Water-wettable filter membrane and preparation thereof

Abstract

The present invention describes a filter membrane prepared by adhering a poloxamer to a preformed sheet of microporous polyolefin. In one embodiment, the poloxamer is supplied with the trade name PLURONICTM P-123, and the sheet is a microporous poly (ethylene). The film provides the advantage of withstanding cleaning agents used in a cleaning-in-place regime.

Description

[0001] This divisional application is a divisional of the patent application with the application number 202080067046.9 and the title "Water-Wettable Filter Membrane and Its Preparation" submitted by the present applicant on August 10, 2020. The entire content of the parent case is incorporated into this divisional application by reference. Technical Field

[0002] The present invention relates to durable filter membranes, filter membrane assemblies comprising such membranes, and their use in recovering water from a feed stream. In particular, the present invention relates to durable filter membranes and their use in recovering water from a feed stream that requires periodic in-situ cleaning of the membrane. Background Art

[0003] The publication of Schmolka (1973) discloses the preparation of polyoxyethylene-polyoxypropylene block polymers represented by the following formula:

[0004] HO(C 2 H 4 O) b (C 3 H 6 O) a (C 2 H 4 O) b H

[0005] wherein a is an integer such that the hydrophobic group represented by (C 3 H 6 O) has a molecular weight of at least 2,250, and b is an integer from about 8 to 180 or higher. These block polymers are used to prepare solids or semi-solid colloids - "gels" or "hydrogels" (where the liquid is water) containing a large amount of liquid, which are particularly suitable for the formulation of topically applied cosmetic and pharmaceutical compositions. These nonionic triblock copolymers are called poloxamers and are available under many trade names, including ACCLAIM TM 、ADEKANOL TM 、ANTAROX TM 、BASOROL TM 、BLAUNON TM 、ETHOX TM 、KOLLIPHORTM、LUTROL TM 、MEROXAPOL TM 、PLURIOL TM 、PLURONIC TM and SYNPERONIC TM。The properties of poloxamers are determined by the ratio and size of the integers a and b. Triblock copolymers in which the order of the polyoxyethylene and polyoxypropylene blocks is reversed are also available under these trade names. These "reverse" triblock copolymers can be identified by using the letter "R" and should not be called "poloxamers".

[0006] The publication by Wang et al. (2006) discloses the formation of membranes from blends of polyethersulfone and different triblock copolymers by a phase inversion method. It was observed that the water flux measured for the membranes depends on the triblock copolymer structure rather than the content. For example, it was observed that the water flux (50.161 LMH) of the membrane formed from the blend with PLURONIC TM 123 was less than the water flux (109.081 LMH) observed in the polyethersulfone control membrane. It was observed that the water flux (218.28 LMH) of the membrane formed from the blend with PLURONIC TM F68 was higher than the water flux of the control membrane.

[0007] The publication by Liu et al. (2014) (machine translation) discloses the preparation of microporous membranes with microstructured surfaces for separating oil from water-in-oil / water emulsions. In the method for preparing the membranes, polyoxyethylene-polyoxypropylene-polyoxyethylene (F127) was used as an additive to prepare a homogeneous solution of the polymer in a solvent. The polymer is selected from polyvinylidene fluoride (PVDF), polysulfone (PSf), polyethersulfone (PES), polyacrylonitrile (PAN), polyvinyl chloride (PVC), polylactic acid (PLA), polyimide (PI), polypropylene (PP) or cellulose acetate, and the solvent is selected from chloroform (CHCl 3 ), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), triethyl phosphate (TEP), trimethyl phosphate (TMP), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), dibutyl phthalate (DBP), dioxane, acetophenone, diphenyl ether and one or more mixtures thereof.

[0008] The publication by Yang et al. (2014) discloses a composite polymer electrolyte for lithium-polymer batteries. The composite material consists of mesoporous modified silica fillers dispersed in a poly(vinylidene fluoride-hexafluoropropylene) matrix. The triblock copolymer PLURONIC TM 123 (Aldrich) was used to prepare the mesoporous silica fillers.

[0009] The publication by Guo et al. (2015) discloses microporous materials for microfiltration and ultrafiltration membranes. The microporous materials comprise finely divided particles, such as water-insoluble silica fillers, distributed throughout a matrix such as poly(ethylene). The material further comprises an interconnected pore network and can be further processed according to the desired application. In this further processing, a triblock copolymer based on poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) can be used as a hydrophilic coating, although polymers containing tertiary amine functional groups are preferred. Without wishing to be bound by theory, it is alleged that the components of the coating can interact with the silica particles in the filler of the microporous material and regulate the surface energy, affecting wettability. Covalent bonding of the hydrophilic coating, such as by grafting, is not disclosed.

[0010] The publication by Cheng et al. (2017) (machine translation) discloses the use of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer as a "structure-directing agent" in the preparation of mesoporous composite membranes. The structure-directing agent is used together with one or more of a catalyst and precursor compounds such as tetraethyl orthosilicate, titanium tetrachloride, titanium n-butoxide acetate, titanium isopropoxide, zinc diacetate phthalate, tin esters, and niobates to provide the mesoporous composite membranes.

[0011] The publication by Carter et al. (2018) discloses the evaluation of the triblock copolymer PLURONIC TM L64 as a solvent for pore filling of regenerated cellulose membranes during initiator immobilization. In this article, glycerol was identified as a more effective pore filling solvent.

[0012] Fouling caused by non-specific adsorption or deposition of proteins requires regular cleaning of the filter membrane. If the filter membrane can be cleaned in situ, the efficiency of plant operation can be achieved. Filter membranes that are tolerant to the reagents (acids, bases, hypochlorites) used in these in-place cleaning (CIP) schemes are needed.

[0013] An object of the present invention is to provide a filter membrane suitable for these and other situations, or at least to provide a useful option in the selection of filter membranes for these and other situations. Summary of the Invention

[0014] In a first aspect, there is provided a water-wettable filter membrane comprising a poloxamer adhered to a substrate consisting of a microporous sheet of polyolefin. The poloxamer is adhered to a preformed microporous sheet of polyolefin. The poloxamer is adhered to the polyolefin matrix of the preformed microporous sheet by the formation of a covalent bond between the two polymers. The covalent bond can be formed directly between the poloxamer and the polyolefin or indirectly through a crosslinking agent.

[0015] Preferably, poloxamer is attached to the substrate by grafting. Most preferably, poloxamer is attached to the substrate by photoinitiated grafting. In the present context, photoinitiated grafting will be understood to encompass the formation of covalent bonds initiated by irradiation with ultraviolet (UV) light in the presence of a suitable photoinitiator. Suitable photoinitiators are type II photoinitiators such as benzophenone (diphenyl ketone; BP). Photoinitiated grafting is advantageously carried out in the presence of a crosslinking agent. Suitable crosslinking agents are low molecular weight divinyl compounds. Low molecular weight divinyl compounds are those having a molecular weight below 150 g mol -1 and such as divinylbenzene (DVB).

[0016] Preferably, the poloxamer is a polymer having the following structure:

[0017] HO(ethylene oxide) m -(propylene oxide) n -(ethylene oxide) m H

[0018] wherein m is in the range of 15 to 25 and n is in the range of 50 to 90. Most preferably, the poloxamer corresponds to the triblock copolymer supplied under the trade name PLURONIC TM P-123 (Sigma-Aldrich). It should be understood that for the polymer sold under the trade name PLURONIC TM P-123 (Sigma-Aldrich), m is 20 and n is 70.

[0019] Preferably, the polyolefin is poly(ethylene) or poly(propylene). More preferably, the polyolefin is poly(ethylene). Most preferably, the polyolefin is virgin poly(ethylene).

[0020] In a first embodiment of the first aspect, there is provided a water-wettable filter membrane composed of a microporous sheet of grafted poly(ethylene), wherein the graft contains a poloxamer having the following structure:

[0021] HO(ethylene oxide) m -(propylene oxide) n -(ethylene oxide) m H

[0022] wherein m is in the range of 15 to 25 and n is in the range of 50 to 90.

[0023] In a second embodiment of the first aspect, there is provided a water-wettable filter membrane composed of a microporous sheet of grafted poly(ethylene), wherein the graft contains divinylbenzene and a poloxamer having the following structure:

[0024] HO(ethylene oxide) m-(Propylene Oxide) n -(Ethylene Oxide) m H

[0025] Wherein m is in the range of 15 to 25 and n is in the range of 50 to 90.

[0026] It is expected that in the first or second embodiment of the first aspect, poly(propylene) can replace poly(ethylene).

[0027] Preferably, the filter membrane is a semi-permeable membrane.

[0028] In a second aspect, a method for preparing a water-wettable filter membrane is provided, wherein the method comprises:

[0029] 1. Contacting a microporous sheet of polyolefin with a solution of poloxamer in a solvent to provide a contacted sheet;

[0030] 2. Irradiating the contacted sheet with ultraviolet light in the presence of a photoinitiator to provide an irradiated sheet; and then

[0031] 3. Washing and drying the irradiated sheet to provide a membrane.

[0032] Preferably, the polyolefin is poly(ethylene) or poly(propylene). More preferably, the polyolefin is poly(ethylene). Most preferably, the polyolefin is unprocessed poly(ethylene).

[0033] Preferably, the solution contains a photoinitiator. More preferably, the solution further contains a crosslinking agent.

[0034] Preferably, poloxamer is a polymer having the following structure:

[0035] HO(Ethylene Oxide) m -(Propylene Oxide) n -(Ethylene Oxide) m H

[0036] Wherein m is in the range of 15 to 25 and n is in the range of 50 to 90. Most preferably, poloxamer corresponds to the triblock copolymer supplied under the trade name PLURONIC TM P-123 (Sigma-Aldrich). It should be understood that for the polymer sold under the trade name PLURONIC TM P-123 (Sigma-Aldrich), m is 20 and n is 70.

[0037] Preferably, the solvent is water-alcohol or water-acetone, wherein the ratio of water to ethanol or acetone (v / v) is in the range of 1:1 to 3:1. More preferably, the ratio of water to ethanol or acetone (v / v) is in the range of 1:1 to 2:1. Most preferably, the solvent is water-ethanol.

[0038] Preferably, the photoinitiator is a type II photoinitiator. Most preferably, the photoinitiator is benzophenone (diphenyl ketone; BP).

[0039] Preferably, the crosslinking agent is a divinyl compound having a molecular weight below 150 g / mol -1 . Most preferably, the crosslinking agent is divinylbenzene (DVB).

[0040] Preferably, the wavelength of the ultraviolet light is in the range of 250 to 360 nm. More preferably, the wavelength of the ultraviolet light is in the range of 250 to 280 nm. Most preferably, the wavelength of the ultraviolet light is 250 nm.

[0041] Preferably, the irradiation duration is between one and a half minutes and two and a half minutes. More preferably, the irradiation duration is 2 minutes plus or minus 10 seconds.

[0042] In one embodiment of the second aspect, a method for preparing a water-wettable membrane is provided, the method comprising irradiating a microporous sheet of poly(ethylene) at a wavelength of 250 nm, the microporous sheet of poly(ethylene) being impregnated with a 30 to 50% (v / v) aqueous ethanol solution of Pluronic TM P-123 provided, 0.5 to 1% (w / v) benzophenone and 0 to 0.5% (w / v) divinylbenzene.

[0043] It is contemplated that in this embodiment of the second aspect poly(propylene) may replace poly(ethylene).

[0044] In a third aspect, a water-wettable filter membrane prepared according to the second aspect is provided.

[0045] In a fourth aspect, a method for recovering water from a feed stream is provided, which comprises contacting a first side of the filter membrane of the first or third aspect with the feed stream at a pressure sufficient to provide permeation.

[0046] Preferably, the feed stream is selected from milk and wastewater. More preferably, the feed stream is skim milk and wastewater containing particulates. Most preferably, the feed stream is selected from wastewater containing suspended particulates. The particulates can be of non-biological or biological origin.

[0047] Preferably, the filter membrane is in the form of a filter membrane module or a filter element. More preferably, the membrane is in the form of a spiral-wound filter membrane module or a filter element.

[0048] Preferably, the method comprises contacting the filter membrane with an acid, a base or a chlorite at least periodically.

[0049] In a fifth aspect, the present invention provides a spiral-wound membrane filtration module or filter element comprising the membrane filtration of the first or third aspect.

[0050] In the specification and claims of this specification, the following abbreviations, acronyms, phrases, and terms have the meanings provided: "block" means a portion of a macromolecule containing many structural units that has a structural or configurational feature not present in at least one adjacent portion; "CAS RN" means the Chemical Abstracts Service (CAS, Columbus, Ohio) registry number; "comprising" means "including", "containing", or "characterized by" and does not exclude any additional element, ingredient, or step; "consisting essentially of" means excluding any element, ingredient, or step not limited by the material; "consisting of" means excluding any unspecified element, ingredient, or step other than impurities and other incidental substances; "crosslinking" means a reaction involving sites or groups on existing macromolecules or an interaction between existing macromolecules that results in the formation of small regions, such as crosslink bridges, from which at least four chains emanate; "crosslinking agent" means a material incorporated into the crosslink bridges of a crosslinked polymer network; "curing" means the chemical process of converting a prepolymer or polymer into a polymer of higher molecular weight and connectivity and ultimately into a network; "filter" means removing particulate matter from a fluid by passing through a porous substrate, and "filtration" has the corresponding meaning; "graft molecule" or "graft polymer molecule" means a macromolecule having one or more blocks attached as side chains to a main chain, the side chains having structural or configurational features different from those in the main chain; "grafting" means the reaction by which one or more blocks are attached as side chains with structural configurational features different from those in the main chain to the main chain of a macromolecule, and "grafted" has the corresponding meaning; "LMH" means liters per square meter per hour; "impregnation" means permeating a substrate, for example, with a solution of a reagent in a solvent; "macromolecule" or "polymer" means a molecule of high relative molecular mass whose structure essentially comprises a plurality of repeating units that are actually or conceptually derived from molecules of low relative molecular mass; "monomer molecule" means a molecule that can undergo a polymerization reaction to provide a structural unit for the basic structure of a macromolecule; "monomeric unit", "monomer unit", or "mer" means the largest structural unit that constitutes the macromolecular structure from a single monomer molecule; "permeable" means allowing the passage of a solvent such as water; "permeation" means complete diffusion; "poloxamer" means a symmetric nonionic triblock copolymer consisting of a central chain of poly(propylene oxide) flanked by two chains of poly(ethylene oxide); "semipermeable" means allowing some substances to pass through but not others, especially allowing a solvent such as water to pass through but not allowing certain solutes such as proteins, salts, or sugars to pass through; "wettable" means becoming permeated by a solvent such as water when in contact with the solvent under standard laboratory conditions (i.e., 25 °C, 100 kPa), and "water-wettable" means being wetted by water.

[0051] The synonyms of any defined term have the corresponding meanings. When there is uncertainty in the meaning of an undefined abbreviation, acronym, phrase or term related to polymer terms and nomenclature, the meaning provided in the publication by Jones et al. (2008) shall prevail.

[0052] It should be recognized that the porosity determined for a substrate will depend at least in part on the method used to determine the porosity. In this specification, the term "microporous" is used to refer to the porosity of a polyolefin sheet, which is equivalent to that of the TM wet-process polyethylene separator, part number SW320H (Targray, Kirkland QC, Canada). In this context, the term "equivalent" means that the porosity determined for the polyolefin sheet is 75 to 125% of the porosity determined for the TM wet-process polyethylene separator, part number SW320H (Targray, Kirkland QC, Canada) by the same method.

[0053] The terms "first", "second", "third", etc. are used with reference to aspects, elements, features or wholes of the subject matter described in the invention specification or defined in the claims, or when used with reference to alternative aspects or embodiments of the present invention, and are not intended to imply a preferred order.

[0054] When defining the concentration or ratio of a reagent, the defined concentration or ratio is the initial concentration or ratio of the reagent. When a value is expressed to one or more decimal places, standard rounding applies. For example, 1.7 encompasses the range from 1.650 cycles to 1.749 cycles.

[0055] The present invention will now be described with reference to embodiments or examples and the drawings on the drawing pages. In the drawings description and the following other descriptions, the "top" (Ctop, Etop, etc.) of a polyolefin filter membrane or microporous sheet prepared according to laboratory methods refers to the face or side of the membrane or sheet that contacts the working solution. The "back" (Cback, Eback, etc.) or "back layer" refers to the opposite face or side. It should be understood that since the membrane or sheet is installed in the filter membrane assembly, the entire face or side is not exposed to the feed stream. A description of this filter membrane assembly (Sterlitech Corp.) and its uses is provided on page 24, line 24 of the specification accompanying International Application No. PCT / NZ2015 / 050034 [Publication No. WO2015 / 147657A1]. Description of the Drawings

[0056] Figure 1 . Exploded view of the filter membrane assembly (Sterlitech Corp.) used in the flux test of a sheet sample of the filter membrane.

[0057] Figure 2 . Untreated microporous poly(ethylene) (TARGRAY TM Wet-processed polyethylene separator, part number SW320H (Targray, Kirkland QC, Canada)) (as-received PE), triblock copolymer (PLURONIC TM P-123; lot# MKCC2305, Sigma-Aldrich) used for sample (P123) preparation, and spectra (3800 cm -1 to 525 cm -1 ) recorded on the top (Etop) and back layer (Eback) sides of each of the samples named 040918Wiv, 040918Wv, and 040918Wvi.

[0058] Figure 3 . Untreated microporous poly(ethylene) (TARGRAY TM Wet-processed polyethylene separator, part number SW320H (Targray, Kirkland QC, Canada)) (as-received PE), triblock copolymer (PLURONIC TM P-123; lot# MKCC2305, Sigma-Aldrich) used for sample (P123) preparation, and extended spectra (1800 cm -1 to 600 cm -1 ) recorded on the top (Etop) and back layer (Eback) sides of each of the samples named 040918Wiv, 040918Wv, and 040918Wvi in the "fingerprint region".

[0059] Figure 4 . Comparison of spectra (3800 cm -1 to 525 cm -1 ) recorded on regions of the sample named 040918Wvi with (Ctop and Cback) exposed to the feed stream and (Etop and Eback) not exposed to the feed stream.

[0060] Figure 5 . Scanning electron micrographs of the top (Etop) side of the sample named 040918Wiv at magnifications of 250,000x (A), 35,000x (B), and 10,000x (C).

[0061] Figure 6 . Scanning electron micrographs of two regions on the top (Etop) side of the sample named 040918Wiv at a magnification of 100,000x.

[0062] Figure 7 . Comparison of the fluxes (LMH) maintained by filter membrane samples (180419Wi and 230419Wii (■); 180419Wii and 230419Wiii (●)) prepared with (solid line) and without (dashed line) crosslinking agent (DVB).

[0063] Figure 8 . Schematic diagram of a prototype production line for preparing a water-wettable filter membrane according to Example C. Detailed Description

[0064] The filter membrane is used in a series of industrial processes including food processing to recover or remove water from a feed stream. In one application, the purpose may be to separate water from contaminated particulates. In another application, the purpose may be to concentrate high-value solutes.

[0065] In either application, efficiency is enhanced by bringing the feed stream into contact with the large surface area of the filter membrane. To this end, the filter membranes are typically assembled into spiral-wound filter elements, which are then installed in industrial plants. Such spiral-wound membrane modules—or “filter elements”—are provided by manufacturers such as Synder Filtration (Vacaville, California, USA).

[0066] Higher efficiency can be achieved if cleaning can be carried out in situ without the need to disassemble and reinstall the filter element. In situ cleaning protocols use chemically aggressive solutions such as acids, bases, and hypochlorites. Alternatively, the feed stream to which the membrane is exposed can be chemically aggressive, and the durability under these conditions reduces the frequency of filter element replacement.

[0067] Microporous sheets of polyolefins such as poly(ethylene) are commercially available from suppliers such as Celgard (Charlotte, North Carolina, USA) and Targray (Kirkland, Quebec, Canada). One obstacle to using these substrates as filter membranes in the above applications is their inherent hydrophobicity. There may also be a lack of the required retention characteristics when the aim is to provide a semipermeable membrane for concentrating high-value solutes.

[0068] It has now been determined that grafting of a microporous sheet of poly(ethylene) with Pluronic supplied under the trade name PLURONIC-P123 provides a filter membrane that is readily wettable with water and provides a high flux rate at a relatively low pressure (5 bar). The filter membranes produced in this way have also been shown to have the required durability when exposed to chemically aggressive liquids.

[0069] Retention of these desired properties is enhanced by adding a crosslinking agent to the working solution used in the preparation method - this is attributable to grafting. Without wishing to be bound by theory, low molecular weight crosslinking agents are advantageous so as not to disrupt the favorable retention properties also exhibited by the membrane.

[0070] The method for preparing the filter membrane is readily applicable to a continuous production process. According to the method, before irradiation with ultraviolet light having a wavelength in the range of 250 nm to 360 nm, a microporous substrate is impregnated with a working solution having the following composition, preferably at a wavelength at or near the lower end of this range (250 nm).

[0071] Working solution:

[0072] 3 to 5% (w / v) poloxamer

[0073] 0.5 to 1% (w / v) photoinitiator

[0074] 0 to 0.5% (w / v) crosslinking agent

[0075] 30 to 50% (v / v) aqueous solution of alcohol or acetone

[0076] The preferred poloxamer for the working solution is available under the trade name PLURONIC® P-123. The preferred photoinitiator for the working solution is benzophenone. The preferred crosslinking agent for the working solution is divinylbenzene.

[0077] Example A

[0078] Preparation of the filter membrane (laboratory method)

[0079] An aqueous solution of 10% (w / v) triblock copolymer (PLURONIC® TM P-123; lot# MKCC2305, Sigma-Aldrich) with a volume of 5 mL was mixed with an equal volume of deionized water. An amount of 0.1 g of the photoinitiator benzophenone (diphenylmethanone; Ph 2 O) was dissolved in a separate volume of 5 mL of ethanol and then added to the diluted solution of the triblock copolymer. The working solution was stored in the dark until use.

[0080] Samples (13.5 × 18.5 cm) were cut from a sheet of microporous poly(ethylene) (TARGRAY TM wet-process polyethylene separator, part number SW320H (Targray, Kirkland QC, Canada)) and each sample was coated with 5 mL of the working solution. Then the coated samples were irradiated with ultraviolet (UV) light in the range of 250 to 360 nm for 2 minutes, then rinsed with water and air-dried on top of a warm oven.

[0081] Four replicate samples prepared according to the method were named 040918Wiv, 040918Wv, 040918Wvi, and 151018Wi. A small piece was cut from the edge of the sample named 040918Wiv and subjected to scanning electron microscopy (SEM).

[0082] Each sample was wetted easily with water and each sample was observed to become uniformly translucent when in contact with the solvent.

[0083] Durability, flux, and protein retention

[0084] Using a membrane filtration assembly (Sterlitech) as shown Figure 1 , the flux (LMH) of each of the samples named 040918Wiv, 040918Wv, and 040918Wvi was determined. The samples were individually mounted in the membrane filtration assembly and the flux was measured 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:

[0085]

[0086] where V is the volume of permeate (L), t is the time to collect V (h), and A is the area of the sample exposed to the feed stream (water or skim milk) (m 2 ). The results are summarized in

[0087] Table 1.

[0088]

[0089] Table 1. Flux (LMH) measured at 0 and 5 bar using water as the feed stream at the specified temperature (°C).

[0090] To evaluate durability, the flux was also measured after a repeated in-situ cleaning (CIP) protocol. The CIP protocol was based on that employed in commercial treatment operations for reverse osmosis (RO) membranes (Anon (2014)) and is summarized in Table 2.

[0091]

[0092] Table 2. In-situ cleaning (CIP) protocol adapted from Anon (2014). "Alkali" is 2% (w / v) sodium hydroxide (NaOH). "Acid" is 1.9% (w / v) nitric acid (H 2 NO 3 ) and 0.6 (w / v) phosphoric acid (H 3 PO 4 ).

[0093] For each sample, multiple CIP protocols were repeated alternately using water or skim milk as the feed stream. Table 3 provides the fluxes and protein rejection percentages (using skim milk as the feed stream) determined for samples named 040918Wv and 040918Wvi. The total protein concentration in the permeate was calculated based on HPLC analysis monitored by UV absorbance.

[0094]

[0095] Table 3. Fluxes (LMH) and protein rejections were determined at 0 and 5 bar using water or skim milk as the feed stream at the specified temperature (°C). Each sample was assayed according to a repeated in-place cleaning (CIP) protocol.

[0096] The durability of the membranes was further evaluated by contacting samples named 151018Wi with 2% (w / v) sodium hydroxide (NaOH) for 7 days. The fluxes and protein rejection percentages (using skim milk as the feed stream) determined for these samples are provided in Table 4.

[0097]

[0098] Table 4. Fluxes (LMH) and protein rejections were determined at 0 and 5 bar using water or skim milk as the feed stream at the specified temperature (°C). Samples were assayed after exposure to 2% (w / v) sodium hydroxide (NaOH) for 7 days.

[0099] Fourier transform infrared (FTIR) spectra

[0100] The spectra of each sample named 040918Wiv, 040918Wv, and 040918Wvi were recorded using a Thermo Electron Nicolet 8700 FTIR spectrometer equipped with a single reflection ATR and a diamond crystal. Each sample was averaged over 32 scans at a resolution of 4 cm -1 . Figure 2 Comparisons of the recorded spectra (from 3800 cm -1 to 525 cm -1 ) are provided: (i) untreated microporous poly(ethylene) (TARGRAY TM wet-process polyethylene separator, part number SW320H (Targray, Kirkland QC, Canada)) (‘as-received PE’); (ii) triblock copolymer used for sample (P123) preparation (PLURONIC TMP-123; lot #MKCC2305, Sigma-Aldrich); and (iii) the top (Etop) and back (Eback) sides of each of the samples named 040918Wiv, 040918Wv, and 040918Wvi.

[0101] Corresponding to the symmetric stretching mode of the C-O-C fragment (1108 cm TM ) present in the spectrum of the triblock copolymer (PLURONIC -1 ) and the signal of the C-H stretching mode of CH 3 (2970 cm -1 ) are also present in the spectra recorded for each sample. Many signal features of the triblock copolymer (PLURONIC TM P-123) are also observed at low intensity in the 'fingerprint' region of the spectra provided in Figure 3 . The signal features of the triblock copolymer (PLURONIC TM P-123) are retained in the spectra recorded for the regions of the sample named 040918Wiv after exposure to the feed stream (water), as shown in Figure 4 .

[0102] ■SEM

[0103] Figure 5 and Figure 6 provide scanning electron micrographs of small pieces cut from the edge of the sample named 040918Wiv. The poly(ethylene) fibers of the microporous sheet appear to be coated.

[0104] The observations from the FTIR spectra and SEM seem to confirm the grafting of poloxamer onto the polyolefin matrix of the microporous sheet. The conversion of the inherently hydrophobic microporous sheet of polyolefin to a water-wettable and permeable membrane is attributed to this grafting.

[0105] Example B

[0106] Preparation of Filter Membrane (Laboratory Method)

[0107] An aqueous solution of 10% (w / v) triblock copolymer (PLURONIC TM P-123; lot #MKCC2305, Sigma-Aldrich) with a volume of 10 mL is mixed with an equal volume of deionized water. An amount of 0.2 g of the photoinitiator benzophenone (diphenylmethanone; Ph 2O) and 0 or 0.1 g of the crosslinking agent divinylbenzene (DVB) was dissolved in a separate volume of 10 mL of ethanol (methylated spirit), and then added to a diluted solution of the triblock copolymer with a volume of 10 mL. These working solutions - with or without the crosslinking agent DVB - were stored in the dark until use.

[0108] Samples (13.5 × 18.5 cm) were cut from sheets of microporous poly(ethylene) (TARGRAY TM Wet polyvinyl alcohol separator, part number SW320H (Targray, Kirkland QC, Canada), and each sample was coated with a certain volume of one of the working solutions. Then the coated samples were irradiated with ultraviolet (UV) light in the range of 250 to 360 nm for 2 minutes, then rinsed with water and air-dried in the open air.

[0109] Three replicate samples prepared using the working solution without DVB according to this method were named 110419Wi, 180419Wi, and 180419Wii. Three replicate samples prepared using the working solution containing DVB according to this method were named 230419Wi, 230419Wii, and 230419Wiii. Each sample was easily wettable with water, and each sample was observed to become uniformly translucent when in contact with this solvent.

[0110] The water flux of each sample was measured using deionized water as the feed stream (DI1). Then the samples were completely dried, and after that, the water flux was measured again using deionized water as the feed stream (DI2). Then each sample was subjected to an in-situ cleaning (CIP) protocol, and then the water flux was measured more than twice using deionized water as the feed stream (DI3 and DI4) and the samples were dried during this period. Each sample remained easily wettable with water. The results are summarized in Tables 5 and 6 and are compared in Figure 7 .

[0111]

[0112] Table 5. Average fluxes (LMH) measured at 0 and 5 bar with water as the feed stream at room temperature (22 to 24 °C) (*membrane failure).

[0113]

[0114] Table 6. Average fluxes (LMH) measured at 0 and 5 bar with water as the feed stream at room temperature (22 to 24 °C).

[0115] Example C

[0116] Preparation of filter membranes (prototype method)

[0117] A distilled aqueous solution of 10% (w / v) triblock copolymer (PLURONIC TM P-123; lot#MKCC2305, Sigma-Aldrich) with a volume of 300 mL was dispensed into a reservoir protected from light exposure. Then an additional 300 mL volume of distilled water was added to provide an initial solution of 5% (w / v) triblock copolymer (PLURONIC TM P-123; lot#MKCC2305, Sigma-Aldrich) in the reservoir. A 1.5% (w / v) solution of benzophenone in ethanol (methylated spirit) was prepared separately, and a certain volume of crosslinking agent divinylbenzene (DVB) was added to provide a final concentration of 0.75% (v / v) DVB. Then a 400 mL volume of this separately prepared solution was mixed with the triblock copolymer (PLURONIC TM P-123; lot#MKCC2305, Sigma-Aldrich) in the reservoir to provide a working solution.

[0118] Referring to the attached drawings Figure 7 , the working solution was pumped from the reservoirs (3, 4) to two semi-cylindrical troughs (5, 6) of the prototype production line using peristaltic pumps (1, 2). During the operation of the prototype production line, the reservoirs were replenished regularly with the working solution.

[0119] Microporous poly(ethylene) in the form of a continuous microporous sheet (7) with a width was fed from a raw material dispensing roller to a first impregnation station, which included an idler roller (8) coaxially mounted in the first of two semi-cylindrical troughs (5). The difference between the radii of the roller (8) and the trough (5) was sufficient to allow the sheet (7) to pass freely around the roller and through the trough, but not so large as to promote evaporation of the working solution in the trough. The surface of the roller (8) through which the sheet (7) passed could be helically engraved to facilitate the passage of the working solution along the length of the surface.

[0120] Then the sheet (7) leaving the first impregnation station was fed vertically to a first irradiation station, which included a slotted chamber (9) containing two opposing arrays of ultraviolet light sources (10, 11). The sheet (7) passed between the opposing arrays (10, 11) such that both sides were irradiated. The feed rate of the sheet (7) was adjusted to provide the required residence time within the slotted chamber (9).

[0121] Then the irradiated sheet (7) is passed through a second impregnation station (12) and a second irradiation station (13) having the same configuration as the first impregnation station and the first irradiation station. After these repeated steps, the irradiated sheet (7) is 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) is circulated by an external pump (18), and the depth of the water is controlled by a combination of a level transmitter and a solenoid valve (19). The combination of the plurality of idler rollers (14, 15, 16) and the water depth ensures sufficient residence time before the water-washed sheet (7) is fed into the drying station.

[0122] The drying station is a forced-air dryer including two air supply chambers (20, 21) having opposing perforated panels through which the base sheet passes. Hot air blowers (22, 23) mounted in the walls of each chamber force air through the perforated panels. Then the dried base sheet (7) is rewound onto a receiving roller (not shown).

[0123] Filter element

[0124] The membrane can be used to fabricate components of various configurations. In one embodiment, the membrane is used to fabricate a spiral-wound filter element. The fabrication of such filter elements is well known in the art.

[0125] Although the present invention has been described with reference to embodiments or examples, it should be understood that variations and modifications can be made to these embodiments or examples without departing from the scope of the present invention. In the presence of known equivalents of specific elements, features or wholes, such equivalents are incorporated as if specifically recited in this specification. Unless otherwise specified, variations and modifications of embodiments or examples including elements, features or wholes disclosed in the cited publications and selected from the cited publications fall within the scope of the present invention. The advantages provided by the present invention and discussed in the specification can be provided in alternative ways or in combination in these different embodiments of the present invention.

[0126] Industrial applicability

[0127] A method for preparing a filter membrane and its use in recovering or removing water from a feed stream are provided. The filter membrane is advantageously used to recover or remove water from a feed stream where in-situ cleaning of the membrane is required to improve the efficiency of plant operation.

[0128] Cross-reference

[0129] In the event that all or part of the claims, specification, or drawings of this specification are missing, pursuant to Articles 4.18, 20.5, and 20.6 of the PCT Rules (effective as of July 1, 2015 or as subsequently amended), the corresponding portions of the specification attached to the most recently filed application claiming priority are incorporated by reference to complete this specification.

[0130] In accordance with 37 C.F.R. 1.57 of the United States Federal Regulations, the disclosures of the following publications (more specifically identified in the "References" section below) are incorporated by reference herein: Jones et al. (2008) and Schmolka (1973).

[0131] References

[0132] Anon (2014) DOW FILMTEC TM Membranes–Cleaning procedures for DOW FILMTEC FT30 elements Tech Fact (Form No. 609-23010-0211).

[0133] Carter et al. (2018) Controlling external versus internal pore modification of ultrafiltration membranes using surface-initiated AGET-ATRP Journal of Membrane Science, 554, 109-116.

[0134] Cheng et al. (2017) Method for preparing mesoporous composite film Chinese Patent Application No. 201611226194 [Publication No. CN 106731886 A].

[0135] Guo et al. (2015) Coated microporous materials having filtration and adsorption properties and their use in fluid purification processes International Application No. PCT / US2014 / 061326 [Publication No. WO 2015 / 073161 A1].

[0136] Jones et al. (2008) Compendium of polymer terminology and nomenclature IUPAC Recommendations, RSC Publishing.

[0137] Liu et al. (2014) With multi-scale gradient microstructure surface preparation method of a microporous membrane Chinese Patent Application No. 201310479920 [Publication No. CN 103611437 A].

[0138] Schmolka (1973) Polyoxyethylene-polyoxypropylene aqueous gels US Patent No. 3,740,421.

[0139] Wang et al. (2006) Pluronic polymers and polyethersulfone blend membranes with improved fouling-resistant ability and ultrafiltration performance Journal of Membrane Science, 283, 440 - 447.

[0140] Yang et al. (2014) Preparation and application of PVDF-HFP composite polymer electrolytes in LiNi 0.5 Co 0.2 Mn 0.3 O 2 lithium-polymer batteries Electrochimica Acta 134, 258 - 265.

Claims

1. A water-wettable filter membrane composed of a microporous sheet of grafted polyolefin, wherein the graft contains a poloxamer having the following structure: HO (ethylene oxide) m -(propylene oxide) n -(ethylene oxide) m H where m is in the range of 15 to 25 and n is in the range of 50 to 90.

2. The membrane according to claim 1, wherein the polyolefin is poly(ethylene).

3. The membrane according to claim 1 or 2, wherein m is 20 and n is 70.

4. The membrane according to any one of claims 1 to 3, wherein the graft contains a crosslinking agent.

5. The membrane according to claim 4, wherein the crosslinking agent has a molecular weight of less than 150 g / mol -1 .

6. The membrane according to claim 5, wherein the crosslinking agent is divinylbenzene.

7. A filter assembly comprising the membrane according to any one of claims 1 to 7.

8. The filter element according to claim 7, wherein the membrane is helically wound.

9. A method for preparing a water-wettable filter membrane, which comprises: (a) contacting a microporous sheet of polyolefin with a solution of poloxamer in a solvent to provide a contacted sheet; (b) irradiating the contacted sheet with ultraviolet light in the presence of a photoinitiator to provide an irradiated sheet; and (c) drying and washing the irradiated sheet to provide the membrane, wherein the poloxamer is a polymer having the following structure HO (ethylene oxide) m -(propylene oxide) n -(ethylene oxide) m H where m is in the range of 15 to 25 and n is in the range of 50 to 90.

10. The method according to claim 9, wherein the polyolefin is poly(ethylene).

11. The method according to claim 9 or 10, wherein m is 20 and n is 70.

12. The method according to any one of claims 9 to 11, wherein the solution contains the photoinitiator.

13. The method according to any one of claims 9 to 12, wherein the photoinitiator is a type II photoinitiator.

14. The method according to any one of claims 9 to 13, wherein the photoinitiator is benzophenone.

15. The method according to any one of claims 9 to 14, wherein the solution contains a low molecular weight crosslinking agent.

16. The method according to claim 15, wherein the crosslinking agent is divinylbenzene.

17. The method according to any one of claims 9 to 16, wherein the solvent is a 30 to 50% (v / v) aqueous solution of alcohol or acetone.

18. The method according to any one of claims 7 to 14, wherein the solvent is a 30 to 50% (v / v) aqueous solution of ethanol.

19. A method for recovering or removing water from a feed stream, which comprises the step of contacting the first side of the membrane according to any one of claims 1 or 8 with the feed stream at a pressure sufficient to provide permeation.

20. The method according to claim 19, wherein the pressure is less than 10 bar and the flux is greater than 500 LMH.

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