DURABLE MEMBRANES, THEIR PREPARATION AND USE

Abstract

Filtration membranes comprising a microporous sheet of polyolefin grafted with a poloxamer are described. In an embodiment, the poloxamer is that supplied under the trade name PLURONIC™ P-123 and the polyolefin is poly(ethylene). The membranes provide the advantage of being tolerant to the cleaning agents used in clean-in-place protocols and can be used to remove particulates from these aqueous feed streams.

Claims

1) A water-wettable filtration membrane consisting essentially of a microporous sheet of grafted polyolefin where the graft comprises a poloxamer of the structure HO(ethylene oxide).sub.m-(propylene oxide).sub.n-(ethylene oxide).sub.mH where m is in the range 15 to 25 and n is in the range 50 to 90.

2) The membrane of claim 1 where the polyolefin is poly(ethylene) or poly(propylene).

3) The membrane of claim 2 where the polyolefin is poly(ethylene).

4) The membrane of claim 3 where m is 20 and n is 70.

5) A spiral wound filter assembly comprising the membrane of claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0094] FIG. 1. Exploded view of the filtration membrane assembly (Sterlitech Corp.) used in the flux testing of samples of sheets of filtration membrane.

[0095] FIG. 2. A comparison of the spectra (3800 cm.sup.−1 to 525 cm.sup.−1) recorded for the untreated microporous poly(ethylene) (TARGRAY™ wet process polyethylene separators, item no. SW320H (Targray, Kirkland QC, Canada)) (PE virgin) and the triblock copolymer (PLURONIC™ P-123; lot #MKCC2305, Sigma-Aldrich) (P123) used in the preparation of the samples, and the top (Etop) and back (Eback) side of each of the samples designated 040918Wiv, 340918Wv and 040918Wvi.

[0096] FIG. 3. A comparison of the spectra from FIG. 2 expanded over the ‘fingerprint region’ (1800 cm.sup.−1 to 600 cm.sup.−1).

[0097] FIG. 4. A comparison of the spectra (3800 cm.sup.−1 to 525 cm.sup.−1) recorded for regions of the sample designated 40918Wvi with (Ctop and Cback) and without (Etop and Eback) exposure to the feed stream.

[0098] FIG. 5. Scanning electron micrographs of the top (Etop) side of the sample designated 040918Wiv at magnifications of 250,000× (A), 35,000× (B) and 10,000× (C).

[0099] FIG. 6. Scanning electron micrographs of two regions of the top (Etop) side the sample designated 040918Wiv at a magnification of 100,000×.

[0100] FIG. 7. Comparison of the flux (LMH) maintained for samples of filtration membrane (1804.19Wi and 230419Wii (.square-solid.); 180419Wii and 230419Wiii (.circle-solid.)) prepared with (solid line) and without (broken line) a crosslinking agent (DVB).

[0101] FIG. 3. Schematic representation of the prototype production line used in the preparation of the water-wettable filtration membrane according to Example C.

[0102] FIG. 9. Photograph of bottles containing samples of used caustic cleaning solution (left bottle) and permeate (right bottle) following filtration of the used caustic cleaning solution as described in Example E.

[0103] FIG. 10. Plot of flow rate (litres/minute) at each of the two inlets (solid and broken lines) of the rate versus reading (seconds) on time during filtration of the used caustic cleaning solution shown in FIG. 9 (left bottle).

[0104] FIG. 11. Plot of flow rate (litres/minute) of the permeate shown in FIG. 9 (right bottle) versus reading (seconds) on timer during filtration of used caustic cleaning solution.

[0105] FIG. 12. Photograph of bottle containing samples of less pigmented used caustic cleaning solution (left bottle) and permeate (right bottle) following filtration of the used caustic cleaning solution as described in Example E.

[0106] FIG. 13. Plot of flow rate (litres/minute) of the permeate shown in FIG. 12 (right bottle) versus reading (seconds) on timer showing filtration of the less pigmented used caustic cleaning solution.

[0107] FIG. 14. Photograph of bottles containing samples of heavily contaminated, i.e. high solids, used caustic cleaning solution (left and middle bottles) and permeate (right bottle) following filtration of the used caustic cleaning solution as described in Example E.

[0108] FIG. 15. Photograph of bottles containing samples of used citric acid cleaning solution (left bottle) and permeate (middle bottle) and concentrate i.e. retentate (right bottle) following filtration of the used citric acid cleaning solution.

[0109] FIG. 16. Plot of flow rate (litres/minute) of the permeate shown in FIG. 15 (middle bottle) versus reading (seconds) on time during filtration of the used citric acid cleaning solution.

[0110] FIG. 17. Appearance of a volume of 10 mL of working solution prepared according to methods 1, 2 and 3 of EXAMPLE G. ‘Working solution A’ contains a quantity of 0.15 g poly(ethenol) (PVA, 65 kDa). ‘Working solution B’ contains a quantity of 0.25 g poly(ethenol) (PVA, 65 kDa). The turbid ‘working solution C’ contains a quantity of 0.5 g poly(ethenol) (PVA, 65 kDa).

[0111] FIG. 18. Appearance of the replicate samples prepared according to method 6 of EXAMPLE G and designated 041918wi, 041918wii and 041918wiii.

[0112] FIG. 19. A comparison of the spectra (3800 cm.sup.−1 to 525 cm.sup.−1) recorded for the untreated microporous poly(ethylene) (TARGRAY™ wet process polyethylene separators, item no. SW320H (Targray, Kirkland QC, Canada)) (PE virgin), the triblock copolymer (PLURONIC™ P-123; lot #MKCC2305, Sigma-Aldrich) (P123) and poly(ethenol) (PVA, 65 kDa) (PVA65) used in the preparation of the samples, and the centre (−C) and edge (−E) of each of the samples designated 310818wi, 030918wii and 030918wi.

[0113] FIG. 20. A comparison of the spectra expanded over the ‘fingerprint region’ (1800 cm.sup.−1 to 600 cm.sup.−1) recorded for the untreated microporous poly(ethylene) (TARGRAY™ wet process polyethylene separators, item no. SW320H (Targray, Kirkland QC, Canada)) (PE virgin), the triblock copolymer (PLURONIC™ P-123; lot #MKCC2305, Sigma-Aldrich) (P123) and poly(ethenol) (PVA, 65 kDa) (PVA65) used in the preparation of the samples, and the centre (−C) and edge (−E) of each of the samples designated 310818wi, 030918wii and 030918wi.

[0114] FIG. 21. Photograph of vials containing partially crosslinked poly(ethenol) (xPVA) prepared according to method 2 of EXAMPLE H. From left to right: Vial 1, Vial 2, Vial 3 and Vial 4.

DESCRIPTION

[0115] Filtration membranes are used in a range of industrial processes, including food processing, to recover or remove water from a feed stream. In one application the objective may be to separate the water from contaminating particulates. In another application the objective may be to concentrate high value solutes. In either application efficiency is increased by contacting the feed stream with a large surface area of the filter membrane. To this end the filtration membrane will often be assembled into a spiral wound filter element, which is then installed in the industrial plant. Such spiral wound membrane assemblies—or “filter elements”—are supplied by manufacturers such as Synder Filtration (Vacaville, Calif., USA).

[0116] Further efficiencies are realised if cleaning can be performed in place without the need for removal and reinstallation of the filter element. Clean-in-place protocols use chemically aggressive solutions such as acid, alkali and hypochlorite. Alternatively, the feed streams to which the membrane is exposed may be chemically aggressive and durability under these conditions reduces the frequency with which the filter element needs to be replaced.

[0117] Microporous sheets of polyolefin, such as poly(ethylene) are available commercially from suppliers such as Celgard (Charlotte, N.C., USA) and Targray (Kirkland, Quebec, Canada). One impediment to the use of these substrates as filtration membranes in the applications alluded to above is there inherent hydrophobicity. Where the objective is to provide a semipermeable membrane for use in concentrating high value solutes the required rejection properties may also be lacking.

[0118] It has now been determined that the grafting of a microporous sheet of poly(ethylene) with a preformed polymer such as the poloxamer supplied under the trade name PLURONIC-P123 provides a filtration membrane that is readily wetted with water and provides high flux rates at relatively low pressures (5 bar). The filtration membranes so produced have also been demonstrated to have the desired durability when exposed to chemically aggressive liquids. The retention of these desirable properties—attributable to the graft—is enhanced by the inclusion of a crosslinking agent in the working solution used in the method of preparation. Without wishing to be bound by theory low molecular weight crosslinking agents are favoured so as not to disrupt the favourable rejection properties also demonstrated for the membranes.

[0119] The method of preparing the filtration membrane is readily adaptable to a continuous production process. In accordance with the methods described, working solutions of the following composition are used to impregnate the microporous substrate before it is irradiated with ultraviolet light at a wavelength in the range 250 nm to 360 nm, wavelengths at or toward the lower end of this range (250 nm) being preferred.

[0120] Working Solution: [0121] 3 to 5% (w/v) poloxamer [0122] 0.5 to 1% (w/v) photoinitiator [0123] 0 to 0.5% (w/v) crosslinking agent [0124] 30 to 50% (v/v) in alcohol or acetone in water (‘solvent’)

[0125] The preferred poloxamer for use in the working solution is that supplied under the trade name PLURONIC P-123. The preferred photoinitiator for use in the working solution is benzophenone. The preferred crosslinking agent for use in the working solution is divinylbenzene.

[0126] The working solution may additionally comprise a second preformed polymer dispersed in the solvent. A suitable second preformed polymer is poly(ethanol). The inclusion of a second preformed polymer may be used to refine the properties (durability, flux or selectivity) of the filtration membrane.

Example A—Preparation of Filtration Membrane (Laboratory Method, Poloxamer Only)

[0127] A volume of 5 ml, of a solution in water of 10% (w/v) triblock copolymer (PLURONIC™ P-123; lot #MKCC2305, Sigma-Aldrich) was mixed with an equal volume of deionised water. A quantity of 0.1 g of the photoinitiator benzophenone (diphenylmethanone; Ph.sub.2O) was dissolved in a separate volume of 5 mL of ethanol before being added to the diluted solution of the triblock copolymer. The working solution was stored in the dark until use.

[0128] Samples (13.5×18.5 cm) were cut from a sheet of microporous poly(ethylene) (TARGRAY™ wet process polyethylene separators, item no. SW320H (Targray, Kirkland QC, Canada)) and each sample coated with a volume of 5 mL of the working solution. The coated samples were then irradiated with ultraviolet (UV) light in the range 250 to 360 nm for a period of time of two minutes before rinsing with water and air-drying on top of a warm oven.

[0129] The four replicate samples prepared according to this method were designated 040918Wiv, 040918Wv, 040918Wvi and 151018Wi. A small piece of the sample designated 040418Wiv was excised from the edge of the sample and submitted to scanning electronic microscopy (SEM).

[0130] Each of the samples was readily wetted with water, being observed to become uniformly translucent when contacted with this solvent.

Durability, Flux and Protein Rejection

[0131] A filtration membrane assembly (Sterlitech) as illustrated in FIG. 1 was used to determine flux (LMH) for each of the samples designated 040916Wiv, 040918Wv and 040918Wvi. Samples were individually mounted in the filtration membrane assembly and the flux determined at 0 and 5 bar. The time to collect a predetermined volume of permeate at the specified pressure and temperature was recorded and the flux (J) was calculated according to the following equation:

[00011]$J=\frac{V}{t\times A}$

where V was the volume of permeate (L), t was the time (h) for the collection of V and A was area of the sample (m.sup.2) exposed to the feed stream (water or skim milk). The results are summarised in Table 1.

TABLE-US-00001 TABLE 1 Fluxes (LMH) determined at 0 and 5 bar with water as the feed stream at the temperatures (° C.) specified. Temperature Flux Sample 0 bar/5 bar 0 bar 5 bar 040918Wiv 9/9 10 367 040918Wv 15/11 33 476 040918Wvi 10/9  32 428

[0132] To assess durability fluxes were also determined after repeated clean-in-place (CIP) protocols. The CIP protocol was based on that employed in a commercial processing operation for reverse osmosis (RO) membranes (Anon (2014)) and is summarised in Table 2.

TABLE-US-00002 TABLE 2 Clean-in-place (CIP) protocol adaptad from Anon (2014). The ‘alkali’ was 2% (w/v) sodium hydroxide (NaOH). The ‘acid’ was 1.9% (w/v) nitric acid (H.sub.2NO.sub.3) and 0.6 (w/v) phosphoric acid (H.sub.3PO.sub.4). Step Feed stream Time (min) Temperature (° C.) 1 water 5 Ambient 2 water 5 35 3 alkali 5 35 4 water 5 35 5 acid 10 35 6 water 5 Ambient 7 hypochlorite 5 35 8 water 5 Ambient

[0133] For each sample, a number of CIP protocols were repeated alternating with the use of water or skim milk as the feed stream. The fluxes and percentage protein rejection (with skim milk as the feed stream) determined for the samples designated 040918Wv and 040918Wvi are provided in Table 3. Total protein concentrations in permeate were calculated on the basis of HPLC analysis with UV absorbance monitoring.

TABLE-US-00003 TABLE 3 Fluxes (LMH) and protein rejection determined at 0 and 5 bar with water or skim milk as the feed stream at the temperatures (° C.) specified. Determinations were made for each of the samples following repeated clean-in-place (CIP) protocols. Feed CIP Temperature (° C.) Flux (LMH) Protein Sample stream protocols 0 bar/5 bar 0 bar 5 bar rejection (%) 040918Wiv water 0 9/9 10 367 040918Wv water 0 15/11 33 476 040918Wv water 1 10/10 6 139 040918Wv water 2 —/12 — 195 040918Wv water 3 —/11 — 171 040918Wv water 6 —/10 — 476 040918Wv water 10 11/10 46 494 040918Wv milk 3 —/11 — 21 040918Wv water 6 —/10 — 476 040918Wv water 10 11/10 46 494 040918Wv milk 10 11/12 4 21 99.4 040918Wvi water 0 10/9 32 428 040918Wvi water 1 19/10 43 642 040918Wvi water 2 13/12 40 714 040918Wvi water 3 10/10 38 644 040918Wvi milk 3 9/11 3 24 040918Wvi water 4 —/9 — 56 (dry) 040918Wvi milk 4 —/10 — 9 99.71 040918Wvi water 5 10/9 38 234 040918Wvi water 7 9/9 60 803 040918Wvi water 10 11/10 64 188 040918Wvi milk 10 —/12 — 9 99.76

[0134] The durability of the filtration membranes was further evaluated by contacting the sample designated 151018Wi with 2% (w/v) sodium hydroxide (NaOH) for 7 days.

[0135] The fluxes and percentage protein rejection (with skim milk as the feed stream) determined for these samples are provided in Table 4.

TABLE-US-00004 TABLE 4 Fluxes (LMH) and protein reledtion determined at 0 and 5 bar with water or skim milk as the feed stream at the temperatures (° C.) specified. Determinations were made for the samples following exposure to 2% (w/v) sodium hydrozide (NaOH) for 7 days. Feed Temperature (° C.) Flux (LMH) Protein Sample stream 0 bar/5 bar 0 bar 5 bar rejection (%) 151016Wi water 9/9 54 257 151016Wi milk 10/10 —  8 99.65
Fourier Transform Infrared (FTIR) Spectroscopy Spectra were recorded for each of the samples designated 040918Wiv, 040918Wv and 040913Wvi using a Thermo Electron Nicolet 8700 FTIR spectrometer equipped with a single bounce ATR and diamond crystal. Thirty-two scans at a resolution of 4 cm.sup.−1 were averaged for each sample. A comparison of the spectra (3800 cm.sup.−1 to 525 cm.sup.−1) recorded for: (i) the untreated microporous poly(ethylene) (TARGRAY™ wet process polyethylene separators, item no. SW320H (Targray, Kirkland QC, Canada)) (‘PE virgin’); (ii) the triblock copolymer (PLURONIC™ P-123; lot #MKCC2305, Sigma-Aldrich) used in the preparation of the samples (‘P123’); and (iii) the top (Etop) and back (Eback) sides of each of the samples designated 040918Wiv, 040918Wv and 040918Wvi is provided in FIG. 2.

[0136] Signals corresponding to the symmetrical stretch mode of C—O—C fragments (1108 cm.sup.−1) and the C—H stretch mode of CH.sub.3 (2970 cm.sup.−1) present in the spectrum of the triblock copolymer (PLURONIC™ P-123) were also present in the spectra recorded for each of the samples. Many signals characteristic of the triblock copolymer (PLURONIC™ P-123) were also observed at low intensity in the ‘fingerprint’ region of the spectra provided in FIG. 31. Signals characteristic of the triblock copolymer (PLURONIC™ P-123) were retained in spectra recorded for regions of the sample designated 040918Wiv following exposure to the feed stream (water) as shown in FIG. 4.

[0137] SEM

[0138] Scanning electron micrographs of the small piece excised from the edge of the sample designated 040918Wiv are provided in FIG. 5 and FIG. 6. The fibres of poly(ethylene) of the microporous sheet appear to be coated.

[0139] The observations from FTIR spectroscopy and SEM appeared to demonstrate the grafting of the poloxamer to the polyolefin matrix of the microporous sheet. The conversion of the inherently hydrophobic microporous sheet of polyolefin to a water-wettable permeable membrane is attributed to this grafting.

Example B—Preparation of Filtration Membrane (Laboratory Method)

[0140] A volume of 10 mL of a solution in water of 10% (w/v) triblock copolymer (PLURONIC™ P-123; lot #MKCC2305, Sigma-Aldrich) was mixed with an equal volume of deionised water. Quantities of 0.2 g of the photoinitiator benzophenone (diphenylmethanone; Ph.sub.2O) and 0 or 0.1 g of the crosslinking agent divinylbenzene (DVB) were dissolved in separate volumes of 10 mL of ethanol (methylated spirits) before being added to a volume of 10 mL of the diluted solution of the triblock copolymer. These working solutions—excluding or including the crosslinking agent. DVB—were stored in the dark until use.

[0141] Samples (13.5×18.5 cm) were cut from a sheet of microporous poly(ethylene) (TARGRAY™ wet process polyethylene separators, item no. SW320H (Targray, Kirkland QC, Canada)) and each sample coated with a volume of one of the working solutions. The coated samples were then irradiated with ultraviolet (UV) light in the range 250 to 360 nm for a period of time of two minutes before rinsing with water and air-drying in open air.

[0142] The three replicate samples prepared according to this method using the working solution excluding DVB were designated 110419Wi, 180419Wi and 180419Wiii. The three replicate samples prepared according to this method with the working solution including DVB were designated 230419Wi, 230415Wii and 230419Wiii. Each of the samples was readily wetted with water, being observed to become uniformly translucent when contacted with this solvent.

[0143] The water flux was determined for each of the samples with deionised water as the feed stream (DI1). The samples were then completely dried before again determining the water flux with deionised water as the feed stream (DI2). Each of the samples were then subjected to a clean-in-place (CIF) protocol before twice more determining the water flux with deionised water as the feed stream (DI3 and DI4) and an intervening drying of the samples. Each of the samples remained readily wettable with water. The results are summarised in Table 5 and Table 6 and compared in FIG. 7.

TABLE-US-00005 TABLE 5 Average fluxes (LMH) determined at room temperature (22 to 24° C.) at 0 and 5 bar with water as the feed stream (*membrane failure). No crosslinking aqent included in the ‘working solution’. Flux Sample DI# 0 bar 5 bar 110419Wi 1 61 964 2 32 771 3 38 964 4 95 1446* 180419Wi 1 70 890 2 35 723 3 48 964 4 —  76 180419Wii 1 62 964 2 34 643 3 36 890 4 —  26

TABLE-US-00006 TABLE 6 Average fluxes (LMH) determined at room temperature (22 to 24° C.) at 0 and 5 bar with water as the feed stream. Crosslinking agent (DVB) included in the ‘working solution’. Flux Sample DI# 0 bar 5 bar 230419Wi 1 43 680 2 15 321 3 24 609 4 15 399 230419Wii 1 345  826 2 28 642 3 34 826 4 17 1285  230419Wiii 1 26 723 2 33 642 3 56 723 4 26 964

Example C—Preparation of Filtration Membrane (Prototype Method)

[0144] A volume of 0.300 mL of a solution of 10% (w/v) triblock copolymer (PLURONIC™ P-123; lot #MKCC2305, Sigma-Aldrich) in distilled water was dispensed into a reservoir protected from exposure to light. A further volume of 300 mL of distilled water was then added to provide an initial solution of 5% (w/v) triblock copolymer (PLURONIC™ P-123; lot #MKCC2305, Sigma-Aldrich) in the reservoir. A solution of 1.5% (w/v) benzophenone in ethanol (methylated spirits) was prepared separately and a volume of the crosslinking agent divinylbenzene (DVB) added to provide a final concentration of 0.75% (v/v) DVB. A volume of 400 mL of this separately prepared solution was then mixed with the solution of triblock copolymer (PLURONIC™ P-123; lot #MKCC2305, Sigma-Aldrich) in a reservoir to provide the working solution.

[0145] Referring to FIG. 8 of the accompanying drawings pages, peristaltic pumps (1,2) were used to deliver the working solution from the reservoirs (3,4) to the two hemicylindrical troughs (5,6) of a prototype production line. The reservoirs were periodically replenished with the working solution during the operation of the prototype production line.

[0146] The width of a continuous microporous sheet (7) of microporous poly(ethylene) was fed from a dispensing roll of stock into a first impregnation station comprising an idler roller (8) co-axially mounted in the first of the two hemicylindrical troughs (5). The difference between the radii of the roller (8) and trough (5) was sufficient to permit free passage of the sheet (7) around the roller and through the trough, but not so great as to promote evaporation of the working solution in the trough. The surface of the roller (8) over which the sheet (7) passes may be spiral engraved to promote passage of the working solution across the length of the surface.

[0147] The sheet (7) exiting the first impregnation station was then fed vertically into a first irradiating station comprising a slotted chamber (9) containing two opposed arrays (10,11) of ultraviolet light sources. The sheet (7) passed between the opposed arrays (10,11) so that both sides were irradiated. The rate at which the sheet (7) was fed was regulated to provide the required residence time within the slotted chamber (9).

[0148] The irradiated sheet (7) was then passed through a second impregnation station (12) and second irradiating station (13) of the same configuration as the first impregnation station and first irradiating station. Following these repeated steps, the irradiated sheet (7) was fed around a plurality of idler rollers (14,15,16) immersed in water in a washing station (17). The water in the washing station (17) was circulated by an external pump (18) and the depth of the water controlled by a combination of level transmitter and solenoid valve (19). The combination of a plurality of idler rollers (14,15,16) and depth of water ensured sufficient residence time before the water washed sheet (7) was fed into the drying station.

[0149] The drying station was a forced air dryer comprising two plenum chambers (20,21) having opposed perforated face plates between which the sheet of substrate passed. Hot air blowers (22,23) mounted in the wall of each chamber forced air through the perforated face plates. The dried sheet (7) of substrate was then rewound onto a receiving roll (not shown).

Example D—Spiral Wound Filter Elements, Housing and Rig

[0150] Spiral-wound filter elements were manufactured using filtration membrane prepared according to the prototype method (EXAMPLE C). The filter elements were wound using type 34 diamond spacers. Two spiral-wound filter elements were mounted in series in each of two housings mounted in an assembly (‘rig’).

Example E—Recovery of Cleaning Solutions

[0151] A volume of 900 litres of caustic cleaning solution that had been used to sanitize wine tanks was collected and transferred in two volumes of 300 litres and 600 litres, respectively, to the reservoir of the rig and delivered via a recirculating pump to the inlet ports of the filter housings. The used caustic solution had a translucent appearance attributed to the suspension of particulates (FIG. 9, left). The solution was pumped under constant pressure from the reservoir to the rig to provide flow rates at the filter housing inlets of 110 to 120 litres per minute (FIG. 10). Permeate was collected from each of the filter housing outlets at an initial rate of around f litres per minute, declining to a near steady rate of 5.3 litres per minute over the duration of the pump run (FIG. 11). The observed decline in flux was attributed to the concentration of the retentate in the closed system (as opposed to fouling of the membrane or spacer). This attribution is supported by the near steady flow rates observed at the housing inlets.

[0152] Over an initial duration of 2.5 hours (including 20 minutes downtime during which the contents of the reservoir were replenished) a volume concentration factor (VCF) of 8.18 was achieved. This equates to the recovery of 88% of the caustic cleaning solution.

[0153] Replenishing the contents of the reservoir with a further volume of 600 litres of caustic cleaning solution that had been used to sanitize wine tanks, but containing less pigments (FIG. 12, left), and repeating the foregoing increased the volume concentration factor to 15. Increases in the permeate flux rates were observed with this second feed stock (FIG. 13) supporting minimal fouling of the membranes and spacers having occurred during the initial run.

[0154] Replenishing the contents of the reservoir with a further volume of 500 litres of caustic cleaning solution that had been used to sanitize wine tanks that were heavily contaminated with solids (FIG. 14, left), a final volume concentration factor of 20 was achieved, albeit with a reduced permeate flux of around 3 litres per minute. A volume concentration factor of 20 equates to a recovery of 95% (w/w) of the caustic cleaning solution.

[0155] Samples of the cumulative volumes (900 L, 1,500 L and 2,000 L) of recovered caustic cleaning solution were titrated to pH 7 using 0.1 N sulphuric acid (H.sub.2SO.sub.4) and an auto-titrator.

TABLE-US-00007 TABLE 7 Recovery of caustic cleaning solution from a series of cleaning operations. (*Dilution of feed stream during processing.) Cumulative volume pH (initial) Titration volume (mL) Permeate (L) of used feed feed recovery cleaning solution stream retentate permeate stream retentate permeate (% (v/v)) 900 N/A N/A N/A — 8.13 8.28 98.2 1,500 11.93 11.94 11.98 3.09  3.09 3.12 99.1 2,000 10.52 — 11.96 0.67* — 3.02 97.7

[0156] To confirm the tolerance of the membrane to multiple chemistries and its utility in the recovery and reuse of the cleaning solutions typically used in beverage and food processing, a volume of citric acid cleaning solution that had been used in the cleaning of a wine tank was collected (FIG. 15, left). The volume was transferred to the cleaned reservoir and delivered via the pump at a similar flow rate to the filter housing inlets. A permeate flow rate averaging around 4 litres per minute for the duration of the run was obtained (FIG. 16). Greater than 95% (w/w) of the citric acid cleaning solution was recovered.

Example F—Reuse of Cleaning Solutions

[0157] Recovered cleaning solutions were used to sanitize wine tanks and the efficacy of these procedures evaluated. The cleaning solutions were repeatedly recovered and reused to confirm the commercial viability of the procedures. In addition to the evaluation of the efficacy of the sanitization operations the content of the recovered and reused cleaning solutions was determined by titration as before (Tables 8 and 9).

TABLE-US-00008 TABLE 8 Recovery and reuse of caustic cleaning solution. Recovery pH (initial) Titration volume (mL) % (reuse) feed stream permeate feed stream permeate recovery First 12.42 12.34 14.02 14.28 102 Second 12.11 12.43 4.81 error n.d. (first) Third 11.94 12.13 5.17 5.13 99.2 (second) Fourth 12.33 13.34 4.61 4.61 100 (third Fifth 12.13 12.09 4.13 3.98 96.5 (fourth)

TABLE-US-00009 TABLE 9 Recovery and reuse of citric acid cleaning solution. Recovery Titration volume (ML) (reuse) feed stream retentate permeate % recovery First 5.71 5.65 5.62 98.4 Second 5.01 5.12 5.08 99.2 (first)

Example G—Preparation of Filtration Membrane (Laboratory Method, Blend of Polymers)

Method 1

[0158] A volume of 5 mL of a solution in water of 10% (w/vi triblock copolymer (PLURONIC™ P-123; lot #MKCC2305, Sigma-Aldrich) was mixed with an equal volume of a solution in water of 0.25 g of poly(ethenol) (PVA, 65 kDa). A quantity of 0.1 g of the photoinitiator benzophenone (diphenylmethanone; Ph.sub.2O) was dissolved in a separate volume of 5 mL, of ethanol before being added to the solution of the triblock copolymer and poly(ethenol) (PVA, 65 kDa). The solution (‘working solution A’) was stored in the dark until use.

Method 2

[0159] A volume of 5 mL of a solution in water of 10% (w/v) triblock copolymer (PLURONIC™ P-123; lot #MKCC2305, Sigma-Aldrich) was mixed with a volume of 3 mL of a solution in water of 0.15 g of poly(ethenol) (PVA, 65 kDa). A quantity of 0.1 g of the photoinitiator benzophenone (diphenylmethanone; Ph.sub.2O) was dissolved in a separate volume of 5 mL of ethanol before being added to the solution of the triblock copolymer and poly(ethenol) (PVA, 65 kDa). The solution (‘working solution B’) was stored in the dark until use.

Method 3

[0160] A quantity of 0.5 g triblock copolymer (PLURONIC™ P-123; lot #MKCC2305, Sigma-Aldrich) was dissolved in a volume of 10 mL, of a solution in water of 0.5 g of poly(ethenol) (PVA, 65 kDa) with the addition of a volume of 5 mL ethanol and at a temperature of 55° C. A quantity of 0.1 g of the photoinitiator benzophenone (diphenylmethanone; Ph.sub.2O) was dissolved in the solution of the triblock copolymer and poly(ethenol) (PVA, 65 kDa) and this turbid, but homogenous solution (‘working solution C’) was stored in the dark until use.

[0161] The appearance of each of the working solutions (A, B and C) prepared according to method 1, 2 and 3 is presented in FIG. 17.

Method 4

[0162] Samples (13.5×18.5 cm) were cut from a microporous sheet of poly(ethylene) (TARGRAY™ wet process polyethylene separators, item no. SW320H (Targray, Kirkland QC, Canada)) and each sample coated with a volume of 5 mL of the working solution. The coated samples were then irradiated with ultraviolet (UV) light in the range 250 to 360 nm for a period of time of two minutes before rinsing with water and air-drying on top of a warm oven. Working solution A was used for the preparation of the sample designated 310818wi, working solution B was used for the preparation of the sample designated 030918wii, working solution C was used for the preparation of the sample designated 030918wi.

[0163] Each of the samples prepared according to method 4 was highly hydrophilic and readily wetted with water.

Method 5

[0164] A quantity of 0.15 g of poly(ethenol) (PVA, 146 to 186 kDa) (PVA180) was dissolved with heating and stirring in a volume of 10 mL of water. A quantity of 0.5 g of triblock copolymer (PLURONIC™ P-123; lot #MKCC2305, Sigma-Aldrich) was then added to the volume and dissolved. A quantity of 0.1 q of the photoinitiator benzophenone (diphenylmethanone; Ph.sub.2O) was dissolved in a separate volume of 5 mL of ethanol before being added to the volume of the triblock copolymer and poly(ethenol) (PVA, 146 to 186 kDa) (PVA180). The solution (‘working solution D’) was stored in the dark until use.

Method 6

[0165] A sample (13.5×18.5 cm) was cut from a microporous sheet of poly(ethylene) (TARGRAY™ wet process polyethylene separators, item no. SW320H (Targray, Kirkland QC, Canada)) and coated with a volume of 5 mL of working solution D. The coated sample was then irradiated with ultraviolet (UV) light in the range 250 to 360 nm for a period of time of two minutes before rinsing with water and air-drying on top of a warm oven.

[0166] Three replicate samples were prepared according to method 5 and designated 041918wi, 041918wii and 041918wiii. The appearance of these samples is provided in Figure S.

[0167] The flux (LMH) was determined for each of the samples designated 310818wi, 039818wii and 030918wi. A summary of the composition of the working solution used to prepare each sample of membrane and the fluxes determined are presented in Table 10.

TABLE-US-00010 TABLE 10 Summary of the composition (g/10 mL) of each working solution used to prepare each sample of membrane (310818wi, 030918wii, 030918wi and 040918wi) and the fluxes (LMB) determined at 0 and 5 bar with water as the feed stream PLURONIC ™ Benzo- Flux Sample P-123 phenone PVA65 PVA180 0 bar 5 bar 030918wi 0.5 0.1 0.15 — 26 340 310818wi 0.5 0.1 0.25 — 22 312 030918wii 0.5 0.1 0.5 — 11 189 040918wi 0.5 0.1 — 0.15 10 361

[0168] Spectra were recorded for each of the samples designated 310818wi, 030918wii and 030918wi, the untreated microporous poly(ethylene) (TARGRAY™ wet process polyethylene separators, item no. SW320H (Targray, Kirkland QC, Canada)), and the triblock copolymer (PLURONIC™ P-123; lot #MKCC2305, Sigma-Aldrich) and poly(ethenol) (PVA, 65 kDa) used in the preparation of the samples. Spectra were also recorded for the centre (−C) and edge (−E) of each of the samples designated 310818wi, 030918wii and 030918wi. A comparison of the recorded spectra is provided in FIG. 19. A comparison of the same spectra over the ‘fingerprint’ region (1800 cm.sup.−1 to 600 cm.sup.−1) is provided in FIG. 20. (The edge of each sample was not exposed to the feed stream (water) during the flux testing.)

Example H—Preparation of Composite Membranes

Method 1

[0169] A series of preliminary experiments were performed to evaluate methods of preparing a film of cross linked poly(ethenol) (xPVA) on a surface. A solution of the radical initiator sodium persulfate (SPS) was prepared by adding a quantity of 0.2 g of SPS to a volume consisting of 10 mL deionised water and 10 mL acetone. The solution of radical initiator was applied onto the surface of each of three glass plates (Plate 1, Plate 2 and Plate 3). Plate 2 and Plate 3 were transferred to an oven and dried at a temperature of 60° C. until all solvent had evaporated to leave a thin layer of the initiator deposited on the surface. Solutions of poly(ethenol) (PVA) were prepared at a concentration of 1% (w/v) in either dimethyl sulfoxide (DMSO) or deionised water. The solution of poly(ethenol) (PVA) in DMSO was sprayed onto the wet surface of Plate 1 and the plate then transferred to an oven and dried at a temperature of 60° C. The solution of poly(ethenol)(PVA) in DMSO was also sprayed onto the dry surface of Plate 2 and the plate then transferred to an oven and dried at a temperature of 60° C. The solution of poly(ethenol) in deionised water was sprayed onto the dry surface of Plate 3 and the plate then transferred to an oven and dried at a temperature of 60° C. The desired film of cross-linked poly(ethenol) was not formed on Plate 1. The failure attributed to the presence of acetone causing the polymer to crash out of solution. The film formed on Plate 2 was too frangible to be useful as a rejection layer of a composite membrane. A clear, peelable film formed on the surface of Plate 3. The film was not brittle, and this method of preparation was adopted for use in the preparation of the composite membrane.

Method 2

[0170] A series of preliminary experiments were performed to evaluate methods of preparing a film of partially cross-linked poly(ethenol) (xPVA) and thereby control the properties of the rejection layer of the composite membrane. Volumes of 10 mL of a 1% (w/v) solution of poly(ethenol) (PVA) in deionised water containing a quantity of 0.1 g of SPS were dispensed into each four vials (Vial 1, Vial 2, Vial 3 and Vial 4). The solution in each vial was heated to a temperature of 75° C. and maintained at this temperature with stirring until the following observations were made (and the vials then cooled): [0171] A yellow solid crashed out of solution (Vial 1; 3 to 4 minutes) [0172] A cloudy white solution with some precipitation formed (Vial 2, around 3 minutes) [0173] A cloudy white solution formed (Vial 3; 1.5 to 2 minutes) [0174] A cloudy solution started to form (Vial 4; 10 to 20 seconds)

[0175] The observations are also presented in FIG. 21. The method of preparing partially cross-linked poly(ethenol) according to that formed in Vial 3 was adapted for use in the preparation of the membrane.

Method 3

[0176] In a proposed alternative method, a volume of 20 mL of the solution of the radical initiator sodium persulfate (SPS) is prepared according to Method 1. A volume of the solution of partially cross-linked poly(ethenol) (xPVA) is prepared according to Method 2 (Vial 3). The solution of the radical initiator is applied to one surface of a hydrophilicitized sheet of microporous poly(ethylene) prepared according to EXAMPLE A. The sheet is then placed on a glass plate and transferred to an oven and dried at a temperature of 60° C. The solution of partially cross-linked poly(ethenol) is applied to the same surface of the dried sheet and the sheet then returned to the oven and dried at 60° C. The dried membrane is then washed with cool water and air dried before evaluation for flux, total solids and salts rejection with different feed streams (water and milk).

Method 4

[0177] A radical initiator containing volume of 8% (w/v) poly(ethenol) (PVA) was prepared by dissolving a quantity of 0.2 g of the radical initiator sodium persulfate (SPS) in a volume of 6.5 mL of distilled water and then adding the solution to a volume of 13.5 mL of 12% (w/v) poly(ethenol)(PVA). The volume of 6% (w/v) poly(ethenol) (PVA) was stirred with heating to 75° C. and monitored until the solution became a pale-yellow colour. The pale-yellow solution was cooled and then applied to a hydrophilicitized sheet of microporous poly(ethylene) prepared according to EXAMPLE A. The sheet was irradiated with ultraviolet (UV) light (250 nm) for 2 minutes before drying on a glass plate in an oven at 60° C.

Method 5

[0178] A radical initiator containing volume of 5% (w/v) poly(ethenol)(PVA) was prepared by dissolving a quantity of 0.2 g of the radical initiator sodium persulfate (SPS) in a volume of 11.5 mL of distilled water and then adding the solution to a volume of 8.5 mL of 12% (w/v) poly(ethenol)(PVA). The volume of 5% (w/v) poly(ethenol) (PVA) was stirred with heating to 15° C. and monitored until the solution became a pale-yellow colour. The pale-yellow solution was cooled and then applied to a hydrophilicitized sheet of microporous poly(ethylene) prepared according to EXAMPLE A. The sheet was irradiated with ultraviolet (UV) light (250 nm) for 2 minutes before drying on a glass plate in an oven at 60° C.

[0179] Samples of membrane prepared according to Method 4 and Method 5 were evaluated. The sample prepared according to Method 4 was also evaluated following exposure to a clean-in-place (CIP) protocol. The results of these evaluations are summarised in Table 11.

TABLE-US-00011 TABLE 11 Mean flux (LMH) determinmd for water as the feed stream and protein rejection (%) and mean flux (LMH) determined for milk as the feed stream for samples of membrane prepared according to the specified methods. Both feed streams at a pressure of 5 bar. (*following exposure to a clean-in-place (CIP) protocol.) Method used to prepare membrane Water Milk Rejection Method 4 7.8 3.8 99.91 Method 4* 11.7 7.8 39.97 Method 5 32.2 11.6 99.92 EXAMPLE A 826 20.6 99.56

[0180] For the manufacture of the composite membranes on an industrial scale it is proposed to prepare a radical initiator, e.g. sodium persulfate (SPS), containing solution of 6 to 10% (w/v) poly(ethenol) (PVA) and apply this directly to a hydrophilicitized sheet of microporous polyolefin before irradiating with ultraviolet (UV) light and drying.

[0181] Although the invention has been described with reference to embodiments or examples it should be appreciated that variations and modifications may be made to these embodiments or examples without departing from the scope of the invention. Where known equivalents exist to specific elements, features or integers, such equivalents are incorporated as if specifically referred to in this specification. Variations and modifications to the embodiments or examples that include elements, features or integers disclosed in and selected from the referenced publications are within the scope of the invention unless specifically disclaimed. The advantages provided by the invention and discussed in the description may be provided in the alternative or in combination in these different embodiments of the invention.

INDUSTRIAL APPLICABILITY

[0182] Methods of preparing membranes and their use in the recovery of aqueous solutions or water from feed streams are provided. The membranes are advantageously used where the membranes are required to be exposed to chemically aggressive feed streams such as those used in clean-in-place operations of the beverage or food processing industries.

INCORPORATION BY REFERENCE

[0183] Where the claims, description or drawings of this specification are missing in their entirety or part, the corresponding portion of the specification accompanying the most recently filed application from which priority is claimed is to be incorporated by reference so as to complete this specification in accordance with Rules 4.18, 20.5 and 20.6 of the PCT Regulations (as in force from 1 Jul. 2015 or subsequently amended).

[0184] For the purposes of 37 C.F.R. 1.57 of the United States Code of Federal Regulations the disclosures of the following publications (as more specifically identified under the heading ‘Referenced Publications’) are incorporated by reference: Jones at al (2008) and Schmolka (1973).

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