Lignin-based slow-release nitrogen fertilizer and preparation method thereof

Abstract

The invention discloses a lignin-based slow-release nitrogen fertilizer and a preparation method thereof, and the preparation method comprises the following steps: mixing lignin, phenol, water and sulfuric acid in proportion, heating, and carrying out pre-phenolation treatment to obtain a phenolated lignin mixed solution; adding acidic water into the phenolated lignin mixed solution, then carrying out solid-liquid separation, washing the solid to be neutral, and drying to obtain phenolated lignin; the phenolated lignin is dissolved in alkali liquor, arginine and formaldehyde are added into the alkali liquor, and the mass ratio of the phenolated lignin to the arginine to the formaldehyde is (1-5): (10-30): (20-35); reacting at 50 to 80 DEG C for 1 to 5 hours; and after the reaction is finished, dialyzing the reacted mixture, collecting a liquid product, and drying to obtain the lignin-based slow-release nitrogen fertilizer. According to the method, active sites of lignin are remarkably increased through phenolation pretreatment, and the nitrogen content of the prepared lignin-based slow-release nitrogen fertilizer can reach 19.27% by combining with optimization of an efficient amination reagent and reaction conditions, so that a new way is provided for high-value utilization of industrial lignin.

Description

Technical Field

[0001] The invention belongs to the technical field of high-value utilization of industrial lignin, and particularly relates to a lignin-based slow-release nitrogen fertilizer and a preparation method thereof. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Lignin, a major component of lignocellulosic biomass, is the second most abundant renewable organic resource in nature, and its efficient utilization is crucial for sustainable development. Currently, industrial lignin primarily originates from black liquor produced during the pulping and papermaking process, which contains a large amount of lignin, along with small amounts of carbohydrates and inorganic salts. Traditional treatment methods typically involve burning black liquor in an alkali recovery system to recover chemicals and energy. However, this method fails to fully utilize the high value-added potential of lignin and results in a waste of biomass resources.

[0004] Lignin, a natural high-molecular compound, acts as a humic acid precursor and can be degraded by microorganisms in the soil and converted into humus, thereby increasing soil organic matter content and improving soil fertility. Lignin-based slow-release fertilizers have become a research hotspot in recent years and are mainly divided into two categories: lignin-coated fertilizers and lignin-based organic nitrogen fertilizers.

[0005] Lignin-coated fertilizers typically combine lignin with additives such as rosin, starch, or vegetable oil, then coat the surface of fertilizer particles like urea to delay nutrient release. However, due to the poor film-forming properties of lignin and the insufficient water resistance and mechanical strength of the coating, the slow-release effect is unstable, making it difficult to meet long-term controlled-release requirements.

[0006] Lignin-based organic nitrogen fertilizers primarily introduce nitrogen into the lignin structure through chemical modification (such as ammonia oxidation). However, lignin's complex molecular structure and low reactivity result in a generally low nitrogen content (typically less than 5%) after modification, limiting its agricultural application value.

[0007] To increase the reactivity of lignin, the Mannich reaction is widely used for amination modification of lignin. This reaction can introduce amino groups into the lignin structure, but due to the limited number of accessible reaction sites in lignin, the nitrogen content of the modified lignin is limited, making it difficult to meet the requirements of high-efficiency slow-release fertilizers. Summary of the Invention

[0008] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide a lignin-based slow-release nitrogen fertilizer and a preparation method thereof. The present invention significantly increases the active sites of lignin through phenolization pretreatment, and combines a high-efficiency amination reagent and optimizes reaction conditions. The nitrogen content of the prepared lignin-based slow-release nitrogen fertilizer can reach 19.27%, providing a new way to high-value utilization of industrial lignin.

[0009] In order to achieve the above object, the present invention is implemented through the following technical solutions: In a first aspect, the present invention provides a method for preparing a lignin-based slow-release nitrogen fertilizer, comprising the following steps: Lignin, phenol, water and sulfuric acid are mixed in proportion, heated, and pre-phenolized to obtain a phenolized lignin mixed solution; Acidic water is added to the phenolic lignin mixture to precipitate the phenolic lignin, followed by solid-liquid separation, and the solid is washed to neutrality and dried to obtain the phenolic lignin; Dissolve phenolic lignin in alkali solution, add arginine and formaldehyde, the mass ratio of phenolic lignin, arginine and formaldehyde is 1-5:10-30:20-35; react at 50-80°C for 1-5h; After the reaction is completed, the reaction mixture is dialyzed, and the liquid product is collected and dried to obtain the lignin-based slow-release nitrogen fertilizer.

[0010] In some embodiments, the alkali solution is a NaOH solution with a concentration of 0.1-0.5 mol / L.

[0011] In some embodiments, the lignin is prepared from hardwood kraft pulping black liquor through acid precipitation, purification, pH balancing, and rotary evaporation.

[0012] Preferably, the acid used in the acid precipitation process is sulfuric acid.

[0013] Preferably, the purification step comprises: dissolving the crude lignin obtained by acid precipitation in a mixture of dioxane and water, wherein the volume ratio of dioxane to water is 2500-3000:100-500; Then, in an inert atmosphere, at 80-95°C, react for 1-3 hours; After the reaction is completed, the solution is cooled and filtered to obtain a purified lignin solution.

[0014] Crude lignin contains some impurities, such as hemicellulose, cellulose, tannin, etc. Lignin dissolved in dioxane can be better separated from other impurities.

[0015] Water, as a polar solvent, enables the reaction to proceed under homogeneous or near-homogeneous conditions, which is beneficial to improving the reaction rate and reaction uniformity.

[0016] Heating can increase the reaction rate and help improve purification efficiency.

[0017] Preferably, the equilibrium pH value is adjusted to neutral pH value of the filtered lignin solution.

[0018] In some embodiments, during the pre-phenolization treatment, the mass ratio of lignin to phenol is 1:2-5.

[0019] Preferably, the temperature of the pre-phenolization treatment is 110-130° C., and the treatment time is 20-40 minutes.

[0020] In some embodiments, the pH value of the acidic water is 1.5-2.5; and the volume ratio of the phenolic lignin mixture to the acidic water is 1.5-2.5:1.

[0021] In some embodiments, the dialysis bag used for dialysis is a dialysis bag with an Mw of 1000.

[0022] In a second aspect, the present invention provides a lignin-based slow-release nitrogen fertilizer prepared by the preparation method.

[0023] The beneficial effects achieved by one or more embodiments of the present invention are as follows: (1) The present invention prepares high-purity lignin by chemical method. The preparation process is simple and the reaction conditions are mild, which is suitable for large-scale application.

[0024] (2) The present invention preliminarily modifies lignin through phenolization pretreatment. By adjusting the amount of phenolization reagent and reaction conditions, the directional preparation of phenolized lignin is achieved to the greatest extent possible. The chemical reactivity of the prepared phenolized lignin is significantly improved, and the content of reaction sites (i.e., specific locations on the lignin molecule that can chemically react with arginine) is increased from 5.79 mmol / g to 25.50 mmol / g.

[0025] (3) The present invention uses arginine as the amination reagent, formaldehyde as the catalyst, the reaction temperature is 75°C, and the reaction time is 3 hours. The lignin-based slow-release nitrogen fertilizer prepared by this method has a higher nitrogen content. DETAILED DESCRIPTION

[0026] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0027] The specific implementation of the present invention is further described below with reference to examples, but the implementation of the present invention is not limited to the scope of the examples.

[0028] The materials involved in the embodiments can all be purchased from the market.

[0029] The present invention has no special restrictions on the type and source of the broadleaf wood used in the kraft pulping black liquor. The following takes the kraft pulping black liquor of Acacia as an example. The relative density of the black liquor is 1.108 (g·cm -3 ), total solid content 25.4%, organic matter 15.32%, inorganic matter 10.00%.

[0030] Example 1 (1) Measure 2000 ml of acacia kraft pulping black liquor, adjust the pH value to 2 with sulfuric acid, and carry out acid precipitation. After acid precipitation, centrifuge to obtain crude lignin.

[0031] Weigh 150 g of crude lignin into a beaker, add 2700 ml of dioxane and 300 ml of deionized water to the beaker, and after the crude lignin is completely dissolved, transfer it to a 3000 ml three-necked flask and react at 87 °C for 2 h under a nitrogen atmosphere.

[0032] After the reaction is completed, the lignin solution is transferred to a beaker, cooled to room temperature, and then filtered. The filtered lignin solution is transferred to a beaker and 17.85 g of sodium bicarbonate is added to adjust the pH. The lignin solution is then transferred to a rotary evaporator and rotary evaporated at 60°C and 108 rpm for 30 minutes. After thorough washing until neutral, the solution is freeze-dried for 48 hours to obtain pure lignin.

[0033] (2) Weigh 1.0 g of the purified lignin obtained in step (1) and transfer it to a reaction vessel. Add 3.5 g of phenol, deionized water, and sulfuric acid to the reaction vessel, with a solid-to-liquid ratio of 1:10. React at 120°C for 30 min to obtain a phenolized lignin mixture with a volume of 40 ml.

[0034] (3) Add 20 ml of acidic deionized water (pH = 2) to the phenolic lignin mixture obtained in step (2).

[0035] (4) The mixture obtained in step (3) was filtered using a Buchner funnel, and the filter residue was washed with deionized water until neutral, and freeze-dried for 48 hours to obtain phenolic lignin.

[0036] (5) The phenolized lignin obtained in step (4) was dissolved in 20 ml of 0.4 mol / L NaOH solution, and then arginine and formaldehyde were added. The mass ratio of phenolized lignin to arginine and formaldehyde was 3:18:24. The reaction was carried out at a temperature of 60°C for 3 h.

[0037] (6) After the reaction is completed, the reaction mixture in step (5) is dialysis filtered using a dialysis bag with an Mw of 1000. The liquid product is collected and freeze-dried for 48 hours to obtain a lignin-based slow-release nitrogen fertilizer.

[0038] The nitrogen content of the lignin-based slow-release nitrogen fertilizer prepared under these conditions was 11.36%.

[0039] A soil column leaching experiment was used to investigate the nitrogen release behavior of lignin-based slow-release nitrogen fertilizer. Soil was collected from the surface layer of farmland (0 cm to 20 cm depth), and the soil was dried at room temperature for 7 days after removing plant roots.

[0040] Then, the soil was sieved with a 10-mesh sieve. 850 g of dry soil was then filled into the bottom of the PVC column (inner diameter = 9.5 cm, height = 25 cm) as the subsoil. The remaining dry soil (650 g) was thoroughly mixed with 10 g of lignin-based slow-release nitrogen fertilizer according to the designed soil bulk density (1.5 g / cm -3 ) is filled to the top of the PVC column. The equivalent dose is 100 mgN kg -1 Different treatments were used for dry soil (dry soil containing 100 mg N per kg was used to treat different soil layers in the soil column leaching experiment).

[0041] In addition, each soil column was covered with a certain amount of quartz sand to reduce interference. A blank experiment (CK) without any fertilizer was conducted under the same conditions for comparison. The entire experiment was conducted at room temperature, with water added as needed to maintain a soil moisture content of approximately 75%. After 1, 4, 7, 13, 19, 28, 48, and 60 days, 200 ml of deionized water was slowly added to each soil column, and the filtrate was collected in a 500 ml conical flask for determination of nitrogen leaching. (Two additional sets of eight soil columns were also set up, each with eight columns. The experimental data were averaged across the three sets to reduce error.)

[0042] Through soil column leaching experiments, it was measured that the nitrogen leaching amounts at 1, 4, 7, 13, 19, 28, 48 and 60 days were 0.01 mg, 0.05 mg, 0.08 mg, 0.10 mg, 0.12 mg, 0.20 mg, 0.22 mg and 0.42 mg respectively.

[0043] Example 2 (1) Measure 2000 ml of acacia kraft pulping black liquor, adjust the pH value to 2 with sulfuric acid, and carry out acid precipitation. After acid precipitation, centrifuge to obtain crude lignin.

[0044] Weigh 150 g of crude lignin into a beaker, add 2700 ml of dioxane and 300 ml of deionized water to the beaker, and after the crude lignin is completely dissolved, transfer it to a 3000 ml three-necked flask and react at 87 °C for 2 h under a nitrogen atmosphere.

[0045] After the reaction is completed, the lignin solution is transferred to a beaker, cooled to room temperature, and then filtered. The filtered lignin solution is transferred to a beaker and 17.85 g of sodium bicarbonate is added to adjust the pH. The lignin solution is then transferred to a rotary evaporator and rotary evaporated at 60°C and 108 rpm for 30 minutes. After thorough washing until neutral, the solution is freeze-dried for 48 hours to obtain pure lignin.

[0046] (2) Weigh 1.0 g of the purified lignin obtained in step (1) and transfer it to a reaction vessel. Add 3.5 g of phenol, deionized water, and sulfuric acid to the reaction vessel, with a solid-to-liquid ratio of 1:10. React at 120°C for 30 min to obtain a phenolized lignin mixture with a volume of 40 ml.

[0047] (3) Add 20 ml of acidic deionized water (pH = 2) to the phenolic lignin mixture obtained in step (2).

[0048] (4) Filter the mixture obtained in step (3) using a Buchner funnel, and wash the filter residue with deionized water until it becomes neutral. After freeze-drying for 48 hours, phenolic lignin is obtained.

[0049] (5) The phenolized lignin obtained in step (4) was dissolved in 20 ml of 0.4 mol / L NaOH solution, and then arginine and formaldehyde were added. The mass ratio of phenolized lignin to arginine and formaldehyde was 3:21:28. The reaction was carried out at a temperature of 60°C for 3 h.

[0050] (6) After the reaction is completed, the reaction mixture in step (5) is dialysis filtered using a dialysis bag with an Mw of 1000. The liquid product is collected and freeze-dried for 48 hours to obtain a lignin-based slow-release nitrogen fertilizer.

[0051] The nitrogen content of the lignin-based slow-release nitrogen fertilizer prepared under these conditions was 16.06%.

[0052] A soil column leaching experiment was used to investigate the nitrogen release behavior of lignin-based slow-release nitrogen fertilizer. Soil was collected from the surface layer of farmland (0 cm to 20 cm deep), plant roots removed, and dried at room temperature for 7 days. The soil was then sieved with a 10-mesh sieve. 850 g of dry soil was then filled into the bottom of a PVC column (inner diameter = 9.5 cm, height = 25 cm) as the subsoil. The remaining dry soil (650 g) was thoroughly mixed with the lignin-based slow-release nitrogen fertilizer and the designed soil bulk density (1.5 g / cm-3 ) is filled to the top of the PVC column. The equivalent dose is 100 mgN kg -1 Dry soil was treated differently. Furthermore, each soil column was covered with a certain amount of quartz sand to minimize interference. A blank experiment (CK) without any fertilizer was conducted under the same conditions for comparison. The entire experiment was conducted at room temperature, with water added as needed to maintain a soil moisture content of approximately 75%. After 1, 4, 7, 13, 19, 28, 48, and 60 days, 200 ml of deionized water was slowly added to the soil columns, and the filtrate was collected in a 500 ml conical flask for determination of nitrogen leaching.

[0053] Through soil column leaching experiments, it was measured that the nitrogen leaching amounts at 1, 4, 7, 13, 19, 28, 48 and 60 days were 0.07 mg, 0.16 mg, 0.20 mg, 0.24 mg, 0.30 mg, 0.33 mg, 0.45 mg and 0.52 mg respectively.

[0054] Example 3 (1) Measure 2000 ml of acacia kraft pulping black liquor, adjust the pH value to 2 with sulfuric acid, and carry out acid precipitation. After acid precipitation, centrifuge to obtain crude lignin.

[0055] Weigh 150 g of crude lignin into a beaker, add 2700 ml of dioxane and 300 ml of deionized water into the beaker, and after the crude lignin is completely dissolved, transfer it to a 3000 ml three-necked flask and react at 87 °C for 2 h under a nitrogen atmosphere.

[0056] After the reaction is completed, the lignin solution is transferred to a beaker, cooled to room temperature, and then filtered. The filtered lignin solution is transferred to a beaker and 17.85 g of sodium bicarbonate is added to adjust the pH. The lignin solution is then transferred to a rotary evaporator and rotary evaporated at 60°C and 108 rpm for 30 minutes. After thorough washing until neutral, the solution is freeze-dried for 48 hours to obtain pure lignin.

[0057] (2) Weigh 1.0 g of the lignin obtained in step (1) and transfer it to a reaction vessel. Add 3.5 g of phenol, deionized water, and sulfuric acid to the reaction vessel, with a solid-to-liquid ratio of 1:10. React at 120°C for 30 min to obtain a phenolized lignin mixture with a volume of 40 ml.

[0058] (3) Add 20 ml of acidic deionized water (pH = 2) to the phenolic lignin mixture obtained in step (2).

[0059] (4) Filter the mixture obtained in step (3) using a Buchner funnel, and wash the filter residue with deionized water until it becomes neutral. After freeze-drying for 48 hours, phenolic lignin is obtained.

[0060] (5) The phenolized lignin obtained in step (4) was dissolved in 20 ml of 0.4 mol / L NaOH solution, and then arginine and formaldehyde were added. The mass ratio of phenolized lignin to arginine and formaldehyde was 3:24:32. The reaction was carried out at 60 °C for 3 h.

[0061] (6) The reaction mixture in step (5) was dialysis filtered using a dialysis bag with an Mw of 1000. The liquid product was collected and freeze-dried for 48 h to obtain a lignin-based slow-release nitrogen fertilizer.

[0062] The nitrogen content of the lignin-based slow-release nitrogen fertilizer prepared under these conditions was 16.15%.

[0063] A soil column leaching experiment was used to investigate the nitrogen release behavior of lignin-based slow-release nitrogen fertilizer. Soil was collected from the surface layer of farmland (0 cm to 20 cm deep), and after removing the plant roots, it was dried at room temperature for 7 days. Then, the soil was sieved with a 10-mesh sieve. Subsequently, 850 g of dry soil was filled into the bottom of a PVC column (inner diameter = 9.5 cm, height = 25 cm) as the lower soil. The remaining dry soil (650 g) was fully mixed with the lignin-based slow-release nitrogen fertilizer and the designed soil bulk density (1.5 g / cm -3 ) is filled to the top of the PVC column. The equivalent dose is 100 mgN kg -1 Dry soil was treated differently. Furthermore, each soil column was covered with a certain amount of quartz sand to minimize interference. A blank experiment (CK) without any fertilizer was conducted under the same conditions for comparison. The entire experiment was conducted at room temperature, with water added as needed to maintain a soil moisture content of approximately 75%. After 1, 4, 7, 13, 19, 28, 48, and 60 days, 200 ml of deionized water was slowly added to the soil columns, and the filtrate was collected in a 500 ml conical flask for determination of nitrogen leaching.

[0064] Through soil column leaching experiments, it was measured that the nitrogen leaching amounts at 1, 4, 7, 13, 19, 28, 48 and 60 days were 0.06 mg, 0.13 mg, 0.15 mg, 0.20 mg, 0.28 mg, 0.30 mg, 0.33 mg and 0.45 mg respectively.

[0065] Example 4 (1) Measure 2000 ml of acacia kraft pulping black liquor, adjust the pH value to 2 with sulfuric acid, and carry out acid precipitation. After acid precipitation, centrifuge to obtain crude lignin.

[0066] Weigh 150 g of crude lignin into a beaker, add 2700 ml of dioxane and 300 ml of deionized water to the beaker, and after the crude lignin is completely dissolved, transfer it to a 3000 ml three-necked flask and react at 87 °C for 2 h under a nitrogen atmosphere.

[0067] After the reaction is completed, the lignin solution is transferred to a beaker, cooled to room temperature, and then filtered. The filtered lignin solution is transferred to a beaker and 17.85 g of sodium bicarbonate is added to adjust the pH. The lignin solution is then transferred to a rotary evaporator and rotary evaporated at 60°C and 108 rpm for 30 minutes. After thorough washing until neutral, the solution is freeze-dried for 48 hours to obtain pure lignin.

[0068] (2) Weigh 1.0 g of the lignin obtained in step (1) and transfer it to a reaction vessel. Add 3.5 g of phenol, deionized water, and sulfuric acid to the reaction vessel, with a solid-to-liquid ratio of 1:10. React at 120°C for 30 min to obtain a phenolized lignin mixture with a volume of 40 ml.

[0069] (3) Add 20 ml of acidic deionized water (pH = 2) to the phenolic lignin mixture obtained in step (2).

[0070] (4) Filter the mixture in (3) using a Buchner funnel, wash the filter residue with deionized water until neutral, and freeze-dry for 48 hours to obtain phenolic lignin.

[0071] (5) The phenolized lignin obtained in step (4) was dissolved in 20 ml of 0.4 mol / L NaOH solution, and then arginine and formaldehyde were added. The mass ratio of phenolized lignin to arginine and formaldehyde was 3:21:28. The reaction was carried out at a temperature of 75 °C for 3 h.

[0072] (6) After the reaction is completed, the reaction mixture in step (5) is dialysis filtered using a dialysis bag with an Mw of 1000. The liquid product is collected and freeze-dried for 48 hours to obtain a lignin-based slow-release nitrogen fertilizer.

[0073] The nitrogen content of the lignin-based slow-release nitrogen fertilizer prepared under these conditions was 19.2%.

[0074] A soil column leaching experiment was used to investigate the nitrogen release behavior of lignin-based slow-release nitrogen fertilizer. Soil was collected from the surface layer of farmland (0 cm to 20 cm deep), and after removing the plant roots, it was dried at room temperature for 7 days. Then, the soil was sieved with a 10-mesh sieve. Subsequently, 850 g of dry soil was filled into the bottom of a PVC column (inner diameter = 9.5 cm, height = 25 cm) as the lower soil. The remaining dry soil (650 g) was fully mixed with the lignin-based slow-release nitrogen fertilizer and the designed soil bulk density (1.5 g / cm -3) is filled to the top of the PVC column. The equivalent dose is 100 mgN kg -1 Dry soil was treated differently. Furthermore, each soil column was covered with a certain amount of quartz sand to minimize interference. A blank experiment (CK) without any fertilizer was conducted under the same conditions for comparison. The entire experiment was conducted at room temperature, with water added as needed to maintain a soil moisture content of approximately 75%. After 1, 4, 7, 13, 19, 28, 48, and 60 days, 200 ml of deionized water was slowly added to the soil columns, and the filtrate was collected in a 500 ml conical flask for determination of nitrogen leaching.

[0075] Through soil column leaching experiments, it was measured that the nitrogen leaching amounts at 1, 4, 7, 13, 19, 28, 48 and 60 days were 0.05 mg, 0.12 mg, 0.13 mg, 0.19 mg, 0.22 mg, 0.34 mg, 0.64 mg and 0.72 mg respectively.

[0076] Example 5 (1) Measure 2000 ml of acacia kraft pulping black liquor, adjust the pH value to 2 with sulfuric acid, and carry out acid precipitation. After acid precipitation, centrifuge to obtain crude lignin.

[0077] Weigh 150 g of crude lignin into a beaker, add 2700 ml of dioxane and 300 ml of deionized water into the beaker, and after the crude lignin is completely dissolved, transfer it to a 3000 ml three-necked flask and react at 87 °C for 2 h under a nitrogen atmosphere.

[0078] After the reaction is completed, the lignin solution is transferred to a beaker, cooled to room temperature, and then filtered. The filtered lignin solution is transferred to a beaker and 17.85 g of sodium bicarbonate is added to adjust the pH. The lignin solution is then transferred to a rotary evaporator and rotary evaporated at 60°C and 108 rpm for 30 minutes. The solution is thoroughly washed until neutral and freeze-dried for 48 hours to obtain lignin.

[0079] (2) Weigh 1.0 g of the purified lignin obtained in step (1) and transfer it to a reaction vessel. Add 3.5 g of phenol, deionized water, and sulfuric acid to the reaction vessel, with a solid-to-liquid ratio of 1:10. React at 120°C for 30 min to obtain a phenolized lignin mixture with a volume of 40 ml.

[0080] (3) Add 20 ml of acidic deionized water (pH = 2) to the phenolic lignin mixture obtained in step (2).

[0081] (4) Filter the mixture from step (3) using a Buchner funnel and wash the residue with deionized water until it is neutral. After freeze-drying for 48 hours, phenolic lignin is obtained.

[0082] (5) The phenolized lignin obtained in step (4) was dissolved in 20 ml of 0.4 mol / L NaOH solution, and then arginine and formaldehyde were added. The mass ratio of phenolized lignin to arginine and formaldehyde was 3:21:28. The reaction was carried out at a temperature of 90 °C for 3 h.

[0083] (6) The reaction mixture in step (5) was dialysis filtered using a dialysis bag with an Mw of 1000. The liquid product was collected and freeze-dried for 48 h to obtain a lignin-based slow-release nitrogen fertilizer.

[0084] The nitrogen content of the lignin-based slow-release nitrogen fertilizer prepared under these conditions was 19.27%.

[0085] A soil column leaching experiment was used to investigate the nitrogen release behavior of lignin-based slow-release nitrogen fertilizer. Soil was collected from the surface layer of farmland (0 cm to 20 cm deep), and after removing the plant roots, it was dried at room temperature for 7 days. Then, the soil was sieved with a 10-mesh sieve. Subsequently, 850 g of dry soil was filled into the bottom of a PVC column (inner diameter = 9.5 cm, height = 25 cm) as the lower soil. The remaining dry soil (650 g) was fully mixed with the lignin-based slow-release nitrogen fertilizer and the designed soil bulk density (1.5 g / cm -3 ) is filled to the top of the PVC column. The equivalent dose is 100 mgN kg -1 Dry soil was treated differently. Furthermore, each soil column was covered with a certain amount of quartz sand to minimize interference. A blank experiment (CK) without any fertilizer was conducted under the same conditions for comparison. The entire experiment was conducted at room temperature, with water added as needed to maintain a soil moisture content of approximately 75%. After 1, 4, 7, 13, 19, 28, 48, and 60 days, 200 ml of deionized water was slowly added to the soil columns, and the filtrate was collected in a 500 ml conical flask for determination of nitrogen leaching.

[0086] Through soil column leaching experiments, it was measured that the nitrogen leaching amounts at 1, 4, 7, 13, 19, 28, 48 and 60 days were 0.08 mg, 0.15 mg, 0.18 mg, 0.25 mg, 0.32 mg, 0.44 mg, 0.64 mg and 0.78 mg respectively.

[0087] Example 6 (1) Measure 2000 ml of acacia kraft pulping black liquor, adjust the pH value to 2 with sulfuric acid, and carry out acid precipitation. After acid precipitation, centrifuge to obtain crude lignin.

[0088] Weigh 150 g of crude lignin into a beaker, add 2700 ml of dioxane and 300 ml of deionized water to the beaker, and after the crude lignin is completely dissolved, transfer it to a 3000 ml three-necked flask and react at 87 °C for 2 h under a nitrogen atmosphere.

[0089] After the reaction is completed, the lignin solution is transferred to a beaker, cooled to room temperature, and then filtered. The filtered lignin solution is transferred to a beaker and 17.85 g of sodium bicarbonate is added to adjust the pH. The lignin solution is then transferred to a rotary evaporator and rotary evaporated at 60°C and 108 rpm for 30 minutes. The solution is thoroughly washed until neutral and freeze-dried for 48 hours to obtain lignin.

[0090] (2) Weigh 1.0 g of the purified lignin obtained in step (1) and transfer it to a reaction vessel. Add 3.5 g of phenol, deionized water, and sulfuric acid to the reaction vessel, with a solid-to-liquid ratio of 1:10. React at 120°C for 30 min to obtain a phenolized lignin mixture with a volume of 40 ml.

[0091] (3) Add 20 ml of acidic deionized water (pH = 2) to the phenolic lignin mixture obtained in step (2).

[0092] (4) The mixture obtained in step (3) was filtered using a Buchner funnel, and the filter residue was washed with deionized water until neutral, and freeze-dried for 48 hours to obtain phenolic lignin.

[0093] (5) The phenolized lignin obtained in step (4) was dissolved in 20 ml of 0.4 mol / L alkaline solution, and then arginine and formaldehyde were added. The mass ratio of phenolized lignin to arginine and formaldehyde was 3:21:28. The reaction was carried out at a temperature of 75°C for 4 h.

[0094] (6) After the reaction is completed, the reaction mixture in step (5) is dialysis filtered using a dialysis bag with an Mw of 1000. The liquid product is collected and freeze-dried for 48 hours to obtain a lignin-based slow-release nitrogen fertilizer.

[0095] The nitrogen content of the lignin-based slow-release nitrogen fertilizer prepared under these conditions was 17.32%.

[0096] A soil column leaching experiment was used to investigate the nitrogen release behavior of lignin-based slow-release nitrogen fertilizer. Soil was collected from the surface layer of farmland (0 cm to 20 cm deep), and after removing the plant roots, it was dried at room temperature for 7 days. Then, the soil was sieved with a 10-mesh sieve. Subsequently, 850 g of dry soil was filled into the bottom of a PVC column (inner diameter = 9.5 cm, height = 25 cm) as the lower soil. The remaining dry soil (650 g) was fully mixed with the lignin-based slow-release nitrogen fertilizer and the designed soil bulk density (1.5 g / cm -3) is filled to the top of the PVC column. The equivalent dose is 100 mgN kg -1 Dry soil was treated differently. Furthermore, each soil column was covered with a certain amount of quartz sand to minimize interference. A blank experiment (CK) without any fertilizer was conducted under the same conditions for comparison. The entire experiment was conducted at room temperature, with water added as needed to maintain a soil moisture content of approximately 75%. After 1, 4, 7, 13, 19, 28, 48, and 60 days, 200 ml of deionized water was slowly added to the soil columns, and the filtrate was collected in a 500 ml conical flask for determination of nitrogen leaching.

[0097] Through soil column leaching experiments, it was measured that the nitrogen leaching amounts at 1, 4, 7, 13, 19, 28, 48 and 60 days were 0.03 mg, 0.10 mg, 0.12 mg, 0.18 mg, 0.25 mg, 0.33 mg, 0.48 mg and 0.53 mg respectively.

[0098] Comparative Example 1 The difference from Example 1 is that the pre-phenolization steps of step (2), step (3) and step (4) are omitted, and the rest are the same as Example 1. The details are as follows: (1) Measure 2000 ml of acacia kraft pulping black liquor, adjust the pH value to 2 with sulfuric acid, and carry out acid precipitation. After acid precipitation, centrifuge to obtain crude lignin.

[0099] Weigh 150 g of crude lignin into a beaker, add 2700 ml of dioxane and 300 ml of deionized water to the beaker, and after the crude lignin is completely dissolved, transfer it to a 3000 ml three-necked flask and react at 87 °C for 2 h under a nitrogen atmosphere.

[0100] After the reaction is completed, the lignin solution is transferred to a beaker, cooled to room temperature, and then filtered. The filtered lignin solution is transferred to a beaker and 17.85 g of sodium bicarbonate is added to adjust the pH. The lignin solution is then transferred to a rotary evaporator and rotary evaporated at 60°C and 108 rpm for 30 minutes. The solution is thoroughly washed until neutral and freeze-dried for 48 hours to obtain lignin.

[0101] (2) The lignin obtained in step (1) was dissolved in 20 ml of 0.4 mol / L alkaline solution, and then arginine and formaldehyde were added. The mass ratio of lignin to arginine and formaldehyde was 3:18:24. The reaction was carried out at a temperature of 60°C for 3 h.

[0102] (3) After the reaction is completed, the reaction mixture in (2) is dialysis filtered using a dialysis bag with an Mw of 1000. The liquid product is collected and freeze-dried for 48 hours to obtain a lignin-based slow-release nitrogen fertilizer.

[0103] The nitrogen content of the lignin-based slow-release nitrogen fertilizer prepared under these conditions is 8.21%. A soil column leaching experiment was used to investigate the nitrogen release behavior of lignin-based slow-release nitrogen fertilizer. Soil was collected from the surface layer of farmland (0 cm to 20 cm deep), and after removing the plant roots, it was dried at room temperature for 7 days. Then, the soil was sieved with a 10-mesh sieve. Subsequently, 850 g of dry soil was filled into the bottom of a PVC column (inner diameter = 9.5 cm, height = 25 cm) as the lower soil. The remaining dry soil (650 g) was fully mixed with the lignin-based slow-release nitrogen fertilizer and the designed soil bulk density (1.5 g / cm -3 ) is filled to the top of the PVC column. The equivalent dose is 100 mgN kg -1 Dry soil was treated differently. Furthermore, each soil column was covered with a certain amount of quartz sand to minimize interference. A blank experiment (CK) without any fertilizer was conducted under the same conditions for comparison. The entire experiment was conducted at room temperature, with water added as needed to maintain a soil moisture content of approximately 75%. After 1, 4, 7, 13, 19, 28, 48, and 60 days, 200 ml of deionized water was slowly added to the soil columns, and the filtrate was collected in a 500 ml conical flask for determination of nitrogen leaching.

[0104] Through soil column leaching experiments, it was measured that the nitrogen leaching amounts at 1, 4, 7, 13, 19, 28, 48 and 60 days were 0.02 mg, 0.08 mg, 0.12 mg, 0.14 mg, 0.18 mg, 0.24 mg, 0.26 mg and 0.28 mg respectively.

[0105] Comparative Example 2 The difference from Example 2 is that the pre-phenolization steps of step (2), step (3) and step (4) are omitted, and the rest are the same as Example 1. The details are as follows: (1) Measure 2000 ml of acacia kraft pulping black liquor, adjust the pH value to 2 with sulfuric acid, and carry out acid precipitation. After acid precipitation, centrifuge to obtain crude lignin.

[0106] Weigh 150 g of crude lignin into a beaker, add 2700 ml of dioxane and 300 ml of deionized water to the beaker, and after the crude lignin is completely dissolved, transfer it to a 3000 ml three-necked flask and react at 87 °C for 2 h under a nitrogen atmosphere.

[0107] After the reaction is completed, the lignin solution is transferred to a beaker, cooled to room temperature, and then filtered. The filtered lignin solution is transferred to a beaker and 17.85 g of sodium bicarbonate is added to adjust the pH. The lignin solution is then transferred to a rotary evaporator and rotary evaporated at 60°C and 108 rpm for 30 minutes. After thorough washing until neutral, the solution is freeze-dried for 48 hours to obtain pure lignin.

[0108] (2) The lignin obtained in step (1) was dissolved in 20 ml of 0.4 mol / L alkaline solution, and then a certain amount of arginine and formaldehyde were added, with the mass ratio of lignin to arginine and formaldehyde being 3:21:28. The reaction was carried out at 60 °C for 3 h.

[0109] (3) The reaction mixture in (2) was dialysis filtered using a dialysis bag with a Mw of 1000. The liquid product was collected and freeze-dried for 48 h to obtain a lignin-based slow-release nitrogen fertilizer.

[0110] The nitrogen content of the lignin-based slow-release nitrogen fertilizer prepared under these conditions was 12.32%.

[0111] A soil column leaching experiment was used to investigate the nitrogen release behavior of lignin-based slow-release nitrogen fertilizer. Soil was collected from the surface layer of farmland (0 cm to 20 cm deep), and after removing the plant roots, it was dried at room temperature for 7 days. Then, the soil was sieved with a 10-mesh sieve. Subsequently, 850 g of dry soil was filled into the bottom of a PVC column (inner diameter = 9.5 cm, height = 25 cm) as the lower soil. The remaining dry soil (650 g) was fully mixed with the lignin-based slow-release nitrogen fertilizer and the designed soil bulk density (1.5 g / cm -3 ) is filled to the top of the PVC column. The equivalent dose is 100 mgN kg -1 Dry soil was treated differently. Furthermore, each soil column was covered with a certain amount of quartz sand to minimize interference. A blank experiment (CK) without any fertilizer was conducted under the same conditions for comparison. The entire experiment was conducted at room temperature, with water added as needed to maintain a soil moisture content of approximately 75%. After 1, 4, 7, 13, 19, 28, 48, and 60 days, 200 ml of deionized water was slowly added to the soil columns, and the filtrate was collected in a 500 ml conical flask for determination of nitrogen leaching.

[0112] Through soil column leaching experiments, it was measured that the nitrogen leaching amounts at 1, 4, 7, 13, 19, 28, 48 and 60 days were 0.04 mg, 0.06 mg, 0.12 mg, 0.15 mg, 0.20 mg, 0.27 mg, 0.31 mg and 0.35 mg respectively.

[0113] Comparative Example 3 The difference from Example 3 is that the pre-phenolization steps of step (2), step (3) and step (4) are omitted, and the rest are the same as Example 1. The details are as follows: (1) Measure 2000 ml of acacia kraft pulping black liquor, adjust the pH value to 2 with sulfuric acid, and carry out acid precipitation. After acid precipitation, centrifuge to obtain crude lignin.

[0114] Weigh 150 g of crude lignin into a beaker, add 2700 ml of dioxane and 300 ml of deionized water into the beaker, and after the crude lignin is completely dissolved, transfer it to a 3000 ml three-necked flask and react at 87 °C for 2 h under a nitrogen atmosphere.

[0115] After the reaction is complete, the lignin solution is transferred to a beaker, cooled to room temperature, and then filtered. The filtered lignin solution is transferred to a beaker, and 17.85 g of sodium bicarbonate is added to adjust the pH. The lignin solution is then transferred to a rotary evaporator and rotary evaporated at 60°C and 108 rpm for 30 minutes. The solution is thoroughly washed until neutral and freeze-dried for 48 hours to obtain lignin.

[0116] (2) The lignin obtained in step (1) was dissolved in 20 ml of 0.4 mol / L alkaline solution, and then arginine and formaldehyde were added. The mass ratio of lignin to arginine and formaldehyde was 3:24:32. The reaction was carried out at 60 °C for 3 h.

[0117] (3) Using a dialysis bag with a Mw of 1000, the reaction mixture in (2) was dialysis filtered. The liquid product was collected and freeze-dried for 48 h to obtain a lignin-based slow-release nitrogen fertilizer.

[0118] The nitrogen content of the lignin-based slow-release nitrogen fertilizer prepared under these conditions was 12.08%.

[0119] A soil column leaching experiment was used to investigate the nitrogen release behavior of lignin-based slow-release nitrogen fertilizer. Soil was collected from the surface layer of farmland (0 cm to 20 cm deep), and after removing the plant roots, it was dried at room temperature for 7 days. Then, the soil was sieved with a 10-mesh sieve. Subsequently, 850 g of dry soil was filled into the bottom of a PVC column (inner diameter = 9.5 cm, height = 25 cm) as the lower soil. The remaining dry soil (650 g) was fully mixed with the lignin-based slow-release nitrogen fertilizer and the designed soil bulk density (1.5 g / cm -3 ) is filled to the top of the PVC column. The equivalent dose is 100 mgN kg -1Dry soil was treated differently. Furthermore, each soil column was covered with a certain amount of quartz sand to minimize interference. A blank experiment (CK) without any fertilizer was conducted under the same conditions for comparison. The entire experiment was conducted at room temperature, with water added as needed to maintain a soil moisture content of approximately 75%. After 1, 4, 7, 13, 19, 28, 48, and 60 days, 200 ml of deionized water was slowly added to the soil columns, and the filtrate was collected in a 500 ml conical flask for determination of nitrogen leaching.

[0120] Through soil column leaching experiments, it was measured that the nitrogen leaching amounts at 1, 4, 7, 13, 19, 28, 48 and 60 days were 0.07 mg, 0.11 mg, 0.15 mg, 0.17 mg, 0.22 mg, 0.24 mg, 0.32 mg and 0.38 mg respectively.

[0121] Comparative Example 4 The difference from Example 4 is that the pre-phenolization steps of step (2), step (3) and step (4) are omitted, and the rest are the same as Example 1. The details are as follows: (1) Measure 2000 ml of acacia kraft pulping black liquor, adjust the pH value to 2 with sulfuric acid, and carry out acid precipitation. After acid precipitation, centrifuge to obtain crude lignin.

[0122] Weigh 150 g of crude lignin into a beaker, add 2700 ml of dioxane and 300 ml of deionized water to the beaker, and after the crude lignin is completely dissolved, transfer it to a 3000 ml three-necked flask and react at 87 °C for 2 h under a nitrogen atmosphere.

[0123] After the reaction is complete, the lignin solution is transferred to a beaker, cooled to room temperature, and then filtered. The filtered lignin solution is transferred to a beaker and 17.85 g of sodium bicarbonate is added to adjust the pH. The lignin solution is then transferred to a rotary evaporator and rotary evaporated at 60°C and 108 rpm for 30 minutes. The solution is thoroughly washed until neutral and freeze-dried for 48 hours to obtain pure lignin.

[0124] (2) The lignin obtained in step (1) was dissolved in 20 ml of 0.4 mol / L alkaline solution, and then arginine and formaldehyde were added. The mass ratio of lignin to arginine and formaldehyde was 3:21:28. The reaction was carried out at 75 °C for 3 h.

[0125] (3) Using a dialysis bag with a Mw of 1000, the reaction mixture in (2) was dialysis filtered. The liquid product was collected and freeze-dried for 48 h to obtain a lignin-based slow-release nitrogen fertilizer.

[0126] The nitrogen content of the lignin-based slow-release nitrogen fertilizer prepared under these conditions was 16.78%.

[0127] A soil column leaching experiment was used to investigate the nitrogen release behavior of lignin-based slow-release nitrogen fertilizer. Soil was collected from the surface layer of farmland (0 cm to 20 cm deep), and after removing the plant roots, it was dried at room temperature for 7 days. Then, the soil was sieved with a 10-mesh sieve. Subsequently, 850 g of dry soil was filled into the bottom of a PVC column (inner diameter = 9.5 cm, height = 25 cm) as the lower soil. The remaining dry soil (650 g) was fully mixed with the lignin-based slow-release nitrogen fertilizer and the designed soil bulk density (1.5 g / cm -3 ) is filled to the top of the PVC column. The equivalent dose is 100 mgN kg -1 Dry soil was treated differently. Furthermore, each soil column was covered with a certain amount of quartz sand to minimize interference. A blank experiment (CK) without any fertilizer was conducted under the same conditions for comparison. The entire experiment was conducted at room temperature, with water added as needed to maintain a soil moisture content of approximately 75%. After 1, 4, 7, 13, 19, 28, 48, and 60 days, 200 ml of deionized water was slowly added to the soil columns, and the filtrate was collected in a 500 ml conical flask for determination of nitrogen leaching.

[0128] Through soil column leaching experiments, it was measured that the nitrogen leaching amounts at 1, 4, 7, 13, 19, 28, 48 and 60 days were 0.09 mg, 0.15 mg, 0.16 mg, 0.19 mg, 0.32 mg, 0.46 mg, 0.52 mg and 0.61 mg respectively.

[0129] Comparative Example 5 The difference from Example 5 is that the pre-phenolization steps of step (2), step (3) and step (4) are omitted, and the rest are the same as Example 1. The details are as follows: (1) Measure 2000 ml of acacia kraft pulping black liquor, adjust the pH value to 2 with sulfuric acid, and carry out acid precipitation. After acid precipitation, centrifuge to obtain crude lignin.

[0130] Weigh 150 g of crude lignin into a beaker, add 2700 ml of dioxane and 300 ml of deionized water into the beaker, and after the crude lignin is completely dissolved, transfer it to a 3000 ml three-necked flask and react at 87 °C for 2 h under a nitrogen atmosphere.

[0131] After the reaction is completed, the lignin solution is transferred to a beaker, cooled to room temperature, and then filtered. The filtered lignin solution is transferred to a beaker and 17.85 g of sodium bicarbonate is added to adjust the pH. The lignin solution is then transferred to a rotary evaporator and rotary evaporated at 60°C and 108 rpm for 30 minutes. The solution is thoroughly washed until neutral and freeze-dried for 48 hours to obtain lignin.

[0132] (2) The lignin obtained in step (1) was dissolved in 20 ml of 0.4 mol / L alkaline solution, and then a certain amount of arginine and formaldehyde were added, with the mass ratio of lignin to arginine and formaldehyde being 3:21:28. The reaction was carried out at 90 °C for 3 h.

[0133] (3) Using a dialysis bag with a Mw of 1000, the reaction mixture in (2) was dialysis filtered. The liquid product was collected and freeze-dried for 48 h to obtain a lignin-based slow-release nitrogen fertilizer.

[0134] The nitrogen content of the lignin-based slow-release nitrogen fertilizer prepared under these conditions was 16.92%.

[0135] A soil column leaching experiment was used to investigate the nitrogen release behavior of lignin-based slow-release nitrogen fertilizer. Soil was collected from the surface layer of farmland (0 cm to 20 cm deep), and after removing the plant roots, it was dried at room temperature for 7 days. Then, the soil was sieved with a 10-mesh sieve. Subsequently, 850 g of dry soil was filled into the bottom of a PVC column (inner diameter = 9.5 cm, height = 25 cm) as the lower soil. The remaining dry soil (650 g) was fully mixed with the lignin-based slow-release nitrogen fertilizer and the designed soil bulk density (1.5 g / cm -3 ) is filled to the top of the PVC column. The equivalent dose is 100 mgN kg -1 Dry soil was treated differently. Furthermore, each soil column was covered with a certain amount of quartz sand to minimize interference. A blank experiment (CK) without any fertilizer was conducted under the same conditions for comparison. The entire experiment was conducted at room temperature, with water added as needed to maintain a soil moisture content of approximately 75%. After 1, 4, 7, 13, 19, 28, 48, and 60 days, 200 ml of deionized water was slowly added to the soil columns, and the filtrate was collected in a 500 ml conical flask for determination of nitrogen leaching.

[0136] Through soil column leaching experiments, it was measured that the nitrogen leaching amounts at 1, 4, 7, 13, 19, 28, 48 and 60 days were 0.10 mg, 0.15 mg, 0.18 mg, 0.26 mg, 0.33 mg, 0.46 mg, 0.55 mg and 0.65 mg respectively.

[0137] Comparative Example 6 The difference from Example 6 is that the pre-phenolization steps of step (2), step (3) and step (4) are omitted, and the rest are the same as Example 1. The details are as follows: (1) Measure 2000 ml of acacia kraft pulping black liquor, adjust the pH value to 2 with sulfuric acid, and carry out acid precipitation. After acid precipitation, centrifuge to obtain crude lignin.

[0138] Weigh 150 g of crude lignin into a beaker, add 2700 ml of dioxane and 300 ml of deionized water to the beaker, and after the crude lignin is completely dissolved, transfer it to a 3000 ml three-necked flask and react at 87 °C for 2 h under a nitrogen atmosphere.

[0139] After the reaction is completed, the lignin solution is transferred to a beaker, cooled to room temperature, and then filtered. The filtered lignin solution is transferred to a beaker and 17.85 g of sodium bicarbonate is added to adjust the pH. The lignin solution is then transferred to a rotary evaporator and rotary evaporated at 60°C and 108 rpm for 30 minutes. The solution is thoroughly washed until neutral and freeze-dried for 48 hours to obtain lignin.

[0140] (2) The lignin obtained in step (1) was dissolved in 20 ml of 0.4 mol / L alkaline solution, and then a certain amount of arginine and formaldehyde were added, with the mass ratio of lignin to arginine and formaldehyde being 3:21:28. The reaction was carried out at 75 °C for 4 h.

[0141] (3) Using a dialysis bag with a Mw of 1000, the reaction mixture in (2) was dialysis filtered. The liquid product was collected and freeze-dried for 48 h to obtain a lignin-based slow-release nitrogen fertilizer.

[0142] The nitrogen content of the lignin-based slow-release nitrogen fertilizer prepared under these conditions was 14.45%.

[0143] A soil column leaching experiment was used to investigate the nitrogen release behavior of lignin-based slow-release nitrogen fertilizer. Soil was collected from the surface layer of farmland (0 cm to 20 cm deep), and after removing the plant roots, it was dried at room temperature for 7 days. Then, the soil was sieved with a 10-mesh sieve. Subsequently, 850 g of dry soil was filled into the bottom of a PVC column (inner diameter = 9.5 cm, height = 25 cm) as the lower soil. The remaining dry soil (650 g) was fully mixed with the lignin-based slow-release nitrogen fertilizer and the designed soil bulk density (1.5 g / cm -3 ) is filled to the top of the PVC column. The equivalent dose is 100 mgN kg -1 Dry soil was treated differently. Furthermore, each soil column was covered with a certain amount of quartz sand to minimize interference. A blank experiment (CK) without any fertilizer was conducted under the same conditions for comparison. The entire experiment was conducted at room temperature, with water added as needed to maintain a soil moisture content of approximately 75%. After 1, 4, 7, 13, 19, 28, 48, and 60 days, 200 ml of deionized water was slowly added to the soil columns, and the filtrate was collected in a 500 ml conical flask for determination of nitrogen leaching.

[0144] Through soil column leaching experiments, it was measured that the nitrogen leaching amounts at 1, 4, 7, 13, 19, 28, 48 and 60 days were 0.04 mg, 0.10 mg, 0.15 mg, 0.22 mg, 0.30 mg, 0.37 mg, 0.46 mg and 0.55 mg respectively.

[0145] Comparative Example 7 The difference from Example 1 is that the arginine in Example 1 is replaced by dimethylamine, and the rest is the same as Example 1.

[0146] The nitrogen content of the lignin-based slow-release nitrogen fertilizer prepared under these conditions was 7.38%.

[0147] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a lignin-based slow-release nitrogen fertilizer, characterized in that: The steps include: Lignin, phenol, water and sulfuric acid are mixed in proportion, heated, and pre-phenolized to obtain a phenolized lignin mixed solution; Acidic water is added to the phenolic lignin mixed solution, followed by solid-liquid separation, and the solid is washed to neutrality and dried to obtain phenolic lignin; Dissolve phenolic lignin in alkali solution, add arginine and formaldehyde, the mass ratio of phenolic lignin, arginine and formaldehyde is 1-5:10-30:20-35; react at 50-80°C for 1-5h; After the reaction is completed, the reaction mixture is dialyzed, and the liquid product is collected and dried to obtain the lignin-based slow-release nitrogen fertilizer.

2. The method for preparing a lignin-based slow-release nitrogen fertilizer according to claim 1, wherein: The alkali solution is a NaOH solution with a concentration of 0.1-0.5 mol / L.

3. The method for preparing the lignin-based slow-release nitrogen fertilizer according to claim 1, wherein: The lignin is prepared by acid precipitation, purification, pH balancing and rotary evaporation of black liquor from hardwood kraft pulping; Preferably, the acid used in the acid precipitation process is sulfuric acid.

4. The method for preparing the lignin-based slow-release nitrogen fertilizer according to claim 3, wherein: The purification step comprises: dissolving the crude lignin obtained by acid precipitation in a mixture of dioxane and water, wherein the volume ratio of dioxane to water is 2500-3000:100-500; Then, in an inert atmosphere, at 80-95°C, react for 1-3 hours; After the reaction is completed, the solution is cooled and filtered to obtain a purified lignin solution.

5. The method for preparing the lignin-based slow-release nitrogen fertilizer according to claim 3, wherein: The equilibrium pH value is to adjust the pH value of the filtered lignin solution to neutral.

6. The method for preparing the lignin-based slow-release nitrogen fertilizer according to claim 1, wherein: During the pre-phenolization treatment, the mass ratio of lignin to phenol is 1:2-5.

7. The method for preparing the lignin-based slow-release nitrogen fertilizer according to claim 1, wherein: The temperature of the pre-phenolization treatment is 110-130°C, and the treatment time is 20-40 minutes.

8. The method for preparing the lignin-based slow-release nitrogen fertilizer according to claim 1, wherein: The pH value of the acidic water is 1.5-2.5; the volume ratio of the phenolic lignin mixed liquid to the acidic water is 1.5-2.5:

1.

9. The method for preparing the lignin-based slow-release nitrogen fertilizer according to claim 1, wherein: The dialysis bag used in the dialysis is a dialysis bag with an Mw of 1000.

10. A lignin-based slow-release nitrogen fertilizer, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.