JPH0765734B2 - Hydrocarbon fuel catalytic combustor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalytic combustor for use in catalytic combustion in which hydrocarbons such as methane and ethane are burned at a low temperature using a catalyst, and particularly to efficiently and completely burn the hydrocarbons. For a catalytic combustor for.

[0002]

2. Description of the Related Art When hydrocarbons such as methane and ethane are combusted, NOx is generated due to the high temperature in combustion, and incomplete combustion occurs, which is a problem. , A catalyst combustion technology was developed to complete combustion by a catalyst surface heterogeneous reaction and a gas phase radical homogeneous reaction in the catalyst layer.This technology is used in catalyst burners, oil stoves, gas turbines for power generation, etc. This concept is also applied to automobile exhaust gas purification equipment. In a catalytic combustor that specifically performs that, after introducing and mixing fuel gas into the air stream in the premixing preheating zone, for example, from a honeycomb catalyst configured by supporting a catalytically active component on a refractory carrier having a honeycomb structure. The catalyst layer is configured to pass through.

[0003]

However, in the case of using a catalyst in which a catalyst layer is uniformly coated on a monolithic carrier such as the above-mentioned refractory carrier having a honeycomb structure, the catalyst layer is heated at the inlet portion thereof. Since the activity of the catalyst is low because it does not exist, the temperature does not rise, whereas in the latter half of the catalyst layer, the temperature rises as the reaction progresses, so the activity of the catalyst becomes larger and the reaction becomes more vigorous. Tends to rise further. Therefore, in this catalyst layer, there is a problem that the difference between the inlet temperature and the outlet temperature becomes large, and the catalyst does not work or deteriorates due to heat depending on the place.

With respect to this problem, especially when the hydrocarbon is methane which is flame retardant, the reaction does not easily occur on the inlet side. Therefore, in JP-A-59-41706, the reaction is caused on the inlet side at a low preheating temperature. There has been proposed a catalyst system for complete combustion of fuel in which a first catalyst layer containing active palladium as an active component is provided, and then a second catalyst layer containing platinum as an active component is provided.

In this catalyst system, the conditions under which a reaction can occur at a low preheating temperature are brought about by selecting the type of the active component of the catalyst, and palladium is selected as the active component having a high activity at a low temperature on the inlet side, Further, in the subsequent second catalyst layer, platinum suitable for completely burning methane is used as an active ingredient.

However, in this catalyst system, the intended action depends mainly on the selection of the type of the active ingredient, so in order to obtain the effect sufficiently, a large amount of expensive palladium or platinum is required as the active ingredient. In addition, there is a problem in that the formation of the distribution must be carefully performed when the active ingredient is loaded on the monolith carrier coated with alumina and / or zirconia.

The present invention enables a reaction to occur at a low preheating temperature on the inlet side in the catalytic combustor, and allows the reaction to sufficiently proceed and burn thereafter and to withstand the high reaction temperature. It is an object of the present invention to provide a catalytic combustor which can be used for a long period of time.

[0008]

The present invention focuses on the fact that the action of the catalyst is determined not only by the active component of the catalyst, but by the total of the active component and the components and structure of the carrier that supports it. Therefore, the above-mentioned object is to be achieved by selecting not only the active ingredient but also the ingredient of the carrier that carries it.

That is, the present invention provides a catalytic combustor for a hydrocarbon fuel, which comprises Pt and / or Pd as an active ingredient and is composed of a monolith carrier coated with alumina-based porous catalyst particles carrying these active ingredients, Si on the inlet side is 0.5 to 20 mol% with respect to the total amount of Al and Si
An alumina-silica-based porous particle containing a first catalyst layer supporting the above active component is provided, and thereafter alumina or alumina containing 0.1 to 20 mol% of La based on the total amount of Al and La. The above object can be achieved by a catalytic combustor for a hydrocarbon fuel, which is characterized in that a second catalyst layer in which the active component is supported by lanthanum oxide-based porous particles is provided.

In a catalyst in which a metal is supported on a carrier such as alumina, it is known that not only the metal acts as an active component, but also the carrier such as alumina acts as a catalytic active component. The combination of the component and the carrier provides a greater catalytic effect than that of the metal active component alone, and the temperature is low at the inlet side of the catalytic combustor, and the reaction is less likely to occur. 0.5 to 2 with respect to the total amount of Al and Si
Alumina-silica based porous particles containing 0 mol% Pt
It has been found that the one carrying Pd and / or the active ingredient of Pd easily causes a combustion reaction even at a low temperature, and using it,
It forms a catalyst layer.

The alumina-silica porous particles containing Si in an amount of 0.5 to 20 mol% with respect to the total amount of Al and Si may be produced by any method, such as aluminum salt-sodium silicate. The silica-alumina wet gel produced from these or silicon alkoxide-aluminum alkoxide may be filled with an organic solvent in its pores, and the organic solvent itself or the organic solvent- It is preferable to use the one obtained by heat-treating the dried gel through the supercritical condition of the CO ₂ mixed system. When the content ratio of Si to the total amount of Al and Si is less than 0.5 mol%, or 2
When it exceeds 0 mol%, the activity for the reaction is too small to be suitable. If necessary, the alumina-silica based porous particles may contain other components such as magnesia and zirconia.

The alumina-silica based porous particles are impregnated with a solution of a platinum salt such as a platinum salt and / or a palladium salt such as palladium nitrate, and then activated to obtain Pt and / or Pd. Are carried. Alternatively, it may be supported by impregnating alumina-silica sol with the salt solution in advance. P is added to the porous particles.
The first catalyst layer is formed on the inlet side of the catalytic combustor by coating the monolith carrier with t and / or Pd supported thereon.

In the present invention, alumina or La is replaced with Al.
Since the second catalyst layer is formed by the alumina-lanthanum oxide-based porous particles containing 0.1 to 20 mol% of the total amount of Al and La, the second catalyst layer is formed, the fire resistance is excellent. It withstands high temperatures in the gas phase combustion reaction and does not lose its catalytic activity for a long time. On the downstream side of the catalytic combustor, it is not necessary to have a high catalytic activity, because the average temperature rises and shows the maximum reaction rate, where it is much higher than in the normal catalytic reaction process. Since the maximum temperature in the combustor is determined by the maximum usable temperature of the catalyst material, alumina or La as porous particles is used here.
The maximum temperature can be increased by using an alumina-lanthanum oxide system containing 0.1 to 20 mol% of Al with respect to the total amount of La. It is well known that alumina has a high melting point and thus is excellent in fire resistance, but an alumina-lanthanum oxide-based alumina containing 0.1 to 20 mol% of La with respect to the total amount of Al and La is used. The ones have stable fire resistance and both are capable of completely burning hydrocarbon fuels at relatively low temperatures.

The alumina used here and the alumina-lanthanum oxide type porous particles may be produced by any method, but as in the case of the alumina-silica type porous particles, the alumina wet gel or alumina- The lanthanum oxide wet gel was filled with an organic solvent in its pores, and they were filled with the organic solvent itself or the organic solvent-CO.
It is preferable to use a gel obtained by heat-treating a dried gel via a supercritical condition of a _two- mix system. The alumina and the alumina-lanthanum oxide-based porous particles may contain other components in order to further improve their properties. The concentration of the active ingredient supported on the second catalyst layer can be lower than the concentration of the active ingredient supported on the first catalyst layer. In the present invention, the alumina-silica-based, alumina, and alumina-lanthanum oxide-based porous particles are collectively referred to as "alumina-based porous particles".

In order to manufacture the catalytic combustor of the present invention, when both catalyst layers are formed on one monolith carrier, alumina-silica based porous particles are coated on the inlet side portion of the monolith carrier, The remaining portion may be coated with alumina or alumina-lanthanum oxide-based porous particles, and the whole may be impregnated with a salt solution of Pt and / or Pd to support the active ingredient. The coated porous particles are preferably coated.
Further, if the active ingredient concentration in each coating layer is made different at that time, each coating layer may be impregnated with a salt solution of Pt and / or Pd having different salt concentrations. Alternatively, the monolith carrier having the first catalyst layer and another monolith carrier having the second catalyst layer may be combined to form a catalytic combustor. An appropriate value for the ratio of the lengths of the first catalyst layer and the second catalyst layer in the flow direction in this catalytic combustor may be determined by an experiment, but for example, the length of the first catalyst layer is the same as that of all the catalyst layers. It can be 10 to 60% of the length. The entire catalyst layer can be formed by providing a third catalyst layer made of, for example, alumina-silica based porous particles after the second catalyst layer, or the number of catalyst layers can be increased.

[0016]

According to the present invention, fuel such as methane can be efficiently and completely combusted in the catalytic combustor by changing the composition of the alumina-based porous particles carrying the active ingredient. That is, since the first catalyst layer supporting the active ingredient with alumina-silica based porous particles containing 0.5 to 20 mol% of Si with respect to the total amount of Al and Si is provided on the inlet side, The reaction can occur at low temperatures. Furthermore, since the active ingredient is supported by alumina-lanthanum oxide-based porous particles containing 0.1 to 20 mol% of alumina or La with respect to the total amount of Al and La in the subsequent second catalyst layer, Since it has a high fire resistance, the reaction proceeds sufficiently, it can be used for a long time, and the reaction can be performed at a high temperature, the fuel can be completely burned.

In particular, when the porous particles produced by the sol-gel method and supercritical drying are used as the carrier for supporting the active ingredient, the above-mentioned action is further enhanced.

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is not limited to this embodiment. Example 1 The following experiment was conducted in order to confirm the effect of the catalytic combustor of the present invention. (1) Alumina porous particles (aerogel) having a particle size of 1 to 3 mm and each carrying 1 wt% of Pd and alumina-
Silica 10 mol% porous particles (aerogel) 120
After heat treatment in air at a temperature of 0 ° C. for 100 hours, these were each formed as a catalyst layer, and catalytic combustion activity was examined in a methane flow system.

Reaction conditions Composition of mixed gas Methane 1 vol% Air 99 vol% Mixed gas flow rate 1 liter / mi
n catalyst loading 1 g space velocity in catalyst bed about 35,000 h ^{-1 When} the methane conversion was measured by changing the temperature in these catalyst layers, the results shown in FIG. 2 were obtained. When the porous particles are alumina, methane can be completely burned at a temperature slightly higher than 600 ° C, but when the temperature becomes low and reaches 350 ° C, it hardly reacts. Further, in the case of alumina-silica, there is an advantage that the reaction starts even at a low temperature of 300 ° C. or lower, but at about 600 to 700 ° C., methane does not completely burn.
It requires a high temperature of 00 ° C. or higher, and at such a high temperature, there is a concern that the structure of alumina-silica is changed and the activity as a catalyst is quickly lost. (2) Next, 0.5 g of the heat-treated alumina-silica porous particles (aerogel) was filled on the inlet side of the catalyst layer, and then the heat-treated alumina porous particles (aerogel) was absent. When 0.5 g was charged and the reaction was performed under the same conditions as in (1) and the conversion rate of methane was measured, the results shown in FIG. 1 were obtained. According to FIG. 1, it is active at a low temperature of about 300 ° C., and methane can be completely burned at a temperature slightly higher than 600 ° C. In FIG. 1, a solid curve a represents the measurement result based on the present invention, and dotted curves b and c represent the curves b and c in FIG.
Are also shown for comparison. According to FIG. 1, the degree of improvement in the present invention is clear.

[0020]

EFFECTS OF THE INVENTION According to the present invention, since the first catalyst layer supporting the active ingredient with specific alumina-silica based porous particles is provided on the inlet side, the reaction can be started at a low temperature. The reaction can be easily initiated, whereby the temperature of the entire catalyst layer can be raised, and the second component in which the active ingredient is supported by alumina or specific alumina-lanthanum oxide-based porous particles after the first catalyst layer Since the catalyst layer is provided, fuel such as methane can be completely burned at a temperature not too high, and since it has high fire resistance, it can be used for a long time.

[Brief description of drawings]

FIG. 1 shows a methane conversion rate in a catalyst layer according to the present invention in Example 1.

FIG. 2 shows the methane conversion rate in the catalyst layer according to the prior art in Example 1.

[Explanation of symbols]

a curve of methane conversion in the catalyst layer according to the present invention. b Curve of methane conversion rate in Pd-supported alumina porous particle catalyst layer. c Curve of methane conversion rate in Pd-supported alumina-silica porous particle catalyst layer.

Claims (3)

[Claims] 1. A hydrocarbon fuel catalyst comprising Pt and / or Pd as an active ingredient and a monolithic carrier coated with alumina-based porous catalyst particles carrying these active ingredients, wherein Si is introduced on the inlet side. A first catalyst layer supporting the above-mentioned active ingredient is provided with alumina-silica based porous particles containing 0.5 to 20 mol% with respect to the total amount of Al and Si, and then alumina or La is added to Al and La. Alumina containing 0.1 to 20 mol% based on the total amount of
A catalytic combustor for a hydrocarbon fuel, comprising a second catalyst layer in which the active component is supported by lanthanum oxide-based porous particles. 2. As the alumina-based porous particles, an alumina-based wet gel whose pores are filled with an organic solvent is passed through a supercritical condition of the organic solvent itself or the organic solvent-CO ₂ mixed system. The catalytic combustor for hydrocarbon fuel according to claim 1, wherein alumina-based porous particles obtained by heat-treating the dried gel are used. 3. Alumina-precious metal wet gel whose pores are filled with an organic solvent is used as the alumina-based porous particles carrying the active ingredient, the organic solvent itself or the organic solvent-CO ₂ mixture. 2. Alumina-based porous particles supporting the active ingredient obtained by heat-treating a gel dried under supercritical conditions of a system are used.
A hydrocarbon fuel catalytic combustor as described.