JP2000084379A - Porous separation membrane and composite reverse osmosis membrane using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a porous separation membrane having high PEG stop-off performance and high water permeating rate, and an excellent composite reverse osmosis membrane using the same as a supporting membrane. SOLUTION: The porous separation membrane has 10-90% polyethylene glycol stop-off ratio in a prescribed measuring condition of the polyethylene glycol stop-off ratio and >=5 m3/m2/D pure water permeating rate at 1 kgf/cm2 evaluating pressure and 25 deg.C. The composite reverse osmosis membrane is obtained by using the porous separation membrane as the supporting membrane and forming a skin layer composed of a synthetic polymer thereon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a dense porous separation membrane and a composite reverse osmosis membrane using the same as a substrate. The composite reverse osmosis membrane of the present invention is excellent in salt rejection, water permeability and pressure resistance. Such a composite reverse osmosis membrane can be stably operated for a long period of time without consolidation even when operated under high pressure conditions.

[0002]

2. Description of the Related Art At present, as a reverse osmosis membrane widely used industrially, there is an asymmetric membrane of cellulose acetate. For example, a lob type membrane described in US Pat. No. 3,133,132 or US Pat. No. 3,133,137 is known. ing. Further, as a reverse osmosis membrane having a different structure from the above, a composite reverse osmosis membrane in which an active thin film having substantially selective separation properties is formed on a microporous support membrane is also known.

[0003] As such a composite reverse osmosis membrane, specifically, a polyamide thin film obtained by interfacial polymerization of a polyfunctional aromatic amine and a polyfunctional aromatic acid halide formed on a support membrane (for example, JP-A-55-l47l06, JP-A-Showa
62-12l603, JP-A-63-2l8208, JP-A-2-l87l35, etc.) or a thin film made of polyamide obtained by interfacial polymerization of a polyfunctional aromatic amine and a polyfunctional alicyclic acid halide. What was formed on the film (for example,
No. l-42308) is known. Usually, these reverse osmosis membranes are formed into a spiral shape or the like and used for various purposes.

However, such porous support membranes
Conventional composite reverse osmosis membranes formed from (e.g., a separation membrane made of polysulfone) and a synthetic polymer skin layer (e.g., an aromatic cross-linked polyamide) cause the consolidation of the porous support membrane layer when used at high pressure, There is a problem that the amount of permeated water is reduced. Although a proposal for solving such a problem has been made (Japanese Patent Laid-Open No. 8-168658), sufficient pressure resistance has not yet been obtained.

In such a conventional composite reverse osmosis membrane,
In order to form a synthetic polymer skin layer on the surface stably and uniformly and to obtain high blocking performance, it is necessary to design the surface structure of the porous support membrane relatively densely. Usually, a wet method is used for producing a porous support membrane, and the pore size increases continuously from the membrane surface to the opposite surface. Therefore, if the surface structure of the film is relatively dense, that is, if the pore size of the surface layer is set small,
The whole supporting membrane becomes dense, and the amount of permeated water decreases. When such a support membrane is compacted, pores are likely to be clogged, and the amount of permeated water of the composite reverse osmosis membrane using this as a base material is significantly reduced.

On the other hand, when the pore size of the surface layer of the porous support membrane is set to be large, a sparse structure is exhibited over the entire support membrane, the pores are blocked and the decrease in the amount of permeated water is reduced, but the pore size of the surface layer is reduced. Is large, the synthetic polymer skin layer cannot be formed stably and uniformly, and as a result, the blocking performance of the composite reverse osmosis membrane is lowered.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a porous separation membrane having a high PEG inhibition performance and a high water permeation rate when polyethylene glycol is used as an index, and a composite reverse osmosis membrane using the same as a base material. Is to provide. In the porous separation membrane of the present invention, only the outermost layer on which the synthetic polymer skin layer is formed is dense, and the other portions have a sparse structure,
A composite reverse osmosis membrane having excellent pressure resistance and exhibiting high rejection performance can be obtained.

According to the present invention, the polyethylene glycol rejection under predetermined polyethylene glycol rejection measurement conditions is 10 to 90%, the evaluation pressure is 1 kgf / cm ² ,
An object of the present invention is to provide a porous separation membrane having a pure water permeated water amount of 5 m ³ / m ² / day or more at a temperature of 25 ° C. More preferably, the amount of permeated pure water is 8 m ³ / m ² / day or more. Further, when the compaction of the porous separation membrane under high pressure of 120 kgf / cm ^2, preferably pure water permeate flow rate at rated pressure 1 kgf / cm ² is 1.0m ³ / m ² / day or more. Further, the present invention also provides a composite reverse osmosis membrane obtained by using the porous separation membrane as a substrate and a support, and forming a skin membrane made of a synthetic polymer thereon.

[0009]

Next, the present invention will be described in detail.
The porous separation membrane of the present invention has a polyethylene glycol rejection measurement condition average molecular weight: 20,000, polyethylene glycol concentration:
0.5% by weight, evaluation pressure: 1 kgf / cm ² , temperature: 25 ° C.
Recirculation flow rate: 10-90% polyethylene glycol rejection at 1 L / min
And the amount of pure water permeated at an evaluation pressure of 1 kgf / cm ² and a temperature of 25 ° C. is 5 m ³ / m ² / day or more. Such a porous membrane can be formed as follows.

[0010] The material of the porous separation membrane is not particularly limited, but examples thereof include cellulose organic polymers, polyamides, polyimides, polysulfones, polyacrylonitriles, polyvinyl alcohols, and ethylene-vinyl alcohol copolymers. .

To prepare these film-forming solutions, a solvent capable of dissolving them, for example, N-methyl-
2-pyrrolidone, N, N-dimethylacetamide, N, N
-Nitrogen-containing compounds such as dimethylformamide, dimethylsulfoxide and pyridine; polyhydric alcohols such as diethylene glycol, diethylene glycol dimethyl ether, diethylene glycol diethyl ether and diethylene glycol dibutyl ether and derivatives thereof; ethers such as 1,4-dioxane, tetrahydrofuran and ethyl-butyl ether; Acetals and the like can be used. These solvents may be used alone or as a mixture of two or more. Further, water, which is a poor solvent, or alcohols such as methanol, ethanol and isopropanol may be added in a range not exceeding 10% by weight.

Using these solvents, the solution concentration is 5 to 20% by weight, preferably 10 to 18% by weight, more preferably 1 to 18% by weight.
It is adjusted to 0 to 16% by weight. If the solution concentration is lower than these ranges, the viscosity is low and a uniform film cannot be formed. On the other hand, if the concentration is higher than this range, the viscosity is too high to make film formation difficult, and the film becomes dense, the desired film structure cannot be obtained, and the amount of permeated water decreases.

The film forming solution used in the present invention is -20 to 6
It is prepared in a temperature range of 0 ° C, preferably 0 to 40 ° C. The wet phase inversion film forming method used in the present invention using this solution is shown below.

[0014] The membrane shape of the composite reverse osmosis membrane of the present invention includes:
It can be in the form of a flat membrane, a hollow fiber, or a tube, and is not particularly limited. In the case of a flat membrane, for example, woven fabric,
After the above solution is applied to a substrate such as a nonwoven fabric by casting or dipping, it is immersed in a coagulation liquid. The coating thickness of the solution on the substrate is 25 to 400 μm, preferably 30 to 2 μm.
It is 50 μm, more preferably 90 to 200 μm.
If the coating thickness is smaller than the above range, defects occur in the porous separation membrane, while if it is too thick, the amount of permeated water decreases.

As the coagulating liquid, water, alcohols such as methanol, ethanol, isopropyl alcohol and the like and a mixed solution comprising at least two kinds thereof are used, but not limited thereto.

The temperature of the coagulating liquid is 0 to 80 ° C., preferably 5 to 80 ° C.
To 50 ° C, more preferably 10 to 30 ° C. If the temperature of the coagulating liquid exceeds 80 ° C., gelation occurs rapidly, and the resulting film has a sparse structure, and a sufficient PEG rejection cannot be obtained. No film. Further, if the solidification temperature is lower than the above range, the membrane becomes dense and the amount of permeated water decreases, while if it is higher than this, the membrane becomes too sparse to form a synthetic polymer skin layer having stable performance on the membrane surface. Can not.

In the present invention, a polyethylene glycol (PEG; average molecular weight: 20,000) solution was used as a method for evaluating the performance of the porous support membrane. An evaluation cell capable of circulating the evaluation solution was used, and the PEG concentration was 0.5% by weight, the evaluation pressure was 1 kgf / cm ² , the temperature was 25 ° C., and the circulation flow rate was 1 L / min. The porous separation membrane of the present invention obtained under the above-mentioned membrane-forming conditions has a PEG rejection under such conditions of 10 to 90%, preferably 10 to 50%. PE
If the G rejection is lower than this range, the film surface is sparse, and a synthetic polymer skin layer having high rejection cannot be formed. On the other hand, if the rejection is higher than the above range, the film surface becomes too dense, and when the consolidation occurs, the clogging of the surface holes is promoted.

The amount of pure water permeated by the porous separation membrane is 5 m ³ /
m ² / day or more (evaluation pressure; 1 kgf / cm ² , temperature: 25 ° C.), preferably 8 m ³ / m ² / day or more. If the amount of permeated water is lower than this, the surface pores are closed due to consolidation, and the amount of permeated water is significantly reduced.

The substrate coated with the film-forming solution needs to be constantly supplied with a new coagulating liquid on the film surface during the coagulation process.
If the supply of the new coagulating liquid to the film surface is not sufficient, a solvent for dissolving the porous film is present in the coagulating liquid on the film surface, solidification is inhibited, and the film surface has a sparse structure. Such a method of constantly supplying a new coagulating liquid to the film surface in the solidification process is not particularly limited. For example, a method in which a substrate such as a woven fabric or a nonwoven fabric coated with a film forming solution is continuously moved in the coagulating solution. Alternatively, a method of circulating the coagulating liquid itself may be employed. When continuously moving a substrate such as a woven or non-woven fabric coated with a film forming solution,
Its speed is 3-100 m / min, preferably 5-50 m / min. Under these conditions, a new coagulating liquid is constantly supplied to the film surface, and the structure of the film surface can be made dense. If the film forming speed is lower than the above range, the film surface becomes sparse, and a desired dense film surface structure cannot be formed. Also, 1
If the speed is higher than 00 m / min, a non-uniform portion occurs on the film surface during film formation.

Further, in order to densify the surface of the porous separation membrane, it may be dried at 30 to 200 ° C., preferably 50 to 150 ° C. In this case, when forming a reverse osmosis membrane, which will be described later, the support membrane is immersed in a mixed solvent (solution concentration: 5 to 70% by weight) of water and alcohol (eg, methanol, ethanol, isopropyl alcohol) for the purpose of moistening the support membrane. Again, a method of replacing with water is used.

Further, the separation layer exhibiting the rejection of PEG is preferably the outermost layer, and the thickness of the layer is 20% of the thickness of the porous separation membrane (not including the base material such as nonwoven fabric).
Or less, preferably 15% or less. If such a layer is thicker than this, the resistance is increased, a sufficient amount of permeated water cannot be secured, and the surface pores are liable to be clogged when compacted.

Further, the porous separation membrane thus obtained has excellent pressure resistance, that is, has a sufficient amount of pure water permeated during compaction. For example, when an impervious film is placed on the surface of a porous separation membrane and a water pressure of 120 kgf / cm ² is applied for 1 hour, the amount of permeated water is 1.0 m ³ / m ² / day or more (evaluation pressure 1 kgf / c 2
m ² , temperature: 25 ° C.), and preferably 3.0 m ³ / m ² /
More than a day. If the amount of permeated water during consolidation is lower than this,
When a composite reverse osmosis membrane is formed using such a porous separation membrane, the amount of permeated water is greatly reduced during high-pressure operation, which is not preferable.

The method for producing a composite reverse osmosis membrane using these porous separation membranes is not particularly limited. The coating (skin layer) formed on the porous separation membrane can be formed by an interfacial polymerization method such as polyamide or polyurea, and can be easily manufactured by a conventionally known method. For example,
Using the porous separation membrane such as a porous polysulfone support membrane as a support membrane, an aqueous solution of a monomer and / or polymer having a reactive amino group such as metaphenylenediamine, piperazine or polyethyleneimine is applied on at least one surface thereof. Then, a solvent such as a polyfunctional acid chloride such as trimesic acid chloride and isophthalic acid chloride or a polyfunctional isocyanate such as tolylene diisocyanate, or a solvent such as hexane of a mixture thereof is contacted, and interfacial polymerization is performed on the porous separation membrane to remove the polymer. A composite reverse osmosis membrane is obtained by forming a film having salt performance.

On such a composite reverse osmosis membrane surface, an organic substance,
And / or an organic polymer, preferably an organic material having a nonionic hydrophilic group, and / or a solution of the organic polymer is applied and then dried to obtain a composite reverse osmosis membrane. It is effective in improving the properties.

As the solvent for the organic substance and / or the organic polymer, a solvent which does not damage the active film layer, for example, water, lower alcohol, halogenated hydrocarbon, aliphatic hydrocarbon, acetone, acetonitrile, or These include mixed solvents. Among them, in particular, aliphatic alcohols such as methanol, ethanol, propanol and butanol, halogenated aliphatic alcohols such as ethylene chlorohydrin, methoxymethanol, methoxyethanol and a mixed solvent of at least one of these lower alcohols with water, etc. May be used. In the case of a mixed solvent, the ratio of the lower alcohol to water is not particularly limited, but the ratio of water is preferably 0 to 90%. When water is used as the solvent, a surfactant may be added for the purpose of improving the wettability with the film.

Examples of such organic substances and / or organic polymers include fluorine-containing polymers such as silicone rubber and polyethylene terephthalate, sulfonic acid group-containing organic polymers such as sulfonated polysulfone and sulfonated polyether sulfone, and polyethyleneimine. Such as amino group-containing organic polymers, polyimides, etc., for the purpose of maintaining high water permeability after coating and suppressing organic substances having hydrophilic groups, and / or organic polymers, particularly, charged adsorption. An organic material having a nonionic hydrophilic group and / or an organic polymer are preferred.

Examples of the organic material having a nonionic hydrophilic group and / or the organic polymer include nonionic surfactants such as polyvinyl alcohol, saponified polyethylene-vinyl acetate copolymer, polyvinylpyrrolidone, hydroxypropylcellulose and polyethylene glycol. Vinyl polymers having a hydrophilic group, condensation polymers, addition polymers, etc. are used.

[0028]

EXAMPLES Next, the present invention will be described more specifically with reference to examples and comparative examples, but these do not limit the present invention at all.

Example 1 Polysulfone (P-3500, manufactured by Amoco) was dissolved in dimethylformamide (DMF) to prepare a film-forming solution (15% by weight) (solution temperature: 25 ° C.). This solution was continuously applied to a roll-shaped nonwoven fabric at a thickness of 130 μm. Next, this nonwoven fabric was continuously immersed in water at 20 ° C. (surface velocity: 8 m / min), coagulated, and wound to prepare a polysulfone porous support membrane.

The obtained porous separation membrane was set in a cell capable of circulating the feed liquid, and evaluated using a polyethylene glycol (average molecular weight: 20,000) solution. Evaluation condition is P
EG concentration: 0.5% by weight, evaluation pressure: 1 kgf / cm ² , measurement temperature: 25 ° C., circulation flow rate: 1 L / min. P of this film
The EG rejection was 23%. The pure water permeated water amount of this membrane was 15 m ³ / m ² / day (evaluation pressure: 1 kgf / cm ² , temperature: 25 ° C.).

On this porous separation membrane (microporous polysulfone support membrane), 3.0% by weight of m-phenylenediamine, 0.15% by weight of sodium lauryl sulfate, 2.0% by weight of triethylamine, 2.0% by weight of camphorsulfonic acid After contacting with an aqueous solution containing 4.0% by weight for several seconds, excess aqueous solution was removed to form a layer of the aqueous solution on the support membrane.

Next, an IP1016 (isoparaffinic hydrocarbon oil manufactured by Idemitsu Chemical Co., Ltd.) solution containing 0.25% by weight of trimesic acid chloride was brought into contact with the surface of the obtained film. Then, it was kept in a hot air dryer at 120 ° C. for 5 minutes to form a skin layer on the support to obtain a composite reverse osmosis membrane. The obtained membrane was treated with a 3.5% by weight aqueous sodium chloride solution at a pressure of 5%.
As a result of evaluation at 6 kgf / cm ² , the inhibition performance was 99.8%, and the amount of permeated water was 0.80 m ³ / m ² / day. After the obtained membrane was pressurized with the aqueous sodium chloride solution under a high pressure of 120 kgf / cm ² for 1 hour, it was evaluated again at a pressure of 56 kgf / cm ^2. As a result, the blocking performance was 99.8% and the permeated water amount was 0. .77m ³
/ M ² / day and no change in performance was observed after exposure to high pressure conditions.

Further, the skin layer portion of the reverse osmosis membrane was removed using an aqueous solution of sodium hypochlorite (1%), and the amount of permeated pure water of the porous support membrane was 1.0 kgf / cm ² , temperature: 25 When evaluated at ℃, it was 5 m ³ / m ² / day, and it was confirmed that the decrease in the amount of permeated water due to the compaction of the support membrane was suppressed.

Comparative Example 1 A polysulfone porous support membrane was prepared in the same manner as in Example 1 except that the surface speed during solidification was 2.5 m / min. The PEG rejection of the obtained separation membrane was 2%. The amount of pure water permeated by this membrane is 27 m ³ /
m ² / day (evaluation pressure: 1 kgf / cm ² , temperature: 25 ° C.). The obtained membrane was treated in the same manner as in Example 1 to form a reverse osmosis membrane. As a result, the inhibition performance was 98.80% and the amount of permeated water was 1.2 m ³ / m ² / day. No performance was obtained.

Comparative Example 2 A porous separation membrane was prepared in the same manner as in Example 1 except that the polysulfone DMF solution concentration was changed to 24% by weight. The PEG rejection of the obtained porous membrane was 95%. The pure water permeation amount of this membrane is 1.
3m ³ / m ² / day (evaluation pressure: 1kgf / cm ² , temperature: 25 ° C)
It was. Using the obtained separation membrane as a support membrane, a reverse osmosis membrane was formed in the same manner as in Example 1 and evaluated.
9.80%, and the permeated water amount was 0.8 m ³ / m ² / day. The obtained membrane was pressurized with the aqueous sodium chloride solution (3.5% by weight) at 120 kgf / cm ^{2 for} 1 hour, and then again pressurized to 56 kg / cm ² .
As a result of evaluation in kgf / cm ² , the blocking performance was 99.82% and the permeated water amount was 0.6 m ³ / m ² / day. Further, the skin layer portion of the reverse osmosis membrane was removed using an aqueous sodium hypochlorite solution (1%), and the amount of pure water permeated through the porous support membrane was adjusted to 1.0 kgf / cm.
^{2. When} evaluated at a temperature of 25 ° C., 0.13 m ³ / m ² /
It was confirmed that the decrease in the amount of permeated water due to the compaction of the support membrane was large.

[0036]

Industrial Applicability The present invention provides a porous separation membrane having high PEG inhibition performance using polyethylene glycol as an index and a high amount of permeated water, and an excellent composite reverse osmosis membrane using the same as a support membrane. In the porous separation membrane of the present invention, only the outermost layer on which the synthetic polymer skin layer is formed is dense, and the other portions have a sparse structure, and a composite reverse osmosis membrane having excellent pressure resistance and high blocking performance is obtained. Can be The porous separation membrane of the present invention and the composite reverse osmosis membrane using the same as a support membrane are subjected to high pressure (for example, 90 kgf / cm ^2).
Even when compressed as described above, excellent pressure resistance (suppression of a decrease in the amount of permeated water of the composite reverse osmosis membrane) and a stable amount of permeated water can be obtained. Such a composite reverse osmosis membrane can be used for high-concentration brine, seawater,
Useful for treating concentrated seawater.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA03 MA03 MA09 MA31 MB02 MB06 MB09 MB18 MC11 MC33 MC34 MC39 MC54 MC58 MC62X NA05 NA10 NA18 NA41 NA46 NA64 PA01 PB03 PB04 PB05 4F074 AA87 CE02 CE16 CE25 CE98 DA20 DA43

Claims (4)

[Claims] 1. A polyethylene glycol rejection rate of 10 to 90% under the following measurement conditions, and an evaluation pressure of 1 kgf.
/ Cm ² , the amount of pure water permeated at a temperature of 25 ° C. is 5 m ³ / m ²
/ Day or more. [Measurement conditions] Average molecular weight: 20,000, polyethylene glycol concentration: 0.5% by weight, evaluation pressure: 1 kgf / cm ² , temperature: 25 ° C, circulation flow rate: 1 L / min 2. The porous separation membrane according to claim 1, wherein the pure water permeated water amount is 8 m ³ / m ² / day or more. 3. A process according to claim pure water permeate flow rate at rated pressure 1 kgf / cm ² when the porous separation membrane was compacted under high pressure of 120 kgf / cm ² is 1.0 m ³ / m ² / day or more 1
Porous separation membrane. 4. A composite reverse osmosis membrane using the porous separation membrane according to claim 1 as a substrate.