KR100784483B1 - A ceramic filter and Preparation method thereof - Google Patents

Abstract

The present invention relates to a ceramic filter using a ceramic paper manufactured using a ceramic fiber as a main raw material, and a method of manufacturing the same, and more particularly, to a ceramic filter including a ceramic paper, a primary coating layer of alumina oxide, and a secondary coating layer of aluminum phosphate. And it provides a preparation method thereof.

The present invention can adjust the pore size, air permeability, strength properties of the ceramic paper, it is possible to provide a ceramic filter having an improved substrate strength.

High Temperature Inorganic Substrates, Alumina Oxide, Aluminum Phosphate, Coatings, Ceramic Paper

Description

A ceramic filter and preparation method thereof

1 is a perspective view schematically showing the structure of a ceramic filter according to the present invention.

<Description of the symbols for the main parts of the drawings>

10: plate-shaped ceramic paper 20: corrugated ceramic paper

The present invention relates to a ceramic filter and a method for manufacturing the same, and more particularly, to a ceramic filter and a method for manufacturing the same, which are suitable for use at high temperatures due to improved pore size, air permeability and strength properties.

Since the late 1970s, a diesel particulate filter (DPF) has been proposed and studied as a device for filtering particulate matter from diesel engines. The DPF can be broadly divided into a honeycomb monolith filter, a ceramic fiber filter, and a metal filter. Of these, honeycomb monolith filters are vulnerable to high temperature thermal shock and have a short lifespan. In addition, the metal filter has advantages of price and ease of manufacture, but has a weak disadvantage in heat resistance and corrosion resistance, and thus, research on nonwoven paper type filters made of ceramic fibers has recently been actively conducted.

In order to use the nonwoven paper made of ceramic fiber as a filter, the wave form is made in the green paper state and the surface area is increased in a single volume. However, in the case of ceramic paper composed only of ceramic fibers, since the paper itself has a small tensile force and a short fiber length, organic fibers such as cellulose fiber, nylon, kevlar (trademark), and various organic chemicals may be used to make continuous paper. It should be used to have tensile force. In addition to the process of making continuous paper, the tensile strength of the organic paper other than the ceramic fiber and various binders are required in the process of corrugating the ceramic paper.

On the other hand, combustion equipment such as combustion engines, thermal power plants, and incinerators include systems capable of evacuating products generated during the combustion process. Such an exhaust system includes a catalyst-supported flow-through type substrate or a wall-flow type filter substrate. Combustion products may include complete combustion or incompletely burned byproducts such as soot particles, CO, NOx, and the like. Soot particles are known to have adverse effects on humans and the environment. The emission levels from internal combustion engines are strictly regulated at national level, and relevant laws and regulations are being enforced. As a result, such regulations have increased interest in exhaust systems that can effectively remove soot particles, and until recently, much effort has been made in developing systems based on particle filters.

In the case of internal combustion engines, the exhaust system consists of a catalyst and a filter component. Catalytic converters typically consist of a flow-through substrate carrying a catalyst having a catalytic monolithic structure. Typical catalyst-supported flow-through substrates are effective for complete oxidation reactions such as CO to CO ₂ oxidation. However, conventionally used flow-through substrates are relatively expensive and are not effective for the combustion of exhaust particles.

In addition, wall-flow type substrates are also commercially available and are manufactured by extrusion using materials having a pore structure such as cordierite or silicon carbide (US Pat. No. 4276071). . Such extruded substrates are very effective and durable, but have a porosity of less than 50%, a small trapping capacity, a very low reactivity through the loading of the catalyst, and a relatively high cost.

In addition, a particle filter made of fibers having an advantage in terms of cost has been produced, but it is still insufficient to commercialize due to the trade-off between durability, pore size, and air permeability (US Pat. Nos. 3,112,184,3899,555). 4608361, 4652286, 47.896, 5194078, 5322537).

In order to solve the problems in the prior art as described above, an object of the present invention is to form alumina layer on the surface of the fiber by coating and heat-treating the ceramic paper first using alumina oxide particles, and then secondly using aluminum phosphate Through the heat treatment after coating, to provide a ceramic filter with improved physical properties by alternating operation between aluminum phosphate and alumina oxide and a method of manufacturing the same.

Another object of the present invention is to provide a ceramic filter applicable to a diesel engine filter and a method of manufacturing the same, by minimizing defects on the surface of the fiber caused by phosphoric acid and changes in strength of the entire web.

Another object of the present invention is to provide a ceramic filter having a high pore size and air permeability through a step-by-step coating process.

In order to achieve the above object, the present invention provides a ceramic filter comprising a ceramic paper, a primary coating layer of alumina oxide and a secondary coating layer of aluminum phosphate.

The present invention also provides a method for preparing a ceramic paper, comprising: (a) preparing a ceramic paper using a slurry solution containing 0.1 to 10 mm of ceramic fiber, organic fiber and organic binder; (b) corrugating the ceramic paper, placing plate-shaped ceramic paper on the lower layer, bonding and winding each other to prepare a ceramic filter having a honeycomb structure, and (c) coating the ceramic filter with an alumina oxide solution first and drying it. ; And (d) coating the first coated ceramic filter with an aluminum phosphate solution, drying, and firing the same.

Hereinafter, the present invention will be described in more detail.

The present invention provides a high temperature ceramic filter comprising a ceramic fiber suitable for use alone or as a reaction support including a catalyst, a thermal power plant exhaust gas purification device, and a vehicle exhaust gas purification device. It is a feature that provides a method of enhancing the strength of the substrate and having sufficient pore size and air flow.

In the present invention, aluminum phosphate (aluminum phosphate) is used as an inorganic binder to form a bond between ceramic fibers, and the inorganic phosphate is first coated on the surface of the fiber first, and then the aluminum phosphate is coated secondly, so that the aluminum phosphate binder and the fiber Substrate strength can be greatly improved by preventing substrate defects through excessive reactions of the liver, and pore size and air flow can be controlled through a two-stage coating.

In the present invention, the primary coating layer of the alumina oxide is formed by a sol solution of 0.1 to 10% by weight containing a nano-size alumina oxide powder. In addition, the secondary coating layer of the aluminum phosphate includes aluminum hydroxide and phosphoric acid, and is formed by a coating solution having an atomic ratio of P / Al of 3 to 50.

In detail, the present invention is prepared using alumina oxide having 40-60 nm, preferably about 50 nano-size as an inorganic particle in the primary coating, a solution in the form of a sol, and then using the primary coating layer To form. The concentration of alumina oxide in the prepared solution is preferably 0.1 to 10% by weight. In this case, when the concentration of the alumina oxide solution is less than 0.1%, excessive repetitive work must be performed to completely coat the fiber surface. In addition, when the concentration is more than 10% by weight, partial pore blockage may occur due to excessive alumina concentration, thereby causing an excessive decrease in permeability.

The inorganic particles used in the secondary coating is an aluminum phosphate solution, which includes aluminum hydroxide and phosphoric acid, it is preferable that the atomic ratio of P / Al is 3 to 50.

Preferably, the ceramic filter of the present invention has a length of 0.1 to 10mm, the ceramic fiber comprising at least one of alumina and silica; Organic fiber; And a corrugated ceramic paper made from a slurry composition comprising an organic binder, and a plate-like ceramic paper made of the same material. 1 is a perspective view schematically showing the structure of a ceramic filter of the present invention. In FIG. 1, reference numeral 10 denotes a plate-shaped ceramic paper, and 20 denotes a corrugated ceramic paper.

At this time, the plate-shaped ceramic paper used in the ceramic filter according to the present invention is not particularly limited as long as it is commonly used in the art, it is also possible to use the ceramic green paper prepared above as it is.

Method for producing a ceramic filter of the present invention, (a) to prepare a ceramic paper using a slurry solution containing 0.1 to 10mm ceramic fiber, organic fiber and organic binder; (b) corrugating the ceramic paper, placing plate-shaped ceramic paper on the lower layer, bonding and winding each other to prepare a ceramic filter having a honeycomb structure, and (c) coating the ceramic filter with an alumina oxide solution first and drying it. ; And (d) second coating the primary coated ceramic filter with an aluminum phosphate solution, drying, and calcining to prepare a ceramic filter usable at high temperature.

The aluminum phosphate solution is used to increase the temperature and structural stability of the ceramic green paper filter structure. The aluminum phosphate solution is prepared by mixing aluminum hydroxide and phosphoric acid, and the P / Al atomic ratio in the solution may be 3 to 50. At this time, when the P / Al atomic ratio is less than 3, there is a concern that the solubility of alumina is very small and the formation of aluminum phosphate may not be smooth. If the P / Al ratio is higher than 50, the concentration of alumina is low due to the excessive amount of phosphoric acid. This damage can weaken the strength. The phosphoric acid serves to carbonize the organic fiber at a low temperature during firing, thereby preventing the organic fiber from burning and flying away.

In addition, if necessary, the surface may be first coated with alumina oxide powder before coating with aluminum phosphate.

In the present invention, the process of coating the ceramic green paper with the aluminum phosphate solution is not particularly limited, and may be performed, for example, by impregnation or spraying. The aluminum phosphate solution may further include a mixed solvent of water and a penetration solvent. Ethanol, isopropyl alcohol, etc. may be used as the penetration solvent, and the content of the penetration solvent may be used in an amount of 1 to 30 wt% based on water. If the content of the penetrating solvent is less than 1% by weight, the role is not smooth, and if it exceeds 30% by weight may cause the precipitation of aluminum phosphate. In addition, the content of aluminum phosphate in the total aluminum phosphate solution may be 1 to 80% by weight based on the solid content, if less than 1% by weight may be repeated several times to coat the required amount, if it exceeds 80% by weight Excess aluminum phosphate remains between the pores, resulting in pore reduction and the impact resistance of the paper may be reduced.

In addition, the heat treatment drying process after the primary coating of the alumina oxide is preferably made in an air atmosphere, the firing temperature may be carried out at 400 to 1200 ℃. If the firing temperature is less than 400 ℃ the removal of the organic component is not completely made, if it exceeds 1200 ℃ may cause a partial melting effect of the fiber used.

The firing step after the secondary coating of the aluminum phosphate can be carried out in a vacuum, inert gas or air, the firing temperature is preferably 400 to 1,100 ℃. When the firing temperature is less than 400 ° C, the organic component is not completely removed. When the firing temperature is above 1,100 ° C, the aluminum phosphate may be deformed, resulting in a decrease in strength.

Through the firing process, the organic fibers are carbonized to form pores, and the aluminum phosphate hollow fibers in the ceramic filter have two phases, Al (PO ₃ ) ₃ (aluminum metaphosphate) and AlPO ₄ (aluminum orthophosphate). It is believed to exist in mixed form.

The ceramic green paper may be prepared from a slurry solution comprising a ceramic fiber, an organic fiber and a small amount of organic binder.

The content of the ceramic fiber is 50-80% by weight, more preferably 70-80% by weight based on the total solids of the slurry. When the content of the ceramic fiber is less than 50% by weight, it may adversely affect the strength and pore characteristics after firing. When the content of the ceramic fiber exceeds 80% by weight, the amount of the organic fiber and the organic binder is too small so that the tensile strength may drop during the wave formation step. There is.

The ceramic fiber is made of a material that can withstand about 1200 ° C or more, and uses at least one of alumina or silica, such as alumina and alumina silicate. For example, ceramic fibers use such as alumina, alumina silicate, alumina borosilicate, mullite, and the like. The ceramic fiber has a diameter of 1-20 microns, more preferably 2-7 microns in diameter, and preferably has a length of 0.1-10 mm.

The organic binder may be used alone or in combination of water-soluble acrylic, polyvinyl alcohol, amphoteric starch and the like, preferably water-soluble acrylic resin. The content of the organic binder is used in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the ceramic fiber. When the content of the organic binder is less than 0.1 parts by weight, the bonding between the fibers is not made, and when the content of the organic binder is greater than 20 parts by weight, the flowability of the ceramic green paper is large and the adhesion is not easy to handle. The organic binder must be flexible in order for the glass transition temperature to be higher than room temperature and to have a three-dimensional structure.

The organic fiber is composed of wood pulp fibers such as cellulose fibers, natural fibers such as hemp, synthetic fibers such as nylon, rayon, polyester, polypropylene, polyethylene, aramid, acrylic fibers, and mixtures thereof. Can be selected from the group, specific examples of the aramid fibers are Kevlar fibers manufactured by Dupont. The wood pulp fiber enhances the web strength of the sheet formed in the papermaking machine. The organic fiber may be used in an amount of 5 to 50 parts by weight, and more preferably 15 to 25 parts by weight, based on 100 parts by weight of the ceramic fiber based on solids in the slurry. When the content of the organic fiber is less than 5 parts by weight, the tensile strength of the ceramic green paper is lowered, and when it exceeds 50 parts by weight, the strength may be reduced due to the presence of excess alumina phosphate hollow fiber after heat treatment.

In addition, the slurry solution may include water, and the amount of water used in the slurry solution is not critical, and may be sufficient to keep the entire process smoothly. The present invention can remove excess water through a vacuum pump connected to the papermaking apparatus and remove excess water remaining through the press to smoothly remove water in the process.

In addition, in the slurry solution of the present invention, in order to improve adhesion of the organic binder to the ceramic fiber or the organic fiber, a conventional pH adjusting agent may be further added. The pH adjusting agent may be used without particular limitation as long as it is commonly used in the art, for example, by using alum (aluminum sulfate), it is possible to maintain the pH of the slurry solution between 5.5-6.5.

The manufacturing method of the ceramic green paper of this invention can use the papermaking method well known in the art normally, The method is not specifically limited. In one preferred embodiment, the ceramic fibers and the organic fibers are mixed to disperse the fibers, and the organic binder having the above-described configuration is mixed to make the fibers aggregated, and then dried to prepare ceramic green paper. Can be.

On the other hand, the ceramic filter according to the present invention is manufactured in the form of honeycomb after the step of corrugating the ceramic green paper as described above, the process of coating the aluminum phosphate solution after the manufacture of the honeycomb type ceramic filter It is preferable to carry out. The waveform may be performed by using a waveform device commonly used in the art, for example, the drum of the waveform device that can be used in the present invention is each of the length of the valley and pitch of 3mm, It is preferable that the surface temperature and the paper feed rate are made to be adjustable.

As described above, the present invention is a uniform coating of alumina oxide particles on the surface of the ceramic paper first, and aluminum phosphate (aluminum phosphate) on the secondary coating to form a bond between the ceramic fibers to form a pore size, air permeability of the ceramic paper In addition, the strength properties can be controlled, and defects of the ceramic fiber itself due to phosphoric acid contained in the aluminum phosphate can be suppressed through the primary coating of nano-sized alumina oxide (also called alumina) and contribute to improving the bonding strength. .

The ceramic filter having the honeycomb structure of the present invention thus obtained can be used as an exhaust gas filter to effectively remove particles contained in diesel exhaust gas. In addition, the ceramic filter of the present invention may be used as a dust removal filter in power plants, chemical plants, cement plants.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

EXAMPLE

Example  One

Ceramic green paper manufacturing

3 g of alumina-silica fiber having an average length of 300 micrometers was added to 2000 ml of water, followed by vigorous stirring to disperse the fibers. Coniferous pulp, an organic fiber, was charged with 25% by weight of the fiber. The acrylic binder, which gives the flexibility of the ceramic paper, was added 20% to the weight of the fiber, and a small amount of 1% aluminum sulfate aqueous solution of pH 3 was added so that the pH of the entire slurry was about 5.5.

Finally, excess water was removed, and ceramic green paper having a diameter of 9.5 cm and a thickness of about 750 micrometers was prepared. The ceramic green paper was naturally dried at room temperature for only 30 minutes and then dried in the drying oven at 100 ° C.

(Primary inorganic coating)

Alumina oxide powder having a size of 50 nm was prepared by mixing with water and isopropyl alcohol to have a concentration of 5%, 10% and 20%, respectively. The prepared ceramic green paper was immersed and coated in the prepared alumina sol solution, and dried at 100 ° C. and finally heat treated at 1,100 ° C.

(Secondary inorganic coating)

Inorganic coating was performed on the heat-treated ceramic paper by using aluminum phosphate solution.

Aluminum phosphate was mixed with Al (OH) ₃ (manufactured by Aldrich) and H ₃ PO ₄ (85%, made by Junsei), quantitatively mixed so that the atomic ratio of P / Al was 23, and stirred while raising the temperature to 150 ° C. The Al (OH) ₃ powder was dissolved in phosphoric acid, thereby producing a high viscosity and clear solution.

In the aluminum phosphate solution for coating, the aluminum phosphate solution prepared above was dissolved in a 3: 1 mixed solvent of water and isopropyl alcohol to prepare a 20% aluminum phosphate solution. The first coated ceramic paper was dip-coated, dried at 110 ° C., and calcined at 800 ° C. under atmospheric conditions.

Example  2 to 9

Except that the composition of the alumina sol of the primary coating solution and the ratio of P / Al of the secondary coating solution was changed as shown in Table 1, it was carried out in the same manner as in Example 1.

Load strength, average pore size and air permeability were measured using the finally obtained ceramic paper of Examples 1 to 9, and the results are shown in Table 1 below.

TABLE 1

Example Al ₂ O ₃ sol concentration AlPO concentration Peak load MFP Permeability One 5% 23 176 28.7 15 2 5% 30 183 31.3 16 3 5% 35 171 34 17.3 4 10% 23 329 32.9 8 5 10% 30 385 21.1 8.8 6 10% 35 343 28.3 9.8 7 20% 23 300 33.8 10 8 20% 30 358 34.1 6.8 9 20% 35 371 30.9 4

Comparative example  One

The ceramic green paper obtained in Example 1 was treated using the primary and secondary coating solutions prepared as follows.

(Primary inorganic coating)

Bentonite clay powder having a size of 40-70 mm was mixed with water and isopropyl alcohol to prepare 2 wt% and 4 wt%, respectively. The prepared ceramic green paper was immersed and coated in the prepared clay powder solution, and dried at 100 ° C. and finally heat treated at 1100 ° C.

(Secondary inorganic coating)

Inorganic coating was performed on the heat-treated ceramic paper by using aluminum phosphate solution.

Aluminum phosphate is mixed with Al (OH) ₃ and H ₃ PO ₄ to have a P / Al ratio of 23, and stirred while raising the temperature to 150 ° C. As a result, Al (OH) ₃ powder is dissolved in phosphoric acid. It was prepared to produce.

The aluminum phosphate solution for coating was dissolved in aluminum phosphate in a mixed solvent of water and isopropyl alcohol (3: 1) to synthesize a 20% solution. The first coated ceramic paper was dip-coated and dried at 110 ° C., and then calcined at 800 ° C. under atmospheric conditions.

Finally, the obtained ceramic paper showed the strength of 61g load strength.

Comparative example  2

The ceramic green paper obtained in Example 1 was coated using only aluminum phosphate solution and heat treated at 800 ° C. The strength showed 87g load strength value.

As described above, the ceramic paper of the present invention minimizes the trade-off between pore size, air permeability, and strength through a two-step coating process using alumina oxide and aluminum phosphate, and easily achieves physical property changes according to application requirements. Substrates can be prepared that can be effectively used at high temperatures.

Claims (11)

A ceramic filter comprising ceramic paper, a primary coating of alumina oxide and a secondary coating of aluminum phosphate. The ceramic filter of claim 1, wherein the primary coating layer of the alumina oxide is formed by a sol solution having a concentration of 0.1 to 10 wt% including 40-60 nanoscale alumina oxide powder. The ceramic filter of claim 1, wherein the secondary coating layer of aluminum phosphate comprises aluminum hydroxide and phosphoric acid, and is formed by a coating solution having an atomic ratio of 3 to 50 of P / Al. The ceramic filter of claim 1, wherein the ceramic filter has a fiber length of 0.1 to 10 mm and includes at least one ceramic fiber selected from the group consisting of alumina and silica; Organic fiber; And a ceramic paper made from a slurry composition comprising an organic binder, and a honeycomb structure consisting of corrugated paper. (a) preparing a ceramic paper using a slurry solution comprising 0.1 to 10 mm of ceramic fiber, organic fiber and organic binder; (b) forming a honeycomb ceramic filter by corrugating and winding the ceramic paper; (c) first coating the ceramic filter with an alumina oxide solution and drying it; And (d) a process of secondary coating, drying and firing the first coated ceramic filter with an aluminum phosphate solution Method of manufacturing a ceramic filter comprising a. The method of manufacturing a ceramic filter according to claim 5, wherein the heat treatment drying step after the coating of the alumina oxide solution is performed in an air atmosphere and is performed at 400 to 1200 ° C. 7. The method of claim 5, wherein the weight of aluminum phosphate in the aluminum phosphate solution is 1-80% by weight based on solids. The method of claim 5, wherein the firing process is performed in a vacuum, inert gas, or air, and is performed at 400 to 1100 ° C. 7. The method of claim 5, wherein the organic binder comprises an acrylic binder, polyvinyl alcohol, amphoteric starch, or a mixture thereof. The method of claim 5, wherein the ceramic fiber is selected from the group consisting of alumina, aluminosilicate, alumino boro silicate and mullite. The method of claim 5, wherein the organic fiber is selected from the group consisting of cellulose fiber, hemp, nylon, rayon, polyester, polypropylene, polyethylene, aramid, acrylic fiber, and mixtures thereof, the organic fiber content of the ceramic fiber 5 to 50 parts by weight based on 100 parts by weight of a ceramic filter manufacturing method.

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