Anti-caking urotropine, preparation method thereof and anti-caking additive used in anti-caking urotropine

Abstract

The invention belongs to the field of fine chemical processing, and particularly relates to anti-caking urotropine, a preparation method thereof and an anti-caking additive used by the anti-caking urotropine. The method comprises the following steps: putting urotropine particles into a fluidized bed for fluidization, taking an anti-caking additive as a spraying agent, carrying out fluidized bed top spraying treatment on the urotropine particles, so that the surfaces of the urotropine particles are uniformly covered with the anti-caking additive, and then drying and curing the urotropine particles to obtain the anti-caking urotropine. According to the invention, a ternary composite anti-caking system is constructed through a multi-stage interface regulation strategy, nano-silica is mixed with zinc stearate and polyethylene glycol, and the mixture uniformly covers the surfaces of urotropine particles to form a composite isolation layer, so that the risk of moisture absorption and caking of urotropine is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of fine chemical processing, and particularly relates to an anti-caking hexamine and its preparation method, and an anti-caking additive used therefor. Background Art

[0002] Hexamine, with the chemical name of hexamethylenetetramine, is in the form of white crystalline powder. Due to its strong hygroscopicity, it is extremely easy to absorb moisture and cake in the air, thereby affecting its quality and use performance. An anti-caking agent is one or more substances, and its function is to ensure the fluidity of hexamine in the form of particles or powder during storage and handling. The action mechanism of the anti-caking agent includes: participating in the crystal formation process, adjusting the crystal growth rate, and thus changing the crystal morphology; forming a hydrophobic layer on the particle surface to hinder the exchange of crystals with external moisture; forming a protective film on the particle surface to achieve mechanical isolation between particles; reducing the surface tension of the solution on the particle surface, changing the solid-liquid contact angle, and thus reducing the capillary adsorption force, etc.

[0003] Patent CN117510510A discloses a method for preparing non-caking sand-like methenamine. The invention belongs to the field of organic synthesis technology and focuses on the preparation process of methenamine. The specific preparation steps are as follows: First, 80-100 mesh hexamine and a nano-inorganic particle nucleating agent are thoroughly mixed in a mass ratio of 100:(0.02-0.08) and stirred to obtain a nucleated hexamine. Next, a saturated hexamine solution is prepared. Subsequently, the saturated hexamine solution is mixed with an anti-caking agent in a volume-to-mass ratio of 20 mL:(0.2-0.8) g to prepare an anti-caking agent solution. The saturated hexamine solution is then added to the nucleated hexamine under continuous stirring to form a hexamine paste. The mixture is then sieved and filtered through a 60-mesh sieve, and the filtrate is returned to the saturated hexamine solution for reuse. Hexamine particles larger than 60 mesh are collected. Finally, a mist of the anti-caking agent solution is sprayed during the dehydration process to obtain the desired product. However, a thorough analysis of this preparation method reveals several areas for improvement. First, the stated ratio of 50 g:100 mL of saturated hexamine solution is inaccurate, potentially adversely affecting subsequent preparation processes. Second, this method is only applicable to finished hexamine products with a particle size greater than 60 mesh, making it relatively narrow in scope. Third, the entire preparation process requires the use of 80-100 mesh hexamine for the preparation of nucleated hexamine, the preparation of saturated hexamine solutions, and the preparation of hexamine pastes. This means that crystallized hexamine must be mixed with water before being crystallized again. This not only duplicates the process but also complicates the operation, increasing production costs and time. Fourth, simply spraying a mist of anti-caking agent solution during the dehydration stage to produce the finished product makes it difficult to effectively control the moisture content. In practice, moisture is the most critical factor causing product agglomeration, and improper moisture control directly impacts product quality and storage stability. Summary of the Invention

[0004] The technical solution of the present invention aims to solve the problem of easy agglomeration of hexamethylenetetramine during airflow drying, storage in silos, warehouses and maritime transportation during production, and to prevent the product from agglomerating and bridging and maintaining its loose state, thereby providing an anti-caking additive.

[0005] The main objectives of the present invention are: 1. A hexamethylenetetramine with good anti-caking performance can be prepared; 2. Optimize the preparation process of anti-caking additives; 3. Improve the preparation process of anti-caking additives.

[0006] To achieve the above objectives, the present invention adopts the following technical solutions.

[0007] A preparation method of anti-caking hexamine The method includes: Placing hexamine particles in a fluidized bed for fluidization, using an anti-caking additive as a spraying agent, performing top spraying treatment on the hexamine particles in the fluidized bed, so that the anti-caking additive uniformly covers the surface of the hexamine particles, and then drying and curing them to obtain anti-caking hexamine.

[0008] Preferably, The fluidization process controls the fluidization air velocity to be 0.8 - 1.2 m / s; The dosage of the anti-caking additive is 0.5 - 1.0 wt% of hexamine; The spraying pressure during the spraying treatment is 0.5 - 0.7 MPa.

[0009] Preferably, The drying and curing adopt gradient heating and heat preservation treatment; The gradient heating and heat preservation treatment is carried out successively with heat preservation at 28 - 32 °C for 25 - 35 min, heat preservation at 42 - 47 °C for 25 - 35 min, and heat preservation at 55 - 65 °C for 55 - 65 min.

[0010] An anti-caking additive The anti-caking additive is prepared by the following method: (1) Mixing a polypeptide and an acyclic carboxylic acid in proportion to form a mixture, and performing heat preservation copolymerization to prepare an organic copolymer; (2) Mixing a non-metal oxide, an organic zinc, and a fatty alcohol derivative in proportion, and performing ultrasonic treatment to prepare a modified inorganic material; (3) Mixing the organic copolymer, the modified inorganic material, and a polymer in proportion to prepare the anti-caking additive.

[0011] Preferably, The polypeptide in step (1) is polyaspartic acid; The acyclic carboxylic acid in step (1) is palmitic acid; The polypeptide and the acyclic carboxylic acid in step (1) are mixed evenly in a mass ratio of (2.4 - 2.8):1.

[0012] Preferably, The heat preservation copolymerization in step (1) is carried out in an inert atmosphere at a temperature of 55 - 65 °C, using 1,2-dichloroethane at 1.5 - 2.5 wt% of the mass of the mixture as a catalyst, and performing a heat preservation reaction for 4 - 6 h.

[0013] Preferably, The non-metal oxide in step (2) is nano-silica; The zinc organic compound described in step (2) is zinc stearate; The fatty alcohol derivative described in step (2) is ethanol; The non-metal oxide, zinc organic compound and fatty alcohol derivative described in step (2) are uniformly mixed in a mass ratio of 1:(0.03 - 0.07):30.

[0014] Preferably, For the ultrasonic treatment in step (2), the ultrasonic power is controlled at 50 - 80 W, and the ultrasonic duration is 0.5 - 1 h.

[0015] Preferably, The organic copolymer, modified inorganic material and polymer described in step (3) are uniformly mixed in a mass ratio of (1.5 - 2.5):1:(3.9 - 4.1).

[0016] An anti-caking hexamine.

[0017] Hexamine, chemically named hexamethylenetetramine, appears as a white crystalline powder. Due to its strong hygroscopic property, when exposed to air, it is extremely easy to absorb water vapor in the air and form lumps. This change will not only have an adverse impact on the chemical quality of hexamine itself, but also significantly weaken its performance in actual application scenarios. To effectively solve the caking problem of hexamine, adding specific types of anti-caking agents to the hexamine system has become one of the commonly used strategies in existing technical solutions. Among them, benzoic acid and some specific surfactants, such as sodium dodecylbenzenesulfonate, OP-10, etc., have been verified by practice to show excellent anti-caking efficiency. Analyzing from the mechanism of action, these anti-caking agents can reduce the surface energy of hexamine particles, thereby reducing their tendency to adsorb moisture in the surrounding environment. Particularly importantly, during the drying process, these anti-caking agents can play a unique role, causing the hexamine particles to bond with each other and finally form a sandy particle structure. This carefully constructed special microstructure essentially further reduces the contact area between hexamine and external water vapor, thereby greatly improving the overall anti-caking ability of hexamine and ensuring its stability and reliability during storage and use.

[0018] The present invention provides an anti-caking additive for surface modification of hexamine and its application process, that is, it is used for the preparation of anti-caking hexamine.

[0019] In the technical solution of the present invention, the core lies in the formation of a hydrogen bond network on the surface of hexamine by organic acids, and a barrier layer is formed through the dual actions of physical adsorption and chemical bond coordination, changing the surface charge distribution of hexamine crystals and reducing the caking rate. This method relies on the free radical graft copolymerization reaction between polyaspartic acid and palmitic acid to successfully synthesize an organic copolymer with an amphiphilic block structure. In this organic copolymer, the palmitic acid chain segment plays a key role. It can provide a hydrophobic surface, reduce the hydrophilicity of hexamine particles, and build an effective hydrophobic barrier around the particles. This greatly reduces the contact opportunity between moisture and hexamine particles, thereby reducing its moisture absorption risk. At the same time, the carboxylic acid groups carried by polyaspartic acid exhibit unique functional characteristics. These carboxylic acid groups have strong adsorption ability and can specifically adsorb trace metal ions on the surface of hexamine particles. Since crystal bridge growth is often triggered by ion migration, the adsorption of polyaspartic acid on metal ions effectively inhibits the ion migration process, and thus inhibits the growth of crystal bridges from the root cause, preventing the caking of hexamine particles due to crystal bridge connection. When the organic copolymer is treated by the spraying process, it will tightly adsorb on the surface of hexamine particles by intermolecular forces such as hydrogen bonds and van der Waals forces. During this process, the organic copolymer will self-assemble on the particle surface to form a dense hydrophobic film, isolating the hexamine particles from the external humid environment and completing the coating of the crystal surface. In addition, the negatively charged carboxylic acid groups carried by polyaspartic acid also have another important function. These negatively charged groups will enhance the electrostatic repulsion between hexamine particles, causing the particles to move away from each other, thus significantly reducing the occurrence of particle agglomeration. Moreover, polyaspartic acid itself has a certain hygroscopicity, and it can locally regulate the humidity of the microenvironment around hexamine particles. When the environmental humidity is high, polyaspartic acid will absorb some moisture and reduce the water vapor concentration around the particles; while when the environmental humidity is low, it will slowly release moisture to maintain the relative stability of the microenvironment humidity. That is, the hygroscopic behavior of polyaspartic acid conforms to the characteristics of the hygroscopic-desorption isotherm. This dynamic humidity regulation mechanism effectively delays the moisture absorption process of hexamine, ensures its good physical stability for a long time, and can effectively reduce the local humidity on the particle surface, further inhibiting the moisture absorption process.

[0020] In the technical solution of the present invention, another core lies in the selection and modification of nano-silica so that it can enhance the anti-caking effect of the organic copolymer on hexamine particles. As a high-performance inorganic nano-material, nano-silica has excellent surface effects, small size effects, macroscopic quantum tunneling effects, and unique physical and chemical properties. These properties enable nano-silica to exhibit great application potential in enhancing material strength, improving material toughness, improving material processing performance, and endowing materials with special functions. Based on the multi-level interface regulation strategy, the present invention constructs a ternary composite anti-caking system of nano-silica-zinc stearate-polyethylene glycol. In the present invention, zinc stearate molecules are anchored on the surface of silica by carboxylate zinc coordination bonds through mechanochemical action. In the present invention, as a special non-metal oxide, nano-silica is precisely mixed with zinc stearate and ethanol in a specific ratio, and an ultrasonic treatment process is implemented, thereby preparing a modified inorganic material. This modification process aims to endow nano-silica with more complex and diverse surface chemical properties, while significantly improving its dispersion performance in the system. The modified nano-silica can uniformly cover the surface of hexamine particles in the actual application scenario. In this way, the action effects of van der Waals forces and capillary forces between particles are effectively weakened, and a physical isolation layer is formed between hexamine particles. At the same time, after zinc stearate participates in the modification, by reducing the surface energy of hexamine particles, the formation of crystal bridges caused by water adsorption is effectively inhibited, a hydrophobic barrier is constructed, and the possibility of hexamine absorbing moisture and caking is greatly reduced. In addition, on the one hand, polyethylene glycol acts as a stabilizer for additives, which can ensure the chemical stability and physical stability of the entire additive system, and ensure the continuous and stable exertion of the synergistic effect between components; on the other hand, polyethylene glycol acts as a trace moisture absorption regulator, preferentially adsorbing moisture in the surrounding environment, forming a local low-humidity microenvironment around hexamine particles, further delaying the moisture absorption process of hexamine, and improving its anti-caking performance.

[0021] The advantages of the present invention are as follows: using organic acids to form hydrogen bond networks, changing the surface charge distribution of hexamine through the dual actions of physical adsorption and chemical bond coordination, and reducing the caking rate; synthesizing an amphiphilic block-structured organic copolymer through the free radical graft copolymerization reaction of polyaspartic acid and palmitic acid, where the palmitic acid chain segment provides a hydrophobic surface, and the carboxyl groups of polyaspartic acid adsorb metal ions to inhibit the growth of crystal bridges, thereby preventing particle caking; modifying nano-silica to enhance the anti-caking effect of the organic copolymer, constructing a ternary composite anti-caking system through a multi-level interface regulation strategy, and after mixing nano-silica with zinc stearate and polyethylene glycol, uniformly covering the surface of hexamine particles to form a composite isolation layer, reducing the risk of moisture absorption and caking. Detailed implementation mode

[0022] The present invention will be further described in detail below in conjunction with specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention described below are generally only a part of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0023] Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available or raw materials that can be obtained by those skilled in the art; unless otherwise specified, the methods used in the embodiments of the present invention are all methods mastered by those skilled in the art.

[0024] Example 1: An anti-caking additive, The method includes: (1) Mix polyaspartic acid and palmitic acid evenly at a mass ratio of 2.4:1 to obtain a mixture. Under the environmental conditions of a nitrogen atmosphere and a temperature of 55 °C, use 1,2-dichloroethane at 2 wt% of the mass of the mixture as a catalyst, and keep the temperature for 6 h to prepare an organic copolymer; (2) Mix nano-silica, zinc stearate and ethanol evenly at a mass ratio of 1:0.03:30, perform ultrasonic treatment at 50 W for 1 h, filter and dry to obtain a modified inorganic material; (3) Mix the organic copolymer, the modified inorganic material and a 0.5% polyethylene glycol aqueous solution evenly at a mass ratio of 1.5:1:3.9 to prepare an anti-caking additive.

[0025] Example 2: An anti-caking additive, The method includes: (1) Mix polyaspartic acid and palmitic acid evenly at a mass ratio of 2.6:1 to obtain a mixture. Under the environmental conditions of a nitrogen atmosphere and a temperature of 60 °C, use 1,2-dichloroethane at 2 wt% of the mass of the mixture as a catalyst, and keep the temperature for 5 h to prepare an organic copolymer; (2) Mix nano-silica, zinc stearate and ethanol evenly at a mass ratio of 1:0.05:30, perform ultrasonic treatment at 60 W for 0.75 h, filter and dry to obtain a modified inorganic material; (3) Mix the organic copolymer, the modified inorganic material and a 0.5% polyethylene glycol aqueous solution evenly at a mass ratio of 2:1:4 to prepare an anti-caking additive.

[0026] Example 3: An anti-caking additive, The method includes: (1)Mix polyaspartic acid and palmitic acid evenly according to a mass ratio of 2.8:1 to obtain a mixture. Under the environmental conditions of a nitrogen atmosphere and a temperature of 65 °C, use 1,2-dichloroethane accounting for 2 wt% of the mixture mass as a catalyst, and keep the temperature for 4 h to prepare an organic copolymer; (2)Mix nano-silica, zinc stearate and ethanol evenly according to a mass ratio of 1:0.07:30, perform ultrasonic treatment at 50 W for 1 h, filter and dry to obtain a modified inorganic material; (3)Mix the organic copolymer, the modified inorganic material and a 0.5% polyethylene glycol aqueous solution evenly according to a mass ratio of 2.5:1:4.1 to prepare an anti-caking additive.

[0027] Application Example 1: A preparation method of anti-caking hexamine, and the specific operation steps are as follows.

[0028] Place 120-mesh hexamine particles in a fluidized bed for fluidization. Use the anti-caking additive prepared in Examples 1 to 3 as a spraying agent, and the addition amount is 1.0 wt% of the hexamine mass. Perform fluidized bed spraying under the environmental conditions of a fluidization gas velocity of 1 m / s and a spraying pressure of 0.5 MPa. After spraying, heat up in three gradients of 30 °C, 45 °C, and 60 °C in sequence and keep the temperature. The heat preservation treatment duration is controlled at 30 min, 30 min, and 45 min in each gradient in sequence to achieve drying and coating curing, and finally obtain an anti-caking hexamine product with a low surface energy and a stable crystal lattice structure as a test sample. Another blank group is set up, without using the additive, and only use 120-mesh hexamine particle products as test samples to directly perform surface energy, caking rate, fluidity detection and biodegradation rate detection. The specific characterization results are as follows.

[0029]

[0030] Caking rate: Weigh the test samples and record the weighing results. Divide each group of test samples into two parts and place them in two simulation boxes with a temperature of 40 °C and an environmental relative humidity of 75% and a temperature of 40 °C and an environmental relative humidity of 90% for 30 d. Finally, place the test samples in a constant temperature environment of 60 °C for 45 min of drying treatment to remove surface moisture. After the test samples are fully dried, quickly pass them through a filter screen with a pore size of 100 meshes for sieving separation. Weigh and record the data of the caked part that fails to pass through the sieve obtained by the filter screen sieving separation, and calculate the caking rate according to the following formula:

[0031] In the formula: ——Mass of the caked part, g; ——Mass of the test sample, g.

[0032]

[0033] Liquidity detection: Referring to the detection standard in ISO 4324 "Surface active agents - Powders and granules - Determination of angle of repose", the performance of Examples 1 to 3 and the blank group was detected, and the characterization results are as follows.

[0034]

[0035] Biodegradation rate detection: Referring to the construction of the microbial flora in ISO-14855-1-2012 "Determination of the ultimate aerobic biodegradability of materials under controlled composting conditions - Method by measuring the evolved carbon dioxide", the test samples in the examples of this application were placed in this microbial environment, and the degradation rate was detected on the 30th day and the 60th day. The characterization results are as follows.

[0036]

[0037] The above standard sample is the anti-caking additive prepared in Example 2.

[0038] Analyzing the above characterization results, compared with the blank control group, after applying the anti-caking additive provided by the present invention, the surface energy of the hexamine particles is significantly reduced, the caking rate drops sharply, the fluidity is significantly optimized, and at the same time, good biodegradability is also exhibited. Specifically analyzing the characterization data, the surface energies of the hexamine particles in Examples 1 to 3 are reduced to 27 mN / m, 26 mN / m, and 28 mN / m respectively, and the surface energy of the blank control group is as high as 72 mN / m. After using the additive of the present invention, the reduction amplitude of the surface energy of the hexamine particles is extremely significant. Under the conditions of simulating different environmental conditions, that is, when the temperature is set at 40 °C and the environmental relative humidity is 75% and 90% respectively, the caking rates of the hexamine in Examples 1 to 3 are far lower than those of the blank group. By comparing the characterization results of multiple fluidity detections such as the angle of repose, Hausner ratio, and compressive strength, after using the anti-caking additive of the present invention, the angle of repose of the hexamine particles is significantly reduced, the Hausner ratio is significantly decreased, and the compressive strength is weakened, resulting in a significant improvement in the fluidity of the hexamine particles. In addition, through in-depth analysis of the characterization data of the control standard samples and the blank group, it is found that the data measured by the blank group reflects the degradation rate of hexamine in the microbial environment. In the microbial environment, the degradation degree of hexamine is extremely limited, and almost no obvious degradation phenomenon can be observed. Hexamine releases formaldehyde during hydrolysis, and almost all bacteria and fungi show a high degree of sensitivity to the formaldehyde produced after hexamine hydrolysis. The non-specific antibacterial properties of formaldehyde can significantly interfere with the physiological metabolism process of microorganisms, thereby inhibiting the growth and reproduction of bacteria and fungi, making it difficult for microorganisms to effectively degrade hexamine. However, the additive prepared by the present invention exhibits excellent biodegradability by reasonably utilizing the synergistic effect of polyaspartic acid and other components. Further analysis of the characterization data of Examples 1 to 3 shows that in the technical system of the present invention, the anti-caking additive can significantly reduce the surface energy of the hexamine particles, fundamentally inhibiting the formation of crystal bridges caused by water adsorption. This additive can build a dense hydrophobic barrier on the surface of the hexamine particles, effectively preventing the intrusion of external moisture, thereby preventing the hydrolysis reaction of hexamine. Due to its unique molecular structure and biodegradation characteristics, polyaspartic acid has a significant synergistic regulation effect in the microbial-mediated degradation system. The amide bonds (peptide bonds) in its main chain can undergo enzymatic hydrolysis through proteases (including peptidases, deaminases) secreted by microorganisms or fungi, and finally be mineralized into environmentally friendly products such as ammonia, carbon dioxide, and water. This degradation process not only realizes the biological elimination of polyaspartic acid itself, but its mineralization products can be used as nitrogen sources, and carbon dioxide participates in the microbial tricarboxylic acid cycle, providing additional energy and synthesis precursors for the metabolism of the microbial community, thereby significantly enhancing the respiratory intensity and metabolic activity of the microorganisms, forming a positive feedback regulation mechanism for the degradation microbial community.In addition, the main chain of polyaspartic acid is rich in carboxylic acid groups and amino groups, which can serve as a high-quality carbon-nitrogen composite nutrient source for microbial growth. By activating the expression of genes related to the proliferation of the microbial community, it promotes the exponential growth of microbial biomass. As the polyaspartic acid chain segment in the copolymer gradually degrades, its original physical coating or spatial shielding effect on hexamine gradually weakens, resulting in the dynamic release of hexamine molecules from the composite system. During this process, the high-density microbial community induced by the degradation products of polyaspartic acid in the early stage has formed a dominant population, and its extracellular enzyme secretion ability and substrate affinity have been significantly improved. At this time, the efficient exposure of hexamine and the synchronous enhancement of the metabolic activity of the microbial community form a spatio-temporal synergistic effect: on the one hand, the probability of interface contact between the microorganisms and hexamine increases geometrically due to the increase in the density of the microbial community; on the other hand, the microbial community accelerates the oxidative ring-opening of the six-membered ring structure of hexamine and the cleavage of the C-N bond by upregulating the expression of degradation-related functional proteins (monooxygenase, dehydrogenase), ultimately achieving an overall improvement in the degradation kinetics. In the technical solution of the present invention, the polar groups of the organic acid interact with the active sites on the surface of hexamine, causing the redistribution of charges, thereby reducing the attraction between particles, and ultimately significantly reducing the caking rate. At the same time, this process involves the balance of intermolecular forces, and the formation of a hydrogen bond network plays a bridging role, tightly connecting the organic acid and hexamine molecules. An amphiphilic block structure is constructed by an organic copolymer synthesized through the free radical graft copolymerization reaction of polyaspartic acid and palmitic acid. In this structure, the palmitic acid chain segment endows the copolymer with hydrophobic surface characteristics. It is speculated from the principle of crystal growth inhibition that the carboxylic acid groups of polyaspartic acid can specifically adsorb metal ions in the system. During the caking process of hexamine, metal ions will promote the growth of crystal bridges, and the adsorption of polyaspartic acid on metal ions effectively inhibits this process, thereby preventing particle caking. In addition, in the ternary composite anti-caking system constructed based on the multi-level interface regulation strategy, after nano-silica is mixed with zinc stearate and polyethylene glycol, a composite system is formed. From a microscopic perspective, this composite system can uniformly cover the surface of hexamine particles, forming a physical isolation layer, effectively preventing the intrusion of external moisture and the direct contact between particles, thereby significantly reducing the risk of moisture absorption and caking.

[0039] Comparative Example 1: An anti-caking additive. In the comparative example, only citric acid was added as the anti-caking additive, and partial performance tests were carried out with reference to Application Example 1. The specific characterization results are as follows.

[0040]

[0041] Analyzing the above characterization results, in the system of the present invention, the core role played by organic acids lies in constructing a hydrogen bond network. Through in-depth analysis of this mechanism of action, it is found that it has an important impact on the system performance. Based on the detailed characterization results of Comparative Example 1, it can be seen that the hydrogen bond network constructed by organic acids does reduce the surface polarity of the system to a certain extent. However, it should be noted that this system only relies on the action of the hydrogen bond network and lacks an effective hydrophobic barrier. This limitation is intuitively reflected in the comparison of the actual caking rate data. Compared with the blank group in the application example, the caking rate of Comparative Example 1 only decreased by 26%. This shows that relying solely on a single mechanism of action - constructing a hydrogen bond network, although it can have a certain effect on reducing the caking rate, the overall effect is relatively limited and it is difficult to meet the requirements of high-efficiency anti-caking performance.

[0042] Comparative Example 2: An anti-caking additive, the specific preparation method of which is the same as that of Example 2. In this example, only the organic copolymer prepared in step (1) of Example 2 is used as the anti-caking additive, and partial performance tests are carried out with reference to Application Example 1. The specific characterization results are as follows.

[0043]

[0044] Analyzing the above characterization results, in the system constructed by the present invention, the hydrophobic segments of the organic copolymer play a crucial role, which can significantly inhibit the growth of crystal bridges. Thanks to this key role, the caking rate of the system has successfully dropped to 24.3%. However, through in-depth analysis of the detailed characterization results of Comparative Example 2, it is found that in the system of Comparative Example 2, although the carboxylic acid groups can effectively adsorb metal ions, which helps to alleviate the caking problem to a certain extent, there are obvious deficiencies in this system, that is, a physical isolation layer fails to form. This lack results in the compressive strength of the system still remaining at a relatively high level of 4.8 kPa. This result fully shows that relying solely on the single mechanism of action of carboxylic acid groups adsorbing metal ions cannot comprehensively and effectively solve the caking problem and reduce the compressive strength of the system, further demonstrating the importance and unique advantages of the synergistic action of multiple mechanisms of action in the system of the present invention to achieve excellent anti-caking performance.

[0045] Comparative Example 3: An anti-caking additive, the specific preparation method of which is the same as that of Example 2. In this example, only the modified nano-silica prepared in step (2) of Example 2 is used as the anti-caking additive, and partial performance tests are carried out with reference to Application Example 1. The specific characterization results are as follows.

[0046]

[0047] Analyzing the above characterization results, in the system constructed in the present invention, the main function of the modified nano-silica is to construct a physical barrier layer. Based on the unique size effect and surface characteristics of nano-materials, the modified nano-silica can be highly dispersed in the system and form a continuous and uniform physical isolation layer at the micro level. This physical isolation layer, by virtue of its steric hindrance effect, significantly reduces the contact probability between particles in the system and effectively inhibits the caking tendency of particles caused by mutual approach and aggregation from a physical perspective. However, analyzing the characterization data of Comparative Example 3, although the physical isolation layer plays an important role in reducing particle contact, there are still obvious deficiencies in the system, which are prominently manifested as the ineffective regulation of surface energy. Surface energy, as a key parameter reflecting the physicochemical properties of particle surfaces, the lack of its regulation makes the particle surfaces in a high-energy state. This high-energy state enhances the activity of the particle surfaces, making them more likely to interact with substances in the surrounding environment, such as adsorbing water vapor, impurities, etc., and then forming a force that is not conducive to dispersion between particles. Even though the physical isolation layer has reduced the possibility of direct particle contact, the particles will still overcome the steric hindrance and approach each other driven by surface energy, ultimately resulting in a caking rate of 31.2% in the system.

[0048] Comparative Example 4: A commercially available anti-caking additive, whose main active ingredient is calcium stearate. Partial performance tests were carried out with reference to Application Example 1, and the specific characterization results are as follows.

[0049]

[0050] Analyzing the above characterization results, in the anti-caking additive system constructed in this invention, compared with the currently commercially available calcium stearate-based anti-caking additives, the additives developed in this invention demonstrate more excellent and comprehensive comprehensive performance. The commercially available calcium stearate-based additives, although having certain efficacy in the anti-caking field and being able to inhibit the caking of hexamine to a certain extent, however, from the perspective of quantitative indicators, their anti-caking effect has obvious limitations, and the caking rate of hexamine is still as high as 29.8%. Moreover, through the determination of key parameters such as the angle of repose and compressive strength, it is found that the values of the angle of repose and compressive strength of hexamine under the action of this type of additive are relatively high. The angle of repose is an important indicator to measure the fluidity of hexamine. A larger value means that the internal friction between hexamine particles is larger and the fluidity is poor; while a higher compressive strength indicates that the compactness of hexamine after caking is higher, further reflecting the insufficiency of its anti-caking effect and the adverse impact on the fluidity of hexamine. In addition, within the 60-day biodegradation test cycle of the calcium stearate-based additives, the biodegradation rate of this type of additive <10%, indicating that it is difficult to be decomposed and utilized by microorganisms in the natural environment and there is a risk of environmental pollution. The anti-caking additive of this invention has remarkable results in reducing the caking rate and can control the caking rate at a level far lower than that of similar products in the market; in improving the fluidity of hexamine, by optimizing the formula and action mechanism, it effectively reduces the angle of repose of hexamine and significantly improves the fluidity performance of hexamine, facilitating the transportation and storage of hexamine; at the same time, it shows good biodegradable characteristics in biodegradability.

Claims

1. A preparation method of anti-caking hexamine, characterized in that, the method comprises: Placing hexamine particles in a fluidized bed for fluidization, using an anti-caking additive as a spraying agent, and performing top-spray spraying treatment on the hexamine particles in the fluidized bed, so that the anti-caking additive uniformly covers the surface of the hexamine particles and then drying and curing them to obtain anti-caking hexamine.

2. The preparation method of anti-caking hexamine according to claim 1, characterized in that, the fluidization process controls the fluidization air velocity to be 0.8 - 1.2 m / s; the dosage of the anti-caking additive is 0.5 - 1.0 wt% of hexamine; the spraying pressure during the spraying treatment process is 0.5 - 0.7 MPa.

3. The preparation method of anti-caking hexamine according to claim 1, characterized in that, the drying and curing adopts gradient heating and heat preservation treatment; the gradient heating and heat preservation treatment is carried out successively with heat preservation at 28 - 32 °C for 25 - 35 min, heat preservation at 42 - 47 °C for 25 - 35 min, and heat preservation at 55 - 65 °C for 55 - 65 min.

4. An anti-caking additive for any one of the methods of claims 1 to 3, characterized in that, the anti-caking additive is prepared by the following method: (1) Mixing a polypeptide and an acyclic carboxylic acid in proportion to form a mixture, and carrying out heat preservation copolymerization to prepare an organic copolymer; (2) Mixing a non-metal oxide, an organic zinc, and a fatty alcohol derivative in proportion, and performing ultrasonic treatment to prepare a modified inorganic material; (3) Mixing the organic copolymer, the modified inorganic material, and a polymer in proportion to prepare the anti-caking additive.

5. The anti-caking additive according to claim 4, characterized in that, the polypeptide in step (1) is polyaspartic acid; the acyclic carboxylic acid in step (1) is palmitic acid; the polypeptide and the acyclic carboxylic acid in step (1) are mixed evenly according to a mass ratio of (2.4 - 2.8):

1.

6. The anti-caking additive according to claim 4 or 5, characterized in that, the heat preservation copolymerization in step (1) is carried out under the environmental conditions of an inert atmosphere and a temperature of 55 - 65 °C, using 1,2-dichloroethane at 1.5 - 2.5 wt% of the mass of the mixture as a catalyst, and carrying out heat preservation reaction for 4 - 6 h.

7. The anti-caking additive according to claim 4, characterized in that, the non-metal oxide in step (2) is nano-silica; the organic zinc in step (2) is zinc stearate; the fatty alcohol derivative in step (2) is ethanol; the non-metal oxide, the organic zinc, and the fatty alcohol derivative in step (2) are mixed evenly according to a mass ratio of 1:(0.03 - 0.07):

30.

8. The anti-caking additive according to claim 4 or 7, characterized in that, the ultrasonic treatment in step (2) controls the ultrasonic power to be 50 - 80 W and the ultrasonic duration to be 0.5 - 1 h.

9. The anti-caking additive according to claim 4, characterized in that, The organic copolymer, modified inorganic material, and polymer described in step (3) are uniformly mixed in a mass ratio of (1.5 to 2.5):1:(3.9 to 4.1).

10. A non-caking hexamine prepared by any of the methods according to claims 1 to 3.

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