METHOD FOR PRODUCING ANTIFOULING COATINGS MADE OF THIN-LAYER COMPOSITE MEMBRANES FOR REVERSE OSMOSIS AND NANOFILTRATION, SUCH THIN-LAYER COMPOSITE MEMBRANES, AND THE USE THEREOF

Abstract

The invention relates to a combined method for gentle molecular surface functionalisation of the very thin, selectively-acting separating layer which preferably consists of aromatic polyamides, polyurethanes and/or polyureas, of thin-film composite membranes for reverse osmosis (hyperfiltration) and for nanofiltration, subsequently collectively termed water-filtration membranes, in order to achieve a passive antifouling effect without impairing the selectivity of the water-selective separating layer made of polyamides and the water-permeability of the membrane.

Claims

1-15. (canceled)

16. A method for the production of antifouling coatings of thin-film composite membranes for reverse osmosis, nanofiltration, or ultrafiltration by modifying a membrane surface, in which in a first step, a primary molecular functionalisation of the membrane in the gas phase is implemented by plasma-chemical and/or photochemical activation of at least one halogen-organic compound which is convertible into gas phase and covalent binding of the plasma-chemical and/or photochemical activated at least one halogen-organic compound to the membrane surface and in a second step, a wet-chemical modification of the functionalised membrane is effected radical graft polymerisation.

17. The method according to claim 16, the at least one halogen-organic compound is selected from the group consisting of allyl halides, C1 to C8 -alkylene halides, C1 to C8 alkyl halides, and mixtures thereof

18. The method according to claim 16, wherein the covalent binding is effected via alkylene bridges and derivatives thereof.

19. The method according to claim 17, wherein the primary molecular functionalisation is effected in the gas phase at atmospheric pressure, a pressure range of 100 to 1,000 mbar, or in a vacuum in a pressure range of 0.01 to 100 mbar and at temperatures in the range of 20 to 150° C. but at most however up to the decomposition temperature of the polymer membrane layer.

20. The method according to claim 17, wherein the plasma-chemical treatment is effected with a direct voltage-, alternating voltage-, high frequency-, or microwave discharge or an electron cyclotron resonance plasma (ECR).

21. The method according to claim 17, wherein the halogen atoms of the halogen-organic compounds are split photochemically or by catalytic effect.

22. The method according to claim 21, wherein starting from the covalently bonded halogen atoms, immobilised radicals are produced, based on which a radical graft polymerisation is started with alkenes.

23. The method according to claim 22, wherein oligomeric or polymeric substances grow, by radical graft polymerisation, beginning on functional groups bonded on the membrane surface and orientated away from the membrane surface.

24. The method according to claim 17, wherein the membrane surface to be modified consists of a material selected from the group consisting of polyamide, polyurethane, and a polyurea, or a composite thereof.

25. A thin-film composite membrane having at least one separating layer with a layer thickness in the range of 10 to 500 nm made of a polyamide, polyurethane, or a polyurea, at least one further polymer layer, and a a polymeric carrier structure, wherein the separating layer has an antifouling coating produced according to claim 16.

26. The thin-film composite membrane according to claim 25, wherein the separating layer has a thickness in the range of 50 to 300 nm and/or the at least one further polymer layer has a thickness in the range of 30 to 100 μm and/or the polymeric carrier structure has a thickness in the range of 50 to 100 μm.

27. The thin-film composite membrane according to claim 26, wherein the at least one separating layer is modified with a terminal polymer chain density between 0.01 and 2 polymer chains, of the polyvinyl-, polyacrylate- and/or polymethacrylates produced by controlled growth polymerisation, without the separation properties and the permeability of the thin-film composite membrane being impaired by more than 20%.

28. The thin-film composite membrane according to claim 26, wherein the at least one further polymer layer comprises a polysulfone, polyethersulfone, polyacrylonitrile, cellulose acetate, polyimide, polyetherimide or any combination of these polymers as mixture or copolymer, or essentially consists of these.

29. The thin-film composite membrane according to claim 26, wherein the at least one carrier structure consists of a sieve mesh, a woven fabric, a porous layer, or a combination thereof.

Description

EXAMPLE 1

[0032] Functionalisation by Introducing Bromine-Containing Molecule Groups in the Gas Phase

[0033] For the bromine functionalisation of reverse osmosis membranes in low pressure plasma, allyl bromide, bromoform and 1-bromopropane were used. The reverse osmosis membranes (for brackish water, high rejection) were provided by IAB Ionenaustauscher GmbH, LANXESS AG. For gentle bromine functionalisation of the membrane surface, the deposition of or modification with brominated hydrocarbons is effected from the low-pressure plasma. The membrane samples were fixed for this purpose on the lower of two plate electrodes (diameter: 150 mm, spacing: 100 mm) and the reaction chamber was sealed hermetically. Allyl bromide, bromoform or bromopropane were introduced via a needle valve after setting a negative pressure of 0.1 Pa until the desired process pressure of 2 to 4 Pa was reached. Ignition of the monomer gas was effected by applying a defined voltage in the range of 900-1,100 V to both electrode plates at 50 Hertz. The indicated process time corresponds to the duration for which a voltage was applied. Respectively 3 membrane samples of one thin-film composite membrane were modified with allyl bromide, bromoform or bromopropane at a voltage of 1,100 V and a process pressure of 4 Pa. Allyl bromide (99%, AB) was obtained from Alfa Aesar and used as obtained. The process duration was 5 seconds. Bromine was able to be detected on the thus coated or treated membranes by means of X-ray photon spectroscopy (XPS).

[0034] Table 1 shows the element composition close to the surface. The data were effected in atomic percentage [at %]. The deviations are standard deviations at 9 measuring positions on 3 parallel samples.

TABLE-US-00001 TABLE 1 Sample Br [at %] C [at %] N [at %] O [at %] untreated — 72.1 ± 0.41 10.4 ± 0.64 14.3 ± 0.65 allyl bromide 3.4 ± 1.18 73.0 ± 0.79  9.0 ± 0.88 11.4 ± 0.75 bromoform 1.6 ± 0.28 66.1 ± 0.75 11.3 ± 0.60 17.9 ± 0.51 bromopropane 4.2 ± 0.62 71.6 ± 0.58  8.6 ± 0.78 12.3 ± 0.91

[0035] There are between 1 and 5 bromine atoms for 100 atoms.

EXAMPLE 2

Radical Graft Polymerisation with Atom Transfer after the Molecular Functionalisation of the Membrane Surface

[0036] The growth of oligomers or polymers on the membrane surface was effected by radical polymerisation with atom transfer (atom transfer radical polymerisation, ATRP) under exclusion of oxygen. The basic course of the method for the examples mentioned here is subsequently described. Copper(I)bromide (CuBr, purity>99.99%) and the ligand 2,2′-bipyridine (bpy, purity 99%, SigmaAldrich) were transferred into a Schlenk flask mixed in the desired quantity and degassed by repeated purging with nitrogen. Analogously, the respectively used monomer 2-hydroxyethylmethacrylate (99+%, HEMA), 2-methacryloyloxyethyl phosphorylcholine (97%, MPC) or [2-(methacryloyloxy) ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide (97%, SBMA) were transferred into a further Schlenk flask and degassed. Methanol (99.9% p.a.) and twice distilled water were filled into respectively a further vessel and likewise degassed. Subsequently, all vessels used were transferred via a lock into a fume hood box with an argon atmosphere (>99%). As next step, the production of reaction solution 1 was effected by dissolving the CuBr and the bpy in methanol. After complete dissolution by agitation, a dark-red reaction solution was obtained. Reaction solution 2 was produced by dissolving the monomer in water. Reaction solution 1 was now added to reaction solution 2 and agitated thoroughly for approx. 30 seconds. Subsequently, the free and dissolved initiator ethyl-α-bromoisobutyrate (98%, EBIB) was added and the resulting solution was agitated for approx. 30 seconds. The solution is placed in a reaction vessel designed especially for the membrane modification. The membrane samples were then either loosely stored or stretched in a differently designed reaction cell which enabled contacting only on one side of membrane samples cut out to be round (diameter approx. 75 mm) with the reaction solution. Temperature-control of the reaction was effected by transferring the reaction vessels into an air thermostat located in the interior of the fume hood box, in which the temperature was adjusted between 10 and 60° C. After expiry of the reaction time, the membrane samples were firstly rinsed carefully in a methanol-water mixture according to the ratio used for the reaction and subsequently in pure water. The samples were subsequently dried.

EXAMPLE 2.1

[0037] Poly-2-hydroxyethylmethacrylate (poly-HEMA) and poly[2-(methacryloyloxy) ethyl]dimethyl-(3-sulfopropane) (poly-SBMA) were polymerised up on membranes functionalised with allyl bromide. The concentrations of agents were 50 mmol/l HEMA or SBMA, 1 mmol/l EBIB, 1 mmol/l CuBr and 2 mmol/l bpy. A 9:1 mixture of water with methanol was used as solvent. The reaction duration was 1.5 h, 3 h and 20 h at 20° C. By means of XPS, an increase in the oxygen content (HEMA) or in the sulphur content (SBMA) of the membrane surface as a function of the reaction time was able to be measured.

[0038] Table 2 shows the surface composition of ATRP-modified membrane samples according to example 2.1. The data are in atomic percentage [at %]. The deviations are standard deviations from analyses implemented at 4 measuring positions.

TABLE-US-00002 TABLE 2 Sample Br [at %] C [at %] N [at %] O [at %] S [at %] PHEMA 1.5 h 0.2 ± 0.12 73.8 ± 0.35 8.9 ± 0.19 15.2 ± 0.19 — PHEMA 3 h 0.1 ± 0.02 72.8 ± 0.26 7.3 ± 0.21 18.5 ± 0.37 — PHEMA 24 h 0.2 ± 0.06 72.8 ± 0.12 6.6 ± 0.19 19.1 ± 0.17 — PSBMA 1.5 h 0.6 ± 0.05 71.7 ± 0.76 8.8 ± 0.39 15.5 ± 0.54  2.2 ± 0.13 PSBMA 3 h 0.5 ± 0.04 70.2 ± 0.34 7.8 ± 0.50 17.6 ± 0.77  2.9 ± 0.34 PSBMA 24 h 0.5 ± 0.06 67.8 ± 0.39 4.6 ± 0.21 22.1 ± 0.30 22.1 ± 0.30

EXAMPLE 2.2

[0039] Poly-2-methacryloyloxyethyl phosphorylcholine (poly-MPC) was polymerised up on membranes functionalised with bromoform (BF) or bromopropane (BP). 50 mmol/l MPC, 1 mmol/l EBIB, 1 mmol/l CuBr and 2 mmol/l bpy were added. A 1:1 mixture of water and methanol was used as solvent. The reaction duration was 2 h at 20° C.

[0040] By means of XPS, an increase in the phosphorus content of the membrane surface, which correlates with the quantity of polymerised monomers could be detected. Since the surface concentration of the available initialisation groups remains virtually constant, conclusions about the average polymerisation degree can also be drawn from the quantity of bonded phosphorus.

[0041] Table 3 shows the surface composition of ATRP-modified membrane samples according to example 2.2. The data are in atomic percentage [at %]. The deviations are standard deviations from analyses implemented at 3 measuring positions.

TABLE-US-00003 TABLE 3 Sample Br [at %] C [at %] N [at %] O [at %] S [at %] PMPC (BF) 1.1 ± 0.09 66.3 ± 0.94 7.9 ± 0.66 21.3 ± 0.04 2.5 ± 0.67 PMPC (BP) 1.6 ± 0.19 68.9 ± 0.48 7.0 ± 0.52 19.2 ± 1.01 2.2 ± 0.11

EXAMPLE 2.3

[0042] Poly-SBMA was polymerised up on membranes functionalised with allyl bromide. 50 mmol/l SBMA, 1 mmol/l EBIB, 1 mmol/l CuBr and 2 mmol/l bpy were used. In addition, 20 mmol/l glucose was added to the reaction solution as reduction agent. A 1:1 mixture of water and methanol was used as solvent. The reaction duration was 20 h. The reaction temperature was 20° C., 35° C. or 50° C. By means of XPS, an increase in the sulphur content of the membrane surface as a function of the reaction temperature could be detected, with which a measure of the achieved molecular weight of the grafted-on polymer chains was provided.

[0043] Table 4 shows the surface composition of ATRP-modified membrane samples according to example 2.3. The data are in atomic percentage [at %]. The indicated standard deviations are produced from the values measured at 3 positions on the membrane surface.

TABLE-US-00004 TABLE 4 Sample Br [at %] C [at %] N [at %] O [at %] S [at %] PSBMA 1.2 ± 0.02 68.2 ± 0.23 5.4 ± 0.11 21.3 ± 0.19 3.9 ± 0.05 (20° C.) PSBMA 1.1 ± 0.06 66.6 ± 0.23 4.7 ± 0.07 23.8 ± 0.18 4.5 ± 0.12 (35° C.) PSBMA 0.4 ± 0.32 67.0 ± 1.10 4.9 ± 0.14 22.S ± 0.81 5.2 ± 0.60 (50° C.)