Bleaching and dyeing; fluid treatment and chemical modification – Fluid treatment – Combined liquid and gas or vapor
Reexamination Certificate
2002-05-14
2003-09-16
Gulakowski, Randy (Department: 1746)
Bleaching and dyeing; fluid treatment and chemical modification
Fluid treatment
Combined liquid and gas or vapor
C008S147000, C008S149200, C008S158000
Reexamination Certificate
active
06620210
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to improvements in the production of ozone (O
3
). More particularly, the invention relates to the electrolytic production of ozone utilizing a proton exchange membrane to separate the anode and depolarized cathode.
Ozone has long been recognized as a useful chemical commodity valued particularly for its outstanding oxidative activity. Because of this activity it finds wide application in disinfection processes. In fact, it kills bacteria more rapidly than chlorine, it decomposes organic molecules, and removes coloration in aqueous systems. Ozonation removes cyanides, phenols, iron, maganese, and detergents. It controls slime formation in aqueous systems, yet maintains a high oxygen content in the system. Unlike chlorination, which may leave undesirable chlorinated organic residues in organic containing systems, ozonation leaves fewer potentially harmful residues. There is evidence that ozone will destroy viruses. It is used for sterilization in the brewing industry and for odor control in sewage treatment and manufacturing. And ozone is employed as a raw material in the manufacture of certain organic compounds, e.g., oleic acid and peroxyacetic acid.
Thus, ozone has widespread application in many diverse activities, and its use would undoubtedly expand if its cost of production could be reduced. In addition, since ozone is explosive when concentrated as either a gas or liquid, or when dissolved into solvents or absorbed into gels, its transportation is potentially hazardous. Therefore, it is generally manufactured on the site where it is used. However, the cost of generating equipment, and poor energy efficiency of production has deterred its use in many applications and in many locations.
On a commercial basis, ozone is currently produced by the silent electric discharge process, otherwise known as corona discharge, wherein air or oxygen is passed through an intense, high frequency alternating current electric field. The corona discharge process forms ozone through the following reaction:
3/20
2
=O
3;
&Dgr;H°
298
=34.1
kcal
Yields in the corona discharge process generally are in the vicinity of 2% ozone, i.e., the exit gas may be about 2% O
3
by weight. Such O
3
concentrations, while quite poor, in an absolute sense, are still sufficiently high to furnish usable quantities of O
3
for the indicated commercial purposes. Another disadvantage of the corona process is the production of harmful NO
x
, otherwise known as nitrogen oxides. Other than the aforementioned electric discharge process, there is no other commercially exploited process for producing large quantities of O
3
.
However, O
3
may also be produced by the electrolytic process, wherein an electric current (normally D.C.) is impressed across electrodes immersed in an electrolyte, i.e., electrically conducting, fluid. The electrolyte includes water, which, in the process, dissociates into its respective elemental species, O
2
and H
2
. Under the proper conditions, the oxygen is also evolved as the O
3
species. The evolution of O
3
may be represented as:
3H
2
O=O
3
+3H
2;
&Dgr;H°
298
=207.5
kcal
It will be noted that the DH° in the electrolytic process is many times greater than that for the electric discharge process. Thus, the electrolytic process appears to be at about a six-fold disadvantage.
More specifically, to compete on an energy cost basis with the electric discharge method, an electrolytic process must yield at least a six-fold increase in ozone. Heretofore, the necessary high yields have not been realized in any foreseeably practical electrolytic system.
The evolution of O
3
by electrolysis of various electrolytes has been known for well over 100 years. High yields up to 35% current efficiency have been noted in the literature. Current efficiency is a measure of ozone production relative to oxygen production for given inputs of electrical current, i.e., 35% current efficiency means that under the conditions stated, the O
2
/O
3
gases evolved at the anode are comprised of 35% O
3
by volume. However, such yields could only be achieved utilizing very low electrolyte temperatures, e.g., in the range from about −30° C. to about −65° C. Maintaining the necessary low temperatures, obviously requires costly refrigeration equipment as well as the attendant additional energy cost of operation.
Ozone, O
3
, is present in large quantities in the upper atmosphere in the earth to protect the earth from the suns harmful ultraviolet rays. In addition, ozone has been used in various chemical processes, is known to be a strong oxidant, having an oxidation potential of 2.07 volts. This potential makes it the fourth strongest oxidizing chemical known.
Because ozone has such a strong oxidation potential, it has a very short half-life. For example, ozone which has been solubilized in waste water may decompose in a matter of 20 minutes. Ozone can decompose into secondary oxidants such as highly reactive hydroxyl (OH*) and peroxyl (HO
2
*) radicals. These radicals are among the most reactive oxidizing species known. They undergo fast, non selective, free radical reactions with dissolved compounds. Hydroxyl radicals have an oxidation potential of 2.8 volts (V), which is higher than most chemical oxidizing species including O
3
. Most of the OH* radicals are produced in chain reactions where OH itself or HO
2
* act as initiators.
Hydroxyl radicals act on organic contaminants either by hydrogen abstraction or by hydrogen addition to a double bond, the resulting radicals disproportionate or combine with each other forming many types of intermediates which react further to produce peroxides, aldehydes and hydrogen peroxide.
Electrochemical cells in which a chemical reaction is forced by added electrical energy are called electrolytic cells. Central to the operation of any cell is the occurrence of oxidation and reduction reactions which produce or consume electrons. These reactions take place at electrode/solution interfaces, where the electrodes must be good electronic conductors. In operation, a cell is connected to an external load or to an external voltage source, and electric charge is transferred by electrons between the anode and the cathode through the external circuit. To complete the electric circuit through the cell, an additional mechanism must exist for internal charge transfer. This is provided by one or more electrolytes, which support charge transfer by ionic conduction. Electrolytes must be poor electronic conductors to prevent internal short circuiting of the cell.
The simplest electrochemical cell consists of at least two electrodes and one or more electrolytes. The electrode at which the electron producing oxidation reaction occurs is the anode. The electrode at which an electron consuming reduction reaction occurs is called the cathode. The direction of the electron flow in the external circuit is always from anode to cathode.
A typical electrochemical cell will have a positively charged anode and a negatively charged cathode. The anode and cathode are typically submerged in a liquid electrolytic solution which may be comprised of water and certain salts, acids or base materials. Generally speaking, gaseous oxygen is released at the anode surface while gaseous hydrogen is released at the cathode surface. A catalyst such as lead dioxide may be used to coat the anode to get greater ozone production. The anode substrate may be another material such as titanium, graphite, or the like.
The cathode and anode are positioned within the electrolytic cell with electrical leads leading to the exterior. The cell is also provided with appropriate plumbing and external structures to permit circulation of the electrolyte to a separate heat exchanger. Suitable inlet and outlet passages are also provided in the cell head space to permit the withdrawal of the gases evolved from the cathode (if gases are to be evolved) and from the anode. The two gas removal systems are typically maintained separate in order to isolate
Hitchens G. Duncan
Murphy Oliver J.
Gulakowski Randy
Lynntech Inc.
Perrin Joseph
Streets Jeffrey L.
Streets & Steele
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