JPH03186319A - Ozone decomposition method - Google Patents

Abstract

PURPOSE:To prevent ozone decomposition power from lowering even if nitrogen oxides coexist with ozone by removing NOx using an adsorbent or a NOx decomposition catalyst before ozone decomposition in the case of decomposition of ozone in a waste gas containing ozone as well as nitrogen oxides. CONSTITUTION:In a method for decomposing ozone in a waste gas containing ozone as well as nitrogen oxides, a NOx removal filter is put in a prior stage to an ozone decomposition catalyst. The filter may be an adsorbent which adsorbs NOx at the temperature of usage condition or a substance which decomposes NOx into N2 and O2 or into NO less reactive with metal oxides than NO2. Alkaline earth metal oxides, alkaline earth hydroxides, alkali metal- zeolite such as Na-X, perovskite compounds such as Y1, Ba2, Cu3, etc., are used as the NOx adsorbent. Ni, Fe, Cu-ZSM-5, etc., are used as the NOx decomposition catalyst. By this method, without the ozone decomposition power being lowered, ozone is decomposed even if nitrogen oxides coexist with ozone.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an ozone decomposition method using a catalyst for decomposing and removing ozone contained in a gas or the like.

<Prior art> Conventionally, as methods for removing ozone, which is a harmful component contained in gases, adsorption methods using porous materials such as activated carbon and zeolite, and oxidative decomposition methods using catalysts such as MnO□ have been proposed. ing.

<Problems to be Solved by the Invention> However, none of the above conventional ozone removal methods can be said to be fully satisfactory.

That is, the adsorption method has a problem in that since the period during which the adsorbent exhibits its adsorption ability is limited, it requires regeneration, etc., and a great deal of labor and cost is required for maintenance of the removal device.

Further, although the oxidative decomposition method does not have the above-mentioned problems, there is a problem in that the activity of the ozone decomposition catalyst deteriorates over time.

The present invention has already applied for various inventions as methods for improving these problems, but it has been found that even these methods cannot sufficiently solve this problem when nitrogen oxides are contained in the exhaust gas. Ta.

This was done to solve these problems,
The purpose is to provide a method in which ozonolysis activity does not decrease even when a trace amount of nitrogen oxides are present.

By the way, the present inventors have already proposed the main cause of the decrease in the activity of the ozone decomposition catalyst.

This is because the desorption of ozone into the gas phase bulk is delayed depending on the catalyst species and the reaction temperature, and the balance of the reaction product system is disrupted due to the accumulation of oxygen in the catalyst.

However, it has become clear that the decrease in activity is not only due to this, but is also greatly influenced by coexisting components in the gas. In particular, when nitrogen oxides coexist, even if the concentration of nitrogen oxides is minute, it will be adsorbed by the ozone decomposition catalyst, and in some cases, it will generate nitrites or nitrates, resulting in active site inhibition or active site destruction. It became clear that the activity changed over time.

The present inventor was made based on such knowledge, and the purpose thereof is to provide a method in which ozone decomposition performance does not deteriorate in the coexistence of nitrogen oxides.

These adsorbents or NOx decomposition catalysts can be used in various shapes in the same way as the ozone decomposition catalysts.

For example, they are honeycomb-shaped, pellet-shaped, foam-shaped, etc.

The adsorbent or NOx decomposition catalyst can be manufactured by appropriately selecting a known manufacturing method such as an impregnation method, a kneading method, a coprecipitation method, a precipitation method, or an oxide mixing method. In the production of catalysts, shaping aids may be added to give the catalyst shapeability, and reinforcing agents such as inorganic fibers, organic binders, etc. may be added as appropriate to improve mechanical strength etc. good.

Furthermore, the contact between the adsorbent and the reaction gas depends on the concentration of nitrogen oxides in the gas, but since the nitrogen oxides normally contained in the ozone-containing exhaust gas are 1 ppm or less, this adsorption operation is performed at 5V=100 It can be carried out for ~100,000 Hr'.

In addition, for NOx decomposition catalysts, NiMetal, Fe
Metal Cu-ZSM-5 or the like can be used. These catalysts do not need to be replaced like adsorbents, but since the ozone concentration is usually extremely low, the adsorbents do not need to be replaced for a long period of time either, so they are all effective in this method.

In addition, the catalyst system that is extremely effective in this method is MnO2-Ag2O, which has high adsorptive reactivity with nitrogen oxides and shows almost no deterioration due to the difficulty in desorbing the generated oxygen mentioned above.
Mn02-Ag20-TiO2, Mn02-Ag20-
Ti02-5in.

MnO2-Ag20-Ti02-ZrO2,Ag20-
Silver thread catalyst such as TiO2.

<Means for Solving the Problem> As the catalyst used in the present invention, catalysts conventionally known as having ozone decomposition ability, such as M n
O2, Cu O+ F e 203 , A g 2
One or two of 0, Nip, Co3O4, Pt, Pd, etc.
Combinations of more than one species, as well as Mn02-TiO2 and MnO2-Ag20-Ti, which the present inventor has already applied for.
O2, Mn02-WO2-Ti02. Mn02-Mo0
3-Ti02 Nemo n et al. 2-Alkali metal and/or alkaline earth metal oxide, oxide formation enthalpy is 10
0Kcal/gff! Examples include zeolite catalysts that support subatomic metals. However, the method of the present invention is not limited thereto.

The shape of the catalyst according to the present invention is not particularly limited, and various shapes such as a honeycomb shape, a pellet shape, a columnar shape, a plate shape, a foam shape, and a pipe shape can be used.

The NOx removal filter used in the present invention is an adsorbent or NOxli which adsorbs NOx at the operating temperature.
Any material may be used as long as it decomposes into N2 and O2 or converts into No, which has inferior reactivity with metal oxides compared to NO2.

Examples of NOx adsorbents include the following. Alkaline earth metal oxides such as MgO, Cub, SrO, BaO, Mg(OH)2tCa(OH
)2, etc. Alkaline earth hydroxides N a-X *
Na-Y + Na-mordenite.

Alkali metal-zeolides such as Na-ZSM-6, Y1+ Ba2. Cu3*07-! /+LaS
r Perovskite compounds such as CaO2, etc.

10 kg of Kyowa Kagaku activated magnesium oxide with a specific surface area of 130w1''/g and 10 kg of activated clay were dry mixed, the appropriate water was added, and the mixture was kneaded using a kneader. After extruding the honeycomb and drying it with ventilation, it was fired at 500°C for 3 hours to eliminate NOx.
An adsorbent was obtained.

(Preparation of catalyst) Example 1 1034 g of titania sol (Ti02 content: 150 g/min) was added to 2704 g of Mn0 with a specific surface area of 48 &/g, and 250 g of glass peas was further added to this.
A slurry was obtained by stirring and mixing for 0 minutes. This slurry was impregnated into a corrugated honeycomb made of ceramic fibers with a porosity of 81% and a pitch of 4.0.
A two-way catalyst was obtained in which 2 (weight ratio: 82:18) was supported at a loading rate of 95%.

Example 2 Manganese acetate (four salt) 17.8g, nitrate cobamelt (
Ropponshio) 282g and nitric acid! ! 1.5g of 500sll
An aqueous solution was prepared. Next, an ammonium carbonate aqueous solution was added to this aqueous solution while stirring to neutralize it, thereby producing a slurry-like precipitate. The final pH at this time was 7.0. Manganese dioxide (M
Add 250 g of nO*) and 103 g of silver oxide (Ag20), and further add 250 g of glass peas and mix with stirring.
A slurry-like precipitate was formed. This slurry was impregnated into a corrugated honeycomb having the same specifications as that used in Example 1. MnO, -Ag20-Ti02 (weight ratio 50:
A three-way catalyst was obtained in which 20:30) was supported at a loading rate of 101%.

First, catalytic activity test For each of the catalysts obtained in Examples 1 and 2 above, a catalytic activity test was conducted under the following reaction conditions using the test apparatus whose flow sheet is shown in FIG. 1) is an ozone generator that generates ozone, and nitrogen oxides include No-N 2 gas added to the downstream stream of the ozone generator so that NOx reaches a predetermined concentration. This air containing ozone and nitrogen oxides is guided to the NOx adsorption layer or decomposition layer (2) and the catalyst layer (3), and the ozone decomposition rate (%) is measured using an ozone analyzer (
It is calculated using the following formula from the ozone concentration values at the inlet and outlet of catalyst N(2) measured in step 4).

Ozone decomposition rate (%) = SV: 100,000Hr' Inlet ozone concentration: 1 OppHl Inlet NOx concentration: 1pp+w Reaction temperature: 20°C Under these conditions, initial and 1 hour elapsed with and without NOx adsorbent After 10 hours, 10
The ozone decomposition rate of each catalyst after 0 hours was measured and the deterioration of each catalyst was investigated. Further, at this time, the NOx concentration after the NOx absorbent was in the range of 20 to 50 PPb during the test.

Figure 1 1 hand Continued Supplementary Positive book (method) %formula% name of invention Ozone decomposition method 3゜ person who makes corrections Relationship with the incident

Claims (1)

[Claims] An ozone decomposition method for decomposing ozone in exhaust gas containing ozone and nitrogen oxides, the method comprising installing a NOx removal filter upstream of an ozone decomposition catalyst.