JPS6050489B2 - Catalyst for purifying exhaust gas containing sulfur compounds - Google Patents

Description

Detailed Description of the Invention The present invention relates to a catalyst for purifying exhaust gas containing sulfur compounds, and in particular, it completely burns combustible components such as hydrogen, carbon monoxide, hydrocarbons, and oxygen-containing organic compounds in the exhaust gas. The present invention relates to a catalyst for purifying exhaust gas containing sulfur compounds that can maintain high performance without being poisoned by the sulfur compounds contained therein.

In recent years, carbon monoxide contained in exhaust gas emitted from various fixed exhaust gas generation sources such as the petrochemical industry, steel industry, painting industry, and printing industry, and from mobile exhaust gas generation sources such as automobiles,
Hydrocarbons, oxygen-containing organic compounds, and the like are harmful or malodorous components, and there is a strong need for countermeasures against air pollution.

Generally, methods for treating exhaust gas include direct combustion exhaust gas purification methods and catalytic combustion exhaust gas purification methods.

However, the former method has the disadvantage of consuming a large amount of fuel due to the high temperature involved, so in recent years, the latter method has been reconsidered over the uneconomical former method, especially from the perspective of energy conservation. . When using a catalytic combustion method to bring various types of exhaust gas into contact with a catalyst to completely burn and purify harmful or malodorous components in the exhaust gas, the performance and lifespan of the catalyst used are the most important factors.

Conventionally, as this type of catalyst, Nj.
Cr. Fe. It contains oxides such as Cu or CO, or platinum elements such as palladium and platinum, and is often used for automobile exhaust gas treatment.

However, when treating industrial plant exhaust gas containing sulfur compounds such as coke oven exhaust gas, the known catalysts described above are poisoned by sulfur oxides and their performance deteriorates over time. Difficult to put into practical use. The deterioration mechanism of such a catalyst is thought to be that alumina, which is a support, and metal oxide, which is an active component, are sulfated by sulfur oxides, and the catalyst loses its activity due to changes in the pore structure or components of the catalyst. . Recently, in order to treat exhaust gas containing sulfur compounds and suppress the emission of SO3 or sulfuric acid mist, catalysts have been developed that can reduce the rate of change from SO2 to SO3 and maintain good oxidation ability of CO and HC (hydrocarbons). As a medium, it has been proposed that a platinum metal element is supported on a carrier mainly composed of activated alumina and modified with titanium oxide and phosphorus pentoxide (Japanese Patent Application Laid-Open No. 52-1
2691), but it cannot be said that it is necessarily satisfactory in terms of the effect of suppressing poisoning of the catalyst by sulfur oxides.

The present invention has been made in view of the current situation, and its purpose is to eliminate hydrogen, carbon monoxide, hydrocarbons, and oxygen-containing organic compounds (such as acetic acid, methanol, and aldehyde 3, etc.) in exhaust gas containing sulfur compounds. ), etc., to completely oxidize the exhaust gas, and maintain high performance stably over a long period of time without being poisoned by sulfur compounds. An object of the present invention is to provide a catalyst capable of recovering thermal energy by completely burning a gas (low calorie gas) η containing a combustible component with poor self-combustibility.

Here, the above-mentioned low-calorie gas is, for example, carbonized gas from municipal waste, low-calorie gas from partial combustion of coal, blast furnace gas from a steel plant, or catalyst regeneration gas from an oil refinery plant (e.g., gas generated from cracking catalyst regeneration), etc. and these usually contain sulfur compounds and sometimes hydrogen sulfide. The present invention has the following configuration to achieve the above object.

That is, the sulfur oxide-containing exhaust gas purifying catalyst of the present invention has a titanium dioxide-alumina mixed molded carrier containing about 70 to 95 weight % titanium dioxide, and about 0.02 to 2 weight % based on the catalyst weight. It is characterized by supporting at least one type of platinum metal element. The present inventors were investigating a catalyst for the catalytic reduction of nitrogen oxides in exhaust gas containing sulfur oxides (SO2 and SO3) with ammonia, and found that a transition metal oxide catalyst containing titanium oxide as the main component was highly resistant. It was found that it has excellent sulfur oxide properties.

In this catalyst, titanium oxide, which is the main component, is difficult to be sulfated by sulfur oxides, and even if the transition metal oxide, which is the second component, is sulfated, titanium oxide is the main component, so the pores of the catalyst It was found that there was little structural change and little decrease in activity due to sulfur compounds. Based on the above facts, the present inventors believe that a catalyst using a carrier mainly composed of titanium oxide is effective as a catalyst for the complete oxidation reaction of hydrogen, carbon monoxide, hydrocarbons, oxygen-containing organic compounds, etc. As a result of further detailed investigation, we found that a catalyst that uses a carrier mainly composed of titanium oxide and supports at least one platinum metal element such as palladium, platinum, and thenium,
It was discovered that the performance could be maintained over a long period of time without being poisoned by sulfur oxides.

By the way, titanium oxide itself has poor formability when molded into various shapes such as spherical or cylindrical shapes, and it is difficult to obtain molded products with sufficient strength. To make it into the body, heat it to a higher temperature (80
must be sintered at temperatures above 0°C).

However, another problem is that titanium oxide tends to grow crystals more easily when treated at high temperatures than alumina etc.
When treated at a temperature of 800'C or higher, the specific surface area becomes less than 1Iy, and the molded product also shrinks significantly, sometimes accompanied by the occurrence of cracks. As a result of our studies taking into consideration the solutions to these problems, the present inventors found that
The present invention was achieved by discovering that the object can be achieved by using a mixed molded carrier of titanium oxide and alumina. The present inventors investigated changes in specific surface area at various firing temperatures depending on the amount of alumina added to titanium oxide.

FIG. 1 is a graph showing the relationship between the alumina content in the carrier and the specific surface area of the carrier when the firing temperature is changed, and the temperature in the figure indicates the firing temperature of the carrier. From this graph, it can be seen that for titanium oxide alone, the specific surface area is approximately 3 Iy when fired at 700°C, but it becomes 1I1f1 when fired at 900°C or higher.
It can be seen that addition of alumina suppresses the decrease in specific surface area. This effect is not simply based on the additivity of alumina, which has a large specific surface area, and titanium oxide, which has a small specific surface area; it also shows that the effect of suppressing the reduction in specific surface area by adding alumina tends to be particularly pronounced at low alumina content. It is clear that there are In this way, titanium oxide
The alumina mixed molded carrier has improved moldability compared to titanium oxide alone, and can also be heated to a higher temperature (90°C).
By performing the firing treatment at temperatures as high as 0°C (0°C is also possible), it has the characteristics of high strength and a larger specific surface area without the occurrence of cracks.

As the carrier for the catalyst of the present invention, it is necessary to use a titanium oxide-alumina mixed molded carrier containing about 70 to 95% by weight of titanium oxide based on the weight of the carrier, taking into account the above properties and a sulfur-resistant compound.

In carriers with a titanium oxide content of approximately 7% by weight or less, alumina, etc. will be sulfated by sulfur oxides in the exhaust gas, and the pore structure of the carrier will change significantly, resulting in a significant decrease in catalytic active sites and a decrease in performance. If the content exceeds about 95% by weight, no strength will be obtained. Further, the specific surface area of the catalyst of the present invention is suitably 1TTII da or more, preferably 10 dIy or more, from the viewpoint of activity and other aspects.

Furthermore, the firing temperature of the shaped carrier or catalyst in the present invention is about 5
The temperature is desirably 00 to 900°C; below about 500'C, sufficient strength cannot be obtained, and above about 900°C, the specific surface area decreases and the activity becomes insufficient.

In addition to titanium oxide powder, the titanium oxide raw materials used in the present invention include hydrated titanium oxide obtained by hydrolysis of orthotitanic acid, metatitanic acid, titanium sulfate, titanium tetrachloride, etc., which are thermally decomposed to titanium oxide at about 150°C or higher. Alternatively, an organic titanium compound such as titanium isopropoxide can be used as a raw material. In addition, the alumina raw material in the present invention has a specific surface area of 10d1y.
1 desirably 50 dIy or more, and alumina hydrate, amorphous alumina gel, alumina sol, etc., which obtain alumina by thermal decomposition such as gypsite, bayerite, and boehmite, can also be used as raw materials.

In addition, as starting materials for alumina production, ordinary nitrates,
Sulfates, chlorides, etc., alkali aluminates, aluminum alkoxides, metallic aluminum, etc. can be used. In addition, a small amount (about several weight %) of other refractory substances such as magnesia, zirconia, silicon carbide, diatomaceous earth, zeolite, mullite, and silica can be added to and mixed with the carrier in the present invention.
In the manufacturing process of the titanium oxide-alumina mixed molded support in the present invention, water is added to a mixture of titanium oxide and alumina powder or a hydrous oxide that is a precursor thereof, and the mixture is sufficiently wet-kneaded and thoroughly mixed through a compaction process. What was done is
It maintains a sufficiently high specific surface area, has high strength, and has excellent resistance to sulfur oxides, so it has high performance and can be used as a stable catalyst carrier for a long period of time.

The catalyst of the present invention has at least one platinum group element supported on the titanium dioxide-alumina mixed molded carrier in an amount of about 0.02 to 2% by weight. Examples of the above-mentioned platinum metal elements in the present invention include palladium, platinum, ruthenium, and rhodium, and these metals are prepared in advance by preparing a mixed support of titanium oxide and alumina, and then impregnated and supported on the support to form a catalyst. Alternatively, a platinum group element compound can be mixed in advance at the stage of obtaining the mixed molded carrier and a final catalyst molded body can be obtained through a wet kneading process.

The amount of platinum group elements supported is about 0.0000000000000000000000000000000000000000000000000000000000000000000000.
A suitable amount is 0.02 to 2% by weight, preferably 0.1 to 1% by weight.

If this amount is less than about 0.0% by weight, the catalytic activity will decrease, and if it is more than about 2% by weight, it will be disadvantageous in terms of cost. The catalyst of the present invention also contains Ni. ．． Cr. ．． Fe.
．． Cu. ．． It is also effective to include a transition metal element such as CO. In this case, it is appropriate that the transition metal element be added in an amount of about 0.01 to 3% based on the white metal element. The means for forming the above-mentioned carrier and catalyst are particularly limited.
Any of the known tableting methods, rolling granulation methods, extrusion molding methods, spray granulation methods, etc. may be used. Further, the shape of the catalyst is not particularly limited, and shapes such as cylindrical, cylindrical, spherical, granular, and honeycomb can be selected as appropriate, and the desired shape is generally determined depending on the properties of exhaust gas, ease of production, etc. determined. Next, the outline of the method for preparing the catalyst of the present invention will be specifically explained by giving an example. First, a predetermined amount of aluminum hydroxide is added to metatitanic acid slurry, and the mixture is sufficiently heated and kneaded using a kneader.

Once everything is thoroughly mixed, heat it to 140°C.
After drying, grind with a ball mill. This powder was granulated into spheres with a diameter of 2 to 4 mm using a rolling granulation method, and then dried.
C. for 6 hours to obtain a titanium oxide-alumina mixed molded support. This carrier is impregnated with a predetermined amount of an aqueous solution of chloroplatinic acid, dried at 120° C. for 5 hours, and then calcined and reduced at 450° C. for 3 hours in a hydrogen stream to obtain a titanium oxide-alumina platinum catalyst. The temperature of the catalyst layer for oxidizing combustible components such as hydrogen, carbon monoxide, hydrocarbons, and oxidized organic compounds using the catalyst thus obtained depends on the composition, properties, and treatment conditions of the exhaust gas. Therefore, the treatment conditions must be determined after fully understanding the composition of the exhaust gas to be treated.

That is, for example, catalyst particle size 2 to 4 TW1, space velocity 2
In the case of 000h-1, 0.2% platinum titanium monoxide-alumina catalyst, the oxidation reaction of hydrogen proceeds sufficiently at temperatures below 100°C, while the oxidation reaction of carbon monoxide proceeds at temperatures above approximately 200°C and for propane above 250°C. , methane is over 400 degrees Celsius! The oxidation reaction of acetic acid proceeds almost completely at temperatures above 300°C (both in the presence of sulfur oxides). The oxidation of these combustible components is an exothermic reaction, and if the concentration of combustible components in the exhaust gas is higher than a certain level, the catalyst layer temperature will rise due to the heat of combustion, causing the exhaust gas to self-combust on the catalyst. , there is a possibility that combustion can be continued, and when treating exhaust gas that can be treated in this way, the characteristics of catalytic combustion purification can be clearly demonstrated, and thermal energy can be effectively recovered. can.

In the combustion type exhaust gas purification method using the catalyst of the present invention,
The amount of secondary air added is 1.5% of the stoichiometric amount of oxygen required to completely oxidize the combustible components in the exhaust gas. An appropriate amount is 1.3 times or more, preferably 1.3 times or more.

The upper limit of the amount of secondary air added is not particularly limited, but in order to achieve the objective of the present invention of effectively recovering thermal energy, it is necessary to add 2.0% of the above stoichiometric amount of oxygen. Below 1, preferably 1. It is better to add air equivalent to less than 100 ml of air. Of course, it is also possible to add oxygen instead of air. Further, the space velocity when carrying out the combustion type exhaust gas purification method using the catalyst of the present invention is preferably in the range of 10,000 to 100,000 h-1.

Next, the present invention will be explained with reference to Examples, but the present invention is not limited to these in any way.

Example 1 1k9 of metatitanic acid slurry containing 35% by weight of titanium oxide and 0.15k9 of γ-alumina powder in a 200 mesh bath were collected in a kneader and mixed for about 1.5 hours.
When the mixture was kneaded at 00 to 200°C and thoroughly mixed to a moisture content of about 30%, it was dried at 140°C for about 2 hours.

After drying, this was ground in a ball mill for 2 hours, and the resulting powder was processed by rolling granulation to a powder size of 2 to 4 Tm! The pellets were granulated into spheres with a diameter of RL and left to stand overnight. This was dried at 140°C for 5 hours and then fired at 500°C for 2 hours to obtain a spherical titanium oxide-alumina mixed molded carrier. This molded carrier was impregnated with 170 ml of a solution prepared by diluting 10 ml of a chloroplatinic acid aqueous solution (10 da Pt/100 ml) with distilled water.

After drying at 120°C for 5 hours, reduction firing was performed at 400°C for 3 hours in a hydrogen stream.

The catalyst thus obtained was 0. It is a platinum-containing titanium oxide (7 weight%)-alumina (3 weight%) catalyst.
24 ml of this catalyst was packed into a quartz reaction tube with an inner diameter of 4 mm,
A gas having the following composition was caused to flow and react at a space velocity of 20,000 h-1.

Carbon monoxide was measured using a non-dispersive infrared analyzer. C
O5OOOppmCO2l5% SO2lOOOOppmsO35OPPmO22%
The oxidation rate of H2OlO%N2 and remaining carbon monoxide was determined by the following formula.

The measurement results of initial activity are shown in Figure 2.

That is, FIG. 2 is a graph showing the relationship between reaction temperature and CO oxidation rate, and as can be seen from this graph, high activity was exhibited even at about 230° C. in the presence of sulfur oxide. Example 2 Example 1 except that the mixing ratio of titanium oxide and alumina was changed
A titanium oxide (95% by weight)-alumina (5% by weight) catalyst containing 0.2% by weight of platinum was prepared in the same manner as described above.

In addition, as a control 1, titanium oxide containing 0.2% by weight platinum (
5% by weight)-alumina (5% by weight) catalyst was prepared. Separately, as a control 2, 2-477177! A spherical alumina carrier of 100 q of diameter was impregnated with 50 ml of a solution of 50 ml of chloroplatinic acid aqueous solution diluted with distilled water, dried at 120°C for 5 hours, and then reduced and calcined at 400°C for 3 hours in a hydrogen stream.
An alumina catalyst containing 0.2% by weight platinum was prepared. Above 3
A 100-hour continuous test of carbon monoxide oxidation reaction at 300°C (space velocity 20,000 h) using the seed catalyst and the catalyst of Example 1 under the same gas composition and measurement conditions as in Example 1.
-1) was carried out.

The durability test results are shown in Figure 3. That is, FIG. 3 is a graph showing the relationship between reaction time and CO oxidation rate, and A
shows the case of the catalyst of Example 1, B shows the case of Example 2, C shows the case of Control 1, and D shows the case of Control 2. As is clear from the graph in Figure 3, the durability of the catalysts of Examples 1 and 2 does not change even after 10 hours, but the CO oxidation rate of the catalysts of Controls 1 and 2 decreases over time. , in the case of Control 2, the durability was significantly lowered.

Example 3 0.5% by weight platinum-containing titanium oxide (7%)-alumina (3%) catalyst prepared in the same manner as in Example 1 except that the firing temperature of the shaped carrier was 900°C. A gas having the following composition was passed at a space velocity to cause a reaction.

C3H3lOOOppmsO25OOppmsO32O
ppmO25% N2 balance propane (C3H3) is FI
Measured using D gas chromatography.

As a result, the oxidation rate of propane at 250°C was 99%.
That's all. On the other hand, 0.5 prepared in the same manner as above
Titanium oxide (sole carrier) catalyst containing wt% platinum (control 3)
When the same reaction as above was carried out using
The oxidation rate of propane was 87%.

In addition, except that the firing temperature of the shaped carrier was 1200°C,
The same reaction as above was carried out using a 0.5% by weight platinum-containing titanium oxide (7% by weight)-alumina (3% by weight) catalyst (Control 4) prepared in the same manner as in Example 1. ,2
The oxidation rate of propane at 50°C was 91%. Example 4 Except that the firing temperature of the shaped carrier was 800'C, and the mixing ratio of titanium oxide and alumina and the type of platinum group element were changed,
A titanium oxide (8% by weight)-alumina (2% by weight) catalyst containing 0.5% by weight palladium was prepared in the same manner as in Example 1, and using this, a gas having the following composition was heated at a space velocity of 10,000.
When the mixture was reacted by flowing through the reactor at h-1, a hydrogen oxidation rate of 95% or more was obtained even at 30°C.

Example 5 Titanium oxide containing 0.2% by weight rhodium was prepared in the same manner as in Example 1, except that the firing temperature of the shaped carrier was 800°C and the mixing ratio of titanium oxide and alumina and the platinum group element and its amount were changed. (8 weight%) - alumina (2 weight%) catalyst was prepared, and using this, a gas having the following composition was heated at a space velocity of 1000.
When reacted by flowing at 0h-1, 99% at 300℃
% or more of acetic acid oxidation rate was obtained).

V2ρ ′υ b〜HPO. Oxidized titanium containing 0.0% rhodium (8% rhodium) prepared in the same manner as above except that rhodium of 0% rhodium was contained.
)-alumina (2% by weight) catalyst and titanium oxide (80% by weight) containing 0.01% by weight rhodium-alumina (2% by weight) catalyst (Control 6) to carry out the same reaction as above. As a result, the acetic acid oxidation rate was 96.5% for the former and 83% for the latter at 300°C.

As can be seen from the results of the above examples and controls, it is appropriate that the titanium oxide in the carrier be about 70 to 95% by weight, and the platinum group element content in the catalyst be 0.02 to 2% by weight. Further, it is preferable that the firing temperature of the carrier is about 500 to 900°C, and if it is out of this range, good effects cannot be obtained.

As described above, according to the present invention, hydrogen, carbon monoxide, hydrocarbons, oxygen-containing organic compounds, etc. in the sulfur oxide-containing exhaust gas are completely oxidized and burned, and moreover, it is possible to completely oxidize and burn the hydrogen, carbon monoxide, hydrocarbons, oxygen-containing organic compounds, etc. in the sulfur oxide-containing exhaust gas, and furthermore, it is possible to prevent poisoning by the sulfur compounds. It is possible to provide a catalyst that can maintain high performance over a long period of time.

Therefore, the catalyst of the present invention can be widely and effectively used for treating exhaust gases emitted from stationary sources in various industries and mobile sources such as automobiles.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the alumina content in the carrier and the specific surface area of the carrier when the firing temperature is changed.
FIG. 2 is a graph showing the relationship between reaction temperature and CO oxidation rate in Example 1, and FIG. 3 is a graph showing the relationship between reaction time and CO oxidation rate in Example 2.

Claims (1)

[Scope of Claims] 1. A titanium dioxide-alumina mixed molded support containing about 70 to 95% by weight of titanium dioxide and supporting about 0.02 to 2% by weight of at least one platinum group element based on the weight of the catalyst. A catalyst for purifying exhaust gas containing sulfur compounds, characterized in that: 2. The sulfur compound-containing exhaust gas purifying catalyst according to claim 1, wherein the shaped carrier is calcined at about 500 to 900°C. 3. The catalyst for purifying exhaust gas containing sulfur compounds according to claim 1 or 2, wherein the carrier or the catalyst is wet-kneaded and compacted. 4. The sulfur compound-containing exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein the platinum metal element is one or more selected from the group consisting of platinum, palladium, ruthenium, and rhodium.