JP4835070B2 - Carbon dioxide absorbent having steam reforming catalyst function, method for producing the same, and method for reforming fuel gas in hydrogen production system - Google Patents

Description

  The present invention relates to a carbon dioxide absorbent having a steam reforming catalyst function used in a hydrogen production system using a steam reforming method, a production method thereof, and a fuel gas reforming method in a hydrogen production system. Carbon dioxide absorbent having a steam reforming catalyst function having a function of generating hydrogen from reforming fuel gas and removing carbon dioxide produced as a secondary, a method for producing the same, and fuel in a hydrogen production system The present invention relates to a gas reforming method.

  As a method for producing hydrogen used in a fuel cell, for example, as shown in FIG. 4, the combustion unit 51 is configured to perform steam reforming using thermal energy generated by burning fuel gas. The reforming section (reformer) 52 is supplied with reforming fuel gas and steam, subjected to steam reforming under high temperature conditions to generate hydrogen, and then the reformed gas is supplied to the CO converter 53. A steam reforming method is known in which high-purity hydrogen is obtained by passing through and removing carbon monoxide (CO) gas contained in the reformed gas.

In this steam reforming method, reactions of the following formulas (1) and (2) proceed in the reforming section (reformer).
CH ₄ + H ₂ O → CO + 3H ₂ (1)
CO + H ₂ O → CO ₂ + H ₂ (2)

  In the CO transformer, the reaction of the above formula (2) proceeds.

As described above, the reformed gas contains CO, CO _2, and unreacted hydrocarbon gas that are generated as a secondary component in addition to hydrogen that can be used as fuel.
Of these, CO, when used in a fuel cell, poisons the electrode and causes a decrease in cell performance. For this reason, in the case of a phosphoric acid fuel cell (PAFC), the CO concentration in the reformed gas is set to 1% or less by using a CO converter that performs a shift reaction from CO to CO ₂ . In the case of a type fuel cell (PEFC), the CO concentration is reduced to 10 ppm or less by a selective oxidation reactor.
In this selective oxidation reaction apparatus, the reaction of the following formula (3) proceeds.
2CO + O ₂ → 2CO ₂ (3)

By the way, when CO ₂ remains in the reformed gas, the reverse reaction of the shift reaction from CO to CO ₂ occurs, and the CO concentration in the fuel gas increases.
Therefore, for the purpose of reducing the load on the CO converter and suppressing the reverse shift reaction, there is a method of using Li ₂ ZrO ₃ or Li ₄ ZrO ₄ as a carbon dioxide absorbent and absorbing carbon dioxide from the reformed gas. It has been proposed (see Patent Document 1).

  However, in the case of this method, it is difficult to absorb carbon dioxide at a high temperature exceeding 700 ° C., regardless of which absorbent material is used.

Further, regarding a method for producing hydrogen by a steam reforming method, a method of simultaneously performing steam reforming and CO ₂ removal at a high temperature has been proposed (see Patent Document 2). The purpose of this method is to improve the hydrogen conversion rate in the fuel reformer, reduce the load in the transformer, and suppress the reverse shift reaction. In addition, a layer in which the steam reforming catalyst and the carbon dioxide absorbent (CaO) are individually filled or a layer in which the steam reforming catalyst and the carbon dioxide absorbent are mixed is provided.

  The method using CaO as a carbon dioxide absorbent is said to be capable of absorbing carbon dioxide even at a high temperature of 700 ° C. or higher.

  However, in order to absorb carbon dioxide at 800 ° C. using CaO, a carbon dioxide concentration of about 40% is required, and even when carbon dioxide is absorbed at 750 ° C., the carbon dioxide concentration should be 10% or less. It is difficult to do. Furthermore, considering that the carbon dioxide concentration after steam reforming is usually about 10%, it is actually difficult to absorb carbon dioxide with CaO under steam reforming conditions.

  Further, a mixed gas comprising at least carbon-containing fuel and water vapor is brought into contact with a reaction layer containing a reforming catalyst and a carbon dioxide adsorption / desorption aid to obtain hydrogen gas and to produce carbon dioxide that is produced as a secondary gas. A hydrogen conversion step for fixing to the adsorption / desorption aid, and a regeneration step for heating the carbon dioxide adsorption / desorption aid to desorb the fixed carbon dioxide and regenerating the carbon dioxide absorption capacity of the carbon dioxide adsorption / desorption aid; An equipped hydrogen production method has been proposed (see Patent Document 3).

In the case of this method, as the carbon dioxide adsorption / desorption aid, oxides of alkaline earth metals such as Mg, Ca and Sr, oxides of alkali metals such as Na, K and Li can be used. ing. However, also in this method, when the above-mentioned substance that can be used as a carbon dioxide adsorption / desorption aid is used, as described with respect to Patent Document 2, carbon dioxide is produced by CaO under steam reforming conditions. It is considered that it is actually difficult to efficiently absorb the water.
JP 2002-255510 A JP 2002-208425 A JP 2002-255508 A

  The invention of the present application solves the above-mentioned problems, and can efficiently remove carbon dioxide that is produced as a secondary product when hydrogen is produced by the steam reforming method. It is an object of the present invention to provide a carbon dioxide absorbent having a function as a steam reforming catalyst for efficiently converting to hydrogen, a method for producing the same, and a method for reforming fuel gas in a hydrogen production system using the steam reforming catalyst. To do.

In order to solve the above problems, the carbon dioxide absorbent having the steam reforming catalyst function of the present invention (Claim 1) has a steam reforming catalyst function used in a hydrogen production system using a steam reforming method. A carbon dioxide absorber provided, wherein a transition metal is supported on the surface of a substance mainly composed of Ba ₂ TiO ₄ .

The carbon dioxide absorbent having a steam reforming catalyst function according to claim 2 is characterized in that, in the configuration of the invention according to claim 1, the transition metal supported on the surface of the substance mainly composed of Ba ₂ TiO ₄ is a Ni, is characterized by a percentage of the total amount of said Ni, said the material mainly containing Ba ₂ TiO ₄ Ni is 1 wt% or more.

Moreover, the method for producing a carbon dioxide absorbent having a steam reforming catalyst function according to the present invention (Claim 3) is characterized in that a powder of transition metal is added to an unfired material that becomes a material mainly composed of Ba ₂ TiO ₄ after firing. Is added, and the transition metal is supported on the surface of the substance containing Ba ₂ TiO ₄ as a main component by baking in a reducing atmosphere.

  According to a fourth aspect of the present invention, there is provided a method for producing a carbon dioxide absorbent having a steam reforming catalyst function, wherein the transition metal powder is Ni powder, and the Ni powder It is characterized in that it is added at a ratio of 1% by weight or more of the whole and fired in a reducing atmosphere.

The reforming method of the fuel gas in the hydrogen production system of the present invention (Claim 5) is a reforming method of the fuel gas for reforming in the hydrogen production system using the steam reforming method, and includes Ba ₂ TiO. It is characterized by using a carbon dioxide absorbent material having a steam reforming catalyst function in which a transition metal is supported on the surface of a substance containing ₄ as a main component.

According to a sixth aspect of the present invention, there is provided a method for reforming a fuel gas in a hydrogen production system according to the fifth aspect of the present invention, wherein the transition metal supported on the surface of the substance containing Ba ₂ TiO ₄ as a main component is Ni. And using a carbon dioxide absorbent having a steam reforming catalyst function, wherein the ratio of the Ni to the total amount of the substance mainly composed of the Ba ₂ TiO ₄ and the Ni is 1% by weight or more. It is a feature.

The carbon dioxide absorbent having the steam reforming catalyst function of the present invention (Claim 1) has a transition metal supported on the surface of a substance mainly composed of Ba ₂ TiO _4. In addition to being able to efficiently remove carbon dioxide that is produced as a secondary product during the production of hydrogen, it has a function as a steam reforming catalyst that efficiently converts the fuel gas for reforming into hydrogen It becomes possible to provide a carbon dioxide absorber. Therefore, by using the carbon dioxide absorbent of the present invention, it is possible to efficiently absorb and remove carbon dioxide in the reformed gas, promote the reforming reaction, and realize a high hydrogen conversion rate. It becomes possible to efficiently produce pure hydrogen gas.

That is, the carbon dioxide absorbent having a steam reforming catalyst function of the present invention is a material in which a transition metal is supported on the surface of a substance mainly composed of Ba ₂ TiO ₄ which is a composite oxide. The carbon absorbent material simultaneously plays a role as a carbon dioxide absorbent and a steam reforming catalyst when producing hydrogen using the steam reforming method. The reforming fuel gas, for example, methane can be steam reformed, and the carbon monoxide concentration can be lowered by the action of absorbing carbon dioxide in the reformed gas. As a result, the reforming reaction of methane is promoted, the concentration of unreacted methane is reduced, a high hydrogen conversion rate can be realized, and high-purity hydrogen gas can be efficiently produced.

Specifically, in the reformer, the reactions of the following formulas (1) and (2) proceed.
CH ₄ + H ₂ O → CO + 3H ₂ (1)
CO + H ₂ O → CO ₂ + H ₂ (2)
And, by removing the CO ₂ in the reformed gas by the carbon dioxide absorbent having the steam reforming catalyst function of the present invention, the equilibrium reaction of (2) proceeds to the right, and the hydrogen conversion rate is increased. While improving, CO density | concentration falls and the load of a CO converter and a CO removal apparatus is reduced.

  In addition, since the CO decreases, the equilibrium reaction (1), which is a basic reforming reaction, also proceeds to the right, so that the hydrogen conversion rate can be further improved.

FIG. 3 is a diagram showing a relationship between temperature and carbon dioxide partial pressure (CO ₂ partial pressure) (a carbon dioxide-absorbable region based on an experiment) when Ba ₂ TiO ₄ is used as an absorbent. As shown in FIG. 3, when Ba ₂ TiO ₄ is used, the partial pressure of carbon dioxide is about 0.003 atm at 700 ° C., the partial pressure of carbon dioxide is about 0.0084 atm at 750 ° C., and the partial pressure of carbon dioxide is 800 ° C. It can be seen that it is as low as about 0.02 atm and has sufficient ability to absorb carbon dioxide at high temperatures.

  In addition, the carbon dioxide absorbent having the steam reforming catalyst function of the present invention can release the carbon dioxide absorbed by heating and recover the carbon dioxide absorption ability.

According to the invention of claim 1 of the present application, by selecting the conditions, the CO concentration in the reformed gas can be reduced to 1% or less without using a CO converter. In that case, it is possible to provide a fuel cell reformer suitable for a phosphoric acid fuel cell (PAFC) that does not require a CO converter.
In addition, a fuel cell reformer suitable for a polymer electrolyte fuel cell (PEFC) that does not require a CO converter when the CO concentration is reduced to 10 ppm or less by a selective oxidation reactor is provided. It is also possible.

  When the carbon dioxide absorbent having the steam reforming catalyst function of the present invention releases carbon dioxide, carbon monoxide and oxygen are generated by thermal decomposition of carbon dioxide. Therefore, by coexisting any gas having high reactivity with carbon monoxide and reacting both with Ni supported on the surface of the carbon dioxide absorbent having the steam reforming catalyst function of the present invention as a catalyst, It is also possible to convert the carbon dioxide released from the carbon dioxide absorbent having the steam reforming catalyst function of the present invention into an intended organic substance, that is, to perform organic synthesis.

Moreover, as a carbon dioxide absorbent having a steam reforming catalyst function according to claim ₂ , in the configuration of the invention according to claim 1, as a transition metal supported on the surface of a substance mainly composed of Ba ₂ TiO ₄ By using Ni and setting the ratio of Ni to the total amount of Ni and the main component of Ba ₂ TiO ₄ and Ni to 1% by weight or more, the above-described effects, that is, the steam reforming method is used. It becomes possible to efficiently generate hydrogen and to efficiently remove carbon dioxide that is generated as a secondary product.
And, by using the carbon dioxide absorbent having the steam reforming catalyst function of the present invention, it is possible to promote the reforming reaction to achieve a high hydrogen conversion rate and efficiently produce high purity hydrogen gas. It becomes possible.

In the carbon dioxide absorbent having the steam reforming catalyst function of the present invention, the amount of Ni supported on the surface of the substance mainly composed of Ba ₂ TiO ₄ is set to 1% by weight or higher. A hydrogen conversion rate can be realized, but even if Ni is supported at a rate exceeding 10% by weight, a significant increase in the effect is not recognized. On the other hand, when the amount of Ni exceeds 10% by weight, the ratio of Ba ₂ TiO ₄ in the carbon dioxide absorbent decreases, and the amount of carbon dioxide that can be absorbed decreases. Therefore, it is usually desirable to support Ni at a ratio of 1 to 10% by weight.

Moreover, the method for producing a carbon dioxide absorbent having a steam reforming catalyst function according to the present invention (Claim 3) is characterized in that a powder of transition metal is added to an unfired material that becomes a material mainly composed of Ba ₂ TiO ₄ after firing. Is added, and the transition metal is supported on the surface of the substance mainly composed of Ba ₂ TiO ₄ by baking in a reducing atmosphere, so that no complicated process is required, and the transition metal is Ba ₂ TiO. A carbon dioxide absorbent having a steam reforming catalyst function supported on the surface of a substance containing ₄ as a main component can be efficiently produced.

That is, according to the method for producing a carbon dioxide absorbent having the steam reforming catalyst function of the present invention (Claim 3), the conventional general method is immersion treatment, that is, Ba ₂ TiO ₄ is added to the transition metal solution. A transition metal such as Ni can be easily supported on the surface of a substance containing Ba ₂ TiO ₄ as a main component without requiring a complicated process such as a process of immersing a substance containing as a main component.

Moreover, like the manufacturing method of the carbon dioxide absorber provided with the steam reforming catalyst function of claim 4, in the configuration of the invention of claim 3, Ni powder is used as the transition metal powder, and Ni powder is used, By adding 1% by weight or more of the total amount, a carbon dioxide absorbent having a steam reforming catalyst function in which a sufficient amount of Ni is supported on the surface of a substance mainly composed of Ba ₂ TiO ₄ is efficiently used. It becomes possible to manufacture well.

The reforming method of the fuel gas in the hydrogen production system of the present invention (Claim 5) is a reforming method of the fuel gas for reforming in the hydrogen production system using the steam reforming method, and includes Ba ₂ TiO. _Since a carbon dioxide absorbent material with a steam reforming catalyst function is used, with the transition metal supported on the surface of the substance whose main component is ₄ , the hydrogen is efficiently generated by the steam reforming method. And carbon dioxide produced as a secondary can be efficiently removed.
Therefore, according to the fuel gas reforming method in the hydrogen production system of the present invention, it is possible to realize a high hydrogen conversion rate and to efficiently produce high-purity hydrogen gas.

Further, in the method for reforming fuel gas in the hydrogen production system according to claim 6, the transition metal supported on the surface of the substance mainly composed of Ba ₂ TiO ₄ is Ni, and Ba ₂ TiO ₄ of Ni is mainly used. Since a carbon dioxide absorbent having a steam reforming catalyst function such that the ratio of the component substance and Ni to the total amount is 1% by weight or more is used, a higher hydrogen conversion rate is ensured. Can be realized, and high-purity hydrogen gas can be efficiently produced.

  The features of the present invention will be described in more detail below with reference to examples of the present invention.

  A powdery material containing metallic Ni was prepared by wet mixing barium titanate, barium carbonate, and Ni powder at a ratio as shown in Table 1 and then drying. In addition, about Ni powder, it added in the ratio of 0.83 weight part, 1.67 weight part, 3.38 weight part, and 8.72 weight part. In addition, the ratio of the Ni powder is such that Ni is 0.5% by weight and 1.0% by weight with respect to the entire carbon dioxide absorbent having a steam reforming catalyst function finally obtained through the firing step, respectively. , 2.0 wt%, and 5.0 wt%.

  Then, granulation was performed by stirring the powdered material while adding a binder to obtain a granule having a particle diameter of about 2 mm.

Next, this granular material was heat treated under conditions of Air atmosphere, 300 ° C. and 5 hours, degreased, and then baked at 1000 ° C. for 2 hours in nitrogen containing 1% hydrogen, and Ba containing 1% Ni. ₂ A carbon dioxide absorbent having a steam reforming catalyst function mainly composed of TiO ₄ was obtained.

FIG. 1 is an SEM photograph showing a state in which Ni is supported on the surface of the absorbent material 3 in Table 1. As shown in FIG. 1, it can be seen that in the absorbent material 3, Ni particles 2 are supported on the surface of a substance mainly composed of Ba ₂ TiO ₄ , that is, the carbon dioxide absorbent main body 1.

  Then, the carbon dioxide absorbent having the steam reforming catalyst function shown in Table 1 is filled in the reformer 13 constituting the fuel cell reformer as shown in FIG. Methane was steam reformed, and the contents of methane, carbon dioxide, carbon monoxide and hydrogen in the reformed gas were measured.

  FIG. 2 is a diagram schematically showing the configuration of a hydrogen production apparatus (fuel cell reforming apparatus) for fuel cells using a carbon dioxide absorbent having a steam reforming catalyst function according to the present invention. . As shown in FIG. 2, this fuel cell reforming apparatus includes a steam reforming catalyst for generating hydrogen by steam reforming a raw material gas (city gas) containing hydrocarbon gas as a main component. In order to remove the carbon monoxide (CO) in the reformer 13 provided with the reaction can 12 filled with the carbon dioxide absorbent 11 having a function and the reformed gas reformed by the reformer 13 The CO transformer 14 is provided.

Further, for comparison, instead of a carbon dioxide absorbent having a steam reforming catalyst function, a catalyst in which a Ni-based reforming catalyst is supported on the surface of an alumina base material, and has a carbon dioxide absorption capability. ₂ Using a catalyst that does not contain TiO ₄ as the main component, steam reforming of methane under the same conditions, and measuring the content of methane, carbon dioxide, carbon monoxide and hydrogen in the reformed gas did.
The results are also shown in Table 2. In Table 2, the test numbers marked with * are outside the scope of the present invention (Claim 2).

  As in the comparative example of test number 5 in Table 2, when a reforming catalyst that does not include a carbon dioxide absorbent and that has a Ni-based reforming catalyst supported on the surface of an alumina base, Although reforming was performed, it was confirmed that the concentration of carbon dioxide and carbon monoxide in the reformed gas was increased. Thus, an increase in the concentration of carbon monoxide is not preferable because the load on the transformer for reducing the concentration of carbon monoxide is large.

  Further, as shown in Test No. 1 in Table 2, a carbon dioxide absorbent having a Ni content of less than 1% by weight and not satisfying the requirements of the present invention (Claim 2) and having a Ni content of 0.5% by weight. When used, the content of carbon dioxide and carbon monoxide was reduced, the function as a carbon dioxide absorbent was good, and it was also confirmed that it had a steam reforming catalyst function, but it contained hydrogen. The rate was slightly low, and it was confirmed that the reforming effect of methane to hydrogen was insufficient and the amount of unreacted methane remained increased.

  On the other hand, the carbon dioxide absorbent provided with the steam reforming catalyst function of the absorbents 2 to 4 in Table 1 that satisfies the requirements of the present invention (Claim 2), that is, a transition metal on the surface of the absorbent. When a carbon dioxide absorbent material having a steam reforming catalyst function in which Ni is supported at a ratio of 1 to 5% by weight is used, steam reforming of methane can be performed without using a reforming catalyst. That is, it was confirmed that the carbon monoxide concentration decreased due to the carbon dioxide absorption action. Furthermore, it was confirmed that by reducing the concentration of carbon monoxide, the reforming reaction of methane was promoted, the concentration of unreacted methane decreased, and a high hydrogen conversion rate could be realized.

  From the above results, by setting the Ni content to 1.0% by weight or more, it becomes possible to perform steam reforming of methane without using a separate reforming catalyst, and by the carbon dioxide absorption effect, It was confirmed that it was possible to obtain high-purity hydrogen efficiently by reducing the carbon concentration.

  In the above embodiment, the case where the transition metal is Ni has been described as an example. However, in the present invention, other transition metals, such as Co, may be used.

As described above, since the carbon dioxide absorbent having the steam reforming catalyst function of the present invention supports the transition metal on the surface of the substance mainly composed of Ba ₂ TiO ₄ , the steam of the present invention is used. By using a carbon dioxide absorbent having a reforming catalyst function, it becomes possible to steam-reform methane without using a reforming catalyst separately, and a substance mainly composed of Ba ₂ TiO ₄ can be used. The carbon dioxide absorption action reduces the carbon monoxide concentration in the reformed gas, promotes the reforming reaction of methane, and realizes a high hydrogen conversion rate.

  Therefore, the present invention can be widely used in reforming processes and reforming apparatuses for fuel cells that produce hydrogen using the steam reforming method.

  According to the present invention, by selecting the conditions, the CO concentration in the reformed gas can be reduced to 1% or less without particularly using a CO converter. Therefore, it is possible to provide a fuel cell reforming apparatus suitable for a phosphoric acid fuel cell (PAFC) that does not require a CO converter. In addition, a fuel cell reformer suitable for a polymer electrolyte fuel cell (PEFC) that does not require a CO converter when the CO concentration is reduced to 10 ppm or less by a selective oxidation reactor is provided. be able to.

Shows a SEM photograph of the carbon dioxide absorbent comprising an embodiment according to the example (Example 1), Ba ₂ TiO ₄ steam reforming catalyst function Ni is supported on the surface of a material composed mainly of the present invention It is. It is a figure which shows typically the structure of the hydrogen manufacturing apparatus (reforming apparatus for fuel cells) for fuel cells using the carbon dioxide absorber provided with the steam reforming catalyst function of this invention. In the case of using Ba ₂ TiO ₄ as an absorbent is a diagram showing relationship between a (carbon dioxide absorption area based on the experiment) of the temperature and carbon dioxide partial pressure (CO ₂ partial pressure). It is a figure which shows the conventional reformer for fuel cells.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Carbon dioxide absorber main body 2 Ni particle 11 Carbon dioxide absorber provided with steam reforming catalyst function 12 Reactor 13 Reformer 14 CO converter

Claims (6)

A carbon dioxide absorbent material having a steam reforming catalyst function, which is used in a hydrogen production system using a steam reforming method, and a transition metal is supported on the surface of a substance mainly composed of Ba ₂ TiO ₄ A carbon dioxide absorbent provided with a steam reforming catalyst function. The transition metal supported on the surface of the substance containing Ba ₂ TiO ₄ as a main component is Ni, and the ratio of Ni to the total amount of the substance containing Ba ₂ TiO ₄ as a main component and Ni is 1 The carbon dioxide absorbent having a steam reforming catalyst function according to claim 1, wherein the carbon dioxide absorbent has a weight% or more. A transition metal powder is added to an unfired material, which is a material containing Ba ₂ TiO ₄ as a main component after firing, and fired in a reducing atmosphere, whereby a transition metal is formed on the surface of the material containing Ba ₂ TiO ₄ as a main component. A method for producing a carbon dioxide absorbent having a steam reforming catalyst function, wherein   The steam reforming catalyst function according to claim 3, wherein the transition metal powder is Ni powder, and the Ni powder is added at a ratio of 1% by weight or more of the whole and fired in a reducing atmosphere. The manufacturing method of the carbon dioxide absorber provided with. A reforming method of a fuel gas for reforming in a hydrogen production system using a steam reforming method, wherein a transition metal is supported on the surface of a substance mainly composed of Ba ₂ TiO _4. A method for reforming a fuel gas in a hydrogen production system, wherein a carbon dioxide absorbent having a catalytic function is used. The transition metal supported on the surface of the substance containing Ba ₂ TiO ₄ as a main component is Ni, and the ratio of Ni to the total amount of the substance containing Ba ₂ TiO ₄ as a main component and Ni is 1 6. The method for reforming a fuel gas in a hydrogen production system according to claim 5, wherein the carbon dioxide absorbent having a steam reforming catalyst function of at least wt% is used.

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