WO2018205251A1

WO2018205251A1 - High flux permeable reverse osmosis membrane and process of making the same

Info

Publication number: WO2018205251A1
Application number: PCT/CN2017/084115
Authority: WO
Inventors: Changquan QIU; Yubin LV; Anna Liu; Lewus LIU
Original assignee: Honeywell International Inc.
Priority date: 2017-05-12
Filing date: 2017-05-12
Publication date: 2018-11-15
Also published as: CN110650789A

Abstract

Highly permeable reverse osmosis (RO) membranes having high flux and methods of making the same are disclosed, which comprising a polyamide layer with embedded oxidized graphene particles.

Description

HIGH FLUX PERMEABLE REVERSE OSMOSIS MEMBRANE AND PROCESS OF MAKING THE SAME

BACKGROUND

Clean drinking water is important for human health, because uncleaned water may contain bacteria, viruses, and heavy metals that are harmful to humans. However, due to the growth of population and development of industry, large amounts of waste or contaminated water are being produced, which deteriorates the environment and threatens people’s health.

In many countries, the quality of the drinking water provided by the government is compromised and citizens need to rely on additional filtration techniques. RO (reverse osmosis) technology, because of its unique advantages in removing almost all salts and contaminants from water, has taken a dominant role in many areas of water treatment.

Therefore it is important to develop ultra-low pressure RO membranes for residential water purification that can be competitive with, or even superior to, commercial RO membranes.

Typically, successful ultra-low pressure RO membrane for residential/commercial water purifiers should meet such requirements as having a water flux of 3.6-7.0 LMH@1bar, and the rejection is larger than 95％. Although many existing ultra-low pressure RO membrane products are prepared using a thin but selective PA (polyamide) layer there is still a need to develop an ultra-low pressure RO membrane that can meet or exceed the above water flux parameters.

SUMMARY OF THE INVENTION

The present invention provides, in one embodiment, a reverse osmosis membrane. The reverse osmosis membrane includes a microporous membrane having a polyamide material thereon, the polyamide material comprising an oxidized graphene, and the reverse osmosis membrane has a water flux of 6.0 to 8.0 L/m²/hour/bar (LMH/bar) .

Unexpectedly and advantageously, some embodiments of the inventive membranes have exceptionally high water fluxes and rejection rates as a result of the presence of oxidized graphene in the polyamide material. It has been surprisingly found that some embodiments of the reverse osmosis membranes made according to the methods described herein are capable of achieving water fluxes that are larger than some of the best commercially available reverse osmosis membranes.

BRIEF DESCRIPTION OF THE FIGURES

The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments of the present invention.

FIG. 1 is an SEM (scanning electron microscope) image of the cross section of porous UF (ultra fine) membrane substrate, in accordance with various embodiments.

FIG. 2 is and SEM image of the surface of the RO membrane, in accordance with various embodiments.

FIG. 3 is the chemical structure of graphene oxide (GO) , in accordance with various embodiments.

FIG. 4 is the structure of traditional RO membrane vs. GO embedded RO membrane, in accordance with various embodiments.

DETAILED DESCRIPTION

Reference will now be made in detail to certain embodiments of the disclosed subject matter, examples of which are illustrated in part in the accompanying drawings. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter.

Throughout this document, values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of “about 0.1％to about 5％” or “about 0.1％to 5％” should be interpreted to include not just about 0.1％to about 5％, but also the individual values (e.g., 1％, 2％, 3％, and 4％) and the sub-ranges (e.g., 0.1％to 0.5％, 1.1％to 2.2％, 3.3％to 4.4％) within the indicated range. The statement “about X to Y” has the same meaning as “about X to about Y, ” unless indicated otherwise. Likewise, the statement “about X, Y, or about Z” has the same meaning as “about X, about Y, or about Z, ” unless indicated otherwise.

In this document, the terms “a, ” “an, ” or “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. The statement “at least one of A and B” or “at least one of A or B” has the same meaning as “A, B, or A and B. ” In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting； information that is relevant to a section heading may occur within or outside of that particular section.

In the methods described herein, the acts can be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Furthermore, specified acts can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed act of doing X and a claimed act of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.

The term “about” as used herein can allow for a degree of variability in a value or range, for example, within 10％, within 5％, or within 1％of a stated value or of a stated limit of a range, and includes the exact stated value or range.

The term “substantially” as used herein refers to a majority of, or mostly, as in at least about 50％, 60％, 70％, 80％, 90％, 95％, 96％, 97％, 98％, 99％, 99.5％, 99.9％, 99.99％, or at least about 99.999％or more, or 100％. The term “substantially free of” as used herein can mean having none or having a trivial amount of, such that the amount of material present does not affect the material properties of the composition including the material, such that the composition is about 0 wt％to about 5 wt％of the material, or about 0 wt％to about 1 wt％, or about 5 wt％or less, or less than, equal to, or greater than about 4.5 wt％, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01, or about 0.001 wt％or less. The term “substantially free of” can mean having a trivial amount of, such that a composition is about 0 wt％to about 5 wt％of the material, or about 0 wt％to about 1 wt％, or about 5 wt％or less, or less than, equal to, or greater than about 4.5 wt％, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01, or about 0.001 wt％or less, or about 0 wt％.

The term “amine” as used herein refers to primary, secondary, and tertiary amines having, e.g., the formula N (group) ₃ wherein each group can independently be H or non-H, such as alkyl, aryl, and the like. Amines can include R-NH₂, for example, alkylamines, arylamines, alkylarylamines； R₂NH wherein each R is independently selected, such as dialkylamines, diarylamines, aralkylamines, heterocyclylamines and the like； and R₃N wherein each R is independently selected, such as trialkylamines, dialkylarylamines, alkyldiarylamines, triarylamines, and the like. The term “amine” also includes ammonium ions as used herein.

The term “amino group” as used herein refers to a substituent of the form -NH₂, -NHR, -NR₂, -NR₃ ⁺, wherein each R is independently selected, and protonated forms of each, except for -NR₃ ⁺, which cannot be protonated. Accordingly, any compound substituted with an amino group can be viewed as an amine. An “amino group” within the meaning herein can be a primary, secondary, tertiary, or quaternary amino group. An “alkylamino” group includes a monoalkylamino, dialkylamino, and trialkylamino group.

The term “solvent” as used herein refers to a liquid that can dissolve a solid, liquid, or gas. Non-limiting examples of solvents are silicones, organic compounds, water, alcohols, ionic liquids, and supercritical fluids.

The term “substituted” as used herein in conjunction with a molecule or an organic group as defined herein refers to the state in which one or more hydrogen atoms contained therein are replaced by one or more non-hydrogen atoms. The term “functional group” or “substituent” as used herein refers to a group that can be or is substituted onto a molecule or onto an organic group. Examples of substituents or functional groups include, but are not limited to, a halogen (e.g., F, Cl, Br, and I) ； an oxygen atom in groups such as hydroxy groups, alkoxy groups, aryloxy groups, aralkyloxy groups, oxo (carbonyl) groups, carboxyl groups including carboxylic acids, carboxylates, and carboxylate esters； a sulfur atom in groups such as thiol groups, alkyl and aryl sulfide groups, sulfoxide groups, sulfone groups, sulfonyl groups, and sulfonamide groups； a nitrogen atom in groups such as amines, hydroxyamines, nitriles, nitro groups, N-oxides, hydrazides, azides, and enamines； and other heteroatoms in various other groups. Non-limiting examples of substituents that can be bonded to a substituted carbon (or other) atom include F, Cl, Br, I, OR, OC (O) N (R) ₂, CN, NO, NO₂, ONO₂, azido, CF₃, OCF₃, R, O (oxo) , S (thiono) , C (O) , S (O) , methylenedioxy, ethylenedioxy, N (R) ₂, SR, SOR, SO₂R, SO₂N (R) ₂, SO₃R, C (O) R, C (O) C (O) R, C (O) CH₂C (O) R, C (S) R, C (O) OR, OC (O) R, C (O) N (R) ₂, OC (O) N (R) ₂, C (S) N (R) ₂, (CH₂) _0-2N (R) C (O) R, (CH₂) _0-2N (R) N (R) ₂, N (R) N (R) C (O) R, N (R) N (R) C (O) OR, N (R) N (R) CON (R) ₂, N (R) SO₂R, N (R) SO₂N (R) ₂, N (R) C (O) OR, N (R) C (O) R, N (R) C (S) R, N (R) C (O) N (R) ₂, N (R) C (S) N (R) ₂, N (COR) COR, N (OR) R, C (＝NH) N (R) ₂, C (O) N (OR) R, and C (＝NOR) R, wherein R can be hydrogen or a carbon-based moiety； for example, R can be hydrogen, (C₁-C₁₀₀) hydrocarbyl, alkyl, acyl, cycloalkyl, aryl, aralkyl, heterocyclyl, heteroaryl, or heteroarylalkyl； or wherein two R groups bonded to a nitrogen atom or to adjacent nitrogen atoms can together with the nitrogen atom or atoms form a heterocyclyl.

The term “aryl” as used herein refers to cyclic aromatic hydrocarbon groups that do not contain heteroatoms in the ring. Thus aryl groups include, but are not limited to, phenyl, azulenyl, heptalenyl, biphenyl, indacenyl, fluorenyl, phenanthrenyl, triphenylenyl, pyrenyl, naphthacenyl, chrysenyl, biphenylenyl, anthracenyl, and naphthyl groups. In some embodiments, aryl groups contain about 6 to about 14 carbons in the ring portions of the groups. Aryl groups can be unsubstituted or substituted, as defined herein. Representative substituted aryl groups can be mono-substituted or substituted more than once, such as, but not limited to, a phenyl group substituted at any one or more of 2-, 3-, 4-, 5-, or 6-positions of the phenyl ring, or a naphthyl group substituted at any one or more of 2-to 8-positions thereof.

The term “alkyl” as used herein refers to straight chain and branched alkyl groups and cycloalkyl groups having from 1 to 40 carbon atoms, 1 to about 20 carbon atoms, 1 to 12 carbons or, in some embodiments, from 1 to 8 carbon atoms. Examples of straight chain alkyl groups include those with from 1 to 8 carbon atoms such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, and n-octyl groups. Examples of branched alkyl groups include, but are not limited to, isopropyl, iso-butyl, sec-butyl, t-butyl, neopentyl, isopentyl, and 2, 2-dimethylpropyl groups. As used herein, the term “alkyl” encompasses n-alkyl, isoalkyl, and anteisoalkyl groups as well as other branched chain forms of alkyl. Representative substituted alkyl groups can be substituted one or more times with any of the groups listed herein, for example, amino, hydroxy, cyano, carboxy, nitro, thio, alkoxy, and halogen groups.

The term “aromatic” as used herein refers to cyclic aromatic hydrocarbon groups that do not contain heteroatoms in the ring. Thus aromatic groups can include phenyl, azulenyl, heptalenyl, biphenyl, indacenyl, fluorenyl, phenanthrenyl, triphenylenyl, pyrenyl, naphthacenyl, chrysenyl, biphenylenyl, anthracenyl, and naphthyl groups. In some embodiments, aromatic groups contain about 6 to about 14 carbons in the ring portions of the groups. Aromatic groups can be unsubstituted or substituted, as defined herein. Representative substituted aromatic groups can be mono-substituted or substituted more than once, such as, but not limited to, a phenyl group substituted at any one or more of 2-, 3-, 4-, 5-, or 6-positions of the phenyl ring, or a naphthyl group substituted at any one or more of 2-to 8-positions thereof.

The term “contact angle” as used herein refers to a measurement of the wettability of a surface by a liquid. The contact angle is θ_C is given by Young’s equation, where γ_SG –γ_SL –γ_LG cos θ_C ＝ 0, and γ_SG, γ_SL, and γ_LG are the solid-vapor, solid-liquid, and liquid-vapor interfacial energies, respectively. Contact angles can be measured by, for example, capturing the profile of a drop of liquid (e.g. water) on a surface (e.g. a membrane) and measuring the angle between the liquid-solid and liquid-vapor interface. A contact angle goniometer can be used for such measurements.

The term “rejection rate” as used herein refers to the ratio of the concentration of solute, such as metal salts, in the permeate (water that has passed through a membrane) to the concentration of solute in the retentate (water that does not pass through the membrane) , expressed as a percentage. The rejection rate can be calculated using the equation R ＝ 100％x (1- (C_p/C_r) ) , where R is the rejection rate, C_p is the concentration of solute in the permeate, and C_r is the concentration of solute in the retentate.

The “LMH/bar” unit used herein is a normalized unit of flux, where the flux is measured in L/m²/hour units per 1 bar of pressure.

Reverse Osmosis Membrane.

In one embodiment, a reverse osmosis membrane is provided. The reverse osmosis membrane includes a microporous membrane having a polyamide material thereon, the polyamide material comprising an oxidized graphene, and the reverse osmosis membrane has a water flux of 6.0 to 8.0 L/m²/hour/bar (LMH/bar) . In some embodiments, the reverse osmosis membrane has a water flux of about 6.25 to about 8.0, about 6.5 to about 8.0, 6.75 to about 8.0, 7.0 to about 8.0, 7.25 to about 8.0, 7.5 to about 8.0, or about 7.5 to about 8.0 LMH/bar. In some embodiments, the reverse osmosis membrane has a water flux less than, equal to, or greater than about 7.1, about 7.2, about 7.3, about 7.4, about 7.5, about 7.6, about 7.7, about 7.8, about 7.9, or about 8.0 LMH/bar, or any range in-between any of these values.

In one embodiment, the microporous membrane has a thickness of about 30 μm to about80 μm, a contact angle of about 60 degrees to about 90 degrees, and a water flux of about 160 to about 350 L/m²/hour/bar (LMH/bar) .

In one embodiment, the reverse osmosis membrane has a rejection rate of at least 95％. In some embodiments, the reverse osmosis membrane has a rejection rate of at least about 95.25, 95.5, 95.75, 96.0, 96.25, 96.5, 96.75, 97.0, 97.25, 97.5, 97.75, 98.0, 98.25, 98.5, 98.75, 99.0, 99.25, 99.5, or about 99.75％, or any range in-between any of these values.

In one embodiment, a method of making the reverse osmosis membrane includes reacting on a microporous membrane a polyfunctional acid chloride composition with a polyfunctional amine composition comprising and oxidized graphene, to form a polyamide material on the microporous membrane. The reverse osmosis membranes described herein, in some embodiments, are suitable for use in residential or commercial water filtration facilities. In some embodiments, the reverse osmosis membranes are suitable for home use by consumers.

Polyfunctional Amine Compositions.

The polyfunctional amine can be any molecule that has two or more amine functional groups. In some embodiments, the amine functional group can be a primary amine or a secondary amine. In one embodiment, the polyfunctional amine can contain both primary and secondary amines. In one embodiment, the polyfunctional amine can be an aromatic diamine or triamine. Examples of aromatic diamines can include substituted or unsubstituted 1, 2-diaminobenzene, 1, 3-diaminobenzene, and 1, 4-diaminobenzene. Examples of aromatic triamines can include 1, 2, 3-triaminobenzene and 1, 3, 5, -triaminobenzene. In one embodiment, the polyfunctional amine is 1, 3-diaminobenzene (m-phenylenediamine, MPD) . The aromatic diamines may be further substituted with one or more groups such as, but not limited to, C₁-₄ alkyl, halogen (F, Cl, or Br) , nitrile (CN) , and nitro (NO₂) .

In another embodiment, the polyfunctional amine is present in an amount from about 0.01 to about 10 wt％of the polyfunctional amine composition. In another embodiment, the polyfunctional amine is present in an amount of from about 0.01 to about 5 wt％, from about 0.01 to about 4 wt％, from about 0.01 to about 3 wt％, from about 0.01 to about 2 wt％, from about 0.01 to about 1.5 wt％, from about 0.01 to about 1 wt％, from about 0.05 to about 5 wt％, from about 0.05 to about 4 wt％, from about 0.05 to about 3 wt％, from about 0.05 to about 2 wt％, from about 0.05 to about 1.5wt％, from about 0.05 to about 1 wt％, from 0.1 to about 5 wt％, from about 0.1 to about 4 wt％, from about 0.1 to about 3 wt％, from about 0.1 to about 2 wt％, from about 0.1 to about 1.5wt％, or from about 0.1 to about 1 wt％of the polyfunctional amine composition. In some embodiments, the polyfunctional amine is present in amount of from about 0.5 to 1.5 wt％of the polyfunctional amine composition. In some embodiments, the polyfunctional amine is present in an amount less than, equal to, or greater than about 0.1 wt％, 0.2 wt％, 0.3 wt％, 0.4 wt％, 0.5 wt％, 0.6 wt％, 0.7 wt％, 0.8 wt％, 0.9 wt％, or about 1.0 wt％. In some embodiments, m-phenylenediamine is present in an amount of about 0.5 wt％.

In one embodiment, the polyfunctional amine composition includes water and at least one water soluble organic solvent. In some embodiments, the water soluble organic solvent is also miscible with water. In some embodiments, the water soluble organic solvent is a polar aprotic solvent. Examples of water soluble organic solvents include, but are not limited to, dimethyl sulfoxide (DMSO) , N, N-dimethylformamide (DMF) , N-methyl-2-pyrrolidone (NMP) , acetonitrile (MeCN) , and tetrahydrofuran (THF) . In some embodiments, the ratio of the water soluble organic solvent to water in the polyfunctional amine composition is about 10: 90, 20: 80, 30:70, 40: 60, 50: 50, 60: 40, 70: 30, 80: 20, or 90: 10. In some embodiments, the ratio of the water soluble organic solvent to water in the polyfunctional amine composition is 1: 99, 2: 98, 3: 97, 4:96, 5: 95, 6: 94, 7: 93, 8: 92, or 9: 91. In some embodiments, the ratio of the water soluble organic solvent to water in the polyfunctional amine composition is 1.5: 98.5, 2.5: 97.5, 3.5: 96.5, 4.5: 95.5, or 5.5: 94.5. In one embodiment, the ratio of DMSO to water is 10: 90. In one embodiment, the ratio of DMF to water is 2.5: 97.5. In one embodiment, the ratio of NMP to water is 2.5: 97.5.

Polyfunctional Acid Chloride Compositions.

The polyfunctional acid chloride can be any molecule that has two or more acid chloride functional groups. In some embodiments, the polyfunctional acid chloride contains two acid chloride functional groups or three acid chloride functional groups. In one embodiment, the polyfunctional acid chloride is polyfunctional aromatic acid chloride. Examples of polyfunctional aromatic acid chlorides include, but are not limited to, 1, 2-benzenedicarbobyl dichloride, 1, 3-benzenedicarbobyl dichloride, 1, 4-benzenedicarbobyl dichloride, or 1, 3, 5- benzenetricarbonyl trichloride. In one embodiment, the polyfunctional acid chloride is 1, 3, 5-benzenetricarbonyl trichloride (trimesoyl chloride, TMC) .

In one embodiment, the polyfunctional acid chloride is present in an amount of from about 0.001 to about 5 wt％of the polyfunctional acid chloride composition. In some embodiments, the polyfunctional acid chloride is present in an amount of from about 0.001 to about 4 wt％, from about 0.001 to about 3 wt％, from about 0.001 to about 2 wt％, from about 0.001 to about 1 wt％, from about 0.01 to about 5 wt％, from about 0.01 to about 4 wt％, from about 0.01 to about 3 wt％, from about 0.01 to about 2 wt％, from about 0.01 to about 1 wt％, from about 0.01 to about 0.9 wt％, from about 0.01 to about 0.8 wt％, from about 0.01 to about 0.7 wt％, from about 0.01 to about 0.6 wt％, from about 0.01 to about 0.5 wt％, from about 0.01 to about 0.4 wt％, from about 0.01 to about 0.3 wt％, from about 0.01 to about 0.2 wt％, from about 0.01 to about 0.1 wt％, from about 0.05 to about 1 wt％, from about 0.05 to about 0.9wt％, from about 0.05 to about 0.8 wt％, from about 0.05 to about 0.7 wt％, from about 0.05 to about 0.6 wt％, from about 0.05 to about 0.5 wt％, from about 0.05 to about0.4 wt％, from about 0.05 to about 0.3 wt％, from about 0.05 to about 0.2 wt％, or from about 0.05 to about 0.1 wt％of the polyfunctional acid chloride composition. In some embodiments, the polyfunctional acid chloride is present in an amount of about 0.01 wt％, 0.02 wt％, 0.3 wt％, 0.04 wt％, 0.05 wt％, 0.06 wt％, 0.07 wt％, 0.08 wt％, 0.09 wt％, or 0.1 wt％of the polyfunctional acid chloride composition. In one embodiment, trimesoyl chloride is present in amount of about 0.08 wt％of the polyfunctional acid chloride composition.

In one embodiment, the acid chloride composition includes at least one organic solvent. In one embodiment, the acid chloride composition includes at least one organic solvent and at least one ketone co-solvent. In some embodiments, the at least one organic solvent is a non-polar solvent. In some embodiments, the at least one organic solvent can be, without limitation, paraffin, pentane, hexane, heptane, octane, nonane, or decane, isomers thereof, and/or mixtures thereof. In one embodiment, the at least organic solvent is paraffin, hexane, decane, or mixtures thereof. In another embodiment, the at least one organic solvent is hexane. In some embodiments, the at least one organic solvent can include petroleum ether or mineral oil.

The ketone co-solvent is any suitable ketone that dissolves in the at least one organic solvent. Examples of ketones include, but are not limited to, acetone, butanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, cyclopentanone, cyclohexanone, or mixtures thereof. In one embodiment, the at least one ketone co-solvent is acetone, butanone, or mixtures thereof. In one embodiment, the ketone co-solvent is present in an amount of from about 0.1 to about 10 wt％of the polyfunctional acid chloride composition. In some embodiments, the ketone co-solvent is present in an amount of from about 0.1 to about 8 wt％, from about 0.1 to about 8 wt％, from about 0.1 to about 6 wt％, from about 0.1 to about 4 wt％, from about 0.1 to about 8 wt％, from about 0.1 to about 2 wt％, or from about 0.1 to about 1 wt％of the polyfunctional acid chloride composition. In some embodiments, the ketone co-solvent is present in an amount of about 0.5 wt％, about 1 wt％, about 1.5 wt％, about 2 wt％, about 2.5 wt％, or about 3 wt％of the polyfunctional acid chloride composition. In one embodiment, the ketone co-solvent is acetone. In one embodiment, the ketone co-solvent is about 2 wt％of the polyfunctional acid chloride composition.

Methods of Forming the Polyamide Material and Reverse Osmosis Membrane.

In one embodiment, the reacting includes an interfacial polymerization process.

In one embodiment, the interfacial polymerization process includes contacting a surface of the microporous membrane with the polyfunctional amine composition to form a coated microporous membrane； and contacting the coated microporous membrane with the polyfunctional acid chloride composition. In some embodiments, the interfacial polymerization process takes place at a solid/liquid interface, where the solid phase can include the microporous membrane coated with polyfunctional amine composition, and the liquid phase can include the polyfunctional acid chloride composition.

In one embodiment, the method includes contacting a surface of the microporous membrane with the polyfunctional amine composition by dipping the microporous membrane in the polyfunctional amine composition. In another embodiment, excess polyfunctional amine composition is removed from the surface of the microporous membrane.

The microporous membrane can act as a substrate for the polyamide material. In some embodiments, the polyamide material is thin relative to the microporous membrane. In some embodiments, the polyamide material has a thickness of about 0.01 μm to about 1 μm. In some embodiments, the polyamide material can have a thickness of about 0.05 μm to 0.9 μm, 0.1 μm to 0.8 μm, 0.15 μm to 0.5 μm, 0.2 μm to 0.4 μm, 0.25 μm to 0.3 μm, or any range or sub-range in between. The interfacial polymerization process can include dipping a portion of the microporous membrane, including the surface of the microporous membrane, into the polyfunctional amine composition. The portion of the microporous membrane that is immersed in the polyfunctional amine composition can remain dipped in the polyfunctional amine composition for between 10 seconds and 5 minutes. In some embodiments, the microporous membrane is dipped into the polyfunctional amine composition for about 2 minutes. After removing the microporous membrane from the polyfunctional amine composition, excess polyfunctional amine composition can be removed from the surface of the microporous membrane

In some embodiments, after the microporous membrane has been dipped in the polyfunctional amine composition, the microporous membrane is dipped into the polyfunctional acid chloride composition for between 10 seconds and 5 minutes to form a reverse osmosis membrane. In some embodiments, the microporous membrane, after having been dipped in the polyfunctional amine compositions, is dipped into the polyfunctional acid chloride composition for about 1 minute. In some embodiments, the interfacial polymerization process occurs while the microporous membrane is dipped in the polyfunctional acid chloride composition. After removing the microporous membrane from the polyfunctional acid chloride composition, which forms the reverse osmosis membrane, the reverse osmosis membrane can be washed with deionized water.

In one embodiment the microporous membrane includes a polysulfone membrane.

The polysulfone membrane can be made from polysulfone (PSf) materials such as PSf-1 or PSf-2, as described herein. Exemplary PSf materials include, but are not limited to,

PSU Resins P-1700, P-1720, P-3500 LCD, GF-110, GF-120, and GF-130 manufactured by Solvay. In some embodiments, the microporous membrane is an ultrafine (UF) membrane.

Methods of making microporous membranes from PSf materials are generally known to those of skill in the art. In an exemplary process, a solution containing about 10 to about 30 wt％of PSf, about 0.5 to 5 wt％of polyethylene glycol (PEG) , and about 70 to about 90 wt％NMP is formed and cast onto a suitable material, such as polyethylene terephthalate (PET) . In some embodiments, the PEG has a molecular weight of less than 2, 000. In some embodiments the PGE has a molecular weight of between about 300 to about 2000. In some embodiments, the PEG has a molecular weight of 300 or 600. In some embodiments, the PET material has a thickness of about 5 μm to about 300 μm. The casting can be performed with a casting knife such as the Elcometer 3700. In one embodiment, the microporous membrane is formed by casting a polysulfone/polyethylene glycol/N-methyl-2-pyrrolidone (PSf/PEG/NMP) solution on a polyethylene terephthalate (PET) material. In one embodiment, solution containing 20 wt％PSf, 2 wt％PEG, and 78 wt％NMP was cast on a PET material. In some embodiments, the polysulfone membrane has a thickness of between about 5 μm and 100 μm. In some embodiments, the polysulfone membrane has a pore size of about 1 nm to about 15 nm. In some embodiments, the polysulfone membrane has a pore size of about 5 nm to about 12 nm, or about 7 nm to about 10 nm.

Oxidized Graphene Compositions.

In one embodiment, the oxidized graphene is graphene oxide (GO) . The chemical structure of graphene oxide is shown in FIG. 3.

In one embodiment, the graphene oxide is present in amount from about 0.1 mg per kilogram to about 100 mg per kilogram of the polyfunctional amine composition. In some embodiments, the graphene oxide forms a dispersion in the polyfunctional amine composition. In some embodiments, the graphene oxide particles in the dispersion have an average particle size (largest dimension of the graphene oxide particle) of from about 100 to 2000 nm.

In one embodiment, the graphene oxide is embedded in the polyamide material. In one embodiment, the graphene oxide becomes embedded in the pores of the polyamide material. In some embodiments, the graphene oxide does not react with either the polyfunctional amine or polyfunctional acid chloride. Without being bound by theory, it is believed that graphene oxide becomes embedded in the structure of the polyamide material and makes the polyamide material looser than polyamide material without graphene oxide. The looser materials allows water to flow more easily, resulting in higher measured water flux values in RO membranes that contain a polyamide layer with embedded GO particles. In some embodiments, the enhancement in water flux through the RO membrane can be primarily caused by a loosening of the polyamide material structure. FIG. 4 shows the structure of traditional RO membrane vs. RO membranes with embedded GO according to some embodiments.

In one embodiment, a method of making the reverse osmosis membrane includes dipping a microporous membrane in a polyfunctional amine composition comprising about 0.01 to about 10 wt％of a polyfunctional amine, water, at least one water soluble organic solvent, and from about 0.1 mg to about 100 mg of graphene oxide per kilogram of polyfunctional amine composition； and contacting the coated microporous membrane with a polyfunctional acid chloride composition comprising from about 0.001 to about 1 wt％of polyfunctional acid chloride, at least one organic solvent, and at least one ketone co-solvent.

In one embodiment, a method of purifying water using a reverse osmosis membrane is provided. The method includes filtering water through the reverse osmosis membrane, to form a purified water.

Examples

Various embodiments of the present invention can be better understood by reference to the following Examples which are offered by way of illustration. The present invention is not limited to the Examples given herein.

A porous PSf or PES (polyethersulfone) membrane substrate was first selected, depending on the most desirable features in the RO membrane. A polyamide selectivity PA layer was fabricated on the PSf or PES membrane by adding graphene oxide (GO) into the aqueous phase during the interfacial polymerization process of polyfunctional amines with polyfunctional acid chlorides as described above. The performance of the finished RO membranes was characterized, including pure water flux, contact angle, thickness, etc.

Example 1: Fabrication of PSf/PES Membrane.

A 20/2/78 wt ％ratio of PSf/PEG/NMP solution was cast on a ～100 μm thick section of PET fabric using a casting knife, and exposed to air for a 30 s period prior to immersion in water at room temperature (25 ℃) to form a PSf porous UF membrane substrate having a membrane thickness of 35-50 μm. The PSf membrane so formed had a pure water flux of ～200 L/m²/hour (LMH) @1 bar, a contact angle of 70-80 ° was obtained (Table 1) , and the cross section SEM image of PSf membrane can be seen in FIG. 1.

Table 1: Characteristics of PSf UF membrane substrate.

A PSf membrane was immersed in an aqueous solution of 0.4-1.5 wt. ％1, 3-phenylenediamine (MPD) for 2 min, using various ratios of graphene oxide/water (mg/g) (e.g., 4/1000, 10/1000, 40/1000) , and with or without different ratios of DMSO/water in the polyfunctional amine composition, as described in Table 2. After removing the excess solution from the PSf membrane’s surface, the PSf membrane was contacted with a polyfunctional acid chloride composition containing 0.04-0.2 wt％1, 3, 5-benzenetricarbonyl trichloride (TMC) solution for 1 minute, and including various amounts of ketone-co solvent (Table 2) . After the PSf membrane was removed from the polyfunctional acid chloride composition, it was washed with DI water and a thin film ultralow pressure RO membrane was obtained. An SEM image of the surface of the RO membrane is shown in FIG. 2. The RO membrane was stored in water for later use. In some embodiments the RO membrane is subjected to a further curing step, which can include a heat curing step.

Example 2: Effect of Graphene Oxide on RO Membrane Water Flux.

The effect of interfacial polymerization conditions on the RO performance, such as amine monomer and reactive acid chloride monomer species, monomer concentration, contact time, co-solvent ratio, so-solvent species, GO concentration, and water soluble organic solvent species in water phase, water soluble organic concentration, etc. Using the disclosed methods, an RO membrane having a water flux of 7.7 LMH/bar with a rejection percentage of greater than 95％was obtained, which was higher than both the TW30-1812-50 (Dow Filmtech) membrane used for residential RO purification, and the XLE-440 (DOW) RO membrane.

Table 2: Performance of thin film composite RO membranes.

Testing conditions for water flux determination: 500 ppm NaCl, 25 ℃, 50 psi water pressure. The water flux and rejection results for the TW30-1812-50 and XLE-440 membranes were taken from the manufacturer’s product catalog.

The terms and expressions that have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the embodiments of the present invention. Thus, it should be understood that although the present invention has been specifically disclosed by specific embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those of ordinary skill in the art, and that such modifications and variations are considered to be within the scope of embodiments of the present invention.

Exemplary Embodiments.

The following exemplary embodiments are provided, the numbering of which is not to be construed as designating levels of importance:

Embodiment 1 provides a reverse osmosis membrane, comprising: a microporous membrane comprising a polyamide material thereon, the polyamide material comprising an oxidized graphene, wherein the reverse osmosis membrane has a water flux of about 6.0 L/m²/hour/bar (LMH/bar) to about 8.0 LMH/bar.

Embodiment 2 provides the reverse osmosis membrane of embodiment 1, wherein the microporous membrane has: a thickness of about 30 μm to about 80 μm, a contact angle of about 60 degrees to about 90 degrees, and a water flux of about 160 LMH/bar to about 350 LMH/bar.

Embodiment 3 provides the reverse osmosis membrane of anyone of embodiments 1-2, wherein the reverse osmosis membrane has a rejection rate of at least 95％.

Embodiment 4 provides a method of making the reverse osmosis membrane of any one of embodiments 1-3, comprising:

reacting on a microporous membrane a polyfunctional acid chloride composition with a polyfunctional amine composition comprising and oxidized graphene, to form a polyamide material on the microporous membrane.

Embodiment 5 provides the method of embodiment 4, wherein the polyfunctional amine composition comprises water and at least one water soluble organic solvent.

Embodiment 6 provides the method of any one of embodiments 4-5, wherein the polyfunctional acid chloride composition comprises at least one organic solvent and at least one ketone co-solvent.

Embodiment 7 provides the method of any one of embodiments 4-6, wherein the at least one ketone co-solvent is acetone, butanone, or mixtures thereof.

Embodiment 8 provides the method of any one of embodiments 4-7, wherein the at least organic solvent is paraffin, hexane, decane, or mixtures thereof.

Embodiment 9 provides the method of any one of embodiments 4-8, wherein the reacting comprises an interfacial polymerization process.

Embodiment 10 provides the method of any one of embodiments 4-9, wherein the interfacial polymerization process comprises:

contacting a surface of the microporous membrane with the polyfunctional amine composition to form a coated microporous membrane； and

contacting the coated microporous membrane with the polyfunctional acid chloride composition.

Embodiment 11 provides the method of any one of embodiments 4-10, wherein the contacting a surface of the microporous membrane with the polyfunctional amine composition comprises:

dipping the microporous membrane in the polyfunctional amine composition.

Embodiment 12 provides the method of any one of embodiments 4-11, wherein the polyfunctional amine comprises from about 0.01 to about 10 wt％of the polyfunctional amine composition.

Embodiment 13 provides the method of any one of embodiments 4-12, wherein the polyfunctional amine is m-phenylenediamine (MPD) .

Embodiment 14 provides the method of any one of embodiments 4-13, wherein the polyfunctional acid chloride composition comprises from about 0.001 to about 5 wt％of polyfunctional acid chloride.

Embodiment 15 provides the method of any one of embodiments 4-14, wherein the polyfunctional acid chloride is trimesoyl chloride (TMC) .

Embodiment 16 provides the method of any one of embodiments 4-15, wherein the microporous membrane comprises a polysulfone.

Embodiment 17 provides the method of any one of embodiments 4-16, wherein the microporous membrane is formed by casting a polysulfone/polyethylene glycol/N-methyl-2-pyrrolidone (PSf/PEG/NMP) solution on a polyethylene terephthalate (PET) material.

Embodiment 18 provides the method of any one of embodiments 4-17, wherein the oxidized graphene is graphene oxide.

Embodiment 19 provides the method of any one of embodiments 4-18, wherein the graphene oxide is present in amount from about 0.1 mg per kilogram to about 100 mg per kilogram of the polyfunctional amine composition.

Embodiment 20 provides the method of any one of embodiments 4-19, wherein the graphene oxide is embedded in the polyamide material.

Embodiment 21 provides a method of making the reverse osmosis membrane of any one of embodiments 1-3, comprising:

dipping a microporous membrane in a polyfunctional amine composition comprising about 0.01 wt％to about 10 wt％of a polyfunctional amine, water, at least one water soluble organic solvent, and from about 0.1 mg to about 100 mg of graphene oxide per kilogram of polyfunctional amine composition； and

contacting the coated microporous membrane with a polyfunctional acid chloride composition comprising from about 0.001 wt％to about 1 wt％of polyfunctional acid chloride, at least one organic solvent, and at least one ketone co-solvent.

Embodiment 22 provides a method of purifying water using the reverse osmosis membrane of any one of embodiments 1-3, comprising: filtering water through the reverse osmosis membrane, to form a purified water.

Claims

A reverse osmosis membrane, comprising:

a microporous membrane comprising a polyamide material thereon, the polyamide material comprising an oxidized graphene, wherein the reverse osmosis membrane has a water flux of about 6.0 /m²/hour/bar (LMH/bar) to about 8.0 LMH/bar.
The reverse osmosis membrane of claim 1, wherein the microporous membrane has:

a thickness of about 30 μm to about 80 μm,

a contact angle of about 60 degrees to about 90 degrees, and

a water flux of about 160 LMH/bar to about 350 LMH/bar.
A method of making the reverse osmosis membrane of claim 1, comprising:

reacting on a microporous membrane a polyfunctional acid chloride composition with a polyfunctional amine composition comprising and oxidized graphene, to form a polyamide material on the microporous membrane.
The method of claim 3, wherein the reacting comprises an interfacial polymerization process.
The method of claim 4, wherein the interfacial polymerization process comprises:

contacting a surface of the microporous membrane with the polyfunctional amine composition to form a coated microporous membrane； and

contacting the coated microporous membrane with the polyfunctional acid chloride composition.
The method of claim 3, wherein the polyfunctional amine is m-phenylenediamine (MPD) .
The method of claim 3, wherein the polyfunctional acid chloride is trimesoyl chloride (TMC) .
The method of claim 3, wherein the microporous membrane comprises a polysulfone.
The method of claim 3, wherein the oxidized graphene is graphene oxide.
A method of making the reverse osmosis membrane of claim 1, comprising:

dipping a microporous membrane in a polyfunctional amine composition comprising about 0.01 wt％to about 10 wt％of a polyfunctional amine, water, at least one water soluble organic solvent, and from about 0.1 mg to about 100 mg of graphene oxide per kilogram of polyfunctional amine composition； and

contacting the coated microporous membrane with a polyfunctional acid chloride composition comprising from about 0.001 wt％to about 1 wt％of polyfunctional acid chloride, at least one organic solvent, and at least one ketone co-solvent.