JP6557181B2 - Method for manufacturing holding material for exhaust gas treatment apparatus - Google Patents

Description

  The present invention relates to a method for manufacturing a holding material for an exhaust gas treatment apparatus that holds an exhaust gas treatment body disposed in a pipe of an exhaust gas exhaust system.

  Various industries are making various efforts to reduce environmental impact on a global scale. Among them, in the automobile industry, not only gasoline engine cars with excellent fuel efficiency, but also hybrid cars and electric cars. The development of the so-called eco-cars such as the above and the further improvement of its performance is being promoted every day.

In addition to the development of such eco-cars, research on catalytic converters that purify exhaust gas discharged from engines is also actively conducted. The exhaust gas purification catalyst constituting this catalytic converter includes an oxidation catalyst, a three-way catalyst, a NOx occlusion reduction catalyst, etc., and it is platinum (Pt) or palladium ( Pd) and noble metal catalysts such as rhodium (Rh), which are generally used in a state where they are supported on a support made of a porous oxide such as alumina (Al ₂ O ₃ ).

The catalytic converter described above is disposed in an exhaust gas exhaust system that connects the vehicle engine and the muffler. Engines may emit substances that are harmful to the environment, such as CO, NOx, unburned HC, and VOCs, and precious metal catalysts such as Rh, Pd, and Pt are used to convert these harmful substances into acceptable substances. By passing the exhaust gas through a catalytic converter in which the catalyst layer supported on the carrier is arranged on the cell wall of the substrate, CO is converted to CO ₂ , NOx is converted to N ₂ and O ₂ , and HC is burned As a result, CO ₂ and H ₂ O are generated. The general configuration of such a catalytic converter is outlined as follows: a honeycomb structure base material having a catalyst coat layer disposed in a hollow pipe (metal case), and an intermediate layer between the outer tube and the base material. And a heat resistant mat (holding material).

  Regarding the catalytic converter described above, in addition to purifying exhaust gas during normal operation, an electrically heated catalytic converter that purifies exhaust gas by activating the catalyst as quickly as possible by raising the temperature by electric heating in cold weather (EHC: Electrically Heated Converter) may be installed.

  This electrically heated catalytic converter has a configuration in which, for example, a pair of electrodes is attached to a honeycomb catalyst arranged in an exhaust gas exhaust system, and the pair of electrodes are connected by an external circuit having a power source. Is heated to increase the activity of the honeycomb catalyst so that the exhaust gas passing therethrough is rendered harmless.

  The general configuration of the electric heating type catalytic converter described above is outlined. Similar to the general catalytic converter described above, heat is generated in a honeycomb structure having a catalyst coating layer arranged in a hollow pipe (metal case). A heat-resistant base material, a heat-resistant and insulating mat (holding material) interposed between the outer tube and the base material, and, for example, a pair of electrodes attached to the surface of the base material in a region without the mat; The structure which consists of an external circuit which connects this pair of electrodes can be mentioned.

  For example, Patent Document 1 discloses a method for producing a catalytic converter holding sealing material.

  According to Patent Document 1, an inorganic particle suspension solution is supplied to a mat-like ceramic fiber assembly that is three-dimensionally assembled and heat-molded so that the inorganic particles contained in the suspension are made of ceramic fibers. An uneven structure is formed by adhering and fixing to the outer surface, which makes it difficult for the single fibers constituting the fiber assembly to slip and shift, and to prevent surface pressure deterioration over time.

JP 2011-231774 A

  According to the holding material disclosed in Patent Document 1, the treatment structure can be safely held with little reduction in surface pressure due to heating even by repeatedly receiving compression accompanying heating in the exhaust system of the exhaust gas.

  However, in Patent Document 1, since the inorganic particle suspension solution is supplied to the fiber assembly, the inorganic particles do not uniformly adhere to the fiber, so that the holding material has a desired repulsive force against repeated compression force. Since it requires a large amount of inorganic particles to be obtained, there is a problem that the manufacturing cost of the holding material increases.

  The present invention has been made in view of the above-described problems, and relates to a method of manufacturing a holding material for an exhaust gas treatment device that holds an exhaust gas treatment body disposed in a pipe of an exhaust gas exhaust system. An object of the present invention is to provide a method for producing a holding material for an exhaust gas treatment apparatus, which can obtain a large repulsive force without increasing the nanostructure and can obtain a holding material with a small decrease in surface pressure.

  In order to achieve the above object, a method for producing a holding material for an exhaust gas treatment apparatus according to the present invention is a method for producing a holding material for an exhaust gas treatment apparatus that holds an exhaust gas treatment body disposed in a pipe of an exhaust gas exhaust system. The holding material is a felt treated with a ceramic fiber needle, and a sol in which inorganic nanofibers having an average fiber diameter of 1 nm to 10 nm and an average length of 1000 nm to 5000 nm are dispersed inside the ceramic fiber felt. The surface of the ceramic fiber is modified by impregnating the solution or impregnating a precursor compound solution that is a precursor of the nanostructure sol, followed by boiling or acid treatment. is there.

  Here, the exhaust gas treatment apparatus includes an exhaust gas treatment body and a holding material. In addition to the catalytic converter described above, the exhaust gas treating body is a concept that includes a DPF that removes fine particles in the exhaust gas by filtering with a filter.

  The holding material manufactured by the manufacturing method of the present invention is made of ceramic fiber felt, and the surface of the ceramic fiber is modified with a nanostructure having a diameter or major axis of 10 nm to 1000 nm, so that the ceramic fibers are intertwined with each other. The frictional force between them can be increased, and by improving the frictional force, a large repulsive force can be exhibited when the holding material is compressed.

  In the production method of the present invention, an aggregate of ceramic fibers is impregnated with a sol solution of inorganic nanofibers or a precursor compound solution of nanostructures. Since the inorganic nanofibers have a large aspect ratio, the directions of the fibers are easily aligned. Therefore, compared to those in which inorganic particles are impregnated and adhered as described in Patent Document 1, they are easily adhered uniformly around the ceramic fibers. . In addition, when impregnated as a precursor compound solution before becoming a sol, since it is in a liquid state, the precursor compound uniformly adheres around the ceramic fiber in this case, and the nanostructure is formed by heating or acid treatment. By changing, a felt in which the nanostructure is uniformly attached around the ceramic fiber can be obtained.

  Thus, in any case, a holding material for an exhaust gas treatment apparatus to which nanostructures are uniformly attached can be obtained. That is, according to the manufacturing method of the present invention, it is possible to manufacture a holding material that exhibits a large repulsive force and has a small decrease in surface pressure without increasing the amount of nanostructure attached.

  In addition, the repulsive force of the holding material is influenced by the return force that tries to return by elastic deformation from the state where the ceramic fibers are bent and entangled in addition to the friction force described above.

  Here, the “ceramic fiber” includes alumina fiber, silica fiber, mullite fiber which is a compound of alumina and silica, and the like.

  “Felt” means a sheet or mat having a dense structure in which ceramic fibers are entangled with each other.

  Furthermore, the “nanostructure” includes nanoparticles, nanofibers, nanoparticle aggregates, nanopetals, and the like. Examples include alumina nanofibers with a fiber diameter of several nanometers and fiber lengths of 3 mm, nanostructures on scales with a size of 100 nm or less or 100 nm or more, and nanostructures with a surface of about 50 nm with petal-like changes. Can be mentioned. In many cases, the crystal structure partially has a boehmite (AlO (OH)) structure.

  According to the present inventors, the holding comprising a felt of ceramic fibers uniformly modified with a nanostructure having a diameter or major axis of several tens to several hundreds nm, specifically 10 nm to 1000 nm, preferably 100 nm to 500 nm. The material is an exhaust gas from a catalytic converter or the like with a fiber amount that is 10% or less less than that of a felt holding material disclosed in Patent Document 1 that is not uniformly modified with such a nanostructure. It has been specified that the repulsive force required to hold the treatment body can be obtained.

  As can be understood from the above description, according to the method for manufacturing a holding material for an exhaust gas treatment apparatus of the present invention, it is composed of a ceramic fiber felt, and the diameter or major axis of the surface of the ceramic fiber is several tens nm to several hundreds nm. Specifically, by obtaining a holding material in which nanostructures of 10 nm to 1000 nm are uniformly modified, it is possible to increase the frictional force between ceramic fibers intertwined with each other, and by improving this frictional force, Without increasing the amount of nanostructures to be adhered, it is possible to produce a holding material that exerts a large repulsive force when the holding material is compressed and has a small decrease in surface pressure.

It is the schematic diagram explaining the state by which the exhaust gas processing apparatus is arrange | positioned in piping. It is a SEM photograph figure of Example 1 of a holding material. (A), (b) is the SEM photograph figure of Example 2 of a holding material. It is a SEM photograph figure of Example 3 of a holding material. It is a SEM photograph figure of Example 4 of a holding material. (A) is the figure explaining the cutting-out method of a test piece, (b) is the figure explaining the condition of the tension test. It is the figure which showed the tension test result.

  Embodiments of a method for manufacturing a holding material for an exhaust gas treatment apparatus of the present invention will be described below with reference to the drawings. Here, a case where a catalytic converter is used as an exhaust gas treatment body used in the exhaust gas treatment apparatus will be described as an example. The illustrated catalytic converter preferably has a cordierite honeycomb carrier excellent in thermal shock resistance, but may be an electrically heated catalytic converter (EHC: Electrically Heated Converter). . Further, the exhaust gas treating body may be a DPF other than the catalytic converter shown in the figure.

(Exhaust gas exhaust system)
First, an exhaust gas exhaust system in which the catalytic converter of the present invention is interposed will be outlined. An exhaust gas exhaust system to which the catalytic converter of the present invention is applied is an engine, a catalytic converter constituting an exhaust gas treatment device, a three-way catalytic converter, a sub muffler, and a main muffler, which are connected to each other by a system pipe. The generated exhaust gas circulates through each part through the system pipe and is exhausted. Next, embodiments of the exhaust gas treatment device, the holding material for the exhaust gas treatment device, and the manufacturing method thereof will be described below.

(Embodiment of exhaust gas treatment apparatus, holding material for exhaust gas treatment apparatus and manufacturing method thereof)
FIG. 1 is a schematic diagram illustrating a state where an exhaust gas treatment device is disposed in a pipe.

  An exhaust gas treatment apparatus 10 shown in FIG. 1 includes a catalytic converter 2 that is an exhaust gas treatment body and a holding material 3, and the catalytic converter 2 is disposed inside the metal pipe 1 via the holding material 3. .

  The catalytic converter 2 is generally composed of a cylindrical base material having a large number of cells and a catalyst layer formed on the surface of the cell wall constituting the cells.

  Here, examples of the material of the base material include materials other than ceramic materials such as cordierite and silicon carbide made of a composite oxide of magnesium oxide, aluminum oxide and silicon dioxide, and metal materials.

  The base material consists of a honeycomb structure having cells having a large number of lattice contours such as quadrangular, hexagonal, octagonal, etc., and flows into the cells at the end on the upstream side (Fr side) in the exhaust gas flow direction in the base material. Exhaust gas (X direction) flows through the inside of the base material and is purified in this flow process, and the exhaust gas purified from the end of the base material on the downstream side (Rr side) in the exhaust gas flow direction flows out. (X direction).

The catalyst layer is composed of a support and a noble metal catalyst supported on the support. As the support, alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), ceria-zirconia composite oxide support (CeO ₂ -ZrO ₂ composite oxide) Examples of the noble metal catalyst include platinum (Pt), palladium (Pd), rhodium (Rh), and the like.

For example, a platinum group element such as palladium (Pd), rhodium (Rh), platinum (Pt), a platinum group element compound, or other noble metals or compounds thereof may be added to an oxide such as alumina (Al ₂ O ₃ ). Ceria zirconia-based composite oxide (CeO ₂ -ZrO ₂ ) is supported on an alumina sol or water to prepare a slurry that is prepared with an alumina sol or water, and the impregnation method, ion exchange method, sol-gel method, washcoat method, etc. By applying, a catalyst layer can be formed.

  When the catalytic converter 2 is an electric heating type catalytic converter, the catalytic converter 2 includes a pair of electrode members (not shown) disposed on the surface of the base material, a cable (not shown) connecting the electrode members, and a middle of the cable. The whole is generally constituted by an external circuit including a power supply (not shown) interposed between the two. Here, the electrode member comprises a surface electrode film disposed on the surface of the substrate, a comb-shaped wiring disposed on the surface of the surface electrode film, and a comb-shaped wiring. The wiring fixing layer fixes a plurality of wirings extending in the circumferential direction. When the power is turned on when starting the engine, a pair of electrode members located in the center of the base material are energized, and the path flowing through the diameter path in the cross section of the base material and the cross section of the base material through the surface electrode film In this way, the current spreading function of the surface electrode film that constitutes the electrode member allows the current to be evenly distributed throughout the entire substrate, and the equivalent current is diffused. And rectification is planned.

  The holding material 3 is made of a ceramic fiber felt, and a nanostructure having a diameter or a major axis of several tens to several hundreds of nanometers, specifically 10 nm to 1,000 nm, is modified on the surface of the ceramic fibers.

  Here, the ceramic fiber includes alumina fiber, silica fiber, mullite fiber which is a compound of alumina and silica, and the like. The felt is a sheet or mat having a dense structure in which ceramic fibers are entangled with each other. Furthermore, nanostructures include nanoparticles, nanofibers, nanoparticle agglomerates, nanopetals, and the like. As an example, alumina nanofibers with a fiber diameter of 4 nm, fiber length of 3000 nm, crystal structure of boehmite (AlO (OH)), nanostructures on scales with a diameter of 100 nm or less or 100 nm or more, and the surface Examples include nanostructures of about 50 nm that change into petals. In many cases, the crystal structure partially has a boehmite (AlO (OH)) structure.

  Thus, the holding material 3 is made of a ceramic fiber felt, and a nanostructure having a diameter or a major axis of several tens of nanometers to several hundreds of nanometers, specifically 10 nm to 1000 nm, is uniformly modified on the surface of the ceramic fibers. Thus, the frictional force between the ceramic fibers that are intertwined with each other can be increased, and the improvement of the frictional force can exert a large repulsive force when the holding material is compressed.

  That is, the illustrated holding material 3 is a holding material that can exert a large repulsive force without increasing the amount of attached nanostructures. The repulsive force of the holding material 3 is exhibited not only by the frictional force described above, but also by a return force that tries to return by elastic deformation from a state where the ceramic fibers are bent and entangled.

  Here, the manufacturing method of the holding material 3 will be outlined. First, the inside of the ceramic fiber felt is impregnated with a sol solution in which inorganic nanofibers having an average fiber diameter of 1 nm to 10 nm and an average length of 1000 nm to 5000 nm are dispersed. Alternatively, a precursor compound solution that is a precursor of the sol of the nanostructure is impregnated. Next, the felt of ceramic fiber impregnated with a sol solution or the like is subjected to boiling treatment or acid treatment, whereby the holding material 3 in which the nanostructure is modified on the surface of the ceramic fiber is manufactured.

(Example of holding material)
The inventors of the present invention are made of ceramic fiber needle-treated felt, and the surface of the ceramic fiber is uniformly modified with nanostructures having a diameter or major axis of several tens to several hundreds of nanometers, specifically 10 nm to 1,000 nm. Various holding materials were manufactured. FIG. 2 is an SEM photograph of Example 1 of the holding material. FIGS. 3A and 3B are both SEM photographs of Example 2 of the holding material. FIG. 4 is an example of Example 3 of the holding material. FIG. 5 is an SEM photograph of Example 4 of the holding material.

  First, the holding material of Example 1 shown in FIG. 2 was modified with alumina nanofibers having an average fiber diameter of 4 nm, an average fiber length of 3000 nm, and a crystal structure of boehmite (AlO (OH)) on the surface of mullite fibers. It is a holding material.

  As shown in the figure, it can be seen that the alumina nanofibers are uniformly attached to the surface of the mullite fiber like a mask melon.

  This holding material is alumina sol F3000 (manufactured by Kawaken Fine Chemical Co., Ltd.) (nanofiber fiber diameter 4 nm, fiber length approximately 3000 nm) in a methanol dilution of 1.0% by mass in sol (solid content) concentration in methanol solvent. The mixture was impregnated with needle treated felt, applied to mullite fiber, and fired at 400 ° C. for 1 hour.

  Next, the holding material of Example 2 shown in FIG. 3 is obtained by modifying the surface of the mullite fiber with a nanostructure. Specifically, the holding materials shown in FIGS. 3A and 3B are made of aluminum chelate (ALCH: aluminum ethyl acetoacetate / diisopropylate) (manufactured by Kawaken Fine Chemical Co., Ltd.) as a precursor compound of the sol. The ceramic fibers are coated and then boiled at 160 ° C. and 180 ° C., respectively, and the ceramic fibers are modified with nanostructures having a size of 100 nm or less and 100 nm or more, respectively.

  Thus, by changing the boiling water treatment temperature at the time of manufacture, the size of the nanostructure can be adjusted as desired, but in any case, it can be seen that the nanostructure is uniformly attached to the mullite fiber.

Next, the holding material of Example 3 shown in FIG. 4 is obtained by modifying the surface of the mullite fiber with a nanostructure by another method. This holding material was produced by adhering a coating solution of aluminum secondary butyrate (ASBD) (manufactured by Kawaken Fine Chemical Co., Ltd.) as a sol precursor compound solution to the surface of mullite fiber and treating it with boiling water.
FIG. 4 shows that ASBD changes to a petal shape of about 50 nm.

  Next, the holding material of Example 4 shown in FIG. 5 is obtained by modifying alumina on the surface of mullite fiber.

  This holding material was produced by attaching alumina sol F1000 (manufactured by Kawaken Fine Chemical Co., Ltd.) (average fiber diameter of nanofiber sol 4 nm, average fiber length of about 1400 nm) to the surface of mullite fiber and treating with phosphoric acid.

  From FIG. 5, it can be seen that uneven alumina having a diameter or major axis of about 100 to 200 nm is produced.

(Tensile test and results)
The present inventors made a holding material, conducted a tensile test, and conducted an experiment to measure the tensile strength of the holding material. Here, FIG. 6A is a diagram illustrating a method for cutting out a test piece, and FIG. 6B is a diagram illustrating a situation of a tensile test.

  A holding material (mat) made of a ceramic fiber felt whose surface was modified with a nanostructure was manufactured, and a test piece (TP: test piece) was cut out as shown in FIG. TP1 coated with 0.01% by weight of alumina sol F3000, TP2 coated with 0.1% by weight of alumina sol F3000, TP3 coated with 0.5% by weight of alumina sol F3000 on mullite fibers having an average diameter of 3 to 15 μm and an average length of several hundreds of nanometers % Applied.

  In addition, as a comparative example, a mullite fiber alone with no nanostructure modification (Comparative Example 1) and an inorganic particle suspension solution described in Patent Document 1 are impregnated in felt, and 1.0% by mass of inorganic particles are adhered. The test of the sample (Comparative Example 2) was also conducted.

  The cut specimen was chucked with a tensile tester as shown in FIG. 6B, and a tensile test was performed. Three test pieces were prepared (TP1 to TP3), and the average value was calculated in addition to the results of the tensile tests. The test results are shown in FIG.

  In FIG. 7, the result without nanostructure modification is the result of producing a holding material (Comparative Example 1) that does not have a nanostructure and conducting a tensile test.

  From FIG. 7, the average value of the tensile strength of TP1 to TP3 was 67.2N, and it was confirmed that the tensile strength was improved by 10% or more with respect to 60N of Comparative Example 1.

  This is because the surface of the ceramic fiber is modified with a nanostructure having a diameter of several tens to several hundreds of nanometers, which increases the frictional force between the ceramic fibers that are intertwined with each other. It is thought that the tensile strength of was improved.

  And the improvement of this tensile strength also leads to the improvement of the repulsive force when a holding material is compressed. Therefore, it can be seen that the repulsive force required when the holding material is compressed can be obtained while reducing the adhesion amount of the nanostructure as compared with the conventional holding material.

  Compared to 65.4N in Comparative Example 2 where the felt was impregnated in the form of a suspension of inorganic particles, TP1 to TP3 obtained a tensile strength equal to or higher than that of the nanostructure, although the amount of nanostructure adhered was much smaller. Therefore, it greatly contributes to reducing the material cost of the holding material.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Piping, 2 ... Catalytic converter (exhaust gas processing body), 3 ... Holding material, 10 ... Exhaust gas processing apparatus

Claims (1)

  A method of manufacturing a holding material for an exhaust gas treatment device that holds an exhaust gas treatment body disposed in a pipe of an exhaust gas exhaust system, wherein the holding material is a felt treated with needles of ceramic fibers, The felt is impregnated with a sol solution in which inorganic nanofibers having an average fiber diameter of 1 nm to 10 nm and an average length of 1000 nm to 5000 nm are dispersed, or a precursor compound solution that is a precursor of a nanostructure sol A method for producing a holding material for an exhaust gas treatment apparatus, wherein a nanostructure is modified on the surface of a ceramic fiber by impregnation and subsequent boiling treatment or acid treatment.

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