U.S. patent application number 17/281239 was filed with the patent office on 2022-03-03 for monovalent selective cation exchange membrane.
The applicant listed for this patent is EVOQUA WATER TECHNOLOGIES LLC. Invention is credited to Simon P. DUKES, George Gu, SAVVAS HADJIKYRIACOU, Michael J. SHAW.
Application Number | 20220062829 17/281239 |
Document ID | / |
Family ID | |
Filed Date | 2022-03-03 |
United States Patent
Application |
20220062829 |
Kind Code |
A1 |
Gu; George ; et al. |
March 3, 2022 |
Monovalent Selective Cation Exchange Membrane
Abstract
A monovalent selective ion exchange membrane is disclosed. The
membrane includes a polymeric microporous substrate, a cross-linked
ion-transferring polymeric layer on a surface of the substrate, and
a charged functionalizing layer covalently bound to the
ion-transferring layer by an acrylic group. A method of producing a
monovalent selective cation exchange membrane is also disclosed.
The method may include chemically adsorbing an acrylic intermediate
layer comprising a chlorosulfonated methacrylate group to a
cross-linked ion-transferring polymeric layer on a surface of a
polymeric microporous substrate, aminating the chlorosulfonated
methacrylate group to attach an amine group layer, and
functionalizing the amine group layer with a charged compound layer
to produce the cation exchange membrane. Water treatment systems
including the monovalent selective cation exchange membrane and
methods of facilitating water treatment including providing the
monovalent selective cation exchange membrane are also
disclosed.
Inventors: |
Gu; George; (ANDOVER,
MA) ; HADJIKYRIACOU; SAVVAS; (TYNGSBORO, MA) ;
DUKES; Simon P.; (CHELMSFORD, MA) ; SHAW; Michael
J.; (DERRY, NH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EVOQUA WATER TECHNOLOGIES LLC |
PITTSBURGH |
PA |
US |
|
|
Appl. No.: |
17/281239 |
Filed: |
September 25, 2019 |
PCT Filed: |
September 25, 2019 |
PCT NO: |
PCT/US2019/052889 |
371 Date: |
September 27, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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62736176 |
Sep 25, 2018 |
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62737373 |
Sep 27, 2018 |
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62861608 |
Jun 14, 2019 |
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International
Class: |
B01D 69/02 20060101
B01D069/02; B01D 61/44 20060101 B01D061/44; B01D 69/10 20060101
B01D069/10; B01D 69/12 20060101 B01D069/12; C02F 1/469 20060101
C02F001/469 |
Claims
1. A method of producing a monovalent selective cation exchange
membrane, comprising: chemically adsorbing an acrylic intermediate
layer comprising a chlorosulfonated methacrylate group to a
cross-linked ion-transferring polymeric layer on a surface of a
polymeric microporous substrate; aminating the chlorosulfonated
methacrylate group to attach an amine group layer to the surface of
the polymeric microporous substrate; and functionalizing the amine
group layer with a charged compound layer to produce the monovalent
selective cation exchange membrane.
2. The method of claim 1, comprising polymerizing the acrylic
intermediate layer by exposure to ultraviolet light.
3. The method of claim 1, comprising chemically adsorbing
2-(methacryloyloxy)-ethylsulfonil chloride to the cross-linked
ion-transferring polymeric layer on a surface of a polymeric
microporous substrate.
4. The method of claim 3, comprising aminating the
2-(methacryloyloxy)-ethylsulfonil chloride with PEI.
5. The method of claim 3, comprising aminating the
2-(methacryloyloxy)-ethylsulfonil chloride with branched PEI having
a molecular weight of at least 600 g/mol.
6. The method of claim 1, comprising functionalizing the amine
group layer with a positively charged group.
7. The method of claim 6, comprising functionalizing the amine
group layer with a positively charged ammonium.
8. The method of claim 1, further comprising soaking the polymeric
microporous substrate with a solution comprising an ionogenic
monomer, a multifunctional monomer, and a polymerization initiator
to produce the cross-linked ion-transferring polymeric layer.
9. A monovalent selective ion exchange membrane, comprising: a
polymeric microporous substrate; a cross-linked ion-transferring
polymeric layer on a surface of the substrate; and a charged
functionalizing layer covalently bound to the cross-linked
ion-transferring polymeric layer by an acrylic group.
10. The monovalent selective ion exchange membrane of claim 9,
wherein the membrane has a total thickness of about 20 .mu.m to
about 155 .mu.m.
11. The monovalent selective ion exchange membrane of claim 10,
wherein the membrane has a total thickness of about 25 .mu.m to
about 55 .mu.m.
12. The monovalent selective ion exchange membrane of claim 9,
wherein the acrylic group is a methacrylate group.
13. The monovalent selective ion exchange membrane of claim 9,
being a cation exchange membrane wherein the charged
functionalizing layer is a positively charged functionalizing
layer.
14. The monovalent selective ion exchange membrane of claim 13,
wherein the positively charged functionalizing layer comprises at
least one of a sulfonic acid group, a carboxylic acid group, a
quaternary ammonium group, and a tertiary amine group hydrolyzed
into a positively charged ammonium.
15. The monovalent selective ion exchange membrane of claim 9,
being an anion exchange membrane wherein the charged
functionalizing layer is a negatively charged functionalizing
layer.
16. The monovalent selective ion exchange membrane of claim 9,
having a counter ion permselectivity of at least 100%.
17. The monovalent selective ion exchange membrane of claim 9,
having a resistivity of less than about 5 .OMEGA.-cm.sup.2.
18. A monovalent selective cation exchange membrane support,
comprising: a polymeric microporous substrate; a cross-linked
ion-transferring polymeric layer on a surface of the substrate; and
an intermediate layer comprising a surface amine group and
covalently bound to the cross-linked ion-transferring polymeric
layer by an acrylic group.
19. The monovalent selective cation exchange membrane support of
claim 18, wherein the acrylic group is a methacrylate group.
20. The monovalent selective cation exchange membrane of claim 19,
wherein the methacrylate group is 2-(methacryloyloxy)-ethylsulfonil
chloride.
21. The monovalent selective cation exchange membrane support of
claim 18, wherein the surface amine group is a primary amine group
or a secondary amine group.
22. The monovalent selective cation exchange membrane support of
claim 21, wherein the intermediate layer comprises polyethylenimine
(PEI).
23. The monovalent selective cation exchange membrane support of
claim 21, wherein the intermediate layer comprises a branched PEI
having a molecular weight of at least 600 g/mol.
24. A water treatment system, comprising: a source of water to be
treated; an electrochemical separation device fluidly connected to
the source of water to be treated and comprising at least one
monovalent selective cation exchange membrane having a charged
functionalizing layer covalently bound to a surface of the cation
exchange membrane by an acrylic group; and a treated water outlet
fluidly connected to the electrochemical separation device.
25. The water treatment system of claim 24, wherein the source of
water to be treated comprises at least one hardness ion selected
from Ca.sup.2+ and Mg'.
26. The water treatment system of claim 24, wherein the charged
functionalizing layer is a positively charged functionalizing layer
comprising at least one of a sulfonic acid group, a carboxylic acid
group, a quaternary ammonium group, and a tertiary amine group
hydrolyzed into a positively charged ammonium.
27. The water treatment system of claim 26, wherein the charged
functionalizing layer is covalently bound to the surface of the
cation exchange membrane by a chemically adsorbed branched PEI
layer.
28. A method of facilitating water treatment with an
electrochemical separation device, comprising: providing a
monovalent selective cation exchange membrane having a charged
functionalizing layer covalently bound to a surface of the cation
exchange membrane by an acrylic group; and instructing a user to
install the monovalent selective cation exchange membrane in the
electrochemical separation device.
29. The method of claim 28, comprising instructing the user to
fluidly connect the electrochemical separation device to a source
of water to be treated comprising at least one hardness ion
selected from Ca.sup.2+ and Mg.sup.2+.
30. The method of claim 28, wherein providing the monovalent
selective cation exchange membrane comprises: providing a
monovalent selective cation exchange membrane support having a
polymeric microporous substrate with an amine group layer
covalently bound to a surface of the polymeric microporous
substrate by an acrylic group; and instructing a user to
functionalize the amine group layer with a charged compound layer
to produce the cation exchange membrane.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. .sctn.
119(e) to U.S. Provisional Application Ser. No. 62/737,373 titled
"Monovalent Selective Cation Exchange Membrane" filed Sep. 27,
2018, U.S. Provisional Application Ser. No. 62/736,176 titled
"Cation Exchange Membrane Through UV Initiated Polymerization"
filed Sep. 25, 2018, and U.S. Provisional Application Ser. No.
62/861,608 titled "Exchange Membrane Preparation by UV Light
Polymerization" filed Jun. 14, 2019, each of which is incorporated
herein by reference in its entirety for all purposes.
FIELD OF TECHNOLOGY
[0002] Aspects and embodiments disclosed herein are generally
related to ion exchange membranes, and more specifically, to
monovalent selective ion exchange membranes.
SUMMARY
[0003] In accordance with one aspect, there is provided a method of
producing a monovalent selective cation exchange membrane. The
method may comprise chemically adsorbing an acrylic intermediate
layer comprising a chlorosulfonated methacrylate group to a
cross-linked ion-transferring polymeric layer on a surface of a
polymeric microporous substrate. The method may comprise aminating
the chlorosulfonated methacrylate group to attach an amine group
layer to the surface of the polymeric microporous substrate. The
method may comprise functionalizing the amine group layer with a
charged compound layer to produce the monovalent selective cation
exchange membrane.
[0004] The method may comprise polymerizing the acrylic
intermediate layer by exposure to ultraviolet (UV) light.
[0005] In some embodiments, the method may comprise chemically
adsorbing 2-(methacryloyloxy)-ethylsulfonil chloride to the
cross-linked ion-transferring polymeric layer on a surface of a
polymeric microporous substrate.
[0006] The method may comprise aminating the
2-(methacryloyloxy)-ethylsulfonil chloride with PEI.
[0007] The method may comprise aminating the
2-(methacryloyloxy)-ethylsulfonil chloride with branched PEI having
a molecular weight of at least 600 g/mol.
[0008] The method may comprise functionalizing the amine group
layer with a positively charged group.
[0009] The method may comprise functionalizing the amine group
layer with a positively charged ammonium.
[0010] The method may further comprise soaking the polymeric
microporous substrate with a solution comprising an ionogenic
monomer, a multifunctional monomer, and a polymerization initiator
to produce the cross-linked ion-transferring polymeric layer.
[0011] In accordance with another aspect, there is provided a
monovalent selective ion exchange membrane. The monovalent
selective ion exchange membrane may comprise a polymeric
microporous substrate. The monovalent selective ion exchange
membrane may comprise a cross-linked ion-transferring polymeric
layer on a surface of the substrate. The monovalent selective ion
exchange membrane may comprise a charged functionalizing layer
covalently bound to the cross-linked ion-transferring polymeric
layer by an acrylic group.
[0012] In some embodiments, the membrane may have a total thickness
of about 20 .mu.m to about 155 .mu.m. the membrane may have a total
thickness of about 25 .mu.m to about 55 .mu.m.
[0013] The acrylic group may be a methacrylate group.
[0014] The monovalent selective ion exchange membrane may be a
cation exchange membrane. The charged functionalizing layer may be
a positively charged functionalizing layer.
[0015] In some embodiments, the positively charged functionalizing
layer may comprise at least one of a sulfonic acid group, a
carboxylic acid group, a quaternary ammonium group, and a tertiary
amine group hydrolyzed into a positively charged ammonium.
[0016] The monovalent selective membrane may be an anion exchange
membrane. The charged functionalizing layer may be a negatively
charged functionalizing layer.
[0017] The monovalent selective ion exchange membrane may have a
counter ion permselectivity of at least 100%.
[0018] The monovalent selective membrane may have a resistivity of
less than about 5 .OMEGA.-cm.sup.2.
[0019] In accordance with another aspect, there is provided a
monovalent selective cation exchange membrane support. The
monovalent selective cation exchange membrane support may comprise
a polymeric microporous substrate. The monovalent selective cation
exchange membrane support may comprise a cross-linked
ion-transferring polymeric layer on a surface of the substrate. The
monovalent selective cation exchange membrane support may comprise
an intermediate layer comprising an amine group covalently bound to
the cross-linked ion-transferring polymeric layer by an acrylic
group.
[0020] In some embodiments, the acrylic group may be a methacrylate
group.
[0021] The methacrylate group may be
2-(methacryloyloxy)-ethylsulfonil chloride.
[0022] In some embodiments, the intermediate layer may comprise a
primary amine group or a secondary amine group.
[0023] The intermediate layer may comprise polyethylenimine
(PEI).
[0024] The intermediate layer may comprise a branched PEI having a
molecular weight of at least 600 g/mol.
[0025] In accordance with another aspect, there is provided a water
treatment system. The water treatment system may comprise a source
of water to be treated. The water treatment system may comprise an
electrochemical separation device fluidly connected to the source
of water to be treated and comprising at least one monovalent
selective cation exchange membrane having a charged functionalizing
layer covalently bound to a surface of the cation exchange membrane
by an acrylic group. The water treatment system may comprise a
treated water outlet fluidly connected to the electrochemical
separation device.
[0026] In some embodiments, the source of water to be treated may
comprise at least one hardness ion selected from Ca.sup.2+ and
Mg.sup.2+.
[0027] In some embodiments, the charged functionalizing layer may
be a positively charged functionalizing layer comprising at least
one of a sulfonic acid group, a carboxylic acid group, a quaternary
ammonium group, and a tertiary amine group hydrolyzed into a
positively charged ammonium.
[0028] In some embodiments, the charged functionalizing layer may
be covalently bound to the surface of the cation exchange membrane
by a chemically adsorbed branched PEI layer.
[0029] In accordance with another aspect, there is provided a
method of facilitating water treatment with an electrochemical
separation device. The method may comprise providing a monovalent
selective cation exchange membrane having a charged functionalizing
layer covalently bound to a surface of the cation exchange membrane
by an acrylic group. The method may comprise instructing a user to
install the monovalent selective cation exchange membrane in the
electrochemical separation device.
[0030] In some embodiments, the method may comprise instructing the
user to fluidly connect the electrochemical separation device to a
source of water to be treated comprising at least one hardness ion
selected from Ca.sup.2+ and Mg.sup.2+.
[0031] The method may comprise providing a monovalent selective
cation exchange membrane support having a polymeric microporous
substrate with an amine group layer covalently bound to a surface
of the polymeric microporous substrate by an acrylic group. The
method may further comprise instructing a user to functionalize the
amine group layer with a charged compound layer to produce the
cation exchange membrane.
[0032] The disclosure contemplates all combinations of any one or
more of the foregoing aspects and/or embodiments, as well as
combinations with any one or more of the embodiments set forth in
the detailed description and any examples.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The accompanying drawings are not intended to be drawn to
scale. In the drawings, each identical or nearly identical
component that is illustrated in various figures is represented by
a like numeral. For purposes of clarity, not every component may be
labeled in every drawing. In the drawings:
[0034] FIG. 1 is a representation of the chemical structure of the
polyethylenimine (PEI) molecule showing primary (--NH.sub.2),
secondary (--NH--), and tertiary amine groups;
[0035] FIG. 2 is a representation of the formation of an ionic bond
by physiosorption between a primary or secondary amine of PEI and a
sulfonic acid group of a cation exchange membrane surface,
according to one embodiment;
[0036] FIG. 3 is a representation of the formation of a covalent
bond by chemisorption between a primary or secondary amine of PEI
and chlorosulfonic acid (ClSO.sub.3H), which occurs as a two-step
process, according to one embodiment;
[0037] FIG. 4A is a graph of concentration of Ca.sup.2+ and
Na.sup.+ in a dilute stream over time for water treatment with a
conventional membrane;
[0038] FIG. 4B is a graph of concentration of Ca.sup.2+ and
Na.sup.+ in a dilute stream over time for water treatment with an
alternate conventional membrane;
[0039] FIG. 5 is a graph of concentration of Ca.sup.2+ and Na.sup.+
in a dilute stream over time for water treatment with a monovalent
selective ion exchange membrane, according to one embodiment;
[0040] FIG. 6A is a graph of ion concentration and sodium
absorption rate (SAR) value of experimental ground water treated
with a monovalent selective ion exchange membrane, according to one
embodiment;
[0041] FIG. 6B is a graph of ion concentration and SAR value of
experimental ground water treated with a conventional cation
exchange membrane;
[0042] FIG. 7 is a graph of ion concentration in experimental
seawater treated with a monovalent selective ion exchange membrane,
according to one embodiment;
[0043] FIG. 8 is a graph of monovalent transport selectivity over
time for water treatment with a monovalent selective ion exchange
membrane, according to one embodiment;
[0044] FIG. 9 is a schematic diagram of a membrane selectivity
experimental apparatus;
[0045] FIG. 10A is a graph showing the concentration of target
cations in a dilute stream desalted by a monovalent selective
cation exchange membrane, according to one embodiment;
[0046] FIG. 10B is a graph showing the concentration of target
cations in a dilute stream desalted by a conventional cation
exchange membrane;
[0047] FIG. 10C is a graph showing the concentration of target
cations in a dilute stream produced by a monovalent selective
cation exchange membrane, according to one embodiment;
[0048] FIG. 10D is a graph showing the concentration of target
cations in a dilute stream produced by a conventional cation
exchange membrane;
[0049] FIG. 11A is a graph of the concentration of select ions in
the concentrate compartment using a monovalent selective anion
exchange membrane for treatment of seawater with an applied density
of 300 A/m.sup.2, according to one embodiment;
[0050] FIG. 11B is a graph of the concentration of select ions in
the concentrate compartment using monovalent selective cation
exchange membrane for treatment of seawater with an applied current
density of 300 A/m.sup.2; according to one embodiment;
[0051] FIG. 12A is a graph showing the lifetime selectivity
(stability) of a conventional/commercially available monovalent
selective membrane and a monovalent selective membrane disclosed
herein at 80.degree. C., according to one embodiment;
[0052] FIG. 12B is a graph showing the lifetime selectivity
(stability) of a conventional/commercially available monovalent
selective membrane and a monovalent selective membrane disclosed
herein at room temperature, according to one embodiment;
[0053] FIG. 13 is a representation of the chemical structure of
2-(methacryloyloxy)-ethylsulfonil chloride;
[0054] FIG. 14 is a representation of the chemical structure of
bis-acylphosphinoxide (BAPO); and
[0055] FIG. 15 is a representation of the composition of
photo-initiator 2,2-dimethoxy-2-phenyl-acetophene (DMPA) after UV
irradiation.
DETAILED DESCRIPTION
[0056] Embodiments disclosed herein provide for ion exchange
membranes and processes for their manufacture. The electrodialysis
(ED) membranes described herein may generally combine low
resistance and high permselectivity. Their properties may make them
highly effective in water desalination applications, particularly
in seawater desalination. Their properties make them highly
effective in treatment of irrigation water, particularly for
adjustment of sodium absorption rate (SAR) value. The ion exchange
membranes described herein may be manufactured by polymerizing one
or more monofunctional ionogenic monomers, optionally a neutral
monomer with at least one multifunctional monomer, in the pores of
a porous substrate.
[0057] Ion exchange membranes are typically employed to transport
cations or anions under an electrical or chemical potential. Ion
exchange membranes may have either negatively or positively charged
groups attached to the polymeric material making up the bulk of the
membrane. The counterion of each group typically functions as the
transferable ion. A cation exchange membrane may have fixed
negative charges and mobile positively charged cations. An anion
exchange membrane may have fixed positively charged groups and
mobile negatively charged anions. Ion exchange membrane properties
may be engineered by controlling the amount, type, and distribution
of the fixed ionic groups. These membranes may be described as
strong acid, strong base, weak acid, or weak base membranes. Strong
acid cation exchange membranes typically have sulfonic acid groups
as the charged group. Weak acid membranes typically have carboxylic
acid groups making up the fixed charged group. Quaternary and
tertiary positively charged ammonium, respectively, may produce the
fixed positive charged groups in strong and weak base anion
exchange membranes.
[0058] Ion exchange membranes may be used for desalination of water
by electrodialysis (ED), as a power generating source in reverse
electrodialysis, or as separators in fuels cells. Thus, water
treatment systems disclosed herein may be or comprise desalination
systems, power generating systems, or reverse electrodialysis
systems. Other applications include recovery of metal ions in the
electroplating and metal finishing industries and applications in
the food and beverage industry. In other embodiments, water
treatment systems disclosed herein may be or comprise metal ion
recovery systems or food and beverage processing systems.
[0059] In a particular exemplary embodiment, ion exchange membranes
disclosed herein may be used for ground water treatment and/or in
agricultural settings. The water treatment systems disclosed herein
may be or comprise ground water treatment systems. The water
treatment systems disclosed herein may be or comprise agricultural
irrigation runoff treatment systems. The methods may comprise
treating ground water. The methods may comprise treating
agricultural water runoff.
[0060] Electrodialysis generally desalinates water by transferring
ions and some charged organics through paired anion- and cation
selective membranes under the motive force of a direct current
voltage. An ED apparatus may include electrically conductive and
substantially water impermeable anion selective and cation
selective membranes arranged as opposing walls of a cell. Adjacent
cells typically form a cell pair. Membrane stacks may include many,
sometime hundreds, of cell pairs. An ED system may include many
stacks. Each membrane stack typically has a DC (direct current)
anode at one end of the stack and a DC cathode at the other end.
Under a DC voltage, ions may move toward the electrode of opposite
charge.
[0061] A cell pair includes two types of cells, diluting cells and
concentrating cells. Each type of cell may be defined by opposing
membranes. One exemplary cell pair may include a common cation
transfer membrane wall and two anion transfer membrane walls
forming the two cells. That is, a first anion transfer membrane and
the cation transfer membrane form the diluting cell, and the cation
transfer membrane and a second anion transfer membrane form the
concentrating cell. In the diluting cell, cations typically pass
through the cation transfer membrane facing the anode, but may be
stopped by the paired anion transfer membrane of the concentrating
cell in that direction facing the cathode. Similarly, anions may
pass through the anion transfer membrane of the diluting cell
facing the cathode, but may be stopped by the cation transfer
membrane of the adjacent pair facing the anode. In this manner,
salt in a diluting cell may be removed. In the adjacent
concentrating cell, cations may enter from one direction and anions
from the opposite direction. Flow in the stack may be arranged so
that the dilute and concentrated flows are kept separate. Thus a
desalinated water stream may be produced from the dilute flow.
[0062] Scarcity of irrigation water of sufficient quality is
deleterious to crop yields and may require choice of crop species
that are of less demand. Newer methods of irrigation that reduce
the amount of water used, using techniques such as drip irrigation,
may also cause a non-sustainable condition due to salt and impurity
buildup in the soil from the water used for irrigation. The soil
salinity may rise to much higher concentrations than in the
irrigation water due to use of most of the water by the crops, and
by evaporation. Conditions of irrigation and soil with inadequate
source water for leaching the soil or insufficient rainfall may
result in soil salinities 4 to 5 times higher than in the
irrigation water itself. Further, should the land consist of
relatively shallow impermeable ground layers, the irrigation water
may raise the water table. When highly saline ground water reaches
crop root levels, the water may be harmful to crop growth. Also,
saline soils may damage leafy crops due to water splash off the
soil surface. Furthermore, if the agricultural land is drained of
the saline water, trace impurities in the soil such as selenium or
boron, or residual contaminants from fertilizer use such as nitrate
may cause contamination of the drainage water and cause
difficulties in safe effluent control.
[0063] When irrigating crops, the yield may be affected by total
dissolved salts (TDS) concentration. The TDS is typically
correlated to conductivity value. For example, a conductivity value
of 1 mS/cm corresponds to approximately 500-700 ppm TDS. Various
plants benefit from low TDS irrigation water. For example, bean,
carrots, and strawberries may benefit from irrigation with water
having a conductivity lower than 1 mS/cm. Other plants may tolerate
irrigation water with a conductivity of about 5 mS/cm. Furthermore,
control of the SAR value at a given TDS and conductivity may affect
soil flocculation and efficient water infiltration. For instance,
irrigation water having a conductivity of less than 1 mS/cm may
benefit from a SAR value of greater than 3 to maintain soil
structure. Irrigation water having a conductivity of 2-3 mS/cm may
benefit from a SAR value of about 10.
[0064] Irrigation water needs also are in competition with potable
drinking water for humans, and water free of contaminants for
livestock, and wildlife. Thus it is commonly the case that a source
of a combination of irrigation water and potable water are needed
in agricultural regions. The membranes described herein may be
employed for agricultural irrigation water treatment. In
particular, the membranes described herein may be employed to
control TDS, conductivity, and SAR value for agricultural
irrigation water. In some embodiments, the membranes described
herein may provide water having a conductivity of less than 1
mS/cm. The membranes described herein may provide water having a
conductivity of between 2-3 mS/cm, between 3-5 mS/cm, or greater
than 5 mS/cm (for example, between 5-7 mS/cm). The membranes
described herein may provide water having a SAR value of greater
than 3, for example, between 3-5. The membranes described herein
may provide water having a SAR value of greater than 5, for
example, between 5-10. The membranes described herein may provide
water having a SAR value of about 10 or greater, for example,
between 10-12.
[0065] Univalent selective or monovalent selective membranes
primarily transfer monovalent ions. Monovalent selective membranes
may separate ions on the basis of charge and/or size. Monovalent
selective membranes may distinguish between monovalent and divalent
ions. Monovalent selective cation transfer membranes may
distinguish between ions having a charge of +1, for example, sodium
and potassium, and ions having a greater positive charge, for
example, magnesium and calcium.
[0066] Thus, monovalent selective cation exchange membranes
described herein may selectively transport monovalent ions such as
sodium and potassium ions, while blocking transport of divalent
ions such as calcium and magnesium ions. Similarly, monovalent
selective anion membranes may separate ions having a charge of -1,
such as chloride, bromide, and nitrate, from ions having a greater
negative charge. Thus, monovalent anion exchange membranes
described herein may selectively transport monovalent ions such as
chloride and nitrate ions, while blocking transport of divalent
ions such as sulfate ions.
[0067] The ion exchange membranes disclosed herein may be used to
treat brackish water and waste water desalination. Even though ED
is generally considered too expensive for seawater use, the ion
exchange membranes disclosed herein may be used efficiently for
seawater desalination. Effective and efficient seawater
desalination may be performed with a membrane resistance of less
than 1 .OMEGA.-cm.sup.2, for example, less than 0.8
.OMEGA.-cm.sup.2, or less than 0.5 .OMEGA.-cm.sup.2. The ion
exchange membranes disclosed herein may also provide an ion
permselectivity of greater than 90%, for example, greater than 95%,
or greater than 98%. Additionally, the ion exchange membranes
disclosed herein have a longer service life and greater physical
strength and chemical durability than comparable conventional ion
exchange membranes. Finally, the ion exchange membranes disclosed
herein may be manufactured at a comparatively low cost.
[0068] As a result, the ion exchange membranes disclosed herein may
be employed in reverse electrodialysis (RED). RED may be used to
convert free energy generated by mixing two aqueous solutions of
different salinities into electrical power. In general, the greater
the difference in salinity, the greater the potential for power
generation. The water treatment systems disclosed herein may be or
comprise RED systems. The methods disclosed herein may be employed
to generate electrical power.
[0069] The ion exchange membranes disclosed herein may be employed
as a polymer electrolyte membrane (PEM). A PEM is a type of ion
exchange membrane that may serve both as the electrolyte and as a
separator to prevent direct physical mixing of the hydrogen from
the anode and oxygen supplied to the cathode. A PEM may contain
negatively charged groups, such as, sulfonic acid groups, attached
or as part of the polymer making up the PEM. Protons typically
migrate through the membrane by jumping from one fixed negative
charge to another to permeate the membrane.
[0070] The membranes disclosed herein may generally comprise an ion
exchange membrane support and a charged functionalizing layer
covalently bound to the ion exchange membrane support. The ion
exchange membrane support may comprise a polymeric microporous
substrate and a cross-linked ion-transferring polymeric layer on a
surface of the substrate. As an intermediate production step, the
membrane support may additionally comprise an amine group layer
covalently bound to the cross-linked ion-transferring polymeric
layer.
[0071] The membranes described herein may generally exhibit good
mechanical strength. The mechanical strength may be sufficient to
allow the membrane to withstand the stresses of a continuous
membrane manufacturing process, and be fabricated and sealed into
the final membrane-holding device or module without overt damage or
hidden damage which could appear after some time of operation. In
addition, the mechanical strength may be sufficient to provide high
dimensional stability. The membrane may generally exhibit minimal
variation in dimensions while working as a desalination apparatus,
during cleaning, sanitizing or defouling regimes, or during
shipping or while in storage. High dimensional stability to changes
in ionic content or temperature, for example, of the fluid
contacting the membrane, may be provided, such that during
operation variations in the distance between membrane pairs which
could lead to current inefficiencies are minimized. Changes in
dimensions during electrodialysis which could cause stresses in the
constrained membrane leading to membrane defects and poor
performance, may also generally be minimized.
[0072] The membranes described herein may exhibit low resistance.
In general, low resistance reduces the electrical energy required
to desalinate and lowers operating cost. Specific membrane
resistance is sometimes measured in .OMEGA.-cm. Another engineering
measure is .OMEGA.-cm.sup.2. Resistance may be measured by a
resistance testing process which uses a cell having two electrodes
of known area in an electrolyte solution. Platinum or black
graphite are typically used for the electrodes. Resistance is then
measured between the electrodes. A membrane sample of known area
may be positioned between the electrodes in the electrolyte
solution. The electrodes do not touch the membrane. Resistance is
then measured again with the membrane in place. Membrane resistance
may then be estimated by subtracting the electrolyte resistance
without the membrane from the test result with the membrane in
place.
[0073] The resistance may also be measured by determining a voltage
vs. current curve in a cell having two well stirred chambers
separated by the membrane. A calomel electrode may be used to
measure the potential drop across the membrane. The slope of the
potential drop vs. current curves may be obtained by varying
voltage and measuring current.
[0074] Electrochemical impedance may also be used for the
calculation. In this method, alternating current may be applied
across the membrane. Measurement at a single frequency gives data
relating to electrochemical properties of the membrane. By using
frequency and amplitude variations, detailed structural information
may be obtained.
[0075] The membranes described herein may have high counter ion
permselectivity. Permselectivity may generally refer to the
relative transport of counterions to co-ions during
electrodialysis. For a theoretically ideal cation exchange membrane
only positively charged ions would pass the membrane, giving a
counter ion permselectivity of 1.0 or 100%. Permselectivity may be
found by measuring the potential across the membrane while it
separates monovalent salt solutions of different
concentrations.
[0076] The ion exchange membranes disclosed herein may have reduced
water permeation. Permeation of the dilute flow through membrane
defects under the driving force of the osmotic pressure difference
between the dilute and concentrated streams may reduce efficiency.
Water permeation may reduce current efficiency and purified water
productivity by removing pure water. Water loss may be particularly
severe in seawater electrodialysis with thin membranes because the
high concentration difference between the concentrate (brine) side
of the membranes and the pure water side of the membrane typically
increases the osmotic driving force. Membrane defects may be
particularly detrimental to operation as the high osmotic pressure
will tend to force pure water through such defects and increase
water loss, increasing power consumption.
[0077] The membranes disclosed herein may generally have a
structure that allows high permeability of cations and low osmotic
flow. Apparent counter ion permselectivity as used herein is the
ratio of transport rate of counter-ions (cations) to co-ions
(anions). Conventional measurement parameters do not indicate the
rate of counter-ion removal. In certain embodiments, the membranes
disclosed herein may be engineered to control cation
permeability.
[0078] Cation permeability may be controlled by the structure of
the ion (molecular size and total charge) and by the effect of
membrane microstructure. The membrane microstructure can retard
counter-ion permeability if the membrane is designed to have pores
that are comparatively small. The relative term can be taken to
mean that the counter-ions encounter high resistance from
interactions with the membrane material in traversing the membrane,
as if they were traversing a tunnel slightly larger than their
apparent diameter. The membrane may have a relatively low water
content, tending to reduce the pathways for counter-ion
permeability. By balancing the content of hydrophilic monomer to
increase counter-ion permeability with the amount and nature of
cross-linking monomer, the water content and effective pore size of
the membrane can be engineered. The cross-linking monomer may be
selected to be a hydrophobic or hydrophilic monomer.
[0079] The membranes disclosed herein may generally comprise an ion
exchange membrane support. The ion exchange membrane support may
comprise a polymeric microporous substrate and a cross-linked
ion-transferring polymeric layer on a surface of the substrate. The
membrane support may be produced by a process comprising selecting
a suitable porous substrate and incorporating a cross-linked
ion-transferring polymeric layer on a surface of the substrate.
[0080] The microporous membrane substrate may be manufactured from
polyolefins, polyvinylidene fluoride, or other polymers. One
exemplary class of substrates comprises thin polyolefin membranes.
Another exemplary class of substrate are manufactured from
high-density polyethylene (HDPE). Another exemplary class of
substrates are manufactured from ultrahigh molecular weight
polyethylene (UHMWPE). The microporous substrate may comprise
microporous membranes of polypropylene, high molecular weight
polyethylene, ultrahigh molecular weight polyethylene or
polyvinylidene fluoride. The substrate may generally have a
thickness of less than about 155 .mu.m, for example, less than
about 55 .mu.m or less than about 25 .mu.m.
[0081] The exemplary microporous membrane materials may be employed
to manufacture very thin ion exchange membranes, for example, as
disclosed in U.S. Pat. No. 8,703,831, incorporated herein by
reference in its entirety for all purposes. The exemplary ion
exchange membranes may have a thickness of 12-100 .mu.m, for
example, 25-32 .mu.m. The thin membrane enables a fast
chlorosulfonation reaction, described in more detail below,
effective throughout a bulk of the membrane. For example, a 5
minute chlorosulfonation reaction may be sufficient to complete
bulk chlorosulfonation. Thus, methods described herein may comprise
performing a chlorosulfonation reaction effective to
chlorosulfonate a bulk of the membrane in about 5 minutes.
[0082] Additionally, certain exemplary microporous membrane
materials may be employed to provide stability against aggressive
chemicals. For example, a membrane substrate of HDPE is generally
stable against ClSO.sub.3H, which may be employed in certain
embodiments. A material such as polypropylene may not be
sufficiently stable against ClSO.sub.3H.
[0083] Embodiments of the substrate membrane may have a porosity
greater than about 45%, for example, greater than about 60%. In
certain embodiments, the substrate membrane may have a porosity
greater than about 70%. The substrate membrane may have a rated
pore size of from about approximately 0.05 .mu.m to about
approximately 10 .mu.m, for example, from about approximately 0.1
.mu.m to about approximately 1.0 .mu.m, or from about approximately
0.1 .mu.m to about approximately 0.2 .mu.m.
[0084] The membrane support may be produced by saturating the
monomer solution in the pores of the substrate. The monomer
solution may be polymerized from functional monomers, a
cross-linking agent, and a polymerization initiator in the pores to
form the cross-linked charged polymer. In certain embodiments, the
functional monomers may include an ionogenic monomer, for example,
a monofunctional ionogenic monomer, and a multifunctional monomer,
for example, a cross-linking agent. As used herein, the term
ionogenic monomer may generally refer to a monomer species having
at least one charged group covalently attached. The charged group
may be positively charged or negatively charged, as described in
more detail below. Monofunctional monomers may generally refer to
monomers which have a single site for carrying forward the
polymerization reaction. Multifunctional monomers may generally
refer to monomers that have more than one polymerization reaction
site and so can form networked or crosslinked polymers.
[0085] The process of polymerizing the cross-linked
ion-transferring polymeric layer in the pores of the substrate may
include saturating the substrate with a solution comprising the
monofunctional ionogenic monomer, the multifunctional monomer, and
the polymerization initiator. The process may include removing
excess solution from the surfaces of the substrate while leaving
the porous volume saturated with solution and initiating
polymerization. Polymerization may be initiated by the application
of heat, ultraviolet (UV) light, or ionizing radiation, optionally
in the absence of substantially all oxygen. The process may be
performed to incorporate the cross-linked ion-transferring
polymeric layer substantially completely filling the pores of the
substrate.
[0086] Thus, in certain embodiments, the membrane support may be
produced by the polymerization of one or more ionogenic monomers, a
neutral monomer, and a suitable crosslinker monomer. Exemplary
neutral monomers are hydroxyethyl acrylate and
hydroxymethylmethacrylate. Other neutral monomers are within the
scope of the disclosure. The ionogenic monomer may be selected to
produce a cation exchange membrane or an anion exchange
membrane.
[0087] Monomers containing negatively charged groups include as
representative examples, without being limited by such examples,
sulfonated acrylic monomers suitable to provide cation exchange
capacity, for example, 2-sulfoethylmethacrylate (2-SEM),
2-Propylacrylic acid, 2-acrylamide-2-methyl propane sulfonic acid
(AMPS), sulfonated glycidylmethacrylate, 3-sulfopropyl
methacrylate, sodium 1-allyloxy-2 hydroxypropyl sulfonate and the
like. Other exemplary monomers are acrylic and methacrylic acid or
their salts, sodium styrene sulfonate, styrene sulfonic acid,
sulfonated vinylbenzyl chloride sodium 1-allyloxy-2 hydroxypropyl
sulfonate, 4-Vinylbenzoic acid, Trichloroacrylic acid, vinyl
phosphoric acid and vinyl sulfonic acid. Preferred monomers are
2-sulfoethylmethacrylate (2-SEM), styrene sulfonic acid and its
salts, and 2-acrylamide-2-methyl propane sulfonic acid (AMPS).
[0088] Cation exchange membrane embodiments described herein may
have a resistivity of less than about approximately 1.0
.OMEGA.-cm.sup.2, for example, less than about approximately 0.5
.OMEGA.-cm.sup.2. Certain embodiments of the cation exchange
membranes described herein may have a permselectivity of greater
than about approximately 95%, for example, greater than about
approximately 99%. In some embodiments, the ionogenic monomers for
the production of cation exchange membranes may be or comprise
2-sulfoethylmethacrylate (2-SEM or 2-acrylamide-2-methyl propane
sulfonic acid (AMPS). One exemplary cross-linker is
ethyleneglycoldimethacrylate. Other ionogenic monomers and
crosslinkers are within the scope of the disclosure.
[0089] Monomers containing positively charged groups include as
representative examples, without being limited by such examples,
Methacrylamidopropyltrimethyl ammonium chloride,
trimethylammoniumethylmethacrylate, quaternary salts of polyamines
and vinylaromatic halides, for example,
1,4-diazabicyclo[2,2,2]octane di(vinylbenzyl chloride) (a
quaternary salt of 1,4-diazabicyclo[2,2,2]octane (DABCO) and
piperazine divinyl chloride), or quaternary salts formed by
reacting cyclic ethers, polyamines and alkyl halides, for example,
Iodoethyldimethylethylenediamino2-hydroxylpropyl methacrylate (a
quaternary ammonium salt formed by reacting glycidylmethacrylate
(GMA) with N,N-dimethylethylenediamine and ethyl iodide), and
vinylbenyltrimethylammonium chloride. Other exemplary monomers for
anion exchange membranes include Trimethylammoniumethylmethacrylic
chloride, 3-(acrylamidopropyl)trimethylammonium chloride,
N,N,N',N',N''-pentamethyldiethylenetriamine di(vinylbenzyl chloride
(a quaternary salt of N,N,N',N',N''-pentamethyldiethylenetriamine
and vinylbenzyl chloride), Glycidyl methacrylate/trimethylamine, or
Glycidyl methacrylate/N, N-dimethylethylenediamine reaction
product.
[0090] Anion exchange membrane embodiments described herein may
have a resistivity of less than about approximately 1.0
.OMEGA.-cm.sup.2, for example, less than about approximately 0.5
.OMEGA.-cm.sup.2. In certain embodiments, the anion exchange
membranes described herein may have a permselectivity of greater
than about approximately 90%, for example, greater than about
approximately 95%. In some embodiments, the ionogenic monomers for
the production of anion exchange membranes may be or comprise
Trimethylammoniumethylmethacrylic chloride crosslinked with
ethyleneglycoldimethacrylate, or glycidyl methacrylate/N,
N-dimethylethylenediamine reaction product crosslinked with
ethyleneglycoldimethacrylate, and the crosslinked ion transferring
polymer formed by polymerization of
N,N,N',N',N''-pentamethyldiethylenetriamine di(vinylbenzyl chloride
(a quaternary salt of N,N,N',N',N''-pentamethyldiethylenetriamine
and vinylbenzyl chloride) or 1,4-diazabicyclo[2,2,2]octane
di(vinylbenzyl chloride) (a quaternary salt of
1,4-diazabicyclo[2,2,2]octane (DABCO) and vinylbenzyl
chloride).
[0091] Multifunctional monomers containing one or more ionic groups
may be used. Without being limited by the example, monomers such as
1,4-divinylbenzene-3 sulfonic acid or its salts may be used. The
degree of crosslinking may range from 2% to 60%. Multifunctional
monomers suitable to provide crosslinking with monomers containing
negatively or positively charged groups include as representative
examples, without being limited by such examples ethyleneglycol
dimethacrylate, 1,3-butanediol dimethacrylate, 1,3-butanediol
diacrylate, 1,4-butanediol dimethacrylate, 1,4-butanediol
diacrylate, 1,6-hexanediol diacrylate, pentaerythritol triacrylate,
tetraethylene glycol dimethacrylate, divinyl benzene,
trimethylolpropane triacrylate, isophorone diisocyanate,
glycidylmethacrylate, trimethylolpropane trimethacrylate,
ethoxylated (n) bisphenol A di(meth)acrylate (n=1.5, 2, 4, 6, 10,
30), ethoxylated (n) trimethylolpropanetri(meth)Acrylate
(n=3,6,9,10,15,20), propoxylated(n) trimethylolpropane triacrylate
(n=3,6), vinylbenzyl chloride, glycidyl methacrylate and the
like.
[0092] The polymerization initiator may be a free radical
polymerization initiator. Free radical polymerization initiators
which may be employed include, for example, benzoyl peroxide (BPO),
ammonium persulfate, 2,2'-azobisisobutyronitrile (AIBN),
2,2'-azobis(2-methylpropionamidine)dihydrochloride,
2,2'-Azobis[2-(2-imidazolin-2yl)propane]dihydrochloride,
2,2'-Azobis[2-(2-imidazolin-2-yl)propane], and dimethyl
2,2'-azobis(2-methylpropionate).
[0093] The substrate pore filling or saturation process may be done
at a slightly elevated temperature (for example, >40.degree. C.)
to reduce air solubility. In other embodiments, the substrate pore
or saturation process may be done after a mild vacuum treatment of
the substrate sample submerged in the formulation solution.
Substrate samples may be presoaked and then placed on a polyester
or similar sheet and covered with a covering sheet. The soaked and
covered substrate may be smoothed out to remove air bubbles.
Several presoaked pieces may be layered and then placed on the
polyester or similar sheet and covered with a covering sheet and
smoothed out to remove air bubbles.
[0094] The soaked substrate may be heated in an oven at a
temperature sufficient and for a time necessary to initiate
complete polymerization. The soaked substrate may be placed on a
heated surface at a temperature sufficient and for a time necessary
to initiate and complete polymerization. Alternate methods for
initiation of the polymerization reaction may be used. Ultraviolet
light or ionizing radiation, such as gamma radiation or electron
beam radiation may be used to initiate the polymerization
reaction.
[0095] A continuous pilot or manufacturing method may comprise
saturating the porous substrate, initiating and completing the
polymerization, and washing or leaching out non-polymerized species
from the now-formed membrane. The membrane may be optionally dried.
Conditioning with a salt solution may be performed in a continuous
immersion process, such as through a tank of a salt solution, or by
soaking a wound-up roll of membrane, or after fabrication into a
module.
[0096] If the monomer solution is formulated with a solvent which
wets out the substrate, the process may start by feeding substrate
from a roll into and through a tank of the monomer formulation and
wiping off excess solution. The soaked substrate may be assembled
between two layers of plastic sheeting fed from rolls and nipped
between two rolls to remove air and produce a smooth multilayered
assembly. One exemplary sheeting material is polyethylene
terephtalate film. Other sheeting materials may be employed. The
assembly may be processed through an oven, or over a heated roll,
to initiate and complete polymerization. One alternative method may
include running the saturated sheet through an oven blanketed with
inert gas. The inert gas may be suitable for use with solvents
having a high boiling point.
[0097] UV light initiation with suitable polymerization initiators
may be used. The method may include irradiating the assembly with
UV light at an intensity sufficient and for a time necessary to
initiate and complete polymerization. For example, the three-layer
assembly described may be run through a tunnel or other process
equipment having an inlet and outlet for the substrate web with UV
light sources on one or both sides of the web. With a high boiling
formulation, the method may be performed in an inert gas
atmosphere.
[0098] The covering sheets may be removed after polymerization. The
now-formed membrane may be washed and optionally dried.
[0099] An organic solvent may be used as a reactant carrier. One
useful class of solvents is dipolar aprotic solvents. Some examples
of suitable solvents include dimethyl acetamide, dimethyl
formamide, dimethyl sulfoxide, hexamethylphosphoramide or
-triamide, acetone acetonitrile, and acetone. The organic solvent
may be employed for solvating ionic group containing monomers and
monomers that are not water soluble. One exemplary solvent is
N-methyl pyrrolidone. Other solvents which may be employed are
N-propanol and dipropylene glycol. Similar hydroxy containing
solvents, such as alcohols, for example isopropanol, butanol, diols
such as various glycols, or polyols, such as glycerine, may be used
in certain embodiments. Other solvents are within the scope of the
disclosure. The solvents discussed may be used alone or in
combination. In some the solvents may be used with water to
increase solubility of ionic containing organics.
[0100] The monomer mixture may be selected to engineer a
cross-linked copolymer to produce a membrane having a desired
balance of properties. For example, combining a water soluble
and/or swellable ionogenic monomer with a non-water swelling
comonomer may produce a copolymer with a high degree of ionic
groups and reduced swelling in water. Such an ion exchange membrane
may be used for desalination. In particular, the exemplary
copolymers may have better physical strength in water and suffer
less dimensional change in use due to changes in water ionic
content or temperature changes. Thus, the exemplary ion exchange
membranes may exhibit a suitable mechanical strength, low
electrical resistance, and high counter ion permselectivity, for
example, for seawater electrodialysis.
[0101] The ion exchange membranes disclosed herein may comprise a
charged functionalizing layer covalently bound to the cross-linked
ion-transferring polymeric layer.
[0102] Many ion exchange membranes are multivalent selective. A
multivalent ion selective membrane may refer to an ion exchange
membrane that selects for transport of a multivalent ion. For
example, a typical cation ion exchange membrane used for ED allows
a multivalent ion transport faster than a monovalent ion. The
faster transport of a multivalent ion typically occurs because the
higher charge number ion is attracted by a larger electrical force
during migration under the same electrical field.
[0103] The ion exchange membranes disclosed herein may be
monovalent selective membranes. The ion exchange membrane may be
engineered to select for monovalent ions against multivalent ions
by controlling charge factors, such as, surface depletion
condition, membrane hydrophobicity, cross-link degree, and membrane
intrinsic charge conditions. For instance, the cross-link degree
and hydrophilicity modifications of a cation exchange membrane may
produce a significant retard of the multivalent ion versus
monovalent ions by creating a low water condition inside the
membrane which is unfavorable to multivalent ions.
[0104] The monovalent selective membranes disclosed herein may have
engineered surface modifications. The surface modification of the
ion exchange membrane may be produced by providing charged
molecules on the surface of the membrane to retard ion transport
with higher valence charge number. A monovalent selective cation
ion exchange membrane may have positively charged molecules on the
surface. For example, a strong acid cation exchange membrane may be
functionalized with sulfonic acid groups as the charged group. A
weak acid membrane may be functionalized with carboxylic acid
groups making up the fixed charged group. Quaternary and tertiary
positively charged ammonium, respectively, may be employed to
functionalize the membrane with positive charged groups in strong
and weak base anion exchange membranes. A monovalent selective
anion ion exchange membrane may have negatively charged molecules
on the surface.
[0105] Furthermore, the strength of the surface charge repellant
may be engineered by controlling charge distribution on the surface
of the membrane. The strength of the charge repellent typically
depends on the charge distribution when the same number of charged
molecules are provided on the surface. Briefly, the electrical
field strength of the ion exchange membrane is defined by dq/dx;
where q is charge number or concentration and x is the depth along
the ion transport.
[0106] Thus, in some embodiments, the charged functionalizing layer
formed on the surface of the membrane may be selected to be a
monolayer, which does not substantially affect the ion transport
resistance significantly while providing a strong barrier or very
large dq/dx value to multivalent ion compared to monovalent ion.
Additionally, a monolayer may not significantly affect the entire
conductance of the membrane. For example, a monolayer may not
significantly impact the water molecule transport with the ion.
[0107] The cross-linked ion-transferring polymeric layer of the ion
exchange membrane support may be functionalized by covalently
binding an intermediate layer to the polymeric layer and reacting
the intermediate layer with a charged functionalizing layer. In
certain embodiments, the intermediate layer may be a molecule
comprising an amine group. During the intermediate reaction, the
amine group may exchange with water to form four covalent bonds or
ammonium. The intermediate layer may comprise surface adsorbed
polyethylenimine (PEI). The various primary, secondary and tertiary
amines may provide a significant selectivity to the multivalent
ions. The PEI molecule structure is shown in FIG. 1.
[0108] As previously described, the charged functionalizing layer
may be selected to be a monolayer. In particular, the charged
functionalizing layer may be a monolayer on a surface of the ion
exchange membrane. Penetration of the functionalizing layer into
the bulk of the membrane may react with the charged
ion-transferring layer, resulting in a reduction of the membrane
permselectivity function. Thus, the intermediate layer may have a
size sufficient to bind to the surface of the microporous polymeric
membrane coated with the cross-linked polymer, without
substantially penetrating the pores of the membrane. For instance,
the intermediate layer may have a size sufficient to be
substantially inhibited from penetrating the micropores of the
polymeric substrate.
[0109] The intermediate layer may be selected to have a size
greater than the pores of the microporous polymeric substrate.
Thus, in some embodiments, the intermediate layer may comprise a
molecule having a molecular weight of at least 100 g/mol, for
example, at least 600 g/mol. The intermediate layer may comprise a
molecule having a molecular weight of at least 1,000 g/mol, for
example, at least 10,000 g/mol. The intermediate layer may comprise
a molecule having a molecular weight of at least 40,000 g/mol, for
example, at least 50,000 g/mol or at least 60,000 g/mol. The
intermediate layer may comprise a molecule having a molecular
weight of at least 70,000 g/mol, at least 80,000 g/mol. The
intermediate layer may comprise a molecule having a molecular
weight of between 60,000 g/mol and 120,000 g/mol. In exemplary
embodiments, the intermediate layer may comprise branched PEI. The
branched PEI may have a molecular weight as described herein.
[0110] Conventionally, PEI may be coated on a surface of a cation
exchange molecule by physisorption. Briefly, physisorption is a
physical adsorption reaction that leads to an ionic bond of PEI on
the cross-linked polymeric layer, as shown in FIG. 2. However, the
ionic bond is generally not stable, such that the surface charged
molecule may dissolve in the water leading to a loss of
selectivity.
[0111] The methods disclosed herein may comprise attaching the
intermediate layer to the cross-linked ion-transferring polymeric
layer by chemisorption. Chemisorption may generally include
chemically adsorbing the intermediate layer to the polymeric layer,
such that the intermediate layer is bound by a covalent bond. Thus,
the ion exchange membrane supports disclosed herein may have an
intermediate layer bound by a covalent bond. The covalent bond may
provide increased surface stability for the ion exchange membrane.
As a result, the covalent bond may increase selectivity of the
membrane for a longer lifespan. In some embodiments, the ion
exchange membrane may have an operational lifespan of more than 150
days, for example, more than 400 days in use at room temperature.
The ion exchange membrane may have an operational lifespan of more
than 2 years or more than 3 years in use at room temperature.
Additionally, the ion exchange membrane may have an operational
lifespan of more than 30 days in use at 80.degree. C.
[0112] The intermediate layer may have an attachment group
configured to covalently bind the intermediate layer to the
cross-linked ion-transferring polymeric layer. The attachment group
may be selected to provide increased stability. For instance, the
attachment group may be selected to provide a bond that is
sufficiently stable to withstand organic compounds in the water to
be treated in use. In particular, the attachment group may be
sufficiently stable to withstand organic contaminants such as
benzyne, toluene, ethylbenzene, and xylene for extended periods of
time while in use. Thus, the ion exchange membranes disclosed
herein may be used to treat wastewater comprising organic
contaminants, such as, produced water, ground water, brackish
water, brine, and seawater. The wastewater may comprise, for
example, between about 100-1000 ppm of TDS. In certain embodiments,
the wastewater may comprise, for example, between about 100-400 ppm
TDS, between about 400-600 ppm TDS, or between about 600-1000 ppm
TDS.
[0113] The monovalent selective cation exchange membranes disclosed
herein may be used to treat water comprising at least one hardness
ion. For instance, the water to be treated may comprise at least
one positively charged divalent ion. In certain embodiments, the
water to be treated may comprise at least one hardness ion selected
from Ca.sup.2+ and Mg'. Additionally, the monovalent selective
cation exchange membranes disclosed herein may be used for
agricultural water treatment, where use of water with a high sodium
content can damage soil, but magnesium and calcium are
beneficial.
[0114] In one exemplary embodiment, the attachment group may be a
styrene group. Chemisorbing the amine intermediate layer to the ion
cross-linked polymeric layer may include plasma grafting the amine
intermediate layer to the surface.
[0115] The chemisorption of the intermediate layer may be performed
in a multi-step method. In one exemplary embodiment, as shown in
FIG. 3, the amine group may react with sulfonyl chloride to form a
stable immobilized amine group in a series of reactions. Briefly,
the method of producing the ion exchange membrane may comprise
covalently binding a styrene layer to the cross-linked polymeric
layer to form a first intermediate layer. The styrene layer may
comprise a sulfonyl chloride group. The reaction may be performed
for an amount of time sufficient to bind the styrene layer to the
bulk of the substrate. For instance, the reaction may be performed
for an amount of time sufficient for the styrene layer to penetrate
the pores of the substrate. The amount of time sufficient may be on
an order of hours, particularly in embodiments wherein the
substrate has a thickness of less than about 155 .mu.m, for
example, less than about 25 .mu.m. For example, the reaction may be
performed in less than about 10 hours. The reaction may be
performed in about 1-2 hours, about 2-5 hours, about 3-6 hours, or
about 4-7 hours.
[0116] In exemplary embodiments, the styrene layer may comprise
divinylbenzene (DVB). In such embodiments, the method may further
comprise attaching a sulfonyl chloride group to the DVB styrene
layer. To attach the sulfonyl chloride group to the DVB styrene
layer, the method may comprise polymerizing and chlorosulfonating
the DVB. In exemplary embodiments, the chlorosulfonation may be
performed by fuming concentrated sulfuric acid or chlorosulfonic
acid (ClSO.sub.3H) on the DVB. The chlorosulfonic acid may be
hydrolyzed with caustic solution. In such exemplary embodiments,
the chlorosulfonation reaction attaches a ClSO.sub.2 group to the
DVB.
[0117] The chlorosulfonation reaction may be performed for an
amount of time sufficient to penetrate the bulk of the substrate.
The amount of time sufficient for the chlorosulfonation reaction
may be on an order of hours. For example, the chlorosulfonation
reaction may be performed in less than about 10 hours. The
chlorosulfonation reaction may be performed in about 1-2 hours,
about 2-5 hours, about 3-6 hours, or about 4-7 hours.
[0118] In another exemplary embodiment, the attachment group may be
an acrylic group. The acrylic group may enable the attachment of a
sulfonated first intermediate layer, while removing the need for a
sulfonation step. The acrylic group may comprise chlorosulfonated
methacrylate group, such that the produced ion exchange membrane
has a methacrylate covalent bond. In one exemplary embodiment, the
acrylic group may comprise 2-(methacryloyloxy)-ethylsulfonil
chloride, as shown in FIG. 13.
[0119] In addition to removing the need for a sulfonation step, the
acrylic group first intermediate layer may enable the
polymerization initiation to be performed with UV light. Thus, the
acrylic group may generally comprise any acrylic group compound
having a surface sulfonyl group and capable of being
photopolymerized by UV light. In particular, the
photopolymerization initiation may be performed as a continuous
process, significantly decreasing production time. The
photopolymerization may be performed with a UV initiator, such as,
2,2-dimethoxy-2-phenyl-acetophene (DMPA), as shown in FIG. 15 or
bis-acylphosphinoxide (BAPO), as shown in FIG. 14. Other UV
initiators are within the scope of the disclosure. The
photopolymerization with DMPA may be performed at room
temperature.
[0120] The method of producing the ion exchange membrane may
comprise aminating the sulfonyl chloride group of the first
intermediate layer with an amine group layer to produce a
chemically immobilized amine containing group on a surface of the
membrane support. The amine group may comprise a primary or
secondary amine. The chemically immobilized amine group may
generally comprise a functionalizable amine. The functionalizable
amine may be selected based on the designed charged molecule.
Furthermore, the amine group may have a size sufficient to bind an
exterior surface of the substrate, while being substantially
inhibited from penetrating the pores of the substrate. The
amination reaction may be performed overnight. For example, the
amination reaction may be performed for an amount of time of
between about 10-18 hours. The chemically immobilized ammine
containing group may be PEI or branched PEI, as previously
described.
[0121] The method may comprise functionalizing the ion exchange
membrane support by reacting the surface intermediate layer with
the charged functionalizing layer. For instance, the method may
comprise binding a charged functionalizing group to the chemically
immobilized amine layer. Any of the charged functionalizing
molecules described above may be attached to the membrane support.
In certain embodiments, for example, to produce a cation exchange
membrane, the method may comprise hydrolyzing PEI with sulfonic
acid group, for example, sulfonyl hydroxide. The produced cation
exchange membrane will generally have the charged functionalizing
layer covalently bound to the ion exchange membrane support. The
covalent bond may provide greater selectivity and stability of the
ion exchange membrane in use, as previously described.
[0122] The monovalent selective ion exchange membranes disclosed
herein may have a counter ion permselectivity of at least 100%. For
example, the monovalent selective ion exchange membranes disclosed
herein may have a counter ion permselectivity of between about
100%-105% or between about 100%-103%. The monovalent selective ion
exchange membranes disclosed herein may have an initial selectivity
of 8-12 fold Na/Ca (ppm) at room temperature. The monovalent
selective membranes disclosed herein may have a resistivity of less
than about 7 .OMEGA.-cm.sup.2, for example, less than about 5
.OMEGA.-cm.sup.2, between about 2-7 .OMEGA.-cm.sup.2, or between
about 3-5 .OMEGA.-cm.sup.2.
[0123] The function and advantages of these and other embodiments
can be better understood from the following examples. These
examples are intended to be illustrative in nature and are not
considered to be limiting the scope of the invention.
EXAMPLES
Example 1: Production of Cation Exchange Membrane Test Coupons
[0124] The following laboratory method was used to investigate
formulation and process effects by producing small coupons for
resistivity and counter ion permselectivity testing. Porous
membrane substrate 43 mm diameter coupons were die cut. Somewhat
larger discs (50 mm or 100 mm diameter) of transparent polyester
sheets were also die cut. A 105 mm aluminum weighing boat was used
to hold a set of coupons. The coupons were sandwiched between two
polyester film discs.
[0125] First, substrate coupons were thoroughly wetted with a
monomer solution to make up a template. This was done by adding the
formulated solution to the aluminum boat, and immersing a polyester
film disc with a substrate coupon layered on it into the solution
so that the porous support is saturated. The saturated support was
then removed from the monomer solution and placed on a piece of
polyester film. Air bubbles were removed from the coupon by, for
example, smoothing or squeezing the coupon with a convenient tool,
such as a small glass rod, or by hand. A second polyester disc was
then layered on top of the first coupon and smoothed to have
complete surface contact between the coupon and the lower and upper
polyester film layers. A second porous substrate was then layered
on the upper polyester film and the saturation, smoothing and
addition of a over layer of polyester film repeated to give a
multilayer sandwich of two coupons and three protective polyester
film layers. A typical experimental run would have a multilayered
sandwich of 10 or more saturated substrate coupon layers. The rim
of the aluminum boat was crimped down to hold the disc/coupon
assembly, if required.
[0126] The sample containing the boat and coupon assembly was
placed into an oven at 80.degree. C. for up to 30 minutes. The bag
was then removed and cooled, and the now reacted cation exchange
membrane coupons were placed in 0.5N NaCl solution at 40.degree.
C.-50.degree. C. for at least 30 minutes, with NaCl soak of up to
18 hours being found satisfactory.
[0127] The described method was suitable to prepare the cation
exchange membrane test coupons.
Example 2: Monovalent Selectivity of the Cation Exchange
Membrane
[0128] To evaluate the selectivity between the monovalent and
multivalent ions, a solution containing 0.15 M NaCl and 0.15
CaCl.sub.2 was used to feed the dilute compartment. The concentrate
and the two electrodes were fed with a 0.30 M KNO.sub.3 solution.
The dilute stream was a 150 ml sample reservoir with a total volume
of about 75 ml. The concentrate stream (0.3M KNO.sub.3) was a 1000
ml solution to ensure a negligible concentration increase.
Typically a 25% salt removal can be reached at 70 mA for a 7
cm.sup.2 membrane sample with an experiment time of 3 hours.
[0129] The current density was 100 A/m.sup.2. All three streams
were circulated by 3 peristaltic pumps, each having a nominal
pumping speed of 200 ml/min. The dilute stream was sampled for ion
chromatography (IC) analysis. Each sample taken was 100.0 .mu.l,
and diluted to 50 ml for analysis. Typically, 4-6 samples were
taken throughout each membrane experiment. The sample removal did
not affect the total volume of the dilute stream. In most cases,
due to the insignificant concentration difference between the
concentrate and dilute stream, the water loss was minor. Volume
adjustment was not required for the IC analysis samples.
[0130] Conventional Cation Exchange Membrane
[0131] FIGS. 4A-4B are graphs of the molar quantity of Ca.sup.2+
and Na.sup.+ ions (mol/L) in the dilute stream over time (seconds)
for desalt using two conventional membranes, as described in the
experimental procedures above. The graphs show selectivity of Ca/Na
(mol/L). The molar transport ratio between Ca.sup.2+ and Na.sup.+
was around 2 for the conventional cation exchange membranes. The
result is mainly due to the charge effect. Ca.sup.2+ migrates in
the electrical field through membrane faster than Na.sup.+ due to
the greater charge of the ion. However, both Ca.sup.2+ ions and
Na.sup.+ ions were steadily removed, as shown by the slopes of the
line.
[0132] Monovalent Selective Cation Exchange Membrane A monovalent
selective cation exchange membrane prepared by the methods
disclosed herein (for example, as described in example 5 below)
with a PEI having a molecular weight of 600 g/mol was tested as
described above. The results are shown in the graph of FIG. 5.
Briefly, the permselectivity of Ca.sup.2+/Na.sup.+ was 11. Thus,
Ca.sup.2+ is 22 times retarded in transport as compared to the
unmodified conventional membranes described above. Accordingly, the
monovalent selective cation exchange membranes described herein
provide an increased permselectivity as compared to conventional
cation exchange membranes.
Example 3: Preparation of Membrane Test Coupons
[0133] A membrane was prepared by soaking a porous polyethylene
(PE) film (having a thickness of 24 or 34 .mu.m) in a styrene
(ST)/divinylbenzene (DVB)/N-Methyl-2-Pyrrolidone (NMP) solution for
0.01-4 hours. The mixture had a polymerization initiator added and
a composition pf ST:DVB:NMP of 7:1:2 (by mass). The PE film was
saturated with the solution and placed between two mylar sheets.
Air bubbles between the mylar sheets were removed. More solution
was added to avoid any "white area" due to evaporation of the
solution after extended exposure. The membrane was heated to about
80-90.degree. C. for 1-4 hours. Typical membrane dimensions for
such an experiment are 4.times.15 inches.
[0134] The membranes so prepared were cut into 1.5 inch disc
coupons. The coupons were soaked in ClSO.sub.3H/CH.sub.3Cl solution
having a composition of ClSO.sub.3H:CH.sub.3Cl of 1:2 (by volume)
for 24 hours at a temperature of 4.degree. C. The membrane was
removed from the solution and rinsed with NMP and methanol. The
rinsed membrane was then dried with a napkin and deemed ready for
subsequent treatment and testing.
[0135] The resistance of such membrane is typically 2500
.OMEGA.-cm.sup.2 and no permselectivity. The resistance reported
was beyond the measurement of the instrument.
Example 4: Preparation of Cation Exchange Membrane from the
Membrane Test Coupons of Example 3
[0136] The membrane test coupons of example 3 were treated to
produce cation exchange membrane test coupons.
[0137] After drying with the napkin the membrane was placed in a 1N
NaOH solution for about 15 minutes. The membrane was removed from
the NaOH solution and rinsed with water and conditioned in a 0.5M
NaCl solution.
[0138] The membrane had a resistance of between 1.8-3
.OMEGA.-cm.sup.2 and a counter ion permselectivity 101%-104%.
Example 5: Surface Modification of the Cation Exchange Membrane
Test Coupons of Example 4
[0139] The cation exchange membrane test coupons of example 4 were
functionalized to prepare monovalent and multivalent selective
cation exchange membrane test coupons.
[0140] After drying with the napkin the membrane was placed in a
PEI water solution overnight (about 15 hours). It was tested that
the PEI solution may have a pH between 8-12.6. The membrane was
removed from the PEI solution and rinsed with water. The membrane
was soaked in a 1N NaOH solution for 15-22 minutes, to ensure the
substrate bulk SO.sub.2Cl groups were converted to SO.sub.3Na
completely.
[0141] The membrane surface was modified with PEI polymer molecule
and subject to various tests. The membrane had a resistance of
between 2.8-7 .OMEGA.-cm.sup.2 and a counter ion permselectivity
100%-103%.
Example 6: Modification of Ground Water
[0142] A sample water containing Na.sup.+ at 800 ppm, Ca.sup.2+ at
250 ppm, and Mg.sup.2+ at 50 ppm was prepared as a representative
ground water. In practice, ground water has a vast variation of the
three cations. The composition tested herein was an average
value.
[0143] The sample ground water was treated with the monovalent
selective cation exchange membrane described in example 5 and a
conventional cation exchange membrane described in example 3. The
results are shown in the graphs of FIGS. 6A-6B. Concentration of
Na.sup.+, Ca.sup.2+, and Mg.sup.2+ ions were measured. Sodium
adsorption ratio (SAR) was also measured. SAR is an important index
for the water hardness requirement of water used for
irrigation.
[0144] Briefly, the results show the monovalent selective membrane
of example 5 can reduce SAR value of the treated water to 3. By
comparison, the cation exchange membrane of example 3 removes all
ions, increasing SAR value due to the removal of the multivalent
ions. Accordingly, the monovalent selective membranes described
herein may decrease SAR value of treated ground water.
Example 7: Treatment of Seawater
[0145] The monovalent selective cation exchange membrane as
described in example 5 was used to treat seawater for hardness
removal. The removal of hardness in seawater may be important for
many processes such as hypochlorite generation, oil extraction, and
table salt production. The results are presented in FIG. 7.
Specifically, the change of concentration of Mg.sup.2+, Ca.sup.2+,
and Na.sup.+ ions in the dilute stream over time is shown in the
graph of FIG. 7. Briefly, the concentration of Mg.sup.2+ and
Ca.sup.2+ remains relatively constant, while the concentration of
Na.sup.+ ions is reduced. Accordingly, the monovalent selective
membranes described herein may be used to reduce Na.sup.+ ion
concentration in seawater.
Example 8: Stability of the Monovalent Selective Cation Exchange
Membrane
[0146] The monovalent selective cation exchange membrane of example
5 was soaked in a 0.5 M NaCl solution at room temperature. A
conventional cation exchange membrane having physiosorbed PEI was
also tested. FIG. 8 is a graph of the change in membrane
permselectivity after time. Briefly, after 150 days of soaking, the
monovalent selective membrane has a permselectivity of greater than
9 for Na.sup.+ ions versus Ca.sup.2+ ions. The monovalent selective
membrane has a higher selectivity than commercially available
conventional product, and also shows significant stability over
time. Accordingly, the monovalent selective membrane has better
selectivity and a longer service life than a conventional membrane,
and remains stable after an extended period of use.
Example 9: Monovalent Selective Cation Membrane Performance
Study
[0147] Monovalent selective cation membrane performance was studied
under laboratory conditions using membrane coupons with a surface
area of 7 cm.sup.2. Selectivity was determined using a lab ED
module (as shown in FIG. 9) containing a diluting and concentrate
compartment. The solutions in these compartments were circulated
independently via peristatic pumps as well as a K.sub.2SO.sub.4
electrolyte circulating through the anodic and cathodic
compartments. The dilute stream had a total volume of about 75 ml
and its ion constituents were monitored by ion chromatography (IC).
Both the cation exchange membrane and the anion exchange membrane
used in testing had a high co-ion exclusivity with a 98%
preferential transport of counterions. Current densities were
chosen to avoid operating beyond limiting current.
[0148] A synthetic ground water composition (having 800 ppm
Na.sup.+, 260 ppm Ca.sup.2+, 76 ppm Mg.sup.2+) was used to test the
selectivity of the monovalent selective cation exchange membrane at
a current density of 30 A/m.sup.2. FIGS. 10A-10B show the
concentrations of target cations in the dilute compartment over
time. FIG. 10B shows all cation concentrations decreasing by
passing through non-selective membrane, while FIG. 10A shows only
the Na.sup.+ being diluted by the monovalent selective cation
exchange membrane. FIGS. 10C-10D show the concentration of target
cations in mol/L in the dilute compartment over time.
[0149] Sea salt recovery is also demonstrated in an experiment. The
dilute compartment contains an initial solution with the major ions
of seawater (having 17000 ppm Cl.sup.-, 2800 ppm SO.sub.4.sup.2-,
9000 ppm Na.sup.+, 1200 ppm Mg.sup.2+ and 300 ppm Ca.sup.2+)
diluted to a TDS of 500 ppm. FIGS. 11A-11B show the concentration
of select ions in the concentrate compartment using a monovalent
selective anion exchange membrane and a monovalent selective cation
exchange membrane with an applied current density of 300 A/m.sup.2.
The blue squares represent the concentrations of the major ions in
raw sea water.
[0150] The graphs clearly demonstrate the increase in concentration
of chloride over sulfate (FIG. 11A) and sodium over calcium (FIG.
11B) in the concentrate compartment over time. The combination of
the monovalent selective anion and cation exchange membranes
demonstrates the applicability to recover sea salt from seawater
using an ED process having both membranes. Moreover, non-selective
and monovalent selective membrane cell pairs can be combined to
produce specifically targeted ionic compositions in EDR product
water.
[0151] Comparison of the initial selectivity and lifetime
selectivity (stability) of a conventional/commercially available
monovalent selective membrane and the monovalent selective membrane
disclosed herein is shown in FIGS. 12A-12B. The selectivity in
FIGS. 12A-12B is expressed in fold change of sodium ion
concentration over calcium ion concentration, on a parts per
million (ppm) or molar (M) concentration scale.
[0152] The conventional/commercially available membrane was
produced by a method including physisorption of PEI. FIG. 12A shows
membrane selectivity over soak time in a 0.5 M NaCl solution at a
temperature of 80.degree. C. The results were extrapolated by using
a temperature correction which was previously derived from
experiment with an Arrhenius plot with a slope of 2.5/10.degree. C.
As shown in the accelerated testing, the loss of selectivity with
the monovalent cation selective membranes disclosed herein is
considerably reduced over time compared to the conventional
membrane. Furthermore, by extrapolating lifetime from high
temperature to normal operation temperature (as shown in FIG. 12B),
an acceptable lifetime for the monovalent selective cation exchange
membrane disclosed herein is determined with a high selectivity of
monovalent cations over divalent cations.
Example 10: Uses of the Monovalent Selective Cation Exchange
Membrane
[0153] Examples of how the monovalent selective cation exchange
membranes disclosed herein can be used in water treatment systems
are described in the following examples. EDR product and reject
water qualities were modeled using in-house finite element analysis
(FEA) projection software for monovalent selective cation exchange
membranes. Scaling indices (SI) for the reject waters were
calculated using the PHREEQC software (a computer program written
in the C++ programming language that is designed to perform a wide
variety of aqueous geochemical calculations) at various
instantaneous EDR recoveries. The results were compared to field
data from non-selective EDR installations as well as FEA
models.
[0154] Application 1: Industrial Water Brine Minimization
[0155] Many industrial applications use reverse osmosis (RO) to
produce low salinity water. Often, the RO systems are limited to
lower recoveries because of potential scale formation, but brine
disposal can be a costly portion of the overall process. Monovalent
selective cation exchange membrane EDR can be used to treat the
brine to achieve discharge limits, greatly reducing the disposal
costs.
[0156] One comparative application site operates an RO at 75%
recovery with a rejected stream TDS of 2297 mg/L. Without further
treatment, 25% of the total feed flow would need to be disposed of
as brine waste. By employing non-selective EDR, this brine can be
reduced to 5.7% of the feed flow. The monovalent selective cation
exchange membranes can further reduce the brine waste to 3.2% of
feed flow by increasing the recovery of the EDR process from 82% to
90% before the danger of precipitating CaCO.sub.3 scale. Table 1
shows the major ion concentrations for the streams from field
testing and monovalent selective cation exchange membrane modeling
as well as the SI for CaCO.sub.3 at the maximum EDR recovery.
TABLE-US-00001 TABLE 1 Industrial brine minimization stream
analysis Non- Non- Monovalent Monovalent Selective Selective
selective selective Product Reject Product Reject 82% 82% 90% 90%
Feed Recovery Recovery Recovery Recovery CaCO.sub.3 0.5 -1.54 2.3
-0.55 2.27 Scaling Index TDS 2297 526 10369 526 18253 (mg/L) pH
(su) 7.98 7.11 8.62 7.11 9.02 Ca (mg/L) 100.9 6.7 564.6 93.2 199.0
Mg (mg/L) 46.6 3.2 358.6 43.4 89.3 Na (mg/L) 638.8 165.9 1820.0
19.9 6223.3 K (mg/L) 24.2 6.4 110.4 0.9 234.3 HCO.sub.3 350.8 115.9
1079.5 87.8 2748.5 (mg/L) Cl (mg/L) 1013.1 182.1 5413 253.7 7937.9
NO.sub.3 4.9 0.6 13.6 1.2 38.7 (mg/L) PO.sub.4 (mg/L) 5.4 2.4 21.0
1.4 42.6 SO.sub.4 (mg/L) 92.8 33.3 281.0 23.2 727.1
[0157] Application 2: Produced Water Discharge
[0158] Processes used to harvest oil and gas can also generate
"produced water" that is a challenge to treat for environmental
discharge. An EDR system was piloted at a produced water facility
where desalination is a major component of the treatment process.
The sample water is a water with high concentrations of silica that
limit pressure driven membrane recoveries.
[0159] The EDR pilot study demonstrated 88% instantaneous recovery
while reducing TDS from 8587 mg/L to 2107 mg/L in the first stage
of a two-stage process, but could not achieve higher recovery due
to the potential formation of BaSO.sub.4 scale. By applying the
selectivity from the monovalent selective cation exchange membrane,
the same TDS reduction can be achieved while operating at an
expected recovery of 98%. Table 2 shows the projected product and
concentrate stream analyses at 97% recovery.
TABLE-US-00002 TABLE 2 Produced water stream analysis Non- Non-
Monovalent Monovalent Selective Selective selective selective
Product Reject Product Reject 88% 88% 97% 97% Feed Recovery
Recovery Recovery Recovery BaSO.sub.4 0.82 -0.64 1.94 0.59 1.59
Scaling Index TDS (mg/l) 8587 2107 54881 2107 218164 pH (su) 7.6
6.9 8.0 6.9 8.68 Ca (mg/l) 20.4 2.8 147.4 16.4 97.1 Mg (mg/l) 3.8
0.3 27.9 3.1 17.7 Na (mg/l) 2670 726 17833 646 68633 K (mg/l) 25.0
7.0 148.5 5.3 670.4 Ba (mg/l) 4.7 0.3 32.5 3.9 19.7 HCO.sub.3 3743
911 19157 921 95671 (mg/l) Cl (mg/l) 2033 414 17003 500 51965
NO.sub.3 (mg/l) 4.7 6.9 7.2 1.2 119.6 SO.sub.4 (mg/l) 34.1 6.4
389.7 8.4 870.8 SiO.sub.2 (mg/l) 24.0 22.7 27.2 22.7 27.2
[0160] Application 3: Agricultural Desalination
[0161] To reduce the load on freshwater sources in agricultural
applications, alternative supplies with brackish water qualities
should be considered. While some crops, like barley and cotton, are
more tolerant to saline water conditions, constant use of a
brackish water will generally accumulate salt in the soil and
negatively affect yield without proper leaching through the
addition of freshwater. For more salt-sensitive crops, including
fruit plants, even greater care must be taken, and desalination is
often required.
[0162] In addition to the overall salt content, cation
concentrations can have varying effects on soil structural
stability. The effect can be expressed by the sodium adsorption
ratio (SAR) and the cation ratio of structural stability (CROSS).
While the effect these parameters can have on agricultural yield
depends on the specific crop and salinity, a lower SAR or CROSS
value typically indicates better soil stability. The equations for
SAR and CROSS are shown below:
SAR = [ Na ] ( [ Ca ] + [ Mg ] ) 0 . 5 ( 1 ) CROSS = [ Na ] + 0.56
.function. [ K ] ( [ Ca ] + 0.6 .function. [ Mg ] ) 0 . 5 ( 2 )
##EQU00001##
[0163] The monovalent selective cation exchange membrane EDR may
selectively remove sodium and potassium over calcium and magnesium.
As a result, it may be suited for reducing TDS for agricultural
applications and maintaining a low SAR value. In particular,
monovalent selective cation exchange membrane EDR maintains low SAR
value throughout the range of product TDS concentrations with low
energy and no additional process steps, as required by many
crops.
[0164] A sample brackish feed water was modeled with non-selective
EDR and monovalent selective EDR with the same product TDS. The
product ion concentrations are presented in Table 3. Monovalent
selective cation exchange product water has a SAR value of 0.16
compared to 6.59 with a non-selective process.
TABLE-US-00003 TABLE 3 Feed and product water analyses for sample
brackish agricultural water. Feed Non-Selective Product MSCEM
Product TDS (mg/L) 5804.6 529.2 556.2 Ca (mg/L) 540.3 3.9 170.9 Mg
(mg/L) 327.3 16.4 3.9 Na (mg/L) 792.3 133.5 7.8 K (mg/L) 3.1 1.7
1.0 Sr (mg/L) 8.4 5.0 7.7 SO.sub.4 (mg/L) 3130.0 199.5 209.0
HCO.sub.3 413.9 147.1 132.0 (mg/L) Cl (mg/L) 582.1 19.5 21.8 Fl
(mg/L) 0.4 0.0 0.0 NO.sub.3 (mg/L) 6.9 2.5 2.0 SAR 6.62 6.59 0.16
CROSS 7.42 8.20 0.17
[0165] Thus, the monovalent selective cation exchange membranes
disclosed herein are suitable for such applications as industrial
water brine minimization, produced water discharge, and
agricultural desalination.
Example 11: Preparation of Monovalent Selective Cation Exchange
Membrane Having an Acrylic Group
[0166] Cation exchange membranes, for example, as described in
example 4, may be functionalized by the method described below.
[0167] Photopolymerization
[0168] A solution comprising 2-(methacryloyloxy)-ethylsulfonyl
chloride may be used to covalently bond acrylic groups to the
membrane substrate. The membrane in solution may be polymerized by
exposure to UV light in the presence of a photo-initiator.
[0169] In general, the use of 2-(methacryloyloxy)-ethylsulfonyl
chloride and UV light polymerization may eliminate the use of
chlorosulfonic acid and batch style production method (used in
production example 5) and allow use of a fast UV polymerization on
a conveyor belt. The production method enables manufacture of
larger quantities of membrane in a shorter amount of time.
[0170] Photopolymerization is an alternative process to thermal
initiation-polymerization, removing the thermal initiator from the
system and replacing it with a UV photo-initiator. The class of
photo-initiation materials may generally absorb UV light and get
excited energetically, which results in their decomposition into
free radicals that can attach the monomers and induce
initiation-polymerization of the system.
[0171] The membrane substrate was exposed to UV light in the
presence of photo-initiator 2,2-dimethoxy-2-phenyl-acetophenone
(DMPA) (known as Omnirad BDK, distributed by IGM Resins, Waalwijk,
Netherlands). The composition of the preparation is shown in Table
4.
TABLE-US-00004 TABLE 4 Formulation for preparation of monovalent
selective cation exchange membrane Concentration Concentration
Material (%) (g) N-methylpyrollidinone 14.71 7.355
Ethyleneglycoldimethacrylate 14.71 7.355 2-(methacryloyloxy)- 68.62
34.10 ethylsulfonyl chloride DMPA 1.96 0.98
[0172] After preparation of the mixture and complete dissolution of
DMPA, the substrate was saturated with the preparation and
irradiated with UV radiation. The saturated membrane became
transparent (from a white non-transparent color), which allows for
UV light penetration. The substrate may be irradiated with UV light
from one or both sides. Irradiation from both sides generally
increases photo-initiator decomposition, making the reaction more
effective and increasing polymer yield and monomer conversion. In
general, the substrate may be irradiated with a lamp of UV light
maxima emissions that matches the maxima of absorption of the
photo-initiator. DMPA absorbs UV light at about 250 nm.
[0173] The reaction is shown in the representation of FIG. 15. From
FIG. 15, it can be seen that upon photolysis, radicals are
generated that can be used to initiate the polymerization of the
chemical mixture. The polymerization can be performed at room
temperature. The polymerization can be performed in an environment
which is substantially free from oxygen, for example, in a
nitrogen-filled chamber. The polymerization may also be performed
between two transparent sheets, without air bubbles, for example,
as described above in example 3. In general, polymerization
continues as long as the mixture is exposed to UV radiation. Upon
removal of the UV radiation, polymerization stops.
[0174] The preparation was polymerized and cross-linked or cured,
to obtain a functional membrane with can be treated further.
[0175] More than one photo-initiator may be used. At short
wavelengths (for example, below 350 nm or below 250 nm), better
surface cure can be achieved with photo-initiators that can be used
at moderately high concentrations. At longer wavelengths (for
example, between 350 nm and 420 nm), better membrane penetration
and better depth curing may be achieved. Other exemplary
photo-initiators include bis-acylphosphinoxide (BAPO) (known as
Omnirad 819), shown in FIG. 14.
[0176] Surface Functionalization
[0177] The photopolymerization was followed by surface
functionalization. The surface may be functionalized by reacting
with an aqueous solution of PEI. The surface functionalization was
performed with a branched PEI having a molecular weight of about
60,000 g/mol. The branching of PEI renders the solution viscous and
more soluble in water, making it easier to handle. The high
molecular weight was used so as to prevent the PEI molecules from
penetrating within the bulk of the substrate. A representative
solution of PEI to be used for surface functionalization is shown
in Table 5.
TABLE-US-00005 TABLE 5 PEI solution for surface functionalization
Branched PEI MW 60,000 g/mol, 50/50 in water 10% 2M NaOH 8% Water
82%
[0178] The substrate was saturated with the solution and placed
under slight stirring for reaction overnight at room temperature.
The following day, the membrane was removed from the solution and
washed with deionized water to remove excess PEI.
[0179] Hydrolysis and Functionalization of the Membrane
[0180] At this stage the substrate is in bulk and not ionic form.
The bulk substrate is not capable of ion exchange. To convert the
substrate to a cation exchange membrane, the substrate was
hydrolyzed to convert --SO.sub.2Cl groups in the bulk of the system
to --SO.sub.3H groups that are very strongly acidic and ionize
immediately. Specifically, after washing with deionized water, the
substrate was placed in a 1M NaOH aqueous solution for 10-15
minutes. After that, the membrane was removed and washed thoroughly
with deionized water to remove excess NaOH. The membrane was stored
in 0.5M NaCl solution, ready for characterization, both chemical
and electrochemical.
[0181] The membrane produced in example 11 is expected to perform
similarly to the membrane produced in example 5 at least because
the surface functionalization groups are similar.
[0182] The phraseology and terminology used herein is for the
purpose of description and should not be regarded as limiting. As
used herein, the term "plurality" refers to two or more items or
components. The terms "comprising," "including," "carrying,"
"having," "containing," and "involving," whether in the written
description or the claims and the like, are open-ended terms, i.e.,
to mean "including but not limited to." Thus, the use of such terms
is meant to encompass the items listed thereafter, and equivalents
thereof, as well as additional items. Only the transitional phrases
"consisting of" and "consisting essentially of," are closed or
semi-closed transitional phrases, respectively, with respect to the
claims. Use of ordinal terms such as "first," "second," "third,"
and the like in the claims to modify a claim element does not by
itself connote any priority, precedence, or order of one claim
element over another or the temporal order in which acts of a
method are performed, but are used merely as labels to distinguish
one claim element having a certain name from another element having
a same name (but for use of the ordinal term) to distinguish the
claim elements.
[0183] Having thus described several aspects of at least one
embodiment, it is to be appreciated various alterations,
modifications, and improvements will readily occur to those skilled
in the art. Any feature described in any embodiment may be included
in or substituted for any feature of any other embodiment. Such
alterations, modifications, and improvements are intended to be
part of this disclosure and are intended to be within the scope of
the invention. Accordingly, the foregoing description and drawings
are by way of example only.
[0184] Those skilled in the art should appreciate that the
parameters and configurations described herein are exemplary and
that actual parameters and/or configurations will depend on the
specific application in which the disclosed methods and materials
are used. Those skilled in the art should also recognize or be able
to ascertain, using no more than routine experimentation,
equivalents to the specific embodiments disclosed.
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