JPS63123406A - Manufacture of semipermeable composite membrane - Google Patents

Abstract

PURPOSE:To enhance the performance of a composite membrane by treating specifically a super-thin film in preparing a semipermeable composite membrane consisting of a porous substrate membrane and a super-thin film constituted mainly of crosslinking polypiperazine amide. CONSTITUTION:In preparing a semipermeable composite membrane consisting of a porous substrate made from polysulfone or the like as stock, having micropores of several tens - several thousands of Angstrom on its surface and a super-thin film of crosslinking polypiperazine amide prepared by the interface reaction of amine carrying two or more secondary amino radicals and a polyfunctional aromatic acid halide, said super-thin film is contacted with water solution containing chlorine of pH 1.0-10 in a state of no pressure difference between both faces of the membrane under the normal pressure giving penetrating flow to the membrane. As a result, the performance of the semipermeable composite membrane, thus prepared particularly salt elution eliminating ratio, can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a semipermeable composite membrane for permselectively separating components of a liquid mixture.

[Conventional technology]

Examples of coating an active layer directly on a porous support membrane include U.S. Pat. No. 3.744.642 and U.S. Pat. No. 3.926.7.
Specification No. 98, JP-A-55-147106, JP-A-53-pH10/16, JP-A-58-2430
In order to achieve high water permeability with this type of composite membrane, the active layer is coated very thinly, so defects are likely to occur due to scratches on the porous support membrane or foreign matter, and it is generally difficult for the industry to achieve high water permeability. It is said that it is difficult to obtain high-performance membranes stably and reproducibly in commercial production.

However, there are many membranes that are said to have chlorine resistance, heat resistance, and chemical resistance, and recently a highly permeable composite membrane in which piperazine is crosslinked with an aromatic polyfunctional acid halide has been proposed and has attracted attention.

(For example, Japanese Patent Publication No. 56-500062, U.S. Patent No. 4.259.183, PB Report 8O-12
7574) Improvements to this piperazine-based composite membrane are also being studied. (For example, JP-A-59-179103, JP-A-57-27101, JP-A-57-27102, JP-A-57-5565) [Problems to be solved by the invention] However, Although this piperazine-based composite membrane has high permeability at low pressure, the sodium chloride rejection rate is 50%.
There was a practical problem in the desalination process because it was as low as about 1.5%. Particularly, in the production of ultrapure water used in the production of semiconductors, there has been a problem in the ability to remove organic components due to this low rejection rate.

In addition, the composite membranes that have been studied for improvement have almost the same performance as the above-mentioned membranes, and also have poor water permeability, resulting in unsatisfactory results.

The present inventors have arrived at the present invention as a result of intensive studies on improving the performance of such semipermeable composite membranes.

[Means for solving problems] In order to achieve the above object, the present invention consists of the following configuration.

That is, in the present invention, when producing a semipermeable composite membrane having an ultra-thin membrane made of cross-linked polypiperazine amide obtained by interfacial reaction with a porous support membrane, the ultra-thin membrane is adjusted to pH'1.
．． The present invention relates to a method for producing a semipermeable composite membrane, which is characterized by contacting with an aqueous solution containing chlorine of O to 10 at normal pressure.

The porous support membrane used in the present invention is a support membrane having micropores of several tens to several angstroms on its surface, and is made of polysulfone, polyvinyl chloride, chlorinated vinyl chloride, polycarbonate, polyacrylonitrile, cellulose. This includes known materials made from esters and the like. Among these, porous polysulfone support membranes are particularly effective in the present invention.

Porous polysulfone membranes can be formed by casting polysulfone in a solution in an aprotic polar solvent such as dimethylformamide onto a nonwoven fabric, and then coagulating it in a medium consisting essentially of water. (
gelation), so-called wet film forming. The porous polysulfone thus obtained has micropores on the surface having a size of several tens to several hundred angstroms and increasing in size from the front surface to the back surface.

In the present invention, the ultra-thin film obtained by interfacial reaction is
The main component is cross-linked polypiperazine amide,
The crosslinked polypiperazine amide can be obtained by an interfacial reaction between an amine having two or more secondary amino groups and a polyfunctional aromatic acid halide.

In the present invention, piperazine has the following structural formula and also has the following structural formula:
5 to 1 carbon atoms having two or more secondary amino groups in one molecule
The polyfunctional amine having 5 and a ring structure is, for example, represented by the following structural formula.

HO-CH2-CH(I)H, HO-CHp-CHz-
CHa-CNH Particularly preferred among these is 1.3
-di(4-piperidyl)-propaneulC)-tC
)+2>, -C>)l.

What is important here is that for piperazine, 2
It is the ratio of polyfunctional amine having a ring structure having two or more grade amino groups, and the weight ratio is 0 to 1 piperazine.
．． It is preferable that it is 05 to 0.7, and roughly 0.1
-0.5 is preferable in view of the balance between membrane performance, desalination rate, and amount of water produced.

The polyfunctional reagent may be any agent that can react with the secondary amine to form a crosslinked polyamide or polyurea, such as trimesic acid halide, benzophenone tetracarboxylic acid halide, trimellitic acid halide, etc. Halide, birometic acid halide, isophthalic acid halide, terephthalic acid halide, naphthalene dicarboxylic acid halide, diphenyldicarboxylic acid halide,
Pyridinedicarboxylic acid halide, benzenedisulfonic acid halide, benzenedisulfonic acid halide, tolylene diisocyanate, bis(P-isocyanate phenyl)
Examples include methane, but trimesic acid chloride, isophthalic acid chloride, terephthalic acid chloride, and mixtures thereof are preferred from the viewpoint of solubility in the membrane forming solvent and performance of the composite reverse osmosis membrane.In particular, from the viewpoint of durability, crosslinked structures are preferred. Trimesoyl chloride is preferred in terms of the introduction of.

In the composite reverse osmosis membrane of the present invention, at least one side of a porous support membrane is coated with an aqueous solution (hereinafter collectively referred to as a composition) containing the piperazine and a secondary amine having a ring structure as main components, and then air-dried and/or Alternatively, after evaporating some or all of the water by heat treatment, a solution mainly composed of a polyfunctional reagent dissolved in a solvent that is immiscible with water and does not dissolve the porous support membrane is applied. , obtained by carrying out a crosslinking reaction and then drying.

The component concentration of the composition for obtaining the composite reverse osmosis membrane of the present invention is 0.1 for the piperazine and the secondary amine having a ring structure.
-10% by weight, preferably 1-4% by weight, and the composition ratio of piperazine and secondary amine having a ring structure is 0.1% by weight of the secondary amine having a ring structure per 1-fold ω part of piperazine.
The amount is preferably 0.5 parts by weight from the viewpoint of membrane performance.

Furthermore, it is effective to add a surfactant to improve the wettability of the composition to the surface of the porous support membrane and make it adhere uniformly.Among them, anionic surfactants are preferred, such as sodium dodecyl sulfate and sodium alkylbenzene sulfonate. Although sodium alkyl diphenyl ether disulfonate is particularly effective in obtaining a membrane with good performance. The surfactant is generally preferably used in an amount of about 0.01 to 2% by weight. A water-soluble organic solvent that does not deteriorate the porous support membrane may be added to these compositions. Additionally, the effect may be further enhanced by adding an alkaline metal compound, such as sodium phosphate.

The polyfunctional reagent is usually used by dissolving 0.01 to 2.0% by weight in n-hexane, trichlorotrifluoroethane, or the like.

Any of the five known coating methods can be applied to coating the porous support membrane with the composition, such as coating the composition on the support membrane, dipping the support membrane in the composition, etc. can be mentioned. Among these methods, the method of coating the composition is preferable from the viewpoint of uniform coating on one side of the porous support membrane, and also from the viewpoint of workability. When the porous support membrane is immersed in the composition, it is preferable to take measures in advance to prevent the composition from adhering to the other side of the porous support membrane in the coating step. In such a coating process, a draining process is generally provided to remove excess composition. As a method for draining the liquid, for example, there is a method of holding the membrane surface vertically and allowing it to flow down by gravity.

The coated porous support membrane is dried using air drying or a heated dryer, etc., usually in the range of room temperature to 150°C, and the drying speed varies depending on the method, that is, the heat introduction method or the type of dryer. Therefore, select a time period of 1 to 60 minutes accordingly. A water-immiscible solution of a polyfunctional reagent is applied to a colander, the liquid is drained off, and a semipermeable membrane is obtained by air drying or heat treatment.

This drying step is usually carried out at a temperature ranging from room temperature to 150°C,
The time is determined depending on the temperature. In this way, an ultra-thin film of cross-linked polypiperazine amide is formed.

When this ultra-thin membrane is immersed in a chlorine-containing aqueous solution with a pH of 1.0 to 10, the performance of the resulting semipermeable composite membrane is improved, particularly the elution exclusion rate. Chlorine generating reagents include chlorine gas, salami powder, sodium hypochlorite, chlorine dioxide, and chloramine B.
Typical examples include chloramine T1 halazone, dichlorodimethylhydantoin, chlorinated isocyanuric acid and its salts, and the concentration is preferably determined depending on the strength of oxidizing power. Among the above-mentioned chlorine generating reagents, a sodium hypochlorite aqueous solution is preferred from the viewpoint of ease of handling. There is an important relationship between the oxidizing power and pH of a chlorine-containing aqueous solution, and the more alkaline II is, the weaker the oxidizing power becomes. This is hypochlorous acid (HCαO), which has strong oxidizing power.
This is because its state of existence changes depending on the pH.

Hypochlorite dissociates into H+ and CQO-. This dissociation occurs at pH
At pH 6.5, hypochlorous acid mostly exists as hypochlorite ion at p) -19 or higher, and at pH 6.5 it is approximately 9
0% is present as undissociated hypochlorous acid.

In the present invention, the preferable chlorination treatment is thought to be caused by ICQO, and at pH 10 or higher, substantially HCrL
O is not present and is not preferred. In addition, if the pH is high, hydrolysis of amide bonds will occur and the ultra-thin film will be damaged.
A chlorine-containing aqueous solution having a pH of 13 or less, preferably 10 or less is suitably used.

Further, in the present invention, the chlorine treatment must be carried out at normal pressure. Atmospheric pressure means that there is no pressure difference between the two sides of the membrane that would provide a permeate flow to the membrane, and does not simply mean that the process is carried out under atmospheric pressure. For example, there is no problem if the pressure on both sides of the membrane is equal. However, the chlorine treatment can be carried out by simply immersing the membrane in a chlorine-containing aqueous solution, and considering this point, there is no need to apply pressure in an autoclave or the like.

In addition, there is a pressure difference on both sides of the membrane, and if water is permeated while being treated with chlorine, the water permeability will generally decrease, which is undesirable. If so, no particular problem will occur.

Chlorination improves the elution exclusion rate.

In addition, water permeability is reduced to such an extent that it does not pose a problem for practical use. Compared to a semipermeable composite membrane without chlorination, the organic component rejection rate is improved and the degree of deterioration of water permeability over time is reduced. The reason for this is that the produced crosslinked polypiperazine amide is not completely bonded only through amide bonds, but has secondary amine terminal groups (>NH>) in some parts.

It is thought that by performing the chlorine treatment, the secondary amine terminal group changes to chloramine (>NCQ), which is further decomposed and reduced, thereby stabilizing the molecular structure of the ultra-thin film layer.

When using sodium hypochlorite as a chlorination agent, the concentration of free chlorine is 10 to 2 oooppm.

Considering the balance of membrane performance, 100 to 1000 ppm
A range of is preferred.

Chlorination time is 2 minutes to 20 hours, free chlorine concentration is low,
When the treatment pH is high, a long treatment time is preferred; on the other hand, when the free chlorine concentration is high and the treatment pH is low, a short treatment time is preferred.

[Examples] The present invention will be specifically explained below using Examples, but the present invention is not limited thereto.

In the following examples, the rejection rate of common salt as selective separation performance was determined by conventional means by measuring electrical conductivity.

In addition, as permeation performance, the water permeation rate was determined by the amount of water permeation per unit area and unit time. Roughly speaking, the degree of deterioration of the transmission performance was shown using m defined by the following formula.

log (J2/Jl) 10(] (T2/TI) Jl: Amount of water permeated after Tt waiting time J2: Amount of water permeated after T2 hours T2 > TI reference example Polyester fiber with a size of 30 cm vertically and 20 cm horizontally Taffeta (multifilament yarn of 150 denier both warp and weft, weave density 90 pieces/inch)
A 16% dimethylformamide (DMF) solution of polysulfone (manufactured by Union Carbide, trade name: Udel P-3500) was fixed at 200 μm on a glass plate. A fiber-reinforced polysulfone support membrane (hereinafter abbreviated as FR-PS support membrane) is produced by casting the membrane at room temperature (20'C) to a thickness of 200C, immediately immersing it in pure water, and leaving it for 5 minutes.

The FR-PS support film thus obtained (thickness: 21
0~215μ) pure water permeability coefficient at a pressure of 1kpH/cl
Measured at TfS temperature 25°C 09OO5~0°01
CI/cJ-sec-atm.

Examples 1 to 4, Comparative Example 1 1.0% by weight of piperazine, 0.2% by weight of 1,3-di(4-piperidyl)-propane, and sodium alkyl diphenyl ether disulfonate were added to the FR-PS support membrane obtained in the reference example. 0.5% by weight, trisodium phosphate 1
．． Apply an aqueous solution (composition) containing 0% by weight and heat at 70'C.
It was dried with hot air for 1 minute.

Thereafter, a solution of 0.5% by weight/volume of a mixture of isophthalic acid chloride and trimesic acid chloride (dew ratio 4:1) dissolved in trichlorotrifluoroethane was applied, and then treated with hot air at 100'C for 5 minutes. .

The composite membrane thus obtained was immersed for 5 minutes in an aqueous solution containing free chlorine and adjusted to pH 7.0 as shown in Table 1, and then washed with running water. 7. Next, this composite membrane was treated with 500 pl)m of saline solution adjusted to pH 6.5 as raw water.
As a result of performing a reverse osmosis test for 20 hours under conditions of 5kMo(, 25°C), the membrane performance shown in Table 1 was obtained.

Examples 5 to 8, Comparative Example 2 In Examples 1 to 4, the samples were immersed for 5 minutes in an aqueous solution adjusted to I)H shown in Table 2 using an aqueous solution with a free chlorine concentration of 500 pl)m. The other properties show the performance of the 1q composite membrane in the same manner.

Example 9 - pH In Examples 1 to 3, the free chlorine concentration was 500 pl) m,
I) immersed in an aqueous solution adjusted to 810 for the time shown in Table 3,
The numbers indicate the performance of composite membranes obtained in the same manner.

Example 12 Using the composite membranes obtained in Example 3 and Comparative Example 1, a reverse osmosis test was conducted for 200 hours under the same conditions as Examples 1 to 4 and Comparative Example 1. The results are shown in Table 4.

Example 13 Using the composite membrane obtained in Example 3 and Comparative Example 1, ioo
7.5k using oppm isopropyl alcohol as raw water
(J/cnf, reverse osmosis test was conducted for 20 hours under the conditions of 25°C. The results are shown in Table 5.

Example 14, Comparative Example 3 A composite membrane was obtained in the same manner except that 1,3-di(4-piperidyl)-propane in the composition of Example 3 and Comparative Example 1 was adjusted to 0% by weight and 1%. Membrane performance is shown in Table 6.

Table 1 Table 2 Table 5 Table 6 [Effects of the invention] In the present invention, the salt rejection rate is improved by 10% compared to the conventional composite membrane manufacturing method, and the organic component rejection rate is improved, and the water It is now possible to provide a membrane with a small degree of permeability deterioration.

Claims (1)

[Claims] When producing a semipermeable composite membrane having a porous support membrane and an ultra-thin membrane mainly composed of cross-linked polypiperazine amide obtained by interfacial reaction, the ultra-thin membrane is heated to pH 1.0 to 1.
1. A method for producing a semipermeable composite membrane, which comprises contacting an aqueous solution containing 0 chlorine at normal pressure.