JPH04267929A - Denitration apparatus and preparation of zeolite azide compound mixed molded body - Google Patents

Abstract

PURPOSE:To remove NOx with high denitration efficiency within a low temp. region over a wide use temp. range by subjecting NOx in the gas flowing through a treatment container to the contact reaction with the zeolite NaN3 mixed molded body in the treatment container. CONSTITUTION:NOx in the gas flowing through a treatment container 1 is subjected to the contact reaction with the zeolite NaN3 mixed molded body 7 in the container 1 to be removed by the removing action of zeolite and NaN3. The aforementioned mixed molded body 7 can be obtained by mixing an org. binder (e.g. polyvinyl alcohol) with a powder mixture of zeolite and NaN3 to mold both of them and baking the molded body in a nitrogen atmosphere. By this denitration apparatus, high denitration efficiency can be realized by the synergistic removing action of zeolite and NaN3 and a use temp. range becomes a wide low temp. region. Further, the convenience and safety of handling are enhanced and the apparatus can be also miniaturized. Since a catalyst is unnecessary, this apparatus is economically advantageous.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for removing NOX from nitrogen oxide (NOX)-containing gas such as exhaust gas from an internal combustion engine.

0002

2. Description of the Related Art Generally, NOX treatment technology has been put to practical use as a flue gas denitrification technology. Flue gas denitrification methods are broadly divided into dry methods and wet methods, and the most advanced method is the selective catalytic reduction method, which is one of the dry methods. The main reaction in this selective selective reduction method is shown in equation (1).

4NO + 4NH3 + O2 → 4N2 + 6H2O... (1) In this selective catalytic reduction method, ammonia, hydrocarbons, and carbon monoxide are used as reducing agents, and ammonia in particular reacts selectively with NOX even if oxygen is present. It is used to treat exhaust gas that contains a lot of oxygen, such as exhaust gas from diesel engines. Further, as a catalyst, noble metals such as Pt, various metal oxides supported on Al2O3, TiO2, etc. are used.

[0004] This selective catalytic reduction method can be carried out using a simple system, provides a high denitrification rate, and also reduces NOx.
Although it has advantages such as eliminating the need for discharge treatment because X can be decomposed into harmless N2 and H2O, it has the following problems. First, since it uses harmful and dangerous ammonia gas, it must be handled with great care. Furthermore, since the NOX reduction reaction is an equimolar reaction, ammonia equal to the amount of NOx to be denitrified must be injected into the exhaust gas, which poses the problem of increasing the size of ammonia storage equipment, catalysts, and the like. In addition, the performance of the reduction catalyst deteriorates due to ammonia gas, and the deterioration of the reduction catalyst progresses due to exhaust gas components, making it necessary to replace the catalyst, which is an economically disadvantageous problem, especially in the case of expensive precious metal catalysts. There is also. In addition, at high temperatures, problems such as sintering of catalyst components occur, and at low temperatures, ammonia reacts with moisture and SOX, reducing the denitrification rate. There are some issues that are limited to.

Since the selective catalytic reduction method has many disadvantages as described above, research on other denitrification methods is currently being conducted. Other denitrification methods include a method of adsorbing and removing NOX. Most of these methods are adsorption methods using activated carbon, but research is also being conducted on adsorption methods using zeolite. When using zeolite, synthetic zeolite is usually used, and there are very few studies using natural zeolite ("Study on the removal of NOx by zeolite", Industrial Development Institute (1984), Ma, Y. H. & C. Ma
ncei; AIchEJ, 18 1148 (1972
)reference). As a denitrification method using synthetic zeolite, research is being conducted using copper ion exchange ZSM-5 type zeolite. This method is reported to have a denitrification rate of nearly 50% at a reaction temperature of 200 to 400°C.

[0006]

[Problems to be Solved by the Invention] However, in the case of the NOX adsorption/removal method using synthetic zeolite, a major problem is that the catalyst performance deteriorates due to oxygen contained in the exhaust gas (several 10% or less) and the denitrification rate decreases. It becomes. Also,
There are various problems such as long activation time, limited reaction temperature range, and limited reaction amount.

[0007] In view of the above circumstances, an object of the present invention is to improve the method of removing NOX using zeolite and to provide a technology that enables simple denitrification treatment with a high denitrification rate.

[0008]

[Means and effects for solving the problems] This invention has the following features:
In order to achieve the above object, a denitrification device is provided which is equipped with a processing vessel through which NOX-containing gas flows, and in which a molded mixture of zeolite and an azide compound is placed inside the processing vessel. According to this device, the zeolite/azide compound mixed molded product catalytically reacts with NOX inside the processing container, and the NOx is removed by the removal action of the zeolite and the azide compound.
is removed.

The zeolite/azide compound mixed molded product described above can be obtained by mixing a binder with a mixed powder of zeolite and an azide compound, molding the mixture, and firing the molded product in a nitrogen atmosphere.

0010

[Embodiments] Examples of the present invention will be described below. In this example, a molded mixture of zeolite and sodium azide (NaN3) was created without using synthetic zeolite.
This mixed molded product is used to remove NOX,
This will be explained in detail below.

First, a commercially available zeolite (Zeolum F-9 manufactured by Tosoh) is prepared, and this zeolite is crushed into powder. Then, add N to 5g of this zeolite powder.
For example, 10% by weight of aN3 is added, and a few% by weight of an organic substance as a binder is mixed therewith and molded into a predetermined shape. Possible shapes include a honeycomb shape, a plate shape, a porous plate shape, and a spherical shape. When making it porous, PVA (polyvinyl alcohol) is used as a binder. After this,
The moldings are fired for 3 hours at low temperature (range 100-300°C) in a N2 atmosphere. Through the above steps, a zeolite/NaN3 mixed molded product was obtained. This mixed molded product is considered to be effective in removing gases such as CO2 in addition to removing NOx.

Next, a denitrification experiment using this mixed molded product will be explained.

FIG. 1 shows the apparatus constructed for the denitrification experiment. A heater 2 is attached to the processing container (glass cylinder) 1, as well as a gas introduction pipe 3 and a gas discharge pipe 4.
are connected. The gas introduction pipe 3 is for introducing a mixture of a standard gas containing NO and moisture into the processing container, and the gas exhaust pipe 4 is for discharging the gas after processing. An introduction pipe 5 for supplying moisture is connected to the gas introduction pipe 3. A NOX concentration analyzer (manufactured by Shimadzu Corporation: NOX analyzer CLM-107) 6 is installed downstream of the gas exhaust pipe 4. Reference numeral 7 denotes the above-mentioned zeolite/NaN3 mixed molded product. This mixed molded product 7 is housed in a mesh case 8 made of stainless steel, and then the mesh case 8 is inserted and installed inside the processing container 1.

In the above configuration, considering that most of the NOX components in the exhaust gas generated by a diesel engine are NO, and that NO2 is about 5%, the NO concentration is 1.
000 ppm NO/N2 gas (manufactured by Nippon Sanso) is used as a standard gas, and this standard gas is fed into the processing container 1 from the gas introduction pipe 2 together with moisture at 1 liter per minute. Inside the processing container 1, NO in the standard gas is removed by contact reaction with the zeolite/NaN3 mixed molded product 7 (contact time: 5 seconds). By measuring the NO concentration of the gas thus treated with the NOX concentration analyzer 6, the NO removal rate can be verified.

[0015] First, a zeolite/NaN3 mixed molded product with a NaN3 mixing ratio of 10% was used at a temperature range of 25 to 250°C.
The NO removal rate at (temperature of the mixed molded product) was verified. As a result, as shown in FIG. 2, it was confirmed that the temperature range in which NO could be removed was wide and in a low temperature range.

Next, the mixing ratio of NaN3 is 10 to 5, respectively.
The NO removal rate was verified using a 0% mixed molding. The results are shown in FIG. It is considered that a good NaN3 mixing ratio is about 1 to 50% due to the relationship between the denitrification rate and the contact area.

[0017]

[Effects of the Invention] As explained above, the denitrification device according to the present invention has the following advantages.

(1) Since denitrification is carried out using a molded mixture of zeolite and azide compound, a high denitrification rate can be achieved due to the synergistic effect of the removal action of zeolite and azide compound.

(2) The operating temperature range is wide, and denitrification is possible in a low temperature range.

(3) There is no need for ammonia gas, which is difficult to handle, and denitrification can be performed using a mixture of azide compound and zeolite in any shape, improving ease of handling and safety, and reducing the need for replacement. These operations are also easy.

(4) There is no need for ammonia gas storage equipment, catalysts, etc., and the device can be made smaller.

(5) Denitration can be carried out without using expensive precious metals, and there is no need for expensive catalysts, which is economically advantageous.

[0023] Furthermore, the method for producing a mixed molded product according to the present invention has the following effects.

(1) Adding a binder to the mixed powder and molding/
A molded mixture for denitrification can be obtained through a simple process of firing.

(2) By adjusting the mixing ratio of the azide compound, the denitrification rate of the mixed molded product can be adjusted.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an outline of a denitrification device according to an embodiment of the present invention.

FIG. 2 is a graph showing the correlation between NOX removal rate and temperature.

FIG. 3 is a graph showing the correlation between NOX removal rate and NaN3 mixing rate.

[Explanation of symbols]

1...Processing container 7... Zeolite/NaN3 mixed molded product

Claims (2)

[Claims] 1. A denitrification device comprising a processing container through which NOX-containing gas flows, and a molded mixture of zeolite and azide compound is placed inside the processing container. 2. A method for producing a zeolite/azide compound mixed molded product, which comprises mixing a binder with a mixed powder of zeolite and an azide compound, molding the mixture, and firing the molded product in a nitrogen atmosphere.