A method for preparing humic acid based on fenton oxidation assisted anaerobic digestion residue

Abstract

The application discloses a method for preparing humic acid based on Fenton oxidation assisted anaerobic digestion residue, and belongs to the technical field of humic acid preparation. In order to solve the problem that current researches are mostly concentrated on the influence effect of single process parameter, and lack of comprehensive optimization research of multiple process parameters for the purpose of shortening reaction time, reducing reaction temperature and improving reaction yield, the anaerobic digestion residue is dried, crushed and sieved to obtain anaerobic digestion residue powder; the anaerobic digestion residue powder is weighed, and Fenton reagent is added; after reaction and cooling, the anaerobic digestion residue is obtained by washing, vacuum filtration and impurity removal, and drying. The reaction substrate is Fenton post-anaerobic digestion residue, the reaction solution is KOH solution, the temperature, reaction time and KOH solution concentration are set, and the humic acid is separated and extracted. Through the cascade linkage mechanism of Fenton oxidation pretreatment-hydrothermal humification key parameter synergistic optimization, the efficient conversion of the anaerobic digestion residue into high-value-added artificial humic acid is realized.

Description

Technical Field

[0001] This invention belongs to the field of humic acid preparation technology, specifically relating to a method for preparing humic acid from anaerobic digestion residues based on Fenton oxidation-assisted oxidation. Background Technology

[0002] Humic acid is a large-molecule organic substance widely found in nature and is widely used in agriculture, forestry, animal husbandry, petroleum, chemical industry, building materials, medicine and health, environmental protection and other fields. Natural humic acid is mainly extracted from non-renewable energy sources such as lignite and peat. However, with the over-exploitation of non-renewable resources, natural resources are becoming scarce. Therefore, the rapid preparation of artificial humic acid from solid waste using hydrothermal humification technology is of great significance.

[0003] In environmental remediation materials: Artificial humic acid, as a functional material with abundant active functional groups (such as carboxyl and phenolic hydroxyl groups) and excellent complexing and adsorption properties, has the potential to be used for the purification of water pollutants. In soil amendment materials: Artificial humic acid improves fertilizer utilization and crop performance through complexation / chelation, ion exchange, pH buffering, improvement of soil aggregates, stimulation of root and nutrient absorption, regulation of microbial communities, and enhancement of stress tolerance. In solid waste resource utilization: Anaerobic digestion residues can be transformed into high-value-added functional materials, achieving the reduction and resource utilization of agricultural solid waste.

[0004] Existing technologies for the preparation of humic acid include:

[0005] 1. Patent application CN202410486244.9: A method and application for improving the yield of hydrothermal humic acid. This method involves first pretreating agricultural solid waste with alkali soaking (stirring in alkali solution for 2 hours followed by soaking for 22 hours), and then preparing humic acid under hydrothermal reaction conditions at 150 ℃ for 4 hours. This method can improve the yield of hydrothermal humic acid without increasing additional costs or hydrothermal reaction conditions, thus enabling the effective resource utilization of agricultural solid waste.

[0006] 2. Patent application CN202510565702.2: A method for preparing humic acid from kitchen waste, the method comprising: (1) drying and pulverizing the kitchen waste to obtain kitchen waste powder; (2) mixing the kitchen waste powder with water, adjusting the pH to acidic, and adding Fenton's reagent to carry out an oxidation reaction (the mass ratio of H2O2 to the mass of the kitchen waste powder is 1:10, Fe 2 +(2) The pretreated kitchen waste is obtained by reacting the pretreated kitchen waste with H2O2 at a molar ratio of 1:7.5 for 1 h; (3) The pretreated kitchen waste is subjected to a hydrothermal reaction (180 °C, 3 h) to obtain a primary hydrothermal product; (4) The primary hydrothermal product is classified and separated, and then subjected to a secondary hydrothermal reaction to obtain different humic acids. This method has great application potential in the field of humic acid production from kitchen waste.

[0007] The aforementioned existing technology has the following technical problems:

[0008] 1. Differences in raw material characteristics: Differences in raw materials significantly affect product characteristics. Current research has shown that humic acid can be prepared using kitchen waste and corn stalks as raw materials, but there is little research on anaerobic digestion residue.

[0009] 2. Pretreatment process: Existing hydrothermal pretreatment methods include alkaline soaking and acid hydrolysis, which require a large amount of acid and alkali chemical reagents, increasing the economic cost of the process. In addition, the pretreatment time is generally long (10-22 h), which increases the time cost and is not conducive to the sustainable development of the overall process.

[0010] 3. Fenton-Hydrothermal Parameter Optimization: Current optimization of Fenton oxidation pretreatment mainly focuses on Fe in the Fenton reaction. 2+ While there is an optimization of the H2O2 ratio, research on the optimization of hydrothermal parameters after Fenton is lacking. Process parameters that significantly affect hydrothermal humification efficiency and product characteristics include temperature, reaction time, and acidity / alkalinity. However, current research mostly focuses on the effects of single process parameters, lacking comprehensive optimization studies of multiple process parameters aimed at shortening reaction time, reducing reaction temperature, and increasing reaction yield. Summary of the Invention

[0011] The problem this invention aims to solve is that current research focuses on the effects of single process parameters, lacking comprehensive optimization studies of multiple process parameters aimed at shortening reaction time, reducing reaction temperature, and increasing reaction yield. Therefore, this invention proposes a method for preparing humic acid from anaerobic digestion residues based on Fenton oxidation-assisted anaerobic digestion.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] A method for preparing humic acid from anaerobic digestion residues based on Fenton oxidation-assisted oxidation includes the following steps:

[0014] Step 1. Physical pretreatment of raw materials: The anaerobic digestion residue produced after anaerobic digestion of cow manure and straw is dried in an oven to constant weight, then crushed by a pulverizer, and then sieved to obtain anaerobic digestion residue powder;

[0015] Step 2. Pretreatment of raw material by Fenton oxidation: Weigh the anaerobic digestion residue powder, add Fenton reagent, react for a certain time, cool, wash, vacuum filter to remove impurities, and dry to obtain the anaerobic digestion residue after Fenton oxidation.

[0016] Step 3. Hydrothermal humification reaction: The substrate of the reaction apparatus is the residue after Fenton's anaerobic digestion, and the reaction solution is KOH solution;

[0017] Step 4. Response surface methodology optimization: Set process parameters including temperature, reaction time, and KOH solution concentration;

[0018] Step 5. Humic acid separation and extraction: After centrifugation of the hydrothermal product, the liquid is retained and the solid is the residue; the pH of the liquid part is adjusted to <2 with hydrochloric acid, and it is allowed to stand for 12 h. After centrifugation, the upper yellow liquid is fulvic acid and the solid is humic acid; the fulvic acid is discarded, and the humic acid is repeatedly washed with deionized water to remove salt ions. After washing, it is dried to constant weight to obtain artificial humic acid.

[0019] Furthermore: the drying temperature in step 1 is 105℃.

[0020] Furthermore: the mesh size of the sieve in step 1 is below 120 mesh.

[0021] Further: In step 2, Fenton's reagent is FeSO4•7H2O + H2O2, and the anaerobic digestion residue powder ratio is FeSO4•7H2O:H2O2 = 22g:3g:70ml, with a reaction time of 2 h.

[0022] Furthermore: In step 2, a 0.45μm filter membrane is used for vacuum filtration.

[0023] Furthermore: the reaction apparatus in step 3 includes a 100 ml liner reactor and an oil bath.

[0024] Furthermore, in step 3, the solid-liquid ratio of the substrate to the reaction solution is 1:12.

[0025] Furthermore, the process parameters in step 4 are: 90℃ temperature, 1 h reaction time, and 0.5 mol / L KOH.

[0026] The beneficial effects of this invention are:

[0027] This invention proposes a method for preparing humic acid from anaerobic digestion residues based on Fenton oxidation-assisted anaerobic digestion. This method achieves efficient conversion of anaerobic digestion residues into high-value-added artificial humic acid through a cascade linkage mechanism of synergistic optimization of key parameters in Fenton oxidation pretreatment and hydrothermal humification. The humic acid yield of the anaerobic digestion residues after Fenton oxidation reaches 21.09%, significantly shortening the reaction time to 1 hour and reducing reaction energy consumption. Furthermore, scanning electron microscopy (SEM) images show that the surface of the prepared artificial humic acid exhibits a blocky polymeric structure with distributed spherical particles, indicating that the prepared artificial humic acid has an appearance structure similar to commercial humic acid. Attached Figure Description

[0028] Figure 1 This is a flowchart of a method for preparing humic acid from anaerobic digestion residues based on Fenton oxidation-assisted oxidation, as described in this invention.

[0029] Figure 2 SEM images: (a) artificial humic acid; (b) commercial humic acid. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described specific embodiments are merely a part of the embodiments of the invention, and not all of them. The components of the specific embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations, and the invention may also have other embodiments.

[0031] Therefore, the following detailed description of specific embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected specific embodiments of the invention. All other specific embodiments obtained by those skilled in the art based on these specific embodiments without inventive effort are within the scope of protection of this invention.

[0032] To further understand the invention's content, features, and effects, the following specific embodiments are provided, along with accompanying drawings. Figure 1 - Appendix Figure 2 Detailed explanation is as follows:

[0033] A method for preparing humic acid from anaerobic digestion residues based on Fenton oxidation-assisted oxidation includes the following steps:

[0034] Step 1. Physical pretreatment of raw materials: The anaerobic digestion residue produced after anaerobic digestion of cow manure and straw is dried in an oven to constant weight (drying temperature is 105℃), then crushed by a pulverizer, and then sieved (sieve mesh number is below 120 mesh) to obtain anaerobic digestion residue powder;

[0035] Step 2. Pretreatment of raw material by Fenton oxidation: Weigh the anaerobic digestion residue powder, add Fenton's reagent (FeSO4•7H2O + H2O2), the ratio of anaerobic digestion residue powder to FeSO4•7H2O to H2O2 is 22g:3g:70ml, the reaction time is 2 h, after cooling, wash and vacuum filter (using a 0.45μm filter membrane for vacuum filtration) to remove impurities, and dry to obtain the anaerobic digestion residue after Fenton oxidation;

[0036] Step 3. Hydrothermal humification reaction: The reaction apparatus consists of a reaction vessel with a 100 ml liner and an oil bath. Figure 2 The substrate was the anaerobic digestion residue after Fenton, the reaction solution was KOH solution (solid-liquid ratio of 1:12), and the hydrothermal control was the anaerobic digestion residue before Fenton.

[0037] Step 4. Response Surface Optimization: Set process parameters including temperature, reaction time, and KOH solution concentration; see Table 1 for the process parameters of each group in the response surface experiment:

[0038] Table 1 Process parameters for each group in the response surface methodology experiment

[0039]

[0040] The specific process parameters were determined to be: 90℃ temperature, 1 h reaction time, and 0.5 mol / L KOH.

[0041] Step 5. Humic Acid Separation and Extraction: After centrifugation of the hydrothermal product, retain the liquid (containing humic acid) and the solid as residue; adjust the pH of the liquid fraction to <2 with hydrochloric acid, let it stand for 12 h, and centrifuge again. The upper yellow liquid is fulvic acid, and the solid is humic acid; discard the fulvic acid, and repeatedly wash the humic acid with deionized water to remove salt ions. After washing, dry to constant weight (drying temperature is 60℃) to obtain artificial humic acid. Humic acid yield (%) = dry weight of humic acid (g) / dry weight of hydrothermal substrate (g).

[0042] The reaction principle of this invention:

[0043] This invention utilizes a tiered, interconnected mechanism of Fenton oxidation pretreatment and hydrothermal humification key parameter optimization to achieve efficient conversion of anaerobic digestion residues into high-value-added artificial humic acid. Firstly, Fenton oxidation utilizes Fe... 2+Catalytic H2O2 generates highly oxidizing hydroxyl radicals (•OH), effectively degrading macromolecular organic matter (such as lignin and proteins) into smaller precursors such as phenolic monomers, amino acids, and reducing sugars. This significantly reduces the mass transfer barriers and activation energy of subsequent hydrothermal reactions and shortens the hydrothermal treatment time. Subsequently, under high temperature and pressure hydrothermal conditions, the H⁺ generated by the self-ionization of H2O accelerates the hydrolysis of macromolecules such as cellulose and hemicellulose, while simultaneously promoting the synthesis of humic acid macromolecules with aromatic and carboxyl functional groups through pathways such as condensation, polymerization, and Maillard reactions. Finally, precise control of process parameters further amplifies this effect. Temperature provides the reaction driving force, time controls the reaction extent, and the alkaline environment provided by KOH promotes lignin removal and cellulose hydrolysis, significantly improving the conversion rate. However, excessively high concentrations increase costs and over-degrade cellulose, thus reducing yield. Therefore, controlling temperature, time, and KOH concentration is crucial. In summary, the Fenton pretreatment method unlocks the release of precursors, and the synergistic control of temperature, time, and KOH concentration in the hydrothermal humification process parameters shortens the traditional humification process, which takes months, to just a few hours, achieving efficient conversion of waste into resources.

[0044] In this example, the humic acid yield was 21.09% for the anaerobic digestion residue after Fenton and 15.17% for the anaerobic digestion residue before Fenton.

[0045] Comparison of process parameters: The reaction parameters for the group with the highest humic acid yield were 90℃ temperature, 1 h reaction time, and 0.5 mol / L KOH. Generally, the hydrothermal humification temperature is higher than 150℃ and the time is longer than 2 h. This invention significantly shortens the reaction time and reduces the reaction energy consumption.

[0046] SEM comparative analysis of the artificial humic acid prepared in this invention and commercial humic acid: Scanning electron microscopy (see [link]). Figure 2 Scanning electron microscopy (SEM) images revealed that the surface of the prepared artificial humic acid exhibited a blocky polymer structure with spherical particles, indicating that the surface structure of the artificial humic acid was similar to that of commercial humic acid.

[0047] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0048] Although this application has been described above with reference to specific embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, as long as there is no structural conflict, the features in the specific embodiments disclosed in this application can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, this application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing humic acid from Fenton oxidation-assisted anaerobic digestion residues, characterized in that, Includes the following steps: Step 1. Physical pretreatment of raw materials: The anaerobic digestion residue produced after anaerobic digestion of cow manure and straw is dried in an oven to constant weight, then crushed by a pulverizer, and then sieved to obtain anaerobic digestion residue powder; Step 2. Pretreatment of raw material by Fenton oxidation: Weigh the anaerobic digestion residue powder, add Fenton reagent, react for a certain time, cool, wash, vacuum filter to remove impurities, and dry to obtain the anaerobic digestion residue after Fenton oxidation. Step 3. Hydrothermal humification reaction: The substrate in the reaction apparatus is the residue from anaerobic digestion after Fenton, and the reaction solution is KOH solution; Step 4. Response surface methodology optimization: Set process parameters including temperature, reaction time, and KOH solution concentration; Step 5. Humic acid separation and extraction: After centrifugation of the hydrothermal product, the liquid is retained and the solid is the residue; the pH of the liquid part is adjusted to <2 with hydrochloric acid, and it is allowed to stand for 12 h. After centrifugation, the upper yellow liquid is fulvic acid and the solid is humic acid; the fulvic acid is discarded, and the humic acid is repeatedly washed with deionized water to remove salt ions. After washing, it is dried to constant weight to obtain artificial humic acid.

2. The method for preparing humic acid from anaerobic digestion residues based on Fenton oxidation-assisted oxidation according to claim 1, characterized in that: The drying temperature in step 1 is 105℃.

3. The method for preparing humic acid from anaerobic digestion residues based on Fenton oxidation-assisted oxidation according to claim 2, characterized in that: In step 1, the sieve mesh size is below 120 mesh.

4. The method for preparing humic acid from anaerobic digestion residues based on Fenton oxidation as described in claim 3, characterized in that: In step 2, Fenton's reagent is FeSO4•7H2O + H2O2, and the ratio of anaerobic digestion residue powder to FeSO4•7H2O to H2O2 is 22g:3g:70ml. The reaction time is 2 hours.

5. The method for preparing humic acid from anaerobic digestion residues based on Fenton oxidation as described in claim 4, characterized in that: In step 2, a 0.45μm filter membrane is used for vacuum filtration.

6. The method for preparing humic acid from anaerobic digestion residues based on Fenton oxidation-assisted oxidation according to claim 5, characterized in that: The reaction apparatus in step 3 includes a 100 ml liner reactor and an oil bath.

7. The method for preparing humic acid from anaerobic digestion residues based on Fenton oxidation as described in claim 6, characterized in that: In step 3, the solid-liquid ratio of the substrate to the reaction solution is 1:

12.

8. The method for preparing humic acid from anaerobic digestion residues based on Fenton oxidation-assisted oxidation according to claim 7, characterized in that: The process parameters in step 4 are 90℃ temperature, 1 h reaction time, and 0.5 mol / L KOH.

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