WO2014098059A1 - Method for hydrophilizing reverse osmosis membrane - Google Patents

Abstract

Provided is a method for hydrophilizing an RO membrane, the method being excellent in terms of the persistence of the hydrophilization effect and flux stability. An RO membrane is brought into contact with a modified polyvinyl alcohol having a polyalkylene oxide chain. The modified polyvinyl alcohol has a degree of saponification of preferably 80% or higher, and the polyalkylene oxide chain preferably is a polyethylene oxide chain. The modified polyvinyl alcohol having a polyalkylene oxide chain has higher adsorbability onto RO membranes than conventional PVAs, and the antifouling properties can hence be maintained over a long period.

Description

Method of hydrophilizing reverse osmosis membrane

The present invention relates to a hydrophilic treatment method for a reverse osmosis (RO) membrane using a modified polyvinyl alcohol having a polyalkylene oxide chain, an RO membrane subjected to a hydrophilic treatment by this method, and a hydrophilic treatment agent for the RO membrane. .

RO membranes have been widely put into practical use in various water treatment fields for the purpose of desalination and concentration, taking advantage of their characteristics.

Conventionally, it is known that polyvinyl alcohol (PVA) is brought into contact with the RO membrane in order to prevent a decrease in permeated water amount (flux) of the RO membrane and a decrease in desalination rate due to use (for example, Patent Documents 1 to 4). 3).

When the PVA is brought into contact with the RO membrane, the RO membrane becomes hydrophilic and the permeation performance of the RO membrane is maintained. That is, since PVA has many OH groups and high hydrophilicity, by attaching PVA to the RO membrane, the RO membrane is hydrophilized, and adsorption of proteins and the like to the RO membrane is suppressed, thereby improving the stain resistance. As a result, the transmission performance can be maintained.

In the conventional hydrophilization treatment of RO membrane using PVA,
(1) PVA peels off from the RO membrane in long-term use, and the hydrophilic effect is lost.
(2) By attaching PVA to the RO membrane, the flux of the RO membrane is greatly reduced compared to before the attachment.
There was a problem.

Japanese Patent Laid-Open No. 51-13388 JP-A-53-28083 Japanese Patent Laid-Open No. 11-28466

The present invention solves the above-mentioned conventional problems, can maintain a hydrophilization effect for a long period of time, and can maintain a relatively high flux, and a hydrophilization treatment method and hydrophilization treatment therefor It is an object to provide an agent.

As a result of intensive studies to solve the above problems, the present inventors have been conventionally used by using modified polyvinyl alcohol having a polyalkylene oxide chain, based on the knowledge that polyethylene glycol has high adsorptivity with RO membranes. It has been found that the adsorptivity to the RO membrane is improved as compared with PVA, and therefore, the contamination resistance can be maintained for a long time as compared with PVA.

The present invention has been achieved on the basis of such knowledge, and the gist thereof is as follows.

[1] A method of hydrophilizing a reverse osmosis membrane, comprising bringing a modified polyvinyl alcohol having a polyalkylene oxide chain into contact with the reverse osmosis membrane.

[2] The method for hydrophilizing a reverse osmosis membrane according to [1], wherein the degree of saponification of the modified polyvinyl alcohol is 80% or more.

[3] The method for hydrophilizing a reverse osmosis membrane according to [1] or [2], wherein the polyalkylene oxide chain is a polyethylene oxide chain.

[4] A container having a liquid inlet and a liquid outlet is partitioned by the reverse osmosis membrane, and the aqueous solution containing the modified polyvinyl alcohol introduced from the liquid inlet is permeated through the reverse osmosis membrane to allow the liquid outlet. The method for hydrophilizing a reverse osmosis membrane according to any one of [1] to [3], wherein the modified polyvinyl alcohol is brought into contact with the reverse osmosis membrane by draining it from water and passing it through.

[5] The method for hydrophilizing a reverse osmosis membrane according to [4], wherein the water-passing pressure is 0.1 to 0.5 MPa.

[6] The hydrophilization of the reverse osmosis membrane according to any one of [1] to [5], wherein the concentration of the modified polyvinyl alcohol in the aqueous solution containing the modified polyvinyl alcohol is 0.1 to 5000 mg / L Processing method.

[7] A reverse osmosis membrane that is hydrophilized by the method of hydrophilizing a reverse osmosis membrane according to any one of [1] to [6].

[8] A hydrophilic treatment agent for a reverse osmosis membrane containing a modified polyvinyl alcohol having a polyalkylene oxide chain.

According to the present invention, by treating the RO membrane with a modified polyvinyl alcohol having a polyalkylene oxide chain, it is possible to impart hydrophilicity and maintain the hydrophilic effect over a long period of time. And if it is a modified polyvinyl alcohol which has a polyalkylene oxide chain, the fall of the flux of RO membrane by a hydrophilic treatment can be suppressed, and the preparation of the aqueous solution is easy compared with conventional PVA. .

6 is a graph showing changes in flux over time in Examples 1 to 3 and Comparative Examples 1 and 2.

Hereinafter, embodiments of the present invention will be described in detail.

<RO membrane>
Examples of the RO membrane to which the present invention is applied include a polyamide-based RO membrane having an aromatic polyamide as a dense layer, but a polyamide-based nanofiltration membrane may also be used. That is, the RO membrane to be treated in the present invention is a broad RO membrane containing a nanofiltration membrane. Also, it can be applied to new films, used films, and deteriorated films without problems.

The structure of the RO membrane is not particularly limited, and a flat membrane module, a spiral type module, a hollow fiber module, or the like can be used.

<Modified polyvinyl alcohol having a polyalkylene oxide chain>
In the present invention, the modified polyvinyl alcohol having a polyalkylene oxide chain used for the hydrophilic treatment of the RO membrane is composed of a vinyl alcohol unit and a unit to which a polyalkylene oxide group is bonded, and optionally further includes a vinyl acetate unit.

As the polyalkylene oxide group of the unit to which the polyalkylene oxide group is bonded, a polyalkylene oxide group having 2 to 4 carbon atoms of an alkylene group such as a polyethylene oxide group, a polypropylene oxide group, or a polybutylene oxide group is preferable. The oxide group is most preferred. The number of repeating alkylene oxide groups in the polyalkylene oxide group is preferably 2 to 300, particularly 4 to 150. If the number of repetitions is too small, the effect of improving the adsorptivity to the RO membrane by the polyalkylene oxide group cannot be sufficiently obtained, and if it is too large, the decrease in the flux of the RO membrane due to the hydrophilization treatment becomes large.

The molar fraction of the unit to which the polyalkylene oxide group is bonded in the modified polyvinyl alcohol having a polyalkylene oxide chain is preferably 0.1 to 50 mol%, more preferably 0.3 to 40 mol%, and 0 Particularly preferred is 5 to 30 mol%. When the molar fraction of the unit to which the polyalkylene oxide group is bonded is smaller than this range, the present invention such as improvement of the adsorptivity to the RO membrane and suppression of flux reduction by introducing the polyalkylene oxide chain into the polyvinyl alcohol. If the amount is too large, the molar fraction of the vinyl alcohol unit is relatively small, and the hydrophilization effect tends to be reduced.

The molar fraction of the vinyl alcohol unit in the modified polyvinyl alcohol having a polyalkylene oxide chain is preferably 50 to 99.9 mol%, more preferably 60 to 99.7 mol%, and particularly preferably 70 to 99.5 mol%. preferable. If the molar fraction of the vinyl alcohol unit is less than this range, the number of hydroxyl groups in the modified polyvinyl alcohol having a polyalkylene oxide chain is reduced, and sufficient hydrophilization effect and flux stability cannot be obtained. If the amount is too large, the molar fraction of the unit to which the polyalkylene oxide group is bonded is relatively small, and the above-described effect due to the introduction of the polyalkylene oxide chain into polyvinyl alcohol may not be sufficiently obtained.

The molar fraction of vinyl acetate units in the modified polyvinyl alcohol having a polyalkylene oxide chain is preferably 0 to 20 mol%, more preferably 0 to 10 mol%, and particularly preferably 0 to 5 mol%.

Saponification degree is an index indicating the properties of polyvinyl alcohol. The saponification degree is obtained by dividing the molar fraction of the vinyl alcohol unit by the sum of the molar fractions of the vinyl alcohol unit and the vinyl acetate unit. In the present invention, the degree of saponification of the modified polyvinyl alcohol having a polyalkylene oxide chain is preferably 80% or more, particularly 85% or more, particularly 95% or more. When the degree of saponification is less than 80%, the number of hydroxyl groups is small, the hydrophilicity is lowered, and sufficient hydrophilization treatment effect and flux stability tend not to be obtained.

The polymerization degree of the modified polyvinyl alcohol having a polyalkylene oxide chain, that is, the total number of units is not particularly limited, but is preferably 20 to 20,000. If the degree of polymerization is too low, the adsorptivity to the membrane is deteriorated, and if the degree of polymerization is too large, the RO membrane flux decreases due to the hydrophilic treatment, which is not preferable.

Such a modified polyvinyl alcohol having a polyalkylene oxide chain can be obtained by a known synthesis method. Commercial products such as “Ecomati WO-320N” and “Ecomati WO-320R” manufactured by Nippon Synthetic Chemical Industry can also be used.

A method for synthesizing a modified polyvinyl alcohol having a polyalkylene oxide chain is a method in which a monomer having a polyalkylene oxide group is polymerized with vinyl acetate, and then a part or all of the vinyl acetate is saponified to obtain a modified polyvinyl alcohol. Although preferred, other synthetic methods may be used.

As the monomer having the above polyalkylene oxide group, polyethylene oxide monovinyl ether, polypropylene oxide monovinyl ether, polyethylene oxide monoallyl ether, polyethylene glycol monomethacrylate, polyethylene glycol monoacrylate, polypropylene glycol monomethacrylate, polypropylene glycol monoacrylate, Polyethylene glycol-polypropylene glycol monomethacrylate, polyethylene glycol-polypropylene glycol monoacrylate, poly (ethylene glycol-tetramethylene glycol) monomethacrylate, poly (ethylene glycol-tetramethylene glycol) monoacrylate, poly (ethylene glycol-propylene glycol) Call) monomethacrylate, methoxy polyethylene glycol - and polypropylene glycol monoacrylate and the like.
These may be used alone or in combination of two or more.

In the present invention, as the modified polyvinyl alcohol having a polyalkylene oxide chain, only one kind may be used, and two or more kinds having different polyalkylene oxide groups, molar fractions of units, polymerization degree, and the like may be used. You may use it in combination.

Such modified polyvinyl alcohol having a polyalkylene oxide chain is usually used for the hydrophilization treatment of the RO membrane as an aqueous solution having a concentration of about 0.1 to 5000 mg / L, preferably about 1 to 1000 mg / L. If this concentration is too low, it takes a long processing time to obtain the desired hydrophilization effect, which is inefficient. Conversely, if this concentration is too high, the viscosity of the aqueous solution increases and the RO membrane is contacted at the time of contact processing. It is not preferable in terms of handling.

The modified polyvinyl alcohol having a polyalkylene oxide chain used in the present invention has sufficient solubility in water of about 40 to 60 ° C. unlike simple polyvinyl alcohol, so that an aqueous solution having a predetermined concentration can be prepared by a simple operation. Can do.

The water used for preparing the aqueous solution of the modified polyvinyl alcohol having a polyalkylene oxide chain is not particularly limited, and water having a low ion load such as desalted water is used. However, the RO membrane feed water has a polyalkylene oxide chain. It is also possible to perform treatment by directly adding polyvinyl alcohol.

<Hydrophilic treatment method>
There is no particular limitation on the method of bringing the modified polyvinyl alcohol having a polyalkylene oxide chain into contact with the RO membrane, but it is preferable to contact the RO membrane with an aqueous solution of the modified polyvinyl alcohol having a polyalkylene oxide chain under pressure. .

For example, a container having a liquid inlet and a liquid outlet is partitioned by a RO membrane to be treated, and an aqueous solution of modified polyvinyl alcohol having a polyalkylene oxide chain is introduced from the liquid inlet and permeated through the RO membrane. The method of discharging is mentioned. In this case, as described above, the modified polyvinyl alcohol having a polyalkylene oxide chain can be directly added to the RO supply water of the RO membrane module of the normal RO membrane separation apparatus to perform the hydrophilic treatment. That is, in the hydrophilization treatment according to the present invention, a modified polyvinyl alcohol having a polyalkylene oxide chain is added to the RO membrane treatment water during the RO membrane separation treatment to the RO membrane module of the existing RO membrane separation apparatus. The RO membrane separation process can be interrupted.

There is no particular limitation on the pressure when an aqueous solution of a modified polyvinyl alcohol having a polyalkylene oxide chain is passed through the RO membrane under pressure, but a range of 0.1 to 2.0 MPa is preferable. In addition, the pump used for the washing | cleaning of RO membrane is normally used for the water flow to the RO membrane of the modified polyvinyl alcohol aqueous solution which has a polyalkylene oxide chain. In this case, from the capability of the pump, the water flow pressure is The range is from 0.1 to 0.5 MPa. There is no particular limitation on the flux when passing water, but it is preferably about 0.1 to 1.0 m / day. If this water flow condition is too low, a sufficient hydrophilic effect cannot be obtained, and if it is too high, there is a concern that the flux will decrease greatly.

The treatment time is not particularly limited, but is preferably 10 minutes or more and less than 48 hours, more preferably 1 hour or more and less than 24 hours. If the treatment time is short, a sufficient hydrophilic effect cannot be obtained. If the treatment time is long, there is a concern that the RO membrane flux is too low.

The temperature (water temperature) during the hydrophilization treatment is preferably 10 to 35 ° C. If the water temperature is too low, the flux decreases and the contact efficiency deteriorates. If the water temperature is too high, problems such as denaturation of the membrane material may occur.

The RO membrane treated by the hydrophilization treatment method of the present invention can be suitably used for an ultrapure water production system, a wastewater collection system, and other water treatment systems.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

[Example 1]
The RO membrane “ES20” (flat membrane, diameter 32 mmφ) manufactured by Nitto Denko Corporation was hydrophilized under the following conditions. The modified polyvinyl alcohol having a polyalkylene oxide chain as a hydrophilic treatment agent was used after being dissolved in ultrapure water (60 ° C.). After hydrophilization treatment, we conducted a water flow test using biologically treated water from the wastewater recovery system of Kurita Industrial Co., Ltd., and verified flux stability.

<Hydrophilic treatment>
Hydrophilization treatment agent: “Ecomati WO-320N” manufactured by Nippon Synthetic Chemical Industry Co., Ltd. (modified polyvinyl alcohol having a polyethylene oxide chain, saponification degree of 98.5% or more)
Concentration: 100 mg / L
Water flow time: 5 hours Inlet pressure: 0.75 MPa
Flux: 1.0m / day
Water temperature: 25 ° C

<Water flow test>
Raw water evaluation raw water: Biologically treated water from the wastewater collection system of Kurita Kogyo Co., Ltd. Development Center ("Kuribata EC-503" manufactured by Kurita Kogyo Co., Ltd. added as a countermeasure against slime, 3 mg / L, pH 6.5)
Inlet pressure: 0.75 MPa
Recovery rate: 60%
Water temperature: 25 ° C

Under the above-mentioned hydrophilization treatment conditions, an aqueous solution of a modified polyvinyl alcohol having a polyalkylene oxide chain is subjected to hydrophilization by passing water through the RO membrane under pressure, and then the above water-flow evaluation raw water is passed through. The change with time (relative value when the flux at the start of water flow is 1) was examined, and the results are shown in FIG.

[Example 2]
The same as in Example 1 except that “Ecomati WO-320R” (modified polyvinyl alcohol having a polyethylene oxide chain, saponification degree: 86.5 to 89.5%) manufactured by Nippon Synthetic Chemical Industry Co., Ltd. was used as the hydrophilic treatment agent. A test was conducted to verify the flux stability. The results are shown in FIG.

[Example 3]
Except that the inlet pressure during the hydrophilization treatment was 0.2 MPa, the same test as in Example 1 was performed to verify the flux stability. The results are shown in FIG.

[Comparative Example 1]
Nitto Denko's “ES20” (flat membrane, 32 mm diameter) was subjected to a water flow test without hydrophilization, and the flux stability was verified. The results are shown in FIG.

[Comparative Example 2]
Except that polyvinyl alcohol (polymerization degree 2,000, saponification degree 99%) was used as the hydrophilic treatment agent, the same test as in Example 1 was performed to verify the flux stability. The results are shown in FIG.

From FIG. 1, it can be seen that by bringing modified polyvinyl alcohol having a polyalkylene oxide chain into contact with the RO membrane, the flux stability is improved and the durability of the stain resistance effect is improved as compared with the conventional PVA treatment. .

Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.
This application is based on Japanese Patent Application No. 2012-279590 filed on Dec. 21, 2012, which is incorporated by reference in its entirety.

Claims (8)

A method for hydrophilizing a reverse osmosis membrane, comprising bringing a modified polyvinyl alcohol having a polyalkylene oxide chain into contact with the reverse osmosis membrane. The method for hydrophilizing a reverse osmosis membrane according to claim 1, wherein the degree of saponification of the modified polyvinyl alcohol is 80% or more. The method for hydrophilizing a reverse osmosis membrane according to claim 1 or 2, wherein the polyalkylene oxide chain is a polyethylene oxide chain. A container having a liquid inlet and a liquid outlet is partitioned by the reverse osmosis membrane, and an aqueous solution containing the modified polyvinyl alcohol introduced from the liquid inlet is permeated through the reverse osmosis membrane and discharged from the liquid outlet. The method of hydrophilizing a reverse osmosis membrane according to any one of claims 1 to 3, wherein the modified polyvinyl alcohol is brought into contact with the reverse osmosis membrane by passing water through the membrane. The hydrophilization of a reverse osmosis membrane according to claim 4, wherein the pressure during water flow is 0.1 to 2.0 MPa, and the water flow flux is 0.1 to 1.0 m / day. Processing method. The method for hydrophilizing a reverse osmosis membrane according to any one of claims 1 to 5, wherein the concentration of the modified polyvinyl alcohol in the aqueous solution containing the modified polyvinyl alcohol is 0.1 to 5000 mg / L. A reverse osmosis membrane which is hydrophilized by the hydrophilization method of a reverse osmosis membrane according to any one of claims 1 to 6. A hydrophilic treatment agent for a reverse osmosis membrane containing a modified polyvinyl alcohol having a polyalkylene oxide chain.

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