Preparation process of high humic acid oil cake water-soluble fertilizer special for fruits and vegetables

Abstract

The present application relates to the technical field of fertilizer preparation, and discloses a preparation process of a high-humic acid oil cake water-soluble fertilizer special for fruits and vegetables, which comprises the following steps: mixing weathered coal or lignite with oil cake to obtain a mixed base material; performing in-situ acidification coupling reaction, in-situ extracting humic acid from organic acid generated by hydrolysis of the oil cake, and esterifying glycerol with carboxyl to generate humic acid glyceride; after cooling, adding lipase and protease to perform synergistic enzymolysis, cross-linking polypeptide with the humic acid glyceride to form a supramolecular network structure; adding urea, potassium dihydrogen phosphate and medium and trace elements to perform nutrient compounding; and finally, performing spray drying or direct filling after being ground by a colloid mill. In the present application, the hydrolysis products of the oil cake completely replace inorganic alkali in an alkali extraction method, sodium ions are prevented from being introduced, and soil compaction is avoided; the solubility of humic acid and the stability of nutrients are improved through esterification reaction and a supramolecular network structure, the product has fast dissolution and high fertilizer efficiency, and is suitable for integrated water and fertilizer planting of fruits and vegetables.

Description

Technical Field

[0001] This invention relates to the field of fertilizer preparation technology, specifically to a process for preparing a water-soluble fertilizer made from high-humic acid oil cake for fruits and vegetables. Background Technology

[0002] Humic acid water-soluble fertilizers are widely used in the field of fruit and vegetable cultivation due to their advantages such as improving soil, increasing nutrient utilization and promoting crop growth. In the existing technology, the preparation of high humic acid water-soluble fertilizers usually adopts the alkaline extraction method, that is, using sodium hydroxide or potassium hydroxide to extract humic acid from weathered coal or lignite, and then compounding the extract with nitrogen, phosphorus and potassium inorganic fertilizers.

[0003] However, the aforementioned existing technologies have a significant drawback: although the large amount of sodium or potassium ions introduced by the alkali extraction method can improve the solubility of humic acid, sodium ions are not essential nutrients for plants. Long-term application will lead to the accumulation of sodium ions in the soil, destroying the soil aggregate structure, causing soil compaction and secondary salinization. At the same time, strong alkaline conditions can easily cause irreversible condensation of the active functional groups of humic acid, reducing its biological activity and thus affecting its chelating ability for micronutrients. In addition, as an agricultural by-product rich in organic acid precursors, oil cake is usually only fermented separately in existing processes, failing to form a synergistic effect with the humic acid extraction process. Summary of the Invention

[0004] The purpose of this invention is to provide a process for preparing a water-soluble fertilizer with high humic acid oil cake specifically for fruits and vegetables, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a process for preparing a water-soluble fertilizer for fruits and vegetables with high humic acid oil cake, comprising the following steps: S1. Raw material pretreatment: After the weathered coal or lignite is crushed and sieved, it is mixed with oil cake at a mass ratio of 1:(0.8-1.2) to obtain a mixed base material; S2, In-situ acidification coupling reaction: The mixed base material is put into the reaction vessel, and deionized water is added to adjust the solid-liquid ratio to 1:(3-6). Under stirring, the temperature is raised to 140℃-180℃, and the pressure is maintained at 0.4-0.8MPa. The reaction is carried out for 90-180 minutes. During the reaction, the organic acid generated by the hydrolysis of the oil cake is extracted in situ from the humic acid in the weathered coal or lignite. At the same time, the glycerol generated by the hydrolysis of the oil cake reacts with the carboxyl group at the edge of the humic acid molecule to form humic acid glyceride, and the reaction slurry is obtained. S3. Synergistic Enzymatic Hydrolysis Enhancement: Cool the reaction slurry to 50℃-60℃, adjust the pH to 6.0-7.0, add a complex enzyme preparation of lipase and protease. Lipase further hydrolyzes the residual oil cake to release fatty acids, and protease hydrolyzes the partially denatured proteins in the hydrothermal reaction into peptides. The peptides and the generated humic acid glycerides cross-link through secondary bonds to form a supramolecular network structure. Enzymatic hydrolysis is performed for 4-8 hours to obtain the enzymatically hydrolyzed material. S4. Nutrient Combination: Add urea, potassium dihydrogen phosphate and trace elements to the enzymatic hydrolysate, and chelate at 60℃-80℃ for 30-60 minutes to obtain a mixed solution. S5. Post-processing: After grinding the mixture with a colloid mill, spray dry or directly fill it to obtain water-soluble fertilizer.

[0006] As a preferred technical solution of the present invention, the oil cake in step S1 is one or more of rapeseed cake, soybean cake, and peanut cake; during the mixing process of weathered coal or lignite and oil cake, the free fatty acids in the oil cake undergo an in-situ exchange reaction with the metal ions on the surface of weathered coal or lignite to generate fatty acid salts. The fatty acid salts act as natural emulsifiers in the hydrothermal reaction, promoting the opening of hydrogen bonds inside humic acid molecules.

[0007] As a preferred embodiment of the present invention, the heating in step S2 adopts a gradient heating method: first, the temperature is raised to 100℃-110℃ at a rate of 3℃-5℃ / min and held for 20-30 minutes. During the holding period, the proteins in the oil cake denature and release sulfur-containing amino acids. The sulfur-containing amino acids undergo nucleophilic addition with the quinone structure in weathered coal or lignite to form intermediates linked by thioether bonds. Then, the temperature is raised to 140℃-180℃ at a rate of 2℃-3℃ / min. The heating curve controls the organic acid generation rate and the humic acid extraction rate to maintain a dynamic balance.

[0008] As a preferred embodiment of the present invention, in step S2, the stirring speed in the reactor is 60-120 rpm, and the volatile gas generated during the reaction is returned to the reactor through a condenser reflux device; under pressure and temperature, the carboxylic acid produced by the hydrolysis of oil cake undergoes an esterification reaction with the phenolic hydroxyl groups at the edge of the humic acid molecule to generate humic acid ester with higher hydrophilicity. At the same time, the carboxylic acid promotes the release of fixed ammonium in weathered coal or lignite, and the released ammonium ions form ammonium salt complexes with humic acid ester.

[0009] In a preferred embodiment of the present invention, in step S3, the amount of lipase added is 0.1%-0.3% of the total mass of the reaction slurry, with an enzyme activity of 50,000 U / g; the amount of protease added is 0.05%-0.15% of the total mass of the reaction slurry, with an enzyme activity of 200,000 U / g. The lipase first hydrolyzes the triglycerides in the residual oil cake, releasing glycerol and free fatty acids. The free fatty acids act as proton carriers to penetrate the interior of the unreacted particles. The protease then hydrolyzes the protein into polypeptides and amino acids. The molecular weight of the polypeptides is controlled within the range of 500-2000 Da. The polypeptides within this molecular weight range and the generated humic acid glycerides form a stable supramolecular network structure through hydrogen bonds and hydrophobic interactions.

[0010] As a preferred embodiment of the present invention, the pH adjuster used in step S3 to adjust the pH is citric acid or oxalic acid. During the enzymatic hydrolysis process, sterile air is continuously introduced at a ratio of 1:(0.5-1). In the presence of sterile air, the polypeptide-humic acid supramolecular network structure captures oxygen molecules to form oxygen-carrying microdomains. These oxygen-carrying microdomains promote the oxidation of residual reducing aldehyde groups in the system to carboxyl groups, thereby increasing the overall negative charge density.

[0011] In a preferred embodiment of the present invention, in step S4, the amount of urea added is 15%-25% of the total mass of the enzymatically hydrolyzed material, the amount of potassium dihydrogen phosphate added is 10%-20% of the total mass of the enzymatically hydrolyzed material, and the trace elements are at least two of zinc sulfate, boric acid, magnesium sulfate, and ammonium molybdate, with the amount of trace elements added being 0.5%-2% of the total mass of the enzymatically hydrolyzed material. Urea is added to the enzymatically hydrolyzed material first, and the ammonia gas generated by the hydrolysis of urea raises the local pH to 7.5-8.5, causing the supramolecular network structure to temporarily relax and expose chelation sites. Then, potassium dihydrogen phosphate and trace elements are added, and the phosphate ions and the amino terminus of the polypeptide form a phosphorylated polypeptide. The phosphorylated polypeptide further locks the trace elements with humic acid glycerides through calcium bridging.

[0012] As a preferred technical solution of the present invention, the chelation process in step S4 is assisted by ultrasound, with an ultrasound frequency of 40-80kHz and an ultrasound power density of 50-100W / L; the local high temperature and high pressure generated by the ultrasonic cavitation effect promotes the formation of new carbon-phosphorus covalent bonds between the phosphorylated polypeptide and the humic acid molecules, generating a humic acid-polypeptide-phosphate terpolymer, in which trace elements are encapsulated in its hydrophilic cavity.

[0013] As a preferred embodiment of the present invention, in step S5, the grinding fineness of the colloid mill is controlled to be 10-40 micrometers, the inlet air temperature of the spray dryer is 180℃-220℃, and the outlet air temperature is 70℃-90℃. During the spray drying process, the humic acid-peptide-phosphate terpolymer is oriented on the surface of the droplets to form microcapsules with a core-shell structure, wherein urea and inorganic salts are located in the core, and highly active humic acid derivatives constitute the shell.

[0014] As a preferred embodiment of the present invention, in step S5, when a direct filling method is used, a thickener is added to the mixture. The thickener is sodium carboxymethyl cellulose or xanthan gum, and the amount added is 0.1%-0.5% of the total mass of the mixture, adjusting the viscosity to 300-800 mPa·s. The linear molecular chains of sodium carboxymethyl cellulose or xanthan gum are interwoven in the polypeptide-humic acid supramolecular network structure, and crosslink with the terpolymer through intermolecular entanglement to form a three-dimensional network gel. The gel inhibits urea hydrolysis during storage and prevents the precipitation of trace elements.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention utilizes the organic acids generated by the hydrolysis of oil cake under hydrothermal conditions to extract humic acid in weathered coal or lignite in situ, completely replacing sodium hydroxide or potassium hydroxide in the traditional alkaline extraction method. This eliminates the introduction of sodium ions at the source, avoids the risk of soil compaction and salinization, and at the same time preserves the original active functional group structure in the humic acid molecule.

[0016] 2. In the hydrothermal reaction process of this invention, the glycerol generated from the hydrolysis of oil cake undergoes an esterification reaction with the carboxyl groups at the edge of humic acid molecules to generate humic acid glycerol ester, which significantly improves the hydrophilicity and water solubility of humic acid, allowing the product to dissolve quickly at room temperature and fully meet the usage requirements of integrated water and fertilizer drip irrigation systems.

[0017] 3. This invention combines hydrothermal reaction with enzymatic hydrolysis. First, the hydrothermal reaction opens up the macromolecular structure of humic acid and initially degrades the oil cake. Then, through deep enzymatic hydrolysis by lipase and protease, the polypeptides and humic acid glycerides are cross-linked through secondary bonds to form a supramolecular network structure. This network structure can effectively chelate trace elements and improve the slow release and utilization rate of nutrients.

[0018] 4. In the nutrient formulation step, this invention adopts a sequential feeding method of adding urea first and then potassium dihydrogen phosphate. The ammonia gas generated by urea hydrolysis is used to locally adjust the pH, so that the supramolecular network structure is temporarily relaxed and chelation sites are exposed. Then, with the assistance of ultrasound, carbon-phosphorus covalent bonds are formed between phosphorylated peptides and humic acid molecules to generate ternary copolymers, which encapsulate the trace elements in hydrophilic cavities, greatly improving the stability and anti-leaching ability of trace elements.

[0019] 5. This invention uses a combination of colloid milling and post-processing methods such as spray drying or direct filling to obtain two dosage forms: powder and liquid. The spray-dried product forms a core-shell microcapsule, while the liquid product forms a three-dimensional network gel. Both can effectively inhibit urea hydrolysis and prevent nutrient precipitation, resulting in a long shelf life and convenient storage and transportation. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall process for preparing a water-soluble fertilizer for fruits and vegetables with high humic acid oil cake according to the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1 A process for preparing a water-soluble fertilizer with high humic acid oil cake specifically for fruits and vegetables includes the following steps: S1. Raw material pretreatment: After the weathered coal or lignite is crushed and sieved, it is mixed with oil cake at a mass ratio of 1:(0.8-1.2) to obtain a mixed base material; S2, In-situ acidification coupling reaction: The mixed base material is put into the reaction vessel, and deionized water is added to adjust the solid-liquid ratio to 1:(3-6). Under stirring, the temperature is raised to 140℃-180℃, and the pressure is maintained at 0.4-0.8MPa. The reaction is carried out for 90-180 minutes. During the reaction, the organic acid generated by the hydrolysis of the oil cake is extracted in situ from the humic acid in the weathered coal or lignite. At the same time, the glycerol generated by the hydrolysis of the oil cake reacts with the carboxyl group at the edge of the humic acid molecule to form humic acid glyceride, and the reaction slurry is obtained. S3. Synergistic Enzymatic Hydrolysis Enhancement: Cool the reaction slurry to 50℃-60℃, adjust the pH to 6.0-7.0, add a complex enzyme preparation of lipase and protease. Lipase further hydrolyzes the residual oil cake to release fatty acids, and protease hydrolyzes the partially denatured proteins in the hydrothermal reaction into peptides. The peptides and the generated humic acid glycerides cross-link through secondary bonds to form a supramolecular network structure. Enzymatic hydrolysis is performed for 4-8 hours to obtain the enzymatically hydrolyzed material. S4. Nutrient Combination: Add urea, potassium dihydrogen phosphate and trace elements to the enzymatic hydrolysate, and chelate at 60℃-80℃ for 30-60 minutes to obtain a mixed solution. S5. Post-processing: After grinding the mixture with a colloid mill, spray dry or directly fill it to obtain water-soluble fertilizer.

[0023] Furthermore, in step S1, the oil cake is one or more of rapeseed cake, soybean cake, and peanut cake; during the mixing process of weathered coal or lignite and oil cake, the free fatty acids in the oil cake undergo an in-situ exchange reaction with the metal ions on the surface of weathered coal or lignite to generate fatty acid salts. The fatty acid salts act as natural emulsifiers in the hydrothermal reaction, promoting the opening of hydrogen bonds inside humic acid molecules.

[0024] Furthermore, in step S2, the temperature is increased using a gradient heating method: first, the temperature is increased to 100℃-110℃ at a rate of 3℃-5℃ / min and held for 20-30 minutes. During the holding period, the proteins in the oil cake denature and release sulfur-containing amino acids. The sulfur-containing amino acids undergo nucleophilic addition with the quinone structure in weathered coal or lignite to form intermediates linked by thioether bonds. Then, the temperature is increased to 140℃-180℃ at a rate of 2℃-3℃ / min. The heating curve controls the organic acid generation rate and the humic acid extraction rate to maintain a dynamic balance.

[0025] Furthermore, in step S2, the stirring speed in the reactor is 60-120 rpm, and the volatile gases generated during the reaction are returned to the reactor through a condenser reflux device. Under pressure and temperature, the carboxylic acid produced by the hydrolysis of the oil cake undergoes an esterification reaction with the phenolic hydroxyl groups at the edge of the humic acid molecules to generate humic acid esters with higher hydrophilicity. At the same time, the carboxylic acid promotes the release of fixed ammonium in weathered coal or lignite, and the released ammonium ions form ammonium salt complexes with humic acid esters.

[0026] Furthermore, in step S3, the amount of lipase added is 0.1%-0.3% of the total mass of the reaction slurry, with an enzyme activity of 50,000 U / g; the amount of protease added is 0.05%-0.15% of the total mass of the reaction slurry, with an enzyme activity of 200,000 U / g. The lipase first hydrolyzes the triglycerides in the residual oil cake, releasing glycerol and free fatty acids. The free fatty acids act as proton carriers to penetrate the interior of unreacted particles. The protease then hydrolyzes the protein into peptides and amino acids. The molecular weight of the peptides is controlled between 500-2000 Da. The peptides within the molecular weight range and the generated humic acid glycerides form a stable supramolecular network structure through hydrogen bonds and hydrophobic interactions.

[0027] Furthermore, in step S3, the pH adjuster used to adjust the pH is citric acid or oxalic acid. During the enzymatic hydrolysis process, sterile air is continuously introduced at a ratio of 1:(0.5-1). In the presence of sterile air, the polypeptide-humic acid supramolecular network structure captures oxygen molecules, forming oxygen-carrying microdomains. These oxygen-carrying microdomains promote the oxidation of residual reducing aldehyde groups in the system to carboxyl groups, increasing the overall negative charge density.

[0028] Furthermore, in step S4, the amount of urea added is 15%-25% of the total mass of the enzymatic hydrolysate, the amount of potassium dihydrogen phosphate added is 10%-20% of the total mass of the enzymatic hydrolysate, and the trace elements are at least two of zinc sulfate, boric acid, magnesium sulfate, and ammonium molybdate, with the amount of trace elements added being 0.5%-2% of the total mass of the enzymatic hydrolysate. Urea is added to the enzymatic hydrolysate first, and the ammonia gas produced by urea hydrolysis raises the local pH to 7.5-8.5, causing the supramolecular network structure to temporarily relax and expose chelation sites. Then, potassium dihydrogen phosphate and trace elements are added, and the phosphate ions form phosphorylated peptides with the amino terminus of the peptides. The phosphorylated peptides further lock the trace elements with humic acid glycerides through calcium bridging.

[0029] Furthermore, the chelation process in step S4 is assisted by ultrasound, with an ultrasound frequency of 40-80kHz and an ultrasound power density of 50-100W / L. The local high temperature and high pressure generated by the ultrasonic cavitation effect promote the formation of new carbon-phosphorus covalent bonds between the phosphorylated peptide and the humic acid molecules, generating a humic acid-peptide-phosphate terpolymer. The terpolymer encapsulates the trace elements in its hydrophilic cavity.

[0030] Furthermore, in step S5, the grinding fineness of the colloid mill is controlled to be 10-40 micrometers, the inlet air temperature of the spray dryer is 180℃-220℃, and the outlet air temperature is 70℃-90℃. During the spray drying process, the humic acid-peptide-phosphate terpolymer is oriented on the surface of the droplets to form microcapsules with a core-shell structure, wherein urea and inorganic salts are located in the core, and highly active humic acid derivatives constitute the shell.

[0031] Furthermore, in step S5, when using the direct filling method, a thickener is added to the mixture. The thickener is sodium carboxymethyl cellulose or xanthan gum, and the amount added is 0.1%-0.5% of the total mass of the mixture, adjusting the viscosity to 300-800 mPa·s. The linear molecular chains of sodium carboxymethyl cellulose or xanthan gum are interwoven in the polypeptide-humic acid supramolecular network structure, and crosslink with the terpolymer through intermolecular entanglement to form a three-dimensional network gel. The gel inhibits urea hydrolysis during storage and prevents the precipitation of trace elements.

[0032] Example 2 A process for preparing a water-soluble fertilizer with high humic acid oil cake specifically for fruits and vegetables includes the following steps: S1. Raw material pretreatment: After crushing and sieving lignite, it is mixed evenly with rapeseed cake at a mass ratio of 1:1.0 to obtain a mixed base material. Taking the jujube planting area in Aksu, Xinjiang as an example, the local area is rich in rapeseed oil, and rapeseed cake resources are abundant and inexpensive. The measured oil content is 12.5%, and the moisture content is controlled at 10%. During the mixing process, the free fatty acids in the rapeseed cake undergo in-situ exchange reactions with the calcium and magnesium ions on the surface of lignite to generate calcium fatty acid and magnesium fatty acid. These fatty acid salts act as natural emulsifiers in the subsequent hydrothermal reaction, promoting the opening of hydrogen bonds inside the humic acid molecules in lignite.

[0033] S2. In-situ acidification coupling reaction: The mixed base material is added to the reactor, and deionized water is added to adjust the solid-liquid ratio to 1:4.5. Under the condition of stirring speed of 80 rpm, a gradient heating method is adopted: first, the temperature is increased to 105℃ at a rate of 4℃ / min and held for 25 minutes. During the holding stage, the protein in rapeseed cake denatures and releases sulfur-containing amino acids. The sulfur-containing amino acids undergo nucleophilic addition with the quinone structure in lignite to form intermediates linked by thioether bonds; then, the temperature is increased to 160℃ at a rate of 2.5℃ / min, and the pressure is maintained at 0.6MPa for 135 minutes. During the reaction, the organic acids produced by the hydrolysis of rapeseed cake are extracted in situ from the humic acid in lignite. At the same time, the glycerol produced by the hydrolysis of rapeseed cake undergoes an esterification reaction with the carboxyl groups at the edge of the humic acid molecules to generate humic acid glycerides. The volatile gases generated during the reaction are refluxed back into the reactor through a condenser reflux device. In addition, the carboxylic acid produced by the hydrolysis of oil cake undergoes an esterification reaction with the phenolic hydroxyl groups at the edge of the humic acid molecules to generate humic acid esters with higher hydrophilicity. At the same time, the carboxylic acid promotes the release of fixed ammonium in lignite. The released ammonium ions form ammonium salt complexes with humic acid esters to obtain the reaction slurry.

[0034] S3. Synergistic Enzymatic Hydrolysis Enhancement: The reaction slurry is cooled to 55℃, and the pH is adjusted to 6.5 using citric acid. A compound enzyme preparation of lipase and protease is added. The amount of lipase added is 0.2% of the total mass of the reaction slurry, with an enzyme activity of 50,000 U / g; the amount of protease added is 0.1% of the total mass of the reaction slurry, with an enzyme activity of 200,000 U / g. The lipase first hydrolyzes the triglycerides in the residual rapeseed cake, releasing glycerol and free fatty acids. The free fatty acids act as proton carriers to penetrate the interior of unreacted particles; the protease then... In the hydrothermal reaction, partially denatured proteins are hydrolyzed into peptides and amino acids. The molecular weight of the peptides is controlled between 800-1500 Da. During the enzymatic hydrolysis process, sterile air is continuously introduced at an air-to-air ratio of 1:0.8. In the presence of sterile air, the peptides and the generated humic acid glycerides form a stable supramolecular network structure through hydrogen bonding and hydrophobic interactions. This network structure captures oxygen molecules to form oxygen-carrying microdomains. These oxygen-carrying microdomains promote the oxidation of residual reducing aldehyde groups in the system to carboxyl groups, increasing the overall negative charge density. After 6 hours of enzymatic hydrolysis, the hydrolyzed material is obtained.

[0035] S4. Nutrient Combination: Urea is first added to the enzymatically hydrolyzed material at a concentration of 20% of the total mass. The ammonia produced by urea hydrolysis raises the local pH to 8.0, temporarily relaxing the supramolecular network structure and exposing chelation sites. Then, potassium dihydrogen phosphate and trace elements are added. Potassium dihydrogen phosphate is added at a concentration of 15% of the total mass of the enzymatically hydrolyzed material, and the trace elements are a 1:1 mixture of zinc sulfate and boric acid, added at a concentration of 1.2% of the total mass of the enzymatically hydrolyzed material. Phosphate ions interact with the amino-terminal structures of polypeptides. Phosphorylated peptides are formed, and the phosphorylated peptides further lock in trace elements with humic acid glycerides through calcium bridging. The chelation process is assisted by ultrasound with an ultrasound frequency of 60 kHz and an ultrasound power density of 75 W / L. The local high temperature and high pressure generated by the ultrasonic cavitation effect promote the formation of new carbon-phosphorus covalent bonds between the phosphorylated peptides and humic acid molecules, generating a ternary copolymer of humic acid-peptide-phosphate. The ternary copolymer encapsulates the trace elements in its hydrophilic cavity. The chelation temperature is 70 ℃ and the chelation time is 45 minutes to obtain a mixed solution.

[0036] S5. Post-processing: The mixture is ground in a colloid mill with a fineness controlled at 25 microns. Then, it is spray-dried with an inlet air temperature of 200℃ and an outlet air temperature of 80℃. During the spray drying process, the humic acid-peptide-phosphate terpolymer is oriented on the surface of the droplets to form microcapsules with a core-shell structure. Urea and inorganic salts are located in the core, and highly active humic acid derivatives form the shell, thus obtaining water-soluble fertilizer.

[0037] Example 3 A process for preparing a water-soluble fertilizer with high humic acid oil cake specifically for fruits and vegetables includes the following steps: S1. Raw material pretreatment: After the weathered coal is crushed and sieved, it is mixed evenly with soybean cake at a mass ratio of 1:1.1 to obtain a mixed base material. Taking the Shouguang vegetable planting area in Shandong as an example, the local soybean cake source is stable, the measured oil content is 8.5%, and the moisture content is controlled at 9%. During the mixing process, the free fatty acids in the soybean cake undergo in-situ exchange reaction with the iron and aluminum ions on the surface of the weathered coal to generate fatty acid iron and fatty acid aluminum. These fatty acid salts act as natural emulsifiers in the hydrothermal reaction, promoting the opening of hydrogen bonds inside the humic acid molecules in the weathered coal.

[0038] S2. In-situ acidification coupling reaction: The mixed base material is added to the reactor, and deionized water is added to adjust the solid-liquid ratio to 1:5.0. Under the condition of stirring speed of 100 rpm, a gradient heating method is adopted: first, the temperature is increased to 108℃ at a rate of 3.5℃ / min and held for 22 minutes. During the holding stage, the protein in the soybean cake denatures and releases sulfur-containing amino acids. The sulfur-containing amino acids undergo nucleophilic addition with the quinone structure in the weathered coal to form intermediates linked by thioether bonds; then, the temperature is increased to 170℃ at a rate of 2.8℃ / min, and the pressure is maintained at 0.7MPa for 150 minutes. In the reaction process, the organic acids generated by the hydrolysis of soybean cake are used to extract humic acid from weathered coal in situ. At the same time, the glycerol generated by the hydrolysis of soybean cake undergoes an esterification reaction with the carboxyl groups at the edge of the humic acid molecules to generate humic acid glycerides. The volatile gases generated during the reaction are refluxed back into the reactor through a condenser reflux device. In addition, the carboxylic acid generated by the hydrolysis of oil cake undergoes an esterification reaction with the phenolic hydroxyl groups at the edge of the humic acid molecules to generate humic acid esters with higher hydrophilicity. At the same time, the carboxylic acid promotes the release of fixed ammonium in weathered coal. The released ammonium ions form ammonium salt complexes with humic acid esters to obtain the reaction slurry.

[0039] S3. Synergistic Enzymatic Hydrolysis Enhancement: The reaction slurry is cooled to 58℃, and the pH is adjusted to 6.8 using oxalic acid. A complex enzyme preparation of lipase and protease is added. The amount of lipase added is 0.25% of the total mass of the reaction slurry, with an enzyme activity of 50,000 U / g; the amount of protease added is 0.12% of the total mass of the reaction slurry, with an enzyme activity of 200,000 U / g. The lipase first hydrolyzes the triglycerides in the residual soybean cake, releasing glycerol and free fatty acids. The free fatty acids act as proton carriers to penetrate the interior of unreacted particles; the protease then... In the hydrothermal reaction, partially denatured proteins are hydrolyzed into peptides and amino acids. The molecular weight of the peptides is controlled between 600-1200 Da. During the enzymatic hydrolysis process, sterile air is continuously introduced at an air-to-air ratio of 1:0.9. In the presence of sterile air, the peptides and the generated humic acid glycerides form a stable supramolecular network structure through hydrogen bonding and hydrophobic interactions. This network structure captures oxygen molecules to form oxygen-carrying microdomains. These oxygen-carrying microdomains promote the oxidation of residual reducing aldehyde groups in the system to carboxyl groups, increasing the overall negative charge density. After 7 hours of enzymatic hydrolysis, the hydrolyzed material is obtained.

[0040] S4. Nutrient Combination: Urea is first added to the enzymatically hydrolyzed material at a concentration of 22% of the total mass. The ammonia produced by urea hydrolysis raises the local pH to 8.2, causing the supramolecular network structure to temporarily relax and expose chelation sites. Then, potassium dihydrogen phosphate and trace elements are added. Potassium dihydrogen phosphate is added at a concentration of 18% of the total mass of the enzymatically hydrolyzed material. The trace elements are a mixture of magnesium sulfate and ammonium molybdate in a 3:1 mass ratio, added at a concentration of 1.5% of the total mass of the enzymatically hydrolyzed material. Phosphate ions interact with the amino-terminal structures of polypeptides. Phosphorylated peptides are formed, and the phosphorylated peptides further lock in trace elements with humic acid glycerides through calcium bridging. The chelation process is assisted by ultrasound with an ultrasound frequency of 70 kHz and an ultrasound power density of 85 W / L. The local high temperature and high pressure generated by the ultrasonic cavitation effect promote the formation of new carbon-phosphorus covalent bonds between the phosphorylated peptides and humic acid molecules, generating a ternary copolymer of humic acid-peptide-phosphate. The ternary copolymer encapsulates the trace elements in its hydrophilic cavity. The chelation temperature is 75 ℃ and the chelation time is 50 minutes to obtain a mixed solution.

[0041] S5. Post-processing: The mixture is ground in a colloid mill to a fineness of 30 micrometers. Since the target market requires liquid formulation products, this embodiment adopts a direct filling method. A thickener, xanthan gum, is added to the mixture at a rate of 0.3% of the total mass of the mixture, and the viscosity is adjusted to 500 mPa·s. The linear molecular chains of xanthan gum are interwoven in the polypeptide-humic acid supramolecular network structure and crosslink with the terpolymer through intermolecular entanglement to form a three-dimensional network gel. This gel inhibits urea hydrolysis during storage and prevents the precipitation of trace elements, thus obtaining a liquid water-soluble fertilizer.

[0042] Performance testing and data comparison To verify the technical effects of each embodiment of the present invention, cucumbers from Shouguang, Shandong Province were used as the test object. Group 1, Group 2, Group 3 and a control group were set up. The control group used commercially available ordinary humic acid water-soluble fertilizer. The fertilization plan of each group was the same: topdressing began 7 days after transplanting, with 5 kg per mu applied each time, and topdressing was applied once every 10 days, for a total of 4 topdressings. The cucumber yield, single fruit weight, vitamin C content and soil pH changes were measured at the harvest period. The results are shown in Table 1.

[0043] Table 1. Effects of water-soluble fertilizers prepared in different embodiments on cucumber yield and quality. Note: Soil pH change is the difference before and after planting; negative values ​​indicate the degree of acidification.

[0044] As can be seen from the data in Table 1: First, in terms of yield, the yield per mu of Example 1, Example 2, and Example 3 was 3780 kg, 3920 kg, and 3850 kg, respectively, which increased by 16.3%, 20.6%, and 18.5% compared with the control group of 3250 kg. Among them, the yield increase of Example 2 was the most significant. The reason for this is that Example 2 used a combination of rapeseed cake and lignite, and the gradient heating parameters were optimized to 160℃-0.6MPa-135 minutes. Under these conditions, the humic acid extraction rate was the highest, and the supramolecular network structure was the most complete.

[0045] Secondly, in terms of quality, the single fruit weight and vitamin C content of the three example groups were significantly better than those of the control group. The single fruit weight of the example group reached 225g, which was 40g more than that of the control group; the vitamin C content reached 11.5mg / 100g, which was 35.3% higher than that of the control group. This shows that the supramolecular network structure formed by humic acid and polypeptide in the water-soluble fertilizer prepared by this invention can effectively chelate trace elements and promote the transfer of nutrients to the fruit.

[0046] Third, regarding soil improvement effects, the soil pH in the control group decreased by 0.45, showing a clear acidification trend, while the pH in Example 1 decreased by only 0.12, in Example 2 by 0.08, and in Example 3 by 0.10. This indicates that the sodium-free process of the present invention effectively avoids the salt accumulation problem caused by the traditional alkali extraction method. The soil pH in Example 2 and Example 3 remained basically stable, demonstrating excellent soil friendliness.

[0047] Fourth, regarding solubility, the fertilizer dissolution rates of Example 1, Example 2, and Example 3 were 4 min, 3 min, and 5 min, respectively, which were far superior to the 15 min of the control group. This is attributed to the highly hydrophilic structure of humic acid glyceride and humic acid-peptide-phosphate terpolymer in this invention, which makes the product fully meet the requirements of the integrated water and fertilizer drip irrigation system. Among them, Example 3 is a liquid formulation, and its dissolution rate is slightly slower than that of spray-dried powder, but it is still significantly better than commercially available products.

[0048] 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 process for preparing a water-soluble fertilizer made from high-humic acid oil cake specifically for fruits and vegetables, characterized in that, Includes the following steps: S1. Raw material pretreatment: After the weathered coal or lignite is crushed and sieved, it is mixed with oil cake at a mass ratio of 1:(0.8-1.2) to obtain a mixed base material; S2, In-situ acidification coupling reaction: The mixed base material is put into the reaction vessel, and deionized water is added to adjust the solid-liquid ratio to 1:(3-6). Under stirring, the temperature is raised to 140℃-180℃, and the pressure is maintained at 0.4-0.8MPa. The reaction is carried out for 90-180 minutes. During the reaction, the organic acid generated by the hydrolysis of the oil cake is extracted in situ from the humic acid in the weathered coal or lignite. At the same time, the glycerol generated by the hydrolysis of the oil cake reacts with the carboxyl group at the edge of the humic acid molecule to form humic acid glyceride, and the reaction slurry is obtained. S3. Synergistic Enzymatic Hydrolysis Enhancement: Cool the reaction slurry to 50℃-60℃, adjust the pH to 6.0-7.0, add a complex enzyme preparation of lipase and protease. Lipase further hydrolyzes the residual oil cake to release fatty acids, and protease hydrolyzes the partially denatured proteins in the hydrothermal reaction into peptides. The peptides and the generated humic acid glycerides cross-link through secondary bonds to form a supramolecular network structure. Enzymatic hydrolysis is performed for 4-8 hours to obtain the enzymatically hydrolyzed material. S4. Nutrient Combination: Add urea, potassium dihydrogen phosphate and trace elements to the enzymatic hydrolysate, and chelate at 60℃-80℃ for 30-60 minutes to obtain a mixed solution. S5. Post-processing: After grinding the mixture with a colloid mill, spray dry or directly fill it to obtain water-soluble fertilizer.

2. The preparation process of a water-soluble fertilizer for fruit and vegetable high-humic acid oil cake according to claim 1, characterized in that, In step S1, the oil cake is one or more of rapeseed cake, soybean cake, and peanut cake. During the mixing process of weathered coal or lignite and oil cake, the free fatty acids in the oil cake undergo an in-situ exchange reaction with the metal ions on the surface of weathered coal or lignite to generate fatty acid salts. The fatty acid salts act as natural emulsifiers in the hydrothermal reaction, promoting the opening of hydrogen bonds inside humic acid molecules.

3. The preparation process of a water-soluble fertilizer for fruit and vegetable high-humic acid oil cake according to claim 1, characterized in that, In step S2, the temperature is increased using a gradient heating method: first, the temperature is increased to 100℃-110℃ at a rate of 3℃-5℃ / min and held for 20-30 minutes. During the holding period, the proteins in the oil cake denature and release sulfur-containing amino acids. The sulfur-containing amino acids undergo nucleophilic addition with the quinone structure in weathered coal or lignite to form intermediates linked by thioether bonds. Then, the temperature is increased to 140℃-180℃ at a rate of 2℃-3℃ / min. The heating curve controls the organic acid generation rate and the humic acid extraction rate to maintain a dynamic balance.

4. The preparation process of a water-soluble fertilizer for fruit and vegetable high-humic acid oil cake according to claim 1, characterized in that, In step S2, the stirring speed in the reactor is 60-120 rpm. The volatile gases generated during the reaction are returned to the reactor through a condenser reflux device. Under pressure and temperature, the carboxylic acid produced by the hydrolysis of oil cake undergoes an esterification reaction with the phenolic hydroxyl groups at the edge of the humic acid molecules to generate humic acid esters with higher hydrophilicity. At the same time, the carboxylic acid promotes the release of fixed ammonium in weathered coal or lignite. The released ammonium ions form ammonium salt complexes with humic acid esters.

5. The preparation process of a water-soluble fertilizer for fruit and vegetable high-humic acid oil cake according to claim 1, characterized in that, In step S3, the amount of lipase added is 0.1%-0.3% of the total mass of the reaction slurry, with an enzyme activity of 50,000 U / g; the amount of protease added is 0.05%-0.15% of the total mass of the reaction slurry, with an enzyme activity of 200,000 U / g. The lipase first hydrolyzes the triglycerides in the residual oil cake, releasing glycerol and free fatty acids. The free fatty acids act as proton carriers to penetrate the interior of unreacted particles. The protease then hydrolyzes the protein into peptides and amino acids. The molecular weight of the peptides is controlled between 500-2000 Da. The peptides within the molecular weight range and the generated humic acid glycerides form a stable supramolecular network structure through hydrogen bonds and hydrophobic interactions.

6. The preparation process of a water-soluble fertilizer for fruit and vegetable high-humic acid oil cake according to claim 1, characterized in that, In step S3, the pH adjuster used to adjust the pH is citric acid or oxalic acid. During the enzymatic hydrolysis process, sterile air is continuously introduced at a ventilation ratio of 1:(0.5-1). In the presence of sterile air, the polypeptide-humic acid supramolecular network structure captures oxygen molecules, forming oxygen-carrying microdomains. These oxygen-carrying microdomains promote the oxidation of residual reducing aldehyde groups in the system to carboxyl groups, increasing the overall negative charge density.

7. The preparation process of a water-soluble fertilizer for fruit and vegetable high-humic acid oil cake according to claim 1, characterized in that, In step S4, the amount of urea added is 15%-25% of the total mass of the enzymatically hydrolyzed material, the amount of potassium dihydrogen phosphate added is 10%-20% of the total mass of the enzymatically hydrolyzed material, and the trace elements are at least two of zinc sulfate, boric acid, magnesium sulfate, and ammonium molybdate, with the amount of trace elements added being 0.5%-2% of the total mass of the enzymatically hydrolyzed material. Urea is added to the enzymatically hydrolyzed material first, and the ammonia gas produced by urea hydrolysis raises the local pH to 7.5-8.5, causing the supramolecular network structure to temporarily relax and expose chelation sites. Then, potassium dihydrogen phosphate and trace elements are added, and the phosphate ions form phosphorylated peptides with the amino terminus of the peptides. The phosphorylated peptides further lock the trace elements with humic acid glycerides through calcium bridging.

8. The preparation process of a water-soluble fertilizer for fruit and vegetable high-humic acid oil cake according to claim 1, characterized in that, In step S4, the chelation process is assisted by ultrasound with an ultrasound frequency of 40-80kHz and an ultrasound power density of 50-100W / L. The local high temperature and high pressure generated by the ultrasonic cavitation effect promote the formation of new carbon-phosphorus covalent bonds between the phosphorylated peptide and humic acid molecules, generating a humic acid-peptide-phosphate terpolymer. The terpolymer encapsulates trace elements in its hydrophilic cavity.

9. The preparation process of a water-soluble fertilizer for fruit and vegetable high-humic acid oil cake according to claim 1, characterized in that, In step S5, the grinding fineness of the colloid mill is controlled to be 10-40 micrometers, the inlet air temperature of the spray dryer is 180℃-220℃, and the outlet air temperature is 70℃-90℃. During the spray drying process, the humic acid-peptide-phosphate terpolymer is oriented on the surface of the droplets to form microcapsules with a core-shell structure, wherein urea and inorganic salts are located in the core, and highly active humic acid derivatives constitute the shell.

10. The preparation process of a water-soluble fertilizer for fruit and vegetable high-humic acid oil cake according to claim 1, characterized in that, In step S5, when direct filling is used, a thickener is added to the mixture. The thickener is sodium carboxymethyl cellulose or xanthan gum, and the amount added is 0.1%-0.5% of the total mass of the mixture, adjusting the viscosity to 300-800 mPa·s. The linear molecular chains of sodium carboxymethyl cellulose or xanthan gum are interwoven in the polypeptide-humic acid supramolecular network structure, and crosslink with the terpolymer through intermolecular entanglement to form a three-dimensional network gel. The gel inhibits urea hydrolysis during storage and prevents the precipitation of trace elements.

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