CN111841495A - Preparation method of porous tea residue biochar with high specific surface area - Google Patents

Abstract

The invention discloses a preparation method of porous high specific surface area tea residue biochar, which belongs to the field of product processing waste recycling. The present invention adopts potassium bicarbonate as modifier. First, the tea residues are washed with hot water, dried and pulverized, and then the tea residues are subjected to hydrothermal treatment. After the hydrothermal treatment, the solid tea residues are dried by hydrothermal charcoal. After drying, it is put into a tubular muffle furnace for pyrolysis. After pyrolysis, the carbonized product is pickled, washed with water, dried and ball-milled to obtain tea residue biochar. The obtained tea residue biochar has a well-developed pore structure. , a large specific surface area, the specific surface area is 1278~1405 m ² /g, and the pore volume is 0.6734~0.8067 cm ³ /g. Tea residue biochar has a good removal effect on tetracycline in water, and the adsorption capacity of tetracycline in water can reach 429-478 mg/g.

Description

A kind of preparation method of porous high specific surface area tea residue biochar

technical field

The invention belongs to the field of product processing waste resource recycling, and specifically designs a method, product and application of a porous high specific surface area tea residue biochar.

Background technique

China is a big country of tea production and consumption. With the rapid development of the tea consumption market, my country's annual tea production has reached more than 2 million tons. After tea production or application, a large amount of tea residues will be produced. How to recycle tea residues and wastes has become a hot spot in the tea industry and the field of ecological environmental protection.

Currently, biochar refers to a class of carbon-rich, highly aromatic solid substances produced by the pyrolysis of biomass at low temperature (<700 °C) in a completely or partially anoxic state. Biochar has good application prospects in the field of water pollution control due to its wide source of raw materials, large specific surface area, well-developed pores, and rich functional groups and minerals. Tea residue contains a large amount of cellulose, hemicellulose, lignin, protein, amino acids, vitamins, tea polyphenols and trace elements, and is a good raw material for biochar preparation.

At present, the preparation method of tea residue biochar is mainly based on direct pyrolysis and carbonization, but the undisturbed tea residue biochar obtained by direct pyrolysis has a small specific surface area (< 100 m²/g) and an underdeveloped pore structure. The removal effect of pollutants in water is not good, so it is necessary to modify the tea residue to improve its adsorption effect. Before direct carbonization, hydrothermal treatment of tea residues can be carried out to make it preliminarily carbonized, which is beneficial to the subsequent thermochemical reaction with the modifier. Commonly used modifiers include phosphoric acid, sulfuric acid, mineral (iron manganese aluminum magnesium) modification, steam, potassium bicarbonate, sodium bicarbonate and other modification methods. However, the above-mentioned activators have problems such as corrosiveness, secondary pollution, and generation of toxic and harmful exhaust gas, and it is urgent to explore new activators.

The removal methods of tetracycline in water mainly include biochemical method, membrane treatment method and photocatalytic oxidation method, all of which have certain limitations. For example, the role of microorganisms in biochemical methods can be inhibited, membrane treatment methods are limited by membrane clogging and efficiency, and photocatalytic degradation methods are limited by the size of the reaction apparatus. The adsorption method has been widely concerned and applied due to its advantages of high efficiency, simple operation, simple process, and no secondary pollution. The key to the adsorption method is the selection and preparation of the adsorbent. Biomass adsorbents with a wide range of sources, low cost and excellent effect have attracted much attention. Therefore, the tea residue waste can be modified by carbonization to prepare porous biochar with high specific surface area, which can be applied to the removal of tetracycline in water.

SUMMARY OF THE INVENTION

In order to realize the resource utilization of waste tea residues, the present invention provides a preparation method of tea residue biochar with porous and high specific surface area.

A specific preparation operation step of tea residue biochar with porous high specific surface area is as follows:

(1) Raw material pretreatment

Wash the tea residue with water, dry it, pulverize it, and pass it through a 60-80 mesh sieve to obtain tea residue powder with impurities and ash removed;

(2) Hydrothermal treatment

Mix 3~5 grams of tea residue powder with 50~80 milliliters of pure water, react in a hydrothermal reactor for 8~10 hours at a temperature of 200 ° C, and separate the solid from liquid to obtain hydrothermal charcoal, which uses anhydrous ethanol for the hydrothermal charcoal. Wash three times and dry to obtain hydrothermal charcoal;

(3) Modifier impregnation treatment

Mix the hydrothermal charcoal and potassium bicarbonate in a mass ratio of 1:4~1:6, add 200 mL of pure water for immersion treatment, stir at a temperature of 15~35 °C for 2~4 h; dry to remove water to obtain hydrothermal charcoal Mixed solids mixed with potassium bicarbonate;

(4) Carbonization treatment

Put the mixed solid into a quartz boat, transfer it to a tubular muffle furnace, raise it to 700 °C at a heating rate of 5 °C/min for carbonization, keep it at 700 °C for 1~3 h, cool it to room temperature and take it out to obtain a carbonized product ;

(5) Washing and drying

Put the charcoal in 100 mL of 0.1 molar hydrochloric acid solution (HCl) for washing, continue to wash after suction filtration, and wash three times in total; then wash with pure water until the pH of the eluate is 6~8, dry, and pulverize by ball milling. , to obtain tea residue biochar; the tea residue biochar has a specific surface area of 1278-1405 m ² /g and a pore volume of 0.6734-0.8067 cm ³ /g.

Further limited technical solutions are as follows:

In step (1), drying is carried out in a blast drying oven, the drying temperature is 100-105°C, and the drying time is 10-24 h.

In step (2), the hydrothermal charcoal is washed three times with absolute ethanol in a volume ratio of 1:20; dried in a blast drying oven, the drying temperature is 100-105 °C, and the time is 10-24 h.

In step (3), drying in a blast drying oven to remove moisture, the drying temperature is 100-105°C, and the time is 10-24 hours.

In step (5), drying is carried out in a blast drying oven, the drying temperature is 100-105° C., and the time is 10-24 h; the ball is milled for 1-5 minutes and pulverized, and passed through a 100-200 mesh sieve.

The beneficial technical effect of the present invention is embodied in the following aspects:

1. The present invention provides a method for preparing tea residue biochar with a simple preparation process, using waste tea residue as a raw material and using potassium bicarbonate as (KHCO ₃ ) as a modifier, KHCO ₃ is a new environmentally friendly The catalyst has the advantages of good effect, no secondary pollution, and low corrosiveness. The preparation process of the invention has low cost and wide raw material sources, and promotes the resource utilization of tea residues and wastes in tea factories or tea processing enterprises, thereby reducing waste of biomass resources and environmental pollution.

2. The obtained tea residue biochar has a developed pore structure and a large specific surface area. The mechanism of forming a developed pore structure and high specific surface area involves reaction formulas (1)-(5): when the pyrolysis temperature exceeds 400 °C, KHCO ₃ will decompose K ₂ CO ₃ and CO ₂ , H ₂ O gas (reaction formula (1)). When the pyrolysis temperature is 700°C, K ₂ CO ₃ will be decomposed into K ₂ O and CO ₂ (reaction (2)), meanwhile, K ₂ CO ₃ and K ₂ O will react with the carbon in the tea residue to form K and CO (reaction equations (3) and (4)), in addition, the generated _CO gas will be reduced to CO gas by the carbon in the tea residue (reaction equation (5)). The H ₂ O, CO ₂ and CO gases generated during the reaction create mesopores and micropores. In addition, K ₂ O and K embedded in the tea residue carbon also formed mesopores and micropores.

2KHCO ₃ →K ₂ CO ₃ + CO ₂ + H ₂ O ——(1)

K ₂ CO ₃ → K ₂ O + CO ₂ —————— (2)

K ₂ CO ₃ +2C → 2K + 3CO ——————(3)

K ₂ O + C → 2K + CO ———————— (4)

CO ₂ + C → 2CO ———————— (5)

The specific surface area of the modified tea residue biochar was as high as 1278-1405 m ² /g, and the pore volume was 0.6734-0.8067 cm ³ /g.

3. The tea residue biochar of the present invention can be used for the removal of pollutants in the water body, so as to realize the resource utilization of waste tea residues and protect the environment. The tea residue biochar of the invention has a good effect of removing tetracycline in water. Within a certain concentration range (0-150 mg/L), the porous tea residue biochar with high specific area of the present invention has a good removal effect on tetracycline in water. When the initial concentration of tetracycline was 10-100 mg/L, the removal rate of tetracycline by tea residue biochar reached 98%. When the initial concentration of tetracycline was 100-150 mg/L, the removal rate of tetracycline by tea residue biochar was above 95%. The tea residue biochar with porous high specific area can adsorb 429-478 mg/g of tetracycline in water, and the removal effect is remarkable, which shows that the tea residue biochar with porous high specific area of the present invention has a very good effect on the treatment of tetracycline in water. great potential. The invention is suitable for the recycling treatment of tea slag, which is a waste of tea factories, reduces resource waste and environmental pollution, and achieves the purpose of "treating waste with waste".

Description of drawings

Figure 1 is the scanning electron microscope image of tea residue biochar at Mag = 10.0k.

Figure 2 is a scanning electron microscope image of tea residue biochar at a magnification of Mag=20.0k.

Figure 3 is a scanning electron microscope image of tea residue biochar at a magnification of Mag=50.0k.

Detailed ways

The present invention will be further described below with reference to specific embodiments.

Example 1

A specific preparation operation step of tea residue biochar with porous high specific surface area is as follows:

(1) Raw material pretreatment

The waste tea residues taken from the tea factory were washed with water to remove impurities. After washing, the tea residues were placed in a blast drying oven for drying. The temperature of the blast drying oven was 100 ° C and the time was 10h. The drying was pulverized with a pulverizer. 60 mesh sieve, save for later use.

(2) Hydrothermal treatment

Mix 3 grams of tea residue with 50 ml of pure water and put it into a hydrothermal reactor, react at 200°C for 8 hours, and separate the solid and liquid to obtain hydrothermal charcoal; the hydrothermal charcoal is washed three times with absolute ethanol, and the The ratio of water to ethanol is 1:20; it is dried in a blast drying oven, the drying temperature is 100 ° C, and the time is 10 h to obtain hydrothermal carbon.

(3) Modifier impregnation treatment

Mix hydrothermal charcoal and potassium bicarbonate in a mass ratio of 5 g: 20 g (1:4), add 200 mL of pure water for immersion treatment, stir at 15 °C for 2 hours, put it in a blast drying box to dry to remove moisture, and dry The temperature is 100°C and the time is 10h; a mixed solid of hydrothermal carbon and potassium bicarbonate is obtained.

(4) Carbonization treatment

The mixed solid was put into a quartz boat, transferred to a tubular muffle furnace, raised to 700°C at a heating rate of 5°C/min for carbonization, kept at 700°C for 1 h, cooled to room temperature and taken out to obtain carbonized material.

(5) Washing and drying

Pour 10 g of carbonized product into 100 mL of 0.1 molar hydrochloric acid solution (HCl) for washing, continue to wash after suction filtration, wash three times in total, and then wash three times with pure water until the pH value of the eluate is 6.84. The solids were dried at a drying temperature of 100°C for 10 hours; ball milled for 1 minute, pulverized, and passed through a 100-mesh sieve to obtain tea residue biochar with high porous and high specific surface area.

It can be seen from Table 1 that the specific surface area of the tea residue biochar in Example 1 is 1278 m ² /g, and the pore volume is 0.6734 cm ³ /g. The adsorption capacity of tetracycline in water was 429 mg/g.

Example 2

A specific preparation operation step of tea residue biochar with porous high specific surface area is as follows:

(1) Raw material pretreatment

The waste tea residues taken from the tea factory were washed with water to remove impurities. After washing, the tea residues were put into a blast drying oven for drying. The temperature of the blast drying oven was 105°C and the time was 15h. 70 mesh sieve to save for future use.

(2) Hydrothermal treatment

4 grams of tea residues and 65 ml of pure water were mixed and put into a hydrothermal reactor, reacted at 200°C for 9 hours, and separated from solid and liquid to obtain hydrothermal charcoal. The hydrothermal charcoal was washed three times with absolute ethanol. The ratio of water to ethanol is 1:20, and it is dried in a blast drying oven, the drying temperature is 105 ° C, and the time is 15 h to obtain hydrothermal charcoal.

(3) Modifier impregnation treatment

Mix hydrothermal charcoal and potassium bicarbonate in a mass ratio of 5 grams: 25 grams (1:5), add 200 mL of pure water for immersion treatment, stir at 20 °C for 3 hours, put it in a blast drying box to dry to remove moisture, and dry The temperature is 105°C and the time is 15h; a mixed solid of hydrothermal charcoal and potassium bicarbonate is obtained.

(4) Carbonization treatment

The mixed solid was put into a quartz boat, transferred to a tubular muffle furnace, raised to 700°C at a heating rate of 5°C/min for carbonization, kept at 700°C for 2 hours, cooled to room temperature and taken out to obtain carbonized material.

(5) Washing and drying

Pour 10 g of carbonized product into 100 mL of 0.1 molar hydrochloric acid solution (HCl) for washing, continue washing after suction filtration, and wash three times in total, and then wash three times with pure water until the pH value of the eluate is 7.04. The solid was dried at a drying temperature of 105°C for 15h; ball milled for 3 minutes and pulverized, and passed through a 150-mesh sieve to obtain tea residue biochar with high porous and high specific surface area.

It can be seen from Table 1 that the specific surface area of the tea residue biochar in Example 2 is 1350 m ² /g, and the pore volume is 0.7215 cm ³ /g. The adsorption capacity of tetracycline in water is 451mg/g.

Example 3

A specific preparation operation step of tea residue biochar with porous high specific surface area is as follows:

(1) Raw material pretreatment

The waste tea residues taken from the tea factory were washed with water to remove impurities. After washing, the tea residues were put into a blast drying oven for drying. The temperature of the blast drying oven was 105 ° C and the time was 24 hours. 80 mesh sieve for future use.

(2) Hydrothermal treatment

Mix 5 grams of tea residue and 80 milliliters of pure water into a hydrothermal reactor, react at 200°C for 10 hours, and separate solid-liquid to obtain hydrothermal charcoal. The hydrothermal charcoal is washed three times with absolute ethanol. The ratio of water to ethanol is 1:20, and it is dried in a blast drying oven, the drying temperature is 105 ° C, and the time is 24 h to obtain hydrothermal charcoal.

(3) Modifier impregnation treatment

Mix hydrothermal charcoal and potassium bicarbonate in a mass ratio of 5 grams: 60 grams (1:6), add 200 mL of pure water for immersion treatment, stir at 25°C for 4 hours, put it in a blast drying box to dry to remove moisture, and dry The temperature is 105°C and the time is 24h; a mixed solid of hydrothermal carbon and potassium bicarbonate is obtained.

(4) Carbonization treatment

The mixed solid was put into a quartz boat, transferred to a tubular muffle furnace, raised to 700°C at a heating rate of 5°C/min for carbonization, kept at 700°C for 3 hours, cooled to room temperature and taken out to obtain carbonized material.

(5) Washing and drying

Pour 10 g of carbonized product into 100 mL of 0.1 molar hydrochloric acid solution (HCl) for washing, continue to wash after suction filtration, wash three times in total, and then wash three times with pure water until the pH of the eluate is 7.23. The solid was dried at a drying temperature of 105°C for 24 hours; ball milled for 5 minutes, pulverized, and passed through a 200-mesh sieve to obtain tea residue biochar with high porous and high specific surface area.

It can be seen from Table 1 that the specific surface area of the tea residue biochar in Example 3 is 1405 m ² /g, and the pore volume is 0.8067 cm ³ /g. The adsorption capacity of tetracycline in water was 478 mg/g.

Referring to Figure 1, when the magnification is 10,000 times, the surface of the tea residue biochar presents rich pore characteristics; see Figure 2, when the magnification is 20,000 times, the surface of the tea residue biochar contains pore structures of different sizes; Referring to Fig. 3, when the magnification is 50000 times, the mesoporous and microporous features on the surface of tea residue biochar are very obvious. It can be seen that the modified tea residue biochar has a well-developed pore structure, obvious honeycomb-like shape, and a large specific surface area, which determines that it has a good adsorption effect on tetracycline in water as an adsorbent.

Claims (5)

1. A preparation method of porous tea residue biochar with high specific surface area is characterized by comprising the following preparation operation steps:

(1) pretreatment of raw materials

Washing tea leaves with water, drying, crushing, and sieving with a 60-80-mesh sieve to obtain tea leaf powder with impurities and ash removed;

(2) hydrothermal treatment

Mixing 3-5 g of tea residue powder and 50-80 ml of pure water, reacting for 8-10 hours at 200 ℃ in a hydrothermal reaction kettle, carrying out solid-liquid separation to obtain hydrothermal carbon, washing the hydrothermal carbon with absolute ethyl alcohol for three times, and drying to obtain hydrothermal carbon;

(3) dipping treatment of modifier

Mixing hydrothermal carbon and potassium bicarbonate according to the mass ratio of 1: 4-1: 6, adding 200 mL of pure water for impregnation treatment, and stirring for 2-4 hours at the temperature of 15-35 ℃; drying to remove water to obtain a mixed solid of the hydrothermal carbon and the potassium bicarbonate;

(4) charring treatment

Putting the mixed solid into a quartz boat, transferring the quartz boat into a tubular muffle furnace, raising the temperature to 700 ℃ at a heating rate of 5 ℃/min, carbonizing, keeping the temperature at 700 ℃ for 1-3 h, cooling to room temperature, and taking out to obtain a carbide;

(5) washing and drying

Pouring the carbide into 100 mL of hydrochloric acid solution (HCl) with the concentration of 0.1 mol for washing, and continuously washing after suction filtration for three times; then washing with pure water until the pH value of the eluate is 6-8, drying, and carrying out ball milling and crushing to obtain tea residue biochar; the specific surface area of the tea residue biochar is 1278-1405 m ²The pore volume is 0.6734-0.8067 cm³/g。

2. The preparation method of the porous high-specific-surface-area tea residue biochar as claimed in claim 1, is characterized in that: and (2) drying in a forced air drying oven at the drying temperature of 100-105 ℃ for 10-24 h in the step (1).

3. The preparation method of the porous high-specific-surface-area tea residue biochar as claimed in claim 1, is characterized in that: in the step (2), the volume ratio of (1): 20 washing the hydrothermal charcoal with absolute ethyl alcohol for three times; and drying in a forced air drying oven at the drying temperature of 100-105 ℃ for 10-24 h.

4. The preparation method of the porous high-specific-surface-area tea residue biochar as claimed in claim 1, is characterized in that: and (3) drying in a forced air drying oven to remove water, wherein the drying temperature is 100-105 ℃, and the drying time is 10-24 hours.

5. The preparation method of the porous high-specific-surface-area tea residue biochar as claimed in claim 1, is characterized in that: drying in a forced air drying oven at 100-105 ℃ for 10-24 h in the step (5); ball milling for 1-5 min, crushing, and sieving with 100-200 mesh sieve.

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