JPS62117620A - Method for removing nitrogen oxide contained in exhaust gas of gasoline engine - Google Patents

Abstract

PURPOSE:To efficiently perform denitration by bringing NOx into contact with a catalyst under the presence of O2 to oxidize and absorb it and stopping the pass of exhaust gas at the point of time when the absorption efficiency of the catalyst is reduced and using a gaseous reducing agent to reduce NO2 of the catalyst. CONSTITUTION:Exhaust gas discharged from a manifold is introduced into an oxidizing catalyst to convert CO into CO2 and introduced into either catalyst of the parallel catalysts A, B and NOx is oxidized and absorbed to the catalyst under the presence of O2. Various metals such as Mn and Fe, oxide thereof and composite oxide are used as the catalyst. When exhaust gas is introduced into the catalyst layer of one hand for a specified time and absorption efficiency is reduced, the flow of exhaust gas is changeovered to the catalyst layer of the other hand and H2 is introduced into the catalyst layer wherein exhaust gas is not flowed from an H2 generator to remove NOx and the catalyst is regenerated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application] The present invention is aimed at reducing nitrogen oxides (hereinafter referred to as NO
It's called X. ).

The engine system, which is located in the gasoline engine J3 and is operated in a fuel lean state, is an engine with low fuel consumption 1a and high fuel efficiency. However, it has been difficult to remove nitrogen oxides due to the excessive presence of oxygen in the exhaust gas.

The present invention addresses this need and relates to a method for removing NOX from acid-containing exhaust gas discharged from gasoline engines and the like.

[Conventional technology 1 Methods for removing NOX from exhaust gas can be broadly classified into adsorption methods, absorption methods, and catalytic reduction methods, but the catalytic reduction method requires a large amount of exhaust gas treatment products, does not require wastewater treatment, and is technically difficult. ,
Because it is economically advantageous, it is currently the mainstream denitrification technique.

The catalytic reduction method uses methane and LPG as reducing agents.

There is a non-selective catalytic reduction method using hydrocarbons such as gasoline, diesel oil, kerosene, hydrogen or carbon monoxide, and a selective catalytic reduction method using ammonia as a binary agent.

In the case of the part name, a reducing agent sufficient to react with oxygen is added to the exhaust gas containing oxygen to reduce NOx, whereas in the latter case, NOx is selectively reduced even in the exhaust gas containing high a degree of oxygen. can be removed.

The former non-selective catalytic reduction method is used to remove NOx from internal combustion engines, mainly automobile exhaust gas, in a reducing atmosphere with almost no oxygen, and the latter selective catalytic reduction method is
NOx is removed from JJT gas discharged from various types of stationary combustion equipment, including thermal power plants.

[Problem 1 to be solved by the invention Although the presently popular denitrification technology is 'Il', the catalytic reduction method is not without its problems.

Regarding the non-selective catalytic reduction method, if the oxygen concentration in the exhaust gas is high, it becomes an economical problem as it requires a human reducing agent, while the selective catalytic reduction method using ammonia has It is difficult to supply C to mobile sources of NOX, such as automobiles, and
There is a problem of secondary pollution in which unreacted ammonia is discharged as the activity of b catalyst decreases for a fixed source of There are still some issues left.

On the other hand, other than the catalytic reduction method, the main oxidation techniques include the absorption method and the adsorption method.

First, the absorption method consists of the oxidation absorption method, which oxidizes and absorbs NOx, and the N
There is a reduction absorption method that absorbs and reduces OX, but the oxidation absorption method uses an oxidizing agent such as chlorine peroxide, sodium dichromate, or potassium permanganate. Other methods include oxidizing with ozone or contact oxidation, then absorbing with an alkaline aqueous solution, and oxidizing with electron beam irradiation, reacting with ammonia, and collecting with ammonium nitrate. In addition, the reduction absorption method is a method in which NOx is reduced to nitrogen by contact with an aqueous solution containing a reducing agent such as sodium sulfite, sodium thiosulfate, and sulfur sulfide. Absorbed by complex salts, etc., and coexisting sulfur dioxide gas)! One method is to absorb the original alkaline aqueous solution.

These absorption methods have poor absorption efficiency in the case of exhaust gas with a large gas volume because the CJ melon of NOX is dilute, the equipment is large-scale, and the oxidizing agent or reducing agent used is expensive, so there are problems in terms of performance. In addition, consideration must be given to wastewater treatment of the aqueous solution used for absorption, and handling of the a1 ammonium salt.

In addition, in the case of iJl gas with many gas parts, or in the case of a moving source, S! The i-stomach is a problem, and neither case has been put to practical use.

Next, the adsorption method uses synthetic zeolite, activated carbon, or ion exchange resin as an absorbent to adsorb and remove NOX. Due to the effects of Due to the small capacity, there are many problems such as the large scale of the equipment, and it has not been put into practical use for professional wrestling.

As mentioned above, there are many problems with either method.

As mentioned above, combustion (N) is present in the oxygen-containing exhaust gas of a gasoline engine operated in a lean state.

There is no suitable removal method, and the present invention (in view of the above points) provides a practical and new denitrification method.

Means for Solving the F Problems] The method of the present invention involves contacting NOx in 11F gas with a catalyst in the presence of 11I2 wood, thereby converting it into an acid (absorbed U,
The oxidation absorption capacity of the catalyst is improved by removing NOx from the JJF gas, stopping the passage of exhaust gas when the absorption efficiency of the catalyst decreases, and reducing and removing the NOx accumulated in the catalyst using a gaseous reducing agent. NO characterized by regenerating
This is a method for removing NOx from X-containing gas. When NOx in exhaust gas is adsorbed using a conventional gas adsorbent, the adsorption mechanism is simple physical adsorption, and due to adsorption equilibrium, there is a limit to the NOx concentration of the residual gas, and there is a limit to the NOx concentration of the residual gas.

Strongly affected by changes in environmental conditions such as humidity and coexisting gases, N
This method has the disadvantage of requiring a large-scale device due to its low Ox absorption capacity.

The first feature of the present invention is that NOx in exhaust gas is oxidized and absorbed by a catalyst in the presence of oxygen.

Since NOX is oxidized and absorbed by a catalyst, the NOx absorption ability is relatively unaffected by external environmental conditions, and even extremely dilute concentrations of NOX can be absorbed and removed. Therefore, compared to methods using conventional gas adsorbents,
This makes it possible to treat exhaust gas with a small-scale device, which is economically advantageous.

Regarding NOx absorption 1 side, tJ! It seems that this is not a physical adsorption, but a chemical adsorption in which the catalyst and 11 were strongly absorbed.

The second feature of the present invention is that a catalyst whose removal efficiency has decreased is regenerated using a gaseous reducing agent such as hydrogen.

The method of reducing NOx using a reducing agent such as hydrogen is widely known as the non-selective catalytic reduction method. , add enough reducing agent to react with oxygen, and
Because it reduces Ox, it consumes a large amount of reducing agent and is not economical, and the use of non-selective catalytic reduction method is recommended only when there is no M cord or when the concentration of oxygen is reduced as much as possible. It was limited.

In the method of the present invention, the consumption of reducing agent is reduced by the amount of N absorbed by the catalyst.
It is a necessary reward to remove 37 yuan of OX, and it is extremely advantageous in terms of generalization since it is extremely 9 yuan.

In addition, the method of the present invention can be said to be a method that yields to the selective catalytic reduction method in that the amount of reducing agent consumed is equivalent to that of the selective 7-component method.

The present invention will be explained in detail below.

A specific usage example is shown in FIG.

The exhaust gas discharged from the manifold is led to an oxidation catalyst - carbon oxides are converted into carbon dioxide, and various hydrocarbons are converted into carbon dioxide and water. Catalyst A, Catalyst B,
are catalysts that oxidize and absorb nitrogen oxides, and are arranged in parallel, and the switching pulp guides the exhaust gas to either the melting medium Δ or the catalyst [8].

After being introduced into one catalyst layer for a certain period of time, it is introduced into the other catalyst layer using a switching valve. lJ [The catalyst layer through which gas has not passed is regenerated by introducing hydrogen generated from the hydrogen generator.

Next, the catalysts used in the present invention are manganese and iron.

Cobalt, nickel, copper, silver, zinc, chromium, molybdenum, tungsten, vanadium, niobium.

Tantalum, cerium, lanthanum, titanium, zirconium, aluminum, silicon, tin, lead, phosphorus.

sulfur, calcium, magnesium, strontium,
A composition consisting of a metal, oxide or composite oxide of at least one element selected from the group of alkaline earth metals consisting of barium, alkali metals J3 and L1 consisting of lithium, helium, potassium, rubidium and cesium. It is a thing.

The shape of the catalyst may be appropriately selected from pellet shapes, pipe shapes, plate shapes, lattice shapes, ribbon shapes, corrugated plate shapes, donut shapes, and other integrally molded shapes. It is also possible to employ a catalyst preparation method in which a lattice-shaped carrier such as cordierite, mullite, or alumina, and a fully curved substrate -F such as a wire mesh or a plate are coated with the catalyst composition.

There are no particular limitations regarding the physical properties of the completed catalyst, but B
Culms with a large ET specific surface area are preferred.

The I)t gas composition applicable to the treatment in which the method of the invention is used is nitrogen oxide (NOI; ?% Di).
L, te) o, ol ~6. OOOppm, fa yellow oxide resistant SO2 l! ! ! ishiT) O~2.500
ppm, oxygen o, 1-21% by volume, carbon dioxide 1-21%
15 volumes f? 1% J3 and water, p air 1-15 volume ψ% culm l
There are 1 and 6 degrees Celsius. Normal boiler [[gas.

Automobile exhaust gas and household heating equipment exhaust gas fall within this range, but the gas composition is not particularly limited. Next, the processing temperature is 1
The temperature is preferably 50 to gooC, especially 200 to 700C, and the space velocity is 1000 to 300,000) (r-', especially 2
．． A range of 000 to 100,000 Hr-1 is suitable. There is no particular limitation on the processing capacity, but it is 0.01 to 10'J
The fourth of /l and i is preferred. The processing time is
Since it is related to the degree of XIIn, there is no particular limitation.

In addition, the processing conditions using the reducing agent include the type of exhaust gas,
Although it varies depending on the properties, conventional reducing agents such as hydrogen, ammonia, carbon oxide, and hydrocarbons such as methane can be used, but hydrogen is most preferred from the viewpoint of handling and secondary pollution. This is because hydrogen can be easily generated by electrolysis of water, steam reforming of methanol, etc.

The concentration of the reducing agent is not particularly limited, but it may be diluted with an inert gas such as nitrogen. Next, the reduction temperature is 15
0 to 800°C, especially 200 to 700°C is preferred, and the space velocity is related to the concentration of the reducing agent, but 10 to 10
A range of 0,0OOHr'' is preferred.

The treatment time is not particularly limited, but is preferably in the range of 1 minute to 1 hour.

The present invention will be explained in more detail below using Examples, but the present invention is not limited to these Examples.

Example 1 Cordierite honeycomb ((6.68 inches x 3.18 inches) φ x 565 inches L manufactured by Nippon Insulators.

400 cells/in2] as a catalytic material.
A catalyst was obtained by supporting 510 g of a composition of F CO3.

I made two of the same type B, installed them in parallel on the exhaust line of a gasoline engine, and passed the exhaust gas in a straight line U at 10 minute intervals.

Catalyst that does not allow gas to pass through, H obtained from water electrolysis
Two gases were supplied at 21'c/min from 2a to 2a to reduce and remove the oxidized and adsorbed NOx. NO in exhaust gas
x 8 degrees was measured using a Chemilumi Ni analyzer. The NOx purification rate was calculated from the NOx concentration in the inlet gas and the NoxQ degree in the outlet gas in one 10-minute accumulation shift.

Gasoline engine and operating conditions used in the experiment.

The exhaust gas conditions are as follows.

Engine used: Exhaust small 2000cc 4 cycles, IEFf specification operating conditions: 2500rpm X-200mX-2
O0 constant rotation catalyst entrance temperature: 400℃ Inlet gas concentration: NOx = 700DIllI+empty
Fuel consumption: A/F = 19.0 NOx & 1 degree in exhaust gas is the average concentration r1oop for 10 minutes
It was pm. Therefore, the NOx purification rate was about 86%.

[Effect of the Invention 1] The nitrogen oxide removal method of the present invention as described above has various features as listed below.

(1) Conventional exhaust gas purification systems were unable to purify nitrogen oxides in an oxygen-rich atmosphere, but the method of the present invention has made it possible to treat nitrogen oxides.

In general, by combining it with an oxidation catalyst, carbon oxides and hydrocarbons can be removed and automobile exhaust gas regulations can be satisfied.

(2) The processing Vi does not require a large scale and is economical.

(3) It is economical because the reducing agent for nitrogen oxides can be treated by walking.

(4) Since no by-products or wastewater are produced, secondary treatment is not necessary.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, C1 and C2 are gas flow path switching valves.

Claims (2)

[Claims] (1) By bringing nitrogen oxides in gasoline engine exhaust gas into contact with a catalyst in the presence of oxygen, the catalyst oxidizes and absorbs the nitrogen oxides, removes nitrogen oxides from the exhaust gas, and reduces the nitrogen oxide absorption efficiency of the catalyst. Gasoline engine exhaust gas characterized in that the exhaust gas is stopped from passing over the catalyst at the point in time, and the nitrogen oxides accumulated on the catalyst are reduced and removed using a gaseous reducing agent, thereby regenerating the oxidation absorption ability of the catalyst. How to remove nitrogen oxides. (2) The catalyst is manganese, iron, cobalt, nickel, copper, silver, zinc, chromium, molybdenum, tungsten,
vanadium, niobium, tantalum, cerium, lanthanum,
titanium, zirconium, aluminum, silicon, tin,
alkaline earth metals consisting of lead, phosphorus, sulfur, calcium, magnesium, strontium, and barium, alkali metals consisting of lithium, sodium, potassium, rubidium, and cesium, and platinum, palladium, rhodium,
The method according to claim (1), characterized in that the method comprises a metal, oxide or composite oxide of at least one element selected from the group of noble metals consisting of ruthenium.