U.S. patent application number 13/570221 was filed with the patent office on 2013-05-09 for filtration membranes, related nano and/or micro fibers, composites methods and systems.
The applicant listed for this patent is Manki CHO, Mamadou S. DIALLO, William A. GODDARD, III, Seong-Jik PARK. Invention is credited to Manki CHO, Mamadou S. DIALLO, William A. GODDARD, III, Seong-Jik PARK.
Application Number | 20130112618 13/570221 |
Document ID | / |
Family ID | 47669218 |
Filed Date | 2013-05-09 |
United States Patent
Application |
20130112618 |
Kind Code |
A1 |
DIALLO; Mamadou S. ; et
al. |
May 9, 2013 |
FILTRATION MEMBRANES, RELATED NANO AND/OR MICRO FIBERS, COMPOSITES
METHODS AND SYSTEMS
Abstract
Filtration membrane comprising polymeric nanofibers and/or
microfibers attaching dendrimer component presenting reactive sites
selective for chemicals to be filtered, and related nanofibers and
microfibers, composite materials, compositions, methods and
system.
Inventors: |
DIALLO; Mamadou S.;
(PASADENA, CA) ; GODDARD, III; William A.;
(PASADENA, CA) ; PARK; Seong-Jik; (SEOUL, KR)
; CHO; Manki; (CHANGWON CITY (Gyungsangnam Do),
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DIALLO; Mamadou S.
GODDARD, III; William A.
PARK; Seong-Jik
CHO; Manki |
PASADENA
PASADENA
SEOUL
CHANGWON CITY (Gyungsangnam Do) |
CA
CA |
US
US
KR
KR |
|
|
Family ID: |
47669218 |
Appl. No.: |
13/570221 |
Filed: |
August 8, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61521290 |
Aug 8, 2011 |
|
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61592409 |
Jan 30, 2012 |
|
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61601410 |
Feb 21, 2012 |
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Current U.S.
Class: |
210/641 ;
210/321.6; 210/321.89; 210/323.1; 210/500.23; 210/500.27;
210/500.33; 210/500.35; 210/500.37; 210/500.42; 210/500.43;
210/654; 264/109; 264/465; 264/484; 427/458; 428/221; 442/1;
525/326.2; 525/328.6; 525/329.1; 525/329.9; 525/330.5; 525/535 |
Current CPC
Class: |
B01D 69/087 20130101;
D01D 5/0007 20130101; B01D 71/76 20130101; B01D 71/82 20130101;
B01D 69/125 20130101; Y10T 428/249921 20150401; B01D 63/021
20130101; D01F 11/04 20130101; B01D 69/12 20130101; B01D 2325/40
20130101; B01D 69/08 20130101; B01D 2325/16 20130101; Y10T 442/10
20150401; B01D 2325/14 20130101; B01D 2323/39 20130101 |
Class at
Publication: |
210/641 ;
210/500.27; 210/500.23; 210/500.33; 210/500.42; 210/500.43;
210/500.35; 210/500.37; 442/1; 428/221; 210/323.1; 210/321.6;
210/321.89; 210/654; 264/465; 427/458; 264/109; 264/484; 525/535;
525/326.2; 525/329.1; 525/330.5; 525/329.9; 525/328.6 |
International
Class: |
B01D 71/82 20060101
B01D071/82 |
Goverment Interests
STATEMENT OF GOVERNMENT GRANT
[0002] This invention was made with government support under
CBET0948485 awarded by the National Science Foundation. The
government has certain rights in the invention.
Claims
1. A filtration membrane comprising: a plurality of nano and/or
micro fibers, each having a polymer component and a dendrimer
component. wherein the polymer component provides a fiber scaffold
and the dendrimer component is attached to the polymer component
and presents reactive sites on the fiber scaffold.
2. The filtration membrane of claim 1, wherein the nanofibers
and/or microfibers are arranged in a composite material layer
having a mesh structure, the composite material layer comprised in
the filtration membrane alone or in combination with one or more
additional layers.
3. The filtration membrane of claim 2, wherein the one or more
additional layers comprise a supporting layer comprising a
supporting layer polymer component, the supporting layer attached
to the composite material layer.
4. The filtration membrane of claim 3 wherein the supporting layer
is functionalized with highly branched dendritic macromolecule or
dendritic nanomaterial.
5. The filtration membrane of claim 2, wherein the one or more
additional layers, comprise a coating layer attached to the
composite material layer, the coating layer comprising a coating
layer dendrimer component comprising cross linked highly branched
dendritic macromolecule or dendritic nanomaterial.
6. The filtration membrane of claim 3, wherein the composite
material layer polymer component and the supporting layer polymer
component are formed by a same polymer.
7. The filtration membrane of claim 5, wherein the one or more
additional layers further comprise a supporting layer polymer
component attached to the coating layer and comprising dendritic
nanomaterial.
8. The filtration membrane of claim 2, further comprising a
scaffold layer comprising nano and/or microfibers including a
polymer component and no dendrimer.
9. The filtration membrane of claim 2, wherein the one or more
additional layers comprise one or more composite material layers
having a mesh structure, wherein the dendritic component of the one
or more composite material layers is either the same or
different.
10. The filtration membrane of claim 1, wherein the plurality of
nano and/or micro fibers are hollow fibers, arranged in a bundle
configuration in which the nano and/or microfibers are
substantially parallel one with another.
11. The filtration membrane of claim 1, wherein the polymer
component is selected from the group consisting of a substituted or
unsubstituted aliphatic polymer, a substituted or unsubstituted
unsaturated polymer and a substituted or unsubstituted aromatic
polymer, and the dendrimer component is selected from a highly
branched dendritic macromolecule or an aggregate nanostructures
and/or microstructure thereof, wherein the polymer component and
the dendrimer component are attached through binding of
corresponding functional group forming a hydrogen bond or a
covalent bond.
12. The filtration membrane of claim 1, wherein the polymer
component is selected from the group consisting of polysulfone
(PS), polyether sulfone (PES), poly(vinylidene)fluoride (PVDF),
poly(tetrafluoroethylene) (PTFE), poly(acrylonitrile) (PAN),
poly(methyl methacrylate) (PMMA), poly(methacrylic acid) (PMAA),
poly(acrylic acid) (PAA), poly(vinyl methyl ketone), and
poly(ethylene terephthalate) (PET).
13. The filtration membrane of claim 11, wherein the dendrimer
component comprises one or more highly branched dendritic
macromolecule selected from the group consisting of generation-3
poly(amidoamine) (PAMAM) dendrimer, generation-4 poly(amidoamine)
(PAMAM) dendrimer, generation-5 poly(amidoamine) (PAMAM) dendrimer,
generation-3 poly(propyleneimine) (PPI) dendrimer, generation-4
poly(propyleneimine) (PPI) dendrimer, generation-5
poly(propyleneimine) (PPI) dendrimer, generation-3
poly(bis(methylol)propionic acid) (MPA) dendrimer, generation-4
poly(bis(methylol)propionic acid) (MPA) dendrimer, generation-5
poly(bis(methylol)propionic acid) (MPA) dendrimer, generation-3
poly(ethyleneimine) dendrimer, generation-4 poly(ethyleneimine)
dendrimer, generation-5 poly(ethyleneimine) dendrimer, and
hyperbranched poly(ethyleneimine), or aggregate nanostructures
and/or microstructure thereof.
14. The filtration membrane of claim 1, wherein the reactive sites
are selected to retain a chemical of interest.
15. The filtration membrane of claim 1, wherein reactive sites are
selected to reject a chemical of interest.
16. The filtration membrane of claim 1, wherein the reactive sites
are electrically charged.
17. A nanofiber or microfiber comprising: a polymeric component
providing a fiber scaffold; and a dendrimer component attached to
the polymeric component to present reactive sites on the fiber
scaffold.
18. The nanofiber or microfiber of claim 17, wherein the dendrimer
component is formed by one or more highly branched dendritic
macromolecules, and/or aggregate nanostructures and/or
microstructure thereof.
19. The nanofiber or microfiber of claim 17, wherein the dendrimer
component attaches the polymer component through hydrogen bond
between corresponding functional groups in the dendrimer component
and in the polymer component.
20. The nanofiber or microfiber of claim 17, wherein the dendrimer
component attaches the polymer component through covalent bond
between corresponding functional groups in the dendrimer component
and in the polymer component.
21. The nanofiber or microfiber of claim 17, wherein the polymer
component has a formula: ##STR00009## (I) wherein: Q, Y, and Z
comprise saturated aliphatic hydrocarbon, aromatic hydrocarbon, or
unsaturated aliphatic hydrocarbons; m, l, and k independently are
integers ranging between 0-50; at least one of m, l, k is not equal
to zero; j is an integer ranging between 50-500; and at least one
of Q (when Q.noteq.0), Y (when Y.noteq.0), or Z (when Z.noteq.0),
comprises the polymer component functional group.
22. The nanofiber or microfiber of claim 21, wherein Q, Y, and Z
are independently selected from the following formulas:
##STR00010## wherein: n=0 or 1; m is an integer ranging from 0-15;
X is a functional group comprising an atom selected from O, S, N,
P, or F; and R.sub.1-R.sub.18 are independently selected from: the
polymer component functional group; hydrogen; C1-C20 linear,
branched, saturated, unsaturated, or aryl hydrocarbon which are
either substituted or unsubstituted with O, N, B, S, P; or
substituted O, N, B, S, or P at least one of R.sub.1-R.sub.18 the
polymer component functional group.
23. The nanofiber or microfiber of claim 17, wherein the polymer
component comprises polysulfone (PS), polyether sulfone (PES),
poly(vinylidene)fluoride (PVDF), poly(tetrafluoroethylene) (PTFE),
poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA),
poly(methacrylic acid) (PMAA), poly(acrylic acid) (PAA), and/or
poly(vinyl methyl ketone).
24. The nanofiber or microfiber of claim 17, wherein the dendrimer
component has a formula: ##STR00011## wherein: n and m are integers
ranging from 2-5; R.sup.1-R.sup.8 are independently selected from
hydrogen or hyperbranched polymer moieties; X.sup.1 and X.sup.2 are
N; and X.sup.4-X.sup.5 are selected from amine, amide, imide, and
carbamate.
25. The nanofiber or microfiber of claim 17, wherein the dendrimer
component comprises highly branched dendritic macromolecules of
formula ##STR00012## wherein n and m are integers ranging from 2-5,
and wherein R.sub.1-R.sub.4 can be independently selected from
hydrogen or hyperbranched polymer moieties.
26. The nanofiber or microfiber of claim 17, wherein the dendrimer
component comprises PEI.
27. The nanofiber or microfiber of claim 17, wherein the reactive
sites are positively and/or negatively charged.
28. The nanofiber or microfiber of claim 17, wherein the reactive
sites comprise N, O and/or S donors.
29. The nanofiber or microfiber of claim 17, wherein the reactive
sites comprise functional groups selected from the group consisting
of amines, quaternary ammonium groups, amides, hydroxyl groups,
ethers, carboxylates, esters, sulfonates, sulfiniates, sulfonate
esters, sulfinate esters, sulfonamides, sulfonamides, phosphates,
carbamates, ureas, imidines, guanidines, oximes, imidazoles,
pyridines, thiols, thioethers, and thiocarboxylates.
30. A composite material comprising: a plurality of the nanofibers
or microfibers of claim 17.
31. The composite material of claim 30, wherein the plurality of
nanofibers or microfibers are arranged in a mesh structure or in a
bundle configuration in which the nano and/or microfibers are
substantially parallel one with the another.
32. A filtration system comprising: at least one filtration
membrane according to claim 1 selective for a first chemical in
combination with one or more additional filtration membranes, each
selective for the first chemical and/or additional chemical.
33. The filtration system of claim 32 wherein the filtration
membranes are arranged in units, wherein a first unit comprises an
alternating series of membranes configured to reject cations and
membranes configured to reject anions, and a second unit comprises
a parallel series of membranes configured to absorb ions of
interest.
34. The filtration system of claim 32, wherein plurality of
nanofibers or microfibers comprising the membranes are arranged in
a mesh structure or in a bundle configuration in which the nano
and/or microfibers are substantially parallel with each other.
35. A process for providing a nanofiber or microfiber, comprising:
mixing a polymer with a highly branched dendritic macromolecule
and/or with an aggregate nanostructure or microstructure thereof,
to provide a liquid mixture and electrospinning the liquid mixture
to provide a nanofiber or microfiber.
36. The process of claim 35, further comprising electrospraying the
nanofiber or microfiber with a highly branched dendritic
macromolecule and/or with an aggregate nanostructure or
microstructure thereof
37. The process of claim 35, wherein the liquid mixture is
electrospun while surrounding a central stream of fluid such that
the nanofiber or microfiber provided is hollow.
38. A process for obtaining a nanofiber or microfiber, comprising:
electrospinning a polymer to provide a nanofiber or a microfiber
and electrospraying the nanofiber or microfiber with a highly
branched dendritic macromolecule and/or with an aggregate
nanostructure or microstructure thereof.
39. The process of claim 38, further comprising electrospraying the
nanofiber or microfiber with a highly branched dendritic
macromolecule and/or with an aggregate nanostructure or
microstructure thereof.
40. The process of claim 38, wherein the liquid mixture is
electrospun while surrounding a central stream of fluid such that
the nanofiber or microfiber provided is hollow.
41. A nanofiber or microfiber obtainable by the process of claim
35.
42. A process for manufacturing a composite material comprising:
aggregating a plurality of nanofibers or microfibers according to
claim 17 in a mesh structure or in a bundle configuration in which
the nanofibers or microfibers are substantially parallel one with
each other.
43. The process of claim 42, wherein the aggregating the plurality
of nanofibers or microfibers in a mesh structure is performed by
mixing a polymeric component dissolved in a suitable solvent with a
dendritic component dissolved in a suitable solvent, and applying
an electrical charge to the liquid mixture of polymeric components
and dendritic components until a continuous stream of the liquid
mixture of polymeric components and dendritic components is pulled
to a rotating collector having an electrical charge opposite that
of the liquid mixture of polymeric components and dendritic
components such that the continuous stream forms a mesh of
nanofibers.
44. A filtration method comprising: filtering a liquid through a
filtration membrane of any one of claim 1.
45. The filtration method of claim 44, wherein the filtration
membrane is formed by a plurality of filtration membranes each
selective for one or more chemicals and the filtering is performed
by passing the liquid through the plurality of filtration membranes
to remove and/or absorb the one or more chemicals in a controlled
fashion.
46. The filtration method of claim 45, wherein at least one of the
plurality of filtration membranes comprises electrically charged
reactive sites and the filtering is performed by passing the liquid
through the plurality of filtration membranes to remove or absorb
electrically charged chemicals.
47. The filtration method of claim 45, wherein the at least one of
the plurality of filtration membranes comprises alternating
positive and negative charged filtration membranes arranged in a
configuration suitable to remove charged chemicals from the
liquid.
48. The filtration method of claim 45 wherein the at least one of
the plurality of filtration membranes comprises alternating
positive and negative charged filtration membranes arranged in a
configuration suitable to absorb charged chemicals from the
liquid.
49. The filtration method of claim 44, further comprising filtering
the liquid through one or more conventional nanofiltration
membranes to remove particles and dissolved organic matter.
50. The filtration method of claim 44, wherein the liquid is water.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Application No. 61/521,290, entitled "Low-Pressure Ion-Selective
Membranes for Water Treatment and Desalination: Synthesis,
Characterization and Multiscale Modeling" filed on Aug. 8, 2011
with docket number CIT-5654-P3, to U.S. Provisional Application No.
61/592,409, entitled "Ion-Selective Nanofiltration Membranes Based
on Polymeric Nanofibrous Scaffolds and Separation Layers Consisting
of Crosslinked Dendritic Macromolecules" filed on Jan. 30, 2012
with docket number CIT-5654-P4, and to U.S. Provisional Application
No. 61/601,410, entitled "Low-Pressure Ion-Selective Membranes for
Water Treatment and Desalination: Synthesis, Characterization and
Multiscale Modeling" filed on Feb. 21, 2012 with docket number
CIT-5654-P5, each of which is incorporated herein by reference in
its entirety.
FIELD
[0003] The present disclosure relates to filtration membrane and
related nano and/or micro fibers, composites, methods and
systems.
BACKGROUND
[0004] Development of efficient membranes has been a challenge in
the field of fluid filtration, in particular when aimed at water
treatment.
[0005] Whether for human consumption, agriculture or industry,
several methods are commonly used for filtration including reverse
osmosis (RO), nanofiltration (NF), ultrafiltration (UF) and
microfiltration (MF) and additional methods identifiable by a
skilled person.
[0006] Despite production and elaboration during the past 20 years
of several filtration concepts/technologies proposed as
improvements or alternatives to the above mentioned approaches,
development of efficient, cost-effective and/or environmental
friendly filtration methods and system has been a challenge in
particular when directed at selective filtration.
SUMMARY
[0007] Provided herein are membranes and related nano- or
micro-fibers, composite materials, methods and systems that allow
in several embodiments to perform selective filtration of a liquid
and in particular of water or aqueous solutions.
[0008] According to a first aspect, a filtration membrane is
described. The filtration membrane comprises a plurality of nano
and/or micro fibers, each having a polymer component and a
dendrimer component. The polymer component provides a fiber
scaffold for attaching the dendrimer component. The dendrimer
component comprises a dendrimer nanomaterial associated to the
fiber scaffold and presenting a reactive site on the fiber scaffold
to allow selective filtration of a chemical capable of interaction
with the reactive site. In some embodiments, in the filtration
membrane, the plurality of nanofibers and/or microfibers is
arranged in a mesh structure forming a layer comprised in the
membrane, alone or in combination with additional layers. In some
embodiments, the plurality of nanofibers and/or microfibers are
arranged in a substantially parallel configuration, in particular
in some of these embodiments, one or more nanofibers and/or
microfibers of the plurality of the nanofibers or microfibers are
hollow.
[0009] According to a second aspect, a nanofiber or microfiber is
described. The nanofiber or microfiber comprises a polymeric
component providing a fiber scaffold and a dendrimer component
attached to the polymeric component to present reactive sites on
the fiber scaffold. In some embodiments in the nanofiber or
microfiber, the reactive sites are positively and/or negatively
charged.
[0010] According to a third aspect, a composite material is
described, which comprises a plurality of the nanofibers and/or
microfibers herein described attaching a dendrimer component and
presenting a reactive site. In some embodiments, in the composite
material, the plurality of nanofiber and/or microfiber are arranged
in a mesh structure forming a layer comprised in the membrane,
alone or in combination with additional layers. In some
embodiments, the plurality of nanofiber and/or microfibers are
arranged in a substantially parallel configuration, in particular
in some of these embodiments, one or more nanofibers and/or
microfibers of the plurality of the nanofibers or microfibers are
hollow.
[0011] According to a fourth aspect, a filtration system is
described. The system comprises at least one filtration membranes
herein described selective for a first chemical in combination with
one or more additional filtration membranes each selective for the
first chemical and/or additional chemicals.
[0012] According to a fifth aspect, a process for providing a
nanofiber or microfiber is described. The process comprises mixing
a polymer with a dendrimer to provide a liquid mixture and
electrospraying and/or electrospinning the liquid mixture to
provide a nanofiber or microfiber.
[0013] According to a sixth aspect a nanofiber or microfiber
obtainable by the process for providing a nanofiber or microfiber
herein described.
[0014] According to a seventh aspect, a process for manufacturing a
composite material herein described. The process comprises
aggregating nano-fiber and/or microfibers herein described.
[0015] Membranes, nano or micro fibers, composite materials and
related methods and systems herein described allow in several
embodiments filtration of fluids without the need for the high
pressures required in conventional fluid purification methods such
as reverse osmosis.
[0016] Membranes, nano or micro fibers, composite materials and
related methods and systems herein described in several embodiments
allow more efficient, cost-effective and/or environmentally sound
technologies to filter fluids including extracting clean water and
valuable chemicals (e.g. critical materials or other elements) from
impaired water including wastewater, brackish water and
seawater.
[0017] Membranes, nano or micro fibers, composite materials and
related methods and systems herein described can be used in
connection with applications wherein water filtration in particular
when aimed at selective filtration is desired. Exemplary
applications comprise fluid purification, and in particular water
filtration, water purification and in particular water desalination
and additional applications associated with
industrial/environmental separations, including chemical and/or
/biological purifications, which are identifiable by a skilled
person. Additional applications comprise gas separations,
additional chemical and/or biological purifications and catalysis
wherein selective absorption, inclusion or removal/conversion of
one or more solutes/compounds is desired.
[0018] The details of one or more embodiments of the disclosure are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages will be apparent from the
description and drawings, and from the claims.
BRIEF DESCRIPTION OF DRAWINGS
[0019] The accompanying drawings, which are incorporated into and
constitute a part of this specification, illustrate one or more
embodiments of the present disclosure and, together with the
detailed description and the examples, serve to explain the
principles and implementations of the disclosure.
[0020] FIG. 1 is a schematic illustrating of an ion-selective UF
membranes for water treatment and desalination according to an
embodiment herein described and related UF membrane module (Panel
A), a related process of manufacturing nano- and/or micro-fibers
according to an embodiment herein described (Panel B) and nano-
and/or micro-fibers according to an embodiment herein described
(Panel C.
[0021] FIG. 2 shows a hyperbranched polyethyleimine (PEI)
macromolecule (Panel A) and related methods of cross linking (Panel
B) and methylation (Panel C) of anion-selective hyperbranched
macromolecules (1.20).
[0022] FIG. 3 shows anion-exchange hyperbranched microparticles
(1.21). In particular, Panel A shows a schematic of an aggregate of
hyperbranched macromolecules forming anion-exchange hyperbranched
microparticles. Panel B shows the interior microenvironment of the
microparticles. Panels C and D show an embodiment where the
reactive site is a quaternary ammonium center.
[0023] FIG. 4 shows the preparation of ion-selective hollow fibers
by electrospinning (Panel A) and a schematic depiction of an
embodiment anion exchanging/cation rejection hollow fiber (Panel
B). (see 1.30).
[0024] FIG. 5 shows a laboratory scale set-up for preparing and
testing anion-exchange hollow fibers according to an embodiment
herein described. In particular, Panel A shows the preparation of a
test membrane of hollow nanofibers. Panel B shows a schematic of
the apparatus for testing the hollow nanofibers according to an
embodiment herein described.
[0025] FIG. 6 shows a depiction of an hyperbranched macromolecules
and a schematic of their use in an ion absorbing microfiltration
(IA.mu.F) membrane [Ref 5.5] according to an embodiment herein
described. Panel A shows a schematic representation of
encapsulation of a molecule by a dendritic component as herein
described. Panel B shows an exemplary membrane comprising a
composite material nano and/or microfiber layer in between two
porous support layers.
[0026] FIG. 7 shows 2-D structures of exemplary poly(amidoamine)
(PAMAM), poly(propyleneimine) (PPI) and bis bis(methylol)propionic
acid (MPA) dendrimers suitable in embodiments herein described.
[0027] FIG. 8 shows a schematic representation of LBL Assembly of
Polyelectrolytes [Ref 2.18]. In particular, Panel A shows the
sequential steps of exposing a substrate surface to different
laying solutions. Panel B shows a schematic of the various layers
deposited by the LBL technique. Panel C shows the repeating monomer
subunits of the positively and negatively charged layers
deposited.
[0028] FIG. 9 shows a general schematic of nanofiber fabrication by
electrospinning [Ref 2.23] according to an embodiment herein
described.
[0029] FIG. 10 shows a cutaway drawing of an embodiment of a
ion-absorbing microfiltration module [Ref 3.5] according to an
embodiment herein described.
[0030] FIG. 11 shows a schematic example preparation of hollow
nanofibers with embedded ion-selective dendritic macromolecules by
electrospinning. (3.22) according to an embodiment herein
described.
[0031] FIG. 12 shows atomistic molecular dynamics simulations of
Cl.sup.- (light gray atoms (151) binding to a fourth generation
(G4-NH.sub.2 poly(amidoamine) (PAMAM)) dendrimer in aqueous
solutions (3.19). The left image shows the dendrimer at approximate
pH 4.0 and the right image shows the dendrimer at approximate pH
7.0.
[0032] FIG. 13 shows photographs of Ion Absorbing Microfiltration
(IA.mu.F) Membrane Module and filtration systems [3.5, 3.4]
suitable in embodiments herein described.
[0033] FIG. 14 shows a schematic diagram of an exemplary
configuration for a low-pressure membrane filtration system and
related method for desalination according to an embodiment herein
described.
[0034] FIG. 15 shows a schematic depiction of an ion rejecting
ultrafiltration membrane module according to an embodiment herein
described. Panel A shows module configuration of an exemplary
module. Panel B shows an exemplary cation rejecting hollow fiber.
Panel C shows an exemplary anion rejecting hollow fiber.
[0035] FIG. 16 shows a depiction of an exemplary ion absorbing
microfiltration membrane module according to an embodiment herein
described. Panel A shows the module configuration. Panel B shows a
schematic of and exemplary anion/cation absorbing hollow fiber.
[0036] FIG. 17 shows functionalized hyperbranched macromolecules as
building blocks for ion-selective hollow fibers according to an
embodiment herein described. Panel A shows schematics of exemplary
anion selective hyperbranched macromolecules with amine and
ammonium reactive sites. Panel B shows schematics of exemplary
cation selective hyperbranched macromolecules with SO.sub.3H and
PO.sub.3H.sub.2 reactive sites.
[0037] FIG. 18 shows the 2-D structures of selected
poly(amidoamine) (PAMAM), poly(propyleneimine) (PPI) dendrimers
suitable in embodiments herein described. Panel A shows a fourth
generation PAMAM dendrimer and Panel B shows a fifth generation PPI
dendrimer.
[0038] FIG. 19 shows a reaction scheme for the synthesis of the
cation-selective macromolecules of FIG. 17 by functionalization of
hyperbranched poly(ethyleneimine) PEI Macromolecules [Ref. 5.16]
suitable in embodiments herein described.
[0039] FIG. 20 shows an example of a cation-selective
bis(methylol)propionic acid (MPA) dendrimer (Panel A) and an
example of its synthesis (Panel B) [Ref. 5.16] suitable in
embodiments herein described.
[0040] FIG. 21 shows a schematic representation of a apparatus,
process and system the preparation of ion-absorbing hollow fibers
by Electrospinning [Ref. 5.19].
[0041] FIG. 22 shows a schematic of a commercial thin film
composite (TFC) nanofiltration membrane [Ref. 6.7] suitable to be
used in connection with membranes, and systems herein
described.
[0042] FIG. 23 shows a depiction of the exemplary nanofibrous
composite (NFC) membranes according to an embodiment herein
described. Panel A shows hollow nanofibers with embedded dendritic
molecules. Panel B shows general schematic depictions of the
dendritic molecules.
[0043] FIG. 24 shows a schematic diagram of the fabrication of
nanofibrous composite (NFC-PVDF-PEI) membranes with PVDF
microporous support, PVDF nanofibrous scaffolds and cross linked
PEI separation layers according to an embodiment herein described.
Panel A shows a schematic example of the electrospinning and
electrospraying of the nanofibers comprising the membrane. Panel B
shows an SEM image of the three layers. Panel C shows the various
chemistries and exemplary structures of the separation layers.
[0044] FIG. 25 shows images of electrospun nanofibers from polymer
solution according to an embodiment herein described. Panel A shows
an SEM image of the electrospun nanofibers from a polymer solution
dissolved in DMF solvent. Panel B shows and SEM image of the
electrospun nanofiber from polymer solution NMP/DMF mixed
solvent.
[0045] FIG. 26 shows SEM images of the surfaces and cross-section
morphologies of composite materials and membranes according to an
embodiment herein described. Panel A (surface) and Panel B
(cross-section) show SEM images of an NFC-PVDF-PEI-1 membrane cross
linked with trimesoyl chloride. Panel C (surface) and Panel D
(cross-section) show SEM images of NFC-PVDF-PEI-2 membrane cross
linked with 1,3-dibromopropane. Panel E (surface) and Panel F
(cross-section) show SEM images of NFC-PVDF-PEI-3 cross linked with
epichlorohydrin. The length of the scale bar is equal=5 .mu.m.
[0046] FIG. 27 shows FTIR-ATR spectra of microporous supports
according to an embodiment herein described. Panel A shows a
spectrum of a PVDF microporous support. Panel B shows a spectrum a
PVDF+PEI nanofibrous scaffold. Panel C shows a spectrum
NFC-PVDF-PEI-1 membrane cross linked with trimesoyl chloride. Panel
D shows a spectrum NFC-PVDF-PEI-2 membrane cross linked with
1,3-dibromopropane. Panel E shows a spectrum NFC-PVDF-PEI-3
membrane cross linked with epichlorohydrin.
[0047] FIG. 28 shows zeta potentials of NFC-PVDF-PEI membranes
according to an embodiment herein described in aqueous solutions as
a function pH.
[0048] FIG. 29 shows a graph of a salt rejection and permeate flux
of NFC-PVDF-PEI-1 at pH 4, 6 and 8 as a function of time. Panels
A-C shows salt rejection at pH 4-8 and Panels D-F show permeat flux
at pH 4-8.
[0049] FIG. 30 shows a diagram illustrating salt rejection and
permeate flux of a NFC-PVDF-PEI-1 membrane as a function of pH
according to an embodiment herein described.
[0050] FIG. 31 shows the distribution of desalination production
capacity by process technology in the word and various regions of
the world where membranes and systems herein described can find
application, where MSF is multi-stage flash distillation, MED is
multi-effect distillation, VCD is vapor composition distillation,
RO is osmosis, NF is nanofiltration, and ED is electrodialysis.
Panel A shows the distribution of desalination production capacity
by process technology for the world in 2005. Panel B shows the
distribution of desalination production capacity by process
technology for the United States in 2005. Panel C shows the
distribution of desalination production capacity by process
technology for the Middle East in 2005 [Ref. 8.4].
[0051] FIG. 32 shows a schematic diagram of membrane filtration
processes [Ref. 8.14].
[0052] FIG. 33 shows several types of membrane filtration processes
[Ref. 8.14].
[0053] FIG. 34 shows schematic pictures of a commercial PA TFC
membrane suitable in filtration methods and systems according to
embodiments herein described.
[0054] FIG. 35 shows separation capabilities of pressure-driven
membrane separation processes [8.7].
[0055] FIG. 36 shows a schematic picture of electrospinning
procedure [Ref. 8.17] suitable in the preparation of fibers,
composites and membranes according to an embodiment herein
described.
[0056] FIG. 37 shows a SEM image of electrospun polystyrene (PS)
nanofibrous membrane.
[0057] FIG. 38 shows representative monomers for interfacial
polymerization in a reverse osmosis membrane
[0058] FIG. 39 shows a schematic depiction of an interfacial
polymerization reaction. TMC is trimesoyl chloride and MPD is
m-phenylenediamine
[0059] FIG. 40 shows a schematic depiction of the Donnan
equilibrium at the initial stage.
[0060] FIG. 41 shows a schematic depiction of the Donnan
equilibrium at equilibrium.
[0061] FIG. 42 shows a schematic depiction of the Donnan
equilibrium under an initial condition.
[0062] FIG. 43 shows a schematic depiction of the Donnan
equilibrium at equilibrium.
[0063] FIG. 44 shows the structure of hyperbranched
polyethyleneimine (PEI). Panel A shows the monomer subunits of and
exemplary PEI molecule. Panel B is a schematic depiction of an
exemplary hyperbranched PEI molecule.
[0064] FIG. 45 shows configuration of an exemplary membrane. Panel
A is a schematic depiction of the membrane and Panel B is the
description of the composition of the layers.
[0065] FIG. 46 shows an SEM picture of the PET paper of an
exemplary membrane as depicted in FIG. 45 at low magnification.
[0066] FIG. 47 shows an SEM image of the PET paper of an exemplary
membrane as depicted in FIG. 45 at high magnification.
[0067] FIG. 48 shows SEM images of electrospun PAN nanofibers from
FIG. 45 at different magnifications. Panel A shows images 20 .mu.m
scale. Panel B shows images at 5 .mu.m scale. Panel C shows images
at 2 .mu.m scale. Panel D shows images at 500 nm scale.
[0068] FIG. 49 shows SEM images of interfacial polymerized top PEI
thin layers (Cross-section views) from an exemplary membrane as
depicted in FIG. 45 according to an embodiment herein described.
Panels A-D show images of a cross-linked PEI coating on a layer of
PAN nano and microfibers.
[0069] FIG. 50 shows SEM images of interfacial polymerized PEI thin
layers from an exemplary membrane as depicted in FIG. 45. Panels
A-B show, according to an embodiment herein described, show images
a top view of a cross-linked PEI coating on a layer of PAN nano and
microfibers.
[0070] FIG. 51 shows a permeable flux of an exemplary membrane as
depicted in FIG. 45 according to an embodiment herein
described.
[0071] FIG. 52 shows a ion rejection trends of an exemplary
membrane as depicted in FIG. 45 according to an embodiment herein
described.
[0072] FIG. 53 shows a schematic (top panel, left) of an
electrospinning apparatus according to some embodiments and five
SEM images of nanofibers at various stages of the methods for
preparing Ion-Selective filtration membranes by electrospinning
using PET, PVDF and hyperbranched PEI macromolecules and
nanoparticles as building blocks according to embodiments herein
described. In particular, the SEM images are taken of PVDF
nanofibers (top panel, middle), composite PVDF+PEI nanofibers (top
panel, right), PET support paper (bottom panel, left), composite
PVDF+HBPEI+PEI NP nanofibers casted onto a PET support, and
cross-linked PVDF+HBPEI+PEI NP nanofibers casted onto a PET
support.
[0073] FIG. 54 shows a schematic flow diagram of various steps
according to some methods herein described. Route-(A) schematically
illustrates a first method according to some embodiments herein
described. The method comprises depositing PEI macromolecules and
nanoparticles on filtration membrane surfaces. Route-(B)
schematically illustrates a second method according to some
embodiments herein described. The method comprises covalently
attaching PEI macromolecules and nanoparticles on filtration
membrane surfaces.
[0074] FIG. 55 shows a schematic illustrating components a film
assembled by a layer-by-layer (LBL) assembly of PEI macromolecules
or nanoparticles according to embodiments of the present
disclosure. In this schematic, the method by which the
layer-by-layer assembly was performed was mediated by a deposition
of poly(methyl methacrylate) [PMMA] followed by thermal amidation
at 110.degree. C. (for 10 hours under nitrogen) to produce films of
cross-linked PVDF nanofibers with high density of reactive amine
groups of the surface of the NF membranes.
[0075] FIG. 56 shows a schematic diagram illustrating various
functionalizations of NFC Membranes according to some embodiments,
including sulfonation, carboxylation, quaternization, and
amidation. As shown here, amine groups of the PEI films of the
filtration membranes can be reacted with functional groups to
produce films with high density of charged groups including
quaternary amines, carboxylic, sulfonate and amide groups to
increase their charge density.
[0076] FIG. 57 shows SEM images of a PAN nanofibrous mid layer of
an HPEI-filtration membrane at two different magnification levels
showing that the average diameter of each PAN fiber in this
example, is approximately 250 nm.
[0077] FIG. 58 shows a SEM image of an interfacial polymerized top
layer (left) and a SEM image of an HPEI top layer of an
HPEI-filtration membrane (right) which show that micro-sized pores
from PAN nanofibrous layers were fully covered by the HPEI-TMC
cross-linked layer by interfacial polymerization in this example.
FIG. 58 also indicates that the concentration of cross-linkers and
reaction time can affect surface morphology in the nano-scale.
[0078] FIG. 59 shows a graph which is a typical graph for pure
water flux versus time (0.05 wt % TMC, 45 s) which can be due to
compaction of HPEI-TMC cross-linked layer by hydraulic pressure.
Stable data of pure water can be obtained after at least 3 hr of
filtration time.
[0079] FIG. 60 shows a plot of TMC concentration versus ion
rejection (around pH 6, no acid or base added) and a corresponding
data table. The plot shows increasing values of ion rejection by
using more TMC due to formation of a dense top layer.
[0080] FIG. 61 shows a plot of ion rejection versus time (saturated
TMC condition, 1 wt %), pH 4, which shows that in this embodiment,
the best performance of the membrane can be obtained at saturated
TMC condition in a short time and that there was not much
difference in the rejection of MgCl.sub.2 and NaCl between 20
seconds reaction time and 10 seconds reaction time.
[0081] FIG. 62 shows a table of X-ray photoelectron spectroscopy
data for characterization of NFC-PAN-PEI-TMC membranes. The data
shows that the nitrogen ratio of the surface was increased with
increasing TMC concentration. The data also shows that the more
cross-linker that is used, the more dense the HPEI layer, at least
in embodiments where interfacial polymerization and highly reactive
cross-linkers are used.
[0082] FIG. 63 shows ATR FT-IR spectrum of PAN support layer with
no active layer. The ATR FT-IR spectrum shows a nitrile group at
2243 cm.sup.-1 and no characteristic bands of amide groups.
[0083] FIG. 64 shows the ATR FT-IR spectrum of HPEI-filtration
membrane, HPEI 10 wt %, 0.05 wt %, 45 s. The ATR FT-IR spectrum
shows characteristic bands of amide groups at 1642 cm.sup.-1
(C.dbd.O stretch), 1560 cm.sup.-1 (N--H stretch).
[0084] FIG. 65 shows the ATR FT-IR spectrum of HPEI-filtration
membrane, HPEI 10 wt %, 2.0 wt %, 45 s at an increased TMC
concentration compared to FIG. 64. The ATR FT-IR spectrum shows
characteristic bands of amide groups at 1642 cm.sup.-1 (C.dbd.O
stretch), 1560 cm.sup.-1 (N--H stretch).
[0085] FIG. 66 shows a schematic showing the synthesis of
hyperbranched PEI nanoparticles using inverse miniemulsion. Panel A
shows the reaction scheme for the formation of hyperbranched PEI
nano/microparticles from hyperbranched PEI macromolecules. Panel B
shows a schematic depiction of the inverse miniemulsion
process.
[0086] FIG. 67 shows a plot indicating a size distribution by
dynamic light scattering of PEI nano/microparticles produced by
inverse miniemulsion.
[0087] FIG. 68 shows a schematic showing a general reaction scheme
of the synthesis of quaternized PEI nano/microparticles.
[0088] FIG. 69 shows a schematic showing general reaction schemes
of the synthesis of boron-selective PEI nano/microparticles. Panel
A shows base PEI beads. Panel B shows Functionalization of Base PEI
Beads with glucono-1,5-D-lactone
[0089] FIG. 70 shows a schematic showing exemplary
cationic-selective PEI nano/microparticles.
[0090] FIG. 71 shows a schematic representation of generation of
metallic clusters/nanoparticles inside NFC-PET-PVDF-PEI membranes
by complexation/encapsulation of target metal ions followed by
reaction with reducing agents (e.g. H.sub.2). Panel A shows a
schematic representation of complexation and/or encapsulation of
target metal ions including, for example, palladium (II) ions.
Panel B shows a schematic representation of the reduction of the
metal ions, for example, the reduction of palladium (II) to
catalytically active palladium (0).
DETAILED DESCRIPTION
[0091] Provided herein are membranes and related nano- or
micro-fiber, composite material, methods and systems that allow in
several embodiment to perform selective filtration of a liquid and
in particular of water.
[0092] The term "filtration" as used herein refers to the
mechanical or physical operation which can be used for separating
components of a homogeneous or heterogeneous solutions. Types of
filtration can be classified by the approximate sizes of chemicals
to be separated and can include particle filtration, or PF (>10
.mu.m); microfiltration, or MF (0.1-10 .mu.m); ultrafiltration, or
UF (0.01-0.1 .mu.m); nanofiltration, or NF (0.001-0.01 .mu.m); and
reverse osmosis, or RO (<0.001 .mu.m).
[0093] The term "chemicals" as used herein indicates a substance
with a distinct composition that is produced by or used in a
chemical process. Exemplary chemicals comprise particles,
molecules, metals, ions, organic compounds, inorganic compounds and
mixture thereof as well as any additional substance detectable
through chemical means identifiable by a skilled person. In
particular, in some embodiments, the chemicals can comprise solutes
dissolved in a fluid (e.g. water), and in particular dissolved
ions.
[0094] The term "membrane" as used herein refers to a porous
structure that is capable of separating components of a homogeneous
or heterogeneous fluid. In particular, "pores" in the sense of the
present disclosure indicate voids allowing fluid communication
between different sides of the structure. More particular in use
when a homogeneous or heterogeneous fluid is passed through the
membrane, some components of the fluid can pass through the pores
of the membrane into a "permeate stream", some components of the
fluid can be retained by the membrane and can thus accumulate in a
"retentate" and/or some components of the fluid can be rejected by
the membrane into a "rejection stream". Membranes can be of various
thickness, with homogeneous or heterogeneous structure. Membranes
can be comprised within, for example, flat sheets or bundles of
hollow fibers. Membranes can also be in various configurations,
including but not limited to spiral wound, tubular, hollow fiber,
and other configurations identifiable to a skilled person upon a
reading of the present disclosure (see, for example the web page
kochmembrane.com/Learning-Center/Configurations.aspx). Membrane can
also be classified according to their pore diameter. According to
IUPAC, there are three different types of pore size
classifications: microporous (dp<2 nm), mesoporous (2
nm<dp<50 nm) and macroporous (dp>50 nm). Membranes can be
neutral or charged, and particles transport can be active or
passive. The latter can be facilitated by pressure, concentration,
chemical or electrical gradients of the membrane process.
[0095] The term "fiber" as used herein indicate a material that is
a continuous filament or is in a discrete elongated piece, similar
to a length of thread. In particular, "nanofiber" as used herein
refer to fibers with a diameter less than approximately 1000 nm and
the term"microfiber" as used herein refer to fibers with a diameter
between approximately 1 .mu.m to approximately 10 .mu.m in size.
More particularly, nanofibers and microfibers in the sense of the
present disclosure comprise a scaffold component providing a
supporting framework for one or more additional components attached
to the scaffold providing functionalities to the scaffold. The
scaffold component and the additional components define features of
the nanofiber and microfiber such as a diameter (or radius), a
mechanical strength, chemical stability, functionalization and
chemical properties which are detectable using techniques and
process identifiable by a skilled person. The features of
nanofibers and microfibers in the sense of the present disclosure
which can also be controlled by modifying the chemical composition
and structure of the fiber during manufacturing of the fiber
according to techniques identifiable by a skilled person upon
reading of the present disclosure.
[0096] In several embodiments, a filtration membrane herein
described comprises a plurality of nano and/or micro fibers, each
having a polymer component providing the fiber scaffold and a
dendrimer component presenting reactive sites on the fiber scaffold
the reactive site selective for a chemical.
[0097] The term "polymeric component" as used herein refers to a
linear polymer comprising repeating structural unit forming long
chains without branches or cross-linked structures. In some
instances molecular chains of a linear polymer can be intertwined,
but in absence of modification or functionalization the forces
holding the polymer together are physical rather than chemical and
thus can be weakened by energy applied in the form of heat. In
particular, polymers forming the polymeric component in the sense
of the disclosure comprise substituted or unsubstituted aliphatic
polymer, a substituted or unsubstituted unsaturated polymer and a
substituted or unsubstituted aromatic polymer identifiable by a
skilled person.
[0098] The term "dendritic component" as used herein refers to a
highly branched dendritic macromolecule or dendritic nanomaterial.
The term "highly branched dendritic macromolecule" as used herein
indicates a macromolecule whose structure is characterized by a
high degree of branching that originates from a central core
region. Exemplary highly branched dendritic macromolecules comprise
dendrimers, hyperbranched polymers, dendrigraft polymers,
dendronized linear polymers, tecto-dendrimers, core-shell (tecto)
dendrimers, hybrid linear-dendritic copolymers, dendronized
polymers and additional molecule identifiable by a skilled person
(see e.g. US 2006/0021938, US 2008/0185341, US 2009/0001802, US
2010/0181257, US 2011/0315636, and US 2012/0035332 each
incorporated by reference in its entirety, also describing method
of making highly branched dendritic macromolecules).
[0099] The term "dendritic nanomaterial" refers to highly branched
dendritic macromolecules linked in aggregate nanostructures and/or
microstructure with a controlled composition, architecture, and/or
size. Exemplary dendritic nanomaterials can include, for example,
any highly branched dendritic macromolecules or mixtures thereof,
in dendrimer-based supramolecular assemblies, 3-D globular
nanoparticles or dendritic nano/microparticles identifiable by a
skilled person (see, for example, US 2006/0021938, US 2008/0185341,
US 2009/0001802, US 2010/0181257, US 2011/0315636, and US
2012/0035332 each incorporated by reference in its entirety).
[0100] In embodiments herein described, the polymer forming the
polymer component has a functional group capable of interacting
with a corresponding functional group on the dendrimer
[0101] The term "functional group" as used herein indicates
specific groups of atoms within a molecular structure that are
responsible for the characteristic chemical reactions of that
structure. Exemplary functional groups include hydrocarbons, groups
containing halogen, groups containing oxygen, groups containing
nitrogen and groups containing phosphorus and sulfur all
identifiable by a skilled person. In particular, functional groups
in the sense of the present disclosure include a carboxylic acid,
amine, triarylphosphine, azide, acetylene, sulfonyl azide, thio
acid and aldehyde. In particular, for example, the first functional
group and the second functional group can be selected to comprise
the following binding partners: carboxylic acid group and amine
group, azide and acetylene groups, azide and triarylphosphine
group, sulfonyl azide and thio acid, and aldehyde and primary
amine. Additional functional groups can be identified by a skilled
person upon reading of the present disclosure. As used herein, the
term "corresponding functional group" refers to a functional group
that can react with another functional group. Thus, functional
groups that can react with each other can be referred to as
corresponding functional groups. In embodiments where the
corresponding functional groups are in the polymer component and in
the dendrimer component the corresponding functional group react to
form a covalent bond, a hydrogen bond or other bond functional to
the attachment of the polymer component and the dendrimer component
identifiable by a skilled person upon reading of the present
disclosure.
[0102] The term "attach" or "attachment" as used herein, refers to
connecting or uniting by a bond, link, force or tie in order to
keep two or more components together, which encompasses either
direct or indirect attachment such that, for example, a first
compound is directly bound to a second compound or material, and
the embodiments wherein one or more intermediate compounds, and in
particular molecules, are disposed between the first compound and
the second compound or material. In particular, in some
embodiments, the dendritic component can be associated with the
polymeric component by, for example, by being physically embedded
in the polymeric component, by being covalently bonded to the
polymeric component, or through a combination of both.
[0103] In some embodiments, the polymer component comprise a
polymer having a formula
##STR00001##
wherein:
[0104] Q, Y, and Z comprise saturated aliphatic hydrocarbon,
aromatic hydrocarbon, or unsaturated aliphatic hydrocarbons;
[0105] m, l, and k independently are integers ranging between
0-50;
[0106] at least one of m, l, k is not equal to zero;
[0107] j is an integer ranging between 50-500; and
[0108] at least one of Q (when Q.noteq.0), Y (when Y.noteq.0), or Z
(when Z.noteq.0), comprises the polymer component functional
group.
[0109] The term "saturated aliphatic hydrocarbon" as used herein
refers to a hydrocarbon comprising, carbon atoms that are joined
together in straight chains, branched chains, or non-aromatic rings
in which the carbon-carbon bonds are saturated with hydrogen (e.g.
methane, ethane, propane, isobutane, and butane). For example, in
saturated aliphatic hydrocarbons have a general formula of
C.sub.nH.sub.2n+2 for acyclic saturated aliphatic hydrocarbons and
C.sub.nH.sub.2n cyclic saturated aliphatic hydrocarbons. Saturated
aliphatic hydrocarbon can be substituted with one or other
elements, for example, N, O, S, P, F, Cl, Br, and I.
[0110] The term "aromatic hydrocarbon" as used herein refers to a
hydrocarbon comprising a conjugated ring of unsaturated bonds, lone
pairs, and/or empty orbitals which can exhibit a stabilization
stronger than expected by the stabilization by conjugation alone.
An exemplary aromatic compounds is benzene which is a six-membered
ring having alternating double and single bonds between carbon
atoms. Aromatic hydrocarbons can be monocyclic (MAH) (e.g. benzene)
or polycyclic (PAH) (e.g. naphthalene, anthracene, pyrene).
Aromatic hydrocarbons can be substituted with one or other
elements, for example, N, O, S, P, F, Cl, Br, and I.
[0111] The term "unsaturated aliphatic hydrocarbon" as used herein
refers to a hydrocarbon comprising carbon atoms that are joined
together in straight chains, branched chains, or non-aromatic rings
and comprise at least one of a double or a triple bond between
adjacent carbon atoms, referred to as "alkenes" and "alkynes",
respectively. An unsaturated hydrocarbon can comprise one or more
of double or triple bonds. In hydrocarbons having more than one
double or triple bond, the unsaturated hydrocarbon can be
conjugated (e.g. 1,4-hexadiene) or can be isolated (e.g.
1,5-hexadiene). In hydrocarbons comprising internal alkenes, the
alkenes can be in a "cis" or a "trans" configuration (e.g.
trans-2-butene or cis-2-butene). Unsaturated aliphatic hydrocarbon
can be substituted with one or other elements, for example, N, O,
S, P, F, Cl, Br, and I.
[0112] In particular in some embodiments, Q, Y, and Z in formula
(I) can independently selected from the following formulas:
##STR00002##
wherein:
[0113] n=0 or 1;
[0114] m is an integer ranging from 0-15;
[0115] X is a functional group comprising an atom selected from O,
S, N, P, or F; and
[0116] R.sub.1-R.sub.18 are independently selected from: the
polymer component functional group; hydrogen; C.sub.1-C.sub.20
linear, branched, saturated, unsaturated, or aryl hydrocarbon which
are either substituted or unsubstituted with O, N, B, S, P; or
substituted O, N, B, S, or P;
[0117] and at least one of R.sub.1-R.sub.18 is the polymer
component functional group attaching the dendrimer component.
[0118] Exemplary polymer materials for polymeric components herein
described comprise polysulfone (PS), polyether sulfone (PES),
poly(vinylidene)fluoride (PVDF), poly(tetrafluoroethylene) (PTFE),
poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA),
poly(methacrylic acid) (PMAA), poly(acrylic acid) (PAA), poly(vinyl
methyl ketone), and poly(ethylene terephthalate) (PET) (see
Examples 1 to 4 and 27). Additional polymers suitable as a polymer
component herein described comprise polymers which can be used as
base polymers in the fabrication of commercial hollow-fiber UF/MF
membranes, polymer which is either partially soluble or can be
dispersed in solvents with different physicochemical properties
together with functionalized anion-selective HPB macromolecules and
nanoparticles according to the disclosure, and polymers which can
be functionalized, which are identifiable by a skilled person upon
reading of the present disclosure.
[0119] Suitable dendrimer components can be selected for a given
polymer component based on compatibility which can be determined
based on the presence of corresponding functional group capable of
attachment as well as possibly other features such as solubility of
the dendritic component together with the polymeric component in a
particular solvent or mixture of solvents, affinity of the
dendritic component for polymeric component, and/or stability of
the dendritic component in a solvent to be used in the fabrication
of the fiber.
[0120] In some embodiments, the dendritic components according to
some embodiments have the general formula (XII)
##STR00003##
wherein: n and m are integers ranging from 2-5; R.sup.1-R.sup.8 are
independently selected from hydrogen or hyperbranched polymer
moieties;
X.sup.1 and X.sup.2 are N; and
[0121] X.sup.4-X.sup.5 are selected from amine, amide, imide, and
carbamate.
[0122] In particular, in some embodiments, the dendritic components
according to some embodiments have the general formulas XIII and
XIV below:
##STR00004##
wherein n and m are integers from 2-5, and wherein R.sub.1-R.sub.4
can be independently hydrogen or hyperbranched polymer moieties
including, but not limited to, polyethyleneimine (PEI) and
derivatives thereof.
[0123] In some embodiments, the dendritic component comprises a
core, a plurality of arms extending from the core, the arms having
a hyperbranched structure, and within the hyperbranched structure,
a plurality of units satisfying having the formula:
##STR00005##
where R.sup.1 comprises no nitrogen atoms that are simultaneously
bound to two or more carbon atoms, for example, secondary and
tertiary amines or amides.
[0124] In some embodiments the dendritic component comprises the
formula:
##STR00006##
where n is an integer ranging from 2-5, each of Q.sub.1 and Q.sub.2
comprises hyperbranched polymer moiety, and R is selected from
hydrogen, an alkyl group, or a 2-hydroxyalkyl group.
[0125] In particular, in some embodiments, when groups
R.sup.1-R.sup.8 and Q of formulas XII-XV comprise hyperbranched
polymer moieties with amino and/or alcohol groups, the molecules
can be converted to nano/microparticles by cross linking the
molecules with cross-linking reagents described herein (e.g.
1,3-dibromopropane or epichlorohydrin) using inverse micelles as
described herein (see e.g. Example 33).
[0126] In particular, in some embodiments, the dendritic component
can comprise various monodisperse generations of poly(amidoamine)
(PAMAM) dendrimers (for example, G3, G4, or G5 PAMAM) or micro
and/or nano aggregates thereof; monodisperse generations of
poly(propyleneimine) (PPI) (for example, G3, G4, or G5 PPI) or
micro and/or nano aggregates thereof; monodisperse generations of
poly(bis(methylol)propionic acid) (MPA) (for example, G3, G4, or G5
MPA) or micro and/or nano aggregates thereof; or monodisperse
generations of poly(ethyleneimine) (PEI) (for example, G3, G4, or
G5 PEI) or micro and/or nano aggregates thereof. In other
embodiments, the dendritic component can be polydisperse
hyperbranched PEI. Hyperbranched PEI can be prepared, for example,
by ring opening polymerization of aziridine also known as ethylene
imine. Additional dendritic components can be selected, for
example, based on compatibility with a polymeric component as
described herein.
[0127] Suitable polymer components can be selected for a given
dendrimer component based on compatibility which can be determined
based on the presence of corresponding functional group capable of
attachment as well as possibly other features such as solubility of
the polymer component together with the dendrimer component in a
particular solvent or mixture of solvents, affinity of the polymer
component for the dendrimer component, and/or stability of the
polymer component in a solvent to be used in the fabrication of the
fiber.
[0128] A method of identifying a compatible polymeric component
according to some embodiments, comprises selecting a dendritic
component to be used for fabricating a membrane; selecting a
polymeric component to be used for fabricating the membrane based
on the compatibility between dendrimer component and polymer
component; selecting a solvent or mixture of solvents; combining
the dendritic component, polymeric component, and solvent or
mixture of solvents and making a multilayer membrane according to
embodiments herein described; and determining whether or not the
layer of the multilayer membrane can be delaminated or peeled away,
under a desired force or pressure applied. If a layer is not able
to be delaminated following application of the force then the
polymeric component can be considered to be compatible. If the
layer is able to be delaminated under the desired force or pressure
then the polymeric component can be considered as being not
compatible.
[0129] In filtration membranes herein described, dendrimer
component is attached to the polymer component typically through a
covalent and/or a hydrogen bond. For example, in some embodiments,
when the polymeric components of formulas I-XI comprise fluorine
and/or carbonyl groups, dendritic components of formulas XII-XV
comprising amino groups can attach to the polymeric component
through hydrogen bonds from the amino hydrogen atoms to the
fluorine or carbonyl oxygen atoms. In other embodiments, when the
polymeric components comprise carboxylic acid groups, dendritic
components comprising amino groups can attach to the polymeric
component through formation of covalent amide bonds.
[0130] In particular in embodiments of the filtration membrane
herein described the dendrimer component is attached to the polymer
component to present reactive sites on the fiber scaffold.
[0131] The term "present" as used herein with reference to a
compound or functional group indicates attachment performed to
maintain the chemical reactivity of the compound or functional
group as attached. Accordingly, a functional group presented on a
surface, is able to perform under the appropriate conditions the
one or more chemical reactions that chemically characterize the
functional group.
[0132] The term "reactive site" as used herein refers to a chemical
functional group capable of attracting, rejecting, and/or binding
to a chemical of interest. In particular, reactive sites herein
described are able to attract, reject or bind selectively a
chemical to be filtered. Exemplary functional groups suitable as
reactive sites include, but are not limited to, amines, quaternary
ammonium groups, amides, hydroxyl groups, ethers, carboxylates,
esters, sulfonates, sulfiniates, sulfonate esters, sulfinate
esters, sulfonamides, sulfonamides, phosphates, carbamates, ureas,
imidines, guanidines, oximes, imidazoles, pyridines, thiols,
thioethers, thiocarboxylates, and phosphines.
[0133] In particular, in some embodiments, the reactive site can be
located on the dendritic component (for example, amino groups on
PEI) without any chemical transformation being necessary. In other
embodiments, one or more reactive sites can be introduced into the
dendritic component after a chemical transformation. Exemplary
chemical transformations suitable for the introduction of a
reactive site comprise reductive amination of amine groups to form
alkylated amino groups, alkylation of amines to form quaternary
ammonium groups, alkylation of hydroxyl groups to form ethers,
reaction of amines or hydroxyls with haloalkyl carboxylic acids
and/or derivatives (such as, for example, 2-chloroacetic acid or
methyl 2-chloroacetate) to form carboxylic acids and/or
derivatives, reaction of amines or hydroxyls with haloalkyl
sulfonic acids and/or derivatives (such as, for example,
2-(chloromethyl)sulfonic acid or methyl 2-(chloromethyl)sulfonate)
to form sulfonic acids and/or derivatives, and reaction of amines
with epoxides to form alcohols. Other transformations are
identifiable to a skilled person upon a reading of the present
disclosure (see, for example, US 2010/0181257 and US 2011/0315636
each incorporated by reference in its entirety). In some
embodiments, the chemical transformation of the reactive site on
the dendritic component can be performed before the dendritic
component is associated with the polymeric component as herein
described. In other embodiments, the chemical transformation of the
reactive site on the dendritic component can be performed after the
dendritic component is associated with the polymeric component as
herein described.
[0134] In embodiments herein described of filtration membrane
herein described the reactive site can be selected and configured
on the fiber scaffold to provide selective filtration of one or
more chemicals of interest. In particular, in some embodiments, the
reactive site can be selected to separate the one or more chemicals
of interest in the rejection stream, permeate stream and/or
retentate of the membrane. In particular, the dimension, chemical
nature, and electrical charge of the reactive site as well as the
location on the dendrimer component can be selected based on the
dimensions, chemical nature and electrical charge of the chemical
to be selectively filtered.
[0135] For example in embodiments wherein selective filtration is
desired to include anions in rejection stream and 2 s metal ions
cations such as Ca.sup.2+ and Mg.sup.2+ in the retentate of the
membrane, reactive sites having negatively charged 0 donors [Ref.
5.17] can be presented on the dendrimer component of the membrane.
As another example, dendritic components having neutral oxygen
donors can be used to coordinate selective retention of 1 s metal
ions such as Na.sup.+ [Ref. 5.17]. As another example, dendritic
components having positively charged nitrogen atoms (e.g.
quaternary ammonium groups) can be used to selectively reject
cations. As another example, dendritic components comprising
vicinal diol groups can be used to coordinate selective retention
of boron (see e.g. Examples 31 and 35)
[0136] In some embodiment, reactive sites retaining one or more
chemical of interest can then be subjected to further reactions to
selectively release some or all of the chemicals forming the
retentate in a permeate stream, and/or to further modify the
retentate as will be understood by a skilled person upon reading of
the present disclosure.
[0137] In particular, membranes herein described including a
suitable retentate can be treated to convert the retentate into a
catalyst thus forming a catalytic membrane. For example, in some
embodiments, a retentate form by metals can be treated with
suitable active agents to change the oxidation state and/or
ligation state to convert the metal to a catalytically active form.
For example, in an embodiment dendritic components having groups
capable of retention of palladium (e.g. amines and phosphines) can
be subjected to reduction (e.g. H.sub.2 or other reducing agents)
to reduce the Pd atoms to produce catalytically active Pd(0) sites.
Additional suitable metals or other materials suitable for
preparation of catalytic membrane and related activating agents
and/or suitable treatments will be identifiable by a skilled
person.
[0138] In some embodiments, the retentate can be subjected to a
selective release before or after an additional treatment. For
example dendritic components having negatively charged 0 donors and
tertiary amine groups can be used to selectively bind Ca.sup.2+ and
Mg.sup.2+ ions at pH .about.7.0, and the ions can later be released
from the dendritic component by washing the dendritic component
with an acidic solution containing a small ligand such as citric
acid.
[0139] In filtration membrane herein described microfiber and/or
nanofiber herein described can be comprised as a composite material
layer having a mesh structure comprised in the filtration membrane
alone or in combination with one or more additional layers.
[0140] The term "composite material" as used herein refers to a
heterogeneous material made from two or more different materials,
the materials having different chemical and/or physical properties
and remaining as separate and distinct materials within the
composite material. For example, according to embodiments herein
described, a composite material can comprise a polymer component
and a dendritic component which is structurally different from the
polymer component. As another example, a composite material can
comprise a dendritic component wherein a portion of the dendritic
component is cross linked through a cross linking agent as
described here, thus providing a material having one or more cross
linked portions and one or more non-cross linked portions. The
composite material according to some embodiments can comprise a
semi-permeable barrier made of overlapping strands of
nanofibers.
[0141] In particular, the composite material comprising a plurality
of nanofibers or microfibers can comprise a plurality of a same
type of fiber or of two or more different types of fibers. In some
embodiments, fibers can be covalently cross-linked to one another.
In some embodiments, nanofibers or microfibers comprised in the
composite material comprise hollow fibers herein described.
[0142] The features of the mesh such as dimension of the pores of
the mesh structure, the strength and resistance of the mesh and
chemical compatibility of the mesh can be controlled by selection
of the diameter of the nanofiber or microfiber, number and
configuration of the nanofiber and/or microfiber forming the mesh
and the specific polymer component and dendrimer component of each
fiber as will be understood by a skilled person upon reading of the
present disclosure.
[0143] In some embodiments, filtration membranes herein described
comprise one or more composite material layers herein described
alone with no additional layer. In some embodiments, the filtration
membrane further comprise one or more support layer and/or one or
more coating layers
[0144] A "support layer" in the sense of the present disclosure is
an aggregate material comprising a polymer component configured to
strengthen the membrane structure. Suitable polymers to be included
in support layers comprise, for example, poly(vinylidene)fluoride
(PVDF), poly(tetrafluoroethylene) (PTFE), poly(acrylonitrile)
(PAN), poly(methyl methacrylate) (PMMA), poly(methacrylic acid)
(PMAA), poly(acrylic acid) (PAA), poly(vinyl methyl ketone), and
poly(ethylene terephthalate) (PET) which can be aggregated by
inverse casting the polymer or by electrospinning. In some
embodiments the support layer includes pores. In some embodiments,
the support layer can be functionalized with a dendrimer component.
For example, in some embodiments, the dendrimer component can be
mixed with a suitable polymer component and electrospun onto a
provided support layer (see e.g. Examples 20-21). In other
embodiments, after a mixture of dendritic component and polymeric
component is electrospun onto a support layer, a further support
layer can be electrospun to provide a top support layer for
providing additional strength or for creating a bipolar
membrane.
[0145] A "coating layer" in the sense of the present disclosure
indicates an aggregate of a dendrimer component configured to
provide a selective filtration of one or more chemicals. Suitable
dendrimer components to be included in a coating layer comprise
monodisperse generations poly(amidoamine) (PAMAM) dendrimers (for
example, G3, G4, or G5 PAMAM) or micro and/or nano aggregates
thereof; monodisperse generations of poly(propyleneimine) (PPI)
(for example, G3, G4, or G5 PPI) or micro and/or nano aggregates
thereof; monodisperse generations of poly(bis(methylol)propionic
acid) (MPA) (for example, G3, G4, or G5 MPA) or micro and/or nano
aggregates thereof; or monodisperse generations of
poly(ethyleneimine) (PEI) (for example, G3, G4, or G5 PEI) or micro
and/or nano aggregates thereof. which can be aggregated by
crosslinking, for example by interfacial polymerization with a
cross linker (e.g. trimesoyl chloride or 1,3-dibromopropane) as
described herein (see, e.g. Examples 20-22)
[0146] In some embodiments, the additional layers can further
comprise a scaffold layer comprising nano and/or microfibers
including a polymer component and no dendrimer. The term "scaffold
layer" refers to a layer of nano and/or microfibers that can
comprise only the polymeric component as herein described, or the
polymeric component and dendritic component as herein describe,
that can serve as a scaffold for a coating layer of cross-linked
dendritic component. For example, in some embodiments, a mixture of
polymer component and dendritic component (e.g. PVDF and
hyperbranched PEI) can be electrospun onto a support layer to
provide a scaffold layer upon which a coating layer can be
deposited (see e.g. Example 20). In other embodiments, a layer of
polymer component (e.g. PAN) can be electrospun onto a support
layer to provide a scaffold layer upon which a coating layer can be
deposited (see e.g. Example 21)
[0147] In embodiments wherein filtration membrane herein described
comprise one or more composite material layers and one or more
additional layers, the one or more composite material layers and
the additional layers can be comprised in the filtration membrane
in various configurations as will be understood by a skilled person
upon reading of the present disclosure. For example in some
embodiments one or more composite layers can be comprised between
two functionalized or unfunctionalized supporting layers. In some
embodiments, one or more composite layers can be comprised between
a supporting layer and a coating layer. In some of these
embodiments a functionalized supporting layer can be further
attached to the coating layer. In some embodiments a coating layer
can be comprised between one or more composite layers a
functionalized supporting layer. Additional configurations can be
identified by a skilled person. In particular, selection of a
configuration of the membrane can be performed by a skilled person
in view of the polymer component and dendrimer component forming
the composite material and/or the support layer and/or coating
layer and in view of a desired selection of one or more chemicals
to be filtered. (see e.g. Examples 20-22 and 27)
[0148] In embodiments, where the filtration membrane comprises a
composites material layer with one or more additional layers, the
polymer component and the dendritic component of the one or more
composite material layers and/or of the one or more additional
layer can be either the same or different. In some of these
embodiments, the polymer component can be polysulfone (PS),
polyether sulfone (PES), poly(vinylidene)fluoride (PVDF),
poly(tetrafluoroethylene) (PTFE), poly(acrylonitrile) (PAN),
poly(methyl methacrylate) (PMMA), poly(methacrylic acid) (PMAA),
poly(acrylic acid) (PAA), and/or poly(vinyl methyl ketone). In some
of these embodiments the dendrimer component can be a highly
branched dendritic macromolecule selected from the group consisting
of generation-3 poly(amidoamine) (PAMAM) dendrimer, generation-4
poly(amidoamine) (PAMAM) dendrimer, generation-5 poly(amidoamine)
(PAMAM) dendrimer, generation-3 poly(propyleneimine) (PPI)
dendrimer, generation-4 poly(propyleneimine) (PPI) dendrimer,
generation-5 poly(propyleneimine) (PPI) dendrimer, generation-3
poly(bis(methylol)propionic acid) (MPA) dendrimer, generation-4
poly(bis(methylol)propionic acid) (MPA) dendrimer, generation-5
poly(bis(methylol)propionic acid) (MPA) dendrimer, generation-3
poly(ethyleneimine) dendrimer, generation-4 poly(ethyleneimine)
dendrimer, generation-5 poly(ethyleneimine) dendrimer, and
hyperbranched poly(ethyleneimine), or aggregate nanostructures
and/or microstructure thereof.
[0149] In some embodiments, the filtration membranes comprise a
plurality of hollow nano and/or micro fibers, arranged in a bundle
configuration in which the nano and/or microfibers are
substantially parallel one with another. In particular, in some
embodiments, the nanofibers and/or microfibers can be hollow
nanofibers comprising a lumen up to approximately 10 microns in
diameter. The hollow nanofibers also comprise a polymeric component
providing a fiber scaffold and a dendritic component attached to
the polymeric component to present reactive sites on the fiber
scaffold. In some of those embodiments the dendrimer component can
be attached to the polymer component to present the reactive sites
in the lumen within the fiber and/or in the outside surface of the
fiber (see e.g. Example 3) In some embodiments, hollow fibers
according the present disclosure can be fabricated, for example, by
electrospinning the polymeric component with a bore fluid
comprising the dendritic component, as exemplified in FIG. 4 and
Example 3. In other embodiments, the hollow fibers can be produced
by electrospinning the polymeric component with an inert bore fluid
to provide hollow fibers of polymeric components which then have
dendritic component attached by, for example, interfacial
polymerization as described herein
[0150] In some embodiments, where the filtration membrane herein
described comprises hollow fibers suitable polymer component
comprises PS, PES, PVDF and/or PAN can be suitable polymer
components for filtration membranes according to the present
disclosure, and can configured to have select chemicals selectable
by UF/MF membranes [Ref. 1.8].
[0151] In particular, in some embodiments, the hollow nanofibers
are ion-exchange hollow fibers comprising polymeric nano and/or
micro fibers ranging from approximately 100-500 nm in diameter. In
these embodiments, the fibers can have large charge densities which
can allow for rejection anions and cations, for example, through
the Donnan Effect [Ref. 1.7, 1.15]. In other embodiments the hollow
fibers are ion-absorbing hollow fibers will comprise polymeric nano
and/or micro fibers which can have a large number of binding sites
which in some embodiments can selectively bind and release target
cations and/or anions. Hollow-fiber configurations according to the
present disclosure allow in some embodiments, large fiber packing
density when used in membrane modules Hollow-fiber configurations
according to the present disclosure also allow for low operating
pressure (e.g. between approximately 0.3-2 bars) and pressure drop
(between approximately 0.1-1 bar) across the membrane module. and
in some embodiments allow for backwashing of the fibers with
aqueous solutions (e.g. acidic, basic or brine from membrane
concentrates).
[0152] In particular, in some embodiments, the hollow nanofibers
can be homogeneous anion-exchange hollow fibers or heterogeneous
anion-exchange hollow fibers. The homogeneous anion-selective
fibers according to the disclosure comprise hollow nanofibers with
an embedded anion-selective dendrimer component (See e.g. FIG. 2).
The heterogeneous anion-exchange fibers according to the disclosure
comprise hollow nanofibers with embedded anion-selective polymeric
nanoparticles (NP). In particular, in these hollow fibers the
polymeric components can be, for example, polysulfone (PS),
polyethersulfone (PES), poly(vinylidenefluoride) (PVDF) or
poly(acrylonitrile) (PAN).
[0153] In particular, in some embodiments, the hollow nanofibers
can have a dendrimer component embedded in outer and/or inner
surfaces of the hollow fibers, for example using membrane surface
modification techniques such as UV-induced graft copolymerization
[Ref. 3.23], layer-by-layer assembly [Ref. 3.24-3.25] (followed by
thermal cross-linking), or interfacial polymerization to covalently
attach and/or graft dendrimer components as exemplified in FIG.
11.
[0154] In some embodiments where PES, PVDF and/or PAN are comprised
as a polymer component of nanofiber or microfiber herein described
in any configuration or as a polymer component of a functionalized
support layer, a dendrimer component attached to the polymer
component can comprise functionalized anion-selective HPB
macromolecules and nanoparticles which according to some
embodiments are used in conjunction with the polymeric component
(See, for example, FIG. 2 and FIG. 3 and Examples 1-4) are either
partially soluble (at least approximately 5-10 wt %) or can be
dispersed in solvents with different physicochemical properties
(e.g. boiling point and surface tension) such as tetrahydrofuran
(THF), dimethyl formamide (DMF), and dimethyl acetamide (DMAc)
[Ref. 1.23-1.24].
[0155] In some embodiments where PES, PVDF and/or PAN are comprised
as a polymer component of nanofiber or microfiber herein described
in any configuration or of the polymer component of a
functionalized support layer PET, PVDF, PS and/or PAN can be
further functionalized (e.g. through UV assisted surface grafting)
with various functional groups (e.g. amines and/or carboxylic
acids) which can be subsequently used for example, for covalent
attachment of ion-selective and macromolecules and nanoparticles
[Refs. 9.9-9.10, 9.21-9.22]. The ability to functionalize can allow
a wider variety of chemical structures for which the physical and
chemical properties of the fibers can be varied, for example by
varying spinning conditions
[0156] In some embodiments, the dendritic component of nanofiber or
microfiber herein described in any configuration, of the a
functionalized support layer and/or of the coating layer can be
formed by dendritic nanomaterials according to the present
disclosure that can range from approximately 1-1000 nm in size and
can in some embodiments can selectively encapsulate and release a
broad range of solutes in water including but not limited to
cations (e.g., copper, silver, gold and uranium), anions (e.g.,
chloride, perchlorate and nitrate) and organic compounds (e.g.,
pharmaceuticals) [Ref. 2.5-2.6].
[0157] In particular in some embodiments, the dendritic component
can comprises hyperbranched PEI macromolecules, water-soluble
branched macromolecules with functional N groups including for
example, Gx-NH.sub.2 PPI dendrimers, Gx-NH.sub.2 PAMAM dendrimers,
hyperbranched and dendrigraft lysine macromolecules, Hybrane
hyperbranched polymers can be used as building blocks separation
layers for the filtration membranes disclosed in this disclosure.
Similarly, base polymers such as polysulfone (PS), polyethersulfone
(PES), and/or poly(vinyl) alcohol can be used in making nanofibrous
scaffolds of the filtration membranes described herein.
[0158] In some embodiments, dendritic nanomaterials can be selected
to retain chemicals and to be used as nanoscale reactors and
catalysts [Ref. 2.5-2.6]. In some embodiments, dendritic
nanomaterial can be selected to be selective for cells, or other
biological material (e.g. to reject or retain such material). For
example, in some embodiments, filtration membranes herein described
can be configured to bind bacteria and viruses possibly followed by
a deactivation of the same [Ref. 2.6]. In other embodiments, the
dendritic nanomaterials can be used as scaffolds and templates for
the preparation of metal-bearing nanoparticles with controllable
electronic, optical and catalytic properties [Refs. 9.13-9.14].
Dendritic nanomaterials can also be used as delivery vehicles or
scaffolds, for example for bioactive compounds [Ref. 9.8].
[0159] According to embodiments herein described, the dendritic
component can be functionalized with surface groups can make the
dendritic component soluble in selected media or bind to surfaces.
According to some embodiments, a first dendritic component can be
covalently linked to one or more further dendritic components or
associated with one or more macromolecules to form supramolecular
assemblies.
[0160] According to some embodiments, a dendritic component can be
used as functional materials, for example, for water treatment
[Refs. 9.15-9.20]. According to some embodiments, the dendritic
component comprises a carbon based structure functionalized with N
or O. In particular, in some embodiments, the dendritic
macromolecules comprise amines, carbonyls, and/or amides. In these
embodiments, the N and O groups can sorb anions and/or cations.
Exemplary dendritic components with N and O groups which can
function as anion and cation sorbents include but is not limited to
poly(amidoamine) [PAMAM], poly(propyleneimine) and bis(methylol)
propionic acid (MPA) dendrimers (see, e.g. FIG. 7). Syntheses of
dendritic component according to the present disclosure can be
carried out, for example, by cross linking of dendritic
macromolecules to form dendritic nano- and/or microparticles (See
e.g. Example 33). Further syntheses of dendritic components will be
apparent to a skilled person upon reading of the present disclosure
(see, for example, references 2.7-2.16
[0161] According to some embodiments, the dendrimer components can
bind and release cations such as Cu.sup.2+, Co.sup.2+, Fe.sup.3+,
Ni.sup.2+ and U.sup.6+] and anions such as Cl.sup.-,
ClO.sub.4.sup.- and SO.sub.4.sup.2--, for example, through a change
of solution pH [Refs. 2.7, 2.9-2.12 and 5.6-5.12]. In particular
PAMAM, PPI, and MPA can in some embodiment bind and release cations
such as Cu.sup.2+, Co.sup.2+, Fe.sup.3+, Ni.sup.2+ and U.sup.6+,
and anions such as Cl.sup.-, ClO.sub.4.sup.- and SO.sub.4.sup.2--.
In some embodiments PAMAM dendrimers are used and the dendrimer can
present for example, an amide, a primary amine, a secondary amine,
and/or a tertiary amine group (see e.g. [FIG. 18] and Example 15).
In some embodiments PPI dendrimers are used. In embodiments where
PPI dendrimers are used, the PPI dendrimers have only primary and
tertiary amine groups. In some embodiments MPA dendrimers are used.
MPA dendrimers can have carbonyl and/or carboxyl groups which can
allow for membranes to have a high capacity, selective, and/or
recyclable ligands for Ca.sup.2+, Mg.sup.2+ and Na.sup.+
(2.17).
[0162] According to further embodiments, dendrimers according to
the present disclosure (e.g. PAMAM, PPI and MPA) can be
functionalized with terminal groups which can allow the dendrimer
to be soluble in a particular solvent to type of solvent, bind onto
one or more targeted surfaces, or cross-link with other dendrimers
to form multifunctional supramolecular assemblies (5.13-5.14) (See
e.g. FIG. 6).
[0163] In some embodiments, the dendritic macromolecules (e.g.,
PAMAM, PEI, and PPI dendrimers) can provide selective and
recyclable high capacity macroligands for anions (for example
Cl.sup.-, Br.sup.-; SO.sub.4.sup.2-; NO.sub.3.sup.-; and
ClO.sub.4.sup.-) and cations (for example, Na.sup.+, Ca.sup.2+, and
Mg.sup.2+) in aqueous solutions [Refs. 1.16-1.19]. Such dendritic
macromolecules can be suitable, for example, in making filtration
membranes for water purification as Na.sup.+, Ca.sup.2+, and
Mg.sup.2+ cations and anions Cl.sup.- and SO.sub.4.sup.2- anions
make-up more than 98% of the total dissolved solids (TDS) in
brackish water and seawater [Ref. 5.15].
[0164] In some embodiments, the dendrimer component comprises
hyperbranched macromolecules, such as polyethyleneimine (PEI) which
can behave similarly to corresponding, dendrimers] [Ref. 1.20].
Hyperbranched PEI has a degree of branching at approximately
65-70%. Hyperbranched PEI are generally soluble (e.g. 5-20 wt %) in
solvents such dimethyl formamide (DMF) and dimethyl acetamide
(DMAc) [Refs. 9.20-9.21] Hyperbranched polyethyleneimine (PEI) can
be useful as a monomer of interfacial polymerization due at least
in part to its high amine density. Generally, hyperbranched PEI
have a large number of amine groups per molecule (e.g. primary,
secondary, and tertiary amine groups in a ratio of approximately
1:2:1), each nitrogen atom is linked each other by an ethylene
group (FIG. 44) [Ref. 8.11] which can allow for a number of
unreacted amine groups, which can be sources of charges (e.g. by pH
change in aqueous solution [8.24] or post-functionalization), for
example, for enhancing Donnan exclusion effects.
[0165] In some embodiments, the dendritic components are capable of
rejecting cations and anions. For example, dendritic components
having negatively charged O donors can be used to coordinate 2s
metal ions such as Ca.sup.2+ and Mg.sup.2+ [Ref. 5.17]. As another
example, dendritic components having neutral oxygen donors can be
used to coordinate with is metal ions such as Na.sup.+ [Ref.
5.17].
[0166] In some embodiments, dendritic components containing
negatively charged 0 donors and tertiary amine groups can be used
to selectively bind Ca.sup.2+ and Mg.sup.2+ ions at pH .about.7.0.
The Ca.sup.2+ and Mg.sup.2+ ions can then be released from the
dendritic component by washing the dendritic component with an
acidic solution containing a small ligand such as citric acid. As
another example, dendritic components containing neutral I donors
and tertiary amine groups can selectively bind Na.sup.+ ions at pH
.about.7.0. The Na.sup.+ ions can then be released from the
dendritic component by washing the dendritic component with an
acidic solution containing a small complexing ligand such as citric
acid. These examples are based on established trends in
coordination chemistry [Ref. 5.17] and accordingly other methods of
making and using dendritic components based on such trends as will
be understood by a skilled person, can be implemented without
departing from the scope of the present disclosure.
[0167] In some embodiments, nanofibers and/or microfibers can be
made using polysulfone (PS), polyether sulfone (PES),
poly(vinylidene)fluoride (PVDF), or poly(acrylonitrile) (PAN) as
the polymeric component and poly(amidoamine) [PAMAM],
poly(propyleneimine), bis(methylol)propionic acid (MPA), or
polyethyleneimine (PEI) as the dendritic component.
[0168] In some embodiments, the dendritic component can be cross
linked to one or more of another dendritic component and/or a
polymeric component by using a cross linking agent. For example, a
dendritic component comprising amine groups (e.g. can be combined
with a cross linking agent which is capable of cross linking
proximate amine groups (amine-amine cross linking agents) to form
nanofibers. The amine-amine cross linking agents can be
bifunctional (e.g. two sites which can form covalent bonds with
amines) or multifunctional (e.g. three or more sites which can form
covalent bonds with amines). The cross linking agents can include
but are not limited to primary bifunctionalized alkanes having the
general formula (XVI) or (XVII) below:
##STR00007##
wherein X.sup.1 and X.sup.2, by way of example, can be
independently selected from (COCl, COBr, COI, Cl, Br, I,
OSO.sub.3CH.sub.3, OSO.sub.3C.sub.7H.sub.7, n can range from 1-15,
and wherein R can be H, alkyl, or epoxy substituted alkyl.
Crosslinking agents can also include imidoesters (e.g. dimethyl
adipimidate.2HCl (DMA), dimethyl pimelimidate.2HCl (DMP), dimethyl
suberimidate.2HCl (DMS), dimethyl 3,3'-dithiobispropionimidate.2HCl
(DTBP)), N-hydroxy succinimide (NHS)-esters (e.g. disuccinimidyl
suberate (DSS), bis(sulfosuccinimidyl) suberate (BS3),
disuccinimidyl glutarate (DSG)), and
1,5-difluoro-2,4-dinitrobenzene (DFDNB). Exemplary amine cross
linking agents comprise in particular, trimesoyl chloride (TMC),
1,3-dibromopropane (DBP), and epichlorohydrin (EPC) to form
nanofibers (see, e.g., Examples 20-22).
[0169] According to some embodiments, a computer aided molecular
design framework can be used to guide a synthesis of ion-selective
UF membranes, for example, for water treatment and desalination
(See e.g. Examples 4 and 10).
[0170] In some embodiments, nanofibers and/or microfibers herein
described are aggregated in a composite material herein described
which is comprised of trimesoyl chloride (TMC) cross-linked
polyethyleneimine (PEI) nanofiber. In another embodiment, the
composite material herein described can be comprised of
1,3-dibromopropane (DBP) cross-linked polyethyleneimine (PEI)
nanofibers. In another embodiment, the composite material is
comprised of epichlorohydrin (ECH) cross-linked polyethyleneimine
(PEI) nanofibers. In another embodiment, the composite material is
comprised of nanofibers of cross-linked polyvinylidene fluoride
(PVDF) nanofibers with embedded polyethyleneimine (PEI)
macromolecules.
[0171] According to a further embodiment of the disclosure, a
filtration membrane comprising layer of the composite material
according to the disclosure in combination with a one or more
additional layers is described. The additional layers can include,
for example, a support layer and/or a separation layer.
[0172] In some embodiments herein described nanofibers or
microfiber suitable as building blocks for nanofiltration membranes
have features such as large surface area to unit volume,
controllable pore size, mechanical strength, chemical stability,
and an ability to be functionalized identifiable by a skilled
person [Ref. 9.11-9.12]. In particular, in some embodiments, fiber
dimensions and characteristics (e.g. mechanical strength, chemical
stability) can be identified in view of a desired selective
filtration and the assembling of the related polymer component and
dendrimer component can be performed through a selection of
chemical conditions and fabricating conditions described herein,
the thickness of the nanofiber composite film and the chemistry of
the dendritic nanomaterials, the filtration membranes described
herein can in some embodiments have high water flux and water
recovery.
[0173] In one embodiment, the membrane has a trimesoyl chloride
(TMC) cross-linked polyethyleneimine (PEI) mesh layer on top of a
polyvinylidine fluoride (PVDF) mesh layer which in turn is on top
of a PVDF microporous support layer (see e.g. Example 20). In
another embodiment, the membrane has a 1,3-dibromopropane (DBP)
cross-linked polyethyleneimine (PEI) mesh layer on top of a
poly(vinylidine fluoride) (PVDF) mesh layer which in turn is on top
of a PVDF microporous support layer (see e.g. Example 20). In
another embodiment, the membrane has an epichlorohydrin (ECH)
cross-linked polyethyleneimine (PEI) mesh layer on top of a
poly(vinylidine fluoride) (PVDF) mesh layer which in turn is on top
of a PVDF microporous support layer (see e.g. Example 20). In
another embodiment, the membrane has a trimesoyl chloride (TMC)
cross-linked polyethyleneimine (PEI) mesh layer on top of a
poly(acrylonitrile) (PAN) nanofibers mesh which in turn is on top
of a polyethylene terephthalate (PET) support paper (see e.g.
Example 21). In another embodiment, the membrane has a mesh of
cross-linked poly(vinylidene fluoride) (PVDF) nanofibers with
embedded polyethyleneimine (PEI) macromolecules and nanoparticles
on top of a polyethylene terephthalate (PET) support paper (see
e.g. Example 25).
[0174] In some embodiments, the membranes are assembled by
layer-by-layer assembly (LBL) (See e.g. Example 5 and Example 27)
LBL assembly of polyelectrolytes onto solid surface [Ref.
2.18-2.19] can be used for building multilayer thin films.
[0175] In particular, in some embodiments, methodology
layer-by-layer assembly can be used to adsorb and deposit
alternating layers of a dendritic component onto a layer of
functionalized porous polymer support. By way of example, and not
of limitation, PAMAM, PPI and/or MPA dendrimers with amino
(NH.sub.2) and carboxyl (COOH) can be adsorbed onto one or more
layers of a functionalized porous polymer support.
[0176] In some embodiments, following a depositing of layers of the
dendritic component onto the layers of porous polymer supports, a
cross linking agent can be used to covalently link the sorbed
layers of the dendritic component to the porous polymer support
layer.
[0177] In these embodiments, cross-linkers can be selected based on
the functionalization of the porous polymer support layer and the
type functionalization on the dendritic component. For example, if
the porous polymer support layer and the dendritic component are
both functionalized with amines then the amine-amine cross-linking
agents described herein with reference to crosslinking within a
dendrimer component can be used. As a further example, if the
porous polymer support is functionalized with carboxylic acids and
the dendritic component is functionalized with amines, then cross
linking agents can comprise reagents suitable for directly coupling
of the amine and the carboxylic acid can be used, for example, to
form an amide bond. Exemplary coupling reagents comprise, for
example, known peptide coupling reagents identifiable by a skilled
person (e.g. 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide
hydrochloride (EDC) and dicyclohexylcarbodiimide (DCC)).
[0178] According to some embodiments, a porous polymer support
which is not functionalized can be functionalized according to
methods identifiable by a skilled person and a functionalization
can be selected based on the functionalization of a corresponding
dendritic component which is selected to be adsorbed on the porous
polymer support. The functionalization can further be selected
based on which type of covalent linkage is to be used to attach the
dendritic component to the porous polymer support. For example, if
a direct cross linking between a dendritic component comprising
primary or secondary amines is used and a porous polymer support is
desired, the polymer can be functionalized with carboxylic acids,
thus allowing for a direct cross linking (e.g. with coupling
reagents). In some embodiments, functionalization of the polymer
support can comprise performing a UV-induced graft copolymerization
with a "2-enoic acid" (e.g. methacrylic acid) [Ref. 2.20]. The
2-enoic acids can comprise a compound according to formula
(XIX):
##STR00008##
where R.sup.1 and R.sup.2 are independently H or a C.sub.1-C.sub.10
alkyl group. Polymeric components which can be used these
embodiments include but is not limited to polyethersulfone (PES and
poly(vinylidene)fluoride (PVDF) [Ref. 2.20] and other suitable
polymer supports according to the disclosure having an abstractable
hydrogen for free radical addition (see, e.g. Example 36).
[0179] In some embodiments, membranes can be fabricated using
electrospinning in combination with LBL deposition and a subsequent
cross linking to covalently attach the dendritic component to
polymeric nanofibers. The cross-linking can be a direct cross
linking (e.g. by formation of an amide bond from an amine and a
carboxylic acid with coupling reagents as herein described) or can
be indirect (e.g. as in an amine-amine crosslinking as herein
described) depending on the functionalization of the dendritic
component and on the functionalization of the polymeric fibers as
will be understood by a skilled person upon reading the present
disclosure. (See e.g. FIG. 9 and Example 6)
[0180] In some embodiments, membranes can be fabricated by casting
a mixture of the polymer component, the dendrimer component, one or
more solvents, and a cross-linking agent onto porous polymeric MF
membrane supports [Ref. 2.24].
[0181] Targeted atomistic molecular dynamics (MD) simulations of
anion and/or cation binding to a dendritic component (e.g. PAMAM,
PPI, and MPA) can be carried out using a Dreiding III force field
(See e.g. Example 10, FIG. 12) [Ref. 2.25] to develop and validate
a computer-aided molecular design framework that can be used to
guide the synthesis of high capacity and recycle low-cost
ion-selective dendritic polymers.
[0182] In some embodiments, membranes can be fabricated by using
bulky hyperbranched polyethyleneimine (PEI) as a monomer of
interfacial polymerization, to make an active layer of a NF
membrane which in some embodiments has a relatively high charge
density and mechanical flexibility. In these embodiments, the NR
membrane can have good charge rejection, for example by enhancement
of Donnan exclusion effects, and can have a higher water flux (see,
e.g. Examples 21-22)
[0183] In these embodiments, NF membranes can be operated at lower
operating pressure and can allow a higher flux compared to RO and
NF membranes, which can be due to its mechanically flexible
membrane structure.
[0184] NF membranes can be in the form of a nanofibrous composite
(NFC) membrane which comprises a thin top layer, a nanofibrous mid
layer, and a backing bottom layer. The mid layer of the NF
filtration membrane comprises a polymer nanofiber mesh which can be
fabricated by an electrospinning technique such that the filtration
membrane can have much higher porosity, which can reduce hydraulic
resistance [Ref. 8.12].
[0185] In some embodiments, poly(acrylonitrile) (PAN), can be used
as a material for polymeric nanofibers and/or microfibers of the
mid layer. PAN can be a suitable mid layer due to its high
mechanical stability and good solvent resistance [Ref 8.13] and
polyethylene terephthalate (PET) paper can be used for bottom
backing layer.
[0186] In some embodiments, the membranes herein described can
comprise at least two components, for example, a microfibrous
polymeric support and a film of cross-linked networks of
functionalized polymeric nanofibers with embedded and/or covalently
attached dendritic macromolecules and nanoparticles that are
functionalized with ion-selective groups including quaternary
amines, carboxyl including quaternary amines, carboxylic, sulfonate
and amide groups.
[0187] In some of these embodiments, the nanofibers are casted onto
the microfibrous using electrospinning. For example, filtration
membranes can be prepared poly(vinylidene fluoride) (PVDF),
polysulfone (PS) and/or poly(acrylonitrile) (PAN) as base polymers
for the nanofibers, hyperbranched polyethyleneimine (PEI) as the
dendritic components and poly(ethylene terephthalate) [PET] as
porous support (see e.g. FIG. 23).
[0188] In some embodiments the nanofibers can be approximately
100-500 nm in diameter.
[0189] According to a further embodiment of the disclosure, a
filtration system is described. The filtration system comprises a
plurality of modules, each module comprising one or more of the
filtration membranes for pretreatment of water according to
embodiments herein described, charged particle rejection of water,
and charged particle absorption of water is described.
[0190] The term "module" as used herein refers to a compartment
comprising a filtration membrane according to the disclosure,
adapted to be used in connection with other modules to perform
parallel and/or sequential filtrations.
[0191] In particular, in some embodiments, a module herein
described can comprise one of the filtration membranes herein
described through which water can pass. For example, if the
membrane in a module is charged particle rejecting, it can remove
charged particles from the water passing through the membrane in
the module such that the charged particles are reduced and/or
substantially eliminated from water exiting the membrane. As
another example, if the membrane in a module is charged particle
absorbing, it can absorb charged particles from the water passing
through the membrane in the module such that the charged particles
are reduced or eliminated from water exiting the membrane.
Exemplary membranes of the disclosure are shown in FIG. 15 and FIG.
16 (see, for example, Example 13).
[0192] In particular, in some embodiments, the filtration within
the modules can operate by size exclusion and/or Donnan exclusion.
The Donnan exclusion can be in operation can when sizes of charged
species are much smaller than the pore size of a membrane [Ref.
8.9]. For example, a more porous membrane than a general NF
membrane can be provided which simultaneously shows rejection for
the charged species by enhancing the Donnan exclusion effect.
[0193] The Donnan equilibrium, also known as the Gibbs-Donnan
effect, Donnan effect, or Gibbs-Donnan equilibrium, refers the
behavior or distribution of charged particles through the both
sides of a semi-permeable membrane when they are not distributed
evenly across the membrane due to the presence of a charged
substances at one side of the membrane. These charged substances
are unable to pass through the membrane and thus generate an
electrical potential. For membranes with fixed positive or negative
charges, the Donnan Effect refers to the repulsion of co-ions,
(anions or cations that have the same charges as the fixed charges
of the membranes).
[0194] At an initial stage, the numbers of ions in both sides can
be represented as (See e.g. FIG. 40): left side: [Na.sup.+]=6,
[Cl.sup.-]=6 and right side: [Na.sup.+]=6
[0195] Since, the electrochemical potentials of both sides are
different, Cl.sup.- at the left side can start to move through the
right side. Due to the movement of anions, electrical potential is
generated between each side separated by the membrane. The left
side will be positively charged and the right side will be
negatively charged. And the cation will also move through the
membrane due to the electrical potential until this system will
reach at electrochemical equilibrium.
[0196] At equilibrium, the numbers of ions in both sides can be
represented as (FIG. 41). left side:
[Na.sup.+]=4, [Cl.sup.-]=4 and right side: [Na.sup.+]=8,
[Cl.sup.-]=2
[0197] In summary, net ion transport across the membrane is 2 pairs
of NaCl among 6 pairs.
[0198] In this example, chloride anions are selectively
rejected
*Initial condition (FIG. 42) Left side: [Na.sup.+].sub.2=c.sub.2,
[Cl.sup.-].sub.2=c.sub.2 Right side: [Na.sup.+].sub.1=c.sub.1,
[P.sup.-]=c.sub.1 (P.sup.-: Big anions which cannot penetrate the
membrane)
*At equilibrium (FIG. 43) Left side: [Na.sup.+].sub.2=c.sub.2-x,
[Cl.sup.-].sub.2=c.sub.2-x Right side:
[Na.sup.+].sub.1=c.sub.1+x[P.sup.-]=c.sub.1, [Cl.sup.-]=x
At equilibrium;
.DELTA.G=.DELTA.G.sub.Na.sub.++.DELTA.G.sub.Cl.sub.-=0
where
.DELTA. G Na + = RT ln [ Na + ] 2 [ Na + ] 1 , .DELTA. G C l - = RT
ln [ Cl - ] 2 [ Cl - ] and ##EQU00001## .DELTA. G = RT ln [ Na + ]
2 [ Na + ] 1 + RT ln [ Cl - ] 2 [ Cl - ] = 0 ##EQU00001.2## RT ln [
Na + ] 2 [ Cl - ] 2 [ Na + ] 1 [ Cl - ] = 0 ##EQU00001.3## [ Na + ]
2 [ Cl - ] 2 [ Na + ] 1 [ Cl - ] = 1 ##EQU00001.4##
with constants and variables,
( c 2 - x ) 2 ( c 1 + x ) x = 1 ##EQU00002##
and solving this equation for x,
x = c 2 2 c 1 + 2 c 2 ##EQU00003##
is obtained.
[0199] Therefore by increasing c.sub.1, in embodiments herein
described, the amount of x (anions which penetrate the membrane)
can be decreased.
[0200] In embodiments, when a charged membrane is used to separate
ionic species in solution, Donnan effects can dominate or
contribute to the separation mechanism of ions. This effect
indicates a distribution of ionic species between the solution and
the charged membrane. For example, if a negatively charged membrane
is used, the co-ions (anions) can be affected by repelling
electro-static force. Consequently, a distribution of ionic species
in membrane and solution can be changed.
[0201] For example, assuming that a negatively charged membrane is
in contact with a sodium chloride solution, at equilibrium, the
chemical potentials of ions at the interface (solution/membrane)
can be considered to be the same.
.mu..sub.i=.mu..sub.i.sup.m
[0202] The electrochemical potential (.PSI.) of an ion in solution
can be described by:
.PSI..sub.i=.mu..sub.i.sup.0+RTlna.sub.i+z.sub.iFE
wherein .mu..sub.i.sup.0 represents reference state, R represents
the gas constant, T represents temperature, a.sub.i represents
activity of ion I, z represents valence of the ion, F represents
the faraday constant, and E represents the measured potential.
[0203] The electrochemical potential of an ion in the membrane can
be described by:
.PSI..sub.i.sup.m=.mu..sub.i.sup.m,0+RTlna.sub.i.sup.m+zFE.sup.m.
[0204] Since the concentration of the ions in solution and membrane
can be different, there can be an electrical potential at the
interface which is called Donnan potential (E.sub.don) which can be
described by:
E don = E n 3 - E = RT z 1 F ln a 1 a 1 m . ##EQU00004##
[0205] Assuming that the chemical potential of the reference state
is same in both phases:
.mu..sub.i.sup.0=.mu..sub.i.sup.m,0
and assuming that the solution is a diluted solution
(a.sub.i.apprxeq.c.sub.i) then the following can be obtained:
c.sub.Na.sub.+.times.c.sub.Cl.sub.-=c.sub.Na.sub.+.sup.m.times.c.sub.Cl.-
sub.-.sup.m
[0206] For electro-neutrality conditions,
.SIGMA.z.sub.ic.sub.i=0
[0207] Electro-neutrality equation for both solution and membrane
phase are,
c.sub.Na.sub.+=c.sub.Cl.sub.-
and
c.sub.Na.sub.+.sup.m=c.sub.Cl.sub.-.sup.m+c.sub.X.sub.-.sup.m
It can thus be obtained that
c.sub.Cl.sup.m.times.c.sub.X.sup.m+(c.sub.Cl.sub.-.sup.m).sup.2=(c.sub.C-
l.sub.-).sup.2
or
c Cl - c Cl - m = c x - m c Cl - m + 1 ##EQU00005##
where X represents membrane charge.
[0208] The above equation can be rewritten As:
* 1 - 1 salt : c Cl - m c Cl - = c Cl - c Cl - m + c x - m .
##EQU00006##
[0209] A similar equation can be derived for a 2-1 salt and a 1-2
salt using the same method to give
* 2 - 1 salt : c Cl - m c Cl - = ( 2 c Cl - ( 2 c Cl - m + c x - m
) ) 2 -> MgCl 2 and ##EQU00007## * 1 - 2 salt : c SO 4 2 - m c
SO 4 2 - = c SO 4 2 - c SO 4 2 - m + c x - m -> Na 2 SO 4 ,
respectively . ##EQU00007.2##
[0210] In some embodiments, the filtration within a module can
operate by ultrafiltration (UF) and microfiltration (MF). UF and MF
membranes can have large pore size (e.g., 5-100 nm) allowing them
to operate pressures between approximately 0.3-5.0 bar). UF and MF
can suitable in embodiments where it desired to generate less
membrane concentrates, for example compared to an RO filtration. UF
and MF are particularly suitable for a pretreatment process to
remove particles from saline water in the desalination of brackish
water and seawater.
[0211] In some embodiments, the ion selective UF/MF membrane
modules (See e.g. FIG. 15) comprise hollow fibers (HF) according to
embodiments herein described which can in some embodiments reject
cations and/or anions, for example through electrostatic (Donnan)
repulsion and can selectively bind and release anions and/or
cations, for example, by complexation and ion exchange.
[0212] A hollow fiber (HF) module configuration can suitable, for
example, because the hollow fiber (HF) module configuration can
have large fiber packing density; a low operating pressure (e.g.
between approximately 0.3-2 bars) and pressure drop (e.g. between
approximately 0.1-1 bar) across the membrane module; and ease of
backwashing the fiber to which can minimize a build-up of ions at
membrane surfaces and/or release bound cations and/or anions. The
hollow fibers of the hollow fiber (HF) module configuration can be
fabricated, for example, using solvent spinning, electrospinning,
or other methods identifiable by a skilled person. Polymers that
can be used to spin the hollow fibers include polyethersulfone
(PES), poly(vinylidene fluoride) (PVDF) and poly(acrylonitrile)
(PAN).
[0213] In some embodiments, the filtration system can be configured
to have three units: a first unit comprising a module, the module
comprising a nanofiltration membrane to remove, for example,
particles and dissolved organic matter; a second unit comprising a
series of alternating positive and negative charged particle
rejecting modules, for example, to remove a majority of the charged
particles; and a third unit comprising a parallel series of modules
capable of absorbing charged particles of interest.
[0214] In some embodiments of the membrane filtration system, the
membranes comprised in the modules comprise hollow fibers with
embedded dendritic component that can reject charged particles. In
other embodiments, the ion-selective hollow fibers can be
backwashed with an acid/base solution or a solution containing
sufficient concentration of an anion/cation selective ligand to
minimize the build-up of ions at the membrane surfaces and/or
release the bound cations/anions. In other embodiments, the
embedded dendritic component can be cross-linked and functionalized
with N and O donors.
[0215] In some embodiments of the membrane filtration system, the
membranes comprised in the modules comprise hollow fibers with
embedded dendritic component that is functionalized with neutral
groups [e.g. polyethylene glycol (PEG)]. In other embodiments, the
ion-selective hollow fibers can be backwashed with an acid/base
solution or a solution containing sufficient concentration of an
anion/cation selective ligand to minimize the build-up of ions at
the membrane surfaces, and/or release the bound cations/anions. In
other embodiments, the embedded dendritic component can be
cross-linked and functionalized with N and O donors.
[0216] In some embodiments of the filtration system, the
ion-rejection filtration stage comprises a conventional
nanofiltration membrane system that can reject dissolved organic
matter, divalent ions and a fraction of the monovalent ions.
[0217] Also provided herein, a process for providing nanofibers or
microfibers is described. In some embodiments, the process
comprises mixing a polymer with a dendrimer in a suitable solvent,
possibly comprising a mixture of solvents, to provide a liquid
mixture and electrospraying and/or electrospinning the liquid
mixture to provide a nanofiber or microfiber.
[0218] In some embodiments, the process for providing a nanofiber
or microfiber comprises mixing a polymeric component dissolved in a
suitable solvent or mixture of solvents with a dendritic component
dissolved in a suitable solvent or mixture of solvents and applying
an electrical charge to the liquid mixture of polymeric components
and dendritic components until a continuous stream of the is pulled
to a collector having an electrical charge opposite that of the
liquid mixture of polymeric components and dendritic components. In
other embodiments, the process for providing a nanofiber or
microfiber comprises mixing a polymeric component having
polymerizable monomer units dissolved in a suitable solvent or
mixture of solvents with a dendritic component dissolved in a
suitable solvent or mixture of solvents and applying an electrical
charge to the liquid mixture of polymeric components and dendritic
components until a continuous stream of the is pulled to a
collector having an electrical charge opposite that of the liquid
mixture of polymeric components and dendritic components
[0219] Also provided herein are nanofibers or microfibers
obtainable by the process for providing a nanofiber in accordance
with the present disclosure.
[0220] Further provided herein, a process for manufacturing a
composite material herein described. The process comprises
aggregating nano-fiber and/or microfibers herein described.
[0221] In some embodiments, the process for aggregating nanofibers
and/or microfibers herein described comprises mixing a polymeric
component having polymerizable monomer units dissolved in a
suitable solvent with a dendritic component dissolved in a suitable
solvent and applying an electrical charge to the liquid mixture of
polymeric components and dendritic components until a continuous
stream of the fibers is pulled to a rotating collector having an
electrical charge opposite that of the liquid mixture of polymeric
components and dendritic components such that the continuous stream
forms a mesh of nanofibers
[0222] Various devices can be used to manufacture and use
composites and membranes herein described. FIG. 36 is a schematic
design of an exemplary apparatus for the process for manufacturing
the composite. It can comprise three parts: a spinneret (where the
solution is ejected), a power supply (apply electrical field
between the spinneret and the collector), and a collector (a
grounded conductor where the electrospun nanofibers are collected)
[Ref. 8.17]. When the solution is ejected by a syringe pump from
the syringe which is connected to spinneret, the solution droplet
(at the tip of spinneret) becomes elongated continuously due to the
high voltage applied between spinneret and collector (for example,
between 1 kV to 30 kV) [Ref. 8.17]. During elongation, the diameter
of fibers can be reduced to as small as nanometer scale and can be
controlled by several parameters including, for example, distance
between the spinneret and collector, applied electrical voltage,
condition of solution, flow rate of ejected solution, temperature,
humidity, and additional parameters identifiable by a skilled
person [see e.g. Refs. 8.17, 8.18]. The elongated fibers can be
deposited onto the grounded collector with random orientations
leading to the formation of the composite material as a non-woven
mesh.
[0223] In particular, in some embodiments, after the nanofibers of
the composite material made by the process described herein can be
collected from the polymer solution, evaporation of the residual
solvents of fibers can make the fibers physically bonded leading to
fabrication of a strong cohesive interconnected porous structure
[Ref. 8.20]. Composite material made by the process disclosed
herein can have features such as, high porosity (compare to
conventional phase-inverted membranes), controllable pore sizes
(e.g. controlled by fiber diameter and can range from tens of
nanometer to several micrometer), interconnected open pore
structure, and high specific area. Due to such features, membranes
comprising these composite materials can show higher water flux and
much suitable functionalization capability than typical UF, MF
membranes.
[0224] In some embodiments, a composite material can be coated with
cross-linked additional dendritic component by interfacial
polymerization. In interfacial polymerization, polymerization
occurs at the interface between two immiscible solvents by the
monomers (reactants) in each solvent. In particular, in some
embodiments, the general procedure of interfacial polymerization
comprised the steps of: immersing the composite material to be
coated in an aqueous solution of the dendritic component; removing
excess aqueous solution from the composite material, for example by
way of a glass roller; immersing the wet composite material in an
organic solvent containing the cross linker; rinsing the coated
composite material with the organic solvent. (See, e.g., Examples
21, 22, and 32)
[0225] Also provided herein, a filtration method comprising,
passing water to be filtered through one or more modules comprising
conventional nanofiltration membranes to remove particles and
dissolved organic matter, passing the water through a series of
alternating positive and negative charged particle rejecting
modules comprising the membranes herein described to remove a
majority of the charged particles, and passing the water through a
parallel series of modules capable of absorbing charged particles
of interest is described.
[0226] In some embodiments, the membrane filtration system for the
desalination of brackish water and seawater comprises: an
ion-rejection filtration stage, wherein saline water passes through
a series of alternating cation/anion selective tight UF membranes
designed to reject 70-90% of dissolved ions; and an ion-absorption
filtration stage, wherein the product water from the ion-rejection
filtration system is split into two streams that pass through a
series of ion-absorbing MF membranes designed to selectively bind
target anions/cations of interest.
[0227] In some embodiments, the filtration membrane comprises of
separation layers made of cross linked dendritic macromolecules
that are supported by polymeric nanofibrous scaffolds electrospun
onto commercial polymeric microporous membrane supports.
[0228] In some embodiments of the filtration membrane, the
separation layers consist of cross linked hyperbranched PEI
macromolecules that are supported by nanofibrous PVDF scaffolds
electrospun onto a PVDF microfiltration membrane support.
[0229] In some embodiments of the filtration membrane, the
separation layers consist of cross linked hyperbranched PEI
macromolecules that are supported by nanofibrous PAN scaffolds
electrospun onto a nonwoven poly(ethylene terephthalate) (PET)
microporous support.
[0230] In some embodiments of the filtration membrane, the
separation layers consist of cross linked low-generation dendrimers
and dendrigraft macromolecules that are supported by polymeric
nanofibrous scaffolds electrospun onto a polymeric microporous
membrane supports.
[0231] Further advantages and characteristics of the present
disclosure will become more apparent hereinafter from the following
detailed disclosure by way or illustration only with reference to
an experimental section.
EXAMPLES
[0232] The nanofibers and microfibers, membranes, and composite
materials and related compositions, methods and systems herein
described are further illustrated in the following examples, which
are provided by way of illustration and are not intended to be
limiting.
[0233] In particular, the following examples illustrate exemplary
nanofibers and microfibers, membranes, and composite materials and
related methods and systems. A person skilled in the art will
appreciate the applicability and the necessary modifications to
adapt the features described in detail in the present section, to
additional nanofibers and microfibers, membranes, and composite
materials, and related methods and systems according to embodiments
of the present disclosure.
Example 1
Synthesis and Characterization of Anion-Exchange Hyperbranched
Macromolecules
[0234] In this example, the Applicants have utilized dendritic
macromolecules (e.g., PAMAM and PPI dendrimers) as selective and
recyclable high capacity macroligands for anions and cations in
aqueous solutions [Refs. 1.16-1.19]. Low-cost hyperbranched
macromolecules, such as polyethyleneimine (PEI), behave very
similarly as the corresponding, but expensive dendrimers [Ref.
1.20]. Hyperbranched PEI has a degree of branching at approximately
65-70%. They comprise of primary, secondary and tertiary amines
linked by C.sub.2 alkyl chains. Two features of hyperbranched PEI
macromolecules are their large N content (18-20 mol/kg) and the
ease of functionalization of their primary and secondary amine
groups. FIG. 2 shows a particular strategy for functionalizing
hyperbranched PEI macromolecules with various functional groups to
synthesize anion-selective macromolecules including macroligands
that can selectively bind anions (e.g., Cl.sup.-, Br.sup.- and
SO.sub.4.sup.2-; NO.sup.3-; and ClO.sup.4-) at pH of approximately
5-6 and release them at pH .about.9.0 [Ref. 1.20]. In this Example,
PEI is reacted with cross-linking agent 1,3-dibromopropane in
methanol at 65.degree. C. to form cross-linked PEI units.
[0235] The Applicants have also synthesized and characterized
functionalized hyperbranched PEI macromolecules that can serve as
high capacity anion-exchange ligands. The anion exchange ligands
were prepared by methylation of hyperbranched PEI using an
Eschweiler-Clarke reaction as shown in the bottom of FIG. 2,
followed by conversion of its tertiary amine groups to quaternary
groups with permanent positive charges (--R.sub.4N.sup.+). In this
example, the chemical compositions and molar masses of the
synthesized hyperbranched macromolecules were characterized using
the appropriate analytical techniques (e.g. NMR, SEC, MALDI-TOF MS,
etc.) The exchange capacity of the anion-exchange hyperbranched
macromolecules was also measured.
Example 2
Synthesis and Characterization of Anion-Exchange Polymeric
Nanoparticles
[0236] In this example, the use of high performance media for water
treatment (patent pending) is described [Ref. 1.21]. (see U.S.
Provisional Patent Application 61/665,749) The media comprise
functionalized polymeric nanoparticles (PNP) which were synthesized
using low-cost hyperbranched polymers HBP as precursor materials as
shown in FIG. 3. Due at least in part to their unique chemistry and
hyperbranched architecture, the media were reacted with a broad
variety of chemical groups to prepare ion-selective media. The
Applicants have synthesized ion-selective hyperbranched
microparticles with a strong base anion-exchange capacity (SBEC) of
2.0 eq/L [Ref. 1.25]. In this example, the exchange capacity is
larger by .about.40% than that of DOWEX.RTM. SAR anion-exchange
resin, which has a SBEC of 1.4 eq/L and is one of the largest
anion-exchange capacity in the market
(dow.com/liquidseps/prod/dx_sar.htm).
[0237] Applicants have prepared anion-exchanged polymeric
nanoparticles (NP) using synthetic strategies similar to those
described in reference 1.21. In this example, the physicochemical
properties of the anion-exchange PNP were characterized using
elemental analysis, FT-IR, SEM and TEM. The exchange capacity of
the anion-exchange PNP can also be measured. The results of this
example provided the building blocks for preparing heterogeneous
anion-exchange hollow fibers with high charge density and Donnan
potential.
Example 3
Synthesis and Characterization of Ion-Selective Hollow Fibers
[0238] The Applicants show in this example that electrospinning
[Refs. 1.22-1.24] can be used to generate anion-exchange hollow
polymeric nanofibers (FIG. 4 and FIG. 1B) by electrospinning a
solution of the polymeric component surrounding a bore fluid
comprising the dendritic component. In this example, two types of
anion-selective fibers can be prepared: homogeneous anion-exchange
hollow fibers and heterogeneous anion-exchange hollow fibers. The
homogeneous anion-selective fibers comprise hollow nanofibers with
embedded anion-selective hyperbranched macromolecules (FIG. 2 and
FIG. 1C). The heterogeneous anion-exchange fibers comprise hollow
nanofibers with embedded anion-selective polymeric nanoparticles
(NP).
[0239] In this example, polysulfone (PS), polyether sulfone (PES),
poly(vinylidene)fluoride (PVDF) and polyacrilonitrile (PAN) can be
used as base polymers for spinning the hollow fibers due to their
wide utilization as base polymers in the fabrication of commercial
hollow-fiber UF/MF membranes (1.8) and because PS, PES, PVDF and
PAN and the functionalized anion-selective HPB macromolecules and
nanoparticles of interest in this example (FIG. 2 and FIG. 3) are
either partially soluble (at least 5-10 wt %) or can be dispersed
in solvents with widely different physicochemical properties (e.g.
boiling point and surface tension) such as tetrahydrofuran (THF),
dimethyl formamide (DMF) and dimethyl acetamide (DMAc) [Refs.
1.23-1.24]. This is expected to provide many degrees of freedom for
optimizing the physical and chemical properties of the fibers by
selecting the appropriate spinning conditions.
[0240] The Applicants provide in this example an exemplary method
for attaching additional layers of positively charged groups on the
surfaces of fibers using standard membrane surface modification
techniques such as reactive coating, interfacial polymerization and
layer-by-layer self-assembly [Refs. 1.25-1.27]. In this Example,
the anion exchange capacity, ion perm-selectivity (e.g.
anion-transfer and cation rejection) and water permeability of the
anion-exchange hollow fibers as shown in FIG. 4, can be measured
using standard techniques [Refs. 1.7-1.9] and the laboratory scale
ultrafiltration set-up is shown in FIG. 5. Selected experiments can
be carried out to characterize the physicochemical properties (e.g.
charge and hydrophobicity), structure and morphology of the fibers
using electrokinetic measurements, contact angle measurements,
spectroscopy (e.g. AT-FTIR and Raman) and imaging (e.g., SEM, TEM
and AFM) [Refs. 1.7, 1.9].
Example 4
Multiscale Modeling Anion-Exchange Polymeric Nanoparticles and
Fibers
[0241] In this example, a computer-aided molecular design framework
for designing ion-selective hyperbranched macromolecules, polymeric
nanoparticles and fibers is described. Using atomistic molecular
dynamics (MD) simulations of the structures and physical/chemical
properties of dendrimers and polymer electrolyte membranes fuel
cells with embedded dendrimers [Refs. 1.28-1.29], multiscale
simulations can be used to determine the structures of
anion-selective hyperbranched polymeric nanoparticles (FIG. 3) and
hollow fibers (FIG. 4) and to probe their interactions with
relevant cations (e.g. Ca.sup.2+, Mg.sup.2+ and Na.sup.+) and
anions (Cl.sup.- and SO.sub.4.sup.2-) in water and model
electrolyte solutions.
[0242] Characterization data from elemental analysis, NMR and size
exclusion chromatography data can be used to build 3-D models of
anion-selective hyperbranched PEI macromolecules and polymeric
nanoparticles (FIG. 2 and FIG. 3). Atomistic MD simulations of
these systems in explicit water with counterions can be carried
out. Following completion of these simulations, 3-D models of
ion-selective hollow fibers by embedding hyperbranched PEI
polymeric nanoparticles (FIG. 3) inside matrices of selected
polymers (e.g. PS, PES, PVDF and PAN) can be built. These systems
can then be used to carry out multiscale modeling ion and water
transport through the model ion-selective hollow fibers and UF
membranes. Parameters that are expected to be determinable from
these simulations include: (1) Ion membrane-water partition
coefficients; (2) Ion diffusion constant and permselectivity; (3)
Water transport (e.g. diffusion) and permeability; and (4)
Electrostatic charge and potential distributions inside the
membranes and at membrane-solution interfaces. The results are
expected provide a computer aided molecular design framework that
can guide the synthesis of ion-selective UF membranes for water
treatment and desalination.
Example 5
Synthesis and Characterization of IA.mu.F Membranes by
Layer-by-Layer (LBL) Deposition and Cross-Linking of Dendrimers
onto Porous Polymeric MF Membrane Supports
[0243] This example provides an exemplary method of using LBL
methodology to adsorb and deposit alternating layers of PAMAM, PPI
and MPA dendrimers (FIG. 7) with amino (NH.sub.2) and carboxyl
(COOH) onto porous polymer supports of commercial MF membranes that
have been functionalized with carboxyl groups by UV-induced graft
copolymerization with methacrylic acid [Ref. 2.20]. Polymer
supports used in this example can include polyethersulfone (PES)
and poly(vinylidene fluoride) (PVDF) [Ref. 2.20]. Following
deposition of the dendrimer layers onto the porous supports,
1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC)
can be used as cross-linker to covalently link the sorbed
dendrimers and attach the multilayer dendrimers films to the porous
polymeric MF membrane supports. Tomalia and Swanson [Ref. 2.21]
have shown that EDC can be used to covalently link PAMAM dendrimers
with terminal NH.sub.2 and COOH groups.
Example 6
Synthesis and Characterization of IA.mu.F Membranes by LBL
[0244] This example provides an exemplary method of using LBL
deposition with EDC coupling to covalently attach PAMAM, PPI and
MPI dendrimers (FIG. 7) to polymeric nanofibers. This example uses
electrospinning (FIG. 9) to generate the PES and PVDF nanofibers
[Ref. 2.22-2.23]. UV-induced graft copolymerization with
methacrylic acid [Ref. 2.20] was used to functionalize the
nanofibers with COOH groups prior to LBL deposition of the
dendrimers.
Example 7
Synthesis and characterization of IA.mu.F Membranes by Phase
Inversion (PI) Casting
[0245] The Applicants have also synthesized and characterized
IA.mu.F membranes by phase inversion (PI) casting of dope solutions
of dendritic macromolecules onto glass supports.
Example 8
Synthesis and Characterization of Ion-Selective Dendritic
Macromolecules (ISDM)
[0246] The Applicants have shown that the cation/anion binding
capacities of PAMAM and PPI dendrimers are very large. The
Applicants have developed a facile and versatile strategy for
synthesizing low-cost ISDM with protonable N groups that can
selectively bind anions (e.g., Cl.sup.-, Br.sup.-, NO.sub.3.sup.-
and ClO.sub.4.sup.-) at pH 5-6 and release them at pH 9.0 [Refs.
3.20-3.21].
Example 9
Synthesis and Characterization of Ion-Absorbing Hollow Fibers
(IAHF)
[0247] This example shows the use of electrospinning to generate
hollow polymeric nanofibers [Ref. 3.22] with embedded ISDM (FIG.
11). Polymers that can be used to prepare the hollow nanofibers in
this example include polyethersulfone (PES),
poly(vinylidene)fluoride (PVDF) and poly(acrylonitrile) (PAN).
[0248] The Applicants have outlined a standard membrane surface
modification techniques (e.g. UV-induced graft copolymerization)
[Ref. 3.23], layer-by-layer assembly [Ref. 3.24-3.25] (followed by
thermal cross-linking) or interfacial polymerization to covalent
attach/graft additional ISDM to the outer and/or inner surfaces of
hollow fibers with embedded ISDM (FIG. 11). In this example, the
physicochemical properties of these IAHF can be characterized using
the appropriate analytical techniques (e.g., AFM, SEM and TEM). The
ion-binding capacity and selectivity of the IAHF can be measured
using standard techniques developed by the Applicants and others
[Refs. 3.10-3.13]. The overall results of these measurements were
used to assess the extent to which the bound cations/anions can be
released by washing the IAHF with acidic/basic solutions.
Example 10
Multiscale Modeling and Computer-Aided Molecular Design of
Ion-Selective Dendritic Macromolecules
[0249] In this example, a computer-aided molecular design framework
for ion-selective dendritic macromolecules (ISDM) and ion-absorbing
hollow fibers (IAHF) can be used. This example uses a modeling and
simulation of the structures and properties of dendritic polymers
[Refs. 3.14-3.19]. The atomistic molecular dynamics (MD)
simulations of the structures and transport properties of polymer
electrolyte membranes fuel cells (PEMFC) with embedded dendrimers
[Ref. 3.18] and the effects of solution pH and counterions (e.g.,
Cl--) on the structure, size and conformation of PAMAM dendrimers
in aqueous solutions (FIG. 12) [Ref. 3.19] are modeled and/or
simulated. Targeted atomistic MD simulations of anion/cation
binding to model low-cost ISD and IAHF synthesized can be carried
out. The computer-aided molecular design framework can be used to
guide the synthesis of low cost ISD and IAHF with high anion/cation
binding capacity and selectivity.
Example 11
Fabrication and Testing of IA.mu.F Membrane Modules and Pilot
Systems for Brackish Water/Seawater Desalination
[0250] The Applicants expect that standard and well establish
methods/procedures can be to fabricate and test IA.mu.F membrane
modules, and to design, construct, and test model filtration
systems (pressurized and submerged) with IA.mu.F membrane modules
(FIG. 13).
Example 12
Example of a Low-Pressure Filtration System that can Desalinate
Brackish Water and Seawater
[0251] In this example, the Applicants have describe a low-pressure
filtration system that can desalinate brackish water and seawater
more efficiently and cost effectively than RO using the filtration
membranes herein described. In some embodiments, the filtration
systems herein described can comprise other membranes in
combination with the filtration membranes herein described. For
example, commercially available membranes can also be included as
will be understood by a skilled person. For example, some suitable
commercial RO membranes comprise a polyamide layer thin film over a
porous polysulfone layer, which in turn is over a polyester support
layer (FIG. 22) In some instances the polyamide layer can face the
incoming feed water (see FIG. 34). In FIG. 32, a general schematic
of the desalination process is shown, wherein feed water,
(comprising chemicals such as dissolved NaCl that is to be removed)
passes through a membrane and the permeate (e.g. water) is passed
through the membrane and the retentate (e.g. NaCl and other salts
in seawater) and can be diverted to a waste stream or elsewhere to
recover the dissolved material not passed by the membrane. The
types of the chemicals to be separated from the feed water depends
on the relative size of the chemicals (FIG. 33 and FIG. 35) In
particular, FIG. 14 shows a typical process configuration of a
desalination system.
[0252] The desalination system illustrated in FIG. 14 can comprise
three units: 1) a pretreatment system to remove particles and
dissolved organic matter, 2) an ion-rejection ultrafiltration (UF)
system and 3) an ion-absorption microfiltration (MF) system.
Various membranes can be included in the three systems, as will be
understood by a skilled person. For example, cation-rejecting and
anion rejecting hollow fibers herein described can be comprised as
a part of the ion-rejection ultrafiltration (UF system) of FIG. 14.
In particular the fibers shown in FIG. 15B-C, and exemplary
ion-absorbing hollow fibers (using, for example, dendritic
component functionalized with poly(ethylene glycol) (PEG)) can be
seen in FIG. 16 (bottom) can be comprised in said system.
Additional membrane and modules can also be used in the system.
[0253] For example in the first unit, saline water can be
pretreated by to remove particulate and dissolved organic matter
using standard pretreatment technologies such as microfiltration
and cartridge filtration. In the second unit, the pretreated saline
water can be passed through a series of alternating cation/anion
selective tight UF membranes designed to reject 70-90% of dissolved
ions. Because of the ion-selective UF membranes can be backwashed
intermittently to control the build-up of ions at the membrane
surfaces, they can be operated at significantly lower pressure
(e.g. 4-10 bar) and much higher water recovery (.about.80-90%) than
RO membranes. Moreover, they are expected to produce significantly
less wastes (e.g. backwash water+dissolved ions) than RO membranes
which generate large amounts of brine (e.g. membrane concentrates).
In the third unit, the product water from the ion-rejection UF
system can be split into two streams and passed through a series of
ion-absorbing MF membranes designed to selectively bind target
anions/cations of interest.
[0254] The ion-selective MF membranes is also expected to be
operable at low pressure (e.g. 0.5-2.0 bar). Moreover, the bound
anions/cations is expected to be released by intermittently
backwashing the MF membranes with an acidic/basic solution, or a
solution containing sufficient concentration of an anion/cation
selective ligand (e.g., citric acid). Following treatment, the
streams from the ion-absorbing MF systems is be expected to yield a
product water with a specified ionic concentration when the streams
are mixed together. The filtration system described is expected to
able widely applicable throughout the world, and in particular in
arid regions such as the Middle East (FIG. 31)
Example 13
Ion Selective UF/MF Membrane Modules
[0255] The Applicants have developed the basic methodology and
building blocks to fabricate ion selective UF/MF membrane modules
(FIG. 10 and FIG. 15) comprising hollow fibers (HF) containing that
can reject cations/anions primarily through electrostatic (Donnan)
repulsion and selectively bind/release anions/cations through
various mechanisms including complexation and ion exchange.
[0256] In this example, the membranes are expected to be fabricated
using solvent spinning or electrospinning. Polymers that expected
to be useful for spinning the HF in this example include
polyethersulfone (PES), poly(vinylidene)fluoride (PVDF) and
polyacrylonitrile (PAN). An exemplary membrane module suitable in
UF filtration is schematically illustrated in FIG. 1A, which also
schematically shows the configuration and possible operation to
perform ultrafiltration of backwash feed to obtain a permeate using
a filtration membrane including hollow fibers (FIG. 1A.)
Example 14
Possible Variations and Modifications on the Low-Pressure Membrane
Desalination System
[0257] The low-pressure membrane desalination system shown FIG. 14
was designed to be flexible, scalable and reconfigurable. The user
can select the number and chemistry of the ion-selective UF/MF
modules that will be deployed to achieve the desired product water
composition. In some cases, a user can select to use a conventional
or improved nanofiltration (NF) membrane system as the first stage
to reject dissolved organic matter, divalent ions and a fraction of
the monovalent ions.
Example 15
Synthesis and Characterization of Ion-Absorbing Hollow-Fibers
(IAHF) with Embedded Hyperbranched Macromolecules that Selectively
Bind and Release Anions and Cations from Aqueous Solutions
[0258] The Applicants have developed the methods/procedures and
building blocks to synthesize ion-absorbing hollow-fibers (IAHF)
with embedded hyperbranched macromolecules that selectively bind
and release anions (e.g., Cl.sup.- and SO.sub.4.sup.2-) and cations
(e.g., Na.sup.+, Ca.sup.2+ and Mg.sup.2+) from aqueous solutions by
intermittently backwashing the hollow-fibers with acidic/basic
solutions. This example was based in part on previous experiments
and multiscale modeling of the supramolecular chemistry of cation
and anion binding to poly(amidoamine) [PAMAM] and
poly(propyleneimine) [PPI] dendrimers in aqueous solutions that
were carried out by the Applicants. PAMAM dendrimers possess amide,
tertiary and primary amine groups; whereas PPI dendrimers have only
primary and tertiary amine groups (FIG. 18). PAMAM and PPI
dendrimers can bind and release a broad range cations (e.g.,
Cu.sup.2+, Co.sup.2+, Fe.sup.3+, Ni.sup.2+ and U.sup.6+) and anions
(e.g., Cl.sup.-,ClO.sub.4.sup.- and SO.sub.4.sup.2-) through a
simple change of solution pH [Refs. 5.6-5.12]. Moreover, dendrimers
such as PAMAM and PPI can be functionalized with terminal groups
that make them soluble in appropriate solvents, bind onto targeted
surfaces or cross-link with other dendrimers to form
multifunctional supramolecular assemblies [Refs. 5.13-5.14].
Example 16
Synthesis and Characterization of Ion-Selective Hyperbranched
Macromolecules and Microparticles
[0259] PAMAM and PPI dendrimers can serve as selective and
recyclable high capacity macroligands for anions and cations in
aqueous solutions [Refs. 5.6-5.12]. Low-cost hyperbranched
macromolecules, such as polyethyleneimine (PEI), behave very
similarly as the corresponding, but expensive dendrimers [Refs.
5.15-5.16]. Hyperbranched PEI has a degree of branching at
approximately 65-70%. Industrial scale quantities of hyperbranched
PEI macromolecules with various molecular weights (MW) ranging from
about 1,000 to several million Daltons are commercially available
from several suppliers. This example shows a strategy for
functionalizing hyperbranched PEI macromolecules (FIG. 2) to
prepare macroligands with very large molar mass that can
selectively bind anions such as Cl.sup.-, Br.sup.- and
SO.sub.4.sup.2- at pH .about.6 and release them at pH .about.9.0
(5.15-5.16).
[0260] The Applicants have also synthesized and characterized
functionalized hyperbranched PEI macromolecules and microparticles
that can selectively bind cations (Na.sup.+, Ca.sup.2+ and
Mg.sup.2+) and anions (Cl.sup.- and SO.sub.4.sup.2-) in aqueous
solutions and release them through a simple change of solution
acidity/basicity. These ions make-up more than 98% of the total
dissolved solids (TDS) in brackish water and seawater [Ref. 5.15].
In this example, further to the synthetic routes shown in FIG. 2
for preparing hyperbranched macromolecules that selectively bind
and release Cl.sup.- and SO.sub.4.sup.2-, recyclable hyperbranched
macromolecules that can selectively bind Na.sup.+, Ca.sup.2+ and
Mg.sup.2+ were synthesized.
[0261] 2s metal ions such as Ca.sup.2+ and Mg.sup.2+ have a strong
preference to coordinate with ligands containing negative O donors
[Ref. 5.17]. Is metal ions such as Na.sup.+ prefer to coordinate
with ligands containing neutral oxygen donors [Ref. 5.17]. Thus,
the following guidelines (based on these well-established trends in
coordination chemistry [Ref. 5.17)]) provides the conceptual
framework for the synthesis of recyclable and selective
hyperbranched macroligands for Na.sup.+, Ca.sup.2+ and
Mg.sup.2+:
[0262] 1. Guideline 1. Hyperbranched macromolecules containing
negative O donors and tertiary amine groups will selectively bind
Ca.sup.2+ and Mg.sup.2+ ions at pH .about.7.0 and release them by
washing with an acid solution containing a small ligand such as
citric acid.
[0263] 2. Guideline 2. Hyperbranched macromolecules containing
neutral O donors and tertiary amine groups will selectively bind
Na+ at pH .about.7.0 and release them by washing with an acid
solution containing a small complexing ligand such as citric
acid.
[0264] To prepare hyperbranched macromolecules containing tertiary
amine and negative O donors, primary/secondary amine groups of
hyperbranched PEI (FIG. 2) were reacted with the appropriate
functional groups (e.g. sulfonate and phosphonate) (FIG. 19).
[0265] For the preparation of hyperbranched macromolecules with
neutral O donors, it is expected that commercially available
2,2-bis(methylol)propionic acid (MPA) hyperbranched macromolecules
can be as starting materials. MPA dendritic macromolecules (FIG.
20) have large numbers of internal O groups and terminal OH groups
[Ref. 5.18]. The terminal OH groups of an MPA hyperbranched
macromolecule (with 64 terminal OH groups) [Ref. 5.18] can be
reacted with the appropriate functional groups (e.g. alcohols,
amines) and is expected to yield hyperbranched macromolecules
containing internal O groups and terminal tertiary amine groups
[FIG. 20].
Example 17
Synthesis and Characterization of Ion-Absorbing Hollow Fibers
(IAHF)
[0266] This example illustrates the use of electrospinning to
generate hollow polymeric nanofibers [Ref. 5.19] with embedded ISHM
as shown in FIG. 21). In this example, PVDF is expected to be
useable as base polymer for the hollow polymeric nanofibers because
it is widely used as base polymer in the fabrication of commercial
hollow-fiber UF/MF membranes and because PVDF and the
functionalized PEI/MPA hyperbranched macromolecules (FIG. 2 to FIG.
20) are partially soluble (at least 5-10 wt %) in polar solvents
with widely different physicochemical properties (e.g. boiling
point and surface tension) such as tetrahydrofuran (THF), dimethyl
formamide (DMF) and dimethyl acetamide (DMAc) [Refs. 5.17,
5.20-5.21]. This is expected to provide many degrees of freedom for
optimizing the physicochemical properties of the proposed IAHF
(FIG. 21) by selecting the appropriate solvents and fiber spinning
conditions [Ref. 5.19].
Example 20
Synthesis, Characterization, and Performance Evaluation of
Ion-Selective Nanofibrous Composite Membranes Using PVDF and
Hyperbranched PEI Macromolecules as Building Blocks
[0267] This example shows the synthesis of nanofibrous composite
(NFC) membranes using polyvinylidene fluoride (PVDF) and
hyperbranched polyethylenimine (PEI) as building blocks. These
NFC-PVDF-PEI membranes comprise cross linked hyperbranched PEI
separation layers supported by PVDF nanofibrous scaffolds that are
electrospun onto commercial PVDF MF membrane supports (FIG. 24)
which in this example allows for fabrication of positively charged
NF membranes with high water flux and improved rejection for
monovalent cations. In order to obtain such membranes, the effects
of cross linker chemistry on membrane properties (morphology,
composition, hydrophobicity and zeta potential) and membrane
performance (salt rejection and permeate flux) was first evaluated.
Three cross linkers tested in this example included trimesoyl
chloride (TMC), 1,3-dibromo propane (DBP) and epichlorohydrin
(ECH). Four salts (NaCl, MgCl.sub.2, Na.sub.2SO.sub.4, and
MgSO.sub.4). The results of this example indicated that PVDF
nanofibers and hyperbranched PEI were suitable s building blocks
for the fabrication of high performance NF membranes for water
purification.
[0268] Materials:
[0269] Poly(vinylidene fluoride) (PVDF) MF membrane supports (0.45
.mu.m pore size) were purchased from Millipore (USA). PVDF powder
(Kynar 761) was provided by Arkema (USA). Hyperbranched
polyethyleneimine (PEI) [M.sub.w: 25,000 and M.sub.n: 10,000] was
provided by BASF (Germany). Dimethylformamide (DMF),
n-methyl-2-pyrrolidone (NMP), trimesoyl chloride (TMC), 1,3-dibromo
propane (DBP) and epichlorohydrin (ECH) were purchased from
Sigma-Aldrich. Analytical grade NaCl, MgCl.sub.2, Na.sub.2SO.sub.4,
MgSO.sub.4, were purchased from Samchon Chemicals (Korea). The
chemicals in this example were used as received. Deionized water
(18.2 M.OMEGA.cm resistivity) was used to rinse the membranes and
prepare the salt solutions.
[0270] Nanofiber and Membrane Synthesis:
[0271] The Applicants utilized blends of PVDF+PEI to spin the
nanofibrous scaffolds of the NFC-PVDF-PEI membranes. A typical
polymer blend was prepared by dissolving PVDF (18.5 wt %) and PEI
(2.5 wt %) in a mixture of DMF and NMP (1:1 w/w). The mixture was
sonicated for 4 hours to obtain a homogeneous PVDF/PEI solution. A
NANON-01A electrospinning (ES) machine (MECC, Japan) was used to
spin the PVDF nanofibrous scaffold of each membrane. The PVDF MF
support was first mounted on the NANON-01A drum collector.
Following this, the PVDF/PEI blend was electrospun onto the PVDF
membrane support using a solution flow rate of 0.7 mL/h and a
voltage of 29 kV. During the ES process, the distance between the
needle and the collector drum was kept constant at 7.5 cm. The
speed of the collector was also kept constant 500 rpm. After the
completion of the ES process, 1.0 mL of a solution of hyperbranched
PEI in methanol (50 wt %) was electrosprayed onto the electrospun
nanofibrous PVDF membranes using a solution flow rate 0.3 mL/h, a
voltage of 29 kV, a needle to collector distance of 7.5 cm and a
collector speed of 2500 rpm. TABLE 1 lists the process parameters
used to (i) spin the PVDF nanofibers and (ii) spray them with PEI.
Following electrospraying, the PEI-coated PVDF nanofibrous
scaffolds were reacted with the cross linkers to generate three
different types of membranes (FIG. 24). To synthesize the
NFC-PVDF-PEI-1 membranes, the PEI-coated nanofibrous scaffolds were
reacted with a solution of TMC in toluene (1% w/v) in a glass
vessel at room temperature for 5 minutes (FIG. 24). Similarly, the
NFC-PVDF-PEI-2 and NFC-PVDF-PEI-3 membranes were synthesized by
reacting the PEI-coated PVDF nanofibrous scaffolds, respectively,
with 20 wt % solutions of 1,3-DBP and ECH in toluene for one hour
at 45.degree. C. Following this, the membranes were rinsed three
times with deionized (DI) water and stored in DI water at room
temperature.
Table 1: List of Electrospinning and Electrospraying Process
Parameters
TABLE-US-00001 [0272] TABLE 1 Process Parameters Electrospinning
Electrospraying Concentration of PVDF (18.5 wt) + PEI 50-wt %
solution Polymer Solution (2.5 wt %) in mixtures of PEI in methanol
of DMF and NMP (1:1 w/w) Amount of 6 mL 1 mL Polymer Solution
Solution Flow Rate 0.7 mL/hr 0.3 mL/hr Applied Voltage 29 kV 29 kV
Needle Diameter (mm) 0.394 mm 0.394 mm Needle Collector 7.5 cm 7.5
cm Distance Drum Collector Speed 500 rpm 2500
[0273] Nanofiber and Membrane Characterization:
[0274] The morphology, chemical composition, hydrophobicity and
zeta potential of the PVDF nanofibers and NFC-PVDF-PEI membranes
were characterized using various analytical tools. The
cross-sectional and surface morphologies of the nanofibers and
membranes were imaged using a field emission scanning electron
microscope (FESEM, FEI, SIRION-100, USA). Before imaging, the
samples in this example were coated with gold at 30 mA for 120
seconds to minimize the charging effect. To obtain the
cross-sectional FESEM images, the membranes were frozen and
fractured following immersion in liquid nitrogen. The SEM images
were subsequently analyzed to estimate the thickness of the
membrane surface layers using the Image J Version 1.45 m image
processing/analysis software. The compositions of the surface
layers of the NFC-PVDF-PEI membranes were characterized by
attenuated total reflectance Fourier transform infrared
spectroscopy (ATR-FTIR) using a JASCO 4100 FT-IR spectrometer
(Japan).
[0275] All samples in this example were scanned from 500 cm.sup.-1
to 4000 cm.sup.-1 with a scanning speed of 2 mm/sec using a zinc
selenide ATR crystal plate with an aperture angle of 45.degree..
The hydrophobicity of each NFC-PEI membrane was determined from
contact angle measurements using a Phoenix 300 contact angle
analyzer (SEQ cooperation, Korea). A microsyringe was utilized to
place a water droplet on the surface of each membrane. After 30
seconds, the image was captured and analyzed using the instrument's
image processing software. Each reported contact angle is the
average of ten different measurements. The zeta potentials of the
membranes were determined using the electrophoresis method [Ref.
7.28].
[0276] This involves measuring the electrophoretic mobility of
monitoring particles inside an electrophoresis chamber having a
membrane and quartz cells [Ref. 7.28]. Due to the sorption and
accumulation of ions at the surface of the membranes, an
electroosmotic flow occurs inside the electrophoresis chamber. This
induced electroosmotic flow causes the particles to undergo
electrophoretic flow (7.28). An ELS-8000 electrophoretic light
scattering spectrophotometer with a plate quartz cell (Otsuka
Electronics, Japan) was used to measure the electrophoretic
mobility of the monitoring particles in 0.01 M KCl solutions as a
function of pH. The monitoring particles consisted of polystyrene
(PS) latex particles (Otsuka Electronics, Japan) with a hydroxy
propyl cellulose surface coating and diameter of 520 nm. The PS
particles were dispersed in 0.01 N KCl solutions. The pH of the KCl
solutions was adjusted with 0.1 N HCl or KOH as needed.
[0277] The measured electrophoretic mobilities (U) [cm.sup.2
V.sup.-1 s.sup.-1] was converted to zeta potentials (.zeta..sub.EP)
[mV] using the Smoluchowski equation as given below (7.28):
.zeta..sub.EP=4.pi..eta.U/.epsilon..sub.r.epsilon..sub.0 Eq 1
where .eta. is the liquid viscosity (0.89.times.10.sup.-3 Pa s),
.epsilon..sub.r is the relative permittivity of the liquid (78.38)
and .epsilon..sub.0 is the vacuum permittivity
(8.854.times.10.sup.-12 s m.sup.-1).
[0278] Filtration Experiments:
[0279] A custom-built filtration system with an effective membrane
area of 24 cm.sup.2 was used to measure the salt rejection and
permeate flux of each NFC-PVDF-PEI membrane. During each filtration
experiment, the Applicants used a feed solution of 10 L with a salt
concentration of 2000 mg/L. The pH of the feed solution was
adjusted with a solution of 0.1 N HCl or 0.1 N NaOH as needed. The
filtration experiments in this example were carried out at room
temperature and at a constant pressure of 7.0 bar. The salt
rejection (R) of each membrane was assayed by electric conductivity
measurements. R was expressed as:
R=(1-C.sub.p/C.sub.f).times.100 Eq. 2
where C.sub.f and C.sub.p are, respectively, the conductivity of
the feed and permeate solutions. The permeate flux (J) [L m.sup.-2
hr.sup.-1] at time t through each membrane was expressed as:
J=V.sub.p/(A.times..DELTA.t) Eq. 3
where V.sub.p is the volume of permeate [L] collected during the
sampling time .DELTA.t [hr] and A is the effective membrane
[m.sup.2].
[0280] Nanofiber Synthesis and Characterization:
[0281] Hyperbranched polyethyleneimine (PEI) and poly(vinylidene
fluoride) (PVDF) were selected as building blocks for the
separation layers, nanofibrous scaffolds and microporous supports
of the filtration membranes (FIG. 24). Due its high density of
reactive amine groups and ready availability from commercial
sources [Refs. 7.13, 2010; 7.9], hyperbranched PEI is a versatile
building block for preparing ion-selective thin films. Other work
has shown that hyperbranched PEI can be used to synthesize NF
membranes with positively charged separation layers [Refs. 7.1;
7.5]. In this example, PVDF was selected as base polymer to
fabricate the nanofibrous scaffolds and microporous supports of the
filtration membranes at least in part because PVDF is widely used
as base polymer in the fabrication of commercial UF/MF membrane
because of its high thermal/chemical resistance and tensile
strength [Refs. 7.20; 7.6] and because PVDF is soluble in a broad
range of solvents including dimethylformamide (DMF),
n-methyl-2-pyrrolidone (NMP) and dimethyl acetamide (DMAc) (Gopal,
2006; 7.6). This provides many degrees of freedom for optimizing
the properties of the microporous supports and nanofibrous
scaffolds of the filtration membranes (FIG. 24) by selecting
appropriate synthetic conditions. However, optimization should take
into account features of the chemical to be selected. For example,
id a membrane is provided for filtering ions, optimization should
take into account that in some instances proteins and other
hydrophobic macromolecular assemblies present in water/wastewater
can foul PVDF membranes due to their hydrophobicity.
[0282] Compared to membrane surface treatment methods such as
chemical oxidation, plasma treatment and polymer grafting [Ref.
7.29], blending hydrophobic polymers such as PVDF with more
hydrophilic polymers can be used as a method for decreasing the
hydrophobicity of polymeric membranes [Ref. 7.19]. Because
hyperbranched PEI and PVDF are both soluble in DMF and NMP, the
blends of PVDF (18.5 w %) and PEI (2.5 w %) were used to synthesize
the nanofibrous scaffolds of the NFC-PVDF-PEI membranes (FIG. 24).
The blends were prepared by dissolving the required amounts of PVDF
and PEI in mixtures of DMF and NMP (1:1 w/w). Consistent with
literature data [Ref. 7.22], the Applicants found that the average
diameter (155.8 nm.+-.44.4 nm) of PVDF nanofibers electrospun using
mixtures DMF/NMP (1:1 w/w) was larger than that of the
corresponding PVDF nanofibers (81.4 nm.+-.21.4 nm) that were
prepared using pure DMF (FIG. 25).
[0283] The utilization of mixtures of solvents for electro spinning
was suitable for this example for at least two reasons [Refs. 7.22;
7.40]. First, using a mixture of solvents can eliminate the
formation of beaded nanofibers [Ref. 7.22]. Beads are defects that
are formed during the electrospinning of polymeric nanofibers
(PNFs) when low-viscosity solvents are utilized to dissolve the
base polymers [Ref. 7.22]. In filtration membranes, beaded
nanofibers decrease the membrane porosity and interrupt the flow of
water through the membrane nanofibrous scaffolds [Ref. 7.22]. The
viscosity of NMP (1.7 cps) is larger than that of DMF (0.9 cps).
Consistent with the observations of Ramakrishna et al. (2005), the
Applicants have found the use of pure DMF as spinning solvent, in
this example, resulted in the formation of beaded PVDF nanofibers
(FIG. 25a). In contrast, in this example, no beaded nanofibers were
observed when mixtures of DMF and NMP (1:1 w/w) were used as
spinning solvents (FIG. 25b). Second, the use of mixtures as
spinning solvents can also increase both the adhesion/tensile
strength of PNFs as well as the strength of their adhesion to
nonwoven microporous supports. Yung et al. [Ref. 7.40], regarding
adhesion/tensile strength of polymeric nanofibers (PNFs) and their
delamination from nonwoven microporous polymeric supports reported
that the adhesion between polyethersulfone (PES) nanofibrous layers
and a nonwoven poly(ethylene terephthalate) (PET) microporous
support was stronger when the base PES polymer was dissolved in
mixtures of DMF and NMP (6:4 w/w). Applicants have also found that
the use of mixtures of DMF and NMP increases the adhesion strength
of PVDF nanofibers to PVDF microporous supports. Consistent with
the observations of Yung et al. [Ref. 7.40], the Applicants have
found the use of pure DMF in this example as spinning solvent
resulted in the formation of PVDF nanofibrous scaffolds that are
easily peeled off by hand from the PVDF microporous supports and
substantially none of the PVDF nanofibrous scaffolds in this
example can be peeled off by hand from their supports when the
fibers were electrospun using mixtures of DMF and NMP (1:1
w/w).
[0284] Membrane Synthesis and Characterization:
[0285] To fabricate ion-selective filtration membranes (FIG. 24),
electrospraying was used to deposit films of hyperbranched PEI onto
PVDF nanofibrous scaffolds that were electrospun onto commercial
PVDF microfiltration membrane supports using mixtures of DMF and
NMP (1:1 w/w). Electrospraying can be a suitable technique for
depositing films onto a broad range of substrates including
polymeric membranes (Jaworek and Sobczyk, 2008). The films can be
deposited from solutions or suspensions of microparticles and/or
nanoparticles with controlled thickness ranging from approximately
10 nm to 100 .mu.m. Roso et al. (2008) have combined
electrospinning with electrospraying to fabricate catalytic
membranes having polysulfone nanofibrous scaffolds with embedded
TiO.sub.2 nanoparticles. TABLE 1 lists the process parameters used
to spray the PVDF nanofibrous scaffolds with hyperbranched PEI.
Based on SEM images (data not shown), the Applicants found the
surfaces of the PVDF nanofibrous scaffolds can be fully covered by
spraying them with 1.0 mL of a 50-wt % solution of PEI in methanol.
Following electrospraying, the PEI-laden nanofibrous PVDF were
reacted, respectively, with trimesoyl chloride (TMC),
1,3-dibromopropane (DBP) and epichlorohydrin (ECH) to produce
filtration membranes with cross linked PEI separation layers (FIG.
24) as described in this example. TABLE 2 lists selected properties
of the NFC-PVDF-PEI membranes that were measured in this example
including contact angle, zeta potential, isoelectric point and
surface layer thickness. FIG. 26 shows the FESEM images of the
surface and cross-section morphology of the NFC-PVDF-PEI membranes.
As shown in FIG. 26a and FIG. 26b, the surface of the
NFC-PVDF-PEI-1 membrane (with TMC cross linker) consists of a film
of PVDF nanofibers with cross linked PEI macromolecules. Due to its
rough/wiggly surface morphology, it was difficult to measure the
thickness of the surface layer of the NFC-PVDF-PEI-1 membrane with
high precision. Using the Image J Version 1.45 m image
processing/analysis software, the thickness of the membrane surface
layer was estimated as being equal to 240 nm.+-.100 nm (TABLE 2).
This value is within the range of the observed thickness (150-2000
nm) of the surface layers of conventional polymeric NF membranes
[Refs. 7.2; 7.18]. FIG. 26 shows that both the surface of the
NFC-PVDF-PEI-2 membrane (with DBP cross linker) and that of the
NFC-PVDF-PEI-3 membrane (with ECH cross linker) consist also of
films of PVDF nanofibers with cross linked PEI macromolecules. The
thickness of the separation layers of the NFC-PVDF-PEI-2 and
NFC-PVDF-PEI-2 membranes can be estimated, respectively, as
approximately equal to 10 .mu.m and 13 .mu.m (TABLE 2). The large
thickness of the surface of these membranes can be attributed to
longer crosslinking reaction times (1 hour) at higher temperature
(45.degree. C.) in the presence of excess reagents (e.g. solutions
of 20 wt % of DBP/ECH in toluene).
TABLE-US-00002 TABLE 2 Table 2: Selected properties of the
NFC-PVDF-PEI membranes synthesized in this example .sup.aContact
Isoelectric Zeta Potential Surface Layer Membrane Surface Layer
Angle Point (pH 6) Thickness NFC-PVDF-PEI-1 Cross linked 38.6 .+-.
1.4.degree. 7.8 39.7 .+-. 3.7 mV 240 .+-. 100 nm PEI/TMC
NFC-PVDF-PEI-2 Cross linked 54.9 .+-. 0.5.degree. 6.4 9.0 .+-. 3.0
mV 10 .mu.m PEI/DBP NFC-PVDF-PEI-3 Cross linked 50.2 .+-.
1.3.degree. 5.7 -4.5 .+-. 0.9 mV 13 .mu.m PEI/ECH .sup.aAll the
contact angles were measured in water. The contact angle of the
PVDF MF membrane support is equal to 130.2.degree. .+-.
0.9.degree..
[0286] FIG. 27 shows the ATR-FTIR spectra of a PVDF membrane
support, a blended PVDF/PEI nanofibrous scaffold and those of the
NFC-PVDF-PEI membranes. FIG. 27a highlights several characteristic
peaks of PVDF surfaces including CF.sub.2 bending (615 and 766
cm.sup.-1), CH.sub.2 rocking (840 cm.sup.-1), CH stretching (976
cm.sup.-1) and CF stretching (1234 and 1279 cm.sup.-1) (7.3). FIG.
27b shows that the blended PVDF/PEI nanofibrous scaffold exhibits
two major peaks including (i) NH.sub.2 bending (1655 cm.sup.-1)
from primary amines and (ii) NH stretching (3255 cm.sup.-1) from
primary/secondary amines. The Applicants assign these peaks to PEI
macromolecules that are embedded in the PVDF nanofibrous scaffold
(FIG. 24). As shown in FIG. 27c, the FT-IR spectrum of the
NFC-PVDF-PEI-1 membrane exhibits some characteristic features of NF
membranes with amide groups including CN stretching (1641
cm.sup.-1) and C.dbd.O stretching (1532 cm.sup.-1) (Setiawan et
al., 2011; Sun et al., 2011). These amide groups are generated when
the PEI macromolecules that are embedded in the membrane PVDF
nanofibrous scaffold react with TMC cross linkers (FIG. 24). The
FT-IR spectrum of the NFC-PVDF-PEI-2 membrane (FIG. 27d) shows no
new characteristic peak. This observation is consistent with the
understanding that mostly secondary/tertiary amines are generated
when the embedded PEI macromolecules of the membrane PVDF
nanofibrous scaffold reacts with 1,3-DBP cross linkers (FIG. 24).
In contrast, the FT-IR spectrum of the NFC-PVDF-PEI-3 membrane
exhibits a new peak, for OH stretching at 3257 cm.sup.-1 indicating
that hydroxyl groups are produced when the PEI macromolecules that
are embedded in the membrane PVDF nanofibrous scaffold reacts with
ECH cross linkers (FIG. 24). TABLE 2 shows significant differences
between the hydrophilicity and zeta potential potentials of
NFC-PVDF-PEI membranes. The contact angle of the PVDF membrane
support is equal to 130.2.degree..+-.0.9.degree. thereby indicating
that the support is very hydrophobic. In contrast, the contact
angles for the NFC-PVDF-PEI-1, NFC-PVDF-PEI-2 and NFC-PVDF-PEI-3
membranes are equal, respectively, to 38.6.+-.1.4.degree.,
54.9.+-.0.5.degree., and 50.2.+-.1.3.degree. thereby indicating
these membranes are hydrophilic and less susceptible to fouling via
sorption of proteins and other hydrophobic macromolecular
assemblies present in water/wastewater. It is worth mentioning that
the contact angle of the NFC-PVDF-PEI-1 membrane
(38.6.degree..+-.1.4.degree.) is smaller by .about.10-20.degree.
than those of commercial thin film composite polyamide NF/RO
membranes with cross linked polyamide separation layers. These
membranes have contact angles of 50-60.degree. [Ref. 7.11]. FIG. 28
shows the zeta potentials of the NFC-PVDF-PEI membranes measured at
various pH. TABLE 2 lists their estimated isoelectric points and
zeta potentials. The isoelectric points of the NFC-PVDF-PEI-1,
NFC-PVDF-PEI-2 and NFC-PVDF-PEI-3 membranes are respectively, equal
to 7.8, 6.4 and 5.7. Their zeta potentials at pH 6 are equal to
39.7.+-.3.7 mV, 9.0.+-.3.0 mV, and -4.5.+-.0.9 mV,
respectively.
[0287] Evaluation of Membrane Performance:
[0288] The overall results of the characterization experiments
indicate that the NFC-PVDF-PEI-1 membrane (with TMC cross linker)
is more hydrophilic than commercial TFC-PA RO/NF membranes. The
large and positive zeta potential of the NFC-PVDF-PEI-1 membrane at
pH 6-7 (FIG. 28) indicates that it has good potential for high
water flux and improved rejection for monovalent cations. To
evaluate the performance of this membrane, cross-flow filtration
experiments were performed to measure its ion rejection and
permeate flux in saline solutions as described in this example.
Aqueous solutions (2000 mg/L) of four salts (NaCl, MgCl.sub.2,
Na.sub.2SO.sub.4, and MgSO.sub.4) were evaluated. FIG. 29 shows the
salt rejection and permeate flux of the NFC-PVDF-PEI-1 membrane
during the course of a typical 12-hr filtration experiment. In
this, the membrane salt rejection and permeate flux reached
constant values after 2 hour of filtration. FIG. 30 shows that the
NFC-PVDF-PEI-1 membrane exhibits higher rejections for the 2-1 salt
(MgCl.sub.2) and 2-2 salt (MgSO.sub.4) than for the 1-1 salt (NaCl)
and 1-2 salt (Na.sub.2SO.sub.4) at pH 4 and 6. This result is
consistent with that of a Donnan exclusion membrane with a positive
surface charge [Ref. 7.23]. As indicated in TABLE 2, the
NFC-PVDF-PEI-1 membrane has an isoelectric point of 7.8. The
isoelectric point of a membrane is the pH at which it has no net
charge in solution. Thus, the NFC-PVDF-PEI-1 membrane is (i)
positively charged at pH 4 and 6 and (ii) negatively charged at pH
8 (FIG. 29). Consistent with the Donnan effect, the NFC-PVDF-PEI-1
membrane will have a higher rejection for divalent cations (e.g.
Mg.sup.2+) over monovalent cations (e.g. Na.sup.+) at pH 4 and 6
[Refs. 7.23; 7.12; 7.4]. A positively charged membrane will also
reject an equivalent amount of anions to maintain overall solution
electroneutrality. Because of this, the Applicants expected the
rejection of a magnesium salt (MgCl.sub.2 MgSO.sub.4) by a
NFC-PVDF-PEI-1 membrane will be larger than that of a sodium salt
(e.g. Na.sub.2SO.sub.4) in aqueous solutions at pH 4 and 6. At pH
8, however, FIG. 30 shows that the salt rejection order of the
NFC-PVDF-PEI-1 membrane is Na.sub.2SO.sub.4>MgCl.sub.2>NaCl.
In this example, the MgCl.sub.2 rejection of the NFC-PVDF-PEI-1
membrane decreased from 87.2% to 76.7% as solution pH water
increased from 4 to 8. In contrast, its Na.sub.2SO.sub.4 rejection
increased significantly from 54.5% to 88.0% with increasing pH from
4 to 8. This higher Na.sub.2SO.sub.4 rejection is consistent with
that of Donnan exclusion membranes with negative surface charges
including thin film composite polyamide NF membranes [Refs. 7.23;
7.34; 7.21] and asymmetric sulfonated polyethersulfone NF membranes
[Refs. 7.32; 7.24].
[0289] The salt rejections and permeate fluxes of the
NFC-PVDF-PEI-2 and NFC-PVDF-PEI-3 membranes were also measured
(TABLE 3TABLE 3). TABLE 3 lists the MgCl.sub.2/NaCl rejections and
permeate fluxes of the NFC-PVDF-PEI membranes at pH 6. The
MgCl.sub.2/NaCl rejections and permeate fluxes of selected
nanofiltration membranes with positively charged surface layers are
also listed in TABLE 3 [Ref. 7.18]. As shown in TABLE 3, the
MgCl.sub.2 rejection of the NFC-PVDF-PEI-1 membrane (87.8%) is
higher than those of the NFC-PVDF-PEI-2 membrane (75.5%) and
NFC-PVDF-PEI-3 membrane (76.4%).
[0290] The NaCl rejections of the NFC-PVDF-PEI-1 and NFC-PVDF-PEI-3
membranes are comparable. They are equal to 64.8% and 62.6%,
respectively. However, the NaCl rejection of the NFC-PVDF-PEI-2 is
lower and equal to 22.9%. TABLE 3 indicates that the permeate flux
of the NFC-PVDF-PEI-3 membrane is relatively low (8-9.0 L m.sup.-2
h.sup.-1). In contrast, the permeate flux of the NFC-PVDF-PEI-1
membrane is relatively high (27-30 L m.sup.-2 h.sup.-1). As shown
in TABLE 3, the permeate flux of the NFC-PVDF-PEI-2 membrane (25-30
L m.sup.-2 h.sup.-1) is comparable to that of the NFC-PVDF-PEI-1
membrane. This result is surprising as the NFC-PVDF-PEI-1 membrane
has a higher surface charge at pH 6 (39.7 mV versus 9.0 mV) with a
lower contact angle (38.6.degree. versus) 54.9.degree. and a
thinner surface layer (200 nm versus 10 .mu.m). The overall results
of this example indicate that nanofibrous composite (NFC) membranes
with PVDF nanofibrous scaffolds and cross linked PEI separation
layers are promising building blocks for the fabrication of high
performance NF membranes for water purification. Without
optimization, the NFC-PVDF-PEI-1 membrane (FIG. 24) already
exhibits a high water flux (.about.30 L m.sup.-2 h.sup.-1) and good
rejections for MgCl.sub.2 (.about.88%) and NaCl (.about.65%)
rejection in salt solutions (2000 mg/L) at pH 6 using a pressure of
7 bar (TABLE 3TABLE 3). The nanofiltration membranes listed in
TABLE 3 that have higher MgCl.sub.2/NaCl rejections that those of
NFC-PVDF-PEI-1 membrane have also lower permeate fluxes
(.about.15.0-19.0 L m.sup.-2 h.sup.-1).
TABLE-US-00003 TABLE 3 R.sub.MgCl2 J.sub.MgCl2 J.sub.NaCl
J.sub.NaCl Experimental Membrane (%) (L m.sup.-2 h.sup.-1) (%) (L
m.sup.-2 h.sup.-1) Separation Layer conditions Reference
NFC-PVDF-PEI-1 87.8 30.5 64.8 27.1 Cross linked 2000 ppm Example 20
PEI/TMC MgCl.sub.2; 2000 ppm NaCl; 7.0 bar NFC-PVDF-PEI-2 75.5 29.8
22.9 24.8 Cross linked 2000 ppm Example 20 PEI/1,3-DBP MgCl.sub.2;
2000 ppm NaCl; 7.0 bar NFC-PVDF-PEI-3 76.4 9.3 62.6 8 Cross linked
2000 ppm Example 20 PEI/ECH MgCl.sub.2; 2000 ppm NaCl; 7.0 bar PPO
73 63 36 63 Poly(2,6-dimethyl-1,4- 1000 ppm 7.31 phenylene oxide)
MgCl.sub.2; 1000 ppm NaCl; 3.5 bar PDMAEMA/PSF 98 8.3 77.8 7.6 Poly
(N,N- 1000 ppm 7.10 dimethylaminoethyl MgCl.sub.2; methacrylate)
1000 ppm NaCl; 8.0 bar HACC/PAN NF-1 94.1 6.9 47.3 12.9
2-hydroxypropyltrimethyl 2000 ppm 7.15 ammonium chloride
MgCl.sub.2; chitosan/hexane diacid/ 2000 ppm acetic anhydride NaCl;
5.0 bar QAPPESK 84 49 31 54 Quaternized 1000 ppm 7.37
poly(phthalazinone MgCl.sub.2; ether sulfone ketone) 1000 ppm NaCl;
4.0 bar GCTACC/ 91.7 8.5 57 8.6 A graft copolymer of 2000 ppm 7.16
PAN trimethylallyl MgCl.sub.2; ammonium chloride 2000 ppm onto
chitosan NaCl; 12.0 bar PEI modified 91.2 15 82.2 15 PEI coating on
75 ppm 7.42 membrane polyamide thin film MgCl.sub.2; composite
membrane 90 ppm NaCl; 8.0 bar PCNFM3 94.3 19.1 60.7 20.6 Poly(2-
1000 ppm 7.18 methacryloyloxy ethyl MgCl.sub.2; trimethylammonium
1000 ppm chloride-co-2- NaCl; 6 bar hydroxyethyl acrylate) M-40
63.3 30.2 36.6 30.2 Poly(arylene ether 1000 ppm 7.41 sulfone) with
pendant MgCl.sub.2; tertiary amine group 1000 ppm NaCl; 5 bar
Example 21
Synthesis, Characterization, and Performance Evaluation of
Ion-Selective Nanofibrous Composite Membranes Using PAN and
Hyperbranched PEI Macromolecules as Building Blocks
[0291] This example show a fabrication of an ion-selective
NFC-PAN-PEI filtration membrane comprising three parts (FIG. 45):
(1) a bottom layer; (2) a mid layer; and (3) a top layer was
fabricated.
[0292] Bottom Layer Fabrication:
[0293] A poly(ethylene terephthalate) (PET) support paper
(3153TH-80S, Basis Weight=80.1 g/m.sup.3, Thickness=109 .mu.m, Air
Permeability=2.71 cc/cm.sup.2/sec, Porosity=5.34
ft.sup.3/ft.sup.2/min) was used as a bottom layer.
[0294] 2) Mid Layer Fabrication:
[0295] Onto the PET paper, the polyacrylonitrile (PAN) mesh mid
layer was fabricated which is composed of PAN nanofibers using
electrospinning technique.
[0296] (a) Materials
[0297] Poly(acrylonitrile) (PAN, powder, M.sub.w=150,000 g/mol),
1,3,5-Benzenetricarbonyl trichloride (trimesoyl chloride or TMC,
98%) were purchased from Sigma-Aldrich (USA). N,N-dimethylformamide
(DMF, 99.5%), 1-Methyl-2-Pyrrolidone (NMP, 99.5%) were purchased
from Dae Jung Chemicals and Metals Co. Ltd (Korea). Toluene (99.5%)
was purchased from Samchun Pure Chemicals Co. Ltd (Korea).
Hyperbranched Polyethyleneimine (PEI, M.sub.n=10,000 g/mol) was
purchased from Nippon Shokubai Co. Ltd (Japan) and the name of
product was SP-200. The reagents and solvents in this example were
used without further purification.
[0298] (b) Preparation of PAN Solution for Electrospinning.
[0299] 1. PAN powder was added into a 30 ml glass vial. 2. DMF and
NMP solvent was added into the vial to make PAN solution. 3. The
solution was put in an oven for 6 h at 80.degree. C. until the
solution become clear. 4. The solution was put in a sonicator for 3
h to make homogeneous solution.
[0300] (c) Fabrication Procedure of Electrospun PAN Mid Layer
[0301] PAN mesh mid layer was fabricated using an electrospinning
machine, `eS-robot` model from NanoNC company. First, a PET support
paper was attached onto the drum collector, and electro spun PAN
nanofibers directly fabricated onto it. Here are the typical
conditions for electrospinning of PAN solution. The applied voltage
is 27 kV, and the distance between the tip and the collector is 10
cm, and the inner diameter of tip is 0.51 mm, and the rotation
speed of drum is 100 rpm, and the flow rate is 1 ml/h. Total
spinning time is depended on the flow rate of spinning solution and
total volume of electrospun solution. Also, the thickness of
nanofiber mesh is depended on the area of the electrospun mesh and
total volume of electrospun solution. The fabricated membrane was
heated 150 C for 1 day in oven.
[0302] Top Layer Fabrication:
[0303] The top layer of the NFC-PAN-PEI membrane was synthesized by
interfacial polymerization onto the electrospun PAN nanofibrous
mesh, using PEI 25k as a monomer of aqueous solution and TMC as a
monomer of organic solution. First, a membrane (the one after
finishing electrospinning) was immersed in the aqueous PEI 25k
solution for 1 h. After that, gently removed the excess solution on
the membrane by glass roller, then it was immersed in the TMC
solution (use Toluene as a organic solvent) for a required reaction
time. After polymerization, the membrane was immersed in the pure
TMC solution for 2 min to get rid of left TMC in it. Subsequently,
the membrane was air-dried for 30 min and it was stored in DI water
before its testing.
[0304] 4) Scanning Electron Microscopy (SEM)
[0305] The morphology of the each layer of the filtration membrane
was investigated by scanning electron microscopy
[0306] The NFC-PAN-PEI membrane fabricated was then characterized
as shown below
[0307] 1) Bottom Layer Characterization
[0308] The PET support paper gives a major mechanical strength to
the filtration membrane, during not only practical water filtration
processes but also fabrication processes. The diameter of fibers is
approximately around 6-7 .mu.m as can be seen in the exemplary
schematic illustration of FIG. 46 and FIG. 47.
[0309] 2) Mid Layer Characterization
[0310] The necessity of mid layer of TFC or filtration membrane
comes from that the thin top layer cannot be fabricated directly
onto PET due to the huge pore size (the empty space between each
fibers) of the PET paper. The smaller pore size in this specific
case associated to a smaller diameter of the fibers, (approximately
200-400 nm), as can be seen from the depiction of FIG. 48A-D The
electrospun nanofiber mesh was used to narrow down the pore size of
the membrane's top part where the synthesis of thin layer actually
occurs. As the diameter of nanofibers is decreased, the pore size
of the nanomesh is also decreased which leads to successful
interfacial polymerization in uniform. Among the conditions of
electrospinning, the diameter of nanofiber is strongly related with
the concentration of polymer solution. In this research, the
minimum concentration for successful electrospinning was 6 wt
%.
[0311] (a) Adhesion Between PAN Nanomesh and PET Support.
[0312] A good adhesion between PAN nanomesh and PET paper is can be
important for further fabrication steps and the filtration test. If
adhesion force is not strong enough, PAN mid layer is expected to
be easily delaminated during the interfacial polymerization step.
Since there are no strong chemical or physical bonds between PAN
mid layer and PET paper, the only major interaction that can
utilize is van der Waals forces. When DMF was solely used as a
solvent for PAN solution, the adhesion was weak due to the highly
volatile nature of DMF (Vapor pressure: 3.85 mmHg at 25.degree. C.)
which makes electrospun fibers too dry even before they arrive on
the PET surface. It is obvious that the good adhesion cannot be
obtained between dry PAN nanofibrous mesh and PET paper. In this
point of view, the Applicants added another solvent, NMP, which is
not only mixable with DMF but also the less volatile (Vapor
pressure: 0.5 mmHg at 25.degree. C.) and also PET is soluble to
NMP. Through many experiments, it was concluded that the
appropriate ratio of these two solvents in PAN solution in this
example is 6:4 (v/v). NMP solvent made electrospun fibers somewhat
wet even after they arrived at the PET surface and residual NMP
solvents contributed to allowing for good adhesion by increasing a
total contact area between PAN electrospun fibers and PET paper.
The adhesion between each nanofiber was also increased which can
contribute to increase the total mechanical integrity of the
membrane.
[0313] Electrospinning conditions also influenced adhesion. When
the mid layer was above certain thickness, the mid layer
delaminated naturally during the air drying after finishing
electrospinning. This happened due to the shrinkage of mid layer
with natural evaporation of organic solvents. When the thickness of
the mid layer was small, the shrinkage of the mid layer was also
small which was not enough to make membrane delaminate. If the
thickness of the mid layer was too small, interfacial
polymerization cannot be successfully done. The thickness of the
mid layer was controlled by controlling total spinning volume. The
speed of drum collector and flow rate also set to certain value to
obtain the membrane with smooth surface and having good adhesion.
Finally, the membrane was heated to 120.degree. C. for a day. This
process significantly increased the adhesion between mid-layer and
PET paper which can due to re-melting process of PAN
nanofibers.
[0314] 3) Top Layer Characterization
[0315] The top layer of membrane can be important to membrane
performances such as water flux and ion rejection. Different from
typical interfacial polymerization, bulky hyperbranched PEI 25k was
used as a monomer in aqueous solution. The concentration of
hyperbranched PEI 25k can be at least 10 wt % for successful
interfacial polymerization which means the covering up of the top
part of PAN nanofibrous layer without cracks. This minimum
concentration can be because there is a certain number of monomer
molecules, depending on the area of pore size, which are needed at
the interface to fully cover up each pore. To be successful in
interfacial polymerization process without cracks, the pore size of
nanofibrous mid layer has to be as small as possible. The
concentration of TMC monomer in Toluene was set to 0.1 wt % which
is typical. The toluene was used since solubility of PEI 25k in
Toluene is quite higher than any other organic solvents. The
reaction time was set to 10 min. This is quite long reaction time
compared to typical interfacial polymerization.
[0316] In SEM images, clear evidence of top thin layer was formed
onto nanofibrous mid layer can be seen. The thickness of PEI thin
film seems less than 100 nm. The conditions of interfacial
polymerization in FIG. 49 and FIG. 50 are PEI 5 wt %, TMC 0.1 wt %,
reaction time 10 min.
Example 22
NFC-PAN-PEI Membrane Evaluation
[0317] The performance of the NFC-PAN-PEI membranes were evaluated
using a custom-made cross-flow filtration equipment. The effective
membrane area of this system was 24 cm.sup.2. The membranes in this
example were operated at 100 psi and an applied cross flow rate was
1.5 LPM. The feed solutions (NaCl, MgSO.sub.4, Na.sub.2SO.sub.4,
MgCl.sub.2) in this example were prepared by dissolving each salt
in distilled water with a concentration of 2000 ppm. NaCl (99.0%)
was purchased from Sigma-Aldrich (USA) and MgSO.sub.4 (99.0%),
Na.sub.2SO.sub.4 (99.0%), MgCl.sub.2 (98.0%) were purchased from
Dae Jung Chemicals Co. Ltd (Korea).
[0318] The water permeability of each membrane was measured in LMH
unit, based on the data of permeate water volume for certain time.
The salt concentration in permeate solutions was measured by a
conductivity measurement equipment (Eutech Instruments, CON 510).
Based on the data of each concentration of permeate (C.sub.p) and
feed (C.sub.f), the rejection (R) was calculated by the equation
below
R ( % ) = [ 1 - ( C p C f ) ] .times. 100. ##EQU00008##
[0319] Permeability Characteristics of NFC-PAN-PEI Membranes:
[0320] Based on the results in this example, it was found that the
water permeability reached at steady state after the 1 h filtration
time which can be due to the membrane, particularly the active
layer, being compacted by pressure. This compaction can increase
the density of thin active layer which led to the decrease of the
water flux. However, the compaction of active layer led to the
increase of ion rejection FIG. 51 and FIG. 52 show a typical water
permeability characteristic and a ion rejection trends with
operating time in the HPEI-filtration membrane.
[0321] Interfacial Polymerization onto Nanofibrous Mid-Layer:
[0322] Typically interfacial polymerization is done onto UF level
membranes which apparently has a much smaller pore size than
electrospun nanofibrous mid-layer. In these examples, somewhat
different monomers and the mid-layer (nanofibrous support) were
applied, which made the conditions of interfacial polymerization
for the PAN filtration membrane to be much different from typical
conditions of interfacial polymerization for commercial RO or NF
membranes. The conditions of interfacial polymerization were
evaluated by water filtration test using MgSO.sub.4 solution (500
ppm) in terms of ion rejection and water flux.
[0323] Morphology of PAN Mid-Layer:
[0324] Since the concentration of PAN spinning solution strongly
affects the fiber diameter of PAN nanofibers, which determines the
pore size of the PAN mid-layer, the performance of membranes were
tested by using the membranes which fabricated by different
spinning solutions. [0325] (A) 10 wt % PAN solution: the chance of
successful interfacial polymerization was inconsistent (at PEI 10
wt %). Ion rejection (MgSO.sub.4) was limited to around 70%.
(300.about.500 nm) [0326] (B) 6 wt % PAN solution: the chance of
successful interfacial polymerization was consistent (at PEI 10 wt
%) Ion rejection (MgSO.sub.4) can be increased to over 90%.
(150.about.200 nm)
[0327] The limitation of ion rejection for the 10 wt % PAN membrane
can be due to the uncovered pores (cracks) in the membrane. Also,
the 10 wt % PAN membrane showed much higher water flux compared to
the 6 wt % PAN membrane at same conditions due to same reason, the
existence of uncovered pores.
[0328] Based on the difference of fiber diameter between 10 wt %
PAN membrane and 6 wt % PAN membrane, the Applicants concluded that
the nanofibrous membrane with smaller diameter is better for
successful interfacial polymerization.
[0329] Concentration of PEI 25k in Aqueous Solution:
[0330] Generally, 1 or 2 wt % of monomers (diamines) are dissolved
in aqueous solution for interfacial polymerization. In this
research, the Applicants observed no ion rejection when using below
10 wt % of PEI 25k regardless of the reaction time and cross linker
concentration. The reason of this phenomenon might be that there is
minimum number of monomer molecules at the interface in the
interfacial polymerization. Due to the difference of molecular
weight between diamines and PEI 25k, which is approximately 1:80,
the Applicants need to dissolve 80 times more to meet the number of
monomers at the interface by simple math. However, the molecular
size of PEI 25k is approximately 4-5 times larger (by radius
assuming that PEI is spherical) so that the concentration can be
increased around 10-20 wt % to meet the number of monomers. In this
example, at least 10 wt % of PEI 25k aqueous solution when 6 wt %
PAN membrane was used. If the monomer is changed to one that has
large molecular weight, the aqueous solution can be more
concentrated then 10 wt %.
TABLE-US-00004 TABLE 4 Performance (Flux, Ion PEI TMC Rxn
rejection) (MgSO.sub.4 PAN Solution Conc. Conc. Time 2000 ppm, pH4,
100 psi) 6 wt % 10 wt % 0.1 wt % 10 min 42 LMH, 90% 6 wt % 5 wt %
0.1 wt % 10 min 77 LMH, 79%
[0331] As shown in TABLE 4, the ion rejection of the membrane
generally cannot reached 80% when 5 wt % PEI was used. Even with
increased reaction time, the ion rejection of this membrane did not
increase very much, largely only the flux was decreased.
[0332] Reaction Time:
[0333] Typical reaction time of interfacial polymerization in this
example is finished in 1-2 min. Typical reaction time was 10 min to
obtain maximum ion rejection. When the reaction time was decreased,
the water flux was much increased; however the ion rejection was
decreased.
TABLE-US-00005 TABLE 5 Performance (Flux, Ion PEI TMC Rxn
rejection) (MgSO.sub.4 PAN Solution Conc. Conc. Time 2000 ppm, pH4,
100 psi) 6 wt % 10 wt % 0.1 wt % 7.5 min 60 LMH, 77% 6 wt % 10 wt %
0.1 wt % 10 min 40 LMH, 90%
[0334] The reaction time determines the thickness of the active
layer. When the 10 min. reaction time, compared to 7.5 min
reaction, the active layer was formed thicker which led to less
water flux and better ion rejection.
[0335] Concentration of Cross-Linker (TMC):
[0336] The concentration of cross-linker in toluene was 0.1 wt %.
The purpose was fabrication of a less cross-linked positive charged
membrane using PEI 25k, so the cross-linker was used as little as
possible. When the monomers are diamine groups, which sizes are
much smaller compared to PEI 25k, there will be no left active
sites of TMC unreacted after the interfacial polymerization of
active layer if diamine molecules are enough. However, PEI 25k
molecules are quite larger and bulky, there is a high possibility
to have unreacted active sites of TMC in active layer even if PEI
25k molecules are enough during the interfacial polymerization
reaction. Because of steric hindrances between PEI 25k, all of the
TMC molecules cannot contribute to make links each PEI 25k
molecule. These unreacted active sites of TMC, which are acyl
groups, turned into carboxylic acid groups when they met water. The
carboxylic acids are a possible source of negative charges at
certain operating pH, the number of these left active sites need to
be decreased as much as possible to make more positive charged
membranes. Also, the amine groups in PEI 25k, which are sources of
positive charge, was not able to survive during the interfacial
polymer reaction if there are a lot of TMC molecules at the
reaction interface.
[0337] Without being limited to a particular hypothesis, it is
thought that when high concentration of TMC was used in interfacial
polymerization reaction, a lot of TMC molecules are attached to
each PEI 25k, which not only induce more dense physical structure
but also decreased the number of amine groups, and unreacted active
sites in each TMC will be converted to carboxylic acid groups
having negative charges. On the contrary, when low concentration of
TMC solution was used, the reaction rate was slow, however, a lot
of amine groups in each PEI were saved and less cross-linked
structure can be obtained. Also, the number of unreacted active
sites of TMC can be decreased since there is not much TMC attached
to single PEI 25k molecule.
[0338] Ion Rejection Characteristics:
[0339] The ion rejection of a PAN filtration membrane was tested by
using four different salts (NaCl, MgSO.sub.4, Na.sub.2SO.sub.4, and
MgCl.sub.2). The feed solutions in this example were prepared by
dissolving each salt in distilled water with a concentration of
2000 ppm. The membrane was made from 6 wt % PAN support and
interfacial polymerized at 10 wt % PEI, 0.1 wt % TMC, and 10 min
reaction time.
TABLE-US-00006 TABLE 6 Permeate Flux (LMH) Ion Rejection (%)
MgCl.sub.2 29 93 MgSO.sub.4 36 90 NaCl 35 75 Na.sub.2SO.sub.4 34
60
[0340] The flux of permeate flow was around 30-35 LMH at 100 psi,
which is similar to commercial NF membranes although the rejection
of MgSO.sub.4 (90%) was lower (97-99% rejection in commercial NF
membranes). However, the rejection of NaCl (75%) was quite higher
than commercial NF membranes (<50% rejection in commercial NF
membranes). The value of permeate flux can be further increased by
controlling reaction time. The record of permeate flux was 42 LMH
at same rejection level (90% rejection for MgSO.sub.4, 77%
rejection for NaCl). The PAN filtration membrane showed good
rejection not only for divalent ions but also for monovalent ions.
Moreover, it is expected that the performance of the membranes, in
terms of permeation flux, can be further increased by changing
conditions of interfacial polymerization.
[0341] The order of the salt rejection was
MgCl.sub.2>MgSO.sub.4>NaCl>Na.sub.2SO.sub.4, which showed
typical rejection order of positively charged membranes with Donnan
exclusion effects. For positively charged membranes, divalent
cations (Mg.sup.2+) is more strongly rejected than monovalent
cations (Na.sup.+) since both ions have similar mass but different
amount of charge (2 times). Consequently, the ion rejections of
magnesium based salt (MgCl.sub.2,MgSO.sub.4) solutions are larger
than sodium based salt (NaCl, Na.sub.2SO.sub.4) solutions because
divalent cations feel two times larger electrostatic repulsion
forces than monovalent cations. Another important phenomenon behind
this rejection order is an electro-neutrality condition. When
cations are rejected from a positive charged membrane, some of the
anions are also rejected to make an electro-neutrality condition.
Between MgCl.sub.2 and MgSO.sub.4, MgCl.sub.2 is expected to be
rejected better since two chloride ions (in MgCl.sub.2), other than
one sulfate ions (in MgSO.sub.4), are repelled when one magnesium
ion is rejected. In the rejection order between NaCl and
Na.sub.2SO.sub.4, NaCl is expected to be rejected better because of
the same electro-neutrality principle.
[0342] There was no evidence about the effects of size exclusion
among the various ion rejection mechanisms. If the size exclusion
effect was one of the ion rejection mechanisms in this membrane,
the ion rejection of Na.sub.2SO.sub.4, which has a large sulfate
ion, is expected to be higher than or even similar to the ion
rejection of NaCl.
Example 23
Procedures Expected to be Suitable for Evaluating Features of
NFC-PAN-PEI Membranes 1. Increase of Permeate Flux:
[0343] The increase of permeate flux can be done by controlling the
conditions of interfacial polymerization. For example, the reaction
time can be decreased to increase the permeate flux. Maintaining
the same level of rejection should also be considered.
[0344] 2. Membrane's pH Dependent Performance:
[0345] This experiment can be used to figure out a relationship
between pH of a feed solution and the ion rejection performance of
the membrane because protonation of amine groups in hyperbranched
PEI can be directly related to a membrane's charge density and can
be largely dependent on pH.
[0346] 3. Pore Size Determination:
[0347] A pore size of a membrane can be determined by testing the
rejection of one or more PEG molecules having different molecular
weights.
[0348] 4. Surface Morphology of the Filtration Membrane:
[0349] Surface morphology of the filtration membrane can be
analyzed by AFM. From this data, information about the interfacial
polymerization reaction can be obtained.
[0350] 5. Zeta Potential Measurement in Filtration Membrane:
[0351] Using a zeta potential measurement system, the relation
between pH and membrane charge can be determined. Also from the
absolute value of zeta potential, the conditions of interfacial
polymerization which can affect the membrane's charge density can
be determined. For example, a quantitative relationship between the
concentration of TMC and the membrane's charge density can be
obtained. These data can help to understand the nature of reaction
characteristics of interfacial polymerization, for example due to
the monomer being bulky.
[0352] 6. Using Bulkier Monomers:
[0353] Different monomers can be used in interfacial polymerization
including higher molecular weight of PEI molecules. They can form a
more loose structure in top layer which can lead to higher flux
good rejection.
Example 25
Synthesis, Characterization, and Performance Evaluation of
Ion-Selective Nanofibrous Composite Membranes Using PET, PVDF, PEI
Macromolecules and PEI Nanoparticles as Building Blocks
[0354] A NANON-01A electrospinning machine was used to fabricate an
ion-selective filtration membrane with a PET backing paper and a
film of cross-linked PVDF nanofibers with embedded PEI
macromolecules and nanoparticles (FIG. 53). Commercially available
PVDF (Kynar 761) provided by Arkema was used to spin the
nanofibers. First, different amounts (15, 18.5, 20 wt %) of PVDF
were dissolved in a mixture (8:2 v/v) of dimethyl formamide (DMF)
and acetone solution. The mixture was stirred overnight to obtain a
homogeneous PVDF solution. Aliquots of the PVDF solutions were then
fed into a 10 mL syringe with a needle of 20 g size. During the
electrospinning, the flow rate of polymer solution was varied from
0.3 to 2 mL/h and the applied voltage was varied from 25 kV to 29
kV. The distance between needle and collector was kept constant at
15 cm. The drum collector operated at 1000 rpm and covered with a
PET support paper placed on an aluminum foil.
[0355] After the completion of the electrospinning, the PVDF
nanofibers were left on the collector to dry overnight at room
temperature. Following this, a solution of hyperbranched PEI (50 wt
%) in methanol was electrosprayed on the PVDF-laden PET support. In
this case, the sample of commercial hyperbranched PEI [Epomin
SP-006 with M.sub.n=600 g/mole] was provided by Nippon Shokubai,
LTD. Epomin SP-006 hyperbranched PEI was used to synthesize the
nanoparticles via an inverse suspension polymerization process
[Refs. 9.26-9.27]. Subsequently, a suspension (10 wt %) of PEI
nanoparticles (500 nm-1000 nm) in DMF was sonicated and
electrosprayed onto the PEI-coated PVDF-laden support (FIG. 53).
The filtration membrane was then reacted with 1,3-dibromopropane at
40.degree. C. to produce a film of network of cross-linked PEI
macromolecules and nanoparticles on the membrane surface. FIG. 53
shows the SEM images of the filtration membrane and its components
including the PET support, the PVDF nanofibers and the composite
film of PVDF nanofibers with embedded cross-linked PEI
macromolecules and nanoparticles.
Example 27
Increasing Ion-Rejection Capability of NFC Membranes
[0356] In order to increase the ion-rejection capability of NFC
membranes, two basic strategies can be used: (1) Covalent
attachment of PEI macromolecules and NP on the filtration membranes
using layer-by-layer assembly followed by cross-linking to increase
the density of reactive amine groups on the filtration membrane
films; and (2) Functionalization of the amine groups of the PEI
macromolecules and nanoparticles with charged groups including
quaternary amines, carboxylic, sulfonate and amide groups to
increase their charge density.
[0357] In this example, the density of reactive amine groups in the
filtration membrane films can be increased by deposition and
covalent attachment of PEI macromolecules with molar mass
(M.sub.w=25000) or by deposition and covalent attachment of PEI
nanoparticles (FIG. 54).
[0358] In both cases, layer-by-layer (LBL) assembly of PEI
macromolecules or nanoparticles (28) mediated by the deposition of
poly(methyl methacrylate) [PMMA] followed by thermal amidation (29)
at 110 C (for 10 hours under nitrogen) can be employed to produce
films of cross-linked PVDF nanofibers with high density of reactive
amine groups of the surface of the NF membranes (FIG. 55).
[0359] The amine groups of the PEI films of the filtration
membranes can be subsequently reacted with the appropriate
functional groups to produce films with high density of charged
groups including quaternary amines, carboxylic, sulfonate and amide
groups to increase their charge density (FIG. 56) using synthetic
methods as described in references 9.23-9.27 to functionalize the
membranes.
Example 28
Further Development of Ion-Selective Filtration Membranes
[0360] Synthesis and characterization of low-pressure and
ion-selective filtration membranes can also be performed using
polysulfone (PS) and polyacrylonitrile (PAN) as base polymers for
the nanofibers. Graft polymerization can be used (e.g. UV induced
polymerization of methylacrylate) to activate the surface of the PS
and PAN nanofibers prior to covalent attachment and functionalizing
of PEI macromolecules and nanoparticles (FIG. 54, to FIG. 56).
Example 29
More HPEI-Filtration Membrane Fabrication and Characterization
[0361] The Applicants have fabricated a HPEI-filtration membrane
comprising three parts: (1) a bottom layer; (2) a mid layer; and
(3) a top layer (FIG. 45).
[0362] 1) Bottom Layer Fabrication:
[0363] A poly(ethylene terephthalate) (PET) support paper (3153
TH-80S, Basis Weight=80.1 g/m.sup.2 Thickness=109 .mu.m Air
Permeability=2.71 cc/cm.sup.2/sec, Porosity=5.34
ft.sup.3/ft.sup.2/min) was used as a bottom layer.
[0364] Mid Layer Fabrication:
[0365] Onto the PET paper, the poly(acrylonitrile) (PAN) mesh mid
layer was fabricated which is composed of PAN nanofibers using
electrospinning technique.
(a) Materials:
[0366] Poly(acrylonitrile) (PAN, powder, M.sub.w=150,000 g/mol),
1,3,5-Benzenetricarbonyl trichloride (Trimesoyl chloride or TMC,
98%) were purchased from Sigma-Aldrich (USA). N,N-Dimethylforamide
(DMF, 99.5%), 1-Methyl-2-Pyrrolidone (NMP, 99.5%) were purchased
from Dae Jung Chemicals and Metals Co. Ltd (Korea). Toluene (99.5%)
was purchased from Samchun Pure Chemicals Co. Ltd (Korea).
Hyperbranched Polyethyleneimine (PEI, M.sub.n=10,000 g/mol) was
purchased from Nippon Shokubai Co. Ltd (Japan) and the name of
product was SP-200. The reagents and solvents in this example were
used without further purification.
(b) Fabrication of Electrospun PAN Mid Layer:
[0367] PAN mesh mid layer was fabricated using an electrospinning
machine, `eS-robot` model from NanoNC company. First, a PET support
paper was attached onto the drum collector, and electrospun PAN
nanofibers directly fabricated onto it. Here are the typical
conditions for electrospinning of PAN solution. PAN solution (9 wt
%) was prepared by dissolving PAN powder into the mixed solvent
(7:3 DMF:NMP). The applied voltage is 17 kV, and the distance
between the tip and the collector is 13 cm, and the inner diameter
of tip is 0.51 mm, and the rotation speed of drum is 120 rpm, and
the flow rate is 0.9 ml/h. Total spinning time is depended on the
flow rate of spinning solution and total volume of electrospun
solution. Also, the thickness of nanofiber mesh is depended on the
area of the electrospun mesh and total volume of electro spun
solution.
[0368] 3) Top Layer Fabrication:
[0369] The top layer of the HPEI-filtration membrane was
synthesized by interfacial polymerization onto the electrospun PAN
nanofibrous mesh, using PEI 25K as a monomer of aqueous solution
and TMC as a monomer of organic solution. First, a membrane (the
one after finishing electrospinning) was immersed in the aqueous 10
wt % of PEI 25k solution for 1 h. After that, gently removed the
excess solution on the membrane by glass roller, then it was
immersed in the TMC solution (0.05-2 wt %) (use Toluene as an
organic solvent) for a required reaction time. After
polymerization, the membrane was immersed in the pure TMC solution
for 1 min to get rid of left TMC in it. Subsequently, the membrane
was immersed in ethanol to wash TMC solvent in the membrane. At
last, the membrane was air-dried for 30 min and it was stored in DI
water for 24 hr before its testing.
[0370] Results:
[0371] According to SEM analysis, the average diameter of each PAN
fiber was approximately 250 nm (FIG. 57).
[0372] From the SEM analysis, it was confirmed that the micro-sized
pores from PAN nanofibrous layer were fully covered by HPEI-TMC
cross linked layer by interfacial polymerization. By changing the
concentration of cross linkers and reaction time, different surface
morphology (in nano-scale) was observed (FIG. 58).
[0373] A water flux vs. time graph is shown in FIG. 59. This is a
typical pure water flux vs. time graph. It is most likely due to
compaction of HPEI-TMC cross linked layer by hydraulic pressure.
The stable data of pure water flux was obtained after at least 3 h
filtration time (FIG. 59).
[0374] The ion rejection values were increasing by using more TMC
due to formation of dense top layer. A saturated concentration of
TMC is expected to be around 1 wt %. It is expected that nitrogen
ratio at the surface and zeta potential value will be increased
with increasing TMC concentration (FIG. 60).
[0375] It was observed that the best performance can be obtained at
saturated TMC condition in short time. Also, there were not much
differences of rejection of MgCl.sub.2, NaCl between 20 s r.times.n
time and 10 s r.times.n time. So, partial conclusion is assembling
HPEI in dense and thin, to make optimized membrane toward
MgCl.sub.2, NaCl (FIG. 61).
[0376] Nitrogen ratio of surface was increased with increasing TMC
concentration (FIG. 62).
[0377] It can be interpreted in this example that the more cross
linker that is used, the denser HPEI layer. This interpretation is
only applied to interfacial polymerization which highly-reactive
cross linkers are used.
[0378] In FIG. 63 it is shown that no characteristic bands of amide
groups were found.
[0379] In FIG. 64 it is shown that characteristic bands of amide
groups were found: 1642 cm.sup.-1 (C.dbd.O stretch), 1560 cm.sup.-1
(N--H stretch).
[0380] In FIG. 65 it is shown that characteristic bands of amide
groups were found: 1642 cm.sup.-1 (C.dbd.O stretch), 1560 cm.sup.-1
(N--H stretch). The intensity of the amide bands also
increased.
Example 33
Synthesis and Characterization of Branched PEI
Micro/Nanoparticles
[0381] Applicants have developed a route for synthesizing dendritic
micro/nanoparticles with controllable size using low-cost
hyperbranched polymers as building blocks (FIG. 66; U.S.
Provisional Patent Application 61/665,749). As an example of this
methodology, the synthesis and characterization of hyperbranched
poly(ethyleneimine) (PEI) nanoparticles (NPs) is described.
[0382] Nanoparticle Synthesis:
[0383] Because hyperbranched PEI macromolecules are water-soluble,
a surfactant-stabilized inverse suspension of water-in-toluene was
used to prepare the base PEI beads with high density of amine
groups. The reaction vessel is charged with hyperbranched
polyethyleneimine (PEI) polymer as the desired amount of HCl is
added over the course of 30 min to an hour under ambient
temperature. Water and surfactant (sodium dodecyl benzene sulfonate
or sodium dodecyl sulfate) is added, followed by addition of
toluene, which serves as continuous phase. The mixture is stirred
for 1 hour until a turbid solution was attained. The solution was
homogenized to induce high shearing and formation of stable mini
emulsions using a stator rotor type homogenizer. The mixture is
then heated to 70-80.degree. C. and followed by drop-wise addition
of cross-linker (epichlorohydrin or dibromopropane). After 2 hours,
the reaction was heated to 120.degree. C. to commence dehydration
of the solution. The reaction end point was considered to be
reached when all the water from the system has been removed. After,
the temperature of the reaction vessel was cooled to ambient
temperature and the suspended particles are collected. The
nanoparticles suspension was separated by centrifugation.
Nanoparticles were neutralized to pH 7 and dialyzed with water to
wash away excess HCl or surfactant.
[0384] Nanoparticle Characterization:
[0385] Dynamic light scattering (DLS) was used to characterize the
size of the PEI nanoparticles. FIG. 67 shows that the PEI NPs have
a bimodal size distribution with the majority of the particles
having an average particle size of 365 nm.
Example 34
Synthesis of Quaternized PEI Microparticles
[0386] Applicants have developed synthetic strategies for
functionalizing PEI macromolecules and PEI microparticles to weak
base and strong base resins with anion high exchange capacity and
controllable size (US Patent Application US 2010/0181257 A1, US
Patent Application US 2011/0315636 A1 and U.S. Patent Application
61/665,749). These strategies can be used to convert membranes to
anion-transfer membranes that can reject cations while allowing
anions to pass through the membranes. As an example of this
methodology, the quaternized PEI microparticles by alkylation of
base PEI microparticles that were synthesized using a inverse
emulsion/suspension process is described (FIG. 17A, FIG. 66 and
FIG. 68).
[0387] Alkylation of PEI Microparticles
[0388] Microparticles were prepared with high anion-exchange
capacity by alkylation of cross linked PEI beads (FIG. 68) that
were synthesized using an inverse suspension process and a
precursor branched PEI macromolecule with molar mass M.sub.n=10,000
Da. Two classes of QPEI resins with monofunctional exchange sites
(1-3) and bifunctional exchange sites (4-5) were prepared (FIG.
68). What follows is a typical preparation procedure for the
quaternized PEI resins (QPEI) with monofunctional exchange sites.
Approximately 20 g of cross-linked PEI beads were mixed with excess
amounts of alkylating reagent (R--I or R--Br) in ethanol (EtOH) or
isopropanol (IPA). 3-5 mL of a proton scavenger (i.e.
diisopropylethylamine [DIPEA]) was added to the mixture, which was
subsequently heated at 75.degree. C. in a pressure vessel for 24 h.
For QPEI resins with bifunctional exchange sites (3 and 4 in FIG.
68), the PEI beads were first alkylated with a bromoalkane with
longer alkyl chain (e.g. hexyl or isobutyl) followed by reaction
with a bromoalkane with shorter alkyl chain (e.g. ethyl or propyl).
The second alkylation step for the QPEI-3 resin was designed to
increase the conversion of amines to quaternary ammonium groups
(QPEI-4).
Example 35
Synthesis of Boron-Selective PEI Microparticles
[0389] Applicants have developed synthetic strategies for
functionalized PEI microparticles and macromolecules with
boron-selective groups. These strategies can be used to convert
membranes to regenerable and boron chelating membranes. FIG. 69
shows the functionalization of base PEI microparticles with organic
compounds (e.g. 2-oxiranylmethanol and glucono-1,5-D-lactone)
containing boron chelating vicinal diol groups. Here again, the
base PEI microparticles were synthesized using an inverse
emulsion/suspension process (FIG. 66 and FIG. 68).
Example 36
Synthesis of Cation-Selective PEI Microparticles
[0390] Applicants have developed synthetic strategies for
functionalized PEI microparticles and macromolecules with
cation-selective groups (FIG. 17B, FIG. 70). Representative
cation-selective ligands that can be linked to PEI microparticles
include compounds with N, O and S donors (FIG. 70) such as
carboxylic acid, carbamate, urea, sulfonic acid, sulfanic acid,
amide, imidine, guanidine, oxime, imidazole, pyridine, thiol,
thio-ether, thio-carboxylic acid. The chemistry for linking these
groups to the primary/secondary amines of base PEI microparticles
(FIG. 19, FIG. 66, and FIG. 69) can be readily implemented due the
superior nucleophilicity of amino groups. This can include halide
substitutions, Michael additions and addition to carboxylates.
These strategies can used to convert membranes to cation transfer
membranes or cation-chelating membranes.
Example 37
Synthesis of Hybrid Inorganic-Organic NFC-PVDF-PEI Membranes
[0391] The NFC-PVDF-PEI membrane platform in this example allows
for building a family of hybrid inorganic-organic membranes. This
example shows an exemplary method of a strategy for synthesizing
such hybrid inorganic-organic NFC-PVDF-PEI. This can include the
following steps (FIG. 54):
1. Synthesizing of NFC-PVDF-PEI membranes (FIG. 54) 2.
Functionalizing of NFC-PVDF-PEI membranes with selective ligands
for the target metal ions of interest (e.g. Cu(II), Ag(I),
Fe(II)/Fe(III), Pd(II), Pt(II)] (FIG. 56) 3. Contacting and
saturating the functionalized NFC-PVDF-PEI membranes with aqueous
solutions of the target metal ions (e.g. Cu(II), Ag(I),
Fe(II)/Fe(III), Pd(II), Pt(II)] 4. Reacting the metal ion laden
with reducing agents such as H.sub.2 to produce NFC-PVDF-PEI
membranes with metallic clusters/nanoparticles.
[0392] In this example (FIG. 54), a PET support was to fabricate
the NFC-PET-PVDF NFC membranes. PVDE can be used as a building
block for both the microfibrous support and nanofibrous scaffold of
the NFC-PVDF-PEI membranes (FIG. 54) due to its high
thermal/chemical resistance and tensile strength, and solubility in
a broad range of solvents including dimethyl formamide (DMF),
N-methyl-2-pyrrolidone (NMP) and dimethyl acetamide (DMAc). These
properties of PVDF provide degrees of freedom for controlling the
properties of the microporous supports and nanofibrous scaffolds of
NFC membranes (FIG. 54) by selecting the appropriate synthesis
conditions. Further the functionalized NFC-PVDF-PEI membranes in
this example can also be loaded with prepared inorganic particles
(e.g. metal oxide/sulfide nanoparticles). By controlling the
structure and chemistry of the membranes and embedded inorganic
nanoparticles (e.g. TiO.sub.2) and/or metal clusters [e.g. Pd(0),
Pt(0) and Fe(0)Pd(0)], other hybrid inorganic-organic membranes can
be fabricated with controllable catalytic/redox activity and,
affinity for gases such as H.sub.2. Such membranes can also be
useful in a broad range of sustainability applications such as
water purification, gas separations, energy conversion and storage,
and chemical manufacturing, for example (FIG. 71).
Example 38
Further Assembly of Multilayer Membrane by Layer-by-Layer
Assembly
[0393] In this example, fabrication of a multilayer membrane by
layer-by-layer assembly is described. In this example, a positively
charged surface (e.g. a layer of nano and/or microfibers with
positively charged dendritic components such as, for example,
quaternary ammonium groups; FIG. 8B, left) is submerged in a
solution containing negatively charged components (e.g. nanofibers
and/or microfibers with negatively charged dendritic components
such as, for example, sulfonate groups; FIG. 8A, beaker 1 and FIG.
8C) and then washed (FIG. 8A, beaker 2) to afford a new layer
comprising the negatively charged component (FIG. 8B, center). The
process is then repeated using a positively charged component (FIG.
8A, beakers 3 and 4, and FIG. 8C right) to afford another layer
comprising the positively charge component (FIG. 8B, right). This
process can be repeated to afford a multi-layer alternating
positive and negative layers.
Example 39
Fabrication of a Membrane with Two Support Layers
[0394] In this example a membrane with two support layers is
described. The membrane can be fabricated by, for example,
electrospinning a support layer (for example, with a polymeric
component and dendritic component as herein described), then
electrospinning a composite layer of nano and/or microfibers
(comprising, for example, ion-absorbing dendritic component), and
then electrospinning a second support layer which can comprise the
same components as the first support layer. An example of this type
of membrane is shown in FIG. 6B using ion-absorbing dendritic
component (FIG. 6A).
[0395] In summary, in several embodiments a filtration membrane is
described comprising polymeric nanofibers and/or microfibers
attaching dendrimer component presenting reactive sites selective
for chemicals to be filtered, and related nanofibers and
microfibers, composite materials, compositions, methods and
systems.
[0396] The examples set forth above are provided to give those of
ordinary skill in the art a complete disclosure and description of
how to make and use the embodiments of filtration membranes and
related, fibers, composites, compositions methods and systems of
the disclosure, and are not intended to limit the scope of what the
Applicants regard as their disclosure. Modifications of the
above-described modes for carrying out the disclosure can be used
by persons of skill in the art, and are intended to be within the
scope of the following claims.
[0397] The entire disclosure of each document cited (including
patents, patent applications, journal articles, abstracts,
laboratory manuals, books, or other disclosures) in the Background,
Summary, Detailed Description, and Examples is hereby incorporated
herein by reference. All references cited in this disclosure are
incorporated by reference to the same extent as if each reference
had been incorporated by reference in its entirety individually.
However, if any inconsistency arises between a cited reference and
the present disclosure, the present disclosure takes
precedence.
[0398] The terms and expressions which have been employed herein
are used as terms of description and not of limitation, and there
is no intention in the use of such terms and expressions of
excluding any equivalents of the features shown and described or
portions thereof, but it is recognized that various modifications
are possible within the scope of the disclosure claimed Thus, it
should be understood that although the disclosure has been
specifically disclosed by preferred embodiments, exemplary
embodiments and optional features, modification and variation of
the concepts herein disclosed can be resorted to by those skilled
in the art, and that such modifications and variations are
considered to be within the scope of this disclosure as defined by
the appended claims.
[0399] 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. As used in this specification and
the appended claims, the singular forms "a," "an," and "the"
include plural referents unless the content clearly dictates
otherwise. The term "plurality" includes two or more referents
unless the content clearly dictates otherwise. Unless defined
otherwise, all technical and scientific terms used herein have the
same meaning as commonly understood by one of ordinary skill in the
art to which the disclosure pertains.
[0400] When a Markush group or other grouping is used herein, all
individual members of the group and all combinations and possible
subcombinations of the group are intended to be individually
included in the disclosure. Every combination of components or
materials described or exemplified herein can be used to practice
the disclosure, unless otherwise stated. One of ordinary skill in
the art will appreciate that methods, device elements, and
materials other than those specifically exemplified can be employed
in the practice of the disclosure without resort to undue
experimentation. All art-known functional equivalents, of any such
methods, device elements, and materials are intended to be included
in this disclosure. Whenever a range is given in the specification,
for example, a temperature range, a frequency range, a time range,
or a composition range, all intermediate ranges and all subranges,
as well as, all individual values included in the ranges given are
intended to be included in the disclosure. Any one or more
individual members of a range or group disclosed herein can be
excluded from a claim of this disclosure. The disclosure
illustratively described herein suitably can be practiced in the
absence of any element or elements, limitation or limitations which
is not specifically disclosed herein.
[0401] A number of embodiments of the disclosure have been
described. The specific embodiments provided herein are examples of
useful embodiments of the disclosure and it will be apparent to one
skilled in the art that the disclosure can be carried out using a
large number of variations of the devices, device components,
methods steps set forth in the present description. As will be
obvious to one of skill in the art, methods and devices useful for
the present methods can include a large number of optional
composition and processing elements and steps.
[0402] In particular, it will be understood that various
modifications may be made without departing from the spirit and
scope of the present disclosure. Accordingly, other embodiments are
within the scope of the following claims.
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