JPH08127545A - Production of methane from carbon dioxide - Google Patents

Abstract

PURPOSE: To selectively obtain methane at a high speed by reacting carbon dioxide with hydrogen in the presence of a catalyst comprising a Co compound containing a rare earth metal. CONSTITUTION: Carbon dioxide is reacted with hydrogen in the presence of an alloy comprising a rare earth metal and Co, especially La and Co, or its oxide as a catalyst to obtain methane. The La-Co alloy catalyst can be prepared by thermally melting La and Co. An alloy prepared by adding at least one of Al, Si, Ti, Mg and Zr as the third component to the above alloy can also be used. The La-Co oxide catalyst carried on at least one of Al2 O3 , SiO2 , TiO2 , MgO, and TiO2 as a carrier can also be used. These catalysts exhibit high conversions for the hydrogenation of the carbon dioxide also under high speed reaction conditions in relatively mild conditions, and can maintain the high activity for a long time.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing methane by reacting carbon dioxide with hydrogen.

[0002]

2. Description of the Related Art In recent years, global warming has become a serious environmental problem. It has been pointed out that carbon dioxide is one of the major contributors to global warming, and especially the rapid rise in atmospheric carbon dioxide concentration is one of the major causes of global warming in recent years. It has been. Therefore, in order to prevent the global environment from further deteriorating, it is urgently necessary to reduce and fix carbon dioxide emissions.

[0003] As a method of immobilizing carbon dioxide, there is a method of catalytically hydrogenating carbon dioxide using a hydrogenation catalyst, and more specifically, a method of reacting carbon dioxide with hydrogen to convert it to methane. is there. For example, there is known a method of hydrogenating carbon dioxide by using a hydrogenation catalyst mainly composed of a transition metal compound such as iron, cobalt and nickel supported on an oxide carrier (CHBarthoromew, Journal o.
f Catalyst, 87 , 352 (1984)).

However, such currently known hydrogenation catalysts generally have low carbon dioxide conversion (conversion) under high-speed reaction conditions and are difficult to maintain high activity for a long time. It is not very effective when carbon dioxide is immobilized industrially.

Therefore, in order to immobilize a large amount of carbon dioxide by catalytic hydrogenation, it is necessary to develop a catalyst that exhibits a high conversion rate even under high-speed reaction conditions and can maintain a high activity for a long period of time.

[0006]

The present invention contributes to the mitigation of global warming by providing a method capable of efficiently converting carbon dioxide to methane, and at the same time achieves the saving of hydrocarbon resources such as petroleum. What you want to do.

More specifically, an object of the present invention is to provide a technique capable of producing methane at high speed and selectively from carbon dioxide and hydrogen.

[0008]

Means for Solving the Problems The present inventor has conducted studies to solve the above problems, and as a result, it has been found that (a) rare earth metals exhibit high affinity for carbon dioxide;
(B) the rare earth metal itself has a low affinity for hydrogen; (c) therefore, the rare earth metal has a low activity for catalytic hydrogenation of carbon dioxide; A catalyst that combines a metal with high affinity, such as Co, exhibits high activity in the catalytic hydrogenation of carbon dioxide even under relatively mild conditions, shows high conversion under high-speed reaction conditions, and has high activity. It was found that time was maintained.

The present invention has been completed based on the above new findings, and is characterized by reacting carbon dioxide with hydrogen using a Co alloy or Co oxide containing a rare earth metal as a catalyst. The present invention provides a method for producing methane.

The reaction for producing methane in the present invention is represented by the following equation.

CO ₂ + 4H ₂ → CH ₄ + 2H ₂ O The present invention accomplishes this reaction by using a specific catalyst as detailed below.

The catalyst used in the present invention is an alloy of a rare earth metal and Co or an oxide containing a rare earth metal and Co, and more preferably an alloy of La and Co or a complex oxide containing La and Co. To mixed oxides. That is, the particularly preferred catalyst used in the present invention is composed of La, which easily adsorbs and activates carbon dioxide, and Co, which easily adsorbs and activates hydrogen.

It is noted that La—Co alloys are known to be excellent in hydrogen storage capacity.
It is expected that it is activated and easily reacts. However, there is no known example in which such an alloy catalyst containing a rare earth metal is used for hydrogenation of carbon dioxide (a methanation reaction), and what effect can be achieved by using such an alloy catalyst is quite low. It is unpredictable.

The La-Co alloy catalyst used in the present invention is L
It can be prepared by heating and melting a and Co. LaCo alloy, the composition ratio of La and _{Co, LaCo 5, LaCo 13,} La 2 Co 7, La 2 C
o ₃ , LaCo ₂ , La ₂ Co ₁₇ , La ₄ Co ₃ , La ₃ Co
There are various things. In the present invention, these alloys may be used alone or in a state where two or more kinds are present. Also, alloys obtained by adding at least one of aluminum, silicon, titanium, magnesium and zirconium as a third component to these alloys can be used as the catalyst. When the obtained alloy is used as a catalyst, it is preferable to pulverize the alloy into granules or powder of 40 to 200 mesh.

When the behavior of the La—Co alloy catalyst in the reaction process was examined in detail by X-ray diffraction, it was found that the alloy itself was a catalyst precursor and was heated in a CO ₂ + 4H ₂ reaction raw material gas under heating. It has been found that it has been activated and changed to compounds such as metallic cobalt and lanthanum hydroxide.

As a method for preparing an oxide catalyst, in addition to the physical mixing of the respective metal oxides, a coprecipitation method in which a metal nitrate is neutralized with an alkali and the formed precipitate is calcined is generally well known. However, even in the present invention, the catalyst prepared by the coprecipitation method is effective. The catalyst by the coprecipitation method is
For example, it is prepared as follows. That is, by adding a necessary amount of sodium carbonate to an aqueous solution of lanthanum and cobalt nitrate and calcining the produced carbonate at about 400 ° C., a mixture of lanthanum oxide and cobalt oxide or a complex oxide or mixture of lanthanum and nickel. An oxide (hereinafter simply referred to as mixed oxide) is obtained. Such an oxide catalyst can be obtained by using conventional methods such as Al ₂ O ₃ , SiO ₂ , TiO ₂ , and Mg.
It can be used in a state in which the catalyst component is supported on carrier particles (about 12 to 200 mesh) such as O and ZrO ₂ . The amount of catalyst supported on the carrier is usually 0.1 to 40%.
It is about 10%, more preferably about 1 to 20%. In addition, such an oxide catalyst is usually mixed with CO ₂ +
It can be obtained as an effective catalyst for methanation by heating at about 400 ° C. in 4H _{2 for} activation. It goes without saying that the catalyst by the coprecipitation method can be produced under conditions other than the above.

In the present invention, methane can be produced by bringing carbon dioxide and hydrogen into contact with the catalyst in the gas phase. The reaction system at this time is not particularly limited, and may be, for example, a fixed bed circulation system in which raw material gases (carbon dioxide and hydrogen) are introduced into a reactor filled with a catalyst to produce methane. Also, regarding the reaction conditions,
Although not particularly limited, generally, the reaction temperature is about 0 to 600 ° C, preferably about 100 to 500 ° C, more preferably about 150 to 400 ° C, and the reaction pressure is 0.1 to 10 ° C.
It is good to be about MPa, preferably about 0.5 to 8 MPa, more preferably about 1 to 6 MPa. Under these reaction conditions, the higher the reaction temperature and the higher the reaction pressure, the higher the methane yield tends to be. However, in consideration of industrial implementation,
As an advantage of the present invention as compared with the conventional method, even under the condition that the reaction temperature and the reaction pressure are relatively low, for example, the reaction temperature is about 250 to 350 ° C., the reaction pressure is 0.5 to 5 MP.
Even at about a, it can be mentioned that methane can be produced with a sufficiently high yield for practical use.

The flow rate of the raw material gas in the case of producing methane by the fixed bed flow method is not particularly limited, but it is determined by the space velocity (SV) in consideration of the packing density (g / ml) of the catalyst in the reactor. 1000 to 100000 ml / g-ca
t · hr, more preferably 2000 to 20000 m
It is preferable to be about 1 / g-cat · hr. In general, it should be noted that if the space velocity is too high, the conversion of carbon dioxide tends to decrease.

The ratio of carbon dioxide to be used as a raw material and hydrogen is not particularly limited, but hydrogen is usually about 2 to 8 mol, preferably about 3 to 6 mol, and particularly preferably about 1 mol of carbon dioxide. It is preferable that the amount is about 4 mol.

[0020]

In the present invention, the catalyst used in the methanation reaction (hydrogenation) of carbon dioxide is a rare earth metal and Co, especially La.
And Co are alloys or oxides. La-Co alloys are known to have high hydrogen storage capacity, but are not known to have high activity in hydrogenation of carbon dioxide.

In the present invention, the alloys and oxides of Co containing a rare earth metal have a high activity at the time of hydrogenating carbon dioxide even at a relatively low temperature because carbon dioxide is a rare earth metal such as lanthanum and hydrogen is cobalt. It is thought that this is because they are easily adsorbed and activated by metals such as (has a high affinity). As a result, it is considered that, for example, in the fixed bed flow reaction system, the state in which the conversion rate of carbon dioxide is high is maintained even when the flow rate of the reaction gas is increased.

The present invention is a method for producing methane at high speed and selectively from carbon dioxide and hydrogen using a highly active catalyst, which not only contributes to alleviation of the global warming problem but also utilizes methane. It also provides useful technologies to various chemical industries such as consumer fuel manufacturing factories, chemical manufacturing industries, and energy conversion industries.

[0023]

The La used as a catalyst in the present invention
Since the -Co alloy and the oxide catalyst show a high conversion rate even under a fast reaction condition under a relatively mild condition for hydrogenation of carbon dioxide, and can maintain a high activity for a long time, the present invention According to this, methane can be efficiently produced from carbon dioxide.

[0024]

The present invention will be described in more detail with reference to the following examples. Needless to say, the present invention is not limited to these examples. Examples 1 and 2 and Comparative Example 1 Regarding the La-Ni alloy and the La.Ni oxide catalyst of the present invention, 40-200 mesh catalyst was packed in a fixed bed flow reactor, and CO ₂ was added under pressure and heating. A mixed gas of H ₂ was introduced to compare the reaction characteristics.

As comparative examples, a nickel powder catalyst, which is well known as an effective hydrogenation catalyst in the CO ₂ methanation reaction, was used, and the LaCo ₅ alloy and the La / Co mixed oxide of the present invention were used. Table 1 shows the activity in comparison with the case.

[0026]

[Table 1] Reaction conditions; catalyst 1 g, H ₂ / CO ₂ = 4, 250 ° C., SV
= 3000 ml / g-cat · hr From the results shown in Table 1, as compared with the catalyst made of Ni powder,
It is clear that the La-Co alloy catalyst and the La-Co mixed oxide catalyst of the present invention have a significantly improved methane yield.

Example 3 LaCo ₅ alloy powder prepared by heating and melting (60-
1 g of 200-mesh) was filled into a stainless steel reaction tube having an inner diameter of 1 cm, and set in a pressurized fixed-bed flow reactor.
Source gas (H ₂ / CO ₂ = 4) 5 MPa, SV = 30
Table 2 shows the methanation yield when it was supplied at 00 ml / g-cat · hr. The analysis of the product was performed by an online gas chromatograph.

[0028]

[Table 2] From the results shown in Table 2, the LaCo ₅ alloy catalyst according to the present invention shows that even under a relatively mild reaction condition of 200 ° C.
It is clear that the catalyst exhibits a catalytic action, and that the catalyst activity sharply increases as the reaction temperature increases.

Example 4 7.5 g of La (NO ₃ ) ₃ .6H ₂ O and Co (N 0 ₃ ) ₂
An aqueous solution in which 25.2 g of 6H ₂ O was dissolved (La:
An aqueous solution of sodium carbonate was added to Co = 1: 5) for neutralization. The lanthanum and cobalt carbonates produced by coprecipitation were filtered off and calcined at 400 ° C. to obtain a mixed oxide. In the same manner as in Example 3, a stainless steel reaction tube having an inner diameter of 1 cm was filled with 1 g of this mixed oxide and set in a pressurized fixed bed flow reactor. Source gas (H ₂ / CO ₂ = 4) 5 MPa, S
Table 3 shows the methanation yield when V was supplied at 3000 ml / g-cat · hr. The analysis of the product was performed by an online gas chromatograph.

[Table 3] From the results shown in Table 3, the La / Ni mixed oxide catalyst according to the present invention begins to show a catalytic action even under a relatively mild reaction condition of 200 ° C., and the catalytic activity dramatically increases as the reaction temperature rises. Is clear.

Example 5 4.3 g of La (NO ₃ ) ₃ .6H ₂ O and Co (N 0 ₃ ) ₂
An aqueous solution in which 11.6 g of 6H ₂ O was dissolved (La:
Aluminum dioxide 30 as a carrier in Co = 1: 4)
g was added, and an aqueous sodium carbonate solution was added with stirring to neutralize. The lanthanum-cobalt carbonate mixture deposited on the support was filtered off and calcined at 400 ° C. to obtain a supported catalyst. As in Example 3, 1 g of this supported catalyst was filled in a stainless steel reaction tube having an inner diameter of 1 cm and set in a pressurized fixed bed flow reactor. Source gas (H ₂ / CO ₂ = 4) 5 MPa, S
Table 4 shows the methanation yield when V was supplied at 3000 ml / g-cat · hr. The analysis of the product was performed by an online gas chromatograph.

[Table 4] From the results shown in Table 4, the La / Ni mixed oxide-supported catalyst according to the present invention begins to show a catalytic action even under a relatively mild reaction condition of 200 ° C., and the catalytic activity dramatically increases as the reaction temperature rises. It is clear.

Front page continued (72) Inventor Hiroshi Miyamura 1-831 Midorigaoka, Ikeda, Osaka Prefecture Industrial Technology Institute, Osaka Institute of Industrial Technology (72) Hideaki Tanaka 1-831 Midorigaoka, Ikeda, Osaka Industry (72) Inventor, Yasuyuki Matsumura, 1-83-1, Midorigaoka, Ikeda-shi, Osaka, Japan

Claims (3)

[Claims] 1. A method for producing methane, which comprises reacting carbon dioxide with hydrogen using a Co compound containing a rare earth metal as a catalyst. 2. The production of methane according to claim 1, wherein a lanthanum-cobalt type alloy is used as an active component of the catalyst, and at least one oxide of aluminum, silicon, titanium, magnesium and zirconium is contained as a third component. Method. 3. A lanthanum-cobalt oxide is used as an active component of a catalyst, and aluminum dioxide is used as a carrier.
The method for producing methane according to claim 1, wherein at least one of silicon dioxide, titanium oxide, magnesium oxide and zirconium oxide is used.