Mineral source enzymatic humic acid and preparation method thereof

Abstract

This invention discloses a method for preparing mineral-derived enzymatically hydrolyzed humic acid, belonging to the field of deep processing technology of mineral-derived humic acid. The preparation method includes the following steps performed sequentially: raw material activation and chain breaking, precise acid adjustment and flocculation, efficient solid-liquid separation, compound emulsification enzymatic hydrolysis, and membrane separation purification. Specifically, the raw material activation and chain breaking uses an alkaline method to gently activate and destroy the cross-linked structure of macromolecules; the compound emulsification enzymatic hydrolysis uses a complex enzyme system composed of protease, cellulase, pectinase, laccase, and lignin peroxidase, combined with a dual emulsification enhancement synergistic effect to achieve the targeted degradation of macromolecular humic acid; the membrane separation purification uses a two-stage membrane filtration process of ultrafiltration and nanofiltration in series for desalination, impurity removal, and concentration. The obtained product, on a dry basis, has the following characteristics: total humic acid ≥70%, fulvic acid ≥35%, water solubility ≥99%, water-insoluble matter ≤1.0%, small molecule humic acid with a molecular weight <3000Da ≥30%, sulfur, chlorine, and sodium content ≤10g / L, total acidic group content ≥3.7mmol / g, and humic acid extraction rate ≥85%. The process of this invention is stable and controllable, and can be continuously industrialized. The product is suitable for agricultural water-soluble fertilizers, soil improvement and ecological restoration.

Description

Technical Field

[0001] This invention relates to the field of deep processing technology of mineral-derived humic acid, specifically to a mineral-derived enzymatic hydrolysis humic acid and its preparation method. The product has the characteristics of high extraction rate, strong activity, good water solubility, and low salt content, and its preparation method is suitable for industrial continuous production. Background Technology

[0002] Humic acid is a class of natural organic polymers rich in active groups such as carboxyl, hydroxyl, and phenolic hydroxyl groups. It is widely found in mineral resources such as weathered coal, lignite, and peat, and has broad application prospects in fields such as agricultural water-soluble fertilizers, soil improvement, ecological restoration, and industrial water treatment. With the increasing demand for high-quality water-soluble fertilizers and low-salt organic fertilizers in modern agriculture, traditional humic acid production processes are no longer sufficient to meet the requirements for high-quality, stable, and continuous production.

[0003] Traditional humic acid preparation methods often employ strong alkali extraction and acid precipitation separation, which generally suffer from problems such as insufficient degradation of macromolecules, poor water solubility, low content of active functional groups, low extraction efficiency, and high levels of water-insoluble matter. When using only enzymatic hydrolysis, the dense structure of the mineral raw materials, small enzyme contact area, and low mass transfer efficiency result in long hydrolysis cycles, uneven degradation, and unstable effects, making it difficult to adapt to continuous industrial production. Existing combined processes generally suffer from inaccurate raw material activation conditions, a single precipitation and flocculation system, unreasonable enzyme formulation, lack of enhanced shear emulsification, and lack of refined membrane separation and purification, leading to poor product quality stability, large fluctuations in indicators, high salt content, and difficulty in guaranteeing application effectiveness.

[0004] The following technological bottlenecks still exist in the industry: The total extraction rate of humic acid is low, resulting in insufficient utilization of raw materials. The macromolecular organic components are not completely degraded, have poor water solubility and are prone to precipitation and stratification. Enzymatic hydrolysis has low catalytic efficiency, uneven reaction, and insufficient content of active functional groups; Industrialized batch production exhibits poor stability, with key indicators fluctuating significantly. Without a standardized continuous production process that couples "raw material activation - precise flocculation - compound emulsification enzymatic hydrolysis - membrane separation and purification", it is difficult to stably supply mineral-derived enzymatically hydrolyzed humic acid with high content, high activity, high water solubility, and low salt content. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing technologies and provide a mineral-derived enzymatic hydrolysis of humic acid and its preparation method. Through a five-step coupled process of raw material activation and chain breaking, precise acid adjustment and flocculation, efficient solid-liquid separation, composite emulsification enzymatic hydrolysis and membrane separation purification, the targeted degradation and activation modification of macromolecular humic acid can be achieved.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing mineral-derived enzymatically hydrolyzed humic acid includes the following steps performed sequentially: (1) Raw material activation and chain breaking One or more of weathered coal, lignite, and peat are selected as raw materials. The total humic acid content in the raw materials is determined according to GB / T11957 and is not less than 40%. The raw materials are crushed to 60–120 mesh. The raw materials, 5%–15% sodium hydroxide solution, and purified water are mixed at a mass ratio of 1:(5–10):20. The mixture is stirred and activated at a constant temperature of 40–75℃ for 1–3 hours to obtain a homogeneous solid-liquid mixture.

[0007] (2) Precise acidity adjustment and flocculation Add sulfuric acid to the solid-liquid mixture to adjust the pH to 4.5–5.5; stir at a constant speed for 30–60 minutes to obtain an acidic homogeneous mixture.

[0008] (3) High-efficiency solid-liquid separation Solid-liquid separation is carried out by one or more of the following methods: plate and frame filtration, centrifugation, or vacuum filtration, to obtain a clear crude humic acid extract.

[0009] (4) Compound emulsified enzymatic hydrolysis The crude humic acid extract was subjected to a first high-speed emulsification for 30–60 minutes, with an emulsification shear speed of 3000–3500 r / min and a feed pressure of 0.3–0.5 MPa. The temperature was controlled at 25–35℃. A compound enzyme preparation was added according to the mass percentage of the crude humic acid extract: protease 0.2%–0.3%, cellulase 0.3%–0.4%, pectinase 0.1%–0.2%, laccase 0.1%–0.15%, and lignin peroxidase 0.15%–0.25%. Among them, the protease activity was ≥100,000 U / g, the cellulase activity was ≥50,000 U / g, the pectinase activity was ≥30,000 U / g, the laccase activity was ≥10,000 U / g, and the lignin peroxidase activity was ≥10,000 U / g. The enzymatic hydrolysis was carried out at a constant temperature for 2–6 hours. Then, a second emulsification was performed for 20–30 minutes, with the same emulsification parameters as the first time.

[0010] (5) Membrane separation and purification The process involves a series of ultrafiltration and nanofiltration membranes for impurity removal, desalination, concentration, and purification. The ultrafiltration pore size is 0.05–0.08 μm, and the nanofiltration pore size is 0.02–0.05 μm, yielding a mineral-derived enzymatically hydrolyzed humic acid product.

[0011] The mineral-derived enzymatically hydrolyzed humic acid prepared by the above method has the following product quality indicators: Total humic acid (dry basis) ≥70%; Fulvic acid (dry basis) ≥35%; Water solubility ≥99%; Water-soluble humic acid accounts for ≥98% of the total humic acid; The number of active functional groups (total acidic groups) is increased by ≥40% compared to the traditional alkaline extraction process; pH 4.5–5.5; Water-insoluble matter ≤1.0%; The content of sulfur, chlorine, and sodium elements is ≤10g / L (ion chromatography). Small molecule humic acid with a molecular weight <3000Da ≥30% (gel chromatography); A uniform brown liquid, odorless, without separation or sedimentation; Fecal coliform count ≤100 CFU / mL, total bacterial count ≤1000 CFU / mL; Heavy metal limits (mg / kg, dry basis): Cadmium (Cd) ≤3, Mercury (Hg) ≤2, Arsenic (As) ≤15, Lead (Pb) ≤50, Chromium (Cr) ≤150, Thallium (Tl) ≤2.5. Beneficial effects

[0012] Compared with the prior art, the present invention has the following beneficial effects: The extraction rate is high. Through the synergistic effect of raw material activation and chain breaking and compound enzymatic hydrolysis, the total humic acid extraction rate of the raw materials can reach more than 85%, and the total humic acid content of the product on a dry basis is not less than 70%.

[0013] It has good water solubility. The product has a water solubility of not less than 99%, water-insoluble matter of not more than 1.0%, and no precipitation or stratification.

[0014] It has a high content of active functional groups. Through the targeted degradation by compound enzymes, the active functional groups (total acidic groups) of the product are increased by more than 40% compared with the traditional alkaline extraction process, and the degree of small molecule size is high.

[0015] The process exhibits good stability. Employing a dual-emulsification enhancement and membrane separation coupling process, key parameters are clearly defined, batch consistency is good, and it is suitable for industrial continuous production.

[0016] Green and environmentally friendly. The reaction conditions are mild (40–75℃), and the permeate produced by membrane separation can be reused in the activation process, achieving water conservation and emission reduction.

[0017] High purity and low salt content. Effective desalination and deashing through two-stage membrane separation, with low sulfur, chlorine, and sodium content, and heavy metal and microbial indicators all meeting relevant requirements.

[0018] It has strong adaptability. The product can be used directly as a raw material for liquid humic acid, or it can be further dried into powder, which is suitable for fertilizers, soil conditioners, ecological restoration and other fields. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. Example

[0020] (1) Raw material activation: 100 mesh lignite (total humic acid content 43.2%), 10% NaOH solution and purified water are mixed in a mass ratio of 1:7:20 and activated at 65℃ for 2h to obtain a homogeneous mixture.

[0021] (2) Acid adjustment and flocculation: Add sulfuric acid to adjust the pH to 5.0 and stir for 45 minutes.

[0022] (3) Solid-liquid separation: Plate and frame filter press combined with centrifugation was used to obtain crude humic acid solution with an extraction rate of 86%.

[0023] (4) Compound emulsification and enzymatic hydrolysis: The first emulsification was carried out at 3200 r / min and 0.4 MPa for 55 min; 0.25% protease, 0.35% cellulase, 0.15% pectinase, 0.12% laccase and 0.20% lignin peroxidase were added at 30℃ and enzymatic hydrolysis was carried out for 4 h; then the second emulsification was carried out for 20 min.

[0024] (5) Membrane purification: 0.05μm ultrafiltration and 0.02μm nanofiltration are connected in series, and the product is obtained after desalting and concentration.

[0025] Finished product testing (dry basis): The total humic acid content was 73.2%, fulvic acid 38.5%, water solubility 99.2%, water insoluble matter 0.8%, total acidic groups 3.86 mmol / g (43% higher than the traditional alkali extraction process), and components with a molecular weight <3000 Da accounted for 32%; sulfur content was 2.3 g / L, chlorine content was 2.8 g / L, and sodium content was 2.9 g / L; heavy metal and microbial indicators all met the requirements. Example

[0026] (1) Raw material activation: Weathered coal and peat are mixed in a mass ratio of 1:1, crushed to 120 mesh (total humic acid content 42.8%), and mixed with 12% NaOH solution and purified water in a mass ratio of 1:6:20. Activation is carried out at 75℃ for 1.5h.

[0027] (2) Acid adjustment and flocculation: Adjust the pH to 5.2 and stir for 40 min.

[0028] (3) Solid-liquid separation: Plate and frame filtration combined with vacuum filtration was used, and the extraction rate was 85.5%.

[0029] (4) Emulsification and enzymatic hydrolysis: The first emulsification was carried out for 40 min at 3500 r / min and 0.5 MPa; the enzymatic hydrolysis was carried out at 28℃ for 3 h; and the second emulsification was carried out for 25 min.

[0030] (5) Membrane purification: 0.06μm ultrafiltration and 0.03μm nanofiltration are connected in series.

[0031] Finished product testing (dry basis): The total humic acid content is 72.5%, fulvic acid content is 38.1%, water solubility is 99.0%, water insoluble matter is 0.9%, total acidic groups are 3.79 mmol / g (41% higher than the traditional alkali extraction process), and the proportion of components with molecular weight <3000 Da is 31%; sulfur content is 2.1 g / L, chlorine content is 2.4 g / L, and sodium content is 2.5 g / L. Example

[0032] (1) Raw material activation: Mix 80 mesh weathered coal (total humic acid content 42.5%), 8% NaOH solution and purified water in a mass ratio of 1:8:20 and activate at 55℃ for 2.5h.

[0033] (2) Acid adjustment and flocculation: Adjust the pH to 4.8 and stir for 50 minutes.

[0034] (3) Solid-liquid separation: Centrifugal separation combined with vacuum filtration was used, and the extraction rate was 85.1%.

[0035] (4) Emulsification and enzymatic hydrolysis: The first emulsification was carried out for 60 min at 3000 r / min and 0.3 MPa; the enzymatic hydrolysis was carried out at 32℃ for 5 h; and the second emulsification was carried out for 30 min.

[0036] (5) Membrane purification: 0.08μm ultrafiltration and 0.04μm nanofiltration are connected in series.

[0037] Finished product testing (dry basis): The total humic acid content is 72.1%, fulvic acid content is 37.8%, water solubility is 99.3%, water insoluble matter content is 0.7%, total acidic groups are 3.83 mmol / g (42% higher than the traditional alkali extraction process), and components with molecular weight <3000 Da account for 33%; sulfur content is 2.5 g / L, chlorine content is 3.1 g / L, and sodium content is 3.4 g / L.

[0038] Comparative Example 1 (Traditional Alkali Extraction Process) Using the same raw materials as in Example 1, the sample was extracted with 10% NaOH, the pH was adjusted to 5.0 for acid precipitation, and the sample was filtered by plate and frame filter press without enzymatic hydrolysis, emulsification, or membrane desalting.

[0039] Test results: total humic acid 58.3%, water solubility 82.5%, water insoluble matter 5.2%, total acidic groups 2.70 mmol / g, and components with molecular weight <3000 Da accounted for 12%.

[0040] Comparative Example 2 (single enzymatic hydrolysis, no activation, no emulsification) Using the same raw materials as in Example 1, without adding alkali, only water and the same compound enzyme as in Example 1, the mixture was enzymatically hydrolyzed at 30°C for 6 hours and then filtered under pressure.

[0041] Test results: Total humic acid 52.6%, water solubility 75.3%, water insoluble matter 8.6%, total acidic groups 1.98 mmol / g, and components with molecular weight <3000 Da accounted for 9%.

[0042] Comparative Example 3 (without secondary emulsification) Compared with Example 1, the second emulsification step was omitted, all other parameters remained the same, and the total enzymatic hydrolysis time remained unchanged.

[0043] Test results: Total humic acid 68.5%, water solubility 94.2%, water insoluble matter 2.8%, total acidic groups 3.16 mmol / g, and components with molecular weight <3000 Da accounted for 23%.

[0044] As can be seen from the comparison between Examples 1–3 and Comparative Examples 1–3, the product obtained by the present invention through five-step coupling process, double emulsification enhancement, composite enzyme directional degradation and membrane separation purification is superior to the comparative examples in terms of humic acid extraction rate, water solubility, content of active functional groups and degree of small molecule formation, while the salt content is effectively controlled.

Claims

1. A method for preparing mineral-derived enzymatically hydrolyzed humic acid, characterized in that, This includes the following steps performed sequentially: (1) Raw material activation and chain breaking: Select one or more of weathered coal, lignite, and peat as raw materials. The total humic acid content shall be not less than 40% as determined by GB / T 11957. Crush the raw materials to 60–120 mesh. Mix the raw materials, 5%–15% sodium hydroxide solution, and purified water at a mass ratio of 1:(5–10):

20. Activate the mixture at a constant temperature of 40–75℃ for 1–3 hours to obtain a homogeneous solid-liquid mixture. (2) Precise acid adjustment and flocculation: Add sulfuric acid to the solid-liquid mixture to adjust the pH to 4.5–5.5, stir at a constant speed for 30–60 minutes to obtain an acidic homogeneous mixture; (3) High-efficiency solid-liquid separation: one or more of plate and frame filter press, centrifugal separation or vacuum filtration are used to remove inorganic impurities, undissolved residues and coarse particles to obtain crude humic acid extract; (4) Compound emulsification and enzymatic hydrolysis: The crude humic acid extract is subjected to high-speed emulsification for 30–60 minutes, with an emulsification shear speed of 3000–3500 r / min and a feed pressure of 0.3–0.5 MPa; the temperature is controlled at 25–35℃, and compound enzymes are added according to the mass percentage of the crude humic acid extract: protease 0.2%–0.3%, cellulase 0.3%–0.4%, pectinase 0.1%–0.2%, laccase 0.1%–0.15%, and lignin peroxidase 0.15%–0.25%; after enzymatic hydrolysis at constant temperature for 2–6 hours, a second emulsification is performed for 20–30 minutes, with the same emulsification parameters as the first time; (5) Membrane separation and purification: Ultrafiltration with a pore size of 0.05–0.08 μm and nanofiltration with a pore size of 0.02–0.05 μm are used for two-stage membrane filtration to remove impurities, desalinate, concentrate and purify, so as to obtain mineral-derived enzymatic hydrolyzed humic acid product.

2. The preparation method according to claim 1, characterized in that, The activity of the protease is ≥100,000 U / g, the activity of the cellulase is ≥50,000 U / g, the activity of the pectinase is ≥30,000 U / g, the activity of the laccase is ≥10,000 U / g, and the activity of the lignin peroxidase is ≥10,000 U / g.

3. The preparation method according to claim 1, characterized in that, The raw material mentioned in step (1) is lignite, or a mixture of weathered coal and peat in a mass ratio of 1:

1.

4. The preparation method according to claim 1, characterized in that, In step (2), adjust the pH to 5.0–5.

2.

5. The preparation method according to claim 1, characterized in that, Step (3) adopts a two-stage combination of plate and frame filtration and centrifugal separation, or a two-stage combination of plate and frame filtration and vacuum filtration.

6. The preparation method according to claim 1, characterized in that, In step (4), the enzymatic hydrolysis temperature is 28–32℃ and the enzymatic hydrolysis time is 3–5 hours.

7. The preparation method according to claim 1, characterized in that, Step (5) The pore size of the ultrafiltration membrane is 0.05–0.06 μm, and the pore size of the nanofiltration membrane is 0.02–0.03 μm.

8. The preparation method according to claim 1, characterized in that, The permeate produced during the membrane separation process is recycled for step (1) raw material activation process.

9. A mineral-derived enzymatically hydrolyzed humic acid, characterized in that, Prepared by the method described in any one of claims 1–8; on a dry basis, the total humic acid content is ≥70%, the fulvic acid content is ≥35%, the water solubility is ≥99%, the water insoluble matter is ≤1.0%, the small molecule humic acid with a molecular weight <3000Da is ≥30%, the sulfur, chlorine and sodium content are all ≤10g / L, and the total acidic group content is ≥3.7mmol / g.

10. The mineral-derived enzymatic hydrolyzed humic acid according to claim 9, characterized in that, The heavy metal content must meet the following requirements: Cd≤3mg / kg, Hg≤2mg / kg, As≤15mg / kg, Pb≤50mg / kg, Cr≤150mg / kg, Tl≤2.5mg / kg; total bacterial count ≤1000CFU / mL, and fecal coliform count ≤100 CFU / mL.