US3657098A

US3657098A - Bipolar electrolysis cells with mercury cathode and having novel amalgam splitting vessel

Info

Publication number: US3657098A
Application number: US795665*A
Authority: US
Inventors: Carl W Raetzsch; John F Van Hoozer; Hugh Cunningham
Original assignee: PPG Industries Inc
Current assignee: PPG Industries Inc
Priority date: 1964-11-12
Filing date: 1969-01-31
Publication date: 1972-04-18
Anticipated expiration: 1989-04-18

Abstract

Disclosed is a bipolar, mercury cathode, electrolytic cell for the electrolysis of brine. Mercury amalgam is removed from each individual cell through separate lines and fed to a mercury amalgam splitter. Mercury amalgam splitter contains a separate compartmentalized wheel for each inlet stream of amalgam. The compartmentalized wheel is caused to rotate and to drop the mercury from separate streams of different electrical potentials into a common mercury pool at a single potential. The mercury pool is electrically insulated from separate streams.

Description

United States Patent Raetzsch et al.

151 3,657,098 [451 Apr. 18, 1972 BIPOLAR ELECTROLYSIS CELLS WITH MERCURY CATHODE AND HAVING NOVEL AMALGAM SPLITTING VESSEL Carl W. Raetzsch; John F. Van Hoozer; Hugh Cunningham, all of Corpus Christi,

Inventors:

Tex.

Assignee: PPG Industries, Inc., Pittsburgh, Pa. Filed: Jan. 31, 1969 Appl. No.: 795,665

Related U.S. Application Data Division of Ser. No. 410,579, Nov. 12, 1964, abandoned.

U.S. Cl ..204/2l9, 204/220, 204/250,

204/268 Int. Cl. ..C22d 1/04, BOlk 3/00 Field of Search ..204/2l9, 220,250, 268

[56] References Cited UNITED STATES PATENTS 3,400,055 9/1968 Messner ..204/220 X Primary Examiner-John H. Mack Assistant Examiner-D. R. Valentine Attorney-Chisholm and Spencer [5 7] ABSTRACT Disclosed is a bipolar, mercury cathode, electrolytic cell for the electrolysis of brine. Mercury amalgam is removed from each individual cell through separate lines and fed to a mercury amalgam splitter. Mercury amalgam splitter contains a separate compartmentalized wheel for each inlet stream of amalgam. The compartmentalized wheel is caused to rotate and to drop the mercury from separate streams of different electrical potentials into a common mercury pool at a single potential. The mercury pool is electrically insulated from separate streams.

1 Claims, 12 Drawing Figures PATENTEDAPR 18 1912 sum 2 OF 9 INVENTORS CARL w. EAETZSCI'I Jul/N )5 WW 1100252, BY #06 CUNNINGHAM MAM! Arm/away PATENTEDAPRWIBYZ 3,657,098

SHEET 70F 9 zl 5 g 6 5 2 m 3 g V i 0 J I U FNIIO'IHQ i X INVENTOR.

CHRL W. fiAfiTZSCH JOHN F. VAN 1/00 zen, Q1 BY H H C NNINGHHM BIPOLAR ELECTROLYSIS CELLS WITH MERCURY CATI-IODE AND HAVING NOVEL AMALGAM SPLITTING VESSEL This application is a division of our copending application Ser. No. 410,579, filed Nov. 12, 1964, now abandoned.

The present invention relates to electrolytic cells. More particularly, the present invention relates to electrolytic cells for the electrolysis of alkali metal chloride solutions. Still more particularly, the present invention relates to electrolytic cells for the electrolysis of alkali metal chloride solutions of the flowing mercury cathode type. 1

In the manufacture of elemental chlorine and caustic soda by the electrolysis of alkali metal chloride solutions, it has become increasingly important that caustic soda of high purity be obtained during such electrolysis. This is particularly true with respect to caustic soda produced for use in the textile industry, and thus in recent years, demand for high grade, ironfree caustic soda has increased tremendously. Caustic soda with these qualifications can be made directly in electrolytic cells having a flowing mercury cathode. While diaphragm cell caustic can be purified to a satisfactory extent for use in the textile industry, purification procedures are costly and complicated, giving rise to an increased demand for caustic soda produced in the flowing mercury cathode cell where the need for such complicated and expensive purification systems are not existent. For this reason, the trend in the chlorine-alkali industry for the past several years has been to manufacture more and more chlorine and caustic soda in mercury cells as opposed to diaphragm cells.

Normally mercury cells operate at slightly higher voltages than diaphragm cells. This higher voltage is due in part to the fact that they are operated at high current densities. High current densities are employed to utilize the cell anodes to a maximum degree since they require a considerable quantity of floor space. Mercury cells require a flowing mercury cathode. Anodes are typically positioned above this cathode to provide an electrolytic surface for decomposing brine which is caused to flow between the anode and cathode. Thus, the minimum cell room floor space required for a given cell is at least equal to the area of the anode of the cell utilized. Since the cells themselves are relatively large in comparison to diaphragm cells, mercury cell installations often require excessively large cell room space in which to operate.

In accordance with the present invention, a novel electrolytic alkali metal-chlorine cell is provided which requires a minimum amount of floor space for successful operation and provides an extremely large electrolytic surface area for electrolysis to take place per unit area of floor space. None of the anode adjustments typically encountered in mercury cell operation are required with this cell. In addition, the cell may be operated at lower current densities than conventional mercury cells without suffering the penalty of excessive floor space requirements while achieving high productivity per cell. This, of course, reduces electrical energy consumption. Bus bar requirements for electrical connection to the cells of this invention are drastically reduced over those necessary for a conventional mercury cell circuit. Further, piping requirements for feed to the cell and removal of product are minimized.

For a more complete understanding of the present invention, reference is made to the accompanying drawings in which:

FIG. 1 represents a side elevation of the bipolar mercury cell of the instant invention showing an anode half cell, a cathode half cell, and an intermediate cell unit having an anode and a cathode disposed between the top half cell and the bottom half cell of the bipolar mercury cell shown.

FIG. 2 is a plan view, partially in perspective, with the cover broken away to show the anode member of the anode half cell and the cathode tray or surface of the intermediate cell unit positioned above the cathode of the bottom half cell, and indicating the flow of brine and mercury.

FIG. 3 is a cross-section of the cell of FIG. 2 taken along lines I-I of FIG. 2, the center section being partially omitted, showing the chlorine outlet and one modification of the anode attachment and electrical connection to the anode.

FIG. 4 is a cross-section of the cell taken along lines Il-II of FIG. 2 the center section being partially omitted, showing the anode half cell of the cell assembly, the cathode half cell of the cell assembly, and the intermediate cell unit, and showing in detail the mercury inlet and outlet and the relationship of the brine and the mercury within the cell.

FIG. 5 is a perspective view partially in section of the mercury inlet 29 of the bottom half cell of the cell assembly shown in FIG. 2.

FIG. 6 is a cross-section of the mercury feed splitter 15 shown in FIG. 1.

FIG. 7 is a cross-section of the amalgam splitter 35 of FIG. 1, taken along the mid line III-III of FIG. 1.

FIG. 8 is a section of the amalgam splitter 35 of FIG. I taken along lines IV-IV showing the details of the lining of the splitter.

FIG. 9 is a cross'section of the amalgam denuder 37 of FIG. 1, taken along the mid line V-V.

FIG. 10 is a cross-section of the cell of FIG. 2 with the center partially omitted taken along the line I-I, and having a further embodiment of the anode support member of the cell in lieu of the support shown in FIG. 2.

FIG. 11 is a cross-section along lines II-II of the cell of FIG. 2 with the center partially omitted and showing the anode support modification of FIG. 10 in lieu of the anode support member of FIG. 2.

FIG. 12 is a further embodiment of a mercury splitter which may be used in lieu of splitter 15 shown in FIG. 1.

Turning now to the drawings, with particular reference to FIGS. 1, 2, 3, and 4, there is shown a bipolar flowing mercury cathode alkali-chlorine cell in which, for illustrative purposes, two cells have been shown. As seen in FIG. 1, the cells are composed of an upper anode containing cover member on anode half cell 1 and a cathode containing bottom member on cathode half cell 8. Intermediate the cover member 1 and the bottom member 8 is disposed a bipolar cell unit generally indicated as 7 which contains on its upper surface a tray 9 for the reception of the mercury cathode and on its bottom side an anode 10 to be used in conjunction with the mercury contained in tray 11 of the bottom member 8. The cover member 1 is lined with a suitable insulating material such as rubber and the lining 6 protects the underside of the cover 1 and electrically insulates it partially from the cell unit 7 placed below it. The cover member 1 is composed of a back up plate 12 of steel or other suitable electrically conductive structural metal. The backer plate 12a contains tapped holes 18 and 18 (See FIG. 3) which are plugged on their upper surface with plugs 19 and 19' and contain within the holes bolts 34 and 34'. The

plugs

19 and 19 may be omitted it desired. Operation of the cell without plugs 19 and 19' has been accomplished and some slight improvement in electrical conductivity observed with no deleterious effects encountered. In such an operation the bolts become covered with mercury which apparently assists in conducting current through the bolts from the cell above. These bolts are affixed to and hold in place against the back plate 12a a titanium sheathed electrically conductive rod member 13a preferably constructed of copper or aluminum. The titanium sheath 14 is intimately afirxed to the rod member by suitable binding material or mechanically attached by compression against the rod so that maximum electrical conductivity between the two metals is realized. The anode 17 of the cell cover 1 is affixed to the titanium sheath 14 such as by welding and when in place is positioned above the tray 9 of the cell unit 7. Affixed to the outer surface of the cover member I is a suitable bus-connector 2 which, during operation of the cell, is suitably bolted to the cell room bus bars (not shown). Several orifices are shown in the cover member of the cell, which orifices are utilized for the performance of certain functions. Thus, in FIG. 2, two orifices 4 and 4 are shown which are utilized as chlorine gas collection points or conduits. Orifices 5 and 5 are utilized for the introduction of brine into the cell, as indicated in FIGS. land 2.

In the over-all operation of the cell, as seen looking at FIG. 1, mercury is introduced into the cell by dropping it into the mercury splitting device 15. The mercury splitting device contains a rotating member generally indicated at which rotates on a vertical axis and has a nozzle member 21 attached on the undersurface thereof which constantly emits a flowing stream of mercury. As the device rotates, it passes a dividing member 22 and the mercury is divided into two separate reservoirs 23 and 24. The contents of reservoir 23 are fed through line 25 to a mercury distributor 27. The contents of reservoir 24 are fed through line 26 to a mercury distributor 29. The mercury passes from

distributors

27 and 29 across the faces of the trays 9 and 11 respectively (See FIG. 4) and flows to the opposite end of the cell. Brine is continuously introduced through

brine feed inlets

5 and 5 during this operation and passes from the upper tray 9 to the lower tray 11 in a manner to be described hereinafter. Current is applied to the cell and electrolysis takes place between the face of the anodes 17 and 10 and the surface of the mercury cathode flowing across the cell in trays 9 and 11. Elemental chlorine formed during the electrolysis is removed from the cell through chlorine outlets 4 and 4 in a manner to be described hereinafter. Sodium-mercury amalgam is formed during the electrolysis on the flowing mercury cathode as it passes across the cell and is collected in the cell in the collection sumps 30 and 31. Thus, the contents of tray 11 collect in sump 31 and those of tray 9 in sump 30. The amalgam in sump 30 is introduced into an amalgam splitter 35 through line 32. The amalgam in sump 31 is introduced into splitter 35 through line 33. After passing through the splitter, the amalgam is passed through line 36 to the mercury denuder 37. In the denuder 37 the amalgam is contacted with water introduced through line 38, and the caustic soda product is removed through line 39. Hydrogen evolved during the denuding operation is removed from the denuder through line 40. The denuded mercury is removed through line 41 and is pumped by means of pump 43 through line 41' to the mercury feed splitter 15, and the process is repeated. Depleted brine is removed from the cell through line 42 after having collected in sump 44. It is, of course, to be understood that the depleted brine removed from the cell may be resaturated and utilized once more in the cell in accordance with conventional practices in the art. The cell is supported on posts 45 and 46 which are anchored to the floor of the cell room on footers 47 and 48.

In accordance with the teachings of this invention, the mercury flows in a longitudinal direction across the cell, as shown in FIG. 2. Preferably the brine flows tangentially to the flow of mercury in the first cell unit to a brine down-comer 49. This brine then reverses its flow on the next lower tray and flows in the opposite direction, but still tangential to the flow of mercury in that tray. The mercury flow in all the trays is preferably in the same direction. Thus, as shown in FIGS. 2 and 5, the mercury introduced through

lines

25 and 26 enters

mercury feed distributors

27 and 29, respectively. As shown in more detail in FIG. 5, which is an enlarged perspective view of the mercury feed distributor 29, this unit contains an elongated slot 50 on its side so that the mercury, when it reaches the level of the slot, flows out of the distributor and across the tray 11 associated with that distributor. An identical configuration of the mercury distributor is contained in the unit 27 of FIG. 2 so that the slotted device constantly provides a film of mercury across the tray 9 with which that distributor is associated. As will be understood by those skilled in the art, the trays themselves are tilted downwardly from the mercury feed point to the collection point or sumps 30 and 31 so that the mercury will flow by gravity from the feed point to the sumps or collection points 30 and 31. Located on the side of the trays between each cell tray are

housings

51, 52, 53, and 54. Contained in each of these housings is an adjusting screw element 55 which rests on an insulated member 56 of the unit immediately below. Suitable electrical insulation, such as micarta, may be employed for this purpose so long as it provides adequate insulation to prevent shorting caused by the differences in potential between the various cell units associated with each of the housing members. These adjustable screw elements are utilized to provide a proper slope for the flowing mercury between the various cell units employed and to provide a means for adjusting the level of the mercury across the width of the cell to thereby insure uniform distribution of mercury across the width of the cell.

Turning now to FIG. 3, the details of the construction and the electrical connection to the cell anodes can be readily seen. In FIG. 3 there is shown the cell cover member generally indicated as 1 which shows two drilled holes 18 and 18' in the back up plate 12 suitably plugged with

plug members

19 and 19. Located immediately below the plug are

bolt elements

34 and 34 which have affixed thereto rod members 13 and 13', preferably constructed of copper and sheathed in a titanium tube or sheath l4 and 14' respectively. The copper rods encased in titanium are sheaths curved at the bottom into a fiat member which is welded to a platinized titanium anode member 17. Thus, the titanium encased copper rods serve as support members for the anode 17 as well as means for distributing current thereto. The mercury contained within the cell, generally indicated by the numeral 38, flows beneath the anode member 17 on a steel tray 9 which, at its peripheral edges, is bonded to a rubber lining 58 of the cell unit 7. The base member 12a of the tray 9 serves as the back plate for the next anode and conducts the electrical current from the cathode of the first cell to the current distributor 13a of the next adjacent cell unit which is located immediately below it and like rod 13 is also encased in a titanium sheath. The insulation 58 and the presence of gasket 60 serves to protect the cell above from shorting out with the cell below. The chlorine from the bottom cell rises up through the brine down-comer 49 as brine from the upper tray falls downwardly through the down-comer 49 in countercurrent contact therewith. Gaseous chlorine ultimately escapes from the cell through outlet 4 located in the cover member 1 of the cell. While in the drawing of FIG. 3 only a single unit of attachment to the cell anode is shown, it is, of course, understood that a plurality of these units extend across the cell to provide adequate support for the flat platinized titanium anode and prevent it from warping during operation. A gasket 59 is placed between the cover member or upper anode containing member of the cell and the tray 9, and a similar gasket 60 is located between the cell unit 7 and the bottom 8 of the cell. These gaskets serve to insulate and seal one cell from the other during operation. To the side of the cell and underneath the adjusting screw member 55 is a nut 61 which is affixed in place when proper adjustment of the slope of the cell trays has been made.

Turning to FIG. 4, there is shown the relationship of the electrical support members or rods 13 to the anodes 17, as well as the relationship of rods 13a to the cell unit anode 10. In addition, the positioning of the

mercury feed reservoirs

27 and 29 and the mercury-amalgam sumps 30 and 31 of the cell are also depicted. The

mercury cell distributors

27 and 29 are bolted to the ends of each tray by suitable tapped bore holes 62 in the cell trays 9 and 11 respectively. These tapped bore holes 62 are provided with bolt elements 64 and the entire units are thus bolted to the cell trays 9 and 11.

As shown in FIGS. 4 and 5, the mercury distributor 29 consists of two

side members

66 and 67; a bottom member 68 and a top member 69 which define a hollow cavity 70. The side member 66 which abuts against the cell tray 11 is slotted at 50 on its long axis so as to be open to the tray 11 with which this distributor 29 is associated. The distributor 29 is also provided with a slotted channel 71 in the vertical direction which channel 71 communicates with the long axis slot 50 and a cavity 72 at the bottom end. Cavity 72 runs parallel to slot 50 along the long axis of the distributor 29. Thus, mercury introduced through line 26 into the cavity 72 traversing the long axis of the distributor 29 rises through the vertical slot or channel 71 to the chamber 70 and from there, by virtue of the slot 50 communicating with the tray 11, mercury is introduced into the cell tray 11 and flows across the tray and the face of the anode placed above the tray. If desired, cavity or channel 72 may be provided with a plurality of drilled holes in lieu of the vertical channel 71 so that a plurality of spaced channels are provided instead of a unitary slot. Similarly channel 72 may be a pipe having a plurality of openings on its upper surface at spaced intervals which communicate with a plurality of spaced vertical holes. Such spaced hole would of course terminate in the chamber 70 in this case as does the vertical slot 71. The mercury, as mercury amalgam, as it reaches the opposite end of the cell, enters the sump 31 formed by the side 73, top member 74, and bottom member 76. The mercury, as it enters this chamber, settles through a vertical slot 77 into a small reservoir member 78 and is ultimately removed from the cell. This mercury collection or amalgam collection member or sump 31 is affixed to the side of the cell as sump 30 is attached. Sump 30 is provided with a tapped bore hole 79 located in the tray 9 and by utilizing suitable bolts 80 is affixed to tray 9. The mercury distributor 27 is of identical construction to the reservoir 29 hereinabove described but as will be obvious, it is associated with tray 9. Similarly, the sump 30 is identical in construction to the sump 31 described above but is associated with tray 9.

Turning now to FIGS. 10 and 11, there is shown another modification of the anode 17 of the cell cover and anode 10 of the cell unit in which the electrical connection and the supporting of the anode is accomplished by means of metal plates 81 in lieu of the titanium sheathed copper rods 13 of FIGS. 3 and 4. In this modification, titanium lugs 82 are affixed to the

backing plates

12 and 12a of the anodes of the cell cover 1 and cell unit 7 respectively, and have attached to them through a suitable screw member 83 a plurality of

metal plates

81 and 81 which are suitably welded to the upper portion of the anodes 17 and 10. A plurality of these

metal plates

81 and 81 are placed across the back of the anodes 17 and 10 to provide suitable electrical distribution to the face of the anodes 17 and 10 to prevent these anodes from warping during cell operation. The relationship of the

brine feed lines

5 and 5 chlorine outlets 4 and 4, and mercury feed lines and 26 remain the same in this modification, the essential difference between this modification and those shown in FIGS. 3 and 4 being in the electrical connection to the anodes 17 and 10. The structure of the

distributors

27 and 29, sumps and 31, and the trays 9 and 11 and all other equipment is essentially the same as described with reference to the embodiment shown in FIGS. 3 and 4.

Turning now to FIG. 6, the mercury splitter 15 of FIG. 1 is shown in cross-sectional detail. This splitting device 15 is comprised of a mercury inlet tube 84 which fills a cavity 85 formed in the center of the device and which rotates around shaft member 86. Shaft 86 is positioned in a suitable housing 87 and held firm by washer 88 and nut 89. A depending nozzle 21 communicates through a channel 91 with the cavity 85. The nozzle 21 rotates in a chamber 90 formed by the sides 92 and 93, and bottom 94 of the splitter 15. The bottom member 94 of the container is divided by a member 22 which rises vertically in the center of the splitter 15 and serves to equally divide mercury entering through the nozzle 21 between chambers 90a and 90b. All portions of the splitter 15 which are in contact with the mercury are rubber covered by rubber linings to provide adequate insulation and assist in breaking the electrical current between the mercury located in each of the individual sections of the splitter 15. The

outlets

25 and 26 of the splitter 15 feed the two individual cells shown in FIG. 1 through the

distributor members

27 and 29. While only two feed units are shown feeding two cells in this figure and in FIG. 1, it is, or course, to be understood that a multiplicity of these cells may be employed, in which case the splitter 15 would be divided into a sufficient number of individual feed units to provide an individual mercury cell feed for each individual mercury cell employed.

Turning to FIGS. 7 and 8, the sodium-mercury amalgam leaving the electrolytic cell is introduced into the splitting device 35 of FIG. 1. This device is shown in two sectional views in FIGS. 7 and 8. In FIG. 7, sodium-mercury amalgam leaving the cell through line 32 enters unit 35 and is dropped into one of the compartments 96 of the

compartmented wheels

97 and 97. As each compartment 96 becomes filled, on the principle of the water-wheel, the mercury amalgam pushes the water-wheels in a clockwise direction, thus electrically splitting it and dropping it into the sump 98, from which it is removed via outlet 36 and introduced into the mercury amalgam denuder 37.

While the wheel 97 can operate on a water-wheel principle, provision may be made to drive it by coupling shaft member to a suitable motor and belt arrangement. As with the mercury splitter 15, the number of compartmented wheels employed will depend on the number of complete cells employed in the completed cell. FIG. 12 shows a further embodiment of the mercury splitter 15 in which there is provided two

sumps

106 and 107. Sump 106 is associated with a wheel 108 and sump 107 with a wheel 109. Wheel 108 is fed through pipe 114 and wheel 109 through pipe 115. The sumps are separated by a wall member 110 and this wall member 110 as well as the walls of the splitter 35 are lined with a rubber lining 111 for insulation purposes. Each sump is provided with an

outlet

112 and 113 for feed to the

mercury reservoirs

27 and 29. Discharge is accomplished by simple overflow into the

open tubes

112 and 113. These open tubes would feed mercury to

lines

25 and 26 for ultimate feed to

reservoirs

27 and 29 respectively. If desired, of course, bottom feeding can be employed rather than an overflow type as shown in FIG. 12. The mercury fed to

pipes

114 and 115 is typically fed from a holding tank.(not shown) provided with two discharge orifices located on the bottom or sides, one orifice being connected to each of

pipes

114 and 115. As with the splitter 15, this device will be provided with sumps and wheels corresponding to the number of complete cells used in the cell assembly.

The denuder 37 shown in FIG. 9 in cross-section is comprised of a steel shell 99 having a perforated baffle 100 located at the bottom thereof and a water inlet 38. The bottom member 101 of the denuder is provided with an outlet 41 for the removal of denuded mercury. In the upper portion of the denuder is located an outlet 39 for the removal of caustic soda. Sodium amalgam is introduced through pipe 36 to a baffle member 102 located in the upper portion of the denuder where it flows downwardly through a perforated plate member 103 and in contact with graphite particles 104 located between perforated baffle 100 and the baffle 102. Hydrogen escapes from the cell through a suitable outlet 40, not shown in FIG. 9.

While the invention has been described with reference to the formation of chlorine and sodium-mercury amalgam from brine, it is of course possible to utilize the instant cell to manufacture other alkali metal hydroxides from the corresponding alkali metal chloride solution. Thus, KCl can be readily electrolyzed to produce chlorine and potassium-mercury amalgam and ultimately potassium hydroxide. Further, while platinum plated titanium has been shown as the preferred anode material, other noble metals may be utilized as the anode surface and can be placed upon other base materials such as tantalum.

While the invention has been described with reference to certain specific and illustrated embodiments, it is not intended that it be so limited except insofar as appears in the accompanying claims.

We claim:

1. A bipolar electrolytic chlorine cell having a series of bipolar cell units, means to flow mercury streams along the cathodic tops of said units, means to impress an electric potential across the series so that the several streams of mercury are at different electric potentials, separate collection means to collect the mercury amalgam at the end of each cell box, individual means to feed the collected mercury amalgam from said collection means to individual inlets in a mercury amalgam splitting vessel, said vessel having a separate compartmentalized wheel for receiving mercury amalgam from each of said inlets positioned above the bottom of said vessel, means for turning said compartmentalized wheels to thereby drop said amalgam from said wheels to the bottom of said vessel, and means for removing mercury amalgam from the bottom of said vessel.