JP4818939B2 - Reinforced porous honeycomb structure - Google Patents

Description

  The present invention relates to a reinforced porous honeycomb structure that can be widely used for an adsorption separation material, a catalyst carrier, and the like and has high strength, and a method for manufacturing the same. The present invention also relates to a sintered reinforced honeycomb structure obtained by firing a reinforced porous honeycomb structure.

  The porous material is a material characterized in that it has innumerable fine pores inside and has a very large internal surface area with respect to the outer surface. Therefore, porous materials are used in a wide range of applications such as adsorbents, catalysts or catalyst carriers, chromatography columns, air conditioners, and filters for water purification devices. When such a porous material is used, it can be properly used as various shapes such as powders, particles, fibers, honeycombs, thin films, and nanotubes depending on the application.

  Here, the filter of an air cleaner is mentioned as a typical thing used for fluid processing. The porous material can also be used as a filter for an air cleaner. The most commonly used porous material for air cleaner filters is granular activated carbon. In order to use the activated carbon for a filter of an air cleaner, a method is used in which the activated carbon is filled in an appropriate container and air as a processing fluid is passed through the container. However, this method has a drawback that the contact area of the processing fluid is very large, but the pressure loss increases and the linear velocity cannot be increased.

For the purpose of reducing such pressure loss, a porous material (hereinafter referred to as a porous honeycomb structure) formed in a honeycomb shape having a straight flow path can be used. Many of the currently used porous honeycomb structures are carriers produced by extruding ceramic. Then, the catalyst component is wash-coated on the carrier and used for, for example, a filter of an air cleaner. The general specific surface area of the porous honeycomb structure is about 100 to 200 m ² / g.

  In general, a porous honeycomb structure has a higher cell density (number of cells per square inch), and the thinner the honeycomb wall thickness, the larger the contact area between the porous material and the treatment liquid, thereby improving the performance.

Therefore, a technique for producing a porous honeycomb-shaped silica gel having a large specific surface area of 800 to 900 m ² / g, which can control the opening diameter to 5 to 50 μm using a sol-gel method, It is disclosed in Patent Document 1.
JP 2004-307294 A

  Since the porous honeycomb structure has a large specific surface area, for example, a large amount of fluid treatment can be performed quickly. On the other hand, however, the porous honeycomb structure has a drawback that since it is porous, its strength is weakened and it is necessary to pay close attention to handling.

  The present invention has been made to solve such problems, and the object of the present invention is to provide a novel reinforced porous honeycomb structure having improved strength as compared with a conventional porous honeycomb structure and The manufacturing method is provided.

  The present invention is composed of a porous honeycomb structure and fine powder, the fine powder is dispersed in the porous honeycomb structure, and has a reinforced porosity having a compressive strength higher than the compressive strength of the porous honeycomb structure. The present invention relates to a quality honeycomb structure.

In the reinforced porous honeycomb structure of the present invention, the compressive strength is preferably 1.0 to 4.5 kg / cm ² .

  In the reinforced porous honeycomb structure of the present invention, the average particle size of the fine powder is preferably 1 to 50 μm.

In the reinforced porous honeycomb structure of the present invention, it is preferable that the average pore diameter is 5 to 150 μm and the specific surface area is 100 to 1000 m ² / g.

  In the reinforced porous honeycomb structure of the present invention, the fine powder is preferably 10 to 120% by weight of the porous honeycomb structure.

  In the reinforced porous honeycomb structure of the present invention, the fine powder preferably contains graphite.

  Further, the reinforced porous honeycomb structure of the present invention is preferably produced by gelling silica sol and molding it by a unidirectional freeze gelation method.

  The reinforced porous honeycomb structure of the present invention is preferably produced by dispersing fine powder in silica sol by ultrasonic waves.

  The reinforced porous honeycomb structure in which the fine powder of the present invention is dispersed has high compressive strength and is easy to handle. Therefore, the reinforced porous honeycomb structure of the present invention can expand the application of the porous material.

<Reinforced porous honeycomb structure>
FIG. 1 is a scanning electron microscope (SEM) photograph showing a partially enlarged reinforced porous honeycomb structure of a preferred example of the present invention. As shown in FIG. 1, the structure of the reinforced porous honeycomb structure according to the present invention is formed in a so-called “honeycomb” shape in which a large number of apertures having a substantially uniform size are formed when viewed from an arbitrary surface. It is a structured. The reinforced porous honeycomb structure is porous as a whole because a large number of pores smaller than the openings are formed in the walls separating the openings (hereinafter also referred to as honeycomb walls).

  The reinforced porous honeycomb structure of the present invention is composed of a porous honeycomb structure and fine powder. The fine powder is dispersed in the porous honeycomb structure. The reinforced porous honeycomb structure is obtained by imparting strength to the porous honeycomb structure. That is, the fine powder of the present invention can impart strength to the porous honeycomb structure. The reinforced porous honeycomb structure contains fine powder. In the present invention, the porous honeycomb structure is preferably made of “porous silica”. This is because it is porous so that its specific surface area is large, a large amount of fluid can be treated, and the surface can be modified using silanol groups on the surface. Usually, such porous silica uses only firing as a method for improving its strength, and therefore its specific surface area tends to be small. On the other hand, the “reinforced porous honeycomb structure” in which the fine powder of the present invention is dispersed can improve the strength while maintaining the porous property.

  In the reinforced porous honeycomb structure of the present invention, the state in which the fine powder is “dispersed” in order to impart strength is the state in which the fine powder is distributed substantially uniformly in the porous honeycomb structure. Sure. Thus, it can be confirmed that the fine powder is dispersed in the reinforced porous honeycomb structure by, for example, observation using an electron microscope.

  The compressive strength of the reinforced porous honeycomb structure is higher than that of the porous honeycomb structure. The amount of the fine powder is not particularly limited as long as the reinforced porous honeycomb structure as a whole can exhibit higher compressive strength than the porous honeycomb structure.

  In order to further increase the compressive strength of the reinforced porous honeycomb structure, it is effective to increase the amount of fine powder constituting the reinforced porous honeycomb structure. However, if the amount of fine powder is excessively increased, the reinforced porous honeycomb structure may not be able to form a “honeycomb” shape.

<Compressive strength of reinforced porous honeycomb structure>
The reinforced porous honeycomb structure of the present invention has higher compressive strength than the porous honeycomb structure. The compressive strength of the reinforced porous honeycomb structure is proportional to the amount of fine powder.

For example, a reinforced porous honeycomb structure made of a porous honeycomb structure made of porous silica and fine powder has a compressive strength of 1.19 to 4.13 kg / cm ² . The compressive strength of the porous honeycomb structure made of porous silica is about 0.5 to 0.9 kg / cm ² .

This compressive strength can be adjusted by the amount of fine powder, and the amount of fine powder is appropriately adjusted according to the type of fine powder used, the material of the porous honeycomb structure, the specific surface area of the reinforced porous honeycomb structure, and the like. However, in the reinforced porous honeycomb structure of the present invention, the compressive strength is preferably in the range of 1.0 to 4.5 kg / cm ² as illustrated above, and 1.1 to 4.2 kg / cm ^2. A range of ² is particularly preferred. When the compressive strength of the reinforced porous honeycomb structure is less than 1.0 kg / cm ² , high strength cannot be expressed as compared with the porous honeycomb structure, while the compressive strength is 4.5 kg / cm ² . In the case of exceeding, the amount of the fine powder of the reinforced porous honeycomb structure is too large, and the “honeycomb” shape cannot be maintained.

Here, the measurement method of the following (1)-(3) is employ | adopted for compressive strength.
(1) A reinforced porous honeycomb structure, which is a columnar material having an appropriate length, is horizontally cut to a length of 1 cm in the longitudinal direction. This cut surface is defined as a horizontal cut surface. And it installs in a load cell in the state which can apply a load (stress) perpendicularly to this horizontal cut surface.

  (2) A load is applied vertically to the horizontal cut surface. The magnitude of the load can be measured with a load cell.

(3) The load applied immediately before the reinforced porous honeycomb structure is completely crushed is converted into a numerical value per 1 cm ^{2 of the} horizontal cut surface, and this is used as the compressive strength.

<Fine powder>
The fine powder described above may be spherical, rectangular parallelepiped, polygonal or those having pores or protrusions, but is preferably spherical. As the size of the fine powder of the present invention, it is preferable to use a micron order size. And when a fine powder is spherical, it is preferable that the average particle diameter exists in the range of 1-50 micrometers. The average particle diameter is particularly preferably 5 to 20 μm, which is considered to be less than the thickness of the honeycomb wall without greatly degrading the specific surface area of the reinforced porous honeycomb structure. When the average particle size is less than 1 μm, the effect of improving the strength may be reduced. When the average particle size is more than 50 μm, it becomes larger than the honeycomb wall, and fine powder protrudes from the wall surface. This is because the fluid processing capability may be reduced.

  In the reinforced porous honeycomb structure of the present invention, the size of the fine powder is an important factor for imparting strength to the porous honeycomb structure. The fine particles have a role of anchoring between molecules of the material of the porous honeycomb structure. Conventionally, a technique of adding a plurality of additives to enhance physical properties such as strength, rigidity, and toughness of a material is still employed. However, as the conventional additive, one having an average particle diameter of about 1 μm is considered to be effective. It is known that the additive having an average particle diameter of about 1 μm is often difficult to uniformly disperse due to aggregation.

  The fine powder imparting strength used in the present invention is not particularly limited. However, it is preferable to use, for example, graphite, carbon nanotube, carbon black, carbon nanofiber, silica fiber or the like used as a raw material for the composite material as a reinforcing material. Among them, it is particularly preferable to use graphite because of its low cost. As the fine powder of the present invention, a commercially available product can be used. For example, graphite (powder, average particle size: 5 to 20 μm) can be used.

  The amount of the fine powder is preferably in the range of 10 to 120% by weight, particularly preferably in the range of 20 to 100% by weight, based on the weight of the reinforced porous honeycomb structure. When the amount of the fine powder is less than 10% by weight, the reinforced porous honeycomb structure as a whole may not be able to exhibit sufficient strength. If the amount of fine powder exceeds 120% by weight, the reinforced porous honeycomb structure itself, particularly the honeycomb wall, may not be formed.

  In addition, the average particle diameter of the fine powder contained in the porous honeycomb structure can be measured, for example, by directly observing with a scanning electron microscope.

<Structure of reinforced porous honeycomb structure>
≪Average pore diameter≫
The average pore diameter in the reinforced porous honeycomb structure of the present invention is not particularly limited, but is preferably in the range of 5 to 150 μm, and particularly preferably in the range of 10 to 100 μm. When the reinforced porous honeycomb structure is used as a filter, the pressure loss tends to increase when the average pore diameter is smaller than 5 μm. When the average pore diameter exceeds 150 μm, the specific surface area of the reinforced porous honeycomb structure may be reduced. As shown in FIG. 1, the average pore diameter of the reinforced porous honeycomb structure is obtained by directly observing a cross section of the porous honeycomb structure with a scanning electron microscope (SEM), taking a photograph, and analyzing the SEM photograph. Can be measured.

≪Specific surface area≫
The specific surface area of the reinforced honeycomb structure of the present invention, but are not particularly limited, is preferably in the range of 100~1000m ² / g, in the range of 140~800m ² / g It is particularly preferred. This is because when the specific surface area is smaller than 100 m ² / g, the fluid processing capacity is lowered, and when the specific surface area is larger than 1000 m ² / g, the amount of fine powder added is small and the effect of improving the strength is lowered. The specific surface area of the reinforced porous honeycomb structure can be measured by performing nitrogen adsorption / desorption measurement at -196 ° C and applying a BET plot to the obtained adsorption / desorption isotherm for analysis.

Generally, as the average pore size of the porous honeycomb structure decreases, the specific surface area increases and the thickness of the honeycomb wall tends to decrease. Accordingly, the surface area to volume ratio is 1 × 10 ^{3 to} 5 × 10 ⁵ m ² / m ³ . However, in the reinforced porous honeycomb structure of the present invention, since the constituent material is more porous than the conventional porous honeycomb structure, the specific surface area does not change greatly even if the average pore diameter changes. Therefore, the surface area to volume ratio is 1 × 10 ⁷ to 1 × 10 ⁸ m ² / m ³ .

Thus, reinforcing honeycomb structure of the present invention is in the range average opening diameter of 5 to 150 m, and a specific surface area of ^{100~1000m 2 / g (1 × 10} 7 ~1 × 10 8 m 2 / It is particularly preferred that it is realized to be in the range of m ³ ). In addition, conditions for producing a porous honeycomb structure having an average pore diameter and a specific surface area within such a preferable range will be described later.

≪Shape≫
The shape of the reinforced porous honeycomb structure of the present invention is not particularly limited. For example, the cross-sectional shape is circular (perfect circle shape, elliptical shape), square shape (triangular shape, square shape, polygonal shape). What was cut into a columnar material such as In this case, it is preferable to cut out the columnar object so that the opening penetrates both sides of the columnar object in the longitudinal direction. The size of the columnar material is not particularly limited, but the length along the longitudinal direction is in the range of 0.5 to 30 cm, and the area of the cut surface horizontal in the longitudinal direction is large. It is preferably within the range of 0.5 to ²⁰ cm2.

≪pores≫
In the reinforced porous honeycomb structure of the present invention, the size of the pores formed in the honeycomb wall separating the openings is preferably 1 to 50 nm. In order to improve the reaction rate and the adsorption capacity, it is necessary to increase the surface area, that is, it is preferable to have many micropores having a diameter of 2 nm or less. On the other hand, since the molecular diffusion rate is very slow in the micropores, the presence of mesopores having a diameter of 2 to 50 nm is also important for efficiency. The pore size and pore size distribution can be calculated, for example, by measuring nitrogen adsorption / desorption at −196 ° C. and applying the Dollimore-Heal method to the obtained adsorption / desorption isotherm and analyzing.

<Sintered reinforced honeycomb structure>
The sintered reinforced honeycomb structure is obtained by firing the reinforced porous honeycomb structure described above. The compressive strength of the sintered reinforced honeycomb structure is higher than the compressive strength of the reinforced porous honeycomb structure before firing the sintered reinforced honeycomb structure.

  The sintered reinforced honeycomb structure is formed by firing the reinforced porous honeycomb structure at 800 to 1100 ° C., particularly preferably 900 to 1000 ° C. for 2 to 4 hours. The firing is preferably performed in a nitrogen atmosphere. When firing is performed at a temperature lower than 800 ° C., there is a problem that the strength is not improved sufficiently. When the firing is performed at a temperature exceeding 1100 ° C., the pores in the porous body disappear and the specific surface area decreases. A malfunction occurs.

  Firing is originally performed to add strength and shape retention to the material. When the reinforced porous honeycomb structure is heated to a high temperature that does not exceed the melting point of its components, each of the reinforced porous honeycomb structures is formed. The atoms in the particle begin to move actively, move along the surface of the particle, and gather at the contact point between the particles to form a neck. After that, as the temperature rises, the movement starts from the inside of the particles, and the particles are firmly bonded to each other. Then, the powder particles are bonded to each other, and at the same time, the voids between the particles are contracted to densify the reinforced porous honeycomb structure, thereby changing to a sintered reinforced honeycomb structure.

  Therefore, the sintered reinforced honeycomb structure has a higher compressive strength than the reinforced porous honeycomb structure. However, when the specific surface area of the reinforced porous honeycomb structure is compared with the specific surface area of the sintered reinforced honeycomb structure obtained by firing the reinforced porous honeycomb structure, the value of the former specific surface area is high.

<Compressive strength of sintered reinforced honeycomb structure>
For example, if the sintered reinforced honeycomb structure is produced by firing a reinforced porous honeycomb structure made of porous silica and fine powder, the reinforced sintering The compressive strength of the honeycomb structure is 4.90 to 6.05 kg / cm ² . This value is higher than the value of the compressive strength of the reinforced porous honeycomb structure composed of a porous honeycomb structure formed of porous silica and fine powder. A sintered honeycomb structure obtained by firing a porous honeycomb structure formed of porous silica in the same manner is about 1.71 kg / cm ² .

<Application>
The reinforced porous honeycomb structure and the sintered reinforced honeycomb structure of the present invention can be suitably used for a filter such as an air cleaner. When the reinforced porous honeycomb structure of the present invention is used as a filter of an air cleaner, a conventionally well-known general structure can be adopted for parts other than the filter. For example, in a housing having an appropriate shape provided with an air inlet and an air outlet, a dust collection filter, a blower (for example, a propeller-shaped fan, a device that compresses air with a pressure nozzle), etc. from the air inlet The passed air is sent to the filter, and the air that has passed through the filter is discharged from the air outlet to the outside of the air cleaner. As the filter, the above-described reinforced porous honeycomb structure cut out in a columnar shape can be used, for example, so that the air passage direction and the aperture are substantially parallel (that is, the columnar longitudinal direction is the air). Are preferably arranged so as to be substantially parallel to the passage direction of In addition, when a reinforced porous honeycomb structure is used, resistance to wind pressure and physical impact is increased, resulting in longer life.

<Method for producing reinforced porous honeycomb structure>
The reinforced porous honeycomb structure of the present invention is not particularly limited with respect to its manufacturing method, but is preferably manufactured using a unidirectional freeze gelation method. This is because the reinforced porous honeycomb structure can be manufactured efficiently.

≪One-way freeze gelation method≫
The unidirectional freeze gelation method is a technique in which the freeze gelation method and the unidirectional freeze method are combined. The freeze gelation method is a gelation method utilizing a freeze concentration effect. When the sol is frozen, phase separation occurs, and it is divided into two phases, a phase in which almost pure water is solidified and a phase in which colloidal particles are concentrated. The effect of accelerating gelation by this concentration is very large, and even at low temperatures, colloidal particles gathered in the gaps between ices are bonded and gelled. At this time, the ice serves as a template, and after thawing and drying, a sample that retains the shape when frozen is obtained. On the other hand, the unidirectional freezing method is a method for controlling the growth of ice. This is a method in which a metal oxide gel is frozen with directionality to grow ice in a columnar shape in one direction to form a plurality of ice columns, and particles are gathered in the gaps between the ice columns. The conventional unidirectional freezing method has been understood as a method for producing polygonal fibers of a metal oxide gel, and has been mainly applied to a hard wet gel having a structure aged for a long time. In the present invention, by combining the freezing gelation method and the unidirectional freezing method, the application range of the conventional unidirectional freezing method is extended to a sol or a wet gel immediately after gelation, thereby applying a reinforced porous honeycomb. A structure can be manufactured.

≪Manufacturing process≫
FIG. 2 is a flowchart schematically showing a preferred example of a method for producing a reinforced porous honeycomb structure. The manufacturing method of the reinforced porous honeycomb structure of the present invention includes the steps (a) to (i) shown in FIG. In FIG. 2, the step in parentheses is a step that is preferably included in the manufacturing method as necessary. The outline of each of the steps (a) to (i) described above is as follows.

  (A) Preparation of silica sol: A step of preparing a silica sol by mixing an ion exchange resin in an aqueous sodium silicate solution.

  (B) Removal of ion exchange resin (and pH adjustment): a step of removing the ion exchange resin from the silica sol and adjusting the pH of the silica sol as necessary.

(C) Fine powder dispersion: A process of producing a composite slurry by dispersing fine powder in silica sol.
(D) Production of silica wet gel: A step of producing a silica wet gel by gelling a composite slurry.

  (E) Unidirectional freezing (and room temperature aging): A step of freezing silica wet gel in one direction and aging at room temperature as necessary.

(F) (Low-temperature aging): A step of low-temperature aging the silica wet gel as necessary.
(G) Thawing (and high temperature aging): A step of thawing a frozen silica wet gel and subjecting it to high temperature aging as necessary.

(H) Solvent replacement: A step of replacing the solvent contained in the silica wet gel.
(I) Drying: A step of drying.

  Hereinafter, based on FIG. 2, each process of the manufacturing method of the reinforcement | strengthening porous honeycomb structure of this invention is demonstrated in detail.

≪ (a) Preparation of silica sol≫
In the production method of the present invention, first, a sodium silicate solution (water glass) is diluted with pure water as a raw material to obtain a sodium silicate aqueous solution. When the concentration of the aqueous sodium silicate solution is low, the solute constituting the honeycomb wall of the reinforced porous honeycomb structure finally produced is insufficient. Moreover, when the density | concentration of sodium silicate aqueous solution is too high, sodium silicate aqueous solution will gelatinize during the ion exchange in a next process. Therefore, the concentration of the aqueous sodium silicate solution is preferably adjusted to a range of 1.0 to 2.0M.

  Next, an ion exchange resin is mixed into the sodium silicate aqueous solution whose concentration is adjusted. This is performed to adjust the pH of the aqueous sodium silicate solution and to remove Na ions that are impurities. Here, Na ions are adsorbed on the surface of the silica particles and have a characteristic of changing the characteristics of the silica. The above pH adjustment and Na ion removal are necessary for producing a porous honeycomb structure having a regular average pore size.

  Specifically, an ion exchange resin is mixed in a sodium silicate aqueous solution accommodated in a container provided with a pH meter (if necessary, an ion meter) until a desired pH (for example, 2 to 3) is reached.

  The ion exchange resin is not particularly limited, but it is preferable to use a strongly acidic ion exchange resin because Na ions can be sufficiently removed while adjusting the pH. Examples of such ion exchange resins include Amberlite IR120B H AG manufactured by Organo Corporation.

  The amount of the ion exchange resin to be mixed in the aqueous sodium silicate solution is not particularly limited, but it is preferable that the volume is from half to almost the same amount as the volume of the aqueous sodium silicate solution. The amount of the ion exchange resin varies depending on the sodium silicate aqueous solution to be adjusted. However, if the amount of the ion exchange resin is small, there is a possibility that Na ions may not be sufficiently removed. This is because when the amount of the ion exchange resin is too large, the pH becomes too low and the time required for gelation in the subsequent step (d) tends to become long.

Through the above steps, the sodium silicate aqueous solution becomes silica sol, and the process proceeds to the next step.
<< (b) Removal of ion exchange resin (and pH adjustment) >>
The ion exchange resin mixed in the silica sol is removed. The ion exchange resin can be removed by using an appropriate sieve, for example. After removing the ion exchange resin, if necessary, an aqueous ammonia solution is added to the silica sol to adjust the pH to about 5.0 to 6.0. The addition of the aqueous ammonia solution is related to the control of the specific surface area and the control of the pore diameter of the reinforced porous honeycomb structure to be manufactured.

≪ (c) Fine powder dispersion≫
A fine powder is dispersed in silica sol. Suitable types and amounts of fine powder are as described above. The fine powder may be dispersed by stirring or using ultrasonic waves, but it is preferable to use ultrasonic waves. If the fine powder is dispersed by stirring, the fine powder distribution may become non-uniform or may precipitate without being dispersed. However, by dispersing the fine powder using ultrasonic waves, the silica sol This is because the fine powder can be uniformly distributed throughout.

  A composite slurry in which fine powder is uniformly dispersed in silica sol can be obtained. For dispersion using the ultrasonic waves, for example, an ultrasonic disperser (VC750, manufactured by SONICS & MATERIALS) can be used.

<< (d) Production of silica wet gel >>
The composite slurry is gelled to obtain a silica wet gel. In the gelation of the composite slurry, the composite slurry obtained in the step (c) is accommodated in a tubular container (cell) used in the step (e) described later, and the temperature is in the range of 20 to 40 ° C. It can be performed by standing for about 8 hours. A silica wet gel in which fine powder is dispersed can be obtained by the above-described gelation. Of course, after the gelation of the composite slurry is performed in another container, the obtained silica wet gel may be accommodated in a tube-shaped container used in step (e).

≪ (e) One-way freezing (and room temperature aging) ≫
The silica wet gel obtained in step (d) is unidirectionally frozen. In the unidirectional freezing of the silica wet gel, each of the above tubular cells is inserted into a refrigerant such as liquid nitrogen at a predetermined insertion speed using a constant speed motor or the like. By inserting the silica wet gel into the refrigerant, the ice in the portion inserted into the refrigerant grows in a columnar shape along the insertion direction.

  In order to obtain a “porous honeycomb-shaped product” after freezing, it is preferable to perform normal temperature aging. Room temperature aging means that the composite slurry is allowed to stand at room temperature from the gelation until the start of freezing. The room temperature aging time is preferably in the range of 0.5 to 12 hours. As the room temperature aging time becomes longer, the shape after freezing changes to a thin film shape, a flat fiber shape, a honeycomb shape, and a polygonal fiber shape (see Patent Document 1 described above). Such a shape change is considered to be based on the ease of movement of the silica particles during freezing. As the normal temperature aging time becomes longer, gelation proceeds and the movement of silica particles is inhibited. When the room temperature aging time is short, the silica particles are relatively easy to move, so that the silica particles are easily aggregated to form a continuously connected thin film or flat fiber. Since the silica particles hardly move before and after the gelation, the silica particles are frozen while remaining around the icicle and become a honeycomb. As the gelation further proceeds, it is divided into fibers by the growth of icicles.

  Moreover, since the diameter of the ice pillar used as a template can be changed by changing freezing conditions, the obtained porous honeycomb structure can be formed to have a desired average pore diameter. Preferable freezing conditions are 0.5 to 70 cm / h at −196 to −10 ° C., more preferably 1 to 20 cm / h at −196 to −20 ° C. As described above, the unidirectional freeze gelation method is a kind of wet synthesis method, and therefore can be used in combination with the excellent nanostructure control technology of the sol-gel method, and a porous material is produced using this technology. In this case, the nanopore characteristics (average pore diameter, specific surface area, pore volume) of the finally obtained honeycomb structure can be precisely controlled by the raw material composition and aging conditions.

≪ (f) Low temperature aging≫
In the method for manufacturing a porous honeycomb structure of the present invention, it is preferable to perform low-temperature aging for a predetermined time in a frozen state of the silica wet gel after the step (e). By performing low-temperature aging, it is possible to reinforce the structure of the silica wet gel in a state where ice is a template. The low temperature aging is preferably performed at a relatively low temperature of −196 to −20 ° C. for 1 to 3 hours.

≪ (g) Defrosting (and high temperature aging) ≫
After the step (e) or low temperature aging, the silica wet gel is thawed by placing the tubular cell containing the silica wet gel in a thermostatic bath at 50 ° C., for example. In the step (b) described above, when the aqueous ammonia solution is not added, the specific surface area can be controlled by performing high temperature aging by immersing the molded silica wet gel in the aqueous ammonia solution for a certain time after thawing. High temperature aging is preferably performed at a temperature of 30 to 90 ° C. for 1 to 3 hours.

≪ (h) Solvent substitution≫
After thawing or high temperature aging, the solvent is replaced. Although it does not restrict | limit especially as a solvent used for solvent substitution, For example, t-butanol is used. The t-butanol is used for the reasons (1) and (2). (1) t-butanol has a small density change at the time of liquid-solid transfer (Δρ = −3.4 × 10 ⁻⁴ g / cm ^{3 at} 299 K), and has a low possibility of breaking the sample during solidification. (2) t-butanol has a large vapor pressure (the vapor pressure of t-butanol at 0 ° C. is p ₀ = 821 Pa, water is 61 Pa), and the drying rate is large.

  Specifically, the silica wet gel is removed from the tubular cell, and immersed in, for example, t-butanol having a volume of 5 times or more of the silica wet gel to stop high-temperature aging, and for 2 to 4 days, Change t-butanol three or more times. By washing with t-butanol, a trace amount of water contained in the silica wet gel is replaced with t-butanol.

≪ (i) Drying≫
It is preferable to dry after solvent substitution. The drying method is not particularly limited and can be dried by a conventionally known appropriate method, but it is difficult to cause cracking of the reinforced porous honeycomb structure or breakage of the pores at the time of drying. It is preferable to carry out drying by freeze-drying. When lyophilization is performed, if the temperature is high, the solvent does not freeze due to a decrease in the freezing point of water contained in a very small amount, and if the temperature is too low, the drying speed is slowed down, so drying is performed in a temperature range of −10 to −30 ° C. It is preferable.

  In addition, it is possible to manufacture a sintering reinforcement | strengthening honeycomb structure by baking the reinforcement | strengthening porous honeycomb structure produced at the above process at 800-1100 degreeC as mentioned above.

[Example]
EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to these.

<Example 1>
A description will be given based on each step shown in FIG.

≪ (a) Preparation of silica sol≫
A 54% sodium silicate solution was diluted with deionized distilled water to obtain 25 mL of an aqueous sodium silicate solution having a SiO ₂ concentration of 1.9 mol / L. A silica sol was obtained by adding 29 mL of H ⁺ type strongly acidic ion exchange resin to the aqueous sodium silicate solution while stirring and adjusting the pH of the aqueous sodium silicate solution to around 2.8.

≪ (b) Removal of ion exchange resin≫
The ion exchange resin was removed from the silica sol using a sieve.

≪ (c) Fine powder dispersion≫
20 parts by weight of graphite powder (manufactured by Wako Pure Chemical Industries, Ltd., average particle size: 10 μm) was added to 100 parts by weight of SiO ₂ contained in the silica sol, and the fine powder was dispersed in the silica sol using an ultrasonic disperser. A composite slurry was made.

<< (d) Production of silica wet gel >>
A polypropylene tube having an inner diameter of 1.3 cm was prepared, and about 1 cm of glass beads were packed in the bottom of the tube. The composite slurry was poured into the tube so as to be 5 cm, covered, and allowed to stand at 30 ° C. The composite slurry became a uniform silica wet gel after 2 hours.

≪ (e) One-way freezing (and room temperature aging) ≫
After performing the normal temperature aging at 30 ° C. for 1 hour after becoming the silica wet gel, the constant speed motor was set so that the tube filled with the silica wet gel was inserted at an insertion speed of 2 cm / h. The tube filled with silica wet gel was inserted into a low temperature ethanol bath controlled to be kept at -20 ° C. In addition, the low temperature aging of the process (f) was abbreviate | omitted.

≪ (g) Defrosting≫
After the silica wet gel was completely frozen, the tube filled with the silica wet gel was placed in a thermostatic bath at 50 ° C. to thaw the silica wet gel.

≪ (h) Solvent substitution≫
After thawing, the silica wet gel was removed from the tube and immersed in t-butanol. Thereafter, washing with t-butanol was carried out three times or more for 3 days to completely replace the water contained in the silica wet gel with t-butanol.

≪ (i) Drying≫
A silica wet gel in which water was sufficiently substituted with t-butanol was freeze-dried at −10 ° C. to obtain a reinforced porous honeycomb structure of the present invention.

<Example 2>
In “Step (c) Fine powder dispersion” in Example 1, 40 parts by weight of graphite powder (manufactured by Wako Pure Chemical Industries, Ltd., average particle size: 10 μm) is added to 100 parts by weight of SiO ₂ contained in silica sol. A reinforced porous honeycomb structure was obtained in the same manner as in Example 1 except that a composite slurry in which fine powder was dispersed in silica sol was produced using a sonic disperser.

<Example 3>
In the “step (c) fine powder dispersion” in Example 1, after removing the ion exchange resin from the silica sol, SiO ₂ containing graphite powder (manufactured by Wako Pure Chemical Industries, Ltd., average particle size: 10 μm) in the silica sol. A reinforced porous honeycomb structure was obtained in the same manner as in Example 1 except that 60 parts by weight was added to 100 parts and a composite slurry in which fine powder was dispersed in silica sol using an ultrasonic disperser was produced. .

<Example 4>
In the “step (c) fine powder dispersion” in Example 1, after removing the ion exchange resin from the silica sol, SiO ₂ containing graphite powder (manufactured by Wako Pure Chemical Industries, Ltd., average particle size: 10 μm) in the silica sol. A reinforced porous honeycomb structure was obtained in the same manner as in Example 1 except that 80 parts by weight with respect to 100 parts by weight and a composite slurry in which fine powder was dispersed in silica sol using an ultrasonic disperser were prepared. .

<Example 5>
In the “step (c) fine powder dispersion” in Example 1, after removing the ion exchange resin from the silica sol, SiO ₂ containing graphite powder (manufactured by Wako Pure Chemical Industries, Ltd., average particle size: 10 μm) in the silica sol. A reinforced porous honeycomb structure was obtained in the same manner as in Example 1 except that 100 parts by weight was added to 100 parts and a composite slurry was prepared by dispersing fine powder in silica sol using an ultrasonic disperser. .

<Comparative Example 1>
A porous honeycomb structure was obtained in the same manner as in Example 1 except that the “step (c) fine powder dispersion” in Example 1 was not performed.

< Reference Examples 1-5 >
In Reference Examples 1 to 5, the reinforced porous honeycomb structures produced in Examples 1 to 5 were fired at 1000 ° C. for 4 hours in a nitrogen atmosphere. This obtained the sintering reinforcement | strengthening honeycomb structure in the reference examples 1-5 .

<Comparative example 2>
The porous honeycomb structure produced in Comparative Example 1 was fired at 1000 ° C. for 4 hours in a nitrogen atmosphere to obtain a sintered honeycomb structure.

≪Evaluation method≫
Regarding the reinforced porous honeycomb structures of Examples 1 to 5 , the sintered reinforced honeycomb structures of Reference Examples 1 to 5 , the porous honeycomb structure of Comparative Example 1, and the sintered honeycomb structure of Comparative Example 2, respectively. What was cut | disconnected horizontally so that the length of the longitudinal direction might be set to 1 cm was prepared, and it installed in the load cell. Then, by applying a load to the horizontal cut surface from the vertical direction, the load when completely broken was measured, and the compressive strength was calculated from the value. In addition, since the reference example 5 did not collapse even when a maximum load was applied, the compressive strength value was not calculated, but the sintered strengthened honeycomb structure has the highest strength.

  Moreover, the average pore diameter, specific surface area, and pore distribution of the reinforced porous honeycomb structures of Examples 1 to 5 and the porous honeycomb structure of Comparative Example 1 were also evaluated. The specific surface area and the pore distribution were determined by performing nitrogen adsorption / desorption measurement at -196 ° C. using BELSORP-mini manufactured by Nippon Bell Co., Ltd. and applying the BET plot to the obtained adsorption / desorption isotherm and analyzing. The average pore diameter was determined by analysis using SEM photographs.

The specific surface areas of the sintered reinforced honeycomb structures of Reference Examples 1 to 5 were also evaluated. The specific surface area was determined by performing nitrogen adsorption / desorption measurement at -196 ° C. using BELSORP-mini manufactured by Nippon Bell Co., Ltd., and applying the BET plot to the obtained adsorption / desorption isotherm and analyzing it.

≪Evaluation results≫
FIG. 3 shows the correlation (diamond mark) between the weight ratio of graphite / porous honeycomb structure and the compressive strength in the reinforced porous honeycomb structures of Examples 1 to 5, and the reinforced porous structures of Reference Examples 1 to 4 The correlation (rectangular mark) between the weight ratio of graphite / porous honeycomb structure and the compressive strength in the honeycomb structure is shown. The horizontal axis in FIG. 3 represents the weight ratio of graphite to the weight of the porous honeycomb structure (graphite weight / porous honeycomb structure weight), and the vertical axis represents the compressive strength. The compressive strength of the porous honeycomb structure of Comparative Example 1 corresponds to the value of the rhombus mark when the horizontal axis is zero. The compressive strength of the sintered honeycomb structure of Comparative Example 2 corresponds to the value of the rectangular mark when the horizontal axis is zero.

  FIG. 4 shows the correlation between the weight ratio of the graphite / porous honeycomb structure and the specific surface area in the reinforced porous honeycomb structures of Examples 1 to 5. The horizontal axis of FIG. 4 represents the weight ratio of graphite to the weight of the porous honeycomb structure (graphite weight / porous honeycomb structure weight), and the vertical axis represents the specific surface area. The specific surface area of the porous honeycomb structure of Comparative Example 1 corresponds to the value when the horizontal axis is zero.

FIG. 5 shows a correlation between the weight ratio of the graphite / porous honeycomb structure and the specific surface area in the reinforced porous honeycomb structures of Reference Examples 1 to 5 . The horizontal axis of FIG. 5 represents the weight ratio of graphite to the weight of the porous honeycomb structure (graphite weight / porous honeycomb structure weight), and the vertical axis represents the specific surface area.

As shown in FIG. 3, it was confirmed that the compressive strength of the reinforced porous honeycomb structures of Examples 1 to 5 was improved in proportion to the increase in the weight ratio of graphite. In FIG. 3, when the reinforced porous honeycomb structure of Example 1 and the porous honeycomb structure of Comparative Example 1 were compared, Example 1 showed a higher compressive strength. Moreover, as shown in FIG. 4, it was confirmed that the reinforced porous honeycomb structures of Examples 1 to 5 all have a specific surface area in the range of 100 to 1000 m ² / g. The reinforced porous honeycomb structures of Examples 1 to 5 all had an average pore diameter of 60 μm and an average pore diameter of 1.72 to 2.51 nm, as analyzed by SEM photographs.

  From the above, it was shown that the reinforced porous honeycomb structure of the present invention has a higher compressive strength and a larger specific surface area than the conventional porous honeycomb structure.

Further, as shown in FIG. 3, when the compression strengths of the sintered reinforced honeycomb structures in Reference Examples 1 to 4 were compared with the compressive strengths of the reinforced porous honeycomb structures in Examples 1 to 4, firing was performed. Thus, it was found that the reinforced porous honeycomb structure becomes a sintered reinforced honeycomb structure having higher compressive strength. However, when FIG. 4 and FIG. 5 are compared, the sintered reinforced honeycomb structures of Reference Examples 1 to 5 have a specific surface area of 40 m ² / g or less, and the reinforced porous honeycomb structures of Examples 1 to 5 are the same. It was suggested that the specific surface area decreases by firing.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

4 is a SEM photograph showing a part of a preferred example of the porous honeycomb structure of the present invention, magnified 600 times. It is a flowchart which shows each process in the preferable manufacturing method of the porous honeycomb structure of this invention. Correlation (diamond mark) between the weight ratio of graphite / porous honeycomb structure and compressive strength in the reinforced porous honeycomb structures of Examples 1 to 5 and the reinforced porous honeycomb structures of Reference Examples 1 to 4 FIG. 4 is a diagram showing a correlation (rectangular mark) between the weight ratio of graphite / porous honeycomb structure and the compressive strength. It is a figure which shows the correlation with the weight ratio and specific surface area of a graphite / porous honeycomb structure in the reinforcement | strengthening porous honeycomb structure of Examples 1-5. It is a figure which shows the correlation with the weight ratio and specific surface area of a graphite / porous honeycomb structure in the reinforced porous honeycomb structure of Reference Examples 1-5 .

Claims (6)

It is composed of a porous honeycomb structure made of porous silica and fine powder containing graphite ,
The fine powder is dispersed in the porous honeycomb structure,
The compressive strength is 1.0 to 4.5 kg / cm ² ;
A reinforced porous honeycomb structure having a specific surface area of 100 to 1000 m ² / g . The reinforced porous honeycomb structure according to claim 1, wherein an average particle diameter of the fine powder is 1 to 50 µm. The average opening size of 5 to 150 m, reinforced porous honeycomb structure according to claim 1 or 2. The reinforced porous honeycomb structure according to any one of claims 1 to 3 , wherein the fine powder is 10 to 120% by weight of the porous honeycomb structure. The reinforced porous honeycomb structure according to any one of claims 1 to 4, which is produced by gelling silica sol and molding the silica sol by a unidirectional freeze gelation method. The reinforced porous honeycomb structure according to claim 5 , wherein the fine powder is produced by dispersing the fine powder in the silica sol using ultrasonic waves.