JPS62266103A - Composite semipermeable membrane - Google Patents

Abstract

PURPOSE:To obtain a composite semipermeable membrane which is effective in both the softening of hard water and the selective separation of a multivalent ion and a monovalent ion and is excellent in water permeability even under the operation conditions in low pressure by coating the surface of an activated layer consisting of a cross-linked organic polymer having a negative fixed charge group by the organic polymer having a positive fixed charge group. CONSTITUTION:A composite membrane where in a cross-linked organic polymer having a negative fixed charge type group is made to an activated layer is obtained for example by allowing piperazine and trimesic acid chloride to react with a support of fiber-reinforced polysulfone by interfacial polycondensation, controlling the interfacial reaction in this case and introducing a carboxyl group into cross-linked pipe-razine polyamide. Then a reverse osmosis method is performed by using this membrane and adding an organic polymer having a positive fixed charge group such as polyethyleneimine to raw water and the organic polymer having the positive fixed charge type group is adsorbed on the surface of the membrane and thereby a composite semipermeable membrane where the activated layer is coated by the organic polymer having positive fixed charge type group is obtained.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to a semipermeable membrane for selectively permeating the components of a liquid I-compound. Can water can be desalinated and desalinated even under low-pressure operation, and is particularly effective in softening hard water.It can also be used to remove pollution-causing sewage, such as dyeing wastewater and electric wastewater. Composite semi-transparent material that selectively removes or recovers contained contaminants or valuable substances, and can also be used in the production of semiconductors and ultrapure water for medical use! It is vaguely related.

[Prior Art] Conventionally, commercially used semipermeable membranes include asymmetric membranes made from cellulose acetate, such as those disclosed in U.S. Patent No. 3,
There are lob-type membranes described in No. 133,132 and No. 3,133.137.

However, this membrane has problems with hydrolysis resistance, microbial resistance, chemical resistance, etc. In particular, when trying to improve permeability, the pressure resistance increases (1) It is not possible to manufacture a membrane that has both durability, and However, it has not yet been put to practical use in a wide range of applications.Research into a new material that eliminates the vacancies in these cellulose acetate asymmetric membranes has been carried out in the US ``1.1-''.
Although it is widely used mainly for 1/A polyamide and polyamide hydrazide (U.S. Special Ha'1 No. 3 and 5)
67.632), polyamide FIi (equity 11r (
No. 50-121168ff1), crosslinked polyamide? !
2 (Japanese Patent Publication No. 52-152879), polyimidazopyrrolone, polysulfone) 7mid, polybenzimidazole, polybenzimidacylon, polyarylene oxide, etc. Although materials that improve some of their drawbacks have been obtained. However, it is inferior to cellulose acetate membranes in terms of selective separation or permeability.

On the other hand, as a semipermeable membrane of a different type from the recent type, a composite membrane in which an active layer and a supporting membrane supporting the active layer are manufactured from different materials has been developed. Some of them are FT-30, PA-
It is already commercially available under trade names such as 300, NF-40, and PEC-1000, and has superior performance in terms of selective separation and permeability compared to asymmetric membranes.
It is opening up new application fields such as one-stage desalination of seawater, separation and recovery of low-molecular-weight organic aqueous solutions, and low-level desalination of canned water. However, from 4K onwards, these composite membranes were mostly developed with desalination as the main focus, and many of them excluded all If-free compounds. Under these circumstances, recently, membranes capable of selectively separating monovalent ions and divalent ions have appeared and are attracting attention. It is disclosed in example 1311, Japanese Patent Publication No. 56-500062, Japanese Patent Application Laid-open No. 57-2'102, Japanese Patent Application Laid-open No. 1830-11-11, October 1987, etc. These membranes have a desalination rate lJ of common salt (a typical example of a monovalent cation, a monovalent anion), a 50% culm, and a typical example of magnesium sulfate (a typical example of a divalent cation, divalent anion).
Since the rejection rate is over 98%, it is suitable for softening hard water. However, when water softening is actually attempted using these membranes, these membranes contain an active layer mainly composed of cross-linked polyamide with acid terminals, that is,
Because it has an n-fixed charge type group, magnesium chloride,
In the case of calcium chloride (divalent cation, monovalent anion), etc., the rejection rate was low and it was found that it was not effective for water softening.

[16 Problems to be Solved by the Invention] The present inventors have developed a semipermeable membrane that is effective in softening hard water and selectively distributing polyvalent ions and monovalent ions, and is permeable even under low pressure operating conditions. As a result of diligently examining as many defective semipermeable membranes as possible, we arrived at the present invention.

[Means for solving the problems] The above object of the present invention is achieved by the following configuration. In other words, it is a composite semipermeable membrane in which the active layer is made of a crosslinked organic polymer having a fixed negative charge group, and the surface thereof is coated with an organic polymer having a fixed positive charge group.

The active layer herein refers to a layer that substantially controls the performance of the composite semipermeable membrane, and is a layer formed thinly on a microporous support membrane such as polysulfone.

In the present invention, the crosslinked organic polymer having a negatively charged group constituting the active layer is mainly composed of a polymer having groups such as carboxylic acid, sulfonic acid, phosphoric acid, and sulfuric acid as the negatively charged group. In particular, in consideration of water permeability and desalting performance as a semipermeable membrane, crosslinked polyamide polymers obtained by interfacial polycondensation, crosslinked sulfonated polysulfone, and the like are preferred.

A typical example of a composite membrane having a crosslinked polyamide polymer as an active layer and having a negatively fixed charged group is, for example, published in Japanese Patent Application Publication No. 1983-1985.
Utilizes the piperazine polyamide shown in Publication No. 0062↑
(A single-layer composite film can be mentioned, in which piperazine, trimesic acid chloride, 5-riI former 21
React with sulfonylinotal acid chloride! ”(le
I can do it. At this time, by carrying out an interfacial reaction, a carboxylic acid group or a sulfonic acid group can be introduced into the crosslinked piperazine polyamide to impart an n fixed charge.

A feature of this type of membrane having a negatively fixed charged group is that the salt removal rate is greatly influenced by the charge of anions, but is not affected much by the charge of cations. Specifically, the desalination rate differs greatly between NaC4 and NaSO4, but the desalination rate does not change much between NaC4 and MqCQ2 or CaCQ+.

In addition, in a composite film with a crosslinked poly(mide) polymer as an active layer, a positively fixed charged group is introduced in the interfacial reaction, and the removal rate of divalent cations A is improved. However, when chlorine is used as a disinfectant, the positively charged groups are selectively destroyed, and the film exhibits the properties of a film containing only negatively charged groups.

Specifically, chlorine treatment reduces MCI, Ca2+, etc. The desalination rate of Na+ decreases, and the desalination rate of Na+ remains unchanged.

The present invention improves the desalination rate of divalent cations by coating the surface of various negatively charged membranes as described above with an organic polymer having a positively fixed charged group. It is.

The organic polymer having a positive fixed charge type group as used herein refers to a crosslinked or non-crosslinked organic polymer having a positive fixed charge type group in its molecular chain and/or terminal and/or side chain. It means a combination, and as a positive fixed charge type group, quaternized ammonium, quaternized pyridinium, etc. are generally used.

Typical examples include homopolymers or copolymers such as quaternized styrene, quaternized vinylpyridine, and quaternized vinylbenzylamine, and amino groups such as polyethyleneimine, amine-modified halogenated polymers, polyallylamine, and polydiallylamine. Examples include polymers or copolymers having the following, and modified products thereof. Preferred positively charged polymers in the present invention include those that improve the exclusion rate of divalent cations without impairing water permeability.
Examples include polyethyleneimine, polyepiaminohydrin, and polyallylamine, with polyethyleneimine being preferred because of its ease of availability.

Here, the active layer can be coated with an a-polymer having a positively fixed charge of 4 groups, by the usual method, but it is more convenient to use the reverse osmosis method. This can also be achieved by adding an organic polymer having a positively fixed charge type group to Zonoikyo water. In addition, even with such a simple operation, the phase with the negatively fixed charged group in the active layer can be reduced! The organic polymer having a positively fixed charged group is well adsorbed to the surface due to the L action, and will not peel off or be washed away during use.

EXAMPLES In the following Examples 83, selective separation performance - C1 common salt or calcium chloride A3 and magnesium chloride rejection rates were determined by conventional means by electrophotographic measurements. In addition, regarding permeation performance, the water passing rate is medium (?
1.November) It was determined by the amount of water permeation per hour.

Reference Example 1 Synthesis of piperazine-modified polyepichlorohydrin from polyepic[1]ruhydrin.

92.5 g of polyepichlorohydrin was dissolved in 280 cc of methyl edyl ketone, 120 CI of sodium iodide was added, stirred and centrifuged for 25 hours, and reprecipitated with water, resulting in polyepiiodohydrin in which 80% of the chloro groups were substituted with iodo groups. was gotten. 10g of this polyepiiodohydrin was added to N-
Dissolved in 90 g of methylpyrrolidone, piperazine 31C1
was added, and the mixture was heated and stirred at 35°C for 2 hours. Leave to cool to room temperature;
When the above solution was added to 500 ml of benzene with rapid stirring, a white polymer could be reprecipitated. This polymer was found to be piperazine-modified polyepichlorohydrin in which approximately 80% of the iodine groups in polyepiiodohydrin were modified with piperazine, as a result of infrared absorption spectroscopy and CNMR spectroscopy. The aqueous solution contained 0.6% by weight of piperazine as determined by Cass chromatography.

Reference Example 2 Tanota (tough yarn) made of polyester fibers with a length of 30 cm and a width of 120 CIR, 150 denier Maru 1 Neiramen I thread, weaving density of 90 yarns/inch (vertical), = 1167 yarns/inch , 160μ thick) on a glass plate, and polysulfone (Union) was placed on top of it.
Carbide's udelP-3500> 16-hand I1
% dimelformamide (DMF) solution to a thickness of 200μ at room temperature (20°C), immersed in pure water and left for 5 minutes to form a fiber-reinforced polysulfone support (hereinafter referred to as FRF). Create an S-poor body and approximately 1). The pure water permeability coefficient of the F' R-I)S support (thickness 210 to 215μ) obtained in this way is 1q at a pressure of 1k.
CJ/d, measured at a temperature of 25°C, 0.005 to 0.
0I Q/cd-Sec-atm.

Example 1 According to Reference Example 2 (obtained F R-P
An aqueous solution containing 1 ΦM% of an anionic surfactant t'l agent (wt%) of phosphoric acid tri)-1 to thulium (wt%) was applied at a rate of 150%/Tn2 and dried with hot air at 95°C. After that, a solution of 0.5% by weight of trimesic acid chloride dissolved in trifluorotrichloroethane was added at 60 mR/T11.
2 coated, and then subjected to dry heat treatment for 5 minutes with hot air at 100°C. The composite membrane thus obtained was coated with 0.15% Na
C, Q aqueous solution as raw water, pressure 15 kcJ/ffl,
When a reverse osmosis test was conducted at a temperature of 25℃, the water velocity overrate was 3.8 m'/TI+2・day, and the rejection rate was 72%.
Met. When a reverse osmosis test was conducted under the same conditions by changing the raw water to a 500 ppm calcium chloride aqueous solution, the water overrate was 3.7 TIl/Tl 12·day, and the rejection rate was 75%.
Met.

Next, raw water polyethyleneimine polymer 1001) I) ■
After treatment, a reverse osmosis test was conducted under the same conditions, and the water overrate after 25 hours was 3.5 pores/m2/day, and the rejection rate was 96.8%. ] improved.

Further, when the surface of this film was analyzed by ESCA, it was found that a layer of polyethyleneimine was present on the surface.

Example 2 11 A composite membrane obtained in the same manner as in Example 1 was coated with 0.15% Na.
A reverse osmosis test was conducted using the CQ aqueous solution as heavy water at a pressure of 15 ki/cffl and a temperature of 25°C.
%Met. When the raw water was changed to an aqueous solution containing 200 ppm of calcium chloride and 2001) of magnesium chloride, and a reverse osmosis test was conducted on the same column A'1, the water velocity overrate was 3°2 m''/m2, and the daily rejection rate was 80%. Next, after continuous operation for 25 hours with residual chlorine 21)I'm, the chlorine was removed and a reverse osmosis test was performed again using a 200 ppm aqueous solution of calcium chloride 21)I)m magnesium chloride as raw water. The water overspeed was 2.8 m''/lr+2·day, and the rejection rate was 80%. Next, after treating the raw water with poly(1-ethyleneimine volima 50Dl) III, a reverse osmosis test was performed under the same conditions, and the water overspeed after 25 hours was 2.6 m'/m?・1-1, the exclusion rate was 98.7%, and the n1 division rate was 1311 people, heading for 11J.

Example 3 When a reverse osmosis test was conducted by repeating chlorine treatment and polyethyleneimine treatment five times in the same manner as in Example 2, the water velocity overrate was 2.5 m''/m2·day and the rejection rate was 98. No deterioration in performance was observed even when the temperature was maintained at 5% and used repeatedly.

Example 4 Reference example 1 was added to the FR-PS support obtained by reference example 2.
Piperazine-modified polyepichlorohydrin double foot% obtained in
Apply the aqueous solution at 150 m1/m2 and 95°C.
It was dried with hot air for 30 seconds. Thereafter, 0.0% trimesic acid chloride was added to trifluorotrichloroethane.
A solution containing 25 wt. The composite membrane thus obtained was treated with 500 pp of calcium chloride.
As a result of a reverse osmosis test using m aqueous solution as raw water at a pressure of 15 h/cot and a temperature of 25°C, the water velocity overrate was 3.1 yn.
'/T112·day, the elimination rate was 97.5%. Next, after 25 hours of continuous operation with residual chlorine 21)i)III, the chlorine was removed, and a reverse osmosis test was performed again under the same conditions using calcium chloride 500 Ell)III aqueous solution as raw water, and the water overrate was 3. 1m'/m2・day, exclusion rate is 91
．． It was 0%. Next, poly 1 tyrene imine volima 11001) l) was added to the raw water and after treatment, a reverse osmosis test was performed under the same conditions. As a result, the rejection rate after 25 hours was 98.7%, and the water velocity overrate was 2.7 m '/m2·day, and the performance recovered to its initial level.

Example 5 When a reverse osmosis test was carried out by repeating chlorine treatment and polyethyleneimine treatment five times in the same manner as in Example 4, the water velocity overrate was 2.5 m'/m2·day and the rejection rate was 97. 7%
No deterioration in performance was observed even after repeated use.

〔Effect of the invention〕

The composite reverse osmosis membrane of the present invention is more effective in desalinating divalent cations than conventional membranes, does not lose its performance due to chlorine treatment, is easy to manufacture, and has excellent durability. I understand. It also has the remarkable effect of being easily applicable to performance recovery treatment for membranes whose separation performance has deteriorated.

Furthermore, it can be processed by a simple operation, and organic polymers having positively charged groups are well adsorbed on the surface due to the phase H interaction with the negatively charged groups in the active layer, and are peeled off and washed away during use. This has the effect that there are fewer problems.

Claims (3)

[Claims] (1) A composite semipermeable membrane in which the active layer is made of a crosslinked organic polymer having a fixed negative charge group, and the surface thereof is coated with an organic polymer having a fixed positive charge group. (2) A composite semipermeable membrane according to claim (1), wherein the active layer is a crosslinked polyamide having carboxylic acid groups and/or sulfonic acid groups. (3) A composite semipermeable membrane according to claim (1), wherein the organic polymer having a positively fixed charged group is selected from polyethyleneimine, amine-modified polyepihalohydrin, and polyallylamine.