Preparation method of lignin-based polyurethane slow-release nitrogen fertilizer

Abstract

The invention provides a preparation method of a lignin-based polyurethane slow-release nitrogen fertilizer, which comprises the following steps: separating and extracting lignosulfonate from papermaking industry waste black liquor by adopting a membrane filtration method, liquefying lignin, polyethylene glycol and ethylene glycol according to a certain proportion, introducing a hydrophobic group through hydroxyl-terminated polydimethylsiloxane, and preparing the lignin-based polyurethane slow-release nitrogen fertilizer. Reacting with castor oil and isophorone diisocyanate to prepare polyurethane, and coating and curing the polyurethane on the surfaces of urea particles in a rotating pot at a certain temperature and rotating speed to prepare the lignin-based polyurethane slow-release nitrogen fertilizer. The polyurethane is wide in raw material source, the preparation method is simple, the bio-based content is high, and the prepared slow-release nitrogen fertilizer is good in slow-release performance.

Description

Technical Field

[0001] The invention relates to a method for preparing a lignin-based polyurethane slow-release nitrogen fertilizer. Biomass lignin and castor oil are used as main raw materials, and hydrophobic groups are introduced to prepare a slow-release nitrogen fertilizer with good slow-release performance by a relatively simple method. Background Art

[0002] Petroleum-based plastics have various excellent properties and can provide various raw materials and products for various industries such as construction, automobiles, machinery manufacturing, and electronic information. They play a very important role in modern social life. As people's understanding of environmental pollution, resource crisis and other issues continues to deepen, the high added value of biomass resources has also been increasingly valued, and people are paying attention to finding renewable biomass resources to replace petroleum products. Most biomaterials are non-toxic and harmless, and are rich in content. They can alleviate the pressure of energy depletion and increased pollution, reduce the plastic industry's dependence on the supply of petroleum-based chemical products, and reduce environmental pollution caused by the production process of polymer materials. At present, research on bio-based polymer materials is mainly limited to some natural polymers or thermoplastic materials such as starch plastics, cellulose-based materials, PHBV, PLA, PBS, and bio-based PE, while research on bio-based thermosetting resins is relatively small.

[0003] Fertilizer plays an important role in increasing crop yields to meet the needs of the world's rapidly growing population. Traditional water-soluble nitrogen fertilizers have low utilization rates (usually only 30-45%), are leached into groundwater by rainwater or irrigation water and pollute the environment, and cannot meet the nitrogen needs of crops throughout their growth period in one fertilization. Excessive fertilization can easily burn seedlings or cause soil compaction. Slow-release nitrogen fertilizers can improve fertilizer utilization and reduce environmental pollution by controlling the fertilizer release rate. Its large-scale promotion is an important way to achieve sustainable agriculture. Coated fertilizers, as the core of slow-release fertilizers (SRFs), account for 95% of the total. In recent decades, the coating materials of SRFs are usually natural sulfur and high molecular polymers. Compared with sulfur coatings that are easy to crack and easily destroyed by microorganisms, high molecular polymers have the advantages of easy control and good hydrophobic effect. Among them, polyurethane has great application prospects in polymer coating materials due to its easy availability, quick preparation, relatively low equipment investment cost and large biodegradation potential. However, traditional polyurethane coating materials are mainly derived from non-renewable petrochemical products, with poor degradability. The residual coating film may have adverse effects on the physical and chemical properties of the soil and the diversity of microbial communities. In response to the above situation, domestic and foreign researchers have accelerated the degradation of polyurethane by introducing natural degradable substances such as starch, cellulose, vegetable oil and lignin into polyurethane. Therefore, bio-based polyurethane coating materials have gradually become a research hotspot due to their better degradability and sustainable raw materials.

[0004] Lignin is one of the most abundant natural polymers in nature, but it has a complex structure. At present, the black liquor produced by papermaking in the world can produce about 50-60 million tons of lignin each year, most of which is burned as energy. Due to the advantages of lignin's wide source, low cost, biodegradability, good hydrophobicity and non-food bio-based and not competing with the people for food, it has good potential in the preparation of polyurethane coating materials. It contains a variety of functional groups, such as carboxyl, hydroxyl, carbonyl and methoxy, but the content of fatty hydroxyl is small, the reactivity of phenolic hydroxyl is low, the molecular weight and steric hindrance are large, and it is difficult to directly participate in the reaction or the performance after the reaction is poor. For the above reasons, domestic and foreign researchers use lignin as filler to prepare composite films, or reasonably modify lignin to improve reactivity and reduce molecular weight, such as esterification modification, hydroxymethylation modification and phenolization modification, which usually have the disadvantages of low conversion rate, complex process, more organic solvents involved, etc. The release mechanism of coated slow-release nitrogen fertilizer is that water enters the interior through the coating layer, and after urea dissolves, it forms a concentration difference with the water in the coating film, and is gradually released into the soil through diffusion. In this process, the fertilizer absorbs water, causing the internal volume to expand and form a large pressure, which may cause the coating film to rupture and lose its slow-release function. Therefore, the properties of the coating film (hydrophilicity or hydrophobicity), its concentration in the coating solution, solution viscosity, added modifiers, number of layers, technology used for coating, and environmental factors and other interdependent parameters jointly determine the release rate of slow-release nitrogen fertilizer.

[0005] The invention provides a method for preparing a lignin-based polyurethane slow-release nitrogen fertilizer, wherein the raw materials are lignin sulfonate, castor oil and IPDI, and a hydrophobic group is introduced through hydroxyl-terminated polydimethylsiloxane, and the lignin-based polyurethane slow-release nitrogen fertilizer is prepared by coating and curing the surface of urea particles at a certain temperature and rotation speed in a rotating pot. The polyurethane has a wide range of raw materials, a relatively simple preparation method, a high bio-based content, and a good slow-release performance of the prepared slow-release nitrogen fertilizer. Summary of the invention

[0006] The purpose of the present invention is to solve the problem that the nitrogen fertilizer release rate is too fast and it is difficult to maintain the nutritional needs during the entire crop growth process, improve the utilization rate of nitrogen fertilizer, and alleviate the environmental pollution caused by excessive application of nitrogen fertilizer. A method for preparing a lignin-based polyurethane slow-release nitrogen fertilizer is provided. The method has a wide range of raw materials, low price, simple steps in the entire reaction process, and does not require harsh reaction conditions. Lignin and castor oil have high utilization rates, a high proportion of bio-based, and the introduced hydrophobic groups can effectively alleviate the diffusion of water in the coating film and prolong the urea release time.

[0007] In order to achieve the above invention objectives, the technical scheme of the present invention is as follows: a lignin-based polyurethane slow-release nitrogen fertilizer, a slow-release layer coated on the surface of urea particles, the slow-release layer is a lignin-based polyurethane, and the specific preparation method is: lignin and polyethylene glycol and ethylene glycol are liquefied into liquefied lignin under the action of catalyst oxalic acid, castor oil reacts with isophorone diisocyanate to form prepolymer 1, and then reacts with liquefied lignin to form prepolymer 2, and then reacts with hydroxyl-terminated polydimethylsiloxane to introduce hydrophobic groups to form polyurethane, and finally in a rotating pot at a certain temperature and rotation speed The coating is solidified on the surface of the urea particles to obtain a lignin-based polyurethane slow-release nitrogen fertilizer.

[0008] The synthesis steps of the lignin-based polyurethane are as follows:

[0009] (1) preparing liquefied lignin: mixing lignin, polyethylene glycol, ethylene glycol and oxalic acid uniformly, heating to react sufficiently, and cooling to room temperature to obtain the product liquefied lignin;

[0010] (2) Preparation of lignin-based polyurethane: Castor oil and isophorone diisocyanate are uniformly mixed, heated under a nitrogen atmosphere for sufficient reaction, and after obtaining prepolymer 1, the liquefied lignin of step (1) and the catalyst dibutyltin dilaurate are poured in, and heated for reaction, after obtaining prepolymer 2, hydroxyl-terminated polydimethylsiloxane is poured in, and the reaction mixture continues to react at this temperature to obtain the product lignin-based polyurethane.

[0011] The mass ratio of lignin, polyethylene glycol and ethylene glycol is 1:2.4:0.6 or 1:1.6:0.4, the mass ratio of castor oil and isophorone diisocyanate is 1:1.5-2, the mass ratio of liquefied lignin to castor oil is 1:1.5-4, and dihydroxymethylsiloxane accounts for 3%-5% of the overall mass of the prepolymer 2.

[0012] In step (1), the reaction temperature is 140-155° C. and the reaction time is 90-120 minutes.

[0013] In step (2), the reaction temperature is 60-80° C. and the reaction time is 120-180 minutes.

[0014] In step (2), a solvent is added to adjust the viscosity, and the solvent used is one of acetone, 2-butanone and tetrahydrofuran.

[0015] The method for preparing the lignin-based polyurethane slow-release nitrogen fertilizer comprises the following steps: first preparing lignin-based polyurethane, and then wrapping the lignin polyurethane around urea particles, wherein the outer layer of the urea particles is wrapped with paraffin.

[0016] More specifically, urea particles are sieved to select a certain size and placed in a rotating pot for preheating. Paraffin is then added and rotated at a certain speed so that the paraffin is evenly wrapped on the surface of the urea. The temperature is then lowered to room temperature, lignin-based polyurethane is added, and a certain rotation speed is maintained so that the lignin-based polyurethane is evenly wrapped on the surface of the urea, and the temperature is raised for curing.

[0017] Beneficial effects:

[0018] (1) The lignin liquefaction catalyst is oxalic acid instead of the traditional 98% concentrated sulfuric acid, which is safer and more environmentally friendly. The source of lignin is waste black liquor from papermaking, which is cheap and widely available, providing a basis for the high-value utilization of lignin. Castor oil is a non-food bio-based product and does not compete with the people for food.

[0019] (2) The liquefied lignin obtained has a high conversion rate, a high hydroxyl content, and a low acid value, which is beneficial to reducing the molecular weight of lignin, increasing the active hydroxyl content, and increasing the proportion of lignin;

[0020] (3) The entire preparation process has few steps, simple process, and no pollutants are generated;

[0021] (4) The introduced siloxane groups can effectively improve the hydrophobicity of the material. DETAILED DESCRIPTION

[0022] The following examples are used to specifically illustrate the preparation method of a lignin-based polyurethane slow-release nitrogen fertilizer of the present invention. The examples are further detailed descriptions of the present invention, but they do not constitute a limitation to the present invention.

[0023] A method for preparing a lignin-based polyurethane slow-release nitrogen fertilizer comprises the following steps: liquefying lignin, polyethylene glycol and ethylene glycol under the action of oxalic acid as a catalyst to form liquefied lignin; reacting castor oil with isophorone diisocyanate (IPDI) to form prepolymer 1, which is then reacted with liquefied lignin to form prepolymer 2; reacting with hydroxyl-terminated polydimethylsiloxane (HTPDMS) to introduce hydrophobic groups to form polyurethane; and finally coating and curing the prepolymer on the surface of urea particles at a certain temperature and rotation speed in a rotating pot to obtain a lignin-based polyurethane slow-release nitrogen fertilizer. The steps for synthesizing the liquefied lignin and polyurethane are as follows:

[0024] (1) A certain amount of lignin, polyethylene glycol, ethylene glycol and oxalic acid are added to a round-bottom flask with a condenser, and the mixture is heated to 150° C. The mixture is kept at this temperature for 90-120 minutes, and cooled to room temperature to obtain a product liquefied lignin. The mass ratio of lignin, polyethylene glycol and ethylene glycol is 1:2.4:0.6 or 1:1.6:0.4.

[0025] (2) A certain amount of castor oil and IPDI are added to a round-bottom flask with a condenser, and the mixture is heated to 60-80°C under a nitrogen atmosphere. The mixture is kept at this temperature for 120-180 minutes to obtain prepolymer 1, and then a certain amount of liquefied lignin and catalyst dibutyltin dilaurate (DBTDL) are poured in. The mixture is reacted at 60-80°C for 120-180 minutes to obtain prepolymer 2, and then a certain amount of dihydroxymethylsiloxane is poured in. The reaction mixture is kept at this temperature for 90 minutes to obtain the product polyurethane, during which the viscosity can be adjusted by a solvent. The mass ratio of castor oil to IPDI is 1:1.5-2, the mass ratio of liquefied lignin to castor oil is 1:1.5-4, and dihydroxymethylsiloxane accounts for 3%-5% of the total mass of prepolymer 2. The solvent used is one of acetone, 2-butanone, and tetrahydrofuran.

[0026] (3) After sieving urea particles of a certain size, put them into a rotating pot for preheating for 10 minutes, and keep the temperature at 80°C. Then, add 1% paraffin of the urea quality, rotate at a certain speed for 30-60 minutes to make it evenly wrapped on the urea surface, and then cool to room temperature. Add a certain amount of polyurethane, keep a certain rotation speed for 30-60 minutes to make it evenly wrapped on the urea surface, heat to 80°C and keep for 120-240 minutes for curing, and finally obtain a completely wrapped slow-release nitrogen fertilizer.

[0027] Embodiment 1:

[0028] (1) 3.5 g of lignin, 8.4 g of polyethylene glycol, 2.1 g of ethylene glycol and 0.42 g of oxalic acid were added to a round-bottom flask with a condenser and heated to 150° C. The mixture was kept at this temperature for 90 minutes and cooled to room temperature to obtain a liquefied lignin product with a liquefaction rate of 95% and a hydroxyl content of 8.38 mmol / g.

[0029] (2) 6 g of castor oil and 6.56 g of IPDI were added to a round-bottom flask with a condenser, and the mixture was heated to 80° C. under a nitrogen atmosphere. The mixture was kept at this temperature for 120 minutes to obtain prepolymer 1. Then, 4 g of liquefied lignin and two drops of catalyst DBTDL were poured into the mixture and reacted at 80° C. for 120 minutes to obtain prepolymer 2. Then, a certain amount of 0.5 g of HTPDMS was poured into the mixture. The reaction mixture was kept at this temperature for 90 minutes to obtain a product polyurethane. During this period, a solvent can be used to adjust the viscosity. The solvent used is tetrahydrofuran.

[0030] (3) After sieving urea particles, about 100 g of a certain size was selected and placed in a rotating pot for preheating for 10 minutes, the temperature was maintained at 80°C, and then 1 g of paraffin was added, and the mixture was rotated at a certain speed for 60 minutes to evenly coat the urea surface, and then cooled to room temperature. 5 g of polyurethane was slowly dripped in, and the rotation speed was maintained for 60 minutes to evenly coat the urea surface, and the temperature was raised to 80°C and maintained for 180 minutes for curing, and finally a completely coated slow-release nitrogen fertilizer was obtained. Compared with uncoated urea, the complete release time in deionized water at room temperature can be extended by up to 8 times.

[0031] Embodiment 2:

[0032] (1) 3.5 g of lignin, 5.6 g of polyethylene glycol, 1.4 g of ethylene glycol and 0.32 g of oxalic acid were added to a round-bottom flask with a condenser and heated to 150° C. The mixture was kept at this temperature for 120 minutes and cooled to room temperature to obtain the product liquefied lignin with a liquefaction rate of up to 95% and a hydroxyl content of 7.64 mmol / g.

[0033] (2) 7 g of castor oil and 5.82 g of IPDI were added to a round-bottom flask with a condenser, and heated to 80° C. under a nitrogen atmosphere. The mixture was kept at this temperature for 120 minutes to obtain prepolymer 1. Then, 3 g of liquefied lignin and two drops of catalyst DBTDL were added, and the mixture was reacted at 80° C. for 120 minutes to obtain prepolymer 2. Then, 0.4 g of HTPDMS was added, and the reaction mixture was kept at this temperature for 90 minutes to obtain a product polyurethane. During this period, a solvent can be used to adjust the viscosity. The solvent used was tetrahydrofuran.

[0034] (3) After sieving urea particles, about 100g of a certain size was selected and placed in a rotating pot for preheating for 10 minutes, the temperature was maintained at 80°C, and then 1g of paraffin was added, and the mixture was rotated at a certain speed for 60 minutes to evenly coat the urea surface, and then cooled to room temperature. 5g of polyurethane was slowly dripped in, and a certain rotation speed was maintained for 60 minutes to evenly coat the urea surface, and the temperature was raised to 60°C and maintained for 120 minutes for curing, and then the temperature was raised to 80°C and maintained for 120 minutes for curing, and finally a completely coated slow-release nitrogen fertilizer was obtained. Compared with uncoated urea, the complete release time can be extended by up to 13 times in deionized water at room temperature.

[0035] Example 3

[0036] (1) 3.5 g of lignin, 8.4 g of polyethylene glycol, 2.1 g of ethylene glycol and 0.42 g of oxalic acid were added to a round-bottom flask with a condenser and heated to 150° C. The mixture was kept at this temperature for 90 minutes and cooled to room temperature to obtain the product liquefied lignin.

[0037] (2) 6 g of castor oil and 6.56 g of IPDI were added to a round-bottom flask with a condenser, and the mixture was heated to 80° C. under a nitrogen atmosphere. The mixture was kept at this temperature for 120 minutes to obtain prepolymer 1. Then, 4 g of liquefied lignin and two drops of catalyst DBTDL were poured into the mixture and reacted at 80° C. for 120 minutes to obtain prepolymer 2. Then, a certain amount of 0.5 g of HTPDMS was poured into the mixture. The reaction mixture was kept at this temperature for 90 minutes to obtain a product polyurethane. During this period, a solvent can be used to adjust the viscosity. The solvent used is tetrahydrofuran.

[0038] (3) After sieving urea particles, about 100g of a certain size was selected and placed in a rotating pot for preheating for 10 minutes, the temperature was maintained at 80°C, and then 1g of paraffin was added, and the mixture was rotated at a certain speed for 60 minutes to evenly coat the urea surface, and then cooled to room temperature. 7g of polyurethane was slowly dripped in, and the rotation speed was maintained for 60 minutes to evenly coat the urea surface, and the temperature was raised to 80°C and maintained for 180 minutes for curing, and finally a completely coated slow-release nitrogen fertilizer was obtained. Compared with uncoated urea, the complete release time in deionized water at room temperature can be extended by up to 25 times.

Claims

1. A lignin-based polyurethane slow-release nitrogen fertilizer, wherein the surface of urea particles is coated with a slow-release layer, characterized in that: The slow-release layer is lignin-based polyurethane, and the specific preparation method is: lignin, polyethylene glycol and ethylene glycol are liquefied into liquefied lignin under the action of catalyst oxalic acid, castor oil reacts with isophorone diisocyanate to form prepolymer 1, which is then reacted with liquefied lignin to form prepolymer 2, and then reacted with hydroxyl-terminated polydimethylsiloxane to introduce hydrophobic groups to form polyurethane, and finally coated and solidified on the surface of urea particles at a certain temperature and rotation speed in a rotating pot to obtain lignin-based polyurethane slow-release nitrogen fertilizer.

2. A lignin-based polyurethane slow-release nitrogen fertilizer according to claim 1, characterized in that: The synthesis steps of the lignin-based polyurethane are as follows: (1) preparing liquefied lignin: mixing lignin, polyethylene glycol, ethylene glycol and oxalic acid uniformly, heating to react sufficiently, and cooling to room temperature to obtain the product liquefied lignin; (2) Preparation of lignin-based polyurethane: Castor oil and isophorone diisocyanate are uniformly mixed, heated under a nitrogen atmosphere for sufficient reaction, and after obtaining prepolymer 1, the liquefied lignin of step (1) and the catalyst dibutyltin dilaurate are poured in, and heated for reaction, after obtaining prepolymer 2, hydroxyl-terminated polydimethylsiloxane is poured in, and the reaction mixture continues to react at this temperature to obtain the product lignin-based polyurethane.

3. A lignin-based polyurethane slow-release nitrogen fertilizer according to claim 1, characterized in that: The mass ratio of lignin, polyethylene glycol and ethylene glycol is 1:2.4:0.6 or 1:1.6:0.4, the mass ratio of castor oil and isophorone diisocyanate is 1:1.5-2, the mass ratio of liquefied lignin to castor oil is 1:1.5-4, and dihydroxymethylsiloxane accounts for 3%-5% of the overall mass of the prepolymer 2.

4. The lignin-based polyurethane slow-release nitrogen fertilizer according to claim 1, characterized in that: In step (1), the reaction temperature is 140-155° C. and the reaction time is 90-120 minutes.

5. The lignin-based polyurethane slow-release nitrogen fertilizer according to claim 1, characterized in that: In step (2), the reaction temperature is 60-80° C. and the reaction time is 120-180 minutes.

6. The lignin-based polyurethane slow-release nitrogen fertilizer according to claim 1, characterized in that: In step (2), a solvent is added to adjust the viscosity, and the solvent used is one of acetone, 2-butanone and tetrahydrofuran.

7. A method for preparing a lignin-based polyurethane slow-release nitrogen fertilizer according to any one of claims 1 to 6, characterized in that: Firstly, lignin-based polyurethane is prepared, and then the lignin-based polyurethane is wrapped outside the urea particles, and the outer layer of the urea particles is wrapped with paraffin.

8. The method according to claim 7, characterized in that More specifically, urea particles are sieved to select a certain size and placed in a rotating pot for preheating. Paraffin is then added and rotated at a certain speed so that the paraffin is evenly wrapped on the surface of the urea. The temperature is then lowered to room temperature, lignin-based polyurethane is added, and a certain rotation speed is maintained so that the lignin-based polyurethane is evenly wrapped on the surface of the urea, and the temperature is raised for curing.