JPS6354905A - Production of semiosmosis composite membrane - Google Patents

Abstract

PURPOSE:To obtain a reverse-osmosis membrane with improved performance, especially water permeability, of the title composite membrane by bringing an ultrathin membrane consisting of cross-linked aromatic polyamide obtained by an interface reaction into contact with an aq. chlorine-contg. soln. at 6-13pH under ordinary pressure. CONSTITUTION:The ultrathin membrane is obtained by the interface reaction between an aromatic amine having >=2 reactive amino groups and a multifunctional aromatic acid halide. when the ultrathin membrane is dipped in the aq. chlorine-contg. soln. at 6.0-1.3pH, the performance, especially water permeability, of the obtained semipermeable composite membrane is improved. Gaseous chlorine, bleaching powder, sodium hypochlorite, chlorine dioxide, chloramine B, etc., are used as the chlorine generating reagent. The chlorine treatment must be carried out under ordinary pressure, and only the dipping of the membrane in the aq. chlorine-contg. soln. is required. The concn. of free chlorine is preferably controlled to 10-2,000ppm, and the treating time is adjusted to 2min-20hr.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is directed to reverse osmosis, which can be used for the desalination of seawater and can water, the recovery of valuables, the reuse of wastewater, the production of ultrapure water, etc. The present invention relates to a method for producing a semipermeable composite membrane for use in a semi-permeable composite membrane.

(Prior Art) Conventionally, semipermeable membranes that have been used industrially include asymmetric membranes made from cellulose acetate, such as those disclosed in U.S. Patent No. 3,
There are lob-type membranes described in Patent No. 133.132 and Patent No. 3.133,137.

However, this membrane has problems with hydrolysis resistance, microbial resistance, chemical resistance, etc. In particular, when trying to improve permeability, it is not possible to manufacture a membrane that has both pressure resistance and durability, so it is not used in some cases. However, it has not yet been put to practical use in a wide range of applications. Research into new materials that eliminate these drawbacks of cellulose acetate asymmetric membranes is being actively conducted mainly in the United States and Japan, but aromatic polyamides, polyamide hydrazide (U.S. Pat. No. 3,567,632), polyamide Acid (Japanese Patent Publication No. 55-37282), crosslinked polyamide 1v2 (Japanese Patent Publication No. 56-3769), polyimidazopyrrolone, polysulfonamide, polybenzimidazole, polybenzimidacylon, polyarylene oxide, etc. Although a material that improves the drawbacks has been obtained, it is inferior to cellulose acetate membranes in terms of selective separation and permeability.

On the other hand, a composite membrane has been developed in which a porous support membrane is coated with an ultra-thin membrane that exhibits substantial membrane performance as a semipermeable membrane different from the lobe type. For composite membranes, it becomes possible to select the optimal material for each application for ultra-thin membranes and porous support membranes, increasing the degree of freedom in membrane manufacturing technology. It also has the advantage of being able to be stored in a dry state, unlike the lobe type, which must be stored in a wet state at all times.

Among such composite membranes, ultra-thin composite membranes made of polyamide or polyurea have high membrane performance, particularly water permeability, and have become the mainstream in the development of semipermeable composite membranes. The method for manufacturing the composite membrane is described in U.S. Pat. No. 3,191.815;
Specification No. 3,744,642, No. 4,039,4
40, No. 4,277.344, and Japanese Patent Application Publication No. 56-500062, an aqueous solution containing a compound having a 7-mino group and a polyfunctional compound on a porous support membrane. There is a method of contacting a hydrocarbon solution containing a reaction reagent to form an ultra-thin film through an interfacial reaction.

[Problem that the invention seeks to solve]

The present inventors have conducted intensive studies to improve the performance of such semipermeable composite membranes, particularly to further improve water permeability, and as a result, they have arrived at the present invention.

[Means for solving problems]

In order to achieve the above object, the present invention consists of the following configuration.

"When producing a semipermeable composite membrane having an ultra-thin membrane made of a cross-linked aromatic polyamide obtained by an interfacial reaction with a porous support membrane, the ultra-thin membrane is brought into contact with a chlorine-containing aqueous solution of 116.0 to 13 at normal pressure. A method for producing a semipermeable composite membrane characterized by , polyvinyl chloride, chlorinated vinyl chloride, polycarbonate, polyacrylonitrile, cellulose ester, and other known materials. Among these, porous polysulfone support membranes are particularly effective in the present invention.

Porous polysulfone films are produced by casting polysulfone as a solution in an aprotic polar solvent such as dimethylformamide onto a woven or nonwoven fabric made of polyester fibers, and then coagulating (gelling) in a medium consisting essentially of water. )
This is done by 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 a crosslinked aromatic polyamide, which can be obtained by an interfacial reaction between an aromatic amine having two or more reactive amino groups and a polyfunctional aromatic acid halide. .

In the present invention, the aromatic amine having two or more reactive 7-mino groups (hereinafter abbreviated as amino compound) refers to an amino compound having two or more amino groups directly connected to an aromatic ring, such as metaphenylene Diamine, paraphenylenediamine, 3,5-diaminobenzoic acid, 2,5-diaminobenzenesulfonic acid, 4.4°-diaminobenzanilide, 3,3°,5.5'-tetraaminobenzanilide, 1,3 .5-triaminobenzene and the like can be exemplified. These amine compounds are generally subjected to the interfacial reaction in the form of an aqueous solution, and the concentration of the amino compound in the aqueous amine compound solution is 0.1 to 10% by weight, preferably 0.5 to 5.0% by weight. . Further, the amino compound aqueous solution may contain a surfactant, an organic solvent, etc. as long as they do not interfere with the reaction between the amine compound and the polyfunctional reaction reagent.

The surface of the porous support membrane may be coated with the amine compound aqueous solution as long as the surface is uniformly and continuously coated with the aqueous solution.
The coating may be carried out by any known coating means, such as coating the surface of the porous support membrane with the aqueous solution or immersing the porous support membrane in the aqueous solution.

The polyfunctional aromatic acid halide in the present invention refers to a compound having two or more acyl halide groups directly connected to an aromatic ring (hereinafter referred to as a polyfunctional reaction reagent), such as trimesic acid chloride, benzophenonetetracarboxylic acid chloride, Examples include trimellitic acid chloride, pyromellitic acid chloride, isophthalic acid chloride, terephthalic acid chloride, naphthalenedicarboxylic acid chloride, diphenyldicarboxylic acid chloride, pyridinedicarboxylic acid chloride, benzenedisulfonic acid chloride, etc., but their solubility in the membrane forming solvent and In consideration of the performance of the semipermeable composite membrane, trimesic acid chloride, isophthalic acid chloride, and terephthalic acid chloride are preferred.

These polyfunctional reaction reagents are generally dissolved in a water-immiscible solvent and subjected to an interfacial reaction, and the solvent is inert to the amino compound and the polyfunctional reaction reagent and water It must be insoluble or poorly soluble in Furthermore, it is preferable that the solvent is inert to the porous support membrane. Typical examples of such solvents include liquid hydrocarbons and halogenated hydrocarbons, such as pentane, hexane,
Heptane, 1,1.2-trichloro-1,2,2-trifluoroethane. The concentration of the polyfunctional reaction reagent is preferably o, oi to 10% by weight, more preferably 0.02
~2% by weight.

The method for contacting the polyfunctional reaction reagent with the aqueous amino compound solution phase may be carried out in the same manner as the method for coating the porous support membrane with the aqueous amino compound solution.

When such an aqueous solution of an amino compound and a solution of a polyfunctional reaction reagent are brought into contact with each other on a porous support membrane, an ultra-thin film of crosslinked aromatic polyamide is formed at the interface due to an interfacial reaction.

When this ultra-thin membrane is immersed in a chlorine-containing aqueous solution with pI-(6,0 to 13), the performance of the resulting semipermeable composite membrane, especially water permeability, is improved. Representative examples include sodium hypochlorite, chlorine dioxide, chloramine B, chloramine T, halazone, dichlorodimethylhydantoin, chlorinated isocyanuric acid and its salts, and the concentration is determined depending on the strength of oxidizing power. is preferred.Among the above chlorine generating reagents, 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 the chlorine-containing aqueous solution, and II is on the alkaline side. I see, the oxidizing power becomes weaker.This is due to the strong oxidizing power of hypochlorous acid (HCD).
This is because the state of existence of O) changes depending on the pH. Hypochlorite dissociates into H+, cD, and o-. This dissociation is affected by pH; at pH 9 or higher, hypochlorous acid mostly exists as hypochlorite ion, and at pH 6.5, about 90% or less exists as hypochlorous acid, which does not dissociate.

In the present invention, the preferable chlorination treatment is thought to be caused by CD, O- ions, and below DH6, substantially CQ
O- does not exist, which is not preferable. Also, if the pH is high, CQ
Even if O- is present, the amide bond will be hydrolyzed and the ultra-thin film will be damaged.
An aqueous solution containing 1 or less chlorine is preferably used.

Further, in the present invention, it is essential that the chlorine treatment be carried out at normal pressure, and chlorine treatment under increased pressure will give unfavorable results. 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 as long as both sides of the membrane are equally pressurized.

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. However, if the pressure difference is O ~ 1.2 kq/-, water velocity overspeed can be ignored. If it is only a small amount, no particular problem will occur.

Chlorination improves water permeability. The reason for this is thought to be that the amide hydrogen of the produced crosslinked aromatic polyamide is replaced by chlorine, which reduces the crystallinity of the crosslinked aromatic polyamide.

In addition, semipermeable composite membranes without chlorine treatment can be used in acidic regions.
For example, when raw water with a pH of 4 is used, the elution exclusion rate is greatly reduced. The treated semipermeable composite membrane suppresses a decrease in elution exclusion rate in an acidic region. The reason for this is that the crosslinked aromatic polyamide produced is completely amide bonds with no aromatic rings, and some of the amine-terminated polyamides have u(-NH
This is thought to be because 2) occurs and this terminal group is ionized. It is thought that by chlorine treatment, the amine end group changes to chloramine (-NHCD), which is roughly decomposed and reduced, thereby suppressing the decrease in elution exclusion rate in the acidic region.

When using sodium hypochlorite as the chlorination agent, the concentration of free chlorine is preferably in the range of 10 to 2000 pl) m, and in consideration of the balance of membrane performance, in the range of 100 to 11000 pp.

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

〔Example〕

The present invention will be specifically explained below using Examples.

Examples 1 to 3, Comparative Example 1 Taffeta made of polyester fibers with a length of 30 cm and a width of 20 cm (multifilament yarn of 150 denier in both warp and weft, weaving density of 90 pieces/inch in length,
A 15% dimethylformamide (DMF) solution of polysulfone (Lldel P3500 manufactured by Union Carboid Co., Ltd.) was fixed on a glass plate to a thickness of 200 μm at room temperature ( 2
A fiber-reinforced polysulfone support (
A FR-PS support (hereinafter abbreviated as FR-PS support) is produced. The FR-PS support obtained in this way (thickness 210-215μ
) has a pure water permeability coefficient of 0.005 to 0.01 C1/- sec ・atm measured at a pressure of 11/-1 and a temperature of 25°C.
Met.

The FR-PS support was immersed as an amino compound in a mixed aqueous solution of 1% by weight of metaphenylenediamine and 1% by weight of 1,3.5-triaminobenzene for 2 minutes. FR-PS
After removing the excess aqueous solution from the support surface, 1,1
．． Trimesic acid chloride 0.0 as a polyfunctional reaction reagent to 2-trichloro-1,2,2-trifluoroethane
A solution containing 5% by weight of terephthalic acid chloride, 0.05% by weight of terephthalic acid chloride, and 300 ppm of dimethylformamide was coated so that the surface was completely wetted and allowed to stand for 1 minute. Next, the membrane was turned vertically to remove excess solution by draining, and then immersed in an aqueous solution containing 0.2% by weight of sodium carbonate for 5 minutes. The solution contained in the membrane was removed with tap water.

The composite membrane thus obtained was immersed in an aqueous solution containing free chlorine shown in Table 1 and adjusted to pH 7.0 for 5 minutes, and then washed with tap water. As a result of performing a reverse osmosis test using 1500 ppm saline solution adjusted to pH 6.5 as raw water under conditions of 15 to 9/cnt and 25°C, the membrane performance shown in Table 1 was obtained.

Examples 4 to 6, Comparative Example 2 In Examples 1 to 3, free chlorine concentration 5001)I)m
The sample was immersed in an aqueous solution whose pH was adjusted to the pH shown in Table 2 for 5 minutes. Other composite membranes were obtained in the same manner.

Membrane performance is shown in Table 2.

Examples 7-9 In Examples 1-3, free chlorine concentration 10001)l)
The performance of composite membranes obtained by immersion in an aqueous solution adjusted to m, 1110.5 for the time shown in Table 3, and otherwise obtained in the same manner is shown.

Example 10 Composite membranes obtained in Comparative Example 2 and Examples 1 to 3 were treated at pH 4,
Using 150 ppm saline solution adjusted to 0 as raw water, 15
As a result of a reverse osmosis test under the conditions of ki/cJ and 25°C, the membrane performance shown in Table 4 was (q).

Example 11 The composite membrane obtained in Comparative Example 1 and Example 2 was treated with 1500 pl) m of saline solution adjusted to pH 6°5 and chlorine concentration 1101) l) as raw water under conditions of 15) cv/cJ and 25°C. So 3
As a result of the 00 hour reverse osmosis test, the membrane performance shown in Table 5 was obtained.

Example 12, Comparative Example 3 In Examples 1 to 3 and Comparative Example 1, a 2% by weight aqueous solution of metaphenylenediamine was used as the amino compound, and 0.1 ff of trimesic acid chloride was used as the polyfunctional reaction reagent.
A composite membrane was obtained in the same manner except that a lffi% 1,1,2-trichloro-1°2,2-trifluoroethane solution was used.

Membrane performance is shown in Table 6.

As shown in the above examples, in the present invention, the water permeation rate was improved by 1.1 to 4.0 times as compared to the conventional method for manufacturing composite membranes.

Table 1 Table 2 Table 3 Table 4 Example 10 Table 5 [Effects of the invention] According to the manufacturing method of the present invention, when manufacturing a composite membrane, the ultra-thin membrane is constantly immersed in a chlorine-containing aqueous solution with a pH of 6.0 to 13. Pressure contact improves the performance of the composite membrane, especially water permeability.

Claims (1)

[Claims] When producing a semipermeable composite membrane having a porous support membrane and an ultra-thin membrane made of cross-linked aromatic polyamide obtained by interfacial reaction, the ultra-thin membrane is constantly immersed in a chlorine-containing aqueous solution with a pH of 6.0 to 13. A method for producing a semipermeable composite membrane characterized by contacting with pressure.