JPH07213864A - Removing method of nitrous oxide - Google Patents

Abstract

PURPOSE:To remove nitrous oxide with a high removing rate even at lox temp. by depositing transition metal on mordenite having specified or higher silica/ alumina ratio or ZSM-5 and bringing a gas to be treated containing nitrous oxide and mixed with hydrocarbon reducing gas into contact with the transition metal. CONSTITUTION:Transition metal is deposited on a mordenite having >10 silica/ alumina ratio or ZSM-5 and a gas to be treated containing nitrous oxide and mixed with hydrocarbon reducing gas is brought into contact with the deposited transition metal. As for the transition metal, cobalt, iron, nickel, manganese, ruthenium, rhodium, iridium, or the like is used. These transition metals are deposited on a catalyst of the mordenite or ZSM-5 by an ion exchange method or the like. The hydrocarbon reducing gas is propane, ethylene, propylene, etc., and is mixed by the number of the moles or larger necessary to decompose N2O. For example, when propane is used, about >=1/5 time as the amt. of N2O is needed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing nitrous oxide which removes nitrous oxide contained in gas.

[0002]

2. Description of the Related Art In recent years, global warming of the climate due to greenhouse effects such as artificially emitted carbon dioxide (CO ₂ ), and destruction of the ozone layer due to stable compounds such as CFCs pose a problem of environmental destruction at the global level. Has become. In particular, it is said that the destruction of the ozone layer increases the amount of ultraviolet rays reaching the surface of the earth, causes frequent skin cancers, and has a serious impact on human health.

As substances that cause the destruction of the ozone layer,
Conventionally, it has been considered that artificially synthesized various CFCs are the main components, and nitrous oxide (N ₂ O) contained in gases emitted from various combustion devices such as boilers, diesel engines, incinerators, etc. It didn't get as much attention. However,
The amount of increase in N ₂ O has been increasing in recent years, and a recent survey revealed that N ₂ O diffuses into the stratosphere and destroys the ozone layer, and also contributes greatly to the greenhouse effect. , Is being highlighted as one of the global environmental problems.

As a technique for removing N ₂ O discharged from a boiler or the like, reduction of N ₂ O generation by improvement of combustion system, decomposition of N ₂ O by plasma irradiation, removal of N ₂ O by a catalyst and the like are considered. . However, there is a problem in practical application in terms of high temperature material, thermal efficiency, cost and the like. It is considered to be relatively practical if N ₂ O can be removed by a catalyst, but it has been confirmed that N ₂ O cannot be removed by a catalyst currently applied to many power plants.

Therefore, it is necessary to develop a new catalyst. For example, it has been proposed to reduce and remove N ₂ O by using mordenite having a silica-alumina ratio of 10 or more or iron-substituted mordenite as a catalyst ( JP-A-2-68120, etc.).

[0006]

However, when N ₂ O is removed by using the above-mentioned mordenite as a catalyst, the reaction temperature is set to about 600 to obtain a high removal rate, for example, 80% or more.
It must be as high as ℃ or higher, and the efficiency is poor.

Therefore, the present invention has been made in view of such circumstances, and an object thereof is to provide a method for removing nitrous oxide which can remove nitrous oxide at a high removal rate even at a low temperature. To provide.

[0008]

As a result of various researches and developments for efficiently removing nitrous oxide (N ₂ O), the present inventors have found that a hydrocarbon to be treated as a gas containing nitrous oxide. Focusing on improving the removal performance of nitrous oxide by mixing the reducing gas of, it has come to complete the present invention, the method of removing nitrous oxide of the present invention, silica alumina ratio Mordenite or Z of 10 or more
The SM-5 is loaded with a transition metal, and a gas to be treated containing nitrous oxide in which a reducing gas of hydrocarbon is mixed is brought into contact therewith.

That is, first, various catalysts (ammonia reduction catalysts (SCs currently used in many power plants)
R), a titania-supported noble metal-based catalyst, a zeolite-based catalyst, etc.) was used to perform an experiment for decomposing N ₂ O, and it was confirmed that the zeolite-based catalyst was useful. Then, several kinds of mordenite were adjusted with transition elements such as cobalt, iron and nickel by ion exchange and the direct decomposition activity of N ₂ O of these catalysts was examined. As a result, it was found that the activation temperature of the catalyst was lowered. It was. N ₂ even at lower temperatures
As a result of research and development for removing O at a high removal rate, a reducing gas of hydrocarbon was mixed into a gas to be treated containing nitrous oxide, and the silica-alumina ratio of which was exchanged with a transition metal cation was 10%. More mordenite or Z
It was found that the activity in the low temperature range is improved by bringing the SM-5 into contact with the catalyst.

In the present invention, mordenite includes those having a general formula of Na ₈ Al ₈ Si ₄₀ O ₉₆ · 24H ₂ O, and its silica-alumina ratio (molar ratio of SiO ₂ / Al ₂ O ₃ ) is 10 or more. If the molar ratio is small, the heat resistance is poor.

ZSM-5 has the general formula M _{12 / n} Al ₂
There are some such as Si ₉₄ O ₁₉₂ · 16H ₂ O (M is a cation and n is its valence), and the silica-alumina ratio must be 10 or more. Inferior to.

Examples of the transition metal include cobalt, iron, nickel, manganese, ruthenium, rhodium and iridium. These transition metals are supported on the catalyst of mordenite or ZSM-5 by ion exchange or the like.

As the reducing gas for hydrocarbon,
Propane, ethylene, propylene and the like can be mentioned, and the mixing amount thereof is at least the number of moles necessary for the reaction of decomposing N ₂ O. For example, in the case of propane, the amount of 1/5 or more with respect to N ₂ O is used. You will need it.

It is considered that the decomposition reaction of N ₂ O is represented by the following formula in the case of propane, for example.

10N ₂ O + 2C ₃ H ₈ + 5O ₂ → 10N
₂ + 6CO ₂ + 8H ₂ O

[0016]

EXAMPLES Examples of the present invention will be described below.

Mordenite (silica-alumina ratio: 15.2)
Cobalt (Co), iron (Fe), nickel (Ni),
Manganese (Mn), Ruthenium (Ru), Rhodium (R
h), iridium (Ir) and ZSM-5 (silica-alumina ratio: 30) are ion-exchanged with iron to form Co / mordenite, Fe / mordenite, Ni / mordenite, Mn / mordenite, Ru / mordenite, Rh /
Mordenite, Ir / mordenite, Fe / ZSM-5
Various catalysts were prepared. For this adjustment, 100 g of a 10% metal salt aqueous solution was prepared, and mordenite and ZSM-5 were added to 30 g of the solution.
Add g and stir for 2 days while keeping the temperature at 80 ℃. After stirring,
Wash with water, filter, dry at 110 ℃ for 1hr, then 350 ℃
Firing for 2 hours at mordenite and ZSM-
A catalyst of 5 was prepared.

The various catalysts thus prepared were brought into contact with a gas to be treated containing nitrous oxide mixed with a reducing gas of propane and ammonia, and the N ₂ O decomposition activity was examined. The results are shown in FIG. ~ Shown in FIG.

The decomposition rate of N ₂ O was investigated as follows.

A quartz glass reactor having an inner diameter of 4 mm, whose temperature can be adjusted by an electric furnace, was filled with 50 mg of the weighed catalyst to form a catalyst layer, and while maintaining this at 600 ° C., He was allowed to flow overnight to perform pretreatment. I went. Next, sample gas (reaction gas)
Is a predetermined composition ratio (N ₂ O 0.78%, C ₃ H ₈ 0.77%, O ₂ 5.6
6% -He balance) was collected in a Tedlar bag, and this was set in the inlet of the reactor. Then, after setting the reactor to a predetermined measurement temperature, the sample gas was flown into the reactor at a flow rate of 30 ml / min. Reaction temperature is 250-500
℃. At this time, the N ₂ O peak area of the bypass line for introducing gas into the reactor, that is, the catalyst layer inlet N ₂
The decomposition rate of N ₂ O was obtained by analyzing the O concentration and the gas after contacting the catalyst layer with a gas chromatograph and the ratio of the N ₂ O peak areas. Gas chromatograph, detector; TC
D, column; using Polapack Q (3m / 3mmφ), column temperature; 80 ℃ or 40 ℃, detector temperature; 120 ℃,
Detector current: 140mA, carry gas flow rate: 45ml / m
The analysis was performed under the conditions of in and 36 ml / min.

In FIG. 1, A is the catalyst Co / mordenite and the reducing gas is propane, B is the catalyst Fe / mordenite and the reducing gas is propane, and C is the catalyst Ni.
/ Mordenite and the reducing gas is propane, D shows the case where the catalyst is Co / mordenite and the reducing gas is ammonia, respectively. In FIG. 2, E shows the case where the catalyst is Mn / mordenite and the reducing gas is propane, and F shows the case where the catalyst is Mn / mordenite and the reducing gas is ammonia.
In FIG. 3, G is the case where the catalyst is Ru / mordenite and the reducing gas is propane, H is the case where the catalyst is Rh / mordenite and the reducing gas is propane, and J is the case where the catalyst is Ir / mordenite and the reducing gas is propane. Show. K in FIG.
Indicates the case where the catalyst is Fe / ZSM-5 and the reducing gas is propane, and L indicates the case where the catalyst is Fe / ZSM-5 and the reducing gas is ammonia.

As is clear from the results shown in FIGS. 1 to 4, when propane is used as the reducing gas (in the case of the propane reduction method), even if the temperature is lower than about 400 ° C., the N ₂ O content is higher than 80%. It can be efficiently decomposed into N ₂ , H ₂ O, and CO ₂ . In particular, Fe / mordenite, Rh / mordenite, and Fe / ZSM-5 catalysts are capable of decomposing 80% or more of N ₂ O at a temperature of about 300 ° C., and have excellent activity in a low temperature range. Further, when ammonia is used as the reducing gas, depending on the catalyst, for example, Co / mordenite or Fe / ZSM
Although the catalyst of -5 has a higher temperature than the case of using propane,
80% or more of N ₂ O can be decomposed at 450 ° C.

Therefore, by depositing a transition metal on mordenite or ZSM-5 having a silica-alumina ratio of 10 or more, and contacting a gas to be treated containing nitrous oxide mixed with propane, which is a hydrocarbon, with ammonia. The removal performance is significantly improved compared to the case of mixing, and nitrous oxide in gas is 80% at low temperature of about 400 ° C or less.
The above can be removed.

Further, since propane is cheaper and less harmful than ammonia and is easy to operate such as handling, the propane reduction method according to the present invention can be applied to other combustion devices of boilers such as diesel engines, incinerators, It can be applied to power plants and is highly industrial.

[0025]

In summary, according to the present invention, the transition metal is supported on mordenite or ZSM-5 having a silica-alumina ratio of 10 or more, and a treated substance containing nitrous oxide is prepared by mixing the transition metal with a reducing gas of hydrocarbon. By bringing the gas into contact with the gas, an excellent effect that nitrous oxide can be removed at a high removal rate even at a low temperature is exhibited.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between reaction temperature and N ₂ O decomposition rate.

FIG. 2 is a diagram showing a relationship between a reaction temperature and an N ₂ O decomposition rate when an Mn / mordenite catalyst is used.

FIG. 3 is a graph showing the relationship between reaction temperature and N ₂ O decomposition rate.

FIG. 4 is a diagram showing a relationship between a reaction temperature and an N ₂ O decomposition rate when an Fe / ZSM-5 catalyst is used.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B01J 29/20 ZAB A

Claims (2)

[Claims] 1. A nitrous oxide comprising a transition metal supported on mordenite having a silica-alumina ratio of 10 or more, and a gas to be treated containing nitrous oxide mixed with a reducing gas of hydrocarbon is brought into contact therewith. Removal method. 2. A ZSM-having a silica-alumina ratio of 10 or more.
5. A method for removing nitrous oxide, which comprises supporting a transition metal on No. 5, and bringing it into contact with a gas to be treated containing nitrous oxide mixed with a reducing gas of hydrocarbon.