WO2018220209A1

WO2018220209A1 - Ultra-stable poly(epoxy)ether thin-film composite membranes made via interfacial initiation

Info

Publication number: WO2018220209A1
Application number: PCT/EP2018/064527
Authority: WO
Inventors: Elke DOM; Ivo Vankelecom; Rhea VERBEKE
Original assignee: Katholieke Universiteit Leuven
Current assignee: Katholieke Universiteit Leuven
Priority date: 2017-06-02
Filing date: 2018-06-01
Publication date: 2018-12-06
Anticipated expiration: 2019-12-02
Also published as: GB201708838D0

Abstract

The present invention relates to a method for the preparation of thin-film composite (TFC) membranes by interfacial initiation of polymerization (IFIP) and the TFC membranes produced by this method. More particularly, the IFIP method of the present invention relates to the use of a ring-opening polymerization reaction of epoxide monomers for making polymer coatings on a porous support membrane. The resulting poly(epoxy)ether TFC membranes are stable in various challenging conditions of extreme pH, in harsh oxidizing environments and in highly demanding aprotic solvents.

Description

ULTRA-STABLE POLY(EPOXY)ETHER THIN-FILM COMPOSITE MEMBRANES MADE VIA INTERFACIAL INITIATION

FIELD OF THE INVENTION

BACKGROUND OF THE INVENTION

Membrane separation technology has gained an important place in the chemical industry. It can be applied in the separation of a range of components of varying molecular weights in gas or liquid phases, including but not limited to nanofiltration, desalination and water treatment. It has several advantages to offer compared to the traditional separation processes, such as distillation, adsorption, absorption or solvent extraction. The benefits include continuous operation, lower energy consumption, possibility of integration with other separation processes, mild conditions and thus more environment friendly, easy but linear up-scaling, feasibility of making tailor-made membranes and less requirement of additives (Basic Principles of Membrane Technology, Second Edition, M. Mulder, Kluwer Academic Press, Dordrecht. 564p).

In membrane separations, the aim is to retain one (or more) component(s) of a mixture, while other components can freely permeate through the membrane under a driving force that can be a pressure, concentration or potential gradient. Membranes are used in many applications, for example as inorganic semiconductors, biosensors, heparinized surfaces, facilitated transport membranes utilizing crown ethers and other carriers, targeted drug delivery systems including membrane-bound antigens, catalyst containing membranes, treated surfaces, sharpened resolution chromatographic packing materials, narrow band optical absorbers, and in various water treatments which involve removal of a solute or contaminant for example dialysis, electrolysis, microfiltration, ultrafiltration and reverse osmosis (Membrane technology and applications, R. Baker, John Wiley & Sons, 2004, 538p). Although membrane separation processes are widely applied in the filtration of mild aqueous fluids, they have not been (widely) used under highly challenging pH or oxidizing conditions, neither for the separation of solutes in organic solvents. Their relatively poor performance and/or stability in these conditions decreases their applicability in more aggressive feeds, despite an enormous potential economical market. For example, chemical and pharmaceutical syntheses or textile dyeing are frequently performed in organic solvents containing products with high added value, like acids and bases or catalysts, which would be recoverable via membrane technology. The recovery of metal salts from acid mine leachates, treatment of harsh waste streams from chemical and pharmaceutical industries and purification of chlorinated water streams in desalination are other examples in which ultra-stable membranes could serve purpose.

Many membranes for aqueous applications are thin film composite (TFC) membranes made by interfacial polymerization (IFP). The IFP technique is well known (Petersen, R. J. "Composite reverse osmosis and nanofiltration membranes". J. Membr. Sci, 83, 81 -150, 1993) and several procedures (e.g. U.S. 3,744,642, U.S. 4,277,244, U.S. 4,950,404) are illustrative of the fundamental method for preparing TFC membranes. One of the earliest patents to describe membranes of the type used in the present invention, U.S. 3,744,642 discloses the process of reacting a broad group of aliphatic or carbocyclic primary diamines with aliphatic or carbocyclic diacyl halides on a porous support membrane to form TFC membranes. In IFP, an aqueous solution of a reactive monomer (often a polyamine (e.g. a diamine)) is first deposited in the pores of a porous support membrane (e.g. a polysulfone ultrafiltration membrane) - this step is also referred to as support membrane impregnation. Then, the porous support membrane, loaded with the first monomer, is immersed in a water-immiscible (organic) solvent solution containing a second reactive monomer (e.g. a tri- or diacid chloride). The two monomers react at the interface of the two immiscible solvents, until a thin film presents a diffusion barrier and the reaction is completed to form a highly cross-linked thin film layer that remains attached to the support membrane. Since membranes synthesized via this technique usually have a very thin top layer, high solvent permeances are expected. High flux is often associated with thin membranes, while high selectivity should not be affected by membrane thickness (Koops, G.H. et al. "Selectivity as a Function of Membrane Thickness: Gas Separation and Pervaporation" Journal of Applied Polymer Science, 53, 1639-1651 , 1994). Since the first successes reached within this field by Loeb and Sourirajan, extensive research has been performed starting from their reverse osmosis membranes disclosed in U.S. 3,133,132. A subsequent breakthrough was achieved by Cadotte. Inspired by the work of Morgan, who was the first to describe "interfacial polymerization", Cadotte produced extremely thin films using the knowledge about interfacial polymerization, as claimed in U.S. 4,277,344.

The thin film layer can be from several tens of nanometers to a few micrometers thick. The thin film is selective between molecules, and this selective layer can be optimized for solute rejection and solvent flux by controlling the coating conditions, the characteristics and concentrations of the reactive monomers, the choice of the support membrane or the use of additives (e.g. acid-acceptors, surfactants ...). The (micro-)porous support can be selectively chosen for porosity, strength and solvent resistance. There is a myriad of supports or substrates for membranes. Specific physical and chemical characteristics to be considered when selecting a suitable substrate include: porosity, surface porosity, pore size distribution of surface and bulk, permeability, solvent resistance, hydrophilicity, flexibility and mechanical integrity. Pore size distribution and overall surface porosity of the surface pores are of great importance when preparing a support for IFP.

An example of interfacial polymerization used to prepare TFC membranes are "Nylons", which belong to a class of polymers referred to as polyamides. One such polyamide is made, for example, by reacting a triacyl chloride, such as trimesoylchloride, with a diamine, such as m- phenylenediamine. The reaction can be carried out at an interface by dissolving the diamine in water and bringing a hexane solution of the triacyl chloride on top of the water phase. The diamine reacts with the triacyl chloride at the interface between these two immiscible solvents, forming a polyamide film at or near the interface which is less permeable to the reactants. Thus, once the film forms, the reaction slows down drastically, leaving a very thin film. In fact, if the film is removed from the interface by mechanical means, fresh film forms almost instantly at the interface, because the reactants are so highly reactive.

Among the products of interfacial polymerization are polyamides, polyureas, polyurethanes, polysulfonamides, polyesters (US 4,917,800), polyacrylates, or β-alkanolamines (US20170065937). Factors affecting the making of continuous, thin interfacial films include temperature, the nature of the solvents and co-solvents (including ionic liquids: Marien et al. "Sustainable Process for the Preparation of High-Performance Thin-Film Composite Membranes using Ionic Liquids as the Reaction Medium" ChemSusChem, 9, 1 101 -1 1 1 , 2016), and the concentration and the reactivity of monomers and additives. These polymers however have various disadvantages. Next to poor stability in for instance chlorinated and oxidizing solvents, the most-widely used polyamides fail to sustain at temperatures higher than 450°C and outside a pH range of 2-12 (Wang et al. "A polyamide-silica composite prepared by the sol-gel process" Polymer Bulletin, 31 , 323-330, 1993). The drawbacks of this traditional IFP product has led to the demand of new, solvent stable membranes with similar performance. Novel membranes are also needed since there is an interest in operating in organic solvent streams to separate small molecules such as synthetic antibiotics and peptides from organic solutions. In these types of applications, a high permeability is required for economical operation. Polar organic solvents, such as dipolar aprotic solvents, particularly solvents such as N-methyl pyrrolidone (NMP), dimethylacetamide (DMAC), dimethyl formamide (DMF) and dimethylsulfoxide (DMSO) are used as solvents or media for chemical reactions to make pharmaceuticals and agrochemicals (for example, pyrethroid insecticides). These powerful solvents will cause severe damage to commonly used polymeric membranes made from polysulfone, polyethersulfone, polyacrylonitrile or polyvinylidene fluoride polymers. TFC membranes based on a β-alkanolamine top layer could overcome some of these challenges and has proven stable in DMF and in extreme acidic conditions (US20170065937), however these TFC membranes are still not stable in several harsh conditions, such as aqueous oxidizing conditions (eg. NaOCI and NaOH).

Other types of polymerization, such as polymerization by interfacial initiation (IFIP) are described in other scientific fields, not related to membrane technology. Here, the reaction can solely begin when the so-called initiator is present at the interface, allowing a localized polymerization. This concept has been described in other fields of science such as in microfluidics and encapsulation technologies (Wei et al., "Novel cationic pH-responsive poly(N,N-dimethylaminoethyl methacrylate) microcapsules prepared by a microfluidic technique" Journal of Colloid and Interface Science, 357, 101 -108; 201 1 , Chen et al., Fabrication and characterization of nanocapsules containing n-dodecanol by miniemulsion polymerization using interfacial redox initiation, Colloid and Polymer Science, 290, 307-314, 2012), and in the resin industry (Imai et al., Importance of polymerization initiator systems and interfacial initiation of polymerization in adhesive bonding of resin to dentin, Journal of Dental research, 70, 1088-91 , 1991 ) but have - up to now - not yet been applied for membranes with purification or separation purposes. Moreover, there is also not any suggestion in these other scientific fields to use IFIP in the field of membrane technology, let alone to use IFIP to generate membranes with improved properties.

Saehan Ind Inc (GB2390042) disclose a composite polyamide reverse osmosis membrane, wherein a polyamide layer is used that reacts with a polyfunctional epoxy compound. Said polyamide layer is the interfacial reaction product of a polyfunctional amine and a polyfunctional amine-reactive reactant. The polyfunctional amines as used in GB2390042 are typically monomeric amines having a primary or secondary, and preferably a primary, amine functional group. Saehan Ind Inc (US2003/0121844) disclose a method for making a coated polyamide reverse osmosis membrane comprising a coating step wherein a polyfunctional epoxy compound is applied to a polyamide film on a porous support, followed by a crosslinking step (or via a homopolymerisation reaction) wherein the polyfunctional epoxy compound is made water- insoluble. The method as disclosed by Saehan Ind inc, does not include an interfacial initiation of the polymerization process and the top (epoxy) layer is used as a coating, not as a selective layer.

In WO2015/127516 a method is described for the synthesis of thin film composite membranes by interfacial polymerization, wherein a polyfunctional nucleophilic monomer is used. Said polyfunctional nucleophilic monomer can be a primary or secondary amine, such that those amines are incorporated in the polymer backbone. There is no suggestion in WO2015/127516 to use a tertiary amine or any other functional group in those polyfunctional nucleophilic monomers so that these monomers could be used as initiators that are not incorporated in the polymer backbone.

In many applications, it would also be useful for the membrane to operate with aqueous mixtures of solvents or with both aqueous solutions and solvent based solutions in series. For such uses, hydrophobic membranes are not useful as they have very low permeabilities for aqueous solutions.

These different requirements have led to a pressing demand of new, broad solvent-stable, oxidation- and pH-resistant membranes. It is an objective of the present invention to provide a highly efficient novel route for the production of such membranes and to obtain TFC membranes with high stability in highly challenging conditions.

SUMMARY OF THE INVENTION

The present invention provides a method for the preparation of thin film composite (TFC) membranes by interfacial initiation of polymerization (IFIP) and the TFC membranes produced by this method. More particularly, the present invention provides an IFIP method using a ring- opening polymerization reaction of epoxide monomers for making a thin film polymer coating on a porous support membrane. The poly(epoxy)ether TFC membranes generated by this method are stable in various challenging conditions of extreme pH, in harsh oxidizing environments and in highly demanding aprotic solvents.

The present invention provides a method for the preparation of TFC membranes by IFIP on the surface of a porous support membrane, comprising the following steps: (a) impregnation of the porous support membrane with an aqueous solution containing an initiator; and (b) contacting the impregnated support membrane with a second substantially water-immiscible solvent containing a polyfunctional epoxide monomer, causing polymerization via a chemical reaction at the interface, called ring-opening of epoxides.

The present invention differs from Saehan Ind Inc (GB2390042) as the polyfunctional amines as used in GB2390042 are typically monomeric amines having a primary or secondary, and preferably a primary, amine functional group. In the present invention an initiator is used that can have different functional groups, including an amine group. The amine group of the present invention is typically a tertiary amine group, such that said initiator comprising said tertiary amine group will not be incorporated in the polymer backbone of the thin film top layer, but could be present at the end of the polymer chain.

The present invention differs from Saehan Ind Inc (US2003/0121844) as they disclose a method for making a coated polyamide reverse osmosis membrane comprising a coating step wherein a polyfunctional epoxy compound is applied to a polyamide film on a porous support, followed by a crosslinking step (or via a homopolymerisation reaction) wherein the polyfunctional epoxy compound is made water-insoluble. The method as disclosed by Saehan Ind inc, does not include an interfacial initiation of the polymerization process and the top (epoxy) layer is used as a coating, not as a selective layer.

The present invention differs from WO2015/127516 as the method as disclosed in WO2015/127516 is a method for the synthesis of thin film composite membranes by interfacial polymerization, wherein a polyfunctional nucleophilic monomer is used. Said polyfunctional nucleophilic monomer can be a primary or secondary amine, such that those amines are incorporated in the polymer backbone. There is no suggestion in WO2015/127516 to use a tertiary amine or any other functional group in those polyfunctional nucleophilic monomers so that these monomers could be used as initiators that are not incorporated in the polymer backbone.

The present invention also relates to the TFC membranes obtained by the methods of the present invention and the use of said TFC membranes.

The present invention more particularly provides poly(epoxy)ether TFC membranes with improved stability in a broad range of pH and chemicals, for use in (nano)filtration of components in aggressive aqueous and organic solvents, such as polar aprotic solvents or chlorinated aqueous feeds.

Numbered statements of this invention are: A method for synthesis of a thin-film composite membrane comprising a poly(epoxy)ether top layer by interfacial initiation of polymerization (IFIP), comprising the following steps: a) impregnation of an ultrafiltration porous support membrane with an aqueous solution containing an initiator; and b) contacting the impregnated support membrane with a second water-immiscible solvent or ionic liquid containing a polyfunctional epoxide monomer, thereby obtaining a membrane, wherein said initiator is not incorporated in the polymer backbone of the thin film top layer, and is optionally present at the end of the polymer chain

The method of statement 1 , wherein the initiator contains a functional group selected from the group consisting of: a tertiary amino, a tertiary thiol, a base, a hydroxyl group and any other (tertiary) nucleophiles.

The method according to statement 1 or 2, wherein the initiator contains a tertiary amino functional group.

The method according to any one of statements 1 to 3, wherein the epoxide monomer is selected from the group:phenyl glycidyl ethers, bisphenol-A-diglycidyl-ether, Tetraphenolethane tetraglycidylether, neopentylglycol diglycidylether, trimetylolpropane triglycidylether, 1 ,4-butanediol diglycidylether, triglycidyl-p- aminophenol, tetraglycidyl-4,4'-diaminodiphenylmethane, and diglycidyl ester of hexahydrophthalic acid.

The method according to any one of statements 1 to 4, wherein the epoxide monomer is Tetraphenolethane tetraglycidylether.

The use of a thin film composite membrane obtained by the method according to any one of the statements 1 to 5 for nanofiltration or reverse osmosis of components.

The use according to statement 6, wherein said components are suspended in organic solvents.

The use according to statement 6, wherein said components are suspended in aqueous solvents of pH ranges pH 0-4 and pH 10-14.

The use according to statement 8, wherein said components are suspended aqueous oxidizing solvents. 10. The use according to statement 9, wherein said aqueous oxidizing solvent is NaOCI.

1 1 . The use according to statement 6 or 7, wherein said components are suspended in polar aprotic solvents.

Further numbered statements of this invention are:

1 . A method for synthesis of a thin-film composite membrane comprising a poly(epoxy)ether top layer by interfacial initiation of polymerization (IFIP), comprising the following steps: a) impregnation of an ultrafiltration porous support membrane with an aqueous solution containing an initiator; and b) contacting the impregnated support membrane with a second water-immiscible solvent or ionic liquid containing a polyfunctional epoxide monomer.

2. The method of statement 1 , wherein the initiator contains a functional group selected from the group consisting: of a tertiary amino, a tertiary thiol, a base, a hydroxyl group and any other (tertiary) nucleophiles.

3. The method of statement 1 , wherein the epoxide monomer is selected from the group:phenyl glycidyl ethers, bisphenol-A-diglycidyl-ether, Tetraphenolethane tetraglycidylether, neopentylglycol diglycidylether, trimetylolpropane triglycidylether, 1 ,4-butanediol diglycidylether, triglycidyl-p-aminophenol, tetraglycidyl-4,4'- diaminodiphenylmethane, and diglycidyl ester of hexahydrophthalic acid.

4. The use of a thin film composite membrane obtained by the method according to any one of the statements 1 to 3 for nanofiltration or reverse osmosis of components.

5. The use according to statement 4, wherein said components are suspended in organic solvents.

6. The use according to statement 4, wherein said components are suspended in aqueous solvents of extreme pH, such as pH(0-4), and pH (10-14).

7. The use according to statement 6, wherein said components are suspended in aqueous oxidizing solvents, such as NaOCI. 8. The use according to statement 4 or 5, wherein said components are suspended in polar aprotic solvents. 9. A thin-film composite membrane comprising a poly(epoxy)ether top layer obtainable via interfacial initiation of polymerization (IFIP), comprising the following steps: a) impregnation of an ultrafiltration porous support membrane with an aqueous solution containing an initiator; and b) contacting the impregnated support membrane with a second water-immiscible solvent or ionic liquid containing a polyfunctional epoxide monomer.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 : ATR-FTIR spectra of poly(3-alkanolamine) TFC-membranes obtained after 6 h IFP, after 24 h immersion in water (pristine), 1 M HCI (pH 0), 0.33 M NaOH (pH 13.5). Figure 2: ATR-FTIR of characteristic peaks for the XL-PAN support-layer and the polyepoxyether top-layer after 24h immersion in 400 ppm NaOCI or in aqueous solutions at pH 0 or 13.5.

DESCRIPTION

The present invention relates to a new method for preparation of thin film composite membranes (TFC) by interfacial initiation polymerization (IFIP) and TFC membranes produced by this method. More particularly, the present invention provides an IFIP method comprising an initiator-induced ring-opening polymerization reaction of epoxide monomers for making an adhesive polymer of a poly(epoxy)ether on a porous support membrane, providing novel TFC membranes.

The scope of the applicability of the present invention will become apparent from the detailed description and drawings provided below. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only since various changes and modifications are also within the spirit and scope of the invention as apparent from this detailed description. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. One aspect of the present invention provides a method for preparation of TFC membranes comprising a thin film layer, preferably a poly(epoxy)ether polymer, formed by IFIP involving a ring-opening polymerization reaction of epoxide monomers with an initiator. Preferably, said method comprises the following steps: (a) impregnation of a porous support membrane with an aqueous solution containing an initiator; and (b) contacting the impregnated support membrane with a second water-immiscible solvent or ionic liquid containing a polyfunctional epoxide monomer.

Alternatively, the method of the present invention comprises the steps of (a) impregnation of a porous support membrane with a substantially water-immiscible solvent containing a polyfunctional epoxide monomer; and (b) contacting the impregnated support membrane with an aqueous solution containing an initiator.

The method of the present invention optionally involves the addition of nanoparticles, phase- transfer catalysts or surfactants to reduce surface tension effects, inorganic salts, co-solvents or a combination thereof. The temperature and time of contacting can vary, depending on the kind of support and the kind and concentration of the reactants, but contacting is generally carried out from about 1 min to 100 hours at room temperature. The method of the present invention optionally involves that the TFC membrane may be washed to remove unreacted monomers, chemically treated with acids, bases, or other reagents to modify performance characteristics, treated with a humectant or protective coating and/or dried, stored in water until tested, further treated for environmental resistance, or otherwise used. Such post-treatments are well-known in the art (U.S. 5,234,598; U.S. 5,085,777; U.S. 5,051 ,178).

One embodiment of the present invention provides the preparation of TFC membranes, preferably a TFC membrane comprising a poly(epoxy)ether polymer, by interfacial initiation, comprising the following steps:

(a) impregnating a porous support membrane, optionally comprising a first conditioning agent, with a polyfunctional initiator solution comprising:

(i) an aqueous first solvent for said initiator; (ii) said initiator; (iii) optionally, an activating solvent; and (iv) optionally, additives including bases, alcohols, ketones, ethers, esters, halogenated hydrocarbons, nitrogen-containing compounds and sulphur-containing compounds, monohydric aromatic compounds; wherein said support membrane is stable in polar aprotic solvents; (b) contacting the impregnated porous support membrane with a polyfunctional epoxide monomer solution comprising:

(i) a substantially water-immiscible second solvent for the polyfunctional epoxide monomer; (ii) a polyfunctional epoxide monomer; (iii) optionally, an activating solvent; and (iv) optionally, additives including alcohols, ketones, ethers, esters, halogenated hydrocarbons, nitrogen- containing compounds and sulphur-containing compounds, monohydric aromatic compounds; wherein the aqueous first solvent ((a)(i)) and the immiscible second solvent ((b)(i)) form a two phase system;

(c) optionally, treating the resulting composite membrane with an activating solvent; and, (d) optionally, impregnating the resulting composite membrane with a second conditioning agent.

The synthesis of a polymeric membrane based on the reaction of an epoxide-compound with an amine-compound have been described in the literature (WO 2010/099387 A1 , USA 4,265,745, CN 104 190 265 A). However, these systems differ from the present invention in that they are either not biphasic, do not contain an initiator, are not based on an interfacial polymerization reaction, or need a cross-linker agent to become selective. Additionally, the amine is often incorporated in the backbone of the polymer. Membrane casting

A porous support membrane for use in the method according to the present invention can be prepared as follows: a polymer solution is casted onto a suitable porous substrate, from which it then may be removed. Casting of the membrane may be performed by any number of casting procedures cited in the literature, for example U.S. 3,556,305; U.S. 3,567,810; U.S. 3,615,024; U.S. 4,029,582 and U.S. 4,188,354; GB-A-2,000,720; Office of Saline Water R & D Progress Report No. 357, October 1967; Reverse Osmosis and Synthetic Membranes, Ed. Sourirajan; Murari et al, J. Membr. Sci. 16: 121 -135 and 181 -193, 1983. Alternatively, a porous support membrane for use in the method according to the present invention can be prepared as follows: once the desired polymer casting solution is prepared (i.e. polymers are dissolved in a suitable solvent system, and optionally organic or inorganic matrices are added into the casting solution so that the matrices are well dispersed) and, optionally, filtered by any of the known processes (e.g. pressure filtration through microporous filters, or by centrifugation), it is casted onto a suitable porous substrate, such as glass, metal, paper, plastic, etc., from which it may then be removed. Preferably, the desired polymer casting solution is casted onto a suitable porous substrate from which the membrane is not removed. Such porous substrate can take the form of an inert porous material which does not hinder the passage of permeate through the membrane and does not react with the membrane material, the casting solution, the gelation bath solvent, or the solvents which the membrane will be permeating in use.

Such porous substrates may be non-woven, or woven, including cellulosics (paper), polyethylene, polypropylene, nylon, vinyl chloride homo-and co-polymers, polystyrene, polyesters such as polyethylene terephthalate, polyvinylidene fluoride, polytetrafluoroethylene, polysulfones, polyether sulfones, poly-ether ketones (PEEK), polyphenylene oxide, polyphenyline sulphide (PPS), Ethylene-(R) ChloroTriFluoroEthylene (Halar ® ECTFE), glass fibers, metal mesh, sintered metal, porous ceramic, sintered glass, porous carbon or carbon fibre material, graphite, inorganic membranes based on alumina and/or silica (possibly coated with zirconium and/or other oxides). The membrane may otherwise be formed as a hollow fiber or tubelet, not requiring a support for practical use; or the support may be of such shape, and the membrane is casted internally thereon.

Conditioning

Optionally, the porous support membrane is impregnated with a first conditioning agent dissolved in a solvent to impregnate the porous support membrane prior to the IFIP reaction. The term "conditioning agent" is used herein to refer to any agent which, when impregnated into the support membrane prior to the IFIP reaction, provides a resulting membrane with a higher rate of flux after drying. This conditioning agent may be, but is not limited to, a low volatility organic liquid. The conditioning agent may be chosen from synthetic oils (e.g., polyolefinic oils, silicone oils, polyalphaolefinic oils, polyisobutylene oils, synthetic wax isomerate oils, ester oils and alkyl aromatic oils), mineral oils (including solvent refined oils and hydroprocessed mineral oils and petroleum wax isomerate oils), vegetable fats and oils, higher alcohols (such as decanol, dodecanol, heptadecanol), glycerols, and glycols (such as polypropylene glycols, polyethylene glycols, polyalkylene glycols). Suitable solvents for dissolving the conditioning agent include water, alcohols, ketones, aromatics, hydrocarbons, or mixtures thereof.

Following treatment with the conditioning agent, the support membrane is typically dried in air at ambient conditions to remove residual solvent. Initiators

The term "initiator" as used herein encompasses any compound able to open an epoxide ring without protonating the formed zwitterion, or to induce the formation of an anion (e.g. alkoxide, hydroxide), which is able to subsequently open the epoxide ring. The initiator will hence not be incorporated in the polymer backbone of the thin film top layer, but could be present at the end of the polymer chain (if reaction path 1 a is followed).

For the purpose of this invention, initiator encompasses any compound which react in a manner analogous to the tertiary amines in the polymerization reactions described herein. Initiator functional groups include but are not restricted to tertiary amino, tertiary thiol, bases, hydroxyl groups, such as NaOH, and other, preferentially tertiary, nucleophiles.

The ring-opening polymerization as used herein refers to the formation of a poly(epoxy)ether formed from a the opening of an epoxide-ring. The epoxide ring needs to be opened by an initiator in order for the polymerization to start. Amongst different initiators, tertiary amines are the most widely studied, and a reaction mechanism is depicted in Scheme 1 . Two types of initiation steps are shown, wherein the first initiation reaction consists of the direct attack of the tertiary amine to the epoxy group resulting in a zwitterion (reaction 1 a). The second initiation reaction uses the presence of alcohols or other proton-donating (acids) compounds to obtain a highly reactive alkoxide ion (reaction 1 b). Caustic compounds are believed to also induce this reaction. Since the initiator is dissolved in an aqueous, polar phase, this solvent will ensure alkoxide formation. Propagation can be conducted through the nucleophilic attack of the alkoxide ions on the epoxy groups. The polymer will grow via chain-growth polymerization.

Once all available epoxy groups are polymerized, termination will occur, wherein the solvent will again form alkoxides.

Scheme 1 .

As example, initiators having amino groups as the functional group include, but are not limited to: (a) linear tertiary amines, such as N,N,N',N'-tetramethyl-1 ,6-hexanediamine and triethylamine; (b) cycloaliphatic tertiary amines, such as 1 ,4-dimethylpiperazine; (c) aromatic tertiary amines, such as (dimethylaminomethyl)phenol, 2,4,6- Tris(dimethylaminomethyl)phenol and dimethylbenzylamine; (d) pyridines, preferentially with tertiairy amines, such as 4(dimethylamino)pyridine; (e) imidazoles, preferentially with tertiairy amines, such as 1 -Benzyl-2-methyl-1 H-imidazol; (f) ammonium salts of the amines described hereinabove (a) to (e).

Preferably, said initiator contains a functional group selected from the group consisting of: a tertiary amino, a tertiary thiol, a base, a hydroxyl group and any other (tertiary) nucleophiles.

In a specific embodiment of the present invention, the initiator functional group is a tertiairy amine.

Aliphatic initiators include both straight chain and branched hydrocarbons containing 2-15 carbon atoms, with at least one initiator functional group that is sufficient nucleophile and/or basic to initiate the polymerization reaction. Determination of the number and size of branches or substitutions is intended to allow high flexibility and hence higher availability of the initiator at the interface, which is also achievable by a high solubility of the initiator in the organic solvent. Initiators which are larger, more polar, more hydrophilic, or a combination thereof are expected to diffuse more slowly into the organic solvent phase and hence decrease the rate of success for initiation. Sterically hindered amines, or a branched structure with substituents on the amino groups very close together should be avoided as initiators.

It is further preferred that, the initiator concentrations are in the range of 0.05-20% by weight. The concentration of the initiator in the aqueous solution is determined, in part, upon the number and nucleophilic strength of the reactive groups per initiator molecule, the method of transferring the initiator to the porous support membrane, and the desired performance characteristics. The pH of the solution should be in the range of from about 7 to about 12. This substantially aqueous solution may or may not contain a solvent capable of dissolving or plasticizing the porous support membrane. U.S. 4,950,404, discloses an enhancement of flux when dissolving or plasticizing solvents such as the polar aprotic tetrahydrofuran, dimethylformamide, N-methylpyrrolidone, acetone and sulfolane are used in concentrations of about 1 -20% in the aqueous initiator solution. Epoxide monomers

The term "epoxide monomer" refers to compounds having at least two or more oxirane rings, highly reactive due to their high ring strain (20 kcal/mol). Due to the electrophilic character of the oxygen atom in the ring, epoxides can react with nucleophiles, which open up the oxirane ring.

A eneral structure for the epoxide monomer can be portrayed as follows by formula (II):

(I D wherein A represents an aliphatic, heterocyclic, or aromatic group, i.e. a group having 2 to 8 carbon atoms, including a divalent alicyclic group, a divalent aromatic group, or a divalent hetero-aromatic group; where Ri and R2 are each an independently selected alkylene or alkenylene group having from 0 to 8 carbons atoms; and wherein R3 and R₄ are independently selected from the group consisting of: hydrogen; halogen; aliphatic, heterocyclic, or aromatic group, i.e. a group having from 2 to 8 carbon atoms, including a divalent alicyclic group, a divalent aromatic group, or a divalent hetero-aromatic group. In addition, Ri and R3, for example, may be taken together to be a heterocyclic or alicyclic group. In addition, R2 and R₄, for example, may be taken together to be a heterocyclic or alicyclic group.

Preferably, the epoxide monomer is selected from the group: phenyl glycidyl ethers, bisphenol- A-diglycidyl-ether, Tetraphenolethane tetraglycidylether, neopentylglycol diglycidylether, trimetylolpropane triglycidylether, 1 ,4-butanediol diglycidylether, triglycidyl-p-aminophenol, tetraglycidyl-4,4'-diaminodiphenylmethane, and diglycidyl ester of hexahydrophthalic acid.

It is further preferred that, the solvent for the epoxide reagents is a relative non-solvent for the reaction product, or oligomer, and is relatively immiscible in the solvent containing the initiator. In a preferred embodiment of the present invention, threshold of immiscibility is as follows: an organic solvent should be soluble in the initiating solvent not more than between 0.01 weight percent and 1 .0 weight percent. Suitable organic solvents for the epoxide include but are not limited to hydrocarbons and halogenated hydrocarbons such as n-pentane, n-hexane, octane, cyclohexane, toluene, naphtha, and carbon tetrachloride.

Poly(epoxy)ether

The term "poly(epoxy)ether" as used herein refers to polymers wherein the main polymer chain fully consists of C-C and C-O-C (ether) bonds and to polymers wherein the main polymer chain mainly consists of C-C and C-O-C (ether) bonds and wherein hydroxyl groups and unreacted epoxides remain present.

Interfacial initiation

As used herein, the term "interfacial initiation" refers to an epoxy ring-opening reaction that occurs at or near the interfacial boundary of two largely immiscible solutions, matching the surface of a porous supporting ultrafiltration membrane. The initiator is present in a phase in which the epoxide-phase is not miscible.

The interfacial initiation reaction is generally held to take place at the interface between an initiating solution, and a polyfunctional epoxide monomer solution, which form two phases. Each phase may include a solution of a single type of dissolved polyfunctional epoxide/initiator or a combination of different types of polyfunctional epoxide/initiator. Concentrations of the dissolved epoxide and initiator may vary. Variables in the system may include, but are not limited to, the nature of the solvents (including ionic liquids), the nature and functionality of the epoxide and initiator, the molar ratio between initiator and epoxide, use of additives in any of the phases, reaction temperature (thermal cycle) that affects the relative rates of different steps and reaction time. Such variables may be controlled to define the properties of the membrane, e.g., membrane selectivity, flux, top layer thickness. The interfacial initiation reaction provides a polymer film on a surface of the porous support membrane.

Treating the resulting asymmetric TFC membrane with an activating solvent

In the method according to the present invention, the post-treatment step (c) preferably includes treating the resulting TFC membranes prior to use for (nano)filtration with an activating solvent, including, but not limited to, polar aprotic solvents. In particular, activating solvents include DMAc, NMP, DMF and DMSO. The "activating solvent" as referred to herein is a liquid that enhances the TFC membrane flux after treatment. The choice of activating solvent depends on the top layer and membrane support stability. Contacting may be effected through any practical means, including passing the TFC membrane through a bath of the activating solvent, or filtering the activating solvent through the composite membrane. More preferably, the composite membrane may be treated with an activating solvent during or after interfacial polymerization. Without wishing to be bound by any particular theory, the use of an activating solvent to treat the membrane is believed to flush out any debris and unreacted material from the pores of the membrane following the interfacial polymerization reaction. The treatment of the composite membrane with an activating solvent provides a membrane with improved properties, including, but not limited to, membrane flux.

TFC-Conditioning

In an embodiment of the present invention, the resulting TFC membrane is impregnated with a second conditioning agent dissolved in a water or organic solvent to impregnate the support membrane after the interfacial polymerization reaction (step (d)). The term "conditioning agent" is used herein to refer to any agent which, when impregnated into the support membrane after the interfacial polymerization reaction, provides a resulting membrane with a higher rate of flux after drying.

The "first conditioning agent" and "second conditioning agent" as referred to herein may be the same, or a different agent. This second conditioning agent may therefore also be, but is not limited to, a low volatility organic liquid. The conditioning agent may be chosen from synthetic oils (e.g., polyolefinic oils, silicone oils, polyalphaolefinic oils, polyisobutylene oils, synthetic wax isomerate oils, ester oils and alkyl aromatic oils), mineral oils (including solvent refined oils and hydro-processed mineral oils and petroleum wax isomerate oils), vegetable fats and oils, higher alcohols (such as decanol, dodecanol, heptadecanol), glycerols, and glycols (such as polypropylene glycols, polyethylene glycols, polyalkylene glycols). Suitable solvents for dissolving the conditioning agent include water, alcohols, ketones, aromatics, hydrocarbons, or mixtures thereof.

Following treatment with the conditioning agent, the TFC membrane is typically dried in air at ambient conditions to remove residual solvent. A second aspect of the present invention relates to the use of the TFC membranes of the present invention, for nanofiltration or reverse osmosis of components. Said components can be suspended in organic solvents or in aqueous solvents of any pH (pHO-14) including in extreme pH conditions, such as pH(0-4), and pH (10-14) or said components can be suspended in aqueous oxidizing solvents, such as NaOCI, or said components can be suspended in polar aprotic solvents.

A third aspect of the present invention relates to the TFC membranes obtainable by the methods of the present invention. Said TFC membranes comprise a poly(epoxy)ether top layer made via interfacial initiation of polymerization (IFIP), comprising the following steps: a) impregnation of an ultrafiltration porous support membrane with an aqueous solution containing an initiator; and b) contacting the impregnated support membrane with a second water-immiscible solvent or ionic liquid containing a polyfunctional epoxide monomer.

Thus the TFC membranes of the present invention are high flux semipermeable and can be used for (nano)filtration operations, particularly in organic solvents, and more particularly (nano)filtration operations in polar aprotic solvents or in challenging pH and/or oxidizing solutions.

EXAMPLES

EXAMPLE 1

A 14wt% PI solution in NMP/THF 3/1 was prepared. The solution was cast onto a porous non- woven PP/PE substrate (Novatex 2471 , Freudenberg). The obtained support membranes were immersed in a 1 w/v% hexanediamine (HDA) in water solution for 1 h. After the cross-linking reaction, the remaining HDA was allowed to diffuse out of the membrane pores by immersion the membrane in distilled water for 5h. The membrane was subsequently transferred to an 1w/v% N,N,N',N'-tetramethyl-1 ,6-hexanediamine in water solution for 1 h. Then the membrane was brought into a specially designed IFIP set-up after which a 0.1w/v% EPON (Tetraphenolethane tetraglycidylether) solution in toluene was poured on the impregnated support and allowed to stand for different polymerization times. The membrane was subsequently filtered with a 35μΜ rose bengal in ethanol solution, of which the results are summarized in table 1 .

Table 1 :

EXAMPLE 2

A 12wt% PAN solution in DMF was prepared. The solution was cast onto a porous non-woven PP/PE substrate (Novatex 2471 , Freudenberg). The obtained support membranes were cross- linked with hydrazine. The membrane was subsequently transferred to an 1w/v% Ν,Ν,Ν',Ν'- tetramethyl-1 ,6-hexanediamine in water solution for 1 h. Then the membrane was brought into a specially designed IFIP set-up after which a 0.1w/v% EPON solution in toluene was poured on the impregnated support for 72h. The membrane was subsequently filtered with a 35μΜ rose bengal in ethanol solution, of which the results are summarized in table 2.

Table 2:

EXAMPLE 3

The membrane synthesized in Example 2 was immersed in a 1 M HCI solution for 120h at 60°C and subsequently re-filtrated with a 35μΜ rose bengal in ethanol solution. Results are shown in table 3.

Table 3:

EXAMPLE 4

The membrane synthesized in Example 2 was immersed in a 400ppm NaOCI solution for 6h at 25°C and subsequently re-filtrated with a 35μΜ rose bengal in ethanol solution. Results are shown in table 4.

Table 4:

EXAMPLE 5

The membrane synthesized in Example 2 was immersed in a 400ppm NaOCI solution for 6h at 60°C and subsequently re-filtrated with a 35μΜ rose bengal in ethanol solution. Results are shown in table 5. Table 5:

EXAMPLE 6: STABILITY OF DIFFERENT TFC MEMBRAN ES.

1 ) Beta-alkanol amine membrane, based on DETA (=diethylenetriamine) (as described WO2015/127516):

The TFC membrane with a β-alkanol amine top-layer on a XL-PI support is stable in pH 0, but unstable in pH 13.5. This is proven by the ATR-FTIR spectra, as the peaks representing the functional groups of the β-alkanol amine top-layer completely vanish after immersion in pH 13.5, while they remain the same after immersion in pH 0 (Figure 1 ).

2) Polyepoxyether membraan, made by the method of the present invention:

The poly(epoxyether) top-layer on a XL-PAN support led to stability of the full TFC-membrane in extremely challenging conditions, i.e. pH 13.5, pH 0 and 400 ppm of the strong oxidant NaOCI. This is proven by the unchanged ATR-FTIR intensity ratios of the infrared signals, compared to the reference C-H stretch signal (Figure 2). The small changes in intensity ratios can be ascribed to practical differences in ATR-FTI R sample manipulations.

Claims

A method for synthesis of a thin-film composite membrane comprising a poly(epoxy)ether top layer by interfacial initiation of polymerization (IFIP), comprising the following steps: a) impregnation of an ultrafiltration porous support membrane with an aqueous solution containing an initiator; and b) contacting the impregnated support membrane with a second water-immiscible solvent or ionic liquid containing a polyfunctional epoxide monomer, thereby obtaining a membrane, wherein said initiator is not incorporated in the polymer backbone of the thin film top layer, and is optionally present at the end of the polymer chain

The method of claim 1 , wherein the initiator contains a functional group selected from the group consisting of: a tertiary amino, a tertiary thiol, a base, a hydroxyl group and any other (tertiary) nucleophiles.

The method according to claim 1 or 2, wherein the initiator contains a tertiary amino functional group.

The method according to any one of claims 1 to 3, wherein the epoxide monomer is selected from the group:phenyl glycidyl ethers, bisphenol-A-diglycidyl-ether, Tetraphenolethane tetraglycidylether, neopentylglycol diglycidylether, trimetylolpropane triglycidylether, 1 ,4-butanediol diglycidylether, triglycidyl-p- aminophenol, tetraglycidyl-4,4'-diaminodiphenylmethane, and diglycidyl ester of hexahydrophthalic acid.

The method according to any one of claims 1 to 4, wherein the epoxide monomer is Tetraphenolethane tetraglycidylether.

The use of a thin film composite membrane obtained by the method according to any one of the claims 1 to 5 for nanofiltration or reverse osmosis of components.

The use according to claim 6, wherein said components are suspended in organic solvents.

The use according to claim 6, wherein said components are suspended in aqueous solvents of pHranges pHO-4 and pH 10-14.

9. The use according to claim 8, wherein said components are suspended in aqueous oxidizing solvents.

10. The use according to claim 9, wherein said aqueous oxidizing solvent is NaOCI.

1 1 . The use according to claim 6 or 7, wherein said components are suspended in polar aprotic solvents.