JPH0970540A - Electric conductive catalyst for combustion of hydrocarbon and its combusting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively oxidize and combust hydrocarbons by using an electric conductive catalyst comprising a specified oxide. SOLUTION: This electric conductive catalyst is used for combustion of hydrocarbons and consists of a multiple oxide expressed by La1-x Ax MO3 , wherein A represents Sr, Ca or Ag, M is Mn, Co or Fe, and X is 0 to 0.8. When A is Sr, M is Mn, Co or Fe, and when A is Ca or Ag, M is Mn. By passing a gas containing hydrocarbons through this electric conductive catalyst, hydrocarbons are oxidized and combusted. This electric conductive catalyst has excellent catalytic performance as a catalyst for oxidation and combustion of hydrocarbons, especially methane or a hydrocarbon containing methane, and the catalyst is rapidly heated and activated by applying an electric current. Thereby, this catalyst is effective to decrease the amt. of hydrocarbons exhausted from a gasoline engine and the like when the engine is started. Thus, a preheating burner or the like is not necessary.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrically conductive catalyst for burning hydrocarbons and a method for burning hydrocarbons using the electrically conductive catalyst.

[0002]

2. Description of the Related Art Catalytic combustion, that is, a method of burning various fuel gases by a catalyst, involves contacting the fuel gas with air on a solid catalyst to cause an oxidation reaction, and converting it into harmless CO ₂ and H ₂ O. Although it generates heat energy at the same time, this catalytic combustion (1) has a wide fuel concentration range (air /
Combustion progresses at a fuel ratio), and combustion is possible even with a lean air-fuel mixture in which flame combustion is not possible. (2) Complete combustion of hydrocarbons (HC) and carbon monoxide (CO) that does not contain heat NOx It is possible to obtain various combustion gases, (3) the combustion starting temperature is low, the temperature of the combustion surface is uniform, and the combustor can have any shape.

Further, in gas engines, gas turbines, boilers for power generation, heating furnaces, etc., city gas and other fuel gases including methane, ethane, propane, butane, etc. are used as the fuel gas. . However, in addition to NOx, SOx, odorous substances, dust, etc., unburned hydrocarbons (H
C) and carbon monoxide (CO) are contained. Of these, particularly unburned hydrocarbons are contained in a large amount in the exhaust gas at the start of cold combustion, and therefore the unburned hydrocarbons need to be oxidized and removed.

One of the methods for oxidizing and removing unburned hydrocarbons in the exhaust gas is to use an appropriate oxidation catalyst for combustion, but few oxidation catalysts are effective at low temperatures. , Works effectively at high temperatures. In this respect, when the hydrocarbons are methane in particular, there is a problem in low temperature ignitability because it is flame retardant,
For this reason, in order to effectively burn and remove unburned hydrocarbons containing methane with an oxidation catalyst, it is necessary to heat the catalyst to raise its temperature. For example, a preheating burner for heating exhaust gas is required. Is.

By the way, an energized catalyst capable of heating the catalyst with the Jule heat generated by energizing the conductive catalyst can be heated by energizing it only when necessary for the reaction to accelerate the catalytic reaction. As a result, combustion of fuel hydrocarbons such as city gas containing methane and others in a closed space,
Alternatively, it is considered to be effective for removing unburned hydrocarbons by oxidation, for example, reducing the amount of hydrocarbons emitted during cold start (that is, at start-up) of a gasoline engine vehicle or the like.

[0006]

The present inventor has previously clarified that the oxide superconductor has excellent characteristics as an electrocatalyst for the CO oxidation reaction. As a result of various experiments and studies on the effectiveness of hydrocarbons as an electrocatalyst for the oxidative combustion of hydrocarbons, specific composite oxides among various composite oxides were found to be hydrocarbons, especially methane and methane. It has been found that it exhibits an excellent energizing catalytic activity for the combustion of hydrocarbons containing. That is, an object of the present invention is to provide an electrically conductive catalyst for combustion of hydrocarbons, which is composed of a specific composite oxide described below, and oxidizes and burns hydrocarbons by using the electrically conductive catalyst. The purpose is to provide a method.

[0007]

[Means for Solving the Problems] That is, the present invention provides an electrically conductive catalyst for burning hydrocarbons, which is La _1-X A _X MO.
₃ (In the formula, A is Sr, Ca or Ag, M is Mn, Co or Fe, and x = 0 to 0.8. However, when A is Sr, M is Mn, Co or Fe, A is Ca or Ag
In this case, M is Mn), and an electrically conductive catalyst for hydrocarbon combustion is provided.

Further, the present invention uses a gas containing hydrocarbons as L
_{a 1-X A X MO 3} ( where, A is Sr, Ca or Ag, M is Mn, is Co or Fe, x = 0~0.8. However, A
When Sr is M, M is Mn, Co or Fe, and when A is Ca or Ag, M is Mn). A method for oxidative combustion of hydrocarbons is provided.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Here, the above composite oxide La _1-X A _X
MO ₃ is mainly a perovskite type (Perovsk
It has a crystal structure of (ite type). In the same equation,
When A is Ca or Ag, M is Mn, which can be specifically shown as La _1-x Ag _x MnO ₃ and La _1-x Ca _x MnO ₃ . When A in the formula is Sr,
M is any one of Mn, Co, and Fe, and specifically, it can be shown as La _1-X Sr _X MnO ₃ , La _1-X Sr _X CoO _3, and La _1-X Sr _X FeO _3. . Further, in these formulas, the value of x is preferably in the range of 0 to 0.8, more preferably in the range of 0 to 0.6.

Further, the above composite oxide La _1-X A _X MO ₃
(In the formula, A is Sr, Ca or Ag, M is Mn, Co or Fe, and x = 0 to 0.8. However, when A is Sr, M is Mn, Co or Fe, and A is Is Ca or Ag
In this case, M is Mn) can be produced by various methods such as a dry evaporation method, a solid phase reaction method, and a coprecipitation method (carbonate method). As an example, to describe the embodiment in the case of the evaporation dryness method, for example, first the acetate of each metal, the salt of each raw material metal such as nitrate is dissolved in water to form a mixed aqueous solution,
Evaporate to dryness with stirring. Next, the metal salt mixture is decomposed at, for example, a temperature of about 350 ° C., pulverized and mixed, and then baked at a temperature of, for example, about 850 ° C.

The composite oxide produced as described above is usually obtained as powdery crystals. At the time of use, it is necessary to heat by energizing, but either direct current or alternating current can be used as the heating power source. As a mode of using this composite oxide in a powder form, it can be used by filling and accommodating the catalyst powder in a layer form, and energizing and heating it. Further, the catalyst powder can be molded into pellets of, for example, a cylindrical shape, and electrodes can be formed at both ends thereof to obtain a molded catalyst for energization. It is desirable to apply an appropriate amount of pressure during this molding as necessary, so that it maintains a certain strength as a molded product, maintains an appropriate air permeability when used as a catalyst, and conducts a current evenly when energized. can do. The powder of the complex oxide according to the present invention can be molded as it is, but if necessary, an appropriate binder may be mixed and used.

FIG. 5 schematically shows one embodiment of an apparatus using the catalyst of the present invention. In FIG. 5, A is a gas flow,
B is a conduit (reaction tube), and C is an electrically conductive oxidation catalyst.
Further, D is a power source, and E is a conducting wire from the power source D. An electric current is applied from the power source D at the time of operation, and the catalyst C is heated to a predetermined temperature through the conductive electrodes on the front and rear surfaces of the catalyst C. F is the oxidation treated gas stream. Although the embodiment shown in FIG. 5 is horizontal, the catalyst of the present invention can be applied in an appropriate format used when using this type of solid catalyst. The heating electric energy is not limited to direct current, and may be induction heating by AC or dielectric heating. In this case, for example, a mode in which electrical energy for heating the catalyst is added from the outside of the conduit reaction tube. Etc.

[0013]

EXAMPLES Examples of the present invention will be described below, but it goes without saying that the present invention is not limited to these examples. In this example, various test catalysts were prepared as follows, and various performance tests were performed on each test catalyst.

<< Preparation of Test Catalyst >> (1) Various composite oxides of perovskite type, K ₂ NiF ₄ type and spinel type were prepared by evaporation to dryness. Acetate or nitrate was used as the starting material, but the following substances were used depending on the type of metal. A mixed aqueous solution of these metal acetate raw materials or metal nitrate raw materials corresponding to various complex oxides was stirred on a hot plate while heating to evaporate water, and then dried overnight at a temperature of 110 ° C. Acetate: La, Na, K, Ca, Sr, Mn, Co, C
u Nitrate: Fe, Ba, Ag

The dried products obtained in (2) and (1) were pulverized and mixed, thermally decomposed at a temperature of 350 ° C. (heating rate 5 ° C./min) for 1 hour, and further pulverized and mixed. (3)
Then, the crushed mixture was placed in an alumina crucible and fired at a temperature of 850 ° C. (heating rate of 10 ° C./min) for 5 hours to obtain powders of various target composite oxides. For the complex oxide containing Co, a Pt crucible was used because Co reacts with alumina. In the following performance test, when a powder catalyst was used as the test catalyst, the powder catalysts at this stage were set in layers in a normal atmospheric fixed bed flow reactor and used.

When the powder catalysts obtained above are molded into cylindrical pellets to be used as test catalysts, the following (4) to
Prepared as in (5). (4), (1) to (3) above
3 g of each catalyst powder obtained in step 1 was molded into a cylindrical pellet (diameter: 13 mm, length: 6 mm), and the pellet was placed on a firing board made of alumina ceramics (Co
For the catalyst containing Pt, a Pt crucible was used for the same reason as above), and the mixture was sintered in air at the same temperature as the above firing temperature of 850 ° C. for 1 hour and then gradually cooled to room temperature to obtain a sintered body. A through hole (diameter: 3 mm) for inserting a thermocouple for temperature measurement was opened in this pellet sintered body.

(5) Next, a conductive adhesive made of silver was applied to the upper surface (one end surface) of each cylindrical pellet sintered body, and then dried in air at a temperature of 650 ° C. for 10 minutes (minutes). Similarly, a conductive adhesive made of silver was applied and dried on the lower surface (the other end surface) to form both electrodes. Conductive wires were fixed to both electrode surfaces with a conductive adhesive, and the thus obtained cylindrical pellet sintered body with a silver electrode was used as a current-carrying catalyst. A test catalyst for the following combustion performance test (combustion activity test) And

<< Performance test >> Each of the energized test catalysts obtained in the above-mentioned steps has an inner diameter of 2 if the catalyst is a cylindrical pellet catalyst.
It is set in a 0 mm stainless steel reaction tube (B in FIG. 7, as an oxidation catalyst layer C therein), and in the case of a powder catalyst, a normal atmospheric fixed bed flow reactor (vertical type) Filling and setting in layers in each, and the presence or absence of changes in the amount of energization (current) and temperature rise under each of the following conditions for each test catalyst,
The combustion performance of methane was investigated. A variable DC power supply was used for energization. 1 to 5 show the results of these tests.

First, FIGS. 1A and 1B show La _1-X Sr _X M.
This is an examination of the x value of the pellet-shaped test catalyst made of nO ₃ and the temperature rise characteristics during energization. Here, the amount of energization (current) and the presence or absence of a temperature rise and changes after the start of energization are shown over time. In this test, helium (He) was used as the passing gas to each test catalyst, the flow rate was 100 cm ³ / min, and the applied voltage was 3 V.
And As shown in FIGS. 1A and 1B, first, x = 1.0.
No current flows (that is, it is not electrically conductive) with the tested catalyst (indicated by a black square in the figure), which means that it is not heated by energization, indicating that it is not suitable as an electrically conductive catalyst. There is.

On the other hand, in the case of x = 0 to 0.5, the amount of energization increases rapidly immediately after the start of energization, and the heating is rapid accordingly. Although there is a slight (slight) difference in the tendency of the temperature rise with respect to the amount of electricity applied, the change in the amount of electricity is directly related to and related to the change in the temperature rise, and the two almost correspond. As shown in FIG. 1 (a), the heating temperature tends to increase at a temperature of about 500 minutes about 10 min (minutes) after the start of energization.
The temperature reached around ℃, and thereafter this temperature was x = 0 (in the figure: ○
), X = 0.3 (in the figure: □), x = 0.4 (in the figure:
Both are marked with ⋄ and x = 0.5 (marked with ∇ in the figure). Also, in the case of x = 0.2 (marked by Δ in the figure), although there is some difference as compared with them, there is a tendency of considerable temperature increase.

FIG. 2 shows the oxidation rate of methane [= conversion rate: C after the start of energization depending on the x value of the pelletized test catalyst also made of La _{1 -X} Sr _x MnO ₃ ].
Shows the results of testing H ₄ conversion (%)]. CH ₄ : 5000 as test gas
A mixed gas of ppm, O ₂ : 10% and He: balance (balance) was used, and this was supplied at a speed of 50 cm ³ / min, and a direct current with a voltage of 3 V was supplied. Here, "CH ₄ oxidation ratio (%)" is, CH ₄ at the outlet portion of the CH ₄ concentration in the feed gas to the catalyst layer D X, the conduit B, and Catalyst C
It is calculated by the following equation (1), where Y is the density,
The same applies to the oxidation performance tests below this point. The CH ₄ concentration Y at the outlet of the catalyst C was analyzed by gas chromatography.

[0022]

[Equation 1]

As shown in FIG. 2, the oxidation rate of methane rises rapidly from the start of energization, and after 10 minutes, x = 0.
In any of the cases of 0.5 to 0.5, the oxidation rate of methane is 60% or more. As shown in FIGS. 1 (a) and 1 (b), the energization amount rapidly increases immediately after the start of energization and is rapidly heated and the temperature rises, but the oxidation rate of methane is almost proportional to this and rises correspondingly rapidly. are doing. It should be noted that this oxidation rate immediately becomes 0% when the supply power is turned off (at the time of 180 min in the figure), but this means that each test catalyst is rapidly cooled by the supply gas and loses its oxidation catalytic ability. Is shown. When x = 1.0 (marked by ■ in the figure), the oxidation rate of methane is zero from the beginning, but this is shown in FIG.
This corresponds to the result shown in (b).

FIG. 3 is a graph showing the La _{1 -X} Sr _X MnO ₃ pellet-shaped test catalysts, which were varied in the range of x = 0 to 1.0, and methane oxidation at reaction temperatures of 500 ° C., 550 ° C. and 600 ° C. It is the result of a test on how to do it.
The gas for testing CH _4: 5000ppm, O _2:
A mixed gas of 10% and He: balance (balance) was used, and this was supplied at a supply rate of 50 cm ³ / min. In this case, the test catalyst was heated while controlling the voltage of the variable DC power supply and adjusting each temperature to the above temperature.

As shown in FIG. 3, the methane (CH ₄ ) oxidation rate (%) of the La _{1 -X} Sr _X MnO ₃ catalyst is more effective when the reaction temperature is higher, but the temperature is 500 ° C. and the temperature is 550 ° C.
And at any temperature of 600 ° C., the CH ₄ oxidation rate (%) showed the maximum at x = 0.5 and before and after that. Further, for example, at a temperature of 600 ° C., x = 0 to 0
CH ₄ oxidation rate of about 58% or more in the range of 0.7,
In the range of x = 0.4 to 0.6 show the CH ₄ oxidation of greater than or equal to about 65%.

FIG. 4 shows La _0.5 Sr _0.5 MnO ₃ (= perovskite type), La _0.8 Sr _0.2 CoO ₃ (= perovskite type), La _0.8 Sr _0.2 FeO ₃ (= perovskite type), La _1.8 Sr _0.2 CuO ₄ ( = K ₂ Ni
F ₄ type), La _1.8 Ba _0.2 CuO ₄ (= K ₂ NiF
₄ type), MnFe ₂ O ₄ (= spinel type) and CuF
These are the results of testing the temperature dependence of the methane oxidation rate using various complex oxide powders of e ₂ O ₄ (= spinel type) as pellet-shaped test catalysts. In this test, the amount of catalyst is 0.05g
Using, as the test gas CH _4: 5000pp
A mixed gas of m, O ₂ : 10% and He: balance (balance) was used, and this was supplied at a supply rate of 50 cm ³ / min.

As shown in FIG. 4, La _0.5 Sr _0.5 MnO ₃
(In the figure: ○), La _0.8 Sr _0.2 CoO ₃ (in the figure: △
Mark) and La _0.8 Sr _0.2 FeO ₃ (in the figure: □ mark), the oxidation rate of methane rapidly increases with increasing temperature, and at a temperature of 650 ° C., the oxidation rate is as high as about 80%. On the other hand, with respect to, the oxidation rate increases somewhat with increasing temperature.
Even with La _1.8 Sr _0.2 CuO ₄ (marked with ⋄ in the figure), the methane oxidation rate reaches only less than 40% even at 650 ° C. As described above, the excellent electrocatalytic oxidation effect of the catalyst according to the present invention is clear.

Table 1 shows the complex compound La _{1 -X} of the present invention.
In A _X MO ₃ , A is Sr, Ca and Ag, respectively.
And shows the conversion rate (oxidation rate) of methane when M is Mn (pellet test catalyst, temperature 500 ° C., 5
50 ° C. and 600 ° C.), and Table 2 shows La _1-X Ag _X M
Self-heating characteristics of nO ₃ pellet-shaped test catalyst by conducting electricity at a voltage of 1.5 V (Self-heati
ng property).

First, as shown in Table 1, La _0.95 Ag _0.05 MnO ₃ and La _0.9 A which are composite compounds containing Ag and Ca.
in the case of g _0.1 MnO ₃ and La _0.9 Ca _0.1 MnO _3, also excellent conduction catalytic effect as that of LaMnO ₃ and La _0.9 Sr _0.1 MnO ₃ is obtained. Also, as shown in Table 2, the temperature of La _1-X Ag _X MnO ₃ increased rapidly upon the start of energization, although there was some difference depending on the x value, and almost corresponded to the catalytic effect shown in Table 1. You can see that

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

As described above, the electrically conductive catalyst according to the present invention has excellent catalytic performance as a catalyst for oxidative combustion of hydrocarbons, particularly methane or hydrocarbons containing methane,
It is rapidly heated by activation of electricity and activated. For this reason, unburned hydrocarbons (mainly methane) in exhaust gas from combustion of city gas using a catalyst (mixing city gas with air to pass through the catalyst), gas engine, gasoline engine, or various combustion equipment. It can be used very effectively as an electrically conductive catalyst for the oxidation and combustion of In addition, since it is effective in reducing the emission of hydrocarbons when starting up a gasoline engine and others, it was necessary in the past.
Excellent effects such as the need for a preheating burner and the like are obtained.

[Brief description of drawings]

FIG. 1 is a graph showing the amount of energization (current) and the presence / absence of a temperature increase in La _{1 -X} Sr _X MnO ₃ depending on the value of x after the start of energization.

FIG. 2 is a graph showing changes in the methane conversion (oxidation) rate of La _{1 -X} Sr _X MnO ₃ after the start of energization depending on the value of x.

FIG. 3: For La _1-X Sr _X MnO ₃ , x = 0 to 1.
Reaction temperature when varied in the range of 0, 500 ° C., 550
The figure which shows the conversion rate of methane in ° C and 600 ° C.

FIG. 4 La _0.5 Sr _0.5 MnO ₃ and La _0.8 Sr
_0.2 CoO ₃ , La _0.8 Sr _0.2 FeO ₃ , La _1.8 S
r _0.2 CuO ₄ , La _1.8 Ba _0.2 CuO ₄ , MnF
e ₂ O ₄ and CuFe ₂ O ₄ of the various composite oxides methane conversion carried out on (oxidation) shows the performance and temperature dependency.

FIG. 5 is a diagram schematically showing one embodiment of an apparatus using the catalyst of the present invention.

[Explanation of symbols]

 A gas flow B conduit (reaction tube) C electrically conductive oxidation catalyst D power source E lead wire from power source D F oxidized gas flow

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location B01J 23/78 ZAB F23C 11/00 306 23/89 ZAB B01D 53/36 ZABZ F23C 11/00 306 104Z

Claims (8)

[Claims] 1. An electrically conductive catalyst for combustion of hydrocarbons, which is La _1-X A _X MO ₃ (wherein A is Sr, Ca or A).
g and M are Mn, Co or Fe, and x = 0 to 0.8.
However, when A is Sr, M is Mn, Co or Fe, and when A is Ca or Ag, M is Mn). Electrically conductive catalyst. 2. The composite oxide is La _1-X Sr _X MnO ₃
The electrically conductive catalyst for hydrocarbon combustion according to claim 1, which is a composite oxide consisting of (in the formula, x = 0 to 0.6). 3. The composite oxide is La _1-X Sr _X MnO ₃
The electrically conductive catalyst for hydrocarbon combustion according to claim 2, which is a composite oxide consisting of (in the formula, x = 0.4 to 0.6). 4. The composite oxide is La _1-X Ca _X MnO ₃
The electrically conductive catalyst for hydrocarbon combustion according to claim 1, which is a composite oxide consisting of (in the formula, x = 0 to 0.6). 5. The composite oxide is La _1-X Ag _X MnO ₃
The electrically conductive catalyst for hydrocarbon combustion according to claim 1, which is a composite oxide consisting of (in the formula, x = 0 to 0.6). 6. The electrically conductive catalyst for hydrocarbon combustion according to claim 1, 2, 3, 4, or 5, wherein the hydrocarbon is methane or a hydrocarbon containing methane as a main component. 7. A gas containing hydrocarbon is La _{1 -X} A _X MO ₃
(In the formula, A is Sr, Ca or Ag, M is Mn, Co or Fe, and x = 0 to 0.8. However, when A is Sr, M is Mn, Co or Fe, and A is Is Ca or Ag
In the case of, M is Mn), and the hydrocarbon is passed through an electrically conductive catalyst composed of a complex oxide. 8. The hydrocarbon combustion method according to claim 7, wherein the hydrocarbon is methane or a hydrocarbon containing methane as a main component.