CN101054174A - Method of preparing biomass high specific surface micro-pore carbon material - Google Patents

Abstract

The invention belongs to the field of preparation of microporous carbon materials, and relates to the preparation of microporous carbon materials with high specific surface area and relatively narrow pore distribution by using biomass. The biomass materials are cleaned and cut into small sections with a length of 1 to 3 centimeters. Carbonize at 300-500°C for 3-4 hours under the protection of an inert atmosphere, then immerse the obtained carbonized product in an alkaline solution for 20-24 hours until the carbonized product is completely infiltrated, separate the carbonized product from the solution, and then under the protection of an inert gas Activate at 700-800°C for 1.5-3 hours, cool down to room temperature naturally, then wash the product with water until the pH of the washing solution is 7-8, soak in dilute acid for 4-5 hours, and wash with water until the pH of the washing solution is 6-7, and then dried at 80-120° C. to obtain a microporous carbon material. The method of the invention has the advantages of simple preparation process, cheap and abundant raw materials, no geographical restrictions on preparation conditions, etc., and is suitable for industrial production.

Description

Preparation method of biomass high specific surface area microporous carbon material

technical field

The invention belongs to the field of preparation of microporous carbon materials, in particular to a method for preparing microporous carbon materials by using biomass, in particular to preparing microporous carbon materials with high specific surface area and narrow pore distribution by using biomass.

Background technique

Due to its special pore structure and high specific surface area, microporous carbon materials play an important role in daily life. Now, microporous carbon materials have been widely used in gas storage and separation, electrode materials for batteries or capacitors, catalysts or catalyst supports for various chemical reactions, sewage treatment, precious metal recovery, etc. In the market, the more common microporous carbon material is activated carbon, which uses charcoal, various fruit shells and high-quality coal as raw materials, and uses physical and chemical methods to crush, sieve, activate catalysts, rinse and dry raw materials. It is processed and manufactured through a series of processes such as screening and screening. However, conventional activated carbon has disadvantages such as non-uniform pore size distribution and small specific surface area, which greatly restrict the application of activated carbon. In order to overcome the shortcomings of activated carbon, people have developed activated carbon fibers, which overcome the shortcomings of activated carbon to a large extent, but a series of new problems have arisen - the preparation process of activated carbon fibers is complicated, the cost is high and the performance development These have seriously restricted the practical application of activated carbon fibers. Therefore, activated carbon still has an absolute advantage in production and life.

In the preparation process of microporous carbon materials, the most important step is the activation process. The activation methods are usually divided into two categories: physical activation method and chemical activation method: ① physical activation method uses water vapor, carbon dioxide and other substances as activators in an inert Activate the carbonized product under the protection of the atmosphere; ②Chemical activation method uses hydroxides of alkali metals or alkaline earth metals such as KOH, NaOH, Ca(OH) ₂ and ZnCl ₂ , CaCl ₂ , H ₂ SO ₄ , H ₃ PO ₄ , etc. The chemical reagent is used as an activator to activate the carbonization under the protection of an inert atmosphere.

Activated carbon prepared by physical activation is mainly microporous carbon material. Although the pore distribution of the prepared activated carbon is relatively narrow, it has good application effect in various application fields, but the ratio of microporous carbon material prepared by this method is With low surface area, these microporous carbon materials are not yet ideal for applications. Although the specific surface area of the activated carbon prepared by the chemical activation method has been greatly improved compared with the activated carbon prepared by the physical activation method, and the use effect is better in many aspects, the pore distribution of the activated carbon prepared by the chemical activation method is generally very poor. wide, which limits the application of activated carbon prepared by chemical activation in some aspects (such as gas separation).

In the present invention, the renewable biomass material is used as the raw material for preparing microporous carbon, and the chemical activation method is used to activate the microporous carbon material, by immersing the carbonization product of the biomass material in an alkaline solution, and then activating it in an inert atmosphere High-quality microporous carbon materials can be obtained by processing. At present, a large part of high-quality activated carbon in the domestic market uses wood and high-quality coal as raw materials, and a large amount of wood and coal are consumed in the preparation of high-quality activated carbon every year. However, the forest coverage rate in our country is not very high. Although our country is Coal is a big country, but coal is a non-renewable resource, and now all countries in the world are facing the crisis of fossil energy. Therefore, if we find renewable raw materials that can replace wood and coal to prepare high-quality microporous carbon materials, it will play a great role in my country's forest protection and reduction of fossil energy consumption.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiency of the current background technology, and use a simple chemical activation method to prepare a microporous carbon material with a high specific surface area and a relatively narrow pore distribution. The invention has high practical application value.

The present invention uses the most common and cheap corn stalks in rural areas as raw materials, carbonizes the stalks in an inert atmosphere, then immerses the carbonized products in an alkaline solution for a period of time, so that the alkali is evenly and fully dispersed in the carbonized products, and then carbonizes The product is taken out from the solution, activated in an inert atmosphere, and then washed with water, treated with acid, washed with water, dried, etc., and finally the microporous carbon material is obtained.

The specific process of preparing microporous carbon materials is as follows:

Clean the straw, cut it into 1-3 cm long sections, and carbonize it at 300-500°C for 3-4 hours under the protection of an inert (nitrogen or argon 99.9%) atmosphere. The ends of the furnace get tar. Then impregnate the obtained carbonized product in 2-13mol/L alkaline solution (KOH or NaOH) (each gram of carbonized product is immersed in 20-25 milliliters of solution) for 20-24 hours until the carbonized product is completely soaked, and use a sieve to The carbonized product is separated from the solution, and then activated at 700-800°C for 1.5-3 hours under the protection of an inert gas (nitrogen or argon 99.9%), and the temperature is naturally cooled to room temperature, and the product is washed with water (or deionized water) until the washing liquid The pH value is 7-8, soaked in dilute acid (hydrochloric acid or nitric acid) with a concentration of 0.05-0.2mol/L for 4-5 hours, then washed with water (or deionized water) until the pH value of the washing solution is 6-7, and finally in 80 Dry at ~120°C to obtain the microporous carbon material with high specific surface area described in this patent.

The invention utilizes common, abundant and renewable biomass corn stalks as raw materials, and prepares microporous carbon materials through simple chemical activation. This carbon material has a large specific surface area (up to 3247m ² /g) and a narrow pore size distribution (1-2nm). The raw materials used in this method are extremely cheap. In the preparation process, unlike the carbonized products of most raw materials, the carbonized products we obtain are mainly loose network structures. At the same time, the activator we use is added in the form of solution impregnation. Therefore, the activator can be uniformly and fully dispersed in the carbonized product, so that the carbonized product can be fully activated and react evenly during the activation process. In the preparation process of most microporous carbons, the activator is added by pulverizing the carbonized product first, and then directly mixed with the solid activator and stirred evenly. The pore size distribution of the reacted product is not uniform. During the carbonization process, many chemical bonds in the main components of the straw are broken to form by-products such as water and tar, while in the activation process, the dehydrogenation reaction and the chemical reaction between the activator and the carbonized product mainly occur.

The method in the present invention has low requirements on equipment, less time consumption, and simple preparation process. The main by-product in the reaction is tar, which is also a product with high utilization value. The cleaning solution of microporous carbon materials is rich in The solution of potassium ions is a good agricultural potassium fertilizer after simple treatment. In addition, the raw materials used have a wide range of sources, are not restricted by regions, are low in price, and are renewable resources, which will save a large amount of wood and high-quality coal. The method of impregnating with KOH (or NaOH) solution is used to dissolve the remaining tar, and KOH (or NaOH) can be better dispersed into the carbon material, which is more uniform than the traditional method of mixing and grinding carbonized products and solid activators, saving energy. process. The microporous carbon material we prepared has rich pore structure, large specific surface area (higher than 3000m ² /g), narrow pore size distribution (1-2nm), and the specific surface area of microporous carbon material can also be adjusted by KOH (or NaOH) solution concentration to adjust.

Therefore, the present invention is extremely suitable for large-scale industrial production, and has very important significance for saving forest resources and coal resources in my country. Especially for the current rural areas where most of the corn stalks are used for heating and livestock feed, the invention can effectively solve this waste phenomenon and open up a new source of economic income for the rural areas. Because the microporous carbon material obtained by the present invention has a higher specific surface area and a narrower pore size distribution, it is suitable for storage and separation of gases, electrode materials for batteries or capacitors, catalysts or carriers in various chemical reactions, and sewage treatment. , precious metal recycling and other fields will have practical application value.

Description of drawings

Figure 1: Nitrogen adsorption/desorption isotherms of microporous carbon materials;

Figure 2: Pore size distribution curve of microporous carbon materials;

Figure 3: High-resolution transmission electron micrographs of microporous carbon materials;

Figure 4: The relationship between the specific surface area of the microporous carbon material and the concentration of KOH solution.

We performed some structural and property characterizations of the obtained microporous carbon materials (Example 12). As shown in Figure 1, it is the nitrogen adsorption/desorption isotherm of the microporous carbon material. The adsorption/desorption isotherm in the figure is a typical type I, and there is no hysteresis loop, indicating that the microporous carbon material contains a large number of hole. Fig. 2 is a pore size distribution diagram of a microporous carbon material. The pore size distribution curve shows that the pore size distribution of this microporous carbon material is relatively narrow, mainly between 1 and 2 nm. Figure 3 is a high-resolution transmission electron microscope photo of the microporous carbon material. In the photo, we can also clearly see that the pore diameter of the microporous carbon material is mainly distributed between 1 and 2 nm. Fig. 4 is the relationship between the specific surface area of the microporous carbon material and the concentration of the KOH solution used. It can be seen from the figure that when the KOH concentration is controlled between 8 and 13 mol/L, the specific surface area of the microporous carbon material can reach 3000m ² /g, and the highest can reach 3247m ² /g.

Detailed ways

The present invention is further elaborated below with regard to embodiment:

Example 1:

Wash the corn stalks, dry them, and cut them into 1.5 cm long pieces. Under the protection of nitrogen, carbonize at 400° C. for 3 hours to obtain carbonized products and by-product tar. The obtained charred product was immersed in 1 mol/L KOH solution (25 ml solution per gram of charred product) for 24 hours. Activate the carbonized product taken out at 750°C for 2 hours, then wash it with deionized water until pH = 7, then soak it with dilute hydrochloric acid (0.1mol/L) for 5 hours, then wash the product with deionized water until The pH of the washing solution was 7, and the microporous carbon material was obtained after drying at 100° C. for 3 hours. The specific surface area of the material was 880 m ² /g, and the pore size was mainly 1.4 nm.

Example 2:

The experimental method is the same as in Example 1, except that the concentration of the activator KOH solution is changed to 2 mol/L, and a microporous carbon material is also obtained. The specific surface area of the material is 1300m ² /g, and the pore size is mainly 1.4nm.

Example 3:

The experimental method is the same as in Example 1, except that the concentration of the activator KOH solution is changed to 3 mol/L, and a microporous carbon material is also obtained. The specific surface area of the material is 1412m ² /g, and the pore size is mainly 1.4nm.

Example 4:

The experimental method is the same as in Example 1, except that the concentration of the activator KOH solution is changed to 4 mol/L, and a microporous carbon material is also obtained. The specific surface area of the material is 1526m ² /g, and the pore size is mainly 1.4nm.

Example 5:

The experimental method was the same as in Example 1, except that the concentration of the activator KOH solution was changed to 5 mol/L, and a microporous carbon material was also obtained. The specific surface area of the material was 1580 m ² /g, and the pore size was mainly 1.4 nm.

Embodiment 6:

The experimental method is the same as in Example 1, except that the concentration of the activator KOH solution is changed to 6 mol/L, and a microporous carbon material is also obtained. The specific surface area of the material is 2201 m ² /g, and the pore size is mainly 1.4 nm.

Embodiment 7:

The experimental method is the same as in Example 1, except that the concentration of the activator KOH solution is changed to 7 mol/L, and a microporous carbon material is also obtained. The specific surface area of the material is 2645 m ² /g, and the pore size is mainly 1.4 nm.

Embodiment 8:

The experimental method is the same as in Example 1, except that the concentration of the activator KOH solution is changed to 8 mol/L, and a microporous carbon material is also obtained. The specific surface area of the material is 2900m ² /g, and the pore size is mainly 1.4nm.

Embodiment 9:

The experimental method was the same as in Example 1, except that the concentration of the activator KOH solution was changed to 9 mol/L, and a microporous carbon material was also obtained. The specific surface area of the material was 2991 m ² /g, and the pore size was mainly 1.4 nm.

Example 10:

The experimental method is the same as in Example 1, except that the concentration of the activator KOH solution is changed to 10 mol/L, and a microporous carbon material is also obtained. The specific surface area of the material is 3247m ² /g, and the pore size is mainly 1.4nm.

Example 11:

The experimental method was the same as in Example 1, except that the concentration of the activator KOH solution was changed to 11 mol/L, and a microporous carbon material was also obtained. The specific surface area of the material was 3103 m ² /g, and the pore size was mainly 1.4 nm.

Example 12:

The experimental method is the same as in Example 1, except that the concentration of the activator KOH solution is changed to 12 mol/L, and a microporous carbon material is also obtained. The specific surface area of the material is 3015m ² /g, and the pore size is mainly 1.4nm.

Example 13:

The experimental method is the same as in Example 1, except that the concentration of the activator KOH solution is changed to 13 mol/L, and a microporous carbon material is also obtained. The specific surface area of the material is 2920 m ² /g, and the pore size is mainly 1.4 nm.

Claims (8)

1. A method for preparing a biomass high specific surface area microporous carbon material, which comprises the following steps: cleaning the biomass material, cutting it into small sections with a length of 1 to 3 cm, and carbonizing the biomass material at 300 to 500 ° C for 3 to 3 cm under the protection of an inert atmosphere 4 hours, then soak the obtained carbonized product in the alkaline solution for 20-24 hours until the carbonized product is completely infiltrated, separate the carbonized product from the solution, and then activate it at 700-800°C under the protection of an inert gas for 1.5-3 hours, Naturally cool down to room temperature, wash the product until the pH value is 7-8, soak in dilute acid for 4-5 hours, then wash the washing solution until the pH value is 6-7, and finally dry at 80-120°C to obtain a high specific surface area microporous carbon materials. 2. The preparation method of biomass high specific surface area microporous carbon material according to claim 1, characterized in that: the biomass material is corn stalks. 3. The method for preparing biomass high specific surface area microporous carbon material according to claim 1, characterized in that: the inert atmosphere is under nitrogen or argon atmosphere. 4. The preparation method of biomass high specific surface area microporous carbon material according to claim 1, characterized in that the alkaline solution is KOH or NaOH. 5. The preparation method of biomass high specific surface area microporous carbon material according to claim 1, characterized in that: each gram of carbonized product is immersed in 20-25 ml of alkaline solution. 6. The method for preparing biomass high specific surface area microporous carbon material according to claim 1, characterized in that the dilute acid is dilute hydrochloric acid or dilute nitric acid with a concentration of 0.05-0.2 mol/L. 7. The method for preparing biomass high specific surface area microporous carbon material according to any one of claims 1-6, characterized in that the concentration of the alkali solution is 2-13 mol/L. 8. The preparation method of biomass high specific surface area microporous carbon material according to claim 7, characterized in that the concentration of the alkali solution is 8-13 mol/L.

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