Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ion-exchange polymer or process of preparing
Reexamination Certificate
2003-01-03
2004-04-06
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ion-exchange polymer or process of preparing
Reexamination Certificate
active
06716888
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention provides unique heterogeneous ion-exchange membranes, methods and apparatus for producing such membranes, and ion-removing apparatus utilizing such membranes.
Purification of fluids such as water, beverages, chemicals and waste streams can be accomplished in a variety of different systems for a plurality of different end results. For ultrapure and drinking water purposes, purification may require the removal of substantial amounts of ions contained within brackish or salt water, may require the removal of turbidity and large particles, or may require the destruction of living organisms. Such purification may also require removal of substantial amounts of ions from reverse osmosis permeate and DI permeate.
For removal of ions, several basic systems have found commercial acceptance: ion-exchange, reverse osmosis, electrodialysis and electrodeionization.
In general, established methods for deionizing fluids include: distillation, ion exchange, electrodialysis, and reverse osmosis. Distillation separates water from contaminants by transferring water into vapor phase, leaving most contaminants behind. Ion-exchange removes ions from solutions by exchange of salts for hydrogen and hydroxide ions. Electrodialysis uses membranes that remove salts by ion transfer under the influence of a direct electrical current. Reverse osmosis uses membranes that are permeable to water but not to solutes, with water being purified as it is driven by pressure through the membranes. Electrodeionization (EDI) processes combine the use of ion-exchange resins and membranes to deionize water. EDI equipment is capable of efficient deionization of a wide range of feeds from bulk salt removal to polishing of reverse osmosis product water.
Typically, in electrodeionization, a number of flat sheets of alternating cation and anion exchange membranes are placed between two electrodes with mixed bed of ion-exchange resins alternately added between the membranes.
The compartments containing the resin beads are generally referred to as the dilute compartments. The adjacent compartments into which ions are transferred for disposal are referred to as the concentrate compartments. The concentrate compartments usually are much thinner than the dilute compartments, and serve to collect the concentrated ions being transferred from the dilute compartments. The concentrate compartment may or may not contain additional ion-exchange resin.
When fluid flow is fed through the system, and electrical potential (voltage) is applied, ions begin to migrate towards the electrodes; the anions to the anode and the cations to the cathode.
In the dilute compartments, ions are able to cross into the neighboring concentrate compartments only when they encounter the ‘right’ membrane; that is, when anions encounter anionic membranes and cations encounter cationic membranes.
In the concentrate compartment, ions continue their migration to the electrodes, but now they encounter the ‘opposite’ membranes; that is, anions encounter cationic membranes while cations encounter anionic membranes. These membranes block their motion, trapping them in the concentrate compartment where they are rinsed out.
The net result of the EDI process is that water is continuously deionized in the dilute compartments, with the unwanted ions exiting from the concentrate compartments.
U.S. Pat. No. 4,465,573 issued to Harry O'Hare for Method and Apparatus for Purification of Water describes such devices and the advent of electrodeionization that continues to gain commercial acceptance among various end users.
A critical element of such purification devices is the membrane that selectively allows diffusion and adsorption of ions while excluding certain other ions and non-ionized solutes and solvents. These membranes have commonly been referred to as ion-exchange membranes and are used in a wide variety of devices for fractionation, transport depletion and electroregeneration, purification for treatment of water, food, beverages, chemicals and waste streams. Such membranes are also used in electrochemical devices and electrophoresis as well as analytical equipment and for treatment applications.
Commercially available ion-exchange membranes are generally classified as two types: homogeneous membranes and heterogeneous membranes. A homogeneous membrane is one in which the entire volume of the membrane (excluding any support material that may be used to improve strength) is made from the reactive polymer. Heterogeneous membranes, on the other hand, are formed of a composite containing an ion-exchange resin to impart electrochemical properties and a binder to impart physical strength and integrity.
The ion-exchange resin particles serve as a path for ion transfer serving as an increased conductivity bridge between the membranes to promote ion movement. Under conditions of reduced liquid salinity, high voltage and low flow, the resins also convert to the H+ and OH− forms due to the splitting of water into its ions in a thin layer at the surface of the resin particles or membranes. This further improves the attainable quality of water. During electrodeionization, the ion concentration within the resin particles is maintained relatively constant and the migration of ions from the resin particles into the concentration compartments is substantially balanced by the migrations of the same, or similar ions from the water being purified into the resin particles.
Such membranes should be resistant to elevated temperatures, result in a low pressure loss, and result in low internal and external leaks. The low pressure loss reduces pumping requirements and also allows the membranes to be spaced more closely to each other, thereby reducing power consumption caused by the electrical resistance of the water streams. For selective ion electrodialysis, selective ion-exchange resins can be used as the resin component of the inventive membrane. For transport depletion electrodialysis, mixed anion and cation resins, or amphoteric resins can be used in place of the resin component of one of the anion or cation membranes. For transport of large, multivalent or slow diffusing ions, low cross-linked ion exchange resins can be used in the membrane.
Typically, the starting ion-exchange resin bead has the physical characteristic in appearance as a translucent, spherical bead with an effective size of from about 0.25 to about 0.75 mm. Chemical stability of ion-exchange resins is dependent among other factors on operating temperatures that generally should not exceed 285 degrees F. for cation exchange resin and 195 degrees F. for anion exchange resin. The resin beads are generally produced by a process incorporating cross-linked polystyrene with an active functional group such as sulfonic acid (cation) or quaternary ammonium functional groups (anion).
The foregoing membranes are useful in apparatus of reverse osmosis (RO), electrodialysis (ED) and electrodialysis reversal (EDR) processes. Such membranes are particularly useful for electrodeionization and electrodeionization reversal applications, where the reduction in leakage and pressure loss is important, along with the advantage of being able to readily bond the membranes within the device. Chemical resistance is particularly important because elements and ions such as hydrogen, hydroxide, hydronium ions, oxygen and chlorine may be produced in situ, in electrodeionization devices. Furthermore, the smoothness of the membrane simplifies automation of resin filling and removal of backwashing of the resin between membranes. Finally, the elimination of adhesives reduces the level of extractables, a significant advantage when electrodeionization apparatus is used in ultrapure water production.
A wide variety of such membranes are known to the art. In this respect, such membranes are described for instance, in U.S. Pat. Nos. 3,627,703; 4,167,551; 3,876,565; 4,294,933; 5,089,187; 5,346,924; 5,683,634; 5,746,916; 5,814,197; 5,833,896; and 5,395,570.
U.S. Pat. No. 5,346,924 to Giuffrida disc
Bernatowicz Joseph M.
O'Hare Ronald J.
Snow Michael J.
Electropure, Inc.
Frisenda Frank
Lipman Bernard
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