JPH05190194A - Inside reforming type molten carbonate type fuel cell - Google Patents

Abstract

PURPOSE:To improve the cell performance and durability by using a platinum group element group regenerating catalyst loaded on a zirconia group carrier and a specific mixed alkaline carbonate electrolyte. CONSTITUTION:As a regenerating catalyst 7, is used a platinum group element group reforming catalyst loaded on a zirconia group carrier. As the zirconia carrier, is used a partially stabilized zirconia, and the yttria containing zirconia is preferable. As the platinum group element, are preferable rhodium and ruthenium. Further, as an electrolyte, is used a two-component substance consisting of lithium carbonate and sodium carbonate, or a mixed substance consisting of the above-described two-component substance as main component and other carbonate compounded. The groove of a fuel gas passge 6 of a regeneration reactor 1 is filled with the catalyst 7, and a Ni porous plate 2 impregnated with the electrolyte and an electrolyte holding plate 3 are laminated, and sealed by a sealing plate 4. Accordingly, performance can be maintained for a long period.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention suppresses deterioration of a catalyst,
The present invention relates to a direct internal reforming molten carbonate fuel cell capable of extending the life of the catalyst and enhancing the cell performance and durability.

[0002]

2. Description of the Related Art A mixture of alkali metal carbonates is usually used as an electrolyte for molten carbonate fuel cells. That is, lithium carbonate-potassium carbonate, lithium carbonate-
Among them, sodium carbonate, lithium carbonate-potassium carbonate-sodium carbonate, etc., and particularly, a binary mixture of lithium carbonate-potassium carbonate (molar ratio 62:38) is most studied and used.

On the other hand, regarding the reforming method of the fuel supplied to the fuel cell, an internal reforming method of reforming the fuel inside the cell is used instead of the external reforming method in which the reforming device is provided separately from the fuel cell body. Since it can be expected to be downsized and power generation efficiency, it has been attracting attention in recent years and is under development. The internal reforming system is a direct internal reforming system in which a reforming catalyst is arranged in a fuel gas chamber opened to the cathode, and a catalyst chamber is provided in a position adjacent to the fuel gas chamber, and the reformed gas is supplied there. It is divided into an indirect internal reforming type that leads to the fuel gas chamber. In the direct internal reforming system, since the catalyst is arranged in the vicinity of the electrolyte layer separated by the porous cathode layer, there is a problem that the catalyst is easily contaminated and poisoned by the alkali carbonate as the electrolyte. Therefore, in order to put a direct internal reforming fuel cell into practical use, it is possible to prevent the catalyst from being deteriorated and the activity from being lowered by the alkali carbonate.
It is an important issue to extend the battery life.

[0004]

SUMMARY OF THE INVENTION The present invention overcomes the disadvantages of the conventional direct internal reforming molten carbonate fuel cell and protects the catalyst from alkali carbonate, and therefore, a special protective material is used. Or suppressing the deterioration of the catalyst without complicated measures such as providing a structure or improving the structure of the fuel gas chamber,
The purpose of the present invention is to provide a direct internal reforming molten carbonate fuel cell having a long catalyst life and excellent cell performance and durability.

[0005]

The inventors of the present invention have conducted various researches to develop a direct internal reforming molten carbonate fuel cell having the above-mentioned preferable characteristics, and as a result, the conventional lithium carbonate was used as an electrolyte. -A mixture of lithium carbonate-sodium carbonate or a mixture system mainly containing this and another carbonate was used instead of the potassium carbonate mixed system, and it was supported on a zirconia-based carrier as a reforming catalyst affected by the electrolyte. It has been found that the object can be achieved by adopting a white metal element-based catalyst and thus using a specific electrolyte and a specific reforming catalyst in combination, and has completed the present invention based on this finding. ..

That is, the present invention has a white metal element reforming catalyst supported on a zirconia-based carrier, and is mainly composed of a two-component system composed of lithium carbonate and sodium carbonate as an electrolyte or another carbonate. The present invention provides a direct internal reforming molten carbonate fuel cell characterized by using a mixed system containing a salt.

As the electrolyte used in the present invention, a mixed system composed of lithium carbonate and sodium carbonate, or a mixed system mainly containing this and another carbonate as a third component is used. The molar ratio of lithium to sodium (Li: Na) is usually selected in the range of 60:40 to 40:60, preferably 55:45 to 45:55.

Rhodium, ruthenium, palladium, platinum or a mixture thereof is used as a white metal element (hereinafter referred to as a catalyst metal) as a catalytically active component of the reforming catalyst used in the present invention, and rhodium or ruthenium is particularly preferable. .. The ratio of the catalyst metal is not particularly limited, but is usually 0.0 with respect to the total amount of the catalyst, that is, the total amount of the catalyst metal and the carrier.
It is selected in the range of 1 to 10% by weight, preferably 0.1 to 3% by weight. If this ratio is too small, the catalytic activity is low and reforming of the hydrocarbon is not sufficient, and if it is too large, the reforming effect commensurate with the amount used cannot be obtained, which is uneconomical.

The carrier on which the catalytic metal is supported is a zirconia-based carrier or a mixed carrier in which the zirconia-based carrier component contains an alumina-based component in a predetermined ratio or less.

Examples of the zirconia-based carrier component include partially stabilized zirconia and stabilized zirconia. Particularly, zirconia containing yttria is advantageously used. In the yttria-containing zirconia, the content ratio of yttria is 0.5 to 20 mol%, preferably 1.5.
It is selected in the range of 10 mol%. If this proportion is less than 0.5 mol%, the effect of inclusion is not sufficient, and if it exceeds 20 mol%, the stabilization of the crystal system becomes insufficient.

To produce zirconia containing yttria, for example, a method of firing a powder mixture of yttria and zirconia in a predetermined ratio, a coprecipitation method using a yttrium compound and a zirconium compound, a hydrolysis method or an alkoxide method is used. Done by. Of these, the coprecipitation method is preferred, particularly yttrium halide such as YCl ₃ and Zr.
A coprecipitation method using zirconium oxyhalide such as OCl ₂ is used.

The alumina-based component in the mixed carrier enhances the mechanical strength of the catalyst carrier, and the ratio of the expensive zirconia-based carrier to the catalytic performance of the zirconia-based carrier such as high activity and the effect of suppressing carbon formation. The amount is reduced within a range not touched, thereby contributing to the cost reduction of the catalyst and thus the fuel cell as a whole.

As the alumina-based component, alumina alone or a mixture of alumina with at least one selected from oxides of metal elements and oxides of metalloid elements is used. Examples of the metal element include Mg, Ca,
Alkaline earth metals such as Ba, Ti, Cr, Mn, Fe
Examples of the semi-metal element include S
i, B, P and the like can be mentioned.

The proportion of the alumina component is preferably 80% by weight or less, more preferably 70% by weight or less, based on the total amount of the carrier. If this proportion exceeds 80% by weight, the reforming characteristics of the catalyst and the effect of suppressing coking are deteriorated.

As a preferable reforming catalyst of the present invention, a zirconia carrier containing yttria, or a carrier prepared by blending the zirconia carrier with an alumina-based component is loaded with rhodium, ruthenium, palladium, platinum or a mixture thereof as a catalyst metal. The most suitable catalyst metal is rhodium or ruthenium.

A conventional method is used for supporting the catalyst metal on the carrier, but an impregnation method is usually used. The shape of the carrier is not particularly limited, and examples thereof include a columnar shape, a ring shape, and a spherical shape. The size of the carrier is 0.5 to 5 mm, preferably 1 to 2 mm for placement in the fuel gas chamber of the fuel cell. It is good to set the range.

The steam reforming reaction using a catalyst is usually 300
It is carried out at ˜1000 ° C., but since the catalyst used in the present invention hardly causes coking even at a reaction temperature of 700 ° C. or lower, it is particularly preferable as an internal reforming catalyst for a molten carbonate fuel cell. In the reforming reaction with a catalyst, the reaction pressure is usually selected in the range of 0.01 to 50 kg / cm ² G, preferably 0.1 to 30 kg / cm ² G. Molar ratio of water vapor and carbon in the source gas (hereinafter referred to as S / C)
Is preferably as small as possible because it is economically advantageous not to use excess steam for the reaction, but on the other hand, if S / C is too small, coking tends to occur, so S / C
Is preferably 1.2 or more, more preferably 1.5 or more, in which caulking is less likely to occur.

The steam reforming reaction in which the catalyst of the present invention is effectively used is not particularly limited. For example, light hydrocarbon-containing gas such as LNG and LPG, petroleum fraction such as naphtha and kerosene, coal liquefied oil and the like. Examples include a reaction in which hydrogen, carbon monoxide, carbon dioxide, or methane is produced by catalytically cracking a raw material mainly composed of a hydrocarbon, particularly a hydrocarbon having a relatively small molecular weight (about C _{1 to} C ₂₀ ). ..

The raw material preferably consists of only hydrocarbons, but may contain a trace amount of different components. The raw materials advantageously have a specific gravity of 0.80 or less, preferably 0.75 or less and a C / H weight ratio of 6.5 or less, preferably 6.0 or less. When the heterogeneous component is a sulfur compound, a raw material with a high content will cause deterioration of the catalyst.
It is preferably 1 ppm or less, more preferably 0.5 ppm or less, due to hydrodesulfurization.

The steam reforming catalyst used in the present invention has a high activity, a high hydrogen production rate, and a low S / C ratio.
And has a very excellent property that coking hardly occurs even in the operating temperature range of a fuel cell of 600 to 700 ° C., and also has excellent stability against an electrolyte mainly composed of lithium carbonate-sodium carbonate. Therefore, it is extremely advantageous as a reforming catalyst for a direct internal reforming fuel cell that is easily affected by electrolyte vapor.

[0021]

INDUSTRIAL APPLICABILITY The internal reforming fuel cell of the present invention has an excellent reforming catalyst which has high reaction activity and hardly causes coking, and a specific mixture which minimizes the influence of pollution and deterioration on the catalyst. The combination with the alkali carbonate electrolyte has the remarkable effect that the performance can be maintained for a long period of time and the durability can be improved.

[0022]

The present invention will be described in more detail with reference to Examples.

Example 2 2.5 parts of zirconia powder containing 3 mol% yttria
Molded into a cylinder with a diameter of 2.5 mm and a length of 2.5 mm, 1000 ° C
It was baked for 3 hours to prepare a carrier. The carrier was impregnated with an aqueous rhodium chloride solution so that 0.5% by weight of rhodium was supported, and dried at 100 ° C. for 3 hours to obtain catalyst particles.

The steam reforming activity of this catalyst was evaluated using propane as a reforming raw material by using a single cell type reactor in which a fuel gas passage groove was provided on a stainless steel disc surface of 10 cm ² .

FIG. 1 shows a schematic view of a vertical cross section perpendicular to the gas flow path of the reforming reactor. That is, in FIG. 1, the reforming catalyst 7 is filled in the groove of the fuel gas flow path 6 of the reactor 1 and is preliminarily impregnated with lithium carbonate-sodium carbonate (Li / Na molar ratio = 52/48) as an electrolyte. The plate 2 and the electrolyte holding plate 3 are stacked and sealed with a stainless steel sealing plate 4.

In the process of raising the temperature of the reactor, first, heated air was supplied, and then heated H ₂ , CO ₂ , H ₂ O mixed gas was switched to reach a steady state of 650 ° C. which is the operating temperature of the fuel cell. After that, the reforming reaction was started. Propane, water vapor and nitrogen gas are 2.5, 21, 48 gas-ml / m, respectively
The reforming reaction was carried out by supplying the reactor at an in ratio. S / C of supply gas is 2.8, space velocity GHSV is 1020h
It was ^-1 . FIG. 2 is a graph showing the relationship between the reaction elapsed time and the propane reaction rate (%).

Reference Example The result of the reforming reaction was carried out in the same manner as in the example except that an electrolyte-free nickel porous plate without an electrolyte was used instead of the electrolyte-impregnated nickel porous plate 2. The test is shown in FIG.

Comparative Example FIG. 2 shows the results of the reforming reaction carried out in the same manner as in the Example except that the electrolyte was changed to lithium carbonate-potassium carbonate (Li / K molar ratio = 62/38).

Therefore, in the embodiment of the present invention using a rhodium catalyst supported on a yttria-containing zirconia carrier and using a lithium carbonate-sodium carbonate binary electrolyte,
The reaction rate is almost constant at about 98% even after the reaction time of 400 hours, and the difference from the blank test is about 2%, which is extremely small, whereas the comparison using other conventional lithium carbonate-potassium carbonate electrolytes In the examples, the reaction rate greatly decreases with the reaction elapsed time, and the reaction rate after the reaction elapsed time of 300 hours does not reach 90%, which shows that the effect of the present invention is unique.

[Brief description of drawings]

FIG. 1 is an explanatory view of a single cell type reactor.

FIG. 2 is a graph showing a relationship between a reaction elapsed time and a propane reaction rate in a single cell type reforming reaction.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor ▲ Sai ▼ Akira Nishitsurugaoka 1-3-1 Oi-cho, Iruma-gun, Saitama Tonen Co., Ltd. Research Institute (72) Satoshi Sakurada Oi-cho, Iruma-gun, Saitama Nishitsurugaoka 1-3-1, Tonen Co., Ltd.

Claims (1)

[Claims] 1. A zirconia-based carrier having a white metal element-based reforming catalyst and a two-component system comprising lithium carbonate and sodium carbonate as an electrolyte, or mainly containing this, and further containing another carbonate. A direct internal reforming molten carbonate fuel cell characterized by using a mixed system.