JPH0755285B2 - Method for removing nitrogen oxides from waste smoke - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION It is well known that nitrogen oxides are contained in waste smoke produced when burning various fuels. Various methods have been put into practical use in order to remove these oxides and render them harmless.

For example, for boiler waste smoke, a selective reduction method using a special catalyst and ammonia gas has been put into practical use. Also, in a normal gasoline engine of the spark ignition system,
While controlling the ratio of air to fuel to keep the oxygen concentration in the exhaust gas within a certain fixed value (called a window), the three-way catalyst removes nitrogen oxides and simultaneously removes carbon monoxide and hydrocarbons. The method of removal has been put to practical use (Reference: Chemistry Review No. 34, Catalyst Design, pages 204-219, Academic Publishing Center, published in 1982, or Chemistry and Industry, Vol. 86, December issue, pages 87-88, 1986) .

However, the former has the advantage that it is also effective for waste smoke under excess oxygen, but since ammonia is essential as a reducing agent, it is effective for special applications but difficult to use for general applications. The denitration method using ammonia has been put to practical use in large-scale boilers for thermal power generation, etc., but cannot be put to practical use in automobiles, generators for private power generation, etc. in terms of safety and the like.

In particular, even a vehicle equipped with a compression ignition type diesel engine or a stationary type is difficult to put into practical use for a general small boiler or the like.

Also, the latter three-way catalyst system is ineffective under excess oxygen,
Not applicable to diesel engine exhaust, etc.

The present inventor has reached various aspects of the invention as a result of various searches for catalysts and reducing agents that are effective in removing nitrogen oxides even when used for waste smoke containing excess oxygen.

According to the present invention, waste smoke produced when burning various fuels is a catalyst composed of hydrogen type mordenite or hydrogen type clinoptilolite, or copper, chromium, manganese, iron, nickel, cobalt, rhodium, palladium, platinum, vanadium. And a catalyst of hydrogen type mordenite or hydrogen type clinoptilolite supporting one or more elements selected from molybdenum and one or more selected from carbon hydrogens, alcohols, ketones and ethers The method is a method for removing nitrogen oxides contained in waste smoke, which is characterized in that they are contacted in the presence of the organic compound.

By using the method of contacting the catalyst of the present invention with waste smoke containing nitrogen oxides in the presence of an organic compound, nitrogen oxides can be selectively removed effectively even if the waste smoke contains a large amount of oxygen. It became clear to get. This is apparent by comparing the examples and control examples described below, and when alumina, silica gel, or non-hydrogenated naturally occurring mordenite or clinoptilolite is used as it is, nitrogen oxides The removal capacity is extremely low.

According to the method of the present invention, it is apparent from the examples described later that nitrogen oxides can be selectively removed regardless of the oxygen concentration in waste smoke, unlike the case of a three-way catalyst. As the organic compound used as the reducing agent, hydrocarbons, alcohols, ketones and ethers are all effective as shown in the examples, and can be used in a far wider range than the known selective reduction method with ammonia.

The hydrogenation method is a direct method in which naturally occurring mordenite or clinoptilolite or synthetic sodium-type mordenite (commercial name Zeolon 900Na, manufactured by Norton, USA) is repeatedly washed with a mineral acid, and once the cations in the zeolite are ammonium ion-containing water. There is an indirect method of substituting ammonium ions by the treatment of the above and then heating and baking to remove ammonia gas to hydrogenate, but any method is effective in the present invention.

Further, as a method for supporting the above-mentioned various elements, a method in which an aqueous solution of a salt thereof is charged with and stirred by hydrogenated zeolites by either of the above two methods (hereinafter referred to as a supporting first method)
Is normal. In some cases, a method of contacting with an aqueous salt solution of a metal on which zeolite is to be supported and then contacting with ammonium ion-containing water and then performing heat deammonia (hereinafter referred to as a second supporting method), or conversely, immediately after substitution of ammonium ion, the metal is immediately removed. A method for supporting a metal component by bringing it into contact with an aqueous salt solution (hereinafter referred to as a supporting third method)
It is also effective to perform hydrogenation by heating and deammonia after the above.

In the following examples, the catalyst bed has an inner diameter of 2 cm and a length of 16 cm.
The column was packed with 10 to 20 mesh catalyst particles for use.

Unless otherwise specified, the gas flow rate of the test gas was 1 liter per minute.

The composition of gas is 80% by volume of nitrogen, 10% of O _{2 and} 10% of CO ₂ ,
A mixture of 0.17% NO and water injected at a rate of 4 grams per hour was used.

The mixed gas was preheated to the reaction temperature, an organic compound as a reducing agent was mixed and then introduced into the catalyst bed.

The nitrogen oxide in the gas was measured by the ozone emission method, and the purification rate was obtained by subtracting 100% from the value obtained by dividing the NO + NO ₂ value in the outlet gas by the value in the inlet gas.

In addition, among the naturally occurring mordenite-containing rocks used in the following Examples or Comparative Examples, those from Akita Prefecture are mainly the first
A kind of tuff which has the X-ray diffraction image as shown in the table, is mainly composed of SiO ₂ , Al ₂ O ₃ and water and contains 1 to 10% by weight of oxide of alkali metal or alkaline earth metal. And
The main component is mordenite. Also, those from Fukushima Prefecture are mainly tuffs that have X-ray diffraction images as shown in Table 2 and have an elemental composition similar to those from Akita Prefecture, and the main component is clinoptilolite. is there.

In this table, the X-ray diffraction image and the value of specific intensity of ₁₀ I / I ₀ may vary slightly depending on the equipment used, humidity, temperature, packing method of crystal powder, etc. Is not essential to prescribe.

Example 1 In this example, as the carrier, the above-mentioned natural mordenite rock produced in Akita prefecture was hydrogenated by the direct method, and a catalyst on which various elements were supported by the above-mentioned supporting first method was used. Direct hydrogenation was carried out by repeatedly washing with 2N hydrochloric acid at 100 ° C for 40 hours. In most cases, nitrate was used as the supported salt, and the supporting method was carried out by contacting with a 3-fold amount of 1 mol / l aqueous solution at 90 ° C. for 2 hours. However, chloride was used for palladium and rhodium, chloroplatinic acid was used for platinum, ammonium metavanadate was used for vanadium, and ammonium molybdate was used for molybdenum.

The results obtained are shown in Table 3. Among the reducing agents, propane is a commercial product for fuel with 8% ethane, 92% propane, and 0.1% isobutane. As the light oil, a commercially available product for diesel vehicles was used. Others used were commercially available as reagents. The mixing amount of the reducing agent is shown in mg / min.

Example 2 This example was exactly the same as Example 1 except that the above-mentioned clinoptilolite rock from Fukushima Prefecture was used as the raw material of the carrier. The execution results are shown in Table 4.

Example 3 In this example, hydrogenated mordenite (commercial name Zeolon 900H) manufactured by Norton Corp., which is said to be hydrogenated of synthetic mordenite (commercial name Zeolon 900Na), was used as it was or as a carrier. It was exactly the same as 1. The results obtained are shown in Table 5.

Example 4 In this example, the same raw material and supporting method as in Example 1 were used, except that the hydrogenation method was the above-mentioned indirect method. The natural mordenite rock was crushed, immersed in a 2 mol / l ammonium chloride aqueous solution at 90 ° C. for 2 hours, and then heated to 600 ° C. for deammonification. The results obtained are shown in Table 5.

Example 5 In this example, a catalyst obtained by the above-mentioned supported second method was used, in which the same raw ore as used in Example 1 was used to initially support the desired element and then hydrogenate by an indirect method of ammonium ion substitution. Using. The results obtained are shown in Table 5.

Example 6 In this example, the same rough as in Example 1 was used to produce a catalyst using the above-mentioned supported third method. The results obtained are shown in Table 5.

Comparative Example Table 6 shows an example of the above-mentioned naturally occurring zeolite or Na type of synthetic mordenite, alumina or the like as it is, or on which various elements are supported.

As shown in this example, when non-hydrogenated zeolite or alumina is used as it is or when various elements are supported, even if a method of using an organic compound as a reducing agent is adopted, an ordinary organic compound reducing agent does not contain oxygen. It is clear that it has little effect on the reduction of nitrogen oxides in smoke. That is, when propane is used as the reducing agent, for example, the mordenite-manganese-supported catalyst shown in Table 5 has a purification rate of 2% at 430 ° C., but the manganese-supported catalyst using hydrogenated mordenite shown in Table 3 is very large. A purification rate as high as% has been obtained.

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Claims (1)

[Claims] 1. A waste smoke produced when a fuel is burned is composed of hydrogen type mordenite or hydrogen type clinoptilolite as a catalyst or copper, chromium, manganese, iron, nickel, cobalt, rhodium, palladium, platinum, vanadium. And a catalyst for hydrogen-type mordenite or hydrogen-type clinoptilolite loaded with one or more elements selected from molybdenum and one or more selected from hydrocarbons, alcohols, ketones and ethers The method for removing nitrogen oxides contained in waste smoke, which comprises contacting the organic compound in the presence of the organic compound.