Solvent resistant polyamide nanofiltration membranes

Abstract

The present invention relates to a composite membrane for nanofiltration of a feed stream solution comprising a solvent and dissolved solutes and showing preferential rejection of the solutes. The composite membrane comprises a thin polymeric film formed by interfacial polymerization on a support membrane. The support membrane is further impregnated with a conditioning agent and is stable in polar aprotic solvents. The composite membrane is optionally treated in a quenching medium, where the interfacial polymerization reaction can be quenched and, in certain embodiments, membrane chemistry can be modified. Finally the composite membrane is treated with an activating solvent prior to nanofiltration.

Claims

1. An interfacial polymerization process for forming a composite membrane suitable for nanofiltration operations in polar aprotic solvents, said process comprising the sequential steps of: (a) impregnating a porous support membrane comprising a first conditioning agent, with a first reactive monomer solution comprising: (i) a first solvent for the said first reactive monomer and (ii) a first reactive monomer; wherein the first conditioning agent is polyethylene glycol, and wherein said support membrane is stable in polar aprotic solvents and is formed from crosslinked polyimide, crosslinked polybenzimidazole, crosslinked polyacrylonitrile, Teflon, polypropylene, or polyether ether ketone (PEEK), or sulfonated polyether ether ketone (S-PEEK); (b) contacting the impregnated support membrane with a second reactive monomer solution comprising: (i) a second solvent for the second reactive monomer and (ii) a second reactive monomer; wherein the first solvent and the second solvent form a two-phase system; (c) after a reaction period, immersing the resulting composite membrane into a quench medium; (d) treating the resulting composite membrane with an activating solvent, wherein the activating solvent is selected from the group consisting of dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, or a mixture thereof, and: (e) optionally, impregnating the resulting composite membrane with a second conditioning agent, wherein the second conditioning agent is a non-volatile liquid, and wherein the use of both the first conditioning agent and the activating solvent increases the organic solvent flux of the composite membrane.

2. A process according to claim 1, wherein the support membrane is formed from crosslinked polyimide.

3. A process according to claim 1, wherein the first reactive monomer solution comprises an aqueous solution of a polyamine.

4. A process according to claim 1, wherein the first reactive monomer solution comprises an aqueous solution of a 1,6 hexenediamine, m-phenylenediamine, or poly(ethyleneimine).

5. A process according to claim 1, wherein the second reactive monomer solution contains a polyacyl chloride.

6. A process according to claim 1, wherein the composite membrane is treated in step (d) with the activating solvent by immersion or by washing in the activating solvent.

7. A process according to claim 1, wherein the composite membrane is treated in step (d) with the activating solvent by filtration through the membrane using the activating solvent.

8. A process according claim 1, wherein the activating solvent is dimethylformamide or dimethyl sulfoxide.

9. A process according to claim 1 in which the contacting in step (b) is performed in a time between about 5 seconds and about 5 hours.

10. A process according to claim 1 in which the temperature of the solution in step (b) is held between about 10 C. and about 100 C.

11. The process according to claim 1, wherein the second reactive monomer solution contains trimesoyl chloride, iso-phthaloyl dichloride, sebacoyl chloride, or a mixture thereof.

12. The process according to claim 1, wherein the activating solvent is dimethylformamide.

13. The process according to claim 1, wherein the concentration of the first reactive monomer in the first reactive monomer solution, and the second reactive monomer in the second reactive monomer solution, is 0.01 to 5 wt. %.

14. The process according to claim 1, wherein the first reactive monomer is m-phenylenediamine, the second reactive monomer is trimesoyl chloride, and the activating solvent is dimethylformamide.

15. The process according to claim 1, wherein the second conditioning agent is selected from one or more of synthetic oils, mineral oils, vegetable fats and oils, higher alcohols, glycerols, and glycols.

16. A method comprising the step of: performing nanofiltration of a feed stream solution using the membrane produced by the process of claim 1, wherein the feed stream solution comprises a solvent and dissolved solutes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows molecular weight cut off (MWCO) curves and fluxes of TFC membranes after treatment with DMF as an activating solvent. Nanofiltration of a feed solution comprising polystyrene oligomers dissolved in DMF has been performed at 30 bar and 30 C.

(2) FIG. 2 shows MWCO curves and fluxes of TFC membranes after treatment with DMF as an activating solvent. Nanofiltration of a feed solution comprising polystyrene oligomers dissolved in THF has been performed at 30 bar and 30 C.

(3) FIG. 3 shows MWCO curves and fluxes of TFC membranes after contacting with DMF as an activating solvent. Nanofiltration of a feed solution comprising alkanes dissolved in THF has been performed at 30 bar and 30 C.

(4) FIG. 4 shows the MWCO curve and flux of a TFC membrane which has not been treated with an activating solvent. Nanofiltration of a feed solution comprising polystyrene oligomers dissolved in acetone has been performed at 30 bar and 30 C.

(5) FIG. 5 shows the MWCO curve and flux of a TFC membrane which has been treated with DMF as an activating solvent. Nanofiltration of a feed solution comprising polystyrene oligomers dissolved in acetone has been performed at 30 bar and 30 C.

(6) FIG. 6 shows MWCO curve and flux of a TFC membrane which has not been treated with an activating solvent. Nanofiltration of a feed solution comprising polystyrene oligomers dissolved in methanol has been performed at 30 bar and 30 C.

(7) FIG. 7 shows MWCO curve and flux of a TFC membrane which has been treated with DMF as an activating solvent. Nanofiltration of a feed solution comprising polystyrene oligomers dissolved in methanol has been performed at 30 bar and 30 C.

(8) FIG. 8 shows MWCO curve and flux of a TFC membrane which has been treated with DMF as an activating solvent. Nanofiltration of a feed solution comprising polystyrene oligomers dissolved in toluene has been performed at 30 bar and 30 C.

(9) FIG. 9 shows MWCO curve and flux of a TFC membrane which has been treated with DMF as an activating solvent. Nanofiltration of a feed solution comprising polystyrene oligomers dissolved in ethyl acetate has been performed at 30 bar and 30 C.

(10) FIG. 10 shows MWCO curves and fluxes of TFC membranes prepared on a crosslinked polyimide support membrane which was not impregnated with a conditioning agent. Nanofiltration of a feed solution comprising polystyrene oligomers dissolved in DMF has been performed at 30 bar and 30 C.

(11) FIG. 11 shows MWCO curve and flux of a TFC membrane prepared on a crosslinked polyimide support membrane which was impregnated with PEG as a conditioning agent. Nanofiltration of a feed solution comprising polystyrene oligomers dissolved in DMF has been performed at 30 bar and 30 C.

(12) FIG. 12 shows MWCO curves and fluxes for TFC membranes prepared on a PEEK support membrane. The TFC membrane has not been treated with DMF as an activating solvent. Nanofiltration of a feed solution comprising polystyrene oligomers dissolved in THF has been performed at 30 bar and 30 C.

(13) FIG. 13 shows MWCO curves and fluxes for TFC membranes prepared on a PEEK support membrane. The TFC membrane has been treated with DMF as an activating solvent. Nanofiltration of a feed solution comprising polystyrene oligomers dissolved in THF has been performed at 30 bar and 30 C.

(14) FIG. 14 shows MWCO curves and fluxes for TFC membranes containing hydrophobic groups added after the interfacial polymerisation reaction. The resulting composite membranes are treated with DMF as an activating solvent. Nanofiltration of a feed solution comprising polystyrene oligomers dissolved in THF has been performed at 30 bar and 30 C.

(15) FIG. 15 shows MWCO curves and fluxes for TFC membranes containing hydrophobic groups added during the interfacial polymerisation reaction. The resulting composite membranes are treated with DMF as an activating solvent. Nanofiltration of a feed solution comprising polystyrene oligomers dissolved in THF has been performed at 30 bar and 30 C.

DESCRIPTION OF VARIOUS EMBODIMENTS

(16) Thin film composite (also referred to as TFC) membranes formed by interfacial polymerisation will be familiar to one of skill in this art and include an entity composed of a dense ultra-thin film layer over a support membrane, where the support membrane is previously formed from a different material.

(17) Suitable support membranes can be produced from polymer materials including crosslinked polyimide, crosslinked polybenzimidazole, crosslinked polyacrylonitrile, Teflon, polypropylene, and polyether ether ketone (PEEK), or sulfonated polyether ether ketone (S-PEEK).

(18) The polymer used to form the support membrane includes but is not limited to polyimide polymer sources. The identities of such polymers are presented in the prior art, U.S. Pat. No. 0,038,306, the entire contents of which are incorporated herein by reference. More preferably, the support membrane of the invention is prepared from a polyimide polymer described in U.S. Pat. No. 3,708,458, assigned to Upjohn, the entire contents of which are incorporated herein by reference. The polymer, available from HP polymers GmbH, Austria as P84, is a copolymer derived from the condensation of benzophenone 3,3,4-4-tetracarboxylic acid dianhydride (BTDA) and a mixture of di(4-aminophenyl) methane and toluene diamine or the corresponding diisocyanates, 4,4-methylenebis(phenyl isocyanate) and toluene diisocyanate. The obtained copolyimide has imide linkages which may be represented by the structural formulae:

(19) ##STR00001##
wherein the copolymer comprises from about 80% I and 20% II.

(20) Support membranes can be prepared following the methods described in GB 2,437,519, the entire contents of which are incorporated herein by reference, and comprise both nanofiltration and ultrafiltration membranes. More preferably, the membranes of the invention used as supports are within the ultrafiltration range. The membrane supports of the invention may be crosslinked using suitable amine crosslinking agents and the crosslinking method and time may be that described in GB 2,437,519.

(21) It is an important feature of the present invention that the support membrane is impregnated with a conditioning agent. The term conditioning agent is used herein to refer to any agent which, when impregnated into the support membrane prior to the interfacial polymerisation reaction, provides a resulting membrane with a higher rate of flux after drying. Any suitable conditioning agent may be used. Suitably, the conditioning agent is 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. The first and second conditioning agents referred to herein may be the same or different.

(22) In this invention, prior to the interfacial polymerization reaction, the support membrane is treated with a first conditioning agent dissolved in a solvent to impregnate the support membrane. Suitably, the first conditioning agent is a low volatility organic liquid as defined above.

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

(24) The interfacial polymerization reaction is generally held to take place at the interface between the first reactive monomer solution, and the second reactive monomer solution, which form two phases. Each phase may include a solution of a dissolved monomer or a combination thereof. Concentrations of the dissolved monomers may vary. Variables in the system may include, but are not limited to, the nature of the solvents, the nature of the monomers, monomer concentrations, use of additives in any of the phases, reaction temperature and reaction time. Such variables may be controlled to define the properties of the membrane, e.g., membrane selectivity, flux, top layer thickness. Monomers used in the reactive monomer solutions may include, but are not limited to, diamines and diacyl halides. The resulting reaction may form a polyamide selective layer on top of the support membrane.

(25) In this invention, the polymer matrix of the top layer can comprise any three-dimensional polymer network known to those of skill in the art. In one aspect, the thin film comprises at least one of an aliphatic or aromatic polyamide, aromatic polyhydrazide, poly-benzimidazolone, polyepiamine/amide, polyepiamine/urea, poly-ethyleneimine/urea, sulfonated polyfurane, polybenzimidazole, polypiperazine isophtalamide, a polyether, a polyether-urea, a polyester, or a polyimide or a copolymer thereof or a mixture thereof. Typically, the polymer selected to form the thin film can be formed by an interfacial polymerization reaction.

(26) In a further embodiment of this invention, the film comprises a polyamide. The polyamide can be an aromatic polyamide or a non-aromatic polyamide. For example, the polyamide can comprise residues of a phthaloyl (e.g. terephthaloyl or isophthaloyl) halide, a trimesyl halide, or a mixture thereof. In another example, the polyamide can comprise residues of diaminobenzene, triaminobenzene, piperazine, poly-piperazine, polyetherimine or a mixture thereof. In a further embodiment, the film comprises residues of a trimesoyl halide and residues of a diaminobenzene. In a further embodiment, the film comprises residues of trimesoyl chloride and m-phenylenediamine. In a further aspect, the film comprises the reaction product of trimesoyl chloride and m-phenylenediamine.

(27) The first reactive monomer solution may comprise an aqueous solution of a polyamine. This aqueous amine solution may also contain other components, such as polyhydric compounds as disclosed in U.S. Pat. No. 4,830,885. Examples of such compounds include ethylene glycol, propylene glycol, glycerine, polyethylene glycol, polypropylene glycol, and copolymers of ethylene glycol and propylene glycol. The aqueous amine solution may also contain polar aprotic solvents.

(28) Aqueous monomer solutions may include, but are not limited to, an aqueous solution containing 1,6 hexenediamine, poly(ethyleneimine), an alternative aqueous monomer solution, and/or combinations thereof. Concentrations of solutions used in the interfacial polymerzation may be in a range from about 0.01 weight % to about 30 weight %. Preferably, concentrations of the interfacial polymerization solutions may be in a range from about 0.1% weight % to about 5 weight %.

(29) The second reactive monomer solution may contain di- or triacyl chlorides such as trimesoyl chloride or other monomers, dissolved in a nonpolar solvent such as hexane, heptane, toluene or xylene. Further, the second reactive monomer solution may include, but is not limited to, a xylene solution of iso-phthaloyl dichloride, sebacoyl chloride, an alternative organic monomer solution, and/or combinations thereof.

(30) The disclosed interfacial polymerization reaction time of step (b) may vary. For example, an interfacial polymerization reaction time may be in a range from about 5 seconds to about 2 hours.

(31) The quenching step (c) includes contacting or treating the membrane after the interfacial polymerisation reaction with a quenching medium. The quenching medium quenches any un-reacted functional groups present following the interfacial polymerisation reaction.

(32) In an embodiment, the quenching medium is water.

(33) The quenching medium may also comprise an alcohol. The presence of an alcohol will cap any unreacted acyl chloride groups present following the interfacial polymerisation reaction. Suitable alcohols include, but are not limited to, ROH, ArOH, alcohols optionally with one or more siloxane-substituents, alcohols with one or more halo-substituents (including fluorinated alcohols R.sub.FOH, where R.sub.F is an alkyl group with one or more hydrogen atoms replaced by fluorine atoms), where R includes but is not limited to alkyl, alkene, haloalkyl (e.g. R.sub.F), or SiOSi; and Ar is aryl (e.g. phenyl).

(34) The quenching medium may also comprise one or more capping monomers as quenching agents. Such capping monomers may include amines. Suitable amines include but are not limited to RNH.sub.2, ArNH.sub.2, amines with siloxane-substituents, alkylamines with halo-substituents including fluorine R.sub.FNH.sub.2 (where R.sub.F is an alkyl group in which one or more hydrogen atoms are replaced by fluorine atoms), where R includes but is not limited to alkyl, alkene, R.sub.F, SiOSi.

(35) The quenching medium may also comprise a solution containing R-acyl halides or Ar-acyl halides, where R includes but is not limited to alkyl, alkene, R.sub.F, SiOSi.

(36) In the above definitions, suitable alkyl groups or moieties comprise 1-20 carbon atoms and suitable alkene groups or moieties comprise 2-20 carbon atoms.

(37) A post treatment step (d) includes contacting the composite membranes prior to use for nanofiltration 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 in this art is defined as a liquid that enhances the composite 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 composite membrane through a bath of the activating solvent, or filtering the activating solvent through the composite membrane.

(38) The second conditioning agent optionally applied in step (e) may be impregnated into the membrane by immersing the TFC membrane in a water or organic solvent bath or baths comprising the second conditioning agent.

(39) The resultant high flux semipermeable TFC membranes of the invention can be used for nanofiltration operations, particularly in organic solvents, and more particularly nanofiltration operations in polar aprotic solvents.

(40) By the term nanofiltration it is meant a membrane process which will allow the passage of solvents while retarding the passage of larger solute molecules, when a pressure gradient is applied across the membrane. This may be defined in terms of membrane rejection R.sub.i, a common measure known by those skilled in the art and defined as:

(41) $\begin{array}{cc}{R}_i=\left(1-\frac{C_{\mathrm{Pi}}}{C_{R_i}}\right)100\%& \left(1\right)\end{array}$
where C.sub.P,i=concentration of species i in the permeate, permeate being the liquid which has passed through the membrane, and C.sub.R,i=concentration of species i in the retentate, retentate being the liquid which has not passed through the membrane. It will be appreciated that a membrane is selectively permeable for a species i if R.sub.i>0. It is well understood by those skilled in the art that nanofiltration is a process in which at least one solute molecule i with a molecular weight in the range 100-2,000 g mol.sup.1 is retained at the surface of the membrane over at least one solvent, so that R.sub.i>0. Typical applied pressures in nanofiltration range from 5 bar to 50 bar.

(42) The term solvent will be well understood by the average skilled reader and includes an organic or aqueous liquid with molecular weight less than 300 Daltons. It is understood that the term solvent also includes a mixture of solvents.

(43) By way of non-limiting example, solvents include aromatics, alkanes, ketones, glycols, chlorinated solvents, esters, ethers, amines, nitriles, aldehydes, phenols, amides, carboxylic acids, alcohols, furans, and polar protic and polar aprotic solvents, water, and mixtures thereof.

(44) By way of non-limiting example, specific examples of solvents include toluene, xylene, benzene, styrene, anisole, chlorobenzene, dichlorobenzene, chloroform, dichloromethane, dichloroethane, methyl acetate, ethyl acetate, butyl acetate, methyl ether ketone (MEK), methyl iso butyl ketone (MIBK), acetone, ethylene glycols, ethanol, methanol, propanol, butanol, hexane, cyclohexane, dimethoxyethane, methyl tert butyl ether (MTBE), diethyl ether, adiponitrile, N,N dimethylformamide, dimethylsulfoxide, N,N dimethylacetamide, dioxane, nitromethane, nitrobenzene, pyridine, carbon disulfide, tetrahydrofuran, methyltetrahydrofuran, N-methyl pyrrolidone, acetonitrile, water, and mixtures thereof.

(45) The term solute will be well understood by the average skilled reader and includes an organic molecule present in a liquid solution comprising a solvent and at least one solute molecule such that the weight fraction of the solute in the liquid is less than the weight fraction of the solvent, and where the molecular weight of the solute is at least 20 g higher than that of the solvent.

(46) The membrane of the present invention can be configured in accordance with any of the designs known to those skilled in the art, such as spiral wound, plate and frame, shell and tube, and derivative designs thereof.

(47) The following examples illustrate the invention.

EXAMPLES

(48) In the following examples, membrane performance was evaluated according to flux profiles and molecular weight cut off (MWCO) curves. All nanofiltration experiments were carried out at 30 bar using a cross-flow filtration system. Membrane discs, of active area 14 cm.sup.2, were cut out from flat sheets and placed into 4 cross flow cells in series. Permeate samples for flux measurements were collected at intervals of 1 h, and samples for rejection evaluations were taken after steady permeate flux was achieved. The MWCO was determined by interpolating from the plot of rejection against molecular weight of marker compounds. The solute rejection test was carried out using two standard solutions. The first was a standard feed solution comprised of a homologous series of styrene oligomers (PS) dissolved in the selected solvent. The styrene oligomer mixture contained 1-2 g L.sup.1 each of PS 580 and PS 1090 (Polymer Labs, UK), and 0.01 g L of -methylstyrene dimer (Sigma-Aldrich, UK). Analysis of the styrene oligomers was done using an Angilent HPLC system with UV/Vis detector set at a wavelength of 264 nm. Separation was achieved using a reverse phase column (C18-300, 2504.6 mm). The mobile phase consisted of 35 vol % analytical grade water and 65 vol % tetrahydrofuran with 0.1 vol % trifluoroacetic acid. The second standard marker solution consisted of a solution of alkanes containing 0.1% (w/v) of each alkane. The alkanes used were: decane, n-hexadecane, n-tetradecane, eicosan, tetracosane, hexacosane. Their MWs are 142.3 Dalton, 198.4 Dalton, 226.4 Dalton, 280.5 Dalton, 338.7 Dalton, and 366.7 Dalton respectively. Analysis of the alkanes was via gas chromatography.

(49) Solvent flux (J) was determined by measuring permeate volume (V) per unit area (A) per unit time (t) according to the following equation:

(50) $\begin{array}{cc}J=\frac{V}{A.Math.t}& \left(1\right)\end{array}$

(51) The rejection (R.sub.i) of markers was calculated from equation 2, where C.sub.P,i and C.sub.F,i correspond to styrene concentrations in the permeate and the feed respectively.

(52) $\begin{array}{cc}{R}_i=\left(1-\frac{C_{P,i}}{C_{F,i}}\right).Math.100\%& \left(2\right)\end{array}$

Example 1

(53) In the following example, membranes of the present invention are formed through interfacial polymerisation to form a polyamide on a crosslinked polyimide support membrane, as follows:

(54) Formation of Crosslinked Polyimide Support Membrane

(55) A polymer dope solution was prepared by dissolving 24% (w/w) polyimide (P84 from Evonik AG) in DMSO and stirring overnight until complete dissolution. A viscous solution was formed, and allowed to stand for 10 hours to remove air bubbles. The dope solution was then cast on a polyester or polypropylene (Viledon, Germany) non-woven backing material taped to a glass plate using a casting knife (Elcometer 3700) set at a thickness of 250 m. Immediately after casting, the membrane was immersed in a water bath where phase inversion occurred. After 15 minutes, it was changed to a new water bath and left for an hour. The wet membrane was then immersed in a solvent exchange bath (isopropanol) to remove any residual water and preparation solvents.

(56) The support membrane was then crosslinked using a solution of hexanediamine in isopropanol, by immersing the support membrane in the solution for 16 hours at room temperature. The support membrane was then removed from the crosslinking bath and washed with isopropanol for 1 h to remove any residual hexanediamine (HDA).

(57) The final step for preparing the crosslinked polyimide support membrane involved immersing the membrane overnight into a conditioning agent bath consisting of a volume ratio of 3:2 polyethylene glycol 400/isopropanol. The membrane was then wiped with tissue paper and air dried.

(58) Formation of Thin Film Composite Membranes by Interfacial Polymerisation:

(59) TFC membranes were hand-cast on the crosslinked polyimide support membrane through interfacial polymerization. The support membrane was taped to a glass plate and placed in an aqueous solution of 2% (w/v) m-phenylenediamine (MPD, >99%, Sigma-Aldrich) for approximately 2 min. The MPD loaded support membrane was then rolled with a roller to remove excess solution. The MPD saturated membrane support was then immersed in a solution of 0.1% (w/v) trimesoyl chloride (TMC, 98%, Sigma-Aldrich) in hexane. After 1 min of reaction, the resulting membranes were withdrawn from the hexane solution and rinsed with water (which corresponds to step (c) of the process defined herein, i.e. immersing the membrane into a quenching medium). The chemical structures of the monomers used for the interfacial polymerization reaction are shown in Scheme 1.

(60) ##STR00002##

(61) Membrane Identification Codes for the TFC Membranes Prepared in this Example are as Follows:

(62) TABLE-US-00001 Entry Membrane No. Membrane code 1 TFC membrane prepared on crosslinked PI as support MPD-n impregnated with polyethylene glycol (PEG)

(63) Where n identifies membranes made in independent batch n.

(64) Treatment of TFC Membranes with Activating Solvent (Step d).

(65) A post-formation treatment step was carried out on the composite membranes in which the membranes were contacted with an activating solvent. In this example the activating solvent was DMF. The contact time was 10 minutes via either filtration or immersion.

(66) Composite Membrane Performance.

(67) The performance of TFC membranes in DMF and in THF were evaluated before and after treatment with DMF as an activating solvent. The rejection curves and fluxes for the TFC membranes in DMF/PS solution and in THF/PS solution after post-treatment with DMF are shown in FIGS. 1 and 2. FIG. 3 shows rejection curves and flux for the TFC membranes in THF/Alkanes solution. The TFC membranes showed no flux with THF before post-treatment with an activating solvent. It is clear that contacting the membrane with the activating solvent enhances flux.

Example 2

(68) TFC membranes were fabricated as per EXAMPLE 1. Post-formation step (d) (contacting with DMF as an activating solvent) was only performed for some of the membranes. The performance of TFC membranes with and without the activation step (d) contacting with DMF was evaluated in different solvents, including acetone, methanol, ethyl acetate and toluene.

(69) For the MWCO curves and flux test in MeOH, acetone, toluene and ethyl acetate with and without contacting with DMF, eight new MPD membranes were tested at each time and the results for both rejection and flux were reproducible.

(70) FIG. 4 shows rejection curves and flux for TFC membranes in acetone/PS without treating the membrane with an activating solvent. FIG. 5 shows rejection curves and flux for TFC membranes during nanofiltration of acetone/PS solution after treating the membranes with DMF.

(71) FIG. 6 shows rejection curves and flux for TFC membranes during nanofiltration of MeOH/PS without treating the membrane with an activating solvent. FIG. 7 shows rejection curves and flux for TFC membranes during nanofiltration of MeOH/PS solution after treating the membranes with DMF.

(72) The TFC membranes that were not treated with DMF showed no flux in toluene and ethyl acetate. FIG. 8 shows rejection curves and flux for TFC membranes in Toluene/PS solution after treating the membranes with DMF.

(73) FIG. 9 shows rejection curves and flux for TFC membranes during nanofiltration of ethyl acetate/PS solution. Without DMF treatment the TFC membranes showed no flux in toluene or ethyl acetate.

Example 3

(74) Membrane supports were fabricated as per EXAMPLE 1 but were not conditioned with PEG. TFC membranes were fabricated on these non-conditioned support membranes as per EXAMPLE 1. The performance of TFC membranes prepared on membrane supports with and without PEG was then evaluated and compared.

(75) Membrane Identification Codes for the TFC Membranes Prepared in this Example are as Follows:

(76) TABLE-US-00002 Entry Membrane No. Membrane code 2 TFC membrane prepared on crosslinked PI as MPD-n support impregnated withPEG 3 TFC membrane prepared on crosslinked PI support MPD-NP-n not impregnated with PEG

(77) Where n identifies membranes made in independent batch n.

(78) FIG. 10 shows rejection curves and flux for TFC membranes prepared on membrane supports without PEG in DMF/PS solution. FIG. 11 shows rejection curves and flux for TFC membranes prepared on membrane supports with PEG in DMF/PS solution. An increase in flux can be observed when TFC membranes are prepared on membrane supports containing PEG.

(79) In this example the salt rejection of TFC membranes prepared with PEG impregnated support membranes was compared with those prepared with non-impregnated supports. For flux and rejection test, 150 mL of 0.2% NaCl (2000 ppm) aqueous solution were used in a dead-end cell filtration set-up at 30 bar pressure. It is clear that impregnating the support with PEG prior to the interfacial polymerisation reaction enhances water flux without changing salt rejection. The choice of the support membrane material depends on the application. For water applications, it is not required to have a solvent stable support membrane, so PEG-impregnated support membranes made from polysulfone and polyethersulfone are suitable and lead to enhanced water flux without changing rejection.

(80) TABLE-US-00003 NaCl NaCl aqueous solution Membrane Rejection (%) Flux (L m.sup.2 h.sup.1) at 30 bar MPD-NP 97.5 6.0 MPD 97.5 22.4

Example 4

(81) In this particular example TFC membranes were prepared on PEEK support membranes, as follows:

(82) Fabrication of Membrane Supports from Polyetheretherketone (PEEK):

(83) A polymer dope solution was prepared by dissolving 12.3% (w/w) PEEK in 79.4% methane sulfonic acid (MSA) and 8.3% sulfuric acid (H.sub.2SO.sub.4). The solution was stirred overnight until complete dissolution. A viscous solution was formed, and allowed to stand for 10 hours to remove air bubbles. The solution was then cast on a polyester non-woven backing material taped to a glass plate using a casting knife (Elcometer 3700) set at a thickness of 250 m. Immediately after casting, the membrane was immersed in a water bath where phase inversion occurred. After 15 minutes, it was changed to a new water bath and left for an hour. The wet membrane was then immersed in a water bath to remove any residual preparation solvents.

(84) The final step for preparing the PEEK support membrane involved immersing the membrane overnight into a conditioning agent bath consisting of a volume ratio of 3:2 polyethylene glycol 400/isopropanol. The membrane was then wiped with tissue paper and air dried. TFC membranes were fabricated as per EXAMPLE 1, section 1.2 on top of the PEEK support membrane. The TFC membranes were treated with DMF as an activating solvent as per EXAMPLE 1. Some of the TFC membranes were not treated with an activating solvent for comparison.

(85) FIG. 12 shows rejection curves and flux for TFC membranes during nanofiltration of THF/PS solution without treating the membrane with an activating solvent. FIG. 13 shows rejection curves and flux for TFC membranes during nanofiltration of THF/PS solution after treating the membranes with DMF as an activating solvent.

Example 5

(86) TFC membranes were fabricated as per EXAMPLE 1. After the interfacial polymerisation reaction the membranes were treated in a quenching medium comprising a reactive monomer dissolved in a solvent (step c).

(87) Treatment of TFC Membranes in Quenching Medium

(88) A post-formation treatment step was carried out on the composite membranes in which the membranes were contacted with a quenching medium. In this example the quenching medium was a solution of a fluoroamine or amino siloxane in hexane. The contact time was 1 minute via immersion. The reactive monomer end-caps the free acyl chloride groups left in the polyamide film. In this example, the quenching step modifies the membrane chemistry, making it more hydrophobic by capping the unreacted acyl chloride groups with amines comprising halo-, silyl- or siloxane-substituents. The chemical structures of the monomers used for the interfacial polymerisation reaction are shown in Scheme 2.

(89) ##STR00003##

(90) ##STR00004##

(91) Membrane Identification Codes for the TFC Membranes Prepared in this Example are as Follows:

(92) TABLE-US-00004 Entry No. Membrane Membrane code 4 TFC membrane prepared on crosslinked PI as MPD-n support impregnated with PEG. 5 TFC membrane prepared on crosslinked PI as Fluoroamine- support impregnated with PEG. The TFC MPD-n membrane is post-treated with a solution of 2,2,3,3,3-pentafluoropropylamine in hexane. 6 TFC membrane prepared on crosslinked PI as Aminosiloxane- support impregnated with PEG. The TFC MPD-n membrane is post-treated with a solution of poly[dimethylsiloxane-co- (3-aminopropyl)methylsiloxane] in hexane.

(93) Where n identifies membranes made in independent batch n.

(94) The performance of the chemically modified TFC membranes was evaluated in toluene. For the MWCO curves and flux test in Toluene eight new TFC membranes were tested at each time and the results for both rejection and flux were reproducible. FIG. 14 shows rejection curves and flux for these hydrophobic TFC membranes in Toluene/PS solution.

Example 6

(95) Crosslinked polyimide supports were fabricated as per EXAMPLE 1 and impregnated with PEG. During the interfacial polymerisation reaction the trimesoyl chlode was blended with a fluoromonoacyl chloride to make the membrane more hydrophobic and more open.

(96) Formation of Thin Film Composite Membranes by Interfacial Polymerisation:

(97) TFC membranes were hand-cast on the crosslinked polyimide support membrane containing PEG through interfacial polymerization. The support membrane was taped to a glass plate and placed in an aqueous solution of 2% (w/v) m-phenylenediamine (MPD, >99%, Sigma-Aldrich) for approximately 2 min. The MPD loaded support membrane was then rolled with a roller to remove excess solution. The MPD saturated membrane support was then immersed in a solution of 0.1% (w/v) trimesoyl chloride (TMC, 98%, Sigma-Aldrich) blended with perfluorooctanoylchloride (7:1) in hexane. After 1 min of reaction, the resulting membranes were withdrawn from the hexane solution and rinsed with water step (c) (immersing membrane into quenching medium). The chemical structures of the monomers used for the interfacial polymerization reaction are shown in Scheme 3.

(98) ##STR00005##

(99) Membrane Identification Codes for the TFC Membranes Prepared in this Example are as Follows:

(100) TABLE-US-00005 Entry No. Membrane Membrane code 7 TFC membrane prepared on crosslinked PI MPD-n as support impregnated with PEG. 8 TFC membrane prepared on crosslinked PI Fluoroacylchloride- as support impregnated with PEG. During MPD-n interfacial polymerisation the TMC is blended with Perfluorooctanoylchloride to render the membrane more hydrophobic and with higher MWCO

(101) Where n identifies membranes made in independent batch n.

(102) The performance of the chemically modified TFC membranes was evaluated in ethyl acetate. For the MWCO curves and flux test in ethyl acetate eight new TFC membranes were tested at each time and the results for both rejection and flux were reproducible. FIG. 15 shows rejection curves and flux for these hydrophobic TFC membranes in ethyl acetate/PS solution.