Liquid purification or separation – Magnetic – With additional separator
Reexamination Certificate
1999-10-29
2002-03-12
Reifsnyder, David A. (Department: 1723)
Liquid purification or separation
Magnetic
With additional separator
C210S222000, C210S243000, C204S280000, C204S283000, C429S010000, C429S010000, C429S047000, C429S127000
Reexamination Certificate
active
06355166
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a method for forming and exploiting fields, e.g., magnetic fields; at the interfaces between components of a composite material, the composite material itself and devices which incorporate the material such as electrochemical systems and separators, including fuel cells, batteries, and separations resulting in enhanced and modified flux and performance. The invention also relates to apparatus, methods of making and methods of using interfacial fields for the separation of transition metals, electrolytic applications such as fuel cells, electrolysis involving free radical products and intermediates, and biological systems.
2. Background of the Related Art
The following discussion provides a brief overview of the current understanding of magnetic properties in composites.
Magnetic Concepts
Magnetic field effects on chemical systems can be divided into several types, including electron transfer (kinetic), mass transport, and thermodynamic. Magnetic effects on homogeneous solutions for electron transfer have been discussed in the background literature, and substantial background research has been conducted on the magnetic effects on mass transport in solutions. Kinetically, reaction rates, reaction pathways, and product distributions can be altered. Macroscopic thermodynamic effects are generally negligible.
(A) Electron Transfer
In electron transfer reactions, an electron is transferred between a molecule or an ion. Electron transfer reactions are ubiquitous throughout natural and technological systems, including biological energy production, ozone depletion, and technologies from photography through batteries, solar cells, fuel cells, and corrosion. Understanding the speed or rates of electron transfer reactions is fundamentally important, since controlling rates can decrease energy consumption, lead to more efficient technologies, and reduce environmental load. For example, approximately 6% of domestic electrical power is used in the chloralkali industry for production of basic chemical stocks, such as hydrochloric acid, sulfuric acid, chlorine gas and sodium hydroxide. Electrochemical refining of aluminum uses a similar amount of power. Any improvement in electron transfer rates for various industrial reactions would significantly reduce energy consumption. Another example involves a fuel cell, which generates power electrically from a fuel (e.g., hydrogen or alcohol) while producing significantly less pollution than an internal combustion engine.
Electron transfer reactions can be characterized as either homogenous or heterogeneous. If the reaction occurs in a single phase (i.e., solid, liquid or gas) between two ions or molecules, the reaction can be characterized as a homogenous electron transfer. Consider two chemically distinct ions, A
z
and B
y
, where z and y are the charges of the species. A
z
and B
y
undergo a homogeneous electron transfer reaction as:
A
z
+B
y
A
z±1
+B
y∓1
. (1)
FIG. 1
shows a homogeneous electron transfer where an electron e transferred from one ion A
z
to another ion B
y
forms the products A
z+1
, B
y−1
. All ions are in solution.
When two different charge states of the same ion undergo homogeneous electron transfer, a self exchange reaction occurs as follows:
A
z+1
+A
z
A
z
+A
z+1
. (2)
While the effects of magnetic fields on homogeneous electron transfer reactions are well-known, little is known about magnetic field effects on heterogeneous reactions due to a lack of sound experimental data and theory.
Electron transfer reaction theory has developed since the 1950s. A model for homogeneous reactions was developed and later modified to describe heterogeneous reactions. Marcus received the Nobel prize in 1991 for theoretical description of those processes based on transition state theory. While the mathematics of Marcus' original theory were done with pencil and paper, the theory has evolved to include quantum mechanical descriptions resolved using sophisticated computer programs.
(B) Mass Transport
Magnetically driven mass transport effects have been studied in electrochemical cells positioned between the poles of large magnets. Effects vary depending on the orientation of the electrode, the relative orientation of the magnetic field and the electrode, forced or natural convection, and the relative concentrations of the redox species and electrolyte.
Paramagnetic molecules have unpaired electrons and are attracted into a magnetic field, while diamagnetic species of molecules possess paired electrons and are slightly repelled by the field. While radicals and oxygen are paramagnetic, most organic molecules are diamagnetic, and metal ions and transition metal complexes can be either para- or diamagnetic. The magnitude of the response of a molecule or species in a solution or fluid to a magnetic field can be parameterized by the molar magnetic susceptibility, &khgr;
m
(cm
3
/mole). For diamagnetic species, &khgr;
m
is between about (−1 to −500)×10
−6
cm
3
/mole, and temperature-independent. For paramagnetic species, &khgr;
m
ranges from 0 to +0.01 cm
3
/mole and, once corrected for its usually small diamagnetic component, varies inversely with temperature in accordance with Curie's Law. Because electrochemistry tends to involve single electron transfer events, the majority of electrochemical reactions should result in a net change in the magnetic susceptibility of species near the electrode.
While ions are monopoles that move either with or against an electric field, depending on the charge of the ion, paramagnetic species are dipoles and will always be aligned in a magnetic field, independent of the direction of the magnetic vector. Those dipoles will experience a net magnetic force if a field gradient exists.
(C) Thermodynamics
A uniformly applied magnetic field created by placing a solution between the poles of a magnet will have a negligible effect on the free energy of reaction. The change in the free energy of the reaction, &Dgr;G
m
, is shown as &Dgr;G
m
=−0.5&Dgr;&khgr;
m
B
2
J/mole, where &Dgr;&khgr;
m
is the difference in magnetic susceptibility of the products and reactants and B is the magnetic induction in Gauss. For the conversion of a diamagnetic species into a paramagnetic species, &Dgr;&khgr;
m
≦0.01 cm
3
/mole. In an applied magnetic field of 1 Tesla (T), where 1 Telsa=10 k Gauss, |&Dgr;G
m
|≦0.05 J/mole. Even in the strongest laboratory fields of 10 T, the effect is negligible compared to typical free energies of reaction.
However, while the macroscopic effects are negligible when the magnet is placed external to the cell and a uniform field is applied to the solution, substantial microscopic effects may exist. The above-discussed effects are most significant in local fields of composites, and in molecules in composites within a short distance of the source of the magnetic field. For example, for a magnetic wire or cylinder, the magnetic field decreases over a distance, x, as x
−3
. Thus the field experienced by a molecule 1 nm from the magnet may be roughly 10
21
times greater than the field experienced at 1 cm.
Fuel Cells
The basic objective of a fuel cell is to allow a reaction between a fuel (e.g., hydrogen) and an oxidant (e.g., oxygen) which normally react spontaneously (and often violently) to discharge in a controlled manner. By containing the fuel and oxidant at separate electrodes, the discharge of the reaction is electrical rather than thermal. A wire coupling the electrodes captures the current and voltage of the discharging system, thus providing power to drive an external device, such as an electric motor.
Fuel cells combine the best characteristics of a battery and a combustion engine. Similar to the combustion engine, they are not recharged electrically and output power as long as fuel is provided. Similar to the battery, fuel cells are electrical devices
Amarasinghe Sudath
Chung Ha-chull
Dunwoody Drew C.
Leddy Johna
Minteer Shelley
Reifsnyder David A.
The University of Iowa Research Foundation
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