Production method of anti-caking potassium nitrate

Abstract

The invention relates to the field of material science and engineering, and particularly discloses an anti-caking potassium nitrate production method which comprises the following steps: taking high-purity potassium nitrate crystals as a base material, selecting lauryl sodium sulfate as an anti-caking agent, and adding 10-100g of sodium dodecyl sulfate into each ton of base material; the production method comprises the following steps: dissolving lauryl sodium sulfate in pure water to prepare a transparent modified solution; uniformly wetting the surface of the crystal with the modification liquid by adopting a layer-paving spraying method; drying the wet material in a non-closed heating environment in which a moisture removal channel is reserved, and inducing the formation of a stable hydrophobic membrane on the surface; and finally, carrying out secondary mechanical mixing and granulating to obtain a finished product. According to the invention, through liquid-phase trace coating and a specific temperature control and moisture removal process, the hygroscopicity and caking tendency of the crystal are remarkably reduced while the water insoluble substance and clarity of the product are ensured to completely meet the analytic purity standard, and the problems of turbid solution, excessive introduction of organic impurities and damaged purity caused by the traditional physical anti-caking technology are effectively solved.

Description

Technical Field

[0001] This application relates to the field of materials science and engineering, and more specifically, to a method for producing potassium nitrate without caking. Background Technology

[0002] Potassium nitrate is an important inorganic chemical raw material widely used in agricultural fertilizers, food preservation, industrial glass manufacturing, ceramic glazes, and daily chemical products. Potassium nitrate typically exists in the form of crystalline powder and has a certain degree of hygroscopicity. During storage, stacking, and transportation after production, changes in ambient temperature and humidity, as well as its own gravity, can cause moisture adsorbed on the crystal surface to dissolve some of the potassium nitrate, forming a saturated solution. When the environment dries or the temperature decreases, the dissolved potassium nitrate redefines and forms liquid bridges between the crystal particles, leading to severe adhesion and agglomeration of the crystals, ultimately forming hard lumps. This not only severely impairs the product's flowability but also alters its physical form.

[0003] To address the clumping problem of potassium nitrate, existing technologies typically employ the addition of anti-caking agents. These include adding inert inorganic powders such as talc, kaolin, diatomaceous earth, or silica. The underlying principle is that through physical mixing, these fine powders adhere to the surface of the potassium nitrate crystals, acting as a physical barrier and reducing the direct contact area between crystals, thereby preventing the formation of crystal bridges.

[0004] In existing technologies, the introduction of water-insoluble substances leads to substandard product clarity. The inorganic anti-caking agents such as talc and kaolin widely used in existing technologies are themselves insoluble in water. Using the above-mentioned physical isolation method will directly cause the solution after potassium nitrate is dissolved to become turbid, and the content of water-insoluble substances will significantly exceed the standard, which will not meet the technical requirements of high-end application fields. Summary of the Invention

[0005] To address the problem of substandard product clarity caused by the introduction of water-insoluble substances in existing technologies, this application provides a silicon carbide-reinforced perfluoroether rubber high-temperature thermally conductive sealing composite material and its preparation process.

[0006] The first aspect of this invention provides a method for producing anti-caking potassium nitrate. This method uses high-purity potassium nitrate crystals as a base material and sodium dodecyl sulfate as an anti-caking agent. The formulation ratio of the anti-caking potassium nitrate is: 10g to 100g of sodium dodecyl sulfate per 1000kg of high-purity potassium nitrate crystals. The production method includes the following steps:

[0007] Step S1: Dissolve the specified amount of sodium dodecyl sulfate in pure water to prepare an anti-caking modified solution;

[0008] Step S2: The anti-caking modified liquid is evenly sprayed onto the surface of the high-purity potassium nitrate crystals and primary mixing is performed to obtain a wet mixture.

[0009] Step S3: Place the wet mixture in a heating environment for dehumidification and drying, so that the moisture evaporates and a hydrophobic film is formed on the crystal surface to obtain the dried material;

[0010] Step S4: Secondary mixing of the dried material yields anti-caking potassium nitrate.

[0011] The method for preparing high-purity potassium nitrate crystals includes: dissolving industrial potassium nitrate in water, adding ammonium nitrate and reacting at 80°C to 90°C to remove nitrite using the principle of redox reaction; then adding ammonium sulfide and reacting at 80°C to precipitate and remove heavy metal ions; then adding potassium carbonate and potassium hydroxide in sequence while maintaining a gentle boil to remove calcium and magnesium ions and ammonium ions using the principles of precipitation and volatilization; finally adding zinc oxide and activated carbon to remove excess sulfur ions and organic impurities, and then neutralizing, concentrating, crystallizing, and centrifuging the filtered liquid to obtain the high-purity potassium nitrate crystals.

[0012] Further, the specific operation for preparing the modified solution in step S1 is as follows: weigh the sodium dodecyl sulfate, add it to pure water at a temperature of 40°C to 50°C and stir until completely dissolved to prepare a transparent solution.

[0013] Sodium dodecyl sulfate has low solubility in cold water and readily forms micelles, while at excessively high temperatures it is prone to producing excessive foam or undergoing hydrolysis. Controlling the dissolution temperature to 40°C to 50°C can yield a true solution with uniform molecular dispersion, which is beneficial for the formation of a uniform monolayer or multilayer on the surface of potassium nitrate crystals during subsequent spraying, avoiding a decrease in product clarity due to excessively high local concentrations.

[0014] Furthermore, the initial mixing and coating operation in step S2 employs a layer-by-layer spraying method, where the high-purity potassium nitrate crystals are laid in layers. A measured amount of the anti-caking modifying liquid is sprayed in after each layer of crystals is laid. After spraying, mechanical stirring is performed at room temperature for at least 2 hours. Preferably, the weight of each layer of high-purity potassium nitrate crystals is 50 kg to 100 kg.

[0015] By layering spraying and long-term room temperature mechanical mixing, the surface tension of water and mechanical friction force are used to force the modified liquid to penetrate into the micropores of the crystal stack, ensuring that the surface of each crystal particle is wetted by the modified liquid, providing a uniform precursor state for subsequent drying and film formation.

[0016] Furthermore, the specific conditions for drying and film formation in step S3 are as follows: the wet mixed material is spread flat on a drying tray and placed in an oven at 90°C for drying for more than 24 hours, and the oven door is kept in a non-sealed state with a dehumidification channel during the drying process.

[0017] A temperature of 90°C is sufficient for rapid evaporation of moisture, while being far below the decomposition temperature of sodium dodecyl sulfate. Maintaining a "non-sealed state with ventilation channels" is crucial, as this creates effective heat and moisture convection. If completely sealed, a high-temperature, high-humidity "steamer effect" would form inside the oven, causing a dissolution-recrystallization cycle on the surface of potassium nitrate crystals. This would not only destroy the existing coating layer but also lead to the formation of hard crystalline bridges between crystals. Non-sealed drying ensures unidirectional moisture escape, allowing surfactant molecules to align and solidify on the crystal surface.

[0018] Furthermore, the specific operation of final mixing and granulation in step S4 is as follows: after passing the dried material through a vibrating screen, it is mechanically rotated and mixed at room temperature for more than 2 hours.

[0019] Even after drying, microscopic point contact adhesion may still exist between crystal particles. By mechanically mixing at room temperature after drying, shear force is applied to break these weak physical connections, eliminate the thermal stress introduced during the drying process, and ultimately give the product excellent looseness and flowability.

[0020] A second aspect of the present invention provides an anti-caking potassium nitrate produced by the above-described production method. This anti-caking potassium nitrate has a core of high-purity potassium nitrate crystals, with a surface coated with a trace amount of sodium dodecyl sulfate hydrophobic film, wherein the content of sodium dodecyl sulfate is 10 ppm to 100 ppm. The water-insoluble matter content of the anti-caking potassium nitrate product is less than or equal to 0.004%.

[0021] In summary, this application has the following beneficial effects:

[0022] 1. This invention uses trace amounts of water-soluble sodium dodecyl sulfate as a modifier. Through liquid-phase spray coating, a hydrophobic film is formed without introducing insoluble impurities, resulting in a very low content of water-insoluble matter in the final product, effectively solving the defect of turbidity caused by traditional anti-caking agents.

[0023] 2. This invention employs a combination of liquid-phase wetting, non-sealed temperature-controlled drying, and secondary depolymerization. Non-sealed drying effectively prevents recrystallization and hardening of the crystal surface under high temperature and high humidity conditions. Secondary room temperature mixing utilizes mechanical shear force to break the microscopic crystal bridges formed during the drying process. This process ensures that a uniform and stable hydrophobic film can be formed on the surface of each crystal, enabling the product to maintain excellent looseness and fluidity during long-term storage. Even if slight agglomeration occurs, it will be a fragile soft block.

[0024] 3. This invention combines deep chemical purification in the front end with trace modification in the back end. The sodium ion and organic carbon content introduced are extremely low, and will not change the main content and chemical properties of potassium nitrate. This makes the product safe to use in the fields of optical glass manufacturing, precision chemical reagents and daily chemical products that are sensitive to impurities, and solves the problem of excessive organic impurities caused by the use of oils or large amounts of surfactants. Attached Figure Description

[0025] Figure 1 This is a flowchart of the preparation process of the anti-caking potassium nitrate production method provided in this application. Detailed Implementation

[0026] The following is in conjunction with the appendix Figure 1 The present application will be further described in detail with reference to the embodiments.

[0027] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0028] Potassium nitrate: Industrial grade, purity ≥99.7%, chloride ion content ≤0.01%.

[0029] Sodium dodecyl sulfate: pharmaceutical grade or daily chemical grade, powder, purity ≥95%.

[0030] Talc powder: chemical grade, fineness 1250 mesh.

[0031] Ammonium nitrate: analytical grade.

[0032] Ammonium sulfide: analytical grade, 20% aqueous solution.

[0033] Potassium carbonate: analytical grade, anhydrous.

[0034] Potassium hydroxide: analytical grade, in flake form.

[0035] Zinc oxide: analytical grade.

[0036] Activated carbon: analytical grade, powder, strong decolorizing power.

[0037] Nitric acid: analytical grade, 65%-68%.

[0038] Example 1: This example provides a method for producing potassium nitrate without caking. See [link to example]. Figure 1 The specific steps are as follows:

[0039] Weigh 40g of sodium dodecyl sulfate and add it to 10kg of pure water at 45℃. Stir until completely dissolved to obtain a transparent and clear modified solution.

[0040] Take 1000 kg of the high-purity potassium nitrate wet crystals prepared above and place them in a stainless steel mixing tank. Using a layer-by-layer spray method, spray approximately 1 kg of modifying liquid evenly for every 100 kg of crystals laid, until all crystals and modifying liquid have been added. Transfer the material to a double-cone rotary mixer and mix at room temperature for 2 hours.

[0041] Spread the wet mixture evenly on a drying tray, about 3cm thick, and place it in the drying oven. Set the temperature to 90℃, and keep the oven door in a non-sealed state with a moisture exhaust channel, leaving a gap of about 5cm in the door. Dry for 36 hours, or until the material is completely dry.

[0042] After drying, remove the material and allow it to cool naturally. Then, pass it through a 20-mesh vibrating screen. The material that passes through the screen is then fed back into the double cone rotary mixer and mixed at room temperature for 2 hours.

[0043] The resulting anti-caking potassium nitrate product is then sealed and packaged. In this example, the K12 addition ratio is 40 ppm.

[0044] Example 2: This example provides a method for producing potassium nitrate without caking. The specific steps are as follows:

[0045] Weigh 10g of sodium dodecyl sulfate and add it to 10kg of pure water at 45℃. Stir until completely dissolved to obtain a transparent and clear modified solution.

[0046] Take 1000 kg of the high-purity potassium nitrate wet crystals prepared above and place them in a stainless steel mixing tank. Using a layer-by-layer spray method, spray approximately 1 kg of modifying liquid evenly for every 100 kg of crystals laid, until all crystals and modifying liquid have been added. Transfer the material to a double-cone rotary mixer and mix at room temperature for 2 hours.

[0047] Spread the wet mixture evenly on a drying tray, about 3cm thick, and place it in the drying oven. Set the temperature to 90℃, and keep the oven door in a non-sealed state with a moisture exhaust channel, leaving a gap of about 5cm in the door. Dry for 36 hours, or until the material is completely dry.

[0048] After drying, remove the material and allow it to cool naturally. Then, pass it through a 20-mesh vibrating screen. The material that passes through the screen is then fed back into the double cone rotary mixer and mixed at room temperature for 2 hours.

[0049] The resulting anti-caking potassium nitrate product is then sealed and packaged. In this example, the K12 addition ratio is 10 ppm.

[0050] Example 3: This example provides a method for producing potassium nitrate without caking. The specific steps are as follows:

[0051] Weigh 100g of sodium dodecyl sulfate and add it to 10kg of pure water at 45℃. Stir until completely dissolved to obtain a transparent and clear modified solution.

[0052] Take 1000 kg of the high-purity potassium nitrate wet crystals prepared above and place them in a stainless steel mixing tank. Using a layer-by-layer spray method, spray approximately 1 kg of modifying liquid evenly for every 100 kg of crystals laid, until all crystals and modifying liquid have been added. Transfer the material to a double-cone rotary mixer and mix at room temperature for 2 hours.

[0053] Spread the wet mixture evenly on a drying tray, about 3cm thick, and place it in the drying oven. Set the temperature to 90℃, and keep the oven door in a non-sealed state with a moisture exhaust channel, leaving a gap of about 5cm in the door. Dry for 36 hours, or until the material is completely dry.

[0054] After drying, remove the material and allow it to cool naturally. Then, pass it through a 20-mesh vibrating screen. The material that passes through the screen is then fed back into the double cone rotary mixer and mixed at room temperature for 2 hours.

[0055] The resulting anti-caking potassium nitrate product is then sealed and packaged. In this example, the K12 addition ratio is 100 ppm.

[0056] Comparative Example 1: Compared with Example 1, the difference is that no anti-caking agent was added, the preparation of modified liquid and spray coating steps were omitted, and high-purity potassium nitrate wet crystals were directly dried, sieved and finally mixed and granulated. All other raw materials and process parameters were the same.

[0057] Comparative Example 2: Compared with Example 1, the difference is that the type and method of adding the anti-caking agent were changed. Sodium dodecyl sulfate was replaced with 1 kg of chemical grade talc powder, and instead of being prepared into a solution, the dry talc powder was added and mixed after the material was dried. All other raw materials and process parameters were the same.

[0058] Comparative Example 3: Compared with Example 1, the difference is that the process of adding the anti-caking agent was changed. Sodium dodecyl sulfate was not prepared into a modified liquid, but was directly sprinkled into high-purity potassium nitrate wet crystals in dry powder form for initial mixing. The dissolution and spraying steps were omitted. All other raw materials and process parameters were the same.

[0059] Experiment Example 1: Detection of Physicochemical Indicators. The specific experimental steps are as follows:

[0060] Weigh approximately 0.3 g of the dried, constant-weight sample and place it in a beaker. Dissolve the sample in water. The potassium nitrate content is determined using the sodium tetraphenylborate gravimetric method. An acetate-sodium acetate buffer solution and a sodium tetraphenylborate solution are added to form a precipitate. After filtration, washing, and drying, the precipitate mass is weighed. The potassium nitrate content is calculated using stoichiometry.

[0061] Determination of water-insoluble matter: Weigh 50g of sample, dissolve in 200mL of hot water, and keep warm in a boiling water bath for 1 hour. Filter through a pre-weighed G4 glass frit funnel, wash with hot water until no nitrate reaction occurs, and dry the filter residue along with the crucible in a 105℃ oven until constant weight. Calculate the percentage of insoluble matter remaining.

[0062] Clarity test: Weigh 10g of sample and dissolve it in 100mL of carbon dioxide-free water. Observe the solution axially against a black background, comparing it to a standard turbidity solution. Assign a grade based on the degree of turbidity; the lower the number, the clearer the solution.

[0063] Sodium content determination: Weigh 1g of sample, dissolve in water, and dilute to 100mL. Use a flame atomic absorption spectrophotometer to measure the absorbance at a wavelength of 589.0nm, and calculate the sodium ion concentration by referring to the standard curve.

[0064] pH value determination: Prepare a 50 g / L sample aqueous solution and measure the pH value of the solution directly using a calibrated pH meter under constant temperature conditions of 25℃.

[0065] The test results are shown in Table 1 below:

[0066] Testing items Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Standard requirements (GB / T647AR) Content (KNO3, %) 99.64 99.71 99.58 99.73 99.12 99.61 ≥99.0 Water-insoluble matter (%) 0.0016 0.0013 0.0028 0.0011 0.0835 0.0018 ≤0.004 Clarity level (number) 2 2 3 1 >5 2 ≤3 Sodium(Na,%) 0.0082 0.0065 0.0124 0.0051 0.0105 0.0088 ≤0.02 pH value (25℃) 7.12 7.05 7.23 7.01 7.55 7.15 5.0-8.0

[0067] As shown in Table 1, the potassium nitrate products prepared in Examples 1 to 3 all had water-insoluble content controlled between 0.0013% and 0.0028%, far below the standard limit of 0.004%, and the solution clarity was all within 3. This indicates that the water-soluble anionic surfactant used in this invention can be completely dissolved in the compound system within a trace addition range, without introducing solid impurities that interfere with optical performance. In contrast, Comparative Example 2 added an insoluble physical anti-caking agent, causing the water-insoluble content to surge to 0.0835%, and the solution exhibited obvious turbidity, failing to meet the requirements for high-purity reagent use. This confirms the necessity of selecting a specific water-soluble modifier to maintain the analytical purity level of the product.

[0068] Analysis of the introduction of impurity ions shows that the sodium ion content in Examples 1 to 3 ranged from 0.0065% to 0.0124%, slightly higher than that of Comparative Example 1 (blank control), but still significantly lower than the standard upper limit of 0.02%. This result verifies the rationality of the formulation ratio described in this invention, namely, by precisely controlling the addition of sodium dodecyl sulfate to an extremely low level, while utilizing its long-chain alkyl groups to form a hydrophobic film, the total amount of sodium ions introduced by its hydrophilic end is insufficient to change the chemical purity level of the base material. Furthermore, although Comparative Example 3 is similar to Example 1 in physicochemical indicators, combined with physical state observation, it indicates that although the dry-mixing process does not exceed the overall chemical composition standard, it cannot reflect the difference in film uniformity, and needs to be comprehensively evaluated in conjunction with subsequent physical performance tests.

[0069] Based on comprehensive physicochemical indicators, the KNO3 content of the product in the example remained above 99.5%, the pH value remained stable within the neutral range, and all impurity indicators were superior to national standards. This is attributed to the removal of base material impurities through chemical precipitation and micro-boiling ammonia removal during the front-end preparation process, and the strict screening of the dosage and type of additives during the back-end modification process. These experimental data confirm that the production method described in this invention successfully solves the problem of sacrificing product purity inherent in traditional anti-caking technologies, achieving surface modification without altering the chemical properties of potassium nitrate as an analytical grade reagent.

[0070] Experiment Example 2: Long-term stacking anti-caking performance test. The specific experimental steps are as follows:

[0071] Each group of test samples was placed into a standard polypropylene woven bag, lined with a polyethylene film bag, with a net weight of 25 kg per bag, and sealed using a mechanical sewing machine.

[0072] In a naturally ventilated warehouse environment, the packaging bags of the same group of samples were stacked vertically, with a stacking layer of 10 layers.

[0073] The storage period was set to 3 months and 6 months. After the specified time, the upper packaging bag was removed, and only the bottom packaging bag was taken as a test sample to examine the clumping situation under the maximum static pressure.

[0074] The sampled packaging bag was dropped horizontally from a height of 1 meter onto a cement floor, repeated 3 times. The bag was then opened, and the contents were poured into a standard sieve with a 5mm aperture for sieving. The mass of the agglomerated material that could not pass through the sieve was weighed, and its percentage of the total weight was calculated and recorded as the agglomeration rate. Simultaneously, the agglomerated material on the sieve was manually pressed, and its hardness was recorded.

[0075] The test results are shown in Table 2 below:

[0076] Sample group 3-month clumping rate (%) Description of 3-month clot status 6-month clumping rate (%) Description of 6-month clot status Example 1 0.12 This tiny soft lump can be crushed by hand. 0.35 A small number of pseudo-agglomerates, which disperse easily with a light tap. Example 2 1.24 Small amount of soft, easily broken pieces 2.87 Some soft lumps, without hard hard crusts Example 3 0.08 Extremely small amount of soft lumps, with excellent fluidity 0.15 Extremely small amount of soft lumps, which can be crushed by hand. Comparative Example 1 45.62 A large number of hard lumps need to be broken by hammering. 88.93 The entire surface is severely compacted and resembles stones. Comparative Example 2 0.21 A small amount of soft lumps, easily crushed by hand. 0.44 A small amount of soft lumps, with good looseness Comparative Example 3 8.45 Mixed state, containing some hard cores 15.72 Obvious lumps, containing hard lumps

[0077] Analysis of the test data in Table 2 shows that after 6 months of high-pressure stacking, the agglomeration rate of the products in Examples 1 to 3 was controlled within 3%, and the residue on the sieve mainly consisted of loose, soft lumps. This is because sodium dodecyl sulfate molecules are oriented on the surface of potassium nitrate crystals, forming a hydrophobic isolation membrane. This membrane effectively reduces the surface energy of the crystal surface, blocking the penetration path of environmental moisture into the crystal interior. When the crystal particles are in close contact under gravity, the hydrophobic membrane prevents the formation of liquid bridges between particles due to capillary adsorption of water, thereby inhibiting the dissolution and recrystallization process. This prevents the formation of high-strength crystal bridges between particles, leaving only weak van der Waals forces or electrostatic adsorption, making them extremely prone to deagglomeration under external forces.

[0078] Comparing the data from Example 1 and Comparative Example 3, it can be seen that although both added the same amount of anti-caking agent, Comparative Example 3, which used a direct dry powder mixing process, had a caking rate as high as 15.72% after 6 months, and hard lumps appeared. This difference confirms the crucial role of the process step of preparing the anti-caking agent into a solution and performing layer-by-layer spraying. Liquid-phase spraying technology utilizes the fluidity and permeability of liquids to uniformly deliver the modifier to the micropores and surface defects of crystal accumulation, forming a continuous coating layer during the subsequent drying process. In contrast, the dry mixing process can only achieve point-contact physical mixing, resulting in a large number of exposed crystal surfaces. These uncoated active sites become growth points for crystal bridging during long-term moisture absorption and desiccation cycles, ultimately leading to localized hardening and caking.

[0079] Furthermore, the severe caking rate of 88.93% in Comparative Example 1 conversely verifies the necessity of the technical solution of this invention. The Example Group and Comparative Example 2 showed comparable anti-caking performance, both maintaining good physical morphology. Considering the physicochemical data of Test Example 1, the method of this invention achieves the same physical anti-caking effect as traditional high-dosage physical anti-caking agents without introducing insoluble impurities and ensuring solution clarity. This comprehensive advantage of low dosage, high purity, and high anti-caking performance also benefits from the synergistic effect of non-closed dehumidification drying and secondary final mixing and granulation processes in the production process. The former avoids damp-heat agglomeration during drying, while the latter eliminates potential microscopic adhesion, ensuring the loose stability of the product during long-term storage.

[0080] Experiment Example 3: Flowability and Hygroscopicity Test. The specific experimental steps are as follows:

[0081] The fixed funnel method was used for measurement. The funnel was fixed to an iron stand, with the lower outlet at a certain height above the horizontally placed coordinate paper base. The sample to be tested was added to the funnel, allowing the material to flow freely down the funnel until the top of the resulting cone-shaped accumulation touched the lower outlet of the funnel. The average diameter of the bottom of the cone was measured, and the angle of repose α was calculated using the formula tanα=H / R. Each sample was measured three times, and the average value was taken.

[0082] Take a clean weighing bottle and dry it at 105℃ to constant weight. Accurately weigh approximately 10g of the sample to be tested and spread it evenly at the bottom of the weighing bottle, recording the net weight M1. Place the open weighing bottle in a constant temperature and humidity chamber, setting the temperature to 30℃ and the relative humidity to 80%. After 24 hours, remove the bottle, immediately tighten the cap, and weigh it again (M2). Calculate the moisture absorption weight gain rate: W = [(M2 - M1) / M1] x 100%.

[0083] The test results are shown in Table 3 below:

[0084] Sample group Angle of repose α (°) 24-hour moisture absorption weight gain rate (%) Physical appearance observation (after moisture absorption) Example 1 28.4 0.13 Dry the surface and keep it loose. Example 2 31.2 0.19 The surface is slightly damp and there is no stickiness. Example 3 27.6 0.11 The surface is dry and has good fluidity. Comparative Example 1 43.5 0.88 The surface is damp, or even liquefied, and clumps together. Comparative Example 2 30.5 0.72 The surface is damp, and the powder adheres. Comparative Example 3 35.8 0.38 Localized dampness, resulting in particle aggregation

[0085] Table 3 reveals the significant impact of the surface modification process on the properties of the microcrystalline interface. The angles of repose in Examples 1 to 3 range from 27.6° to 31.2°, significantly lower than the 43.5° in Comparative Example 1. The decrease in the angle of repose directly reflects the reduction in interparticle friction, which is attributed to the monolayer or multilayer film formed by sodium dodecyl sulfate molecules on the crystal surface. This film shields the highly active ionic bonding sites on the potassium nitrate crystal surface, smooths the micro-roughness of the crystal surface, and reduces the surface energy by introducing long-chain alkyl groups. Furthermore, the secondary mechanical mixing step at the end of the production process eliminates the fine connections that may form during the drying process through shearing action, further improving the dispersion and flowability of the powder.

[0086] The difference in moisture absorption weight gain rate verifies the effectiveness of the liquid-phase spray film formation process in constructing a hydrophobic barrier. The moisture absorption weight gain rate of the example group remained low at 0.11% to 0.19%, while the moisture absorption weight gain rate of Comparative Example 3, which used direct mixing of dry powder, reached 0.38%, nearly three times that of Example 1; and the completely untreated Comparative Example 1 reached as high as 0.88%. This difference indicates that by simply using physical dry mixing, surfactant molecules are unlikely to cover all crystal surfaces with trace amounts, and the exposed potassium nitrate crystal faces rapidly absorb moisture to form a liquid film in a high-humidity environment. The method described in this invention, by dissolving the modifier into a true solution and spraying it, utilizes the wetting effect of the liquid to ensure the complete coverage of the hydrophobic groups on the crystal surface, thereby effectively blocking the diffusion path of environmental moisture into the crystal interior.

[0087] Although the angle of repose of Comparative Example 2 is close to that of the Example Group, showing a better physical flow-aiding effect, its moisture absorption and weight gain rate remains high. This indicates that the main mechanism of action of insoluble inorganic powders such as talc is to reduce the particle contact area through geometric spacing, rather than changing the surface hydrophilic properties of the base material itself. In contrast, the chemical adsorption film formed by sodium dodecyl sulfate in this invention has the dual functions of reducing friction and hydrophobic moisture barrier. This mechanism based on microscopic surface modification enables the product to achieve anti-caking performance superior to traditional physical mixing techniques without introducing a large amount of insoluble impurities.

[0088] 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. Potassium nitrate with anti-caking properties, characterized in that, The anti-caking potassium nitrate is made by mixing high-purity potassium nitrate crystals and sodium dodecyl sulfate. The high-purity potassium nitrate crystals are the base material, and the sodium dodecyl sulfate is the anti-caking agent. The formulation ratio of the anti-caking potassium nitrate is 10g to 100g of sodium dodecyl sulfate per 1000kg of high-purity potassium nitrate crystals.

2. A method for producing anti-caking potassium nitrate, according to claim 1, characterized in that, Includes the following steps: S1. Dissolve the sodium dodecyl sulfate in pure water according to the formula to prepare an anti-caking modified solution; S2. The anti-caking modified liquid is evenly sprayed onto the surface of the high-purity potassium nitrate crystals and primary mixing is performed to obtain a wet mixed material. S3. Place the wet mixture in a heating environment to remove moisture and dry it, so that the moisture evaporates and a hydrophobic film is formed on the crystal surface to obtain the dried material. S4. The dried material is then subjected to secondary mixing to obtain anti-caking potassium nitrate.

3. The method for producing potassium nitrate with anti-caking properties according to claim 2, characterized in that, The method for preparing the high-purity potassium nitrate crystals is as follows: Industrial potassium nitrate is dissolved in water, and ammonium nitrate is added to react at 80°C to 90°C to remove nitrite. Ammonium sulfide was then added and reacted at 80°C to 90°C to remove heavy metal ions; Then add potassium carbonate and potassium hydroxide in sequence and keep it at a gentle boil to remove calcium and magnesium ions and ammonium ions; Finally, zinc oxide and activated carbon are added to remove excess sulfur ions and organic impurities. The filtered clear liquid is then neutralized, concentrated, crystallized, and centrifuged to obtain the high-purity potassium nitrate crystals.

4. The method for producing potassium nitrate with anti-caking properties according to claim 2, characterized in that, The specific operation for preparing the modified solution in step S1 is as follows: weigh the sodium dodecyl sulfate, add it to pure water at a temperature of 40°C to 50°C and stir until it is completely dissolved to prepare a transparent solution.

5. The method for producing potassium nitrate with anti-caking properties according to claim 3, characterized in that, The specific steps for removing calcium and magnesium ions and ammonium ions are as follows: First, add potassium carbonate to adjust the pH of the solution to 8.5 to 9.0, then add potassium hydroxide to adjust the pH of the solution to be greater than 12, and keep it at a gentle boil until no ammonia smell is emitted.

6. The method for producing potassium nitrate with anti-caking properties according to claim 3, characterized in that, The specific steps for neutralization, concentration, crystallization, and centrifugation of the filtered clear liquid are as follows: The pH of the filtered clear liquid was adjusted to 7.0 to 7.2 using analytical grade nitric acid. The pH-adjusted solution was concentrated under reduced pressure to a density of 1.30 g / cm³ to 1.32 g / cm³. The high-purity potassium nitrate crystals were obtained by cooling and crystallizing and centrifuging.

7. The method for producing potassium nitrate with anti-caking properties according to claim 2, characterized in that, The specific operation of the initial mixing and coating in step S2 adopts the layer-laying spray method, in which the high-purity potassium nitrate crystals are laid in layers, and a certain amount of the anti-caking modification liquid is sprayed in after each layer of crystals is laid. After spraying, mechanical stirring and mixing are carried out at room temperature for more than 2 hours.

8. The method for producing potassium nitrate with anti-caking properties according to claim 7, characterized in that, In the layer-laying spray method, the weight of each layer of high-purity potassium nitrate crystals is 50kg to 100kg, and the amount of the anti-caking modifying liquid used is such that 10g to 100g of sodium dodecyl sulfate is consumed for every 1000kg of high-purity potassium nitrate crystals.

9. The method for producing potassium nitrate with anti-caking properties according to claim 2, characterized in that, The specific conditions for drying and film formation in step S3 are as follows: the wet mixed material is spread flat on a drying tray and placed in an oven at 90°C for drying for more than 24 hours, and the oven door is kept in a non-sealed state with a dehumidification channel during the drying process.

10. The method for producing potassium nitrate with anti-caking properties according to claim 2, characterized in that, The specific operation of final mixing and granulation in step S4 is as follows: after passing the dried material through a vibrating screen, it is mechanically rotated and mixed at room temperature for more than 2 hours.

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