CN1583550A - Preparing method for porous carbon with high specific surface area - Google Patents

Abstract

A method for preparing mesoporous carbon with a high specific surface area is to dissolve KOH in water until the KOH is completely dissolved, the concentration of which is 500g-1000gKOH/L water, and immerse the microporous carbon in the KOH solution according to the alkali-carbon mass ratio of 1-10:1 , impregnated at room temperature for 1-48 hours; raise the impregnated microporous carbon to 600-900°C at a rate of 2-20°C in an inert atmosphere, then react at a constant temperature for 10-150min, and then cool naturally; take out the reactant , washed with water until no OH ^- was detected. The invention has the advantages of abundant raw material source, simple process and low cost in the KOH secondary activation method, and the porous carbon prepared by the method has extremely rich mesopores, narrow pore diameter distribution and high specific surface area.

Description

A kind of preparation method of high specific surface area mesoporous carbon

technical field

The invention belongs to a method for preparing porous carbon, in particular to a method for preparing mesoporous carbon with high specific surface area.

Background technique

Porous carbons have been applied in many fields, such as environment, medicine, energy, etc., due to their abundant raw material sources and low price. However, different application fields have different requirements for technical parameters of porous carbon. As a supercapacitor electrode material, although microporous carbon has an ultra-high specific surface area, its small pore size (below 2nm) is not conducive to the rapid penetration and free entry and exit of the electrolyte, which seriously affects the power characteristics of the supercapacitor. So that a considerable part of the micropores can not be effectively used. Therefore, it is necessary to develop a method for the preparation of porous carbons with both high specific surface area and abundant mesopores.

There have been many reports on the preparation of mesoporous carbons, and there are three main directions of thinking:

(1) Raw material direct activation method. For example, the proportion of mesopores obtained by steam activation and ZnCl ₂ activation is relatively high, but the specific surface area is not high (mostly less than 1000m ² /g).

(2) Add porogen or catalyst to the organic precursor and activate it by carbonization. The method used in the invention patent entitled "Method for Manufacturing Mesoporous Carbon" applied by Americans Gadkae and Hickman et al. is to add metal organic or inorganic compounds to the carbon precursor resole resin with high carbon yield , carbonization and steam activation after a series of treatments, the resulting mesoporous carbon has only a low specific surface area (450-800m ² /g).

(3) Deposit organic raw materials on the porous molecular sieve template, and then remove the template after carbonization treatment. Typical examples, such as Korean Wu Chengmo, mixed inorganic templates (such as silica) and carbon precursors to form template/carbon precursor composite materials, obtained carbon/template materials after carbonization, and then obtained mesoporous carbon after removing the template. Although the mesoporous carbon can control the pore size and shape, its specific surface area is not high, and the raw material adaptability is narrow, the process is cumbersome, and the cost is high.

In addition to the shortcomings of the above-mentioned methods (such as high cost, narrow application range of raw materials, etc.), it is difficult to meet the high specific surface area activated carbon required by supercapacitors.

Contents of the invention

The object of the present invention is to provide a method for preparing porous carbon with high specific surface area and abundant mesopores.

The present invention uses various plant shells, anthracite, bituminous coal, lignite, petroleum coke, needle coke, carbon fiber, etc. as raw materials. The principle of secondary activation is that when KOH reacts with carbon, it can be inserted into the C layer, and the carbon layer can be stretched to create micropores, so that a higher specific surface area can be obtained. In addition, KOH can also penetrate into the existing micropores and cause some micropores to collapse through the reaction, thereby creating mesopores. Since the porosity of the porous carbon obtained by the first activation is already very high, a large number of new pores will not be generated during the second activation, and almost all the activators at this time are used to expand the pores. Therefore, the obtained porous carbon has both high specific surface area and abundant mesopores.

The present invention prepares the method for mesoporous carbon, and its whole preparation process is as follows:

(1) Dissolve KOH with water until KOH is completely dissolved (concentration is 500g-1000gKOH/L water). Immerse the microporous carbon in the KOH solution according to the alkali-carbon mass ratio of 1-10:1, and immerse at room temperature for 1-48 hours;

(2) Raise the impregnated microporous carbon to 600-900°C at a rate of 2-20°C in an inert atmosphere, then react at a constant temperature for 10-150min, and then cool naturally;

(3) Take out the reactant, wash with water until no ^OH- is detected, and dry to obtain the product.

The above-mentioned microporous carbon is obtained from plant shells, anthracite, bituminous coal, lignite, petroleum coke, needle coke, or carbon fiber through activation treatment. Although the specific surface area of the activated carbon reaches 2700-3500m ² /g , but more than 85% of the pores have a diameter below 2nm.

After secondary activation and pore expansion, although the specific surface area of the obtained porous carbon has decreased to varying degrees, the mesopores have increased significantly, and the mesopore volume accounts for about 65-85% of the total pore volume.

The present invention has the following advantages

1. KOH secondary activation method has rich sources of raw materials, simple process and low cost;

2. The porous carbon prepared by this method has extremely rich mesopores, narrow pore size distribution and high specific surface area.

Detailed ways

Example 1

Dissolve KOH in water, take petroleum coke as raw material with the mass ratio of alkali-carbon ratio of 5:1 (the specific surface area is 3024m ² , the micropores with pore diameter ≤ 2nm account for 86% of the total pore volume) and immerse in the KOH solution , fully soaked at room temperature for 18h. Then transfer the above-mentioned impregnation into an activation furnace for activation, the heating rate is 20°C/min, and it is activated at 900°C for 0.5h, and the activation process is protected by an inert gas. The BET specific surface area of the prepared activated carbon is about 2700m ² , the pore volume is 1.9cm ³ /g, and the mesopore volume accounts for 70% of the total pore volume.

Example 2

Activated carbon (the specific surface area is 2840m ² , and micropores with a pore diameter ≤ 2nm account for 82% of the total pore volume) prepared from anthracite fine powder as a raw material is mixed with KOH at a mass ratio of 1:8. The method is the same as in Example 1. Immerse at room temperature for 6h. Then transfer the above-mentioned impregnation into an activation furnace for activation, the heating rate is 10°C/min, and the activation is at 800°C for 1 hour, and the activation process is protected by an inert gas. The BET specific surface area of the prepared activated carbon is about 2580m ² , the pore volume is 1.8cm ³ /g, and the mesopore volume accounts for 72% of the total pore volume.

Example 3

Viscose-based activated carbon fiber (with a specific surface area of 2680m ² , and micropores with a pore diameter of ≤2nm accounting for 90% of the total pore volume) is used as a raw material, mixed with KOH at a mass ratio of 1:1, the method is the same as in Example 1, at room temperature Dipping for 48h. Then transfer the above-mentioned impregnation into an activation furnace for activation, the heating rate is 2°C/min, and it is activated at 600°C for 1.5h, and the activation process is protected by an inert gas. The BET specific surface area of the prepared activated carbon fiber is about 1880m ² , the pore volume is 1.4cm ³ /g, and the mesopore volume accounts for 68% of the total pore volume.

Example 4

Activated carbon prepared from walnut shells (the specific surface area is 3105m ² , and micropores with a pore diameter≤2nm account for 92% of the total pore volume) and KOH are mixed in a mass ratio of 1:6. The method is the same as in Example 1. 24h. Then transfer the impregnated material into the activation furnace for activation, the heating rate is 8°C/min, activate at 750°C for 2.5h, and the activation process is protected by inert gas. The BET specific surface area of the prepared activated carbon is about 2760m ² , the pore volume is 2.1cm ³ /g, and the mesopore volume accounts for 83% of the total pore volume.

Example 5

Activated carbon prepared from needle coke (green coke) (with a specific surface area of 3496m ² and micropores with a pore diameter of ≤2nm accounting for 89% of the total pore volume) was mixed with KOH at a mass ratio of 1:1, and the method was the same as in Example 1. , soaked at room temperature for 36h. Then transfer the above-mentioned impregnation into an activation furnace for activation at a heating rate of 15°C/min, and activate at 900°C for 1 hour, and the activation process is protected by an inert gas. The BET specific surface area of the prepared activated carbon is about 3010m ² , the pore volume is 2.4cm ³ /g, and the mesopore volume accounts for 65% of the total pore volume.

Example 6

Activated carbon prepared from needle coke (green coke) (with a specific surface area of 3293m ² and micropores with a pore diameter of ≤2nm accounting for 88% of the total pore volume) was mixed with KOH at a mass ratio of 1:5, and the method was the same as in Example 1. , soaked at room temperature for 24h. Then transfer the above-mentioned impregnation into an activation furnace for activation, the heating rate is 5°C/min, and the activation is at 800°C for 1.5h, and the activation process is protected by an inert gas. The BET specific surface area of the prepared activated carbon is about 2800m ² , the pore volume is 2.2cm ³ /g, and the mesopore volume accounts for 81% of the total pore volume.

Example 7

Activated carbon prepared from needle coke (green coke) (with a specific surface area of 2751 m ² , micropores with a pore diameter of ≤2 nm accounting for 81% of the total pore volume) and KOH are mixed in a mass ratio of 1:10, and the method is the same as in Example 1. , soaked at room temperature for 1h. Then transfer the above-mentioned impregnation into an activation furnace for activation, the heating rate is 10°C/min, activate at 850°C for 2h, and the activation process is protected by inert gas. The BET specific surface area of the prepared activated carbon is about 2350m ² , the pore volume is 1.6cm ³ /g, and the mesopore volume accounts for 83% of the total pore volume.

Claims (3)

1, a kind of preparation method of high specific surface area mesoporous carbon, it is characterized in comprising the steps: (1) Dissolve KOH with water until KOH is completely dissolved, the concentration is 500g-1000gKOH/L water, and the microporous carbon is immersed in the KOH solution according to the mass ratio of alkali to carbon at 1-10:1, and soaked at room temperature for 1-48 hours ; (2) Raise the impregnated microporous carbon to 600-900°C at a rate of 2-20°C in an inert atmosphere, then react at a constant temperature for 10-150min, and then cool naturally; (3) Take out the reactant, wash with water until no ^OH- is detected, and dry to obtain the product. 2. A method for preparing mesoporous carbon with high specific surface area as claimed in claim 1, characterized in that said microporous carbon is made of plant shell, anthracite, bituminous coal, lignite, petroleum coke, needle coke or carbon fiber As a raw material, it can be obtained by activation treatment. 3. A method for preparing mesoporous carbon with high specific surface area as claimed in claim 2, characterized in that the specific surface area of the microporous carbon is ^2700-3500m2 /g, and the pore diameter of more than 85% of the pores is below 2nm .