JPS6137735B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to fuel cells.

Since the oil crisis, there has been a desire to develop power converters with excellent thermal efficiency from the standpoint of energy conservation.
Among them, H ₂ - O ₂ fuel cells have a theoretical energy conversion efficiency of about 83%, which makes them much superior compared to other heat engines, and their activity performance as a fuel cell is also better than other types. Due to its excellent features, interest in using it for transportation is increasing.

However, when adapting fuel cells for transportation, there are difficulties in how to store hydrogen as fuel.
That is, storage as cylinders of _H2 gas or metal hydrides does not result in total energy savings due to their large weight.

Therefore, in order to reduce the total weight (mobile vehicle body, fuel cell main body, fuel storage or converter), it is necessary to take special measures to store and convert fuel.

Therefore, hydrogen as a fuel can be generated by catalytic pyrolysis or catalytic reforming of liquid hydrocarbons or alcohols, and these liquid hydrocarbons or alcohols do not require special precautions in storage. The development of fuel cells for transportation that use liquid hydrocarbons containing alcohol as fuel is attracting attention at home and abroad because it has the advantage of being able to supply fuel for transportation as easily as in conventional gasoline-powered vehicles.

However, when liquid hydrocarbons are used as fuel, methanol and liquefied natural gas are promising as alternative fuels for petroleum, and the basic system of conventional fuel cells using these as fuel is as shown in Figure 1. It was summer. That is, fuel from a fuel tank 1 is supplied to a reformer 2 containing a catalyst, and reformed in this reformer 2 according to the following reaction formula.

In the case of methanol a・CH ₃ OH→b・H ₂ +c・CO+d・CH ₄ (catalytic reforming) a・CH ₃ OH+b・H ₂ O→c・H ₂ +d・CO ₂ +
e・CO+f・CH (catalytic steam reforming) For liquefied natural gas a・CH ₄ +b・H ₂ O→c・H ₂ +d・CO+e・
CO ₂ (catalytic steam reforming) where a, b, cd, e, f are stoichiometric numbers.

In the unpurified gas obtained in reformer 2 in this way,
In order to purify H ₂ (particularly because CO in the unpurified gas is highly active and is a poisonous substance that adsorbs to the H ₂ fuel electrode and significantly reduces the activation performance), a shift device 3 and a methanator device 4 are used. Alternatively, the fuel is introduced into the fuel electrode chamber 6 through a large-scale purifier such as a purifier 5 using a Pd--Ag alloy membrane.

Therefore, since the fuel gas purification part is significantly larger than other components, there is a drawback that it is not an energy-saving fuel cell that uses liquid hydrocarbon containing alcohol as fuel.

Therefore, it is required to reduce the total weight by making the gas purification part, which is essential for maintaining the life of the battery, compact, or by performing purification using a better method.

The shift device 3 is a device that, when CO and water vapor are reacted on a catalyst, becomes CO+H ₂ O→CO ₂ +H ₂ and removes CO according to this reaction formula. In addition, the methanator device 4 is
CO is reacted with H ₂ and CO is removed according to the following reaction formula: CO + 3H ₂ → CH ₄ + H ₂ O.

Also, what is hydrogen purifier 5 using Pd-Ag alloy membrane?
It is a system that selectively allows only H ₂ gas to pass through, and has the drawbacks of being large-sized and expensive because it uses a large amount of precious metals for purification.

In view of the above-mentioned conventional drawbacks, the present invention provides a mobile fuel cell using liquid hydrocarbon as fuel.
In front of the H ₂ - O ₂ fuel cell, another stage of fuel cells for oxidizing CO generated when reforming liquid hydrocarbons can be installed, and the second stage can improve the thermal efficiency of the system's energy use. There is a way to get a fuel cell.

The present invention will be explained in detail below with reference to embodiments shown in FIGS. 2 to 4.

In the embodiment shown in FIG. 2, numeral 11 is a fuel tank containing liquid hydrocarbon fuel 12 containing alcohol. 13 is a fuel pump that supplies the fuel in the fuel tank 11 to the heat exchanger 14. The heat exchanger 14 heats and vaporizes a portion of the fuel using solar heat. 15 is a fuel gas generation device for decomposing or reforming fuel, and the heat exchanger 14
The partially heated and vaporized fuel is supplied to a heating burner 18 and a fuel heating vaporizer 19 via cylinders 16 and 17. 20 is a fuel air supply pump that supplies air to the fuel gas generation device 15. 2
1 is a catalyst bed for decomposing or reforming fuel, and this catalyst bed 21 includes a fuel heating vaporizer 22 and a heat insulating material 23.
The fuel heating vaporizer 19 is connected to the fuel heating vaporizer 19 through a pipe 24 covered with a pipe 24. 25 is a heat exchange part for utilizing the fuel gas used for heating the reforming or decomposition reaction for heating and keeping warm (80 to 160°C) the electrolyte aqueous solution of the fuel cell. Reference numeral 26 denotes a porous filter made of glass or a polymer membrane to facilitate diffusion of H ₂ and CO gas from the fuel gas generating device 15 into the solution. 27 is a carbon monoxide oxidizing electrode chamber having a carbon monoxide oxidizing electrode 28 that selectively and electrochemically oxidizes carbon monoxide. Reference numeral 29 denotes an oxygen electrode chamber having a first oxygen reduction electrode 32 and a second oxygen reduction electrode 33 into which air is introduced through an air introduction pipe 30 through a porous filter 31 and which reduces oxygen in the air. A diaphragm 34 made of an ion exchange membrane is provided at the bottom of the oxygen electrode chamber 29. Reference numeral 35 denotes a fuel electrode chamber having an electrode 39 for guiding H ₂ and CO ₂ gases from the carbon monoxide oxidizing electrode chamber 27 through a pipe 36 and a porous filter 37 to oxidize hydrogen in the electrolyte aqueous solution 38 . The electrolyte aqueous solution 38 is the carbon monoxide oxidizing electrode 2
7. When a common electrolyte aqueous solution is used for both the oxygen electrode chamber 29 and the fuel electrode chamber 35, an acid aqueous solution such as 2 to 5N orthophosphoric acid or sulfuric acid is used. Further, for the fuel electrode chamber 35 and the oxygen electrode chamber 29, an alkaline electrolyte aqueous solution may be used. Reference numeral 40 denotes a changeover switch that selectively switches the carbon monoxide oxidation electrode 28 and the first oxygen reduction electrode 32 to a variable resistor 41 or an external load 42, mainly auxiliary equipment. The electrodes 33, 39 are connected to an external load 43 (main load).

In the above configuration, a portion of the alcohol-containing liquid hydrocarbon fuel supplied from the fuel tank 11 via the fuel pump 13 is heated and vaporized by the heat exchanger 14 . This partially heated and vaporized fuel is supplied to the fuel heating vaporizers 19 and 22 via the tank 17. On the other hand, the heat exchanger 14
A part of the fuel is supplied via the fuel tank 16 to the heating fuel burner 18 of the catalyst bed 21 that decomposes or reforms the fuel, and is burned together with the air sent from the air supply pump 20. In addition, the fuel heated and vaporized via the fuel heating vaporizers 19 and 22 is decomposed or reformed by the catalyst bed 21, which has been previously heated to a temperature of 200° to 800°C, and is transformed into a hydrogen-rich mixed gas. The fuel is heated and cooled by heat exchange (70° to 150° C.) by the fuel heating vaporizer 19. This cooled gas mixture is selective for CO;
Then, the gas is introduced into a carbon monoxide oxidizing electrode chamber 27 equipped with an electrode 28 that can be electrochemically oxidized via a filter 26 that is effective for diffusing and dissolving the gas into the solution. Then, CO is selectively and electrochemically oxidized on the electrode 28. That is, the reaction of CO + H ₂ O → CO ₂ + 2H ⁺ 2e ^- results in carbon dioxide gas. In order to cause this electrochemical reaction, an external load 42 or a variable resistor 4 is connected between the electrode 32 of the oxygen electrode chamber 29 separated by a diaphragm 44 and this CO selective oxidation electrode 28.
By connecting any one of 1 with a changeover switch 40, a set of batteries can be formed, and selective oxidation of CO can be performed.

In this case, the changeover switch 40 determines whether the gas introduced into the CO selective oxidation electrode 28 is connected to the variable resistor 41 or the external load 42.
Depends on CO concentration. That is, when the CO concentration is 3 to 10% or higher, the system is connected to an external load 42 (for example, a fuel supply pump as an auxiliary device) to increase the energy utilization efficiency of the system. In this way, the CO concentration can be converted into an output or just a variable resistor 41
CO is either consumed by or
The selective oxidation of the gas progresses, and the gas containing CO obtained from the fuel gas generator 15 is purified ( _H2 gas with a purity of 99.9% to 99.99% relative to CO) and introduced into the fuel electrode chamber 35 through a pipe 36. do. This introduced fuel gas is electrochemically oxidized on the electrode 39, and the diaphragm 4
forming a set of H ₂ -O ₂ fuel cells with a second oxygen reduction electrode 33 located on the opposite side via 5;
Electrical energy is supplied to external load 43. In this case, water generated in the oxygen electrode chamber 26 where the first oxygen reduction electrode 32 and the second oxygen reduction electrode 33 are present is removed via the ion exchange membrane 34 for removing generated water. There is also a heat exchange section 2 that heats the electrolyte of the fuel cell to a high temperature of 80° to 160°C using the combustion gas provided to promote the decomposition or reforming reaction of the fuel.
5 is provided around the fuel cell chamber, the output of the battery can be improved.

Next, different embodiments of the present invention shown in FIGS. 3 and 4 will be explained. In the description of these embodiments, the same parts as those of the above embodiments are given the same reference numerals and redundant explanations will be omitted.

The embodiment shown in FIG. 3 is mainly different from the previous embodiment in that a set of cells for selectively electrochemically oxidizing CO and a H ₂ -O ₂ fuel cell are separated. By separating in this way, existing H ₂ - O ₂ fuel cells can be replaced by simply adding a set of cells that selectively and electrochemically oxidize CO to existing H ₂ - O ₂ fuel cells. Can be used without major modification. Note that the operation of this embodiment is essentially the same as that of the previous embodiment, but the heating of the battery electrolyte from the waste gas generated from the fuel gas generation device 15 is performed using H ₂ -
The difference is that it is applied only to _O2 fuel cells. This is because the modified CO concentration is low (3~
10% or less), this is to prevent the oxidation efficiency of the carbon monoxide oxidation electrode 28 that selectively oxidizes CO from increasing unnecessarily and increasing the size of the device.

The main difference between the embodiment shown in Figure 4 and the previous embodiment is that in order to increase the effective surface area of the carbon monoxide oxidation electrode that selectively and electrochemically oxidizes CO, the surface of the porous spherical alumina carrier is Ru is supported and dispersed as a catalyst to form a pellet-like electrode 46, and this pellet-like electrode 46 is made to flow within the carbon monoxide oxidizing electrode chamber 27 by circulation of an electrolytic solution, a so-called reticular fluidized bed type electrode 47. . In addition, 48 is a porous membrane for improving the stirring and mixing effect of the electrolyte solution, 49 is an electromagnetic pump for stirring and circulating the electrolyte solution, 50 is an AC converter, and 51 is an ion-conductive alumina or ion exchange resin, etc. It is a diaphragm consisting of With this configuration, the fluidized bed electrode 47 and the first oxygen reduction electrode 32 form a pair of batteries, and selectively reduce CO.
In addition, since electrochemical oxidation is performed and the resulting current is taken out as an output to operate the electromagnetic pump 49, the efficiency of selective oxidation of CO can be further improved than in the previous embodiment.

In addition, in the above embodiment, the carbon monoxide oxidation electrode 28
Ru has excellent performance in selective oxidation of CO
(ruthenium), WC (tungsten carbide), or a mixture thereof may be used as the catalyst. Moreover, as the liquid hydrocarbon containing alcohol, alcohol containing methanol and liquefied natural gas (LNG) may be used. Furthermore, copper oxide, zinc oxide, chromium oxide, and platinum are used as catalysts for reforming or decomposing liquid hydrocarbons and converting them into hydrogen-rich gas.
It is best to use nickel as the main source of LNG. In addition, as a method for reforming or decomposing liquid hydrocarbons, catalytic reforming or catalytic steam reforming is used for alcohols.
Catalytic steam reforming will be used for LNG. Further, as a method for supporting and dispersing the catalyst (Ru, WC) used in the CO selective oxidation electrode 28, for Ru, carbon powder is impregnated with an aqueous solution containing Ru ions, dried, and pressed onto a nickel mesh. Furthermore, Ru is deposited on an inexpensive tungsten thin plate (0.1 to 0.3 mm) by electrodeposition of several atomic layers, ion plating, or chemical vapor deposition. Regarding WC, tungsten powder is heated in a CO atmosphere (300° to 600°C), the resulting WC powder is mixed with carbon powder, and this is pressed onto a nickel mesh.

In addition, the fluidized bed type CO selective oxidation electrode 46 is a CO
Ru, which has excellent selective oxidation of
℃, 15-60 minutes), then baking (250℃-600℃ in air)
℃ for 1 to 5 hours). Furthermore, if the surface of the porous spherical alumina support is impregnated with an Ru ion aqueous solution in the presence of ammonium thiosulfate at a temperature range of 25°C to 60°C, Ru can be attached to the very surface layer of the alumina, and CO
It is highly effective against oxidation.

As is clear from the above description, in the present invention, a fuel cell that uses liquid hydrocarbon as fuel is a fuel cell that generates fuel gas containing carbon monoxide and hydrogen by decomposing or reforming liquid hydrocarbon. a carbon monoxide oxidizing electrode chamber having a carbon monoxide oxidizing electrode that selectively and electrochemically oxidizes carbon monoxide in the fuel gas supplied from the fuel gas generating device; An electrode having a first oxygen reduction electrode electrically connected to a carbon oxidation electrode, an oxygen electrode chamber to which oxygen is supplied, and an electrode that oxidizes hydrogen in the fuel gas supplied from the carbon monoxide oxidation electrode chamber. H ₂ −
In front of the O ₂ fuel cell, another stage of fuel cells is installed to oxidize carbon monoxide generated when reforming liquid hydrocarbons, and the second stage aims to improve the thermal efficiency of the system's energy use. I can do it. In addition, the present invention can be used for small mobile power sources including electric vehicles and on-site (nuclear power plants) that utilize hydrocarbon fuels with an extremely high total conversion efficiency of 40 to 50%.
It has excellent advantages such as being able to be used for power generation, etc.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing a conventional embodiment; Figure 2 is a system diagram showing a conventional embodiment;
The figure is a schematic explanatory diagram showing one embodiment of the present invention, and FIGS. 3 and 4 are schematic explanatory diagrams showing different embodiments of the present invention, respectively. 11...Fuel tank, 12...Liquid hydrocarbon fuel,
13... Fuel pump, 14... Heat exchanger, 15... Fuel gas generator, 18... Heating burner, 19... Fuel heating vaporizer, 20... Air supply pump, 21... Catalyst bed, 27... Carbon monoxide oxidizing electrode chamber, 28... Carbon monoxide oxidation electrode, 29... Oxygen electrode chamber, 32... First oxygen reduction electrode, 33... Second oxygen reduction electrode, 35... Fuel electrode chamber, 38... Electrolyte aqueous solution, 39... Electrode for oxidizing hydrogen , 40... Selector switch, 41... Variable resistor, 42... External load, 43... External load, 44,
45...Diaphragm, 46...Pellet electrode, 47...Reticular fluidized bed electrode.

Claims (1)

[Claims] 1. A fuel gas generation device that generates a fuel gas containing carbon monoxide and hydrogen by decomposing or reforming liquid hydrocarbons, and monoxide in the fuel gas supplied from this fuel gas generation device. A carbon monoxide oxidation electrode chamber having a carbon monoxide oxidation electrode that selectively and electrochemically oxidizes carbon, and a first oxygen reduction electrode electrically connected to the carbon monoxide oxidation electrode. , an oxygen electrode chamber to which oxygen is supplied, a fuel electrode chamber having an electrode that oxidizes hydrogen in the fuel gas supplied from the carbon monoxide oxide electrode chamber, and a second electrode connected to the electrode that oxidizes the hydrogen. 1. A fuel cell comprising: an oxygen reduction electrode, and an oxygen electrode chamber to which oxygen is supplied. 2. The fuel cell according to claim 1, wherein the carbon monoxide oxidation electrode uses ruthenium, tungsten carbide (WC), or a mixture of ruthenium and tungsten carbide as a catalyst. 3. The fuel cell according to claim 1 or 2, wherein the carbon monoxide oxidation electrode is a reticular fluidized bed type electrode.