US3475313A - Electrolytic cell for chlorate manufacture - Google Patents

Description

Oct. 28, 1969 e. o. WESTERLUND 3,475,313

ELECTROLYTIC CELL FOR CHLORATE MANUFACTURE FiledJuly 6, 1964 6 Sheets-Sheet l STORAGE HEAT EXCHANGER HEADER REACTOR DEGASSIFIER REACTOR ELECTROLYHC ceu.

FIG

ln uenlzor buae, wes evluno E/Jw 10M, MQLM pforneys 1969 'G. o. WESTERLUND ELECTROLYTIC CELL FOR CHLORATE MANUFACTURE Filed July 6, 1964 6 Sheets-Sheet 2 In uenfor i e. lt lsier/und \oct- 1969 G. o. WESTERLUND 3,475,313

ELECTROLYTIC CELL FOR CHLORATE MANUFACTURE FiledJuly 6, 1964 6 Sheets-Sheet 3 flue/2AM Gb'Me (Q h/esvem/ nd Oct. 3. 1969 G. o. WESTERLUND 3,475,313

ELECTROLYTIC CELL FOR CHLORATE MANUFACTURE Filed July 6, 1964 6 Sheets-Sheet 4 v L5 i2 58 E 9 3 Ln m m o m Inventor- /7 o neys Oct. 28, 1969 Q Q WESTERLUND 35475313 ELECTROLYTIC CELL FOR CHLORATE MANUFACTURE Filed July 6, 1964 6 Sheets-Sheet 5 36 82 i 'x l/ A l/l/l /l/i/l/lll J84 r g] 93 2 85 i! 79 86 \I FIG. 5

FIG.6

no FIG.7

fm/enlror Oct. 28, 1969 G. O. WESTERLUND ELECTROLYTIC CELL FOR CHLORATE MANUFACTURE Filed July 6, 1964 S SheetS-Sheet 6 m\ gm fm/enl c @Bflqa WesLer/un m-i-ome ys United States Patent 3,475,313 ELECTROLYTIC CELL FOR CHLORATE MANUFACTURE Giithe Oscar Westerlund, Vancouver, British Columbia,

Canada, assignor to Chemech Engineering Ltd., Vancouver, British Columbia, Canada Filed July 6, 1964, Ser. No. 380,518 Claims priority, application Canada, July 3, 1964,

Int. Cl. C01b 11 /26; B01k 1/60 US. Cl. 204-234 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the production of metal chlorates, particularly alkali metal chlorates. It relates, more specifically, to an improved electrolytic cell and method of operating such cell. The present invention also relates to an improved electrolysis apparatus and improved electrolysis process. The present invention also relates to novel means for providing spacers and seals for the electrodes.

Known electrolytic cells for the production of metal chlorates and rising carbon electrodes have certain disadvantages. Monopolar cells inherently have many power connections and electrolyte branches, high electrode stub losses, high voltage drop and high power loss. Furthermore, many units are' required in commercial production and much larger building spaces are required.

Bipolar electrolytic cells designed to avoid many of the above difficulties have brought about one major problem. Such cells are designed to operate with a gas phase above the level of the liquid and below the cell cover. The electrical connections to the graphite electrode is situated in this phase and accordingly, the danger of sparks occurring, with the resultant explosion is always present.

One feature of the present invention is the provision of a bipolar electrolytic cell in which the danger of sparkinduced explosion is essentially avoided.

Another feature of the present invention is the provision of a bipolar electrolytic cell in which electrode wear or disintegration is essentially uniform over the active surface of the electrodes.

Another feature of the present invention is the provision of a bipolar electrolytic cell in which local overheating and differential rates of reaction are essentially minimized.

Another feature of this invention is the provision of a bipolar electrolytic cell in which improved current elliciencies and minimized current leakage from cell to cell are attained.

Another feature of the present invention is the provision of an improved electrolysis apparatus including a bipolar electrolytic cell.

A further feature of the present invention is the provision of an improved electrolysis procedure.

By one aspect of the present invention there is provided an electrolytic metal chlorate cell comprising a cell box including a closure; a plurality of bipolar electrodes positioned in said box and constructed and arranged to 3,475,313 Patented Oct. 28, 1969 conduct electric current through said box and through a circulating electrolyte; means associated with said closure providing a distribution means for electrolyte inlet; means inhibiting the accumulation of gaseous products of electrolysis within a zone adjacent said closure; and means associated with, but external of, said closure providing an outlet for said electrolyte and gaseous products of said electrolysis and for at least partial separation of said electrolyte from said gaseous products of said electrolysis.

By another aspect of the present invention there is provided an electrolytic metal chlorate cell comprising a cell box including a closure; a plurality of bipolar electrodes positioned in said box and constructed and arranged to conduct electric current through cell box and through a circulating electrolyte; inlet means to said box; outlet means from said box; and circulation means provided by combined enforced external pumping means and internal pumping action due to the construction and arrangement of said bipolar electrodes and the rising gaseous products of said electrolysis.

By yet another aspect of this invention there is provided an electrolytic metal chlorate cell comprising: a cell box including a closure; a plurality of groups of bipolar electrodes positioned in said box and so constructed and arranged to conduct electric current through said box and through a circulating electrolyte; means spacing said electrodes from the bottom of said box and from said closure; current leakage preventing fluid-tight seals between said closure and said spacing means, between said spacing means and an upper electrode of said group of electrodes, between adjacent electrodes in said group of electrodes, between a lower electrode of said group of electrodes and said spacing means, and between said spacing means and said bottom; inlet means to said cell; and outlet means from said cell.

By still another aspect of this invention there is provided an electrolytic metal chlorate cell comprising: a cell box including a closure; a plurality of groups of bipolar electrodes positioned in said box and so constructed and arranged to conduct electric current through said box and through a circulating electrolyte; electrical connection means provided by a platinized titanium electrode connected directly to said electrodes and arranged to be submerged within said electrolyte; means spacing said electrodes from the bottom of said box and from said closure; current leakage preventing fluid-tight seals between said closure and said spacing means, between said spacing means and an upper electrode of said group of electrodes, between adjacent electrodes in said group of electrodes, between a lower electrode of said group of electrodes and said spacing means, and between said spacing means and said bottom; inlet means to said cell; and outlet means from said cell.

By a still further aspect of this invention there is provided an electrolysis apparatus comprising: an enclosed bipolar electrolytic cell provided with inlet and outlet means; means associated with said outlet means providing at least a partial separation of the gaseous products of electrolysis from the eflluent electrolyte; vent means for said gases; means conducting said efliuent electrolyte to a reacting and degassifying chamber; gaseous vent means on said reacting and degassifying chamber; recycle means for conducting efliuent from said reacting and degassifying chamber to a heat exchanger; means conducting the effluent from said heat exchanger to a header tank and reacting chamber; and means conducting effluent from said header tank and reacting chamber together with fresh electrolyte to said enclosed bipolar electrolyte. This aspect of this invention provides as a subsidiary aspect, the inclusion of a branch line from said reacting and degassifying chamber to a filter; of conduit means from said filter; and storage means for eflluent from said filter.

By another aspect of this invention there is provided an electrolysis procedure comprising effecting an electrolysis reaction of an aqueous solution of a metal halide; effecting a partial separation of the liquid products of said electrolysis from the gaseous products of said electrolysis, effecting a degassification and reaction between primary products of said electrolysis, adjusting the temperature of the products of reaction, effecting a further reaction of said products of reaction and recycling a major amount of said reaction products to said electrolysis reaction. This aspect of this invention provides as a subsidiary aspect the additional step of withdrawing and storing a minor proportion of said reaction products.

The present invention, thus, is concerned with the wellknown procedure for the production of metal chlorates, particularly alkali metal chlorates. It is well-known that alkali metal chlorates may be prepared by electrolysis of an aqueous solution of an alkali metal chloride. In this process elemental chlorine is evolved at the anode and alkali metal hydroxide at the cathode. However, in the conventional cells, since there is no diaphragm between the cathode and the anode, the primary products of the electrolysis react to form the alkali metal chlorate.

The simplified reaction in the aforesaid electrolysis may be summarized as:

MtCl+ 3H O+6 Faradays MtClO 3H wherein Mt is a metal.

The main reactions in the electrolytic preparation of the metal chlorate from the metal chloride may be represented as follows:

PRIMARY REACTIONS (A) At the anode:

2MtCl 2Mt++2Cl- Cl +2e-+2Na+ (l) (B) At the cathode:

2H O22H++2OH-+2e- H +2OH (2) SECONDARY REACTIONS Cl +OH- ClOH+Cl (3) ClOH2H +OCl- (D) 2ClOH+ClO- C1O3 201- (5) UNDESIRABLE SIDE REACTIONS (E) Oxidation at the anode:

HClO+H O O +3H+-|-Cl--|-2e- (6) 2H O O +4H++4e- (7) (F) Reduction at the cathode:

ClO+H O+2e Cl-+2OH- (8) ClO +3H O+6e Cl+6OH (9) (G) Hypochlorite attack by nascent hydrogen:

ClO+2H H O+Cl (10) (H) Breakdown reactions in sunlight:

2HClO 2HCl+O (l1) HClO+HCl H O+C1 (12) (I) Breakdown reaction in the presence of catalysts: 2MtClO 2MtCl+O (13) (J) Breakdown due to vapor pressure:

C1 (in solution)- Cl (gaseous) (14) It is manifest that conditions within the electrolysis system in general and in the electrolytic cell in particular must be carefully controlled in order to obtain the optimum desired final product and to obtain a high current efficiency. As has been noted before, the present electrolytic cell provides the following novel features which may be used either singly or in various permutations and combinations:

(i) means associated with the cell closure providing a distribution means for electrolyte inlet together with means inhibiting the accumulation of gaseous products of electrolysis within a zone adjacent the closure, coupled with means associated with, but external of, the closure providing an outlet for the electrolyte and the gaseous products of the electrolysis and for at least partially separating the liquid electrolyte from the gaseous products of the electrolysis.

This provides an important feature of the present invention in that it prevents the electrolyte from proceeding directly to the cell. It is desirable to proceed in this manner in order to prevent high current leakage. This is provided by a hanging distribution channel for the inlet of fresh electrolyte to the cell and for the outlet of the products of the electrolysis.

In addition, the cell is specifically and expressly filled with the electrolyte. Operation of the cell should be carried out at a high velocity throughput so that the gaseous products of the electrolysis is retained in the electrolyte as finely divided bubbles. Such electrolyte liquor with the gas bubbles therein is permitted to enter a small confined space associated with but external of the cell cover where the gas bubbles separate. As regards to this small confined space, the cross-sectional area should be slightly larger than necessary in order to prevent foaming when the gas escapes.

(ii) circulation means provided by combined enforced external pumping means and internal pumping action due to the construction and arrangement of the bipolar electrodes and the rising gaseous products of the electrolysis.

It is important to provide a high circulation rate in the cell in order to prevent local high concentrations of hypochlorite which both decomposes to chlorides (see Equation 8) and also corrodes the graphite. The use of the inherent internal circulation alone by means of an external circulation tank is unsatisfactory while the use of an external pump is unsuitable due to the high capital cost and high cost of power for driving the pumps. This aspect of the present invention combines enforced external pumping action with the natural pumping action due to rising gases, coupled with the directed internal circulation due to the particular construction and arrangement of the bipolar electrodes and the hanging distributor.

(iii) means spacing the bipolar electrodes from the bottom of the cell and from the cell closure, current leakage preventing fluid tight means between the closure and the spacing means, between the spacing means and the upper bipolar electrode, between adjacent bipolar electrodes, between the bottom bipolar electrode and the spacing means and between the spacing means and the bottom.

It is important to provide these seals in order to provide improved circulation as previously noted. This results in uniform electrode wear or disintegration. Spalling of the bipolar electrodes and uneven Wear are minimized and, as a result, local overheating and different rates or reaction are minimized. Improved current efficiencies are attained by cquallizing electrolyte composition, pH and temperature throughout the cell. Harmful and undesirable side reactions are reduced and positively controlled. The seals used as cell dividers reduce current leakage from cell to cell.

The actual construction of the seal and dividers will be described hereinafter.

(iv) electrical connections provided by a platinized titanium connector connected directly to the monopolar electrodes and arranged to be submerged Within the electrolyte.

The power connectors should have a core of a high conductivity metal in order to minimize power losses. A suitable metal for the connector is titanium. In addition, the possibility of having poor contacts between the connector and the electrode is minimized by the fact that the platinized coatings are resistant to oxidation and reaction with the cell liquor. Using this type of connectors, cell gas explosions which might occur when the electrodes extend through the gas zone due to electrical sparks at the liquor surface and/ or cover are, of course, eliminated.

Further features of the present invention will be described with reference to the accompanying drawings, in which FIGURE 1 is a schematic flow diagram of the process and apparatus of the present invention;

FIGURE 2 is a central longitudinal side cross-section of one embodiment of the electrolytic cell of the present invention;

FIGURE 3 is a top plan view of the electrolytic cell of FIGURE 2 with the cover removed;

FIGURE 4 is a central longitudinal side cross-section of one embodiment of the electrolytic cell of the present invention;

FIGURE 5 is a central longitudinal cross-section of a series of top fluid tight seals and dividers according to the present invention;

FIGURE 6 is a central longitudinal cross-section of a further series of top fluid tight seals and dividers according to the present invention;

FIGURE 7 is a central longitudinal cross-section of a typical fluid tight seal between a divider and an upper electrode;

FIGURE 8 is a central longitudinal cross-section of a typical fluid tight seal between adjacent electrodes;

FIGURE 9 is a central longitudinal cross-section of a typical fluid tight seal between the bottom of the cell and a lower divider;

FIGURE 10 is a typical packing box assembly for the electrode connectors; and

FIGURE 11 is an isometric view of the central well equipped with side channels.

Referring to FIGURE 1, electrolyte, consisting of fresh electrolyte from line 11 and recycled electrolyte from line 12 enters the electrolytic cell 13 through inlet header 14. Electrolysis proceeds, and effluent, consisting of C1 Na+, H 0H1 ClOH, Cl, H+, and OCl" leaves via outlet header to T-separator 15. Entrained gases, permitted to separate in T-separator 15 and which consist of H H O (vapor), 0 CO and C1 leave via vent line 16. The eflluent liquor passes from T-separator 15 via line 17 to degassifier-reactor 18.

The cross-sectional area of the degassifier-reactor 18 is specifically designed and is of such a size that the liquor velocity is reduced to such an extent that optimum separation of the entrained gases takes place without short circuiting through the tank, which would result from too low a liquor velocity. The velocity, on the other hand, must be suflicient to utilize the entire vessel but not too rapid to inhibit the expulsion of the entrained gases. The optimum velocity is a function of the apparent density of the liquor, which, in turn, is dependent on the amount of entrained gases and the bubble size. It has been found that a liquor velocity of about 2 ft./ min. can separate more than 95% of the entrapped gases.

The degassifier-reactor 18 also is for the purpose of permitting the reaction centration of ClOH and C10" present in the liquor which in turn is directly related to the current density. Thus, it

was found that to yield a current efficiency of greater than with a constant recirculation of liquor and a pH of 6.5, the current density should be less than 4.5 amps/litre at 50 C. or less than 3 amps/litre at 35 C. The current density (in amps/litre) is the main determining factor in calculating the reacting chamber volume. The retention time, on the other hand, is dependent on the rate of the liquor circulation, as well as on the volume of the reaction vessel. For convenience, the reaction vessel is divided into two vessels, i.e. degassifier-reactor 18 and header-reactor 19, which will be described hereinafter.

The particular arrangement of the degassifier-reactor 18 enables it to be used as a liquor seal for the cell gases carried off through line 16. In addition, the degassifierreactor 18 is provided with a vent line 20 where gases have been released from the liquor. These gases are combined with the gases in line 16 and may be vented as waste, or may be oxidized, as will be described hereinafter.

The liquor entering the degassifier-reactor 18, in a preferred embodiment, has a temperature of about 45 C. As a result of the reaction therein, the eflluent liquor has a temperature of about 45.5 C. The eflluent liquor passes via line 21 to pump 22 to the heat exchanger 23 where it is again cooled to about 45 C. The pump provides the enforced circulation to overcome the drag of the heat exchanger. The eflluent from the heat exchange 23 passes via line 24 to the header-reactor 19.

Header-reactor 19 is a second reacting chamber where Equation 5 takes place. Care is taken to avoid shortcircuiting and channelling to maintain a constant reaction or retention time. It is important to control precisely the temperature in header-reactor 19. The higher the temperature, the lower the volume of the header-reactor 19, with its attendant upsetting of the retention time. A longer retention time favors the desirable reaction It is also important to minimize the concentration of the hypochlorite for if itis too high it will decompose, as shown in Equation 8.

In addition, the pH must be less than 7 and preferably between about 5 and 7. At a pH of 6.8, the optimum reaction of two moles of HClO to 1 mole of NaOCl takes place.

It is also noted that the header-reader 19 serves, in addition to being a reaction vessel, as a header and pipeline for the recycle of the liquor.

From header-reactor 19, the liquor proceeds via line 12 to the cell 13.

A branch line 25 leads from degassifier-reactor 18 to a filter 26, where particles of graphite are filtered out, and then through line 27 to a chlorate storage tank 28. It is preferred that a recycle rate of from 200:1 to 500:1 takes place, i.e. 200 to 500 parts recycled for each part to storage.

It is desired to oxidize the gases from lines 16 and 20, it is noted that the gases have the following ranges of proportions:

Percent by volume Hydrogen, H 89-94 Water vapor, H O 3-6 Oxygen, O 2-4 Carbon dioxide, CO 0.3-0.6 Chlorine, C1 0.2-1

In combusting the gasses the following reaction will take place:

H +Cl 2HCl (producing hydrogen chloride) ZH +O 2H O (producing water vapor) The hydrogen chloride is recovered as hydrochloric acid by scrubbing with water. The excess hydrogen is recovered by absorbing the CO in an absorbent and then dehydrating the residual gas.

It is generally known that the oxygen content of the cell gas decreases with lower pH of electrolyte simultaneously as chloride losses increases. Using a combustion chamber for recovery of chlorine losses as hydrochloric acid may be operated at low pH and thus benefit by resulting improved current efliciency as well as lower electrode consumption. In fact, as shown in FIGURE 1 chlorine may be added to the cell gases through line 29 for complete combustion of all hydrogen to hydrochloric acid and water vapor. The residual gas, mainly containing water vapor and carbon dioxide may be partly recirculated for control of hydrogen and chlorine concentrations to avoid an explosive gas composition.

Referring now to FIGURES 2, 3, 4, it is seen that there is provided a generally rectangular closed vessel 30 provided with side walls 31 and 32, back wall 33, front wall 34, bottom wall 35 and top closure 36. The cell 30 itself is made of non-conducting and cell-liquor inert material; such as unplasticized polyvinyl chloride, or steel lined with an non-conducting and cell liquor inert material such as Penton. One suitable unplasticized polyvinyl chloride which may be used is that known by the registered trademark of Darvic which has the following properties.

Mechanical.Hard material with very high impact-resistance. At 68 F. it has the following mechanical properties:

Tensile strength, lb./in. 8,000 Youngs modulus, lb./in. 4.8X105 Impact strength, ft. lb. 12 Brinell Hardness (3 kg., 2 mm. ball) 17-18 Specific gravity (average) 1.44

. tivity and specific heat, but compared to metals, it has a high coefiicient of expansion.

Penton is the registered trademark of Hercules Powder Co. for a chlorinated polyester of high molecule weight, linear in nature, crystalline in character and extremely resistant to thermal degradation at molding and extrusion temperatures.

The vessel 30 is divided in this embodiment although numerous other subdivisions may be made, into four quadrants 37, 38, 39 and 40 by means of longitudinal cell divider 41 and four transverse electrode end walls 42, 43, 44 and 45, spaced in such a way as to provide a central well 46.

Atop the top closure and extending along the central longitudinal axis of the vessel is a header 47 divided by a central longitudinal wall 50 into an inlet header 48 and an outlet header 49. Inlet header is connected via coupling 51 to inlet conduit 12 heretofore described with reference to FIGURE 1. From the inlet header 48 inlet liquid enters cell 36 via inlet 52, flows along the top layer 53 of the cell downwardly channel 54 between wall 31 and quadrants 37 and 40 to bottom layer 55 where it may mix with residual solution in the cell. Solution may travel downwardly in the channel 56 between wall 32 and quadrants 38 and 39 to cause an internal recirculation. Solution and cell gases enter top layer 57 to flow along the layer to outlet 58 into the outlet heater 49. From outlet header 49 efiluent is led through coupling 59 to T-joint 15 and outlet conduits 14 and 15 described heretofore for FIGURE 1.

Within each quadrant of the cell is a plurality of closely spaced apart, transversely extending, horizontally stacked, bipolar graphic electrodes 60. Each set of transversely extending, horizontally stacked bipolar electrodes 60 is maintained in the necessary spaced apart relationship by means of upper end seals and spacers 61, to be more fully described hereinafter with reference to FIGURES 5 and 6. The adjacent sets of such electrodes 64 in different quadrants are maintained in their essential spaced apart relationship by means of centre and intermediate seals and spacers 62 to be more fully described with reference to FIGURES 5 and 6. Each such set of electrodes 60 is maintained in liquid tight sealed relationship with adjacent such sets by graphite receptacle closures to be more fully described with reference to FIG- URES 5, 6 and 7. The upper bipolar electrode of each such set of electrodes is maintained in liquid tight sealed relationship to its associated graphite receptacle closure 63 by means of a gasket 64 to be described hereinafter with reference to FIGURE 7. Each vicinal bipolar electrode 60 in each set is fluid-tight sealably connected to its neighbor by means of seal 100 to be described hereinafter with reference to FIGURE 8. Finally, the bottom bipolar electrode of each such set is maintained in its liquid-tight sealed relationship to its adjacent set by means of seal 66 to be described in greater detail hereinafter with reference to FIGURES 9 and 11. The cell 30 is provided with central current connector for the monopolar electrode having a horizontal segment 67 and a vertical section 68. As shown in FIGURE 4, there are two such current connectors, joined by a clamp 69. The central current connector enters the cell by means of a sealing means 70A to be more fully explained with reference to FIGURE 10. The vertical section of the connector is connected to each of its associated adjacent monopolar electrodes 60 by means of a clamp 70 of U-shaped crosssection which is bolted by bolts 71 (preferably of titanium). Each monopolar electrode is provided with a semicylindrical vertically extending groove 72 so that the cylindrical connector may abut snuggly and be retained thereon by bolts 73 (preferably of titanium) threaded into clamp 70 and abutting connector 68.

It is to be noted that central current connector 67 and 68 is a titanium tube with a highly conductive core such as copper or aluminum and is platinized to provide a high conducting and an oxidation resistant metal skin. There is, thus, a platinum surface between the titanium and the graphite to inhibit oxidation of the titanium.

It is noted that while the cell has been shown with a central current connector having a horizontal and a vertical section, the connector may be designed using the horizontal section only and installing the monopolar electrodes in upright position.

It is to be noted that while the cell has been shown divided into four quadrants (or compartments), the cell may also be designed for one compartment by using only one of the central electrodes or for multi-compartments using more than two such electrodes.

It is also to be noted that the size of the compartments may be adjusted at will. If the end connectors have the same polarity, and if the number and spacing of the bipolar electrodes is equal, then the voltage pressure and current flow would be equal in all compartments.

As shown in FIGURE 2, the ends of the bipolar electrode assembly have monopolar electrodes connected to a carbon connector by face-to-face contact therewith, and is bolted or otherwise secured to a connector 75, which is permitted to enter the cell in the manner shown in FIGURE 10. Connector 75 as shown, is titanium having a highly conductive core 76 and an oxidation resistant platinum skin 77 therearound.

Referring now to FIGURES 5 and 6, hanging from the top closure 36 is a central channel 78. This central channel is connected (see FIG. 4) both to the inlet header 48 via inlet 52 to provide a header channel 53, and to the outlet header 49 via outlet 58 to provide header channel 57. It is noted that channel 78 is generally U- shaped and that each of the upstanding legs of the U is provided with a downwardly extending flange 82. Disposed in the channel 83 between the legs of the U and flange 82 is the upper portion of a graphite receptacle closure divider plate 79.

Adjacent to channel 78 and plate 79 is an intermediate sealing U-shaped channel 80. One of its legs 86 is provided with a pair of horizontally extending sealing ridges 85 and terminates in a downwardly extending flange 84. The channel space between such leg and the flange 84 is just wide enough to permit the entry therein of the flange 82 of channel 78, which itself embraces divider 79. Divider 79 is kissed by ridges 85. The other leg 87 is provided at its terminus with a downwardly extending flange 88. The channel space between leg 87 and flange 88 is just wide enough to embrace plate 79. A plurality of such channel 80-plate 79 units is provided, the number being equal to the number of sets of bipolar graphite electrodes. The marginal terminal channel at the edge of the side walls is shown in FIGURE 6.

Thus, it is seen that the margin channel 81 has one leg 89 provided on its outer surface with a horizontally extending sealing ridge 85 and it terminates in a downwardly extending flange 90. The channel space between leg 89 and flange 90 is just wide enough to permit the entry thereof of the flange 84 of the adjacent channel 80, which in turn embraces plate 79. The divider plate 79 is kissed by ridge 85. The other leg 91 is provided with a downwardly extending flange 92 whose channel space is just wide enough to embrace marginal divider plate 94. An upper end closure 93 is provided integral with the side walls, which closure is provided with a longitudinally extending groove 95 whose Width is just enough snugly to embrace flange 92.

Each channel 80 has a pair of upwardly extending ridges associated with its flange 84 to assure better sealing contact between the channels 80 and the top closure 36.

As seen in FIGURE 7, the lower end of each divider plate 79 is embraced by a longitudinally extending slot 96 in a sealing member 97. An Oring 98 provides sealing between the sealing member 97 and the divider plate 79. The sealing member is itself received in a slot 99 in graphite electrode 60.

As seen in FIGURE 8, the upper edge of the lower graphite electrode 60 is provided with a longitudinally extending slot 104 into which the downwardly extending leg 101 of a T-shaped seal 100 is placed. The horizontal portion of seal 100 is provided with three upper longitudinally extending sealing ridges 10.2 and with two lower longitudinally extending sealing ridges 3. Lower ridges 103 are adapted to kiss the upper edge 105 of the lower electrode 60 while the upper ridges 102 are adapted to kiss the lower edge .106 of the upper electrode 60.

As seen in FIGURES 9 and 11, a bottom seal 107 is provided with three longitudinally extending sealing ridges 109, adapted to kiss the bottom wall 35, and a slot 110 extending longitudinally downwardly from the top thereof. Within slot 110 is snugly inserted circulating chamber divider 108. At the marginal edges of each such divider 108 is a U-channel seal 111, adapted to abut the side walls of the vessel.

It is seen, therefore, that the lower electrode 60 of the set ofelectrodes rests with its weight on circulating chamber divider 108, which weight is transferred through ridges 109 to the bototm wall 35. Each superposed electrode 60 adds its weight to the lower one through ridges 102 and 103. The weight of the divider Wall 79 is transmitted to the upper electrode through slot 99. Again, the combined weight of the hanging channels 78, 80* and 81 is transmitted to the upper edge of divider 79 and 94. Finally, a portion of the weight of the top closure 36 is transmitted via ridges on flanges 84. Thus, an eflicient seal is provided.

It is obvious that the materials out of which 78, 80, 81, 79, 94, 97, 100, 108, .107 and 111 are made must be a non-conductor and cell liquor inert material. Thus dividers 108, 94 and 79 may be made of a rigid methacrylate polymer such as that known by the registered trademark of Plexiglas or Lucite or alternately may be made of a rigid polyvinyl chloride. The seals 107, 100, and 97 and the channels 78, and 81 may be made of natural or synthetic rubber or of the material known by the registered trademark of Hypalon, or of polyvinyl chloride, or polyethylene or polyproplylene.

Referring now to FIGURE 10, the monopoar electrode connector 75 consists of titanium 76 and a core of high conductive metal such as copper, and a skin of high corrosion resistant metal such as platinum. The wall 31 of the cell 30 may be lined with a non-corrosive lining 31a such as saran. A collar 112 is secured to the outside of wall 31 and a gland bushing with chevron packing 114 is placed around electrode connector 75. The bushing and packing are held to the collar and also secure the connector 75 thereto by means of bolts 115.

In operation the electric current flows from one cell to the other due to the potential diiferences and voltage pressure. Electric current enters the cell unit at the anode power connector 70, travels along the monopolar electrodes 67 and 69 to the bipolar electrodes 60. The current flows along electrodes 60 to leave the cell via electrode (cathode) 75. It is to be observed that the current may be reversed in the cell, thereby maintaining near equal wear and consumption on both sides of the bipolar electrodes 60 and for the monopolar electrodes 67 and 6-8. It is noted that while the cell has been shown with special end electrode connectors, the cell may also be designed using the central electrode connectors for the ends as well.

A prime feature in the operation is the internal circulation, shown by the arrows in FIGURE 4. Internal circulation is maintained because of gas left due to formation of cell gases in the cell. The flow of electrolyte, starting at the bottom of the cell 30 is upwardly between the sets of bipolar electrodes 60, across the top, downwardly through well 46 and then along bottom 55. Additional circulation may be achieved by designing the cell with a channel 56.

The liquor flows downwardly along channel 56 and along the bottom 55 and upwardly through electrodes 60. A portion of the liquor is removed from the cell along channel 57 and outlet 58. Fresh liquor, to compensate for removed liquor enters via inlet header 48, inlet '52, inlet channel 33 and downwardly in channel 54. Thus, the forced circulation is obtained by the head diflerence of liquor between inlet header 48 and outlet header 49. It is noted that while the cell has been shown with a central inlet and outlet header, these headers may be separated and designed for any position along the cell cover.

The cell gases are entrapped in the liquor and leave the cell unit together with the liquor, as described above, through outlet header 49, thence through coupling 59 to T-joint 15. The gases are partly separated from the liquor and are led off by conduit 16. The liquor is discharged through outlet 14 for treatment as described with reference to FIGURE 1.

The following Experiment A indicates the utility of such an electrolytic cell.

EXPERIMENT A The electrodes consisted of a sheet of plantinised titanium bolted to a graphite electrode in sodium chloride solution. The current density used was amperes/ square inch, contact pressure approximately 100 psi. and the contact resistance was determined to 0.001-001 ohm for 1 square inch. There was no indication that the platinum would dissolve; the test was run for a total of 80 hours.

Four cells were employed in the unit using the end monopolar graphite electrodes and in-between bipolar graphite electrodes. The width of the electrodes was 6 and the height 48". The circulating chamber was A" X 2 in cross area. The electrolyte at start-up contained 300 g.p.l. NaCl and 3 g.p.l. Na Cr O pH was approximately 6.5, and temperature 4050 C. At 0.5 amp/sq. in., the cells internal circulation was approximately 5 feet/ minute between the electrodes, /2" apart, and the anode current eificiency, based on gas analysis, was approximately 94%. When the circulating chamber was closed the efiiciency dropped to 91%.

The hypochlorite concentration was 1.5 g.p.l. and cell unit voltage was 12 volts; i.e., 3 volt/cell.

I claim:

1. An electrolytic metal chlorate cell comprising a cell box including a closure; an electrolytic zone defined by a plurality of bipolar electrodes positioned in said box and constructed and arranged to conduct electric current through said box and through a circulating electrolyte; means associated with said closure providing a distribution means for electrolyte inlet; outlet means for removing electrolyte and gaseous products of electrolysis entrained therein; means for channelling said product, consisting of said electrolyte and said gaseous products of electrolysis entrained therein, from said electrolytic zone to said outlet means, thereby inhibiting the formation and accumulation of gaseous products of electrolysis within a zone immediately below and adjacent said closure; and means associated with, but external of, said closure and connected to said outlet means for receiving said electrolyte and entrained gaseous products of said electrolysis for at least partially separating said electrolyte from said entrained gaseous products of said electrolysis.

2. An electrolytic metal chlorate cell comprising a cell box including a closure; a plurality of bipolar electrodes positioned in said box and constructed and arranged to conduct electric current through cell box and through a circulating electrolyte; inlet means to said box; outlet means from said box; and circulation means provided by combined enforced external pumping means and internal pumping action due to the construction and arrangement of said bipolar electrodes and the rising gaseous products of said electrolysis.

3. An electrolytic metal chlorate cell comprising: a cell box including a closure; a plurality of groups of bipolar electrodes positioned in said box and so constructed and arranged to conduct electric current through said box and through a circulating electrolyte; means spacing said electrodes from the bottom of said box and from said closure; current leakage preventing fluid-tight seals bebetween said closure and said spacing means, between said spacing means and an upper electrode of said group of electrodes, between adjacent electrodes in said group of electrodes, between a lower electrode of said group of electrodes and said spacing means, and between said spacing means and said bottom; inlet means to said cell; and outlet means from said cell.

4. An electrolytic metal chlorate cell comprising; a cell box including a closure; a plurality of groups of bipolar electrodes positioned in said box and so constructed and arranged to conduct electric current through said box and through a circulating electrolyte; electrical connection means provided by a platinized titanium electrode connected directly to said electrodes and arranged to be submerged within said electrolyte; means spacing said electrodes from the bottom of said box and from said closure; current leakage preventing fluid-tight seals between said closure and said spacing means, between said spacing means and an upper electrode of said group of electrodes, between adjacent electrodes in said group of electrodes, between a lower electrode of said group of electrodes and said spacing means, and between said spacing means and said bottom; inlet means to said cell; and outlet means from said cell.

5. An electrolysis apparatus comprising: an enclosed bipolar electrolytic cell provided with a closure and an electrolytic zone therewithin; inlet means for electrolyte substantially free of entrained gaseous products of electrolysis; outlet means for electrolyte and gaseous products of electrolysis entrained therein; means for channelling said product, consisting of electrolyte and gaseous products of electrolysis entrained therein, from said electrolytic zone to said outlet means, thereby inhibiting the formation and accumulation of gaseous products of electrolysis within a zone immediately below and adjacent said closure; means associated with said outlet means providing at least a partial separation of the gaseous products of electrolysis from the diluent electrolyte; vent means for said gases; means conducting said efiiuent electrolyte to a reacting and degasifying chamber; gaseous vent means on said reacting and degasifying chamber; recycle means for conducting effluent from said reacting and degasifying chamber to a heat exchanger, means conducting the effiuent from said heat exchanger to a header tank and reacting chamber; and means conducting efliuent from said header tank and reacting chamber together with fresh electrolyte to said enclosed bipolar electrolytic cell.

6. The apparatus of claim 5 including a branch line from said reacting and degassifying chamber to a filter; conduit means from said filter; and storage means for effluent from said filter.

References Cited UNITED STATES PATENTS 1,023,545 4/1912 Bates et al. 20495 1,173,346 2/1916 Gibbs 20495 3,298,946 1/1967 Forbes ZO4-268 JOHN H. MACK, Primary Examiner H. M. FLOURNOY, Assistant Examiner U.S. Cl. X.R. 20495, 269, 270

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