JPH0630580B2 - Method for producing porous ceramics for microorganism carrier - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a porous ceramic for a microorganism carrier, and more specifically, a bioreactor or biosensor used in the food industry or a biochemical treatment of wastewater. The present invention relates to a method for producing porous ceramics used as a carrier for microorganisms and enzymes used in.

[Conventional technology]

In recent years, with the use of bioreactors and biosensors, research on the microbial carrier used for this has been advanced,
Various products have been developed, including natural products such as alginic acid and kappa carrageenan, synthetic polymers, activated carbon and charcoal, and inorganic foam glass.

The basic function of the microorganism carrier is the microorganism (fungus body)
In addition to having a large number of surface openings capable of supporting cells, each surface opening allows easy entry and exit of substrates and reaction products, and once the bacterial cells (colony) that have once grown are subjected to washing work or continuous liquid passing work, etc. Therefore, it is required that the microstructure of the porous body does not easily flow out. Therefore, as a microbial carrier, there are some differences depending on the type of reactor, the nature of the substrate such as the fermentation liquid, and the microorganisms used,
Generally, it is desirable that the porous body has a large number of communicating pores having a pore size distribution of about 3 μm to 300 μm.

Although surface pores with a pore size of 100 μm or more have a drawback that the bacterial cells can easily flow out, on the other hand, since the substrate can easily enter and leave the pores, the substrate can be easily taken in and out. Since an effective surface equivalent to the outer surface of the body is expanded to the inside of the opening, a few μm capable of supporting cells on the inner surface of the opening.
If a hole having a diameter of ˜several tens of μm is opened as a communication hole, the volume of the chamber in which the bacterial cells proliferate and accumulate is large when viewed from the entire volume of the carrier.

Further, the opening area of the carrier is required to be 20% or more of the surface area of the carrier and to have a sufficient number of openings. If the surface area of the carrier is small compared to the total volume of the carrier, or if the number of pores is small, the area where the cells easily act on the substrate, that is, the effective volume in which the cells reside, responds quickly to the reaction. It is impossible to secure a possible effective area.

Furthermore, the carrier is also required to have sufficient mechanical strength. That is, when using a tower-shaped large tank filled with the carrier, when removing sludge adhering to the surface of the carrier with jet water, or when the carriers collide / contact each other or collide with the reactor wall surface. -When it is used in a fluidized bed reactor that causes contact, it is desirable that it will not be easily damaged or generate abrasion powder even when it is put in or taken out of a tank or during transportation work.

For this purpose, it is necessary that the surface of the carrier has no protrusions, it is as smooth as possible, the honeycomb-shaped opening wall has high strength, and it has an appropriate thickness. In terms of load / bead projected area when the carrier is destroyed by applying pressure, 40 kg / cm ² or more is generally required.

Further, in a fluidized bed reactor, it is desirable that the carrier has an apparent density similar to that of the substrate in order to reduce the power for flowing.

[Problems to be Solved by the Invention]

However, conventionally used supports made of natural products such as alginic acid and kappa carrageenan have problems in mechanical strength and durability in long-term use. In addition, those obtained by cross-linking synthetic polymers are not suitable for use in the food industry because of concern about the toxicity of synthetic substances, and they cannot be steam sterilized or reformed at 700 ° C or higher. Furthermore, activated carbon and charcoal are insufficient in terms of pore size and number.

Further, in the case of using foamed glass with water glass or glass powder as a base material, when the support is fluidized and used, or when the support is collided with or brought into contact with the support during transportation into or out of the tank, the wall portion is It easily wears and breaks and cannot withstand long-term use. This is due to the nature of the material
This is because if the surface aperture ratio is set to 20% or more, the thickness of the honeycomb wall becomes thin, and if the strength is increased, the surface aperture area ratio becomes extremely small, which is not suitable for the purpose. This is because it ends up. Further, it is impossible to incinerate the organic matter at 700 ° C. or higher for reuse, because the fine honeycomb structure made by foaming is softened and deformed.

In addition, there are known lightweight aggregates and heat insulating materials obtained by firing and foaming various inorganic materials by the action of alkali metal salts or alkaline earth salts, but these have openings that allow bacteria and substrates to easily enter and leave the surface. Rather, it has a surface film having no openings and is intended to reduce the water absorption rate and secure the strength according to the purpose of use, and cannot be used as a microorganism carrier.

The present invention provides a method for producing a porous ceramic for a microorganism carrier, which has excellent mechanical strength, is chemically stable, has no fear of toxicity, can be reformed at 700 ° C. or higher, and is inexpensive. The purpose is to do.

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides 100 parts by weight of a base material mainly composed of finely powdered high melting point material selected carefully to 40 mesh or less, and a melting material 5 comprising an alkali metal salt having a melting point lower than that of the base material.
˜30 parts by weight and 25 to 40 parts by weight of water are uniformly mixed, and after molding and drying, the melting point of the melt is 100 to 100%.
It is characterized by obtaining a porous ceramics having a surface opening diameter of 3 to 300 μm, a surface opening area ratio of 20% or more, and a compressive fracture strength of 40 kg / cm ² or more by firing at a high temperature of 350 ° C. It is a thing.

It is important to use a fine powdery high melting point material as the base material, which is finely powdered and has a good particle size distribution. For example, clay selected carefully to 40 mesh or less, such as clay or kneaded clay which is a raw material powder for general-purpose porcelain Is preferably used. Also, silica,
As fine powders such as alumina and zirconia, those having an appropriate particle size distribution are commercially available, and those can also be used. It should be noted that the ultrafine particle size (7-5
Various materials such as silica (0 nm), alumina, zirconia, etc. can be used, but like those using water glass or glass powder, these have weak strength when the aperture ratio is set to several tens of percent or more. It is not preferable because it is easy to make things. Further, although the exhaust dust powder during the production of ferrosilicon by the electrothermometallurgical method can be used, it is not preferable to use it because it contains a substance harmful to the human body.

Regarding the particle size distribution of the base material, it is necessary that an appropriate amount of submicron (0.1 to 1 μm) or more particles be mixed in order to form a honeycomb shape having a preferable aperture ratio and strength as a carrier. . For example, when a base material having a particle size of 50 nm or less is used, the expandability is good, but the conditions for obtaining a surface opening area ratio suitable for the purpose are satisfied, and a honeycomb structure having a strong compressive strength cannot be formed, and the wall thickness is It is easy to make thin, weak materials and those covered with a surface film without openings.

The melting material to be blended with the base material is an alkali metal salt having a melting point lower than that of the base material, and among them, potassium sulfate salt or potassium phosphate salt is preferable. The compounding ratio is the base material 1 by weight ratio.
It is 5 to 30 parts in total or in combination with 00 parts, but 1
5 to 20 parts is optimal. In addition, add water to this
40 parts by weight is added to form an aqueous solution, which is mixed with the base material and kneaded to uniformly mix the base material and the melting material.

Next, after performing a molding process such as granulating the mixture,
Dry at 100-250 ° C. Furthermore, at 700 ℃ 30
By pre-baking for about a minute, complete drying can be performed and impurities such as organic substances in the raw material can be removed.

Firing is the melting point of the melt (about 1100 ° C for potassium sulfate)
100-350 ℃ higher temperature as soon as possible,
The temperature is raised within 30 minutes, preferably within 10 minutes.
Further, the raw material may be supplied after raising the temperature by 100 to 350 ° C. above the melting point of the melting material. The melting point of the melting material is
The temperature at which the melting material itself is liquefied inside and having two melting points of a low temperature liquefaction point and a high temperature liquefaction point indicates the high temperature side.

And it hold | maintains at the said temperature for 5 to 60 minutes, and bakes. It is preferable that the base material is fired on the low temperature side when the melting material is added in a large amount, and on the high temperature side when it is added in a small amount.

The raw material base material has its structure softened by the melting material melted at the time of firing, and a mixed liquid of a molten salt and a base material having a fine diameter of submicron (0.1 μm to 1 μm) or less due to the reaction-generated gas or the vapor pressure of the melting material. Bubbles are formed in the part to form a vitrified thin film honeycomb. Sub-micron or larger base particles do not fluidize in the initial stage of foam film formation, and when alumina or zirconia having a higher melting point than silica is added as a sub-base material, those sub-micron or smaller are foamed. Viscosity increases during the film formation stage, resulting in an increase in film thickness and increased strength of the carrier. This provides self-supporting properties in the foaming temperature range. Particularly, it is satisfactorily expressed on a sub-micron or larger particle base material.

For example, when firing a large amount of raw materials in a stacked state from the viewpoint of manufacturing efficiency, the self-supporting property in the foaming temperature zone prevents deformation in this state.

Silica or alumina fine powder made by the vapor phase method of 50 nm or less,
Further, in the case of using water glass, glass powder, or the like as a raw material, for example, firing a cup-shaped one is inferior in self-sustainability in the firing temperature range, so that only dimensional accuracy is extremely poor.

The temperature and rate of temperature increase during firing must be appropriately selected depending on the type of the base material, the particle size distribution, the type of the melting material and the blending ratio thereof.

The foaming temperature at which a large number of honeycomb-shaped holes are formed on the surface is
The mixing ratio of the flux and the particle size distribution of the base material have a great influence. Foaming at low temperature as the blending ratio of the melting material is increased,
Further, the larger the ratio of the base particles having a particle size of 100 nm or less, the lower the temperature at which foaming occurs.

On the other hand, the strength of the porous ceramics (support) after firing is generally higher as the firing temperature is higher. For example, 100 parts by weight of the base material may contain 15 to 20 parts by weight of potassium sulfate as a flux. If part is added, it is 3 from the melting point.
On the other hand, firing at a temperature higher than 50 ° C. is not preferable because it weakens, a coarse honeycomb structure is formed, or deformation is reduced. When the blending ratio of the melting material is increased, the same is true even if firing is performed at a temperature of 350 ° C. higher than the melting point. In addition, the smaller the blending ratio of the fusing material, the higher the strength.

The heating rate varies depending on the blending ratio of the melting material, but the smaller the blending ratio is, the less foaming occurs unless the temperature is raised rapidly. When the mixing ratio of the melting material is increased and the temperature is slowly raised, it is difficult to set the apparent density to 1.0 or less, and the strength becomes small. Therefore, in order to obtain a lightweight and durable carrier for use in a fluidized bed, it is absolutely necessary to reduce the amount of the melting material and increase the foamability, and for this purpose, increase the heating rate. Is effective.

The thus-produced porous ceramic is porous having semi-independent pores and communicating pores, has a surface opening diameter of 3 to 300 μm, a surface opening area ratio of 20% or more, and an apparent density. It floats lightly on water and has high strength. Furthermore, the outer surface is smooth with no protrusions,
When fluidized and used, since degassing will cause it to sink in water, the in-liquid weight can be adjusted by the degassing strength.

Also, when a larger surface opening area ratio is required, self-polishing with a porcelain pot mill, etc.
The epidermis may be removed. At this time, an abrasive may be mixed, but the yield is better if it is not used. Since the porous ceramics obtained by the above-mentioned manufacturing method has a high strength in the honeycomb structure portion, even if it is subjected to such finishing treatment, abrasion powder is hardly generated during various operations.

〔Example〕

Examples and comparative examples of the present invention will be shown below, but the present invention is not limited thereto.

Example 1 As a sub-base material, the main material is elutriated clay (5% or less in particle size 99%) of the Seto region mixed with 10 parts by weight of alumina having a diameter of several tens of micrometers (trade name A21 manufactured by Sumitomo Chemical Co., Ltd.). Main substrate 1
After blending 20 parts by weight of K ₂ S ₂ O ₅ as a melting material with respect to 00 parts by weight and adding 40 parts by weight of water thereto and sufficiently wet-kneading so that the base material and the melting material are uniformly mixed, a diameter of 8 mm Was formed into a granular shape. This was dried at 120 to 230 ° C for 3 hours and then prebaked at 700 ° C for 20 minutes.

Next, after firing for 10 minutes in a furnace that has already reached 1380 ° C, the temperature is raised to 1420 ° C in 5 minutes while still in the furnace.
It was fired for 5 minutes to obtain a porous ceramics for supporting a microorganism.

Furthermore, the obtained porous ceramics were air-cooled and then self-polished for 2 hours with a porcelain pot mill. When alumina having a diameter of several tens of μm is mixed as a sub-base material in the base material, the foaming becomes uniform, dry cracking during drying after wet molding is prevented, and partial coarse foaming is effectively prevented.

Example 2 Using the Seto local kibushi clay selected as a base material with a sieve of 40 mesh or less, an aqueous solution consisting of 15 parts by weight of KHSO ₄ as a melting material and 30 parts by weight of water was added to 100 parts by weight of the base material. After thoroughly wet-kneading the base material and the melting material, they were formed into particles having a diameter of 8 mm. This was dried at 120 to 230 ° C for 3 hours and then prebaked at 700 ° C for 30 minutes. Then directly 142
It was fired at 0 ° C. for 20 minutes to obtain a porous ceramics for supporting a microorganism.

Comparative Example 1 Alumina having a particle size of 20 nm (Al, manufactured by Nippon Aerosil Co., Ltd.,
C) Silica having a particle diameter of 40 nm (OX50 manufactured by Nippon Aerosil Co., Ltd.) mixed with 2 parts by weight as a sub-base material is used as a main base material, and 100 parts by weight of the main base material is used as NaAlO ₂ 8 as a melting material.
After 150 parts of water was added together with 8 parts by weight of K ₂ S ₂ O _{7 and 1} part by weight of the base material and the melt material, the mixture was sufficiently kneaded, and then formed into particles having a diameter of 8 mm.

It is dried at 120-230 ° C for 3 hours and then at 700 ° C for 1 hour.
After pre-calcined for 0 minutes, it was directly calcined at 1450 ° C. for 15 minutes to obtain a porous ceramic for a microorganism carrier.

Alumina having a particle diameter of 20 nm mixed in the base material has the effect of increasing the strength by sliding the surface during foaming, but if 5 parts by weight or more is mixed in, the surface area ratio of the surface opening will decrease, so care must be taken.

The results of Examples 1 and 2 and Comparative Example 1 are shown in Table 1. From Table 1, it can be seen that the one obtained in Comparative Example 1 has a lower strength than the ones obtained in Examples 1 and 2.

Further, photographs (scanning electron micrographs) of the surface texture and texture of the porous ceramics for microbial carrier produced in Examples 1 and 2 and Comparative Example 1 are shown in FIGS. 1 to 6. . That is, FIGS. 1 and 2 are photographs of the surface and the skin of Example 1 removed by self-polishing, and FIGS. 3 and 4 are the photographs of the surface and skin of Example 2 removed by self-polishing. Photo,
5 and 6 are photographs in which the surface and the photographic skin of Comparative Example 1 were removed by self-polishing.

[Effects of the Invention] As described above, according to the present invention, the surface opening diameter is 3
.About.300 .mu.m, surface area ratio is 20% or more, and
A porous ceramic suitable for use as a microorganism carrier having a compressive fracture strength of 40 kg / cm ² or more can be efficiently produced. Moreover, it is possible to use clay, which is available in large quantities and is inexpensive, as a raw material that has been carefully selected by a simple method such as sieving. Furthermore, by using a material with an appropriate particle size distribution, the molded product can be self-supported during firing. Good and high manufacturing efficiency.

Further, the porous ceramics for microorganism carrier obtained by the method of the present invention has excellent mechanical strength despite the large number of communicating holes of about several tens of μm, and the weight in liquid can be appropriately adjusted, so that it can be used in various reactors. In addition, since the wall of the porous body is thick and durable and the surface is smooth, there is no damage or abrasion due to collision or contact between the carriers, chemically stable, no toxicity problem, durability Since it is excellent, it is suitable for use in the food industry, and is particularly effective as a microbial carrier used in a fluidized bed reactor.

Further, when sludge or the like adheres to the carrier made of the porous ceramics obtained by the method of the present invention, if sludge or the like is sprayed, heated with water or steam, or heated to 700 ° C. or higher in the furnace, the sludge is removed again. It can be used and is economically excellent.

[Brief description of drawings]

1 to 4 show the surface texture and the texture of the porous ceramic produced by the method of the present invention,
FIG. 1 is an electron micrograph of the surface texture of the porous ceramics produced in Example 1, and FIG. 2 is an electron micrograph of the texture of the porous ceramics of Example 1 after self-polishing and removing. FIG. 4 is an electron micrograph of the surface structure of the porous ceramics produced in Example 2, FIG. 4 is an electron micrograph of the structure of the porous ceramics of Example 2 in which the skin was removed by self-polishing, FIG. 5 and FIG. FIG. 6 shows the surface texture of the porous ceramics produced in the comparative example of the present invention and the texture obtained by removing the skin, and FIG. 5 is an electron micrograph of the surface texture of the porous ceramics produced in Comparative Example 1. FIG. 6 is an electron micrograph of a structure obtained by self-polishing and removing the skin of the porous ceramic of Comparative Example 1.

Claims (1)

[Claims] 1. A base material containing a fine powdery high melting point material selected to 40 mesh or less as a main component, 5 to 30 parts by weight of a melting material composed of an alkali metal salt having a melting point lower than that of the base material, and water. 25 to 40 parts by weight are uniformly mixed, molded and dried, and then fired at a temperature 100 to 350 ° C. higher than the melting point of the melting material to have a surface opening diameter of 3 to 300 μm and a surface opening area ratio. Is 20% or more and the compressive fracture strength is 40
A method for producing a porous ceramics for a microorganism carrier, which comprises obtaining a porous ceramics of kg / cm ² or more.