Preparation method and application of crop straw humic acid

Abstract

The invention provides a crop straw humic acid preparation method, which comprises: carrying out biomass pretreatment, alkali treatment and carbonization to obtain a humic acid precursor substance, carrying out acid water pyrolysis extraction, carrying out alkaline water pyrolysis extraction, carrying out centrifugation to retain the centrifugate, adjusting the pH value, collecting the precipitate, and purifying to obtain the crop straw humic acid. The invention also provides a method for promoting the growth of pakchoi by applying the crop straw humic acid. The crop straw humic acid prepared by the invention is very similar to commercial mineral source humic acid in structure, element composition and surface functional group, and can solve the problems that lignite is non-renewable, humic acid raw materials are deficient, and the humic acid industry is difficult to continuously develop.

Description

Technical Field

[0001] The invention belongs to the technical field of humic matter resource utilization, and particularly relates to a preparation method of crop straw humic acid and application thereof. Background Art

[0002] Humic acid is an important natural organic polymer widely used in agriculture, environmental protection, medicine, and other fields. It plays a vital role in agricultural production and environmental protection. Its unique chemical structure and properties endow it with diverse functions, such as soil improvement, fertilizer efficiency enhancement, and heavy metal adsorption. In today's critical situation, where excessive and extensive application of chemical fertilizers has led to a decline in arable land quality, the application of mineral-derived humic acid plays a vital role in maintaining soil fertility and ensuring sustainable agricultural development. With the increasing demand for sustainable resources and environmentally friendly technologies, the humic acid industry, particularly mineral-derived humic acid, is rapidly developing but also faces a series of challenges and problems. On the one hand, since humic acid raw materials are derived from natural resources such as lignite and peat, the mining and utilization of these materials not only depletes resources but also damages the ecology and pollutes the environment. On the other hand, the production and manufacturing of humic acid still faces technical bottlenecks, such as low production efficiency and unstable product quality. Therefore, methods for producing humic acid from biomass resources have attracted widespread attention. Brown charcoal is a hydrothermal decomposition and low-temperature carbonization technology, an effective method for converting biomass into mineral-based humic acid raw materials. To promote the sustainable development of the humic acid industry, this patent invents a method for preparing humic acid using brown charcoal as a raw material.

[0003] In summary, the problems faced by the humic acid industry and urgently need to be solved are as follows: (1) Raw materials are non-renewable, and the contradiction between raw material mining and environmental protection is becoming increasingly acute. The raw materials of humic acid come from natural resources such as lignite and peat, but the reserves of lignite and peat in my country and even the world are limited and non-renewable resources. In addition, the mining and utilization of lignite and peat often cause environmental damage, land swamping and water pollution. How to solve the problem of non-renewable raw materials and how to ensure that the humic acid manufacturing process does not damage and pollute the environment are the primary problems facing the humic acid industry. (2) There are technical bottlenecks in the production and manufacturing process of humic acid, such as low production efficiency, unstable product quality, and difficulty in utilizing by-products. This not only increases the production cost of humic acid, but also affects the market competitiveness of the product. (3) With the deepening of environmental protection and farmland conservation projects and the continuous development of ecological agriculture, the demand for humic acid in agriculture is increasing. However, due to the limitation of raw materials, the production scale of the humic acid industry is relatively small, the quality is uneven, and it is difficult to meet market demand. Therefore, a large number of biological humic acids have appeared on the market. However, biological humic acid does not have the same structure and function as mineral-derived humic acid, so the product's effects, functions, and application effectiveness are significantly reduced. Therefore, the key to ensuring the quantity and quality of the humic acid industry lies in utilizing biomass resources to develop humic acid raw materials, prepare humic acid, and develop corresponding humic acid manufacturing technologies and processes.

[0004] The formation processes of lignite and peat reveal that they are the product of long-term biochemical, geochemical, and physicochemical reactions that transform the remains of terrestrial and bog plants, respectively, into primary coal, rich in organic matter and charcoal. Peat formation begins in bogs and wetlands, where abundant water and poor air circulation provide ideal conditions for the accumulation and incomplete decomposition of plant remains. During peatification, plant debris is first acted upon by microorganisms such as aerobic bacteria and fungi, partially breaking down into gases and water while others are converted into simpler organic compounds. As bog water covers the area, anoxic conditions gradually develop, and anaerobic bacteria begin to dominate the decomposition process, further converting organic matter into stable substances such as humic acid. The key to peatification is the slow oxidation of lignin and cellulose in plant cell walls by microorganisms, transforming them into humus. In a weakly oxidizing or reducing environment, these humus undergoes gelation to form colloidal substances, ultimately constituting the primary component of peat. The formation of lignite is the result of further peat transformation. Over geological history, peat layers gradually compact and lose water under the influence of geothermal heat and pressure. Through a series of physical and chemical changes, such as aging and hardening, they eventually transform into lignite. Lignite is denser than peat, with an increased carbon content and relatively reduced humic acid and oxygen contents. The formation of lignite is a long and complex physical and chemical process involving multiple stages, including compaction, dehydration, and coalification. These processes act together on peat layers, gradually transforming them into lignite. Peatification and lignification are two key stages in coal formation, each of which evolves over a vast timescale in nature. Starting with plant remains, peatification forms peat, and then lignification forms lignite. The entire process takes millions to hundreds of millions of years. Therefore, once depleted, the resource will become scarce.

[0005] Analyzing the formation process of humic acid, humification is the decomposition, combination, and aggregation of organic matter in plants under the influence of biochemistry, geochemistry, physicochemistry, and geothermal heat. Therefore, theoretically, if specific physical and chemical methods can be used to achieve the decomposition, combination, and aggregation of biomass materials, the lengthy humification process in nature can be shortened and completed in a factory. This would enable the production of humic acid raw materials and the artificial synthesis of humic acid. This would represent an innovation and advancement in humic acid raw material substitution and the humic acid industry.

[0006] A Chinese patent (publication number: CN 107915215B) discloses a method for preparing biochar and its application. Although banana peels are used as biomass and undergo pretreatment and acid washing of the carbonized product, the carbonization temperature is between 500 and 1000°C. The resulting product is a biochar of relatively high purity, which is an adsorbent for particulate matter in the atmosphere and organic matter in water. Chinese patent (publication number: CN 107364860B) A method for preparing straw biochar by carbonization at low temperature and high efficiency provides a method for preparing straw biochar by carbonization at low temperature. Chinese patent CN201310643730.9 relates to a method for preparing biochar using straw. Chinese patent CN201610650186.4 discloses a method for preparing water hyacinth biochar. Chinese patent CN201710030796.9 relates to a carbonization device and process for preparing biochar at low temperature. Chinese patent CN201510410635.3 proposes a new method for producing biochar from tobacco waste. Although these patents aim to provide a method for preparing straw biochar by reducing the carbonization temperature, their purpose is to produce biochar, and the products are all biochar of relatively high purity. Although the above patents involve biomass such as banana peels and carbonization treatment, none of them involve the preparation of humic acid from biomass. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for preparing humic acid from crop straw and its application in view of the above-mentioned deficiencies in the prior art. The method can solve the problems of non-renewable lignite, lack of humic acid raw materials, and difficulty in sustainable development of the humic acid industry.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing humic acid from crop straw, the method comprising:

[0009] S1. Pretreatment of biomass:

[0010] The crop straw is washed and then naturally air-dried to obtain washed biomass;

[0011] S2, drying the washed biomass obtained in S1 to obtain dried biomass;

[0012] S3. Alkali treatment:

[0013] The dried biomass obtained in S2 is soaked in an alkaline solution, filtered and then filter-pressed to make the mass of the dried biomass and the adsorbed alkaline solution equal, and dried to obtain an alkali-treated biomass;

[0014] S4, carbonization:

[0015] Under anaerobic conditions with a vacuum pressure of -0.1 MPa, the alkali-treated biomass obtained in S3 is heated from room temperature to 150°C to 330°C at a heating rate of 3°C / min, carbonized at a constant temperature for 0.5h to 4h, and naturally cooled to room temperature to obtain a humic acid precursor;

[0016] S5. Acid-water pyrolysis extraction:

[0017] Deionized water is added to the humic acid precursor obtained in S4, the pH value of the system is adjusted to 1-6.5, and an acid pyrolysis reaction is carried out at a temperature of 100° C. to 300° C. for 5-6 hours. After naturally cooling to room temperature, an acid hydrolyzate is obtained;

[0018] S6. Alkaline water pyrolysis extraction:

[0019] The pH value of the acid hydrolyzate in S5 is adjusted to 8 to 14, and an alkaline pyrolysis reaction is carried out at a temperature of 60° C. to 280° C. for 1 to 5 hours, and then naturally cooled to room temperature to obtain an alkaline hydrolyzate;

[0020] S7, centrifuging the alkaline hydrolyzate obtained in S6, and retaining the centrifuge;

[0021] S8, adjusting the pH of the centrifuge obtained in S7 to 1-4 with a sulfuric acid aqueous solution, centrifuging, and collecting the precipitate;

[0022] S9, purification:

[0023] The precipitate obtained in S8 is washed with deionized water, centrifuged, collected, and dried to obtain crop straw humic acid.

[0024] Preferably, the crops in S1 are banana trees.

[0025] Preferably, in S2, the washed biomass obtained in S1 can be cut into a length of 2 to 5 cm, dried, and crushed to obtain dried biomass; the drying temperature in S2 is 105°C.

[0026] Preferably, the concentration of the alkaline solution in S3 is 0.05 mol / L to 1.50 mol / L; the alkaline solution is a KOH aqueous solution, a NaOH aqueous solution, a Na2CO3 aqueous solution or a NaHCO3 aqueous solution; the mass ratio of the dried biomass to the alkaline solution is 1:10; the soaking time in S3 is 1 h to 24 h; the filtration method in S3 is filtering with a nylon mesh with a pore size of 0.075 mm; the drying temperature in S3 is 105°C.

[0027] Preferably, the concentration of the aqueous sulfuric acid solution in S5 is 6 mol / L to 12 mol / L; the usage ratio of the humic acid precursor and deionized water in S5 is 1 g:20 mL; and the concentration of the aqueous sulfuric acid solution in S8 is 6 mol / L.

[0028] Preferably, the pH value is adjusted with a KOH solution in S6; the concentration of the KOH solution is 0.2 mol / L to 0.3 mol / L.

[0029] Preferably, the centrifugal speed in S7 to S9 is 4000 r / min, and the centrifugal time is 5 min to 30 min.

[0030] Preferably, the number of deionized water washing in S9 is 3 times; and the drying temperature is 40° C. to 60° C.

[0031] The present invention also provides an application of the crop straw humic acid prepared by the above-mentioned preparation method, wherein the crop straw humic acid is used to promote the growth of pakchoy.

[0032] Preferably, the concentration of the crop straw humic acid is 500 mg / L.

[0033] After drying, the dried biomass S2 is obtained. The dried biomass is conditioned with a sulfuric acid aqueous solution for 5 to 6 hours. The present invention has the following advantages over the prior art:

[0034] The present invention uses field crop straw as a biomass raw material, causes the straw to undergo a physical and chemical reaction under anaerobic conditions, high temperature, and supercharged conditions, and converts it into a substance similar to peat and lignite. This substance is referred to as a humic acid precursor in the present invention. The humic acid precursor is the raw material for artificially synthesizing humic acid. Humic acid is then extracted using the humic acid precursor. The crop straw humic acid prepared by the present invention is very similar to commercial mineral-source humic acid in structure, elemental composition, and surface functional groups. The present invention can solve the problems of the non-renewable nature of lignite, the scarcity of humic acid raw materials, and the difficulty of sustainable development of the humic acid industry. It has important practical significance and far-reaching historical significance for solving the sustainable development of modern agriculture and addressing food and food security.

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a SEM image of the humic acid precursor prepared in step S4 of Example 1 of the present invention.

[0037] Figure 2 This is a morphological diagram of the humic acid precursor prepared in step S4 of Example 1 of the present invention.

[0038] Figure 3 1 is a scanning electron microscope image of the banana straw humic acid prepared in Example 1 of the present invention and commercial mineral-source humic acid.

[0039] Figure 4 1 is an infrared spectrum of banana straw humic acid prepared in Example 1 of the present invention and commercial mineral source humic acid.

[0040] Figure 5 This is a morphological diagram of the humic acid precursor prepared in step S4 of Comparative Example 1 of the present invention.

[0041] Figure 6 This is a morphological diagram of the humic acid precursor prepared in step S4 of Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0042] Example 1

[0043] The preparation method of banana straw humic acid of the present embodiment is as follows:

[0044] S1. Pretreatment of biomass:

[0045] Washing banana straw (stems and leaves) to remove dirt and dust, and air-drying the banana straw to obtain washed biomass;

[0046] S2. Dry the washed biomass obtained in S1 at 105° C. for 2 h to obtain dried biomass. In the present invention, the washed biomass is dried using the original sample when manufactured using an industrial device. If the washed biomass is dried using a laboratory device, the washed biomass is cut into a length of 2 to 5 cm, dried, crushed, and passed through a 20-mesh sieve to obtain dried biomass before performing subsequent operations.

[0047] S3. Alkali treatment:

[0048] The dried biomass obtained in S2 was soaked in an alkaline solution for 2 hours, filtered through a nylon mesh with a pore size of 0.075 mm and then filtered to make the mass of the dried biomass and the adsorbed alkaline solution equal, and then air-dried and dried at a temperature of 105°C for 1 hour to obtain an alkaline-treated biomass; the alkaline solution was a KOH aqueous solution with a concentration of 0.25 mol / L; the mass ratio of the dried biomass to the alkaline solution was 1:10;

[0049] S4, carbonization:

[0050] Under anaerobic conditions at a vacuum pressure of -0.1 MPa, the alkali-treated biomass obtained in S3 was heated from room temperature to 225°C at a heating rate of 3°C / min, carbonized at this constant temperature for 2 hours, and naturally cooled to room temperature to obtain a humic acid precursor. The yield (%) of the humic acid precursor was calculated as follows: mass of the humic acid precursor / mass of the banana straw × 100%.

[0051] The yield of humic acid precursors was 27.8%;

[0052] S5. Acid-water pyrolysis extraction:

[0053] To 20 g of the humic acid precursor obtained in S4, 400 mL of deionized water was added, and the pH value of the system was adjusted to 4 with a 6 mol / L sulfuric acid aqueous solution. The mixture was subjected to acid pyrolysis at 200°C for 6 h, and then naturally cooled to room temperature to obtain an acid hydrolyzate.

[0054] The core function of acid hydrolysis is to remove impurities from humic acid precursors through protonation and hydrolysis, release humic acid, improve the purity of humic acid, change the molecular structure and the final application effect. What is different from the general industrial humic acid acid hydrolysis of this patent is that sulfuric acid is used throughout the process because sulfur is an essential nutrient element; the concentration of sulfuric acid in the acid hydrolysis is high, which improves work efficiency. Specifically: 1) It can effectively dissolve inorganic minerals such as bound calcium, magnesium, iron and other metal ions in the humic acid precursor to release humic substances. 2) It can hydrolyze non-humic organic matter such as polysaccharides and proteins in the raw materials, reducing the interference of impurities in the extraction of humic acid. 3) Acid hydrolysis may break some ester bonds and glycosidic bonds, increase humic acid production and improve the activity of humic acid. 4) Acid hydrolysis facilitates the dissolution of humic acid in the form of carboxylate (-COO-), which is beneficial to the subsequent precipitation and purification of humic acid.

[0055] S6. Alkaline water pyrolysis extraction:

[0056] The pH value of the acid hydrolyzate in S5 was adjusted to 12 with a 0.25 mol / L KOH aqueous solution, and alkaline pyrolysis reaction was carried out at a temperature of 200°C for 4 hours. After naturally cooling to room temperature, an alkaline hydrolyzate was obtained;

[0057] The core function of alkaline hydrolysis is to convert humic acid into soluble salts under alkaline conditions, achieving efficient extraction and providing a foundation for subsequent purification. KOH is used throughout the alkaline hydrolysis process because potassium is an essential nutrient. A relatively low KOH concentration (0.2 mol / L to 0.3 mol / L) prevents excessive alkaline hydrolysis from potentially affecting humic acid activity, such as molecular chain breakage and molecular weight reduction. Specifically: 1) Dissolving humic acid: Under alkaline conditions, humic acid dissolves as carboxylates (-COO-) and phenolates (-O-), separating them from insoluble impurities (such as cellulose and lignin residues) for efficient extraction. Alkaline hydrolysis converts insoluble, macromolecular humic acid into soluble potassium salts. 2) Alkaline conditions break hydrogen bonds between humic acid molecules and promote hydrophobic aggregation, promoting humic acid dispersion and solubility. 3) Alkaline hydrolysis partially hydrolyzes non-humic components such as proteins and esters in the humic acid precursor, reducing the impact of impurities on humic acid purity and solubility. 4) The solution after alkaline hydrolysis can be further purified by acid precipitation to reprecipitate humic acid.

[0058] S7. Centrifuge the alkaline hydrolyzate obtained in S6 at a speed of 4000 r / min for 10 min, and retain the centrifuge (marked as L);

[0059] S8. The centrifuge obtained in S7 is adjusted to pH 3 with a 6 mol / L sulfuric acid aqueous solution. Substances precipitate and are centrifuged at 4000 rpm for 10 min. The precipitate (labeled as D1) is collected. D1 is a mixture of humic acid and salt.

[0060] S9, purification:

[0061] The precipitate obtained in S8 was washed three times with deionized water, each time with 400 mL of deionized water. After washing, the precipitate was centrifuged at a speed of 4000 r / min for 10 min, and the precipitate (marked as D2) was collected and dried at a temperature of 60°C for 6 h to obtain banana straw humic acid.

[0062] Yield (%) of humic acid from crop straw = mass of D2 / mass of humic acid precursor × 100%.

[0063] The yield of banana straw humic acid in this embodiment is 22.5%.

[0064] The humic acid precursor obtained after carbonization in step S4 of this embodiment is brown in color, similar to the color of lignite, and the SEM morphology shows that the stem ( Figure 1 A) Leaf Figure 1 B) The semi-carbonized biomass tissue structure has a carbon content of 71.6% as determined by the C / N analyzer. The humic acid precursor still retains the original form of the stems and leaves, and its apparent morphology is as follows: Figure 2 shown.

[0065] The performance test of banana straw humic acid prepared in this embodiment is as follows:

[0066] (1) Scanning electron microscopy

[0067] The banana straw humic acid prepared in this example and the commercial mineral humic acid were compared. Samples for electron microscopy were prepared with reference to the sample preparation method for scanning electron microscopy. After gold plating, the morphological characteristics and surface elemental composition of the biochar were determined using a scanning electron microscope-energy dispersive spectrometer (SEM-EDS) (CARL ZEISS EVO 10, Germany) at an operating voltage of 10.0 kV. Figure 3 ) It can be seen that the structures of banana straw humic acid (A) and commercial humic acid (B) are similar, both of which are irregular blocks with rough surfaces and pores inside.

[0068] Commercial mineral humic acid was purchased from Shanxi Huasheng Humic Acid Co., Ltd.

[0069] (2) Energy spectrum analysis

[0070] Energy dispersive spectrometry (EDS) was used to determine the elemental composition of banana straw humic acid (A) and commercial mineral humic acid (B). The results showed that the elemental compositions of the two samples were very similar, with carbon contents of 62.55% (A) and 64.42% (B), hydrogen contents of 5.13% (A) and 5.31% (B), oxygen contents of 29.92% (A) and 28.5% (B), and nitrogen contents of 1.22% (A) and 1.38% (B). These results are consistent with the elemental content ranges reported for lignite humic acid in the literature (Francioso et al., 2005; Allard, 2006; Nasir et al., 2011). et al., 2018).

[0071] (3) Fourier transform infrared test

[0072] Fourier transform infrared (FTIR) spectrometer (Vertex 70, Bruker, Germany) was used to measure the wavelengths between 4000 and 400 cm -1 The surface functional groups of banana straw humic acid and commercial mineral humic acid within the wavelength range. Figure 4 As shown in the figure, the functional groups of banana straw humic acid (A) and commercial humic acid (B) are very similar. They both include 6 main characteristic peaks: at 3434 and 3431 cm -1 , 2918 and 2912 cm -1 , 1625 and 1617cm-1 , 1372 and 1435cm -1 , 1217 and 1201cm -1 , 599 and 588cm -1 Place.

[0073] (IV) Evaluation of the application effect of banana straw humic acid

[0074] Using large field plots (plot area of 9m 2 Each treatment was repeated three times, i.e., three plots were used. The banana straw humic acid (HA) prepared in this example and commercial mineral-source humic acid (FA) were used as materials to evaluate the effects of humic acid on pakchoy. The effects on pakchoy yield, root development, and nitrogen fertilizer agronomic efficiency were evaluated. The pakchoy variety in this example was Shanghai green.

[0075] The field experiment was conducted at the experimental base of South China Agricultural University on Wushan Road, Tianhe District, Guangzhou. The soil pH was 5.37, the total nitrogen content was 0.59%, and the available phosphorus content was 228.22 mg·kg -1 , fast-acting potassium content 170.33 mg·kg -1 The test crop was Shanghai green. The base fertilizer used in the experiment was a mixture of urea (46% N) and compound fertilizer (15-15-15) at a mass ratio of 2:1. The fertilizer application rate was 375 kg ha. -1 Nitrogen. Using water as a control, the effects of banana straw humic acid (HA) and commercial mineral humic acid (FA) on the yield, root length and agronomic efficiency of Chinese cabbage were studied by seed soaking, foliar spraying and root application (irrigation). The application concentrations of both humic acids included low concentration (50 mg L -1 ) and high concentrations (500 mg L -1 Seeds for the soaking treatment were soaked in HA, FA, and water for 24 hours before sowing. Seeds for the foliar spraying and root irrigation treatments were sown together. Seeds for the foliar spraying and root irrigation treatments were applied 10 days after emergence. Seedlings were harvested 40 days after emergence.

[0076] During the harvest period, the pakchoy trees in each plot were harvested, the yield was measured, and the effect of humic acid on the pakchoy yield was calculated (the results are shown in Table 1).

[0077] Two weeks after the application of humic acid, the entire root system was collected to investigate the effect of humic acid on promoting root development of pakchoi (results are shown in Table 1). Root length was measured using a root scanner.

[0078] At the harvest period, the pakchoy plants of each treatment were collected, the total nitrogen content of the pakchoy plants was determined, the nitrogen recovery rate of the pakchoy plants was calculated, and the effect of humic acid on the nitrogen fertilizer utilization rate of the pakchoy plants was evaluated (the results are shown in Table 1).

[0079] The results showed that, on the basis of uniform application of chemical fertilizers, whether 50 mg L -1 Or 500mg L -1 The results showed that the application of humic acid in the three methods of seed soaking, foliar spraying and root application significantly increased the yield of Chinese cabbage (except for the high concentration FA root application treatment), root length and nitrogen fertilizer agronomic efficiency, indicating that biomass humic acid (banana straw humic acid) has a significant growth-promoting effect. The results also showed that even at a concentration of 50 mg L -1 Under the condition of HA, the growth-promoting effect of HA on Chinese cabbage is generally not as good as that of FA. -1 Under the conditions of HA, the growth-promoting effect of HA on pakchoi is generally better than that of FA. It can be seen that the growth-promoting effect of brown charcoal humic acid prepared from biomass such as straw is significantly better than that of commercial mineral-source humic acid at a higher concentration.

[0080] Table 1 Comparison of the application effects of banana straw humic acid (HA) and commercial humic acid (FA) on pakchoy

[0081]

[0082] Comparative Example 1

[0083] The preparation method of banana straw humic acid in this comparative example is the same as that in Example 1, except that the carbonization temperature in step S4 is 500°C. Although the humic acid precursor obtained by carbonization at 500°C retains the original form of the stems and leaves, only a small amount of the product is similar to lignite. Most of the straw has been completely carbonized, and the product is black in color, similar to straw biochar, with a surface morphology like Figure 5 As shown, the yield of the humic acid precursor is lower than that of Example 1. The yield of the humic acid precursor prepared in step S4 is 19.3%; and the yield of banana straw humic acid calculated in step S9 is 0.36%.

[0084] Comparative Example 2

[0085] The preparation method of banana straw humic acid in this comparative example is the same as that in Example 1, except that the carbonization temperature in step S4 is 800°C. Although the banana straw product carbonized at 800°C still retains the original shape of the stems and leaves, the straw has been completely carbonized. The product after carbonization in step S4 is banana straw biochar, not the humic acid precursor required by the present invention. The banana straw biochar is black in color and has a shape like Figure 6 The yield of banana straw biochar obtained after carbonization in step S4 is significantly lower than that in Example 1, with a yield of 15.7%; and the yield of banana straw humic acid calculated in step S9 is 0.

[0086] As can be seen from Example 1 of the present invention and Comparative Examples 1-2, as the carbonization temperature gradually increases, the carbonization product undergoes significant changes. At the temperature of Example 1 (225°C), a lignite-like substance can be produced, which can serve as a precursor to humic acid. However, after the temperature exceeds 500°C, the biomass undergoes thorough pyrolysis (especially above 800°C), and the product is a high-purity charcoal that has almost lost the functional groups of humic acid. The obvious difference between the acid pyrolysis of the humic acid precursor obtained in Example 1 and the existing acid hydrolysis is that sulfuric acid is used throughout the process instead of hydrochloric acid, so that the product contains the essential nutrient element sulfur. The high concentration of sulfuric acid used (6-12 mol / L) improves the efficiency of the industrial process. The difference between this patent and the general industrial humic acid alkaline hydrolysis is that KOH is used throughout the process instead of NaOH, so that the product contains the essential nutrient element K. The low concentration of KOH used (0.2 mol / L-0.3 mol / L) prevents excessive alkaline hydrolysis from causing humic acid molecular chain breakage and molecular weight reduction, which reduces the activity of humic acid.

[0087] Example 2

[0088] The preparation method of banana straw humic acid of the present embodiment is as follows:

[0089] S1. Pretreatment of biomass:

[0090] Washing banana straw (stems and leaves) to remove dirt and dust, and naturally air-drying to obtain washed biomass; the crop is a banana tree;

[0091] S2. Cut the washed biomass obtained in S1 into a length of 2 to 5 cm, dry it at 105° C. for 2 h, crush it, and pass it through a 20-mesh sieve to obtain dried biomass;

[0092] S3. Alkali treatment:

[0093] The dried biomass obtained in S2 was soaked in an alkaline solution for 1 hour, filtered through a nylon mesh with a pore size of 0.075 mm and then filtered to make the mass of the dried biomass and the adsorbed alkaline solution equal, and dried at a temperature of 105°C for 1 hour to obtain an alkaline-treated biomass; the alkaline solution was a NaOH aqueous solution with a concentration of 1.50 mol / L; the mass ratio of the dried biomass to the alkaline solution was 1:10;

[0094] S4, carbonization:

[0095] Under anaerobic conditions with a vacuum pressure of -0.1 MPa, the alkali-treated biomass obtained in S3 was heated from room temperature to 330°C at a heating rate of 3°C / min, carbonized at a constant temperature for 4 hours, and naturally cooled to room temperature to obtain a humic acid precursor.

[0096] S5. Acid-water pyrolysis extraction:

[0097] To 20 g of the humic acid precursor obtained in S4, 400 mL of deionized water was added, and the pH value of the system was adjusted to 1 with a 12 mol / L sulfuric acid aqueous solution. The mixture was subjected to acid pyrolysis at 300°C for 6 h, and then naturally cooled to room temperature to obtain an acid hydrolyzate.

[0098] S6. Alkaline water pyrolysis extraction:

[0099] The pH value of the acid hydrolyzate in S5 was adjusted to 14 with a 0.20 mol / L KOH aqueous solution, and the system was subjected to alkaline pyrolysis at 60°C for 5 h. After naturally cooling to room temperature, an alkaline hydrolyzate was obtained.

[0100] S7. Centrifuge the alkaline hydrolyzate obtained in S6 at a speed of 4000 r / min for 30 min, and retain the centrifuge;

[0101] S8, adjusting the pH of the centrifuge obtained in S7 to 1 with a 6 mol / L aqueous sulfuric acid solution, causing a substance to precipitate. After centrifugation at a speed of 4000 r / min for 30 min, the precipitate was collected;

[0102] S9, purification:

[0103] The precipitate obtained in S8 was washed three times with deionized water, each time with 400 mL of deionized water. After washing, the precipitate was centrifuged at a speed of 4000 r / min for 30 min, and the precipitate was collected and dried at a temperature of 40° C. for 8 h to obtain banana straw humic acid.

[0104] In this embodiment, the yield of the humic acid precursor prepared in step S4 is 24.2%; and the yield of banana straw humic acid calculated in the final step S9 is 12.6%.

[0105] The banana straw humic acid prepared in this example is used to promote the growth of pakchoy (variety: Shanghai green).

[0106] Use a small area (the area of the small area is 9m 2 Each treatment was repeated three times, i.e., three plots. The experiment used banana straw humic acid (HA) prepared in Example 2 and commercial mineral humic acid (FA) as humic acid, and Shanghai green pakchoy as the listed crop. The effects of humic acid seed soaking and foliar spraying, as well as the application concentration, on pakchoy yield, root development, and agronomic efficiency of nitrogen fertilizer were evaluated. The results are shown in Table 2. The results showed that even at a concentration of 50 mg L -1 Under the condition of HA, the growth-promoting effect of HA on Chinese cabbage is generally not as good as that of FA. -1Under the condition of HA, the effect of promoting the growth of Chinese cabbage and improving the agronomic efficiency of nitrogen fertilizer is generally better than that of FA. -1 The growth-promoting effect of the above concentrations is significantly better than that of commercial mineral humic acid.

[0107] Table 2 Comparison of the application effects of banana brown charcoal humic acid (HA) and commercial humic acid (FA) on pakchoy

[0108]

[0109] Example 3

[0110] The preparation method of banana straw humic acid of the present embodiment is as follows:

[0111] S1. Pretreatment of biomass:

[0112] Washing banana straw (stems and leaves) to remove dirt and dust, and naturally air-drying to obtain washed biomass; the crop is a banana tree;

[0113] S2, cutting the washed biomass obtained in S1 into a length of 2 to 5 cm, drying at 105° C. for 2 h, crushing it, and passing it through a 20-mesh sieve to obtain crushed biomass;

[0114] S3. Alkali treatment:

[0115] The dried biomass obtained in S2 was soaked in an alkaline solution for 24 hours, filtered through a nylon mesh with a pore size of 0.075 mm and then filtered to make the mass of the dried biomass and the adsorbed alkaline solution equal, and dried at a temperature of 105°C for 1 hour to obtain an alkaline-treated biomass; the alkaline solution was a 0.05 mol / L Na2CO3 aqueous solution; the mass ratio of the dried biomass to the alkaline solution was 1:10;

[0116] The alkaline solution in this embodiment can also be a 0.05 mol / L NaHCO3 aqueous solution;

[0117] S4, carbonization:

[0118] Under anaerobic conditions with a vacuum pressure of -0.1 MPa, the alkali-treated biomass obtained in S3 was heated from room temperature to 150°C at a heating rate of 3°C / min, carbonized at a constant temperature for 0.5 h, and naturally cooled to room temperature to obtain a humic acid precursor.

[0119] S5. Acid-water pyrolysis extraction:

[0120] To 20 g of the humic acid precursor obtained in S4, 400 mL of deionized water was added, and the pH value of the system was adjusted to 6.5 with a 12 mol / L sulfuric acid aqueous solution. The mixture was subjected to acid pyrolysis at 100°C for 5 h, and then naturally cooled to room temperature to obtain an acid hydrolyzate.

[0121] S6. Alkaline water pyrolysis extraction:

[0122] The pH value of the acid hydrolyzate in S5 was adjusted to 8 with a 0.30 mol / L KOH aqueous solution, and the alkaline pyrolysis reaction was carried out at a temperature of 280°C for 1 hour. After naturally cooling to room temperature, an alkaline hydrolyzate was obtained;

[0123] S7. Centrifuge the alkaline hydrolyzate obtained in S6 at a speed of 4000 r / min for 5 min, and retain the centrifuge;

[0124] S8, adjusting the pH of the centrifuge obtained in S7 to 4 with a 6 mol / L aqueous sulfuric acid solution, causing precipitation of the substance, and centrifuging at 4000 rpm for 5 min to collect the precipitated substance;

[0125] S9, purification:

[0126] The precipitate obtained in S8 was washed three times with deionized water, each time with 400 mL of deionized water. After washing, the precipitate was centrifuged at a speed of 4000 r / min for 5 minutes, and the precipitate was collected and dried at a temperature of 60° C. for 8 hours to obtain banana straw humic acid.

[0127] In this embodiment, the yield of the humic acid precursor prepared in step S4 is 30.7%; and the yield of banana straw humic acid calculated in the final step S9 is 7.1%.

[0128] Use a small area (the area of the small area is 9m 2 Each treatment was repeated three times, i.e., three plots. The experiment used banana straw humic acid (HA) prepared in Example 3 and commercial mineral humic acid (FA) as humic acid, and Shanghai green pakchoy as the listed crop. The effects of humic acid seed soaking and foliar spraying, as well as the application concentration, on pakchoy yield, root development, and agronomic efficiency of nitrogen fertilizer were evaluated. The results are shown in Table 3. The results showed that even at a concentration of 50 mg L -1 Under the condition of HA, the growth-promoting effect of HA on Chinese cabbage is generally not as good as that of FA. -1 Under the condition of HA, the effect of promoting the growth of Chinese cabbage and improving the agronomic efficiency of nitrogen fertilizer is generally better than that of FA. -1The growth-promoting effect of the above concentrations is significantly better than that of commercial mineral humic acid.

[0129] Table 3 Comparison of the application effects of banana brown charcoal humic acid (HA) and commercial humic acid (FA) on pakchoy

[0130]

[0131]

[0132] The method for preparing humic acid from banana straw of the present invention can also be used to prepare humic acid from other crops, such as rice straw, corn straw, rubber trees, fruit tree trunks, etc., and the method of the present invention can be used to prepare humic acid precursors. The morphology of the phytic acid precursor is a semi-carbonized product that retains the original biomass structure, and humic acid is finally extracted from the humic acid precursor.

[0133] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing humic acid from crop straw, characterized in that: The method is: S1. Pretreatment of biomass: The crop straw is washed and then naturally air-dried to obtain washed biomass; S2, drying the washed biomass obtained in S1 to obtain dried biomass; S3. Alkali treatment: The dried biomass obtained in S2 is soaked in an alkaline solution, filtered and then filter-pressed to make the mass of the dried biomass and the adsorbed alkaline solution equal, and dried to obtain an alkali-treated biomass; S4, carbonization: Under anaerobic conditions with a vacuum pressure of -0.1 MPa, the alkali-treated biomass obtained in S3 is heated from room temperature to 150°C to 330°C at a heating rate of 3°C / min, carbonized at a constant temperature for 0.5h to 4h, and naturally cooled to room temperature to obtain a humic acid precursor; S5. Acid-water pyrolysis extraction: Deionized water is added to the humic acid precursor obtained in S4, the pH value of the system is adjusted to 1-6.5, and an acid pyrolysis reaction is carried out at a temperature of 100° C. to 300° C. for 5-6 hours. After naturally cooling to room temperature, an acid hydrolyzate is obtained; S6. Alkaline water pyrolysis extraction: The pH value of the acid hydrolyzate in S5 is adjusted to 8 to 14, and an alkaline pyrolysis reaction is carried out at a temperature of 60° C. to 280° C. for 1 to 5 hours, and then naturally cooled to room temperature to obtain an alkaline hydrolyzate; S7, centrifuging the alkaline hydrolyzate obtained in S6, and retaining the centrifuge; S8, adjusting the pH of the centrifuge obtained in S7 to 1-4 with a sulfuric acid aqueous solution, centrifuging, and collecting the precipitate; S9, purification: The precipitate obtained in S8 is washed with deionized water, centrifuged, collected, and dried to obtain crop straw humic acid.

2. The method for preparing humic acid from crop straw according to claim 1, wherein: The crops described in S1 are banana trees.

3. The method for preparing humic acid from crop straw according to claim 1, wherein: In S2, the washed biomass obtained in S1 can be cut into a length of 2 to 5 cm, dried, and crushed to obtain dried biomass; the drying temperature in S2 is 105°C.

4. The method for preparing humic acid from crop straw according to claim 1, wherein: The concentration of the alkaline solution in S3 is 0.05 mol / L to 1.50 mol / L; the alkaline solution is a KOH aqueous solution, a NaOH aqueous solution, a Na2CO3 aqueous solution or a NaHCO3 aqueous solution; the mass ratio of the dried biomass to the alkaline solution is 1:10; the soaking time in S3 is 1 h to 24 h; the filtration method in S3 is filtering with a nylon mesh with a pore size of 0.075 mm; the drying temperature in S3 is 105°C.

5. The method for preparing humic acid from crop straw according to claim 1, characterized in that: The concentration of the sulfuric acid aqueous solution in S5 is 6 mol / L to 12 mol / L; the usage ratio of the humic acid precursor and deionized water in S5 is 1 g:20 mL; the concentration of the sulfuric acid aqueous solution in S8 is 6 mol / L.

6. The method for preparing humic acid from crop straw according to claim 1, characterized in that: In S6, the pH value is adjusted with a KOH solution; the concentration of the KOH solution is 0.2 mol / L to 0.3 mol / L.

7. The method for preparing humic acid from crop straw according to claim 1, characterized in that: The centrifugal speed in S7 to S9 is 4000 r / min, and the centrifugal time is 5 min to 30 min.

8. The method for preparing humic acid from crop straw according to claim 1, characterized in that: The number of deionized water washing in S9 is 3 times; the drying temperature is 40°C to 60°C.

9. An application of crop straw humic acid prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The crop straw humic acid is used to promote the growth of Chinese cabbage.

10. The use according to claim 9, characterized in that The concentration of the crop straw humic acid is 500 mg / L.

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