Membranes for removing anionic substances

Abstract

The present disclosure provides a porous polymeric membrane having ionizable nitrogen functional groups at least on its surface, such groups being associated with hydroxide anions. The membrane is useful in the purification of polar solvents such as water and alcohols, and is capable of removing trace amounts of anionic contaminants such as halides, phosphates, nitrates, nitrites, sulfites, and sulfates.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to filtration membranes and their use in removing anionic impurities from polar solvents, particularly solvents useful in semiconductor manufacturing processes including photoresist applications. [Background technology]

[0002] Filter products are essential tools in modern industry and are used to remove unwanted materials from useful fluid streams. Useful fluids that are treated using filters include water, liquid industrial solvents and process fluids, industrial gases used in manufacturing or processing (e.g., in semiconductor fabrication), and liquids with medical or pharmaceutical uses. Unwanted materials that are removed from fluids include impurities and contaminants such as particles, microorganisms, and dissolved chemical species. Specific examples of filter applications include use with liquid materials for semiconductor and microelectronic device manufacturing.

[0003] To perform the filtering function, a filter generally includes a filter membrane that is responsible for removing undesired substances from the fluid passing through the filter membrane. The filter membrane may be in the form of a flat sheet that may be wound (e.g., spirally wound), flat, pleated, or disk-shaped, as desired. Alternatively, the filter membrane may be in the form of a hollow fiber. The filter membrane may be contained within a housing or otherwise supported such that the fluid being filtered is required to enter the filter inlet, pass through the filter membrane, and then pass through the filter outlet.

[0004] Filtration membranes can be constructed from porous structures with average pore sizes that can be selected based on the filter's application, i.e., the type of filtration performed by the filter. Typical pore sizes are in the micron or submicron range, such as about 0.001 microns to about 10 microns. Membranes with average pore sizes of about 0.001 to about 0.05 microns are sometimes classified as ultrafiltration membranes. Membranes with pore sizes between about 0.05 and 10 microns are sometimes referred to as microporous membranes.

[0005] Filtration membranes with micron or submicron range pore sizes can be effective in removing unwanted materials from a fluid stream, either by sieving or non-sieving mechanisms, or both. Sieving mechanisms are a type of filtration in which particles are removed from a liquid stream by mechanical retention of the particles on the surface of the filtration membrane, which acts to mechanically interfere with the movement of the particles and retain them within the filter, mechanically preventing the flow of the particles through the filter. Typically, the particles can be larger than the pores of the filter. "Non-sieving" filtration mechanisms are a type of filtration in which the filtration membrane retains suspended particles or dissolved materials contained in the fluid stream passing through the filtration membrane in a manner that is not solely mechanical, including, for example, electrostatic mechanisms in which particulate matter or dissolved impurities are electrostatically attracted to the filter surface and retained there for removal from the fluid stream; the particles can be dissolved or solid with a particle size smaller than the pores of the filter media.

[0006] The removal of ionic materials, such as dissolved anions or cations, from solutions is important in many industries, such as the microelectronics industry, where very low concentrations of ionic contaminants and particles can adversely affect the quality and performance of microprocessors and memory devices. The ability to prepare positive and negative photoresists with low levels of metal ion contaminants, or to deliver isopropyl alcohol used in Maragoni drying for wafer cleaning with low parts per billion or parts per trillion levels of metal ion contaminants, is highly desirable and are just two examples of the need for contamination control in semiconductor manufacturing. Colloidal particles, which can be positively or negatively charged depending on the colloid chemistry and solution pH, can also contaminate process fluids and need to be removed. Dissolved ionic materials can be removed by microporous filtration membranes made of polymeric materials that attract dissolved ionic materials by a non-sieving filtration mechanism. Examples of such microporous membranes are made from chemically inert, low surface energy polymers such as ultra-high molecular weight polyethylene ("UPE"), polytetrafluoroethylene, and the like. Membranes have been used to remove metal contaminants from liquids in industries such as the microelectronic device industry. For example, photoresist solutions with ultra-low levels of metal ion contaminants are desirable for lower wafer defect rates and higher yields during mass production of integrated circuits. Cation exchange membranes (i.e., negatively charged membranes) are the industry standard for removing such metal contamination from photoresist solutions used in the manufacture of microchips.

[0007] Also desirable in the microelectronic device industry are various solvents used in photoresist applications, especially polar solvents, that have minimal anionic impurities. In particular, it is highly desirable for polar solvents such as water and isopropanol to have minimal anionic impurities--impurities such as halides (e.g., chlorides), phosphates, nitrates, nitrites, sulfites, and sulfates. Summary of the Invention

[0008] The field of microelectronic device processing requires steady improvements in processing materials and methods to maintain a parallel steady improvement in the performance (e.g., speed and reliability) of microelectronic devices. Opportunities for improving microelectronic device fabrication exist in all aspects of the manufacturing process, including methods and systems for filtering liquid materials.

[0009] A wide variety of different liquid materials are used as process solvents, cleaners, and other processing solutions in microelectronic device processing. Many, if not most, of these materials are used at very high levels of purity. As an example, liquid materials (e.g., solvents) used in photolithographic processing of microelectronic devices must be of very high purity. Specific examples of liquids used in microelectronic device processing include processing solutions for spin-on-glass (SOG) techniques, for back surface antireflective coating (BARC) processes, and for photolithography or wet etch and clean.

[0010] The present disclosure provides a porous membrane having ionizable nitrogen functional groups at least at the surface of the membrane, at least a portion of the ionizable nitrogen functional groups being associated with hydroxide anions. As described more fully below, these ionizable functional groups can be introduced to the surface of the membrane either by a grafting process or by coating with a curable coating prepared from a monomeric species having the desired functional groups. In this way, at least a portion of the membrane thus has this coating and then has available ionizable nitrogen functional groups that can interact with the fluid passing through the membrane, thereby removing undesirable anionic contaminants.

[0011] The membranes are thus useful in the purification of polar solvents such as water and alcohols, and are capable of removing trace amounts of anionic contaminants such as halides, phosphates, nitrates, nitrites, sulfites, and sulfates. [Brief description of the drawings]

[0012] [Figure 1] 4 illustrates the removal of chloride ions from deionized water (DIW) samples. [Diagram 2] 1 illustrates the removal of chloride ions from an isopropanol (IPA) sample. [Diagram 3] 1 shows the results of an experiment involving a control membrane, i.e., before treatment with a hydroxide compound, indicating that no effective chloride removal occurred, see Comparative Example 1. [Figure 4] 1 shows the results of an experiment involving a control membrane, i.e., before treatment with a hydroxide compound, indicating that no effective chloride removal occurred, see Comparative Example 2. [Diagram 5] 1 shows the results of an experiment involving a control membrane, i.e., before treatment with a hydroxide compound, indicating that no effective chloride removal occurred, see Comparative Example 3. [Figure 6] 1 shows the results of an experiment in which the control membrane referred to above was treated with ammonium hydroxide, demonstrating that effective chloride removal occurred, see Example 1. [Figure 7] 1 is a plot of percent removal of bromide, chloride, fluoride, nitrate, nitrite, phosphate, and sulfate anions as a function of tank turnover. [Figure 8] 1 is a plot of the percent removal of bromide, chloride, fluoride, nitrate, sulfate, and phosphate from 100% isopropanol in a single pass of the solvent through the membrane. [Figure 9] 1 shows (schematic and not necessarily to scale) examples of filter products as described herein. [Figure 10] 1 is a plot of the percent removal of fluoride, chloride, nitrite, sulfate, bromide, nitrate, and phosphate from a 50 ppb multi-anion exposure by a polyallylamine coated UPE membrane. [Figure 11]1 is a plot of percent removal of fluoride, chloride, nitrite, sulfate, bromide, nitrate, and phosphate from a 2500 ppb multi-anion exposure by polyallylamine coated UPE membrane. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term "or" is generally utilized in its sense including "and / or" unless the content clearly dictates otherwise.

[0014] The term "about" generally refers to a range of numbers that are considered to be equal to the recited value (e.g., having the same function or result). In many instances, the term "about" may include numbers that are rounded to the nearest significant figure.

[0015] Numerical ranges expressed using endpoints include all numbers subsumed within that range (eg, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5).

[0016] In one aspect, the present disclosure provides a porous membrane having ionizable nitrogen functional groups at least at a surface of the membrane, at least a portion of the ionizable nitrogen functional groups being associated with hydroxide anions.

[0017] The porous membranes contemplated herein are not limited by the underlying material that constitutes the membrane. The porous membrane can be any suitable porous membrane, which can be amorphous, crystalline, or any suitable morphological combination thereof in structure. The porous polymer membrane can be made of any suitable polymer, such as, for example, polyolefins (including fluorinated polyolefins), polyamides, polyacrylates, polyesters, nylons, polysulfones (PS), polyethersulfones (PES), cellulose, polycarbonates, single polymers, copolymers, composites, and combinations thereof. Particular embodiments include membranes that include polyolefins. Suitable polyolefins include, but are not limited to, polyethylene, high density polyethylene, ultra-high molecular weight polyethylene, and combinations thereof. Suitable halocarbon polymers include, but are not limited to, polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), fluorinated ethylene polymers (FEP), polyhexafluoropropylene, and polyvinylidene fluoride, and combinations of two or more thereof. In another embodiment, the membrane is composed of polytetrafluorethyene.

[0018] In one embodiment, the porous polymer membrane comprises a polyethylene-based membrane referred to as ultra-high molecular weight polyethylene (UPE). UPE filter materials, such as UPE membranes, typically have a molecular weight of about 1×10 6 ~9×10 6 Da, or 1.5 × 10 6 ~9×10 6 Da range, e.g., about 1×10 6 It is made from a resin having a molecular weight (viscosity average molecular weight) higher than Dalton (Da).

[0019] To introduce ionizable nitrogen functional groups at or near the surface of the membrane, such groups can be grafted onto the polymer membrane or introduced by a coating. In some embodiments, the coating can be a crosslinked polymer, such as a polymer such as polyallylamine or polyvinylamine mixed with a crosslinker, such as a bifunctional crosslinker, such as poly(ethylene glycol) diglycidyl ether or 1,4-butanediol diglycidyl ether. In some embodiments, the coating can be the result of free radical polymerization of ionizable nitrogen-containing ethylenically unsaturated monomers and optionally other ethylenically unsaturated monomers. The polymerization results in a coating that covers at least a portion of the polymer membrane surface, thereby resulting in ionizable nitrogen functional groups at least on the surface, which allows the interaction of these ionizable nitrogen groups to interact with the fluid being purified by passing through the membrane.

[0020] In certain embodiments, the ethylenically unsaturated monomer having an ionizable nitrogen functionality is selected from 2-(dimethylamino)ethyl hydrochloride acrylate, [2-(acryloyloxy)ethyl]trimethylammonium chloride, 2-aminoethyl methacrylate hydrochloride, N-(3-aminopropyl)methacrylate hydrochloride, 2-(dimethylamino)ethyl methacrylate hydrochloride, [3-(methacryloylamino)propyl]trimethylammonium chloride solution, [2-(methacryloyloxy)ethyl]trimethylammonium chloride, acrylamidopropyltrimethylammonium chloride, 2-aminoethyl methacrylamide hydrochloride, N-(2-aminoethyl)methacrylamide hydrochloride, N-(3-aminopropyl)-methacrylamide hydrochloride, diallyldimethylammonium chloride, allylamine hydrochloride, vinylimidazolium hydrochloride, vinylpyridinium hydrochloride, and vinylbenzyltrimethylammonium chloride, etc., either individually or in combination of two or more thereof. In a particular embodiment, the ethylenically unsaturated monomer with ionizable nitrogen functionality comprises acrylamidopropyltrimethylammonium chloride (APTAC).It should be appreciated that some ethylenically unsaturated monomers with at least one ionizable nitrogen functionality mentioned above contain quaternary ammonium groups and are naturally charged in polar solvents, while other monomers with positive charges, such as those containing primary, secondary and tertiary amines, can be adjusted to create a charge by treatment with acid.It should also be appreciated that this free radical polymerized coating can be prepared using the chloride or hydrochloride forms of the monomers listed above, or can be converted to different halide or hydrohalide forms, or converted to hydroxide forms before polymerization.In any event, as described more fully below, the coating once formed will be treated with a hydroxide compound, such as an alkyl or aryl phosphonium hydroxide, ammonium hydroxide, or an organic ammonium hydroxide, to convert the ionizable nitrogen-containing functional groups to those that associate with hydroxide anions and thus become useful in the present invention to reduce or remove anionic contaminants, such as halides, phosphates, nitrates, nitrites, sulfites, and sulfates, from polar solvents.

[0021] In certain embodiments, the underlying polymeric membrane has a free radical polymerized coating prepared from about 1 to about 25 weight percent of an ethylenically unsaturated monomer having an ionizable nitrogen functional group. In other embodiments, the underlying polymeric membrane has a free radical polymerized coating prepared from about 2 to about 15 weight percent of an ethylenically unsaturated monomer having an ionizable nitrogen functional group. In other embodiments, the underlying polymeric membrane has a free radical polymerized coating prepared from about 3 to about 10 weight percent of an ethylenically unsaturated monomer having an ionizable nitrogen functional group. As referred to herein, the weight percent of the ethylenically unsaturated monomer is the weight of the monomer based on the total weight of the solution, i.e., the reaction solvent and all other monomers utilized in the polymerization reaction.

[0022] In addition to the ethylenically unsaturated monomers having at least one ionizable nitrogen functional group, the free radically polymerized coatings can be prepared from additional ethylenically unsaturated monomers that do not have at least one ionizable nitrogen functional group and can be classified as uncharged, negatively charged, or zwitterionic in nature. Such monomers are well known and include various vinyl and (meth)acrylic monomers that can be charged, e.g., acrylic acid or methacrylic acid, or uncharged, e.g., acrylic or methacrylic esters, or zwitterionic in nature. Additionally, the free radically polymerized coatings can contain difunctional compounds to effectively act as crosslinkers.

[0023] Exemplary crosslinkers include methylene bisacrylamide (MBAm), triallylamine, tetraethylene glycol diacrylate, tetraethylene glycol diamethacrylate, divinyl sulfone, divinylbenzene, 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione 98%, and ethylene glycol divinyl ether. In one embodiment, the crosslinker is methylene bisacrylamide.

[0024] Examples of monomers with negative charge in organic liquids that can be used for coating include, but are not limited to, 2-ethylacrylic acid, acrylic acid, 2-carboxyethyl acrylate, 3-sulfopropyl acrylate potassium salt, 2-propylacrylic acid, 2-(trifluoromethyl)acrylic acid, methacrylic acid, 2-methyl-2-propene-1-sulfonic acid sodium salt, mono-2-(methacryloyloxy)ethyl maleate, 3-sulfopropyl methacrylate potassium salt, 2-acrylamido-2-methyl-1-propanesulfonic acid, 3-methacrylamidophenylboronic acid, vinylsulfonic acid, and vinylphosphonic acid, either individually or in combination of two or more thereof. In a particular embodiment, the monomer with negative charge comprises a sulfonic acid. In one embodiment, the monomer with negative charge is vinylsulfonic acid or a salt thereof. It should be recognized that some of the monomers with negative charge listed above contain strong acid groups and are naturally charged in organic solvents, while other monomers with negative charge comprising weak acids are adjusted to create a charge by treatment with a base. Monomers that are negatively charged in organic solvents, either naturally or by processing, can be polymerized and crosslinked with a crosslinker to form a coating for the porous membrane that is negatively charged in organic solvents.

[0025] Examples of non-charged ethylenically unsaturated monomers are vinyl acetate, butyl butyrate, vinyl caprylate, and C1-C 18 Alkyl (meth)acrylates. Further examples include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, ethylhexyl acrylate, ethylhexyl methacrylate, octyl acrylate, octyl methacrylate, styrene, α-methylstyrene, glycidyl methacrylate, alkyl crotonates, vinyl acetate, vinyl caprylate, di-n-butyl maleate, di-octyl maleate, and the like.

[0026] Examples of zwitterionic monomers include, either individually or in combination of two or more thereof, [3-(methacryloylamino)propyl]di-methyl(3-sulfopropyl)ammonium hydroxide; [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide; 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate; and 1-(3-sulfopropyl)-2-vinylpyridinium hydroxide.

[0027] In one embodiment, the underlying polymer membrane is at least partially coated with a free radically polymerized polymer prepared from about 3 to about 10 weight percent acrylamidopropyltrimethylammonium chloride, and monomers including dimethylacrylamide and methylenebisacrylamide.

[0028] As an example, polymerization and crosslinking of the polymerizable monomer to the porous membrane substrate can be performed such that selected portions or the entire surface of the porous membrane, including the inner surface of the porous membrane, are modified with crosslinked polymer. It should be understood that various embodiments of the coated porous polymer membrane include crosslinking as much of the membrane surface as desired, from greater than 0% to 100%. It should also be understood that embodiments include other techniques such as grafting (as discussed further below) and combinations of techniques, such as some crosslinked and some grafted. Embodiments also include crosslinking the grafted portion.

[0029] As an example, a reagent bath consisting of (1) at least one polymerizable monomer that is an ethylenically unsaturated monomer having at least one ionizable nitrogen functional group, and optionally another ethylenically unsaturated monomer, (2) if necessary, and optionally a polymerization initiator, (3) a cross-linking agent in a polar solvent, such as a water-soluble solvent for these three components, is contacted with the porous polymeric membrane substrate under conditions that cause polymerization and cross-linking of the monomers and deposition of the resulting cross-linked polymer on the porous polymeric membrane substrate. Even if the solvent is a polar solvent, the required degree of membrane surface modification can and will be obtained. If the monomer is difunctional or has higher functionality, an additional cross-linking agent is not required, but may be used. Representative suitable polar solvents include polyols, including 2-methyl-2,4-pentanediol, 2,4 pentanedione, glycerin or 2,2'-thiodiethanol; amides, such as formamide, dimethylformamide, dimethylacetamide; alcohols, such as methanol; and solvents having a dielectric constant greater than 25 at room temperature, such as nitro-substituted aromatics, including nitrobenzene, 2-furaldehyde, acetonitrile, 1-methylpyrrolidone, etc. The particular solvent is selected to solubilize the crosslinking agent, monomer, and, if present, the initiator.

[0030] Suitable initiators and crosslinking agents for the above-mentioned monomers can be used. For example, when a charged alkyl group is utilized as the polymerizable monomer, suitable photoinitiators include benzophenone, 4-(2-hyroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, azoisopropane, or 2,2-dimethoxy-2-phenylacetophenone. Suitable thermal initiators include organic peroxides such as dibenzoyl peroxide, t-butyl hydroperoxide, cumyl peroxide, or t-butyl perbenzoate, and azo compounds such as azobisisobutyronitrile (AIBN) or 4,4,'-azobis(4-cyanovaleric acid). Representative suitable crosslinking agents include 1,6-hexanediol diacrylate, tetraethylene glycol diacrylate, 1,1,1-trimethylolpropane triacrylate, and the like; N,N'-methylenebisacrylamide, and the like, either individually or in combination of two or more thereof.

[0031] In one embodiment, the polymerizable monomer is present in the reactant solution at a concentration of about 2% to about 20% based on the weight of the total solution, or alternately at a concentration of about 3% to about 10%. The crosslinking agent is present in one embodiment in an amount of about 2% to about 10% by weight based on the weight of the polymerizable monomer. Larger amounts of crosslinking agent can be used. The polymerization initiator is present in an amount of about 1% to about 10% by weight based on the weight of the polymerizable monomer. As mentioned above, the crosslinking agent can be utilized without a monomer, thereby acting as a polymerizable monomer.

[0032] Polymerization and crosslinking can be carried out by exposing the monomer reaction system to ultraviolet (UV) light, a heat source, or ionizing radiation. Polymerization and crosslinking are carried out in an environment where oxygen does not inhibit polymerization or crosslinking. The process is conveniently carried out by immersing the membrane substrate in a solution containing the monomer, crosslinking agent, and initiator, sandwiching the membrane between two sheets transparent to UV light, such as polyethylene, or within a blanket of an inert gas, such as nitrogen, and exposing to UV light. The process can be carried out continuously, with the desired crosslinked coating forming after UV exposure begins. By controlling the reactant concentrations and UV exposure as described above, a composite membrane is produced that is free of clogging and has essentially the same porous structure as the membrane substrate.

[0033] Further disclosure regarding the formation and composition of such coatings on the surface of porous polymeric membranes can be found in U.S. Patent Publication No. 2020 / 0206691, which is incorporated herein in its entirety for all purposes.

[0034] In further embodiments, membranes that can be treated with hydroxide compounds and utilized as described herein include those available from Entegris, Inc. under the name Purasol™ SN.

[0035] Exemplary hydroxide compounds that can be used to convert a coating to one that contains an ionizable nitrogen functional group associated with a hydroxide ion include hydroxide compounds that also do not contain an alkali or alkaline earth metal counterion, and thus include ammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tributylmethylammonium hydroxide, benzyltrimethylammonium hydroxide, choline hydroxide, tetrabutylphosphonium hydroxide, tetramethylphosphonium hydroxide, tetraethylphosphonium hydroxide, tetrapropylphosphonium hydroxide, benzyltriphenylphosphonium hydroxide, methyltriphenylphosphonium hydroxide, ethyltriphenylphosphonium hydroxide, and N-propyltriphenylphosphonium hydroxide.

[0036] In another embodiment, the ionizable nitrogen functional group is grafted to the membrane. In this process, the desired ionizable nitrogen-containing ethylenically unsaturated monomer can be attached to the filter material by grafting from the membrane. Grafting refers to chemically linking a moiety such as a monomer or other molecule to the polymeric porous membrane surface, including the inner pore surface of the porous membrane. "Grafting" in this context can be accomplished by irradiation of the filter material in the presence of a photoinitiator and an unsaturated monomer containing the desired polycarboxyl ligand (see, e.g., WO 2016 / 081729 A1 (Jaber et al.), U.S. Patent Publication Nos. 2021 / 0260537; 2020 / 0406201; 2020 / 0254398; 2020 / 0206691; 20200171442; 2019 / 0282961; 2018 / 0290109; 2018 / 0185835; 2016 / 0144322; and U.S. Patent No. 10,792,620, each of which is incorporated by reference in its entirety for all purposes). In another mode of practice, the filter material can be attached to the desired ionizable nitrogen-containing ethylenically unsaturated monomers by grafting from the membrane using electron beam or gamma radiation. Grafting using electron beam or gamma radiation can be accomplished using techniques known as pre-irradiation grafting or co-irradiation grafting.

[0037] For grafting of functional groups to polymers with hydrophobic surfaces, such as polyethylene, the use of hydrophobic photoinitiators can be effective. For other polymers, particularly polymers such as nylon that exhibit hydrophilic surfaces, these techniques are less effective. In such cases, the method described in U.S. Patent Publication No. 2020 / 01714422, which is incorporated herein by reference, can be utilized. In general, the technique involves applying a hydrophobic photoinitiator in a dissolved state to the surface of a hydrophilic polymer, followed by an optional drying step, and then rewetting the surface with a monomer solution. The technique can ensure that a relatively high level of photoinitiator is deposited on the surface of the hydrophilic polymer. The level of photoinitiator presented on the surface is sufficient to allow grafting of charged monomers to the hydrophilic surface in an amount that would be usefully or advantageously high in terms of allowing the hydrophilic polymer (as part of the filtration membrane) to be effective as a filtration membrane. The process of chemically bonding ionic groups to the hydrophilic polymer of a filtration membrane does not have a significant effect on the amount (flow rate or flux) of fluid that can pass through the filtration membrane - the amount (velocity or flow rate) of fluid that can pass through the filtration membrane is not substantially adversely affected by chemically attaching ionic groups to the filtration membrane. At the same time, the filtration performance of the filtration membrane, particularly non-sieving filtration as measured by dye binding capacity, particle retention, and metal ion rejection, can be improved by significant amounts.

[0038] The filtration membrane thus provided by the present disclosure is useful for removing at least a portion of anionic species in polar solvent.Accordingly, in another aspect, the present disclosure provides a method for removing anionic contaminants from a polar solvent composition, comprising passing the composition through the membrane of the present disclosure.In this manner, 50 (weight) percent, 60 percent, 70 percent, 80 percent, 90 percent, 95 percent, or even about 99 percent of the anionic contaminants in polar solvent can be removed.

[0039] In certain embodiments, the polar solvent composition is comprised of a solvent selected from at least one of water, C1-C6 alcohols, glycols, and glycol ethers. Exemplary solvents include water, methanol, ethanol, isopropanol, butanol, C2-C4 diols, C2-C4 triols, tetrahydrofurfuryl alcohol, 3-chloro-1,2-propanediol, 3-chloro-1-propanethiol, 1-chloro-2-propanol, 2-chloro-1-propanol, 3-chloro-1-propanol, 3-bromo-1,2-propanediol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-iodo-1-propanol, 4-chloro-1-butanol, 2-chloroethanol), dichloromethane, and the like. , chloroform, acetic acid, propionic acid, trifluoroacetic acid, tetrahydrofuran, N-methylpyrrolidinone, cyclohexylpyrrolidinone, N-octylpyrrolidinone, N-phenylpyrrolidinone, methyldiethanolamine, methyl formate, N,N-dimethylformamide, dimethylsulfoxide, tetramethylene sulfone, diethyl ether, phenoxy-2-propanol, propriophenone, ethyl lactate, ethyl acetate, ethyl benzoate, acetonitrile, acetone, ethylene glycol, propylene glycol, 1,3-Propanediol, dioxane, butyryllactone, butylene carbonate, ethylene carbonate, propylene carbonate, dipropylene glycol, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol phenyl ether, propylene glycol methyl ether, dipropylene glycol methyl ether, tripropylene glycol methyl ether, dipropylene glycol Examples of the glyceryl ethers include propylene glycol dimethyl ether, dipropylene glycol ethyl ether, propylene glycol n-propyl ether, dipropylene glycol n-propyl ether, tripropylene glycol n-propyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, tripropylene glycol n-butyl ether, propylene glycol phenyl ether, ethylene glycol monophenyl ether, diethylene glycol monophenyl ether, hexaethylene glycol monophenyl ether, dipropylene glycol methyl ether acetate, tetraethylene glycol dimethyl ether, dibasic esters, glycerin carbonate, N-formyl morpholine, triethyl phosphate, and combinations thereof.

[0040] In one embodiment, the C1-C6 alcohol is isopropanol.

[0041] In one embodiment, the anionic contaminants to be removed by the membranes of the present disclosure are selected from one or more of halides, phosphates, nitrates, nitrites, sulfites, and sulfates, hi another embodiment, the anionic contaminants to be removed are selected from phosphate, chloride, and fluoride ions.

[0042] The membranes of the present disclosure can be utilized with one or more filters or membranes other than the membranes of the present disclosure. This utilization can range from simply using such other filters and membranes in series with the membranes of the present disclosure to combining such other filters and membranes with the membranes of the present disclosure in a unitary structure. Thus, in a further aspect, the present disclosure provides a composite membrane comprising a first membrane and a second membrane, the output facing surface of the first membrane being in contact with the input facing surface of the second membrane; the first membrane or the second membrane comprises a porous membrane having ionizable nitrogen functional groups at or near a surface of the membrane, at least a portion of the ionizable nitrogen functional groups being associated with hydroxide anions; and providing a composite membrane in which the second membrane is different from the first membrane.

[0043] In one embodiment, the second membrane is capable of removing cationic materials from polar solvents. Many such filter materials are commercially available or otherwise known. See, for example, PURASOL™ SP solvent purifiers, Protego Plus HT and HTX Purifiers, and Protego Plus LT Purifiers available from Entegris, Inc. See also U.S. Patent Publication No. 2020 / 0206691 and U.S. Patent No. 10,792,620, which are incorporated herein by reference in their entirety for all purposes.

[0044] The membranes described herein may have a variety of geometric configurations, such as flat sheets, corrugated sheets, pleated sheets, and hollow fibers, among others. The porous polymeric membranes may have pore structures that may be isotropic or anisotropic, skinned or unskinned, symmetric or asymmetric, any combination thereof, or may be composite membranes that include one or more retaining layers and one or more supporting layers. Additionally, coated porous membranes may be supported or unsupported, such as by webs, nets, and cages, among others.

[0045] The described membranes can be housed in a larger filter structure, such as a multi-layer filter assembly or filter cartridge used in a filtration system. A filtration system places the filtration membrane in a filter housing, for example as part of a multi-layer filter assembly or as part of a filter cartridge, and exposes the filtration membrane to a liquid chemical flow path, so that at least a portion of the liquid chemical flow passes through the filtration membrane, so that the filtration membrane removes a certain amount of impurities or contaminants from the liquid chemical. The structure of the multi-layer filter assembly or filter cartridge can include one or more of a variety of additional materials and structures that support the composite filtration membrane in the filter assembly or filter cartridge, allowing the fluid to flow from the filter inlet, through the composite membrane (including the filter layer), and through the filter outlet, thereby passing through the composite filtration membrane as it passes through the filter. The filtration membrane supported by the filter assembly or filter cartridge can be any useful shape, such as a pleated cylinder, a cylindrical pad, a cylindrical sheet without one or more pleats (flat), a pleated sheet, among others. Thus, in a further aspect, the present disclosure provides a filter that includes one or more of the membranes or composite membranes described herein.

[0046] An example of a filter structure containing a filtration membrane in the form of a pleated cylinder can be prepared to include the following components, any of which may be included in the filter structure but may not be required: a rigid or semi-rigid core supporting the pleated cylindrical coated filtration membrane at the inner inlet of the pleated cylindrical coated filtration membrane; a rigid or semi-rigid cage supporting or surrounding the outside of the pleated cylindrical coated filtration membrane at the outside of the filtration membrane; optional terminal pieces or "pucks" located at each of the two opposite ends of the pleated cylindrical coated filtration membrane; and a filter housing including an inlet and an outlet. The filter housing can be of any useful and desired size, shape and material, and preferably made of a suitable polymeric material.

[0047] As an example, FIG. 9 shows a filter component 30 that is the product of a pleated cylindrical component 10 and end piece 22 with optional other components. The cylindrical component 10 includes a filtration membrane 12 as described herein and is pleated. The end piece 22 is bonded (e.g., "potted") to one end of the cylindrical filter component 10. The end piece 22 may preferably be made of a melt-processable polymeric material. A core (not shown) may be disposed in the interior opening 24 of the pleated cylindrical component 10 and a cage (not shown) may be disposed around the outside of the pleated cylindrical component 10. A second end piece (not shown) may be bonded ("potted") to a second end of the pleated cylindrical component 30. The resulting pleated cylindrical component 30 with two opposing potted ends and optional core and cage may then be placed into a filter housing that includes an inlet and an outlet and is configured such that all of the fluid entering the inlet must pass through the filtration membrane 12 before exiting the filter at the outlet.

[0048] An additional filter structure may be that shown in FIG. 1B of U.S. Patent Publication No. 2020 / 0206691. EXAMPLES

[0049] As mentioned above, exemplary membranes having ionizable nitrogen functional groups can be prepared as described in U.S. Patent Publication No. 2020 / 0206691, which is incorporated herein in its entirety for all purposes. Examples 2 and 4 of this publication are described below as Preparations 1 and 2.

[0050] Preparation 1 This example illustrates the preparation of a surface modification solution containing a positively charged monomer as well as a radical initiator, a material for forming a coating. In a representative experiment, a solution was made containing 0.3% Irgacure 2959, 3.5% methanol, 5.6% acrylamidopropyltrimethylammonium chloride (APTAC), 1.2% dimethylacrylamide (DMAm) and 1.2% methylenebisacrylamide (MBAm) crosslinkers, 88.2% water.

[0051] Preparation 2 This example illustrates how a polyethylene film can be surface modified by coating with a polymerized monomer that carries a positive charge.

[0052] In a typical experiment, a 47 mm disk of UPE membrane (9 psi average mean bubble point in isopropanol (IPA) (Entegris, Inc.) was wetted with IPA solution for 25 seconds. A replacement solution containing 10% hexylene glycol and 90% water was used to rinse the membrane to remove the IPA. The membrane disk was then introduced into the surface modification solution described in Preparation 1. The dish was covered and the membrane was allowed to soak in the solution for 2 minutes. The membrane disk was removed and placed between 1 mil polyethylene sheets. The polyethylene / membrane disk / polyethylene sandwich was placed flat on a table and excess solution was removed by rolling a rubber roller over the sandwich. The polyethylene sandwich was then taped to a transport unit and the assembly was transferred to a Fusion 3000 NMR spectroscopy (DMAC) ... The membrane was then transported into a 350 nm UV-exposure lab unit operated at 50° C. The duration of exposure was controlled by the speed at which the assembly moved through the UV unit. In this example, the assembly moved through the UV chamber at 10 feet per minute. After exiting the UV unit, the membrane was removed from the sandwich and immediately placed in DI water; there it was washed by swirling for 5 minutes. The treated membrane sample was then washed in methanol for 5 minutes. After this washing procedure, the membrane was dried on the holder in an oven operating at 50° C. for 10 minutes. The IPA flow time for the membrane modified as described above was 240 seconds.

[0053] Comparative Example 1 A filter device (Device 1) containing a membrane prepared according to a process similar to Preparation 1 above was pretreated with a deionized water (DIW) flush only (5 min) and then exposed to a DIW solution spiked with chloride ions. The results, set forth in Figure 3, show that there was no removal of chloride over the period of exposure, and in act, a release of chloride ions was observed, resulting in a negative removal percentage during the early stages of the experiment.

[0054] Comparative Example 2 A filter device (Device 3) containing a membrane prepared according to a process similar to Preparation 1 above was pretreated twice with a DIW soaking step, once at room temperature (16 hours) and once at elevated temperature (50°C for 16 hours), and then exposed to a DIW solution spiked with chloride ions. The results, set forth in Figure 4, show that there is no removal of chloride, and in fact a release of chloride ions is observed, resulting in a negative removal percentage during the early stages of the experiment.

[0055] Comparative Example 3 A filter device (Device 2) containing a membrane prepared according to a process similar to Preparation 1 above was pretreated with a DIW flush (5 min) followed by a hot DIW soak (50° C. for 24 hrs) and then exposed to a DIW solution spiked with chloride ions. The results, set forth in FIG. 5, show that there is no removal of chloride over the period of exposure, and in fact a release of chloride ions is observed, resulting in a negative removal percentage during the early stages of the experiment.

[0056] Example 1 A filter device (Device 4) containing a membrane prepared according to a process similar to Preparation 1 above was pretreated with multiple 1% NH4OH and DIW soaks only (1% NH4OH 30 min soak, 16 hour 50°C DIW soak followed by 1% NH4OH 30 min flush, then 30 min DIW flush) and then exposed to a DIW solution spiked with chloride ions (soaks / flushes described herein were performed after the membrane was placed in the filter structure). The results, depicted in Figure 6, show good removal of chloride ions over the period of exposure.

[0057] Referring to the data in Figure 1, a filter device containing the treated membrane of Example 1 is exposed to a DIW solution spiked with 150 ppb chloride ions in a recirculation system and samples are taken at periodic time intervals represented by the tank turnover rate at that time. The tank turnover rate is defined as the ratio of the feed volume to the recirculation flow rate (e.g., with a feed volume of 500 mL and a recirculation flow rate of 100 mL / min, one tank turnover rate corresponds to 5 minutes). The results show that there is greater than 94% removal of chloride over the duration of the test.

[0058] Referring to the data in Figure 2, a filter device containing the treated membrane of Example 1 is exposed to a 100% isopropanol solution spiked with 75 ppb chloride ion in a recirculation system and samples are taken at periodic time intervals represented by the tank turnover rate at that time. The tank turnover rate is defined as the ratio of the feed volume to the recirculation flow rate (e.g., with a feed volume of 500 mL and a recirculation flow rate of 100 mL / min, one tank turnover rate corresponds to 5 minutes). The results show that there is greater than 92% removal of chloride over the duration of the test.

[0059] FIG. 7 is a plot of the percent removal of anions, namely bromide, chloride, fluoride, nitrate, nitrite, phosphate, and sulfate, as a function of tank turnover. Here, a filter device containing treated membranes (same as in FIG. 1) is exposed to DIW containing each of the specified ions spiked at various levels (each ion concentration is 20 ppb to 250 ppb) in a recirculation system, and samples are taken at periodic time intervals represented by the tank turnover at the time. The results show that the percent removal of an ion is a strong function of its oxidation state. Ions such as sulfate and phosphate, which have higher absolute oxidation states of 2 and 3, respectively, are completely (100%) and stably removed as a function of tank turnover. For other ions such as bromide, chloride, fluoride, nitrate, and nitrite, we see a range of absolute removal as a function of tank turnover, but the final removal depends on the particular anion. Specifically, bromide, nitrite and nitrate show approximately 60% removal; while chloride and fluoride have approximately 40% removal.

[0060] Figure 8 is a plot of the percent removal of bromide, chloride, fluoride, nitrate, sulfate, and phosphate anions from 100% isopropanol in a single pass of solvent through the membrane. Here, a 47 mm (diameter) coupon of treated membrane (same as that of Figure 1) is exposed to 100% isopropanol spiked with 20 ppb of each of the specified ions in a single pass system and samples are taken at periodic intervals based on volume. The results show that the percent removal of an ion depends on the particular anion. For sulfate and phosphate, the removal is greater than 95%; for bromide, chloride, and nitrate, the removal is >80%; for fluoride, the removal depends on the volume of spiked 100% isopropanol passed through the membrane - the higher the volume passed, the lower the removal.

[0061] Example 2 A hydrophilic ultra-high molecular weight polyethylene (UPE) membrane sheet with a pore size of about 0.65 microns was surface modified with a cross-linked polyallylamine coating using the following method. First, a coating solution was made containing 10% polyallylamine (average MW about 15,000) and 0.5% poly(ethylene) glycol diglycidyl ether (MW about 500) by weight. To soak the membrane in the solution, the hydrophilic UPE membrane sheet was submerged in the coating solution for about 1 minute. The membrane was then removed from the coating solution and placed between two polyethylene sheets, and excess coating solution was removed with a rubber roller. The membrane was then clamped between two Teflon-coated metal frames and allowed to dry at room temperature for about 16 hours to allow curing to occur. The membrane was removed from the frames and washed several times with deionized water and 10% hydrochloric acid, then washed with methanol and placed again between the Teflon-coated metal frames and allowed to dry. The resulting hydrophilic UPE membrane coated with cross-linked polyallylamine (PAA membrane) was cut into 47 mm diameter coupons.

[0062] The coupons were immersed in jars containing exposure solutions containing fluoride, chloride, nitrite, sulfate, bromide, nitrate, and phosphate anions at two different concentrations (50 ppb and 2500 ppb of each ion). A sample of each exposure solution was collected in a sample jar for analysis to act as the "feed" value. The solution containing the membrane was placed on a rotary mixer and left to mix for about 24 hours, then the deionized water solution was aliquoted into a sample jar and the solution was analyzed by ion chromatography (IC). Figure 10 shows the % removal of ions versus the "feed" concentration in the exposure solution at 50 ppb exposure, and Figure 11 shows that at 2500 ppb exposure. As can be seen, the PAA membrane has high rejection of sulfate and phosphate anions.

[0063] Aspects In a first aspect, the present disclosure provides a porous membrane having ionizable nitrogen functional groups at least at a surface of the membrane, at least a portion of the ionizable nitrogen functional groups being associated with hydroxide anions.

[0064] In a second aspect, the present disclosure provides a membrane of the first aspect, capable of removing anionic contaminants from a polar solvent composition.

[0065] In a third aspect, the present disclosure provides the membrane of the first or second aspect, wherein the anionic contaminant is selected from chloride, fluoride, bromide, nitrate, nitrite, sulfate, and phosphate ions.

[0066] In a fourth aspect, the present disclosure provides a membrane of any one of the first, second, or third aspects, wherein ionizable nitrogen functional groups are grafted to the membrane.

[0067] In a fifth aspect, the present disclosure provides a membrane of any one of the first, second, or third aspects, having a coating, and wherein the ionizable nitrogen functional groups are at least on a surface of the coating of the membrane.

[0068] In a sixth aspect, the present disclosure provides the membrane of the fifth aspect, wherein the coating is a polymeric material formed from a free radical reaction of ethylenically unsaturated monomers, at least a portion of which are ethylenically unsaturated monomers having an ionizable nitrogen functional group.

[0069] In a seventh aspect, the present disclosure provides the membrane of the sixth aspect, wherein the ethylenically unsaturated monomer having an ionizable nitrogen functional group is selected from 2-(dimethylamino)ethyl acrylate, [2-(acryloyloxy)ethyl]trimethylammonium, 2-aminoethyl methacrylate, N-(3-aminopropyl)methacrylate, 2-(dimethylamino)ethyl methacrylate, [3-(methacryloylamino)propyl]trimethylammonium, [2-(methacryloyloxy)ethyl]trimethylammonium, acrylamidopropyltrimethylammonium, 2-aminoethyl methacrylamide, N-(2-aminoethyl)methacrylamide, N-(3-aminopropyl)-methacrylamide, diallyldimethylammonium, allylamine, vinylimidazolium, vinylpyridinium, and vinylbenzyltrimethylammonium, or hydroxides, or halide or hydrohalide salts thereof.

[0070] In an eighth aspect, the present disclosure provides the membrane of the sixth or seventh aspect, wherein the ethylenically unsaturated monomer having an ionizable nitrogen functional group comprises acrylamidopropyltrimethylammonium chloride.

[0071] In a ninth aspect, the present disclosure provides the membrane of any one of the sixth, seventh, or eighth aspects, wherein the ethylenically unsaturated monomer is further selected from monomers that are uncharged, negatively charged, or zwitterionic.

[0072] In a tenth aspect, the present disclosure provides the membrane of the fifth aspect, wherein the coating is a polyallylamine or a polyvinylamine.

[0073] In an eleventh aspect, the present disclosure provides a membrane of any one of the first to ninth aspects, treated with an alkyl or aryl phosphonium hydroxide, ammonium hydroxide, or an organic ammonium hydroxide.

[0074] In a twelfth aspect, the present disclosure provides the membrane of the eleventh aspect, wherein the hydroxide compound is selected from ammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tributylmethylammonium hydroxide, benzyltrimethylammonium hydroxide, choline hydroxide, tetrabutylphosphonium hydroxide, tetramethylphosphonium hydroxide, tetraethylphosphonium hydroxide, tetrapropylphosphonium hydroxide, benzyltriphenylphosphonium hydroxide, methyltriphenylphosphonium hydroxide, ethyltriphenylphosphonium hydroxide, N-propyltriphenylphosphonium hydroxide.

[0075] In a thirteenth aspect, the present disclosure provides the membrane of any one of the sixth, seventh, or eighth aspects, wherein the ethylenically unsaturated monomer having an ionizable nitrogen functional group is a quaternary ammonium group associated with a hydroxyl anion.

[0076] In a fourteenth aspect, the present disclosure provides the membrane of any one of the sixth, seventh, or eighth aspects, wherein the underlying polymeric membrane is at least partially coated with a free-radically polymerized polymer, the polymer being prepared from monomers comprising about 3 to about 10 weight percent acrylamidopropyltrimethylammonium chloride, and the ethylenically unsaturated monomers further comprise dimethylacrylamide and methylenebisacrylamide.

[0077] In a fifteenth aspect, the present disclosure provides a method for removing anionic contaminants from a polar solvent composition comprising passing said composition through a membrane of any one of the first to thirteenth aspects.

[0078] In a sixteenth aspect, the present disclosure provides the method of the fifteenth aspect, wherein the polar solvent composition is comprised of a solvent selected from at least one of water, a C1-C6 alcohol, a glycol, and a glycol ether.

[0079] In a seventeenth aspect, the present disclosure provides a polar solvent composition comprising any one of methanol, ethanol, isopropanol, butanol, C2-C4 diols, C2-C4 triols, tetrahydrofurfuryl alcohol, 3-chloro-1,2-propanediol, 3-chloro-1-propanethiol, 1-chloro-2-propanol, 2-chloro-1-propanol, 3-chloro-1-propanol, 3-bromo-1,2-propanediol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-iodo-1-propanol, 4-chloro-1-butanol, 2 ... ethanol), dichloromethane, chloroform, acetic acid, propionic acid, trifluoroacetic acid, tetrahydrofuran, N-methylpyrrolidinone, cyclohexylpyrrolidinone, N-octylpyrrolidinone, N-phenylpyrrolidinone, methyldiethanolamine, methyl formate, N,N-dimethylformamide, dimethylsulfoxide, tetramethylene sulfone, diethyl ether, phenoxy-2-propanol, propriophenone, ethyl lactate, ethyl acetate, ethyl benzoate, acetonitrile, acetone, ethylene glycol, propylene glycol, 1,3-Propanediol, dioxane, butyryllactone, butylene carbonate, ethylene carbonate, propylene carbonate, dipropylene glycol, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol phenyl ether, propylene glycol methyl ether, dipropylene glycol methyl ether, tripropylene glycol methyl ether, dipropylene glycol dimethyl ether, dipropylene The method of the fifteenth aspect is provided, wherein the solvent is selected from at least one of pyrene glycol ethyl ether, propylene glycol n-propyl ether, dipropylene glycol n-propyl ether, tripropylene glycol n-propyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, tripropylene glycol n-butyl ether, propylene glycol phenyl ether, ethylene glycol monophenyl ether, diethylene glycol monophenyl ether, hexaethylene glycol monophenyl ether, dipropylene glycol methyl ether acetate, tetraethylene glycol dimethyl ether, dibasic esters, glycerin carbonate, N-formyl morpholine, triethyl phosphate, and combinations thereof.

[0080] In an eighteenth aspect, the present disclosure provides the method of the sixteenth aspect, wherein the C1-C6 alcohol is isopropanol.

[0081] In a nineteenth aspect, the present disclosure provides the method of any one of the fifteenth to eighteenth aspects, wherein the anionic contaminant is selected from one or more of halides, phosphates, nitrates, nitrites, sulfites, and sulfates.

[0082] In a twentieth aspect, the present disclosure provides the method of any one of the fifteenth to eighteenth aspects, wherein the anionic contaminant is selected from fluoride, chloride, and phosphate ions.

[0083] In a twenty-first embodiment, the present disclosure provides a composite membrane comprising a first membrane and a second membrane, wherein an outlet surface of the first membrane is in contact with an input surface of the second membrane; the first membrane or the second membrane comprises a porous membrane having ionizable nitrogen functional groups at least at a surface of the membrane, at least a portion of the ionizable nitrogen functional groups being associated with hydroxide anions; and providing a composite membrane in which the second membrane is different from the first membrane.

[0084] In a twenty-second aspect, the present disclosure provides the composite membrane of the twenty-first aspect, wherein the membrane is capable of removing anionic contaminants from a polar solvent composition.

[0085] In a twenty-third aspect, the present disclosure provides a filter comprising the membrane of any one of the first to fourteenth aspects, the twenty-first or the twenty-second aspects.

[0086] Having thus described several illustrative embodiments of the present disclosure, those skilled in the art will readily recognize that still other embodiments may be made and used within the scope of the claims appended hereto. Many advantages of the present disclosure, which are covered by this document, have been set forth in the foregoing description. It will be understood, however, that the present disclosure is in many respects merely illustrative. The scope of the present disclosure is, of course, to be defined in the language in which the appended claims are expressed.

Claims

1. A porous membrane comprising ionizable nitrogen functional groups at least on a surface of the membrane, at least a portion of the ionizable nitrogen functional groups being associated with hydroxide anions.

2. 10. The membrane of claim 1, capable of removing anionic contaminants from a polar solvent composition.

3. 3. The membrane of claim 2, wherein the anionic contaminants are selected from chloride, fluoride, bromide, nitrate, nitrite, sulfate, and phosphate ions.

4. 4. The membrane according to claim 1, wherein ionizable nitrogen functional groups are grafted onto the membrane.

5. 4. The membrane of claim 1 having a coating, the ionizable nitrogen functional groups being at least on the surface of the coating of the membrane.

6. 6. The membrane of claim 5, wherein the coating is a polymeric material formed from a free radical reaction of ethylenically unsaturated monomers, at least a portion of which are ethylenically unsaturated monomers having ionizable nitrogen functional groups.

7. 7. The membrane of claim 6, wherein the ethylenically unsaturated monomer having an ionizable nitrogen functionality is selected from 2-(dimethylamino)ethyl acrylate, [2-(acryloyloxy)ethyl]trimethylammonium, 2-aminoethyl methacrylate, N-(3-aminopropyl)methacrylate, 2-(dimethylamino)ethyl methacrylate, [3-(methacryloylamino)propyl]trimethylammonium, [2-(methacryloyloxy)ethyl]trimethylammonium, acrylamidopropyltrimethylammonium, 2-aminoethyl methacrylamide, N-(2-aminoethyl)methacrylamide, N-(3-aminopropyl)-methacrylamide, diallyldimethylammonium, allylamine, vinylimidazolium, vinylpyridinium, and vinylbenzyltrimethylammonium, or hydroxides, or halides, or hydrohalides thereof.

8. 7. The membrane of claim 6, wherein the ethylenically unsaturated monomer having an ionizable nitrogen functional group comprises acrylamidopropyltrimethylammonium chloride.

9. 7. The membrane of claim 6, wherein the ethylenically unsaturated monomer is further selected from monomers that are uncharged, negatively charged, or zwitterionic.

10. 7. The membrane of claim 6, wherein the ethylenically unsaturated monomer having an ionizable nitrogen functionality is a quaternary ammonium group associated with a hydroxyl anion.

11. 6. The membrane of claim 5, wherein the coating is a polyallylamine or a polyvinylamine.

12. 12. The membrane of any one of claims 1 to 11, treated with an alkyl or aryl phosphonium hydroxide, ammonium hydroxide, or an organic ammonium hydroxide.

13. 13. The membrane of claim 12, wherein the hydroxide compound is selected from ammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tributylmethylammonium hydroxide, benzyltrimethylammonium hydroxide, choline hydroxide, tetrabutylphosphonium hydroxide, tetramethylphosphonium hydroxide, tetraethylphosphonium hydroxide, tetrapropylphosphonium hydroxide, benzyltriphenylphosphonium hydroxide, methyltriphenylphosphonium hydroxide, ethyltriphenylphosphonium hydroxide, N-propyltriphenylphosphonium hydroxide.

14. 14. The membrane of any one of claims 1 to 13, wherein the underlying polymer membrane is at least partially coated with a free radically polymerized polymer, the polymer being prepared from monomers comprising about 3 to about 10 weight percent acrylamidopropyltrimethylammonium chloride, and the ethylenically unsaturated monomers further comprise dimethylacrylamide and methylenebisacrylamide.

15. 15. A method for removing anionic contaminants from a polar solvent composition comprising passing the polar solvent composition through a membrane according to any one of claims 1 to 14.

16. The polar solvent composition is water, C １ ~C ６ 16. The method of claim 15, comprising a solvent selected from at least one of an alcohol, a glycol, and a glycol ether.

17. The polar solvent composition is methanol, ethanol, isopropanol, butanol, C ２ ~C ４ Diol, C ２ ~C ４ triol, tetrahydrofurfuryl alcohol, 3-chloro-1,2-propanediol, 3-chloro-1-propanethiol, 1-chloro-2-propanol, 2-chloro-1-propanol, 3-chloro-1-propanol, 3-bromo-1,2-propanediol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-iodo-1-propanol, 4-chloro-1-butanol, 2-chloroethanol), dichloromethane, chloroform, acetic acid, propionic acid , trifluoroacetic acid, tetrahydrofuran, N-methylpyrrolidinone, cyclohexylpyrrolidinone, N-octylpyrrolidinone, N-phenylpyrrolidinone, methyldiethanolamine, methyl formate, N,N-dimethylformamide, dimethylsulfoxide, tetramethylene sulfone, diethyl ether, phenoxy-2-propanol, propriophenone, ethyl lactate, ethyl acetate, ethyl benzoate, acetonitrile, acetone, ethylene glycol, propylene glycol, 1,3-propanediol, dioxane, butyryllactone, butylene carbonate, ethylene carbonate, propylene carbonate, dipropylene glycol, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol phenyl ether, propylene glycol methyl ether, dipropylene glycol methyl ether, tripropylene glycol methyl ether, dipropylene glycol dimethyl ether, dipropylene 16. The method of claim 15, wherein the solvent is selected from at least one of propylene glycol ethyl ether, propylene glycol n-propyl ether, dipropylene glycol n-propyl ether, tripropylene glycol n-propyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, tripropylene glycol n-butyl ether, propylene glycol phenyl ether, ethylene glycol monophenyl ether, diethylene glycol monophenyl ether, hexaethylene glycol monophenyl ether, dipropylene glycol methyl ether acetate, tetraethylene glycol dimethyl ether, dibasic esters, glycerin carbonate, N-formylmorpholine, triethyl phosphate, and combinations thereof.

18. C １ ~C ６ 17. The method of claim 16, wherein the alcohol is isopropanol.

19. 19. The method of any one of claims 15 to 18, wherein the anionic contaminants are selected from one or more of halides, phosphates, nitrates, nitrites, sulfites, and sulfates.

20. 19. The method of any one of claims 15 to 18, wherein the anionic contaminants are selected from fluoride, chloride, and phosphate ions.

21. A first membrane; and Second membrane A composite membrane comprising: a discharge surface of the first membrane contacting an input surface of the second membrane; The first or second membrane comprises a porous membrane having ionizable nitrogen functional groups at least at a surface of the membrane, at least a portion of the ionizable nitrogen functional groups being associated with hydroxide anions; and A composite membrane wherein the second membrane is different from the first membrane.

22. 22. The composite membrane of claim 21, wherein the membrane is capable of removing anionic contaminants from a polar solvent composition.

23. 23. A filter comprising a membrane according to any one of claims 1 to 14 or 21 to 22.

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