Eutectic solvent / bimetal organic framework co-catalyzed straw polyol as well as preparation method and application thereof

Abstract

The invention discloses a deep eutectic solvent / bimetal organic framework co-catalyzed straw polyol as well as a preparation method and application thereof, the straw polyol is prepared by the following method: uniformly mixing straw powder, small molecular alcohol, an acid catalyst and a deep eutectic solvent in a nitrogen atmosphere, and reacting to obtain a reaction product; and adding a bimetal organic framework catalyst into the reaction product, and reacting to obtain the straw polyol. A green, natural and pollution-free eutectic solvent catalytic liquefaction technology is adopted, lignin and hemicellulose can be dissolved, the cross-linking effect between lignin and hemicellulose and cellulose is reduced, the crystalline structure of cellulose can be destroyed, the available surface area is increased, the contact with a liquefying agent is enhanced, the conversion efficiency is improved, and the residue rate is reduced; the bimetallic organic framework catalyst is added in the middle and later periods of the reaction, aldehydes, ketones and acid and ester substances can be reduced and upgraded into alcohols, the hydroxyl value of the liquefied polyol is greatly increased, and the film-forming crosslinking degree is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of controlled-release fertilizer production, and particularly relates to a eutectic solvent / bimetallic organic framework co-catalyzed straw polyol and a preparation method and application thereof. Background Art

[0002] Coated controlled-release fertilizers are fertilizers that gradually release and slowly release nutrients in the fertilizer by wrapping a thin film material on the surface of the fertilizer. They have the effects of improving fertilizer utilization efficiency, reducing nutrient loss, improving the soil environment, and reducing the negative impact on the environment. However, currently commercially available coated controlled-release fertilizers often use petrochemical-derived polymer materials, which have high production costs and poor biodegradability of the film materials. They often result in high energy consumption and environmental protection costs during production and application, and they remain in the environment for a long time, which will cause a burden on the soil ecology and environment in the long term.

[0003] Liquefied biomass coating materials are prepared by converting biomass, especially crop straw, into low-molecular-weight, fluid biomass liquefied polyols through chemical or physical methods such as pyrolysis and acidolysis, and then preparing controlled-release fertilizer film materials through cross-linking reactions with curing agents. Because they are derived from natural renewable resources, they can not only effectively utilize agricultural waste and reduce resource waste, but are also more easily degraded than traditional petrochemical film materials, effectively reducing the environmental risk of film shell residues. Therefore, they have attracted extensive attention in the field of agricultural fertilizers in recent years. However, straw contains a large amount of cellulose, hemicellulose, and lignin. Due to the large differences in activation energy and crystallinity of these components, it is difficult to control their reaction kinetics. When the liquefaction degree is low, the prepared polyols usually have problems such as incomplete liquefaction and high residue rate. When the liquefaction degree is too high, phenolic, aldehyde, and acid by-products will be generated, affecting the purity and reactivity of the polyols, thus making the prepared coated controlled-release fertilizer film structure loose, with more pores and a shorter controlled-release period. The hydrogenation technology is the key method for improving the quality of liquefied products. This method can convert carbonyl compounds in polyols, but different catalysts have different hydrogenation and quality improvement performances. Unreasonable quality improvement will lead to over-reduction and the generation of inert hydrocarbons, which is not conducive to the film formation of polyurethane-coated controlled-release fertilizers. Therefore, preparing catalysts with good performance is particularly important for improving the performance of polyols.

[0004] Patent ZL 201210261735.0 discloses a coated controlled-release fertilizer using crop straw as a degradable film and its production method. This method directly liquefies crop straw. The resulting biomass polyol has poor film-forming denseness due to low liquefaction rate, and due to side reactions during the liquefaction process, a large number of groups that do not participate or have high reaction steric hindrance will be generated, resulting in low crosslinking degree and short nutrient controlled-release period. Patent ZL 202111540324.0 discloses a steam explosion pretreatment of crop straw-based polyurethane coated slow and controlled-release fertilizer and its preparation method. This method requires special blasting equipment, and after blasting, processes such as cleaning and drying are required. The process is complex, the treatment energy consumption is high, and the production efficiency is low. Patent ZL201510416904.7 discloses a straw liquefaction coating liquid and its preparation method and application. This method does not reduce and upgrade the by-products, and a large amount of substances that do not participate in film formation will be contained in the liquefaction product, affecting the quality of the liquefaction product. Moreover, wax-like auxiliaries and a large amount of polyether polyols are used in this method, which will affect the degradation performance of the film material. Patent CN 105646090 B discloses a controlled-release fertilizer obtained by modifying agricultural organic waste into a degradable film and its preparation method. This method uses siloxane as an auxiliary agent, which is recognized as an emerging organic pollutant or listed as a priority control chemical by countries such as the European Union, and its environmental residues pose ecological environment risks and human health risks. Summary of the Invention

[0005] In view of the above-mentioned prior art, the object of the present invention is to provide a eutectic solvent / bimetallic organic framework co-catalyzed straw polyol and its preparation method and application.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In the first aspect of the present invention, a straw polyol is provided, which is prepared by the following method:

[0008] (1) Under a nitrogen atmosphere, mix straw powder, small molecule alcohol, acid catalyst and eutectic solvent in a mass ratio of (5 - 45):(80 - 120):(0.1 - 5):(0.1 - 5) evenly, and react at 100 - 180 °C for 0.5 - 2 h to obtain a reaction product;

[0009] (2) Under a nitrogen atmosphere, add a bimetallic organic framework catalyst accounting for 0.1% - 3.0% of the mass of the small molecule alcohol to the reaction product obtained in step (1), and react at 100 - 180 °C for 0.5 - 5 h to obtain the straw polyol.

[0010] Preferably, the small molecule alcohol is one or more of methanol, ethanol, propylene glycol, diethylene glycol, glycerol, isopropanol, isobutanol, 1,4-butanediol, pentanediol, 2-methyl-1-propanol.

[0011] Preferably, the acid catalyst is one or more of sulfuric acid, hydrochloric acid, phosphoric acid, formic acid, and acetic acid.

[0012] Preferably, the deep eutectic solvent is prepared by the following method:

[0013] Mix a hydrogen donor and a hydrogen acceptor in a molar ratio of (75 - 100):(69 - 287), react at 50 - 120 °C for 15 - 120 min to form a homogeneous liquid, and cool to obtain the deep eutectic solvent;

[0014] The hydrogen donor is one or more of tetrabutylammonium bromide, 1 - ethyl - 3 - methylimidazolium salt, cetyltrimethylammonium bromide, dodecyldimethylbenzylammonium chloride, didodecyldimethylammonium bromide, octadecyldimethyl(2 - hydroxyethyl)ammonium nitrate, benzalkonium chloride, and triphenylcycloimidazoline quaternary ammonium salt;

[0015] The hydrogen acceptor is selected from one or more of urea, ethylene glycol, glycerol, formic acid, acetic acid, citric acid, N,N - dimethylformamide, N,N - dimethylacetamide, and acrylamide.

[0016] Preferably, the bimetallic organic framework is prepared by the following method:

[0017] (1) Mix the first metal salt, the organic ligand, and the solvent in a mass ratio of (1 - 2):(20 - 35):(300 - 500), react at 120 - 160 °C for 2 - 6 h, cool after the reaction, and obtain the monometallic organic framework through centrifugation, washing, and drying;

[0018] (2) Use the prepared monometallic organic framework as a precursor, then add the second metal salt, stir for 20 - 28 h, dry, and calcine the obtained solid in nitrogen at 450 - 550 °C for 1 - 3 h to obtain the bimetallic organic framework.

[0019] Preferably, the molar ratio of the first metal salt to the second metal salt is 0.2 - 3:1.

[0020] Preferably, the first metal salt is Co(NO 3 ) 2 ·6H 2 O, Ni(NO 3 ) 2 ·6H 2 O, Na 2 MoO 4 , Fe 2 Mo 3 O 12 one of them;

[0021] The second metal salt is Zn(NO3 ) 2 ·6H 2 O, Cu(NO 3 ) 2 ·6H 2 O, ZnCl 2 , AlCl 3 , Al 2 (SO 4 ) 3 , Al(NO 3 ) 3 One of the following:

[0022] The organic ligand is one or more of terephthalic acid, trimesic acid, 5-hydroxyphthalic acid, 5-benzyloxymethyldicarboxylic acid, lauric acid, citric acid, benzene-1,3,5-tricarboxylic acid.

[0023] The solvent is one or more of N,N-dimethylformamide, methanol, ethanol, dimethyl sulfoxide, n-butanol, cetyltrimethylammonium bromide.

[0024] In a second aspect of the present invention, there is provided the use of the above-mentioned straw polyol in the preparation of coated controlled-release fertilizers.

[0025] In a third aspect of the present invention, there is provided a coated controlled-release fertilizer, which is prepared by the following method:

[0026] Fertilizer particles with a size of 2-6 mm are preheated to 50-80 °C in a rotary drum, and then the above-mentioned straw polyol, curing agent, and chain extender are mixed in a mass ratio of (45-82):(28-60):(3-12), sprayed onto the surface of the fertilizer particles, and the spraying amount each time is 0.5-2% of the mass of the fertilizer particles. Spraying is repeated multiple times to obtain the coated controlled-release fertilizer.

[0027] Preferably, the curing agent is one or more of toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), hexamethylene diisocyanate (HDI), L-lysine diisocyanate (LDI).

[0028] The chain extender is one or several of 1,4-butanediamine, 1,6-hexanediamine, diethylenetriamine, 1,4-butanediol, polyethylene glycol, phenylenediamine.

[0029] The fertilizer is urea, diammonium phosphate, potassium chloride, potassium sulfate or compound fertilizer.

[0030] Advantages of the present invention:

[0031] 1. The present invention adopts the eutectic solvent catalytic liquefaction technology which is green, natural and pollution-free. This technology can dissolve lignin and hemicellulose, reduce their cross-linking with cellulose, and is also conducive to destroying the crystalline structure of cellulose, reducing its crystallinity, exposing more amorphous regions, increasing the available surface area, enhancing the contact with the liquefying agent, improving the conversion efficiency and reducing the residue rate.

[0032] 2. The present invention adds a bimetallic organic framework catalyst in the middle and later stages of the reaction. Traditional upgrading catalysts have poor catalytic specificity and are difficult to reduce substances with large steric hindrance such as acids and esters. However, the present invention uses a bimetallic catalyst. The first metal can specifically reduce aldehydes and ketones, while the second metal has higher catalytic performance and can specifically reduce acids and esters. Through the combined action of the two, the hydroxyl value of the liquefied polyol can be greatly increased, which is beneficial to improving the film-forming cross-linking degree, and avoids problems such as the reduction of hydroxyl content and the increase of saturated hydrocarbons caused by over-reduction. It can also control the selectivity of by-products, thus being beneficial to the high-quality production of polyols. In addition, the bimetallic catalyst adopts the MOF structure, which has the characteristics of high specific surface area, multiple adsorption sites and high catalytic activity compared with traditional metal catalysts, and has good thermal stability under the complex conditions of strong acid and high temperature in biomass liquefaction, maintaining its stable structure and chemical properties.

[0033] 3. The straw-based polyol prepared by the present invention has the characteristics of green safety, without the need to add high-dose petrochemical modification materials additionally. The process is simple and easy to operate, without the need for repeated cleaning and drying, and has the characteristics of production continuity and low energy consumption. The prepared polyol has the characteristics of high reaction activity, high cross-linking degree and low non-film-forming substance content, which is beneficial to the uniform and dense film formation of the controlled-release fertilizer film material and can effectively extend the nutrient release period. Description of the Drawings

[0034] Figure 1 : Residue rate of straw polyols prepared under different conditions;

[0035] Figure 2 : Hydroxyl value of straw polyols prepared under different conditions;

[0036] Figure 3 : Component types and proportions of straw polyols prepared under the same conditions;

[0037] Figure 4 : Nutrient release characteristics of controlled-release fertilizers coated with different polyols. Detailed Embodiments

[0038] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0039] As described in the background art, straw contains a large amount of cellulose, hemicellulose and lignin. Due to the large differences in activation energy and crystallinity of these components, it is difficult to control their reaction kinetics. When the liquefaction degree is low, the polyols prepared usually have problems such as incomplete liquefaction and high residue rate. When the liquefaction degree is too high, phenolic, aldehydic, acidic and other undesirable by-products will be produced, affecting the purity and reactivity of the polyols, and thus making the film structure of the prepared coated controlled-release fertilizer loose, with more pores and a shorter controlled-release period. Based on this, the present invention first uses a renewable, inexpensive and green deep eutectic solvent as a catalyst to liquefy straw. By simulating the process of releasing hydrogen bonds in enzymatic catalysis and adopting the co-melting method of hydrogen donors and hydrogen acceptors, the destruction of the internal hydrogen bond network of cellulose is promoted, the liquefaction process is accelerated and the residue rate is reduced, and the depth of the reaction is promoted to prepare a biomass polyol rich in active hydroxyl groups. In addition, during the liquefaction process, due to the differences in activation energy and molecular structure of cellulose, hemicellulose and lignin in straw, the liquefaction efficiency of different components is different, and a large amount of insoluble unsaturated carbonyl compounds such as aldehydes, ketones, carboxylic acids and esters are produced, thus affecting the purity and quality of the polyol. Therefore, a bimetallic organic framework catalyst is added in the middle and later stages of the reaction. This catalyst is composed of two reducing metals. One metal is selected from metals such as Co, Ni, Na, Fe, etc., which can hydrogenate unsaturated aldehydes and ketones to saturated alcohols. Since carbonyl compounds such as acids and esters have large steric hindrance and weak polarity, it is very difficult to reduce and upgrade them. Therefore, the other metal is selected from metals such as Cu, Zn, Al, etc. This type of metal has a high activation energy and can promote the reaction. In addition, the catalyst used adopts a MOF structure, which can provide abundant active reaction sites and can maintain its structural stability at a higher temperature, helping to precisely control the reaction path. Therefore, by coupling the above two catalytic technologies, the complete liquefaction of biomass can be promoted, the hydroxyl value of the polyol can be increased, the non-film-forming residue can be reduced, and thus the denseness of the film material of the coated controlled-release fertilizer and the nutrient controlled-release performance can be improved.

[0040] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below in conjunction with specific embodiments.

[0041] The test materials used in the embodiments of the present invention are all conventional test materials in the art and can be obtained through commercial channels.

[0042] Example 1: Preparation of straw polyol:

[0043] (1) Preparation of deep eutectic solvent:

[0044] Choline chloride and citric acid were mixed at a molar ratio of 1:2 and stirred and reacted at 85 °C for 70 min to form a homogeneous liquid. The homogeneous liquid was cooled to room temperature to obtain a deep eutectic solvent;

[0045] (2) The bimetallic organic framework is prepared by the following method:

[0046] Mix Ni(NO 3 ) 2 ·6H 2 O, terephthalic acid, and N,N-dimethylformamide in a mass ratio of 1:20:300. Stir the mixture for 20 minutes, transfer it to a Teflon-lined stainless steel autoclave, seal it, and react at 140 °C for 4 h. After the reaction, naturally cool it to room temperature. Centrifuge the solution, wash the precipitate several times with anhydrous ethanol and water to remove possible residues, and dry it under vacuum at 65 °C for 8 h to obtain a monometallic organic framework;

[0047] Use the prepared monometallic organic framework as a precursor, and then add Cu(NO 3 ) 2 ·6H 2 O, Ni(NO 3 ) 2 ·6H 2 O, and Cu(NO 3 ) 2 ·6H 2 O with a molar ratio of 1:1. Stir for 24 h, dry, and calcine the obtained solid in nitrogen at 500 °C for 2 h to obtain the bimetallic organic framework.

[0048] (3) Preparation of straw polyol:

[0049] Under a nitrogen atmosphere, mix corn straw powder, 1,2-propanediol, diethylene glycol, sulfuric acid with a mass concentration of 98%, and a deep eutectic solvent in a mass ratio of 12:50:30:0.1:0.1, and mix them evenly. React at 150 °C for 1.5 h to obtain straw polyol; then, under a nitrogen atmosphere, add a bimetallic organic framework catalyst accounting for 0.1% of the mass of the small molecule alcohol to the reaction product, and react at 110 °C for 3 h to obtain straw polyol.

[0050] Example 2: Preparation of straw polyol:

[0051] (1) Preparation of deep eutectic solvent:

[0052] Mix choline chloride and urea in a molar ratio of 75:69, stir and react at 85 °C for 70 min to form a homogeneous liquid, and cool the homogeneous liquid to room temperature to obtain the deep eutectic solvent;

[0053] (2) The bimetallic organic framework is prepared by the following method:

[0054] Mix Ni(NO 3 ) 2 ·6H 2O, citric acid and N,N-dimethylformamide are mixed in a mass ratio of 1:20:300. The mixture is stirred for 20 minutes and transferred to a Teflon-lined stainless steel autoclave, sealed and reacted at 140 °C for 4 h. After the reaction, it is naturally cooled to room temperature. The solution is centrifuged, and the precipitate is washed several times with anhydrous ethanol and water to remove possible residues, and dried under vacuum at 65 °C for 8 h to obtain a single metal-organic framework;

[0055] The prepared single metal-organic framework is used as a precursor, and then Cu(NO 3 ) 2 ·6H 2 O, Ni(NO 3 ) 2 ·6H 2 O and Cu(NO 3 ) 2 ·6H 2 O are added in a molar ratio of 1:1, stirred for 24 h, dried, and the obtained solid is calcined in nitrogen at 500 °C for 2 h to obtain a bimetallic metal-organic framework.

[0056] (3) Preparation of straw polyol:

[0057] Under a nitrogen atmosphere, corn straw powder, glycerol, butanediol, and a deep eutectic solvent of 98% mass concentration sulfuric acid are mixed evenly in a mass ratio of 10:20:60:0.1:0.1, and reacted at 150 °C for 1.5 h to obtain a reaction product;

[0058] Under a nitrogen atmosphere, a bimetallic metal-organic framework catalyst of 0.1% of the mass of small molecule alcohol is added to the reaction product, and reacted at 110 °C for 3 h to obtain straw polyol.

[0059] Example 3: Preparation of straw polyol:

[0060] (1) Preparation of deep eutectic solvent:

[0061] Tetrabutylammonium bromide and citric acid are mixed in a molar ratio of 90:150, stirred and reacted at 85 °C for 70 min to form a homogeneous liquid, and the homogeneous liquid is cooled to room temperature to obtain a deep eutectic solvent;

[0062] (2) The bimetallic metal-organic framework is prepared by the following method:

[0063] Co(NO 3 ) 2 ·6H 2O, terephthalic acid, and dimethyl sulfoxide were mixed in a mass ratio of 1.5:28:400. The mixture was stirred for 20 minutes and transferred to a Teflon-lined stainless steel autoclave, sealed, and reacted at 140 °C for 4 h. After the reaction, it was naturally cooled to room temperature. The solution was centrifuged, and the precipitate was washed several times with absolute ethanol and water to remove possible residues, and then dried under vacuum at 65 °C for 8 h to obtain a single metal-organic framework;

[0064] The prepared single metal-organic framework was used as a precursor, and then ZnCl 2 , Co(NO 3 ) 2 ·6H 2 O and ZnCl 2 were added in a molar ratio of 2:1, stirred for 24 h, dried, and the obtained solid was calcined in nitrogen at 500 °C for 2 h to obtain a bimetallic metal-organic framework.

[0065] (3) Preparation of straw polyol:

[0066] Under a nitrogen atmosphere, corn straw powder, propylene glycol, phosphoric acid, and a deep eutectic solvent were mixed evenly in a mass ratio of 40:100:3:3 and reacted at 110 °C for 1.5 h to obtain a reaction product;

[0067] Under a nitrogen atmosphere, a bimetallic metal-organic framework catalyst accounting for 2% of the mass of the small molecule alcohol was added to the reaction product, and the reaction was carried out at 110 °C for 3 h to obtain straw polyol.

[0068] Example 4: Preparation of straw polyol:

[0069] (1) Preparation of deep eutectic solvent:

[0070] Benzalkonium chloride and ethylene glycol were mixed in a molar ratio of 100:287, stirred and reacted at 85 °C for 70 min to form a homogeneous liquid, and the homogeneous liquid was cooled to room temperature to obtain a deep eutectic solvent;

[0071] (2) The bimetallic metal-organic framework was prepared by the following method:

[0072] Ni(NO 3 ) 2 ·6H 2 O, trimesic acid, and n-butanol were mixed in a mass ratio of 2:35:500. The mixture was stirred for 20 minutes and transferred to a Teflon-lined stainless steel autoclave, sealed, and reacted at 140 °C for 4 h. After the reaction, it was naturally cooled to room temperature. The solution was centrifuged, and the precipitate was washed several times with absolute ethanol and water to remove possible residues, and then dried under vacuum at 65 °C for 8 h to obtain a single metal-organic framework;

[0073] The prepared single metal-organic framework was used as a precursor, and then Cu(NO3 ) 2 ·6H 2 O, Ni(NO 3 ) 2 ·6H 2 O and Cu(NO 3 ) 2 ·6H 2 O are in a molar ratio of 3:1, stirred for 24 h, dried, and the obtained solid is calcined in nitrogen at 500 °C for 2 h to obtain a bimetallic organic framework.

[0074] (3) Preparation of straw polyol:

[0075] Under a nitrogen atmosphere, corn straw powder, pentanediol, sulfuric acid with a mass concentration of 98%, and a deep eutectic solvent are mixed evenly in a mass ratio of 25:120:5:5, and reacted at 150 °C for 1.5 h to obtain a reaction product;

[0076] Then, a bimetallic organic framework catalyst accounting for 3.0% of the mass of the small molecule alcohol is added to the reaction product, and the reaction is carried out for 3 h to obtain straw polyol.

[0077] Comparative Example 1: Preparation of straw polyol:

[0078] Under a nitrogen atmosphere, corn straw powder, 1,2-propanediol, diethylene glycol, and sulfuric acid with a mass concentration of 98% are mixed evenly in a mass ratio of 12:50:30:0.1, and reacted at 150 °C for 1.5 h to obtain straw polyol.

[0079] Comparative Example 2: Preparation of straw polyol:

[0080] (1) Preparation of deep eutectic solvent:

[0081] Choline chloride and citric acid are mixed in a molar ratio of 1:2, stirred and reacted at 85 °C for 70 min to form a homogeneous liquid, and the homogeneous liquid is cooled to room temperature to obtain a deep eutectic solvent;

[0082] (2) Preparation of straw polyol:

[0083] Under a nitrogen atmosphere, corn straw powder, 1,2-propanediol, diethylene glycol, sulfuric acid with a mass concentration of 98%, and a deep eutectic solvent are mixed evenly in a mass ratio of 12:50:30:0.1:0.1, and reacted at 150 °C for 1.5 h to obtain straw polyol;

[0084] Comparative Example 3: Preparation of straw polyol:

[0085] (1) Preparation of deep eutectic solvent:

[0086] Mix choline chloride and citric acid in a molar ratio of 1:2, stir and react at 85 °C for 70 min to form a homogeneous liquid, and cool the homogeneous liquid to room temperature to obtain a deep eutectic solvent;

[0087] (2) The Ni-based single metal-organic framework is prepared by the following method:

[0088] Mix Ni(NO 3 ) 2 ·6H 2 O, terephthalic acid and N,N-dimethylformamide in a mass ratio of 1:20:300, stir the mixture for 20 minutes, transfer it to a Teflon-lined stainless steel autoclave, seal it and react at 140 °C for 4 h. After the reaction, naturally cool it to room temperature, centrifuge the solution, wash the precipitate several times with anhydrous ethanol and water to remove possible residues, and dry it under vacuum at 65 °C for 8 h to obtain a single metal-organic framework;

[0089] (3) Preparation of straw polyol:

[0090] Under a nitrogen atmosphere, mix corn straw powder, 1,2-propanediol, diethylene glycol, sulfuric acid with a mass concentration of 98% and the deep eutectic solvent in a mass ratio of 12:50:30:0.1:0.1, react at 150 °C for 1.5 h to obtain straw polyol; then, under a nitrogen atmosphere, add a Ni-based single metal-organic framework catalyst accounting for 0.1% of the mass of the small molecule alcohol to the reaction product, and react at 110 °C for 3 h to obtain straw polyol.

[0091] Comparative Example 4: Preparation of straw polyol:

[0092] (1) Preparation of deep eutectic solvent:

[0093] Mix choline chloride and citric acid in a molar ratio of 1:2, stir and react at 85 °C for 70 min to form a homogeneous liquid, and cool the homogeneous liquid to room temperature to obtain a deep eutectic solvent;

[0094] (2) The Cu-based single metal-organic framework is prepared by the following method:

[0095] Mix Cu(NO 3 ) 2 ·6H 2 O, terephthalic acid and N,N-dimethylformamide in a mass ratio of 1:20:300, stir the mixture for 20 minutes, transfer it to a Teflon-lined stainless steel autoclave, seal it and react at 140 °C for 4 h. After the reaction, naturally cool it to room temperature, centrifuge the solution, wash the precipitate several times with anhydrous ethanol and water to remove possible residues, and dry it under vacuum at 65 °C for 8 h to obtain a Cu-based single metal-organic framework;

[0096] (3) Preparation of straw polyol:

[0097] Under a nitrogen atmosphere, corn straw powder, 1,2 - propanediol, diethylene glycol, sulfuric acid with a mass concentration of 98%, and a deep eutectic solvent were mixed evenly in a mass ratio of 12:50:30:0.1:0.1, and reacted at 150 °C for 1.5 h to obtain straw polyol; then, under a nitrogen atmosphere, a Ni - based single - metal organic framework catalyst accounting for 0.1% of the mass of the small molecule alcohol was added to the reaction product, and the reaction was carried out at 110 °C for 3 h to obtain straw polyol.

[0098] Comparative Example 5: Preparation of straw polyol:

[0099] (1) The bimetallic organic framework was prepared by the following method:

[0100] Ni(NO 3 ) 2 ·6H 2 O, terephthalic acid, and N,N - dimethylformamide were mixed in a mass ratio of 1:20:300, the mixture was stirred for 20 minutes, and transferred to a Teflon - lined stainless - steel autoclave, sealed and reacted at 140 °C for 4 h. After the reaction, it was naturally cooled to room temperature, the solution was centrifuged, and the precipitate was washed several times with anhydrous ethanol and water to remove possible residues, and dried under vacuum at 65 °C for 8 h to obtain a single - metal organic framework;

[0101] Taking the prepared single - metal organic framework as a precursor, then adding Cu(NO 3 ) 2 ·6H 2 O, Ni(NO 3 ) 2 ·6H 2 O and Cu(NO 3 ) 2 ·6H 2 O with a molar ratio of 1:1, stirred for 24 h, dried, and the obtained solid was calcined with nitrogen at 500 °C for 2 h to obtain a bimetallic organic framework.

[0102] (2) Preparation of straw polyol:

[0103] Under a nitrogen atmosphere, corn straw powder, 1,2 - propanediol, diethylene glycol, and sulfuric acid were mixed evenly in a mass ratio of 12:50:30:0.1, and reacted at 150 °C for 1.5 h to obtain straw polyol; then, under a nitrogen atmosphere, a bimetallic organic framework catalyst accounting for 0.1% of the mass of the small molecule alcohol was added to the reaction product, and the reaction was carried out at 110 °C for 3 h to obtain straw polyol.

[0104] Application Example 1:

[0105] Preheat 2 - 6 mm of urea to 65°C in a rotary drum, and then mix the straw polyol prepared in Example 1 with diphenylmethane diisocyanate (MDI) and 1,4 - butanediamine in a mass ratio of 65:54:8. As the coating material, spray it onto the surface of the urea, with each spraying amount being 1% of the mass of the urea. Repeat spraying the coating material multiple times so that the coating material accounts for 3% of the total mass of the coated controlled - release fertilizer to obtain the coated controlled - release fertilizer.

[0106] Application Example 2:

[0107] Preheat 2 - 6 mm of urea to 65°C in a rotary drum, and then mix the straw polyol prepared in Example 2 with toluene diisocyanate (TDI) and 1,4 - butanediamine in a mass ratio of 65:54:8. As the coating material, spray it onto the surface of the urea, with each spraying amount being 1% of the mass of the urea. Repeat spraying the coating material multiple times so that the coating material accounts for 4% of the total mass of the coated controlled - release fertilizer to obtain the coated controlled - release fertilizer.

[0108] Application Example 3:

[0109] Preheat 2 - 6 mm of urea to 65°C in a rotary drum, and then mix the straw polyol prepared in Example 3 with diphenylmethane diisocyanate (MDI) and 1,4 - butanediol in a mass ratio of 65:54:8. As the coating material, spray it onto the surface of the urea, with each spraying amount being 1% of the mass of the urea. Repeat spraying the coating material multiple times so that the coating material accounts for 3% of the total mass of the coated controlled - release fertilizer to obtain the coated controlled - release fertilizer.

[0110] Application Example 4:

[0111] Preheat 2 - 6 mm of urea to 65°C in a rotary drum, and then mix the straw polyol prepared in Example 4 with isophorone diisocyanate (IPDI) and 1,4 - hexanediamine in a mass ratio of 65:54:8. As the coating material, spray it onto the surface of the urea, with each spraying amount being 1% of the mass of the urea. Repeat spraying the coating material multiple times so that the coating material accounts for 2.5% of the total mass of the coated controlled - release fertilizer to obtain the coated controlled - release fertilizer.

[0112] Application Example 5:

[0113] Preheat 2 - 6 mm of urea to 65°C in a rotary drum, and then mix the straw polyol prepared in Comparative Example 1 with diphenylmethane diisocyanate (MDI) and 1,4 - butanediamine in a mass ratio of 65:54:8. As the coating material, spray it onto the surface of the urea, with each spraying amount being 1% of the mass of the urea. Repeat spraying the coating material multiple times so that the coating material accounts for 3% of the total mass of the coated controlled - release fertilizer to obtain the coated controlled - release fertilizer.

[0114] Application Example 6:

[0115] Preheat 2 - 6 mm urea to 65 °C in a rotary drum. Then, mix the straw polyol prepared in Comparative Example 2 with diphenylmethane diisocyanate (MDI) and 1,4 - butanediamine in a mass ratio of 65:54:8. Use this as the coating material and spray it onto the surface of the urea. The spraying amount each time is 1% of the mass of the urea. Repeat spraying the coating material multiple times so that the coating material accounts for 3% of the total mass of the coated controlled - release fertilizer, and obtain the coated controlled - release fertilizer.

[0116] Application Example 7:

[0117] Preheat 2 - 6 mm urea to 65 °C in a rotary drum. Then, mix the straw polyol prepared in Comparative Example 5 with diphenylmethane diisocyanate (MDI) and 1,4 - butanediamine in a mass ratio of 65:54:8. Use this as the coating material and spray it onto the surface of the urea. The spraying amount each time is 1% of the mass of the urea. Repeat spraying the coating material multiple times so that the coating material accounts for 3% of the total mass of the coated controlled - release fertilizer, and obtain the coated controlled - release fertilizer.

[0118] Test Example 1:

[0119] Test the residue rate, hydroxyl value, and the composition of the liquefied product of the straw polyol prepared in Example 1 and the comparative examples:

[0120] 1. Residue rate: Weigh 2.0 g of the liquefied product (accurate to 0.0001 g). Then, measure 20 mL of a mixed solution of 1,4 - dioxane and water (volume ratio 4:1) with a measuring cylinder. Place the two in a beaker and stir in a water bath at 80 °C for 30 min. Filter while it is hot, and rinse the residue with 1,4 - dioxane until the filtrate is colorless.

[0121] Put the filter paper with the residue into a drying oven at 120 °C and dry for 4 h. After drying, weigh its mass.

[0122] The formula for calculating the residue rate is as follows:

[0123] Residue rate (%) = (m3 - m2) / m1 × 100;

[0124] Where, m1: represents the mass of the liquefied product; m2: represents the mass of the filter paper; m3: represents the mass of the residue and the filter paper.

[0125] Hydroxyl value: The measurement method refers to GB / T 12008.3 - 2009.

[0126] Composition of the liquefied product: The method refers to Section 2.5.2 of Xiaojing Yu, Xiao Sun, Jingjing Dong, Liang Wu, Wusong Guo, Yanfeng Wang, Xuju Jiang, Zhiguang Liu, Min Zhang. Instant catapult steam explosion pretreatment of wheat straw liquefied polyols to prolong the slow-release longevity of bio-based polyurethane-coated fertilizers. Chemical Engineering Journal, 2022, 435, 134985.

[0127] It can be seen from Figures 1-3 that the residue rate of the straw polyol prepared in Example 1 of the present invention is the lowest, the hydroxyl value is the highest, and among the components of the liquefied product, the alcohol content is the highest, indicating that the present invention uses the green, natural, pollution-free and recyclable deep eutectic solvent catalytic liquefaction technology combined with the bimetallic organic framework catalyst, which significantly improves the quality of the prepared straw polyol.

[0128] Test Example 2:

[0129] According to the "National Standard for Slow-release Fertilizers GB / T 23348-2009", the nitrogen release rate of the coated controlled-release fertilizers prepared in Application Example 1, Application Example 5, Application Example 6 and Application Example 7 was measured, and the time required for the nutrient cumulative release rate to reach 80% was recorded as the controlled-release period.

[0130] It can be seen from Figure 4 that the controlled-release period of the coated controlled-release fertilizer prepared in Application Example 1 using the straw polyol prepared in Example 1 of the present invention is the longest, which is 55 days; the controlled-release period of the coated controlled-release fertilizer prepared in Application Example 5 using the straw polyol prepared in Comparative Example 1 is 19 days; the controlled-release period of the coated controlled-release fertilizer prepared in Application Example 6 using the straw polyol prepared in Comparative Example 2 is 40 days; the controlled-release period of the coated controlled-release fertilizer prepared in Application Example 7 using the straw polyol prepared in Comparative Example 5 is 32 days, indicating that the present invention uses the deep eutectic solvent and the bimetallic organic framework to jointly catalyze the preparation of straw polyol, which has a synergistic effect on improving the controlled-release period of the coated controlled-release fertilizer.

[0131] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A straw polyol, characterized in that: Prepared by the following method: (1) Under a nitrogen atmosphere, straw powder, a small molecule alcohol, an acid catalyst and a low eutectic solvent are uniformly mixed in a mass ratio of (5-45): (80-120): (0.1-5): (0.1-5), and reacted at 100-180° C. for 0.5-2 h to obtain a reaction product; (2) Under a nitrogen atmosphere, a bimetallic organic framework catalyst in an amount of 0.1% to 3.0% by mass of the small molecule alcohol is added to the reaction product obtained in step (1), and the mixture is reacted at 100 to 180° C. for 0.5 to 5 hours to obtain a straw polyol.

2. The straw polyol according to claim 1, characterized in that The small molecule alcohol is one or more of methanol, ethanol, propylene glycol, diethylene glycol, glycerol, isopropanol, isobutanol, 1,4-butanediol, pentanediol, and 2-methyl-1-propanol.

3. The straw polyol according to claim 1, characterized in that The acid catalyst is one or more of sulfuric acid, hydrochloric acid, phosphoric acid, formic acid and acetic acid.

4. The straw polyol according to claim 1, characterized in that The deep eutectic solvent is prepared by the following method: The hydrogen donor and the hydrogen acceptor are mixed in a molar ratio of (75-100): (69-287), reacted at 50-120° C. for 15-120 min to form a homogeneous liquid, and cooled to obtain a deep eutectic solvent; The hydrogen donor is one or more of tetrabutylammonium bromide, choline chloride, 1-ethyl-3-methylimidazolium salt, hexadecyltrimethylammonium bromide, dodecyldimethylbenzylammonium chloride, dioctadecyldimethylammonium bromide, octadecyldimethylhydroxyethylammonium nitrate, benzalkonium chloride, and triphenylcyclic imidazoline quaternary ammonium salt; The hydrogen acceptor is selected from one or more of urea, ethylene glycol, glycerol, formic acid, acetic acid, citric acid, N,N-dimethylformamide, N,N-dimethylacetamide, and acrylamide.

5. The straw polyol according to claim 1, characterized in that: The bimetallic organic framework is prepared by the following method: (1) mixing a first metal salt, an organic ligand and a solvent in a mass ratio of (1-2): (20-35): (300-500) uniformly, reacting at 120-160° C. for 2-6 hours, cooling after the reaction, centrifuging, washing and drying to obtain a single metal organic framework; (2) The prepared single metal organic framework is used as a precursor, and then a second metal salt is added, stirred for 20-28 hours, dried, and the resulting solid is calcined at 450-550° C. with nitrogen for 1-3 hours to obtain a bimetallic organic framework.

6. The straw polyol according to claim 5, characterized in that: The molar ratio of the first metal salt to the second metal salt is 0.2-3:1; The first metal salt is Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Na2MoO4, Fe2Mo3O 12 One of; The second metal salt is one of Zn(NO3)2·6H2O, Cu(NO3)2·6H2O, ZnCl2, AlCl3, Al2(SO4)3, and Al(NO3)3.

7. The straw polyol according to claim 5, characterized in that: The organic ligand is one or more of terephthalic acid, trimesic acid, 5-hydroxyphthalic acid, 5-benzyloxymethyl dicarboxylic acid, lauric acid, citric acid, and benzene-1,3,5-tricarboxylic acid; The solvent is one or more of N,N-dimethylformamide, methanol, ethanol, dimethyl sulfoxide, n-butanol, and hexadecyltrimethylammonium bromide.

8. Use of the straw polyol according to any one of claims 1 to 7 in the preparation of coated controlled-release fertilizer.

9. A coated controlled-release fertilizer, characterized in that: Prepared by the following method: Preheat the fertilizer particles of 2-6 mm in a drum to 50-80° C., then mix the straw polyol described in any one of claims 1-7 with a curing agent and a chain extender in a mass ratio of (45-82): (28-60): (3-12), and spray them onto the surface of the fertilizer particles. The spraying amount each time is 0.5-2% of the mass of the fertilizer particles. Repeat the spraying multiple times to obtain a coated controlled-release fertilizer.

10. The coated controlled-release fertilizer according to claim 9, characterized in that: The curing agent is one or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and L-lysine diisocyanate. The chain extender is one or more of 1,4-butanediamine, 1,6-hexanediamine, diethylenetriamine, 1,4-butanediol, polyethylene glycol, and phenylenediamine.

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