KR20050059367A - Porous ceramic filter and method of producing the same - Google Patents

Abstract

The present invention relates to a porous ceramic filter for filtration and a method for producing the same, comprising 50 wt% or more of sub-micron silica particles such as fumed silica or colloidal silica. It relates to a dispersion process for producing a slurry with the above composition as a main component, a molding process for forming a molded body using a mold, a drying process for separating the molded product from the mold and drying, and firing the dried product at 500-1200 ° C. It characterized by including a process. The present invention is a useful method for producing a porous ceramic filter exhibiting excellent filtration performance of pore size of 0.1 micrometer (μm) or less.

Description

Porous ceramic filter and method of producing the same

The present invention relates to a porous ceramic filter for filtration and a method of manufacturing the same.

In general, the filtration ceramic filter is widely used because of the advantages of the ceramic material, such as heat resistance, corrosion resistance, chemical resistance, acid resistance and excellent durability, unlike general synthetic membrane filter. In addition, the pore size of 0.1-1 micrometer (㎛) has been widely used in water purification systems for beverages as well as general filtration due to the advantage of filtering out suspended matter and foreign matter and passing minerals beneficial to the human body.

       In general, the manufacturing method of the ceramic filter goes through a manufacturing process similar to the manufacturing step of a general ceramic molded body, and consists of the steps of dispersion (mixing), molding, drying and firing (heat treatment). The composition of the material used at this time determines the performance of the filter.

       There are no particular restrictions on ceramic materials such as silica, alumina, zirconia, clay, lignite, and chamotte, and molded articles of various characteristics are manufactured according to the type and physical properties of the material.

       The dispersing (mixing) step is a step of mixing the ceramic material powder and an organic solvent such as water or alcohol as a base, and sometimes additives such as a dispersant, a binder, and a pore agent may be added.

       The dispersant prevents agglomeration of the powder particles in water or a solvent and improves dispersibility, the binder improves the binding force between the powder particles of the molded body, and the pore agent is used for improving the porosity of the molded body.

       The composition of the composition is uniformly dispersed (mixed) by using a device such as a stirrer, a blender, an ultrasonic wave, or a ceramic slurry is prepared through a centrifugation process to remove impurities.

       The molding step is a step of preparing a molded body by using the molding method of the various methods, such as molding method, extrusion method, centrifugal molding method, press molding method, injection molding method and the like.

       The gelling agent is added immediately before molding for molding, and the finished product is separated from the mold for drying.

       The drying step is a process of removing the water or the organic solvent of the molded product, which is performed under constant temperature and humidity conditions in which natural drying or temperature humidity is controlled.

       The sintering step is a process for improving the strength of the dried molded body is heat-treated under the conditions of 500-1500 ℃ to improve the bonding force by moving the material between the particles.

       When the organic additive is added, the organic matter removing process may be further performed (120 to 600 ° C.).

       Porous ceramic filters for filtration should be small, uniform and porous in pore size and have strength to withstand a certain pressure.

       The high porosity of the filter represents a high filtration treatment per unit area, so it is desirable to fabricate the filter as high as possible.

       The pore size of the ceramic filter is very important by determining the filtration capacity of the ceramic filter, and the uniform distribution of the pores is also important.

       On the other hand, the conventional filtration ceramic filter has a pore size of 0.1-1 micrometer (µm), porosity is limited to within 50% and pore distribution is also uneven.

       This problem can be overcome in manufacturing using ceramic powder having a small particle size (0.1 micrometer (μm) or less), but the material having the above characteristics is not diverse and has difficulty in manufacturing process.

       In general, when the particle size is reduced in the ceramic process (0.1 micrometer (μm) or less), there is a problem of causing cracks due to uneven dispersion and high capillary pressure and high shrinkage rate caused by small pores in the drying process.

       Therefore, the present invention uniformly distributes micropores of 0.1 micrometer (μm) or less with high porosity, exhibits high filtration capability, and also requires a relatively low firing temperature due to the use of fine particles in the manufacturing process, resulting in high yield. It is an object of the present invention to provide a porous ceramic filter and a method of manufacturing the same that can achieve the effect of cost reduction.

 In order to achieve the object of the present invention, by using nano-sized silica particles such as fumed silica or colloidal silica, fine pores of 0.1 micrometer (μm) or less are uniformly distributed at high porosity. It provides a porous ceramic filter for filtration and a method of manufacturing the same.

       Porous ceramic filter manufacturing method according to the present invention comprises a dispersion (mixing), molding, drying, firing step similar to the manufacturing process of the general ceramic filter.

       In order to maintain a high porosity and have pores of 0.1 micrometer (µm) or less, it is preferable to use a ceramic powder material having a particle size of 0.1 micrometer (µm) or less.

       Therefore, the present invention provides fumed silica and colloidal silica as main materials.

 Fumed silica is a method of producing spherical fine silica particles by flame hydrolysis of silicon tetrachloride in an oxygen and hydrogen environment, and commercially available products having a particle size of several nm to 40 nm are sold. (Manufacturer: Degussa.Cabot, Wacker, etc.)

       Colloidal silica, on the other hand, is an alkoxysilane compound such as sodium silicate, potassium silicate, or tetramethyl orthosilicate, or tetraethyl orthosilicate. Is hydrolyzed with water under an acid or base catalyst to produce a colloidal slurry called silica sol, which contains silica particles of various sizes, and various particle sizes (from several nm to several micrometers) from various companies. Products of and content (5% to 50% by weight) are commercially available.

       In the dispersion step, fumed silica is mixed with water to prepare a uniform phase having a content and viscosity suitable for molding using a high performance blender or the like.

       In order to have the strength of the wet molded product and a low shrinkage rate during drying, a higher content of fumed silica is preferable, and a high dry yield may be obtained at 40% or more.

       Therefore, when the content is high, a dispersant may be added to induce charge on the particle surface to generate repulsion between particles, and sodium hydroxide, aqueous ammonia, and tetramethylammonium hydroxide to induce a pH value of the slurry of 10 or more. Alkali substances such as (Tetramethylammonium hydorxide) are also used, and there is no limitation on the type of organic-inorganic compounds.

       In addition, a binder may be added to improve the wet strength and drying ability of the molded body, and polyvinyl alcohol (Polyvinylalcohol), poly 2 ethyl 2 oxazoline (Poly (2-ethyl-2-oxazoline)), polyethylene imine (Polyethylenimine), etc. Organic polymers are used.

       The binder not only improves the binding force between the particles, but also decreases the hydrophilicity of the particle surface and serves to shorten the drying time.

       In addition, a plasticizer such as glycerin may be added to improve the flexibility of the wet formed body.

       Depending on the purpose of manufacture, the above materials can be selectively mixed and dispersed and added, and a high performance blender is used or an ultrasonic dispersion device is used. In some cases, additional processes such as centrifugation to remove aggregates or high specific impurities are performed. Can also be used.

       Colloidal silica, on the other hand, is sold in the form of a slurry of 5% to 50% by weight due to the manufacturing characteristics. Therefore, what is necessary is just to add the said additive selectively.

       However, for high silica content, it may be concentrated or dispersed after adding additional fumed silica.

       The slurry produced by the above method is subjected to a molding process. The molding process may be a molding method, an extrusion method, a centrifugal molding method, etc. and may be selected in consideration of the composition, the size and shape of the molded body, and the like.

       In order to induce molding, a gelling agent may be added, and in the case of a slurry having a pH of 10 or more, ester compounds such as ethyl lactate and methyl lactate are mainly used. Fluorine compounds such as ammonium fluoride are used. Silver is used regardless of the pH of the slurry.

       The molded product is prepared by putting a gelling agent into a silica slurry and then molding the mold after stirring.

       The molded product is separated from the mold for drying after a certain time of aging for strengthening the strength of the wet molded body.

       The wet molded body separated from the mold is subjected to a drying process in a constant temperature and humidity chamber in which natural drying or temperature humidity is controlled.

       The dry environment is preferably a temperature of 10-70 ° C. and a relative humidity of 20-90% depending on the composition and the size of the wet molded body.

       The drying process preferably proceeds to the point where the weight reduction rate of the wet molded body reaches equilibrium.

       The drying process therefore takes several hours to several tens of days depending on the size of the wet molded body.

       After the drying process, the molded product is subjected to a heat treatment process to remove residual moisture, organic matter, and bond between particles by viscous flow, that is, to secure the strength of the molded product.

       Residual water is removed at 120-150 ° C and organics removal is at 300-600 ° C.

       Finally, the firing process for strengthening the strength of the molded body depends on the size of the material particles and the like and is processed in an electric furnace at 500-1200 ° C.

       It is preferable to perform a baking process in the range which porosity does not reduce by excessive heat processing.

       The present invention will be described in more detail with reference to Examples.

       Example 1

       0.3 kg of Aerosil OX-50 (fumed silica Degussa. Particle diameter 40 nm) and 0.3 kg of deionized water were mixed and dispersed using a high performance blend to prepare a silica slurry. 10 cc of an aqueous solution of 50% by weight of ammonium fluoride was added to the slurry, followed by stirring using a stirrer. During stirring, the viscosity of the slurry was lowered to 50 cps or less, and when the stirring was stopped, the viscosity increased with time, losing fluidity and a wet molded body was produced. Therefore, the silica slurry, which secured fluidity through stirring, was injected into the prepared mold and molded. For the production of tubular filters, the mold consisted of an acrylic bottom (5 cm in diameter), an acrylic tube (5 cm inside) mounted on the floor, and a suss rod (3 cm in diameter) installed in the center of the floor. The molded body which lost fluidity and completed molding was removed from the mold for drying after removing the sussing rod in the center of the mold and aging for 5 hours for strength. The separated silica compact was subjected to natural drying for 4 days, and the dried silica compact was calcined at 900 ° C. for 1 hour after 3 hours treatment at 150 ° C. to remove residual moisture. The manufactured tubular filtration porous silica ceramic filter had a length of 27 cm, a thickness of 0.9 cm, an average pore size of 38 nm, and a porosity of 65%.

       Example 2

       1.1 kg of Aerosil OX-50, 1 kg of deionized water, and 0.12 kg of tetramethylammonium hydroxide (Tetramehylammonium hydroxide) were mixed and dispersed in the same manner as in Example 1 to prepare a silica slurry. After the silica slurry was aged for 12 hours (pH = 11.90), 80 cc of ethyl lactate was added thereto, stirred, and injected into a prepared tubular mold. After 2 hours of molding, the susps were removed and separated from the mold. The drying process and the residual water removal process were performed in the same manner as in Example 1. The temperature was maintained at 600 ° C. for 3 hours to remove the added organic matter (dispersant). The firing process was performed in the same manner as in Example 1, and the manufactured tubular filtration silica ceramic filter showed an average pore size of 34 nm and a porosity of 66%.

      Example 3

      The mixed dispersion process was performed in the same manner as in Example 2. The prepared silica slurry was added to a mold for centrifugal molding, ethyl lactate was added thereto, a stopper was closed, and the tube was rotated at 1500 rpm for 20 minutes to form a tubular ceramic filter. The wet formed body was dried, removed residual water, removed organic matter, and calcined in the same manner as in Example 2. The manufactured tubular filtration silica ceramic filter showed an average pore size of 34 nm and a porosity of 67%.

       Example 4

       0.3 kg of Aerosil 90 (fumed silica Degussa. Particle diameter 20 nm), 0.4 kg of deionized water, and 0.04 kg of tetramethylammonium hydroxide were mixed and dispersed in the same manner as in Example 2 to disperse the silica slurry. Prepared. The silica slurry was molded in the same manner as in Example 3 after aging for 12 hours (pH = 11.5). The wet molded body separated from the mold was dried for 5 days in a constant temperature and humidity chamber at a temperature of 20 ° C. and a relative humidity of 80%. Residual water removal and organic matter removal process were the same as Example 2, and the baking process was hold | maintained at 700 degreeC for 1 hour. The manufactured tubular filtration silica ceramic filter showed an average pore size of 18 nm and porosity of 70%.

       Example 5

       Into a colloidal silica (OX-K50 Dupont, silica 49.8% by weight, average particle diameter 40nm) 0.6kg tetramethylammonium hydorxide 15cc was added to the silica slurry in the same manner as in Example 2 (PH = 11.8) 25 cc of ethyl lactate was added to the silica slurry prepared by the method described above, followed by stirring and molding, mold release, and drying in the same mold as in Example 1. The firing process was maintained at 850 ° C. for 1 hour. The manufactured tubular filtration silica ceramic filter showed an average pore size of 35 nm and porosity of 65%.

       Example 6

       Colloidal silica (Nyacol 2040, Nyacol Product, Inc. silica 40% by weight, average particle diameter 20nm) 0.6kg of tetramethylammonium hydroxide (15% Tetramethylammonium hydorxide) in the same manner as in Example 2 Silica slurry was prepared. (PH = 11.6)

       20 cc of ethyl lactate was added to the silica slurry prepared by the above method, followed by molding, mold release, and drying in the same mold as in Example 3. The firing process was maintained at 650 ° C. for 1 hour. The manufactured tubular filtration silica ceramic filter showed an average pore size of 15 nm and a porosity of 70%.

       Example 7

       0.9 kg of Aerosil OX-50, 0.1 kg of Aerosil 90, 1 kg of deionized water, and 0.12 kg of tetramethylammonium hydroxide (Tetramehylammonium hydroxide) were mixed and dispersed in the same manner as in Example 2 to prepare a silica slurry. After the silica slurry was aged for 12 hours (pH = 11.60), 80 cc of ethyl lactate was added thereto, stirred, and injected into the prepared tubular mold. After 2 hours of molding, the susps were removed and separated from the mold. The drying process and the residual water removal process were performed in the same manner as in Example 2. The temperature was maintained at 600 ° C. for 3 hours to remove the added organic matter (dispersant).

       The firing process was performed in the same manner as in Example 2, and the manufactured tubular filtration silica ceramic filter was widely distributed from the average pore size of 10 nm or less to 40 nm and exhibited a porosity of 60%.

The present invention has a pore size of 0.1 micrometer (μm) or less by producing a porous ceramic filter for filtration mainly composed of nano-sized silica particles such as fumed silica or colloidal silica. It is possible to produce a ceramic filter with excellent performance that is uniformly distributed.

In particular, regardless of the type of phase (phase), unlike the conventional ceramic filter, due to the very small pore size (0.1 micrometer (μm) or less) high filtration ability.

In addition, the use of fine particles in the manufacturing process requires a relatively low firing temperature, resulting in high yield and cost savings.

Claims (2)

A porous ceramic filter comprising at least 50% by weight of nano-sized (sub-micron) fume silica or colloidal silica particles. Method for producing a porous ceramic filter, characterized in that it comprises the above step (a) preparing a ceramic slurry comprising at least 50% by weight of nano-sized fume silica or colloidal silica particles; (b) preparing a molded article using the slurry prepared in step (a) (c) drying the molded body (d) heat-treating the dried formed body at 1200 ° C or less