Bio-based coated controlled-release fertilizer and preparation method thereof

Abstract

The present invention discloses a bio-based coated controlled-release fertilizer and a preparation method thereof, and relates to the field of novel fertilizers, the bio-based coated controlled-release fertilizer comprises: a fertilizer core comprising at least one nutrient element of nitrogen, phosphorus and potassium; the bio-based controlled release coating layer is coated outside the fertilizer core, and the coating layer comprises the following components by dry weight: 50-80wt% of a non-modified natural biomass material which is selected from at least one of rice hull powder, straw powder and manioc waste and has a particle size of less than or equal to 100 meshes; 15-40 wt% of a natural vegetable fat derivative selected from at least one of epoxidized soybean oil, vulcanized palm oil and cashew nut shell oil; 5-15 wt% of a biomass source binder, which is defatted bean flour or corn protein powder; according to the bio-based coated controlled-release fertilizer and the preparation method thereof, a chemically synthesized cross-linking agent is abandoned on the basis of unmodified agricultural wastes and natural grease, a film layer can be completely biodegraded in soil, and micro-plastic and formaldehyde residue pollution can be thoroughly eliminated.

Description

Technical Field

[0001] The present invention relates to novel fertilizer technology, and in particular to a bio-based coated controlled-release fertilizer and a preparation method thereof. Background Art

[0002] Current fertilizer coating technologies generally rely on petroleum-based polymers or chemically modified natural materials, which are subject to bottlenecks such as non-degradable residues, complex production processes, and high costs. Traditional slow-release fertilizers are often coated with epoxy resins or plastic polymers. While these can delay nutrient release, the coatings are difficult to decompose naturally, leading to microplastic contamination in the soil over time. Bio-based coating materials, such as modified starch and chitosan, while somewhat biodegradable, are susceptible to mechanical damage due to their lack of strength and require high-temperature and high-pressure modification, resulting in significant energy consumption.

[0003] In particular, existing oil-based coating systems suffer from critical flaws. Plant oils alone have poor hydrophobicity after film formation, swelling upon exposure to moisture and triggering a rapid release of nutrients. While synthetic cross-linkers can strengthen the structure, they also introduce toxic residues such as formaldehyde. More critically, existing fluidized bed processes are poorly adapted to bio-based emulsions. Top-spraying methods result in incomplete coating of small particles, and the lack of layered drying can cause stress cracking within the film. These deficiencies collectively hinder the large-scale application of bio-based controlled-release fertilizers, necessitating the development of a fully bio-based, low-energy, and high-precision controlled-release fertilizer solution. Summary of the Invention

[0004] The purpose of the present invention is to provide a bio-based coated controlled-release fertilizer and a preparation method thereof, so as to solve the above-mentioned deficiencies in the prior art.

[0005] In order to achieve the above-mentioned object, the present invention provides the following technical solution: a bio-based coated controlled-release fertilizer, comprising:

[0006] A fertilizer core comprising at least one nutrient element selected from nitrogen, phosphorus, and potassium;

[0007] The bio-based controlled-release coating layer coated on the outside of the fertilizer core is composed of the following components by dry weight:

[0008] 50-80 wt% of unmodified natural biomass material, selected from at least one of rice husk powder, straw powder, and cassava residue, with a particle size of ≤100 mesh;

[0009] 15-40 wt% of a natural plant oil derivative, selected from at least one of epoxidized soybean oil, sulfurized palm oil, and cashew nut shell liquid;

[0010] 5-15 wt% of the biomass source binder is defatted soybean flour or corn gluten meal.

[0011] Furthermore, the fertilizer core is one or more composite particles of urea, diammonium phosphate, and potassium chloride, and the particle size of the composite particles is 2-4 mm.

[0012] Furthermore, the dry weight of the bio-based controlled-release coating layer accounts for 3-8% of the total weight of the fertilizer, and the coating layer is composed of 3-8 sub-film layers.

[0013] Furthermore, the natural plant oil derivative is a mixture of epoxidized soybean oil and sulfurized palm oil, and the weight ratio of epoxidized soybean oil to sulfurized palm oil is 1:1 to 3:1.

[0014] A method for preparing the bio-based coated controlled-release fertilizer as described above comprises the following steps:

[0015] S1. Preparation of coating solution: Mix unmodified natural biomass material, natural plant oil derivative, biomass-derived binder and water, control the solid content of the mixture to 20-35 wt%, and stir at 50-60° C. to form a homogeneous emulsion to obtain a coating solution;

[0016] S2. Fluidized bed coating: Place the fertilizer kernel in a fluidized bed, preheat to 50-65°C, and spray the coating solution obtained in step S1 in batches using a bottom spraying process. After each spraying, pass hot air at 60-80°C to dry for 5-10 minutes;

[0017] S3. Curing treatment: After all the coating is completed, hot air curing is carried out at 45-55℃ for 0.5-1 hour.

[0018] Furthermore, in step S2, the spraying pressure is 0.2-0.4 MPa, and the weight gain of a single spraying is 0.5-1.2% of the weight of the fertilizer kernel.

[0019] Furthermore, in step S1, food-grade monoglyceride is added to the mixed solution as an emulsifier, and the amount of food-grade monoglyceride added is 0.1-0.5 wt% of the dry weight of the bio-based controlled-release coating layer.

[0020] Furthermore, after step S3, the method further includes spraying a beeswax ethanol solution onto the surface of the coated fertilizer particles, followed by flash drying at 40-45° C. for 1-2 minutes; wherein the beeswax concentration in the beeswax ethanol solution is 3-8wt%, and the spraying amount is 0.05-0.15% of the total weight of the fertilizer.

[0021] Compared with the existing technology, the bio-based coated controlled-release fertilizer and its preparation method provided by the present invention are based on unmodified agricultural waste and natural oils, and abandon chemical synthetic cross-linking agents. The film layer can be completely biodegraded in the soil, completely eliminating microplastics and formaldehyde residual pollution.

[0022] The polysulfide bonds of sulfurized palm oil and the epoxy groups of epoxidized soybean oil form an in-situ hydrolysis-resistant network. Combined with the efficient micropore sealing of beeswax, the nutrient release curve is precisely matched to crop needs, and the initial burst release is reduced by more than three times compared to traditional processes.

[0023] By directly utilizing non-modified biomass raw materials, eliminating the chemical modification process, and combining it with the bottom-spray fluidized bed layered drying process, the equipment modification cost is extremely low, and the overall production cost is effectively reduced compared to petroleum-based coated fertilizers. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments described in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0025] Figure 1 This is a flowchart of the method for preparing the bio-based coated controlled-release fertilizer provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0027] Example 1

[0028] Bio-based coated controlled-release fertilizers, including:

[0029] Fertilizer core: urea granules, particle size: 3.0±0.2mm, nitrogen content 46%;

[0030] Bio-based controlled-release coating layer (5.0% of the total fertilizer weight):

[0031] Unmodified natural biomass material: rice husk powder (200 mesh) 65wt%;

[0032] Natural plant oil derivatives: epoxidized soybean oil 15wt%, sulfurized palm oil (sulfur content 1.0wt%) 7.5wt%;

[0033] Biomass-derived binder: defatted soy flour 12.5 wt%;

[0034] Auxiliary additives: food grade monoglyceride 0.3wt% (accounting for the dry weight of the coating layer).

[0035] See also Figure 1 A method for preparing the above-mentioned bio-based coated controlled-release fertilizer comprises the following steps:

[0036] S1. Preparation of coating solution: Rice husk powder, epoxy soybean oil, sulfurized palm oil, defatted soybean flour, monoglyceride and deionized water were mixed to control the solid content of the mixture to 28 wt %, and stirred at 300 rpm for 30 min at 55° C. to form a homogeneous emulsion to obtain the coating solution;

[0037] S2. Fluidized bed coating: Place the fertilizer kernel in a fluidized bed (using FLP-10 bottom spray fluidized bed, nozzle diameter 1.2mm) and preheat to 60±1℃;

[0038] Use bottom spraying process, pressure 0.30MPa, atomizing gas volume 40L / min, spray coating liquid in 5 times;

[0039] The coating liquid obtained in step S1 was sprayed in batches using a bottom spraying process at a spraying pressure of 0.30 MPa and an atomizing gas volume of 40 L / min. After spraying, hot air at 70±2°C was introduced for drying for 8 minutes at a wind speed of 8 m / s.

[0040] S3. Curing treatment: After all the coating is completed, hot air curing is carried out at 50±1℃ for 45 minutes and relative humidity is 30%;

[0041] After solidification, 5 wt% beeswax ethanol solution (0.1% of the total weight of the fertilizer) was sprayed and flash dried at 40±1°C for 1.5 min.

[0042] Example 2

[0043] Bio-based coated controlled-release fertilizers, including:

[0044] Fertilizer core: same as in Example 1;

[0045] Bio-based controlled-release coating layer: 5.0% of the total fertilizer weight, including:

[0046] Unmodified natural biomass material: rice husk powder (200 mesh) 65wt%;

[0047] Natural plant oil derivatives: epoxidized soybean oil 10wt%, sulfurized palm oil (sulfur content 1.2wt%) 10wt%;

[0048] Biomass-derived binder: defatted soy flour 12.5 wt%;

[0049] Auxiliary additives: food grade monoglyceride 0.3wt% (accounting for the dry weight of the coating layer).

[0050] A method for preparing the above-mentioned bio-based coated controlled-release fertilizer comprises the following steps:

[0051] S1. Preparation of coating solution: Mix unmodified natural biomass material, natural plant oil derivative, biomass-derived binder and water, control the solid content of the mixture to 28 wt %, and stir at 55° C. to form a homogeneous emulsion to obtain a coating solution;

[0052] S2. Fluidized bed coating: Place the fertilizer kernel in a fluidized bed (using an FLP-10 bottom spray fluidized bed with a nozzle diameter of 1.2 mm), preheat to 60±1°C, spray at a pressure of 0.30 MPa, and an atomizing gas volume of 40 L / min. Apply the coating solution obtained in step S1 in batches using a bottom spraying process. After each spraying, dry the kernel with hot air at 70±2°C for 8 minutes at a wind speed of 8 m / s.

[0053] S3. Curing treatment: After all the coating is completed, hot air curing is carried out at 50±1℃ for 45 minutes and relative humidity is 30%;

[0054] After solidification, spray 5 wt% beeswax ethanol solution (0.1% fertilizer weight) and flash dry at 40±1°C for 1.5 min.

[0055] Example 3

[0056] Bio-based coated controlled-release fertilizers, including:

[0057] Fertilizer core: same as in Example 1;

[0058] Bio-based controlled-release coating layer: same as in Example 1.

[0059] A method for preparing the above-mentioned bio-based coated controlled-release fertilizer comprises the following steps:

[0060] S1. Preparation of coating solution: Mix unmodified natural biomass material, natural plant oil derivative, biomass-derived binder and water, control the solid content of the mixture to 28 wt %, and stir at 55° C. to form a homogeneous emulsion to obtain a coating solution;

[0061] S2. Fluidized bed coating: Place the fertilizer kernel in a fluidized bed (using an FLP-10 bottom spray fluidized bed with a nozzle diameter of 1.2 mm), preheat to 60±1°C, spray at a pressure of 0.30 MPa, and an atomizing gas volume of 40 L / min. Apply the coating solution obtained in step S1 in batches using a bottom spraying process. After each spraying, dry the kernel with hot air at 80±1°C for 8 minutes at a wind speed of 8 m / s.

[0062] S3. Curing treatment: After all the coating is completed, hot air curing is carried out at 50±1℃ for 30 minutes and the relative humidity is 30%.

[0063] Comparative Example 1

[0064] Components:

[0065] Fertilizer core: same as in Example 1;

[0066] Bio-based controlled-release coating layer: 5.0% of the total fertilizer weight, including:

[0067] Unmodified natural biomass material: rice husk powder (200 mesh) 65wt%;

[0068] Natural plant oil derivatives: epoxidized soybean oil 22.5wt%;

[0069] Biomass-derived binder: defatted soy flour 12.5 wt%;

[0070] Auxiliary additives: food grade monoglyceride 0.3wt% (accounting for the dry weight of the coating layer)

[0071] Preparation method: same as Example 1.

[0072] Comparative Example 2

[0073] Components: same as Comparative Example 1;

[0074] Preparation method:

[0075] S1. Preparation of coating solution: Mix unmodified natural biomass material, natural plant oil derivative, biomass-derived binder and water, control the solid content of the mixture to 28 wt %, and stir at 55° C. to form a homogeneous emulsion to obtain a coating solution;

[0076] S2. Fluidized bed coating: Place the fertilizer kernel in a fluidized bed (using an FLP-10 bottom spray fluidized bed with a nozzle diameter of 1.2 mm), preheat to 60±1°C, spray at a pressure of 0.30 MPa, and an atomizing gas volume of 40 L / min. Apply the coating solution obtained in step S1 in batches using a bottom spraying process. After each spraying, dry the kernel with hot air at 70±2°C for 8 minutes at a wind speed of 8 m / s.

[0077] S3. Curing treatment: After all the coating is completed, hot air curing is carried out at 50±1℃ for 45 minutes and relative humidity is 30%;

[0078] After solidification, spray 5 wt% beeswax ethanol solution (0.1% fertilizer weight) and flash dry at 40±1°C for 1.5 min.

[0079] Comparative Example 3

[0080] Fertilizer core: urea granules, particle size 3.0±0.2mm, nitrogen 46%;

[0081] Coating layer: accounts for 5.0% of the total weight of the fertilizer, including: 70wt% of modified corn starch (gelatinized and modified at 130°C), 25wt% of epoxidized soybean oil, and 5wt% of chitosan.

[0082] Preparation method:

[0083] Starch pretreatment: corn starch and deionized water were mixed in a ratio of 1:3, reacted at 130°C for 30 min, and cooled to 60°C to form gelatinized starch colloid;

[0084] Coating fluid preparation:

[0085] Gelatinized starch colloid, epoxidized soybean oil, chitosan, water;

[0086] Solid content 25wt%;

[0087] Stir at 60°C and 250 rpm for 20 min (viscosity 420 cP);

[0088] Fluidized bed coating (top spray process):

[0089] Equipment: GPCG-5 top-spray fluidized bed (nozzle position: top center)

[0090] Preheat to 70°C;

[0091] Spraying parameters: pressure 0.4MPa, single weight gain 2.5% (in 2 layers);

[0092] Drying: 85℃ hot air drying for 30 minutes;

[0093] Surface treatment: spraying 1 wt% silane coupling agent (γ-aminopropyltriethoxysilane) ethanol solution and drying in an 80° C. oven for 20 min.

[0094] Control experiment example

[0095] 1. Test object:

[0096] Experimental group: Example 1;

[0097] Control group: Comparative Example 1, Comparative Example 2, Comparative Example 3.

[0098] 2. Test standards:

[0099] Release rate: GB / T 23348-2021 "Slow-release fertilizers";

[0100] Biodegradation rate: ISO 17556:2019;

[0101] Film damage rate: simulated transportation vibration test (amplitude 5mm, frequency 10Hz, 30min).

[0102] 3. Fairness Guarantee:

[0103] The dry weight of the coating layer of all samples accounted for 5.0%;

[0104] Same urea core (particle size 3 mm, nitrogen 46%);

[0105] Same batch test environment (25℃ static water dissolution method).

[0106] The test results are shown in the following table:

[0107]

[0108] From the above, we can see that by compounding epoxidized soybean oil and sulfurized palm oil (1:1 to 3:1) in conjunction with beeswax micropore sealing technology, a breakthrough improvement in controlled release performance can be achieved:

[0109] In terms of controlled-release accuracy, the initial release rate of Example 1 was only 8.3%, a 209.6% decrease from Comparative Example 1 (no sulfurized palm oil, release rate 25.7%), and a 243.4% decrease from Comparative Example 2 (no sulfurized oil and no beeswax, release rate 28.5%). Furthermore, the 28-day cumulative release rate of 42.5% precisely met the national standard for controlled-release fertilizers (40-70%), while Comparative Example 3 was as high as 72.4%, only reaching the level of slow-release fertilizers.

[0110] In terms of physical stability, the membrane breakage rate of Example 1 was 2.1% (vibration test), which was much lower than the 15.4% of Comparative Example 1 (porosity increased by 220% due to lack of sulfur crosslinking) and the 9.8% of Comparative Example 3 (top spray process defects).

[0111] In terms of environmental friendliness, the biodegradation rate of Example 1 was 85.3%, which was 88.7% higher than that of Comparative Example 3 (silane treatment, degradation rate 45.2%), and no heavy metal or formaldehyde residues were detected.

[0112] Through the epoxy groups (—CH(O)CH—) of epoxidized soybean oil and the polysulfide bonds (—S x The molecular synergistic effect of the epoxidized palm oil (S-S-) achieves a breakthrough in controlled-release membrane performance: During the fluidized bed drying process at 60-80°C, the polysulfide bonds (—S—S—) of the sulphurized palm oil break to produce sulfhydryl radicals (·S—). These radicals attack the ternary epoxy groups of the epoxidized soybean oil, triggering a ring-opening reaction and forming C—S—C covalent bonds, thereby constructing a three-dimensional network with controllable crosslinking density.

[0113] The long-chain alkanes (C16-C18) of sulfurized palm oil are embedded in the interstices of the crosslinked network, forming a dense physical barrier. The low polarity of sulfur atoms (compared to oxygen atoms) reduces the membrane's surface energy from 38mN / m to 28mN / m, increasing the contact angle from 75° to 105°, and thus blocking the permeation path of water molecules. This synergistic mechanism simultaneously improves the membrane's mechanical strength and reduces the nutrient diffusion coefficient without the use of chemical crosslinkers, overcoming the dual technical bottlenecks of insufficient strength and poor controlled-release precision of bio-based coating materials.

[0114] This application is based on unmodified agricultural waste (rice husk powder / straw powder) and natural oils, abandoning chemical synthetic cross-linking agents. The film layer is completely biodegradable in the soil, completely eliminating microplastics and formaldehyde residual pollution;

[0115] The polysulfide bonds of sulfurized palm oil and the epoxy groups of epoxidized soybean oil form an in-situ hydrolysis-resistant network. Combined with the efficient micropore sealing of beeswax, the nutrient release curve precisely matches crop needs, reducing initial burst release by more than three times compared to traditional processes.

[0116] By directly utilizing non-modified biomass raw materials and eliminating the chemical modification process, combined with the bottom-spray fluidized bed layered drying process, the equipment modification cost is extremely low, and the overall production cost is reduced by more than 60% compared to petroleum-based coated fertilizers.

[0117] The above description is merely illustrative of certain exemplary embodiments of the present invention. It goes without saying that those skilled in the art will be able to modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims.

Claims

1. Bio-based coated controlled-release fertilizer, characterized in that: include: A fertilizer core comprising at least one nutrient element selected from nitrogen, phosphorus, and potassium; The bio-based controlled-release coating layer coated on the outside of the fertilizer core is composed of the following components by dry weight: 50-80 wt% of unmodified natural biomass material, selected from at least one of rice husk powder, straw powder, and cassava residue, with a particle size of ≤100 mesh; 15-40 wt% of a natural plant oil derivative, selected from at least one of epoxidized soybean oil, sulfurized palm oil, and cashew nut shell liquid; 5-15 wt% of the biomass source binder is defatted soybean flour or corn gluten meal.

2. The bio-based coated controlled-release fertilizer according to claim 1, characterized in that: The fertilizer core is one or more composite particles of urea, diammonium phosphate and potassium chloride, and the particle size of the composite particles is 2-4 mm.

3. The bio-based coated controlled-release fertilizer according to claim 1, characterized in that: The dry weight of the bio-based controlled-release coating layer accounts for 3-8% of the total weight of the fertilizer, and the coating layer is composed of 3-8 sub-film layers.

4. The bio-based coated controlled-release fertilizer according to claim 1, characterized in that: The natural plant oil derivative is a mixture of epoxidized soybean oil and sulfurized palm oil, and the weight ratio of the epoxidized soybean oil to the sulfurized palm oil is 1:1 to 3:

1.

5. A method for preparing the bio-based coated controlled-release fertilizer according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Preparation of coating solution: Mix unmodified natural biomass material, natural plant oil derivative, biomass-derived binder and water, control the solid content of the mixture to 20-35 wt%, and stir at 50-60° C. to form a homogeneous emulsion to obtain a coating solution; S2. Fluidized bed coating: Place the fertilizer kernel in a fluidized bed, preheat to 50-65°C, and spray the coating solution obtained in step S1 in batches using a bottom spraying process. After each spraying, pass hot air at 60-80°C to dry for 5-10 minutes; S3. Curing treatment: After all the coating is completed, hot air curing is carried out at 45-55℃ for 0.5-1 hour.

6. The method for preparing the bio-based coated controlled-release fertilizer according to claim 5, characterized in that: In step S2, the spraying pressure is 0.2-0.4 MPa, and the weight gain of a single spraying is 0.5-1.2% of the weight of the fertilizer kernel.

7. The method for preparing the bio-based coated controlled-release fertilizer according to claim 5, characterized in that: In step S1, food-grade monoglyceride is added to the mixed solution as an emulsifier, and the amount of food-grade monoglyceride added is 0.1-0.5 wt % of the dry weight of the bio-based controlled-release coating layer.

8. The method for preparing the bio-based coated controlled-release fertilizer according to claim 5, characterized in that: After step S3, the process also includes spraying a beeswax ethanol solution onto the surface of the coated fertilizer particles, followed by flash drying at 40-45° C. for 1-2 minutes; wherein the beeswax concentration in the beeswax ethanol solution is 3-8wt%, and the spraying amount is 0.05-0.15% of the total weight of the fertilizer.

Images