JP2005071970A - Fuel cell that utilizes methanol - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that, when compared with an inside reformation type fuel cell, the portability of an outside reformation type portable fuel cell that utilizes methanol is hindered by a reforming device though it is efficient. <P>SOLUTION: On the fuel cell system including a methanol oxidation type steam reforming device, the methanol reformation at the outside of the fuel cell is carried out by setting a reformation temperature for restraining the generation of CO to 180 to 250°C, and reformation of steam and oxidation of CO are simultaneously proceeded in a reforming catalyst by mixing air in reformed gas. The quantity of the fuel and the air to be supplied to the fuel cell is controlled only by a pressurized air. The efficiency of the reformation is improved and starting period is shortened by heating the catalyst directly. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

Detailed Description of the Invention

  The present invention is a portable fuel cell that uses methanol as a fuel and is portable or in-vehicle.

In a fuel cell using a hydrocarbon-based fuel, steam reforming is advantageous in order to increase the hydrogen conversion rate obtained from the supplied fuel.
On the other hand, in the steam reforming of hydrocarbons, H ₂ and CO are generated, and CO is further shift-reacted to H ₂ and CO ₂ by steam, and the remaining CO is selectively oxidized by air to be CO ₂ . Need a reaction process.
As described above, the reformer becomes complicated and increases costs.

Problems to be solved by the invention

  In order to make the fuel cell portable and in-vehicle portable, the fuel reformer and the fuel cell must be suitable for miniaturization and earthquake resistance. For this purpose, the gas reformer, the fuel, water and air supply pumps, and valves need to be as simple as possible, and a solution to that problem is required.

Means for solving the problem

In order to solve the above objects and problems, the present invention is as follows.
In the miniaturization of the fuel cell, methanol is used as the fuel, and the method according to the formula (1) is normally used for methanol steam reforming.
CH ₃ OH + H ₂ O → 3H ₂ + CO ₂ ......... (1)
Since this reaction is an endothermic reaction, the higher the temperature, the better the equilibrium. However, at a high temperature, CO is produced by the reaction of the aqueous conversion reverse reaction (2).
CO ₂ + H ₂ → CO + H ₂ O ………… (2)
When CO is contained in H ₂ supplied to the fuel cell, the fuel cell electrode catalyst is poisoned by CO. Therefore, it is required to reduce the CO concentration as much as possible.
As a countermeasure for the above problems, the methanol reforming reaction temperature was made as low as possible to 180 to 250 ° C. so as not to cause the aqueous conversion reverse reaction, and the selective oxidation of CO by-product was promoted.

In the reforming catalyst of methanol, a catalyst for complete oxidation of methanol proceeds according to the formula (3) at 160 ° C. according to the formula (3), and the partial oxidation of formula (4) selectively proceeds at 180 ° C. or higher. I found it.
At 160 ° C. CH ₃ OH + 3 / 2O ₂ → 2H ₂ O + CO ₂ ............ (3)
At 180 ° C. CH ₃ OH + 1 / 2O ₂ → 2H ₂ + CO ₂ ............ (4)
When the reaction is carried out by supplying only CH ₃ OH and O ₂ on this catalyst, CO ₂ and H ₂ O are generated at 160 ° C., and H ₂ and CO ₂ are H ₂ / CO ₂ = 2 was generated.
From the above experimental results, it has been found that the formulas (3) and (4) proceed selectively depending on the temperature on the same catalyst, so that the structure of the reactor can be simplified and reduced in size, and the hydrogen production rate can be reduced at a low temperature. It provides a methanol reformer having a high level.

  That is, according to the first invention of the present invention, methanol and water are vaporized and entrained at a molar ratio of 1: 1, air is mixed in a weight ratio of 20 to 30%, and methanol is subjected to oxidative steam reforming. When CO is supplied to the fuel cell, the by-produced CO is allowed to proceed with selective reforming by air in the reforming reactor at the same time as the reforming reaction, and the catalyst is Cu supported on ZnO. When the reaction temperature is 180 to 250 ° C., the reforming heat is supplied by methanol combustion, the catalyst is indirectly heated, but when a part of the fuel cell output is used, the electric heating element loaded in the catalyst filling section A methanol-based fuel cell characterized by oxidative steam reforming of methanol, which is directly heated to reduce the startup time, is provided.

  According to the second aspect of the present invention, in the first aspect of the present invention, in the fuel and air supply, the methanol / water mixture, the reforming air, and the fuel cell air flow rate control are controlled by methanol / water. The liquid surface of the water mixture is pressurized with air, and the pressurized air is used to adjust the air pressure of the reforming air and the fuel cell air. In addition, a fuel cell is provided in which the moisture for wetting the fuel cell electrode is supplied by a jet pump using fuel gas or air as a working medium.

  According to the third aspect of the present invention, in the first aspect, the flow control of the fuel methanol and water mixture, the reforming air, and the fuel cell air is controlled at the liquid level of the methanol / water mixture. The air is pressurized, and the air pressure of the reforming air and the fuel cell air is adjusted by the pressurized air. In addition, a fuel cell is provided in which the moisture for wetting the fuel cell electrode is supplied by a jet pump using fuel gas or air as a working medium.

  Further, according to the fourth aspect of the present invention, in the direct heating system of the catalyst in which the reforming reaction section heating is electric heating in the first aspect, the power supply to the electric heating load at all times is the output of the fuel cell. However, when the fuel cell is started, it is supplied by a storage battery connected in parallel to the fuel cell or an external power source, and unreacted hydrogen of the fuel cell is supplied by a suction pump through a hydrogen permeation filter. A fuel cell is provided that is bleed and recirculated to the fuel cell.

Hereinafter, embodiments of the present invention will be described based on experimental data.
The following three types of methanol steam reforming catalysts were prepared and used. Cu / ZnO, Cu / ZrO, Cu / SiO ₂ .
FIG. 1 shows the relationship between temperature and hydrogen conversion rate in a reforming reaction using a Cu / ZnO catalyst with vaporization of methanol and water (H ₂ O / CH ₃ OH = 1.0). FIG. 1 shows the effect of O ₂ coexistence in a Cu / ZnO catalyst. At a temperature of 180 ° C. or higher, the methanol conversion rate is remarkably increased by the coexistence of O ₂ . Comparing the O ₂ concentrations of 0%, 1%, and 5%, at 180 ° C., the hydrogen conversion rate increases 4 times in the case of 5% O _{2 and in} the absence of O ₂ .

FIG. 2 shows the product composition and conversion rate in the presence of 5% O _{2 with} respect to the reaction temperature.
At a reaction temperature of 160 ° C., CO ₂ and CO are only produced, but H ₂ is not produced. Above 180 ° C., H ₂ and CO ₂ are produced with H ₂ / CO ₂ = 2.

Further, FIG. 3 shows Cu / _{ZnO, O} 2 5% presence of Cu / ZrO 2, Cu / SiO 2 as the reforming catalyst, methanol hydrogen conversion in _{O 2} non coexistence. In any catalyst, the hydrogen conversion rate increases due to the coexistence of O ₂ , but the temperature at which the increase becomes significant differs depending on the Cu support. In Cu / ZnO 180 ℃, Cu / ZrO 2 at 220 ℃, Cu / SiO ₂ at 250 ° C., and the than Cu / ZnO shift to the high temperature side.

Based on the above experimental results, FIG. 4 shows a system configuration in which a methanol reformer using Cu / ZnO as a reforming catalyst and a solid polymer type (PEFC) as a fuel cell are combined. Details of the reforming section are shown in FIGS. 5, 6, 7, and 8.
The fuel is a mixed liquid of methanol and water, supplied from the fuel tank 2, and the space portion of the fuel tank 2 is used as a storage portion for compressed air supplied from the air compressor 1.
The air pressure of the air reservoir is adjusted by the pressure detector 1a, and the supply flow rate is controlled by the throttle valve settings of the fuel supply throttle valve 2a, the reforming air throttle valve 2b, and the fuel cell air throttle valve 2c. It is supposed to be.
The fuel is reformed into gas by the reformer 3, the pressure of the reformed gas is given by the vapor pressure of the vaporizer 33 of the reformer, and the reformed gas is supplied to the fuel cell 4 by the electrode wetting jet pump 3a. The discharged water is sucked and supplied to the fuel cell.
A part of the electric output 5 of the fuel cell 4 is consumed for charging the storage battery 6, and a part is supplied for heating the catalyst of the reformer 3.
When the fuel cell 4 is started, it can be supplied from the storage battery 6 to the catalyst heating, and can be supplied from the external power source 7 to the catalyst heating by the power switch 8, in which case the unreacted hydrogen of the fuel cell is Hydrogen is extracted from the fuel cell exhaust through the hydrogen permeable filter 9 by the suction pump 10 and recirculated to the fuel cell.

  The details of the reformer 3 will be described with reference to FIGS. 4, 5, 6, and 7. Methanol, water, and air are supplied to the fuel vaporization unit 33 from the fuel supply port 32 housed in the reformer case 31. Then, it is heated by the heating electric heater 38 for vaporization, and is supplied to the reforming catalyst 36 through the fuel passage 34 by the vaporization vapor pressure. The reforming catalyst 36 is filled in an annular portion formed by the porous outer cylindrical tube 35 and the porous inner cylindrical tube 37, and a heating element 38 for heating the catalyst is disposed on the same axis as the annular portion. As a result, the catalyst is directly heated and the start-up time of the reformer 3 is shortened.

Further, unreacted hydrogen of the fuel cell is separated into hydrogen by a hydrogen permeable membrane 92 such as palladium supported by the porous ceramic tube 93 from the cell exhaust gas passage 91 in the hydrogen permeable filter 9, and the fuel cell by the suction pump 10. Recirculate to
This is a fuel cell using methanol, which combines the above oxidative steam reforming of methanol and a fuel cell.

The invention's effect

The present invention is configured as described above and has the following effects.
In the conventional methanol reforming, the reforming reaction and the CO selective oxidation reaction required each reaction section. However, by supplying a mixed gas of methanol, water, and air to a single reforming reactor, CO is added as a secondary reaction. It was possible to produce H ₂ and CO ₂ that did not occur.
As a result, the reforming reactor is simple and downsized, and the hydrogen conversion rate can be improved.
Further, since the catalyst is directly heated by using electric heat as the heating method of the reforming reactor, it is possible to improve the reforming heat efficiency and shorten the start-up time delay.

It is a graph showing the relationship between the _{O 2} coexist effect and temperature by Cu / ZnO catalyst. It is a graph which shows the temperature dependence of the reformer product composition by a Cu / ZnO catalyst. _ZnO carrier of Cu catalyst is a graph showing the ZrO 2, ZnSiO ₂ and the effect of the carrier case, and _{O 2} coexist effects versus temperature. It is a block diagram of a methanol fuel cell. The longitudinal cross-sectional view of a hydrogen permeation filter. The longitudinal cross-sectional view of the steam reforming apparatus of methanol. FIG. 7 is a cross-sectional view taken along line A-A ′ of FIG. 6. FIG. 7 is a sectional view taken along line B-B ′ of FIG. 6.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Air compressor 31 Reformer case 2 Fuel tank 32 Fuel supply port 2a Fuel supply throttle valve 33 Fuel vaporization part 2b Reform air throttle valve 34 Fuel passage 2c Fuel cell air throttle valve 35 Porous outer cylinder 3 Reformer 36 Reforming Catalyst 3a Electrode Wetting Jet Pump 37 Porous Inner Tube 4 Fuel Cell 38 Heating Heater 5 Electrical Output End 39 Reformed Gas Outlet 6 Storage Battery 91 Battery Exhaust Gas Passage 7 External Power Supply 92 Hydrogen Permeation Membrane 8 Power Supply Switching switch 93 Porous ceramic tube 9 Hydrogen permeation filter 94 Hydrogen extraction port 10 Suction pump

Claims (4)

  When methanol and water are vaporized together at a molar ratio of 1: 1, air is mixed in a weight ratio of 20 to 30% with methanol, and methanol is oxidatively steam reformed and supplied to the fuel cell, the by-product CO is The selective oxidation by air is allowed to proceed simultaneously with the reforming reaction in the reforming reactor, and the catalyst is Cu supported on ZnO, and the reforming reaction temperature is 180 to 250 ° C. In the case of methanol combustion for the supply of the catalyst, the catalyst is indirectly heated, but when a part of the output of the fuel cell is used, it is directly heated by an electric heating element loaded in the catalyst filling portion to shorten the start-up time. A methanol-based fuel cell characterized by oxidative steam reforming of methanol.   Control of the flow rate of the fuel methanol / water mixture, reforming air, and fuel cell air is performed by pressurizing the liquid level of the methanol / water mixture and using the pressurized air for reforming air and the fuel cell. By adjusting the air pressure of the service air. The fuel cell electrode is supplied with wet moisture by a jet pump using fuel gas or air as a working medium.   In a fuel cell using methanol, the moisture content of the fuel cell electrode is supplied by using a mixture of methanol and water as the fuel. To supply via.   In the catalyst direct heating method in which the heating of the reforming reaction section in claim 1 is electric heating, the power supply to the electric heating load at the normal time supplies a part of the output of the fuel cell, but at the time of starting the fuel cell Is supplied by a storage battery connected in parallel to the fuel cell or an external power source, and unreacted hydrogen of the fuel cell is extracted by a suction pump through a hydrogen permeation filter and recirculated to the fuel cell.

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