Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
1998-12-17
2001-04-17
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S747300, C210S908000, C588S253000
Reexamination Certificate
active
06217779
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method for the dehalogenation of halogenated aliphatic and alicyclic hydrocarbons in aqueous compositions. In one aspect, this invention relates to a method utilizing a mixed metal composition to dehalogenate halogenated aliphatic and alicyclic hydrocarbons in an aqueous composition. In another aspect, this invention relates to a method of contacting a mixed metal composition prepared by contacting a metal or a soluble metal salt with an anchor metal to deposit the metal on an anchor metal with a halogenated aliphatic and alicyclic hydrocarbon contaminated aqueous composition to dehalogenate the halogenated aliphatic and alicyclic hydrocarbon. In a further aspect, this invention is utilized in situ to dehalogenate halogenated aliphatic and alicyclic hydrocarbons in groundwater.
Halogenated aliphatic and alicyclic hydrocarbons, particularly chlorinated aliphatic and alicyclic hydrocarbons such as carbon tetrachloride, chloroform, trichloroethylene and tetrachloroethylene, have been widely used as chemical intermediates, solvents for dry cleaning of clothing, degreasing, and a variety of other applications. Halogenated aliphatic and alicyclic hydrocarbons are very stable and persistent in the environment, and are relatively toxic at low levels.
Over the years, halogenated aliphatic and alicyclic hydrocarbons have been accumulating in the environment, particularly in groundwater. As a result, pollution of water by chlorinated hydrocarbons has become an important environmental problem and contaminated groundwater represent a large portion of environmental action plans throughout the world.
It is known that chlorinated compounds can be degraded by reductive dechlorination, i.e. replacement of chlorine substituents by hydrogen. Evidence indicates that many of the chlorinated solvents are degraded under anaerobic conditions in sediments and in systems simulating anaerobic wastewater treatment. Current theory suggests that some of these anaerobic dechlorinations are not strictly biological in nature, but are catalyzed by metallic iron. While the use of iron in the dechlorination affords little environmental threat, its use suffers from certain problems.
Recently, Gillham and O'Hannesin disclosed in U.S. Pat. No. 5,266,213, a method for cleaning halogenated contaminants from groundwater. The process involves feeding contaminated groundwater through a trench containing a metal such as iron, under strict exclusion of oxygen, and over a lengthy period of time. Disadvantages of this system include the fact that large amounts of iron and substantial periods of time are needed for completion of the reactions.
In U.S. Pat. Nos. 4,219,419 and 4,382,865 (Sweeny), there is disclosed a system for treating the effluent created during the production of halogenated pesticides. In that process, the effluent water stream containing the halogenated waste material is required to be buffered to near neutral pH prior to passing the waste stream over a metal couple.
There is a need for an enhanced method for dehalogenating aliphatic and alicyclic hydrocarbons in contaminated aqueous solutions so as to diminish the amount of metallic iron needed to complete the dehalogenation. There is also a need for a dehalogenation method where the rate of dehalogenation is increased and innocuous reaction products are generated. It has now been found that a mixed metal composition prepared by contacting a metal or a soluble metal salt with an anchor metal to deposit the metal on an anchor metal while controlling the portion of the surface area of the anchor metal which has a second metal deposited thereon solves the above-described problems.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved method for dehalogenating halogenated aliphatic and alicyclic hydrocarbons in aqueous compositions. It is a further object of the invention to provide a method for detoxifying groundwater contaminated with halogenated aliphatic and alicyclic hydrocarbons, particularly chlorinated aliphatic and alicyclic hydrocarbons. It is yet a further object of the invention to provide a method for dehalogenating halogenated aliphatic and alicyclic hydrocarbons in groundwater which can be used in situ, particularly in conjunction with in situ soil and groundwater remediation processes.
According to the invention, a method for dehalogenation of aqueous compositions contaminated with halogenated aliphatic and alicyclic hydrocarbons is provided which comprises contacting the aqueous composition with an amount of a mixed metal composition effective to dehalogenate the halogenated aliphatic and alicyclic hydrocarbons at a temperature of at least 10° C., wherein the mixed metal composition comprises a second metal deposited on an anchor metal consisting essentially of iron metal and wherein the amount of second metal in the mixed metal composition is an amount effective to increase the dehalogenation rate compared to use of iron alone, and the surface of the mixed metal composition has exposed iron metal.
In one embodiment, the mixed metal composition is prepared by contacting an anchor metal consisting essentially of iron metal with a soluble metal salt in the presence of a liquid comprising water for a time sufficient to deposit metal derived from the soluble metal salt on the anchor metal wherein the metal in the soluble salt is copper, nickel, molybdenum, tin, lead, silver, chromium, palladium, platinum or gold. In another embodiment, the mixed metal composition is prepared by contacting an anchor metal consisting essentially of iron metal with a second metal selected from the group consisting of copper and nickel in the presence of a liquid comprising water for a time sufficient to deposit the second metal on the anchor metal. In a further embodiment, the mixed metal composition is prepared by contacting an anchor metal consisting essentially of iron metal with a nonaqueous electroless plating solution comprising a soluble metal halide salt complex and a suitable solvent for a time sufficient to deposit metal derived from the soluble metal salt on the anchor metal wherein the metal in the soluble salt is cobalt, copper, nickel, bismuth or lead, and recovering the mixed metal composition.
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of the invention relates to a method for dehalogenation of aqueous compositions contaminated with halogenated aliphatic and alicyclic hydrocarbons comprising contacting an aqueous composition with an amount of a mixed metal composition effective to dehalogenate the halogenated aliphatic and alicyclic hydrocarbons at a temperature of at least 10° C., wherein the mixed metal composition comprises a second metal selected from the group consisting of copper, cobalt, nickel, molybdenum, bismuth, tin, lead, silver, chromium, palladium, platinum and gold deposited on an anchor metal consisting essentially of iron metal and wherein the amount of second metal in the mixed metal composition is an amount effective to increase the dehalogenation rate compared to use of iron alone, and the surface of the mixed metal composition has exposed iron metal.
A second embodiment of the invention relates to a method for dehalogenation of aqueous compositions contaminated with halogenated aliphatic and alicyclic hydrocarbons comprising: (a) contacting an anchor metal consisting essentially of iron metal with a soluble metal salt in the presence of a liquid comprising water for a time sufficient to deposit metal derived from the soluble metal salt on the anchor metal to produce a mixed metal composition wherein the amount of metal derived from the soluble metal salt in the mixed metal composition is an amount effective to increase the dehalogenation rate compared to use of iron alone, and the surface of the mixed metal composition has exposed iron metal, and wherein the metal in the soluble salt is copper, nickel, molybdenum, tin, lead, silver, chromium, palladium, platinum or gold, and (b) contacting the aqueous composition with an amount of
Ho Sa Van
McKenzie David E.
Orth Robert G.
Astaris LLC
Hruskoci Peter A.
Thompson & Coburn LLP
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