Method for converting plant waste into mineral-like source humic acid through hydrothermal catalysis

Abstract

The invention relates to a method for converting Chinese herbal medicine waste into mineral-like source humic acid through two-stage heating hydrothermal catalysis and a preparation method of an iron-doped nitrogen-phosphorus modified montmorillonite catalyst. Under hydrothermal conditions of two different temperature stages, by adding an organic acid catalyst and an iron-doped nitrogen-phosphorus modified montmorillonite novel catalyst, Chinese herbal medicine wastes are effectively converted into artificial humic acid similar to mineral source humic acid.

Description

Technical Field

[0001] The invention relates to the field of hydrothermal catalysis, and in particular to a method for converting plant waste, in particular Chinese herbal medicine waste, into mineral-based humic acid by heating hydrothermal catalysis, and the preparation of an iron-doped nitrogen-phosphorus modified clay mineral catalyst. Background Art

[0002] Plant waste, especially Chinese herbal medicine waste, refers to the waste generated during the processing of Chinese herbal medicines, the production of Chinese patent medicines, and the production and processing of other Chinese herbal medicine-related products. It is usually a mixture of roots, stems, leaves, etc. of plants after extraction. Chinese herbal medicines are natural traditional medicinal materials with a wide variety of types, but Chinese herbal medicine waste generally has the following characteristics: First, it is difficult to degrade, has a high fiber content, is seriously lignified, and is hindered by dense structures such as cellulose, hemicellulose and lignin in plant cell walls. The effective active ingredients in the cell cytoplasm are difficult to be fully extracted, resulting in a waste of medicinal resources. Second, it is rich in a variety of active substances such as amino acids, polysaccharides, alkaloids, fats, saponins, vitamins, organic acids, trace elements, etc., and has high reusability value. Third, the high water content (the mass fraction of water is greater than 80%) increases the difficulty of collection, transportation and treatment. Long-term stacking of Chinese herbal medicine waste will produce odor and affect air quality. The waste liquid after corruption is easy to penetrate into groundwater or flow into rivers, polluting water resources. Fourth, low toxicity. Chinese herbal medicine waste contains some unextracted organic acids and alkaloids, which threaten the safety of human and animal life and are not conducive to microbial treatment. How to fully utilize Chinese herbal medicine waste is an important link in the ecological chain of the Chinese medicine industry.

[0003] At present, there are many methods for treating Chinese herbal medicine waste, and the traditional methods include sanitary landfill and fixed-point incineration. As the most commonly used garbage disposal method, sanitary landfill has the characteristics of low cost, large disposal volume, and simple operation. However, in the process of degradation of Chinese herbal medicine waste, a large amount of odor, sewage, etc. will be generated, which will not only occupy a large amount of land resources, but also pollute the surrounding soil, atmosphere, and water environment, causing damage to the local ecology. Fixed-point incineration refers to the process of centralized treatment of Chinese herbal medicine waste at a fixed time and point, and through thermal decomposition, combustion, melting and other reactions, the Chinese herbal medicine waste becomes residue under high temperature. This process can convert toxic and harmful components in Chinese herbal medicine waste into harmless substances and significantly reduce the volume. However, Chinese herbal medicine waste has a large water content and low calorific value. When using this method, additional auxiliary fuel needs to be added, the investment is large, and a large amount of difficult-to-control waste gas will be generated during the incineration process, which is difficult to apply universally. These methods not only fail to effectively achieve the reduction and resource-based coordinated treatment of Chinese herbal medicine waste, but also lead to serious waste of resources and pollution of the surrounding ecological environment. Therefore, to accurately understand the economic value of Chinese herbal medicine waste, it is urgent to find a feasible resource treatment solution. In view of the richness of this kind of herbal waste, finding a universal treatment method has also become a difficult problem that needs to be solved urgently.

[0004] Humic acid is a high molecular weight organic acid composed of aromatics and multiple functional groups. It has good physiological activity and absorption, complexation, exchange and other functions. It is widely used as a soil remediation agent or organic fertilizer. Humic acid is divided into two categories according to its source: mineral-derived humic acid and biological-derived humic acid. Mineral-derived humic acid is generally extracted from low calorific value coal such as weathered coal and lignite, while biological-derived humic acid is obtained by microbial decomposition (fermentation, composting, landfill, etc.) of waste biomass (including human and animal feces, kitchen waste and other wastes containing high concentrations of organic matter). Compared with biological-derived humic acid, mineral-derived humic acid has more aromatic structures and active functional groups, which makes mineral-derived humic acid more suitable for soil remediation, improvement of saline-alkali land, promotion of plant growth, and avoidance of pests than biological-derived humic acid. However, traditional mineral-based humic acid relies solely on extraction from low calorific value coal, a process that is limited by low humic acid yield, high pollution during coal mining, and damage to the environment. In addition, coal takes more than 10,000 years (greater than 15,000 years) to form, and extracting humic acid from coal is an unsustainable process in a short time dimension. In addition, in the field of artificial synthesis of humic acid, strong acid and strong base catalysts are widely used, which is extremely unfavorable to the environment. In the soil, layered aluminosilicate minerals and iron oxides are often cemented together by various forces to form a complex. The silicate mineral-iron oxide complex is the basic unit of soil aggregate structure and controls many soil micro-interface processes, such as the fixation of nutrients, pollutants and organic carbon. The rational use of natural mineral materials as catalysts can not only increase the yield of humic acid, but also will not have an adverse effect on the subsequent application of humic acid. Therefore, it is urgent to develop a new technology for the sustainable production of mineral-based humic acid.

[0005] If we can simulate the natural process, use environmentally friendly hydrothermal reactions, take Chinese herbal medicine waste as substrate, and use modified natural clay structure minerals as catalysts to convert it into mineral-like humic acid, then we will achieve two birds with one stone. This will not only solve the problem of Chinese herbal medicine waste treatment, but also solve the high pollution problem that may be caused by the traditional humic acid preparation process. Summary of the invention

[0006] In order to overcome the above-mentioned defects of the prior art, the present invention provides a method for hydrothermal catalytic conversion of plant waste, especially Chinese herbal medicine waste, into mineral-based humic acid, and provides an iron-doped nitrogen-phosphorus modified clay structure mineral catalyst used in the above method, especially a montmorillonite catalyst and a preparation method thereof.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A method for hydrothermal catalytic conversion of plant waste into mineral-like humic acid, the method comprising converting the plant waste into mineral-like humic acid under hydrothermal conditions by adding an organic acid or inorganic weak acid catalyst A and an iron-doped nitrogen-phosphorus modified clay structure mineral catalyst B.

[0009] The mineral-source-like humic acid described in the present invention refers to humic acid obtained by a non-mineral extraction method and having a chemical structure that is identical or similar to that of mineral-source humic acid.

[0010] Preferably, the clay structure mineral is selected from: montmorillonite, kaolinite, illite and the like.

[0011] Preferably, the plant waste is Chinese herbal medicine waste.

[0012] Preferably, the catalyst A is selected from: a mixture of one or more organic acids such as citric acid, oxalic acid, malic acid, formic acid, and inorganic weak acids such as phosphoric acid.

[0013] Preferably, the hydrothermal condition is a two-stage hydrothermal condition, and the two-stage hydrothermal condition is: firstly, heating to 100-150°C and reacting for 10-60 minutes; then heating to 180-250°C and reacting for 10-60 minutes.

[0014] Preferably, the mass ratio of catalyst A to the waste is 1:20-1:1, the mass ratio of catalyst B to the waste is 1:20-1:5, and the mass ratio of the waste to water is 1:1-1:5.

[0015] The present invention also provides a method for preparing an iron-doped nitrogen-phosphorus modified clay structure mineral catalyst, the method comprising the following steps:

[0016] 1) Adding hydrogen phosphate solution to clay structure mineral, stirring in a water bath at 85-100° C. for 4-8 hours. After centrifugation, freeze drying for 12-16 hours to obtain phosphorus-modified clay structure mineral;

[0017] 2) dispersing the phosphorus-modified clay structure mineral in deionized water, adding a nitrogen-containing compound, wherein the mass ratio of the nitrogen-containing compound to the phosphorus-modified clay structure mineral is 1:10-1:20, adding the mixture into a hydrothermal reactor, and heating the mixture at 150-180° C. for 18-24 hours to obtain a nitrogen-phosphorus-modified clay structure mineral;

[0018] 3) Dispersing the nitrogen-phosphorus modified clay structure mineral in deionized water, adding iron salt to the suspension, stirring at room temperature, adding urea, the mass ratio of urea to the nitrogen-phosphorus modified clay structure mineral is 11:1-15:1, stirring at 80-100°C for 4-8h, washing, centrifuging, drying the product, and calcining in air for 6-12h to prepare an iron-doped nitrogen-phosphorus modified clay structure mineral catalyst.

[0019] Preferably, the clay structure mineral is selected from: montmorillonite, kaolinite, and illite.

[0020] Preferably, the hydrogen phosphate is selected from: K2HPO4, Na2HPO4.

[0021] Preferably, the nitrogen-containing compound is selected from: ammonia, ferrocenyldimethylamine, and glycine.

[0022] Preferably, the iron salt is selected from: ferric chloride, ferric nitrate, and ferric sulfate.

[0023] Preferably, the concentration of the hydrogen phosphate solution is 800-1500 mg / l, and is added to the clay structure mineral in a ratio of 10:1-20:1 (ml:g).

[0024] The present invention further provides an iron-doped nitrogen-phosphorus modified clay structure mineral catalyst, which is prepared by the method as described above.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1) For the first time, a non-strong acid or strong base catalyst is used in the field of artificial synthesis of humic acid. The main catalyst is a natural clay-structured mineral, especially montmorillonite, and the catalyst does not affect the application of humic acid in the soil.

[0027] 2) Clay structure minerals such as montmorillonite have a layered structure and good properties for promoting coupling reactions. They have the following properties: ① Adsorption and fixation of reactants: They have a large surface area and pore structure, and can adsorb and fix organic molecules or metal ions. In the coupling reaction, montmorillonite can adsorb reactants onto its surface or internal cavity, increase the concentration and contact rate of reactants, and facilitate the reaction. ② Enhance reaction selectivity: As a solid carrier, it can regulate the reaction conditions and environment to improve the selectivity of the coupling reaction. Provide a local environment, promote a specific reaction path, avoid the occurrence of side reactions, and thus improve the purity and yield of the reaction product. ③ Catalytic effect: It has catalytic activity itself and can promote the coupling reaction. For example, functional groups such as metal ions or hydroxides in montmorillonite can react with reactants, reduce activation energy, and accelerate the reaction rate. ④ Provide a stable reaction environment: It has a stable structure and chemical properties, and can provide a stable reaction environment during the reaction, which helps prevent the decomposition of reactants or the occurrence of adverse reactions, and ensure the efficiency and controllability of the reaction.

[0028] 3) Clay-structured minerals such as nitrogen-phosphorus-modified montmorillonite have nitrogen and phosphorus functional groups. Compared with clay-structured minerals such as ordinary montmorillonite, nitrogen-phosphorus-modified minerals have higher surface activity and richer chemical reaction sites, which are conducive to promoting coupling reactions: The key points are: ① Adsorption performance: It has more functional groups and active sites, stronger adsorption capacity and higher surface area, and significantly improves adsorption and catalytic performance. ② Selectivity and activity: Since nitrogen-phosphorus-modified montmorillonite has specific functional groups and structural characteristics, it has higher selectivity and activity for coupling reactions. ③ Thermal stability: Nitrogen-phosphorus-modified montmorillonite has better thermal stability and high temperature resistance. The nitrogen and phosphorus elements introduced during the modification process can enhance the thermal stability of montmorillonite, so that it still maintains good catalytic activity and structural stability under high temperature conditions. Iron can effectively catalyze the humification reaction. On the other hand, the adsorption and fixation of clay mineral catalysts makes it almost impossible for elements such as iron, nitrogen, and phosphorus to enter the reaction waste liquid, so it has good environmental friendliness, does not produce additional wastewater, and reduces the cost of wastewater treatment.

[0029] 4) Compared with traditional humic acid preparation methods, this technology uses plant waste, especially Chinese herbal medicine waste and other general industrial waste as raw materials, avoiding the use of non-renewable fossil energy-coal to prepare humic acid, thereby avoiding the pollution and environmental damage that may be caused by high coal mining. At the same time, this technology can obtain a higher yield of mineral-based humic acid.

[0030] 5) There are no special requirements for plant waste, especially Chinese herbal medicine waste, which can be used after simple crushing and a higher humic acid yield is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a representative FITR spectrum of the mineral-like humic acid described in the present invention;

[0032] Figure 2 This is a representative NMR spectrum of the mineral-based humic acid described in the present invention; DETAILED DESCRIPTION

[0033] Unless otherwise stated, implied from the context, or customary in the art, all parts and percentages in this application are based on weight, and the tests and characterization methods used are current as of the filing date of this application. If the definition of a specific term disclosed in the prior art is inconsistent with any definition provided in this application, the definition of the term provided in this application shall prevail.

[0034] The words "preferred", "preferably", "more preferably", etc. in the present invention refer to embodiments of the present invention that can provide certain beneficial effects in certain circumstances. However, other embodiments may also be preferred under the same circumstances or other circumstances. In addition, the statement of one or more preferred embodiments does not imply that other embodiments are not applicable, nor is it intended to exclude other embodiments from the scope of the present invention. The sources of components not mentioned in the present invention are all commercially available.

[0035] The following is a further clear and complete description of the technical features in the technical solution provided by the present invention in conjunction with specific implementation methods, which is not intended to limit the scope of protection thereof.

[0036] Embodiment 1:

[0037] Synthesis of iron-doped nitrogen-phosphorus-modified catalysts.

[0038] Step 1: Add 1000 mg / l K2HPO4 solution (pH 7) to natural montmorillonite at a ratio of 20:1 (ml:g), and stir in a 100°C water bath for 8 h. After centrifugation, freeze-dry for 12 h to obtain P-Mnt.

[0039] Step 2: Disperse 1g P-Mnt in 100ml deionized water, add appropriate amount of glycine, the ratio of glycine to montmorillonite is 1:20, add into Teflon hydrothermal reactor, heat at 180℃ for 24h to obtain PN-Mnt.

[0040] Step 3: Disperse 1g of P-N-Mnt in 1000ml of deionized water. Add 30mmol of FeCl3 to the suspension, stir at room temperature for 1h, add an appropriate amount of urea, the ratio of urea to montmorillonite is 5:1, stir at 100℃ for 4h, rinse the sample with deionized water and centrifuge, dry and calcine in air at 300℃ for 12h to prepare Fe@PN-Mnt.

[0041] Embodiment 2:

[0042] Use pure Radix Isatidis as Chinese herbal medicine waste.

[0043] Add 5g of Radix Isatidis, 10ml of deionized water, 2ml of phosphoric acid, and 0.5g of Fe@PN-Mnt to the reactor to make the filling rate reach 50%. After sealing the reactor, heat it to 120°C in the first stage and react for 1h. Heat it to 220°C in the second stage and react for 1h, and then cool it to room temperature. The solid humic acid content is quantified according to the determination method of total humic acid content of mineral sources in GBT34766-2017, and the yield of humic acid is calculated. The extracted humic acid is compared with natural mineral humic acid and biogenic humic acid by FITR, NMR and other characterizations. The characterization spectrum is attached. Figure 1-2.

[0044] The results showed that the humic acid yield was 21.5%, and the generated humic acid had a high degree of similarity with mineral source humic acid.

[0045] Embodiment 3:

[0046] According to the method of Example 2, the substrate was changed to betel nut shell. 5g of betel nut shell, 10ml of deionized water, 2ml of phosphoric acid, and 0.5g of Fe@PN-Mnt were added to the reactor to make the filling rate reach 50%. After the reactor was sealed, the temperature was raised to 120°C in the first stage, reacted for 1h, and the temperature was raised to 220°C in the second stage, reacted for 1h, and then cooled to room temperature. The solid humic acid content was quantified according to the determination method of total humic acid content of mineral sources in GBT34766-2017, and the yield of humic acid was calculated.

[0047] The results showed that the humic acid yield was 18.5%.

[0048] Embodiment 4:

[0049] According to the method of Example 2, the substrate was changed to Pinellia. 5g of Pinellia, 10ml of deionized water, 2ml of phosphoric acid, and 0.5g of Fe@PN-Mnt were added to the reactor to make the filling rate reach 50%. After the reactor was sealed, the temperature was raised to 120°C in the first stage, reacted for 1h, and the temperature was raised to 220°C in the second stage, reacted for 1h, and then cooled to room temperature. The solid humic acid content was quantified according to the determination method of total humic acid content of mineral sources in GBT34766-2017, and the yield of humic acid was calculated.

[0050] The results showed that the humic acid yield was 22%.

[0051] Embodiment 5:

[0052] According to the method of Example 2, the added acid was replaced with citric acid. 5 g of Radix Isatidis, 10 ml of deionized water, 2 ml of citric acid, and 0.5 g of Fe@PN-Mnt were added to the reactor to make the filling rate reach 50%. After the reactor was sealed, the temperature was raised to 120 ° C in the first stage, reacted for 1 h, and the temperature was raised to 220 ° C in the second stage, reacted for 1 h, and then cooled to room temperature. The solid humic acid content was quantified according to the determination method of total humic acid content of mineral sources in GBT34766-2017, and the yield of humic acid was calculated.

[0053] The results showed that the humic acid yield was 34.9%.

[0054] Embodiment 6:

[0055] A comparative experiment between organic acid and inorganic strong acid was conducted. According to the method of Example 5, the added acid was replaced with sulfuric acid. 5 g of Radix Isatidis, 10 ml of deionized water, 2 ml of sulfuric acid, and 0.5 g of Fe@PN-Mnt were added to the reactor to make the filling rate reach 50%. After the reactor was sealed, the temperature was raised to 120 ° C for one stage, reacted for 1 h, and the temperature was raised to 220 ° C for two stages, reacted for 1 h, and then cooled to room temperature. The solid humic acid content was quantified according to the determination method of total humic acid content of mineral sources in GBT34766-2017, and the yield of humic acid was calculated.

[0056] The results showed that the yield of humic acid was 17%. The results showed that the yield of strong acid was significantly lower than that of organic weak acid and it was corrosive to the reaction vessel.

[0057] Embodiment 7:

[0058] According to the method of Example 4, the amount of Fe@PN-Mnt added was increased. 5 g of Radix Isatidis, 10 ml of deionized water, 2 ml of citric acid, and 1 g of Fe@PN-Mnt were added to the reactor to make the filling rate reach 50%. After the reactor was sealed, the temperature was raised to 120 ° C in the first stage, reacted for 1 h, and the temperature was raised to 220 ° C in the second stage, reacted for 1 h, and then cooled to room temperature. The solid humic acid content was quantified according to the determination method of total humic acid content of mineral sources in GBT34766-2017, and the yield of humic acid was calculated.

[0059] The results showed that the humic acid yield was 39%.

[0060] Embodiment 8:

[0061] According to the method of Example 6, a solid mixture of Chinese herbal medicine waste was used as a reaction substrate. 5g of Chinese herbal medicine waste mixture, 10ml of deionized water, 2ml of citric acid, and 1g of Fe@PN-Mnt were added to the reactor to make the filling rate reach 50%. After the reactor was sealed, the temperature was raised to 120°C in the first stage, reacted for 1h, and the temperature was raised to 220°C in the second stage, reacted for 1h, and then cooled to room temperature. The solid humic acid content was quantified according to the determination method of total humic acid content of mineral sources in GBT34766-2017, and the yield of humic acid was calculated.

[0062] The results showed that the humic acid yield was 33%.

[0063] Embodiment 9:

[0064] According to the method of Example 1, the catalyst substrate montmorillonite was changed to kaolinite (Klt). 5g of Radix Isatidis, 10ml of deionized water, 2ml of phosphoric acid, and 0.5g of Fe@PN-Klt were added to the reactor to make the filling rate reach 50%. After the reactor was sealed, the temperature was raised to 120°C in the first stage, reacted for 1h, and the temperature was raised to 220°C in the second stage, reacted for 1h, and then cooled to room temperature. The solid humic acid content was quantified according to the determination method of total humic acid content of mineral sources in GBT34766-2017, and the yield of humic acid was calculated.

[0065] The results showed that the humic acid yield was 20.1%.

[0066] The above description of the embodiments is to facilitate the understanding and use of the invention by ordinary technicians in the technical field. It is obvious that those familiar with the technology in the field can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention. Any equivalent structure or equivalent process transformation made using the specification of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for hydrothermal catalytic conversion of plant waste into mineral-like humic acid, the method comprising converting plant waste into mineral-like humic acid under hydrothermal conditions by adding a weak acid catalyst A and an iron-doped nitrogen-phosphorus modified clay structure mineral catalyst B.

2. The method according to claim 1, characterized in that The clay structure mineral is selected from: montmorillonite, kaolinite, illite and the like.

3. The method according to claim 1, characterized in that The plant waste is Chinese herbal medicine waste.

4. The method according to claim 1, characterized in that The catalyst A is selected from one or more mixtures of organic weak acids or inorganic weak acids, and the catalyst A is preferably an organic weak acid.

5. The method according to claim 4, wherein the organic weak acid is selected from citric acid, oxalic acid, malic acid or formic acid, and the inorganic weak acid is phosphoric acid.

6. The method according to claim 1, characterized in that The hydrothermal conditions are two-stage hydrothermal, and the two-stage hydrothermal conditions are: firstly, heating to 100-150° C. and reacting for 10-60 minutes; then heating to 180-250° C. and reacting for 10-60 minutes.

7. The method according to claim 1, characterized in that The mass ratio of the catalyst A to the waste is 1:20-1:1, the mass ratio of the catalyst B to the waste is 1:20-1:5, and the mass ratio of the waste to water is 1:1-1:

5.

8. A method for preparing an iron-doped nitrogen-phosphorus modified clay structure mineral catalyst, the method comprising the following steps: 1) Adding hydrogen phosphate solution to clay structure mineral, stirring in a water bath at 85-100°C for 4-8h. After centrifugation, freeze drying for 12-16h to obtain phosphorus-modified clay structure mineral, preferably the hydrogen phosphate is selected from: K2HPO4, Na2HPO4; preferably the clay structure mineral is selected from: montmorillonite, kaolinite, illite; 2) dispersing the phosphorus-modified clay structure mineral in deionized water, adding a nitrogen-containing compound, wherein the mass ratio of the nitrogen-containing compound to the phosphorus-modified clay structure mineral is 1:10-1:20, adding the mixture into a hydrothermal reactor, and heating the mixture at 150-180° C. for 18-24 hours to obtain a nitrogen-phosphorus-modified clay structure mineral, wherein the nitrogen-containing compound is preferably selected from the group consisting of ammonia water, ferrocene dimethylamine, and glycine; 3) Dispersing the nitrogen-phosphorus modified clay structure mineral in deionized water, adding iron salt to the suspension, stirring at room temperature, adding urea, the mass ratio of urea to the nitrogen-phosphorus modified clay structure mineral is 11:1-15:1, stirring at 80-100°C for 4-8h, washing, centrifuging, drying the product, and calcining in air for 6-12h to prepare an iron-doped nitrogen-phosphorus modified clay structure mineral catalyst.

9. The method according to claim 7, characterized in that The iron salt is selected from: ferric chloride, ferric nitrate or ferric sulfate.

10. An iron-doped nitrogen-phosphorus modified clay structure mineral catalyst prepared by the method according to any one of claims 8 to 9.

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