A method for preparing high-purity potassium nitrate by material balance control

Abstract

This application relates to the field of chemical production, specifically disclosing a method for preparing high-purity potassium nitrate through material balance control, comprising the following steps: S1, preparing a potassium nitrate reaction solution by mixing potassium chloride, ammonium nitrate, and water, adding modified activated carbon to the reaction solution, allowing it to stand and filter, and then heating and stirring the filtrate with steam; S2, adding a separation agent, filtering the mother liquor containing potassium nitrate crystals, and then performing foam flotation to obtain crude potassium nitrate and a mother liquor containing ammonium chloride; S3, refining the crude potassium nitrate; wherein, the modified activated carbon in step S1 is obtained by polymerizing styrene and divinylbenzene monomers with activated carbon as a framework, followed by chloromethylation and sulfonation treatment. This application achieves a molar balance between potassium chloride and ammonium nitrate in the potassium nitrate production process, ensures the complete dissolution of potassium chloride, and alleviates the problem of ammonium chloride crystal precipitation and difficulty in separating from potassium nitrate during potassium nitrate crystallization due to ammonium chloride supersaturation.

Description

Technical Field

[0001] This application relates to the field of chemical production, and more specifically, it relates to a method for preparing high-purity potassium nitrate through material balance control. Background Technology

[0002] Potassium nitrate is a colorless orthorhombic crystal or white powder, and is an important inorganic chemical product with wide applications in agriculture and industry. In recent years, with the development of science and technology, the demand for potassium nitrate in the Chinese market has been increasing, and higher requirements have been placed on its quality.

[0003] The main production processes for potassium nitrate include acid-base neutralization of nitric acid and potassium hydroxide to produce potassium nitrate, metathesis of ammonium nitrate and potassium chloride to produce potassium nitrate, and ion exchange. Among these, the metathesis method is widely used because the raw material price is relatively low and the by-product ammonium chloride has a certain market value.

[0004] For example, Chinese patent application publication number CN105060317A discloses a method for producing high-quality potassium nitrate by a double decomposition cycle of potassium chloride and ammonium nitrate, including the following steps: (1) Preparation: Mix potassium chloride, ammonium nitrate and water to prepare KNO3 reaction solution, place it in the mixing tank, and add NH4+ to the KNO3 reaction solution. + With Cl - The molar ratio is 1 to 1.6:1, heated with steam and stirred; (2) Addition of flotation reagents: When the KNO3 reaction solution in the mixing tank is heated to ≥40℃, the flotation reagents are added to the mixing tank and the temperature is continued to rise so that they are completely dispersed and dissolved in the KNO3 reaction solution; during this process, the pH value of the system is adjusted to be between 4.0 and 7.0. (3) KNO3 crystallization: Control the temperature of the KNO3 reaction solution to 70℃~110℃. After the KNO3 reaction solution evaporates to 38Be~44Be, filter to remove impurities, and cool to 30℃~36℃ to obtain the mother liquor in which potassium nitrate crystals are precipitated. (4) Foam flotation separation: The mother liquor from which potassium nitrate crystals precipitate is pumped to a centrifugal filter. Ammonium chloride crystals mixed in the mother liquor from which potassium nitrate crystals precipitate float naturally to the upper layer of the mother liquor from which potassium nitrate crystals precipitate. The foam layer is separated by overflow. The mother liquor from which potassium nitrate crystals precipitate is centrifuged and dehydrated to obtain crude potassium nitrate crystals. The foam liquid after separation is an ammonium chloride-containing mother liquor, which is ready for use. (5) Dehydration and washing of crude potassium nitrate crystals: The crude potassium nitrate crystals were placed in a centrifuge lined with filter cloth. After dehydration by centrifugation, the residual ammonium chloride adsorbed on the surface of the crude potassium nitrate was rinsed with water. After dehydration by centrifugation, crude potassium nitrate was obtained. The separation liquid and washing liquid were combined to form mother liquor I, which was set aside for later use. (6) Refining of crude potassium nitrate: Dissolve the separated crude potassium nitrate, determine the amount of NH4+ in it, and express the result as n(Na2CO3):n(NH4+). + Sodium carbonate is added to potassium nitrate solution at a molar ratio of 1:2; the steam heating temperature is controlled between 100℃ and 115℃, and the solution concentration is 48Be to 52Be; after the solution is cooled and recrystallized, it is centrifuged and dried to obtain high-quality potassium nitrate; part of the recrystallized mother liquor III will be used for washing crude potassium nitrate in the next cycle, and part will be combined with ammonium chloride mother liquor; (7) NH4Cl crystallization: Mix ammonium chloride mother liquor with mother liquor I and mother liquor III, heat to 120-130℃, evaporate and concentrate, and add ammonium nitrate to control NH4. + With Cl - The molar ratio was 2:1, the concentration of the reaction solution was adjusted to 36Be~38Be, and after cooling, ammonium chloride crystals precipitated. (8) NH4Cl product: The solution from which ammonium chloride crystals precipitate is placed in a centrifuge lined with filter cloth, and after centrifugation and dehydration, ammonium chloride product is obtained; the NH4Cl separated is added as mother liquor II to the KNO3 reaction solution to replace part of the ammonium nitrate.

[0005] In the above-mentioned potassium nitrate production process, maintaining the material balance between ammonium nitrate and potassium chloride is crucial. There are two conventional control methods: one is to use reagent analysis to simply analyze the molar concentrations of ammonium and chloride ions in the solution to determine the concentration of NH4NO3, calculate the amount of NH4NO3, and then determine the amount of KCl to be added. The other method is to directly detect the molar concentrations of various ions in the solution using a chromatograph to determine the amount of NH4NO3 to be added with KCl.

[0006] Following the above method for proportioning and feeding materials can certainly achieve material reaction equilibrium. However, in existing potassium nitrate production processes, the concentration of the mother liquor is often too high. If the above method is used for feeding materials, considering only the ionic balance of the material reaction, two other problems will arise. First, if KCl is added to the reactor according to the calculation formula, but the concentration of NaCl and NH4Cl in the mother liquor is too high, meaning the Cl ion concentration in the mother liquor is too high, the added KCl may not dissolve completely due to the common ion effect. Incomplete dissolution of KCl will affect the crystal formation of crude KNO3. The residual KCl solid will act as a seed crystal for KNO3, contained within the crude KNO3 crystals, leading to excessive chloride levels in the crude KNO3. The second problem is that if the NH4Cl in the mother liquor becomes supersaturated after the KCl reaction in the reactor, a large amount of NH4Cl crystals will precipitate. When the crude KNO3 is dehydrated using a centrifuge, some NH4Cl crystals will remain mixed in and cannot be separated, affecting the purity of the crude KNO3.

[0007] In summary, the key issues we need to address are: achieving material balance, meaning the molar amounts of KCl and NH4NO3 must be equal—this is a prerequisite. We also need to ensure that the KCl added during the reaction dissolves completely, even under the influence of common ion effects. Furthermore, after the KCl reaction, when the mother liquor is cooled to the temperature at which crude KNO3 is produced, the mother liquor should not be saturated with NH4Cl, preventing the precipitation of NH4Cl crystals. Solving these problems is crucial for obtaining high-purity potassium nitrate. Summary of the Invention

[0008] In order to achieve a molar balance between potassium chloride and ammonium nitrate in the potassium nitrate production process, ensure the complete dissolution of potassium chloride, and alleviate the problem of ammonium chloride crystal precipitation and difficulty in separating from potassium nitrate during the cooling and crystallization of potassium nitrate due to ammonium chloride supersaturation, this application provides a method for preparing high-purity potassium nitrate through material balance control.

[0009] This application provides a method for preparing high-purity potassium nitrate through material balance control, employing the following technical solution: A method for preparing high-purity potassium nitrate through material balance control includes the following steps: S1. Prepare a potassium nitrate reaction solution by mixing potassium chloride, ammonium nitrate and water, add modified activated carbon to the reaction solution, let it stand for 10-20 minutes and then filter it. Heat the filtrate with steam and stir. S2. When the filtrate is heated to ≥40℃, emulsion separation agent is added to adjust the pH value. Then, the mother liquor containing potassium nitrate crystals is obtained by heating and then cooling. The mother liquor containing potassium nitrate crystals is then filtered and subjected to foam flotation to obtain crude potassium nitrate and mother liquor containing ammonium chloride. S3. Refine crude potassium nitrate to obtain refined potassium nitrate, and crystallize ammonium chloride-containing mother liquor to obtain ammonium chloride crystals; In step S1, the modified activated carbon is prepared by polymerizing styrene and divinylbenzene monomers with activated carbon as the skeleton, followed by chloromethylation and sulfonation.

[0010] By adopting the above technical solution, this application first adds modified activated carbon to the reaction solution prepared with potassium chloride and ammonium nitrate as reaction raw materials. After selective adsorption of chloride ions, the solution is filtered to remove the activated carbon that has adsorbed some chloride ions before proceeding with the subsequent heating reaction. On the one hand, the modified activated carbon adsorbs some chloride ions to reduce the chloride ion concentration in the reaction mother liquor, thereby solving the problem that potassium chloride cannot be completely dissolved due to the copper ion effect, which affects the excessive chloride content of potassium nitrate crystals. On the other hand, it also solves the problem that the precipitation of supersaturated ammonium chloride in the mother liquor reduces the purity of potassium nitrate crystals.

[0011] In this application, the modified activated carbon uses activated carbon as a matrix. Activated carbon itself has a certain adsorption capacity for chloride ions. Based on the polymerization of styrene and divinylbenzene as monomers to form a styrene-divinylbenzene copolymer, chloromethylation and sulfonamide treatments are then applied to introduce chloromethyl functional groups and sulfonamide groups. The bond between the styrene-divinylbenzene copolymer and chloride ions is more stable, resulting in stable adsorption. Furthermore, the introduction of chloromethyl functional groups into the copolymer alters the surface charge distribution due to the electronegativity of chloride atoms, enhancing the affinity for chloride ions. Moreover, by adjusting the number and distribution of chloromethyl functional groups, preferential adsorption of specific chloride ions is achieved. Combined with the sulfonamide groups, this results in a strong affinity for chloride ions. The adsorption performance was investigated, and it was found that the modified activated carbon treated with acyl chloride and sulfonamide could specifically adsorb chloride ions after the reaction solution was treated. This reduced the chloride ion concentration to alleviate the incomplete dissolution of potassium chloride and the supersaturation precipitation of ammonium chloride caused by the common ion effect of chloride ions, without changing the presence of other ions. This resulted in the improvement of potassium nitrate purity without significantly reducing the yield of potassium nitrate. Finally, through material balance control, the subsequent reaction system under the condition of multiphase ions such as NH4NO3, KNO3, KCl, NH4Cl, and NaCl underwent metathesis reaction and crystallization to obtain high-purity potassium nitrate product and ammonium chloride byproduct, thereby reducing the chloride and ammonia content in potassium nitrate crystals.

[0012] Optionally, the modified activated carbon is prepared by the following method: 1) Dissolve the first styrene monomer in an ethanol solution of 4-6 times its mass, then add activated carbon for ultrasonic impregnation, filter and dry to obtain pretreated activated carbon; 2) Mix the second styrene monomer, 4-aminostyrene and divinylbenzene monomer, then add dimethylformamide, mix with the pretreated activated carbon obtained in step 1), then add initiator and pore-forming agent, react at 90-100℃ for 1.5-2.5h, wash with water and dry to obtain primary modified activated carbon; 3) Mix primary modified activated carbon with chloromethyl methyl ether, then add anhydrous zinc chloride, and react at 30-50℃ for 5-8 hours to obtain chloromethyl modified activated carbon; 4) Mix the prepared chloromethyl modified activated carbon with methanesulfonic anhydride, then add pyridine, react at 40-50℃ for 1-2 hours, then filter and dry to obtain modified activated carbon.

[0013] By adopting the above technical solution, activated carbon is first soaked in a first styrene monomer solution, and the first styrene monomer is loaded on the surface of the activated carbon. Then, it is mixed with a solution containing second styrene monomer, 4-aminostyrene and divinylbenzene monomer. Under the action of an initiator, based on the styrene monomer on the surface of the pretreated activated carbon, styrene monomer, 4-aminostyrene and divinylbenzene monomer copolymerize on the surface of the activated carbon to form a copolymer. During the process, the addition of a pore-forming agent produces a porous copolymer, thereby achieving the adsorption of chloride ions. Then, the primary activated carbon is chloromethylated with chloromethyl ether as a chloromethyl reagent to introduce chloromethyl groups. Then, with methanesulfonic anhydride as a sulfonating agent, under alkaline conditions in the presence of pyridine, it reacts with the amino group introduced in the copolymer to generate methanesulfonamide, thereby introducing methanesulfonamide groups, and thus introducing sulfonic acid and amino groups to achieve specific adsorption of chloride ions.

[0014] Optionally, in preparing modified activated carbon, the mass ratio of the first styrene monomer to activated carbon in step 1) is 1:(1.2-1.5). In step 2), each ingredient is added according to the following weight proportions: 15-25 parts divinylbenzene monomer, 12-20 parts 4-aminostyrene, 8-15 parts divinylbenzene monomer, 15-25 parts dimethylformamide, 1-3 parts initiator, 3-5 parts porogen, 10-20 parts pretreated activated carbon; In step 3), the amount of chloromethyl methyl ether added is 10-15 wt% of the amount of primary modified activated carbon added, and the amount of anhydrous zinc chloride added is 1-3 wt% of the amount of chloromethyl methyl ether added. In step 4), the mass ratio of methanesulfonic anhydride to chloromethyl modified activated carbon is 1:(5-6), and the amount of pyridine added is 3-5 wt% of the amount of methanesulfonic anhydride added.

[0015] By adopting the above technical solution, the modified activated carbon prepared with the above raw material addition amount has better specific adsorption performance for chloride ions and has the least impact on the multiphase system.

[0016] Optionally, the porogen in step 2) may be one or both of toluene and cyclohexane.

[0017] Optionally, the amount of modified activated carbon added in step S1 is 1.3-2.5 wt% of the amount of potassium chloride added.

[0018] By controlling the amount of modified activated carbon added, a small amount of chloride ions are removed, ensuring that the activated carbon remains a complete solvent for potassium chloride. This prevents ammonium chloride from becoming supersaturated and precipitating into potassium nitrate crystals. Furthermore, the reaction system allows for normal metathesis reactions to produce potassium nitrate crystals, ultimately improving the purity of potassium nitrate without affecting its yield.

[0019] Optionally, in step 1), the activated carbon is added after being soaked in a hydrogen peroxide solution with a mass concentration of 30-40%.

[0020] By adopting the above technical solution, activated carbon is soaked in hydrogen peroxide solution and then added as a copolymer skeleton to increase oxygen-containing functional groups on the surface of activated carbon, thereby enhancing its adsorption capacity for chloride ions.

[0021] Optionally, the flotation reagent in step S2 includes the following parts by weight of raw materials: 20-30 servings of C 12 - C 20 Higher linear fatty amines, 3-5 parts glycerol, 5-8 parts sodium dodecyl sulfate and 0.2-0.5 parts 1-butyl-3-methylimidazolium hexafluorophosphate.

[0022] By adopting the above technical solution, C in this application 12 - C 20 Advanced linear aliphatic amines can selectively adsorb onto the surface of ammonium chloride crystals, altering their surface properties from hydrophilic to hydrophobic. Simultaneously, potassium nitrate crystals remain hydrophilic, unaffected by the linear aliphatic amines. This allows for separation of potassium nitrate crystals during subsequent flotation under the action of flotation reagents and the overflow of ammonium chloride with the foam, yielding potassium nitrate crystals and a mother liquor containing ammonium chloride. In this application, a small amount of glycerol is added to the flotation reagent, which is primarily composed of linear aliphatic amines, as a co-solvent to increase the solubility of both potassium chloride and ammonium chloride. This prevents ammonium chloride from precipitating due to supersaturation and adhering to potassium nitrate crystals, thus affecting its purity. Furthermore, sodium dodecyl sulfate can interact with ammonium chloride crystals through electrostatic action, thereby inhibiting ammonium chloride crystallization, while potassium nitrate remains unaffected, thus influencing the crystallization process. The growth of ammonium crystals reduces their crystallization and adhesion to potassium nitrate crystals. 1-Butyl-3-methylimidazolium hexafluorophosphate, as a hydrophobic ionic liquid, further improves the solubility of both potassium chloride and ammonium chloride, thereby reducing the risk of excessive chloride content on potassium nitrate crystals due to incomplete dissolution of potassium chloride. It also further reduces the impact on the purity of potassium nitrate crystals caused by supersaturated ammonium chloride crystallization adhering to them. More importantly, the addition of glycerol, sodium dodecyl sulfate, and the hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid in this application allows these substances to float with the foam and separate from the potassium nitrate crystals during flotation. Subsequent crystallization then prepares ammonium chloride crystals. The addition of these substances significantly improves the separation efficiency of potassium nitrate crystals during flotation and significantly reduces the chloride content in the potassium nitrate crystals.

[0023] Optionally, the amount of flotation reagent added is 0.01-0.015 wt% of the amount of potassium chloride added.

[0024] By adopting the above technical solution, this application achieves better flotation effect with less flotation reagent dosage, significantly reduces the problem of potassium chloride precipitating with potassium nitrate due to incomplete dissolution caused by common ion effect and ammonium chloride precipitating with potassium nitrate due to supersaturation, and improves the purity of potassium nitrate.

[0025] Optionally, the C 12 - C 20 The advanced linear fatty amines are selected from one or more of laurylamine, tetradecylamine, and octadecylamine.

[0026] In summary, this application has the following beneficial effects: 1. In this application, modified activated carbon is first added to the reaction solution prepared with potassium chloride and ammonium nitrate as reaction raw materials to selectively adsorb chloride ions. After filtration, the activated carbon with some chloride ions adsorbed is removed before subsequent heating reaction. On the one hand, the modified activated carbon adsorbs some chloride ions to reduce the chloride ion concentration in the reaction mother liquor, thereby solving the problem that potassium chloride cannot be completely dissolved due to the copper ion effect, which affects the excessive chloride content of potassium nitrate crystals. On the other hand, it also solves the problem that the supersaturation of ammonium chloride in the mother liquor reduces the purity of potassium nitrate crystals. 2. In this application, the modified activated carbon uses activated carbon as a matrix. Activated carbon itself has a certain adsorption capacity for chloride ions. Based on the polymerization of styrene and divinylbenzene as monomers to form a styrene-divinylbenzene copolymer, chloromethylation and sulfonamide treatments are then applied to introduce chloromethyl functional groups and sulfonamide groups. The bond between the styrene-divinylbenzene copolymer and chloride ions is more stable, resulting in stable adsorption. Furthermore, the introduction of chloromethyl functional groups into the copolymer alters the surface charge distribution due to the electronegativity of chloride atoms, enhancing the affinity for chloride ions. Moreover, by adjusting the number and distribution of chloromethyl functional groups, the adsorption capacity for chloride ions is further improved. The preferential adsorption of chloride ions, combined with the strong adsorption performance of sulfonamide groups for chloride ions, led to the discovery that modified activated carbon treated with acyl chloride and sulfonamides can specifically adsorb chloride ions after treatment of the reaction solution. This reduces the chloride ion concentration, alleviating the incomplete dissolution of potassium chloride and the supersaturation precipitation of ammonium chloride caused by the common ion effect of chloride ions, without changing the presence of other ions. As a result, it can improve the purity of potassium nitrate without significantly reducing the yield of potassium nitrate. Finally, through material balance control, high-purity potassium nitrate product and ammonium chloride byproduct are obtained, while reducing the chloride and ammonia content in potassium nitrate crystals. Detailed Implementation

[0027] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0028] The following preparation examples are examples of the preparation of modified activated carbon. Preparation Example 1 A method for preparing modified activated carbon includes the following steps: 1) The first styrene monomer is dissolved in 5 times the mass of ethanol, then activated carbon is added and ultrasonically impregnated, then filtered and dried to obtain pretreated activated carbon, wherein the mass ratio of the first styrene monomer to the activated carbon is 1:1.3. 2) Mix 20 kg of divinylbenzene monomer, 16 kg of 4-aminostyrene and 12 kg of divinylbenzene monomer, then add 20 kg of dimethylformamide, mix with 15 kg of the pretreated activated carbon obtained in step 1), then add 2 kg of initiator benzoyl peroxide and 4 kg of pore-forming agent toluene, react at 95 °C for 2 h, wash with water and dry to obtain primary modified activated carbon; 3) The prepared primary modified activated carbon is mixed with chloromethyl methyl ether, and then anhydrous zinc chloride is added. The mixture is reacted at 40°C for 6 hours to obtain chloromethyl modified activated carbon. The amount of chloromethyl methyl ether added is 12 wt% of the amount of primary modified activated carbon, and the amount of anhydrous zinc chloride added is 2 wt% of the amount of chloromethyl methyl ether. 4) The prepared chloromethyl modified activated carbon was mixed with methanesulfonic anhydride, and then pyridine was added. The mixture was reacted at 45°C for 1.5 h, and then filtered and dried to obtain modified activated carbon. The mass ratio of methanesulfonic anhydride to chloromethyl modified activated carbon was 1:5.5, and the amount of pyridine added was 4 wt% of the amount of methanesulfonic anhydride added.

[0029] Preparation Example 2 A method for preparing modified activated carbon includes the following steps: 1) The first styrene monomer is dissolved in 4 times the mass of ethanol, then activated carbon is added and ultrasonically impregnated, then filtered and dried to obtain pretreated activated carbon, wherein the mass ratio of the first styrene monomer to the activated carbon is 1:1.2. 2) Mix 15 kg of divinylbenzene monomer, 12 kg of 4-aminostyrene and 8 kg of divinylbenzene monomer, then add 15 kg of dimethylformamide, mix with 10 kg of the pretreated activated carbon obtained in step 1), then add 1 kg of initiator benzoyl peroxide and 3 kg of pore-forming agent toluene, react at 90 °C for 2.5 h, wash with water and dry to obtain primary modified activated carbon; 3) The prepared primary modified activated carbon is mixed with chloromethyl methyl ether, and then anhydrous zinc chloride is added. The mixture is reacted at 30°C for 8 hours to obtain chloromethyl modified activated carbon. The amount of chloromethyl methyl ether added is 10 wt% of the amount of primary modified activated carbon, and the amount of anhydrous zinc chloride added is 1 wt% of the amount of chloromethyl methyl ether. 4) The prepared chloromethyl modified activated carbon was mixed with methanesulfonic anhydride, and then pyridine was added. The mixture was reacted at 40°C for 2 hours, and then filtered and dried to obtain modified activated carbon. The mass ratio of methanesulfonic anhydride to chloromethyl modified activated carbon was 1:5, and the amount of pyridine added was 3wt% of the amount of methanesulfonic anhydride added.

[0030] Preparation Example 3 A method for preparing modified activated carbon includes the following steps: 1) The first styrene monomer is dissolved in 6 times the mass of ethanol, then activated carbon is added and ultrasonically impregnated, then filtered and dried to obtain pretreated activated carbon, wherein the mass ratio of the first styrene monomer to the activated carbon is 1:1.5. 2) Mix 25 kg of divinylbenzene monomer, 20 kg of 4-aminostyrene and 15 kg of divinylbenzene monomer, then add 25 kg of dimethylformamide, mix with 20 kg of pretreated activated carbon obtained in step 1), then add 3 kg of initiator benzoyl peroxide and 5 kg of pore-forming agent toluene, react at 100 °C for 1.5 h, wash with water and dry to obtain primary modified activated carbon; 3) The prepared primary modified activated carbon is mixed with chloromethyl methyl ether, and then anhydrous zinc chloride is added. The mixture is reacted at 50°C for 5 hours to obtain chloromethyl modified activated carbon. The amount of chloromethyl methyl ether added is 15 wt% of the amount of primary modified activated carbon, and the amount of anhydrous zinc chloride added is 3 wt% of the amount of chloromethyl methyl ether added. 4) The prepared chloromethyl modified activated carbon was mixed with methanesulfonic anhydride, and then pyridine was added. The mixture was reacted at 50°C for 1 hour, and then filtered and dried to obtain modified activated carbon. The mass ratio of methanesulfonic anhydride to chloromethyl modified activated carbon was 1:5, and the amount of pyridine added was 3wt% of the amount of methanesulfonic anhydride added.

[0031] Preparation Example 4 A method for preparing modified activated carbon is carried out according to the method in Preparation Example 1, except that in step 1), the activated carbon is added after being soaked in a hydrogen peroxide solution with a mass concentration of 30%.

[0032] Preparation Example 5 A method for preparing modified activated carbon is carried out according to the method in Preparation Example 1, except that in step 1), the activated carbon is added after being soaked in a hydrogen peroxide solution with a mass concentration of 40%.

[0033] Comparative Preparation Example 1 A method for preparing modified activated carbon is carried out according to the method in Preparation Example 1, except that in step 2), 4-aminostyrene is replaced by an equal amount of styrene monomer.

[0034] Comparative Preparation Example 2 A method for preparing modified activated carbon is carried out according to the method in Preparation Example 1, except that in step 2), the activated carbon is added directly to a mixed solution of styrene monomer, 4-aminostyrene and divinylbenzene monomer without being treated in step 1).

[0035] Comparative preparation example 3 A method for preparing modified activated carbon is carried out according to the method in Preparation Example 1, except that step 4) is not performed, and step 3) is performed by drying after chloromethyl modification.

[0036] Comparative preparation example 4 A method for preparing modified activated carbon is carried out according to the method in Preparation Example 1, except that the primary modified activated carbon obtained in step 2) is directly subjected to the modification treatment in step 4) without step 3).

[0037] Example 1 A method for preparing high-purity potassium nitrate through material balance control includes the following steps: S1. Prepare a potassium nitrate reaction solution by mixing potassium chloride, ammonium nitrate, and water (the circulating mother liquor from step S3 is added during circulation) to control NH4+. 4+ With Cl - The molar ratio of the substances is 1.5:1. Then, the modified activated carbon prepared in Preparation Example 1 is added to the reaction solution. The amount of modified activated carbon added is 2wt% of the amount of potassium chloride added. After standing for 15 minutes, the solution is filtered, and the resulting reaction filtrate is heated and stirred with steam. S2. When the filtrate is heated to 40°C, emulsion flotation reagent is added. The amount of flotation reagent added is 0.012 wt% of the amount of potassium chloride added. The temperature is continued to rise while the pH value is adjusted to 5. When the temperature of the reaction filtrate is controlled to rise to 100°C, and the reaction filtrate is evaporated to a concentration of 40 Be (Baumé), the reaction filtrate is cooled to 35°C by vacuum cooling, and potassium nitrate crystals are precipitated to obtain a mother liquor containing potassium nitrate crystals. The mother liquor containing potassium nitrate crystals was centrifuged and filtered. During the process, the ammonium chloride crystals mixed in with the potassium nitrate crystals floated on the upper layer of the mother liquor after the potassium nitrate precipitated due to the entrainment effect of the foam. They were then separated from the potassium nitrate crystals by overflow, yielding crude potassium nitrate and mother liquor A containing ammonium chloride. S3. Dissolve the obtained crude potassium nitrate to determine the presence of NH4+. 4+ The amounts of substance, expressed as n(Na₂CO₃):n(NH₃) 4+Sodium carbonate was added to a KNO3 solution at a molar ratio of 1:2. The steam heating temperature was controlled at 110℃, and the solution was evaporated to a concentration of 50Be. After cooling and recrystallization, the solution was centrifuged and dried to obtain high-quality potassium nitrate with a KNO3 content ≥ 99.7%. The recrystallized mother liquor B was combined with the ammonium chloride-containing mother liquor A to obtain an ammonium-containing mother liquor. The ammonium-containing mother liquor was heated to 125°C, evaporated and concentrated, and ammonium nitrate was added. The NH4+ content in the system was controlled. 4+ With Cl - The molar ratio is 2:1. The mixture is evaporated to a concentration of 36Be, cooled, and ammonium chloride crystals are precipitated to obtain a solution containing ammonium chloride crystals. The solution containing ammonium chloride crystals is centrifuged and dehydrated to obtain ammonium chloride product and circulating mother liquor. The circulating mother liquor is added to step S1 for recycling.

[0038] The flotation reagent in step S2 is prepared by mixing the following raw materials by weight (kg): 25 kg laurylamine, 4 kg glycerol, 6 kg sodium dodecyl sulfate and 0.3 kg 1-butyl-3-methylimidazolium hexafluorophosphate.

[0039] Example 2 A method for preparing high-purity potassium nitrate by controlling material balance is carried out according to the method in Example 1, except that: The modified activated carbon added in step S1 is the modified activated carbon prepared in Preparation Example 2, and the amount of modified activated carbon added is 1.3 wt% of the amount of potassium chloride added. After standing for 10 min, the mixture is filtered, and the resulting reaction filtrate is heated and stirred with steam. In step S2, the amount of flotation reagent added is 0.01 wt% of the amount of potassium chloride added, and the flotation reagent is prepared by mixing the following raw materials by weight (kg): 20 kg octadecylamine, 3 kg glycerol, 5 kg sodium dodecyl sulfate and 0.2 kg 1-butyl-3-methylimidazolium hexafluorophosphate.

[0040] Example 3 A method for preparing high-purity potassium nitrate by controlling material balance is carried out according to the method in Example 1, except that: The modified activated carbon added in step S1 is the modified activated carbon prepared in Preparation Example 3, and the amount of modified activated carbon added is 2.5 wt% of the amount of potassium chloride added. After standing for 20 minutes, the mixture is filtered, and the resulting reaction filtrate is heated and stirred with steam. In step S2, the amount of flotation reagent added is 0.015 wt% of the amount of potassium chloride added, and the flotation reagent is prepared by mixing the following raw materials by weight (kg): 30 kg tetradecylamine, 5 kg glycerol, 8 kg sodium dodecyl sulfate and 0.5 kg 1-butyl-3-methylimidazolium hexafluorophosphate.

[0041] Examples 4-5 A method for preparing high-purity potassium nitrate by material balance control is carried out according to the method in Example 1, except that the modified activated carbon added in step S1 is the modified activated carbon obtained in Preparation Examples 4-5.

[0042] Example 6 A method for preparing high-purity potassium nitrate by material balance control is carried out according to the method in Example 1, except that laurylamine is used as the flotation reagent in step S2.

[0043] Example 7 A method for preparing high-purity potassium nitrate by material balance control is carried out according to the method in Example 1, except that 1-butyl-3-methylimidazolium hexafluorophosphate is not added to the flotation reagent in step S2.

[0044] Example 8 A method for preparing high-purity potassium nitrate by material balance control is carried out according to the method in Example 1, except that glycerol is not added to the flotation reagent in step S2.

[0045] Comparative Examples 1-4 A method for preparing high-purity potassium nitrate by material balance control is carried out according to the method in Example 1, except that the modified activated carbon in step S1 is the modified activated carbon obtained in Comparative Preparation Examples 1-4.

[0046] Comparative Example 5 A method for preparing high-purity potassium nitrate by controlling material balance is carried out according to the method in Example 1, except that the modified activated carbon in step S1 is replaced by activated carbon in equal amounts.

[0047] Comparative Example 6 A method for preparing high-purity potassium nitrate by material balance control is carried out according to the method in Example 1, except that modified activated carbon is not added in step S1, and laurylamine is used as the flotation reagent in step S2.

[0048] Performance testing The chloride and ammonium ion contents in the high-quality potassium nitrate prepared in the above examples and comparative examples were detected, and the results are shown in Table 1 below.

[0049] Table 1: Testing items Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 <![CDATA[Cl - Content / % 0.002 0.004 0.003 0.002 0.001 0.004 0.005 <![CDATA[NH 4+ Content / % 0.008 0.010 0.008 0.005 0.004 0.014 0.016 Testing items Example 8 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 <![CDATA[Cl - Content / % 0.004 0.006 0.006 0.007 0.007 0.007 0.008 <![CDATA[NH 4+ Content / % 0.015 0.020 0.022 0.023 0.023 0.026 0.027 Referring to the test results in Table 1 above, the potassium nitrate prepared by the method of this application has high purity. The refined potassium nitrate obtained in the examples has a content ≥ 99.7%, and the refined potassium nitrate obtained in Example 1 has a content greater than 99.8%. The chloride and ammonium ion contents are low, and the purity is higher. Combining the test results of Example 1 and Examples 4-5, the addition of activated carbon after oxidation treatment further reduces the entry of potassium chloride and ammonium chloride crystals into potassium nitrate crystals, thereby reducing the chloride and ammonium ion contents. Referring to the test results in Example 6 and Example 1, it can be seen that when only fatty amines are used as the flotation reagent, compared with the flotation reagent provided in this application, the flotation reagent containing glycerol and 1-butyl-3-methylimidazolium hexafluorophosphate added in this application has a better separation effect for the flotation separation of ammonium chloride and potassium nitrate, thereby significantly reducing the ammonium ion content.

[0050] Referring to the test results of Example 1 and Comparative Examples 1-4, in Comparative Example 1, when no 4-aminostyrene monomer was added to the modified activated carbon, the chloride ion adsorption effect in the system was affected, thus affecting the dissolution of potassium chloride and the supersaturation precipitation of ammonium chloride. Ultimately, the chloride and ammonium ion contents in potassium nitrate were high. Combining this with the test results of Comparative Example 6, where no modified activated carbon was added and only fatty amines were added as flotation reagents, the chloride and ammonium ion contents were high. Furthermore, combining this with the test results of Comparative Example 2, where the activated carbon was directly subjected to step 2) copolymerization without prior treatment in the monomer solution, the final chloride and ammonium ion contents were significantly higher. This is because the monomer on the activated carbon acts as a crystal nucleus. The role of the spot is to help the monomer mixture in step 2) copolymerize on the surface of activated carbon to form a copolymer film. Combined with the role of the pore-forming agent, the pore structure of the modified activated carbon is built, thereby achieving efficient adsorption of chloride ions. Combined with the test results of Comparative Examples 3 and 4, when the modified activated carbon is copolymerized and only chloromethylated or sulfonamide treated, its adsorption effect of chloride is reduced, thus affecting the chloride and ammonia content in the final potassium nitrate. Referring to the test results of Comparative Example 5, when activated carbon is added directly without modification, the adsorption effect of chloride is weak. More importantly, the amount of high-quality potassium nitrate obtained is significantly reduced compared with the example. Activated carbon also adsorbs other elements in the reaction filtrate system, resulting in a decrease in yield.

[0051] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing high-purity potassium nitrate through material balance control, characterized in that, Includes the following steps: S1. Prepare a potassium nitrate reaction solution by mixing potassium chloride, ammonium nitrate and water, add modified activated carbon to the reaction solution, let it stand for 10-20 minutes and then filter it. Heat the filtrate with steam and stir. S2. When the filtrate is heated to ≥40℃, emulsion separation agent is added to adjust the pH value. Then, the mother liquor containing potassium nitrate crystals is obtained by heating and then cooling. The mother liquor containing potassium nitrate crystals is then filtered and subjected to foam flotation to obtain crude potassium nitrate and mother liquor containing ammonium chloride. S3. Refine crude potassium nitrate to obtain refined potassium nitrate, and crystallize ammonium chloride-containing mother liquor to obtain ammonium chloride crystals; In step S1, the modified activated carbon is prepared by polymerizing styrene and divinylbenzene monomers with activated carbon as the skeleton, followed by chloromethylation and sulfonation.

2. The method for preparing high-purity potassium nitrate by controlling material balance according to claim 1, characterized in that: The modified activated carbon is prepared by the following method: 1) Dissolve the first styrene monomer in an ethanol solution of 4-6 times its mass, then add activated carbon for ultrasonic impregnation, filter and dry to obtain pretreated activated carbon; 2) Mix the second styrene monomer, 4-aminostyrene and divinylbenzene monomer, then add dimethylformamide, mix with the pretreated activated carbon obtained in step 1), then add initiator and pore-forming agent, react at 90-100℃ for 1.5-2.5h, wash with water and dry to obtain primary modified activated carbon; 3) Mix primary modified activated carbon with chloromethyl methyl ether, then add anhydrous zinc chloride, and react at 30-50℃ for 5-8 hours to obtain chloromethyl modified activated carbon; 4) Mix the prepared chloromethyl modified activated carbon with methanesulfonic anhydride, then add pyridine, react at 40-50℃ for 1-2 hours, then filter and dry to obtain modified activated carbon.

3. The method for preparing high-purity potassium nitrate by controlling material balance according to claim 2, characterized in that: When preparing modified activated carbon, the mass ratio of the first styrene monomer to activated carbon in step 1) is 1:(1.2-1.5). In step 3), the amount of chloromethyl methyl ether added is 10-15 wt% of the amount of primary modified activated carbon added, and the amount of anhydrous zinc chloride added is 1-3 wt% of the amount of chloromethyl methyl ether added. In step 4), the mass ratio of methanesulfonic anhydride to chloromethyl modified activated carbon is 1:(5-6), and the amount of pyridine added is 3-5 wt% of the amount of methanesulfonic anhydride added.

4. The method for preparing high-purity potassium nitrate by controlling material balance according to claim 2, characterized in that: In step 2), each ingredient is added according to the following weight proportions: 15-25 parts divinylbenzene monomer, 12-20 parts 4-aminostyrene, 8-15 parts divinylbenzene monomer, 15-25 parts dimethylformamide, 1-3 parts initiator, 3-5 parts porogen, and 10-20 parts pretreated activated carbon.

5. The method for preparing high-purity potassium nitrate by controlling material balance according to claim 2, characterized in that: In step 2), the porogen can be one or both of toluene and cyclohexane.

6. The method for preparing high-purity potassium nitrate by controlling material balance according to claim 1, characterized in that: In step S1, the amount of modified activated carbon added is 1.3-2.5 wt% of the amount of potassium chloride added.

7. The method for preparing high-purity potassium nitrate by controlling material balance according to claim 2, characterized in that: In step 1), the activated carbon is added after being soaked in a hydrogen peroxide solution with a mass concentration of 30-40%.

8. The method for preparing high-purity potassium nitrate by controlling material balance according to claim 1, characterized in that: The flotation reagent in step S2 includes the following parts by weight of raw materials: 20-30 servings of C 12 - C 20 Higher linear fatty amines, 3-5 parts glycerol, 5-8 parts sodium dodecyl sulfate and 0.2-0.5 parts 1-butyl-3-methylimidazolium hexafluorophosphate.

9. The method for preparing high-purity potassium nitrate by controlling material balance according to claim 1, characterized in that: The amount of flotation reagent added is 0.01-0.015 wt% of the amount of potassium chloride added.

10. A method for preparing high-purity potassium nitrate by controlling material balance according to claim 8, characterized in that: The C 12 - C 20 The advanced linear fatty amines are selected from one or more of laurylamine, tetradecylamine, and octadecylamine.