US2598228A - Electrolytic apparatus - Google Patents

Description

May 27, 1952 R. a. cox

ELECTROLYTIC APPARATUS 5 Sheets-Sheet 1 Filed Feb. 5, 1945 FIG. 1

FIG. 3

INVENTOR. Robert 8. Cox flwm 08 ORNEY May 27, 1952 cox 2,598,228

ELECTROLYTIC APPARATUS Filed-Feb. 5, 1945 3 Sheets-Sheet 2 INVENTOR.

BY W I Rfobert B. Cox

ZATTORNEY May 27, 1952 cox 2,598,228

ELECTROLYTIC APPARATUS Filed Feb. 5, 1945 3 Sheets-Sheet 3 Water Drip s 4s 39 3e FIG. 7

INVENTOR. Robel t B. 00x BY W R Patented May 27, 1 952 UNITED STATES ATENT QFFICE ELECTROLYTIC arranarns Application February 3, 1945, Serial No. 576,041

Claims.

The present invention, relating as indicated to an alkali-:chlorine electrolytic apparatus and electrolytic process, has particular reference to a mercury cathode type electrolytic cell and process in which the cathode is in the form of a vertidaily moving film of mercury. In the commercially operable mercury cell'process type installations heretgfore made, the mercury cathode has be in the form of a horizontally disposed pool owing stream above which is located the anode, the latter being the form of a graphite block or plate. The"cl1ief objections to such horizontal mercury cells have been the relatively high electric power consumption due to the voltage drop across the cell (4 to 4.4 volts), the relatively large capital expenditure involved'in the cost of th'e'mercury.

' it is, therefore, the general object and nature of myinye'ntion to provide a mercury type electrolytic cell and process, particularly adapted for the production of chlorine and caustic soda from brine, in which the voltage drop throughout the indiv'dual cell'is substantially reduced, thus contribut ng to the'energy efliciency of the cell; and in which the amount of mercury and floor space per cell are reduced to a fraction of that heretofore required.

' Previous attempts have heretofore been made to devise a vertical mercury film typeof electrolytic cell. German Patent No. 692,954 discloses such a cell in which the film of mercury flows down the surface of a supporting sheet. Other attempts have been made wherein the vertical film of mercury is supported on the inside of a tube or on a cylindrical surface. However, none of these prior attempts'have been sufiiciently successful or feasible, primarily because mercury, due to its relatively high surface tension, tends to draw itself up into a moving body or stream of minimum surface area, thereby producing an uneven and discontinuous flow of the mercury body along the surface of the supporting element. I have discovered that a downwardly flowing stream of mercury can most satisfactorily and successfully be supported upon a rod-like element, viz: a solid rod or a hollow .rod or wire of relatively small cross section (hereinafter referred to as a rod), whereby the mercury film thereon remains uniform and unbroken throughout the path of flow.

A further object of my invention is to provide an anode surface for the electrolytic cell which is considerably greater than that of the mercury cathode, whereby the voltage drop through the" electrolyte, e. g. brine inthe'case bf an alkalichlorine electrolytic cell,,is considerably reduced because the current per unit cross sectional area of its path through the electrolyte is reduced. In addition, by providing an anode which has relatively greater electrolyte contacting surface area than the cathode, the corrosion and wearing away of the anode surface, requiring periodic readjustment and replacement of the anode elements in the cell, are greatly minimized.

A further object of my invention is to provide a novel means for mounting the mercury cathode supporting rods in the cell and for introducing the mercury to such rods whereby the rate of mercury flow is efiiciently controlled within the optimum, desired range; and in the cas of a plurality of vertical cathode rod supports to which the mercury is supplied from a single source, the amount of mercury introduced to each individual rod is substantially uniform and equal.

Another object of my invention is-to provide an amalgam denuding or stripping cell wherein the mercury body containing the amalgamated metal, such as sodium, is caused to flow vertically through a packing of carbon or graphite particles in which there are interspersed particles of a material which readily becomes wetted by mercury, e. g. iron, steel, nickel, "Monel metal, etc., whereby a highly efficient rate of metallic ion removal from the amalgam is obtained as well as a relatively high strength caustic alkali liquor.

My invention also provides for the complete removal of alkali metal from the mercury body as the latter is circulated through the process system thus preventing the formation of any solid material which would tend to clog or contaminate the apparatus.

Another object of my invention is to provide an apparatus and process in which the equipment is assembled in a vertical arrangement, thereby reducing by many times the amount of floor space required for a given cell production as compared to the prior commercial, horizontal mercury cell installations. Moreover, such a vertical arrangement permits an interior circulation within the electrolyte in both the brine decomposition cell and in the sodium amalgam stripping cell, due to the pneumatic lift action of the gases formed. This interior circulation in the vertical cells not only contributes to the uniform and efficient contact of the electrolyte with the electrodes, but also prevents the formation of static and clinginggas bubbles which reduce available working surface of the elctrodesandincrease the electrical resistance within the cell.

Additional objects and advantages of my invention shall become apparent as the following description proceeds.

To the accomplishment of these and additional objectives and to enable any person skilled in the art readily to understand and practice the invention, the following full and concise description and annexed drawing set forth the best mode in which I have contemplated applying the principle of my invention.

Fig. 1 is an elevational view of an apparatus embodying the principle of my invention, showing the vertically arranged brine decomposition cell, amalgam denuding cell and the circulatory connections Fig. 2 is an enlarged cross sectional view of the brine decomposition cell of Fig. 1;

Fig. 3 is an enlarged cross sectional view of the amalgam denuding cell of Fig. 1;

Fig. 4 is a horizontal cross section taken substantially along line 4-4 of Fig. 2; and

Figs. 5 and 6 are horizontal cross sectional views through the vertically disposed brine decomposition cell, illustrating alternative forms of arrangement of the cathodes and anodes.

Now referring more particularly to the drawing, the apparatus embodying the principle of my invention comprises an electrolytic cell i into the bottom of which the electrolyte, such as brine, is introduced into the inlet 2 and the spent electrolyte or brine withdrawn at the outlet 3 near the top of the cell. A gas outlet 4 is provided for the withdrawal of the gaseous product of electrolysis, e. g. chlorine. Vertical supporting rods 21 (which are preferably of Monel metal) for the mercury film cathodes extend within the cell I and are mounted on the supports or nozzles 5 on the top thereof. Mercury is introduced from the distributor 6 through the conduit 1 to each one of the nozzles 5, whence it flows through the interior of the cell 1 and out of the bottom of the latter to the conduit 8. The nozzles 5 are made of an electrically conductive material which is also wettable by mercury, at least in the area surrounding the rods 21. The electric current (direct current) connections for the cell l are made at the nozzles 5 and electric cable connection 9 for the cathodic connection, and to the bus bar In extending along the length of the cell body I, the latter being preferably fabricated from graphite.

The voltage drop across the above described cell is on the order of 3.75 volts, substantially less than that heretofore encountered in the horizontal mercury cells. This reduction in the voltage drop contributes to the energy efiiciency of the cells as well as to the economy of its operation.

The mercury leaving the cell I contains sodium by reason of the dissolution of the liberated sodium ions from the brine in the flowing mercury cathode. Water or a solution of caustic soda is introduced from the line H of Fig. 3 and admixed with the amalgam in the distributor l2. Preferably about a 30% NaOI-I content solution is employed due to the improved electrical conductivity thereof as compared to water alone. From the distributor 12, the amalgam together with the water or aqueous NaOl-I solution is fed to the nozzles I3 leading into the caustic or amalgam denuding cell I4 where the sodium of the amalgam reacts with water to form sodium hydroxide and hydrogen. The hydrogen outlet is provided at and the caustic soda outlet is at l6.

The denuded mercury flows down to the bottom of the cell M, to the conduit l1, thence to the mercury reservoir 18. A pump l9, connected to the reservoir 13 returns the mercury to the line 20, thence through the line 22 to the distributor 6 for the recycling in the process system. An overflow line 2| returns excess flow or head of mercury from the line 20 to the reservoir l8. An excess of the mercury body, circulated through the system, is thus caused to be by-passed from the cells I and I4 and conducted through the line 21 and the reservoir 18. It will be noted that the upper end of the line 2| leads from a riser which is open to the atmosphere. This permits air to come into contact with the by-passed portion of the mercury going through the line 2i, so that a portion of the mercury body circulating through the system is continuously subjected to an oxidation action which in turn results in the removal of any possible entrained impurities, such as iron, which impurities would otherwise tend to contaminate the NaOH product.

At the conduit connection 23, a small amount of water is permitted to drip into the mercury stream. The so-added water is carried along with the moving body of mercury and into the cell 1. This is for the purpose of dissolving any solid substances, such as sodium oxide, which might form due to whatever trace of sodium there might be left in the mercury as it is recirculated, and which might tend to clog the apparatus and equipment.

The body of the brine decomposition cell i may suitably be made from a block of graphite through which the bores or passages 26 are formed. The passages 24 constitute the electrolysis chambers and the central bore 25 forms a return circulation flow chamber for the electrolyte which is maintained at a level indicated at 26.

The mercury film cathode supporting rods 21 extend through the chambers 24, being supported at their upper ends by the supporting elements or nozzles 5. The nozzles 5 in turn are mounted in the top wall or cover 28 of cell i. This cover is fabricated from a chlorine resistant, electric insulating material such as stoneware, glass or concrete. Rubber gaskets 29 and 30 are disposed on the top and bottom of the cover 28. A metallic plate 3| on the top of the gasket 29 serves as a convenient bus bar for distributing electric current to the nozzles 5 and thence to the cathodes 21. As indicated at 32, the nozzles 5 have an enlarged inner diameter portion which provides a space around each of the rods 21. Near the lower terminal ends of the nozzles 5, this space is reduced substantially in size leaving a clearance on the order of ,6 of an inch between the rods 21 and the inside spaces of the nozzles 5 and through which the mercury is permitted to flow. The interior of the larger diameter spaces in the nozzles 5 serve as excess mercury reservoirs for the mercury which is delivered to the conduit 1 and cannot immediately pass out through the smaller annular spaces at 33.

I have determined that the optimum size for the diameter of the rods 21 is on the order of of an inch. If substantially larger than this, there is a tendency for the mercury film to break or become uneven. I have also determined that the rate of mercury flow along the rods 21 should be in the range of 30 to 250 cc. per minute. If above this range, there will be a tendency for the mercury to lose its adherence to the rod and if below this range, there will be a tendency for the mercury .film to break.

It will thus be seen that the individual reser-Q voirs provided at the spaces 32 function to effect an automatic control of the rate of feed within this range and through the annular orifices at 33. If the flow rate through the orifices 33 tends to decrease, a greater head or pressure will be built up in the reservoirs 32, thus tending to counteract any drop-off in flow rate and to increase it to within the desired range. a

It will be noted that the lower ends of the nozzles 5 are submerged below the brine level 26. Since it is normal practice to build up a subate mospheric pressure within the cell to effect re.- moval of the chlorine, and prevent its escape into the cell room, the mercury within the individual reservoirs 32 also serves as a sealing means for preventing air from being drawn into the cells at the point of introduction of the mercury.

Such submersion of the nozzle ends also prevents a chlorine film from forming there.

It will thus be seen that the novel construction of the above described nozzles 5 serves the multiple functions of: supporting the rods 21; controlling the desired fioW rate of mercury onto and down the rods; preventing a leakage of air into the cell which would otherwise dilute the educed chlorine gas; and conducting current from the bus bar plate 3| to the rods 21.

A bottom cap 34 of refractory or insulating material is mounted on the cell l in a manner similar to that of the previously described top cover The supporting rods 21 extend through the bottom cover 34 to the metal plate 35 to which the cathodic electrical connection is made as indicated at 9.

The mercury iiow distributor 6 comprises a vertical, rotatable hollow shaft 36 which is mounted in the bearing 37. Laterally, extending arms 88, terminating in small discharge orifices or jets project from the shaft 36. Thus, as mercury flows down into the shaft 85 and out the ends or orifices of the arms 38, the shaft 36 is caused to rotate (by the Bakers Mill or jet reaction principle of physics) whereby the mercury flow is uniformly distributed upon the floor or the bottom 32 of the distributor housing 6. The bottom has collecting recesses at each of the connecting points of the inlet ends of the conduits I.

In the denuding cell, as illustrated in greater detail in Fig. 3, the weak caustic solution is introduced from the line H and goes through the distributor i2 and the vent line it! leading directly into the top of the cell. of the caustic solution is maintained at the point t! or just above the bottom ends of the nozzles l3. These nozzles are similar in construction to the nozzles 5 as hereinabove described. The rods which they support, however, are in the form of pig tails as indicated at 42 which aid in the distribution of the incoming sodium-containing mercury stream over the bed or mass of packing This packing 43 is composed of relatively small carbon or graphite particles (preferably about My mesh size) and metal particles which readily become wetted by mercury, such as iron, steel, nickel, Monel, etc. Baffie rings 44 are located at spaced intervals within the cell M and tend to redirect the mercury stream back away The liquid level liquid mercury, viz; to prevent the mercury col-. lecting on the rings 44 and from dropping off at a single point on the inner periphery.

The denuding cell I4 as above described, has been found to be most eflicient in promoting the reaction of the metallic sodium in the mercury with water. Tests have shown that the sodium is so efficiently removed from the amalgamation or dissolution of the mercury that only one part per million (by weight) sodium remains after passage through the denuding cell. Although I do not wish to be limited to any scientific theory, it is believed that this unusualdenuding or stripping efilciency of the sodium from the mercury is promoted by the combination of the small par-, ticles of carbon together with the small particles of iron or steel, the latter wetted with mercury and thus tending to distribute the mercury and the mercury amalgam thoroughly throughout the packing and the liquid solution with which the chemical reaction is taking place, this in turn results in a substantial reduction of current density and voltage drop through the caustic.

It will also be noted, that both in the brine decomposition cell i and in the denuding cell 94, the liberated gases rise vertically from the bottom to the top thereof, thus producing a pneumatic lift action upon the electrolyte which in turn results in an interior circulation within the cells. This interior circulation in turn produces both a turbulence and a flow which increases the uniformity of contact of the electrolyte with the electrode surfaces and sweeps away any pockets or bubbles which would otherwise tend to adhere to the electrode surfaces. This interior brine circulation action also aids in keepin any graphite particles (from the anodes) in suspension until removed from the cell with the spent brine. Thus, in the case of the brine decomposition cell I, the interior circulation due to the pneumatic lift action (and as illustrated by the dotted-line arrows therein) causes a circulation of the brine electrolyte up through the passages 24 and down through the central passage 25.

In Fig. 5 an alternating arrangement for the mercury film cathode supporting rods and the graphite anodes is illustrated. The cell housing 50 is of circular cross sectional shape and fabricated from a suitable corrosion resistant material such as rubber covered steel, porcelain, concrete or stoneware. The cathode rods 51 are mounted in groups of four, each group being radially disposed with respect to the center of the housin 5%. The anodes 52, which may be fabricated from graphite blocks, are in turn radially disposed and are located alternately between the groups of cathodes 5|.

6 shows an arrangement wherein the vertical cathodes and anodes are assembled in a housing of rectangular cross section. Thus, the rectangular housing 55 has the series of parallel, horizontally alined cathode rods 56, between which are mounted the graphite anode plates or blocks 51. In the case of both Figs. 5 and 6, it will be seen that central open spaces 53 and 58, respectively, are provided for the return flow or interior circulation of the electrolyte, thus functioning in the same manner as the central passage 25 as heretofore described and illustrated in connection with Figs. 2 and 4.

My above described apparatus and process embodying this invention, is also applicable to the electrolysis of chemical compounds other than sodium chloride, to which the foregoing detailed description has been directed for the purpose of 7 convenience in explanation, rather than by way of limitation. Any chemical compound containing a metallic ion or a radical which is capable of forming an amalgam with mercury, can be used as the electrolyte in the apparatus and process of my invention. As examples of such compounds there may be mentioned those containing the alkali metals and alkaline earth metals, ammonium and the metals of gr-cups 1 and 2 of the periodic table.

Equivalent modes of practicing my invention may be followed provided that they are within the scope and purview of the appended claims.

I, therefore, distinctly claim and particularly point out as my invention:

1. An electrolytic cell of the moving mercury cathode type comprising an electrolyte chamber, a vertical rod extending within said chamber, a tubular supporting element for said rod mounted in the top wall of said chamber, said tubular supporting element holding and making electrical contact with the upper end of said rod, a portion of the inner surface of said supporting element being spaced from said rod, and a conduit for mercury leading to the space between said supporting element and said rod, said space extending to the lower end of said supporting element whereby mercury introduced therein flows down the surface of said rod.

2. An electrolytic cell of the moving mercury cathode type comprising an electrolyte chamber, a vertical rod extending within said chamber, a tubular supporting element for said rod mounted in the top wall of said chamber, said tubular supporting element holding andmaking electrical contact with the upper end of said rod, a portion of the inner surface of said supporting element being spaced from said rod, a conduit for mercury leading to the space between said supporting element and said rod, said space extending to the lower end of said supporting element whereby mercury introduced therein flows down the surface of said rod, and means for maintaining a fixed liquid level of the electrolyte in said chamber, the lower end of said supporting element extending below such liquid level.

3. An electrolytic cell of the moving mercury cathode type comprising an electrolyte chamber, a vertical rod extending Within said chamber, a tubular supporting element for said rod mounted in the top wall of said chamber, said tubular supporting element holding and making electrical contact with the upper end of said rod, a portion of the inner surface of said supporting element being spaced from said rod, a conduit for mercury leading to the space between said supporting element and said rod, said space having an enlarged diameter at the point of entry of said conduit and reducing in diameter at its terminus at the lower end of said supporting element, whereby mercury introduced from said conduit flows out of said space and down said rod, such enlarged diameter portion of said space constituting a mercury reservoir.

4. An electrolytic cell of the moving mercury cathode type comprising an electrolyte chamber, a plurality of rods vertically extending within said chamber, a tubular supporting element for each of said rods mounted in the top wall of said chamber, each of said tubular supporting elements holding and making electrical contact with the upper end of each of said rods, a portion of the inner surface of each of said supporting elements being spaced from each of said rods, such space extending to the lower end of each said supporting elements whereby mercury introduced therein flows down the surface of each of said rods, conduits leading to each of such spaces, a single source of mercury supply, a distributing chamber connected at its bottom to said conduits, a rotatable hollow shaft vertically mounted in said distributing chamber, and laterally projecting discharge arms on the bottom end of said shaft, the upper end of said shaft being connected to said mercury supply source whereby the flow of mercury through said shaft and said arms induces rotation thereof and discharges the mer cury fiow uniformly on the bottom of said distributing chamber.

5. An electrolytic cell of the moving mercury cathode type comprising an electrolyte chamber, a plurality of rods vertically extending within said chamber, a tubular supporting element for each of said rods mounted in the top wall of said chamber, each of said tubular supporting elements holding and making electrical contact with the upper end of each of said rods, a portion of the inner surface of each of said supporting elements being spaced from each of said rods, a conduit for mercury leading to each of the spaces between said supporting elements and said rods, such space extending to the lower end of each of said supporting elements whereby mercury introduced therein flows down the surface of each of said rods, and a distributing reservoir having its bottom well connected to the upper end of each of said conduits for uniformly distributing the flow of mercury to the latter.

ROBERT BRUCE COX.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 661,188 Nettl NOV. 6, 1900 673,754 Bell May 7, 1901 709,971 E'dser et al Sept. 30, 1902 784,592 Phillip Mar. 14, 1905 908,545 Carrier Jan. 5, 1909 947,741 Rink Jan. 25, 1910 1,411,507 Paulus Apr. 4, 1922 1,712,952 Creighton May 14, 1929 1,784,066 Heinze Dec. 9, 1930 1,900,996 Palmaer Mar. 14, 1933 2,083,648 Gorke June 15, 1937 2,234,967 Gilbert Mar. 18, 1941 2,248,363 Kuenhold July 8, 1941 2,316,685 Gardiner Apr. 13, 1943 2,336,045 Taylor Dec. 7, 1943 FOREIGN PATENTS Number Country Date 20,768 Great Britain of 1890 17,415 Great Britain of 1898 490,911 Great Britain Aug. 23, 1938 836,742 France Jan. 25, 1939

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