JPH0691931B2 - Gas separation membrane and manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas separation membrane and a method for producing the same. More specifically, it relates to a gas separation membrane that mainly separates hydrogen from a mixed gas and a method for producing the same.

(B) Conventional technology There are polymer non-porous membranes and porous membranes in gas separation membranes that mainly separate hydrogen from a mixed gas. Polymer non-porous multi-membranes have a large separation coefficient but a small permeation amount, while porous membranes. The membrane has a small separation coefficient but a relatively large permeation amount. Among them, as a gas separation membrane made of a porous membrane, one using a porous glass membrane is known. This porous glass film is formed by using borosilicate glass through a process of high temperature melting, molding, phase separation, and elution to form a porous film.

(C) Problems to be Solved by the Invention However, the porous glass membrane formed in the above process has a considerably large thickness of 0.2 mm or more and does not have sufficient separability, and has a large hydrogen permeability. Also 200 × 10 ^-9 m ³ / m ²
・ The limit is about s ・ Pa.

The present invention has been made in view of the above circumstances, and particularly aims to provide a gas separation membrane having a thin film thickness and a uniform pore diameter.

(D) Means for Solving the Problems Thus, according to the present invention, a uniform membrane having a predetermined gas selective permeability is closely formed on the surface of the porous support which can freely permeate gas. Thus, there is provided a gas separation membrane, wherein the membrane is a porous gel having a film thickness of 1 to 10 μm made of a hydrolyzate of a metal alkoxide.

The most characteristic point of the present invention is that a wet gel obtained from a metal alkoxide solution is applied to a porous support and heated and dried at a low temperature in a non-aqueous solvent to form a thin and uniform porous layer. That is, a gas separation membrane having a dry gel membrane is obtained.

The metal alkoxide used in the present invention is not particularly limited as long as it can give a gel by hydrolysis and further dehydration, for example, silicon alkoxide, aluminum alkoxide, titanium alkoxide,
Examples thereof include boron alkoxide, sodium alkoxide, calcium alkoxide, lithium alkoxide and the like, and silicon alkoxide, aluminum alkoxide and titanium alkoxide are preferable.

Further, a lower alkoxy group is suitable for the alkoxy group,
For example, a methoxy group, an ethoxy group, a propoxy group and the like can be mentioned.

Examples of the metal alkoxide include silicon tetraethoxide Si (OC ₂ H ₅ ) ₄ and triethoxyaluminum Al (OC
₂ H _{5) 3,} include tetra propyl oxytitanium Ti (OC ₃ H _{7) 4} and the like, silicon tetraethoxide is preferred.

Further, one alkoxide group of the above metal alkoxide used in the present invention may be a substituted alkoxy group in which an aliphatic or aromatic hydrocarbon group, an amino group or an alkylamino group is substituted.

As the aqueous solvent for the metal alkoxide, a mixture of water and a lower alcohol such as methanol, ethanol or propanol is used as in the conventional method.

As the hydrolysis catalyst, hydrochloric acid, sulfuric acid, aqueous ammonia solution or the like is used as in the conventional method.

When the metal alkoxide is hydrolyzed to form a sol, the hydrolysis catalyst may be added to the metal alkoxide-containing aqueous solution and stirred at room temperature, but the temperature may be slightly elevated to accelerate the hydrolysis reaction. . In addition, the hydrolysis reaction
The metal alkoxide, water or aqueous solvent and the hydrolysis catalyst may be added and mixed at the same time.

The sol thus obtained is applied to the intended porous support and left at a predetermined temperature (for example, at room temperature to 80 ° C. for 1 to 60 minutes) to form a wet gel molded body.

In the present invention, the porous support on which the obtained wet gel is closely formed is subsequently immersed in a non-aqueous solvent and subjected to heating / drying treatment to dehydrate the wet gel to obtain a dry gel. The wet gel is dehydrated slowly in the solvent due to the viscosity of the solvent, and as a result, the porosity and the pore diameter of the resulting dry gel are kept substantially uniform, which is important.

The non-aqueous solvent is substantially immiscible with water and has a boiling point of about
Any liquid that is stable above 200 ° C. and at least about 200 ° C. and is inert to the wet gel may be used, and examples thereof include liquid paraffin, silicone oil, and rapeseed oil.

The heating / drying conditions are appropriately selected so that the dehydration of the wet gel is uniformly performed and the intended porosity is obtained, but in order to obtain a porosity of 30 to 80%, the non-aqueous solvent is usually used. It is processed at 200 ℃ or below for about 24 hours, especially at a temperature of 1
It is preferable to carry out at 00 to 200 ° C because the dehydration time becomes short. Further, if the temperature exceeds 200 ° C, the product may be deformed or cracks may start to occur, which is not preferable.

In the present invention, in order to increase the strength of the dry gel, the gel may be further heat-treated, if necessary.

The above heating conditions are preferably carried out gradually at a high temperature of about 300 to 900 ° C., in view of the uniformity of the porosity of the gel obtained. In this case, if the treatment is performed at 1000 ° C. or higher for 24 hours or longer, the porosity is lost, which is not preferable. As the pore size of the dry gel obtained as described above, 200 Å or less is suitable, which is preferable when mainly separating hydrogen. The pore size is adjusted by adjusting the gelling condition and the drying condition during the above treatment.

The gas separation membrane of the present invention is formed by applying the sol to the intended porous support and then treating as described above. In this case, the thickness of the formed coating film is retained by the film. Although it is selected slightly depending on the porosity, for example, those having the above porosity and not impairing the transmittance are 0.1 to 100.
μm is suitable and 1 to 10 μm is preferable.

Further, the gas separation membrane of the present invention is formed by coating the surface of an intended support while the sol constituting the membrane has fluidity, leaving it to stand, and then heating and drying it as described above.

Suitable materials for the porous support used in the gas separation membrane of the present invention are ceramics such as alumina, zirconia, mullite, magnesia, and silicon nitride.

The pore size of the porous support is preferably 0.1 to 100 μm, and is preferably 1 to 10 μm when mainly separating hydrogen.

The above-mentioned porous support may be used in any shape, and examples thereof include a plate shape, a tube shape, and a particle shape, which are appropriately selected depending on the application.

(E) Action According to the present invention, a thin wet gel film can be obtained by applying a sol comprising a hydrolyzate of a metal alkoxide. This gel film is heated and dried in a viscous non-aqueous solvent to gradually dehydrate the gel, and the evaporation of water produced by the dehydration is suppressed by the viscosity, resulting in the gel as a whole. Dehydration is performed from the uniformly dispersed portion to obtain a porous dry gel film having a uniform pore size and a uniform dispersion.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

(F) Example 10 ml of Si (OC ₂ H ₅ ) ₄ , 5 ml of water and 0.1 ml of 1.0N-HCl were mixed and stirred for hydrolysis to obtain a uniform sol solution. 0.1 NN for this
After adjusting the pH to 5.0 with H ₄ OH, pour this sol solution onto a porous alumina support (pore size about 1.5 to 4.0 μm) and apply it, and leave it at room temperature for about 30 minutes to gel it to a thickness. About 2.0μ
m wet gel film was formed.

Thereafter, this support was placed so that the entire wet gel film was immersed in liquid paraffin, and dehydrated by heating and drying at 80 ° C. for 24 hours. During this time, the gel apparently did not shrink and did not crack. This was taken out from the liquid paraffin, washed with acetone, and then dried in air at 120 ° C for 1 hour.
A porous dry gel film was obtained. The obtained gel had a pore size of 160 to 30Å and a porosity of about 76.4%.

The porous dry gel film (thickness 0.
The gas separation membrane (a) in which 9 μm) is closely formed is used as shown in FIG. 1, and pure gases of H ₂ , He, N ₂ , and O ₂ are introduced from one of the flow paths (1), and the gas separation membrane (a) is introduced. The amount of gas passing through the other channel (3) across (2) was measured by a soap membrane flow meter (not shown) connected to the channel (3).
The gas separation membrane (a) used for this measurement had a diameter of 30 mm (≈
7.1 cm ² ).

Since each of the above gases flowing through the porous membrane in this example can be treated as a Knudsen flow, from the above results, the reciprocal of the square root of the permeation rate (m ³ / m ² · s · Pa) and the gas molecular weight M (M ^{−1). / 2} ) and the results shown in Fig. 2 were obtained.

The separation coefficient at this time was H ₂ / N ₂ = 3.18 using the gas separation membrane (a). The theoretical value is H ₂ / N ₂ = 3.74.

From this result, the permeability of each of the gas separation membranes of the present invention is increased by about 10,000 times as compared with the conventional gas separation membrane formed of the porous glass.

(G) Effect of the Invention According to the present invention, a wet gel obtained by hydrolysis of a metal alkoxide is heated and dried in a non-aqueous solvent to be dehydrated to have a uniform porosity composed of pore diameters. A dry gel is obtained, and since this dry gel can be formed into a thin layer in close contact with the surface of the porous support, a gas separation membrane with an increased amount of permeation can be obtained, which is particularly suitable as a hydrogen separation membrane. .

[Brief description of drawings]

FIG. 1 is a structural explanatory view illustrating an apparatus for measuring the gas permeation amount of a gas separation membrane of the present invention, and FIG. 2 is the reciprocal of the square root of the molecular weight of the gas corresponding to the permeation rate of each gas by the apparatus of FIG. It is a graph which shows the relationship with.

Claims (4)

[Claims] 1. A uniform film having a predetermined gas selective permeability is adhered and formed on the surface of a porous support which is freely permeable to gas, and the film is composed of a hydrolyzate of a metal alkoxide. A gas separation membrane which is a porous gel having a thickness of 1 to 10 μm. 2. The gas separation membrane according to claim 1, wherein the predetermined gas is hydrogen. 3. A sol is prepared by hydrolyzing a metal alkoxide, and the sol is applied onto a porous support and left at a predetermined temperature to form a wet gel film, and the wet gel film is heated to 200 ° C.
The surface of the support is heated to a dry gel film by heating and drying in a state of being immersed in a non-aqueous solvent having a boiling point higher than the heating temperature up to a heating temperature of up to A method for producing a gas separation membrane, which comprises closely forming a selectively permeable membrane made of a porous gel having a uniform thickness of 1 to 10 μm on the top. 4. The method according to claim 3, wherein the non-aqueous solvent is liquid paraffin or silicone oil.