JPH0938467A - Purifying device for exhaust gas and purifying method of exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reducing and purifying device of NOx and a purifying method in which a hydrocarbon component as a reducing agent can be increased without requiring a complicated system, reforming of a large capacity or a decomposition catalyst. SOLUTION: In this purifying device for exhaust gas, exhaust gas is purified by a reduction catalyst device for nitrogen oxides which uses hydrocarbons as a reducing agent. The device is equipped with a device consisting of a hydrocarbon injecting nozzle and a catalyst layer for decomposition of hydrocarbons in order to add hydrocarbons on the upstream side of the flow passage of the exhaust gas in the reduction catalyst device for nitrogen oxides. The hydrocarbons supplied from the hydrocarbon injecting nozzle are controlled to be as a hydrocarbon flow having a larger content of lower hydrocarbons than in the hydrocarbons supplied from the catalyst layer for decomposition of hydrocarbons, and then the hydrocarbon flow is added to the exhaust gas flow. If necessary, this device or method is provided with a catalyst for decomposition of HC on the downstream side of the NOx reducing catalyst, so that hydrocarbons, CO, and SOF in exhaust gas can also be oxidized and removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for purifying exhaust gas from vehicles such as automobiles, construction machinery and ships, generators, etc. The present invention relates to a purification device for nitrogen oxides (NOx) in the exhaust gas and a purification method for these.

[0002]

2. Description of the Related Art A diesel engine operates at a lean air-fuel ratio, consumes less fossil fuel per work than a conventional gasoline engine, and can suppress the emission of carbon dioxide (CO ₂ ) which is a global warming substance. There are advantages. However, the exhaust gas contains oxygen in excess of the stoichiometric amount required to completely oxidize reducing components such as hydrocarbons (hereinafter sometimes referred to as HC) and carbon monoxide (CO). Removal of NOx in exhaust gas has been difficult with conventional techniques.

In recent years, a zeolite catalyst, a metallosilicate catalyst or an aluminophosphate catalyst, in which exhaust gas having such a lean air-fuel ratio is ion-exchanged with a transition metal such as Cu or Co (US Pat. No. 4,297,328, Japanese Patent Laid-Open No. 63-328328).
No. 100919, JP-A-3-127628, JP-A-3-229620, JP-A-1-112488), or a catalyst in which a noble metal such as Pt, Pd, Rh is supported on a porous metal oxide such as zeolite or alumina. (JP-A-3-
No. 221143 and JP-A-3-221144), various HC selective reduction methods have been proposed in which NOx is selectively reduced and removed by HC in exhaust gas. However, all of these catalysts have low selectivity for NOx reduction of HC,
In particular, the amount of methane-converted hydrocarbons that remains like diesel engine exhaust gas (hereinafter also referred to as THC).
When the molar ratio of NOx to NOx was 1 or less, the removal rate of NOx was insufficient. Therefore, there has been proposed a method of increasing the NOx removal rate by adding a slight amount of HC to the exhaust gas before bringing the diesel engine exhaust gas into contact with the NOx reduction catalyst (for example, JP-A-5-44444).

However, kerosene, light oil, and heavy oil are usually used as fuels for diesel engines. Such high boiling point hydrocarbons are not always effective as NOx reducing agents, and NOx reduction selectivity is low. for,
Excessive hydrocarbon is required, which leads to deterioration of fuel efficiency and an increase in suspended particulate matter (hereinafter sometimes referred to as PM). On the other hand, the addition of a C _{2 to} C ₅ hydrocarbon, especially olefins, suitable as a reducing agent for NOx to the exhaust gas means that a storage container for these reducing agents is provided separately from the fuel storage container for the diesel engine. Needed and not practical.

Then, the diesel engine fuel is reformed or decomposed into hydrocarbons suitable for NOx reduction, and NOx is converted.
Various methods of contacting with a reducing catalyst have been devised. (1) In JP-A-5-59933, a reactor housing provided with a reaction tube filled with a hydrocarbon reforming catalyst and a heater for heating the hydrocarbon is used, and the hydrocarbon is fed to the reforming reaction tube by a pump. , An exhaust gas purification device that adds reformed hydrocarbons to exhaust gas from an injection nozzle,
(2) JP-A-5-222923 and JP-A-6-1088
In No. 25, a device for preliminarily reforming a liquid fuel of an engine with a reforming catalyst and separating or storing the reformed hydrocarbon, and then injecting and adding the reformed hydrocarbon from an injection nozzle via a pressure pump,
(3) Japanese Examined Patent Publication No. 6-61427 discloses that a fuel hydrocarbon is introduced into an exhaust gas from a fuel introducing part to form a mixture of the exhaust gas and the hydrocarbon, and the mixture is composed of a hydrocarbon decomposition catalyst.
There has been disclosed a method of bringing the fuel into contact with the catalyst layer to reform the fuel mainly into C _{2 to} C ₄ unsaturated hydrocarbon, and then bringing it into contact with the second catalyst layer composed of the NOx reduction catalyst.

[0006]

As described above, all of the conventional NOx reduction methods by adding hydrocarbons have problems. Generally, in the catalytic cracking reaction of hydrocarbons used in the above (1) and (2), gas is generated and the volume is significantly expanded with the molar expansion. It was not practical to control the gas-solid reaction in a non-open system and temporarily store and inject the produced gaseous hydrocarbons, which complicates the system. Further, in the above (3), since the fuel hydrocarbons are diluted with a large excess of exhaust gas in the first catalyst layer, a large-capacity reforming catalyst is required to reform or decompose the hydrocarbons. Depending on the type of catalyst required or excess oxygen in the exhaust gas, a considerable proportion of the hydrocarbons is completely oxidized to CO ₂ and H ₂ O and NO
It was not an efficient method for supplying hydrocarbons for x reduction. INDUSTRIAL APPLICABILITY The present invention does not require a complicated system or a large-capacity reforming or cracking catalyst when adding higher hydrocarbons as a reducing agent to exhaust gas in a NOx reduction method in various exhaust gases, particularly exhaust gas of a diesel engine. To
An object of the present invention is to provide an exhaust gas purifying apparatus and method for reducing NOx by using a method of efficiently increasing a hydrocarbon component effective for improving the NOx removal rate by a simple method.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventor has found that hydrocarbons are converted into NOx.
A hydrocarbon decomposition catalyst is provided in or near the exhaust gas flow channel when added to the exhaust gas as a reducing agent for the hydrocarbon injection nozzle by closing one end face of the hydrocarbon decomposition catalyst layer to the exhaust gas flow channel. Are placed facing each other, and the other end face is opened to the exhaust gas flow path, and hydrocarbons discharged from the injection port are catalytically decomposed to cause molar expansion of hydrocarbons and mixed with engine exhaust gas, and then nitrogen oxides are mixed. They have found that the above problems can be solved by bringing them into contact with a reducing catalyst, and have completed the present invention.

That is, according to the present invention, in an exhaust gas purifying apparatus for purifying exhaust gas by a nitrogen oxide reduction catalyst device using hydrocarbon as a reducing agent, carbonization is performed on the upstream side of the exhaust gas passage of the nitrogen oxide reduction catalyst device. A device for adding hydrocarbons consisting of a hydrogen injection nozzle and a hydrocarbon decomposition catalyst layer is installed, and hydrocarbons supplied from the hydrocarbon injection nozzle are converted into hydrocarbons lower than the supplied hydrocarbons by the hydrocarbon decomposition catalyst layer. The present invention relates to an exhaust gas purifying apparatus, characterized in that a hydrocarbon stream having an increased content of is added to the exhaust gas stream, and an exhaust gas purifying method using the apparatus. More specifically, the present invention provides an exhaust gas purifying apparatus having a device for adding a hydrocarbon to the upstream side of the exhaust gas flow passage, provided with a nitrogen oxide reduction catalyst device in the exhaust gas flow passage of a diesel engine, The apparatus for adding the hydrocarbon comprises a hydrocarbon injection nozzle and a hydrocarbon decomposition catalyst layer, one end surface of the hydrocarbon decomposition catalyst layer is arranged facing the hydrocarbon injection nozzle, and the other end surface is an exhaust gas passage. The present invention relates to a diesel engine exhaust gas purifying apparatus, which is open to the public, and an exhaust gas purifying method using the apparatus. More specifically, the present invention provides a nitrogen oxide reduction catalyst in the exhaust gas of a diesel engine, and the C oxide in the engine exhaust gas is provided upstream of the catalyst.
When O and hydrocarbons are insufficient for the reduction of nitrogen oxides, when adding hydrocarbons to the engine exhaust gas from the injection nozzle, the hydrocarbons discharged from the injection nozzle may be mixed with the hydrocarbon decomposition catalyst before mixing with the engine exhaust gas. TECHNICAL FIELD The present invention relates to an exhaust gas purifying apparatus for bringing a hydrocarbon that has been brought into contact with and catalytically cracked and has been subjected to molar expansion to be mixed with an engine exhaust gas, and then brought into contact with a nitrogen oxide reduction catalyst, and an exhaust gas purifying method using the apparatus. Further, the present invention relates to an exhaust gas purifying apparatus, characterized in that the exhaust gas discharged from the nitrogen oxide reduction catalyst layer is further contacted with an oxidation catalyst on the downstream side thereof, and an exhaust gas purifying method using the apparatus.

In the present invention, unlike the prior art, higher hydrocarbons are not previously catalytically cracked and / or catalytically reformed at a place different from the exhaust gas passage and then injected from the injection nozzle into the exhaust passage. According to the method of the present invention, (1) in a state where there is substantially no flow of exhaust gas in the hydrocarbon decomposition catalyst layer,
(2) Injecting higher hydrocarbons from the injection nozzle toward the hydrocarbon decomposition catalyst, and (3) mixing the hydrocarbons having an increased content of decomposed lower hydrocarbons directly with the exhaust gas along with the molar expansion. Clearly different from the prior art. The purification apparatus and the purification method of the present invention have a simpler structure and higher operation reliability than those of the prior art. In particular, when the amount of added hydrocarbon is controlled depending on the THC / NOx molar ratio in the engine exhaust gas or the NOx concentration, for example,
THC / NO in exhaust gas during diesel engine operation
If the x molar ratio is 1 or more or the NOx concentration is less than 100 ppm, no hydrocarbon is added and the THC / NOx molar ratio is 1
When performing control such as adding hydrocarbons when the concentration is less than or when the NOx concentration is 100 ppm or more,
The response of the change in the amount of hydrocarbon added is quick, and as a result, a high NOx removal rate can be obtained by the NOx reduction catalyst in the latter stage.

Generally, among petroleum fractions, the fraction having a boiling point of about 30 ° C to 216 ° C is gasoline and 160 ° C to 3 ° C.
The fraction at 00 ° C is called kerosene, the fraction at 220 ° C to 350 ° C is called light oil, and the fraction at 317 ° C or higher is called heavy oil. Today, kerosene, light oil, and heavy fuel oil A (corresponding to heavy oil having a relatively low boiling point, low flash point, low pour point, and JIS class 1 heavy oil) are used as fuels for diesel engines. NOx is usually 30 in the exhaust gas of diesel engines.
0 to 1000 ppm, CO 100 to 400 ppm, hydrocarbons (as THC) 50 to 300 ppm, O ₂ 6 to 14%, H ₂ O 6 to 12%, and other CO ₂ , particulates and nitrogen are included. The composition of these components changes depending on the fuel used and the operating condition (rotation speed and load) of the engine. Generally, except when the engine is started or when the engine is lightly loaded, the molar ratio of CO and hydrocarbons in the exhaust gas, which should be NOx reducing agents, to NOx is as low as 1 or less, and only such hydrocarbons in the exhaust gas are used. It was not possible to obtain a high NOx removal rate. Therefore, when it is determined that the concentration of the reducing agent such as hydrocarbon is insufficient as compared with the NOx concentration, the hydrocarbon such as diesel fuel is injected and added to the flow path of the exhaust gas, and THC / NOx of the exhaust gas contacting the NOx reduction catalyst is added. It was necessary to increase the molar ratio. However, adding a large amount of hydrocarbons unnecessarily leads to a deterioration in the fuel economy of the entire system and also tends to increase the particulates at the outlet of the NOx reduction catalyst, which is not preferable, and depends on the state of the exhaust gas. The supply of reducing agent was required. In the present invention, preferably THC
/ NOx molar ratio of 1 to 6 equivalent hydrocarbon, if necessary,
It can be fed to the exhaust gas stream.

As a device for supplying higher hydrocarbons to the hydrocarbon cracking catalyst layer, a device known as a fuel injection nozzle for diesel engines can be used. The hydrocarbon catalytic cracking catalyst used in the present invention is not limited as long as it is a catalyst capable of catalytically cracking a higher hydrocarbon such as a diesel engine fuel such as light oil or kerosene into a lower hydrocarbon having a short carbon chain. That is, the hydrocarbon catalytic cracking catalyst may be any one that decomposes hydrocarbons constituting fuel oil and increases paraffin components, naphthene components, aromatics components or olefin components having a smaller number of carbon atoms. However, in order to obtain a high NOx conversion rate by selectively reducing NOx with hydrocarbons in an oxygen-excess atmosphere such as exhaust gas of diesel engine, in general, lower hydrocarbons having about C ₂ to C ₉ as hydrocarbon species, especially It is known that olefins are good. Therefore, the boiling point of diesel fuel oil is mainly 21
Fractions above 6 ° C (boiling point of dodecane C ₁₂ H ₂₄ ) are decomposed and the total fraction of gas components above C ₂ and gasoline fractions below boiling point 216 ° C is increased from that of hydrocarbons before catalytic cracking. Hydrocarbon cracking catalysts, especially C ₂ to C ₅
The hydrocarbon cracking catalyst that gives a large amount of the olefin component of is preferable.

As such catalysts, silica, silica-alumina, aluminosilicate zeolite, and porous metal oxides such as aluminophosphate and silicoaluminophosphate, which have been conventionally used as a main component of a fluid catalytic cracking (FCC) catalyst, are used. Used. Among them, Y-zeolite, ultra-stabilized Y-zeolite and high silica zeolite such as ZSM-5 and zeolite beta are particularly preferable, and particularly preferable are those which produce a large amount of a low boiling point olefin fraction of C _{2 to} C _5. It is a stabilized H-type Y-zeolite. As the ultra-stabilized Y-zeolite, the Y-zeolite obtained by hydrothermal synthesis is dealuminated by a known method, for example, dealumination under hydrothermal conditions of 500 ° C. to 800 ° C. or tetrachlorosilane treatment (R. A. Corbet
t, oil Gas J .; , 84 (41), 55 (19
86)) is manufactured. The hydrocarbon decomposition catalyst may be used in the form of powder, or may be preliminarily molded into an appropriate shape such as spheres, rings, pellets or granules. Alternatively, the surface of a refractory support substrate having a certain shape may be coated and used. The refractory support substrate has a cross section perpendicular to the flow direction of the injected hydrocarbon of 300 to 600 cells / square inch (cpsi).
Particularly preferred are cordierite or stainless monolith support substrates having a cell density of. The coating amount of the catalyst is preferably 50 to 250 g per 1 L of the supporting substrate.

In the present invention, a device for adding hydrocarbons is provided on or near the exhaust gas passage extending from the exhaust manifold of the engine to the NOx reduction catalyst, and one end face of the hydrocarbon decomposition catalyst layer is provided with the exhaust gas passage. It is arranged so as to face the hydrocarbon injection nozzle in a closed state, and the other end surface is opened to the exhaust gas flow path, and the hydrocarbon injected from the injection nozzle is catalytically decomposed and the It is mixed with engine exhaust gas by expansion. Conversely, if the hydrocarbon cracking catalyst layer is provided in such a position and manner that at least most of the injected hydrocarbons do not substantially mix with the engine exhaust gas without passing through this hydrocarbon cracking catalyst layer. Good. As for the method of combining the hydrocarbon stream emitted from the device for adding hydrocarbons with the exhaust gas, in addition to the method shown in FIG. 1, any method may be used as long as a hydrocarbon stream as a reducing agent of the exhaust gas stream is supplied. It may be of any type and is not particularly limited.

The hydrocarbon catalytic cracking catalyst layer of the present invention is provided in the exhaust gas flow passage or in the vicinity of the exhaust gas flow passage, and heat is transferred from the exhaust gas flowing through the exhaust flow passage to 200 ° C. to 700 ° C. during engine operation. Heated to ℃. The temperature of the hydrocarbon decomposition catalyst layer may be the same as the temperature of the exhaust pipe of the engine during operation, and is not particularly limited, but is preferably in the range of 300 ° C to 600 ° C. When a diesel engine fuel such as light oil or kerosene is injected into the catalytic cracking catalyst layer at such a temperature, hydrocarbon molecules having a large C number such as C _{12 to} C ₃₀ in the fuel undergo catalytic cracking and undergo hydrogen and C. It is decomposed into hydrocarbons of about _{1 to} C ₁₁ . In the hydrocarbon decomposition product, the optimum hydrocarbon decomposition catalyst layer temperature is 400 ° C. to 600 ° C. for increasing the yield of C _{2 to} C ₅ olefins that can increase the NOx removal rate of the NOx reduction catalyst in the subsequent stage. ℃,
Particularly preferably, it is 450 ° C to 550 ° C.

Since the gaseous hydrocarbons generated by the catalytic cracking of hydrocarbons are immediately mixed with the exhaust gas, there is no difficulty in controlling the catalytic cracking reaction in a closed system as in the conventional method. Further, the heat of the exhaust gas in the exhaust passage can be used as it is as the reaction heat necessary for the catalytic cracking of hydrocarbons, and it is not always necessary to provide a special heater. However, in order to control the conversion rate of the catalytic cracking reaction of hydrocarbons and the selectivity to olefins, a heater may be provided around the hydrocarbon cracking catalyst layer, if necessary. The volume of the hydrocarbon cracking catalyst is such that the contact time of the injected hydrocarbon with the catalyst is 5 to 5.
It is preferable that the amount of catalyst is 500 g · sec / g hydrocarbon. However, in the case of a monolithic coated catalyst, the contact time shall be expressed as the net weight of the catalyst coated on the monolithic structure. The difference of the method of the present invention from the conventional method (3) is that the catalytic cracking (reforming) reaction of hydrocarbons is carried out before the hydrocarbons are mixed with the exhaust gas.

The catalytic cracking catalyst layer faces the hydrocarbon injection nozzle with one end face closed to the exhaust gas passage,
The other end face is installed in a state of being opened to the exhaust flow path.
When no hydrocarbon is added to the exhaust gas, the hydrocarbon injection nozzle is closed and there is no substantial flow of exhaust gas in the catalytic cracking catalyst layer. The NOx concentration in the engine exhaust gas becomes relatively higher than the exhaust gas hydrocarbon concentration, and NOx
When it is determined that the addition of hydrocarbons is necessary for the reduction, the hydrocarbon injection nozzle opens and the hydrocarbons are injected into the exhaust passage. Thus, the device for adding hydrocarbons can be supplied with hydrocarbons as necessary. For example, the concentration of nitrogen oxides in the exhaust gas is measured, and the hydrocarbons are supplied according to the measured values. You can also Generally kerosene,
Aromatic components of hydrocarbons in light oil and heavy oil A are 20-40
%, Naphthene component 20 to 40%, paraffin component 20
~ 40%, olefin component is 10% or less, NOx
The olefin component and paraffin component having C ₁₁ or less effective for the selective reduction of is extremely small. By catalytically cracking this kerosene or light oil, the fraction of C ₁₁ or less olefin or paraffin can be increased to at least 30% or more, preferably 50% or more, and more preferably 60% or more. Among the fractions having C ₁₁ or less, C ₁ methane, C ₆ benzene, and C ₁₀ naphthalene are relatively inactive in NOx reduction, so that it is preferable to suppress the production of these components. The ratio of hydrocarbons effective for NOx reduction can be increased to 70% to 80% by devising reaction conditions and decomposition catalysts that suppress excessive decomposition and hydrogen transfer reaction that easily generate methane, benzene, and naphthalene. be able to. Further, by using a cracking catalyst having high olefin selectivity, the proportion of C _{2 to} C ₅ olefins in cracked hydrocarbon can be increased from about 30% to about 50%.

The NOx reduction catalyst used in the present invention is a so-called lean NOx reduction catalyst capable of selectively reducing NOx by CO and hydrocarbons in the presence of excess oxygen to decompose it into N ₂ and H ₂ O. Then, it is not particularly limited. However, the effective hydrocarbon species for NOx reduction is NO
It also depends on the type of x reduction catalyst. A large amount of paraffin is produced in the case of a NOx reduction catalyst which is effective for paraffin hydrocarbons such as Cu / ZSM-5 catalyst (US Pat. No. 4,297,328) and Ag / Al ₂ O ₃ catalyst (JP-A-4-281844). A combination of cracking reaction conditions and cracking catalysts may be used. Ir / SiC catalyst (JP-A-6-311)
No. 73), a NOx reduction catalyst showing a remarkably high activity for olefinic hydrocarbons is preferably selected as a combination of a cracking reaction condition and a cracking catalyst that produce a large amount of olefinic hydrocarbon species. Each of these NOx reduction catalysts is prepared by the method described in the above literature. N
The volume of the Ox reduction catalyst is not particularly limited, but the space velocity SV is 7,000 to 15 with respect to the exhaust gas to which hydrocarbon is added.
50,000 / hr, preferably 10,000 to 100,0
00 / hr. However, in the case of the SV of the monolithic structure coated catalyst, the volume of the monolithic structure is used (the same applies hereinafter). The inlet gas temperature of the NOx reduction catalyst is not particularly limited, but is preferably set to a temperature range where the NOx reduction catalyst has the highest denitration rate. In general, the most frequent exhaust gas temperature changes depending on the distance of the exhaust gas flow path from the engine manifold, so that it is possible to set a preferable temperature range by optimizing the mounting position of the converter filled with the NOx reduction catalyst. The preferable temperature range is 200 ° C. to 300 ° C. for Pt / zeolite type catalyst, 350 ° C. to 450 ° C. for Cu / zeolite type catalyst, and 4 ° C. for Ir / Si type catalyst.
The temperature is 00 ° C to 500 ° C.

In the present invention, since the selectivity of hydrocarbons for NOx reduction is enhanced, the amount of hydrocarbons required to obtain a constant NOx removal rate is 1/2 to 1 of that of the conventional method.
Significantly less than / 3. The small amount of added hydrocarbons also has the effect of reducing the residual hydrocarbons and CO concentrations in the outlet gas of the NOx reduction catalyst and the soluble organic compounds (SOF) in the particulates. The present invention further provides N
Provided are an exhaust gas purifying device in which an oxidation catalyst for oxidizing hydrocarbons is installed behind an Ox reduction catalyst, and an exhaust gas purifying method using the device. As the oxidation catalyst, various kinds of catalysts that have been conventionally known as oxidation catalysts for diesel exhaust gas can be used. Among them, a catalyst that can oxidize and remove gas-phase hydrocarbons and CO and SOF in particulates and does not generate sulfate is preferable. For example, a catalyst in which at least one of Pt, Pd, and Rh is supported on a porous carrier such as alumina, silica, zirconia, titania, aluminosilicate zeolite (S
AE. , 932720 (1993)), Cu, Fe,
At least one of Ni, Ce, Mg, and Ca is alumina,
A catalyst supported on titania or the like (JP-A-6-6888).
A catalyst such as 6) can be used. The oxidation catalysts are prepared by the methods described in the above literature, such as ion exchange and impregnation. Like the NOx reduction catalyst, these are preferably used by coating them on a support substrate having an integral structure made of cordierite or metal.

By simply adding the hydrocarbon of the fuel to the exhaust system, the hydrocarbon having a high boiling point is partially oxidized and decomposed by the NOx reduction catalyst. Even if an oxidation catalyst is installed behind the NOx reduction catalyst, high boiling point hydrocarbons are less likely to undergo oxidative decomposition. When the added hydrocarbon is brought into contact with the hydrocarbon decomposition catalyst and added to the exhaust gas, the molecular weight of the hydrocarbon becomes small and the NOx reduction catalyst alone improves the removal rate of hydrocarbons considerably.
When the oxidation catalyst is installed behind the reduction catalyst, the removal rate of hydrocarbons is further improved. The volume of the oxidation catalyst is not limited, but N
SV 10,000 to exhaust gas emitted from the Ox reduction catalyst
It is preferably set to 1500000 / hr. The temperature of the gas at the entrance of the oxidation catalyst is not particularly limited, but is 200 ° C to 4 ° C.
00 ° C is preferred.

[0020]

EXAMPLES Next, examples of the present invention will be described, but the present invention is not limited to these examples.

Example 1 (gas oil addition / hydrocarbon decomposition catalyst) → (NOx reduction catalyst) (1) Preparation of catalyst 400 cpsi cordierite honeycomb with a volume of 500 mL and 3 L (respectively referred to as honeycomb A and honeycomb B)
Prepared. H-type USY-zeolite (lattice constant 2.
430 nm) 100 parts by weight of silica sol (solid content 20
%) 20 parts by weight and 100 parts by weight of deionized water are wet pulverized by a ball mill to immerse the honeycomb A in a slurry, and excess slurry is removed by air blow, and after drying, 500
USY-zeolite coated honeycomb A after firing at 30 ° C for 30 minutes
A hydrocarbon decomposition catalyst composed of (catalyst honeycomb A) was obtained.
Further, an aqueous solution of chloroiridate is added to the SiC slurry, heated and dried up, and then baked (see JP-A-6-3117).
No. 3, Example 1) Then, 100 parts by weight of an Ir-supported SiC powder catalyst prepared by hydrogen reduction at 700 ° C. was mixed with a mixture of 20 parts by weight of alumina sol (solid content 20%) and 100 parts by weight of deionized water in a ball mill. Honeycomb B is immersed in the slurry obtained by wet pulverization, the excess slurry is removed by air blow, dried and then baked at 500 ° C. for 30 minutes to make Ir / Si.
A NOx reduction catalyst composed of C-coated honeycomb B (catalyst honeycomb B) was obtained. (2) Preparation of device As shown in FIG. 1, a side pipe having one end opened is attached to the exhaust pipe at a position 1 m downstream of the manifold of the exhaust pipe of a naturally aspirated diesel engine with an engine displacement of 8 L, and the other end is attached. A fuel injection nozzle capable of injecting fuel from the fuel tank to the exhaust pipe side pipe was attached to the section. A hydrocarbon decomposition catalyst (catalyst honeycomb A) was filled in the central portion of the side tube so that the channels of the honeycomb were parallel to the injected hydrocarbon flow and no blow-through of the hydrocarbon flow occurred. Furthermore, in the engine exhaust gas flow path, 50 from the position of the side pipe.
A catalytic converter filled with a NOx reduction catalyst (catalyst honeycomb B) was attached to the rear of the cm to prepare the purification device shown in FIG. (3) Measurement of Exhaust Gas NOx, hydrocarbons, and CO in exhaust gas before and after the NOx reduction catalyst were analyzed by an automobile exhaust gas analyzer. When low-sulfur gas oil (S = 0.05%) is used as fuel and the engine is operated in a steady state at a load of 90%, when light oil is not added from the hydrocarbon injection nozzle (case 1), the NOx reduction catalyst NOx concentration at the inlet is 512ppm, NO at the outlet
The x concentration was 475 ppm, and the NOx conversion rate was 7%. When the same diesel fuel as the fuel, which is equivalent to 1500 ppm of C _{1 is} injected from the hydrocarbon injection nozzle (case 2),
The NOx concentration at the outlet of the NOx reduction catalyst is 177 ppm,
The denitration rate improved to 65%. At this time, the hydrocarbon concentration at the inlet and the outlet of the NOx reduction catalyst was 1610 p each.
The hydrocarbon purification rate was 78% at 352 ppm of pm. At this time, the hydrocarbon decomposition catalyst bed temperature was 490 ° C.
The gas temperature at the entrance of the Ox reduction catalyst was 450 ° C.

Example 2 (gas oil addition / hydrocarbon decomposition catalyst) → (NOx reduction catalyst) → (oxidation catalyst) (1) Preparation of oxidation catalyst H-type ZSM-5 of SiO ₂ / Al ₂ O ₃ = 60 was added to tetraammine. After ion exchange with platinum (II) ions, washing, drying, and calcination at 500 ° C., 0.5% Pt / ZSM-5 catalyst was obtained, and this was coated on a 400 cpsi 3L cordierite honeycomb at 120 g / L. (2) Preparation of device The converter filled with the catalyst prepared in (1) was attached to the downstream side of the converter of the NOx reduction catalyst of Example 1 to prepare the purification device shown in FIG. (3) Measurement of Exhaust Gas As in Case 2 of Example 1, the engine was operated at 90% load, 1500 ppm of light oil was injected from the hydrocarbon injection nozzle, and added to the exhaust gas via the hydrocarbon decomposition catalyst (Case 3). When the exhaust gas composition at the inlet of the NOx decomposition catalyst and the outlet of the subsequent oxidation catalyst were analyzed in the same manner as in Example 1, the denitration rate was 67% and the hydrocarbon purification rate was 90%.

Comparative Example 1 (Addition of light oil) → (NOx reduction catalyst) In the same manner as in Example 1 except that the side tube is not filled with the hydrocarbon decomposition catalyst, the engine is operated in a normal operation. The NOx conversion rate before and after the NOx reduction catalyst was measured. First, when light oil was not injected, the NOx conversion was 7% as in Case 1 of Example 1, but the light oil was converted to C ₁ and the NOx conversion rate was 150%.
Even with 0 ppm injection (case 4), the NOx concentration at the NOx reduction catalyst outlet is 353 ppm and the hydrocarbon concentration is 515.
In ppm, denitration rate is 31%, hydrocarbon purification rate is 68%
Met. The following points were clarified by comparing Cases 1, 2 and 4 of Example 1 and Comparative Example 1. (1) When the hydrocarbon concentration in the exhaust gas is lower than the NOx concentration and the THC / NOx ratio is 0.3 or less, the NOx conversion rate is low only by bringing the exhaust gas into contact with the NOx reduction catalyst. (2) When hydrocarbons are added to the exhaust gas before the NOx reduction catalyst to increase the THC / NOx ratio to 1 or more, the conversion rate of NOx before and after the NOx reduction catalyst is improved as compared with the case where no hydrocarbon is added, but Not enough. (3) When the hydrocarbon is injected from the injection nozzle toward the hydrocarbon decomposition catalyst, brought into contact with the hydrocarbon decomposition catalyst and mixed with the exhaust gas together with the molar expansion, and then brought into contact with the NOx reduction catalyst, it does not come into contact with the hydrocarbon decomposition catalyst. In comparison with the case where hydrocarbon is added, the NOx conversion rate is significantly improved. Further, comparing the hydrocarbon purification rates of Cases 2 and 3 of Examples 1 and 2 and Case 4 of the comparative example, the hydrocarbon purification rate of 68% (by NOx reduction catalyst) without the hydrocarbon decomposition catalyst was found to be the hydrocarbon decomposition catalyst. It was found that the value was improved to 78% with the addition of oxidization, and to 90% with the addition of the oxidation catalyst.

Comparative Example 2 (Addition of light oil) → (Hydrocarbon decomposition catalyst) → (NOx reduction catalyst) Two 3 L 400 cpsi cordierite honeycombs were prepared, and the first one was coated with H-type USY zeolite (catalyst honeycomb). C), and the second is Ir /
A SiC catalyst was coated (catalyst honeycomb D). The hydrocarbon decomposition catalyst of the side pipe of the diesel engine exhaust system of Example 1 was removed, and the catalyst honeycomb C was first moved backward from the position of this side pipe.
Further, a catalytic converter filled with the catalyst honeycomb D was attached further downstream. First, as in Case 1 of Example 1, the diesel engine was operated at a load of 90% and the exhaust gas composition before and after the catalyst honeycomb D was analyzed without addition of hydrocarbons (Case 5). The NOx concentration at the inlet was 490 p.
pm, the NOx concentration at the outlet was 455 ppm, and the NOx conversion rate was 7%. Then, light oil was measured from the injection nozzle of the side pipe while adding THC / NOx ratio of 1500 ppm equivalent (case 6). As a result, the NOx concentration at the inlet of the catalyst honeycomb D was 484 ppm, and the NOx concentration at the outlet was 330.
The denitrification rate was 32% in ppm. Case 2 of Example 1
In comparison with Case 6 of Comparative Example 2, when light oil is added and a hydrocarbon cracking catalyst is used, as in Case 6, the light oil is mixed with the exhaust gas body and then comes into contact with the hydrocarbon cracking catalyst. The denitrification rate hardly improves, but when light oil comes into contact with the hydrocarbon cracking catalyst before mixing with the exhaust gas main body as in Case 2, the hydrocarbon cracking reaction proceeds with high efficiency and the high NOx removal rate is high. It became clear that it was obtained.

Comparative Example 3 (Addition of light oil) → (“hydrocarbon cracking catalyst”) → (NOx reduction catalyst) Two 400 cpsi honeycombs were prepared, and the first one was an example of Japanese Patent Publication No. 6-61427 (preparation of catalyst). ) Fe / Al ₂ O ₃ powder prepared according to [Catalyst (A)] is coated to form a “hydrocarbon reforming catalyst”. Cu / ZSM-5 prepared according to (B)] was coated to obtain a NOx reduction catalyst. Downstream of exhaust system manifold of diesel engine 1.
A hydrocarbon reforming catalyst was installed at a position of 5 m, and a NOx reduction catalyst was installed further downstream thereof. Similar to the evaluation example of Example 1, the engine load was 90% and the THC / NOx1 was measured from the side pipe.
When light oil equivalent to 500 ppm was added by injection, the NOx concentration at the inlet of the hydrocarbon decomposition catalyst was 490 ppm and the hydrocarbon concentration was 1650 ppm, whereas the NOx concentration at the outlet of the NOx reduction catalyst was 353 ppm and the hydrocarbon concentration was 429 pp.
In m, the denitration rate was 28% and the hydrocarbon purification rate was 74%. That is, after adding hydrocarbons to the exhaust gas, Fe /
It has been found that when the catalyst is brought into contact with the Al ₂ O ₃ catalyst, the hydrocarbon is oxidized more than the hydrocarbon is reformed and does not contribute to the improvement of the NOx conversion rate.

Reference Example 1 Hydrocarbon Decomposition Reaction From 500 mL of the hydrocarbon decomposition catalyst honeycomb of Example 1, a core having a diameter of 3/4 inch (19 mm) was cored and cut into a length of 30 mm. The catalyst core was filled in a stainless steel reaction tube having an inner diameter of 20 mm, which was manufactured according to ASTM-Standard D-3907 for a micro reaction test device for fluid catalytic cracking reaction catalyst, and the catalyst bed temperature was maintained at 480 ° C. by a heater. 1.5g of low sulfur gas oil to the above hydrocarbon cracking catalyst
Was supplied at a constant rate for 60 seconds, and the gas components produced during this period were collected in a collection bottle and analyzed by gas analyzer E-gas chromatography, and the distillate oil was gas mass, and each component was identified and quantified to determine the composition. . The results are shown in Tables 1 and 2.

[0027]

[Table 1]

[0028]

[Table 2]

From these results, the hydrocarbon cracking catalyst decomposes the light oil mainly into the C _{2 to} C ₄ gaseous hydrocarbon fraction and the gasoline fraction, and further, the paraffin and naphthene contents in the light oil are reduced and the olefin is reduced. It turns out that the minutes are increasing. Such a hydrocarbon rich in olefin is a preferable hydrocarbon species for the NOx reduction catalyst in the latter stage, and it is presumed that a high denitration rate was obtained in Case 2 of Example 1 for this reason.

[0030]

According to the exhaust gas purifying apparatus of the present invention,
Compared to the conventional technology that decomposes / reforms hydrocarbons in a reactor that is separate from the exhaust gas flow path, stores it once, and injects it into the exhaust gas flow path, the operation is simple and highly reliable and responsive. An exhaust gas purifying device having good properties and a purifying method using the same are provided. Also, since NOx in diesel engine exhaust gas can be efficiently removed by adding as little reducing agent hydrocarbon as possible, it is possible to improve the fuel economy of the entire system without adding more hydrocarbon than necessary, and Since the above hydrocarbons are not added, the unburned fuel and incomplete combustion products, that is, suspended particulate matter, CO and hydrocarbons can be oxidized and removed with high efficiency by the oxidation catalyst in the latter stage of the NOx reduction catalyst.

[Brief description of drawings]

FIG. 1 is a diagram showing a method of applying a hydrocarbon decomposition catalyst and a NOx reduction catalyst of Example 1 of the present invention to exhaust gas threads. FIG.
In the figure, 1 is an engine, 2 is an exhaust manifold, 3 is a hydrocarbon injector, 4 is a hydrocarbon decomposition catalyst, 5 is a NOx reduction catalyst, and 6 is an exhaust pipe. FIG. 2 is a diagram showing a method of applying the hydrocarbon decomposition catalyst, NOx reduction catalyst and hydrocarbon oxidation catalyst of Example 2 of the present invention to an exhaust gas system. In FIG. 2, 1 is an engine, 2 is an exhaust manifold, 3 is a hydrocarbon injector, 4 is a hydrocarbon decomposition catalyst, and 5 is NOx.
A reduction catalyst, 6 is an exhaust pipe, and 7 is a hydrocarbon oxidation catalyst.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B01D 53/36 102A 102D

Claims (9)

[Claims] 1. In an exhaust gas purifying apparatus for purifying exhaust gas with a nitrogen oxide reduction catalyst device using hydrocarbon as a reducing agent, a hydrocarbon injection nozzle is provided upstream of a flow path of the exhaust gas of the nitrogen oxide reduction catalyst device. A device for adding hydrocarbons consisting of a hydrocarbon decomposition catalyst layer is installed, and the hydrocarbons supplied from the hydrocarbon injection nozzles have a hydrocarbon content lower than that of the supplied hydrocarbons due to the hydrocarbon decomposition catalyst layer. An exhaust gas purifying apparatus, characterized in that an increased hydrocarbon flow is provided, and the hydrocarbon flow is merged with the exhaust gas flow. 2. An exhaust gas purifying apparatus having a device for adding a nitrogen oxide reduction catalyst in a flow path of exhaust gas of a diesel engine and adding hydrocarbons upstream of the flow path of the exhaust gas. The adding device is composed of a hydrocarbon injection nozzle and a hydrocarbon decomposition catalyst layer, one end surface of the hydrocarbon decomposition catalyst layer is arranged facing the hydrocarbon injection nozzle, and the other end surface is open to the exhaust gas passage. A diesel engine exhaust gas purification device characterized by being arranged. 3. The exhaust gas purifying apparatus according to claim 1, further comprising a hydrocarbon oxidation catalyst device provided downstream of the nitrogen oxide reduction catalyst device. 4. The exhaust gas purifying apparatus according to claim 1, 2 or 3, wherein the hydrocarbon supplied to the apparatus for adding hydrocarbon is fuel oil. 5. A hydrocarbon catalytic cracking catalyst layer of a device for adding hydrocarbons decomposes hydrocarbons constituting fuel oil to increase paraffin components, naphthene components, aromatics components or olefin components having a smaller carbon number. The exhaust gas purifying apparatus according to claim 1, 2, 3, or 4, wherein the exhaust gas purifying apparatus is provided. 6. The catalyst according to claim 1, wherein the catalyst of the hydrocarbon catalytic cracking catalyst layer of the apparatus for adding hydrocarbons contains ultra-stabilized Y-zeolite as a main component. Exhaust gas purification device. 7. The exhaust gas purifying apparatus according to claim 1, wherein the catalyst of the nitrogen oxide reduction catalyst device has an iridium-supporting metal carbide as a main component. 8. A method for purifying exhaust gas, which comprises purifying the exhaust gas by the apparatus according to claim 1. 9. The method for purifying exhaust gas according to claim 8, wherein the exhaust gas is exhaust gas of diesel engine.