JP3174394B2 - Method for treating nitrogen oxides in diesel engine exhaust gas - 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 decomposing nitrogen oxides in a diesel engine exhaust gas, and more particularly, to bringing a diesel engine exhaust gas into contact with wear-resistant catalytic cracking catalyst particles in a centrifugal fluidized bed. And a method for effectively decomposing nitrogen oxides in exhaust gas.

[0002]

2. Description of the Related Art Nitrogen oxides in flue gas emitted from industrial plants and automobiles are substances that cause photochemical smog, and the amount of such emissions has recently been strictly regulated from the standpoint of environmental protection. It will be strengthened later. Reducing the emission of nitrogen oxides and dust in the exhaust gas of a diesel engine, which is one of the emission sources, has become a serious and urgent social issue.

[0003] Therefore, various measures have been proposed and implemented, including means for improving the engine structure and exhaust gas recirculation. However, these methods are in conflict with the reduction of the amount of nitrogen oxides and the reduction of suspended particles, so it is difficult to significantly reduce the amount of nitrogen oxides, and this problem has not yet been completely solved. .

[0004] Among the means for reducing nitrogen oxides in exhaust gas, the method of decomposing or reducing nitrogen oxides has been noted as the most effective and drastic means, and various studies and proposals have been made. . For example, a method of reducing and removing nitrogen oxides using a reducing agent such as ammonia, hydrogen, or carbon monoxide has been proposed as one of effective removing means and development has been attempted. In addition to the need for a suitable reducing agent, the disadvantage of requiring an apparatus and a mechanism for collecting or decomposing the unreacted reducing agent is inevitable.

On the other hand, the method of decomposing nitrogen oxides using a catalytic catalyst or the like is a simple and effective method in terms of process without requiring a special reducing agent or a device for recovery or decomposition. . However, the combustion of diesel engines is carried out under the condition of excess oxygen, the presence of about 10% oxygen in the exhaust gas, the relatively low temperature of the exhaust gas, the presence of suspended particles and sulfuric acid contained in the exhaust gas. Due to the relatively large amount of salts and the like, these poison the catalyst, and it has been very difficult to develop a catalyst having sufficient activity and durability for the purpose of removing nitrogen oxides in exhaust gas. It was supposed to be.

[0006] However, recently, a catalyst having an activity sufficient for decomposing and removing nitrogen oxides in exhaust gas of a diesel engine or the like has been found at least with respect to the initial activity of the catalyst. For example, JP-A-60-1
Japanese Patent No. 25250 proposes a nitrogen oxide contact catalyst having a specific crystalline aluminosilicate containing copper ions. ZSM-5 (Z), ferrierite (F), mordenite (M ), L type (L), Y type (Y)
, Zeolite, etc., with Cu, Co, Ag or Zn ions exchanged, or Al ₂ O ₃ with Cu, Fe, C
It has also been reported that those supporting o and Cr are effective as catalysts.

[0007]

However, when these contact catalyst particles are filled in a reactor and the exhaust gas is contact-reacted as a fixed-bed catalyst layer in a fixed-bed flow-type reactor, the exhaust gas in the diesel engine exhaust gas Such as suspended particles such as hydrocarbons, tar, carbon particles, etc., adhering to the catalyst surface layer in a relatively short period of time, covering the surface layer and deactivating the catalytic active sites. Is generated. Also, many diesel engines, such as automobile diesel engines and vehicle diesel engines, are not constant in operating state, but rather constantly fluctuate. Therefore, not only the exhaust gas amount but also the nitrogen oxide content, In many cases, the composition of the exhaust gas also changes.

Therefore, when the catalyst layer is a fixed bed, the contact time during which the exhaust gas effectively contacts the catalyst layer constantly changes,
The linear velocity of the catalyst also varies. Therefore, the conversion of nitrogen oxides in the exhaust gas necessarily fluctuates, and as a result,
The average nitrogen oxides removal rate during the operation period is reduced, and there is a disadvantage that the object cannot be effectively achieved. The above-mentioned disadvantages can be avoided to some extent by extending the catalyst layer and filling a large amount of the catalyst, but in this case, the device container becomes excessively large, which not only increases the weight but also increases the differential pressure at the time of exhaust gas circulation. Such as the problem of becoming too large,
Practically has various disadvantages.

Therefore, when the exhaust gas of a diesel engine is usually treated with a fixed bed catalyst, a filtration device such as a strainer or a filter is installed in order to remove most of these suspended particles in advance to protect the fixed catalyst layer. Have been. However, the installation of such an apparatus increases the cost of the exhaust gas treatment apparatus, and causes various inconveniences, such as the necessity of replacing or cleaning the filter with considerable frequency due to clogging of the filter and the like. The present invention avoids the above-mentioned drawbacks of the conventional fixed bed contact circulation system, can effectively decompose and remove nitrogen oxides in exhaust gas at a high conversion rate for a long time, and operates in response to fluctuations in the amount of exhaust gas. It is an object of the present invention to provide a method for removing nitrogen oxides of a diesel engine, which has a remarkably wide range, as a result, a high conversion can be maintained for a long time, and the apparatus is compact.

[0010]

According to the present invention, a metal bearing is provided.
COMPOSITION CONTAINING FINE ZEOLITE PARTICLES AND SILICA SOL
Volume obtained by spray granulating and firing
Catalytic cracking catalyst particles having a quasi-median diameter of 20 to 500 µm
Contains carbon particles in a centrifugal fluidized bed using
The diesel engine exhaust gas is mixed with the carbon particles in a fluid medium.
Disclosed is a method for treating exhaust gas of a diesel engine, which comprises decomposing nitrogen oxides in the exhaust gas while being in contact with a body .

In the method of the present invention, an extremely large catalytically active surface per unit weight of the catalyst can be obtained as compared with a fixed-bed catalytic cracking method such as a normal catalyst particle filling method or a honeycomb molded catalyst method. Also, since the suspended catalyst particles are constantly flowing at random, the particle surface is less likely to be contaminated by the adhesion of suspended solids etc. due to collisions between the particles, etc. It exhibits a variety of superior properties for fixed bed catalysts that can be maintained. As described above, the centrifugal fluidized contact method of the present invention exhibits superior performance as compared with the denitration method using a fixed bed catalyst.
The relationship between (SV) and the nitrogen oxide conversion of the exhaust gas is clear by referring to the graph shown.

That is, FIG. 3 shows the exhaust gas space velocity (W) at 420 ° C. in the centrifugal fluidized bed contactor of the present invention packed with the ZSM-5 type zeolite catalyst in an amount of 200 g.
HSV h ^{- 1)} is a data obtained by measuring the nitrogen oxide conversion varied in the range of about 10,000 to 60,000 (stable operating range), the conversion of this apparatus of the present invention WHSV15000hr ^{- 1} near at about 0.8
(80%) WHSV 25000 hr ^{- 1} even about 0.65
(65%), which is much higher than the conversion (0.35, 0.29) at the corresponding WHSV value under the same catalyst and temperature conditions in the fixed bed catalyst shown as a reference value. Is shown. This specifically shows the above-mentioned specific effects of the fluidized bed such as the size of the active surface per unit weight of the catalyst and the avoidance of deactivation of the active surface due to the attachment of tar-like substances and solid suspended matters. .

Furthermore, the method of the present invention has several advantages as described below due to its large centrifugal force, even when compared to a fluidized bed in a normal moving field. That is, since the gas flow rate can be increased, not only can the apparatus volume per exhaust gas throughput be reduced, but also the particle ejection speed is large and the operation range of the fluidized bed can be significantly widened. In the case of diesel engine exhaust gas, this is a great advantage in following up the change of the exhaust gas emission amount due to the change of the operating condition. Further, as the catalyst particles, it is possible to use fine catalyst particles having a considerably small particle diameter, so that the active surface area per unit weight of the used catalyst can be remarkably increased, and the used catalyst can be saved. Not only contributes to the downsizing of the device.

In addition to the advantages described above, the most important feature of the method of the present invention is that, in the method of the present invention, suspended particles and the like in the exhaust gas of a diesel engine are not filtered and separated in advance by a strainer, a filter or the like. In particular, the point that it is possible to treat the carbon particles that are present in a large amount in the suspended particles while coexisting in the exhaust gas,
This means that there is no need for a strainer, a filter, and the like, which are usually required for filtration and removal of suspended particles, particularly carbon particles, and the like, which are required in the case of fixed-bed exhaust gas treatment. Moreover, surprisingly, in the case of the present invention, it has been found that the presence of carbon particles mixed into the exhaust gas has a promoter-like effect of promoting catalytic cracking of nitrogen oxides. . The detailed mechanism has not been fully elucidated yet, but probably,
Under the conditions in the centrifugal fluidized bed of the present invention, soot contained in the exhaust gas, fine particles such as unburned hydrocarbons quickly become agglomerated, and do not adhere to the catalyst surface and weaken the catalytic activity. In addition, it is presumed that the aggregated particles act to adsorb nitrogen oxides and the like, and when the adsorbed particles come into contact with the catalyst surface, they may exhibit some kind of decomposition reaction accelerating effect.

In any case, in the method of the present invention, it is a very remarkable feature that the presence of suspended particles such as soot, which is usually an inhibitor of the catalytic cracking reaction, rather promotes the cracking reaction.

Further, in the method of the present invention, even if the amount of exhaust gas increases and the linear velocity in the apparatus increases, it is possible that the pressure difference between the inlet and the outlet of the processing apparatus hardly increases beyond a certain value. It is one of the features, and as is apparent from the attached FIG. 2, in the centrifugal fluidized bed of the present invention, the range where the linear velocity of the exhaust gas is small (in the case of the figure, Ug = about 0.05 m. Although the differential pressure rises in accordance with the linear velocity, the stage after the stage where the flow of the catalyst particles becomes almost complete (the state where the rigid rotation state is achieved in the particle layer) (Ug = in the figure)
(0.1 or more), the differential pressure is substantially constant regardless of the linear velocity. Moreover the centrifugal fluidized bed, centrifugal force (in this case of figure speed) can reduce the differential pressure for the same linear velocity by increasing the, yet of the NO _x, as will be readily understood with reference to the accompanying drawings The conversion is the same independently of the speed.

This means that in the exhaust gas treatment, the treatment amount is hardly restricted at least from the pressure difference surface of the catalyst layer, which is a remarkable advantage as compared with the case of the fixed bed catalyst layer.

[0018]

Preferred embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing an example of a centrifugal fluidized bed catalytic cracking device used in the method of the present invention. Exhaust gas from diesel engines is discharged directly from the engine exhaust port, or if
The temperature is adjusted to about 0 ° C. and introduced into a container gas inlet of a centrifugal flow device incorporating a catalyst-filled rotor. The introduced exhaust gas is sucked into the rotor from the distributor (2) provided on the outer peripheral surface of the rotor (1) in the container, and flows through the centrifugal fluidized bed of catalyst particles formed on the inner surface side of the distributor. pass.

The nitrogen oxides present in the exhaust gas undergo a decomposition reaction in the fluidized bed due to the interaction of the accompanying catalyst with the carbon particles in the suspended particles and the contact catalyst to be decomposed into N ₂ and O _2. . In the case of the apparatus shown in the figure, the exhaust gas denitrified by the decomposition reaction in this manner is a suspended particle which has been agglomerated from the exhaust gas outlet provided in the rotating rotor core,
And some scattered catalyst fine particles.

The contact catalyst used in the method of the present invention may be any catalyst particles capable of effectively decomposing nitrogen oxides, and known catalyst particles can be used. In view of the fact that the catalyst particles are used by forming a centrifugal fluidized bed, it is of course necessary to have a high activity against nitrogen oxide decomposition reaction, but it is excellent in sustaining activity stability and durability. You need to be good.

Usually, a centrifugal fluidized bed is often formed in a rotating container such as a rotor in order to generate the centrifugal force. Therefore, particles that are resistant to collision with the container wall and the like and collision between particles, that is, It is preferable that the particles have excellent wear durability.

From this viewpoint, the catalyst particles used in the present invention should have a volume-based median diameter of 20 to 500 μm, and more preferably, the following formula: F = (W ₀ −W ₁ ) × 100 / W _In Formula ₀ , W ₀ is the initial filling amount (g) of the catalyst particles in the centrifugal abrasion test, and W ₁ is at a centrifugal force of 100 G and a gas streamline velocity of 0.2 to 0.3 m / s. This is the weight (g) of the residual catalyst after the treatment for 3 hours. It is better that the wear rate (F) defined by is 10% or less, especially 5% or less.
No. When the median diameter of the catalyst particles is smaller than the above range, the catalyst particles escape, it is difficult to maintain the fluidized state, and when the median diameter of the catalyst particles is larger than the above range, it is only difficult to set the fluidizing conditions. Therefore, the surface area of the active catalyst is small, and a sufficient conversion cannot be achieved.

The shape of the catalyst particles is not particularly limited. However, from the viewpoint of reducing the abrasion resistance of the particles themselves and the abrasion loss of the rotating container in the apparatus, the shape of the catalyst particles may be spherical or the like. It is preferable to have an angled shape. In the present invention, as a denitration catalyst,
In order to use a known ZSM-5 type zeolite supporting copper metal as a catalyst, this zeolite powder is subjected to spray granulation using colloidal silica as a binder, and this is used as catalyst particles.

According to the present invention, the hydrothermal synthesis of SiO
_Two(84.16% by weight), Al_TwoO _Three(6.94 weight
%), Na_TwoZS composed of O (1.29% by weight)
M-5 type zeolite was synthesized, and then 5% by weight of water
Na in zeolite_Two1. For O content.
Five moles of copper complex was added, and the mixture was stirred at room temperature for 24 hours.
1.24 weight as CuO without ion exchange
% ZSM-5 zeolite is prepared.

[0025] Then 4 with respect to the zeolite 20% by weight of colloidal silica as SiO ₂ as SiO ₂
An aqueous slurry of 0% by weight is prepared, the slurry is granulated by spray drying, and then 400 to 600 ° C.
For 2 to 6 hours to obtain catalyst particles having a particle diameter of 20 to 500 μm (volume-based median diameter).

Further, in the present invention, various zeolite single crystal particles having excellent wear resistance are used as catalyst particles.
Preferable examples thereof include an analcyme-type zeolite having a clear 24-hedron or a 24-hedral shape with rounded corners, and acid-treated particles thereof or metal-supported particles thereof.

In the present invention, sodium silicate or activated silicate gel, sodium aluminate and sodium hydroxide are satisfactorily mixed to form an alkali aluminosilicate gel, and after homogenizing the gel, Crystallization at normal temperature or hydrothermal condition at a temperature of from 200 ° C. to 200 ° C. produces a single crystal analcyme type zeolite having a primary particle size of 10 to 60 μm. The single-crystal zeolite particles are usually subjected to an acid treatment using a mineral acid such as hydrochloric acid, sulfuric acid, or nitric acid to elute a part or most of the sodium and alumina components in the zeolite.
The particles obtained here have the same clear particle shape as zeolite particles, and have a BET specific surface of 100 to 500.
It is an acid-treated particle of an analcyme type zeolite having an m ² / g (active analcyme). In addition, as for the wear resistance of these zeolite single crystals and the acid-treated particles thereof, the wear rate (F) defined by "Equation 1" was almost zero.

In the present invention, metal species such as copper, nickel, chromium, vanadin and platinum are supported on the single crystal zeolite and the acid-treated particles thereof.

Zeolite particles carrying the above metal species
Is mixed with silica sol, spray granulated and fired.
Are used as contact catalyst particles.

Examples of the zeolites include various zeolites and metal ion exchangers of those zeolites, such as ferrierite, mordenite,
Zeolites such as A-type, Y-type, X-type, P-type, offretite-type, erionite-type, and shabazite-type, and metal ion exchangers thereof can be exemplified. In particular, among them, as described above, single crystal zeolite or its metal ion exchanger is preferable. Further, various metal silicates, for example, silicates such as iron silicate, chromium silicate, and manganese silicate can also be suitably used.

Further, the above-mentioned metal-supported zeolite,
Fine particles such as metal silicates and perovskite-type composite oxides are spray-granulated using a suitable binder, and those obtained by firing are suitably used as catalyst particles. Natural or synthetic smectite-type clay minerals such as tronite, saponite, hectorite, sauconite, and stevensite can be used.

In the present invention, the reaction temperature of the centrifugal fluidized catalyst bed varies depending on various factors such as the activity of the catalyst to be used and the flow rate of the exhaust gas, but it can be usually operated at a diesel engine exhaust gas temperature of 250 to 600 ° C. In addition, the contact reaction conditions between the exhaust gas and the catalyst are as follows: centrifugal fluidization conditions such as the flow start speed of catalyst particles, the particle ejection speed, etc., catalytic activity, equipment structure, reaction temperature, exhaust gas composition, and required nitrogen oxide decomposition Although it is difficult to display a unique display depending on various factors such as the conversion rate, the normal space velocity (WSHV) is 1 unit.
It is operated at about 0000 to 60,000 h ^{- 1} .

Furthermore, in the present catalytic cracking, conventionally known reducing components such as NH ₅ and hydrocarbons may be newly mixed into the exhaust gas as required. Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

[0034]

【Example】

(Preparation of catalyst particles) ZSM-5 type zeolite was synthesized by a hydrothermal method, filtered, sufficiently washed with water, and the obtained zeolite was made into a 5% suspension with water. To this suspension was added copper acetate 1.5 times the molar amount of Na ₂ O in the zeolite.
The mixture was stirred at room temperature for 4 hours to perform ion exchange, filtered, sufficiently washed with water, and stirred at 110 ° C. Table 1 shows the chemical analysis values of the obtained copper-exchanged zeolite.

[0035]

[Table 1]

This copper-exchanged zeolite was pulverized, and colloidal silica (SiO ₂ content 20%) used as a binder was used.
w%) and granulated by spray drying. The amount of colloidal silica added was 40% of zeolite as SiO ₂ . This is fired at 500 ° C. for 4 hours,
After air classification, it was used as sample catalyst A. Table 2 shows the average particle size, apparent density, porosity, and wear rate of the sample catalyst A measured by a Coulter counter.

[0037]

[Table 2]

The copper-exchanged ZSM-5 zeolite is made of colloidal silica as a binder and has a particle size of 0.5 to 1.
The catalyst particles obtained by granulating into 0 mm granules and sizing are mixed at 500 ° C for 4 hours.
What was calcined for a time was used as sample catalyst B.

(Experimental Apparatus) (a) Centrifugal fluidized bed catalytic cracking apparatus The experimental apparatus shown in FIG. 1 was used. In this device, a rotor (1) and a wind box (3) are made of stainless steel, and a heater and a heat insulating material are attached to a pipe and a main body to control exhaust gas temperature. The rotor (1) is provided with a cylindrical distributor (2). The distributor (2) is a sintered stainless steel having an inner diameter of 184 mm and a thickness of 3 mm and a filtration accuracy of 100 mm. Rotor (1)
The number of revolutions is adjusted arbitrarily by an inverter. The rotation speed during the experiment was measured with a stroboscope. The exhaust gas used was the exhaust gas of a diesel engine described below, and the flow rate was measured by an orifice flow meter.

(B) Exhaust gas generator Diesel engine (Yanmar Diesel Co., Ltd.
Exhaust gas was directly used when operating under a no-load condition with a displacement of 1429 ml, a compression ratio of 18.0, and a direct injection type. Note NOx concentration of the exhaust gas was measured by before and after Yanagimoto Seisakusho NO _X meter ECL-77A passing through the fluidized catalyst bed.

[Example 1] The NO concentration discharged from the exhaust gas generator was about 470 to 530 ppm, and the oxygen concentration was about 10
% And suspended particles, 200 g of the catalyst A was charged into the rotor of the centrifugal fluidized bed catalytic cracker, and the gas flow rate and the rotor speed were set to the values shown in Table 3 at a fluidized bed temperature of 420 ° C. It was set and the NO conversion was measured. Table 3 shows the results.

Example 2 The same exhaust gas as in Example 1 was used, 300 g of the catalyst A in the rotor was filled, the fluidized bed temperature was set to 380 ° C., and the gas flow rate and the rotor speed were each set in the same manner as in Example 1. The values were set to the values shown in Table 3 and the NO conversion was measured. Table 3 shows the results.

[0043]

[Table 3]

[Comparative Example 1] 200 g of the catalyst B was charged into a cylindrical normal-pressure fixed-bed flow-type reactor, and a contact reaction was carried out at 420 ° C. using the same exhaust gas as in Example 1, and the NO _x conversion was as shown in Table 4. Table 4 shows the results measured for each of the described space velocities (WHSV).

[0045]

[Table 4]

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an example of a centrifugal fluidized bed catalytic cracking device used in the method of the present invention.

FIG. 2 is a diagram showing a relationship between a gas linear velocity and a pressure loss in the centrifugal fluidized bed catalytic cracking device of the present invention.

FIG. 3 is a diagram showing a relationship between exhaust gas space velocity (WHSV) and NO conversion in the centrifugal fluidized bed catalytic cracking device of the present invention.

FIG. 4 shows N in the catalytic cracking apparatus for centrifugal fluidized bed of the present invention.
FIG. 3 is a diagram showing a relationship among an O conversion, a reaction temperature, and an exhaust gas linear velocity.

[Explanation of symbols]

1 Rotor 2 distributors terpolymers 3 wind box 4 heater 5 manometer 6 orifices 7 flow rate control valve 8 roots blower 9 diesel engine 10 NO _x meter

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Atsushi Tsutsumi Misato Sky Mansion 1009 1-2-4 Misato, Misato-shi, Saitama (56) References JP-A-55-86529 (JP, A) JP-A-53 JP-A-44473 (JP, A) JP-A-4-322725 (JP, A) JP-A-4-322724 (JP, A) JP-A-4-118030 (JP, A) JP-A-60-125250 (JP, A) ) Japanese Utility Model Application 58-108132 (JP, U) Eiichi Kikuchi. et. al, "Selective Reduction of NO with Propylene on Fe-silicate Catalysts", CHEMISTRY LETTE RS, 1991, p. 1063-1066 (58) Field surveyed (Int.Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/86-53/94 F01N 3/00

Claims (2)

(57) [Claims] The present invention relates to a metal-supported zeolite fine particle and silica zeolite.
Granulation and baking of a composition containing
Therefore, the obtained volume-based median diameter is 20 to 500 μ
m catalytic cracking catalyst particles in a centrifugal fluidized bed using a fluidized medium.
Exhaust gas from a diesel engine containing carbon particles.
A method for treating exhaust gas of a diesel engine, comprising decomposing nitrogen oxides in exhaust gas while contacting the fluid medium with carbon particles . 2. The catalytic cracking catalyst particles have the following formula : F = (W ₀ −W ₁ ) × 100 / W ₀ where W ₀ is the initial amount of catalyst particles (g) in a centrifugal wear test. W ₁ is under a centrifugal force of 100 G and the gas streamline velocity is 0.2
This is the weight (g) of the residual catalyst when treated for 3 hours in the range of ~ 0.3 m / s. Wear rate (F) defined by
The treatment method according to claim 1, wherein the particles are spherical particles of not more than%.