Composite reverse osmosis membrane and process for preparing...

Details Composite reverse osmosis membrane and process for preparing... Composite reverse osmosis membrane and process for preparing...

1999-12-30

2004-04-20

Zirker, Daniel (Department: 1771)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Composite having voids in a component

C428S319700, C428S318400, C210S652000, C210S653000, C210S500240, C210S500270, C210S500380, C210S506000

Reexamination Certificate

active

06723422

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a composite reverse osmosis membrane for selectively separating components in a liquid mixture, and a method of producing the membrane. More specifically, the present invention relates to a composite reverse osmosis membrane having a porous support on which a polyamide skin layer mainly comprising polyamide is formed to provide both high salt rejection and high permeability, and a method of producing the same.
Such a composite reverse osmosis membrane can be used for many purposes, including the manufacture of ultra-pure water and the desalination of sea water or brackish water. This membrane also can be used to remove contamination from a source or withdraw purified materials from contaminated dyeing waste or electrochemical deposition coating waste. Such wastes may cause pollution. Thus the present invention will clean contaminated water to be reused. The membrane of the present invention also can be used for other purposes like condensing effective components for food.
BACKGROUND ART
Conventionally, composite reverse osmosis membranes have been known as reverse osmosis membranes which differ in structure from asymmetric reverse osmosis membranes. Such composite reverse osmosis membranes are produced by forming active thin films (skin layers) which possess the ability to selectively separate materials, on porous supports.
Applications disclose membranes comprising polyamide obtainable by interfacial polymerization between polyfunctional aromatic amines and polyfunctional aromatic acid halide compounds formed on porous supports. The examples of such applications are, JP-A-(Unexamined Published Japanese Patent Application) 55-147106, JP-A-62-121603, JP-A-63-218208, and JP-A-2-187135. Other prior art references disclose composite reverse osmosis membranes wherein skin layers comprising polyamide are formed on porous supports, and the polyamide is obtained by an interfacial polymerization of a polyfunctional aromatic amine and a polyfunctional alicyclic acid halide compound (cf. JP-A-61-42308).
The composite reverse osmosis membranes described above have a high desalination property and a high water permeability, but it is desirable to improve the water permeability while keeping the high desalination property from the standpoint of the efficiency and so on. For these requirements, various kinds of additives are proposed e.g., in JP-A-63-12310. However, in the conventional composite reverse osmosis membranes, the improvement of the properties of the composite reverse osmosis membranes are still insufficient.
JP-A-63-178805 discloses a method of forming a membrane in a two-stage reaction. In this method, a polyfunctional reaction reagent of a low concentration is added in the second stage. A composite reverse osmosis membrane obtained in this method is improved slightly in the salt rejection, but the permeation speed is lowered instead. This method cannot provide a composite reverse osmosis membrane to conform to the requirements.
The present invention aims to provide a composite reverse osmosis membrane having a high salt rejection and high water permeability, and a method of producing the same.
DISCLOSURE OF THE INVENTION
In order to accomplish these objects, a composite reverse osmosis membrane of the present invention comprises a polyamide skin layer formed on a porous support, and the contact angle between the polyamide skin layer surface and water is defined not to exceed 45°.
When the contact angle is no more than 45°, a high salt rejection is maintained, a flux is improved and thus, the membrane has excellent water permeability. The contact angle is preferably 40° or less.
In the present invention, the contact angle is measured in the following manner. First, the polyamide skin layer surface is cleansed and dried. Then, pure water is dropped on the surface in order to measure the angle (the internal angle of the water drop) formed by the water drop and the polyamide skin layer. The angle is measured preferably about 15 seconds after the dropping of the water.
The composite reverse osmosis membrane preferably includes a polyamide skin layer formed by a reaction of one or more compounds having at least two reactive amino groups and one or more polyfunctional acid halide compounds having at least two reactive acid halide groups.
Preferably, the composite reverse osmosis membrane provides a salt rejection of at least 98% and a permeate flow rate of at least 0.5 m
3
/m
2
·day when evaluated by using feed water having pH 6.5 containing 0.05 weight % of salt at an operation pressure of 5 kgf/cm
2
and a temperature of 25° C. If the salt rejection and the permeate flow rate are within these ranges, ions can be removed if an actual operation pressure is low as 5 kgf/cm
2
or less, for example, about 3 kgf/cm
2
. Therefore, facilities comprising the composite reverse osmosis membranes can be built by using pipes made of inexpensive materials such as polyvinyl chloride. This offers a significant cost advantage. The composite reverse osmosis membrane can be used at city water level pressures. Preferably, the salt rejection is at least 98%, the permeate flow rate is at least 0.6 m
3
/m
2
·day under the above-identified condition. Most preferable is if the salt rejection is at least 99% and the permeate flow rate is at least 0.7 m
3
/m
2
·day.
A method of producing a composite reverse osmosis membrane of the present invention includes the steps of:
forming a layer by coating on a porous support a solution A comprising one or more compounds having at least two reactive amino groups;
contacting this layer with a solution B comprising one or more polyfunctional acid halide compounds; and
further contacting the layer with another solution C comprising one or more polyfunctional acid halide compounds of a concentration higher than the solution B in order to form a polyamide skin layer on the porous support.
The above-identified composite reverse osmosis membrane can be produced in this method.
The composite reverse osmosis membrane of the present invention is preferably produced in this method, but it is not limited thereto.
In the producing method, preferably, the concentration of the polyfunctional acid halide compound in the solution C is at least 1.2 times of the polyfunctional acid halide compound in the solution B. More specifically, the difference in the concentration ranges from 1.3 times to 5000 times. When the concentration of the solution C is less than 1.2 times of the solution C, the obtained composite reverse osmosis membrane may not have a high salt rejection or a high permeate flow rate. On the other hand, when the concentration of the solution C exceeds 5000 times of the solution B, the properties cannot be improved to match with the difference, and it causes disadvantages in costs and efficiency. The standard of the concentration is not specifically limited, but it can be, for example, based on weight.
Preferably in the producing method, solution B remains partially rejected at a contact with the solution C.
The remaining solution B can be observed visually after a contact with the solution C. A composite reverse osmosis membrane having a high salt rejection and a high permeate flow rate can be obtained even if the solution B does not remain. However, the properties of the composite reverse osmosis membrane can be improved if some solution B remains.
In the present invention, the compound included in the solution A preferably has at least two amino groups and the compound is at least one selected from the group consisting of aromatic polyfunctional amine, aliphatic polyfunctional amine and alicyclic polyfunctional amine.
A preferable aromatic polyfunctional amine is selected from the group consisting of m-phenylenediamine, p-phenylenediamine, 1,3,5-triaminobenzene, 1,2,4,-triaminobenzene, 3,5-diamino benzoic acid, 2,4-diaminotoluene, 2,4-diaminoanisole, amidol, and xylenediamine. These amines can be used either alone or as mixtures thereof.
A preferable aliphatic polyfunctional amine is selected from the group consisting of

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