JPH051051B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention provides a semipermeable composite membrane for reverse osmosis that can be used for desalination of seawater and can water, recovery of valuables, reuse of wastewater, production of ultrapure water, etc. Relating to a manufacturing method. [Prior Art] Conventionally, semipermeable membranes that have been used industrially include asymmetric membranes made from cellulose acetate, such as the Robo membrane described in U.S. Pat. No. 3,133,132 and U.S. Pat. There is a type membrane. 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 into practical use in a wide range of applications. Research into new materials that eliminate the drawbacks of these asymmetric cellulose acetate membranes is being actively conducted mainly in the United States and Japan, but aromatic polyamides, polyamide hydrazide (US Pat. No. 3,567,632), polyamic acid (Japanese Patent Publication) 55-37282), crosslinked polyamic acid (Japanese Patent Publication No. 56-3769), polyimidazopyrrolone, polysulfonamide, polybenzimidazole, polybenzimidazolone, polyarylene oxide, etc. Materials that improve some of their drawbacks. However, 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 therefore become the mainstream in the development of semipermeable composite membranes. The method for manufacturing the composite membrane is described in U.S. Patent No.
Specification No. 3191815, Specification No. 3744642, Specification No. 3191815, Specification No. 3744642, Same No.
Carbonization containing an aqueous solution containing a compound having an amino group and a polyfunctional reaction reagent on a porous support membrane as disclosed in Specification No. 4039440, Specification No. 4277344, and Japanese Patent Publication No. 56-500062. There is a method of forming an ultra-thin film through interfacial reaction by bringing it into contact with a hydrogen-based solution. [Problems to be Solved by the Invention] The present inventors have arrived at the present invention as a result of extensive studies aimed at further improving the performance of such semipermeable composite membranes, particularly the water permeability. [Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration. "When manufacturing a semipermeable composite membrane having an ultra-thin membrane made of a cross-linked aromatic polyamide obtained by interfacial reaction with a porous support membrane, the ultra-thin membrane is
A method for producing a semipermeable composite membrane, which comprises contacting a chlorine-containing aqueous solution at normal pressure. ” The porous support membrane used in the present invention is a support membrane having micropores of several tens to several thousand angstroms on its surface, and is made of polysulfone, polyvinyl chloride, chlorinated vinyl chloride, polycarbonate, polyacrylonitrile, This includes known materials made from cellulose ester and the like. 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. ), or 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 mainly composed of a crosslinked aromatic polyamide, and the crosslinked aromatic polyamide contains an aromatic amine having two or more reactive amino groups, It can be obtained by interfacial reaction of polyfunctional aromatic acid halides. In the present invention, aromatic amines having two or more reactive amino groups (hereinafter abbreviated as amino compounds)
indicates an amino compound having two or more amino groups directly connected to an aromatic ring, such as metaphenylenediamine, paraphenylenediamine, 3,5-
Diaminobenzoic acid, 2,5-diaminobenzenesulfonic acid, 4,4'-diaminobenzanilide,
3,3',5,5'-tetraaminobenzanilide,
Examples include 1,3,5-triaminobenzene. These amino 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 amino 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 amino compound and the polyfunctional reaction reagent. The aqueous solution of the amino compound may be coated on the surface of the porous support membrane as long as the aqueous solution is uniformly and continuously coated on the surface. This may be carried out by a method such as immersing a 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 Examples include chloride, 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 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
- There is trifluoroethane. The concentration of the polyfunctional reaction reagent is preferably 0.01 to 10% by weight, more preferably 0.02 to 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 a pH of 6.0 to 13, the performance of the resulting semipermeable composite membrane improves, especially its water permeability. Typical examples of chlorine generating reagents include chlorine gas, salami powder, sodium hypochlorite, chlorine dioxide, chloramine B, chloramine T, halazone, dichlorodimethylhydantoin, chlorinated isocyanuric acid and its salts, etc. It is preferable to determine the concentration 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. Oxidizing power and pH of chlorine-containing aqueous solutions
There is an important relationship between the two; the more alkaline the pH, the weaker the oxidizing power. This is because the state of existence of hypochlorous acid (HClO), which has strong oxidizing power, changes depending on the pH. Hypochlorite is H ⁺ and ClO ^-
dissociates into This dissociation is affected by pH; at pH 9 or above, most hypochlorous acid exists as hypochlorite ions, and at pH 6.5, about 90% exists as undissociated hypochlorous acid. In the present invention, the preferred chlorination treatment is thought to be caused by ClO ^- ions, and at pH below 6 there is substantially no ClO ^- , which is not preferred. In addition, if the pH is high, even if ClO ^- is present, hydrolysis of the amide bond will occur and the ultra-thin film will be damaged.
Preferably, a chlorine-containing aqueous solution with a pH of 11 or less is suitably 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 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, but if the pressure difference is 0 to 1.2 Kg/ ^cm2 , the water permeation rate is negligible. If so, 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, resulting in a decrease in the crystallinity of the crosslinked aromatic polyamide. Furthermore, a semipermeable composite membrane that is not subjected to chlorine treatment has a large drop in elution exclusion rate when raw water in an acidic region, for example, pH 4, is used. The treated semipermeable composite membrane suppresses a decrease in elution exclusion rate in an acidic region. The reason for this is thought to be that the produced crosslinked aromatic polyamide is completely bonded only with amide bonds and has no aromatic rings, and some amine terminal groups ( _-NH2 ) are generated, and these terminal groups are ionized. It is thought that by chlorine treatment, the amine end group changes to chloramine (-NHCl), which is further 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 10 to 2000 ppm, and in consideration of the balance of membrane performance, the range is preferably 100 to 1000 ppm. The chlorine treatment time is 2 minutes to 20 hours. If the free chlorine concentration is low and the treatment PH is high, the treatment time is preferably long. Conversely, if the free chlorine concentration is high and the treatment PH is low, the treatment time is short. is preferred. [Example] The present invention will be specifically described below with reference to 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 in length/
inch, width 67 pieces/inch, thickness 160μ) was fixed on a glass plate, and 15% by weight of polysulfone (Udel p3500 manufactured by Union Carboid) was placed on it.
A fiber-reinforced polysulfone support (hereinafter abbreviated as FR-PS support) was prepared by casting dimethylformamide (DMF) solution to a thickness of 200μ at room temperature (20°C), immediately immersing it in pure water, and leaving it for 5 minutes. ). FR− obtained in this way
The pure water permeability coefficient of the PS support (thickness 210-215μ) is
0.005 to 0.01 when measured at a pressure of 1Kg/cm ² and a temperature of 25℃
g/ ^cm2・sec・atm. 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. After removing the excess aqueous solution from the surface of the FR-PS support, 1,1,2-trichloro-1,
Coat the surface with a solution containing 0.05% by weight of trimesic acid chloride, 0.05% by weight of terephthalic acid chloride, and 300 ppm of dimethylformamide as polyfunctional reaction reagents in 2,2-trifluoroethane so that the surface is completely wet, and leave it for 1 minute. did. 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 a reverse osmosis test using 1500 ppm saline solution adjusted to pH 6.5 as raw water at 15 kg/cm ² and 25°C, the membrane performance shown in Table 1 was obtained. Examples 4 to 6, Comparative Example 2 In Examples 1 to 3 and Comparative Example 1, the samples were immersed for 5 minutes in an aqueous solution having a free chlorine concentration of 500 ppm and adjusted to the pH shown in Table 2. 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
The performance of composite membranes obtained by immersing in an aqueous solution adjusted to 1000 ppm and pH 10.5 for the time shown in Table 3, and otherwise obtained in the same manner is shown. Example 10 Composite membranes obtained in Comparative Example 1 and Examples 1 to 3 were
Use 1500ppm saline solution adjusted to PH4.0 as raw water15
As a result of reverse osmosis test under the conditions of Kg/cm ² and 25℃,
The membrane performance shown in Table 4 was obtained. Example 11 The composite membranes obtained in Comparative Example 1 and Example 2 were heated to PH6.5,
As a result of a reverse osmosis test using 1500 ppm saline solution adjusted to a chlorine concentration of 10 ppm as raw water at 15 kg/cm ² and 25° C. for 300 hours, the membrane performance shown in Table 5 was obtained. Example 12, Comparative Example 3 In Example 2 and Comparative Example 1, a 2% by weight aqueous solution of metaphenylenediamine was used as the amino compound, and 0.1% by weight of 1,1,2- trimesic acid chloride was used as the polyfunctional reaction reagent. trichloro-1,
A composite membrane was obtained in the same manner except for using a 2,2-trifluoroethane solution. Membrane performance is shown in Table 6. As shown in the above examples, in the present invention, the water permeation rate is 1.1 compared to the conventional composite membrane manufacturing method.
Improved by ~4.0 times.

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〔Effect of the invention〕

According to the manufacturing method of the present invention, when manufacturing a composite membrane, the performance of the composite membrane, especially water permeability, is improved by contacting the ultra-thin membrane with a chlorine-containing aqueous solution with a pH of 6.0 to 13 at normal pressure. do.

Claims (1)

[Claims] 1. When producing a semipermeable composite membrane having a porous support membrane and an ultra-thin membrane made of crosslinked aromatic polyamide obtained by interfacial reaction, the ultra-thin membrane is heated to pH 6.0.
A method for producing a semipermeable composite membrane, which comprises bringing it into contact with a chlorine-containing aqueous solution of ~13 at normal pressure.