Crop straw modification method and application thereof in carbon capture

Abstract

The invention relates to a crop straw modification method and application thereof in carbon capture. The crop straw modification method comprises the following steps: S1, crushing crop straw to obtain a fibrous straw raw material; s2, uniformly mixing a cellulosic straw raw material with blocking agent powder, spraying a composite surfactant, and performing chemical passivation treatment by adopting a sealed rotary heating mode to obtain carbonized cellulosic straw; s3, sprinkling water to the carbonized cellulosic straw, cooling to 100 DEG C, and modifying the carbonized cellulosic straw by using a composite surfactant aqueous solution; s4, flattening and drying the treated carbonized cellulosic straw in the open air to obtain the modified crop cellulosic straw. The crop straw is treated through chemical passivation and modification, efficient recycling and matrix utilization of the crop straw are achieved, carbon capture and storage are promoted, and the method has the advantages of being low in cost, high in speed, environmentally friendly and the like.

Description

Technical Field

[0001] The invention relates to the field of agricultural waste treatment and resource utilization, in particular to a crop straw modification method and application thereof in carbon capture. Background Art

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

[0003] The main ways to use crop straw include fertilizer, feed, fuel, raw material, base material, etc. Many scholars at home and abroad have conducted research in the above aspects, such as "Preparation of modified straw-based hydrothermal charcoal and its application in carbon dioxide fixation (patent number: ZL202311415117.1)", which converts straw into hydrothermal charcoal through hydrothermal carbonization technology, reduces the preparation temperature of straw-based carbon materials, and improves the carbon dioxide fixation capacity through modification. Another example is "A modified sugarcane bagasse-based material and its application in environmental protection (patent number: ZL201810202401.3)", which develops sugarcane bagasse into a new material through chemical modification to effectively remove pesticide residues in the soil. Although the above technologies can effectively realize the fuel and base material of crop straw and improve the utilization rate of straw resources, the above preparation methods all need to be carried out under relatively high temperature (above 150°C), and there are problems such as harsh preparation conditions, long high temperature reaction time, and high energy consumption. The shortcomings of the above technologies significantly increase their operating costs, thereby limiting their promotion and application. However, by chemically passivating and modifying crop straw, not only is the operation method simple and easy to control, but also the carbonization effect and carbon dioxide capture and storage capacity are improved. More importantly, the product obtained by the reaction has good stability and chemical inertness, is suitable for long-term storage, and effectively solves the problems of recycling and high-value conversion of agricultural waste, and can effectively replace non-renewable resources such as traditional peat and peat, which has important practical value and social significance. In view of this, the present invention provides a method for modifying crop straw and its application in carbon capture. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a low-cost, efficient and environmentally friendly method for resource utilization of crop straw, in particular a method for modifying crop straw and its application in carbon capture. The method can not only effectively improve the utilization rate of crop straw, but also play an important role in carbon capture and storage. The crop straw treated by the method of the present invention can be converted into modified fibrous straw with high value, providing a new way for resource utilization of agricultural waste.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a crop straw modification method and application thereof in carbon capture, wherein the crop straw modification method comprises the following steps:

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

[0008] S2: adding blocking agent powder to the fibrous straw raw material obtained in step S1 at room temperature, spraying the composite surfactant after mixing evenly, leaving it to balance for 12 hours, and then performing chemical passivation treatment by sealed rotary heating to obtain carbonized fibrous straw;

[0009] S3: Sprinkle water on the carbonized fibrous straw in step S2 to cool it down to 100° C., modify the carbonized fibrous straw using a composite surfactant aqueous solution, and place it for equilibrium for 12 hours;

[0010] S4: Spreading the carbonized fibrous straw treated in step S3 and air-drying it in the open air to obtain modified fibrous straw.

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

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

[0013] Preferably, the blocking agent powder in step S2 is one or more of calcium carbonate, diatomaceous earth and kaolin, and the adding 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 and improve the carbonization effect. It has a certain filling and reinforcing effect and can improve the strength and stability of the modified straw. Diatomaceous earth, due to its high specific surface area and porosity, can increase the adsorption capacity of straw, help 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. At the same time, it also has a certain adhesiveness, which helps to enhance the binding force between straw particles and improve the overall performance of modified straw.

[0015] Preferably, the chemical passivation treatment described in step S2 is specifically performed as follows: the fibrous straw raw material after being equilibrated for 12 hours is placed in 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 described in step S2 is compounded by C12-18 alkyl betaines and N-alkyl amino acids in a mass fraction ratio of 1:1; the C12-18 alkyl betaines are preferably cocamidopropyl betaine, and the N-alkyl amino acid is preferably sodium lauroyl sarcosinate; the spraying ratio is 50-100 ml of 1% 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 mass fraction ratio of 1:1, which can effectively reduce the surface tension of fibrous straw, allowing water to quickly penetrate the surface of fibrous straw, making the fibrous straw more quickly and evenly soaked by water, and effectively solving the water repellency problem of the matrix. Cocamidopropyl betaine and sodium lauroyl sarcosinate have mild effects, low irritation, low toxicity, good biodegradability, safety and excellent compatibility. The two surfactants are compounded in a mass fraction ratio of 1:1, which can greatly reduce the irritation of a single surfactant and obtain a milder composite surfactant solution.

[0018] Preferably, the modification treatment described in step S3 is specifically performed as follows: after the carbonized fibrous straw obtained in step S2 is cooled to 100° C. by sprinkling water, it is poured into a mixer and sprayed with a 1% concentration of a composite surfactant while stirring until the humidity of the carbonized fibrous straw is 30-40%, and then left to balance 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 air and dried until its water content is The modified fibrous straw can be obtained.

[0020] The present invention also provides modified fibrous straw obtained by the modification method described in the above scheme and its application in carbon capture. In the chemical passivation process of the present invention, the fibrous straw undergoes a carbonization reaction under high temperature oxygen-isolating conditions, the carbon element in the straw reacts with carbon dioxide, and the carbon dioxide is fixed in the biochar in the form of chemical bonding, and the composite surfactant improves the reaction efficiency of carbon dioxide and the carbon element in the straw by reducing surface tension, increasing reactive sites, etc., and further improves the carbon dioxide fixation and storage content during the carbonization process. The fibrous straw after the modification treatment has changed its pore structure and surface properties, and has stronger adsorption and fixation capabilities. These modified fibrous straws can be used as carbon sink materials to store captured carbon dioxide and prevent it from being released back 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) The present invention first forms a chemical barrier by mixing a blocking agent with crop fibrous straw, effectively blocking the active sites in the straw, reducing the decomposition and volatilization of the straw during the carbonization process, thereby improving the stability and performance of the carbonized fibrous straw. The surfactant is then used to significantly improve the wettability and dispersibility of the straw surface, so that the blocking agent powder is 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 cost for subsequent passivation treatment.

[0023] (2) The present invention can quickly convert crop straw into an organic matrix, with a fast production speed, low cost, and easy promotion and implementation. The present invention adopts high-temperature passivation treatment, and the active groups of the cellulose are passivated by a blocking agent, resulting in the appearance of phenolic hydroxyl groups to reduce the breakage of CO and CH bonds, dehydration, cellulose cracking, silicon-oxygen reaction to form Si-O-Si bonds, and sugar aromatization, thereby maintaining the straw gap, mechanical strength, and hydrophilicity characteristics, eliminating insect eggs and harmful microorganisms in mixed straw, and effectively blocking and inhibiting the occurrence of epidemics. However, it takes 2 to 3 months to convert crop straw into an organic matrix by composting, fermenting, etc., and the smell is unpleasant. Compared with the current fully decomposed fermentation products used as cultivation substrates, the preparation process of the present invention is simple, time-saving, and efficient.

[0024] (3) The raw materials used in the present invention are widely available, low in cost, and have strong carbon fixation capacity. Common ways to treat straw include burning, returning to the field, papermaking, power generation, etc., but there are secondary pollution or disease transmission. The present invention adopts chemical passivation treatment to effectively enhance the anti-decomposition ability of crop straw fiber, and then uses surfactant to modify the crop straw. It only takes 24 hours from crop straw to qualified matrix. After modification, the straw has a water holding rate of 186% to 230%, a porosity of 54% to 78%, a total carbon content of 34% to 45%, and an easily decomposable carbon content of 5% to 16%. The fiber decomposition rate is 2.3 to 18.3 g / g·year, which is 92% to 98% lower than the normal decomposition rate, and 340 to 460 g / kg of carbon storage is achieved. According to the agricultural crop yield of 600 kg / mu, 50 tons of carbon dioxide can be captured per hectare of crop planting and transferred, which is equivalent to the carbon dioxide capture capacity of 20 to 40 tons of forest carbon. Therefore, through the application of the technology of the present invention, crop straw can be directly converted into organic matrix, thereby realizing efficient resource utilization of crop straw.

[0025] (4) The modified fibrous straw obtained by the present invention is green, environmentally friendly and recyclable. The present invention utilizes high temperature conversion and non-toxic, pollution-free surfactants to treat crop straws, and no new pollutants are generated in the process. The hemicellulose and lignin in the straws are slowly decomposed and converted into humic acid under natural conditions, and mixed with perlite, clay, sand, organic fertilizer, etc., which can meet the needs of plant growth for water, air and fertilizer, effectively promote plant growth, and form a long-term and balanced nutrient supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Process flow chart for crop straw modification

[0027] Figure 2 -A is an enlarged picture of bagasse fiber before modification (magnified 40 times)

[0028] Figure 2 -B is a cultivation medium made of modified bagasse mixed with other materials

[0029] Figure 3 The growth status of cabbage planted in the cultivation medium formed by mixing and compounding the modified fibers in Examples 1-3 of the present invention

[0030] Figure 4 The root growth diagram of the cabbage planted in the cultivation medium formed by mixing and compounding the modified fibers in Examples 1-3 of the present invention DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Example 1

[0033] A modification method using bagasse as raw material comprises the following steps:

[0034] S1: Preliminarily screen and dry the bagasse raw material, crush it with a crusher, and sieve it with a 10-mesh sieve to obtain a bagasse fibrous straw raw material with a fiber length of 8 to 10 mm;

[0035] S2: At room temperature, 5 g of calcium carbonate powder is added to each kg of bagasse fibrous straw raw material for uniform mixing, 100 ml of a mixed aqueous solution of 1% cocamidopropyl betaine and sodium lauroyl sarcosinate (mass fraction ratio is 1:1) is sprayed on each kg of bagasse fibrous straw, and the mixture is allowed to stand for 12 hours for equilibrium, and then sealed in an externally heated rotary kiln, heated to 135° C. at a speed of 60 rpm, and passivated for 30 minutes to obtain carbonized bagasse fibrous straw;

[0036] S3: Sprinkle water on the carbonized bagasse fiber in step S2 to cool it down. After the temperature drops to 100° C., pour it into a mixer, spray it again with a 1% mixed aqueous solution of cocamidopropyl betaine and sodium lauroyl sarcosinate (mass fraction ratio is 1:1) until the humidity of the carbonized bagasse fiber is 30-40%, stir it evenly, and leave it to balance for 12 hours;

[0037] S4: Spread the carbonized bagasse fibers treated in step S3 in the open air and air dry them until the moisture content is 25% to obtain modified bagasse fibers (such as Figure 2 -A).

[0038] Example 2

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

[0040] S1: Preliminarily screen and dry raw materials such as corn stalks, bagasse, and soybean stalks, crush them using a crusher, and sieve them using a 15-mesh sieve to obtain mixed fibrous stalks with a fiber length of 5 to 8 mm;

[0041] S2: at room temperature, 3 g of diatomaceous earth powder was added to each kg of mixed fibrous straw for uniform mixing, 100 ml of 1% sodium lauroyl sarcosinate aqueous solution was sprayed on each kg of mixed fibrous straw, and the mixture was allowed to stand for 12 h for equilibrium, and then sealed in an externally heated rotary kiln, heated to 130° C. at a speed of 30 rpm, and passivated for 20 min to obtain carbonized fibrous straw;

[0042] S3: Sprinkle water on the carbonized fibrous straw in step S2 to cool it down. After the temperature drops to 100° C., pour it into a mixer and spray 1% sodium lauroyl sarcosinate aqueous solution again until the humidity of the carbonized bagasse fiber is 30-40%. Stir it thoroughly and evenly, and leave it to balance for 12 hours.

[0043] S4: Spreading the carbonized fibrous straw treated in step S3 in the open air, and air-drying it to a moisture content of 25%, thereby obtaining a modified mixed fibrous straw using corn straw, bagasse, and soybean straw as raw materials.

[0044] Example 3

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

[0046] S1: Preliminarily screen and dry the corn stalks and sorghum stalks, crush them with a pulverizer, and sieve them with a 15-mesh sieve to obtain mixed fibrous stalks with a fiber length of 8 to 10 mm;

[0047] S2: At room temperature, 1 gram of calcium carbonate powder is added to each kilogram of mixed fibrous straw for uniform mixing, and 50 ml of a mixed aqueous solution of 1% cocamidopropyl betaine and sodium lauroyl sarcosinate (mass fraction ratio is 1:1) is sprayed on each kilogram of fibrous straw, and the mixture is allowed to stand for 12 hours for equilibrium, and then sealed in an externally heated rotary kiln, heated to 120°C at a speed of 30 rpm, and passivated for 30 minutes to obtain carbonized fibrous straw;

[0048] S3: Sprinkle water on the carbonized fibrous straw in step S2 to cool it down. After the temperature drops to 100° C., pour it into a mixer and spray 1% sodium lauroyl sarcosinate aqueous solution on it again until the humidity of the carbonized fibrous straw reaches 30-40%. Stir it thoroughly and evenly, and place it for equilibrium for 12 hours.

[0049] S4: Spreading the carbonized fibrous straw treated in step S3 in the open air, and air-drying it to a moisture content of 15%, thereby obtaining a modified mixed fibrous straw using corn straw and sorghum straw as raw materials.

[0050] Example 4

[0051] A modification method using bagasse as raw material, wherein in step 2, the fiber is directly passivated for 30 minutes without adding a blocking agent and a surfactant, and other specific operation processes are the same as those in Example 1 to obtain modified bagasse fiber.

[0052] Example 5

[0053] A modification method using wheat straw, barley straw and rice straw (weight ratio is 1:1:1) as raw materials, wherein the specific operation process is the same as that of Example 2, and modified mixed fibrous straw using wheat straw, barley straw and rice straw as raw materials is obtained.

[0054] Example 6

[0055] A modification method using bagasse as raw material, wherein the passivation treatment temperature in step S2 is increased to 150° C., and other specific operation processes are the same as those in Example 1, to obtain modified bagasse fiber.

[0056] Comparative Example 1

[0057] Bagasse is used as raw material, the bagasse raw material is preliminarily screened and dried, crushed by a pulverizer, and sieved with a 10-mesh sieve to obtain bagasse fiber raw material with a fiber length of 8-10 mm; then it is loaded into an externally heated rotary kiln and sealed, heated to 135°C at a speed of 60 rpm, and treated for 30 minutes to obtain carbonized bagasse fiber; the carbonized fibrous straw is sprinkled with water to cool down, and air-dried to a moisture content of 15% to obtain carbonized bagasse fiber.

[0058] Comparative Example 2

[0059] Corn stalks, bagasse and soybean stalks (weight ratio of 1:1:1) are used as raw materials, the stalk raw materials are preliminarily screened and dried, crushed by a pulverizer, and sieved with a 12-mesh sieve to obtain a mixed fibrous straw with a fiber length of 8 to 10 mm; then the mixed fibrous straw is loaded into an externally heated rotary kiln and sealed, heated to 130°C at a speed of 30 rpm, and treated for 20 minutes to obtain carbonized fibrous straw; the carbonized fibrous straw is cooled by sprinkling water, and air-dried to a moisture content of 25% to obtain a carbonized mixed fibrous straw using corn stalks, bagasse and soybean stalks as raw materials.

[0060] Comparative Example 3

[0061] Wheat straw, barley straw and rice straw (weight ratio of 1:1:1) were used as raw materials, and the specific processing steps were the same as those in Comparative Example 2 to obtain carbonized mixed fibrous straw using wheat straw, barley straw and rice straw as raw materials.

[0062] 1000 kg of crop straw was used as raw material, and different methods of embodiments (1-6) and comparative examples (1-3) were used to prepare fibrous straw. 60% fibrous straw, 5% organic fertilizer, 10% perlite, 20% coconut bran, and 5% river sand were used as a cultivation matrix by volume, and 300-500 g of potassium sulfate compound fertilizer was added to each cubic meter of the cultivation matrix. Finally, the carbonization rate (%), total porosity (%), ventilation pores (%), large and small pore ratio, water holding capacity and other indicators were compared, and the results are shown in Table 1 below:

[0063] Table 1 Analysis of physical properties of different fibrous straws

[0064]

[0065] From the results in Table 1, it can be seen that different raw material ratios, passivation treatments (passivation temperature, passivation time), and modification treatments have a significant effect on the carbonization yield, total porosity, large and small pore ratio, water holding capacity and other indicators of fibrous straw. Example 1-3 was first subjected to chemical passivation treatment and then to modification treatment, and its carbonization yield was significantly better than that of other test groups. Although Example 6 was also subjected to chemical passivation and modification treatment, its carbonization yield was low due to the excessively high passivation temperature (150°C), which was not conducive to the capture and storage of carbon dioxide. Therefore, the cultivation substrate prepared with the modified fibrous straw of Example 1-3 has the best physical properties, and the large and small pore ratio is 0.34-0.35, which meets the ratio requirements of excellent substrates. The modified straw has a water holding rate of 186% to 230%, a porosity of 54% to 78%, a total carbon content of 34% to 45%, an easily decomposable carbon content of 5% to 16%, and a fiber decomposition rate of 2.3 to 18.3 g / g·year, which is 92% to 98% lower than the normal decomposition rate, and can store 340 to 460 g / kg of carbon. Based on the agricultural crop yield of 600 kg / mu, 50 tons of carbon dioxide can be captured per hectare of crop planting and transferred, which is equivalent to the forest carbon dioxide capture capacity of 20 to 40 tons.

[0066] By using the composite matrix prepared in Examples 1-3 for the cultivation of Chinese cabbage, the matrix has significant fertilizer effect and good performance (such as Figure 2 -B); the germination rate of Chinese cabbage is high and the seedling effect is good (as shown in Figure 3 As shown), it can effectively increase the number of fibrous roots in the seedling stage and improve the quality of cabbage seedlings (as shown Figure 4 As shown); compared with the traditional substrate peat, the above substrate used to plant Chinese cabbage has high plant morphological indicators, good quality, high yield, and 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 and its application in carbon capture, characterized in that: The modification method comprises: S1: Preliminary screening, drying and crushing of crop straw to obtain fibrous straw raw materials; S2: adding blocking agent powder to the fibrous straw raw material obtained in step S1 at room temperature, spraying the composite surfactant after mixing evenly, leaving it to balance for 12 hours, and then performing chemical passivation treatment by sealed rotary heating to obtain carbonized fibrous straw; S3: Sprinkle water on the carbonized fibrous straw in step S2 to cool it down to 100° C., modify the carbonized fibrous straw using a composite surfactant aqueous solution, and place it for equilibrium for 12 hours; S4: Spreading the carbonized fibrous straw treated in step S3 and air-drying it in the open air to obtain modified fibrous straw.

2. The modification method according to claim 1, characterized in that The crop straw described in step S1 is selected from one or more of wheat straw, corn straw, rice straw, sugarcane bagasse from sugar factories, barley straw, sorghum straw, soybean straw, rape straw, and cotton straw; preferably one or more of sugarcane bagasse, corn straw, sorghum straw, and soybean straw from sugar factories.

3. The modification method according to claim 1, characterized in that: The fibrous straw raw material described in step S1 is sieved through a 10-15 mesh sieve and has a length of 5-10 mm.

4. The modification method according to claim 1, characterized in that: The blocking agent powder in step S2 is one or more of calcium carbonate, diatomaceous earth, and kaolin; the adding ratio is 1 to 5 grams of blocking agent powder per kilogram of fibrous straw.

5. The modification method according to claim 1, characterized in that: The composite surfactant described in step S2 is prepared by compounding C12-18 alkyl betaines and N-alkyl amino acids in a mass fraction ratio of 1:1; the C12-18 alkyl betaines are 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 raw material.

6. The modification method according to claim 1, characterized in that: The specific operation of the chemical passivation treatment described in step S2 is as follows: the fibrous straw raw material after being placed for 12 hours of equilibrium is placed in an externally heated rotary kiln and sealed, and heated to 120-135° C. at a speed of 30-60 rpm, and the passivation treatment is performed for 10-30 minutes.

7. The modification method according to claim 1, characterized in that: The modification treatment described in step S3 is specifically performed as follows: after the carbonized fibrous straw obtained in step S2 is cooled to 100° C. by sprinkling water, it is poured into a mixer and sprayed with a 1% concentration of a composite surfactant while stirring until the humidity is 30-40%, and then left to balance for 12 hours.

8. The modification method according to claim 1, characterized in that: The specific operation in step S4 is as follows: the carbonized fibrous straw treated in step S3 is spread out in the open air and dried until the water content thereof is 10%-15%, thereby obtaining the modified fibrous straw.

9. Use of the modified fibrous straw obtained by the modification method according to any one of claims 1 to 8 in carbon dioxide capture.

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