U.S. patent application number 16/831347 was filed with the patent office on 2020-08-06 for nanocomposite membranes and methods of making and using same.
The applicant listed for this patent is THE REGENTS OF THE UNIVERSITY OF CALIFORNIA. Invention is credited to Eric M.V. Hoek, Byeong-Heon Jeong, Yushan Yan.
Application Number | 20200246757 16/831347 |
Document ID | / |
Family ID | 1000004765463 |
Filed Date | 2020-08-06 |
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United States Patent
Application |
20200246757 |
Kind Code |
A1 |
Hoek; Eric M.V. ; et
al. |
August 6, 2020 |
NANOCOMPOSITE MEMBRANES AND METHODS OF MAKING AND USING SAME
Abstract
Disclosed are nanocomposite membranes and methods for making and
using same. In one aspect, the nanocomposite membrane comprises a
film comprising a polymer matrix and nanoparticles disposed within
the polymer matrix, wherein the film is substantially permeable to
water and substantially impermeable to impurities. In a further
aspect, the membrane can further comprise a hydrophilic layer. In a
further aspect, the nanocomposite membrane comprises a film having
a face, the film comprising a polymer matrix, a hydrophilic layer
proximate to the face, and nanoparticles disposed within the
hydrophilic layer, wherein the film is substantially permeable to
water and substantially impermeable to impurities. This abstract is
intended as a scanning tool for purposes of searching in the
particular art and is not intended to be limiting of the present
invention.
Inventors: |
Hoek; Eric M.V.; (Los
Angeles, CA) ; Yan; Yushan; (Los Angeles, CA)
; Jeong; Byeong-Heon; (Los Angeles, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THE REGENTS OF THE UNIVERSITY OF CALIFORNIA |
Oakland |
CA |
US |
|
|
Family ID: |
1000004765463 |
Appl. No.: |
16/831347 |
Filed: |
March 26, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11364885 |
Feb 27, 2006 |
10618013 |
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16831347 |
|
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60660428 |
Mar 9, 2005 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y10T 428/3175 20150401;
C02F 2001/4619 20130101; C02F 1/4618 20130101; C02F 1/44 20130101;
B01D 67/0079 20130101; B01D 61/027 20130101; B01D 65/08 20130101;
B01D 67/0093 20130101; Y02A 20/131 20180101; B01D 69/141 20130101;
B82Y 30/00 20130101; C02F 2305/08 20130101; B01D 71/38 20130101;
B01D 2323/30 20130101; B01D 71/56 20130101; B01D 2321/168 20130101;
B01D 2325/48 20130101 |
International
Class: |
B01D 69/14 20060101
B01D069/14; B01D 61/02 20060101 B01D061/02; C02F 1/461 20060101
C02F001/461; B01D 65/08 20060101 B01D065/08; B01D 67/00 20060101
B01D067/00; B01D 71/38 20060101 B01D071/38; B82Y 30/00 20060101
B82Y030/00; B01D 71/56 20060101 B01D071/56 |
Claims
1. A nanocomposite membrane comprising a film comprising: a. a
polymer matrix and b. nanoparticles disposed within the polymer
matrix, wherein the film is substantially permeable to water and
substantially impermeable to impurities, and wherein the
nanoparticles are encapsulated within the film such that at least
80% of a volume of at least 50% of the nanoparticles is positioned
between surfaces of the film, and the film has a thickness from 1
nm to 1000 nm.
2. The membrane of claim 1, wherein the nanoparticles are
hydrophilic nanoparticles.
3. The membrane of claim 1, wherein the film has a face and wherein
the membrane further comprises a hydrophilic layer proximate to the
film.
4. The method of claim 1, wherein the hydrophilic layer comprises
at least one of polyvinyl alcohol, polyvinyl pyrrole, polyvinyl
pyrrolidone, hydroxypropyl cellulose, polyethylene glycol,
saponified polyethylene-vinyl acetate copolymer, triethylene
glycol, or diethylene glycol or a mixture thereof.
5. The membrane of claim 3, wherein the hydrophilic layer comprises
crosslinked polyvinyl alcohol.
6. The membrane of claim 3, wherein the hydrophilic layer further
comprises nanoparticles disposed within the layer.
7. The membrane of claim 1, wherein the film comprises a
polyamide.
8. The membrane of claim 1, wherein the nanoparticles have an
average hydrodynamic diameter nanoparticles from 1 nm to 1000
nm.
9. (canceled)
10. The membrane of claim 1, wherein the nanoparticles comprise a
mesoporous molecular sieve comprising at least one of an oxide of
aluminum or silicon, an aluminosilicate, or an aluminophopsphate or
a mixture thereof.
11. The membrane of claim 1, wherein the nanoparticles comprise at
least one zeolite.
12. The membrane of claim 11, wherein the nanoparticles comprise
Zeolite A.
13. The membrane of claim 1, wherein the nanoparticles comprise an
interconnected porous material.
14. A nanocomposite membrane comprising a film comprising: a. an
interfacially-polymerized polyamide matrix and b. zeolite
nanoparticles dispersed within the polymer matrix, wherein the film
is substantially permeable to water and substantially impermeable
to sodium ions wherein the nanoparticles are encapsulated within
the film such that at least 80% of a volume of at least 50% of the
nanoparticles is positioned between surfaces of the film, and the
film has a thickness from 1 nm to 1000 nm.
15. The membrane of claim 14, wherein the nanoparticles comprise
Zeolite A.
16. The membrane of claim 14, wherein the nanoparticles further
comprise silver ions.
17. The membrane of claim 14, wherein the film comprises residues
oftrimesoyl chloride and m-phenylenediamine.
18-40. (canceled)
41. The membrane of claim 1, wherein the polymer matrix comprises a
crosslinked film comprising a polyamide matrix.
42. The membrane of claim 1, wherein the polymer matrix comprises a
polymerized polyamine and polyfunctional acyl halide.
43. The membrane of claim 1, wherein a thickness of the film
matches a size of the nanoparticles.
44. The membrane of claim 14, wherein a thickness of the film
matches a size of the nanoparticles.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of United States
Application No. 60/660,428 filed Mar. 9, 2005, which is hereby
incorporated herein by reference in its entirety.
BACKGROUND
[0002] Biofouling is a major concern with modern desalination
membranes (e.g., reverse osmosis (RO) or nanofiltration (NF)
membranes) because it cannot be easily eliminated and plagues many
applications such as seawater and brackish water desalination, as
well as conventional water and wastewater treatment. A breakthrough
in the field of membrane separations was the development of thin
film composite membranes, which are characterized by an ultra-thin
"barrier" layer supported on a porous substrate. Among thin film
composite membranes, polyamide thin film composite membranes have
been widely commercialized for water purification applications such
as seawater desalination, surface water treatment, and wastewater
reclamation due to their excellent separation performance and
energy efficiency.
[0003] In recent years, the water permeability of conventional
polyamide thin film composite membranes has improved dramatically
without an appreciable change in solute rejection. Polyamide thin
film composite membranes are widely commercialized for use in RO
separations such as seawater desalination, water treatment, and
wastewater reclamation due to their excellent membrane selectivity.
Despite this advantage, one concern with conventional polyamide
(PA) thin film composite (TFC) membranes in these applications is
their loss of performance due to biofouling, which typically cannot
be eliminated by feed water pretreatment, membrane surface
modification, module and process optimization, or chemical
cleaning. S. Kang et al., Direct Observation of Biofouling in
Cross-flow Microfiltration: Mechanisms of Deposition and Release,
Journal of Membrane Science 244 (2004) 151. A small amount of
microbial deposition can result in extensive biofilm growth, which
in RO processes leads to higher operating pressures and more
frequent chemical cleanings. This in turn can shorten membrane life
and compromise product water quality.
[0004] Therefore, there remains a need for methods and compositions
that overcome these deficiencies and that effectively provide for
membranes having improved fouling resistance, anti-microbial
(biocidal) activity, water permeability, and salt rejection.
SUMMARY
[0005] In accordance with the purpose(s) of the invention, as
embodied and broadly described herein, the invention, in one
aspect, relates to a nanocomposite membrane comprising a film
comprising a polymer matrix comprising and nanoparticles disposed
within the polymer matrix, wherein the film is substantially
permeable to water and substantially impermeable to impurities. In
a further aspect, the membrane can further comprise a hydrophilic
layer.
[0006] In a further aspect, the invention relates to a
nanocomposite membrane comprising a film comprising an
interfacially-polymerized polyamide matrix and zeolite
nanoparticles dispersed within the polymer matrix, wherein the film
is substantially permeable to water and substantially impermeable
to sodium ions. In a further aspect, the membrane can further
comprise a hydrophilic layer.
[0007] In a further aspect, the invention relates to a method for
preparing a nanocomposite membrane comprising the steps of
providing a polar mixture comprising a polar liquid and a first
monomer that is miscible with the polar liquid; providing an apolar
mixture comprising an apolar liquid substantially immiscible with
the polar liquid and a second monomer that is miscible with the
apolar liquid; providing nanoparticles in either the polar mixture
or the apolar mixture, wherein the nanoparticles are miscible with
the apolar liquid and miscible with the polar liquid; and
contacting the polar mixture and the apolar mixture at a
temperature sufficient to react the first monomer with the second
monomer, thereby interfacially-polymerizing the first monomer and
the second monomer to form a polymer matrix, wherein the
nanoparticles are disposed within the polymer matrix.
[0008] In a further aspect, the invention relates to a method for
preparing a nanocomposite membrane comprising the steps of soaking
a polysulfone membrane in an aqueous solution comprising
m-phenylenediamine, and pouring onto the soaked polysulfone
membrane a hexane solution comprising trimesoyl chloride and
zeolite nanoparticles suspended in the hexane solution, thereby
interfacially-polymerizing the m-phenylenediamine and the trimesoyl
chloride to form a film, wherein the zeolite nanoparticles are
dispersed within the film.
[0009] In a further aspect, the invention relates to a
nanocomposite membrane comprising a film having a face, wherein the
film comprises a polymer matrix; a hydrophilic layer proximate to
the face; and nanoparticles disposed within the hydrophilic layer,
wherein the film is substantially permeable to water and
substantially impermeable to impurities.
[0010] In a further aspect, the invention relates to a method for
preparing a nanocomposite membrane comprising the steps of
providing an aqueous mixture comprising water, a hydrophilic
polymer, nanoparticles, and optionally, at least one crosslinking
agent; providing a polymer film that is substantially permeable to
water and substantially impermeable to impurities; contacting the
mixture and the film, thereby forming a hydrophilic nanocomposite
layer in contact with the film; and evaporating at least a portion
of the water from the hydrophilic nanocomposite layer.
[0011] In a further aspect, the invention relates to the products
produced by the methods of the invention.
[0012] In a further aspect, the invention relates to methods for
purifying water comprising the steps of providing the nanocomposite
membranes of the invention or the products of the invention,
wherein the membrane has a first face and a second face; contacting
the first face of the membrane with a first solution of a first
volume having a first salt concentration at a first pressure; and
contacting the second face of the membrane with a second solution
of a second volume having a second salt concentration at a second
pressure; wherein the first solution is in fluid communication with
the second solution through the membrane, wherein the first salt
concentration is higher than the second salt concentration, thereby
creating an osmotic pressure across the membrane, and wherein the
first pressure is sufficiently higher than the second pressure to
overcome the osmotic pressure, thereby increasing the second volume
and decreasing the first volume.
[0013] In a further aspect, the invention relates to methods for
concentrating an impurity comprising the steps of providing the
nanocomposite membranes of the invention, wherein the membrane has
a first face and a second face; contacting the first face of the
membrane with a first mixture of a first volume having a first
impurity concentration at a first pressure; contacting the second
face of the membrane with a second mixture of a second volume
having a second impurity concentration at a second pressure; and
collecting the impurity, wherein the first mixture is in fluid
communication with the second solution through the membrane,
wherein the first impurity concentration is higher than the second
impurity concentration, thereby creating an osmotic pressure across
the membrane, and wherein the first pressure is sufficiently higher
than the second pressure to overcome the osmotic pressure, thereby
increasing the second volume and decreasing the first volume.
[0014] Additional advantages of the invention will be set forth in
part in the description which follows, and in part will be obvious
from the description, or may be learned by practice of the
invention. The advantages of the invention will be realized and
attained by means of the elements and combinations particularly
pointed out in the appended claims. It is to be understood that
both the foregoing general description and the following detailed
description are exemplary and explanatory only and are not
restrictive of the invention, as claimed.
BRIEF DESCRIPTION OF THE FIGURES
[0015] The accompanying figures, which are incorporated in and
constitute a part of this specification, illustrate several
embodiments and together with the description serve to explain the
principles of the invention.
[0016] FIG. 1 shows SEM images of as synthesized Zeolite A
nanoparticles.
[0017] FIG. 2 shows representative SEM images of synthesized pure
polyamide and zeolite-polyamide nanocomposite membranes. A hand
cast thin film composite (TFC) polyamide membrane is shown in (a)
and hand cast thin film nanocomposite (TFN) membranes synthesized
with increasing concentrations zeolite nanoparticles are shown in
(b) through (f).
[0018] FIG. 3 shows representative TEM images of hand cast pure
polyamide TFC at magnifications of (a) 48 k.times. and (b) 100
k.times. and hand cast and zeolite-polyamide TFN membranes at
magnifications of (c) 48 k.times. and (d) 100 k.times..
DETAILED DESCRIPTION
[0019] The present invention may be understood more readily by
reference to the following detailed description of aspects of the
invention and the Examples included therein and to the Figures and
their previous and following description.
[0020] Before the present compounds, compositions, articles,
devices, and/or methods are disclosed and described, it is to be
understood that they are not limited to specific synthetic methods
unless otherwise specified, or to particular reagents unless
otherwise specified, as such may, of course, vary. It is also to be
understood that the terminology used herein is for the purpose of
describing particular embodiments only and is not intended to be
limiting.
A. Definitions
[0021] Although any methods and materials similar or equivalent to
those described herein can be used in the practice or testing of
the present invention, example methods and materials are now
described.
[0022] All publications mentioned herein are incorporated herein by
reference to disclose and describe the methods and/or materials in
connection with which the publications are cited. The publications
discussed herein are provided solely for their disclosure prior to
the filing date of the present application. Nothing herein is to be
construed as an admission that the present invention is not
entitled to antedate such publication by virtue of prior invention.
Further, the dates of publication provided herein may be different
from the actual publication dates, which may need to be
independently confirmed.
[0023] As used in the specification and the appended claims, the
singular forms "a," "an" and "the" include plural referents unless
the context clearly dictates otherwise. Thus, for example,
reference to "a component," "a polymer," or "a particle" includes
mixtures of two or more such components, polymers, or particles,
and the like.
[0024] Ranges can be expressed herein as from "about" one
particular value, and/or to "about" another particular value. When
such a range is expressed, another embodiment includes from the one
particular value and/or to the other particular value. Similarly,
when values are expressed as approximations, by use of the
antecedent "about," it will be understood that the particular value
forms another embodiment. It will be further understood that the
endpoints of each of the ranges are significant both in relation to
the other endpoint, and independently of the other endpoint. It is
also understood that there are a number of values disclosed herein,
and that each value is also herein disclosed as "about" that
particular value in addition to the value itself. For example, if
the value "10" is disclosed, then "about 10" is also disclosed. It
is also understood that when a value is disclosed that "less than
or equal to" the value, "greater than or equal to the value" and
possible ranges between values are also disclosed, as appropriately
understood by the skilled artisan. For example, if the value "10"
is disclosed the "less than or equal to 10" as well as "greater
than or equal to 10" is also disclosed. It is also understood that
throughout the application, data is provided in a number of
different formats and that this data represents endpoints and
starting points, and ranges for any combination of the data points.
For example, if a particular data point "10" and a particular data
point 15 are disclosed, it is understood that greater than, greater
than or equal to, less than, less than or equal to, and equal to 10
and 15 are considered disclosed as well as between 10 and 15. It is
also understood that each unit between two particular units are
also disclosed. For example, if 10 and 15 are disclosed, then 11,
12, 13, and 14 are also disclosed.
[0025] A residue of a chemical species, as used in the
specification and concluding claims, refers to the moiety that is
the resulting product of the chemical species in a particular
reaction scheme or subsequent formulation or chemical product,
regardless of whether the moiety is actually obtained from the
chemical species. Thus, an ethylene glycol residue in a polyester
refers to one or more --OCH.sub.2CH.sub.2O-- units in the
polyester, regardless of whether ethylene glycol was used to
prepare the polyester. Similarly, a sebacic acid residue in a
polyester refers to one or more --CO(CH.sub.2).sub.8CO-- moieties
in the polyester, regardless of whether the residue is obtained by
reacting sebacic acid or an ester thereof to obtain the
polyester.
[0026] As used herein, the terms "optional" or "optionally" means
that the subsequently described event or circumstance may or may
not occur, and that the description includes instances where said
event or circumstance occurs and instances where it does not.
[0027] Disclosed are the components to be used to prepare the
compositions of the invention as well as the compositions
themselves to be used within the methods disclosed herein.
[0028] These and other materials are disclosed herein, and it is
understood that when combinations, subsets, interactions, groups,
etc. of these materials are disclosed that while specific reference
of each various individual and collective combinations and
permutation of these compounds may not be explicitly disclosed,
each is specifically contemplated and described herein. For
example, if a particular compound is disclosed and discussed and a
number of modifications that can be made to a number of molecules
including the compounds are discussed, specifically contemplated is
each and every combination and permutation of the compound and the
modifications that are possible unless specifically indicated to
the contrary. Thus, if a class of molecules A, B, and C are
disclosed as well as a class of molecules D, E, and F and an
example of a combination molecule, A-D is disclosed, then even if
each is not individually recited each is individually and
collectively contemplated meaning combinations, A-E, A-F, B-D, B-E,
B-F, C-D, C-E, and C-F are considered disclosed. Likewise, any
subset or combination of these is also disclosed. Thus, for
example, the sub-group of A-E, B-F, and C-E would be considered
disclosed. This concept applies to all aspects of this application
including, but not limited to, steps in methods of making and using
the compositions of the invention. Thus, if there are a variety of
additional steps that can be performed it is understood that each
of these additional steps can be performed with any specific
embodiment or combination of embodiments of the methods of the
invention.
[0029] It is understood that the compositions disclosed herein have
certain functions. Disclosed herein are certain structural
requirements for performing the disclosed functions, and it is
understood that there are a variety of structures that can perform
the same function that are related to the disclosed structures, and
that these structures will typically achieve the same result.
B. Reverse Osmosis and Nanofiltration Membranes
[0030] Reverse osmosis membranes and nanofiltration membranes can
be used to separate dissolved or dispersed materials from feed
streams. The separation process typically involves bringing an
aqueous feed solution into contact with one surface of the membrane
under pressure so as to effect permeation of the aqueous phase
through the membrane while permeation of the dissolved or dispersed
materials is prevented.
[0031] Both reverse osmosis and nanofiltration membranes typically
include a thin film discriminating layer fixed to a porous support,
collectively referred to as a "composite membrane." Ultrafiltration
and microfiltration membranes may also have a composite
arrangement. The support provides physical strength but offers
little resistance to flow due to its porosity. On the other hand,
the discriminating layer can be less porous and can provide the
primary means of separation of dissolved or dispersed materials.
Therefore, it is generally the discriminating layer which
determines a given membrane's "rejection rate"--the percentage of
the particular dissolved material (i.e., solute) rejected, and
"flux"--the flow rate per unit area at which the solvent passes
through the membrane.
[0032] Reverse osmosis membranes and nanofiltration membranes vary
from each other with respect to their degree of permeability to
different ions and organic compounds. Reverse osmosis membranes are
relatively impermeable to virtually all ions, including sodium and
chloride ions, as well as uncharged solutes with molecular weights
above about 200 Daltons. Therefore, reverse osmosis membranes are
widely used for the desalination of brackish water or seawater to
provide a highly purified water for industrial, commercial, or
domestic use because the rejection rate of sodium and chlorine ions
for reverse osmosis membranes is usually greater than about 90
percent.
[0033] Conventional nanofiltration membranes are more specific for
the rejection of ions. Generally, nanofiltration membranes reject
divalent ions, including radium, magnesium, calcium, sulfate, and
carbonate. In addition, nanofiltration membranes are generally
impermeable to organic compounds having molecular weights above
about 1,000 Daltons. Additionally, nanofiltration membranes
generally have higher fluxes at comparable pressures than reverse
osmosis membranes. These characteristics render nanofiltration
membranes useful in such diverse applications as the "softening" of
water and the removal of pesticides from water. As an example,
nanofiltration membranes generally have a sodium chloride rejection
rate of from about 0 to about 50 percent but can reject salts such
as magnesium sulfate from about 50 to about 99 percent.
[0034] Among particularly useful membranes for reverse osmosis and
nanofiltration applications are those in which the discriminating
layer is a polyamide. The polyamide discriminating layer for
reverse osmosis membranes is often obtained by an interfacial
polycondensation reaction between a polyfunctional amine monomer
and a polyfunctional acyl halide monomer (also referred to as a
polyfunctional acid halide) as described in, for example, U.S. Pat.
No. 4,277,344. The polyamide discriminating layer for
nanofiltration membranes is typically obtained via an interfacial
polymerization between a piperazine or an amine substituted
piperidine or cyclohexane and a polyfunctional acyl halide as
described in U.S. Pat. Nos. 4,769,148 and 4,859,384. Another way of
obtaining polyamide discriminating layers suitable for
nanofiltration is via the methods described in, for example, U.S.
Pat. Nos. 4,765,897; 4,812,270; and 4,824,574. These patents
describe changing a reverse osmosis membrane, such as those of U.S.
Pat. No. 4,277,344, into a nanofiltration membrane.
[0035] Composite polyamide membranes are typically prepared by
coating a porous support with a polyfunctional amine monomer, most
commonly coated from an aqueous solution: Although water is a
preferred solvent, non-aqueous solvents may be utilized, such as
acetyl nitrile and dimethylformamide (DMF). A polyfunctional acyl
halide monomer (also referred to as acid halide) is subsequently
coated on the support, typically from an organic solution. Although
no specific order of addition is necessarily required, the amine
solution is typically coated first on the porous support followed
by the acyl halide solution. Although one or both of the
polyfunctional amine and acyl halide may be applied to the porous
support from a solution, they may alternatively be applied by other
means such as by vapor deposition, or neat.
[0036] Means for improving the performance of membranes by the
addition of constituents to the amine and/or acyl halide solutions
are described in the literature. For example, U.S. Pat. No.
4,950,404, issued to Chau, describes a method for increasing flux
of a composite membrane by adding a polar aprotic solvent and an
optional acid acceptor to the aqueous amine solution prior to
interfacially polymerizing the amine with a polycarboxylic acid
halide. Similarly, U.S. Pat. Nos. 6,024,873; 5,989,426; 5,843,351;
5,733,602; 5,614,099; and 5,576,057 to Hirose et al. describe the
addition of selected alcohols, ethers, ketones, esters, halogenated
hydrocarbons, nitrogen-containing compounds and sulfur-containing
compounds having a solubility parameter of 8 to 14
(cal/cm.sup.3).sup.1/2 to the aqueous amine solution and/or organic
acid halide solution prior to interfacial polymerization.
[0037] Methods of improving membrane performance by post-treatment
are also known. For example, U.S. Pat. No. 5,876,602 to Jons et al.
describes treating a polyamide composite membrane with an aqueous
chlorinating agent to improve flux, lower salt passage, and/or
increase membrane stability to base. U.S. Pat. No. 5,755,964 to
Mickols discloses a process wherein the polyamide discriminating
layer is treated with ammonia or selected amines, e.g., butylamine,
cyclohexylamine, and 1,6 hexane diamine. U.S. Pat. No. 4,765,897 to
Cadotte discloses the post treatment of a membrane with a strong
mineral acid followed by treatment with a rejection enhancing
agent.
C. Nanocomposite Membranes
[0038] In one aspect, the membranes of the invention are a new
class of filtration materials, for example, desalination membrane
materials. In particular, the membranes of the invention can be
inorganic-organic thin film nanocomposite membranes, which can
result from the dispersion of inorganic nanoparticles such as
zeolite or metal oxide nanoparticles in a starting monomer
solution. The invention takes advantage of inherently advantageous
properties of organic membranes (such as flexibility, high packing
density in spiral wound elements, ease of manufacture, and good
permeability and selectivity) with those of inorganic nanoparticles
(such as high surface charge density, ion-exchange capacity,
hydrophilicity, and biocidal capability). These inorganic-organic
nanocomposite membranes can be prepared, for example, by an
interfacial polymerization reaction, as is used in forming pure
polyamide thin film composite membranes. The membranes of the
invention can be used in conjunction with any of a large number of
available nanomaterials that offer a wide range of possible
particle sizes, hydrophilicity/hydrophobicity, pore sizes,
porosity, interfacial reactivity, and chemical compositions.
[0039] One advantage of traditional thin film composite membranes
is that the thin barrier layer and porous support layer can be
independently modified to achieve an optimal mechanical, chemical,
and thermal stability as well as flux and rejection, a.k.a.,
"selectivity."
[0040] A new advantage of thin film nanocomposite membranes
involves independent selection and modification of nanoparticles to
optimize further the selectivity of the membrane. As a result, the
synthesized membrane structure can comprise inorganic nanoparticles
embedded within a semi-permeable polymer film. The presence of
nanoparticles, for example inorganic nanoparticles, can modify the
membrane structure formed during interfacial polymerization and
alter the macroscopic surface properties (e.g., surface charge,
hydrophilicity, porosity, thickness, and roughness) in a favorable
manner, which can lead to improved selectivity.
[0041] Another advantage of thin film nanocomposite membranes
involves the potential to impart active fouling resistance or
passive fouling resistance or both types of fouling resistance to
the formed film. Passive fouling resistance, sometimes referred to
as "passivation," describes modification of a surface to reduce
surface reactivity and promote hydrophilicity. Passive fouling
resistance can prevent unwanted deposition of dissolved, colloidal,
or microbial matter on the membrane surface, which tends to foul
the membrane and negatively influence flux and rejection. Active
fouling resistance involves the modification of a surface to
promote a selective, beneficial reactivity between the surface and
a dissolved, colloidal, or microbial constituent. An example is the
modification of nanoparticles to possess biocidal properties, and
subsequently, embedding the nanoparticles in a polyamide film to
produce a reverse osmosis or nanofiltration membrane with inherent
antimicrobial properties.
[0042] The present invention provides a new class of "thin film
nanocomposite" membranes with improved water permeability, solute
rejection, and fouling resistance over conventional polyamide thin
film composite membranes. Development of more efficient, more
selective, and antimicrobial desalination membranes can
revolutionize water and wastewater treatment practice. An
additional advantage of the nanocomposite approach is that
nanoparticles can be functionalized to produce practically any
desired membrane surface properties, and thus, are easily dispersed
in the initiator solution regardless of the solvent used.
Therefore, the methods of the invention are amenable to immediate
introduction into existing commercial membrane manufacturing
processes without significant process modification.
[0043] In one aspect, the invention relates to a nanocomposite
membrane comprising a film comprising a polymer matrix and
nanoparticles disposed within the polymer matrix, wherein the film
is substantially permeable to water and substantially impermeable
to impurities. By "disposed," it is meant that at least about 50%
of the volume of at least about 50% the nanoparticles are
positioned between the surfaces of the film. For example, at least
about 60%, at least about 70%, at least about 80%, or at least
about 90% of the volume of at least about 50% the nanoparticles can
be positioned between the surfaces of the film. As another example,
at least about 50% of the volume of at least about 60%, at least
about 70%, at least about 80%, or at least about 90% of the
nanoparticles can be positioned between the surfaces of the film.
In a further aspect, the nanoparticles can be substantially
encapsulated within the film. By "encapsulated," it is meant that
at least about 80% of the volume of at least about 50% of the
nanoparticles is positioned between the surfaces of the film. For
example, at least about 80% or at least about 90% of the volume of
at least about 50% the nanoparticles can be positioned between the
surfaces of the film.
[0044] Typically, the film can have at least two surfaces or faces;
one of the surfaces or faces can be proximate a porous support. In
one aspect, one of the surfaces or faces can be in contact with the
support. In a further aspect, the membrane can further comprise a
polysulfone, polyethersulfone, poly(ether sulfone ketone),
poly(ether ethyl ketone), poly(phthalazinone ether sulfone ketone),
polyacrylonitrile, polypropylene, cellulose acetate, cellulose
diacetate, cellulose triacetate, or other porous polymeric support
membrane.
[0045] In a further aspect, the membrane can comprise a film
comprising an interfacially-polymerized polyamide matrix and
zeolite nanoparticles dispersed within the polymer matrix, wherein
the film is substantially permeable to water and substantially
impermeable to sodium ions.
[0046] In a further aspect, the membrane can comprise a film having
a face, wherein the film comprises a polymer matrix; a hydrophilic
layer proximate to the face; and nanoparticles disposed within the
hydrophilic layer, wherein the film is substantially permeable to
water and substantially impermeable to impurities. In one aspect,
the hydrophilic layer can be adjacent to the face. In a further
aspect, the hydrophilic layer can be in contact with the face.
[0047] 1. Impurities
[0048] Typically, the membranes of the invention can be prepared so
as to be substantially impermeable to impurities. As used herein,
"impurities" generally refers to materials dissolved, dispersed, or
suspended in a liquid. The materials can be undesired; in such a
case, the membranes can be used to remove the undesired impurities
from the liquid, thereby purifying the liquid, and the liquid can
be subsequently collected. The materials can be desired; in such a
case, the membranes can be used to decrease the volume of the
liquid, thereby concentrating the impurities, and the impurities
can be subsequently collected. In one aspect, the membranes can be
provided to be substantially impermeable to particular impurities,
which can be selected from among impurities known to those of skill
in the art. In a further aspect, the impurities can comprise at
least one of sodium ions, potassium ions, magnesium ions, calcium
ions, silicates, organic acids, or nonionized dissolved solids with
a molecular weight of greater than about 200 Daltons or a mixture
thereof. The impurities can be dissolved or dispersed within a
liquid. The impurities can be hydrophobic or hydrophilic or neither
or a mixture thereof. Exemplary impurities can include ions,
neutral species, silicates, and organic compounds, for example,
amines or carboxylic acids.
[0049] Ions can be monovalent ions, divalent ions, trivalent ions,
higher valent ions, or a mixture thereof. In one aspect, the
impurities comprise monovalent ions. The ions can be positive ions,
negative ions, or a mixture thereof. Monovalent metal ions include
lithium ions, sodium ions, potassium ions, rubidium ions, cesium
ions, francium ions, ammonium ions, protonated primary amine ions,
protonated secondary amine ions, and protonated tertiary amine
ions. In addition, monovalent ions can be dissociated mineral or
organic acids. In a further aspect, one or more of these types of
ions are not among the impurities wherein a membrane of the
invention is substantially impermeable.
[0050] In a further aspect, the impurities comprise divalent ions.
The ions can be positive ions, negative ions, or a mixture thereof.
Divalent ions include beryllium ions, magnesium ions, calcium ions,
strontium ions, radium ions, ferrous iron, barium ions, strontium
ions, and protonated diamines. In addition, divalent ions can be
dissociated mineral or organic acids. In a further aspect, one or
more of these types of ions are not among the impurities wherein a
membrane of the invention is substantially impermeable.
[0051] In a further aspect, the impurities comprise higher valent
ions. The ions can be positive ions, negative ions, or a mixture
thereof. Higher valent ions include aluminum ions, ferric iron
ions, or silica ions. In a further aspect, one or more of these
types of ions are not among the impurities wherein a membrane of
the invention is substantially impermeable.
[0052] Neutral species can include, for example, nonionized solids
with a molecular weight of greater than about 200 Daltons. The
molecular weight can be, for example, at least about 200 Daltons,
at least about 250 Daltons, at least about 300 Daltons, at least
about 350
[0053] Daltons, at least about 400 Daltons, at least about 500
Daltons, at least about 600 Daltons, at least about 700 Daltons, at
least about 800 Daltons, at least about 900 Daltons, or at least
about 1,000 Daltons. The neutral species can be dissolved or
suspended. The neutral species can be hydrophobic, hydrophilic,
both, or neither. In a further aspect, one or more of these types
of neutral species are not among the impurities wherein a membrane
of the invention is substantially impermeable.
[0054] Silicates can include all known compounds of Silicon and
Oxygen based upon the SiO.sub.4 tetrahedron-shaped anionic group,
with or without one or more metal ions present. It is understood
that the silicates can be present as solids with a molecular weight
of greater than about 200 Daltons and can be dissolved or
suspended. The molecular weight can be, for example, at least about
200 Daltons, at least about 250 Daltons, at least about 300
Daltons, at least about 350 Daltons, at least about 400 Daltons, at
least about 500 Daltons, at least about 600 Daltons, at least about
700 Daltons, at least about 800 Daltons, at least about 900
Daltons, or at least about 1,000 Daltons. In a further aspect, one
or more of these types of silicates are not among the impurities
wherein a membrane of the invention is substantially
impermeable.
[0055] Organic acids can include formic acid, acetic acid,
propionic acid, butyric acid, pentanoic acid, hexanoic acid,
heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, and
lactic acid and derivatives and mixtures thereof. Also included are
phenols and derivatives and mixtures thereof in addition to
naturally occurring humic and fulvic acids or biopolymers
comprising amino acids, proteins, or complex polysaccharidic acids.
The acids can be protonated or deprotonated. In a further aspect,
one or more of these types of organic acids are not among the
impurities wherein a membrane of the invention is substantially
impermeable.
[0056] In a further aspect, the impurities can be the product of a
chemical or biological reaction, screening assay, or isolation
technique. For example, the impurities can be a chemically active
agent, a pharmaceutically active agent, or a biologically active
agent or a mixture thereof. In a yet further aspect, one or more of
these types of agents are not among the impurities wherein a
membrane of the invention is substantially impermeable.
[0057] 2. Nanoparticles
[0058] Generally, the nanoparticles of the invention can be any
nanoparticles known to those of skill in the art. However, in one
aspect, the nanoparticles used in connection with the membranes of
the invention can be selected based upon a number of criteria,
including one or more of: (1) an average particle size in the
nanoscale regime (i.e., having at least one dimension of a size of
from about 1 nm to about 1,000 nm, for example, from about 1 nm to
about 500 nm, from about 1 nm to about 250 nm, or from about 1 nm
to about 100 nm); (2) an average hydrophilicity greater than that
of the polymer matrix comprising the membrane, thereby enhancing
the passive fouling resistance of the resulting membrane (e.g., a
surface film consisting essentially of suitable nanoparticulate
material would be completely wetted with a pure water contact angle
less than about 5.degree. to 10.degree.); (3) a nanoscale porosity
with characteristic pore dimensions of from about 3 .ANG. to about
30 .ANG.; and/or (4) dispersibility in both the polar liquid and
the apolar liquid. Optionally, the nanoparticles can be selected so
as to be modifiable to impart biocidal or antimicrobial reactivity
to the membrane. [0059] a. Particle Composition
[0060] In one aspect, the nanoparticles of the invention can be a
metallic species. The metallic species can be any metallic species
known to those of skill in the art and meeting the nanoparticle
selection criteria of the invention. For example, the nanoparticles
can comprise at least one of gold, silver, copper, zinc, titanium,
iron, aluminum, zirconium, indium, tin, magnesium, or calcium or an
alloy thereof or an oxide thereof or a mixture thereof. It is also
contemplated that metallic species can be absent from the
compositions and/or methods of the invention.
[0061] In a further aspect, the nanoparticles can be a nonmetallic
species. The nonmetallic species can be any nonmetallic species
known to those of skill in the art and meeting the nanoparticle
selection criteria of the invention. For example, the nanoparticles
can comprise at least one of Si.sub.3N.sub.4, SiC, BN, B.sub.4C, or
TiC or an alloy thereof or a mixture thereof. It is also
contemplated that nonmetallic species can be absent from the
compositions and/or methods of the invention.
[0062] In a further aspect, the nanoparticles can be a carbon-based
species. The carbon-based species can be any carbon-based species
known to those of skill in the art and meeting the nanoparticle
selection criteria of the invention. For example, the nanoparticles
can comprise at least one of graphite, carbon glass, a carbon
cluster of at least C.sub.2, buckminsterfullerene, a higher
fullerene, a carbon nanotube, a carbon nanoparticle, or a mixture
thereof Such materials, in nanoparticulate form, can be surface
modified to enable compatibility with the non-aqueous solvent as
well as to promote hydrophilicity by attaching molecules
containing, for example, phenethyl sulfonic acid moieties where the
phenethyl group promotes compatibility with the apolar solvent and
the acid group promotes compatibility with water. The relative
compatibility with aqueous and non-aqueous phases can be tuned by
changing the hydrocarbon chain length. It is also contemplated that
carbon-based species can be absent from the compositions and/or
methods of the invention.
[0063] In a further aspect, the nanoparticles can comprise a
dendrimer. The dendrimer can be any dendrimer known to those of
skill in the art and meeting the nanoparticle selection criteria of
the invention. For example, the dendrimer can comprise at least one
of primary amino (PAMAM) dendrimers with amino, carboxylate,
hydroxyl, succinamic acid, organisilicon or other surface groups,
cyclotriphosphazene dendrimers, thiophoshphoryl-PMMH dendrimers
with aldehyde surface groups, polypropylenimine dendrimers with
amino surface groups, poly(vinyl alcohol)-divinylsulfone,
N-isopropyl acrylamide-acrylic acid or a mixture thereof. It is
also contemplated that dendrimers can be absent from the
compositions and/or methods of the invention.
[0064] In a further aspect, the nanoparticles can comprise at least
one zeolite. The zeolite can be any zeolite known to those of skill
in the art and meeting the nanoparticle selection criteria of the
invention. A zeolite can be natural or synthetic. Zeolites can also
be referred to as "molecular sieves." It is also contemplated that
zeolites or "molecular sieves" can be absent from the compositions
and/or methods of the invention.
[0065] A zeolite structure can be referred to by a designation
consisting of three capital letters used to describe and define the
network of the corner sharing tetrahedrally coordinated framework
atoms. Such designation follows the rules set up by an IUPAC
Commission on Zeolite Nomenclature in 1978. The three letter codes
are generally derived from the names of the type materials. Known
synthetic zeolites that are considered suitable porous
nanoparticulate materials include: ABW, ACO, AEI, AEL, AEN, AET,
AFG, AFI, AFN, AFO, AFR, AFS, AFT, AFX, AFY, AHT, ANA, APC, APD,
AST, ASV, ATN, ATO, ATS, ATT, ATV, AWO, AWW, BCT, BEA, BEC, BIK,
BOG, BPH, BRE, CAN, CAS, CDO, CFI, CGF, CGS, CHA, -CHI, -CLO, CON,
CZP, DAC, DDR, DFO, DFT, DOH, DON, EAB, EDI, EMT, EON, EPI, ERI,
ESV, ETR, EUO, FAU, FER, FRA, GIS, GHJ, GME, GON, GOO, HEU, IFR,
IHW, ISV, ITE, ITH, ITW, IWR, IWW, JBW, KFI, LAU, LEV, LIO, -LIT,
LOS, LOV, LTA, LTL, LTN, MAR, MAZ, MEI, MEL, MEP, MER, MFI, MFS,
MON, MOR, MOZ, MSO, MTF, MTN, MTT, MTW, MWW, NAB, NAT, NES, NON,
NPO, NSI, OBW, OFF, OSI, OSO, OWE, -PAR, PAU, PHI, PON, RHO, -RON,
RRO, RSN, RTE, RTH, RUT, RWR, RWY, SAO, SAS, SAT, SAV, SBE, SBS,
SBT, SFE, SFF, SFG, SFH, SFN, SFO, SGT, SOD, SOS, SSY, STF, STI,
STT, TER, THO, TON, TSC, UEI, UFI, UOZ, USI, UTL, VET, VFI, VNI,
VSV, WEI, -WEN, YUG, and ZON. As well known to those of skill in
the art, an up-to-date list of known synthetic zeolites can be
accessed at http://topaz.ethz.ch/IZA-SC/StdAtlas.htm. It is also
contemplated that zeolites having structures of other than the
structures expressly disclosed herein, but otherwise meeting the
nanoparticle selection criteria of the invention, can also be
employed in connection with the membranes of the invention.
[0066] In one aspect, the nanoparticles comprise a porous
structure. That is, the pores of the nanoparticle provide an open
structure in one dimension or direction. In a further aspect, the
nanoparticles can comprise an interconnected porous material. That
is, the pores of the nanoparticle can be "linked" to provide an
open structure in more than one dimension or direction. An example
of a porous material can be found in zeolitic materials. A specific
example of an interconnected porous material can be found in
Zeolite A. In such an aspect, the nanoparticles can comprise
preferential flow paths for liquids permeating the membranes of the
invention.
[0067] The size of the pores in the nanoparticles can be described
in terms of average pore diameter and can be expressed in angstroms
(.ANG.). In a further aspect, the nanoparticles can have a
nanoscale porosity with characteristic pore dimensions of from
about 3 .ANG. to about 30 .ANG., for example, from about 3 .ANG. to
about 10 .ANG., from about 10 .ANG. to about 20 .ANG., from about
20 .ANG. to about 30 .ANG., from about 3 .ANG. to about 20 .ANG.,
or from about 10 .ANG. to about 30 .ANG.. In a further aspect, the
nanoparticles can have an interconnected pore structure; that is,
adjacent pores are linked or coupled to produce a network of
channels throughout the nanoparticle structure. In a yet further
aspect, the nanoparticles can have a substantially
non-interconnected pore structure; for example, the pores can
comprise substantially parallel channels extending through the
nanoparticles. In further aspects, the nanoparticles can comprise
an about 1 .ANG. to an about 50 .ANG. porous material, an about 2
.ANG. to an about 40 .ANG. porous material, an about 3 .ANG. to an
about 12 .ANG. porous material, an about 3 .ANG. to an about 30
.ANG. porous material, an about 1 .ANG. to an about 20 .ANG. porous
material, an about 2 .ANG. to an about 20 .ANG. porous material, an
about 2 .ANG. to an about 40 .ANG. porous material, an about 5
.ANG. to an about 50 .ANG. porous material, or an about 5 .ANG. to
an about 20 .ANG. porous material.
[0068] Generally, zeolites or molecular sieves are materials with
selective sorption properties capable of separating components of a
mixture on the basis of a difference in molecular size, charge, and
shape. Zeolites can be crystalline aluminosilicates with fully
cross-linked, open framework structures made up of corner-sharing
SiO.sub.4 and AlO.sub.4 tetrahedra. A representative empirical
formula of a zeolite is
M.sub.2/nmO.Al.sub.2O.sub.3.xSiO.sub.2.yH.sub.2O where M represents
the exchangeable cation of valence n. M is generally a Group I or
II ion, although other metal, non-metal, and organic cations can
also balance the negative charge created by the presence of Al in
the structure. The framework can contain cages and channels of
discrete size, which are normally occupied by water. In addition to
Si.sup.4+ and Al.sup.3+ , other elements can also be present in the
zeolitic framework. They need not be isoelectronic with Si.sup.4+
or Al.sup.3+, but are able to occupy framework sites.
Aluminosilicate zeolites typically display a net negative framework
charge, but other molecular sieve frameworks can be electrically
neutral.
[0069] Zeolites can also include minerals that have similar
cage-like framework structures or have similar properties and/or
are associated with aluminosilicates. These include the phosphates:
kehoeite, pahasapaite and tiptopite; and the silicates:
hsianghualite, lovdarite, viseite, partheite, prehnite, roggianite,
apophyllite, gyrolite, maricopaite, okenite, tacharanite and
tobermorite. Thus, zeolites can also comprise molecular sieves
based on AlPO.sub.4. These aluminophosphates,
silicoaluminophosphates, metalloaluminophosphates and
metallosilicoaluminophosphates are denoted as AlPO.sub.4-n, SAPO-n,
MeAPO-n and MeAPSO-n, respectively, where n is an integer
indicating the structure type. AlPO.sub.4 molecular sieves can have
the structure of known zeolites, but many have novel structures.
When Si is incorporated in an AlPO.sub.4-n, framework, the product
is known as SAPO. MeAPO or MeAPSO sieves are formed by the
incorporation of a metal atom (Me) into an AlPO.sub.4-n or SAPO
framework. These metal atoms include Li, Be, Mg, Co, Fe, Mn, Zn, B,
Ga, Fe, Ge, Ti, and As. Most substituted AlPO.sub.4-n's have the
same structure as AlPO.sub.4-n, but several new structures are only
found in SAPO, MeAPO and MeAPSO materials. Their frameworks
typically carry an electric charge. Thus, zeolite chemistry is not
confined to aluminosilicates.
[0070] The framework of a molecular sieve typically contains cages
and channels of discrete size and generally from about 3 to about
30 .ANG. in diameter. In certain aspects, the primary building unit
of a molecular sieve is the individual tetrahedral unit, with
topology described in terms of a finite number of specific
combinations of tetrahedra called "secondary building units"
(SBU's).
[0071] In these aspects, description of the framework topology of a
molecular sieve can also involve "tertiary" building units
corresponding to different arrangements of the SBU's in space. The
framework can be considered in terms of large polyhedral building
blocks forming characteristic cages. For example, sodalite, Zeolite
A, and Zeolite Y can all be generated by the truncated octahedron
known as the [[beta]]-cage. An alternative method of describing
extended structures uses the two-dimensional sheet building units.
Various kinds of chains can also be used as the basis for
constructing a molecular sieve framework.
[0072] For example, the zeolites can be at least one zeolite from
the Analcime Family: Analcime (Hydrated Sodium Aluminum Silicate),
Pollucite (Hydrated Cesium Sodium Aluminum Silicate), and Wairakite
(Hydrated Calcium Sodium Aluminum Silicate); Bellbergite (Hydrated
Potassium Barium Strontium Sodium Aluminum Silicate); Bikitaite
(Hydrated Lithium Aluminum Silicate); Boggsite (Hydrated calcium
Sodium Aluminum Silicate); Brewsterite (Hydrated Strontium Barium
Sodium Calcium Aluminum Silicate); the Chabazite Family: Chabazite
(Hydrated Calcium Aluminum Silicate) and Willhendersonite (Hydrated
Potassium Calcium Aluminum Silicate); Cowlesite (Hydrated Calcium
Aluminum Silicate); Dachiardite (Hydrated calcium Sodium Potassium
Aluminum Silicate); Edingtonite (Hydrated Barium Calcium Aluminum
Silicate); Epistilbite (Hydrated Calcium Aluminum
[0073] Silicate); Erionite (Hydrated Sodium Potassium Calcium
Aluminum Silicate); Faujasite (Hydrated Sodium Calcium Magnesium
Aluminum Silicate); Ferrierite (Hydrated Sodium Potassium Magnesium
Calcium Aluminum Silicate); the Gismondine Family: Amicite
(Hydrated Potassium Sodium Aluminum Silicate), Garronite (Hydrated
Calcium Aluminum Silicate), Gismondine (Hydrated Barium Calcium
Aluminum Silicate), and Gobbinsite (Hydrated Sodium Potassium
Calcium Aluminum Silicate); Gmelinite (Hydrated Sodium Calcium
Aluminum Silicate); Gonnardite (Hydrated Sodium Calcium Aluminum
Silicate); Goosecreekite (Hydrated Calcium Aluminum Silicate); the
Harmotome Family: Harmotome (Hydrated Barium Potassium Aluminum
Silicate), Phillipsite (Hydrated Potassium Sodium Calcium Aluminum
Silicate), Wellsite (Hydrated Barium Calcium Potassium Aluminum
Silicate); The Heulandite Family: Clinoptilolite (Hydrated Sodium
Potassium Calcium Aluminum Silicate) and Heulandite (Hydrated
Sodium Calcium Aluminum Silicate); Laumontite (Hydrated Calcium
Aluminum Silicate); Levyne (Hydrated Calcium Sodium Potassium
Aluminum Silicate); Mazzite (Hydrated Potassium Sodium Magnesium
Calcium Aluminum Silicate); Merlinoite (Hydrated Potassium Sodium
Calcium Barium Aluminum Silicate); Montesommaite (Hydrated
Potassium Sodium Aluminum Silicate); Mordenite (Hydrated Sodium
Potassium Calcium Aluminum Silicate); the Natrolite Family:
Mesolite (Hydrated Sodium Calcium Aluminum Silicate), Natrolite
(Hydrated Sodium Aluminum Silicate), and Scolecite (Hydrated
Calcium Aluminum Silicate); Offretite (Hydrated Calcium Potassium
Magnesium Aluminum Silicate); Paranatrolite (Hydrated Sodium
Aluminum Silicate); Paulingite (Hydrated Potassium Calcium Sodium
Barium Aluminum Silicate); Perlialite (Hydrated Potassium Sodium
Calcium Strontium Aluminum Silicate); the Stilbite Family:
Barrerite (Hydrated Sodium Potassium Calcium Aluminum Silicate),
Stilbite (Hydrated Sodium Calcium Aluminum Silicate), and
Stellerite (Hydrated Calcium Aluminum Silicate); Thomsonite
(Hydrated Sodium Calcium Aluminum Silicate); Tschernichite
(Hydrated Calcium Aluminum Silicate); Yugawaralite (Hydrated
Calcium Aluminum Silicate) or a mixture thereof.
[0074] In one aspect, the nanoparticles can comprise Zeolite A. In
a further aspect, the nanoparticles can comprise one or more of
Zeolite A (also referred to as Linde Type A or LTA), MFI, FAU, or
CLO or a mixture thereof.
[0075] In a further aspect, the zeolite comprises a negatively
charged functionality. That is, in one aspect, the zeolite can have
negatively charged species within the crystalline framework, while
the framework maintains an overall net neutral charge. In a further
aspect, the zeolite can have a net charge on the crystalline
framework. One example wherein the zeolite comprises a negatively
charged functionality is Zeolite A. In such an aspect, the
negatively charged functionality can bind cations, including for
example silver ions. Thus, the zeolite nanoparticles can be subject
to ion-exchange with silver ions. The nanocomposite membranes can
thereby acquire antimicrobial properties. A. M. P. McDonnell et
al., Hydrophilic and antimicrobial zeolite coatings for
gravity-independent water separation, Adv. Functional Mater. 15
(2005) 336. [0076] b. Particle Size
[0077] Particle size for nanoparticles is often described in terms
of average hydrodynamic diameter, assuming a substantially
spherical shape of the particles. While it is contemplated that the
nanoparticles of the invention can be provided in any particle size
known to those of skill in the art, the nanoparticles of the
invention are, in one aspect, with an average hydrodynamic diameter
of from about 1 nm to about 1000 nm, from about 10 nm to about 1000
nm, from about 20 nm to about 1000 nm, from about 50 nm to about
1000 nm, from about 1 nm to about 500 nm, from about 10 nm to about
500 nm, from about 50 nm to about 200 nm, from about 200 nm to
about 300 nm, or from about 50 nm to about 500 nm.
[0078] In a further aspect, the particle size of the nanoparticles
can be selected to match the thickness of the film layer. For
example, for a film thickness of from about 200 nm to about 300 nm,
the nanoparticles of the invention can be selected to have an
average hydrodynamic diameter of from about 200 nm to about 300 nm.
As another example, for a film thickness of from about 50 nm to
about 200 nm, the nanoparticles of the invention can be selected to
have an average hydrodynamic diameter of from about 50 nm to about
200 nm.
[0079] 3. Hydrophilic Layer
[0080] In one aspect, the membranes of the invention can comprise a
film having a face, wherein the film comprises a polymer matrix,
and can further comprise a hydrophilic layer proximate to the face.
In a further aspect, the hydrophilic layer can be adjacent to the
face. In a yet further aspect, the hydrophilic layer can be in
contact with the face.
[0081] While it is contemplated that the hydrophilic layer can
comprise any hydrophilic material known to those of skill in the
art, the layer, in one aspect, comprises a water-soluble polymer.
In a further aspect, the hydrophilic layer can comprise at least
one of polyvinyl alcohol, polyvinyl pyrrole, polyvinyl pyrrolidone,
hydroxypropyl cellulose, polyethylene glycol, saponified
polyethylene-vinyl acetate copolymer, triethylene glycol, or
diethylene glycol or a mixture thereof.
[0082] It is contemplated that the hydrophilic layer can comprise a
crosslinked hydrophilic polymeric material. In a further aspect,
the hydrophilic layer can comprise a non-crosslinked hydrophilic
polymeric material. In one aspect, the hydrophilic layer comprises
crosslinked polyvinyl alcohol. It is also understood that the
hydrophilic layer can further comprise the nanoparticles of the
invention disposed within the layer. In a further aspect, the
nanoparticles can be substantially encapsulated within the
hydrophilic layer. For example, the film can comprise a
cross-linked polymer, and the nanoparticles can be substantially
encapsulated within the polymer.
[0083] 4. Film
[0084] In one aspect, the membranes of the invention can comprise a
film comprising a polymer matrix, wherein the film is substantially
permeable to water and substantially impermeable to impurities. By
"polymer matrix" it is meant that the polymeric material can
comprise a three-dimensional polymer network. For example, the
polymer network can be a crosslinked polymer formed from reaction
of at least one polyfunctional monomer with a difunctional or
polyfunctional monomer.
[0085] In one aspect, the nanoparticles of the invention are
disposed within the polymer matrix. By disposed "within the polymer
matrix," it is meant that the nanoparticles are mechanically
entrapped within the strands of the three-dimensional polymer
network. For example, the polymer matrix can be crosslinked around
the nanoparticles. Such mechanical entrapment can occur during, for
example, interfacial polymerization, wherein the nanoparticles are
present during the polymerization reaction. Another example of such
mechanical entrapment is wherein the nanoparticles are added to a
non-crosslinked polymeric material after the polymerization
reaction has occurred, but a subsequent crosslinking reaction is
performed while the nanoparticles are present. It is understood
that the invention can include both of the foregoing examples or
can be limited to one of the foregoing examples, as desired.
[0086] In one aspect, when nanoparticles are disposed "within the
polymer matrix," at least about 50% of the volume of at least about
50% the nanoparticles is mechanically entrapped within the strands
of the three-dimensional polymer network. For example, at least
about 60%, at least about 70%, at least about 80%, or at least
about 90% of the volume of at least about 50% the nanoparticles can
be mechanically entrapped within the strands of the
three-dimensional polymer network. As another example, at least
about 50% of the volume of at least about 60%, at least about 70%,
at least about 80%, or at least about 90% of the nanoparticles can
be mechanically entrapped within the strands of the
three-dimensional polymer network.
[0087] Such examples are in contrast to a condition wherein a
particle is merely physically located within a polymeric material.
A particle being merely physically located within a polymeric
material can occur, for example, when a particle is physically
mixed with a bulk polymeric material after the polymerization
reaction has occurred.
[0088] One example wherein mechanical entrapment of particles
within the polymer matrix is typically absent from a film is a
procedure wherein particles are positioned within a polymer by a
solution casting method, with or without a "compatiblizing" or
"priming" step. For example, in a solution casting method disclosed
in U.S. Pat. No. 6,585,802 to Koros et al., particles are "primed"
(or "sized") by adding a small amount of the desired matrix polymer
or any suitable "sizing agent" that will be miscible with the
organic polymer to be used for the matrix phase, thereby making the
particles more compatible with the polymer film. In such a
technique, the particles are typically positioned within the
polymer subsequent to any polymerization step and/or a crosslinking
step is absent from the technique. In such techniques, the
particles are not mechanically entrapped within the strands of a
three-dimensional polymer network. Accordingly, in such a
technique, the particles are not disposed "within the polymer
matrix." It is understood that such an example can, in one aspect,
be excluded from the invention.
[0089] In a further aspect, the nanoparticles can be "substantially
encapsulated within the polymer matrix." By "substantially
encapsulated within the polymer matrix," it is meant that at least
about 80% of the volume of at least about 50% the nanoparticles can
be mechanically entrapped within the strands of the
three-dimensional polymer network. For example, at least about 80%
or at least about 90% of the volume of at least about 50% the
nanoparticles can be mechanically entrapped within the strands of
the three-dimensional polymer network.
[0090] In a further aspect, the film has a face and at least a
portion of the nanoparticles penetrate the face. That is, all or
less than all of the nanoparticles penetrates the face. By
"penetrate," it is meant that a portion of each nanoparticle is
positioned exterior to the surface of the film. [0091] a. Polymer
Composition
[0092] While it is contemplated that the polymer matrix can
comprise any three-dimensional polymer network known to those of
skill in the art, in one aspect, the film comprises at least one of
an aliphatic or aromatic polyamide, aromatic polyhydrazide,
poly-bensimidazolone, polyepiamine/amide, polyepiamine/urea,
poly-ethyleneimine/urea, sulfonated polyfurane, polybenzimidazole,
polypiperazine isophtalamide, a polyether, a polyether-urea, a
polyester, or a polyimide or a copolymer thereof or a mixture
thereof. Typically, the polymer is selected to be a polymer that
can be formed by an interfacial polymerization reaction or a
polymer that can be crosslinked subsequent to polymerization.
[0093] In a further aspect, the film comprises a polyamide. The
polyamide can be an aromatic polyamide or a non-aromatic polyamide.
For example, the polyamide can comprise residues of a phthaloyl
(e.g., isophthaloyl or terephthaloyl) halide, a trimesyl halide, or
a mixture thereof. In another example, the polyamide can comprise
residues of diaminobenzene, triaminobenzene, polyetherimine,
piperazine or poly-piperazine or a mixture thereof. In a further
aspect, the film comprises residues of a trimesoyl halide and
residues of a diaminobenzene. In a further aspect, the film
comprises residues of trimesoyl chloride and m-phenylenediamine. In
a further aspect, the film comprises the reaction product of
trimesoyl chloride and m-phenylenediamine. [0094] b. Film
Thickness
[0095] While the polymer film can be provided at any desired film
thickness, the films of the invention are, in one aspect, provided
at a thickness of from about 1 nm to about 1000 nm. For example,
the film can be provided at a thickness of from about 10 nm to
about 1000 nm, from about 100 nm to about 1000 nm, from about 1 nm
to about 500 nm, from about 10 nm to about 500 nm, from about 50 nm
to about 500 nm, from about 50 nm to about 200 nm, from about 50 nm
to about 250 nm, from about 50 nm to about 300 nm, or from about
200 nm to about 300 nm.
[0096] In a further aspect, the thickness of the film layer can be
selected to match the particle size of the nanoparticles. For
example, for nanoparticles having an average hydrodynamic diameter
of from about 200 nm to about 300 nm, the film thickness can be
selected to have a film thickness of from about 200 nm to about 300
nm. As another example, for nanoparticles having an average
hydrodynamic diameter of from about 50 nm to about 200 nm, the film
thickness can be selected to have a film thickness of from about 50
nm to about 200 nm. As another example, for nanoparticles having an
average hydrodynamic diameter of from about 1 nm to about 100 nm,
the film thickness can be selected to have a film thickness of from
about 1 nm to about 100 nm.
[0097] The film thickness can be visually confirmed and quantified,
for example, by using transmission electron microscopy (TEM).
Freger V, Gilron J, Belfer S, "TFC polyamide membranes modified by
grafting of hydrophilic polymers: an FT-IR/AFM/TEM study," Journal
of Membrane Science 209 (2002) 283-292. For TEM observations, the
polyester backing of both TFC and TFN membranes was peeled off so
that polysulfone and polyamide layers remained together. Small
pieces of the two membrane layers were embedded in epoxy resin
(e.g., Eponate 12, Ted Pella, Inc.). Approximately 60-80 nm thick
sections were cut on a Reichert-Jung Ultracut E ultramicrotome and
placed on FORMVAR.RTM. (i.e., poly-vinylformal)-coated copper
grids. The sections either unstained or stained with 8% uranyl
acetate for 30 min were examined on a JEOL 100CX transmission
electron microscope (TEM) at an accelerating voltage of 80 kV.
[0098] 5. Properties
[0099] In various aspects, the nanocomposite membranes of the
invention can have various properties that provide the superior
function of the membranes, including excellent flux, high
hydrophilicity, negative zeta potential, surface smoothness, an
excellent rejection rate, improved resistance to fouling, and the
ability to be provided in various shapes. It is also understood
that the membranes have other properties. [0100] a. Flux
[0101] The pure water flux of the membranes can be measured in a
laboratory scale cross-flow membrane filtration apparatus. For
example, the pure water flux can be measured in a high-pressure
chemical resistant stirred cell (Sterlitech HP4750 Stirred Cell).
In one aspect, the membranes can have a flux of from about 0.02 to
about 0.4 GFD (gallons per square foot of membrane per day) per psi
(pound per square inch) of applied pressure. For example, the flux
can be from about 0.03 to about 0.1, from about 0.1 to about 0.3,
from about 0.1 to about 0.2, from about 0.2 to about 0.4, from
about 0.05 to about 0.1, from about 0.05 to about 0.2, from about
0.03 to about 0.2, from about 0.5 to about 0.4, from about 0.1 to
about 0.4, from about 0.03 to about 0.3 gallons per square foot of
membrane per day per psi of applied pressure. [0102] b.
Hydrophilicity
[0103] The hydrophilicity of the membranes can be expressed in
terms of the pure water equilibrium contact angle. The contact
angles of the membranes of the invention can be measured using a
contact angle goniometer (DSA10, KRUSS GmbH). In one aspect, a
membrane of the invention can have a pure water equilibrium contact
angle of less than about 90.degree.. For example, the contact angle
can be less than about 75.degree., less than about 60.degree., less
than about 45.degree., or less than about 30.degree.. In a further
aspect, the contact angle can be from about 60.degree. to about
90.degree., from about 50.degree. to about 80.degree., from about
40.degree. to about 70.degree., from about 30.degree. to about
60.degree., from about 20.degree. to about 50.degree., or below
20.degree.. [0104] c. Zeta Potential
[0105] The surface (zeta) potential of the membranes of the
invention can be measured by streaming potential analysis (BI-EKA,
Brookhaven Instrument Corp). In one aspect, a membrane of the
invention can have a zeta potential of from about +10 to about -50
mV depending on solution pH, type of counter-ions present, and
total solution ionic strength. For example, in 10 mM NaCl solution
the zeta potential can be at least as negative as about -5 mV, at
least as negative as about -15 mV, at least as negative as about
-30 mV, or at least as negative as about -45 mV for pHs range of
from about 4 to about 10. [0106] d. Roughness
[0107] The surface topography of the synthesized membranes can be
investigated by atomic force microscopy (AFM). Such investigation
allows calculation of a root mean squared (RMS) roughness value for
a membrane surface. Hoek, E. M. V., S. Bhattacharjee, and M.
Elimelech, "Effect of Surface Roughness on Colloid-Membrane DLVO
Interactions," Langmuir 19 (2003) 4836-4847. In one aspect, a
membrane of the invention can have an RMS surface roughness of less
than about 100 nm. For example, the RMS surface roughness can be
less than about 65 nm, less than about 60 nm, less than about 55
nm, less than about 50 nm, less than about 45 nm, or less than
about 40 nm. [0108] e. Rejection
[0109] Salt water rejection of the membranes of the invention can
be measured in the same high-pressure chemical resistant stirred
cell used to measure flux, for example, using approximately 2,000
ppm NaCl. The salt concentrations in the feed and permeate water
can then be measured by a digital conductivity meter and the
rejection is defined as R=1-c.sub.p/c.sub.f, where c.sub.p is the
salt concentration in the permeated solution and c.sub.f is the
salt concentration in the feed solution. In one aspect, a membrane
of the invention can have a salt water rejection of from about 75
to greater than about 95 percent. [0110] f. Resistance to
Fouling
[0111] The relative biofouling potentials of the membranes of the
invention can be evaluated by direct microscopic observation of
microbial deposition and adhesion. S. Kang, A. Subramani, E. M. V.
Hoek, M. R. Matsumoto, and M. A. Deshusses, Direct observation of
biofouling in cross-flow microfiltration: mechanisms of deposition
and release, Journal of Membrane Science 244 (2004) 151-165.
Viability of bacteria adhered to Zeolite A-polyamide (ZA-PA) and
polyamide (PA) membranes can be verified with a commercial
viability staining kit (e.g., LIVE/DEAD.RTM. BacLight.TM. Bacterial
Viability Kit, Molecular Probes, Inc., Eugene Oreg.) for 2-4
minutes, followed by observation using a fluorescence microscope
(e.g., BX51, Olympus America, Inc., Melville, N.Y.). Living cells
can be observed as green spots and dead (inactivated) cells are
seen as red spots. B. K. Li and B. E. Logan, The impact of
ultraviolet light on bacterial adhesion to glass and metal
oxide-coated surface, Colloids and Surfaces B-Biointerfaces 41
(2005) 153-161. [0112] g. Shape
[0113] A variety of membrane shapes are useful and can be provided
using the present invention. These include spiral wound, hollow
fiber, tubular, or flat sheet type membranes.
D. Preparation of Nanocomposite Membranes
[0114] In one aspect, the membranes of the invention are prepared
by a method distinct from the conventional RO membrane preparation
processes. However, many of the techniques used in conventional RO
membrane preparation can be applicable to the methods of the
invention.
[0115] 1. Thin Film Composite Membrane Formation Techniques
[0116] Thin film composite membranes can be formed on the surface
of a microporous support membrane via interfacial polymerization.
See U.S. Pat. No. 6,562,266. One suitable microporous support for
the composite membrane is a polysulfone "ultrafiltration" membrane
with molecular cutoff value of .about.60 kDa and water permeability
of .about.100-150 l/m.sup.2hbar. Zhang, W., G. H. He, P. Gao, and
G. H. Chen, Development and characterization of composite
nanofiltration membranes and their application in concentration of
antibiotics, Separation and Purification Technology, 30 (2003) 27;
Rao, A. P., S. V. Joshi, J. J. Trivedi, C. V. Devmurari, and V. J.
Shah, Structure-performance correlation of polyamide thin film
composite membranes: Effect of coating conditions on film
formation, Journal of Membrane Science, 211 (2003) 13. The support
membrane can be immersed in an aqueous solution containing a first
reactant (e.g., 1,3-diaminobenzene or "MPD" monomer). The substrate
can then be put in contact with an organic solution containing a
second reactant (e.g., trimesoyl chloride or "TMC" initiator).
Typically, the organic or apolar liquid is immiscible with the
polar or aqueous liquid, so that the reaction occurs at the
interface between the two solutions to form a dense polymer layer
on the support membrane surface.
[0117] The standard conditions for the reaction of MPD and TMC to
form a fully aromatic, polyamide thin film composite membrane
include an MPD to TMC concentration ratio of .about.20 with MPD at
about 1 to 3 percent by weight in the polar phase. The reaction can
be carried out at room temperature in an open environment, but the
temperature of either the polar or the apolar liquid or both can be
controlled. Once formed, the dense polymer layer can act as a
barrier to inhibit the contact between reactants and to slow down
the reaction; hence, the selective dense layer so formed is
typically very thin and permeable to water, but relatively
impermeable to dissolved, dispersed, or suspended solids. This type
of membrane is conventionally described as a reverse osmosis (RO)
membrane.
[0118] 2. Nanofiltration Membrane Formation Techniques
[0119] Unlike conventional RO membranes, nanofiltration (NF)
membranes typically have the ability to selectively separate
divalent and monovalent ions. A nanofiltration membrane exhibits a
preferential removal of divalents over monovalents, while a
conventional reverse osmosis membrane typically does not exhibit
significant selectivity. A conventional thin film composite
nanofiltration (NF) membrane can be made as follows. Piperazine,
together with a hydrophilic monomer or polymer containing amine
groups (e.g., tri-ethylamine or "TEA" catalyst), is dissolved in
water. The microporous support membrane can then be immersed in the
aqueous solution with a piperazine concentration of .about.1-2 wt %
at room temperature for a desired amount of time. Next, the
membrane is put in contact with the organic solution containing
.about.0.1-1 wt % of TMC at room temperature for about a minute
after the excess solution on the membrane surface is removed. Other
changes to water flux and solute rejection can be accomplished by
using different monomers and initiators, changing the structure of
the microporous support membrane, altering the ratio of monomer to
initiator in the reaction solutions, blending multiple monomers and
initiators, changing structure of the organic solvent or using
blends of different organic solvents, controlling reaction
temperature and time, or adding catalysts (e.g., metals, acids,
bases, or chelators). In general, polyfunctional amines are
dissolved in water and polyfunctional acid chlorides are dissolved
in a suitable nonpolar solvent, which is immiscible with water
like, for example, hexane, heptane, naptha, cyclohexane, or
isoparaffin based hydrocarbon oil. While not wishing to be bound by
theory, it is believed that the interfacial polycondensation
reaction does not take place in the water phase, because a highly
unfavorable partition coefficient for acid chloride limits its
availability in the aqueous phase. For film thickness to build up,
the amine monomer crosses the water-organic solvent interface,
diffuses through the polyamide layer already formed, and then comes
into contact with acid chloride on the organic solvent side of the
polyamide layer. Thus, new polymer forms on the organic solvent
side of the polyamide film. While not wishing to be bound by
theory, it is believed that the thickness of the thin film formed
at the interface is primarily determined by the rate of diffusion
of the amine to the organic phase via water-organic media
interface. See, e.g., Rao, A. P., S. V. Joshi, J. J. Trivedi, C. V.
Devmurari, and V. J. Shah, Structure-performance correlation of
polyamide thin film composite membranes: Effect of coating
conditions on film formation, Journal of Membrane Science, 211
(2003) 13; Kwak, S. Y., S. G. Jung, and S. H. Kim,
Structure-motion-performance relationship of flux-enhanced reverse
osmosis (RO) membranes composed of aromatic polyamide thin films,
Environmental Science &Technology, 35 (2001) 4334; Kwak, S. Y.,
Relationship of relaxation property to reverse osmosis permeability
in aromatic polyamide thin-film-composite membranes, Polymer, 40
(1999) 6361; Kwak, S. Y. and D. W. Ihm, Use of atomic force
microscopy and solid-state NMR spectroscopy to characterize
structure-property-performance correlation in high-flux reverse
osmosis (RO) membranes, Journal of Membrane Science, 158 (1999)
143; U.S. Pat. No. 5,028,337; Mulder, M., Basic principles of
membrane technology, Second, Kluwer Academic Publishers, Dordrecht,
N L, 1996; Petersen, R. J., Composite reverse-osmosis and
nanofiltration membranes, Journal of Membrane Science, 83 (1993)
81; Kurihara, M., Y. Fusaoka, T. Sasaki, R. Bairinji, and T.
Uemura, Development of cross-linked fully aromatic polyamide
ultra-thin composite membranes for seawater desalination,
Desalination, 96 (1994) 133; Kim, C. K., J. H. Kim, I. J. Roh, and
J. J. Kim, The changes of membrane performance with polyamide
molecular structure in the reverse osmosis process, Journal of
Membrane Science, 165 (2000) 189; Hoek, E. M. V., Colloidal fouling
mechanisms in reverse osmosis and nanofiltration, Ph.D., Chem.
Eng., Yale University, New Haven, Conn., 2002; U.S. Pat. No.
6,413,425; Comstock, D. L., Desal-5 membrane for water softening,
Desalination, 76 (1989) 61; Cadotte, J. E., R. J. Petersen, R. E.
Larson, and E. E. Erickson, New thin-film composite seawater
reverse-osmosis membrane, Desalination, 32 (1980) 25; Cadotte, J.,
R. Forester, M. Kim, R. Petersen, and T. Stocker, Nanofiltration
membranes broaden the use of membrane separation technology,
Desalination, 70 (1988) 77; Belfer, S., Y. Purinson, and O. Kedem,
Surface modification of commercial polyamide reverse osmosis
membranes by radical grafting: An ATR-FTIR study, Acta Polymerica,
49 (1998) 574; Belfer, S., Y. Purinson, R. Fainshtein, Y.
Radchenko, and O. Kedem, Surface modification of commercial
composite polyamide reverse osmosis membranes, Journal of Membrane
Science, 139 (1998) 175; Belfer, S., J. Gilron, Y. Purinson, R.
Fainshtain, N. Daltrophe, M. Priel, B. Tenzer, and A. Toma, Effect
of surface modification in preventing fouling of commercial SWRO
membranes at the Eilat seawater desalination pilot plant,
Desalination, 139 (2001) 169.
[0120] 3. Post-Treatment Techniques
[0121] Various post-treatments can be employed to enhance water
permeability, solute rejection, or fouling resistance of a formed
TFC membrane. See, e.g., U.S. Pat. No. 5,755,964. For example, a
membrane can be immersed in an acidic and/or basic solution to
remove residual, unreacted acid chlorides and diamines. While not
wishing to be bound by theory, it is believed that such treatments
can improve the flux of the formed composite membrane.
Additionally, heat treatment, or curing, can also be applied to
promote contact between the polyamide film and polysulfone support
(e.g., at low temperature) or to promote cross-linking within the
formed polyamide film. Generally, curing increases solute
rejection, but often at the cost of lower water permeability.
Finally, a membrane can be exposed to an oxidant such as chlorine
by filtering a 10-20 ppm solution of, for example, sodium
hypochlorite through the membrane for 30-60 minutes.
Post-chlorination of a fully aromatic polyamide thin film
composites forms chloramines as free chlorine reacts with pendant
amine functional groups within the polyamide film. This can
increase the negative charge density, by neutralizing
positively-charged pendant amine groups, and the result is a more
hydrophilic, negatively charged RO membrane with higher flux, salt
rejection, and fouling resistance.
[0122] Membrane surface properties, such as hydrophilicity, charge,
and roughness, typically correlate with RO/NF membrane fouling.
Zhu, X. H. and M. Elimelech, Colloidal fouling of reverse osmosis
membranes: Measurements and fouling mechanisms, Environmental
Science & Technology, 31 (1997) 3654; Vrijenhoek, E. M., S.
Hong, and M. Elimelech, Influence of membrane surface properties on
initial rate of colloidal fouling of reverse osmosis and
nanofiltration membranes, Journal of Membrane Science, 188 (2001)
115; Elimelech, M., X. Zhu, A. E. Childress, and S. Hong, Role of
membrane surface morphology in colloidal fouling of cellulose
acetate and composite aromatic polyamide reverse osmosis membranes,
Journal of Membrane Science, 127 (1997) 101; Brant, J. A. and A. E.
Childress, Assessing short-range membrane-colloid interactions
using surface energetics, Journal of Membrane Science, 203 (2002)
257; Flemming, H. C., Mechanistic aspects of reverse osmosis
membrane biofouling and prevention, in Z. Amjad (Ed.), Membrane
technology, Van Nostrand Reinhold, New York, 1992, pp. 163;
Flemming, H. C., G. Schaule, T. Griebe, J. Schmitt, and A.
Tamachkiarowa, Biofouling--the achilles heel of membrane processes,
Desalination, 113 (1997) 215. Generally, membranes with highly
hydrophilic, negatively charged, and smooth surfaces yield good
permeability, rejection, and fouling behavior. However, important
surface attributes of RO and NF membranes--to promote fouling
resistance--include hydrophilicity and smoothness. Membrane surface
charge can also be a factor when solution ionic strength is
significantly less than 100 mM because at or above this ionic
strength electrical double layer interactions are negligible.
Israelachvili, J. N., Intermolecular and surface forces, 2nd Ed.,
Academic Press, London, 1992; Probstein, R. F., Physicochemical
hydrodynamics, 2nd, John Wiley & Sons, Inc., New York, N.Y.,
1994; Stumm, W. and J. J. Morgan, Aquatic chemistry, 1st,
Wiley-Interscience, New York, N.Y., 1996. Since many RO and NF
applications involve highly saline waters, one cannot always rely
on electrostatic interactions to inhibit foulant deposition.
Moreover, it has been demonstrated that polyamide composite
membrane fouling by natural organic matter (NOM) is typically
mediated by calcium complexation reactions occurring between
carboxylic acid functional groups of the NOM macromolecules and
pendant carboxylic acid functional groups on the membrane surface.
Li, Q.L. and M. Elimelech, Organic fouling and chemical cleaning of
nanofiltration membranes: Measurements and mechanisms,
Environmental Science & Technology, 38 (2004) 4683; Hong, S. K.
and M. Elimelech, Chemical and physical aspects of natural organic
matter (nom) fouling of nanofiltration membranes, Journal of
Membrane Science, 132 (1997) 159.
[0123] 4. Hydrophilic Layer Formation Techniques
[0124] Creation of a non-reactive, hydrophilic, smooth composite
membrane surface typically includes applying an additional coating
layer comprised of a water-soluble (super-hydrophilic) polymer such
as polyvinyl alcohol (PVA), polyvinyl pyrrole (PVP), or
polyethylene glycol (PEG) on the surface of a polyamide composite
RO membrane. In recent years, several methods of composite membrane
surface modification have been introduced in membrane preparation
beyond simple dip-coating and interfacial polymerization methods of
the past. These advanced methods include plasma, photochemical, and
redox initiated graft polymerization, drying-leaching (two-step),
electrostatically self-assembled multi-layers, Gilron J, Belfer S,
Vaisanen P, Nystrom M, Effects of surface modification on
antifouling and performance properties of reverse osmosis
membranes, Desalination 140 (2001) 167-179; Hammond P. T., Recent
explorations in electrostatic multilayer thin film assembly,
Current Opinion in Colloid & Interface Science 4 (1999)
430-442; Gilron, J; Belfer, S; Vaisanen, P; et al. Effects of
surface modification on antifouling and performance properties of
reverse osmosis membranes, Desalination, 140 (2001) 167-179. Ma, H
M; Nielsen, D R; Bowman, C N; et al. Membrane surface modification
and backpulsing for wastewater treatment, Separation Science and
Technology, 36 (2001) 1557-1573. Ma, H M; Bowman, C N; Davis, R H,
Membrane fouling reduction by backpulsing and surface modification,
Journal of Membrane Science, 173 (2000) 191-200. Chiang W. Y. and
Hu C. M., Separation of liquid-mixtures by using polymer membranes:
1. Water alcohol separation by pervaporation through PVA-g-MMA MA
membrane, Journal of Applied Polymer Science 43 (1991) 2005-2012.
Advantages of these surface modification approaches include
well-controlled coating layer thickness, permeability, charge,
functionality, smoothness, and hydrophilicity. However, a drawback
of all of these sophisticated surface modification methods is the
inability to economically incorporate them into existing commercial
manufacturing systems.
[0125] Currently, one preferred approach to surface modification of
thin film composite membranes remains the simple dip coating-drying
approach. In addition, polyvinyl alcohol can be an attractive
option for modification of composite membranes because of its high
water solubility and good film-forming properties. It is known that
polyvinyl alcohol is little affected by grease, hydrocarbons, and
animal or vegetable oils; it has outstanding physical and chemical
stability against organic solvents. Thus, polyvinyl alcohol can be
used as a protective skin layer in the formation of thin-film
composite membranes for many reverse osmosis applications, as well
as an ultra-thin selective layer in many pervaporation
applications. K. Lang, S. Sourirajan, T. Matsuura, G. Chowdhury, A
study on the preparation of polyvinyl alcohol thin-film composite
membranes and reverse osmosis testing, Desalination 104 (1996)
185-196. Kim I C, Ka Y H, Park J Y, Lee K H, Preparation of fouling
resistant nanofiltration and reverse osmosis membranes and their
use for dyeing wastewater effluent, Journal of Industrial and
Engineering Chemistry 10 (2004) 115-121.
[0126] A PVA coating layer can be formed on the surface of a
polyamide composite membrane as follows. An aqueous PVA solution
with .about.0.1-1 wt % PVA with molecular weight ranging from 2,000
to over 70,000 can be prepared by dissolving the polymer in
distilled/deionized water. Lang, K., T. Matsuura, G. Chowdhury, and
S. Sourirajan, Preparation and testing of polyvinyl-alcohol
composite membranes for reverse-osmosis, Canadian Journal of
Chemical Engineering, 73 (1995) 686; Lang, K., G. Chowdhury, T.
Matsuura, and S. Sourirajan, Reverse-osmosis performance of
modified polyvinyl-alcohol thin-film composite membranes, Journal
of Colloid and Interface Science, 166 (1994) 239; Lang, K., S.
Sourirajan, T. Matsuura, and G. Chowdhury, A study on the
preparation of polyvinyl alcohol thin-film composite membranes and
reverse osmosis testing, Desalination, 104 (1996) 185. PVA powder
is easily dissolved in water by stirring at .about.90.degree. C.
for .about.5 hours. The already formed polyamide composite membrane
is contacted with the PVA solution and the deposited film is dried
overnight. Subsequently, the membrane can be brought into contact
(e.g., from the PVA side) with a solution containing a
cross-linking agent (e.g., dialdehydes and dibasic acids) and
catalyst (e.g., .about.2.4 wt % acetic acid) for about 1 second.
The membrane may then be heated in an oven at a predetermined
temperature for a predetermined period. Various cross-linking
agents (glutaraldehyde, PVA-glutaraldehyde mixture,
paraformaldehyde, formaldehyde, glyoxal) and additives in the PVA
solution (formaldehyde, ethyl alcohol, tetrahydrofuran, manganese
chloride, and cyclohexane) can be used to prepare PVA films cast
over existing membranes in combination with heat treatment of
prepared PVA films to modify film properties. Lang, K., S.
Sourirajan, T. Matsuura, and G. Chowdhury, A study on the
preparation of polyvinyl alcohol thin-film composite membranes and
reverse osmosis testing, Desalination, 104 (1996) 185.
[0127] 5. Nanocomposite Membrane Formation
[0128] In one aspect, the invention relates to a method for
preparing a nanocomposite membrane comprising the steps of
providing a polar mixture comprising a polar liquid and a first
monomer that is miscible with the polar liquid; providing an apolar
mixture comprising an apolar liquid substantially immiscible with
the polar liquid and a second monomer that is miscible with the
apolar liquid; providing nanoparticles in either the polar mixture
or the apolar mixture, wherein the nanoparticles are miscible with
the apolar liquid and miscible with the polar liquid; and
contacting the polar mixture and the apolar mixture at a
temperature sufficient to react the first monomer with the second
monomer, thereby interfacially-polymerizing the first monomer and
the second monomer to form a polymer matrix, wherein the
nanoparticles are disposed within the polymer matrix.
[0129] By "miscible," it is meant that the respective phases can
mix and form a homogeneous mixture or dispersion at the relevant
temperature and pressure. Unless otherwise specified, the relevant
temperature and pressure are at room temperature and at atmospheric
pressure. Particles can be termed miscible in a liquid if the
particles can form a uniform and stable dispersion in the liquid.
An example of a particle being miscible in an apolar liquid is
Zeolite A nanoparticles in hexane. A further example of a particle
being miscible in a polar liquid is Zeolite A nanoparticles in
water. By "immiscible," it is meant that the respective phases do
not appreciably mix and do not appreciably form a homogeneous
mixture at the relevant temperature and pressure. Two liquids can
be termed immiscible if neither liquid is appreciably soluble in
the other liquid. An example of two immiscible liquids is hexane
and water. [0130] a. Molar Liquid
[0131] While it is contemplated that the apolar liquid can be any
apolar liquid known to those of skill in the art, typically, an
apolar liquid of the invention is selected such that it is
immiscible with a particular polar liquid used in a method of the
invention. Further, an apolar liquid of the invention is typically
selected such that it is miscible with particular nanoparticles of
the invention: For example, if the particular polar liquid is water
and the particular nanoparticles are Zeolite A, the apolar liquid
can be selected to be hexane.
[0132] In one aspect, the apolar liquid can comprise at least one
of a C.sub.5 to C.sub.24 hydrocarbon. The hydrocarbon can be an
alkane, an alkene, or an alkyne. The hydrocarbon can be cyclic or
acyclic. The hydrocarbon can be straight chain or branched. The
hydrocarbon can be substituted or unsubstituted. In further
aspects, the apolar liquid can comprise at least one of a linear
hydrocarbon, a branched hydrocarbon, a cyclic hydrocarbon, naptha,
heavy naptha, paraffin, or isoparaffin or a mixture thereof. In one
aspect, the apolar liquid comprises hexane.
[0133] It is understood that the nanoparticles of the invention
can, in one aspect, be provided as part of the apolar mixture. For
example, the nanoparticles can be dispersed within the apolar
liquid. [0134] b. Polar Liquid
[0135] While it is contemplated that the polar liquid can be any
polar liquid known to those of skill in the art, typically, a polar
liquid of the invention is selected such that it is immiscible with
a particular apolar liquid used in a method of the invention.
Further, a polar liquid of the invention is typically selected such
that it is miscible with particular nanoparticles of the invention.
For example, if the particular apolar liquid is hexane and the
particular nanoparticles are Zeolite A, the polar liquid can be
selected to be water.
[0136] In one aspect, the polar liquid can comprise at least one of
a C.sub.5 to C.sub.24 alcohol. The alcohol can be an alkane, an
alkene, or an alkyne. The alcohol can be cyclic or acyclic. The
alcohol can be straight chain or branched. The alcohol can be
substituted or unsubstituted. In a further aspect, the polar liquid
comprises water.
[0137] It is understood that the nanoparticles of the invention
can, in one aspect, be provided as part of the polar mixture. For
example, the nanoparticles can be dispersed within the polar
liquid.
[0138] In one aspect, the polar mixture can be adsorbed upon a
substantially insoluble support membrane prior to the contacting
step. The support membrane can comprise, for example, a polysulfone
or polyethersulfone webbing. [0139] c. Monomers
[0140] Generally, the polymer matrix of the invention is prepared
by reaction of two or more monomers. In one aspect, the first
monomer is a dinucleophilic or a polynucleophilic monomer and the
second monomer is a dielectrophilic or a polyelectrophilic monomer.
That is, each monomer can have two or more reactive (e.g.,
nucleophilic or electrophilic) groups.
[0141] Both nucleophiles and electrophiles are well known in the
art, and one of skill in the art can select suitable monomers for
use in the methods of the invention. In one aspect, the first and
second monomers can be chosen so as to be capable of undergoing an
interfacial polymerization reaction to form a polymer matrix (i.e.,
a three-dimensional polymer network) when brought into contact. In
a further aspect, the first and second monomers can be chosen so as
to be capable of undergoing a polymerization reaction when brought
into contact to form a polymer product that is capable of
subsequent crosslinking by, for example, exposure to heat, light
radiation, or a chemical crosslinking agent.
[0142] In one aspect, a first monomer is selected so as to be
miscible with a polar liquid and, with the polar liquid, can form a
polar mixture. The first monomer can optionally also be selected so
as to be immiscible with an apolar liquid. Typically, the first
monomer is a dinucleophilic or a polynucleophilic monomer. In a
further aspect, the first monomer can comprise a diaminobenzene.
For example, the first monomer can comprise m-phenylenediamine. As
a further example, the first monomer can comprise a
triaminobenzene. In a yet further aspect, the polar liquid and the
first monomer can be the same compound; that is, the first monomer
is not dissolved in a separate polar liquid.
[0143] In one aspect, a second monomer is selected so as to be
miscible with an apolar liquid and, with the apolar liquid, can
form an apolar mixture. The second monomer can optionally also be
selected so as to be immiscible with a polar liquid. Typically, the
second monomer is a dielectrophilic or a polyelectrophilic monomer.
In a further aspect, the second monomer can comprise a trimesoyl
halide. For example, the second monomer can comprise trimesoyl
chloride. As a further example, the second monomer can comprise a
phthaloyl halide. In a yet further aspect, the apolar liquid and
the second monomer can be the same compound; that is, the second
monomer is not dissolved in a separate apolar liquid.
[0144] Generally, the difunctional or polyfunctional nucleophilic
monomer used in the present invention can have primary or secondary
amino groups and may be aromatic (e.g.,
m-phenylenediamine,p-phenyenediamine, 1,3,5-triaminobenzene,
1,3,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene,
2,4-diaminoanisole, and xylylenediamine) or aliphatic (e.g.,
ethylenediamine, propylenediamine, and tris(2-diaminoethyl)amine).
Examples of suitable amine species include primary aromatic amines
having two or three amino groups, for example m-phenylene diamine,
and secondary aliphatic amines having two amino groups, for example
piperazine. The amine can typically be applied to the microporous
support as a solution in a polar liquid, for example water. The
resulting polar mixture typically includes from about 0.1 to about
20 weight percent, for example from about 0.5 to about 6 weight
percent, amine. Once coated on the microporous support, excess
polar mixture may be optionally removed. The polar mixture need not
be aqueous but is typically immiscible with the apolar liquid.
[0145] Generally, difunctional or polyfunctional electrophilic
monomer is preferably coated from an apolar liquid, although the
monomer can optionally be delivered from a vapor phase (for
monomers having sufficient vapor pressure). The electrophilic
monomer can be aromatic in nature and can contain two or more, for
example three, electrophilic groups per molecule. In the case of
acyl halide electrophilic monomers, because of the relatively lower
cost and greater availability, acyl chlorides are generally more
suitable than the corresponding bromides or iodides. A suitable
polyfunctional acyl halide is trimesoyl chloride (TMC). The
polyfunctional acyl halide can be dissolved in an apolar organic
liquid in a range of, for example, from about 0.01 to about 10.0
weight percent or from about 0.05 to about 3 weight percent, and
delivered as part of a continuous coating operation. Suitable
apolar liquids are those which are capable of dissolving the
electrophilic monomers, for example polyfunctional acyl halides,
and which are immiscible with a polar liquid, for example water. In
particular, suitable polar and apolar liquids can include those
which do not pose a threat to the ozone layer and yet are
sufficiently safe in terms of their flashpoints and flammability to
undergo routine processing without having to undertake extreme
precautions. Higher boiling hydrocarbons, i.e., those with boiling
points greater than about 90.degree. C., such as C.sub.8-C.sub.24
hydrocarbons and mixtures thereof, have more suitable flashpoints
than their C.sub.5 -C.sub.7 counterparts, but they are less
volatile.
[0146] Once brought into contact with one another, the
electrophilic monomer and nucleophilic monomer react at the surface
interface between the polar mixture and the apolar mixture to form
a polymer, for example polyamide, discriminating layer. The
reaction time is typically less than one second, but contact time
is often longer, for example from one to sixty seconds, after which
excess liquid may optionally be removed, e.g., by way of an air
knife, water bath(s), dryer, and the like. The removal of the
excess polar mixture and/or apolar mixture can be conveniently
achieved by drying at elevated temperatures, e.g., from about
40.degree. C. to about 120.degree. C., although air drying at
ambient temperatures may be used.
[0147] Through routine experimentation, those skilled in the art
will appreciate the optimum concentration of the monomers, given
the specific nature and concentration of the other monomer,
nanoparticles, reaction conditions, and desired membrane
performance.
[0148] In a further aspect, the method comprises the steps of
soaking a polysulfone membrane in an aqueous solution comprising
m-phenylenediamine, and pouring onto the soaked polysulfone
membrane a hexane solution comprising trimesoyl chloride and
zeolite nanoparticles suspended in the hexane solution, thereby
interfacially-polymerizing the m-phenylenediamine and the trimesoyl
chloride to form a film, wherein the zeolite nanoparticles are
dispersed within the film. In a yet further aspect, the
nanoparticles comprise Zeolite A. In a yet further aspect, the
method can further comprise the step of contacting the zeolite
nanoparticles with a silver salt. For example, the zeolite can be
contacted with a silver salt prior to interfacially polymerizing a
first monomer (e.g., m-phenylenediamine) and a second monomer
(e.g., trimesoyl chloride) to form a film, thereby producing
silver-exchanged zeolite nanoparticles dispersed within the film.
[0149] d. Nanoparticles
[0150] In one aspect, nanoparticles used in connection with the
membranes of the invention can be used in connection with the
methods of the invention. Typically, the nanoparticles are provided
as part of the polar mixture or as part of the apolar mixture. In
one aspect, the nanoparticles are selected so as to be miscible
with both the polar liquid and the apolar liquid.
[0151] Through routine experimentation, those skilled in the art
will appreciate the optimum concentration of the nanoparticles,
given the specific nature and concentration of the first monomer,
second monomer, reaction conditions, and desired membrane
performance.
[0152] 6. Nanocomposite Membrane with Hydrophilic Layer
[0153] In a further aspect, the method of the invention comprises
the steps of providing an aqueous mixture comprising water, a
hydrophilic polymer, nanoparticles, and optionally, at least one
crosslinking agent; providing a polymer film that is substantially
permeable to water and substantially impermeable to impurities;
contacting the mixture and the film, thereby forming a hydrophilic
nanocomposite layer in contact with the film; and evaporating at
least a portion of the water from the hydrophilic nanocomposite
layer. In a yet further aspect, the method further comprises the
step of heating the layer to a temperature sufficient to crosslink
the crosslinking agent. [0154] a. Aqueous Mixture
[0155] In one aspect, the method involves providing an aqueous
mixture comprising water, a hydrophilic polymer, nanoparticles, and
optionally, at least one crosslinking agent. The components can be
combined in any order; however, in one aspect, the nanoparticles
can be added to a mixture of the hydrophilic polymer and water. In
one aspect, the crosslinking agent can be added after the other
three components have been combined.
[0156] Typically, the water is fresh water; however, in one aspect,
the water can be salt water. Similarly, the water can include other
dissolved materials.
[0157] While it is contemplated that the hydrophilic polymer can
comprise any hydrophilic polymer known to those of skill in the
art, the polymer, in one aspect, can comprise at least one of
polyvinyl alcohol, polyvinyl pyrrole, polyvinyl pyrrolidone,
hydroxypropyl cellulose, acrylic acids, poly(acrylic acids),
polyethylene glycol, saponified polyethylene-vinyl acetate
copolymer, triethylene glycol, or diethylene glycol or a mixture
thereof. In one aspect, the hydrophilic polymer comprises
crosslinked polyvinyl alcohol.
[0158] It is also understood that the hydrophilic polymer can
further comprise the nanoparticles of the invention disposed within
the polymer. In a further aspect, the nanoparticles can be
substantially encapsulated within the hydrophilic polymer. For
example, the film can comprise a crosslinked polymer, and the
nanoparticles can be substantially encapsulated within the polymer
matrix of the polymer.
[0159] At least one crosslinking agent is optionally provided in
the method. That is, in one aspect, the hydrophilic polymer can
comprise a crosslinked hydrophilic polymer. In a further aspect,
the hydrophilic layer can comprise a non-crosslinked hydrophilic
polymer. [0160] b. Polymer Film
[0161] In one aspect, the method involves providing a polymer film
that is substantially permeable to water and substantially
impermeable to impurities. The polymer film can comprise any film
known to those of skill in the art; however, in one aspect,
suitable films include known thin film composite membranes,
nanofiltration membranes, as well as the nanocomposite membranes of
the invention. That is, it is contemplated that the nanoparticles
of the invention can be optionally provided with the polymer film
of the invention and that, in one aspect, the polymer film can have
the components and properties of the nanocomposite membranes of the
invention. In a further aspect, the nanoparticles of the invention
can be absent from the polymer film of the invention, and the
polymer film can have the components and properties of known thin
film composite membranes or nanofiltration membranes. [0162] c.
Contacting Step
[0163] In one aspect, nanoparticles of the invention can be
dispersed in a stirred polyvinyl alcohol (PVA) aqueous solution to
form a PNA-nanoparticle aqueous suspension. Ultrasonication can be
used to ensure complete dispersion of the nanoparticles. A given
amount of cross-linking agent (CL) (e.g., fumaric acid, maleic
anhydride, or malic acid) can be dissolved in the aqueous
suspension with stirring at 50.degree. C. overnight, and then
cooled and degassed.
[0164] Next, a thin film nanocomposite membrane, a thin film
composite membrane or a nanofiltration membrane can be contacted
with the PVA-nanoparticle-CL aqueous suspension, allowing water to
evaporate at room temperature, and then cross-linking PVA at
increased temperature over approximately 5 to 10 minutes. The
resulting thin film nanocomposite membranes possess superior flux,
rejection, and fouling resistance.
E. Methods of Using the Membranes
[0165] In certain aspects, the membranes of the invention can be
used in filtration methods that are well-known to those of skill in
the arts of filtration techniques. For example, the membranes can
be used to purify a liquid by removing impurities dissolved,
suspended, or dispersed within the liquid as it is passed through
the membrane. In a further example, the membranes can be used to
concentrate impurities by retaining the impurities dissolved,
suspended, or dispersed within a liquid as the liquid is passed
through the membrane. [0166] 1. Purifying Liquids
[0167] In one aspect, the invention can be used for reverse osmosis
separations including seawater desalination, brackish water
desalination, surface and ground water purification, cooling tower
water hardness removal, drinking water softening, and ultra-pure
water production.
[0168] The feasibility of a membrane separation process is mainly
determined by stability in water flux and solute retention with
time. Fouling, and in particular biological fouling, can alter the
selectivity of a membrane and causes membrane degradation either
directly by microbial action or indirectly through increased
cleaning requirements. These characteristics can have a direct
effect on the size of the membrane filtration plant, the overall
investment costs, and operating and maintenance expenses. By
applying the membranes and methods of the invention to commercial
membrane and desalination processes, the overall costs can be
significantly reduced due to the improved selectivity and fouling
resistance of the nanocomposite membranes of the invention. Due to
antibiotic properties of the nanoparticles, in particular
silver-exchanged Zeolite A nanoparticles, disposed within the
nanocomposite membranes, less frequent chemical cleanings and lower
operating pressures are typically required, thereby offering
additional savings to owners and operators of these processes.
[0169] In one aspect, the membranes of the invention can be used in
a method for purifying water comprising the steps of providing a
nanocomposite membrane of the invention or a product of the methods
of the invention, wherein the membrane has a first face and a
second face; contacting the first face of the membrane with a first
solution of a first volume having a first salt concentration at a
first pressure; and contacting the second face of the membrane with
a second solution of a second volume having a second salt
concentration at a second pressure; wherein the first solution is
in fluid communication with the second solution through the
membrane, wherein the first salt concentration is higher than the
second salt concentration, thereby creating an osmotic pressure
across the membrane, and wherein the first pressure is sufficiently
higher than the second pressure to overcome the osmotic pressure,
thereby increasing the second volume and decreasing the first
volume.
[0170] In further aspects, the invention can be used for reverse
osmosis separations including liquids other than water. For
example, the membranes can be used to remove impurities from
alcohols, including methanol, ethanol, n-propanol, isopropanol, or
butanol. Typically, suitable liquids are selected from among
liquids that do not substantially react with or solvate the
membranes.
[0171] 2. Concentrating Impurities
[0172] In one aspect, the invention can be used in isolation
techniques for recovering an impurity--for example a valuable
product--from a liquid, for example water or one or more alcohols.
The impurities thereby collected can be the product of a chemical
or biological reaction, screening assay, or isolation technique,
for example, a pharmaceutically active agent, or a biologically
active agent or a mixture thereof.
[0173] In one aspect, the membranes of the invention can be used in
a method for concentrating an impurity comprising the steps of
providing a nanocomposite membrane of the invention or a product of
the methods of the invention, wherein the membrane has a first face
and a second face; contacting the first face of the membrane with a
first mixture of a first volume having a first impurity
concentration at a first pressure; contacting the second face of
the membrane with a second mixture of a second volume having a
second impurity concentration at a second pressure; and collecting
the impurity, wherein the first mixture is in fluid communication
with the second solution through the membrane, wherein the first
impurity concentration is higher than the second impurity
concentration, thereby creating an osmotic pressure across the
membrane, and wherein the first pressure is sufficiently higher
than the second pressure to overcome the osmotic pressure, thereby
increasing the second volume and decreasing the first volume.
F. Experimental
[0174] The following examples are put forth so as to provide those
of ordinary skill in the art with a complete disclosure and
description of how the compounds, compositions, articles, devices
and/or methods claimed herein are made and evaluated, and are
intended to be purely exemplary of the invention and are not
intended to limit the scope of what the inventors regard as their
invention. Efforts have been made to ensure accuracy with respect
to numbers (e.g., amounts, temperature, etc.), but some errors and
deviations should be accounted for. Unless indicated otherwise,
parts are parts by weight, temperature is in .degree. C. and is at
ambient temperature, and pressure is at or near atmospheric.
[0175] 1. Preparation of Nanoparticles
[0176] Zeolite A (ZA) nanoparticles were synthesized by
hydrothermal synthesis from a clear solution with a molar
composition of 1.00 Al.sub.2O.sub.3: 6.12 SiO.sub.2: 7.17
(TMA).sub.2O: 0.16 Na.sub.2O: 345 H.sub.2O. H. Wang et al.,
Homogeneous Polymer-zeolite Nanocomposite Membranes by
Incorporating Dispersible Template-removed Zeolite Nanocrystals, J.
Mater. Chem., 12 (2002) 3640. First, aluminum isopropoxide (+98%,
Aldrich) was dissolved in a solution made from 25 wt. % aqueous
tetramethylammonium hydroxide (TMA, Aldrich), 97 wt. % sodium
hydroxide (Aldrich) and distilled water. Once the solution became
clear, Ludox HS-30 colloidal silica (Aldrich) was added to begin a
two-day aging process. The solution was then heated with stirring
at 100.degree. C. for 1 day. The colloidal ZA-water suspension was
obtained by centrifugation, careful decanting, and ultrasonic
re-dispersion in water.
[0177] In order to remove TMA without inducing nanoparticle
aggregation, a polymer network was introduced into the colloidal
ZA-water suspension. An acrylamide monomer (AM, 97%, Aldrich),
crosslinker N,N'-methylenebiscarylamide (MBAM, 99%, Aldrich), and
diaminosulfate initiator (NH.sub.4).sub.2S.sub.2O.sub.8, (AS, +98%,
Aldrich) were added to the nanoparticle suspension in water. After
the monomer had dissolved, the mixture was ultrasonicated for 30
minutes to ensure complete dispersion of ZA nanoparticles. The
monomer aqueous solution was then heated to 50.degree. C. for 2
hours and 12 hours, respectively, at a heating rate of 2.degree. C.
per minute. Template-removed ZA nanoparticles can be given their
antibacterial property by an ion exchange process with silver salt.
This was carried out by adding ZA nanoparticles to a gently stirred
0.1 M solution of A.sub.gNO.sub.3 at room temperature for 12 h. A.
M. P. McDonnell et al., Hydrophilic and antimicrobial zeolite
coatings for gravity-independent water separation, Adv. Functional
Mater. 15 (2005) 336.
[0178] 2. Preparation of Nanocomposite Membrane [0179] a.
Synthesis
[0180] ZA-PA thin film nanocomposite membranes were cast on
pre-formed polysulfone ultrafiltration (UF) membranes through an
interfacial polymerization reaction. The UF membranes were placed
in aqueous solution of 2% (w/v) m-phenylenediamine (MPD, 99%,
Aldrich) for approximately 10 minutes and the MPD soaked support
membranes were then placed on a paper towel and rolled with a soft
rubber roller to remove excess solution. For the interfacial
polymerization reaction, a hexane solution consisting of 0.1% (w/v)
trimesoly chloride (TMC, 98%, Aldrich) was poured on top. A. P. Rao
et al., Structure-performance Correlation of Polyamide Thin Film
Composite Membranes: Effect of Coating Conditions on Film
Formation, Journal of Membrane Science, 211 (2003) 13. For the
ZA-PA nanocomposite membranes, a measured amount of ZA
nanoparticles were added to the TMC-hexane solution, and the
resultant suspension was ultrasonicated for 1 h in order to ensure
good dispersion of the ZA nanoparticles. The MPD-water soaked UF
support membrane as then contacted with the ZA-TMC-hexane solution.
After 1 minute of reaction, the TMC solution was poured off, and
the resulting membranes were then rinsed with 18 M-ohm de-ionized
water. In some cases, the formed membranes may be contacted with a
0.2 wt % sodium carbonate solution for about 3 hours. The membranes
were then thoroughly washed with and stored in a sterile container
of deionized water. [0181] b. Characterization
[0182] X-ray diffraction and energy dispersive X-ray spectroscopy
(EDX) were used to confirm the crystalline structure, the Si/Al
ratio, and the degree of silver exchanged into ZA nanoparticles.
Morphological characterization of synthesized nanoparticles and
membranes was carried out using scanning electron microscopy (SEM).
Zeta potential of the nanoparticles was measured by particle
electrophoresis. The surface (zeta) potential and the (sessile
drop) contact angles of the synthesized membranes were measured by
streaming potential analyzer and contact angle goniometer,
respectively. Surface topography of synthesized membranes was
determined by atomic force microscopy (AFM). [0183] c.
Performance
[0184] The PA and ZA-PA nanocomposite membranes were evaluated for
pure water permeability and solute rejection. The pure water flux
was measured using a high-pressure chemical resistant dead-end
stirred cell (Sterlitech HP4750 Stirred Cell). Circular membrane
samples with a diameter of 49 mm were placed in the test cell with
the active separation layer facing the cell reservoir. The membrane
was supported on the porous stainless steel membrane disc with a
Buna-N O-ring around it to ensure leak-free operation. The
effective membrane area for water and solute permeation was
approximately 14.6 cm.sup.2. One distinction is that the dead-end
filtration configuration leads to higher concentration in the feed
reservoir as water permeated through the membrane, and hence, flux
decreases with time as the feed reservoir solute concentration (and
resulting trans-membrane osmotic pressure) increases. Without
wishing to be bound by theory, since solute rejection is known to
decrease as feed concentration increases and as water flux
decreases (M. Mulder, Principles of Membrane Technology, 2.sup.nd
Edition, 1996, Kluwer Press, Amsterdam, The Netherlands), it is
believed that the values of solute rejection are substantially
lower than those that would be achieved in a hydrodynamically
optimized spiral wound element.
[0185] Pure water flux experiments were performed using 18 M-ohm
de-ionized water. The operating pressure was set at 180 psi and the
flow of water was measured volumetrically and by mass determination
on a calibrated electronic balance. Solute rejection tests were
performed using separate 2,000 mg/L solutions of NaCl, MgSO.sub.4,
and poly(ethylene glycol) (PEG). Salt concentrations in the feed
and permeate water measured by a digital conductivity meter that
was calibrated daily. PEG concentrations in the feed and permeate
were determined by total organic carbon analysis. Solute rejections
were determined from 1-C.sub.p/(C.sub.f,0-C.sub.f,e), where C.sub.p
is the permeate (filtered) water concentration, C.sub.f,0 is the
initial feed water concentration, and C.sub.f,e is the final feed
water concentration. During the entire test, a high rate of
stirring was maintained using a Teflon-coated magnetic stir bar to
reduce concentration polarization.
[0186] An experimental system designed to facilitate visual
quantification of microbial cell deposition onto synthesized
membranes was employed. S. Kang et al., Direct Observation of
Biofouling in Cross-flow Microfiltration: Mechanisms of Deposition
and Release, Journal of Membrane Science, 244 (2004) 151-165. The
experimental system described in Kang et al., was operated without
flux through the membrane in order to determine the rate and extent
of heterogeneous adsorption of bacteria cells onto the synthesized
membranes. S. Wang et al., Direct Observation of Microbial Adhesion
to Membranes, Environmental Science & Technology 39 (2005)
6461-6469. Without wishing to be bound by theory, it is believed
that visual confirmation of cell deposition onto membranes provides
a more direct quantification of the propensity of a membrane to
foul than simple of flux decline while filtering a suspension of
fouling material. Without wishing to be bound by theory, it is also
believed that flux decline is an indirect and misleading measure of
fouling because it can be biased by various factors such as
membrane hydraulic resistance, salt rejection, and concentration
polarization. E. M. V. Hoek and M. Elimelech, Cake-Enhanced
Concentration Polarization: A New Mechanism of Fouling for Salt
Rejecting Membranes 37 (2003) 5581-5588.
[0187] In selected experiments, as synthesized and silver exchanged
(AgX) Zeolite A nanoparticles were convectively deposited onto the
surfaces of pure polyamide composite membrane samples in order to
quantify (visually) the antimicrobial efficacy of the silver
exchanged nanoparticles. Live bacteria cell, Pseudomonas putida,
suspension in water with NaCl concentration of 10 mM (58.5 mg/L)
and unadjusted pH were pumped through the direct microscopic
observation filtration cell in three separate experiments. In the
first experiment, a sample of pure PA composite membrane was
tested. In the second experiment, a sample of ZA-PA nanocomposite
membrane was tested. In the third experiment, a sample of AgX-ZA-PA
nanocomposite membrane was tested. The cell suspension was filtered
through the system for 30 minutes, at which time the experiment was
stopped and the membrane samples were stained using the Live/Dead
BacLight bacterial viability kit. B. K. Li and B. E. Logan, The
impact of ultraviolet light on bacterial adhesion to glass and
metal oxide-coated surface, Colloids and Surfaces B-Biointerfaces
41 (2005) 153-161. [0188] d. Results
[0189] The crystal structure of synthesized ZA nanoparticles was
confirmed by matching the X-ray diffraction (XRD) patterns (not
shown) with the Joint Committee on Powder Diffraction Standards
(JCPDS) files. FIG. 1 shows that as formed LTA-type zeolite
nanoparticles exhibit particles sizes ranging from about 50 to
about 200 nm in this example. According to energy dispersive X-ray
spectroscopic analysis, the Si/Al ratio of as synthesized Zeolite A
was 1.5 and the degree of silver ion exchange was 90%. Additional
characterization data is provided in Table 1. Dynamic light
scattering confirmed the average hydrodynamic radius in de-ionized
water to be 140 nm, thus, indicating good dispersability of ZA
nanoparticles in water. Zeta potential of the nanoparticles
determined from measured electrophoretic mobility was -45.+-.2 mV,
when dispersed in an aqueous 10 mM NaCl electrolyte at unadjusted
pH of 6.
TABLE-US-00001 TABLE 1 Properties of synthesized ZA nanoparticles
Particle DLS Zeta Crystal size by SEM datum potential Structure
[nm] [nm] [mV] A 50-200 140 -45 .+-. 2
[0190] FIG. 2 (a) and (b) show representative SEM images of PA and
ZA-PA nanocomposite membranes, respectively. Also generally shown
are TEM images of TFC/TFN-0.04% membranes. XYZ indicates the
concentration (w/v) of zeolite dispersed in the hexane-TMC
initiator solution: (a) XYZ=0.000%, (b) XYZ=0.004%, (c) XYZ=0.010%,
(d) XYZ=0.040%, (e) XYZ=0.100%, and (f) XYZ=0.400%. The surface of
the PA membrane exhibited the familiar "hill and valley" structure.
For the ZA-PA membrane, however, nanoparticles appeared well
dispersed in the polyamide film and the typical surface structure
of an interfacially polymerized RO membrane was not found.
Furthermore, at high magnification no voids were observed between
nanoparticles and the polyamide matrix, suggesting good
zeolite-polymer contact.
[0191] Table 2 shows the three key properties that are
representative of PA and ZA-PA membranes. Pure water contact angle
and surface (zeta) potential for the ZA-PA membrane were 10 degrees
lower and 4 mV more negative, respectively, suggesting a more
hydrophilic surface. There was a decrease in the surface roughness
(R.sub.RMS, z-data standard deviation) for the ZA-PA membrane
compared to the pure PA membrane, indicating that the surface of
the ZA-PA membrane is much smoother. Thus, ZA-PA membranes provide
improved energy efficiency, separation performance, and fouling
resistance in water purification processes.
TABLE-US-00002 TABLE 2 Surface Properties of Synthesized Membranes.
Pure Water Surface (zeta) potential Surface roughness Membrane
Contact angle [.degree.] @ pH 7 [mV] R[nm] PA 77.6 .+-. 0.4 -13.1
73.0 ZA-PA 62.2 .+-. 0.8 -17.4 65.6
TABLE-US-00003 TABLE 3 Performance and Properties of Synthesized
Membranes Membrane NP Loading Permeability Solute Reje
References