A dual-effect modified biochar as well as a preparation method and application thereof

Abstract

The present application relates to a kind of double-effect modified biochar and its preparation method and application, which comprises: with the crop straw treated with cellulase, or saccharification residue as raw material, anaerobic pyrolysis obtains biochar;Biochar is obtained by low-temperature air thermal oxidation to obtain modified biochar.Compared with prior art, the present application greatly reduces the amount of soluble release, effectively improves the hydrophobicity, and then improves the environmental friendliness, stability of biochar, and increases its adsorption organic pollutant performance.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization of waste agricultural crops and adsorption and removal of organic pollutants, and relates to a dual-function modified biochar, its preparation method and application. Background Technology

[0002] Crop straw is one of the most abundant renewable lignocellulose raw materials in nature. As a major agricultural country, my country produces over 800 million tons of crop straw annually, but the waste rate exceeds 30%, indicating that its utilization rate needs improvement. Effective utilization of straw resources can achieve carbon emission reduction, reduce pollutant emissions (such as PM2.5), and generate economically valuable products.

[0003] Biochar, a straw product, is currently a global research hotspot, with various applications in the environmental field. However, biochar releases a large amount of soluble substances over a long period, affecting not only its performance and stability but also its environmental impact. Straw is mainly composed of cellulose, hemicellulose, and lignin, among which lignin has the most stable pyrolysis characteristics and is easily carbonized during pyrolysis, forming a stable carbon skeleton. Treating straw samples with cellulase can effectively convert cellulose and hemicellulose in straw into economically valuable monosaccharides and significantly increase the proportion of lignin in straw components. Biochar prepared from straw treated with cellulase has a lower amount of soluble released substances. Air thermal oxidation, as a method for modifying biochar, can effectively improve the specific surface area, porosity, and oxygen-containing functional groups on the surface of biochar. However, since its modification temperature is usually above 400℃, and its main purpose is to improve the specific surface area and hydrophilicity of biochar, the mass loss of biochar during the modification process is relatively large, usually 25-30%, and in some cases, more soluble exogenous substances are generated. This not only results in low product yield and negatively affects adsorption stability, but may also bring more serious potential environmental risks.

[0004] Patent CN108315354A discloses a method for preparing biochar using straw saccharification residue and the application of the prepared biochar. The method includes the following steps: crushing straw; treating the straw powder with cellulase through a saccharification process; collecting the saccharification residue by centrifugation or sieving after treatment; using the dried saccharification residue, whose main component is lignin, as a raw material for preparing biochar; the method for preparing biochar from the saccharification residue is to place the obtained saccharification residue in a heating device and treat it at 300-600℃ for no less than 2 hours in an anaerobic environment to finally obtain biochar.

[0005] Patent CN115092904A discloses a method for increasing the proportion of persistent functional groups on the surface of biochar, the prepared biochar and its application. The method involves crushing crop straw and ball milling it to allow the straw powder to pass through a sieve, obtaining straw powder. Cellulase treatment is then used to degrade the cellulose and hemicellulose components of the straw powder into various monosaccharides. The straw powder is collected, washed, and then dried to obtain dried straw powder. The straw powder is then placed in a heating device and treated at 500-700℃ for at least 2 hours in an anaerobic environment to obtain biochar with a high proportion of persistent functional groups on its surface.

[0006] However, the biochar prepared by the aforementioned patents still contains a certain concentration of soluble releases, which not only affects its performance and stability but also has an impact on the environment. Summary of the Invention

[0007] The purpose of this invention is to overcome at least one defect of the prior art by providing a dual-function modified biochar, its preparation method and application. This invention significantly reduces the amount of soluble releases, effectively improves hydrophobicity, thereby enhancing the environmental friendliness and stability of the biochar, as well as increasing its adsorption performance of organic pollutants.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] One of the technical solutions of the present invention is to provide a method for preparing dual-functional modified biochar, the method comprising the following steps:

[0010] (1) Using cellulase-treated crop straw or saccharification residue (waste material from the process of producing bioethanol from crop straw) as raw materials, the biochar obtained by anaerobic pyrolysis is used as a precursor for modified biochar. Through cellulase treatment, the cellulose and hemicellulose components in the straw are degraded into soluble monosaccharides. Cellulose and hemicellulose are the main causes of soluble releases during the preparation of biochar.

[0011] (2) Modified biochar is obtained by low-temperature air thermal oxidation of biochar. Within the low-temperature range of this invention, air thermal oxidation modification is beneficial to reduce the soluble release of biochar, which has not been the focus of previous studies. The effect of enhanced hydrophobicity of modified biochar is also completely opposite to the effect of conventional high-temperature air thermal oxidation modification (the hydrophilicity of modified biochar increases). Moreover, step (2) is based on step (1). The combined effect of the two makes the amount of soluble release of biochar close to the limit low value (1-2 mg / L), which is 90% less than that of the prior art. At the same time, the hydrophobic force in adsorption is strengthened, and the hydrophobicity is also enhanced. Moreover, the mass loss during the biochar modification process is extremely low, only 1-2%.

[0012] Activated carbon adsorption of organic pollutants is considered a very effective method for environmental remediation. Compared to activated carbon, biochar has a lower preparation cost and can be combined with the production process of bioethanol. By using the waste residue from the straw production of bioethanol, namely the saccharification residue, as a raw material, it is possible not only to theoretically achieve full carbon utilization of straw as agricultural waste, but also to significantly reduce the preparation cost of biochar.

[0013] This invention modifies biochar prepared from cellulase-treated straw (similar to waste products generated during bioethanol production) through relatively low-temperature air thermal oxidation. By improving its hydrophobicity, it enhances the adsorption capacity of organic pollutants and significantly reduces the amount of soluble releases, thereby improving its environmental friendliness and stability, performance, and expanding its application range. Furthermore, the mass loss of biochar during the modification process is extremely low. Under the modification conditions of this invention, effects completely different from existing technologies can be achieved. This invention has a positive impact on national carbon targets, biomass energy goals, and environmental governance.

[0014] Furthermore, in step (1), the crop straw is selected from one or more of rice, wheat, barley and corn straw, and the lignin content is more than 50%.

[0015] As a preferred technical solution, the lignin content of crop straw in step (1) is 50-75%.

[0016] Furthermore, the cellulase treatment step of crop straw in step (1) includes:

[0017] (a) Drying, coarsely grinding, and crushing crop straw to obtain crop straw powder;

[0018] (b) Add cellulase to crop straw powder and use cellulase to treat crop straw powder through a saccharification process to obtain cellulase-treated crop straw.

[0019] Furthermore, in step (b), the material ratio of cellulase (based on enzyme activity) to crop straw powder (based on mass) is 2-300 FPU / g;

[0020] The saccharification temperature is 40-60℃, the rotation speed is 50-200 r / min, and the time is 12-72 h.

[0021] As a preferred technical solution, the drying temperature in step (a) is 60-80℃, and the particle size is less than 50 mesh.

[0022] As a preferred technical solution, the particle size in step (a) is 50-400 mesh.

[0023] Furthermore, in step (1), the anaerobic pyrolysis temperature is 500-600℃ and the time is 2-3h.

[0024] Furthermore, in step (2), the air flow rate is 200-500 mL / min.

[0025] As a preferred technical solution, the air flow rate in step (2) is 300-400 mL / min.

[0026] Furthermore, in step (2), the thermal oxidation temperature is 150-300℃ and the time is 20-60min.

[0027] As a preferred technical solution, the thermal oxidation temperature in step (2) is 220-280℃.

[0028] As a preferred technical solution, the thermal oxidation temperature in step (2) is 220-260℃.

[0029] As a preferred technical solution, the thermal oxidation time in step (2) is 30-45 min.

[0030] Furthermore, after step (2), the modified biochar is placed for more than a week. When the freshly prepared biochar is used directly, its adsorption performance is unstable, but after being placed, its adsorption performance is more stable.

[0031] One of the technical solutions of the present invention is to provide a dual-function modified biochar prepared by the method, wherein the amount of soluble release product of the modified biochar is 0.5-3 mg / L and has strong hydrophobicity.

[0032] As a preferred technical solution, the amount of soluble release from the modified biochar is 1-2 mg / L.

[0033] One of the technical solutions of the present invention is to provide an application of dual-function modified biochar, wherein the modified biochar is used for the adsorption of organic pollutants.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) Resource utilization of agricultural waste: This invention prepares biochar from waste crop straw, realizing the transformation of waste into treasure;

[0036] (2) Reduce the cost of biochar preparation: The cellulase treatment of straw in this invention is similar to the process of producing bioethanol. Therefore, the waste tailings from the production of bioethanol can be used as the raw materials for the preparation of this invention, thereby saving one-third of the collection and logistics costs of biochar preparation. Furthermore, the combination of the two processes enables the production of multiple products and can also reduce the price of bioethanol.

[0037] (3) Improve the adsorption performance and environmental friendliness of biochar: This invention modifies biochar by air thermal oxidation at a relatively low temperature, which effectively improves the hydrophobicity of biochar and enhances its hydrophobic adsorption effect, thereby improving its adsorption performance of low water-soluble organic pollutants; and the significant reduction in the amount of soluble releases in this invention not only improves its stability, but also prevents pollution problems caused by the large loss of components in practical applications.

[0038] (4) The present invention exhibits extremely low mass loss during the biochar modification process;

[0039] (5) The present invention improves the stability of adsorption performance by placing the freshly prepared biochar after it has been placed. Attached Figure Description

[0040] Figure 1 This is a graph showing the amount of soluble released product from dual-function modified biochar at different air flow rates and temperatures in Example 1 of the present invention.

[0041] Figure 2 This is a diagram showing the equilibrium adsorption capacity of phenol by dual-functional modified biochar at different treatment times and temperatures in Example 3 of the present invention. Detailed Implementation

[0042] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0043] Unless otherwise specified, the equipment used in the following embodiments is conventional equipment in the art; unless otherwise specified, the reagents used are commercially available products or prepared by conventional methods in the art. In the following embodiments, unless otherwise described in detail, conventional experimental methods in the art can be used.

[0044] A method for cellulase treatment of crop straw, the specific steps of which are as follows:

[0045] (a) Dry the crop straw at 80°C, coarsely grind it with a pulverizer, crush the crop straw and pass it through a 50-mesh sieve (particle size less than 0.28 mm) to obtain crop straw powder;

[0046] (b) Add 200 FPU of cellulase to 100g of crop straw powder and saccharify it in a shaker at 55℃ and 200r / min for 48h. Use cellulase to treat the crop straw powder through the saccharification process to obtain 70g of cellulase-treated crop straw.

[0047] Example 1:

[0048] A dual-functional modified biochar and its preparation method are disclosed, with the specific steps as follows:

[0049] 100g of corn stalks were obtained from Yancheng City, Jiangsu Province. After treatment with cellulase, the lignin content was 63%. Biochar was prepared by anaerobic pyrolysis at 500℃ for 2h, which is the precursor of modified biochar. 5.00g of biochar was placed in a tubular furnace with an air flow rate of 300mL / min and treated at 200℃ for 30min to finally obtain 4.95g of modified biochar.

[0050] Comparative Example 1:

[0051] A common type of biochar is biochar prepared directly from untreated straw through anaerobic pyrolysis at 500°C for 2 hours.

[0052] Comparative Example 2:

[0053] A precursor biochar is prepared by anaerobic pyrolysis of enzyme-treated straw at 500°C for 2 hours.

[0054] The specific steps for testing the soluble release content of biochar are as follows:

[0055] Weigh 0.03 g of biochar and place it in a 100 mL stoppered conical flask. Add 60 mL of ultrapure water to prepare a 0.5 g / L biochar solution. Place the solution in a constant temperature shaker at 30 °C and 200 r / min for 1 h, and then measure the total dissolved solids (TDS) of the sample. All experiments were repeated three times, and the average value of the soluble release content was calculated.

[0056] Experimental results: The soluble release amount of ordinary biochar was 44.17 mg / L; the soluble release amount of precursor biochar was 11.00 mg / L; and the soluble release amount of modified biochar was 1.29 mg / L. The soluble release amount of modified biochar was significantly reduced, decreasing by 97.08% compared to ordinary biochar and by 88.27% compared to precursor biochar.

[0057] like Figure 1 As shown, when the processing time is 30 min, the concentration of soluble released substances in the modified biochar increases with the increase of air flow rate and temperature. Under the modification conditions of this invention, the concentration of soluble released substances in the modified biochar is generally below 2 mg / L, and under some conditions, it can even be below 1 mg / L. It can be seen that these modification conditions can effectively reduce the concentration of soluble released substances in biochar. From the trend in the figure, it can be inferred that if the air flow rate and temperature continue to increase, the effect of reducing the concentration of soluble released substances in biochar will become worse. The preferred air flow rate is 300-400 mL / min, and the preferred temperature is 220-260℃.

[0058] Example 2:

[0059] A dual-functional modified biochar and its preparation method are disclosed, with the specific steps as follows:

[0060] 100g of corn stalks were obtained from Yancheng City, Jiangsu Province. After treatment with cellulase, the lignin content was 63%. Biochar was prepared by anaerobic pyrolysis at 500℃ for 2h, which is the precursor of modified biochar. 5.00g of biochar was placed in a tubular furnace with an air flow rate of 400mL / min and treated at 250℃ for 45min, finally yielding 4.90g of modified biochar.

[0061] A dynamic contact angle test for biochar, the specific steps of which are as follows:

[0062] Biochar was placed tightly and flat on the measuring stage, and the contact angle of the material surface was measured using the seated drop method with an Attension Theta Flex optical contact angle meter (Biolin, Sweden). The volume of the ultrapure water droplet was 5 μL, and the contact angle was dynamically measured from 0 to 10 s. All experiments were repeated three times, and the average value of the dynamic contact angle was calculated.

[0063] Experimental results: The soluble release amount of ordinary biochar was 44.17 mg / L, and the dynamic contact angle was 80.3°; the soluble release amount of precursor biochar was 11.00 mg / L, and the dynamic contact angle was 102.3°; the soluble release amount of modified biochar was 1.53 mg / L, and the dynamic contact angle was 108.7°. Its soluble release amount was significantly reduced, and its dynamic contact angle increased, indicating enhanced hydrophobicity.

[0064] Example 3:

[0065] A dual-functional modified biochar and its preparation method are disclosed, with the specific steps as follows:

[0066] 100g of corn stalks were obtained from Yancheng City, Jiangsu Province. After treatment with cellulase, the lignin content was 63%. Biochar, a precursor of modified biochar, was prepared by anaerobic pyrolysis at 500℃ for 2 hours. 5.00g of biochar was placed in a tubular furnace with an air flow rate of 400mL / min and treated at 250℃ for 20 minutes to obtain 4.90g of modified biochar. After preparation, the biochar was left to stand for one week before use (at which time its adsorption performance was relatively stable).

[0067] Comparative Example 3:

[0068] A common biochar, namely the biochar of Comparative Example 1, is prepared directly from untreated straw by anaerobic pyrolysis at 500℃ for 2 hours. After preparation, it is left to stand for one week before use.

[0069] Comparative Example 4:

[0070] A precursor biochar, namely the biochar of Comparative Example 2, is prepared by anaerobic pyrolysis of enzyme-treated straw at 500℃ for 2 hours. After preparation, it is left to stand for one week before use.

[0071] The specific steps for testing the adsorption performance of phenol by biochar are as follows:

[0072] 0.03 g of biochar was placed in a 100 mL stoppered conical flask containing 50 mL of phenol solution and placed in a constant temperature shaker at 25 °C. The mixture was shaken at 150 r / min for 48 h. All experiments were repeated three times, and the average value of phenol adsorption was calculated.

[0073] Experimental results: After 48 hours (all reached adsorption equilibrium), the equilibrium adsorption capacity of ordinary biochar was 9.38 mg / g; the equilibrium adsorption capacity of precursor biochar was 18.73 mg / g; and the equilibrium adsorption capacity of modified biochar was 25.47 mg / g. Its adsorption capacity increased significantly, by 172% compared with ordinary biochar and by 36% compared with precursor biochar.

[0074] like Figure 2 As shown, at an air flow rate of 400 mL / min, the equilibrium adsorption capacity of biochar generally increases with increasing temperature, but begins to decrease after the temperature exceeds 280℃. Between 200-280℃, the equilibrium adsorption capacity also increases with increasing modification time, but begins to decrease after 48 min. The preferred modification time is 30-45 min, and the preferred temperature is 220-280℃.

[0075] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing dual-functional modified biochar, characterized in that, The method includes the following steps: (1) Biochar is obtained by anaerobic pyrolysis of crop straw treated with cellulase or saccharification residue; (2) Modified biochar is obtained by low-temperature air thermal oxidation of biochar; In step (2), the air flow rate is 200-500 mL / min. The thermal oxidation temperature is 150-300 ℃. The soluble release amount of modified biochar is 0.5-3 mg / L; Within the low temperature range, air thermal oxidation modification is beneficial to reduce the soluble release of biochar. The effect of enhanced hydrophobicity of modified biochar is completely opposite to that of conventional high temperature air thermal oxidation modification, i.e., the increase in hydrophilicity of modified biochar. Moreover, step (2) is based on step (1). The combined effect of the two allows the amount of soluble release of biochar to approach the limit low value. At the same time, the hydrophobic force in adsorption is strengthened, and the hydrophobicity is also enhanced. Furthermore, the mass loss during biochar modification is extremely low.

2. The method for preparing a dual-functional modified biochar according to claim 1, characterized in that, In step (1), the crop straw is selected from one or more of rice, wheat, barley and corn straw, and the lignin content is more than 50%.

3. The method for preparing a dual-functional modified biochar according to claim 1, characterized in that, The cellulase treatment of crop straw in step (1) includes: (a) Dry the crop straw, coarsely grind it, and crush it to obtain crop straw powder; (b) Add cellulase to crop straw powder and saccharify to obtain cellulase-treated crop straw.

4. The method for preparing a dual-functional modified biochar according to claim 3, characterized in that, In step (b), the material ratio of cellulase to crop straw powder is 2-300 FPU / g; The saccharification temperature is 40-60 ℃, the rotation speed is 50-200 r / min, and the time is 12-72 h.

5. The method for preparing a dual-functional modified biochar according to claim 1, characterized in that, In step (1), the anaerobic pyrolysis temperature is 500-600 ℃ and the time is 2-3 h.

6. The method for preparing a dual-functional modified biochar according to claim 1, characterized in that, The thermal oxidation time in step (2) is 20-60 min.

7. The method for preparing a dual-functional modified biochar according to claim 1, characterized in that, After step (2), the modified biochar is placed for more than one week.

8. A dual-functional modified biochar prepared by the method according to any one of claims 1 to 7.

9. An application of the dual-functional modified biochar as described in claim 8, characterized in that, The modified biochar is used for the adsorption of organic pollutants.

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