JP6192090B2 - Method for producing porous body - Google Patents

Description

  The present invention is a useful method for producing a filter for decomposing volatile organic gas containing a porous material used when decomposing a volatile organic substance contained in a gas discharged from an automobile or a chemical factory by a combustion catalyst method. And a volatile organic gas decomposition filter.

  Gases emitted from automobiles and chemical factories contain various volatile organic compounds (VOC) such as toluene, ethyl acetate, isopropanol, and so on. Causes photochemical oxidants. Many of these VOCs have their emissions regulated by the Air Pollution Control Act, and various efforts to reduce VOC emissions are being made.

  Various methods such as a combustion method (direct combustion method, catalytic combustion method), an adsorption method, a plasma decomposition method, and a photocatalytic method are known as methods for decomposing harmful components in gas. Of these methods, the combustion method is basically a method of decomposing and removing harmful components by heating and burning a target gas.

  This combustion method is roughly classified into a direct combustion method and a catalytic combustion method. The direct combustion method directly heats and decomposes a target gas component in a high temperature atmosphere of about 800 ° C. or higher. However, in this method, there is a concern that not only the apparatus for decomposing harmful components is enlarged, but also nitrogen compounds are generated.

  On the other hand, in the catalytic combustion method, by using a catalyst, decomposition proceeds even at relatively low temperature heating (for example, 500 ° C. or less), so that a nitrogen compound is not generated and the direct combustion method is performed. There is an advantage that it becomes smaller than the device. There is also an advantage that the replacement frequency of the catalyst in the catalytic combustion method is lower than the replacement frequency of the adsorbent in the adsorption method using the adsorbent.

Catalysts used in conventional catalytic combustion methods basically use expensive noble metal elements, and these elements are generally supported on a support mainly composed of zeolite or zirconia. . As such a technique, for example, Patent Document 1 discloses that “a metal oxide containing at least one platinum group element at the front stage and a mixture of a metal oxide part containing at least one platinum group element and a zeolite at the rear stage. The organic compound combustion removal catalyst arranged in the above.

  However, since the catalyst as described above contains an expensive metal element, the cost becomes high and it is difficult to reuse the catalyst after using the catalyst. Further, discarding the used catalyst as it is after being used as a catalyst has an adverse effect on the environment.

  As a method of treating a gas using a catalyst, a method using a photocatalyst (photocatalytic method) is also known. This method uses a metal oxide having a photocatalytic action to treat a gas without heating. As a photocatalyst used in such a technique, for example, Patent Document 2 discloses “a photocatalytic apatite composition comprising a photocatalytic apatite in which a metal oxide having a photocatalytic action and a metal ion having antibacterial properties are incorporated in an apatite crystal structure. Is disclosed.

  On the other hand, in consideration of the influence on the environment, a technique using hydroxyapatite as a catalyst has also been proposed. As such a technique, for example, Patent Document 3 proposes “a method for decomposing and removing trichloroethylene gas or tetrachloroethylene gas in which trichloroethylene gas or tetrachloroethylene gas is contacted with hydroxyapatite in a heated state”. This technique is basically a technique for removing organic chlorine compounds such as trichlorethylene and tetrachloroethylene, and its removal effect on VOC has not been confirmed.

  In addition, as a technique related to hydroxyapatite, it has been reported that phosphorus resources recovered from sewage sludge incineration ash are effectively used (for example, Non-Patent Document 1). In this document, it is disclosed that sewage sludge incineration ash contains hydroxyapatite and calcium hydrogen phosphate, and effective reuse of these substances is expected.

  By the way, when processing a gas using a catalyst, there exists a problem that handling with a powder is difficult as a property of the catalyst to be used. Further, the contact efficiency with the processing gas is poor, and there is a problem in the gas purification ability. For these reasons, realization of a catalyst formed into a porous body is desired. However, the actual situation is that a porous body capable of effectively decomposing and removing VOC has not been realized.

  On the other hand, as a method for producing a ceramic fired body, a so-called gel casting molding method is known. In this method, ceramic particles are dispersed in an organic monomer (polymerizable resin) aqueous solution to form a slurry, the slurry is poured into a mold, and a polymerization reaction of the organic monomer proceeds to form a wet polymer gel-like molded body containing ceramic particles. Is the way to get. And a ceramic fired body can be obtained by drying and firing this molded body.

  As a technique applying such a gel casting molding method, for example, Patent Document 4 discloses that “a slurry in which a ceramic, a monomer, a crosslinking agent, and a metal source are dissolved in an ion, chelate, and micelle state is mixed. A method for producing a metal-encapsulated conductive ceramic is proposed by placing in a mold, adding a disclosure agent and a catalyst to the mold, taking out the molded product from the mold, drying, and performing reduction firing. .

Japanese Patent Laid-Open No. 2001-219058 JP 2007-260587 A Japanese Examined Patent Publication No. 6-59386 JP 2007-153646 A

Gifu Prefectural Institute of Public Health and Environment No. 18 (2010) pp. 13-17

  The present invention has been made paying attention to the above-mentioned circumstances, and its purpose is to apply a gel casting molding method, and to apply a porous body that can be applied as a catalyst capable of efficiently decomposing a gas containing a volatile organic substance. It is an object of the present invention to provide a useful method for producing a volatile organic gas decomposition filter using such a porous body.

  The method for producing a porous body of the present invention that has achieved the above object includes adding a hydroxyapatite powder, a dispersant, water, a crosslinking agent, a polymerizable resin, a polymerization initiator, and an anionic surfactant to a foam. It is characterized in that a porous body is produced by preparing a slurry and drying and firing.

  Preferred examples of the hydroxyapatite powder used in the method of the present invention include those having a molar ratio of Ca to P (Ca / P) of 1.67 to 2.50. Examples of the dispersant used in the present invention include polycarboxylic acid surfactants, polyvinyl alcohol as a crosslinking agent, and water-soluble epoxy resin as a polymerizable resin. Furthermore, as a polymerization initiator used in the present invention, triethyltetramine is preferable.

  The porous body obtained by the method of the present invention is useful as a material for a filter for decomposing volatile organic gas that can effectively decompose volatile organic gas. Moreover, when using as a filter for volatile organic gas decomposition | disassembly, it is preferable that the average porosity of a porous body is 65-95 volume%.

  In the present invention, a foamed slurry is prepared by adding a powder, a dispersant, water, a crosslinking agent, a polymerizable resin, a polymerization initiator and an anionic surfactant, and then dried and fired to obtain a porous body. Since it was manufactured, a porous body useful as a volatile organic gas decomposition filter can be obtained.

4 is a drawing-substituting micrograph showing a pore observation image by an optical microscope in each sample obtained in Example 1. FIG. 3 is a drawing-substituting micrograph showing a pore observation image by X-ray CT scan in each sample obtained in Example 1. FIG. It is a graph which shows the distribution measurement result of a pore diameter using the pore observation image shown in FIG. It is a graph which shows the relationship between the gas flow rate (liter / min) and differential pressure (DELTA) P (kPa) in each sample AC obtained in Example 1. FIG. It is a graph which shows the relationship between the flow velocity (gas flow velocity v: m / sec) of the gas which flowed to each sample AC, and a pressure drop (pressure drop amount per sample length: (DELTA) P / L). And Darcy permeability K ₁ and non-Darcy permeability K ₂ determined in samples A through C, is a graph showing the relationship between the porosity. It is a drawing-substituting micrograph showing a pore observation image of a porous body (test No. 6 equivalent product) produced using an anionic surfactant. It is a drawing-substituting micrograph showing a pore observation image of a porous body produced using an amphoteric surfactant. It is a drawing-substituting micrograph showing a pore observation image of a porous body produced using a nonionic surfactant.

  The present inventors have been further researching on a method capable of efficiently decomposing VOC by a catalytic combustion method. As part of the research, it has been found that if hydroxyapatite is used as a catalyst used in the catalytic combustion method, VOC can be efficiently decomposed by the catalytic combustion method, and the same applicant filed earlier (Japanese Patent Application No. 2012-055125). issue). This technique shows that VOC can be efficiently decomposed by using hydroxyapatite as a catalyst used in the catalytic combustion method.

  The present inventors have further studied a method for obtaining a porous material useful as a material for a filter for decomposing volatile organic gas that can effectively decompose volatile organic gas even after the above-described technology is completed. It was.

  The characteristics required of a porous body as a material for a volatile organic gas decomposition filter are required to have as high a porosity as possible. In addition, when producing a porous body using a hydroxyapatite powder as a raw material and applying a gel cast molding method, the amount of the hydroxyapatite powder added to the slurry is increased as much as possible so that it is uniformly dispersed in the slurry. There is a need. In order to produce a porous body, it is necessary to generate a large number of bubbles in the slurry.

  Under such an idea, manufacturing conditions for manufacturing a porous body were examined from various angles. As a result, when preparing a slurry using a hydroxyapatite powder, water (dispersion medium), a crosslinking agent, a polymerizable resin, and a polymerization initiator as basic components, a dispersant is added to appropriately disperse the hydroxyapatite powder. The present inventors have found that a porous body capable of exhibiting desired properties can be produced by adding a foamed slurry by adding an anionic surfactant and foaming, thereby completing the present invention.

  The raw material components used in the present invention are a hydroxyapatite powder, a dispersant, a crosslinking agent, a polymerizable resin, a polymerization initiator, and an anionic surfactant, and these are added to water to form a slurry.

Hydroxyapatite powder is a complex of hydroxyapatite and calcium hydroxide. This hydroxyapatite powder is a compound represented by the general formula [Ca ₁₀ (HPO ₄ ) ₆ (OH) ₂ ]. It is known that this hydroxyapatite powder is produced in various ways with a molar ratio of Ca and P (Ca / P) in the range of 1.55 to 2.5 depending on the conditions such as the production method. .

  The molar ratio of Ca to P (Ca / P) in the hydroxyapatite powder is about 1.67 stoichiometrically. Hydroxyapatite preferable as a catalyst used for decomposing VOC by the catalytic combustion method has a molar ratio of Ca to P (Ca / P) of 1.67 to 2.50. The molar ratio (Ca / P) is more preferably 1.71 to 2.50. However, when the molar ratio (Ca / P) exceeds 2.50, the crystal structure as the hydroxyapatite cannot be maintained, and the function as the catalyst is hardly exhibited.

  The hydroxyapatite powder preferably has an average particle size of about 100 nm or less in consideration of dispersibility in the slurry. Further, the mixing ratio (volume ratio) of the hydroxyapatite powder in the slurry is preferably about 5.0 to 50% by volume, more preferably about 25 to 45% by volume with respect to the whole slurry. In order to further refine the hydroxyapatite powder, a method of pulverizing with a ball mill can be used.

  The dispersant used in the present invention has good dispersion in the slurry of the hydroxyapatite powder. As such a dispersant, a polycarboxylic acid surfactant is preferably used. Specifically, “Serena D-305” (trade name: manufactured by Chukyo Yushi Co., Ltd.) can be mentioned. The amount of the dispersing agent is preferably about 0.5 to 20 parts by mass (more preferably about 2.0 to 10 parts by mass) with respect to 100 parts by mass of the hydroxyapatite powder.

  The crosslinking agent used in the present invention is for crosslinking a polymerizable resin. For example, polyvinyl alcohol is preferable, and specifically, “polyvinyl alcohol (degree of polymerization: about 500)” (trade name: Japanese) Kojun Yakuhin Co., Ltd.). The amount of the crosslinking agent is preferably about 0.05 to 2.0 parts by mass with respect to 100 parts by mass of the polymerizable resin (more preferably about 0.2 to 1.0 part by mass).

  The polymerizable resin forms a porous skeleton, and a water-soluble epoxy resin is preferable. The term “water-soluble” means “water dispersibility”. Specific examples of such water-soluble epoxy resins include “Deconal EX-1410” (trade name: manufactured by Nagase ChemteX Corporation). It is preferable that the compounding quantity of polymeric resin is about 0.5-20 volume% with respect to the whole slurry (more preferably about 2.0-10 volume%).

  The polymerization initiator is for initiating polymerization of the polymerizable resin, and examples thereof include triethyltetramine (TETA).

  In the present invention, it is necessary to prepare a foamy slurry by generating bubbles in the slurry. For this purpose, it is necessary to add an anionic surfactant to the slurry. By using this anionic surfactant, a large number of bubbles having a large diameter can be generated in the slurry to form a foamy slurry. As a result, the average porosity and pore diameter of the finally obtained porous body can be increased. On the other hand, when a nonionic surfactant or an amphoteric surfactant is used, bubbles are not sufficiently generated, and a porous body with an increased average porosity or pore diameter cannot be obtained (Examples described later). 3).

  Specific examples of the anionic surfactant used in the present invention include “Latemul AD-25” (trade name: manufactured by Kao Corporation). It is preferable that the compounding quantity of an anionic surfactant is about 0.2-5.0 mass% with respect to the whole slurry (more preferably about 0.5-3.0 mass%).

  In addition, the order of addition of the compounding raw materials when preparing the foamy slurry is not limited at all, but in short, in order to complete the solidification (polymerization) of the polymerizable resin, bubbles are generated in the slurry, What is necessary is just to adjust the addition time of an anionic surfactant. In addition, before adding the anionic surfactant, the slurry may be deaerated from the viewpoint of removing the gas existing in the raw material powder from the slurry (powder dispersibility becomes good). preferable.

  A porous body can be produced by drying and firing the foamy slurry prepared as described above. What is necessary is just to follow a conventional method about the drying conditions and baking conditions at this time. The porous body thus obtained is useful as a material for a volatile organic gas decomposition filter that can effectively decompose volatile organic gas. An average porosity of the porous body is 65 to 95% by volume, which is optimal as a material for a volatile organic gas decomposition filter.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Example 1
Using a hydroxyapatite powder having a Ca / P molar ratio of 1.67 (“HAP-100”, trade name: Taihei Chemical Sangyo Co., Ltd.), a slurry for gel casting was prepared using distilled water as a dispersion medium. . At this time, the polymerizable monomer (gelling agent) was a water-soluble epoxy resin monomer (“Deconal EX-1410”, trade name: manufactured by Nagase ChemteX Corporation), a crosslinking agent with a polyvinyl alcohol having an average molecular weight of about 500 (“polyvinyl alcohol ( The degree of polymerization was about 500) "trade name: Wako Pure Chemical Industries, Ltd.), and triethyltetramine (TETA) was used as the polymerization initiator. As the dispersant, a polycarboxylic acid surfactant (“Celna D-305”, trade name: manufactured by Chukyo Yushi Co., Ltd.) was used. The mixing ratio (mass% and volume%) of the raw material components at this time is shown in Table 1 below.

  A polycarboxylic acid surfactant (dispersant) was dissolved in distilled water, and then a hydroxyapatite powder was added and kneaded by a ball mill. In preparing a 1 kg slurry, a 5 liter diameter zirconia ball (613 g) having the same mass as a hydroxyapatite powder and 5 zirconia balls having a diameter of 25 mm were charged in a 1 liter container made of polystyrene resin. Was kneaded at 60 rpm. The hydroxyapatite powder is charged in four times, the first time being 1/2 of the total mass, the second time being 1/4 of the total mass, and the third time being 1/8 of the total mass. The amount was charged. After each amount of the hydroxyapatite powder was charged, the next amount was charged after ball mill kneading for 30 minutes. Further, after the entire amount of the hydroxyapatite powder was charged, the kneading was performed for 12 hours. Next, after adding polyvinyl alcohol and kneading for 1 hour, a polymerizable monomer (gelator) was added, and stirring was further performed for 30 minutes.

  After deaeration from the resulting slurry with a self-revolving stirrer, 296.4 g was collected, an anionic surfactant ("Latemul AD-25", trade name: manufactured by Kao Corporation), and a polymerization initiator 3.56 g of triethyltetramine (TETA) was added and stirred with a hand mixer to generate bubbles in the slurry to prepare a bubble-containing slurry (foam slurry). At this time, three types of bubble-containing slurries were prepared by changing the amount of the anionic surfactant added to 0.3 g (sample A) and 1.0 g (sample B) 0.7 g (sample C).

  The foam-containing slurry was poured into a vinyl chloride mold (cylindrical shape with an inner diameter of 25 mmφ × length of 20 mm), allowed to stand at 40 ° C. for 24 hours, and then taken out from the mold after confirming the completion of solidification (polymerization). . The obtained molded body was dried in a constant temperature and humidity chamber while keeping the temperature constant at 25 ° C. and decreasing the humidity from 90% to 50% by 10% every 12 hours. Thereafter, the dried molded body was fired at 1000 ° C. in an air atmosphere to obtain a porous body.

  The obtained porous body (samples A to C) was cut and processed into a cylindrical shape (length 20 mm) having a diameter of 19 mmφ to obtain a sample for characteristic evaluation. Using this sample, the porosity was measured and the pore shape was observed by the following method, and the gas permeability was measured.

(Measurement of porosity and average pore diameter)
The pore shape was observed and the pore diameter distribution was measured with an image taken using an optical microscope and an X-ray CT scanning apparatus “inspexIO SMX-90CT” (trade name: manufactured by Shimadzu Corporation). At this time, the image resolution was 5 μm / pix, the pores having a diameter of 20 μm or more were measured, and the porosity and the average pore diameter were calculated. The average diameter of the pores is the one having a small pore size (area), and the pore diameter when the number of pores corresponds to 50% of the whole (area standard integrated frequency is 50%) when the number of pores is counted. (Median diameter: hereinafter sometimes referred to as “D50”).

(Measurement of gas permeability)
The flow rate of gas (high purity nitrogen) was changed by a mass flow controller, and the differential pressure when flowing in the length direction (20 mm) of the sample was measured. The sample shape and measurement items are shown in Table 2 below.

  Pore observation images by an optical microscope in each sample are shown in FIGS. Moreover, the pore observation image by X-ray CT scan is shown to Fig.2 (a)-(c) [(a)-(c) respond | corresponds to sample AC respectively].

  As is clear from this result, a clear difference in pore structure can be confirmed for each sample. FIG. 3 shows the results of pore size distribution measurement using the pore observation image shown in FIG. Moreover, in each sample AC, the value of the average diameter (pore diameter: D50) of the porosity obtained from the porosity and the pore diameter distribution measurement is shown in Table 3 below together with the porosity (volume%).

  From these results, it can be considered as follows. Sample A shows a moderate porosity and pore diameter (D50), and shows a slightly wider pore diameter distribution than other samples B and C. Sample B has the largest porosity and pore diameter, and sample C has the smallest. That is, the porosity depends on the amount of bubbles introduced in the slurry preparation stage, and by controlling the amount of bubbles by increasing / decreasing the amount of anionic surfactant added and stirring time, samples with different porosity are used. (Porous body). In the gelation process of the slurry, the bubble diameter increases as a plurality of bubbles gather and become one. Since the higher the porosity, the easier the bubbles are collected, it is considered that Sample B has the largest pore diameter (D50).

FIG. 4 shows the relationship between the gas flow rate (liters / minute) and the differential pressure ΔP (kPa) in each of the samples A to C with respect to the gas permeability measurement results. It can be seen that different relationships are obtained for the respective samples A to C. It can be seen that the sample B having the highest porosity has the highest gas flow and the sample C is less likely to flow. From this result, it is clear that the relationship between the gas flow rate and the differential pressure is not linear. That is, it is predicted that the gas permeability (K ₁ ) in the porous body cannot be approximated by the Darcy law (Darcy law) expressed by the following equation (1). The Darcy rule is described in detail in “Materials Chemistry of Powder” Yasuo Arai (Author), Baifukan (published September 10, 1987) P184-188.
ΔP = (μL / K ₁ ) v (1)

Therefore, the above equation (1) was corrected, and the properties of the porous body were evaluated based on the gas permeability (K ₂ ) represented by the following equation (2).
(ΔP / L) = (μ / K ₁ ) v + (ρ / K ₂ ) v ² (2)

In the above equation (2), the first term [(μ / K ₁ ) v] on the right side is a Darcy term, which depends on the viscosity of the fluid and the size of the flow path. The second term on the right side ((ρ / K ₂ ) v ² : hereinafter referred to as “non-Darcy term”) depends on the shape resistance of the flow path, and as the Reynolds number increases (that is, the gas flow) As it approaches turbulence, the effect becomes stronger. The non-Darcy term is described in “Jour HTST”, vol. 39, no. 154, 47-48 (Journal of Heat Transfer Society).

FIG. 5 shows the relationship between the flow velocity of the gas flowing through the sample (gas flow velocity v: m / second) and the pressure drop (pressure drop amount per sample length: ΔP / L). A quadratic equation is approximated to the plot of the pressure drop (ΔP / L) with respect to the gas flow velocity v shown in FIG. 5, and the transmittance K ₁ (K ₁ is expressed as “Darcy transmittance” from the equation (2). And transmittance K ₂ (K _{2 is referred} to as “non-Darcy transmittance”). As a result, the curve based on the approximate expression and the actually measured value were in good agreement. The calculated values of Darcy transmittance K ₁ and non-Darcy transmittance K ₂ are shown in Table 4 below. Both values indicate that the larger the value, the smaller the resistance during gas permeation.

FIG. 6 shows the relationship between the Darcy transmittance K ₁ and the non-Darcy transmittance K ₂ obtained in the samples A to C and the porosity (Table 4). The value of the Darcy transmittance K ₁ is greatly different for each of the samples A to C, and decreases in the order of sample B> sample A> sample C. The sample having a higher porosity has a larger value. Further, the value of the non-Darky transmittance K ₂ is smaller in the order of sample B> sample C> sample A, and the resistance due to the pore shape of sample A is extremely larger than the other samples B and C. I understand that. From this, the sample B is presumed to have a structure in which large pores preferentially become channels and the diameter of the portion where bubbles communicated is large, so that the shape of the channel is small and turbulence is unlikely to occur.

On the other hand, in the sample C, since the pore diameter itself is small and the rate of gas permeation is limited (the value of the Darcy transmittance K ₁ is small), the influence of the channel shape is difficult to occur, and the non-Darcy transmittance K ₂ is small. It is thought that it has become. In sample A, as can be seen from the image analysis of X-ray CT scan and the pore size distribution, pores of various sizes coexist, the shape of the flow channel is greatly changed, and turbulent flow is likely to occur. For this reason, it is considered that the non-Darcy transmittance K ₂ is small (the flow path resistance is large). When the calculation based on the approximate expression shown in FIG. 5 is performed, the magnitude relationship between the pressure drop (ΔP / L) of sample A and sample C is reversed from when the gas flow velocity exceeds 5 m / sec, The penetration resistance is expected to be the largest.

  From the above results, the difference in gas permeation behavior due to the pore structure of the produced samples A to C was clarified. When the inside of the pores is considered as a reaction field of the catalyst, it is conceivable that the contact time with the porous body wall surface serving as the catalyst and the state of gas flow influence the reaction rate.

(Example 2)
Prepare various hydroxyapatites with different molar ratios of Ca and P (Ca / P) [Ca / P ratio], and prepare slurries with various amounts of anionic surfactants. The type and the amount thereof are the same as in Example 1 (the total may exceed 100%). Hereinafter, various porous bodies (samples) are basically formed in the same manner as in Example 1 except for the conditions specified later. Produced. The slurry composition (Ca / P ratio of the hydroxyapatite powder, the amount of the anionic surfactant) and the slurry stirring time are shown in Table 5 below (Test Nos. 1 to 11).

  About each obtained sample, the porosity and the pore diameter (D50) were measured like Example 1. FIG. Moreover, about each obtained sample (diameter 19 mm diameter and 20-mm-length cylinder shape), the gas which adjusted VOC (ethyl acetate) to 25 ppm was continuously flowed to the length direction, and was made to contact. The temperature during decomposition (heating temperature) was 500 ° C. Then, based on the VOC concentration before and after the reaction, the decomposition ratio of the VOC component (this is referred to as “VOC mineralization ratio”) was measured.

  The results are shown in Table 6 below together with the firing temperature at the time of producing the porous body. In Table 6, “impossible to measure” means that the ventilation resistance is large and cannot be measured stably.

  As is clear from the results, an appropriate amount of an anionic surfactant is contained to prepare a foam slurry, and a porous material is produced from the foam slurry to obtain an appropriate porosity and pore diameter (D50). The porous body which has is obtained. Such a porous body is useful as a material for a volatile organic gas decomposition filter.

(Example 3)
Test No. 2 in Example 2 In preparing the slurry shown in FIG. 6, instead of using an anionic surfactant, an amphoteric surfactant (“Amphitor 24B”, trade name: manufactured by Kao Corporation) or a nonionic surfactant (“Emulgen 420”) is used. Using a product name: Kao Corporation, a foam slurry was prepared, dried, and fired to produce various porous bodies (the other components are the same as in Examples 1 and 2). The firing temperature at this time was 800 ° C. for all. The addition amount of each surfactant was 0.3 g (0.3 mass%) with respect to the whole slurry (100 g).

  About each obtained porous body, the shape of the pore was observed with the optical microscope. A pore observation image of a porous body produced using an anionic surfactant (test No. 6 equivalent) is shown in FIG. 7 (drawing substitute micrograph), and a pore observation image of the porous body produced using an amphoteric surfactant is shown in FIG. FIG. 8 (drawing substitute micrograph) and FIG. 9 (drawing substitute micrograph) show pore observation images of the porous body produced using the nonionic surfactant, respectively. 7-9, the observation image shown by (a) is a thing at the time of magnification 25, and the observation image shown by (b) is a thing at the time of magnification 50.

  7-9, it can consider as follows from the magnitude | size of a bubble and the thickness of the wall which exists between a bubble and a bubble. In the case of using a nonionic surfactant (FIG. 9), the bubbles are fine, but the wall between the bubbles is thick, and the porous body is so thick that a gas permeation test cannot be performed. Is unsuitable. Further, in the case of using an amphoteric surfactant (FIG. 8), the wall between the bubbles is thin, and it is easy to form an open cell, but using an anionic surfactant (FIG. 7). ), The bubbles tend to be large, and there is a concern that the contact time of the gas will be shortened.

  As is apparent from this result, bubbles were generated using an anionic surfactant to form a foam slurry, and a porous material was produced from this foam slurry, and pores of an appropriate size were formed on the surface of the porous material. It can be seen that is formed. On the other hand, in the case where bubbles are generated by using an amphoteric surfactant or a nonionic surfactant to form a foam slurry, and the porous body is produced from this foam slurry, the pore diameter becomes too small or large. It turns out that it has become a thing of the form which is hard to apply as a filter for volatile organic gas decomposition | disassembly.

Claims (4)

  Preparation of foam slurry by adding hydroxyapatite powder, dispersant, water, crosslinking agent, polymerizable resin, polymerization initiator and anionic surfactant, followed by drying and firing to produce a porous body A method for producing a porous body.   2. The method for producing a porous body according to claim 1, wherein the hydroxyapatite powder has a Ca to P molar ratio (Ca / P) of 1.67 to 2.50.   The method for producing a porous body according to claim 1 or 2, wherein the dispersant is a polycarboxylic acid surfactant, the cross-linking agent is polyvinyl alcohol, and the polymerizable resin is a water-soluble epoxy resin.   The method for producing a porous body according to any one of claims 1 to 3, wherein the polymerization initiator is triethyltetramine.