JP2024166831A - Direct cracking of hydrocarbons - Google Patents

Abstract

[Problem] To provide a direct decomposition method for hydrocarbons with improved conversion rate of hydrocarbons. [Solution] The direct decomposition method for hydrocarbons, which directly decomposes hydrocarbons into carbon and hydrogen, comprises a step of contacting a feed gas containing methane and hydrocarbons having two or more carbon atoms with a catalyst that is an unsupported catalyst consisting of an aggregate of multiple iron particles, and the concentration of the hydrocarbons having two or more carbon atoms in the feed gas is 0.02 to 10 vol %. [Selected Figure] Figure 4

Description

This disclosure relates to a method for directly cracking hydrocarbons.

Currently, the production of various forms of energy is heavily dependent on fossil fuels such as oil, coal, and natural gas, but from the perspective of protecting the global environment, the increase in carbon dioxide emissions released from the combustion of fossil fuels is seen as a problem. The Paris Agreement, which was agreed upon in 2015, calls for a reduction in carbon dioxide emissions in order to address the issue of climate change, and reducing carbon dioxide emissions from the combustion of fossil fuels is a major issue for thermal power plants and other facilities. While processes for separating and capturing emitted carbon dioxide are being actively studied, technologies for producing energy without emitting carbon dioxide by using alternative fuels to fossil fuels are also being considered.

Hydrogen, a clean fuel that does not emit carbon dioxide when burned, has therefore been attracting attention as an alternative to fossil fuels. Hydrogen can be produced, for example, by steam reforming methane contained in natural gas. However, this production method produces carbon monoxide as a by-product, which is ultimately oxidized and emitted as carbon dioxide. Meanwhile, methods such as water electrolysis and photocatalysis are being considered as methods for producing hydrogen from water without using fossil fuels, but these methods require a large amount of energy and are therefore economically problematic.

In response to this, a method has been developed to produce hydrogen and carbon by directly decomposing methane. The features of direct decomposition of methane are that hydrogen fuel can be obtained without emitting carbon dioxide, and that the by-product carbon is solid and can be easily immobilized, and the carbon itself can be effectively used for a wide range of applications such as electrode materials, tire materials, and building materials. Up until now, methods have been developed to directly decompose hydrocarbons into hydrogen and carbon by contacting a supported catalyst with a hydrocarbon gas, but there has been a problem in that the carbon, which is a product of the direct decomposition reaction of hydrocarbons, adheres to the catalyst, causing the catalytic activity to decrease in a short period of time.

In response to this, the applicant of the present disclosure has developed a method for directly decomposing hydrocarbons into carbon and hydrogen using a catalyst that is an unsupported catalyst consisting of an aggregate of multiple iron particles, as described in Patent Document 1. With this method, even if carbon, the product of the direct decomposition reaction of hydrocarbons, adheres to the catalyst, activity is maintained by creating new active sites, and it was considered that the activity of this reaction can be maintained for a long time.

Patent No. 7089235

The applicant of the present disclosure has further developed the direct cracking method of hydrocarbons described in Patent Document 1 and discovered a method for improving the conversion rate of hydrocarbons.

In view of the above, at least one embodiment of the present disclosure aims to provide a method for direct cracking of hydrocarbons that improves the conversion rate of the hydrocarbons.

To achieve the above object, the direct decomposition method of hydrocarbons disclosed herein is a direct decomposition method of hydrocarbons that directly decomposes hydrocarbons into carbon and hydrogen, and includes a step of contacting a feed gas containing methane and a hydrocarbon having two or more carbon atoms with a catalyst that is an unsupported catalyst consisting of an aggregate of multiple iron particles, and the concentration of the hydrocarbons having two or more carbon atoms in the feed gas is 0.02 to 10 vol%.

The direct cracking method for hydrocarbons disclosed herein can improve the conversion rate of hydrocarbons compared to using a feed gas containing only methane.

FIG. 1 is a schematic diagram showing the configuration of an apparatus for carrying out a method for direct cracking of hydrocarbons according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram showing a configuration of a modified example of an apparatus for carrying out a method for direct cracking of hydrocarbons according to an embodiment of the present disclosure. FIG. 1 is a schematic diagram showing the configuration of an experimental apparatus for verifying the effect of a method for direct cracking of hydrocarbons according to an embodiment of the present disclosure. FIG. 2 is a diagram showing the experimental results of Examples 1 to 3 and Comparative Example 1 (the relationship between the concentration of hydrocarbons having two or more carbon atoms in the feed gas and the peak value of the methane conversion rate).

The direct cracking method for hydrocarbons according to an embodiment of the present disclosure will be described below with reference to the drawings. The embodiment described below shows one aspect of the present disclosure, does not limit the disclosure, and can be modified as desired within the scope of the technical concept of the present disclosure.

<Configuration of an apparatus for carrying out a direct cracking method for hydrocarbons according to an embodiment of the present disclosure>
As shown in Fig. 1, an apparatus 1 for carrying out a direct cracking method for hydrocarbons according to an embodiment of the present disclosure includes, as an essential component, a reactor 3 containing a catalyst 2. The reactor 3 is provided with a heating device 4 (e.g., a jacket through which steam flows) for heating the inside of the reactor 3, particularly the catalyst 2. The reactor 3 is connected to a raw material supply line 5 for supplying a raw material gas to the reactor 3, and a reaction gas distribution line 6 through which a reaction gas containing hydrogen produced by the reaction of the hydrocarbons in the raw material gas with the catalyst 2 flows after flowing out of the reactor 3.

The hydrocarbons in the raw material gas include methane and hydrocarbons having two or more carbon atoms, such as ethane, propane, and butane. The concentration of the hydrocarbons having two or more carbon atoms in the raw material gas is 0.02 to 10 vol%, preferably 5 to 10 vol%, and more preferably 5 to 9.7 vol%. As such a raw material gas, for example, city gas in which the concentration of hydrocarbons having two or more carbon atoms is about 10 vol%, can be used, but it is not limited to city gas, and any raw material gas prepared so that the concentration of hydrocarbons having two or more carbon atoms is within the above-mentioned range can be used.

Catalyst 2 is an unsupported catalyst consisting of an aggregate of multiple iron particles. In reactor 3, each particle of catalyst 2 may be stationary, or the particles may be suspended in the raw gas by ejecting the raw gas upward, forming a fluidized bed. Carbon produced by the reaction of hydrocarbons in the raw gas with catalyst 2 adheres to the particles of catalyst 2, but when catalyst 2 forms a fluidized bed, the particles of catalyst 2 rub against each other, physically removing the carbon that adheres to the particles of catalyst 2. When a fixed-bed reactor is used as reactor 3, for example, a carbon removal device may be provided outside reactor 3 to remove the carbon that adheres to catalyst 2 from catalyst 2.

The reaction gas flow line 6 may be provided with a solid-gas separator 7 such as a bag filter or a cyclone. Depending on the concentration of hydrogen in the reaction gas, if necessary, a hydrogen purifier 11 for purifying hydrogen in the reaction gas, i.e., for increasing the hydrogen concentration, may be provided in the reaction gas flow line 6. The configuration of the hydrogen purifier 11 is not particularly limited, but for example, a pressure swing adsorption (PSA) device or the like may be used.

As shown in FIG. 2, a recycle line 8 may be provided to connect the raw material supply line 5 and the reaction gas flow line 6. The recycle line 8 may be provided with a flow control valve 9 for controlling the flow rate of the gas (part of the reaction gas) flowing through the recycle line 8.

<Method for direct cracking of hydrocarbons according to an embodiment of the present disclosure>
Next, the operation of the apparatus 1 shown in Fig. 1 (method for directly decomposing hydrocarbons) will be described. A raw material gas containing hydrocarbons such as methane is supplied to the reactor 3 via a raw material supply line 5. The raw material gas that has flowed into the reactor 3 passes through the catalyst 2 while coming into contact with the catalyst 2. At this time, the hydrocarbons in the raw material gas are directly decomposed into hydrogen and carbon (hereinafter, this reaction will be referred to as a "direct decomposition reaction"). Taking methane as an example of a hydrocarbon in the direct decomposition reaction, the reaction represented by the following reaction formula (1) occurs in the reactor 3.
CH ₄ → 2H ₂ +C ... (1)

The principle by which the activity of the direct decomposition reaction is maintained for a long time is explained in detail by the applicant of the present disclosure in Patent Document 1. Similarly, in order to promote the direct decomposition reaction, it is preferable to maintain the temperature of the catalyst 2 in the range of 600°C to 900°C by the heating device 4.

Carbon produced by the direct decomposition method adheres to the catalyst 2, and the produced hydrogen flows out of the reactor 3 as a reaction gas together with unreacted hydrocarbons (and inert gases) and flows through the reaction gas distribution line 6. Carbon can be recovered by stopping the supply of reaction gas to the reactor 3, recovering the catalyst 2 from the reactor 3, and removing the carbon adhered to the catalyst 2 by a carbon removal device, if necessary. Hydrogen is recovered by recovering the reaction gas flowing through the reaction gas distribution line 6. If a hydrogen purification device 11 is provided in the reaction gas distribution line 6, hydrogen is purified. When the conversion rate of hydrocarbons is low, the hydrogen concentration in the reaction gas is low, but the hydrogen purification device 11 can increase the concentration of hydrogen as the final product.

In the device 1 shown in FIG. 2, a part of the reaction gas flows into the raw material supply line 5 through the recycle line 8, and flows into the reactor 3 as a mixed gas mixed with the raw material gas flowing through the raw material supply line 5. In this device 1, a direct decomposition reaction occurs when the mixed gas, which is a mixture of a part of the reaction gas and the raw material gas, comes into contact with the catalyst 2. Since the reaction gas contains hydrogen produced by direct decomposition of the hydrocarbons, the concentration of the hydrocarbons having two or more carbon atoms in the reaction gas is lower than the concentration of the hydrocarbons having two or more carbon atoms in the raw material gas. Therefore, the concentration of the hydrocarbons having two or more carbon atoms in the mixed gas is lower than the concentration of the hydrocarbons having two or more carbon atoms in the raw material gas. For example, when city gas is used as the raw material gas, the concentration of the hydrocarbons having two or more carbon atoms in the city gas is about 10 vol%, but the concentration of the hydrocarbons having two or more carbon atoms in the mixed gas that comes into contact with the catalyst in the reactor 3 is lower than 10 vol%. The more the flow rate of the reaction gas flowing through the recycle line 8 is increased by the flow rate control valve 9, the more the concentration of the hydrocarbons having two or more carbon atoms in the mixed gas can be reduced.

As will be verified by the examples described later, the conversion rate of hydrocarbons is improved by directly cracking a gas with a concentration of 0.02 to 10 vol%, preferably 5 to 10 vol%, of hydrocarbons having two or more carbon atoms compared to the conversion rate of methane obtained by directly cracking a gas containing only methane. However, when the concentration of hydrocarbons having two or more carbon atoms is 10 vol% (equivalent to the case where city gas is used as the raw gas), the effect of improving the conversion rate of hydrocarbons is somewhat lower than when the concentration is 5 to 9.7 vol%. However, even if city gas is used as the raw gas, if a direct cracking reaction is caused in the device 1 shown in FIG. 2, the concentration of hydrocarbons having two or more carbon atoms in the mixed gas is lower than 10 vol%, so that the conversion rate of hydrocarbons can be improved compared to the case where city gas is used as the raw gas in the device 1 shown in FIG. 1. Furthermore, raw material gas with a concentration of hydrocarbons having two or more carbon atoms less than 10 vol% must be prepared separately, for example by mixing city gas with methane gas. However, if city gas can be used, this preparation of raw material gas becomes unnecessary, improving the workability of carrying out the direct decomposition method of hydrocarbons.

The inventors of the present disclosure clarify the effect of the direct cracking method of hydrocarbons of the present disclosure by comparing Examples 1 to 4, which correspond to the direct cracking method of hydrocarbons of the present disclosure, with Comparative Example 1, which does not correspond to the direct cracking method of hydrocarbons of the present disclosure. The configuration of the experimental apparatus for comparing Examples 1 to 4 and Comparative Example 1 is shown in FIG. 3. The experimental apparatus 20 is equipped with a quartz reactor 23 with an inner diameter of 16 mm that contains the catalysts 22 of Examples 1 to 4 and Comparative Example 1. The reactor 23 can be heated by an electric furnace 24. As the catalyst 22, electrolytic iron particles obtained from Nilaco Corporation were used, which were classified to have a particle size in the range of 32 μm to 40 μm.

The reactor 23 is connected to a raw material supply line 25 for supplying methane and city gas, respectively, and a reaction gas distribution line 26 through which the reaction gas containing hydrogen generated by the direct decomposition reaction of hydrocarbons flows after it leaves the reactor 23. That is, the raw material gas supplied to the reactor 23 can be methane, city gas, or a mixed gas of methane and city gas. The reaction gas distribution line 26 is connected to a gas chromatograph 27 for measuring the composition of the reaction gas. The experimental conditions for each of Examples 1 to 4 and Comparative Example 1 are summarized in Table 1 below. In Comparative Example 1, only city gas was supplied to the reactor 23, and in Example 3, only methane was supplied to the reactor 23. In Examples 1 and 2, the amounts of methane and city gas supplied to the reactor 23 were adjusted so that the concentration of hydrocarbons having two or more carbon atoms in the raw material gas was the value in Table 1.

The experimental results of each of Examples 1 to 4 and Comparative Example 1 are shown in Figure 4. In each of the experiments of Examples 1 to 4 and Comparative Example 1, the change in methane conversion rate over time was measured, and the peak value of the methane conversion rate was identified. Figure 4 shows the relationship between the concentration of hydrocarbons having two or more carbon atoms in the feed gas and the peak value of the methane conversion rate. The methane conversion rate is defined by the following formula (2).
Conversion rate = (1 - (amount of unreacted methane / amount of methane in raw material)) x 100 (2)

The results in Figure 4 show that when the concentration of hydrocarbons having two or more carbon atoms in the feed gas is 0.02 to 10 vol%, the conversion rate of the hydrocarbons, especially when it is 5 to 10 vol%, is higher than the conversion rate of methane when a feed gas containing only methane is used.

Furthermore, the results in Figure 4 show that when the concentration of hydrocarbons with two or more carbon atoms is 10 vol%, the effect of improving the hydrocarbon conversion rate is somewhat lower than when the concentration is 5 to 9.7 vol%. Since the concentration of hydrocarbons with two or more carbon atoms contained in city gas is approximately 10 vol%, when city gas is used as the feed gas, there is a risk that the effect of improving the hydrocarbon conversion rate will be lower than expected compared to when a feed gas containing only methane is used.

In contrast, when the direct decomposition method of hydrocarbons of the present disclosure is carried out using city gas as the raw material gas in the device 1 having the configuration shown in FIG. 2, a part of the reaction gas flowing out from the reactor 3 is mixed with the raw material gas and flows into the reactor 3, and contacts the catalyst 2 in the reactor 3. As described above, the reaction gas contains hydrogen produced by the direct decomposition of hydrocarbons, so the concentration of hydrocarbons having two or more carbon atoms in the reaction gas is lower than the concentration of hydrocarbons having two or more carbon atoms in the raw material gas. Therefore, the concentration of hydrocarbons having two or more carbon atoms in the mixed gas is lower than the concentration of hydrocarbons having two or more carbon atoms in the raw material gas. In other words, even if city gas, which has a concentration of hydrocarbons having two or more carbon atoms of 10 vol%, is used as the raw material gas, the concentration of hydrocarbons having two or more carbon atoms in the mixed gas that contacts the catalyst 2 in the reactor 3 can be in the range of 5 to 9.7 vol%. Then, from the results of FIG. 4, it can be said that even if city gas is used as the raw material gas, the expected effect of improving the conversion rate of hydrocarbons can be obtained compared to the use of a raw material gas containing only methane.

The contents described in each of the above embodiments can be understood, for example, as follows:

[1] A method for direct cracking of hydrocarbons according to one embodiment includes the steps of:
A method for directly cracking hydrocarbons into carbon and hydrogen, comprising the steps of:
The method includes a step of contacting a feed gas containing methane and a hydrocarbon having two or more carbon atoms with a catalyst (2), which is an unsupported catalyst consisting of an aggregate of a plurality of iron particles;
The concentration of the hydrocarbon having two or more carbon atoms in the raw material gas is 0.02 to 10 vol %.

The direct cracking method for hydrocarbons disclosed herein can improve the conversion rate of hydrocarbons compared to using a feed gas containing only methane.

[2] A direct cracking method for hydrocarbons according to another embodiment is the direct cracking method for hydrocarbons according to [1],
The concentration of the hydrocarbon having two or more carbon atoms in the feed gas is 0.5 to 9.7 vol %.

This configuration allows for a higher conversion rate of hydrocarbons than when using a feed gas containing only methane.

[3] A method for direct cracking of hydrocarbons according to yet another embodiment is the method for direct cracking of hydrocarbons according to [1] or [2],
The particle sizes of the particles range from 32 to 180 μm.

This configuration allows for a higher conversion rate of hydrocarbons than when using a feed gas containing only methane.

[4] A direct cracking method for hydrocarbons according to yet another embodiment is the direct cracking method for hydrocarbons according to any one of [1] to [3],
The step of contacting the feed gas with the catalyst (2) is carried out at a temperature in the range of 700 to 800°C.

This configuration allows for a higher conversion rate of hydrocarbons than when using a feed gas containing only methane.

[5] A direct cracking method for hydrocarbons according to yet another embodiment is the direct cracking method for hydrocarbons according to any one of [1] to [4],
A part of the gas remaining after the raw material gas has been brought into contact with the catalyst (2) is mixed with the raw material gas and brought into contact with the catalyst (2).

By setting the concentration of hydrocarbons having two or more carbon atoms in the feed gas to 0.02-10 vol%, it is possible to improve the conversion rate of the hydrocarbons compared to using a feed gas containing only methane, but when the concentration of hydrocarbons having two or more carbon atoms is 10 vol%, the effect of improving the conversion rate of the hydrocarbons is somewhat lower than when the concentration is 5 vol%. Because the gas after the feed gas has been brought into contact with the catalyst contains hydrogen produced by the direct decomposition of the hydrocarbons, even if the concentration of hydrocarbons having two or more carbon atoms in the feed gas is 10 vol%, the concentration of hydrocarbons having two or more carbon atoms in the gas after the feed gas has been brought into contact with the catalyst will be lower than 10 vol%. Therefore, according to the configuration of [5], even if a raw material gas with a concentration of hydrocarbons having two or more carbon atoms of 10 vol% is used, the gas after contacting the raw material gas with the catalyst is mixed with the raw material gas and then contacts the catalyst, so that the raw material gas and the catalyst come into contact with each other in a state where the concentration of hydrocarbons having two or more carbon atoms is lower than 10 vol%. As a result, even if a raw material gas with a concentration of hydrocarbons having two or more carbon atoms of 10 vol% is used, it is possible to obtain an effect similar to the improvement in the conversion rate of hydrocarbons obtained when the concentration is 5 vol%.

[6] A direct cracking method for hydrocarbons according to yet another embodiment is any of the direct cracking methods for hydrocarbons according to [5],
The raw gas is city gas.

The concentration of hydrocarbons having two or more carbon atoms in city gas is approximately 10 vol%, so the effect of improving the conversion rate of the hydrocarbons is somewhat lower than when using a raw material gas in which the concentration of hydrocarbons having two or more carbon atoms is 5 vol%. However, for the same reason that the above-mentioned effect is obtained from the configuration [5] above, even when city gas is used, an effect similar to the improvement effect of the conversion rate of the hydrocarbons obtained when the concentration is 5 vol% can be obtained. Note that while a raw material gas in which the concentration of hydrocarbons having two or more carbon atoms is lower than 10 vol% must be prepared separately, if city gas can be used, the work of preparing the raw material gas is unnecessary, and the workability of carrying out the direct decomposition method of hydrocarbons can be improved.

2 Catalysts

Claims (6)

A method for directly cracking hydrocarbons into carbon and hydrogen, comprising the steps of:
The method includes contacting a feed gas containing methane and a hydrocarbon having two or more carbon atoms with a catalyst that is an unsupported catalyst of an aggregate of a plurality of iron particles,
A method for direct cracking of hydrocarbons, wherein the concentration of the hydrocarbons having two or more carbon atoms in the feed gas is 0.02 to 10 vol %. The direct decomposition method for hydrocarbons according to claim 1, wherein the concentration of the hydrocarbons having two or more carbon atoms in the feed gas is 0.5 to 9.7 vol%. The method for direct decomposition of hydrocarbons according to claim 1, wherein the particle sizes of the particles range from 32 to 180 μm. The method for direct decomposition of hydrocarbons according to claim 1 or 2, wherein the step of contacting the feed gas with the catalyst is carried out at a temperature range of 700 to 800°C. The method for direct decomposition of hydrocarbons according to claim 1 or 2, in which a portion of the gas remaining after the feed gas has been brought into contact with the catalyst is mixed with the feed gas and brought into contact with the catalyst. The method for direct decomposition of hydrocarbons according to claim 5, wherein the raw gas is city gas.

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