U.S. patent application number 12/436063 was filed with the patent office on 2009-11-05 for thin film membranes with additives for forward and pressure retarded osmosis.
This patent application is currently assigned to NANOH20 INC.. Invention is credited to Robert Leon Burk, Christopher James Kurth.
Application Number | 20090272692 12/436063 |
Document ID | / |
Family ID | 41799524 |
Filed Date | 2009-11-05 |
United States Patent
Application |
20090272692 |
Kind Code |
A1 |
Kurth; Christopher James ;
et al. |
November 5, 2009 |
THIN FILM MEMBRANES WITH ADDITIVES FOR FORWARD AND PRESSURE
RETARDED OSMOSIS
Abstract
A thin film composite or TFC membrane formed by interfacial
polymerization of an organic and aqueous phase on a support
membrane with nanoparticles in the discrimination layer and/or the
support membrane, optimized by the selection of nanoparticles for
membrane flux, hydrophilicity and to minimize thickness of the
support membrane while maintaining the strength and ruggedness
characteristics required for forward osmosis (FO) and/or pressure
retarded osmosis (PRO) so that the flux flow paths are less
tortuous than conventional support membranes and thereby provide
increased flux flow.
Inventors: |
Kurth; Christopher James;
(Eden Prairie, MN) ; Burk; Robert Leon; (Seattle,
WA) |
Correspondence
Address: |
IRELL & MANELLA LLP
1800 AVENUE OF THE STARS, SUITE 900
LOS ANGELES
CA
90067
US
|
Assignee: |
NANOH20 INC.
Los Angeles
CA
|
Family ID: |
41799524 |
Appl. No.: |
12/436063 |
Filed: |
May 5, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12424533 |
Apr 15, 2009 |
|
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12436063 |
|
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61050572 |
May 5, 2008 |
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Current U.S.
Class: |
210/652 |
Current CPC
Class: |
B01D 69/148 20130101;
B01D 61/002 20130101; B01D 67/0006 20130101; B01D 71/60 20130101;
C02F 1/441 20130101; B05D 5/00 20130101; B01D 67/0079 20130101;
B01D 69/141 20130101; B01D 61/025 20130101; C02F 1/445 20130101;
B01D 2323/36 20130101; B01D 2325/48 20130101; Y02A 20/131 20180101;
B01D 71/82 20130101; B01D 71/56 20130101; B01D 63/10 20130101; C02F
2103/08 20130101; B01D 69/125 20130101 |
Class at
Publication: |
210/652 |
International
Class: |
B01D 61/02 20060101
B01D061/02; C02F 1/44 20060101 C02F001/44 |
Claims
1. A forward or pressure retarded osmosis process, comprising:
providing a porous support membrane having nanoparticles disposed
therein; applying a draw solution to a discrimination membrane
interfacially polymerized on the porous support membrane; and
applying a feed solution to the discrimination layer for diffusion
there through to the draw solution to remove contaminants from, or
utilize increased pressure in, the draw solution.
2. The forward or pressure retarded osmosis process of claim 1,
wherein applying a draw solution to a discrimination membrane
interfacially polymerized on the porous support membrane further
comprises: applying the draw solution to the porous support
membrane for diffusion there through to the discrimination
layer.
3. The forward or pressure retarded osmosis process of claim 1,
wherein applying a feed solution to the discrimination layer for
diffusion there through into the draw solution, comprising:
applying the feed solution to the porous support membrane for
diffusion there through to the discrimination layer.
4. The forward or pressure retarded osmosis process of claim 1,
further comprising: utilizing increased pressure in the draw
solution resulting from transport of the feed solution across the
discrimination membrane into the draw solution.
5. The forward or pressure retarded osmosis process of claim 1,
further comprising: contaminants may be removed from the feed
solution resulting from transport of the contaminants across the
discrimination membrane into the draw solution.
6. The process of claim 1, wherein providing a porous support
membrane having nanoparticles disposed therein further comprises:
providing a porous support membrane having the structural strength
of a thicker porous support membrane as a result of having the
nanoparticles disposed therein.
7. The process of claim 1, wherein providing a porous support
membrane having nanoparticles disposed therein further comprises:
providing a porous support membrane having the structural strength
of a more porous support membrane as a result of having the
nanoparticles disposed therein.
8. The process of claim 1, wherein providing a porous support
membrane having nanoparticles disposed therein further comprises:
providing a thinner porous support membrane having the required
structural strength for the process as a result of having the
nanoparticles disposed therein.
9. The process of claim 1, wherein providing a porous support
membrane having nanoparticles disposed therein further comprises:
providing a porous support membrane having less tortuous feed
solution transport paths as a result of having the nanoparticles
disposed therein.
10. The process of claim 1, wherein providing a porous support
membrane having nanoparticles disposed therein further comprises:
providing a porous support membrane having increased hydrophilicity
as a result of having the nanoparticles disposed therein.
11. The process of claim 1, further comprising: providing the
discrimination membrane including additives dispersed therein added
to an organic and/or an aqueous phase before the organic and
aqueous phases were contacted during the interfacial polymerization
so that the discrimination layer has increased solvent permeability
as a result of the additives therein.
12. The process of claim 11 wherein providing the discrimination
membrane including additives dispersed therein further comprises:
providing the discrimination membrane including the same or
different nanoparticles dispersed therein.
13. The process of claim 12 wherein providing the discrimination
membrane including the same or different nanoparticles dispersed
therein further comprises: providing the discrimination membrane
also including alkaline earth metals dispersed therein.
14. The process of claim 12 wherein providing the discrimination
membrane including the same or different nanoparticles dispersed
therein further comprises: providing the discrimination membrane
also including alkaline earth metals dispersed therein.
15. The process of claim 13 wherein providing the discrimination
membrane also including alkaline earth metals dispersed therein
further comprises: providing the discrimination membrane also
including mhTMC as an additive dispersed therein.
16. The process of claim 11 wherein providing the discrimination
membrane including additives dispersed therein further comprises:
providing the discrimination membrane including alkaline earth
metals dispersed therein.
17. The process of claim 16 wherein providing the discrimination
membrane including alkaline earth metals dispersed therein further
comprises: providing the discrimination membrane also including
mhTMC as an additive dispersed therein.
18. The process of claim 11 herein providing the discrimination
membrane including additives dispersed therein further comprises:
providing the discrimination membrane including mhTMC as an
additive dispersed therein.
19. The process of the claim 1, further comprising: providing the
discrimination membrane including additives dispersed therein added
to an organic and/or an aqueous phase before the organic and
aqueous phases were contacted during the interfacial polymerization
so that the discrimination layer has increased solvent permeability
as a result of the additives therein.
20. The process of claim 1, wherein the draw solution is seawater
and the feed solution is fresh water.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the priority of provisional
application 61/050,572, filed May 5, 2008 and Ser. No.12/424,533
filed Apr. 15, 2009, incorporated in herein in full and attached
hereto as Appendix A for that purpose.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention is related to thin film composite membranes,
which may be called TFC membranes, and more particularly to such
membranes used for forward osmosis or FO, for example to purify
water, or for pressure retarded osmosis or PRO, for example to
generate power from the mixing of salt water and pure water.
[0004] 2. Description of the Prior Art
[0005] RO membranes are often made by interfacial polymerization or
IFP of a monomer in a nonpolar (e.g. organic) phase together with a
monomer in a polar (e.g. aqueous) phase on a porous support
membrane. The support membrane is used for structural support of
the IFP membrane during manufacturing and during operation. RO
membranes, such as IFP RO membranes (that is, RO membranes made by
interfacial polymerization processes), may be used for osmosis
where water flows naturally from a pure solvent or feed solution,
to a less pure solution or draw solution. However, when IFP RO
membranes are used for FO or PRO, the solvent, typically water, and
the solute, typically water diluted with inorganic or organic
salts, or other soluble molecules, tend to dilute each other and
reduce membrane efficiency. Further, the support membrane, which is
used primarily for structural support, reduces water flux to some
degree, and the solvent and solute become mixed in solution in the
thickness of the support membrane structure including a fabric,
further reducing membrane efficiency for both FO and PRO
processes.
[0006] What are needed are improved membranes with enhanced
efficiency for use in FO and PRO processes.
SUMMARY OF THE INVENTION
[0007] In one aspect, a forward or pressure retarded osmosis
process may include providing a porous support membrane having
nanoparticles and/or other additives disposed therein, applying a
draw solution to one side of a discrimination membrane
interfacially polymerized on the porous support membrane and
applying a feed solution to another side of the discrimination
layer for diffusion there through to remove contaminants from, or
utilize increased pressure in, the draw solution. The feed solution
may be applied to the porous support membrane for the another side
of the discrimination layer.
[0008] The increased pressure in the draw solution resulting from
transport of the feed solution across the discrimination membrane
into the draw solution may be used. Contaminants from the feed
solution may be removed resulting from transport of the
contaminants across the discrimination membrane into the draw
solution.
[0009] The porous support membrane may have the structural strength
of a thicker porous support membrane or a less porous support
membrane as a result of having the nanoparticles and/or other
additives disposed therein. A thinner support membrane, and/or a
membrane with less tortuous feed solution transport paths may be
used as a result of having the nanoparticles and/or other additives
disposed therein.
[0010] The discrimination membrane may including additives
dispersed therein added to an organic and/or an aqueous phase
before the organic and aqueous phases were contacted during the
interfacial polymerization so that the discrimination layer has
increased feed solution permeability as a result of the additives
therein. The discrimination membrane may include the same or
different nanoparticles and/or alkaline earth metals and/or other
metals and/or mhTMC as an additive dispersed therein. The membrane
may have increased feed solution permeability as a result of the
additives therein. The draw solution may be seawater and the feed
solution may be fresh water.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is an exploded diagrammatic view of membrane 10
during a fabrication processing including nanoparticle/additives 16
in aqueous phase 14 and/or organic phase 18 and/or porous support
12 and/or fabric 20.
[0012] FIG. 2 is a cross-sectional view of membrane 10 with
nanoparticle/additives 16 dispersed in discrimination layer 24 and
support layer 12.
[0013] FIG. 3 is a graph of resistance to flow, illustrating
compaction as a function of time, during initial operations of
control membrane 52--without nanoparticles/additives 16--and for
membranes 54, 56 and 58 with nanoparticle/additives 16 dispersed in
various layers.
[0014] FIG. 4 is a photomicrograph illustrating the operation of
the dual beam FIB-SEM technique used for FIGS. 5-7.
[0015] FIG. 5 is an FIB-SEM of support membrane 12--with
nanoparticle/additives 16 dispersed therein--after 8 hours of
operation of membrane 12 at 800 psi.
[0016] FIGS. 6,7 are FIB-SEMs of support membrane 64, without
nanoparticle/additives 16 dispersed therein, after 1 and 8 hours of
operation, respectively.
[0017] FIG. 8 is a diagrammatic view of an IFP FO/PRO membrane in a
conventional cylindrical housing, canister 66.
[0018] FIG. 9 is a diagrammatic view of membrane 10 during
operation as an FO or RO membrane including a graph of salinity
superimposed thereon.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0019] Referring now to FIG. 1, an exploded view of membrane 10
illustrating the fabrication process is shown in which membrane 10
may include organic phase layer 18, aqueous phase layer 14, porous
support membrane 12 and fabric layer 20. One or more types of
nanoparticles 16, or other additives as discussed below in greater
detail, may be included in aqueous or organic phases 14, 18 before
contact there between for interfacial polymerization so that
nanoparticles 16 are dispersed in discrimination layer 24 as shown
in FIG. 2. Nanoparticles/additives 16 may also be dispersed in
support layer 12 and fabric 20.
[0020] Referring now also to FIG. 2, a portion of membrane 10 is
illustrated after fabrication including nanoparticles and/or other
additives 16, in discrimination layer 24 as well as
nanoparticles/additives 16 in support layer 12 which may be the
same or different than those--if any--used in discrimination layer
24. In a conventional thin film composite or TFC membrane, made
without nanoparticles/additives 16, the typical layer thicknesses
are as shown, the discrimination layer is on the order of 0.1
microns (100 nm) thick, the support layer is typically on the order
of 50 microns thick and the fabric layer is typically on the order
of 100 microns thick. These thicknesses of layers are
conventionally required for structural support.
[0021] Nanoparticles/additives 16, which may used in porous support
layer 12 to add strength to support membrane 12, advantageously may
permit a substantially thinner support membrane to be used under
the same conditions as a conventionally made support membrane is
used as discussed in more detail below. Similarly, the same or
different nanoparticles 16 may be added to fabric layer 20 to
provide further structure support and ease of handling for support
membrane 12 and membrane 10. For example, the conventionally used
50 micron thickness of support layer for TFC membranes, such as
membrane 10, when strengthened by the addition of nanoparticles 16,
provides perhaps twice as much structural strength as provided by
the same support layer without nanoparticles/additives 16 and may
be replaced by a substantially thinner layer such as a 25 micron
layer without any loss of required strength as shown below with
regard to FIG. 9. Similarly, when nanoparticles/additives 16 are
added, the thickness of fabric 20 may be reduced by perhaps about
25% to 50% as also shown below in FIG. 9.
[0022] During fabrication, support membrane 12 is often formed by
casting on fabric 20. Nanoparticles/additives 16 may be added to
aqueous phase 14 and/or organic phase 18 before such phases are
contacted together for IFP. Aqueous phase 14 is typically applied
to support 12 and then organic phase 18 is applied to aqueous phase
14 which begins the IFP process, forming discrimination layer
24.
[0023] In particular with regard to the process of forming membrane
10 by IFP, aqueous phase 14 may also include one of the reactants
or monomers, and other processing aids such as surfactants, drying
agents, catalysts, coreactants, cosolvents, etc. A first reactant
or monomer can be selected so as to be miscible with a polar liquid
to form a polar mixture. Typically, the first monomer can be a
dinucleophilic or a polynucleophilic monomer. Generally, the
difunctional or polyfunctional nucleophilic monomer can have a
primary or secondary amino group and can be aromatic (eg,
m-phenylenediamine (MPD), pphenylenediamine, 1,3,5-triaminobenzene,
1,3,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene,
2,4-diaminoanisole, and xylylenediamine) or aliphatic (e.g.,
ethylenediamine, propylenediamine, piperazine, and
tris(2-diaminoethyl)amine).
[0024] The polar mixture for aqueous phase 14 need not be aqueous,
but the polar liquid should be immiscible with the apolar liquid of
organic phase 18. Although water is a preferred solvent for aqueous
phase 14, non-aqueous solvents can be utilized, such as
acetonitrile and dimethylformamide (DMF). The resulting polar
mixture typically includes from about 0.1% to about 20% by weight,
preferably from about 0.5% to about 6% weight, of amine. The polar
mixture can typically be applied to the micro-porous support
membrane 12 by dipping, immersing, coating, spraying or other
conventional techniques. Once coated on porous support membrane 12,
excess polar mixture can be optionally removed by evaporation,
drainage, air knife, rubber wiper blade, nip roller, sponge, or
other devices or processes.
[0025] Organic phase 18 used during IFP may also include one of the
reactants and other processing aids such as catalysts,
co-reactants, co-solvents, etc. A second monomer can be selected so
as to be miscible with an apolar liquid forming an apolar mixture
for organic phase 18, although for monomers having sufficient vapor
pressure, the monomer can be optionally delivered from a vapor
phase. Typically, the second monomer can be a dielectrophilic or a
polyelectrophilic monomer. The electrophilic monomer can be
aromatic in nature and can contain two or more, for example three,
electrophilic groups per molecule. For the case of acyl halide
electrophilic monomers, acyl chlorides are generally more suitable
than the corresponding bromides or iodides because of the
relatively lower cost and greater availability.
[0026] Suitable polyfunctional acyl halides include trimesoyl
chloride or TMC, trimellitic acid chloride, isophthaloyl chloride,
terephthaloyl chloride and similar compounds or blends of suitable
acyl halides. The polyfunctional acyl halide can be dissolved in an
apolar organic liquid for organic phase 18 in a range of, for
example, from about 0.01% to about 10.0% by weight or from about
0.05% to about 3% weight percent, preferably about 08.%-5.0%.
Suitable apolar liquids are those which are capable of dissolving
the electrophilic monomers, for example polyfunctional acyl
halides, and which are immiscible with a polar liquid, for example
water. In particular, suitable apolar liquids can include those
which do not pose a threat to the ozone layer and yet are
sufficiently safe in terms of their flashpoints and flammability to
undergo routine processing without having to undertake extreme
precautions. Higher boiling hydrocarbons, e.g., those with boiling
points greater than about 90.degree. C., such as C8-C24
hydrocarbons and mixtures thereof, have more suitable flashpoints
than their C5-C7 counterparts, but they are less volatile. The
apolar mixture for organic phase 18 can typically be applied to
microporous support membrane 12 by dipping, immersing, coating or
other conventional techniques.
[0027] During fabrication of membrane 10, interfacial
polymerization--or IFP--occurs at the interface between aqueous
phase layer 14 and organic phase layer 18 to form discrimination
layer 24 shown in FIG. 2. The conventional conditions for the
reaction of MPD and TMC to form a fully aromatic, polyamide thin
film composite membrane 10 include an MPD to TMC concentration
ratio of 10-30 with MPD at about 1% to 6% by weight in polar phase
14, preferably about 2.0-4.0% by weight MPD. The reaction can be
carried out at room temperature in an open environment, or the
temperature of either the polar or the apolar liquid or both may be
controlled.
[0028] Once formed, the dense polymer layer, which becomes
discrimination layer 24, can advantageously act as a barrier to
inhibit the contact between reactants and to slow down the
reaction. The selective dense layer, discrimination layer 24 so
formed, is typically very thin and permeable to water, but
relatively impermeable to dissolved, dispersed, or suspended solids
such as salts. Once the polymer layer 24 is formed, the apolar
liquid or residue of organic phase 18 can be removed by evaporation
or mechanical removal. It is often convenient to remove the residue
of organic phase 18 by evaporation at elevated temperatures, for
instance in a drying oven.
[0029] Nanoparticles/additives 16 may be added to aqueous phase 14
and/or organic phase 18 for several reasons; to increase water
permeability, to increase hydrophilicity, and/or to control surface
morphology (for example to increase or decrease the smoothness of
the membrane surface). Changes to the membrane smoothness can alter
the rate at which materials rejected by the membrane are
transported from the membrane, that is, higher smoothness can both
improve process efficiency and/or reduce fouling.
[0030] In some cases, performance can be further improved by the
addition of a rinse in a high pH aqueous solution after membrane 10
is formed. For example, membrane 10 can be rinsed in a sodium
carbonate solution. The pH is preferably from 8-12, and exposure
time may vary from 10 seconds to 30 minutes or more. Alternatively
the membrane may be rinsed at high temperatures, or exposed to
chlorinating agents.
[0031] Support membrane 12, on which discrimination layer 24 is
formed by IFP, is typically a polymeric microporous support
membrane, which may or may not be supported by a nonwoven or woven
fabric, such as fabric 20, for further mechanical strength and
structural support. Support membrane 12 may conventionally be made
from polysulfone or other suitably porous membranes, such as
polyethersulfone, poly(ether sulfone ketone), poly(ether ethyl
ketone), poly(phthalazinone ether sulfone ketone),
polyacrylonitrile, polypropylene, cellulose acetate, cellulose
diacetate, or cellulose triacetate. These conventional microporous
support membranes 12 are typically 25-250 microns in thickness, for
example 50 microns, and have been found to have the smallest pores
located very near their upper surface. Porosity at the surface of
membrane 12 is often low, for instance from 5-15% of the total
surface area. Nanoparticles/additives 16, such as zeolites,
particularly LTA, may be added to support membrane 12 during
processing to improve flux by, perhaps, improving porosity, e.g. at
the surface of support membrane 12 and/or by making membrane 12
more resistant to compaction and/or mechanical strengthening of the
membrane.
[0032] Support membrane 12 including nanoparticles/additives 16
will have greater strength and toughness and therefore may be made
thinner than conventional support membranes made for the same
service. As a result of being thinner, support membranes 12 with
nanoparticles/additives 16 imbedded therein are able to minimize
mixing within the support and fabric layer, possibly from the
decreased diffusion path length. Further, addition of nanoparticles
16 to the support membrane 12 may lead to a more highly porous
structure, with fluid transport paths of relatively low tortuosity,
when compared with a conventional support membrane.
[0033] In other words, support membrane 12 with
nanoparticles/additives 16 may be made thinner using less material
(and thus possessing more porosity, less thickness and less
tortuosity of water flow path) while still providing the required
mechanical properties to serve as an appropriate support. In one
embodiment, this may be accomplished, for example, by forming
porous support membrane 12 from a polymer and nanoparticle/additive
solution containing less polymer, for example 5-15%, than would be
used in conventional support membranes 12, such as 15-20%. In
another embodiment, this may be accomplished, for example, by
casting a thinner layer directly, for instance by changing the gap
used for slot die or knife over roll casting, or by decreasing the
flow rate or increasing the web speed for slot die casting.
[0034] Support layers 12--including well dispersed
nanoparticles/additives 16 therein--may also be hydrophilic, e.g.,
with surfaces more readily wet with water and/or displacing air or
gasses entrained within the body of support 12. Such entrained
gasses may make support 12 less efficient by blocking portions of
support 12 to water flow, reducing effective porosity of support 12
to water or other fluid flow. By selecting nanoparticles/additives
16 for use within support membrane 12 that result in hydrophilicity
of membrane 12 (for example nanoparticle zeolites such LTA),
increased hydrophilicity of support 12 may result in reduced water
contact angles at the surfaces of support 12.
[0035] In some instances, fabric layer 20 may also have
nanoparticles/additives 16 incorporated therein for added strength,
as shown for example below with regard to FIG. 9. Fabric layer 20
may be woven or non-woven layers typically of polymeric fibers. It
is desirable that fabric layer 20 be permeable to the fluid or
water being processed, flat and without stray fibers that could
penetrate support 12 and/or thin film 24 and relative thin to
decrease cost and to maximize the surface area of membrane 10 for a
given diameter housing as discussed below in greater detail with
regard to FIG. 8, strong against extension and mechanically
resistant to deformation at high pressures which is useful for PRO
processes in which the draw solution is often pressurized to enable
more efficient system performance. Adding nanoparticles/additives
16 to the polymer fibers of layer 20 produces a more mechanically
robust backing that may allow thinner, less expensive, or tougher
support layers to be manufactured as well as help increase the
surface area of membrane 10 for a given diameter housing as
described with regard to FIG. 8. In some cases it may be preferable
that fabric layer 20 is contained within the support layer 12.
[0036] In some instances, membrane 10 may be used to treat waters
that contain materials that have a tendency to accumulate on the
membrane surface, decreasing the effective permeability of the
membrane. These materials can include but are not limited to
natural organic matter, partially insoluble inorganic materials,
organic surfactants, silt, colloidal material, microbial species
including biofilms, and organic materials either excreted or
released from microbial species such as proteins, polysaccharides,
nucleic acids, metabolites, and the like. This drop in permeability
is often smaller for membranes prepared as disclosed herein than
for membranes prepared by conventional techniques due to a
decreased amount, density, viability, thickness and/or nature of
accumulated material. Membrane surface properties, such as
hydrophilicity, charge, and roughness, often affect this
accumulation and permeability change.
[0037] Generally, membranes with highly hydrophilic, negatively
charged and smooth surfaces yield good permeability, rejection, and
fouling behavior. The improved resistance to accumulation for
membranes of the type disclosed herein can in part be related to
the increased hydrophilicity of these membranes. The increased
hydrophilicity can be measured by the equilibrium contact angle of
the membrane surface with a drop of distilled water at a controlled
temperature. Membranes prepared with nanoparticles/additives 16
present during IFP polymerization can have a contact angle that is
reduced by 5.degree., 15.degree. or even 25.degree. or more
relative to a similarly prepared membrane without
nanoparticles/additives 16. The equilibrium contact angle can be
less than 45.degree., less than 40.degree., or even less than
25.degree..
[0038] Contact angles of distilled, or DI, water at room
temperature may be measured. Membrane 10 may be thoroughly rinsed
with water, and then allowed to dry in a vacuum desiccator to
dryness. Membrane 10 may be dried in a vertical position to prevent
re-deposition of any extracted compounds that may impact contact
angle. Due to the occasional variability in contact angle
measurements, 12 angles may be measured at different spots on
membrane 10 with the high and low angles being excluded and the
remaining angles averaged.
[0039] Referring now to FIGS. 3-6, the addition of
nanoparticles/additives 16 to support layer 12, and/or fabric layer
20, may reduce the tendency of membrane 10 to become compacted
overtime and lose permeability during operation.
[0040] Compaction is a somewhat different function or result than
the increased strength of support membrane 12 discussed above. The
increased strength of support 12 discussed above resulting from the
addition of nanoparticles/additives 16 refers to the fact that
membrane 12 with nanoparticles/additives 16 dispersed therein
provides greater support and resistance against damage and
distortion. As a result, for example, a typical 50 micron thickness
of support membrane 12, fabricated without nanoparticles/additives
16 may be replaced with a 25 micron thickness of the same membrane
with nanoparticles/additives 16 dispersed therein without loss of
the necessary structural strength or rigidity.
[0041] As described immediately below, resistance to compaction
refers to the ability of membrane 12, with nanoparticles/additives
16 dispersed therein, to resist being compacted, i.e., being
squeezed to a thinner dimension by pressure and remaining at a
thinner dimension. As shown below with regard to the graph of FIG.
3, membrane 12 with nanoparticles/additives 16 is substantially
less compacted over time during operation as a result of applied
pressure. The advantage of resistance to compaction is a reduction
in the common loss, after initial operation, of substantial
permeability or flux flow. The advantage of increased strength by
adding nanoparticles/additives 16 to support membrane 12, and/or
fabric 20, is that a thinner support membrane, with shorter and
less tortuous flow paths, may be used and provides better operating
efficiency for FO and PRO processes both during initial operation
and also thereafter.
[0042] Referring now in particular to FIG. 3, graph 50 illustrates
flow compaction by graphing resistance to flow through membrane 12
with nanoparticles/additives 16, as a function of time. The
experimental conditions were a differential pressure of 500 pounds
per square inch or psi, a temperature of 25.degree. C. and 585 ppm
NaCl. For control membrane 52, a TFC membrane similar to membrane
10 except without nanoparticles/additives 16 dispersed therein was
used, as shown by the graph line for membrane 52. Resistance
increased from just above 6 units to about 12.5 or so units in
about 2 hours. That is, after initial operation, the TFC membrane
made in accordance with the present disclosure but without
nanoparticles/additives 16 lost about half of its permeability in
about 2 hours. Membrane salt rejection was on the order of 91%.
[0043] The graph line for membrane 54, with nanoparticles/additives
16 dispersed in discrimination layer 24, indicates that the
resistance to flow in membrane 54 started at a much lower
resistance to flow, just over 4 units, and lost very little
permeability over the 4 hour test. Membrane salt rejection was on
the order of 90%.
[0044] The graph line for membrane 56, with nanoparticles/additives
16 in support layer 12 and discrimination layer 24, indicates that
the resistance to flow in membrane 56 started at an even lower
resistance to flow, about 1.5 units, and also lost very little
permeability over the 4 hour test. Membrane salt rejection was on
the order of 94%.
[0045] The graph line for membrane 58, with nanoparticles/additives
16 in support layer 12, indicates that the resistance to flow in
membrane 58 started at an even lower resistance to flow, just about
1 unit, and lost a little permeability over the 4 hour test, to
reach the same level as membrane 56 in about 1 hour. Membrane salt
rejection was on the order of 92%.
[0046] Graph lines for the 4 membranes shown in graph 50 illustrate
the reduced resistance to flow for a TFC membrane, such as membrane
52, when nanoparticles/additives 16 are added to the various layers
in membranes 54, 56 and 58, indicating that the addition of
nanoparticles/additives 16 increases the resistance to compaction
of these membranes.
[0047] Referring now in particular to FIGS. 4-7, a series of
photomicrographs are shown of various support membranes taken by a
focused ion beam scanning electron microscope or FIB-SEM technique,
to illustrate the physical effect of the presence of
nanoparticles/additives 16 in support membrane 12 over time. In
this technique, as shown in FIG. 4, platinum deposition Pt 60 was
made on a sample polysulfone support membrane 64 and a dual ion
beam was used to cut a cross sectional view of the polysulfone
support to a depth of approximately 5 microns. A portion of cut 62
for 3 different membranes is shown by FIB-SEM in FIGS. 5-7.
[0048] Referring now specifically to FIGS. 5-7, a segment of
support membrane 12--with nanoparticles/additives 16 dispersed
therein--is shown by FIB-SEM after 16 hours of operation at 800
psi. For comparison, control membrane 64, made in the same manner
as membrane 12 but without nanoparticles/additives 16, is also
shown after 1 hour of operation at 800 psi. The openings in
membranes 12 and 64 are generally of the same shape and
orientations. FIG. 7 shows membrane 64 after 8 hours of operation
at the same pressure, 800 psi. The shape and orientation of the
openings within membrane 64 have clearly been degraded during the
subsequent operations. In particular, the openings shown in FIG. 7
are primarily in a horizontal orientation indicating that
substantial compaction has occurred compared to the openings in
membrane 64 shown in FIG. 6.
[0049] It is clear by comparing support membrane 12 in FIG. 5 that
very little compaction has occurred in the membrane with
nanoparticles/additives 16 after 16 hours because at least a fair
number of the openings are clearly oriented in a vertical direction
as also shown in membrane 64 in FIG. 6 rather than primarily in a
horizontal orientation as shown by membrane 64 in FIG. 7 after 8
hours.
[0050] In operation, saltwater 26 could also be a relatively high
concentration stream of any solute rejected by membrane 10, such as
less pure water, and able to generate a spontaneous flow into pure
fluid 28. Similarly, pure fluid 28 could be any stream relatively
low in concentration of solutes rejected by membrane 10, for
example a freshwater solution. In some instances, pure water 28
could even be seawater if a sufficient concentration of solutes are
added to saltwater 26 to cause water to flow from fluid 28 to 26.
Alternately, saltwater 26 could be relatively pure water with a
high quantity of sugars present to desalinate a seawater stream
into a potable mixture, or a high quantity of ammonium carbonate
which can easily be removed by subsequent processing to generate a
purified water stream. In a PRO system, the pressure could be
utilized at tap 68.
[0051] Support membranes 12 with nanoparticles/additives 16
imbedded therein may be able to minimize mixing losses from
purified water 28 and seawater 26 by maximizing diffusive transport
of solutes within support 12. Inclusion of nanoparticles/additives
16 in support 12 may add strength and toughness allowing useful
support membranes 12 to be created from materials that would
conventionally be ineffective such as polypropylene,
polyethyleneterepthalate, polyvinylchloride, or polystyrene.
[0052] Referring now to FIG. 8, canister 66 may be a conventional
membrane canister such as a 8'' diameter, 40'' long sealed tube
containing solute, such as seawater 26, surrounding membrane
structure 72 wound in a spiral around flow tube 70 carrying the
solvent, such as purified water 28. Membrane structure 72 may
include one or more sheets of 12''-40'' wide sheets of membrane 10
that are 20''-80'' long, providing a wide range of total surface
areas from about 5 square feet to 1600 square feet or more, plus
conventional spacers, permitting membrane 10 to be wound in a
spiral form. Membrane 10 may include support layer 12 with
nanoparticles/additives 16 dispersed therein having a reduced
thickness, for example, of 25 microns rather than the conventional
50 microns as shown in FIG. 2 as well as fabric 20 with
nanoparticles/additives 16 dispersed therein having a reduced
thickness of for example 75 microns rather than the conventional
100 microns also as shown in FIG. 2.
[0053] Because of the spiral winding, the benefit of the additional
strength provided by nanoparticles/additives 16 reduces the
diameter of the spiral wound membrane structure 72 by 50 microns
for each winding. A conventional membrane of the same type as
membrane 10 having a 50 micron support membrane and a 100 micron
fabric backing that would fit in conventional canister 66 would
have the same 40'' width as membrane 10 but the total square
footage of membrane available for osmosis would be reduced by
.about.3-10% compared to a membrane fabricated according to the
present disclosure. In other words, the use of
nanoparticles/additives 16 in support membrane 12 and/or fabric 20
may provide a .about.3-10% improvement in the membrane area
available for osmosis when used in a standard size canister.
[0054] Referring now to FIG. 9, FO/PRO membrane 10 is shown in
operation between draw solution 26 and feed solution 28 to
illustrate a further advantage, related to salinity, of the
addition nanoparticles/additives 16 to permit the use of thinner
support layers 12 and/or thinner fabric layers 20. Membrane 10 may
be used for FO or PRO processes in which feed solution 28 may be
allowed to spontaneously flow through membrane 10 to dilute draw
solution 26 on the other side of membrane 10. To a small degree,
salt or other contaminants from draw solution 26 can also diffuse
into feed solution 28 and vice versa. These processes lead to
regions within draw solution 26 diluted with feed solution 28 and
regions in support membrane 12, fabric 20 and feed solution 28
contaminated with draw solution 26. FIG. 9 includes a graph of
salinity 25 superimposed on the illustration of FO/PRO membrane 10
in use.
[0055] In the graph, salinity 25 increases from the left hand side
to a maximum, such as 32,000 ppm of salt in saltwater 25. The
increasing salinity shown is the salinity of the fluid at the
vertical position within saltwater 26, membrane 10 including
support 12 and fabric 10, and fresh water 28. Graph segment 25a
represents a portion of the salinity curve where saltwater 26
contacts discrimination membrane 24. As shown by segment 25a,
salinity decreases from the maximum salinity of the saltwater to a
lower salinity where pure water 28, having penetrated
discrimination membrane 24, is not yet fully in solution with
saltwater 26. Below discrimination membrane 24, graph segment 25b
illustrates salinity 25 substantially reduced by membrane 10 but
still higher than the salinity of pure water 28. The salinity
gradually reduces as the salt from saltwater 26, leaking backwards
through membrane 10, is dissolved in pure water 28 until it reaches
the typically non-zero level of salt in pure water 28. The salinity
for segment 25b is also higher than that in pure water 28 from
removal of water through the discrimination membrane 24.
[0056] Although membrane 10 is shown with discrimination membrane
24 in contact with seawater 26, fabric 20 in contact with fresh
water 28, and with support membrane 12 there between, it is
conventional in some situations to use membrane 10 in the opposite
orientation. That is, discrimination membrane 24 may be in contact
with fresh water 28, fabric 20 in contact with seawater 26, and
support membrane 12 there between.
[0057] Referring again to the orientation shown in FIG. 9, the
presence of pure water 28 in saltwater 26 above membrane 10, and of
salt from saltwater 26 in pure water 28 near the bottom of
discrimination layer 24, reduces the efficiency of FO and PRO
processes across membrane 10 by reducing the salinity differential
there across. It should be noted that among the advantages of
membrane 10 as described herein, the presence of
nanoparticles/additives 16 in support layer 12 (and/or fabric 20)
enhance the strength of these structural layers permitting the use
of thinner layers. Further, in addition to support layer 12 being
thinner, the water transport paths there through may become less
tortuous, i.e., less resistant to flow, and therefore make support
layer 12 more permeable than a conventional porous support
membrane.
[0058] Although the exact thickness dimensions of the various
layers of conventional FO and PRO membranes depend on many factors,
the following table shows some relatively reasonable,
representative values of the thicknesses and salinity of
conventional IFP RO membranes and IFP RO membranes 10--with
nanoparticles/additives 16 dispersed therein--in accordance with
the present disclosure as a guide to one of the improvement
provided by the present design. A salinity of 32,000 parts per
million, or ppm, for saltwater 26 and 500 ppm for fresh water 28
was used.
TABLE-US-00001 Salinity ppm at IFP FO/PRO Support Fabric Membrane
10 Salinity Membranes (in Microns) Top Bottom Differential
Conventional 50 75 25K 5K 20K Nanoparticle 25 50 25K 1.5K 23.5K
[0059] Although the mixing of fresh water and salt water in FO and
PRO processes conventionally leads to decreased driving forces for
water transport, leading to decreased process efficiencies, the use
of nanoparticles in discrimination layer 24, support layer 12
and/or in other layers such as fabric layer 20, as described
herein, may increase the concentration driving force and improve
process efficiencies. For example, use of nanoparticles and/or
other additives dispersed in discrimination layer 24 and/or support
layer 12 may lead to increased flux flow or permeability to further
increase process efficiencies.
[0060] Referring now to Appendix A, and in particular to Section D:
Tables I-XII, Examples 1-172, pages 66-77, par.s [00047]-[000259],
the related portions of the specification and drawings of Appendix
A, and FIGS. 1 and 2 of the present application,
nanoparticles/additives 16, particularly for addition to aqueous
phase 14 and/or organic phase 18 before IFP in order to be
dispersed in discrimination layer 24, may include [0061] LTA
nanoparticles 16 in aqueous phase 14 as indicated in examples 23-25
and/or in organic phase 18 as shown in examples 26-28; [0062] CuMOF
nanoparticles in organic phase 18 as indicated in example 36;
[0063] SiO2 nanoparticles 16 in aqueous phase 14 as indicated in
example 38; [0064] Zeolite BETA nanoparticles 16 in aqueous phase
14 as indicated in example 40; [0065] additives such as Al, Fe, Sn,
Cu, Co, Pr, Zn, Cr, In, V, Sn, Ru, Mo, Cd, Pd, Hf, Nd, Na, Yb, Er,
Zn, K and/or Li in organic phase 18 as indicated in examples
94-118; [0066] mhTMC in organic phase 18 as indicated in examples
122-136; [0067] Alkaline earth additives in organic phase 18, such
as Ca, Sr, Mg or Be as indicated in examples 29-34; [0068]
Nanotubes in organic phase 18 as indicated in example 44; [0069]
mhTMC (monohydrolyzed TMC) in organic phase 18 as shown in examples
122-136; as well as [0070] combinations of these
nanoparticle/additives, such as nanoparticles (including FAU) or
nanotubes with metal additives or alkaline earth additive and/or
with mhTMC as indicated in the remaining examples in Tables
I-X.
[0071] Further, the concentration of TMC may be adjusted in
accordance with the ranges indicated in examples 137-166 in Table
XI, as described in greater detail in Appendix A, and the MPD to
TMC ratio may be adjusted in accordance with the ratios shown in
Table XII, as described in greater detail in Appendix A.
[0072] Further, the combination of nanoparticle and other additive
reduces flux loss during initial operation as shown in FIG. 5, as
described in greater detail in Appendix A.
[0073] Still further, the concentration of additives and
combinations thereof, such as mhTMC, can be adjusted, tested and
compared to identify the deflection point as shown in FIG. 26, as
described in greater detail in Appendix A. Knowledge of the
deflection point, where one can be clearly determined, for a
particular additive or combination of additives, permits optimizing
the select of the additives, whether nanoparticles or tubes,
alkaline earth or other metals, mhTMC and/or various combinations
thereof.
* * * * *