U.S. patent number RE35,741 [Application Number 08/778,714] was granted by the patent office on 1998-03-10 for process for purifying water.
This patent grant is currently assigned to Millipore Corporation. Invention is credited to Stephen M. Ciaccio, Gary C. Ganzi, Anthony J. Giuffrida, Yoram Oren.
United States Patent |
RE35,741 |
Oren , et al. |
March 10, 1998 |
Process for purifying water
Abstract
A process is provided for removing ions from water which is
passed through an ion depletion compartment of an
electrodeionization apparatus. The electrodeionization apparatus
contains an ion depletion compartment containing mixed ion exchange
resin beads and an ion concentration compartment which may contain
ion exchange resin beads in a given separation stage having an
anode and a cathode. The anion resin beads and cation resin beads
utilized each comprise beams of substantially uniform size. A
second liquid is passed through the ion concentration compartment
to collect ions under the influence of DC potential which pass from
the depletion compartments into the concentration compartments
through ion permeable membranes. The electrodeionization apparatus
can be operated continuously since resin regeneration is not
required.
Inventors: |
Oren; Yoram (Beer Sheva,
IL), Giuffrida; Anthony J. (Andover, MA), Ciaccio;
Stephen M. (Londonderry, NH), Ganzi; Gary C. (Lexington,
MA) |
Assignee: |
Millipore Corporation (Bedford,
MA)
|
Family
ID: |
27574340 |
Appl.
No.: |
08/778,714 |
Filed: |
December 27, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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613075 |
Mar 8, 1996 |
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322187 |
Oct 12, 1994 |
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908913 |
Sep 18, 1986 |
4925541 |
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762804 |
Aug 2, 1985 |
4632745 |
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628930 |
Jul 9, 1984 |
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417950 |
Oct 6, 1989 |
5154809 |
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275314 |
Nov 23, 1988 |
4931160 |
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48161 |
May 11, 1987 |
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Reissue of: |
417950 |
Oct 6, 1989 |
05154809 |
Oct 13, 1992 |
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Current U.S.
Class: |
204/524; 204/533;
204/536; 204/632; 204/647 |
Current CPC
Class: |
B01D
61/48 (20130101); B01J 47/08 (20130101); C02F
1/4695 (20130101); C02F 1/42 (20130101); C02F
1/4604 (20130101); C02F 2201/46115 (20130101); C02F
2201/4612 (20130101); C02F 2201/4613 (20130101); C02F
2209/05 (20130101) |
Current International
Class: |
B01J
47/08 (20060101); B01J 47/00 (20060101); B01D
61/42 (20060101); B01D 61/48 (20060101); C02F
1/469 (20060101); C02F 1/42 (20060101); C02F
1/46 (20060101); B01D 061/48 () |
Field of
Search: |
;204/524,533,536,632,647 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
SM. Jain, "Electrodialysis and its Applications " (no date). .
D.C. Sammon et al., "An Experimental Study of Electrodeionisation
and its Application to the Treatment of Radioactive Wastes",
Chemistry Division, Atomic Energy Research Establishment, Harwell,
Berkshire, 1960 (no month). .
G.J. Gittens et al., "Some Experimental Studies of
Electrodeionisation Through Resin Packed Beds", Chemistry Division,
Atomic Energy Research Establishment, Harwell, Berkshire, 1964 (no
month). .
Dow Advertising Material--New Dowex Monosphere TG, 1984 (no month).
.
E. Glueckauf, "Electro-Deionisation Through a Packed Bed", British
Chemical Engineering, Dec. 1959, pp. 646-651 (no month). .
G.J. Gittens, et al. "The Applicaation of Electrodialysis to
Demineralisation", A.1,Ch.E.-1, Chem.E. Symposium Series, No 9,
1965 (no month). .
Mateika, Z., Continuous Production of High-Purity Water by
Electrodeionisation, J. Appl. Chem. Biotechnol 1971, vol. 21
(Apr.). .
Sotskova, T. et al., The Mechanism of the Conduction of Electric
Current Through a Mixed Resin Bed, Russian Journal of Physical
Chemistry, 47 (11) 1973, pp. 1596-1599. .
R. Byron Bird, et al., Transport Phenomena, John Wiley & Sons,
Inc., 1960, pp. 40, 41, 198-201, (Department of Chemical
Engineering, University of Wisconsin) (no month). .
Robert Kunin, Ion Exchange Resins, Second Edition, Wiley &
Sons, INc., 1958, pp. 52, 53, 80-83, 320-323, 330-333, 336, 337 (no
month). .
Konrad Dorfner, Ph.D., Ion Exchangers Properties and Applications,
Ann Arbor Science Publishers Inc., 1972, pp. 12, 13, 28-33, 56, 57
(no month). .
Product Brochure, With High-Performance DOWEX MONOSPHERE Resins,
1984, The Dow Chemical Company (no month). .
Product Brochure, Deionization with Amberlite Ion Exchange Resins
in Monobed Ion Exchange Resin Systems, Apr. 1974, Rohn & Haas,
pp. 2-15. .
Product Brochure, Ion Exchange with the Amberlite Resins, Apr.
1974, Rohm and Haas, pp. 1-5. .
Peter-Michael Lange and Friedrich Martinola, Monodisperse
Ionenaustauscher und Absorber, neue Varianten in de
Austauschertechnik, 1987, Vom Wasser, 69 (1987) pp. 203-215 (no
month). .
D. Klempner, L. Berkowski, "Ion-Exchange Polymers," John Wiley
& Sons, in Encyclopedia of Polymer Science and Engineering,
(1987) vol. 8, pp. 341-347, 355-359, 365-378, 388-393 (no month).
.
Unprecedented Bead Size Uniformity Provides Near-Perfect Separation
in Condensate Polishers pp. 2-9, The Dow Chemical Company, 1983 (no
month). .
Jack B. Prentiss, Michael D. Mayne, Evaluation of Uniform Mesh Ion
Exchange Resins for Condensate Polishing, 1984, 179-189 (no month).
.
Uniform Particle Size Ion Exchange Resins in Water Demoralization
Wilson & McNutty, Rohm & Hass Co., Watertech (1993, ) pp.
114-120. .
Dowex Monosphere Resins, Better Water Chemistry Through Total
Control of Bead Size Mar. 1988. .
The Effect of Bead Size and Hydrated Bead Density on the
Separability of Mixed Beds, Fisher & Otten, Puricons, Inc.,
409-415 (no date). .
New Dowex Monoshpere TG, Tough Gel (TG) ion exchange resins for
high-performance systems, (1984). .
Evaluation of Uniform Particle Size Type II Anion Resin, Usitalo,
et al., 49th Annual Meeting INt'l Water Conf., (Oct. 24-26, 1988).
.
Impact of Particle Size on Single Bed Demineralizer Performance,
Daniel B. Rice, 51st Annual Mtg. Int'l Water Conf., (Oct. 21-24,
1990). .
Ion Exchange: A New Sphere of Action, Dow Chemical CO., Chemical
Engineering, (Sep. 1992) pp. 63-71. .
The Properties & Advantages of Uniform Particle Size
Ion-Exchange Resins, Wrigley, et al., Ion Exchange Adv., Proc. IEX
(1992,) 65-72. .
Ion Exchange Mechanism in Condensate Polishing, JR Emmett, et al.
Combustion, (Aug. 1980) pp. 12-18. .
Mixed-Bed Performance in a Condensate Polishing Plant, K. Tittle,
vol. 43, Proceedings of the American Power Conf., (1981) 1126-1130.
.
A Different Approach to Condensate Polishing, R.E. Mickel, et al,
42nd Annual Meeting Int'l Water Conference, (Oct. 26-28, 1981).
.
An INtroduction to Condensate Polishing, H. L. Aronovitch, 20th
Annual Liberty Bell Corrosion Course IV, (Sep. 23, 1982). .
Recent Trends in Condensate Treatment, C. Calmon, Environment
Protection Engineering, vol. 8, No. 1-4, (1982,) pp.
55-66..
|
Primary Examiner: Phasge; Arun S.
Attorney, Agent or Firm: Wolf, Greenfield & Sacks,
P.C.
Parent Case Text
REFERENCE TO RELATED APPLICATIONS
.[.This application is a.]. .Iadd.This application is a
continuation of application Ser. No. 08/613,075, filed Mar. 8,
1996, now abandoned, which was a continuation of application Ser.
No. 08/322,187, filed Oct. 12, 1994, now abandoned, which is a
reissue of 07/417,950, filed Oct. 6, 1989, now U.S. Pat. No.
5,154,809, which is a .Iaddend.continuation in part of application
Ser. No. 908,913, filed Sep. 18, 1986, now U.S. Pat. No. 4,925,541
which is a divisional application of Ser. No. 762,804, filed Aug.
2, 1985, now U.S. Pat. No. 4,632,745 which is a continuation of
application Ser. No. 628,930, filed Jul. 9, 1984, now
abandoned.
.[.The.]. .Iadd.Said .Iaddend.application also is a continuation in
part of co-pending application Ser. No. 275,314, filed Nov. 23,
1988, now U.S. Pat. No. 4,931,160 which is a continuation of
application Ser. No. 048,161, filed May 11, 1987, now abandoned.
Claims
We claim:
1. .[.The process for purifying water to remove organics and ionic
species therein which comprises:
passing said water through ion depletion compartments of an
electrodeionization apparatus, said electrodeionization apparatus
comprising;.]..Iadd.A process for removing organic and ionic
species from a liquid which comprises the steps of:
a) providing an electrodeionization apparatus which comprises:
i.Iaddend.) a cathode compartment at a first end of .[.said.].
.Iadd.the .Iaddend.apparatus,
.Iadd.ii.Iaddend.) an anode compartment at .[.an.]. .Iadd.a second
.Iaddend.end of .[.said.]. .Iadd.the .Iaddend.apparatus opposite
.[.said.]. .Iadd.the .Iaddend.first end,
.[.a plurality of said ion depletion compartments alternating with
ion concentration compartments positioned between said cathode
compartment and said anode compartment,
an anion permeable membrane and a cation permeable membrane,
said anion permeable membrane and said cation permeable membrane
being bonded to a spacer to effect sealing against water leakage
between said ion depletion compartment and
each of said ion depletion compartments containing a mixture of
anion resin beads of substantially uniform size and cation resin
beads of substantially uniform size,.].
.Iadd.iii) at least one ion concentrating compartment positioned
adjacent to at least one ion depleting compartment, the ion
depleting compartment comprising a mixture of anion exchange resin
beads having a substantially uniform size and cation exchange resin
beads having a substantially uniform size positioned between an
anion exchange membrane and a cation exchange membrane, the ion
depleting and ion concentrating compartments being positioned
between the cathode compartment and the anode compartment, wherein
the ion concentrating compartments are free of ion exchange
resin,
b) passing a first liquid through the ion depleting
compartments,
c) simultaneously .Iaddend.passing a second liquid for accepting
ions from .[.said water,.]. .Iadd.the first liquid .Iaddend.through
.[.said.]. .Iadd.the .Iaddend.concentration compartments .[.while
said water is passed through said ion depletion
compartments.].,
.Iadd.d.Iaddend.) applying an electrical voltage between an anode
in .[.said.]. .Iadd.the .Iaddend.anode compartment and a cathode in
.[.said.]. .Iadd.the .Iaddend.cathode compartment, and
.Iadd.e.Iaddend.) recovering .[.purified water.]. .Iadd.the first
liquid .Iaddend.from .[.said depletion.]. .Iadd.the depleting
.Iaddend.compartment.
2. The process of claim 1 wherein .[.the ion exchange comprises a
mixture of anion exchange resin beads and cation exchange resin
beads and wherein.]. the volume ratio of anion exchange resin beads
to cation exchange resin beads in said ion depiction compartments
is between 4.0 and 0.5.
3. The process of claim 1 wherein said water is passed through at
least two ion depletion compartments in series positioned between
said anode and said cathode.
4. .[.The process for purifying water to remove organics and ionic
species therein which comprises:
passing said water through ion depletion compartments of an
electrodeionization apparatus comprising,
said electrodeionization apparatus comprising;
a cathode compartment at a first end of said apparatus,
an anode compartment at an end of said apparatus opposite said
first end,
a plurality of said ion depletion compartments alternating with ion
concentration compartments positioned between said cathode
compartment and said anode compartment,.]. .Iadd.The process of
claim 1 wherein .Iaddend.
each of .[.said.]. .Iadd.the .Iaddend.ion .[.depletion.].
.Iadd.depleting .Iaddend.compartments comprising a spacer and a
plurality of subcompartments formed by a plurality of ribs
extending along the length of each of .[.said.]. .Iadd.the
.Iaddend.ion .[.depletion.]. .Iadd.depleting .Iaddend.compartments
each of .[.said.]. .Iadd.the .Iaddend.subcompartment .[.containing
an ion exchange solid composition, each of said subcompartments.].
having a width defined by the distance between .[.said.]. .Iadd.the
.Iaddend.ribs of between about 0.3 and 4 inches and a thickness
between about 0.05 and 0.25 inches.[...]..Iadd., .Iaddend.
.[.an anion permeable membrane and a cation permeable membrane,
said anion permeable membrane and said cation permeable membrane
being bonded.]. .Iadd.the anion exchange membrane and the cation
exchange membrane each being secured .Iaddend.to a spacer to
.[.effect sealing against water.]. .Iadd.create a seal against
liquid .Iaddend.leakage between .[.said.]. .Iadd.the .Iaddend.ion
.[.depletion.]. .Iadd.depleting .Iaddend.compartment .[.and
each of said ion depletion compartments containing a mixture of
anion resin beads of substantially uniform size and cation resin
beads of substantially uniform size,
passing a second liquid for accepting ions from said water, through
said concentration compartments while said water is passed through
said ion depletion compartments,
applying an electrical voltage between an anode in said anode
compartment and a cathode in said cathode compartment, and
recovering purified water from said depletion compartment.]..
5. The process of claim 4 wherein the width of said subcompartment
is between about 0.5 and 1.5 inches.
6. The process of claim 4 wherein the thickness of said
subcompartment is between about 0.06 and 0.125 inches.
7. The process of claims 4, 5, or 6 wherein .[.the ion exchangers
comprise a mixture of anion exchange resin beads and cation
exchange resin beads and wherein.]. the volume ratio of anion
exchange resin beads to cation exchange resin beads in said ion
depletion compartments is between 4.0 and 0.5.
8. The process of claim 4 wherein said .[.water.]. .Iadd.liquid
.Iaddend.is passed through at least two ion depiction compartments
in series positioned between said anode and said cathode. .[.9. The
process of claim 4 wherein said ion concentration compartments
contain a mixture or anion exchange beads of substantially uniform
size and cation exchange beads of substantially uniform size and
wherein electrical voltage supplied to said anode and said cathode
is reversed periodically to convert said anode to a second cathode
and to convert said cathode to a second anode and to convert said
ion depletion compartment to a second ion concentration compartment
and to convert said ion concentration compartment to a second ion
depiction compartment and recovering a water having low
conductivity continuously from said ion depletion compartment and
said second ion depiction compartment..]..[.10. The process of
claim 8 wherein electrical voltage supplied to said anode and said
cathode is reversed periodically to convert said anode to a second
cathode and to convert said cathode to a second anode and to
convert said ion depletion compartment to a second ion
concentration compartment and to convert said ion concentration
compartment in a second ion depletion compartment and recovering a
water having low conductivity continuously from said ion depiction
compartment
and said second ion depiction compartment..].11. A dual compartment
construction adapted to remove ions from a liquid which
comprises:
an ion depletion compartment and an ion concentration compartment
and an odd number of at least three ion permeable membranes,
.[.said.]. .Iadd.the .Iaddend.ion permeable membranes comprising
anion permeable membranes alternately positioned with respect to
cation permeable membranes,
each of .[.said.]. .Iadd.the .Iaddend.ion depletion compartments
and each of .[.said.]. .Iadd.the .Iaddend.ion concentration
compartments comprising a spacer and a plurality of ion depletion
subcompartments and ion concentration subcompartments,
.[.said.]. .Iadd.the .Iaddend.subcompartments being formed by a
plurality of ribs extending along the length of each of .[.said.].
.Iadd.the .Iaddend.ion depletion compartments and .[.said.].
.Iadd.the .Iaddend.ion concentration compartments,
each of .[.said.]. .Iadd.the .Iaddend.ion depletion subcompartments
and .[.said.]. .Iadd.the .Iaddend.ion concentration subcompartments
containing a mixture of anion exchange resin beads .[.of.].
.Iadd.having a .Iaddend.substantially uniform size and cation
exchange resin beads of substantially uniform size,
each of .[.said.]. .Iadd.the .Iaddend.ion depletion subcompartments
and .[.said.]. .Iadd.the .Iaddend.ion concentration subcompartments
.Iadd.formed by a plurality of ribs extending along the length of
each of the ion depletion compartments, each of the subcompartments
.Iaddend.having .[.a rib.]. .Iadd.a width .Iaddend.defined by the
distance between .[.said.]. .Iadd.the .Iaddend.ribs .[.or.].
.Iadd.of .Iaddend.between about 0.3 and 4 inches and a thickness
between about 0.05 and 0.25 inches wherein the thickness of
.[.said.]. .Iadd.the .Iaddend.subcompartments is defined by the
distance between .[.an.]. .Iadd.the .Iaddend.anion permeable
membrane and .[.a.]. .Iadd.the .Iaddend.cation permeable
membrane,
each of .[.said.]. .Iadd.the .Iaddend.ion permeable membranes being
.[.bonded.]. .Iadd.secured .Iaddend.to a spacer and .[.said.].
.Iadd.the .Iaddend.ribs within .[.a.]. .Iadd.the .Iaddend.spacer
such that the anion permeable membrane and .Iadd.the
.Iaddend.cation permeable membrane are positioned alternatively
along the length of .[.said.]. .Iadd.the .Iaddend.dual
compartment,
.[.means.]. .Iadd.a port .Iaddend.for passing a first liquid to be
purified through each ion depletion compartment,
and .[.means.]. .Iadd.a port .Iaddend.for passing a second liquid
for accepting ions from .[.said.]. .Iadd.the .Iaddend.first liquid
through
each ion concentration compartment. 12. The construction of claim
11 wherein the width of said subcompartments is between about 0.5
and 1.5
inches. 13. The construction of claim 11 wherein the thickness of
said
subcompartments is between about 0.06 and 0.125 inches. 14. The
construction of any one of claims 11, 12, or 13 wherein .[.the ion
exchange composition comprises a mixture of anionic exchange resin
beads and cationic exchange resin beads and wherein.]. the volume
ratio of .[.anionic.]. .Iadd.anion exchange .Iaddend.resin beads to
.[.cationic.]. .Iadd.cation .Iaddend.exchange resin beads .[.and.].
.Iadd.in .Iaddend.said ion depletion compartments and in said ion
concentration
compartments is between about 4.0 and 0.5. 15. The process of any
one of claims 1,2,3,4,5,6, .Iadd.or .Iaddend.8, .[.9 or 10.].
wherein the anion resin beads and the cation resin beads are of
substantially equal average
size. 16. The construction of any one of claims 11,12 or 13 wherein
the anion resin beads and the cation resin beads are of
substantially equal
size. 17. The process of claim 7 wherein the anion resin beads and
the
cation resin beads are of substantially equal average size. 18. The
construction of claim 14 wherein the anion resin beads and the
cation resin beads are of substantially equal size. .Iadd.19. An
electrodeionization apparatus comprising at least one ion
concentrating compartment positioned adjacent to at least one ion
depleting compartment, the ion depleting compartment comprising an
ion exchange resin positioned, between an anion exchange membrane
and a cation exchange membrane, wherein the ion exchange resin
comprises a mixture of anion exchange resin beads having a
substantially uniform size and cation exchange resin beads having a
substantially uniform size, and the ion concentrating compartment
being
free of ion exchange resin. .Iaddend..Iadd.20. An
electrodeionization apparatus as in claim 19 wherein the volume
ratio of anion exchange resin beads to cation exchange resin beads
is between about 4.0 and 0.5. .Iaddend..Iadd.21. A process for
removing organic and ionic species from a liquid which comprises
the steps of:
a) providing an electrodeionization apparatus which comprises:
i) a cathode compartment at a first end of the apparatus,
ii) an anode compartment at a second end of the apparatus opposite
the first end,
iii) at least one ion concentrating compartment positioned adjacent
to at least one ion depleting compartment, the ion concentrating
compartment and the ion depleting compartment comprising a mixture
of anion exchange resin beads having a substantially uniform size
and cation exchange resin beads having a substantially uniform size
positioned between an anion exchange membrane and a cation exchange
membrane, the ion depleting and ion concentrating compartments
being positioned between the cathode compartment and the anode
compartment,
b) passing a first liquid through the ion depleting
compartments,
c) simultaneously passing a second liquid for accepting ions from
the first liquid through the concentration compartments,
d) applying an electrical voltage between an anode in the anode
compartment and a cathode in the cathode compartment, and
e) recovering the first liquid from the depleting compartment.
.Iaddend..Iadd.22. The process of claim 21 wherein the volume ratio
of anion exchange resin beads cation exchange resin beads in said
ion concentration compartments and said ion depletion compartments
is between 4.0 and 0.5. .Iaddend..Iadd.23. The process of claim 21
wherein said water is passed through at least two ion depletion
compartments in series positioned between said anode and said
cathode. .Iaddend..Iadd.24. The process of claim 21 wherein each of
the ion depleting compartments comprising a spacer and a plurality
of subcompartments formed by a plurality of ribs extending along
the length of each of the ion depleting compartments each of the
subcompartment having a width defined by the distance between the
ribs of between about 0.3 and 4 inches and a thickness 0.05 and
0.25 inches,
the anion exchange membrane and the cation exchange membrane each
being secured to a spacer to create a seal against liquid leakage
between the ion depleting compartments. .Iaddend..Iadd.25. The
process of claim 24 wherein the width of said subcompartment is
between about 0.5 and 1.5 inches. .Iaddend..Iadd.26. The process of
claim 24 wherein the thickness of said subcompartment is between
about 0.06 and 0.125 inches. .Iaddend..Iadd.27. The process of
claims 24, 25 or 26 wherein the volume ratio of anion exchange
resin beads to cation exchange resin beads in said ion
concentration compartments and in said ion depletion compartments
is between 4.0 and 0.5. .Iaddend..Iadd.28. The process of claim 24
wherein said water is passed through at least two ion depletion
compartments in series positioned between said anode and said
cathode. .Iaddend..Iadd.29. The process of claim 24 wherein
electrical voltage supplied to said anode and said cathode is
reversed periodically to convert said anode to a second cathode and
to convert said cathode to a second anode and to convert said ion
depletion compartment to a second ion concentration compartment and
to convert said ion concentration compartment to a second ion
depletion compartment and recovering a water having low
conductivity continuously from said ion depletion compartment and
said second ion depletion compartment. .Iaddend..Iadd.30. The
process of claim 28 wherein electrical voltage supplied to said
anode and said cathode is reversed periodically to convert said
anode to a second cathode and to convert said cathode to a second
anode and to convert said ion depletion compartment to a second ion
concentration compartment and to convert said ion concentration
compartment to a second ion depletion compartment and recovering a
water having low conductivity continuously from said ion depletion
compartment and said second ion depletion compartment. .Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates to an electrodeionization process wherein
liquid to be purified is passed through an ion depletion
compartment containing substantially uniform sized anion resin
beads and uniform sized cation resin beads under the influence of a
polar field in order to effect ion transfer from the liquid in the
ion depletion compartment to liquid in an ion concentration
compartment.
The purification of a liquid by reducing the concentration of ions
or molecules in the liquid has been an area of substantial
technological interest. Many techniques have been used to purify
and isolate liquids or to obtain concentrated pools of specific
ions or molecules from a liquid mixture.
The most well known processes include distillation,
electrodialysis, reverse osmosis, liquid chromatography, membrane
filtration and ion exchange. A lesser known method is
electrodeionization, occasionally mis-termed filled cell
electrodialysis.
The first apparatus and method for treating liquids by
electrodeionization was described by Kollsman in U.S. Pat. Nos.
2,689,826 and 2,815,320. The first of these patents describes an
apparatus and process for the removal of ions within a liquid
mixture in a depletion chamber through a series of anionic and
cationic diaphragms into a second volume of liquid in a
concentration chamber under the influence of an electrical
potential which causes the prelected ions to travel in a
predetermined direction. The volume of the liquid being treated is
depleted of ions while the volume of the second liquid becomes
enriched with the transferred ions and carries them in concentrated
form. The second of these patents describes the use of macroporous
beads formed of ion exchange resins as a filler material positioned
between the anionic or cationic diaphragms. This ion exchange resin
acts as a path for ion transfer and also serves as an increased
conductivity bridge between the membranes for the movement of
ions.
The term "electrodeionization" refers to the process wherein an ion
exchange material is positioned between anionic and cationic
diaphragms. The term "electrodialysis" refers to such a process
which does not utilize ion exchange resins between the anionic and
cationic diaphragms. Illustrative of other prior art attempts to
use a combination of electrodialysis and ion exchange materials or
resins to purify saline from brackish are described in U.S. Pat.
Nos. 2,794,770; 2,796,395; 2,947,688; 3,384,568; 2,923,674;
3,014,855 and 4,165,273. Attempts to improve electrodeionization
apparatus are shown in U.S. Pat. Nos. 3,149,061; 3,291,713;
3,515,664; 3,562,139; 3,993,517 and 4,284,492.
A commercially successful electrodeionization apparatus and process
is described in U.S. Pat. No. 4,632,745. The apparatus utilizes ion
depletion compartments containing an ion exchange solid composition
and a concentration compartment which is free of ion exchange solid
material. The electrodeionization apparatus includes two terminal
electrode chambers containing an anode and a cathode respectively
which are utilized to pass direct current transversely through the
body Of the apparatus containing a plurality of ion depletion
compartments and ion concentration compartments. In operation, the
dissolved ion salts of the liquid are transferred through the
appropriate membranes from the ion depletion compartments to the
ion concentration compartments. The ions collected in the ion
concentration compartments are removed through discharge outlets
and are directed to waste.
At the present time, anion exchange beads and cation exchange beads
having a substantially uniform bead size are available for use in
ion exchange processes that is, in processes wherein an ion
dissolved in a liquid can be exchanged with an ion ionically bonded
to the beads. Prior to their use, the regenerated beads must be
washed with water in order to remove leachable components in the
beads such as, residual regenerant, total organic carbon components
and polymeric leachables such as sulfonated polystyrene. These
leachable components must be removed prior to use in order to
prevent contamination of the aqueous medium being treated or
contaminating downstream apparatus or processes. It has been found
that when utilizing the substantially uniform size ion exchange
beads, the rinse or flush out time required can be as low as about
1/3 the flush out time required to clean commercially available
beads having a non-uniform bead size. By the phrase, "flush out
time" as used herein means the time required to obtain a quality
improvement of effluent water contacting the beads before the water
quality reaches a substantially constant level. Prior to the
present invention, a substantially uniform sized ion exchange beads
have not been utilized in an electrodeionization process.
SUMMARY OF THE INVENTION
This invention is based upon the discovery that substantially
uniform sized ion exchange beads can be utilized in an
electrodeionization process and can be rinsed to remove
extractables, prior to use in a time of from about one fourth to
about one third or less of the time required to flush out
non-uniformly sized ion exchange beads normally utilized in an
electrodeionization process. By the phrase "substantially uniform
size" as applied to the anion resin beads or the cation resin beads
as used herein means that 90% of the beads are within .+-.10% of
the mean bead size and that the relative average size of one ionic
form of resin beads to a second ionic form of resin beads in a
mixture of resin beads is at least 0.8. In the process of this
invention, the uniform size resin beads are introduced into the ion
depletion compartments of an electrodeionization apparatus and also
can be introduced into the ion concentration compartments, if
desired, depending upon the mode of electrodeionization. Water is
then introduced into the compartments containing the resin beads
and is passed therethrough for a period of time needed to effect
substantially constant levels of measured extractable in the water
removed from the compartments. This flushing is effected while an
electrical voltage is applied between an anode and a cathode
positioned on either side of the compartments containing the resin
beads. Water to be purified then continues to be passed through the
ion depletion compartments while water after accepting ions from
the ion depletion compartments is discarded. The
electrodeionization step can be operated by passing the water being
treated in one pass through a given ion depletion compartment or by
effecting serpentine flow within two adjacent ion depletion
compartments. In addition, the electrodeionization step can be
conducted under conditions where voltage polarity is reversed
periodically. Additional process steps can be added such as an
ultrafiltration step in order to further improve product purity or
by a preliminary step wherein water to be purified is exposed to
ultraviolet radiation under a wave length that promotes oxidation
of organics, e.g., 185 nm so that substantially complete removal of
total organic carbon (TOG) can be effected.
BRIEF DESCRIPTION OF THE DRAWINGS.
FIG. 1 is a schematic view illustrating the operation of one
embodiment of the electrodeionization process of this
invention.
FIG. 2 is a schematic view of a second embodiment of this
invention.
FIGS. 3 and 4 are schematic views illustrating an embodiment of
this invention wherein polarity is reversed during operation of the
electrodeionization step.
FIG. 5 is a schematic view showing one flow path arrangement useful
when reversing polarity.
FIG. 6 is a schematic view showing an alternative flow path
arrangement useful for reversing polarity.
DESCRIPTION OF SPECIFIC EMBODIMENTS
Suitable ionic resin beads for use in the present invention are
DOWEX MONOSPHERE resin beads 550A and 650C available from Dow
Chemical Company, Midland, Mich. The 550A beads and 650C beads have
90% of the beads within .+-.10% of the mean bead size. The mean
bead size of the 550A anionic resin beads is 550 micrometers while
the 650C cationic resin beads has a mean bead size of 650
micrometers. The relative average size of the cationic resin beads
to the anionic resin beads or vise versa should be at least about
80 percent of the other resin beads, preferably of substantially
equal average size. In use, anionic resin beads, cationic resin
beads or a mixture of anionic resin beads and cationic resin beads
are placed into ion depletion compartments and may be placed into
ion concentration compartments prior to passing water through the
electrodeionization device. Water is then passed through the
compartments containing the resin beads until the extractables
removed from the beads into the water reaches a substantially
constant low level. Water to be purified then is passed through the
ion depletion compartment of the electrodeionization apparatus in
the manner described below. The electrodeionization step is
comprised of ion depletion compartments which are positioned in
alternating relationship with ion concentration compartments. The
ion depletion compartments are defined by alternating anion
permeable membranes and cation permeable membranes which are sealed
in a manner to prevent leakage between ion depletion compartments
and ion concentration comments. The ion depletion compartments
contain a mixture of anion resin beads and cation resin beads to
promote ion transfer from water in the ion depletion compartments.
The alternating ion depletion compartments and ion concentration
compartments are positioned between an anode and a cathode. Water
to be purified is passed through the ion depletion compartments
while water used to accept ions from the ion depletion compartments
is passed through the ion concentration compartments. In operation,
an electrical voltage is applied between the anode and cathode
which promotes ion transfer from the water in the ion depletion
compartments through the anion permeable membrane and the cation
permeable membrane and into the water passing through the adjacent
ion concentration compartments. In the electrodeionization step,
the ions removed from the water are not retained by the membranes
or resin beads but are removed with the water passing through the
ion concentration compartments. Therefore, the electrodeionization
step ca be operated continuously without the need to replace or
regenerate the resin particles or membranes.
Prior to conducting the electrodeionization process of this
invention with ion exchange resin beads of substantially uniform
size, the beads are flushed out with water under a voltage gradient
between the cathode and the anode in order to remove extractables
from the beads. With standard nonuniform size resins, the procedure
requires an average of about two hours to generate a product stream
having a satisfactory low extractables concentration. With the
uniform sized beads utilized in the present invention, anionic and
cationic resin beads of substantially equal average size, e.g. 550
micrometers-550 micrometers, have a flush out time as quickly as
one minute or less varying from about 50 seconds to about 20
minutes, depending on voltage and flow conditions, cell design and
construction and water quality desired while anionic and cationic
resin beads having an average size of about 4/5 give a flush out
time of about 8 minutes. This compares to an average flush out time
with standard nonuniform size resin beads of about 1 hour to 4
hours or more.
In a specific embodiment of this invention, the electrodeionization
step is conducted by the process and with the apparatus disclosed
in U.S. Pat. No. 4,632,745, issued Dec. 30, 1986 which is
incorporated herein by reference. As disclosed in the patent, an
electrodeionization apparatus is provided wherein each
electrodeionization electrical stage includes an anode and a
cathode, and their compartments, a series of ion concentration
compartments and a series of ion depletion compartments that
contain a mixture of anion exchange resin and cation exchange
resin. The depletion compartments are formed so that the ion
exchange resin mixture is housed within independent discrete
subcompartments each of which has a width between about 0.3 and 4
inches, preferably between about 0.5 and 1.5 inches. The discrete
subcompartments are formed by securing, such as by bonding, both
the anion permeable membrane and the cation permeable membrane to
the periphery of the depletion compartment and to ribs which extend
across the thickness of and along the entire length of the
depletion compartment so that each subcompartment is defined by a
pair of ribs, the anion permeable membrane and the cation permeable
membrane. The thickness of the subcompartments as defined by the
distance between the anion permeable membrane and the cation
permeable membrane is between about 0.05 and 0.25 inches,
preferably between about 0.06 and 0.125 inches. In this embodiment,
it has been found that the thickness and width of the depletion
compartments are critical to achieving efficient operation of the
electrodeionization apparatus. The solid ion exchange material
positioned within the subcompartments are constrained from moving
between subcompartments by the ribs and ion permeable
membranes.
The electrodeionization apparatus can comprise one or a plurality
of stages. In each stage, an anode is positioned at an opposite end
of a stack of depletion and concentration compartments from an end
at which a cathode is positioned. Each anode and cathode is
provided with an adjacent electrode spacer and an ion permeable
membrane wherein an electrolyte passes through the electrode
spacer. The remaining portion of each stage comprises a series of
alternating depletion and concentration compartments constructed as
set forth herein. The liquid to be depleted of ions can be passed
in parallel through each depletion compartment in each stage and a
second liquid can be passed through each concentration compartment
in parallel in each stage in order to effect removal of ions from
the first liquid in the depletion compartments into the second
liquid in the concentration compartments. When a plurality of
stages are utilized, the liquid removed from the depletion
compartments in an upstream stage can be directed in series into
the depletion compartments in the next adjacent downstream stage.
Similarly, the liquid removed from the concentration compartments
of an upstream stage can be directed in series to the concentration
compartments in the next adjacent downstream stage. Electrolyte can
be passed through the spacer adjacent each electrode in the
electrodeionization apparatus and is removed from the
electrodeionization apparatus.
The subcompartments in the depletion compartments have a controlled
thickness and width in order to sustain high efficiency for ion
depletion over long periods. There is no limit on the length of the
compartment other than as dictated by practical construction and
fluid pressure loss considerations. Obviously, the longer the
subcompartment length, the greater the ion removal from the liquid
therein. Generally, the length of the subcompartments are between
about 5 inches and about 70 inches. When it is desired to remove
only a particular anion or particular cation, 100% of the
appropriate exchange material is used. Usually it is desired to
remove both cations and anions in order to produce a purified
liquid product. The ratio of anion exchange resin beads to cation
exchange resin beads generally are about 60 to 40 by volume. By
utilizing the subcompartment structure in the depletion
compartments, efficient mixing of the liquid and the beads therein
is attained while avoiding channeling of the liquid through the
depleting compartment. Thus, efficient interchange of the ions and
the liquid in the depletion compartment with the ions in the beads
to effect ion removal from the liquid in the depletion compartment
is attained. Furthermore, it has been found that by controlling the
geometry of the subcompartments as set forth herein, relatively low
energy requirements for the electrodeionization apparatus can be
utilized even over long periods to attain desired liquid
purity.
Referring to FIG. 1, the flowpaths of the liquids in the various
compartment are explained. Liquid to be purified enters inlet 40,
passes through depletion compartments 42, is then passed through
depletion compartments 44 and is recovered from outlet 46.
Concentrating liquid is passed through inlet 48 through
concentration compartments 50 and 52 and hence through outlet 54 to
drain. Liquid electrolyte is circulated through electrode
compartments 56, 58, 60 and 62 from inlets 64 and is discarded to
drain through outlets 66.
Any anion permeable membrane or cation permeable membrane having
the strength to withstand the operating pressure differential,
typically up to about 5 psi, can be utilized in the present
invention. It should be pointed out that sealing of the membranes
to the ribs forming the subcompartments permits the us of higher
operating pressures and enhances the apparatus of the prior art
since the assembly strength is thereby increased. Representative
suitable anion permeable membranes include a homogeneous type web
supported styrene-divinylbenzene based with sulfonic acid or
quarternary ammonium functional groups sold under the
identifications CR61-CZL-386 and AR 103-CZL-386 by Ionics, Inc.; a
heterogeneous type web supported using styrene-divinylbenzene based
resins in a polyvinylidene fluoride binder sold under the
identifications MC-3470 and MA-3475 by Sybron/Ionac; homogeneous
type unsupported-sulfonated styrene and quaternized
vinylbenzylamine grafts of polyethyene sheet sold under the name,
Raipore by RAI Research Corporation; a homogeneous type web
supported styrene-divinylbenzene based with sulfonic acid or
quaternary ammonium functional groups sold under the name Aciplex
by Asahi Chemical Industry, Ltd.
The electrodeionization step can be controlled by measuring product
water conductivity from all or any one of the stages and adjusting
the process parameters including process voltage, liquid flow
velocities, temperatures, pressures, and electrical current
accordingly.
The following is a description of two methods for controlling the
demineralization of an electrodeionization system. The methods can
be used separately or in combination in a single or
multi-electrical staged system. The first method senses the
resistivity and temperature of the feed water and the appropriate
cell pair voltage is applied to demineralize the liquid to the
desired fraction salt removal.
The second method senses the product resistivity and temperature
that is used to control the voltage of the stage to produce water
of the desired quality. This type of voltage control can be used to
provide product water of a pre-selected quality.
An example of a two-stage system is as follows: The first stage is
operated at a valuable voltage based on the feed water quality
(about 0.5 to 5.0 volts per cell pair) appropriate to achieve
approximately 70-90 percent salt removal by using a predetermined
resistivity/temperature/percent salt removal relationship. The
automatically applied voltage permits operation below the
polarization point, thus assuring efficient operation without
scaling. The second stage is operated at a variable voltage based
on the product water quality (about 0.5 to 5.0 volts per cell
pair), appropriate to provide water of a pre-selected quality.
Since the feed water to the second stage is product water from the
first, the second stage feed is less prone to scaling. For this
reason polarization in the second stage is acceptable, and the
voltage can therefore be varied to any degree to provide the
required product quality.
In another aspect of this invention, the electrodeionization step
can be operated under conditions of serpentine flow between an
anode and a cathode. In accordance with one aspect of this
invention, the depletion compartments are arranged and are provided
with inlet and outlet means so that water to be purified is passed
through at least two depletion compartments between a given set of
an anode and a cathode in each stage. Improved ion removal
efficiency is attained with the multiple pass process of this
embodiment of the invention as compared to a process wherein water
to be purified is passed through one depletion compartment in each
stage having a length equal to the combined lengths of the multi
depletion compartments in each stage. The depletion compartments
also are formed so that the ion exchange resin mixture is housed
within independent discrete subcompartments each of which has a
width of about 0.3 to 4 inches, preferably between about 0.5 and
about 1.5 inches. The discrete subcompartments also are formed by
securing, such as by bonding both the anion permeable membrane and
the cation permeable membrane to the periphery of the depletion
compartment and to ribs which extend across the thickness of and
along the entire length of the depletion compartment so that each
subcompartment is defined by a pair of ribs, the anion permeable
exchange membrane and the cation permeable membrane.
In this embodiment electrodeionization apparatus can comprise one
or a plurality of stages. In each stage, an anode is positioned at
an opposite end of a stack of depleting and concentrating
compartments from an end at which a cathode is positioned. Each
anode and cathode is provided with an adjacent electrode spacer and
an ion permeable membrane wherein an electrolyte passes through the
electrode spacer. The remaining portion of each stage comprises a
series of alternating depletion and concentrating compartments
constructed as set forth herein. The liquid to be depleted of ions
can be passed in parallel through each depletion compartment in
each stage in order to effect removal of ions from the first liquid
in the depletion compartments into the second liquid in the
concentration compartments. In any event, the liquid to be purified
in this embodiment is passed through at least two depletion
compartments in each stage. The direction of flow within the
depletion compartments is not critical and can be in the same
direction or in an opposite direction to the flow in an adjacent
compartment or concentration compartment. When a plurality of
stages are utilized, the liquid removed from the depleting
compartments in an upstream stage can be directed in series into
the depleting compartments in the next adjacent downstream stage.
Alternatively, feed water can be directed in a counter flow
arrangement in depleting compartments comprising a second stage.
Electrolyte can be passed through the spacer adjacent each
electrode in the electrodeionization apparatus and is removed from
the electrodeionization apparatus. It is preferred that the
subcompartment in the depleting compartments have a controlled
thickness and width as stated above in order to sustain high
efficiency for ion depletion over long periods.
As shown in FIG. 2, water to be purified 70 enters depletion
compartments 72 and 74 which contains substantially uniform size
resin beads. Concentration water feed stream 68 enters
concentration compartments 76, 78 and 80. The concentration water
passes from concentration compartments 76, 78, and 80 into anode
compartment 82 and thence to cathode compartment 84 and to drain
86. The water to be purified passes from depletion compartments 72
and 74 through depletion compartments 88 and 90 and then is
recovered from stream 92.
In another aspect of this invention, the electrodeionization steps
described above can be operated under conditions of voltage
polarity reversal during water purification. During operation, the
polarity of voltage applied to the electrodes in the
electrodeionization apparatus is reversed in order to dissolve and
desorb organics at the cathode, to oxidize deposits and dissolve
any scale at the anode, to dissolve any scale from prior cycles in
the newly formed depletion compartments and to desorb any adsorbed
foulants that may be deposited during use of the apparatus in the
newly formed concentration compartments. As a result of voltage
polarity reversal, the compartments which were initially ion
depleting compartments become ion concentrating compartments. There
is no need to direct product liquid to waste as a consequence of
voltage polarity reversal since there is an unexpected rapid ion
migration and ion depletion within the newly formed ion depletion
compartments combined with a time delay in the increase of
concentration in the newly formed concentration compartments such
that the product liquid never attains an unacceptably high
concentration of ions. Also, the time between reversal cycles can
be extended due to an unexpected time delay of any pH shifts in the
concentrating and cathode streams thereby decreasing the scaling
potential in the device.
As set forth herein, the term "dual compartment" means a
compartment formed of an odd number of permeable membranes, at
least one depletion compartment and at least one concentration
compartment, each of which compartments are divided into
subcompartments, as described above. The ion permeable membranes
are arranged so that the anion permeable membrane and the cation
permeable membrane alternate along the thickness of the dual
compartment. Thus, the dual compartment can include one more cation
permeable membrane than anion permeable membrane or can include one
more anion permeable membrane than cation permeable membrane of the
odd number ion permeable membranes. It has been found in accordance
with this invention that the dual compartment structure permits
reversing voltage polarity in a manner which does not require
directing a portion of the liquid product to waste due to the
presence of the solid ion exchange material positioned within the
subcompartments by the ribs and by the ion permeable membranes.
The electrodeionization apparatus can comprise one of a plurality
of stages. In each stage, the anode is positioned at an opposite
end of a stack of depleting and concentrating compartments from an
end at which the cathode is positioned. Each anode and cathode is
provided with an adjacent electrode spacer and an ion permeable
membrane wherein an electrolyte passes through the electrode
spacer. The remaining portion of each stage comprises a series of
alternating depletion and concentration compartments constructed as
set forth herein. The liquid to be depleted of ions can be passed
in parallel through each depletion compartment in each stage and a
second liquid can be passed through each concentration compartment
in parallel in each stage in order to effect removal of ions from
the first liquid in the depletion compartment into the second
liquid into the concentration compartment. When a plurality of
stages are utilized, the liquid removed from the depletion
compartments in an upstream stage can be directed in series into
the depletion compartments of the next adjacent downstream stage.
Similarly, the liquid removed from the concentration compartments
of an upstream stage can be directed in series to the concentration
compartments in the next adjacent downstream stage. Electrolyte can
be obtained from the feed, product, neutral, or concentrate streams
or from an independent source and passed through the spacer
adjacent to each electrode in the electrodeionization apparatus and
is removed from the electrodeionization apparatus. Optionally,
electrolyte from the spacer adjacent the electrode can be passed
through one or more neutral zones prior to being directed to waste.
Scale and organics build up within the electrodeionization
apparatus, particularly at the electrodes, is prevented by
periodically reversing the voltage polarity such that the original
anode becomes a cathode and the original cathode becomes the anode.
When voltage polarity is reversed, the original depletion
compartments become concentration compartments and concentration
compartments become depletion compartments. At the electrodes any
accumulated scale is cleaned during the anodic cycle and any
accumulated organics are dissolved during the cathodic cycle and
are removed. Also any accumulated scale in the concentrating
compartments is dissolved during the initial period of the diluting
cycle and is rinsed to drain. In addition, any organic foulants
accumulated during the diluting cycle are desorbed from the resin
and membranes during the concentrating cycle by the action of
increased salinity and pH and removed in the waste stream so that
their presence does not adversely affect the quality of the water
or function of the equipment.
During voltage polarity reversal, it would be expected that a
portion of the liquid recovered from the compartments would need be
discarded since ion removal would not be sufficiently rapid during
the polarity reversal. However, surprisingly, the ion removal from
the newly formed depletion compartments is sufficiently rapid and
during the initial period after reversal there is a delay time
between polarity removal and deterioration of water quality in the
newly formed concentration stream so that the liquid product need
not be discarded at any time during or between any cycle. In other
words, the conductivity of the liquid product from either or both
of the newly formed depletion or concentration compartments are
sufficiently low as to render the liquid product acceptable in one
stream or the other stream or both. This result is very desirable
since it eliminates the need for valving and conduit means for
directing a portion of the liquid product from the newly formed
depletion compartment to waste followed by a reversal of the system
flow to effect recovery of the liquid product from the newly formed
depletion compartments. Also since polarity reversal in accordance
with this invention permits continuous recovery of high quality
product, the prior art need for a holding tank system with
associated pumping capacity is desirably eliminated.
In addition, it would be expected that the time between polarity
reversal would be short, to prevent the immediate localized
formation of scale on surfaces such as the cathode and anion
membranes. However, localized scaling is minimized by the pH
buffering action of the ion-exchangers in the concentrating and/or
electrode streams. Therefore the time between polarity reversal can
be extended resulting in purer product on the average. It is
essential that the subcompartments in the depletion and
concentration compartments have a controlled thickness and width in
order to sustain high efficiency of ion depletion over long periods
as set forth above.
Furthermore, as shown in the example below, the flush out time
needed to initiate the water purification process of this invention
is unexpectedly short when utilizing ion exchange resin beads of
substantially uniform size.
Referring to FIG. 3, liquid to be purified enters inlet 10 and
passes through depletion compartments 12, through depletion
compartments 14 and then is recovered from outlet 16. Concentrating
liquid is passed through inlet 18, through concentration
compartments 20 and 22 thence through outlet 24 to drain. Liquid
electrolyte is circulated through electrode compartments 26, 28, 30
and 32 from inlets 34 and is discarded to drain through outlets 36.
When operated in the mode shown in FIG. 1, electrode compartments
26 and 30 comprise cathodes and electrode compartments 28 and 32
comprise anodes.
Referring to FIG. 4, the polarity of the electrodes is reversed
such that electrodes 26 and 30 comprise anodes and electrodes 28
and 32 comprise cathodes where a liquid electrolyte is circulated
therethrough from inlets 34 and is discarded to drain through
outlets 36. Because of the polarity reversal, the depletion
compartments 12 of FIG. 3 now become concentration compartments 13
and the depletion compartments 14 of FIG. 3 become concentration
compartments 15. Similarly, the concentration compartments 20 and
22 of FIG. 3 become concentration compartments 15. Similarily, the
concentration compartments 20 and 22 of FIG. 3 become depletion
compartments 21 and 23. Therefore, the product outlets 16 of FIG. 3
becomes a waste stream 17 while the waste stream 24 of FIG. 4
becomes a product stream 25.
Referring to FIG. 5, an arrangement of dual compartments is shown
each of which includes two cation permeable membranes 69 and 71 and
anion permeable membrane 73 separated by and bonded to spacers 75
and 77 as set forth above. When the polarity of electrode 79 is
negative the compartments including spacer 75 is an ion depleting
compartment while the compartment including spacer 77 is an ion
concentration compartment When the polarity of electrode 79 is
positive and the polarity of electrode 81 is negative, the
compartments including spacer 75 become ion concentration
compartments and the compartments including spacer 77 comprise ion
depletion compartments. The liquid for the depletion and
concentration compartments passing through 75 and 77 can be passed
in series as shown in FIG. 5 or in parallel as shown in FIG. 6
therethrough or combination of series and parallel flow. An
optional construction is shown in FIG. 5 wherein the dual
compartment structures are separated by neutral zones 83 which
include screens 85. The neutral zones 83 merely function to prevent
contact between membranes of adjacent dual compartments. The liquid
for the neutral zones 83 can be passed in series or in parallel
therethrough and can be fed by the feed stream, electrode streams,
depletion or concentration streams as desired and can be directed
to waste or fed to the anode or cathode compartments as desired
prior to exiting the apparatus.
The following examples illustrate the present invention and are not
intended to limit the same.
EXAMPLE 1
A series of electrodeionization units comprised of 4 depletion
cells and 4 alternating concentration cells, each 30 cm long and
having three subcompartments 0.23 cm thick and 3.3 cm width are
positioned between a cathode and an anode. The depletion
subcompartments were filled either with conventional Dow MR-3 beads
or a mixture of Dowex Monosphere cation and anion beads, both 550
micrometers in diameter.
Both units were tested under the following conditions: challenge
solution: Nacl; feed conductivity: 100 us/cm; Product flow rate:
190-200 ml/min; Voltage: 12-13.5 V.
______________________________________ Product Quality Conventional
Monosphere Ratio ______________________________________ Time to 2
Megaohm-cm 36 1.6 22 reach 4 Megaohm-cm 96 2.8 34 (min)
______________________________________
The table demonstrates that the flushout time with the monospheres
was 22 times faster to reach 2 Megohm and 34 times faster to reach
4 Megohm compared with conventional resin.
EXAMPLE II
Two electrodeionization modules having the following geometry: Two
series stages with 10 depleting cells per stage and 10
concentrating screen type spacers per stage; both stages positioned
between one anode and one cathode; each depleting cell having a
flow path length of 13 inches and having three subcompartments
0.090 inches thick and 1.3 inches wide. The depletion compartments
were filled with Dowex monosphere resin beads (both 550 micrometers
in diameter) at a volume ratio of 70/30 anion to cation. The feed
water to the modules was tap water adjusted to 120 microsiemens/cm
with the addition of sodium chloride. Both modules produced water
in the megohm quality range within 1 to 3 minutes after start up.
The fast flushout was unexpected since these stacks with 20 cell
pairs contain a large quantity of resin. The response was 20-50
times faster than that observed with similar units containing
standard resin mixtures such as Dowex MR-3 beads.
EXAMPLE III
Two electrodeionization modules, 5 GPM and 10 GPM capacity having
the following geometry: Each having a single stage with 30 and 60
depleting cells with respectively 31 and 61 concentrating screen
type spacers, each depleting cell having a 26 inch flowpath length,
and having ten subcompartments 0.090 inch thick and 1.1 inches
wide. The depletion compartments were filled with Dowex monosphere
beads (550A and XUS40369, both 550 micrometers in diameter) at a
volume ratio of 70/30 anion to cation. The feed water to both
modules had a conductivity of 80 microsiemens/cm.
EXAMPLE IV
An electrodeionization module having the following geometry: Four
stages in series positioned between one anode and one cathode, each
stage consisting of one depleting cell, each depleting cell having
a flowpath length of 13 inches with three subcompartments of 0.090
inches thick and 1.3 inches wide. The depleting cells in the module
were filled with standard Dowex monosphere resins having bead
diameter size of 550 micrometers for the anion and 650 micrometers
for the cation. The resin ratio in the depleting cells was 70/30 by
volume anion to cation. The module contained three concentrating
screen-type cells. The feed water to the module was 550
microsiemens/cm of equal parts of sodium chloride and sodium
bicarbonate. The required time to megohm quality was eight minutes
which although longer than other modules containing both anion and
cation beads of 550 micrometers in diameter, was still
substantially shorter than the approximately one hour required for
similar modules using standard Dowex MR-3.
EXAMPLE V
The performance of two electrodeionization units were compared,
each comprised of 8 cells, each cell 30 cm long, and with each cell
containing 3 subcompartments each 3.3 cm wide and 0.23 cm thick.
Each unit contained two electrodes. All compartments were filled
with a mixture of cation and anion exchange resins: one unit with
conventional Dow MR-3 and the other unit with Dowex Monospheres,
550 micrometers in diameter. In each unit, four alternate
compartments were used as depletion compartments and the other four
as concentration compartments. Every 40 minutes the polarity of the
electrodes to the two units was reversed. Accordingly, the
depletion and the concentration compartments reversed function.
Both units had 4 series stages, and were tested under the following
conditions:
Feed solution: NaCl; feed conductivity: 60 microsiemens/cm; product
flow: 200 ml/min; voltage applied: 16 volts. The response time for
each unit, i.e., the improvement in product resistivity as a
function of time, over the 40 minute period between polarity
reversals was monitored.
The initial slope for the unit built with the conventional resin
was 0.024 normalized resistivity units/min, compared with 0.103
normalized resistivity units/min for the unit built with the Dow
monosphere resin. The ratio between the slopes of the two units was
4.3:1 in favor of the unit built with the Dow monosphere resin.
* * * * *