JPH0518613B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD OF THE INVENTION The present invention relates to an improved method for manufacturing a filter medium made of a glass-ceramic laminate. More specifically, the present invention provides a filter material in which a porous glass thin film is laminated on the surface of a porous ceramic support having a high permeation rate and good mechanical strength. This article relates to a manufacturing method that prevents such problems from occurring. BACKGROUND ART It has been known that porous glass membranes are useful as separation membranes because they have a narrow pore size distribution and excellent heat resistance. However, when this porous glass membrane is normally used as a separation membrane, it has to be thickened to about 0.5 mm from the viewpoint of strength, which has the disadvantage that the permeation rate is inevitably reduced significantly. ing. In order to compensate for these drawbacks, attempts have been made to reduce the film thickness and increase the permeation rate by using porous ceramics as a support and laminating the porous glass thin film thereon. For example, soluble components can be eluted by melting and applying an extraphase-forming glass slip to the surface of a porous ceramic support, or by immersing the support in a melt and then treating it with an acid. A method has been proposed in which a porous glass thin film is laminated on the surface of a porous ceramic support by forming a porous glass thin film, then evaporating the attached water under atmospheric pressure and drying it (see " Verres Refract”, Volume 31, No. 4, No.
pages 405-432). Problems to be Solved by the Invention However, in the above method, the viscosity of the glass melt is high and the thickness of the glass layer adhering to the support surface increases, so this must be thinned by polishing. In addition to its shortcomings,
During the drying process of water after treatment, a porous glass thin film and
The disadvantage is that stress is generated due to the difference in shrinkage rate with the porous ceramic support, which inevitably causes cracks in the porous glass thin film. The present invention overcomes the drawbacks of such conventional methods and provides a filter material that has a high permeation rate and good mechanical strength, and is made by laminating a porous glass thin film on the surface of a porous ceramic support. The purpose of this invention is to provide a method for manufacturing the glass thin film using simple operations and without cracking the glass thin film. Means for Solving the Problems The present inventors have developed a filter medium consisting of a porous glass thin film laminated on the surface of a porous ceramic support.
As a result of intensive research to develop a manufacturing method that would prevent the formation of cracks in the glass thin film, we spray-coated a porosity-forming glass powder onto the surface of the support, phase-separated it after firing, and After the acid treatment, before drying the laminate provided with the porous glass thin film, replace the water contained in the laminate with an organic solvent with low surface tension, and then dry by a supercritical point drying method. The inventors have discovered that the object can be achieved, and have completed the present invention based on this knowledge. That is, the present invention spray-coats a porosity-forming glass powder onto the surface of a porous ceramic support to form a coating layer, which is then fired, further subjected to phase separation treatment and acid treatment, and then dried. When manufacturing a filter material consisting of a laminate having a porous glass thin film on the surface of the support, the water contained in the laminate is replaced with an organic solvent before drying, and then supercritical point drying is performed. The present invention provides a method for producing a filter material made of a glass-ceramic laminate, which is dried by a drying method. The present invention will be explained in detail below. In the method of the present invention, porous ceramics are used as a support for the filter medium. There are no particular restrictions on the porous ceramics, including conventionally known ones such as oxides such as alumina, zirconia, titania, magnesia, beryllia, and sillimanite, and non-oxidized materials such as silicon carbide, silicon nitride, sialon, and boron nitride. Any material selected from physical porous ceramics can be used. Further, there is no particular restriction on its shape, but a plate-like or cylindrical shape is usually used.
Further, regarding the pore diameter, it is preferable that the average pore diameter is about 0.5 to 20 μm. In the method of the present invention, the porosity-forming glass powder for forming a coating layer on the surface of these porous ceramic supports may be those conventionally used in the production of porous glasses, such as SiO ₂ ,
B ₂ O ₃ and Na ₂ O are the main components, and if necessary, add
Slips vitrified by adding CaO, ZrO ₂ , Al ₂ O ₃ , MgO, Li ₂ O, K ₂ O, etc. can be used, but the coefficient of thermal expansion is the same as that of the support or not.
It is desirable that the composition has a composition that is up to 60% and that the expansion/contraction rate during acid treatment is usually 0.3% or less, preferably 0.1% or less. If the difference in thermal expansion coefficient from the support is large, the thin glass film is likely to crack after firing, and if the expansion/contraction ratio during acid treatment exceeds 0.3%, the porous thin glass film created by the acid treatment may become unsupported. This is undesirable as it may peel off from the body or cause cracks in the porous glass thin film. For example, when porous alumina ceramics is used as a support, glass powder that satisfies the conditions for the thermal expansion coefficient and expansion/contraction ratio may be, for example, 62% by weight of SiO ₂ , 27% by weight of B ₂ O ₃ , and Na _{2 .} O8 weight%
and 3% by weight of Al ₂ O ₃ . In the method of the present invention, water is added to the glass powder to form a slip, a uniform coating layer is applied to the surface of the porous ceramic support by means such as spraying, and after drying, the slip is baked. , further subjected to phase separation treatment. The heating temperature and time for baking and the heating temperature and time for phase separation treatment are as follows:
Although it depends on the composition of the glass powder used and the desired pore size of the porous glass thin film, the firing treatment for baking is generally performed at a temperature in the range of 700 to 1000°C, and the phase separation treatment is performed at a temperature in the range of 500 to 800°C. Each is carried out at a range of temperatures for an appropriate period of time. Through such treatment, a glass thin film is laminated on the support, but it is necessary to perform acid treatment on this glass thin film to elute phase-separated soluble components such as sodium borate. Examples of acids used in the acid treatment include inorganic acids such as hydrochloric acid and sulfuric acid;
An aqueous solution containing an organic acid such as acetic acid or citric acid can be used. The acid concentration of this aqueous solution is 0.1
The treatment temperature is preferably selected within the range of 60 to 100°C, preferably 80 to 100°C. Such acid treatment makes the glass thin film porous. In the method of the present invention, the laminate provided with the porous glass thin film obtained as described above is washed with water if desired, and then the water contained in the laminate is replaced with an organic solvent. It is necessary to dry by spot drying method. When the laminate is dried without replacing the water contained therein with an organic solvent, as the water in the pores evaporates,
Because stress is generated in the laminate due to drying shrinkage,
Cracks occur in the porous glass thin film. The organic solvent preferably has a low surface tension and is hydrophilic, such as methanol,
Examples include ethanol, propanol, butanol, acetone, methyl ethyl ketone, and diethylamine. Next, a preferred example of substitution with an organic solvent and drying treatment using a critical point drying method will be explained. First, the laminate is immersed in the organic solvent, and the water in the pores is removed from the organic solvent. After complete replacement with
A method of applying high pressure to completely vaporize the organic solvent, then gradually releasing the pressure to atmospheric pressure while maintaining the temperature, and then lowering the temperature.
Alternatively, since the critical temperature of the organic solvent is as high as about 270°C even in methanol, compounds that have a low critical temperature and critical pressure and are gaseous at room temperature and easily liquefy, such as trifluoromonochloromethane, trifluoromethane, hexafluoroethane, etc. The transition liquid is made by liquefying fluorinated hydrocarbons such as carbon dioxide, nitrous oxide, etc., and the laminate in which the water in the pores has been completely replaced with an organic solvent is immersed in the transition liquid. After replacing the solvent with the transition liquid, a drying process is performed, such as by a method in which the transition liquid is completely vaporized at a temperature 10 to 20° C. higher than the critical temperature of the transition liquid. In the latter supercritical point drying method, surface modification methods commonly used for silica gel and porous glass can be applied since high temperatures are not required. In this way, a filter medium is obtained in which a porous glass thin film is laminated on the surface of a porous ceramic support. The thickness of the porous glass thin film is usually 30~
The range is 300 μm. Effects of the Invention According to the method of the present invention, a filter medium consisting of a porous glass thin film laminated on the surface of a porous ceramic support having a high permeation rate and good mechanical strength can be used without cracks in the porous glass thin film. It can be manufactured in such a way that it does not occur. EXAMPLES Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way. Example 1 SiO ₂ 62% by weight, B ₂ O ₃ 27% by weight, Na ₂ O 8% by weight
and glass consisting of 3% by weight of Al ₂ O ₃ with a particle size of 590μ
To this 100 parts by weight, add 30 parts by weight of colloidal silica [manufactured by Nissan Chemical Co., Ltd., trade name Snowtex 20] and an appropriate amount of water, and grind and mix with a grinder to form a slip. Prepared. Next, this was applied to the surface of a porous alumina tube having an average permeation pore diameter of 1.5 μm by spraying to cover it. The thickness of the coating layer was approximately 100 μm. After drying the tube at 130° C. for 15 minutes, it was heated at 800° C. for 30 minutes using an electric furnace, thereby laminating a glass thin film on the surface of the porous alumina tube. The sample thus obtained was kept in an electric furnace at 550°C for 20 hours, and the glass thin film was phase-separated into an alkali metal borate phase and a silica phase. Then 90
After immersing in a 0.25NH ₂ SO ₄ solution at ℃ for 20 hours to elute the phase-separated soluble components in the glass thin film,
Washed with water. At this time, the weight of the glass thin film relative to 1 sulfuric acid was about 1 g. After washing the laminate with water several times with methanol, it was immersed in methanol for 24 hours to replace the contained water with methanol, and then, while immersed in methanol, it was heated to 300°C in an autoclave and held for 30 minutes. . The equilibrium pressure at that time is approximately 80
It was hot due to atmospheric pressure. Thereafter, the leak valve was opened, and the pressure inside the autoclave was lowered to atmospheric pressure over 30 minutes, and then the autoclave was cooled to room temperature to complete drying, and a filter medium made of a laminated tube was produced. No cracks were observed in the porous glass thin film in this laminate tube. Comparative Example 1 A filter medium made of a laminate tube was produced in the same manner as in Example 1, except that the laminate was dried in the air after washing with water. The porous glass thin film in this laminate tube began to crack several minutes after the start of drying, and eventually the cracks spread over the entire surface. Comparative Example 2 A laminate was prepared in the same manner as in Example 1, except that the laminate in which water and methanol had been replaced in Example 1 was transferred to a beaker, covered with a lid with small holes, and slowly dried for two days. A filter material consisting of a tube was created. As a result, the yield of the filter medium having a porous glass thin film without any cracks was approximately 50%. Test Example 1 The laminate tube obtained in Example 1, the laminate tube with no visible cracks obtained in Comparative Example 2, and the center pore diameter (150 Å) comparable to that of the porous glass thin film in these laminate tubes. ) and pore volume (0.35cc/g)
Porous glass tube with a wall thickness of 0.5 mm (Comparative Example 3)
Using this method, a separation experiment of a N ₂ -H ₂ (H ₂ :50 vol%) mixed gas was carried out, and the permeation rate of H ₂ was measured for the separated sample. The results are shown in Table 1. From Table 1, it can be seen that in Comparative Example 2, gas cannot be separated because there are minute cracks that are invisible to the naked eye, whereas in Example 1, there are no minute cracks and there are no porous holes. It can be seen that a separation ratio comparable to that of porous glass can be obtained, and in addition, a permeation rate approximately 14 times higher than that of porous glass can be obtained.

[Table] Example 2 In Example 1, the glass thin film laminated alumina tube before the phase separation treatment was subjected to phase separation treatment in an electric furnace at 540°C.
After holding for a certain period of time, the sample was immersed in 1N sulfuric acid for 24 hours to elute soluble components. At this time, the weight of the glass thin film relative to 1 sulfuric acid was 15 g. After washing the glass thin film laminate thus made porous, it was immersed in acetone to replace the acetone in the porous glass laminate. Next, trimethylchlorosilane (hereinafter abbreviated as TMS)
The laminate was immersed in a toluene solution (concentration: 5 wt%) and refluxed for 24 hours. After washing this with absolute ethanol, before the absolute ethanol evaporated and dried, it was immediately placed in a pressure-resistant container (volume: 100 ml) with a temperature controllable valve and sealed. Next, this container was lowered to 10°C from room temperature, carbon dioxide was introduced, and held for 10 minutes. After replacing the anhydrous ethanol in the pores of the laminate with liquefied carbon dioxide, the container was heated to 40°C.
℃ and released carbon dioxide gas at a rate of about 2/min using a valve, and after about 30 minutes, all the carbon dioxide gas was released and drying was completed. The porous glass laminated filter material obtained in this way has no cracks.
The central pore diameter of the porous glass area was about 40 Å, the pore volume was 0.28 cc/g, and the specific surface area was 229 m ² /g.
In addition, the total amount of TMS is 1 m ² of the surface of porous glass.
It was about 4 μmol per portion. Performance test 2 It has a center pore diameter (approximately 40 Å), pore volume (0.29 cc/g), and specific surface area (214 m ² /g) similar to the porous glass layer of the porous glass laminated filter material of Example 2. A porous glass with a wall thickness of 0.5 mm was refluxed for 24 hours in a toluene solution of TMS (concentration 5 wt%), washed with absolute ethanol, and then dried to obtain a surface-modified porous glass. This porous glass
The amount of TMS bound was approximately 4 μmol per m ² of the surface of the porous glass (Comparative Example 4). Using those of Example 2 and Comparative Example 4, THF was separated from an aqueous solution (concentration 0.2 mol/) of tetrahydrofuran (hereinafter abbreviated as THF) at an operating pressure of 30 atm. The results are shown in Table 2. Here, the separation rate α was determined by the following formula, where X _p is the THF concentration of the original solution, and X is the THF concentration of the filtrate. α=X _p −X/X _p ×100 (%) From Table 2, it can be seen that the sample in Example 2 had a separation rate similar to that in Comparative Example 4, and the permeation rate was significantly higher, about 10 times. I can see that

【table】

Claims (1)

[Claims] 1. A porosity-forming glass powder is spray-coated on the surface of a porous ceramic support to form a coating layer, then fired, further subjected to phase separation treatment and acid treatment, and then dried to form the support. When manufacturing a filter material consisting of a laminate with a porous glass thin film on the surface, the water contained in the laminate is replaced with an organic solvent before drying, and then dried by a supercritical point drying method. A method for producing a filter medium made of a glass-ceramic laminate, characterized by: