Method for extracting humic acid from biological waste

Abstract

The invention discloses a method for extracting humic acid from biological waste, and belongs to the technical field of humic acid extraction, the method comprises the following steps: S2, dissolving pretreated biomass waste with an alkaline ionic liquid to obtain a lignin solute and solid residues rich in cellulose and hemicelluloses; the alkaline ionic liquid is alkaline imidazole ionic liquid; s3, the solid residues rich in cellulose and hemicellulose are subjected to acidic hydrothermal treatment, cellulose and hemicellulose are converted into liquid products rich in micromolecular saccharides and organic acids, and acidic hydrothermal treatment liquid is obtained; after hydrothermal treatment, fructose phosphorylase and glucose oxidase are added into the acidic hydrothermal treatment liquid, incubation is carried out for 30 min at the temperature of 30-40 DEG C, and an enzymolysis conversion mixture is obtained. The humic acid can be extracted from the biological waste, and the yield and quality of the humic acid are improved.

Description

Technical Field

[0001] The invention relates to the technical field of humic acid extraction, and in particular to a method for extracting humic acid from biological waste. Background Art

[0002] Biowaste mainly includes organic waste generated in agricultural and industrial production, such as crop straw, livestock and poultry manure, and food processing waste. These wastes are rich in cellulose and lignin organic components, which can be converted into humic acid through proper treatment. There are currently three methods for extracting humic acid from biowaste: (1) mixing biowaste with an alkaline solution (such as sodium hydroxide or potassium hydroxide) to dissolve humic acid in the alkaline solution, and then precipitating the humic acid through acidification. (2) subjecting biowaste to a hydrothermal reaction under high temperature, high pressure and water conditions to promote the humification process of organic matter and generate humic acid. (3) utilizing the metabolic action of microorganisms to decompose organic matter in biowaste and generate humic acid. Among the above three methods, hydrothermal treatment has the highest efficiency.

[0003] Lignin is a complex amorphous biopolymer composed of phenylpropane subunits connected by ether and C-C bonds, with a molecular weight ranging from 2,500 to 10,000 g / mol. Lignin is mainly formed by the free radical polymerization of three hydroxycinnamyl alcohols (monolignols), namely guaiacyl, p-coumaryl and neonaphthoyl alcohols. Lignin can be cross-linked with carbohydrates (mainly hemicellulose, but also to a certain extent with cellulose) to form so-called lignin-carbohydrate complexes (LCCs). Studies have shown that the level of cross-linking through LCCs is directly related to the cell wall hardness and resistance to enzymatic attack of the biomass. In softwoods, all lignin fragments are linked to carbohydrates, with up to 50% linked to cellulose. In hardwoods, 47% to 66% of the lignin fragments are associated with carbohydrates, with up to 17% being associated with them.

[0004] During hydrothermal treatment, lignin degrades, producing inhibitory substances such as polyphenols and organic acids. These substances can inhibit the activity of hydrolytic enzymes, reducing their catalytic efficiency. For example, phenolic compounds produced by lignin degradation may bind to the active sites of enzymes, altering their conformation and rendering them inactive. As a key component of lignocellulosic biomass, lignin plays a key role in the humification process. Lignin can undergo humification through either a top-down or bottom-up pathway: lignin is broken down into larger fragments, which are then oxidized and humified, or it can be first broken down into small phenolic compounds, which are then oxidized and polymerized into humic substances. Cellulose and hemicellulose, two other important components of lignocellulosic biomass, can also undergo humification. During hydrothermal treatment, cellulose and hemicellulose are hydrolyzed into monosaccharides (i.e., glucose and fructose), which are then further dehydrated and oxidized into organic acids or furanic compounds. Finally, these small molecules can undergo condensation reactions to form humic substances, primarily fulvic acid. During hydrothermal treatment, the decomposition products of cellulose, hemicellulose, and lignin can react with each other and participate in the synthesis of humic acid. The humification mechanisms of these three biomass components differ during hydrothermal treatment at different pH ranges. At neutral pH, hemicellulose undergoes a certain degree of hydrolysis to produce pentoses, and lignin is broken down into smaller fragments. However, cellulose has a weaker decomposition ability, resulting in lignin and hemicellulose being the main components involved in the humification reaction. Under acidic conditions, a large number of free hydrogen ions readily react with cellulose, causing it to undergo a strong hydrolysis-condensation reaction. However, due to the acid insolubility of lignin, the decomposition of cellulose is limited. In an alkaline hydrothermal environment, cellulose, hemicellulose, and lignin can undergo hydrolysis and cleavage reactions to produce small molecular compounds or fragments, which can then undergo condensation reactions to form humic acid. However, compared with traditional coal extraction, the humic acid yield obtained by direct alkaline thermal treatment of biomass waste is not ideal. The researchers developed a two-step hydrothermal humification process for biomass waste. First, the biomass waste is treated under acidic hydrothermal conditions to produce a large number of humic acid precursors, including sugars, furan compounds, organic acids, and coal-like hydrocarbons. These substances are then humified under alkaline hydrothermal conditions, successfully improving the efficiency of the hydrothermal humification process. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the object of the present invention is to provide a method for extracting humic acid from biological waste, which can achieve the extraction of humic acid from biological waste and improve the yield and quality of humic acid.

[0006] The purpose of the present invention is achieved by adopting the following technical solutions:

[0007] A method for extracting humic acid from biological waste comprises the following steps:

[0008] S1. crushing and drying the biomass waste to obtain pretreated biomass waste;

[0009] S2. Solving the pretreated biomass waste with an alkaline ionic liquid to obtain a lignin solution and a solid residue rich in cellulose and hemicellulose; the alkaline ionic liquid is an alkaline imidazole ionic liquid;

[0010] S3. Subjecting the solid residue rich in cellulose and hemicellulose to an acidic hydrothermal treatment to convert the cellulose and hemicellulose into a liquid product rich in small molecule sugars and organic acids, thereby obtaining an acidic hydrothermal treatment solution, wherein the acidic hydrothermal treatment is performed under the following conditions: a temperature of 140-180° C., a pH of 3-4, a pressure of 0.5-1 MPa, and a time of 30-60 min. After the hydrothermal treatment, the pH of the solution is adjusted to 5-7, and fructose phosphorylase and glucose oxidase are added to the acidic hydrothermal treatment solution, and the mixture is incubated at a temperature of 30-40° C. for 30 min to obtain an enzymatic conversion mixture.

[0011] S4. Adding the lignin solubilizer obtained in step S2 to the enzymatic conversion mixture obtained in step S2, and performing alkaline hydrothermal treatment to obtain a mixture containing humic acid; wherein the conditions of the alkaline hydrothermal treatment are: temperature 200-230° C., pH 10-11, reaction time 2-3 hours, and pressure 1-2 MPa;

[0012] S5. Acidifying the mixture containing humic acid obtained in step S4, adjusting the pH value to 1-2, so that humic acid is precipitated from the solution, filtering, and washing to obtain humic acid.

[0013] Furthermore, the biological waste is crop straw, forestry residues, and agricultural processing waste.

[0014] Furthermore, in step S5, metal ions that form precipitates with polyphenol compounds are first added, and the polyphenol compounds react with the metal ions to form a water-insoluble precipitate. The precipitate is removed by filtration to remove the polyphenol compounds, and then the mixture containing humic acid obtained in step S4 is acidified to obtain high-purity humic acid.

[0015] Furthermore, the metal ion is one of aluminum ion and iron ion.

[0016] Furthermore, the alkaline imidazolium ionic liquid is [C2C1im][C1CO2].

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention provides a method for extracting humic acid from biological waste. Alkaline ionic liquid has good dissolving selectivity for lignin and can preferentially dissolve lignin, thereby achieving separation of lignin from cellulose and hemicellulose. This step greatly reduces the content of lignin polyphenols in the solid residue rich in cellulose and hemicellulose. Therefore, when the acidic hydrothermal treatment is performed in step S3, the amount of lignin polyphenols has been significantly reduced, and the effect on the hydrolysis of cellulose and hemicellulose and the activity of fructose phosphorylase and glucose oxidase is relatively small; and the alkaline ionic liquid treatment destroys the close structure between lignin and cellulose and hemicellulose. The acidic hydrothermal treatment can more efficiently hydrolyze cellulose and hemicellulose to generate glucose and fructose monosaccharides, thereby improving the yield of carbohydrate products.

[0019] Glucose and fructose, the hydrolysis products of cellulose and hemicellulose after acidic hydrothermal treatment, serve as substrates for fructose phosphorylase and glucose oxidase, further converting them into organic acids and alcohols. For example, glucose oxidase can oxidize glucose to gluconic acid, which further participates in the formation of humic acid. The converted small-molecule sugars and organic acids can more effectively undergo condensation and polymerization reactions with lignin solubilizers to form the macromolecular structure of humic acid, thereby improving the efficiency of the humification reaction and the yield of humic acid during alkaline hydrothermal treatment.

[0020] (2) The present invention provides a method for extracting humic acid from biological waste. In step S5, when the mixture containing humic acid is subjected to acidification treatment, polyphenolic compounds may precipitate together with the humic acid, resulting in a decrease in the purity of the humic acid product. This is because polyphenolic compounds contain multiple phenolic hydroxyl groups, which may cause them to form precipitates with other substances under acidic conditions. In addition, polyphenolic compounds have a certain water solubility and may not be completely separated from humic acid during acidification treatment. This may cause the extracted humic acid product to contain polyphenolic compound impurities, affecting its purity and quality. Metal ion precipitation method: first, metal ions that form precipitates with polyphenolic compounds are added, and the polyphenolic compounds react with the metal ions to form a water-insoluble precipitate. The precipitate is removed by filtration, thereby removing the polyphenolic compounds and improving the purity of the humic acid product. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific embodiments. It should be noted that, under the premise of no conflict, the embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0022] Example 1

[0023] The present invention provides a method for extracting humic acid from crop straw, comprising the following steps:

[0024] S1. crushing and drying the biomass waste to obtain pretreated biomass waste;

[0025] S2. Solving the pretreated biomass waste with an alkaline ionic liquid to obtain a lignin solution and a solid residue rich in cellulose and hemicellulose; the alkaline ionic liquid is an alkaline imidazole ionic liquid, and the concentration of the alkaline ionic liquid is 1 mol / L;

[0026] S3. subjecting the solid residue rich in cellulose and hemicellulose to an acidic hydrothermal treatment to convert the cellulose and hemicellulose into a liquid product rich in small molecular sugars and organic acids, thereby obtaining an acidic hydrothermal treatment solution, wherein the conditions for the acidic hydrothermal treatment are: temperature 140° C., pH 3, pressure 0.8 MPa, and time 50 min. After the hydrothermal treatment, the pH of the solution is adjusted to 5, and fructose phosphorylase and glucose oxidase are added to the acidic hydrothermal treatment solution, and the mixture is incubated at 30° C. for 30 min to obtain an enzymatic conversion mixture.

[0027] S4. Adding the lignin solubilizer obtained in step S2 to the enzymatic conversion mixture obtained in step S2, and performing alkaline hydrothermal treatment to obtain a mixture containing humic acid; wherein the conditions of the alkaline hydrothermal treatment are: temperature 200° C., pH 10, reaction time 2.5 hours, and pressure 1 MPa;

[0028] S5. Acidifying the mixture containing humic acid obtained in step S4, adjusting the pH value to 1, precipitating humic acid from the solution, filtering, and washing to obtain humic acid.

[0029] In this embodiment, interaction with the aromatic ring of lignin: the cations of the ionic liquid (such as imidazole cations) can interact with the aromatic ring of lignin through π-π stacking and electrostatic effects, destroying the stacking between lignin molecules, helping to destroy the three-dimensional network structure of lignin, making the structure of lignin loose, and increasing the solubility and reactivity of lignin.

[0030] In this embodiment, the alkaline imidazole ionic liquid is [C2C1im][C1CO2], which is a type of alkaline ionic liquid and its chemical name is 1-ethyl-3-methylimidazolium acetate.

[0031] Example 2

[0032] The present embodiment provides a method for extracting humic acid from forestry residues, comprising the following steps:

[0033] S1. crushing and drying the biomass waste to obtain pretreated biomass waste;

[0034] S2. Solving the pretreated biomass waste with an alkaline ionic liquid to obtain a lignin solution and a solid residue rich in cellulose and hemicellulose; the alkaline ionic liquid is an alkaline imidazole ionic liquid, and the concentration of the alkaline ionic liquid is 2 mol / L;

[0035] S3. Subjecting the solid residue rich in cellulose and hemicellulose to an acidic hydrothermal treatment to convert the cellulose and hemicellulose into a liquid product rich in small molecular sugars and organic acids, thereby obtaining an acidic hydrothermal treatment solution. The conditions for the acidic hydrothermal treatment are: temperature 160° C., pH 3.5, pressure 0.5 MPa, and time 30 min. After the hydrothermal treatment, the pH of the solution is adjusted to 6, and fructose phosphorylase and glucose oxidase are added to the acidic hydrothermal treatment solution. The mixture is incubated at 40° C. for 30 min to obtain an enzymatic conversion mixture.

[0036] S4. Adding the lignin solubilizer obtained in step S2 to the enzymatic conversion mixture obtained in step S2, and performing alkaline hydrothermal treatment to obtain a mixture containing humic acid; wherein the conditions of the alkaline hydrothermal treatment are: temperature 210° C., pH 11, reaction time 2 hours, and pressure 1.5 MPa;

[0037] S5. Acidifying the mixture containing humic acid obtained in step S4, adjusting the pH value to 1.5, so that humic acid is precipitated from the solution, filtering, and washing to obtain humic acid.

[0038] In this embodiment, the alkaline imidazole ionic liquid is [C2C1im][C1CO2], which is a type of alkaline ionic liquid and its chemical name is 1-ethyl-3-methylimidazolium acetate.

[0039] Example 3

[0040] The present embodiment provides a method for extracting humic acid from agricultural processing waste, comprising the following steps:

[0041] S1. crushing and drying the biomass waste to obtain pretreated biomass waste;

[0042] S2. Solving the pretreated biomass waste with an alkaline ionic liquid to obtain a lignin solution and a solid residue rich in cellulose and hemicellulose; the alkaline ionic liquid is an alkaline imidazole ionic liquid, and the concentration of the alkaline ionic liquid is 5 mol / L;

[0043] S3. subjecting the solid residue rich in cellulose and hemicellulose to an acidic hydrothermal treatment to convert the cellulose and hemicellulose into a liquid product rich in small molecular sugars and organic acids, thereby obtaining an acidic hydrothermal treatment solution, wherein the conditions for the acidic hydrothermal treatment are: temperature 180° C., pH 4, pressure 1 MPa, and time 60 min; after the hydrothermal treatment, adjusting the pH of the solution to 7, adding fructose phosphorylase and glucose oxidase to the acidic hydrothermal treatment solution, and incubating at 35° C. for 30 min to obtain an enzymatic conversion mixture;

[0044] S4. Adding the lignin solubilizer obtained in step S2 to the enzymatic conversion mixture obtained in step S2, and performing alkaline hydrothermal treatment to obtain a mixture containing humic acid; wherein the conditions of the alkaline hydrothermal treatment are: temperature 230° C., pH 10.5, reaction time 3 hours, and pressure 2 MPa;

[0045] S5. Acidifying the mixture containing humic acid obtained in step S4, adjusting the pH value to 2, so that humic acid is precipitated from the solution, filtering, and washing to obtain humic acid.

[0046] In this embodiment, the alkaline imidazole ionic liquid is [C2C1im][C1CO2], which is a type of alkaline ionic liquid and its chemical name is 1-ethyl-3-methylimidazolium acetate.

[0047] Example 4

[0048] The present invention provides a method for extracting humic acid from crop straw, comprising the following steps:

[0049] S1. crushing and drying the biomass waste to obtain pretreated biomass waste;

[0050] S2. Solving the pretreated biomass waste with an alkaline ionic liquid to obtain a lignin solution and a solid residue rich in cellulose and hemicellulose; the alkaline ionic liquid is an alkaline imidazole ionic liquid, and the concentration of the alkaline ionic liquid is 1 mol / L;

[0051] S3. subjecting the solid residue rich in cellulose and hemicellulose to an acidic hydrothermal treatment to convert the cellulose and hemicellulose into a liquid product rich in small molecular sugars and organic acids, thereby obtaining an acidic hydrothermal treatment solution, wherein the conditions for the acidic hydrothermal treatment are: temperature 140° C., pH 3, pressure 0.8 MPa, and time 50 min. After the hydrothermal treatment, the pH of the solution is adjusted to 5, and fructose phosphorylase and glucose oxidase are added to the acidic hydrothermal treatment solution, and the mixture is incubated at 30° C. for 30 min to obtain an enzymatic conversion mixture.

[0052] S4. Adding the lignin solubilizer obtained in step S2 to the enzymatic conversion mixture obtained in step S2, and performing alkaline hydrothermal treatment to obtain a mixture containing humic acid; wherein the conditions of the alkaline hydrothermal treatment are: temperature 200° C., pH 10, reaction time 2.5 hours, and pressure 1 MPa;

[0053] S5. First, ferric chloride and aluminum chloride are added to form a precipitate with the polyphenol compound. The polyphenol compound reacts with the ferric chloride and aluminum chloride to form a water-insoluble precipitate. The precipitate is removed by filtering to remove the polyphenol compound. The mixture containing humic acid obtained in step S4 is acidified and the pH value is adjusted to 1 to precipitate humic acid from the solution. After filtering, the mixture is washed to obtain humic acid.

[0054] In this embodiment, the alkaline imidazole ionic liquid is [C2C1im][C1CO2], which is a type of alkaline ionic liquid and its chemical name is 1-ethyl-3-methylimidazolium acetate.

[0055] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A method for extracting humic acid from biological waste, characterized in that: The following steps are involved: S1. crushing and drying the biomass waste to obtain pretreated biomass waste; S2. Solving the pretreated biomass waste with an alkaline ionic liquid to obtain a lignin solution and a solid residue rich in cellulose and hemicellulose; the alkaline ionic liquid is an alkaline imidazole ionic liquid; S3. Subjecting the solid residue rich in cellulose and hemicellulose to an acidic hydrothermal treatment to convert the cellulose and hemicellulose into a liquid product rich in small molecule sugars and organic acids, thereby obtaining an acidic hydrothermal treatment solution, wherein the acidic hydrothermal treatment is performed under the following conditions: a temperature of 140-180° C., a pH of 3-4, a pressure of 0.5-1 MPa, and a time of 30-60 min. After the hydrothermal treatment, the pH of the solution is adjusted to 5-7, and fructose phosphorylase and glucose oxidase are added to the acidic hydrothermal treatment solution, and the mixture is incubated at a temperature of 30-40° C. for 30 min to obtain an enzymatic conversion mixture. S4. Adding the lignin solubilizer obtained in step S2 to the enzymatic conversion mixture obtained in step S2, and performing alkaline hydrothermal treatment to obtain a mixture containing humic acid; wherein the conditions of the alkaline hydrothermal treatment are: temperature 200-230° C., pH 10-11, reaction time 2-3 hours, and pressure 1-2 MPa; S5. Acidifying the mixture containing humic acid obtained in step S4, adjusting the pH value to 1-2, so that humic acid is precipitated from the solution, filtering, and washing to obtain humic acid.

2. The method for extracting humic acid from biological waste according to claim 1, wherein: The biological waste is crop straw, forestry residues, and agricultural processing waste.

3. The method for extracting humic acid from biological waste according to claim 1, wherein: In step S5, metal ions that form precipitates with polyphenol compounds are first added, and the polyphenol compounds react with the metal ions to form a water-insoluble precipitate. The precipitate is removed by filtration to remove the polyphenol compounds. Then, the mixture containing humic acid obtained in step S4 is acidified to obtain high-purity humic acid.

4. The method for extracting humic acid from biological waste according to claim 3, wherein: The metal ion is one of aluminum ion and iron ion.

5. The method for extracting humic acid from biological waste according to claim 1, wherein: The concentration of the alkaline ionic liquid in step S2 is 1-5 mol / L.

6. The method for extracting humic acid from biological waste according to claim 1, wherein: The alkaline imidazolium ionic liquid is [C2C1im][C1CO2].