JP2002208425A - Fuel reformer for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel reformer which can generate high-purity hydrogen or even, does not need outer heating. SOLUTION: The fuel reformer generates hydrogen from fuel and steam, and is equipped with a fuel reforming catalyst layer filled with steam reforming catalyst of fuel, a reforming fuel gas supply means introducing fuel and reforming fuel gas containing steam to the fuel reforming catalyst layer, a reforming fuel gas exhausting means exhausting hydrogen principal component gas generated by steam reforming from the fuel reforming catalyst layer, and a metal oxide layer provided at downstream of the fuel reforming catalyst layer to absorb carbon dioxide contained in the reforming fuel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel reformer for a fuel cell, and more particularly to a fuel reformer for a fuel cell using a metal oxide and a fuel reforming method using the same.

[0002]

2. Description of the Related Art A fuel reformer for producing hydrogen and carbon dioxide from a fuel such as methane or methanol and water (steam) is known as a device for supplying a fuel gas to a fuel cell. In a fuel cell, a fuel gas containing hydrogen is supplied to a cathode side, and an oxidizing gas containing oxygen is supplied to an anode side, and an electromotive force is obtained by an electrochemical reaction occurring at both electrodes.

First, in a fuel reformer using methane-containing gas and steam, the following methane reforming reaction is generally performed to produce hydrogen and carbon dioxide. CH4 + 2H2O → CO2 + 4H2 ΔH = + 164.8 KJ / mol (1) This reaction is an endothermic reaction, and is usually carried out at about 800 ° C. while using a packed bed reactor containing a nickel catalyst and heating gas fuel from the outside. The reaction reforms the fuel at a ratio of 4 moles of hydrogen and 1 mole of carbon dioxide, and this mixed gas is used as a fuel in a fuel cell.

On the other hand, in a fuel reformer using methanol and steam, the following methanol reforming reaction is generally performed to produce hydrogen and carbon dioxide. CH3OH (g) + H2O (g) → CO2 + 3H2 ΔH = + 49.5 KJ / mol (2) This reaction is an endothermic reaction, and similarly to the case of methane, a packed bed reactor containing a nickel catalyst is used. The reaction is performed while heating the gaseous fuel. In this case, the reaction is carried out at about 200 to 300 ° C., the fuel is reformed at a ratio of 3 mol of hydrogen and 1 mol of carbon dioxide, and this mixed gas is used as a fuel in a fuel cell.

[0005]

As described above, since the above-mentioned reforming reaction is an endothermic reaction, it is necessary to supply thermal energy to make the reforming reaction proceed. For example, a burner or a heater is provided to perform external heating. Since this method is usually performed, and furthermore, carbon dioxide is generated together, high-concentration hydrogen is desired to improve the performance of the fuel cell.

Accordingly, the present inventors have conducted various studies in order to obtain a fuel reformer which can produce high-purity hydrogen or which does not require external heating, and arrived at the present invention.

[0007]

A fuel reformer for a fuel cell according to a first aspect of the present invention is a fuel reformer for producing hydrogen from fuel and steam, and comprises a catalyst for steam reforming of fuel. A filled fuel reforming catalyst layer, a reforming fuel gas supply means for introducing a reforming fuel gas containing fuel and steam into the fuel reforming catalyst layer, and a hydrogen-containing gas generated by steam reforming into the fuel reforming catalyst layer. Means for discharging reformed fuel gas from the reformed catalyst layer, and a metal oxide layer provided downstream of the fuel reformed catalyst layer for absorbing carbon dioxide contained in the reformed fuel. The gist is a fuel reformer for a fuel cell.

In the present invention, the fuel to be reformed includes methane-containing gas such as methane and natural gas, gasoline, naphtha,
Although hydrocarbons such as light oil and LP gas, and methanol are common, the case of methane and methanol will be described below. Further, as the metal oxide, those that react with carbon dioxide to generate a metal carbonate are used, and calcium, magnesium, copper,
Oxides such as iron and nickel are preferred. The choice depends on the type of fuel and the like, but calcium oxide for methane and magnesium oxide for methanol are particularly suitable for obtaining a fuel reformer that does not require external heating.

In the fuel reformer configured as described above, when methane and steam are introduced into the methane reforming catalyst layer, hydrogen and carbon dioxide are generated at about 800.degree. Then, when these are introduced into the calcium oxide layer, 80
At around 0 ° C., calcium oxide reacts with carbon dioxide to produce calcium carbonate. CaO + CO2 → CaCO3 ΔH = −178.1 kJ / mol (3) As described above, carbon dioxide is selectively absorbed by the calcium oxide layer, and hydrogen flows out of the calcium layer. Therefore, a high concentration of hydrogen is obtained, and the performance of the fuel cell is improved. Furthermore, carbon dioxide can be recovered without releasing it to the atmosphere. On the other hand, when methanol and water vapor are introduced into the methanol reforming catalyst layer, hydrogen and carbon dioxide are generated at about 200 ° C. to 300 ° C., which is suitable for achieving a practical level of reaction rate. Equilibrium proceeds even at 100 ° C. or less). Then, when these are introduced into the magnesium oxide layer, 300 ° C. to 45 ° C.
At around 0 ° C., magnesium oxide reacts with carbon dioxide to produce magnesium carbonate.

MgO + CO 2 → MgCO 3 ΔH = −118.2 kJ / mol (4) As described above, carbon dioxide is selectively absorbed by the magnesium oxide layer, and hydrogen flows out of the magnesium layer. Therefore, a high concentration of hydrogen is obtained, and the performance of the fuel cell is improved. Furthermore, carbon dioxide can be recovered without releasing it to the atmosphere. A fuel reformer for a fuel cell according to a second aspect of the present invention is a fuel reformer for producing hydrogen from fuel and steam, and a fuel reforming catalyst layer filled with a catalyst for steam reforming of fuel; Fuel gas supply means for introducing a reforming fuel gas containing water and steam into the fuel reforming catalyst layer, and a reformed fuel discharging hydrogen main component gas generated by steam reforming from the fuel reforming catalyst layer A gas exhaust means, and a metal oxide layer provided downstream of the fuel reforming catalyst layer for absorbing carbon dioxide contained in the reformed fuel, wherein the fuel reforming catalyst layer and the metal oxidation A gist of the present invention is a fuel reformer for a fuel cell, in which at least two sets of material layers are alternately stacked. In the fuel reformer configured as described above, when methane and steam are introduced into the methane reforming catalyst layer, hydrogen and carbon dioxide are generated at about 800 ° C. Since the catalyst layer is alternately stacked with the downstream calcium oxide layer, the generated carbon dioxide is absorbed by the downstream calcium oxide layer. At this time, as described above, the exothermic reaction heat of carbonation (178.1 kJ / mo)
1) is generated. Since this heat of formation is larger than the required calorie (-164.8 kJ / mol) of the methane reforming endothermic reaction,
The heat of carbonation may provide the heat of the subsequent reforming reaction. The following reaction formula is satisfied in the whole layer.

CaO + CH4 + 2H2O → CaCO3 + 4H2O ΔH = −13.3 kJ / mol (5) That is, there is an exotherm of 13.3 kJ / mol, and this reaction proceeds without external heat supply. In this way, it is possible to realize that the fuel reformer can supply necessary heat by itself without external heating. On the other hand, when methanol and steam are introduced into the methanol reforming catalyst layer, hydrogen and carbon dioxide are preferably generated at about 200 ° C. to 300 ° C. Since the catalyst layer is alternately stacked with the magnesium oxide layer on the downstream side, the generated carbon dioxide is absorbed by the magnesium oxide layer on the downstream side. At this time, the exothermic heat of carbonation (118.2 kJ / mol) is generated as described above. Since the heat of formation is larger than the required heat of the endothermic methanol reforming reaction (-49.5 kJ / mol), the heat of reforming can be supplied by the heat of carbonation. The following reaction formula is satisfied in the whole layer.

MgO + CH3OH + H2O → MgCO3 + 3H2 ΔH = −68.7 kJ / mol (6) That is, there is a heat generation of 68.7 kJ / mol, and this reaction proceeds without external heat supply. In this way, it is possible to realize that the fuel reformer can supply necessary heat by itself without external heating.

Further, a fuel reformer for a fuel cell according to a third aspect of the present invention is a fuel reformer for producing hydrogen from fuel and steam, which comprises a catalyst for steam reforming of fuel and a metal oxide. A filled fuel reforming catalyst layer, a reforming fuel gas supply means for introducing a reforming fuel gas containing fuel and steam into the fuel reforming catalyst layer, and a hydrogen-containing gas produced by steam reforming. A gist of the present invention is a fuel cell fuel reformer including a reformed fuel gas discharging unit that discharges gas from a reforming catalyst layer. In this embodiment, since the catalyst and calcium oxide are mixed and filled in the methane reforming catalyst layer, the reaction heat self-supply type fuel reforming can be performed more quickly. In this embodiment, since the catalyst and the magnesium oxide are mixed and filled in the methanol reforming catalyst layer, the reaction heat self-supply type fuel reforming can be performed more quickly.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION First, the case where a methane-containing gas is used as a fuel gas in the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing a reformer according to the first to third embodiments of the present invention. Reference numeral a denotes a carbon dioxide absorption type reformer requiring heating, in which methane is introduced into the reaction tube (1) together with steam as a methane-containing gas. The reaction tube (1) is maintained at a predetermined temperature in a heating furnace (4), and the catalyst layer (2) is filled with Ni-supported alumina as a steam reforming catalyst. In the catalyst layer, a reforming reaction is performed at about 800 ° C., and a product gas containing hydrogen and carbon dioxide flows out and is introduced into a downstream metal oxide layer (3) filled with calcium oxide. There, carbon dioxide is selectively absorbed, and a high concentration of hydrogen flows out of the metal oxide layer. The catalyst is not limited to Ni, and the carrier may be silica or the like instead of alumina. b indicates a stacked reformer in which two or more sets of Ni-supported catalyst layers (2) and metal oxide layers (3) filled with calcium oxide are alternately stacked, and c indicates a catalyst obtained by mixing Ni-supported alumina and calcium oxide. 5 shows a mixed reformer having a / metal oxide mixed layer (5). Both b and c are self-supplying types of reaction heat, basically do not require heating, and only have a preheater (not shown) for starting.

In the fuel reforming of the present invention, a small amount of carbon monoxide is generated as in the conventional fuel reforming. This carbon monoxide poisons the catalyst and has an adverse effect, so it is necessary to convert it to carbon dioxide. Therefore, it is converted to carbon dioxide by a converter provided downstream of the reformer. In the reformer of the present invention, carbon dioxide generated in the Ni catalyst layer is absorbed by carbonation and its concentration decreases, so that the reaction of carbon monoxide to carbon dioxide proceeds more equilibrium theoretically. For this reason, generation of carbon monoxide is suppressed. Since carbon monoxide poisons the electrode catalyst (platinum-based) of the fuel cell and lowers the cell characteristics, a carbon monoxide converter is usually provided downstream of the reformer. The load on the vessel may be reduced or eliminated.

FIG. 2 shows the progress of the main reaction in the fuel reformer of the present invention by a chemical reaction equilibrium line.
3 shows an equilibrium relationship between calcium oxide / carbon dioxide, calcium oxide / water, and a fuel reforming reaction. The calcium oxide / carbon dioxide system is the reaction of interest, and the calcium oxide / water system is a competitive reaction expected from the gas used. The pressure P on the vertical axis indicates the carbon dioxide pressure and the water vapor pressure in each reaction, and indicates the degree of progress of the degree of decomposition (leftward reaction) (the larger the P, the better the decomposition). Only the reforming reaction shows a reaction equilibrium constant K. For example, at around 700 ° C., calcium carbonate hardly decomposes. That is, carbonation of calcium oxide proceeds well. Further, it can be seen that the fuel reforming reaction proceeds rightward (on the hydrogen generation side). On the other hand, calcium hydroxide is almost completely decomposed into calcium oxide, so that absorption of water into calcium oxide hardly occurs. From this, it can be thermodynamically confirmed that the reforming reaction proceeds well in this temperature range, and the generated carbon dioxide undergoes a carbonation reaction with calcium oxide.

FIG. 3 shows a change in the temperature of the reaction layer due to a change in the carbonation pressure at an initial reaction temperature of 650 ° C.
That is, in a packed-bed reactor of about 1 kg of a calcium oxide reaction sample, when carbon dioxide is introduced into the reaction layer at an initial temperature of 650 ° C. at a reaction time of 0 minutes, the reaction proceeds promptly. Then, the reaction layer is rapidly heated to 900 to 1000 ° C. by the reaction heat.
Temperature rises. From this, absorption of carbon dioxide into calcium oxide at about 700 to 800 ° C. (carbonation)
Progressed sufficiently, indicating that self-reaction heat supply was possible.

On the other hand, when methanol fuel is used in the present invention, the reaction temperature is different in place of methanol / magnesium oxide instead of methane / calcium oxide as described above, but the above-mentioned FIGS. FIG. 4 shows the progress of the main reaction in the fuel reformer of the present invention using a chemical reaction equilibrium line when methanol fuel is used, and shows the relationship between magnesium oxide / carbon dioxide, magnesium oxide / water and the fuel reforming reaction. Shows the equilibrium relationship of The magnesium oxide / carbon dioxide system is the relevant reaction, and the magnesium oxide / water system is a competitive reaction expected from the gas used. The pressure P on the vertical axis indicates the carbon dioxide pressure and water vapor pressure in each reaction,
The degree of progress (leftward reaction) is shown (the larger the P, the better the decomposition). Only the reforming reaction shows a reaction equilibrium constant K. For example, at around 300 ° C., magnesium carbonate hardly decomposes. That is, the carbonation of magnesium oxide proceeds well. Further, it can be seen that the fuel reforming reaction proceeds rightward (on the hydrogen generation side). On the other hand, magnesium hydroxide is almost completely decomposed into magnesium oxide, so that almost no water is absorbed into magnesium oxide. From this, it can be thermodynamically confirmed that the reforming reaction proceeds well in this temperature range, and the generated carbon dioxide undergoes a carbonation reaction with magnesium oxide.

Since the magnesium carbonate produced by the formula (6) is decomposed at normal pressure by heating and returns to magnesium oxide,
It can be used again for fuel reforming. Equation (2)
Is different depending on the phase of the reaction raw material.
For example, when methanol is in the liquid phase, CH3OH (L) + H2O (g) → CO2 + 3H2 ΔH = + 87.0 KJ / mol (2-2), and when both methanol and water are in the liquid phase, CH3OH (L) +
H2O (L) → CO2 + 3H2 ΔH = + 131.0K
J / mol (2-3). Mg represented by formula (6)
The calorific value in O-carbonation is larger than the calorific value required for the reaction of the formula (2), and the exothermic temperature is about 300 ° C. Therefore,
The reforming reaction heat of the formula (2) can be sufficiently supplied, and a self-reaction that does not require external heating is also possible. Furthermore, equation (6)
Is larger than the amount of heat required for the reaction of the formula (2-2), and the excess heat can be used for vaporization of methanol.
On the other hand, the reaction of the formula (2-3) including the heat of vaporization of water is represented by the formula
Although the calorific value of (6) is insufficient, by using waste heat from a fuel cell (for example, a fuel cell for an automobile) together, the expression (2-
3) Self-progression is also possible.

As described above, according to the present invention, it is possible to provide a fuel reformer that can produce high-purity hydrogen or that does not require external heating.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an embodiment of a fuel reformer of the present invention.

FIG. 2 is a diagram showing a chemical reaction equilibrium line of a main reaction in the fuel reformer of the present invention.

FIG. 3 is a diagram showing a change in a reaction layer temperature accompanying a change in carbonation pressure in the fuel reformer of the present invention.

FIG. 4 is a diagram showing a chemical reaction equilibrium line of a main reaction in the fuel reformer of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reaction tube 2 ... Catalyst layer 3 ... Metal oxide layer 4 ... Heating furnace 5 ... Catalyst / metal oxide mixed layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C10K 3/04 C10K 3/04 F term (Reference) 4G040 EA02 EA03 EA06 EB23 EC07 FA02 FB04 FC02 FD07 FE03 4G140 EA02 EA03 EA06 EB23 EC07 FA02 FB04 FC02 FD07 FE03 4H060 AA01 AA02 BB22 BB33 DD02 EE03 FF03 GG02 5H027 AA02 BA01 BA08 BA16

Claims (7)

[Claims] 1. A fuel reformer for producing hydrogen from a fuel and steam, comprising: a fuel reforming catalyst layer filled with a fuel steam reforming catalyst; and a fuel gas for reforming containing fuel and steam. Reforming fuel gas supply means for introducing into the reforming catalyst layer, reformed fuel gas discharging means for discharging hydrogen main component gas generated by steam reforming from the fuel reforming catalyst layer, and contained in the reformed fuel In order to absorb carbon dioxide,
A fuel reformer for a fuel cell, comprising: a metal oxide layer provided downstream of the fuel reforming catalyst layer. 2. A fuel reformer for producing hydrogen from a fuel and steam, comprising: a fuel reforming catalyst layer filled with a steam reforming catalyst for fuel; and a fuel gas for reforming containing fuel and steam. Reforming fuel gas supply means for introducing into the reforming catalyst layer, reformed fuel gas discharging means for discharging hydrogen main component gas generated by steam reforming from the fuel reforming catalyst layer, and contained in the reformed fuel In order to absorb carbon dioxide,
A metal oxide layer provided downstream of the fuel reforming catalyst layer, wherein at least two or more sets of the fuel reforming catalyst layer and the metal oxide layer are alternately laminated. vessel. 3. A fuel reformer for producing hydrogen from a fuel and steam, comprising a fuel reforming catalyst layer filled with a fuel steam reforming catalyst and a metal oxide, a fuel and a reforming fuel containing steam. A reforming fuel gas supply means for introducing gas into the fuel reforming catalyst layer, and a reformed fuel gas discharging means for discharging hydrogen-based gas generated by steam reforming from the fuel reforming catalyst layer. A fuel reformer for fuel cells. 4. In a fuel reforming method for producing hydrogen from fuel and steam, a metal oxide layer is provided downstream of the fuel reforming catalyst layer, and the fuel and steam are introduced into the fuel reforming catalyst layer.
A method for reforming a fuel, comprising: introducing generated hydrogen and carbon dioxide into the metal oxide layer to selectively absorb carbon dioxide and allowing hydrogen to flow out of the metal oxide layer. 5. In a fuel reforming method for producing hydrogen from fuel and steam, at least two or more sets of a fuel reforming catalyst layer and a metal oxide layer downstream thereof are alternately stacked to convert the fuel and steam into the fuel. Introduced to the reforming catalyst layer, then, the generated hydrogen and carbon dioxide are introduced into the metal oxide layer to selectively absorb carbon dioxide, allow hydrogen to flow out of the metal oxide layer, and A method for reforming a fuel, characterized in that reaction heat generated in the fuel is supplied to the reforming catalyst layer further downstream as reforming reaction heat. 6. A fuel reforming method for producing hydrogen from fuel and water vapor, wherein a fuel reforming catalyst layer in which a metal oxide is mixed with a catalyst is provided, and fuel and water are introduced into the reforming catalyst layer. A fuel reforming method, characterized in that only hydrogen is discharged from the fuel reforming catalyst layer. 7. The fuel reforming catalyst layer according to claim 6, wherein after the reaction is completed, the fuel reforming catalyst layer is heated from the outside, a decarboxylation reaction of the generated metal carbonate proceeds, carbon dioxide is recovered, and the metal oxide is removed. A fuel reforming method characterized by regenerating.