[0118] Reactor II: Temperature 70°C, KOH concentration 20 wt%, stirring speed 100 rpm, residence time 29.2 min.

[0119] Reactor III: Temperature 85°C, KOH concentration 24 wt%, stirring speed 120 rpm, residence time 32.5 min.

[0120] Reactor IV: Temperature 90°C, KOH concentration 24 wt%, stirring speed 100 rpm, residence time 35.8 min.

[0121] Through continuous steady-state sampling and analysis, the mass ratio of potassium phosphite to potassium hypophosphite in the product is approximately 2:1 (i.e., the content of potassium phosphite is approximately the main product).

[0122] Example 4 (Recycling of Phosphoric Acid Byproducts) The method for co-producing potassium hypophosphite from potassium phosphite in this embodiment: The phosphoric acid solution (concentration 41wt%) obtained from the tail gas combustion-absorption process in Example 1 was neutralized by adding solid potassium hydroxide at a molar ratio of KOH: H3PO4 of 1:1. The reaction temperature was 75°C, and the reaction was stirred for 1 hour. After cooling and crystallization, centrifugation and drying, industrial-grade potassium dihydrogen phosphate (KH2PO4) with a purity ≥98% was obtained, which can be used to formulate high phosphorus and potassium compound fertilizers.

[0123] Comparative Example 1 Unlike Example 1, one reactor was removed, and only a three-stage reaction was carried out. Five consecutive batches of product were tested. The average phosphorus (P₂O₅) content of the potassium phosphite-potassium hypophosphite co-produced product was <245 g / L, the average potassium (K₂O) content was <330 g / L, the average water-insoluble matter content was <6.8 g / L, and the average pH (1% aqueous solution) was <6.8. It is evident that, compared to Example 1, only a three-stage reaction was carried out, resulting in insufficient reaction depth and failing to meet the standards for a qualified product.

[0124] Therefore, the embodiments of the present invention bring the following beneficial effects: (1) Production efficiency is significantly improved. From the input of yellow phosphorus and potassium hydroxide to the continuous output of the final product, uninterrupted continuous production is achieved. Compared with the intermittent method, a lot of auxiliary time such as unloading, cleaning and re-feeding between batches is saved, and the equipment utilization rate and unit time capacity are greatly improved.

[0125] (2) Reduced raw material costs. By directly using yellow phosphorus and potassium hydroxide as raw materials, the preparation of phosphorous acid intermediates is eliminated, resulting in a significant reduction in raw material costs compared to the phosphorous acid neutralization route.

[0126] (3) Excellent product quality. Through stepped temperature control and precise management of alkali concentration under four-stage series conditions, side reactions such as deep oxidation are effectively suppressed. As verified by Example 1, the potassium phosphite content in the product is ≥50 wt%, and the potassium hypophosphite content can be adjusted within the range of 10-40 wt% according to the process conditions. The total proportion of +3 valent phosphorus and +1 valent phosphorus is much higher than the effective phosphorus content in the prior art. The harmful impurities in the product meet the requirements of the "Limit Requirements for Toxic and Hazardous Substances in Fertilizers" (GB38400-2019) and the relevant standards for industrial sodium hypophosphite (HG / T 3253-2023 "Industrial Sodium Hypophosphite").

[0127] (4) High process safety. The entire process is under N2 protection and positive pressure operation. Phosphine and hydrogen are collected centrally and then treated by controlled combustion, avoiding the risk of leakage of toxic and harmful gases. The process is inherently safer than the direct oxidation of yellow phosphorus.

[0128] (5) High resource utilization rate. The by-product phosphine is recovered by combustion and is used as a by-product of phosphoric acid. The heat from the combustion of the by-product hydrogen is used for heating and preheating of the reaction system. The comprehensive utilization rate of phosphorus (based on the products entering the product) can reach a high level. At the same time, the total amount of waste gas emissions is reduced, which has good environmental benefits.

[0129] (6) The product meets fertilizer standards. The potassium phosphite and potassium hypophosphite co-produced by this process meet the requirements of the group standard T / HNFLXH 001-2024 "Agricultural Potassium Phosphite" for potassium phosphite; if potassium hypophosphite is separated into a single product, its indicators can meet the requirements of HG / T 3253-2023 "Industrial Sodium Hypophosphite".

[0130] (7) Wider range of product applications. The co-product of this invention—a mixed solution of potassium phosphite and potassium hypophosphite—combines the characteristics of both compounds: potassium phosphite provides rapid supply of +3 valent phosphorus nutrients and has bactericidal and disease-preventing functions, while potassium hypophosphite provides slow-release +1 valent phosphorus nutrients (which can be slowly oxidized in the soil to a form that can be absorbed by plants) and has industrial application value (such as a reducing agent for chemical nickel plating, a polymer heat stabilizer, etc.). Users can directly use the mixed product as needed, or separate it into single components through simple post-processing. It has strong market adaptability and significant comprehensive economic benefits.

[0131] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for co-producing potassium hypophosphite from potassium phosphite, characterized in that: Specifically, the following steps are included: Step (1) Replace all reactors and pipelines with nitrogen to maintain a slight positive pressure in the system; Step (2) The potassium hydroxide aqueous solution and molten yellow phosphorus are continuously fed into the first-stage reactor to undergo a disproportionation reaction, generating potassium hypophosphite and phosphine; Step (3) The reaction solution from step (2) enters the second-stage reactor, and the alkali concentration gradually increases, with some potassium hypophosphite beginning to be converted into potassium phosphite; Step (4) The reaction solution from step (3) enters the third-stage reactor, where the alkali concentration is maintained at a certain level. Potassium hypophosphite is partially converted into potassium phosphite and hydrogen gas is released. Step (5) The reaction solution from step (4) enters the fourth stage reactor. The alkali concentration is maintained at a certain level. After the reaction approaches equilibrium, the product is continuously discharged from the fourth stage reactor to obtain a mixed solution product containing potassium phosphite and potassium hypophosphite.

2. The method according to claim 1, characterized in that: In step (2), the concentration of potassium hydroxide aqueous solution is 12-16wt%, the reaction temperature is controlled at 55-65°C, the stirring speed is 80-120 rpm, the molar ratio of yellow phosphorus to KOH is 1:3-3.5, and the residence time is 21.3-24.8 min.

3. The method according to claim 1, characterized in that: In step (3), the reaction temperature is controlled at 65-75°C, the stirring speed is 80-120 rpm, the alkali concentration is gradually increased to 16-19 wt%, and the residence time is 27-29.2 min.

4. The method according to claim 1, characterized in that: In step (4), the reaction temperature is controlled at 75-95°C, the stirring speed is 100-150 rpm, the alkali concentration is maintained at 19-22 wt%, potassium hypophosphite is partially converted into potassium phosphite and hydrogen is released, and the residence time is 29.5-32.5 min.

5. The method according to claim 1, characterized in that: In step (5), the reaction temperature is controlled at 80-95°C, the stirring speed is 80-120 rpm, the alkali concentration is maintained at 19-22 wt%, and the residence time is 33.7-35.8 min.

6. The method according to claim 1, characterized in that: In steps (3) and (4), the alkali concentration in the reaction solution is monitored in real time, and potassium hydroxide is automatically added when the alkali concentration is lower than the lower limit of the target range. The potassium hydroxide added in steps (3) and (4) is added in solid form or in the form of a concentrated solution with a concentration of ≥30 wt%.

7. The method according to claim 1, characterized in that: By adjusting the reaction temperature and / or alkali concentration and / or material residence time in the third and fourth stage reactors, the conversion depth of potassium hypophosphite to potassium phosphite can be controlled, so that the mass ratio of potassium phosphite to potassium hypophosphite in the product can be continuously adjusted within the range of 1:3 to 10:

1.

8. The method according to claim 1, characterized in that: It also includes step (6), where all gaseous products are collected from the top of each vessel and then subjected to combustion absorption treatment. The gaseous products include phosphine and hydrogen. The specific method of combustion absorption treatment is as follows: The mixed gas collected in the gas tank is sent into the combustion chamber for controlled combustion, and the P4O generated by the combustion of phosphine is produced. 10 Phosphoric acid solution is obtained through water absorption. Hydrogen is burned to generate water vapor and recover heat. The residual tail gas is washed with alkaline solution and discharged in compliance with standards. The heat generated by combustion is recovered as by-product low-pressure steam through a waste heat boiler. The phosphoric acid solution obtained through water absorption is further reacted with potassium hydroxide to produce potassium dihydrogen phosphate fertilizer.

9. A system for the co-production of potassium hypophosphite from potassium phosphite, characterized in that: include: Four-stage reactors, with decreasing height, and adjacent reactors are connected by overflow pipes; A yellow phosphorus feed metering pump and a KOH solution feed metering pump are connected to the primary reactor; A continuous discharge metering valve connected to the bottom of the four-stage reactor; Gas outlet pipes installed at the top of each reactor collect gas into a gas collection tank. The online monitoring system adjusts the temperature, alkali concentration, and feed rate of each reactor in real time. Aqueous potassium hydroxide solution and molten yellow phosphorus are continuously fed into the first-stage reactor, where a disproportionation reaction occurs to produce potassium hypophosphite and phosphine. The reaction solution enters the second-stage reactor, where the alkali concentration gradually increases, and some potassium hypophosphite begins to be converted into potassium phosphite. Then, the reaction solution enters the third-stage reactor, where the alkali concentration is maintained at a certain level, and potassium hypophosphite is partially converted into potassium phosphite and hydrogen gas is released. Then, the reaction solution enters the fourth-stage reactor, the alkali concentration is maintained at a certain concentration, and after the reaction approaches equilibrium, the product is continuously discharged from the fourth-stage reactor to obtain a mixed solution product containing potassium phosphite and potassium hypophosphite. The four glass-jacketed reactors have decreasing heights and are connected to each other. The reaction liquid flows automatically in stages by relying on the gravity difference.

10. The system according to claim 9, characterized in that: Also includes: Gas outlet pipes installed at the top of each reactor collect gas into a main gas pipe; gas collection tanks are connected to the main gas pipe. Combustion chamber and waste heat boiler; Phosphoric acid absorption tower and alkaline scrubbing tower; A heat transfer oil heating / cooling system connected to the jackets of each reactor; The mixed gas collected in the gas tank is sent into the combustion chamber for controlled combustion, and the P4O generated by the combustion of phosphine is produced. 10 Phosphoric acid solution is obtained through water absorption. Hydrogen is burned to generate water vapor and recover heat. The residual tail gas is washed with alkaline solution and discharged in compliance with standards. The heat generated by combustion is recovered as by-product low-pressure steam through a waste heat boiler and reused for preheating and heating of the reaction vessel. The phosphoric acid solution obtained through water absorption is further reacted with potassium hydroxide to produce potassium dihydrogen phosphate fertilizer.

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