Straw-derived polyol co-catalyzed by deep eutectic solvent / bimetallic metal-organic framework, preparation method therefor and use thereof

Abstract

Disclosed in the present invention is a straw-derived polyol co-catalyzed by a deep eutectic solvent / a bimetallic metal-organic framework, a preparation method therefor, and a use thereof. The straw-derived polyol is prepared by means of a method comprising: in a nitrogen atmosphere, uniformly mixing straw powder, a small-molecule alcohol, an acid catalyst, and a deep eutectic solvent for reaction to obtain a reaction product; and then adding a bimetallic organic framework catalyst to the reaction product for a reaction to obtain the straw-derived polyol. In the present invention, by means of a green, natural, and pollution-free deep eutectic solvent-catalyzed liquefaction technique, lignin and hemicellulose can be dissolved, thereby reducing cross-linking interactions thereof with cellulose, facilitating disruption of the crystalline structure of cellulose, increasing the available surface area, enhancing the contact with a liquefying agent, improving the conversion efficiency, and reducing the residue rate. By adding a bimetallic organic framework catalyst in the middle and later stages of the reaction, aldehydes, ketones, acids, and esters can all be reduced and upgraded to alcohols, thereby significantly increasing the hydroxyl value of liquefied polyols and facilitating an increase in the degree of cross-linking of formed films.

Description

A straw polyol co-catalyzed by a eutectic solvent / bimetallic organic framework, its preparation method and application Technical Field

[0001] This invention relates to the technical field of controlled-release fertilizer production, specifically to a straw polyol co-catalyzed by a eutectic solvent / bimetallic organic framework, its preparation method, and its application. Background Technology

[0002] Coated controlled-release fertilizers are fertilizers that release nutrients gradually or slowly by coating the fertilizer surface with a thin film material. This improves fertilizer utilization efficiency, reduces nutrient loss, improves soil conditions, and minimizes negative environmental impacts. However, commercially available coated controlled-release fertilizers often use petrochemical-derived polymer materials, which have high production costs and poor biodegradability. This often leads to high energy consumption and environmental costs during production and application, and their long-term environmental residues place a burden on soil ecology and the environment.

[0003] Liquefied biomass coating materials are produced by converting biomass, especially crop straw, into low-molecular-weight, fluid biomass liquefied polyols through chemical or physical methods such as pyrolysis and acid hydrolysis. These polyols are then cross-linked with a curing agent to create controlled-release fertilizer films. Because they originate from natural renewable resources, they not only effectively utilize agricultural waste and reduce resource waste, but are also more easily degraded than traditional petrochemical films, effectively reducing the environmental risks associated with film residues. Therefore, they have attracted widespread attention in the agricultural fertilizer field in recent years. However, straw contains large amounts of cellulose, hemicellulose, and lignin. Due to significant differences in activation energy and crystallinity, the reaction kinetics of these components are difficult to control. When the degree of liquefaction is low, the prepared polyols often suffer from incomplete liquefaction and high residue rates. Conversely, excessively high liquefaction levels produce undesirable byproducts such as phenols, aldehydes, and acids, affecting the purity and reactivity of the polyols. This results in a loose structure, numerous pores, and a short controlled-release period in the prepared coated controlled-release fertilizer film. Hydrogenation technology is a key method for upgrading liquefied products. This method can convert carbonyl compounds in polyols. However, different catalysts have different hydrogenation performance. Inappropriate upgrading can lead to excessive reduction and the generation of inert hydrocarbons, which is not conducive to the film formation of polyurethane-coated controlled-release fertilizers. Therefore, it is particularly important to prepare catalysts with good performance to improve the performance of polyols.

[0004] Patent ZL 201210261735.0 discloses a coated controlled-release fertilizer using crop straw as a biodegradable film and its production method. This method directly liquefies crop straw, resulting in poor film density due to low liquefaction rates. Furthermore, side reactions during liquefaction generate numerous unreacted or sterically hindered groups, leading to low cross-linking and a short nutrient release period. Patent ZL 202111540324.0 discloses a bio-based polyurethane coated slow-release fertilizer pretreated with steam explosion and its preparation method. This method requires specialized explosion equipment and post-explosion cleaning and drying processes, making it complex, energy-intensive, and inefficient. Patent ZL 201510416904.7 discloses a straw liquefaction coating liquid, its preparation method, and its application. This method does not reduce and upgrade the by-products, resulting in a large amount of non-film-forming substances in the liquefied product, affecting its quality. Furthermore, the method uses wax-based additives and a large amount of polyether polyols, which will affect the degradation performance of the membrane material. Patent CN 105646090 B discloses a controlled-release fertilizer modified from agricultural organic waste into a biodegradable membrane and its preparation method. This method uses siloxanes as additives, which are identified as emerging organic pollutants or listed as priority controlled chemicals by countries such as the EU, posing environmental and ecological risks and human health risks due to their environmental residues. Summary of the Invention

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

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a straw polyol prepared by the following method:

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

[0009] (2) Under a nitrogen atmosphere, add 0.1%-3.0% of a small molecule alcohol by mass of a bimetallic organic framework catalyst to the reaction product obtained in step (1), and react at 100-180℃ for 0.5-5h to obtain 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, and 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 eutectic solvent is prepared by the following method:

[0013] The hydrogen donor and the hydrogen acceptor were mixed at a molar ratio of (75-100):(69-287) and reacted at 50-120℃ for 15-120 min to form a homogeneous liquid. After cooling, a eutectic solvent was obtained.

[0014] The hydrogen donor is one or more of the following: tetrabutylammonium bromide, 1-ethyl-3-methylimidazolium salt, hexadecyltrimethylammonium bromide, dodecyl dimethyl benzylammonium chloride, bis(octadecyl dimethylammonium bromide) 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) The first metal salt, organic ligand and solvent are mixed evenly in a mass ratio of (1-2):(20-35):(300-500), and reacted at 120-160℃ for 2-6 hours. After the reaction, the mixture is cooled, centrifuged, washed and dried to obtain a single metal organic framework.

[0018] (2) The prepared monometallic organic framework is used as a precursor, and then a second metal salt is added. The mixture is stirred for 20-28 hours, dried, and the resulting solid is calcined with nitrogen at 450-550℃ for 1-3 hours to obtain a 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(NO3)2·6H2O, Ni(NO3)2·6H2O, Na2MoO4, or Fe2Mo3O4. 12 One of them;

[0021] The second metal salt is one of Zn(NO3)2·6H2O, Cu(NO3)2·6H2O, ZnCl2, AlCl3, Al2(SO4)3, and Al(NO3)3.

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

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

[0024] A second aspect of the present invention provides the application of the above-mentioned straw polyol in the preparation of coated controlled-release fertilizer.

[0025] A third aspect of the present invention provides a coated controlled-release fertilizer, prepared by the following method:

[0026] Preheat 2-6mm fertilizer granules to 50-80℃ in a rotating drum. Then mix the above-mentioned straw polyol with curing agent and chain extender in a mass ratio of (45-82):(28-60):(3-12) and spray it onto the surface of the fertilizer granules. Each spraying amount is 0.5-2% of the mass of the fertilizer granules. Repeat the spraying multiple times to obtain 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), and L-lysine diisocyanate (LDI).

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

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

[0030] The beneficial effects of this invention are:

[0031] 1. This invention employs a green, natural, and pollution-free low-eutectic solvent catalytic liquefaction technology. This technology can dissolve lignin and hemicellulose, reduce their cross-linking with cellulose, and also helps to destroy the crystalline structure of cellulose, reduce its crystallinity, expose more amorphous regions, increase the usable surface area, enhance contact with the liquefying agent, improve conversion efficiency, and reduce residue rate.

[0032] 2. This invention incorporates a bimetallic organic framework catalyst in the 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, this 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 significantly increased, which is beneficial to improving the degree of film crosslinking and avoiding problems such as reduced hydroxyl content and increased saturated hydrocarbons caused by excessive reduction. It can also control the selectivity of by-products, thus facilitating the high-quality production of polyols. In addition, the bimetallic catalyst adopts a MOF structure, which has the characteristics of high specific surface area, multiple adsorption sites, and high catalytic activity compared with traditional metal catalysts. It also 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 polyols prepared using this invention are green and safe, requiring no additional high-dose petrochemical modifying materials. The process is simple and easy to operate, eliminating the need for repeated washing and drying, and features continuous production and low energy consumption. The prepared polyols exhibit high reactivity, high cross-linking degree, and low content of non-film-forming substances, which is beneficial for the uniform and dense film formation of controlled-release fertilizer films and can effectively prolong the nutrient release period. Attached Figure Description

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

[0035] Figure 2: Hydroxyl values ​​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 with different polyol coatings. Detailed Implementation

[0038] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0039] As described in the background section, straw contains a large amount of cellulose, hemicellulose, and lignin. Due to the large differences in activation energy and crystallinity, the reaction kinetics of these components are difficult to control. When the degree of liquefaction is low, the prepared polyols usually have problems such as incomplete liquefaction and high residue rate. When the degree of liquefaction is too high, undesirable byproducts such as phenols, aldehydes, and acids will be produced, affecting the purity and reactivity of the polyols. As a result, the prepared coated controlled-release fertilizer film has a loose structure, many pores, and a short controlled-release period. Based on this, this invention first uses a renewable, inexpensive, and environmentally friendly eutectic solvent as a catalyst to liquefy straw. By simulating the process of releasing hydrogen bonds through enzyme catalysis, a hydrogen donor and acceptor eutectic method is employed to promote the disruption of the intrinsic hydrogen bond network of cellulose, accelerating the liquefaction process, reducing residue, and promoting the depth of the reaction, thus preparing a biomass polyol rich in active hydroxyl groups. Furthermore, during the liquefaction process, the differences in activation energy and molecular structure of cellulose, hemicellulose, and lignin in the straw lead to varying liquefaction efficiencies for different components, generating a large number of insoluble unsaturated carbonyl compounds such as aldehydes, ketones, carboxylic acids, and esters, thereby affecting the purity and quality of the polyol. Therefore, this invention adds a bimetallic organic framework catalyst in the later stages of the reaction. This catalyst consists of two reducing agents... The catalyst is composed of two metals. One metal is selected from Co, Ni, Na, Fe, etc., which can hydrogenate unsaturated aldehydes and ketones to prepare saturated alcohols. However, due to the large steric hindrance and weak polarity of carbonyl compounds, the reduction and upgrading of acids and esters is very difficult. Therefore, the other metal is selected from Cu, Zn, Al, etc., which have high activation energies and can promote the reaction. In addition, the catalyst used adopts a MOF structure, which can provide abundant active reaction sites and maintain its structural stability at high temperatures, which helps 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 polyols can be increased, and non-film-forming residues can be reduced, thereby improving the density and nutrient release performance of the coated controlled-release fertilizer film.

[0040] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

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

[0042] Example 1: Preparation of straw polyols:

[0043] (1) Preparation of eutectic solvent:

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

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

[0046] Ni(NO3)2·6H2O, terephthalic acid and N,N-dimethylformamide were mixed at a mass ratio of 1:20:300. The mixture was stirred for 20 minutes and then transferred to a Teflon-lined stainless steel autoclave. The autoclave was sealed and reacted at 140°C for 4 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The solution was centrifuged and the precipitate was washed several times with anhydrous ethanol and water to remove any possible residues. The precipitate was then dried under vacuum at 65°C for 8 hours to obtain a single metal organic framework.

[0047] The prepared monometallic organic framework was used as a precursor, and then Cu(NO3)2·6H2O, Ni(NO3)2·6H2O and Cu(NO3)2·6H2O were added in a molar ratio of 1:1. The mixture was stirred for 24 h, dried, and the resulting solid was calcined at 500 °C with nitrogen for 2 h to obtain a bimetallic organic framework.

[0048] (3) Preparation of straw polyols:

[0049] Under a nitrogen atmosphere, corn stalk powder, 1,2-propanediol, diethylene glycol, 98% sulfuric acid, and eutectic solvent were mixed uniformly at a mass ratio of 12:50:30:0.1:0.1 and reacted at 150°C for 1.5 h to obtain stalk polyol. Then, under a nitrogen atmosphere, 0.1% by mass of a bimetallic organic framework catalyst of small molecule alcohol was added to the reaction product, and the reaction was carried out at 110°C for 3 h to obtain stalk polyol.

[0050] Example 2: Preparation of straw polyols:

[0051] (1) Preparation of eutectic solvent:

[0052] Choline chloride and urea were mixed at a molar ratio of 75:69 and stirred at 85°C for 70 min to form a homogeneous liquid. The homogeneous liquid was then cooled to room temperature to obtain a eutectic solvent.

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

[0054] Ni(NO3)2·6H2O, citric acid and N,N-dimethylformamide were mixed at a mass ratio of 1:20:300. The mixture was stirred for 20 minutes and then transferred to a Teflon-lined stainless steel autoclave. The autoclave was sealed and reacted at 140°C for 4 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The solution was centrifuged and the precipitate was washed several times with anhydrous ethanol and water to remove any possible residues. The precipitate was then dried under vacuum at 65°C for 8 hours to obtain a single metal organic framework.

[0055] The prepared monometallic organic framework was used as a precursor, and then Cu(NO3)2·6H2O, Ni(NO3)2·6H2O and Cu(NO3)2·6H2O were added in a molar ratio of 1:1. The mixture was stirred for 24 h, dried, and the resulting solid was calcined at 500 °C with nitrogen for 2 h to obtain a bimetallic organic framework.

[0056] (3) Preparation of straw polyols:

[0057] Under a nitrogen atmosphere, corn stalk powder, glycerol, butanediol, and 98% sulfuric acid eutectic solvent were 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 the reaction product.

[0058] Under a nitrogen atmosphere, 0.1% by mass of a small molecule alcohol and a bimetallic organic framework catalyst were added to the reaction product, and the reaction was carried out at 110°C for 3 hours to obtain straw polyol.

[0059] Example 3: Preparation of straw polyols:

[0060] (1) Preparation of eutectic solvent:

[0061] Tetrabutylammonium bromide and citric acid were mixed at a molar ratio of 90:150 and stirred at 85°C for 70 min to form a homogeneous liquid. The homogeneous liquid was then cooled to room temperature to obtain a eutectic solvent.

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

[0063] Co(NO3)2·6H2O, terephthalic acid, and dimethyl sulfoxide were mixed in a mass ratio of 1.5:28:400. The mixture was stirred for 20 minutes and then transferred to a Teflon-lined stainless steel autoclave. The autoclave was sealed and reacted at 140°C for 4 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The solution was centrifuged, and the precipitate was washed several times with anhydrous ethanol and water to remove any possible residues. The precipitate was then dried under vacuum at 65°C for 8 hours to obtain a single metal organic framework.

[0064] The prepared monometallic organic framework was used as a precursor, and then ZnCl2 was added. The molar ratio of Co(NO3)2·6H2O to ZnCl2 was 2:1. The mixture was stirred for 24 h, dried, and the resulting solid was calcined at 500 °C with nitrogen for 2 h to obtain a bimetallic organic framework.

[0065] (3) Preparation of straw polyols:

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

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

[0068] Example 4: Preparation of straw polyols:

[0069] (1) Preparation of eutectic solvent:

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

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

[0072] Ni(NO3)2·6H2O, trimesic acid and n-butanol were mixed in a mass ratio of 2:35:500. The mixture was stirred for 20 minutes and then transferred to a Teflon-lined stainless steel autoclave. The autoclave was sealed and reacted at 140°C for 4 hours. After the reaction, the autoclave was allowed to cool naturally to room temperature. The solution was centrifuged and the precipitate was washed several times with anhydrous ethanol and water to remove any possible residues. The precipitate was then dried under vacuum at 65°C for 8 hours to obtain a single metal organic framework.

[0073] The prepared monometallic organic framework was used as a precursor, and then Cu(NO3)2·6H2O, Ni(NO3)2·6H2O and Cu(NO3)2·6H2O were added in a molar ratio of 3:1. The mixture was stirred for 24 h, dried, and the resulting solid was calcined at 500 °C with nitrogen for 2 h to obtain a bimetallic organic framework.

[0074] (3) Preparation of straw polyols:

[0075] Under a nitrogen atmosphere, corn stalk powder, pentylene glycol, 98% sulfuric acid and eutectic solvent were mixed evenly in a mass ratio of 25:120:5:5 and reacted at 150°C for 1.5 h to obtain the reaction product.

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

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

[0078] Under a nitrogen atmosphere, corn stalk powder, 1,2-propanediol, diethylene glycol, and 98% 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 stalk polyol.

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

[0080] (1) Preparation of eutectic solvent:

[0081] Choline chloride and citric acid were mixed at a molar ratio of 1:2 and stirred at 85°C for 70 min to form a homogeneous liquid. The homogeneous liquid was then cooled to room temperature to obtain a eutectic solvent.

[0082] (2) Preparation of straw polyols:

[0083] Under a nitrogen atmosphere, corn stalk powder, 1,2-propanediol, diethylene glycol, 98% sulfuric acid and 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 stalk polyol;

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

[0085] (1) Preparation of eutectic solvent:

[0086] Choline chloride and citric acid were mixed at a molar ratio of 1:2 and stirred at 85°C for 70 min to form a homogeneous liquid. The homogeneous liquid was then cooled to room temperature to obtain a eutectic solvent.

[0087] (2) Ni-based single-metal organic frameworks are prepared by the following methods:

[0088] Ni(NO3)2·6H2O, terephthalic acid and N,N-dimethylformamide were mixed at a mass ratio of 1:20:300. The mixture was stirred for 20 minutes and then transferred to a Teflon-lined stainless steel autoclave. The autoclave was sealed and reacted at 140°C for 4 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The solution was centrifuged and the precipitate was washed several times with anhydrous ethanol and water to remove any possible residues. The precipitate was then dried under vacuum at 65°C for 8 hours to obtain a single metal organic framework.

[0089] (3) Preparation of straw polyols:

[0090] Under a nitrogen atmosphere, corn stalk powder, 1,2-propanediol, diethylene glycol, 98% sulfuric acid, and a eutectic solvent were mixed uniformly at a mass ratio of 12:50:30:0.1:0.1 and reacted at 150°C for 1.5 h to obtain stalk polyol. Then, under a nitrogen atmosphere, 0.1% by mass of a Ni-based monometallic organic framework catalyst of small molecule alcohol was added to the reaction product, and the reaction was carried out at 110°C for 3 h to obtain stalk polyol.

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

[0092] (1) Preparation of eutectic solvent:

[0093] Choline chloride and citric acid were mixed at a molar ratio of 1:2 and stirred at 85°C for 70 min to form a homogeneous liquid. The homogeneous liquid was then cooled to room temperature to obtain a eutectic solvent.

[0094] (2) Cu-based single-metal organic frameworks are prepared by the following method:

[0095] Cu(NO3)2·6H2O, terephthalic acid and N,N-dimethylformamide were mixed at a mass ratio of 1:20:300. The mixture was stirred for 20 minutes and then transferred to a Teflon-lined stainless steel autoclave. The autoclave was sealed and reacted at 140°C for 4 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The solution was centrifuged and the precipitate was washed several times with anhydrous ethanol and water to remove any possible residues. The precipitate was then dried under vacuum at 65°C for 8 hours to obtain a Cu-based monometallic organic framework.

[0096] (3) Preparation of straw polyols:

[0097] Under a nitrogen atmosphere, corn stalk powder, 1,2-propanediol, diethylene glycol, 98% sulfuric acid, and a eutectic solvent were mixed uniformly at a mass ratio of 12:50:30:0.1:0.1 and reacted at 150°C for 1.5 h to obtain stalk polyol. Then, under a nitrogen atmosphere, 0.1% by mass of a Ni-based monometallic organic framework catalyst of small molecule alcohol was added to the reaction product, and the reaction was carried out at 110°C for 3 h to obtain stalk polyol.

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

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

[0100] Ni(NO3)2·6H2O, terephthalic acid and N,N-dimethylformamide were mixed at a mass ratio of 1:20:300. The mixture was stirred for 20 minutes and then transferred to a Teflon-lined stainless steel autoclave. The autoclave was sealed and reacted at 140°C for 4 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The solution was centrifuged and the precipitate was washed several times with anhydrous ethanol and water to remove any possible residues. The precipitate was then dried under vacuum at 65°C for 8 hours to obtain a single metal organic framework.

[0101] The prepared monometallic organic framework was used as a precursor, and then Cu(NO3)2·6H2O, Ni(NO3)2·6H2O and Cu(NO3)2·6H2O were added in a molar ratio of 1:1. The mixture was stirred for 24 h, dried, and the resulting solid was calcined at 500 °C with nitrogen for 2 h to obtain a bimetallic organic framework.

[0102] (2) Preparation of straw polyols:

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

[0104] Application Example 1:

[0105] Urea of ​​2-6 mm thickness was preheated to 65°C in a rotating drum. Then, the straw polyol prepared in Example 1 was mixed with diphenylmethane diisocyanate (MDI) and 1,4-butanediamine at a mass ratio of 65:54:8 and used as a coating material. The mixture was sprayed onto the surface of the urea, with each spray amount being 1% of the urea mass. The coating material was sprayed repeatedly until it accounted for 3% of the total mass of the coated controlled-release fertilizer, thus obtaining the coated controlled-release fertilizer.

[0106] Application Example 2:

[0107] Urea of ​​2-6 mm thickness was preheated to 65°C in a rotating drum. Then, the straw polyol prepared in Example 2 was mixed with toluene diisocyanate (TDI) and 1,4-butanediamine at a mass ratio of 65:54:8 and used as a coating material. The mixture was sprayed onto the surface of the urea, with each spray amount being 1% of the urea mass. The coating material was sprayed repeatedly until it accounted for 4% of the total mass of the coated controlled-release fertilizer, thus obtaining the coated controlled-release fertilizer.

[0108] Application Example 3:

[0109] Urea of ​​2-6 mm thickness was preheated to 65°C in a rotating drum. Then, the straw polyol prepared in Example 3 was mixed with diphenylmethane diisocyanate (MDI) and 1,4-butanediol at a mass ratio of 65:54:8 and used as a coating material. The mixture was sprayed onto the surface of the urea, with each spray amount being 1% of the urea mass. The coating material was sprayed repeatedly until it accounted for 3% of the total mass of the coated controlled-release fertilizer, thus obtaining the coated controlled-release fertilizer.

[0110] Application Example 4:

[0111] Urea of ​​2-6 mm thickness was preheated to 65°C in a rotating drum. Then, the straw polyol prepared in Example 4 was mixed with isophorone diisocyanate (IPDI) and 1,4-hexanediamine at a mass ratio of 65:54:8. This mixture was used as a coating material and sprayed onto the surface of the urea. Each spraying amount was 1% of the urea mass. The coating material was sprayed repeatedly until it accounted for 2.5% of the total mass of the coated controlled-release fertilizer, thus obtaining the coated controlled-release fertilizer.

[0112] Application Example 5:

[0113] Urea (2-6 mm thick) was preheated to 65°C in a rotating drum. Then, straw polyol prepared in Comparative Example 1 was mixed with diphenylmethane diisocyanate (MDI) and 1,4-butanediamine in a mass ratio of 65:54:8. This mixture was used as a coating material and sprayed onto the surface of the urea. Each spraying amount was 1% of the urea mass. The coating material was sprayed repeatedly until it accounted for 3% of the total mass of the coated controlled-release fertilizer, thus obtaining the coated controlled-release fertilizer.

[0114] Application Example 6:

[0115] Urea of ​​2-6 mm thickness was preheated to 65°C in a rotating drum. Then, the straw polyol prepared in Comparative Example 2 was mixed with diphenylmethane diisocyanate (MDI) and 1,4-butanediamine in a mass ratio of 65:54:8. This mixture was used as a coating material and sprayed onto the surface of the urea. Each spraying amount was 1% of the urea mass. The coating material was sprayed repeatedly until it accounted for 3% of the total mass of the coated controlled-release fertilizer, thus obtaining the coated controlled-release fertilizer.

[0116] Application Example 7:

[0117] Urea with a thickness of 2-6 mm was preheated to 65°C in a rotating drum. Then, the straw polyol prepared in Comparative Example 5 was mixed with diphenylmethane diisocyanate (MDI) and 1,4-butanediamine in a mass ratio of 65:54:8. This mixture was used as a coating material and sprayed onto the surface of the urea. Each spraying amount was 1% of the urea mass. The coating material was sprayed repeatedly until it accounted for 3% of the total mass of the coated controlled-release fertilizer, thus obtaining the coated controlled-release fertilizer.

[0118] Experimental Example 1:

[0119] The residue rate, hydroxyl value, and composition of the liquefaction products of the straw polyols prepared in Example 1 and the comparative example were tested:

[0120] 1. Residue rate: Weigh 2.0g of liquefied product (accurate to 0.0001g), and then weigh 20mL of a mixed solution of 1,4-dioxane and water (volume ratio 4:1) using a graduated cylinder. Place both solutions in a beaker and stir in an 80℃ water bath for 30min. Filter while hot, and wash the residue with dioxane until the filtrate is colorless.

[0121] Place the filter paper with residue into a 120℃ drying oven and dry for 4 hours. After drying, weigh the paper.

[0122] The formula for calculating the residue ratio 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; and m3 represents the mass of the residue and the filter paper.

[0125] Hydroxyl value: The determination method is in accordance with GB / T 12008.3-2009.

[0126] Composition of liquefaction products: The method was based on Xiaojing Yu, Xiao Sun, Jingjing Dong, Liang Wu, Wusong Guo, Yanfeng Wang, Xuju Jiang, Zhiguang Liu, Min Zhang. Instant catapultsteam explosion pretreatment of wheat straw liquefied polyols to prolong the slow-release longevity of bio-based polyurethane-coated fertilizers. Chemical Engineering Journal, 2022, 435, 134985.2.5.2.

[0127] As shown in Figures 1-3, the straw polyol prepared in Example 1 of this invention has the lowest residue rate, the highest hydroxyl value, and the highest alcohol content among the liquefaction products. This indicates that the present invention uses a green, natural, pollution-free, and recyclable eutectic solvent catalytic liquefaction technology combined with a bimetallic organic framework catalyst, which significantly improves the quality of the prepared straw polyol.

[0128] Experimental Example 2:

[0129] According to the national standard GB / T 23348-2009 for slow-release fertilizers, the nitrogen release rate of the coated controlled-release fertilizers prepared using Application Examples 1, 5, 6 and 7 was determined, and the time required for the cumulative nutrient release rate to reach 80% was recorded as the controlled-release period.

[0130] As shown in Figure 4, the controlled-release fertilizer prepared using straw polyol prepared in Example 1 of this invention has the longest controlled-release period, at 55 days; the controlled-release fertilizer prepared using straw polyol prepared in Comparative Example 5 has a controlled-release period of 19 days; the controlled-release fertilizer prepared using straw polyol prepared in Comparative Example 2 has a controlled-release period of 40 days; and the controlled-release fertilizer prepared using straw polyol prepared in Comparative Example 5 has a controlled-release period of 32 days. This indicates that the present invention utilizes a eutectic solvent and a bimetallic organic framework to co-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 description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A straw polyol, characterized by, Prepared by the following method: (1) Under a nitrogen atmosphere, straw powder, small molecule alcohol, acid catalyst and eutectic solvent are mixed evenly in a mass ratio of (5-45):(80-120):(0.1-5):(0.1-5), and reacted at 100-180℃ for 0.5-2h to obtain the reaction product; (2) Under a nitrogen atmosphere, add 0.1%-3.0% of a small molecule alcohol by mass of a bimetallic organic framework catalyst to the reaction product obtained in step (1), and react at 100-180℃ for 0.5-5h to obtain 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 of claim 1, wherein, The eutectic solvent is prepared by the following method: The hydrogen donor and the hydrogen acceptor were mixed at a molar ratio of (75-100):(69-287) and reacted at 50-120℃ for 15-120 min to form a homogeneous liquid. After cooling, a eutectic solvent was obtained. The hydrogen donor is one or more of the following: tetrabutylammonium bromide, choline chloride, 1-ethyl-3-methylimidazolium salt, hexadecyltrimethylammonium bromide, dodecyldimethylbenzylammonium chloride, dioctadecyldimethylammonium bromide, octadecyldimethylhydroxyethylammonium nitrate, benzalkonium chloride, and triphenylcycloimidazoline 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 of claim 1, wherein, The bimetallic organic framework is prepared by the following method: (1) The first metal salt, organic ligand and solvent are mixed evenly in a mass ratio of (1-2):(20-35):(300-500), and reacted at 120-160℃ for 2-6 hours. After the reaction, the mixture is cooled, centrifuged, washed and dried to obtain a single metal organic framework. (2) The prepared monometallic organic framework is used as a precursor, and then a second metal salt is added. The mixture is stirred for 20-28 hours, dried, and the resulting solid is calcined with nitrogen at 450-550℃ for 1-3 hours to obtain a bimetallic organic framework.

6. The straw polyol according to claim 5, wherein, The molar ratio of the first metal salt to the second metal salt is 0.2-3:1; the first metal salt is one of Co(N03)2-6H20, Ni(N03)2-6H20, Na2Mo04, Fe2Mo30 12 4, and Co(N03)2-6H20. 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, wherein, The organic ligand is one or more of the following: terephthalic acid, pyromellitic acid, 5-hydroxyphthalic acid, 5-benzyloxymethyldicarboxylic acid, lauric acid, citric acid, and phenyl-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. The application of the straw polyol according to any one of claims 1-7 in the preparation of coated controlled-release fertilizer.

9. A coated controlled release fertilizer, characterized in that, Prepared by the following method: Fertilizer granules of 2-6 mm are preheated to 50-80°C in a rotating drum. Then, the straw polyol described in any one of claims 1-7 is mixed with a curing agent and a chain extender in a mass ratio of (45-82):(28-60):(3-12) and sprayed onto the surface of the fertilizer granules. Each spraying amount is 0.5-2% of the mass of the fertilizer granules. The spraying is repeated multiple times to obtain a coated controlled-release fertilizer.

10. The coated controlled-release fertilizer of claim 9, wherein, 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.

Images