A method for producing potassium dihydrogen phosphate by solvent extraction

Abstract

The application provides a method for producing potassium dihydrogen phosphate by a solvent extraction method, comprising the following steps: (1) preparing a clarified raw material solution; (2) adding the clarified raw material solution and an extractant into an extraction crystallizer to perform an extraction reaction; (3) allowing the solution to stand and separate, conveying the extracted organic phase to a back-extraction tank, and conveying the raffinate aqueous phase to a cooling crystallization tank; (4) performing cooling crystallization on the raffinate aqueous phase in the cooling crystallization tank, and after the cooling crystallization is completed, performing solid-liquid separation, and the obtained solid is potassium dihydrogen phosphate; (5) adding ammonia water into the back-extraction tank to perform a neutralization reaction, after the neutralization reaction is completed, allowing the solution to stand and separate, the obtained organic phase after the separation is the extractant, the extractant is stored in a storage tank and recycled, the obtained aqueous phase after the separation is concentrated and cooled and crystallized, and solid-liquid separation is performed, and the obtained solid phase is ammonium chloride. The application can simplify the process flow of the existing solvent extraction method for producing potassium dihydrogen phosphate, reduce equipment investment and operation cost, reduce the requirement for raw material acid, and reduce production cost.

Description

Technical Field

[0001] This invention belongs to the field of extraction separation and inorganic chemistry, and relates to a method for producing potassium dihydrogen phosphate by solvent extraction. Background Technology

[0002] Potassium dihydrogen phosphate (KH₂PO₄) is an important chemical raw material widely used in agriculture, food, pharmaceuticals, electronics, ceramics, and feed additives, especially in fine chemicals and high-tech fields. The main methods for preparing potassium dihydrogen phosphate include neutralization, solvent extraction, electrochemical methods, and metathesis methods. Currently, the mainstream industrial method for preparing potassium dihydrogen phosphate is the neutralization method, which has advantages such as a short process, high product purity, and simple process. However, its high raw material cost limits its further widespread application.

[0003] Solvent extraction is a method to obtain high-purity potassium dihydrogen phosphate by extracting it from hydrochloric acid after the reaction of phosphoric acid and potassium chloride. This method has advantages such as low energy consumption and good product quality, and has received increasing attention in recent years. For example, Xue Henan et al. (see Xue Henan et al., Solvent Extraction Technology for Potassium Dihydrogen Phosphate Production, Phosphate Fertilizer and Compound Fertilizer, 2023, Vol. 2, pp. 16-18) reported a process for preparing potassium dihydrogen phosphate from wet-process phosphoric acid by solvent extraction. In this process, wet-process phosphoric acid is desulfurized from phosphate rock slurry to obtain pretreated phosphoric acid. Then, the pretreated phosphoric acid, potassium chloride solution, and potassium dihydrogen phosphate mother liquor are mixed, and HCl is extracted using an extractant. The aqueous phase obtained after extraction and phase separation is the potassium dihydrogen phosphate feed solution. The potassium dihydrogen phosphate feed solution is then pressure filtered, and the filtrate is vacuum concentrated, cooled and crystallized, centrifuged, and fluidized bed dried to obtain the potassium dihydrogen phosphate product. The filter cake obtained from the pressure filtration is dried to obtain a phosphate and potassium fertilizer byproduct. Ammonia and water are added to the organic phase obtained from the extraction and phase separation for back-extraction. The extractant obtained after phase separation is returned to the extraction process for recycling. The resulting aqueous phase is an ammonium chloride solution, which is vacuum concentrated, cooled and crystallized, and centrifuged to obtain an ammonium chloride byproduct. Although the process yields high-quality potassium dihydrogen phosphate and produces ammonium chloride as a byproduct, the following problems still exist: (1) As shown in Figure 1 of the literature, the process includes a salt washing operation. This is mainly because the extractant extracts a certain amount of phosphoric acid during the extraction of hydrochloric acid. In order to avoid the phosphoric acid from having an adverse effect on the subsequent extraction, the extractant needs to be salt washed with saturated potassium chloride solution before back-extraction to remove the phosphoric acid. However, the salt washing step has strict requirements and is prone to problems such as emulsification, inability to separate phases, and entrainment, which leads to a complex process flow and difficulty in control, increasing equipment and operating costs; (2) The process directly introduces ammonia and water into the back-extraction tank for neutralization reaction. Because ammonia The process of dissolving gas in water and neutralizing it with hydrochloric acid are both strongly exothermic reactions, which makes it difficult to control the entire process of back-extraction to prepare ammonium chloride. In addition, the temperature of the extractant obtained after back-extraction is high, and it must be cooled by water washing before it can be used for subsequent extraction, which indirectly increases energy consumption and equipment investment and operating costs. (3) Existing methods generally use industrial-grade phosphoric acid as raw material acid when preparing potassium dihydrogen phosphate. Although the process reported in the above literature uses lower-cost wet phosphoric acid, it requires pretreatment of wet phosphoric acid, which leads to a complex process flow and increased costs. It cannot be used for low-quality raw material acid containing nitric acid or sulfuric acid and metal impurity ions. In summary, the above-reported processes have problems such as long process flow, large equipment investment and operating costs, and high requirements for raw material acid, which greatly limit the large-scale promotion and application of solvent extraction method for preparing potassium dihydrogen phosphate. Summary of the Invention

[0004] To address the problems of long process flow, high equipment investment and operating costs, and high requirements for raw acid in the existing solvent extraction method for preparing potassium dihydrogen phosphate, this invention provides a method for producing potassium dihydrogen phosphate by solvent extraction, which simplifies the process flow, reduces equipment investment and operating costs, and lowers the requirements for raw acid, thereby reducing the production cost of potassium dihydrogen phosphate.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for producing potassium dihydrogen phosphate by solvent extraction includes the following steps:

[0007] (1) The raw acid and potassium chloride are dissolved in the first mother liquor to prepare a crude raw material solution at a temperature of 40-70℃. The molar ratio of phosphoric acid to potassium chloride in the crude raw material solution is controlled to be (0.85-1.3):1. A filter aid is added to the crude raw material solution, and after thorough stirring, the solution is filtered to obtain a clear raw material solution. The raw acid contains 30wt%-60wt% P2O5, 1wt%-1.5wt% nitric acid, 0.05wt%-0.1% iron ions, and 0.3wt%-1wt% sulfuric acid.

[0008] (2) The clarified raw material solution and the extractant are added to an extraction crystallizer for extraction reaction. The pH value of the extraction reaction is controlled between 3.5 and 4.5 by controlling the addition ratio of the clarified raw material solution and the extractant. The extractant consists of a main agent and an auxiliary agent. The main agent is N,N-diisooctylethanolamine and trioctylmethylammonium chloride, and the auxiliary agent is xylene and C8-C9 ... 16 Alkanes, C8-C 16 The alkane is at least one of the alkanes having 8 to 16 carbon atoms, and the volume ratio of the main agent to the auxiliary agent is (0.2 to 0.6):1;

[0009] (3) After the extraction reaction is completed, the phases are separated by standing. The extracted organic phase is transferred to the back-extraction tank, and the raffinate aqueous phase is transferred to the cooling crystallization tank.

[0010] (4) Cool the aqueous phase in the cooling crystallizer to crystallize. After the cooling crystallization is completed, the solid and liquid are separated. The obtained solid is potassium dihydrogen phosphate and the obtained liquid phase is the first mother liquor. The first mother liquor is sent to step (1) to prepare the crude raw material liquid.

[0011] (5) Add ammonia water to the back-extraction tank for neutralization reaction. During the neutralization reaction, the pH value of the mixture in the back-extraction tank is maintained at 6.5-7.5 by adding ammonia water. After the neutralization reaction is completed, the resulting reaction solution is input into the back-extraction phase separation tank and allowed to stand for phase separation. The organic phase obtained by phase separation is the extractant. The extractant is stored in the storage tank and the extractant in the storage tank is transported to step (2) for extraction reaction. The aqueous phase obtained by phase separation is concentrated, cooled and crystallized, and the solid and liquid are separated. The obtained solid phase is ammonium chloride and the obtained liquid phase is the second mother liquor. The second mother liquor is transported to the back-extraction tank.

[0012] In the above technical solution, the preferred volume ratio of N,N-diisooctylethanolamine to trioctylmethylammonium chloride in the main component of the extractant is (0.5-1.2):1.

[0013] In the above technical solution, xylene and C8-C964 are used as auxiliary agents in the extractant. 16 The preferred volume ratio of alkanes is (0.8–2):1.

[0014] In the above technical solution, the volume ratio of the main agent to the auxiliary agent in the extractant is preferably (0.4-0.6):1.

[0015] In step (1) of the above technical solution, the main function of adding a filter aid for filtration is to change the color of the low-quality raw material acid and increase the clarity of the crude raw material liquid. The filter aid is activated carbon, and the preferred amount of filter aid added is 0.1% to 0.5% of the mass of the crude raw material liquid.

[0016] In step (1) of the above technical solution, filtration is usually carried out after adding the filter aid and stirring for 30 to 60 minutes.

[0017] In step (1) of the above technical solution, the concentration of chloride ions in the crude raw material liquid is controlled to be 1.5 to 3.2 mol / L.

[0018] In step (2) of the above technical solution, the pH value of the extraction reaction is controlled between 3.5 and 4.5 by controlling the addition ratio of the clarified raw material liquid and the extractant. That is, the pH value of the mixture of the clarified raw material and the extractant is controlled between 3.5 and 4.5 by adjusting the addition ratio of the clarified raw material liquid and the extractant. Preferably, the volume ratio of the clarified raw material liquid to the extractant in the extraction crystallizer is controlled to be (1 to 2.5):1.

[0019] In step (2) of the above technical solution, it is preferred to control the extraction reaction temperature to be 20-60℃ and the extraction reaction time to be 10-60min.

[0020] In step (4) of the above technical solution, the raffinate in the cooling crystallizer is cooled to 20-35°C and kept for 30-90 minutes for cooling crystallization of potassium dihydrogen phosphate. During the cooling crystallization process, it is best to apply stirring at a speed of 10-100 rpm.

[0021] In step (4) of the above technical solution, the obtained potassium dihydrogen phosphate is transported to a drying bed for drying, thereby obtaining the potassium dihydrogen phosphate product.

[0022] In step (5) of the above technical solution, the temperature of the neutralization reaction is maintained by the heat released by the neutralization reaction itself, without the need for additional heating or cooling, that is, the temperature of the neutralization reaction is naturally maintained at 40-70℃; in this step, it is preferred to control the neutralization reaction time to 30-60min.

[0023] In step (5) of the above technical solution, the aqueous phase obtained by phase separation is vacuum concentrated, then cooled to 20-35°C and kept for 30-90 minutes to perform cooling crystallization of ammonium chloride. During the cooling crystallization process, it is best to apply stirring at a speed of 10-100 rpm.

[0024] Compared with the prior art, the technical solution provided by the present invention has the following beneficial technical effects:

[0025] 1. This invention provides a method for producing potassium dihydrogen phosphate by solvent extraction. Its main feature is the use of a composite extractant, which uses N,N-diisooctylethanolamine and trioctylmethylammonium chloride as the main agents. The extractant utilizes the ion exchange effect of trioctylmethylammonium chloride to extract hydrochloric acid, and utilizes the combination of N,N-diisooctylethanolamine with Cl after protonation. - The extraction of hydrochloric acid is achieved by adjusting the ratio of the two compounds, resulting in a synergistic effect between the two mechanisms. This effectively enhances the selective separation performance of the extractant for hydrochloric acid and phosphoric acid. Simultaneously, low-viscosity xylene and C8-C964 are used. 16 Alkanes are used as auxiliary agents to adjust the viscosity and density of the extractant to appropriate levels, promoting phase separation of the oil and water phases after extraction. Compared to tert-butylamine extractants used in the existing industrial production of potassium dihydrogen phosphate, the composite extractant used in this invention enhances the extraction effect on hydrochloric acid while almost completely eliminating the extraction of phosphoric acid, exhibiting excellent selective separation performance. Based on this composite extractant, the method of this invention effectively avoids the problem of simultaneous extraction of hydrochloric acid and phosphoric acid, thus eliminating the salt washing operation in the existing potassium dihydrogen phosphate production process. This avoids the problems of emulsification, inability to separate phases, and entrainment that can easily occur during salt washing, simplifying the process flow, increasing process controllability, and reducing equipment and operating costs.

[0026] 2. The method described in this invention is well-suited for low-quality raw material acids containing nitric acid, sulfuric acid, and metal ions (raw material acid with P2O5 content of 30wt%–60wt%, nitric acid content of 1wt%–1.5wt%, iron ion content of 0.05wt%–0.1%, and sulfuric acid content of 0.3wt%–1wt%). Using low-quality raw material acids can effectively reduce the cost of raw material acids. This invention can solve the problem of excessively high raw material acid costs caused by the use of industrial-grade phosphoric acid as a raw material acid in existing potassium dihydrogen phosphate industrial production methods. It can also solve the problem of increased process complexity and cost caused by the need for pretreatment when using wet-process phosphoric acid as a raw material acid in existing potassium dihydrogen phosphate industrial production methods.

[0027] 3. Experiments have confirmed that the potassium dihydrogen phosphate produced by the method described in this invention meets the superior grade requirements of HG / T2321-2016 ("Fertilizer Grade Potassium Dihydrogen Phosphate"). Furthermore, even after recycling the composite extractant described in this invention 100 times, potassium dihydrogen phosphate products meeting the superior grade requirements of HG / T2321-2016 ("Fertilizer Grade Potassium Dihydrogen Phosphate") can still be produced. This indicates that the composite extractant used in this invention has excellent cycle stability, and the extractant with accumulated impurities still exhibits excellent extraction performance after back-extraction and regeneration. This is extremely beneficial for reducing the production cost of potassium dihydrogen phosphate.

[0028] 4. The method of the present invention directly adds ammonia water to the back-extraction tank for neutralization reaction in the back-extraction step, which changes the existing process of directly introducing ammonia gas into the back-extraction tank for neutralization reaction. This avoids the problem that the temperature in the back-extraction tank rises due to the exothermic reaction of ammonia gas during liquefaction, which makes it difficult to control the ammonium chloride preparation process. It effectively controls the temperature of the extractant after back-extraction, so there is no need to wash and cool the extractant with water after back-extraction, which simplifies the process and can save equipment and operating costs. Detailed Implementation

[0029] The following examples further illustrate the solvent extraction method for producing potassium dihydrogen phosphate provided by the present invention. It should be noted that the following examples are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description are still within the scope of protection of the present invention.

[0030] Example 1

[0031] The ability of the extractant used in this invention to selectively separate hydrochloric acid and phosphoric acid was investigated.

[0032] A special extractant for preparing potassium dihydrogen phosphate by solvent extraction is composed of a main agent and an auxiliary agent in a volume ratio of 0.43:1. The main agent consists of N,N-diisooctylethanolamine and trioctylmethylammonium chloride in a volume ratio of 1:1, and the auxiliary agent consists of xylene and dodecane in a volume ratio of 1:1.

[0033] Phosphoric acid and potassium chloride were dissolved in deionized water at a molar ratio of 1:1 to form an aqueous solution with a chloride ion concentration of 2.29 mol / L. The extractant described in this example was used as the organic phase. The aqueous and organic phases were added to a 500 mL separatory funnel at a volume ratio of 1:1. The mixture was shaken and reacted for 6 min at room temperature and atmospheric pressure. After settling, timing was started. Timing was stopped when both the extracted organic phase and the remaining aqueous phase were completely clear. The phase separation time was found to be 28 s.

[0034] Based on sampling and testing, the extraction rate of hydrochloric acid in this embodiment was 99.5%, and the extraction rate of phosphoric acid was 1.0%. The raffinate was evaporated, concentrated, and crystallized to obtain potassium dihydrogen phosphate product, with a yield of 98.3%. Sampling and testing showed that the purity of potassium dihydrogen phosphate was 99.5%.

[0035] Comparative Example 1

[0036] In this comparative example, the ability of existing extractants to selectively separate hydrochloric acid and phosphoric acid was examined.

[0037] The extractant used in this comparative example was a mixture of trioctylamine, cyclohexane, and isoamyl alcohol in a volume ratio of 2:4:1.

[0038] Phosphoric acid and potassium chloride were dissolved in deionized water at a molar ratio of 1:1 to form an aqueous solution with a chloride ion concentration of 2.29 mol / L. The above-mentioned extractant from this comparative example was used as the organic phase. The aqueous and organic phases were added to a 500 mL separatory funnel at a volume ratio of 1:1. The mixture was shaken and reacted for 10 min at room temperature and atmospheric pressure. After standing, timing was started. Timing was stopped when the extracted organic phase and the raffinate aqueous phase were completely clear. The phase separation time was found to be 6 min.

[0039] Based on sampling and testing, the extraction rate of the above-mentioned extractant for hydrochloric acid was 95.7%, and the extraction rate for phosphoric acid was 4.5%. The raffinate was evaporated, concentrated, and crystallized to obtain potassium dihydrogen phosphate product, with a yield of 91.3%. Sampling and testing showed that the purity of potassium dihydrogen phosphate was 97.2%.

[0040] As can be seen from Example 1 and Comparative Example 1, compared with existing extractants, the composite extractant used in this invention can improve the separation selectivity of hydrochloric acid and phosphoric acid when preparing potassium dihydrogen phosphate by solvent extraction. While ensuring a high extraction rate for hydrochloric acid, it can effectively reduce the extraction rate for phosphoric acid and effectively shorten the phase separation time of oil and water after extraction.

[0041] Example 2

[0042] In this embodiment, a method for producing potassium dihydrogen phosphate by solvent extraction according to the present invention is provided, comprising the following steps:

[0043] (1) Dissolve the raw acid and potassium chloride in the first mother liquor to prepare a crude raw material solution at a temperature of 50℃. Control the molar ratio of phosphoric acid to potassium chloride in the crude raw material solution to be 1:1 and control the concentration of chloride ions in the crude raw material solution to be 2.4 mol / L. Add activated carbon filter aid to the crude raw material solution, the amount of activated carbon added is 0.5% of the mass of the crude raw material solution, stir for 30 min and then filter to obtain a clear raw material solution.

[0044] The raw acid contains 60 wt% P2O5, 1.5 wt% nitric acid, 0.1 wt% iron ions, and 0.5 wt% sulfate ions. The first mother liquor originates from step (4), and in the initial stage of the entire process, the first mother liquor is water.

[0045] (2) Add the clarified raw material liquid and the extractant to the extraction crystallizer for extraction reaction. Control the volume ratio of the clarified raw material liquid to the extractant in the extraction crystallizer to be 1.3:1. Control the pH value of the extraction reaction to be about 4. Control the extraction reaction temperature to be 50℃ and the extraction reaction time to be 30min.

[0046] The extractant is a mixture of a main agent and an auxiliary agent in a volume ratio of 0.43:1. The main agent is composed of N,N-diisooctylethanolamine and trioctylmethylammonium chloride in a volume ratio of 1:1, and the auxiliary agent is composed of xylene and dodecane in a volume ratio of 1:1.

[0047] (3) After the extraction reaction is completed, the phases are separated by standing. The extracted organic phase (located in the upper layer) is transported to the back-extraction tank, and the raffinate aqueous phase (located in the lower layer) is transported to the cooling crystallization tank.

[0048] (4) Cool the raffinate in the cooling crystallizer to 35°C and maintain this temperature for 60 min to perform cooling crystallization of potassium dihydrogen phosphate. During the cooling crystallization process, stir at a speed of 50 rpm. After cooling crystallization is completed, the resulting liquid containing potassium dihydrogen phosphate crystals is sent to a centrifugal decanter for continuous solid-liquid separation. The separated solid phase is sent to a drying bed and dried at 80°C to obtain potassium dihydrogen phosphate product. The separated liquid phase is recorded as the first mother liquor and returned to step (1) for the preparation of crude raw material liquid.

[0049] (5) Add ammonia water to the back-extraction tank for neutralization reaction. During the neutralization reaction, control the amount of ammonia water added to keep the pH value of the mixture in the back-extraction tank at 6.5 to 7.5. Control the neutralization reaction time to 60 min. The temperature of the neutralization reaction is maintained by the heat released by the neutralization reaction itself. No additional heating or cooling is required. The temperature of the neutralization reaction is naturally maintained in the range of 55 to 65℃.

[0050] After the neutralization reaction is completed, the resulting reaction solution is fed into the back-extraction phase separation tank and allowed to stand for phase separation. The organic phase obtained from the phase separation (located in the upper layer) is the extractant. This extractant is stored in a storage tank and then transported to step (2) for extraction reaction. The aqueous phase obtained from the phase separation (located in the lower layer) is fed into a vacuum concentrator and concentrated to a solid content of 20 wt% under 50 kPa conditions. The concentrated solution is then transported to an ammonium chloride cooling crystallizer, cooled to 35°C, and maintained at this temperature for 90 min for ammonium chloride cooling crystallization. During the cooling crystallization process, stirring is applied at a speed of 50 rpm. After cooling crystallization is completed, the resulting solution containing ammonium chloride crystals is separated by a centrifuge. The resulting solid phase is the ammonium chloride product, and the resulting liquid phase is the second mother liquor. The second mother liquor is then transported to the back-extraction tank.

[0051] The potassium dihydrogen phosphate product prepared in step (4) was tested, and the results showed that the mass fraction of potassium dihydrogen phosphate was 99.8% and the mass fraction of phosphorus pentoxide was 52.1%, which met the superior grade index in HG / T2321-2016 ("Fertilizer Grade Potassium Dihydrogen Phosphate"). Based on the yield of potassium dihydrogen phosphate and ammonium chloride products in steps (4) and (5), approximately 0.6 tons of ammonium chloride products will be produced as a byproduct for every ton of potassium dihydrogen phosphate product produced.

[0052] Comparative Example 2

[0053] In this comparative example, potassium dihydrogen phosphate is produced using an existing extractant in combination with industrial-grade phosphoric acid. The steps are as follows:

[0054] (1) Industrial-grade phosphoric acid and potassium chloride are dissolved in the first mother liquor to prepare a crude raw material solution at a temperature of 50°C. The molar ratio of phosphoric acid to potassium chloride in the crude raw material solution is controlled at 1:1, and the concentration of chloride ions in the crude raw material solution is controlled at 2.4 mol / L. Activated carbon filter aid is added to the raw material solution, and the amount of activated carbon added is 0.5% of the mass of the crude raw material solution. After stirring for 30 min, the solution is filtered to obtain a clear raw material solution. The industrial-grade phosphoric acid contains 60 wt% P2O5, 0.001 wt% nitric acid, 0.001 wt% iron ions, and 0.005 wt% sulfate ions. The first mother liquor is derived from step (4). In the initial stage of the entire process, the first mother liquor is water.

[0055] (2) The clarified raw material solution and the extractant are added to an extraction crystallizer for extraction reaction. The volume ratio of the clarified raw material solution to the extractant in the extraction crystallizer is controlled at 1.3:1. The pH value of the extraction reaction is controlled at approximately 4. The extraction reaction temperature is controlled at 50℃ and the extraction reaction time is controlled at 30 min. The extractant is a mixture of trioctylamine, cyclohexane, and isoamyl alcohol in a volume ratio of 2:4:1.

[0056] (3) After the extraction reaction is completed, the phases are separated by standing. The extracted organic phase (located in the upper layer) is transported to the washing tank, and the raffinate aqueous phase (located in the lower layer) is transported to the cooling crystallization tank.

[0057] (4) Cool the raffinate in the cooling crystallizer to 35°C and maintain this temperature for 60 min to perform cooling crystallization of potassium dihydrogen phosphate. During the cooling crystallization process, stir at a speed of 50 rpm. After cooling crystallization is completed, the resulting liquid containing potassium dihydrogen phosphate crystals is sent to a centrifugal decanter for continuous solid-liquid separation. The separated solid phase is sent to a drying bed and dried at 80°C to obtain potassium dihydrogen phosphate product. The separated liquid phase is recorded as the first mother liquor and returned to step (1) for the preparation of crude raw material liquid.

[0058] (5) In the washing tank, the organic phase of extraction (saturated loaded extractant) is washed with saturated potassium chloride at a temperature of 50°C for 60 minutes. The washed extractant and washing mother liquor are allowed to stand in the washing phase separation tank for phase separation. The washing mother liquor is returned to the washing liquid preparation tank for the preparation of saturated potassium chloride. The extractant is then transported to the back-extraction tank.

[0059] (6) Add ammonia water to the back-extraction tank for neutralization reaction. During the neutralization reaction, control the amount of ammonia water added to keep the pH value of the mixture in the back-extraction tank at 6.5 to 7.5. Control the neutralization reaction time to 60 min. The temperature of the neutralization reaction is maintained by the heat released by the neutralization reaction itself. No additional heating or cooling is required. The temperature of the neutralization reaction is naturally maintained in the range of 55 to 65℃.

[0060] After the neutralization reaction is completed, the resulting reaction solution is fed into the back-extraction phase separation tank and allowed to stand for phase separation. The organic phase obtained from the phase separation (located in the upper layer) is the extractant. This extractant is stored in a storage tank and then transported to step (2) for extraction reaction. The aqueous phase obtained from the phase separation (located in the lower layer) is fed into a vacuum concentrator and concentrated to a solid content of 20 wt% under 50 kPa conditions. The concentrated solution is then transported to an ammonium chloride cooling crystallizer, cooled to 35°C, and maintained at this temperature for 90 min for ammonium chloride cooling crystallization. During the cooling crystallization process, stirring is applied at a speed of 50 rpm. After cooling crystallization is completed, the resulting solution containing ammonium chloride crystals is separated by a centrifuge. The resulting solid phase is the ammonium chloride product, and the resulting liquid phase is the second mother liquor. The second mother liquor is then transported to the back-extraction tank.

[0061] The potassium dihydrogen phosphate product prepared in step (4) was tested, and the results showed that the mass fraction of potassium dihydrogen phosphate was 99.5% and the mass fraction of phosphorus pentoxide was 52.1%, which met the superior grade index in HG / T2321-2016 ("Fertilizer Grade Potassium Dihydrogen Phosphate"). Based on the yield of potassium dihydrogen phosphate and ammonium chloride products in steps (4) and (6), approximately 0.6 tons of ammonium chloride products will be produced as a byproduct for every ton of potassium dihydrogen phosphate product produced.

[0062] Comparative Example 3

[0063] In this comparative example, potassium dihydrogen phosphate is produced using an existing extractant in combination with low-quality phosphoric acid. The steps are as follows:

[0064] (1) Dissolve the raw acid and potassium chloride in the first mother liquor to prepare a crude raw material solution at a temperature of 50℃. Control the molar ratio of phosphoric acid to potassium chloride in the crude raw material solution to be 1:1 and control the concentration of chloride ions in the crude raw material solution to be 2.4 mol / L. Add activated carbon filter aid to the crude raw material solution, the amount of activated carbon added is 0.5% of the mass of the crude raw material solution, stir for 30 min and then filter to obtain a clear raw material solution.

[0065] The raw acid contains 60 wt% P2O5, 1.5 wt% nitric acid, 0.1 wt% iron ions, and 0.5 wt% sulfate ions. The first mother liquor originates from step (4), and in the initial stage of the entire process, the first mother liquor is water.

[0066] (2) The clarified raw material solution and the extractant are added to an extraction crystallizer for extraction reaction. The volume ratio of the clarified raw material solution to the extractant in the extraction crystallizer is controlled at 1.3:1. The pH value of the extraction reaction is controlled at approximately 4. The extraction reaction temperature is controlled at 50℃ and the extraction reaction time is controlled at 30 min. The extractant is a mixture of trioctylamine, cyclohexane, and isoamyl alcohol in a volume ratio of 2:4:1.

[0067] (3) After the extraction reaction is completed, the phases are separated by standing. The extracted organic phase (located in the upper layer) is transported to the washing tank, and the raffinate aqueous phase (located in the lower layer) is transported to the cooling crystallization tank.

[0068] (4) Cool the raffinate in the cooling crystallizer to 35°C and maintain this temperature for 60 min to perform cooling crystallization of potassium dihydrogen phosphate. During the cooling crystallization process, stir at a speed of 50 rpm. After cooling crystallization is completed, the resulting liquid containing potassium dihydrogen phosphate crystals is sent to a centrifugal decanter for continuous solid-liquid separation. The separated solid phase is sent to a drying bed and dried at 80°C to obtain potassium dihydrogen phosphate product. The separated liquid phase is recorded as the first mother liquor and returned to step (1) for the preparation of crude raw material liquid.

[0069] (5) In the washing tank, the organic phase of extraction (saturated loaded extractant) is washed with saturated potassium chloride at a temperature of 50°C for 60 minutes. The washed extractant and washing mother liquor are allowed to stand in the washing phase separation tank for phase separation. The washing mother liquor is returned to the washing liquid preparation tank for the preparation of saturated potassium chloride. The extractant is then transported to the back-extraction tank.

[0070] (6) Add ammonia water to the back-extraction tank for neutralization reaction. During the neutralization reaction, control the amount of ammonia water added to keep the pH value of the mixture in the back-extraction tank at 6.5 to 7.5. Control the neutralization reaction time to 60 min. The temperature of the neutralization reaction is maintained by the heat released by the neutralization reaction itself. No additional heating or cooling is required. The temperature of the neutralization reaction is naturally maintained in the range of 55 to 65℃.

[0071] After the neutralization reaction is completed, the resulting reaction solution is fed into the back-extraction phase separation tank and allowed to stand for phase separation. The organic phase obtained from the phase separation (located in the upper layer) is the extractant. This extractant is stored in a storage tank and then transported to step (2) for extraction reaction. The aqueous phase obtained from the phase separation (located in the lower layer) is fed into a vacuum concentrator and concentrated to a solid content of 20 wt% under 50 kPa conditions. The concentrated solution is then transported to an ammonium chloride cooling crystallizer, cooled to 35°C, and maintained at this temperature for 90 min for ammonium chloride cooling crystallization. During the cooling crystallization process, stirring is applied at a speed of 50 rpm. After cooling crystallization is completed, the resulting solution containing ammonium chloride crystals is separated by a centrifuge. The resulting solid phase is the ammonium chloride product, and the resulting liquid phase is the second mother liquor. The second mother liquor is then transported to the back-extraction tank.

[0072] The potassium dihydrogen phosphate product prepared in step (4) was tested, and the results showed that the mass fraction of potassium dihydrogen phosphate was 95.3% and the mass fraction of phosphorus pentoxide was 50.1%, which met the first-class product index in HG / T2312-2016 ("Fertilizer Grade Potassium Dihydrogen Phosphate"). Based on the yield of potassium dihydrogen phosphate and ammonium chloride products in steps (4) and (6), approximately 0.6 tons of ammonium chloride products will be produced as a byproduct for every ton of potassium dihydrogen phosphate product produced.

[0073] As can be seen from Examples 2 and 2-3, when using existing extractants in combination with industrial-grade phosphoric acid to produce potassium dihydrogen phosphate, although the prepared potassium dihydrogen phosphate can meet the requirements of superior grade, the existing extractant trioctylamine has poor selective separation performance for hydrochloric acid and phosphoric acid. During the extraction of hydrochloric acid, a certain amount of phosphoric acid is extracted. To avoid the phosphoric acid entering the extractant and adversely affecting subsequent extraction, the extractant needs to be salt-washed with a saturated potassium chloride solution before back-extraction. This increases the process steps and equipment and operating costs. When using existing extractants in combination with low-quality phosphoric acid to produce potassium dihydrogen phosphate, although a salt-washing operation is added before back-extraction, the quality of the prepared potassium dihydrogen phosphate is still reduced. The above experimental results demonstrate that when using the composite extractant to prepare potassium dihydrogen phosphate, the salt washing operation before back-extraction can be omitted, and the requirements for raw material acid can be reduced. When using low-quality acid as raw material acid, the composite extractant with a certain amount of impurities can be recycled after back-extraction without significantly reducing the quality of potassium dihydrogen phosphate. High-quality potassium dihydrogen phosphate can still be prepared. This is mainly due to the improved selective separation performance of the composite extractant of the present invention for hydrochloric acid and phosphoric acid.

[0074] Comparative Example 4

[0075] In this comparative example, ammonia gas was directly introduced into the back-extraction tank during the back-extraction step to investigate its effect on the temperature of the neutralization reaction system.

[0076] Steps (1) to (4) are the same as steps (1) to (4) in Example 2.

[0077] (5) Ammonia gas is introduced into the back-extraction tank for neutralization. During the neutralization reaction, the amount of ammonia introduced is controlled to maintain the pH value of the mixture in the back-extraction tank at 6.5-7.5, and the neutralization reaction time is controlled to be 60 min. Since the process of ammonia dissolving in water and the process of ammonia water reacting with hydrochloric acid both release a large amount of heat, if no special cooling operation is performed in this step, the temperature of the neutralization reaction will naturally remain at 80-100℃, which will make it difficult to control the system temperature. A special water washing step is required to lower the temperature of the extractant. Since the temperature of the extraction reaction needs to be controlled within the range of 20-60℃, the pressure of subsequent water washing heat exchange is relatively large.

[0078] After the neutralization reaction is completed, the resulting reaction solution is fed into the back-extraction phase separation tank and allowed to stand for phase separation. The organic phase obtained from the phase separation (located in the upper layer) is the extractant. This extractant is stored in a storage tank. The extractant in the storage tank is washed with water and heated to a temperature of 50°C before being sent to step (2) for extraction reaction. The aqueous phase obtained from the phase separation (located in the lower layer) is fed into a vacuum concentrator. The aqueous phase in the vacuum concentrator is concentrated to a solid content of 20 wt% under a condition of 50 kPa. The concentrated solution is then sent to an ammonium chloride cooling crystallizer and cooled to 35°C. This temperature is maintained for 90 min to perform ammonium chloride cooling crystallization. During the cooling crystallization process, stirring is applied at a speed of 50 rpm. After the cooling crystallization is completed, the solution containing ammonium chloride crystals is separated by a centrifuge. The resulting solid phase is the ammonium chloride product, and the resulting liquid phase is the second mother liquor. The second mother liquor is sent to the back-extraction tank.

[0079] As can be seen from Example 2 and Comparative Example 4, this application uses ammonia water instead of ammonia gas in the back-extraction process, which eliminates the need for additional heating or cooling operations. The temperature of the neutralization reaction can be naturally maintained in the range of 55-65°C, which can effectively reduce the difficulty of controlling the back-extraction process to prepare ammonium chloride. It can also eliminate the process of washing and cooling the high-temperature extractant with water, which not only reduces the process operations, but also reduces energy consumption and equipment investment and operating costs.

[0080] Example 3

[0081] In this embodiment, potassium dihydrogen phosphate is produced using the method described in this invention, and the recycling performance of the extractant is investigated. The steps are as follows:

[0082] The operations of steps (1) to (5) are the same as those of steps (1) to (5) in Example 2.

[0083] (6) Following steps (1) to (5), the extractant is recycled 100 times. The potassium dihydrogen phosphate product prepared in step (4) after the 100th recycling of the extractant is tested. The results show that the mass fraction of potassium dihydrogen phosphate in the product is 99.7%, and the mass fraction of phosphorus pentoxide is 52.0%, which meets the superior grade index in HG / T2321-2016 ("Fertilizer Grade Potassium Dihydrogen Phosphate"). Based on the yield of potassium dihydrogen phosphate and ammonium chloride products in steps (4) and (5), approximately 0.6 tons of ammonium chloride products are produced as a byproduct for every ton of potassium dihydrogen phosphate product produced, which is comparable to the effect when the extractant is used for the first time. This indicates that the composite extractant used in this invention can be repeatedly recycled and has good stability.

[0084] Example 4

[0085] In this embodiment, a method for producing potassium dihydrogen phosphate by solvent extraction according to the present invention is provided, comprising the following steps:

[0086] (1) The raw acid and potassium chloride were dissolved in the first mother liquor to prepare a crude raw material solution at a temperature of 70°C. The molar ratio of phosphoric acid to potassium chloride in the crude raw material solution was controlled at 0.85:1, and the concentration of chloride ions in the crude raw material solution was controlled at 3.2 mol / L. Activated carbon filter aid was added to the crude raw material solution at a concentration of 0.3% of the mass of the crude raw material solution. After stirring for 60 min, the solution was filtered to obtain a clear raw material solution.

[0087] The raw acid contains 50 wt% P2O5, 1 wt% nitric acid, 0.05 wt% iron ions, and 0.3 wt% sulfate ions. The first mother liquor originates from step (4), and in the initial stage of the entire process, the first mother liquor is water.

[0088] (2) Add the clarified raw material liquid and the extractant to the extraction crystallizer for extraction reaction. Control the volume ratio of the clarified raw material liquid to the extractant in the extraction crystallizer to be 2.5:1. Control the pH value of the extraction reaction to be about 3.5. Control the extraction reaction temperature to be 60℃ and the extraction reaction time to be 10min.

[0089] The extractant is a mixture of a main agent and an auxiliary agent in a volume ratio of 0.5:1. The main agent is composed of N,N-diisooctylethanolamine and trioctylmethylammonium chloride in a volume ratio of 0.5:1, and the auxiliary agent is composed of xylene and hexadecane in a volume ratio of 1:1.

[0090] (3) After the extraction reaction is completed, the phases are separated by standing. The extracted organic phase (located in the upper layer) is transported to the back-extraction tank, and the raffinate aqueous phase (located in the lower layer) is transported to the cooling crystallization tank.

[0091] (4) Cool the raffinate in the cooling crystallizer to 35°C and maintain this temperature for 60 min to perform cooling crystallization of potassium dihydrogen phosphate. During the cooling crystallization process, stir at a speed of 50 rpm. After cooling crystallization is completed, the resulting liquid containing potassium dihydrogen phosphate crystals is sent to a centrifugal decanter for continuous solid-liquid separation. The separated solid phase is sent to a drying bed and dried at 80°C to obtain potassium dihydrogen phosphate product. The separated liquid phase is recorded as the first mother liquor and returned to step (1) for the preparation of crude raw material liquid.

[0092] (5) Add ammonia water to the back-extraction tank for neutralization reaction. During the neutralization reaction, control the amount of ammonia water added to keep the pH value of the mixture in the back-extraction tank at 6.5 to 7.5. Control the neutralization reaction time to 50 min. The temperature of the neutralization reaction is maintained by the heat released by the neutralization reaction itself. No additional heating or cooling is required. The temperature of the neutralization reaction is naturally maintained in the range of 55 to 65℃.

[0093] After the neutralization reaction is completed, the resulting reaction solution is fed into the back-extraction phase separation tank and allowed to stand for phase separation. The organic phase obtained from the phase separation (located in the upper layer) is the extractant. This extractant is stored in a storage tank and then transported to step (2) for extraction reaction. The aqueous phase obtained from the phase separation (located in the lower layer) is fed into a vacuum concentrator and concentrated to a solid content of 20 wt% under 50 kPa conditions. The concentrated solution is then transported to an ammonium chloride cooling crystallizer, cooled to 35°C, and maintained at this temperature for 90 min for ammonium chloride cooling crystallization. During the cooling crystallization process, stirring is applied at a speed of 50 rpm. After cooling crystallization is completed, the resulting solution containing ammonium chloride crystals is separated by a centrifuge. The resulting solid phase is the ammonium chloride product, and the resulting liquid phase is the second mother liquor. The second mother liquor is then transported to the back-extraction tank.

[0094] The potassium dihydrogen phosphate product prepared in step (4) was tested, and the results showed that the mass fraction of potassium dihydrogen phosphate was 99.9% and the mass fraction of phosphorus pentoxide was 52.1%, which met the superior grade index in HG / T2312-2016 ("Fertilizer Grade Potassium Dihydrogen Phosphate"). Based on the yield of potassium dihydrogen phosphate and ammonium chloride products in steps (4) and (5), approximately 0.6 tons of ammonium chloride products will be produced as a byproduct for every ton of potassium dihydrogen phosphate product produced.

[0095] Example 5

[0096] In this embodiment, a method for producing potassium dihydrogen phosphate by solvent extraction according to the present invention is provided, comprising the following steps:

[0097] (1) Dissolve the raw acid and potassium chloride in the first mother liquor to prepare a crude raw material solution at a temperature of 40℃. Control the molar ratio of phosphoric acid to potassium chloride in the crude raw material solution to be 1.3:1, and control the concentration of chloride ions in the crude raw material solution to be 1.5 mol / L. Add activated carbon filter aid to the crude raw material solution, with the amount of activated carbon added being 0.1% of the mass of the crude raw material solution. Stir for 60 min and then filter to obtain a clear raw material solution.

[0098] The raw acid contains 60 wt% P2O5, 1.5 wt% nitric acid, 0.1 wt% iron ions, and 0.5 wt% sulfate ions. The first mother liquor originates from step (4), and in the initial stage of the entire process, the first mother liquor is water.

[0099] (2) Add the clarified raw material liquid and the extractant to the extraction crystallizer for extraction reaction. Control the volume ratio of the clarified raw material liquid to the extractant in the extraction crystallizer to be 1:1. Control the pH value of the extraction reaction to be about 4.5. Control the extraction reaction temperature to be 20℃ and the extraction reaction time to be 60min.

[0100] The extractant is a mixture of a main agent and an auxiliary agent in a volume ratio of 0.2:1. The main agent is composed of N,N-diisooctylethanolamine and trioctylmethylammonium chloride in a volume ratio of 1.2:1, and the auxiliary agent is composed of xylene and octane in a volume ratio of 2:1.

[0101] (3) After the extraction reaction is completed, the phases are separated by standing. The extracted organic phase (located in the upper layer) is transported to the back-extraction tank, and the raffinate aqueous phase (located in the lower layer) is transported to the cooling crystallization tank.

[0102] (4) Cool the raffinate in the cooling crystallizer to 35°C and maintain this temperature for 60 minutes to perform cooling crystallization of potassium dihydrogen phosphate. During the cooling crystallization process, stir at a speed of 50 rpm. After cooling crystallization is completed, the liquid containing potassium dihydrogen phosphate crystals is sent to a centrifugal decanter for continuous solid-liquid separation. The separated solid phase is sent to a drying bed and dried at 80°C to obtain potassium dihydrogen phosphate product. The separated liquid phase is recorded as the first mother liquor and returned to step (1) for the preparation of crude raw material liquid.

[0103] (5) Add ammonia water to the back-extraction tank for neutralization reaction. During the neutralization reaction, control the amount of ammonia water added to keep the pH value of the mixture in the back-extraction tank at 6.5 to 7.5. Control the neutralization reaction time to 50 min. The temperature of the neutralization reaction is maintained by the heat released by the neutralization reaction itself. No additional heating or cooling is required. The temperature of the neutralization reaction is naturally maintained in the range of 55 to 65℃.

[0104] After the neutralization reaction is completed, the resulting reaction solution is fed into the back-extraction phase separation tank and allowed to stand for phase separation. The organic phase obtained from the phase separation (located in the upper layer) is the extractant. This extractant is stored in a storage tank and then transported to step (2) for extraction reaction. The aqueous phase obtained from the phase separation (located in the lower layer) is fed into a vacuum concentrator and concentrated to a solid content of 20 wt% under 50 kPa conditions. The concentrated solution is then transported to an ammonium chloride cooling crystallizer, cooled to 35°C, and maintained at this temperature for 90 min for ammonium chloride cooling crystallization. During the cooling crystallization process, stirring is applied at a speed of 50 rpm. After cooling crystallization is completed, the resulting solution containing ammonium chloride crystals is separated by a centrifuge. The resulting solid phase is the ammonium chloride product, and the resulting liquid phase is the second mother liquor. The second mother liquor is then transported to the back-extraction tank.

[0105] The potassium dihydrogen phosphate product prepared in step (4) was tested, and the results showed that the mass fraction of potassium dihydrogen phosphate was 99.8% and the mass fraction of phosphorus pentoxide was 52.0%, which met the superior grade index in HG / T2312-2016 ("Fertilizer Grade Potassium Dihydrogen Phosphate"). Based on the yield of potassium dihydrogen phosphate and ammonium chloride products in steps (4) and (5), approximately 0.6 tons of ammonium chloride products will be produced as a byproduct for every ton of potassium dihydrogen phosphate product produced.

[0106] Example 6

[0107] In this embodiment, a method for producing potassium dihydrogen phosphate by solvent extraction according to the present invention is provided, comprising the following steps:

[0108] (1) Dissolve the raw acid and potassium chloride in the first mother liquor to prepare a crude raw material solution at a temperature of 60℃. Control the molar ratio of phosphoric acid to potassium chloride in the crude raw material solution to be 1:1, and control the concentration of chloride ions in the crude raw material solution to be 2 mol / L. Add activated carbon filter aid to the crude raw material solution, with the amount of activated carbon added being 0.5% of the mass of the crude raw material solution. Stir for 30 min and then filter to obtain a clear raw material solution.

[0109] The raw acid contains 30 wt% P2O5, 1.1 wt% nitric acid, 0.08 wt% iron ions, and 1 wt% sulfate ions. The first mother liquor originates from step (4), and in the initial stage of the entire process, the first mother liquor is water.

[0110] (2) Add the clarified raw material liquid and the extractant to the extraction crystallizer for extraction reaction. Control the volume ratio of the clarified raw material liquid to the extractant in the extraction crystallizer to be 1.8:1. Control the pH value of the extraction reaction to be about 4. Control the extraction reaction temperature to be 50℃ and the extraction reaction time to be 30min.

[0111] The extractant is a mixture of a main agent and an auxiliary agent in a volume ratio of 0.6:1. The main agent is composed of N,N-diisooctylethanolamine and trioctylmethylammonium chloride in a volume ratio of 0.5:1, and the auxiliary agent is composed of xylene and undecane in a volume ratio of 0.8:1.

[0112] (3) After the extraction reaction is completed, the phases are separated by standing. The extracted organic phase (located in the upper layer) is transported to the back-extraction tank, and the raffinate aqueous phase (located in the lower layer) is transported to the cooling crystallization tank.

[0113] (4) Cool the raffinate in the cooling crystallizer to 35°C and maintain this temperature for 60 minutes to perform cooling crystallization of potassium dihydrogen phosphate. During the cooling crystallization process, stir at a speed of 50 rpm. After cooling crystallization is completed, the liquid containing potassium dihydrogen phosphate crystals is sent to a centrifugal decanter for continuous solid-liquid separation. The separated solid phase is sent to a drying bed and dried at 80°C to obtain potassium dihydrogen phosphate product. The separated liquid phase is recorded as the first mother liquor and returned to step (1) for the preparation of crude raw material liquid.

[0114] (5) Add ammonia water to the back-extraction tank for neutralization reaction. During the neutralization reaction, control the amount of ammonia water added to keep the pH value of the mixture in the back-extraction tank at 6.5 to 7.5. Control the neutralization reaction time to 50 min. The temperature of the neutralization reaction is maintained by the heat released by the neutralization reaction itself. No additional heating or cooling is required. The temperature of the neutralization reaction is naturally maintained in the range of 55 to 65℃.

[0115] The potassium dihydrogen phosphate product prepared in step (4) was tested, and the results showed that the mass fraction of potassium dihydrogen phosphate was 98.0% and the mass fraction of phosphorus pentoxide was 51.5%, which met the superior grade index in HG / T2321-2016 ("Fertilizer Grade Potassium Dihydrogen Phosphate"). Based on the yield of potassium dihydrogen phosphate and ammonium chloride products in steps (4) and (5), approximately 0.6 tons of ammonium chloride products will be produced as a byproduct for every ton of potassium dihydrogen phosphate product produced.

Claims

1. A method for producing potassium dihydrogen phosphate by solvent extraction, characterized in that, Includes the following steps: (1) The raw acid and potassium chloride are dissolved in the first mother liquor to prepare a crude raw material solution at a temperature of 40~70 ℃. The molar ratio of phosphoric acid to potassium chloride in the crude raw material solution is controlled to be (0.85~1.3):

1. Filter aid is added to the crude raw material solution, and after thorough stirring, it is filtered to obtain a clear raw material solution. The raw acid contains 30 wt%~60 wt% P2O5, 1 wt%~1.5 wt% nitric acid, 0.05 wt%~0.1 wt% iron ions, and 0.3 wt%~1 wt% sulfuric acid. (2) The clarified raw material solution and the extractant are added to the extraction crystallizer for extraction reaction. The pH value of the extraction reaction is controlled between 3.5 and 4.5 by controlling the addition ratio of the clarified raw material solution and the extractant. The extractant consists of a main agent and an auxiliary agent. The main agent is N,N-diisooctylethanolamine and trioctylmethylammonium chloride, and the auxiliary agent is xylene and C8~C 16 Alkanes, the C8~C 16 The alkane is at least one of the alkanes having 8 to 16 carbon atoms, and the volume ratio of the main agent to the auxiliary agent is (0.2 to 0.6): 1; in the main agent of the extractant, the volume ratio of N,N-diisooctylethanolamine to trioctylmethylammonium chloride is (0.5 to 1.2): 1; in the auxiliary agent of the extractant, xylene and C8~C 16 The volume ratio of alkanes is (0.8~2):1; (3) After the extraction reaction is completed, the phases are allowed to separate. The extracted organic phase is transferred to the back-extraction tank, and the raffinate aqueous phase is transferred to the cooling crystallization tank. (4) Cool the aqueous phase in the cooling crystallizer to crystallize. After cooling and crystallization, the solid and liquid are separated. The solid obtained is potassium dihydrogen phosphate, and the liquid obtained is the first mother liquor. The first mother liquor is sent to step (1) to prepare the crude raw material liquid. (5) Add ammonia water to the back-extraction tank for neutralization reaction. During the neutralization reaction, the pH value of the mixture in the back-extraction tank is maintained at 6.5~7.5 by adding ammonia water. After the neutralization reaction is completed, the resulting reaction solution is input into the back-extraction phase separation tank and allowed to stand for phase separation. The organic phase obtained by phase separation is the extractant. The extractant is stored in the storage tank and the extractant in the storage tank is transported to step (2) for extraction reaction. The aqueous phase obtained by phase separation is concentrated, cooled and crystallized, and the solid and liquid are separated. The obtained solid phase is ammonium chloride and the obtained liquid phase is the second mother liquor. The second mother liquor is transported to the back-extraction tank.

2. The method for producing potassium dihydrogen phosphate by solvent extraction according to claim 1, characterized in that, In the extractant, the volume ratio of the main agent to the auxiliary agent is (0.4~0.6):

1.

3. The method for producing potassium dihydrogen phosphate by solvent extraction according to claim 1 or 2, characterized in that, In step (1), the filter aid is activated carbon, and the amount of filter aid added is 0.1% to 0.5% of the mass of the crude raw material liquid.

4. The method for producing potassium dihydrogen phosphate by solvent extraction according to claim 1 or 2, characterized in that, In step (1), the concentration of chloride ions in the crude raw material liquid is controlled to be 1.5~3.2 mol / L.

5. The method for producing potassium dihydrogen phosphate by solvent extraction according to claim 1 or 2, characterized in that, In step (2), the volume ratio of the clarified raw material liquid to the extractant in the extraction crystallizer is controlled to be (1~2.5):

1.

6. The method for producing potassium dihydrogen phosphate by solvent extraction according to claim 1 or 2, characterized in that, In step (2), the extraction reaction temperature is controlled at 20~60 ℃ and the extraction reaction time is controlled at 10~60 min.

7. The method for producing potassium dihydrogen phosphate by solvent extraction according to claim 1 or 2, characterized in that, In step (5), the temperature of the neutralization reaction is naturally maintained between 40 and 70 °C, and the time of the neutralization reaction is controlled to be between 30 and 60 min.