Process for the preparation of high purity ammonium chloride

Abstract

The application discloses a preparation method of high-purity ammonium chloride and relates to the technical field of ammonium chloride production. The preparation method of the high-purity ammonium chloride adopts a multi-stage process of chemical adsorption impurity removal, evaporation concentration, cooling crystallization and secondary recrystallization to cooperatively purify the ammonium chloride, removes different types of impurities step by step, and purifies the agricultural ammonium chloride to AR grade. In addition, the process adopted by the application has the advantages of low cost, low requirement for equipment, high yield, high purity, high yield and low cost.

Description

Technical Field

[0001] This invention relates to the field of ammonium chloride production technology, and in particular to a method for preparing high-purity ammonium chloride. Background Technology

[0002] Ammonium chloride is an important inorganic chemical product widely used in agriculture, batteries, pharmaceuticals, and electronic chemicals. With the development of high-end manufacturing, the market demand for high-purity ammonium chloride (purity ≥99.5%, or even electronic grade ≥99.9%) continues to grow, and the requirements for impurity content (especially sodium, potassium, sulfate, and heavy metals) are becoming increasingly stringent.

[0003] Currently, domestic ammonium chloride mainly originates from the byproducts of soda ash production via the combined alkali process. Due to impurities in the raw material sodium chloride, the sulfate content in the product is typically 0.04%–0.06%, and the sodium salt content is also relatively high, making it difficult to meet the demands of high-end applications. Furthermore, some ammonium chloride is derived from byproducts generated during the preparation of potassium nitrate, meta-aramid fibers, etc., resulting in even more complex impurity compositions.

[0004] The existing technologies for preparing high-purity ammonium chloride mainly include the following: (I) Recrystallization Method. The process flow of this method is as follows: industrial ammonium chloride is dissolved, cooled, and crystallized; the product is obtained by centrifugation and drying. This method is simple, but due to the presence of ammonium ions (NH4+),... + Radius and potassium ion (K) + Sodium ions (Na) + Since their radii are close, they easily form double salts or eutectics. Conventional recrystallization is difficult to effectively separate alkali metal impurities, and their ability to remove anionic impurities such as sulfate is also limited.

[0005] (II) Combined Chemical Precipitation-Recrystallization Method. The process flow of this method is as follows: barium chloride (BaCl2) is added during recrystallization, causing sulfate ions to be removed as barium sulfate precipitate. This method has a certain removal effect on sulfate ions, but it introduces new barium ion impurities, requiring additional treatment for removal; barium chloride is a toxic chemical, posing environmental pressures and safety risks; furthermore, this method is essentially ineffective in removing sodium and potassium ions.

[0006] (III) Washing Method. The process flow of this method is as follows: a multi-stage countercurrent washing process is used to wash ammonium chloride with ammonia mother liquor and hot deionized water. This method is relatively simple to operate, but its effect on removing eutectic alkali metal ions is limited, and the product can usually only meet the first-class standard.

[0007] (iv) Sublimation method. This method utilizes the principle that ammonium chloride decomposes into ammonia and hydrogen chloride upon heating, and then recombines them in a low-temperature region for purification. Theoretically, it can yield products with extremely high purity. However, this method consumes a great deal of energy, causes severe equipment corrosion, and has a low product yield, making it difficult to achieve industrial-scale production.

[0008] (v) Membrane separation method. This method utilizes the differentiated interfacial interactions between ammonium and sodium ions using specialized membranes to achieve separation, yielding an ammonium chloride solution with a purity of up to 99.5%. While this method has low energy consumption, its ability to remove impurities such as sulfate and heavy metals is limited, and it suffers from problems such as membrane fouling, membrane flux decline, and insufficient stability during long-term industrial operation.

[0009] In summary, existing technologies generally have the following shortcomings: First, the removal of impurities is incomplete, making it difficult to effectively remove alkali metal ions and anionic impurities such as sulfate ions simultaneously; second, energy consumption and costs are relatively high; third, it is difficult to balance purity and yield; fourth, some processes involve the use of toxic reagents, resulting in significant environmental pressure; and fifth, the process flow is complex, leading to poor industrial adaptability.

[0010] Therefore, developing a method that is simple, has high impurity removal efficiency, moderate energy consumption, is environmentally friendly, and can stably produce high-purity ammonium chloride has significant industrial application value. Summary of the Invention

[0011] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing high-purity ammonium chloride, which aims to solve the technical problem that it is difficult to balance the purity, yield and cost of ammonium chloride preparation in the prior art.

[0012] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing high-purity ammonium chloride, comprising the following steps: S1. Heating and dissolving: Add agricultural ammonium chloride to deionized water or recycled mother liquor, heat and stir until completely dissolved to obtain a hot ammonium chloride solution; S2. Impurity Removal and Adsorption: An impurity removal agent is added to the above-mentioned hot ammonium chloride solution to form a precipitate or flocculent containing impurities, thereby obtaining a mixed solution; the impurity removal agent includes one or more of ammonium carbonate, ammonia, ammonium sulfide, and ammonium oxalate; the amount of the impurity removal agent added is 0.5% to 5.0% of the mass of agricultural ammonium chloride, the reaction temperature is 60℃ to 95℃, and the stirring reaction time is 10 to 60 minutes; S3. Filtration and separation: The mixture obtained in S2 is filtered to separate and remove precipitates or flocculants containing impurities, and purified ammonium chloride filtrate is obtained. S4. Evaporation and concentration: The purified ammonium chloride filtrate obtained in S3 is evaporated and concentrated to remove some water, resulting in ammonium chloride concentrate. S5. Cooling and crystallization: Cool the ammonium chloride concentrate obtained in S4 to allow ammonium chloride to crystallize and precipitate, resulting in an ammonium chloride slurry; S6. Centrifugal separation: The ammonium chloride crystal slurry obtained in S5 is centrifuged to obtain crude ammonium chloride and crystallization mother liquor; S7. Secondary recrystallization: Dissolve the crude ammonium chloride obtained in S6 by heating with deionized water or high-purity water, cool and crystallize again, and centrifuge to obtain the refined ammonium chloride product. S8. Drying: Drying process to obtain AR grade high-purity ammonium chloride product.

[0013] The method for preparing high-purity ammonium chloride, wherein the impurity removal agent is a combination of ammonium carbonate and ammonia.

[0014] In the method for preparing high-purity ammonium chloride, in step S1, the heating temperature is 60℃~100℃.

[0015] In the method for preparing high-purity ammonium chloride, in step S1, the heating temperature is 80℃~95℃.

[0016] In the method for preparing high-purity ammonium chloride, in step S1, the mass ratio of agricultural ammonium chloride to deionized water or recycled mother liquor is 1:(1.5-3.0).

[0017] In the method for preparing high-purity ammonium chloride, in step S2, the impurity removal agent is added in the form of an aqueous solution, wherein the mass fraction of the solute in the aqueous solution is 5% to 20%.

[0018] In the method for preparing high-purity ammonium chloride, in step S4, the evaporation and concentration are carried out under normal pressure or reduced pressure, evaporating until the solution density is 1.10–1.35 g / cm³. 3 .

[0019] In the method for preparing high-purity ammonium chloride, in step S5, the cooling endpoint temperature for crystallization is 10℃~40℃, the cooling rate is 1℃ / hour~10℃ / hour, and the crystallization time is 1~8 hours.

[0020] In the method for preparing high-purity ammonium chloride, in step S7, the dissolution temperature for secondary recrystallization is 60℃~95℃, the mass ratio of crude ammonium chloride to deionized water or high-purity water is 1:(1.2~2.5), and the cooling crystallization temperature is 5℃~20℃.

[0021] In the method for preparing high-purity ammonium chloride, in step S8, the drying temperature is 80℃~120℃ and the drying time is 2~8 hours.

[0022] Beneficial Effects: This invention provides a method for preparing high-purity ammonium chloride. The method employs a multi-stage synergistic purification process involving "chemical adsorption for impurity removal—evaporation and concentration—cooling and crystallization—secondary recrystallization," removing different types of impurities step by step. Specifically, the impurity remover selectively removes sulfate and heavy metal ions; the initial crystallization and centrifugation remove most soluble alkali metal salts; and the secondary recrystallization further removes residual Na+ co-crystallized with ammonium chloride. + K + Plasma ionization. Through coordinated and progressively purified steps, AR-grade high-purity ammonium chloride products can be stably produced, with a main content ≥99.5% (dry basis), sulfate content ≤0.002%, sodium content ≤0.005%, potassium content ≤0.005%, heavy metal content ≤0.0005%, and ignition residue ≤0.01%. All indicators meet the requirements for analytical grade reagents. Compared to the limitations of existing recrystallization methods, which struggle to remove alkali metal ions, and chemical precipitation methods, which struggle to remove multiple impurities simultaneously, this invention offers significant advantages in impurity removal.

[0023] Meanwhile, the process is simple, the operating conditions are mild, it is suitable for industrial production, and the raw materials are widely available and inexpensive, solving the technical problem of balancing purity, yield and cost. Detailed Implementation

[0024] This invention provides a method for preparing high-purity ammonium chloride. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following embodiments are provided to further illustrate the invention in detail. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0025] This invention provides a method for preparing high-purity ammonium chloride, comprising the following steps: S1. Heating and dissolving: Add agricultural ammonium chloride to deionized water or recycled mother liquor, heat and stir until completely dissolved to obtain a hot ammonium chloride solution; S2. Impurity Removal and Adsorption: An impurity remover is added to the above-mentioned hot ammonium chloride solution to form a precipitate or flocculant containing impurities, thereby obtaining a mixed solution. The impurity remover includes one or more of diatomaceous earth, ammonium carbonate, silica gel, ammonia, ammonium sulfide, and ammonium oxalate. The amount of the impurity remover added is 0.5% to 5.0% of the mass of agricultural ammonium chloride, the reaction temperature is 60℃ to 95℃, and the stirring reaction time is 10 to 60 minutes. The selected impurity remover can form insoluble precipitates or complexes with impurities such as sulfate and heavy metal ions, while not introducing new metal ion impurities into the system, thus avoiding the drawbacks of introducing barium ions in the traditional barium chloride impurity removal method. S3. Filtration and separation: The mixture obtained in S2 is filtered to separate and remove precipitates or flocculants containing impurities, and purified ammonium chloride filtrate is obtained. S4. Evaporation and concentration: The purified ammonium chloride filtrate obtained in S3 is evaporated and concentrated to remove some water, resulting in ammonium chloride concentrate. S5. Cooling and crystallization: Cool the ammonium chloride concentrate obtained in S4 to allow ammonium chloride to crystallize and precipitate, resulting in an ammonium chloride slurry; S6. Centrifugal separation: The ammonium chloride slurry obtained in S5 is centrifuged to obtain crude ammonium chloride and crystallization mother liquor; the crystallization mother liquor can be partially or completely recycled back to the heating and dissolving process in S1, so as to realize the effective utilization of the mother liquor, improve the overall yield, and reduce waste liquid discharge; S7. Secondary recrystallization: Dissolve the crude ammonium chloride obtained in S6 by heating with deionized water or high-purity water, cool and crystallize again, and centrifuge to obtain the refined ammonium chloride product. S8. Drying: Drying process to obtain AR grade high-purity ammonium chloride product.

[0026] The method for preparing high-purity ammonium chloride in this invention employs a combined process route of "chemical adsorption for impurity removal, evaporation and concentration, cooling and crystallization, and secondary recrystallization." First, ammonium chloride is fully dissolved by heating, and the hot solution is used to reduce the solution viscosity and improve filtration performance. Then, impurity removers free of metal ions, such as diatomaceous earth, ammonium carbonate, silica gel, ammonia, ammonium sulfide, and ammonium oxalate, are selected to remove sulfate and heavy metal ions through precipitation reactions, while avoiding the introduction of new metal impurities. Next, the filtrate is treated by evaporation and concentration, which not only provides supersaturation for subsequent crystallization but also removes free ammonia and some volatile impurities during the evaporation process. The first crystallization is used to precipitate a large amount of ammonium chloride bulk, while most soluble alkali metal impurities are enriched in the mother liquor and removed by centrifugation. The second recrystallization further removes residual alkali metal ions (Na+) that co-crystallize with ammonium chloride. + K + This ensures that the product purity reaches AR grade. Each step works synergistically and is indispensable, achieving efficient conversion of agricultural ammonium chloride into high-purity AR grade products.

[0027] This invention utilizes widely available and inexpensive raw materials, resulting in significant economic benefits. Agricultural ammonium chloride (market price approximately 800 RMB / ton) is used as the starting material. This raw material is a major byproduct of soda ash production via the combined alkali process, with ample market supply and stable prices. After purification using the method of this invention, AR-grade high-purity ammonium chloride with a market value of approximately 8000 RMB / ton can be obtained, increasing the product's added value by about 10 times. This significantly improves the resource utilization value of agricultural ammonium chloride, bringing substantial economic benefits. Compared to existing technologies that use industrial-grade or chemically pure ammonium chloride as raw materials, this invention has clear advantages in raw material costs and profit margins.

[0028] Furthermore, the technical solution of this invention avoids the introduction of new metal ion impurities, ensuring high product safety. Existing chemical precipitation methods often use barium chloride as a purifying agent to remove sulfate ions, but this method inevitably introduces barium ions, a new toxic impurity, requiring additional processing steps and increasing process complexity and product safety risks. In contrast, this invention uses diatomaceous earth, ammonium carbonate, silica gel, ammonia, ammonium sulfide, and ammonium oxalate as purifying agents, none of which contain metal cations. During the purifying process, only ammonium ions and corresponding acid radicals are introduced into the system. The ammonium ions are ammonium chloride's own cations, and excess ammonia can completely evaporate and escape during subsequent evaporation, concentration, and drying processes, leaving no residue in the product and ensuring product purity and safety.

[0029] In terms of process flow, the operating conditions are mild and suitable for industrial production. The processes of heating and dissolving, impurity removal and filtration, evaporation and concentration, cooling and crystallization, centrifugation, secondary recrystallization, and drying are all routine and mature operations in the field of inorganic salt purification. They do not require harsh conditions such as high pressure or high temperature (not exceeding 120℃), resulting in lower equipment investment, easier control of operating parameters, and lower operator training costs. Compared to the high-temperature equipment and special corrosion-resistant materials required for sublimation methods, and the special membrane modules and precision control systems required for membrane separation methods, this process is easier to implement and has lower equipment investment costs.

[0030] In terms of energy consumption, this invention eliminates the need for the high-temperature (above 300°C) heating conditions required by sublimation and the repeated heating-cooling cycles of multi-stage recrystallization. It requires only two crystallization operations, and the evaporation and concentration are carried out under normal or low pressure conditions. Therefore, the overall thermal energy consumption is significantly lower than that of sublimation and multi-stage recrystallization. Furthermore, the mother liquor from crystallization can be partially or completely recycled back to the dissolution process, which not only improves the overall yield of ammonium chloride (total yield can reach over 85%) but also reduces the consumption of raw materials and deionized water, effectively controlling overall production costs.

[0031] In terms of environmental protection, the impurity removal agents used in this invention (diatomaceous earth, ammonium carbonate, silica gel, ammonia, ammonium sulfide, ammonium oxalate, etc.) are all conventional chemical raw materials. The impurity precipitates generated by the reaction (such as sulfates, carbonates, oxalates, etc.) are not highly toxic and are easy to filter, separate, and dispose of. In addition, the evaporation condensate and crystallization mother liquor in this invention can be recycled and reused, and the waste liquid discharge of the entire process is extremely small, which meets the environmental protection requirements of green and clean production.

[0032] Regarding product yield, this invention achieves an overall ammonium chloride yield of 85%–92% by controlling crystallization conditions, recycling mother liquor, and optimizing secondary recrystallization conditions, while ensuring product purity reaches AR level. Combined with extremely low raw material costs (approximately 800 RMB / ton), low impurity removal agent usage (only 0.5%–5.0% of raw material mass), moderate energy consumption, and reasonable equipment investment, the overall production cost per unit of product in this invention is significantly lower than existing technologies, giving it greater market competitiveness.

[0033] Preferably, the impurity removal agent is a combination of ammonium carbonate and ammonia. Ammonium carbonate can form carbonate precipitates with cations such as calcium, magnesium, and heavy metals, and simultaneously removes sulfate ions through co-precipitation. Ammonia can adjust the pH of the solution, promote the formation and flocculation of impurities, and since ammonia itself is a volatile substance, any excess can be removed during subsequent evaporation, concentration, and drying processes, leaving no residue in the product.

[0034] Preferably, in step S1, the heating temperature is 60℃~100℃. Appropriate heating can increase the solubility of ammonium chloride, accelerate the dissolution rate, ensure the complete dissolution of agricultural ammonium chloride, and reduce the residue of insoluble impurities. However, the temperature should not be too high, otherwise it will not only increase energy consumption and cause excessive water evaporation, but may also lead to the decomposition of ammonium chloride.

[0035] Preferably, in step S1, the heating temperature is 80℃~95℃.

[0036] Preferably, in step S1, the mass ratio of agricultural ammonium chloride to deionized water or recycled mother liquor is 1:(1.5-3.0). If there is too much solvent, the energy consumption for subsequent evaporation and concentration will increase, and the production efficiency will decrease; if there is too little solvent, the agricultural ammonium chloride will not dissolve sufficiently, affecting the yield.

[0037] Preferably, in step S2, the impurity remover is added in the form of an aqueous solution, wherein the mass fraction of the solute in the aqueous solution is 5% to 20%. Adding the impurity remover in the form of an aqueous solution ensures that the impurity remover is uniformly dispersed in the solution and that the reaction is complete. If the concentration of the impurity remover is too high when added, it can easily cause excessive local alkalinity, resulting in colloidal impurities that are difficult to filter.

[0038] Preferably, in step S4, the evaporation and concentration are performed under normal pressure or reduced pressure, evaporating until the solution density is 1.10–1.35 g / cm³. 3 During the evaporation process, excess ammonia and some volatile impurities can escape with the water vapor, further purifying the system.

[0039] Preferably, in step S5, the final cooling temperature for crystallization is 10°C to 40°C, the cooling rate is 1°C / hour to 10°C / hour, and the crystallization time is 1 to 8 hours. Slow cooling reduces the formation of fine microcrystals from rapid cooling, promotes the formation of large, well-crystallized ammonium chloride crystals, and reduces impurity encapsulation and adsorption.

[0040] Preferably, in step S7, the dissolution temperature for secondary recrystallization is 60℃~95℃, the mass ratio of crude ammonium chloride to deionized water or high-purity water is 1:(1.2~2.5), and the cooling crystallization temperature is 5℃~20℃. Suitable temperature and feed-to-liquid ratio allow for complete redissolution of the crude ammonium chloride and ensure that impurities remain in the mother liquor during secondary recrystallization, achieving deep purification.

[0041] Preferably, in step S8, the drying temperature is 80℃~120℃ and the drying time is 2~8 hours.

[0042] The present invention will be further illustrated by the following examples and comparative examples.

[0043] Example 1 A method for preparing high-purity ammonium chloride, comprising the following steps: S1. Heating and dissolving: Add agricultural ammonium chloride to deionized water at a mass ratio of 1:2, heat and stir until completely dissolved at a temperature of 85°C to obtain a hot ammonium chloride solution. S2. Impurity Removal and Adsorption: An impurity remover is added to the above-mentioned hot ammonium chloride solution to form a precipitate or flocculent containing impurities, thereby obtaining a mixed solution; the impurity remover is a combination of ammonium carbonate and ammonia water, with a mass ratio of ammonium carbonate to ammonia water of 2:1; the amount of the impurity remover added is 3.0% of the mass of agricultural ammonium chloride; before adding the impurity remover, it is diluted with deionized water to make the mass fraction of solute in the obtained aqueous solution 15%; after adding the impurity remover, the reaction temperature is 75℃, and the stirring reaction time is 50 minutes; S3. Filtration and separation: The mixture obtained in S2 is filtered to separate and remove precipitates or flocculants containing impurities, and purified ammonium chloride filtrate is obtained. S4. Evaporation and Concentration: The purified ammonium chloride filtrate obtained in S3 is evaporated and concentrated under normal pressure to remove some water, yielding a concentrated ammonium chloride solution with a density of 1.35 g / cm³. 3 ; S5. Cooling and crystallization: Cool the ammonium chloride concentrate obtained in S4 at a cooling rate of 5℃ / hour, with the final cooling temperature being 20℃, so that ammonium chloride crystals precipitate out to obtain an ammonium chloride slurry. S6. Centrifugal separation: The ammonium chloride crystal slurry obtained in S5 is centrifuged to obtain crude ammonium chloride and crystallization mother liquor; S7. Secondary recrystallization: The crude ammonium chloride obtained in S6 is dissolved in deionized water by heating. The mass ratio of crude ammonium chloride to deionized water is 1:1.5, and the dissolution temperature is 70℃. The product is then cooled and crystallized again at a cooling rate of 5℃ / hour and a final cooling temperature of 20℃. The product is then separated by centrifugation to obtain the refined ammonium chloride product. S8. Drying: Drying treatment, drying temperature is 90℃, drying time is 6 hours, to obtain AR grade high-purity ammonium chloride product.

[0044] Example 2 A method for preparing high-purity ammonium chloride, comprising the following steps: S1. Heating and dissolving: Add agricultural ammonium chloride to deionized water at a mass ratio of 1:2, heat and stir until completely dissolved at a temperature of 85°C to obtain a hot ammonium chloride solution. S2. Impurity Removal and Adsorption: An impurity remover is added to the above-mentioned hot ammonium chloride solution to form a precipitate or flocculent containing impurities, thereby obtaining a mixed solution; the impurity remover is a combination of ammonium carbonate and ammonia water, with a mass ratio of ammonium carbonate to ammonia water of 2:1; the amount of the impurity remover added is 3.0% of the mass of agricultural ammonium chloride; before adding the impurity remover, it is diluted with deionized water to make the mass fraction of solute in the obtained aqueous solution 15%; after adding the impurity remover, the reaction temperature is 75℃, and the stirring reaction time is 50 minutes; S3. Filtration and separation: The mixture obtained in S2 is filtered to separate and remove precipitates or flocculants containing impurities, and purified ammonium chloride filtrate is obtained. S4. Evaporation and Concentration: The purified ammonium chloride filtrate obtained in S3 is evaporated and concentrated under normal pressure to remove some water, yielding a concentrated ammonium chloride solution with a density of 1.21 g / cm³. 3 ; S5. Cooling and crystallization: Cool the ammonium chloride concentrate obtained in S4 at a cooling rate of 5℃ / hour, with the final cooling temperature being 20℃, so that ammonium chloride crystals precipitate out to obtain an ammonium chloride slurry. S6. Centrifugal separation: The ammonium chloride crystal slurry obtained in S5 is centrifuged to obtain crude ammonium chloride and crystallization mother liquor; S7. Secondary recrystallization: The crude ammonium chloride obtained in S6 is dissolved in deionized water by heating. The mass ratio of crude ammonium chloride to deionized water is 1:1.5, and the dissolution temperature is 70℃. The product is then cooled and crystallized again. The cooling rate is 5℃ / hour, and the final cooling temperature is 5℃. The product is then separated by centrifugation to obtain the refined ammonium chloride product. S8. Drying: Drying treatment, drying temperature is 90℃, drying time is 6 hours, to obtain AR grade high-purity ammonium chloride product.

[0045] Example 3 A method for preparing high-purity ammonium chloride, comprising the following steps: S1. Heating and dissolving: Add agricultural ammonium chloride to deionized water at a mass ratio of 1:1.5, heat and stir until completely dissolved at a temperature of 90°C to obtain a hot ammonium chloride solution; S2. Impurity Removal and Adsorption: An impurity remover is added to the above-mentioned hot ammonium chloride solution to form a precipitate or flocculent containing impurities, resulting in a mixed solution; the impurity remover is a combination of ammonium carbonate and diatomaceous earth, with a mass ratio of ammonium carbonate to diatomaceous earth of 1:2; the amount of the impurity remover added is 3.0% of the mass of agricultural ammonium chloride; before adding the impurity remover, the ammonium carbonate is diluted with deionized water to obtain an aqueous solution with a solute mass fraction of 15%; after adding the ammonium carbonate, the diatomaceous earth is added; after adding the impurity remover, the reaction temperature is 75℃, and the stirring reaction time is 50 minutes; S3. Filtration and separation: The mixture obtained in S2 is filtered to separate and remove the precipitate or flocculent containing impurities, and purified ammonium chloride filtrate is obtained. Then, AR hydrochloric acid is added to acidify the pH to 1. S4. Evaporation and Concentration: The purified ammonium chloride filtrate obtained in S3 is evaporated and concentrated under normal pressure to remove some water, yielding a concentrated ammonium chloride solution with a density of 1.21 g / cm³. 3 ; S5. Cooling and crystallization: Cool the ammonium chloride concentrate obtained in S4 at a cooling rate of 5℃ / hour, with the final cooling temperature being 20℃, so that ammonium chloride crystals precipitate out to obtain an ammonium chloride slurry. S6. Centrifugal separation: The ammonium chloride crystal slurry obtained in S5 is centrifuged to obtain crude ammonium chloride and crystallization mother liquor; S7. Secondary recrystallization: The crude ammonium chloride obtained in S6 is dissolved in deionized water by heating. The mass ratio of crude ammonium chloride to deionized water is 1:1.5, and the dissolution temperature is 70℃. The product is then cooled and crystallized again at a cooling rate of 5℃ / hour and a final cooling temperature of 20℃. The product is then separated by centrifugation to obtain the refined ammonium chloride product. S8. Drying: Drying treatment, drying temperature is 90℃, drying time is 6 hours, to obtain AR grade high-purity ammonium chloride product.

[0046] Example 4 A method for preparing high-purity ammonium chloride, comprising the following steps: S1. Heating and dissolving: Add agricultural ammonium chloride to deionized water at a mass ratio of 1:1.5, heat and stir until completely dissolved at a temperature of 90°C to obtain a hot ammonium chloride solution; S2. Impurity Removal and Adsorption: An impurity remover is added to the above-mentioned hot ammonium chloride solution to form a precipitate or flocculent containing impurities, thereby obtaining a mixed solution; the impurity remover is a combination of silica gel and ammonia water, with a mass ratio of silica gel to ammonia water of 1:2; the amount of the impurity remover added is 3.0% of the mass of agricultural ammonium chloride; before adding the impurity remover, the ammonia water is first diluted with deionized water to make the mass fraction of solute in the resulting aqueous solution 15%; after adding the impurity remover, the reaction temperature is 75℃, and the stirring reaction time is 50 minutes; S3. Filtration and separation: The mixture obtained in S2 is filtered to separate and remove the precipitate or flocculent containing impurities, and purified ammonium chloride filtrate is obtained. Then, AR hydrochloric acid is added to acidify the pH to 1. S4. Evaporation and Concentration: The purified ammonium chloride filtrate obtained in S3 is evaporated and concentrated under normal pressure to remove some water, yielding a concentrated ammonium chloride solution with a density of 1.21 g / cm³. 3 ; S5. Cooling and crystallization: Cool the ammonium chloride concentrate obtained in S4 at a cooling rate of 5℃ / hour, with the final cooling temperature being 20℃, so that ammonium chloride crystals precipitate out to obtain an ammonium chloride slurry. S6. Centrifugal separation: The ammonium chloride crystal slurry obtained in S5 is centrifuged to obtain crude ammonium chloride and crystallization mother liquor; S7. Secondary recrystallization: The crude ammonium chloride obtained in S6 is dissolved in deionized water by heating. The mass ratio of crude ammonium chloride to deionized water is 1:1.5, and the dissolution temperature is 70℃. The product is then cooled and crystallized again at a cooling rate of 5℃ / hour and a final cooling temperature of 20℃. The product is then separated by centrifugation to obtain the refined ammonium chloride product. S8. Drying: Drying treatment, drying temperature is 90℃, drying time is 6 hours, to obtain AR grade high-purity ammonium chloride product.

[0047] Example 5 A method for preparing high-purity ammonium chloride, comprising the following steps: S1. Heating and dissolving: Add agricultural ammonium chloride to deionized water at a mass ratio of 1:2, heat and stir until completely dissolved at a temperature of 85°C to obtain a hot ammonium chloride solution. S2. Impurity Removal and Adsorption: An impurity remover is added to the above-mentioned hot ammonium chloride solution to form a precipitate or flocculent containing impurities, thereby obtaining a mixed solution; the impurity remover is a combination of ammonium carbonate and ammonia water, with a mass ratio of ammonium carbonate to ammonia water of 1:2; the amount of the impurity remover added is 3.0% of the mass of agricultural ammonium chloride; before adding the impurity remover, it is diluted with deionized water to make the mass fraction of solute in the obtained aqueous solution 15%; after adding the impurity remover, the reaction temperature is 75℃, and the stirring reaction time is 50 minutes; S3. Filtration and separation: The mixture obtained in S2 is filtered to separate and remove precipitates or flocculants containing impurities, and purified ammonium chloride filtrate is obtained. S4. Evaporation and Concentration: The purified ammonium chloride filtrate obtained in S3 is evaporated and concentrated under normal pressure to remove some water, yielding a concentrated ammonium chloride solution with a density of 1.21 g / cm³. 3 ; S5. Cooling and crystallization: Cool the ammonium chloride concentrate obtained in S4 at a cooling rate of 5℃ / hour, with the final cooling temperature being 20℃, so that ammonium chloride crystals precipitate out to obtain an ammonium chloride slurry. S6. Centrifugal separation: The ammonium chloride crystal slurry obtained in S5 is centrifuged to obtain crude ammonium chloride and crystallization mother liquor; S7. Secondary recrystallization: The crude ammonium chloride obtained in S6 is dissolved in deionized water by heating. The mass ratio of crude ammonium chloride to deionized water is 1:1.5, and the dissolution temperature is 70℃. The product is then cooled and crystallized again at a cooling rate of 5℃ / hour and a final cooling temperature of 20℃. The product is then separated by centrifugation to obtain the refined ammonium chloride product. S8. Drying: Drying treatment, drying temperature is 90℃, drying time is 6 hours, to obtain AR grade high-purity ammonium chloride product.

[0048] Comparative Example 1 A method for preparing high-purity ammonium chloride, comprising the following steps: S1. Heating and dissolving: Add agricultural ammonium chloride to deionized water at a mass ratio of 1:2, heat and stir until completely dissolved at a temperature of 85°C to obtain a hot ammonium chloride solution. S2. Impurity Removal and Adsorption: An impurity remover is added to the above-mentioned hot ammonium chloride solution to form a precipitate or flocculent containing impurities, thereby obtaining a mixed solution; the impurity remover is a combination of ammonium carbonate and ammonia water, with a mass ratio of ammonium carbonate to ammonia water of 2:1; the amount of the impurity remover added is 3.0% of the mass of agricultural ammonium chloride; before adding the impurity remover, it is diluted with deionized water to make the mass fraction of solute in the obtained aqueous solution 15%; after adding the impurity remover, the reaction temperature is 75℃, and the stirring reaction time is 50 minutes; S3. Filtration and separation: The mixture obtained in S2 is filtered to separate and remove precipitates or flocculants containing impurities, and purified ammonium chloride filtrate is obtained. S4. Evaporation and Concentration: The purified ammonium chloride filtrate obtained in S3 is evaporated and concentrated under normal pressure to remove some water, yielding a concentrated ammonium chloride solution with a density of 1.21 g / cm³. 3 ; S5. Cooling and crystallization: Cool the ammonium chloride concentrate obtained in S4 at a cooling rate of 5℃ / hour, with the final cooling temperature being 20℃, so that ammonium chloride crystals precipitate out to obtain an ammonium chloride slurry. S6. Centrifugal separation: The ammonium chloride crystal slurry obtained in S5 is centrifuged to obtain crude ammonium chloride and crystallization mother liquor; S7. Secondary recrystallization: The crude ammonium chloride obtained in S6 is dissolved in deionized water by heating. The mass ratio of crude ammonium chloride to deionized water is 1:1.5, and the dissolution temperature is 70℃. The product is then cooled and crystallized again at a cooling rate of 5℃ / hour and a final cooling temperature of 20℃. The product is then separated by centrifugation to obtain the refined ammonium chloride product. S8. Drying: Drying treatment, drying temperature is 90℃, drying time is 6 hours, to obtain AR grade high-purity ammonium chloride product.

[0049] Comparative Example 2 A method for preparing high-purity ammonium chloride, comprising the following steps: S1. Heating and dissolving: Add agricultural ammonium chloride to deionized water at a mass ratio of 1:1.5, heat and stir until completely dissolved at a temperature of 90°C to obtain a hot ammonium chloride solution; S2. Impurity Removal and Adsorption: An impurity remover is added to the above-mentioned hot ammonium chloride solution to form a precipitate or flocculent containing impurities, resulting in a mixed solution; the impurity remover is a combination of ammonium sulfide and ammonium oxalate, with a mass ratio of ammonium sulfide to ammonium oxalate of 1:2; the amount of the impurity remover added is 3.0% of the mass of agricultural ammonium chloride; before adding the impurity remover, it is diluted with deionized water to make the mass fraction of solute in the resulting aqueous solution 15%; after adding the impurity remover, the reaction temperature is 75℃, and the stirring reaction time is 50 minutes; S3. Filtration and separation: The mixture obtained in S2 is filtered to separate and remove the precipitate or flocculent containing impurities, and purified ammonium chloride filtrate is obtained. Then, AR hydrochloric acid is added to acidify the pH to 1. S4. Evaporation and Concentration: The purified ammonium chloride filtrate obtained in S3 is evaporated and concentrated under normal pressure to remove some water, yielding a concentrated ammonium chloride solution with a density of 1.21 g / cm³. 3 ; S5. Cooling and crystallization: Cool the ammonium chloride concentrate obtained in S4 at a cooling rate of 5℃ / hour, with the final cooling temperature being 20℃, so that ammonium chloride crystals precipitate out to obtain an ammonium chloride slurry. S6. Centrifugal separation: The ammonium chloride crystal slurry obtained in S5 is centrifuged to obtain crude ammonium chloride and crystallization mother liquor; S7. Secondary recrystallization: The crude ammonium chloride obtained in S6 is dissolved in deionized water by heating. The mass ratio of crude ammonium chloride to deionized water is 1:1.5, and the dissolution temperature is 70℃. The product is then cooled and crystallized again at a cooling rate of 5℃ / hour and a final cooling temperature of 20℃. The product is then separated by centrifugation to obtain the refined ammonium chloride product. S8. Drying: Drying treatment, drying temperature is 90℃, drying time is 6 hours, to obtain AR grade high-purity ammonium chloride product.

[0050] Comparative Example 3 A method for preparing high-purity ammonium chloride, comprising the following steps: S1. Heating and dissolving: Add agricultural ammonium chloride to deionized water at a mass ratio of 1:2, heat and stir until completely dissolved at a temperature of 85°C to obtain a hot ammonium chloride solution. S2. Impurity Removal and Adsorption: An impurity remover is added to the above-mentioned hot ammonium chloride solution to form a precipitate or flocculent containing impurities, thereby obtaining a mixed solution; the impurity remover is a combination of ammonium carbonate and ammonia water, with a mass ratio of ammonium carbonate to ammonia water of 2:1; the amount of the impurity remover added is 3.0% of the mass of agricultural ammonium chloride; before adding the impurity remover, it is diluted with deionized water to make the mass fraction of solute in the obtained aqueous solution 15%; after adding the impurity remover, the reaction temperature is 75℃, and the stirring reaction time is 50 minutes; S3. Filtration and separation: The mixture obtained in S2 is filtered to separate and remove precipitates or flocculants containing impurities, and purified ammonium chloride filtrate is obtained. S4. Evaporation and Concentration: The purified ammonium chloride filtrate obtained in S3 is evaporated and concentrated under normal pressure to remove some water, yielding a concentrated ammonium chloride solution with a density of 1.21 g / cm³. 3 ; S5. Cooling and crystallization: Cool the ammonium chloride concentrate obtained in S4 at a cooling rate of 5℃ / hour, with the final cooling temperature being 20℃, so that ammonium chloride crystals precipitate out to obtain an ammonium chloride slurry. S6. Centrifugal separation: The ammonium chloride crystal slurry obtained in S5 is centrifuged to obtain crude ammonium chloride and crystallization mother liquor; S7. Secondary recrystallization: The crude ammonium chloride obtained in S6 is dissolved in deionized water by heating. The mass ratio of crude ammonium chloride to deionized water is 1:1.5, and the dissolution temperature is 70℃. The product is then cooled and crystallized again at a cooling rate of 10℃ / hour and a final cooling temperature of 20℃. The product is then separated by centrifugation to obtain the refined ammonium chloride product. S8. Drying: Drying treatment, drying temperature is 90℃, drying time is 6 hours, to obtain AR grade high-purity ammonium chloride product.

[0051] The purity of the high-purity ammonium chloride prepared in the above examples and comparative examples was tested, and the results are shown in Table 1.

[0052] Table 1

[0053] As can be seen from the results in Table 1, the purity of the ammonium chloride prepared in Examples 1-5 all met the requirements.

[0054] The main difference between Example 2 and Example 1 is that the mass ratio of ammonium carbonate to ammonia is 1:2; and in S4, the density of the concentrated solution is adjusted to 1.21 g / cm³. 3 The final ammonium chloride content was the same as in Example 1.

[0055] The main difference between Examples 3 and 4 and Example 1 is that different impurity removal agents are used. Judging from the final results, silica gel and ammonia are the most effective impurity removal agents.

[0056] The main difference between Example 5 and Example 1 is that in S4, the density of the concentrate is adjusted to 1.21 g / cm³. 3 Meanwhile, the final cooling temperature in S7 was 5°C, and the final ammonium chloride content was the same as in Example 1.

[0057] The main difference between Comparative Example 1 and Example 1 is that, in S4, the density of the concentrate was adjusted to 1.21 g / cm³. 3 The results show that under these process conditions, changes in the density of the concentrate negatively impact the purity of the product.

[0058] The main difference between Comparative Example 2 and Example 1 is that the impurity remover used was a combination of ammonium oxalate and ammonium sulfide. As a result, the ammonium chloride content did not meet the standard, and the sulfate content also did not meet the standard.

[0059] Compared with Comparative Example 1, the main difference of Comparative Example 3 is that in S7, the cooling rate was 10℃ / hour. The results show that the change in the cooling rate in S7 did not affect the change in ammonium chloride content.

[0060] It is understood that those skilled in the art can make equivalent substitutions or modifications to the technical solution and inventive concept of the present invention, and all such substitutions or modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing high-purity ammonium chloride, characterized in that, Includes the following steps: S1. Heating and dissolving: Add agricultural ammonium chloride to deionized water or recycled mother liquor, heat and stir until completely dissolved to obtain a hot ammonium chloride solution; S2. Impurity Removal and Adsorption: An impurity removal agent is added to the above-mentioned hot ammonium chloride solution to form a precipitate or flocculent containing impurities, thereby obtaining a mixed solution; the impurity removal agent includes one or more of diatomaceous earth, ammonium carbonate, silica gel, ammonia water, ammonium sulfide, and ammonium oxalate; the amount of the impurity removal agent added is 0.5% to 5.0% of the mass of agricultural ammonium chloride, the reaction temperature is 60℃ to 95℃, and the stirring reaction time is 10 to 60 minutes; S3. Filtration and separation: The mixture obtained in S2 is filtered to separate and remove precipitates or flocculants containing impurities, and purified ammonium chloride filtrate is obtained. S4. Evaporation and concentration: The purified ammonium chloride filtrate obtained in S3 is evaporated and concentrated to remove some water, resulting in ammonium chloride concentrate. S5. Cooling and crystallization: Cool the ammonium chloride concentrate obtained in S4 to allow ammonium chloride to crystallize and precipitate, resulting in an ammonium chloride slurry; S6. Centrifugal separation: The ammonium chloride crystal slurry obtained in S5 is centrifuged to obtain crude ammonium chloride and crystallization mother liquor; S7. Secondary recrystallization: Dissolve the crude ammonium chloride obtained in S6 by heating with deionized water or high-purity water, cool and crystallize again, and centrifuge to obtain the refined ammonium chloride product. S8. Drying: Drying process to obtain AR grade high-purity ammonium chloride product.

2. The method for preparing high-purity ammonium chloride according to claim 1, characterized in that, The impurity removal agent is a combination of ammonium carbonate and ammonia.

3. The method for preparing high-purity ammonium chloride according to claim 1, characterized in that, In S1, the heating temperature is 60℃~100℃.

4. The method for preparing high-purity ammonium chloride according to claim 3, characterized in that, In S1, the heating temperature is 80℃~95℃.

5. The method for preparing high-purity ammonium chloride according to claim 1, characterized in that, In step S1, the mass ratio of agricultural ammonium chloride to deionized water or recycled mother liquor is 1:(1.5-3.0).

6. The method for preparing high-purity ammonium chloride according to claim 1, characterized in that, In step S2, the impurity remover is added in the form of an aqueous solution, wherein the mass fraction of the solute in the aqueous solution is 5% to 20%.

7. The method for preparing high-purity ammonium chloride according to claim 1, characterized in that, In step S4, the evaporation and concentration are performed under normal pressure or reduced pressure, evaporating until the solution density is 1.10–1.35 g / cm³. 3 .

8. The method for preparing high-purity ammonium chloride according to claim 1, characterized in that, In step S5, the final temperature of cooling crystallization is 10℃~40℃, the cooling rate is 1℃ / hour~10℃ / hour, and the crystallization time is 1~8 hours.

9. The method for preparing high-purity ammonium chloride according to claim 1, characterized in that, In S7, the dissolution temperature for secondary recrystallization is 60℃~95℃, the mass ratio of crude ammonium chloride to deionized water or high-purity water is 1:(1.2~2.5), and the cooling crystallization temperature is 5℃~20℃.

10. The method for preparing high-purity ammonium chloride according to claim 1, characterized in that, In step S8, the drying temperature is 80℃~120℃, and the drying time is 2~8 hours.

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