JP3051493B2 - Nitrogen oxide purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying exhaust gas, and in particular, to nitrogen oxides (hereinafter abbreviated as NOx) in exhaust gas.
A method of purifying water.

[0002]

2. Description of the Related Art In the treatment of exhaust gas from automobiles and the like, it is general to purify NOx, hydrocarbons and CO in exhaust gas using a catalyst. Currently, in the used catalyst, Pt, NOx Rh system of the three-way catalyst in the vicinity of the stoichiometric air-fuel ratio, hydrocarbons, although simultaneous removal of CO, that the O ₂ concentration fuel consumption due to the low deteriorate I have a problem.

[0003]

On the other hand, the development of a catalyst capable of removing NOx at an O ₂ concentration of 1% or more has been urgently promoted in order to improve fuel efficiency, but it has not yet been put to practical use. In addition, 4
If a 1-liter class honeycomb catalyst of 00 cells is used, the pressure loss in the exhaust gas line becomes large, and there are problems such as deterioration of engine performance and damage of the muffler. Therefore, a method for removing NOx in exhaust gas without using a catalyst is desired.

The present invention has been made in view of the above-mentioned state of the art, and aims to provide a method capable of removing NOx in exhaust gas without using a catalyst.

[0005]

Means for Solving the Problems The present inventors have eagerly prepared a catalyst.
Investigation of a method to remove NOx in exhaust gas without using
As a result, I found a surprising phenomenon. It's a blind spot so far
It seems that hydrocarbons in the exhaust gas
That is, ethylene and propylene are at a certain temperature under oxygen content.
NOx reacts efficiently with NOx in the range
_TwoAnd the hydrocarbon is H _TwoO and CO_TwoIs a phenomenon that converts to
You.

The present invention has been completed based on the above findings, and the present invention provides a method for purifying automobile exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons and having a high O ₂ concentration. At 400 to 700 ° C.
The method for purifying nitrogen oxides is characterized in that nitrogen oxides in the exhaust gas are reduced and made harmless by keeping the temperature within the range described above and maintaining the exhaust gas in the temperature range for a residence time of 0.5 seconds or more. .

[0007]

The gasoline vehicle usually has a wide temperature distribution from the engine to the muffler from about 800 to 200 ° C., and the residence time in the exhaust gas pipe is usually 0.5.
Seconds or less. In the present invention, the exhaust gas pipe has a temperature of 4
The exhaust gas pipe is reciprocated several times so that the temperature is uniformly maintained at 00 to 700 ° C. and the residence time of the exhaust gas is 0.5 seconds or more.

In the exhaust gas purification reaction formula of the present invention, for example (assuming that the hydrocarbon in the exhaust gas is C ₂ H ₄ ), 2NO + C ₂ H ₄ + 2O ₂ → N ₂ + 2CO ₂ + 2H ₂
The temperature at which NO is selectively reduced to N ₂ without using a catalyst is 400 to 700 ° C., preferably 450 to 7
00 ° C, especially 450-650 ° C. At a temperature other than this reaction temperature, the reducing agent is not activated or the reducing agent (C
_No denitration occurs because only the combustion reaction of ₂ H ₄ etc. occurs. In order to smoothly perform the denitration according to the above equation (1), the residence time in the exhaust pipe at a uniform temperature is 0.5 seconds or more.
Preferably it is 1 second or more.

According to the method of the present invention, denitration in a lean burn region having a high O ₂ concentration, which has not been realized conventionally, is made possible without using a catalyst.

[0010]

【Example】

(Example 1) As a simulated exhaust gas composition of a lean burn gasoline engine, NO: 400 ppm, CO: 1000 pp
_{m, C 2 H 4: 1500ppm} , CO 2: 10%, H 2
_{O: 10%, O 2:} 8%, was fed at a predetermined residence time to within the reaction tube was uniformly kept the raw material gas remaining N _2. Each temperature,
Table 1 shows the denitration rate and ethylene removal rate in each GHSV. Note that the residence time indicated here refers to the time during which the exhaust gas remains in a uniform temperature range.

[0011] From the results shown in Table 1, mainly the temperature 400-70
At 0 ° C., it was found that the denitration was sufficiently performed with the above exhaust gas composition, and it was found that as the residence time was further increased, the denitration rate was improved. Further, even in the presence of a hydrocarbon other than C ₂ H ₄ , almost the same effect as in Example 1 was obtained.

[Table 1]

(Example 2) Based on the results of Example 1, the exhaust gas pipe of an actual lean-burn gasoline engine can be kept uniformly at 550 ° C and the exhaust gas is reciprocated to maintain a residence time longer than a predetermined value. It was discharged outside.

A schematic diagram of this system is shown in FIG. As a result of keeping the residence time at 1 second, the catalyst was not used, and as shown in FIG.
As a result, a new 10-mode operation (certified by the Ministry of International Trade and Industry) resulted in a denitration rate of 30%. The average composition of the inlet exhaust gas was the same as the simulated gas composition shown in Example 1.

Comparative Example 1 A conventional exhaust gas line is shown in FIG.
Shown in In this conventional method, the exhaust gas pipe has a non-uniform temperature of 800 to 200 ° C., and the residence time of the exhaust gas in the exhaust pipe is 0.2 seconds. As a result of performing a new 10-mode operation without using a catalyst, the denitration rate was 2%. The average composition of the exhaust gas is the same as that of the simulation gas of Example 1.

[0015]

As shown in the examples, by keeping exhaust gas containing nitrogen oxides and hydrocarbons at an exhaust temperature of 400 to 700 ° C. for a predetermined residence time or more (0.5 seconds or more), a catalyst can be used without using a catalyst. It has been clarified that denitration is possible.

As a result, it has been found that it is effective as a method for purifying exhaust gas of a conventional lean burn gasoline engine or diesel engine as an alternative to a method using a catalyst.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention.

FIG. 2 is a chart showing vehicle speeds in a new 10-mode driving mode.

FIG. 3 is an explanatory diagram of one embodiment of a conventional nitrogen oxide purification method.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B01D 53/56 F01N 3/08 F01N 3/10

Claims (1)

(57) [Claims] 1. A method for purifying automobile exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons and having a high O ₂ concentration, wherein the exhaust passage is kept in a temperature range of 400 to 700 ° C. A method for purifying nitrogen oxides, comprising reducing and detoxifying nitrogen oxides in exhaust gas by maintaining the gas in the above temperature range for a residence time of 0.5 seconds or more.