Method for producing phosphoric acid by using ammonium dihydrogen phosphate

Abstract

The invention discloses a method for producing phosphoric acid by using ammonium dihydrogen phosphate, and belongs to the technical field of chemical engineering. The method comprises the following steps: mixing ammonium dihydrogen phosphate with hydrochloric acid or introducing HCl gas into an ammonium dihydrogen phosphate solution for transformation so that ammonium dihydrogen phosphate is converted into phosphoric acid and ammonium chloride, cooling after transformation so that ammonium chloride is crystallized and separated out, and then carrying out solid-liquid separation so as to respectively obtain ammonium chloride crystals and a phosphoric acid solution; evaporating and concentrating the phosphoric acid solution to volatilize HCl gas to obtain a phosphoric acid product; and the obtained HCl gas is collected and returned to the transformation process for recycling. The invention provides a method for producing phosphoric acid by taking ammonium dihydrogen phosphate as a raw material. The novel method for preparing phosphoric acid has the advantages of simple process, good product quality, low production cost, environmental friendliness and the like.

Description

Technical Field

[0001] The present invention relates to a method for producing phosphoric acid from ammonium dihydrogen phosphate, belonging to the technical field of chemical engineering. Background Art

[0002] Ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ), also known as monoammonium phosphate, is an important phosphate, mainly used as a fire retardant for wood, fabrics, and paper, and can also be used as a fertilizer, bread improver, and food additive. Industrially, ammonium dihydrogen phosphate can be used to prepare various phosphate products, such as potassium dihydrogen phosphate. The production of ammonium dihydrogen phosphate usually uses phosphoric acid as a raw material, and there are mainly two production methods: one is to react phosphoric acid with ammonium chloride at a temperature of 150 °C, and then obtain the finished product after cooling, centrifugal separation, and drying; the other is to add liquid ammonia and phosphoric acid to a reactor, heat to above 130 °C for reaction, and obtain the finished product after cooling, crystallization, centrifugal separation, and drying. In addition, ammonium dihydrogen phosphate can also be prepared using ammonium phosphate and diammonium phosphate as raw materials. For example, adding phosphoric acid to acidify the solution of ammonium phosphate or diammonium phosphate can crystallize out ammonium dihydrogen phosphate, and heating and decomposing ammonium phosphate or diammonium phosphate can also obtain ammonium dihydrogen phosphate.

[0003] Phosphoric acid, also known as orthophosphoric acid, is a common inorganic acid with the chemical formula H 3 PO 4 . Phosphoric acid is mainly used in industries such as pharmaceuticals, food, and fertilizers, including as an anti-rust agent, food additive, dentistry and orthopedics, EDIC corrosion inhibitor, electrolyte, soldering flux, dispersant, industrial corrosion inhibitor, raw material for fertilizers and components of household cleaning products, and can also be used as a chemical reagent. There are two main categories of industrial production methods for phosphoric acid: one is thermal production, and the obtained product is called thermal phosphoric acid. The process is to first thermally reduce phosphate rock to prepare elemental phosphorus, and then oxidize elemental phosphorus to make phosphoric acid; the other is wet production, and the obtained product is called wet-process phosphoric acid. The process is to first decompose phosphate rock with an acid, such as nitric acid, hydrochloric acid, sulfuric acid, etc., and then separate and recover phosphoric acid from the decomposition solution. However, currently, the acid mainly used for decomposing phosphate rock in industry is sulfuric acid, so generally speaking, wet-process phosphoric acid actually refers to phosphoric acid prepared by decomposing phosphate rock with sulfuric acid.

[0004] The advantages of thermal phosphoric acid are that the obtained phosphoric acid has a high concentration and good quality. The disadvantages are that the preparation of elemental phosphorus by thermal decomposition of phosphate rock relies on electric furnace production, and about 12,500 - 15,000 kWh of electricity is consumed to produce 1 ton of elemental phosphorus. The power consumption of thermal phosphoric acid is large and the production cost is high.

[0005] The advantages of wet-process phosphoric acid are that its energy consumption is low and production cost is low compared with thermal-process phosphoric acid. Its disadvantages are that the concentration of the produced phosphoric acid solution is dilute, there are many impurities, and the evaporation and concentration burden in the phosphoric acid production process is heavy. In the evaporation and concentration process of the dilute phosphoric acid solution, not only fluorine-containing compound vapors with strong corrosiveness escape, but also a large amount of precipitates are generated, resulting in scaling of equipment and pipelines. Some precipitates will also be suspended in the acid and it is very difficult to remove them from the concentrated phosphoric acid. In addition, secondary precipitated salts will be generated after the dilute phosphoric acid solution is concentrated. The process conditions for separating trace impurities in wet-process phosphoric acid are harsh and deep separation is very difficult. Adding ammonia to neutralize the phosphoric acid solution to produce ammonium phosphate salts, and through crystallization and recrystallization, the residual trace impurities in the phosphoric acid solution can be easily removed. If ammonium phosphate salts can be used as raw materials to prepare phosphoric acid in turn, this will open up a new way for the production of high-quality phosphoric acid. Summary of the Invention

[0006] In order to overcome the disadvantages of existing phosphoric acid production methods, the present invention proposes a method for producing phosphoric acid using ammonium dihydrogen phosphate as a raw material, which is a new method for preparing phosphoric acid with the advantages of simple process, good product quality, low production cost, environmental friendliness, etc.

[0007] In order to achieve the above object, the first aspect of the present invention is to provide a method for producing phosphoric acid using ammonium dihydrogen phosphate, and the method includes:

[0008] Mix ammonium dihydrogen phosphate with hydrochloric acid or introduce HCl gas into the ammonium dihydrogen phosphate solution for transformation to convert ammonium dihydrogen phosphate into phosphoric acid and ammonium chloride. After transformation, cool to precipitate ammonium chloride crystals, and then obtain ammonium chloride crystals and phosphoric acid solution respectively through solid-liquid separation;

[0009] The obtained phosphoric acid solution is evaporated and concentrated to volatilize HCl gas to obtain a phosphoric acid product; and the obtained HCl gas is collected and returned to the transformation process for recycling.

[0010] The present invention ingeniously uses ammonium dihydrogen phosphate and its recrystallized product as raw materials for the production of wet-process phosphoric acid, greatly simplifies the production process of high-quality wet-process phosphoric acid, uses hydrochloric acid or HCl gas as a transformation agent, and utilizes the principle of strong acid displacing weak acid. First, ammonium dihydrogen phosphate is converted into a phosphoric acid solution and ammonium chloride crystals, and then the obtained phosphoric acid solution is evaporated and concentrated to obtain a high-quality phosphoric acid product. The obtained HCl gas is collected and returned to the transformation process for recycling, and the recycling of HCl in the phosphoric acid production process is also realized. It has the advantages of simple process, good product quality, low production cost, environmental friendliness, etc.

[0011] A method for producing high-quality phosphoric acid using ammonium dihydrogen phosphate according to the present invention has the following basic principle:

[0012] NH 4 H 2 PO 4 + H+ = H 3 PO 4 + NH 4 + (1)

[0013] NH 4 + + HCl (excess) = NH 4 Cl↓ + H + (2)

[0014] NH 4 + + NH 4 HSO 4 = (NH 4 ) 2 SO 4 + H + (3)

[0015] NH 4 + + NaHSO 4 = NH 4 NaSO 4 + H + (4)

[0016] (5)

[0017] (6)

[0018] (7)

[0019] As a preferred embodiment, the temperature for mixing ammonium dihydrogen phosphate and hydrochloric acid is 40 - 80 °C.

[0020] As a preferred embodiment, the ammonium chloride crystals are thermally decomposed to release HCl gas and ammonia gas, and the obtained HCl gas is collected and returned to the transformation process for recycling.

[0021] It should be noted that the present invention has no special requirements for the source of the ammonium dihydrogen phosphate. Exemplarily, it can be industrial ammonium dihydrogen phosphate and its recrystallized products, or ammonium dihydrogen phosphate prepared from ammonium phosphate or diammonium phosphate.

[0022] As a preferred embodiment, the specific steps of the thermal decomposition specifically include: mixing ammonium chloride crystals with water and then adding them to a thermal decomposition medium to obtain a mixture, heating the mixture to 110 - 210 °C, completely releasing the HCl gas and then heating to 250 - 350 °C to release ammonia gas; the thermal decomposition medium is hydrogen sulfate.

[0023] The HCl gas generated by pyrolysis is collected and returned to the transformation process for recycling.

[0024] In the present invention, the ammonium chloride crystals obtained are pyrolyzed to sequentially release HCl gas and ammonia gas. This not only eliminates the cumbersome purification process in the traditional wet-process phosphoric acid production process, but also realizes the recycling of HCl in the phosphoric acid production process.

[0025] As a preferred embodiment, the bisulfate is sodium bisulfate and / or ammonium bisulfate.

[0026] As a preferred embodiment, the ammonia gas generated by pyrolysis is used for producing ammonia water, producing ammonium carbonate products, or producing agricultural fertilizers. The ammonia gas generated by the present invention can also be recycled, further improving the resource utilization rate.

[0027] As a preferred embodiment, the solid-liquid ratio of the ammonium chloride crystal to the water is 1:0.5 - 1.5 g / mL.

[0028] As a preferred embodiment, the molar ratio of the amount of ammonium dihydrogen phosphate to HCl based on dry basis is 1:1 - 3.

[0029] As a preferred embodiment, the step of crystallizing out ammonium chloride includes: placing the solution obtained after transformation under the condition of -35°C to 9°C to crystallize out ammonium chloride.

[0030] As a more preferred embodiment, the solution obtained after transformation is first cooled to 10 - 30°C, and ammonium chloride is crystallized out under the action of the common ion effect of Cl - ions. After solid-liquid separation, the filtrate is further crystallized out ammonium chloride under the condition of -35°C to 9°C.

[0031] As a preferred embodiment, the time for the deep crystallization is 4 - 24 h.

[0032] Compared with the prior art, the present invention has at least the following advantages:

[0033] Ammonium dihydrogen phosphate is a phosphate product that can be easily purified by crystallization and recrystallization. In the present invention, ammonium dihydrogen phosphate and its recrystallized product are ingeniously used as raw materials for the production of wet-process phosphoric acid, greatly simplifying the production process of high-quality wet-process phosphoric acid. Hydrochloric acid or HCl gas is used as a transformation agent. First, ammonium dihydrogen phosphate is converted into a phosphoric acid solution and ammonium chloride crystals, and then the obtained phosphoric acid solution is evaporated and concentrated to obtain a high-quality phosphoric acid product. The obtained ammonium chloride crystals are pyrolyzed to sequentially release HCl gas and ammonia gas. This not only eliminates the cumbersome purification process in the traditional wet-process phosphoric acid production process, but also realizes the recycling of HCl in the phosphoric acid production process, having the advantages of simple process, good product quality, low production cost, and environmental friendliness. The phosphoric acid produced by the method of the present invention can meet the quality standard of food additive - phosphoric acid specified in the national food safety standard GB 1886.15 - 2015. Detailed implementation manners

[0034] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0035] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments. All other embodiments obtained by those skilled in the art without creative efforts still fall within the protection scope of the present invention.

[0036] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0037] Example 1

[0038] Take 500 g of ammonium dihydrogen phosphate obtained by pyrolyzing diammonium phosphate and add it to 500 mL of concentrated hydrochloric acid (36 - 37%). Heat and stir (at a temperature of 65 °C) to completely dissolve the crystals therein, then cool and crystallize, filter to obtain ammonium chloride crystals, and place the obtained filtrate at -25 °C and add a little ammonium chloride crystal as a seed for freeze crystallization for 20 h to deeply crystallize and precipitate the remaining ammonium chloride therein, filter. Finally, heat and evaporate the obtained filtrate to concentrate it, forcing the excess HCl to completely volatilize. When the specific gravity of the solution rises to 1.55 g / mL, stop heating, cool, and take the supernatant for testing after standing. Its quality meets the quality standard of food additive - phosphoric acid specified in the national food safety standard GB 1886.15 - 2015. After the obtained ammonium chloride crystals are recrystallized, adjust the slurry by adding water according to a solid-liquid ratio of 1:1 g / mL, and then slowly add it to the ammonium bisulfate melt, allowing it to rapidly decompose and release HCl gas at a temperature of 150 - 165 °C. The obtained HCl gas is collected and returned to the transformation process for recycling. After the HCl gas is completely released, raise the temperature of the melt to 280 - 330 °C, and blast in CO 2 gas, so that the NH 3 generated in the melt can volatilize smoothly under the action of the carrier gas, and the NH 2 carried out by the CO 3 gas is absorbed by water cooling to obtain ammonium bicarbonate crystals.

[0039] Example 2

[0040] Take 1000 g of the recrystallized product of industrial ammonium dihydrogen phosphate and add it to 600 mL of deionized water. Heat and stir to dissolve it. At room temperature, introduce HCl gas into the solution according to an NH 4 H 2 PO 4 / HCl molar ratio of 1:1.5, cool to lower the temperature of the slurry to room temperature, then place it at -15 °C for freeze stirring crystallization for 10 h to deeply crystallize and precipitate the remaining ammonium chloride, filter. Finally, heat and evaporate the obtained filtrate to concentrate it, forcing the excess HCl to completely volatilize. When the specific gravity of the solution rises to 1.58 g / mL, stop heating, cool, and take the supernatant for testing after standing. Its quality meets the quality standard of food additive - phosphoric acid specified in the national food safety standard GB 1886.15 - 2015. After the obtained ammonium chloride crystals are recrystallized, add water and heat with stirring to dissolve according to a solid-liquid ratio of 1:1.2 g / mL, and then slowly add the obtained solution to the sodium bisulfate melt so as to rapidly release HCl gas at a temperature of 130 - 150 °C. The obtained HCl gas is collected and returned to the transformation process for recycling. After the HCl gas is completely released, raise the temperature of the melt to 290 - 350 °C, and blast in N 2 as the carrier gas, so that the NH 3 generated in the melt can volatilize smoothly under the action of the carrier gas, and the volatilized NH 3Absorb with the magnesium sulfate solution produced by flue gas desulfurization, and filter to obtain a liquid agricultural fertilizer containing ammonium sulfate.

[0041] Comparative example

[0042] Weigh 500 g of phosphate rock powder with a P 2 O 5 content of 31.48 wt% and a CaO content of 48.97 wt%. Adjust the slurry with water according to a solid-liquid ratio of 1:1 g / mL, and then slowly add 98% concentrated sulfuric acid according to a Ca / S molar ratio of 1:1.3. Maintain the temperature of the reaction solution at 68-81 °C, stir and react for 1 h, filter while it is hot to obtain a filtrate and a filter residue. Wash the filter residue with water to obtain phosphogypsum. Add 350 g of phosphate rock powder to the obtained filtrate and stir and react at 73 °C for 1 h for desulfurization, filter and wash to obtain a P 2 O 5 phosphoric acid solution with a concentration of 32.84%. The wet-process phosphoric acid obtained by evaporating, concentrating and purifying and removing impurities from the phosphoric acid solution has a H 3 PO 4 concentration of 76.5 wt%, and its quality can only meet the quality requirements of Specification 1 qualified products in the industry standard of "HG / T 4069-2022 Industrial Wet-process Purified Phosphoric Acid".

[0043] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for producing phosphoric acid using diammonium phosphate, characterized in that: The method includes: The ammonium dihydrogen phosphate is mixed with hydrochloric acid or HCl gas is introduced into the ammonium dihydrogen phosphate solution to convert the ammonium dihydrogen phosphate into phosphoric acid and ammonium chloride, and after the conversion, the ammonium chloride is cooled to crystallize and precipitate, and then the ammonium chloride crystals and the phosphoric acid solution are obtained after solid-liquid separation; The phosphoric acid solution is evaporated and concentrated to volatilize HCl gas to obtain a phosphoric acid product; and the obtained HCl gas is collected and returned to the transformation process for recycling.

2. A method for producing phosphoric acid using diammonium phosphate according to claim 1, characterized in that: The ammonium chloride crystals are pyrolyzed to release HCl gas and ammonia gas, and the obtained HCl gas is collected and returned to the transformation process for recycling.

3. A method for producing phosphoric acid using diammonium phosphate according to claim 2, characterized in that: The specific steps of the pyrolysis specifically include: The ammonium chloride crystals are mixed with water and then added to a pyrolysis medium to obtain a mixture, the mixture is heated to 110-210° C., the HCl gas is completely released, and then heated to 250-350° C. to release ammonia gas; the pyrolysis medium is bisulfate; The HCl gas produced by pyrolysis is collected and returned to the transformation process for recycling.

4. A method for producing phosphoric acid using diammonium phosphate according to claim 3, characterized in that: The ammonia produced by pyrolysis is used to produce ammonia water, ammonium carbonate products or agricultural fertilizers.

5. A method for producing phosphoric acid using diammonium phosphate according to claim 3, characterized in that: The solid-to-liquid ratio of the ammonium chloride crystals to the water is 1:0.5-1.5 g / mL.

6. A method for producing phosphoric acid using diammonium phosphate according to any one of claims 1 to 5, characterized in that: The molar ratio of the ammonium dihydrogen phosphate to HCl on a dry basis is 1:1-3.

7. A method for producing phosphoric acid using diammonium phosphate according to any one of claims 1 to 5, characterized in that: The step of crystallizing ammonium chloride comprises: The solution obtained after the transformation is placed at -35°C ~ 9°C to crystallize ammonium chloride.

8. A method for producing phosphoric acid using diammonium phosphate according to claim 7, characterized in that: The step of crystallizing ammonium chloride specifically comprises: The solution obtained after transformation was cooled to 10-30°C and then - Ammonium chloride is crystallized under the common ion effect of ions, and after solid-liquid separation, the filtrate is deeply crystallized at -35℃~9℃ to precipitate ammonium chloride.

9. A method for producing phosphoric acid using diammonium phosphate according to claim 8, characterized in that: The time of the deep crystallization is 4 to 24 hours.