JPH05293343A - Gas separation composite membrane - Google Patents

Abstract

PURPOSE:To obtain such a membrane as a gas separation composite membrane that the efficiency of gas separation can arbitrarily be controlled while the mechanical strength of the membrane is maintained, by combining microbial cellulose or its deriv. and polymer material. CONSTITUTION:Microbes such as acetobacters and glyconobacters which produce microbial cellulose are used to produce microbial cellulose by static calturing method or the like. The microbial cellulose thus prepared may be chemically modified to obtain a cllulose deriv so as to change the gas permeation characteristics. The polymer material used is such a material which gives gas permeation selectivity to the microbial cellulose, such as chitin and carboxymethylchitin. Then both materials are formed into the composite membrane by mixing, combining, laminating, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas separation composite membrane, and more particularly to a gas separation composite membrane containing (a) microbial cellulose or its derivative and (b) a polymeric substance as main components. This membrane can separate gases such as oxygen, carbon dioxide and nitrogen selectively and efficiently.

[0002]

2. Description of the Related Art Conventionally, materials such as porous polysulfone, cellulose acetate, polyimide, polyethersulfone, poly-4-methylpentene-1, and polyphenylene oxide have been selected as gas permeable membranes. It is appropriately used depending on the gas to be separated.

However, although the above materials have a high selectivity for the target gas, they have a low mechanical strength, so that it is necessary to increase the film thickness. However, when the film thickness is increased, the gas separation efficiency is increased, but the gas permeation rate (flow rate) is decreased, so that industrial improvement has been desired.

Therefore, a material having a high selectivity for a specific gas and a gas having a low gas separation efficiency but having a high mechanical strength can be composited by a method such as laminating or polymerization to obtain a high selectivity. A film having properties and capable of imparting a practical permeation rate has been developed. However, depending on the gases to be separated, those combinations had to be considered individually.

[0005]

[Means for Solving the Problems] The present inventors have previously described a dialysis membrane, a ultrafiltration membrane, a reverse osmosis membrane, a pervaporation membrane, which contains microbial cellulose or a derivative thereof and a polymeric substance as a main component,
A composite separation membrane effective as a vaporization permeation membrane and a method for producing the same have been developed (JP-A-3-32726).

However, although the composite separation membrane has been studied for liquid-liquid separation or gas-liquid separation, it has not been studied for gas-gas separation at all, and its usefulness has been completely unknown. .. Generally, for liquid-liquid separation or gas-liquid separation and gas-liquid separation, the separation mechanism is not the same, so a separation membrane having high separation ability for liquid-liquid separation or gas-liquid separation is not necessarily gas-liquid separation. It is known that the gas separation power is not high.

The present inventors have examined the gas separation ability of the microbial cellulose membrane, and have found that the microbial cellulose membrane itself has no selectivity for gases such as oxygen, carbon dioxide and nitrogen. ..

Furthermore, by mixing or compositing the microbial cellulose membrane with a material having gas permeation selectivity, the mechanical strength of the membrane can be obtained without affecting the separation efficiency of the material having gas permeation selectivity. It was found that the gas separation efficiency can be arbitrarily controlled while maintaining the mechanical strength by changing the mixing ratio or the method of compounding or changing the film thickness. completed.

That is, the present invention provides a composite membrane for gas separation containing (a) microbial cellulose or its derivative and (a) a polymeric substance as main components.

The gas separation composite membrane of the present invention is mainly composed of (a) microbial cellulose or its derivative and (a) a polymeric substance. The microbial cellulose used in the present invention is not particularly limited as long as it is produced by a microorganism that produces microbial cellulose, and examples of the microbial cellulose-producing bacterium include Acetobacter, Gluconobacter,
Microorganisms belonging to the genus Pseudomonas and the genus Agrobacterium can be used. Among them, microorganisms belonging to the genus Acetobacter are particularly preferable because they have a high ability to produce microbial cellulose.

Specific examples of microbial cellulose-producing bacteria include Acetobacter pastorianus ATCC 102.
45 and the like.

As a medium used for culturing the microbial cellulose-producing bacterium to produce microbial cellulose, a general medium used for culturing ordinary bacteria may be used, and carbon source, nitrogen source, inorganic salts , Others include amino acids, vitamins, and other nutritional sources as needed. In the case of microorganisms belonging to the genus Acetobacter,
Hestrin-Schramm medium (Biochem. J., 58, 34)
5 (1954)) is particularly preferably used.

Next, the culture conditions may be those for culturing ordinary bacteria, and the pH is preferably such that microbial cellulose-producing bacteria grow and produce microbial cellulose, usually 5 to 9, and the culture temperature is 20 to 40. A range of ° C is suitable.

The culture method may be either aeration stirring culture or static culture. When a microorganism belonging to the genus Acetobacter is used, the productivity of the target product is high and the gas permeable membrane can be easily molded. Therefore, a method of culturing in stationary culture and producing it on the surface of the culture solution is desirable. The microbial cellulose produced is usually deproteinized and then washed with water before use.

The thus-prepared microbial cellulose can be used as a cellulose derivative by changing the gas permeation characteristics by chemical modification such as acetylation treatment or nitrification treatment by a conventional method.

The polymer substance used in the present invention is not particularly limited as long as it imparts gas permeation selectivity to microbial cellulose, but from the viewpoint of strength and life of the produced gas permeable membrane, microbial cellulose. Those exhibiting some interaction with are preferably used.

Specific examples thereof include chitin, carboxymethyl chitin, sulfated chitin, chitin glycine ester, chitosan, sulfated chitosan, nitrified chitosan, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and the like. One kind or two or more kinds of molecular substances can be used.

It is desirable that the above-mentioned microbial cellulose and its derivatives and polymer substances have a high purity as much as possible, but they may contain impurities to some extent depending on the application.

As a method for preparing the composite membrane for gas separation containing (a) microbial cellulose or its derivative and (a) a polymeric substance as main components in the present invention, for example, the following three methods can be mentioned. The first method is a method in which a polymeric substance is laminated on a microbial cellulose membrane, which is disclosed in JP-A-3-32726, specifically, the membranes are separately prepared in advance, and these are laminated. Alternatively, there is a method of preparing either film and then laminating the other film on the film.

The second method is a method in which the disaggregated microbial cellulose is mixed with a polymer substance to form a composite, and the method disclosed in JP-A-3-157402, specifically, the produced microbial cellulose is used. After cutting with a mechanical shearing force such as a mixer or disintegration with a valve disintegrator, homogenization treatment with a high-pressure homogenizer is performed to form microfibrils, and the resulting suspension is centrifuged to obtain paste-like disintegrants. In this method, the polymer substance to be composited with the paste-like disaggregated material is mixed well with a mixer or a homogenizer.

In the third method, in culturing a microbial cellulose-producing bacterium to produce microbial cellulose, a polymer substance is added to the medium to combine the cellulose with the polymer substance during the production of the cellulose. It is a method for producing a complexed compound, which is specifically described in JP-A-3-15
The method disclosed in 7402 is used.

As a method of molding the above composite into a membrane, the polymer and the polymer substance are produced during the production of the cellulose by laminating the polymer substance or adding the polymer substance to the medium. In the case of forming a composite compound, a method of dehydrating and drying by a method such as air-drying or freeze-drying that does not decompose microbial cellulose to form a film can be applied. Also, once disintegrate with a pulp disintegrator, etc.,
When mixing homogenized microbial cellulose and polymeric substances to form a composite, there is a method such as placing the composite on the glass plate according to the shape you want to mold and dehydrating and drying by air drying, freeze drying, etc. is there.

Further, when a high molecular substance is added to the medium to form a complex compound of the cellulose and the high molecular substance during the production of the cellulose, the shape of the container to be cultured is desired to be molded. With such a film, films of various shapes can be easily produced.

[0024]

EXAMPLES The present invention will be specifically described with reference to the following examples. Example 1 Acetobacter pastorianus ATCC 10245
Hestrin-Schramm medium (D-glucose 2.0 g, Bactopeptone (manufactured by Difco) 0.5 g, yeast extract (manufactured by Difco) 0.5 g, citric acid 0.115 g, disodium hydrogen phosphate 0.27 g, Distilled water 100ml, pH 6.
The cells were inoculated in 0) and statically cultured at 28 ° C. for 96 hours.

After completion of the culture, the membrane containing microbial cellulose produced on the surface of the culture solution as a main component was taken out, and 1% Na was added.
After immersing in OH aqueous solution and treating at room temperature for 24 hours, 1
% Acetic acid solution and neutralized at room temperature for 24 hours. This treatment was repeated, and after it was confirmed that the deproteinization treatment was completely completed, it was thoroughly washed with water.

The obtained microbial cellulose film has a solid content of
Suspend to 0.3% in distilled water, cut with a food cutter, and then use a high-pressure homogenizer (Gorlin model 1
5-15 MR-8TBA), pressure 500kg / cm
^The treatment was performed 30 times at ² to make microfibrils.

The suspension of microfibrillated microbial cellulose was centrifuged (6,000 rpm, 15 minutes),
The obtained paste-like material was applied onto a glass plate and air-dried to prepare a microbial cellulose film. The thickness of the prepared dry microbial cellulose membrane was 22 g / m ² . By the same method, a microbial cellulose membrane having a membrane thickness of 11 g / m ² was prepared.

Next, a suspension of the above microfibrillated microbial cellulose and a liquid obtained by disaggregating squid chitin powder prepared by the method disclosed in Japanese Patent Laid-Open No. 3-32726 into water are present in a weight ratio of 1 to 2. The mixture was mixed at a ratio of 1 and the resulting mixed solution was paper-made by a conventional method and dried to prepare a composite membrane composed of microbial cellulose and squid chitin. The thickness of the composite film composed of the dry microbial cellulose and squid chitin thus prepared was 22 g / m ² . In a similar manner, a composite membrane composed of microbial cellulose and squid chitin having a membrane thickness of 11 g / m ² was prepared.

On the other hand, we were prepared two kinds of films having a thickness of 10.5 g / m ² and 22 g / m ² consisting of only squid chitin as a control. The oxygen permeability of the prepared membrane was measured by the gas permeability test method of plastic films and sheets (JIS K 7126-
1987) at a test temperature of 23 ± 0.5 ° C by the differential pressure method.

In the case of a membrane consisting only of microbial cellulose, the permeability was large irrespective of the thickness and it was impossible to measure, but in the case of a composite membrane consisting of microbial cellulose and squid, the thickness was 11 g / m ^2. Then 1100cm ³ / m ² · 24h · at
It was 94 cm ³ / m ² · 24 h · atm at m ² and a thickness of 22 g / m ² . On the other hand, in the case of the control film composed only of squid chitin, the thickness of 10.5 g / m ² is 4400 cm ³ / m ² · 24 h · atm
When the thickness was 22 g / m ² , it was 72 cm ³ / m ² · 24 h · atm.

Further, when the tear strength of the above-mentioned membrane was measured by a conventional method, the specific tear of the membrane consisting only of microbial cellulose, the composite membrane consisting of microbial cellulose and squid chitin, and the membrane consisting only of squid chitin was 11 g / m ² ( In the case of squid chitin alone, it is 22.5 at 10.5 g / m ² )
At 18.1 and 8.65, the composite membrane composed of microbial cellulose and squid chitin was about the same as the membrane composed of microbial cellulose only.

Example 2 Microbial cellulose membrane prepared in the same manner as in Example 1,
The permeability of carbon dioxide gas and the permeability of nitrogen gas of a composite membrane composed of microbial cellulose and squid chitin and a membrane composed only of squid chitin were measured according to the gas permeability test method for plastic films and sheets (JIS K 7126-1987) and JIS Z 1707. did. The results are shown in Table 1.

[0033]

[Table 1]

Next, the permeability of nitrogen gas was measured in the same manner as above. The results are shown in Table 2.

[0035]

[Table 2]

Therefore, the composite membrane of the present invention composed of microbial cellulose and squid chitin can increase the nitrogen gas permeability while retaining the carbon dioxide gas permeability as compared with the membrane composed only of squid chitin, and lower than the membrane composed of only microbial cellulose. It shows that the gas permeability can be selectively controlled.

Example 3 Acetobacter pastorianus ATCC 10245
The cells were inoculated into a Hestrin-Schramm medium containing 0.5% of carboxymethyl cellulose (sodium salt, molecular weight 130,000) and statically cultured at 28 ° C. for 96 hours.

After completion of the culture, deproteinization treatment was carried out in the same manner as in Example 1 and air drying was carried out to obtain a membrane in which microbial cellulose and carboxymethyl cellulose were complexed. The oxygen gas permeability and the carbon dioxide gas permeability of the obtained film were measured in the same manner as in Example 1 and Example 2. As a result, permeability of the oxygen gas is ^{320cm 3 / m 2 · 24h ·} atm, permeability of carbon dioxide is ^{190cm 3 / m 2 · 24h ·} atm. Further, the dynamic Young's modulus of the membrane in which the microbial cellulose and carboxymethyl cellulose were complex was measured by a conventional method and found to be 58.4 GPa. On the other hand, the dynamic Young's modulus of the film containing only microbial cellulose was 25.7 GPa.

EXAMPLE 4 Carboxymethyl chitin (substitution degree 0.7) prepared by the method disclosed in JP-A-3-32726 was added to the medium in place of the carboxymethyl cellulose of Example 3 by adding 0.5% to the medium. The culture was carried out in the same manner as in No. 3, followed by deproteinization and drying to obtain a membrane in which microbial cellulose and carboxymethyl chitin were complexed.

The oxygen gas permeability and the carbon dioxide gas permeability of the obtained composite membrane were measured by the same method as in Examples 1 and 2. As a result, the permeability of oxygen gas is 3.4 cm ³ / m ² ·
24h ・ atm, carbon dioxide permeability is 5.0cm ³ / m ²・
It was 24h • atm. The dynamic Young's modulus of the membrane in which microbial cellulose and carboxymethyl chitin were complex was measured by a conventional method, and was 23.5 GPa.

Example 5 Methylcellulose (molecular weight: 13000) was added to the medium in an amount of 0.5% instead of carboxymethylcellulose of Example 3, cultured in the same manner as in Example 3, deproteinized,
It was dried to obtain a membrane in which microbial cellulose and methyl cellulose were complexed.

Oxygen gas permeability, carbon dioxide gas permeability and nitrogen permeability of the obtained composite membrane were measured by the same method as in Examples 1 and 2. As a result, the permeability of oxygen gas was 33 cm ³ / m ² · 24h · atm, the permeability of carbon dioxide was 330 cm ³ / m ² · 24h · atm, and the permeability of nitrogen gas was 20.
It was cm ³ / m ² · 24h · atm. The dynamic Young's modulus of this composite film was measured according to a conventional method to find that it was 15.6 GPa.
Met.

Example 6 Hydroxyethyl cellulose SP600 (molecular weight of 1,000,000) was used in place of carboxymethyl cellulose of Example 3.
Was added to the medium at 0.5% and cultured in the same manner as in Example 3, followed by deproteinization and drying to obtain a membrane in which microbial cellulose and hydroxyethyl cellulose were complexed.

The oxygen gas permeability and carbon dioxide gas permeability of the obtained composite membrane were measured by the same method as in Examples 1 and 2. As a result, the permeability of oxygen gas is 6.1 cm ³ / m ² ·
24h ・ atm, carbon dioxide permeability is 2.2cm ³ / m ²・
It was 24h • atm. The dynamic Young's modulus of this composite film was measured by a conventional method and found to be 24.3 GPa.

[0045]

According to the present invention, the mechanical strength of the composite membrane for gas separation can be improved without affecting the gas separation efficiency of the material having gas permeation selectivity. Also, by changing the mixing ratio of each material, the method of compounding, the thickness of the membrane, etc., the gas separation efficiency can be arbitrarily controlled while maintaining the mechanical strength, and efficient gas separation or selective gas separation can be achieved. Separation is possible.

Claims (3)

[Claims] 1. A composite membrane for gas separation comprising (a) microbial cellulose or a derivative thereof and (a) a polymeric substance as main components. 2. The composite membrane for gas separation according to claim 1, wherein the microbial cellulose or a derivative thereof is laminated with a polymer substance. 3. The composite membrane for gas separation according to claim 1, wherein the polymer substance is at least one selected from chitin, chitosan, methylcellulose and carboxymethylcellulose.