JPH0367991B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing ceramic membranes for use in separating condensable components.

A porous diaphragm with ultra-fine pores with an average pore diameter of several tens to several hundreds of angstroms is used for separation, which is made by sintering metal powder or ceramic powder, or compression molding organic synthetic resin powder such as fluorine resin. Therefore, it was difficult to mold it into an arbitrary shape. Therefore, in many cases, in order to have sufficient strength,
Measures have been taken to reinforce the above-mentioned thin porous diaphragm having micropores with a porous body or wire mesh-like material having a certain thickness and high gas permeability to form a multilayer structure.

For example, there are various methods to make a multilayered porous membrane into a tubular shape, but in general, a sheet-like multilayer porous diaphragm is formed into a circular tube shape, and the ends are butt welded or overlapped and bonded. I'm going.
However, although it is possible to form a circular tube when the porous material is highly flexible such as metal, it is extremely difficult to form a circular tube when the porous material is inflexible such as ceramic.
In addition, since porous metals are porous materials, their strength is lower than that of non-porous materials due to the presence of pores, and there is a limit to the radius of curvature that can be formed into a circular shape. It was extremely difficult to mold.

Therefore, as a method to solve such difficulties, the porous support tube and the pipe or core metal placed inside or outside of it are held in the same circular shape, and the porous support tube and the pipe or core metal are vibrated. while giving
Gas is ejected into the gap between the porous support tube and the pipe or core metal to uniformly fill the gap with powder, and the powder filled in the gap is crimped onto the porous support tube by static pressure forming. However, a method of forming a tubular porous membrane in which a compressed layer of powder is formed on a porous support tube is known (see Japanese Patent Application Laid-open No. 77410/1983), but it is difficult to fill the powder uniformly and to make it extremely thin. In practice, there are many difficulties, such as creating a membrane.

The present invention was made in view of the current situation, and it is possible to freely select the size and shape, and the present invention is a porous diaphragm having a very small pore diameter of about 10 Å. This paper proposes a manufacturing method.

That is, the present invention involves impregnating the pores of a ceramic porous body with an alumina sol obtained by hydrolyzing aluminum alcoholate or aluminum chelate, drying and firing, and then impregnating aluminum alcoholate or aluminum chelate dissolved in an organic solvent. The present invention relates to a method for producing a ceramic membrane for separating condensed components, which comprises hydrolyzing the membrane and then firing it.

In the method of the present invention, first, an aluminum alcoholate or an aluminum chelate compound is added to a porous base material of any shape having relatively large pores (usually a pore diameter of 1000 Å or more) such as foamed silica, sintered alumina, and mullite. After being impregnated with alumina sol (AlOOH) obtained by decomposition, drying and firing are performed to produce alumina (Al ₂ O ₃ ). The above hydrolysis is performed in water or saturated steam at 60 to 100°C, and after the hydrolysis, nitric acid, hydrochloric acid, etc. are added to peptize the sol to improve the uniformity and strength of the resulting solid. The above drying is 80-120℃
The firing time is 400-600℃, 1-24 hours.
Prefiring is preferably performed at a lower temperature than this, and pre-firing can also be performed at a lower temperature.

This operation is repeated several times because cracks may occur due to drying shrinkage or the pores cannot be filled sufficiently with the sol.

Next, the pores whose pore diameter has been reduced by the above operation are impregnated with aluminum alcoholate or aluminum chelate dissolved in an organic solvent,
After removing the organic solvent by volatilization, the aluminum alcoholate or aluminum chelate in the pores is hydrolyzed with water vapor to form an alumina sol,
Dry and bake.

Examples of aluminum alcoholates used in the present invention include aluminum isopropoxide and aluminum-2-butyrate, and examples of aluminum chelates include aluminum tris (ethylacetoacetate) and ethylacetoacetate aluminum diisopropylate. Further, the organic solvents used include normal hexane, cyclohexane, benzene, toluene, xylene, isopropanol, and trichlene.

According to the method of the present invention, it is possible to produce a ceramic membrane having pores with a pore diameter of 10 Å or less.

By using the ceramic membrane obtained by the method of the present invention, it is possible to separate condensable components in a gas. For example, in order to separate moisture (water vapor) from the air, one side of a ceramic membrane is filled with air containing water vapor, and the other side of the membrane is evacuated.The moisture in the air condenses into the pores. However, since it comes out on the vacuum side, the water vapor in the air decreases. Possible uses for such a membrane include use in a dehumidifying device in a closed system.

Hereinafter, the present invention will be explained according to examples.

Example 1 After mixing kaolin and graphite at a weight ratio of 2:1, water was added to form a mixture with a diameter of 12 mm and a thickness of 1.2 mm.
mm, and a length of 12 cm, a clay tube with one side plugged was molded. After drying this indoors, the temperature was raised to 1250°C at a rate of 200°C/h and held at 1250°C for 10 hours to obtain a fired clay body. The firing atmosphere was air. As a result, the pore diameter was 0.8 μm (8000
A porous sintered body with a pore volume of 0.2 cc/g, a diameter of 10 mm, a thickness of 1 mm, and a length of 10 cm was obtained.

Add 5g of aluminum isopropoxide to 100g of water maintained at 80-90℃,
Hydrolyzed aluminum isopropoxide.
0.6 ml of concentrated nitric acid was added to this, kept at 80 to 90°C for 24 hours, and peptized to obtain an alumina sol.

The porous sintered body obtained above was added to this alumina sol.
After soaking in batches, dry indoors for 24 hours, and then dry at 80℃ for 2 hours.
After drying for 1 hour, further dry at 350℃ for 2 hours and at 600℃ for 2 hours.
Baked for an hour. This operation was repeated four times to obtain a microporous body. Figure 1 shows the change in average pore diameter measured by mercury intrusion method. In FIG. 1, the horizontal axis represents the number of impregnations, and the vertical axis represents the average pore diameter. It is clearly seen that the pores are filled with alumina by impregnation.

Next, aluminum isopropoxide was dissolved in a weight ratio of 5 parts to 100 parts of trichlene, and the tube filled with alumina was immersed in this solution. was precipitated. Next, while the inside of this tube is under reduced pressure, it is placed in steam at 100℃ to hydrolyze the aluminum isopropoxide.
After drying at room temperature, baking at 350℃ for 2 hours, and then
It was baked at 600°C for 1 hour. This operation was repeated three times to obtain a microporous body.

The pore distribution of the finally obtained microporous ceramic material was determined by water vapor adsorption, and the results are shown in FIG. In FIG. 2, the horizontal axis is the relative humidity, and the vertical axis is the dimensionless water vapor adsorption amount. This measurement was carried out at 32℃, and the 94Å, 24Å, and 10Å in the figure
The value of Å is the pore diameter determined from the Kelvin equation for capillary condensation. It is clear from this figure that the ceramic membrane prepared by the method of the present invention has pores of 10 Å or less. That is, the Kelvin equation gives the pore radius (condensation radius) when the components begin to condense, and is expressed by the following equation.

r=2Vσ/RTln(P/P _p ) where, r: Condensation radius σ: Surface tension of liquid v: Molecular volume of liquid P _p : Saturated vapor pressure P: Pressure that causes capillary condensation The relative humidity at a certain temperature is , when expressed in terms of pressure, it is expressed as P/P _p , and by entering these values into the Kelvin equation and calculating, the pore radius can be obtained. In Fig. 2, 10 Å, 24 Å, and 94 Å shown with arrows are the condensation radii for relative humidity of 13%, 50%, and 80%, respectively, and since condensation adsorption is clearly observed at 10 Å, in the present invention, It can be seen that pores with a diameter of 10 Å are formed.

Regarding this ceramic membrane, a condensable component separation evaluation test was conducted using a water vapor separation test apparatus shown in FIGS. 3A and 3B.

In FIG. 3A, 1 and 2 are corrugated pipes for gas heating, 3 and 4 are condensable component gas addition parts, and in the case of this test, water (steam) was used as the condensable component. 5 is a condensable component separation part,
6 and 7 are condensable component condensing sections, and 8 is a vacuum pump. FIG. 3B is an enlarged view of the membrane portion of the condensable component separation section 5 described above. 9 is alumina having fine pores filled in pores 11, and 10 is a base material.

In the test, nitrogen gas is impregnated with water vapor using a gas heating coil 1 and a condensable component adding section 3, and then the nitrogen gas is evacuated via a ceramic membrane 5 using a vacuum pump 8. The water vapor that has passed through the ceramic membrane 5 is
The condensable components are condensed using liquid nitrogen filled in the condensing section 6 or 7.

The water permeation rate was determined by weighing the condensed water.

Figure 4 shows the results of measuring the water permeation rate. In FIG. 4, the horizontal axis is relative humidity (%), the vertical axis is permeation rate (mol/m ² hr), and the measurement temperature was 76.2°C. In FIG. 4, curve 1 is the water vapor permeation rate, and curve 2 is the nitrogen permeation rate. As is clear from the figure, the permeation rate of water vapor is greater than the permeation rate of nitrogen at relative humidity of 20% or higher. Furthermore, as the relative humidity increases, the water vapor permeation rate increases and the nitrogen permeation rate decreases.

Example 2 An alumina porous sintered body with a pore diameter of 1500 Å and a pore volume of 0.18 cc/g was filled with alumina sol four times in the same manner as in Example 1, and then aluminum isopropoxide dissolved in an organic solvent was added with water. The decomposition operation was performed five times to obtain a ceramic membrane.

The water vapor equilibrium adsorption curve (32°C) of the obtained ceramic membrane is shown in Figure 5. In FIG. 5, the horizontal axis is relative humidity (%), and the vertical axis is dimensionless water vapor adsorption amount. Pore diameter value 10 Å according to Kelvin equation,
24 Å is shown in the figure. As a result of water vapor equilibrium adsorption curve measurement, it was revealed that the pore diameter of the obtained ceramic porous material was smaller than 10 Å.

Next, Example 1 about the obtained ceramic film
A condensable component (water vapor) separation performance evaluation test was conducted in the same manner as above. The test results are shown in Figure 6.

In Figure 6, the horizontal axis is the relative humidity (%),
The vertical axis is the permeation rate (mol/m ² ·hr). In Figure 6, ○: 76.8℃ water vapor, △: 76.8℃ air, ●:
58.0℃ water vapor, △・ is the permeation rate data of 58.0℃ air.

In this case as well, it has become clear that at relative humidity levels of 20% or higher, more water vapor permeates than air. Furthermore, as the humidity increases, the air permeation rate decreases, but the water vapor permeation rate increases. Also, when comparing the amount of water vapor permeation depending on temperature,
The amount of water vapor permeated at 76.8°C was greater than the amount of water vapor permeated at 58.0°C, and it was found that the higher the temperature, the greater the amount of water vapor permeated.

As detailed above, the ceramic membrane obtained by the method of the present invention has good separation performance for condensable components, although its performance varies slightly depending on the gas temperature and the content of condensable components. The method for producing the membrane is also easy, and the method of the present invention is industrially useful.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the results obtained in Examples of the present invention, and is a diagram showing the change in average pore diameter when impregnated with alumina sol. Figures 2 and 5
The figure shows a water vapor equilibrium adsorption curve of a ceramic membrane prototyped according to the method of the present invention. In FIG. 3, A is a schematic diagram of a condensable component separation test device for evaluating ceramic membranes obtained by the method of the present invention, and FIG.
It is a partially enlarged view of figure A. Figures 4 and 6 show the results of a gas permeation test using a prototype ceramic membrane.

Claims (1)

[Claims] 1 After impregnating the pores of a ceramic porous body with alumina sol obtained by hydrolyzing aluminum alcoholate or aluminum chelate, drying and firing, then impregnating aluminum alcoholate or aluminum chelate dissolved in an organic solvent and hydrolyzing. 1. A method for producing a ceramic membrane for condensed component separation, which is characterized in that the ceramic membrane is then fired.