JPS62282604A - Composite semipermeable membrane for separating material and its production - Google Patents

Abstract

PURPOSE:To obtain a composite semipermeable membrane which can maintain high sepn. performance for a long period of time by interposing metal near the surface of the semipermeable membrane and forming an ultra-thin film layer consisting of a high polymer having affinity to the semipermeable membrane and metal onto said semipermeable membrane. CONSTITUTION:The semipermeable membrane of the asymmetrical structure formed by casting a film forming soln. of cellulose acetate, etc., on a glass plate and immersing the same in cold water, etc., is heat-teated in a hot water bath cong. metallic ions of ferric sulfate, etc., and is washed; thereafter, the membrane is immersed into a high-polymer soln. of a PVA, etc. The composite semipermeable membrane which contains average >=100ppm metal near the surface of the membrane (active layer side) and has further the ultra-thin film layer of the high-polymer for immobilizing the metal onto the surface is thus obtd.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention provides a novel semipermeable membrane with excellent substance separation properties and a method for producing the same. More specifically, the present invention provides a composite semipermeable membrane in which a metal is present near the surface of the semipermeable membrane and an ultra-thin membrane layer on the semipermeable membrane, and a novel method for producing the same.

[Prior Art 1 Separation membranes are becoming increasingly important in various fields such as substance separation, shrinkage, and purification.

Typical examples include desalination of seawater and brine using reverse osmosis membranes, production of ultrapure water, artificial kidneys using dialysis membranes,
Extreme: Juice concentration using filtration membranes, etc., and the development of oxygen enrichment membranes, oxygen fixation membranes, etc. is also progressing.

Generally 1 minute! There are two types of If membranes: asymmetric semipermeable membranes consisting of a dense layer and a porous layer, and composite semipermeable membranes in which an ultra-thin layer of about 0.01 to 0.1μ is formed on a porous base membrane. Membranes are said to have an advantage in that the active layer, which governs separation performance, can be made thinner.

Conventionally, the following methods are typical as methods for shaping composite semipermeable membranes.

(1) A dilute solution of a polymer is coated on a porous base film, and the solvent is evaporated to form an ultra-thin film.

(2) Coating a mono- and/or propolymer onto a porous base film and forming an ultra-thin film by interfacial polymerization reaction or the like.

(3) An ultra-thin film formed by a water surface spreading method or the like is laminated on a porous base film.

However, in (1), it is generally difficult to produce an ultra-thin film without defects, and in (2), it is difficult to control the reaction conditions, making it difficult to produce an ultra-thin film with good reproducibility. In addition, in (3), there is a risk of damaging the ultra-thin film when it is laminated on another base film. Moreover, the currently proposed composite membranes have limited combinations of materials for the support membrane and super 8 membrane layers, and this poses a major problem that requires improvement in solvent resistance, dissolved oxygen resistance, and chlorine resistance.

As one method to solve these problems, in the field of reverse osmosis membranes, methods have been researched and proposed in which the membrane is treated with various semipermeable membrane treatment agents after V membrane production (Dee, Bergmanra, Eating of the Seventh International Symposium on Fresh Water from the Sea> (D, Bargeman
etc.

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h International Sympusi
um Orl Fresh water from
the 3ea, Vol, 2.99-104.1
980>.

This method improves membrane performance by immersing a semipermeable membrane in a suitable polymer solution and filling the relatively large pores in the semipermeable membrane with polymer, which reduce separation performance. However, in this case, there is a problem that the membrane i performance rapidly decreases due to desorption of the treated polymer from the membrane during membrane performance evaluation. As a countermeasure to this problem, the authors propose to roughly coat the treated polymer. However, in the case of crosslinking reactions,
It is difficult to complete the reaction uniformly and sufficiently, unreacted parts remain as defects, and there is a limit to the effect of improving performance. Not yet reached. Moreover, the processing steps before and after the crosslinking reaction become complicated, resulting in a production loss of 1 or more.

In addition, as a method for improving the permeation performance of an asymmetric membrane, the present inventors have proposed a method for improving the permeation performance of an asymmetric membrane. In No. 21969, they proposed a semipermeable membrane characterized by containing metal in an asymmetric membrane and distributing the metal at a high temperature on the surface. Special request 1976
The invention described in No. 0-21969 relates to a method for significantly improving membrane performance. However, it has been found that when this method is used under long exposure conditions, the metal gradually dissolves and the initial separation performance gradually deteriorates.

[Problems to be solved by the invention] In view of these circumstances, the inventors of the present invention have improved the conventional technology as described in (a) above and conducted intensive studies to create a high-performance membrane of 1q, and as a result, they have arrived at the present invention. It is something.

That is, the object of the present invention is to provide a high-performance composite semipermeable membrane in which a metal is present near the surface of the membrane and a predetermined polymer is formed into an ultra-thin film to fix the metal layer, and a method for manufacturing the same. It is about providing.

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

[(1) In a semipermeable membrane having substance separation ability, the protective membrane is
A semipermeable membrane (B) containing a metal (A> with an average value of 10 pμm or more, and a semipermeable membrane (B) containing a polymer (B) having an affinity for the metal (A>) on the semipermeable membrane (B) A composite semipermeable membrane for substance separation, characterized in that it is provided with the 7i4 membrane of C).

(2) In the production of composite semipermeable membranes with substance separation ability, a semipermeable membrane with an asymmetric structure is created by evaporating the raw material casting liquid and then solidifying it, and then heat-treating it. ! 1. A method for producing a composite semipermeable membrane for substance separation, characterized in that the membrane is treated by containing metal ions in a bath and then treated with a dilute solution of a polymer. ” In the present invention, the semipermeable membrane for substance separation refers to a membrane with semipermeability that is used to separate, concentrate, or purify a specific substance by utilizing the difference in permeability of substances. permeable membrane,
Extreme: Semipermeable membranes for liquid separation such as filtration membranes and dialysis membranes, semipermeable membranes for gas separation, ion exchange membranes, etc. can be used.

The shape of these semipermeable membranes is not particularly limited, and various shapes such as a flat membrane, a tubular shape, and a hollow fiber shape can be applied.

Regarding membrane materials and membrane structures, semipermeable membranes with asymmetric structures and composite semipermeable membranes made of polyacrylonitrile, polysulfone, polyamide, polybenzimidazole, etc. in addition to cellulose acetate are also applicable.

In the present invention, the metal may be any metal, but preferably has a specific gravity of 4.0 or more, and more preferably one or more selected from Fe, Ti, Pb, and Cr.

The reason for this is not clear, but it has been confirmed by experimental facts. The metal may be in any ionic, chelated, or elemental form.

In the present invention, it is preferable that the 'Q degree of the metal in the surface layer of the membrane is 10 times or more as compared to the center of the membrane in order to improve the separation ability, particularly 100 times or more.

Further, as the metal immobilizing polymer in the present invention, a polymer having polar and non-polar parts and having adsorption ability to the semipermeable membrane and the surface metal is used.

The above-mentioned polymer is composed of the polymer and a solvent as a dilute solution in the form of a treatment solution, but other additives may be included as required. The polymer is selected depending on the semipermeable membrane and the type of metal, but typical examples include polyvinyl alcohol, partially carbonated polyvinyl acetate, partially carbonated polyvinyl acetate and maleic anhydride. Esterified products, copolymers of vinyl acetate and maleic anhydride or vinyl pyrrolidone, polyethyleneimine, etc. are required, but they have an affinity for the membrane to be treated and the metals contained in the membrane, and The polymers are not limited to those listed here as long as they exhibit appropriate affinity.

The method for forming a film in the method of the present invention is not particularly limited, but a film of 1q can be formed by a normal wet-forming method in which after casting on a support, part of the solvent is evaporated and the film is introduced into a coagulation bath. Preferable for invention.

Roughly speaking, the method of adsorbing gold glaze onto the film, which is a feature of the present invention, is possible before or after the protective film is introduced into the heat treatment process, or after heat treatment. 2! Although it may be carried out in a bath, it is preferably carried out in a heat treatment step. The form of metal added to the treatment bath is
As a specific example, for trivalent iron ions, ferric sulfate,
Inorganic salts such as ferric chloride and ferric nitrate, purified salts such as potassium ferricyanide and sodium ferricyanide, bases such as ferric hydroxide, and organic metal salts such as ferric acetylacetone and ferric thiocyanate. can be mentioned. Among them, inorganic salts such as ferric sulfate, ferric chloride, and ferric nitrate are suitable for the present invention.

Next, a method for forming a thin film for the metal immobilization process will be described. The treatment liquid consists of a semipermeable membrane (B) and a polymer that has an affinity for the metal (A>) contained in the semipermeable membrane, and a solution thereof. Aliphatic alcohols such as methanol and ethanol, mixed solvents of the aliphatic alcohol and water, etc. are commonly used for various membrane materials. Any other solvent can be used as long as it does not have a substantial effect on the solvent.

The temperature of the treatment liquid is reduced to 5% or less, preferably 2% or less. If the temperature exceeds 5%, the thin film formed will become too thick and the water permeability will deteriorate, which is not preferable.

Thin film formation is performed by bringing a semipermeable membrane containing a predetermined metal into contact with the treatment liquid.

The method includes a dipping treatment, a method of applying a treatment solution to the surface of the semipermeable membrane using substantially the same conditions and times as the aforementioned dipping treatment method, and the like.

The thin film formed by these treatments has an affinity for the semipermeable membrane and the metal contained in the semipermeable membrane, so it will not peel off during use. Moreover, the metal contained in the semipermeable membrane does not desorb during use due to the presence of the thin film provided on the semipermeable membrane, and the initial performance can be maintained.

Next, the composite semipermeable membrane according to the present invention will be explained using figures. FIG. 1 shows a schematic cross-sectional view of the composite semipermeable membrane of the present invention, and FIG. 2 shows an enlarged cross-sectional view of the vicinity of the active layer. As shown in this figure, the composite semipermeable membrane according to the present invention contains metal near the surface of the membrane (on the active layer side) and further has an ultra-thin film on the surface for fixing the metal. It costs ¥f.

Next, we will discuss the analysis of the metals contained in the semipermeable membrane and the polymers in the thin film layer on the surface of the semipermeable membrane.

The amount of metal present in the cross-sectional direction of the membrane was measured using a secondary ion spectrometer SIMS (SecondaryJom M
ass 3pectroscope V).

Manufactured by CAMECA in France, type IMS-3F, the thin polymer layer is an X-ray photoelectron spectrometer ESCA (E
l ectron '5pect roscOp
y for ChemRCA+ Analysis
), Shimadzu Corporation, type ESCA750, etc., to specifically confirm the abundance.

Examples] The present invention will be explained below using examples.

In the examples, the reverse osmosis membrane performance is shown by the water permeation amount and salt rejection rate when a saline solution containing 1500 pμm of salt is pressurized at 30 −/− and flowed over the membrane surface at a flow rate of 10 m/min.

The performance of reverse osmosis membranes usually changes with the amount of water permeation and the salt rejection rate, but the performance index specific to the membrane is A2/B or A3/B (A is the water permeation coefficient (Q/cnf -sec
-atm>, B is the salt permeability coefficient<cm/sec
＞ remains almost constant. In this example, A3/B was used as an index of membrane performance, and the membrane performance improvement effect by forming a composite semipermeable membrane was confirmed by comparing the ratio values. The film thickness was measured using a dial gauge. Although a reverse osmosis membrane is only illustrated as an example, the present invention is not limited to reverse osmosis membranes.

Example 1 Cellulose triacetate with acedylation degree of 43.2% and cellulose diacetate with acedylation degree of 39.8% were
20 parts of dioxane mixed in a ratio of 26 parts, 40 parts of dioxane,
A film-forming solution consisting of 27 parts of acetone, 3 parts of butanetetracarboxylic acid, and 10 parts of methanol was prepared. The coating is 30'
The solution was cast onto a glass plate to a thickness of 0.2 mm using an applicator in an atmosphere of C, and after drying for about 1 minute, it was immersed together with the glass plate in cold water at 10'C for about 20 minutes, and peeled off from the glass plate. I let him do it.

The untreated membrane thus obtained was treated with 5 m of ferric sulfate.
Heat treated for 5 minutes in a hot water bath (temperature 75 °C) containing m%,
Next, after rinsing in cold water, the membrane was further immersed in a 0.3% polyvinyl alcohol solution (water as a solvent) with a degree of polymerization of 1000 and a degree of viscoelasticity of 80% for 1 hour, and then the membrane was taken out, immersed in water for 1 hour, and left to stand. did.

The amount of water permeated through the membrane thus obtained was 0°70tn.
'/m2·day, the salt rejection rate was 99.3%.

A membrane with a high water permeation rate despite a high salt rejection rate was obtained. Also, the value of A3/B is 43X10-10g3
/cm 7. It was sec-atm 3.

This film was evaluated intermittently for 9 hours a day for a total of 300 hours to confirm its durability. Moisture permeation amount after 300 hours is 0
．． 71ml/m2. The salt rejection rate is 99.3%.
The membrane performance was maintained at the initial level, and it was confirmed that it was durable.

In addition, the amount of metal present in the cross-sectional direction of this film was measured using a secondary ion mass spectrometer SIMS (Sec.

ndary ) on Mass 3pectr.

5copy), manufactured by CAMECA in France, type I
When confirmed using MS-3F, it was found that 1μ from the surface of the membrane.
About 11,000 pp of Fe exists in m, and 1 from the surface of the film.
The amount of Fe present in the ~10 μm region was about 40 pμm.

Further, on the semipermeable membrane, the degree of polymerization is 1000. X indicates that a layer of polyvinyl alcohol with a saponification degree of 80% is formed.
Line photoelectron spectrometer ESCA (E 1ectron)
5pectroscopy f.

r Chemical Analysis), manufactured by Shimadzu Corporation, type ESCA750. Confirmed by.

The film thickness before and after the polyvinyl alcohol solution treatment was 75 μm, which was the same. Therefore, it can be seen that an ultra-thin film of the polyvinyl alcohol used above was formed.

Comparative Example 1 An untreated membrane obtained by the same method as in Example 1 was heat-treated for 5 minutes in a hot water bath (temperature 75°C) to which iron ions were not added.The amount of water permeation of the membrane was 0. .95m3/m2
．． The salt rejection rate was 97.3%. In addition, the value of A3/B, which is an index of membrane performance, is 20X 10 g/cm
, there were 3 sec-atm.

Comparative Example 2 Comparative Example 2 An unheated film obtained by the same method as in Example 1 was treated with sulfuric acid
After just 5 minutes of heat treatment in a hot water bath (temperature 75°C) containing 5% iron, the amount of water permeation through the membrane, which had not been thinned with a polymer solution, was 0°81m! /m2. The salt rejection rate was 98.6%.

Also, the value of A3/B is 29 x 10” Q3/cm7
It was sec-atm 3. Furthermore, in the durability evaluation of the membrane performance using the same method as in Example 1, there was almost no change up to 100 hours, but after that, the membrane performance gradually decreased and after 300 hours, the salt rejection rate reached 98.2%. decreased.

Example 2 Using a semipermeable membrane treated with iron ions obtained in the same manner as in Example 1, this membrane was heated to a degree of polymerization of 1700. After immersing for 30 seconds in a 0°3% solution of partial/vvated polyvinyl acetate with a degree of saponification of 40% (solvent is a mixed system of water:ethanol = 1:1 (gravity ω ratio)), the membrane was taken out and left for 1 hour. It was immersed in water and left standing.

In this way (the water permeation m of the q membrane is 0.71 m
! /Tr12·days, the salt rejection rate was 99.2%. Also, the value of A3/B is 39X 10 CJ/cm
, there were 3 sec-atm. In addition, the durability performance after 100 hours using the same method as in Example 1 showed that the amount of water permeation was 0.
The initial performance was maintained at 72Tr13/Tr12·day with a salt rejection rate of 99.1%.

A membrane with higher performance than Comparative Example 1.2 could be obtained. Further, the presence of metal in the thin film of partially saponified polyvinyl acetate in this film was analyzed using the same analyzer as in Example 1, and the same distribution as in Example 1 was confirmed.

Example 3 Using a semipermeable membrane treated with iron ions obtained in the same manner as in Example 1, this membrane was immersed in a 0.3% solution of polyethyleneimine (the solvent was water (by weight)) for 16 hours. Then, the membrane was taken out, immersed in water for 1 hour, and left to stand. The water permeation rate of the membrane thus obtained was 0.94 m'/m2. On Sunday, the salt rejection rate was 98.7%. Also A3/B(7)(142
X10-" CJ3/cm, SeC, atm 3 teats. The durability performance after 100 hours using the same method as in Example 1 was as follows: water permeation! ii 0.94 m'/m2 day, salt rejection rate 98.6%. The initial performance was maintained.Compared to Comparative Examples 1 and 2, it was possible to produce a membrane with higher performance.

In addition, the amount of metal present in this film and the presence of a polyethyleneimine thin film were analyzed using the same analyzer as in Example 1.
A similar distribution was confirmed.

Example 4 Reverse osmosis module ROGA8800HRM manufactured by UOP using a cellulose diacetate membrane having an asymmetric structure
AGNUM@Membrane obtained by disassembly (membrane performance is water permeation amount 0.
84m'/Tr+2・day, salt rejection rate 98.0%, A3
/B=21 X1O-10/C13/g(, SeC
-atm 3) was heat-treated in a hot water bath (temperature 75°C) containing 5% by weight of ferric sulfate for 5 minutes in the same manner as in Example 1, and after washing in cold water, it was used in Example 2. The sample was immersed in a partially saponified polyvinyl acetate solution for 30 seconds.

In this way, the amount of water permeation through the q membrane was 0.68 m
! /m2・day, the salt rejection rate is 99.2%, and A3/B
The value is 36X10-g3/Cm7. sec-atm
I got i-+ at 3.

It can be seen that the performance is significantly improved compared to the disassembled membrane before treatment. Furthermore, the durability performance after 300 hours using the same method as in Example 1 was as follows: moisture permeation @0.69T113/Tr12
・The salt rejection rate was 99.1%, maintaining the initial performance. Compared to Comparative Examples 1 and 2, we were able to produce 1 q of membranes with higher performance. In addition, the amount of metal present in this film and the presence of a thin film of partially saponified polyvinyl acetate were analyzed using the same analyzer as in Example 1.
The same distribution as in Example 1 was confirmed.

[Effects of the Invention] In the present invention, the metal exists at a high temperature near the surface of the film, and the film has an ultra-thin film of rough polymer. As a result, the liquid separation performance is significantly improved, and an unprecedentedly excellent separation membrane that can maintain extremely high separation characteristics over a long period of time can be provided.

[Brief explanation of the drawing]

FIG. 1 shows a schematic cross-sectional view of the composite semipermeable membrane of the present invention, and FIG.
The figure shows an enlarged cross-sectional view of the vicinity of the active layer.

Claims (8)

[Claims] (1) In a semipermeable membrane having substance separation ability, the membrane is a semipermeable membrane (B) containing metal (A) with an average value of 10 pμm or more, and the semipermeable membrane (B) ) and a thin film layer of a polymer (C) having an affinity for metals (A). (2) The composite semipermeable membrane for substance separation according to claim 1, wherein the semipermeable membrane (B) is cellulose acetate having an asymmetric structure. (3) The metal (A) contained in the semipermeable membrane (B) is Fe,
The composite semipermeable membrane for substance separation according to claim (1), characterized in that the semipermeable membrane is one or more selected from Ti, Pb, and Cr. (4) The polymer (C) is selected from polyvinyl alcohol, partially saponified polyvinyl acetate, esterified product of partially saponified polyvinyl acetate and maleic anhydride, copolymer of vinyl acetate and maleic anhydride or vinyl pyrrolidone, and polyethyleneimine. The composite semipermeable membrane for substance separation according to claim (1), characterized in that the membrane is one or more of: (5) In manufacturing a composite semipermeable membrane with substance separation ability,
A semipermeable membrane with an asymmetric structure is created by evaporating the raw material casting liquid and then solidifying it, and then heat-treating it by incorporating metal ions into the heat-treating bath. A method for producing a composite semipermeable membrane for substance separation, characterized by treatment with a dilute solution of molecules. (6) The metal ion is sulfate, acetate, hydrate, hydrochloride,
The method for producing a composite semipermeable membrane for substance separation according to claim (5), characterized in that the membrane is one or more selected from nitrates, oxalates, and ammonium salts. (7) The dilute polymer solution is selected from polyvinyl alcohol, partially saponified polyvinyl acetate, an ester of partially saponified polyvinyl acetate and maleic anhydride, a copolymer of vinyl acetate and maleic anhydride or vinylpyrrolidone, and polyethyleneimine. The method for producing a composite semipermeable membrane for substance separation according to claim (5), characterized in that the method is one or more kinds of solutions. (8) A method for producing a composite semipermeable membrane for substance separation according to claim (5), wherein the temperature of the polymer is 5% by weight or less.