Highly loose, long-shelf-life powdered potassium nitrate, water-soluble anti-caking agent

Abstract

This invention provides a water-soluble anti-caking agent for preparing highly loose, long-shelf-life powdered potassium nitrate. Its key feature is that the anti-caking agent is composed of a crystal stabilizer, an anti-adhesion wetting agent, a lubricating and water-repellent agent, and a high-heat resistant agent. It addresses the shortcomings of previous anti-caking agents for powdered potassium nitrate, such as high dosage, poor anti-caking effect, presence of undissolved floating matter in aqueous solutions, and short shelf life of the resulting powdered potassium nitrate. This invention uses a crystal stabilizer as an effective anti-crystallization material for powdered potassium nitrate; and adds a key non-ionic, low-melting-point lubricating and water-repellent agent. This allows the invention to be implemented using a safe post-addition process below 60°C after potassium nitrate drying, resulting in powdered, loose potassium nitrate with a shelf life of six months and a looseness maintained above 95%. This invention is suitable as an effective moisture-proof and anti-caking agent for preparing powdered, loose potassium nitrate. The addition concentration of this invention is 0.07%–0.15%.

Description

Technical Field

[0001] This invention relates to an anti-caking agent for potassium nitrate, specifically a surfactant for improving the moisture-proof and anti-caking properties of easily agglomerated solid inorganic salt powders. More particularly, it is a water-soluble anti-caking agent for preparing highly loose, long-shelf-life powdered potassium nitrate, which can also be used as a dispersant and anti-caking agent in the processing of inorganic water-soluble fertilizers. This anti-caking agent is composed of a crystal stabilizer, an anti-adhesion wetting agent, a lubricating and water-repellent agent, and a high-heat resistant agent. Technical Background

[0002] In modern times, many scientists and engineers both domestically and internationally have conducted extensive research on additives to address the caking defects of potassium nitrate. Currently, domestic and international manufacturers commonly use potassium carbonate as an anti-caking agent, with an addition concentration of approximately 1.0% to 2.0%. However, a serious defect still exists: swelling occurs during storage due to the low thermal decomposition temperature of carbonates. Many potassium nitrate manufacturers currently add 0.5% magnesium sulfate as an anti-caking agent, but its shelf life is only about one month, which cannot meet the requirement of at least three months for long-distance overseas transport. Extensive research has revealed that using various surfactants is an effective technical approach to improve the caking defects of potassium nitrate. Since the early 1990s, specialized research has been conducted on the engineering application of various surfactants to solve the caking defects of inorganic salts, and certain technological progress has been achieved. In recent years, Chinese invention patent ZL201010294980.2 (authorized on May 2, 2012) describes a composite modifier that uses a cationic surfactant, a primary amine weak acid salt, as an effective anti-crystallization agent for potassium nitrate. This allows for the production of highly loose powdered potassium nitrate with a shelf life exceeding six months. Domestic production has already begun, with exports to over ten countries. However, the poor water solubility of this cationic surfactant results in trace amounts of floating matter in the aqueous solution of the loose potassium nitrate, hindering its use in drip irrigation fertilizers where complete water solubility is required, leading to user dissatisfaction. In the past two years, foreign researchers have successfully developed a highly water-soluble powder called AkzoAg, which is imported in large quantities. However, its practical application suffers from significant drawbacks, including a strong, irritating odor due to the presence of highly toxic coagulant and a flammable hazard. While these technological advancements and inventions have made some improvements, none have achieved complete success. Therefore, further research into anti-caking technology for powdered potassium nitrate has become an urgent and pressing technical challenge. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and to design a moisture-proof and anti-caking agent that enables powdered potassium nitrate to maintain excellent looseness, complete water solubility, and resistance to moisture absorption and clumping during a six-month storage period, while meeting environmental protection requirements and achieving excellent overall performance.

[0004] The invention aims to design and prepare a multi-component anti-caking system with complementary properties to address the agglomeration defect of powdered potassium nitrate. The goal is to create a homogeneous mixed-crystal structure between potassium nitrate and the anti-caking agent, forming a moisture-proof and anti-caking potassium nitrate particle molecular model. To this end, the surface of the mixed-crystal must be coated or encapsulated with a water-resistant and moisture-proof film, and the stabilizer and wetting agent inside the mixed crystal must be able to control the crystal transformation characteristics of potassium nitrate. Therefore, the anti-caking agent system must consist of a lubricating and water-resistant agent, a high-heat resistant agent, a crystal form stabilizer that controls crystal form, and an anti-adhesion wetting agent that assists in controlling crystal form. The design of crystal stabilizers and lubricating water-resistant agents is the most critical: the main function of crystal stabilizers is to control the irreversible or slowed change of potassium nitrate crystal form near the phase transition point, maintaining the modified loose potassium nitrate with a good stable crystal form; another key low-melting-point nonionic organic lubricating water-resistant agent can form a water-resistant and moisture-proof film, effectively coating the surface of easily agglomerated inorganic potassium nitrate particles, preventing the intrusion of environmental moisture, and keeping the modified loose potassium in a stable loose state during storage, without agglomeration or hardening; the role of high-heat resistant agents is to ensure and provide thermal safety for the modification process of flammable oxidizing potassium nitrate.

[0005] Based on the above concept, a multi-component, fully water-soluble, powdered anti-caking system with complementary component properties was designed and prepared: the stabilizer, which plays a major role in crystal control, must be water-soluble, heat-resistant, and have high diffusion capacity, containing polar groups -SO4H, -SO3H, and -PO4H. Planar anionic surfactants; anti-adhesion wetting agents that reduce the coefficient of intermolecular friction, generally using water-soluble detergents or leveling agents with different cloud points, such as alkylphenol polyoxyethylene ethers, alkyl phosphates or sodium isobutylnaphthalene sulfonate, sodium p-methyl fatty amide benzene sulfonate, fatty alcohol polyoxyethylene ethers, OP-35, saponins, etc.; lubricating and water-repellent agents using low-melting-point nonionic film-forming materials, such as sodium polybutenoate, fatty alcohol and propylene oxide condensate dispersants, sodium dodecylbenzene sulfonate, carboxymethyl cellulose, sodium polyacrylate, polyester, alginic acid, hydroxypropyl cellulose, etc.; high-heat resistant agents mostly have high heat capacity and difficult-to-burn chemical flame-retardant functional additives, such as decabromodiphenyl ether, brominated polystyrene, dibromopropyl isocyanate, sodium methylene benzyl naphthalene sulfonate, sodium benzyl naphthalene sulfonate formaldehyde condensate, sodium benzyl naphthalene sulfonate condensate, etc.

[0006] The composition of the water-soluble anti-caking agent for powdered potassium nitrate of this invention, by mass %, is as follows:

[0007] 30-65 Crystal form stabilizers: sodium lignosulfonate, sodium methylene disulfonate, sodium diphenyl succinate sulfonate, or sodium fatty acid formaldehyde sulfonate;

[0008] 5-15 Anti-adhesion wetting agents: alkylphenol polyoxyethylene ether or alkyl phosphate or sodium isobutylnaphthalene sulfonate or sodium p-methyl fatty amide benzene sulfonate;

[0009] 28-50 Lubricating and water-repellent agents: sodium polybutenoate or fatty alcohol condensate with propylene oxide or sodium dodecylbenzene sulfonate or carboxymethyl cellulose;

[0010] 2-5 High-heat resistant agents: sodium methylene benzyl naphthalene sulfonate or sodium benzyl naphthalene sulfonate formaldehyde condensate or sodium benzyl naphthalene sulfonate condensate or dispersant S.

[0011] The optimal components of this invention, by mass % are:

[0012]

[0013] The concept of the preparation method of the present invention is as follows: First, the high-heat resistant agent is dried. Then, the anti-adhesion wetting agent and the lubricating water-resistant agent are pulverized to a specified fineness in a pulverizer. Then, according to the composition (mass %) ratio, the measured crystal stabilizer, anti-adhesion wetting agent, lubricating water-resistant agent and high-heat resistant agent are added together into a mixer and stirred for a specified time to obtain the powdered anti-caking agent of the present invention.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] 1. Planar anionic surfactants containing polar groups -SO4H, -SO3H, and -PO4H were successfully used as crystal stabilizers for potassium nitrate.

[0016] 2. The invention successfully utilizes nonionic surfactants containing fatty alcohols and propylene oxide condensates as low-melting-point lubricating and water-repellent agents for powdered potassium nitrate, enabling the invention to be implemented using a safe post-addition process at temperatures below 60°C after potassium nitrate drying.

[0017] 3. The water-soluble, 100% loose potassium nitrate product prepared by this invention has a shelf life of six months without clumping or hardening, and its looseness is above 95%.

[0018] 4. The loose potassium nitrate products prepared by this invention can be obtained by dry mixing or by spray feeding in an aqueous phase to modify powdered potassium nitrate, thus making it easy to promote and apply.

[0019] 5. The raw materials are abundant and entirely sourced domestically. The dosage is small (the concentration added is 0.07% to 0.15% of the mass of powdered potassium nitrate) but the application effect is obvious. Example

[0020] 1. Implement according to the following optimal composition (mass%):

[0021]

[0022] Preparation of the present invention: 30g of sodium benzyl naphthalene sulfonate formaldehyde condensate was dried in an oven at 60-70°C for 4 hours. Then, it was added together with 600g of sodium fatty acid formaldehyde sulfonate, 300g of carboxymethyl cellulose (crushed to a fineness of 60 mesh), and 70g of alkylphenol polyoxyethylene ether into a double-helix mixing mixer and stirred at room temperature for 20-25 minutes. The resulting product was the water-soluble anti-caking agent of the present invention.

[0023] This invention enables the production of loose, powdered potassium nitrate using a post-addition process after the material has been dried and the temperature is below 60°C. Specifically, in a heat-dissipating mixing tank, 0.7 tons of dried potassium nitrate and 0.7 kg of the anti-caking agent (concentration of 0.07%–0.15%) of this invention are simultaneously added to each tank. The material is stirred and mixed at 50–56°C for 5–10 minutes, then discharged and packaged (50 kg per bag). The product is white in appearance. According to the industrial potassium nitrate technical standard GB1918-2911, on-site testing shows a looseness of 100%, moisture of 0.18%, water-insoluble matter of 0.05%, water solubility of 100%, and a pH of 6.5, indicating neutrality. After six months of storage, the product's physical appearance remains unchanged, with a looseness of 95% (high-quality product looseness index ≥80%), without clumping or hardening.

[0024] 2. Implement according to the following composition (mass%):

[0025]

[0026] The preparation of the present invention is described in Example 1.

[0027] Using the product of this invention, the water solubility of this invention was tested using conventional methods for testing the solubility of solid powders in water. The test results are shown in Table 1.

[0028] Table 1 Water solubility properties of the product

[0029]

[0030] 3. Implement according to the following composition (mass%):

[0031]

[0032] The preparation of the present invention is described in Example 1.

[0033] Using this invention, loose potassium nitrate is produced by an aqueous phase method.

[0034] Implementation method: This refers to the aqueous phase method for producing powdered potassium nitrate, and the implementation process is as follows:

[0035] First, prepare the aqueous solution (also known as a spray): Before use, dissolve the anti-caking powder in water at a ratio of 1:2. Add a certain amount of demineralized water to the mixing equipment according to the ratio, start stirring, and then slowly add the anti-caking agent. Stir for approximately 10 minutes every two hours. It will completely dissolve in about 16 hours, resulting in a transparent, pale yellow solution with a pH of approximately 6.5, indicating neutrality. The dosage is 0.12%–0.15%. Then, apply nitric acid as a spray agent. Potassium modification: A variable frequency peristaltic pump with a pneumatic spraying device must be used. The addition amount should be controlled at 0.12% to 0.15%. The completely dissolved anti-caking agent solution should be added evenly from the dryer inlet using a pneumatic spraying device and thoroughly mixed with the centrifuged wet material (containing approximately 3.0% to 3.5% water) to achieve the modification effect. Then, the material enters the dryer (hot air temperature approximately 180℃). After drying, the material enters a cooling fluidized bed. It is best to reduce the temperature of the modified potassium nitrate material to below 45℃ before packaging (50Kg per bag). The product has a white appearance. According to the technical standard GB1918-2011 for industrial potassium nitrate, the on-site test showed a looseness of 100%, moisture of 0.19%, chloride ion content of 0.08%, water-insoluble matter of 0.01%, water solubility of 100%, and a solution pH of 6.5, indicating neutrality. Storage performance: After six months of storage, the product's physical appearance remained unchanged, with a looseness of 95% (high-quality products have a looseness index ≥80%). A comparison of the looseness during storage with products without anti-caking agents or without the anti-caking agent of this invention is shown in Table 2.

[0036] Table 2. Looseness of the product during storage period

[0037]

[0038] 4. Implement according to the following composition (mass%):

[0039]

[0040] The preparation of the present invention is described in Example 1.

[0041] The thermal decomposition kinetics of the product of this invention were studied using a combined thermogravimetric analysis (TGA-DTA) method with a Q600 differential scanning calorimeter. The results of the thermal decomposition temperature detection are shown in Table 3.

[0042] Table 3 Thermal decomposition properties of the products

[0043]

[0044] As can be seen from Table 3, the product of this invention is more heat-resistant than previous products. Its initial thermal decomposition temperature of 349.57℃ is much higher than the hot air drying temperature of potassium nitrate (170-180℃), so it is safe to use during production.

Claims

1. A water-soluble anti-caking agent for powdered potassium nitrate, characterized in that: This anti-caking agent is composed of a crystal stabilizer, an anti-adhesion wetting agent, a lubricating and water-repellent agent, and a high-heat resistant agent. Its components, by mass % are: 60 Crystalline stabilizer: Sodium fatty acid formaldehyde sulfonate; 7. Anti-adhesion wetting agent: Alkylphenol polyoxyethylene ether; 30. Lubricating and water-repellent agent: Carboxymethyl cellulose; 3. High-heat resistant agent: sodium benzyl naphthalene sulfonate formaldehyde condensate; During the use of the anti-caking agent, a post-addition process is adopted after the material is dried and the temperature is below 60°C: that is, in each heat dissipation mixing tank, 0.7t of dried potassium nitrate and 0.7kg of anti-caking agent are added simultaneously. The concentration of the anti-caking agent is 0.1%. The material temperature is 50-56°C and the mixture is stirred for 5-10 minutes to obtain the product. The potassium nitrate and anti-caking agent in the product form a uniform mixed crystal structure. The product is white in appearance, 100% water-soluble, and its physical appearance remains unchanged after 6 months of storage, with a looseness of 95%.

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