MEMBRANES AND METHOD FOR THE PRODUCTION THEREOF

Abstract

The invention concerns the field of polymer chemistry and relates to membranes, such as those used as membranes for the preparation of aqueous solutions by means of reverse osmosis or microfiltration, ultrafiltration or nanofiltration, for example.

The object of the present invention is the specification of membranes that exhibit a reduced fouling tendency with equally suitable or improved filtration properties, as well as the specification of a simple and cost-effective method for the production thereof.

The object is attained with membranes comprising a substrate on which a porous supporting layer is arranged, on which supporting layer a separation-active layer is arranged, and on which separation-active layer a cover layer is also arranged, wherein the material of the separation-active layer comprises functional groups which primarily have carbon-carbon triple bonds and/or carbon-nitrogen triple bonds, and wherein the material of the cover layer has functional groups which are primarily at least azide groups, and the functional groups having at least carbon-carbon triple bonds and/or carbon-nitrogen triple bonds are chemically coupled covalently with the azide groups.

Claims

1. Membranes comprising at least one substrate on which a porous supporting layer is arranged, on which supporting layer at least one separation-active layer is arranged, and on which separation-active layer at least one cover layer is also arranged, wherein the separation-active layer is composed of polymers applied by means of interfacial polymerization or of the material of the porous supporting layer and is an integral part of the porous supporting layer, and wherein the material of the separation-active layer comprises functional groups which primarily have carbon-carbon triple bonds and/or carbon-nitrogen triple bonds, and wherein the material of the cover layer has functional groups which are primarily at least azide groups, and the functional groups having at least carbon-carbon triple bonds and/or carbon-nitrogen triple bonds of the material of the separation-active layer are chemically coupled covalently with the azide groups of the material of the cover layer in the region of contact between the separation-active layer and the cover layer.

2. The membranes according to claim 1 in which the substrate is a textile fabric, advantageously a fleece.

3. The membranes according to claim 1 in which the material of the porous supporting layer and/or the separation-active layer is polysulfone or polyethersulfone or polyacrylonitrile or polyvinylidene fluoride or polyester.

4. The membranes according to claim 1 in which the material of the separation-active layer is composed of polymers applied by means of interfacial polymerization, such as advantageously polyamide, polyester, polyurethane, polysulfonamide and/or polyurea.

5. The membranes according to claim 1 in which the cover layer is composed of a hydrophilic multifunctional material that is water soluble and/or alcohol soluble and/or soluble in a water/alcohol mix and is advantageously highly branched.

6. The membranes according to claim 1 in which the cover layer is composed of polyethyleneimine and/or polypropylene and/or poly(amide amine) and/or polyamine and/or polyetherol and/or polyol and/or polysaccharide and/or chitosan and/or polyalkyloxazoline.

7. The membranes according to claim 1 in which the concentration of the functional groups of the material of the separation-active layer is between 1% and 10%, wherein at least 75% to 100% of these functional groups are functional groups with at least carbon-carbon triple bonds and/or carbon-nitrogen triple bonds.

8. The membranes according to claim 7 in which the concentration of the functional groups having at least carbon-carbon triple bonds and/or carbon-nitrogen triple bonds in the material of the separation-active layer is 75% to 100% of the functional groups.

9. The membranes according to claim 1 in which the functional groups having at least carbon-carbon triple bonds and/or carbon-nitrogen triple bonds are ethynyl groups or nitrile groups.

10. The membranes according to claim 1 in which each molecule of the material forming the cover layer contains at least one azide group.

11. A method for producing membranes, in which at least one porous supporting layer is applied to a substrate, onto which supporting layer at least one separation-active layer is subsequently applied which is an integral part of the porous supporting layer, and onto which separation-active layer at least one cover layer is then also directly applied, wherein a material having functional groups is used as material of the separation-active layer, or functional groups are polymerized into the material of the separation-active layer before the application of the cover layer, wherein the functional groups of the material of the separation-active layer comprise primarily carbon-carbon triple bonds and/or carbon-nitrogen triple bonds, and wherein the material of the cover layer comprises functional groups which are primarily at least azide groups, and the functional groups having at least carbon-carbon triple bonds and/or carbon-nitrogen triple bonds of the material of the separation-active layer are chemically coupled covalently with the azide groups of the material of the cover layer in the region of contact between the separation-active layer and the cover layer via a 1,3-dipolar cycloaddition reaction during and/or after the application of the cover layer.

12. The method according to claim 11 in which polysulfone or polyethersulfone or polyacrylonitrile or polyvinylidene fluoride or polyester is used as material of the porous supporting layer and/or the separation-active layer.

13. The method according to claim 11 in which the separation-active layer is produced by means of interfacial polymerization.

14. The method according to claim 11 in which the functional groups are introduced into the material during the production of the material of the separation-active layer by the use of monomers containing functional groups.

15. The method according to claim 11 in which the cover layer is applied to the separation-active layer in the form of an aqueous solution and/or an alcoholic solution and/or a solution in a water/alcohol mix of the materials of the cover layer using a spraying method or a drawdown method or a dipping method, advantageously immediately following the interfacial polymerization of the separation-active layer.

16. The method according to claim 11 in which a material having a concentration of the functional groups of between 1% and 10% is used as material of the separation-active layer, wherein at least 75% to 100% of these functional groups are functional groups with at least carbon-carbon triple bonds and/or carbon-nitrogen triple bonds.

17. The method according to claim 16 in which, as material of the separation-active layer, a material is used in which the concentration of the functional groups with at least carbon-carbon triple bonds and/or carbon-nitrogen triple bonds is 75% to 100% of the functional groups.

18. The method according to claim 16 in which, as material of the separation-active layer, a material having functional groups with at least carbon-carbon triple bonds and/or carbon-nitrogen triple bonds is used, wherein the functional groups are ethynyl groups or nitrile groups.

19. The method according to claim 11 in which an aqueous solution and/or an alcoholic solution and/or a solution in a water/alcohol mix of the cover layer material is used as material of the cover layer, in which each molecule of the material forming the cover layer contains at least one azide group.

20. The method according to claim 11 in which the chemically covalent coupling of the functional groups having at least carbon-carbon triple bonds and/or carbon-nitrogen triple bonds of the material of the separation-active layer with the azide groups of the material of the cover layer is achieved via a copper-catalyzed 1,3-dipolar cycloaddition reaction.

21. The method according to claim 11 in which a catalyst, advantageously a copper(I) salt, is applied to the separation-active layer with the material of the cover layer.

22. A use of membranes according to claim 1 produced for the preparation of aqueous solutions by means of reverse osmosis or microfiltration or nanofiltration or ultrafiltration.

Description

[0063] The invention is explained below in greater detail with the aid of several exemplary embodiments.

COMPARATIVE EXAMPLE 1

Production of an RO Membrane without a Cover Layer (MEM-1)

[0064] An ultrafiltration membrane (UF membrane) comprising a fleece as a substrate and a polyether sulfone located thereon as a porous supporting layer is impregnated with a solution of 20 g/L m-phenylenediamine in water. The excess solution is removed from the surface by a roller. The impregnated UF membrane is then coated with a solution of 1 g/L trimesoyl chloride (TMC) in a hexane/tetrahydrofuran (THF) mixture with 0.5% THF for the production of the separation-active layer. After a duration of 180 s, the excess solution is removed and the crude membrane is dried at room temperature for 30 s and at a temperature of 80 C. for 120 s. The reverse osmosis (RO) membrane produced in this manner is first washed with fully desalinated (FD) water for 2 h, then with 1 mM hydrochloric acid (pH=3) for 20 h, and then again with FD water for 2 h.

EXAMPLE 2

Production of an RO Membrane with a Coupled Cover Layer (MEM-2)

[0065] An ultrafiltration membrane (UF membrane) comprising a fleece as a substrate and a polyethersulfone located thereon as a porous supporting layer is impregnated with a solution of 20 g/L m-phenylenediamine and ethynylaniline in water/acetonitrile (3:1 mass/mass). The excess solution is removed from the surface by a roller. The impregnated UF membrane is then coated with a solution of 1 g/L TMC in a hexane/THF mixture with 0.5% THF for the production of the separation-active layer. After a duration of 180 s, the excess solution is removed and the crude membrane is dried at room temperature for 30 s and at a temperature of 80 C. for 120 s. The RO membrane produced in this manner is first washed with FD water for 2 h, then with 1 mM hydrochloric acid (pH=3) for 20 h, and then again with FD water for 2 h. The RO membrane is then coated with an aqueous solution of 1 g/L azide-terminated polyethylene glycol monoethyl ether for the production of the cover layer. Following the application of the aqueous solution, 1 mL of a solution of 0.8 g/L CuSO.sub.4.5H.sub.2O and 6.4 g/L sodium ascorbate is applied to the surface as a catalyst. After 4 hours, the excess solution is poured off from the membrane and the membrane is once again washed with FD water for 2 h, then with 1 mM hydrochloric acid (pH =3) for 20 h, and then again with FD water for 2 h.

EXAMPLE 3

Production of an RO Membrane with a Coupled Cover Layer (MEM-3)

[0066] A UF membrane comprising a fleece as a substrate and a polyethersulfone located thereon as a porous supporting layer is impregnated with a solution of 20 g/L m-phenylenediamine and ethynylaniline in water/acetonitrile (3:1 mass/mass). The excess solution is removed from the surface by a roller. The impregnated UF membrane is then coated with a solution of 1 g/L TMC in a hexane/THF mixture with 0.5% THF for the production of the separation-active layer. After a duration of 180 s, the excess solution is removed and the crude membrane is dried at room temperature for 30 s and at a temperature of 80 C. for 120 s. The RO membrane produced in this manner is first washed with FD water for 2 h, then with 1 mM hydrochloric acid (pH=3) for 20 h, and then again with FD water for 2 h. The RO membrane is then coated with an aqueous solution of 1 g/L azide-terminated polymethyloxazoline for the production of a cover layer. Following the application of the aqueous solution, 1 mL of a solution of 0.8 g/L CuSO.sub.4.5H.sub.2O and 6.4 g/L sodium ascorbate is applied to the surface as a catalyst. After 4 hours, the excess solution is poured off from the membrane and the membrane is once again washed with FD water for 2 h, then with 1 mM hydrochloric acid (pH=3) for 20 h, and then again with FD water for 2 h.

COMPARATIVE EXAMPLE 4

Production of an Ultrafiltration (UF) Membrane without a Cover Layer (MEM-4)

[0067] A polyester fleece as is fixed to a glass plate as a substrate and impregnated with a mixture of 60 vol % N-methylpyrrolidone (NMP) and 40 vol % water. After 1 min, the excess mixture is removed by a roller. A solution of polyethersulfone with 10 mol % ethynyl groups, which corresponds to a concentration of 200 g/L ethynyl groups in NMP, is applied to the impregnated polyester fleece at a thickness of 80 m using a doctor blade and subsequently transferred to a water bath in order to precipitate out the polymer. After 30 min, the membrane is washed with FD water and stored in FD water at 4 C. The separation-active layer is an integral part of the porous supporting layer.

EXAMPLE 5

Production of a UF Membrane with a Cover Layer (MEM-5)

[0068] A polyester fleece as is fixed to a glass plate as a substrate and impregnated with a mixture of 60 vol % N-methylpyrrolidone (NMP) and 40 vol % water. After 1 min, the excess mixture is removed by a roller. A solution of polyethersulfone with 10 mol % ethynyl groups, which corresponds to a concentration of 200 g/L ethynyl groups in NMP, is applied to the impregnated polyester fleece at a thickness of 80 m using a doctor blade and subsequently transferred to a water bath in order to precipitate out the polymer. After 30 min, the membrane is washed with FD water. The separation-active layer is an integral part of the porous supporting layer. The membrane is then placed in a frame and coated with an aqueous solution of 1 g/L azide-terminated polyethylene glycol monomethyl ether for the production of the cover layer. Following the application of the aqueous solution, 1 mL of a solution of 0.8 g/L CuSO.sub.4.5H.sub.2O and 6.4 g/L sodium ascorbate is applied to the surface as a catalyst. After 4 hours, the excess solution is poured off from the membrane and the membrane is washed with FD water for 2 h.

Testing the RO Membranes MEM-1 through MEM-3

[0069] To analyze the performance of the membranes, the membranes were tested with an aqueous solution of 3.5 g/L sodium chloride at a pressure of 5 MPa and a flow rate of 90 kg/h. For this purpose permeability and salt rejection were measured.

[0070] To determine the fouling tendency of the membranes, the water flow was measured before and after the filtration of a protein solution with 1 g/L bovine serum albumin (BSA) at a pH of 7. Before the start of filtration, the membranes were conditioned at a pressure of 5 MPa for 16 h. The results are indicated in Table 1.

TABLE-US-00001 TABLE 1 Permeability Salt after protein Permeability rejection fouling Membrane (L/m.sup.2hbar) (%) (%) MEM-1 0.71 98.2 90 MEM-2 0.85 98.0 99 MEM-3 0.88 98.5 99

Testing the UF Membranes MEM-4 and MEM-5

[0071] To analyze the performance of the membranes, the membranes were tested with FD water to determine the permeability and with aqueous solutions of 1 g/L polyethylene glycol with molecular weights between 1000 and 100000 g/mol to determine the cut off (MWCO) (90% rejection of PEG 50000 g/mol) at a pressure of 0.3 MPa.

[0072] To determine the fouling tendency of the membranes, the water flow was measured before and after the filtration of a protein solution with 1 g/L bovine serum albumin (BSA) at a pH of 7. Before the start of filtration, the membranes were conditioned at a pressure of 0.4 MPa for 4 h. The results are indicated in Table 2.

TABLE-US-00002 TABLE 2 Permeability after protein Permeability MWCO fouling Membrane (L/m.sup.2hbar) (g/mol) (%) MEM-4 235 50000 50 MEM-5 199 50000 98