JPH0240224A - Semipermeable membrane to be used for gas separation - Google Patents

Abstract

PURPOSE:To improve permeation velocity of a semipermeable membrane for a condensible gas without impairing a permselectivity coefft. of the membrane by constituting the semipermeable membrane of at least one roughened surface, wherein the surface area of the roughened surface is >=5 times of a projected area of the surface. CONSTITUTION:A semipermeable membrane to be used for gas separation is constituted to have at least one roughened surface and the surface area of the roughened surface is regulated to be >=5 times of a projected area of the surface. Preferred surface roughness of the semipermeable membrane is 0.5-100mum, particularly 1-50mum. The roughened surface area is regulated to be >=5 times, pref. >=10 times basing on the projected area of the surface by regulating the number of fine unevennesses to 10<3>-10<15> per 1cm<2> of the area of the membrane. The semipermeable membrane is constituted pref. of a high molecular film capable of contg. dissolved condensible gas such as steam, ammonia. The semipermeable membrane obtd. by this method has improved permeation velocity without impairing permselective coeffts. for condensible gases.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a separation membrane that permeates and separates specific components from a mixed gas using a semipermeable membrane, and particularly relates to a separation membrane that permeates and separates specific components from a gas mixture, and in particular, it permeates and separates specific components from a gas mixture. This invention relates to a semipermeable membrane used for gas separation that selectively allows condensable gases such as ammonia, carbon dioxide, and sulfur dioxide to pass through.

More specifically, we manufacture air with reduced humidity such as air conditioning for buildings and compressed air for instrumentation, remove moisture from natural gas,
In addition, in the production of gases that control humidity, which are used in a wide range of fields such as the chemical industry, the electrical and electronics industry, the precision machinery industry, the food industry, and the textile industry, semipermeable membranes are used to convert moisture-containing gases into water-containing gases. , a method of selectively permeating and separating water vapor, a method of selectively permeating and separating carbon dioxide gas from methane/carbon dioxide gas such as natural gas and methane fermentation, and a method of selectively permeating and separating sulfur dioxide gas contained in flue gas. The present invention relates to a semipermeable membrane used in the method.

[Prior art] Methods for removing condensable gas from gas can be broadly classified into (
Four methods are known: 1) compression method, (2) cooling method, (3) adsorption method, and (4) membrane separation method.

The membrane separation method is a method in which a gas containing a specific component is brought into contact with one side of a semipermeable membrane, and the specific component is selectively permeated and separated from the other side.In principle, the running cost is lower than the other three methods. Although it has the advantages of being inexpensive, having a simple device structure, and being able to continuously obtain purified gas without contaminating the gas, there are currently few semipermeable membranes with excellent selective permselectivity, and it is rarely put to practical use. has not been standardized.

For example, JP-A-53-97246. Japanese Patent Publication No. 54-114
81゜ Japanese Patent Publication No. 54-152679, Japanese Patent Application Publication No. 60-18
3025, JP-A-61-195117, JP-A-62
-42723 describes water vapor separation membranes made of hydrophilic polymer membranes and membrane materials with high gas permeability used for oxygen separation and hydrogen separation, but the amount of water vapor permeation is small, and the separation coefficient of water vapor and gas is is also not enough.

In addition, for the purpose of improving water vapor permeation and membrane strength, composite membranes using the above-mentioned membrane materials as thin films with polysulfone porous membranes, polypropylene porous membranes, and polytetrafluoroethylene porous membranes are disclosed in JP-A-53-86684 and JP-A-60. -25781
9, JP-A-60-261503° JP-A-62-427
72, etc., although the membrane strength has been improved, the amount of water vapor permeation did not improve as expected.
The water vapor selective permeability coefficient is also small.

On the other hand, it is used in diaphragms for fuel cells and diaphragms for electrolysis.
Perfluoro ion exchange membranes containing sulfonic acid groups in their side chains are considered effective as water vapor separation membrane materials because of their high water absorption and high water permeation rate through polymers.
A dehumidifier using hollow tubes of perfluorosulfonic acid polymer is described in USP 3735558 and is available as PermaPure Dry. However, since this method has a small amount of water vapor permeation, it has the disadvantage that it cannot be used as a substitute for conventional refrigeration or adsorption methods in industrial applications that process large amounts of gas.

Furthermore, although the roughened semipermeable membrane of the present invention has a different structure and purpose,
14036. Japanese Patent Publication No. 62-58623 describes a diaphragm for alkali chloride electrolysis that has at least one surface roughened. The membrane surface is roughened to prevent chlorine gas or hydrogen gas generated during electrolysis from adhering to the membrane surface and increasing the voltage; it does not improve the membrane's permeability to substances. . Moreover, these membranes are made to block the permeation of hydroxide ions or chloride ions, and have low water absorption rates, so they cannot be used as semipermeable membranes for gas separation.

[Problems to be Solved by the Invention] The present invention attempts to solve the above-mentioned drawbacks of the prior art, and is aimed at solving the above-mentioned drawbacks of the prior art. It is an object of the present invention to provide an improved semipermeable membrane that increases the permeation rate of cohesive gas without reducing the selective permeation coefficient.

When the semipermeable membrane of the present invention is used for water vapor separation, it can replace the production of compressed air for air conditioners and instrumentation using conventional technology, and can also be used for dehumidifying natural gas and removing carbon dioxide. The purpose is to provide.

[Means for Solving the Problems] The above object of the present invention is to provide a semipermeable membrane for gas separation in which at least one surface is roughened, and the roughened surface area is 5 times or more the transparent area of the membrane. This is achieved by a semi-permeable membrane.

The semipermeable membrane of the present invention is basically a semipermeable membrane whose gas contact side surface and/or gas permeation side surface condition is specified, and this is based on novel ideas and knowledge that have not existed before. It is.

In other words, conventional semipermeable membranes for gas separation are made of materials with large selective permeability coefficients such as cellulose, polyvinyl alcohol, acrylic, polysulfone, polyimide, silicone, and perfluoro ion exchange membranes.
It is used after being formed into a thin film of 100 μm to several 100 μm. In order to further increase the amount of permeation, it is used as an asymmetric porous membrane with an extremely thin dense layer on the membrane surface, or as a composite membrane in which a membrane with a thickness of several 10 angstroms to several tens of microns is laminated on a porous support membrane. This is also being implemented.

However, these asymmetric porous membranes and composite membranes with extremely thin layers can increase permeation rates without compromising permselectivity when used for common gases such as oxygen/nitrogen separations, hydrogen or helium/air separations. can be done, but
It has been found that even when a membrane having an ultra-thin layer is used to separate a cohesive gas such as water vapor, the increase in permeation rate is small and rather the permselectivity is reduced.

As a result of intensive research into a method for manufacturing a semipermeable membrane that increases the permeation rate without impairing permselectivity in a method for separating cohesive gases such as water vapor from gases that contain them, the present inventor discovered that We have discovered that this can be achieved by making the surface of the membrane rough.

It is not clear why making the surface of a semipermeable membrane rough increases the permeation rate of cohesive gases such as water vapor, but it is thought to be due to the following reasons.

That is, the gas permeation rate is determined by the following three steps. The first step is the rate of gas dissolution and adsorption on the membrane surface;
The second step is the diffusive permeation rate of gas within the membrane, and the third step is the rate of gas desorption at the permeate surface of the membrane. The permeation rate of gases such as hydrogen, helium, nitrogen, and oxygen is inversely proportional to the thickness of the semipermeable membrane, and if the thickness is halved, the permeation rate doubles, so the permeation rate of these gases is The diffusion permeation rate is effectively rate-limiting. However, in the case of condensable gases such as water vapor, the thickness of the semipermeable membrane is not inversely proportional to the thickness of the semipermeable membrane, and especially for membranes containing hydrophilic groups such as ion exchange groups, the membrane thickness increases. However, since the decrease in water vapor permeation and superspeed is slight, it may be that the water vapor permeation rate is rate-limiting, or that it is not the diffusion permeation rate within the membrane (or that it is dominated by dissolved adsorption and/or desorption on the membrane surface). This explains that by roughening the surface of a semipermeable membrane, the surface area increases, which increases the rate of dissolution and adsorption to the membrane surface and/or the rate of desorption of gas, thereby increasing the permeation rate. However, this explanation is provided for the purpose of understanding the present invention, and does not limit the present invention in any way.

As the roughened semipermeable membrane of the present invention, one whose roughened surface area is 5 times or more, preferably 10 times or more of its transparent area is used. Here, the term "roughened" refers to a state in which the surface of the film is irregular, that is, the surface of the film is not smooth and has minute irregularities.
"Surface roughness of 2 μm" means that the sum of the depth of one peak and the adjacent valley in the unevenness of the surface of the film is
It represents 2 μm on average. Moreover, the "roughened surface area" is expressed by finding the surface length between two points on two orthogonal sides using a stylus type surface area meter, and multiplying it by that length. In the present invention, the semipermeable membrane may be made of various materials without any limitation, but in particular water vapor, which is a condensable gas,
Ammonia, carbon dioxide.

A vine polymer membrane in which sulfur dioxide is dissolved is preferable, and a semipermeable polymer membrane having ion exchange groups is a particularly preferable membrane material because it has a high solubility for these condensable gases.

Examples of ion exchange membrane types include cation exchange groups such as sulfonic acid, sulfonate, carboxylic acid, carboxylate, phosphoric acid, phosphate, acidic hydroxyl, and salts of acidic hydroxyl;
Examples include anion exchange groups such as a tertiary amino group and a quaternary ammonium group. Semipermeable membranes with these ion exchange groups have a water absorption rate of 40 when immersed in water at 25°C for 16 hours.
Volume % or more, fixed ion concentration 6 meq/g H2
0 or less and a film thickness of 2 to 200 μm is used. When the water absorption rate is less than 40% by volume or the fixed ion concentration is more than 6 meq/gHzO, the gas solubility is small (the permeation rate is also low. If the membrane thickness is less than 2 μm, the membrane Parts with extremely small thickness occur, resulting in a decrease in permselectivity and, in some cases, causing problems such as pinholes.

As a method for obtaining a roughened semipermeable membrane in the present invention, when the semipermeable membrane or the precursor of the semipermeable membrane has thermoplasticity,
It is also possible to use other materials with rough surfaces, such as blasted metal plates, rolls, blasted films, porous metal plates, porous films, and the like. In addition, the surface of the semipermeable membrane is roughened by mechanically scraping it with an abrasive such as sandblasting,
In addition to chemically roughening the surface in an ionizing atmosphere such as plasma etching or sputtering, methods to obtain a semipermeable membrane with a rough surface include casting or polymerizing a polymer solution or monomer solution on the rough surface. It will be done. Another preferred surface roughening method is to embed soluble particles or fibers in a semipermeable membrane, or apply an ion exchange polymer solution containing soluble particles or fibers to a semipermeable membrane, and then A method of eluating fibers and roughening the surface can also be used.

The surface roughness of the roughened semipermeable membrane obtained by (2) is preferably 0.5 to 100 μm, particularly 1 to 50 μm,
In addition, the fine irregularities are preferably 10" to 1O'1 on average per 1 ca+" of membrane area, preferably 10'-1 on average.
By having 0" pieces, the roughened surface area is formed to be 5 times or more, preferably 10 times or more, the transparent area (that is, the surface area of an ideal smooth film).

If the surface roughness is large, such as 100 μm or more, the amount of gas that you do not want to permeate from the recesses where the film thickness is the smallest increases, resulting in a decrease in selective permeability, or a decrease in gas flow to the recesses, resulting in a permeation rate. For the same reason, the ratio of the thickness of the convex portions to the thickness of the concave portions of the semipermeable membrane is preferably 1/2 or less.

The roughened semipermeable membrane of the present invention thus obtained is brought into contact with water vapor or a gas containing a condensable gas such as ammonia, carbon dioxide, or sulfur dioxide, and the other side is brought into contact with a dry gas. Alternatively, these cohesive gases can be selectively permeated by reducing the pressure.

The roughened surface of the semipermeable membrane may be on either the raw material mixed gas side or the permeated gas side, but it is often preferable to have both surfaces roughened. In particular, by using the roughened semipermeable membrane of the present invention for a gas containing water vapor as a cohesive gas, the water vapor permeation rate and water vapor selective permeability coefficient are lower than that of a semipermeable membrane with a smooth surface. It can be used as a much improved dehumidification membrane.

The roughened semi-permeable membrane also has a high water absorption rate.

It can be used as a multilayer membrane with two or more layers with different fixed ion concentrations, or as a composite membrane reinforced with a porous support.

Next, the present invention will be explained with reference to examples, but the present invention is not limited to these examples.

Prior to the examples, various measurement methods used in the following examples will be summarized.

(1) Measurement of water absorption rate W A film layer produced under the same conditions as the semipermeable membrane used to measure permeability was immersed in pure water at 25°C for 16 hours to determine the weight W1.
Dry weight of the film layer dried under vacuum W2. and the density ρ after drying, it is calculated from the following formula.

W=100(Wl-W2)/W, ÷ρ (2) Calculation of fixed ion concentration Aw Ion exchange capacity (meq/g resin) A, I and above W1
It is determined from the following equation from and W2.

A-=AR/ (WI W2) ÷ W2 (3) Water vapor transmission rate Q (rd(STP)/rrfura r, at
Measurement of m) Using the apparatus shown in FIG. 1, the water vapor permeation rate with 100% purity is calculated.

(4) Water vapor selective permeability coefficient α The permeation rate QA of gas A is determined using a Seikagaku-style gas permeation measuring device, and calculated using the following formula.

α,=Q/QA [Example] Example I CFi=CFOCFzCF (CFi)0 (CFz)
Copolymerizing zsOJ and tetrafluoroethylene,
A copolymer with an ion exchange capacity of 1.1 meq/g resin was obtained.

The copolymer was melt-extruded to a roughness of 5μ on one side and both sides.
By hot pressing a roll with a rough surface, the thickness of 8
A film of 0 μm was obtained.

The film obtained in the above manner was hydrolyzed with an aqueous alkali hydroxide solution, and then converted into an acid form with an aqueous hydrochloric acid solution, and the water vapor permeation rate and water vapor/nitrogen selective permeability coefficient of each were determined.The results are shown in the table below. Shown in 1.

The water absorption rate of the acid type membrane was 60.8% by volume, the fixed ion concentration was 3.6 meq/g HzO, and the surface area of the rough surface was determined to be 16 times the transparent area.

Comparative Example 1 Comparative Example 1 was carried out in exactly the same manner as in Example 1 except that a smooth film without roughening treatment was used.

Note that the water absorption rate and fixed ion concentration were exactly the same. The results are shown in Table-1.

Table 1 Example 2 CF,=CFO (CF3COOCH) and tetrafluoroethylene were copolymerized to obtain a copolymer with an ion exchange capacity of 1.8 milliequivalents/g resin.

The copolymer was melt-molded to obtain a roughened film having a roughness of 5 μm on one side and both sides with a roughness of 5 μm.

The film thus obtained was hydrolyzed with an aqueous sodium hydroxide solution to obtain a Na salt type carboxylic acid film. The water absorption rate of the peritoneum is 75.2% by volume, and the fixed ion concentration is 4.7 meq.
/g H2O. The water vapor transmission rate was determined in the same manner as in Example-1. For comparison, a smooth film that was not subjected to surface roughening treatment was also measured. Table 2 of the results
Shown below.

Table-2

[Brief explanation of the drawing]

FIG. 1 shows a schematic diagram of a water vapor transmission rate measuring device. 1... Water vapor permeation measurement cell 2... Steam chamber side pressure gauge 3...Transmission chamber side pressure gauge 4... Moisture aggregation trap 11...Porous support 12...Test membrane for measurement 13... water vapor 14...Pure water Engraving of drawings (no changes to content) 1 concave Procedural amendment phantom November 8, 1986

Claims (1)

[Scope of Claims] (1) A semipermeable membrane for gas separation, characterized in that at least one surface is roughened, and the roughened surface area is 5 times or more the transparent area of the membrane. Semipermeable membrane (2) The semipermeable membrane has a water absorption rate of 40% by volume or more, a fixed ion concentration of 6 milliequivalents/gH_2O or less, and a membrane thickness of 2 to 200%.
The roughened semipermeable membrane according to claim (1), characterized in that it has a resin layer containing ion exchange groups of μm in diameter. Patent claim (1) or (2), characterized in that it is a water vapor selectively permeable membrane that selectively allows water and water vapor to permeate by contacting the other surface with dry gas or by reducing the pressure. roughened semipermeable membrane