Method for preparing monopotassium phosphate from wet-process phosphoric acid

Abstract

The invention belongs to the field of chemical processes, and particularly relates to a method for preparing monopotassium phosphate from wet-process phosphoric acid, which comprises the following steps: a) mixing semi-hydrated wet-process phosphoric acid and barium carbonate, heating to react, and carrying out solid-liquid separation to obtain a first liquid phase; b) mixing the first liquid phase with dibutyl phosphate, carrying out heating reaction, and carrying out solid-liquid separation to respectively obtain a second liquid phase and a pasty solid; c) carrying out mixed reaction on the second liquid phase and KOH, and carrying out solid-liquid separation to obtain a third liquid phase; d) carrying out cooling crystallization and solid-liquid separation on the third liquid phase to respectively obtain a crystallized product and a fourth liquid phase; and e) drying the crystallized product to obtain a monopotassium phosphate product. The method can be used for simply and efficiently removing impurities from wet-process phosphoric acid and producing high-quality industrial-grade monopotassium phosphate, and is relatively low in implementation cost and wide in industrialization prospect.

Description

Technical Field

[0001] The invention belongs to the field of chemical technology, and in particular relates to a method for preparing potassium dihydrogen phosphate by using wet-process phosphoric acid. Background Art

[0002] Potassium dihydrogen phosphate (MKP for short, molecular formula: KH2PO4) is an important phosphorus chemical product, widely used in fertilizer, metallurgy, medicine, food, electronics and other industries. The main specifications available on the market are agricultural grade, industrial grade, feed grade and food grade. Its production methods include neutralization method, extraction method, ion exchange method, double decomposition method, direct method, crystallization method and electrolysis method. However, the most widely used method in production is the neutralization method of "thermal phosphoric acid or industrial grade phosphoric acid-potassium hydroxide".

[0003] The thermal phosphoric acid process has been gradually phased out due to high energy consumption and high pollution. Currently, most phosphoric acid and phosphate products are produced by the wet phosphoric acid production process. Wet phosphoric acid is produced by decomposing phosphate rock with sulfuric acid, nitric acid or hydrochloric acid. Since phosphate rock contains a large amount of SO4 2- , Fe and other impurities, so these impurities will also enter the wet-process phosphoric acid during the acid hydrolysis process, resulting in a high impurity content in the wet-process phosphoric acid, which needs to be removed to produce a higher quality purified phosphoric acid product. At present, the most widely used method in production is to use solvent extraction to prepare industrial-grade phosphoric acid. However, the preparation process of industrial-grade phosphoric acid has problems such as complex process, high cost, and low phosphoric acid yield. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a method for preparing potassium dihydrogen phosphate from wet-process phosphoric acid, which can simply and efficiently remove impurities from wet-process phosphoric acid and produce high-quality industrial-grade potassium dihydrogen phosphate.

[0005] The present invention provides a method for preparing potassium dihydrogen phosphate by wet-process phosphoric acid, comprising the following steps:

[0006] a) mixing semi-aqueous wet-process phosphoric acid and barium carbonate, heating for reaction, and performing solid-liquid separation to obtain a first liquid phase;

[0007] b) mixing the first liquid phase with dibutyl phosphate, heating for reaction, and performing solid-liquid separation to obtain a second liquid phase and a paste-like solid respectively;

[0008] c) mixing the second liquid phase with KOH for reaction, and performing solid-liquid separation to obtain a third liquid phase;

[0009] d) cooling the third liquid phase for crystallization and solid-liquid separation to obtain a crystal product and a fourth liquid phase respectively;

[0010] e) drying the crystalline product to obtain a potassium dihydrogen phosphate product.

[0011] Preferably, in step a), the P2O5 content of the semi-aqueous wet-process phosphoric acid is 40-42 wt%.

[0012] Preferably, in step a), the SO4 in the semi-aqueous wet-process phosphoric acid 2- The Ba in the barium carbonate 2+ The molar ratio is 1:(1~1.2).

[0013] Preferably, in step a), the heating reaction is carried out at a temperature of 60 to 70° C. and for a time of 10 to 40 minutes.

[0014] Preferably, in step b), before mixing with the dibutyl phosphate, the P2O5 content of the first liquid phase is diluted to 20-25 wt%.

[0015] Preferably, in step b), the content of dibutyl phosphate in the mixed system is 10-20 wt%.

[0016] Preferably, in step b), the heating reaction is carried out at a temperature of 50 to 70° C. and for a time of 10 to 20 minutes.

[0017] Preferably, in step c), the molar ratio of H3PO4 to KOH in the second liquid phase is 1:(0.95-1.2).

[0018] Preferably, in step c), the pH value of the system after the mixed reaction is 4 to 4.5.

[0019] Preferably, the method further comprises the following steps:

[0020] Incinerating the paste solid to obtain ash;

[0021] And / or, the fourth liquid phase is concentrated and then returned to the third liquid phase for cyclic treatment.

[0022] Compared with the prior art, the present invention provides a method for preparing potassium dihydrogen phosphate from wet-process phosphoric acid, comprising the following steps: a) mixing semi-aqueous wet-process phosphoric acid with barium carbonate, heating for reaction, and solid-liquid separation to obtain a first liquid phase; b) mixing the first liquid phase with dibutyl phosphate, heating for reaction, and solid-liquid separation to obtain a second liquid phase and a paste solid respectively; c) mixing the second liquid phase with KOH for reaction, and solid-liquid separation to obtain a third liquid phase; d) cooling and crystallizing the third liquid phase, and solid-liquid separation to obtain a crystalline product and a fourth liquid phase respectively; e) drying the crystalline product to obtain a potassium dihydrogen phosphate product. The present invention first uses barium carbonate to desulfurize semi-aqueous wet-process phosphoric acid, and then uses dibutyl phosphate (DBP) and Fe to form a solid complex Fe-DBP to efficiently remove Fe impurities in wet-process phosphoric acid, and then uses the impurity-removed wet-process phosphoric acid to react with KOH to prepare potassium dihydrogen phosphate. The method can simply and efficiently remove impurities from wet-process phosphoric acid and produce high-quality industrial-grade potassium dihydrogen phosphate, with low implementation costs and broad industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0024] Figure 1 It is a process flow chart provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The present invention provides a method for preparing potassium dihydrogen phosphate by wet-process phosphoric acid, comprising the following steps:

[0027] a) mixing semi-aqueous wet-process phosphoric acid and barium carbonate, heating for reaction, and performing solid-liquid separation to obtain a first liquid phase;

[0028] b) mixing the first liquid phase with dibutyl phosphate, heating for reaction, and performing solid-liquid separation to obtain a second liquid phase and a paste-like solid respectively;

[0029] c) mixing the second liquid phase with KOH for reaction, and performing solid-liquid separation to obtain a third liquid phase;

[0030] d) cooling the third liquid phase for crystallization and solid-liquid separation to obtain a crystal product and a fourth liquid phase respectively;

[0031] e) drying the crystalline product to obtain a potassium dihydrogen phosphate product.

[0032] In the method provided by the present invention, in step a), the P2O5 content of the semi-aqueous wet-process phosphoric acid is preferably 40 to 42 wt%, specifically 40 wt%, 40.1 wt%, 40.2 wt%, 40.3 wt%, 40.4 wt%, 40.5 wt%, 40.6 wt%, 40.7 wt%, 40.8 wt%, 40.9 wt%, 41 wt%, 41.1 wt%, 41.2 wt%, 41.3 wt%, 41.4 wt%, 41.5 wt%, 41.6 wt%, 41.7 wt%, 41.8 wt%, 41.9 wt% or 42 wt%; the SO4 2- The content is preferably 10000-15000ppm, specifically 11000ppm, 12000ppm, 13000ppm, 14000ppm, 14370ppm or 15000ppm; the Fe content of the semi-aqueous wet-process phosphoric acid is preferably 3000-4000ppm, specifically 3000ppm, 3100ppm, 3200ppm, 3300ppm, 3400ppm, 3500ppm, 3548ppm, 3600ppm, 3700ppm, 3800ppm, 3900ppm or 4000ppm.

[0033] In the method provided by the present invention, in step a), the barium carbonate is preferably mixed with semi-aqueous wet-process phosphoric acid in the form of a barium carbonate slurry; the barium carbonate slurry has a Ba 2+ The content is preferably 5-7wt%, specifically 5wt%, 5.5wt%, 6wt%, 6.5wt% or 7wt%.

[0034] In the method provided by the present invention, in step a), the SO4 2- The Ba in the barium carbonate 2+ The molar ratio of is preferably 1:(1-1.2), specifically 1:1, 1:1.05, 1:1.1, 1:1.15 or 1:1.2.

[0035] In the method provided by the present invention, in step a), the temperature of the heating reaction is preferably 60-70°C, specifically 60°C, 65°C or 70°C; the stirring rate of the heating reaction is preferably 300-400r / min, specifically 300r / min, 350r / min or 400r / min; the time of the heating reaction is preferably 10-40min, specifically 10min, 15min, 20min, 25min, 30min, 35min or 40min.

[0036] In the method provided by the present invention, in step b), before mixing with the dibutyl phosphate, the P2O5 content of the first liquid phase is preferably diluted to 20-25wt%, specifically 20wt%, 20.5wt%, 21wt%, 21.5wt%, 22wt%, 22.5wt%, 23wt%, 23.5wt%, 24wt%, 24.36wt%, 24.5wt% or 25wt%.

[0037] In the method provided by the present invention, in step b), the content of dibutyl phosphate in the mixed system is preferably 10-20wt%, specifically 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%.

[0038] In the method provided by the present invention, in step b), the temperature of the heating reaction is preferably 50-70°C, specifically 50°C, 55°C, 60°C, 65°C or 70°C; the stirring rate of the heating reaction is preferably 300-400r / min, specifically 300r / min, 350r / min or 400r / min; the time of the heating reaction is preferably 10-20min, specifically 10min, 15min or 20min.

[0039] In the method provided by the present invention, in step c), the KOH is preferably mixed with the second liquid phase in the form of a KOH aqueous solution; the concentration of the KOH aqueous solution is preferably 40-60wt%, specifically 40wt%, 45wt%, 50wt%, 55wt% or 60wt%.

[0040] In the method provided by the present invention, in step c), the molar ratio of H3PO4 to KOH in the second liquid phase is preferably 1:(0.95-1.2), specifically 1:0.95, 1:0.97, 1:1, 1:1.02, 1:1.05, 1:1.07, 1:1.1, 1:1.12, 1:1.15, 1:1.17 or 1:1.2.

[0041] In the method provided by the present invention, in step c), the pH value of the system after the mixed reaction is preferably 4 to 4.5.

[0042] In the method provided by the present invention, it is preferred to further include the following steps: incinerating the paste solid in step b) to obtain ash. In the present invention, the main component of the paste solid is a Fe-DBP complex, and the ash after incineration can be used to prepare white fertilizer.

[0043] In the method provided by the present invention, it is preferred to further include the following steps: concentrating the fourth liquid phase obtained in step d), and then returning it to the third liquid phase for cyclic treatment in step d).

[0044] The method provided by the present invention can simply and efficiently remove impurities from wet-process phosphoric acid and produce high-quality industrial-grade potassium dihydrogen phosphate. More specifically, it has at least the following advantages:

[0045] (1) The Fe impurities in wet-process phosphoric acid are removed by forming a solid complex Fe-DBP with DBP. The removal effect is good, and the Fe removal rate can reach more than 99.5%, which can reduce the Fe content to below 10 ppm.

[0046] (2) The wet-process phosphoric acid Fe impurity removal process produces a solid complex Fe-DBP, which is easy to remove by phase separation; and the solid complex can be subsequently incinerated and used to prepare white fertilizer, thus realizing resource utilization.

[0047] (3) The P2O5 content in wet-process phosphoric acid remains basically unchanged before and after Fe removal, and no phosphorus loss will occur.

[0048] (4) The impurity content of wet-process phosphoric acid after impurity removal is extremely low, and the obtained potassium dihydrogen phosphate is of excellent quality.

[0049] For the purpose of greater clarity, the invention is described in detail through the following examples.

[0050] Example 1

[0051] A method for preparing potassium dihydrogen phosphate by wet phosphoric acid, the process flow is as follows Figure 1 As shown, the specific process includes:

[0052] Semi-aqueous wet-process phosphoric acid (P2O5 content 41.4wt%, SO4 2- content 14370ppm, Fe content 3548ppm) was added to the reaction tank, and then SO4 2- :Ba 2+ Ba was added to the reaction tank at a molar ratio of 1:1.1. 2+The semi-aqueous wet-process phosphoric acid was desulfurized by a 6.5wt% barium carbonate slurry; the reaction temperature was maintained at 60°C, the stirring rate was 300r / min, and the reaction lasted for 15min after the addition of the barium carbonate slurry; the filtered acid solution SO4 2- The content is 346ppm.

[0053] The filtered acid solution was diluted to a P2O5 content of 24.36wt% and added to a reactor, and then DBP was added to the reactor at a mass ratio of diluted acid solution:DBP of 10:1.6, the reaction temperature was maintained at 60°C, the stirring rate was 300r / min, and the reaction was carried out for 15min after the addition of DBP was completed; the phases were allowed to stand for phase separation to obtain an upper paste (Fe-DBP complex) and a lower clear liquid, and then solid-liquid separation was performed; the separated paste was incinerated at high temperature, and the ash after incineration was used to prepare white fertilizer; the Fe content of the separated clear liquid was 46ppm.

[0054] Take the above-mentioned clear liquid after Fe removal and add it into a reaction tank, then add 50wt% KOH solution into the reaction tank for neutralization reaction according to the KOH:H3PO4 molar ratio of 1.2:1, and the stirring rate is 300r / min; when the pH value of the mixed slurry reaches 4-4.5, filter it once, cool the filtrate for crystallization, and then filter it twice to obtain potassium dihydrogen phosphate crystals and mother liquor; the mother liquor is concentrated and returned to the filtrate before cooling and crystallization for circulation treatment; the potassium dihydrogen phosphate crystals are dried to obtain potassium dihydrogen phosphate products.

[0055] The main content indicators of the potassium dihydrogen phosphate product prepared in this embodiment are shown in the following table:

[0056] <![CDATA[KH2PO4 / %]]> <![CDATA[P2O5 / %]]> <![CDATA[K2O / %]]> <![CDATA[Cl - / ppm]]> Fe / ppm As / ppm Pb / ppm Water insoluble matter / % Moisture / % 99.13 51.82 34.25 204 16 9.3 Not detected 0.15 0.28

[0057] Example 2

[0058] A method for preparing potassium dihydrogen phosphate by wet phosphoric acid, the process flow is as follows Figure 1 As shown, the specific process includes:

[0059] Semi-aqueous wet-process phosphoric acid (P2O5 content 41.4wt%, SO4 2- content 14370ppm, Fe content 3548ppm) was added to the reaction tank, and then SO4 2- :Ba 2+ Ba was added to the reaction tank at a molar ratio of 1:1.2. 2+ The semi-aqueous wet-process phosphoric acid is desulfurized by a 6.5wt% barium carbonate slurry; the reaction temperature is maintained at 60°C, the stirring rate is 300r / min, and the reaction is continued for 30 minutes after the addition of the barium carbonate slurry; the filtered acid solution SO4 2- The content is 158ppm.

[0060] The filtered acid solution was diluted to a P2O5 content of 24.36wt% and added to a reactor, and then DBP was added to the reactor at a mass ratio of diluted acid solution:DBP of 10:1.8, the reaction temperature was maintained at 60°C, the stirring rate was 300r / min, and the reaction was carried out for 15min after the addition of DBP was completed; the phases were allowed to stand for phase separation to obtain an upper paste (Fe-DBP complex) and a lower clear liquid, and then solid-liquid separation was performed; the separated paste was incinerated at high temperature, and the ash after incineration was used to prepare white fertilizer; the Fe content of the separated clear liquid was 6ppm.

[0061] The clear liquid after the above-mentioned Fe removal is added into a reaction tank, and then 50wt% KOH solution is added into the reaction tank for neutralization reaction according to the KOH:H3PO4 molar ratio of 1.1:1, and the stirring rate is 300r / min; when the pH value of the mixed slurry reaches 4-4.5, it is filtered once, the filtrate is cooled and crystallized, and then filtered twice to obtain potassium dihydrogen phosphate crystals and mother liquor; the mother liquor is concentrated and returned to the filtrate before cooling and crystallization for circulation treatment; the potassium dihydrogen phosphate crystals are dried to obtain potassium dihydrogen phosphate products.

[0062] The main content indicators of the potassium dihydrogen phosphate product prepared in this embodiment are shown in the following table:

[0063] <![CDATA[KH2PO4 / %]]> <![CDATA[P2O5 / %]]> <![CDATA[K2O / %]]> <![CDATA[Cl - / ppm]]> Fe / ppm As / ppm Pb / ppm Water insoluble matter / % Moisture / % 99.54 52.32 33.82 196 8 8.2 Not detected 0.1 0.24

[0064] Example 3

[0065] A method for preparing potassium dihydrogen phosphate by wet phosphoric acid, the process flow is as follows Figure 1 As shown, the specific process includes:

[0066] Semi-aqueous wet-process phosphoric acid (P2O5 content 41.4wt%, SO4 2- content 14370ppm, Fe content 3548ppm) was added to the reaction tank, and then SO4 2- :Ba 2+ Ba was added to the reaction tank at a molar ratio of 1:1. 2+ The semi-aqueous wet-process phosphoric acid was desulfurized by a 6.5wt% barium carbonate slurry; the reaction temperature was maintained at 60°C, the stirring rate was 300r / min, and the reaction lasted for 15min after the addition of the barium carbonate slurry; the filtered acid solution SO4 2- The content is 446ppm.

[0067] The filtered acid solution was diluted to a P2O5 content of 24.36wt% and added to a reactor, and then DBP was added to the reactor at a mass ratio of diluted acid solution:DBP of 10:1.4, the reaction temperature was maintained at 60°C, the stirring rate was 300r / min, and the reaction was carried out for 15min after the addition of DBP was completed; the phases were allowed to stand for phase separation to obtain an upper paste (Fe-DBP complex) and a lower clear liquid, and then solid-liquid separation was performed; the separated paste was incinerated at high temperature, and the ash after incineration was used to prepare white fertilizer; the Fe content of the separated clear liquid was 58ppm.

[0068] The clear liquid after the above-mentioned Fe removal is added into a reaction tank, and then a 50wt% KOH solution is added into the reaction tank for neutralization reaction according to a KOH:H3PO4 molar ratio of 0.95:1, and the stirring rate is 300r / min; when the pH value of the mixed slurry reaches 4-4.5, it is filtered once, the filtrate is cooled and crystallized, and then filtered twice to obtain potassium dihydrogen phosphate crystals and mother liquor; the mother liquor is concentrated and returned to the filtrate before cooling and crystallization for circulation treatment; the potassium dihydrogen phosphate crystals are dried to obtain potassium dihydrogen phosphate products.

[0069] The main content indicators of the potassium dihydrogen phosphate product prepared in this embodiment are shown in the following table:

[0070] <![CDATA[KH2PO4 / %]]> <![CDATA[P2O5 / %]]> <![CDATA[K2O / %]]> <![CDATA[Cl - / ppm]]> Fe / ppm As / ppm Pb / ppm Water insoluble matter / % Moisture / % 99.01 50.17 33.03 188 27 8.6 Not detected 0.2 0.28

[0071] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing potassium dihydrogen phosphate by wet-process phosphoric acid, characterized in that: The following steps are involved: a) mixing semi-aqueous wet-process phosphoric acid and barium carbonate, heating for reaction, and performing solid-liquid separation to obtain a first liquid phase; b) mixing the first liquid phase with dibutyl phosphate, heating for reaction, and performing solid-liquid separation to obtain a second liquid phase and a paste-like solid respectively; c) mixing the second liquid phase with KOH for reaction, and performing solid-liquid separation to obtain a third liquid phase; d) cooling the third liquid phase for crystallization and solid-liquid separation to obtain a crystal product and a fourth liquid phase respectively; e) drying the crystalline product to obtain a potassium dihydrogen phosphate product.

2. The method according to claim 1, characterized in that In step a), the P2O5 content of the semi-aqueous wet-process phosphoric acid is 40-42 wt%.

3. The method according to claim 1, characterized in that: In step a), the SO4 in the semi-aqueous wet-process phosphoric acid 2- The Ba in the barium carbonate 2+ The molar ratio is 1:(1~1.2).

4. The method according to claim 1, characterized in that: In step a), the heating reaction is carried out at a temperature of 60 to 70° C. and for a time of 10 to 40 minutes.

5. The method according to claim 1, characterized in that: In step b), before mixing with the dibutyl phosphate, the P2O5 content of the first liquid phase is diluted to 20-25 wt%.

6. The method according to claim 1, characterized in that In step b), the content of dibutyl phosphate in the mixed system is 10-20 wt%.

7. The method according to claim 1, characterized in that In step b), the heating reaction is carried out at a temperature of 50 to 70° C. for 10 to 20 minutes.

8. The method according to claim 1, characterized in that In step c), the molar ratio of H3PO4 to KOH in the second liquid phase is 1:(0.95-1.2).

9. The method according to claim 1, characterized in that: In step c), the pH value of the system after the mixed reaction is 4 to 4.

5.

10. The method according to claim 1, characterized in that The following steps are also included: Incinerating the paste solid to obtain ash; And / or, the fourth liquid phase is concentrated and then returned to the third liquid phase for cyclic treatment.

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