WO2002000814A1 - Fuel for fuel cell system - Google Patents

Abstract

A fuel for a fuel cell system which takes a gaseous state at ordinary temperature under atmospheric pressure, contains hydrocarbon compounds in an amount of 5 mol % or more and oxygen-containing compounds in an amount of 0.5 to 20 mass % in terms of oxygen atoms relative to the total amount of the fuel, wherein the hydrocarbon compound component contains 5 mol % or less of hydrocarbons having two or less carbon atoms, 90 mol % or more of hydrocarbons having three or four carbon atoms, and 5 mol % or less of hydrocarbons having five or more carbon atoms. The fuel exhibits an increased energy output generated per its weight and per amount of CO2 formed, an improved fuel consumption, a decreased evaporative emission, good handling properties such as good storage stability and a suitable flash point, and reduced calories required for preheating. Further, the fuel allows a fuel cell system using the fuel to keep its initial performance for a long period of time, since it reduces the deterioration of a fuel cell system such as a reforming catalyst, a water gas shift reaction catalyst, a carbon monoxide removal catalyst and a fuel cell stack.

Description

 Description Fuel technology for fuel cell systems

 The present invention relates to a fuel used for a fuel cell system. Background art

In recent years, the growing sense of danger to the global environment in the future has demanded the development of an energy supply system that is kind to the earth. In particular, reduce CO _{2 to} prevent global warming, THC (unreacted hydrocarbons in exhaust gas), NOx, PM (particulate matter in exhaust gas: soot, fuel 'High boiling point of lubricating oil · It is required to achieve a high degree of reduction of harmful substances such as unburned polymer components. Specific examples of such a system include an automotive power system that replaces the conventional Otto's diesel system or a power generation system that replaces thermal power.

Therefore, a fuel cell that has energy efficiency close to ideal and emits only H ₂ O and CO ₂ is expected to be a promising system for meeting the needs of society. To achieve such a system, it is essential not only to develop equipment technology but also to develop the optimal fuel.

 Conventionally, hydrogen, methanol, and hydrocarbon fuels have been considered as fuels for fuel cell systems.

 As fuel for fuel cell systems, there is methanol in addition to hydrogen. Although methanol is advantageous in that it can be relatively easily reformed to hydrogen, it must be handled with care because it produces a small amount of power per weight and is toxic. Also, due to its corrosiveness, special equipment is required for storage and supply.

Thus, no fuel has yet been developed to fully exploit the capabilities of the fuel cell system. In particular, heavy fuels for fuel cell systems High power generation per unit, high power generation per CO ₂ generation, good fuel efficiency of the fuel cell system as a whole, low evaporation gas (evaporation), reforming catalyst, water gas shift reaction Low degradation of fuel cell system such as catalyst, carbon monoxide removal catalyst, fuel cell stack, etc., so that initial performance can be maintained for a long time, system startup time is short, system loading, storage stability and ignition Good handling properties such as points are required.

 In a fuel cell system, it is necessary to maintain the fuel and reformer at a given temperature, so the amount of power generated by subtracting the required amount of heat (the amount of heat that balances the preheating and endothermic heat associated with the reaction) from the amount of generated power is This is the amount of power generated by the entire fuel cell system. Therefore, the lower the temperature required for reforming the fuel, the smaller the amount of preheating and the more advantageous the system, the shorter the startup time of the system, and the lower the amount of heat per weight required for the preheating of the fuel. Is also necessary. Insufficient preheating can lead to high levels of unreacted hydrocarbons (THC) in the exhaust gas, not only reducing power generation per weight, but also causing air pollution. Conversely, when the same system is operated at the same temperature, it is advantageous for the exhaust gas to have a small amount of THC and a high conversion rate to hydrogen.

 In view of such circumstances, an object of the present invention is to provide a fuel suitable for a fuel cell system that satisfies the above-mentioned required properties in a good balance. Disclosure of the invention

 The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, a fuel containing a specific amount of an oxygen-containing compound and having a specific composition of hydrocarbon compounds for each carbon number has been known as a fuel cell. We found that it was suitable for the system. That is, the fuel for a fuel cell system according to the present invention is:

(1) Contain at least 5 mol% of a hydrocarbon compound, contain 0.5 to 20% by mass of oxygenated compound based on the total amount of fuel in oxygen element conversion, and conduct hydrocarbon conversion. 5 mol% or less of hydrocarbons having 2 or less carbon atoms in the compound, 90 mol% or more of hydrocarbons having 3 carbon atoms and hydrocarbons having 4 carbon atoms, and 5 mol% of hydrocarbons having 5 or more carbon atoms % Or less, and is a gas at normal temperature and normal pressure.

It is more preferable that the fuel containing the oxygen-containing compound in a specific amount and the hydrocarbon compound having a specific composition for each carbon number further satisfy the following additional requirements. ₀

(2) The sulfur content is 50 mass ppm or less.

 (3) The hydrocarbon compound has a saturated content of 60 mol% or more, an olefin component of 40 mol% or less, a butadiene component of 0.5 mol% or less, and 0.1% of isoparaffin in the saturated component having 4 or more carbon atoms. Mol% or more.

 (4) The vapor pressure at 40 ° C is; L. 55 MPa or less.

(5) The density at 15 of the hydrocarbon compound is 0.500 to 0.620 g / cm ³ .

 (6) Corrosion rate of copper plate for 1 hour at 40 is 1 or less.

 (7) The gas has a heat capacity of less than 1.7 kJkg '° C at 15 ° C. '' Brief description of the drawings

 FIG. 1 is a flowchart of a steam reforming type fuel cell system used for evaluating the fuel for a fuel cell system of the present invention. FIG. 2 is a flow chart of a partial oxidation fuel cell system used for evaluating the fuel for a fuel cell system of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, the contents of the present invention will be described in more detail.

In the present invention, the oxygen-containing compound contained in a specific amount means alcohols having 2 to 4 carbon atoms, ethers having 2 to 8 carbon atoms, and the like. For example, methanol, ethanol, dimethyl ether, methyl tert-butyl ether (MTBE), ethyl tertiary butyl ether, Yuichi Ichiri amyl methyl ether (T AM E), tertiary amyl ethyl ether and the like.

 The content of these oxygen-containing compounds is 0 .0 in terms of oxygen element, based on the total fuel amount, because of the good fuel efficiency of the entire fuel cell system, the small amount of THC in the exhaust gas, and the short system startup time. It must be at least 5% by mass, and in consideration of the balance with the power generation per weight, it must be at most 20% by mass.

The fuel for a fuel cell system according to the present invention includes, in addition to the oxygen-containing compounds described above, oxygen-containing compounds and hydrocarbons because of their large power generation per weight and large power generation per CO ₂ generation. It is a mixture with oil, and the blended amount of hydrocarbon oil is 5 mol% or more based on the total amount of fuel.

 In the present invention, the composition for each carbon number in the hydrocarbon compound means that the hydrocarbon compound has 5 mol% or less of hydrocarbons having 2 or less carbon atoms and the hydrocarbon compound has 3 carbon atoms and 4 carbon atoms. The total amount is 90 mol% or more, and hydrocarbons with 5 or more carbon atoms are 5 mol% or less.

Hydrocarbons having 2 or less carbon atoms are 5 mol% or less, preferably 3 mol% or less, from the viewpoint of mountability, flammability, evaporation, and the like. The total amount of hydrocarbons coal hydrocarbons and 4 carbon atoms of 3 carbon atoms, often power generation amount per weight, it generation amount of ₂ generation amount per CO is large, that overall fuel consumption of the fuel cell system is a good Since the amount of THC in the exhaust gas is small, the system startup time is short, the deterioration of the reforming catalyst is small, and the initial performance can be maintained for a long time. % Or more is preferable. Hydrocarbons with 5 or more carbon atoms have a large amount of power generation per weight, a large amount of power generation corresponding to the amount of CO ₂ generated, good fuel economy as a whole fuel cell system, and low THC in exhaust gas. Since the system startup time is short, the deterioration of the reforming catalyst is small, and the initial performance can be maintained for a long time, the content is 5 mol% or less, preferably 2 mol% or less. .

The above composition for each carbon number is a value measured by JISK2240 “Liquid fossil-gas 5.9 composition analysis method”. Further, the sulfur content of the fuel of the present invention is not limited at all. Since the performance can be maintained for a long time, it is preferably 50 mass ppm or less, more preferably 10 mass ppm or less, and most preferably 1 mass ppm or less, based on the total amount of fuel. preferable.

 Here, the sulfur content means the sulfur content measured by JIS K 2240 "Liquefied petroleum gas 5.5 or 5.6 sulfur content test method". In the present invention, the component composition of the hydrocarbon compound is not limited at all, but the saturated component (M (S)) is preferably 60 mol% or more, and the olefin component (M (O)) is preferably 40 mol% or less, butadiene. The content (M (B)) is preferably 0.5 mol% or less, and the content of isoparaffin (M (IP)) in the saturated component having 4 or more carbon atoms is preferably 0.1 mol% or more. Hereinafter, these will be individually described.

The saturation M (O) means that the power generation per weight is large, the power generation per CO ₂ generation is large, the fuel efficiency of the fuel cell system as a whole is good, the THC in the exhaust gas is small, the system 60 mol% or more is preferable, more preferably 80 mol% or more, even more preferably 95 mol% or more, and most preferably 99 mol% or more. preferable.

The olefin component (M (O)) has a large amount of power generation per weight, a large amount of power generation per CO ₂ generation, good fuel economy of the fuel cell system as a whole, and low THC in the exhaust gas. However, the starting time of the system is short, the deterioration of the reforming catalyst is small, the initial performance can be maintained for a long time, and the storage stability is preferably 40 mol% or less, more preferably 10 mol% or less. Preferably, it is most preferably 1 mol% or less.

Butadiene (M (B)) has a large amount of power generation per weight, a large amount of power generation per CO ₂ generation, good fuel economy of the fuel cell system as a whole, and low THC in exhaust gas. The system startup time is short, the deterioration of the reforming catalyst is small, and the initial performance can be maintained for a long time. From the viewpoint of storage stability and the like, the content is preferably 0.5 mol% or less, and most preferably 0.1 mol% or less.

 Isoparaffins (M (IP)) in saturated components with 4 or more carbon atoms have good fuel efficiency as a whole fuel cell system, low THC in exhaust gas, short system startup time, reforming catalyst 0.1 mol% or more, more preferably 1 mol% or more, even more preferably 10 mol% or more, because the deterioration of the metal is small and the initial performance can be maintained for a long time. % Or more, and most preferably 30 mol% or more.

 The above M (S), M (B), M (IP) and M (O) are values measured by JIS K 2240 “liquefied petroleum gas 5.9 composition analysis method”.

 Further, satisfying both the preferred range of the sulfur content and the preferred range of the composition described above may cause deterioration of a fuel cell system such as a reforming catalyst, a water gas shift reaction catalyst, a carbon monoxide removal catalyst, and a fuel cell stack. Most preferred because it is small and the initial performance can be maintained for a long time.

 The vapor pressure of the fuel of the present invention is not limited at all. However, from the viewpoint of mountability, flammability, evaporative emission, etc., the vapor pressure at 40 ° C is preferably 1.55 MPa or less, and 1.53 MPa or less. a or less is more preferable.

 In addition, the vapor pressure at 40T: is measured by JIS K 2240 “liquefied petroleum gas 5.4 vapor pressure test method”.

Further, although not what we limitation on the density of the hydrocarbon compounds contained in the fuel of the present invention, many power generation amount per weight, more power generation amount per C0 ₂ generation amount, overall fuel consumption of a fuel cell system From the point that the reforming catalyst is less deteriorated and the initial performance can be maintained for a long time because of the good performance, the low THC in the exhaust gas, and the short system startup time. It is preferably 620 g / cm ³ or less, and most preferably 0.50 g / cm ³ or more in order to achieve the effects of the present invention.

The density at 15 ° C is based on JISK 2249 `` liquefied petroleum gas 5. 7 or 5.8 Density test method ”.

 Further, there is no limitation on the copper plate corrosivity of the fuel of the present invention, but the fuel cell system, such as a reforming catalyst, a water gas shift reaction catalyst, a carbon monoxide removal catalyst, and a fuel cell stack, has little deterioration and has a long initial performance. From the viewpoint of sustaining the time, it is preferable that the corrosion rate of the board per hour at 40 ° C is 1 or less.

 The corrosion rate of the copper plate at 40 ° C for 1 hour is measured by JIS K2240 “Liquid petroleum gas 5.10 Copper plate corrosion test method”.

 Further, in the present invention, the heat capacity of the fuel is not limited at all. However, since the fuel efficiency of the fuel cell system as a whole is good, the amount of heat in gaseous state at 15 is 1.7 kJZ kg The following is preferred.

 This heat capacity is measured by a calorimeter such as a water calorimeter, an ice calorimeter, a vacuum calorimeter, or an adiabatic calorimeter.

 There is no particular limitation on the method for producing the fuel of the present invention. Specifically, for example, a straight-line propane fraction mainly composed of propane obtained from a crude oil distillation unit and a naphtha reformer, a straight-line desulfurized propane fraction obtained by desulfurizing it, a crude oil distillation unit, a naphtha reformer -Based butane fraction mainly consisting of butane obtained from a gasification apparatus, an alkylation apparatus, etc., a straight-line desulfurized butane fraction obtained by desulfurizing the straight-line butane fraction, and propane obtained from a catalytic cracking unit. One or more base materials such as a cracked propane fraction mainly composed of propylene, a cracked butane fraction mainly composed of butane / butene obtained from a catalytic cracking unit, etc., are included in the present invention. It is produced by containing a specific amount of an oxygen compound.

 Among these, preferred as a base material for producing the fuel of the present invention include dimethyl ether and methyl alcohol such as a straight-run desulfurized propane fraction and a straight-run desulfurized butane fraction.

The fuel of the present invention is used as a fuel for a fuel cell system. The fuel cell system referred to in the present invention includes a fuel reformer, a carbon monoxide purification device, a fuel cell, and the like. The fuel of the present invention is applicable to any fuel cell system. It is preferably used.

 The fuel reformer is for reforming the fuel to obtain hydrogen, which is the fuel of the fuel cell. As a reformer, specifically, for example,

 (1) A steam reforming reformer that mixes heated and vaporized fuel with steam and reacts by heating in a catalyst such as copper, nickel, platinum, and ruthenium to obtain hydrogen-based products. ,

 (2) Partial oxidation reforming that mixes heated and vaporized fuel with air and reacts with or without a catalyst such as copper, nickel, platinum, ruthenium, etc. to obtain a product containing hydrogen as a main component. Bowl,

: (3) The heated and vaporized fuel is mixed with steam and air, and subjected to partial oxidation reforming of (2) in the first stage of the catalyst layer of nickel, platinum, ruthenium, etc., and in the second stage. By utilizing the heat generation of the oxidation reaction to perform the steam type reforming of (1), a partial oxidation / steam reforming type reformer that obtains a product containing hydrogen as a main component,

 And the like.

 The carbon monoxide purifier removes carbon monoxide contained in the gas generated by the above reformer and becomes a catalyst poison of the fuel cell.

 (1) Water gas shift reaction in which reformed gas and heated vaporized water are mixed and reacted in a catalyst such as copper, nickel, platinum, and ruthenium to produce carbon dioxide and hydrogen as products from carbon oxide and water vapor. Vessel,,

(2) Selective oxidation reactors that convert carbon monoxide to carbon dioxide by mixing reformed gas with compressed air and reacting in a catalyst such as platinum or ruthenium, etc. Used. .

 Specific examples of the fuel cell include polymer electrolyte fuel cells (PEFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), and solid oxide fuel cells ( SOFC).

In addition, the fuel cell system as described above includes electric vehicles, conventional engine-electric hybrid vehicles, portable power sources, distributed power sources, home power sources, Used for cogeneration systems and the like. Example

 Table 1 shows the properties of the base material (LPG) used for each fuel in the examples and comparative examples.

Table 2 shows the composition and properties of each fuel used in Examples and Comparative Examples.

Table 1

O

Table 2 Example 1 Example 2 Comparative Example 1 Comparative Example 2 Mixing ratio (% by volume)

 Straight run 20

 Straight run · Desulfurized ethane 90 90

 Cracking vutane fraction 100

DME 10 5

 Methanol 100 properties analysis results

 Sulfur content 虛 ppm <1 1 <1 34 Density (hydrocarbon part) g / cm3 0.509 0.563 0.796 0.591 Vapor pressure Mpa 0.40 0.57 0.03 0.36 Carbon number distribution (hydrocarbon part) Hydrocarbons with 2 or less carbon mole% 2.5 0.6 -0.0 Hydrocarbons with 3 carbons mol% 96.6 23.0-12.4 Hydrocarbons with 4 carbons mol% 0.9 76.4-12.4 Hydrocarbons with 5 or more carbons mol% 0.0 0.1 5.2 Composition (hydrocarbon part) Saturation mol% 99.9 99.9 53.9

 Olefin content mol% 0.1 0.1 46.1 phthalocyanine mol% 0.0 0.0 0.2

Isoharafffin mol% in C4 or more saturated content 78.2 35.9 80.6 Oxygen ratio Mass ·% 4.0 2.1 49.9 0.0 Copper plate corrosion 1 a 1 a 1 Net calorific value kJ / kg 43750 44800 19920 45440 Heat volume 5 kJ / kg- ° C 1.60 1.61 1.34 1.55

For each of these fuels, a fuel cell system evaluation test was performed.

Fuel cell system evaluation test

 (1) Steam reforming type

 Fuel and water were vaporized by electric heating, and led to a reformer filled with a noble metal-based catalyst and maintained at a predetermined temperature by electric heating to generate a hydrogen-rich reformed gas.

 The temperature of the reformer was set to the lowest temperature at which reforming was completely performed in the initial stage of the test (the lowest temperature at which THC was not contained in the reformed gas).

 The reformed gas is led to a carbon monoxide treatment device (water gas shift reaction) together with water vapor to convert carbon monoxide in the reformed gas into carbon dioxide, and the generated gas is guided to a polymer electrolyte fuel cell to generate electricity. Was.

 Diagram of the flow chart of the steam reforming type fuel cell system used for evaluation

Shown in 1.

 (2) Partial oxidation type

 The fuel was vaporized by electric heating, filled with a precious metal-based catalyst together with preheated air, and led to a reformer maintained at 110 by an electric heater to generate a reformed gas rich in hydrogen.

 The reformed gas is led to a carbon monoxide treatment device (water gas shift reaction) together with water vapor to convert carbon monoxide in the reformed gas into carbon dioxide, and the generated gas is guided to a polymer electrolyte fuel cell to generate electricity. Was.

 Figure 2 shows a flowchart of the partial oxidation fuel cell system used for the evaluation.

 (3) Evaluation method

Immediately after the start of the evaluation test, the amounts of H ₂ , CO, CO ₂ , and THC in the reformed gas generated from the reformer were measured. Similarly, the amounts of H ₂ , CO, CO ₂ , and THC in the reformed gas generated from the carbon monoxide treatment equipment were measured immediately after the start of the evaluation test.

Immediately after and 100 hours after the start of the evaluation test, measurements were made of the amount of power generation, fuel consumption, and CO ₂ emitted from the fuel cell. became.

 The amount of heat (preheat) required to guide each fuel to the specified reformer temperature was calculated from the heat capacity and latent heat of vaporization.

 In addition, the performance degradation rate of the reforming catalyst (the amount of power generated 100 hours after the start of the test, the amount of power generated immediately after the start of the test), the thermal efficiency (the amount of power generated immediately after the start of the test, "The calorific value of the fuel) and the preheat ratio (preheat / power generation) were calculated.

Table 3 shows the measured values and calculated values.

Table 3 Example 1 Example 2 Comparative Example 1 Comparative Example 2 Parity result

Water steam 発 電 Power generation by the reforming method (reformer temperature ^: = optimal reformer temperature)

 Optimal reformer temperature. c 540 590 360 670 Electric energy KJ / fuel kg Initial performance 29580 30200 17140 29460

After 100 hours 29580 30190 17140 28520 Performance degradation ratio After 100 hours 0.00% 0.03% 0.00% 3.19% Thermal efficiency ²⁾ Initial performance 68% 67% 86% 65%

G02 generation kg / fuel kg Initial performance 2.901 2.956 1.374 3.079

Energy per C02 KJ / C02-kg Initial performance 10196 10217 12475 9568 Pre-ripening KJ / Fuel kg 830 910 1590 1000 Preheating ratio ⁴⁾ 2.8% 3.0% 9.3% 3.4% Power generation by partial oxidation reforming (reformer) (Temperature 1100 ° C)

 Electric energy KJ / material kg Initial performance 15100 15440 10280 14420

After 100 hours 15 100 15 430 10 280 14 220 Performance degradation ratio After 100 hours 0.00% 0.06% 0.00% 1.39% Thermal efficiency ^a Initial performance 35% 34% 52% 32%

C02 generation kg / fuel kg Initial performance 2.900 2.955 1.373 3.077

Energy per G02 * One KJ / C02-kg Initial performance 5207 5225 7487 4686 Preheating amount ³⁾ KJ / fuel kg 1720 1729 2590 1670 Preheating ratio ⁴⁾ 1 1.4% 1 1.2% 25.2% 1 1.6%

1) Minimum temperature at which THC is not contained in the reformed gas

 2) Electric energy twisting calorific value

 3) The amount of heat required to bring the fuel to the specified reformer temperature

4) Preheating amount, electric energy

Industrial applicability

 As described above, a fuel containing a specific amount of the oxygen-containing compound of the present invention and having a hydrocarbon compound having a specific composition for each number of carbon atoms can be used in a fuel cell to provide an electric engine with a low performance deterioration ratio. In addition to being able to obtain high energy, it satisfies various performances for fuel cells.

Claims

The scope of the claims 1. Carbon containing at least 5 mol% of hydrocarbon compounds, 0.5 to 20 mass% of oxygenated compounds based on the total amount of fuel in oxygen element conversion, and carbon number of 2 or less in hydrocarbon compounds Hydrogen is 5 mol% or less, the total amount of hydrocarbons having 3 carbon atoms and hydrocarbons having 4 carbon atoms is 90 mol% or more, and hydrocarbons having 5 or more carbon atoms is 5 mol% or less. A fuel for a fuel cell system.  2. The fuel for a fuel cell system according to claim 1, having a sulfur content of 50 mass ppm or less.  3. Hydrocarbon compounds have a saturated content of 60 mol% or more, an olefin component of 40 mol% or less, a butadiene component of 0.5 mol% or less, and 0.1 mol of isoparaffin in a saturated component having 4 or more carbon atoms. 3. The fuel for a fuel cell system according to claim 1, wherein the amount is not less than 0.1%. 4. The fuel for a fuel cell system according to any one of claims 1 to 3, wherein the vapor pressure at 4.40 is 1.55 MPa or less. 5. density at a hydrocarbon compound content of 15, 0. 500~0. 620 g / cm 3 a fuel cell fuel system according to any one of claims first to fourth terms are. 6. The fuel for a fuel cell system according to any one of claims 1 to 5, wherein a copper plate corrosion rate per hour at 40 is 1 or less. 7. The fuel for a fuel cell system according to any one of claims 1 to 6, wherein the gas has a heat capacity at 15 of 1.7 kJZkg * ° C or less.