Anti-crystallization marine urea and preparation method thereof

Abstract

The invention relates to the technical field of urea, in particular to anti-crystallization marine urea and a preparation method thereof.The anti-crystallization marine urea is prepared from, by weight, 320-335 parts of urea, 665-680 parts of deionized water, 5-15 parts of an additive A, 1-5 parts of an additive B, 0.5-2 parts of a corrosion inhibitor and 0.1-0.5 part of a pH stabilizer. The additive A is an aramid fiber compounded and modified by lac and is polymerized with 2-acrylamide-2-methylpropanesulfonic acid, a polymer structure with steric hindrance and hydrogen-bond interaction is formed, ordered arrangement of urea molecules can be interfered, so that formation and growth of crystal nucleuses are inhibited, the additive B is an aramid fiber compounded and modified by lac, and a hydrophobic chain segment and a rigid aromatic ring structure are introduced in the preparation process, so that the hydrophobic property of the aramid fiber is improved. The dispersion stability of the solution can be improved, a barrier can be formed on a urea crystallization interface, the crystallization process is delayed, and the crystallization resistance of the marine urea is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of urea technology, specifically to an anti-crystallization marine urea and its preparation method. Background Technology

[0002] Marine urea solution is a high-purity aqueous solution of urea. As a reducing agent, it is specifically used in the exhaust gas treatment system of marine diesel engines. It can selectively catalytically reduce nitrogen oxides in exhaust gas into harmless nitrogen and water to meet the stringent emission regulations of the International Maritime Organization. It is a key consumable for ships to achieve green emission reduction.

[0003] In existing technologies, marine urea suffers from the problem of easy crystallization at low temperatures during practical applications. The solubility of marine urea decreases as the temperature drops. When the ambient temperature is below -11°C, urea crystals will precipitate in the marine urea solution, leading to pipeline blockage and injection system malfunctions. Adding anti-crystallization agents to address this problem, however, affects the stability of marine urea. Based on this, the present invention provides an anti-crystallization marine urea and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide an anti-crystallization marine urea and its preparation method. The anti-crystallization marine urea prepared by this invention not only has good anti-crystallization properties, but also good dispersion stability, effectively improving the performance of marine urea.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In the first aspect, an anti-crystallization marine urea comprises the following raw materials in parts by weight: 320-335 parts urea, 665-680 parts deionized water, 5-15 parts additive A, 1-5 parts additive B, 0.5-2 parts corrosion inhibitor and 0.1-0.5 parts pH stabilizer. The raw materials for additive A include L-theanine, a compound acid solution, 2-acrylamide-2-methylpropanesulfonic acid, and a compound material; The raw materials for additive B include maleic anhydride, additives, xylene, and benzoyl peroxide.

[0006] Further, the additive A is prepared by the following method: L-theanine, deionized water and compound acid solution are mixed at a mass ratio of (8-12):(15-25):(0.5-1.5), reacted at 90-110℃ for 2-4 hours, cooled to 50-70℃ to obtain a slurry, which is then set aside. 2-Acrylamide-2-methylpropanesulfonic acid and deionized water are mixed at a mass ratio of 1:(2-3) to obtain a first mixture. The first mixture is mixed with the slurry at a mass ratio of (0.4-0.6):1, and the compound material is added. The mixture is reacted at 60-80℃ for 1-2 hours. Sodium hydroxide solution is added to adjust the pH value to 9-11, and the mixture is hydrolyzed at 80-90℃ for 2-3 hours. The mixture is filtered, and the filtrate is concentrated under reduced pressure at 60-80℃ to 30-50% of its original volume to obtain additive A, wherein the mass concentration of the sodium hydroxide solution is 10-20%.

[0007] Further, the composite material is prepared by the following method: tea polyphenols and deionized water are mixed at a mass ratio of 1:(6-9) to obtain a tea polyphenol solution; the tea polyphenol solution is mixed with diatomaceous earth at a mass ratio of 1:3 to obtain an intermediate product; the intermediate product is mixed with anhydrous ethanol at a solid-liquid ratio of 1g:(8-10)mL, transferred into an ultrasonic device, and ultrasonically treated for 30-45 minutes at a power of 200-300W; glutaraldehyde is added, and the mixture is reacted at 50-60℃ for 1-2 hours; subsequently, it is spray-dried at an inlet air temperature of 160-180℃ and an outlet air temperature of 80-90℃ to obtain the composite material, wherein the mass of the glutaraldehyde is 8-12% of the mass of the tea polyphenols.

[0008] Further, the additive B is prepared by the following method: the additive is mixed with maleic anhydride at a mass ratio of 1:(0.8-1.2) to obtain a mixture; the mixture is mixed with xylene at a solid-liquid ratio of 1g:(15-20)mL; benzoyl peroxide is added; and the mixture is reacted at 110-120℃ for 4-6h. After the reaction is completed, the mixture is cooled, filtered, and the residue is obtained. The residue is washed with acetone 3-4 times and vacuum dried at 80-90℃ for 3h to obtain additive B, wherein the mass of the benzoyl peroxide is 0.5-1.0% of the mass of the additive.

[0009] Further, the additive is prepared by the following method: aramid fiber and sodium hydroxide solution are mixed at a mass ratio of 1:(8-12), stirred at 55-65℃ and 100-200 rpm for 2 hours, filtered, and the filter residue is washed with deionized water until neutral, and then vacuum dried at 80℃ to constant weight for later use. The dried filter residue is mixed with the treatment liquid at a mass ratio of 1:(10-15), stirred at 60-70℃ and 150-200 rpm for 1-2 hours, filtered, and the filter residue is washed once with anhydrous ethanol, then twice with deionized water, and then vacuum dried at 80℃ to constant weight to obtain the additive, wherein the mass concentration of the sodium hydroxide solution is 5-8%.

[0010] Further, the treatment solution is prepared by the following method: shellac and citric acid aqueous solution are mixed at a mass ratio of 1:(7-9), reacted at 60-80℃ for 2h to obtain a second mixture, perilla seed oil and lecithin are added to the second mixture, and ultrasonic treatment is performed at 250W power for 20-30min to obtain the treatment solution.

[0011] Furthermore, the citric acid aqueous solution has a mass concentration of 5%, the perilla seed oil has a volume of 0.5-1.0% of the volume of the second mixture, and the lecithin has a mass of 5% of the perilla seed oil.

[0012] Furthermore, the composite acid solution is prepared by mixing phytic acid and citric acid in a mass ratio of 1:1.

[0013] Furthermore, the corrosion inhibitor is a mixture of sodium molybdate and benzotriazole in a mass ratio of (1-2):1, and the pH stabilizer is analytical grade ammonia with a mass concentration of 25%.

[0014] Secondly, the present invention provides a method for preparing anti-crystallization marine urea, comprising the following steps: Step 1: Raw material pretreatment. Add deionized water to the preparation vessel and heat it to 40-50℃. Add urea while stirring to obtain urea base material. Step 2: Additive compounding. Reduce the temperature of the preparation vessel to 25-35℃, and add additive A, additive B, corrosion inhibitor and pH stabilizer in sequence while stirring. After each additive is added, continue stirring for 10-15 minutes to obtain a premixed solution. Step 3: Precision filtration. The premixed solution is filtered sequentially through 1μm and 0.22μm tubular filters. The filtrate is collected, passed through an ion exchange resin column, and then filled into a clean container. Dry nitrogen gas is introduced into the upper space of the container for protection. The container is then sealed to obtain anti-crystallization marine urea.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. In this invention, additive A uses L-theanine as a raw material. It utilizes the amino and carboxyl active sites in its molecular structure to react with the polyphosphate groups in the composite acid solution and polymerize with 2-acrylamide-2-methylpropanesulfonic acid to generate a polymer with hydrogen bonding and steric hindrance effects. This polymer can be effectively adsorbed on the surface of urea crystal nuclei, interfering with the regular stacking and lattice growth of urea molecules, reducing the crystallization activation energy, thereby inhibiting the initiation and expansion of crystallization, and improving the anti-crystallization performance and low-temperature stability of urea.

[0016] 2. In this invention, additive B uses aramid fibers with surface alkali activation and shellac composite modification as a carrier. It utilizes glutaraldehyde crosslinking reaction to form a stable composite structure, introduces hydrophobic segments through maleic anhydride, and retains the rigid skeleton of aramid. The hydrophobic segments on its surface can reduce interfacial energy and form a stable dispersion system in solution. The rigid structure forms a physical barrier layer at the solid-liquid interface, effectively delaying the advancement of the crystallization front, while improving the overall system's dispersion uniformity and long-term storage stability.

[0017] 3. In this invention, additive A and additive B work together to resist crystallization. Additive A mainly acts on the nucleation and growth stages of the crystallization process, while additive B focuses on interface modification and physical barrier. The two intervene in the formation of crystals from different mechanism levels, so that the resulting marine urea solution maintains good anti-crystallization performance in low-temperature environments, while also having metal corrosion inhibition and pH stability, meeting the long-term reliable operation requirements of the ship selective catalytic reduction technology system. Attached Figure Description

[0018] Figure 1 The present invention provides a flowchart of an anti-crystallization marine urea and its preparation method. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that the raw materials used in the following embodiments are all commercially available.

[0021] Example 1

[0022] Preparation of the composite material: Tea polyphenols and deionized water were mixed at a mass ratio of 1:6 to obtain a tea polyphenol solution. The tea polyphenol solution was mixed with diatomaceous earth at a mass ratio of 1:3 to obtain an intermediate product. The intermediate product was mixed with anhydrous ethanol at a solid-liquid ratio of 1g:8mL and transferred into an ultrasonic device. The mixture was ultrasonically treated for 30 minutes at a power of 200W. Glutaraldehyde was added and reacted at 50℃ for 1 hour. Subsequently, the mixture was spray-dried at an inlet air temperature of 160℃ and an outlet air temperature of 80℃ to obtain the composite material. The mass of the glutaraldehyde was 8% of the mass of the tea polyphenols.

[0023] Preparation of Additive A: L-theanine, deionized water, and a compound acid solution were mixed at a mass ratio of 8:15:0.5 and reacted at 90°C for 2 hours. The mixture was then cooled to 50°C to obtain a slurry, which was set aside for later use. 2-Acrylamide-2-methylpropanesulfonic acid and deionized water were mixed at a mass ratio of 1:2 to obtain a first mixture. The first mixture was then mixed with the slurry at a mass ratio of 0.4:1. The compound material was added, and the mixture was reacted at 60°C for 1 hour. Sodium hydroxide solution was added to adjust the pH to 9, and the mixture was hydrolyzed at 80°C for 2 hours. The mixture was filtered, and the filtrate was concentrated under reduced pressure at 60°C to 30% of its original volume to obtain Additive A. The mass concentration of the sodium hydroxide solution was 10%.

[0024] The composite acid solution is prepared by mixing phytic acid and citric acid in a mass ratio of 1:1.

[0025] Preparation of the treatment solution: Shellac and citric acid aqueous solution were mixed at a mass ratio of 1:7 and reacted at 60℃ for 2 hours to obtain a second mixture. Perilla seed oil and lecithin were added to the second mixture and ultrasonically treated with a power of 250W for 20 minutes to obtain the treatment solution.

[0026] The citric acid aqueous solution has a mass concentration of 5%, the perilla seed oil has a volume of 0.5% of the volume of the second mixture, and the lecithin has a mass of 5% of the perilla seed oil.

[0027] Preparation of the additive: Aramid fiber and sodium hydroxide solution were mixed at a mass ratio of 1:8 and stirred at 100 rpm for 2 hours at 55°C. The mixture was then filtered, and the filter residue was washed with deionized water until neutral. It was then vacuum dried at 80°C to constant weight and set aside for later use. The dried filter residue was mixed with the treatment liquid at a mass ratio of 1:10 and stirred at 150 rpm for 1 hour at 60°C. The mixture was then filtered, and the filter residue was washed once with anhydrous ethanol and twice with deionized water. It was then vacuum dried at 80°C to constant weight to obtain the additive. The mass concentration of the sodium hydroxide solution was 5%.

[0028] Preparation of Additive B: The additive and maleic anhydride were mixed at a mass ratio of 1:0.8 to obtain a mixture. The mixture was then mixed with xylene at a solid-liquid ratio of 1g:15mL. Benzoyl peroxide was added, and the mixture was reacted at 110℃ for 4h. After the reaction was completed, the mixture was cooled, filtered, and the residue was obtained. The residue was washed three times with acetone and dried under vacuum at 80℃ for 3h to obtain Additive B. The mass of benzoyl peroxide was 0.5% of the mass of the additive.

[0029] Raw material preparation: 320 parts urea, 665 parts deionized water, 5 parts additive A, 1 part additive B, 0.5 parts corrosion inhibitor and 0.1 parts pH stabilizer.

[0030] The corrosion inhibitor is a mixture of sodium molybdate and benzotriazole in a mass ratio of 1:1, and the pH stabilizer is analytical grade ammonia with a mass concentration of 25%.

[0031] Preparation of anti-crystallization marine urea: Step 1: Raw material pretreatment. Add deionized water to the preparation vessel, heat to 40°C, and add urea while stirring to obtain urea base material. Step 2: Additive compounding. The temperature of the preparation vessel is lowered to 25°C. Additive A, additive B, corrosion inhibitor and pH stabilizer are added in sequence with stirring. After each additive is added, stirring is continued for 10 minutes to obtain a premixed solution. Step 3: Precision filtration. The premixed solution is filtered sequentially through 1μm and 0.22μm tubular filters. The filtrate is collected, passed through an ion exchange resin column, and then filled into a clean container. Dry nitrogen gas is introduced into the upper space of the container for protection. The container is then sealed to obtain anti-crystallization marine urea.

[0032] Example 2

[0033] Preparation of the composite material: Tea polyphenols and deionized water were mixed at a mass ratio of 1:7 to obtain a tea polyphenol solution. The tea polyphenol solution was mixed with diatomaceous earth at a mass ratio of 1:3 to obtain an intermediate product. The intermediate product was mixed with anhydrous ethanol at a solid-liquid ratio of 1g:9mL and transferred into an ultrasonic device. The mixture was ultrasonically treated for 35 minutes at a power of 250W. Glutaraldehyde was added and reacted at 55℃ for 1.5 hours. Subsequently, the mixture was spray-dried at an inlet air temperature of 170℃ and an outlet air temperature of 85℃ to obtain the composite material. The mass of glutaraldehyde was 10% of the mass of tea polyphenols.

[0034] Preparation of Additive A: L-theanine, deionized water, and a compound acid solution were mixed at a mass ratio of 10:20:1 and reacted at 100℃ for 3 hours. The mixture was then cooled to 60℃ to obtain a slurry, which was set aside for later use. 2-Acrylamide-2-methylpropanesulfonic acid and deionized water were mixed at a mass ratio of 1:2.5 to obtain a first mixture. The first mixture was then mixed with the slurry at a mass ratio of 0.5:1. The compound material was added, and the mixture was reacted at 70℃ for 1.5 hours. Sodium hydroxide solution was added to adjust the pH to 10, and the mixture was hydrolyzed at 85℃ for 2.5 hours. The mixture was filtered, and the filtrate was concentrated under reduced pressure at 70℃ to 40% of its original volume to obtain Additive A. The mass concentration of the sodium hydroxide solution was 15%.

[0035] The composite acid solution is prepared by mixing phytic acid and citric acid in a mass ratio of 1:1.

[0036] Preparation of the treatment solution: Shellac and citric acid aqueous solution were mixed at a mass ratio of 1:8 and reacted at 70℃ for 2 hours to obtain a second mixture. Perilla seed oil and lecithin were added to the second mixture and ultrasonically treated with a power of 250W for 25 minutes to obtain the treatment solution.

[0037] The citric acid aqueous solution has a mass concentration of 5%, the perilla seed oil has a volume of 0.8% of the volume of the second mixture, and the lecithin has a mass of 5% of the perilla seed oil.

[0038] Preparation of the additive: Aramid fiber and sodium hydroxide solution were mixed at a mass ratio of 1:10 and stirred at 150 rpm for 2 hours at 60°C. The mixture was filtered, and the filter residue was washed with deionized water until neutral. It was then vacuum dried at 80°C to constant weight and set aside for later use. The dried filter residue was mixed with the treatment liquid at a mass ratio of 1:12 and stirred at 180 rpm for 1.5 hours at 65°C. The mixture was filtered, and the filter residue was washed once with anhydrous ethanol and twice with deionized water. It was then vacuum dried at 80°C to constant weight to obtain the additive. The mass concentration of the sodium hydroxide solution was 6%.

[0039] Preparation of Additive B: The additive and maleic anhydride were mixed at a mass ratio of 1:1 to obtain a mixture. The mixture was then mixed with xylene at a solid-liquid ratio of 1g:17mL. Benzoyl peroxide was added, and the mixture was reacted at 115℃ for 5h. After the reaction was completed, the mixture was cooled, filtered, and the residue was obtained. The residue was washed four times with acetone and dried under vacuum at 85℃ for 3h to obtain Additive B. The mass of benzoyl peroxide was 0.8% of the mass of the additive.

[0040] Raw material preparation: 330 parts urea, 670 parts deionized water, 10 parts additive A, 3 parts additive B, 1 part corrosion inhibitor and 0.3 parts pH stabilizer.

[0041] The corrosion inhibitor is a mixture of sodium molybdate and benzotriazole at a mass ratio of 1.5:1, and the pH stabilizer is analytical grade ammonia with a mass concentration of 25%.

[0042] Preparation of anti-crystallization marine urea: Step 1: Raw material pretreatment. Deionized water is added to the preparation vessel and heated to 45°C. Urea is added while stirring to obtain urea base material. Step 2: Additive compounding. The temperature of the preparation vessel is reduced to 30°C. Additive A, additive B, corrosion inhibitor and pH stabilizer are added in sequence with stirring. After each additive is added, stirring is continued for 12 minutes to obtain a premixed solution. Step 3: Precision filtration. The premixed solution is filtered sequentially through 1μm and 0.22μm tubular filters. The filtrate is collected, passed through an ion exchange resin column, and then filled into a clean container. Dry nitrogen gas is introduced into the upper space of the container for protection. The container is then sealed to obtain anti-crystallization marine urea.

[0043] Example 3

[0044] Preparation of the composite material: Tea polyphenols and deionized water were mixed at a mass ratio of 1:9 to obtain a tea polyphenol solution. The tea polyphenol solution was mixed with diatomaceous earth at a mass ratio of 1:3 to obtain an intermediate product. The intermediate product was mixed with anhydrous ethanol at a solid-liquid ratio of 1g:10mL and transferred to an ultrasonic device. The mixture was ultrasonically treated at a power of 300W for 45min. Glutaraldehyde was added and reacted at 60℃ for 2h. Subsequently, the mixture was spray-dried at an inlet air temperature of 180℃ and an outlet air temperature of 90℃ to obtain the composite material. The mass of glutaraldehyde was 12% of the mass of tea polyphenols.

[0045] Preparation of Additive A: L-theanine, deionized water, and a compound acid solution were mixed at a mass ratio of 12:25:1.5 and reacted at 110°C for 4 hours. The mixture was then cooled to 70°C to obtain a slurry, which was set aside for later use. 2-Acrylamide-2-methylpropanesulfonic acid and deionized water were mixed at a mass ratio of 1:3 to obtain a first mixture. The first mixture was then mixed with the slurry at a mass ratio of 0.6:1. The compound material was added, and the mixture was reacted at 80°C for 2 hours. Sodium hydroxide solution was added to adjust the pH to 11, and the mixture was hydrolyzed at 90°C for 3 hours. The mixture was filtered, and the filtrate was concentrated under reduced pressure at 80°C to 50% of its original volume to obtain Additive A. The mass concentration of the sodium hydroxide solution was 20%.

[0046] The composite acid solution is prepared by mixing phytic acid and citric acid in a mass ratio of 1:1.

[0047] Preparation of the treatment solution: Shellac and citric acid aqueous solution were mixed at a mass ratio of 1:9 and reacted at 80℃ for 2 hours to obtain a second mixture. Perilla seed oil and lecithin were added to the second mixture and ultrasonically treated with a power of 250W for 30 minutes to obtain the treatment solution.

[0048] The citric acid aqueous solution has a mass concentration of 5%, the perilla seed oil has a volume of 1.0% of the volume of the second mixture, and the lecithin has a mass of 5% of the perilla seed oil.

[0049] Preparation of the additive: Aramid fiber and sodium hydroxide solution were mixed at a mass ratio of 1:12 and stirred at 200 rpm for 2 hours at 65°C. The mixture was filtered, and the filter residue was washed with deionized water until neutral. It was then vacuum dried at 80°C to constant weight and set aside for later use. The dried filter residue was mixed with the treatment liquid at a mass ratio of 1:15 and stirred at 200 rpm for 2 hours at 70°C. The mixture was filtered, and the filter residue was washed once with anhydrous ethanol and twice with deionized water. It was then vacuum dried at 80°C to constant weight to obtain the additive. The mass concentration of the sodium hydroxide solution was 8%.

[0050] Preparation of Additive B: The additive and maleic anhydride were mixed at a mass ratio of 1:1.2 to obtain a mixture. The mixture was then mixed with xylene at a solid-liquid ratio of 1g:20mL. Benzoyl peroxide was added, and the mixture was reacted at 120℃ for 6h. After the reaction was completed, the mixture was cooled and filtered to obtain a filter residue. The filter residue was washed four times with acetone and dried under vacuum at 90℃ for 3h to obtain Additive B. The mass of benzoyl peroxide was 1.0% of the mass of the additive.

[0051] Raw material preparation: 335 parts urea, 680 parts deionized water, 15 parts additive A, 5 parts additive B, 2 parts corrosion inhibitor and 0.5 parts pH stabilizer.

[0052] The corrosion inhibitor is a mixture of sodium molybdate and benzotriazole in a mass ratio of 2:1, and the pH stabilizer is analytical grade ammonia with a mass concentration of 25%.

[0053] Preparation of anti-crystallization marine urea: Step 1: Raw material pretreatment. Add deionized water to the preparation vessel, heat to 50°C, and add urea while stirring to obtain urea base material. Step 2: Additive compounding. The temperature of the preparation vessel is lowered to 35°C. Additive A, additive B, corrosion inhibitor and pH stabilizer are added in sequence with stirring. After each additive is added, stirring is continued for 15 minutes to obtain a premixed solution. Step 3: Precision filtration. The premixed solution is filtered sequentially through 1μm and 0.22μm tubular filters. The filtrate is collected, passed through an ion exchange resin column, and then filled into a clean container. Dry nitrogen gas is introduced into the upper space of the container for protection. The container is then sealed to obtain anti-crystallization marine urea.

[0054] Comparative Example 1: The difference between this comparative example and Example 1 is that this comparative example does not contain additive A.

[0055] Comparative Example 2 differs from Example 1 in that it does not contain additive B.

[0056] Comparative Example 3 differs from Example 1 in that no composite material was used in the preparation of additive A in this comparative example.

[0057] Performance testing: The anti-crystallization marine urea prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing, and the test data are recorded in the table below: Table 1 Testing items Low-temperature crystallization temperature (°C) Turbidity change rate (%) Corrosion weight loss (mg) Example 1 -18.5 3.2 0.85 Example 2 -19.2 2.8 0.78 Example 3 -18.8 3.5 0.92 Comparative Example 1 -9.7 12.5 2.89 Comparative Example 2 -8.3 18.6 2.17 Comparative Example 3 -11.2 8.7 2.20 In the performance test, the following steps were performed: Low-temperature crystallization temperature determination: Referring to the general method for crystallization temperature determination, differential scanning calorimetry was used to cool the sample. The temperature at which crystals began to precipitate was recorded as the crystallization temperature. The lower the crystallization temperature, the stronger the anti-crystallization performance. Turbidity change rate determination: The sample was placed in a constant temperature and humidity chamber and subjected to 10 cycles of testing within a temperature range of -10℃ to 40℃, with each cycle lasting 24 hours. After the test, the turbidity of the solution was measured at 25℃ using a turbidimeter and compared with the initial turbidity to calculate the turbidity change rate. Corrosion weight loss: A standard carbon steel test piece was completely immersed in the sample and soaked at 40℃ for 30 days. The test piece was then removed, cleaned, dried, and weighed. The corrosion weight loss per unit surface area was calculated.

[0058] According to the data in the table obtained from the performance test, the low-temperature crystallization temperature of the anti-crystallization marine urea prepared in Examples 1-3 is significantly lower than that of Comparative Examples 1-3, and the turbidity change rate and corrosion weight loss are also significantly lower than those of each comparative example. This is mainly attributed to the mechanism of action of additives A and B in inhibiting crystallization, stabilizing the system and synergistic corrosion prevention.

[0059] Additive A, through the formation of hydrogen bond networks and steric hindrance in urea solution by L-theanine-derived polymers, interferes with the nucleation and growth of urea crystals at the molecular level, thereby lowering the crystallization temperature. Additive B, with its modified hydrophobic surface and rigid structure of aramid fibers, constructs a physical barrier layer, delaying the crystallization process and improving the dispersion stability of the system. The two work together to not only improve the low-temperature crystallization resistance of marine urea, but also reduce the increase in turbidity caused by component aggregation by improving the uniformity of the system.

[0060] Comparative Example 1, which does not contain additive A, shows a significant increase in crystallization temperature, indicating that it loses its ability to interfere with crystallization at the molecular level, making the system more prone to crystallization. Comparative Example 2, which does not contain additive B, shows a significant increase in turbidity change rate, indicating a lack of physical barrier and dispersion stabilization effects, resulting in decreased stability of the system under temperature cycling. In Comparative Example 3, additive A was not used in the composite material, and its crystallization inhibition and system stabilization effects were weaker than those of the complete formulation, further confirming the key role of composite materials in constructing an effective polymer structure.

[0061] By comparing and analyzing the relevant data in the table, it can be seen that the anti-crystallization marine urea prepared by this invention not only has good anti-crystallization properties but also good dispersion stability. This indicates that the anti-crystallization marine urea provided by this invention has a broader market prospect and is more suitable for widespread application.

[0062] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0063] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A type of anti-crystallization marine urea, characterized in that, The raw materials include the following parts by weight: 320-335 parts urea, 665-680 parts deionized water, 5-15 parts additive A, 1-5 parts additive B, 0.5-2 parts corrosion inhibitor and 0.1-0.5 parts pH stabilizer; The raw materials for additive A include L-theanine, a compound acid solution, 2-acrylamide-2-methylpropanesulfonic acid, and a compound material; The raw materials for additive B include maleic anhydride, additives, xylene, and benzoyl peroxide.

2. The anti-crystallization marine urea according to claim 1, characterized in that, Additive A is prepared by the following method: L-theanine, deionized water and compound acid solution are mixed at a mass ratio of (8-12):(15-25):(0.5-1.5), reacted at 90-110℃ for 2-4 hours, cooled to 50-70℃ to obtain a slurry, which is then set aside. 2-Acrylamide-2-methylpropanesulfonic acid and deionized water are mixed at a mass ratio of 1:(2-3) to obtain a first mixture. The first mixture is mixed with the slurry at a mass ratio of (0.4-0.6):1, and the compound material is added. The mixture is reacted at 60-80℃ for 1-2 hours. Sodium hydroxide solution is added to adjust the pH to 9-11, and the mixture is hydrolyzed at 80-90℃ for 2-3 hours. The mixture is filtered, and the filtrate is concentrated under reduced pressure at 60-80℃ to 30-50% of its original volume to obtain additive A. The mass concentration of the sodium hydroxide solution is 10-20%.

3. The anti-crystallization marine urea according to claim 2, characterized in that, The composite material is prepared by the following method: tea polyphenols and deionized water are mixed at a mass ratio of 1:(6-9) to obtain a tea polyphenol solution. The tea polyphenol solution is mixed with diatomaceous earth at a mass ratio of 1:3 to obtain an intermediate product. The intermediate product is mixed with anhydrous ethanol at a solid-liquid ratio of 1g:(8-10)mL. The mixture is then transferred to an ultrasonic device and ultrasonically treated for 30-45 minutes at a power of 200-300W. Glutaraldehyde is added and reacted at 50-60℃ for 1-2 hours. Subsequently, the mixture is spray-dried at an inlet air temperature of 160-180℃ and an outlet air temperature of 80-90℃ to obtain the composite material. The mass of the glutaraldehyde is 8-12% of the mass of the tea polyphenols.

4. The anti-crystallization marine urea according to claim 1, characterized in that, Additive B is prepared by the following method: the additive is mixed with maleic anhydride at a mass ratio of 1:(0.8-1.2) to obtain a mixture; the mixture is mixed with xylene at a solid-liquid ratio of 1g:(15-20)mL; benzoyl peroxide is added; and the mixture is reacted at 110-120℃ for 4-6h. After the reaction is completed, the mixture is cooled and filtered to obtain a filter residue. The filter residue is washed with acetone 3-4 times and vacuum dried at 80-90℃ for 3h to obtain additive B. The mass of benzoyl peroxide is 0.5-1.0% of the mass of the additive.

5. The anti-crystallization marine urea according to claim 4, characterized in that, The additive is prepared by the following method: aramid fiber and sodium hydroxide solution are mixed at a mass ratio of 1:(8-12), stirred at 55-65℃ and 100-200 rpm for 2 hours, filtered, and the filter residue is washed with deionized water until neutral, and then vacuum dried at 80℃ to constant weight for later use. The dried filter residue is mixed with the treatment liquid at a mass ratio of 1:(10-15), stirred at 60-70℃ and 150-200 rpm for 1-2 hours, filtered, and the filter residue is washed once with anhydrous ethanol, then washed twice with deionized water, and then vacuum dried at 80℃ to constant weight to obtain the additive. The mass concentration of the sodium hydroxide solution is 5-8%.

6. The anti-crystallization marine urea according to claim 5, characterized in that, The treatment solution is prepared by the following method: shellac and citric acid aqueous solution are mixed at a mass ratio of 1:(7-9) and reacted at 60-80℃ for 2 hours to obtain a second mixture. Perilla seed oil and lecithin are added to the second mixture and ultrasonically treated with a power of 250W for 20-30 minutes to obtain the treatment solution.

7. The anti-crystallization marine urea according to claim 6, characterized in that, The citric acid aqueous solution has a mass concentration of 5%, the volume of perilla seed oil is 0.5-1.0% of the volume of the second mixture, and the mass of lecithin is 5% of the mass of perilla seed oil.

8. The anti-crystallization marine urea according to claim 2, characterized in that, The composite acid solution is prepared by mixing phytic acid and citric acid in a mass ratio of 1:

1.

9. The anti-crystallization marine urea according to claim 1, characterized in that, The corrosion inhibitor is a mixture of sodium molybdate and benzotriazole in a mass ratio of (1-2):1, and the pH stabilizer is analytical grade ammonia with a mass concentration of 25%.

10. The method for preparing anti-crystallization marine urea according to any one of claims 1-9, characterized in that, Includes the following steps: Step 1: Raw material pretreatment. Add deionized water to the preparation vessel and heat it to 40-50℃. Add urea while stirring to obtain urea base material. Step 2: Additive compounding. Reduce the temperature of the preparation vessel to 25-35℃, and add additive A, additive B, corrosion inhibitor and pH stabilizer in sequence while stirring. After each additive is added, continue stirring for 10-15 minutes to obtain a premixed solution. Step 3: Precision filtration. The prepared premixed solution is filtered sequentially through 1μm and 0.22μm tubular filters. The filtrate is collected, passed through an ion exchange resin column, filled into a clean container, and filled with dry nitrogen gas for protection. The container is then sealed to obtain anti-crystallization marine urea.

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