JPH0555175B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a composite semipermeable membrane for selectively permeating components of a fluid mixture.

[Prior Art] Conventionally, many composite membranes have been developed as semipermeable membranes for reverse osmosis, in which an ultra-thin semipermeable membrane is formed on a microporous support membrane. Polyacrylonitrile is widely used as the support film because it has excellent chemical resistance, heat resistance, durability, and the like. For example, Japanese Unexamined Patent Publication No. 172311/1983 discloses a technique for forming a cellulose acetate thin film on the surface of polyacrylonitrile.

[Problems to be Solved by the Invention] However, when a film containing polyacrylonitrile as a main component is used as a support film, the adhesion between the microporous support film and the ultra-thin film material is poor, resulting in the support film being damaged during use. The problem was that the ultra-thin film peeled off and the performance deteriorated.

The present invention aims to solve the drawbacks of the prior art, and aims to provide a composite semipermeable membrane whose performance is less degraded due to peeling of the ultra-thin membrane.

[Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration.

"In a composite membrane consisting of a microporous support membrane mainly composed of polyacrylonitrile and an ultra-thin membrane covering the support membrane, the support membrane has at least one substituent selected from an ionic group and a nonionic polar group. In the present invention, the porous support membrane is mainly composed of polyacrylonitrile having at least one selected from ionic groups and nonionic polar groups. An ionic group is at least partially
Refers to a functional group that can form a positive or negative ionic state, such as sulfonic acid, carboxylic acid, phosphoric acid,
Examples include amines and quaternary ammonium.

In addition, the nonionic polar group refers to a functional group that can cause significant charge polarization in at least a portion thereof, such as an ester group, an amide group, an amino group, a urea group,
Examples include urethane groups and nitrile groups.

Further, in the present invention, it is preferable that the polyacrylonitrile polymer has such an ionic group and a nonionic polar group in the side chain.

One method for introducing ionic groups and nonionic polar groups into a polyacrylonitrile support membrane is to copolymerize acrylonitrile with a polymerizable substance having ionic groups and/or nonionic polar groups. One method is to do so. Examples of such polymerizable substances include acrylic monomers and vinyl monomers, such as acrylic acid,
Methacrylic acid, acrylic ester, methacrylic ester, acrylamide, methacrylamide, vinyl acetate, hydroxystyrene, p-vinylbenzenesulfonic acid, p-vinylbenzenecarboxylic acid, p-vinylbenzene boric acid, p-vinylbenzene phosphoric acid , maleic acid, fumaric acid, maleic ester, fumaric ester, maleic anhydride, vinyl chloride, N-vinylpyrrolidone, methyl vinyl ketone, vinyl sulfonic acid monomer,
Examples include vinyl silane monomers. Further, the polymerization ratio of the polymerizable substance is preferably less than 30 mol% in the support film.

Another method for introducing ionic groups and/or nonionic polar groups into the polyacrylonitrile support membrane is to chemically modify and introduce acrylonitrile. Chemical modification refers to chemically changing the nitrile moiety of polyacrylonitrile, or the functional group moiety of a copolymer component, if any, and is not limited to the treatment method that brings about such a change. Alternatively, it is preferable to treat with an alkali.
Acids are not particularly limited, but include sulfuric acid, nitric acid,
Hydrochloric acid and phosphoric acid are preferably used. Alkalies include sodium hydroxide, potassium hydroxide,
Caustic alkalis such as sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate,
Also, amines such as ammonia, aqueous ammonia, monomethylamine, hydrazine, and hydroxylamine are preferably used.

A modified polyacrylonitrile support membrane can be obtained by immersion in an acid or alkaline solution.

The treatment concentration of acids or alkalis is 1
A concentration range of ~30% by weight is preferred. 1
Less than 30% by weight, the effect is poor;
Exceeding this may damage the supporting membrane.

Such chemical modification may be performed on the polyacrylonitrile raw material itself before film formation, or may be performed on polyacrylonitrile in a microporous support membrane after film formation.

It is preferable to use polyacrylonitrile in which the ionic groups and/or nonionic polar groups contained in the support membrane are uniformly distributed within the support membrane or are mainly distributed on the surface of the support membrane.

As the structure of the microporous support membrane of the present invention, a membrane having an asymmetric structure is preferable. Furthermore, 30Kg/ ^cm2
It is desirable that it can withstand the following pressures. Its shape may be either a flat membrane or a hollow fiber membrane. Considering the workability of forming an ultra-thin membrane and the membrane area of the module, the hollow fiber membrane has an inner diameter of 300~
1200 (μm), with an outer diameter in the range of 400 to 1400 (μm). Furthermore, in the case of a hollow fiber shape, the ultra-thin film can be applied to its outer surface, inner surface, or both surfaces.

The production of the microporous support membrane of the present invention is not particularly limited, and may be carried out in accordance with a conventional method, that is, a general wet film production method.

In the present invention, the ultra-thin membrane is a membrane that covers a support membrane and has substantial separation performance, and may be any conventionally known ultra-thin membrane. The formation of the ultra-thin film of the present invention is not particularly limited, but may be performed using a solution in which a polymer, which is the main component of the ultra-thin film, is dissolved, or by in-situ polymerization. The main component of the ultra-thin film of the present invention may be either a synthetic polymer or a natural polymer. It can be arbitrarily selected depending on the purpose.
Synthetic polymers include polyamide, polysulfonamide, polyurea, polyurethane, polyester, polyvinyl alcohol, polyvinyl chloride,
Examples include vinyl polymers such as polyvinyl acetate and polystyrene, acrylic polymers such as polyacrylic esters, polymethacrylic esters, and polyacrylonitrile, and silicone polymers. Among these, crosslinked polyethyleneimine, crosslinked polyvinyl alcohol, or crosslinked polyamide are preferred, and those containing crosslinked polyamide as a main component are particularly preferred. The ultra-thin film mainly composed of crosslinked polyamide is a film formed by an interfacial condensation reaction between a diamine and a polyfunctional acid halide. The diamine may be any diamine as long as it reacts with the polyfunctional acid halide to form a crosslinked polyamide film, and may be either an aliphatic diamine or an aromatic diamine, but an aliphatic diamine is preferred. Furthermore, it is preferable that it is a secondary amine,
For example, N,N'-dimethylethylenediamine,
N,N'-dimethylpropanediamine, N,N'-
Dimethyl-m-phenylenediamine, N,N'-
Dimethyl-p-phenylenediamine, piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, 1,3-bis(4-piperidyl)methane, 1,3-bis(4-piperidyl)ethane,
Examples include 1,3-bis(4-piperidylpropane). Among them, piperazine diamines that can form a crosslinked piperazine polyamide having a structural moiety represented by -N N- are most preferably used.

The diamine is used after being dissolved in water, and the concentration of the diamine coated on the support film is preferably in the range of 0.2 to 10% by weight. If the concentration of diamine is less than 0.2% by weight, it is difficult to form an ultra-thin film, and if it exceeds 10% by weight, it is difficult to obtain a uniform ultra-thin film.

Any polyfunctional acid halide may be used as long as it reacts with the diamine to form an ultra-thin crosslinked polyamide film, such as trimesic acid halide, benzophenone tetracarboxylic acid halide, isophthalic acid halide, and trimellitic acid. Halide, pyromellitic acid halide, terephthalic acid halide, naphthalenedicarboxylic acid halide, diphenyldicarboxylic acid halide, pyridinedicarboxylic acid halide, benzenedisulfonic acid halide,
Examples include aromatic polyfunctional acid halides such as chlorosulfonylisophthalic acid halide, but trimesic acid chloride is preferable in consideration of solubility in the membrane forming solvent.

The concentration of the polyfunctional acid halide is preferably 0.1% by weight or more and 2% by weight or less.
If it is less than 0.1% by weight, the crosslinking density will decrease and stable membrane performance will not be obtained. Moreover, if it exceeds 2% by weight, there is a risk of damaging the hollow fiber support membrane whose main component is polyacrylonitrile.

The polyfunctional acid halide is used after being dissolved in an organic solvent. Such organic solvents are immiscible with water;
It is also necessary to dissolve the polyfunctional acid halide and not destroy the microporous polyacrylonitrile support membrane, and any material may be used as long as it can form a crosslinked polyamide by interfacial condensation polymerization. Preferred examples include n-hexane, trichlorotrifluoroethane, and the like.

Examples of natural polymers include cellulose polymers such as cellulose, cellulose triacetate, carboxymethyl cellulose, cellulose acetate butyrate, cellulose propionate, ethyl cellulose, methyl cellulose, nitrocellulose, chitin, chitosan alginic acid, and the like.

A preferred requirement of the present invention is that the ultra-thin film is mainly composed of a polymer having ionic groups and/or nonionic polar groups from the viewpoint of improving adhesion and membrane performance. The definitions and specific examples of such ionic groups and nonionic polar groups are the same as those described above. It is more preferable that the ionic groups of the polymer constituting the ultra-thin film have the opposite sign to the ionic groups of the support membrane polymer.

The thickness of the ultra-thin film can be arbitrarily selected depending on the purpose, but it is preferably between 10 nm and 1000 nm; if it is too thin, the film will not be able to exhibit its performance, and if it is too thick, the permeation rate will decrease. Therefore, it is more preferable that the thickness is 20 nm to 30 nm.

A preferred example of forming the ultra-thin film of the present invention on the inner surface of a hollow fiber-like support membrane mainly composed of polyacrylonitrile is to apply an aqueous solution containing 0.5 to 5% by weight of piperazine as a main component to the support membrane. After that, 0.1 to 0.5% by weight of a trichlorotrifluoroethane solution of a polyfunctional acid halide is injected into the lumen, kept in the lumen for a certain period of time, and the crosslinking condensation reaction proceeds instantaneously at room temperature. can be mentioned.

The composite membrane obtained by the present invention includes a reverse osmosis membrane, an ultrafiltration membrane, which supplies a liquid and has the liquid as a permeation side.
Alternatively, it is used for fluid separation, such as a pervaporation membrane that supplies a liquid and has a gas permeate side, or a gas separation membrane that supplies a gas and has a gas permeate side.

[Example] In the following examples, the selective separation performance of reverse osmosis membranes or ultrafiltration membranes is determined by measuring the salt rejection rate by measuring electrical conductivity, and by measuring the rejection rate of water-soluble organic substances by measuring refractive index. Measured by. In addition, as permeation performance, the water permeation rate was determined by the amount of water permeation per unit area and per unit day. As pervaporation performance, selective separation performance was determined by gas chromatography.

Example 1 A flat microporous support membrane of a copolymer consisting of 80 parts of acrylonitrile and 20 parts of acrylic acid was coated with piperazine.
After immersion in an aqueous solution containing 1.0% by weight and 1.0% by weight of trisodium phosphate, excess droplets of the amine aqueous solution adhering to the surface of the dense layer of the support membrane were removed and air-dried for 1 minute at room temperature. After that, add 0.2 of trimesic acid chloride to trichlorotrifluoroethane.
A solution in which the weight percent was dissolved was cast onto the surface of the dense layer of the support membrane, and a polycondensation reaction was performed. This support membrane was lifted from the acid chloride solution to volatilize the solvent adhering to the membrane surface, and then immersed in an aqueous solution containing 0.2% by weight of sodium carbonate, followed by thorough washing with water.

The composite membrane thus obtained was heated at a pressure of 4 kg/
As ^a result of an ultrafiltration test of a 500 ppm NaCl aqueous solution at 25°C, the desalination rate was 43% and the water permeation rate was 43%.
It showed a performance of 0.8m ³ /m ² ·day.

Example 2 An aqueous solution containing 1.0% by weight of piperazine and 1.0% by weight of trisodium phosphate was injected into the lumen of a hollow fiber microporous support membrane made of a copolymer consisting of 80 parts of acrylonitrile and 20 parts of acrylic acid. applied to the inner surface. After draining off the excess aqueous solution adhering to the inner surface by blowing nitrogen gas under pressure at room temperature, a solution of 0.2% by weight of trimesic acid chloride dissolved in trichlorotrifluoroethane was poured into the hollow fiber lumen. for 1 minute. The solvent adhering to the inner surface was evaporated by blowing nitrogen gas into the inner cavity under pressure. Thereafter, an aqueous solution containing 0.2% by weight of sodium carbonate was injected, and distilled water was further allowed to flow down into the hollow fiber lumen for washing.

The composite hollow fiber membrane obtained in this way was
500ppm NaCl under the conditions of ℃, operating pressure 3Kg/ ^cm2
As a result of ultrafiltration test of aqueous solution, desalination rate was 45%.
It exhibited a water permeation rate of 0.6 m ³ /m ² ·day.

Example 3 A flat microporous support membrane made of polyacrylonitrile was immersed in 10% sulfuric acid for 1 hour at room temperature, thoroughly washed with water, and prepared in an aqueous solution containing 1.0% by weight of piperazine and 1.0% by weight of trisodium phosphate. immersed in it. lifting the support membrane from the amine aqueous solution,
The droplets adhering to the surface of the support membrane having a dense layer were removed and air-dried for 1 minute at room temperature. After that, add trimesic acid chloride to trichlorotrifluoroethane.
A solution containing 0.2% by weight was cast onto the surface and reacted for 1 minute. After volatilizing the solvent adhering to the membrane surface, the membrane was immersed in an aqueous solution containing 0.2% by weight of sodium carbonate for 1 minute, and then thoroughly washed with water.

The thus obtained composite membrane was subjected to an ultrafiltration test of a 500 ppm NaCl aqueous solution under the same conditions as in Example 1. As a result, the desalination rate was 41% and the water permeation rate was 0.7 m ³ /
It showed performance of ^m2・day.

Example 4 A hollow fiber microporous support membrane made of polyacrylonitrile was immersed in 10% by weight sulfuric acid at room temperature for 1 hour, and then thoroughly washed with water to form a membrane containing 1.0% by weight of piperazine and 1.0% by weight of trisodium phosphate. Immersed in amine aqueous solution. The support membrane was lifted from the amine aqueous solution, droplets adhering to the surface of the hollow fiber membrane were removed, and the membrane was air-dried for 2 minutes at room temperature. Thereafter, the hollow fiber membrane was immersed in a solution of 0.2% by weight of trimesic acid chloride dissolved in trichlorotrifluoroethane and allowed to react for 1 minute. After volatilizing the solvent adhering to the membrane surface, the membrane was immersed in an aqueous solution containing 0.2% by weight of sodium carbonate for 1 minute, and thoroughly washed with water.

The thus obtained composite hollow fiber membrane was subjected to an ultrafiltration test for a 500 ppm NaCl aqueous solution under the same conditions as in Example 2. As a result, the salt removal rate was 47%, and the water permeation rate was 47%.
It showed a performance of 0.4m ³ /m ² ·day.

Furthermore, when the surface of this composite hollow fiber membrane was rubbed with a finger and dipped in an aqueous solution containing methyl violet B to perform a dyeing test, it was observed that the surface of the composite hollow fiber membrane had no peeling of the ultra-thin membrane layer. .

Example 5 Copoly(acrylonitrile-) with a molar ratio of 95:5
maleimide) in dimethyl sulfoxide (concentration
15% by weight) on polyester taffeta and then immersed in water to obtain a flat microporous support membrane. An ultra-thin film of crosslinked piperazine polyamide was formed thereon according to the method described in Example 1.
When ultrafiltration was evaluated using a 500 ppm NaCl aqueous solution at 25°C under a pressure of 2.5 Kg/ ^cm2 , the desalination rate was 60.
%, and a water permeation rate of 0.68 m ³ /m ² ·day was obtained.

Example 6 The pervaporation performance was evaluated using a composite hollow fiber membrane obtained by coating the hollow fiber microporous support membrane obtained in Example 4 with an ultra-thin film made of crosslinked polyvinyl alcohol. Using 80% alcohol aqueous solution as the feed liquid, under conditions of temperature 20℃ and permeation pressure 2torr, water separation coefficient is 97 and permeation rate is 0.04Kg/m ³
hr performance was obtained.

Comparative Example 1 A hollow fiber microporous support membrane made of polyacrylonitrile was immersed in an amine aqueous solution containing 1.0% by weight of piperazine and 1.0% by weight of trisodium phosphate. An ultra-thin film of cross-linked piperazine polyamide was formed on the outer surface of the membrane.

The thus obtained composite hollow fiber membrane was subjected to an ultrafiltration test of a 500 ppm NaCl aqueous solution under the same conditions as in Example 2. As a result, the desalination rate was 30%, and the water permeation rate was 30%.
It showed a performance of 0.7m ³ /m ² ·day. Further, when the outer surface of this composite hollow fiber membrane was rubbed with a finger and subjected to a staining test with methyl violet B, clear peeling of the ultra-thin membrane layer was observed.

[Effects of the Invention] According to the present invention, the adhesiveness between the support membrane and the ultra-thin membrane having a separation function is excellent, and the peelability is extremely low.
A composite semipermeable membrane with excellent removal performance is provided.

Claims (1)

[Claims] 1. A composite membrane consisting of a microporous support membrane mainly composed of polyacrylonitrile and an ultra-thin membrane covering the support membrane, wherein the support membrane has at least one substituent selected from an ionic group and a nonionic polar group. A composite semipermeable membrane comprising: