US3476675A - An electrolytic cell for chlorine production - Google Patents

Description

4, 1969 D- COLVIN ET A 3, 6,

ELECTROLYTIC CELL FOR CHLOHINE PRODUCTION Fil'ed March22', 1966 I NVENTORS DONALD COL VIN VERNON A. SCHULTZ '1 E Arromvsvs United States Patent 3,476,675 AN ELECTROLYTIC CELL FOR CHLORINE PRODUCTION Donald Calvin, San Francisco, and Vernon A. Schultz,

El Sobrante, Califl, assignors to Simplex Manufacturing (30., Richmond, Califi, a corporation of California Filed Mar. 22, 1966, Ser. No. 536,439 Int. Cl. Bfllk 3/04; C22d 1/02 U.S. 'Cl. 204-242 9 Claims ABSTRACT OF THE DISCLOSURE An electrolytic cell for making chlorine suitable for the chlorination of swimming pools, comprising a metallic tube having a section thereof flattened on two sides to form two parallel walls, said tube being the cathode and preferably of non-corrosive metal such as stainless steel, an anode structure containing a tantalum frame mounted within and insulated from said tube, a rectangular corrugated platinum sheet electrically connected to and carried on the tantalum frame midway between the flat walls of the tube, and a pair of foraminous polyethylene covers overlaying the platinum sheet on each side thereof; said cell being supplied through an electric circuit formed to short circuit the anode and cathode during the off time.

The present invention relates to improvements in an electrolytic cell, and more particularly to an improved electrolytic cell for making chlorine from chloride solutions by electrolysis.

It is well known that chlorine is made by electrolytic processes, and it is also known to make chlorine electrolytically where it is needed for immediate use. In general, the electrolytic cell of the present invention is suitable for making chlorine electrolytically regardless of the use therefor. However, the cell has been found to be particularly valuable when utilized to provide chlorine for the chlorination of swimming pools. A typical set-up for the utilization of this cell in swimming pools will be illustrated herein, but it should be appreciated that this particular utility should in no way limit the invention.

One of the very serious problems encountered in making electrolytic cells for the manufacture of chlorine is the deterioration of the anode where the chlorine is formed. Various systems have been developed and various types of anodes have been utilized, including graphite and other relatively inexpensive materials which are quite expendible, to extremely corrosion-resistant materials such as platinum. No matter what material is used, the cell has a limited life, and in certain applications this limited life should be as long as possible.

In other words, where chlorine is made industrially, it is quite possible to utilize materials such as graphite effectively because the system is under the control of trained, qualified technicians and repair of the cell and maintenance thereof may be provided from time to time to keep the system operating. However, where the cell is to be utilized by relatively untrained personnel, it is desirable to provide a cell having an especially long life of operation, with little or no maintenance problems. The

cell of the present invention is developed to fit the latter category, where a long life of trouble-free maintenance is desirable.

In such cases, it is customary to utilize platinum or members of the platinum family as the anode since platinum is extremely corrosion resistant and will serve for rather long periods of time before it deteriorates beyond serviceable use.

It will be appreciated, however, that platinum and members of the platinum family are rather expensive and therefore efiicient use of the platinum should be achieved. In the past, various systems have been suggested, such as plating the platinum onto other materials, but these systems have the disadvantage of providing rather expensive, sophisticated structures which still have limited life.

Thus, it is a primary object of the present invention to provide a relatively simple electrolytic cell structure which is constructed with a platinum anode formed for efl'lcient utilization of platinum and giving a relatively long life of trouble-free service.

Another problem which has been encountered in electrolytic cells suitable for making chlorine, and particularly for cells making chlorine from chloride solutions in swimming pools and the like, is that of the formation of scale on the cathode which changes the internal conductivity in the cells and causes serious problems such as localized overheating unless the scale is reduced to a minimum or eliminated. In prior cells, it has been customary to provide a transparent housing so that scale conditions can be observed visually, and the scale is removed by various systems when the buildup becomes too great. However, it has been found that the scale may be removed through the use of a galvanic action which takes place during the off time of the cell in combination with the hydrogen production which takes place during the on time of the cell and other forms of agitation likely to be present. The present invention utilizes this principle to avoid the need for transparent housings and to solve the problem of scale build-up.

Accordingly, it is another object of the invention to provide an electrolytic cell which is simple in structure and yet which is capable of operating without the formation of excessive scale on the cathode.

A further object of the invention is to provide an ele trolytic cell of the character described which is capable of being placed in a fluid stream of chloride solution ard withstand rather strong current flow without danger of injury to the cell structure.

Yet another object of the invention is to provide an electrolytic cell of the character described having a novel cathode structure which is formed for cooperation with the novel anode for obtaining the most efiicient use of the anode and yet providing the cathode in a relatively inexpensive but reliable form.

Further objects and advantages of the invention will be apparent as the specification progresses, and the new and useful features of the electrolytic cell will be fully described in the claims attached hereto.

The preferred form of the invention is illustrated in the accompanying drawings forming a part of this description in which:

FIGURE 1 is a perspective view of a typical cell constructed according to the invention, with parts broken away to illustrate internal structure, and including a typical circuit diagram utilized in the preferred form of the invention;

FIGURE 2, a cross-sectional elevational view of the electrolytic cell of FIGURE 1 with the cell being broken away to illustrate adjustment in the length thereof;

FIGURE 3, a cross-sectional top view of the cell illus trated in FIGURE 2; and

FIGURE 4, an enlarged sectional view taken substantially in the line 44 of FIGURE 2.

While only the preferred form of the invention is shown, it sould be understood that various changes or modifications may be made within the scope of the claims attached hereto without departing from the spirit of the invention.

'Referring to the drawings in greater detail, there is shown an electrolytic cell 11 comprising a metallic housing 12 formed to serve as the cathode and containing a section having two substantially flat walls 13 and 14 in substantially parallel relation for providing active cathodic surfaces, and a fiat anode plate 16 (see FIGURE 4) mounted in substantially evenly spaced relation between the flat walls 13 and 14 of the housing. The anode plate is fabricated of a single sheet of material of the platinum family, such as platinum or platinum-iridium alloy. As best seen in FIGURE 4, the anode plate 16 has each side facing one of the cathode plates 13 or 14 so that a single sheet is operative to provide two cell areas 17 and 18. Preferably, the anode plate 16 is corrugated to provide added strength thereto and also to provide an increased active surface.

The anode plate is securely held in position by holding means 19 comprising a corrosion-resistant frame 21 mounted in the housing through suitable mounting means 22.

In general, this corrosion-resistant frame can be any suitable member capable of supporting the anode plate securely in its proper position and carrying an electrical connection thereto. Accordingly, the frame could be made of plastic with any type of wire sealingly encased therein or a corrosion-resistant electrical conductor such as tantalum or titanium which is capable of supporting the anode plate and also bringing an electric current thereto. The preferred structure is shown in the drawings in which a tantalum frame is shown which is substantially rectangular with parallel sides 23 and 24 disposed in a centrally aligned position between plates 13 and 14. The sides 23 are disposed substantially axially on the housing 12 and have the anode plate wrapped therearound as shown at 26 in FIGURE 4. In this way, the connection is axial to the flow of liquid through the housing and provides a secure fastening, in Which the corrugations also have their long axis corresponding with the flow of the current of water through the electrolytic cell.

The sides 24 have V-shaped support members 27 attached thereto, with the support members preferably being centrally aligned, as shown, and passing through the inclined surface of the housing between the flattened section and tubular portion, as best seen in FIGURE 2.

The frame 21 is preferably sized just slightly smaller than the diameter of the tube from which honing 12 is made so that it may be fit therethrough and into position as best seen in FIGURE 3. The support members 27 can be temporarily bent out of shape and seated through the mounting means 22, or one of the support members welded in place by spot welding or the like at the bend thereof. The preferred form of mounting means is shown in FIGURE 2 where there is provided a threaded fitting 28 in the form of a threaded sleeve passing through the housing to provide an opening therethrough and a Teflon plug 29 having a shoulder portion 31 adapted to fit within nut 32. With the frame properly positioned, nut 32 is tightened to provide a sealing grip on support memher 27 so that the member may act as an electrical conductor insulated from the housing by the Teflon plug 29 and remain sealingly in place. The angular offset of the support members assists in providing a secure anchoring through the Teflon plug.

In order to protect the anode plate 16 from physical damage when strong currents of liquid are pumped through the cell structure, a pair of cover plates 33 are disposed on each side of the anode plate. These cover plates may be formed of any corrosion-resistant material which is capa-ble of providing added strength, such as tantalum mesh or a suitable plastic such as any of the polyolefin plastics, including but not limited to polyethylene, polypropylene, polytetrafluoroethylene, and polystyrene.

As shown in the drawings, the cover plates are made of a polyethylene plastic and are constructed to be held securely in place by the tantalum frame in suflicient spaced relation to fit against the corrugations of the anode plate on each side. The cover plates are also equipped with holes 34 to allow better movement of gases such as hydrogen and chlorine therethrough, if and when necessary. With this construction, the platinum anode is thoroughly protected and will continue operation until substantially all of the platinum has been eaten away by use. When this happens, it is seen that the cell may be easily reconstructed to include another anode plate.

As indicated above, the housing 12 serves as a cathode and therefore should be of metallic or electrically conducting construction. It is also important to provide a cathode of a material which will slough off scale through the mechanism of reversed polarity between the on period and the off period, as hereinafter explained. Thus, it is important to utilize a metal cathode having an especially smooth surface whereby metal oxide formed on the cathode may be sloughed off from the cathode surface along with the scale to effect removal therefrom.

Thus, in its broad aspect, the metal may -be any metal which is capable of a long life in the electrolytic solution containing chloride ion, and has the property of being higher than platinum on the electromotive series. In other words, metals higher than platinum will form oxide coatings through the galvanic effect when the cell is turned off so that even materials such as copper, which is below hydrogen, will form such an oxide coating. However, it is important that the oxide coating be relatively removeable from the base metal, and copper has not been found to be very satisfactory in this respect. Metals such as iron, nickel and chromium have been found to be excellent; however, exteremly resistant alloys such as stainless steel are preferred. In general, any type of stainless steel will achieve this result since all of the stainless steels contain high percentages of iron, nickel and chromium. Accordingly, the stainless steel selected should be one which is praticularly resistive to attack by the chloride ion.

It will be appreciated that the housing will also be slowly deteriorated away by the formation of oxide coating through the galvanic effect, but the housing can be made of sufficiently thick walls that this slow process is unimportant as compared to the anode damage mentioned above. In addition, it will be appreciated that this housing may be fabricated quite easily and inexpensively simply by taking a standard tube of stainless steel of suitable dimensions and flattening the center section thereof by means of a suitable press to the degree indicated in FIGURE 2. Simple pressing will provide the desired configuration and the tube will tend to flatten symmetrically to the form shown.

The operation achieved by the galvanic effect is believed to take place substantially as follows: During the off period of the cell, oxide coatings form on the smooth cathode surface through the galvanic effect and build up to an amount suflicient that they will assist in the removal of scale as they themselves are dislodged from the surface of the base metal. This dislodgement tends to occur during the on operation due to the physical action provided by the turbulence of moving water and, more important, by the production of hydrogen gas on the surface of the cathode. In this way, the scale is removed as it is formed during the on period. With this construction, it has been found in practice that the cell will operate through many hours of useful service without any build-up of excessive scale.

In order to assist in the galvanic action mentioned above, it is preferred to utilize the circuit illustrated in FIGURE 1. As there shown, an alternating current is provided by any suitable source 36 through lines 37 and 38, with one of the lines containing a switch 39 and a fuse 41. This line then passes through a clock timer 42 or other control device that will provide the desired line output. When control device 42 and switch 39 are on, relay 44 is actuated to the position shown in phantom in FIG- URE 1, and current is supplied to the primary coil 46 of transformer 47. Seconday coils 48 and 49 are then each operative to pick up a half wave of the alternating current which will pass through silicon diodes 51 contained in lines 52 and 53 and thence to the cathode. Anode lead 54 provides the other tap for direct current to the anode and may be equipped with an ammeter 56 as shown.

When the cell is switched to the olf position, either through the switch 39 or the control device 42, relay 44 moves to the position shown in solid lines and provides a short circuit between the anode and cathode through lines 57 and 58, as shown. With this load, the cell functions in a manner similar to a battery during this off period and builds up the oxide coating through the galvanic effect mentioned above. The short circuiting system is particularly valuable in increasing this galvanic action which occurs during the off period, and therefore a circuit of this nature is preferred.

It will be appreciated that a suitable relay which is operative to provide and eliminate the short circuit illustrated could be placed at other positions in the circuit, as long as it is controlled by a relay or other device operative when the cell is turned on and off.

It will also be appreciated that the cell will only op erate when electrolyte is present between the anode and the cathode and this will be provided in accordance with the use designed for the particular cell. In FIGURE 1, there is a diagrammatic illustration of the use of the cell in a system for chlorinating a swimming pool 59. Briefly speaking, the operation includes the use of a conduit or pipe 61 which will draw liquid from the swimming pool and recycle it thereto. Typically, this conduit could be the conduit utilized in the filter system of the swimming pool. As shown in FIGURE 1, the conduit contains a filter 62 upstream of a pump 63 which in turn is upstream of the electrolytic cell 11 so that the efiluent from the cell 11 is returned directly to the swimming pool.

Suitable amounts of chloride ion are added to the swimming pool water in the form of sodium chloride, and preferably suflicient salt is added to retain the salt content above about 0.4% in order to achieve good descaling in the system here shown. Control for the system is provided by the clock timer 42 or by other suitable means. A more complete description of a system suitable for chlorinating swimming pools is shown in our co-pending United States application Ser. No. 378,411 entitled Electrolytic Cell in Chlorinating System Using Same, filed June 26, 1964, now Patent No. 3,378,479 issued Apr. 16, 1968.

Since the preferred conduit includes a pair of silicon diodes suitable for rectifying the alternating current, the electrolytic cell 11 preferably includes these diodes in mounted position thereon. As shown in FIGURE 2, a terminal block 64 is securely welded, brazed or otherwise secured to the housing 12 and contains a pair of 6 wells 66 in which the silicon diodes fit, with the diodes being connected on one side to the main body of the terminal block and on the other side to lead wires 52 and 53. The entire assembly is fit into the well with suitable insulating materials such as a ceramic insulating material. As here shown, the terminal block is made of copper, and line 58 is simple attached thereto to allow reverse flow in the short circuit system mentioned above.

It has been found by testing that the cell constructed as shown in the drawings will operate for many hours of trouble-free service. It has also been found that very little scale builds up within the cell. In fact, more scale builds up at the ends than within the cell areas. In order to reduce this scale build-up at the ends of the cells, it is proposed to cover the central section of support members 27 with platinum, but this is not essential.

From the foregoing description, it is seen that we have provided an improved electrolytic cell which is relatively simple and inexpensive in construction, rugged and durable in operation, and yet provides excellent economy of expensive platinum material.

We claim:

1. An electrolytic cell for making chlorine from chloride solutions by electrolysis, comprising a metallic tubular housing formed to serve as a cathode and containing a flattened section having two substantially flat walls in substantially parallel relation for providing active cathodic surfaces, and a flat anode plate mounted in substantially evenly spaced relation between the fiat walls of the housing, said anode plate being constructed of a single sheet of a material selected from the platinum family with each side of said sheet being operatively disposed with one of the fiat walls of the cathode.

2. The electrolytic cell defined in claim 1, in which a corrosion-resistant frame is provided to hold the anode plate securely in position, with the frame being mounted in said housing and carrying an electrical lead connection to the anode plate in insulated fashion through the housing.

3. The electrolytic cell defined in claim 2, in which the corrosion-resistant frame includes a rectangular tan talum rod and the anode plate is a corrugated platinum sheet wrapped around the tantalum rod at opposite ends for good electrical contact therewith.

4. The electrolytic cell defined in claim 3, in which covers are provided to completely overlay and protect the platinum sheet on each side, said covers being formed of a corrosion-resistant material containing sufficient openings to allow gases formed at the anode to pass therethrough.

5. The electrolytic cell defined in claim 4, in which the covers are made of polyolefin plastic.

6. An electrolytic cell for making chlorine from chloride solutions by electrolysis, comprising a stainless steel tube having a section thereof flattened on two sides to form two substantially fiat walls in substantially parallel relation, said tube adapted to serve as a cathode with the flat walls providing plate surfaces, an anode structure containing a tantalum frame mounted within and insulated from the stainless steel tube, and a rectangular platinum sheet carried on the tantalum frame in substantially evenly spaced relation between the flat walls of the housing.

7. The electrolytic cell defined in claim 6, in which covers are provided to completely overlay and protect the platinum sheet on each side, said covers being formed of corrosion-resistive material and containing sufficient openings to allow gases formed at the anode to pass therethrough.

'8. The electrolytic cell defined in claim 7, in which the covers are made of polyolefin plastic.

9. The electrolytic cell defined in claim 6, in which an electric supply circuit is provided for providing direct current to said anode and cathode, said electric supply circuit including switch means for controlling the on and 011 condition of the circuit, and a relay behind the switch operative when the supply circuit is in the OE condition to close a short circuit between the anode and cathode and operative when the supply circuit is in the on condition to open the short circuit.

References Cited UNITED STATES PATENTS 12/1893 Cutten 204-278 8/1904 Nelson 204242 XR 11/1921 Slater 204275 XR 12/ 1940 Paul.

5 JOHN H. MACK, Primary Examiner D. R. VALENTINE, Assistant Examiner US. Cl. X.R.

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