US3725223A - Baffles for dimensionally stable metal anodes and methods of using same - Google Patents

Abstract

DESCRIBES BAFFLES FOR USE WITH DIMENSIONALLY STABLE METAL ANODES IN FLOWING MERCURY CATHODE ELECTROLYSIS CELLS TO CONTROL THE FLOW OF THE ELECTROLYTE THROUGH THE ELECTROLYSIS GAP AND UPWARDLY THROUGH THE OPENINGS IN THE ANODE WORKING SURFACES TO IMPROVE THE OPERATION OF THE CELLS, AND THE METHOD OF CONTROLLING THE FLOW OF THE ELECTROLYTE THROUGH THE CELLS BY THE USE OF SAID BAFFLES OR SIMILAR FLOW CONTROLLING DEVICES.

Description

April 3, 1973 v, DE A ET AL 3,725,223

BAFFLES FOR DIMENSIONALLY STABLE METAL ANODES AND METHODS OF USING SAME Filed March 2, 1971 5 Sheets-Sheet 1 INVENTORS v I TTORIO dc NRA April 3, 1973 DE NORA ET AL 3,725,223

BAFFLES FOR DIMENSIONALLY STABLE METAL ANODES AND METHODS OF USING SAME Filed March 2, 1971 3 Sheets-Sheet 2 INVENTORS V ITTORIO de NORA F l G .9

' GIOVANNI TR ISOGLIQ Aprll 3, 1973 v, DE NORA ET AL 3,725,223

BAFFLES FOR DIMENSLONALLY STABLE METAL ANODES AND METHODS OF USING SAME Filed March 2, 1971 3 Sheets-Sheet 5 INVENTORS 1 vmomo de NORA nsos l0 United States Patent 3,725,223 BAFFLES FOR DIMENSIONALLY STABLE METAL ANODES AND METHODS OF USING SAME Vittorio de Nora, Nassau, Bahama Islands, and Giovanni Trisoglio, Como, Italy, assignors to Electronor Corporation, Panama City, Panama Filed Mar. 2, 1971, Ser. No. 120,247 Claims priority, application Italy, Jan. 18, 1971, 19 473/71 Int. Cl. 001a 1/08; C22d 1/04 US. Cl. 204-99 12 Claims ABSTRACT OF THE DISCLOSURE Describes baflles for use with dimensionally stable metal anodes in flowing mercury cathode electrolysis cells to control the flow or" the electrolyte through the electrolysis gap and upwardly through the openings in the anode working surfaces to improve the operation of the cells, and the method of controlling the flow of the electrolyte through the cells by the use of said batiies or similar flow controlling devices.

This invention relates to dimensionally stable anodes used in mercury cell electrolysis processes and to methods of electrolysis using dimensionally stable anodes.

Dimensionally stable anodes are metal anodes which do not change in dimension during an electrolysis process, as distinguished from graphite anodes which gradually wear away during electrolysis, due to the corrosive conditions in an electrolysis cell, thereby causing enlargement of the electrolysis gap and reducing the efficiency of the electrolysis process.

Dimensionally stable anodes are usually made from a valve metal, such as titanium or tantalum, which is resistant to electrolysis cell conditions, and the working faces of the titanium or tantalum anodes are coated with an electrically conducting electrocatalytic coating of a platinum group metal, or an oxide of a platinum group metal or a mixture of oxides of a platinum group metal with oxides of titanium, tantalum or other metals.

Electrolysis cells equipped with dimensionally stable anodes are operated at considerably higher current densities than similar cells equipped with graphite anodes and hence operate at higher temperatures. While graphite anodes in mercury cells offer some obstruction to the flow of brine from the inlet to the outlet of the cells due to the thickness of the graphite anodes, dimensionally stable anodes offer less obstruction to said brine flow especially in cells of a high slope and hence encounter greater temperature differentials. Baflles have been used on graphite anodes in flowing mercury cathode electrolysis cells as shown, for example, in Swiss Pat. No. 235,756, issued Apr. 16, 1945, in Japanese Pat. No. 436,023, issued Dec. 26, 1964 and in Italian Pat. No. 790,278, issued Nov. 2, 1967. These baffles were, however, used for a different purpose than the baflies described herein, for use with relatively thin dimensionally stable metal anodes in mercury cathode electrolysis cells operated at higher current densities than permisible with graphite anodes.

One of the objects of this invention is to provide battles for use with dimensionally stable anodes in horizontal mercury cells which will retard the flow of brine from the inlet to the outlet end of such cells and hence provide for more uniform heat distribution in the brine from end to end of the cell, and greater heat dissipation.

Another object is to provide dimensionally stable anodes in horizontal mercury cells which will direct the flow of brine into and through the electrolysis gap between the active or working face of the anodes and the flowing mercury cathode surface.

3,725,223 Patented Apr. 3, 1973 Another object of the invention is to provide baffles in a substantially horizontal mercury cell equipped with dimensionally stable anodes which will speed up the flow of the electrolyte through the anode gap and upwardly through the anode structure to promote rapid renewal of the electrolyte in the anode gap and more uniform electrolyte temperature.

Another object of this invention is to give an upward component of flow to the electrolyte flowing through the open mesh or opening in the working face of a dimensionally stable metal anode so as to give greater sweep to the electrolyte flowing through the opening of the anode.

Another object of the invention is to provide baflies for use with dimensionally stable anodes which can be installed on such anodes in existing mercury cells Without having to remove the anodes from the cells.

Another object is to provide bafiles for use with dimensionally stable anodes which will. increase the efiiciency of the electrolysis process.

Another object is to provide battles for use with dimensionally stable anodes in horizontal mercury cells with overflow openings which will control the level of the electrolyte dammed up behind each baffle and promote steady operation of the cell.

Another object is to provide baflles to accomplish the above-stated objects which can also be used to prevent the cell cover in cells equipped with flexible cell covers, from dipping into the electrolyte and interferring with gas release from the anode space.

Various other objects and advantages of the invention will appear as this description proceeds.

Referring now to the drawings which show several embodiments of the invention:

FIG. 1 is a perspective view of a typical form of dimensionally stable metal anode with a bafiie installed thereon;

FIG. 2 is a partial sectional view along the line 22 of FIG. 1;

FIG. 2a is a view similar to FIG. 2, showing a modification;

FIG. 3 is a partial perspective view of one form of anode working face;

FIG. 4 is a perspective view of another form of anode having a coated titanium rod working face with a bafiie installed on the anode;

FIG. 5 is a partial perspective view of a rod form of anode working face;

FIG. 6 is a perspective view of the baflle illustrated in FIGS. 1 and 4;

FIG. 7 is a sectional view along the line 7-7 of FIG. 6;

FIG. 8 is a perspective side view of one side of the battle of FIG. 6;

FIG. 9 is a view of a bafiie showing clips for securing the baffle on the lead-in-stems of the anode;

FIG. 10 is a part perspective, part sectional view of a typical horizontal mercury cell showing a baflie applied to a dimensionally stable anode used therein;

FIG. 11 is a sectional view substantially along the line 11-11 of FIG. 12;

FIG. 12 is a modified sectional view of a typical horizontal mercury cell substantially along the line 12-12 of FIG. 10.

One form of dimensionally stable metal anode A with which this invention is used, comprises a working face 1 or 2, comprising a titanium or tantalum mesh base covered with an electrically conductive coating capable,

mixture of oxides of a platinum group metal capable of catalyzing chloride ion discharge from the face of the anode. Other dimensionally stable anodes and other electrocatalytically active coatings such as electro-deposited or chemi-deposited platinum group metal coatings may be used. The working faces 1 or 2 are of an approximate thickness of 1 to 3 mm. and the voids or open spaces between the mesh or rods of the working faces constitute from 40 to 60%, preferably 50 to 53%, of the surface area of the working faces 1 or 2. The term mes used to describe the working faces of the anodes is intended to include thin sheets of titanium or tantalum or of alloys of titanium or tantalum in foraminous or expanded form, wire mesh and gauze, rolled wire mesh, punched and slotted sheet titanium or tantalum, spaced rods or half-round forms, etc., and the words titanium and tantalum are intended to include alloys of these metals with other metals.

The working faces 1 or 2 are connected by welding, riveting or other connections, to a plurality of secondary current conducting cross bars 3 extending transversely of the electrolytic cell and the bars 3 are connected to primary current conducting bars 4 running longitudinally of the cell, which, in turn, are connected to the copper lead-ins 5 by which the current is conducted into the cell. The copper lead-ins 5 are connected to the conductor bars 4 by internally screw threaded titanium bosses 6, welded or otherwise secured to the primary conductor bars 4. Eight secondary conductor cross bars 3 and two primary conductor bars 4 have been shown, but the number of primary and secondary conductor bars is not critical, and will vary depending on the size and design of the cell, nor is their direction within the cell critical. The number of primary and secondary conductor bars may be increased or decreased, but they should be proportioned in size according to the conductive capacity of the metal to convey the required amount of current to the anode face and distribute it uniformly over the anode working face. The primary conductor bars 4 may sit on top of the secondary conductor bars 3 and be welded thereto or they may be notched into the bars 3 and welded thereto. The secondary and primary conductor bars are preferably arranged at right angles to each other for better current distribution, but a slight deviation from a 90 connection is permissible.

As illustrated in FIG. 3, the expanded titanium mesh used for the working face 1 is provided witth diamondshaped openings 1a in the mesh. The open areas 1a of the working faces may be from 40 to 60% (preferably 50 to 53%) of the total surface area of the working face 1. The secondary conducting bars 3 are preferably welded as at 3a to the working face 1 at right angles to the long way of the diamond-shaped opening, while the primary conducting bars 4 run parallel to the long way of the diamond-shaped opening. This leads to better current distribution along the working face 1 and to better release or escape of gas from the face of the anodes.

The bosses 6 are preferably internally screw threaded to receive the screw threads at the bottom of the copper lead-ins 5, and the lead-ins 5 seat firmly against the primary conducting bars 4 as shown in FIG. 2. Titanium sleeves 7 surround the copper lead-ins 5 inside the cell and extend from the bosses 6 to the flexible cell cover 8 (FIGS. 11 and 12) to protect the lead-ins from the corrosive effect of the electrolyte and the cell gases. Other protective insulation, such as rubber, neoprene or other plastics which are resistant to electrolytic cell conditions, may be used in place of sleeves 7 to protect the lead-ins 5. The sleeves 7 are sealed to the bosses 6 and to the flexible cover 8 to prevent the entrance of gas or liquid into the interior of the sleeves 7. The sleeves 7 may be welded to the bosses 6, or may be separate from the bosses 6, as illustrated at 7a in the exploded left portion of FIG. 1. The use of separate sleeves 7 permits the anode portions 1, 2, 3 and 4. to be assembled Or Welded together as a flat unit which occupies little space in shipping and allows the sleeves 7 to be shipped separately and assembled on the bosses 6 at the place of use. The sleeves 7 or 7a have been omitted from the right side of FIGS. 1 and 4 for better illustration of the assembly.

When the sleeves 7a are separate from the bosses 6, they are sealed to the bosses and to the flexible cell cover 8 with a fluid tight seal. The sleeves 7 or 7a may fit around the bosses 6 as illustrated in FIG. 2 and instead of screwing the copper lead-ins 5 into threaded titanium bosses 6, the lead-ins 5 may be screwed into holes 6a in the conductor bars 4 as illustrated in FIG. 2a and the sleeves 7 welded directly on the conductor bars 4.

In the assembled structure, the liquid and gas-proof titanium sleeves 7 or 7a surround and protect the copper lead-ins 5 from the corrosive conditions inside the cell.

As illustrated in FIGS. 4 and 5, the working faces 2 of the anodes A may be formed of round, square or other shaped rods 2a, welded at 9 to the secondary conducting bars 3 and providing with an electrically conducting electrocatalytic coating.

In use, a plurality of dimensionally stable metal anodes, such as described above, are suspended in the trough 10a of a flowing mercury cathode electrolysis cell 10, as indicated in FIG. 10, in which mercury flowing along the cell bottom 11 constitutes the cathode of the cell and the electrolysis gap is formed between the working faces of the anodes A and the flowing mercury cathode. The cell trough 10a slopes from end to end, so that the mercury flows by gravity along the cell bottom and the electrolyte is usually introduced into the upper end of the cell and discharged at the lower end, so that it flows concurrently with the mercury while the cell gases released at the anodes, rise through the meshes of the anodes and through the electrolyte above the working faces of the anodes to a gas release space at the top of the cell from which the gas flows through an outlet 8a in the cell cover to the gas recovery system. When cells of this type are used for the production of chlorine, the electrolyte is a saturated solution of sodium chloride. Cells of this type are, however, used for the production of other electrolysis products and the reference to chlorine and sodium chloride brine herein is only for purposes of illustration. The slope of these cells may be from 025 to 15 or more.

A typically mercury cell in which the baffles of the present invention may be used is illustrated in outline in FIGS. 10, 11 and 12, in which many parts not necessary to the understanding of this invention have been omitted or illustrated only diagrammatically.

The cell illustrated consists of a trough 10a of steel over which the mercury cathode layer flows. The tops of each side and each end of the trough 10a has a flange 12 and the walls of the trough are protected from chemical attack by an insulating lining 13. The anodes A, illustrated in FIGS. 1 and 4, are suspended in the trough 10a by means of the copper lead-ins 5, which are connected to the positive bus bars 14 by means of nuts 15 screw threaded on the copper lead-ins 5.

The lead-ins 5 and anodes A are suspended and supported from a metal frame spider 16 which consists of transverse arms 17 mounted on a longitudinal beam 18. The transverse arms 17 are adjustably supported on posts 19 mounted on the top flange 12 of the cell trough or on separate supports at each side of the cell trough, so that the height of the spider 16 and of the anodes A supported therefrom may be adjusted relative to the cell trough. Eyes 20 are provided on the beam 18 so that an entire anode bank can be lifted from the cell trough when necessary. The anodes suspended from the lead-ins 5 are adjustably suspended from support bars 21, carried by the spider 16, by nuts 15 so that the entire anode bank or any individual anode may be adjusted within the cell trough. The flexible cell cover 8 made of sheet rubber or other sheet plastic permits this adjustment, and

is held on the cell trough by means of pressing bars 22 and removable clips 22a. A similar mercury cell with graphite anodes is shown in U.S. Pat. No. 2,958,635. The flexible cover 8 is sealed against the escape of gas around the lead-ins by nuts and flexible washers b.

-Brine feed pipies 23 feed brine or other electrolyte into the upper end 24 of the cell and also (if desired) into intermediate points along the cell.

Titanium or other valve metal bafile plates 25 are provided on the upstream side of several of the anodes A. These baflle plates may be mounted on the 3rd, 5th, 7th, 9th, 11th and 13th row of the anodes of a fourteen row anode cell, for example, or in any other position or on any other rows of anodes in a cell. The bafile plates essentially act as a series of dams, damming the flow of electrolyte on the upstream side of each dam and causing the electrolyte to flow under each dam, into the electrode gap, between the working faces of the anodes and the flowing mercury cathode, and upward through open spaces in the working faces of the anodes, as indicated by the arrows in FIGS. 1, 2, 3, 11, etc., to help sweep the gas bubbles from the working faces and prevent gas blanketing of the anodes.

'Upstream of each dam formed by a battle plate 25, the level of the electrolyte is raised, as indicated by the lines b, FIGS. 1, 4 and 10, and downstream of each dam a cavitation trough is formed in which the relative electrolyte level is lower, as indicated by the lines 0. The average electrolyte level is indicated by the line d. The lines b, c and d are only illustrative of the relative electrolyte levels which may in fact be higher or lower than indicated.

The damming of the electrolyte by the battles 25 increases the speed of flow through the electrolyte gaps, by the higher pressure of the higher electrolyte level upstream of each dam 25, and increases the upward flow of the electrolyte through the working faces of the anodes, to sweep the gas bubbles from the working faces of the anodes.

The bafiles prevents the electrolyte from by-passing the electrolyte gap in cells equipped with dimensionally stable anodes and provide rapid renewal of the electrolyte in the gap. As these cells are operated at considerably higher current density than the cells equipped with graphite anodes, rapid flow through the electrolyte gap and rapid renewal of the electrolyte in the gap provides higher efliciency in these cells.

The bafiles may be mounted at substantially right angles (90) to the working face of the anodes or may be mounted at an angle of approximately 30 to 90 to the working face as illustrated in FIG. 2a. When mounted at an acute angle to the working faces, the baffles act somewhat as a sluice or funnel to increase the rate of flow of the electrolyte through the interelectrodic gap.

The amount of electrolyte held on the upstream side of each bafile increases the overall volume of electrolyte in the cell, while the free escape of gas bubbles from beneath the working faces of the anodes, through the perforation therein keeps the electrolyte above the working faces in a high state of agitation and circulation within the cell to thereby keep the temperature of the electrolyte lower and to prevent differences in the temperature and composition of the electrolyte in various parts of the cell. In cells of this type, the electrolyte is usually cooled before introduction into the cell and is heated Within the cell by the electrolysis reaction taking place.

The use of bafiies with dimensionally stable anodes in mercury cells provides more uniform concentration and temperature of all the brine in each compartment created by the baffles including the interelectrodic gap and the surface of the cathode in the areas immediately adjacent to the baffle is swept by brine so that a lower production of mercury butter and a better current distribution is obtained.

The use of baflie plates on various types of mercury cells equipped with dimensionally stable anodes has shown an improvement in Faraday eificiency of 1% or more and the voltage on the cells has been reduced by millivolts in cells operating at 13 ka./m. current density.

The baffile 25 may be mounted on the anodes in variousways. In the embodiments of FIGS. 1, 2, 4, 6, 7 and 8, the baflles 25 are provided with mounting clips 25a having spring fingers 25b which slip over the conductor bars 4 and hold the baflies on the anodes. In FIG. 9, the bafiles 25 are provided with vertical spring clips 250 which slip over the titanium sleeves 7 or 7a surrounding the lead-ins 5 to hold the baffles on the anodes, the slots 25 fitting over the conductor bars 4. The bafiies may also be provided withoutwardly projecting ears 25d (FIG. 4 and 10) which rest on the flanges 12 of the cell trough below the cell cover 8 to hold the bafiles in position. The bafiles may also be welded to the ends of the conductor bars 4 or otherwise made integral with the anodes.

The lower edge of the baflles 25 end slightly above the electrolyte gap between the working faces of the anodes and the flowing mercury cathode, to promote the flow of electrolyte into and through the gap, and to give greater speed to the electrolyte flowing through the gap by virtue of the dammed pools of electrolyte upstream of each dam.

The bafiies 25 are preferably provided with a turned over lip or lips 26 at the top, which bear against the cell cover 8 and keep the cell cover from sagging and contacting the brine. A series of slots 27 provide openings through which anodic gas may flow to the gas outlet 8a, and through which electrolyte may overflow from pool to pool, in case the level of the electrolyte in any dammed portion rises above the level of the bottom of slots 27. The crimp 25a gives greater strength to the relatively thin titanium or tantalum sheets used to make the baffles.

While the use of battles on one particular form of dimensionally stable metal anode has been described, it will be understood that the battles may be used with other forms and designs of dimensionally stable anodes and in other types of mercury cells and that various modifications of the invention described herein may be made within the scope of the appended claims.

What is claimed is:

1. In a flowing mercury cathode electrolysis cell provided with a plurality of dimensionally stable metal anodes having open mesh working faces and an electrolysis gap between the anode faces and the mercury cathode adapted for the flow of the electrolyte to be electrolyzed through said gap, the improvement which comprises providing a plurality of battles upstream from at least some of the dimensionally stable metal anodes and extending upward from about the working face of the anode whereby the electrolyte volume in the cell is increased upstream of each baflle, providing secondary conducting bars attached to said working faces and primary conducting bars attached to said secondary conducting bars, said secondary conducting bars spacing the primary conducting bars from the anode working faces and providing 40 to 60% of open spaces in the total surface of the anode working faces, whereby gases released at the anode working faces are swept upwardly past said secondary and primary conducting bars and out of the electrolyte, and renewal of the electrolyte and removal of heat and gas bubbles from the electrolysis gap is accelerated.

2. The combination of claim 1, in which the bafiles are arranged on spaced rows of anodes.

3. The combination of claim 1, in which the baffles are removably supported on the anodes.

4. The combination of claim 3, in which the baffles are removably clipped on the anodes by spring clips.

5. The combination of claim 4, in which the baffles are clipped on conductor bars of the anodes by spring clips.

6. The combination of claim 1, in which the bafiles are welded on the anodes.

7. The combination of claim 1, in which the baflies are supported from the cell trough.

8. The combination of claim 1, in which the baffles are mounted at substantially a right angle to the working faces of the anodes.

9. The combination of claim 1, in which the baffies are mounted at an angle of substantially 30 to 90 to the working faces of the anodes.

10. The combination of claim 1, in which the cell has a flexible cell cover and the baffles extend to the cell cover and keep the cover from sagging into the electrolyte.

11. The combination of claim 10, in which the battles have a turned over top edge with openings to permit flow of gas and electrolyte through the top portion of the baffles.

12. The method of controlling the flow of electrolyte through a flowing mercury cathode electrolysis cell provided with a plurality of dimensionally stable anodes having the open mesh working faces having from 40 to 60% of open spaces in the total surface area of the anode working faces and primary conducting bars spaced from the working faces by secondary conducting bars, and an electrolysis gap between each anode working face and the mercury cathode which comprises passing an electrolyte into the electrolysis cell, through the electrolysis gaps and out of the cell, and providing bafiles upstream from at least some of the anodes whereby the electrolyte is dammed and forced through the electrolyte gap at a greater velocity and upward through the open mesh working faces and past said secondary and primary conducting bars to sweep the gas bubbles from the working face of the anodes and to increase the brine flow rate through the electrolysis gap and keep the electrolyte concentration and temperature gradient within the gap substantially the same as in the remainder of the cell.

References Cited UNITED STATES PATENTS 3,409,519 11/1968 'Gallone et al. 204-2l9 X 3,409,533 11/1968 Murayama et al. 204-219 FOREIGN PATENTS 1,203,361 8/1970 Great Britain 204-219 JOHN H. MACK, Primary Examiner D.. R. VALENTINE, Assistant Examiner US. Cl. X.R.

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