WO1998045583A1

WO1998045583A1 - Catalyst converter

Info

Publication number: WO1998045583A1
Application number: PCT/JP1998/001636
Authority: WO
Inventors: Mamoru Shoji; Toshiaki Sasaki
Original assignee: Mitsubishi Chemical Corporation
Priority date: 1997-04-10
Filing date: 1998-04-09
Publication date: 1998-10-15
Also published as: AU6747898A

Abstract

A catalyst converter in which a monolith is stably fixed by a specific monolith support and from which no exhaust gas leaks at all through the outer periphery of the monolith. The monolith support (3) comprises a compressed crystalline alumina fiber mat and an organic binder, and has a large number of grooves (3c) orthogonal to the winding direction in the surface thereof. The monolith support (3) follows up changes in the clearance between the outer peripheral surface of the monolith and the inner surface of the casing resulting from the temperature change of the monolith (1) and the casing (2) after the organic binder is thermally decomposed, supports the monolith (1) by its restoring elastic force, and exhibits strong adhesion to the outer peripheral surface of the monolith (1) thanks to the grooves (3c).

Description

Description Catalytic converter

Technical field

The present invention relates to a catalytic converter, and more particularly, to a catalytic converter mainly used for automobiles, in which a monolith is stably fixed by a specific monolith holding material, and exhaust gas from the outer periphery of the monolith is fixed. The present invention relates to a catalytic converter that reliably prevents leakage.

Background

As is well known, a catalytic converter is a device that removes harmful components such as carbon monoxide, hydrocarbons, and nitrogen oxides contained in exhaust gas of an internal combustion engine using a noble metal catalyst. Japanese Patent Application Laid-Open No. 9-946 discloses a so-called integrated catalyst in which a catalyst metal is supported on a cylindrical monolithic carrier (hereinafter, referred to as "monolith") provided with a large number of exhaust gas passages. In addition, the technology of a catalytic converter as shown in FIGS. 3 to 5, which aims at improving durability and miniaturization, is disclosed.

The catalytic converter described in the above-mentioned publication contains a monolith (1) formed in a cylindrical shape and carrying an exhaust gas purifying catalyst, and a monolith (1), and both ends thereof are connected to an exhaust gas conduit. And a monolith holding material (3) wound around the monolith (1) and interposed in the gap between the monolith and the casing (2).

The monolith (1) usually has a honeycomb structure that can secure a larger surface area in the exhaust gas flow path in order to reduce the resistance when passing exhaust gas and increase catalyst efficiency. Have been. The monolith holding material (3) is composed of an alumina fiber mat containing an organic binder, and is restored in the casing (2) by thermal decomposition to hold the monolith (1) with an appropriate force. It has the function to do.

The first reason that the monolith holding material (3) as described above is interposed in the gap between the monolith (1) and the casing (2) is that the heat of the honeycomb is transmitted directly to the metal casing (2). This is to prevent the temperature of the monolith (1) from dropping during idling. The second reason is that the monolith (1) is properly fixed to prevent the monolith (1) from detaching or shifting. Therefore, the monolith holding material (3) needs to maintain a predetermined holding force from normal temperature to high temperature during operation. That is, it is necessary to follow the change in the gap caused by the thermal expansion of the monolith (1) ゃ casing (2) due to the passage of exhaust gas.

By the way, in the catalytic converter described in JP-A-9-1946, as shown in FIG. 5, when a monolith holding material (3) is wound around a cylindrical monolith (1), a monolith holding material is used. Depending on the thickness of (3), a shim (3d) is formed on the inner peripheral side, and a minute gap is formed between the monolith (1) and the monolith holding material (3). Exhaust gas may leak slightly. In addition, the formation of the non-uniform shies (3d) may cause the holding material to be non-uniformly filled.

The present invention has been made in view of the above circumstances, and has as its object to stably fix a monolith by a specific monolith holding material and to more reliably prevent leakage of exhaust gas from the outer periphery of the monolith. An object of the present invention is to provide an improved catalytic converter. Disclosure of the invention

The catalytic converter of the present invention is formed in a tubular shape and serves as an exhaust gas purifying catalyst. A monolith that holds the monolith, a metal casing that houses the monolith and is connected to an exhaust gas conduit, and a monolith holding material that is wound around the monolith and interposed in a gap between the monolith and the casing. In the catalytic converter composed of: the monolith holding material, the crystalline alumina fiber mat compressed in the thickness direction and the organic fiber uniformly impregnated in the alumina fiber mat and disappeared by thermal decomposition. The monolith holding member on the side in contact with the monolith has a large number of grooves orthogonal to the winding direction of the monolith holding member. Features.

In the above-described catalytic converter, the monolith holding material is formed by the gap between the outer peripheral surface of the monolith and the inner surface of the casing based on a change in temperature of the monolith casing after the organic binder contained therein disappears due to thermal decomposition. And supports the monolith with its restoring elasticity. In addition, the monolith holding material provided with the specific groove does not generate a shear when it is wound around the monolith, and exhibits high adhesion to the outer peripheral surface of the monolith. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view showing a monolith holding material used in the catalytic converter 1 of the present invention. FIG. 2 is a front view showing a wound state of the monolith holding material in the catalytic converter of the present invention, and the monolith in the figure shows a ceramic monolith as an example. FIG. 3 is an assembled perspective view showing a general structure of the catalytic converter 1, and the monolith in the figure shows a metal monolith as an example. FIG. 4 is a perspective view showing a general procedure for winding a monolith holding material on a monolith. Fig. 5 is a front view showing the wound state of the monolith holding material in the conventional catalytic converter. BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described with reference to the drawings. In the description of the embodiment, FIG. 3 and FIG. 4 used in the background description of the related art are used together.

As shown in FIG. 3, a catalytic converter 1 according to the present invention has a monolith (1), which is formed substantially in a tubular shape and carries an exhaust gas purifying catalyst, A metal casing (2) connected to the gas conduit, and a monolith holding material (3) wound around the monolith (1) and interposed in the gap between the monolith and the casing (2) Be composed.

As the monolith (1), a monolith composed of ceramics mainly composed of cordierite or the like, or a monolith composed of a metal foil material can be used. In particular, fly-based stainless steel foil containing Fe, Cr, A1 or Si as a basic component has good compatibility with the coating material and the catalyst when supporting the catalyst, and has relatively little thermal change after the catalyst is supported. Since it is small, it is a suitable material for constructing metal monoliths. The monolith (1) is usually provided with a catalyst function by supporting a noble metal layer such as Pt and Ph.

The casing (2) has a two-part clamshell structure that combines and integrates two members, a casing member (2a) constituting the upper half of the casing and a casing member (2b) constituting the lower half. . The casing members (2a) and (2b) have flange portions (21a) and (21b), respectively, and the flange portions (21a) and (21b) weld the casing members (2a) and (2b). It functions as a joining surface in the case. At both ends of one casing member (2b), connection ports (4) and (5) for connecting to an exhaust gas conduit are provided. In FIG. 3, reference numerals (22a) and (22b) denote bolt holes for fixing to a vehicle body or the like. As the metal casing, a casing having a stuffing structure, which is formed in a tubular shape in advance and into which a monolith is inserted, is used. Can also be adopted.

One feature of the present invention is that a specific monolith holding material (3) is employed. That is, the monolith holding material (3) is made of a non-expandable crystalline alumina fiber mat (hereinafter abbreviated as “mat”) compressed in the thickness direction and uniformly impregnated into the mat. And an organic binder that is eliminated by thermal decomposition. The above mat exhibits a specific restoring force when compressed to a thickness corresponding to the gap between the monolith (1) outer peripheral surface and the casing (2) inner surface, and does not destroy the monolith (1) and The effect of supporting the monolith is fully exhibited.

Specifically, the above mat is preferably 0.1 to 10.0 _kg fZcm ² , more preferably 0.1 mm, in a compressed state having a thickness corresponding to a gap between the outer peripheral surface of the monolith (1) and the inner surface of the casing (2). and a restoring force of ~8.0kgf / cm ^2. Such a restoring force, monolith (1) 0.5~10.0kgf / cm ² approximately in the case of ceramics, preferably is a 0.5~8.0kgf / cm ² or so, when the monolith (1) is made of metal 0.1 It is ~4.0kgf / cm ² about.

The above-mentioned restoring force is developed after the organic binder uniformly impregnated in the mat disappears by thermal decomposition. The resilience of the mat is equivalent to the force (compression force) required to compress the mat to a thickness corresponding to the gap between the monolith (1) outer surface and the casing (2) inner surface. Accordingly, in the present invention, the above-mentioned index of the restoring force is determined by the compressive force at the time of mat formation.

In other words, the thickness of the mat is determined by the elasticity, the monolith (1) the gap between the outer peripheral surface and the casing (2) the inner surface, the amount of thermal change, gas sealability, and the breaking strength of the monolith (1). However, the monolith (1) is set to have a compressive force equivalent to the above-mentioned restoring force when compressed to a thickness corresponding to the gap between the outer peripheral surface and the casing (2) the inner surface. The mat as the base material of the monolith holding material (3) refers to an aggregate of alumina fibers that are substantially uniformly laminated in the thickness direction, and includes a so-called blanket or block. As the alumina fiber, usually, a fiber diameter of l to 50 / m and a fiber length of 0.5 to 500 mm is used, but from the viewpoint of restoring force and shape retention, the fiber diameter is 3 to 8 / zm, Fibers having a fiber length of 0.5 to 300 mm are particularly preferred.

The composition of the above-mentioned alumina fiber is alumina-silicone crystalline short fiber, having an alumina content of 5% by weight or less, that is, high alumina having an alumina content of 95% by weight or more, and having an alumina content of 70 to 70% by weight. A typical material is 95% by weight and the balance is composed of sili force. In particular, a fiber having a mullite composition of 72 to 85% by weight of alumina is excellent in high-temperature stability and elasticity, and a preferred alumina fiber is a crystalline alumina fiber which is the same as an alumina-silica non-crystalline ceramic fiber. Compared to ceramic fibers, they have excellent heat resistance and extremely low thermal degradation such as softening and shrinkage, so they have high elasticity when used as a compressed mat. That is, mat has a property that it generates a high holding force at a low bulk density and its temperature change is small. Therefore, even if the gap between the monolith (1) and the casing (2) changes due to the difference in thermal expansion between the monolith (1) and the metal casing (2), and the bulk density increases, The holding pressure against the monolith (1) does not change rapidly. The organic binder can be used without particular limitation as long as it can maintain the thickness of the compressed mat at room temperature and can restore the thickness of the above mat after disappearance by thermal decomposition. A material that does not decompose even at the operating temperature or higher, and further impregnates organic knives to impair the flexibility and restoring surface pressure characteristics of the mat and promote the destruction of the monolith (1) The use of organic binders must be avoided. Various organic rubbers, water-soluble organic Polymer compounds, thermoplastic resins, thermosetting resins, and the like can be used.

Examples of the rubbers include natural rubbers; copolymers of ethyl acrylate and chloroethyl vinyl ether, copolymers of n-butyl acrylate and acrylonitrile, and copolymers of ethyl acrylate and acrylonitrile. Acryl rubber; nitrile rubber of a copolymer of butadiene and acrylonitrile; butadiene rubber; and the like. Examples of the water-soluble organic high molecular compound include carboxymethyl cellulose and polyvinyl alcohol. Examples of the thermoplastic resin include acryl resin which is a homopolymer or a copolymer of acrylic acid, acrylic acid ester, acrylamide, acrylonitrile, methacrylic acid, methacrylic acid ester, etc .; acrylonitrile styrene copolymer; acrylonitrile Butadiene / styrene copolymer. Examples of the thermosetting resin include a bisphenol-type epoxy resin and a novolak-type epoxy resin.

Aqueous solutions, water-dispersed emulsions, latex, and organic solvent solutions (collectively referred to as "binder solutions") containing the above-mentioned organic binder as an active ingredient are commercially available. Since it can be used after being diluted with a solvent, it can be applied at relatively low cost. The organic binder does not need to be one kind, and may be a mixture of two kinds.

Among the above organic binders, at least one selected from the group consisting of acrylyl rubber, nitrile rubber, carboxymethylcellulose, polyvinyl alcohol and acrylyl resin other than acrylyl rubber is preferable, and particularly, synthetic rubber such as acrylic rubber and nitrile rubber. Of these, flexible rubber is effective.

The content of the organic binder is not particularly limited, and the type and shape of the fiber constituting the mat, the absolute thickness of the mat, and the molded product including the organic binder before being incorporated into the casing (2). Determined by the thickness and the repulsive force. Organic bi Usually, the content of the organic binder is preferably 3 to 30 parts by weight based on 100 parts by weight of the alumina fiber. If the content of the organic binder is less than 3 parts by weight, the thickness of the molded body may not be maintained due to repulsion of the mat. There is a risk that flexibility may be impaired. From such a viewpoint, the ratio of the organic binder is preferably in the range of 5 to 20 parts by weight.

The greatest feature of the present invention is that the monolith holding material (3) is formed in a specific shape. That is, on the surface of the monolith holding member (3) on the side that comes into contact with the monolith (1), a number of grooves (3c) orthogonal to the winding direction of the monolith holding member are provided. The cross section of the groove (3c) is usually formed in a substantially V shape or a substantially U shape. According to such a configuration, when the monolith holding material (3) is wound around the monolith (1), it is possible to prevent the occurrence of a screen on the inner peripheral surface of the monolith holding material (3), thereby preventing the exhaust gas from leaking. It can be prevented more reliably. Further, in the monolith holding material (3), the depth of the groove (3c) is 130 to 12 of the thickness of the monolith holding material (3) in order to further enhance the adhesion to the monolith (1). In addition, it is preferable that the width of the groove (3c) (the maximum width of the opening of the groove) is 130 to 1/2 of the thickness of the monolith holding material (3). Further, in the monolith holding material (3), it is preferable that the arrangement pitch of the grooves (3c) is 1 to 20 to 2 which is the radius of curvature of the monolith (1). The radius of curvature of the monolith (1) is usually 10 to 80 mm.

The monolith holding material (3) is prepared by (a) a step of impregnating the organic binder liquid into the mat, (b) a step of compressing the mat impregnated with the organic binder liquid in the thickness direction, and (c) a step of compressing the mat. It is produced through a process of removing the solvent component of the organic binder liquid as it is. Then, the groove (3c) on the surface of the monolith holding material (3) was formed by applying a smooth forming plate to one surface of the mat in the above-mentioned step (b) and having a ridge corresponding to the groove (3c). Formed by pressing the board against the other side of the mat, or Alternatively, after the step (c), it is formed by subjecting the obtained molded body to grooving. In addition, as shown in Fig. 1, the obtained monolith holding material (3) has a connection that can be combined with each other when it is wound around the monolith (1) to prevent twisting and displacement during assembly. The portions are provided at both ends in the winding direction by cutting or the like.

The monolith holding material (3) obtained by the above steps is wound around the outer periphery of the monolith (1) as shown in FIG. In this case, the monolith holding member (3) can be extremely easily and accurately wound since a large number of grooves (3c) are provided on one surface corresponding to the inner peripheral side of the monolith holding member (3). In addition, when the monolith holding material (3) is wound, as shown in Fig. 2, the difference in the length between the outer circumference and the inner circumference caused by the thickness of the monolith holding material (3) causes a large number of grooves (3c). Because it is complemented by the monolith (3), it can be wound close to the monolith (3). Then, the monolith (1) on which the monolith holding material (3) is wound is accommodated in the casing (2) shown in FIG.

The catalytic converter illustrated in FIG. 3 has a two-part structure in which the flange (21a) of the casing member (2a) and the flange (21b) of the casing member (2b) are welded to each other as a joint surface. The case (2) is adopted. When the monolith (1) is housed in the casing (2), the thickness of the monolith holding material (3) is the same as the gap formed by the outer surface of the monolith (1) and the inner surface of the casing (2). It is not necessary to have a small thickness. However, if it is too thick, if the sliding with the casing (2) is poor, some of the fibers of the monolith holding material (3) will protrude to the joint surface of the flanges (21a) and (21b). However, the thickness is set to 1.0 to 2.0 times the above gap to cause inconveniences such as making welding impossible. The upper limit of such a set value is preferably 1.7 times, more preferably 1.6 times.

As shown in the figure, in the catalytic converter of the present invention, the monolith (1) is directly supported by the monolith holding material (3) made of a crystalline alumina fiber mat. Is preferred. That is, in the structure in which the monolith (1) is directly supported by the specific monolith holding material (3) as described above, an appropriate tightening force can be exerted on the monolith (1) and the monolith (1) There is no fear of destroying.

The catalytic converter of the present invention is mainly attached to an exhaust gas pipe of an automobile. In the catalytic converter of the present invention, when the high temperature exhaust gas discharged from the internal combustion engine is passed, the temperature of the monolith (1), the casing (2) and the monolith holding material (3) rises, and the monolith is held. In material (3), the organic binder impregnated in the mat disappears due to thermal decomposition, and the monolith (1) is fixed by restoring its thickness.

In other words, when the monolith (1) is made of ceramics due to the passage of exhaust gas, the metal casing (2) has a larger thermal expansion than the monolith (1), so that the monolith (1) is Casing (2) The distance between the casing and the inner surface increases. On the other hand, when the monolith (1) is made of a metal as described above, the thermal expansion of the monolith (1) is larger than that of the metal casing (2). (2) The distance between the inner surface and the case is narrow. On the other hand, the above specific monolith holding material (3) follows the change in the gap between the monolith (1) outer peripheral surface and the casing (2) inner surface based on the temperature change of the monolith (1) ゃ casing (2). Then, directly fix the monolith (1) elastically in the casing (2).

In other words, the monolith holding material (3) is formed by uniformly impregnating the compressed mat with the organic binder. At the time of assembly, the resilience of the thickness is suppressed by the binding force of the organic binder, so that the monolith holding material (3) can be easily formed. The monolith (1) can be fixed very stably because the organic binder disappears due to thermal decomposition and exhibits a restoring elasticity of its thickness when it is put into operation.

The monolith holding material (3) has a large number of grooves (3c) on the surface of the monolith (1). What High adhesion to the outer peripheral surface of the monolith (1). As a result, the gap between the monolith (1) and the casing (2) can be completely sealed, and leakage of exhaust gas from the outer periphery of the monolith (1) can be more reliably prevented. Industrial applicability

As described above, according to the catalytic converter of the present invention, since the specific monolith holding material that is restored in the thickness direction by the thermal decomposition of the binder is used, the monolith is fixed easily and stably. it can. In addition, since the surface of the monolith holding member that is in contact with the monolith has a large number of grooves, the monolith holding member can be easily wound around the monolith during assembly, and Since the adhesion of the monolith supporting material to the squirrel can be further enhanced, the leakage of exhaust gas from the gap between the outer peripheral surface of the monolith and the inner surface of the casing can be more reliably prevented.

Therefore, the catalytic converter of the present invention is useful as a device for more reliably removing harmful components such as carbon monoxide, hydrocarbons and nitrogen oxides contained in the exhaust gas of an internal combustion engine.

Claims

The scope of the claims

1. A monolith (1) formed in a cylindrical shape and carrying an exhaust gas purifying catalyst; a metal casing (2) containing the monolith (1) and connected to an exhaust gas conduit; In a catalytic converter composed of a monolith holding material (3) wound around (1) and interposed in the gap between the monolith and the casing (2), the monolith holding material (3) has a thickness direction. It is composed of a crystalline alumina fiber mat compressed to a low temperature and an organic binder that is uniformly impregnated in the alumina fiber mat and disappears by thermal decomposition. A catalytic converter characterized in that the surface of the monolith holding member (3) is provided with a large number of grooves (3c) orthogonal to the winding direction of the monolith holding member.

2. The depth of the groove (3c) is 130 to 1/2 of the thickness of the monolith holding material (3), and the width of the groove (3c) is 1/30 to 1/30 of the thickness of the monolith holding material (3). 2. The catalytic converter according to claim 1, wherein the ratio is 1/2.

3. The catalytic converter according to claim 1, wherein an arrangement pitch of the grooves (3c) is 120 to 2 having a radius of curvature of the monolith (1).

4. The alumina fiber mat constituting the monolith holding material (3) has a thickness of 0.1 lO.OkgfZcm ² in a compressed state with a thickness corresponding to the gap between the monolith (1) outer peripheral surface and the casing (2) inner surface. 4. The catalytic converter according to claim 1, which has a restoring force.