JPS59147605A - Preparation of porous diaphragm for gas separation - Google Patents

Abstract

PURPOSE:To prepare a porous diaphragm of pure alumina having suitable pore size for gas separation and sufficiently high strength by molding and drying a mixture of calcined and uncalcined alumina sol, and calcining the product. CONSTITUTION:A mixture of 25-75wt% calcined alumina sol with residual wt% uncalcined alumina sol is molded and dried; the product is calcined at 500-900 deg.C for 2-24hr to obtain a target porous diaphragm for gas separation. The average pore size of the diaphragm is about 50-300Angstrom . Satisfactory results may be attained when the diaphragm is used for gas separation, for example, selective separation of H2 from a gaseous mixture of H2 and N2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a porous diaphragm used for gas separation and the like.

A porous diaphragm with micro pores, especially ultra-fine pores with an average size of several tens to several tens of OA, using a porous body base material made by completely sintering metal powder or ceramic powder, or compression molding organic synthetic resin powder such as fluororesin. For example, by gas diffusion method? When separating and concentrating, it is necessary to make the porous diaphragm as thin as possible in order to perform it efficiently, but from the viewpoint of strength it cannot be made extremely thin. or,
In such cases, it is difficult to mold into any desired shape.

Therefore, in the past, in order to have a large pore size and sufficient strength so as not to interfere with gas diffusion, a porous material with a certain thickness and high gas permeability, or a thin porous material similar to a wire mesh with fine pores was used. Measures have been taken to strengthen the diaphragm and create a multilayer structure.

For example, there are various methods for making a multilayered porous membrane into a tubular shape, but generally a sheet-like multilayer porous diaphragm is formed into a circular tube shape, and the ends are butt welded or overlapped and bonded. is being carried out. However, if the porous body is highly flexible such as metal, it is possible to form a circular tube, but if the porous body is inflexible such as ceramic, it is extremely difficult. In addition, since porous metals are porous bodies even if they are metals, their strength is lower than that of non-porous bodies due to the presence of pores, and there is a limit to the radius of curvature that can be formed into circular tubes. It was extremely difficult to form it into a thin tube shape.

Therefore, as a method to solve these difficulties, the porous support tube and the pipe or core placed inside or outside of it are held in the same circular shape, and vibration is applied to the porous support tube and the pipe or core. While applying the pressure, 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 for forming a tubular porous membrane by forming a compressed layer of powder on a porous support tube is known (Japanese Unexamined Patent Application Publication No. 1989-1993).
77410), but there are actually many difficulties in filling the powder uniformly and producing a very thin film.

The inventors of the present invention have developed the present invention as a result of conducting extensive research in order to overcome the above-mentioned problems regarding porous diaphragms used for gas separation and the like.

That is, the present invention relates to a method for producing a porous membrane for gas separation, which comprises completely mixing an uncalcined alumina sol and a calcined product of finely pulverized alumina sol, forming, drying, and firing the porous diaphragm. be.

Until now, it has been extremely difficult to mold a single alumina sol due to the rheological properties of alumina sol. Even if a molded alumina sol could be made, it would shrink significantly during the drying and firing process, resulting in many cracks, making it impossible to produce a product that could be used as a porous diaphragm. Furthermore, since the calcined product of finely pulverized alumina sol alone does not have adhesive properties, it is impossible to manufacture the entire porous diaphragm.

In the method of the present invention, the mixing ratio of calcined alumina sol and uncalcined alumina sol is 25 to 75%.
It is preferable that the remainder of the weight percentage be an uncalcined alumina sol.

The optimum mixing ratio is approximately equal weight ratio of calcined alumina sol and uncalcined alumina sol.・The average pore diameter of the porous diaphragm obtained with such a mixing ratio is 50
~300A, and if this is used as a porous diaphragm for gas separation, good gas separation can be achieved.

In addition, the alumina sol burnt in the method of the present invention, 50
It is carried out at a temperature of 0 to 900°C for 2 to 24 hours.

According to the method of the present invention, it is possible to easily produce a sufficiently strong porous diaphragm made of pure alumina and having a pore size that allows gas separation.

Hereinafter, the method of the present invention will be explained in full detail according to Examples.

Example 1 Aluminum isopropoxide 500F (z) was poured into 2000 CC of warm water heated to 70°C and hydrolyzed with stirring. After the hydrolysis was completed, autoclave treatment was performed at 150°C for 24 hours, but 1N salt e 'k HC1/A
Add so that the molar ratio of t0OH is 0.05, 95
It was peptized for 24 hours at 'C. After obtaining the alumina sol in this manner, it was left in a dryer kept at 150° C. to remove water and dry, and then pulverized using a hammer-type pulverizer to obtain boehmite powder. Next, it was calcined for 2 hours in 1600'c of finely pulverized boehmite powder, and
- Made of alumina.

A small amount of water was added to the boehmite powder described above, and it was formed into a flat plate with a thickness of 1 inch. In this case, if a little more water was added, the boehmite became very soft and it was difficult to maintain its shape after molding. 1c, when there was little water, it was dry and difficult to mold. Furthermore, even when molding was successfully performed with a moderate amount of water, shrinkage occurred during drying, resulting in deformation and cracking of the molded product.

Next, 50 pieces of boehmite powder and boehmite f600
Mixing γ-alumina 501 obtained by calcining at °C,
A small amount of water was added to form a flat plate with a thickness of one layer. In this case, moldability was very good. After molding, it was air dried. No deformation was observed during this drying.

After air drying, place in an electric furnace and heat at 900°C at a heating rate of +00'C/h.
After holding for a period of time, the mixture was cooled in a furnace and the porous diaphragm was completely removed.

The porous diaphragm thus obtained was subjected to pore size distribution anvil using mercury intrusion method. The results are shown in Figure 1. 1st
In the figure, the horizontal axis shows the pore radius (distance), and the vertical axis shows the cumulative pore volume (cC7y).

Further, as a result of measurement, it was found that the average pore radius of the prototype porous diaphragm was 210A, and the pore volume was 0.5'[] CC/9.

Regarding this porous diaphragm, a gas separation test was conducted using a gas separation test device with a mixed gas of 50% hydrogen and 50% nitrogen set at an inlet pressure of 3K17cm2 and an outlet pressure of IK9/Crn2. The gas composition of the gas after passing through the porous diaphragm was found to be 67% hydrogen and 33% nitrogen, indicating that hydrogen selectively permeated through the porous diaphragm.

Ushita, using the same gas separation test equipment, 50% hydrogen
, for a mixed gas of 50 g of methane, the inlet pressure is 3 K9
7cm2, outlet side pressure 1 was set to 9/α2, and a gas separation test was conducted, and it was found that the gas composition of the gas after passing through the porous diaphragm was 63% hydrogen and 3Z methane. In some cases, selective permeation of hydrogen through the porous membrane was also observed.

As is clear from this example, according to the method of the present invention, it is possible to obtain a porous diaphragm that is excellent in shape, strength, and gas separation performance.

Example 2 Commercially available alumina sol (manufactured by Hinami Chemical Co., Ltd.) f I It was held in a drying layer kept at 50°C to remove moisture and was pulverized using a hammer-type pulverizer to obtain boehmite powder. . Next, the finely pulverized boehmite powder was baked at 600° C. for 2 hours to obtain γ-alumina.

A small amount of water was added to the boehmite powder described above, and it was formed into a flat plate with a thickness of 1 square inch. In this case, if a little more water was added, the boehmite became extremely soft, making it difficult to maintain its shape after molding. When the mixture was slender or had little water, it was dry and difficult to mold. It has become clear that the range of appropriate water amounts for molding is very narrow. Further, even when the molding was successfully performed using an appropriate amount of water, shrinkage occurred during drying, and the molded product was deformed and cracked.

Next, boehmite powder 509 and boehmite) i600
Mixing γ-alumina 502 obtained by calcining at °C,
A small amount of water and gold was added and formed into a flat plate with a thickness of one inch. The moldability during molding was very good. After molding, it was air-dried, but no deformation was observed during drying.

After natural drying, it was placed in an electric furnace and heated to 900°C at a heating rate of 100°C/h, held at 900°C for 2 hours, and then cooled in the oven to obtain a porous diaphragm.

The pore size distribution of the porous diaphragm thus obtained was determined by mercury intrusion method. The results are shown in FIG. Second
In the figure, the horizontal axis shows the pore radius (A), and the vertical axis shows the cumulative pore volume (CO/f).

Further, as a result of measurement, it was found that the average pore radius of the prototype porous diaphragm was 70A, and the pore volume was 0.520O/9.

All gas separation tests were conducted on the porous diaphragm using the gas separation test equipment, setting the inlet side pressure to 3 to 9/cn12 and the outlet side pressure to IK97cm2 for a mixed gas of 50% hydrogen and 50% nitrogen. However, the gas composition of the gas after passing through the porous diaphragm was 70% hydrogen and 30% nitrogen, and selective permeation of hydrogen through the porous diaphragm was observed.

′! , using the same gas separation test equipment, hydrogen 5
Inlet side pressure 3 for mixed gas of 0% and 50% methane
Set K17cm2, outlet side pressure IK9/(1)2,
When a gas separation test was conducted, the gas composition of the gas after passing through the porous diaphragm was 65% hydrogen and 35% methane, and selective permeation of hydrogen through the porous diaphragm was also observed in this case.

As is clear from this example, according to the method of the present invention,
A porous diaphragm excellent in shape, strength, and gas separation performance can be obtained.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams showing the pore size distribution of a porous diaphragm prototyped by the method of the present invention. Sub-agents 1) Meifuku agent Ryo Hagiwara -

Claims (1)

[Claims] A method for producing a porous diaphragm for gas separation, which comprises mixing calcined alumina sol and uncalcined alumina sol, forming, drying, and firing the mixture.