A production method of nitro-sulfur base controlled-release compound fertilizer

Abstract

The present application relates to the field of agricultural fertilizer, controlled release material and polymer coating technology, in particular to a production method of nitro-sulfur base slow / controlled release compound fertilizer; the method first loads porous starch with double inhibitors and coats with ethyl cellulose to prepare protective granules, then drum granulation is carried out to obtain fertilizer core particles, and finally the surface of the core particles is sprayed with a solidified inner film layer, an intermediate film layer containing protective granules and an outer film layer in sequence; the present application constructs a three-layer compound coating structure, the mass ratio of the inner film layer, the intermediate film layer and the outer film layer is (20-35):(35-55):(20-35), the physical controlled release of the particle scale is combined with the soil micro-domain nitrogen conversion inhibition; the present application effectively isolates the cross reaction of the granulation heat environment and the coating, reduces the initial nutrient release rate through the double slow release synergistic mechanism, prolongs the nutrient release period, maintains the urease and nitrification inhibition effect, inhibits the nitrogen conversion loss and prolongs the effective release period to 80-90 days.

Description

Technical Field

[0001] This invention relates to the fields of agricultural fertilizers, controlled-release materials, and polymer coating technology, specifically a method for producing a nitrate-sulfur-based slow-release compound fertilizer. Background Technology

[0002] Nitrogen-sulfur-based compound fertilizers contain nitrate nitrogen and sulfur, and are characterized by high initial effective nutrient release rate, good nutrient water solubility, and suitability for chlorine-sensitive crops. They have been widely used in food crops, cash crops, and horticultural crops. However, ordinary nitrate-sulfur-based compound fertilizers have a high water solubility rate after being applied to the soil. Nitrate nitrogen is easily migrated and leached by water, and ammonium nitrogen and ammonium nitrogen produced by the hydrolysis of amide nitrogen will further undergo nitrification reactions, resulting in a short nutrient supply cycle, serious nitrogen loss, and may cause nitrate accumulation in groundwater and agricultural non-point source pollution. Existing slow-release fertilizers mainly delay nutrient dissolution through inorganic precipitation, sulfur coating, or single polymer coating. For example, some disclosed technologies use sparingly soluble inorganic phases such as magnesium ammonium phosphate to regulate nitrogen release. The solubility and dissolution behavior of such inorganic slow-release structures are significantly constrained by soil pH, temperature, and moisture conditions, and the adjustable range of the release cycle is limited. Although single polymer coating can reduce the initial dissolution rate of fertilizer, it mainly controls the physical diffusion of nutrients from inside the fertilizer particles to the outside. Once nutrients pass through the membrane and enter the soil, processes such as amide nitrogen hydrolysis, ammonium nitrogen nitrification, and nitrate nitrogen migration will continue to occur. Therefore, relying solely on physical coating cannot simultaneously solve the problems of excessively rapid nutrient dissolution and excessively rapid nitrogen transformation and loss. Furthermore, urease inhibitors and nitrification inhibitors are generally sensitive to temperature, humidity, and chemical environment; if directly added to a high-temperature granulation system, thermal inactivation may occur; if directly exposed to isocyanate-coated precursors, the active groups in the inhibitor molecules may undergo side reactions with isocyanates, thereby reducing the effective content and biological activity; therefore, it is necessary to construct suitable inhibitor protection, isolation, and release structures; based on the above problems, it is necessary to develop a compound fertilizer that combines particle-scale physical controlled release with nitrogen transformation inhibition in soil microdomains, so as to achieve slow dissolution of fertilizer nutrients while ensuring processing stability and storage stability. Summary of the Invention

[0003] Given the inherent limitations of existing nitrate-sulfur-based compound fertilizers and slow-release fertilizers, such as initial nutrient burst release, high nitrogen transformation and loss rates, and the sensitivity of inhibitors to high temperatures and chemical environments, the present invention aims to provide a nitrate-sulfur-based compound fertilizer with a dual slow-release synergistic mechanism. This compound fertilizer combines particle-scale physical controlled release with nitrogen transformation inhibition in the soil micro-domain, ensuring processing and storage stability, and achieving a synergistic and long-lasting effect of dual inhibitors and a three-layer coating structure. The specific technical solution is as follows: A method for producing a nitrate-sulfur-based slow-release compound fertilizer includes the following steps: S1: N-n-butylthiophosphoric triamine, 3,4-dimethylpyrazole phosphate, and porous starch are added to an ethanol-water solution at a mass ratio of 1:(0.5-2):(4-10) in 3-8 times the total mass of the N-n-butylthiophosphoric triamine, 3,4-dimethylpyrazole phosphate, and porous starch. The mixture is stirred, vacuum impregnated at -0.09 to -0.06 MPa, and dried to obtain a loaded powder. Ethyl cellulose solution is sprayed onto the surface of the loaded powder in a fluidized bed to obtain inhibitor protective particles. S2: Mix nitrate nitrogen source, urea, ammonium sulfate, potassium sulfate, phosphorus source and binder, and granulate by drum granulation to obtain fertilizer core particles; S3: Castor oil, polycaprolactone diol and polyethylene glycol are dehydrated and then polyisocyanate is added. The mixture is reacted at 70-85℃ to obtain a coated prepolymer. S4: Preheat the fertilizer core and keep it rolling, then spray the coating prepolymer, the mixture of inhibitor protective particles and coating prepolymer, and the coating prepolymer in sequence, and cure them to form an inner film layer, an intermediate film layer and an outer film layer, with the total mass of the three layers being 3%-10% of the mass of the fertilizer core.

[0004] Preferably, in S3, the amount of polyisocyanate added is determined according to the molar ratio of isocyanate group to hydroxyl group (1.05-1.30):1.

[0005] Preferably, the stirring and dispersion time in S1 is 15-40 min, the volume fraction of ethanol in the ethanol-water solution is 40%-70%, the vacuum degree of vacuum impregnation is -0.09 to -0.06 MPa, and the time is 20-60 min; the drying temperature is 35-50℃, until the moisture content of the loaded powder is not higher than 3%.

[0006] Preferably, the ethyl cellulose solution in S1 is a 6%-15% (w / w) ethyl cellulose ethyl acetate solution; the fluidized bed inlet air temperature is 45-60℃, the loaded powder temperature is 35-45℃, and the atomization pressure is 0.15-0.35MPa; the amount of ethyl cellulose used is 8%-25% of the loaded powder mass, and the particle size of the resulting inhibitor protective particles is 80-300μm.

[0007] Preferably, in S2, by weight, the nitrate nitrogen source is 20-35 parts, urea is 15-30 parts, ammonium sulfate is 15-30 parts, potassium sulfate is 10-25 parts, phosphorus source is 5-15 parts, and binder is 1-5 parts; the nitrate nitrogen source is at least one of potassium nitrate and ammonium nitrate, the phosphorus source is at least one of monoammonium phosphate and diammonium phosphate, and the binder is at least one of lignin sulfonate and starch.

[0008] Preferably, during the S2 drum granulation, the material temperature is 35-42℃ and the drum speed is 10-25 r / min. After granulation, the material is dried at 40-45℃ until the moisture content is not higher than 2%, and the particles with a particle size of 2-5 mm are screened out as fertilizer core particles.

[0009] Preferably, in S3, by weight, the castor oil comprises 40-60 parts, the polycaprolactone diol comprises 20-35 parts, and the polyethylene glycol comprises 5-15 parts; the number average molecular weight of the polyethylene glycol is 400-2000, and the number average molecular weight of the polycaprolactone diol is 500-3000; the polyisocyanate is 4,4-diphenylmethane diisocyanate.

[0010] Preferably, the dehydration in S3 is carried out by vacuum dehydration, with a vacuum dehydration temperature of 80-105℃, a vacuum degree of -0.095 to -0.07MPa, and a time of 30-90min. After vacuum dehydration, the temperature is lowered to 45-60℃ and 4,4-diphenylmethane diisocyanate is added. The temperature is then increased to 70-85℃ at a rate of 0.5-2℃ / min and the reaction is maintained at this temperature for 60-150min. The temperature is then lowered to 40-55℃ to obtain the coated prepolymer.

[0011] Preferably, the preheating temperature of the fertilizer core particles in S4 is 40-55℃; the mass ratio of the inner membrane layer, the intermediate membrane layer and the outer membrane layer is (20-35):(35-55):(20-35); the weight ratio of the inhibitor protective particles to the coating prepolymer used in the intermediate membrane layer is (5-20):100, and each membrane layer is formed by 2-6 atomization sprayings, and after each spraying, it is rolled and cured at 45-65℃ for 5-20 minutes.

[0012] Preferably, after completing the atomized spraying of the outer film layer and the rolling curing after each spraying in S4, the coated particles are finally rolled and cured at 50-65℃ for 20-60 minutes, and then left to stand and mature for 12-36 hours at 20-35℃ and relative humidity not exceeding 60%. After maturation, the particles are cooled and sieved to obtain nitrate-sulfur-based slow-release compound fertilizer with a particle size of 2-5 mm.

[0013] The beneficial effects of this invention are as follows: This invention involves vacuum impregnating N-n-butylthiophosphoric triamine, 3,4-dimethylpyrazole phosphate, and porous starch, then spraying ethyl cellulose onto the surface to form protective granules, which are finally placed in the intermediate membrane layer of a three-layer structure. This multi-layer coating structure and loading process effectively isolate the high-temperature environment of the granulation process and the isocyanate groups in the coating prepolymer, avoiding side reactions or thermal deactivation of the inhibitor. Combined with the controlled release effect of the multi-layer membrane, a synergistic effect of soil micro-domain nitrogen transformation inhibition and particle-scale physical controlled release is achieved, significantly reducing nutrient loss and nitrogen transformation loss. It should be noted that the mass transfer pathways and release sequences of the inhibitor and nutrients in this invention are specifically designed: the inhibitor protective particles are located in the intermediate membrane layer, and their outward release only requires crossing the outer membrane layer, while the nutrients such as nitrate nitrogen and ammonium nitrogen in the core particles require sequentially crossing the inner membrane layer, intermediate membrane layer, and outer membrane layer for outward release. The mass transfer pathway of the inhibitor is shorter than that of the nutrients. After the fertilizer is applied to the soil, water preferentially penetrates into the outer and intermediate membrane layers under osmotic pressure. The porous starch absorbs water and swells, and the pores expand. After the ethyl cellulose membrane absorbs water, it forms microporous channels. The inhibitor then diffuses outward through the short path driven by the concentration gradient. The nutrients enter the outer membrane layer and soil micro-domains before the large amount of nutrients in the core particles dissolve; while the nutrients need to penetrate the complete and dense inner membrane layer under the drive of osmotic pressure before they can be gradually dissolved, and their release starts later than that of the inhibitors; the amount of ethyl cellulose is limited to 8%-25% of the weight of the loaded powder, and its role is only to avoid the loss of inhibitors during processing and storage and instantaneous dissolution at the beginning of application, without causing release lag, so as to ensure that the urease inhibitor and nitrification inhibitor reach the effective concentration within the effective window of amide nitrogen hydrolysis and ammonium nitrogen nitrification, and achieve the synergistic effect of physical controlled release and nitrogen transformation inhibition in time.

[0014] This invention prepares a coated prepolymer by reacting castor oil, polycaprolactone diol, polyethylene glycol, and polyisocyanate, and then sequentially sprays and cures it on the surface of fertilizer core particles to form an inner membrane layer, an intermediate membrane layer, and an outer membrane layer. This specific prepolymer material and three-layer coating structure have continuous and dense physical characteristics, which can effectively slow down the diffusion of nutrients to the outside. This structure significantly reduces the initial nutrient release rate, overcomes the defects of ordinary fertilizers such as excessively high initial water solubility rate and sudden nutrient release, and significantly prolongs the effective release period of nitrogen. Detailed Implementation

[0015] The technical solutions in the embodiments of the present invention are described clearly and completely below; the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention; to ensure the repeatability and implementation effect of the technical solutions of the present invention, the porous starch of the present invention has a porosity of 40%-60%, a specific surface area of ​​8-15 m² / g, and an average pore size of 1-5 μm. The porosity and average pore size are determined by mercury intrusion porosimetry, and the specific surface area is determined by BET nitrogen adsorption method; the ethyl cellulose is pharmaceutical grade, and its viscosity in a 5% toluene / ethanol (mass ratio 80:20) mixed solvent at 25°C is 10-20 mPa·s.

[0016] Example 1:

[0017] This embodiment provides a nitrate-sulfur-based compound fertilizer with a dual slow-release synergistic mechanism, specifically including the following steps: S1, Preparation of Inhibitor Protective Particles N-n-butylthiophosphoric triamine, 3,4-dimethylpyrazole phosphate, and porous starch were added to an ethanol-water solution at a weight ratio of 1:1:6, with an ethanol volume fraction of 55% and the amount of ethanol-water solution being 5 times the total mass of the three materials. The mixture was stirred and dispersed for 30 min. The dispersion was then vacuum impregnated at a vacuum degree of -0.08 MPa for 40 min. After filtration, the mixture was dried at a low temperature of 42°C until the moisture content of the loaded powder was 2.1%. A 10% (w / w) ethyl cellulose ethyl acetate solution was atomized and sprayed onto the surface of a fluidized loaded powder. The fluidized bed inlet air temperature was 52℃, the loaded powder temperature was 40℃, the atomization pressure was 0.25MPa, and the amount of ethyl cellulose was 16% of the loaded powder mass. After drying and sieving, inhibitor protective particles with a particle size of 150-250μm were obtained. S2, Fertilizer Pellet Preparation By weight, 30 parts potassium nitrate, 22 parts urea, 22 parts ammonium sulfate, 15 parts potassium sulfate, 9 parts monoammonium phosphate, and 2 parts lignin sulfonate are mixed and added to a rotary drum granulator for granulation. The material temperature during granulation is 42℃, and the drum speed is 18r / min. After granulation, the material is dried at 45℃ until the moisture content is 1.4%, and granules with a particle size of 2-5mm are screened out as fertilizer core particles. S3, Preparation of coated prepolymer By weight, 50 parts castor oil, 28 parts polycaprolactone diol with a number average molecular weight of 1500, and 10 parts polyethylene glycol with a number average molecular weight of 1000 were mixed and vacuum dehydrated at 95°C and -0.085 MPa for 60 min. After dehydration, the mixture was cooled to 52°C, and 4,4-diphenylmethane diisocyanate was added, with a molar ratio of isocyanate groups to hydroxyl groups of 1.18:1. Under nitrogen protection, the mixture was heated to 78°C at a heating rate of 1°C / min, held at that temperature for 100 min, and then cooled to 48°C to obtain the coated prepolymer. In this embodiment, the hydroxyl value of castor oil is 163 mg KOH / g, the hydroxyl value of polycaprolactone diol is 75 mg KOH / g, the hydroxyl value of polyethylene glycol is 112 mg KOH / g, and the NCO mass fraction of 4,4-diphenylmethane diisocyanate is 31%. Based on the molar ratio of isocyanate group to hydroxyl group of 1.18:1, the specific amount of 4,4-diphenylmethane diisocyanate added is 32.4 parts. S4, Composite Coating Preheat the fertilizer core to 48°C and keep it in a rolling state; coat it with an inner film layer, an intermediate film layer and an outer film layer in a mass ratio of 30:40:30. The inner membrane layer is formed by spraying a coating prepolymer, which is applied in three coats, and each coat is cured by rolling at 55°C for 10 minutes. The middle membrane layer is formed by spraying a mixture of inhibitor protective particles and coating prepolymer, with a weight ratio of inhibitor protective particles to coating prepolymer of 12:100. The mixture is applied in four coats, and each coat is cured by rolling at 55°C for 10 minutes. The outer membrane layer is formed by spraying a coating prepolymer, which is applied in three coats, and each coat is cured by rolling at 55°C for 10 minutes. The total mass of the three-layer membrane is 6% of the mass of the fertilizer core particles. After the outer membrane layer is sprayed, it is rolled and cured at 58℃ for 40 minutes, and then left to mature at 25℃ and relative humidity not higher than 60% for 24 hours. After maturation, it is cooled and sieved to obtain nitrate-sulfur-based slow-release compound fertilizer with a particle size of 2-5mm. Performance evaluation of the product in this embodiment: Using the 25℃ static water extraction method, the initial nutrient release rate was 1.2%, the nutrient release rate after 28 days was 35%, and the nutrient release cycle was as long as 90 days. The membrane structure was dense and undamaged. Using the phenol-sodium hypochlorite colorimetric method and the soil culture method, the urease inhibition rate was 85% and the nitrification inhibition rate was 88% on the 28th day of culture, respectively, which effectively confirmed the synergistic long-term effect of the dual inhibitors and the three-layer membrane structure. The specific testing conditions for the soil culture method are as follows: take air-dried soil that has passed through a 2mm sieve, adjust the soil moisture content to 60% of the field capacity, add fertilizer sample according to the set ratio and mix well, then culture at a constant temperature of 25℃ and in the dark, and periodically sample, extract and determine the content of ammonium nitrogen and nitrate nitrogen in the soil.

[0018] In addition, to characterize the temporal synchronicity of inhibitor release and nutrient release, dynamic release data were determined using a 25℃ static water extraction method: fertilizer samples were placed in deionized water and soaked at a constant temperature. The extract was changed and samples were taken on days 1, 3, 7, 14, 28, 45, 60, and 90. The contents of N-n-butylthiophosphoric acid triamine and 3,4-dimethylpyrazole phosphate in the extract were determined using high-performance liquid chromatography (HPLC), and the total nitrogen content in the extract was also determined. The cumulative release rate at each sampling point was calculated using the following formula: R(t) = M t / M0×100%, where M t M0 represents the cumulative mass of the target compound in the extract on day t, and M0 represents the initial mass of the target compound in the fertilizer. And the Ritger-Peppas equation M is adopted. t / M∞=kt nThe obtained dynamic release data are fitted, where M∞ is the equilibrium cumulative release, K is the release rate constant, and n is the diffusion index. The results were as follows: the cumulative release rates of nitrogen nutrients on days 1, 3, 7, 14, 28, 45, 60, and 90 were 1.2%, 4.5%, 10.2%, 18.5%, 35%, 52%, 70%, and 88%, respectively. M∞ was set to 100%, and the data range with a cumulative release rate not exceeding 60% was fitted, yielding n=0.52. The cumulative release rates of N-n-butylthiophosphoric acid triamine were 6.1%, 15.3%, 28.4%, 42.5%, 60.2%, 75.1%, 86.3%, and 94.8%, respectively, yielding n=0.58. The cumulative release rates of 3,4-dimethylpyrazole phosphate were 5.2%, 13.1%, 25.6%, 38.9%, 55.4%, 71.8%, 84.0%, and 93.5%, respectively, yielding n=0.56.

[0019] The time required for the cumulative release rate to reach 50% is denoted as the half-release period t. 50 nitrogen nutrient t 50 Approximately 42 days, the t-test results for both inhibitors 50 The inhibitor's t-days were approximately 22 days and 26 days, respectively. 50 Significantly smaller than nutrient t 50 Define the release synchronization exponent S(t) = R i (t) / R n (t), where R is a t), i (t) represents the arithmetic mean of the cumulative release rates of the two inhibitors on day t, R n S(t) represents the cumulative release rate of nitrogen nutrients on day t. In this example, S(t) was greater than 1.5 from day 1 to day 28, indicating that the release of the inhibitor preceded the release of nutrients rather than lagged behind. This experimentally verified the existence of a synergistic mechanism between physical controlled release and nitrogen conversion inhibition.

[0020] Meanwhile, using the aforementioned soil culture method, samples were taken on days 7, 14, 28, 45, 60, and 90 of culture to determine the urease inhibition rate and nitrification inhibition rate. The results showed that the urease inhibition rates were 92%, 90%, 85%, 80%, 74%, and 68%, respectively, and the nitrification inhibition rates were 94%, 91%, 88%, 83%, 77%, and 70%, respectively. It can be seen that throughout the entire cycle of continuous nutrient release, both inhibitors maintained effective inhibition levels, and the duration of the inhibitory effect completely covered the high incidence periods of amide nitrogen hydrolysis and ammonium nitrogen nitrification, which matched the nutrient release data on a time scale.

[0021] Example 2:

[0022] This embodiment uses the same raw materials and operating steps as Embodiment 1, only changing some process parameters; In S1, the weight ratio of N-n-butylthiophosphoric triamine, 3,4-dimethylpyrazole phosphate, and porous starch is 1:0.5:4. The volume fraction of ethanol in the aqueous ethanol solution is 40%, and the amount of aqueous ethanol solution used is 3 times the total mass of the three materials. The stirring and dispersion time is 15 min, the vacuum degree is -0.06 MPa, the vacuum impregnation time is 20 min, the low temperature drying temperature is 35℃, and the moisture content of the loaded powder is 2.8%. The mass fraction of ethyl cellulose ethyl acetate solution was 6%, the amount of ethyl cellulose was 8% of the mass of the loaded powder, the fluidized bed inlet air temperature was 45℃, the loaded powder temperature was 35℃, the atomization pressure was 0.15MPa, and the particle size of the resulting inhibitor protective particles was 80-150μm. In S2, 20 parts potassium nitrate, 30 parts urea, 15 parts ammonium sulfate, 25 parts potassium sulfate, 5 parts diammonium phosphate, and 5 parts starch are mixed and granulated. The material temperature during granulation is 35℃, the drum speed is 10r / min, the drying temperature is 45℃, the moisture content after drying is 1.9%, and fertilizer core particles with a particle size of 2-5mm are screened out. In S3, 40 parts of castor oil, 35 parts of polycaprolactone diol with a number average molecular weight of 500, and 15 parts of polyethylene glycol with a number average molecular weight of 400 are mixed; the vacuum dehydration temperature is 80℃, the vacuum degree is -0.07MPa, and the dehydration time is 30min; after cooling to 45℃, 4,4-diphenylmethane diisocyanate is added, with a molar ratio of isocyanate groups to hydroxyl groups of 1.05:1; the temperature is increased to 70℃ at 0.5℃ / min, and the reaction is maintained at this temperature for 60min; then the temperature is cooled to 40℃ to obtain the coated prepolymer. Among them, the hydroxyl value of castor oil is 163 mg KOH / g, the hydroxyl value of polycaprolactone diol is 224 mg KOH / g, the hydroxyl value of polyethylene glycol is 280 mg KOH / g, and the NCO mass fraction of 4,4-diphenylmethane diisocyanate is 31%. The amount added is 47.1 parts according to the above molar ratio of 1.05:1. In S4, the preheating temperature of the fertilizer core is 40℃, and the mass ratio of the inner membrane layer, the middle membrane layer, and the outer membrane layer is 20:55:25; the weight ratio of the inhibitor protective particles to the coating prepolymer is 5:100, each membrane layer is sprayed twice, and after each spraying, it is rolled and cured at 45℃ for 5 minutes; the total mass of the three membrane layers is 3% of the mass of the fertilizer core. After the outer film layer is completed, it is rolled and cured at 50°C for 20 minutes, and then allowed to stand and mature for 12 hours at 20°C and relative humidity not exceeding 60% to obtain nitrate-sulfur-based slow-release compound fertilizer. Evaluated using the same test method as in Example 1, the initial nutrient release rate of the product in this example is 1.5%, the nutrient release rate after 28 days is 38%, and the nutrient release cycle reaches 80 days; the urease inhibition rate is 82%, and the nitrification inhibition rate is 84%.

[0023] The cumulative release rates of nitrogen nutrients on days 1, 7, 14, 28, 60, and 80 were measured using the same method as in Example 1: 1.5%, 11.0%, 19.8%, 38%, 72%, and 86%, respectively; the cumulative release rates of N-n-butylthiophosphoric acid triamine were 6.5%, 29.5%, 43.8%, 62.0%, 87.5%, and 94.0%, respectively; and the cumulative release rates of 3,4-dimethylpyrazole phosphate were 5.6%, 26.8%, 40.2%, 57.5%, 85.0%, and 92.8%, respectively. The t-day values ​​of nitrogen nutrients were also measured. 50 Approximately 38 days, the t-test results for both inhibitors 50 The incubation periods were approximately 20 days and 24 days, respectively, with S(t) greater than 1.4 from day 1 to day 28. The urease inhibition rates on days 7, 14, 28, 45, 60, and 80 were 90%, 88%, 82%, 77%, 71%, and 65%, respectively, while the nitrification inhibition rates were 92%, 89%, 84%, 80%, 74%, and 67%, respectively.

[0024] Example 3:

[0025] This embodiment uses the same raw materials and operating steps as Embodiment 1, only changing some process parameters; In S1, the weight ratio of N-n-butylthiophosphoric triamine, 3,4-dimethylpyrazole phosphate, and porous starch is 1:2:10. The volume fraction of ethanol in the aqueous ethanol solution is 70%, and the amount of aqueous ethanol solution used is 8 times the total mass of the three materials. The stirring and dispersion time is 40 min, the vacuum degree is -0.09 MPa, the vacuum impregnation time is 60 min, the low temperature drying temperature is 50℃, and the moisture content of the loaded powder is 1.5%. The mass fraction of ethyl cellulose ethyl acetate solution is 15%, the amount of ethyl cellulose is 25% of the mass of the loaded powder, the fluidized bed inlet air temperature is 60℃, the loaded powder temperature is 45℃, the atomization pressure is 0.35MPa, and the particle size of the resulting inhibitor protective particles is 250-300μm. In S2, there are 35 parts of ammonium nitrate, 15 parts of urea, 30 parts of ammonium sulfate, 10 parts of potassium sulfate, 15 parts of diammonium phosphate, and 1 part of a mixed binder of lignin sulfonate and starch, of which 0.5 parts are lignin sulfonate and 0.5 parts are starch. The mixture is granulated. The material temperature during granulation is 42℃, the drum speed is 25r / min, the drying temperature is 45℃, the moisture content after drying is 1.2%, and fertilizer core particles with a particle size of 2-5mm are screened out. In S3, 60 parts of castor oil, 20 parts of polycaprolactone diol with a number average molecular weight of 3000, and 5 parts of polyethylene glycol with a number average molecular weight of 2000 are mixed; the vacuum dehydration temperature is 105℃, the vacuum degree is -0.095MPa, and the dehydration time is 90min; after cooling to 60℃, 4,4-diphenylmethane diisocyanate is added, with a molar ratio of isocyanate groups to hydroxyl groups of 1.30:1; the temperature is increased to 85℃ at 2℃ / min, and the reaction is maintained at this temperature for 150min; then the temperature is cooled to 55℃ to obtain the coated prepolymer. In this embodiment, the hydroxyl value of castor oil is 163 mg KOH / g, the hydroxyl value of polycaprolactone diol is 37 mg KOH / g, the hydroxyl value of polyethylene glycol is 56 mg KOH / g, and the NCO mass fraction of 4,4-diphenylmethane diisocyanate is 31%. Based on the above molar ratio of 1.30:1, the amount added is 33.9 parts. In S4, the preheating temperature of the fertilizer core particles is 55℃, and the mass ratio of the inner membrane layer, the middle membrane layer, and the outer membrane layer is 35:35:30; the weight ratio of the inhibitor protective particles to the coating prepolymer is 20:100. Each membrane layer is sprayed 6 times, and after each spraying, it is rolled and cured at 65℃ for 20 minutes; the total mass of the three membrane layers is 10% of the mass of the fertilizer core particles; after the outer membrane layer is completed, it is rolled and cured at 65℃ for 60 minutes, and then allowed to stand and mature for 36 hours at 35℃ and an ambient relative humidity not exceeding 60% to obtain the nitrate-sulfur-based slow-release compound fertilizer. The product of this example was evaluated using the same test methods as in Example 1. The initial nutrient release rate was 1.3%, the 28-day nutrient release rate was 36%, and the nutrient release cycle was 85 days. The urease inhibition rate was 84%, and the nitrification inhibition rate was 86%. The cumulative release rates of nitrogen nutrients on days 1, 7, 14, 28, 60, and 85 were measured using the same method as in Example 1: 1.3%, 10.5%, 19.0%, 36%, 71%, and 87%, respectively; the cumulative release rates of N-n-butylthiophosphoric triamine were 6.3%, 28.8%, 43.0%, 61.0%, 86.8%, and 94.2%, respectively; and the cumulative release rates of 3,4-dimethylpyrazole phosphate were 5.4%, 26.2%, 39.5%, 56.8%, 84.5%, and 93.0%, respectively. The t-day values ​​of nitrogen nutrients were also measured. 50 Approximately 40 days, the t-test results for both inhibitors 50 The incubation periods were approximately 21 and 25 days, respectively, with S(t) greater than 1.4 from day 1 to day 28. The urease inhibition rates on days 7, 14, 28, 45, 60, and 85 were 91%, 89%, 84%, 79%, 73%, and 66%, respectively, while the nitrification inhibition rates were 93%, 90%, 86%, 81%, 75%, and 68%, respectively.

[0026] Example 4:

[0027] This embodiment uses similar operating steps to Embodiment 1, only changing some raw material types and process parameters; In S1, the weight ratio of N-n-butylthiophosphoric triamine, 3,4-dimethylpyrazole phosphate, and porous starch is 1:1.5:8. The volume fraction of ethanol in the aqueous ethanol solution is 60%, and the amount of aqueous ethanol solution used is 6 times the total mass of the three materials. The stirring and dispersion time is 25 min, the vacuum degree is -0.075 MPa, the vacuum impregnation time is 45 min, the low temperature drying temperature is 45℃, and the moisture content of the loaded powder is 2.0%. The mass fraction of ethyl cellulose ethyl acetate solution was 12%, the amount of ethyl cellulose was 20% of the mass of the loaded powder, the fluidized bed inlet air temperature was 55℃, the loaded powder temperature was 42℃, the atomization pressure was 0.30MPa, and the particle size of the resulting inhibitor protective particles was 180-280μm. In S2, there are 28 parts of a mixed nitrate nitrogen source of potassium nitrate and ammonium nitrate, including 14 parts of potassium nitrate and 14 parts of ammonium nitrate; 25 parts of urea; 24 parts of ammonium sulfate; 18 parts of potassium sulfate; 12 parts of a mixed phosphorus source of monoammonium phosphate and diammonium phosphate, including 6 parts of monoammonium phosphate and 6 parts of diammonium phosphate; and 3 parts of a mixed binder of lignin sulfonate and starch, including 1.5 parts of lignin sulfonate and 1.5 parts of starch, which are mixed and granulated. The material temperature during granulation is 40℃, the drum speed is 20r / min, the drying temperature is 45℃, the moisture content after drying is 1.5%, and fertilizer core particles with a particle size of 2-5mm are screened out. In S3, 55 parts of castor oil, 25 parts of polycaprolactone diol with a number average molecular weight of 2000, and 12 parts of polyethylene glycol with a number average molecular weight of 1500 were mixed; the vacuum dehydration temperature was 100℃, the vacuum degree was -0.09MPa, and the dehydration time was 70min; after cooling to 55℃, 4,4-diphenylmethane diisocyanate was added, with a molar ratio of isocyanate groups to hydroxyl groups of 1.22:1; the temperature was increased to 80℃ at 1.5℃ / min, and the reaction was maintained at this temperature for 120min; then the temperature was lowered to 50℃ to obtain the coated prepolymer. In this embodiment, the hydroxyl value of castor oil is 163 mg KOH / g, the hydroxyl value of polycaprolactone diol is 56 mg KOH / g, the hydroxyl value of polyethylene glycol is 75 mg KOH / g, and the NCO mass fraction of 4,4-diphenylmethane diisocyanate is 31%. Based on the above molar ratio of 1.22:1, the amount added is 33.2 parts. In S4, the preheating temperature of the fertilizer core is 50℃, and the mass ratio of the inner membrane layer, the middle membrane layer, and the outer membrane layer is 30:45:25; the weight ratio of the inhibitor protective particles to the coating prepolymer is 15:100. Each membrane layer is sprayed 4 times, and after each spraying, it is rolled and cured at 60℃ for 15 minutes; the total mass of the three membrane layers is 7% of the mass of the fertilizer core; after the outer membrane layer is completed, it is rolled and cured at 60℃ for 45 minutes, and then allowed to stand and mature for 24 hours at 30℃ and an ambient relative humidity not exceeding 60% to obtain the nitrate-sulfur-based slow-release compound fertilizer. The product of this example was evaluated using the same test method as in Example 1. The initial nutrient release rate was 1.4%, the nutrient release rate after 28 days was 37%, and the nutrient release cycle was 88 days. The urease inhibition rate was 83% and the nitrification inhibition rate was 87% on the 28th day of culture.

[0028] Comparative Example 1: The difference between this comparative example and Example 1 is that the ethyl cellulose atomization spraying, drying and sieving operations in step S1 are omitted, and the loaded powder after vacuum impregnation and low temperature drying is directly added as the inhibitor-containing material to the intermediate film layer in step S4; other operation steps and process parameters are exactly the same as in Example 1.

[0029] Comparative Example 2: The difference between this comparative example and Example 1 is that the porous starch in step S1 is replaced with the same mass of ordinary starch, while the other operating steps and process parameters are exactly the same as in Example 1. Following the same performance evaluation as Example 1, Comparative Example 2 showed an initial nutrient release rate of 2.0%, a nutrient release rate of 40% after 28 days, and a nutrient release cycle of 78 days. However, the cumulative release rate of the inhibitors on day 1 reached 32%, and the urease inhibition rate and nitrification inhibition rate on day 28 were 57% and 60%, respectively, indicating that ordinary starch was insufficient for loading and sustained-release protection of the two inhibitors.

[0030] Comparative Example 3: The difference between this comparative example and Example 1 is that the inner film layer spraying and curing operation in step S4 is omitted, and the intermediate film layer containing inhibitor is directly sprayed on the surface of the fertilizer core, followed by the outer film layer spraying; the mass ratio of the intermediate film layer to the outer film layer is adjusted to 40:30, and the total mass of the two film layers is maintained at 6% of the mass of the fertilizer core. Other operation steps and process parameters are exactly the same as in Example 1. Following the same performance evaluation as Example 1, Comparative Example 3 showed an initial nutrient release rate of 7.6%, a 28-day nutrient release rate of 69%, and a nutrient release cycle of 55 days. On day 7, S(t) was 0.8, and on day 28, the urease inhibition rate and nitrification inhibition rate were 62% and 64%, respectively. This indicates that the lack of an inner membrane layer weakens the nutrient slow-release barrier effect and disrupts the time matching relationship between inhibitor release and nutrient release.

[0031] Comparative Example 4: The difference between this comparative example and Example 1 is that the outer film layer spraying and curing operation in step S4 is omitted, the mass ratio of the inner film layer and the inhibitor-containing intermediate film layer is adjusted to 30:40, the total mass of the film layer is maintained at 6% of the mass of the fertilizer core particles, and other operation steps and process parameters are exactly the same as in Example 1.

[0032] Comparative Example 5: The difference between this comparative example and Example 1 is that N-n-butylthiophosphoric triamine in step S1 is omitted, and only 3,4-dimethylpyrazole phosphate and porous starch are used to prepare inhibitor protective particles, and the mass of N-n-butylthiophosphoric triamine is reduced accordingly. Other operating steps and process parameters are exactly the same as in Example 1.

[0033] Comparative Example 6: The difference between this comparative example and Example 1 is that 3,4-dimethylpyrazole phosphate in step S1 is omitted, and only N-n-butylthiophosphoric triamine and porous starch are used to prepare inhibitor protective particles, and the mass of 3,4-dimethylpyrazole phosphate is reduced accordingly. Other operating steps and process parameters are exactly the same as in Example 1.

[0034] Following the same dynamic release test as in Example 1, Comparative Example 1, lacking ethyl cellulose coating, showed a cumulative release rate of 45% for the inhibitor on day 1, but no effective inhibitory concentration was detected in the soil after day 28, with a urease inhibition rate of only 50% on day 28, exhibiting a disconnect between initial instantaneous release and later ineffectiveness. Comparative Example 2, using ordinary starch, had insufficient inhibitor loading stability, with a cumulative release rate of 32% on day 1, and urease inhibition rate and nitrification inhibition rate decreasing to 57% and 60% on day 28, respectively. Comparative Example 3, lacking an inner membrane layer, achieved an initial nutrient release rate of 7.6%, reaching 69% after 28 days, with an S(t) of 0.8 on day 7. This significantly accelerated nutrient release and weakened the synergistic effect of the dual slow-release mechanism. Comparative Example 4, lacking an outer membrane layer, achieved an initial nutrient release rate of 8.2%, but its S(t) dropped below 0.6 from day 7 onwards, indicating that inhibitor release lagged behind nutrient burst release. Comparative Examples 5 and 6, containing only a single inhibitor, showed that by day 28, the urease inhibition rate and nitrification inhibition rate decreased to 52% and 54%, respectively, failing to maintain effective inhibition throughout the entire nutrient release cycle. These comparisons demonstrate that only when porous starch loading, ethyl cellulose protection, a three-layer membrane structure, and a dual-inhibitor combination are simultaneously present can the release of inhibitors and nutrients be synchronized.

[0035] Comparative Example 7: The difference between this comparative example and Example 1 is that the molar ratio of isocyanate group to hydroxyl group in step S3 is adjusted from 1.18:1 to 0.95:1, while the remaining operation steps and process parameters are exactly the same as in Example 1. Based on the hydroxyl value parameters of each raw material in Example 1, the specific amount of 4,4-diphenylmethane diisocyanate added at this time is approximately 26.1 parts. Performance evaluation under the same conditions showed that insufficient isocyanate group content led to a decrease in the degree of crosslinking of the prepolymer and incomplete curing, resulting in an increase in membrane pore defects. Its initial nutrient release rate was 12.5%, and the nutrient release rate reached 78% after 28 days, with a nutrient release cycle of only 40 days. Furthermore, the urease inhibition rate dropped to 55%, and the nitration inhibition rate dropped to 58%, failing to achieve the long-term sustained-release and dual-inhibitor synergistic protection effects described in the examples.

[0036] The above are merely specific embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any conventional modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for producing a nitrate-sulfur-based slow-release compound fertilizer, characterized in that, Includes the following steps: S1: N-n-butylthiophosphoric triamine, 3,4-dimethylpyrazole phosphate, and porous starch are added to an ethanol-water solution at a mass ratio of 1:(0.5-2):(4-10) in 3-8 times the total mass of the N-n-butylthiophosphoric triamine, 3,4-dimethylpyrazole phosphate, and porous starch. The mixture is stirred, vacuum impregnated at -0.09 to -0.06 MPa, and dried to obtain a loaded powder. Ethyl cellulose solution is sprayed onto the surface of the loaded powder in a fluidized bed to obtain inhibitor protective particles. S2: Mix nitrate nitrogen source, urea, ammonium sulfate, potassium sulfate, phosphorus source and binder, and granulate by drum granulation to obtain fertilizer core particles; S3: Castor oil, polycaprolactone diol and polyethylene glycol are dehydrated and then polyisocyanate is added. The mixture is reacted at 70-85℃ to obtain a coated prepolymer. S4: Preheat the fertilizer core and keep it rolling, then spray the coating prepolymer, the mixture of inhibitor protective particles and coating prepolymer, and the coating prepolymer in sequence, and cure them to form an inner film layer, an intermediate film layer and an outer film layer, with the total mass of the three layers being 3%-10% of the mass of the fertilizer core.

2. The production method of a nitrate-sulfur-based slow-release compound fertilizer as described in claim 1, characterized in that, In S3, the amount of polyisocyanate added is determined according to the molar ratio of isocyanate group to hydroxyl group (1.05-1.30):

1.

3. The production method of a nitrate-sulfur-based slow-release compound fertilizer as described in claim 1, characterized in that, The stirring and dispersion time in S1 is 15-40 min, the volume fraction of ethanol in the ethanol aqueous solution is 40%-70%, the vacuum degree of vacuum impregnation is -0.09 to -0.06 MPa, and the time is 20-60 min; the drying temperature is 35-50℃, until the moisture content of the loaded powder is not higher than 3%.

4. The production method of a nitrate-sulfur-based slow-release compound fertilizer as described in claim 1, characterized in that, The ethyl cellulose solution mentioned in S1 is a 6%-15% (w / w) ethyl cellulose ethyl acetate solution; the fluidized bed inlet air temperature is 45-60℃, the loaded powder temperature is 35-45℃, and the atomization pressure is 0.15-0.35MPa; the amount of ethyl cellulose used is 8%-25% of the loaded powder mass, and the particle size of the resulting inhibitor protective particles is 80-300μm.

5. The production method of a nitrate-sulfur-based slow-release compound fertilizer as described in claim 1, characterized in that, In S2, by weight, the nitrate nitrogen source is 20-35 parts, urea is 15-30 parts, ammonium sulfate is 15-30 parts, potassium sulfate is 10-25 parts, phosphorus source is 5-15 parts, and binder is 1-5 parts; the nitrate nitrogen source is at least one of potassium nitrate and ammonium nitrate, the phosphorus source is at least one of monoammonium phosphate and diammonium phosphate, and the binder is at least one of lignin sulfonate and starch.

6. The production method of a nitrate-sulfur-based slow-release compound fertilizer as described in claim 5, characterized in that, During S2 rotary drum granulation, the material temperature is 35-42℃ and the drum speed is 10-25r / min. After granulation, the material is dried at 40-45℃ until the moisture content is not higher than 2%. Particles with a diameter of 2-5mm are screened out as fertilizer core particles.

7. The production method of a nitrate-sulfur-based slow-release compound fertilizer as described in claim 2, characterized in that, In S3, by weight, the castor oil comprises 40-60 parts, the polycaprolactone diol comprises 20-35 parts, and the polyethylene glycol comprises 5-15 parts; the number average molecular weight of the polyethylene glycol is 400-2000, and the number average molecular weight of the polycaprolactone diol is 500-3000; the polyisocyanate is 4,4-diphenylmethane diisocyanate.

8. The production method of a nitrate-sulfur-based slow-release compound fertilizer as described in claim 7, characterized in that, The dehydration described in S3 is performed using vacuum dehydration at a temperature of 80-105℃, a vacuum degree of -0.095 to -0.07 MPa, and a time of 30-90 min. After vacuum dehydration, the temperature is lowered to 45-60℃ and 4,4-diphenylmethane diisocyanate is added. The temperature is then increased to 70-85℃ at a rate of 0.5-2℃ / min and maintained for 60-150 min. The temperature is then lowered to 40-55℃ to obtain the coated prepolymer.

9. The production method of a nitrate-sulfur-based slow-release compound fertilizer as described in claim 1, characterized in that, The preheating temperature of the fertilizer core particles in S4 is 40-55℃; the mass ratio of the inner membrane layer, the intermediate membrane layer and the outer membrane layer is (20-35):(35-55):(20-35); the weight ratio of the inhibitor protective particles to the coating prepolymer used in the intermediate membrane layer is (5-20):

100. Each membrane layer is formed by 2-6 atomization sprayings, and after each spraying, it is rolled and cured at 45-65℃ for 5-20 minutes.

10. The production method of a nitrate-sulfur-based slow-release compound fertilizer as described in claim 9, characterized in that, After completing the atomized spraying of the outer film layer in S4 and the rolling curing after each spraying, the coated particles are rolled and cured at 50-65℃ for 20-60 minutes, and then left to stand and mature for 12-36 hours at 20-35℃ and relative humidity not exceeding 60%. After maturation, the particles are cooled and sieved to obtain nitrate-sulfur-based slow-release compound fertilizer with a particle size of 2-5mm.