Highly permeable composite reverse osmosis membrane and method of producing the same

Abstract: The present invention provides a composite reverse osmosis membrane as a polyamide membrane including a side chain amino group such as a residue of a polyvinyl alcohol-based amine compound represented by Formula 1. Such a membrane can remove organic impurities under a low pressure, providing an economical method for removal of impurities. An aqueous solution including a polyvinyl alcohol-based amine compound having a side chain amino group represented by Formula 1 is applied on a polysulfone-based ultrafiltration membrane as a microporous support. Next, trimesic acid chloride solution is applied causing interfacial polycondensation, which generates a reverse osmosis membrane. When this composite reverse osmosis membrane is evaluated by using a pH 6.5 aqueous solution including 500mg/l of sodium chloride at an operation pressure of 5kg/cm 2 and at a temperature of 25°C, the permeable flux is at least 1.5m 3 /m 2 ·d, and the salt rejection is 80% or less. wherein 0<a, 0≦b, 2<c, 1≦x≦5, 0≦y≦4; R 1 is at least one group selected from the group consisting of an ether group, an alkylene group and an ester group; and R 2 is at least one group selected from the group consisting of an alkyl group and a halogen group.

Description: The following disclosure relates to a composite reverse osmosis membrane for selective permeation and separation of ingredients included in a liquid mixture. Specifically, a composite reverse osmosis membrane is used for the removal of toxic substances such as trihalomethane precursors and agricultural chemicals. This is useful for example, in water purification or recovery of effective substances in food production and the like. Conventionally, composite reverse osmosis membranes have been known as reverse osmosis membranes which differ in structure from asymmetric reverse osmosis membranes. Such composite reverse osmosis membranes are produced by forming active thin films having selective separativeness on microporous supports. Applications disclose membranes comprising polyamide obtainable by interfacial polymerization between polyfunctional aromatic amines and polyfunctional aromatic acid halides formed on supports. The examples of such applications are, Unexamined Published Japanese Patent Application (Tokkai-Sho) 55-147106, Tokkai-Sho 62-121603, Tokkai-Sho 63-218208, and Unexamined Published Japanese Patent Application (Tokkai-Hei) 2-187135. Inclusion of hydrophilic groups in membranes to improve water permeability is disclosed by, for example, Tokkai-Sho 57-119928, Tokkai-Sho 59-179103, and Tokkai-Sho 62-53703. It is also disclosed that water permeability is further improved by a treatment with an aqueous alkaline solution after including hydrophilic groups in the membrane (see Tokkai-Sho 63-7807 etc.). Highly hydrophilic polyimide-based reverse osmosis membranes, which include polyvinyl alcohols, are also disclosed in Examined Published Japanese Patent Application (Tokko-Sho) 59-27202, Tokko-Sho 61-17521, Examined Published Japanese Patent Application (Tokko-Hei) 2-32009, Tokkai-Sho 63-17521 and the like. However, these membranes have a salt rejection factor greater than 90%, and the permeable water quantity is no more than 0.2m 2 /m 2 ·d·kg/cm 2 . This indicates that the permeable water quantity level is as low as 0.4m 3 /m 2 ·d at a pressure level of city water (2kg/cm 2 ). When such membranes are used, the membrane area should be enlarged or pumps should be employed to raise pressure to obtain a proper permeable water quantity. Because these materials reject such a high percentage of salt, salt concentration in the concentrated water is increased at an operation with a high recovery rate, so that insoluble ingredients such as CaCO 3 and SiO 2 are deposited on the membrane surface and cause troubles such as a decrease in permeable water quantity. In general, the above-mentioned composite reverse osmosis membranes cannot function sufficiently until they are operated under a pressure of at least 10kg/cm 2 . This raises costs for facilities and operation. To solve this problem, more improved composite reverse osmosis membranes are required. An ideal membrane would remove toxic substances and maintain economical permeation water level at low pressures. Improvement in the recovery rate (=permeable water quantity / supplied water quantity) can reduce the quantity of supplied water and of condensed water for obtaining a predetermined quantity of permeable water. This results in a smaller apparatus as well as lowering costs for running and treatment of waste water. However, a high recovery rate causes the concentration of insoluble ingredients to rise, causing clogging of the surface. A membrane, which retards deposition of insoluble ingredients even in a high recovery rate of no less than 80%, is required. EP 0 010 425 A1 discloses a semipermeable composite membrane comprising a thin semipermeable film of a polymeric material deposited on one side of a microphorous substrate, said polymeric material being prepared by crosslinking a soluble polymer containing at least 30 mole % of a recurring unit of an amino ether or an amino ester defined by a formula and having at least 0,5 milliequivalent, per gram or said polymer, of an amino group containing 1 or 2 active hydrogen atoms with a polyfunctional compound containing at least two functional groups capable of reacting with the amino group having 1 or 2 active hydrogen atoms. In EP 0 056 175 A1, an amphoteric ion-permeable composite membrane is disclosed, which comprises a microporous substrate, and supported on the substrate, a thin amphoteric ion-exchange film formed of an active amino group-containing polymer which has been interfacially crosslinked at least at the surface portion of the thin film, said membrane being produced by forming a thin layer comprising an active amino group-containing polymer containing 1.0 to 23 milliequivalents/g, as amino equivalent, of an active amino group selected from primary and secondary amino groups and 0 to 18 milliequivalents/g, as amino equivalent, of a tertiary amino group and/or an ammonium salt group per molecule with the total amino content thereof being in the range of 2.0 to 23 milliequivalents/g on the microporous substrate and then contacting the thin layer on the substrate interfacially with a polyfunctional aromatic compound containing at least two functional groups. EP 0 031 730 A2 discloses a process for producing a semipermeable composite membrane which comprises forming on a microporous substrate a thin layer of a polymeric material comprising a polyamino polymer containing at least 1 milliequivalent, per gram of the polymer in the dry state, of active amino groups selected from primary amino groups and secondary amino groups, and thereafter interfacially crosslinking a surface portion of said thin layer with a crosslinking agent having at least two functional groups (a) capable of easily reacting with either the primary or secondary amino groups or both in said polymer; characterised in that (1) said polymeric material contains dispersed therein a polyfunctional compound having at least two functional groups (b) substantially incapable of reacting with the primary or secondary amino groups in said polymer at a temperature at which the interfacial crosslinking is carried out, but capable of reacting easily with either the primary or secondary amino groups or both in said polymer at a temperature at least 30 DEG C. higher than said crosslinking temperature, and (2) the interfacially crosslinked thin layer is heated to a temperature at which said polyfunctional compound reacts with the primary or secondary amino groups or both in said polymer. This application discloses a composite reverse osmosis membrane that can remove organic matters even in an operation under a low operation pressure (e.g., 3kg/cm 2 ). The membrane also provides an economical permeable water level, while preventing deposition of insoluble materials even for high recovery rates. This composite reverse osmosis membrane comprises a thin film and a microporous support to support the film. The thin film is obtainable by a process comprising contacting (a) an amine component represented by the following formula 1 wherein 0<a, 0≦b, 2<c, 1≦x≦5, 0≦y≦4; R 1 is at least one group selected from the group consisting of an ether group, an alkylene group and an ester group; and R 2 is at least one group selected from the group consisting of an alkyl group and a halogen group on a microporous support with (b) a component comprising at least one substantially monomeric compound having at least two groups that react with the amino groups. The amine component can also include at least one amine compound selected from the group consisting of aromatic, aliphatic and alicyclic polyfunctional amines together with the (a) amine compound. It is preferable that the (b) compound is an acid halide. Preferably, the (b) compound is at least one polyfunctional acid halide compound selected from the group consisting of aromatic, aliphatic, and alicyclic polyfunctional acid halide compounds. Preferably, the microporous support is an ultrafiltration membrane on which pores of 1-50nm in diameter are formed. Preferably, when the composite reverse osmosis membrane is used, the permeable flux is at least 1.0m 3 /m 2 ·d in an evaluation using a pH 6.5 aqueous solution comprising 500mg/liter of sodium chloride at a pressure of 5kg/cm 2 and at a temperature of 25°C. Preferably, the salt rejection when using said membrane is no more than 80% in an evaluation using a pH 6.5 aqueous solution comprising 500mg/liter of sodium chloride at a pressure of 5kg/cm 2 and at a temperature of 25°C. A method of producing such a highly permeable composite reverse osmosis membrane includes contacting on a microporous support (a) a polar solvent solution with (b) at least one organic solvent solution, in order to carry out an interfacial polymerization reaction. The (a) polar solvent solution comprises an amine component of formula 1 while the (b) organic solvent solution is selected from the group consisting of compounds of substantial monomers having at least two groups that react with the amino groups. In this example, at least one amine compound is used for producing thin films. The amine compound is selected from polyvinyl alcohol-based amine compounds having at least two primary and secondary side chain amino groups. When an acid halide group reacts with the amine compound, a polyamide membrane is obtained by an interfacial polycondensation. Additionally, aromatic, aliphatic and alicyclic polyfunctional amines can be used together with these amine compounds. Such aromatic polyfunctional amine compounds include, for example, m-phenylenediamine, p-phenylenediamine, 1,3,5-triaminobenzene, 1,2,4,-triaminobenzene, 3,5-diamino benzoic acid, 2,6-diaminotoluene, 2,4-diaminoanisole, and xylenediamine. The aliphatic polyfunctional amines include, for example, ethylenediamine, propylenediamine, and tris(2-aminoethyl)amine. The alicyclic polyfunctional amines include, for example, 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 2,5-dimethylpiperazine, and 4-aminomethylpiperazine. Accordingly, groups that can react with an amino group including at least one compound can be selected from the group consisting of substantially monomeric compounds having at least two groups that can react with amino groups comprise, for example, an acid halide group, an isocyanate group, and a carboxylic acid group. An acid halide group is preferred in light of the reactivity. Specifically, an acid chloride group is preferred. Polyfunctional acid halide groups that can be used include, but are not limited to aromatic, aliphatic and alicyclic polyfunctional acid halides can be used. Examples of the aromatic polyfunctional acid halides utilized include trimesic acid chloride, terephthalic acid chloride, isophthalic acid chloride, biphenyldicarboxylic acid chloride, naphthalenedicarboxylic acid chloride, benzene trisulfonic acid chloride, benzene disulfonic acid chloride, and chlorosulfonium benzene dicarboxylic acid chloride. Examples of the aliphatic polyfunctional acid halides include propanetricarboxylic acid chloride, butanetricarboxylic acid chloride, pentanetricarboxylic acid chloride, glutaryl halide, and adipoyl halide. Examples of the alicyclic polyfunctional acid halides include 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. According to this disclosure, a composite reverse osmosis membrane having a thin film comprising a crosslinked polymer as the main component on a microporous support is obtained by interfacial polymerization of the above-described amine component and a component that can react with the amine component. Typically, interfacial polymerization involves an interfacial reaction between a polar solution containing an amine component with an organic solution containing a suitable compound. The compound has a group that can react with the amine component on the interface. It is preferable that the permeable flux is at least 1.5m 3 /m 2 ·d when the composite reverse osmosis membrane is evaluated by using a pH 6.5 aqueous solution including 500mg/l of sodium chloride at an operation pressure of 5kg/cm 2 and at a temperature of 25°C. When the permeable flux is less than 1.0m 3 /m 2 ·d, sufficient permeable flux cannot be obtained when the operation pressure is as low as 3kg/cm 2 (city water level). For this purpose, more preferable permeable flux is 1.5m 3 /m 2 ·d or more. The salt rejection is preferably 80% or less when the composite reverse osmosis membrane is evaluated by using a pH 6.5 aqueous solution including 500mg/l of sodium chloride at an operation pressure of 5kg/cm 2 and at a temperature of 25°C. When the salt rejection exceeds 80%, insoluble ingredients are easily deposited under a high recovery condition, and the surface of the reverse osmosis membrane is easily polluted and clogged. It is further preferable that the salt rejection is no more than 70%. A microporous support used according to this disclosure is not specifically limited as long as it can support the thin film. Typically, an ultrafiltration membrane having pores of 1-50nm in diameter on the surface is used. Materials for such a support include, for example, polysulfone, polyethersulfone, polyimide, polyamide, polyvinylidene fluoride, ethylene-vinylalcohol copolymer, and cellulose acetate. Ultrafiltration membranes comprising polysulfone, polyethersulfone and the like are specifically preferred in light of the chemical, mechanical and thermal stability. Such an ultrafiltration membrane can be reinforced with woven fabric, non-woven fabric and the like. The amine salts described in Tokkai-Hei 2-187135, such as a salt of a tetraalkylammonium halide or a trialkylamine, and an organic acid can also be suitably used for the solution to facilitate the film formation, improve the absorption of the amine solution in the support film, and accelerate the condensation reaction. Addition of a material whose solubility parameter ranges from 8 to 14 (cal/cm 3 ) 1/2 for the crosslinking reaction is also effective to increase the permeable water quantity. The solution can further contain a surfactant such as sodium dodecylbenzenesulfonate, sodium dodecylsulfonate, and sodium laurylsulfonate. Such a surfactant has an effect for improving the wettability of the polar solvent solution including the amine component for the microporous support. Furthermore, for accelerating the polycondensation reaction at the interface, it is effective to use sodium hydroxide or sodium tertiary phosphate capable of removing a hydrogen halide formed by the interfacial reaction or to use an acylation catalyst as a catalyst. The concentration of the amine compound is not particularly limited to the solution including the amine component described above, but the concentration is usually from 0.01 to 20 weight %, and preferably from 0.1 to 10 weight %. Any polar solvent can be used for the polar solvent solution including amine component as long as the solvent dissolves the amine component well without dissolving the microporous support. For example, water can be used for this purpose. The concentration of the amine-reactive compound in an organic solvent is not specifically limited, but typically, it ranges from 0.001 to 10 weight %, preferably, from 0.01 to 5 weight %. Any organic solvent solutions containing acid halide components are allowable as long as they dissolve the acid halide component while remaining immiscible with the polar solvent. For example, aliphatic or alicyclic hydrocarbons having 5-10 carbons can be used. More specifically, pentane, hexane, heptane, octane, and cyclopentane etc. can be used. A thin film is formed by applying the polar solution onto a microporous support and by removing excess solution. To this, the organic solution containing an acid halide component is added, and excess solution is removed, so that interfacial polymerization is performed. Heating can be carried out as required. The heating temperature ranges from 40 to 180°C, preferably, from 50 to 150°C. The heating time ranges from 10 seconds to 60 minutes, more preferably, 1 to 30 minutes. The method is further described by referring to Examples 1-4, but the disclosure is not limited thereby. In the following examples a polysulfone-based ultrafiltration membrane was used for the microporous support. The performance of the obtained composite reverse osmosis membrane was evaluated with respect to the sodium chloride rejection and permeable flux after passing through the membrane a pH 6.5 aqueous solution including 500mg/l of sodium chloride for one hour at an operation pressure of 5kgf/cm 2 , and at an temperature of 25°C. The rejection was obtained in a common measurement depending on the electric conductivity. (Example 1) An aqueous solution including 2 weight % of polyvinyl alcohol-based amine compound having a side chain amino group represented by Formula 3, 0.5 weight % of sodium lauryl sulfate and 0.5 weight % of sodium hydrocarbon was applied on a polysulfone-based ultrafiltration membrane (microporous support) before removing extra aqueous solution, so that a layer of the aqueous solution was formed on the support: wherein a=8, b=10 and c=500. Subsequently, the layer was contacted with an isooctane solution including 1 weight % of trimesic acid chloride for interfacial polycondensation on the support, and maintaining for three minutes in a 120°C dryer so that a polymer membrane was formed on the microporous support, generating a composite reverse osmosis membrane. The product was then evaluated. The salt rejection was 50%, and the permeable flux was 3.2m 3 /m 2 ·d. When the performance was evaluated again under the same condition after passing pH 12 alkaline solution through this membrane for three days, the salt rejection was 48% and the permeable flux was 3.3m 3 /m 2 ·d. This illustrated that the membrane had sufficient resistance against alkali. (Examples 2-4) Composite reverse osmosis membranes were formed in the same manner as described in Example 1 except that the concentration of the trimesic acid chloride was varied. The performance of the obtained composite reverse osmosis membranes is shown in Table 1. Trimesic acid chloride concentration (wt%) Salt rejection (%) Permeable flux (m 3 /m 2 ·d) Example 2 0.1 34 3.7 Example 3 0.25 50 2.5 Example 4 3 38 5.3 As shown in Table 1, products of the present invention provide high permeable flux under a low pressure of 5kg/cm 2 . Moreover, sufficiently high permeable flux was obtained even under an operation pressure of 3kg/cm 2 (city water level). (Comparative Example 1) A composite reverse osmosis membrane was obtained in a manner similar to Example 1 except that the polyvinyl alcohol-based amine compound was replaced by m-phenylenediamine. When the composite reverse osmosis membrane was evaluated, the salt rejection was 99% and the permeable flux was extremely low as 0.05m 3 /m 2 ·d. This disclosure also provides a method of efficiently producing a composite reverse osmosis membrane with the aforementioned desired properties.

Claims: A highly permeable composite reverse osmosis membrane comprising a thin film and a microporous support to support the thin film, the thin film is obtainable by a process comprising contacting (a) an amine component represented by the following Formula 1 wherein 0 < a, 0 ≤ b, 2 < c, 1 ≤ x ≤ 5, 0 ≤ y ≤ 4; R 1 is at least one group selected from the group consisting of an ether group, an alkylene group and an ester group; and R 2 is at least one group selected from the group consisting of an alkyl group and a halogen group on a microporous support with (b) a component comprising at least one monomeric compound having at least two groups that react with the amino groups. The highly permeable composite reverse osmosis membrane according to claim 1, wherein an amine component comprising at least one amine compound selected from the group consisting of aromatic, aliphatic and alicyclic polyfunctional amines is further comprised in addition to the (a) amine compound. The highly permeable composite reverse osmosis membrane according to claim 1 or claim 2, wherein the component (b) is an acid halide. The highly permeable composite reverse osmosis membrane according to claim 3, wherein the component (b) is at least one polyfunctional acid halide compound selected from the group consisting of aromatic, aliphatic and alicyclic polyfunctional acid halide compounds. A method for producing a highly permeable composite reverse osmosis membrane according to any of claims 1 to 4, wherein a reverse osmosis membrane is formed on a microporous support by contacting for interfacial polymerization reaction on a microporous support (a) a polar solvent solution comprising an amine component represented by the following Formula 2: wherein 0 < a, 0 ≤ b, 2 < c, 1 ≤ x ≤ 5, 0 ≤ y ≤ 4; R 1 is at least one group selected from the group consisting of an ether group, an alkylene group and an ester group; and R 2 is at least one group selected from the group consisting of an alkyl group and a halogen group and (b) at least one organic solvent solution selected from the group of monomeric compounds having at least two groups that react with the amino groups. Use of the highly permeable composite reverse osmosis membrane according to any of claims 1 to 4 for selective permeation and separation of ingredients included in a liquid mixture. The use according to claim 6, wherein toxic substances are removed from the liquid mixture. The use according to claim 6 or claim 7, wherein trihalomethane precursors or agricultural chemicals are removed from the liquid mixture. The use according to any of claims 6 to 8, wherein the permeable flux is at least 1.0 m 3 /m 2 · d at an evaluation where a pH 6.5 aqueous solution comprising 500 mg/liter of sodium chloride is used at an operation pressure of 5 kg/cm 2 and at a temperature of 25 °C. The use according to any of claims 6 to 9, wherein the salt rejection is no more than 80 % at an evaluation where a pH 6.5 aqueous solution comprising 500 mg/liter of sodium chloride is used at an operation pressure of 5 kg/cm 2 and at a temperature of 25 °C.

Inventors: HIROSE MASAHIKO, HIROSE, MASAHIKO
Applicants: NITTO DENKO CORP, NITTO DENKO CORPORATION
Application year: 1999
Main classification: B01D71
IPC codes: B01D69, B01D71