KR102198796B1 - Preparation method of activated carbon using reducing atmosphere - Google Patents

Abstract

The present invention relates to a method of manufacturing activated carbon, and more particularly, to a method of manufacturing activated carbon having mesopores by heat-treating a metal organic skeleton in a reducing atmosphere. In order to achieve the above object, the present invention comprises the steps of (Step 1) preparing an organic metal skeleton; (Step 2) raising the temperature of the organic metal skeleton to a range of 750 ~ 850 ℃ while injecting an inert gas; And (Step 3) performing heat treatment while replacing and injecting an inert gas with a reducing gas after the temperature is raised.

Description

Preparation method of activated carbon using reducing atmosphere {Preparation method of activated carbon using reducing atmosphere}

The present invention relates to a method of manufacturing activated carbon, and more particularly, to a method of manufacturing activated carbon having mesopores by heat-treating a metal organic skeleton in a reducing atmosphere.

Activated carbon is an amorphous carbon having a porous pore structure of various sizes, not only used as an adsorbent due to physical adsorption occurring on the inner surface, but also widely used as deodorization, decolorization, and catalyst, etc. As for the use of activated carbon, waste gas treatment, recovery of volatile solvents, removal of toxic organic substances, and agricultural water treatment, the use and use of activated carbon are gradually increasing, and the demand is increasing day by day.

However, conventional activated carbon has a high surface area, but can only adsorb small molecules due to its narrow pore size, and its pore volume is relatively small, so it cannot adsorb a large amount of material, causing clogging, etc. The problem of is being pointed out.

Accordingly, a method of increasing the specific surface area and pore volume by modifying the surface characteristics of the existing activated carbon is being studied. For example, a chemical treatment is performed using chemical substances such as potassium carbonate and zinc chloride, and under nitrogen gas injection conditions. A method of modifying the surface properties of activated carbon by calcining at a high temperature of 600 to 900°C or higher has been provided.

However, the conventional method of modifying the surface properties of activated carbon has a problem in that the mesopores are not properly secured, only a slight increase in the specific surface area and pore volume. Therefore, adsorption of macromolecular substances is still difficult, and there is a problem in that effective use is limited because it takes a long time for the target substance to penetrate into the pores due to no mesopores. Therefore, recently, a carbon material having mesopores is attracting attention.

On the other hand, the metal organic framework is a three-dimensional porous material in which micropores of the same size are evenly arranged. Is achieved. Accordingly, the present inventors have developed a method for producing activated carbon having mesopores by carbonizing an organic ligand material of a metal organic framework and simultaneously removing central metal ions.

Republic of Korea Patent Registration No. 10-0715873 (Name of invention: method of increasing the mesopore content of carbon materials for supercapacitor electrodes, Applicant: Pohang Institute of Industrial Science and Technology, registration date: May 1, 2007) Republic of Korea Patent Registration No. 10-0885191 (Name of invention: Mesopoa activated carbon manufacturing method using iron catalyst ion exchange method, Applicant: Chungbuk National University Industry-Academic Cooperation Foundation, registration date: February 17, 2009)

An object of the present invention is to provide a method for producing activated carbon having excellent specific surface area even at low temperature using a metal organic skeleton.

Another object of the present invention is to provide an activated carbon having mesopores manufactured through the above manufacturing method.

The present invention (step 1) preparing a metal organic skeleton;

(Step 2) raising the temperature of the organic metal skeleton to a range of 750 ~ 850 ℃ while injecting an inert gas; And

It provides a method for producing activated carbon comprising: (Step 3) heat treatment while injecting and replacing the inert gas with a reducing gas after heating.

In the second step, the inert gas is preferably nitrogen, and the heating rate is more preferably 3 to 7° C./min.

In the third step, the reducing gas is preferably a mixture of hydrogen and argon, and more preferably, the mixed gas contains 3 to 7% by volume of hydrogen.

In addition, the heat treatment in step 3 is preferably performed for 2 to 4 hours.

The gas injection rate in the second or third step is preferably 250 to 350 ml/min, and the gas injection rate in the second or third step may be the same or different.

The method of manufacturing activated carbon of the present invention may further include performing heat treatment in an inert gas atmosphere for an additional 2 to 4 hours after heating in the third step and before replacing the inert gas with a reducing gas.

Activated carbon prepared through the manufacturing method of the present invention is characterized by having mesopores of 4.5 nm or more. In addition, the activated carbon is characterized by having a total specific surface area of 1600 to 1700 m ² /g and a specific surface area due to mesopores of 300 m ² /g or more.

Hereinafter, the present invention will be described in detail.

In order to achieve the above object, the present invention comprises the steps of (Step 1) preparing an organic metal skeleton;

(Step 2) raising the temperature of the organic metal skeleton to a range of 750 ~ 850 ℃ while injecting an inert gas; And

It provides a method for producing activated carbon comprising: (Step 3) heat treatment while injecting and replacing the inert gas with a reducing gas after heating.

That is, the present invention relates to a method of producing activated carbon having mesopores by carbonizing an organic ligand material that binds to a central metal component of a metal organic skeleton in a reducing atmosphere and removing the central metal at the same time.

In the first step, the metal organic skeleton may be prepared by mixing a zinc precursor, terephthalic acid, and a solvent, followed by heating, and the metal organic skeleton has zinc or zinc oxide as a central metal component. At this time, the solvent is preferably not to destroy the structure of the metal organic skeleton, for example, chloroform, tetrahydrofuran, benzene, water, ethanol, methanol, acetone, dimethyl sulfoxide, N,N-Dimethylformamide and N,N It may be one or more selected from the group consisting of -Diethylformamide.

In the second step, the inert gas is preferably nitrogen.

In addition, in the second step, the heating rate is preferably 3 to 7°C/min, and the temperature raising temperature range is preferably 750 to 850°C. If the heating temperature is less than 750° C., zinc does not evaporate, so that the specific surface area of the activated carbon is not sufficient, and if it exceeds 850° C., mesopores are not sufficiently formed, which is not preferable.

In the third step, the reducing gas is preferably a mixture of hydrogen and argon, and more preferably, the mixed gas contains 3 to 7% by volume of hydrogen. If the content of hydrogen in the mixed gas is less than 3% by volume, it is difficult for zinc to lower the evaporation temperature, and if it exceeds 7% by volume, the mesopores in the activated carbon are not sufficiently formed, which is not preferable.

In addition, the heat treatment in step 3 is preferably performed for 2 to 4 hours. If the heat treatment time is less than 2 hours, zinc is not sufficiently evaporated, and if it exceeds 4 hours, it is not economical and thus is not preferable.

The gas injection rate in the second or third step is preferably 250 to 350 ml/min, and the gas injection rate in the second or third step may be the same or different.

The method of manufacturing activated carbon of the present invention may further include performing heat treatment in an inert gas atmosphere for an additional 2 to 4 hours after heating in the third step and before replacing the inert gas with a reducing gas.

Activated carbon prepared through the manufacturing method of the present invention is characterized by having mesopores of 4.5 nm or more.

In addition, the activated carbon has a total specific surface area of 1600 to 1700 m ² /g, and a specific surface area due to mesopores of 300 m ² /g or more. More preferably, the specific surface area of the mesopores may be 350m ² /g or more.

The method for producing activated carbon provided in the present invention is a suitable method for producing activated carbon having sufficient mesopores by carbonizing a metal organic skeleton in a reducing atmosphere.

In addition, through the above manufacturing method, activated carbon having an excellent specific surface area can be manufactured at a low temperature, which is economical.

1 is a graph showing TGA measurement results of activated carbon prepared according to Examples and Comparative Examples.
2 is a graph showing the results of adsorption isotherms of activated carbon prepared according to Examples and Comparative Examples.
3 is a graph showing the results of porosity distribution of activated carbon prepared according to Examples and Comparative Examples.

Hereinafter, a preferred embodiment of the present invention will be described in detail. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, it is provided to sufficiently convey the spirit of the present invention to those skilled in the art so that the contents introduced herein are thorough and complete.

Manufacturing example. MOF-5 manufacturing

11.9 g of zinc nitrate hexahydrate, 2.3 g of terephthalic acid and 160 ml of dimethylformamide (DMF) were put in an autoclave, sealed, heated at 120° C. for 24 hours, Crystals were prepared. Subsequently, the crystals were washed several times with DMF and then washed with chloroform (CHCl ₃ ) to remove unreacted impurities. Thereafter, the crystals from which impurities were removed were vacuum-dried at 150° C. for 24 hours to prepare MOF-5.

Examples and Comparative Examples. Activated carbon manufacturing

Example 1 (800° C., inert gas injection, then replacement injection with reducing gas)

After putting 2 g of MOF-5 prepared above into a tube furnace, it was heated to 800° C. at a rate of 5° C. per minute while injecting N ₂ gas at a rate of 300 ml/min. Subsequently, after further heating for 3 hours under N ₂ gas conditions at 800° C., H ₂ /Ar mix gas (H ₂ 4 vol%) was injected instead of N ₂ gas at a rate of 300 ml/min, followed by heat treatment for 3 hours. Then, it was naturally cooled to prepare activated carbon.

Comparative Example 1 (700° C., inert gas injection and then replacement injection with reducing gas)

Activated carbon was prepared in the same manner as in Example 1, but the temperature was raised to 700°C to prepare activated carbon.

Comparative Example 2 (900° C., inert gas injection and then replacement injection with reducing gas)

Activated carbon was prepared in the same manner as in Example 1, but heated to 900°C to prepare activated carbon.

Comparative Example 3 (800°C, inert gas injection)

After putting 2 g of MOF-5 prepared above into a tube furnace, it was heated to 800° C. at a rate of 5° C. per minute while injecting N ₂ gas at a rate of 300 ml/min. Subsequently, after further heating for 6 hours under 700° C. N ₂ gas condition, it was naturally cooled to prepare activated carbon.

Comparative Example 4 (900°C, inert gas injection)

Activated carbon was prepared in the same manner as in Comparative Example 3, but the temperature was raised to 900°C to prepare activated carbon.

Comparative Example 5 (1000° C., inert gas injection)

Activated carbon was prepared in the same manner as in Comparative Example 3, but the temperature was raised to 100°C to prepare activated carbon.

Experimental Example 1. Measurement of specific surface area of activated carbon

Specific surface area was measured through the results of nitrogen adsorption-desorption isotherm analysis of the activated carbons prepared in Example 1 and Comparative Examples 1 to 5, and the results are shown in Table 1 and FIG. .

Reducing atmosphere Nitrogen atmosphere Comparative Example 1
(700℃) Example 1
(800℃) Comparative Example 2
(900℃) Comparative Example 3
(800℃) Comparative Example 4
(900℃) Comparative Example 5
(1000℃) S _BET (m ² /g) 157.3 1673.1 1742.4 187.69 1616.9 2376.5

Referring to Table 1 and FIG. 1, in the case of activated carbon prepared under nitrogen conditions, the specific surface area tended to increase from 900°C or higher, and from 800°C in the case of activated carbon prepared under reducing gas.

Experimental Example 2. TGA measurement of activated carbon

In order to check the presence or absence of zinc in the activated carbon prepared in Example 1 and Comparative Examples 1 to 5, thermogravimetric analysis (TGA) was performed under air conditions containing oxygen, and the results are shown in Tables 2 and 2 below. Shown in. At this time, carbon is thermally decomposed below 600°C, and the material remaining at a temperature above that is zinc oxide (ZnO).

Reducing atmosphere Nitrogen atmosphere Comparative Example 1
(700℃) Example 1
(800℃) Comparative Example 2
(900℃) Comparative Example 3
(800℃) Comparative Example 4
(900℃) Comparative Example 5
(1000℃) yield(%) 52.3 11.6 7.4 42.0 7.6 3.3 TGA-air
Remaining Amount (%) 77.9 7.2 0 80.8 26.1 5.2

Referring to Table 2 and FIG. 2, in the case of activated carbon prepared in a reducing atmosphere, it was confirmed that zinc was almost evaporated at 800°C.

On the other hand, in the case of activated carbon produced only in a nitrogen atmosphere, only carbon was thermally decomposed at 800°C, but zinc did not evaporate, and zinc began to evaporate above 900°C.

Accordingly, it was confirmed that the present invention provides a method for producing activated carbon having an excellent specific surface area at a relatively low temperature.

Experimental Example 3. Measurement of specific surface area according to pore size of activated carbon

Specific surface area and pore volume were measured through the results of nitrogen adsorption-desorption isotherm analysis of the activated carbons prepared in Example 1, Comparative Example 2, Comparative Example 4, and Comparative Example 5. It is shown in Table 3 and FIG. 3 below.

V _total
(cm ³ /g) S _BET
(m ² /g) S _Micro
(m ² /g) S _Meso
(m ² /g) S _Macro
(m ² /g) D _p
(nm) Example 1 1.97 1673.1 1025.0 388.7 259.4 4.73 Comparative Example 2 1.82 1742.4 1421.0 195.6 125.8 4.18 Comparative Example 4 1.61 1616.9 1288.2 208.9 119.8 3.98 Comparative Example 5 2.24 2376.5 1983.5 252.7 140.3 3.77 micro pore (<2nm), meso pore (2 ~ 50nm), macro pore (> 50nm)
S _BET : specific surface area calculated using Brunauer-Emmett-Teller (BET) equation at a relative pressure range of 0.04-0.2.
V _Total : total pore volume is estimated at a relative pressure P/P ₀ = 0.990.
S _Micro : t-plot micropore area.
S _Meso : calculated from desorption curve by BJH-method.
S _Macro : calculated from BET surface area subtracting to micropore and mesopore area.
D _P : average pore diameter

Referring to Table 3, of activated carbon prepared in a reducing atmosphere, activated carbon prepared in a reducing atmosphere at 800° C. (Example 1) had a specific surface area of 1673.1 mg ² /g, and activated carbon prepared in a nitrogen atmosphere at 900° C. (Comparative Example Results similar to 4) were shown. That is, the present invention can provide activated carbon having an excellent specific surface area at a relatively low temperature by preparing activated carbon in a reducing atmosphere.

In addition, in the case of Example 1, the specific surface area due to mesopores was 388.7 m ² /g, which was prepared in the same reducing atmosphere, but the activated carbon of Comparative Example 2 having a heating temperature of 900°C was 195.6 m ² /g showed a very large difference. Accordingly, the present invention is suitable for producing activated carbon having mesopores.

Claims (12)

(Step 1) preparing a metal organic framework containing zinc or zinc oxide as a core metal;
(Step 2) raising the temperature of the organic metal skeleton to a range of 750 ~ 850 ℃ while injecting an inert gas; And
(Step 3) heat-treating for 2 to 4 hours while injecting and replacing the inert gas with a reducing gas after the temperature is raised; includes,
A method for producing activated carbon, characterized in that the total specific surface area of the activated carbon is 1600 to 1700 m ² /g, and the specific surface area by mesopores is 300 m ² /g or more. delete The method of claim 1,
An organic ligand material that binds to the central metal component of the organic metal framework is carbonized, and the central metal is evaporated to form mesopores. The method of claim 1,
The method for producing activated carbon, characterized in that the activated carbon has mesopores of 4.5 nm or more. delete The method of claim 1,
The method of manufacturing activated carbon having mesopores, characterized in that the inert gas in the second step is nitrogen. The method of claim 1,
In the third step, the reducing gas is a mixed gas of hydrogen and argon. The method of claim 7,
The method for producing activated carbon, characterized in that the mixed gas contains 3 to 7% by volume of hydrogen. The method of claim 1,
The method of manufacturing activated carbon, characterized in that the injection rate of the gas in the second or third step is 250 to 350 ml/min. The method of claim 1,
The method for producing activated carbon, characterized in that the temperature increase rate in the second step is 3 to 7°C/min. The method of claim 1,
The method for producing activated carbon, characterized in that the heat treatment in the third step is performed for 2 to 4 hours. The method of claim 1,
The method of manufacturing activated carbon, characterized in that heat treatment is further performed for 2 to 4 hours in an inert gas atmosphere after the temperature is raised in the third step before replacing with a reducing gas.

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