A system for reducing the content of phosphorus pentoxide in a crude phosphoric acid organic extraction phase

Abstract

A system for reducing the content of P2O5 in a crude phosphoric acid organic extraction phase, comprising a main extraction tank for obtaining a crude liquid containing hydrochloric acid extraction phase and KH2PO4 by hydrochloric acid extraction phase separation; a 1# washing tank and a 2# washing tank connected in sequence for removing P2O5 droplets entrained in the hydrochloric acid extraction phase by two-stage countercurrent washing; a 1# supergravity washing tank and a 2# supergravity washing tank connected in sequence for removing P2O5 associated with the extractant by two-stage countercurrent washing of the extraction phase treated by the washing tank; a potassium chloride solution supply unit connected to the 2# supergravity washing tank; and a potassium dihydrogen phosphate mother liquor supply unit mixed with the washing liquid from the 1# supergravity washing tank and then entering the 2# washing tank. The P2O5 entrained and associated in the hydrochloric acid extraction phase is effectively removed, the content of P2O5 in the extraction phase is reduced to 0.002%-0.009%, the product yield and purity are improved, the equipment corrosion is reduced, and the solvent regeneration efficiency is improved.

Description

Technical Field

[0001] This utility model belongs to the technical field of producing potassium dihydrogen phosphate by organic extraction of crude phosphoric acid, specifically relating to a system for reducing the phosphorus pentoxide content in the hydrochloric acid-containing extract phase during the process of producing potassium dihydrogen phosphate by organic extraction of crude phosphoric acid. Background Technology

[0002] Solvent extraction is a crucial process for producing high-purity potassium dihydrogen phosphate (KH₂PO₄). Typically, phosphate rock is decomposed with sulfuric acid to obtain crude phosphoric acid, which is then reacted with potassium chloride through an extraction reaction to generate KH₂PO₄. After the reaction, the mixture is separated into two phases: a lower layer is crude KH₂PO₄, and an upper layer is an organic extract phase containing hydrochloric acid. This hydrochloric acid-containing extract phase contains unreacted P₂O₅, with a content of approximately 0.6%-1.0%. This extract phase needs to be subsequently sent to a solvent regeneration section to recover the extractant and produce ammonium chloride as a byproduct. If the P₂O₅ content is too high, the following problems will occur: 1) In the regeneration section, P₂O₅ reacts with ammonia to produce ammonium phosphate, which mixes into the byproduct ammonium chloride, severely reducing the purity of the ammonium chloride product; 2) It leads to a decrease in the phosphorus yield of the main product, potassium dihydrogen phosphate; 3) P₂O₅ accumulates in the system, exacerbating equipment corrosion; 4) It affects the regeneration efficiency and service life of the extractant.

[0003] Existing technologies typically involve directly regenerating or using a single-stage washing process with a P2O5 content of 0.6%-1.0% containing hydrochloric acid as the extractant. The single-stage washing equipment is a mixing and clarification tank. However, due to the strong association between P2O5 and the organic extractant, conventional physical washing methods have limited mass transfer efficiency, making it difficult to break this association and reduce the P2O5 content to below 0.01%, thus failing to meet the requirements for producing high-quality potassium dihydrogen phosphate. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies. In the process of producing potassium dihydrogen phosphate from crude phosphoric acid through organic extraction, conventional washing methods have low efficiency in removing associated P2O5. This invention provides a coupled system that combines conventional washing with high-gravity chemical washing to improve mass transfer efficiency, reduce the P2O5 content in the hydrochloric acid-containing extract phase, increase product yield and purity, and reduce equipment corrosion.

[0005] The technical solution adopted by this utility model is as follows: A system for reducing the phosphorus pentoxide content in the organic extract phase of crude phosphoric acid, comprising: The main extraction tank is used for hydrochloric acid extraction and phase separation. The upper layer is the hydrochloric acid extraction phase, and the lower layer is the crude KH2PO4 solution. Washing tanks #1 and #2, which are connected in sequence to the hydrochloric acid-containing extract phase, are used to perform two-stage countercurrent washing of the hydrochloric acid-containing extract phase to remove entrained phosphorus pentoxide droplets. The No. 1 and No. 2 supergravity washing tanks, connected in sequence, are used to perform two-stage countercurrent washing on the extract phase after it has been treated in the washing tanks, and to remove phosphorus pentoxide associated with the extractant through a chemical reaction. The potassium chloride solution supply unit is connected to the No. 2 gravity washing tank; The potassium dihydrogen phosphate mother liquor supply unit mixes with the washing liquid from the No. 1 super gravity washing tank and then enters the No. 2 washing tank.

[0006] The system consists of a main extraction tank, two-stage conventional washing tanks (washing tanks #1 and #2), and two-stage high-gravity washing tanks (high-gravity washing tanks #1 and #2). The hydrochloric acid-containing extract phase is sequentially washed by conventional washing and high-gravity washing. Through a combination of countercurrent washing and chemical reaction, entrained and associated phosphorus pentoxide is removed.

[0007] Furthermore, the No. 1 and No. 2 supergravity washing tanks are rotating filled bed mixers with a rotor speed of 2600~3600 rpm, generating 1000~1500 times the gravitational acceleration. The supergravity washing tanks adopt a rotating filled bed structure, which generates a supergravity environment through high-speed rotation, thereby enhancing the mass transfer and reaction process.

[0008] Furthermore, this system also includes: The first regulating valve is used to regulate the flow rate of potassium dihydrogen phosphate mother liquor; The second regulating valve is used to regulate the flow rate of the washing liquid from the No. 1 super gravity washing tank, and to control the flow rate of the washing liquid relative to the fluctuation of phosphorus pentoxide content.

[0009] Furthermore, the volume ratio of the potassium dihydrogen phosphate mother liquor to the No. 1 washing liquid from the No. 1 supergravity washing tank is (34):2.

[0010] Furthermore, the volume ratio of the hydrochloric acid-containing extraction phase, extraction phase 1, extraction phase 2, extraction phase 3, extraction phase 4 to the potassium chloride solution is (7~9):(7~8.9):(7~8.8):(7~8.7):(7~8.6):1.

[0011] Furthermore, the operating temperatures of the No. 1 washing tank, No. 2 washing tank, No. 1 super gravity washing tank, and No. 2 super gravity washing tank are controlled at 25~30℃, 20~25℃, 15~20℃, and 10~15℃, respectively. The temperatures of the washing tank and the super gravity washing tank are controlled within different ranges to balance washing effect and energy consumption control.

[0012] Furthermore, the No. 1 washing tank and the No. 2 washing tank are mixing and clarification tanks, and the stirring speed is 200~300 rpm.

[0013] Furthermore, the mass concentration of the potassium chloride solution is 10% to 20%.

[0014] The beneficial effects of this utility model are: 1. This utility model combines two washing methods: conventional washing (mixing and clarifying tank) is used to remove most of the free P2O5 first, and then the strong shear force and mass transfer efficiency of high gravity washing (rotating packed bed) are used to remove the difficult-to-remove associated P2O5, thereby reducing the P2O5 content in the hydrochloric acid extraction phase.

[0015] 2. Under hypergravity conditions, the liquid film is extremely thin, the mass transfer distance is extremely short, and the phase interface is updated extremely quickly. This invention can efficiently break the association between P2O5 and the extractant, reducing the P2O5 content in the final extract phase from 0.6%-1.0% to 0.002%-0.009%.

[0016] 3. After deep dephosphorization, the purity of the by-product ammonium chloride is significantly improved, the yield of the main product potassium dihydrogen phosphate is increased, equipment corrosion is reduced, and the regeneration efficiency of the extractant is increased by 1-2 times.

[0017] 4. This utility model uses potassium chloride solution and potassium dihydrogen phosphate mother liquor generated in the system as washing liquid. All washing liquid #4 is returned to the main process as raw material, realizing a closed-loop cycle of phosphorus element, generating no additional waste, and is green and environmentally friendly. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of this utility model. Detailed Implementation

[0019] The content of this utility model will be further described below with reference to the accompanying drawings and embodiments.

[0020] like Figure 1 As shown, a system for reducing the phosphorus pentoxide content in the crude phosphoric acid organic extract phase includes: Main extraction tank 1 is used for hydrochloric acid extraction reaction and phase separation. After crude phosphoric acid 11 and extractant 12 are extracted in main extraction tank 1, the upper layer is hydrochloric acid extraction phase 2 and the lower layer is crude KH2PO4 liquid 13. Washing tanks 1#3 and 2#4, connected in sequence, are used for two-stage countercurrent washing of the hydrochloric acid extract phase 2 to remove entrained phosphorus pentoxide droplets. The hydrochloric acid extract phase 2 is fed into washing tanks 1#3 and 2#4 for two-stage countercurrent washing to remove entrained phosphorus pentoxide droplets. In washing tank 2#4, the mixed washing solution comes into contact with the extract phase 21 from washing tank 1#3. After phase separation, washing solution 3#33 is generated and sent to washing tank 1#, while the extract phase is sent to washing tank 1#5. In washing tank 1#3, washing solution 3#33 comes into contact with the hydrochloric acid extract phase 2. After phase separation, the extract phase is sent to washing tank 2#, while washing solution 4#34 is generated and returned to the main extraction tank 1 as raw material. The 1# supergravity washing tank 5 and the 2# supergravity washing tank 6, connected in sequence, are used to perform two-stage countercurrent washing on the extract phase after the washing tank is treated, and to remove phosphorus pentoxide associated with the extractant through chemical reaction. The potassium chloride solution supply unit 61 is connected to the 2# hypergravity washing tank 6. The potassium chloride solution enters the 2# hypergravity washing tank 6 and comes into contact with the 3# extraction phase 23 from the 1# hypergravity washing tank 5. After phase separation, the generated 2# washing liquid 32 enters the 1# hypergravity washing tank 5. The 4# extraction phase 24 generated after washing is sent to the solvent regeneration unit 7.

[0021] The potassium dihydrogen phosphate mother liquor supply unit 41 mixes with the 1# washing liquid 31 from the 1# supergravity washing tank 5 and then enters the 2# washing tank 4; the 2# washing liquid 32 comes into contact with the 2# extraction phase 22 from the 2# washing tank 4, and after phase separation, the 1# washing liquid 31 is generated and sent to mix with the potassium dihydrogen phosphate mother liquor 41 to generate the 3# extraction phase 23, which is sent to the 2# supergravity washing tank 6.

[0022] After two stages of countercurrent washing in super gravity washing tank 5 (1#) and super gravity washing tank 6 (2#), phosphorus pentoxide associated with the extractant is removed through chemical reaction.

[0023] The No. 1 supergravity washing tank 5 and the No. 2 supergravity washing tank 6 are rotary packed bed mixers with rotor speeds of 2600~3600 rpm, generating 1000~1500 times the gravitational acceleration. The high-speed rotation of the rotor generates a centrifugal force field, forming a supergravity environment. Different materials are mixed in a complex flow channel. The strong shear force breaks the liquid phase material into micron-sized liquid films or droplets, generating a rapidly renewed phase interface, shortening the liquid-liquid mass transfer distance, and enhancing the mixing efficiency.

[0024] To optimize the washing effect, based on the fluctuation of phosphorus pentoxide content in the hydrochloric acid-containing extract phase, the system further includes: a first regulating valve 2a for regulating the flow rate of the potassium dihydrogen phosphate mother liquor; and a second regulating valve 4a for regulating the flow rate of the washing liquid from the No. 1 supergravity washing tank, so that the volume ratio of the potassium dihydrogen phosphate mother liquor to the No. 1 washing liquid from the No. 1 supergravity washing tank is (3~4):2.

[0025] To optimize the washing effect, an excess of potassium chloride is beneficial for the chemical reaction to proceed in the direction of reducing phosphorus pentoxide, so that the molar ratio of phosphorus pentoxide to potassium chloride in the hydrochloric acid extract phase is 1:3, and the volume ratio of the hydrochloric acid extract phase, extract phase 1, extract phase 2, extract phase 3, extract phase 4 to potassium chloride solution is (7~9):(7~8.9):(7~8.8):(7~8.7):(7~8.6):1.

[0026] Low temperature is beneficial to reduce equipment corrosion, and the higher temperature setting of washing tank 3 and washing tank 4 is beneficial to washing away phosphorus pentoxide entrained in the extractant. The lower temperature setting of washing tank 5 and washing tank 6 is to save energy. The operating temperatures of washing tank 3, washing tank 4, washing tank 5, and washing tank 6 are controlled at 25~30℃, 20~25℃, 15~20℃, and 10~15℃, respectively.

[0027] The No. 1 washing tank 3 and No. 2 washing tank 4 of this utility model can be mixing and clarifying tanks, with a stirring speed of 200~300 rpm for regular cleaning.

[0028] The potassium chloride solution has a mass concentration of 10%~20%, and a chemical reaction occurs: KCl + H3PO4 = KH2PO4 + HCl. This allows the Cl⁻ in the potassium chloride solution to react with the phosphate ions (H2PO4) in the hydrochloric acid-containing extractant. - The competitive action of phosphorus pentoxide selectively replaces phosphorus pentoxide in the organic phase, generating potassium dihydrogen phosphate which enters the aqueous phase, and the generated hydrochloric acid which enters the extraction phase. Example 1

[0029] The flow rate of the hydrochloric acid-containing extractant phase from the main extraction tank is 9 m³ / s. 3 The sample was fed into the system at a temperature of 40°C and a P2O5 content of 0.8% per hour.

[0030] First, it enters the first-stage mixing and clarification tank (conventional washing), where it comes into countercurrent contact with the No. 3 washing liquid from the second-stage mixing and clarification tank. The stirring speed is controlled at 250 rpm and the temperature at 28℃.

[0031] After the first stage of washing, the flow rate of extraction phase #1 is 8.9 m³ / s. 3At a rate of 1 h, the P2O5 content decreases to 0.5%, and the solution enters the second-stage mixing and clarification tank, where it comes into countercurrent contact with a washing solution made from potassium dihydrogen phosphate mother liquor and washing solution #1 from the supergravity unit at a volume ratio of 3.5:2. The stirring speed is controlled at 250 rpm and the temperature at 22℃.

[0032] After the second stage of washing, the flow rate of extraction phase #2 was 8.8 m³ / s. 3 The P2O5 content decreased to 0.1% per hour, and the solution entered the first-stage rotating packed bed (hypergravity washing). In the first-stage rotating packed bed, it came into countercurrent contact with the No. 2 washing solution from the second-stage rotating packed bed. The rotor speed was controlled at 3200 rpm (creating a hypergravity environment of approximately 1300g), and the temperature was 18℃, resulting in a No. 3 extraction phase flow rate of 8.7 m³ / h. 3 / h, the P2O5 content decreased to 0.01%.

[0033] Subsequently, the No. 3 extraction phase enters the second-stage rotating packed bed, with a flow rate of 1 m³ / min. 3 The rotor is contacted countercurrently with a 10% potassium chloride solution at a constant speed of 3200 rpm and a temperature of 12℃.

[0034] Ultimately, the purified extract phase #4 was 8.6 μm. 3 / h, the P2O5 content drops to 0.005%, and it is sent to the solvent regeneration section.

[0035] The entire system achieves efficient removal of P2O5 with a removal rate of 99.4%, and all washing liquid is returned to the front end as raw material, increasing the total phosphorus yield by about 2.5%. Example 2

[0036] The flow rate of the hydrochloric acid-containing extractant phase from the main extraction tank is 9 m³ / s. 3 The sample was fed into the system at a temperature of 40°C and a P2O5 content of 0.8% per hour.

[0037] First, it enters the first-stage mixing and clarification tank (conventional washing), where it comes into countercurrent contact with the No. 3 washing liquid from the second-stage mixing and clarification tank. The stirring speed is controlled at 250 rpm and the temperature at 28℃.

[0038] After the first stage of washing, the flow rate of extraction phase #1 is 8.9 m³ / s. 3 At a rate of 1 h, the P2O5 content decreases to 0.5%, and the solution enters the second-stage mixing and clarification tank, where it comes into countercurrent contact with a washing solution made from potassium dihydrogen phosphate mother liquor and washing solution #1 from the supergravity unit at a volume ratio of 3.5:2. The stirring speed is controlled at 250 rpm and the temperature at 22℃.

[0039] After the second stage of washing, the flow rate of extraction phase #2 was 8.8 m³ / s. 3The P2O5 content decreased to 0.1% per hour, and the solution entered the first-stage rotating packed bed (hypergravity washing). In the first-stage rotating packed bed, it came into countercurrent contact with the No. 2 washing liquid from the second-stage rotating packed bed. The rotor speed was controlled at 3600 rpm (creating a hypergravity environment of approximately 1500g), and the temperature was 18℃, resulting in a No. 3 extraction phase flow rate of 8.7m³. 3 / h, the P2O5 content decreased to 0.007%.

[0040] Subsequently, the No. 3 extraction phase enters the second-stage rotating packed bed, with a flow rate of 1 m³ / min. 3 / h, 10% potassium chloride solution countercurrent contact; rotor speed controlled at 3600 rpm, temperature 12℃.

[0041] Ultimately, the purified extract phase #4 was 8.6 μm. 3 / h, the P2O5 content drops to 0.002%, and it is sent to the solvent regeneration section.

[0042] The entire system achieves efficient removal of P2O5 with a removal rate of 99.7%, and all washing liquid is returned to the front end as raw material, increasing the total phosphorus yield by about 2.5%.

[0043] The embodiments described above are merely preferred embodiments of the present utility model and are not intended to limit the scope of the present utility model. Various modifications and improvements made to the technical solutions of the present utility model by those skilled in the art without departing from the spirit of the present utility model should fall within the protection scope defined by the claims of the present utility model.

Claims

1. A system for reducing the phosphorus pentoxide content in the organic extract phase of crude phosphoric acid, characterized in that, include: The main extraction tank is used for hydrochloric acid extraction and phase separation. The upper layer is the hydrochloric acid extraction phase, and the lower layer is the crude KH2PO4 solution. Washing tanks #1 and #2, which are connected in sequence to the hydrochloric acid-containing extract phase, are used to perform two-stage countercurrent washing of the hydrochloric acid-containing extract phase to remove entrained phosphorus pentoxide droplets. The No. 1 and No. 2 supergravity washing tanks, connected in sequence, are used to perform two-stage countercurrent washing on the extract phase after it has been treated in the washing tanks, and to remove phosphorus pentoxide associated with the extractant through chemical reaction. The potassium chloride solution supply unit is connected to the No. 2 gravity washing tank; The potassium dihydrogen phosphate mother liquor supply unit mixes with the washing liquid from the No. 1 super gravity washing tank and then enters the No. 2 washing tank.

2. The system according to claim 1, characterized in that, The No. 1 and No. 2 supergravity washing tanks are rotary filled bed mixers with a rotor speed of 2600~3600 rpm.

3. The system according to claim 1, characterized in that, Also includes: The first regulating valve (2a) is used to regulate the flow rate of potassium dihydrogen phosphate mother liquor; The second regulating valve (4a) is used to regulate the flow rate of the washing liquid from the No. 1 super gravity washing tank.

4. The system according to claim 1, characterized in that, The volume ratio of the potassium dihydrogen phosphate mother liquor to the No. 1 washing liquid from the No. 1 supergravity washing tank is (3-4):

2.

5. The system according to claim 1, characterized in that, The volume ratio of the hydrochloric acid-containing extract phase, extract phase 1, extract phase 2, extract phase 3, extract phase 4 to the potassium chloride solution is (7~9):(7~8.9):(7~8.8):(7~8.7):(7~8.6):

1.

6. The system according to claim 1, characterized in that, The operating temperatures of the No. 1 washing tank, No. 2 washing tank, No. 1 super gravity washing tank, and No. 2 super gravity washing tank are controlled at 25~30℃, 20~25℃, 15~20℃, and 10~15℃, respectively.

7. The system according to claim 1, characterized in that, The No. 1 and No. 2 washing tanks are mixing and clarification tanks with a stirring speed of 200~300 rpm.

8. The system according to claim 1, characterized in that, The potassium chloride solution has a mass concentration of 10% to 20%.

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