CN116726880A - Magnetic biochar and preparation method and application thereof - Google Patents

Abstract

The invention discloses a magnetic biochar and its preparation method and application. The preparation includes the following steps: fully grind and mix waste biomass, ammonium oxalate monohydrate and potassium bicarbonate in proportion, and the mixture is calcined in a nitrogen environment to obtain After the calcined product is washed, dried and ground, weigh 0.5-1g of the ground product and disperse it into 25-35ml of ethylene glycol. Add sodium acetate and ferric chloride hexahydrate with a mass ratio of (1-1.5): 1. , hydrothermal reaction at 210°C for 8-20 hours, the hydrothermal reaction product obtained is washed, separated and dried with a magnet, and magnetic biochar is obtained. This magnetic biochar has a large specific surface area, pore volume and saturation magnetization. It can be used in flue gas treatment to adsorb dioxin with an efficiency of 99.8%. It can be regenerated in a nitrogen environment and complete the degradation of dioxin to achieve activated carbon. The material is reused and the pore structure is still maintained after regeneration in nitrogen environment.

Description

Magnetic biochar and preparation method and application thereof

Technical field

The invention belongs to the technical field of biochar, and specifically relates to a magnetic biochar and its preparation method and application.

Background technique

Biochar refers to biomass raw materials such as agricultural and forestry wastes that are thermally decomposed at high temperatures to produce stable porous carbon-rich carbon-fixing materials under anoxic or anaerobic conditions. Biochar is often used in water pollution treatment. However, the particle size of biochar is small, and it is difficult to recover and easy to lose in practical applications. Magnetic biochar is prepared by loading magnetic substances on biochar.

Since magnetic biochar has excellent characteristics such as high carbon content, large specific surface area, and secondary separation, based on these characteristics, magnetic separation technology can be used to separate magnetic substances from the system by applying an external magnetic field after application. Come out to realize the recycling and reuse of magnetic biochar materials. It has the characteristics of simple operation, fast and efficient. Therefore, magnetic biochar and the application of magnetic biochar have received greater attention.

Dioxins (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, PCDD/Fs) in smoke are semi-volatile organic compounds with strong biological toxicity and irreversible "Teratogenic, carcinogenic, mutagenic" toxicity, and will be enriched in organisms. Dioxins in the atmosphere are mainly produced by solid waste incineration and metal smelting. In industry, activated carbon injection is generally used to remove dioxins produced by waste incineration. Although activated carbon injection can remove most dioxin from flue gas, the activated carbon after adsorbing dioxin is usually landfilled together with fly ash, causing a waste of activated carbon and possibly causing dioxin to accumulate in soil and groundwater. leakage, causing secondary pollution to the environment. At present, magnetic activated carbon materials are mainly used in the field of wastewater treatment, and there are few reports on their application in the field of flue gas treatment.

Contents of the invention

In view of the current technical problems, the present invention provides a magnetic biochar and its preparation method and application. The magnetic biochar prepared by this method has a large specific surface area, pore volume and saturation magnetization intensity, and still retains its magnetic properties after regeneration in a nitrogen environment. Maintain better pore structure.

In order to achieve the above objects, the present invention adopts the following technical means:

A first aspect of the present invention provides a preparation method of magnetic biochar, including the following steps:

(1) Thoroughly grind and mix waste biomass, ammonium oxalate monohydrate and potassium bicarbonate in a mass ratio of 1: (2-4): 1 to obtain a mixture;

(2) Calcining the mixture in (1) under a nitrogen environment to obtain a calcined product;

(3) Clean, dry and grind the calcined product in (2) to obtain a ground product;

(4) Weigh 0.5-1g of the ground product obtained in (3), disperse it into 25-35ml of ethylene glycol, and then add sodium acetate and ferric chloride hexahydrate with a mass ratio of (1-1.5):1, Hydrothermal reaction is carried out at 210°C for 8-20 hours to obtain the hydrothermal reaction product;

(5) Clean the hydrothermal reaction product of (4), separate and dry with a magnet to obtain magnetic biochar.

Further, the waste biomass in step (1) is one or more of corn cob powder, straw powder, bamboo powder, and wood powder, and the fineness is 50-70 mesh.

Further, the calcination treatment in step (2) is as follows: the mixture in step (1) is added to the muffle furnace, raised to 800-900°C at a rate of 10°C/min in a nitrogen environment, calcined for 1 hour and then cooled naturally.

Further, the cleaning method in step (3) is: disperse the calcined product obtained in step (2) in deionized water, add 8-12 ml of hydrochloric acid, stir for 12-15 hours, and filter with suction until the filtrate becomes neutral.

Further, in step (4), the mass ratio of the ground product to ferric chloride hexahydrate is 1: (2-4).

Further, in step (5), the cleaning method is: centrifugal cleaning with absolute ethanol and then centrifugal cleaning with deionized water.

The second aspect of this aspect provides a magnetic biochar prepared by the preparation method described above. The magnetic biochar uses waste biomass as raw material, is mixed and calcined with ammonium oxalate monohydrate and potassium bicarbonate, and is prepared with ethanol. Diol is used as a reducing agent, sodium acetate is used as a stabilizer, and ferric chloride hexahydrate is used as a metal source. It is prepared through hydrothermal reaction. This magnetic biochar material has a large specific surface area: 1157-1957m ² /g, and a micropore area : 724-1428m ² /g, total pore volume: 0.62-0.95cm ³ /g, micropore volume: 0.26-0.61cm ³ /g, average pore diameter: 1.94-2.27nm and saturation magnetization 2.0-3.4emu/g.

The third aspect of the present invention provides an application of magnetic biochar in the removal of dioxin from flue gas. The magnetic biochar has a dioxin adsorption efficiency of 99.8% and can be regenerated and completed in a nitrogen environment. Degradation of dioxin enables the reuse of activated carbon materials, and maintains a good pore structure after regeneration in a nitrogen environment.

Beneficial effects of the invention

Compared with the existing technology, the present invention has the following beneficial effects: the magnetic biochar material obtained by using the activator and preparation method provided by the present invention has a large specific surface area: 1157-1957m ² /g, and a micropore area: 724-1428m ² /g, total pore volume: 0.62-0.95cm ³ /g, micropore volume: 0.26-0.61cm ³ /g, average pore diameter: 1.94-2.27nm and saturation magnetization 2.0-3.4emu/g, which is currently used in Compared with the 90.3% adsorption efficiency of common activated carbon materials for dioxin removal from flue gas, the adsorption efficiency of magnetic biochar materials for dioxin reaches 99.8%. While ensuring the efficient removal of dioxin in flue gas, magnetic biochar materials can be used Separation technology can not only recover magnetic biochar and dioxins mixed in fly ash to avoid secondary environmental pollution, but also separate low-toxic fly ash at the same time, which can be further utilized as resources.

The magnetic biochar after adsorbing dioxin can be regenerated and complete the degradation of dioxin by heating and desorption in a nitrogen environment. The desorption rate is as high as 99.8% at 400°C without destroying the pore structure of the material. Regeneration The resulting activated carbon material can still efficiently adsorb dioxins, enabling the reuse of activated carbon materials and having excellent economic value. The magnetic biochar material still maintains a good pore structure after regeneration in a nitrogen environment.

Magnetic activated carbon is used in flue gas dioxin removal. Through the coordinated use of magnetic separation technology and nitrogen environmental regeneration technology, the reuse of magnetic activated carbon materials and efficient removal of flue gas dioxin can be achieved.

Description of drawings

Figure 1 shows a scanning electron microscope (SEM) image of magnetic biochar, in which (a), (c), (e), and (g) are electron microscope images of the product MBC1 of Example 1; (b), (d) ), (f), (h) are electron microscope pictures of MBC2, the product of Example 2;

Figure 2 shows the hysteresis curve (VSM) diagram of magnetic biochar;

Figure 3 shows the nitrogen adsorption-desorption isotherm and pore size distribution diagram of magnetic biochar;

Figure 4 shows the X-ray diffraction (XRD) pattern of magnetic biochar;

Figure 5 shows a schematic diagram of the application of magnetic biochar in flue gas dioxin removal.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to examples.

Example

The following examples are provided herein to demonstrate preferred embodiments of the invention. Those skilled in the art will appreciate that the techniques disclosed in the following examples represent techniques discovered by the inventors to be useful in practicing the invention, and therefore may be considered preferred arrangements for practicing the invention. However, those skilled in the art will understand from this description that many modifications can be made to the specific embodiments disclosed herein and still obtain the same or similar results without departing from the spirit or scope of the invention.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and the disclosures and materials cited in them are hereby incorporated by reference. . Those skilled in the art will recognize, or be able to learn through routine experimentation, many equivalents to many of the specific embodiments of the invention described herein. These equivalents are intended to be included in the claims.

Example 1

(1) Weigh 6g of corn cob powder with a fineness of 60 mesh, 18g of ammonium oxalate monohydrate, and 6g of potassium bicarbonate. After thorough grinding and mixing, add them to the muffle furnace, and raise to Calculate at 800°C for 1 hour and then cool naturally. The cooled product after calcination is dispersed in deionized water, add 10 ml of hydrochloric acid, stir for 12 hours, and filter until the filtrate becomes neutral. The solid is dried and ground to obtain product A.

(2) Weigh 1.5g of ferric chloride hexahydrate and ultrasonically disperse it in 30ml of ethylene glycol. Add 1.8g of anhydrous sodium acetate and 0.75g of the obtained product A. Stir for 30 minutes at room temperature and then react hydrothermally at 210°C for 18 hours. Hydrothermal reaction The product was washed three times with absolute ethanol and three times with deionized water. After drying, magnetic biochar MBC1 was obtained. The saturation magnetization intensity was 2.0 emu/g. The pore parameters are shown in Table 1.

Example 2

(1) Weigh 6g of corn cob powder with a fineness of 60 mesh, 18g of ammonium oxalate monohydrate, and 6g of potassium bicarbonate. After thorough grinding and mixing, add them to the muffle furnace, and raise to Calculate at 800°C for 1 hour and then cool naturally. The cooled product after calcination is dispersed in deionized water. Add 10 ml of hydrochloric acid and stir for 12 hours. Filter until the filtrate is neutral. The solid is dried and ground to obtain product B.

(2) Weigh 3g of ferric chloride hexahydrate and ultrasonically disperse it in 30ml of ethylene glycol. Add 3.6g of anhydrous sodium acetate and 0.75g of the obtained product B. Stir for 30 minutes at room temperature and then react hydrothermally at 210°C for 18h. The hydrothermal reaction product Wash three times with absolute ethanol and three times with deionized water. After drying, the magnetic biochar MBC2 is obtained. The saturation magnetization intensity is 3.4 emu/g. The pore parameters are shown in Table 1.

Example 3

(1) Weigh 6g of straw powder with a fineness of 60 mesh, 18g of ammonium oxalate monohydrate, and 6g of potassium bicarbonate. After thorough grinding and mixing, add them to the muffle furnace and raise the temperature to 800 at a heating rate of 10°C/min in a nitrogen environment. After calcining for 1 hour, cool naturally. The cooled product after calcination is dispersed in deionized water. Add 10 ml of hydrochloric acid and stir for 12 hours. Filter until the filtrate becomes neutral. The solid is dried and ground to obtain product C.

(2) Weigh 1.5g of ferric chloride hexahydrate and ultrasonically disperse it in 30ml of ethylene glycol. Add 1.8g of anhydrous sodium acetate and 0.75g of the obtained product C. Stir for 30 minutes at room temperature and then react hydrothermally at 210°C for 18 hours. Hydrothermal reaction The product was washed three times with absolute ethanol and three times with deionized water. After drying, magnetic biochar MBC3 was obtained. The saturation magnetization intensity was 1.8 emu/g. The pore parameters are shown in Table 1.

Example 4

(1) Weigh 6g of bamboo powder with a fineness of 60 mesh, 18g of ammonium oxalate monohydrate, and 6g of potassium bicarbonate. After thorough grinding and mixing, add them to the muffle furnace and raise the temperature to 800 at a heating rate of 10°C/min in a nitrogen environment. Calculate at ℃ for 1 hour and then cool naturally. The cooled product after calcination is dispersed in deionized water. Add 10 ml of hydrochloric acid and stir for 12 hours. Filter until the filtrate is neutral. The solid is dried and ground to obtain product D.

(2) Weigh 1.5g of ferric chloride hexahydrate and ultrasonically disperse it in 30ml of ethylene glycol. Add 1.8g of anhydrous sodium acetate and 0.75g of the obtained product D. Stir for 30 minutes at room temperature and then react hydrothermally at 210°C for 18 hours. Hydrothermal reaction The product was washed three times with absolute ethanol and three times with deionized water. After drying, magnetic biochar MBC4 was obtained. The saturation magnetization intensity was 2.0 emu/g. The pore parameters are shown in Table 1.

Example 5

(1) Weigh 6g of wood powder with a fineness of 60 mesh, 18g of ammonium oxalate monohydrate, and 6g of potassium bicarbonate. After thorough grinding and mixing, add them to the muffle furnace and raise the temperature to 800 at a heating rate of 10°C/min in a nitrogen environment. Calculate at ℃ for 1 hour and then cool naturally. The cooled product after calcination is dispersed in deionized water. Add 10 ml of hydrochloric acid and stir for 12 hours. Filter until the filtrate becomes neutral. The solid is dried and ground to obtain product E.

(2) Weigh 1.5g of ferric chloride hexahydrate and ultrasonically disperse it in 30ml of ethylene glycol. Add 1.8g of anhydrous sodium acetate and 0.75g of the obtained product E. Stir for 30 minutes at room temperature and then react hydrothermally at 210°C for 18 hours. Hydrothermal reaction The product was washed three times with absolute ethanol and three times with deionized water. After drying, magnetic biochar MBC5 was obtained. The saturation magnetization intensity was 2.1 emu/g. The pore parameters are shown in Table 1.

Example 6

(1) Weigh 6g of corn cob and straw mixed powder with a fineness of 60 mesh, 18g of ammonium oxalate monohydrate, and 6g of potassium bicarbonate. After thorough grinding and mixing, add them to the muffle furnace and heat them up at 10°C/min in a nitrogen environment. The rate was increased to 800°C and calcined for 1 hour and then cooled naturally. The cooled product after calcination was dispersed in deionized water, added with 10 ml of hydrochloric acid, stirred for 12 hours, filtered until the filtrate was neutral, and the solid was dried and ground to obtain product F.

(2) Weigh 1.5g of ferric chloride hexahydrate and ultrasonically disperse it in 30ml of ethylene glycol. Add 1.8g of anhydrous sodium acetate and 0.75g of the obtained product F. Stir for 30 minutes at room temperature and then react hydrothermally at 210°C for 18 hours. Hydrothermal reaction The product was washed three times with absolute ethanol and three times with deionized water. After drying, magnetic biochar MBC6 was obtained. The saturation magnetization intensity was 2.0emu/g. The pore parameters are shown in Table 1.

Comparative example 1

Weigh 6g of cellulose powder, 6g of ammonium oxalate monohydrate, and 18g of sodium bicarbonate. After thorough grinding and mixing, add them to the muffle furnace, raise them to 900°C at a heating rate of 10°C/min in a nitrogen environment, calcine for 1 hour, and then cool naturally. , the calcined cooled product was dispersed in deionized water, 10 ml of hydrochloric acid was added, stirred for 12 hours, filtered until the filtrate was neutral, and the solid was dried and ground to obtain unloaded magnetic biochar BC1. The pore parameters are shown in Table 1.

Comparative example 2

Weigh 6g of corncob powder with a fineness of 60 mesh and 24g of potassium bicarbonate. After thorough grinding and mixing, add it to the muffle furnace. In a nitrogen environment, raise it to 900°C at a heating rate of 10°C/min. Calculate for 1 hour and then cool naturally. The calcined cooled product was dispersed in deionized water, 10 ml of hydrochloric acid was added, stirred for 12 hours, filtered until the filtrate was neutral, and the solid was dried and ground to obtain unloaded magnetic biochar BC2. The pore parameters are shown in Table 1.

Comparative example 3

Weigh 6g of wheat straw powder with a fineness of 60 mesh, 6g of potassium carbonate, and 12g of potassium hydroxide. After thorough grinding and mixing, add them to the muffle furnace and heat them up to 900°C for 1 hour in a nitrogen environment at a heating rate of 10°C/min. After cooling naturally, the calcined cooled product was dispersed in deionized water, 10 ml of hydrochloric acid was added, stirred for 12 hours, filtered until the filtrate was neutral, and the solid was dried and ground to obtain unloaded magnetic biochar BC3. The pore parameters are shown in Table 1.

Table 1 Pore parameters of biochar materials

Among them, a scanning tunneling microscope was used to characterize the magnetic biochars MBC1 and MBC2 prepared in Example 1 and Example 2. The results are shown in Figure 1. A vibrating sample magnetometer was used to characterize the magnetic biochars MBC1 and MBC2 prepared in Example 1 and Example 2. The magnetic biochar MBC1 and MBC2 were characterized, and the results are shown in Figure 2. The magnetic biochar MBC1 and MBC2 prepared in Example 1 and Example 2 were characterized using a nitrogen isothermal adsorption-desorption test, and the results are shown in Figure 3 As shown in Figure 4, the magnetic biochars MBC1 and MBC2 prepared in Example 1 and Example 2 were characterized using X-ray diffraction.

Example 7

Weigh 100 mg of magnetic biochar MBC1-MBC6 and unloaded magnetic biochar BC1-BC3 obtained in the example, and conduct a dioxin adsorption experiment at 160°C. Set the carrier gas flow rate to 500 ml/min and the oxygen content to 11%. , adsorption for 1h. The dioxin removal efficiency of biochar materials is shown in Table 2.

Table 2 Dioxin removal efficiency of biochar materials

The results show that although MBC1-MBC6 use different raw materials, they use the same activator. The prepared magnetic biochar has better dioxin removal efficiency, and the difference is not significant, indicating that the raw materials in this method have a better effect on biochar. The adsorption effect has little impact. The biochars prepared by BC1-BC3 using different activators have poor dioxin removal efficiency and significant differences, indicating that the activators in this method have a greater impact on the adsorption effect of biochar. Using the activator of the present invention and The magnetic biochar prepared by this method has better dioxin removal efficiency.

Example 8

The dioxin-adsorbed magnetic biochar MBC1-MBC6 and the unloaded magnetic biochar BC1-BC3 were heated at 400°C for 1 hour in a nitrogen environment, and the nitrogen flow rate was set to 200 ml/min. The dioxin desorption rate of biochar materials and the pore loss rate of the material after regeneration are shown in Table 3.

Table 3 Dioxin desorption rate and material pore loss rate after regeneration

Dioxin desorption rate (%) pore loss rate MBC1 99.5 0.7 MBC2 99.8 0.8 MBC3 99.8 0.4 MBC4 99.4 0.4 MBC5 99.5 0.9 MBC6 99.7 0.5 BC1 99.8 0.5 BC2 99.3 1.2 BC3 99.4 0.7

The results showed that magnetic biochar and biochar without magnetic loading desorbed dioxin after adsorption. There was little difference in dioxin desorption rate and biochar pore loss rate, and both were suitable for reuse.

Example 9

Magnetic biochar can be reused in the removal of dioxin from incineration flue gas. As shown in Figure 5, the incineration flue gas and fly ash in the boiler enter the quench tower and are deacidified dryly. The magnetic activated carbon is then incinerated after deacidification. The flue gas and fly ash enter the dust bag for dioxin adsorption. The adsorbed flue gas enters wet deacidification and is discharged from the chimney.

The magnetic biochar after adsorbing dioxin enters the low-temperature pyrolysis furnace for desorption and low-temperature degradation of dioxin. The magnetic biochar with fly ash enters the magnetic separator for separation. At the same time, low-toxic fly ash and low-toxicity can be obtained. Fly ash can be further utilized as a resource, and the obtained magnetic biochar is supplied to the activated carbon injector and recycled for adsorption of dioxins in the deacidified incineration flue gas.

All documents mentioned in this application are incorporated by reference in this application to the same extent as if each individual document was individually incorporated by reference. In addition, it should be understood that after reading the above teaching content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims (8)

1. A method for preparing magnetic biochar, characterized in that it includes the following steps: (1) Thoroughly grind and mix waste biomass, ammonium oxalate monohydrate and potassium bicarbonate in a mass ratio of 1: (2-4): 1 to obtain a mixture; (2) Calcining the mixture in (1) under a nitrogen environment to obtain a calcined product; (3) Clean, dry and grind the calcined product in (2) to obtain a ground product; (4) Weigh 0.5-1g of the ground product obtained in (3), disperse it into 25-35ml of ethylene glycol, and then add sodium acetate and ferric chloride hexahydrate with a mass ratio of (1-1.5): 1, 210 ℃ hydrothermal reaction for 8-20 hours to obtain the hydrothermal reaction product; (5) Clean the hydrothermal reaction product of (4), separate and dry with a magnet to obtain magnetic biochar. 2. A method for preparing magnetic biochar according to claim 1, wherein the waste biomass in step (1) is one or more of corn cob powder, straw powder, bamboo powder, and wood powder. , the fineness is 50-70 mesh. 3. The preparation method of magnetic biochar according to claim 1, characterized in that the calcination treatment in step (2) is: the mixture in step (1) is added to a muffle furnace, and in a nitrogen environment, Rise to 800-900°C at a rate of 10°C/min, calcine for 1 hour and then cool naturally. 4. The preparation method of magnetic biochar according to claim 1, characterized in that: the cleaning method in step (3) is: dispersing the calcined product obtained in step (2) in deionized water, adding 8- 12ml hydrochloric acid, stir for 12-15h, filter with suction until the filtrate becomes neutral. 5. The preparation method of magnetic biochar according to claim 1, characterized in that: in step (4), the mass ratio of the ground product and ferric trichloride hexahydrate is 1: (2-4). 6. The preparation method of magnetic biochar according to claim 1, characterized in that in step (5), the cleaning method is: centrifugal cleaning with absolute ethanol and then centrifugal cleaning with deionized water. 7. A magnetic biochar prepared by the preparation method according to any one of claims 1-6. 8. Application of the magnetic biochar according to claim 7 in the removal of dioxin from flue gas.