CN115092904A - Method for increasing the ratio of persistent functional groups on the surface of biochar, prepared biochar and application thereof - Google Patents

Abstract

The invention discloses a method for improving the proportion of persistent functional groups on the surface of biochar, the prepared biochar and application thereof, wherein crop straws are crushed and subjected to ball milling to enable straw powder to be sieved to obtain straw powder; cellulose and hemicellulose components of the straw powder are degraded into various monosaccharides through cellulase treatment; collecting straw powder, cleaning and drying to obtain dried straw powder; then placing the straw powder into heating equipment, and treating for at least 2 hours at the temperature of 500-700 ℃ in an oxygen-free environment to obtain the biochar with high-proportion durable functional groups on the surface. The biochar with high-proportion of persistent functional groups on the surface is used as an activating agent in the advanced oxidation method. According to the invention, the lignin content is increased, the proportion of the persistent functional groups on the surface of the biochar is improved, the group loss is reduced, and the method can be applied to an advanced oxidation technology to stably, continuously and efficiently repair organic pollutants, so that the effect of treating wastes with processes of wastes against one another is achieved.

Description

Method for increasing the proportion of persistent functional groups on the surface of biochar, and prepared biochar Carbon and its applications

technical field

The invention belongs to the field of comprehensive utilization of waste crops and advanced oxidation treatment of organic pollutants, and particularly relates to a preparation method for increasing the proportion of persistent functional groups on the surface of biochar and its application in advanced oxidation technology.

Background technique

As a major agricultural country, my country's main food crops and other agricultural and sideline products have maintained a global leading level all year round, and the amount of crop waste that followed has also maintained a relatively high level. For example, the annual output of straw is about 800 million tons. . Direct burning of crop straws will produce a large amount of carbon dioxide and other pollutants. The country has been committed to improving the comprehensive utilization rate of straw across the country, and aims to achieve a comprehensive utilization rate of 97% of straw by 2025. Effective utilization of straw resources can achieve carbon emission reduction, reduce pollutant emissions (such as PM2.5), and produce economically valuable products.

Biochar is one of the most studied straw products. Straw is mainly composed of cellulose, hemicellulose, and lignin. After the crop straw with high cellulose and hemicellulose content is prepared into biochar, the surface groups of the finished carbon are easily lost. The pyrolysis characteristics of lignin are the most stable. Lignin has a large temperature span in the pyrolysis process, and is easily carbonized during the pyrolysis process to form a stable carbon skeleton. Therefore, if biochar is prepared from raw materials with high lignin content, the properties of the biochar should be more stable and will not cause the loss of groups.

Advanced persulfate oxidation technology has become a kind of organic pollution remediation technology that is highly concerned at home and abroad due to its advantages of short cycle, quick effect, low cost and high treatment efficiency. As an economical, green and environmentally friendly carbon-based material activator, biochar has the same activation performance as metal materials, making it possible to replace metal activators to activate persulfate to degrade organic pollutants. It has been reported that biochar contains a certain amount of soluble and insoluble components, and the soluble component contains a large number of groups. In the actual in-situ advanced oxidation remediation, after the biochar is input into the in-situ system, its soluble components will be separated from the large biochar particles due to hydraulic flushing, which will lead to a large loss of biochar groups and reduce the remediation efficiency. Moreover, the lost groups will cooperate with heavy metals and organic pollutants to migrate to non-polluted areas in groundwater, causing secondary pollution.

SUMMARY OF THE INVENTION

In order to solve the problems of the prior art, the purpose of the present invention is to overcome the deficiencies of the prior art, and to provide a method for increasing the ratio of persistent functional groups on the surface of biochar, the prepared biochar and its application. It is converted into biochar and treated with cellulase to increase the proportion of lignin content of straw, reduce the loss of surface groups of biochar, and be used in the field of advanced oxidation treatment of organic pollutants with high efficiency and long-term stability, so as to achieve the purpose of treating waste with waste.

In order to achieve the above-mentioned purpose of invention and creation, the present invention adopts the following technical solutions:

A method for increasing the ratio of persistent functional groups on the surface of biochar, comprising the steps of:

(1) Pulverize the crop stalks, and further ball mill them through a ball mill, so that the stalk powder can pass through a screen with a mesh size of not more than 100 meshes to obtain the sifted and collected stalk powder for use; straw-like;

(2) The straw powder obtained in the step (1) is treated with cellulase, and the cellulose and hemicellulose components of the straw powder are degraded into various monosaccharides, so as to increase the lignin content, according to the quality Percentage calculation, the total amount of lignin in the treated straw powder shall not be less than 50%;

(3) collecting the straw powder obtained in the step (2), washing with water at least twice, and then drying at 60-80° C. for at least 24 hours to obtain dry straw powder;

(4) Using the straw powder obtained in the step (3) as a raw material for preparing biochar, placing the straw powder in a heating device, and treating the straw powder at 500-700 ° C for at least 2 hours in an oxygen-free environment, Thus, biochar with a high proportion of persistent functional groups on the surface is obtained.

Preferably, in the step (1), the crop straw is at least one of barley straw, wheat straw and rice straw.

Preferably, in the step (1), the crop straw is dried and then pulverized. Further preferably, the drying temperature is not lower than 60°C.

Preferably, in the step (2), when the straw powder is treated with cellulase, the reaction is carried out at a temperature of not lower than 45° C. in a shaker of not lower than 200 rpm for at least 48 hours to obtain Enzyme-treated straw powder.

Preferably, in the step (2), calculated by mass percentage, the total amount of lignin in the treated straw powder reaches 50-80%.

Preferably, in the step (4), the heating device adopts a tube furnace.

A biochar with a high proportion of persistent functional groups on the surface is prepared by the method for increasing the proportion of persistent functional groups on the surface of biochar according to the present invention.

Preferably, in the biochar with a high proportion of persistent functional groups on the surface of the present invention, the mass percentage content of lignin is not less than 50.66%, and the concentration of water-soluble exudates is not higher than 24.22 mg/L.

Preferably, in the biochar with a high proportion of persistent functional groups on the surface of the present invention, the content of carboxyl groups in the persistent functional groups is not less than 0.10 mmol/g, the content of lactone groups is not less than 0.12 mmol/g, and the content of phenolic hydroxyl groups is not less than 0.12 mmol/g. Not less than 0.14 mmol/g, and carbonyl content of not less than 1.19×10 ⁹ groups/cm ² .

Preferably, under normal temperature and pressure, after the biochar having a high proportion of persistent functional groups on the surface of the present invention is vortexed and stirred in water for 1 hour, the loss rate of persistent functional groups is not higher than 12%.

An application of the biochar with a high proportion of persistent functional groups on the surface of the present invention is characterized in that the biochar with a high proportion of persistent functional groups on the surface is used as an activator in an advanced oxidation method.

Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant advantages:

1. The present invention uses crop straw as a raw material to make biochar, which can achieve the purpose of recycling agricultural waste, reduces the environmental pollution generated during incineration, and realizes turning waste into treasure;

2. The present invention increases the proportion of lignin content through cellulase hydrolysis, the pyrolysis characteristics of lignin are the most stable, and the proportion of persistent functional groups on the surface of biochar can be significantly increased. Persistent functional groups will not be lost with hydraulic scouring, and can activate peroxides for a long time, providing theoretical basis and guidance for the actual application of advanced oxidation and remediation of organic pollution;

3. Because the biochar has high stability, the content of its water-soluble exudates is extremely low, and a large amount of organic components will not be lost, thus reducing the risk of secondary pollution in practical applications.

Description of drawings

Fig. 1 is a recycling effect diagram of biochar activation of peracetic acid to degrade triclosan in Example 3 of the present invention.

Detailed ways

The above scheme will be further described below in conjunction with specific embodiments, and preferred embodiments of the present invention are described in detail as follows:

Example 1

In this embodiment, the treatment target is barley straw, and a method for increasing the ratio of persistent functional groups on the surface of biochar includes the following steps:

(1) The barley straw is from Yancheng City, Jiangsu Province, dried at 60°C, and the barley straw is coarsely ground and pulverized by a pulverizer, and further finely ground by a ball mill, so that the straw powder can pass through a 100-mesh sieve, and the straw powder collected by the sieve is obtained. ,spare;

(2) adding cellulase, treating the straw powder obtained in the step (1) with cellulase, reacting at 45° C. in a shaking table at 200 rpm for 48 hours, and collecting after the enzyme treatment The cellulose and hemicellulose components of the straw powder are degraded into various monosaccharides by enzyme treatment, thereby increasing the lignin content;

(3) collecting the straw powder obtained in the step (2), washing with water at least twice, and then drying at 60° C. for 24 hours to obtain dry straw powder;

(4) Using the straw powder obtained in the step (3) as a raw material for preparing biochar, placing the straw powder in a heating device, and treating it at 500° C. for 2 hours in an oxygen-free environment to obtain a surface Biochar with a high proportion of persistent functional groups.

Experimental test analysis:

1. Detection of lignin content after enzyme treatment:

Taking the barley straw without enzyme treatment as a comparison sample, under the same conditions as a comparison, the lignin content of each sample was detected by biomass component analysis.

Experimental results: The lignin content of the biochar samples prepared in this example increased from 37% to 58% of the comparative sample, and the concentration of water-soluble exudates decreased from 71.26 mg/L of the comparative sample to 24.22 mg/L.

It can be seen that the biochar prepared in this example has good stability and high lignin content.

Compared with the biochar made from barley straw without enzyme treatment under the same conditions, the surface group content of biochar was measured by Boehm titration method and fluorescent labeling method.

2. The content of each group on the surface of biochar:

The biochar surface group content of biochar was measured by Boehm titration method and fluorescent labeling method compared with the biochar made from untreated straw under the same conditions.

Experimental results: the carboxyl group content of the biochar in this example is 0.37mmol/g, the lactone group content is 0.12mmol/g, the phenolic hydroxyl group content is 0.19mmol/g, and the carbonyl group content is 1.34×10 ⁹ groups/cm ² . At normal temperature and pressure, the comparative sample and the biochar with a high proportion of persistent functional groups on the surface prepared in this example were swirled in water for 1 hour, and the groups were measured again. It was found as a comparative test of ordinary biochar The group loss rate of the sample reached more than 34%, while the group loss rate of the biochar in this example was 9%, and the group loss rate was reduced by 25%. In this example, by increasing the lignin content, the ratio of persistent functional groups on the surface of the biochar is increased, and the loss of groups is reduced.

3. As an activator effect and the number of times of reuse:

By the method of this example, the barley straw was used as the raw material to prepare biochar at 500°C. The finished charcoal is used to activate peracetic acid to degrade triclosan:

The experiment was carried out in a wide-mouth conical flask with a capacity of 100mL, the total liquid volume was 50mL; the amount of biochar was 2.9g/L, the amount of peracetic acid was 1.3mM, the concentration of pollutant triclosan was 10mg/L, and the reaction was carried out at room temperature. Normal pressure, 200 rpm on a magnetic stirrer for 2 hours; at regular intervals, use a pipette to sample, then filter 1 mL of the reaction solution through a 0.22 μm filter; absolute ethanol is used as a free radical scavenger.

The concentration of pollutants in the samples was detected by high performance liquid chromatography. The biochar after the above reaction is cleaned by suction filtration, dried, collected and reused. Repeat the above operation steps to conduct a research on the effect of reuse.

Experimental results: The biochar in this example has a lasting, stable and efficient activation ability. When used for the first time, the degradation rate of triclosan can reach 94.6% after 2 hours of reaction, and it can still reach 81.3% after repeated use for ten times. This is because the biochar has a high proportion of persistent functional groups, which can lastingly and efficiently activate peracetic acid to generate reactive oxygen species (CH ₃ COO , CH ₃ COOO , OH and ¹ O ₂ ) and maintain high-efficiency removal. Effect.

Example 2

This embodiment is basically the same as Embodiment 1, and the special features are:

In this embodiment, the treatment target is wheat straw, and a method for increasing the ratio of persistent functional groups on the surface of biochar includes the following steps:

(1) The wheat straw is from Yancheng City, Jiangsu Province, dried at 60°C, the wheat straw is coarsely ground and pulverized by a pulverizer, and further finely ground by a ball mill, so that the straw powder can pass through a 100-mesh sieve, and the straw powder collected by the sieve is obtained. ,spare;

(2) adding cellulase, treating the straw powder obtained in the step (1) with cellulase, reacting at 45° C. in a shaking table at 200 rpm for 48 hours, and collecting after the enzyme treatment The cellulose and hemicellulose components of the straw powder are degraded into various monosaccharides by enzyme treatment, thereby increasing the lignin content;

(3) collecting the straw powder obtained in the step (2), washing with water at least twice, and then drying at 60° C. for 24 hours to obtain dry straw powder;

(4) Using the straw powder obtained in the step (3) as a raw material for preparing biochar, placing the straw powder in a heating device, and treating it at 500° C. for 2 hours in an oxygen-free environment to obtain a surface Biochar with a high proportion of persistent functional groups.

Experimental test analysis:

1. Detection of lignin content after enzyme treatment:

Taking the wheat straw without enzyme treatment as a comparison sample, under the same conditions as a comparison, the lignin content of each sample was detected by biomass component analysis.

Experimental results: The lignin content of the biochar samples prepared in this example increased from 38.29% to 50.66% of the comparative sample, and the concentration of water-soluble exudates decreased from 45.83 mg/L to 12.02 mg/L of the comparative sample.

It can be seen that the biochar prepared in this example has good stability and high lignin content.

Compared with biochar made from wheat straw without enzyme treatment under the same conditions, the surface group content of biochar was measured by Boehm titration method and fluorescent labeling method.

2. The content of each group on the surface of biochar:

The biochar surface group content of biochar was measured by Boehm titration method and fluorescent labeling method compared with the biochar made from untreated straw under the same conditions.

Experimental results: the carboxyl group content of the biochar in this example is 0.22mmol/g, the lactone group content is 0.20mmol/g, the phenolic hydroxyl group content is 0.14mmol/g, and the carbonyl group content is 1.19×10 ⁹ groups/cm ² . At normal temperature and pressure, the comparative sample and the biochar with a high proportion of persistent functional groups on the surface prepared in this example were swirled in water for 1 hour, and the groups were measured again. It was found as a comparative test of ordinary biochar The group loss rate of the sample reached more than 33%, while the group loss rate of the biochar in this example was 12%, and the group loss rate was reduced by 21%. In this example, by increasing the lignin content, the ratio of persistent functional groups on the surface of the biochar is increased, and the loss of groups is reduced.

3. As an activator effect and the number of times of reuse:

By the method of this example, wheat straw was used as raw material to prepare biochar at 500°C. The finished charcoal is used to activate peracetic acid to degrade triclosan:

The experiment was carried out in a wide-mouth conical flask with a capacity of 100mL, the total liquid volume was 50mL; the amount of biochar was 2.9g/L, the amount of peracetic acid was 1.3mM, the concentration of pollutant triclosan was 10mg/L, and the reaction was carried out at room temperature. Normal pressure, 200 rpm on a magnetic stirrer for 2 hours; at regular intervals, use a pipette to sample, then filter 1 mL of the reaction solution through a 0.22 μm filter; absolute ethanol is used as a free radical scavenger.

The concentration of pollutants in the samples was detected by high performance liquid chromatography. The biochar after the above reaction is cleaned by suction filtration, dried, collected and reused. Repeat the above operation steps to conduct a research on the effect of reuse.

Experimental results: The biochar in this example has a lasting, stable and efficient activation ability. When used for the first time, the degradation rate of triclosan can reach 92.2% after 2 hours of reaction, and it can still reach 78.1% after repeated use for ten times. This is because the biochar has a high proportion of persistent functional groups, which can lastingly and efficiently activate peracetic acid to generate reactive oxygen species (CH ₃ COO , CH ₃ COOO , OH and ¹ O ₂ ) and maintain high-efficiency removal. Effect.

Example 3

This embodiment is basically the same as the above-mentioned embodiment, and the special features are:

In this embodiment, the treatment target is rice straw, and a method for increasing the ratio of persistent functional groups on the surface of biochar includes the following steps:

(1) The rice straw is from Yancheng City, Jiangsu Province, dried at 60°C, the rice straw is coarsely ground and pulverized by a pulverizer, and further finely ground by a ball mill, so that the straw powder can pass through a 100-mesh sieve, and the straw powder collected by the sieve is obtained. ,spare;

(2) adding cellulase, treating the straw powder obtained in the step (1) with cellulase, reacting at 45° C. in a shaking table at 200 rpm for 48 hours, and collecting after the enzyme treatment The cellulose and hemicellulose components of the straw powder are degraded into various monosaccharides by enzyme treatment, thereby increasing the lignin content;

(3) collecting the straw powder obtained in the step (2), washing with water at least twice, and then drying at 80° C. for 24 hours to obtain dry straw powder;

(4) Using the straw powder obtained in the step (3) as a raw material for preparing biochar, placing the straw powder in a heating device, and treating it at 700° C. for 2 hours in an oxygen-free environment to obtain a surface Biochar with a high proportion of persistent functional groups.

Experimental test analysis:

1. Detection of lignin content after enzyme treatment:

Taking the rice straw without enzyme treatment as a comparison sample, under the same conditions as a comparison, the lignin content of each sample was detected by biomass component analysis.

Experimental results: The lignin content of the biochar samples prepared in this example increased from 39% to 51% of the comparative sample, and the concentration of water-soluble exudates decreased from 34.44 mg/L of the comparative sample to 11.81 mg/L.

It can be seen that the biochar prepared in this example has good stability and high lignin content.

Compared with the biochar made from rice straw without enzyme treatment under the same conditions, the surface group content of biochar was measured by Boehm titration method and fluorescent labeling method.

2. The content of each group on the surface of biochar:

The biochar surface group content of biochar was measured by Boehm titration method and fluorescent labeling method compared with the biochar made from untreated straw under the same conditions.

Experimental results: the carboxyl group content of the biochar in this example was 0.10 mmol/g, the lactone group content was 0.22 mmol/g, the phenolic hydroxyl group content was 0.24 mmol/g, and the carbonyl group content was 1.58×10 ⁹ groups/cm ² . At normal temperature and pressure, the comparative sample and the biochar with a high proportion of persistent functional groups on the surface prepared in this example were swirled in water for 1 hour, and the groups were measured again. It was found as a comparative test of ordinary biochar The group loss rate of the sample reached more than 29%, while the group loss rate of the biochar in this example was 10%, and the group loss rate was reduced by 19%. In this example, by increasing the lignin content, the ratio of persistent functional groups on the surface of the biochar is increased, and the loss of groups is reduced.

3. As an activator effect and the number of times of reuse:

By the method of this example, rice straw was used as raw material to prepare biochar at 500°C. The finished charcoal is used to activate peracetic acid to degrade triclosan:

The experiment was carried out in a wide-mouth conical flask with a capacity of 100mL, the total liquid volume was 50mL; the amount of biochar was 2.9g/L, the amount of peracetic acid was 1.3mM, the concentration of pollutant triclosan was 10mg/L, and the reaction was carried out at room temperature. Normal pressure, 200 rpm on a magnetic stirrer for 2 hours; at regular intervals, use a pipette to sample, then filter 1 mL of the reaction solution through a 0.22 μm filter; absolute ethanol is used as a free radical scavenger.

The concentration of pollutants in the samples was detected by high performance liquid chromatography. The biochar after the above reaction is cleaned by suction filtration, dried, collected and reused. Repeat the above operation steps to conduct a research on the effect of reuse.

Experimental results: The biochar in this example has a lasting, stable and efficient activation ability. As shown in Fig. 1, when used for the first time, the degradation rate of triclosan can reach 99% after 2 hours of reaction, and it can still reach 77% after repeated use for ten times. This is because the biochar has a high proportion of persistent functional groups, which can lastingly and efficiently activate peracetic acid to generate reactive oxygen species (CH ₃ COO , CH ₃ COOO , OH and ¹ O ₂ ) and maintain high-efficiency removal. Effect.

By increasing the lignin content, increasing the proportion of persistent functional groups on the surface of biochar, and reducing the loss of groups, the above embodiment can be applied to advanced oxidation technology to stably, continuously and efficiently repair organic pollutants, and achieve the effect of treating waste with waste.

The embodiments of the present invention have been described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned embodiments, and various changes can also be made according to the purpose of the invention and creation of the present invention. Changes, modifications, substitutions, combinations or simplifications should be equivalent substitution methods, as long as they meet the purpose of the present invention, as long as they do not deviate from the technical principles and inventive concepts of the present invention, all belong to the protection scope of the present invention.

Claims (10)

1. A method for improving the proportion of the persistent functional groups on the surface of the biochar is characterized by comprising the following steps:

(1) crushing crop straws, and further ball-milling the crushed crop straws by a ball mill to ensure that the straw powder can be sieved by a screen with the size of a sieve hole not larger than 100 meshes to obtain the sieved and collected straw powder for later use; the crop straw is gramineous crop straw or leguminous straw;

(2) treating the straw powder obtained in the step (1) by cellulase, and degrading cellulose and hemicellulose components of the straw powder into various monosaccharides so as to improve the lignin content, wherein the total amount of lignin in the treated straw powder is not less than 50% by mass percent;

(3) collecting the straw powder obtained in the step (2), washing with water at least twice, and drying at 60-80 ℃ for at least 24 hours to obtain dried straw powder;

(4) and (4) taking the straw powder obtained in the step (3) as a raw material for preparing the biochar, placing the straw powder in heating equipment, and treating at 500-700 ℃ for at least 2 hours in an oxygen-free environment, thereby obtaining the biochar with high-proportion durable functional groups on the surface.

2. The method for increasing the proportion of the permanent functional groups on the surface of the biochar as claimed in claim 1, wherein the method comprises the following steps: in the step (1), the crop straw is at least one of barley straw, wheat straw and rice straw.

3. The method for increasing the proportion of the permanent functional groups on the surface of the biochar as claimed in claim 1, wherein the method comprises the following steps: in the step (2), when the straw powder is treated by cellulase, the reaction is carried out in a shaking table with the speed of not less than 200 revolutions per minute for at least 48 hours at the temperature of not less than 45 ℃ to obtain the straw powder after enzyme treatment.

4. The method for increasing the proportion of the permanent functional groups on the surface of the biochar as claimed in claim 1, wherein: in the step (2), the total amount of lignin in the treated straw powder is 50-80% by mass.

5. The method for increasing the proportion of the permanent functional groups on the surface of the biochar as claimed in claim 1, wherein: in the step (4), the heating device is a tube furnace.

6. A biochar with a high proportion of persistent functional groups on the surface is characterized in that: the biochar is prepared by the method for improving the proportion of the persistent functional groups on the biochar surface according to claim 1.

7. Biochar having a high proportion of persistent functional groups on its surface according to claim 6, characterized in that: wherein the mass percent content of the lignin is not less than 50.66 percent, and the concentration of the water-soluble release substance is not more than 24.22 mg/L.

8. Biochar having a high proportion of persistent functional groups on its surface according to claim 6, characterized in that: the content of carboxyl group in the persistent functional group is not less than 0.10mmol/g, the content of lactone group is not less than 0.12mmol/g, the content of phenolic hydroxyl group is not less than 0.14mmol/g, and the content of carbonyl group is not less than 1.19 multiplied by 10 ⁹ groups/cm ² 。

9. Biochar having a high proportion of persistent functional groups on its surface according to claim 6, characterized in that: and (3) stirring the biochar with the high-proportion permanent functional groups on the surface in water at normal temperature and normal pressure for 1 hour in a vortex manner, wherein the loss rate of the permanent functional groups is not higher than 12%.

10. Use of biochar according to claim 6 having a high proportion of permanent functional groups on its surface, characterized in that: biochar having a high proportion of persistent functional groups on its surface is used as an activator in advanced oxidation processes.

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