KR100665525B1 - Ceramic filter and its manufacturing method - Google Patents

Abstract

The present invention relates to a porous ceramic filter capable of controlling pores of various sizes with silica particles as its main component, and a method of manufacturing the same. The present invention relates to a membrane having silica particles as a main component to prepare asymmetric nanomembrane or ultrafiltration membrane with relatively small pores. Preparing a first dispersion slurry using silica particles to coat a nano-sized silica asymmetric layer on a support and then dry it and heat-treat it at 1400 ° C. or less to prepare a micro-filter having relatively large pores. Controlling the size of the secondary silica agglomerate through physical grinding after drying or calcining the first dispersion slurry, adding a solvent and an additive to the secondary silica agglomerate powder to prepare a second dispersion slurry, and the second dispersion Forming a slurry by adding a coagulant to the slurry, and It provides a method of manufacturing a micro filter comprising the step of drying, heat treatment at 500 ℃-1400 ℃ range of porosity reduction of the dried molded body is insignificant.

Nano membrane, ultrafiltration membrane, micro filter, silica                                                                                                                                                

Description

CERAMIC FILTER AND METHOD OF PRODUCING THE SAME

The present invention relates to a silica microfiltration membrane having various pore sizes and a method of manufacturing the same. In general, the filtration ceramic filter has been 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. In addition, recently, as ceramic particles, which are materials of ceramic filters, are widely provided from several nanometers to several micrometers, their utilization in precision filtration areas is increasing. In general, the manufacture of a ceramic filter goes through a manufacturing process similar to the manufacturing step of a ceramic molded body, and consists of the steps of dispersion (mixing), molding, drying, and heat treatment (firing). In the case of the ultrafiltration membrane and the nanomembrane, a coating layer having pores of about 1-100 nm is additionally formed on the surface of the ceramic support. The composition of the material used at this time determines the performance of the ceramic filter. Generally, the material of the support and the coating layer is used without particular limitations such as alumina, zirconia, clay, lignite, and chamotte, and molded bodies having various characteristics are manufactured according to the type and physical properties of the material. In particular, a microfiltration ceramic filter using fume silica or colloidal silica and a method of manufacturing the same are described in detail in the previously filed "Porous Ceramic Filter and its Manufacturing Method" (Application No. 1020020032729).

The dispersing (mixing) step is a step of mixing the ceramic material powder and an organic solvent such as water or alcohol based on the additive, and in some cases, additives such as a dispersant, a binder, a pore agent, and a plasticizer may be added. The composition is a ceramic slurry through a process of uniformly dispersed (mixed) using a device such as a stirrer, blender, ultrasonic waves.

The molding step is a step of preparing a molded body by using a variety of molding 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 usually heat treatment at 1600 ℃ or less to induce mass transfer between particles to improve the bonding force.

In the case of asymmetric membrane production, a reverse immersion pulling method or the like is used to form a coating layer having pores smaller than pores of the ceramic support on the surface. The ceramic slurry in which particles of a smaller size than the particles of the ceramic support are dispersed is brought into contact with the surface of the ceramic support and coated using capillary pressure. Formation of the coating layer can be selectively applied after the drying or heat treatment process of the ceramic support, and the asymmetric membrane in which the coating layer is additionally formed is completed through drying and heat treatment.

Ceramic filters for filtration should be small, uniform and porous. It should also have strength to withstand a certain pressure. The pore size 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, in the case of the conventional filtration ceramic filter, the type and size of the material powder is not various, so it is not easy to control various pore sizes, the porosity is limited to within 50%, and the pore size is also not uniform. In addition, the performance of the filtration filter can be evaluated by the ability to remove and concentrate fine particles by pore size and throughput per unit time. However, as the pore size decreases, the ability to remove fine substances increases, but the throughput per unit time decreases, so that the proper pore size control of the filter is achieved. It is important. Despite the many advantages of ceramic filters, the absence of materials having various ceramic particle sizes has made it difficult to fabricate an optimal filter for a particular process.

Accordingly, the present invention provides a high porosity and provides a relatively high yield and cost reduction effect by providing an asymmetric nanomembrane using an silica, an ultrafiltration membrane and a method for manufacturing the same, and a silica microfilter and a method for producing the pore size which can be easily adjusted. To provide a silica microfiltration membrane and a method for producing the same.

The present invention provides a micro filter, an ultrafiltration membrane, a nano membrane, and a method of manufacturing the same, using a silica particle such as fume silica or colloidal silica to easily control various pore sizes and achieve high porosity. .

The method for producing a microfilter according to the present invention is a primary dispersion (mixing), the production of secondary aggregates by physical grinding after drying or firing, secondary dispersion step using secondary aggregates, forming step, drying step, heat treatment (firing Step).

The main materials used in the manufacture of the ceramic filter in the present invention are fumed silica and colloidal silica. Fumed silica is a method of producing spherical fine silica particles by flame hydrolysis of silicon tetrachloride in an oxygen and hydrogen environment. Commercial products have a particle size of several nm to about 40 nm. Colloidal silicas, on the other hand, are sodium silicate, potassium silicate, or tetramethylorthosilicate, tetraethyl. By hydrolyzing an alkoxysilane compound, such as orthosilicate, or tetraethylorthosilicate, under an acid or base catalyst, a colloidal silica slurry called silica sol containing silica particles of various sizes is prepared, and at various nm Various particle sizes of several μm and various contents from 5% to 60% by weight This product is commercialized. In the first dispersion step, the fumed silica is uniformly dispersed using a high performance blender after mixing with a solvent of water or alcohol. At this time, the amount of fumed silica to be mixed is not limited but should be an amount easy to obtain a uniform phase. Inorganic-inorganic alkali compounds such as ammonia water, tetramethylammonium hydroxide, and sodium hydroxide are added as a dispersant to maintain a pH of 11 or more, thus making it possible to prepare a uniform slurry having a low viscosity of about 50% by weight or more. Do. Colloidal silica, on the other hand, is dispersed in various concentrations of slurry and provided by the manufacturer, and can be used after purchase of a product having a desired particle size and particle content without additional physicochemical process. In addition, a mixture of primary dispersion slurry made of fumed silica or fumed silica and colloidal silica may be used.

The primary dispersion slurry prepared in the same manner is subjected to a dry step to form a secondary aggregate. In the drying step, rapid drying is performed at 100 ° C. or less in a natural drying to a constant temperature / humidity chamber or oven. The dried powder has the shape of one or several agglomerates of powder agglomerates and undergoes physical grinding to control secondary agglomerate sizes. As a physical grinding method, a high speed rotary grinder composed of a rotor and a state, a ceramic ball mill such as a ball mill, a high speed grinder, and the like are used, and the grinding method is not limited. However, it is preferable to finely adjust the size of the secondary aggregate by using a process such as a ball mill or a high speed mill after mechanical grinding. The balls used in the inferior process are not particularly limited, such as quartz balls, alumina balls, zirconia balls, but the size of balls used determines the size of secondary aggregates, and also affects the rotational speed and the structure of jars. . When the size of the total ball is small and ball milling for a long time, the size of the secondary agglomerates is reduced to adjust the above conditions to induce a desired particle size distribution. In addition, the size control of the secondary aggregate is possible even after calcination. The first dispersed slurry is dried and then subjected to a calcination step, wherein the calcination temperature is determined by particle size and the like, and is generally performed at 500 ° C.-1300 ° C. And the calcination temperature is preferably made in a range that does not significantly reduce the size of the unit particles, that is, the particles used during the primary dispersion. After calcination, the size of the secondary aggregate is controlled by a process such as mechanical grinding, ball mill, etc. as described above. However, if the size of the secondary aggregates is adjusted after calcination, the binding force of the secondary aggregates increases, but requires more energy.

The secondary dispersion step is to prepare a slurry of uniform phase using sized secondary silica agglomerates. It is prepared in the same manner as in the step of preparing the primary dispersion slurry, except that the sized secondary aggregates are added in place of the raw materials. Sometimes an ultrasonic treatment process or the like may be added to improve dispersibility. However, in order to secure the strength of the molded body, it is advantageous to prepare a high concentration of slurry, and preferably 40% by weight or more. In the second dispersion step, in addition to the water and the dispersant, inorganic and inorganic additives may be added for cracking of the molded body and for special purposes. As the organic additive, a polymer binder and a plasticizer for improving the bonding force between the silica particles may be used. As the inorganic additive, an inorganic additive such as titania used as a photocatalyst for environmental purification may be used.

The molding step is a step of producing a molded body using the slurry of the low viscosity uniform phase prepared through the secondary dispersion step. 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. In order to induce molding, gel lowering agent may be added. For slurry above pH 10, ester compounds such as ethyl lactate and methyl lactate, which lower the pH value, are mainly used and ammonium fluoride (NH4F) is used. Fluorine compounds are used regardless of the pH value of the slurry. The molded product is prepared by injecting a gelling agent into the slurry dispersed second and then molding the mold after stirring. The molded product is separated from the mold for drying after a certain period of time to enhance the strength of the wet molded body.

The wet molded body separated from the mold is subjected to a drying process under natural drying or constant temperature and humidity conditions. The drying environment is made at a temperature of 10 ° C.-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 of the wet formed body reaches zero. The drying process therefore takes from several hours to several ten 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, remove unnecessary organic matter, and bond particles by viscous flow, that is, to strengthen the molded product. Residual water is removed at 120 ° C-150 ° C and organics are mostly removed at 300 ° C-600 ° C. Finally, the plastic heat treatment process for strengthening the strength of the molded body is processed in an electric furnace at 500 ° C.-1300 ° C. depending on the size of the material particles and the like. The calcining heat treatment step is preferably performed within a range in which the porosity does not decrease due to excessive heat treatment.

The method for producing an asymmetric nanomembrane and ultrafiltration membrane according to the present invention comprises a preparation of a silica support, a preparation of a coating layer, drying, and a heat treatment (firing) step.

The silica support may be prepared by using the silica ceramic filter mentioned in the previously filed 'Porous Ceramic Filter and Manufacturing Method thereof' (Application No. 1020020032729) or the silica ceramic filter whose pore is controlled by the secondary dispersion described above. It is used after manufacture. The formation of the asymmetric coating layer of the silica support prepared by the above method may use a reverse immersion pulling method or a coating method using centrifugal force. First, in the reverse immersion pulling method, the silica particles are coated on the surface of the support by using capillary pressure by contacting a slurry in which silica particles having a small size are dispersed on the surface of the silica support. In this case, the silica slurry used for forming the coating layer uses particles smaller than those of the particles constituting the silica support, and fumed silica or colloidal silica of various particle sizes may be used. The particle size used determines the nanomembrane or ultrafiltration membrane. In the case of nanomembrane, the particles of silica forming the coating layer should be within several nm. Thus, it is prepared using a slurry containing silica particles within several nm. The slurry in which silica particles of several nm or less are dispersed may be prepared by hydrolyzing an alkoxysilane compound under an acid catalyst. When the hydrolyzate hydrolyzed under an acid catalyst is used instead of the silica slurry, the surface of the silica support is coated, dried, and heat treated to form a layer of silica particles of several nm or less, thereby producing an asymmetric nanofilm. The asymmetric membrane prepared by the above method is subjected to a drying step. The drying step is carried out in a constant temperature and humidity chamber in which temperature and humidity are controlled so that the coating layer does not separate or crack.

When drying is complete, heat treatment is performed to remove organics and to enhance strength. Organic matter removal is performed at about 600 ° C or less, and heat treatment for strengthening strength is preferably performed at about 1200 ° C within a range in which the porosity of the coating layer does not decrease.

The present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

Example 1

Preparation of Micro Filter

400 g of fumed silica, Aerosil OX-50 (Degussa., Specific surface area 50 m 2 / g, average particle size 40 nm) was dispersed in 400 g of deionized water. At this time, ammonia water was added together as a dispersant, but was added until the pH of the slurry was 11 or more, and dispersed in a high speed blender to prepare a uniform slurry having a low viscosity. The prepared primary dispersion slurry was placed in an oven and dried at 90 ° C. until moisture was removed. Silica agglomerates from which water was removed were pulverized using a grinder and filtered using a 500 mesh sieve to obtain a uniform secondary aggregate. 300 g of the recovered secondary aggregate powder was added with 250 g of deionized water and 25 cc of 25% aqueous tetramethylammonium hydorxide solution, and then the quartz dispersion was used to adjust the size of the secondary dispersion and the secondary aggregate. Ball milling time. The secondary dispersion slurry prepared by the above method showed high fluidity and had a pH value of 11.8. 16 cc of ethyl lactate was added to the prepared secondary dispersion slurry as a gelling agent, stirred for about 3 minutes, and then injected into a prepared mold. As the slurry into which ethyl lactate was added, the pH value was lowered to 9 or less and the viscosity was increased over time, resulting in loss of fluidity and a molded product. The prepared mold consisted of an acrylic bottom cap (5 cm diameter), an acrylic tube (5 cm inside diameter) mounted on the floor, and a sussing rod (3 cm diameter) installed in the center of the acrylic floor to manufacture a tubular ceramic filter. 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 12 hours for strength. The separated wet molded product was dried for 4 days under natural drying conditions to remove moisture. The dried ceramic filter molded body was calcined at 900 ° C. for 1 hour after heat treatment at 150 ° C. for 5 hours to remove residual moisture. The manufactured tubular silica filter had a geometry of 30 cm in length, 4.7 cm in outer diameter and 0.6 cm in thickness. The porosity of the filter was measured using a porosimeter, a porosimeter. The porosity distribution with two centerlines was found at 38nm and 200nm. Therefore, the pores having a size of about 38 nm are due to the particle size of the fumed silica Aerosil OX-50, which is a starting material, while the pores having a relatively wide distribution around 200 nm are due to the size of the secondary aggregate.

Example 2

Preparation of Micro Filter

500 g of fumed silica Aerosil OX-50 and 1 liter of deionized water were dispersed using a high speed blender. In order to secure the fluidity of the slurry, 15 cc of 10% aqueous solution of ammonium fluoride (NH 4 F) was added and dispersed in a high speed blender. The slurry had very good flowability during dispersion in a high speed blender but soon lost flowability when stirring was stopped. Therefore, the mixture was immediately transferred to a drying vessel for drying after stirring at high speed, and dried in an oven. The dried silica mass was filtered using mechanical grinding and shredding in the same manner as in Example 1, and then heat-treated at 900 ° C. for 1 hour to obtain a relatively hard powder. 300 g of the collected secondary aggregate powder and 300 cc of deionized water were mixed and ball milled for 24 hours in the same manner as in Example 1. The prepared secondary dispersion slurry was formed by adding 10 cc of an aqueous 10% aqueous solution of ammonium fluoride (NH 4 F) and stirring to ensure fluidity and injecting the same mold as in Example 1. The slurry injected into the mold lost fluidity within 5 minutes and a molded body was produced. Drying and heat treatment were carried out in the same manner as in Example 1. The manufactured tubular silica filter showed porosity distribution with two centerlines at 38 nm and 310 nm. Thus, the pores with a size of about 38 nm are due to the particle size of the starting material, fumed silica, Aerosil OX-50, whereas the pores with a relatively wide distribution of about 310 nm are due to the size of the secondary aggregates.

Example 3

Preparation of Micro Filter

Commercial colloidal silica (colloidal silica) OX-K50 (manufactured by Dupont, silica content 49% by weight, average particle size 40nm) 1kg was dried in an oven at 95 ℃ to recover the dried silica mass. The recovered silica mass was ground and ball milled in the same manner as in Example 1 to control the size of the secondary aggregates. The amount of deionized water and tetramethylammonium hydorxide 25% aqueous solution added to the secondary aggregate powder during ball milling was added in the same ratio as in Example 1 to prepare a secondary slurry. Molding and drying step was carried out in the same manner as in Example 1 and the firing process was heat-treated for 2 hours at 850 ℃. The tubular silica filter produced showed porosity distribution with two centerlines at 35 nm and 150 nm. Thus, pores with a size of about 35 nm are due to the particle size of the starting material OX-K50 (average particle size 40 nm), while pores with a relatively wide distribution of about 150 nm are due to the size of the secondary aggregates.

Example 4

Preparation of Micro Filter

Silica filters were prepared in the same manner as in Example 3, using commercial colloidal silica Nycol 2040 (Nycol product, silica content 40 wt%, average particle size 20 nm) as a primary dispersion slurry. As a result of measuring the porosity of the manufactured tubular silica filter, porosity distribution having two center lines was shown at 18 nm and 110 nm. Thus, pores having a size of about 18 nm are due to the particle size of the starting material Nycol 2040 (average particle size 20 nm), while pores having a relatively wide distribution of about 110 nm are due to the size of the secondary aggregate.

Example 5

Preparation of Micro Filter

A primary dispersion slurry was prepared in the same manner as in Example 2, except that ammonium fluoride ((NH 4 F) was added.) Tetraethylortho silicate, an alkoxysilane compound, was chemically equivalent to 4 times the equivalent ratio. The deionized water was hydrolyzed while stirring under a small amount of hydrochloric acid solution catalyst, and as time passed, the temperature was increased by an exothermic reaction and a clear solution of a uniform phase was prepared to prepare an alkoxide hydrolyzate. An amount corresponding to 20% by weight of the primary dispersion slurry was mixed and again uniformly mixed and dispersed with a high speed blender.The slurry in which the hydrolyzate of fumed silica and the alkoxide compound was mixed and dispersed was the same method as in Example 1. The secondary dispersion slurry was prepared by drying with a secondary aggregate size control process. The heat treatment was also performed in the same manner as in Example 1. The prepared silica filter had a porosity distribution having two centerlines at 50 nm and 250 nm, so that the pores having a size of about 50 nm were formed from the starting material Aerosil OX-50. The pores with a relatively wide distribution near about 250 nm are due to the size of the secondary aggregates, while the grain growth is due to hydrolysis of the alkoxide compound.

Example 6

Preparation of Asymmetric Membrane

The silica filter provided in the previously applied "porous ceramic filter and its manufacturing method" (application number 1020020032729) was used as a support. According to the application details, the tubular silica filter (length 50 cm, outer diameter 4 cm, inner diameter 3 cm) made of fumed silica OX-50 exhibited an average pore size of 38 nm and a porosity of 65%. The preparation of the slurry for the asymmetric coating layer is as follows. 20 g of fumed silica Aerosil 300 (Degussa., Particle size 7 nm) was dispersed in 180 g of deionized water, and a pH value of 11 or more was added by adding tetramethylammonium hydroxide, a strong alkali, to improve dispersibility. Adjusted to. A high speed blender was used and additionally processed in an ultrasonic apparatus to grind aggregates to produce well dispersed low viscosity silica slurry. The asymmetric coating using the above slurry used a reverse immersion pulling method. Fill the slurry inside the silica filter support and open the lower valve to allow the slurry to slowly drain out. At this time, the particles of the slurry were coated on the surface of the support by capillary pressure of the support. The filter on which the coating layer was formed was dried in a constant temperature and humidity chamber having a temperature of 30 ° C. and a relative humidity of 70%. The dried filter was heat-treated at 850 ° C. to secure strength. The coating layer of the prepared asymmetric filtration membrane showed an average pore size of 6nm.

Example 7

Preparation of Asymmetric Membrane

As the silica support, the filter prepared in Example 1 was used. As a slurry for coating the asymmetric membrane, a commercial colloidal silica Nycol 1440 (Nycol, particle size 14nm, concentration 40% by weight) was used. The coating and drying were carried out in the same manner as in Example 6, and the heat treatment was performed at 870 ° C. The average pore size of the coating layer of the prepared asymmetric filtration membrane was 13nm.

Example 8

Preparation of Asymmetric Membrane

The silica support was prepared in the same manner as in Example 6. The slurry for preparing the asymmetric coating layer was prepared by the following method. 100 cc of tetraethylortho silicate, an alkoxysilane compound, 20 cc of deionized water, and 100 cc of ethyl alcohol were mixed and stirred, and 16 cc of hydrochloric acid having 0.1 normal concentration was added little by little as a catalyst for the hydrolysis reaction. The mixture was allowed to stand for 2 hours more after stirring until the hydrolysis reaction was completed to eliminate layer separation and to form a transparent single phase.

The solution containing the prepared alkoxide hydrolyzate was used as a coating slurry and coated on the surface of the support by the reverse immersion pulling method in the same manner as in Example 6. After drying in the same manner as in Example 6 to heat treatment at 700 ℃ to prepare an asymmetric membrane. In the prepared asymmetric membrane, the average pore size of the coating layer was 2 nm.

The present invention provides silica fine filtration membranes having various pore sizes such as nano membranes, ultrafiltration membranes, micro filters, etc. based on silica particles, and a method for producing the same.

Claims (6)

a) preparing a first dispersion slurry in which silica particles are uniformly dispersed as a main component: b) controlling the size of the secondary aggregates by drying and pulverizing the first dispersed silica slurry or by calcination and calcination: c) preparing a secondary dispersed silica slurry using the pulverized secondary aggregate as a main component: d) step of forming a molded product by molding a gelling agent into the secondary dispersion silica slurry: e) separating the molded body from the mold and drying: f) heat treatment step of thermally treating the dried formed body at 500 ℃ -1300 ℃ to induce interparticle bonding: Method for producing a ceramic filter comprising a The method of manufacturing a ceramic filter according to claim 1, wherein the silica particles of step a) comprise fumed silica or colloidal silica. a) silica support mainly composed of fume silica or colloidal silica b) ceramic coating layer having pores smaller than the pores of the silica support Ceramic asymmetric filtration membrane comprising the configuration of a) and b) a) preparing a silica support based mainly on fume silica or colloidal silica: b) preparing a ceramic slurry to form a coating layer: c) coating the ceramic slurry of b) on the surface of the silica support: d) drying the asymmetric filtration membrane: e) heat-treating the dried asymmetric filtration membrane at 1300 ° C. or below: Method for producing an asymmetric filtration membrane comprising the above step The method of claim 4, wherein the ceramic slurry forming the coating layer comprises nano-sized fume silica or colloidal silica. The method of claim 4, wherein the slurry forming the coating layer comprises a hydrolyzate of a metal alkoxide compound.