High utilization rate compound fertilizer with protective layer and preparation method thereof

Abstract

The present application relates to a high utilization rate compound fertilizer with a protective layer and a preparation method thereof, and belongs to the technical field of agricultural fertilizers. Bio-based polyols prepared by liquefaction of corn cobs are compounded with natural epoxy soybean oil to serve as a coating core raw material. Both of them contain functional groups such as hydroxyl groups and ester groups that can be degraded by soil microorganisms. The membrane shell has a high biodegradation rate, and will not accumulate residues during long-term use. Meanwhile, the polyurethane crosslinking network cooperates with soil microorganisms to maintain soil aggregate structure, improve air and water permeability, effectively avoid soil compaction, and form stable chelates with magnesium and iron ions to avoid the precipitation of trace elements in the soil with clay minerals and phosphate, thereby improving the absorption rate of crops. In combination with the inhibitory effect of urease inhibitors on urease activity, a dual controlled release system of physical barrier and biological inhibition is constructed to prolong the release period of nitrogen and match the nutrient requirements of crops during the growth period.

Description

Technical Field

[0001] This invention belongs to the field of agricultural fertilizer technology, and relates to a high-utilization compound fertilizer with a protective layer and its preparation method. Background Technology

[0002] In modern agricultural production, compound fertilizer is a core input to ensure high crop yields. However, the performance shortcomings of traditional products have become a constraint on industrial upgrading. On the one hand, the nutrients in conventional compound fertilizers exist in a fast-acting form and are easily lost through ammonia volatilization and nitrate leaching after being applied to the soil. Especially in sandy soils or rainy areas, the nutrient utilization rate is less than 35%, which increases planting costs and exacerbates agricultural non-point source pollution. On the other hand, compound fertilizers produced by traditional granulation processes have many pores on the surface of the particles and strong hygroscopicity. After being stored for more than 30 days, the clumping rate can reach more than 30%. They need to be crushed before application, which reduces the uniformity of nutrients and increases labor costs.

[0003] Chinese invention patent application CN121063974A discloses a compound fertilizer for improving the utilization rate of nutrient elements and its preparation method. The compound fertilizer includes, by weight, 10-30 parts of nitrogen source, 5-20 parts of phosphorus source, 10-25 parts of potassium source, 3-15 parts of synergist, 1-5 parts of trace elements, 2-8 parts of coating material, and 8-15 parts of plant growth promoter. The plant growth promoter is a specific deuterated benzene ring derivative. The preparation method includes processes such as raw material mixing and crushing, microbial pre-fermentation, granulation of coating liquid, and fluidized bed coating. Through humic acid chelation, microbial agent activation, and synergistic effect of deuterated molecular structure, the utilization rate of nitrogen, phosphorus, and potassium is increased to more than 1.5 times that of conventional fertilizers. At the same time, it improves the soil microbial environment and realizes intelligent slow release of nutrients.

[0004] The above scheme uses petrochemical-based materials such as polyacrylate or polyvinyl alcohol as coating materials. Because the molecular structure contains stable carbon-carbon covalent bonds and ether bonds, soil microorganisms lack the corresponding degradation enzyme system. After these coating materials are applied to the soil with chemical fertilizers, they are difficult to be decomposed and mineralized by microorganisms. Long-term application will lead to soil compaction and affect crop root extension and nutrient absorption. Summary of the Invention

[0005] The purpose of this invention is to provide a high-utilization compound fertilizer with a protective layer and its preparation method. By immobilizing trace elements with chelates and bio-based coatings, a slow-release effect is achieved, which improves the nutrient utilization rate of the compound fertilizer and solves the problem of soil pollution caused by petrochemical-based coatings.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing a high-utilization compound fertilizer with a protective layer includes the following steps: Step 1: Combine the metal ions of ammonium polyphosphate with magnesium salt solution and iron salt solution through coordination bonds to obtain chelates.

[0007] Step 2: The corn cob is liquefied using polyethylene glycol 400, glycerol and catalyst H-ZSM-5 to obtain a bio-based polyol.

[0008] Step 3: Mix urea, potassium dihydrogen phosphate, chelate, potassium sulfate, quartz sand and urease inhibitor evenly, and then granulate by extrusion using a granulator to obtain granular compound fertilizer.

[0009] Step 4: Coat the surface of the granular compound fertilizer with bio-based polyol, epoxidized soybean oil, stannous octanoate and isopropyl isocyanate coating material using a coating machine. After cross-linking and curing, a high-utilization compound fertilizer with a protective layer is obtained.

[0010] Furthermore, the specific preparation process of the chelate is as follows: Ammonium polyphosphate and deionized water were added to a reaction vessel and stirred to dissolve. The pH of the solution was adjusted to 6.8-7.2 with 10wt% ammonia water. Magnesium salt solution and iron salt solution were added at 35-37℃ and stirred for 45-55 minutes. Then anhydrous ethanol was added to precipitate the mixture. The precipitate was then centrifuged, filtered, dried, pulverized, and sieved to obtain the chelate.

[0011] The adjacent P=O and P-OH groups in the ammonium polyphosphate molecule form bidentate ligands, providing stable binding sites for metal ions. The pH range of 6.8-7.2 can prevent the hydrolysis of metal ions and enhance the efficiency of coordination bond formation. Magnesium ions in magnesium salt solutions and iron ions in iron salt solutions are bound to the bidentate polyphosphate through coordination bonds to form structurally stable chelates, preventing metal ions from reacting with clay minerals and phosphates in the soil and precipitating.

[0012] Furthermore, the ratio of ammonium polyphosphate, deionized water, magnesium salt solution, and iron salt solution is 0.95-1.15 kg : 2.1-2.5 L : 0.2-0.3 kg : 0.25-0.45 kg. This ratio ensures that the coordination chelation reaction proceeds fully and improves the chelation rate of metal ions.

[0013] Furthermore, the magnesium salt solution is one of magnesium chloride solution and magnesium sulfate solution.

[0014] Furthermore, the iron salt solution is one of ferrous sulfate solution and ferrous ammonium sulfate solution.

[0015] Furthermore, the specific preparation method of bio-based polyols is as follows: Corn cobs were added to a high-pressure reactor, along with liquefying agents polyethylene glycol 400 and glycerol, and then calcined and activated catalyst H-ZSM-5. The mixture was thoroughly mixed, and the air inside the reactor was replaced three times with nitrogen. The reaction was carried out at 300-500 r / min and 180-190℃ for 100-120 min, during which the pressure inside the reactor naturally rose to 0.3-0.5 MPa. After the reaction was completed, the reactor was cooled to room temperature, the pressure was released, and 1,4-dioxane was added. The mixture was stirred for 30-40 min, centrifuged, and rotary evaporated to obtain bio-based polyols.

[0016] Corn cobs have a high cellulose content, which provides sufficient active groups for the liquefaction reaction. The liquefying agents polyethylene glycol 400 and glycerol can synergistically improve the dissolution efficiency of corn cob lignocellulose. The catalyst H-ZSM-5 has many acidic sites, which can reduce the activation energy of lignocellulose decomposition. Under the synergistic effect of the liquefying agent and the catalyst, the cellulose, hemicellulose and lignin in the corn cob decompose into bio-based polyols containing multiple hydroxyl groups. The hydroxyl groups can provide active sites for the subsequent polyurethane reaction.

[0017] Furthermore, the ratio of corn cob, polyethylene glycol 400, glycerol, H-ZSM-5 and 1,4-dioxane is 100-120g: 350-400g: 150-180g: 50-60g: 300-400mL.

[0018] This ratio ensures high liquefaction efficiency of corn cobs, guaranteeing that the yield and purity of bio-based polyols meet coating requirements.

[0019] Furthermore, the mass ratio of urea, potassium dihydrogen phosphate, chelate, potassium sulfate, quartz sand and urease inhibitor is 3.91-4.31: 1.92-2.12: 0.54-0.64: ​​2.4-2.8: 1.76-1.96: 0.005-0.007.

[0020] The nutrient ratio is suitable for the growth needs of most crops. Among them, urease inhibitors can inhibit urease activity and reduce ammonia volatilization loss, while quartz sand acts as a weighting agent and filler to improve the mechanical strength of the particles.

[0021] Furthermore, the specific preparation process of the high-utilization compound fertilizer with a protective layer is as follows: Preheat the coating machine to 68-72℃ with a blower. Add granular compound fertilizer at 30-50 r / min, then add the coating material: bio-based polyol, epoxidized soybean oil, stannous octanoate, and isopropyl isocyanate. Let it react fully for 15-20 minutes, then add the coating material again and repeat the reaction 3 times. Maintain the temperature at 68-72℃ and continue stirring for 30-40 minutes to ensure that the membrane is completely cross-linked and cured. Allow it to cool naturally to room temperature to obtain a high-utilization compound fertilizer with a protective layer.

[0022] A temperature range of 68-72℃ can accelerate the formation of polyurethane while avoiding uneven coating caused by excessively rapid curing of the membrane. The hydroxyl groups of the bio-based polyol and the isopropyl isocyanate groups of isopropyl octoate undergo a stepwise addition polymerization reaction under the catalysis of stannous octoate to form a polyurethane network containing urethane bonds. The epoxy groups of epoxidized soybean oil can undergo cross-linking reactions with the hydroxyl and isopropyl isocyanate groups. At the same time, the long-chain structure fills the gaps in the polyurethane network. The phased addition can avoid local aggregation of the membrane material and ensure uniform membrane thickness.

[0023] Furthermore, the mass ratio of bio-based polyol, epoxidized soybean oil, stannous octanoate, and isopropyl isocyanate is 7-11:3-5:0.01-0.02:2.2-3.2.

[0024] Furthermore, the membrane thickness of the high-utilization compound fertilizer with a protective layer is 0.3-0.6 mm.

[0025] This thickness allows for slow nutrient release while ensuring the mechanical strength of the membrane shell, preventing damage during transportation.

[0026] This invention also provides a high-utilization compound fertilizer with a protective layer. A coating material consisting of bio-based polyol, epoxidized soybean oil, stannous octanoate, and isopropyl isocyanate is coated onto the surface of a granular compound fertilizer. After cross-linking and curing, a high-utilization compound fertilizer with a protective layer can be obtained.

[0027] The beneficial effects of this invention are: 1. This invention uses a combination of bio-based polyol prepared by corn cob liquefaction and natural epoxidized soybean oil as the core raw material for coating. Both contain functional groups such as hydroxyl and ester groups that can be degraded by soil microorganisms. The membrane has a high biodegradability rate and will not accumulate residues after long-term application. Moreover, the coating process does not require organic solvents, thus avoiding VOC emissions. At the same time, the polyurethane cross-linking network works synergistically with soil microorganisms to maintain soil aggregate structure, improve air permeability and water permeability, effectively prevent soil compaction, protect the soil micro-ecological balance, and meet the needs of sustainable development in modern agriculture.

[0028] 2. This invention utilizes the bidentate coordination structure of ammonium polyphosphate (P=O and P-OH) to form stable chelates with magnesium and iron ions in magnesium and iron salt solutions. This prevents trace elements from reacting and precipitating with clay minerals and phosphates in the soil, thereby improving crop absorption. At the same time, the polyphosphate ions themselves can slow down the release rate of phosphorus, achieving synchronous and appropriate supply of phosphorus and magnesium and iron trace elements. This precisely matches the needs of crops for trace elements throughout their entire growth period, improving the utilization rate of trace elements in compound fertilizers.

[0029] 3. The dense polyurethane protective layer formed by the bio-based polyol and isopropyl isocyanate under the catalysis of stannous octoate in this invention delays nutrient dissolution through physical barrier, and, combined with the inhibitory effect of urease inhibitor on urease activity, constructs a dual controlled-release system of physical barrier and biological inhibition, prolonging the nitrogen release cycle, matching the nutrient requirements of crop growth period, reducing the number of fertilizations and labor input, realizing simplified cultivation, and adapting to large-scale agricultural production.

[0030] 4. In the granulation process of this invention, quartz sand acts as a weighting agent and filler, significantly improving the mechanical strength of the granular compound fertilizer and preventing breakage during transportation, storage, and mechanized fertilization. Urea, potassium dihydrogen phosphate, and other macroelements, along with chelates and urease inhibitors, are uniformly mixed after pulverization, sieving, and high-temperature drying, and then extruded to ensure uniform nutrient distribution. The coating layer and the granular core material are tightly bonded, synergistically achieving efficient absorption of trace elements and slow release of macroelements such as nitrogen, phosphorus, and potassium, thus improving the overall utilization rate of the compound fertilizer. Furthermore, the acid-base buffering capacity of the bio-based coating and chelates allows the compound fertilizer to adapt to various soil environments, including alkaline, heavy, and arid conditions, while preventing localized soil acidification or salinization. Combined with urease inhibitors and the chelation system, it promotes crop yield while improving soil fertility, achieving a balance between crop yield increase and soil ecological protection. Detailed Implementation

[0031] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0032] Example 1: This example provides a high-utilization compound fertilizer with a protective layer, prepared through the following steps: S1: Add 1.05 kg of ammonium polyphosphate (purchased from Zhengzhou Jiajie Chemical Products Co., Ltd.) and 2.3 L of deionized water to the reactor and stir to dissolve at 165 r / min. Adjust the pH of the solution to 7.0 with 10 wt% ammonia water. Add 0.25 kg of magnesium chloride solution (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) and 0.35 kg of ferrous sulfate solution (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) at 36℃ and react at 250 r / min for 50 min. The adjacent P=O and P-OH groups in the ammonium polyphosphate can act as bidentate ligands and combine with magnesium ions of magnesium sulfate and iron ions of ferrous sulfate through coordinate bonds to form chelates. Then add 4.0 L of anhydrous ethanol to precipitate the chelate. Centrifuge at 4000 r / min for 12 min, filter, dry the filter cake at 42℃ for 5 h, pulverize, and pass through a 100 mesh sieve to obtain the chelate.

[0033] S2: 110g of corn cobs crushed to below 20 mesh and with a moisture content ≤2% were added to a high-pressure reactor. 375g of liquefying agent polyethylene glycol 400 (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), 165g of glycerol (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), and 55g of calcined and activated catalyst H-ZSM-5 (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) were added. The mixture was thoroughly mixed, and the air inside the reactor was replaced with nitrogen three times. The reaction was carried out at 400r / min and 185℃ for 110min. During the reaction, the pressure inside the reactor naturally rose to 0.4MPa. After the reaction, the mixture was cooled to room temperature and depressurized to atmospheric pressure. 350mL of 1,4-dioxane (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) was added, and the mixture was stirred for 35min. The mixture was centrifuged at 2500r / min for 17min. The supernatant was collected and rotary evaporated at 42℃ to recover 1,4-dioxane, yielding a bio-based polyol.

[0034] S3: Crush 4.11 kg of urea, 2.02 kg of potassium dihydrogen phosphate, 0.59 kg of chelate and 2.6 kg of potassium sulfate separately, pass them through an 80-mesh sieve, and dry them to constant weight at 62℃. Then add 1.86 kg of quartz sand and stir at 175 r / min for 17 min. Then add 6 g of urease inhibitor (94317-64-3, purchased from Wuhan Linglingfa Technology Co., Ltd.), mix evenly, and extrude the mixture into granules under 10 MPa pressure using a four-column hydraulic granulator. Allow it to cool naturally to room temperature to obtain granular compound fertilizer.

[0035] S4: Preheat the coating machine to 70℃ with a blower. Add 1.1kg of granular compound fertilizer at 40r / min, then add 9g of coating material (bio-based polyol), 4g of epoxidized soybean oil (8013-07-8, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.), 0.015g of stannous octoate (purchased from Tengyi Material Supply Station, Xigong District, Luoyang City), and 2.7g of isopropyl isocyanate (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.). React for 17min, then add the coating material again and repeat the reaction 3 times. After all the coating material has been added, maintain the temperature at 70℃ and continue stirring for 35min to ensure that the membrane is completely cross-linked and cured. The membrane thickness is 0.45mm. Allow it to cool naturally to room temperature to obtain a high-utilization compound fertilizer with a protective layer.

[0036] Under the catalysis of stannous octoate, the -OH group of bio-based polyol and the -NCO group of isopropyl isocyanate undergo a stepwise addition polymerization reaction to form a polyurethane cross-linked network with urethane bonds as the main chain, which constitutes the core skeleton of the protective layer. Epoxidized soybean oil, as a modifying agent, undergoes a cross-linking reaction with the -OH group of bio-based polyol and the -NCO group of isopropyl isocyanate to form a shell. Its long-chain structure fills the gaps in the polyurethane network, improves the flexibility of the membrane shell, and delays the dissolution and release of nutrients in the compound fertilizer through physical barrier effect, ultimately improving the fertilizer utilization rate.

[0037] Example 2: This example provides a high-utilization compound fertilizer with a protective layer, prepared through the following steps: S1: Add 0.95 kg of ammonium polyphosphate (purchased from Zhengzhou Jiajie Chemical Products Co., Ltd.) and 2.1 L of deionized water to the reactor and stir to dissolve at 150 r / min. Adjust the pH of the solution to 6.8 with 10 wt% ammonia water. Add 0.2 kg of magnesium chloride solution (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) and 0.25 kg of ferrous sulfate solution (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) at 35℃ and react at 200 r / min for 45 min. The adjacent P=O and P-OH groups in the ammonium polyphosphate can act as bidentate ligands and combine with magnesium ions of magnesium sulfate and iron ions of ferrous sulfate through coordinate bonds to form chelates. Add 3.5 L of anhydrous ethanol to precipitate the chelate. Centrifuge at 4000 r / min for 10 min, filter, dry the filter cake at 40℃ for 4 h, pulverize, and pass through a 100 mesh sieve to obtain the chelate.

[0038] S2: 100g of corn cobs crushed to below 20 mesh and with a moisture content ≤2% were added to a high-pressure reactor. 350g of liquefying agent polyethylene glycol 400 (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), 150g of glycerol (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), and 50g of calcined and activated catalyst H-ZSM-5 (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) were added. The mixture was stirred until homogeneous. The air inside the reactor was replaced with nitrogen three times. The reaction was carried out at 300r / min and 180℃ for 100min. During the reaction, the pressure inside the reactor naturally rose to 0.3MPa. After the reaction, the mixture was cooled to room temperature and depressurized to atmospheric pressure. 300mL of 1,4-dioxane (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) was added and stirred for 30min. The mixture was then centrifuged at 2500r / min for 15min. The supernatant was collected and rotary evaporated at 40℃ to recover 1,4-dioxane, yielding a bio-based polyol.

[0039] S3: Crush 3.91 kg of urea, 1.92 kg of potassium dihydrogen phosphate, 0.54 kg of chelate and 2.4 kg of potassium sulfate separately, pass them through an 80-mesh sieve, dry them at 60℃ to constant weight, then add 1.76 kg of quartz sand, stir at 150 r / min for 15 min, then add 5 g of urease inhibitor (94317-64-3, purchased from Wuhan Linglingfa Technology Co., Ltd.), mix evenly, and extrude the mixture into granules under 10 MPa pressure using a four-column hydraulic granulator, and allow it to cool naturally to room temperature to obtain granular compound fertilizer.

[0040] S4: Preheat the coating machine to 68℃ with a blower. Add 1kg of granular compound fertilizer at 30r / min, then add 7g of coating material (bio-based polyol), 3g of epoxidized soybean oil (8013-07-8, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.), 0.01g of stannous octoate (purchased from Tengyi Material Supply Station, Xigong District, Luoyang City), and 2.2g of isopropyl isocyanate (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.). React for 15min, then add the coating material again and repeat the reaction 3 times. After all the coating material has been added, maintain the temperature at 68℃ and continue stirring for 30min to ensure that the membrane is completely cross-linked and cured. The membrane thickness is 0.3mm. Allow it to cool naturally to room temperature to obtain a high-utilization compound fertilizer with a protective layer.

[0041] Example 3: This example provides a high-utilization compound fertilizer with a protective layer, prepared through the following steps: S1: Add 1.15 kg of ammonium polyphosphate (purchased from Zhengzhou Jiajie Chemical Products Co., Ltd.) and 2.5 L of deionized water to the reactor and stir to dissolve at 180 r / min. Adjust the pH of the solution to 7.2 with 10 wt% ammonia water. Add 0.3 kg of magnesium chloride solution (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) and 0.45 kg of ferrous sulfate solution (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) at 37℃. React at 300 r / min for 55 min. The adjacent P=O and P-OH groups in the ammonium polyphosphate can act as bidentate ligands and combine with magnesium ions of magnesium sulfate and iron ions of ferrous sulfate through coordinate bonds to form chelates. Add 4.5 L of anhydrous ethanol to precipitate the chelate. Centrifuge at 4000 r / min for 14 min, filter, dry the filter cake at 45℃ for 6 h, pulverize, and pass through a 100 mesh sieve to obtain the chelate.

[0042] S2: 120g of corn cobs crushed to below 20 mesh and with a moisture content ≤2% were added to a high-pressure reactor. 400g of liquefying agent polyethylene glycol 400 (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), 180g of glycerol (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), and 60g of calcined and activated catalyst H-ZSM-5 (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) were added. The mixture was thoroughly mixed, and the air inside the reactor was replaced with nitrogen three times. The reaction was carried out at 500r / min and 190℃ for 120min. During the reaction, the pressure inside the reactor naturally rose to 0.5MPa. After the reaction, the mixture was cooled to room temperature and depressurized to atmospheric pressure. 400mL of 1,4-dioxane (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) was added, and the mixture was stirred for 40min. The mixture was then centrifuged at 2500r / min for 20min. The supernatant was collected and rotary evaporated at 45℃ to recover 1,4-dioxane, yielding a bio-based polyol.

[0043] S3: Crush 4.31 kg of urea, 2.12 kg of potassium dihydrogen phosphate, 0.64 kg of chelate and 2.8 kg of potassium sulfate separately, pass them through an 80-mesh sieve, dry them at 65℃ to constant weight, then add 1.96 kg of quartz sand, stir at 200 r / min for 20 min, then add 7 g of urease inhibitor (94317-64-3, purchased from Wuhan Linglingfa Technology Co., Ltd.), mix evenly, and extrude the mixture into granules under 10 MPa pressure using a four-column hydraulic granulator, and allow it to cool naturally to room temperature to obtain granular compound fertilizer.

[0044] S4: Preheat the coating machine to 72℃ with a blower. Add 1.2kg of granular compound fertilizer at 50r / min, then add 11g of coating material bio-based polyol, 5g of epoxidized soybean oil (8013-07-8, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.), 0.02g of stannous octoate (purchased from Tengyi Material Supply Station, Xigong District, Luoyang City), and 3.2g of isopropyl isocyanate (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.). React for 20min, then add the coating material again and repeat the reaction 3 times. After all the coating material has been added, maintain the temperature at 72℃ and continue stirring for 40min to ensure that the membrane is completely cross-linked and cured. The membrane thickness is 0.6mm. Allow it to cool naturally to room temperature to obtain a high-utilization compound fertilizer with a protective layer.

[0045] Example 4: This example provides a high-utilization compound fertilizer with a protective layer. The difference from Example 1 is that magnesium sulfate solution is used instead of magnesium chloride solution in step S1.

[0046] Example 5: This example provides a high-utilization compound fertilizer with a protective layer. The difference from Example 1 is that ferrous ammonium sulfate solution is used instead of ferrous sulfate solution in step S1.

[0047] Example 6: This example provides a high-utilization compound fertilizer with a protective layer. The difference from Example 1 is that in step S1, magnesium sulfate solution is used instead of magnesium chloride solution, and ferrous ammonium sulfate solution is used instead of ferrous sulfate solution.

[0048] Comparative Example 1: This comparative example provides a high-utilization compound fertilizer with a protective layer. The difference from Example 1 is that the chelate is removed in step S3, while the amount of other raw materials and process parameters are the same as in Example 1.

[0049] Comparative Example 2: This comparative example provides a high-utilization compound fertilizer with a protective layer. The difference from Example 1 is that polyethylene glycol 400 is used instead of bio-based polyol in step S4.

[0050] Comparative Example 3: This comparative example provides a high-utilization compound fertilizer with a protective layer. The difference from Example 1 is that step S4 is not performed. The granular compound fertilizer prepared in step S3 is the high-utilization compound fertilizer with a protective layer.

[0051] The high-utilization compound fertilizers with protective layers prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to pot experiments: The experiment was conducted in pots. Each pot was treated with the same amount of 3.7g urea, 2.6g diammonium phosphate, and 2.4g potassium chloride, along with three high-utilization compound fertilizer pellets with a protective layer. Plastic flower pots were used. Depending on the treatment, the potting soil was filled into the pots, which were 30cm in diameter and 22cm in height. Each pot contained 10kg of soil, which was compacted appropriately. Fertilizer was then applied at a lateral distance of 5cm and at depths of 5cm and 10cm. The pots were then thoroughly watered. Two Chinese cabbage plants were planted in each pot. Each treatment was replicated four times, and the average value was taken.

[0052] Nutrient utilization: Soil and plant nitrogen content was determined by the Kjeldahl method, phosphorus content by the vanadium-molybdenum blue colorimetric method, and potassium content by the flame spectrophotometry method. The utilization rates of nitrogen (N), phosphorus (P2O5), and potassium (K2O) were calculated.

[0053] Soil compaction degree: After harvest, the soil bulk density is measured using the ring cutter method. The higher the bulk density, the more severe the compaction.

[0054] Crop yield: The fresh weight of the above-ground parts is measured at harvest, and the yield per pot is calculated.

[0055] Coating degradation rate: The amount of coating residue was determined by gravimetric method after 90 days, and the degradation rate was calculated.

[0056] Trace element absorption rate: Magnesium and iron content in plants were determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0057] The test results are shown in the table below: Table 1 Performance Test Overview As shown in Table 1, the nitrogen, phosphorus and potassium utilization rates of Examples 1-6 were all higher than those of Comparative Examples 1-3. This may be because the chelate prevents the fixation of trace elements and promotes the synergistic absorption of macronutrients by crops. The bio-based polyurethane coating delays nutrient dissolution through physical barriers, and the urease inhibitor inhibits urease activity to reduce nitrogen volatilization, thereby improving the utilization rate of compound fertilizer.

[0058] The soil bulk density of Examples 1-6 is lower than that of Comparative Example 2, possibly because the bio-based polyol prepared by corn cob liquefaction and the epoxidized soybean oil are coated together. Both can be degraded by soil microorganisms, maintain soil aggregate structure, and improve air permeability and water permeability.

[0059] The 90-day degradation rate of the coatings in Examples 1-6 was higher than that in Comparative Example 2, possibly because the core of the coating material is a bio-based polyol, which contains biodegradable functional groups such as hydroxyl and ester groups, and can be recognized and decomposed by soil microorganisms.

[0060] The magnesium and iron absorption rates of plants in Examples 1-6 were higher than those in Comparative Example 3. This may be because the P=O and P-OH bidentate coordination structure of ammonium polyphosphate forms stable chelates with magnesium and iron ions, preventing them from reacting and precipitating with clay minerals and phosphates in the soil. At the same time, the bio-based coating delays nutrient release and ensures a continuous supply of trace elements.

[0061] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0062] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a high-utilization compound fertilizer with a protective layer, characterized in that, Includes the following steps: Step 1: Combine the metal ions of ammonium polyphosphate with magnesium salt solution and iron salt solution through coordinate bonds to obtain chelates; Step 2: The corn cob is liquefied using polyethylene glycol 400, glycerol and catalyst H-ZSM-5 to obtain a bio-based polyol; Step 3: Mix urea, potassium dihydrogen phosphate, chelate, potassium sulfate, quartz sand and urease inhibitor evenly, and then granulate by extrusion using a granulator to obtain granular compound fertilizer; Step 4: Coat the surface of the granular compound fertilizer with bio-based polyol, epoxidized soybean oil, stannous octanoate and isopropyl isocyanate coating material using a coating machine. After cross-linking and curing, a high-utilization compound fertilizer with a protective layer is obtained.

2. The method for preparing a high-utilization compound fertilizer with a protective layer according to claim 1, characterized in that, The specific preparation process of the chelate described in step one is as follows: Ammonium polyphosphate and deionized water were added to a reaction vessel and stirred to dissolve. The pH of the solution was adjusted to 6.8-7.2 with 10wt% ammonia water. Magnesium salt solution and iron salt solution were added at 35-37℃ and stirred for 45-55 minutes. Then anhydrous ethanol was added to precipitate the mixture. The precipitate was then centrifuged, filtered, dried, pulverized, and sieved to obtain the chelate.

3. The method for preparing a high-utilization compound fertilizer with a protective layer according to claim 2, characterized in that, The ratio of the amount of ammonium polyphosphate, deionized water, magnesium salt solution and iron salt solution used is 0.95-1.15 kg: 2.1-2.5 L: 0.2-0.3 kg: 0.25-0.45 kg.

4. The method for preparing a high-utilization compound fertilizer with a protective layer according to claim 3, characterized in that, The magnesium salt solution is one of magnesium chloride solution and magnesium sulfate solution; The iron salt solution is either ferrous sulfate solution or ferrous ammonium sulfate solution.

5. The method for preparing a high-utilization compound fertilizer with a protective layer according to claim 1, characterized in that, The specific preparation method of the bio-based polyol mentioned in step two is as follows: Corn cobs were added to a high-pressure reactor, along with liquefying agents polyethylene glycol 400 and glycerol, and then calcined and activated catalyst H-ZSM-5. The mixture was thoroughly mixed, and the air inside the reactor was replaced three times with nitrogen. The reaction was carried out at 300-500 r / min and 180-190℃ for 100-120 min, during which the pressure inside the reactor naturally rose to 0.3-0.5 MPa. After the reaction was completed, the reactor was cooled to room temperature, the pressure was released, and 1,4-dioxane was added. The mixture was stirred for 30-40 min, centrifuged, and rotary evaporated to obtain bio-based polyols.

6. The method for preparing a high-utilization compound fertilizer with a protective layer according to claim 5, characterized in that, The ratio of corn cob, polyethylene glycol 400, glycerol, H-ZSM-5 and 1,4-dioxane is 100-120g: 350-400g: 150-180g: 50-60g: 300-400mL.

7. The method for preparing a high-utilization compound fertilizer with a protective layer according to claim 1, characterized in that, The mass ratio of urea, potassium dihydrogen phosphate, chelate, potassium sulfate, quartz sand and urease inhibitor in step three is 3.91-4.31: 1.92-2.12: 0.54-0.64: ​​2.4-2.8: 1.76-1.96: 0.005-0.

007.

8. The method for preparing a high-utilization compound fertilizer with a protective layer according to claim 1, characterized in that, The specific preparation process of the high-utilization compound fertilizer with a protective layer described in step four is as follows: Preheat the coating machine to 68-72℃ with a blower. Add granular compound fertilizer at 30-50 r / min, then add the coating material: bio-based polyol, epoxidized soybean oil, stannous octanoate, and isopropyl isocyanate. Let it react fully for 15-20 minutes, then add the coating material again and repeat the reaction 3 times. Maintain the temperature at 68-72℃ and continue stirring for 30-40 minutes to ensure that the membrane is completely cross-linked and cured. Allow it to cool naturally to room temperature to obtain a high-utilization compound fertilizer with a protective layer.

9. The method for preparing a high-utilization compound fertilizer with a protective layer according to claim 8, characterized in that, The mass ratio of the bio-based polyol, epoxidized soybean oil, stannous octanoate, and isopropyl isocyanate is 7-11:3-5:0.01-0.02:2.2-3.

2. The membrane thickness of the high-utilization compound fertilizer with a protective layer is 0.3-0.6 mm.

10. A high-utilization compound fertilizer with a protective layer, characterized in that, It is prepared by the method for preparing a high-utilization compound fertilizer with a protective layer as described in any one of claims 1-9.

Images