Method for producing highly permeable composite reverse osmosis membrane

Abstract: Disclosed is a method for producing a composite reverse osmosis membrane comprising the steps of coating a porous support with (A) a solution containing a compound having at least two reactive amino groups per molecule and bringing (B) a solution containing a polyfunctional acid halide into contact with the solution (A) to induce crosslinking to form a crosslinked polyamide skin layer, in which the crosslinking is carried out in the presence of a substance having a solubility parameter of 8 to 14 (cal/cm 3 ) 1/2 . The resulting composite reverse osmosis membrane exhibits high salt rejection and high water permeability.

Description: This invention relates to a method for producing a composite reverse osmosis membrane for selectively separating a component of a liquid mixture. More particularly, it relates to a method for producing a composite reverse osmosis membrane which is composed of a porous support having a thin film consisting mainly of a polyamide and which exhibits both high salt rejection and high permeability. The composite reverse osmosis membrane is suitable for production of ultra-pure water or desalting of seawater or brackish water. It makes a contribution to water reclamation in a closed system, in which waste water which would cause environmental pollution, such as waste water from dyeing or waste water from electrodeposition coating, is treated to remove contaminants or to recover effective substances. It is also useful for concentration of an effective ingredient in food industry. A composite reverse osmosis membrane composed of a porous support having formed thereon a thin film capable of selective separation is known as a reverse osmosis membrane, which is structurally different from an asymmetric composite reverse osmosis membrane. At present, many composite reverse osmosis membranes each having formed on a support a thin film comprising a polyamide obtained by interfacial polymerization of a polyfunctional aromatic amine and a polyfunctional aromatic acid halide are known, e.g., in JP-A-55-147106 (corresponding to US-A-4,277,344), JP-A-62-121603 (corresponding to US-A-4,761,234), and JP-A-63-218208 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). In addition, a support having thereon a polyamide thin film obtained by interfacial polymerization of a polyfunctional aromatic amine and a polyfunctional alicyclic acid halide has also been proposed as disclosed, e.g., in JP-A-61-42308 (corresponding to US 4 520 044 A) and in US-A-5,254,261. The conventional composite reverse osmosis membranes have high desalting performance and water permeability, and yet it has been demanded to improve the water permeability while retaining the high desalting performance for attaining higher efficiency. While various additives have been proposed as described, e.g., in JP-A-2-187135 (corresponding to US-A-4,872,984) in order to meet the demand, the conventional composite reverse osmosis membranes are insufficient, still leaving the demand for higher water permeability unfulfilled. EP-A-498596 discloses a method for producing a composite reverse osmosis membrane by interfacial polymerization comprising coating a porous support with a solution (A) containing a compound having at least two reactive amino groups per molecule and bringing a solution (B) containing a polyfunctional acid halide into contact with solution (A) to form a crosslinked polyamide layer. The crosslinking is carried out in the presence of a substance which is added to solution (B) in an amount of 1 to 25%, preferably 5 to 10%, said substance including ethers such as methyl t-butylether and dimethyl ether. US-A-4772394 discloses a similar method whereby alcohols such as ethanol, propanol isomers (e.g. isopropanol) and butanols are added to solution (A). According to the method disclosed in US-A-4772394 the solutions (A) and (B) are contacted at ambient temperature and curing is effected at a temperature from ambient temperature up to 150°C, preferably at 70°C. The object of the present invention is to provide a method for producing a composite reverse osmosis membrane possessing both high salt rejection and high water permeability. The object of the present invention is accomplished by a method for producing a composite reverse osmosis membrane by interfacial polymerization comprising the steps of coating a porous support with (A) a solution containing a compound having at least two reactive amino groups per molecule and bringing (B) a solution containing a polyfunctional acid halide into contact with the solution (A) to induce a crosslinking reaction to form a crosslinked polyamide skin layer, wherein the step of bringing solutions (A) and (B) into contact with each other to induce the crosslinking reaction is conducted at a temperature of 30 to 90°C, and wherein the crosslinking reaction is carried out in the presence of an alcohol and/or an ether having a solubility parameter of 16.4·10 3 to 28.7·10 3 (J/m 3 ) 1/2 [8 to 14 (cal/cm 3 ) 1/2 ] selected from the group consisting of ethanol, propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, t-amyl alcohol, isoamyl alcohol, isobutyl alcohol, isopropyl alcohol, undecanol, 2-ethylbutanol, 2-ethylhexanol, octanol, cyclohexanol, tetrahydrofurfuryl alcohol, t-butanol, benzyl alcohol, 4-methyl-2-pentanol, 3-methyl-2-butanol, pentyl alcohol, allyl alcohol, ethyl isoamyl ether, ethyl t-butyl ether, ethyl benzyl ether, diisoamyl ether, diisopropyl ether, diglycidyl ether, diphenyl ether, dibutyl ether, dipropyl ether, dibenzyl ether, dimethyl ether, dichloroethyl ether, butyl phenyl ether, methyl t-butyl ether, monodichlorodiethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether and diethylene glycol monobutyl ether, with the proviso that when the substance is added to solution B, it is added in an amount of 0.001 to 10 % by weight. Preferred embodiments of the present invention are set forth in the sub-claims. In the following the above alcohols and ethers are simply referred to as "substance S". The term "solubility parameter" as used herein denotes the value (ΔH/V) 1/2 (J/m 3 ) 1/2 ((cal/cm 3 ) 1/2 ), wherein ΔH is the molar heat of evaporation (J/mol) ((cal/mol)) of a liquid, and V is the molar volume (m 3 /mol) ((cm 3 /mol)). The solubility parameter can be obtained, for example, according to the method described in the item "Solubility Parameter Values" of "Polymer Handbook", third edition, edited by J. Brandrup and E.H. Immergut and published by John Willey & Sons, Inc. in 1989, and the solubility parameters of various solvents are shown on pages VII-526 to VII-532 of the document. According to the constitution of the present invention, in a method for producing a composite reverse osmosis membrane comprising the steps of coating a porous support with (A) a solution containing a compound having at least two reactive amino groups per molecule and bringing (B) a solution containing a polyfunctional acid halide into contact with the solution (A) to induce crosslinking to form a crosslinked polyamide skin layer, the presence of substance S in the site of the crosslinking reaction realizes production of a composite reverse osmosis membrane having both high salt rejection and high water permeability. The use of substance S assures a particularly high salt rejection and particularly high water permeability. It is preferable for obtaining an increased permeation flux to add substance S to at least one of solution B and solution A. Where substance S is added to solution A, it is preferably added in an amount of 10 to 50% by weight. If the amount is less than 10% by weight, the effect of increasing the permeation flux is liable to be insufficient. If it exceeds 50% by weight, the rejection tends to be reduced. If added to solution B, substance S is added in an amount of 0.001 to 10% by weight. If the amount is less than 0.001% by weight, the effect of increasing the permeation flux is be liable to be insufficient. If it exceeds 10% by weight, the rejection tends to be reduced. It is preferable for obtaining a particularly high salt rejection and particularly high water permeability to previously impregnate a porous support with substance S before the step of bringing solution A and solution B into contact with each other. Impregnation of a porous support with substance S is carried out by, for example, dipping, coating or spraying. Impregnation may be conducted in an arbitrary stage before or during crosslinking. For achieving an increased permeation flux solution A and solution B are brought into contact with each other to induce crosslinking at a temperature of 30 to 90°C, preferably 30 to 60°C. It is preferable for attaining a particularly high salt rejection and a particularly high permeation flux to bring solution A and solution B into contact with each other to induce crosslinking in a gas phase of substance S. The method of the present invention is characterized in that the interfacial polycondensation reaction between a polyfunctional acid halide and a compound having at least two reactive amino groups per molecule is performed in the presence of substance S, i.e., a specific alcohol and/or ether having a solubility parameter of 16.4·10 3 to 28.7·10 3 (J/m 3 ) 1/2 (8 to 14 (cal/cm 3 ) 1/2 ), preferably 16.4·10 3 to 26.7·10 3 (J/m 3 ) 1/2 (8 to 13 (cal/cm 3 ) 1/2 ). Presence of a substance having a solubility parameter of less than 16.4·10 3 (J/m 3 ) 1/2 (8 (cal/cm 3 ) 1/2 ) produces no substantial effect of improving water permeability. A substance having a solubility parameter of more than 28.7·10 3 (J/m 3 ) 1/2 (14 (cal/cm 3 ) 1/2 ) is difficult to mix with solution B. Where substance S is added to solution B, the amount to be added is from 0.001 to 10% by weight, preferably 0.05 to 5% by weight. If the amount is less than 0.001% by weight, there is a possibility that the effect of increasing the permeation flux is insubstantial. If it exceeds 10% by weight, there is a possibility that an interfacial membrane is not formed satisfactorily. Examples of alcohols suitable as substance S are ethanol, propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, t-amyl alcohol, isoamyl alcohol, isobutyl alcohol, isopropyl alcohol, undecanol, 2-ethylbutanol, 2-ethylhexanol, octanol, cyclohexanol, tetrahydrofurfuryl alcohol, t-butanol, benzyl alcohol, 4-methyl-2-pentanol, 3-methyl-2-butanol, pentyl alcohol and allyl alcohol. Examples of suitable ethers are ethyl isoamyl ether, ethyl t-butyl ether, ethyl benzyl ether, diisoamyl ether, diisopropyl ether, diglycidyl ether, diphenyl ether, dibutyl ether, dipropyl ether, dibenzyl ether, dimethyl ether, dichloroethyl ether, butyl phenyl ether, methyl t-butyl ether, monodichlorodiethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether and diethylene glycol monbobutyl ether. These compounds may be used either individually or in combination of two or more thereof. The amine component contained in solution A is not particularly limited as long as it is a polyfunctional compound having two or more reactive amino groups per molecule, and includes aromatic, aliphatic or alicyclic polyfunctional amines. Examples of the aromatic polyfunctional amines are m-phenylenediamine, p-phenylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,4-diaminoanisole, amidol, and xylylenediamine. Examples of the aliphatic polyfunctional amines are ethylenediamine, propylene diamine, and tris(2-aminoethyl)amine. Examples of the alicyclic polyfunctional amines are 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 2,5-dimethylpiperazine, and 4-aminomethylpiperazine. These amines may be used either individually or as a mixture thereof. The polyfunctional acid halide which is contained in solution B is not particularly limited and includes aromatic, aliphatic or alicyclic polyfunctional acid halides. Examples of the aromatic polyfunctional acid halides are trimesic acid chloride, terephthalic acid chloride, isophthalic acid chloride, biphenyldicarboxylic acid chloride, naphthalenedicarboxylic acid dichloride, benzenetrisulfonic acid chloride, benzenedisulfonic acid chloride, and chlorosulfonylbenzenedicarboxylic acid chloride. Examples of the aliphatic polyfunctional acid halides include propanetricarboxylic acid chloride, butanetricarboxylic acid chloride, pentanetricarboxylic acid chloride, a glutaryl halide, and an adipoyl halide. Examples of the alicyclic polyfunctional acid halides are cyclopropanetricarboxylic acid chloride, cyclobutanetetracarboxylic acid chloride, cyclopentanetricarboxylic acid chloride, cyclopentanetetracarboxylic acid chloride, cyclohexanetricarboxylic acid chloride, tetrahydrofurantetracarboxylic acid chloride, cyclopentanedicarboxylic acid chloride, cyclobutanedicarboxylic acid chloride, cyclohexanedicarboxylic acid chloride, and tetrahydrofurandicarboxylic acid chloride. The above-mentioned amine component and acid halide component are subjected to interfacial polymerization to form a thin film consisting mainly of a crosslinked polyamide on a porous support thereby providing a composite reverse osmosis membrane. The porous support which can be used in the present invention is not particularly limited as far as it can support the thin film. For example, polysulfone, polyaryl ether sulfone such as polyether sulfone, polyimide, and polyvinylidene fluoride may be mentioned. In particular, a porous support comprised of polysulfone or polyaryl ether sulfone is preferred for their chemical, mechanical and thermal stability. While not limiting, the porous support usually has a thickness of 25 to 125 µm, preferably 40 to 75 µm. In carrying out the interfacial polymerization, solution A containing the amine component is applied to the porous support to form a first layer, and a layer consisting of solution B containing the acid halide component is then formed on the first layer to conduct interfacial polycondensation to form a thin film composed of a crosslinked polyamide on the porous support. In order to facilitate film formation or to improve the performance of the resulting composite reverse osmosis membrane, solution A containing the polyfunctional amine may contain a small amount of a polymer, such as polyvinyl alcohol, polyvinylpyrrolidone or polyacrylic acid, or a polyhydric alcohol, such as sorbitol or glycerol. The amine salts described in JP-A-2-187135 (corresponding to US-A-4,872,984), such as salts of tetraalkylammonium halides or trialkylamines with organic acids, may also be added to solution A for the purpose of facilitating film formation, improving penetrability of the amine solution into the support, and accelerating the condensation reaction. Surface active agents, such as sodium dodecylbenzenesulfonate, sodium dodecylsulfate, and sodium lauryl sulfate, may also be incorporated into solution A. These surface active agents are effective to improve wettability of solution A to a porous support. In order to accelerate the polycondensation in the interface, it is beneficial to use sodium hydroxide or sodium tertiary phosphate, which is capable of removing a hydrogen halide generated from the interfacial reaction, or an acylation catalyst. As stated above, solution A may contain substance S in order to improve the permeation flux. The concentrations of the acid halide or polyfunctional amine in solutions B or A are not particularly limited. In general, the concentration of the acid halide in solution B is 0.01 to 5% by weight, preferably 0.05 to 1% by weight, and that of the polyfunctional amine in solution A is 0.1 to 10% by weight, preferably 0.5 to 5% by weight. After solution A is applied to the porous support and solution B is applied thereon, excess of the solvent is removed from both solutions, and the coating layers are heat dried generally in the range of 20 to 150°C, preferably 70 to 130°C, for 1 to 10 minutes, preferably 2 to 8 minutes, to form a water-permeable thin film consisting of a crosslinked polyamide. The thin film usually has a thickness of 0.05 to 2 µm, preferably 0.1 to 1 µm. If desired, the resulting composite reverse osmosis membrane may be subjected to a chlorine treatment with hypochlorous acid for further improving the salt rejection performance as described in JP-B-63-36803 (the term "JP-B" as used herein means an "examined published Japanese patent application"). The present invention will now be illustrated in greater detail with reference to Examples. Unless otherwise indicated, all the percents are by weight. EXAMPLE 1 Aqueous solution A containing 2.0% m-phenylenediamine, 0.15% sodium lauryl sulfate, 2.0% triethylamine, 4.0% camphorsulfonic acid, and 20% isopropyl alcohol was applied to a porous polysulfone supporting membrane, and excess of solution A was removed to form a layer of solution A on the supporting membrane. A 0.15% solution of trimesic acid chloride in IP 1016 (isoparaffinic hydrocarbon oil produced by Idemitsu Petrochemical Co., Ltd.) was prepared as solution B. Solution B was heated to 40°C and brought into contact with the layer of solution A at that temperature, and the coated supporting membrane was maintained in a hot air drier at 120°C for 3 minutes to form a polymer thin film on the supporting membrane. The performance of the resulting composite reverse osmosis membrane was evaluated by testing against an aqueous solution containing 1500 ppm of sodium chloride (pH 6.5) under a pressure of 15 kgf/cm 2 . As a result, the salt rejection was 99.7% as measured from the conductivity of the permeated liquid, and the permeation flux was 1.7 m 3 /m 2 •day. These results are shown in Table 1 below. EXAMPLES 2 AND 3 AND COMPARATIVE EXAMPLE 1 Composite reverse osmosis membranes were prepared in the same manner as in Example 1, except for changing the temperature of solution B as shown in Table 1. The test results are also shown in Table 1. COMPARATIVE EXAMPLES 2 AND 3 Composite reverse osmosis membranes were prepared in the same manner as in Example 1, except that solution A contained no isopropyl alcohol, and the temperature of solution B was changed as shown in Table 1. The test results obtained are shown in Table 1. Example No. Additive in Solution A (Concn.; wt%) Temp. of Solution B 1500ppm NaCl Ag. Soln. Salt Rejection Permeation Flux (°C) (%) (m 3 /m 2 •day) Example 1 isopropyl alcohol (20) 40 99.7 1.7 Compara. Example 1 isopropyl alcohol (20) 20 99.7 1.4 Example 2 isopropyl alcohol (20) 50 99.5 1.6 Example 3 isopropyl alcohol (20) 60 99.5 1.6 Compara. Example 2 none 20 99.6 0.9 Compara. Example 3 none 50 99.7 0.9 COMPARATIVE EXAMPLE 4 Aqueous solution A containing 2.0% m-phenylenediamine, 0.15% sodium lauryl sulfate, 2.0% triethylamine, and 4.0% camphorsulfonic acid was brought into contact with a porous polysulfone supporting membrane for several seconds, and excess of solution A was removed to form a layer of solution A on the supporting membrane. Isopropyl alcohol was heated to generate isopropyl alcohol vapor, and a 0.20% hexane solution of trimesic acid chloride (solution B) was brought into contact with the layer of solution A in the isopropyl alcohol vapor atmosphere. The coated supporting membrane was maintained in a hot air drier at 120°C for 3 minutes to form a polymer thin film on the supporting membrane. The performance of the resulting composite reverse osmosis membrane was evaluated by testing against an aqueous solution containing 1500 ppm of sodium chloride (pH 6.5) under a pressure of 15 kgf/cm 2 . As a result, the salt rejection was 99.6% as measured from the conductivity of the permeated liquid, and the permeation flux was 1.0 m 3 /m 2 •day. COMPARATIVE EXAMPLE 5 A composite reverse osmosis membrane was prepared in the same manner as in Comparative Example 4, except that the contact of solution B was not in an isopropyl alcohol atmosphere. When evaluated in the same manner as in Comparative Example 4, the resulting membrane had a salt rejection of 99.7% and a permeation flux of 0.7 m 3 /m 2 •day. The composite reverse osmosis membrane prepared according to the method of the present invention exhibits both high salt rejection and high permeability and makes it possible to conduct practical desalting under a relatively low pressure. Accordingly, the membrane is suited for desalting of brackish water or seawater to obtain fresh water and preparation of ultra-pure water necessary for semiconductor manufacturing.

Claims: A method for producing a composite reverse osmosis membrane by interfacial polymerization comprising the steps of coating a porous support with (A) a solution containing a compound having at least two reactive amino groups per molecule and bringing (B) a solution containing a polyfunctional acid halide into contact with the solution (A) to induce a crosslinking reaction to form a crosslinked polyamide skin layer, wherein the step of bringing solutions (A) and (B) into contact with each other to induce the crosslinking reaction is conducted at a temperature of 30 to 90°C, and wherein the crosslinking reaction is carried out in the presence of an alcohol and/or an ether having a solubility parameter of 16.4·10 3 to 28.7·10 3 (J/m 3 ) 1/2 [8 to 14 (cal/cm 3 ) 1/2 ] selected from the group consisting of ethanol, propanol, 1-butanal, 2-butanol, 1-pentanol, 2-pentanol, t-amyl alcohol, isoamyl alcohol, isobutyl alcohol, isopropyl alcohol, undecanol, 2-ethylbutanol, 2-ethylhexanol, octanol, cyclohexanol, tetrahydrofurfuryl alcohol, t-butanol, benzyl alcohol, 4-methyl-2-pentanol, 3-methyl-2-butanol, pentyl alcohol, allyl alcohol, ethyl isoamyl ether, ethyl t-butyl ether, ethyl benzyl ether, diisoamyl ether, diisopropyl ether, diglycidyl ether, diphenyl ether, dibutyl ether, dipropyl ether, dibenzyl ether, dimethyl ether, dichloroethyl ether, butyl phenyl ether, methyl t-butyl ether, monodichiorodiethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether and diethylene glycol monobutyl ether, with the proviso that when the substance is added to solution B, it is added in an amount of 0.001 to 10 % by weight. The method of claim 1, wherein said alcohol and/or ether is present in at least one of solution (A) and solution (B). The method of claim 1, wherein the porous support is previously impregnated with said alcohol and/or ether before the contact between solution (A) and solution (B). The method of claim 1, wherein the crosslinking reaction is carried out by bringing solution (A) and solution (B) into contact with each other in a gas phase of said alcohol and/or ether.

Inventors: HIROSE MASAHIKO, ITO HIROKI, OHARA TOMOMI, HIROSE, MASAHIKO, ITO, HIROKI, OHARA, TOMOMI
Applicants: NITTO DENKO CORP, NITTO DENKO CORPORATION
Application year: 1995
Main classification: B01D67
IPC codes: B01D71, B01D69