WO2024003352A1 - Use of polymer additive comprising zwitterionic moieties in pvdf membranes for decreasing the transmembrane pressure at constant flux of said membranes - Google Patents

Use of polymer additive comprising zwitterionic moieties in pvdf membranes for decreasing the transmembrane pressure at constant flux of said membranes Download PDF

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Publication number
WO2024003352A1
WO2024003352A1 PCT/EP2023/068003 EP2023068003W WO2024003352A1 WO 2024003352 A1 WO2024003352 A1 WO 2024003352A1 EP 2023068003 W EP2023068003 W EP 2023068003W WO 2024003352 A1 WO2024003352 A1 WO 2024003352A1
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polymer
units
vdf
monomer
acrylate
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PCT/EP2023/068003
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French (fr)
Inventor
Emanuele DI NICOLO'
Charles LOUSSERT
Alice BODIN
Xavier REVEST
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Solvay Sa
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0002—Organic membrane manufacture
    • B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/30—Polyalkenyl halides
    • B01D71/32—Polyalkenyl halides containing fluorine atoms
    • B01D71/34—Polyvinylidene fluoride
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/76—Macromolecular material not specifically provided for in a single one of groups B01D71/08 - B01D71/74
    • B01D71/82—Macromolecular material not specifically provided for in a single one of groups B01D71/08 - B01D71/74 characterised by the presence of specified groups, e.g. introduced by chemical after-treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2323/00—Details relating to membrane preparation
    • B01D2323/02—Hydrophilization
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2323/00—Details relating to membrane preparation
    • B01D2323/12—Specific ratios of components used
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2323/00—Details relating to membrane preparation
    • B01D2323/15—Use of additives
    • B01D2323/18—Pore-control agents or pore formers

Definitions

  • the present invention relates to the use of a composition comprising zwitterionic moieties in membranes based on vinylidene fluoride (VDF) polymers for decreasing the transmembrane pressure at constant flux.
  • VDF vinylidene fluoride
  • Porous membrane is a thin object whose key property is its ability to control the permeation rate of chemical species through itself. This feature is exploited in applications like separation applications (for example liquid, like water, and gas).
  • Fluorinated polymers are widely used in the preparation of microfiltration and ultrafiltration membranes due to their good mechanical strength, high chemical resistance and thermal stability.
  • partially fluorinated polymers based on vinylidene fluoride (VDF) are particularly convenient for controlling porosity and morphology of said membranes.
  • Membranes made from vinylidene fluorine polymers [polymer (VDF)] are hydrophobic in nature and therefore endowed with water repellency, low water permeability and subject to fouling of particles, proteins at their surface. Hydrophobicity impedes water to penetrate into the fluoropolymer membrane and therefore water permeability requires higher pressure and consumes more energy. Fouling reduces temporarily or permanently the flux of permeation of water through the membrane e.g. in ultrafiltration or microfiltration processes.
  • VDF vinylidene fluorine polymers
  • WO 2015/070004 discloses zwitterionic containing membranes wherein a selective layer formed of a statistical copolymer comprising zwitterionic repeat units and hydrophobic repeat units such as p(MMA-s-SBMA) is disposed on a support layer formed of porous PVDF membrane.
  • a selective layer formed of a statistical copolymer comprising zwitterionic repeat units and hydrophobic repeat units such as p(MMA-s-SBMA) is disposed on a support layer formed of porous PVDF membrane.
  • p(MMA-s-SBMA) hydrophobic repeat units
  • Hydrophilization additives for PVDF based membranes is proposed in US 2018/0001278 which discloses comb-shaped and random zwitterionic copolymers (e.g. p(MMA-r-SBMA)) useful to enhance hydrophilicity of PVDF membranes.
  • Resulting additivated PVDF membranes show good resistance against fouling and improved permeability when compared to PVDF membranes.
  • a relatively high amount of additive that can impair mechanical, chemical resistance of the PVDF membrane as well as its economical attractiveness, is required.
  • SUBSTITUTE SHEET (RULE 26) to be very efficient hydrophilization agents in order to be used sparingly, thus avoiding any detrimental effect due to their presence in too large amount on the mechanical, thermal and chemical resistance of the porous PVDF membrane.
  • TMP transmembrane pressure
  • bar or in Pascal, Pa
  • composition (C) in a membrane makes it possible to reduce the transmembrane pressure at constant flux during the filtration process instead of traditional PVDF membranes, thus making it possible to reduce the number of washing cycles. Furthermore, it appears surprisingly that the use of the composition (C) according to the invention leads to better recovery of the membrane, i.e. once the membrane has undergone several repeated complete washing cycles during the filtration process, the transmembrane pressure falls back to values close to the starting transmembrane pressure and therefore that leads to lower cleaning frequency and thus lower energy and chemical consumptions. Finally, the use of the composition (C) according to the invention allows better resistance of this membrane to chemical washing, the latter degrading less than the membranes of the prior art.
  • the present invention leads to a more sustainable solution for filtration processes.
  • the present invention makes it possible to decrease the transmembrane pressure at constant flux over time during the filtration process of the porous membrane, while maintaining high filtration properties and performances, and reducing energy consumption and cleaning maintenance cycles and thus chemicals consumption for cleaning.
  • Figure l is a simplified scheme of the hollow fiber spinning machine used for manufacturing hollow fiber membranes.
  • Figure 2 is a schematic cut of the spinneret (annular die), through a plane parallel to the fiber extrusion flow.
  • Figure 3 is a schematic cut of the spinneret (annular die), through a plane perpendicular to the fiber extrusion flow.
  • Figure 4 and 5 are graphs representing the TMP evolution versus time.
  • Figure 6 is a graph representing the need for backwashes in the filtration of diluted sewage water.
  • Figure 7 is a graph that represents the transmembrane pressure after chemical cleaning as a function of time.
  • composition (C) in a porous membrane for decreasing the transmembrane pressure (TMP) at constant flux of said membrane wherein the porous membrane comprises the composition (C) comprising:
  • VDF vinylidene fluoride
  • the invention also refers to a method for decreasing the transmembrane pressure (TMP) at constant flux of a porous membrane comprising at least one vinylidene fluoride (VDF) polymer [polymer (VDF)], in which said porous membrane further comprises at least one copolymer [copolymer (N-ZW)] comprising:
  • SUBSTITUTE SHEET (RULE 26) wherein units (Rzw) represent 0.1 to 7 mol %, preferably 0.1 to 5 mol % based on the molar composition of the copolymer (N-ZW), and wherein the molecular weight of the copolymer (N-ZW) measured by gel permeation chromatography ranges from 25000 g/mol to 350000 g/mol, and wherein the weight ratio copolymer (N-ZW) /polymer (VDF) is at least 0.1/99.9 and/or is less than 25/75.
  • composition (C) is particularly effective for decreasing the transmembrane pressure at constant flux over time during filtration operation while delivering outstanding permeability performances in aqueous media filtration and separation processes.
  • VDF vinylidene fluoride polymer
  • VDF polymer
  • VDF Polymer
  • Polymer (VDF) may further comprise recurring units derived from at least one fluorinated monomer different from VDF and/or may further comprise recurring units derived from a fluorine-free monomer (also referred to as “hydrogenated monomer”).
  • fluorinated monomer is hereby intended to denote an ethylenically unsaturated monomer comprising at least one fluorine atom.
  • the fluorinated monomer may further comprise one or more other halogen atoms (Cl, Br, I).
  • polymer (VDF) is generally selected among polyaddition polymers comprising recurring units derived from VDF and, optionally, recurring units derived from at least one ethylenically unsaturated monomer comprising fluorine atom(s) different from VDF, which is generally selected from the group consisting of:
  • C2-C8 perfluoroolefins such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoroisobutylene;
  • VDF vinyl fluoride
  • TrFE trifluoroethylene
  • HFIB hexafluoroisobutylene
  • CEb CE[-Rn, wherein Rn is a Ci-Ce perfluoroalkyl group;
  • C2-C8 chloro- and/or bromo-containing fluoroolefms such as chlorotrifluoroethylene (CTFE);
  • each of Rr,. Rf4, Rfs and Rf6, equal to or different from each other, is independently a fluorine atom, a Ci-Ce perfluoro(oxy)alkyl group, optionally comprising one or more oxygen atoms, such as -CF3, -C2F5, -C3F7, -OCF3 or - OCF2CF2OCF3
  • the vinylidene fluoride polymer is preferably a polymer comprising:
  • (a’) at least 60 % by moles, preferably at least 75 % by moles, more preferably 85 % by moles of recurring units derived from vinylidene fluoride (VDF);
  • (b’) optionally from 0.1 to 30%, preferably from 0.1 to 20%, more preferably from 0.1 to 15%, by moles of recurring units derived from a fluorinated monomer different from VDF;
  • (c’) optionally from 0.1 to 10 %, by moles, preferably 0.1 to 5 % by moles, more preferably 0.1 to 1% by moles of recurring units derived from one or more hydrogenated monomer(s),
  • the said fluorinated monomer is advantageously selected in the group consisting of vinyl fluoride (VFi); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl)vinyl ethers, such as perfluoro(methyl)vinyl ether (PMVE), perfluoro(ethyl) vinyl ether (PEVE) and perfluoro(propyl)vinyl ether (PPVE); perfluoro(l,3-dioxole); perfluoro(2,2- dimethyl-l,3-dioxole) (PDD).
  • the possible additional fluorinated monomer is chosen from chlorotrifluoroethylene (CTFE), hexafluoroproylene (HFP), trifluoroethylene (VF3) and tetrafluoroethylene (TFE).
  • the choice of the said hydrogenated monomer(s) is not particularly limited; alpha-olefins, (meth)acrylic monomers, vinyl ether monomers, styrenic mononomers may be used; nevertheless, to the sake of optimizing chemical resistance, embodiments wherein the polymer (F) is essentially free from recurring units derived from said hydrogenated comonomer(s) are preferred.
  • the vinylidene fluoride polymer [polymer (VDF)] is more preferably a polymer consisting essentially of:
  • (a’) at least 60 % by moles, preferably at least 75 % by moles, more preferably 85 % by moles of recurring units derived from vinylidene fluoride (VDF);
  • (b’) optionally from 0.1 to 30%, preferably from 0.1 to 20%, more preferably from 0.1 to 15% by moles of a fluorinated monomer different from VDF; said fluorinated monomer being preferably selected in the group consisting of vinylfluoride (VFi), chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), tetrafluoroethylene (TFE), perfluoromethylvinylether (MVE), trifluoroethylene (TrFE) and mixtures therefrom, all the aforementioned % by moles being referred to the total moles of recurring units of the polymer (VDF).
  • VFi vinylfluoride
  • CTFE chlorotrifluoroethylene
  • HFP hexafluoropropene
  • TFE tetrafluoroethylene
  • MVE perfluoromethylvinylether
  • TrFE trifluoroethylene
  • VDF polymer
  • VDF polymers useful in the present invention
  • VDF homopolymers are particularly advantageous for being used as polymer (VDF) in the composition (C).
  • the melt index of the polymer (VDF) is advantageously at least 0.01, preferably at least 0.05, more preferably at least 0.1 g/10 min and advantageously less than 50, preferably less than 30, more preferably less than 20 g/10 min, when measured in accordance with ASTM test No. 1238, run at 230°C, under a piston load of 2.16 kg.
  • the melt index of the polymer (VDF) is advantageously at least 0.1, preferably at least 1, more preferably at least 5 g/10 min and advantageously less than 70, preferably less than 50, more preferably less than 40 g/10 min, when measured in accordance with ASTM test No. 1238, run at 230°C, under a piston load of 5 kg.
  • the melt index of the polymer (VDF) is advantageously at least 0.1, preferably at least 0.5, more preferably at least 1 g/10 min and advantageously less than 30, preferably less than 20, more preferably less than 10 g/10 min, when measured in accordance with ASTM test No. 1238, run at 230°C, under a piston load of 21.6 kg.
  • the polymer (VDF) has advantageously a melting point (T m ) advantageously of at least 120°C, preferably at least 125°C, more preferably at least 130°C and of at most 190°C, preferably at most 185°C, more preferably at most 180°C, when determined by DSC, at a heating rate of 10°C/min, according to ASTM D 3418.
  • T m melting point
  • Composition (C) used in the present invention for decreasing the transmembrane pressure (TMP) at constant flux of a porous membrane comprises at least one copolymer [copolymer (N-ZW)] comprising:
  • zwitterionic recurring units are derived from at least one zwitterionic monomer (A) that is neutral in overall charge but contains a number of group (C+) equal to the number of group (A-).
  • the cationic charge(s) may be contributed by at least one onium or inium cation of nitrogen, such as ammonium, pyridinium and imidazolinium cation; phosphorus, such as phosphonium; and/or sulfur, such as sulfonium.
  • the anionic charge(s) may be contributed by at least one carbonate, sulfonate, phosphate, phosphonate, phosphinate or ethenolate anion, and the like.
  • Suitable zwitterionic monomers include, but are not limited to, betaine monomers, which are zwitterionic and comprise an onium atom that bears no hydrogen atoms and that is not adjacent to the anionic atom.
  • units (Rzw) are derived from at least one monomer (A) selected from the list consisting of a) alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl acrylates or methacrylates, acrylamido or methacrylamido, typically
  • heterocyclic betaine monomers typically
  • - sulfobetaines derived from 2-vinylpyridine and 4-vinylpyridine, more typically 2- vinyl- 1 -(3 -sulfopropyl )pyridinium betaine or 4-vinyl-l-(3- sulfopropyl)pyridinium betaine,
  • SUBSTITUTE SHEET (RULE 26) and g) betaines resulting from cyclic acetals, typically ((dicyanoethanolate)ethoxy)dimethylammoniopropylmethacrylamide.
  • units (Rzw) are derived from at least one monomer (A) selected from the list consisting of
  • units (Rzw) are derived from at least one monomer (A) selected from the list consisting of
  • units (Rzw) are derived from
  • Copolymer (N-ZW) according to the invention, besides comprising recurring units (Rzw) derived from at least one zwitterionic monomer (A), also comprises recurring units (RN) derived from at least one at least one additional monomer (B) different from monomer (A).
  • units are derived from at least one monomer deprived of ionisable groups.
  • units (RN) are derived from at least one monomer selected from the list consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, vinyl acetate and N,N-dimethylacrylamide [units (RN-I)].
  • units (RN-I) are derived from methyl methacrylate, ethyl methacrylate or mixture thereof. More preferably, units (RN-I) are derived from methyl methacrylate.
  • units (RN) are derived from at least one monomer selected from the list consisting of 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2-hydroxyethyl acrylate (ELEA), hydroxypropyl acrylate, 4-hydroxybutyl acrylate, polyethylene glycol) methacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (mPEGMA), poly(ethylene glycol) ethyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate and poly(ethylene glycol) ethyl ether acrylate [units (RN-2)].
  • HEMA 2-hydroxyethyl methacrylate
  • EUA 2-hydroxyethyl acrylate
  • mPEGMA poly(ethylene glycol) methyl ether methacrylate
  • mPEGMA poly(ethylene glycol) ethyl ether methacrylate
  • units (RN-2) are derived from 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate or mixture thereof. More preferably, units (RN-2) are derived from 2-hydroxyethyl methacrylate (HEMA).
  • HEMA 2-hydroxyethyl methacrylate
  • units (RN) are derived from at least one monomer selected from at least one monomer selected from the list consisting of methyl methacrylate, ethyl methacrylate, butyl acrylate, methyl acrylate, ethyl acrylate, butyl acrylate, vinyl acetate and N,N-dimethylacrylamide [units (RN-I)] and from at least one monomer selected from the list consisting of 2-
  • HEMA hydroxyethyl methacrylate
  • HEMA hydroxypropyl methacrylate
  • 2- hydroxyethyl acrylate HSA
  • HEMA hydroxypropyl acrylate
  • 4-hydroxybutyl acrylate polyethylene glycol) methacrylate
  • PEGMA poly(ethylene glycol) methyl ether methacrylate
  • mPEGMA poly(ethylene glycol) ethyl ether methacrylate
  • R-2 poly(ethylene glycol) ethyl ether acrylate [units (RN-2)].
  • units (RN-I) are derived from methyl methacrylate, ethyl methacrylate or mixture thereof and units (RN-2) are derived from 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate or mixture thereof. More preferably, units (RN-I) are derived from methyl methacrylate and units (RN-2) are derived from 2-hydroxyethyl methacrylate (HEMA).
  • the copolymer (N-ZW) of the composition (C) used in the present invention comprises recurring units (Rzw) derived from sulfopropyl dimethylammonioethyl methacrylate (SPE), l-(3- Sulphonatopropyl)-2-vinylpyridinium (2SPV) or mixtures thereof and recurring units (RN-I) derived from methyl methacrylate.
  • Rzw sulfopropyl dimethylammonioethyl methacrylate
  • 2SPV l-(3- Sulphonatopropyl)-2-vinylpyridinium
  • the copolymer (N-ZW) of the present disclosure comprises recurring units (Rzw) derived from sulfopropyldimethylammonioethyl methacrylate (SPE) and recurring units (RN-I) derived from methyl methacrylate.
  • the copolymer (N-ZW) of the composition (C) used in the present invention comprises recurring units (Rzw) derived from (SPE) or (2SPV), recurring units (RN-I) derived from methyl methacrylate and recurring units (RN-2) derived from 2-hydroxyethyl methacrylate (HEMA).
  • the copolymer (N-ZW) of the composition (C) according to the present disclosure generally comprises 80 % or more by moles, preferably 90% or more by moles, more preferably 93% or more by moles and even more preferably 95% or more by moles of units (RN), with respect to the total moles of recurring units of copolymer (N-ZW).
  • copolymer (N-ZW) When recurring units (RN-I) and recurring units (RN-2) are present, copolymer (N-ZW) generally comprises from 0.1 to 50 % by moles, preferably from 0.1 to 40 % by moles, more preferably from 0.1 to 30% by moles and even more preferably from 0.1 to 20 % by moles of recurring units (Rzw) and (RN-2), with respect to the total moles of recurring units of copolymer (N-ZW).
  • SUBSTITUTE SHEET (RULE 26) Copolymer (N-ZW) of the composition (C) used in the present invention for decreasing the transmembrane pressure (TMP) at constant flux is a block copolymer, a branched copolymer or a statistical copolymer. Good results were obtained with copolymer (N-ZW) being a statistical copolymer.
  • molar mass when molar mass is referred to, the reference will be to the weight-average molar mass, expressed in g/mol.
  • the latter can be determined by gel permeation chromatography (GPC) with light scattering detection (DLS or alternatively MALLS) or refractive index detection, with an aqueous eluent or an organic eluent (for example dimethylacetamide, dimethylformamide, and the like), depending on the copolymer (N-ZW).
  • the weight-average molar mass (Mw) of the copolymer (N-ZW) is in the range of from 25,000 to 350,000 g/mol, typically from about 35,000 to about 300,000, g/mol, more typically from about 70,000 to 250,000 g/mol, even more typically 80,000 to 200,000 g/mol.
  • the copolymer (N-ZW) of the composition (C) used in the present invention for decreasing the transmembrane pressure (TMP) at constant flux of the membrane may be obtained by any polymerization process known to those of ordinary skill.
  • the copolymer (N-ZW) may be obtained by radical polymerization or controlled radical polymerization in aqueous solution, in dispersed media, in organic solution or in organic/water solution (miscible phase).
  • the monomer deprived of ionisable groups from which can be derived units (RN) may be obtained from commercial sources.
  • the zwitterionic monomer from which are derived units may be obtained from commercial sources or synthesized according to methods known to those of ordinary skill in the art.
  • Suitable zwitterionic monomers from which can be derived units include, but are not limited to monomers selected from the list consisting of: a) alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl acrylates or methacrylates, acrylamido or methacrylamido, typically:
  • SPV 2-vinyl-l-(3-sulfopropyl)pyridinium betaine
  • SUBSTITUTE SHEET (RULE 26) and 4-vinyl-l -(3 -sulfopropyl )pyridinium betaine (4SPV), the synthesis of which is disclosed in the paper “Evidence of ionic aggregates in some ampholytic polymers by transmission electron microscopy”, V. M. Castano and A. E. Gonzalez, J. Cardoso, O. Manero and V. M. Monroy, J. Mater. Res., 5 (3), 654-657 (1990), and other hydroxyalkyl sulfonates derived from 2-vinylpyridine and 4vinylpyridine of formulae below
  • SUBSTITUTE SHEET (RULE 26) the synthesis of which are disclosed in EP 810 239 Bl (Biocompatibles, Alister et al.); g) betaines resulting from cyclic acetals, typically ((dicyanoethanolate)ethoxy)dimethylammoniumpropylmethacrylamide: the synthesis of which is described by M-L.
  • Suitable monomers comprising hydroxyalkyl sulfonate moi eties from which can be derived units (Rzw) can be obtained by reaction of sodium 3- chloro-2-hydroxypropane-l -sulfonate (CHPSNa) with monomer bearing tertiary amino group, as described in US20080045420 for the synthesis of SHPP, starting from dimethylaminopropylmethacrylamide according to the reaction scheme:
  • SUBSTITUTE SHEET (RULE 26) directly obtained from polymerizing the said monomer, and the same recurring units (Rzw) obtained by modification of an existing polymer.
  • recurring units may be obtained by modification of a polymer referred to as a precursor polymer comprising recurring units bearing tertiary amino groups through the reaction with sodium 3-chloro-2- hydroxypropane-1 -sulfonate (CHPSNa). Similar modification was described in sodium 3 -chloropropane- 1 -sulfonate in place of CHPSNa:
  • recurring units (Rzw) may be obtained by chemical modification of a polymer referred to as a precursor polymer with a sultone, such as propane sultone or butane sultone, a haloalkylsulfonate or any other sulfonated electrophilic compound known to those of ordinary skill in the art.
  • a sultone such as propane sultone or butane sultone
  • a haloalkylsulfonate such as any other sulfonated electrophilic compound known to those of ordinary skill in the art.
  • Exemplary synthetic steps are shown below:
  • recurring units (Rzw) may be obtained by modification of a polymer referred to as a precursor polymer comprising recurring units bearing tertiary amino groups, pyridine groups, imidazole group or mixtures thereof through the reaction with sodium 3 -chloro-2-hydroxypropane-l -sulfonate (CHPSNa), a sultone, such as propane sultone or butane sultone, or a haloalkylsulfonate.
  • CHPSNa sodium 3 -chloro-2-hydroxypropane-l -sulfonate
  • a sultone such as propane sultone or butane sultone
  • haloalkylsulfonate a sultone
  • copolymer (N-ZW) is used as an additive for polymer (VDF)
  • the polymer (VDF) is generally present in predominant amount over copolymer (N- ZW) in composition (C).
  • the weight ratio copolymer (N-ZW)/polymer (VDF) is of at least 0.1/99.9 wt/wt, preferably at least 1/99 wt/wt, more preferably at least 3/97 wt/wt and/or it is less than 25/75 wt/wt, preferably less than 20/80 wt/wt, more preferably less than 15/85 wt/wt and even more preferably less than 10/90 wt/wt.
  • Composition (C) may optionally comprise at least one further ingredient.
  • Said further ingredient can preferably be selected in the group consisting of nonsolvents (water, alcohols...), co-solvents (e.g. ketones), pore forming agents, nucleating agents, fillers, nanoparticles, salts, surfactants.
  • pore forming agents are typically added to the composition (C) in amounts usually ranging from 1% to 30% by weight, preferably from 2% to 20% by weight, based on the total weight of the composition (C).
  • Suitable pore forming agents are for instance polyvinyl alcohol (PVA), polyvinyl-pyrrolidone (PVP) and polyethylene glycol (PEG).
  • composition (C) further comprises at least one liquid medium [medium (L)] comprising at least one organic solvent [composition (C L )].
  • solvent is used herein in its usual meaning, that is, it indicates a substance capable of dissolving another substance (solute) to form a uniformly dispersed mixture at the molecular level.
  • solvent indicates a substance capable of dissolving another substance (solute) to form a uniformly dispersed mixture at the molecular level.
  • a polymeric solute it is common practice to refer to a solution of the polymer in a solvent when the resulting mixture is transparent and no phase separation is visible in the system. Phase separation is taken to be the point, often referred to as “cloud point”, at which the solution becomes turbid or cloudy due to the formation of polymer aggregates.
  • medium (L) comprises at least one solvent (S) for polymer (VDF).
  • the medium (L) typically comprises at least one organic solvent selected from the group comprising:
  • aliphatic hydrocarbons including, more particularly, the paraffins such as, in particular, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane or cyclohexane, and naphthalene and aromatic hydrocarbons and more particularly aromatic hydrocarbons such as, in particular, benzene, toluene, xylenes, cumene, petroleum fractions composed of a mixture of alkylbenzenes;
  • - aliphatic or aromatic halogenated hydrocarbons including more particularly, perchlorinated hydrocarbons such as, in particular, tetrachloroethylene, hexachloroethane;
  • - partially chlorinated hydrocarbons such as di chloromethane, chloroform, 1,2- di chloroethane, 1,1,1 -tri chloroethane, 1 , 1 ,2,2-tetrachloroethane, pentachloroethane, trichloroethylene, 1 -chlorobutane, 1,2-di chlorobutane, monochlorobenzene, 1,2-di chlorobenzene, 1,3-dichlorobenzene, 1,4- di chlorobenzene, 1, 2, 4-tri chlorobenzene or mixture of different chlorobenzenes;
  • ether oxides more particularly, diethyl oxide, dipropyl oxide, diisopropyl oxide, dibutyl oxide, methyltertiobutyl ether, dipentyl oxide, diisopentyl oxide, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether benzyl oxide; dioxane, tetrahydrofuran (THF);
  • glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n- butyl ether;
  • glycol ether esters such as ethylene glycol methyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate;
  • - alcohols including polyhydric alcohols, such as methyl alcohol, ethyl alcohol, diacetone alcohol, ethylene glycol;
  • ketones such as acetone, methylethylketone, methylisobutyl ketone, diisobutylketone, cyclohexanone, isophorone;
  • SUBSTITUTE SHEET (RULE 26) di ethyl acetamide, dimethylformamide (DMF), diethylformamide or N-methyl-2- pyrrolidone (NMP);
  • organic carbonates for example dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, ethylmethyl carbonate, ethylene carbonate, vinylene carbonate;
  • - phosphoric esters such as trimethyl phosphate, triethyl phosphate (TEP);
  • ureas such as tetramethylurea, tetraethylurea
  • linear or cyclic carboxamides such as N,N- dimethylacetamide (DMAc), N,N-di ethyl acetamide, dimethylformamide (DMF), diethylformamide or N-methyl-2-pyrrolidone (NMP), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), methyl-5-dimethylamino-2-methyl-5- oxopentanoate (commercially available under the trademark Rhodialsov Polarclean®) and triethylphosphate (TEP).
  • DMAc N,N- dimethylacetamide
  • DMF dimethylformamide
  • NMP N-methyl-2-pyrrolidone
  • DMSO dimethylsulfoxide
  • THF tetrahydrofuran
  • TEP triethylphosphate
  • Linear or cyclic carboxamides such as N,N-dimethylacetamide (DMAc),
  • N,N-di ethyl acetamide, dimethylformamide (DMF), diethylformamide or N- methyl-2-pyrrolidone (NMP) are particularly preferred.
  • NMP N-methyl-pyrrolidone
  • DMAc dimethyl acetamide
  • the medium (L) may further comprise at least one additional liquid component different from solvent (S) (or in other terms, a non-solvent).
  • Said additional liquid component which does not have ability to dissolve polymer (VDF) may be added to composition (C L ), in an amount generally below the level required to reach the cloud point, typically in amount of from
  • composition (C L ) O.1% to 40% by weight, preferably in an amount of from 0.1% to 20% by weight, based on the total weight of medium (L) of the composition (C L ).
  • L medium
  • C L solvent
  • the composition (C L ) comprises an overall amount of copolymer (N-ZW) and polymer (VDF) of at least 1 wt.%, more preferably of at least 3 wt.%, even more preferably of at least 5 wt.%, based on the total weight of medium (L), copolymer (N-ZW) and polymer (VDF), and/or composition (C L )
  • SUBSTITUTE SHEET preferably comprises an overall amount of copolymer (N-ZW) and polymer (VDF) of at most 60 wt.%, more preferably of at most 50 wt.%, even more preferably at most 30 wt.%, based on the total weight of medium (L), copolymer (N-ZW) and polymer (VDF) and/or composition (C L ).
  • the amount of medium (L) in composition (C L ) is of at least 40 wt.%, preferably at least 50 wt.%, even more preferably at least 70 wt.%, based on the total weight of medium (L), copolymer (N-ZW) and polymer (VDF), and/or the amount of medium (L) in composition (C L ) is of at most 99 wt.%, preferably at most 97 wt.%, even more preferably at most 95 wt.%, based on the total weight of medium (L), copolymer (N-ZW) and polymer (VDF).
  • Composition (C L ) may optionally comprise at least one further ingredient.
  • Said further ingredient is preferably selected in the group consisting of pore forming agents, nucleating agents, fillers, salts, surfactants.
  • pore forming agents are typically added to the composition (C L ) in amounts usually ranging from 0.1% to 30% by weight, preferably from 0.5% to 20% by weight, based on the total weight of the composition (C L ).
  • Suitable pore forming agents are for instance polyvinyl alcohol (PVA), cellulose acetate, polyvinyl-pyrrolidone (PVP) and polyethyleneglycol (PEG).
  • the composition (C) is used in a porous membrane for decreasing the transmembrane pressure (TMP) at constant flux, said porous membrane comprising:
  • VDF vinylidene fluoride polymer
  • porous membrane is used according to its usual meaning in this technical field, i.e. to denote membrane including pores, i.e. voids or cavities of any shape and size.
  • the porous membrane used in the present invention is obtainable from the composition (C L ) as detailed above and/or can be manufactured using the method as below detailed.
  • the porous membrane of the invention may be in the form of flat membranes or in the form of tubular membranes.
  • Flat membranes preferably have a thickness comprised between 10 pm and 200 pm, more preferably between 15 pm and 150 pm.
  • Tubular membranes typically have an outer diameter greater than 3 mm.
  • Tubular membranes having an outer diameter comprised between 0.5 mm and 3 mm are typically referred to as hollow fibers membranes.
  • Tubular membranes having a diameter of less than 0.5 mm are typically referred to as capillary membranes.
  • Membranes containing pores homogeneously distributed throughout their thickness are generally known as symmetric (or isotropic) membranes; membranes containing pores which are heterogeneously distributed throughout their thickness are generally known as asymmetric (or anisotropic) membranes.
  • the porous membrane according to the present invention may be either a symmetric membrane or an asymmetric membrane.
  • the asymmetric porous membrane typically consists of one or more layers containing pores which are heterogeneously distributed throughout their thickness.
  • the asymmetric porous membrane typically comprises an outer layer containing pores having an average pore diameter smaller than the average pore diameter of the pores in one or more inner layers.
  • the porous membrane of the invention preferably has an average pore diameter of at least 0.001 pm, more preferably of at least 0.005 pm, and even more preferably of at least 0.01 pm.
  • the porous membrane of the invention preferably has an average pore diameter of at most 50 pm, more preferably of at most 20 pm and even more preferably of at most 15 pm.
  • the porous membrane typically has a gravimetric porosity comprised between 5% and 90%, preferably between 10% and 85% by volume, more preferably between 30% and 90%, based on the total volume of the membrane.
  • the term “gravimetric porosity” is intended to denote the fraction of voids over the total volume of the porous membrane.
  • the porous membrane of the invention may be either a self-standing porous membrane or a porous membrane supported onto a substrate and/or comprising a backing layer.
  • the porous membrane comprises at least one layer comprising at least one polymer (VDF) and at least one copolymer (N-ZW).
  • a porous membrane supported onto a substrate is typically obtainable by laminating said substrate and/or backing with a pre-formed porous membrane or by manufacturing the porous membrane directly onto said substrate and/or said backing.
  • porous membrane may be composed of one sole layer comprising polymer (VDF) and copolymer (N-ZW) or may comprise additional layers.
  • the porous membrane of the invention may further comprise at least one substrate.
  • the substrate may be partially or fully interpenetrated by the porous membrane of the invention.
  • the nature of the substrate/backing is not particularly limited.
  • the substrate generally consists of materials having a minimal influence on the selectivity of the porous membrane.
  • the substrate layer preferably consists of non-woven materials, polymeric materials such as, for example, polypropylene, glass, glass fibers.
  • tubular braid or threads/fabric reinforcing the substrate layer such as polyethylene terephthalate (PET) braid
  • SUBSTITUTE SHEET (RULE 26) particularly for improving the mechanical properties of polymer (VDF) porous membranes.
  • the porous membrane of the invention is a porous composite membrane assembly comprising:
  • At least one substrate layer preferably a non-woven substrate
  • At least one layer comprising at least one polymer (VDF) and at least one copolymer (N-ZW).
  • Typical examples of such porous composite membrane assembly are the so-called Thin Film Composite (TFC) structures which are typically used in reverse osmosis or nanofiltration applications.
  • TFC Thin Film Composite
  • top layers suitable for use in the porous composite membrane assemblies of the invention include those made of polymers selected from the group consisting of polyamides, polyimides, polyacrylonitriles, polybenzimidazoles, cellulose acetates and polyolefins.
  • Porous membrane layers comprising polymer (VDF) and copolymer (N- ZW) may additionally comprise one or more than one additional ingredient. Nevertheless, embodiments whereas porous membrane comprises at least one layer consisting essentially of polymer (VDF) and copolymer (N-ZW) are preferred, being understood that additives, and/or residues of pore forming agents may be present, in amounts not exceeding 5 wt.% of the said layer.
  • copolymer (N-ZW) is used as an additive for polymer (VDF), so it is generally understood that polymer (VDF) is present in predominant amount over copolymer (N-ZW).
  • the weight ratio copolymer (N-ZW)/polymer (VDF) is of at least 0.1/99.9 wt/wt, preferably at least 1/99 wt/wt, more preferably at least 3/97 wt/wt and/or it is less than 50/50 wt/wt, preferably less than 40/60 wt/wt, preferably less than 30/70 wt/wt.
  • the composition (C) is used in a porous membrane for decreasing the transmembrane pressure (TMP) at constant flux.
  • the porous membrane is generally manufactured by a manufacturing method comprising: step (i): preparing a composition (C L ) as defined above; step (ii): processing the composition provided in step (i) thereby providing a film; and,
  • a non-solvent medium medium (NS)
  • composition (C L ) is manufactured by any conventional techniques.
  • medium (L) may be added to polymer (VDF) and copolymer (N-ZW), or, preferably, polymer (VDF) and copolymer (N-ZW) are added to medium (L), or even polymer (VDF), copolymer (N-ZW) and medium (L) are simultaneously mixed.
  • any suitable mixing equipment may be used.
  • the mixing equipment is selected to reduce the amount of air entrapped in composition (C L ) which may cause defects in the final membrane.
  • the mixing of polymer (VDF), copolymer (N-ZW) and the medium (L) may be conveniently carried out in a sealed container, optionally held under an inert atmosphere. Inert atmosphere, and more precisely nitrogen atmosphere has been found particularly advantageous for the manufacture of composition (C L ).
  • step (i) the mixing time and stirring rate required to obtain a clear homogeneous composition (C L ) can vary widely depending upon the rate of dissolution of the components, the temperature, the efficiency of the mixing apparatus, the viscosity of composition (C L ) and the like.
  • step (ii) of the manufacturing process conventional techniques can be used for processing the composition (C L ) for providing a film.
  • composition (C L ) is typically processed by casting thereby providing a film.
  • Casting generally involves solution casting, wherein typically a casting knife, a draw-down bar or a slot die is used to spread an even film of composition (C L ) across a suitable support.
  • the temperature at which composition (C L ) is processed by casting may be or may be not the same as the temperature at which composition (C L ) is mixed under stirring.
  • composition (C L ) is cast as a film over a flat supporting substrate, typically a plate, a belt or a fabric, or
  • SUBSTITUTE SHEET (RULE 26) another microporous supporting membrane, typically by means of a casting knife, a draw-down bar or a slot die.
  • composition (C L ) is processed by casting onto a flat supporting substrate to provide a flat film.
  • composition (C L ) is processed by casting to provide a tubular film.
  • the tubular film is manufactured using a spinneret, this technique being otherwise generally referred to as "spinning method". Hollow fibers and capillary membranes may be manufactured according to the spinning method.
  • spinneret is hereby understood to mean an annular nozzle comprising at least two concentric capillaries: a first outer capillary for the passage of composition (C L ) and a second inner (generally referred to as “lumen”) for the passage of a supporting fluid, also referred to as “bore fluid”.
  • Figure l is a simplified scheme of the hollow fiber spinning machine (“Effect of spinning conditions on the structure and performance of hydrophobic PVDF hollow fiber membranes for membrane distillation”, Desalination, 287, 326-339 (15 February 2012)) which can be used for manufacturing hollow fiber membranes, wherein 3 is the dope solution tank equipped with a feeding pump 5, 1 is the nitrogen cylinder, 2 is the bore fluid cylinder, 6 is the spinneret or annular die, 7 is the coagulation bath where is depicted the nascent hollow fiber and 8 is the take-up wheel. Dope solution is pushed for the tank to the filter 4 and then pumped with the gear pump 5 through the nozzle 6. Air gap (distance between the nozzle and the coagulation bath) could be varied from 1 to several cm.
  • Figure 2 is a schematic cut of the spinneret (annular die), through a plane parallel to the fiber extrusion flow, wherein 1 is the bore fluid die, and 2 is the annular die feeding the dope solution.
  • Figure 3 is a schematic cut of the spinneret (annular die), through a plane perpendicular to the fiber extrusion flow, wherein 1 is the extruded/spinned bore fluid, 2 is the extruded/spinned dope solution, and 3 is the body of the spinner et/annul ar die.
  • composition (C L ) is generally pumped through the spinneret, together with at least one supporting fluid (so called “bore fluid”).
  • the supporting fluid acts as the support for the casting of the composition (C L ) and maintains the bore of the hollow fiber or
  • the supporting fluid may be a gas, or, preferably, a non-solvent medium [medium (NS)] or a mixture of the medium (NS) with a medium (L).
  • NS non-solvent medium
  • L medium
  • the selection of the supporting fluid and its temperature depends on the required characteristics of the final membrane as they may have a significant effect on the size and distribution of the pores in the membrane.
  • Step (iii) generally includes a step of contacting the film provided in step (ii) with a non-solvent medium [medium (NS)] thereby providing a porous membrane.
  • a non-solvent medium [medium (NS)]
  • Such step of contacting with a medium (NS) is generally effective for precipitating and coagulating the composition (C L ) constituting the film of step (ii) into a porous membrane.
  • the film may be precipitated in said medium (NS) by immersion in a medium (NS) bath, which is often referred to as a coagulation bath.
  • contacting the film with the medium (NS) can be accomplished by exposing the said film to a gaseous phase comprising vapors of said medium (NS).
  • a gaseous phase is prepared e.g. by at least partial saturation with vapors of medium (NS), and the said film is exposed to said gaseous phase.
  • a relative humidity of higher than 10 %, generally higher than 50 % i.e. comprising water vapor
  • the film Prior to being contacted with the non-solvent medium (by whichever technique as explained above), the film may be exposed during a given residence time to air and/or to a controlled atmosphere, in substantial absence of said medium (NS). Such an additional step may be beneficial for creating a skin on the exposed surface of the film through alternative mechanisms.
  • this may be accomplished by imposing an air-gap in the path that the spinned hollow tubular precursor follows before being driven into a coagulation bath.
  • step (iii) coagulation/precipitation of the composition (C L ) may be promoted by cooling.
  • the cooling of the film provided in step (ii) can be typically using any conventional techniques.
  • the solvent (S) of medium (L) of composition (C L ) is advantageously a “latent” solvent [solvent (LT)], i.e. a solvent which behaves as an active solvent towards polymer (VDF) only when heated above a certain temperature, and which is not able to solubilize the polymer (VDF) below the said temperature.
  • solvent (LT) solvent
  • step (i) and step (ii) of the manufacturing method are generally carried out at a temperature high enough to maintain composition (C L ) as a homogeneous solution.
  • the film may be typically processed at a temperature comprised between 60°C and 250°C, preferably between 70°C and 220°C, more preferably between 80°C and 200°C, and under step (iii), the film may be typically precipitated by cooling to a temperature below 100°C, preferably below 60°C, more preferably below 40°C.
  • Cooling may be achieved by contacting the film provided in step (ii) with a cooling fluid, which may be a gaseous fluid (i.e. cooled air or cooled modified atmosphere) or may be a liquid fluid.
  • a cooling fluid which may be a gaseous fluid (i.e. cooled air or cooled modified atmosphere) or may be a liquid fluid.
  • the medium (L) comprises both a solvent (S) and a nonsolvent for polymer (VDF)
  • at least partially selective evaporation of solvent (S) may be used for promoting coagulation/precipitation of polymer (VDF).
  • solvent (S) and non-solvent components of medium (L) are typically selected so as to ensure solvent (S) having higher volatility than non-solvent, so that progressive evaporation, generally under controlled conditions, of the solvent (S) leads to polymer (VDF) precipitation, and hence actual contact of the film with the medium (NS).
  • pore forming agents are generally at least partially, if not completely, removed from the porous membrane in the medium (NS), in step (iii) of the method of the invention.
  • the manufacturing method may include additional post treatment steps, for instance steps of rinsing and/or stretching the porous membrane and/or a step of drying the same.
  • the porous membrane may be additionally rinsed using a liquid medium miscible with the medium (L).
  • porous membrane may be advantageously stretched so as to increase its average porosity.
  • the porous membrane is dried at a temperature of advantageously at least 30°C.
  • Drying can be performed under air or a modified atmosphere, e.g. under an inert gas, typically exempt from moisture (water vapor content of less than 0.001% v/v). Drying can alternatively be performed under vacuum.
  • an inert gas typically exempt from moisture (water vapor content of less than 0.001% v/v). Drying can alternatively be performed under vacuum.
  • non-solvent medium a medium consisting of one or more liquid substances incapable of dissolving the polymer (VDF) of composition (C) or (C L ), and which advantageously promotes the coagulation/precipitation of polymer (VDF) from liquid medium of composition (C L ).
  • the medium (NS) typically comprises water and, optionally, at least one organic solvent selected from alcohols or polyalcohols, preferably aliphatic alcohols having a short chain, for example from 1 to 6 carbon atoms, more preferably methanol, ethanol, isopropanol and ethylene glycol.
  • organic solvent selected from alcohols or polyalcohols, preferably aliphatic alcohols having a short chain, for example from 1 to 6 carbon atoms, more preferably methanol, ethanol, isopropanol and ethylene glycol.
  • the medium (NS) is generally selected among those miscible with the medium (L) used for the preparation of composition (C L ).
  • the medium (NS) may further comprise a solvent (S), as above detailed.
  • the medium (NS) consists of water.
  • Water is the most inexpensive non-solvent medium and can be used in large amounts.
  • TMP transmembrane pressure
  • a second aspect of the invention relates a method for decreasing the transmembrane pressure (TMP) at constant flux of a porous membrane comprising at least one vinylidene fluoride (VDF) polymer [polymer (VDF)], in which said porous membrane further comprises at least one copolymer [copolymer (N-ZW)] comprising:
  • SUBSTITUTE SHEET (b) recurring units [units (RN)] derived from at least one additional monomer [monomer (B)] different from monomer (A), wherein units (Rzw) represent 0.1 to 7 mol %, preferably 0.1 to 5 mol % based on the molar composition of the copolymer (N-ZW), and wherein the molecular weight of the copolymer (N-ZW) measured by gel permeation chromatography ranges from 25000 g/mol to 350000 g/mol, and wherein the weight ratio copolymer (N-ZW) /polymer (VDF) is at least 0.1/99.9 and/or is less than 25/75.
  • the composition (C) comprising at least one vinylidene fluoride (VDF) polymer [polymer (VDF)], and at least one copolymer [copolymer (N-ZW)] as detailed above is present.
  • VDF vinylidene fluoride
  • VDF polymer
  • N-ZW copolymer
  • the porous membrane comprising composition (C) that makes it possible to decrease the transmembrane pressure (TMP) at constant flux can be used for separating an aqueous medium, by contacting said aqueous medium with the porous membrane as described above.
  • the aqueous phase may be notably a water-based phase comprising one or more contaminants.
  • the aqueous phase may be a particulate suspension of contaminants, i.e. a suspension comprising chemical or physical pollutants (e.g. inorganic particles such as sand, grit, metal particles, ceramics; organic solids, such as polymers, paper fibers, plants’ and animals’ residues; biological pollutants such as bacteria, viruses, protozoa, parasites).
  • chemical or physical pollutants e.g. inorganic particles such as sand, grit, metal particles, ceramics; organic solids, such as polymers, paper fibers, plants’ and animals’ residues; biological pollutants such as bacteria, viruses, protozoa, parasites).
  • this may be notably a method for filtrating water suspensions from suspended particulates; in this case, the used porous membrane generally possesses an average pore diameter of from 5 pm to 50 pm.
  • PVDF Solef® 1015 provided by Solvay Specialty Polymers was used as VDF homopolymer.
  • a 2 1 jacketed reactor with a five-necked kettle head was set with an overhead teflon pitch blade stirrer in the center port.
  • the second port was used for the addition of chemicals.
  • the third port was connected to a nitrogen inlet, while the fourth port was used to connect the double walled condenser.
  • the fifth port was fixed with a temperature probe.
  • MMA Methyl methacrylate (MMA) monomer (156.94 g) dissolved in 400 ml DMSO, was added into the reactor by transfer funnel. The quantity of MMA that adhered to the weighing container was transferred by additional 100 ml DMSO. Then, the N,N-Dimethyl- N-(2 -methacryloyl oxy ethyl)-N-(3 -sulfopropyl) ammonium betaine (SPE) monomer (23.052 g) dissolved in a mixture of 50 ml of water and 200 ml of dimethyl sulfoxide (DMSO) (under sonication), was added to the methyl methacrylate (MMA) solution in the reactor under constant stirring. The remaining quantity that adhered to the weighing container was transferred to the reactor by rinsing with 81 ml DMSO. The reaction mixture was stirred using the overhead stirrer (maintained at 250 rpm) and N2 gas was purged
  • SUBSTITUTE SHEET (RULE 26) for 1 h to remove dissolved oxygen in the solution. Simultaneously, the temperature of the solution (measured via the temperature probe) was increased from room temperature to 70 °C. Once the temperature of the solution reached 70 °C, initiator AIBN (1.084 g) was added to the reaction mixture by dissolving it in 19 ml DMSO. Nitrogen purging was continued for another 15 minutes after which the nitrogen purger was kept above the solution level. Addition of the initiator was considered as starting of polymerization and the reaction was continued for further 12 h. Kinetics of the polymerization was monitored by drawing out samples at every one hour interval and taking NMR spectra of the collected aliquots in DMSO-d 6 .
  • reaction mass was collected in a beaker and kept in the refrigerator overnight.
  • the obtained precipitate exhibited a DMSO content of 12% (data obtained from GC-FID) after drying.
  • the solid polymer was further crushed using a mortar and pestle and was redispersed in 1.5 1 of water/isopropanol 90: 10 v / v mixture and stirred for 2 h.
  • the solid was filtered using a Buchner funnel and dried at 60 °C under vacuum for 3 days. This process was repeated again to completely remove DMSO from the polymer.
  • MMA monomer conversion was equal to 93 %
  • SPE monomer conversion was equal to 94 %
  • High-performance liquid chromatography was performed at 35°C using a HPLC 1290 Infinity F30 equipped with Poroshell 120 columns.
  • the mobile phase was composed of H2O + H3PO4 0.05% (v/v) and ACN (acetonitrile) and the flow rate was 2.0 ml/min. 5 pl samples were injected, calibration was obtained with PMMA narrow standards.
  • MMA monomer conversion was equal to 96.1%
  • SPE monomer conversion was equal to 94.3%
  • reaction mixture was then diluted with 81.2 kg of DMSO, to obtain a solution of polymer in DMSO at 10%. After cooling down to room temperature, 197.5 kg of polymer solution was recovered in steel drums.
  • the opportune amount of PVDF, pore forming agents (PVP K30/PEG400/EG) and eventually zwitterionic additive were added in a glass tank of DMAC (equipped with a mechanical anchor) and stirred at approximately 65°C.
  • Dope solution quantity was 2 liters. The stirring lasted for several hours at 65°C. Then solutions were left at rest at 65°C for some hours to remove eventual air bubbles.
  • Dope solutions were always homogeneous, transparent and stable for several days at temperatures equal or higher than 40°C.
  • Membranes were spun from dope solutions containing blends of PVDF Solef® 1015 and of the synthesized zwitterionic p(MMA-s-SPE) copolymers in N,N-dimethylacetamide (DMAc) and immersed in a coagulation bath in order to induce phase separation (NIPS for non-solvent induced phase separation).
  • DMAc N,N-dimethylacetamide
  • polymeric hollow fibers were manufactured by extruding the dope solutions, as detailed in figures 1 to 3, through an annular aperture. Hollow fibers were prevented from collapsing by coextruding water as bore fluid in the center of the annulus. The coagulation water bath enabled producing coagulation by phase inversion. Take up wheel allowed the collection of the fiber. Dope and spinneret temperatures were maintained at 70°C for the formulation Reference Solef® 1015 and 40°C for the formulation with zwitterionic additive in order to match the viscosities. All the other conditions were the same as illustrated in Table 1 below. The spinneret geometry used in the extrusion part had an internal diameter (ID) of 700 pm, an external one of 1300 pm (OD).
  • the formulation prepared as reference had 18% wt/wt of Solef® 1015.
  • the formulations (referred as Fl or F2) according to the invention had 16,2% wt/wt of Solef® 1015 and 1,8% of zwitterionic additive (referred as sample Pl or P2 respectively), in order to have a ratio of 90/10 PVDF/zwitterionic additive).
  • Table 1 Main process conditions of the spinning trials.
  • rejection rate also inversely called retention rate
  • Rejection rate is defined as below: 100, wherein Cpermeate corresponds to the concentration of the substance in the permeate and Cretentate corresponds to the concentration of the same substance in the retentate.
  • a rejection rate of 100% means that the solute is perfectly retained by the membrane whereas a rejection rate of 0 corresponds to a solute not at all retained by the membrane.
  • foulant solution is filtered through the hollow-fiber membrane in total recirculating mode: both retentate
  • TOC total organic carbon
  • Rotational steady state shear measurements were performed at temperatures of interest using a Rheometric Scientific “RFS III” rheogoniometer in the concentric cylinder configuration (Couette). Flow curves were obtained with a sweep performed from the lowest attainable shear rate (0.02 s' 1 ) to the highest defined by the maximum torque that the instrument can reach. In all the considered cases, a quite large Newtonian range was observed. Viscosity values in the text represent the Newtonian plateau of the flow curves and are expressed in cpoises (cP).
  • Procedure is based on the same principles of the air-liquid porometry described above, both methods using the correlation between the applied pressure and the pore radio open to flux as given by Washbum equation.
  • the pore size distribution is tested with liquid-liquid displacement porometer (LLDP) (model PRM-8710®) which consists of an automated pressure constant device suitable for gas/liquid and liquid/liquid tests.
  • the device is configured for testing pore sizes down to 4 nm and uses relatively low pressures (maximum 10 bars) for the characterization of porous membranes in the high MF/UF-NF range.
  • the equipment allows for implementing very stable pressure and leads to very accurate measurement of resulting fluxes by using an analytical balance (Sartorius® Practum, accuracy of 10 mg).
  • Example 1 the zwitterionic additive prepared in Example 1 (Pl) is used. Fibers are in the range of large pore ultrafiltration membranes.
  • permeability of fibers was measured by using the Convergence Inspector tool (from Convergence Industry B. V - Enschede-The Netherlands) and working again in cross-flow mode. Modules of 5 fibers with a length of 27 cm each (typical surfaces 50 cm 2 ) were tested in Out- In configuration, with a feed throughput equal to 2 1/h, a transmembrane pressure equal to 0.5 bar was applied and flux through the membrane was monitored.
  • An out-in mode means the separation layer is on the outside surface of the fiber and the feed water flows outside the fibers.
  • Table 2 sets out the rejection rate of BSA (bovine serum albumin) solution permeability data of the hollow fiber membranes on the samples without zwitterionic additive, Ref. Solef® 1015, and with zwitterionic additive Pl and this illustrates the difference between membranes comprising or not the zwitterionic additive.
  • BSA bovine serum albumin
  • Example 2 the zwitterionic additive prepared in Example 2 (P2) is used. Fibers are in the range of small pore ultrafiltration membranes.
  • the conditions for preparing hollow fibers membrane in this case are the same as those mentioned in Table 1, except that the formulation is in pure water and the dope temperature is 40°C.
  • permeability measurement consists of imposing a constant pressure upstream the membrane fibers surface (module of 220 fibers, typical surfaces 1866 cm 2 , out-in configuration, dead-end filtration) and increasing progressively the inlet pressure by recording the permeate water flow. As the outlet pressure is at the atmospheric pressure, the outlet pressure is considered equal to 0 and inlet pressure equivalent to the differential pressure to be applied. Time was fixed every 30 seconds for each inlet pressure constant step and test was carried out by dead-end filtration. Hydraulic water permeability is calculated by adjusting data points to linear relationship through permeate flow (Q) in mg/s versus differential pressure from 300 mbar to 1300 mbar.
  • Q permeate flow
  • Table 3 sets out the rejection rate of BSA and permeability data of the hollow fiber membranes without zwitterionic additive, Ref. Solef® 1015, and with zwitterionic additive, P2 and this illustrates the difference between membranes comprising or not the zwitterionic additive.
  • Fouling tests were performed using the Poseidon module (Convergence industry B.V).
  • the module is managed by computer and a specific software Osmo inspector software v6.2.0.2.
  • Fouling tests were performed at room temperature (22-24 °C) in out/in mode with straight hollow-fiber membranes of 50 cm 2 . Feed was circulating at 5 1/h. Permeate was recirculated in the feed tank in order to keep constant feed concentration. The filtration was performed at a constant flow rate of 0.1 1/h (20 LMH) regulated by Coriolis mass flowmeter. Transmembrane pressure was monitored to evaluate permeability and fouling. When transmembrane pressure reached 400 mbar, backwash was performed. Procedure for backwash was: 30 seconds of relaxation, 2 minutes of backwash at 0.15 1/h (30 LMH) with distilled water, 30 seconds of relaxation. Fouling tests lasted 24h to have several filtration and backwash cycles.
  • the first one was straight hollow-fiber membranes (5 fibers, with surface 50 cm 2 ), with reference Solef® 1015 (Ref. Solef® 1015), as described above.
  • the second one was straight hollow-fiber membranes (5 fibers, with surface 50 cm 2 ) with Pl as detailed above, according to the invention.
  • Table 4 shows the results of fouling tests. The rejection of foulants with different foulants was measured before pressure reached the limit of 400 mbar and the required number of backwash (BW) per 24h was measured when the transmembrane pressure reached the limit of 400 mbar.
  • Fouling tests were performed at temperatures around 16-20°C in out/in mode with straight hollow-fiber modules of 220 fibers with a surface of 1866 cm 2 .
  • the filtration was performed at a constant flux of 10 1/h (53.6 LMH).
  • Transmembrane pressure was monitored to evaluate permeability and fouling. When transmembrane pressure reached 800 mbar, backwash was performed. The continuous filtration test was performed during 4 weeks.
  • Procedure for backwash cycles was: water backwash of 5 minutes at 14 1/h and chemical backwash of 8 minutes with NaOCl (around 250 ppm) at 14 1/h, with a frequency of 6 water backwashes for 1 chemical backwash.
  • SUBSTITUTE SHEET (RULE 26) Modules have been fed with two types of water: drinking water and diluted sewage water coming through the output wastewater treatment plant (Rouquet Agent, France). The sewage water was mixed with drinking water in order to have good fouling conditions for the membrane tested. The mixing ratio is 80% drinking water and 20% treated water.
  • the first one was straight hollow-fiber membranes (220 fibers with surface of 1866 cm 2 ), with reference Solef® 1015 (Ref. Solef® 1015), as described above.
  • the second one was straight hollow-fiber membranes F2 (220 fibers with surface of 1866 cm 2 ) with P2, as detailed above, according to the invention.
  • TMP transmembrane pressure
  • transmembrane pressure decreases more strongly after cleaning cycle (repeating sequence of 6 pure water backwash and 1 chemical backwash) for the membrane F2 with the zwitterionic additive (P2), getting much closer to the value of the initial transmembrane pressure, compared to reference membrane Solef® 1015.
  • the gap widens after a month. It becomes more and more difficult to recover a transmembrane pressure close to that initial for the reference membrane after repeated washing cycles.
  • Table 5 below also shows the results of fouling tests after 4 weeks run on diluted sewage water and on drinking water.
  • Table 5 Number of physical and chemical backwashes after 4 weeks run for samples Ref. Solef® 1015 (without additive) and F2 (with zwitterionic additive P2).
  • the hollow-fiber membranes comprising P2 according to the invention shows a less frequent need of backwashes, whether for physical backwashes with water or for chemical backwashes with NaOCl for the filtration of diluted sewage water and also of drinking water.
  • the difference in the number of backwashes reaches 28% less for the module F2.
  • the evolution over time of this difference in frequency of backwashes in Figure 6 for the filtration of diluted sewage water that represents the number of physical backwashes versus time.
  • the required number of chemical washes is much lower using the membrane according to the invention.
  • a procedure for accelerated aging test was performed on the reference module (Ref. Solef® 1015) and on the module F2 with zwitteionic additive (P2) according to the invention.
  • the filtration was performed during 10 minutes with drinking water at a constant flow rate of 10 1/h (53.6 LMH) in out- in mode (dead-end configuration).
  • a chemical backwash was carried out with NaOCl at 2000 ppm at a constant flow rate of 14 1/h in in- out mode. This aging test was continued for 1 week (24/24h).
  • Pore size before and after aging test was measured using liquid-liquid porosimeter.
  • fouling tests demonstrate superior performances of membranes with a zwitterionic additive according to the invention regardless of fiber selectivity, water feed and tests conditions.
  • long lasting tests show higher permeability and lower fouling propensity which was evident by the lower cleaning frequency (physical and chemical backwashes).
  • composition (C) comprising a zwitterionic copolymer
  • VDF polymer
  • membrane filtration properties particles selectivity, resistance to various foulants, mechanical and chemical resistance. . .
  • VDF vinylidene fluorine polymers
  • SUBSTITUTE SHEET (RULE 26) performances of the membranes can position them as a very attractive solution for willing to install high flux filtration systems, able to deal with high solid contents liquid influx, where lower cleaning maintenance is needed, and with an extended lifetime of the overall device.
  • Such invention therefore also allows membrane users to lower their specific energy consumption (due to lower pressure needed for the same filtration rate)

Abstract

The present invention pertains to the use of polymer additive comprising zwitterionic moieties in membranes based on vinylidene fluoride (VDF) polymers for decreasing transmembrane pressure at constant flux of said membranes. Said composition comprising vinylidene fluoride (VDF) polymers and polymer additives comprising zwitterionic moieties delivers outstanding hydrophilization performances of manufactured membranes.

Description

Use of polymer additive comprising zwitterionic moieties in PVDF membranes for decreasing the transmembrane pressure at constant flux of said membranes.
This application claims priority from EP application Nr. 22182705.8, filed on 01 July 2022, the whole content of this application being incorporated herein by reference for all purposes.
The present invention relates to the use of a composition comprising zwitterionic moieties in membranes based on vinylidene fluoride (VDF) polymers for decreasing the transmembrane pressure at constant flux. Background
Porous membrane is a thin object whose key property is its ability to control the permeation rate of chemical species through itself. This feature is exploited in applications like separation applications (for example liquid, like water, and gas).
Fluorinated polymers are widely used in the preparation of microfiltration and ultrafiltration membranes due to their good mechanical strength, high chemical resistance and thermal stability. Among them, partially fluorinated polymers based on vinylidene fluoride (VDF) are particularly convenient for controlling porosity and morphology of said membranes. Membranes made from vinylidene fluorine polymers [polymer (VDF)] are hydrophobic in nature and therefore endowed with water repellency, low water permeability and subject to fouling of particles, proteins at their surface. Hydrophobicity impedes water to penetrate into the fluoropolymer membrane and therefore water permeability requires higher pressure and consumes more energy. Fouling reduces temporarily or permanently the flux of permeation of water through the membrane e.g. in ultrafiltration or microfiltration processes.
Membranes made from vinylidene fluorine polymers [polymer (VDF)] are also widely used in beer brewing, removal of contaminants and spoilage organisms from food and beverage items and more and more in biopharmaceutical industry as a result of increasing disease prevalence, and therefore a surge in the demand for more purified drugs and vaccines.
Capability of permeating water through porous PVDF membrane is generally improved by making outer surfaces of the inner pores hydrophilic. Besides, it is generally accepted that an increase of the hydrophilicity of PVDF
SUBSTITUTE SHEET (RULE 26) membranes offers better fouling resistance because most of proteins and other foulants are hydrophobic in nature.
Several strategies have been employed to make the porous PVDF membrane hydrophilic and thus rendering said membrane highly water permeable and highly resistant to fouling. Among approaches that have been pursued, one can cite approaches based on grafting hydrophilic species on the surface of membranes, incorporation of hydrophilic comonomers in polymer chain of main vinylidenefluoride polymer, incorporation of hydrophilization additives, etc. . . These approaches are reviewed e.g. in Surface Modifications for Antifouling Membranes, Chemical Reviews, 2010, Vol. 110, No. 4, p.2448- 2471. The use of zwitterionic structures for hydrophilization of PVDF based membranes is part of these approaches and of the greatest interest.
WO 2015/070004 discloses zwitterionic containing membranes wherein a selective layer formed of a statistical copolymer comprising zwitterionic repeat units and hydrophobic repeat units such as p(MMA-s-SBMA) is disposed on a support layer formed of porous PVDF membrane. However, nothing is said neither about durability of the resulting membrane nor about their resistance to chemical aging.
Hydrophilization additives for PVDF based membranes is proposed in US 2018/0001278 which discloses comb-shaped and random zwitterionic copolymers (e.g. p(MMA-r-SBMA)) useful to enhance hydrophilicity of PVDF membranes. Resulting additivated PVDF membranes show good resistance against fouling and improved permeability when compared to PVDF membranes. However, to obtain such results, a relatively high amount of additive, that can impair mechanical, chemical resistance of the PVDF membrane as well as its economical attractiveness, is required.
It is therefore essential to develop a highly permeable porous membrane, with controlled pores size and demonstrating anti-fouling behavior. Said membrane should show high thermal and chemical stabilities which can ensure durable properties. It is also essential to develop additives, having high thermal and chemical stabilities, capable of hydrophilizing PVDF membranes into which they are dispersed. These additives have to be easily and durably incorporated in the vinylidenefluoride polymer membrane in order to enhance their hydrophilicity, water permeability and anti-fouling behavior on the long term without impairing inherent properties of vinylidenefluoride polymers which are, high mechanical, thermal and chemical properties. In addition, the additives have
SUBSTITUTE SHEET (RULE 26) to be very efficient hydrophilization agents in order to be used sparingly, thus avoiding any detrimental effect due to their presence in too large amount on the mechanical, thermal and chemical resistance of the porous PVDF membrane.
In addition to this, there is a continuous need for providing more sustainable solutions for porous membranes, both in terms of durability of their properties over time and increasing their lifetime while reducing the frequency of cleaning washes required.
As mentioned above, a common phenomenon is observed over time, namely fouling resulting in the reduction of the flux of permeation at constant concentration and pressure and which can go as far as complete blockage of the membrane. Thus, the unavoidable external surface fouling leads to increase the required pressure in order to continue the filtration operation.
Due to fouling that occurs, it is necessary to carry out regular washing cycles of the membrane, in particular with physical backwashes (which consists of reversing the pressures to return the water produced through the membrane for eliminating fouling) to eliminate most surface fouling. Nevertheless, it is sometimes unavoidable to have to carry out a chemical cleaning to clean the membrane more thoroughly in order to achieve as much as possible the initial properties of the membrane. These washing cycles, even if they are necessary, consume a lot of energy, water and also chemical products for chemical cleaning and the repetition of these can moreover in the long term damage the membranes.
There is therefore an essential need to minimize the need to carry out these washing cycles and therefore to reduce the number of backwashes and chemical cleanings, while maintaining high filtration properties, in order to preserve the properties of the membrane for as long as possible and also to have a more sustainable solution both in terms of energy consumption but also with a longer lifetime of the membranes since by reducing the number of needed washing cycles, they are subjected to less stress during their uses.
One of the criteria for monitoring the impact of this fouling when using the membrane is the pressure difference between the inlet and the outlet of the filtration module. This pressure gradient is called the transmembrane pressure (TMP) or transmembrane differential pressure, expressed in bar (or in Pascal, Pa). This transmembrane pressure can be defined as follows:
Figure imgf000004_0001
SUBSTITUTE SHEET (RULE 26) Thus, the greater the fouling, the more the transmembrane pressure at constant flux will increase over time during the filtration process. It is therefore important to be able to reduce the transmembrane pressure at constant flux as much as possible over time during the filtration process before it becomes necessary to run a cycle of cleaning washes and also to decrease the transmembrane pressure after each cycle of cleaning washes so that it comes as close as possible to the initial transmembrane pressure.
The Applicant has found that the use of the composition (C) in a membrane makes it possible to reduce the transmembrane pressure at constant flux during the filtration process instead of traditional PVDF membranes, thus making it possible to reduce the number of washing cycles. Furthermore, it appears surprisingly that the use of the composition (C) according to the invention leads to better recovery of the membrane, i.e. once the membrane has undergone several repeated complete washing cycles during the filtration process, the transmembrane pressure falls back to values close to the starting transmembrane pressure and therefore that leads to lower cleaning frequency and thus lower energy and chemical consumptions. Finally, the use of the composition (C) according to the invention allows better resistance of this membrane to chemical washing, the latter degrading less than the membranes of the prior art.
Therefore, the present invention leads to a more sustainable solution for filtration processes.
The present invention makes it possible to decrease the transmembrane pressure at constant flux over time during the filtration process of the porous membrane, while maintaining high filtration properties and performances, and reducing energy consumption and cleaning maintenance cycles and thus chemicals consumption for cleaning.
These long-lasting performances of the membranes can position them as a very attractive solution for water and waste water treatment companies and for biopharmaceutical, and food and beverage companies, willing to install high flux filtration systems, able to deal with high solid contents liquid influx, where lower cleaning maintenance is needed, and with an extended lifetime of the overall device.
Brief description of drawings
Figure l is a simplified scheme of the hollow fiber spinning machine used for manufacturing hollow fiber membranes.
SUBSTITUTE SHEET (RULE 26) Figure 2 is a schematic cut of the spinneret (annular die), through a plane parallel to the fiber extrusion flow.
Figure 3 is a schematic cut of the spinneret (annular die), through a plane perpendicular to the fiber extrusion flow.
Figure 4 and 5 are graphs representing the TMP evolution versus time.
Figure 6 is a graph representing the need for backwashes in the filtration of diluted sewage water.
Figure 7 is a graph that represents the transmembrane pressure after chemical cleaning as a function of time.
Summary of invention
Thus, the present invention relates to the use of a composition [composition (C)] in a porous membrane for decreasing the transmembrane pressure (TMP) at constant flux of said membrane wherein the porous membrane comprises the composition (C) comprising:
- at least one vinylidene fluoride (VDF) polymer [polymer (VDF)], and
- at least one copolymer [copolymer (N-ZW)] comprising
(a) recurring units [units (Rzw)] derived from at least one zwitterionic monomer [monomer (A)], and
(b) recurring units[units (RN)] derived from at least one at least one additional monomer [monomer (B)] different from monomer (A), wherein units (Rzw) represent 0.1 to 7 mol %, preferably 0.1 to 5 mol % based on the molar composition of the copolymer (N-ZW), and wherein the molecular weight of the copolymer (N-ZW) measured by gel permeation chromatography ranges from 25000 g/mol to 350000 g/mol, and wherein the weight ratio copolymer (N-ZW) /polymer (VDF) is at least 0.1/99.9 and/or is less than 25/75.
The invention also refers to a method for decreasing the transmembrane pressure (TMP) at constant flux of a porous membrane comprising at least one vinylidene fluoride (VDF) polymer [polymer (VDF)], in which said porous membrane further comprises at least one copolymer [copolymer (N-ZW)] comprising:
(a) recurring units [units (Rzw)] derived from at least one zwitterionic monomer [monomer (A)], and
(b) recurring units[units (RN)] derived from at least one at least one additional monomer [monomer (B)] different from monomer (A),
SUBSTITUTE SHEET (RULE 26) wherein units (Rzw) represent 0.1 to 7 mol %, preferably 0.1 to 5 mol % based on the molar composition of the copolymer (N-ZW), and wherein the molecular weight of the copolymer (N-ZW) measured by gel permeation chromatography ranges from 25000 g/mol to 350000 g/mol, and wherein the weight ratio copolymer (N-ZW) /polymer (VDF) is at least 0.1/99.9 and/or is less than 25/75.
The Applicant has surprisingly found that the use of at least one copolymer [copolymer (N-ZW)] in composition (C) as detailed above in membranes, is particularly effective for decreasing the transmembrane pressure at constant flux over time during filtration operation while delivering outstanding permeability performances in aqueous media filtration and separation processes.
The fact to use the copolymer |copolymer (N-ZW)] in addition to vinylidene fluoride (VDF) polymer in the manufacture of membranes makes it possible to decrease the transmembrane pressure at constant flux of the porous membrane.
The polymer (VDF)
The expression “vinylidene fluoride polymer” and “polymer (VDF)” are used, within the frame of the present invention for designating polymers comprising recurring units derived from vinylidene fluoride, generally as major recurring units components. So, polymer (VDF) is generally a polymer essentially made of recurring units, more that 50 % by moles of said recurring units being derived from vinylidene fluoride (VDF).
Polymer (VDF) may further comprise recurring units derived from at least one fluorinated monomer different from VDF and/or may further comprise recurring units derived from a fluorine-free monomer (also referred to as “hydrogenated monomer”). The term “fluorinated monomer” is hereby intended to denote an ethylenically unsaturated monomer comprising at least one fluorine atom. The fluorinated monomer may further comprise one or more other halogen atoms (Cl, Br, I).
In particular, polymer (VDF) is generally selected among polyaddition polymers comprising recurring units derived from VDF and, optionally, recurring units derived from at least one ethylenically unsaturated monomer comprising fluorine atom(s) different from VDF, which is generally selected from the group consisting of:
(a) C2-C8 perfluoroolefins such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoroisobutylene;
SUBSTITUTE SHEET (RULE 26) (b) hydrogen-containing C2-C8 fluoroolefms different from VDF, such as vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutylene (HFIB), perfluoroalkyl ethylenes of formula CEb=CE[-Rn, wherein Rn is a Ci-Ce perfluoroalkyl group;
(c) C2-C8 chloro- and/or bromo-containing fluoroolefms such as chlorotrifluoroethylene (CTFE);
(d) perfluoroalkyl vinyl ethers (PAVE) of formula CF2=CFORfi, wherein Rn is a Ci-Ce perfluoroalkyl group, such as CF3 (PMVE), C2F5 or C3F7;
(e) perfluorooxyalkylvinylethers of formula CF2=CFOXo, wherein Xo is a a Ci- C12 perfluorooxyalkyl group comprising one or more than one ethereal oxygen atom, including notably perfluoromethoxyalkylvinylethers of formula CF2=CFOCF2ORf2, with Rf2 being a C1-C3 perfluoro(oxy)alkyl group, such as - CF2CF3, -CF2CF2-O-CF3 and -CF3; and
(f) (per)fluorodioxoles of formula:
Figure imgf000008_0001
wherein each of Rr,. Rf4, Rfs and Rf6, equal to or different from each other, is independently a fluorine atom, a Ci-Ce perfluoro(oxy)alkyl group, optionally comprising one or more oxygen atoms, such as -CF3, -C2F5, -C3F7, -OCF3 or - OCF2CF2OCF3
The vinylidene fluoride polymer [polymer (VDF)] is preferably a polymer comprising:
(a’) at least 60 % by moles, preferably at least 75 % by moles, more preferably 85 % by moles of recurring units derived from vinylidene fluoride (VDF);
(b’) optionally from 0.1 to 30%, preferably from 0.1 to 20%, more preferably from 0.1 to 15%, by moles of recurring units derived from a fluorinated monomer different from VDF; and
(c’) optionally from 0.1 to 10 %, by moles, preferably 0.1 to 5 % by moles, more preferably 0.1 to 1% by moles of recurring units derived from one or more hydrogenated monomer(s),
SUBSTITUTE SHEET (RULE 26) all the aforementioned % by moles being referred to the total moles of recurring units of the polymer (VDF).
The said fluorinated monomer is advantageously selected in the group consisting of vinyl fluoride (VFi); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl)vinyl ethers, such as perfluoro(methyl)vinyl ether (PMVE), perfluoro(ethyl) vinyl ether (PEVE) and perfluoro(propyl)vinyl ether (PPVE); perfluoro(l,3-dioxole); perfluoro(2,2- dimethyl-l,3-dioxole) (PDD). Preferably, the possible additional fluorinated monomer is chosen from chlorotrifluoroethylene (CTFE), hexafluoroproylene (HFP), trifluoroethylene (VF3) and tetrafluoroethylene (TFE).
The choice of the said hydrogenated monomer(s) is not particularly limited; alpha-olefins, (meth)acrylic monomers, vinyl ether monomers, styrenic mononomers may be used; nevertheless, to the sake of optimizing chemical resistance, embodiments wherein the polymer (F) is essentially free from recurring units derived from said hydrogenated comonomer(s) are preferred.
Accordingly, the vinylidene fluoride polymer [polymer (VDF)] is more preferably a polymer consisting essentially of:
(a’) at least 60 % by moles, preferably at least 75 % by moles, more preferably 85 % by moles of recurring units derived from vinylidene fluoride (VDF);
(b’) optionally from 0.1 to 30%, preferably from 0.1 to 20%, more preferably from 0.1 to 15% by moles of a fluorinated monomer different from VDF; said fluorinated monomer being preferably selected in the group consisting of vinylfluoride (VFi), chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), tetrafluoroethylene (TFE), perfluoromethylvinylether (MVE), trifluoroethylene (TrFE) and mixtures therefrom, all the aforementioned % by moles being referred to the total moles of recurring units of the polymer (VDF).
Defects, end chains, impurities, chains inversions or branchings and the like may be additionally present in the polymer (VDF) in addition to the said recurring units, without these components substantially modifying the behavior and properties of the polymer (VDF).
As non-limitative examples of polymers (VDF) useful in the present invention, mention can be notably made of homopolymers of VDF, VDF/TFE copolymers, VDF/TFE/HFP copolymers, VDF/TFE/CTFE copolymers,
SUBSTITUTE SHEET (RULE 26) VDF/TFE/TrFE copolymers, VDF/CTFE copolymers, VDF/HFP copolymers, VDF/TFE/HFP/CTFE copolymers and the like.
VDF homopolymers are particularly advantageous for being used as polymer (VDF) in the composition (C).
The melt index of the polymer (VDF) is advantageously at least 0.01, preferably at least 0.05, more preferably at least 0.1 g/10 min and advantageously less than 50, preferably less than 30, more preferably less than 20 g/10 min, when measured in accordance with ASTM test No. 1238, run at 230°C, under a piston load of 2.16 kg.
The melt index of the polymer (VDF) is advantageously at least 0.1, preferably at least 1, more preferably at least 5 g/10 min and advantageously less than 70, preferably less than 50, more preferably less than 40 g/10 min, when measured in accordance with ASTM test No. 1238, run at 230°C, under a piston load of 5 kg.
The melt index of the polymer (VDF) is advantageously at least 0.1, preferably at least 0.5, more preferably at least 1 g/10 min and advantageously less than 30, preferably less than 20, more preferably less than 10 g/10 min, when measured in accordance with ASTM test No. 1238, run at 230°C, under a piston load of 21.6 kg.
The polymer (VDF) has advantageously a melting point (Tm) advantageously of at least 120°C, preferably at least 125°C, more preferably at least 130°C and of at most 190°C, preferably at most 185°C, more preferably at most 180°C, when determined by DSC, at a heating rate of 10°C/min, according to ASTM D 3418.
Copolymer (N-ZW) comprising zwitterionic recurring units
Composition (C) used in the present invention for decreasing the transmembrane pressure (TMP) at constant flux of a porous membrane comprises at least one copolymer [copolymer (N-ZW)] comprising:
(a) recurring units [units (Rzw)] derived from at least one zwitterionic monomer [monomer (A)], and
(b) recurring units[units (RN)] derived from at least one at least one additional monomer [monomer (B)] different from monomer (A).
The term “flux” is the mass flow through a solid divided by the solid surface (measurement of volume per unit area of membrane and time (1/h/m2 = LMH)) and is used herein in its usual meaning that is it indicates the permeation flux of the membrane in its conditions of use.
SUBSTITUTE SHEET (RULE 26) Generally, zwitterionic recurring units (Rzw) are derived from at least one zwitterionic monomer (A) that is neutral in overall charge but contains a number of group (C+) equal to the number of group (A-). The cationic charge(s) may be contributed by at least one onium or inium cation of nitrogen, such as ammonium, pyridinium and imidazolinium cation; phosphorus, such as phosphonium; and/or sulfur, such as sulfonium. The anionic charge(s) may be contributed by at least one carbonate, sulfonate, phosphate, phosphonate, phosphinate or ethenolate anion, and the like. Suitable zwitterionic monomers include, but are not limited to, betaine monomers, which are zwitterionic and comprise an onium atom that bears no hydrogen atoms and that is not adjacent to the anionic atom.
In some embodiments, units (Rzw) are derived from at least one monomer (A) selected from the list consisting of a) alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl acrylates or methacrylates, acrylamido or methacrylamido, typically
- sulfopropyldimethylammonioethyl (meth)acrylate,
- sulfoethyldimethylammonioethyl (meth)acrylate,
- sulfobutyldimethylammonioethyl (meth)acrylate,
- sulfohydroxypropyldimethylammonioethyl (meth)acrylate,
- sulfopropyldimethylammoniopropylacrylamide,
- sulfopropyldimethylammoniopropylmethacrylamide,
- sulfohydroxypropyldimethylammoniopropyl(meth)acrylamide,
- sulfopropyldiethylammonio ethoxyethyl methacrylate. b) heterocyclic betaine monomers, typically
- sulfobetaines derived from piperazine,
- sulfobetaines derived from 2-vinylpyridine and 4-vinylpyridine, more typically 2- vinyl- 1 -(3 -sulfopropyl )pyridinium betaine or 4-vinyl-l-(3- sulfopropyl)pyridinium betaine,
- 1 -vinyl-3 -(3 -sulfopropyl)imidazolium betaine; c) alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl allylics, typically sulfopropylmethyldiallylammonium betaine; d) alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl styrenes; e) betaines resulting from ethylenically unsaturated anhydrides and dienes; f) phosphobetaines of formulae
SUBSTITUTE SHEET (RULE 26)
Figure imgf000012_0001
and g) betaines resulting from cyclic acetals, typically ((dicyanoethanolate)ethoxy)dimethylammoniopropylmethacrylamide.
In some preferred embodiments, units (Rzw) are derived from at least one monomer (A) selected from the list consisting of
- sulfopropyldimethylammonioethyl acrylate,
- sulfopropyldimethylammonioethyl methacrylate (SPE),
Figure imgf000012_0002
- sulfopropyldimethylammoniopropyl acrylamide,
- sulfopropyldimethylammoniopropyl methacrylamide,
- sulfohydroxypropyldimethylammonioethyl acrylate,
- sulfohydroxypropyldimethylammonioethyl methacrylate (SHPE),
- sulfohydroxypropyldimethylammoniopropyl acrylamide (AHPS),
- sulfohydroxypropyldimethylammoniopropyl methacrylamide (SHPP)
- l-(3-Sulphonatopropyl)-2-vinylpyridinium (2SPV), and
Figure imgf000012_0003
- l-(3-Sulphonatopropyl)-4-vinylpyridinium (4SPV).
SUBSTITUTE SHEET (RULE 26) In some more preferred embodiments, units (Rzw) are derived from at least one monomer (A) selected from the list consisting of
- sulfopropyldimethylammonioethyl acrylate,
- sulfopropyldimethylammonioethyl methacrylate,
- l-(3-Sulphonatopropyl)-2-vinylpyridinium, and
- l-(3-Sulphonatopropyl)-4-vinylpyridinium.
In some even more preferred embodiments, units (Rzw) are derived from
- sulfopropyldimethylammonioethyl methacrylate (SPE), or
- l-(3-Sulphonatopropyl)-2-vinylpyridinium (2SPV).
Copolymer (N-ZW) according to the invention, besides comprising recurring units (Rzw) derived from at least one zwitterionic monomer (A), also comprises recurring units (RN) derived from at least one at least one additional monomer (B) different from monomer (A).
Often, units (RN) are derived from at least one monomer deprived of ionisable groups.
In some embodiments, units (RN) are derived from at least one monomer selected from the list consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, vinyl acetate and N,N-dimethylacrylamide [units (RN-I)]. Preferably, units (RN-I) are derived from methyl methacrylate, ethyl methacrylate or mixture thereof. More preferably, units (RN-I) are derived from methyl methacrylate.
In some other embodiments, units (RN) are derived from at least one monomer selected from the list consisting of 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2-hydroxyethyl acrylate (ELEA), hydroxypropyl acrylate, 4-hydroxybutyl acrylate, polyethylene glycol) methacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (mPEGMA), poly(ethylene glycol) ethyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate and poly(ethylene glycol) ethyl ether acrylate [units (RN-2)]. Preferably, units (RN-2) are derived from 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate or mixture thereof. More preferably, units (RN-2) are derived from 2-hydroxyethyl methacrylate (HEMA).
Still in some other embodiment, units (RN) are derived from at least one monomer selected from at least one monomer selected from the list consisting of methyl methacrylate, ethyl methacrylate, butyl acrylate, methyl acrylate, ethyl acrylate, butyl acrylate, vinyl acetate and N,N-dimethylacrylamide [units (RN-I)] and from at least one monomer selected from the list consisting of 2-
SUBSTITUTE SHEET (RULE 26) hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2- hydroxyethyl acrylate (HEA), hydroxypropyl acrylate, 4-hydroxybutyl acrylate, polyethylene glycol) methacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (mPEGMA), poly(ethylene glycol) ethyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate and poly(ethylene glycol) ethyl ether acrylate [units (RN-2)]. Preferably, units (RN-I) are derived from methyl methacrylate, ethyl methacrylate or mixture thereof and units (RN-2) are derived from 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate or mixture thereof. More preferably, units (RN-I) are derived from methyl methacrylate and units (RN-2) are derived from 2-hydroxyethyl methacrylate (HEMA).
In some preferred embodiments, the copolymer (N-ZW) of the composition (C) used in the present invention comprises recurring units (Rzw) derived from sulfopropyl dimethylammonioethyl methacrylate (SPE), l-(3- Sulphonatopropyl)-2-vinylpyridinium (2SPV) or mixtures thereof and recurring units (RN-I) derived from methyl methacrylate.
In some more preferred embodiments, the copolymer (N-ZW) of the present disclosure comprises recurring units (Rzw) derived from sulfopropyldimethylammonioethyl methacrylate (SPE) and recurring units (RN-I) derived from methyl methacrylate.
Still in some more preferred embodiments, the copolymer (N-ZW) of the composition (C) used in the present invention comprises recurring units (Rzw) derived from (SPE) or (2SPV), recurring units (RN-I) derived from methyl methacrylate and recurring units (RN-2) derived from 2-hydroxyethyl methacrylate (HEMA).
The copolymer (N-ZW) of the composition (C) according to the present disclosure generally comprises 80 % or more by moles, preferably 90% or more by moles, more preferably 93% or more by moles and even more preferably 95% or more by moles of units (RN), with respect to the total moles of recurring units of copolymer (N-ZW).
When recurring units (RN-I) and recurring units (RN-2) are present, copolymer (N-ZW) generally comprises from 0.1 to 50 % by moles, preferably from 0.1 to 40 % by moles, more preferably from 0.1 to 30% by moles and even more preferably from 0.1 to 20 % by moles of recurring units (Rzw) and (RN-2), with respect to the total moles of recurring units of copolymer (N-ZW).
SUBSTITUTE SHEET (RULE 26) Copolymer (N-ZW) of the composition (C) used in the present invention for decreasing the transmembrane pressure (TMP) at constant flux is a block copolymer, a branched copolymer or a statistical copolymer. Good results were obtained with copolymer (N-ZW) being a statistical copolymer.
Unless otherwise indicated, when molar mass is referred to, the reference will be to the weight-average molar mass, expressed in g/mol. The latter can be determined by gel permeation chromatography (GPC) with light scattering detection (DLS or alternatively MALLS) or refractive index detection, with an aqueous eluent or an organic eluent (for example dimethylacetamide, dimethylformamide, and the like), depending on the copolymer (N-ZW). The weight-average molar mass (Mw) of the copolymer (N-ZW) is in the range of from 25,000 to 350,000 g/mol, typically from about 35,000 to about 300,000, g/mol, more typically from about 70,000 to 250,000 g/mol, even more typically 80,000 to 200,000 g/mol.
The copolymer (N-ZW) of the composition (C) used in the present invention for decreasing the transmembrane pressure (TMP) at constant flux of the membrane may be obtained by any polymerization process known to those of ordinary skill. For example, the copolymer (N-ZW) may be obtained by radical polymerization or controlled radical polymerization in aqueous solution, in dispersed media, in organic solution or in organic/water solution (miscible phase).
The monomer deprived of ionisable groups from which can be derived units (RN) may be obtained from commercial sources.
The zwitterionic monomer from which are derived units (Rzw) may be obtained from commercial sources or synthesized according to methods known to those of ordinary skill in the art.
Suitable zwitterionic monomers from which can be derived units (Rzw) include, but are not limited to monomers selected from the list consisting of: a) alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl acrylates or methacrylates, acrylamido or methacrylamido, typically:
- sulfopropyldimethylammonioethyl methacrylate, sold by Raschig under the name RALU®MER SPE
SUBSTITUTE SHEET (RULE 26)
Figure imgf000016_0001
- sulfoethyldimethylammonioethyl methacrylate,
Figure imgf000016_0002
- sulfobutyldimethylammonioethyl methacrylate:
Figure imgf000016_0003
the synthesis of which is described in the paper “Sulfobetaine zwitterionomers based on n-butyl acrylate and 2-ethoxyethyl acrylate: monomer synthesis and copolymerization behavior”, Journal of Polymer Science, 40, 511-523 (2002),
- sulfohydroxypropyldimethylammonioethyl methacrylate,
Figure imgf000016_0004
and other hydroxyalkyl sulfonates of dialkylammonium alkyl acrylates or methacrylates, acrylamido or methacrylamido of formulae below
SUBSTITUTE SHEET (RULE 26)
Figure imgf000017_0001
- sulfopropyldimethylammoniopropylacrylamide, the synthesis of which is described in the paper “Synthesis and solubility of the poly(sulfobetaine)s and the corresponding cationic polymers: 1. Synthesis and characterization of sulfobetaines and the corresponding cationic monomers by nuclear magnetic resonance spectra”, Wen-Fu Lee and Chan- Chang Tsai, Polymer, 35 (10), 2210-2217 (1994),
- sulfopropyldimethylammoniopropylmethacrylamide, sold by Raschig under the name SPP:
Figure imgf000017_0002
- sulfopropyldiethylammonio ethoxyethyl methacrylate:
SUBSTITUTE SHEET (RULE 26)
Figure imgf000018_0001
the synthesis of which is described in the paper “Poly(sulphopropylbetaines): 1. Synthesis and characterization”, V. M. Monroy Soto and J. C. Galin, Polymer, 1984, Vol. 25, 121-128; b) heterocyclic betaine monomers, typically:
- sulfobetaines derived from piperazine having any one of the following structures
Figure imgf000018_0002
the synthesis of which is described in the paper “Hydrophobically Modified Zwitterionic Polymers: Synthesis, Bulk Properties, and Miscibility with Inorganic Salts”, P. Koberle and A. Laschewsky, Macromolecules, 27, 2165-2173 (1994), and other hydroxyalkyl sulfonates derived from piperazine of formulae below
SUBSTITUTE SHEET (RULE 26)
Figure imgf000019_0001
- sulfobetaines derived from 2-vinylpyridine and 4vinylpyridine, such as 2-vinyl-l-(3-sulfopropyl)pyridinium betaine (2SPV), sold by Raschig under the name SPV:
SUBSTITUTE SHEET (RULE 26)
Figure imgf000020_0001
and 4-vinyl-l -(3 -sulfopropyl )pyridinium betaine (4SPV),
Figure imgf000020_0002
the synthesis of which is disclosed in the paper “Evidence of ionic aggregates in some ampholytic polymers by transmission electron microscopy”, V. M. Castano and A. E. Gonzalez, J. Cardoso, O. Manero and V. M. Monroy, J. Mater. Res., 5 (3), 654-657 (1990), and other hydroxyalkyl sulfonates derived from 2-vinylpyridine and 4vinylpyridine of formulae below
Figure imgf000020_0003
- 1 -vinyl-3 -(3 -sulfopropyl)imidazolium betaine:
Figure imgf000020_0004
SUBSTITUTE SHEET (RULE 26) the synthesis of which is described in the paper “Aqueous solution properties of a poly(vinyl imidazolium sulphobetaine)”, J. C. Salamone, W. Volkson, A.P. Oison, S.C. Israel, Polymer, 19, 1157-1162 (1978), and corresponding hydroxyalkyl sulfonate of formula below
Figure imgf000021_0001
c) alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl allylics, typically sulfopropylmethyldiallylammonium betaine:
Figure imgf000021_0002
the synthesis of which is described in the paper “New poly(carbobetaine)s made from zwitterionic diallylammonium monomers”, Favresse, Philippe; Laschewsky, Andre, Macromolecular Chemistry and Physics, 200(4), 887-895 (1999), d) alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl styrenes, typically compounds having any one of the following structures:
Figure imgf000021_0003
SUBSTITUTE SHEET (RULE 26) the synthesis of which is described in the paper “Hydrophobically Modified Zwitterionic Polymers: Synthesis, Bulk Properties, and Miscibility with Inorganic Salts”, P. Koberle and A. Laschewsky, Macromolecules, 27, 2165-2173 (1994), and other hydroxyalkyl sulfonates of dialkylammonium alkyl styrenes of formulae below
Figure imgf000022_0001
e) betaines resulting from ethylenically unsaturated anhydrides and dienes, typically compounds having any one of the following structures:
Figure imgf000022_0002
the synthesis of which is described in the paper “Hydrophobically Modified Zwitterionic Polymers: Synthesis, Bulk Properties, and Miscibility with Inorganic Salts”, P. Koberle and A. Laschewsky, Macromolecules, 27, 2165-2173 (1994), f) phosphobetaines having any one of the following structures:
SUBSTITUTE SHEET (RULE 26)
Figure imgf000023_0001
the synthesis of which are disclosed in EP 810 239 Bl (Biocompatibles, Alister et al.); g) betaines resulting from cyclic acetals, typically ((dicyanoethanolate)ethoxy)dimethylammoniumpropylmethacrylamide:
Figure imgf000023_0002
the synthesis of which is described by M-L. Pujol-Fortin et al. in the paper entitled “Poly(ammonium alkoxydicyanatoethenolates) as new hydrophobic and highly dipolar poly(zwitterions). 1. Synthesis”, Macromolecules, 24, 4523-4530 (1991).
Suitable monomers comprising hydroxyalkyl sulfonate moi eties from which can be derived units (Rzw) can be obtained by reaction of sodium 3- chloro-2-hydroxypropane-l -sulfonate (CHPSNa) with monomer bearing tertiary amino group, as described in US20080045420 for the synthesis of SHPP, starting from dimethylaminopropylmethacrylamide according to the reaction scheme:
Figure imgf000023_0003
SUBSTITUTE SHEET (RULE 26) Other monomers bearing tertiary amino group may be involved in reaction with CHPSNa to obtain suitable monomers from which are derived units (Rzw) :
Figure imgf000024_0001
Suitable monomers from which are derived units (Rzw) may be also obtained by reaction of sodium 3 -chloro-2-hydroxypropane-l -sulfonate (CHPSNa) with monomer bearing pyridine or imidazole group:
Figure imgf000024_0002
The expression “derived from” which puts recurring units (Rzw) in connection with a monomer is intended to define both recurring units (Rzw)
SUBSTITUTE SHEET (RULE 26) directly obtained from polymerizing the said monomer, and the same recurring units (Rzw) obtained by modification of an existing polymer.
Accordingly, recurring units (Rzw) may be obtained by modification of a polymer referred to as a precursor polymer comprising recurring units bearing tertiary amino groups through the reaction with sodium 3-chloro-2- hydroxypropane-1 -sulfonate (CHPSNa). Similar modification was described in sodium 3 -chloropropane- 1 -sulfonate in place of CHPSNa:
Figure imgf000025_0001
Figure imgf000025_0002
Finally, recurring units (Rzw) may be obtained by chemical modification of a polymer referred to as a precursor polymer with a sultone, such as propane sultone or butane sultone, a haloalkylsulfonate or any other sulfonated electrophilic compound known to those of ordinary skill in the art. Exemplary synthetic steps are shown below:
SUBSTITUTE SHEET (RULE 26)
Figure imgf000026_0001
SUBSTITUTE SHEET (RULE 26) Similarly, recurring units (Rzw) may be obtained by modification of a polymer referred to as a precursor polymer comprising recurring units bearing tertiary amino groups, pyridine groups, imidazole group or mixtures thereof through the reaction with sodium 3 -chloro-2-hydroxypropane-l -sulfonate (CHPSNa), a sultone, such as propane sultone or butane sultone, or a haloalkylsulfonate.
As copolymer (N-ZW) is used as an additive for polymer (VDF), the polymer (VDF) is generally present in predominant amount over copolymer (N- ZW) in composition (C). Generally the weight ratio copolymer (N-ZW)/polymer (VDF) is of at least 0.1/99.9 wt/wt, preferably at least 1/99 wt/wt, more preferably at least 3/97 wt/wt and/or it is less than 25/75 wt/wt, preferably less than 20/80 wt/wt, more preferably less than 15/85 wt/wt and even more preferably less than 10/90 wt/wt.
Composition (C) may optionally comprise at least one further ingredient. Said further ingredient can preferably be selected in the group consisting of nonsolvents (water, alcohols...), co-solvents (e.g. ketones), pore forming agents, nucleating agents, fillers, nanoparticles, salts, surfactants.
When used, pore forming agents are typically added to the composition (C) in amounts usually ranging from 1% to 30% by weight, preferably from 2% to 20% by weight, based on the total weight of the composition (C). Suitable pore forming agents are for instance polyvinyl alcohol (PVA), polyvinyl-pyrrolidone (PVP) and polyethylene glycol (PEG).
Liquid medium
In some embodiments, composition (C) further comprises at least one liquid medium [medium (L)] comprising at least one organic solvent [composition (CL)].
The term “solvent” is used herein in its usual meaning, that is, it indicates a substance capable of dissolving another substance (solute) to form a uniformly dispersed mixture at the molecular level. In the case of a polymeric solute, it is common practice to refer to a solution of the polymer in a solvent when the resulting mixture is transparent and no phase separation is visible in the system. Phase separation is taken to be the point, often referred to as “cloud point”, at which the solution becomes turbid or cloudy due to the formation of polymer aggregates.
Generally, in composition (CL), medium (L) comprises at least one solvent (S) for polymer (VDF).
SUBSTITUTE SHEET (RULE 26) The medium (L) typically comprises at least one organic solvent selected from the group comprising:
- aliphatic hydrocarbons including, more particularly, the paraffins such as, in particular, pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane or cyclohexane, and naphthalene and aromatic hydrocarbons and more particularly aromatic hydrocarbons such as, in particular, benzene, toluene, xylenes, cumene, petroleum fractions composed of a mixture of alkylbenzenes;
- aliphatic or aromatic halogenated hydrocarbons including more particularly, perchlorinated hydrocarbons such as, in particular, tetrachloroethylene, hexachloroethane;
- partially chlorinated hydrocarbons such as di chloromethane, chloroform, 1,2- di chloroethane, 1,1,1 -tri chloroethane, 1 , 1 ,2,2-tetrachloroethane, pentachloroethane, trichloroethylene, 1 -chlorobutane, 1,2-di chlorobutane, monochlorobenzene, 1,2-di chlorobenzene, 1,3-dichlorobenzene, 1,4- di chlorobenzene, 1, 2, 4-tri chlorobenzene or mixture of different chlorobenzenes;
- aliphatic, cycloaliphatic or aromatic ether oxides, more particularly, diethyl oxide, dipropyl oxide, diisopropyl oxide, dibutyl oxide, methyltertiobutyl ether, dipentyl oxide, diisopentyl oxide, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether benzyl oxide; dioxane, tetrahydrofuran (THF);
- dimethylsulfoxide (DMSO);
- glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n- butyl ether;
- glycol ether esters such as ethylene glycol methyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate;
- alcohols, including polyhydric alcohols, such as methyl alcohol, ethyl alcohol, diacetone alcohol, ethylene glycol;
- ketones such as acetone, methylethylketone, methylisobutyl ketone, diisobutylketone, cyclohexanone, isophorone;
- linear or cyclic esters such as isopropyl acetate, n-butyl acetate, methyl acetoacetate, dimethyl phthalate, y-butyrolactone;
- linear or cyclic carboxamides such as N,N-dimethylacetamide (DMAc), N,N-
SUBSTITUTE SHEET (RULE 26) di ethyl acetamide, dimethylformamide (DMF), diethylformamide or N-methyl-2- pyrrolidone (NMP);
- organic carbonates for example dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, ethylmethyl carbonate, ethylene carbonate, vinylene carbonate;
- phosphoric esters such as trimethyl phosphate, triethyl phosphate (TEP);
- ureas such as tetramethylurea, tetraethylurea;
- methyl-5-dimethylamino-2-methyl-5-oxopentanoate (commercially available under the trademark Rhodialsov Polarclean®).
The following are preferred: linear or cyclic carboxamides such as N,N- dimethylacetamide (DMAc), N,N-di ethyl acetamide, dimethylformamide (DMF), diethylformamide or N-methyl-2-pyrrolidone (NMP), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), methyl-5-dimethylamino-2-methyl-5- oxopentanoate (commercially available under the trademark Rhodialsov Polarclean®) and triethylphosphate (TEP).
Linear or cyclic carboxamides such as N,N-dimethylacetamide (DMAc),
N,N-di ethyl acetamide, dimethylformamide (DMF), diethylformamide or N- methyl-2-pyrrolidone (NMP) are particularly preferred.
N-methyl-pyrrolidone (NMP) and dimethyl acetamide (DMAc) are even more preferred.
The medium (L) may further comprise at least one additional liquid component different from solvent (S) (or in other terms, a non-solvent).
Said additional liquid component, which does not have ability to dissolve polymer (VDF), may be added to composition (CL), in an amount generally below the level required to reach the cloud point, typically in amount of from
O.1% to 40% by weight, preferably in an amount of from 0.1% to 20% by weight, based on the total weight of medium (L) of the composition (CL). Without being bound by this theory, it is generally understood that the addition of a non-solvent to composition (CL) could be advantageously beneficial in increasing rate of demixing/coagulation in processes for manufacturing porous membranes, and/or for promoting coagulation by removal of solvent (S) by evaporation.
Generally, the composition (CL) comprises an overall amount of copolymer (N-ZW) and polymer (VDF) of at least 1 wt.%, more preferably of at least 3 wt.%, even more preferably of at least 5 wt.%, based on the total weight of medium (L), copolymer (N-ZW) and polymer (VDF), and/or composition (CL)
SUBSTITUTE SHEET (RULE 26) preferably comprises an overall amount of copolymer (N-ZW) and polymer (VDF) of at most 60 wt.%, more preferably of at most 50 wt.%, even more preferably at most 30 wt.%, based on the total weight of medium (L), copolymer (N-ZW) and polymer (VDF) and/or composition (CL).
Conversely, the amount of medium (L) in composition (CL) is of at least 40 wt.%, preferably at least 50 wt.%, even more preferably at least 70 wt.%, based on the total weight of medium (L), copolymer (N-ZW) and polymer (VDF), and/or the amount of medium (L) in composition (CL) is of at most 99 wt.%, preferably at most 97 wt.%, even more preferably at most 95 wt.%, based on the total weight of medium (L), copolymer (N-ZW) and polymer (VDF).
Composition (CL) may optionally comprise at least one further ingredient. Said further ingredient is preferably selected in the group consisting of pore forming agents, nucleating agents, fillers, salts, surfactants.
When used, pore forming agents are typically added to the composition (CL) in amounts usually ranging from 0.1% to 30% by weight, preferably from 0.5% to 20% by weight, based on the total weight of the composition (CL). Suitable pore forming agents are for instance polyvinyl alcohol (PVA), cellulose acetate, polyvinyl-pyrrolidone (PVP) and polyethyleneglycol (PEG).
Porous membranes
According to the present invention, the composition (C) is used in a porous membrane for decreasing the transmembrane pressure (TMP) at constant flux, said porous membrane comprising:
- at least one vinylidene fluoride polymer [polymer (VDF)], and
- at least one copolymer [copolymer (N-ZW)] comprising
(a) recurring units [units (Rzw)] derived from at least one zwitterionic monomer [monomer (A)], and
(b) recurring units [units (RN)] derived from at least one additional monomer [monomer (B)] different from monomer (A), wherein units (Rzw) represent 0.1 to 7 mol %, preferably 0.1 to 5 mol % based on the molar composition of the copolymer (N-ZW), and wherein the molecular weight of the copolymer (N-ZW) measured by gel permeation chromatography (GPC) ranges from 25000 g/mol to 350000 g/mol, and wherein the weight ratio copolymer (N-ZW) /polymer (VDF) is at least 0.1/99.9 and/or is less than 25/75.
SUBSTITUTE SHEET (RULE 26) The expression “porous membrane" is used according to its usual meaning in this technical field, i.e. to denote membrane including pores, i.e. voids or cavities of any shape and size.
As said, the porous membrane used in the present invention is obtainable from the composition (CL) as detailed above and/or can be manufactured using the method as below detailed.
The porous membrane of the invention may be in the form of flat membranes or in the form of tubular membranes.
Flat membranes are generally preferred when high fluxes are required whereas hollow fibers membranes are particularly advantageous in applications wherein compact modules having high surface areas are required.
Flat membranes preferably have a thickness comprised between 10 pm and 200 pm, more preferably between 15 pm and 150 pm.
Tubular membranes typically have an outer diameter greater than 3 mm. Tubular membranes having an outer diameter comprised between 0.5 mm and 3 mm are typically referred to as hollow fibers membranes. Tubular membranes having a diameter of less than 0.5 mm are typically referred to as capillary membranes.
Membranes containing pores homogeneously distributed throughout their thickness are generally known as symmetric (or isotropic) membranes; membranes containing pores which are heterogeneously distributed throughout their thickness are generally known as asymmetric (or anisotropic) membranes.
The porous membrane according to the present invention may be either a symmetric membrane or an asymmetric membrane.
The asymmetric porous membrane typically consists of one or more layers containing pores which are heterogeneously distributed throughout their thickness.
The asymmetric porous membrane typically comprises an outer layer containing pores having an average pore diameter smaller than the average pore diameter of the pores in one or more inner layers.
The porous membrane of the invention preferably has an average pore diameter of at least 0.001 pm, more preferably of at least 0.005 pm, and even more preferably of at least 0.01 pm. The porous membrane of the invention preferably has an average pore diameter of at most 50 pm, more preferably of at most 20 pm and even more preferably of at most 15 pm.
SUBSTITUTE SHEET (RULE 26) Suitable techniques for the determination of the average pore diameter in the porous membranes of the invention are described for instance in the Handbook of Industrial Membrane Technology, edited by PORTER. Mark C. Noyes Publications, 1990. p.70-78.
In the present invention, the porous membrane typically has a gravimetric porosity comprised between 5% and 90%, preferably between 10% and 85% by volume, more preferably between 30% and 90%, based on the total volume of the membrane.
For the purpose of the present invention, the term “gravimetric porosity” is intended to denote the fraction of voids over the total volume of the porous membrane.
Suitable techniques for the determination of the gravimetric porosity in the porous membranes of the invention are described for instance in SMOLDERS K., et al. Terminology for membrane distillation. Desalination. 1989, vol.72, p.249-262.
The porous membrane of the invention may be either a self-standing porous membrane or a porous membrane supported onto a substrate and/or comprising a backing layer.
The porous membrane comprises at least one layer comprising at least one polymer (VDF) and at least one copolymer (N-ZW).
A porous membrane supported onto a substrate is typically obtainable by laminating said substrate and/or backing with a pre-formed porous membrane or by manufacturing the porous membrane directly onto said substrate and/or said backing.
Hence, porous membrane may be composed of one sole layer comprising polymer (VDF) and copolymer (N-ZW) or may comprise additional layers.
In particular, the porous membrane of the invention may further comprise at least one substrate. The substrate may be partially or fully interpenetrated by the porous membrane of the invention.
The nature of the substrate/backing is not particularly limited. The substrate generally consists of materials having a minimal influence on the selectivity of the porous membrane. The substrate layer preferably consists of non-woven materials, polymeric materials such as, for example, polypropylene, glass, glass fibers.
One can also mention the incorporation of tubular braid or threads/fabric reinforcing the substrate layer, such as polyethylene terephthalate (PET) braid,
SUBSTITUTE SHEET (RULE 26) particularly for improving the mechanical properties of polymer (VDF) porous membranes.
In some embodiments, the porous membrane of the invention is a porous composite membrane assembly comprising:
- at least one substrate layer, preferably a non-woven substrate,
- at least one top layer, and
- between said at least one substrate layer and said at least one top layer, at least one layer comprising at least one polymer (VDF) and at least one copolymer (N-ZW).
Typical examples of such porous composite membrane assembly are the so-called Thin Film Composite (TFC) structures which are typically used in reverse osmosis or nanofiltration applications.
Non limiting examples of top layers suitable for use in the porous composite membrane assemblies of the invention include those made of polymers selected from the group consisting of polyamides, polyimides, polyacrylonitriles, polybenzimidazoles, cellulose acetates and polyolefins.
Porous membrane layers comprising polymer (VDF) and copolymer (N- ZW) may additionally comprise one or more than one additional ingredient. Nevertheless, embodiments whereas porous membrane comprises at least one layer consisting essentially of polymer (VDF) and copolymer (N-ZW) are preferred, being understood that additives, and/or residues of pore forming agents may be present, in amounts not exceeding 5 wt.% of the said layer.
In the porous membrane, copolymer (N-ZW) is used as an additive for polymer (VDF), so it is generally understood that polymer (VDF) is present in predominant amount over copolymer (N-ZW). Generally, the weight ratio copolymer (N-ZW)/polymer (VDF) is of at least 0.1/99.9 wt/wt, preferably at least 1/99 wt/wt, more preferably at least 3/97 wt/wt and/or it is less than 50/50 wt/wt, preferably less than 40/60 wt/wt, preferably less than 30/70 wt/wt.
Manufacturing of porous membrane
According to the present invention, the composition (C) is used in a porous membrane for decreasing the transmembrane pressure (TMP) at constant flux.
The porous membrane is generally manufactured by a manufacturing method comprising: step (i): preparing a composition (CL) as defined above; step (ii): processing the composition provided in step (i) thereby providing a film; and,
SUBSTITUTE SHEET (RULE 26) step (iii): processing the film provided in step (ii), generally including contacting the film with a non-solvent medium [medium (NS)], thereby providing a porous membrane.
Under step (i), composition (CL) is manufactured by any conventional techniques. For instance, medium (L) may be added to polymer (VDF) and copolymer (N-ZW), or, preferably, polymer (VDF) and copolymer (N-ZW) are added to medium (L), or even polymer (VDF), copolymer (N-ZW) and medium (L) are simultaneously mixed.
Any suitable mixing equipment may be used. Preferably, the mixing equipment is selected to reduce the amount of air entrapped in composition (CL) which may cause defects in the final membrane. The mixing of polymer (VDF), copolymer (N-ZW) and the medium (L) may be conveniently carried out in a sealed container, optionally held under an inert atmosphere. Inert atmosphere, and more precisely nitrogen atmosphere has been found particularly advantageous for the manufacture of composition (CL).
Under step (i), the mixing time and stirring rate required to obtain a clear homogeneous composition (CL) can vary widely depending upon the rate of dissolution of the components, the temperature, the efficiency of the mixing apparatus, the viscosity of composition (CL) and the like.
Under step (ii) of the manufacturing process, conventional techniques can be used for processing the composition (CL) for providing a film.
The term “film” is used herein to refer to a layer of composition (CL) obtained after processing of the same under step (ii) of the process of the invention. The term “film” is used herein in its usual meaning, that is to say that it refers to a discrete, generally thin, dense layer. Under step (ii), composition (CL) is typically processed by casting thereby providing a film.
Casting generally involves solution casting, wherein typically a casting knife, a draw-down bar or a slot die is used to spread an even film of composition (CL) across a suitable support.
Under step (ii), the temperature at which composition (CL) is processed by casting may be or may be not the same as the temperature at which composition (CL) is mixed under stirring.
Different casting techniques are used depending on the final form of the membrane to be manufactured.
When the final product is a flat membrane, composition (CL) is cast as a film over a flat supporting substrate, typically a plate, a belt or a fabric, or
SUBSTITUTE SHEET (RULE 26) another microporous supporting membrane, typically by means of a casting knife, a draw-down bar or a slot die.
According to a first embodiment of step (ii), composition (CL) is processed by casting onto a flat supporting substrate to provide a flat film.
According to a second embodiment of step (ii), composition (CL) is processed by casting to provide a tubular film.
According to a variant of this second embodiment, the tubular film is manufactured using a spinneret, this technique being otherwise generally referred to as "spinning method". Hollow fibers and capillary membranes may be manufactured according to the spinning method.
The term “spinneret” is hereby understood to mean an annular nozzle comprising at least two concentric capillaries: a first outer capillary for the passage of composition (CL) and a second inner (generally referred to as “lumen”) for the passage of a supporting fluid, also referred to as “bore fluid”.
Figure l is a simplified scheme of the hollow fiber spinning machine (“Effect of spinning conditions on the structure and performance of hydrophobic PVDF hollow fiber membranes for membrane distillation”, Desalination, 287, 326-339 (15 February 2012)) which can be used for manufacturing hollow fiber membranes, wherein 3 is the dope solution tank equipped with a feeding pump 5, 1 is the nitrogen cylinder, 2 is the bore fluid cylinder, 6 is the spinneret or annular die, 7 is the coagulation bath where is depicted the nascent hollow fiber and 8 is the take-up wheel. Dope solution is pushed for the tank to the filter 4 and then pumped with the gear pump 5 through the nozzle 6. Air gap (distance between the nozzle and the coagulation bath) could be varied from 1 to several cm.
Figure 2 is a schematic cut of the spinneret (annular die), through a plane parallel to the fiber extrusion flow, wherein 1 is the bore fluid die, and 2 is the annular die feeding the dope solution.
Figure 3 is a schematic cut of the spinneret (annular die), through a plane perpendicular to the fiber extrusion flow, wherein 1 is the extruded/spinned bore fluid, 2 is the extruded/spinned dope solution, and 3 is the body of the spinner et/annul ar die.
According to this variant of the second embodiment, composition (CL) is generally pumped through the spinneret, together with at least one supporting fluid (so called “bore fluid”). The supporting fluid acts as the support for the casting of the composition (CL) and maintains the bore of the hollow fiber or
SUBSTITUTE SHEET (RULE 26) capillary precursor open. The supporting fluid may be a gas, or, preferably, a non-solvent medium [medium (NS)] or a mixture of the medium (NS) with a medium (L). The selection of the supporting fluid and its temperature depends on the required characteristics of the final membrane as they may have a significant effect on the size and distribution of the pores in the membrane.
Step (iii) generally includes a step of contacting the film provided in step (ii) with a non-solvent medium [medium (NS)] thereby providing a porous membrane.
Such step of contacting with a medium (NS) is generally effective for precipitating and coagulating the composition (CL) constituting the film of step (ii) into a porous membrane.
The film may be precipitated in said medium (NS) by immersion in a medium (NS) bath, which is often referred to as a coagulation bath.
As an alternative (or usually before immersing in a coagulation bath), contacting the film with the medium (NS) can be accomplished by exposing the said film to a gaseous phase comprising vapors of said medium (NS).
Typically, a gaseous phase is prepared e.g. by at least partial saturation with vapors of medium (NS), and the said film is exposed to said gaseous phase. For instance, air possessing a relative humidity of higher than 10 %, generally higher than 50 % (i.e. comprising water vapor) can be used.
Prior to being contacted with the non-solvent medium (by whichever technique as explained above), the film may be exposed during a given residence time to air and/or to a controlled atmosphere, in substantial absence of said medium (NS). Such an additional step may be beneficial for creating a skin on the exposed surface of the film through alternative mechanisms.
For instance, in the spinning method, this may be accomplished by imposing an air-gap in the path that the spinned hollow tubular precursor follows before being driven into a coagulation bath.
According to certain embodiments, in step (iii), coagulation/precipitation of the composition (CL) may be promoted by cooling. In this case, the cooling of the film provided in step (ii) can be typically using any conventional techniques.
Generally, when the coagulation/precipitation is thermally induced, the solvent (S) of medium (L) of composition (CL) is advantageously a “latent” solvent [solvent (LT)], i.e. a solvent which behaves as an active solvent towards polymer (VDF) only when heated above a certain temperature, and which is not able to solubilize the polymer (VDF) below the said temperature.
SUBSTITUTE SHEET (RULE 26) When medium (L) comprises a latent solvent or solvent (LT), step (i) and step (ii) of the manufacturing method are generally carried out at a temperature high enough to maintain composition (CL) as a homogeneous solution.
For instance, under step (ii), according to this embodiment, the film may be typically processed at a temperature comprised between 60°C and 250°C, preferably between 70°C and 220°C, more preferably between 80°C and 200°C, and under step (iii), the film may be typically precipitated by cooling to a temperature below 100°C, preferably below 60°C, more preferably below 40°C.
Cooling may be achieved by contacting the film provided in step (ii) with a cooling fluid, which may be a gaseous fluid (i.e. cooled air or cooled modified atmosphere) or may be a liquid fluid.
In this latter case, it is usual to make use of a medium (NS) as above detailed, so that the phenomena of non solvent-induced and thermally-induced precipitation may simultaneously occur.
It is nevertheless generally understood that even in circumstances where the precipitation is induced thermally, a further step of contacting with a medium (NS) is carried out, e.g. for finalizing precipitation and facilitating removal of medium (L).
In cases where the medium (L) comprises both a solvent (S) and a nonsolvent for polymer (VDF), at least partially selective evaporation of solvent (S) may be used for promoting coagulation/precipitation of polymer (VDF). In this case, solvent (S) and non-solvent components of medium (L) are typically selected so as to ensure solvent (S) having higher volatility than non-solvent, so that progressive evaporation, generally under controlled conditions, of the solvent (S) leads to polymer (VDF) precipitation, and hence actual contact of the film with the medium (NS).
When present in composition (CL), pore forming agents are generally at least partially, if not completely, removed from the porous membrane in the medium (NS), in step (iii) of the method of the invention.
In all these approaches, it is generally understood that the temperature gradient during steps (ii) and (iii), the nature of medium (NS) and medium (L), including the presence of non-solvent in medium (L) are all parameters known to one of ordinary skills in the art for controlling the morphology of the final porous membrane including its average porosity.
SUBSTITUTE SHEET (RULE 26) The manufacturing method may include additional post treatment steps, for instance steps of rinsing and/or stretching the porous membrane and/or a step of drying the same.
For instance, the porous membrane may be additionally rinsed using a liquid medium miscible with the medium (L).
Further, the porous membrane may be advantageously stretched so as to increase its average porosity.
Generally, the porous membrane is dried at a temperature of advantageously at least 30°C.
Drying can be performed under air or a modified atmosphere, e.g. under an inert gas, typically exempt from moisture (water vapor content of less than 0.001% v/v). Drying can alternatively be performed under vacuum.
For the purpose of the present invention, by the term “non-solvent medium [medium (NS)]” it is meant a medium consisting of one or more liquid substances incapable of dissolving the polymer (VDF) of composition (C) or (CL), and which advantageously promotes the coagulation/precipitation of polymer (VDF) from liquid medium of composition (CL).
The medium (NS) typically comprises water and, optionally, at least one organic solvent selected from alcohols or polyalcohols, preferably aliphatic alcohols having a short chain, for example from 1 to 6 carbon atoms, more preferably methanol, ethanol, isopropanol and ethylene glycol.
The medium (NS) is generally selected among those miscible with the medium (L) used for the preparation of composition (CL).
The medium (NS) may further comprise a solvent (S), as above detailed.
More preferably, the medium (NS) consists of water. Water is the most inexpensive non-solvent medium and can be used in large amounts.
Method for decreasing the transmembrane pressure (TMP) at constant flux of a porous membrane
A second aspect of the invention relates a method for decreasing the transmembrane pressure (TMP) at constant flux of a porous membrane comprising at least one vinylidene fluoride (VDF) polymer [polymer (VDF)], in which said porous membrane further comprises at least one copolymer [copolymer (N-ZW)] comprising:
(a) recurring units [units (Rzw)] derived from at least one zwitterionic monomer [monomer (A)], and
SUBSTITUTE SHEET (RULE 26) (b) recurring units [units (RN)] derived from at least one additional monomer [monomer (B)] different from monomer (A), wherein units (Rzw) represent 0.1 to 7 mol %, preferably 0.1 to 5 mol % based on the molar composition of the copolymer (N-ZW), and wherein the molecular weight of the copolymer (N-ZW) measured by gel permeation chromatography ranges from 25000 g/mol to 350000 g/mol, and wherein the weight ratio copolymer (N-ZW) /polymer (VDF) is at least 0.1/99.9 and/or is less than 25/75.
Thus, as this is the case for the first aspect of the invention relating to the use of the composition (C) in porous membrane, in this method, the composition (C) comprising at least one vinylidene fluoride (VDF) polymer [polymer (VDF)], and at least one copolymer [copolymer (N-ZW)] as detailed above is present.
All features above described in connection with the use of the composition (C) for decreasing the transmembrane pressure (TMP) at constant flux of the invention and with the porous membrane are applicable in connection to this method hereby described.
Separation of an aqueous medium
The porous membrane comprising composition (C) that makes it possible to decrease the transmembrane pressure (TMP) at constant flux can be used for separating an aqueous medium, by contacting said aqueous medium with the porous membrane as described above.
All features above described in connection with the porous membrane are applicable here.
According to certain embodiments, the aqueous phase may be notably a water-based phase comprising one or more contaminants.
The aqueous phase may be a particulate suspension of contaminants, i.e. a suspension comprising chemical or physical pollutants (e.g. inorganic particles such as sand, grit, metal particles, ceramics; organic solids, such as polymers, paper fibers, plants’ and animals’ residues; biological pollutants such as bacteria, viruses, protozoa, parasites).
Otherwise, this may be notably a method for filtrating water suspensions from suspended particulates; in this case, the used porous membrane generally possesses an average pore diameter of from 5 pm to 50 pm.
Should the disclosure of any patents, patent applications, andpublications which are incorporated herein by reference conflict with the description of the
SUBSTITUTE SHEET (RULE 26) present application to the extent that it may render a term unclear, the present description shall take precedence.
The invention will now be described in connection with the following examples, whose scope is merely illustrative and not intended to limit the scope of the invention.
Experimental
Raw Materials
PVDF Solef® 1015 provided by Solvay Specialty Polymers was used as VDF homopolymer.
The following solvents reactants and solvents were obtained from Sigma Aldrich and used as received: 2,2'-Azobis(2-methylbutyronitrile) (AMBN), Azobisisobutyronitrile (AIBN), methyl methacrylate (MMA), 3-((2- (methacryloyloxy)ethyl)dimethylammonio)propane-l -sulfonate also named N,N- Dimethyl- N-(2-methacryloyloxyethyl)-N-(3-sulfopropyl) ammonium betaine (SPE), dimethylsulfoxide (DMSO), N,N-dimethylacetamide (DMAc), N-methyl- 2-pyrrolidone (NMP), Polyethylene glycol 100 (PEG 100), Polyethylene glycol 200 (PEG 200), Polyethylene glycol 400 (PEG 400), Ethylene Glycol (EG), Polyvinylpyrrolidone (PVP) K 30 and isopropyl alcohol (IP A).
Example 1: Synthesis of poly(MMA-stat-SPE) 95/5 mol/mol (MW = 161000 g/mol) - Pl
A 2 1 jacketed reactor with a five-necked kettle head was set with an overhead teflon pitch blade stirrer in the center port. The second port was used for the addition of chemicals. The third port was connected to a nitrogen inlet, while the fourth port was used to connect the double walled condenser. The fifth port was fixed with a temperature probe.
Methyl methacrylate (MMA) monomer (156.94 g) dissolved in 400 ml DMSO, was added into the reactor by transfer funnel. The quantity of MMA that adhered to the weighing container was transferred by additional 100 ml DMSO. Then, the N,N-Dimethyl- N-(2 -methacryloyl oxy ethyl)-N-(3 -sulfopropyl) ammonium betaine (SPE) monomer (23.052 g) dissolved in a mixture of 50 ml of water and 200 ml of dimethyl sulfoxide (DMSO) (under sonication), was added to the methyl methacrylate (MMA) solution in the reactor under constant stirring. The remaining quantity that adhered to the weighing container was transferred to the reactor by rinsing with 81 ml DMSO. The reaction mixture was stirred using the overhead stirrer (maintained at 250 rpm) and N2 gas was purged
SUBSTITUTE SHEET (RULE 26) for 1 h to remove dissolved oxygen in the solution. Simultaneously, the temperature of the solution (measured via the temperature probe) was increased from room temperature to 70 °C. Once the temperature of the solution reached 70 °C, initiator AIBN (1.084 g) was added to the reaction mixture by dissolving it in 19 ml DMSO. Nitrogen purging was continued for another 15 minutes after which the nitrogen purger was kept above the solution level. Addition of the initiator was considered as starting of polymerization and the reaction was continued for further 12 h. Kinetics of the polymerization was monitored by drawing out samples at every one hour interval and taking
Figure imgf000041_0001
NMR spectra of the collected aliquots in DMSO-d6. Final conversion of the monomers was calculated from
Figure imgf000041_0002
spectrum and molecular weight was measured via GPC (DMF as solvent). Gel permeation chromatography (GPC) was performed at 40°C using a Jasco PU-2080 Plus HPLC pump equipped with 2 SHODEX KD- 804 columns and a Jasco Refractive index-4030 detector. The mobile phase was composed of 1.5 % LiBr in DMF and the flow rate was 1.0 ml/min. 100 pl samples (concentration of approximatively 5.0 mg/ml) were injected, calibration was obtained with PMMA narrow standards.
After the polymerization the reaction mass was collected in a beaker and kept in the refrigerator overnight.
In this case, to purify the polymer, crude was precipitated in 6.5 1 of water/isopropanol 90: 10 v/v mixture under constant stirring (overhead fitted with half-moon stirrer blade) with the help of a peristaltic pump (feed rate of 10 ml/min). After the precipitation, the stirring continued for an additional 2 h. Subsequently, the precipitate was filtered using a Buchner funnel, under vacuum. The precipitate was then dried at 60°C under vacuum for 3 days.
The obtained precipitate exhibited a DMSO content of 12% (data obtained from GC-FID) after drying. The solid polymer was further crushed using a mortar and pestle and was redispersed in 1.5 1 of water/isopropanol 90: 10 v / v mixture and stirred for 2 h. The solid was filtered using a Buchner funnel and dried at 60 °C under vacuum for 3 days. This process was repeated again to completely remove DMSO from the polymer.
After the polymerization, a sample was taken for 'H NMR analysis to determine the MMA and SPE conversions.
The results were the following: MMA monomer conversion was equal to 93 %, SPE monomer conversion was equal to 94 % and molecular weight was of MWPI = 161000 g/mol.
SUBSTITUTE SHEET (RULE 26) Example 2: Synthesis of poly(MMA-stat-SPE) 95/5 mol/mol (MW = 131000 g/mol) - P2
In a stainless steel tank with a capacity of 250 1 were introduced, at room temperature (22°C), 81.0 kg of dimethyl sulfoxide (DMSO, at 99% purity), followed by the successive addition of 17.0 kg of methyl methacrylate (MMA) and a solution of 3-((2-(methacryloyloxy)ethyl)dimethylammonio)propane-l- sulfonate (SPE) in water (dissolution of 2.5 kg of SPE in 4.0 kg of water). The reaction mixture was de-oxygenated by nitrogen bubbling (flow: 10 1/h) for 1 hour. After 1 hour of bubbling, the reaction mixture was heated to 70°C and a solution of AMBN initiator in DMSO (137.5 g of AMBN in 1.8 kg of DMSO) was introduced.
The reaction was monitored by HPLC (High-performance liquid chromatography) for 10 hours to observe the conversion of MMA and SPE.
High-performance liquid chromatography was performed at 35°C using a HPLC 1290 Infinity F30 equipped with Poroshell 120 columns. The mobile phase was composed of H2O + H3PO4 0.05% (v/v) and ACN (acetonitrile) and the flow rate was 2.0 ml/min. 5 pl samples were injected, calibration was obtained with PMMA narrow standards.
The results were the following: MMA monomer conversion was equal to 96.1%; SPE monomer conversion was equal to 94.3% and molecular weight was of MWP2 = 130000 g/mol.
The reaction mixture was then diluted with 81.2 kg of DMSO, to obtain a solution of polymer in DMSO at 10%. After cooling down to room temperature, 197.5 kg of polymer solution was recovered in steel drums.
From the previous solution of polymer, the co-polymer MMA/SPE 95/5 was recovered by precipitation. An amount of 34.4 kg of polymer solution was used for this precipitation. The solution of polymer was added to a heel of water at 50°C. The introduction of polymer solution was performed using a pump over about 3 hours for a global flow rate of 174 g/min. Filtration, washes and drying were performed on Cogeim (S13000) with a surface of filtration of 0.24 m2. The slurry was filtered under 1.0 bar of nitrogen at 50°C and with 250 mbar of vacuum under the filter to recover 177.8 kg of a clear filtrate. Five successive washes with a water were done at 70°C. The five washes allow to remove the DMSO and to reach a level of DMSO residual of 300 ppm. Then, drying of the polymer was performed at 80°C for 18 hours under 10 mbar. 3.1 kg of the final white powder were recovered.
SUBSTITUTE SHEET (RULE 26) The washing step and the removal of DMSO were followed by GC (gas chromatography). Gas chromatography was performed using HP6890 Series (CPG 1) F28 equipped with DB-5MS columns, a FID detector, and with helium as gas vector. The flow rate was 1.0 mL/min. 1 pl samples were injected.
General method for preparing dope solutions (for fiber spinning)
To prepare the dope solutions, the opportune amount of PVDF, pore forming agents (PVP K30/PEG400/EG) and eventually zwitterionic additive were added in a glass tank of DMAC (equipped with a mechanical anchor) and stirred at approximately 65°C. Dope solution quantity was 2 liters. The stirring lasted for several hours at 65°C. Then solutions were left at rest at 65°C for some hours to remove eventual air bubbles. Dope solutions were always homogeneous, transparent and stable for several days at temperatures equal or higher than 40°C.
Method for preparing hollow fibers membranes containing zwitterionic additive
Membranes were spun from dope solutions containing blends of PVDF Solef® 1015 and of the synthesized zwitterionic p(MMA-s-SPE) copolymers in N,N-dimethylacetamide (DMAc) and immersed in a coagulation bath in order to induce phase separation (NIPS for non-solvent induced phase separation).
Thus, polymeric hollow fibers were manufactured by extruding the dope solutions, as detailed in figures 1 to 3, through an annular aperture. Hollow fibers were prevented from collapsing by coextruding water as bore fluid in the center of the annulus. The coagulation water bath enabled producing coagulation by phase inversion. Take up wheel allowed the collection of the fiber. Dope and spinneret temperatures were maintained at 70°C for the formulation Reference Solef® 1015 and 40°C for the formulation with zwitterionic additive in order to match the viscosities. All the other conditions were the same as illustrated in Table 1 below. The spinneret geometry used in the extrusion part had an internal diameter (ID) of 700 pm, an external one of 1300 pm (OD).
The formulation prepared as reference had 18% wt/wt of Solef® 1015. The formulations (referred as Fl or F2) according to the invention had 16,2% wt/wt of Solef® 1015 and 1,8% of zwitterionic additive (referred as sample Pl or P2 respectively), in order to have a ratio of 90/10 PVDF/zwitterionic additive).
SUBSTITUTE SHEET (RULE 26)
Figure imgf000044_0002
Table 1 : Main process conditions of the spinning trials.
Characterization of the hollow fiber membranes Rejection of foulants
The selectivity of a membrane for a given substance is generally defined by the rejection rate R (also inversely called retention rate) and depends on its nature and structure, the chemical environment near the membrane and the properties of the substance to be separated. Rejection rate is defined as below: 100,
Figure imgf000044_0001
wherein Cpermeate corresponds to the concentration of the substance in the permeate and Cretentate corresponds to the concentration of the same substance in the retentate. A rejection rate of 100% means that the solute is perfectly retained by the membrane whereas a rejection rate of 0 corresponds to a solute not at all retained by the membrane.
To determine rejection in the present invention, foulant solution is filtered through the hollow-fiber membrane in total recirculating mode: both retentate
SUBSTITUTE SHEET (RULE 26) and permeate are recirculated in the feed tank. After 30 minutes of filtration, samples are withdrawn at permeate and retentate outlets.
Concentrations are measured by TOC (total organic carbon) in permeate and retentate samples with a Shimadzu TOC-L.
Viscosity measurements
Rotational steady state shear measurements were performed at temperatures of interest using a Rheometric Scientific “RFS III” rheogoniometer in the concentric cylinder configuration (Couette). Flow curves were obtained with a sweep performed from the lowest attainable shear rate (0.02 s'1) to the highest defined by the maximum torque that the instrument can reach. In all the considered cases, a quite large Newtonian range was observed. Viscosity values in the text represent the Newtonian plateau of the flow curves and are expressed in cpoises (cP).
Pore size measurements
Procedure is based on the same principles of the air-liquid porometry described above, both methods using the correlation between the applied pressure and the pore radio open to flux as given by Washbum equation. The pore size distribution is tested with liquid-liquid displacement porometer (LLDP) (model PRM-8710®) which consists of an automated pressure constant device suitable for gas/liquid and liquid/liquid tests. The device is configured for testing pore sizes down to 4 nm and uses relatively low pressures (maximum 10 bars) for the characterization of porous membranes in the high MF/UF-NF range. The equipment allows for implementing very stable pressure and leads to very accurate measurement of resulting fluxes by using an analytical balance (Sartorius® Practum, accuracy of 10 mg).
The pore size distribution test is performed according to the capillary principle, the media are previously wet in a liquid (wetting phase): by increasing the pressure of wetting liquid upstream to the membrane at a predetermined rate, the first droplets downstream are observed to indicate the passage of displacement liquid through the maximum diameter hollow fiber pores. Both wetting and displacement liquids are immiscible between them. In case of these measurements, a very stable and immiscible 5/3.5/1.5 (v/v) ternary mixture composed by water/isobutanol/isopropanol (y = 0.75 mN/m) was used. All liquids were of reagent grade and used as received without further purification
SUBSTITUTE SHEET (RULE 26) (Sigma- Aldrich®: Purity > 98.5 %). For these measurements, organic phase (lighter phase) has been used as a wetting liquid during 30 minutes at 150 mbar of inlet pressure and aqueous phase (heavier phase) as displacement ones. The temperature was kept constant at 22 °C (± 0.1 °C).
Results
In this first set of samples, the zwitterionic additive prepared in Example 1 (Pl) is used. Fibers are in the range of large pore ultrafiltration membranes.
For these samples, permeability of fibers (flux/pressure) was measured by using the Convergence Inspector tool (from Convergence Industry B. V - Enschede-The Netherlands) and working again in cross-flow mode. Modules of 5 fibers with a length of 27 cm each (typical surfaces 50 cm2) were tested in Out- In configuration, with a feed throughput equal to 2 1/h, a transmembrane pressure equal to 0.5 bar was applied and flux through the membrane was monitored. An out-in mode means the separation layer is on the outside surface of the fiber and the feed water flows outside the fibers.
With this automated system permeate flow and retentate flow can be directly measured and collected.
Table 2 sets out the rejection rate of BSA (bovine serum albumin) solution permeability data of the hollow fiber membranes on the samples without zwitterionic additive, Ref. Solef® 1015, and with zwitterionic additive Pl and this illustrates the difference between membranes comprising or not the zwitterionic additive.
Figure imgf000046_0001
Table 2: Rejection rate and permeability of samples Ref. Solef® 1015 (without additive), and Fl (with additive Pl) - Permeability (flux/pressure) measured at 0,5 bar in cross flow configuration
SUBSTITUTE SHEET (RULE 26) In this table 2, it is clearly demonstrated that the use of the zwitterionic additive Pl in membranes according to the invention makes it possible to obtain a much better permeability compared to membranes without any additive, in out- in configuration. At the same time, a higher rejection to BSA is obtained for the membrane Fl with the zwitterionic additive (Pl), according to the invention.
In this second set of samples, the zwitterionic additive prepared in Example 2 (P2) is used. Fibers are in the range of small pore ultrafiltration membranes. The conditions for preparing hollow fibers membrane in this case are the same as those mentioned in Table 1, except that the formulation is in pure water and the dope temperature is 40°C.
For these samples, permeability measurement consists of imposing a constant pressure upstream the membrane fibers surface (module of 220 fibers, typical surfaces 1866 cm2, out-in configuration, dead-end filtration) and increasing progressively the inlet pressure by recording the permeate water flow. As the outlet pressure is at the atmospheric pressure, the outlet pressure is considered equal to 0 and inlet pressure equivalent to the differential pressure to be applied. Time was fixed every 30 seconds for each inlet pressure constant step and test was carried out by dead-end filtration. Hydraulic water permeability is calculated by adjusting data points to linear relationship through permeate flow (Q) in mg/s versus differential pressure from 300 mbar to 1300 mbar.
Table 3 sets out the rejection rate of BSA and permeability data of the hollow fiber membranes without zwitterionic additive, Ref. Solef® 1015, and with zwitterionic additive, P2 and this illustrates the difference between membranes comprising or not the zwitterionic additive.
Figure imgf000047_0001
Table 3: Rejection rate and permeability of samples Ref. Solef® 1015 (without additive) and F2 (with zwitterionic additive P2)
SUBSTITUTE SHEET (RULE 26) In this table, it is clearly demonstrated that the use of the zwitterionic additive P2 in membranes according to the invention makes it possible to obtain a much better permeability compared to membranes without any additive, in out- in configuration.
Fouling tests method description
Fouling tests with hollow-fiber membrane Fl
Fouling tests were performed using the Poseidon module (Convergence industry B.V). The module is managed by computer and a specific software Osmo inspector software v6.2.0.2.
Fouling tests were performed at room temperature (22-24 °C) in out/in mode with straight hollow-fiber membranes of 50 cm2. Feed was circulating at 5 1/h. Permeate was recirculated in the feed tank in order to keep constant feed concentration. The filtration was performed at a constant flow rate of 0.1 1/h (20 LMH) regulated by Coriolis mass flowmeter. Transmembrane pressure was monitored to evaluate permeability and fouling. When transmembrane pressure reached 400 mbar, backwash was performed. Procedure for backwash was: 30 seconds of relaxation, 2 minutes of backwash at 0.15 1/h (30 LMH) with distilled water, 30 seconds of relaxation. Fouling tests lasted 24h to have several filtration and backwash cycles.
Different foulants were used: PEG 100 kDa at 1 g/1, PEG 200 kDa at 1 g/1, PEG 400 kDa at 1 g/1 and sludge from wastewater treatment plant at 2 g/1 (Biological sludge at 2 g/1 of TSS (total suspended solids) from an aeration pond of a municipal wastewater treatment plant (Ecostation, Saint-Fons, France)).
Two types of membrane were tested during fouling test:
The first one was straight hollow-fiber membranes (5 fibers, with surface 50 cm2), with reference Solef® 1015 (Ref. Solef® 1015), as described above.
The second one was straight hollow-fiber membranes (5 fibers, with surface 50 cm2) with Pl as detailed above, according to the invention.
Results of fouling tests for membrane Fl
Table 4 below shows the results of fouling tests. The rejection of foulants with different foulants was measured before pressure reached the limit of 400 mbar and the required number of backwash (BW) per 24h was measured when the transmembrane pressure reached the limit of 400 mbar.
SUBSTITUTE SHEET (RULE 26)
Figure imgf000049_0001
Table 4: Rejection of foulants and required number of BW per 24h with the different foulants for samples Ref. Solef® 1015 (without additive) and Fl (with zwitterionic additive Pl).
For all foulants, rejections were slightly higher with hollow fibers membranes Fl with the zwitterionic additive (Pl), according to the invention, compared to the reference membrane. In addition, for all foulants, the number of required backwashes per 24h is lower for membranes Pl with the zwitterionic additive, according to the invention, compared to the reference membrane. This underlines the fact that the transmembrane pressure decreases with the use of the composition (C) comprising the zwitterionic additive Pl in the membrane, and in particular that the upper limit of 400 mbar for the transmembrane pressure is reached less quickly. These results highlight the better resistance to fouling of modified PVDF.
Fouling tests with hollow-fiber membrane F2
Fouling tests were performed at temperatures around 16-20°C in out/in mode with straight hollow-fiber modules of 220 fibers with a surface of 1866 cm2. The filtration was performed at a constant flux of 10 1/h (53.6 LMH). Transmembrane pressure was monitored to evaluate permeability and fouling. When transmembrane pressure reached 800 mbar, backwash was performed. The continuous filtration test was performed during 4 weeks.
Procedure for backwash cycles was: water backwash of 5 minutes at 14 1/h and chemical backwash of 8 minutes with NaOCl (around 250 ppm) at 14 1/h, with a frequency of 6 water backwashes for 1 chemical backwash.
SUBSTITUTE SHEET (RULE 26) Modules have been fed with two types of water: drinking water and diluted sewage water coming through the output wastewater treatment plant (Rouquet Agent, France). The sewage water was mixed with drinking water in order to have good fouling conditions for the membrane tested. The mixing ratio is 80% drinking water and 20% treated water.
Two types of membrane modules were tested during this fouling test:
The first one was straight hollow-fiber membranes (220 fibers with surface of 1866 cm2), with reference Solef® 1015 (Ref. Solef® 1015), as described above.
The second one was straight hollow-fiber membranes F2 (220 fibers with surface of 1866 cm2) with P2, as detailed above, according to the invention.
Results of fouling tests for membrane F2
The evolution of transmembrane pressure (TMP) at constant flux over time was followed during the 4 weeks. The Figure 4 represents the TMP evolution versus time for 3 days during the first testing week. The Figure 5 represents for its parts the TMP evolution versus time for 3 days during the last testing week (fourth week of test). One can see that the transmembrane pressure increases due to membrane fouling which requires to proceed to backwash cycles as detailed above. It is clearly demonstrated that the required number of physical and chemical washes is much less with the membrane F2 with the zwitterionic additive (P) (composition (C)). In addition, it is also observed that the transmembrane pressure decreases more strongly after cleaning cycle (repeating sequence of 6 pure water backwash and 1 chemical backwash) for the membrane F2 with the zwitterionic additive (P2), getting much closer to the value of the initial transmembrane pressure, compared to reference membrane Solef® 1015. This illustrates a better transmembrane flux recovery after repeated backwash cycles. In particular, it can be observed that the gap widens after a month. It becomes more and more difficult to recover a transmembrane pressure close to that initial for the reference membrane after repeated washing cycles.
Table 5 below also shows the results of fouling tests after 4 weeks run on diluted sewage water and on drinking water.
SUBSTITUTE SHEET (RULE 26)
Figure imgf000051_0001
Table 5: Number of physical and chemical backwashes after 4 weeks run for samples Ref. Solef® 1015 (without additive) and F2 (with zwitterionic additive P2).
It is clearly demonstrated in Table 5, that after 4 weeks, the hollow-fiber membranes comprising P2 according to the invention shows a less frequent need of backwashes, whether for physical backwashes with water or for chemical backwashes with NaOCl for the filtration of diluted sewage water and also of drinking water. In particular, for the filtration of diluted sewage water, the difference in the number of backwashes reaches 28% less for the module F2. It is also possible to see the evolution over time of this difference in frequency of backwashes in Figure 6 for the filtration of diluted sewage water, that represents the number of physical backwashes versus time. Similarly, the required number of chemical washes is much lower using the membrane according to the invention.
It is the same with the filtration of drinking water with a reduction of 40% of backwashes frequency after 4 weeks, even if obviously in this case the phenomenon of fouling is much less present.
All of these results demonstrate that the membrane F2 with zwitterionic additive, according to the invention, clogs less than the reference membrane (Ref. Solef® 1015) and therefore presents a lower propensity to fouling.
The decrease in transmembrane pressure at constant flux over time is also illustrated in Figure 7 that represents the transmembrane pressure after chemical cleaning as a function of time. It is clearly demonstrated that the transmembrane
SUBSTITUTE SHEET (RULE 26) pressure decreases more strongly after chemical backwash for the membrane F2, getting much closer to the value of the initial transmembrane pressure, compared to reference membrane Solef® 1015. Thus, the membrane F2 (with zwitterionic additive P2) according to the invention recovers better compared to the reference membrane (Solef® 1015) and therefore is easier to wash. This is a striking increase in flux recovery after chemical cleaning phases.
Aging test for module F2
A procedure for accelerated aging test was performed on the reference module (Ref. Solef® 1015) and on the module F2 with zwitteionic additive (P2) according to the invention. For this test, the filtration was performed during 10 minutes with drinking water at a constant flow rate of 10 1/h (53.6 LMH) in out- in mode (dead-end configuration). Then, during 5 minutes, a chemical backwash was carried out with NaOCl at 2000 ppm at a constant flow rate of 14 1/h in in- out mode. This aging test was continued for 1 week (24/24h).
This is equivalent to around 3350 chemical backwashes as described above for the fouling tests.
Pore size before and after aging test was measured using liquid-liquid porosimeter.
The results are presented in table 6 below.
Figure imgf000052_0001
Table 6: Effects of aging test on water permeability and larger pore size for samples Ref. Solef® 1015 (without additive) and F2 (with zwitterionic additive P2)
SUBSTITUTE SHEET (RULE 26) It is clearly shown in this Table 6 that, after the accelerated aging test, the impact of the same chemical treatments for the same duration on the permeability properties and on the modification of maximal larger pore size is much less significant for the membrane F2 with zwitterionic additive (P2) according to the invention. Indeed, the initial membrane permeability for this membrane F2 is increased up until 21 %, contrary to the reference membrane (Ref. Solef® 1015) for which, the increase of the permeability is much higher 77%. The same is true for the maximal larger pore size with a lower impact of the aging test on the membrane F2 according to the invention. The high increase of permeability of reference membrane (Ref. Solef® 1015) after the aging test is due to the increase of pore size and therefore to a degradation of membrane property and performances.
Therefore, fouling tests demonstrate superior performances of membranes with a zwitterionic additive according to the invention regardless of fiber selectivity, water feed and tests conditions. In particular, long lasting tests show higher permeability and lower fouling propensity which was evident by the lower cleaning frequency (physical and chemical backwashes). These results translate into an overall reduction of energy consumption and of chemicals for cleaning during filtration operation, due to decreasing transmembrane pressure (TMP) at constant flux of porous membrane comprising the composition (C) as claimed in the present invention. Moreover, both lower cleaning frequency and higher chemical resistance suggest longer life expectancy for membranes with the zwitterionic additive as claimed in the present invention.
All these results position this invention as a much more sustainable solution, especially for waste water filtration companies.
Indeed, it has been shown by using the composition (C) comprising a zwitterionic copolymer, a much better resistance over time of polymer (VDF) membrane filtration properties (particles selectivity, resistance to various foulants, mechanical and chemical resistance. . .), in particular after repeated washing cycles (both physical backwash, and chemical cleanings), instead of traditional membranes made from vinylidene fluorine polymers [polymer (VDF)] for which properties are being progressively altered due to repeated cleaning maintenance cycles, both because of progressive permanent obstruction of the membranes pores and of the degradation of membrane mechanical resistance consecutive to aggressive chemical cleaning conditions. These long-lasting
SUBSTITUTE SHEET (RULE 26) performances of the membranes can position them as a very attractive solution for willing to install high flux filtration systems, able to deal with high solid contents liquid influx, where lower cleaning maintenance is needed, and with an extended lifetime of the overall device. Such invention therefore also allows membrane users to lower their specific energy consumption (due to lower pressure needed for the same filtration rate)
SUBSTITUTE SHEET (RULE 26)

Claims

- 55 -
C L A I M S
1- Use of a composition [composition (C)] in a porous membrane for decreasing transmembrane pressure (TMP) at constant flux of said membrane, wherein the porous membrane comprises the composition (C) comprising:
- at least one vinylidene fluoride (VDF) polymer [polymer (VDF)], and
- at least one copolymer [copolymer (N-ZW)] comprising
(a) recurring units [units (Rzw)] derived from at least one zwitterionic monomer [monomer (A)], and
(b) recurring units [units (RN)] derived from at least one additional monomer [monomer (B)], different from monomer (A), wherein units (Rzw) represent 0.1 to 7 mol %, preferably 0.1 to 5 mol % based on the molar composition of the copolymer (N-ZW), and wherein the molecular weight of the copolymer (N-ZW) measured by gel permeation chromatography ranges from 25,000 g/mol to 350,000 g/mol, and wherein the weight ratio polymer (N-ZW) /polymer (VDF) is at least 0.1/99.9 and/or is less than 25/75.
2- The use according to claim 1, wherein polymer (VDF) is selected among poly addition polymers comprising units derived from VDF and, optionally, units derived from at least one ethylenically unsaturated monomer comprising fluorine atom(s) different from VDF, which is generally selected from the group consisting of:
(a) C2-C8 perfluoroolefms such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoroisobutylene;
(b) hydrogen-containing C2-C8 fluoroolefms different from VDF, such as vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutylene (HFIB), perfluoroalkyl ethylenes of formula CH2=CH-Rfi, wherein Ru is a Ci-Ce perfluoroalkyl group; - 56 -
(c) C2-C8 chloro- and/or bromo-containing fluoroolefins such as chlorotrifluoroethylene (CTFE);
(d) perfluoroalkylvinylethers (PAVE) of formula CF2=CFORn, wherein Rfi is a Ci-Ce perfluoroalkyl group, such as CF3 (PMVE), C2F5 or C3F7;
(e) perfluorooxyalkylvinylethers of formula CF2=CFOXQ, wherein Xo is a a C1-C12 perfluorooxyalkyl group comprising one or more than one ethereal oxygen atom, including notably perfluoromethoxyalkylvinylethers of formula CF2=CFOCF2ORf2, with Rf2 being a C1-C3 perfluoro(oxy)alkyl group, such as - CF2CF3, -CF2CF2-O-CF3 and -CF3; and
(f) (per)fluorodioxoles of formula:
Figure imgf000056_0001
wherein each of Rf3, Rf4, Rfs and Rf6, equal to or different from each other, is independently a fluorine atom, a Ci-Ce perfluoro(oxy)alkyl group, optionally comprising one or more oxygen atoms, such as -CF3, -C2F5, -C3F7, -OCF3 or - OCF2CF2OCF3.
3- The use according to claim 2, wherein polymer (VDF) is a polymer comprising :
(a’) at least 60 % by moles, preferably at least 75 % by moles, more preferably 85 % by moles of units derived from vinylidene fluoride (VDF);
(b’) optionally from 0.1 to 30%, preferably from 0.1 to 20%, more preferably from 0.1 to 15%, by moles of units derived from a fluorinated monomer different from VDF; and
(c’) optionally from 0.1 to 10 %, by moles, preferably 0.1 to 5 % by moles, more preferably 0.1 to 1% by moles of units derived from one or more hydrogenated monomer(s), - 57 - all the aforementioned % by moles being referred to the total moles of units of the polymer (VDF).
4- The use according to any one of the preceding claims, wherein units (Rzw) are derived from at least one monomer (A) selected from the list consisting of a) alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl acrylates or methacrylates, acrylamido or methacrylamido, typically
- sulfopropyldimethylammonioethyl (meth)acrylate,
- sulfoethyldimethylammonioethyl (meth)acrylate,
- sulfobutyldimethylammonioethyl (meth)acrylate,
- sulfohydroxypropyldimethylammonioethyl (meth)acrylate,
- sulfopropyl dimethyl ammoni opropy 1 aery 1 ami de,
- sulfopropyldimethylammoniopropylmethacrylamide,
- sulfohydroxypropyldimethylammoniopropyl(meth)acrylamide,
- sulfopropyldiethylammonio ethoxyethyl methacrylate. b) heterocyclic betaine monomers, typically
- sulfobetaines derived from piperazine,
- sulfobetaines derived from 2-vinylpyridine and 4-vinylpyridine, more typically 2- vinyl-l-(3-sulfopropyl)pyridinium betaine or 4-vinyl-l-(3- sulfopropyl)pyridinium betaine,
- 1 -vinyl-3 -(3 -sulfopropyl)imidazolium betaine; c) alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl allylics, typically sulfopropylmethyldiallylammonium betaine; d) alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl styrenes; - 58 - e) betaines resulting from ethylenically unsaturated anhydrides and dienes; f) phosphobetaines of formulae
Figure imgf000058_0001
; and g) betaines resulting from cyclic acetals, typically ((dicyanoethanolate)ethoxy)dimethylammoniopropylmethacrylamide.
5- The use according to any one of the preceding claims, wherein units (RN) are derived from at least one monomer deprived of ionisable groups.
6- The use according to claim 5, wherein units (RN) are derived
- from at least one monomer selected from the list consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl methacrylate, vinyl acetate and N,N-dimethylacrylamide [units (RN-I)];
- from at least one monomer selected from the list consisting of 2- hydroxy ethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2- hydroxyethyl acrylate (HEA), hydroxypropyl acrylate, 4-hydroxybutyl acrylate, polyethylene glycol) methacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (mPEGMA), poly(ethylene glycol) ethyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate and poly(ethylene glycol) ethyl ether acrylate [units (RN-2)];
- from at least one monomer selected from the list consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, vinyl acetate and N,N-dimethylacrylamide [units (RN-I)] and from at least one additional monomer selected from the list consisting of 2- hydroxy ethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2- hydroxyethyl acrylate (HEA), hydroxypropyl acrylate, 4-hydroxybutyl acrylate, polyethylene glycol) methacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (mPEGMA), poly(ethylene glycol) ethyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate and poly(ethylene glycol) ethyl ether acrylate [units (RN-2)].
7- The use according to any one of the preceding claims, wherein polymer (N-ZW) comprises 80 % or more by moles, preferably 90 % or more by moles of units (RN), with respect to the total moles of recurring units of polymer (N-ZW).
8- The use according to any one of claim 6 or 7, wherein polymer (N-ZW) comprises recurring units (RN-I) and comprises from 0.1 to 50 % by moles, preferably from 0.1 to 40 % by moles, more preferably from 0.1 to 30% by moles and even more preferably from 0.1 to 20 % by moles of recurring units (Rzw) and (RN-2), with respect to the total moles of recurring units of polymer (N-ZW).
9- The use according to any one of claims 5 to 7, wherein units (RN) are composed of units (RN-I).
10- The use according to any one of the preceding claims, wherein polymer (N-ZW) is a statistical copolymer.
11- The use according to any one of the preceding claims, wherein the composition (C) further comprises at least one liquid medium [medium (L)] comprising at least one organic solvent [composition (CL)].
12- The use according to claim 11, wherein composition (CL) comprises an overall amount of polymer (N-ZW) and polymer (VDF) of at least 1 wt.%, more preferably of at least 3 wt.%, even more preferably of at least 5 wt.%, based on the total weight of medium (L), polymer (N-ZW) and polymer (VDF), and/or composition (CL) preferably comprises an overall amount of polymer (N- ZW) and polymer (VDF) of at most 60 wt.%, more preferably of at most 50 wt.%, even more preferably at most 30 wt.%, based on the total weight of medium (L), polymer (N-ZW) and polymer (VDF) and/or composition (CL). 13- A method for decreasing transmembrane pressure (TMP) at constant flux of a porous membrane comprising at least one vinylidene fluoride (VDF) polymer [polymer (VDF)], in which said porous membrane further comprises at least one copolymer [copolymer (N-ZW)] comprising: (a) recurring units [units (Rzw)] derived from at least one zwitterionic monomer [monomer (A)], and
(b) recurring units [units (RN)] derived from at least one additional monomer [monomer (B)] different from monomer (A), wherein units (Rzw) represent 0.1 to 7 mol %, preferably 0.1 to 5 mol % based on the molar composition of the copolymer (N-ZW), and wherein the molecular weight of the copolymer (N-ZW) measured by gel permeation chromatography ranges from 25000 g/mol to 350000 g/mol, and wherein the weight ratio copolymer (N-ZW) /polymer (VDF) is at least 0.1/99.9 and/or is less than 25/75.
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