JP2000254501A - Production of catalyst for removing hydrocarbon in exhaust gas containing methane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To have high removing performance in exhaust gas having a high methane content and to demonstrate stable catalytic activity in the presence of sulfur oxide by immersing a fire resistant honeycomb base material in slurry in which zirconium oxide, a binder, and a solvent are mixed, drying and carry ing palladium. SOLUTION: A series of operations in which it is immersed in slurry obtained by mixing zirconium oxide, a binder such as zirconia sol, and a solvent for coating to a fire resistant honeycomb base material, taken out, and dried is repeated prescribed times. Next, the honeycomb base material coated with the slurry is immersed in a solution of a salt which dissolves palladium or palladium and platinum, dried preferably in air, and burned to obtain a desired honeycomb catalyst. In this way, since the obtained catalyst is resistant to activity lowering by sulfur components in exhaust gas, a stable, high hydrocarbon removing ratio is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a methane-containing composition,
The present invention relates to a method for producing a catalyst for removing hydrocarbons from an exhaust gas containing excess oxygen.

[0002] In the present specification, "exhaust gas containing excess oxygen" or "exhaust gas containing excess oxygen" means that the exhaust gas to be treated is necessary for completely oxidizing methane and other reducing substances contained therein. It means that it contains more than a certain amount of oxygen.

[0003]

2. Description of the Related Art It has been known that a catalyst supporting a platinum group metal such as platinum and palladium exhibits high performance in oxidizing and removing hydrocarbons other than methane in exhaust gas containing excess oxygen. For example, JP-A-51-106691 discloses an exhaust gas purification catalyst in which platinum or palladium is supported on an alumina carrier. However, when the main component of hydrocarbons is methane, such as the exhaust gas from natural gas, a sufficient purification effect is achieved even with such a catalyst because of the high chemical stability of methane. There is a problem that is not done.

[0004] Further, since poisoning substances such as sulfur oxides are usually present in the combustion exhaust gas, it is inevitable that the catalytic activity significantly decreases with time. Since petroleum-based fuels such as kerosene and light oil contain sulfur-containing compounds, it is natural that the combustion exhaust gas contains sulfur oxides. In addition, natural gas-derived fuels that essentially do not contain sulfur compounds, such as city gas supplied in Japan, contain compounds containing sulfur as odorants. The generated sulfur oxides are inevitably included.

Japanese Patent Application Laid-Open No. 8-332392 discloses a catalyst for oxidizing low-concentration hydrocarbons in an oxygen-excess exhaust gas, in which a honeycomb substrate is provided with at least 7 g / l of palladium and 3 to 20 g / l of platinum via an alumina carrier. 1 discloses a supported catalyst. However, even in the case of this catalyst, long-term durability is not sufficient in the presence of a sulfur component, and deterioration of the catalyst activity with time cannot be avoided.

As described above, the catalyst according to the prior art has a serious problem that the removal rate of hydrocarbons such as methane is low and the catalyst activity is greatly reduced within a short time under the condition where sulfur oxides coexist. Exists.

[0007]

DISCLOSURE OF THE INVENTION The present invention exhibits high removal performance even for exhaust gas having a high methane content in all hydrocarbons, and is stable over a long period of time even in the presence of sulfur oxides. A main object of the present invention is to provide a method for producing a catalyst for removing low-concentration hydrocarbons in exhaust gas containing excess oxygen, which exhibits catalytic activity.

[0008]

Means for Solving the Problems As a result of repeated studies in view of the problems of the prior art, the present inventors have immersed a refractory honeycomb substrate in a slurry formed by mixing zirconium oxide, a binder and a solvent. Then, after drying, the catalyst prepared by supporting palladium, preferably by drying or calcining, shows high resistance to poisoning of the catalytic activity by sulfur oxides. Also found that a stable high hydrocarbon removal rate was maintained over a long period of time. It has also been found that when platinum is supported together with palladium, a higher hydrocarbon conversion is exhibited.

The present invention has been completed on the basis of such new findings, and provides the following method for producing a catalyst for removing hydrocarbons from methane-containing exhaust gas. 1. A method for producing a catalyst for removing hydrocarbons in a methane-containing exhaust gas, comprising immersing a refractory honeycomb substrate in a slurry formed by mixing zirconium oxide, a binder and a solvent, drying and supporting palladium. . 2. A catalyst for removing hydrocarbons in a methane-containing exhaust gas, characterized by immersing a refractory honeycomb substrate in a slurry formed by mixing zirconium oxide, a binder and a solvent, drying and supporting palladium and platinum. Manufacturing method. 3. The method for producing a catalyst for removing hydrocarbons in methane-containing exhaust gas according to claim 1, wherein the amount of supported palladium is 5 to 100 g / l with respect to the volume of the honeycomb catalyst. 4. With respect to the volume of the honeycomb catalyst, the supported amount of palladium is 5 to 100 g / l, and the supported amount of platinum is 0.25 to 100 g / l.
3. The method for producing a catalyst for removing hydrocarbons in methane-containing exhaust gas according to claim 2, wherein 5. The binder is a zirconia sol.
The method for producing a catalyst for removing hydrocarbons in a methane-containing exhaust gas according to any one of the above.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION As zirconium oxide used in the present invention, commercially available zirconium oxide can be used as it is, and zirconium oxide which has been subjected to a treatment for increasing acidity in advance can also be used.

The zirconium oxide treated to increase the acidity is not particularly limited.
Zirconium oxide supporting sulfate, zirconium oxide supporting tungsten, and the like can be given. The zirconium oxide that has been treated to increase the acidity can be prepared by a known method. For example, zirconium oxide carrying a sulfate group is amorphous zirconium oxide,
It is obtained by bringing sulfuric acid into contact with zirconium hydroxide or the like, or impregnating amorphous zirconium oxide or zirconium hydroxide with ammonium sulfate and then calcining at a temperature in the range of about 500 to 650 ° C. Further, zirconium oxide supporting tungsten can be obtained by, for example, wet-kneading amorphous zirconium oxide, zirconium hydroxide, or the like with tungstic acid, followed by firing at about 650 to 850 ° C.

The supporting of palladium and platinum can be carried out by immersing a honeycomb substrate coated with zirconium oxide in a solution of a soluble salt such as a nitrate salt or an ammine complex salt.

The binder is not particularly limited, but zirconia sol, silica sol, alumina sol, titania sol or a mixed sol thereof can be used. Among these binders, zirconia sol is more preferred.

As the solvent, at least one kind of organic solvent miscible with water and water, such as acetone, ethanol and ethylene glycol, in an arbitrary ratio can be used. Of these, water is more preferred. Mixing is sufficiently performed by a ball mill or the like.

The coating of a slurry formed by mixing zirconium oxide with a binder and a solvent on a refractory honeycomb substrate is performed by immersing the refractory honeycomb substrate in the formed slurry, removing the substrate, and drying. This is performed by repeating the required number of times. The required coating amount can be adjusted by the number of repetitions and the slurry concentration. The material of the refractory honeycomb substrate to be used is not particularly limited, but is usually cordierite or metal.
(Such as stainless steel) is used.

Next, the honeycomb substrate coated with the slurry is impregnated with palladium or a soluble salt solution of palladium and platinum, preferably dried in air, and calcined to obtain a desired honeycomb catalyst. If the firing temperature is too high, the supported noble metal component grows in grains, while if too low, the supported noble metal component is less likely to be sufficiently activated. Therefore, in order to stably obtain a high catalytic activity, the calcination is performed at 450 to 650.
It is preferable to carry out at a temperature of about 500C, more preferably at about 500-600C.

If the amount of supported palladium in the honeycomb catalyst is too small, the catalytic activity will be low, whereas if it is too large, the particle size of palladium will be so large that palladium cannot be used effectively. Therefore, the amount of supported palladium is usually 5 to 100 g / l based on the volume of the honeycomb catalyst.
And more preferably about 10 to 70 g / l.

When palladium and platinum are used together,
If the amount of platinum is too small, the effect of the combined use is not sufficiently exhibited, whereas if the amount of platinum is too large, the function of palladium as an active metal may be impaired.Therefore, platinum is contained in the entire volume of the honeycomb catalyst. 0.25 ~
The range is 100 g / l, more preferably 0.5 to 70 g / l of platinum.

When the catalyst obtained by the production method of the present invention is used to remove hydrocarbons from the methane-containing exhaust gas, if the amount of the catalyst is too small, a predetermined removal rate cannot be obtained. 50000 per space velocity (GHSV)
It is desirable to use it under the condition of 0h ^-1 or less. As the amount of catalyst increases, the space velocity (G
(HSV) is reduced and the removal rate is improved, which is advantageous, but on the other hand, when GHSV is used under conditions of 1000 h ^-1 or less, it is economically disadvantageous and the pressure in the catalyst layer is low. The loss increases. Therefore, the amount of catalyst used is GH
What is necessary is just to select suitably under the condition that SV becomes 500,000-1000h ^-1 .

If the oxygen concentration in the methane-containing exhaust gas is extremely low, the rate of the methane decomposition reaction decreases.
The oxygen concentration in the exhaust gas is at least 2% by volume and at least the oxidation equivalent of reducing components such as hydrocarbons in the exhaust gas,
More preferably, it is desirable that oxygen is present in an amount equal to or more than 5 times the oxidation equivalent. If the oxygen concentration in the exhaust gas is too low, the exhaust gas may be mixed with a required amount of an oxygen-containing gas (usually air) before or during the treatment.

The catalyst for removing hydrocarbons from methane-containing exhaust gas obtained according to the present invention has high activity. However, when the use temperature is too low, the activity is not sufficiently exhibited, and it is difficult to obtain a desired hydrocarbon removal rate. On the other hand, if the operating temperature is too high, the durability of the catalyst may be deteriorated. Further, when the hydrocarbon concentration in the exhaust gas is extremely high, a rapid reaction occurs in the catalyst layer, and there is a risk that the durability of the catalyst is adversely affected. In consideration of these points, the temperature of the catalyst layer is maintained within the temperature range of 300 to 700 ° C., and the temperature rise (difference between the outlet temperature and the inlet temperature of the catalyst layer) in the catalyst layer becomes 150 ° C. or less. It is desirable to treat the exhaust gas while adjusting the reaction conditions as described above.

Further, the combustion exhaust gas usually contains sulfur oxides which significantly reduce the catalytic activity. However, the catalyst produced according to the present invention has a high resistance to the decrease in the activity due to the sulfur component. High hydrocarbon removal rates are substantially unaffected.

Further, the combustion exhaust gas usually contains about 5 to 15% of water vapor, but when the catalyst produced according to the present invention is used, the exhaust gas containing water vapor as described above does not cause any trouble. , Can be removed.

[0024]

According to the present invention, the following remarkable effects are achieved. (1) The catalyst for removing hydrocarbons in methane-containing exhaust gas produced by the method of the present invention has a long-term stable oxidation activity against hydrocarbons such as methane even in exhaust gas containing a large amount of water vapor such as combustion exhaust gas. Shown. (2) The catalyst of the present invention is also excellent in resistance to sulfur oxides. (3) Therefore, according to the present invention, it is possible to stably purify an exhaust gas containing a large amount of methane for a long period of time, which has been particularly difficult to treat with a conventional catalyst.

[0025]

The present invention will be described below in more detail with reference to Examples and Comparative Examples, but the present invention is not limited by these Examples. Example 1 50 g of zirconium oxide, 100 g of commercially available zirconia sol, and 1 part of water
00g was charged into a ball mill and mixed for 12 hours to produce a slurry.

The resulting slurry is coated on a cordierite honeycomb substrate (200 cell honeycomb, size diameter 20 mm, length 30 m).
m) was immersed, taken out, and the excess slurry was removed by air blowing and dried. A series of operations from immersion in the slurry to drying was repeated to perform coating at a weight ratio of about 122.7% to the honeycomb substrate.
After coating, it was baked at 550 ° C. for 4 hours.

A honeycomb coated with zirconium oxide was immersed in 1.5 cc of a 23.91% palladium nitrate solution, and water was absorbed and impregnated at room temperature by a capillary effect. Then 8
It was dried at 0 ° C. overnight and calcined at 550 ° C. for 4 hours to prepare a Pd / zirconium oxide honeycomb catalyst.

The catalyst thus prepared contained 55.0 g of palladium per liter of the honeycomb catalyst (catalyst 1). Example 2 100 g of zirconium oxide, 100 g of commercially available zirconia sol and water
100 g was charged into a ball mill and mixed for 12 hours to produce a slurry.

The resulting slurry was coated on a cordierite honeycomb substrate (200 cell honeycomb, size diameter 20 mm, length 30 m).
m) was immersed, taken out, and the excess slurry was removed by air blowing and dried. A series of operations from dipping in the slurry to drying was repeated to perform coating at a weight ratio of about 98.7% to the honeycomb substrate.

Cis [Pt (NO ₂ ) ₂ (NH ₃ ) ₂ ] (containing 60.63% Pt)
Weigh 142 g and add 23.91% palladium nitrate solution 1.1 c to this
c was added and dissolved by heating. Further, 0.18 cc of water was added and mixed well. A honeycomb coated with zirconium oxide was immersed in this solution, and water was absorbed and impregnated at room temperature by a capillary effect. Next, after drying at 80 ° C. overnight, it was further calcined at 550 ° C. for 4 hours to prepare a Pd—Pt / zirconium oxide honeycomb catalyst.

The catalyst thus prepared was prepared by adding 45.7 g of palladium and platinum to 1 liter of the honeycomb catalyst.
It contained 9.2 g (catalyst 2). Example 3 2000 ppm of methane, 1000 ppm of carbon monoxide, 10% of oxygen, 10% of carbon dioxide in a reactor catalyst layer (maintained at about 450 ° C.) each filled with the honeycomb catalysts (catalysts 1 and 2) obtained in Examples 1 and 2. A gas having a composition of 6% carbon, 10% steam, 0.3 ppm sulfur dioxide, and the balance of helium gas was allowed to flow under the condition of GHSV (space time per gas hour) of 80,000 h- ¹ , and the temperature of the catalyst layer was maintained at about 450 ° C. The methane conversion was measured. The result is shown in FIG.

As is clear from the results shown in FIG. 1, the catalyst obtained by the method of the present invention exhibits high catalytic activity (methane conversion) even in the presence of sulfur dioxide, which significantly inhibits catalytic activity.

[Brief description of the drawings]

FIG. 1 is a graph showing the methane conversion over time by the catalysts obtained in Examples 1 and 2 of the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Ken Tabata 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi, Osaka Inside Osaka Gas Co., Ltd. (72) Inventor Hirofumi Otsuka 4-chome, Hirano-cho, Chuo-ku, Osaka-shi, Osaka No. 1-2 Osaka Gas Co., Ltd. (72) Inventor Takenori Hirano 1385-2 Kami-Sabuchi, Izumi-shi F-term (reference) 3G091 AA12 AB02 BA04 BA11 BA15 BA39 FB10 GA07 GB01X GB06W GB07W GB10X GB17X 4G069 AA03 AA08 BA05A BA05B BA05C BA13B BA37 BB02A BB02B BC72A BC72B BC75A BC75B CA02 CA03 CA07 CA15 EA18 EA19 EB14Y ED07 FA03 FB06 FB15 FC02 FC08

Claims (5)

[Claims] 1. Removal of hydrocarbons in a methane-containing exhaust gas, wherein a refractory honeycomb substrate is immersed in a slurry formed by mixing zirconium oxide, a binder and a solvent, dried and loaded with palladium. Production method for catalysts. 2. A carbonized gas in a methane-containing exhaust gas, wherein a refractory honeycomb substrate is immersed in a slurry formed by mixing zirconium oxide, a binder and a solvent, dried, and palladium and platinum are supported. A method for producing a catalyst for removing hydrogen. 3. The method for producing a catalyst for removing hydrocarbons in methane-containing exhaust gas according to claim 1, wherein the amount of palladium carried is 5 to 100 g / l based on the volume of the honeycomb catalyst. 4. The amount of palladium carried is 5 to 100 g / l and the amount of platinum carried is 0.25 g / l based on the volume of the honeycomb catalyst.
The method for producing a catalyst for removing hydrocarbons in methane-containing exhaust gas according to claim 2, wherein the amount is from 100 to 100 g / l. 5. The method for producing a catalyst for removing hydrocarbons from methane-containing exhaust gas according to claim 1, wherein the binder is a zirconia sol.