KR20090022040A - Preparation of high porous activated carbon for methane storage - Google Patents

Abstract

A method for manufacturing high porous activated carbon for methane storage is provided to maintain great storage capacity of methane by activating an activated charcoal precursor to potassium hydroxide chemically. A method for manufacturing high porous activated carbon for methane storage comprises the following steps of: mixing and pulverizing an activated carbon precursor with potassium hydroxide to 1:2~5 weight ratio; performing dehydration the mixed and pulverized compounds at 350~450°C; performing heat treatment of the dehydrated compounds at 700~900°C and activating the compounds; cooling, washing, and drying the activated compounds.

Description

Manufacturing method of high carbon activated carbon for methane storage {Preparation of high porous activated carbon for methane storage}

The present invention relates to a method of manufacturing a high porosity activated carbon for methane storage, and more particularly, by dehydrating and activating the activated carbon precursor under specific conditions with potassium hydroxide under an inert atmosphere to highly develop porosity such as surface area. It is easy to carry out the adsorption and desorption process, and it is easy to store and repeat the adsorption of methane. It relates to a storage method.

Since methane is inexpensive and can lower the dependence on imported oil, it also has less environmental pollution than gasoline or diesel, so it has been increasingly used as an automobile fuel in the form of natural gas since the 1980s. However, under standard conditions, methane is a gas and the volume energy density, defined as the heat of combustion per unit volume, is 0.038 MJ / liter, which is so small that it is only 0.11% of gasoline. Therefore, it is necessary to increase the volume energy density for efficient storage and transportation. have. If methane can be liquefied in a pure state, a high energy density of 22.44 MJ / liter can be achieved. The critical temperature of methane is -82 ° C, which is very low, and can not be liquefied at room temperature alone. It is possible to liquefy at low temperature below -82 ℃, but special container design and energy loss are not technically easy to apply to automobiles.

Accordingly, different methods for increasing the volumetric energy density of methane have been considered. Currently, the compression storage method widely used all over the world is pressurized methane and stored at room temperature as a supercritical fluid of 250 atm, and in this case, it is necessary to use a high pressure container, which may cause difficulties in cylinder design, excessive container weight and fuel economy. I'm taking it. And high pressure compression to about 250 atmospheres requires expensive multistage compression. These problems may be solved if a sufficient amount of natural gas can be stored at room temperature and low pressure. As one method, the adsorption methane storage method may be considered.

Methane gas is adsorbed by the porous material, but the adsorbed methane exists in the liquid state, so if the adsorption amount is increased, the volume energy density may be higher than that of the gas phase compression storage method.

Activated carbon is generally an environmentally functional material, and has excellent adsorption capacity and adsorption rate according to the development of surface area and pore structure, and according to the purpose of use, gas separation, removal and deodorization in gas phase, organic solvent and heavy metal recovery in liquid phase, and purification It is widely used for adsorption filters, catalysts and catalyst carriers for concentration and decolorization. Currently, widely used activated carbon is mainly manufactured from coconut shell, sawdust, coal, etc., and recently, agricultural by-products such as rice hulls, crests, etc. Many techniques for producing activated carbon using waste resources such as coffee waste have been reported.

Porosity is well developed, and high porosity activated carbon with a total surface area of more than 2,000 m 2 / g is likely to exhibit high methane storage capacity.

Such activated carbon is generally manufactured by carbonizing and activating an organic substance containing carbon as a main component, and carbonization is a form in which carbon is concentrated through various chemical reactions such as pyrolysis, polycondensation, and aromatic carbonization when the organic substance is heated in an inert atmosphere. It means to be.

There are gas activation and chemical activation methods for producing activated carbon by activating carbide.

First, in the gas activation method, when the carbide is contacted with an oxidizing gas such as water vapor, carbon dioxide, or air at a high temperature, the carbide reacts with the oxidizing gas to be removed in the form of carbon dioxide and carbon monoxide, thereby forming fine pores in place. The gas activation process is known to proceed in two steps.

In the first step, the active site (unstructured portion) of the carbide is selectively reacted and removed to generate fine pores and open pores closed between the carbon crystals to rapidly increase porosity. In the second step, the pore size increases as the carbon crystal and the fine pores react with the oxidative gas.

This gas activation method is simple in the reaction process, less corrosion of the device and easy to mass production, most of the commercial activated carbon is produced by the gas activation method, but to obtain activated carbon having high surface area and well developed fine pores Since it must be accompanied by the vaporization of fixed carbon, it is not economical because the activation yield is low, the pore structure is difficult to control, and a lot of energy is required through high temperature heat treatment. In addition, in the case of the activated carbon produced is not high porosity, generally activated carbon having a total surface area of 1,500 m ² / g or less.

Second, the chemical activation method is to include a chemical activator in the carbonaceous raw material and then heated in an inert atmosphere to produce porous activated carbon as the dehydration and oxidation reaction proceeds. Generally as a chemical activator, acidic solutions, such as phosphoric acid, zinc chloride, a metal hydroxide, and basic solution are used.

One example of such chemical activation method is to mix wood such as sawdust with phosphoric acid, a chemical activator, and then calcinate at 350 to 500 ° C. to produce a high porosity activated carbon having a specific surface area of about 2,000 m ² / g.

Accordingly, the present inventors have made efforts to solve the problems of the conventional methane storage method is a high energy loss, safety weakness due to high pressure and excessive container weight, as a result, the activated carbon precursor is converted to potassium hydroxide under inert atmosphere under specific conditions. When activated scientifically, the activated carbon prepared therefrom has been found to increase porosity such as total surface area and to easily absorb and desorb methane, and in particular, to significantly reduce the methane storage pressure, thereby completing the present invention. .

Therefore, an object of the present invention is to provide a method for producing a meat ball activated carbon for methane storage.

In addition, the present invention has another object to provide a storage method of methane using the meat ball activated carbon prepared by the above method.

The present invention

1 step of mixing and grinding the activated carbon precursor and potassium hydroxide in a weight ratio of 1: 2 to 5;

Dehydrating the mixed and pulverized mixture at 350 to 450 ° C .;

3 steps of activating the dehydrated mixture by heat treatment at 700 ~ 900 ℃; And

Four steps of cooling, washing and drying the activated product

There is also a feature in the manufacturing method of activated carbon for methane storage made of activated carbon.

In the present invention, the high-molecular-weight activated carbon prepared by chemically activating the activated carbon precursor with potassium hydroxide has a high methane storage capacity, thereby promoting the practical use of natural gas vehicles, fuel cells, etc., and improving the methane transport efficiency, and ultimately environmental pollution. The effect is to prepare for the decline.

Hereinafter, the present invention will be described in detail.

The present invention relates to a method for preparing a high porosity activated carbon that can be used for methane storage with excellent methane adsorption capacity and a method for storing methane using the activated carbon prepared therefrom.

In the present invention, the porosity and the methane adsorption capacity are greatly improved by chemically activating various precursors such as green state and carbide under specific conditions. In addition, since the adsorption and desorption processes can be freely performed, the methane can be repeatedly adsorbed and stored.

When explaining the high porosity activated carbon for methane storage according to the present invention in more detail.

As the activated carbon precursor, lignocellulosic, polymer resin, coal, or the like can be used. As the lignocellulosic system, nuts such as oak and bamboo and nuts such as walnut shell, pine nut, almond shell, pistachio shell, palm shell, ginkgo shell, hazel shell and cashew nut shell can be used. Phenolic resin, polyacrylonitrile, rayon or the like may be used as the polymer resin. Bituminous coal, lignite coal, anthracite coal, etc. can be used as a coal system.

In the present invention, the use of coconut shell, oak, phenol resin, bituminous carbon, etc. as the activated carbon precursor, they are easy to supply in large quantities compared to other raw materials, and the price is low and economically suitable for activated carbon for methane storage.

In addition, as an activator such as sodium compounds, potassium compounds and ammonium compounds which are widely used for the activation of carbonaceous raw materials, for example, NaOH, NaCl, NaHCO ₃ , KOH, K ₂ CO ₃ , KClO ₃ , KCl, NH ₄ OH, NH ₄ Cl, NH ₄ HCO ₃ may be used, but during the activation, the potassium compound is intercalated into the microcrystalline structure present in the activated carbon while chemically activating the activated carbon precursor, which may contribute to the enhancement of methane adsorption capacity. It is preferable to use it because it exists. Among these potassium compounds, potassium hydroxide is mixed with a precursor to complete dehydration reaction such as pyrolysis and polycondensation, and then removed at the activation stage to generate narrow pores in the form of an ink-bottle inlet having good methane adsorption. It is most preferable to use it selectively. Such potassium hydroxide may be used in the form of an anhydride or a hydrate having a water content of 2 to 25% by weight.

On the other hand, the method of manufacturing the methane storage meat ball activated carbon according to the present invention in detail.

First, the precursor and potassium hydroxide are added in a constant ratio, and then mixed uniformly while grinding. The precursor and potassium hydroxide may maintain a weight ratio of 1: 2 to 5, preferably 1: 3 to 4 weight ratio. If the amount of potassium hydroxide is less than 2% by weight of the chemical activation is incomplete to reduce the pore production, if the amount exceeds 5% by weight excess pore wall due to the excessive activation reaction to reduce the porosity rather than the yield of activated carbon and There is a problem of poor economic efficiency.

At this time, the reaction mixture composed of the precursor and potassium hydroxide is preferably pulverized so that the particle size is 44 ~ 420 ㎛ size, more preferably it is preferable to maintain the 74 ~ 177 ㎛ size. If the size of the finely pulverized reactant particles is larger than 420 μm, it is difficult for the chemical activator to diffuse into the nut shell particles, resulting in incomplete activation reactions, resulting in reduced porosity and methane adsorption capacity and smaller size of the reactant particles than 44 μm. In this case, the power cost for grinding is increased. The fine pulverization can be performed with a device such as a crusher, a mill, a cutter, or the like.

As described above, the pulverized precursor and potassium hydroxide undergo a mixed grinding process and then dehydrate the precursor. This is to obtain the effect of suppressing the clogging of the pores by the polycondensation at the same time as the pyrolysis precursor to crosslinking.

At this time, the dehydration reaction is heated from room temperature to perform 1 to 2 hours in the range of 350 ~ 450 ℃ to remove the potassium hydroxide melting and reaction water. When the temperature is less than 350 ℃ during the dehydration reaction, the dehydration reaction rate is slow, if the temperature exceeds 450 ℃ cross-linking is difficult to be made stable. In addition, if the dehydration reaction is less than 1 hour, the dehydration reaction may not be completed, and subsequent activation reaction may not be satisfactory. If the dehydration reaction is longer than 2 hours, the physical properties of the product may not be affected, but the productivity of the process may be reduced and the energy requirement may be increased. There is.

After the dehydration reaction, the temperature is raised to 700 ~ 900 ℃ and the activation reaction is carried out for 2 to 3 hours. If the temperature of the activation reaction is less than 700 ℃, the activation reaction rate is slow to take excessive activation time, if it exceeds 900 ℃ the control of the process is difficult due to excessive activation reaction and the pore wall is destroyed to reduce the porosity The problem occurs that the mechanical strength of activated carbon is reduced. That is, the activation temperature is a factor that greatly affects the porosity of the produced activated carbon, it is preferable to maintain the above range. Common rotary rotary kilns, batch kilns and multiple-hearth furnaces are used for heating in the dehydration and activation processes.

In general, the chemical activation is performed after the carbonization process in the range of 800 ~ 900 ℃, heat treatment at 400 ~ 1000 ℃ to perform the activation reaction, the present invention uses a precursor that is a non-heat treatment raw material as an activation raw material different from the other method To produce activated carbon.

After the activation reaction, the product is cooled to room temperature (20 ~ 30 ℃) and washed with water until the hydrogen ion concentration of the filtrate is neutral. At this time, the filtration is performed using a centrifuge or a filter press. The washed activated carbon cake is dried for 2 to 3 hours at 115-150 ° C. using a batch or continuous dryer to remove moisture, and then sealed and used as a methane adsorbent.

As described above, the activated carbon prepared by chemically activating the precursor with potassium hydroxide has a highly developed porosity (total surface area of 2,000 to 3,500 m 2 / g, total pore volume of 0.8 to 2.5 cc / g) and high methane adsorption capacity at a relatively low pressure. (Methane adsorption capacity 12.0 ~ 25.0 wt%). In the case of activated carbon according to the present invention, the storage capacity of methane at room temperature (20 ~ 30 ℃), atmospheric pressure ~ 60 atm is 12 to 25% by weight, which corresponds to the storage capacity of methane corresponding to 150 atm in the conventional high pressure storage method. The effect is to reduce the pressure by about a quarter. In addition, since the adsorption and desorption of methane is easy because of the physical adsorption behavior, the methane can be repeatedly adsorbed and stored.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

Example 1

10.0 g of bituminous coal and 30.0 g of potassium hydroxide (coconut shell: potassium hydroxide = 1: 3) were added to a vibrating mill, mixed and pulverized, and put in a sample container and placed in a tubular furnace. The heating was started while flowing argon gas, and sufficient dehydration reaction was performed at 400 ° C. for 1 hour, and then, the temperature was raised to 700 ° C., which is an activation reaction temperature, and activated for 2 hours. The activated reaction product was cooled to 25 ° C., 2,000 g of water was added and stirred to elute the remaining potassium hydroxide, then filtered and washed with 3,000 g of water. The filtered activated carbon cake was dried at 150 ° C. for 3 hours to prepare activated carbon.

The porosity and methane adsorption capacity of the activated carbon prepared above are measured and shown in Table 1 below.

Example 2

In the same manner as in Example 1, the activation was performed by raising the activation reaction temperature to 800 ℃.

The porosity and methane adsorption capacity of the activated carbon prepared above are measured and shown in Table 1 below.

Example 3

In the same manner as in Example 1, the activation was performed by raising the activation reaction temperature to 900 ℃.

The porosity and methane adsorption capacity of the activated carbon prepared above are measured and shown in Table 1 below.

Example 4

In the same manner as in Example 1, but instead of bituminous coal was used coconut grenade.

The porosity and methane adsorption capacity of the activated carbon prepared above are measured and shown in Table 1 below.

Example 5

In the same manner as in Example 1, instead of bituminous coal, coconut coal was used, and activation was performed by raising the activation reaction temperature to 800 ° C.

The porosity and methane adsorption capacity of the activated carbon prepared above are measured and shown in Table 1 below.

Example 6

In the same manner as in Example 1, instead of bituminous coal, coconut coal was used, and activation was performed by raising the activation reaction temperature to 900 ° C.

The porosity and methane adsorption capacity of the activated carbon prepared above are measured and shown in Table 1 below.

Example 7

In the same manner as in Example 1, phenol resin powder was used instead of bituminous coal.

The porosity and methane adsorption capacity of the activated carbon prepared above are measured and shown in Table 1 below.

Example 8

In the same manner as in Example 1, in place of bituminous coal, phenol resin powder was used, and activation was performed by raising the activation reaction temperature to 800 ° C.

The porosity and methane adsorption capacity of the activated carbon prepared above are measured and shown in Table 1 below.

Example 9

In the same manner as in Example 1, instead of the bituminous coal, phenol resin powder was used, and activation was performed by raising the activation reaction temperature to 900 ° C.

The porosity and methane adsorption capacity of the activated carbon prepared above are measured and shown in Table 1 below.

As shown in Table 1, Examples 1 to 3 in which the bituminous coal was chemically activated with potassium hydroxide according to the present invention showed a maximum total surface area of 3,149 m ² / g and a maximum methane adsorption capacity of 20.5% by weight. In addition, in the case of palm kernel coal and phenol resin, porosity such as surface area and pore volume tended to decrease slightly compared with bituminous coal, and methane adsorption capacity was also decreased.

The bituminous coal, palm kernel and phenol resin all have a pore structure of 98% or more in the total surface area, and have a pore structure that is advantageous for adsorption and storage of methane molecules having a small molecular size and difficult to liquefy.

1 shows a manufacturing process chart of the methane storage meat ball activated carbon according to the present invention.

In addition, the methane adsorption isotherm of the activated carbon prepared in Example 1 and Example 2 is measured and shown in the range of 10 to 60 atmospheres at 25 ° C., which shows a type 1 adsorption isotherm by BDDT classification. As the adsorption pressure increases, the methane adsorption amount increases rapidly at low pressure, but at high pressures above 60 atm, the methane adsorption amount no longer increases.

Comparative Example 1

10.0 g of bituminous coal was placed in a tubular furnace, and heating was started while flowing argon gas. After sufficient carbonization reaction was performed at 950 ° C. for 1 hour, the argon gas flow was stopped and carbon dioxide was flowed and activated at 950 ° C. for 1 hour. The porosity and methane adsorption capacity of the activated carbon prepared above are measured and shown in Table 2 below.

Comparative Example 2

10.0 g of coconut coal was placed in a tubular furnace and started heating while flowing argon gas to stop the argon gas flow when reaching the activation temperature of 950 ° C. and activated at 950 ° C. for 1 hour while flowing carbon dioxide. The porosity and methane adsorption capacity of the activated carbon prepared above are measured and shown in Table 2 below.

Comparative Example 3

In the same manner as in Comparative Example 1, a phenol resin powder was used instead of bituminous coal.

The porosity and methane adsorption capacity of the activated carbon prepared above are measured and shown in Table 2 below.

As shown in Table 2, when activated carbon precursor is activated by gas with carbon dioxide, water vapor, etc., it can be seen that the porosity of surface area, pore volume, etc. is significantly reduced and methane adsorption capacity is smaller than that of chemical activation shown in Table 1. .

Comparative Example 4

The methane storage efficiencies of various methane storage methods currently used or considered as methane storage methods are shown in Table 3 below.

Assuming that the volumetric density of a normal gas at 25 ° C and 1 atm is 1, the volumetric density of liquefied methane is 600, the highest among all storage methods. However, the liquefied storage method is difficult to be commercialized due to energy loss, so when considering the next best compression storage method, the volume relative density is 150 at 25 ° C. and 150 atm. Density can be obtained at 40 atmospheres. That is, since the compression storage method requiring 150 atm can be replaced by the adsorption method of 40 atm, it is possible to reduce the weight of the container, improve fuel efficiency, and increase safety.

Example 10

By using the activated carbon prepared in Example 1, the change of methane adsorption capacity during the repeated adsorption and desorption of methane was measured and the results are shown in Table 4 below.

At this time, repeated adsorption and desorption conditions were subjected to 40 atmosphere adsorption, atmospheric desorption, and vacuum desorption processes 100 times at 25 ° C constant temperature conditions.

Adsorption Recovery Methane adsorption capacity, weight percent (room temperature, 40 atmospheres) One 20.5 50 20.4 100 20.4

As shown in Table 4, when the repeated adsorption and desorption of methane using the activated carbon according to the present invention, the amount of reduction in the methane adsorption capacity is within 0.1% within the measurement error range, and thus the methane adsorption follows physical adsorption behavior and repeated use at room temperature. Even though the methane storage capacity was maintained.

3 shows the methane adsorption capacity of the activated carbons prepared in Examples 1 to 9 with respect to the total surface area. The results showed that the overall methane adsorption capacity was proportional to the total surface area, and it was confirmed that the activated carbon in the meat plot was useful as a methane reservoir.

1 is a manufacturing process chart of the methane storage meat ball activated carbon according to the present invention.

Figure 2 shows the methane isothermal adsorption line (25 ℃) according to the pressure change of the activated carbon prepared according to the present invention (activated carbon of Example 1 and Example 2).

Figure 3 shows the correlation between the total surface area and the methane adsorption capacity according to the activated carbon type for the activated carbon of Examples 1 to 9.

Claims (6)

1 step of mixing and grinding the activated carbon precursor and potassium hydroxide in a weight ratio of 1: 2 to 5; Dehydrating the mixed and pulverized mixture at 350 to 450 ° C .; 3 steps of activating the dehydrated mixture by heat treatment at 700 ~ 900 ℃; And 4 steps of cooling, washing and drying the activated product; Method for producing a methane storage meat ball activated carbon, characterized in that made. According to claim 1, wherein the activated carbon precursor is bituminous coal, lignite, anthracite coal, oak wood, bamboo wood, walnut shell, pine nut, almond shell, pistachio shell, palm shell, ginkgo shell, hazel and cashew nut shell, phenol resin, poly At least one selected from acrylonitrile resin and rayon resin. The method of claim 1, wherein the pulverization of the activated carbon precursor and potassium hydroxide is pulverized to have a particle size of 44 ~ 420 ㎛. The method according to claim 1, wherein the potassium hydroxide is an anhydride or a hydrate containing 2 to 25% by weight of water. According to claim 1, The porosity of the activated carbon has a total surface area of 2,000 ~ 3,500 m 2 / g, the total pore volume of 0.8 ~ 2.5 cc / g, the methane adsorption capacity of the activated carbon is 10.0 ~ 25.0 wt% Manufacturing method. Method for storing methane by adsorbing methane to the meat ball activated carbon prepared by the method of any one of claims 1 to 5 under atmospheric pressure ~ 60 atm.

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