Method for producing monopotassium phosphate by solvent extraction method

Abstract

The invention provides a method for producing monopotassium phosphate by a solvent extraction method. The method comprises the following steps: (1) preparing a clear raw material solution; (2) adding the clarified raw material liquid and an extraction agent into an extraction crystallizer for extraction reaction; (3) standing for phase splitting, conveying an extracted organic phase into a reverse extraction tank, and conveying a raffinate water phase into a cooling crystallization tank; (4) carrying out cooling crystallization on the raffinate water phase in the cooling crystallization tank, and after cooling crystallization is completed, carrying out solid-liquid separation to obtain a solid which is monopotassium phosphate; (5) ammonia water is added into the reverse extraction tank for a neutralization reaction, after the neutralization reaction is completed, standing and phase splitting are carried out, an organic phase obtained through phase splitting is an extraction agent, and the extraction agent is stored in a storage tank and recycled; and concentrating the water phase obtained by phase splitting, cooling and crystallizing, and carrying out solid-liquid separation to obtain a solid phase which is ammonium chloride. According to the invention, the process flow for producing monopotassium phosphate by the existing solvent extraction method can be simplified, the equipment investment and operation cost are reduced, the requirement on raw material acid is reduced, and the production cost is reduced.

Description

Technical Field

[0001] The 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 Art

[0002] Potassium dihydrogen phosphate (KH2PO4), as an important chemical raw material, is widely used in agriculture, food, medicine, electronics, ceramics, feed additives and other industries, especially in fine chemicals and high-tech fields. The preparation methods of potassium dihydrogen phosphate mainly include neutralization method, solvent extraction method, electrochemical method and double decomposition method. At present, the mainstream method for preparing potassium dihydrogen phosphate in industry is neutralization method, which has the advantages of short process, high product purity and simple process, but there is a problem of high raw material cost, which limits its further promotion and application.

[0003] The solvent extraction method is a method of obtaining high-purity potassium dihydrogen phosphate by extracting hydrochloric acid after the reaction of phosphoric acid and potassium chloride. This method has the advantages of 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., Technology for producing potassium dihydrogen phosphate by solvent extraction, "Phosphate Fertilizers and Compound Fertilizers", Issue 2, 2023, pp. 16-18) reported a process for preparing potassium dihydrogen phosphate using wet phosphoric acid by solvent extraction. In this process, wet phosphoric acid is desulfurized through phosphate slurry to obtain pretreated phosphoric acid, and then the pretreated phosphoric acid, potassium chloride solution, potassium dihydrogen phosphate mother liquor, etc. are mixed, and HCl is extracted by an extractant. The aqueous phase obtained after extraction and phase separation is the potassium dihydrogen phosphate feed liquid. The potassium dihydrogen phosphate feed liquid is filtered, and the filtrate obtained by filtration is vacuum concentrated, cooled and crystallized, centrifuged, and fluidized dried to obtain a potassium dihydrogen phosphate product. The filter cake obtained by filtration is dried to obtain a phosphate and potassium fertilizer by-product; ammonia and water are added to the organic phase obtained by extraction and phase separation for back extraction, and the extractant obtained after phase separation is returned to the extraction process for recycling, and the obtained aqueous phase is ammonium chloride solution, which is vacuum concentrated, cooled and crystallized, and centrifuged to obtain an ammonium chloride by-product. Although this process obtains high-quality potassium dihydrogen phosphate and produces ammonium chloride as a by-product, the following problems still exist: (1) As can be seen from the process flow shown in Figure 1 of the document, it 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 adverse effect of phosphoric acid on subsequent extraction, the extractant needs to be salt washed with a saturated potassium chloride solution before stripping to remove the phosphoric acid. However, the conditions of the salt washing step are demanding, which can easily cause problems such as emulsification failure and entrainment, which in turn leads to complex process flow and difficulty in regulation, and increases equipment and operating costs; (2) This process directly introduces ammonia and water into the stripping tank for neutralization reaction. Due to the ammonia The process of dissolving the gas in water and neutralizing it with hydrochloric acid is a strong exothermic reaction, which makes it difficult to control the entire stripping process to prepare ammonium chloride. In addition, the temperature of the extractant obtained after stripping is high, and it must be washed and cooled to reduce its temperature for subsequent extraction, which indirectly causes energy consumption and increased equipment investment and operating costs; (3) In the existing method, industrial-grade phosphoric acid is generally used as the raw acid for preparing potassium dihydrogen phosphate. Although the process reported in the above literature uses wet-process phosphoric acid with lower cost, it requires pretreatment of the wet-process phosphoric acid, resulting in a complicated process flow and increased costs. Low-quality raw acid containing nitric acid or sulfuric acid and metal impurity ions cannot be used. In general, the process reported above has the problems of long process flow, high equipment investment and operating costs, and high requirements for raw acid, which greatly limits the large-scale promotion and application of solvent extraction technology for preparing potassium dihydrogen phosphate. Summary of the invention

[0004] In view of the problems that the prior art uses a solvent extraction method to prepare potassium dihydrogen phosphate, such as a long process flow, high equipment investment and operating costs, and high requirements for raw acid, the present invention provides a method for producing potassium dihydrogen phosphate by a solvent extraction method, so as to simplify the process flow, reduce equipment investment and operating costs, and lower the requirements for raw acid, thereby reducing the production cost of potassium dihydrogen phosphate.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

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

[0007] (1) dissolving a raw acid and potassium chloride in a first mother liquor to prepare a crude raw liquid at a temperature of 40 to 70° C., controlling the molar ratio of phosphoric acid to potassium chloride in the crude raw liquid to be (0.85 to 1.3):1, adding a filter aid to the crude raw liquid, stirring the mixture sufficiently and filtering the mixture to obtain a clarified raw liquid; wherein the raw acid has a P2O5 content of 30 wt% to 60 wt%, a nitric acid content of 1 wt% to 1.5 wt%, an iron ion content of 0.05 wt% to 0.1%, and a sulfuric acid content of 0.3 wt% to 1 wt%;

[0008] (2) adding the clarified raw liquid and the extractant into an extraction crystallizer for extraction reaction, controlling the addition ratio of the clarified raw liquid to the extractant to control the pH value of the extraction reaction between 3.5 and 4.5; the extractant is composed 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 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 allowed to stand for phase separation, the extracted organic phase is transported to the stripping tank, and the residual water phase is transported to the cooling crystallization tank;

[0010] (4) cooling and crystallizing the raffinate water phase in the cooling crystallization tank. After the cooling and crystallization is completed, the solid and liquid are separated, and the obtained solid is potassium dihydrogen phosphate, and the obtained liquid phase is the first mother liquor. The first mother liquor is transported to step (1) for preparing the crude raw material liquid;

[0011] (5) adding aqueous ammonia to the stripping tank for neutralization reaction. During the neutralization reaction, the pH value of the mixed solution in the stripping tank is regulated and maintained at 6.5-7.5 by adding aqueous ammonia. After the neutralization reaction is completed, the obtained reaction solution is input into the stripping phase separation tank, and the phases are allowed to stand for phase separation. The organic phase obtained by phase separation is the extractant, which is stored in a storage tank. 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-liquid separation is performed. 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 stripping tank.

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

[0013] In the above technical solution, in the auxiliary agent of the extractant, xylene and C8~C 16 The volume ratio of alkanes is preferably (0.8-2):1.

[0014] In the above technical solution, in the extractant, the volume ratio of the main agent to the auxiliary agent 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 acid and increase the clarity of the crude raw liquid. The filter aid is activated carbon, and the amount of the filter aid added is preferably 0.1% to 0.5% of the mass of the crude liquid.

[0016] In step (1) of the above technical solution, filtering is usually performed after adding a 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 mixed solution 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 and the extractant in the extraction crystallizer is controlled to be (1 to 2.5):1.

[0019] In step (2) of the above technical solution, the extraction reaction temperature is preferably controlled to be 20 to 60° C., and the extraction reaction time is preferably controlled to be 10 to 60 min.

[0020] In step (4) of the above technical solution, the raffinate water phase in the cooling crystallization tank is cooled to 20-35°C and maintained for 30-90 minutes for cooling crystallization of potassium dihydrogen phosphate. During the cooling crystallization process, stirring is preferably applied 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 a 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 to 70°C; in this step, the time of the neutralization reaction is preferably controlled to be 30 to 60 minutes.

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

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

[0025] 1. The present invention provides a method for producing potassium dihydrogen phosphate by solvent extraction, the main feature of which is that the extractant used is a composite extractant, the composite extractant is a main agent of N, N-diisooctylethanolamine and trioctylmethylammonium chloride, the ion exchange effect of trioctylmethylammonium chloride is used to extract hydrochloric acid, and N, N-diisooctylethanolamine is used to bind Cl after protonation. - The two mechanisms are synergistically effective in extracting hydrochloric acid and phosphoric acid by adjusting the ratio of the two. The selective separation performance of the extractant for hydrochloric acid and phosphoric acid is effectively enhanced. At the same time, the low viscosity xylene and C8~C 16 Alkanes are used as auxiliary agents to adjust the viscosity and density of the extractant to appropriate levels, which can promote the phase separation of the oil and water phases after extraction. Compared with the tert-butylamine extractants used in the existing industrial production of potassium dihydrogen phosphate, the composite extractant used in the present invention enhances the extraction effect on hydrochloric acid, but hardly extracts phosphoric acid, and has excellent selective separation performance. The method of the present invention is based on the composite extractant, which effectively avoids the problem of extracting hydrochloric acid and phosphoric acid at the same time, thereby omitting the salt washing operation in the production of potassium dihydrogen phosphate in the prior art, and further avoiding the problems of emulsification unable to separate phases and entrainment caused by the salt washing operation, which is conducive to simplifying the process flow and increasing the controllability of the process, and can reduce equipment and operating costs.

[0026] 2. The method of the present invention has good applicability to low-quality raw acid containing nitric acid, sulfuric acid and metal ions (P2O5 content is 30wt% to 60wt%, nitric acid content is 1wt% to 1.5wt%, iron ion content is 0.05wt% to 0.1%, and sulfuric acid content is 0.3wt% to 1wt%), and the use of low-quality raw acid can effectively reduce the cost of raw acid. The present invention can solve the problem of high cost of raw acid caused by the need to use industrial-grade phosphoric acid as raw acid in the existing industrial production method of potassium dihydrogen phosphate, and can also solve the problem that the existing industrial production method of potassium dihydrogen phosphate needs to pre-treat it when using wet-process phosphoric acid as raw acid, thereby increasing the complexity of the process flow and the problem of process cost.

[0027] 3. The present invention has been experimentally confirmed that the quality of potassium dihydrogen phosphate produced by the method of the present invention meets the requirements of superior products in HG / T2321-2016 ("fertilizer grade potassium dihydrogen phosphate"), and the composite extractant of the present invention can be recycled 100 times to prepare a potassium dihydrogen phosphate product that meets the requirements of superior products in HG / T2321-2016 ("fertilizer grade potassium dihydrogen phosphate"), that is, the composite extractant used in the present invention has excellent cyclic stability, and the extractant that accumulates a certain amount of impurities still has excellent extraction performance after stripping and regeneration, which is extremely beneficial to reducing the production cost of potassium dihydrogen phosphate.

[0028] 4. The method of the present invention directly adds ammonia water to the stripping tank for neutralization reaction in the stripping step, which changes the existing process of directly introducing ammonia gas into the stripping tank for neutralization reaction, avoids the problem that the temperature in the stripping tank increases due to heat release during the liquefaction process of ammonia gas, thereby causing the difficulty in regulating the ammonium chloride preparation process, and effectively controls the temperature of the extractant after stripping, so there is no need to wash and cool the extractant after stripping, which simplifies the process flow and can save equipment and operating costs. DETAILED DESCRIPTION

[0029] The method for producing potassium dihydrogen phosphate by solvent extraction provided by the present invention is further described below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art may make some non-essential improvements and adjustments to the present invention according to the above invention content and implement them specifically, which still falls within the scope of protection of the present invention.

[0030] Example 1

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

[0032] The special extractant for preparing potassium dihydrogen phosphate by solvent extraction is prepared by fully mixing a main agent and an auxiliary agent in a volume ratio of 0.43:1, wherein 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.

[0033] Phosphoric acid and potassium chloride were dissolved in deionized water at a molar ratio of 1:1 to form an aqueous solution, in which the concentration of chloride ions was 2.29 mol / L. The above-mentioned extractant of this embodiment was used as the organic phase. The aqueous phase and the organic phase were added to a 500 mL separatory funnel at a volume ratio of 1:1, and the reaction was oscillated for 6 minutes at room temperature and normal pressure, and then allowed to stand and the timing was started. The timing was stopped when the extracted organic phase and the residual aqueous phase were completely clarified. It was found that the phase separation time was 28 seconds.

[0034] According to the sampling test and calculation, the extraction rate of hydrochloric acid in this embodiment is 99.5%, and the extraction rate of phosphoric acid is 1.0%. The raffinate aqueous phase is evaporated, concentrated, and crystallized to obtain a potassium dihydrogen phosphate product, and the yield of potassium dihydrogen phosphate is 98.3%. Sampling and testing show that the purity of potassium dihydrogen phosphate is 99.5%.

[0035] Comparative Example 1

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

[0037] The extractant used in this comparative example is prepared by fully mixing 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 phase solution, in which the concentration of chloride ions was 2.29 mol / L. The above-mentioned extractant of this comparative example was used as the organic phase. The aqueous phase and the organic phase were added to a 500 mL separatory funnel at a volume ratio of 1:1, and the reaction was oscillated for 10 minutes at room temperature and normal pressure, and then allowed to stand and the timing was started. The timing was stopped when the extracted organic phase and the residual aqueous phase were completely clear. It was found that the phase separation time was 6 minutes.

[0039] After sampling and testing, the extraction rate of the above extractant for hydrochloric acid is 95.7%, and the extraction rate for phosphoric acid is 4.5%. The residual water phase is evaporated, concentrated and crystallized to obtain potassium dihydrogen phosphate product, and the yield of potassium dihydrogen phosphate is 91.3%. After sampling and testing, the purity of potassium dihydrogen phosphate is 97.2%.

[0040] In combination with Example 1 and Comparative Example 1, it can be seen that, compared with the existing extractants, the composite extractant used in the present invention can improve the separation selectivity of hydrochloric acid and phosphoric acid when preparing potassium dihydrogen phosphate by solvent extraction, effectively reduce the extraction rate of phosphoric acid on the basis of ensuring a high extraction rate of hydrochloric acid, and can also effectively shorten the phase separation time of the oil-water phase 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, and the steps are as follows:

[0043] (1) The raw acid and potassium chloride are dissolved in the first mother liquor to prepare a crude raw liquid at a temperature of 50° C. The molar ratio of phosphoric acid to potassium chloride in the crude raw liquid is controlled to be 1:1, and the concentration of chloride ions in the crude raw liquid is controlled to be 2.4 mol / L. Activated carbon filter aid is added to the crude raw liquid, and the amount of activated carbon added is 0.5% of the mass of the crude raw liquid. After stirring for 30 minutes, the mixture is filtered to obtain a clarified raw liquid.

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

[0045] (2) adding the clarified raw liquid and the extractant into an extraction crystallizer for extraction reaction, controlling the volume ratio of the clarified raw liquid to the extractant in the extraction crystallizer to be 1.3:1, controlling the pH value of the extraction reaction to be about 4, controlling the extraction reaction temperature to be 50° C., and controlling the extraction reaction time to be 30 min.

[0046] The extractant is formed by fully mixing a main agent and an auxiliary agent in a volume ratio of 0.43:1, wherein 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 allowed to stand and separated, and the extracted organic phase (located on the upper layer) is transported to the stripping tank, and the raffinate aqueous phase (located on the lower layer) is transported to the cooling crystallization tank.

[0048] (4) The raffinate water phase in the cooling crystallization tank is cooled to 35°C and maintained at this temperature for 60 minutes to perform cooling crystallization of potassium dihydrogen phosphate, and stirring is applied at a speed of 50 rpm during the cooling crystallization process. After the cooling crystallization is completed, the obtained feed liquid containing potassium dihydrogen phosphate crystals is transported to a centrifugal horizontal screw machine for continuous solid-liquid separation, and the separated solid phase is transported to a drying bed for drying at 80°C to obtain a potassium dihydrogen phosphate product, and the separated liquid phase is recorded as the first mother liquor, and the first mother liquor is returned to step (1) for preparing the crude raw material liquid.

[0049] (5) Ammonia water is added to the stripping tank for neutralization reaction. During the neutralization reaction, the amount of ammonia water added is controlled to keep the pH value of the mixed solution in the stripping tank at a level of 6.5 to 7.5. The neutralization reaction time is controlled to be 60 minutes. 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°C.

[0050] After the neutralization reaction is completed, the obtained reaction solution is input into the back extraction phase separation tank, and the phase separation is allowed to stand. The organic phase obtained by phase separation (located on the upper layer) is the extraction agent, and the extraction agent is stored in the storage tank. The extraction agent in the storage tank is transported to step (2) for extraction reaction. The aqueous phase obtained by phase separation (located on the lower layer) is input into a vacuum concentrator, and the aqueous phase in the vacuum concentrator is concentrated to a solid content of 20wt% under the condition of 50kPa. The concentrated feed liquid is transported to the ammonium chloride cooling crystallizer, cooled to 35°C and maintained at this temperature for 90min to carry out cooling crystallization of ammonium chloride, and stirring is applied at a speed of 50rpm during the cooling crystallization process. After the cooling crystallization is completed, the obtained feed liquid containing ammonium chloride crystals is separated by a centrifuge, and the obtained solid phase is the ammonium chloride product, and the obtained liquid phase is the second mother liquor, and the second mother liquor is 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 in the potassium dihydrogen phosphate product was 99.8%, and the mass fraction of phosphorus pentoxide was 52.1%, reaching the index of superior products in HG / T2321-2016 ("fertilizer grade potassium dihydrogen phosphate"). According to the output calculation of the potassium dihydrogen phosphate product and the ammonium chloride product in step (4) and step (5), about 0.6 tons of ammonium chloride product will be produced as a by-product for every 1 ton of potassium dihydrogen phosphate product produced.

[0052] Comparative Example 2

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

[0054] (1) Dissolve industrial-grade phosphoric acid and potassium chloride in the first mother liquor to prepare a crude raw material liquid at a temperature of 50°C, control the molar ratio of phosphoric acid to potassium chloride in the crude raw material liquid to be 1:1, and control the concentration of chloride ions in the crude raw material liquid to be 2.4 mol / L. Add activated carbon filter aid to the raw material liquid, the amount of activated carbon added is 0.5% of the mass of the crude raw material solution, stir for 30 minutes and filter to obtain a clarified raw material liquid. The industrial-grade phosphoric acid has a P2O5 content of 60wt%, a nitric acid content of 0.001wt%, an iron ion content of 0.001wt%, and a sulfate ion content of 0.005wt%. The first mother liquor is derived from step (4). At the initial stage of the entire process, the first mother liquor is water.

[0055] (2) adding the clarified raw liquid and the extractant to an extraction crystallizer for extraction reaction, controlling the volume ratio of the clarified raw liquid to the extractant in the extraction crystallizer to be 1.3:1, controlling the pH value of the extraction reaction to be about 4, controlling the extraction reaction temperature to be 50° C., and the extraction reaction time to be 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 allowed to stand and separated, and the extracted organic phase (located on the upper layer) is transported to the washing tank, and the raffinate water phase (located on the lower layer) is transported to the cooling crystallization tank.

[0057] (4) The raffinate water phase in the cooling crystallization tank is cooled to 35°C and maintained at this temperature for 60 minutes to perform cooling crystallization of potassium dihydrogen phosphate, and stirring is applied at a speed of 50 rpm during the cooling crystallization process. After the cooling crystallization is completed, the obtained feed liquid containing potassium dihydrogen phosphate crystals is transported to a centrifugal horizontal screw machine for continuous solid-liquid separation, and the separated solid phase is transported to a drying bed for drying at 80°C to obtain a potassium dihydrogen phosphate product, and the separated liquid phase is recorded as the first mother liquor, and the first mother liquor is returned to step (1) for preparing the crude raw material liquid.

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

[0059] (6) Aqueous ammonia is added to the stripping tank for neutralization reaction. During the neutralization reaction, the amount of aqueous ammonia added is controlled to keep the pH value of the mixed solution in the stripping tank at a level of 6.5 to 7.5. The time of the neutralization reaction is controlled to be 60 minutes. 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°C.

[0060] After the neutralization reaction is completed, the obtained reaction solution is input into the back extraction phase separation tank, and the phase separation is allowed to stand. The organic phase obtained by phase separation (located on the upper layer) is the extraction agent, and the extraction agent is stored in the storage tank. The extraction agent in the storage tank is transported to step (2) for extraction reaction. The aqueous phase obtained by phase separation (located on the lower layer) is input into a vacuum concentrator, and the aqueous phase in the vacuum concentrator is concentrated to a solid content of 20wt% under the condition of 50kPa. The concentrated feed liquid is transported to the ammonium chloride cooling crystallizer, cooled to 35°C and maintained at this temperature for 90min to carry out cooling crystallization of ammonium chloride, and stirring is applied at a speed of 50rpm during the cooling crystallization process. After the cooling crystallization is completed, the obtained feed liquid containing ammonium chloride crystals is separated by a centrifuge, and the obtained solid phase is the ammonium chloride product, and the obtained liquid phase is the second mother liquor, and the second mother liquor is 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 in the potassium dihydrogen phosphate product was 99.5%, and the mass fraction of phosphorus pentoxide was 52.1%, reaching the index of superior products in HG / T2321-2016 ("fertilizer grade potassium dihydrogen phosphate"). According to the output calculation of the potassium dihydrogen phosphate product and the ammonium chloride product in step (4) and step (6), about 0.6 tons of ammonium chloride product will be produced as a by-product for every 1 ton of potassium dihydrogen phosphate product produced.

[0062] Comparative Example 3

[0063] In this comparative example, the existing extractant is used in combination with low-quality phosphoric acid to produce potassium dihydrogen phosphate, and the steps are as follows:

[0064] (1) The raw acid and potassium chloride are dissolved in the first mother liquor to prepare a crude raw liquid at a temperature of 50° C. The molar ratio of phosphoric acid to potassium chloride in the crude raw liquid is controlled to be 1:1, and the concentration of chloride ions in the crude raw liquid is controlled to be 2.4 mol / L. Activated carbon filter aid is added to the crude raw liquid, and the amount of activated carbon added is 0.5% of the mass of the crude raw liquid. After stirring for 30 minutes, the mixture is filtered to obtain a clarified raw liquid.

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

[0066] (2) adding the clarified raw liquid and the extractant to an extraction crystallizer for extraction reaction, controlling the volume ratio of the clarified raw liquid to the extractant in the extraction crystallizer to be 1.3:1, controlling the pH value of the extraction reaction to be about 4, controlling the extraction reaction temperature to be 50° C., and the extraction reaction time to be 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 allowed to stand and separated, and the extracted organic phase (located on the upper layer) is transported to the washing tank, and the raffinate water phase (located on the lower layer) is transported to the cooling crystallization tank.

[0068] (4) The raffinate water phase in the cooling crystallization tank is cooled to 35°C and maintained at this temperature for 60 minutes to perform cooling crystallization of potassium dihydrogen phosphate, and stirring is applied at a speed of 50 rpm during the cooling crystallization process. After the cooling crystallization is completed, the obtained feed liquid containing potassium dihydrogen phosphate crystals is transported to a centrifugal horizontal screw machine for continuous solid-liquid separation, and the separated solid phase is transported to a drying bed for drying at 80°C to obtain a potassium dihydrogen phosphate product, and the separated liquid phase is recorded as the first mother liquor, and the first mother liquor is returned to step (1) for preparing the crude raw material liquid.

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

[0070] (6) Aqueous ammonia is added to the stripping tank for neutralization reaction. During the neutralization reaction, the amount of aqueous ammonia added is controlled to keep the pH value of the mixed solution in the stripping tank at a level of 6.5 to 7.5. The time of the neutralization reaction is controlled to be 60 minutes. 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°C.

[0071] After the neutralization reaction is completed, the obtained reaction solution is input into the back extraction phase separation tank, and the phase separation is allowed to stand. The organic phase obtained by phase separation (located on the upper layer) is the extraction agent, and the extraction agent is stored in the storage tank. The extraction agent in the storage tank is transported to step (2) for extraction reaction. The aqueous phase obtained by phase separation (located on the lower layer) is input into a vacuum concentrator, and the aqueous phase in the vacuum concentrator is concentrated to a solid content of 20wt% under the condition of 50kPa. The concentrated feed liquid is transported to the ammonium chloride cooling crystallizer, cooled to 35°C and maintained at this temperature for 90min to carry out cooling crystallization of ammonium chloride, and stirring is applied at a speed of 50rpm during the cooling crystallization process. After the cooling crystallization is completed, the obtained feed liquid containing ammonium chloride crystals is separated by a centrifuge, and the obtained solid phase is the ammonium chloride product, and the obtained liquid phase is the second mother liquor, and the second mother liquor is 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 in the potassium dihydrogen phosphate product was 95.3%, and the mass fraction of phosphorus pentoxide was 50.1%, reaching the index of first-class products in HG / T2312-2016 ("fertilizer-grade potassium dihydrogen phosphate"). According to the output calculation of the potassium dihydrogen phosphate product and the ammonium chloride product in step (4) and step (6), about 0.6 tons of ammonium chloride product will be produced as a by-product for every 1 ton of potassium dihydrogen phosphate product produced.

[0073] Combining Example 2 and Comparative Examples 2 to 3, it can be seen that when the existing extractant is used in combination with industrial-grade phosphoric acid to produce potassium dihydrogen phosphate, although the prepared potassium dihydrogen phosphate can meet the requirements of superior products, due to the poor selective separation performance of the existing extractant trioctylamine for hydrochloric acid and phosphoric acid, a certain amount of phosphoric acid will be extracted when extracting hydrochloric acid. In order to avoid the phosphoric acid entering the extractant from adversely affecting the subsequent extraction, the extractant needs to be salt-washed with a saturated potassium chloride solution before stripping, which will increase the process operation flow and increase equipment and operating costs. When the existing extractant is used in combination with low-quality phosphoric acid to produce potassium dihydrogen phosphate, although the salt washing operation is added before stripping, the quality of the prepared potassium dihydrogen phosphate will still be reduced. The above experimental results show that when the composite extractant is used to prepare potassium dihydrogen phosphate in the present invention, not only can the salt washing operation before stripping be omitted, but also the requirements for the raw acid can be reduced. When low-quality acid is used as the raw acid, the composite extractant that has accumulated a certain amount of impurities can be recycled after stripping, and the quality of potassium dihydrogen phosphate will not be significantly reduced. High-quality potassium dihydrogen phosphate can still be prepared. This is mainly due to the improvement of the 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 stripping tank in the stripping step to examine its effect on the temperature of the neutralization reaction system.

[0076] The operations of steps (1) to (4) are the same as steps (1) to (4) of Example 2.

[0077] (5) Ammonia is introduced into the stripping tank for neutralization reaction. During the neutralization reaction, the amount of ammonia introduced is controlled to keep the pH value of the mixed solution in the stripping tank at a level of 6.5 to 7.5, and the neutralization reaction time is controlled to be 60 minutes. Since a large amount of heat is released during the process of ammonia dissolving in water and the process of ammonia water reacting with hydrochloric acid, if no special cooling operation is performed in this step, the temperature of the neutralization reaction will naturally be maintained at 80 to 100°C, which will make the system temperature difficult to control. A special water washing step needs to be added later to reduce the temperature of the extractant. Since the temperature of the extraction reaction needs to be controlled within the range of 20 to 60°C, the pressure of the subsequent water washing heat exchange is relatively high.

[0078] After the neutralization reaction is completed, the obtained reaction solution is input into the stripping phase separation tank, and the phase separation is allowed to stand. The organic phase obtained by phase separation (located on the upper layer) is the extractant, and the extractant is stored in the storage tank. The extractant in the storage tank is washed with water and heat exchanged to the extractant temperature of 50°C and then transported to step (2) for extraction reaction. The aqueous phase obtained by phase separation (located on the lower layer) is input into a vacuum concentrator, and the aqueous phase in the vacuum concentrator is concentrated to a solid content of 20wt% under the condition of 50kPa. The concentrated feed liquid is transported to the ammonium chloride cooling crystallizer, cooled to 35°C and maintained at this temperature for 90min for cooling crystallization of ammonium chloride, and stirring is applied at a speed of 50rpm during the cooling crystallization process. After the cooling crystallization is completed, the obtained feed liquid containing ammonium chloride crystals is separated by a centrifuge, and the obtained solid phase is the ammonium chloride product, and the obtained liquid phase is the second mother liquor, and the second mother liquor is transported to the stripping tank.

[0079] In combination with Example 2 and Comparative Example 4, it can be seen that the present application uses ammonia water instead of ammonia gas in the stripping process, and the temperature of the neutralization reaction can be naturally maintained in the range of 55 to 65° C. without additional heating or cooling operations, which can effectively reduce the difficulty of regulating the stripping process for preparing ammonium chloride, and can also omit the process of washing and cooling the high-temperature extractant, which not only reduces the process operation, but also reduces energy consumption and equipment investment and operating costs.

[0080] Example 3

[0081] In this example, potassium dihydrogen phosphate was produced by the method of the present invention, and the recycling performance of the extractant was investigated. The steps are as follows:

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

[0083] (6) According to the operation of steps (1) to (5), the extractant is recycled for 100 times, and the potassium dihydrogen phosphate product prepared in step (4) when the extractant is recycled for the 100th time is tested. The results show that the mass fraction of potassium dihydrogen phosphate in the potassium dihydrogen phosphate product is 99.7%, and the mass fraction of phosphorus pentoxide is 52.0%, reaching the index of superior products in HG / T2321-2016 ("fertilizer grade potassium dihydrogen phosphate"). According to the output calculation of the potassium dihydrogen phosphate product and the ammonium chloride product in steps (4) and (5), about 0.6 tons of ammonium chloride product will be produced as a by-product for every 1 ton of potassium dihydrogen phosphate product produced, which is equivalent to the effect when the extractant is used for the first time, indicating that the composite extractant used in the present invention can be recycled repeatedly 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, and the steps are as follows:

[0086] (1) The raw acid and potassium chloride are dissolved in the first mother liquor to prepare a crude raw liquid at a temperature of 70° C. The molar ratio of phosphoric acid to potassium chloride in the crude raw liquid is controlled to be 0.85:1, and the concentration of chloride ions in the crude raw liquid is controlled to be 3.2 mol / L. Activated carbon filter aid is added to the crude raw liquid, and the amount of activated carbon added is 0.3% of the mass of the crude raw liquid. After stirring for 60 minutes, the mixture is filtered to obtain a clarified raw liquid.

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

[0088] (2) Adding the clarified raw liquid and the extractant into an extraction crystallizer for extraction reaction, controlling the volume ratio of the clarified raw liquid to the extractant in the extraction crystallizer to be 2.5:1, controlling the pH value of the extraction reaction to be about 3.5, controlling the extraction reaction temperature to be 60° C., and controlling the extraction reaction time to be 10 min.

[0089] The extractant is formed by fully mixing a main agent and an auxiliary agent in a volume ratio of 0.5:1, wherein 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 allowed to stand and separated, and the extracted organic phase (located on the upper layer) is transported to the stripping tank, and the raffinate aqueous phase (located on the lower layer) is transported to the cooling crystallization tank.

[0091] (4) The raffinate water phase in the cooling crystallization tank is cooled to 35°C and maintained at this temperature for 60 minutes to perform cooling crystallization of potassium dihydrogen phosphate, and stirring is applied at a speed of 50 rpm during the cooling crystallization process. After the cooling crystallization is completed, the obtained feed liquid containing potassium dihydrogen phosphate crystals is transported to a centrifugal horizontal screw machine for continuous solid-liquid separation, and the separated solid phase is transported to a drying bed for drying at 80°C to obtain a potassium dihydrogen phosphate product, and the separated liquid phase is recorded as the first mother liquor, and the first mother liquor is returned to step (1) for preparing the crude raw material liquid.

[0092] (5) Ammonia water is added to the stripping tank for neutralization reaction. During the neutralization reaction, the amount of ammonia water added is controlled so that the pH value of the mixed solution in the stripping tank is maintained at a level of 6.5 to 7.5. The neutralization reaction time is controlled to be 50 minutes. 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°C.

[0093] After the neutralization reaction is completed, the obtained reaction solution is input into the back extraction phase separation tank, and the phase separation is allowed to stand. The organic phase obtained by phase separation (located on the upper layer) is the extraction agent, and the extraction agent is stored in the storage tank. The extraction agent in the storage tank is transported to step (2) for extraction reaction. The aqueous phase obtained by phase separation (located on the lower layer) is input into a vacuum concentrator, and the aqueous phase in the vacuum concentrator is concentrated to a solid content of 20wt% under the condition of 50kPa. The concentrated feed liquid is transported to the ammonium chloride cooling crystallizer, cooled to 35°C and maintained at this temperature for 90min to carry out cooling crystallization of ammonium chloride, and stirring is applied at a speed of 50rpm during the cooling crystallization process. After the cooling crystallization is completed, the obtained feed liquid containing ammonium chloride crystals is separated by a centrifuge, and the obtained solid phase is the ammonium chloride product, and the obtained liquid phase is the second mother liquor, and the second mother liquor is 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 in the potassium dihydrogen phosphate product was 99.9%, and the mass fraction of phosphorus pentoxide was 52.1%, reaching the index of superior products in HG / T2312-2016 ("fertilizer grade potassium dihydrogen phosphate"). According to the output calculation of the potassium dihydrogen phosphate product and the ammonium chloride product in step (4) and step (5), about 0.6 tons of ammonium chloride product will be produced as a by-product for every 1 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, and the steps are as follows:

[0097] (1) The raw acid and potassium chloride are dissolved in the first mother liquor to prepare a crude raw liquid at a temperature of 40° C. The molar ratio of phosphoric acid to potassium chloride in the crude raw liquid is controlled to be 1.3:1, and the concentration of chloride ions in the crude raw liquid is controlled to be 1.5 mol / L. Activated carbon filter aid is added to the crude raw liquid, the amount of activated carbon added is 0.1% of the mass of the crude raw liquid, and the mixture is stirred for 60 minutes and then filtered to obtain a clarified raw liquid.

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

[0099] (2) Adding the clarified raw liquid and the extractant into an extraction crystallizer for extraction reaction, controlling the volume ratio of the clarified raw liquid to the extractant in the extraction crystallizer to be 1:1, controlling the pH value of the extraction reaction to be about 4.5, controlling the extraction reaction temperature to be 20° C., and controlling the extraction reaction time to be 60 min.

[0100] The extractant is formed by fully mixing a main agent and an auxiliary agent in a volume ratio of 0.2:1, wherein 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 allowed to stand and separated, and the extracted organic phase (located on the upper layer) is transported to the stripping tank, and the raffinate aqueous phase (located on the lower layer) is transported to the cooling crystallization tank.

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

[0103] (5) Ammonia water is added to the stripping tank for neutralization reaction. During the neutralization reaction, the amount of ammonia water added is controlled so that the pH value of the mixed solution in the stripping tank is maintained at a level of 6.5 to 7.5. The neutralization reaction time is controlled to be 50 minutes. 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°C.

[0104] After the neutralization reaction is completed, the obtained reaction solution is input into the back extraction phase separation tank, and the phase separation is allowed to stand. The organic phase obtained by phase separation (located on the upper layer) is the extraction agent, and the extraction agent is stored in the storage tank. The extraction agent in the storage tank is transported to step (2) for extraction reaction. The aqueous phase obtained by phase separation (located on the lower layer) is input into a vacuum concentrator, and the aqueous phase in the vacuum concentrator is concentrated to a solid content of 20wt% under the condition of 50kPa. The concentrated feed liquid is transported to the ammonium chloride cooling crystallizer, cooled to 35°C and maintained at this temperature for 90min to carry out cooling crystallization of ammonium chloride, and stirring is applied at a speed of 50rpm during the cooling crystallization process. After the cooling crystallization is completed, the obtained feed liquid containing ammonium chloride crystals is separated by a centrifuge, and the obtained solid phase is the ammonium chloride product, and the obtained liquid phase is the second mother liquor, and the second mother liquor is 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 in the potassium dihydrogen phosphate product was 99.8%, and the mass fraction of phosphorus pentoxide was 52.0%, reaching the index of superior products in HG / T2312-2016 ("fertilizer grade potassium dihydrogen phosphate"). According to the output calculation of the potassium dihydrogen phosphate product and the ammonium chloride product in step (4) and step (5), about 0.6 tons of ammonium chloride product will be produced as a by-product for every 1 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, and the steps are as follows:

[0108] (1) The raw acid and potassium chloride are dissolved in the first mother liquor to prepare a crude raw liquid at a temperature of 60° C. The molar ratio of phosphoric acid to potassium chloride in the crude raw liquid is controlled to be 1:1, and the concentration of chloride ions in the crude raw liquid is controlled to be 2 mol / L. Activated carbon filter aid is added to the crude raw liquid, and the amount of activated carbon added is 0.5% of the mass of the crude raw liquid. After stirring for 30 minutes, the mixture is filtered to obtain a clarified raw liquid.

[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 is derived from step (4). At the initial stage of the entire process, the first mother liquor is water.

[0110] (2) adding the clarified raw liquid and the extractant into an extraction crystallizer for extraction reaction, controlling the volume ratio of the clarified raw liquid to the extractant in the extraction crystallizer to be 1.8:1, controlling the pH value of the extraction reaction to be about 4, controlling the extraction reaction temperature to be 50° C., and controlling the extraction reaction time to be 30 min.

[0111] The extractant is formed by fully mixing a main agent and an auxiliary agent in a volume ratio of 0.6:1, wherein 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 allowed to stand and separated, and the extracted organic phase (located on the upper layer) is transported to the stripping tank, and the raffinate aqueous phase (located on the lower layer) is transported to the cooling crystallization tank.

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

[0114] (5) Ammonia water is added to the stripping tank for neutralization reaction. During the neutralization reaction, the amount of ammonia water added is controlled so that the pH value of the mixed solution in the stripping tank is maintained at a level of 6.5 to 7.5. The neutralization reaction time is controlled to be 50 minutes. 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°C.

[0115] The potassium dihydrogen phosphate product prepared in step (4) was tested, and the results showed that the mass fraction of potassium dihydrogen phosphate in the potassium dihydrogen phosphate product was 98.0%, and the mass fraction of phosphorus pentoxide was 51.5%, reaching the index of superior products in HG / T2321-2016 ("fertilizer grade potassium dihydrogen phosphate"). According to the output calculation of the potassium dihydrogen phosphate product and the ammonium chloride product in step (4) and step (5), about 0.6 tons of ammonium chloride product will be produced as a by-product for every 1 ton of potassium dihydrogen phosphate product produced.

Claims

1. A method for producing potassium dihydrogen phosphate by solvent extraction, characterized in that: The following steps are involved: (1) dissolving a raw acid and potassium chloride in a first mother liquor to prepare a crude raw liquid at a temperature of 40 to 70° C., controlling the molar ratio of phosphoric acid to potassium chloride in the crude raw liquid to be (0.85 to 1.3):1, adding a filter aid to the crude raw liquid, stirring the mixture sufficiently and filtering the mixture to obtain a clarified raw liquid; wherein the raw acid has a P2O5 content of 30 wt% to 60 wt%, a nitric acid content of 1 wt% to 1.5 wt%, an iron ion content of 0.05 wt% to 0.1%, and a sulfuric acid content of 0.3 wt% to 1 wt%; (2) adding the clarified raw liquid and the extractant into an extraction crystallizer for extraction reaction, controlling the addition ratio of the clarified raw liquid to the extractant to control the pH value of the extraction reaction between 3.5 and 4.5; the extractant is composed 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 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; (3) After the extraction reaction is completed, the phases are allowed to stand for phase separation, the extracted organic phase is transported to the stripping tank, and the residual water phase is transported to the cooling crystallization tank; (4) cooling and crystallizing the raffinate water phase in the cooling crystallization tank. After the cooling and crystallization is completed, the solid and liquid are separated, and the obtained solid is potassium dihydrogen phosphate, and the obtained liquid phase is the first mother liquor. The first mother liquor is transported to step (1) for preparing the crude raw material liquid; (5) adding aqueous ammonia to the stripping tank for neutralization reaction. During the neutralization reaction, the pH value of the mixed solution in the stripping tank is regulated and maintained at 6.5-7.5 by adding aqueous ammonia. After the neutralization reaction is completed, the obtained reaction solution is input into the stripping phase separation tank, and the phases are allowed to stand for phase separation. The organic phase obtained by phase separation is the extractant, which is stored in a storage tank. 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-liquid separation is performed. 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 stripping tank.

2. The method for producing potassium dihydrogen phosphate by solvent extraction according to claim 1, characterized in that: In the main agent of the extractant, the volume ratio of N,N-diisooctylethanolamine to trioctylmethylammonium chloride is (0.5-1.2):

1.

3. The method for producing potassium dihydrogen phosphate by solvent extraction according to claim 1, characterized in that: Among the auxiliary agents of the extractant, xylene and C8~C 16 The volume ratio of alkanes is (0.8~2):

1.

4. 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.

5. The method for producing potassium dihydrogen phosphate by solvent extraction according to any one of claims 1 to 4, characterized in that: In step (1), the filter aid is activated carbon, and the amount of the filter aid added is 0.1% to 0.5% of the mass of the crude raw material liquid.

6. The method for producing potassium dihydrogen phosphate by solvent extraction according to any one of claims 1 to 4, characterized in that: In step (1), the concentration of chloride ions in the crude raw material solution is controlled to be 1.5 to 3.2 mol / L.

7. The method for producing potassium dihydrogen phosphate by solvent extraction according to any one of claims 1 to 4, characterized in that: In step (2), the volume ratio of the clarified raw liquid to the extractant in the extraction crystallizer is controlled to be (1-2.5):

1.

8. The method for producing potassium dihydrogen phosphate by solvent extraction according to any one of claims 1 to 4, characterized in that: In step (2), the extraction reaction temperature is controlled to be 20-60° C. and the extraction reaction time is controlled to be 10-60 min.

9. The method for producing potassium dihydrogen phosphate by solvent extraction according to any one of claims 1 to 4, 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 30 to 60 minutes.