Preparation method of bio-based polyurethane slow-release fertilizer
By hydrogenating and catalytically reducing lignocellulose, bio-based polyurethane slow-release fertilizer was prepared, solving the problems of structural damage to coating materials and competition for farmland during liquefaction, and achieving high performance and environmentally friendly slow-release effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-12
- Publication Date
- 2026-04-14
AI Technical Summary
Existing bio-based coating materials generate carboxylic acid compounds during liquefaction, which damages the polyurethane coating network structure, reduces sustained-release performance, and raises concerns about the source of raw materials competing with food supplies.
Using lignocellulose as raw material, carboxylic acid compounds are converted into alcohols or esters through the hydrogenation catalytic reduction technology of polyols. The acid value of the refined bio-based polyol is controlled to be less than 5 mg KOH/g, and it reacts with isocyanate to form a polyurethane coating.
The formation of a dense, non-porous polyurethane coating improves the controlled-release performance of slow-release fertilizers, solves the problem of coating structure integrity, achieves high-performance and environmentally friendly slow-release effects, and avoids the risk of raw materials competing for farmland.
Smart Images
Figure CN121850791A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of agricultural slow-release fertilizer technology, specifically relating to a method for preparing a bio-based polyurethane slow-release fertilizer. Background Technology
[0002] Grain yield is closely related to fertilizer application. Typically, after fertilizer is applied to the soil, crops can only absorb and utilize 30% to 50% of the nutrients, with the remainder lost through leaching, volatilization, and nitrification-denitrification processes. To ensure nutrient supply throughout the crop's growth cycle, agricultural production often increases fertilizer application; however, excessive fertilizer application can easily lead to a series of ecological problems such as soil compaction, eutrophication of water bodies, and environmental pollution. Slow-release fertilizers improve utilization efficiency by regulating the nutrient release rate to match the crop's nutrient requirements during growth. Among various slow-release fertilizers, coated slow-release fertilizers have been studied more extensively, mainly divided into inorganic and organic coated types. Organic coated slow-release fertilizers involve coating urea granules with a polymer film to control their dissolution and release rate. The slow-release performance of this type of fertilizer depends crucially on the properties of the coating material; common polymers include resins and polyurethanes. However, most polymer materials are difficult to degrade in the environment, and large-scale use can cause new forms of white pollution.
[0003] Therefore, biodegradable bio-based coating materials have become an important research direction. For example, coating materials are prepared using corn starch and vegetable oil as raw materials. However, these bio-based materials present a contradiction of competing with food production. In recent years, researchers have turned their attention to the more abundant, non-food-grade lignocellulose resources. Lignocellulose is mainly composed of cellulose (40%~50%), hemicellulose (20%~35%), and lignin (20%~40%). However, during thermochemical liquefaction in a polyol medium, lignocellulose generates high levels of carboxylic acids such as formic acid, acetic acid, and levulinic acid, leading to an increase in the acid value of the liquefied polyol. When these residual carboxylic acid components react with isocyanates, carbon dioxide gas is released, causing the final polyurethane coating layer to develop pores, severely damaging the integrity of the polyurethane coating network structure, and thus significantly reducing the mechanical strength and controlled-release function of the coating. In view of this, this application is proposed to overcome the limitations of existing bio-based coating materials in terms of raw material sources and performance control. Summary of the Invention
[0004] To address the shortcomings of existing technologies, the technical problem to be solved by this invention is to provide a method for preparing bio-based polyurethane slow-release fertilizer, which uses lignocellulose as raw material and regulates the slow-release performance of the polyurethane coating by moderately hydrogenating its full-component liquefied polyol, ultimately obtaining a high-performance, environmentally friendly slow-release fertilizer.
[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing a bio-based polyurethane slow-release fertilizer, comprising the following steps: (1) Using lignocellulose as raw material and polyol as liquefaction solvent, a liquefaction reaction is carried out under the action of acid catalyst to obtain liquefied polyol; (2) In the presence of a hydrogenation catalyst, the liquefied polyol is subjected to a moderate hydrogenation reaction to selectively reduce the organic carboxylic acid contained therein to the corresponding alcohol or ester compound. After the reaction is completed, the reaction solvent is removed to obtain a refined bio-based polyol. The acid value of the refined bio-based polyol is controlled to be less than 5 mg KOH / g. (3) Place 25-150 parts by weight of urea granules in a coating device, and then add a mixture consisting of 0-0.3 parts by weight of catalyst, 8-20 parts by weight of the refined bio-based polyol and 6-25 parts by weight of isocyanate. After stirring and reacting, the mixture is dried to obtain the bio-based polyurethane slow-release fertilizer.
[0006] Optionally, in step (1), the liquid-to-solid mass ratio of the liquefaction reaction is (4:1) to (8:1), the reaction temperature is 140℃ to 200℃, and the reaction time is 1h to 5h.
[0007] Optionally, in step (1), the lignocellulose is one of wheat straw, corn straw, sugarcane bagasse, bamboo powder and wood powder; The polyol is one or a mixture of polyethylene glycol 400, ethylene glycol and glycerin, wherein the ratio of the mixture is optional, for example: a mixture of polyethylene glycol 400 and glycerin, preferably with a mass ratio of (1:2) to (2:1); or a mixture of ethylene glycol and glycerin, preferably with a mass ratio of (1:2) to (2:1); The acid catalyst is one of sulfuric acid, nitric acid, and hydrochloric acid, and the amount of the acid catalyst is 1 to 5% of the mass of the polyol.
[0008] Optionally, in step (2), the conditions for the hydrogenation reduction reaction are: reaction temperature of 160℃~240℃, reaction time of 4~12h, reaction pressure of 2-6 MPa, and reaction solvent of water, methanol, or n-hexane; the concentration of the liquefied polyol is 5-50%, and the amount of the hydrogenation catalyst is 1-10% of the mass of the liquefied polyol.
[0009] Optionally, in step (2), the hydrogenation catalyst is a porous CuZnAl catalyst; The porous CuZnAl catalyst is prepared by: providing 100 parts by weight of water, 10-30 parts by weight of sodium hydroxide and 100 parts by weight of Divide alloy, reacting in an ice-water bath for 0.5-4 hours, and washing until neutral after the reaction is complete.
[0010] Optionally, in step (3), the stirring reaction is carried out at room temperature, with a rotation speed of 40 to 100 rpm and a time of 10 to 30 min; The drying process involves natural air drying for 6 to 36 hours.
[0011] Optionally, in step (3), after the stirring reaction and before drying, the mixture is cured at 80°C for 0 to 60 minutes, preferably 25 to 60 minutes.
[0012] Optionally, the catalyst is a mixture of a tertiary amine and an organotin compound, wherein the weight ratio of the tertiary amine to the organotin compound is (1:2) to (2:1); wherein the tertiary amine is triethylenediamine or triethylamine, and the organotin compound is dibutyltin dilaurate or stannous octoate.
[0013] Optionally, the isocyanate is at least one selected from toluene diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate.
[0014] Optionally, before hydrogenation purification in step (2) or before coating preparation in step (3), an alkaline compound is added to the system to neutralize the inorganic acids contained therein.
[0015] The alkaline compounds can be common neutralizing agents such as sodium hydroxide and potassium hydroxide. After neutralization, the pH of the system can be adjusted to 6-8, preferably 7. The inorganic acids in the system mainly come from the acid catalyst used in the liquefaction reaction in step (1).
[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a method for preparing a bio-based polyurethane slow-release fertilizer. The method first converts lignocellulose into a liquefied polyol through thermochemical liquefaction; then, it refines the liquefied polyol using catalytic hydrogenation technology, hydrogenating carboxylic acid compounds such as formic acid, acetic acid, and levulinic acid into their corresponding alcohols or esters, controlling the acid value of the refined bio-based polyol to be less than 5 mg KOH / g; finally, using this refined bio-based polyol as a raw material, it forms a polyurethane coating on the surface of urea particles through in-situ polymerization with isocyanate, thus obtaining the slow-release fertilizer. Through the organic combination of the above steps, this invention controls the acid value of the refined bio-based polyol at an appropriate level, fundamentally suppressing the foaming problem caused by the reaction of carboxylic acid compounds in the liquefied polyol with isocyanate to release carbon dioxide. This results in a dense, pore-free, and structurally complete polyurethane coating layer, ensuring the controlled-release performance of the fertilizer. The prepared bio-based polyurethane slow-release fertilizer exhibits excellent slow-release performance.
[0017] This invention uses abundant and renewable lignocellulose as raw material to prepare bio-based polyols, which are then used in the synthesis of polyurethane coating materials. This avoids the problem of "competing with people for food" that may be caused by the application of bio-based raw materials such as vegetable oil and starch, and realizes the high-value utilization of lignocellulose resources.
[0018] This invention employs catalytic hydrogenation technology to reduce carboxylic acid compounds such as formic acid, acetic acid, and levulinic acid in bio-based polyols to the corresponding alcohols or esters. By moderately hydrogenating, the acid value of the refined bio-based polyol is controlled to be less than 5 mg KOH / g, which not only effectively reduces the content of by-reactive components but also significantly improves the storage stability and chemical reactivity of the polyol product.
[0019] The preparation process of the porous CuZnAl catalyst used in this invention also has significant advantages. This catalyst is synthesized in one step via a simple alkaline etching method, avoiding the complexity of traditional multi-step processes such as impregnation, calcination, and reduction. This shortens the preparation cycle, reduces energy consumption, and facilitates the formation of a stable porous structure with fully exposed active sites, thus providing efficient and stable catalytic support for the hydrorefining process. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0021] Figure 1 Image of the bio-based polyurethane slow-release fertilizer product prepared in Example 1 of this invention; Figure 2 Photograph of the bio-based polyurethane slow-release fertilizer product prepared in Comparative Example 1. Detailed Implementation
[0022] To better understand the present invention, the following embodiments further illustrate the content of the invention, but the scope of protection of the present invention is not limited to the following embodiments. Numerous specific details are set forth in the following description to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the present invention can be practiced without one or more of these details.
[0023] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.
[0024] Unless otherwise specified, all raw materials are derived from commercially available products and do not contain any unspecified components other than unavoidable impurities.
[0025] In the following embodiments, "parts" refers to parts by weight.
[0026] Room temperature refers to 25±5℃.
[0027] The particle size of wheat straw, corn straw, sugarcane bagasse, bamboo powder, or wood powder is 80 mesh.
[0028] Example 1 A method for preparing a bio-based polyurethane slow-release fertilizer includes the following steps: Step (1) Liquefaction: Take 100 parts of corn stalk powder and mix it with 600 parts of polyethylene glycol 400 (liquid-solid ratio 6:1). Add sulfuric acid at 2% of the mass of polyethylene glycol 400 as a catalyst and liquefy at 160℃ for 3 hours. Cool to obtain liquefied polyol. Step (2) Hydrogenation purification: The above-mentioned liquefied polyol is dissolved in methanol at a concentration of 20%, and the pH value of the solution is adjusted to 7 using sodium hydroxide. 5% of the mass of the liquefied polyol porous CuZnAl catalyst is added, and the reaction is carried out at 180℃ and 4MPa hydrogen pressure for 6 hours. After the reaction, the solvent is removed by filtration and evaporation to obtain purified bio-based polyol. Step (3) Coating preparation: Take 100 parts of urea granules and place them in a rotary drum coating machine (speed 60 rpm). Spray the mixture consisting of 15 parts of refined bio-based polyol and 14 parts of diphenylmethane diisocyanate evenly onto the surface of the urea granules. After spraying, mix at room temperature for 15 minutes, then stop stirring and solidify the granules at 80°C for 60 minutes, and then air dry naturally for 24 hours to obtain bio-based polyurethane urea slow-release fertilizer.
[0029] In this embodiment, the porous CuZnAl catalyst was prepared by adding 100 parts by weight of water and 20 parts by weight of sodium oxide to the reactor in an ice-water bath, followed by adding 100 parts by weight of Dewey alloy, reacting for 3 hours, and washing until neutral after the reaction was completed, thus obtaining the porous CuZnAl catalyst.
[0030] Example 2 A method for preparing a bio-based polyurethane slow-release fertilizer includes the following steps: Step (1) Liquefaction: Take 100 parts of sugarcane bagasse powder and mix it with 800 parts of a mixed solvent of ethylene glycol and glycerol (mass ratio 1:1) (liquid-solid ratio 8:1). Add hydrochloric acid accounting for 5% of the total mass of the solvent as a catalyst, and liquefy the reaction at 140℃ for 5 hours. After cooling, liquefied polyol is obtained. Step (2) Hydrogenation purification: Dissolve the liquefied polyol in water at a concentration of 5%, and adjust the pH of the solution to 7 using sodium hydroxide. Add 1% of the mass of the liquefied polyol porous CuZnAl catalyst. After hydrogenation reaction at 200℃ and 5MPa hydrogen pressure for 12 hours, filter and evaporate the solvent after the reaction to obtain purified bio-based polyol. Step (3) Coating preparation: Take 25 parts of urea granules and place them in a rotary drum coating machine (speed 60 rpm). Spray the mixture consisting of 0.1 parts of triethylenediamine, 0.2 parts of dibutyltin dilaurate, 8 parts of refined bio-based polyol and 6 parts of toluene diisocyanate evenly onto the surface of the urea granules. After spraying, continue mixing at room temperature for 30 minutes, then stop stirring and air dry the granules at room temperature for 36 hours to obtain bio-based polyurethane urea slow-release fertilizer.
[0031] In this embodiment, the porous CuZnAl catalyst is prepared by adding 100 parts by weight of water and 10 parts by weight of sodium oxide to the reactor in an ice-water bath, then adding 100 parts by weight of Dewey alloy, reacting for 3 h, and washing until neutral after the reaction is complete, thus obtaining the porous CuZnAl catalyst.
[0032] Example 3 A method for preparing a bio-based polyurethane slow-release fertilizer includes the following steps: Step (1) Liquefaction: Take 100 parts of wood powder and mix it with 400 parts of glycerol (liquid-solid ratio 4:1). Add nitric acid accounting for 3% of the mass of glycerol, liquefy at 180℃ for 4 hours, cool, and obtain liquefied polyol; Step (2) Hydrogenation purification: Dissolve the liquefied polyol in methanol at a concentration of 30%, and adjust the pH of the solution to 7 using sodium hydroxide. Add 8% of the mass of the liquefied polyol porous CuZnAl catalyst and react at 240℃ and 6MPa hydrogen pressure for 12 hours. After the reaction, filter and evaporate the solvent to obtain purified bio-based polyol. Step (3) Coating preparation: Take 80 parts of urea granules and place them in a rotary drum coating machine (rotation speed 80 rpm). Spray the mixture consisting of 0.3 parts of triethylenediamine, 12 parts of refined bio-based polyol and 9 parts of toluene diisocyanate evenly onto the surface of the urea granules. After spraying, continue mixing for 25 minutes. Then, solidify the granules at 80°C for 25 minutes and air dry them naturally for 18 hours to obtain bio-based polyurethane urea slow-release fertilizer.
[0033] In this embodiment, the porous CuZnAl catalyst was prepared by adding 100 parts by weight of water and 30 parts by weight of sodium oxide to the reactor in an ice-water bath, followed by adding 100 parts by weight of Dewey alloy, reacting for 3 hours, and washing until neutral after the reaction was completed, thus obtaining the porous CuZnAl catalyst.
[0034] The porous CuZnAl catalysts used in Examples 4-7 and Comparative Example 2 are the same as those in Example 1.
[0035] Example 4 A method for preparing a bio-based polyurethane slow-release fertilizer includes the following steps: Step (1) Liquefaction: Take 100 parts of wheat straw powder and 700 parts of polyethylene glycol 400 (liquid-solid ratio 7:1), add sulfuric acid accounting for 2.5% of the mass of polyethylene glycol 400, liquefy at 150℃ for 2.5 hours, cool, and obtain liquefied polyol; Step (2) Hydrogenation purification: Dissolve the liquefied polyol in water at a concentration of 15%, and adjust the pH of the solution to 7 using sodium hydroxide. Add 3% of the mass of the liquefied polyol to a porous CuZnAl catalyst, and react at 190℃ and 3MPa hydrogen pressure for 8 hours. After the reaction, filter and evaporate the solvent to obtain purified bio-based polyol. Step (3) Coating preparation: Take 100 parts of urea granules and add them to a rotary drum coating machine. Then add a mixture consisting of 20 parts of refined bio-based polyol, 6 parts of isophorone diisocyanate, 0.3 parts of triethylamine and stannous octoate (mass ratio 1:2). Mix at 50 rpm and room temperature for 20 minutes, cure at 80°C for 50 minutes, and air dry for 24 hours to obtain bio-based polyurethane urea slow-release fertilizer.
[0036] Example 5 A method for preparing a bio-based polyurethane slow-release fertilizer includes the following steps: Step (1) Liquefaction: Take 100 parts of bamboo powder and 500 parts of ethylene glycol (liquid-solid ratio 5:1), add 4% hydrochloric acid (by mass of ethylene glycol), liquefy at 170℃ for 3 hours, cool, and obtain liquefied polyol; Step (2) Hydrogenation purification: Dissolve the liquefied polyol in methanol at a concentration of 25%, and adjust the pH of the solution to 7 using sodium hydroxide. Add 10% of the mass of the liquefied polyol porous CuZnAl catalyst, and hydrogenate at 180℃ and 2.5MPa for 7 hours. After the reaction, filter and evaporate the solvent to obtain purified bio-based polyol. Step (3) Coating preparation: Take 100 parts of urea granules and add them to a rotary drum coating machine. Then add a mixture consisting of 8 parts of refined bio-based polyol, 10 parts of toluene diisocyanate, 10 parts of diphenylmethane diisocyanate, and 0.1 parts of dibutyltin dilaurate. Mix at 40 rpm and room temperature for 30 minutes. Then stop stirring and cure the granules at 80°C for 60 minutes and air dry for 12 hours to obtain bio-based polyurethane urea slow-release fertilizer.
[0037] Example 6 A method for preparing a bio-based polyurethane slow-release fertilizer includes the following steps: Step (1) Liquefaction: Take 100 parts of wheat straw powder and mix it with 600 parts of a mixed solvent of glycerol and polyethylene glycol 400 (mass ratio 2:1) (liquid-solid ratio 6:1). Add sulfuric acid accounting for 1% of the mass of the mixed solvent, liquefy at 200℃ for 1 hour, cool, and obtain liquefied polyol. Step (2) Hydrogenation purification: Dissolve the liquefied polyol in n-hexane at a concentration of 10%, and adjust the pH of the solution to 7 using sodium hydroxide. Add 2% of the mass of the liquefied polyol to a porous CuZnAl catalyst, and react at 160°C and 2MPa hydrogen pressure for 4 hours. After the reaction, filter and evaporate the solvent to obtain the purified bio-based polyol. Step (3) Coating preparation: Take 120 parts of urea granules and add them to a rotary drum coating machine. Then add a mixture consisting of 16 parts of refined bio-based polyol, 15 parts of toluene diisocyanate, 0.1 parts of triethylenediamine, and 0.1 parts of dibutyltin dilaurate. Mix at 40 rpm for 25 minutes at room temperature. Then stop stirring and solidify the granules at 80°C for 45 minutes. Then continue to air dry the granules naturally for 24 hours to obtain bio-based polyurethane urea slow-release fertilizer.
[0038] Example 7 A method for preparing a bio-based polyurethane slow-release fertilizer includes the following steps: Step (1) Liquefaction: Same as in Example 1; Step (2) Hydrogenation purification: Dissolve the liquefied polyol in methanol at a concentration of 40%, and adjust the pH of the solution to 7 using sodium hydroxide. Add 4% of the mass of the liquefied polyol porous CuZnAl catalyst, and hydrogenate at 220℃ and 2MPa for 9 hours. After the reaction, filter and evaporate the solvent to obtain purified bio-based polyol. Step (3) Coating preparation: Take 150 parts of urea granules and add them to a rotary drum coating machine. Then add a mixture consisting of 18 parts of refined bio-based polyol, 25 parts of mixed isocyanate (the mass ratio of isophorone diisocyanate to diphenylmethane diisocyanate is 1:1) and 0.3 parts of triethylenediamine. Mix at 100 rpm and room temperature for 10 minutes. Then stop stirring and solidify the granules at 80°C for 60 minutes. Then air dry naturally for 24 hours to obtain bio-based polyurethane urea slow-release fertilizer.
[0039] Comparative Example 1 A method for preparing a bio-based polyurethane slow-release fertilizer includes the following steps: Step (1) Liquefaction: Same as in Example 1, liquefied polyol is obtained, and the pH value of the polyol is adjusted to 7 using sodium hydroxide; Step (2) Hydrogenation purification: Not used; Step (3) Coating preparation: Take 100 parts of urea granules and place them in a rotary drum coating machine (speed 60 rpm). Spray the mixture consisting of 15 parts of liquefied polyol and 14 parts of diphenylmethane diisocyanate evenly onto the surface of the urea granules. After spraying, mix at room temperature for 15 minutes. After discharge, cure at 80℃ for 60 minutes and then air dry naturally for 24 hours to obtain bio-based polyurethane urea slow-release fertilizer.
[0040] like Figure 1 and Figure 2 As shown, Comparative Example 1 ( Figure 2 The bio-based polyurethane slow-release fertilizer prepared in Example 1 showed significant damage after being soaked in water for 24 hours; while in Example 1... Figure 1 The color and coating integrity of the obtained slow-release fertilizer were significantly better than those of the control sample 1.
[0041] Comparative Example 2 A method for preparing a bio-based polyurethane slow-release fertilizer includes the following steps: Step (1) Liquefaction: Take 100 parts of bamboo powder and 400 parts of polyethylene glycol 400 (liquid-solid ratio 4:1), add sulfuric acid accounting for 5% of the mass of polyethylene glycol 400, liquefy efficiently at 200℃ for 1 hour, cool, and obtain liquefied polyol; Step (2) Hydrogenation purification: The liquefied polyol is dissolved in n-hexane at a high concentration of 50%, and the pH of the solution is adjusted to 7 using sodium hydroxide. A porous CuZnAl catalyst of 10% by weight of the liquefied polyol is added, and hydrogen is added at 160℃ and 1MPa hydrogen pressure for 4 hours. After the reaction, the solvent is removed by filtration and evaporation to obtain the purified bio-based polyol. Step (3) Coating preparation: Take 25 parts of urea granules and place them in a rotary drum coating machine (speed 100 rpm). Spray the mixture consisting of 0.2 parts of stannous octoate, 0.1 parts of triethylamine, 20 parts of refined bio-based polyol and 25 parts of isophorone diisocyanate evenly onto the surface of the urea granules. After spraying, continue mixing for 10 minutes, then stop stirring and solidify the granules at 80°C for 30 minutes. Air dry at room temperature for 6 hours to obtain bio-based polyurethane urea slow-release fertilizer.
[0042] The following explains the content of the evaluation test.
[0043] 1. The hydroxyl value and acid value of the liquefied polyols and / or purified bio-based polyols prepared in Examples 1-7 and Comparative Examples 1-2 were tested, and the results are shown in Table 1.
[0044] 2. The initial nutrient release rate of the slow-release fertilizers prepared in Examples 1-7 and Comparative Examples 1-2 was measured according to the method specified in GB / T23348-2009, and expressed as %. The results are shown in Table 1.
[0045] Table 1 Test Results
[0046] The above results show that when the acid value of the refined bio-based polyol in Examples 1-7 of the present invention is controlled within 5 mg KOH / g, the initial nutrient release rate of the prepared slow-release fertilizer is within 13%.
[0047] Comparative Example 1, which did not employ hydrogenation refining, produced a slow-release fertilizer with an initial nutrient release rate as high as 72.74%, significantly higher than that of Example 1. This demonstrates that hydrogenation refining can significantly reduce the initial nutrient release rate of slow-release fertilizer.
[0048] After hydrogenation and refining, the acid value of the refined bio-based polyol in Comparative Example 2 was 14.82 mg KOH / g, and the initial nutrient release rate of the prepared slow-release fertilizer was 56.78%, which was significantly higher than that in the Example.
[0049] In summary, in this invention, when the liquefied polyol obtained by liquefying lignocellulose is not hydrogenated and refined, or when the acid value of the refined bio-based polyol exceeds the control range of this invention, the initial nutrient release rate of the prepared slow-release fertilizer is significantly increased, failing to meet the application expectations.
[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.
Claims
1. A method for preparing a bio-based polyurethane slow-release fertilizer, characterized in that: Includes the following steps: (1) Using lignocellulose as raw material and polyol as liquefaction solvent, a liquefaction reaction is carried out under the action of acid catalyst to obtain liquefied polyol; (2) In the presence of a hydrogenation catalyst, the liquefied polyol is subjected to a moderate hydrogenation reaction to selectively reduce the organic carboxylic acid contained therein to the corresponding alcohol or ester compound. After the reaction is completed, the reaction solvent is removed to obtain a refined bio-based polyol. The acid value of the refined bio-based polyol is controlled to be less than 5 mg KOH / g. (3) Place 25-150 parts by weight of urea granules in a coating device, and then add a mixture consisting of 0-0.3 parts by weight of catalyst, 8-20 parts by weight of the refined bio-based polyol and 6-25 parts by weight of isocyanate. After stirring and reacting, the mixture is dried to obtain the bio-based polyurethane slow-release fertilizer.
2. The method for preparing a bio-based polyurethane slow-release fertilizer as described in claim 1, characterized in that: In step (1), the liquid-to-solid mass ratio of the liquefaction reaction is (4:1) to (8:1), the reaction temperature is 140℃ to 200℃, and the reaction time is 1h to 5h.
3. The method for preparing a bio-based polyurethane slow-release fertilizer as described in claim 2, characterized in that: In step (1), the lignocellulose is one of wheat straw, corn straw, sugarcane bagasse, bamboo powder and wood powder; the polyol is one or a mixture of polyethylene glycol 400, ethylene glycol and glycerol; the acid catalyst is one of sulfuric acid, nitric acid and hydrochloric acid, and the amount of the acid catalyst is 1 to 5% of the mass of the polyol.
4. The method for preparing a bio-based polyurethane slow-release fertilizer as described in claim 1, characterized in that: In step (2), the conditions for the hydrogenation reduction reaction are: reaction temperature of 160℃~240℃, reaction time of 4~12h, reaction pressure of 2-6MPa, and reaction solvent of water, methanol, and n-hexane; the concentration of the liquefied polyol is 5-50%, and the amount of the hydrogenation catalyst is 1-10% of the mass of the liquefied polyol.
5. The method for preparing a bio-based polyurethane slow-release fertilizer as described in claim 4, characterized in that: In step (2), the hydrogenation catalyst is a porous CuZnAl catalyst; The porous CuZnAl catalyst is prepared by: providing 100 parts by weight of water, 10-30 parts by weight of sodium hydroxide and 100 parts by weight of Divide alloy, reacting in an ice-water bath for 0.5-4 hours, and washing until neutral after the reaction is complete.
6. The method for preparing a bio-based polyurethane slow-release fertilizer as described in claim 1, characterized in that: In step (3), the stirring reaction is carried out at room temperature, with a rotation speed of 40-100 rpm and a time of 10-30 min; The drying process involves natural air drying for 6 to 36 hours.
7. The method for preparing a bio-based polyurethane slow-release fertilizer as described in claim 6, characterized in that: In step (3), after the stirring reaction and before drying, the process also includes curing at 80°C for 0 to 60 minutes, preferably 25 to 60 minutes.
8. The method for preparing a bio-based polyurethane slow-release fertilizer as described in claim 1, characterized in that: In step (3), the catalyst is a mixture of tertiary amine and organotin, and the weight ratio of the tertiary amine to organotin is (1:2) to (2:1). Wherein: the tertiary amine is triethylenediamine or triethylamine, and the organotin is dibutyltin dilaurate or stannous octoate.
9. The method for preparing a bio-based polyurethane slow-release fertilizer as described in claim 1, characterized in that: The isocyanate is at least one of toluene diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate.
10. The method for preparing a bio-based polyurethane slow-release fertilizer as described in claim 1, characterized in that: Before hydrogenation purification in step (2) or before coating preparation in step (3), an alkaline compound is added to the system to neutralize the inorganic acids contained therein.