Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Involving measuring – analyzing – or testing during synthesis
Reexamination Certificate
2000-08-22
2002-03-26
Bell, Bruce F. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Involving measuring, analyzing, or testing during synthesis
C205S336000, C204S222000, C204S223000, C204S230400, C204S261000, C204S273000
Reexamination Certificate
active
06361678
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for detecting a short incident during electrochemical processing and a system therefor.
BACKGROUND OF THE INVENTION
One industrial process for producing fluorochemical compounds is the electrochemical fluorination process commercialized initially in the 1950s by Minnesota Mining and Manufacturing Company which comprises passing a direct electric current through an electrolyte, (i.e., a mixture of fluorinatable organic starting compound, liquid anhydrous hydrogen fluoride, and perhaps a conductivity additive), to produce the desired fluorinated compound or fluorochemical. This process is commonly referred to as the “Simons electrochemical fluorination process” or “Simons ECF”. Simons ECF cells typically utilize a monopolar electrode assembly, i.e., electrodes connected in parallel through electrode posts to a source of direct current at a low voltage (e.g., four to eight volts). Simons ECF cells are generally undivided, single-compartment cells, i.e., the cells typically do not contain anode or cathode compartments separated by a membrane or diaphragm. The Simons ECF process is disclosed in U.S. Pat. No. 2,519,983 (Simons) and is also described in some detail by J. Burdon and J. C. Tatlow in
Advances in Fluorine Chemistry
(M. Stacey, J. C. Tatlow, and A. G. Sharpe, editors) Volume 1, pages 129-37, Buttersworths Scientific Publications, London (1960); by W. V. Childs, L. Christensen, F. W. Klink, and C. F. Kolpin in
Organic Electrochemistry
(H. Lund and M. M. Baizer, editors), Third Edition, pages 1103-12, Marcel Dekker, Inc., New York (1991); by A. J. Rudge in
Industrial Electrochemical Processes
(A. T. Kuhn, editor), pages 71-75, Marcel Dekker, Inc., New York (1967); and by F. G. Drakesmith,
Topics Curr. Chem
., 193, 197, (1997).
Various modifications and/or improvements have been introduced to the Simons ECF process since the 1950s including, but not limited to, those described in U.S. Pat. No. 3,753,976 (Voss et al.); U.S. Pat. No. 3,957,596 (Seto); U.S. Pat. No. 4,203,821 (Cramer et al.); U.S. Pat. No. 4,406,768 (King); Japanese Patent Application No. 2-30785 (Tokuyama Soda KK); SU 1,666,581 (Gribel et al.); U.S. Pat. No. 4,139,447 (Faron et al.); and U.S. Pat. No. 4,950,370 (Tarancon).
U.S. Pat. No. 5,322,597 (Childs et al.) more recently describes the practice in a bipolar flow cell of an electrochemical fluorination process comprising passing by forced convection a liquid mixture comprising anhydrous hydrogen fluoride and fluorinatable organic compound at a temperature and a pressure at which a substantially continuous liquid phase is maintained between the electrodes of a bipolar electrode stack. The bipolar electrode stack comprises a plurality of substantially parallel, spaced-apart electrodes made of an electrically-conductive material, e.g., nickel, which is essentially inert to anhydrous hydrogen fluoride and which, when used as an anode, is active for electrochemical fluorination. The electrodes of the stack are arranged in either a series or a series-parallel electrical configuration. The bipolar electrode stack has an applied voltage difference which produces a direct current which can cause the production of fluorinated organic compound.
Another example of a bipolar flow cell is the Solutia EHD (electrohydrodimerization) cell. See
J. Electrochem. Soc
.: REVIEWS AND NEWS, D. E. Danly, 131(10), 435C-42C (1984) and
Emerging Opportunities for Electroorganic Processes
, D. E. Danly, pages 132-36, Marcel Dekker, Inc., New York (1984).
Yet another electrochemical cell is an electrolyzer such as those described by Wullenweber et al. in U.S. Pat. No. 5,174,878. Wullenweber et al. disclose an electrolyzer having bipolar cells arranged in a row and consisting each of two metallic partitions, spring-elastic electrodes bearing on the partitions, and a diaphragm which is disposed between the electrodes and spaced from the electrodes by spacers.
Although electrochemical processing is an effective method to manufacture chemicals, for example fluorochemicals, on occasion the electrochemical cell(s) may experience a “short incident”. A “short incident” is defined herein as an event such as for example, a run-away chemical reaction, unstable two-phase flow, or plate flexing which ultimately may lead to a connection of comparatively low resistance made between points on a circuit between which the resistance is normally much greater than zero. The ultimate cause of serious damage from a short incident is current flow through plate-to-plate contacts and the deposition of sufficient energy at those contacts to melt the electrode (e.g., a metal plate, such as nickel). A short incident can result in considerable damage to the electrochemical cell which often means lost time during manufacturing and expense to repair the cell. Thus, it is desirable to eliminate such short incidents or to the extent possible to reduce damage caused by these short incidents. Detecting a short incident as soon as possible helps to reduce damage to the cell caused by the short incident and in turn helps to minimize lost time during manufacturing. Detecting short incidents before plate-to-plate contact occurs substantially lessens damage.
One method of detecting a short incident is to use a mechanics stethoscope, a device much like the familiar physician's stethoscope, but which uses a pointed solid rod instead of the familiar bell for making contact with the body being examined. With the Simons ECF cell or with low voltage conventional cells, a mechanics stethoscope can be used to detect vibration in the audible frequencies. However, with a bipolar flow cell where the voltage is possibly higher, perhaps several hundred volts, a mechanics stethoscope should not be used for safety reasons. Further, the ability to detect a short incident using a mechanics stethoscope varies with the user's ability and thus may at times not be reliable, and it is not practical.
Another method of detecting a short incident is to use a large plastic-handled screwdriver in the same manner as a mechanics stethoscope.
These methods require an operator's attention, are not reliable, and may take a long time to detect the onset of a short incident. Damage to the cell pack and lost production time is often considerable before a short incident is confirmed and a cell is taken out of service.
Another method of detecting a short incident is to monitor current and voltage responses. If the current is set, the voltage fluctuates. However, the “noise” in the voltage can be relatively large as compared to the fluctuation in the voltage due to an individual short incident (for example a 2 to 3 volt drop out of 500 to 600 volts). Thus, it is often difficult, if not impossible to detect a problem until several plates in a cell are affected. It may be possible to monitor voltages between individual plates or set of plates. However, this may be difficult to engineer, may lead to leaks in the system, and involves more data collection, storage, etc.
Thus, the need exists for a method of detecting a short incident in an electrochemical cell which is safe for lower voltage electrochemical cells and for higher voltage electrochemical cells; is reliable; and preferably is inexpensive.
SUMMARY OF THE INVENTION
The present invention provides a method for detecting a short incident in an electrochemical cell. The method of the present invention advantageously detects a short incident soon after initiation and thus limits damage, is safe for both low and high voltage electrochemical cells, and is reliable. Further, the method of the present invention is inexpensive to install and to operate.
The method of the present invention utilizes a means for detecting vibration (e.g., an accelerometer) of sufficient sensitivity to detect movement of an externally-located piece of the cell system.
The method of the present invention is a method of detecting a short incident in an electrochemical cell comprising the steps of:
(a) providing an electrochemical cell system having a cell pac
Childs William V.
Gross Christopher L.
Schotz Eric A.
Smith Mark P.
3M Innovative Properties Company
Bell Bruce F.
Fagan Lisa M.
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