Process for producing molten salt-grade potassium nitrate by ammonia process

Abstract

The invention discloses a process for producing molten salt-grade potassium nitrate by an ammonia process, and relates to the technical field of potassium nitrate production. An existing ammonium nitrate-potassium chloride four-step cyclic double decomposition method is improved, nitric acid and ammonia gas are introduced into the ammonium chloride mother liquor instead of directly adding the finished product ammonium nitrate, so that the concentration of ammonium nitrate is about 40% after the nitric acid and the ammonia gas in the mother liquor I react, and the reaction risk is reduced. Moreover, finished ammonium nitrate is not used in the production process, so that an ammonium nitrate production device does not need to be independently built or ammonium nitrate does not need to be purchased, and the production cost is reduced. In addition, nitric acid and ammonia gas are introduced into the mother liquor I, so that crystallization and separation of ammonium chloride are promoted, the separation effect of ammonium chloride and potassium nitrate is enhanced, the product quality of potassium nitrate is improved, and high-quality molten salt-grade potassium nitrate is efficiently and continuously produced.

Description

Technical Field

[0001] The invention relates to the technical field of potassium nitrate production, and in particular to a process for producing molten salt-grade potassium nitrate by an ammonia process. Background Art

[0002] The existing process flow of producing potassium nitrate by the ammonium nitrate-potassium chloride four-step cyclic double decomposition method is as follows: potassium chloride, ammonium nitrate and water are reacted as raw materials to obtain a synthetic feed liquid, the synthetic feed liquid is filtered, crystallized and centrifuged to obtain a crude potassium nitrate product and a primary mother liquor; the crude potassium nitrate product is washed, dried and packaged to obtain a finished potassium nitrate product; the primary mother liquor is evaporated and concentrated and ammonium nitrate is added, followed by crystallization and centrifugation to obtain ammonium chloride and a secondary mother liquor; the secondary mother liquor replaces ammonium nitrate, reacts with potassium chloride in a reactor, and is recycled.

[0003] However, the above process has the following problems: 1) Ammonium nitrate is highly dangerous, which makes storage difficult; 2) It is necessary to build an ammonium nitrate production plant or purchase ammonium nitrate from outside, and the project investment is relatively high; 3) During the production process, other substances need to be added to treat the water wash liquid, which increases the complexity of the process and production costs; 4) The potassium nitrate produced is not molten salt grade. Therefore, it is necessary to provide a new production process to solve the problems of the above potassium nitrate production process. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a process for producing molten salt-grade potassium nitrate by the ammonia process, wherein nitric acid and ammonia gas are introduced into the mother liquor I instead of directly adding the finished ammonium nitrate, so that the concentration of ammonium nitrate is about 40%, the danger of the reaction is reduced, the production cost is reduced, the product quality of potassium nitrate is improved, and the efficient and continuous production of high-quality molten salt-grade potassium nitrate is achieved.

[0005] The technical solution of the present invention is: The process of producing molten salt grade potassium nitrate by ammonia process comprises the following steps: S1 Initial start-up phase Potassium chloride, nitric acid and water are used as raw materials to react, and after the reaction is complete, ammonia gas is introduced to react to obtain a synthetic feed liquid; S2 Potassium Nitrate Crystals The synthetic feed liquid is filtered and then crystallized to precipitate potassium nitrate, and then the crude potassium nitrate is refined after solid-liquid separation, and the filtrate obtained is mother liquor I; S3 Potassium Nitrate Refining The crude potassium nitrate is heated and dissolved, the dissolved solution is filtered and then crystallized, and then the solid-liquid separation is performed, and the obtained solid potassium nitrate is dried and packaged to obtain a molten salt grade potassium nitrate product; S4 Ammonium chloride evaporation and crystallization Nitric acid and ammonia are added to the mother liquor I, and the reaction is carried out under stirring. After the mother liquor I reaches neutrality, it is evaporated and concentrated, and then crystallized, and then solid-liquid separation is performed. The obtained ammonium chloride is packaged to obtain the finished ammonium chloride product, and the obtained filtrate is the mother liquor II and enters step S5; S5 Stable production stage Potassium chloride, mother liquor II and process condensate are added into a reactor as raw materials, and reacted under stirring to obtain a synthetic feed liquid, and then the above steps S2-S4 are repeated.

[0006] Preferably, in step S1, Cl is controlled during the reaction process. - The concentration is 10-15wt.%, NH 4 + The concentration is 5-8wt.%, and the pH is neutral.

[0007] Preferably, in step S3, the heating and dissolving temperature of the crude potassium nitrate is 80-100°C.

[0008] Preferably, in step S3, the crystallization temperature is ≤30°C.

[0009] Preferably, in step S4, the molar ratio of nitric acid to ammonia is 1:1.

[0010] Preferably, in step S4, the crystallization temperature is 60-70°C.

[0011] Preferably, in step S4, crystallization is performed after evaporation and concentration until the solution has a specific gravity of 1.33-1.37.

[0012] Preferably, in step S5, the reaction temperature is 50-80°C.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The present invention improves the existing ammonium nitrate-potassium chloride four-step cycle double decomposition method, and introduces nitric acid and ammonia into the ammonium chloride mother liquor (i.e., the mother liquor I in the present invention) instead of directly adding the finished ammonium nitrate, so that after the reaction of nitric acid and ammonia in the mother liquor I, the concentration of ammonium nitrate is about 40%, which reduces the danger of the reaction. In addition, since the finished ammonium nitrate is not used in the production process, there is no need to separately build an ammonium nitrate production device or purchase ammonium nitrate from outside, which reduces the production cost. In addition, the present invention introduces nitric acid and ammonia into the mother liquor I, which promotes the crystallization and precipitation of ammonium chloride, enhances the separation effect of ammonium chloride and potassium nitrate, improves the product quality of potassium nitrate, and realizes efficient and continuous production of high-quality molten salt grade potassium nitrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The present invention is a process flow chart for producing molten salt-grade potassium nitrate by the ammonia process.

[0015] Figure 2 It is a process flow chart for producing industrial-grade potassium nitrate by the existing ammonium nitrate-potassium chloride four-step cyclic double decomposition method. DETAILED DESCRIPTION

[0016] In order to enable persons skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0017] Example 1 like Figure 1 As shown, the process for producing molten salt-grade potassium nitrate by the ammonia process of this embodiment comprises the following steps: S1 Initial start-up phase Potassium chloride, nitric acid and water are used as raw materials for reaction. After the reaction is complete, ammonia is introduced to obtain a synthetic liquid. During the reaction, Cl is controlled. - The concentration is 10wt.%, NH 4 + The concentration is 5wt.%, and the pH is neutral; S2 Potassium Nitrate Crystals The synthetic liquid is filtered through a filter press and then enters a crystallizer for crystallization, the temperature is lowered to precipitate potassium nitrate, the solid-liquid mixture after crystallization is separated into solid and liquid by a centrifuge, the obtained crude potassium nitrate is refined, and the obtained filtrate is mother liquor I; S3 Potassium Nitrate Refining The crude potassium nitrate is heated and dissolved at a temperature of 80°C. The dissolved solution is filtered and then enters a crystallizer, where it is cooled to 30°C for crystallization. The solid-liquid mixture is separated into solid and liquid by a centrifuge. The obtained solid potassium nitrate is dried and packaged to obtain a molten salt grade potassium nitrate product. S4 Ammonium chloride evaporation and crystallization Add nitric acid and ammonia gas in a molar ratio of 1:1 to the mother liquor I, and react under stirring. After the mother liquor I reaches neutrality, enter the evaporator for evaporation and concentration, and then crystallize. After evaporation to a solution specific gravity of 1.37, enter the crystallization process, the crystallization temperature is 70° C., the suspension is separated into solid and liquid by a centrifuge, and the obtained ammonium chloride is packaged to obtain an ammonium chloride product, and the obtained filtrate is the mother liquor II and enters step S5; S5 Stable production stage Potassium chloride, mother liquor II and the process condensate of step S4 are added into a reactor as raw materials, and reacted under stirring at a reaction temperature of 60° C. to obtain a synthetic feed liquid, and then the above steps S2-S4 are repeated.

[0018] Example 2 like Figure 1 As shown, the process for producing molten salt-grade potassium nitrate by the ammonia process of this embodiment comprises the following steps: S1 Initial start-up phase Potassium chloride, nitric acid and water are used as raw materials for reaction. After the reaction is complete, ammonia is introduced to obtain a synthetic liquid. During the reaction, Cl is controlled. - The concentration is 15wt.%, NH 4 + The concentration is 8wt.%, and the pH is neutral; S2 Potassium Nitrate Crystals The synthetic liquid is filtered through a filter press and then enters a crystallizer for crystallization, the temperature is lowered to precipitate potassium nitrate, the solid-liquid mixture after crystallization is separated into solid and liquid by a centrifuge, the obtained crude potassium nitrate is refined, and the obtained filtrate is mother liquor I; S3 Potassium Nitrate Refining The crude potassium nitrate is heated and dissolved at a temperature of 100°C. The dissolved solution is filtered and then enters a crystallizer, where it is cooled to 25°C for crystallization. The solid-liquid mixture is separated into solid and liquid by a centrifuge. The obtained solid potassium nitrate is dried and packaged to obtain a molten salt grade potassium nitrate product. S4 Ammonium chloride evaporation and crystallization Add nitric acid and ammonia gas in a molar ratio of 1:1 to the mother liquor I, and react under stirring. After the mother liquor I reaches neutrality, enter the evaporator for evaporation and concentration, and then crystallize. After evaporation to a solution specific gravity of 1.33, enter the crystallization process, the crystallization temperature is 60° C., the suspension is separated into solid and liquid by a centrifuge, and the obtained ammonium chloride is packaged to obtain an ammonium chloride product, and the obtained filtrate is the mother liquor II and enters step S5; S5 Stable production stage Potassium chloride, mother liquor II and the process condensate of step S4 are added into a reactor as raw materials, and reacted under stirring at a reaction temperature of 80° C. to obtain a synthetic feed liquid, and then the above steps S2-S4 are repeated.

[0019] Example 3 like Figure 1 As shown, the process for producing molten salt-grade potassium nitrate by the ammonia process of this embodiment comprises the following steps: S1 Initial start-up phase Potassium chloride, nitric acid and water are used as raw materials for reaction. After the reaction is complete, ammonia is introduced to obtain a synthetic liquid. During the reaction, Cl is controlled. - The concentration is 12wt.%, NH 4 + The concentration is 6wt.%, and the pH is neutral; S2 Potassium Nitrate Crystals The synthetic liquid is filtered through a filter press and then enters a crystallizer for crystallization, the temperature is lowered to precipitate potassium nitrate, the solid-liquid mixture after crystallization is separated into solid and liquid by a centrifuge, the obtained crude potassium nitrate is refined, and the obtained filtrate is mother liquor I; S3 Potassium Nitrate Refining The crude potassium nitrate is heated and dissolved at a temperature of 90°C. The dissolved solution is filtered and then enters a crystallizer, where it is cooled to 30°C for crystallization. The solid-liquid mixture is separated into solid and liquid by a centrifuge. The obtained solid potassium nitrate is dried and packaged to obtain a molten salt grade potassium nitrate product. S4 Ammonium chloride evaporation and crystallization Add nitric acid and ammonia gas in a molar ratio of 1:1 to the mother liquor I, and react under stirring. After the mother liquor I reaches neutrality, enter the evaporator for evaporation and concentration, and then crystallize. After evaporation to a solution specific gravity of 1.35, enter the crystallization process, the crystallization temperature is 65° C., the suspension is separated into solid and liquid by a centrifuge, and the obtained ammonium chloride is packaged to obtain an ammonium chloride product, and the obtained filtrate is the mother liquor II and enters step S5; S5 Stable production stage Potassium chloride, mother liquor II and the process condensate of step S4 are added into a reactor as raw materials, and reacted under stirring at a reaction temperature of 50° C. to obtain a synthetic feed liquid, and then the above steps S2-S4 are repeated.

[0020] Comparative Example 1 like Figure 2 As shown, Comparative Example 1 uses the existing ammonium nitrate-potassium chloride four-step cycle double decomposition method to produce potassium nitrate, and the process steps are as follows: S1 uses potassium chloride, ammonium nitrate and water as raw materials to react to obtain a synthetic liquid; S2 filters, crystallizes and centrifuges the synthetic liquid to obtain crude potassium nitrate and a primary mother liquor; S3 washes, dries and packages the crude potassium nitrate to obtain a finished potassium nitrate product; S4 evaporates and concentrates the primary mother liquor and adds ammonium nitrate, followed by crystallization and centrifugation to obtain ammonium chloride and a secondary mother liquor; The S5 secondary mother liquor replaces ammonium nitrate and reacts with potassium chloride in the reactor for cyclic use.

[0021] The standards for different potassium nitrate product categories are shown in Table 1: Table 1 Standards for different potassium nitrate product categories

[0022] The composition test results of the potassium nitrate products produced in Examples 1-3 and Comparative Example 1 are shown in Table 2: Table 2 Composition test results of potassium nitrate products produced in Examples 1-3 and Comparative Example 1

[0023] It can be seen from the test results in Table 2 that the potassium nitrate produced by the process of the present invention is of Class I molten salt grade, while the potassium nitrate produced by the existing process in Comparative Example 1 is of Class II ordinary industrial grade potassium nitrate, so the potassium nitrate produced by the process of the present invention has higher purity.

Claims

1. A process for producing molten salt-grade potassium nitrate by the ammonia process, characterized in that: The following steps are involved: S1 Initial start-up phase Potassium chloride, nitric acid and water are used as raw materials to react, and after the reaction is complete, ammonia gas is introduced to react to obtain a synthetic feed liquid; S2 Potassium Nitrate Crystals The synthetic feed liquid is filtered and then crystallized to precipitate potassium nitrate, and then the crude potassium nitrate is refined after solid-liquid separation, and the filtrate obtained is mother liquor I; S3 Potassium Nitrate Refining The crude potassium nitrate is heated and dissolved, the dissolved solution is filtered and then crystallized, and then the solid-liquid separation is performed, and the obtained solid potassium nitrate is dried and packaged to obtain a molten salt grade potassium nitrate product; S4 Ammonium chloride evaporation and crystallization Nitric acid and ammonia are added to the mother liquor I, and the reaction is carried out under stirring. After the mother liquor I reaches neutrality, it is evaporated and concentrated, and then crystallized, and then solid-liquid separation is performed. The obtained ammonium chloride is packaged to obtain the finished ammonium chloride product, and the obtained filtrate is the mother liquor II and enters step S5; S5 Stable production stage Potassium chloride, mother liquor II and process condensate are added into a reactor as raw materials, and reacted under stirring to obtain a synthetic feed liquid, and then the above steps S2-S4 are repeated.

2. The process for producing molten salt-grade potassium nitrate by the ammonia process as claimed in claim 1, characterized in that: In step S1, Cl is controlled during the reaction process. - Concentration is 10-15wt.%, NH4 + The concentration is 5-8wt.%, and the pH is neutral.

3. The process for producing molten salt-grade potassium nitrate by the ammonia process as claimed in claim 1, characterized in that: In step S3, the heating and dissolving temperature of the crude potassium nitrate is 80-100°C.

4. The process for producing molten salt-grade potassium nitrate by the ammonia process as claimed in claim 1, characterized in that: In step S3, the crystallization temperature is ≤30°C.

5. The process for producing molten salt-grade potassium nitrate by the ammonia process as claimed in claim 1, characterized in that: In step S4, the molar ratio of nitric acid to ammonia is 1:

1.

6. The process for producing molten salt-grade potassium nitrate by the ammonia process as claimed in claim 1, characterized in that: In step S4, the crystallization temperature is 60-70°C.

7. The process for producing molten salt-grade potassium nitrate by the ammonia process as claimed in claim 1, characterized in that: In step S4, the solution is concentrated by evaporation until the specific gravity of the solution is 1.33-1.37, and then crystallized.

8. The process for producing molten salt-grade potassium nitrate by the ammonia process as claimed in claim 1, characterized in that: In step S5, the reaction temperature is 50-80°C.

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