NOVEL MEMBRANES AND PREPARATION THEREOF

Abstract

Novel membranes suitable for use in separation applications are described, as well as processes by which the membranes are made and uses of the membranes in a range of separation applications. The membranes are obtainable by an interfacial polymerisation reaction involving two monomers, in which at least one of the monomers comprises oligomeric portions that are suitable for tuning the separation characteristics of the membrane, particularly in liquid separations, such as organic solvent nanofiltration.

Claims

1. An interfacial polymerisation process for the preparation of a thin film membrane, the process comprising the step of reacting a first monomer and a second monomer at the interface of two immiscible liquids to produce a crosslinked polymeric film; wherein the crosslinked polymeric film is composed of at least one crosslinked polymer; and at least one of the first monomer and second monomer is a compound of formula (I) shown below:
T-Q-L-Y-L-Q-T   (I) in which each Q is a chemically-inert oligomer having a predetermined number of repeating units, m; Y is a reactive moiety comprising at least 2 groups capable of reacting with the other of the first monomer and second monomer to produce the crosslinked polymeric film; each L is a linking moiety through which each Q is covalently bonded to Y; and each T is a chemically-inert terminating group.

2. The process of claim 1, wherein the crosslinked polymeric film is composed of at least one crosslinked polymer selected from the group consisting of polyamide, polyester and polyether.

3. The process of claim 1 or 2, wherein m is 2 to 20.

4. The process of claim 1, 2 or 3, wherein Q is selected from the group consisting of: ##STR00045##

5. The process of any preceding claim, wherein the compound of formula (I) has a hydrophilic-lipophilic balance of <10

6. The process of claim 5, wherein Q is selected from the group consisting of: ##STR00046##

7. The process of any preceding claim, wherein Y comprises 3-10 reactive groups.

8. The process of any preceding claim, wherein the reactive groups present in Y are independently selected from the group consisting of —NH.sub.2, —NH—, —OH and —C(═O)X, wherein X is halo.

9. The process of any preceding claim, wherein Y is oligomeric having n number of repeating units, and wherein each repeating unit n comprises one of the reactive groups, such that Y has the following structure: ##STR00047## wherein and each Z is independently selected from the group consisting of: ##STR00048## where R is selected from the group consisting of —(CH.sub.2).sub.vOH, —(CH.sub.2).sub.vNH.sub.2, —(CH.sub.2).sub.vC(═O)X and —(CH.sub.2).sub.vC(═O)NHNH.sub.2, in which v is 0-4 and X is halo.

10. The process of any preceding claim, wherein the compound of formula (I) has a structure according to any of the following: ##STR00049## ##STR00050## wherein T, m, Z and n are as defined in any preceding claim.

11. The process of any preceding claim, wherein the compound of formula (I) has either of the following structures: ##STR00051## wherein m, n and Z are as defined in any preceding claim.

12. The process of claim 10 or 11, wherein Z is —NH—, —CH(OH)— or —CH(R)—, where R is a group —C(═O)Cl, m is 2-6, and n is 3-5.

13. The process of any preceding claim, wherein only the first monomer is a compound of formula (I) and the second monomer is a polyacylhalide, a polyamine or a polyhydroxy compound.

14. The process of claim 13, wherein (A) the first monomer is a compound of formula (I) in which Y comprises 3-6 reactive groups selected from the group consisting of —NH.sub.2, —NH—, and —OH, and the second monomer is a polyacylhalide; or (B) the first monomer is a compound of formula (I) in which Y comprises 3-6 reactive groups selected from the group consisting of —NH.sub.2 and —NH—, and the second monomer is a polyacylhalide.

15. The process of claim 14, wherein the polyacylhalide is trimesoylchloride, isophthaloyl chloride or sebacoyl chloride.

16. The process of any preceding claim, wherein the step of reacting a first monomer and a second monomer at the interface of two immiscible liquids to produce a crosslinked polymeric film comprises the steps of: (a) providing a first solution comprising: (i) a first solvent, and (ii) the first monomer; (b) contacting the first solution with a second solution, the second solution comprising: (i) a second solvent, the second solvent being immiscible in the first solvent, and (ii) the second monomer; wherein reaction of the first monomer with the second monomer in step (b) results in the formation of the crosslinked polymeric film at the interface of the first solvent and the second solvent.

17. The process of claim 16, wherein (A) the first solution comprises 0.005-30.0 wt. % of the first monomer; and/or (B) the second solution comprises 0.005-30.0 wt. % of the second monomer.

18. The process of claim 16 or 17, wherein (A) the crosslinked polymeric film is formed on a supporting membrane during step (b); or (B) the crosslinked polymeric film is formed at the free interface between the first solvent and second solvent during step (b) and is subsequently transferred onto a supporting membrane.

19. The process of claim 16, 17 or 18, wherein the process further comprises the step (c) of isolating and drying the crosslinked polymeric film.

20. The process of claim 19, wherein the isolated and dried crosslinked polymeric film is contacted with a hydrophilic solvent.

21. The process of claim 20, wherein the hydrophilic solvent is one or more solvents selected from the group consisting of acetone, ethanol, methanol, isopropanol and water.

22. A thin film membrane obtained, directly obtained or obtainable by the process of any preceding claim.

23. A thin film membrane comprising a plurality of interconnected moieties, each of formula (Ia), linked to one another to provide a crosslinked polymer:
T-Q-L-Y.sub.a-L-Q-T   (Ia) in which each Q is a chemically-inert oligomer having a predetermined number of repeating units, m; each L is a linking moiety through which each Q is covalently bonded to Y.sub.a; each T is a chemically-inert terminating group; and Y.sub.a is a group comprising at least two crosslinking moieties Z.sub.a, wherein each crosslinking moiety Z.sub.a links one moiety of formula (Ia) to another moiety of formula (Ia).

24. Use of the thin film membrane of claim 22 or 23 in a process for isolating one or more components from a mixture.

25. The use of claim 24, wherein the process for isolating one or more components from a mixture is a process selected from the list consisting of gas separation, pervaporation, reverse osmosis, nanofiltration, desalination and water treatment.

Description

EXAMPLES

[0119] One or more examples of the invention will now be described, for the purpose of illustration only, with reference to the accompanying figures, in which:

[0120] FIG. 1 shows permeances of a TFC-1-MOM-1 membrane prepared from MOM-1 on PAN support for a range of solvents tested in the order water, methanol, acetone, hexane, heptane, and toluene. Nanofiltration of a pure solution has been performed at 10 bar and 25° C.

[0121] FIG. 2 shows the molecular weight cut-off (MWCO) curve of a TFC-1-MOM-1 membrane prepared from MOM-1 on PAN support for a range of dyes with molecular weight varying from ˜200 to 800 g.Math.mol.sup.−1. Nanofiltration of a feed solution comprising dye molecules dissolved in methanol has been performed at 10 bar and 25° C., after testing with pure solvents in the order water, methanol, acetone, hexane, heptane, and toluene.

[0122] FIG. 3 shows permeances of a TFC-1-MOM-2 membrane prepared from MOM-2 on PAN support for a range of solvents including water, methanol, acetone, hexane, heptane, and toluene. The solvents were tested in the order water, methanol, acetone, hexane, heptane and toluene. Nanofiltration of a pure solution has been performed at 10 bar and 25° C.

[0123] FIG. 4 shows the MWCO curve of a TFC-1-MOM-2 membrane prepared from MOM-2 on PAN support for a range of dyes with molecular weight varying from ˜200 to 800 g.Math.mol.sup.−1. Nanofiltration of a feed solution comprising dye molecules dissolved in methanol has been performed at 10 bar and 25° C. after testing with pure solvents in the order water, methanol, acetone, hexane, heptane, and toluene

[0124] FIG. 5 shows permeances of a TFC-1-MOM-3 membrane prepared from MOM-3 on PAN support for a range of solvents tested in the order water, methanol, acetone, hexane, heptane, and toluene. Nanofiltration of a pure solution has been performed at 10 bar and 25° C.

[0125] FIG. 6 shows the MWCO curve of a TFC-1-MOM-3 membrane prepared from MOM-3 on PAN support for a range of dyes with molecular weight varying from ˜200 to 800 g.Math.mol.sup.−1. Nanofiltration of a feed solution comprising dye molecules dissolved in methanol has been performed at 10 bar and 25° C. after testing with pure solvents in the order water, methanol, acetone, hexane, heptane, and toluene

[0126] FIG. 7 shows permeances of a TFC-2-MOM-3 membrane prepared from MOM-4 on PAN support for a range of solvents tested in the order water, methanol, acetone, hexane, heptane, and toluene. Nanofiltration of a pure solution has been performed at 10 bar and 25° C.

[0127] FIG. 8 shows the MWCO curve of a TFC-2-MOM-3 membrane prepared from MOM-4 on PAN support fora range of dyes with molecular weight varying from ˜200 to 800 g.Math.mol.sup.−1. Nanofiltration of a feed solution comprising dye molecules dissolved in methanol has been performed at 10 bar and 25° C. after testing with pure solvents in the order water, methanol, acetone, hexane, heptane, and toluene

[0128] FIG. 9 shows permeances of a TFC-1-MOM-4 membrane prepared from MOM-5 on PAN support for a range of solvents tested in the order water, methanol, acetone, hexane, heptane, and toluene. Nanofiltration of a pure solution has been performed at 10 bar and 25° C.

[0129] FIG. 10 shows the MWCO curve of a TFC-1-MOM-4 membrane prepared from MOM-5 on PAN support for a range of dyes with molecular weight varying from ˜200 to 800 g.Math.mol.sup.−1. Nanofiltration of a feed solution comprising dye molecules dissolved in methanol has been performed at 10 bar and 25° C. after testing with pure solvents in the order water, methanol, acetone, hexane, heptane, and toluene

[0130] FIG. 11 shows the MWCO curve of a TFC-1-MOM-1 membrane prepared from MOM-1 on PAN support for a mixture of polystyrene (PS) with molecular weight varying from ˜300 to 1000 g.Math.mol.sup.−1. Nanofiltration of a feed solution comprising PS molecules dissolved in heptane has been performed at 10 bar and 25° C.

[0131] FIG. 12 shows the MWCO curve of a TFC-1-MOM-2 membrane prepared from MOM-2 on PAN support for a mixture of polystyrene (PS) with molecular weight varying from ˜300 to 1000 g.Math.mol.sup.−1. Nanofiltration of a feed solution comprising PS molecules dissolved in heptane has been performed at 10 bar and 25° C.

[0132] FIG. 13 shows (a) exemplary preparation of a polyamide crosslinked polymer according to the invention; (b) exemplary preparation of a polyester crosslinked polymer according to the invention; (c) exemplary preparation of an aromatic polyhydrazide crosslinked polymer according to the invention; (d) exemplary preparation of a sulfonated polyfurane crosslinked polymer according to the invention; (e) exemplary preparation of a polypiperazine isophthalamide crosslinked polymer according to the invention; (f) exemplary preparation of a polyepiamine-amide crosslinked polymer according to the invention; (g) exemplary preparation of a polyepiamine-urea crosslinked polymer according to the invention; (h) exemplary preparation of a polyethyleneimine-urea crosslinked polymer according to the invention; (i) exemplary preparation of a polyether-amide crosslinked polymer according to the invention; (j) exemplary preparation of a polyether-urea crosslinked polymer according to the invention; (k) exemplary preparation of a polyester-amide crosslinked polymer according to the invention.

[0133] FIG. 14 shows the visual difference between permeate and retentate in Example 4.

[0134] FIG. 15 shows a simulated distillation of feed, permeate and retentate samples in Example 4.

[0135] FIG. 16a-c show GC×GC difference plot showing molecules that are enhanced in the permeate (red) and molecules that are enhanced in the retentate (green) in Example 4.

EXAMPLE 1—SYNTHESIS OF MOMS

[0136] In the following example, MOMs comprising halogenated hydrocarbon oligomers were synthesised including a reaction step and a purification step.

1.1—MOM-2—Reaction Step

[0137] In brief, a 1H, 1H-Perfluoro-1-pentanol (1 equivalent) and carbonyldiimidazole (1.2 equivalents) were dissolved in dimethylformamide (DMF) in a flask with strong magnetic stirring. The reaction took place under nitrogen atmosphere and a specific temperature was applied by using an oil bath. After stirring for a certain period of time, pentaethylenehexamine was added to the mixture and the reaction was left for a certain reaction time, after which the colour of the resulting mixture changed from colourless to light yellow.

1.2—MOM-2—Purification Step

[0138] Precipitation: After cooling down to the room temperature, the mixture was slowly added to the excess amount of hexane and dichloromethane (DCM) mixture under strong magnetic stirring. The yellow precipitate was collected by separatory funnel and dissolved by DCM subsequently.

[0139] Extraction: A Semi-saturated saline was added to the solution and well mixed for a certain period. The supernatant was removed while the underlying layer was extracted again by saturated saline. The procedure was repeated several times to remove water soluble by-products. The remaining small amount of water was removed by sodium sulphate anhydrous and filtered by filter paper subsequently.

[0140] Concentration: The excess amount of solvent was removed by rotary evaporator and further dried under high vacuum at certain temperature.

[0141] Finally, the yellow gel-like product MOM-2, with chemical structure shown in Scheme 1, was obtained with ˜30-35% yield, and stored in 4° C. environment.

##STR00042##

1.3—MOM-1, MOM-3, and MOM-4

[0142] The synthetic procedure outlined in Examples 1.1 and 1.2 was adapted to prepare MOM-1, MOM-3 and MOM-4:

##STR00043##

EXAMPLE 2—PREPARATION OF TFC MEMBRANE

[0143] In the following example, membranes of the present invention are formed through interfacial polymerisation to form a polyamide separating layer on a polyacrylonitrile support membrane.

2.1—Formation of Polyacrylonitrile Support Membrane

[0144] Polyacrylonitrile membranes were cast using a continuous casting machine (Sepratek, South Korea). The dope solution was prepared by dissolving 11 wt % polyacrylonitrile powder in a mixture of 44.5 wt. % DMSO and 44.5 wt. % 1,3-dioxolane, and stirred overnight at 75° C. Prior to casting, the dope solution was filtered through 41 μm filter (NY4104700, Merck), and subsequently through 11 μm filter (NY1104700, Merck) using a nitrogen pressurised filtration cell (XX4004740, Merck) at pressures of up to 70 psi. The membrane was cast on to a PET non-woven fabric (Hirose RO grade). The gap between the casting knife and the backing was set at 120 μm. The casting speed was controlled by the winder tension. After casting on the backing, the dope/non-woven composite underwent phase inversion through tangential entry into the water bath. After casting, the support was immediately immersed in water at 60° C. for 3 h, followed by drying at room temperature.

2.2—Formation of TFC Membranes by Interfacial Polymerisation

[0145] TFC membranes in this Example were labelled TFC-x-MOM-n, where x represents the specific interfacial polymerisation conditions employed for each membrane, and n represents the oligomeric MOM moiety employed.

[0146] The separating polyamide layer was made through interfacial polymerization at a free liquid-liquid interface. A given MOM synthesized in Example 1 was dissolved in an aqueous solution, preferentially more than 25 ml, with THF as an additive bi-solvent. TFC-1 used a ratio of 0.02 wt. % MOM: 5 wt. % THF: 94.98 wt. % water. TFC-2 used a ratio of 0.05 wt. % MOM: 5 wt. % THF: 94.95 wt. % water. TFC-3 used a ratio of 0.025 wt. % MOM: 5 wt. % THF: 94.975 wt. % water. These solutions were added into MOM dropwise applying ultrasonication. The solution comprising MOM was added into a glassware container where an inert substrate was immersed in. An organic solution containing 0.1 wt. % trimesoyl chloride (TMC, 98%, Sigma-Aldrich) was poured into the container carefully and left to be in contact with aqueous solution. After 7 min reaction, the immersed substrate was lifted to pick up the polyamide film formed at the free liquid-liquid interface, and subsequently re-floated the film on a bulk water surface, followed by fishing and adhering the film on a polyacrylonitrile support for an incorporation of thin film composite (TFC) membrane. TFC membrane was rest to be dried in room conditions. The chemical structures of the monomers used for the interfacial polymerization reaction are shown in Scheme 2.

##STR00044##

EXAMPLE 3—TFC MEMBRANE PERFORMANCE

[0147] The nanofiltration separation properties, in terms of permeance profiles and molecular weight cut off (MWCO) curves, of the TFC membranes of Example 2 was evaluated.

3.1—Testing Protocols

[0148] Nanofiltration experiments involving dye separations were carried out under 10 bar at 25° C. in a dead-end cell, and nanofiltration experiments involving polystyrene separations were carried out at 10 bar at 25° C. using a cross-flow filtration system.

[0149] For each filtration experiment in dead-end cell, one membrane disc, of active area 12.6 cm.sup.2, was cut out from flat sheets and placed into the cell, and at least three membranes made from identical conditions were used to demonstrate the reproducibility. Solvents were contacted with the membrane in the order water, methanol, acetonitrile, hexane, heptane, and toluene. Permeate samples for permeance measurements were collected at intervals of 10 min, and samples for rejection evaluations were taken after steady permeance was achieved. The MWCO was then determined by interpolating from the plot of rejection against molecular weight of dye compounds. Each rejection test comprised one dye solute with a constant concentration of 20 mg.Math.L.sup.−1 in methanol. Analysis of dye concentrations was done using an UV-vis detector in the wavelength ranging from 200 to 800 nm.

[0150] For crossflow filtration, the membrane discs, of active area 13.8 cm.sup.2, were cut out from flat sheets and placed into 4 cross flow cells in series. Solvent was heptane. Permeate samples for permeance 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 a standard feed solution comprised of a homologous series of styrene oligomers (PS) dissolved in heptane. 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.sup.−1 of α-methylstyrene dimer (Sigma-Aldrich, UK). Analysis of the styrene oligomers was done using an Agilent HPLC system with UV/Vis detector set at a wavelength of 264 nm. Separation was achieved using a reverse phase column (C18-300, 250×4.6 mm). The mobile phase consisted of 35 vol % analytical grade water and 65 vol % tetrahydrofuran with 0.1 vol % trifluoroacetic acid.

[0151] Solvent permeance (J) was determined by measuring permeate volume (V) per unit area (A) per unit time (t) per unit transmembrane pressure (ΔP) according to the following equation:

[00001]$\begin{array}{cc}J=\frac{V}{A.t.\Delta P}& \left(1\right)\end{array}$

[0152] The rejection (R) of markers was calculated from equation 2, where C.sub.p and C.sub.f correspond to solute concentrations in the permeate and the feed respectively.

[00002]$\begin{array}{cc}R=\left(1-\frac{C_p}{C_f}\right)\times 100\%& \left(2\right)\end{array}$

3.2—Results

[0153] The performance of TFC membranes was evaluated in the dead end cell by filtering solvents in the order water, methanol, acetonitrile, hexane, heptane, and toluene. The rejection curves and permeances for the TFC membranes made from different types (n) of MOM were shown in FIG. 1-10 for the separation of dye solutes in methanol, after passing pure solvents through the membrane in the order given above. The rejection curves for the TFC-x-MOM-n membranes are shown in FIG. 11-12 for the separation of polystyrene (PS) solutes in heptane. It is clearly shown that the performance of TFC membranes changed with the type of MOM used for interfacial polymerisation.

EXAMPLE 4—CRUDE OIL SEPARATION BY TFC MEMBRANE

4.1—Testing Protocol

[0154] Separation of a light shale-based crude oil was carried out in a Sterlitech HP4750X dead-end cell. A coupon of TFC-3-MOM-3 membrane with active area of 14.8 cm.sup.2 was cut out from flat sheets and placed into the cell. Initially, 200 ml each of water, acetone and toluene (in that order) were filtered through the membrane at room temperature and 10 bar. Following this “activation” procedure, the cell was charged with 100 g of a light shale-based crude oil. Using nitrogen head pressure, the crude oil feed was pressurized to 43 bar and maintained at room temperature (22° C.). The cell was stirred at a constant rate of 400 rpm. The weight of permeate (converted to volume (V)) was measured as a function of time (t) and using the membrane active area (A) and transmembrane pressure (ΔP), the average membrane permeance (J) was calculated according to equation (1) in Example 3.

[0155] The permeate, feed and retentate samples were analysed using a standardized simulated distillation technique to determine their boiling point distributions and a standard two-dimensional gas chromatography technique to visualize separation based on class and molecular weight.

4.2—Results

[0156] The permeate was collected until a stage cut of 15% was obtained. The membrane flux remained relatively constant throughout the run at 3.6 L/m.sup.2/h. The permeance calculated from equation (1) was 0.083 L/m.sup.2/h/bar, which is much higher than many commercial RO/NF membranes. From FIG. 14, a visual difference between permeate and retentate is observed, with the permeate appearing lighter (closer to naphtha/kero/jet range) than the retentate. This is further supported by the dynamic viscosity of the permeate at 30° C. (1.2 mPa.Math.s) being less than half that of the retentate (2.5 mPa.Math.s). The specific gravity of the permeate is also lower than that of the retentate—0.78 vs 0.80 at 30° C. These measurements indicate that the membrane selectively permeates lighter, higher value molecules while rejecting the heavier fractions.

[0157] FIG. 15 shows the simulated distillation of the crude feed, permeate and retentate, which represents the boiling point distribution of each of the samples. The permeate has a cut-off at 550° C. while the feed and retentate boiling point range extends to 700° C. This demonstrates that the membrane rejects the heavy (residue) fraction. At the same time, there is enhancement of the light fractions including napththa/kero/jet fuel. FIG. 15 shows that 48wt % of the feed has boiling point lower than 400° C. vs 60wt % of the permeate has boiling point below 400° C., demonstrating that the light fractions become concentrated in the permeate and the heavy fractions in the retentate.

[0158] FIG. 16a shows the GC×GC difference plot for the permeate and retentate samples. Peaks that have higher intensity (and hence concentration) in the permeate appear green while those that have higher concentration in the retentate appear red. This further demonstrates that the permeate is lighter than the retentate, with high concentrations of light saturate and light aromatic molecules in the permeate while there is rejection of heavier 3- and 4-ring aromatics. There is a cut-off near the normal paraffin with carbon number 17 which corresponds to a molecular weight of 240 Da. The normal paraffins continue beyond carbon number 30 since they are able to diffuse through the polymer matrix due to a small kinetic diameter in one dimension. FIGS. 16b and 16c are a representation of FIG. 16a in 3-dimensional form.

[0159] This experiment clearly demonstrates the utility of MOM membranes for the separation of complex hydrocarbon feeds such as crude oil, leading to enhancement of high-value molecules and rejection of low-value, heavier molecules while exhibiting permeances of industrial relevance.

[0160] While specific embodiments of the invention have been described herein for the purpose of reference and illustration, various modifications will be apparent to a person skilled in the art without departing from the scope of the invention as defined by the appended claims.