High-activity carboxymethylated water-soluble lignin potassium fertilizer and preparation method thereof

Abstract

The application discloses a high-activity carboxymethylated water-soluble lignin potassium fertilizer and a preparation method thereof, and belongs to the technical field of high-value utilization of biomass resources. The method uses lignin as raw material, adopts potassium hydroxide instead of traditional sodium hydroxide as alkalization medium, and adds acetic anhydride under inert atmosphere; then, etherification reaction is carried out with monochloroacetic acid. After the reaction is completed, dilute ammonia water is added, and pH is adjusted, solid-liquid separation and drying are carried out to obtain the high-water-solubility carboxymethylated lignin potassium fertilizer. The application can efficiently introduce carboxymethyl groups to improve water solubility, and the obtained product has double functions of potassium fertilizer supply and plant growth regulation, and provides a green and efficient technical path for high-value conversion of lignin into efficient green agricultural fertilizer.

Description

Technical Field

[0001] This invention belongs to the field of high-value utilization technology of biomass resources, specifically relating to a chemical modification method of lignin and the resulting product, especially a highly active carboxymethylated water-soluble lignin potassium fertilizer and its preparation method. Background Technology

[0002] Lignin, as the second largest renewable organic resource in nature, faces the core challenge of efficient and high-value utilization in the field of biomass refining. With the development of the biofuel and bio-based chemical industries, biorefining processes, exemplified by cellulosic ethanol, generate large amounts of enzymatic hydrolysis residues. These residues are rich in unused lignin, representing a new and high-purity source of lignin. Compared to traditional alkali lignin from papermaking black liquor, enzymatic hydrolysis residue lignin, having not undergone strong alkali cooking, retains a more complete natural structure and abundant reaction sites. However, its high molecular weight and complex cross-linking structure also lead to poor solubility and low reaction uniformity, limiting its direct application. Chemically modifying the lignin in enzymatic hydrolysis residues to transform it into water-soluble functional materials is a key step in achieving full-component utilization and improving process economy. Carboxymethylation is an effective means of improving lignin's water solubility and introducing functional groups. By introducing hydrophilic carboxymethyl groups onto the benzene rings and side chains of lignin, it can be transformed into anionic polymers with good water solubility, chelation, and dispersibility. Modified lignins of this type can serve as highly efficient fertilizer synergists and soil conditioners in agriculture. Their carboxyl and phenolic hydroxyl groups effectively complex micronutrients, preventing nutrient fixation and possessing certain plant growth-stimulating activity. However, existing carboxymethylation modification processes typically use sodium hydroxide as an alkalizing agent and conduct etherification reactions under strongly alkaline conditions (pH>12) and relatively high temperatures (80-95℃). While this strongly alkaline system is highly effective in promoting lignin dissolution and introducing carboxyl groups, it irreversibly destroys the naturally occurring phenolic hydroxyl structure in the lignin molecule, leading to oxidation or condensation reactions and significantly reducing the phenolic hydroxyl content of the product. Phenolic hydroxyl groups are key functional groups for lignin to exert its antioxidant, stress-resistant, and plant growth-promoting physiological activities. Their loss means that while traditional carboxymethylated lignin has increased water solubility, it loses the inherent biostimulant function of lignin, limiting its potential application as a multifunctional fertilizer synergist in green agriculture.

[0003] To address the aforementioned problems in existing technologies, this invention proposes an improved carboxymethylation modification method. This method uses KOH as an alkalizing agent to modify lignin through carboxymethylation, and introduces acetic anhydride during the alkalization stage. After the etherification reaction, dilute ammonia is added to prepare a lignin potassium fertilizer with high phenolic hydroxyl activity. This product simultaneously possesses the functions of a water-soluble lignin organic chelate carrier and potassium fertilizer nutritional efficacy, while retaining the natural biostimulating activity of lignin. This achieves integrated synthesis of lignin modification and quality improvement with fertilizer nutritional enhancement, opening up a new technological direction with greater application value and market competitiveness for the high-value utilization of lignin resources. Summary of the Invention

[0004] The purpose of this invention is to overcome the defect of strong alkali system destroying the natural phenolic hydroxyl structure in the existing lignin carboxymethylation modification process, and to provide a highly active carboxymethylated water-soluble lignin potassium fertilizer and its preparation method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A highly active carboxymethylated water-soluble lignin potassium fertilizer is prepared by the following method: lignin raw material is mixed with potassium hydroxide and acetic anhydride, and then alkalized and dissolved under an inert atmosphere; monochloroacetic acid is added to the resulting alkalized lignin solution to carry out an etherification reaction; after the reaction is completed, dilute ammonia water is added, and then the pH is adjusted. After solid-liquid separation and drying, the lignin potassium fertilizer with dual functions of potassium fertilizer supply and plant growth regulation is obtained.

[0007] The mass ratio of the lignin raw material, potassium hydroxide and monochloroacetic acid is 1:(0.2-0.5):(0.2-0.5); the pH is adjusted to 5.5-6.5.

[0008] A method for preparing a highly active carboxymethylated water-soluble lignin potassium fertilizer includes the following steps:

[0009] S1. Alkali dissolution: Mix the lignin raw material, alkali and the first portion of deionized water, and add acetic anhydride. Stir at 60-90 °C for 20-40 min under an inert gas atmosphere to fully dissolve and activate the lignin, and obtain a homogeneous alkalized lignin solution.

[0010] S2. Etherification reaction: Dissolve monochloroacetic acid in a second part of deionized water to prepare an aqueous solution of monochloroacetic acid; cool the alkalized lignin solution system obtained in step S1 to 35-45℃, and then slowly add the aqueous solution of monochloroacetic acid dropwise over 20-40 min; after the addition is complete, heat the reaction system to 60-80℃ and maintain the temperature at this temperature for 60-120 min to obtain the carboxymethylated reaction solution;

[0011] S3. Post-processing purification: Cool the reaction solution obtained in step S2 to room temperature, add dilute ammonia, and stir the reaction at 30-50℃ for 30-60 min; then adjust its pH value to 5.5-6.5 with acid solution, achieve solid-liquid separation by centrifugation, discard insoluble impurities, and collect the liquid phase component; dry the liquid phase component to obtain powdered carboxymethylated water-soluble lignin potassium fertilizer product.

[0012] Preferably, in step S1, the lignin raw material is one of the following: straw enzymatic hydrolysis residue, wood enzymatic hydrolysis residue, and agricultural processing by-product enzymatic hydrolysis residue.

[0013] Preferably, in step S1, the alkali is potassium hydroxide.

[0014] Preferably, in step S1, the amount of acetic anhydride used is 0.1-0.5 times the mass of the lignin raw material; the inert gas is nitrogen or argon.

[0015] Preferably, in step S1, the mass ratio of the lignin raw material, alkali, and monochloroacetic acid is 1:(0.2-0.5):(0.2-0.5). More preferably, the mass ratio is 1:(0.25-0.35):(0.25-0.35).

[0016] Preferably, in step S1, the mass of the first portion of deionized water is 5-15 times the mass of the lignin raw material.

[0017] Preferably, in step S2, the mass of the second portion of deionized water is 20-40 times the mass of monochloroacetic acid.

[0018] Preferably, in step S3, the acid used to adjust the pH is a hydrochloric acid or sulfuric acid solution.

[0019] Preferably, in step S3, the solid-liquid separation method is centrifugation, with a rotation speed of 10000 r / min and a time of 5 min.

[0020] Preferably, in step S3, the drying method is blower drying, vacuum drying, spray drying, or freeze drying at 40-60 °C.

[0021] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0022] 1. High product activity and excellent structural retention: This invention overcomes the defects of traditional carboxymethylation modification processes by introducing acetic anhydride during the alkalization stage and adding dilute ammonia after the etherification reaction. It effectively solves the problem of easy destruction and loss of activity of natural phenolic hydroxyl groups in lignin under strong alkaline systems. While efficiently completing lignin modification and introducing functional groups, it retains the inherently highly active phenolic hydroxyl structure of lignin to the greatest extent, avoiding the drawbacks of low activity and single function in conventional modified lignin, and effectively improving the native biological activity and structural integrity of the modified product.

[0023] 2. Dual Functional Synergy and Outstanding Application Performance: This invention introduces carboxymethyl groups through carboxymethylation and employs a structural design that retains a high content of phenolic hydroxyl groups. This allows the modified product to possess both excellent water solubility and high bioactivity. The ample carboxymethyl groups endow the product with good water solubility, chelation, and dispersibility, resulting in uniform dissolution without precipitation. Simultaneously, the high retention of phenolic hydroxyl groups endows the product with excellent antioxidant, stress-resistant, and growth-promoting physiological activities. The product can simultaneously achieve potassium nutrient supply, activation of trace elements in the soil, and regulation of crop growth. Multiple functions work synergistically, and compared with lignin salt products that have not undergone phenolic hydroxyl group retention modification, the product of this invention performs better in promoting crop growth (see Table 1 for a comparison between Example 1 and Comparative Example 3).

[0024] 3. Wide range of applicable scenarios and significant industrialization advantages: The highly active and water-soluble carboxymethylated lignin potassium fertilizer produced integrates multiple properties such as organic chelation, nutrient enhancement, soil improvement, and biostimulation. It can be widely used in functional water-soluble fertilizers, pesticide slow-release carriers, soil improvement and remediation, etc. It has good market competitiveness and broad industrial application prospects in the fields of green agriculture and high-value utilization of biomass. Attached Figure Description

[0025] Figure 1 shows the appearance and dissolution diagram of the carboxymethylated water-soluble lignin potassium fertilizer prepared according to the present invention;

[0026] Figure 2 shows the infrared spectrum of the carboxymethylated water-soluble lignin potassium fertilizer prepared according to the present invention;

[0027] Figure 3 This is a schematic diagram of lettuce plant growth 14 days after applying different fertilizers in Example 4 of the present invention. From left to right, they are CK, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Example 1. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] Weigh 1.0 g of enzymatically hydrolyzed lignin, 0.3 g of potassium hydroxide, 10.0 g of deionized water, and 0.15 g of acetic anhydride, purge with nitrogen for protection, and add to a 100 mL three-necked flask. Stir in an 80 °C water bath for 30 min to obtain a dark brown solution. Dissolve 0.3 g of monochloroacetic acid in 10.0 g of deionized water to prepare a solution. Cool the above alkali lignin solution system to 40 °C. Slowly add the monochloroacetic acid aqueous solution dropwise using a peristaltic pump over 30 min. After the addition is complete, raise the water bath temperature to 70 °C and continue stirring at this temperature for 90 min. After the reaction is complete, cool the reaction solution to room temperature, add 10 mL of 5% dilute ammonia water, and stir at 40 °C for 40 min. Then adjust the pH of the reaction solution to 6.0 with 2 mol / L hydrochloric acid solution. Centrifuge the pH-adjusted solution at 10000 rpm for 5 min and collect the supernatant. The supernatant was dried in a 50 °C oven to constant weight to obtain a brown solid. The phenolic hydroxyl content was determined to be 2.17 mmol / g, the carboxyl content to be 2.83 mmol / g, and the potassium content to be 12.34% by titration.

[0031] Example 2

[0032] Weigh 1.0 g of alkali lignin, 0.2 g of potassium hydroxide, 10.0 g of deionized water, and 0.10 g of acetic anhydride, and under nitrogen protection, add them to a 100 mL three-necked flask. Stir in an 80 °C water bath for 30 min to obtain a dark brown solution. Dissolve 0.3 g of monochloroacetic acid in 10.0 g of deionized water to prepare a solution. Cool the above alkali lignin solution system to 40 °C. Slowly add the monochloroacetic acid aqueous solution dropwise using a peristaltic pump over 30 min. After the addition is complete, raise the water bath temperature to 70 °C and continue stirring at this temperature for 90 min. After the reaction is complete, cool the reaction solution to room temperature, add 10 mL of 5% dilute ammonia water, and stir at 40 °C for 40 min. Then adjust the pH of the reaction solution to 6.0 with 2 mol / L hydrochloric acid solution. Centrifuge the pH-adjusted solution at 10000 rpm for 5 min and collect the supernatant. The supernatant was dried in a 50 °C oven to constant weight to obtain a brown solid. The phenolic hydroxyl content was determined to be 2.14 mmol / g, the carboxyl content to be 2.64 mmol / g, and the potassium content to be 10.86% by titration.

[0033] Example 3

[0034] Weigh 1.0 g of organic solvent lignin, 0.4 g of potassium hydroxide, 10.0 g of deionized water, and 0.20 g of acetic anhydride, and add them to a 100 mL three-necked flask under nitrogen protection. Stir in an 80 °C water bath for 30 min to obtain a dark brown solution. Dissolve 0.3 g of monochloroacetic acid in 10.0 g of deionized water to prepare a solution. Cool the above alkali lignin solution system to 40 °C. Slowly add the monochloroacetic acid aqueous solution dropwise using a peristaltic pump over 30 min. After the addition is complete, raise the water bath temperature to 70 °C and continue stirring at this temperature for 90 min. After the reaction is complete, cool the reaction solution to room temperature, add 10 mL of 5% dilute ammonia water, and stir at 40 °C for 40 min. Then adjust the pH of the reaction solution to 6.0 with 2 mol / L hydrochloric acid solution. Centrifuge the pH-adjusted solution at 10000 rpm for 5 min and collect the supernatant. The supernatant was dried in a 50 °C oven to constant weight to obtain a brown solid. The phenolic hydroxyl content was determined to be 1.97 mmol / g, the carboxyl content to be 2.76 mmol / g, and the potassium content to be 12.46% by titration.

[0035] Example 4 (Fertilizer Efficiency Experiment in Potted Plants)

[0036] Select plump and uniform butter lettuce seeds, disinfect them by soaking in 3% H2O2 for 15 minutes, then rinse them thoroughly with distilled water. After soaking in distilled water for 24 hours, place the seeds in a germination box lined with germination paper and incubate them in the dark at 30℃ for germination treatment. Select seeds with uniform growth and transplant them into 6-cell hydroponic boxes. Cultivate them with Hoagland's nutrient solution and place them in a light incubator (culture temperature: daytime 25℃ / nighttime 20℃, light cycle: 14h light / 10h darkness, light intensity 10000lx, relative humidity 60~80%). Change the nutrient solution every 4 days. After the lettuce plants were transplanted and allowed to acclimate to the hydroponic environment for 3 days, different treatment groups were set up: CK, control group 2 (unmodified enzymatically hydrolyzed potassium fertilizer residue), control group 3 (unblocked phenolic hydroxyl carboxymethylated modified lignin potassium fertilizer), control group 4 (blocked but not restored carboxymethylated modified lignin potassium fertilizer), and control group 5 (blocked phenolic hydroxyl carboxymethylated modified lignin potassium fertilizer, Example 1). The fertilizer concentration for each treatment group was set at 200 mg / L. After 14 days of cultivation, lettuce plants were collected, and physiological indicators such as stem length and root length were measured. A comparison of stem and root length growth of lettuce plants 14 days after application of different lignin potassium fertilizers is shown in the attached figure. Figure 3 , Figure 3 The images shown are from this embodiment. The actual measurement data is shown in Table 1 below.

[0037] Table 1. Comparison of lettuce plant growth 14 days after application of different concentrations of carboxymethylated modified lignin potassium fertilizer. Stem length (cm) 4.25 10.11 11.42 7.32 12.60 Root length (cm) 14.86 15.22 15.56 14.22 16.95

[0038] Experimental analysis showed that, compared to the unfertilized control group (CK), the stem and root lengths of all fertilized treatment groups were increased. The most significant increase was observed in the application of the patented product with phenolic hydroxyl group blocking (Example 1), with a stem length of 12.60 cm and a root length of 16.95 cm. In contrast, the control group without phenolic hydroxyl group blocking showed a lower growth-promoting effect than the treatment group of the same concentration. This demonstrates that the present invention, through the sequential addition of acetic anhydride followed by dilute ammonia, successfully preserves the natural phenolic hydroxyl activity of lignin, thereby providing additional growth-promoting effects on top of providing potassium and a chelating carrier.

[0039] Comparative Example 1

[0040] Lignin raw material comparison: The sample (control group) prepared by the same method as Comparative Example 3 without phenolic hydroxyl blocking and direct carboxymethylation was compared with the product of Example 1 of the present invention.

[0041] Water solubility test: Take 0.1g of each sample and add it to 10mL of deionized water with pH=7. Stir magnetically for 1 hour at room temperature. The product of Example 1 completely dissolved, and the solution was clear and transparent; most of the unmodified lignin precipitated, and the solution was turbid; the control sample without phenolic hydroxyl blocking showed a small amount of precipitation after dissolution, and the solution was darker in color.

[0042] Comparative Example 2

[0043] Weigh 1.0 g of unmodified enzymatic hydrolysis residue and add 15.0 g of deionized water, stirring to disperse evenly. At room temperature, slowly add 0.3 g of potassium hydroxide and continue stirring for 30 min to allow the free phenolic hydroxyl groups, carboxyl groups, and other active groups in the enzymatic hydrolysis residue to chelate with potassium ions. During the reaction, the pH of the system is approximately 10-11. After the reaction, adjust the pH to 6.0-6.5 with 2 mol / L hydrochloric acid solution. Centrifuge the mixture at 10000 rpm for 5 min, discarding the insoluble precipitate (mostly unreacted enzymatic hydrolysis residue), and collect the supernatant. Place the supernatant in a 50 ℃ forced-air drying oven and dry to constant weight to obtain a dark brown solid product, which is the unmodified enzymatic hydrolysis residue-potassium chelate fertilizer.

[0044] Comparative Example 3

[0045] Weigh 1.0 g of enzymatically hydrolyzed lignin, 0.3 g of potassium hydroxide, and 10.0 g of deionized water, and add them to a 100 mL three-necked flask. Stir in an 80 °C water bath for 30 min until the lignin is completely dissolved, yielding a dark brown solution. Dissolve 0.3 g of monochloroacetic acid in 10.0 g of deionized water to prepare a solution. Cool the above alkali lignin solution system to 40 °C. Slowly add the monochloroacetic acid aqueous solution dropwise using a peristaltic pump over 30 min. After the addition is complete, raise the water bath temperature to 70 °C and continue stirring at this temperature for 90 min. After the reaction is complete, cool the reaction solution to room temperature and adjust the pH of the reaction solution to 6.0 with 2 mol / L hydrochloric acid solution. Centrifuge the pH-adjusted solution at 10,000 rpm for 5 min and collect the supernatant. Place the supernatant in a 50 °C forced-air drying oven and dry to constant weight to obtain a brown solid, which is the crude carboxymethylated lignin. The phenolic hydroxyl content was determined to be 1.48 mmol / g, the carboxyl content to be 2.56 mmol / g, and the potassium content to be 9.67% by titration.

[0046] Comparative Example 4

[0047] Weigh 1.0 g of enzymatically hydrolyzed lignin, 0.3 g of potassium hydroxide, 10.0 g of deionized water, and 0.15 g of acetic anhydride, purge with nitrogen, and add to a 100 mL three-necked flask. Stir in an 80 °C water bath for 30 min to obtain a dark brown solution. Dissolve 0.3 g of monochloroacetic acid in 10.0 g of deionized water to prepare a solution. Cool the above alkali lignin solution system to 40 °C. Slowly add the monochloroacetic acid aqueous solution dropwise using a peristaltic pump over 30 min. After the addition is complete, raise the water bath temperature to 70 °C and continue stirring at this temperature for 90 min. After the reaction is complete, adjust the pH of the reaction solution to 6.0 with 2 mol / L hydrochloric acid solution. Centrifuge the pH-adjusted solution at 10000 rpm for 5 min and collect the supernatant. Place the supernatant in a 50 °C forced-air drying oven and dry to constant weight to obtain a brown solid. The phenolic hydroxyl content was determined to be 1.22 mmol / g, the carboxyl content to be 2.63 mmol / g, and the potassium content to be 9.14% by titration.

[0048] In summary, the highly water-soluble carboxymethylated lignin potassium fertilizer rich in phenolic hydroxyl groups prepared by this invention can effectively promote crop growth and development and improve nutrient conversion and utilization. The preparation method is environmentally friendly, simple to operate, and low in cost, making it suitable for large-scale industrial application. The above description is merely a preferred embodiment of this invention, but the scope of protection of this invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in this invention, based on the technical solution and inventive concept of this invention, should be covered within the scope of protection of this invention.

Claims

1. A highly active carboxymethylated water-soluble lignin potassium fertilizer, characterized in that, The product is prepared by the following method: lignin raw material is mixed with potassium hydroxide and acetic anhydride, and then alkalized and dissolved under an inert atmosphere; monochloroacetic acid is added to the resulting alkalized lignin solution to carry out an etherification reaction; after the reaction is completed, dilute ammonia water is added, and then the pH is adjusted. After solid-liquid separation and drying, a lignin potassium fertilizer with dual functions of potassium fertilizer supply and plant growth regulation is obtained; wherein, the mass ratio of the lignin raw material, potassium hydroxide and monochloroacetic acid is 1:(0.2-0.5):(0.2-0.5); The method includes the following steps: S1. Alkali dissolution: Mix lignin raw material, potassium hydroxide and the first portion of deionized water, add acetic anhydride, and stir at 60-90 ℃ for 20-40 min under an inert gas atmosphere to obtain a homogeneous alkalized lignin solution; S2. Etherification reaction: Dissolve monochloroacetic acid in a second part of deionized water to prepare an aqueous solution of monochloroacetic acid; cool the alkalized lignin solution system obtained in step S1 to 35-45℃, and then slowly add the aqueous solution of monochloroacetic acid dropwise over 20-40 min; after the addition is complete, heat the reaction system to 60-80℃ and maintain the temperature at this temperature for 60-120 min to obtain the carboxymethylated reaction solution; S3. Post-processing purification: Cool the reaction solution obtained in step S2 to room temperature, add dilute ammonia, stir the reaction at 30-50 °C for 30-60 min, then adjust the pH value to 5.5-6.5 with acid solution, achieve solid-liquid separation by centrifugation, discard insoluble impurities, and collect the liquid phase component; dry the liquid phase component to obtain powdered carboxymethylated modified lignin product.

2. The highly active carboxymethylated water-soluble lignin potassium fertilizer according to claim 1, characterized in that: The lignin raw material in step S1 of the method is one of alkali lignin, enzymatically hydrolyzed lignin, organic solvent lignin, or sulfate lignin.

3. The highly active carboxymethylated water-soluble lignin potassium fertilizer according to claim 1, characterized in that: In step S1 of the method, the amount of acetic anhydride used is 0.1-0.5 times the mass of the lignin raw material; the inert gas is nitrogen or argon.

4. The highly active carboxymethylated water-soluble lignin potassium fertilizer according to claim 1, characterized in that: In the method, the mass ratio of lignin raw material, potassium hydroxide and monochloroacetic acid is 1:(0.25-0.35):(0.25-0.35).

5. The highly active carboxymethylated water-soluble lignin potassium fertilizer according to claim 1, characterized in that: In step S1 of the method, the mass of the first portion of deionized water is 5-15 times the mass of the lignin raw material; in step S2, the mass of the second portion of deionized water is 20-40 times the mass of monochloroacetic acid.

6. The highly active carboxymethylated water-soluble lignin potassium fertilizer according to claim 1, characterized in that: In step S3 of the method, the acid used to adjust the pH is hydrochloric acid or sulfuric acid solution.

7. The highly active carboxymethylated water-soluble lignin potassium fertilizer according to claim 1, characterized in that: The solid-liquid separation method in step S3 of the method is centrifugal separation.

8. The highly active carboxymethylated water-soluble lignin potassium fertilizer according to claim 1, characterized in that: The drying method described in step S3 of the method is any one of blower drying, vacuum drying, spray drying, or freeze drying.

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