Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating moving substrate
Reexamination Certificate
2000-05-16
2002-08-13
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating moving substrate
C205S144000, C205S149000
Reexamination Certificate
active
06432292
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to an apparatus and method for performing an electrochemical process on electrically conductive particles, and, in particular, to an electrolyzer and method for electrodeposition on electrically conducting particles.
2. Related Art
One of the more promising alternatives to conventional power sources in existence today is the metal/air fuel cell. These fuel cells have tremendous potential because they are efficient, environmentally safe and completely renewable. Metal/air fuel cells can be used for both stationary and motile applications, and are especially suitable for use in all types of electric vehicles.
Metal/air fuel cells and batteries produce electricity by electrochemically combining metal with oxygen from the air. Zinc, iron, lithium, and aluminum are some of the metals that can be used. Oxidants other than air, such as pure oxygen, bromine, or hydrogen peroxide can also be used. Zinc/air fuel cells and batteries produce electricity by the same electrochemical processes. But zinc/air fuel cells are not discarded like primary batteries. They are not slowly recharged like secondary batteries, nor are they rebuilt like “mechanically recharged” batteries. Instead, zinc/air fuel cells are conveniently refueled in minutes or seconds by adding additional zinc when necessary. Further, the zinc used to generate electricity is completely recoverable and reusable.
The zinc/air fuel cell is expected to displace lead-acid batteries where higher specific energies are required and/or rapid recharging is desired. Further, the zinc/air fuel cell is expected to displace internal combustion engines where zero emissions, quiet operation, and/or lower maintenance costs are important.
In one example embodiment, the zinc “fuel” is in the form of particles. Zinc is consumed and releases electrons to drive a load (the anodic part of the electrochemical process), and oxygen from ambient air accepts electrons from the load (the cathodic part). The overall chemical reaction produces zincate or its precipitate zinc oxide, a non-toxic white powder. When all or part of the zinc has been consumed and, hence, transformed into zincate or zinc oxide, the fuel cell can be refueled by removing the reaction product and adding fresh zinc particles and electrolyte.
The zincate or zinc oxide (ZnO) product is typically reprocessed into zinc particles and oxygen in a separate, stand-alone recycling unit using electrolysis. The whole processing a closed cycle for zinc and oxygen, which can be recycled indefinitely.
In general, a zinc/air fuel cell system comprises two principal components: the fuel cell itself and a zinc recovery apparatus. The recovery apparatus is generally stationary and serves to supply the fuel cell with zinc particles, remove the zinc oxide, and convert it back into zinc metal fuel particles. A metal recovery apparatus may also be used to recover zinc, copper, or other metals from solution for any other purpose. In particular, a metal recovery apparatus may be used to economically recover metals from scrap or from processed ore.
The benefits of zinc/air fuel cell technology over rechargeable batteries such as lead-acid batteries are numerous. These benefits include very high specific energies, high energy densities, and the de-coupling of energy and power densities. Further, these systems provide rapid on-site refueling that requires only a standard electrical supply at the recovery apparatus. Still further, these systems provide longer life potentials, and the availability of a reliable and accurate measure of remaining energy at all times.
The benefits over internal combustion engines include zero emissions, quiet operation, lower maintenance costs, and higher specific energies. When replacing lead-acid batteries, zinc/air fuel cells can be used to extend the range of a vehicle or reduce the weight for increased payload capability and/or enhanced performance. The zinc/air fuel cell gives vehicle designers additional flexibility to distribute weight for optimizing vehicle dynamics.
The benefits of using an electrolyzer with a moving particulate bed for metal recovery from processed ore or scrap include the following: 1) The energy consumption per unit of metal produced can be far lower than with traditional techniques; 2) The apparatus can be run continuously without periodic labor intensive shutdowns for removing recovered metal in slab form, as with traditional techniques; 3) The particulate form of the metal produced is much more convenient to store, distribute, ship, and use than are the metal slabs produced using traditional apparatus.
The recovery apparatus uses an electrolyzer to reprocess dissolved zinc oxide into zinc particles for eventual use in the fuel cells (or, in the case of a metal processing or recovery application, into metal particles that can be conveniently stored, shipped, and introduced into metal refining, casting, or fabrication processes). The electrolyzer accomplishes this by electrodepositing zinc from the zinc oxide on electrically conducting particles. Fluidized bed electrolyzers and spouted bed electrolyzers are examples of two types of technologies used for the electrodeposition of metals on conducting particles (see for example U.S. Pat. No. 5,695,629, Nadkami et al.; “Spouted Bed Electrowinning of Zinc: Part I, Juan Carlos Salas-Morales et al., Metall. Trans. B, 1997, vol. 28B, pp. 59-68; U.S. Pat. No. 4,272,333, Scott et al.; and U.S. Pat. No. 5,958,210, Siu et al.). In both a fluidized bed electrolyzer and spouted bed electrolyzer, the anodes are separated from the fluidized particles by a separator. The separator must be an ionic conductor but not an electrical conductor and must be resistant to erosion and dendrite growth for the electrolyzer to perform reliably. The dendrite problem is particularly difficult to avoid since if a single conducting particle becomes trapped in or on the separator, and if the particle remains in electrical contact with the bed of moving particles, it will grow through the separator toward the anode and cause an electrical short. At this point, the electrolyzer may have to be disassembled and rebuilt with a new separator. Another problem with some electrolyzers is the low volumetric efficiency or low space time yield of the device. In other words, a device of a given size does not produce enough metal per unit time to be economically viable or practical. This results from the fact that In a conventional “plate” electrolyzer the cathode is a zinc plate, which has a much lower surface area on which electrodeposition can take place than does a bed of particles occupying a similar volume. Therefore the yield of electrodeposited material per unit volume may be very low in a conventional flat plate system.
A problem with a traditional fluidized bed electrolyzer is the high pumping energy required to maintain the cathode particle bed in fluid motion, thereby decreasing the overall efficiency of the system. Yet another disadvantage of the traditional fluidized bed electrolyzer is the poor average electrical contact made by the fluidized cathode particles with the current collector, further reducing the energy efficiency of the system.
Thus, what is needed is an electrolyzer for electrodeposition on electrically conductive particles that maintains good electrical contact between the power supply and the conducting particles, does not require unacceptably high pumping power, and eliminates the need for a separator, thereby avoiding the aforementioned problems with separator erosion through contact with the moving particles, and the growth of dendritic particles which penetrate the separator and cause an electrical short between the anode and cathode. The electrolyzer should also have a high yield of electrodeposited material per unit volume.
SUMMARY OF THE INVENTION
Accordingly, the present invention eliminates the need for a separator in an electrolyzer for electrodeposition on electrically conductive particles, thereby avoiding sepa
Colborn Jeffrey A.
Evans James W.
Pinto Martin
Smedley Stuart
Howrey Simon Arnold & White , LLP
Leader William T.
Metallic Power, Inc.
Valentine Donald R.
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