Ion exchange and electrochemical methods and devices...

Details Ion exchange and electrochemical methods and devices... Ion exchange and electrochemical methods and devices...

1999-07-28

2002-06-25

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S290000, C526S293000, C526S303100, C526S307200, C526S307800, C526S310000, C526S318100, C526S326000, C526S346000, C521S025000, C521S038000

Reexamination Certificate

active

06410672

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of ion exchange and electrochemical methods and devices, and, in particular, to such methods and devices employing anion selective polymers produced by substantially simultaneous quaternization and polymerization reactions.
BACKGROUND OF THE INVENTION
Ion exchange (“IX”) and electrochemical methods and devices using ion exchange structures were initially developed more than 50 years ago, and have since that time been improved to the point that such systems are commonly employed to purify fluids for a variety of applications. Typically, IX and electrochemical membrane methods and devices such as electrodialysis (“ED”) and reversing type electrodialysis (“EDR”) purify fluid through ion exchange or electric field-mediated transfer of ions through membranes from diluting or permeate streams passing through “less concentrated” compartments to concentrating or brine streams passing through “more concentrated” compartments. Generally, anion transfer and cation transfer membranes are alternated in ED methods and devices, the membranes being placed between an anode (positive electrode) and a cathode (negative electrode) across which a DC electric field is applied transverse to the fluid flow directions. Anion transfer membranes allow passage only of low molecular weight negatively charged species (anions), and cation transfer membranes allow passage only of low molecular weight positively charged species (cations). Transfer of ions across membranes is mediated by the attraction of anions to the anode and cations to the cathode. The combination of an anode, a cathode, and alternating anion and cation transfer membranes therebetween is commonly referred to as an ED “stack” or pack.
FIG. 1
depicts a schematic view of an exemplary ED unit
10
having a cathode
12
and an anode
14
and cation transfer membranes
20
alternating with anion transfer membranes
22
. Cation transfer membranes
20
and anion transfer membranes
22
form a plurality of alternating ED diluting compartments
24
and ED concentrating or brine compartments
26
. A fluid, for example water, enters the ED unit
10
at electrode stream inlets
52
and exits ED unit
10
at electrode stream outlets
54
to form electrode streams
50
. The electrode streams
50
that comes into contact with cathode
12
or with anode
14
do not mix with, and are not in fluid communication with, fluid in ED feed stream
30
or with fluid in ED brine stream
40
(see below).
Fluid to be purified flows into ED unit
10
in the form of ED feed stream
30
which enters the unit at ED feed stream inlet
32
. ED feed stream inlet
32
is in fluid communication with ED feed stream inlet manifold
34
, through which fluid to be purified is delivered to one or more ED diluting (less concentrated) compartments
24
. The number of diluting compartments
24
in an ED unit can vary according to the application in which the ED unit is used. Determinations of the appropriate number of diluting compartments for a particular application can be accomplished empirically, on the basis of the desired capacity of the fluid purification system and the amount and identity of contaminants in the feed stream. As defined herein, diluting compartment
24
of ED unit
10
involves the sum of all diluting compartments contained within the unit. After traversing the diluting compartment
24
, fluid from ED feed stream
30
enters ED product stream outlet manifold
36
, exiting the ED unit as less concentrated product stream
30
a
at ED product stream outlet
38
. Fluid is purified in the ED diluting compartments
24
by virtue of passage of ions out of the ED diluting compartments
24
into the more concentrated ED concentrating or brine compartments
26
.
In parallel to the flow of ED feed stream
30
, an ED concentrate or brine influent
40
flows into unit
10
at ED concentrate or brine stream inlet
42
. ED concentrate or brine stream inlet
42
is in fluid communication with ED concentrate or brine stream inlet manifold
44
, through which fluid that receives ions from the ED diluting compartments
24
is delivered to one or more ED concentrating or brine compartments
26
. The number of concentrating or brine compartments in an ED unit may vary according to the application in which the ED unit is used, but will be equal to (or±1) the number of diluting compartments in the unit. In accordance with the invention, concentrating or brine compartment
26
of ED unit
10
comprises the sum of all concentrating or brine compartments contained within the unit. After traversing the ED concentrating compartment
26
, fluid from ED concentrate or brine influent
40
enters ED concentrate or brine stream outlet manifold
46
, exiting the ED unit at ED concentrate or brine stream outlet
48
. After exiting from ED concentrate or brine stream outlet
48
, all or at least a portion of the brine stream is discarded as “blowdown”, and the remainder, if any, of the effluent brine stream is recycled into concentrate or brine influent
40
, upstream of brine stream inlet
42
.
Anion selective polymers for use in anion exchange resins or transfer membranes involved in the electrochemical devices and processes described above may be manufactured via a variety of techniques. For example, anion selective polymers may be prepared by co-polymerizing methacrylate esters containing amine groups of the tertiary type, with cross-linking methacrylate esters (see for example U.S. Pat. No. 4,231,855 by Hodgdon et al.). The resulting polymer with pendant tertiary amine groups may be quaternized with an alkyl halide, such as methyl chloride, so that the tertiary amine groups are converted to quaternary ammonium salts.
The above-described technique may require washing steps between process steps and requires chemical reactions on polymerized sheets. Further, exchange resins and transfer membranes formed of methacrylate esters may degrade rapidly in the presence of caustic solutions. In addition, exchange resins and transfer membranes formed by the above-identified technique may lack resiliency and further, the membranes may leak, because the post-polymerization quaternization reactions may weaken the resin.
Anion selective polymers for use in anion exchange resin particulates or transfer membranes employed in electrochemical devices and methods may also be prepared by solubilizing a cross-linking monomer such as methylene bisacrylamide (MBA), by pre-treatment with a caustic solution. The solubilized MBA may then be combined with an acrylic monomer, such as dimethylaminopropylmethacrylamide, in a water soluble solvent and polymerized. See U.S. Pat. Nos. 5,037,858 and 5,354,903 to MacDonald. As in the previously identified technique, the resulting polymer may have to be further reacted so that its pendant tertiary amine group is converted to a quaternary ammonium salt to form the anion selective polymer. Alternatively, these patents teach combining the solubilized MBA with an ionogenous acrylic monomer which has already undergone quaternization, such as methacrylamido-propyltrimethylammonium chloride, in a water soluble solvent and polymerizing the liquid mixture.
Accordingly, the above-identified technique requires a caustic solution pretreatment step for solubilizing the cross-linking monomer. Further, as in the previously described technique, post-polymerization quaternization may weaken the exchange resins and transfer membranes made from such polymers. The alternative process involving use of an ionogenous acrylic monomer requires a special solvent to prevent the quaternary ammonium salt from precipitating out of the liquid solution before the polymerization occurs.
Thus, there is a need to develop caustic stable anion exchange resins and transfer membranes with resilient surfaces and substantially leak-free transfer membranes for use in ion exchange and electrochemical methods and devices. Further, there is a need to develop simplified methods of forming such exchange resins and transfer membranes which avoid precipi

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