JPH0615153A - Production of drying separation membrane - Google Patents

Abstract

PURPOSE:To provide a production method for a gas separation membrane simplified in production process, reduced in treating time, thereby decreased in production cost and capable of completely removing water. CONSTITUTION:The gas separation membrane is produced by bringing a hydrous cellulose acetate semipermeable membrane into contact with the mixed solution of a water miscible organic solvent, a non-polar organic solvent and a surfactant to substitute water of the semipermeable membrane by the mixed solution.

Description

Detailed Description of the Invention

[Object of the Invention]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a gas separation membrane, and more particularly to a method for producing a gas separation membrane effective for separating oxygen and nitrogen.

[0003]

2. Description of the Related Art Cellulose acetate membranes have already been widely put to practical use for desalination of water by the reverse osmosis method. Therefore, various methods for producing a dry gas separation membrane have been studied, which are dried without destroying the asymmetric structure of the hydrous cellulose acetate membrane and the original reverse osmosis performance is not impaired even when rewetting. A typical example is U.S. Pat. No. 3,842,5.
No. 15, JP-A-56-197204, a hydrous cellulose acetate membrane is first treated with a water-miscible organic solvent, then with a non-polar organic solvent and then dried. That is, a dry film can be obtained by this method without significantly destroying the film structure.

[0004]

However, the dry film obtained by this method had to be subjected to a displacement treatment with a water-miscible organic solvent and then further treated with a nonpolar organic solvent. For this reason, not only the continuous processing or the batch processing, but also the displacement processing apparatus becomes excessively large, and the amount of solvent used increases and the processing time becomes long. Therefore, there is a problem that the manufacturing cost of the dry film increases. One-step replacement with a mixed solvent of a water-miscible organic solvent and a non-polar organic solvent is also conceivable, but depending on the replacement conditions, water phase-separates in the mixed solvent and water adheres to the film during drying, resulting in There was a problem of causing destruction. The present invention has been made to solve such conventional problems, and a gas separation membrane capable of simplifying the manufacturing process, thereby shortening the processing time, reducing the manufacturing cost, and completely removing water. It aims at providing the manufacturing method of.
[Constitution of Invention]

[0005]

In order to achieve the above object, the present invention comprises contacting a hydrous cellulose acetate semipermeable membrane with a mixed solution of a water-miscible organic solvent, a non-polar organic solvent and a surfactant. The water in the semipermeable membrane is replaced with the mixed solution, and then dried.

As the cellulose acetate membrane in the present invention, a cellulose diacetate membrane, a cellulose triacetate membrane or a membrane composed of a mixture of cellulose diacetate and cellulose triacetate is preferably used, but the cellulose triacetate membrane has gas separation performance and gas permeability performance. It is excellent in balance and is particularly preferable.

The surfactant used in the present invention is a compound miscible with or partially miscible with a water-miscible organic solvent, a non-polar organic solvent, or a mixture thereof, and water is added to the mixed solvent containing the surfactant. There is no particular limitation as long as it can be emulsified or solubilized. Specifically, an anionic surfactant and a cationic surfactant can be used.

Examples of anionic surfactants include sodium oleate for soaps, sodium lauryl sulfate ester for sulfates, and sodium laurylbenzenesulfonate for sulfonates.
The more preferable anionic surfactant is sodium oleate.

Examples of the cationic surfactant include laurylamine acetate in the amine salt type, cetylethyldimethylammonium bromide, cetyltrimethylammonium chloride in the quaternary ammonium salt type, ammonium stearate, cetylpyridinium chloride and the like. . Cationic surfactants are generally suitable for the present invention.

The concentration of the surfactant contained in the mixed solvent in the present invention varies depending on the surfactant used, but is preferably at least 1% by weight, more preferably 2% by weight.
It is from 5% to 5% by weight. If the content concentration is lower than 1% by weight, the merit in manufacturing the separation membrane tends to be lost.

The water-miscible organic solvent used in the production of the gas separation membrane of the present invention must be a non-solvent for the cellulose acetate membrane. That is, a solvent that dissolves the film or densifies the film structure is not suitable.

Specifically, pentane, hexane, heptane, octane, cyclobutane, cyclopentane, cyclohexane, 1,3-dimethylcyclohexane, benzene, toluene, ethyl ether, isopropyl ether, carbon tetrachloride, 1,1,2- Examples include trichlorofluoroethane and carbon disulfide.

The time and temperature for the substitution treatment vary depending on the type of water-miscible organic solvent, nonpolar organic solvent and surfactant used and the composition of the treatment liquid, but the time is 30 to 120 minutes. If the substitution time is shorter than 30 minutes, the water content of the membrane after the substitution treatment will exceed 2.5% and the performance will not be exhibited.
Also, even if the replacement time is increased by 120 minutes or more, the replacement does not proceed any further. The substitution temperature is preferably -10 ° C to 20 ° C. If it is out of this range, the film structure may be destroyed.

The drying temperature may be a temperature at which the cellulose acetate film is not densified, and it is preferable to dry at 30 ° C to 100 ° C. The drying time may be the time required for the mixed solvent in the cellulose acetate film to completely evaporate.

The composition of the water-miscible organic solvent and the non-polar organic solvent of the mixed solvent in the present invention is preferably 40/60 to 10/90, more preferably 30/70 to 15/85. When the water-miscible organic solvent is more than 40%, the shrinkage of the membrane becomes large when dried. If the amount of non-polar organic solvent is more than 90%, the water content of the water-containing film will not be sufficiently dissolved in the mixed solvent, and the water content of the film after the replacement will be
If it exceeds 2.5%, no performance will appear after drying.

The hydrous cellulose acetate membrane in the present invention may be in the form of either a flat membrane or a hollow fiber membrane, but the effect of the present invention is greater in the hollow fiber membrane in which it is difficult to replace water in the membrane.

[0017]

In the present invention, by adding a surfactant to the water-miscible organic solvent and the non-polar organic solvent, the water in the membrane pores of the hydrous cellulose acetate semipermeable membrane becomes an emulsified state and the organic solvent. It is extracted inside, and in this state is dried and removed together with the organic solvent.

[0018]

The present invention will be described in more detail with reference to the following examples.
The present invention is not limited to these.

The hydrous cellulose acetate membrane used in the examples is "Horosep" (trade name) manufactured by Toyobo Co., Ltd.
The one used for the element was used. This membrane was made of cellulose triacetate, and its performance as a reverse osmosis membrane was a salt removal rate of 99.9%. (Using 1500ppm saline,
It was measured at an evaluation pressure of 30 kg / cm ² and 25 ° C. ) In addition, the gas permeability of the dry membrane is different from pure gases such as oxygen and nitrogen.
Pressurized at 5.0 kg / cm ² and measured at a temperature of 25 ℃.
The flow rate of the gas passing through ² ) was measured using a thin film flow meter. Oxygen permeation rate KO ₂ (cc (st
p) / cm ² · s · cmHg), nitrogen permeation rate KN ₂ (cc (stp) / c
m ² · s · cmHg) and the separation coefficient α (KO ₂ / KN ₂ ) was calculated from the ratio of the permeation rates.

Example 1 A mixed solvent containing 2-propanol (hereinafter, IPA) and cyclohexane (hereinafter, CHX) 20/80 was prepared, and 2% by weight of laurylamine acetate was added to the mixed solvent. The liquid temperature was maintained at 15 ° C. Next, the hydrous cellulose acetate membrane was dipped, and the solution was occasionally stirred and held for 60 minutes.

However, at this time, the water content of the membrane is 40 per 1 m ² of the membrane.
cc, and the amount of liquid used for the substitution treatment was 1600 per 1 m ² of the membrane.
cc

After the substitution treatment, it was dried at 50 ° C. for 24 hours to obtain a dry film. The measurement results of the gas permeation performance of this dried membrane are shown in Table 1.

Comparative Example 1 Using the same cellulose triacetate membrane as used in Example 1, the ratio of 2-propanol and cyclohexane was 80.
Changed to / 20. The substitution operation and the drying operation were performed under the same conditions as in Example 1 without using a surfactant.

The measurement results of the gas permeation performance of this dry membrane are shown in Table 1.

Comparative Example 2 Using the same cellulose triacetate membrane as used in Example 1, the proportions of 2-propanol and cyclohexane were 20%.
I changed it to / 80. The substitution operation and the drying operation were performed under the same conditions as in Example 1 without using a surfactant.

Table 1 shows the measurement results of the gas permeation performance of this dry membrane.

Comparative Example 3 The same cellulose triacetate membrane as that used in Example 1 was used and separately dipped in 2-propanol and cyclohexane (two-stage substitution). That is, first, a water-containing cellulose acetate membrane was added to 2-propanol whose liquid temperature was kept at 15 ° C.
Soak for 60 minutes, then change the solvent to cyclohexane
Soaked for 60 minutes. After the completion of the substitution, it was dried at 50 ° C. for 24 hours to obtain a dry film.

The measurement results of the gas permeation performance of this dry membrane are shown in Table 1.

[0029]

[Table 1]

[0030]

EFFECTS OF THE INVENTION The gas separation membrane of the present invention does not significantly deteriorate in gas permeation performance and membrane performance even though it is used in a single-stage substitution by using a mixed solvent containing a surfactant. In addition, because of the one-stage substitution, the manufacturing process can be greatly simplified as compared with the conventional method for drying a hydrous cellulose acetate membrane. Therefore, reduction of the amount of solvent used,
It is possible to provide a gas separation membrane and a method for manufacturing the same, which can reduce the processing time and can be manufactured at low cost.

[0031]

Claims (1)

[Claims] 1. A hydrous cellulose acetate semipermeable membrane is contacted with a mixed solution of a water-miscible organic solvent, a nonpolar organic solvent and a surfactant, and the water in the semipermeable membrane is replaced with the mixed solution. ,
A method for producing a gas separation membrane, which comprises drying.