Manufacturing method of ceramic support body for membrane separation

Abstract

To provide a manufacturing method of a ceramic support body for membrane separation obtained by focusing on a hydrothermal synthetic condition for uniformly generating a bore diameter.SOLUTION: A nonoxide porous ceramic is used in a ceramic support body for membrane separation constituting a molecular sieve filter obtained by forming a separation membrane such as zeolite on a surface of the ceramic support, and therefore, a process of hydrothermal synthesis is performed in a minus potential region where a zeta potential (mV) is equal to or less than 0 mV in the relation of a pH value-zeta potential (mV) in hydrothermal synthesis.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a ceramic support for membrane separation of a porous filter for supporting a separation membrane, also known as a "molecular sieve." [Background technology]

[0002] For example, known ceramic membranes that contribute to membrane separation of fluids include zeolite, silica (silicon), silicalite, carbon, etc. These separation membranes are formed on the surface of a ceramic support to create a molecular sieve filter.

[0003] Zeolite, a typical molecular sieve filter, has a particle size of 1 nm (10 -9 A crystal with micropores of μm (10 -6 The membrane is formed on a porous support (filter substrate) with pore sizes on the order of 1 nm. By using such a porous filter, inorganic and organic molecules of 1 nm or less can be separated based on their size difference.

[0004] As a disclosure of prior art relating to this type of molecular sieve filter (membrane separation filter), for example, a ceramic separator using a hollow ceramic rod as a fluid membrane separation filter is disclosed in Patent Document 1. The membrane separation filter disclosed in Patent Document 1 has a zeolite layer formed on the surface of a porous tube made of alumina (oxide) by hydrothermal synthesis. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-66528 Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, ceramic supports for membrane separation include non-oxide types such as silicon nitride (SiN) and silicon carbide (SiC) in addition to oxide types. Generally, ceramics are manufactured using hydrothermal synthesis, but oxide-based ceramics undergo an atmospheric change from a strong alkaline to a strong acidic region during the synthesis process. As a result, the zeta potential of the oxide surface changes to a positive region at a pH of 7, causing a change in the composition of the ceramic pores. The elution of the oxide material used as the base material acts as a catalyst, inhibiting the deposition of membrane formation and causing fluctuations in the permeation flow rate of the support.

[0007] In contrast, in the case of a support made of a non-oxide material, the amount of change is small, and the zeta potential during the manufacturing process is always stable in the negative range. In porous ceramic supports made of non-oxide materials, the particle diameter of the aggregate is D, and the interparticle pore diameter d that occurs after molding and firing generally falls within the range of d = 0.15D to 0.45D depending on the density.

[0008] In order to generate pores with a uniform diameter, the selection of the particle size of the aggregate is the most important factor, and various molding conditions such as the amount of sintering matrix and the sintering temperature must be controlled. An object of the present invention is to provide a method for producing a ceramic support for membrane separation, focusing on various conditions for producing the above-mentioned pores with a uniform diameter. [Means for solving the problem]

[0009] The means for achieving the above object of the present invention are listed below. Note that the present invention is not limited to the configurations described below and in the embodiments described below, and it goes without saying that various modifications are possible within the scope of the technical concept of the present invention.

[0010] The method for producing a ceramic support for membrane separation according to the present invention comprises the steps of: (1) The method is characterized by using non-oxide porous ceramic materials and carrying out the hydrothermal synthesis process in a negative potential range where the zeta potential (mV) is below 0 mV in the relationship between the pH value and the zeta potential (mV) in hydrothermal synthesis. Further, the method for producing a ceramic support for membrane separation according to the present invention comprises the steps of: (2) The method is characterized in that a non-oxide porous ceramic material is used, and the hydrothermal synthesis process is carried out at a pH value in the range of 3 to 10 in terms of the relationship between the pH value and the zeta potential (mV) in the hydrothermal synthesis.

[0011] By carrying out the manufacturing process while synergistically considering the above (1) and (2), a ceramic support for membrane separation with good separation efficiency can be obtained.

[0012] In the examples described below, silicon carbide is used as the non-oxide porous ceramic material, although silicon nitride (SiN) can also be used.

[0013] The configurations of a single-tube filter element using a ceramic support manufactured by the manufacturing method according to the present invention and a filter module formed by bundling filter elements are as follows.

[0014] (3) The ceramic filter element manufactured using the manufacturing method of the ceramic support for membrane separation according to the present invention is composed of a hollow single-tube support formed of a non-oxide porous ceramic produced by hydrothermal synthesis in a pH range where the zeta potential in the hydrothermal synthesis is negative, using the manufacturing method described in (1) above.

[0015] (4) Furthermore, using the manufacturing method of the present invention described in (2) above, the support is constructed of a hollow single tube manufactured so that the relationship between pH value and zeta potential (mV) during hydrothermal synthesis is in the range of pH value 3 to 10.

[0016] Then, a ceramic filter element for membrane separation is constructed using a hollow single-tube support having good separation efficiency, which is manufactured by synergistically considering the above (3) and (4).

[0017] The hollow single pipe may have both hollow ends open, or one end may be closed with the ceramic itself.

[0018] The surface or inner surface of the hollow single tube is then coated with a thin film material having a pore size of 1 nm or less, preferably zeolite, which allows only specific molecules / particles to pass through, to form a molecular sieve filter.

[0019] A molecular sieve filter can be constructed by bundling a plurality of the above ceramic filter elements into one unit.

[0020] That is, a filter module can be constructed by bundling a plurality of ceramic filter elements manufactured using the manufacturing method of the ceramic support for membrane separation according to the present invention, aligning their longitudinal directions, and connecting at least both ends of the elements with a matrix material to form a unit, covering both ends connected with the matrix material with cap members, leaving only the hollow open ends of the ceramic single-tube filter elements exposed, and fixing both ends and the cap members with a fixing material having a thermal expansion coefficient similar to that of the constituent material of the ceramic filter elements. [Effects of the Invention]

[0021] The manufacturing method according to the present invention makes it possible to obtain a ceramic support for membrane separation with good pore size uniformity and high strength. By coating this ceramic support with a separation membrane made of dense polycrystalline material such as zeolite, a molecular sieve filter support with pore sizes on the order of micrometers can be obtained. A thin zeolite membrane is then formed on the surface of this support. This allows for stable screening of organic and inorganic molecules of 1 nm or less based on their size differences.

[0022] Furthermore, it is possible to provide a filter module in which ceramic single-tube filter elements manufactured by this method are bundled together to form an easily handled filtering member.

[0023] In addition, the widely used monolithic (lotus root type, honeycomb type, etc.) molecular sieve filters are entirely block-shaped, so the communication distance between the inside and outside of the filter is long and varies, resulting in a small filter area per unit volume and a heavy weight, which means that the filter efficiency cannot be said to be good.

[0024] In contrast, when single-tube filters using supports manufactured using the manufacturing method of the present invention are bundled together to form a module, the communication distance between the inside and outside of each filter is uniform, the weight is light, and the internal and external areas of the filter are uniform overall, so the filter efficiency per unit volume is extremely high compared to monolithic filters. Therefore, when used in a water purification device, for example, the device becomes small and lightweight overall, making it easy to transport and operate in disaster areas or areas with water shortages. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a cross-sectional view of a molecular sieve illustrating a method for producing a ceramic support for membrane separation according to the present invention; [Figure 2] An explanatory diagram of manufacturing conditions in the method for manufacturing a ceramic support for membrane separation according to the present invention. [Figure 3] Schematic diagram of a ceramic single-tube filter element manufactured by the method for manufacturing a ceramic support for membrane separation according to the present invention. [Figure 4] Schematic diagram of the shape of the other end of the ceramic single-tube filter element shown in Figure 3. [Figure 5] FIG. 1 is an explanatory diagram of an inter-element gap formed by bundling and fixing a plurality of ceramic single-tube filter elements manufactured by the method for manufacturing a ceramic support for membrane separation according to the present invention. [Figure 6] FIG. 1 is a perspective view illustrating the schematic structure of a filter module using a ceramic single-tube filter element manufactured by the method for manufacturing a ceramic support for membrane separation according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. [Example]

[0027] 1 is an explanatory diagram of a cross section of a main part of a molecular sieve to explain the manufacturing method of a ceramic support for membrane separation according to the present invention, showing a state in which a thin film material 13 for the molecular sieve is formed on one surface of a wall 18 of the ceramic support for membrane separation filter. This thin film material 13 is preferably a zeolite membrane, with a pore size of 1 nm or less and a thickness of about 0.1 μm, and in FIG. 1 it is fixed to the grain boundaries of the surface layer of the wall 18 by the anchor effect AN.

[0028] The fluid to be filtered is filtered through the pores of the wall 18, which have a diameter of 10 ―6 By passing from the bottom of the ceramic support (bottom of the paper) of about μm to the thin film material 13, the molecules are separated by their molecular size.

[0029] 2 is an explanatory diagram of the production conditions in the method for producing a ceramic support for membrane separation according to the present invention, in which the horizontal axis represents the pH value of the solution in the hydrothermal synthesis process, and the vertical axis represents the zeta potential (mV).

[0030] Figure 2 shows the relationship between pH and zeta potential for silicon carbide (SiC), alumina (Al2O3), yttrium oxide (YO3), and indium tin oxide (ITO) as hydrothermal synthesis targets. In this example, a 0.01M NH4NO3 solution (0.01M solution of ammonium nitrate) was used. As shown in the figure, the zeta potentials of silicon carbide and yttrium oxide are negative over a wide range in the solution pH range of 3 to 10 (range indicated by double-headed arrow B). Also, in the negative zeta potential range below 0 mV (arrow C), silicon carbide and yttrium oxide are present in a wide pH range.

[0031] From this characteristic, it can be seen that silicon carbide is most stable when the pH of the hydrothermal synthesis solution is in the range of 3 to 10. From another perspective, it can also be seen that silicon carbide is most stable in the negative range where the zeta potential is 0 mV or less. It is preferable to use silicon carbide (SiC) under process conditions in which the pH is in the range of 3 to 10 and the zeta potential is in the range of 0 mV or less in FIG.

[0032] In this example, taking this into consideration, silicon carbide was used as the substrate in the manufacture of a ceramic support for membrane separation. In the case of porous ceramic supports hydrothermally synthesized using silicon carbide (SiC) as a non-oxide material, if the particle diameter of the aggregate is D and the diameter of the interparticle pores generated after molding and firing is d, the pore diameter is generally within the range of d = 0.15 to 0.45D depending on the density, and a uniform pore diameter is generated.

[0033] Next, specific examples of molecular sieve filters manufactured by the above-described method for manufacturing a ceramic support for membrane separation according to the present invention will be described with reference to FIGS.

[0034] FIG. 3 is a schematic diagram of a ceramic single-tube filter element 10 manufactured by the method for manufacturing a ceramic support for membrane separation according to the present invention, with FIG. 3(a) being an explanatory diagram of a first configuration example and FIG. 3(b) being an explanatory diagram of a second configuration example. The thin arrow → indicates an open end. FIG. 4 is a schematic diagram of the shape of each other end of a stack of multiple single-tube filter elements shown in FIG. 3(a) and (b). Note that for the sake of explanation, the thickness of the thin film material 13 is exaggerated in FIG. 3. The thin film material 13 is not shown in FIG. 4.

[0035] In the configuration example shown in Figure 3(a), one end (the end on the left side of the drawing) and the other end (the end on the right side of the drawing) of the hollow single-tube support 11 are both open ends, as indicated by thin arrows →. In the configuration example shown in Fig. 1(b), one end (the end on the left side of the drawing) of the hollow single pipe support 11 is an open end, and the other end (the end on the right side of the drawing) is a closed end 14. This closed end 14 is formed as a bag-shaped terminal end using only the constituent material of the hollow single pipe support 11 itself.

[0036] Fig. 5 is an explanatory diagram of the inter-element gap formed by bundling and fixing a plurality of ceramic single-tube filter elements manufactured by the method for manufacturing a ceramic support for membrane separation according to the present invention. Fig. 5 is a schematic diagram of a state in which a plurality of single-tube filter elements 10 are stacked and bundled in the longitudinal direction, with the side surfaces of adjacent single tubes joined with a matrix material 15, as viewed from one end (open end) of the single tubes, and the spacing between the single tubes is exaggerated for illustrative purposes. The matrix material 15 is formed by applying and firing a ceramic material having the same thermal expansion coefficient as the material of the support 11 of the single-tube filter element 10 . The same applies to the adjustment of the diameter of the pores formed between the ceramic particles that constitute the ceramic support.

[0037] This matrix material 15 is made by applying a matrix material dispersant of the matrix material component to the periphery of the single-tube filter element 10 to a predetermined thickness (adjustable by the amount of application), and then sintering it in a firing process to bond the opposing surfaces of the supports 11 of adjacent filter elements.

[0038] When the applied matrix material dispersion is in a fluid state, its surface energy (surface tension) causes it to assume the cross-sectional shape shown in the figure, and sintering controls the size of the gap G to the desired size. These gaps G (G1, G2, G3) become passages for the filtrate that has passed through the wall of the support 11 of the single-tube filter element 10, and Figure 5 shows that increasing the amount of application increases the diameter of the gap G in the order (a) → (b) → (c).

[0039] Figure 6 is a perspective view illustrating the schematic structure of a filter module using a ceramic single-tube filter element manufactured by the method for manufacturing a ceramic support for membrane separation according to the present invention, and is a suitable configuration for a filter in a water purification device. In the figure, several single-tube filter elements 10 are bundled together to form a triangular unit. The module is then constructed by bundling several units together and securing their ends with caps 16 and fasteners 17.

[0040] In Figure 6, ten filter elements 10 are stacked to form a unit with a triangular cross section, and six of these units are combined to form one module. Since this type of ceramic member may break if there is any rattle between them, in Figure 6 each unit is held together with intermediate fixing material 17a.

[0041] The fixing material 17 and the intermediate fixing material 17a, which are filled between the units and the caps 16 to fix the single-pipe filter elements 10 of each unit, are preferably made of a material with the same thermal expansion coefficient as the single-pipe filter elements 10, and are preferably made of the same ceramic as the single-pipe filter elements 10. The caps 16 also have the function of protecting the module from external forces, and can be made of stainless steel, plastic, etc., but are not particularly limited thereto.

[0042] By setting the number of units per unit to, for example, 3, 6, 10, 15, 21, 33, etc., the volume of the module can be minimized and the water purification capacity per module can be adjusted. Although FIG. 6 shows a substantially cylindrical module, the present invention is not limited to this, and stacks of modules with rectangular cross sections can be used as appropriate depending on the application.

[0043] By installing at least two of these filter modules and backwashing one with the purified water of the other, filter replacement is no longer necessary, making it possible to provide an inexpensive, easy-to-use, and highly efficient water purification device to disaster-stricken areas and countries and regions around the world suffering from shortages of drinking water.

[0044] According to this example, a ceramic support for membrane separation having uniform pore size, high strength, and high filtration performance can be produced. Furthermore, a ceramic single-tube filter element using a ceramic support for membrane separation manufactured by the manufacturing method of the present invention can provide a filter module that is easy to handle and exhibits stable filtration performance. [Industrial Applicability]

[0045] The present invention relates to a method for manufacturing a ceramic support for membrane separation, and is not limited to filters for water purifiers, such as the ceramic single-tube filter elements given in the examples, but can also be applied to molecular sieve filters used in filter treatment equipment for various liquids and gases that require separation of components. [Explanation of symbols]

[0046] 10 Single-tube filter element 11 Support 12 Open end 13 Thin film material (zeolite) 14 Closed end 15 Matrix material 16 Cap material 17 Fixing material 17a Intermediate fixing material 18 Wall

Claims

1. A method for producing a ceramic support for membrane separation, comprising: A method for producing a ceramic support for membrane separation, characterized in that a non-oxide porous ceramic material is used, and the hydrothermal synthesis process is carried out in a negative potential region where the pH value-zeta potential (mV) relationship in the hydrothermal synthesis is such that the zeta potential (mV) is 0 mV or less.

2. A method for producing a ceramic support for membrane separation, comprising: A method for producing a ceramic support for membrane separation, characterized in that a non-oxide porous ceramic material is used, and the hydrothermal synthesis process is carried out at a pH value in the range of 3 to 10, where the relationship between the pH value and the zeta potential (mV) in the hydrothermal synthesis is the pH value.

3. 3. The method for producing a ceramic support for membrane separation according to claim 1, wherein the non-oxide porous ceramic material is silicon carbide.

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