A method for modifying crop straw and application thereof in carbon capture

Abstract

The present application relates to a kind of crop straw modification method and its application in carbon capture, the crop straw modification method includes the following steps: S1: crop straw is crushed to obtain fibrous straw raw material;S2: fibrous straw raw material is mixed with blocking agent powder, sprays composite surfactant, using sealed rotary heating mode is carried out chemical passivation treatment, obtains carbonized fibrous straw;S3: carbonized fibrous straw is cooled to 100 DEG C by watering, using composite surfactant aqueous solution is modified to carbonized fibrous straw;S4: after treatment, carbonized fibrous straw is open-air flat drying, and obtain modified crop fibrous straw.The present application is modified to crop straw by chemical passivation, realizes the efficient resource of crop straw and matrix utilization, promotes carbon capture and storage, with low cost, fast, green environmental protection and the like advantages.

Description

Technical Field

[0001] This invention relates to the field of agricultural waste treatment and resource utilization, and in particular to a method for modifying crop straw and its application in carbon capture. Background Technology

[0002] Crop straw refers to the remaining stems and leaves of crops after the grains are harvested, such as wheat, rice, corn, and sugarcane. It mainly consists of hollow, hard-walled, segmented stems and leaves, primarily composed of cellulose (40%–50%), hemicellulose (25%–30%), and lignin (15%–20%). Although straw resources are abundant, their utilization rate is very low. Large quantities of straw cannot be effectively recycled and are directly burned or discarded, causing environmental pollution and resource waste. Processing these crop straws into biochar can effectively realize the resource utilization of solid waste.

[0003] The main ways to utilize crop straw include fertilizer, feed, fuel, raw material, and substrate. Numerous scholars both domestically and internationally have conducted research in these areas. For example, the patent "Preparation of Modified Straw-Based Hydrothermal Carbon and Its Application in Carbon Dioxide Fixation (Patent No.: ZL202311415117.1)" converts straw into hydrothermal carbon using hydrothermal carbonization technology, lowering the preparation temperature of straw-based carbon materials and improving carbon dioxide fixation capacity through modification treatment. Another example is "A Modified Sugarcane Bagasse-Based Material and Its Application in Environmental Protection (Patent No.: ZL201810202401.3)" which develops sugarcane bagasse into a novel material through chemical modification, effectively removing pesticide residues from the soil. While the above technologies effectively realize the fuel and substrate utilization of crop straw, improving the utilization rate of straw resources, these preparation methods all require high temperatures (above 150℃), resulting in harsh preparation conditions, long high-temperature reaction times, and high energy consumption. These drawbacks significantly increase operating costs, thus limiting their promotion and application. However, chemical passivation and modification of crop straw not only offers simple and easy-to-control operation but also improves carbonization efficiency and carbon dioxide capture and storage capacity. More importantly, the reaction products exhibit good stability and chemical inertness, making them suitable for long-term storage. This effectively solves the problems of recycling and high-value conversion of agricultural waste, and can effectively replace traditional non-renewable resources such as peat and sphagnum moss, possessing significant practical value and social significance. Therefore, this invention provides a method for modifying crop straw and its application in carbon capture. Summary of the Invention

[0004] To address the problems existing in current technologies, this invention provides a low-cost, efficient, and environmentally friendly method for the resource utilization of crop straw, particularly a method for modifying crop straw and its application in carbon capture and storage. This method not only effectively improves the utilization rate of crop straw but also plays a crucial role in carbon capture and storage. Crop straw treated using the method of this invention can be transformed into high-value modified fibrous straw, providing a new pathway for the resource utilization of agricultural waste.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for modifying crop straw and its application in carbon capture, characterized in that the method for modifying crop straw includes the following steps:

[0007] S1: Initially screen and dry the crop straw raw material, crush it using a crusher, and sieve it through a 10-15 mesh sieve to obtain fibrous straw raw material;

[0008] S2: At room temperature, add the blocking agent powder to the fibrous straw raw material obtained in step S1, mix evenly, then spray the composite surfactant, let it stand for equilibration for 12 hours, and then use a sealed rotary heating method to carry out chemical passivation treatment to obtain carbonized fibrous straw.

[0009] S3: Spray water to cool the carbonized fibrous straw from step S2 to 100℃, then use a composite surfactant aqueous solution to modify the carbonized fibrous straw and let it stand for 12 hours to reach equilibrium.

[0010] S4: Spread the carbonized fibrous straw treated in step S3 out in the open air to air dry, and obtain modified fibrous straw.

[0011] Preferably, the crop straw mentioned in step S1 is selected from one or more of wheat straw, corn straw, rice straw, sugarcane bagasse from sugar mills, barley straw, sorghum straw, soybean straw, rapeseed straw, and cotton straw; more preferably, sugarcane bagasse from sugar mills, corn straw, sorghum straw, and soybean straw are selected from one or more of them.

[0012] Preferably, the length of the fibrous straw in step S1 is 5-10 mm;

[0013] Preferably, the blocking agent powder mentioned in step S2 is one or more of calcium carbonate, diatomaceous earth, and kaolin, and the addition ratio is 1 to 5 grams of blocking agent powder per kilogram of fibrous straw raw material.

[0014] Calcium carbonate is used to adjust the pH value of straw, improve carbonization, and has a certain filling and reinforcing effect, which can improve the strength and stability of modified straw. Diatomaceous earth, due to its high specific surface area and porosity, can increase the adsorption capacity of straw, helping to adsorb and fix harmful substances and improve carbonization efficiency. Kaolin has good adsorption and ion exchange properties and can be used to improve the adsorption performance of straw. It also has a certain binding property, which helps to enhance the binding force between straw particles and improve the overall performance of modified straw.

[0015] Preferably, the chemical passivation treatment in step S2 is specifically operated as follows: the fibrous straw raw material, after being placed and balanced for 12 hours, is loaded into an externally heated rotary kiln and sealed, and heated to 120-135°C at a speed of 30-60 rpm, and passivated for 10-30 minutes.

[0016] Preferably, the composite surfactant in step S2 is composed of C12-18 alkyl betaine and N-alkyl amino acid in a mass ratio of 1:1; the C12-18 alkyl betaine is preferably cocamidopropyl betaine, and the N-alkyl amino acid is preferably sodium lauroyl sarcosinate; the spraying ratio is 50-100 ml of a 1% concentration composite surfactant aqueous solution per kilogram of fibrous straw.

[0017] The composite surfactant is mainly composed of C12-18 alkyl betaines and N-alkyl amino acids in a 1:1 mass ratio. It effectively reduces the surface tension of fibrous straw, allowing water to quickly penetrate the surface and wetting the straw more rapidly and evenly, effectively solving the problem of water repulsion in the substrate. Cocamidopropyl betaine and sodium lauroyl sarcosinate are mild, have low irritation, low toxicity, good biodegradability, are safe, and have excellent compatibility. The 1:1 mass ratio of these two surfactants significantly reduces the irritation of individual surfactants, resulting in a milder composite surfactant solution.

[0018] Preferably, the modification treatment in step S3 is specifically carried out as follows: After the carbonized fibrous straw obtained in step S2 is sprayed with water to cool down to 100°C, it is poured into a mixer, and a 1% concentration of compound surfactant is sprayed while stirring until the humidity of the carbonized fibrous straw is 30-40%, and then left to equilibrate for 12 hours.

[0019] Preferably, the specific operation in step S4 is as follows: The carbonized fibrous straw treated in step S3 is spread out in the open to dry until its moisture content is [missing information]. Modified fibrous straw can then be obtained.

[0020] This invention also provides modified fibrous straw obtained by the modification method described above and its application in carbon capture. In the chemical passivation process, the fibrous straw undergoes a carbonization reaction under high-temperature, oxygen-free conditions. The carbon elements in the straw react with carbon dioxide, fixing the carbon dioxide in the biochar in a chemically bonded form. The composite surfactant improves the reaction efficiency between carbon dioxide and carbon elements in the straw by reducing surface tension and increasing reactive sites, further enhancing the carbon dioxide fixation and storage content during the carbonization process. After modification, the pore structure and surface properties of the fibrous straw change, resulting in stronger adsorption and fixation capabilities. These modified fibrous straws can serve as carbon sink materials to store captured carbon dioxide and prevent its re-release into the atmosphere. Therefore, the modified fibrous straw obtained by the above method can achieve carbon dioxide capture and storage during the modification process.

[0021] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0022] (1) This invention first forms a chemical barrier by mixing the blocking agent with crop fibrous straw, effectively blocking the active sites in the straw and reducing the decomposition and volatilization of the straw during the carbonization process, thereby improving the stability and performance of the carbonized fibrous straw. Then, the surfactant significantly improves the wettability and dispersibility of the straw surface, making the blocking agent powder more evenly distributed on the straw surface, thereby further improving the blocking effect. More importantly, the surfactant can promote the carbonization process of the straw, reduce the temperature and pressure required for straw carbonization, and save energy and costs for subsequent passivation treatment.

[0023] (2) This invention can rapidly convert crop straw into an organic matrix, with fast production speed, low cost, and easy promotion and implementation. This invention uses high-temperature passivation treatment, which uses an inhibitor to passivate the active groups of the cellulose, resulting in the appearance of phenolic hydroxyl groups, reducing CO and CH bond breakage, dehydration, cellulose pyrolysis, silicon-oxygen reaction to form Si-O-Si bonds, and glycosylation. This preserves the straw's porosity, mechanical strength, and hydrophilicity, eliminates insect eggs and harmful microorganisms in the mixed straw, and effectively blocks and inhibits the occurrence of diseases. In contrast, converting crop straw into an organic matrix using composting or fermentation methods takes 2-3 months and produces an unpleasant odor. Compared with the current use of fully decomposed fermentation products as cultivation substrates, this invention has a simpler, more time-saving, and more efficient preparation process.

[0024] (3) The raw materials used in this invention are widely available, low in cost, and have strong carbon sequestration capabilities. Common methods of straw disposal include burning, returning to the field, papermaking, and power generation, but all of these involve secondary pollution or disease transmission. This invention uses chemical passivation treatment to effectively enhance the anti-decomposition ability of crop straw fibers. Then, surfactants are used to modify the crop straw. It only takes 24 hours to transform the crop straw into a qualified substrate. After modification, the straw has a water holding capacity of 186%–230%, a porosity of 54%–78%, a total carbon content of 34%–45%, an easily decomposable carbon content of 5%–16%, and a fiber decomposition rate of 2.3–18.3 g / g·year, which is 92%–98% lower than the normal decomposition rate. It also achieves carbon storage of 340–460 g / kg. Based on an agricultural crop yield of 600 kg / mu, each hectare of crop planting can capture 50 tons of carbon dioxide and achieve storage, which is equivalent to the carbon dioxide capture capacity of 20–40 tons of forest carbon. Therefore, by applying the technology of this invention, crop straw can be directly converted into organic matter matrix, thereby realizing the efficient resource utilization of crop straw.

[0025] (4) The modified fibrous straw obtained by this invention is green, environmentally friendly, and recyclable. This invention uses high-temperature conversion and non-toxic, pollution-free surfactants to treat crop straw. The process does not generate new pollutants. The hemicellulose and lignin in the straw slowly decompose and transform into humic acid under natural conditions. When mixed with perlite, clay, sand, organic fertilizer, etc., it can meet the needs of plants for water, air, and fertilizer, effectively promote plant growth, and form a long-term and balanced nutrient supply system. Attached Figure Description

[0026] Figure 1 Process flow diagram for modifying crop straw

[0027] Figure 2 -A is a magnified image of sugarcane bagasse fiber before modification (magnified 40 times).

[0028] Figure 2 -B is a diagram of a cultivation substrate made from a mixture of modified sugarcane bagasse.

[0029] Figure 3 These are images showing the growth of Chinese cabbage grown in the cultivation substrate prepared by the modified fiber mixture in Examples 1-3 of this invention.

[0030] Figure 4 This is a diagram showing the root growth of Chinese cabbage grown in the cultivation substrate prepared by the modified fiber mixture in Examples 1-3 of this invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] A method for modifying sugarcane bagasse as raw material includes the following steps:

[0034] S1: The sugarcane bagasse raw material is initially screened and dried, crushed using a crusher, and sieved through a 10-mesh sieve to obtain sugarcane bagasse fibrous straw raw material with a fiber length of 8-10mm.

[0035] S2: At room temperature, mix 5 grams of calcium carbonate powder per kilogram of sugarcane bagasse fibrous straw raw material, spray 100 ml of a mixed aqueous solution of 1% cocamidopropyl betaine and sodium lauroyl sarcosinate (mass fraction ratio of 1:1) per kilogram of sugarcane bagasse fibrous straw, let it stand for equilibration for 12 hours, then put it into an externally heated rotary kiln and seal it, rotate and heat it to 135°C at a speed of 60 rpm, passivate it for 30 minutes, and obtain carbonized sugarcane bagasse fibrous straw;

[0036] S3: Spray water to cool down the carbonized sugarcane bagasse fiber from step S2. After the temperature drops to 100℃, pour it into a mixer and spray it again with a 1% cocamidopropyl betaine and sodium lauroyl sarcosinate mixed aqueous solution (mass fraction ratio of 1:1) until the moisture content of the carbonized sugarcane bagasse fiber is 30-40%. Stir it thoroughly and let it stand for 12 hours to reach equilibrium.

[0037] S4: Spread the carbonized bagasse fiber treated in step S3 out in the open and air-dry it until the moisture content is 25% to obtain modified bagasse fiber (e.g., Figure 2 -A is shown).

[0038] Example 2

[0039] A modification method using corn stalks, sugarcane bagasse, and soybean stalks (in a weight ratio of 1:1:1) as raw materials includes the following steps:

[0040] S1: The raw materials such as corn stalks, sugarcane bagasse, and soybean stalks are initially screened and dried, then crushed using a crusher and sieved through a 15-mesh sieve to obtain mixed fibrous straw with a fiber length of 5-8mm.

[0041] S2: At room temperature, mix 3 grams of diatomaceous earth powder per kilogram of mixed fibrous straw, spray 100 ml of 1% sodium lauroyl sarcosinate aqueous solution per kilogram of mixed fibrous straw, let it stand for equilibration for 12 hours, then put it into an externally heated rotary kiln and seal it. Rotate and heat it to 130°C at 30 rpm and passivate it for 20 minutes to obtain carbonized fibrous straw.

[0042] S3: Spray water to cool down the carbonized fibrous straw from step S2. After the temperature drops to 100℃, pour it into the mixer and spray it again with a 1% concentration of sodium lauroyl sarcosinate solution until the moisture content of the carbonized sugarcane bagasse fiber is 30-40%. Stir it thoroughly and let it stand for 12 hours to reach equilibrium.

[0043] S4: Spread the carbonized fibrous straw treated in step S3 out in the open and air dry it until the moisture content is 25% to obtain modified mixed fibrous straw made from corn straw, sugarcane bagasse and soybean straw.

[0044] Example 3

[0045] A modification method using corn stalks and sorghum stalks (by weight 1:1) as raw materials includes the following steps:

[0046] S1: The corn stalks and sorghum stalks raw materials are initially screened and dried, crushed using a crusher, and sieved through a 15-mesh sieve to obtain mixed fibrous straw with a fiber length of 8-10mm.

[0047] S2: At room temperature, mix 1 gram of calcium carbonate powder per kilogram of mixed fibrous straw, spray 50 ml of a mixed aqueous solution of 1% cocamidopropyl betaine and sodium lauroyl sarcosinate (mass fraction ratio of 1:1) per kilogram of fibrous straw, let it stand for equilibration for 12 hours, then put it into an externally heated rotary kiln and seal it, rotate and heat it to 120°C at a speed of 30 rpm, passivate it for 30 minutes, and obtain carbonized fibrous straw;

[0048] S3: Spray water to cool down the carbonized fibrous straw from step S2. After the temperature drops to 100℃, pour it into the mixer and spray it again with a 1% concentration of sodium lauroyl sarcosinate solution until the humidity of the carbonized fibrous straw is 30-40%. Mix it thoroughly and let it stand for 12 hours to reach equilibrium.

[0049] S4: Spread the carbonized fibrous straw treated in step S3 out in the open and air dry it until the moisture content is 15% to obtain modified mixed fibrous straw made from corn straw and sorghum straw.

[0050] Example 4

[0051] A modification method using bagasse as raw material involves direct passivation treatment for 30 minutes in step 2 without adding blocking agents and surfactants. Other specific operations are the same as in Example 1, resulting in modified bagasse fiber.

[0052] Example 5

[0053] A modification method using wheat straw, barley straw, and rice straw (in a weight ratio of 1:1:1) as raw materials is described. The specific operation process is the same as in Example 2, resulting in modified mixed fibrous straw made from wheat straw, barley straw, and rice straw.

[0054] Example 6

[0055] A modification method using bagasse as raw material involves increasing the passivation treatment temperature in step S2 to 150°C, while other specific operations are the same as in Example 1, to obtain modified bagasse fiber.

[0056] Comparative Example 1

[0057] Using bagasse as raw material, the bagasse is initially screened and dried, then crushed using a pulverizer and sieved through a 10-mesh sieve to obtain bagasse fiber raw material with a fiber length of 8-10 mm. It is then placed in an externally heated rotary kiln and sealed, and heated to 135°C at a speed of 60 rpm for 30 minutes to obtain carbonized bagasse fiber. The carbonized fibrous straw is then sprayed with water to cool it down and air-dried until the moisture content is 15% to obtain carbonized bagasse fiber.

[0058] Comparative Example 2

[0059] Using corn stalks, sugarcane bagasse, and soybean stalks (in a weight ratio of 1:1:1) as raw materials, the stalks are initially screened and dried, then crushed using a pulverizer and sieved through a 12-mesh sieve to obtain mixed fibrous stalks with a fiber length of 8-10 mm. These stalks are then placed in an externally heated rotary kiln and sealed, heated to 130°C at 30 rpm for 20 minutes to obtain carbonized fibrous stalks. The carbonized fibrous stalks are then sprayed with water to cool them down and air-dried until the moisture content is 25%, resulting in carbonized mixed fibrous stalks made from corn stalks, sugarcane bagasse, and soybean stalks.

[0060] Comparative Example 3

[0061] Using wheat straw, barley straw, and rice straw (in a weight ratio of 1:1:1) as raw materials, the specific processing steps are the same as those in Comparative Example 2, to obtain carbonized mixed fibrous straw made from wheat straw, barley straw, and rice straw.

[0062] Using 1000 kg of crop straw as raw material, fibrous straw was prepared using different methods in Examples (1-6) and Comparative Examples (1-3). A cultivation substrate was prepared by mixing 60% fibrous straw, 5% organic fertilizer, 10% perlite, 20% coconut coir, and 5% river sand by volume. 300-500 g of potassium sulfate compound fertilizer was added per cubic meter of cultivation substrate. Finally, the carbonization yield (%), total porosity (%), aeration porosity (%), large and small pore ratio, and water holding capacity were compared. The results are shown in Table 1 below.

[0063] Table 1. Physical property analysis of straws with different fiber content

[0064]

[0065] Table 1 shows that different raw material ratios, passivation treatments (passivation temperature and time), and modification treatments significantly affect the carbonization yield, total porosity, macropore ratio, and water-holding capacity of fibrous straw. Examples 1-3, which underwent chemical passivation followed by modification, showed significantly higher carbonization yields than other experimental groups. While Example 6 also underwent chemical passivation and modification, its high passivation temperature (150℃) resulted in a lower carbonization yield, which is detrimental to carbon dioxide capture and storage. Therefore, the cultivation substrate prepared from the modified fibrous straw of Examples 1-3 exhibits the best physical properties, with a macropore ratio of 0.34–0.35, meeting the requirements for an excellent substrate. The modified straw has a water holding capacity of 186%–230%, a porosity of 54%–78%, a total carbon content of 34%–45%, a readily decomposable carbon content of 5%–16%, and a fiber decomposition rate of 2.3–18.3 g / g·year, which is 92%–98% lower than the normal decomposition rate. It also achieves carbon storage of 340–460 g / kg. Based on an agricultural crop yield of 600 kg / mu, each hectare of crop planting can capture and store 50 tons of carbon dioxide, equivalent to the 20–40 tons of carbon dioxide capture capacity of forests.

[0066] By applying the composite substrates prepared in Examples 1-3 to the cultivation of pak choy, the substrates showed significant fertilization effects and good performance (e.g., Figure 2 -B as shown); the germination rate of bok choy is high, and the seedling effect is good (as shown in B). Figure 3 As shown), it can effectively increase the number of fibrous roots during the seedling stage and improve the quality of cabbage seedlings (e.g., Figure 4 (As shown); Compared with traditional peat substrate, the above-mentioned substrate produces bok choy with higher morphological indicators, better quality, and higher yield. It also has the advantages of saving water resources, shortening the growth cycle, and reducing the occurrence of diseases and pests.

Claims

1. A method for modifying crop straw, characterized in that, The modification method includes: S1: Initially screen, dry and crush crop straw to obtain fibrous straw raw materials; S2: At room temperature, add the blocking agent powder to the fibrous straw raw material obtained in step S1, mix evenly, then spray with a composite surfactant, let it stand for equilibration for 12 hours, and then perform chemical passivation treatment using a sealed rotary heating method to obtain carbonized fibrous straw; wherein, the blocking agent powder is one or more of calcium carbonate, diatomaceous earth, and kaolin; the addition ratio is 1-5 grams of blocking agent powder per kilogram of fibrous straw; the composite surfactant is composed of cocamidopropyl betaine and sodium lauroyl sarcosinate in a mass fraction ratio of 1:1; the spraying ratio is 50-100 ml of a 1% concentration composite surfactant aqueous solution per kilogram of fibrous straw raw material; the specific operation of the chemical passivation treatment is as follows: the fibrous straw raw material after standing for equilibration for 12 hours is placed in an externally heated rotary kiln and sealed, and heated at a speed of 30-60 rpm to 120-135°C, and passivated for 10-30 minutes; S3: Spray water to cool the carbonized fibrous straw obtained in step S2 to 100°C, and use a composite surfactant aqueous solution to modify the carbonized fibrous straw. Let it stand for 12 hours to equilibrate. The specific operation of the modification treatment is as follows: After the carbonized fibrous straw obtained in step S2 is sprayed with water to cool it to 100°C, it is poured into a mixer, and a 1% concentration of composite surfactant is sprayed while stirring until its humidity is 30-40%. Let it stand for 12 hours to equilibrate. S4: Spread the carbonized fibrous straw treated in step S3 out in the open air to air dry, and obtain modified fibrous straw.

2. The modification method as described in claim 1, characterized in that, The crop straw mentioned in step S1 is selected from one or more of the following: sugarcane bagasse, corn straw, sorghum straw, and soybean straw.

3. The modification method as described in claim 1, characterized in that, The fibrous straw raw material mentioned in step S1 is obtained by sieving through a 10-15 mesh sieve, and its length is 5-10 mm.

4. The modification method as described in claim 1, characterized in that, The specific operation in step S4 is as follows: Spread the carbonized fibrous straw treated in step S3 out in the open to dry until its moisture content is 10%-15%, and the modified fibrous straw can be obtained.

5. The modified fibrous straw obtained by any of the modification methods described in claims 1-4 is used in carbon dioxide capture.

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