JP7705356B2 - Dehydrogenation catalyst, pyrolysis tube for producing olefins, and method for producing olefins - Google Patents

Description

The present invention relates to a dehydrogenation catalyst, etc.

Olefins such as ethylene and propylene are used in industry to produce a wide variety of chemical synthesis products. Olefins are produced by passing petroleum-derived hydrocarbons such as ethane and naphtha through a pyrolysis tube (cracking tube) and heating them to 700-900°C to cause thermal decomposition in the gas phase. This production method requires a large amount of energy to reach high temperatures. For this reason, a technology is known in which a dehydrogenation catalyst is supported on the inner surface of the pyrolysis tube.

Patent Document 1 discloses a dehydrogenation catalyst containing, as a catalytic component, at least one of the group consisting of oxides of metal elements in Group 2B, Group 3B, and Group 4B of the periodic table.

JP 2017-209661 A

However, the dehydrogenation catalyst described in Patent Document 1 may not provide sufficient performance depending on the olefin production conditions, and the development of further dehydrogenation catalysts is desired.

One aspect of the present invention was made in consideration of the above problems, and its purpose is to provide a dehydrogenation catalyst that has high catalytic activity in the thermal cracking reaction of a hydrocarbon feedstock.

In order to solve the above problems, a dehydrogenation catalyst according to one embodiment of the present invention is represented by the general _formula M11 _{- xM2xOy} , in which M1 is at least one element selected from a first group consisting of Ce, Sr, Ca, La, and Ba, M2 is at least one element selected from a second group consisting of Co, Fe, Cr, and Mn, and x is 0.01 to 0.5.

According to one aspect of the present invention, it is possible to realize a dehydrogenation catalyst that has high catalytic activity in the thermal decomposition reaction of a hydrocarbon feedstock.

FIG. 1 is a schematic cross-sectional view showing the configuration of a pyrolysis tube for producing olefins according to a first embodiment of the present invention. FIG. 2 is an enlarged view of the inner surface of the pyrolysis tube for producing olefins. FIG. 2 is a schematic cross-sectional view showing the configuration of a pyrolysis tube for producing olefins according to a second embodiment of the present invention. FIG. 2 is an enlarged view of the inner surface of the pyrolysis tube for producing olefins. 1 is a graph showing the production rate of ethylene when a thermal decomposition experiment was carried out using the dehydrogenation catalysts of the examples of the present invention and the comparative examples. FIG. 1 is a graph created using data obtained from a thermal cracking experiment using dehydrogenation catalysts according to examples of the present invention and comparative examples, in which the horizontal axis represents ethane conversion and the vertical axis represents ethylene selectivity. 1 is a graph showing the production rate of ethylene when a thermal decomposition experiment was carried out using the dehydrogenation catalysts of the examples of the present invention and the comparative examples. FIG. 1 is a graph created using data obtained from a thermal cracking experiment using dehydrogenation catalysts according to examples of the present invention and comparative examples, in which the horizontal axis represents ethane conversion and the vertical axis represents ethylene selectivity.

[Embodiment 1]
Hereinafter, the pyrolysis tube 1A for olefin production and the dehydrogenation catalyst 4 in the first embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a schematic cross-sectional view showing the configuration of the pyrolysis tube 1A for olefin production in this embodiment. Fig. 2 is an enlarged view of the inner surface of the pyrolysis tube 1A for olefin production.

As shown in FIG. 1 and FIG. 2, the pyrolysis tube 1A for olefin production has an alumina coating 3 formed on the inner surface of a tubular base material 2 and a plate-like body (insert material) 5. The base material 2 and the plate-like body 5 are made of a heat-resistant metal material. The alumina coating 3 is a metal oxide coating containing Al ₂ O _3. A dehydrogenation catalyst 4 is supported on the surface of the alumina coating 3. In this application, the metal oxide coating containing Al ₂ O ₃ is called an "alumina coating". With the above configuration, the pyrolysis tube 1A for olefin production can improve the olefin yield from a hydrocarbon raw material such as ethane or naphtha by adding a dehydrogenation catalytic reaction to the pyrolysis reaction. The base material 2, the plate-like body 5, the alumina coating 3, and the dehydrogenation catalyst 4 in the pyrolysis tube 1A for olefin production will be described in detail below.

(Base material 2 and plate-like body 5)
The base material 2 in this embodiment is a casting made of a heat-resistant metal material with an alumina film 3 formed on the surface of the base material 2. The plate-like body 5 in this embodiment is a casting made of a heat-resistant metal material or a stainless steel plate provided inside the base material 2 and with an alumina film 3 formed on the surface of the plate-like body 5. In this embodiment, the pyrolysis tube for producing olefins 1A includes the plate-like body 5, but the plate-like body 5 is not an essential member, and the plate-like body 5 may not be included. The base material 2 and the plate-like body 5 may be, for example, castings made of a conventionally known heat-resistant metal material, and are preferably castings made of a heat-resistant metal material containing at least chromium (Cr), nickel (Ni), and aluminum (Al).

In this embodiment, the alumina film 3 is formed on the inner surface of the base material 2 and the surface of the plate-like body 5, but the alumina film 3 may be formed only on the inner surface of the base material 2, or the alumina film 3 may be formed only on the surface of the plate-like body 5. In addition, in this embodiment, the dehydrogenation catalyst 4 is supported on the inner surface of the base material 2 and the surface of the plate-like body 5, but the dehydrogenation catalyst 4 may be supported only on the inner surface of the base material 2, or the dehydrogenation catalyst 4 may be supported only on the surface of the plate-like body 5.

It is preferable that at least a portion of the inner surface of the base material 2 and/or the surface of the plate-like body 5 form recesses and/or protrusions. This improves the heat transfer efficiency and allows the fluid in the tubular base material 2 to be heated uniformly.

(Alumina coating 3)
The alumina coating 3 is highly dense and acts as a barrier to prevent oxygen, carbon, and nitrogen from penetrating into the base material 2 and the plate-like body 5 from the outside. In a typical pyrolysis tube for producing olefins, no metal oxide coating is formed on the inner surface of the base material 2 and the surface of the plate-like body 5. Therefore, excessive decomposition of the hydrocarbon raw material occurs during pyrolysis due to the catalytic action of nickel (Ni), iron (Fe), cobalt (Co), and the like, which are the constituent elements of the surface of the base material 2 and the plate-like body 5, and coke is generated on the inner surface of the base material 2 and the surface of the plate-like body 5. When the coke generated on the inner surface of the base material 2 and the surface of the plate-like body 5 accumulates, the heat transfer resistance increases, and there is a problem that the temperature of the outer surface of the pyrolysis tube for producing olefins increases in order to maintain the reaction temperature in the olefin pyrolysis tube. In addition, when coke accumulates on the inner surface of the base material 2 and the surface of the plate-like body 5, the cross-sectional area of the flow path through which the gas passes becomes smaller, and the pressure loss increases. For these reasons, typical olefin production pyrolysis tubes require frequent removal of accumulated coke (decokking).

In contrast, in the pyrolysis tube 1A for producing olefins of this embodiment, the alumina coating 3 is formed on the inner surface of the base material 2 and on the surface of the plate-like body 5, which can suppress the formation of coke on the inner surface of the base material 2 and on the surface of the plate-like body 5. As a result, the frequency of decoking can be reduced.

The alumina coating 3 of the present invention is formed by a surface treatment process and a first heat treatment process. The surface treatment process is a process in which the target areas of the base material 2 and the plate-like body 5 that come into contact with a high-temperature atmosphere when the product is in use are surface-treated to adjust the surface roughness of the areas. An example of the surface treatment of the base material 2 and the plate-like body 5 is a polishing process. The surface treatment can be performed so that the surface roughness (Ra) of the target areas is 0.05 to 2.5 μm. More preferably, the surface roughness (Ra) is 0.5 to 2.0 μm. In addition, by adjusting the surface roughness by the surface treatment, residual stress and distortion in the heat-affected zone can also be removed at the same time.

The first heat treatment step is a step of subjecting the base material 2 and the plate-like body 5 after the surface treatment step to a heat treatment in an oxidizing atmosphere. The oxidizing atmosphere is an oxidizing environment in which an oxidizing gas containing 20 volume % or more of oxygen or steam or _CO2 is mixed. The heat treatment is performed at a temperature of 900°C or more, preferably 1000°C or more, and the heating time is 1 hour or more.

By sequentially carrying out the surface treatment process and the first heat treatment process on the base material 2 and the plate-like body 5 as described above, it is possible to manufacture a pyrolysis tube for producing olefins in which the alumina coating 3 is stably formed on the inner surface of the base material 2 and the surface of the plate-like body 5.

The thickness of the alumina coating 3 formed on the inner surface of the base material 2 and the surface of the plate-like body 5 is preferably 0.5 μm or more and 6 μm or less in order to effectively exert the barrier function. If the thickness of the alumina coating 3 is less than 0.5 μm, there is a risk that the carburization resistance will decrease. If the thickness of the alumina coating 3 exceeds 6 μm, there is a risk that the alumina coating 3 will be easily peeled off due to the influence of the difference in thermal expansion coefficient between the base material 2 and the plate-like body 5 and the coating. For the above reasons, it is more preferable that the thickness of the alumina coating 3 be 0.5 μm or more and 2.5 μm or less.

Note that chromium oxide scale may be partially formed on the alumina film 3. This is because the chromium oxide scale formed near the surface of the base material 2 and the plate-like body 5 is pushed up to the product surface by Al ₂ O _3. The less chromium oxide scale, the better, and it is preferable that it occupies less than 20 area % of the product surface, with Al ₂ O ₃ occupying 80 area % or more.

(Dehydrogenation catalyst 4)
The dehydrogenation catalyst 4 is a catalyst used for olefin production. The dehydrogenation catalyst 4 is a catalyst for improving the yield of olefins in a thermal cracking reaction (specifically, a reaction for thermally decomposing a hydrocarbon raw material such as naphtha or ethane into olefins) using the olefin production pyrolysis tube 1A, and is supported on the surface of the alumina coating 3.

The dehydrogenation catalyst 4 contains at least one element selected from a first group consisting of Ce, Sr, Ca, La, and Ba (hereinafter also referred to as the first group element), and at least one element selected from a second group consisting of Co, Fe, Cr, and Mn (hereinafter also referred to as the second group element). In addition, the dehydrogenation catalyst 4 has a molar ratio of the total of the second group elements of 0.01 to 0.5 when the sum of the molar ratios of the total of the first group elements and the second group elements is 1. This configuration makes it easier for the dehydrogenation catalyst 4 to take oxygen in and out of its structure. This makes it possible to promote the dehydrogenation reaction of the hydrocarbon feedstock, and therefore has high catalytic activity in the dehydrogenation reaction.

The dehydrogenation catalyst 4 can also be expressed as follows. That is, the dehydrogenation catalyst 4 is represented by the general formula M1 _1-x M2 _x O _y , where M1 is at least one element selected from the first group consisting of Ce, Sr, Ca, La, and Ba, M2 is at least one element selected from the second group consisting of Co, Fe, Cr, and Mn, and x is 0.01 to 0.5. The lower limit of x is preferably 0.1. The upper limit of x is preferably 0.4, and more preferably 0.2. The value of y is determined by the first group elements and the second group elements.

In the dehydrogenation catalyst 4, the element selected from the first group is preferably Ce, and the element selected from the second group is preferably Co. This configuration further improves the catalytic ability in the dehydrogenation reaction. In addition, in the case of this configuration, when the sum of the molar ratio of Ce and the molar ratio of Co is 1, the molar ratio of Co is preferably 0.1 to 0.4. In this case, the dehydrogenation catalyst 4 can be expressed as Ce _1-x Co _x O ₂ (x is 0.1 to 0.4).

<Method for producing dehydrogenation catalyst 4>
The method for producing the dehydrogenation catalyst 4 is not particularly limited, but it can be produced, for example, by a citric acid complex polymerization method, a solid phase method, etc. Hereinafter, the methods for producing the dehydrogenation catalyst 4 using the citric acid complex polymerization method and the solid phase method will be described.

(Citric acid complex polymerization method)
The citric acid complex polymerization method includes a mixing and stirring step, a drying step, a pre-baking step, and a main baking step.

In the mixing and stirring step, a salt (e.g., nitrate, acetate, etc.) containing the elements constituting the dehydrogenation catalyst 4, citric acid monohydrate, ethylene glycol, and distilled water are mixed to obtain a mixed liquid. The salt is weighed so that the first group elements and the second group elements have the desired molar ratio. Citric acid monohydrate is preferably added in an amount 3 to 4 times the total molar amount of the first group elements and the second group elements contained in the salt. Ethylene glycol is preferably added in an amount 3 to 4 times the total molar amount of the first group elements and the second group elements contained in the salt. Distilled water is preferably added in an amount 1200 to 1600 times the total molar amount of the first group elements and the second group elements contained in the salt. The mixed liquid is preferably stirred at 60 to 70°C for 10 to 17 hours.

In the drying process, the mixture is dried to obtain a powder. For example, it can be heated and dried on a hot plate while stirring.

In the pre-firing step, the powder is pre-fired to obtain a pre-firing body. The pre-firing step is carried out in air or oxygen, and the pre-firing temperature is preferably 400 to 450°C and the holding time is preferably 2 to 3 hours. The firing temperature and holding time may be appropriately adjusted within the ranges according to the amount of catalyst to be prepared.

In the firing process, the pre-fired body is fired to obtain an oxide. The firing process is carried out in air or oxygen, and the firing temperature is preferably 850 to 900°C and the holding time is preferably 8 to 12 hours. The firing temperature and holding time may be appropriately adjusted within the ranges depending on the amount of catalyst to be prepared.

(solid phase method)
The solid phase method includes a grinding and mixing step, a drying step, and a calcination step.

In the grinding and mixing step, compounds (e.g., oxides, carbonate compounds) containing the elements that make up the dehydrogenation catalyst 4 are mixed, and the mixture is ground and mixed to obtain a ground and mixed powder. The compounds are mixed so that the first group elements and the second group elements are in the desired molar ratio. For example, grinding and mixing can be performed using a wet bead mill.

In the drying process, the pulverized and mixed powder is dried to obtain a dried body. In the calcination process, the dried body is calcined to obtain an oxide. The calcination process is carried out in air or oxygen, and the calcination temperature is preferably 500 to 1300°C and the holding time is preferably 1 to 10 hours. The calcination temperature and holding time may be appropriately adjusted within the ranges depending on the amount of catalyst to be prepared.

<Method of supporting dehydrogenation catalyst 4>
Next, a method for supporting the dehydrogenation catalyst 4 on the alumina film 3 will be described. The method for supporting the dehydrogenation catalyst 4 on the alumina film 3 includes a coating step and a second heat treatment step. The coating step and the second heat treatment step will be described in detail below.

(a) Coating Step The coating step is a step of coating the surface of the alumina film 3 formed in the surface treatment step and the first heat treatment step with a slurry containing a dehydrogenation catalyst 4 prepared in advance.

(b) Second Heat Treatment Step The second heat treatment step is a step of heat treating the base material 2 and the plate-like body 5 having the alumina film 3 coated with the slurry in the coating step.

The heat treatment in the second heat treatment step is carried out in air or an acidic atmosphere. The heat treatment temperature in the second heat treatment step is in the range of 500 to 900°C, and the heat treatment time is 1 to 6 hours.

By carrying out the second heat treatment step under the above heat treatment conditions, the dehydrogenation catalyst 4 can be supported on the alumina coating 3.

In addition, by adjusting the concentration of the slurry applied in the above-mentioned application process, the dehydrogenation catalyst 4 can be supported on the alumina coating 3 at an appropriate concentration (amount).

In this way, in the pyrolysis tube 1A for producing olefins in this embodiment, an alumina coating 3 is formed on the inner surface of a tubular base material 2 made of a heat-resistant metal material and on the surface of a plate-shaped body 5, and a dehydrogenation catalyst 4 is supported on the surface of the alumina coating 3.

According to the above configuration, the pyrolysis tube 1A for producing olefins of the present invention has an alumina coating 3 formed on the inner surface of the base material 2 and on the surface of the plate-like body 5. This makes it possible to suppress the formation of coke on the surface of the alumina coating 3 (base material 2 and plate-like body 5). The surface of this alumina coating 3 is supported with a dehydrogenation catalyst 4. This makes it possible to produce ethylene from ethane, for example, by a dehydrogenation reaction, when the dehydrogenation catalyst 4 acts as a dehydrogenation catalyst in pyrolysis using the pyrolysis tube 1A for producing olefins. As a result, it is possible to improve the yield of olefins from hydrocarbon raw materials such as ethane and naphtha by pyrolysis.

In this embodiment, the alumina film 3 formed on the inner surface of the base material 2 and the surface of the plate-like body 5 by the surface treatment process and the first heat treatment process is subjected to the coating process and the second heat treatment process to support the dehydrogenation catalyst 4 on the alumina film 3, but the pyrolysis tube for olefin production of the present invention is not limited to this. For example, the coating process and the heat treatment process may be performed after the surface treatment process. In this case, the alumina film 3 is formed on the inner surface of the base material 2 and the surface of the plate-like body 5 in the heat treatment process, and the dehydrogenation catalyst 4 is supported on the alumina film 3. As a result, the alumina film 3 can be formed on the inner surface of the base material 2 and the surface of the plate-like body 5, and the dehydrogenation catalyst 4 can be supported on the alumina film 3 by performing the heat treatment process only once.

In addition, in this embodiment, the dehydrogenation catalyst 4 is supported on the surface of the alumina coating 3 formed on the inner surface of the base material 2 and the surface of the plate-like body ₅ , but the pyrolysis tube for olefin production 1A of the present invention is not limited to this. That is, the pyrolysis tube for olefin production of the present invention may have a configuration in which the dehydrogenation catalyst 4 is supported on the surface _of a metal oxide coating (e.g., _Cr2O3 , _MnCr2O4 , _etc. ) other than _Al2O3 that has a barrier function and can support the dehydrogenation catalyst 4.

The olefin production method according to one embodiment of the present invention is a method for producing olefins using the above-mentioned pyrolysis tube for olefin production 1A. Examples of olefins include ethylene and propylene. Examples of hydrocarbon raw materials include ethane and naphtha. Olefins are produced by passing the hydrocarbon raw material through the pyrolysis tube for olefin production 1A, heating it to 700 to 900°C, and pyrolyzing it in the gas phase.

[Embodiment 2]
Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

Figure 3 is a schematic cross-sectional view showing the configuration of a pyrolysis tube 1B for producing olefins in this embodiment. Figure 4 is an enlarged view of the inner surface of the pyrolysis tube 1B for producing olefins.

In the pyrolysis tube for olefin production 1A in the first embodiment, an alumina film 3 as a metal oxide film containing Al ₂ O ₃ is formed on the inner surface of the base material 2 and on the surface of the plate-like body 5, and a dehydrogenation catalyst 4 is supported on the surface of the alumina film 3. In contrast, the pyrolysis tube for olefin production 1B in the present embodiment differs from the pyrolysis tube for olefin production 1A in that the dehydrogenation catalyst 4 is directly supported on the inner surface of the tubular base material 2 made of a heat-resistant metallic material and on the surface of the plate-like body 5, as shown in Figs. 3 and 4.

The pyrolysis tube 1B for producing olefins can be manufactured by applying a slurry containing a previously prepared dehydrogenation catalyst 4 to the inner surface of the base material 2 and the surface of the plate-shaped body 5, and then heat treating the slurry under appropriate conditions such as air or nitrogen atmosphere to support the dehydrogenation catalyst 4 on the inner surface of the base material 2 and the surface of the plate-shaped body 5.

As described above, the pyrolysis tube 1B for olefin production has the dehydrogenation catalyst 4 supported on the inner surface of the base material 2 and on the surface of the plate-like body 5. This allows, for example, ethylene to be produced from ethane by a dehydrogenation reaction when the dehydrogenation catalyst 4 acts as a dehydrogenation catalyst in pyrolysis using the pyrolysis tube 1B for olefin production. As a result, it is possible to improve the yield of olefins from hydrocarbon raw materials such as ethane and naphtha by pyrolysis.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in different embodiments.

Below, we will explain the dehydrogenation catalysts of Examples 1 to 8 as examples of the dehydrogenation catalyst of the present invention, and the dehydrogenation catalyst of Comparative Example 1 as a comparative example. First, we will explain the methods for producing the dehydrogenation catalysts of Examples 1 to 8 and Comparative Example 1.

Example 1
The dehydrogenation catalyst of Example 1 was prepared by a citric acid complex polymerization method. Specifically, cerium nitrate hexahydrate (Ce(NO ₃ ) _{3.6H 2} O) and chromium nitrate (Cr(NO ₃ ) ₃ ) were first weighed out to a molar ratio of Ce:Cr=0.9:0.1 to prepare a solute. Citric acid monohydrate and ethylene glycol in a molar amount three times the total molar amount of Ce and Cr in the solute were dissolved in distilled water in a molar amount 1500 times the total molar amount, and thoroughly stirred (hereinafter referred to as the solvent). The solute was mixed into the solvent, and heated and stirred at 70° C. overnight. The mixture was then heated and dried on a pot plate while stirring to obtain a powder. The powder was pre-calcined at 400° C. for 2 hours, and then calcined at 850° C. for 10 hours to prepare Ce _0.9 Cr _0.1 O ₂ as the dehydrogenation catalyst of Example 1.

Example 2
Ce0.9Mn0.1O2 as the dehydrogenation catalyst of _Example 2 was prepared in the same manner as _{in Example 1, except that cerium nitrate hexahydrate (Ce(NO3)3.6H2O ) and} manganese nitrate hexahydrate (Mn( _NO3 ) _{2.6H2O )} were weighed out to give a molar ratio of Ce:Mn = _0.9 : _0.1 and used as the solute.

Example 3
Ce0.9Fe0.1O2 as the dehydrogenation catalyst of Example 3 was prepared in the same manner as in Example 1 _, except that cerium nitrate hexahydrate (Ce( _NO3 ) _3.6H2O ) and iron nitrate (Fe( _NO3 ) ₃ ) were weighed out to have a molar ratio of Ce:Fe = _0.9 : _0.1 and used as the _solute .

Example 4
Ce0.9Co0.1O2 as the dehydrogenation catalyst of Example 4 was prepared in the same manner as in Example 1 _, except that cerium nitrate hexahydrate (Ce( _NO3 ) _3.6H2O ) and cobalt nitrate (Co( _NO3 ) ₂ ) were weighed out to have a molar ratio of Ce:Co= _0.9 : _0.1 and used as the _solute .

Example 5
Ce0.9Ni0.1O2 _{as the dehydrogenation catalyst of Example 5 was prepared in the same manner as in Example 1, except that cerium nitrate hexahydrate (Ce(NO3)3.6H2O ) and nickel} nitrate hexahydrate (Ni( _NO3 ) _{2.6H2O )} were weighed out to give a molar ratio of Ce:Ni = _0.9 : _0.1 and used as the solute.

Example 6
Ce0.8Co0.2O2 as the dehydrogenation catalyst of Example 6 was prepared in the same manner as in Example 1 _{, except that cerium nitrate hexahydrate (Ce(NO3)3.6H2O ) and} cobalt nitrate (Co( _NO3 ) _{2 )} were weighed out to have a molar ratio of Ce:Fe= _0.8 : _0.2 and used as the solute.

(Example 7)
Ce0.7Co0.3O2 as the dehydrogenation catalyst of Example 7 was prepared in the same manner as in Example 1 _{, except that cerium nitrate hexahydrate (Ce(NO3)3.6H2O ) and} cobalt nitrate (Co( _NO3 ) _{2 )} were weighed out to have a molar ratio of Ce:Fe= _0.7 : _0.3 and used as the solute.

(Example 8)
Ce0.6Co0.4O2 as the dehydrogenation catalyst of Example 8 was prepared in the same manner as in Example 1 _{, except that cerium nitrate hexahydrate (Ce(NO3)3.6H2O ) and} cobalt nitrate (Co( _NO3 ) _{2 )} were weighed out to have a molar ratio of Ce:Fe= _0.6 : _0.4 and used as the solute.

(Comparative Example 1)
The dehydrogenation catalyst of Comparative Example 1 was prepared by a citric acid complex polymerization method. Cerium nitrate hexahydrate (Ce(NO ₃ ) _{3.6H 2} O) was used as a solute, and citric acid monohydrate and ethylene glycol were dissolved in distilled water in an amount of 1500 times the molar amount of Ce in the solute and thoroughly stirred (hereinafter referred to as solvent). The solute was mixed into the solvent and heated and stirred at 70° C. overnight. After that, the mixture was heated and dried while stirring on a pot plate to obtain a powder. The powder was pre-calcined at 400° C. for 2 hours, and then calcined at 850° C. for 10 hours to produce CeO ₂ .

<Ethane pyrolysis experiment>
Next, an ethane thermal decomposition experiment using the dehydrogenation catalysts of Examples 1 to 5 and Comparative Example 1 will be described. In the ethane thermal decomposition experiment, a mixture of 100 mg of the dehydrogenation catalyst and 392 mg of an inactive solid SiC was first filled in a quartz tube (inner diameter 4 mm, length 180 mm) to a height of 30 mm. Next, the quartz tube was inserted into a tubular furnace, and the temperature in the tubular furnace was increased to 600° C. Next, a raw material gas adjusted to a volume ratio of ethane (C ₂ H ₆ ): water vapor (H ₂ O): nitrogen (N ₂ ) = 1.0: 1.4: 5.6 was supplied to the quartz tube at a flow rate of 118 mL/min to perform a thermal decomposition reaction of ethane. Among the gases flowing out of the quartz tube, hydrogen (H ₂ ) and nitrogen (N ₂ ) were analyzed by a TCG gas chromatograph (Shimadzu, GC-8A). Among the gases flowing out of the quartz tube, ethane (C ₂ H ₆ ), ethylene (C ₂ H ₄ ), carbon monoxide (CO), and methane (CH ₄ ) were analyzed by an FID gas chromatograph (Shimadzu, GC-8A) equipped with a methanizer. From these analysis results, the production rate of ethylene (C ₂ H ₄ ), the conversion rate of ethane (C ₃ H ₆ ), and the selectivity of ethylene (C ₂ H ₄ ) were calculated.

Fig. 5 is a graph showing the ethylene production rate when a thermal decomposition experiment was conducted using the dehydrogenation catalysts of Examples 1 to 5 and Comparative Example 1. Fig. 6 is a graph prepared using data obtained from a thermal decomposition experiment using the dehydrogenation catalysts of Examples 1 to 4 and Comparative Example 1, with the ethane conversion rate on the horizontal axis and the ethylene selectivity on the vertical axis. Figs. 5 and 6 are graphs prepared using data obtained from a thermal decomposition experiment using a dehydrogenation catalyst represented by Ce _0.9 M _0.1 O ₂ (M is a group 2 element) and the dehydrogenation catalyst of Comparative Example 1.

As shown in Figure 5, when the dehydrogenation catalysts of Examples 1 to 5 containing Ce and a second group element were used, the ethylene production rate was higher than when the dehydrogenation catalyst of Comparative Example 1, which does not contain a second group element, was used. In particular, the ethylene production rate was highest when the dehydrogenation catalyst of Example 4, which contains Co, was used.

As shown in Figure 6, when the dehydrogenation catalysts of Examples 1 to 5 containing Ce and a second group element were used, the ethane conversion was higher than when the dehydrogenation catalyst of Comparative Example 1, which did not contain a second group element, was used. In addition, when the dehydrogenation catalysts of Examples 2 to 4 containing Mn, Fe, or Co as the second group element were used, the ethylene selectivity was higher than when the dehydrogenation catalyst of Comparative Example 1 was used.

Fig. 7 is a graph showing the ethylene production rate when a thermal decomposition experiment was conducted using the dehydrogenation catalysts of Examples 4, 6 to 8, and Comparative Example 1. Fig. 8 is a graph created using data obtained from a thermal decomposition experiment using the dehydrogenation catalysts of Examples 4, 6 to ₈ , and Comparative Example 1, with the ethane conversion rate on the horizontal axis and the ethylene selectivity on the vertical axis. Figs. 7 and 8 are graphs created using data obtained from a thermal decomposition experiment using the dehydrogenation catalyst represented by Ce1 _{- xCoxO2} and the dehydrogenation catalyst of Comparative Example 1.

7, when the dehydrogenation catalysts containing Ce and Co of Examples 4 and 6 to 8 were used, the ethylene production rate was higher than when the dehydrogenation catalyst _CeO2 of Comparative Example 1 was used. In particular, the ethylene production rate was highest when the _{dehydrogenation} catalyst of Example 6, _{Ce0.8Co0.2O2 ,} was used.

8, when the dehydrogenation catalysts of Examples 4 and 6 to 8 containing Ce and Co were used, both the ethane conversion and the ethylene selectivity were higher than when the dehydrogenation catalyst of Comparative Example 1, _CeO2 , was used. In particular, when the _{dehydrogenation} catalyst of Example ₆ , _Ce0.8Co0.2O2 , was used, the ethane conversion and ethylene selectivity were the highest.

1A, 1B Pyrolysis tube for olefin production 2 Base material 3 Alumina coating (metal oxide coating)
4 Dehydrogenation catalyst 5 Plate

Claims (4)

It is represented by the general formula M1 _1-x M2 _x O _y ,
The M1 is at least one element selected from a first group consisting of Ce, Sr, Ca, La, and Ba,
The M2 is at least one element selected from a second group consisting of Co, Fe, Cr, and Mn,
The x is 0.01 to 0.5,
the element selected from the first group is Ce,
The element selected from the second group is Co;
Dehydrogenation catalyst. The dehydrogenation catalyst according to claim 1 , wherein x is 0.1 to 0.4. The dehydrogenation catalyst according to claim 1 or 2 is supported on the inner surface of a tubular base material made of a heat-resistant metal material and/or on the surface of a plate-like body made of a heat-resistant metal material.
Pyrolysis tubes for olefin production. A method for producing olefins, comprising producing olefins using the pyrolysis tube for olefin production according to claim 3 .

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