JP2008144668A - Power system and ethanol conversion catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power system improved in fuel economy by efficiently utilizing exhaust heat and an ethanol conversion catalyst used for the power system and capable of efficiently converting an ethanol-containing fuel. <P>SOLUTION: This power system comprises a power source in which an ethanol-containing fuel is used as the fuel and a catalyst device for converting an ethanol by utilizing exhaust heat. The catalyst device has an ethanol conversion catalyst containing the oxide of at least one of a group of the elements comprising platinum, cerium, titanium, and niobium. The ethanol conversion catalyst performs the conversion of the ethanol-containing fuel under the conditions that the mole ratio of water (S) to carbon (C) in the ethanol-containing fuel is 1.5 or higher, the liquid space velocity is 10 h<SP>-1</SP>or higher, and the reaction temperature is 500°C or lower. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power system and an ethanol conversion catalyst, and more specifically, a power system including a catalyst device that converts ethanol-containing fuel using exhaust heat from a power source such as an internal combustion engine or a fuel cell, And an ethanol conversion catalyst used therefor.

In recent years, reduction of carbon dioxide (CO ₂ ) emissions has been screamed in consideration of the global environment, and various attempts have been made for the purpose of improving the fuel consumption of internal combustion engines such as automobiles.
For example, high pressure injection technology for gasoline lean burn engines, direct injection engines, and diesel engines is known, and various measures such as addition of an octane number improver for fuel have been taken.

  On the other hand, as a fuel side approach, hydrogen, alcohol (methanol, ethanol, etc.), ether (dimethyl ether, methyl tertiary butyl ether, etc.), biodiesel, synthetic fuel (GTL) as well as gasoline and light oil that have been used Alternative fuels such as) have also been considered.

For example, ethanol has gained attention in recent years as a carbon neutral fuel that can be produced from bio origin and is therefore renewable and does not increase CO ₂ in the atmosphere. In some countries, such as Brazil and the United States, a gas hole, which is 100% ethanol fuel or a fuel in which a certain amount of ethanol is mixed with gasoline, is used as a fuel for an internal combustion engine.

Alcohols are high-octane fuels that contain oxygen atoms in their molecules, so mixing with gasoline is expected to improve the octane number and contribute to improved fuel combustibility.
However, since alcohol, for example ethanol, has only about 60% of the heat of gasoline, the output of the mixed fuel is simply reduced by the amount of the mixed fuel. This becomes a cause of deterioration in fuel consumption, and although CO ₂ emissions are reduced, it is difficult to say that it leads to saving of fuel itself.

Under such circumstances, the supply when supplying these mixed fuels to the internal combustion engine for the purpose of optimizing various conditions when supplying the mixed fuel of gasoline or light oil and alcohol to the internal combustion engine. Various techniques such as a method and an injection method have been proposed. (For example, see Patent Document 1 and Patent Document 2).
Japanese Examined Patent Publication No. 60-47469 JP-A-6-10787

  Specifically, the invention described in Patent Document 1 heats an alcohol-mixed gasoline fuel to a temperature higher than the reforming temperature of alcohol, obtains reformed gas, gasifies the gasoline at the same time, and then cools the gasified gasoline fuel. It condenses and separates from the reformed gas and supplies them to the engine in a separate system.

  However, the present invention seems to be effective when methanol, which is relatively easy to reform as an alcohol, is used as a fuel. However, in the case of ethanol that requires a higher reforming temperature, it can be converted into a reformed gas. It becomes difficult. Further, the relationship between the operating conditions of the internal combustion engine and the supply of the reformed gas is not taken into consideration, and it is unclear whether the obtained reformed gas can contribute to improving the efficiency of the internal combustion engine.

On the other hand, Patent Document 2 proposes a compact double fuel injection valve in order to effectively supply and inject, for example, alcohol-mixed light oil.
In this case as well, if a fuel component advantageous for diesel engine combustion is obtained from the mixed alcohol fuel, it is considered that the conventional injection device can also improve the combustion efficiency.
However, the invention described in Patent Document 2 focuses on the fuel injection valve, and does not consider the characteristics of the fuel, that is, the alcohol species to be mixed.

  As described above, the proposals related to the supply of the conventional alcohol fuel or the alcohol-mixed fuel to the internal combustion engine have been made with a focus on methanol that is relatively easy to reform as alcohol, Relationships are not fully considered and are not being used effectively.

In other words, a fuel conversion supply catalyst that works efficiently from low temperatures has not been proposed for biofuel-derived ethanol, which has been attracting attention as a renewable energy fuel, as a fuel or a mixed fuel. The effective use was not made.
In particular, considering the on-board fuel conversion, the catalyst device mounting capability is an important factor, but no proposal has been made in consideration of its compactness.

  The present invention has been made in view of such problems of the prior art, and the object of the present invention is a power system that can efficiently use exhaust heat and improve fuel efficiency, and can be used for this. An object of the present invention is to provide an ethanol conversion catalyst capable of efficiently converting an ethanol-containing fuel.

  As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved by using a predetermined ethanol conversion catalyst, and have completed the present invention.

That is, the power system of the present invention is a power system including a power source using ethanol-containing fuel as a fuel, and a catalyst device for converting ethanol using exhaust heat,
The catalyst device includes an ethanol conversion catalyst containing platinum and an oxide of at least one element selected from the group consisting of cerium, titanium, and niobium,
This ethanol conversion catalyst has a water (S) / ethanol-containing fuel carbon (C) molar ratio of 1.5 or less, a liquid space velocity (LHSV) of 10 h ⁻¹ or more, and a reaction temperature of 500 ° C. or less. The ethanol-containing fuel is converted.

Moreover, the ethanol conversion catalyst of the present invention is an ethanol conversion catalyst used in the catalyst device of the power system as described above,
Containing an oxide of platinum and at least one element selected from the group consisting of cerium, titanium, and niobium, and a carbon (C) molar ratio in a water (S) / ethanol-containing fuel of 1.5 or less, a liquid The conversion of the ethanol-containing fuel is performed under conditions where the space velocity (LHSV) is 10 h ⁻¹ or more and the reaction temperature is 500 ° C. or less.

  According to the present invention, since a predetermined ethanol conversion catalyst is used, etc., a power system that can efficiently use exhaust heat and improve fuel efficiency, and an ethanol-containing fuel that can be efficiently converted can be used in this system. An ethanol conversion catalyst can be provided.

  Hereinafter, the power system of the present invention will be described in detail. In the present specification, “%” for the concentration, the blending amount, the loading amount, and the like represents a mass percentage unless otherwise specified.

FIG. 1 is a configuration diagram showing an embodiment of a power system of the present invention.
In this figure, this power system includes an internal combustion engine having a combustion chamber 10 and a fuel tank 11 as an example of a power source, and a catalyst device 20 having an ethanol conversion catalyst of the present invention to be described later.
The fuel tank 11 stores ethanol-containing fuel, and the fuel supply passage 12 is provided with direct injection means 30 for directly injecting fuel into the combustion chamber 10.

In the present embodiment, roughly two ethanol-containing fuel supply systems are provided.
One of the systems is a system in which ethanol-containing fuel is sucked into the combustion chamber 10 from the fuel tank 11 via the fuel supply channel 12, and the other system uses exhaust heat, and the ethanol-containing fuel supplies fuel. It passes through the catalyst device 20 installed in the exhaust passage 14 via the passage 13, is temporarily stored in a storage tank 22 as needed, and is supplied to the combustion chamber 10.

  For example, when the power system is started, first, ethanol mixed fuel is directly injected and supplied to the combustion chamber 10 by the direct injection means 30 via the fuel supply flow path 12a. Next, when the exhaust gas temperature rises, the fuel supply system is switched to the supply system via the fuel supply flow path 13, the ethanol-containing fuel is supplied to the catalyst device 20, and the operation of the power system is continued.

  The above-described catalyst device 20 is provided with the ethanol conversion catalyst of the present invention, and can perform fuel conversion using exhaust gas heat, as will be described later. When the heat required for the fuel conversion reaction is insufficient, the catalyst device 20 can be heated by incorporating a heater.

  The fuel component that has passed through the catalyst device 20 having the ethanol conversion catalyst is in the form of gas and can be directly injected into the combustion chamber 10, but in this embodiment, in the middle of the fuel supply system, specifically, It is also possible to carry out heat exchange or cooling in the storage tank 22 and separate and inject the gas component into the liquid component. Therefore, as the direct injection means, a direct injection means 32 for gas and a direct injection means 30 for liquid are provided, and in the present embodiment, both can be used together.

That is, the liquid component reformed and discharged by the catalyst device 20 and gas-liquid separated by the storage tank 22 is supplied to the combustion chamber 10 by the direct injection means 30 through the supply flow path 13b. The supply flow path 13b may be joined with the fuel supply flow path 12a, whereby the liquid component can be directly injected together with the ethanol-containing fuel from the fuel tank 11.
On the other hand, the gas component that has been gas-liquid separated is directly injected into the combustion chamber 10 by the direct injection means 32 via the supply flow path 13a simultaneously or separately from the liquid component as described above.

In the power system of the present embodiment, the catalyst device 20 is preferably installed at a position where exhaust heat from the exhaust gas in the fuel chamber 10 can be utilized.
Normally, this exhaust heat is applied to the catalyst layer of the ethanol conversion catalyst in the catalyst device 20 via a heat exchanger or the like, but the catalyst device 20 itself is used as a heat exchanger in the exhaust flow path 14 or the exhaust flow path 14. Can be installed around.

  In order to increase the efficiency of the fuel conversion reaction in the catalyst device 20, a part of the exhaust gas can be supplied to the catalyst layer via the bypass 14a, thereby controlling the pressure and oxygen. However (this will be described later), at this time, if at least one of the exhaust passage 14 and the bypass 14a is appropriately kept warm, the exhaust heat can be simultaneously applied to the catalyst layer for heating.

In the power system of this embodiment, since the ethanol conversion catalyst of the present invention is used, hydrogen can be efficiently generated from the contained alcohol even at low exhaust conditions during low speed operation with a low load on the internal combustion engine, and at the same time carbon monoxide. (CO), methane (CH ₄ ) and the like can be generated. Furthermore, hydrogen, ethylene, etc. can be generated from some gasoline other than alcohol, which can contribute to the expansion of the lean burn area of the internal combustion engine.
Moreover, since these reactions are endothermic reactions, the exhaust heat of the exhaust gas can be recovered as a result, and the fuel efficiency improvement effect is increased.

In the power system of this embodiment, the ethanol conversion catalyst of the catalyst device 20 has a water (S) / carbon (C) molar ratio in the ethanol-containing fuel of 1.5 or less, a liquid space velocity of 10 h ⁻¹ or more, and a reaction. It is important to convert the ethanol-containing fuel under a temperature of 500 ° C. or lower.
In order to ensure such conditions, a water sensor, a flow meter, and a temperature sensor may be added to control the amount of water, the amount of fuel, and the reaction temperature supplied to the ethanol conversion catalyst.

Next, the ethanol conversion catalyst of the present invention will be described.
The ethanol conversion catalyst of the present invention is an ethanol conversion catalyst used in the catalyst device of the power system as described above.
The ethanol conversion catalyst contains cerium (Ce), titanium (Ti), niobium (Nb) or an oxide of any mixture thereof, platinum (Pt), and water (S) / ethanol-containing fuel. The ethanol-containing fuel is converted under the conditions of a carbon (C) molar ratio (S / C) of 1.5 or less, a liquid space velocity of 10 h ⁻¹ or more, and a reaction temperature of 500 ° C. or less.

Here, even if the above molar ratio (S / C) exceeds 1.5, the conversion efficiency does not increase, and more energy is required to evaporate the water, and the efficiency is lowered. Therefore, the molar ratio (S / C) needs to be 1.5 or less.
Further, if the liquid space velocity is less than 10 h ⁻¹ , the reactor becomes large and heat exchange becomes insufficient and the conversion efficiency is lowered. Therefore, it is important that the liquid space velocity is 10 h ⁻¹ or more.
Furthermore, when the reaction temperature exceeds 500 ° C., problems such as the catalyst starting to deteriorate and the methane production reaction predominate and the production amounts of hydrogen and CO are reduced, resulting in a decrease in efficiency. .

By using this ethanol conversion catalyst, it is possible to convert ethanol in the mixed fuel into a fuel having a high combustion rate such as hydrogen and CO with high efficiency even from a low temperature condition of about 200 ° C. with a compact device.
When this catalyst is used, the heat required for the catalytic reaction can be covered by exhaust heat from a power source such as an internal combustion engine. This makes it possible to recover heat, thereby increasing the fuel efficiency improvement effect.

The heat recovery efficiency of each reforming reaction starting from ethanol is shown below.
The heat recovery efficiency is a value calculated on the basis of the lower heating value standard shown below.
Heat recovery efficiency η = [LHV (reformed gas) −LHV (ethanol)] / LHV (ethanol) × 100%
Here, LHV is a low calorific value, and means a value obtained by subtracting the heat of condensation of the water vapor generated by combustion (latent heat of vaporization) from the calorific value of the fuel.

C ₂ H ₅ OH + 3H ₂ O → 6H ₂ + 2CO ₂ (1); η = 118%
C ₂ H ₅ OH + H ₂ O → 4H ₂ + 2CO (2); η = 125%
C ₂ H ₅ OH → H ₂ + CH ₄ + CO (3); η = 108%
C ₂ H ₅ OH → H ₂ + CH ₃ CHO (4); η = 109%

Reaction formula (1) is a so-called normal steam reforming reaction, and the condition is S / C = 3/2 = 1.5. In this reaction, although the yield of hydrogen is high, a relatively large amount of water needs to be added, and energy is required to evaporate the water. Therefore, there is a concern that the overall heat recovery efficiency is lowered.
On the other hand, the reaction formula (2) is a condition of S / C = 1/2 = 0.5, and is a reaction that can realize a relatively high heat recovery efficiency under a condition of less water addition.

Reaction formula (3) is a condition of S / C = 0, which is a so-called ethanol decomposition reaction. This is preferable because water is unnecessary and it is not necessary to consider the heat of vaporization of water, but a large amount of methane (CH ₄ ) is generated. However, if the combustion heat of CH ₄ can also be used, the heat recovery efficiency becomes 108%, which is useful for improving the efficiency of the internal combustion engine.

Reaction formula (4) is a dehydrogenation reaction, which generates acetaldehyde (CH ₃ CHO) together with hydrogen. When CH ₃ CHO is decomposed, reaction formula (3) is obtained, and water is added to CH ₃ CHO to improve steam. When a quality reaction is caused, the reaction formula (2) is obtained. That is, the reaction can be said to be the first stage of the reactions (2) and (3). Even if the reaction is stopped at this stage, the heat recovery efficiency is 109%, which is useful for improving the efficiency of the internal combustion engine.

The ethanol conversion catalyst of the present invention is effective for the reaction formula (4) and can cause a reaction even at a low temperature of about 200 ° C. However, CH ₃ CHO generated in the reaction formula (4) is easily decomposed on the catalyst and easily becomes CH ₄ and CO. Further, when water is added, the reactions (1) and (2) are obtained. Therefore, by selecting the conditions, it is possible to eventually cause the various reactions (1) to (3).

When the above reaction takes place, at least a part of exhaust gas from an internal combustion engine or the like is mixed with ethanol-containing fuel and supplied to the catalyst layer, so that moisture, nitrogen oxides, CO and HC (hydrocarbon) in the exhaust gas are mixed. In addition to being useful for heat recovery, it can also contribute to cleaner exhaust gas.
Furthermore, when a part of the exhaust gas is mixed with the ethanol-containing fuel, the fuel conversion reaction can be performed more effectively by controlling the oxygen concentration. Further, the controllability of the conversion reaction can be improved by controlling the pressure of the reaction field in the catalyst layer in the same manner.

The ethanol conversion catalyst of the present invention contains Pt and the above-mentioned predetermined oxide, and these oxides typically function as a Pt supporting substrate. The use of such an oxide is one of the features of the present invention.
In the case where Ce oxide is used, a great effect is exhibited by using it in combination with Ti oxide and / or Nb oxide rather than using it alone. The reason why these oxides are effective is unknown, but it seems to be important to have a characteristic that oxygen vacancies are easily formed.
Regarding the Ti oxide, a rutile type is effective, and a high specific surface area exceeding 60 m ² / g is preferable.

  The effective mass concentration of Pt supported on the oxide is in the range of 0.5 to 4%. If it is less than 0.5%, the catalytic action cannot be exerted, and if it exceeds 4%, the decomposition activity of ethanol is too high, and carbon deposition occurs and it becomes easy to deactivate.

  It should be noted that at least one of rhodium (Rh) and palladium (Pd) can be further added to the ethanol conversion catalyst of the present invention, whereby the reactions (1) and (2) can be promoted. It is preferable from the viewpoint of recovery.

As for the above-mentioned addition of Rh and / or Pd, they may be added by themselves, but may be added in the form of a Pt-containing catalyst and / or an Rh-containing catalyst.
For such a Pd-containing catalyst, alumina (Al ₂ O ₃ ) or the like is used as a supporting substrate in addition to the Ce oxide as described above, and the supporting concentration (%) of Rh and Pd is the same as in the case of Pt. It is preferable to set it as 0.5 to 4% of range.

  In addition, about arrangement | positioning of a noble metal component, ie, Pt, Rh, and Pd, each can be performed with the form of a single-piece | unit or a noble metal containing catalyst, and these 2 types or 3 types of noble metal components exist in the same catalyst layer. It is also possible to arrange each noble metal catalyst separately or as a separate catalyst layer.

  The ethanol conversion catalyst of the present invention is particularly effective for a fuel containing ethanol, but of course, it contains conventional methanol, MTBE (methyl-tertiary-butyl ether), ETBE (ethyl-tertiary-butyl ether) and the like. It is also effective for mixed fuels in which oxygen compounds are added to gasoline fuel.

The above-mentioned ethanol conversion catalyst is applied to a catalyst support having ceramic or metal three-dimensional continuous pores, for example, a metal foam made of Ni alloy having pores of 30 ppi. The catalyst utilization rate is improved.
Examples of such a catalyst support include a metal foam support such as a nickel alloy, that is, a monolith support having three-dimensional continuous pores and a porosity of 80% or more. A sufficient conversion function can be obtained with a small amount of catalyst, and light-off characteristics and responsiveness are enhanced.

The reactions (1) to (4) can be controlled by reaction conditions. In particular, the amount of water, the reaction temperature, the pressure, and the amount of fuel supplied to the catalyst are important, and a desired reaction can be selected by controlling according to operating conditions.
For example, reaction (3) predominates in the absence of water, and reaction (4) predominates at lower temperatures. Although the reaction of (1) or (2) can be promoted by supplying the moisture of the exhaust gas to the catalyst, the reaction (2) becomes dominant particularly when the fuel supply rate is increased.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.

(Examples 1-7, Comparative Example 1)
A power system as shown in FIG. 1 was produced, and an ethanol conversion catalyst having the specifications shown in Table 1 below was installed in the catalyst device to construct a power system of each example.
As shown in Table 1, the catalyst powder used in the power system of each example includes a combination of Ce, Nb, and Ti oxides, a change in Pt loading, and Rh, Pd. A combination of catalysts was prepared, and about 120 g / L was applied to a monolithic carrier made of Ni alloy having pores of 30 ppi to prepare a test catalyst.

  In applying the catalyst powder to the monolith support, the catalyst powder is mixed with water and an alumina binder, and the slurry obtained by applying a pot mill grinder is sprayed onto the monolith support, and the excess slurry is blown off and removed, followed by drying and firing. Through this process, the catalyst was formed. The amount of the alumina binder added was 3%.

Prior to the performance evaluation, the catalyst used in each example was treated in a nitrogen balance gas containing 10% hydrogen at 450 ° C. for 1 hour.
For the evaluation of the catalyst, water was added under the condition of S (water) / C (C in ethanol) molar ratio = 0.5 using an atmospheric pressure flow type reactor, and ethanol was LHSV = on the volume basis of the monolith catalyst. The reaction was conducted at 25 h ⁻¹ , using nitrogen as the carrier gas, and the catalyst inlet temperature of 250 ° C. and 340 ° C.

Table 1 also shows the ethanol conversion rate and hydrogen generation amount under each temperature condition. The amount of hydrogen produced was shown by the gas volume composition excluding water and nitrogen.
As a comparative example, the performance of Pt / alumina catalyst and Pt / Ce oxide obtained in the same manner was shown. However, the catalyst of the present invention has a high hydrogen generating ability and can effectively supply hydrogen even at a low temperature. Therefore, it is possible to improve efficiency by recovering relatively low quality exhaust heat.

As mentioned above, although this invention was demonstrated in detail by suitable embodiment and an Example, this invention is not limited to these embodiment and an Example, A various deformation | transformation is possible within the range of the summary of this invention. .
For example, as a power source, not only an internal combustion engine but also a fuel cell can be applied. Further, the direct injection means and the EGR bypass are not essential members.

It is a lineblock diagram showing one embodiment of the power system of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Combustion chamber 11 Fuel tank 12 Fuel supply flow path 14 Exhaust flow path 20 Catalytic device 22 Storage tanks 30 and 32 Direct injection means

Claims (10)

A power system comprising a power source that uses ethanol-containing fuel as a fuel, and a catalyst device that converts ethanol using exhaust heat,
The catalyst device includes an ethanol conversion catalyst containing platinum and an oxide of at least one element selected from the group consisting of cerium, titanium, and niobium,
This ethanol conversion catalyst is obtained under the conditions that the molar ratio of carbon (C) in the water (S) / ethanol-containing fuel is 1.5 or less, the liquid space velocity is 10 h ⁻¹ or more, and the reaction temperature is 500 ° C. or less. A power system characterized by converting the contained fuel. The power source is an internal combustion engine or a fuel cell device;
2. The power system according to claim 1, wherein the ethanol fuel conversion catalyst is disposed at a position where heat exchange can be performed with a catalyst that processes exhaust gas from the internal combustion engine or the fuel cell device. An ethanol conversion catalyst used in the catalyst device of the power system according to claim 1 or 2,
Containing an oxide of platinum and at least one element selected from the group consisting of cerium, titanium and niobium, and a carbon (C) molar ratio in the water (S) / ethanol-containing fuel is 1.5 or less, An ethanol conversion catalyst characterized in that the ethanol-containing fuel is converted under conditions of a liquid space velocity of 10 h ^-1 or more and a reaction temperature of 500 ° C or less.   4. The ethanol conversion catalyst according to claim 3, wherein platinum is supported on an oxide of at least one element selected from the group consisting of cerium, titanium and niobium.   The ethanol conversion catalyst according to claim 4, wherein platinum is supported at a ratio of 0.5 to 4%.   The ethanol conversion catalyst according to claim 3, comprising cerium oxide and at least one of titanium oxide and niobium oxide.   The catalyst for ethanol conversion according to any one of claims 3 to 6, further comprising a catalyst containing rhodium.   The ethanol conversion catalyst according to any one of claims 3 to 7, further comprising a catalyst containing palladium.   The ethanol conversion catalyst according to any one of claims 3 to 8, wherein the titanium oxide has a rutile structure.   The ethanol conversion catalyst according to any one of claims 3 to 9, wherein the ethanol conversion catalyst is formed on a metal monolith support having a three-dimensional pore structure.

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