Method of making and using nanoscale metal

Details Method of making and using nanoscale metal Method of making and using nanoscale metal

2001-12-19

2004-08-17

Metzmaier, Daniel S. (Department: 1712)

Colloid systems and wetting agents; subcombinations thereof; pro

Continuous liquid or supercritical phase: colloid systems;...

Primarily organic continuous liquid phase

C516S033000, C241S016000, C241S021000, C502S151000, C502S159000, C502S172000

Reexamination Certificate

active

06777449

ABSTRACT:

BACKGROUND AND SUMMARY OF THE INVENTION
Since the mid-1990's, there have been a series of dramatic developments for the in-situ treatment of chlorinated solvents. The approach of the present invention is based on the sequential reduction of chlorinated hydrocarbons to innocuous end products such as methane, ethane or ethene. In principal the process has been recognized in scientific circles but, it is just beginning to be investigated for environmental application. The process exploits the use of zero valence state elemental metals to reductively dehalogenate halogenated hydrocarbons. In addition, elemental metals may be used to reduce soluble metals such as chromate to insoluble species (Cr (III)) or metalloids such as arsenic or selenium.
The most common metal being utilized for this purpose is iron. But other metals including tin, zinc, and palladium have also shown to be effective. The process may be best described as anaerobic corrosion of the metal by the chlorinated hydrocarbon. During this process, the hydrocarbon is adsorbed directly to the metal surface where the dehalogenation reactions occur. Increasing surface area (by reducing the size of iron particles) increases the effectiveness of the process.
The variations of the process are complex. Recent research on iron systems indicates three mechanisms at work in the reductive process.
Metallic iron may act as a reductant by supplying electrons directly from the metal surface to the adsorbed halogenated compound.
Metallic iron may act as a catalyst for the reaction of hydrogen with the halogenated hydrocarbon. The hydrogen is produced on the surface of the iron metal as the result of corrosion with water.
Also ferrous iron solubilized from the iron metal due the above reactions may act as a reductant for the dehalogenation of halogenated hydrocarbons.
The rate of the reaction of the metallic iron with halogenated hydrocarbons has been demonstrated to be partially dependent upon the surface area of the metallic iron. As the size of the metallic iron is reduced, surface area goes up as well as chemical reactivity. Initial applications of this technology used iron filings. More recent applications have used iron colloids in the micron size range. The applications of the metallic iron reduction of the present invention incorporate nanoscale colloids. These are colloids that range in size from 1 to 999 nanometers. A colloid of this size may have several advantages in application for in-situ groundwater treatment or for use in above ground treatment reactors. These advantages include:
High surface area with greater reaction kinetics as a result. The increase in kinetics allows for a lower mass loading of iron in the treatment zone or reactor because the residence time required for complete dehalogenation is decreased.
The small size and greater reactivity of the colloid allows for the application of the technology through direct in-situ injection into the subsurface.
The smaller size allows for advective colloidal transport.
The greater reactivity, due to the small size, allows for much lower overall iron mass requirements.
To further enhance the physical and chemical character of the colloid, a metallic catalyst may be used to create a bimetallic colloid. The catalyst further increases the rates of reactions, which further lowers the amount of iron colloid that must be used to create an effective reductive dehalogenation treatment zone in the subsurface or a surface reactor. Metals that may be used as a catalyst with the iron include palladium, platinum, nickel, zinc, and tin.
Production of Nano-Scale Iron Colloids
Introduction
A key limitation on the development of the technology of the present invention is the lack of availability of nanoscale metallic colloids. Research, driven primarily by the materials science needs (hi-tech electronic chips or component industry products), has, over the last decade, contributed to general technologies designed to produce nanoscale colloids. Although, generally the research has been in the area of colloids that are composed of ceramic or other non-metallic inorganic materials and not metal colloids. A significant part of the development effort for the technology of the present invention was the adaptation of the non-metallic nanoscale colloid production methods to the production of metallic nanoscale colloids of the present invention.
The method for the production of metal colloids in the nanoscale range may be divided into two primary approaches:
“Bottom Up” in which colloids of the appropriate size are produced by being assembled from individual atoms.
“Top Down” in which colloids of the appropriate size are produced by attrition of larger existing particles of the metal.
The “Bottom Up” approach has a greater number of potentially applicable methods, including:
Chemical reduction using sodium borohydride; various soluble metal salts (such as ferrous or ferric chloride for iron) in suspensions of water or various hydrocarbon solvents. This process may or may not be enhanced with sonofication during reaction processes.
Other chemical precipitation reactions in aqueous or hydrocarbon solutions capable of producing metals from soluble salts that may or may not include sonofication during reaction processes.
Various methods of metal volatilization and subsequent deposition, typically under vacuum. These include:
Gas Evaporation
Active Hydrogen-Molten Metal Reactions
Sputtering
Vacuum Evaporation to Running Oil Surface
Evaporation Using Direct Electrical Current Heating
Hybrid Plasmas
The “Top Down” approach uses two primary variations of milling or mechanical comminuation, this includes:
Using mechanical agitation of a mixture of the desired colloidal metal, a grinding media, and an organic or aqueous suspension fluid. Examples include ball mills and rod mills.
Systems similar to the above where the mechanical agitation is provided by high-speed gas jets.
Upon searching for a supply of nanoscale colloids the inventors of the present invention found that the only method of production capable of producing nanoscale colloids in large kilogram amounts was the sodium borohydride reduction method. However, this was expensive (up to $5,000 per kilogram) and not practical for full-scale application of the technology.
After an evaluation of other production methods the following determinations were made:
Metal volatilization was also expensive, the reactors available for the production of colloids were limited to kilogram capacities, and the colloids produced are at the lower end of the nanoscale range (typically less than 10 nanometers). With time and further development these technologies may also be applied to the production of nanoscale iron colloids for environmental use.
“Top Down” mechanical attrition had the potential of:
Generating colloids of the proper size
Colloid production at a reasonable cost ($100 a kilogram or less)
Production capacity in the 100 to 1000 kilogram range.
However, at the time of the evaluation there was no existing capacity (of any size) for the production of iron colloids using mechanical attrition. All work in the field was being performed on ceramics or other non-metallic inorganic materials. The inventors of the present invention sought a provider of nanoscale ceramic production and generated the specifications and requirements for the production of nanoscale iron colloids.
Production of Nanoscale Colloids by Mechanical Attrition
Nanoscale colloids have been produced in amounts up to 10 kilograms, with scale-up production volumes readily and cost effectively available. The process developed to date includes the following components:
Feed material consisting of approximately <325 mesh sized iron particles.
Organic suspension solvent fluids that:
Have high flash points to prevent explosions; and
Are not reactive to the surface of the iron colloid
Examples may include dodecane, butyl acetate, and polypropylene glycol ethyl ether acetate
Dispersants to act as surface acting agents to prevent the agglomeration of the colloids during the milling process wer

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