Clean production method for preparing artificial humic acid from straw raw material

Abstract

The invention relates to the technical field of resource utilization of straw biomass energy, and discloses a clean production method for preparing artificial humic acid by using straw raw materials, which comprises the following steps: step 1, acidic hydrolysis: mixing straw raw material powder and water to obtain a raw material solution, heating and carrying out acidolysis on the straw raw materials to obtain an acidolysis solution and hydrothermal carbon mixture system; step 2, alkaline humic acidification: adjusting the pH value of the system, and heating for reaction to obtain an alkaline extraction solution; step 3, acidification solid-liquid separation: carrying out suction filtration on the alkali extraction solution to obtain hydrothermal carbon and suction filtration liquid; adjusting the pH value of the suction filtrate, filtering and separating the suction filtrate to obtain a humic acid product and acid liquor, and circulating the acid liquor for the mixed straw raw materials in the step 1. According to the scheme, the acidic wastewater generated during humic acid production is circularly used for acidic hydrolysis of the straw raw material in the first stage, so that the recycling effect of the acidic wastewater is effectively improved, the dosage of an acidic reagent can be effectively reduced, the cost is remarkably reduced, and the production benefit is improved.

Description

Technical Field

[0001] The invention relates to the technical field of resource utilization of straw biomass energy, and in particular to a clean production method for preparing artificial humic acid using straw raw materials. Background Art

[0002] Humic acid has been widely used in agricultural production in recent years due to its unique functions in improving soil, increasing the efficiency of fertilizers, enhancing crop resistance, and improving crop quality. Currently, humic acid is usually extracted from non-renewable raw materials such as peat and lignite, which has poor sustainability. Microbial fermentation methods such as composting are not only inefficient and highly polluting, but the fermentation products are organic materials rich in humic acid, not humic acid products.

[0003] In recent years, hydrothermal humification technology using biomass straw as raw material has provided feasibility for the preparation of artificial humic acid. The biomass is hydrolyzed and humified under alkaline conditions to produce humic acid products. However, this method faces the problem of alkaline humification and acid separation of the product, resulting in the generation of a large amount of acid-base waste liquid. For example, the prior art CN108753324A discloses a method for producing humic acid and block fuel by hydrothermal carbonization of corn straw. After the hydrothermal reaction, humic acid is extracted by alkaline humification, and the liquid phase product is concentrated and dried to obtain a sodium humate mixture. However, the prior art has the following technical problems: (1) The solid-liquid ratio of the hydrolyzed raw material in the prior art is as high as 1:25, and the pH of the solution in the alkaline humification reaction is relatively high (the pH of the alkaline solution in the embodiment is 13-14), which means that a large amount of acid solution is required for pH adjustment during the acidification and separation process, which increases the cost; (2) The prior art generates a large amount of inorganic acid waste liquid after humic acid extraction, and the concentration and drying process requires a large amount of liquid to be evaporated and concentrated, which consumes a lot of energy and greatly reduces the production efficiency; (3) When the pH is too high during alkaline humification, a large amount of lignin will be contained in the liquid phase after the reaction. Lignin and humic acid have similar molecular weight and solubility, and are difficult to separate in the extraction and purification stage, resulting in a large amount of lignin remaining in the product, thereby reducing the purity of the product, affecting its fertility, biological activity and chemical stability, and reducing the use effect of humic acid.

[0004] In view of this, developing a zero-emission, clean production method for preparing artificial humic acid using straw raw materials can not only effectively make up for the shortcomings of existing technologies, but also effectively reduce the energy consumption of waste liquid treatment, while achieving green production and improving production efficiency. Summary of the invention

[0005] The present invention aims to provide a clean production method for preparing artificial humic acid using straw raw materials, so as to solve the technical problem that a large amount of acid and alkali waste liquid is generated in the existing humic acid production process, which needs to be evaporated and concentrated, resulting in high energy consumption and greatly reducing the production efficiency.

[0006] To achieve the above object, the present invention adopts the following technical scheme: a clean production method for preparing artificial humic acid using straw raw materials, comprising the following steps:

[0007] Step 1, acid hydrolysis: mixing straw raw material powder and water to obtain a raw material solution, adjusting the pH of the raw material solution to 1-3, heating the straw raw material to acid hydrolyze the straw raw material, and obtaining an acid hydrolysis solution and a hydrothermal carbon mixture system;

[0008] Step 2: Alkaline humification: adjusting the pH of the acid hydrolysis solution and the hydrothermal carbon mixture system to 11-13, and heating the system to obtain an alkaline extraction solution;

[0009] Step 3: Acidification and solid-liquid separation: Filter the alkaline extraction solution to obtain hydrothermal charcoal and filtrate; adjust the pH of the filtrate to 1-3, filter and separate the filtrate into humic acid product and acid solution, and recycle the acid solution for mixing straw raw materials in step 1.

[0010] The principle of this scheme is:

[0011] This scheme uses acidic high-temperature hydrolysis to decompose macromolecules such as straw cellulose, hemicellulose, and lignin to produce glucose, 5-hydroxymethylfurfural, furfural, acetic acid, levulinic acid and other humic acid synthesis precursors, and then synthesizes and dissolves humic acid through alkaline humic acidification. The reason for the analysis is that under alkaline conditions, functional groups such as carboxyl groups in humic acid molecules will dissociate and produce negative ions, making humic acid more soluble in water. Subsequently, the alkali extraction solution is filtered to remove the undecomposed and alkaline-insoluble hydrothermal carbon in the solution, and finally the pH of the filtrate is adjusted to acidic. The functional groups in the humic acid molecules are affected by hydrogen ions, resulting in reduced solubility. After the humic acid precipitates, artificial humic acid is obtained by filtration, and the remaining acid solution contains partially dissolved fulvic acid, which is recycled in step one to continue acid hydrolysis of the straw raw material and regenerate humic acid, which not only realizes the full utilization of the acid solution, but also effectively saves the energy consumption of acid solution evaporation and concentration, and further improves production efficiency.

[0012] The advantages of this solution are:

[0013] 1. Compared with the existing humic acid production process, which generates a large amount of acidic and alkaline waste liquid and requires evaporation and concentration with high energy consumption, this scheme adjusts the solutions of the first stage (acidic hydrolysis) and the final stage (acidification solid-liquid separation) of humic acid production to acidic, and recycles the acidic wastewater generated during the production of humic acid for the acidic hydrolysis of straw raw materials in the first stage. On the one hand, the recycling effect of acidic wastewater is effectively improved, and no waste acid liquid is generated; on the other hand, the amount of acidic reagent used in acidic hydrolysis is effectively reduced, thereby significantly reducing costs and significantly improving production efficiency.

[0014] 2. In the present invention, the pH of the liquid after acidic hydrolysis is 4 to 6 (the decomposition of macromolecules consumes concentrated acid during the reaction, and a small amount of acid is produced for self-neutralization reaction), and the pH of the alkali extraction solution in the second stage is relatively low (pH 11 to 13), which significantly reduces the amount of alkali solution used and reduces costs. In addition, the acid used for acid correction in the third stage is an organic acid, which can be easily used as a precursor for humic acid synthesis. When the liquid phase product (i.e., acidic waste liquid) after humic acid is recycled into the first stage acidic hydrolysis straw raw material, the yield of humic acid after circulation is effectively improved.

[0015] 3. Compared with the reference document that adds sodium hydroxide alkali solution for humic acid extraction after the hydrothermal reaction, the present solution adds potassium hydroxide before the humification reaction, which can effectively improve the humification degree and thus improve the yield of humic acid. The applicant analyzed that the reason is that the humified precursor obtained after acid hydrolysis is more easily polymerized into humic acid macromolecules under alkaline conditions. Therefore, before extracting humic acid, adding potassium hydroxide can effectively increase the content of humic acid macromolecules in the system, thereby improving the yield of humic acid.

[0016] 4. This scheme effectively decomposes and extracts highly nutritious humic acid from straw raw materials by combining the stages of acid hydrolysis-alkaline extraction-solid-liquid separation after acid precipitation. In particular, the acidic initial pH of this scheme (i.e., the acidic pH in step 1) can provide more precursors for the subsequent humification process, thereby obtaining a higher humic acid yield. In this way, on the one hand, this scheme not only effectively improves the resource utilization effect of straw, but also, on the other hand, by optimizing the process conditions of each stage, effectively reduces impurities in humic acid, improves the purity of humic acid, and facilitates its direct application to the soil or application to the leaves after dilution to promote plant growth. The applicant has found through long-term experiments that if the pH in step one is too low, the humic acid precursor will decompose and accumulate due to excessive hydrolysis of the straw, thereby reducing the humic acid yield; if the pH in step one is too high, the humic acid precursor will accumulate insufficiently due to insufficient hydrolysis of the straw, thereby reducing the humic acid yield; if the pH in step two is too low, the humic acid yield will decrease due to further hydrolysis of the humified product at high temperature; if the pH in step two is too high, the subsequent humic acid acid precipitation extraction process will increase the amount of acid used, resulting in insufficient economy and environmental protection; if the pH in step three is too low, and the humic acid yield does not increase significantly when the pH continues to decrease, but leads to acid waste, which is not worth the loss; and if the pH in step three is too high, the salt ions in the humate cannot be completely exchanged by the hydrogen ions of the organic acid, and the extraction is not thorough, resulting in a reduction in the humic acid yield.

[0017] Preferably, as an improvement, in step one, the straw raw material is a combination of one or more of corn straw powder and sunflower straw powder.

[0018] Technical effect: This scheme adopts the above-mentioned setting, which makes it easy to fully utilize the organic matter in the straw raw material to produce humic acid products, thereby not only effectively improving the resource utilization rate of the straw, but also effectively turning waste into treasure.

[0019] Preferably, as an improvement, in step one, the particle size of the straw raw material powder is 0.15 to 0.425 mm.

[0020] Technical effect: This scheme adopts the above-mentioned setting to effectively improve the exposure of organic matter in the raw material, facilitate the full decomposition of organic matter in the straw raw material, improve the utilization rate of raw materials, and improve the yield of humic acid. The applicant has found through long-term experiments that if the particle size of the straw raw material powder is too large, it will not be able to fully contact the acid solution for hydrolysis due to the low exposure of organic matter in the raw material; and if the particle size of the straw raw material powder is too small, it will cause a waste of crushing energy.

[0021] Preferably, as an improvement, in step one, the solid-liquid mass ratio of the straw raw material mixed with water or acid solution is 1:8-12.

[0022] Technical effect: This scheme adopts the above-mentioned setting, which is convenient for fully acidifying and hydrolyzing the organic matter in the straw raw material powder, while reducing the amount of acid and subsequent alkali solution, thereby reducing costs. Specifically, using the solid-liquid ratio in this scheme, 10 to 120 kg of formic acid and 0.3 to 67 kg of potassium hydroxide are consumed for processing each ton (or KG) of straw raw material powder. The applicant has found through long-term experiments that if the solid-liquid ratio is too high (that is, too much straw raw material powder is used), the straw raw material powder will be poorly dissolved, which will affect the full contact and hydrolysis between the straw raw material powder and the acid solution, thereby reducing the humic acid yield; and if the solid-liquid ratio is too low (that is, too little straw raw material powder is used), the acid and alkali will be wasted due to the excessive volume of the solution and the heating reaction time will be prolonged, which will reduce efficiency, increase energy consumption and costs, and reduce production benefits.

[0023] Preferably, as an improvement, in step 1, the acid hydrolysis is carried out by heating the temperature to 180-240° C. for 2-6 hours.

[0024] Technical effect: This scheme adopts the above-mentioned setting, which is convenient for fully acidifying the organic matter in the straw raw material and improving the yield of humic acid products. The applicant found through long-term experiments that if the temperature of acid hydrolysis is too low, it will take a long time due to the slow decomposition of cellulose, hemicellulose and lignin in the straw; if the temperature of acid hydrolysis is too high, the hydrolysis products in the straw, such as monosaccharides, organic acids, furfural, and phenols, will be excessively decomposed into carbon dioxide and water, resulting in ineffective acid hydrolysis treatment and excessive energy consumption; if the acid hydrolysis time is too short, the accumulation of humic acid precursors will be insufficient due to insufficient decomposition of macromolecules in the straw; and if the acid hydrolysis time is too long, the treatment energy consumption will be high and the efficiency will be low because there is no need to further extend the reaction time after the macromolecules in the straw are completely decomposed.

[0025] Preferably, as an improvement, in step 2, the temperature-raising reaction is carried out at 180-240° C. for 6-20 hours.

[0026] Technical effect: This scheme adopts the above-mentioned setting, which is convenient for synthesizing humic acid from the humic acid precursor obtained by acidic hydrolysis and fully dissolving it, so as to improve the humic acid yield. The applicant has found through long-term experiments that if the temperature of alkaline humic acidification is too low, the humic acid yield will be low due to insufficient polymerization of humic acid precursor substances; if the temperature of alkaline humic acidification is too high, the humic acid yield will be low due to the decomposition of humification products; if the time of alkaline humic acidification is too short, the humic acid yield will be low due to insufficient polymerization of humic acid precursor substances; and if the time of alkaline humic acidification is too long, high energy consumption will result due to ineffective treatment.

[0027] Preferably, as an improvement, in step 1 and step 3, the acid used to adjust the pH is formic acid, acetic acid or a mixture of the two in any proportion, and in step 2, the base used to adjust the pH is potassium hydroxide.

[0028] Technical effect: This scheme adopts the above-mentioned setting, which is convenient for effectively adjusting the pH of the solution while avoiding the introduction of new impurities (such as chloride salts) into the humic acid product, and formic acid and acetic acid can be easily used as precursors for the synthesis of humic acid, which not only effectively improves the quality of the humic acid products produced, but also improves the yield of humic acid products. The applicant found through long-term experiments that if hydrochloric acid is used to adjust the pH, it will cause the chloride ions in the humic acid to be higher and harm the plants when applied, and will gradually accumulate the chloride ion content in the acid solution, so that some chloride ions will be entrained in the humic acid obtained by acid precipitation, which is not conducive to the growth of chlorine-avoiding crops. Specifically, the applicant has also tried to use hydrochloric acid and sodium hydroxide to adjust the pH of each step, but with the repeated acid-base adjustment of sodium hydroxide and hydrochloric acid, if the subsequent acid solution is reused, it is easy to cause a large amount of salt sodium chloride to accumulate in the acid solution, which is not only easily transferred to the humic acid product, affecting the product quality; and the acid solution must be discarded after being reused several times to avoid the chloride content in the humic acid product produced being too high and unable to meet the fertilization needs of "chlorine-avoiding crops".

[0029] Preferably, as an improvement, the present scheme also provides an artificial humic acid prepared using straw raw material, including the humic acid produced by the above method.

[0030] Preferably, as an improvement, the humic acid is high-purity palmitic acid.

[0031] Technical effect: This scheme adopts the above-mentioned setting to facilitate the acquisition of humic acid products that meet the national standard "GB / T33804-2017 Potassium Humate for Agricultural Use". BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the artificial humic acid obtained by hydrothermal humification-acid precipitation of corn stalks in the embodiment of the present invention.

[0033] Figure 2 This is a Fourier transform infrared absorption spectrum of artificial humic acid produced from corn stalks in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following examples and experimental examples are conventional means well known to those skilled in the art, and the materials, reagents, etc. used can be obtained from commercial sources.

[0035] Program Overview

[0036] This scheme provides a clean production method for preparing artificial humic acid using straw raw materials, comprising the following steps:

[0037] Step 1, acid hydrolysis: mixing straw raw material powder and water to obtain a raw material solution, adjusting the pH of the raw material solution to 1-3, heating the straw raw material to acid hydrolyze the straw raw material to obtain an acid hydrolysis solution;

[0038] As a reference, the straw raw material is one or more combinations of corn straw powder and sunflower straw powder. The particle size of the straw raw material powder is 0.15-0.425 mm (i.e. 40-100 mesh). The solid-liquid mass ratio of the straw raw material mixed with water or acid is 1:8-12. The temperature-raising acid hydrolysis is to heat the temperature to 180-240℃ for 2-6 hours. The acid used to adjust the pH is one of formic acid and acetic acid or a mixture of the two in any proportion.

[0039] Step 2: Alkaline humification: adjusting the pH of the acid solution to 11-13, heating the solution to obtain an alkaline extraction solution;

[0040] As a reference, the acid hydrolysis products of step 1, including the acid hydrolysis solution and the hydrothermal carbon solid, are all transferred to the alkaline hydrolysis system of step 2 for humification reaction. KOH is selected as the base for adjusting pH. The temperature reaction is carried out at 180-240°C for 6-20h.

[0041] Step 3: Acidification and solid-liquid separation: Filter the alkaline extraction solution to obtain hydrothermal charcoal and filtrate; adjust the pH of the filtrate to 1-3, filter and separate the filtrate into humic acid product and acid solution, and recycle the acid solution for mixing straw raw materials in step 1.

[0042] As a reference, the acid used to adjust the pH is formic acid, acetic acid, or a mixture of the two in any proportion.

[0043] This scheme also provides an artificial humic acid prepared by using straw raw materials, characterized in that: the humic acid produced by the method described in any one of claims 1 to 7 is a high-purity palmitic acid, such as Figure 1 As shown, after testing, the Fourier transform infrared absorption spectrum of the prepared artificial humic acid is as follows Figure 2 shown.

[0044] The present scheme also provides a method for treating acid waste liquid from humic acid production, including recycling the acid waste liquid for mixing with straw raw materials, extracting humic acid according to the above method, and regulating the acid waste liquid after recycling 3-4 times.

[0045] The conditioning treatment includes appropriate dilution according to the total dissolved solids (TDS) of the recycled acid to reduce the viscosity. As a reference, the total dissolved solids (TDS) of the recycled acid can be adjusted to 40,000 mg / L to avoid the increase in liquid viscosity caused by the accumulation of hydrolysis products such as sugars due to high reaction temperature and long reaction time, which affects the production of a new round of humic acid. This solution removes impurities and regulates the acid waste liquid after multiple cycles, so as to improve the humic acid yield during the recycling of the acid waste liquid and reduce the impact of impurities on the humic acid product, thereby effectively improving the purity of the humic acid product.

[0046] Example 1

[0047] The present invention provides a clean production method for preparing artificial humic acid using straw raw materials, comprising the following steps: (1) acid hydrolysis: first, 30g corn straw powder is mixed with a formic acid solution with a pH of 1 at a solid-liquid ratio of 1:10, and reacted at 200°C for 4h; (2) alkaline hydrothermal humification: after the acid hydrolysis is completed, KOH is added to the reaction system until the pH of the system is 13, and the reaction is continued at 200°C for 20h; (3) separation and purification: solid-liquid separation is performed by suction filtration through a Buchner funnel to obtain 8.6g of hydrothermal charcoal, and formic acid is continuously added to the filtrate until the pH is 1, and 5.2g of artificial humic acid is obtained by suction filtration and separation. The humic acid yield of the first time is: 5.2 / 30*100%=17.3%; (4) acid liquid circulation: liquid phase circulation is used for a total of 5 reactions, and the humic acid yields of the second to fifth times are 14.1%, 11.2%, 8.8% and 9.5% respectively.

[0048] The scheme also provides an artificial humic acid prepared by using straw raw materials, including the humic acid produced by the above method.

[0049] Example 2

[0050] The scheme provides a clean production method for preparing artificial humic acid using straw raw materials. First, 30g corn straw powder is mixed with a formic acid solution with a pH of 2 at a solid-liquid ratio of 1:8, and the mixture is reacted at 180°C for 6h. After the acidic hydrolysis is completed, KOH is added to the reaction system until the pH of the system is 12, and the reaction is continued at 240°C for 12h. The solid-liquid separation is performed by suction filtration through a Buchner funnel to obtain 9.1g of hydrothermal charcoal, and formic acid is added to the filtrate until the pH is 2. The artificial humic acid is separated by suction filtration to obtain 5.9g, and the humic acid yield of the first time is 19.7%; the liquid phase circulation reaction is performed for 5 times, and the humic acid yields of the second to fifth times are 15.5%, 9.7%, 9.8% and 8.5%, respectively.

[0051] The scheme also provides an artificial humic acid prepared by using straw raw materials, including the humic acid produced by the above method.

[0052] Example 3

[0053] The present invention provides a clean production method for preparing artificial humic acid using straw raw materials. First, 30g corn straw powder is mixed with a formic acid-acetic acid (molar ratio 1:1) mixed solution with a pH value of 2 at a solid-liquid ratio of 1:9, and reacted at 200°C for 4h; after the acidic hydrolysis is completed, KOH is added to the reaction system until the pH value of the system is 13, and the reaction is continued at 220°C for 8h; solid-liquid separation is performed by suction filtration through a Buchner funnel to obtain 6.4g of hydrothermal charcoal, and the filtrate is further added with a formic acid-acetic acid (molar ratio 1:1) mixed solution until the pH value is 1, and suction filtration is performed to separate and obtain 4.4g of artificial humic acid, and the first humic acid yield is 14.7%; liquid phase circulation is used for a total reaction for 5 times, and the humic acid yields of the 2nd to 5th times are 14.8%, 11.2%, 12.6% and 12.4%, respectively.

[0054] The scheme also provides an artificial humic acid prepared by using straw raw materials, including the humic acid produced by the above method.

[0055] Example 4

[0056] The scheme provides a clean production method for preparing artificial humic acid using straw raw materials. First, 30g of sunflower straw powder is mixed with a formic acid solution with a pH value of 1 at a solid-liquid ratio of 1:8, and the mixture is reacted at 200°C for 4 hours; after the acidic hydrolysis is completed, KOH is added to the reaction system until the pH value of the system is 13, and the reaction is continued at 200°C for 12 hours; solid-liquid separation is performed by suction filtration through a Buchner funnel to obtain 6.9g of hydrothermal charcoal, and formic acid is continuously added to the filtrate until the pH value is 1, and suction filtration and separation are performed to obtain 7.9g of artificial humic acid, and the first humic acid yield is 26.3%; liquid phase circulation is used for a total reaction for 5 times, and the humic acid yields of the second to fifth times are 28.9%, 31.5%, 33.8% and 36.1%, respectively.

[0057] The scheme also provides an artificial humic acid prepared by using straw raw materials, including the humic acid produced by the above method.

[0058] Example 5

[0059] The scheme provides a clean production method for preparing artificial humic acid using straw raw materials. First, 30g of sunflower straw powder is mixed with a formic acid solution with a pH value of 2 at a solid-liquid ratio of 1:8, and the mixture is reacted at 200°C for 6 hours; after the acidic hydrolysis is completed, KOH is added to the reaction system until the pH value of the system is 13, and the reaction is continued at 200°C for 8 hours; solid-liquid separation is performed by suction filtration through a Buchner funnel to obtain 7.7g of hydrothermal charcoal, and formic acid is continuously added to the filtrate until the pH value is 2, and suction filtration and separation are performed to obtain 8.1g of artificial humic acid, and the first humic acid yield is 27%; liquid phase circulation is used for a total reaction for 5 times, and the humic acid yields of the second to fifth times are 29.9%, 33.2%, 34.8% and 39.1%, respectively.

[0060] The scheme also provides an artificial humic acid prepared by using straw raw materials, including the humic acid produced by the above method.

[0061] Comparative Example 1

[0062] This comparative example is basically the same as Example 1, except that the pH in step 1 is 4.

[0063] According to the test, the humic acid yields in the first to fifth times in this comparative example were 14.5%, 12.1%, 11.2%, 9.8% and 8.2% respectively.

[0064] Comparative Example 2 This comparative example is basically the same as Example 1, except that the solid-to-liquid ratio in step 1 is 1:14.

[0065] According to the test, the humic acid yields in the first to fifth times in this comparative example were 15.8%, 10.5%, 9.8%, 8.2% and 8.6% respectively.

[0066] Comparative Example 3

[0067] This comparative example is basically the same as Example 1, except that the solid-liquid ratio in step 1 is 1:7.

[0068] According to the test, the humic acid yields from the 1st to the 5th times in this comparative example were 15.9%, 15.2%, 11.2%, 9.9% and 9.4% respectively.

[0069] Comparative Example 4

[0070] This comparative example is basically the same as Example 1, except that the pH in step 2 is 14.

[0071] According to the test, the humic acid yields in the first to fifth times in this comparative example were 17.2%, 15.5%, 10.8%, 11.2% and 9.5% respectively.

[0072] Comparative Example 5

[0073] This comparative example is basically the same as Example 1, except that the recycled acid solution is not diluted to reduce viscosity.

[0074] According to the test, the humic acid yields in the first to fifth times in this comparative example were 17.7%, 14.5%, 9.2%, 6.5% and 5.2% respectively.

[0075] Comparative Example 6

[0076] The present invention provides a clean production method for preparing artificial humic acid using straw raw materials. First, 30g corn straw powder is mixed with an acetic acid solution with a pH value of 3 at a solid-liquid ratio of 1:12, and the mixture is reacted at 240°C for 2h. After the acidic hydrolysis is completed, KOH is added to the reaction system until the pH value of the system is 11, and the reaction is continued at 200°C for 12h. The solid-liquid separation is performed by suction filtration through a Buchner funnel to obtain 9.3g of hydrothermal charcoal. Acetic acid is further added to the filtrate until the pH value is 3, and the artificial humic acid is obtained by suction filtration and separation. The humic acid yield of the first time is 10.7%. The liquid phase circulation reaction is performed for 5 times, and the humic acid yields of the second to fifth times are 8.8%, 9.1%, 9.8% and 7.2%, respectively.

[0077] Experimental data show that the yield of humic acid obtained from different straws as raw materials varies greatly. According to the applicant's analysis, when humic acid is produced from corn straw as raw material, the yield of humic acid products shows a downward trend as the acid solution is circulated more times. The applicant believes that the reason is that the effective utilization of humic acid precursors decreases during the recycling of acid solution with high cellulose content raw materials; while when sunflower straw is used as raw material, the yield of humic acid products shows an upward trend as the acid solution is circulated more times. The applicant believes that the reason is that the effective utilization of humic acid precursors is higher during the recycling of acid solution with high lignin content raw materials.

[0078] In addition, if the solid-liquid ratio of this solution is too high (such as in comparative example 3) or too low (such as in comparative example 2), the humic acid yield will be reduced. The applicant analyzed that if the solid-liquid ratio is too high (i.e., the amount of straw raw material powder is too much), the straw raw material powder will be poorly dissolved, which will affect the full contact and hydrolysis between the straw raw material powder and the acid solution, thereby reducing the humic acid yield; and if the solid-liquid ratio is too low (i.e., the amount of straw raw material powder is too little), the concentration of humic acid precursors after acid hydrolysis is too low, which makes it difficult to aggregate into large molecules during alkaline humification, resulting in deviation in its extraction efficiency, thereby reducing the humic acid yield.

[0079] Furthermore, the acidic initial pH (i.e., the acidic pH in step 1) can provide more precursors for the subsequent humification process, thereby obtaining a higher humic acid yield. If the pH in step 1 is too high (such as in comparative example 1), insufficient accumulation of humic acid precursors will occur due to insufficient hydrolysis of the straw, thereby reducing the humic acid yield.

[0080] In the acid hydrolysis, too high a temperature will also significantly affect the yield of humic acid. For example, in Comparative Example 6, the hydrolysis was carried out at 240°C for 2 hours. Although the other conditions were suitable, the acid hydrolysis temperature was too high. Even if the acid hydrolysis time was shortened, it could not make up for the damage to the structure of the humic acid precursor caused by the high temperature, resulting in a significant decrease in the yield of humic acid produced.

[0081] Furthermore, in this scheme, by adding potassium hydroxide before the humification reaction, the degree of humification can be effectively improved, thereby increasing the yield of humic acid. The applicant analyzed that the reason is that the humified precursor obtained after acid hydrolysis is more easily polymerized into humic acid macromolecules under alkaline conditions. Therefore, before extracting humic acid, the content of humic acid macromolecules in the system can be effectively increased by adding potassium hydroxide, thereby increasing the yield of humic acid. If the amount of potassium hydroxide is too much (such as pH to 14 in step 2 of comparative example 4), under extremely alkaline conditions, some functional groups of humic acid (such as carboxyl, phenolic hydroxyl, etc.) may undergo reactions such as decarboxylation and dehydration, resulting in the degradation of humic acid molecules, which may not only destroy the structure of humic acid molecules and reduce the yield; it will also increase the amount of acid used in the subsequent humic acid acid precipitation extraction process, resulting in insufficient economy and environmental protection.

[0082] Finally, during the continuous reuse of acid, appropriately diluting the acid to reduce its viscosity before reuse can also effectively increase the yield of humic acid after reuse.

[0083] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A clean production method for preparing artificial humic acid using straw raw materials, characterized in that: The steps include: Step 1, acid hydrolysis: mixing straw raw material powder and water to obtain a raw material solution, adjusting the pH of the raw material solution to 1-3, heating the straw raw material to acid hydrolyze the straw raw material, and obtaining an acid hydrolysis solution and a hydrothermal carbon mixture system; Step 2: Alkaline humification: adjusting the pH of the acid hydrolysis solution and the hydrothermal carbon mixture system to 11-13, and heating the system to obtain an alkaline extraction solution; Step 3: Acidification and solid-liquid separation: Filter the alkaline extraction solution to obtain hydrothermal charcoal and filtrate; adjust the pH of the filtrate to 1-3, filter and separate the filtrate into humic acid product and acid solution, and recycle the acid solution for mixing straw raw materials in step 1.

2. The clean production method for preparing artificial humic acid using straw raw materials according to claim 1, characterized in that: In step one, the straw raw material is one or more combinations of corn straw powder and sunflower straw powder.

3. The clean production method for preparing artificial humic acid using straw raw materials according to claim 1, characterized in that: In step 1, the particle size of the straw raw material powder is 0.15 to 0.425 mm.

4. The clean production method for preparing artificial humic acid using straw raw materials according to claim 1, characterized in that: In step 1, the solid-liquid mass ratio of the straw raw material mixed with water or acid liquid is 1:8-12.

5. The clean production method for preparing artificial humic acid using straw raw materials according to claim 1, characterized in that: In step 1, the acid hydrolysis is carried out by heating the temperature to 180-240° C. for 2-6 hours.

6. The clean production method for preparing artificial humic acid using straw raw materials according to claim 1, characterized in that: In step 2, the temperature rise reaction is carried out at 180-240° C. for 6-20 hours.

7. The clean production method for preparing artificial humic acid using straw raw materials according to claim 1, characterized in that: In step 1 and step 3, the acid used to adjust the pH is formic acid, acetic acid or a mixture of the two in any proportion. In step 2, the base used to adjust the pH is potassium hydroxide.

8. An artificial humic acid prepared using straw raw materials, characterized in that: The humic acid is produced by the method described in any one of claims 1 to 7.

9. The method for preparing artificial humic acid using straw raw materials according to claim 8, characterized in that: The humic acid is palmitic acid, which has the characteristics of alkali dissolution and acid precipitation.

10. A method for treating waste acid liquid from humic acid production, comprising recycling the waste acid liquid in the method according to any one of claims 1 to 7 for mixing with straw raw materials to extract humic acid 3-4 times, and then adjusting the waste acid liquid to reduce its viscosity.

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