Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-02-25
2001-06-19
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S332200, C525S338000, C525S375000, C525S381000, C526S261000
Reexamination Certificate
active
06248842
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to metal chelation and more specifically to the selective and reversible removal or concentration of a target metal ion.
2. Description of the Background Art
Most commercial methods for removing undesirable metal ions are presently done using reverse osmosis (RO) and/or ion-exchange columns. However, RO is expensive, requires several precleaning stages (that is, it cannot be used in a cost-effective way to treat heavily contaminated waters), and is very susceptible to fouling. Ion-exchange columns can be used for many applications where selectivity and the exchange of one kind of ion for another are not critical factors, but could present problems in other situations. The materials for these columns also do not have a very high binding constant.
In order to get around the above issues, strong chelating agents, such as crown ethers or cyclic amines, can be used. Chelating agents have the advantage of being selective for transition metal ions over most group IA and IIA metal ions and of possessing very high binding (formation) constants, both of which are useful properties for selectively taking up metal ions in a mixed ion system.
These crown ethers or cyclic amines achieve their top formation constants and selectivity through the preorganization of their electron-donors into conformations that are optimal for particular metal ion sizes and coordination geometries. However, the high expense and general unavailability of these materials on a commercial scale preclude their common usage. On the other hand, acyclic chelating agents are common and very low cost compared to the macrocycles. Their disadvantages are their lower binding constants and selectivities in comparison to those of the macrocycles.
Ideally, acyclic chelating agents could be locked into an optimal geometry such that a target metal ion, and no other ion, could fit into that nanoscale receptacle. Current knowledge of the required conformations and thermodynamics needed for optimization is inadequate for designing sites having those optimal geometries. Additionally, the cost of such a “chelation by design” approach would be prohibitive and would eliminate the cost advantage possessed by acyclic chelating agents.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to selectively and reversibly bind metals to an acyclic chelating agent.
It is another object of the present invention to inexpensively optimize the selectivity and metal binding efficiency of an acyclic chelating agent.
It is a further object of the present invention to inexpensively provide a chelating agent in a conformation that selectively binds to only a single metal a narrow range of target metal ions.
These and additional objects of the invention are accomplished by substituting an acyclic chelating agent with at least one polymerizable functional group. The resulting functional group-substituted chelating agent monomer is then reacted with the target metal. During complexation, the acyclic chelating moiety forms chelation rings that are dependent on target metal-ion size and geometry and are thus optimized for the target metal. In this way, the functional group-substituted chelating agent is “templated” for the target metal. The complexed functional group-substituted chelating agent is then reacted with a crosslinking monomer to form a crosslinked polymer including the chelating moiety. The crosslinking step locks in the templating that occurs during complexation. The metal is then removed from the crosslinked polymer, for example, by acid washing.
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Singh, et al., “Incorporation of Nano-particle Sites in Polymer Matrix by Metal Ion Imprinting,”Mat. Res. Soc. Symp. Proc.,vol. 501, Materials Research Society, 1998.
Chang Eddie L.
Singh Alok
Karasek John J.
Ketner Philip E.
The United States of America as represented by the Secretary of
Wu David W.
Zalukaeva Tanya
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