A corncob sugar residue / castor oil-based coated controlled-release fertilizer and a preparation method thereof

Abstract

The application discloses a corncob sugar residue / castor oil-based coated controlled-release fertilizer and a preparation method thereof. The coated controlled-release fertilizer is prepared by the following method: (1) mixing corncob sugar residue and a polyol to carry out a liquefaction reaction to obtain liquefied corncob sugar residue-based polyol A; (2) mixing the liquefied corncob sugar residue-based polyol A and castor oil at room temperature to obtain coated raw material B; (3) mixing isocyanate and an organic metal catalyst at room temperature to obtain coated raw material C; (4) mixing the coated raw material B and the coated raw material C at room temperature to obtain coated controlled-release raw material D; and spraying the coated controlled-release raw material D on the surface of core fertilizer particles to carry out an in-situ polymerization reaction, so that the corncob sugar residue / castor oil-based coated controlled-release fertilizer is prepared. The fertilizer is not only green and environment-friendly, but also can effectively improve the utilization rate of the fertilizer, the initial release rate of nutrients is less than 10%, and the cumulative release period is more than 30 days.

Description

Technical Field

[0001] This invention relates to the field of biomass resource utilization and green new fertilizer technology. More specifically, it relates to a controlled-release fertilizer coated with corn cob sugar residue / castor oil and its preparation method. Background Technology

[0002] Currently, global agricultural production heavily relies on chemical fertilizers to ensure food security. However, traditional fast-acting fertilizers have extremely low nutrient utilization rates, with approximately 50-60% of nitrogen and a large amount of other nutrients lost through leaching and volatilization. This not only results in enormous economic waste but also triggers a series of severe environmental problems such as eutrophication, soil compaction, and soil acidification. Against this backdrop, coated controlled-release fertilizers, by coating the fertilizer surface with a polymer film, achieve slow and controlled nutrient release, significantly improving nutrient utilization and considered one of the effective ways to solve these problems. However, most mainstream coated fertilizers on the market currently use petroleum-based polymers such as polyethylene and polypropylene as the film material. These materials originate from non-renewable fossil resources and are extremely difficult to degrade in the natural environment. After the nutrients are released, the waste film fragments remain in the soil for a long time, not only damaging the soil structure but also potentially affecting soil ecological health. Furthermore, these fragments can spread with agricultural activities, posing a potential threat to the sustainable use of arable land and creating a significant "secondary pollution" hazard.

[0003] To fundamentally address the environmental unfriendliness of existing coated fertilizers, developing novel coating materials that combine excellent controlled-release performance with complete biodegradability has become a critical technological bottleneck in this field. Although researchers have attempted to use natural or biosynthetic polymers such as starch, chitosan, and polylactic acid (PLA) as alternatives, these materials generally suffer from drawbacks such as high raw material costs, poor film-forming properties, insufficient mechanical strength, or unstable controlled-release performance, severely restricting their large-scale commercial application. Therefore, finding a widely available, low-cost, environmentally friendly, and easily modifiable biomass raw material to replace traditional petroleum-based coating materials is of great practical significance. Against this backdrop, corn cob residue demonstrates enormous application potential. Corn cob residue is a bulk solid byproduct generated from the production of xylose or xylitol from corn cobs, with an annual output of millions of tons in my country, representing a vast and extremely low-cost industrial waste. However, currently, the vast majority of corn cob residue is used only as low-value-added fuel or directly discarded, resulting in serious resource waste. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned defects of the prior art and to provide a corn cob sugar residue / castor oil-based coated controlled-release fertilizer that combines excellent nutrient controlled-release performance and biodegradability through a green and efficient process.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: a method for preparing a corn cob sugar residue / castor oil-based coated controlled-release fertilizer, comprising the following steps:

[0006] S1 mixes corn cob sugar residue, siloxane and polyol, adds acid solution as catalyst, and adds it to the reaction vessel for liquefaction reaction to obtain liquefied corn cob sugar residue-based polyol A; S2 mixes the liquefied corn cob sugar residue-based polyol A with castor oil to obtain coating material B; S3 mixes isocyanate with organometallic catalyst at room temperature to obtain coating material C; S4. The coating material B and the coating material C are mixed at room temperature to obtain the coating controlled-release material D; S5 loads the core fertilizer into a rotary drum coating machine for preheating. Using an in-situ coating process, the coating controlled-release raw material D is uniformly dripped onto the fertilizer surface. Through in-situ polymerization reaction, a film is formed, thus preparing corn cob sugar residue / castor oil-based coated controlled-release fertilizer.

[0007] The core technical concept of this invention lies in the high-value utilization of inexpensive and readily available corn cob residue. Chemical analysis reveals that corn cob residue is mainly composed of lignin and cellulose, with its molecular skeleton naturally rich in active functional groups such as hydroxyl and carboxyl groups. These functional groups provide ideal sites for chemical modification reactions such as esterification, grafting, and cross-linking, giving it great potential for chemically controlling its film-forming properties, hydrophobicity, mechanical strength, and degradation rate, thus enabling its transformation into a high-performance fertilizer coating material. Therefore, this invention aims to successfully transform industrial waste corn cob residue into a novel, biodegradable, controlled-release fertilizer film material through a specific chemical modification and composite preparation process, thereby achieving "waste treatment of waste" and turning waste into treasure.

[0008] Corn cob residue is a bulk solid byproduct generated from the industrial production of xylose / xylitol from corn cobs through acid or enzymatic hydrolysis. Currently, the vast majority of corn cob residue is used as low-value boiler fuel, cheap animal feed, or simply discarded, resulting in significant resource waste and environmental disposal pressure. Appropriate chemical modification can effectively improve its film-forming properties, hydrophobicity, and mechanical strength, transforming it into a high-performance controlled-release fertilizer coating material.

[0009] This invention utilizes corn cob sugar residue as raw material and modifies it with siloxane to obtain liquefied corn cob sugar residue-based polyol. By combining the liquefied corn cob sugar residue-based polyol with castor oil, the molding properties and hydrophobicity of the coating material are further enhanced, and a low-cost and environmentally friendly corn cob sugar residue / castor oil-based coated controlled-release fertilizer is successfully prepared, effectively prolonging the controlled-release effect of the coated fertilizer.

[0010] Preferably, in step S1, the corn cob sugar residue accounts for 20-40% of the mass fraction of corn cob sugar residue-based polyol A; the siloxane accounts for 2-5% of the mass fraction of corn cob sugar residue-based polyol A; and the acid solution catalyst accounts for 1-3% of the mass fraction of corn cob sugar residue-based polyol A.

[0011] Preferably, the mass ratio of liquefied corn cob sugar residue-based polyol A to castor oil in step S2 is 1~5:0~2.

[0012] Preferably, the mass ratio of isocyanate to organometallic catalyst in step S3 is 22~44:1.

[0013] Preferably, the mass ratio of coating material B to coating material C in step S4 is 1:0.8~1.5.

[0014] Preferably, in the corn cob sugar residue-based coated controlled-release fertilizer described in step S5, the coating material accounts for 2-8% of the core fertilizer.

[0015] Preferably, the corn cob sugar residue is the waste residue generated during the preparation of xylose from corn cobs.

[0016] Preferably, the siloxane is selected from one or more of linear polydimethylsiloxane, cyclic polydimethylsiloxane, hydroxyl-terminated polydimethylsiloxane, vinyl-terminated polydimethylsiloxane, hydrogen-containing silicone oil, amino-modified silicone oil, epoxy-modified silicone oil, and phenyl silicone oil.

[0017] Preferably, the polyol is one or more selected from polyethylene glycol, polyvinyl lactone glycol, glycerol, and ethylene glycol.

[0018] Preferably, the acid solution is one or more of concentrated sulfuric acid, hydrochloric acid, and nitric acid.

[0019] Preferably, the castor oil is selected from one or more of industrial grade castor oil, pharmaceutical grade castor oil, cold-pressed castor oil, hydrogenated castor oil, sulfonated castor oil, and dehydrated castor oil.

[0020] Preferably, the isocyanate is selected from one or more of hexamethylene diisocyanate (HDI), polymeric DMI 200, polymeric DMI 400, polymeric DMI 600 and polymeric DMI 700.

[0021] Preferably, the organometallic catalyst is selected from one or more of dibutyltin dilaurate, stannous octanoate, dibutyltin diacetate, stannous oleate, zinc naphthenate, zinc isooctanoate, bismuth carboxylate, bismuth isooctanoate, zirconium carboxylate, phenylmercuric propionate, and phenylmercuric acetate.

[0022] Preferably, the core fertilizer is one or more of the following: large-particle urea, sulfur-coated urea, ammonium carbonate, ammonium nitrate, ammonium sulfate, potassium chloride, potassium nitrate, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate, with an average particle size of 2-5 mm.

[0023] Another objective of this invention is to provide a corn cob sugar residue / castor oil-based coated controlled-release fertilizer.

[0024] The corn cob sugar residue / castor oil-based coated controlled-release fertilizer provided by this invention is prepared by the above method. The beneficial effects of this invention compared to the prior art are as follows: (1) This invention uses corn cob sugar residue as raw material to prepare corn cob sugar residue / castor oil-based coated controlled-release fertilizer. Corn cob sugar residue raw material is not only widely available, inexpensive, and renewable, but the reuse of corn cob sugar residue raw material can solve its environmental pollution problem. (2) The present invention improves the hydrophobicity of the fertilizer by coating the core fertilizer with a polyurethane compound of corn cob sugar residue and castor oil, and also improves the hardness of the fertilizer particles, thereby reducing the nutrient release rate in the coated controlled-release fertilizer. (3) The preparation process of the present invention is simple, the raw material preparation and coating process is green and environmentally friendly, and it meets the nutrient requirements of crops throughout the entire growth period while greatly reducing production costs.

[0025] This invention not only eliminates the residual pollution problem caused by the use of traditional coating materials at the source, but also provides modern green agriculture with a cost-effective, environmentally friendly, and highly efficient fertilizer solution that fully complies with the circular economy and sustainable development strategy. Attached Figure Description

[0026] Figure 1 The cumulative nitrogen release at different times of the coated controlled-release fertilizers prepared in Examples 1-6 of this invention. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments. Unless otherwise specified, the methods, reagents and equipment used in the present invention are all conventional methods, reagents and equipment in the art, and the materials described in the present invention are all commercially available.

[0028] Example 1 Preparation of liquefied corn cob sugar residue-based polyol: 32 parts of corn cob sugar residue powder and 3 parts of siloxane were added to 65 parts of polyol solution, specifically 25.4 parts of ethylene glycol, 38.1 parts of polyethylene glycol, and 1.5 parts of concentrated sulfuric acid as a catalyst. After thorough mixing, the solution was added to a reaction vessel for liquefaction. The liquefaction conditions were 160 ℃, 500 rpm, and 3 h, yielding liquefied corn cob sugar residue-based polyol A.

[0029] Preparation of coating material B: Take 100 parts of liquefied corn cob sugar residue-based polyol A and 0 parts of castor oil and stir and mix at room temperature to obtain coating material B.

[0030] Preparation of coating material C: Take 29 parts of hexamethylene diisocyanate (HDI) and 1 part of stannous octoate and place them in a 50 mL plastic bottle. Mix them by ultrasonic vibration for 5 min to obtain coating material C.

[0031] Preparation of coating material D: Take 50 parts of coating material B and 50 parts of coating material C and mix them evenly at room temperature to obtain coating material D.

[0032] Preparation of coated controlled-release fertilizer: Weigh 1000 g of large-particle urea with an average particle size of 3.00~5.00 mm and preheat it in a rotary drum coating machine. Accurately weigh 18.33 g of coating material D and spray it evenly onto the fully preheated urea surface. React at 75 ℃ for 10 minutes to form a film on the urea particle surface. Repeat adding coating material D and spraying a total of 3 times until the fertilizer particle surface is cured and no longer sticky, thus obtaining corn cob sugar residue / castor oil-based coated controlled-release fertilizer.

[0033] Example 2 Preparation of liquefied corn cob sugar residue-based polyol: 32 parts of corn cob sugar residue powder and 3 parts of siloxane were added to 65 parts of polyol solution, specifically 25.4 parts of ethylene glycol, 38.1 parts of polyethylene glycol, and 1.5 parts of concentrated sulfuric acid as a catalyst. After thorough mixing, the solution was added to a reaction vessel for liquefaction. The liquefaction conditions were 160 ℃, 500 rpm, and 3 h, yielding liquefied corn cob sugar residue-based polyol A.

[0034] Preparation of coating material B: Take 90 parts of liquefied corn cob sugar residue-based polyol and 10 parts of castor oil and stir and mix at room temperature to obtain coating material B.

[0035] Preparation of coating material C: Take 29 parts of hexamethylene diisocyanate (HDI) and 1 part of stannous octoate and place them in a 50 mL plastic bottle. Mix them by ultrasonic vibration for 5 min to obtain coating material C.

[0036] Preparation of coating material D: Take 50 parts of coating material B and 50 parts of coating material C and mix them evenly at room temperature to obtain coating material D.

[0037] Preparation of coated controlled-release fertilizer: Weigh 1000 g of large-particle urea with an average particle size of 3.00~5.00 mm and place it in a rotary drum coating machine for preheating. Accurately weigh 18.33 g of coating material D and spray it uniformly onto the surface of the preheated urea. React at 75 ℃ for 10 minutes to form a film on the surface of the urea particles. Repeat adding coating material D and spraying a total of 3 times until the surface of the fertilizer particles is cured and no longer sticky. This yields corn cob sugar residue / castor oil-based coated controlled-release fertilizer.

[0038] Example 3 Preparation of liquefied corn cob sugar residue-based polyol: 32 parts of corn cob sugar residue powder and 3 parts of siloxane were added to 65 parts of polyol solution, specifically 25.4 parts of ethylene glycol, 38.1 parts of polyethylene glycol, and 1.5 parts of concentrated sulfuric acid as a catalyst. After thorough mixing, the solution was added to a reaction vessel for liquefaction. The liquefaction conditions were 160 ℃, 500 rpm, and 3 h, yielding liquefied corn cob sugar residue-based polyol A.

[0039] Preparation of coating material B: Take 85 parts of liquefied corn cob sugar residue-based polyol and 15 parts of castor oil and stir and mix at room temperature to obtain coating material B.

[0040] Preparation of coating material C: Take 29 parts of hexamethylene diisocyanate (HDI) and 1 part of stannous octoate and place them in a 50 mL plastic bottle. Mix them by ultrasonic vibration for 5 min to obtain coating material C.

[0041] Preparation of coating material D: Take 50 parts of coating material B and 50 parts of coating material C and mix them evenly at room temperature to obtain coating material D.

[0042] Preparation of coated controlled-release fertilizer: Weigh 1000 g of large-particle urea with an average particle size of 3.00~5.00 mm and place it in a rotary drum coating machine for preheating. Accurately weigh 18.33 g of coating material D and spray it evenly onto the fully preheated urea surface. React at 75 ℃ for 10 minutes to form a film on the urea particle surface. Repeat the addition of coating material D, spraying a total of 3 times until the fertilizer particle surface is cured and no longer sticky, thus obtaining corn cob sugar residue / castor oil-based coated controlled-release fertilizer.

[0043] Example 4 Preparation of liquefied corn cob sugar residue-based polyol: 32 parts of corn cob sugar residue powder and 3 parts of siloxane were added to 65 parts of polyol solution, specifically 25.4 parts of ethylene glycol, 38.1 parts of polyethylene glycol, and 1.5 parts of concentrated sulfuric acid as a catalyst. After thorough mixing, the solution was added to a reaction vessel for liquefaction. The liquefaction conditions were 160 ℃, 500 rpm, and 3 h, yielding liquefied corn cob sugar residue-based polyol A.

[0044] Preparation of coating material B: Take 80 parts of liquefied corn cob sugar residue-based polyol and 20 parts of castor oil and stir and mix at room temperature to obtain coating material B.

[0045] Preparation of coating material C: Take 29 parts of hexamethylene diisocyanate (HDI) and 1 part of stannous octoate and place them in a 50 mL plastic bottle. Mix them by ultrasonic vibration for 5 min to obtain coating material C.

[0046] Preparation of coating material D: Take 50 parts of coating material B and 50 parts of coating material C and mix them evenly at room temperature to obtain coating material D.

[0047] Preparation of coated controlled-release fertilizer: Weigh 1000 g of large-particle urea with an average particle size of 3.00~5.00 mm and place it in a rotary drum coating machine for preheating. Accurately weigh 18.33 g of coating material D and spray it evenly onto the fully preheated urea surface. React at 75 ℃ for 10 minutes to form a film on the urea particle surface. Repeat the addition of coating material D, spraying a total of 3 times until the fertilizer particle surface is cured and no longer sticky, thus obtaining corn cob sugar residue / castor oil-based coated controlled-release fertilizer.

[0048] Example 5 Preparation of liquefied corn cob sugar residue-based polyol: 32 parts of corn cob sugar residue powder and 3 parts of siloxane were added to 65 parts of polyol solution, specifically 25.4 parts of ethylene glycol, 38.1 parts of polyethylene glycol, and 1.5 parts of concentrated sulfuric acid as a catalyst. After thorough mixing, the solution was added to a reaction vessel for liquefaction. The liquefaction conditions were 160 ℃, 500 rpm, and 3 h, yielding liquefied corn cob sugar residue-based polyol A.

[0049] Preparation of coating material B: Take 75 parts of liquefied corn cob sugar residue-based polyol and 25 parts of castor oil and stir and mix at room temperature to obtain coating material B.

[0050] Preparation of coating material C: Take 29 parts of hexamethylene diisocyanate (HDI) and 1 part of stannous octoate and place them in a 50 mL plastic bottle. Mix them by ultrasonic vibration for 5 min to obtain coating material C.

[0051] Preparation of coating material D: Take 50 parts of coating material B and 50 parts of coating material C and mix them evenly at room temperature to obtain coating material D.

[0052] Preparation of coated controlled-release fertilizer: Weigh 1000 g of large urea particles with an average particle size of 3.00~5.00 mm and place them in a rotary drum coating machine for preheating. Accurately weigh 18.33 g of coating material D and spray it evenly onto the surface of the preheated urea. React at 75 ℃ for 10 minutes to form a film on the surface of the urea particles. Repeat the addition of coating material D and spray a total of 3 times until the surface of the fertilizer particles is cured and no longer sticky. This yields corn cob sugar residue / castor oil-based coated controlled-release fertilizer.

[0053] Example 6 Preparation of liquefied corn cob sugar residue-based polyol: 32 parts of corn cob sugar residue powder and 3 parts of siloxane were added to 65 parts of polyol solution, specifically 25.4 parts of ethylene glycol, 38.1 parts of polyethylene glycol, and 1.5 parts of concentrated sulfuric acid as a catalyst. After thorough mixing, the solution was added to a reaction vessel for liquefaction. The liquefaction conditions were 160 ℃, 500 rpm, and 3 h, yielding liquefied corn cob sugar residue-based polyol A.

[0054] Preparation of coating material B: Take 75 parts of liquefied corn cob sugar residue-based polyol and 25 parts of castor oil and stir and mix at room temperature to obtain coating material B.

[0055] Preparation of coating material C: Take 29 parts of hexamethylene diisocyanate (HDI) and 1 part of stannous octoate and place them in a 50 mL plastic bottle. Mix them by ultrasonic vibration for 5 min to obtain coating material C.

[0056] Preparation of coating material D: Take 45.5 parts of coating material B and 54.5 parts of coating material C and mix them evenly at room temperature to obtain coating material D.

[0057] Preparation of coated controlled-release fertilizer: Weigh 1000 g of large-particle urea with an average particle size of 3.00~5.00 mm and preheat it in a rotary drum coating machine; accurately weigh 18.33 g of coating material D and spray it evenly onto the fully preheated urea surface. React at 75 ℃ for 10 minutes to form a film on the urea particle surface. Repeat adding coating material D and spraying a total of 3 times until the fertilizer particle surface is cured and no longer sticky, thus obtaining corn cob sugar residue / castor oil-based coated controlled-release fertilizer.

[0058] In this invention, the controlled-release performance of the obtained coated fertilizer was tested according to industry standard GB / T 23348~2009. The steps are as follows: Weigh 10.00 g of coated fertilizer (accurate to 0.01 g) and place it in a 100-mesh nylon mesh bag. After sealing, place the mesh bag containing the coated fertilizer into a plastic bottle containing 200 mL of water that has been pre-placed at 25 ℃. Seal the bottle and incubate it in a biochemical incubator at 25 ℃. Samples were taken at regular intervals (sampling times are 1 day, 3 days, 5 days, 7 days, 14 days, 21 days, 28 days, 35 days, 42 days, 49 days, ..., 60 days). During sampling, the bottle was inverted three times to ensure a consistent liquid concentration. Subsequently, the nylon mesh bag was removed, the solution was shaken well, and the sample to be tested was collected and stored for determining the refractive index or conductivity value. The initial release rate is represented by the mass fraction of the amount of nutrients released by the coated fertilizer after 24 hours of extraction in still water at 25 ℃. The date corresponding to 80% cumulative nutrient release is defined as the cumulative nutrient release period of the fertilizer, as shown in Table 1.

[0059] Table 1 Nutrient release rates of corn cob sugar residue / castor oil-based coated controlled-release fertilizers from different embodiments deal with Particle hardness (N) Nitrogen release rate (%) in 24 hours Nutrient release 80% (controlled release period) Example 1 38.73 34.77 14 days Example 2 39.76 18.87 21 days Example 3 41.60 5.64 35 days Example 4 42.36 5.31 42 days Example 5 43.20 1.46 49 days Example 6 46.75 0.37 49 days

Claims

1. A method for preparing a corn cob sugar residue / castor oil-based coated controlled-release fertilizer, characterized in that, Includes the following steps: S1 mixes corn cob sugar residue, siloxane and polyol, adds acid solution as catalyst, and adds it to the reaction vessel for liquefaction reaction to obtain liquefied corn cob sugar residue-based polyol A; S2 mixes the liquefied corn cob sugar residue-based polyol A with castor oil to obtain coating material B; S3 mixes isocyanate with organometallic catalyst at room temperature to obtain coating material C; S4. The coating material B and the coating material C are mixed at room temperature to obtain the coating controlled-release material D; S5 The fertilizer is preheated in a rotary drum coating machine. Using an in-situ coating process, the coating controlled-release raw material D is uniformly dripped onto the surface of the core fertilizer. The film is formed through in-situ polymerization reaction, thus preparing corn cob sugar residue / castor oil-based coated controlled-release fertilizer.

2. The method for preparing the corn cob sugar residue / castor oil-based coated controlled-release fertilizer according to claim 1, characterized in that: In step S1, the corn cob sugar residue accounts for 20-40% of the mass fraction of the corn cob sugar residue-based polyol A; the siloxane accounts for 2-5% of the mass fraction of the corn cob sugar residue-based polyol A; and the acid solution catalyst accounts for 1-3% of the mass fraction of the corn cob sugar residue-based polyol A. In step S2, the mass ratio of liquefied corn cob sugar residue-based polyol A to castor oil is 1~5:0~2; In step S3, the mass ratio of isocyanate to organometallic catalyst is 22~44:1; In step S4, the mass ratio of coating material B to coating material C is 1:0.8~1.5; In step S5, the coated controlled-release raw material D is 2-8% of the mass of the core fertilizer.

3. The method for preparing the corn cob sugar residue / castor oil-based coated controlled-release fertilizer according to claim 1, characterized in that, The corn cob sugar residue mentioned above is the waste residue generated during the preparation of xylose from corn cobs.

4. The method for preparing the corn cob sugar residue / castor oil-based coated controlled-release fertilizer according to claim 1, characterized in that, The polyol is one or more of polyethylene glycol, polyvinyl lactone glycol, glycerol, or ethylene glycol.

5. The method for preparing the corn cob sugar residue / castor oil-based coated controlled-release fertilizer according to claim 1, characterized in that, The castor oil is selected from one or more of the following: industrial grade castor oil, pharmaceutical grade castor oil, cold-pressed castor oil, hydrogenated castor oil, sulfonated castor oil, and dehydrated castor oil.

6. The method for preparing the corn cob sugar residue / castor oil-based coated controlled-release fertilizer according to claim 1, characterized in that, The isocyanate is selected from one or more of hexamethylene diisocyanate, polymeric DMI 200, polymeric DMI 400, polymeric DMI 600 and polymeric DMI 700.

7. The method for preparing the corn cob sugar residue / castor oil-based coated controlled-release fertilizer according to claim 1, characterized in that, The organometallic catalyst is selected from one or more of the following: dibutyltin dilaurate, stannous octanoate, dibutyltin diacetate, stannous oleate, zinc naphthenate, zinc isooctanoate, bismuth carboxylate, bismuth isooctanoate, zirconium carboxylate, phenylmercuric propionate, and phenylmercuric acetate.

8. The method for preparing the corn cob sugar residue / castor oil-based coated controlled-release fertilizer according to claim 1, characterized in that, The fertilizer is one or more of the following: large-particle urea, sulfur-coated urea, ammonium carbonate, ammonium nitrate, ammonium sulfate, potassium chloride, potassium nitrate, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate, with an average particle size of 2-5 mm.

9. The method for preparing the corn cob sugar residue / castor oil-based coated controlled-release fertilizer according to claim 1, characterized in that, In step S1, the liquefaction reaction conditions are 2~4 h, 140~170 ℃, and 500~700 rpm; in step S5, the rotation speed is 300~400 rpm, the temperature is 70~100 ℃, and the time is 10~30 min.

10. Corn cob sugar residue / castor oil-based coated controlled-release fertilizer prepared by any of the preparation methods described in claims 1 to 9.

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