Preparation method of a water-soluble lignin oligomer potassium fertilizer

Abstract

The present invention relates to the fields of high-value utilization of lignin and fertilizers, and specifically relates to the preparation of a water-soluble lignin oligomer potassium fertilizer. Aiming at the molecular weight inhomogeneity and hydrophobicity of lignin, an environmentally friendly new potassium fertilizer was prepared from the water-soluble oligomers produced by mild oxidative depolymerization of lignin. The main steps include: dissolving lignin in an NaOH solution, adding a catalyst CuO, and carrying out oxidative depolymerization in an oxygen atmosphere. After the reaction is completed, the catalyst is filtered out, the reaction liquid is acidified to pH 5, the precipitate is removed by centrifugation, the supernatant is further acidified to pH 2, the precipitate is centrifuged out, the precipitate is washed and extracted with an organic solvent. After extraction, the solid is dispersed in water, KOH is added to adjust the pH to 7, and after concentration, it is spray-dried to obtain the water-soluble lignin oligomer potassium fertilizer. The present invention provides a method for preparing lignin potassium fertilizer with a simple preparation process, low cost and easy large-scale production, providing a simple and effective utilization route for the application of lignin in the field of fertilizers.

Description

Technical Field

[0001] The present invention relates to the field of high-value utilization of lignin and the field of fertilizers, and specifically relates to the preparation of a water-soluble lignin oligomer potassium fertilizer.

Background Art

[0002] Lignin is the most abundant aromatic polymer in nature and is one of the three major components of lignocellulosic biomass. Three C6-C3 phenylpropane units containing phenolic hydroxyl groups, namely syringyl alcohol (S), guaiacyl alcohol (G), and p-hydroxyphenyl alcohol (H), form a random three-dimensional network structure of the lignin polymer. Lignin is a high-molecular-weight polymer rich in chemical groups such as phenolic hydroxyl groups, carboxyl groups, benzyl alcohol groups, and methoxy groups. It can undergo various reactions such as oxidation, reduction, sulfonation, nitration, polycondensation, graft copolymerization, etc. Currently, lignin can be applied in agriculture as a plant growth stimulant, fertilizer, soil conditioner, chelating agent, etc. In particular, lignin-based fertilizers have attracted much attention due to their characteristics of being cheap and easily available, having a good slow-release effect, and being environmentally friendly. However, the complex structure, molecular weight heterogeneity, and hydrophobicity of lignin greatly limit its further promotion, reduce its utilization rate, and also limit its high-value utilization in the agricultural field.

[0003] Oxidative depolymerization is one of the effective ways to achieve the high-value utilization of lignin. At a certain temperature, macromolecular lignin is catalytically oxidized to produce small-molecule aromatic monomer compounds and oligomers. Currently, a large number of studies have focused on how to effectively utilize the depolymerized aromatic monomers of lignin, but little attention has been paid to the further high-value utilization of oligomers. At the same time, due to the fact that the target product of current lignin oxidative depolymerization is phenolic monomers, the general reaction conditions are relatively severe.

[0004] Potassium fertilizer is one of the important elements for plant growth and can significantly improve the stress resistance of crops, improve the quality, and increase the yield in agricultural practices. Different from traditional potassium fertilizers, in addition to providing the necessary potassium element for crop growth, lignin potassium fertilizers can also improve acidic soil, improve the physical and chemical properties of the soil, increase the types and quantities of beneficial microorganisms in the soil, and improve the soil microecological environment, thereby stimulating crop growth and increasing the yield of crops. Aiming at the molecular weight heterogeneity and hydrophobicity of lignin, the present invention prepares an environmentally friendly new potassium fertilizer through water-soluble oligomers produced by mild oxidative depolymerization of lignin, realizes the high-value utilization of lignin, provides a potassium fertilizer preparation method with a reasonable design and scientific formula, and its preparation process is simple to operate, low in cost, high in efficiency, and easy to scale up production.

Summary of the Invention

[0005] The present invention relates to the preparation of a water-soluble lignin oligomer potassium fertilizer. The oligomer is derived from lignin small molecules after the oxidative depolymerization of lignin rich in aryl ether bonds (such as organosolv lignin, enzymatically hydrolyzed lignin, and native lignin in wood powder) under mild conditions. The main steps are as follows:

[0006] (1) Dissolve a certain amount of lignin in 1%-2% (w / v) NaOH aqueous solution according to the solid-liquid ratio of 1:10 - 30 (mass / volume ratio), stir evenly until fully dissolved, then pour it into a reaction kettle, and add the catalyst CuO in a ratio of 1:4 - 10 (mass ratio of catalyst to lignin).

[0007] (2) Introduce oxygen into the reaction kettle to reach a total pressure of 0.5 - 2 MPa, and carry out oxidative depolymerization under the conditions of 80 - 120 °C for 1 - 3 h, with a rotation speed of 200 - 700 r / min;

[0008] (3) After the oxygenolysis reaction is completed, cool the reaction kettle to a certain temperature and discharge the material, filter out the catalyst. At this temperature, acidify the reaction liquid with HCl to pH = 5, centrifuge to remove the precipitate, continue to add HCl to the supernatant to pH = 2, centrifuge to separate the precipitate, wash the precipitate and extract it with an organic solvent. The remaining solid after extraction is dispersed in water according to the solid-liquid ratio of 1:5 - 10, add 4M KOH to adjust the pH to 7.0, concentrate and then spray-dry to obtain the water-soluble lignin oligomer potassium fertilizer.

Specific Embodiment

[0009] Example 1

[0010] Dissolve 0.5 g of organosolv lignin in 2% (w / v) NaOH aqueous solution according to the solid-liquid ratio of 1:10, stir evenly until fully dissolved, then pour it into a reaction kettle, and add 125 mg of catalyst CuO. Introduce oxygen into the reaction kettle to reach a total pressure of 0.5 MPa, and carry out oxidative depolymerization under the conditions of 120 °C for 1.5 h, with a rotation speed of 700 r / min.

[0011] After the oxygenolysis reaction is completed, cool the reaction kettle to 60 °C, filter out the catalyst. At this temperature, acidify the reaction liquid with HCl to pH = 5, centrifuge to remove the precipitate, continue to add HCl to the supernatant to pH = 2, centrifuge to separate the precipitate, wash it and extract it with ether. The remaining solid after extraction is dispersed in water according to the solid-liquid ratio of 1:5, add 4M KOH to adjust the pH to 7.0, concentrate and then spray-dry to obtain the water-soluble lignin oligomer potassium fertilizer. The yield of the oligomer potassium fertilizer is 30.19% (relative to the mass of lignin). When applied to hydroponic wheat, compared with the unoxidized organosolv lignin potassium fertilizer, the germination rate increased by 40.3%, the stem length increased from 9.8 ± 0.3 cm to 14.2 ± 0.4 cm, and the fresh weight increased from 0.15 ± 0.08 g to 0.36 ± 0.07 g.

[0012] Example 2

[0013] 0.5 g of hardwood sawdust was dispersed in 1.5% (w / v) aqueous NaOH solution at a solid-liquid ratio of 1:20. After stirring evenly, it was poured into a reaction kettle, and 100 mg of catalyst CuO was added. Oxygen was introduced into the reaction kettle until the total pressure reached 1 MPa, and oxidative depolymerization was carried out at 100 °C for 2 h with a rotation speed of 500 r / min.

[0014] After the oxygenolysis reaction ended, the reaction kettle was cooled to 70 °C, and the catalyst was filtered out. At this temperature, the reaction liquid was acidified with HCl to pH = 5, the precipitate was removed by centrifugation, the supernatant was continuously added with HCl to pH = 2, the precipitate was separated by centrifugation, washed and then extracted with petroleum ether. The remaining solid after extraction was dispersed in water at a solid-liquid ratio of 1:7, 4 M KOH was added to adjust the pH to 7.0, and after concentration, it was spray-dried to obtain water-soluble lignin oligomer potassium fertilizer. The yield of oligomer potassium fertilizer was 29.77% (relative to the mass of lignin), the germination rate increased by 38.5%, the stem length increased from 9.8 ± 0.3 cm to 15.7 ± 0.4 cm, and the fresh weight increased from 0.15 ± 0.08 g to 0.32 ± 0.05 g.

[0015] Example 3

[0016] 0.5 g of enzymatically hydrolyzed lignin was dissolved in 1% (w / v) aqueous NaOH solution at a solid-liquid ratio of 1:25. After stirring evenly and fully dissolving, it was poured into a reaction kettle, and 62 mg of catalyst CuO was added. Oxygen was introduced into the reaction kettle until the total pressure reached 1.5 MPa, and oxidative depolymerization was carried out at 100 °C for 1.5 h with a rotation speed of 400 r / min.

[0017] After the oxygenolysis reaction ended, the reaction kettle was cooled to 80 °C, and the catalyst was filtered out. At this temperature, the reaction liquid was acidified with HCl to pH = 5, the precipitate was removed by centrifugation, the supernatant was continuously added with HCl to pH = 2, the precipitate was separated by centrifugation, washed and then extracted with ether. The remaining solid after extraction was dispersed in water at a solid-liquid ratio of 1:8, 4 M KOH was added to adjust the pH to 7.0, and after concentration, it was spray-dried to obtain water-soluble lignin oligomer potassium fertilizer. The yield of oligomer potassium fertilizer was 31.22% (relative to the mass of lignin), the germination rate increased by 41.2%, the stem length increased from 9.8 ± 0.3 cm to 15.1 ± 0.5 cm, and the fresh weight increased from 0.15 ± 0.08 g to 0.30 ± 0.04 g.

[0018] Example 4

[0019] Dissolve 0.5 g of enzymatically hydrolyzed lignin in 1% (w / v) NaOH aqueous solution according to a solid-liquid ratio of 1:30. After stirring evenly and fully dissolving, pour it into a reaction kettle, add 50 mg of catalyst CuO, introduce oxygen into the reaction kettle until the total pressure reaches 2 MPa, and carry out oxidative depolymerization at 80 °C for 2.5 h with a rotation speed of 300 r / min.

[0020] After the oxygenolysis reaction is completed, cool the reaction kettle to 75 °C, filter out the catalyst. At this temperature, acidify the reaction liquid with HCl to pH = 5, centrifuge to remove the precipitate, continue to add HCl to the supernatant to pH = 2, centrifuge to separate the precipitate, wash it, and extract it with petroleum ether. The remaining solid after extraction is dispersed in water according to a solid-liquid ratio of 1:10, add 4 M KOH to adjust the pH to 7.0, concentrate and then spray-dry to obtain water-soluble lignin oligomer potassium fertilizer. The yield of oligomer potassium fertilizer is 32.23% (relative to the mass of lignin), the germination rate is increased by 38.5%, the stem length is increased from 9.8 ± 0.3 cm to 14.8 ± 0.4 cm, and the fresh weight is increased from 0.15 ± 0.08 g to 0.29 ± 0.05 g.

Claims

1. A preparation method of a water-soluble lignin oligomer potassium fertilizer, the method comprising the following steps: (1) Dissolve 0.5 g of enzymatically hydrolyzed lignin in 1% (w / v) NaOH aqueous solution according to a solid-liquid ratio of 1:25, stir evenly and fully dissolve, then pour it into a reaction kettle, and add 62 mg of catalyst CuO; (2) Introduce oxygen into the reaction kettle to reach a total pressure of 1.5 MPa, and carry out oxidative depolymerization at 100 °C for 1.5 h, with a rotation speed of 400 r / min; (3) After the oxygenolysis reaction is completed, cool the reaction kettle to 80 °C, filter out the catalyst. At this temperature, acidify the reaction liquid with HCl to pH = 5, centrifuge to remove the precipitate, continue to add HCl to the supernatant to pH = 2, centrifuge to separate the precipitate, wash it and extract it with ether. The remaining solid after extraction is dispersed in water according to a solid-liquid ratio of 1:8, add 4 M KOH to adjust the pH to 7.0, concentrate and then spray dry to obtain the water-soluble lignin oligomer potassium fertilizer.