JPS6147568B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention deals with hydrogen, carbon monoxide, and
This invention relates to a method for catalytically oxidizing combustion components such as hydrocarbons and oxygenated hydrocarbons. Exhaust gas containing carbon monoxide and unburned fuel components resulting from incomplete combustion of internal combustion engines, or various industrial plants, such as coke oven exhaust gas, organic solvents from the paint industry, or chemical plants with harmful or foul odors. Exhaust gases and exhaust gases from waste treatment equipment that utilize microorganisms are a cause of air pollution. One of the methods for removing harmful components from these exhaust gases is a catalytic reduction method using a catalyst. Catalysts often use alumina carriers, and alumina with Ni and Cr oxides (Special Publications 1972-
3632, 52-3633) Alumina with Fe oxides (Special Publication No. 51-4715) Alumina with Cu, Co oxides, and platinum group elements such as palladium and platinum (Ind.Eng.Chem.
, Prod.Res.Dev., Vol. 15, No. 3, 1976), as well as those in which Ti.P oxide and platinum group elements (Japanese Patent Application Laid-open No. 12691-1976) are added to alumina are known.
Other known catalysts include _Fe2O3 + _Cr2O3 , _CuO + _{Cr2O3 ,} and _silica - _MnO2 . These catalysts are particularly intended for automotive exhaust gas treatment. However, when treating industrial plant exhaust gas, for example exhaust gas containing sulfur oxides such as coke oven exhaust gas, the above-mentioned known catalysts are poisoned by sulfur oxides and their performance deteriorates over time, so they cannot be put to practical use. is difficult. The mechanism of this deterioration is thought to be that alumina, which is a support, and a metal oxide, which is an active component, are sulfated by sulfur oxides, and the oxidation activity is lost due to changes in the pore structure and components of the catalyst. For these reasons, precious metal group catalysts have rarely been used as catalysts for treating gases containing sulfur oxides. An object of the present invention is to provide a method for burning combustion components in gas using an improved catalyst that can provide stable catalytic activity over a long period of time even in gas containing sulfur oxides. . The present invention is a combustion method that uses a catalyst in which a platinum group element is supported on a titanium carrier that is highly active and resistant to sulfur oxides, in order to burn combustion components in gas. The combustion components contained in the gas to be treated are near or below the lower flammability limit concentration, such as gas generated by carbonized decomposition of municipal waste, low-calorie gas generated by partial combustion of coal, blast furnace gas from steel plants, or petroleum. These include catalyst regeneration gas (e.g. gas containing CO generated during cracking catalyst regeneration) in refinery plants. These usually contain 5 to 10 ppm or more of sulfur oxides (SO ₃ ) and sometimes hydrogen sulfide (H ₂ S) in addition to hydrogen, carbon monoxide, hydrocarbons, or oxygenated hydrocarbons. Complete combustion of the combustible components in the gas as described above not only removes polluting components, but also allows thermal energy to be extracted from low-calorie gas, making effective use of thermal energy possible. Ru. The catalyst used in the present invention uses titanium oxide as a carrier, which is highly active and has resistance to sulfur oxides. Such titanium oxide is obtained by thermally decomposing orthotitanic acid, metatitanic acid, etc., or by hydrolyzing titanium sulfate, titanium tetrachloride, etc., and is heat-treated in a temperature range of 400 to 800°C. The lower the heat treatment temperature, the larger the pore volume of titanium oxide, the larger its specific surface area, and the higher the catalytic activity. However, since the resistance to sulfur oxides becomes poor, it is necessary to add a temperature history of at least 400°C. However, if the concentration of sulfur oxides, especially sulfuric acid, is low and the processing gas temperature is 400° C. or higher, the pre-calcination can be omitted.
When the titanium oxide support is heated to 800° C. or higher, sintering progresses rapidly and the specific surface area becomes 20 m ² /g or less. Then, the catalytic activity of the platinum group catalyst supported thereon is significantly reduced. It is of course possible to add refractory substances to prevent sintering of titanium oxide, and transition metals and rare earth elements that act as co-catalysts for platinum group catalysts, but the amount of addition is limited to the weight of the catalyst using the normal addition method. Must be less than 25% by weight. The supported amount of platinum group elements such as palladium, platinum, ruthenium, and rhodium, which are active components of the catalyst, is preferably in the range of 0.02 to 2% by weight as a metal.
If it is less than 0.02%, the catalyst activity will be low, and if it is more than 2%, the activity will not improve much. Considering economy and long life, it is preferable to set the content to 0.1 to 1% by weight industrially. The catalyst can be manufactured by any of the known tabletting methods, rolling granulation methods, extrusion molding methods, spray granulation methods, or other molding methods. Further, for platinum group metals, it is preferable to prepare a carrier containing titanium oxide as a main component in advance and then impregnate it with a solution of a water-soluble platinum group compound. However, the catalyst can also be produced by mixing a powder containing titanium oxide as a main component and a solution of a water-soluble platinum group compound and using the above-described production method. The impregnated or mixed-molded catalyst can be calcined at 400-800°C to obtain the oxidation catalyst according to the invention. The shape of the catalyst can be cylindrical, cylindrical, spherical, plate-like, or honeycomb-shaped by the production method described above. The desired structure is
It is determined by the composition of the exhaust gas and the ease of production. For example, in the case of a dust-free gas, a fixed bed reactor is used with a cylindrical or cylindrical pellet catalyst. In cases where dust is contained, it is desirable to use a spherical moving bed type reactor, or a parallel flow type reactor using a plate-shaped or honeycomb-shaped catalyst. The temperature of the catalyst layer for oxidizing carbon monoxide, hydrocarbons, etc. using this titanium oxide-platinum group catalyst varies depending on the composition of the exhaust gas. For example, when the catalyst particle size is 2 to 4 mm and the space velocity is 10,000 h ^-1 , an oxidation rate of 95% or more can be obtained for carbon monoxide at 250° C. or higher, and for hydrocarbons at 300° C. or higher. However, the oxidation of carbon monoxide, hydrocarbons, etc. is an exothermic reaction, and the temperature of the catalyst layer increases as the reaction progresses. The temperature rise varies depending on the concentration, but at 1000 ppm, the temperature rise reaches about 9°C for carbon monoxide and about 80 to 100°C for hydrocarbons. When the concentration of combustion components in the gas is high, the gas is diluted as necessary to prevent temperature rise. The temperature conditions for the reaction are determined by taking into account the heat of reaction and fluctuations in the capacity of the equipment.
Select so that the temperature of the catalyst itself does not exceed 800°C. When the combustion component is hydrogen, if the palladium-supported titanium oxide catalyst of the present invention is used, the combustion reaction will proceed even at room temperature (15 to 30°C). In the combustion of hydrocarbons, methane is the most difficult to react with, but in the case of propane and butane, the reaction proceeds quickly with a platinum-supported titanium oxide catalyst at temperatures above 250°C. As mentioned above, the reaction temperature differs depending on the type of combustion component. The space velocity when performing combustion using the combustion of the present invention is 1000 to 500000 m ³ /m ³ /h. space velocity
When it is less than 1000, the amount of catalyst becomes large and becomes uneconomical. The upper limit of the space velocity varies depending on the catalyst particle size, but is 500000 m ³ /m ³ /h. Next, the present invention will be explained by giving examples. However, the following examples specifically explain the present invention, and the present invention is not limited thereto. Example 1 Metatitanic acid slurry 10 containing 35% by weight of titanium oxide is placed in a kneader and heated and kneaded for 2 hours to bring the water content to about 35%. This was dried at 140°C for 5 hours and ground in a ball mill for 2 hours. The obtained powder is calcined in air at 350°C for 2 hours. This powder is granulated into spheres with a diameter of 2 to 4 mm using a rolling granulation method and left to stand overnight. Heat this at 140℃ for 5
After drying for an hour and then baking at 450℃ for 2 hours,
Spherical titanium oxide is obtained. Next, 5 ml of hexachloroplatinate (H ₂ PtCl ₆ ) aqueous solution (10 g Pt/100 g solution) is diluted with distilled water to make a total volume of 35 ml, and this is impregnated into the spherical titanium oxide obtained by the above production method. After drying at 120℃ for 5 hours,
Calcination reduction is carried out at 450° C. for 3 hours in a stream of steam. This catalyst is a titanium oxide-platinum (0.5% by weight) catalyst. A quartz reaction tube with an inner diameter of 40 mm was filled with 24 ml of the catalyst prepared in the above manner, and a gas having the composition shown below was reacted at a space velocity of about 10,000 h ^-1 . Carbon monoxide was measured with a non-dispersive infrared spectrophotometer. SO ₂ 1000ppm SO ₃ 50ppm CO 5000ppm CO ₂ 15% O ₂ 2% H ₂ O 10% N ₂ balance The oxidation rate of carbon monoxide was determined from the following formula. CO reduction rate (%) = (1 - outlet CO concentration/inlet CO concentration)
×100 The results of measuring the initial activity are shown in FIG. 1 by solid line A. At temperatures above 250℃, the oxidation rate of carbon monoxide is 95
% or more. The durability of the catalyst was investigated after approximately 100 hours of continuous operation, and the results are shown in A in Figure 2. The activity of this catalyst does not decrease even under severe conditions of 1000 ppm SO ₂ and 50 ppm SO ₃ . Reference example 1 Hexachloroplatinate (H ₂ PtCl ₆ ) aqueous solution (10
gPt/1000g solution) 5ml was diluted with distilled water to make a total volume of 70ml. This was impregnated into 100 g each of a spherical activated alumina carrier with a diameter of 2 to 4 mm and an alumina-titanium mixed carrier (Al ₂ O ₃ -TiO ₂ equimolar mixture),
After drying at 120℃ for 5 hours, drying at 450℃ in a steam stream for 3 hours.
Reduce baking time. This catalyst is a 0.5% by weight platinized catalyst. 24 ml of the catalyst prepared in the above manner was filled into a quartz reaction tube with an inner diameter of 40 mm, and the initial activity was measured using the same gas composition as in Example 1. The results are shown by dotted line B in FIG.
As shown in Figure 1, the initial activity is
Shows an oxidation rate of 95% or more at temperatures above 250℃. However, as shown in FIG. 2B, in the case of using an alumina carrier, the oxidation rate rapidly decreased as the reaction time progressed. In addition, as shown by dotted line C, the catalyst supported on an alumina-titanium support (TiO ₂ 48% by weight)
After some time had passed, the activity began to gradually decrease. Example 2 The CO oxidation rate was measured in the same manner as in the first example except that the platinum content was changed. Results first
Shown in the table.

[Table] This shows that the platinum content is effective when it is 0.02% by weight or more, and it shows almost the same level of activity when it is 0.1% by weight or more. Example 3 The impregnating solution was prepared in exactly the same manner as in Example 1, except that 35 ml of an aqueous palladium nitrate solution (containing 0.5 g of palladium metal) was used, and the CO oxidation rate was measured. The results are shown in Table 2.

[Table] As shown in D in Figure 2, the oxidation rate at a reaction temperature of 300°C shows no decrease even after 100 hours. Example 4 The impregnating solution was prepared in exactly the same manner as in the first example except that it was 35 ml of ruthenium tetrachloride aqueous solution (containing 0.5 g of ruthenium metal), and the results of measuring the CO oxidation rate are shown in Table 3. Shown below.

[Table] As shown in E in Figure 2, no decrease in oxidation rate was observed even after 100 hours in the reaction at 300°C. According to the present invention, since the catalyst is made of titanium oxide and platinum group elements that are difficult to convert into sulfates, carbon monoxide and hydrocarbons in gas containing sulfur oxides can be completely oxidized and removed for a long time. , there is almost no change in the pore structure or composition of the catalyst, and a high oxidation rate can be maintained. Example 5 In this example, the results of experiments in which various combustion components were combusted will be described. The reaction gas used in Example 1 was obtained by replacing carbon monoxide with hydrogen (1%), methane (1%), butane (0.5%), or methanol (2%). Table 4 shows the results obtained under the same reaction conditions as in Example 1.

[Table] Example 6 A titanium oxide carrier was prepared in the same manner as in Example 1 except that the firing temperature was changed, and a total amount of 0.2 g of ruthenium and palladium was supported to prepare a catalyst. The reaction rate at 300° C. was determined in the same manner as in Example 1 using a reaction gas having the following composition. SO ₂ 500ppm SO ₃ 500ppm CO 1% O ₂ 15% N ₂ remaining The results are shown in Table 5.

【table】

[Table] Those with a calcination temperature of 250 and 1100°C are reference examples. If the calcination temperature is low, the catalyst activity will decrease. On the other hand, those fired at high temperatures have essentially low activity, although there is no decrease in activity. Note that the activity of the catalyst calcined at 1100°C was approximately the same as that when a commercially available titanium carrier was used. Example 7 Using the catalysts of Example 1 and Reference Example 1, the influence of the SOx concentration contained in the reaction gas was investigated. SO ₂ and
The same conditions as in Example 6 were used except that the concentration of SO ₃ was changed. The results are shown in Table 6.

[Table] Among SOx, _SO3 has the greatest poisoning effect, especially
At 5 ppm or more, the alumina support becomes poisoned and shows a significant decrease in activity. As described above in detail, the method of the present invention makes it possible to burn low-concentration combustion components in gas over a long period of time at a high reaction rate without being affected by sulfur oxides.

[Brief explanation of the drawing]

FIG. 1 shows the initial activity of the titanium oxide-platinum catalyst according to the present invention and the alumina-supported platinum catalyst according to Reference Example 1. Figure 2 shows Reference Example 1, Example 1,
3 and 4 show the durability of the catalyst against sulfur oxides.

Claims (1)

[Scope of Claims] 1. A method for catalytically oxidizing combustion components in a gas containing at least one of hydrogen, carbon monoxide, hydrocarbons, and sulfur oxides, wherein the gas is
A platinum group metal catalyst supported on a titanium oxide support calcined at 400 to 800°C was heated to 800°C in the presence of an oxidizing agent.
A method for combustion of combustion components in a gas, characterized by bringing them into contact at a temperature below ℃. 2. The method for combustion of combustion components in a gas according to claim 1, wherein the platinum group metal catalyst is at least one metal catalyst selected from platinum, palladium, and ruthenium.