JPS5814929A - Gas-permeable membrane - Google Patents

Abstract

PURPOSE:To obtain a gas-permeable membrane having a high gas permeation coefficient and excellent in selectivity, by a method wherein a membrane is prepared from a material comprising polyorganosiloxane and supported by a porous support film directly or after formed into an extremely thin membrane to prepare a composite membrane. CONSTITUTION:Polymethylhydrogensiloxane and an olefine such as pentene -1 are reacted in the presence of a platinum catalyst to obtain polyorganosiloxane having structure shown by the general formula (wherein R is a 4-9C alkyl group, n is an integer exclusive of zero, m is an integer inclusive of zero). When the carbon number of the substituent R is 3 or less, the selectivity of the obtained polymer is low and when it exceeds 9, selectivity thereof is saturated and oxygen permeability is lowered. In addition, the polymerization degree n of said polymer should be at least 10. The above polyorganosiloxane is soluble in an aromatic solvent and can be formed into a membrane by a casting method and, after the membrane is formed into an extremely thin membrane with a thickness of 1mum or less, this thin membrane is supported by a porous film to make it possible to form a composite membrane.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas permeable membrane that allows more of a specific component to pass through than a mixed gas. In particular, the present invention provides a gas permeable membrane that is easy to manufacture as an ultra-thin membrane of 1 μm or less, has a large gas permeability coefficient, and has improved selectivity.

Continuous concentration methods using thin polymer films have recently been attracting attention as a means of separating and concentrating a specific gas from a gas mixture. For example, when separating oxygen or nitrogen from the air, a continuous concentration method using a thin polymer membrane is preferable to the conventional cryogenic liquefaction method or batch separation method using zeolite adsorption. It is expected that energy saving and production equipment will be made smaller and simpler, and therefore oxygen-enriched air can be easily produced at low cost. This method generally has the advantage that it can be used not only for separating oxygen and nitrogen from air, but also for separating a specific gas from a mixture of various gases.

When a gas is permeated through a polymer membrane, the factors that influence the permeability are said to be the interaction between the target gas and the polymer membrane, that is, the diffusion coefficient and solubility. As mentioned above, although membrane separation methods are expected to have many advantages, the reason why they have not yet been put into practical use is that the balance between gas permeability and selectivity, which is influenced by these two factors, is This is because it is not fully demonstrated.

For example, silicone (polydimethylsiloxane) has 10-7 to 10-8 cc-crry'crl for oxygen.
・Although it exhibits permeability of about sea-cJ (g), its selectivity with nitrogen is as small as about 2, and the concentration ratio cannot be increased.

The present inventors conducted various studies in order to obtain a gas-permeable membrane material with excellent gas permeability and selectivity from the above viewpoint, and as a result, a gas-permeable membrane was fabricated using a material made of polyorganosiloxane whose structure is represented by the general formula. We have also found that a composite membrane in which this material is supported on a porous support membrane has excellent permeability and can improve selectivity. Here, R represents an alkyl group having 4 to 9 carbon atoms, n is an integer not including 0, and m is an integer including 0.

These materials are easily obtained by reacting polymethyl, hydrogensiloxant, and olefins such as t-pentene-1 under a platinum catalyst. Alternatively, methyl or alkyldichlorosilane may be synthesized in advance and subjected to condensation polymerization using a conventional method.

In the former method, a small amount of unreacted hydrogen may remain in the molecule, and in the latter method, gelation may occur if the degree of polymerization increases too much, so careful attention is required.

As for the effects of substituents, in propylmethylsiloxane in which R has 3 carbon atoms, the selectivity for oxygen and nitrogen is as small as 2.2, and the oxygen permeability is 2.5
-8cc ham/cram sec @amHq, which is worse than simple polydimethylsiloxane. However, when R became an alkyl group having 4 carbon atoms, the selectivity began to improve to 2.4, and it was observed that as the number of carbon atoms further increased and the number of branches increased, the selectivity improved further. When R exceeds 9 carbon atoms, selectivity is almost saturated and oxygen permeability tends to decrease. Also, materials with residual hydrogen.

circle. ,,,Ka8-o□Eyao. □In the polymer, all substituents R may be the same, or may be partially different as long as the number of carbon atoms is 4 to 9.

The degree of polymerization n of the polyorganosiloxane must be at least 10 mer or more, and the higher the degree of polymerization n, the better as long as gelation is possible.

In addition, when starting from substituted monomers to obtain polyorganosiloxane, co-hydrolysis is possible as is well known, and at this time, oligocyclic dimethylsiloxane is used as a partner for co-hydrolysis to control the degree of polymerization. can be improved.

The obtained polyorganosiloxane is soluble in common aromatic hydrocarbons such as benzene, toluene, xylene, etc., and can be easily formed into a film by a casting method.

Moreover, the polyorganosiloxane according to the present invention has a thickness of 1
It can also be made into an ultra-thin film of μm or less.

That is, when a dilute solution consisting of polyorganosiloxane and an aromatic solvent is spread on a water surface, it spreads uniformly on the water surface at a fast spreading speed, making it possible to produce an ultra-thin film of 0.1 μm or less. Since such ultra-thin films have weak mechanical strength, they usually require a support film to hold them, and such support films include porous films, such as Nippon Polyplastics' product name DURAGAT, which is made of porous polypropylene material. ' etc. are suitable. The polymer material according to the present invention has excellent adhesion to this porous membrane, and can be easily attached to the water surface.
By simply bringing the porous membrane into contact with the developed ultra-thin polymer membrane, an integrated composite membrane with sufficient strength can be obtained.

Specific examples of the present invention will be described below.

<Example 1> 38 parts of polymethylhydrodiene silane (17-mer),
15 parts of 1-butene and 1 me of a propatool solution containing 6 parts of chloroplatinic acid were sealed in a sealed tube, and reacted in a water bath at 60'C for 8 hours. Thereafter, the sealed tube was cooled to room temperature, and after opening, the contents were distilled under reduced pressure to remove low-boiling compounds, and the remaining viscous liquid was washed with methanol.

This was dissolved in benzene, added with backward benzoyl oxide, cast on a glass plate, and heated at 100° C. for 1 hour to obtain a film. When this film was removed from a glass plate, the amount of gas permeation was measured, and the amount of oxygen permeation was 2.3 x 10
-"cc-cm/cm'set·cmHq, and the separation coefficient between oxygen and nitrogen was 2.4.

<Example 2> ゛ 35 parts of methyldichlorosilane, 26 parts of isobutyne,
6% chloroplatinic acid gropanol solution 1 shoulder A! Seal the tube, 6
The reaction was carried out in a water bath at 0°C for 8 hours. After the reaction was completed, the contents were distilled to obtain methyl-isobutyldichlorosilane having a boiling point of 61°C/28mmHg.This was dissolved in dioxane, 50ml of water was added, and the mixture was reacted at 20''C for 3 hours. After completion of the reaction, distillation was carried out under reduced pressure to obtain tetramethyl, tetraisopdelcyclosiloxane (boiling point 120°C/4tan
10 parts of H(1) were obtained. The obtained product was polymerized under a KOH catalyst to obtain polymethyl isobutylsiloxane with a molecular weight of 18,000. The gas permeability of this polymer is 3.4x 10-8 cc-cml for oxygen
oll・set,・cmH(J, selectivity with nitrogen is 2
．． It was 6.

<Example 3> Example 1. Polymethylalkylsiloxane was synthesized by the same method as in Example 2. The transmittance of the obtained polymethylalkylsiloxane is shown in Table 1 (Example 4) Polymethylhebutylsiloxane was dissolved in benzene to prepare a 10% solution. This polymer and child solution were heated at 26°
It was dropped with a syringe onto the stationary water surface at C and allowed to spread. The developed area was 3od. This developed surface was brought into contact with "Duraguard Membrane" manufactured by Nippon Polyplastics Co., Ltd. to create a composite membrane with the polymer membrane.

The oxygen permeability and selectivity of this composite membrane were as shown in Table 2.

Table 2 (Example 6) Polymethylisobutylsiloxane was dissolved in benzene and 1
A 0% solution was created. This polymer solution was spread on the water surface in the same manner as in Example 4, and a composite membrane was prepared by adhering it to a Millipore filter tube manufactured by Nippon Millipore Limited by vacuum suction. The gas permeability and selectivity of this composite membrane were as shown in Table 2.

More than! However, the chemical structure of the present invention is of the general formula (where R
represents an alkyl group having 4 to 9 carbon atoms, n is an integer not containing O, and m is an integer containing O. ) A gas-permeable membrane made of a polyorganosiloxane shown in For example, oxygen-enriched air, which has more oxygen than air, can be easily obtained, so it has extremely high utility value for various internal combustion engines, various industries, medical applications, etc.

Claims (2)

[Claims] (1) A gas permeable membrane composed of polyorganosiloxane whose structure is represented by the following general formula (where R represents an alkyl group having 4 to 9 carbon atoms, and n is an integer not containing O) , m indicates an integer of 0 or 1 or more.) (2) The gas permeable membrane according to claim 1, which is constructed as a composite membrane in which the polyorganosiloxane is supported on a porous support membrane.