JPH0820054B2 - Catalytic combustion method of combustible gas - Google Patents

Description

The present invention relates to a method of burning a combustible gas, for example, a gas such as carbon monoxide, hydrogen, or a hydrocarbon, using a catalyst, and particularly to a method for burning methane, which is the most difficult to burn. The present invention relates to a catalytic combustion method capable of stable combustion in a wide temperature range from low temperature to high temperature.

[Conventional technology]

Conventionally, a catalytic combustion method for obtaining a high temperature gas by using a lower hydrocarbon gas such as methane as a fuel and performing a combustion reaction in a diluted state that is not generally in a combustion condition range has been conventionally known. .

As the combustion catalyst in this conventional method, a honeycomb type cordierite or mullite is used as a base material, and alumina, zirconia, magnesia or the like carrier is coated with a washcoat as the active ingredient, and Pt, Pt + Pd as an active ingredient,
Noble metals such as Pd, Pt + Rh, or cobalt, nickel,
A catalyst supporting an oxide of a base metal such as manganese has been proposed.

Recently, a perovskite type oxide (Japanese Patent Laid-Open No. 61-
33232,61636), or a catalyst having a catalytically active component supported on a carrier mainly composed of a composite oxide of aluminum and lanthanum (JP-A-60-12132), or a catalyst containing palladium, platinum and nickel (JP 61-33233), and a catalyst containing a composite oxide of an alkaline earth metal element and aluminum as a main component (JP-A-62-153158) has been proposed.

However, only using the above catalyst leaves various problems such as excellent low temperature ignitability but no heat resistance, or conversely heat resistance but poor low temperature ignitability.

[Problems to be solved by the invention]

However, in the combustion method of a flammable gas using the above-mentioned catalyst alone, low-temperature ignitability is excellent like a palladium-based catalyst, but the agglomeration of palladium occurs at 800 ° C. or higher and the activity decreases, and On the contrary, the heat-resistant catalyst has a problem that the low temperature ignitability is poor.

[Object of the Invention]

In view of the above-mentioned state of the art, the present invention is intended to provide a method capable of burning a combustible gas even at a low temperature and stably performing a complete oxidative combustion at a high temperature.

[Means for solving problems]

The present invention is characterized in that a flammable gas is contacted with a catalyst containing palladium in the first stage and then with a catalyst containing a complex oxide of an alkaline earth metal element, aluminum and manganese in the second stage. This is a catalytic combustion method of gas.

The catalyst containing palladium as referred to in the present invention is a pellet (sphere or cylinder, etc.)-Shaped or honeycomb-type carrier which is loaded with 0.01 to 10% by weight of palladium to stabilize the properties other than palladium. In addition, a group VIII element such as platinum, a rare earth element such as lanthanum, or rhenium is added.

As used herein, the carrier means a heat-resistant base material such as mullite, cordierite, aluminum titanate, zirconia, zirconia spinel, zircon-mullite, etc., and alumina, titania, silica, etc. coated with a washcoat on the heat-resistant base material, or generally a carrier. Means alumina, titania, silica and the like used as.

The complex oxide of the alkaline earth metal element, aluminum and manganese referred to in the present invention is a magnetobrumbite
etoplumbite) type layered aluminate structure, which is represented by the general formula MeMn _x Al _12-x O _19-α (Me: alkaline earth metal element, x = 1 to 3, 0 <α <1) It is a thing. This can be manufactured by the following method.

It was produced by dropping an aqueous solution of manganese nitrate into an alcohol solution containing 1 mol to 11 mol of alkaline earth metal isoproxide and aluminum isobropoxide in an amount such that the alkaline earth metal element and manganese have the same molar ratio. The gel is dried and calcined at 1200 ° C or above.

Powders of a compound of an alkaline earth metal element, a compound of manganese and a compound of aluminum are mixed at a predetermined ratio, pulverized and mixed in a ball mill, and fired at 1200 ° C or higher.

A basic precipitant is added to an aqueous solution of a compound of an alkaline earth metal element, a compound of manganese and a compound of aluminum, the precipitate formed is washed, dried, and calcined at 1200 ° C or higher.

The alkaline earth element, a catalyst containing a composite oxide of aluminum and manganese is formed by adding a binder to the composite oxide, or the heat-resistant base material described above is coated with a washcoat of the composite oxide. Point For example, a composite oxide using barium as an alkaline earth element will be described as an example. BaMn _x Al _12-x O is obtained by substituting a part of Al ions of BaO.6Al ₂ O ₃ layered aluminate with Mn.
It is displayed as _19-α (x: substitution amount). BaMnAl ₁₁ O _{19 − α} = 1
The catalyst calcined at 300 ° C for 5 hours has a high specific surface area of 13.7 m ² / g, and when the gas of 1 g of methane and 99% of air is brought into contact with the catalyst under the conditions of SV 48000h ^-1 , the conversion rate reaches 10%. Temperature is 540
℃ (3rd symposium on catalytic combustion, P.32, 1987).

[Action]

In the combustible gas catalytic combustion method of the present invention, a catalyst containing palladium in the first stage (gas inlet side) and a catalyst containing a complex oxide of an alkaline earth metal element, aluminum and manganese in the second stage (gas outlet side) Since we will place
Good low temperature ignitability and stable combustion even at high temperature.

Taking the combustion of methane, which is the most difficult to burn, as an example, the catalyst containing palladium in the first stage starts the oxidation of methane at 400 ° C or lower, and the temperature of the catalyst layer in the first stage is controlled to fall within the temperature range of 300 to 800 ° C. , A catalyst containing a mixed oxide of alkaline earth elements, aluminum and manganese in the latter stage 60
Stable combustion can be maintained by controlling the temperature within the range of 0 to 1300 ° C.

 Hereinafter, the present invention will be specifically described with reference to examples.

[Example 1] An aqueous solution of manganese nitrate was added dropwise to an isopropyl alcohol solution containing barium isopropoxide and aluminum isopropoxide in a ratio of 1 mol to 11 mol by an amount such that the atomic ratio of barium and manganese was the same. The gel is dried and calcined at 1300 ℃ for 5 hours, and the Mn-based composite oxide 1 (Ba
MnAl ₁₁ O _19−α ) was obtained.

Next, powders of calcium carbonate, manganese carbonate and alumina were mixed in a molar ratio of CaO: Mn ₂ O ₃ : Al ₂ O ₃ = 1: 1: 5, pulverized and mixed in a ball mill for 24 hours, and ℃ and calcined 5 hours at obtain a Mn-based composite oxide _{2 (CaMn 2 Al 10 O 19} -α).

Next, an aqueous solution of strontium nitrate, manganese nitrate, and aluminum nitrate Aqueous solution of sodium carbonate to produce a precipitate, which is washed, dried and calcined at 1300 ° C. for 5 hours.
Mn-based composite oxide 3 (SrMn ₂ Al ₉ O _19-α ) was obtained.

It was confirmed by X-ray diffraction that the above complex oxides 1, 2 and 3 each had a magnetoplumbite structure.

1 inch diameter with 200 openings per square inch (2
Honeycomb-shaped cordierite (2MgO.
2Al ₂ O ₃ · 5SiO ₂ ) base material is immersed in a slurry solution of Mn-based composite oxide 1 (wash coat) and baked at 1400 ° C to coat Mn-based composite oxide 1 on a cordierite base material. 1 (complex oxide 18 per 100 carriers) was obtained.

Catalyst 2 in which cordierite base material was coated with Mn-based composite oxide 2 by the same method as described above (composite oxide 16 per 100 supports)
And a catalyst 3 in which a cordierite base material was coated with Mn-based composite oxide 3 (complex oxide 16 per 100 supports).

1 inch diameter with 200 openings per square inch (2
Honeycomb-shaped cordierite (2MgO.
2Al ₂ O ₃ · 5SiO ₂ ) substrate or aluminum titanate (MgO
4Al ₂ O ₃ .6TiO ₂ ) base material was used to prepare carriers A, B and C by the following method.

Powders of barium carbonate and alumina were mixed in a ratio of BaO: Al ₂ O ₃ = 1: 6, crushed and mixed in a ball mill for 24 hours, then 1300
Barium aluminate (BaO ・ 6
Al ₂ O ₃ ) is coated on the cordierite base material in a wash coat, and 1
A carrier A coated with barium aluminate was obtained by baking at 400 ° C. Further, a carrier B in which barium aluminate was coated on the aluminum titanate substrate was obtained by the same method as above except that the aluminum titanate substrate was used instead of the cordierite substrate. In addition, using a slurry of alumina powder, a cordierite substrate was wash-coated and
A carrier C coated with alumina was obtained by baking at 0 ° C.

Each of the above carriers A, B and C was dipped in an aqueous solution of palladium chloride, dried, calcined at 500 ° C. for 5 hours, hydrogen reduced at 400 ° C. for 3 hours, and a catalyst 4 carrying 1.5% by weight of palladium (Pd) A), catalyst (carrier B), and catalyst 6 (carrier C) were obtained.

The obtained catalyst 4, 5 or 6 was placed in the front stage, and the catalyst 1, 2 or 3 was placed in the rear stage, and the oxidation (combustion) of methane was carried out under the conditions of Table 1.

As a result of conducting the combustion test under the conditions of Table 1, the results shown in Table 2 were obtained.

In this state, it was confirmed that even if combustion was continued for 1000 hours, neither the methane conversion rate nor the outlet gas temperature changed, and stable combustion performance was obtained.

<Comparative Example> In Example 1, the combustion test was conducted under the conditions shown in Table 1 with the catalyst of only the first stage (23.3 ml) or the catalyst of only the second stage (23.3 ml), and the results shown in Table 3 were obtained.

As described above, only the catalyst containing palladium (first stage) is not durable, and the low temperature ignitability is poor only with the catalyst containing Mn-based complex oxide (second stage).

[Example 2] The test was conducted under the same conditions as in Table 1 except that the gas flow rate was 3.57 m ³ N / h (GHSV 150,000h ^-1 ), with the catalyst 4 in the front stage and the catalyst 3 in the rear stage. As a result, the ignition temperature was 270 ° C, the methane conversion rate was 95%, and the catalyst layer outlet gas temperature was 1140 ° C.
It was confirmed that even if combustion was continued for 1000 hours in this state, neither methane conversion rate nor outlet gas temperature changed, and stable combustion performance was obtained.

〔The invention's effect〕

As described above in detail, according to the present invention, it is possible to provide a method of completely oxidizing and burning a combustible gas with a low oxidation start temperature (good ignitability) and at a high temperature.

Claims (1)

[Claims] 1. A method in which a combustible gas is brought into contact with a catalyst containing palladium in the first stage, and then an alkaline earth metal element in the second stage,
A catalytic combustion method for combustible gas, which comprises contacting with a catalyst containing a composite oxide of aluminum and manganese.