KR20230076222A - A method for simultaneously producing hydrogen and carbon materials for electrodes with high specific surface area and high conductivity from activated carbon through methane decomposition - Google Patents

Abstract

According to the present invention, a high value-added, high-conductivity carbon material for electrodes can be provided by producing hydrogen, which is a clean fuel, from methane and simultaneously reforming activated carbon used as a methane decomposition reaction catalyst into high-conductivity activated carbon having a high added value. In addition, according to the present invention, an electrode material having an improved sensitivity change rate can be provided by using the high-conductivity carbon material. To this end, a method for producing the high-conductivity carbon material for electrodes includes a step (a) of performing methane decomposition reaction by supplying a methane-containing gaseous reactant into a reactor containing a carbon-based catalyst, and a step (b) of separating hydrogen-containing gaseous products and the carbon-based catalyst after reaction.

Description

A method for simultaneously producing hydrogen and carbon materials for electrodes with high specific surface area and high conductivity from activated carbon through methane decomposition}

The present invention relates to a method for simultaneously preparing a carbon material for a high specific surface area and high conductivity electrode and hydrogen from activated carbon through a methane decomposition reaction. More specifically, it relates to a method for producing a highly conductive carbon material for a highly sensitive gas sensor electrode and at the same time producing hydrogen, a clean gas, by utilizing carbon generated from a methane decomposition reaction to reform activated carbon as a reaction catalyst.

In a recent report by the Intergovernmental Panel on Climate Change (IPCC), it was pointed out that the short-term greenhouse effect of methane (CH ₄ ) is more than 80 times that of carbon dioxide (CO ₂ ), the main greenhouse gas. According to the total methane emission data, the share of methane, which has a strong greenhouse effect, by sector is 43.9% in the agricultural sector, 31.0% in the waste sector, 22.9% in the energy sector, and 2.2% in the industrial process sector. Methane was found to be released. In order to reduce methane emissions essential to human activities, an eco-friendly methane conversion technology is required.

On the other hand, methane as an energy source is in the spotlight as a resource to replace traditional fossil fuels in that it is a major component of natural gas and has abundant reserves and can be obtained from biological resources. In particular, research and development to convert methane into hydrogen, which is attracting attention as a clean fuel, is being attempted.

Conventional studies on converting methane into hydrogen gas have been largely conducted in two ways. The process that has been mainly used so far is the steam methane reforming (SMR) process, which is a process in which high-temperature steam is introduced into a methane reforming reaction that requires endothermic heat. In the SMR process, since CO ₂ and CO gas, which are greenhouse gases derived from water vapor, are simultaneously generated, there is a problem in that a complicated purification process is required and the environmental load is large.

As an alternative to the SMR, a thermo-catalytic decomposition (TCD) process requiring relatively little energy has been proposed. Unlike the SMR process, the TCD process does not convert into CO ₂ and CO gas, and the product is separated into carbon deposits and hydrogen gas, which is a clean fuel, thereby simplifying the purification process and being environmentally friendly.

Catalysts used in the TCD process are classified into metal-based catalysts and carbon-based catalysts. The carbon-based catalyst has advantages of low price, excellent high-temperature stability, and resistance to impurities such as sulfur compared to metal-based catalysts.

However, while the price of the carbon-based catalyst is lower than that of the metal-based catalyst, the price competitiveness of the methane decomposition process is inevitably reduced by only hydrogen gas production in that a process that requires a high-temperature condition of 800 to 1,000 ° C. is required. Therefore, it is necessary to accompany the high addition of materials produced from the methane decomposition reaction.

On the other hand, as the demand for activated carbon as an electrode material increases, the demand for activated carbon with high energy density, high power, and high conductivity is also increasing. There is a problem called

In this regard, International Patent Publication WO2021/102521 A1 (published on June 3, 2021) relates to thermal decomposition and carbon decomposition, in detail, by thermal decomposition of resources such as biomass through thermal decomposition to generate activated carbon, followed by activated carbon. A technique for manufacturing a high-quality crystalline carbon material by depositing carbon generated by decomposing methane is disclosed. However, according to prior literature, the crystalline carbon material has a very low specific surface area of 200 m ² /g or less, and there is a problem in that it is unlikely to be used as an electrode material requiring a high specific surface area and conductivity.

There is a need for a highly conductive carbon material manufacturing technology that can be used for a highly sensitive gas sensor electrode by reforming activated carbon used in the TCD process while solving environmental problems including global warming.

International Patent Publication WO2021/102521 A1 (2021.06.03. Publication)

An object of the present invention is to provide a method for producing hydrogen and at the same time producing a highly conductive carbon material for a high value-added, highly sensitive gas sensor electrode by performing a methane decomposition reaction under optimal reaction time and temperature conditions.

In addition, an object of the present invention is to provide a highly sensitive gas sensor using the highly conductive carbon material produced from the above method.

In order to solve the above problems, the present invention provides a method for producing a highly conductive carbon material for a highly sensitive gas sensor electrode from activated carbon through a methane decomposition reaction, (a) supplying a gas reactant containing methane in a reactor containing a carbon-based catalyst Performing a methane decomposition reaction; and (b) separating the carbon-based catalyst and the hydrogen-containing gas product after the reaction, wherein after the reaction in step (b), the carbon-based catalyst has double bonds between carbons on all or at least part of the surface and inside the pores. As it is formed, it can be characterized as a carbon material with improved crystallinity and conductivity.

The carbon-based catalyst in step (a) may be activated carbon, activated carbon fiber, carbon black, amorphous carbon material, turbostratic carbon material, or mixtures thereof.

As an embodiment of the present invention, the carbon-based catalyst in step (a) is activated carbon, and the specific surface area of the activated carbon may be 2,000 m ² /g or more.

The methanolysis reaction of step (a) may be characterized in that it is carried out at a temperature of 850 to 950 ° C for 4 to 20 minutes, preferably, at a temperature of 900 to 950 ° C for 10 to 20 minutes.

After the reaction in step (b), the electrical conductivity of the carbon-based catalyst may be in the range of 10 to 19 S/cm.

The reduction rate of the specific surface area of the carbon-based catalyst after the reaction in the step (b) may be 25% or less compared to the carbon-based catalyst before the reaction in the step (a).

It is possible to provide an electrode material using the carbon material for a high specific surface area and high conductivity electrode prepared from the above method.

According to the present invention, carbon materials for electrodes such as capacitors, CDIs, gas sensors, etc. There is a remarkable effect that can be produced.

In addition, it is possible to provide an electrode material using the carbon material for an electrode manufactured by the manufacturing method of the present invention, and a gas sensor, which is an example of using the electrode material, exhibits a remarkable effect of improving the sensitivity change rate.

1 is a graph showing (a) storage amount and (b) electrical conductivity according to the reaction time of a highly conductive carbon material for an electrode from activated carbon through a methane decomposition reaction prepared according to the present invention.
2(a) to 2(b) show SEM and TEM images of the carbon materials of Comparative Example 1 in which the methanolysis reaction was not performed and Comparative Example 3 in which excessive methanolysis reaction was performed.
3(a) to 3(e) are XPS measurement results of the carbon materials of Comparative Example 2 and Examples 1 to 4.
Figure 4 is a graph showing (a) methane conversion rate, (b) hydrogen composition and (c) storage amount in gaseous products according to the reaction temperature of the carbon-based catalyst introduced into the methane decomposition reaction, (d) reaction tube with a reaction temperature of 800 ° C. and (e) a photograph of a reaction tube having a reaction temperature of 1,000 °C.
5 is a graph showing the amount of occlusion according to the reaction time of the highly conductive carbon material for an electrode from activated carbon through a methane decomposition reaction prepared according to the present invention.
6 is a graph showing the sensitivity when the highly conductive carbon material for an electrode manufactured according to the present invention is used as a gas sensor electrode material.

Hereinafter, the present invention will be described in detail so that those skilled in the art can easily practice the present invention. Prior to this, the terms or words used in this specification and claims should not be construed as being limited to the usual or dictionary meaning, and the inventor appropriately uses the concept of the term in order to explain his/her invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined. Therefore, since the configurations of the embodiments described in this specification are only the most preferred examples of the present invention and do not represent all of the technical spirit of the present invention, there are various equivalents and modifications that can replace them at the time of this application. You need to understand that you can.

In describing the principles of preferred embodiments of the present invention in detail, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted.

The present invention provides a high value-added carbon material for physicochemical electrodes by producing hydrogen, a clean fuel, through methane decomposition reaction and reforming activated carbon used as a reaction catalyst into activated carbon having a high specific surface area and high conductivity. to be

The methane decomposition reaction represented by Equation 1 below generates hydrogen gas and carbon as a result of an endothermic reaction.

CH ₄ (g) → C(s) + 2H ₂ (g) (ΔH = 18.0 kcal/mol) [Equation 1]

However, it is known that carbon, which is a product of the methane decomposition reaction, reduces the catalyst activity by causing a coking phenomenon due to carbon deposition on the reaction catalyst. In order to reduce the coking phenomenon, research and development to use a metal-based catalyst capable of suppressing coking continued, but completely suppressing the coking phenomenon is not only technically difficult, but also economically deteriorated due to the expensive metal included in the metal-based catalyst. In this respect, there is a need for a method to utilize a relatively inexpensive carbon-based catalyst.

Accordingly, the applicant of the present invention adopts a relatively inexpensive carbon-based catalyst as a reaction catalyst for the methane decomposition reaction, and utilizes the coking phenomenon of the catalyst, which had to be avoided or suppressed in the conventional methanation reaction process, for reforming the carbon-based catalyst and At the same time, by applying the optimal conditions for the methane decomposition reaction for this purpose, a method of manufacturing a high value-added carbon material with high conductivity while maintaining a high specific surface area was completed.

Hereinafter, a method for preparing a highly conductive carbon material for an electrode from activated carbon through the methanolysis reaction of the present invention will be described.

The method of preparing a highly conductive carbon material for an electrode from activated carbon through a methanolysis reaction of the present invention includes the steps of (a) supplying a gaseous reactant containing methane to a reactor containing a carbon-based catalyst to perform a methane decomposition reaction; and (b) separating the carbon-based catalyst and the hydrogen-containing gas product after the reaction, wherein after the reaction in step (b), the carbon-based catalyst has double bonds between carbons on all or at least part of the surface and inside the pores. Characterized in that it is a carbon material with improved crystallinity and conductivity as it is formed.

The carbon-based catalyst in step (a) may be, but is not limited to, activated carbon, activated carbon fiber, carbon black, amorphous carbon material, turbostratic carbon material, and mixtures thereof, but preferably activated carbon. can be used.

The activated carbon used as the carbon-based catalyst in step (a) is a porous material containing micropores and has a specific surface area of 2,000 m ² /g or more. When the specific surface area of the activated carbon is less than 2,000 m ² /g, the initial methane decomposition activity is rapidly reduced, and there is a problem in that it cannot be used as an electrode material requiring a high specific surface area, such as a capacitor, a CDI, or a gas sensor.

According to the present invention, the carbon-based catalyst in step (a) has a reduced specific surface area due to a coking phenomenon in which carbon is deposited in the methanolysis reaction, but all or at least part of the surface of the carbon-based catalyst and the inside of the pores are doubled between carbon As bonds are formed, crystallinity and conductivity are improved.

The methanolysis reaction of step (a) is characterized in that it is carried out at a temperature of 850 to 950 ° C for 1 to 50 minutes, preferably at a temperature of 900 to 950 ° C for 10 to 50 minutes. If the time of the methanolysis reaction is less than 1 minute, there is a problem that the crystallinity and conductivity of the carbon material are not improved due to insignificant carbon deposition, and if the time exceeds 50 minutes, the specific surface area is not controlled by excessive carbon deposition. In addition, when used as an electrode material such as a gas sensor, a sensitivity change rate may be reduced. In addition, when the temperature of the methane decomposition reaction is less than 850 ° C., there is a problem that methane is not decomposed and hydrogen simultaneous production is impossible, and when the temperature exceeds 950 ° C., excessive heat supply causes methane to decompose on the catalyst In addition, there is a problem that continuous process operation is difficult, such as clogging of the reaction tube due to deposition of carbon products on the inner wall of the reaction tube.

The step (b) is a step of separating the carbon-based catalyst and the hydrogen-containing gaseous product after the reaction of the methane decomposition of the step (a). After the reaction, the carbon-based catalyst is a carbon material having improved crystallinity and conductivity as double bonds between carbons are formed on all or at least part of the inside of the surface and pores, and can be used for electrodes such as capacitors, CDIs, and gas sensors.

After the reaction, the separation of the carbon-based catalyst and the hydrogen-containing gas product can be applied without limitation as long as it is a solid-gas separation method such as filtration or dust collection, and through this, a carbon material including a carbon-based catalyst can be obtained after the reaction.

Produced hydrogen and unreacted methane can be separated using adsorption and membrane technology. Among them, membrane technology is small in scale and energy efficient, so hydrogen (2.89 Å) and methane (3.8 Å), which have a large gas size difference, can be separated. Very suitable for separation. In particular, when applied to a separation membrane process using a hydrogen permselective membrane such as polyimide or polysulfone, high purity hydrogen can be produced.

In addition to the separation membrane, it is possible to apply a process alone or a combined process to separate a mixed gas such as PSA (Pressure Swing Adsorption).

In the obtained carbon material, crystallinity and conductivity are improved as double bonds between carbons are formed on all or at least part of the inside of the surface and pores during the reaction, while the specific surface area is reduced, so appropriate reaction time and temperature conditions are set. Therefore, it is important to control the crystallinity, conductivity and specific surface area so as to have an excellent sensitivity change rate.

The carbon-based catalyst after the reaction in step (b) produced by performing the methane decomposition reaction under the above-described temperature and time conditions is a carbon material with an electrical conductivity in the range of 10 to 19 S / cm, and the specific surface area reduction rate is that of step (a) It is characterized in that it is 25% or less compared to the carbon-based catalyst before the reaction.

Accordingly, the present invention can provide an electrode material using the highly conductive carbon material produced by the above method, and the carbon material having the above electrical conductivity range while the specific surface area reduction rate due to the methane decomposition reaction does not exceed 25% is a gas sensor When used as a material for an electrode, there is an advantage of having an excellent sensitivity change rate.

Hereinafter, a method for preparing a highly conductive carbon material for an electrode from activated carbon through a methanolysis reaction of the present invention will be described in more detail through preferred examples and comparative examples.

Comparative Example 1

2.0 g of activated carbon (MSP20) having a specific surface area of 2,283 m ² /g was prepared.

Examples 1 to 4, Comparative Examples 2 and 3

After filling the reactor with 2.0 g of the activated carbon of Comparative Example 1, the temperature was raised to 900 ° C at a rate of 10 ° C / min in an argon atmosphere, and then methane gas 100 mL / min, space velocity 3,000 mL / g _cat h conditions After the decomposition reaction was performed for the reaction time shown in Table 1 below, a carbon material was obtained by separating the hydrogen-containing gas product and the carbon-based catalyst after the reaction by filtration or dust collection.

Experimental Example 1

The specific surface area, microporosity, pore volume and size of the carbon-based catalysts or carbon materials of Examples and Comparative Examples were measured and listed in Table 1 below, and the storage amount of the carbon-based catalysts or carbon materials was shown in FIG. shown in

division reaction temperature
(℃) reaction time
(minute) specific surface area
(m²/g) Microporosity
(%) pore volume
(cm³/g) pore size
(nm) Comparative Example 1 - - 2283.508 98.767 1.419143 1.5170 Comparative Example 2 900 0 2197.361 98.866 0.942711 1.71608 Example 1 4 2159.196 98.904 0.927175 1.71763 Example 2 8 2034.565 98.926 0.873455 1.71723 Example 3 10 1968.705 98.972 0.845210 1.71729 Example 4 20 1728.642 99.006 0.741116 1.71491 Comparative Example 3 60 1048.948 99.303 0.458869 1.74983

According to Table 1, the pore volume and size of the carbon-based catalyst or carbon material increased while the specific surface area decreased as the reaction time increased in the methanolysis reaction.

In particular, the specific surface area of Comparative Example 3, in which the methane decomposition reaction time was 60 minutes, was found to be reduced by more than 50% compared to Comparative Examples 1 and 2 in which the methane decomposition reaction was not performed.

Experimental Example 2

The electrical conductivity according to the reaction time was measured for the carbon-based catalysts or carbon materials of Examples and Comparative Examples, and is shown in FIG. 1(b).

According to FIG. 1(b), it was shown that the electrical conductivity of the carbon-based catalyst or carbon material increases as the reaction time increases in the methanolysis reaction.

In particular, the electrical conductivity of Example 4 in which the methanolysis reaction time was 20 minutes was 18.866 S/cm, which was increased by more than 85% compared to the electrical conductivity of 10.185 S/cm of Comparative Example 1 in which the methanolysis reaction was not performed.

Experimental Example 3

SEM and TEM images of the carbon-based catalysts or carbon materials of Comparative Examples 1 and 3 are shown in FIGS. 2(a) to 2(b).

According to FIGS. 2(a) to 2(b), it can be confirmed that crystals are formed on a part of the carbonaceous material of Comparative Example 3 as the reaction time elapses for 60 minutes in the methane decomposition reaction.

Experimental Example 4

XPS measurement results for the carbon-based catalysts or carbon materials of Comparative Example 2 and Examples 1 to 4 are shown in FIGS. 3(a) to 3(e).

3(a) to 3(e), Examples 1 to 4 show that the intensity of the double bond peak (C = C peak) between carbons gradually increases as the reaction time increases in the methanolysis reaction. It is believed that crystallinity and conductivity increase.

Experimental Example 5

The results of measuring the methane conversion rate according to the reaction temperature and the hydrogen composition and storage amount in the gas product for the carbon-based catalysts or carbon materials of Examples 5 to 7 are shown in FIGS. 4(a) to 4(c).

According to FIGS. 4(a) to 4(c), it was shown that the methane conversion rate, the hydrogen composition in the gas product, and the storage amount increased as the reaction temperature increased in the methane decomposition reaction.

In addition, according to FIG. 4 (d) and FIG. 4 (e), when the reaction temperature is 800 ℃, methane decomposition reaction does not occur and the mass of carbon does not increase, and when the reaction temperature is 1,000 ℃ methane catalyst In addition to the red conversion, it was confirmed that thermal decomposition occurred and carbon was deposited on the inner wall of the reactor. If the reaction temperature of the present invention is out of the range of 850 to 950 ° C., it is considered that the clogging of the reactor, which is undesirable in process operation, will be caused by the deposition of the carbon.

Experimental Example 6

The results of measuring the electrical conductivity according to the reaction temperature for the carbon-based catalysts or carbon materials of Comparative Example 1 and Examples 5 to 7 are shown in FIG. 5 .

According to FIG. 5, the electrical conductivity of the carbon materials of Examples 5 to 7 increased as the reaction temperature increased in the methanolysis reaction.

Experimental Example 7

The results of measuring the sensitivity of the gas sensor using the carbon-based catalyst or carbon material of Comparative Examples 1 and 3 and Examples 1 to 4 as an electrode material are shown in FIG. 6 .

According to FIG. 6, the slope is a sensitivity change rate, and in the case of the gas sensor using the carbon material of Examples 1 to 4 as an electrode material, the sensitivity change rate is excellent compared to Comparative Examples 1 and 3 outside the temperature and reaction time ranges of the present invention. appear.

All simple modifications or changes of the present invention can be easily performed by those skilled in the art, and all such modifications or changes can be considered to be included in the scope of the present invention.

Claims (8)

In the method for producing a highly conductive carbon material for an electrode from activated carbon through a methane decomposition reaction,
(a) performing a methane decomposition reaction by supplying a gas reactant containing methane into a reactor containing a carbon-based catalyst; and
(b) separating the carbon-based catalyst and the hydrogen-containing gas product after the reaction;
After the reaction in step (b), the carbon-based catalyst is a carbon material with improved crystallinity and conductivity as double bonds between carbons are formed on all or at least part of the surface and inside the pores Activated carbon through methanolysis reaction A method for producing a highly conductive carbon material for an electrode from
According to claim 1,
The carbon-based catalyst in step (a) is activated carbon, activated carbon fiber, carbon black, amorphous carbon material, turbostratic carbon material, and mixtures thereof. A method for producing a highly conductive carbon material for an electrode from
According to claim 1,
The carbon-based catalyst in step (a) is activated carbon, and the activated carbon has a specific surface area of 2,000 m ² /g or more.
According to claim 1,
The method for producing a highly conductive carbon material for an electrode from activated carbon through methanolysis, characterized in that the methanolysis reaction of step (a) is performed at a temperature of 850 to 950 ° C. for 1 to 50 minutes.
According to claim 1,
The method for producing a highly conductive carbon material for an electrode from activated carbon through a methanolysis reaction, characterized in that the methanolysis reaction in step (a) is performed at a temperature of 900 to 950 ° C. for 10 to 50 minutes.
According to claim 1,
After the reaction in step (b), the carbon-based catalyst is a carbon material having an electrical conductivity in the range of 10 to 19 S / cm.
According to claim 1,
After the reaction in step (b), the specific surface area reduction rate of the carbon-based catalyst is 25% or less compared to the carbon-based catalyst before the reaction in step (a). How to manufacture.
An electrode material using the highly conductive carbon material for an electrode manufactured by the method of any one of claims 1 to 7.

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