U.S. patent application number 12/967092 was filed with the patent office on 2011-06-30 for modified membrane.
Invention is credited to Carleton L. Gaupp, Richard C. Krauss, William E. Mickols, Qingshan Jason Niu.
Application Number | 20110155660 12/967092 |
Document ID | / |
Family ID | 38433998 |
Filed Date | 2011-06-30 |
United States Patent
Application |
20110155660 |
Kind Code |
A1 |
Mickols; William E. ; et
al. |
June 30, 2011 |
MODIFIED MEMBRANE
Abstract
A multilayered modified membrane and method for making the same,
comprising a modified discriminating layer that can have a fouling
resistant surface, improved salt rejection, antimicrobial
properties, and/or improved solute, and/or small organics rejection
as compared to membranes with unmodified discriminating layers.
Inventors: |
Mickols; William E.;
(Chanhassen, MN) ; Krauss; Richard C.; (Fort
Myers, FL) ; Niu; Qingshan Jason; (Excelsior, MN)
; Gaupp; Carleton L.; (Midland, MI) |
Family ID: |
38433998 |
Appl. No.: |
12/967092 |
Filed: |
December 14, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12299849 |
Nov 6, 2008 |
7882963 |
|
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PCT/US2007/009001 |
Apr 12, 2007 |
|
|
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12967092 |
|
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60799863 |
May 12, 2006 |
|
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Current U.S.
Class: |
210/500.28 ;
427/245 |
Current CPC
Class: |
B01D 2323/02 20130101;
B01D 2323/12 20130101; B01D 61/025 20130101; B01D 71/56 20130101;
B01D 67/0093 20130101; B01D 69/125 20130101; B01D 2325/28 20130101;
B01D 2325/48 20130101 |
Class at
Publication: |
210/500.28 ;
427/245 |
International
Class: |
B01D 39/16 20060101
B01D039/16; B05D 7/24 20060101 B05D007/24 |
Claims
1-35. (canceled)
36. A method for making a composite membrane by interfacially
polymerizing a polyfunctional amine and a polyfunctional acid
halide to form a polyamide discriminating layer upon a porous
support, wherein the method is characterized by applying the
polyfunctional acid halide to the porous support from a composition
comprising an organic solvent and pyridine.
37. A composite membrane comprising a porous support and a
polyamide discriminating layer having an inner side and outer side,
the inner side of the discriminating layer in contact with the
porous support, and wherein the membrane is characterized by the
polyamide discriminating layer having a relatively higher
concentration of moieties derived from pyridine in a region near
the outer side of the discriminating layer as compared with a
region near the inner side.
38. The membrane of claim 37 wherein the ratio of moieties derived
from pyridine in the region near the outer side of the
discriminating layer as compared to the region near the inner side
of the discriminating layer is approximately 1.5:1.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 12/299,849, filed Nov. 6, 2008, which is a National Stage
application filed pursuant to 35 U.S.C. 371 and claims the benefit
of international application no. PCT/USUS/2007/009001, filed Apr.
12, 2007, which claims benefit of U.S. 60/799,863, filed May 12,
2006. The entire contents of Ser. No. 12/299,849,
PCT/US2007/009001, and 60/799,863 are incorporated herein by
reference.
FIELD OF THE DISCLOSURE
[0002] The present disclosure generally relates to membranes for
use in separating liquid components and methods of making such
membranes. The membranes of the present disclosure are particularly
useful in purifying water.
BACKGROUND
[0003] Reverse osmosis and nanofiltration membranes are 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.
[0004] 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 is less porous and provides 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," i.e., the percentage of the particular
dissolved material (i.e., solute) rejected, and "flux," i.e., the
flow rate per unit area at which the solvent passes through the
membrane.
[0005] Membrane manufacturers optimize the discriminating layer for
a desired combination of solvent flux and solute rejection, while
also optimizing the porous support layer for maximum strength and
compression resistance combined with a minimum resistance to
permeate flow. In theory, a large variety of chemical compositions
could be formed into thin barrier layers, however, only a few
polymers offer the right combination of flux and solute rejection
to generate commercially attractive reverse osmosis or
nanofiltration membranes. Reverse osmosis membranes and
nanofiltration membranes vary from each other with respect to their
degree of permeability to different ions and compounds.
[0006] Reverse osmosis membranes are relatively impermeable to
virtually all ions, including sodium and chlorine ions. Therefore,
reverse osmosis membranes are widely used for the desalination of
brackish water or seawater to provide relatively non-salty water
for industrial, commercial, or domestic use, because the rejection
rate of sodium and chlorine ions for reverse osmosis membranes is
usually from about ninety-five (95) to about one hundred (100)
percent.
[0007] Nanofiltration membranes are usually more specific for the
rejection of ions including radium, magnesium, calcium, sulfate,
and carbonate. In addition, nanofiltration membranes can be
impermeable to organic compounds having molecular weights above
about two hundred (200) Daltons. Additionally, nanofiltration
membranes can 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 can have a sodium chloride
rejection rate of from about zero (0) to about ninety-five (95)
percent but have a relatively high rejection rate for salts such as
magnesium sulfate and in some cases organic compounds such as
atrazine.
[0008] Some membranes can be useful for reverse osmosis and
nanofiltration applications by including a polyamide discriminating
layer. The polyamide discriminating layer for reverse osmosis
membranes is often obtained by an interfacial polycondensation
reaction between a polyfunctional amine monomer and a
polyfunctional acid halide monomer as described in, for example,
U.S. Pat. No. 4,277,344. The polyamide discriminating layer for
nanofiltration membranes can be obtained via an interfacial
polymerization between a piperazine, a cyclohexane bearing at least
two reactive amine or aminoalkyl groups, or a piperidine bearing at
least one reactive amine or aminoalkyl group and a polyfunctional
acid 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.
[0009] Composite polyamide membranes can be prepared by coating a
porous support with a polyfunctional amine monomer, for example,
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 acid halide monomer can
subsequently be coated on the support, for example, from an organic
solution. Although no specific order of addition is necessarily
required, the amine solution can be coated first on the porous
support followed by the acid halide solution. Although one or both
of the polyfunctional amine and acid 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.
[0010] Membrane fouling can occur from adhesion of suspended
particles, scaling by insoluble salts, and bacterial fouling. While
changing the polymer of the membrane may change properties such as
the permeability to various ions, the membrane surface energy, or
the membrane surface charge, it would also require large changes in
membrane fabrication.
[0011] Membrane manufacture can be done in a dedicated facility
with lines operating in a semi-continuous process. Introducing
membranes with new starting materials and membrane coating
processes can be time-consuming and expensive. It can be less
expensive to make use of existing process lines and materials to
make a variety of different composite membranes.
[0012] Means for improving the performance of membranes by the
addition of constituents to the amine and/or acid 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.
[0013] 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.
SUMMARY
[0014] Embodiments of the present disclosure provide multilayered
membranes including a modified discriminating layer that can have
improved rejection as compared to a membrane with an unmodified
discriminating layer. Embodiments also include methods for making
such membranes, including methods which are adaptable to commercial
scale membrane manufacturing. In addition, embodiments of the
present disclosure can be suited for making both nanofiltration and
reverse osmosis membranes.
BRIEF DESCRIPTION OF FIGURES
[0015] FIG. 1 presents the sodium chloride, isopropyl alcohol, and
nitrate passage percentage in membranes with a modified
discriminating layer.
[0016] FIG. 2 presents the cryo-sectioning analysis resulting from
each membrane.
DETAILED DESCRIPTION
[0017] Embodiments of the present disclosure include a multilayered
membrane with a modified discriminating layer and methods for
making the same. Embodiments also include a membrane with a
modified discriminating layer having improved rejection. Further,
embodiments include a membrane with a modified discriminating layer
having improved antimicrobial properties. Embodiments of the
present disclosure exhibit improvements over membranes with
unmodified discriminating layers.
[0018] The membrane of the present disclosure can include a
modified discriminating layer, where the discriminating layer is
modified by applying a modifying composition to the discriminating
layer. The modifying composition is disposed on at least the
surface portion of the discriminating layer to form a modifying
composition layer secured to the discriminating layer by at least
one of hydrogen bonding, ionic bonding, covalent bonding, physical
entanglement, and chemical linkage. As used herein, "physical
entanglement" refers to the process of having long chains of
molecules, for example, polymers such as a phenyl amine becoming
entangled in each other or, for example, a polyamide contained in a
polyamide discriminating layer instead of becoming chemically
bonded to the discriminating layer. In some embodiments, the
chemical linkage can be at least one of amides, sulfamides,
urethanes, ureas, thioesters, and amines, including secondary
amines, ternary amines, quarternary amines, and beta
hydroxylamines.
[0019] In some embodiments, the membrane of the present disclosure
can be prepared by a post-treatment on an already formed
discriminating layer, such as a composite polyamide reverse osmosis
membrane (e.g., "FT-30.TM." available from FilmTec Corporation). In
some embodiments, the post-treatment can be performed by adding the
various compounds to an aqueous solution and coating the aqueous
solution onto the already formed discriminating layer. Further
process steps can then also be performed, as discussed herein. In
various embodiments, the modification can be accomplished during
membrane fabrication, (e.g., just after the initiation of the
interfacial polymerization of the polyamine and polyfunctional acid
halide reaction, as discussed herein). In embodiments where the
modifying composition is not soluble in an aqueous solution, the
modification can be accomplished during membrane fabrication by
adding the various compounds to the aqueous solution. As the
aqueous solution goes through the membrane, the various compounds
may be at a higher concentration on the surface of the
discriminating layer, and may become secured to the discriminating
layer by hydrogen bonding, ionic bonding, covalent bonding,
physical entanglement and/or by forming chemical linkages. In some
embodiments, the type of securing and/or the degree of securing can
depend on the molecular weight and the chemical composition of the
various compounds that are applied to the discriminating layer,
and/or the molecular weight and the chemical composition of
reaction products formed from mixing the various compounds. The
presence of the various compounds used to modify the surface of the
discriminating layer, as discussed herein, can provide the membrane
with one or more improvements including: a fouling resistant
surface, improved salt rejection, improved solute rejection,
improved small organic rejection, and/or improved antimicrobial
properties as compared to membranes with unmodified discriminating
layers. As used herein, "rejection" refers to the percentage of
solute concentration removed from system feed water by the
membranes.
[0020] The membrane of the present disclosure can be prepared by
applying an aqueous coating composition to at least a surface
portion of a porous substrate to form a first-coated substrate. The
aqueous coating composition can include at least one polyfunctional
compound selected from a polyfunctional amine, a polyfunctional
alcohol, a polyfunctional thiol, and a polyfunctional
anhydride.
[0021] In some embodiments, the concentration of the polyfunctional
compound in the aqueous coating composition can be in a range of
approximately 0.1 to ten (10) weight percent, and preferably in a
range of approximately 0.5 to seven (7.0) weight percent, based on
total aqueous coating composition weight. In addition, coating can
be accomplished by spraying, film coating, rolling, or through the
use of a dip tank, among other coating techniques. Excess solution
can be removed from the support by air and/or water knifes, dryers,
or ovens, among others.
[0022] Next, an organic solvent composition can be applied to the
first-coated substrate to form a discriminating layer on at least
the surface portion of the porous substrate. The organic solvent
composition can include an organic solvent and at least one of a
polyfunctional acid halide, a polyfunctional anhydride, and a
polyfunctional dianhydride. The polyfunctional acid halide can be
dissolved in the non-polar organic solvent in a range from about
0.01 to five (5) weight percent, preferably 0.02 to two (2) weight
percent, based on total non-polar organic solvent weight, and
delivered as part of a continuous coating operation.
[0023] The discriminating layer formed from the interfacial
polymerization of the aqueous coating composition and the organic
solvent composition can comprise a reaction product of the
polyfunctional compound and at least one of the polyfunctional acid
halide, the polyfunctional anhydride, and the polyfunctional
dianhydride and a residual reactive moiety, as discussed further
herein.
[0024] In some embodiments, the discriminating layer can be a
polyamide discriminating layer. A polyamide discriminating layer
can be prepared by interfacially polymerizing a polyfunctional
compound, (e.g., a polyfunctional amine monomer) with a
polyfunctional acid halide, wherein each term is intended to refer
both to the use of a single species or multiple species of amines
in combination or acid halides in combination, on at least one
surface of a porous support. As used herein, "polyamide" is a
polymer in which amide linkages (--C(O)NH--) occur along the
molecular chain.
[0025] As discussed herein, the polyfunctional amine monomer and
polyfunctional acid halide can be delivered to the porous support
by way of a coating step from solution, where the polyfunctional
amine monomer can be coated from an aqueous solution and the
polyfunctional acid halide can be coated from an organic solvent.
Although the coating steps can be "non-sequential" (i.e., follow no
specific order), the polyfunctional amine monomer is preferably
coated on the porous support first followed by the polyfunctional
acid halide.
[0026] The polyfunctional amine monomer used in the present
disclosure to form a polyamide discriminating layer may have
primary or secondary amino groups and may be aromatic (e.g.,
m-phenylenediamine, p-phenylenediamine, 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 preferred polyfunctional amine monomers include primary
amines having two or three amino groups, for example, m-phenylene
diamine (MPD), and secondary aliphatic amines having two amino
groups, for example, piperazine. As discussed herein, the
polyfunctional amine monomer can be applied to the porous support
as an aqueous coating composition. Once coated on the porous
support, excess aqueous coating composition may be optionally
removed.
[0027] As discussed herein, the polyfunctional acid halide is
preferably coated from an organic solvent, although the
polyfunctional acid halide may be delivered from a vapor phase
(e.g., for polyfunctional acid halides having sufficient vapor
pressure). The polyfunctional acid halide is not particularly
limited, and aromatic or alicyclic polyfunctional acid halides can
be used. Non-limiting examples of aromatic polyfunctional acid
halides include, trimesic acid chloride, terephthalic acid
chloride, iso-phthalic acid chloride, biphenyl dicarboxylic acid
chloride, and naphthalene dicarboxylic acid dichloride.
Non-limiting examples of alicyclic polyfunctional acid halides
include cyclopropane tri carboxylic acid chloride, cyclo butane
tetra carboxylic acid chloride, cyclo pentane tri carboxylic acid
chloride, cyclo pentane tetra carboxylic acid chloride, cyclo
hexane tri carboxylic acid chloride, tetrahydrofuran tetra
carboxylic acid chloride, cyclo pentane dicarboxylic acid chloride,
cyclo butane dicarboxylic acid chloride, cyclo hexane dicarboxylic
acid chloride, and tetrahydrofuran dicarboxylic acid chloride. One
preferred polyfunctional acid halide is trimesoyl chloride
(TMC).
[0028] Suitable organic solvents are those which are capable of
dissolving the polyfunctional acid halide and are immiscible with
water. Preferred solvents 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
ninety (90).degree. C. such as hydrocarbons with eight to fourteen
carbon atoms, and mixtures thereof, have more favorable flashpoints
than hydrocarbons containing five to seven carbon atoms, but they
are less volatile. As such, useful organic solvents include
hydrocarbons such as n-hexane or cyclo-hexane, high purity
isoparaffinic materials such as Isopar.TM. (Exxon), or halogenated
hydrocarbons such as Freon.TM. (E.I. DuPont Co.), which includes
trifluorotrichloroethane.
[0029] Once brought into contact with one another, the
polyfunctional acid halide and the polyfunctional amine monomer
react at their surface interface to form the polyamide
discriminating layer.
[0030] The reaction time of the polyfunctional acid halide and the
polyfunctional amine monomer can be less than one second but
contact time ranges from one to sixty seconds, after which excess
liquid may optionally be removed, by way of an air knife, water
bath(s), dryer, and the like. The removal of the excess water
and/or organic solvent can be achieved by drying at elevated
temperatures, for example, from about forty (40).degree. C. to
about one hundred twenty (120).degree. C., although air drying at
ambient temperatures may be used.
[0031] Embodiments of the present disclosure include methods of
modifying the discriminating layer, prepared as discussed herein,
by applying a modifying composition to at least a surface portion
of the discriminating layer to form a modified discriminating
layer. The modifying composition can include an organic solvent and
a reactive modifying compound including a functional group, as
discussed further herein.
[0032] As discussed herein, the discriminating layer can include a
reaction product of the polyfunctional compound and at least one of
the polyfunctional acid halide, the polyfunctional anhydride, and
the polyfunctional dianhydride and residual reactive moieties. The
residual reactive moiety can be at least one of an unreacted
functional group on the polyfunctional compound, an unreacted
functional group on the polyfunctional acid halide, an unreacted
functional group on the polyfunctional anhydride, and an unreacted
functional group on the polyfunctional dianhydride. The residual
reactive moiety can also be a hydrolysis product of the
polyfunctional compound, a hydrolysis product of the polyfunctional
acid halide, a hydrolysis product of the polyfunctional anhydride,
and/or the hydrolysis product of the polyfunctional
dianhydride.
[0033] Preferably, the modifying composition can be applied after
interfacial polymerization to form the discriminating layer, but
before steps that might limit or remove residual reactive moieties
on the discriminating layer, such as rinsing or drying steps. In
addition, by applying the modifying composition at such a point in
the method, fewer changes may be needed to an existing membrane
manufacturing process. However, embodiments include processes where
the modifying composition is applied to the discriminating layer at
any time in the process after the organic solvent composition
containing the polyfunctional acid halide is applied, as discussed
herein. The method of the present disclosure merely requires that a
sufficient number of residual reactive moieties are available on
the discriminating layer. In some embodiments, the appropriate
number of residual reactive moieties will depend on the desired
changes.
[0034] To modify the discriminating layer, embodiments of the
present disclosure take advantage of the residual reactive moieties
on the discriminating layer that remain after the interfacial
polymerization reaction step, as discussed herein. In some
embodiments, the residual reactive moieties available on the
discriminating layer can depend on the starting materials for the
interfacial polymerization. For example, in embodiments where the
polyfunctional amine monomer is meta-phenylene diamine (MPD) and
the polyfunctional acid halide is trimesic acid chloride (TMC), the
reactive moieties on the discriminating layer can include derivates
of polyfunctional amines and polyfunctional acid chlorides.
Therefore, the discriminating layer can include two sites (e.g., Y
and Z), for added groups shown in formula (I):
##STR00001##
Separately, the polyfunctional amine can be represented by formula
(II):
##STR00002##
and carboxylic acids present as a reactive moiety on the
discriminating layer, resulting from the hydrolysis of the
polyfunctional acid chloride, can be represented by formula
(III):
##STR00003##
[0035] As discussed herein, the method of making the membrane
includes applying a modifying composition to at least a surface
portion of the discriminating layer to form a modified
discriminating layer. In some embodiments, the modifying
composition can include an organic solvent and a reactive modifying
compound including a functional group. In some embodiments, the
organic solvent of the modifying compositions can be the same as
the solvent used for the polyfunctional acid halide, as discussed
herein.
[0036] In previous approaches to improve rejection of an existing
membrane, modifying the membrane involved adding modifiers to the
aqueous phase, usually in, or after, a rinse or hydrolysis step.
Therefore, the modifiers were limited to water-soluble polymers and
chemicals, limiting the selection of functional groups that can be
used with the membrane. Embodiments of the present disclosure,
however, include reactive modifying compounds that are soluble, or
at least dispersible, in an organic solvent. The use of organic
solvents can allow for the use of a wide selection of reactive
modifying compounds and can dissolve higher molecular weight
reactive modifying compounds, such as aromatics and aliphatics
having five (5) or more carbon atoms. In addition, since organic
solvents are less soluble in water, organic soluble reactive
modifying compounds can be less likely to be removed and/or washed
out during the use of the resulting multilayered membrane in water
purification processes.
[0037] In addition, an aspect of embodiments of the present
disclosure is selecting reactive modifying compounds that change
the selectivity properties of the discriminating layer without
significantly reducing the flux below commercial requirements
across the membrane. The reactive modifying compound can be
selected from substituted or unsubstituted aromatic compounds,
cyclo-aliphatic compounds, pyridines, or linear aliphatic compounds
having five (5) or more members.
[0038] In embodiments where the reactive modifying compound
includes a functional group that reacts with the discriminating
layer to secure the modifying composition to the discriminating
layer through chemical linkage, the reactive modifying compound can
include a functional group that will form an amine, an amide, a
sulfamide, a urethane, a urea, a thioester, an aminoester, an
esteramide, an imide, a secondary amine, a ternary amine, a
quarternary amine, or a beta hydroxyl amine linkage with the
residual reactive moieties on the discriminating layer. Preferable
reactive modifying compounds can be selected from aniline
derivatives and linear or cyclic amines having five (5) or more
carbon atoms.
[0039] In some embodiments, it is preferable to select reactive
modifying compounds that can provide a rigid linkage between the
amide, isocyanate, urethane, urea, sulfamide, thioester,
aminoester, esteramide, imide, secondary amine, ternary amine,
quarternary amine, or beta hydroxyl amine and the functional group.
This can allow for more improved rejection and selectivity.
[0040] As discussed herein, the reactive modifying compound can
include a functional group. The functional group can be selected
from the group consisting of amine, aminoalcohol, aminoester,
ester, thioester, ether, alcohol, anhydride, epoxide, acid halide,
isocyanate, 2-oxazoline, thiol, thiophenol, disulfide, and azide.
In addition, also discussed herein, in some embodiments the
functional group can react with residual reactive moieties on the
discriminating layer to form chemical linkages.
[0041] In embodiments where the functional group reacts with the
residual reactive moieties on the discriminating layer to form
chemical linkages, the modifying compound can include a functional
group selected based on the residual reactive moiety that the
functional group is most likely to react with. For example, as
discussed herein, a residual reactive moiety can be an amine in a
polyamide discriminating layer. Possible functional groups that can
react efficiently with such amines can include acid halides,
epoxides, isocyanates, diisocyanates, and azides. For example, an
aliphatic epoxy modifying compound can react with a residual amine
moiety to form a beta hydroxyl amine. Similarly, an aliphatic
isocyanate modifying compound can react with a residual amine
moiety to form a substituted urea, and a diisocyanate modifying
compound can react with a residual amine moiety to form a
urethane.
[0042] In some embodiments, the residual reactive moiety can be an
acid halide and/or a carboxylic acid in the polyamide
discriminating layer. In such embodiments, amines, 2-oxazolines,
and alcohols are among the available basic and/or nucleophilic,
organic soluble compounds that can be selected for a functional
group on the modifying compound. In various embodiments, aromatic
structures are preferred, as they are stable enough to be handled
without extreme health and safety concerns. Additionally, larger
modifying compounds can create more significant changes in
selectivity properties in the modified discriminating layer, and
thus the membrane, as compared to smaller modifying compounds.
[0043] An example of a modifying compound to react with a residual
acid halide moiety and/or residual carboxylic acid moiety is
aniline. The amine on the aniline can react with an unreacted acid
chloride and/or carboxylic acid on the discriminating layer. Other
suitable reactive modifying compounds for reacting with acid
halides and/or carboxylic acids include, but are not limited to,
aliphatic secondary amines, aromatic amines, tertiary amines, and
amides.
[0044] Other embodiments include a modifying compound with a
functional group selected from the group including ester,
thioester, ether, alcohol, anhydride, 2-oxazoline, thiol,
thiophenol, and disulfide. It follows, then, that the reactive
modifying compound can be selected from aliphatic amines, aromatic
amines, azides, isocyanates, esters, anhydrides, epoxides,
2-oxazolines, amides, tresylates, tosylates, and mesylates, among
others.
[0045] In some embodiments, the reactive modifying compound can
include the functional group, as discussed herein, and a pendent
functional group. In some embodiments, the pendent functional group
can be chosen to change one or more properties of the
discriminating layer. For example, a pendent functional group can
be an organometallic that will provide a discriminating layer with
antimicrobial properties. In some embodiments, the reactive
modifying compound can include the functional group to react with
residual reactive moieties on the discriminating layer to create
chemical linkages and the pendent functional group to change
properties of the discriminating layer.
[0046] In some embodiments, the reactive modifying compound can
include one pendent functional group. However, embodiments also
include reactive modifying compounds with multiple pendent
functional groups. In addition, the reactive modifying compound can
include multiple pendent functional groups of the same compound
and/or multiple pendent functional groups that are different
compounds.
[0047] In some embodiments, the reactive modifying compound can
include a pendent functional group selected from alkyl group,
alkene group, alkyne group, aliphatic amine (including primary,
secondary, or ternary amine), aromatic amine, ester, ketone,
aldehyde, thioester, amide, sulfamide, alcohol, ether, isocyanate,
thiol, sulfide, disulfide, sulfate, sulfite, thiophenol, thiophene,
halogen, silyl, silicone containing organometallic compounds,
phosphorous containing organometallic compounds, other
organometallic compounds, and metal complexes. The pendent
functional group can also be selected from organometallic
derivatives of aliphatic amines, aromatic amines, amides,
sulfamides, ureas, esters, ethers, acids, alcohol, and urethanes.
In embodiments where the reactive modifying compound is an
aliphatic or aromatic thiol, the pendent functional group(s) can be
a metal ion. In addition, in embodiments where the reactive
modifying compound is an aliphatic with five (5) or more carbons,
the pendent functional group can be a quaternary amine, which is a
biocidal group and can give the resulting membrane biocidal
properties.
[0048] In embodiments where the functional group is an amine, the
reactive modifying compound can be a phenyl amine and the pendent
functional group can be selected from halides, ethers, esters,
ketones, aldehydes, alcohols, thiols, methiols, amines,
phosphorous, metal complexes, and organometallics. Formula (IV)
represents possible candidate positions for the pendent functional
groups, where the reactive modifying compound is a phenyl and the
functional group is an amine.
##STR00004##
In formula (IV), A, B, C, D, and E represent the various positions
that a pendent functional group on an aromatic ring can occupy. As
discussed herein, more than one pendent functional group can be
attached to the ring, and each pendent functional group can be the
same or different. In some embodiments, two and/or three of the
same pendent functional group can be attached to the ring to more
effectively change the property of the discriminating layer, as
compared to using one pendent functional group attached to the
ring. As discussed herein, pendent functional groups can also be
attached to aliphatic reactive modifying compounds.
[0049] In embodiments where the reactive modifying compound is a
phenyl amine, a non-IUPAC name that identifies the resultant
pendent functional group will be used. For example, m-phenetidine
would be named 3-ethoxyaniline or m-ethoxyaniline, which leaves an
ethoxy pendent functional group. Similarly, 3-aminothiophenol would
be named 3-thioaniline, and the resultant pendent functional group
is a thiol. Finally if MPD is used, it would be named
3-aminoaniline and the pendent functional group would be an
amine.
[0050] In some embodiments, the reactive modifying compound can be
a phenyl amine, and the pendent functional group can be selected
from halides and thiols. Such embodiments include, but are not
limited to, reactive modifying compounds selected from: 2 chloro
aniline, 3 chloro aniline, 4 chloro aniline, 2,3 dichloro aniline,
2,4 dichloro aniline, 2,5 dichloro aniline, 3,4 dichloro aniline,
3,5 dichloro aniline, 2,6 dichloro aniline, 2,3,4 trichloro
aniline, 3,4,5 trichloro aniline, 2,4,5 trichloro aniline, 2,4,6
trichloro aniline, 3,4,5,6 tetrachloro aniline, 2,4,5,6 tetrachloro
aniline, 2,3,5,6 tetrachloro aniline, 2,3,4,5,6 pentachloro
aniline, 2 bromo aniline, 3 bromo aniline, 4 bromo aniline, 2,3
dibromo aniline, 2,4 dibromo aniline, 2,5 dibromo aniline, 2,6
dibromo aniline, 3,4 dibromo aniline, 3,5 dibromo aniline, 2,3,4
tribromo aniline, 3,4,5 tribromo aniline, 2,4,5 tribromo aniline,
2,4,6 tribromo aniline, 3,4,5,6 tetrabromo aniline, 2,4,5,6
tetrabromo aniline, 2,3,5,6 tetrabromo aniline, 2,3,4,5,6
pentabromo aniline, 2 fluoro aniline, 3 fluoro aniline, 4 fluoro
aniline, 2,3 difluoro aniline, 2,4 difluoro aniline, 2,5 difluoro
aniline, 2,6 difluoro aniline, 3,4 difluoro aniline, 3,5 difluoro
aniline, 2,3,4 trifluoro aniline, 3,4,5 trifluoro aniline, 2,4,5
trifluoro aniline, 2,4,6 trifluoro aniline, 3,4,5,6 tetrafluoro
aniline, 2,4,5,6 tetrafluoro aniline, 2,3,5,6 tetrafluoro aniline,
2,3,4,5,6 pentafluoro aniline, 2 iodo aniline, 3 iodo aniline, 4
iodo aniline, 2,3 diiodo aniline, 2,4 diiodo aniline, 2,5 diiodo
aniline, 2,6 diiodo aniline, 3,4 diiodo aniline, 3,5 diiodo
aniline, 2,3,4 triiodo aniline, 3,4,5 triiodo aniline, 2,4,5
triiodo aniline, 2,4,6 triiodo aniline, 3,4,5,6 tetraiodo aniline,
2,4,5,6 tetraiodo aniline, 2,3,5,6 tetraiodo aniline, 2,3,4,5,6
pentaiodo aniline, 2 methoxy aniline, 3 methoxy aniline, 4 methoxy
aniline, 2,3 dimethoxy aniline, 2,4 dimethoxy aniline, 2,5
dimethoxy aniline, 2,6 dimethoxy aniline, 3,4 dimethoxy aniline,
3,5 dimethoxy aniline, 2,3,4 trimethoxy aniline, 3,4,5 trimethoxy
aniline, 2,4,5 trimethoxy aniline, 2,4,6 trimethoxy aniline,
2,3,4,5 tetramethoxy aniline, 2,3,4,5,6 pentamethoxy aniline, 2
ethoxy aniline, 3 ethoxy aniline, 4 ethoxy aniline, 2,3 diethoxy
aniline, 2,4 diethoxy aniline, 2,5 diethoxy aniline, 2,6 diethoxy
aniline, 3,4 diethoxy aniline, 3,5 diethoxy aniline, 2,3,4
triethoxy aniline, 3,4,5 triethoxy aniline, 2,4,5 triethoxy
aniline, 2,4,6 triethoxy aniline, 2 propoxy aniline, 3 propoxy
aniline, 4 propoxy aniline, 2,3 dipropoxy aniline, 2,4 dipropoxy
aniline, 2,5 dipropoxy aniline, 2,6 dipropoxy aniline, 3,4
dipropoxy aniline, 3,5 dipropoxy aniline, 2,3,4 tripropoxy aniline,
3,4,5 tripropoxy aniline, 2,4,5 tripropoxy aniline, 2,4,6
tripropoxy aniline, 2 butoxy aniline, 3 butoxy aniline, 4 butoxy
aniline, 2,3 dibutoxy aniline, 3,4 dibutoxy aniline, 3,5 dibutoxy
aniline, 2,3,4 tributoxy aniline, 3,4,5 tributoxy aniline, 2
hydrothio aniline, 3 hydrothio aniline, 4 hydrothio aniline, 2,3
dihydrothio aniline, 2,4 dihydrothio aniline, 2,5 dihydrothio
aniline, 2,6 dihydrothio aniline, 3,4 dihydrothio aniline, 3,5
dihydrothio aniline, 2 methylthio aniline, 3 methylthio aniline, 4
methylthio aniline, 2 acetyl aniline, 3 acetyl aniline, 4 acetyl
aniline, 2,3 diacetyl aniline, 3,4 diacetyl aniline, 3,5 diacetyl
aniline, 2 carbmethoxy aniline, 3 carbmethoxy aniline, 4
carbmethoxy aniline, 2 carbethoxy aniline, 3 carbethoxy aniline, 4
carbethoxy aniline, 3 hydroxy aniline, 4 hydroxy aniline, 2
carbmethoxy-4-bromoaniline, 2 carbmethoxy-5-bromoaniline, 2
carbmethoxy-6-bromoaniline, 2 carbmethoxy-3-bromoaniline, 2
carbmethoxy-4-chloroaniline, 2 carbmethoxy-5-chloroaniline, 2
carbmethoxy-6-chloroaniline, 2 carbmethoxy-3-chloroaniline, 2
carbethoxy-4-bromoaniline, 2 carbethoxy-5-bromoaniline, 2
carbethoxy-6-bromoaniline, 2 carbethoxy-3-bromoaniline, 2
carbethoxy-4-chloroaniline, 2 carbethoxy-5-chloroaniline, 2
carbethoxy-6-chloroaniline, 2 carbethoxy-3-chloroaniline, 2
acetyl-4-bromoaniline, 2 acetyl-5-bromoaniline, 2
acetyl-6-bromoaniline, 2 acetyl-3-bromoaniline, 2
acetyl-4-chloroaniline, 2 acetyl-5-chloroaniline, 2
acetyl-6-chloroaniline, 2 acetyl-3-chloroaniline, 2
methoxy-4-bromoaniline, 2 methoxy-5-bromoaniline, 2
methoxy-6-bromoaniline, 2 methoxy-3-bromoaniline, 2
methoxy-4-chloroaniline, 2 methoxy-5-chloroaniline, 2
methoxy-6-chloroaniline, 2 methoxy-3-chloroaniline, mixed
halogenated anilines such as 2-halo aniline, 3-halo aniline, 4-halo
aniline, 2,3 diahalo aniline, 2,4 diahalo aniline, 2,5 diahalo
aniline, 2,6 diahalo aniline, 3,4 diahalo aniline, 3,5 diahalo
aniline, 2,3,4 trihalo aniline, 3,4,5 trihalo aniline, 2,4,5
trihalo aniline, 2,4,6 trihalo aniline, 3,4,5,6 tetrahalo aniline,
2,4,5,6 tetrahalo aniline, 2,3,5,6 tetrahalo aniline, and,
2,3,4,5,6 pentahalo aniline, N,N-ethyl ethyl amine, N,N ethanol
ethyl amine, di ethanol amine, N,N propyl propyl amine, N,N propyl
propoanol amine, di propanol amine, N,N butyl butyl amine, N,N
butyl butanolamine, di propanol amine, di methyl amine, di ethyl
amine, di propyl amine, and di butyl amine, among others.
[0051] In some embodiments where the functional group is an amine,
the reactive modifying compound can include the pendent functional
group, as discussed herein, and non-limiting examples of such
reactive compounds include:
##STR00005##
[0052] In some embodiments, the modifying composition containing an
organic solvent and a reactive modifying compound can be a
dehydration composition, where the modifying composition drives
water from the discriminating layer using a condensation reagent
such as N,N'-dicyclohexylcarbodimide (DCC). In various embodiments,
by driving the water from the discriminating layer, unreacted
functional groups on the polyfunctional compound can react with a
hydrolysis product of the polyfunctional acid halide (i.e.,
carboxylic acid) to form an amide linkage, an ester linkage, or an
ether linkage.
[0053] Those skilled in the art will recognize that method
embodiments of the present disclosure may be modified to include
other steps. Coating procedures, such as the use of surfactants or
other wetting agents to coat the porous support layer, post
treatment of the membrane, rinsing the membrane with water, and so
forth may also be used in the embodiments of the present
disclosure.
[0054] In addition, as discussed herein, the membrane can include a
porous support. The porous support can be a microporous support. In
various embodiments, the microporous support can be a polymeric
material containing pore sizes which are of sufficient size to
permit the passage of permeate there through but not large enough
so as to interfere with the bridging over of a thin polyamide
membrane formed thereon. For example, the pore size of the support
can range from one (1) nanometer (nm) to five hundred (500) nm.
Pore diameters larger than five hundred (500) nm, can, in some
instances, permit the polyamide membrane to sag into the pores,
thus disrupting the flat sheet configuration desired in some
embodiments. Examples of porous supports include those made of a
polysulfone, a polyether sulfone, a polyimide, a polyamide, a
polyetherimide, polyacrylonitrile, a poly(methyl methacrylate), a
polyethylene, a polypropylene, and various halogenated polymers,
such as polyvinylidene fluoride. The porous support can also be
made of other materials. In some embodiments, the porous support
can have a thickness in a range of twenty-five (25) micrometers
(.mu.m) to one hundred twenty five (125) .mu.m. As used herein,
"permeate" refers to the purified product water produced by a
membrane system.
[0055] Embodiments of the present disclosure also include
multilayered membranes. In some instances, the multilayered
membranes can be produced according to methods described herein.
The multilayered membrane can include a porous substrate having a
first side parallel to a second side and a modified discriminating
layer including an inner side and an outer side, where the inner
side is in operative contact with at least one side of the porous
substrate. The outer side and a portion of the modified
discriminating layer disposed between the inner side and the outer
side include a plurality of pendent functional groups. The pendent
functional groups can be connected to the modified discriminating
layer by way of at least one of hydrogen bonding, ionic bonding,
covalent bonding, physical entanglement, and chemical linkages, the
chemical linkages being at least one of amides, sulfamides,
urethanes, ureas, thioesters, and amines, including secondary
amines, ternary amines, quaternary amines, and beta hydroxyl
amines.
[0056] As discussed herein, in embodiments where the pendent
functional groups are connected to the modified discriminating
layer by way of chemical linkages, the reactive modifying compound
can be connected to the discriminating layer by reacting the
functional group with residual reactive moieties on the
discriminating layer. Therefore, the pendent functional groups on
the modified discriminating layer correspond to the pendent
functional groups attached to the reactive modifying compound, as
discussed herein.
[0057] In some embodiments, the pendent functional group can be
characterized as a moiety that changes the properties of the
discriminating layer, compared to an unmodified discriminating
layer. For example, the pendent functional group may alter the
selectivity properties of the discriminating layer to solute
molecules.
[0058] In some embodiments, the pendent functional groups can be
connected to the modified discriminating layer by way of covalently
bonding to the discriminating layer, making the pendent functional
groups difficult to wash off the multilayered membrane. In
addition, the pendent functional groups can form a thin layer at
the top of the modified discriminating layer. By forming a thin
layer of pendent functional groups at the top (i.e., outer side) of
the modified discriminating layer, the pendent functional groups
can be present in small amounts as compared to methods where the
pendent functional groups are dispersed throughout a discriminating
layer. Thus, a thin layer of pendent functional groups on the
surface can decrease flux loss in embodiments where the selected
pendent functional groups are known to cause flux loss.
[0059] In some embodiments, certain pendent functional groups can
be chosen that, although not useful for making membranes alone, can
be used to impart properties that would not otherwise be available
in a membrane. For example, biocidal groups and metal-binding sites
can be added. In additional embodiments, pendent functional groups
can be chosen that are linking groups, where the pendent functional
group can be used to attach other polymers to the modified
discriminating layer surface.
[0060] Surface analysis techniques such as Secondary Ion Mass
Spectroscopy (SIMS), Electron Scanning Chemical Analysis (ESCA),
X-Ray Microscopy, Energy Dispersive X-Ray Analysis (EDX), and
Scanning Transmission Electron Microscopy with Electron Energy Loss
(TEM/EEL) can show the percentage of pendent functional groups in
the discriminating layer.
[0061] In addition, SIMS analysis can be used to demonstrate that
pendent functional groups are somewhat more concentrated near the
surface of the discriminating layer, but also are connected to the
discriminating layer through chemical linkages. Depending on the
size and chemistry of the reactive modifying compound, pendent
functional groups can be found throughout the discriminating layer,
with slightly higher concentrations in the upper half of the depth
of the discriminating layer, creating a multilayered membrane. This
is in contrast with other methods of modifying a discriminating
layer such as direct chlorination of polyamide discriminating
layers where the chlorine groups attach to the discriminating layer
throughout all portions of the discriminating layer.
[0062] As discussed herein, surface analysis techniques can be used
to show the percentage of pendent functional groups in the
discriminating layer. In some embodiments, ESCA can be used to
quantify atomic surface percentages. For example, for modified
MPD-TMC membranes, the percentage of pendent functional groups to
MPD derived groups on the surface of the discriminating layer can
be estimated. In some embodiments, anilines with halogens and
thiols can be used as the reactive modifying compound and readily
quantified by ESCA.
[0063] In such membranes, the atomic percentage of nitrogen and
thus, the total number of amines on the surface of the
discriminating layer before applying the modifying composition is
due only to the MPD. However, after applying the modifying
composition, the atomic percentage of nitrogen is from both the MPD
and the anilines in the reactive modifying compound. To calculate
the total surface percent of nitrogen, two considerations are
important; first, an MPD derived moiety contains two nitrogens, and
second, the depth of penetration of ESCA is on average most likely
large enough to incorporate both nitrogens on the MPD. Using these
considerations, the total nitrogen in terms of MPD and aniline can
be written as shown in Equation 1:
Percent Total Surface Nitrogen(% TSN)=N from MPD+N from
Aniline=2.times.surface MPD+Anilines Equation 1
Then, if a thiol or a halogen is derived from a pendent functional
group on the aniline, the atomic percentage of the sulfur or the
halogen is a direct measure of the surface coverage of the
anilines. As used herein, the atomic percentage of mono-thiol or
mono-halogenated anilines will be represented as the atomic
percentage, X %. In embodiments where anilines contain multiple
pendent functional groups, the atomic percentage (X %) can be
divided by the average number of pendent functional groups per
reactive modifying compound. For mono-pendent functional group
anilines, the surface coverage can be estimated using Equation
2:
Aniline MPD = % X ( % TSN - Aniline ) .times. 0.5 = % X ( % TSN - %
X ) .times. 0.5 Equation 2 ##EQU00001##
[0064] The approach described above is used in the examples below,
in the Examples Section, to estimate the surface coverage for
3-thio aniline and for 3-chloro aniline on a membrane with a
MPD-TMC discriminating layer. For example, in some embodiments the
pendent functional groups comprise from about ten (10) to
forty-five (45) percent of the modified discriminating layer,
calculated as a percent added pendent functional groups to a
chemical group of the discriminating layer, as discussed herein. In
addition, in some embodiments the modified discriminating layer can
have a ratio of a moiety derived from the pendent functional group
in a region near the outer side of the modified discriminating
layer as compared to a region near the inner side of the
discriminating layer equal to approximately 1.5:1.
[0065] In some embodiments, the multilayered membrane can have a
modified surface charge as compared to a membrane with an
unmodified discriminating layer. Reducing the surface charge can
reduce the organic fouling of a membrane, as well as producing
other effects. For example, polyamide membranes produced by the
interfacial polymerization of MPD and TMC can have two
surface-bound changed species, due to the residual amine and acid.
However, some operating conditions to produce the polyamide
discriminating layer can produce MPD-TMC discriminating layers with
negative surface charge due to residual acid groups. In embodiments
of the present disclosure, however, the multilayered membrane can
have a nearly neutral charge as the residual acids are reacted with
the functional group on the reactive modifying compound, as
discussed herein, or as carboxylic acid groups are reacted with MPD
via an additional condensation reagent such as
N,N'-dicyclohexylcarbodimide (DCC), as discussed herein.
[0066] Another important property of membranes is the surface
energy of a membrane. Surface energy is a main effect controlling
flux across a membrane, therefore, the surface energy of the
membrane can be measured to determine whether a pendent functional
group may cause a change in flux as compared to similar membranes
without such functional groups.
[0067] By measuring how the surface energy changes when pendent
functional groups are changed, the usefulness of pendent functional
groups on the reactive modifying compound can be measured. In some
embodiments, the order of improvement in flux by pendent functional
groups on an aniline reactive modifying compound can be can be
measured. In some embodiments, ketone can be approximately equal to
multiple methyl ethers and thiol, ketone can be more useful than
single methyl ethers, single methyl ethers can be more useful than
esters, esters can be more useful than methiols, methiols can be
more useful than primary amines, primary amines can be more useful
than secondary amines, and secondary amines can be more useful than
ternary amines. Or, ketone.about.multiple methyl
ethers.about.thiol>single methyl
ethers>esters>methiols>primary amines>secondary
amines>ternary amines. In addition, in some embodiments,
multiple pendent functional groups on a single reactive modifying
compound can increase the effect on the flux improvement.
[0068] In some embodiments, when the pendent functional group on
the modified discriminating layer is selected from ethers, ketones,
and thiols, the multilayered membrane including the modified
discriminating layer can improve the rejection rate for solutes
including at least one of nitrate, silica, boric acid, arsenic, and
selenium and metal salts as compared to membranes without a
modified discriminating layer. In addition, the multilayered
membrane can improve the rejection rate for small organics
including at least one of alcohols, disinfection byproducts,
halogenated solvents, pharmaceuticals, and endocrine disruptors. As
used herein, "disinfection byproducts" refer to byproducts formed
when disinfectants used in water treatment plants react with
bromide and/or natural organic matter (i.e., decaying vegetation)
present in source water. Different disinfectants produce different
types or amounts of disinfection byproducts. Disinfection
byproducts can include, but are not limited to, trihalomethanes,
haloacetic acids, bromate, and chlorite. In addition, halogenated
solvents can include, but are not limited to, methylene chloride
(dichloromethane), methyl chloroform (1,1,1-Trichloroethane),
perchloroethylene (tetrachloroethylene), and trichloroethylene, and
pharmaceuticals can include antibiotics, anti-depressants, birth
control pills, seizure medication, chemotherapy drugs, antibiotics,
hormones, analgesics, ibuprofen, aspirin, tranquilizers,
cholesterol-lowering compounds, and caffeine, among others. Also,
as used herein, an "endocrine disruptor" is a synthetic chemical
that when absorbed into the body either mimics or blocks hormones
and disrupts the body's normal functions. This disruption can
happen through altering normal hormone levels, halting or
stimulating the production of hormones, or changing the way
hormones travel through the body, thus affecting the functions that
these hormones control. Endocrine disruptors can include
diethylstilbesterol, dioxin, polychlorinated biphenyls (PCBs),
dichloro-diphenyl-trichloroethane (DDT), and some other pesticides,
among others.
[0069] As discussed herein, in some embodiments, the chemical
linkage in the modified discriminating layer can be made more rigid
by using certain reactive modifying compounds. For example, a
chemical linkage between the discriminating layer and an amide
functional group on an aromatic reactive modifying compound can be
more rigid than a chemical linkage between the discriminating layer
and an amide functional group on an aliphatic reactive modifying
compound. In some embodiments, more rigid chemical linkages can
produce multilayered membranes with a higher flux as compared to
multilayered membranes with less rigid chemical linkages.
[0070] In some embodiments, the multilayered membrane of the
present disclosure can be designed to reduce fouling. Fouling of
membranes in water systems can limit the flux through the membrane,
and ultimately, the service life of membranes. Fouling problems can
include natural organic matter in the water, man-made matter such
as soaps and oils, and bacterial growth. Fouling may also be caused
by chemical or physical attraction of the membrane surface to
chemicals in the retentate side of a membrane filtration unit. In
addition, fouling from growth of microbes can increase when
additional organic matter serves as food to the microbes.
[0071] The problem of fouling has previously been extensively
studied and, although not wishing to be bound by theory, several
"rules" for lower fouling have been suggested. Such rules can
include aromatic surfaces (e.g., MPD-TMC) are more fouling than
aliphatic surfaces (e.g., piperazine discriminating layers).
Positively charged surfaces are more fouling than negatively
charged surfaces. Smooth surfaces are less fouling than rough
surfaces. Surfaces with biocides attached with specific linking
group lengths remain biocidal. Specific metal ions on the surface
have been shown to stop fouling of surfaces in seawater.
[0072] These generalities, however, are mostly for specific
foulants. Natural organic matter like that found in surface waters
can have different fouling solutions than fouling in oceans,
bio-fouling, and fouling from synthetic contaminates like oil and
surfactants.
[0073] Embodiments of the present disclosure can be designed to
reduce fouling. In some embodiments, fouling can be reduced by
creating a modified discriminating layer surface that is physically
or chemically resistant to fouling, and/or by creating a biocidal
membrane surface to kill microbes. In some embodiments, adding
piperazine derived pendent functional groups to a discriminating
layer can allow the surface charge to change from positive to
negative, it can smooth the surface, and it can change the surface
from aromatic to mostly aliphatic. In some embodiments, adding
biocidal pendent functional groups can also change the surface
charge.
[0074] As discussed herein, multilayered membranes of the present
disclosure can allow for a greater range of selectivity toward
different chemical compounds and ions. The selectivity can depend
on which pendent functional group is linked to the modified
discriminating layer. For example, for MPD-TMC discriminating
layers, pendent functional groups such as 3-aminoacetophenone and
3-methoxyaniline can give significant improvements in sodium
chloride, isopropyl alcohol, and sodium nitrate rejection.
[0075] A variety of membrane shapes are commercially available and
useful in the present invention. These include spiral wound, hollow
fiber, tubular, or flat sheet type membranes. In regard to the
composition of the membrane, often the membrane has hygroscopic
polymers other than the discriminating layer coated upon the
surface of the discriminating layer. Among these polymers are
polymeric surfactants, polyvinyl alcohol, poly vinyl pyrrolidone,
and polyacrylic acid or polyhydric alcohols such as orbital and
glycerin. In some embodiments, the formation of the discriminating
layer can include contacting a complexing agent with the organic
solvent prior to substantial reaction between the polyfunctional
compound and at least one of a polyfunctional acid halide, a
polyfunctional anhydride, and a polyfunctional dianhydride.
Complexing agents can include those methods as described in, for
example, U.S. Pat. No. 6,562,266. The presence of these polymers
and complexing agents will generally not affect the embodiments of
the present disclosure so long as the various reactive modifying
compounds and the discriminating layer come into contact. If the
discriminating layer is to be contacted after it is in final
membrane form, then the shape and composition of the membrane
should be such that the membrane is capable of being contacted with
the described modifying composition and reactive modifying
compounds.
[0076] As used herein, the following terms have the definitions
provided: "rejection rate" is the percentage of a particular
dissolved or dispersed material (i.e., solute) which does not flow
through the membrane with the solvent. The rejection rate is equal
to 100 minus the percentage of dissolved or dispersed material
which passes through the membrane, i.e., solute passage, "salt
passage" if the dissolved material is a salt. "Flux" is the flow
rate at which solvent, typically water, passes through the
membrane. "Reverse osmosis membrane" is a membrane which has a
rejection rate for NaCl of from about 95 to 100 percent.
"Nanofiltration membrane" is a membrane which has a rejection rate
for NaCl of from about 0 to about 95 percent and has a rejection
rate for at least one divalent ion or organic compound of from
about 20 to about 100 percent.
Specific Embodiments of the Disclosure
[0077] The following examples are provided for illustrative
purposes only and are not intended to limit the scope of the
present disclosure. In addition, some examples provided herein
include the addition of complexing agents, as discussed herein, to
improve the membrane flux obtained.
Example 1
[0078] On a pilot plant membrane fabrication system, commercial
polysulfone supports (i.e., porous substrates) are soaked in an
aqueous solution of 5.2 weight per volume percent (wt./vol. %)
meth-phenylene diamine (MPD), with the pH adjusted to a pH of
approximately ten (10) by the addition of two (2) molar (M) sodium
hydroxide. The support roll is pulled through a reaction table at
constant speed. Following the MPD soaking, a thin, uniform layer of
0.14 wt./vol. % trimesoyl chloride (TMC) in high purity
isoparaffinic solvent (ISOPAR L, Exxon) is applied to the membrane.
Excess TMC solution is removed via air knife and suction cup. Then,
after the TMC/solvent layer is applied, a ten (10) millimolar (mM)
solution of a reactive modifying compound in the same solvent is
applied on top of the polyamide discriminating layer in a thin,
uniform layer. The line speed of the pilot plant machine is kept
constant. Excess liquid is removed by an air knife and suction
pump. The membrane is then passed through a water rinse tank and a
drying oven, followed by a coating of a hygroscopic polymer.
[0079] Sample coupons are then cut from the roll and tested.
[0080] Table 1 presents data evaluating a MPD-TMC discriminating
layer modified by a reactive modifying compound utilizing a test
solution comprising an aqueous solution containing approximately
thirty-two thousand (32,000) parts per million (ppm) sodium
chloride (NaCl) at a transmembrane pressure of eight hundred (800)
pounds per square inch (psi) (5,515,805.83 pascals) with a feed pH
between seven (7) and eight (8). The flow through the samples is
allowed to run for approximately thirty (30) minutes before
testing.
TABLE-US-00001 TABLE 1 Flux of Membranes with a Modified
Discriminating Layer. Reactive modifying compound (10 mM) Flux
(gfd) 4-isopropylaniline 9.9 Piperazine 17.6 Control 16.0
[0081] As can be seen from Table 1, the MPD-TMC discriminating
layer loses a considerable amount of flux when the reactive
modifying compound is 4-isopropylaniline. However, the flux of the
membrane improves when the reactive modifying compound is
piperazine.
Example 2
[0082] Samples of polysulfone support are stored in water for at
least three (3) hours. The polysulfone support is a non-woven web
made of polyethylene terephthalate (PET), coated with a polysulfone
solution from dimethyl formamide (DMF), and formed by processing in
water. Samples of the polysulfone support are clipped to a metal
frame and immersed in a 2.5 wt./vol. % solution of MPD for at least
five (5) minutes. The support is placed on a paper sheet, and
excess amine solution is nipped off, using a latex rubber
roller.
[0083] Membranes 1, 2, 3, and 4 are prepared using a fifty (50)
milliliter (ml) solution of TMC and ISOPAR L. The solution is
prepared by adding approximately 49.3 ml of ISOPAR L to 0.86 ml of
5.2 wt./vol. % stock TMC solution. A rubber barrier is placed on
the MPD coated support to form a well. The TMC solution is then
poured into the well, left on the MPD-coated support for
approximately one (1) minute, and then poured off. The
MPD-TMC-coated support is rinsed with hexane for approximately
thirty (30) seconds, and allowed to air dry for approximately one
(1) minute before being placed in water. The samples are stored in
water until tested.
[0084] Membrane 5 is prepared as described above for membranes 1,
2, 3, and 4 above using a solution of TMC, pyridine, and ISOPAR L.
The solution is prepared by adding 0.86 ml of the 5.2 wt./vol. %
TMC to 49.3 ml of a solution made from five (5) ml of fifty (50) mM
pyridine in ISOPAR L.
[0085] Membrane 6 is prepared as described above for membranes 1,
2, 3, and 4 above using an approximately fifty (50) ml solution of
TMC and ISOPAR L. However, after the draining off of the TMC
solution after the approximately one (1) minute of contact, a five
(5) mM pyridine solution is applied to the membrane and reacted for
approximately thirty (30) seconds. Then, the pyridine solution is
drained off and the membrane is rinsed with hexane for
approximately thirty (30) seconds, followed by placing the membrane
in water.
[0086] Membrane 7 is prepared as described above for membrane 5,
however the TMC, pyridine, and ISOPAR L solution is made from
adding twenty-five (25) ml of five (5) mM pyridine to a solution of
0.43 ml TMC in approximately 24.5 ml ISOPAR L.
[0087] Membranes 8 and 9 are prepared as described above for
membrane 5. Membrane 8 is prepared by adding 0.85 ml TMC to 49.3 ml
of a solution made from 12.4 ml of 5.2 mM dibutyl amine added to
ISOPAR L. Membrane 9 is prepared by adding 0.85 ml TMC to 49.3 ml
of a solution made from 6.25 ml of 5.2 mM dibutyl amine added to
ISOPAR L.
[0088] Table 2 presents data evaluating the above prepared
membranes utilizing a test solution comprising an aqueous solution
containing approximately one thousand five hundred (1,500) ppm NaCl
at a transmembrane pressure of one hundred fifty (150) psi
(1,034,213.59 pascals).
TABLE-US-00002 TABLE 2 Sodium Chloride Rejection and Flux for
Membranes with a Modified Discriminating Layer NaCl Rejection
Membrane (wt. %) Flux (gfd) 1 99.16 13.6 2 99.25 16.3 3 99.25 5.1 4
99.38 15.0 5 99.23 25.0 6 99.34 15.9 7 99.22 19.6 8 99.58 4.17 9
99.53 6.37
[0089] As can be seen from Table 2, the addition of pyridine to the
TMC solution, as shown by membrane 5, can enhance the flux of
TMC-MPD membranes, however adding pyridine to the membrane after
the TMC-MPD process, as shown by membrane 6, does not have the same
effect on the flux. In addition, a greater concentration of
pyridine in the TMC solution, as shown by membrane 7, enhances the
flux of the TMC-MPD membrane, however, it is more significant with
a smaller concentration of pyridine, as shown by membrane 5.
[0090] Also, the addition of dibutyl amine to the TMC solution
enhances the sodium chloride (NaCl) rejection, as shown by
membranes 8 and 9, however, membrane 9 shows an improvement in NaCl
rejection while reducing the flux by less than membrane 8.
Example 3
[0091] Membranes are prepared on a standard pilot coater as a
continuous process at thirteen (13) feet per minute (fpm) (0.066
meters per second), using a formulation for a high-flux seawater
membrane on a polysulfone porous substrate. First, a 3.5 weight
percent (wt. %) solution of MPD is applied in water to the pre-made
polysulfone porous substrate. The MPD application has a residence
time of 156 seconds and the excess MPD solution is removed using a
nip roller. A TMC dissolved in ISOPAR L is applied at 118 ml per
square feet with a residence time of 132 seconds. At the oil-water
interface a polyamide is formed.
[0092] The oil is then removed using an air knife and pump. Next, a
modifying compound is applied. A series of runs are done with
different concentrations of 3-chloro aniline and 3-thiol aniline.
The concentrations vary from one (1) to fifteen (15) mM. The
application rate of the modifying compound is the same as that used
for the TMC solution and has a residence time of one hundred eighty
(180) seconds. The excess modifying compound is removed using an
air knife and pump. The membrane then travels through a
room-temperature water bath to remove excess oil, then a
ninety-eight (98) degrees Celsius (.degree. C.) bath containing
3.5% glycerine. The residence time in the dip baths is thirty-seven
(37) minutes. The membrane is then dried through an air-floatation
dryer at a temperature of ninety-five (95).degree. C. for 10.6
minutes.
[0093] Tables 3 and 4 present data evaluating the above prepared
membranes utilizing a test solution comprising an aqueous solution
containing approximately two thousand (2,000) ppm NaCl at a
transmembrane pressure of one hundred twenty-five (125) psi
(861,844.662 pascals), five (5) ppm boric acid, one hundred (100)
ppm isopropyl alcohol, and one hundred (100) ppm sodium
nitrate.
TABLE-US-00003 TABLE 3 Flux of Membranes with Increasing Modifying
Compound Concentration 3-Thiol Aniline (mM) Flux (gfd) 0 43.7 1
31.5 5 27.7 10 25.2 15 23.9
TABLE-US-00004 TABLE 4 Flux of Membrane with Increasing Modifying
Compound Concentration 3-Chloro Aniline (mM) Flux (gfd) 0 43.7 1
30.6 5 19.5 10 17.5 15 18.4
[0094] As can be seen from both Table 3 and Table 4, a plateau is
seen after the 10 mM is reached.
[0095] Tables 5 and 6 show ESCA analysis of the membranes
prepared.
TABLE-US-00005 TABLE 5 ESCA of Membranes with a Modified
Discriminating Layer 3-Thiol Aniline % Surface (mM) [C] [O] [N] [S]
Aniline/MPD 0 73.0 13.0 13.8 ND 0 1 71.9 13.4 12.6 1.4 25.0 5 72.2
13.5 12.1 2.2 44.4 10 73.0 12.1 12.5 2.0 38.1 15 72.5 14.0 11.1 1.8
38.7
[0096] As can been seen from Table 5, the percent of carbon and
oxygen, although showing some variation, stays relatively constant.
Nitrogen-to-carbon ratio can be used to determine the structure of
the polyamide discriminating layer. The ratio eliminates the
effects on the atomic percentage due to various amounts of water
absorbed into the surface of the discriminating layer. The sulfur
percentage is a direct measure of the percentage of the aniline
(3-thiol aniline) on the surface and ND indicates the nondetectable
level of sulfur found in the control membrane.
[0097] Similarly, nitrogen is a measure of MPD exposed on the
surface of the discriminating layer. For this analysis, it is
assumed that if one nitrogen of a MPD moiety is exposed, then, on
average, the other half can also be measured by ESCA, i.e., the
other half is exposed or it is within the depth of penetration of
the ESCA. Similarly, if the sulfur is exposed, then the nitrogen
from the amide bond is also exposed. Any error due to some
percentage not being accessible should be similar for both species.
If the flow loss from Table 3 is taken together with the data from
Table 5, for the highest concentration of 3-thio aniline (e.g., 15
mM), a 58% flow loss is due to 39% incorporation of the 3-thiol
aniline. In addition, at an approximate saturation level (10 mM) of
42% flow loss, there is 38% aniline incorporation.
TABLE-US-00006 TABLE 6 ESCA of Membranes with a Modified
Discriminating Layer 3-chloro aniline % Surface (mM) [C] [O] [N]
[Cl] Aniline/MPD 0 73.0 13.0 13.8 0.1 1.5 1 71.4 14.3 13.4 0.7 11.0
5 72.2 13.8 12.8 1.3 22.6 10 73.2 13.3 12.3 1.2 21.6 15 72.4 13.3
13.0 1.3 22.2
[0098] As can be seen from Table 6 and Table 4, Table 6 shows a
saturation level of both the aniline incorporation and the flux
reduction. Table 6 shows a ratio of aniline to MPD of 11% (3-chloro
aniline) and flow loss of 30%. The flow loss is calculated, for
example, by subtracting the flux (gfd) of the membrane when one (1)
mM 3-chloro aniline is applied from the flux (gfd) of the membrane
when no 3-chloro aniline is applied to obtain a flux reduction
amount. The flow loss is then equal to the percentage of the flux
reduction amount as compared to the flux of the membrane when no
3-chloro aniline is applied. This calculation is shown below:
Flux(0 mM 3-chloro aniline)-Flux(1 mM 3-chloroaniline)=flux
reduction amount Flow loss=100(flux reduction amount/Flux(0 mM
3-chloroaniline))
At a saturation level of approximately 22% incorporation, there is
a limiting flux loss of 58%, which is an average of the flow loss
for the membranes with 5 mM, 10 mM, and 15 mM 3-chloro aniline
applied.
[0099] The ESCA presented in Table 6 also allows for the
examination of the atomic percentages directly. Since the
saturation percentage of chlorine incorporated is about 1.3% and
the sulfur incorporation is 2%, the extent of reaction is higher
with 3-thio aniline than with 3-chloro aniline. The comparison of
the Chlorine (Cl) or Sulfur (S) to Nitrogen (N) is important
because surface contamination and water absorption affect the
carbon and oxygen atomic percentages. By taking the Cl and S to N
ratio, the excess carbon and oxygen from surface contamination and
water will not affect the ratios.
Example 4
[0100] BW30 membranes are obtained from FilmTec Corporation of
Edina, Minn. A BW30 membrane is a commercial MPD-polyamide membrane
designated commercially as BW30LE and BW30XLE. A formulation of
MPD-polyamide membrane BW30XLE is modified by the method of the
present disclosure by coating with reactive modifying compounds. In
this example, the BW30 membrane is designated as a control.
[0101] FIG. 1 and Tables 7-12 present data evaluating the above
prepared membranes utilizing a test solution comprising an aqueous
solution containing approximately 2,000 ppm NaCl at a transmembrane
pressure of 225 psi (1,551,320.39 pascals), 5 ppm boric acid, 100
ppm isopropyl alcohol, and 100 ppm sodium nitrate.
[0102] As can be seen from FIG. 1, the IPA passage of several
non-aromatic amines is close to 10-15%. However, these are the
uncoated controls, the BW30 control membrane, and the BW30LE
control membrane. The modified membranes have relatively consistent
sodium nitrate passage with a passage as low as 2.5%. In addition,
the IPA passage for the membrane modified with 3-aminoacetophenone
is 7%.
TABLE-US-00007 TABLE 7 Flux and Sodium Chloride, Isopropyl Alcohol,
and Nitrate Passage Percentage in Membranes with a Modified
Discriminating Layer Reactive NaCl Nitrate IPA modifying Contact
Flux Passage Passage Passage compound Angle (gfd) (wt. %) (wt. %)
(wt. %) Control 62.7 .+-. 1.6 32.7 .+-. 1.3 1.08 .+-. 0.06 4.27
.+-. 0.21 13.61 .+-. 1.60 3-Br 91.3 .+-. 4.0 12.7 .+-. 0.9 0.79
.+-. 0.05 2.00 .+-. 0.47 8.23 .+-. 0.99 Aniline Tri- Cl 90.3 .+-.
2.0 25.0 .+-. 1.2 0.85 .+-. 0.07 2.55 .+-. 0.05 10.74 .+-. 1.02
aniline 4-amino 78.3 .+-. 0.6 15.9 .+-. 2.4 0.80 .+-. 0.05 1.78
.+-. 0.21 13.68 .+-. 3.61 phenyl disulfide N-methyl 67.0 .+-. 2.6
25.6 .+-. 1.5 0.81 .+-. 0.04 3.01 .+-. 0.12 10.78 .+-. 0.78
4-methoxy aniline 4-methoxy 63.3 .+-. 2.1 23.5 .+-. 1.3 0.77 .+-.
0.05 2.52 .+-. 0.15 12.18 .+-. 3.11 aniline amino 47.8 .+-. 3.3
35.4 .+-. 0.2 1.21 .+-. 0.05 5.14 .+-. 0.12 14.24 .+-. 0.23
ademantane alcohol amino 49.8 .+-. 1.0 34.6 .+-. 2.7 1.06 .+-. 0.05
4.46 .+-. 0.42 13.83 .+-. 0.45 crotenoic acid methyl ester N-methyl
45.7 .+-. 1.5 34.6 .+-. 0.9 1.07 .+-. 0.13 4.53 .+-. 0.22 16.80
.+-. 0.48 homoveratryl amine Control 60.2 .+-. 0.3 36.4 .+-. 1.5
0.94 .+-. 0.03 4.07 .+-. 7.11 17.68 .+-. 5.30
[0103] As can be seen from Table 7, the aromatic disulfide behaves
similarly to the standard halogenated aniline. The 4-methoxy
aniline and the N-methyl versions are also similar to the
halogenated aniline. The three other variations with large amounts
of aliphatic nature and high mobility result in little change in
performance, in contrast to the dimethoxy anilines, which show
large flux changes and large improvements in solute passage.
TABLE-US-00008 TABLE 8 Flux and Sodium Chloride, Isopropyl Alcohol,
and Nitrate Passage Percentage in Membranes with a Modified
Discriminating Layer Reactive NaCl IPA Nitrate Modifying Flux
Passage Passage Passage Compound (gfd) (wt. %) (wt. %) (wt. %) None
30.97 .+-. 2.88 3.05 .+-. 0.12 21.00 .+-. 1.18 10.42 .+-. 0.76
1-acetyl- 35.96 .+-. 4.11 2.93 .+-. 0.28 20.31 .+-. 1.31 13.16 .+-.
0.45 piperazine (10 mM) 3-amino 19.47 .+-. 1.05 0.99 .+-. 0.17 6.99
.+-. 2.34 3.02 .+-. 0.32 acetophenone (5 mM) Morpholine 36.75 .+-.
1.55 2.92 .+-. 0.25 21.31 .+-. 2.36 13.53 .+-. 1.08 (15 mM)
m-Phenetidine 17.13 .+-. 0.94 0.88 .+-. 0.03 9.42 .+-. 2.96 2.56
.+-. 0.50 (5 mM) Bis (2- 29.99 .+-. 1.54 2.26 .+-. 0.08 19.61 .+-.
1.35 10.54 .+-. 0.86 methoxyethyl) amine (15 mM) Ethyl 3- 13.40
.+-. 0.66 1.64 .+-. 1.83 9.84 .+-. 1.91 2.82 .+-. 1.73
aminobenzoate (5 mM) None 37.25 .+-. 2.92 2.62 .+-. 0.40 18.64 .+-.
1.69 9.58 .+-. 0.69
[0104] As can be seen from Table 8, three anilines (3-amino
acetophonone, m-phenetidine, ethyl 3-amino benzoate) show
substantial improvement in the solute passage. These are anilines
with aromatic amides, ketones, ethers, and esters. Both morpholine
and bis(2-methoxyethyl) amine show no substantial changes in
performance, although there is a slight improvement in solute
passage with the diether.
TABLE-US-00009 TABLE 9 Flux and Sodium Chloride, Isopropyl Alcohol,
and Nitrate Passage Percentage in Membranes with a Modified
Discriminating Layer Reactive NaCl IPA Nitrate Modifying Flux
Passage Passage Passage Compound (gfd) (wt. %) (wt. %) (wt. %)
Control 37.85 .+-. 1.23 5.32 .+-. 0.80 21.76 .+-. 1.97 11.85 .+-.
0.65 3-methoxy aniline 23.72 .+-. 1.19 2.77 .+-. 1.90 7.66 .+-.
3.60 4.33 .+-. 1.08 4-methoxy aniline 26.46 .+-. 1.18 2.66 .+-.
0.24 14.15 .+-. 1.01 6.28 .+-. 0.36 3,5 dimethoxy 27.94 .+-. 1.95
1.84 .+-. 0.44 11.00 .+-. 0.58 4.81 .+-. 0.29 aniline 3,4 ether
ring 28.14 .+-. 2.59 2.86 .+-. 0.74 12.57 .+-. 3.54 6.49 .+-. 0.48
aniline 3-amino 19.79 .+-. 0.83 1.57 .+-. 0.04 6.67 .+-. 3.49 3.60
.+-. 0.44 acetophenone 4-amino methyl 24.30 .+-. 1.31 2.02 .+-.
0.23 10.73 .+-. 2.10 5.07 .+-. 0.47 benzoate 4-amino ethyl 21.78
.+-. 0.98 2.24 .+-. 0.82 10.51 .+-. 2.41 4.41 .+-. 0.73 benzoate 3
F aniline 29.98 .+-. 1.13 2.40 .+-. 0.28 12.38 .+-. 1.52 5.52 .+-.
0.18 3 Cl aniline 24.34 .+-. 1.31 2.00 .+-. 0.18 11.40 .+-. 1.75
4.09 .+-. 0.47 3 Br aniline 45.75 .+-. 4.25 3.79 .+-. 0.45 22.92
.+-. 5.64 11.44 .+-. 0.26 control 21.26 .+-. 1.18 1.25 .+-. 0.20
13.05 .+-. 2.30 4.10 .+-. 0.38
[0105] As can be seen from Table 9, the experiment compares the
effect of different halogenated aniline and oxygen containing
aliphatic derivatives of aniline. As shown, 3 amino acetophenone, 3
methoxy aniline, and 3,5 dimethoxy aniline demonstrate reduce NaCl,
IPA, and sodium nitrate passage.
TABLE-US-00010 TABLE 10 Flux and Sodium Chloride, Borate, Isopropyl
Alcohol, and Nitrate Passage Percentage in Membranes with a
Modified Discriminating Layer Reactive NaCl Borate Nitrate IPA
Modifying Flux Passage Passage Passage Passage Compound (gfd) (wt.
%) (wt %) (wt %) (wt %) Control 34.33 .+-. 1.05 0.79 .+-. 0.04 43.3
.+-. 6.66 3.66 .+-. 0.57 12.3 .+-. 2.20 3- 9.76 .+-. 0.45 0.81 .+-.
0.14 28.8 .+-. 9.23 1.74 .+-. 0.54 10.3 .+-. 2.44 (methylthiol)
aniline Thio 34.67 .+-. 0.99 1.09 .+-. 0.14 38.3 .+-. 4.84 3.43
.+-. 0.91 11.0 .+-. 0.90 morpholine hexanoyl 30.79 .+-. 1.68 0.83
.+-. 0.08 37.4 .+-. 0.91 2.75 .+-. 0.95 10.5 .+-. 1.10 chloride
1,9-diamino 23.89 .+-. 0.99 2.04 .+-. 0.11 37.7 .+-. 1.82 6.49 .+-.
3.50 13.6 .+-. 3.23 nonane morpholine 39.61 .+-. 1.07 1.51 .+-.
0.21 48.2 .+-. 2.46 6.57 .+-. 2.15 15.7 .+-. 3.74 control 35.93
.+-. 1.42 1.04 .+-. 0.05 45.3 .+-. 1.22 4.37 .+-. 1.07 13.8 .+-.
1.35
[0106] As can be seen from Table 10, a comparison of NaCl, sodium
nitrate, borate (pH 8), and IPA passage for an aniline and three
aliphatic pendent modified membranes is given. The 3-(methyl thiol)
aniline has the lowest flux (10 gfd) and much better borate passage
29% vs. 43%, and nitrate passage 1.7% vs. 3.7%. Table 10 also shows
the comparison of an aliphatic amide with a cyclic ether or thiol.
This is the comparison of morpholine and thiomorpholine. The
morpholine modified membrane shows worse solute passage, while the
thiomorpholine shows improved solute passage. Table 10 also shows
an increased solute passage when 1, 9 diamino nonane is used.
TABLE-US-00011 TABLE 11 Isopropyl Alcohol, Borate, and Nitrate
Passage Percentage in Membranes with a Modified Discriminating
Layer Reactive Borate Nitrate IPA Modifying Concentration Passage
Passage Passage Compound (mM) (wt %) (wt %) (wt %) 3-amino thio 1
20.1 .+-. 0.2 2.52 .+-. 2.30 7.57 .+-. 2.45 phenol 5 21.3 .+-. 0.5
2.56 .+-. 1.79 6.39 .+-. 0.66 10 21.1 .+-. 0.4 1.40 .+-. 0.08 6.58
.+-. 0.90 15 20.3 .+-. 0.4 3.14 .+-. 1.51 9.30 .+-. 2.30 3-Chloro 1
21.1 .+-. 0.4 1.54 .+-. 0.17 7.18 .+-. 2.24 aniline 5 17.0 .+-. 0.0
1.63 .+-. 0.32 8.37 .+-. 1.94 10 16.2 .+-. 0.4 1.46 .+-. 0.36 6.52
.+-. 0.95 15 16.5 .+-. 0.5 1.68 .+-. 0.84 5.96 .+-. 1.01 Acetyl 1
28.3 .+-. 0.5 2.19 .+-. 1.14 7.84 .+-. 2.25 piperazine 5 28.0 .+-.
0.2 2.98 .+-. 1.58 7.89 .+-. 1.42 10 30.3 .+-. 0.2 2.87 .+-. 1.59
10.34 .+-. 3.12 15 m 30.8 .+-. 0.7 4.04 .+-. 2.16 10.53 .+-.
3.85
[0107] As can be seen from Table 11, the addition of 3-chloro
aniline reduces the Borate passage to a certain extent as the
concentration increases, from 21.1 wt % to 16.5 wt %. Also, the
addition of 3-chloro aniline reduces the IPA passage as the
concentration increases, from 7.18 wt % to 5.96 wt %. However,
adding increasing concentrations of acetyl piperazine and
3-aminothiophenol did not seem to significantly improve borate,
nitrate, or IPA passage. In the example of acetyl piperazine, on
the other hand, keeping the concentration of acetyl piperazine low,
(i.e., 1 mM) decreased the nitrate passage more dramatically than
having higher concentrations of acetyl piperazine, as compared to
the control in Table 10.
TABLE-US-00012 TABLE 12 Flux and Sodium Chloride Passage Percentage
in Membranes with a Modified Discriminating Layer Reactive
Modifying Concentration NaCl Passage Compound (mM) Flux (wt. %)
None 41.32 .+-. 1.47 4.12 .+-. 2.31 4-piperazine 2.5 39.61 .+-.
0.92 3.35 .+-. 0.44 acetophenone 1-piperazine 10 41.69 .+-. 2.27
3.06 .+-. 0.66 carboxaldehyde 3-amino 10 18.83 .+-. 0.15 0.80 .+-.
0.04 acetophonone 3,5 dimethoxy 10 23.57 .+-. 2.65 1.38 .+-. 0.10
aniline 3,4 methylenedioxy 10 29.41 .+-. 0.49 1.47 .+-. 0.10
aniline piperonyl piperazine 10 25.41 .+-. 0.63 6.13 .+-. 2.32 None
41.37 .+-. 1.50 4.26 .+-. 3.13
[0108] As can be seen from Table 12, the use of piperazine as a
linking group between phenyl groups has been shown to improve the
solute passage. Table 12 has a comparison of 4-piperazine
acetophenone and piperonyl piperazine to 3,4 methylenedioxy
aniline, 3,5 dimethoxy aniline, and 3-amino acetophenone. The
presence of the ternary amine in both cases causes either worse
solute passage (piperonyl piperazine) or only slightly better
solute passage (4-piperazine acetophenone). The flux is only
slightly reduced when 4-piperazine acetophenone (40 gfd vs. 41 gfd)
is used, but much lower for 3-amino acetophenone (19 gfd).
Piperonyl piperazine, as the modifying compound, reduces the flux
from 41 gfd to 25 gfd, and using 3,4 methylenedioxy aniline the
flux is 29 gfd.
Example 5
[0109] Membranes are prepared on a standard pilot coater as a
continuous process at thirteen (13) feet per minute (fpm) (0.066
meters per second), using a formulation for a high-flux seawater
membrane on a polysulfone porous substrate. First, a 3.5 weight
percent (wt. %) solution of MPD is applied in water to the pre-made
polysulfone porous substrate. The MPD application has a residence
time of 156 seconds and the excess MPD solution is removed using a
nip roller. A TMC dissolved in ISOPAR L is applied at 118 ml per
square feet with a residence time of 132 seconds. At the oil-water
interface a polyamide is formed.
[0110] The oil is then removed using an air knife and pump. In some
instances, a modifying compound is applied. A series of runs are
done with 3-aminothiophenol, 3-chloroaniline, acetyl piperazine,
amino crotenoic acid methyl ester, 3,5-dimethoxy aniline, and
3-aminoacetophenone at a concentration of 5 mM. The application
rate of the modifying compound is the same as that used for the TMC
solution and has a residence time of 180 seconds. The excess
modifying compound is removed using an air knife and pump. The
membrane then travels through a room-temperature water bath to
remove excess oil, then a ninety-eight (98) degrees Celsius
(.degree. C.) bath containing 3.5% glycerine. The residence times
in the dip baths is thirty-seven (37) minutes. The membrane is then
dried through an air-floatation dryer at a temperature of
ninety-five (95).degree. C. for 10.6 minutes.
[0111] Table 13 presents the membrane designations.
TABLE-US-00013 TABLE 13 Membrane Designations, Type, and Modifying
Compound Membrane Designation Membrane Type and Modifying Compound
RO-1 BW30XLE (FilmTec Corp., Edina, MN) RO-2 BW30 Membrane (FilmTec
Corp., Edina, MN) RO-3 Polyamide membrane of the present disclosure
modified with 3-aminothiophenol RO-4 Polyamide membrane of the
present disclosure modified with 3-chloroaniline RO-5 Polyamide
membrane of the present disclosure modified with acetyl piperazine
RO-6 Polyamide membrane of the present disclosure modified with
amino crotenoic acid methyl ester RO-7 Polyamide membrane of the
present disclosure modified with 3,5-dimethoxy aniline RO-8
Polyamide membrane of the present disclosure modified with
3-aminoacetophenone NF NF-200 Membrane (FilmTec Corp., Edina,
MN)
[0112] To observe biofilm formation potential on the surface of
Reverse Osmosis (RO) and Nano-filtration (NF) membranes, a biofilm
formation study is carried out in a rotating disk reactor (RDR)
system. Three RDR are used and nine (RO and NF) membrane swatches
are adhered onto polycarbonate coupons by silicon rubber sealant in
RDR systems. Table 14 shows the distribution of RO and NF membranes
in the different reactors.
TABLE-US-00014 TABLE 14 Distribution of Membranes in Rotating Disk
Reactor Systems Reactor 1 (R1) Reactor 2 (R2) Reactor 3 (R3) RO-1
RO-1 RO-1 RO-2 RO-2 RO-2 NF NF RO-3 RO-4 RO-5 RO-6 RO-7 RO-8
[0113] Each reactor is operated for thirty-one (31) days. The feed
to the reactors is biological activated carbon (BAC) treated water.
To enhance the growth of biofilm, nutrients (Carbon: Nitrogen:
Potassium), are added to the reactors. Glutamic acid, glucose,
galactose, and arabinose are used for a carbon source, potassium
nitrate (KNO.sub.3) is used for a nitrogen source, and potassium
phosphate (K.sub.2HPO.sub.4) is used for a potassium source. The
carbon source, nitrogen source, and potassium source are added to
the reactors in a molar ratio of 100:10:1 corresponding to 5.54 ml
carbon source, 16.88 ml nitrogen source, and 4.00 ml potassium
source in a twenty (20) liter (L) container of nanopure water. The
flow rate of nutrient (C:N:P) and BAC treated water are 0.50 ml/min
and 0.70 ml/min, respectively. The average culture-forming unit per
milliliter (CFU/ml) in the BAC treated water is 1.35 to about
1.9.times.10.sup.4 CFU/ml during the experiment. The temperature
inside the reactor is maintained at twenty-five (25).degree. C.
throughout the experiment to nullify the effect of temperature of
biofilm growth, the ambient temperature is also close to
twenty-five (25).degree. C. The rotation speed of the rotor in the
RDR is fifty (50) rotations per minute (rpm) in all reactors.
[0114] The RO and NF membranes in the three RDR reactors are
examined after thirty-one (31) days of operation using the
cryo-sectioning (cryo) and live/dead staining (L/D). Table 15 shows
what analysis is performed on each membrane.
TABLE-US-00015 TABLE 15 Designation of Type of Membrane Analysis
for each Membrane Reactor 1 (R1) Reactor 2 (R2) Reactor 3 (R3) Cryo
& L/D Cryo & L/D Cryo & L/D Cryo & L/D Cryo &
L/D Cryo & L/D Cryo & L/D Cryo & L/D Cryo & L/D
The membranes are taken out from coupons using sterilized razor
blade and hemostats without disturbing the surface of membrane
containing biofilm. For membrane cryo-sectioning analysis, a
Cryostate Series #Leica CM 1850 is used and the thickness of each
membrane slice is 5.0 micrometers (.mu.m).
[0115] LIVE/DEAD BacLight.TM. is used for Live/Dead staining of
cells on the surface of the membrane. This kit contains SYTO 9
(3.34 mM) and propidium iodide (20 mM) dyes. To stain the cells on
the membrane, the same amount, 1.5 .mu.l/ml of SYTO 9 and propidium
iodide dyes, are diluted in one (1) ml of nanopure water and after
proper dilution, dyes are added to the top surface of a membrane
and incubated for one hour. After incubation, the excess dye is
washed off and the stained membranes are observed under
epiflourescence microscope (Microscope Series # Nikon, Eclipse E
800, Japan) by 100.times. object.
[0116] For the cryo-sectioning analysis, 15 cryo-sections are taken
from each slice of membrane which are 5-.mu.m thick, and one line
scan images of live and dead cells are taken. The values are then
turned into a data set using Metamorph surface topography image
analysis software. Each image gives different distributions of live
and dead cells along the thickness of biofilm on the membrane. To
calculate the thickness at which live and dead cells occur in each
image, the width at the mid-height is taken. FIG. 2 shows a summary
of cryo-sectioning analyses results of all membranes. Each bar for
each membrane represents average thickness (15 slices of membranes)
of either live or dead cells.
[0117] As can be seen in FIG. 2, on the surface of RO-1 and RO-7,
the relative number of live cells is more than that of dead cells.
In addition, if the results of the commercial membranes, RO-1 and
RO-2, are compared to the membranes with a modifying compound, the
membrane that has 3-amino acetophenone as the modifying compound,
RO-9, has the lowest number of live cells and one of the lowest
numbers of dead cells. The only other membrane that shows better
cell counts is the NF membrane.
[0118] Based upon the thickness of the cryo-sectioning images, the
approximate accumulation rate of the biofilm is calculated as shown
in Equation 3:
Average Growth of Biofilm = Average thickness of biofilm ( m )
Period of operation ( days ) Equation 3 ##EQU00002##
This analysis is simplistic since a membrane biofilm is a complex,
heterogeneous, and multilayer-mixed structure. However, Table 16
shows the average growth of biofilm for each membrane in descending
growth rate order.
TABLE-US-00016 TABLE 16 Average Growth of Biofilm for each Membrane
Average growth of Average Growth of Membrane Dead cells (.mu.m/day)
Membrane Live Cells (.mu.m/day) RO-3 1.82 RO-3 1.73 RO-5 1.78 RO-5
1.53 RO-7 1.30 RO-7 1.34 RO-4 1.18 RO-1 1.21 RO-1 1.17 RO-4 1.08
RO-6 0.97 RO-6 0.86 RO-8 0.76 RO-2 0.75 RO-2 0.74 NF 0.64 NF 067
RO-8 0.61
Based on the cryo-sectioning analysis and the number of days of
observation, it appears that the maximum average growth of biofilm
is less than 1 .mu.m/day on the surface of membranes RO-6, RO-2,
NF, and RO-8. In addition, it appears from Table 16 that using
3-aminoacetophenone and 3-chloroaniline as the modifying compound
reduces bio-growth on the surface of the membranes.
* * * * *