POROUS MEMBRANES FOR HIGH PRESSURE FILTRATION

Abstract

The present invention relates to a porous membrane suitable for use in high pressure filtration method.

Claims

1.-15. (canceled)

16. A method for purifying a fluid containing at least one contaminant, said method comprising the steps of (i) providing a fluid containing at least one contaminant; (ii) providing a membrane [membrane (PP)] comprising at least one porous layer [layer (PP)] comprising at least one polyphenylene polymer [polymer (PP)]; (iii) contacting said fluid containing at least one contaminant and said membrane (PP) by applying a pressure higher than 1 bar to said fluid; and (iv) recovering the fluid free from said at least one contaminant.

17. The method according to claim 16, wherein said membrane (PP) comprises said layer (PP) as the only layer or said membrane (PP) is a multi-layered membrane.

18. The method according to claim 16, wherein said polymer (PP) comprises at least about 10 mole percent (per 100 moles of polymer (PP)) of repeating units (R.sub.pm) represented by the following formula: ##STR00008## and at least about 10 mol percent repeat units (R.sub.pp) represented by the following formula: ##STR00009## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4 R.sup.5, R.sup.6, R.sup.1, and R.sup.8 are each independently selected from the group consisting of hydrogen, alkyl, aryl, alkoxy, aryloxy, alkylketone, arylketone, fluoroalkyl, fluoroaryl, bromoalkyl, bromoaryl, chloroalkyl, chloroaryl, alkylsulfone, arylsulfone, alkylamide, arylamide, alkylester, arylester, fluorine, chlorine, and bromine.

19. The method according to claim 18, wherein one or more of R.sup.1, R.sup.2, R.sup.3, and R.sup.4 is independently represented by formula Ar-T-, wherein Ar is represented by a formula selected from the following group of formulae: ##STR00010## wherein each R.sub.j, R.sub.k and R.sub.l is independently selected from the group consisting of hydrogen, halogen, alkyl, alkenyl, alkynyl, aryl, ether, thioether, carboxylic acid, ester, amide, imide, alkali or alkaline earth metal sulfonate, alkyl sulfonate, alkali or alkaline earth metal phosphonate, alkyl phosphonate, amine and quaternary ammonium, with j and l, equal or different from each other, being independently 0, 1, 2, 3, 4, or 5 and, k, equal or different from j or l, being independently 0, 1, 2, 3 or 4; T is selected from the group consisting of —CH.sub.2—; —O—; —SO.sub.2—; —S—; —C(O)—; —C(CH.sub.3).sub.2—; —C(CF.sub.3).sub.2—; —C(═CCl.sub.2)—; —C(CH.sub.3)(CH.sub.2CH.sub.2COOH)—; —N═N—; —R.sup.aC═CR.sup.b—, wherein each R.sup.a and R.sup.b, independently of one another, is hydrogen, C.sub.1-C.sub.12-alkyl, C.sub.1-C.sub.12-alkoxy, or C.sub.6-C.sub.18-aryl group; —(CH.sub.2).sub.n— and —(CF.sub.2).sub.n— with n being an integer from 1 to 6; a linear or branched aliphatic divalent group having from 1 to 6 carbon atoms.

20. The method according to claim 19, wherein one or more of R.sup.1, R.sup.2, R.sup.3, and R.sup.4 is represented by formula: ##STR00011##

21. The method according to claim 18, wherein the repeat unit (R.sub.pm) is represented by the formula ##STR00012##

22. The method according to claim 18, wherein said polymer (PP) comprises at least about 30 mole percent of repeating units (R.sub.pm).

23. The method according to claim 18, wherein one or more of R.sup.5, R.sup.6, R.sup.7, and R.sup.8 is independently represented by formula Ar″-T″-, wherein Ar″ is represented by a formula selected from the following group of formulae ##STR00013## wherein each R.sub.j″, R.sub.k″ and R.sub.l″ is independently selected from the group consisting of hydrogen, halogen, alkyl, alkenyl, alkynyl, aryl, ether, thioether, carboxylic acid, ester, amide, imide, alkali or alkaline earth metal sulfonate, alkyl sulfonate, alkali or alkaline earth metal phosphonate, alkyl phosphonate, amine and quaternary ammonium, j″ and i″, equal or different from each other being independently 0, 1, 2, 3, 4, or 5 and, k″, equal or different from j″ or l″, being independently 0, 1, 2, 3 or 4; T″ is selected from the group consisting of —CH.sub.2—; —O—; —SO.sub.2—; —S—; —C(O)—; —C(CH.sub.3).sub.2—; —C(CF.sub.3).sub.2—; —C(═CCl.sub.2)—; —C(CH.sub.3)(CH.sub.2CH.sub.2COOH)—; —N═N—; —R.sup.aC═CR.sup.b—, wherein each R.sup.a and R.sup.b, independently of one another, is hydrogen, C.sub.1-C.sub.12-alkyl, C.sub.1-C.sub.12-alkoxy, or C.sub.6-C.sub.18-aryl group; —(CH.sub.2).sub.n— and —(CF.sub.2).sub.n— with n being an integer from 1 to 6; a linear or branched aliphatic divalent group having from 1 to 6 carbon atoms.

24. The method according to claim 18, wherein the repeat unit (R.sub.pp) is represented by the formula: ##STR00014##

25. The method according to claim 18, wherein said polymer (PP) comprises at least about 40 mole percent repeat units (R.sub.pp).

26. The method according to claim 16, wherein said method is for purifying non-drinkable water, said fluid is saline water or brackish water, said contaminant is the salts content dissolved into said fluid, and said membrane (PP) is a multi-layered membrane comprising (I) a substrate layer, (II) an outer layer consisting of aromatic polyamides and (Ill) the layer (PP), said layer (PP) being interposed between said substrate layer and said outer layer.

27. The method according to claim 16, wherein said fluid containing at least one contaminant is a liquid phase or a gas phase.

28. The method according to claim 16, wherein said membrane (PP) is obtained from a liquid composition [composition (C.sup.L)] comprising said polymer (PP) in an amount of from 7 to less than 60 wt. % based on the total weight of said composition (C.sup.L) or a solid composition [composition (C.sup.S)] comprising said polymer (PP) in an amount of from 1 to 85 wt. % based on the total weight of said composition (C.sup.S).

29. A membrane [membrane (PP*)] comprising at least one porous layer [layer (PP*)] obtained from a composition [composition (C*)] comprising at least one polyphenylene polymer [polymer (PP)] and at least one solvent [medium (L)], wherein said polymer (PP) is in an amount from 7 wt. % to less than 60 wt. % based on the weight of said composition (C*).

30. The membrane according to claim 29, said membrane being characterized by a tensile modulus (measured according to ASTM D638 type V) of at least 201 MPa; and/or by a gravimetric porosity of at least 0.55.

Description

DESCRIPTION OF EMBODIMENTS

[0046] For the purposes of the present description:

[0047] the use of parentheses before and after symbols or numbers identifying compounds, chemical formulae or parts of formulae has the mere purpose of better distinguishing those symbols or numbers from the rest of the text and hence said parentheses can also be omitted;

[0048] the term “membrane” is intended to indicate to a discrete, generally thin, interface that moderates the permeation of chemical species in contact with it, said membrane containing pores of finite dimensions;

[0049] the term “gravimetric porosity” is intended to denote the fraction of voids over the total volume of the porous membrane;

[0050] the term “solvent” is used herein in its usual meaning, that is it indicates a substance capable of dissolving another substance (solute) to form an 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.

[0051] 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.

[0052] Said membrane (PP) may be either a symmetric membrane or an asymmetric membrane.

[0053] The asymmetric porous membrane (PP) 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.

[0054] The membrane (PP) preferably has an average pore diameter of at least 0.001 μm, more preferably of at least 0.005 μm, and even more preferably of at least 0.01 μm. The membrane (PP) preferably has an average pore diameter of at most 50 μm, more preferably of at most 20 μm and even more preferably of at most 15 μm.

[0055] Suitable techniques for the determination of the average pore diameter in the porous membranes of the invention are described for instance in Handbook of Industrial Membrane Technology. Edited by PORTER, Mark C. Noyes Publications, 1990. p.70-78. Average pore diameter is preferably determined by scanning electron microscopy (SEM).

[0056] The membrane (PP) 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.

[0057] Suitable techniques for the determination of the gravimetric porosity in membrane (PP) are described for instance by SMOLDERS, K., et al. Terminology for membrane distillation. Desalination. 1989, vol.72, p.249-262.

[0058] Membrane (PP) may be either a self-standing porous membrane comprising said layer (PP) as the only layer or a multi-layered membrane, preferably comprising said layer (PP) supported onto a substrate.

[0059] Said substrate layer may be partially or fully interpenetrated by said layer (PP).

[0060] A multi-layered membrane is typically obtained by coating said substrate with said layer (PP) or by impregnating or dipping said substrate with said composition (C) as defined above.

[0061] The nature of the substrate 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, glass fibers and/or polymeric material such as for example polypropylene, polyethylene, polyethyleneterephthalate.

[0062] In addition to the substrate, membrane (PP) can comprise an additional layer, which is preferably a coating with aromatic polyamides.

[0063] Depending on its final intended use, membrane (PP) can be flat, when flat membranes are required, or tubular in shape, when tubular or hollow fiber membranes are required.

[0064] 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.

[0065] Flat membranes preferably have a thickness comprised between 10 μm and 200 μm, more preferably between 15 μm and 150 μm.

[0066] 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.

[0067] Polymer (PP) preferably comprises at least about 10 mole percent (per 100 moles of polymer (PP)), more preferably at least 12 mole percent and even more preferably at least 15 mole percent, of repeating units (R.sub.pm) represented by the following formula:

##STR00001##

[0068] and at least about 10 mol percent repeat units (R.sub.pp) represented by the following formula:

##STR00002##

[0069] wherein

[0070] R.sup.1, R.sup.2, R.sup.3, R.sup.4 R.sup.5, R.sup.6, R.sup.7, and R.sup.8 are each independently selected from the group consisting of hydrogen, alkyl, aryl, alkoxy, aryloxy, alkylketone, arylketone, fluoroalkyl, fluoroaryl, bromoalkyl, bromoaryl, chloroalkyl, chloroaryl, alkylsulfone, arylsulfone, alkylamide, arylamide, alkylester, arylester, fluorine, chlorine, and bromine.

[0071] Preferably, one or more of R.sup.1, R.sup.2, R.sup.3, and R.sup.4 is independently represented by formula Ar-T-,

[0072] wherein

[0073] Ar is represented by a formula selected from the following group of formulae:

##STR00003##

[0074] wherein

[0075] each R.sub.j, R.sub.k and R.sub.l is independently selected from the group consisting of hydrogen, halogen, alkyl, alkenyl, alkynyl, aryl, ether, thioether, carboxylic acid, ester, amide, imide, alkali or alkaline earth metal sulfonate, alkyl sulfonate, alkali or alkaline earth metal phosphonate, alkyl phosphonate, amine and quaternary ammonium,

[0076] with j and i, equal or different from each other, being independently 0, 1, 2, 3, 4, or 5 and,

[0077] k, equal or different from j or l, being independently 0, 1, 2, 3 or 4; T is selected from the group consisting of —CH.sub.2—; —O—; —SO.sub.2—; —S—; —C(O)—; —C(CH.sub.3).sub.2—; —C(CF.sub.3).sub.2—; —C(═CCl.sub.2)—; —C(CH.sub.3)(CH.sub.2CH.sub.2COOH)—; —N═N—; —R.sup.aC═CR.sub.b—, [0078] wherein

[0079] each R.sup.a and R.sup.b, independently of one another, is hydrogen, C.sub.1-C.sub.12-alkyl, C.sub.1-C.sub.12-alkoxy, or C.sub.6-C.sub.18-aryl group; —(CH.sub.2).sub.n— and —(CF.sub.2).sub.n— with n being an integer from 1 to 6; a linear or branched aliphatic divalent group having from 1 to 6 carbon atoms.

[0080] In some embodiments, one or more of R.sup.1, R.sup.2, R.sup.3, and R.sup.4 is represented by formula:

##STR00004##

[0081] In some embodiments, the repeat unit (R.sub.pm) is represented by the formula

##STR00005##

[0082] In some embodiments, the polymer (PP) comprises at least about 30 mole percent, preferably at least about 40 mole percent of repeating units (R.sub.pm).

[0083] In some embodiments, one or more of R.sup.5, R.sup.6, R.sup.7, and R.sup.8 is independently represented by formula Ar″-T″-,

[0084] wherein

[0085] Ar″ is represented by a formula selected from the following group of formulae

##STR00006##

[0086] wherein

[0087] each R.sub.j″, R.sub.k″ and R.sub.l″ is independently selected from the group consisting of hydrogen, halogen, alkyl, alkenyl, alkynyl, aryl, ether, thioether, carboxylic acid, ester, amide, imide, alkali or alkaline earth metal sulfonate, alkyl sulfonate, alkali or alkaline earth metal phosphonate, alkyl phosphonate, amine and quaternary ammonium,

[0088] j″ and i″, equal or different from each other being independently 0, 1, 2, 3, 4, or 5 and,

[0089] k″, equal or different from j″ or l″, being independently 0, 1, 2, 3 or 4; T″ is selected from the group consisting of —CH.sub.2—; —O—; —SO.sub.2—; —A—; —C(O)—; —C(CH.sub.3).sub.2—;

[0090] —C(CF.sub.3).sub.2—; —C(═CCl.sub.2)—; —C(CH.sub.3)(CH.sub.2CH.sub.2COOH)—; —N═N—; —R.sub.aC═CR.sup.b—, wherein each R.sup.a and R.sup.b, independently of one another, is hydrogen, C.sub.1-C.sub.12-alkyl, C.sub.1-C.sub.12-alkoxy, or C.sub.6-C.sub.18-aryl group; —(CH.sub.2).sub.n— and —(CF.sub.2).sub.n— with n being an integer from 1 to 6; a linear or branched aliphatic divalent group having from 1 to 6 carbon atoms.

[0091] In some embodiments, the repeat unit (R.sub.pp) is represented by the formula:

##STR00007##

[0092] In some embodiments, the polymer (PP) comprises at least about 40 mole percent repeat units (R.sub.pp).

[0093] In a preferred embodiment, said polymer (PP) is commercially available from Solvay Specialty Polymers, under the tradename PrimoSpire® SRP.

[0094] Said medium (L) is advantageously selected from polar aprotic solvents.

[0095] The medium (L) preferably comprises at least one organic solvent.

[0096] Suitable examples of organic solvents are:

[0097] 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;

[0098] aliphatic or aromatic halogenated hydrocarbons including more particularly, perchlorinated hydrocarbons such as, in particular, tetrachloroethylene, hexachloroethane;

[0099] partially chlorinated hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane, trichloroethylene, 1-chlorobutane, 1,2-dichlorobutane, monochlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,4-trichlorobenzene or mixture of different chlorobenzenes;

[0100] aliphatic, cycloaliphatic or aromatic ether oxides, more particularly, diethyl oxide, dipropyl oxide, diisopropyl oxide, dibutyl oxide, methylterbutyl ether, dipentyl oxide, diisopentyl oxide, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether benzyl oxide; dioxane, tetrahydrofuran (THF);

[0101] dimethylsulfoxide (DMSO);

[0102] 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;

[0103] glycol ether esters such as ethylene glycol methyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate;

[0104] alcohols, including polyhydric alcohols, such as methyl alcohol, ethyl alcohol, diacetone alcohol, ethylene glycol;

[0105] ketones such as acetone, methylethylketone, methylisobutyl ketone, diisobutylketone, cyclohexanone, isophorone;

[0106] linear or cyclic esters such as isopropyl acetate, n-butyl acetate, methyl acetoacetate, dimethyl phthalate, γ-butyrolactone;

[0107] linear or cyclic carboxamides such as N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, dimethylformamide (DMF), diethylformamide or N-methyl-2-pyrrolidone (NMP);

[0108] organic carbonates for example dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, ethylmethyl carbonate, ethylene carbonate, vinylene carbonate;

[0109] phosphoric esters such as trimethyl phosphate, triethyl phosphate (TEP);

[0110] ureas such as tetramethylurea, tetraethylurea;

[0111] methyl-5-dimethylamino-2-methyl-5-oxopentanoate (commercially available under the tradename Rhodialsov Polarclean®).

[0112] Preferably, said at least one organic solvent is selected from polar aprotic solvents and even more preferably in the group consisting of: N-methyl-pyrrolidone (NMP), dimethyl acetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), methyl-5-dimethylamino-2-methyl-5-oxopentanoate (commercially available under the tradename Rhodialsov Polarclean®) and triethylphosphate (TEP).

[0113] The medium (L) preferably comprises at least 40 wt. %, more preferably at least 50 wt. % based on the total weight of said medium (L), of at least one organic solvent. Medium (L) preferably comprises at most 100 wt. %, more preferably at most 99 wt. % based on the total weight of said medium (L), of at least one organic solvent.

[0114] The medium (L) may further comprise at least one non-solvent medium [medium (NS)]. The medium (NS) may comprise water.

[0115] Preferably, said fluid containing at least one contaminant is a liquid phase or a gas phase.

[0116] Said contaminant can be a solid contaminant. According to this embodiment, liquid and gas phases comprising one or more solid contaminants are also referred to as “suspensions”, i.e. heterogeneous mixtures comprising at least one solid particle (the contaminant) dispersed into a continuous phase (or “dispersion medium”, which is in the form of liquid or gas).

[0117] Said at least one solid contaminant preferably comprises comprising microorganisms, preferably selected from the group consisting of bacteria such as Staphylococcus aureus and Pseudomonas aeruginosa, algae, fungi, protozoa and viruses.

[0118] According to another embodiment, when saline water is the liquid phase, said contaminant is the dissolved salt content in the saline water itself.

[0119] According to this embodiment, the liquid phase is an “aqueous solution”, i.e. a homogeneous mixture wherein salts (the solute) are dissolved into water (the solvent).

[0120] In a preferred embodiment, the method of the present invention is a method for purifying non-drinkable water, wherein said fluid is saline water or brackish water, said contaminant is the dissolved salts content, and said membrane (PP) comprises (I) a substrate layer, (II) an outer layer consisting of aromatic polyamides and (III) a layer (PP) as defined above, said layer (PP) being interposed between said substrate layer and said outer layer.

[0121] In one embodiment, two or more membranes (PP) can be used in series for the filtration of a liquid and/or gas phase. Advantageously, a first filtration step is performed by contacting liquid and/or gas phases comprising one or more solid contaminants with a first membrane [membrane (PP1)] having an average pore diameter higher than 5 μm, more preferably from 5 to 50 μm; and a second filtration step is performed after said first filtration step, by contacting the same liquid and/or gas phase with a second membrane [membrane (PP2)] having an average pore diameter of from 0.001 to 5 μm.

[0122] Alternatively, at least one membrane (PP) is used in series with at least one porous membrane obtained from a composition different composition (C) according to the present invention.

[0123] Preferably, said step (iii) is performed by applying a pressure of at least 2 bar, preferably of at least 4 bars. Preferably, said step (iii) is performed by applying a pressure up to 50 bar, more preferably up to 100 bar.

[0124] Membrane (PP) can be manufactured according to techniques known in the art, for example in liquid phase or in molten phase.

[0125] According to a first embodiment of the invention, the process for manufacturing a porous membrane is carried out in liquid phase.

[0126] The process according to this first embodiment preferably comprises:

[0127] (i{circumflex over ( )}) providing a liquid composition [composition (C.sub.L)] comprising:

[0128] polymer (PP) as defined above, and

[0129] a liquid medium [medium (L)] as defined above;

[0130] (ii{circumflex over ( )}) processing composition (C.sup.L) provided in step (i) thereby providing a film; and

[0131] (iii{circumflex over ( )}) precipitating the film provided in step (ii) thereby providing a porous membrane.

[0132] Under step (i{circumflex over ( )}), composition (C.sup.L) is manufactured by any conventional techniques. For instance, the medium (L) may be added to polymer (PP), or, preferably, polymer (PP) may be added to the medium (L), or even polymer (PP) and the medium (L) may be simultaneously mixed.

[0133] Any suitable mixing equipment may be used. Preferably, the mixing equipment is selected to reduce the amount of air entrapped in composition (C.sup.L) which may cause defects in the final membrane. The mixing of polymer (PP) 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.sup.L).

[0134] Under step (i{circumflex over ( )}), the mixing time during stirring required to obtain a clear homogeneous composition (C.sup.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.sup.L) and the like.

[0135] Under step (ii{circumflex over ( )}), composition (C.sup.L) is typically processed in liquid phase.

[0136] Under step (ii{circumflex over ( )}), composition (C.sup.L) is typically processed by casting thereby providing a film.

[0137] 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 a liquid composition comprising a suitable medium (L) across a suitable support.

[0138] Under step (ii{circumflex over ( )}), the temperature at which composition (C.sup.L) is processed by casting may be or may be not the same as the temperature at which composition (C.sup.L) is mixed under stirring.

[0139] Different casting techniques are used depending on the final form of the membrane to be manufactured.

[0140] When the final product is a flat membrane, composition (C.sup.L) is cast as a film over a flat supporting substrate, typically a plate, a belt or a fabric, or another microporous supporting membrane, typically by means of a casting knife, a draw-down bar or a slot die.

[0141] According to a first embodiment of step (ii{circumflex over ( )}), composition (C.sup.L) is processed by casting onto a flat supporting substrate to provide a flat film.

[0142] According to a second embodiment of step (ii{circumflex over ( )}), composition (C.sup.L) is processed to provide a tubular film.

[0143] According to a variant of this second embodiment of step (ii{circumflex over ( )}), the tubular film is manufactured using a spinneret.

[0144] 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 (C.sup.L) and a second inner one for the passage of a supporting fluid, generally referred to as “lumen”.

[0145] Hollow fibers and capillary membranes may be manufactured by the so-called spinning process according to this variant of the second embodiment of step (ii{circumflex over ( )}). According to this variant of the second embodiment of the invention, composition (C.sup.L) is generally pumped through the spinneret. The lumen acts as the support for the casting of composition (C.sup.L) and maintains the bore of the hollow fiber or capillary precursor open. The lumen may be a gas, or, preferably, a medium (NS) or a mixture of the medium (NS) with a medium (L). The selection of the lumen 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.

[0146] At the exit of the spinneret, after a short residence time in air or in a controlled atmosphere, under step (iii^) of the process for manufacturing a porous membrane according to this first embodiment of the invention, the hollow fiber or capillary precursor is precipitated thereby providing the hollow fiber or capillary membrane.

[0147] The supporting fluid forms the bore of the final hollow fiber or capillary membrane.

[0148] Tubular membranes, because of their larger diameter, are generally manufactured using a different process from the one employed for the production of hollow fiber membranes.

[0149] The Applicant has found that use of solvent/non-solvent mixtures at a given temperature, in any one of steps (ii{circumflex over ( )}) and (iii{circumflex over ( )}) of the process according to the invention, advantageously allows controlling the morphology of the final porous membrane including its average porosity.

[0150] The temperature gradient between the film provided in any one of steps (ii{circumflex over ( )}) and (iii{circumflex over ( )}) of the process according to the first embodiment of the invention and the medium (NS) may also influence the pore size and/or pore distribution in the final porous membrane as it generally affects the rate of precipitation of the polymer (A) from composition (C.sup.L).

[0151] According to a second embodiment of the invention, the process for manufacturing a porous membrane is carried out in molten phase.

[0152] The process according to the second embodiment of the invention preferably comprises the following steps:

[0153] (i{circumflex over ( )}{circumflex over ( )}) providing a solid composition [composition (C.sup.S)] comprising at least one polymer (PP) as defined above;

[0154] (ii{circumflex over ( )}{circumflex over ( )}-A) processing the composition (C.sup.S) provided in step (i{circumflex over ( )}{circumflex over ( )}) thereby providing a film and (iii{circumflex over ( )}{circumflex over ( )}-A) stretching the film provided in step (ii{circumflex over ( )}{circumflex over ( )}-A) thereby providing a porous membrane; or

[0155] (ii{circumflex over ( )}{circumflex over ( )}-B) processing the composition (C.sup.S) provided in step (i{circumflex over ( )}{circumflex over ( )}) thereby providing fibers and (iii{circumflex over ( )}{circumflex over ( )}-B) processing the fibers provided in (ii{circumflex over ( )}{circumflex over ( )}-B) thereby providing a porous membrane.

[0156] Under step (ii{circumflex over ( )}{circumflex over ( )}-A), composition (C.sup.S) is preferably processed in molten phase.

[0157] Melt forming is commonly used to make dense films by film extrusion, preferably by flat cast film extrusion or by blown film extrusion.

[0158] According to this technique, composition (C.sup.S) is extruded through a die so as to obtain a molten tape, which is then calibrated and stretched in the two directions until obtaining the required thickness and wideness. Composition (C.sup.S) is melt compounded for obtaining a molten composition. Generally, melt compounding is carried out in an extruder. Composition (C.sup.S) is typically extruded through a die at temperatures of generally lower than 250° C., preferably lower than 200° C. thereby providing strands which are typically cut thereby providing pellets.

[0159] Twin screw extruders are preferred devices for accomplishing melt compounding of composition (C.sup.S).

[0160] Films can then be manufactured by processing the pellets so obtained through traditional film extrusion techniques. Film extrusion is preferably accomplished through a flat cast film extrusion process or a hot blown film extrusion process. Film extrusion is more preferably accomplished by a hot blown film extrusion process.

[0161] Under step (iii{circumflex over ( )}{circumflex over ( )}-A), the film provided in step (ii{circumflex over ( )}{circumflex over ( )}-A) may be stretched either in molten phase or after its solidification upon cooling.

[0162] The porous membrane obtainable by the process of the invention is typically dried, preferably at a temperature of at least 30° C.

[0163] Drying can be performed under air or a modified atmosphere, e.g. under an inert gas, typically exempt from moisture (water vapour content of less than 0.001% v/v). Drying can alternatively be performed under vacuum.

[0164] As used within the present description, “composition (C)” is intended to include both the liquid composition [composition (C.sup.L)] and the solid composition [composition (C.sup.S)], unless otherwise specified.

[0165] According to a preferred embodiment, composition (C) is free of plasticizer agents, i.e. plasticizer agents are not added to composition (C) or they are present in an amount of less than 1 wt. %, more preferably less than 0.1 wt. % based on the total weight of said composition (C).

[0166] Preferably, said composition (C.sup.L) comprises said polymer (PP) in an amount of from 7 to less than 60 wt. %, more preferably from 8 to 55 wt. % and even more preferably from 10 to 50 wt. %, based on the total weight of said composition (C.sup.L).

[0167] Preferably, said composition (C.sup.L) comprises said medium (L) in an amount of 40 wt. % or higher, more preferably of at least 45 wt. % and even more preferably of at least 50 wt. % based on the total weight of said composition (C.sup.L). Preferably, said composition (C.sup.L) comprises said medium (L) in an amount up to 93 wt. %, more preferably of 92 wt. % and even more preferably of 90 wt. % based on the total weight of said composition (C.sup.L).

[0168] Preferably, said composition (C.sup.S) comprises said polymer (PP) in an amount of from 1 to 85 wt. % based on the total weight of said composition (C.sup.S).

[0169] A preferred embodiment of membrane (PP) according to the present invention is the embodiment referred to as membrane (PP*)).

[0170] Preferably, composition (C*) has the features described above for composition (C.sup.L).

[0171] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0172] The invention will be herein after illustrated in greater detail by means of the Examples contained in the following Experimental Section; the Examples are merely illustrative and are by no means to be interpreted as limiting the scope of the invention.

Experimental Section

[0173] Raw Materials

[0174] Dimethylacetamide (DMAC), N-Methyl pirrolidone (NMP), isopropyl alcohol (IPA) and PolyVinyl Pirrolidone (PVP) K10 were obtained from Sigma Aldrich.

[0175] Veradel® 3000P (polyethersulfone—PESU) and Primospire® PR 250 (polyphenylene) were obtained from Solvay Specialty Polymers.

[0176] Methods

[0177] Mechanical (Tensile) Test on Flat Sheet Membranes

[0178] Mechanical properties on flat sheet porous membranes were assessed at room temperature (23° C.) following ASTM norm D638 type V, with a Grip distance=25.4 mm, and initial length L.sub.0=21.5 mm. Velocity was between 1 and 50 mm/min.

[0179] The samples stored in water were took out from the container boxes and immediately tested to determine apparent modulus and stress at break.

[0180] Mechanical (Tensile) Test on Hollow Fiber Membranes

[0181] All the tests on the extruded fibers were performed following the ASTM D3032 method with an initial length L.sub.0=125 mm and velocity of 125 mm/min.

[0182] All the tested fibers were stored in water without any supplementary treatment. During the tests the fibers were maintained wet: each test involved at least four-five iterations on several fiber specimens. Apparent modulus and stress at break were determined.

[0183] Measurement of Porosity and Pore Sizes

[0184] Gravimetric porosity of the membrane is defined as the volume of the pores divided by the total volume of the membrane. The porosities were measured using IPA (isopropyl alcohol) as wetting fluid according to the procedure described in Appendix of Desalination, 72 (1989) 249-262.

[00001]$\mathrm{.Math.}=\frac{\frac{\left(\mathrm{Wet}-\mathrm{Dry}\right)}{{\rho }_{\mathrm{liquid}}}}{\frac{\left(\mathrm{Wet}-\mathrm{Dry}\right)}{{\rho }_{\mathrm{liquid}}}-\frac{\mathrm{Dry}}{{\rho }_{polymer}}}$

[0185] where

[0186] Wet is the weight of the wetted membrane,

[0187] Dry is the weight of dry membrane,

[0188] ρ.sub.polymer is the density of the polymer, (1.19 g/cm.sup.3 PrimoSpire®; 1.36 g/cm.sup.3 of PESU) and

[0189] ρ.sub.liquid is the density of IPA (0.78 g/cm.sup.3).

[0190] Measurement of Water Permeability

[0191] The pure water permeability was measured according to the technique known in the art. Water flux (J) through each membrane at given pressure, was defined as the volume which permeates per unit area and per unit time. The flux is calculated by the following equation:

[00002]$J=\frac{V}{A\Delta t}$

[0192] where V (L) is the volume of permeate, A is the membrane area, and Δt is the operation time.

[0193] Water flux measurements on flat sheet membranes were conducted at room temperature using a dead-end configuration under a constant nitrogen.

[0194] Flux Decay Tests (“Compaction Tests”)

[0195] This test was performed to assess the propensity of the produced items to pressure compaction. This test was performed only on some selected flat sheet items and consists in measuring the flux (as defined above) for prolonged times (about 45 minutes) for each of three pre-determined consecutive steps at 1-2 and 4 bar of applied pressure. The first flux measurement at 1 bar was performed after roughly 11 minutes of holding the pressure. The entire test lasted for 135 minutes. At the end, it was possible to assess the flux decay during the duration of each pressure step and also check the eventual proportionality between flux and applied pressure.

[0196] Preparation of Dope Solutions

[0197] Solutions were prepared at 30° C., by adding the amount of polymer detailed in the examples that follows and optional additives in the solvent (DMAC or NMP as detailed below) and stirring with a mechanical anchor for several hours until a clear and homogeneous system for each solution was obtained. When necessary, the temperature of the system was raised to 50° C-60° C. in order to speed up the dissolution process.

[0198] Preparation of Membranes in the Form of Flat Sheet

[0199] Porous membranes in the form of flat sheets were prepared by filming the dope solution prepared as described above over a suitable smooth glass support, by means of an automatized casting knife.

[0200] Membrane casting was performed by holding the dope solution, the casting knife and the support temperatures at 25° C., so as to prevent premature precipitation of the polymer. The knife gap was set at 250 μm. After casting, polymeric films were immediately immersed in a coagulation bath (either of pure de-ionized water or a mixture IPA/water 50:50 v/v) in order to induce phase inversion.

[0201] After coagulation the membranes were washed several times in pure water in the following days to remove residual traces of solvent.

[0202] Preparation of Membranes in the Form of Hollow Fibers

[0203] Porous membranes in the form of hollow fibers were prepared by extruding the dope solution, prepared as detailed above, through a spinneret (3 in FIG. 1).

[0204] Hollow fibers were prevented from collapsing by coextruding water as bore fluid in the center of the annulus, which was fed at a flow rate ranging from 1-10 ml/min.

[0205] The rotating (coagulation) water bath (6 in FIG. 1) enabled producing coagulation by phase inversion. The temperature of the apparatus was controlled by a PID system. The spinneret geometry used in the extrusion part had an internal diameter (IDsp) of 800 μm, an external one of 1600 μm (ODsp) and a bore diameter of 300 μm (indicated later in the text as 0.3-0.8-1.6).

EXAMPLE 1

[0206] Porous membranes according to the invention in the form of flat sheets were prepared using DMAC solvent and Primospire® PR-250 in the following concentrations: 15%, 20% and 25% w/w.

[0207] (a) The nascent membrane was coagulated in water.

[0208] (b) the nascent membrane was coagulated in a blend of 50/50 v/v IPA/water.

EXAMPLE 1C

[0209] As comparison, porous membranes in the form of flat sheets were prepared using DMAC solvent and Veradel® PESU (polyethersulfone) 3000 MP in the following concentrations: 15% and 20% w/w.

[0210] (a) The nascent membrane was coagulated in water.

[0211] (b) the nascent membrane was coagulated in a blend of 50/50 v/v IPA/water.

[0212] The mechanical properties for the membranes obtained are shown in the following Table 1.

TABLE-US-00001 TABLE 1 Example1 Example 1C(*) (a) (b) (a) (b) Concentration = 15% w/w Modulus (MPa) 201 317 100 147 Stress at break 9.9 12.8 5.0 6.5 (MPa) Porosity 0.824 0.796 0.815 0.780 Concentration = 20% w/w Modulus (MPa) 380 549 141 175 Stress at break 12.4 17.5 7.3 8.2 (MPa) Porosity 0.764 0.727 0.780 0.731 Concentration = 25% w/w Modulus (MPa) 529 630 — — Stress at break 16.5 19.6 — — (MPa) Porosity 0.713 0.672 — — (*)comparison

[0213] The results in Table 1 show that the membranes prepared according to the invention had improved mechanical properties.

[0214] Compaction test was performed using membranes prepared according to Example 1 method (a) with concentration 15% w/w and Example 1C(*) method (a) with concentration 15% w/w. The results are shown in the following Table 2.

TABLE-US-00002 TABLE 2 Example 1 Example 1C(*) Applied Time Flux/(initial Flux/(initial pressure (bar) (min) flux at 1 bar) flux at 1 bar) 1 11 1.00 1.00 1 21 0.95 0.90 1 31 0.95 0.84 1 41 0.93 0.79 2 56 1.80 1.25 2 66 1.74 1.16 2 76 1.71 1.09 2 86 1.67 1.06 4 101 3.34 1.59 4 111 3.17 1.51 4 121 3.05 1.44 4 131 2.95 1.38 (*)comparison

[0215] The above results showed that the membrane prepared according to the invention retained a better flux at each pressure step and notably at 2 bar and above, and that, as pressure increased, a proportionality between flux and pressure was maintained. On the contrary, as pressure increased, the flux measured for the comparative membrane was strongly affected by pressure compaction.

EXAMPLE 2

[0216] Porous membranes according to the invention in the form of flat sheets were prepared using DMAC solvent and a blend comprising 5% w/w of PVP K10 and 20% w/w Primospire® PR-250.

[0217] (a) The nascent membrane was coagulated in water.

[0218] (b) the nascent membrane was coagulated in a blend of 50/50 v/v IPA/water.

EXAMPLE 2C

[0219] As comparison, porous membranes in the form of flat sheets were prepared using DMAC solvent and a blend comprising of 5% w/w of PVP K10 and 20% w/w Veradel® PESU (polyethersulfone) 3000 MP.

[0220] (a) The nascent membrane was coagulated in water.

[0221] (b) the nascent membrane was coagulated in a blend of 50/50 v/v IPA/water.

[0222] The mechanical properties for the membranes obtained are shown in the following Table 3.

TABLE-US-00003 TABLE 3 Example 2 Example 2C(*) (a) (b) (a) (b) Concentration = 20% w/w Modulus (MPa) 210 302 71 119 Stress at break 8.3 12.1 3.4 6.7 (MPa) Porosity 0.81 0.78 0.82 0.77 (*)comparison

[0223] The results in Table 3 showed that the membranes prepared according to the invention had improved mechanical properties.

[0224] Compaction test was performed using membranes prepared according to Example 2 method (a) and Example 2C(*) method (a). The results are shown in the following Table 4.

TABLE-US-00004 TABLE 4 Example 2 Example 2C(*) Applied Time Flux/(initial Flux/(initial pressure (bar) (min) flux at 1 bar) flux at 1 bar) 1 11 1.00 1.00 1 21 1.00 0.97 1 31 0.97 0.94 1 41 0.96 0.93 2 56 1.94 1.71 2 66 1.89 1.69 2 76 1.86 1.65 2 86 1.83 1.61 4 101 3.56 2.25 4 111 3.47 1.96 4 121 3.39 1.79 4 131 3.34 1.66 (*)comparison

[0225] The above results showed that the membrane prepared according to the invention retained a better flux at each pressure step and notably at 2 bar and above, and that, as pressure increased, a proportionality between flux and pressure was maintained. On the contrary, as pressure increased, the flux measured for the comparative membrane was strongly affected by pressure compaction.

EXAMPLE 3

[0226] Porous membranes according to the invention in the form of hollow fibers were prepared using DMAC solvent and 25% w/w Primospire® PR-250.

EXAMPLE 3C

[0227] As comparison, porous membranes in the form of hollow fibers were prepared using DMAC solvent and 25% w/w Veradel® PESU 3000 MP (polyethersulfone).

[0228] The experimental conditions for the preparation of the membranes of Example 3 and Example 3C were the following:

[0229] dope composition/T° C. extrusion: 25 wt. %/30° C.

[0230] nozzle (mm): 0.3-0.8-1.6

[0231] bore fluid: pure water

[0232] coagulation bath temperature: water at 25° C.

[0233] ratio of Dope throughput (g/min) to Bore throughput (D/B ratio): 0.6-3.5

[0234] air gap: 9 cm

[0235] The mechanical properties for the membranes obtained are shown in the following Table 5.

TABLE-US-00005 TABLE 5 Example 3 Example 3C(*) Modulus (MPa) 320 215 Stress at break (MPa) 18 11 Porosity (%) 0.73 0.61 (*)comparison

[0236] The results in Table 5 showed that the membranes prepared according to the invention had improved mechanical properties.

EXAMPLES 4C

[0237] Porous membranes in the form of flat sheet was prepared using DMAC solvent and PrimoSpire® PR250 5% w/w.

[0238] The membrane was coagulated in water.

[0239] The membrane thus obtained showed no mechanical integrity upon handling and hence it was not possible to measure its mechanical properties.

EXAMPLE 5C

[0240] A composition comprising DMAC solvent and PrimoSpire® PR250 60% w/w was prepared.

[0241] From the abovementioned composition, it was not possible to cast film a membrane. Indeed, either using a magnetic or a mechanical stirrer and heating up to 130° C., it was not possible to dissolve the PrimoSpire® PR250 polymer into the DMAC solvent.