JP3261192B2 - Method for desulfurizing hydrocarbon feedstock for fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for desulfurizing a hydrocarbon raw material for a fuel cell. More specifically, the present invention relates to a method for converting hydrocarbons into a fuel gas mainly composed of hydrogen by at least a steam reforming reaction. The present invention relates to an efficient method for desulfurizing a hydrocarbon raw material, which is a method extremely advantageously used for a fuel cell system using hydrogen as a fuel.

[0002]

2. Description of the Related Art Fuel cells using hydrogen as fuel have already been put into practical use and are expected to become more and more popular in the future.
Hydrogen or a hydrogen-containing fuel gas used in this fuel cell can be obtained by various methods.A general-purpose fuel cell system uses relatively light hydrocarbons such as kerosene or naphtha as a raw material, and uses this as a raw material. Attention has been paid to a method obtained by steam reforming with a suitable catalyst. In addition, in the steam reforming reaction of hydrocarbons, carbon monoxide and the like are generally generated in addition to hydrogen. Therefore, the product of the steam reforming reaction is further subjected to a denaturation treatment with a suitable catalyst, and the carbon monoxide is converted to an aqueous solution. It is also common practice to react with water by gas shift reaction to convert it to carbon dioxide and hydrogen, further improve the yield of hydrogen, and reduce carbon monoxide, which is harmful and tends to cause a decrease in the activity of fuel cell electrodes. .

[0003] As described above, a fuel cell system using a hydrocarbon as a raw material and provided with a steam reforming means and a denaturing means has been developed and its use has been promoted.

In such a fuel cell system, various hydrocarbons (eg, natural gas, city gas, etc.) including petroleum hydrocarbons such as LPG, naphtha, kerosene, etc. are used as a raw material for producing hydrogen by steam reforming. Hydrocarbon-containing gas and synthetic petroleum) can be used, but such hydrocarbon feedstocks still contain a considerable concentration of sulfur even in commercial products desulfurized in advance by hydrorefining. Even in the case of kerosene (commercially available desulfurized kerosene), usually several ppm
It contains about 100 ppm sulfur. This sulfur content, even as an organic sulfur compound or as hydrogen sulfide by hydrodesulfurization, becomes a poison for the steam reforming reaction catalyst and the modification catalyst unless it is removed from the system, and reduces the activity of the fuel cell electrode. Adversely affect.

Therefore, in such a fuel cell system using hydrocarbons as a raw material, it is important to sufficiently remove the sulfur content in the raw material in order to protect the steam reforming catalyst, the reforming catalyst, and the electrodes in the subsequent stage. Technology. In addition,
Prior to the steam reforming reaction, the sulfur content is usually 0.1 p
pm or less.

In such a fuel cell system, the raw materials
As a method of removing sulfur content, raw material hydrocarbons are suitable.
Hydrodesulfurization with appropriate desulfurization catalyst to remove organic sulfur compounds
H that is easy to remove by adsorption _TwoH instead of S _TwoS is a suitable adsorbent
It seems to be effective to remove it. So, hydrogen
Co-Mo, N commonly used as hydrodesulfurization catalysts
Using a desulfurization catalyst such as i-Mo and zinc oxide as an adsorbent
And combine them to obtain the sulfur content of the raw material (organic
Sulfur compounds and H_TwoA method of removing S) is conceivable.
However, using such a general hydrodesulfurization catalyst,
With the above desulfurizing agents, hydrodesulfurization itself increases the hydrogen pressure considerably.
Pressure is not effective and the desulfurization performance is inadequate
To reduce the sulfur content to the target 0.1 ppm or less.
It is difficult to do. Therefore, such desulfurizing agents
Fuel cell system, especially, when the operating pressure is atmospheric pressure to 10 kg /
cm^Two It is applicable to general-purpose fuel cell systems as low as G
It is hard.

Accordingly, a desulfurizing agent having a high desulfurization ability, which has a sufficient hydrodesulfurization function and a function of adsorbing and removing sulfur even at such a low pressure and capable of efficiently reducing the sulfur content to 0.1 ppm or less. Development is an important issue.

[0008] In view of these points, the present inventors have widely investigated and studied what has conventionally been proposed as a desulfurizing agent for hydrocarbons. as a result,
It has been found that the conventional desulfurizing agent is insufficient to realize the intended advanced desulfurization technology.

For example, Japanese Unexamined Patent Publication (Kokai) No. 2-204301 proposes a Ni-based desulfurizing agent as a desulfurizing agent for kerosene. In the description, the Ni content is 30-70.
%, The addition of Cu and the use of zinc oxide as a carrier are described, but there is no specific description of a specific method for preparing the desulfurizing agent or desulfurization performance.

Japanese Unexamined Patent Publication (Kokai) No. 2-302302 discloses a Cu—Zn-based or Cu—Zn—based desulfurizing agent for city gas (13A), LPG, and full-range naphtha.
It is said that an Al ₂ O ₃ type is effective. However, these conventional desulfurizing agents have insufficient desulfurization results.

That is, when such a desulfurizing agent having insufficient desulfurization performance is used in the above-described fuel cell system, it is necessary to ensure sufficient activity and life of the catalyst such as a steam reforming catalyst in the subsequent stage. However, there is a problem that it is economically disadvantageous because a large amount of desulfurizing agent must be used, and it is difficult to make the system compact.

[0012]

An object of the present invention is to develop a high-performance desulfurizing agent capable of efficiently and sufficiently removing sulfur from hydrocarbons even at a relatively low pressure, and to use the desulfurizing agent. A method for efficiently removing sulfur from various hydrocarbon fuel materials for fuel cells, that is, converting hydrocarbons into a fuel gas mainly composed of hydrogen by at least a steam reforming reaction, and using the obtained hydrogen as a fuel An object of the present invention is to provide a method for desulfurizing a hydrocarbon raw material, which is a method that can be used very advantageously in a battery system.

[0013]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a desulfurizing agent comprising a specific component prepared by a specific preparation method called a coprecipitation method (namely, copper , Nickel and zinc oxide) are extremely effective as desulfurizing agents for various fuel cell hydrocarbon materials such as kerosene, LPG, and naphtha. It has been found that the sulfur content can be easily removed and reduced to a low concentration of 0.1 ppm or less. So, in fact,
The desulfurizing treatment of the hydrocarbon raw material for the fuel cell is performed prior to the steam reforming reaction by using this novel high-performance desulfurizing agent, and the reformed gas is treated with a denaturing catalyst as required, and the fuel for a hydrogen-containing fuel cell is produced. As a result of configuring and evaluating a fuel cell system using gas, the performance of the desulfurizing agent has been significantly improved.
It was confirmed that the activity of a catalyst such as a steam reforming catalyst in the latter stage was sufficiently exhibited, and the life of the catalyst was significantly extended. Also,
In the case of this desulfurizing agent, it has also been found that a small amount of the desulfurizing agent exhibits a sufficient effect, so that the fuel cell system can be easily made compact. We have:
The present invention has been completed mainly based on these findings and facts.

That is, according to the present invention, prior to reforming a hydrocarbon raw material into a fuel gas containing hydrogen as a main component by a steam reforming reaction, the hydrocarbon raw material is brought into contact with a desulfurizing agent comprising copper, nickel and zinc oxide produced by a coprecipitation method. It is intended to provide a method for desulfurizing a hydrocarbon raw material for a fuel cell, wherein

In this desulfurization method, various hydrocarbons are converted into a reformed gas containing hydrogen as a main component by a steam reforming reaction, and the reformed gas is subjected to a denaturation treatment as required, so that the hydrogen-containing fuel for a fuel cell can be obtained. In various fuel cell systems of the type used by converting to gas, it is suitable as a means for sufficiently removing the sulfur content from a hydrocarbon-containing raw material used for producing the hydrogen-containing fuel gas (that is, a hydrocarbon raw material for a fuel cell). Can be used. In this case, the desulfurization treatment is performed prior to the steam reforming reaction.

In the desulfurization method of the present invention, in order to sufficiently remove sulfur from the hydrocarbon raw material, at least the desulfurization agent comprising at least the specific desulfurization agent, ie, copper, nickel and zinc oxide produced by a coprecipitation method. (Hereinafter, may be referred to as a desulfurizing agent [A] to distinguish it from a general desulfurizing agent).

It is important that the desulfurizing agent [A] is prepared by a coprecipitation method, and generally it can be suitably obtained by the following method.

That is, in order to produce the desulfurizing agent [A], first, a precipitate comprising at least a copper component, a nickel component and a zinc component is made to act on an aqueous solution of these starting metal compounds with an appropriate precipitant. The precipitate is formed by co-precipitation (the details of the raw material metal compound, precipitant and co-precipitation method used for forming the precipitate will be described later).
The precipitate thus formed by the coprecipitation method is aged, if necessary, and then separated from the liquid by filtration or the like,
Wash if necessary. In this way, a particulate solid is usually obtained. The solid thus obtained is usually preferably dried at an appropriate temperature (preferably 100 to 120 ° C.) and then calcined at an appropriate temperature (preferably 300 to 600 ° C.). In addition, this baking is generally preferably performed in an air stream. Further, it is preferable that the particulate solid such as the calcined product obtained as described above is added to an additive such as graphite if necessary, and then formed into an appropriate size by, for example, tableting or the like.

As described above, the desired precursor of the desulfurizing agent [A] can be suitably produced. The precursor thus obtained usually comprises at least copper oxide, nickel oxide and zinc oxide. The desired desulfurizing agent [A] converts the composite oxide precursor into, for example, hydrogen,
An appropriate temperature (preferably 200 to 500) in a reducing gas atmosphere such as carbon monoxide or a mixed gas thereof.
(Temperature of ° C.) to reduce copper oxide and nickel oxide to a metal state, respectively, to obtain copper-nickel-zinc oxide. This reduction is
The reduction gas may be appropriately diluted with an inert gas such as nitrogen, for example. This reduction treatment may be performed in a desulfurization reactor in the fuel cell system, or may be separately performed in advance.

In producing the desulfurizing agent [A], each metal compound (copper compound, nickel compound and zinc compound) used for forming a precipitate by the coprecipitation method is as follows:
There is no particular limitation as long as a predetermined aqueous solution is obtained and can be subjected to the coprecipitation method.For example, nitrates, sulfates, inorganic acid salts such as chlorides, organic acid salts such as acetates, alkoxides, A wide variety of compounds can use ammine complexes and the like. Among these, copper nitrate, nickel nitrate and zinc nitrate are particularly preferably used.

On the other hand, the precipitant used for the formation of the precipitate by the coprecipitation method is not particularly limited, and may be appropriately selected depending on other conditions such as the kind of the starting metal compound used and the composition of the aqueous solution. It is sufficient to select and use those, but usually, a hydroxide or carbonate of an alkali metal element such as sodium or potassium or an alkaline earth metal element is preferably used, and these may be used as they are or as an aqueous solution. Can be used. Ammonia water or the like is also preferably used.

In the coprecipitation method, as in the case of a general coprecipitation method, the types of raw metal compounds (in this case, copper compound, nickel compound and zinc compound) to be used and the composition, addition or There are various modifications depending on the type of the precipitant to be mixed, its use form (for example, whether it is added as an aqueous solution or as it is, etc.), the method of mixing the aqueous solution of the metal compound and the precipitant, and the like. Can be applied. Generally, for example, an aqueous solution in which a copper compound, a nickel compound, and a zinc compound are dissolved, such as an aqueous solution in which copper nitrate, nickel nitrate, and zinc nitrate are dissolved, is prepared. The method of mixing and coprecipitating is preferably adopted, but the method is not necessarily limited to the method using an aqueous solution containing three kinds of metal components of a copper compound, a nickel compound, and a zinc compound. Various modifications are possible, such as a method of mixing an aqueous solution of ammonia such as nickel nitrate and an aqueous solution of zinc nitrate.

As described above, the desulfurizing agent [A] comprising at least copper, nickel and zinc oxide can be suitably obtained by the coprecipitation method. The ratio of the copper component, the nickel component and the zinc component in the desulfurizing agent [A] is usually [(1-3):
(1-5): (3-7)], preferably [(0.5-
2.0): (2.0-4.0): (5.0-7.0)]
It is appropriate to select within the range.

In the desulfurization method of the present invention, the desulfurizing agent [A] produced as described above is brought into contact with a predetermined hydrocarbon material (various fuel cell hydrocarbon materials) under appropriate reaction conditions. It desulfurizes and sufficiently removes the sulfur content in the raw material.

Here, the hydrocarbon raw materials to be subjected to desulfurization are hydrocarbon raw materials of various compositions containing one or more hydrocarbons which can be converted into a fuel gas mainly composed of hydrogen by a steam reforming reaction. And usually
Hydrocarbon-based raw materials containing one or more hydrocarbons having various boiling points ranging from methane to gas oil fractions (preferably those mainly containing alkanes) are suitably used. Such hydrocarbon raw materials are not limited to petroleum-based materials, and various types of hydrocarbon materials such as natural gas-based materials and coal-based materials can be applied. Among them, those which can be particularly preferably used include, for example, hydrocarbon-containing gas mainly composed of relatively lower alkanes such as methane, ethane, propane and butane, natural gas or LNG, and various city gases. , LP
G, naphtha, kerosene, various light oils and the like can be exemplified. In addition, these hydrocarbon raw materials may be those whose sulfur content has been reduced in advance by ordinary hydrodesulfurization.

In this desulfurization method, the concentration of sulfur contained in the raw material to be subjected to the desulfurization is usually in the range of 0.1 to 100 ppm, preferably 5 to 65 ppm, based on the weight in terms of sulfur S. Some are good targets. Here, these raw materials may contain only an organic sulfur compound (or mercaptan) as the sulfur component, may contain only hydrogen sulfide, or may contain both of them. Good.

The desulfurization treatment performed using the desulfurizing agent [A] can usually be suitably carried out under the following reaction conditions.

When the raw material to be supplied contains an organic sulfur compound, it is usually desirable to carry out the desulfurization treatment in the presence of hydrogen. That is, the desulfurizing agent [A] produced by the coprecipitation method as described above has a high chemical adsorption capacity for sulfur (particularly hydrogen sulfide). On the other hand, when only hydrogen sulfide is contained as the sulfur content, it can be sufficiently removed by the adsorption reaction without necessarily adding hydrogen. Therefore, hydrogen may be added and subjected to desulfurization treatment as occasion demands. At that time, the hydrogen or the hydrogen-containing gas to be added may be one that is easily prepared separately, or a part of the hydrogen or the hydrogen-containing gas contained in the product after the steam reforming reaction in the latter stage may be recycled. Or a combination of these.

The reaction temperature in the desulfurization treatment is usually 2
It is suitable to select the temperature in the range of 80 to 380 ° C, preferably 330 to 360 ° C.

The reaction pressure is usually 1.0 to 10.0 kg
/ Cm ² G, preferably 5.0 to 6.0 kg / cm ²
It is preferable to select in the range of G.

The space velocity of the feed is determined by the liquid space velocity (LHS) calculated from the apparent volume of the desulfurizing agent [A] used and the volume of hydrocarbons in the feed when the hydrocarbons are liquefied.
V) is usually 0.1 to 2.0 h ^-1 , preferably
It is preferable to select from the range of 0.2 to 1.0 h ^-1 .

The proportion of hydrogen added is usually at least equimolar to the sulfur content (sulfur S) contained as an organic sulfur compound in the raw material, preferably 0.05 to 0.5 H _2.
It is preferable to select within the range of Nl / kerosene · g.

As a reaction system in this desulfurization treatment,
Although there is no particular limitation, usually, a continuous flow method using a fixed bed method is suitably used.

As described above, the sulfur content (organic sulfur compound and hydrogen sulfide) in the raw material can be easily reduced to a sufficiently low concentration, and the low sulfur content suitable as the raw material for the steam reforming reaction in the fuel cell system can be obtained. A hydrocarbon-containing product containing sulfur can be obtained efficiently. It is desirable that the sulfur content be reduced to 0.1 ppm or less, usually on a weight basis in terms of sulfur S. By this desulfurization method, hydrocarbons suitable for such a low sulfur content steam reforming reaction are used. The inclusion can be easily obtained.

That is, by applying the desulfurization method of the present invention prior to the conventional steam reforming reaction in a fuel cell system, the sulfur content of various hydrocarbon fuel materials for fuel cells can be efficiently reduced to a sufficiently low concentration. Therefore, the subsequent decrease in the activity of the steam reforming catalyst or the modified catalyst can be significantly suppressed, and the catalyst life can be significantly increased. In addition, the desulfurizing agent [A] used in this method has a remarkably superior desulfurizing performance as compared with the conventional desulfurizing agent, so that the amount of the desulfurizing agent used can be much reduced, and therefore, the desulfurizing device and thus the fuel cell system can be used. Compactness can be easily realized.

The steam reforming reaction and the modification treatment in the latter stage can be carried out by a conventional method, and the desulfurization step using this desulfurizing agent [A] is performed in the former stage of the steam reforming reaction step in the conventional fuel cell system. A fuel cell system that is far superior to the conventional one can be configured simply by incorporating it as a desulfurization step.

[0037]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples of the present invention and Comparative Examples thereof, but the present invention is not limited to these Examples.

EXAMPLE 1 36.2 g of copper nitrate (trihydrate) and nickel nitrate (hexahydrate)
130.8 g and zinc nitrate (hexahydrate) 267.7 g were dissolved in ion-exchanged water to prepare 1.5 liter of a mixed aqueous solution of these metal nitrates, while 159 g of sodium carbonate (anhydrous salt) was added to ion-exchanged water. After dissolving, 1.5 liters of an aqueous solution of sodium carbonate was prepared.
Heated to 0 ° C. Next, these aqueous solutions were quickly mixed to form a precipitate under stirring at 80 ° C. After the formation of the precipitate was completed, stirring was continued at 80 ° C for 2 hours to ripen.

Thereafter, the precipitate was separated from the liquid by filtration and washed several times with an appropriate amount of ion-exchanged water. The solid thus obtained was dried at 120 ° C. for 12 hours, and then dried in an air stream for 4 hours.
The mixture was calcined at 50 ° C. for 2 hours to obtain a powdery solid. Graphite was added to this powder and mixed so that the graphite content was 5% by weight, and the mixture was tableted to obtain a precursor of a desired desulfurizing agent (average particle size: about 5 mm). The desulfurizing agent precursor obtained here is a composite oxide composition composed of copper oxide, nickel oxide, and zinc oxide, and the composition is Cu: Ni: Zn = 1: 3: 6 in atomic ratio. there were.

A predetermined amount of the desulfurizing agent precursor produced by the coprecipitation method as described below is filled in a reaction tube of a continuous flow type evaluation tester for a desulfurization test, and is previously placed in a hydrogen stream.
After reducing at 300 ° C. for 1 hour to obtain a desired desulfurizing agent (Cu—Ni—ZnO), a mixture of a hydrocarbon material and hydrogen is continuously passed through the desulfurizing agent layer under the following reaction conditions, and a predetermined desulfurization test is performed. (Acceleration evaluation test) was performed.

(Conditions for Accelerated Evaluation Test) Desulfurization test apparatus: Continuous flow type evaluation tester (1 inch inner diameter,
A reaction tube with a length of 90 cm is provided.) Desulfurizing agent usage: 60 g (weight as a desulfurizing agent precursor) Supply hydrocarbon material: kerosene (containing sulfur concentration: 62 ppm) Reaction temperature: 330 ° C; Reaction pressure: 6 kg / cm ² G LHSV: 1 h ^-1 ; supply H ₂ / oil ratio: 0.36 Nl
/ G The results of this desulfurization test (accelerated evaluation test) are shown in Table 1.

Comparative Example 1 Copper nitrate (trihydrate) 36.2 g and nickel nitrate (hexahydrate)
130.8 g was dissolved in ion-exchanged water, and 121 g of powdered zinc oxide was added as a carrier to the aqueous solution, evaporated to dryness, and the obtained solid was calcined at 450 ° C. for 2 hours in an air stream to obtain a powder. A solid was obtained. Graphite was added to this powder and mixed so that the graphite content was 5% by weight, and the mixture was tableted to obtain a precursor of a desired desulfurizing agent (average particle size: about 5 mm). The desulfurizing agent precursor obtained here is a supported composition in which copper oxide and nickel oxide are supported on zinc oxide, and the composition is Cu: Ni: Z in atomic ratio.
n = 1: 3: 6.

The conventional desulfurizing agent precursor thus produced by the impregnation method was used, and was changed to a desulfurizing agent (in this case, Cu-Ni / ZnO) in the same manner as in Example 1; A desulfurization test (acceleration evaluation test) was carried out under the same conditions as in Example 1 using the desulfurizing agent of Example 1.

Table 1 shows the results of the desulfurization test (acceleration evaluation test).

Comparative Examples 2 to 4 A desulfurization test (acceleration evaluation test) was performed under the same conditions as in Example 1 except that the respective commercially available catalysts (manufactured by Nissan Gardler Co., Ltd.) shown in Table 1 were used as desulfurizing agents. Was.

Table 1 shows the results of these desulfurization tests (accelerated evaluation tests).

[0047]

[Table 1] * Sulfur was analyzed by coulometry and conductivity.

Example 2 The same procedure as in Example 1 was repeated except that the desulfurizing agent precursor prepared by the coprecipitation method was used.
A desulfurization test (accelerated life evaluation test) was carried out under the same conditions as in Example 1 using this desulfurizing agent instead of (Ni-ZnO).

Table 2 shows the results of the desulfurization test (accelerated life evaluation test).

[0050]

[Table 2]

[0051]

According to the desulfurization method of the present invention, a high-performance desulfurizing agent capable of efficiently and sufficiently removing sulfur (organic sulfur compounds and hydrogen sulfide) from a hydrocarbon-containing raw material even at a relatively low pressure (ie, The desulfurizing agent [A]) consisting of copper, nickel and zinc oxide produced by the coprecipitation method was developed,
Since it uses a desulfurizing agent, for example, kerosene, light oil,
It is possible to efficiently remove sulfur from various kinds of hydrocarbon feedstocks for fuel cells such as LPG, city gas, and natural gas.
Therefore, by performing this desulfurization treatment prior to subjecting the hydrocarbon raw material to a steam reforming reaction to reform the fuel gas containing hydrogen as a main component, the activity of the steam reforming catalyst or the reforming catalyst due to sulfur content decreases. Can be greatly reduced,
Their catalyst life can be significantly increased. Further, since the desulfurizing agent [A] used in the method of the present invention has a remarkably high desulfurizing ability as compared with the conventional desulfurizing agent, the amount of the desulfurizing agent used can be reduced. Can be significantly compacted as compared with conventional ones.

That is, according to the present invention, in particular, various hydrocarbon-containing raw materials in various hydrogen-burning fuel cell systems including a fuel cell system when the operating pressure is relatively low at about 10 kg / cm ² G or less. It is possible to provide an excellent method for desulfurizing a hydrocarbon raw material for a fuel cell, which can be suitably used as a desulfurization means.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-188405 (JP, A) JP-A-2-204301 (JP, A) JP-A-2-302303 (JP, A) JP-A-2- 302302 (JP, A) JP-A-1-123627 (JP, A) JP-A-5-70780 (JP, A) JP-A-6-212173 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) C10G 29/04 B01D 53/46 C10G 29/16

Claims (1)

(57) [Claims] 1. Prior to reforming a hydrocarbon raw material into a fuel gas mainly composed of hydrogen by a steam reforming reaction, the hydrocarbon raw material is brought into contact with a desulfurizing agent comprising copper, nickel and zinc oxide produced by a coprecipitation method. Method for desulfurizing a hydrocarbon raw material for a fuel cell.