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Researchers Submit Patent Application, "Composite Filtration Membranes and Methods of Preparation Thereof", for Approval

August 28, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Na, Young-Hye (San Jose, CA); Nelson, Alshakim (Fremont, CA); Sooriyakumaran, Ratnam (San Jose, CA); Vora, Ankit (San Jose, CA), filed on April 5, 2014, was made available online on August 14, 2014.

The patent's assignee is International Business Machines Corporation.

News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to composite filtration membranes, methods of their preparation, and uses thereof, and more specifically, to anti-fouling membranes for ultrafiltration comprising a layer of interfacially crosslinked poly(meth)acrylates and/or poly(meth)acrylamides.

"Membrane technologies such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) are widely used for water purification because they are energy efficient, cost-effective and simple to operate. However, many commercial membranes experience substantial flux declines when they are exposed to a mixture of inorganic salt, emulsified oil droplets, and natural organic matters (dissolved organic compounds, various proteins, and other bio-materials). These contaminants in water cause membrane fouling (deposition on membrane surface and/or blocking membrane pores), shortening the lifetime of the membrane. Current approaches to address the fouling problem include pretreatment of the feed, periodic depressurization of the membrane tube, flow reversal, and use of cleaning agents to remove fouled films from the membrane surface. These techniques require additional energy and reduce the productive operating time of the membrane, thereby directly contributing to operating cost.

"Various materials and methods have also been used to modify membrane surfaces in an effort to enhance fouling resistance. These include coating membrane surfaces with nanoparticles, enzymes, and epoxy compounds; coating membrane surfaces with poly(ethylene glycol) (PEG) based brush copolymers made by atom transfer radical polymerization (ATRP); forming a crosslinked coating based on cyclooctene monomers comprising PEO chains; growing sulfobetaine methacrylate (SBMA) copolymers by ATRP polymerization initiated on a membrane surface; covalently grafting poly(ethylene oxide) (PEO) derivatives comprising epoxy groups to a membrane surface; and employing interfacial polymerization of a difunctional aromatic amine monomer with a multifunctional acid chloride monomer to form a crosslinked polyamide network on a polysulfone UF support for reverse osmosis and nanofiltration membranes, but commercial RO and NF membranes made by interfacial polymerization do not yet provide fouling resistance. The monomers are coated in tandem layers and react without a drying step. Although the above-described materials and techniques are efficient in reducing membrane fouling, generally they are not well-suited for large scale manufacturing. The methods of preparing the modified membranes often require additional steps of casting, drying and curing to form thin selective layers on support membranes. For example, the ATRP based polymers are disadvantaged by the use of a copper catalyst, which is removed at the end of the reaction by passing the ATRP polymers through alumina columns multiple times. In another example, azide-functional cyclooctene monomers, used in making ultraviolet radiation crosslinkable polymers on UF support, are particularly hazardous for large scale industrial applications.

"Consequently, a continuing need exists for filtration membranes, particularly for water purification, having enhanced fouling resistance, anti-microbial properties, and/or enhanced salt rejection properties."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "Accordingly, a method is disclosed, comprising:

"disposing, on a porous support membrane, an aqueous mixture comprising a crosslinkable polymer comprising a poly(meth)acrylate and/or poly(meth)acrylamide backbone, thereby forming an initial film layer, wherein the crosslinkable polymer comprises a side chain nucleophilic amine group capable of interfacially reacting with a multi-functional acid halide crosslinking agent to form a crosslinked polymer;

"contacting the initial film layer with a mixture comprising i) the multi-functional acid halide crosslinking agent, ii) an optional accelerator, and iii) an organic solvent, the organic solvent being a non-solvent for the crosslinkable polymer; and

"allowing the crosslinkable polymer to interfacially react with the crosslinking agent, thereby forming a composite filtration membrane comprising an anti-fouling selective layer comprising the crosslinked polymer.

"Further disclosed is a composite filtration membrane, comprising:

"a porous support membrane layer; and

"an anti-fouling selective layer disposed on the porous support membrane layer; the selective layer comprising a crosslinked polymer of formula (15):

"##STR00001##

"wherein

"each --R.sup.1 is independently a hydrogen or a methyl group,

"--R.sup.2-- is a linear, branched or cyclic divalent radical selected from the group consisting of alkylenes, fluoroalkylenes, arylenes, arylalkylenes, alkylarylenes, and silicon containing groups,

"R.sup.3 is a bridging group having a valency of m and comprising 1 to 10,000 carbons,

"--X.sup.1-- is a divalent radical selected from the group consisting of --O--, --N(H)--, and --N(R.sup.5)--,

"--R.sup.5 is a monovalent radical comprising 1 to 20 carbons,

"m is a positive integer greater than or equal to 2,

"j represents a number of bridging groups R.sup.3 which are bound to one backbone of the crosslinked polymer, j being a number greater than or equal to 1,

"k represents a number of backbones of the crosslinked polymer which are bound to one bridging group R.sup.3, k being a positive number greater than or equal to 2,

"a', b', c', and y' are positive numbers,

"n is a positive integer greater than 1,

"--K.sup.1 is a monovalent radical selected from the group consisting of --NH.sub.2-- and --N(H)(R.sup.4)--,

"--R.sup.4 is a monovalent radical comprising 1 to 50 carbons,

"--R.sup.6-- is a divalent radical selected from the group consisting of a ethylene, 2-propylene, butylene, and combinations thereof,

"--Z.sup.1 is a monovalent radical selected from the group consisting of --H, --R.sup.7, -L.sup.1-NH.sub.2, -L.sup.1-N(H)(R.sup.7), -L.sup.1-N(R.sup.7).sub.2, and hydrogen salt forms of any of the foregoing amine groups,

"--R.sup.7 is a monovalent hydrocarbon radical comprising 1 to 20 carbons,

"-L.sup.1- is a divalent radical comprising 1 to 20 carbons,

"--R.sup.8 is a cationic monovalent radical comprising a member selected from the group consisting of quaternary amine salts, sulfonium salts, phosphonium salts, and combination thereof, wherein --R.sup.8 has a net positive charge,

"-D'-Q.sup.1- is a divalent linking group selected from the group consisting of amides, sulfonamides, sulfinamides, and functional groups having a phosphorous-nitrogen bond,

"-Q.sup.1- is a divalent radical independently selected from the group consisting of --N(H)-- and --N(R.sup.4)--,

"--R.sup.4 is a monovalent radical comprising 1 to 50 carbons, and

"-D'- is a divalent radical independently selected from the group consisting of --C(.dbd.O)--, --S(.dbd.O).sub.2--, and --S(.dbd.O)--, and groups comprising a phosphorous bonded to a nitrogen of -Q.sup.1-.

"Also disclosed is a composite filtration membrane, comprising:

"a porous support membrane layer; and

"an anti-fouling selective layer disposed on the porous support membrane layer; the selective layer comprising a crosslinked polymer of formula (16):

"##STR00002##

"wherein

"each --R.sup.1 is independently a hydrogen or a methyl group,

"--R.sup.2-- is a linear, branched or cyclic divalent radical selected from the group consisting of alkylenes, fluoroalkylenes, arylenes, arylalkylenes, alkylarylenes, and silicon containing groups,

"R.sup.3 is a bridging group having a valency of m and comprising 1 to 10,000 carbons,

"--X.sup.1-- is a divalent radical selected from the group consisting of --O--, --N(H)--, and --N(R.sup.5)--,

"--R.sup.5 is a monovalent radical comprising 1 to 20 carbons,

"m is a positive integer greater than or equal to 2,

"j represents a number of bridging groups R.sup.3 which are bound to one backbone of the crosslinked polymer, j being a number greater than or equal to 1,

"k represents a number of backbones of the crosslinked polymer which are bound to one bridging group R.sup.3, k being a positive number greater than or equal to 2,

"d', e', f', and y' are positive numbers,

"n is a positive integer greater than 1,

"--K.sup.1 is a monovalent radical selected from the group consisting of --NH.sub.2-- and --NH(R.sup.4)--,

"--R.sup.4 is a monovalent radical comprising 1 to 50 carbons,

"--R.sup.6-- is a divalent radical selected from the group consisting of a ethylene, 2-propylene, butylene, and combinations thereof,

"--Z.sup.1 is a monovalent radical selected from the group consisting of --H, --R.sup.7, -L.sup.1-NH.sub.2, L.sup.1-NHR.sup.7, -L.sup.1-N(R.sup.7).sub.2, and hydrogen salt forms of any of the foregoing amine groups,

"--R.sup.7 is a monovalent radical comprising 1 to 20 carbons,

"-L.sup.1- is a divalent radical comprising 1 to 20 carbons,

"--R.sup.9 is a zwitterionic monovalent radical comprising i) a cationic group selected from the group consisting of quaternary amines, sulfonium groups, phosphonium groups, and combinations thereof, and ii) an anionic group selected from the group consisting of carboxylate (--CO.sub.2.sup.-), sulphonate (--SO.sub.3.sup.-), and sulfinate (--SO.sub.2.sup.-), wherein --R.sup.9-- has a net zero charge,

"-D'-Q.sup.1- is a divalent linking group selected from the group consisting of amides, sulfonamides, sulfinamides, and functional groups having a phosphorous-nitrogen bond,

"-Q.sup.1- is a divalent radical selected from the group consisting of --N(H)-- and --N(R.sup.4)--,

"--R.sup.4 is a monovalent radical comprising 1 to 50 carbons, and

"-D'- is a divalent radical selected from the group consisting of --C(.dbd.O)--, --S(.dbd.O).sub.2--, and --S(.dbd.O)--, and groups comprising a phosphorous bonded to a nitrogen of -Q.sup.1-.

"The above-described and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

"In the drawings, like parts are numbered alike.

"FIG. 1 is a cross-sectional layer diagram of a composite filtration membrane having a selective layer disposed on a porous support membrane.

"FIG. 2 is a cross-sectional layer diagram of a composite filtration membrane having two selective layers disposed on different faces of a porous support membrane.

"FIG. 3 is a photograph of an atomic force microscope image of the surface of a polysulfone support membrane.

"FIG. 4 is a photograph of an atomic force microscope image of the surface of the composite filtration membrane of Example 4, made by interfacially crosslinking polymer P-1 with isophthaloyl chloride. The selective layer comprising the crosslinked polymer was too thin to be measured.

"FIG. 5 is a graph comparing permeate flux with time of the composite membrane prepared in Example 4 (top curve) with an untreated polysulfone ultrafiltration membrane (bottom curve), using an oil/water emulsion in a cross-flow filtration test, at a constant pressure of 100 psi. The permeate flux of the composite membrane, which has a selective layer of crosslinked sulfobetaine copolymer (Example 1), is consistently higher than the control polysulfone membrane over a 4 hour period.

"FIG. 6 is a graph showing the pressure differential across several membranes as a function of time at constant flux using a cross-flow filtration setup. The top curve corresponds to untreated polysulfone ultrafiltration membrane. The middle curve corresponds to the composite membrane of Example 5. The bottom curve, showing the least pressure drop, corresponds to composite membrane of Example 4.

"FIG. 7 is a cross-sectional scanning electron micrograph (SEM) image of the composite membrane of Comparative Example 2. The pores of the PSF support membrane are clogged.

"FIG. 8 is a cross-sectional SEM image of the composite membrane of Comparative Example 3, and shows a thick coating of the crosslinked polymer layer.

"FIG. 9 is a cross-sectional SEM of the composite membrane of Comparative Example 4. The thickness of the crosslinked polymer layer is about 637 nm.

"FIG. 10 is a cross-sectional SEM of the composite membrane of Comparative Example 6. The thickness of the crosslinked polymer layer is about 1 micrometer. The pores of the PSF support membrane are clogged.

"FIG. 11 is a graph showing the permeate flux with time of the composite membrane formed by interfacially reacting 1,3-phenylenediamine with trimesoyl chloride in Comparative Example 7 at a constant pressure of 200 psi."

For additional information on this patent application, see: Na, Young-Hye; Nelson, Alshakim; Sooriyakumaran, Ratnam; Vora, Ankit. Composite Filtration Membranes and Methods of Preparation Thereof. Filed April 5, 2014 and posted August 14, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=6611&p=133&f=G&l=50&d=PG01&S1=20140807.PD.&OS=PD/20140807&RS=PD/20140807

Keywords for this news article include: Gases, Alkenes, Elements, Hydrogen, Nitrogen, Ethylenes, Nanofiltration, Nanotechnology, Inorganic Chemicals, Emerging Technologies, International Business Machines Corporation.

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