US2415135A

US2415135A - Brine flush out for electrolytic cells

Info

Publication number: US2415135A
Application number: US458845A
Authority: US
Inventors: Roy A Horst; Eugene B Port
Original assignee: Solvay Process Co
Current assignee: Solvay Process Co
Priority date: 1942-09-18
Filing date: 1942-09-18
Publication date: 1947-02-04
Anticipated expiration: 1964-02-04

Description

Feb. 4, 1947. R. A. HORST ETAL 2, 3

BRINE FLUSH-OUT FQR ELECTROLYTIC CELLS m mw M h N05 R m m4 e n Filed Sept. 18, 1942 l IQUOR LEVEL :1 1947- R. A. HORST ETAL ,41 35 BRINE FLUSH-OUT'FQR ELECTROLYTIC CELLS Filed Sept. 18, 1942 4 Sheets-Sheet 2 INVENTORS Roy A. Ham:

0 5. For?! 1 22v sv 7 6 /9 ATTORNEY Fgb. 4, i947. R. A. HORST ETAL 5, 3

BRINE FLUSH-OUT FOR ELECTROLYTIC CELLS I Filed Sept. 18, 1942 4 Sheet s-Sheet s INVENTORS flay Allan-z: [gene 6. P072! BY 1 Patented Feb. 4-, 1947 BRINE FLUSH OUT FOR ELECTROLYTIC CELLS Roy A. Horst, Syracuse, and Eugene B. Port, Baldwinsville, N. Y., assignors to The Solvay Process Company, New York, N. Y., a corporation of New York Application September 18, 1942, Serial 0. 458,845

5 Claims. 1

This invention relates to improvements in mercury cathode electrolytic cells. Such cells normally involve a brine chamber, in which a salt is electrolyzed and a metal is collected as an amalgam in a mercury cathode, and a regenerator, in which the metal is removed from the mercury, as by washing the mercury with water thereby forming a hydroxide of the metal.

In the manufacture of chlorine and alkalimetal hydroxides from alkali-metal chlorides by electrolysis in mercury cathode cells various foreign materials find their way into the mercury forming impurities therein. These impurities may consist of particles of carbon from the carbon anodes of the cell, metallic or metal oxide impurities either from the brine employed or from the cell itself, and amalgams formed by metallic impurities. The various impurities, referred to in the claims as foreign material," either alone or in admixture with mercury, form a sludge which is substantially heavier than the brine and substantially lighter than the mercury and accordingly floats upon the surface of the mercury.

This sludge forms on the surface of the mercury a layer which, by increasing the electrical resistance of the cell, may substantially reduce its electrical efiiciency. Furthermore, some of these impurities accelerate the reaction of alkalimetals with water and thus cause alkali-metal present in the mercury to react with brine solution to form hydrogen, which in contact with the chlorine produced constitutes an explosion hazard, as well as alkali-metal hydroxide. The

alkali-metal hydroxide reacts with chlorine to form alkali-metal hydpochlorite and chlorate which salts may be electrolyzed to give nascent oxygen at the anodes, which oxygen reacts with the anodes and appreciably shortens their useful life. Eventually the sludge may become sufiiciently pasty and sufficiently voluminous to cause irregularties or even stoppages of mercury fiow through the cell.

In the past the accumulations of sludge have been removed by skimming operations carried out manually. For instance, at some point in the cell where the mercury is readily accessible, the operator of the cell skims off the sludge taking with it substantial quantities of the mercury.

It is an object of the present invention to facilitate the removal of sludge-forming impurities from the mercury employed as the cathode in electrolytic cells, to reduce the labor cost for this operation and to provide a structure which accomplishes the removal of the sludgev semi- 2 automatically and thus reduces the time C011?- sumed in the operation.

A further object is the provision of such a structure that removal of sludge may be accomplished without interference with the operation of the cell, thus permitting frequent sludge removal and maintenance of high efficiency and output of the cell.

Further advantages of the invention will be apparent from the specification which follows.

.The structure of our invention comprises a mercury cell which normally contains a pool of mercury. A low ceiling is provided over the pool of mercury which with appropriate side walls cooperates with the mercury to define a constricted passageway communicating at one end with the brine chamber or the regenerator chamber, preferably the brine chamber, and at the other end with a suitable-outlet through which electrolyte and sludge may be withdrawn. By such a construction a sufficient velocity of electrolyte over the surface of the mercury can be obtained to effectively fiush accumulations of impurities on the mercury surface out through the aforementioned outlet.

Since the introduction of impurities into the mercury usually occurs primarily in the brine chamber of the electrolytic cell, it is preferred to place the, sludge removal structure :at the mercury outlet. end of thebrine chamber so that it receives the mercury from this chamber and permits removal of sludgebefore the mercury enters the regenerator chamber. A similar sludge removal structure might be placed at the mercury outlet end of the regenerator. Since for most purposes a single sludge removal unit at the mercury outlet of the brine chamber is adequate for a satisfactorily low content of impurities in the mercury throughout the electrolytic cell, such a structure has been selected to illustrate the practical application of the invention. The following description of several embodiments of the invention should be read in connection with the accompanying drawings, wherein Fig. 1 is a sectionon line li of Fig. 2 and shows a plan view of a preferred, structure including fragmentarily the end of the electrolytic cell to which it isattached;

Fig. 2 is a vertical section on line 2 Z of Fig. 1;

Fig. 3 is an end view of the electrolytic cell with the skimming unit of the invention removed to show the relative positions of the brine chamber and regenerator and attachments for securing the skimming unit;

Figs. 4, 5, 6, and 7 are cross-sections on lines 4-4, 55, 6-6, and 'I-'I, respectively, of Figs. 1 and 2;

Fig. 8 is a schematic diagram of an alternative structure shown in cross-section;

Fig. 9 is a schematic diagram of a second alternative structure, also shown in cross-section.

The skimming and mercury sealunit of the present invention is especially adapted for use with an electrolytic cell of the type described and claimed in application Serial No. 458,844 of even date and will be described in conjunction with such a cell.

With especial reference to Figs. 1 to 7, the preferred structure is secured to the end of the mercury cathode electrolytic apparatus, comprising a brine chamber I and a regenerator 2 directly beneath the brine chamber. The brine chamber I comprises a mercury cathode supporting bed 3 and carbon anodes'4 supported by anode supporting stems 5 extending through brine chamber cover 6 and the regenerator 2 comprises a grooved graphite floor I and sidewalls 8. The bottom of the brine chamber I serves as the top for the regenerator 2.

It will be understood that the electrolytic cell has a length many times its width and comprises a large number of anodes 4 disposed side by side along the length of the chamber. The end of the cell is provided with supporting flanges 9 having holes Ill for securing the unit of the present invention thereto by means of bolts (not shown).

The unitof the invention, which may be in the form of a metal casting suitably lined or coated to withstand corrosion of the chlorinesaturated brine, has a flange II fitting the supporting flange 9 of the cell. The unit has a floor I2 which in conjunction with bed 3 of the brine chamber forms a transverse groove or chan- 4 23 which terminates short of the bottom of reser voir I4. T the rear of wall 23 a second wall 24 unites with the side walls of reservoir I4 to form a back and partial bottom for the reservoir. The top of wall 24 preferably is at least 6 inches above the bottom of wall 23 and at a level such that the head of mercury between this wall and wall 23 balances the head of mercury in reservoir I4 and the head of brine in the brine chamber and maintains the normal level of mercury in reservoir I4 slightly below ceiling I8, for example, between a half inch and one inch therebelow; in this way a pool of mercury is maintained in reservoir I4, which forms a seal between the brine chamber and the regenerator chamber. The position and slope of floor I2 are such that the normal mercury level is above the margin of the reservoir 14 nel I3 extending the width of the brine chamber and providing a small mercury reservoir at this point (see Fig. 2); From this reservoir the floor I2 slopes gently in a diagonal direction toward a kidney-shaped recess or mercury reservoir I4. The sloped floor I2, toward the right-hand side of the unit as viewed in Figs. 3 to 7, rises to a level slightly'above the lip of channel I3 and forms a horizontal shelf I5. The kidney-shaped reservoir I4 partly surrounds a cylinder I6. The shelf l5, as viewed in Fig. l, is bounded by channel I3, floor I2, cylinder I6 and the upper left hand portion of kidney-shaped reservoir I4. The shelf I5 and a ledge I'I together support a horizontally disposed closure plate I8, which, as shown in Figs. 2 to 7 inclusive, forms a ceiling at least co-extensive in area with the surface of the mercury in reservoir I4 and co-operates with the side walls of reservoir I4 to form a constricted passageway over said mercury surface. Extending through shelf I5 is a vertically disposed overflow pipe I9 which has its mouth at approximately the brine level desired in the brine chamber. The ceiling I8 is provided with apertures through which cylinder I6 and pipe I9 extend. Shelf I5 is provided with a depression 20 which rises'gradually from the edge of reservoir I4 at a level below the normal level of mercury in said reservoir to a level somewhat above the normal mercury level. At a point slightly above the mercury level the depression has a step-up 2I and then continues to an outlet pipe 22 having valve 22V.

The cylinder I 6 extends downwardly into reservoir I4 and finally merges'therewith to form wall and fioor I2. The normal shore line of the mercury has been shown in Fig. 1 by a broken contour line 25.

A conduit 26 merges with wall 24 and cylinder I6. This conduit 26 expands from a width equal to the diameter of cylinder I6 to awidth substantially the width of the regenerator 2 and thus provides a channel from which mercury overflowing wall 24 is conveyed to the regenerator. The conduit 26 and the floor I of the regenerator are slightly depressed where they meet, to provide a transverse depression 21, which serves to distribute mercury transversely of the regenerator and thus to provide an equal distribution to the channels or grooves formed in the floor of thischamber. A conduit 28 extends up through the bottom of channel 26 approximately to the desired level of regenerating fluid in the regenerator. The position of this conduit is such that it tends to divide the flow of mercury and aid in distributing the latter toward the sides of the chamber and at the same time to reduce the velocity of the mercury flowingto the central portion of the chamber.

The entire unit is provided with a suitable cover 29 which may be caulked with putty in order to avoid leakage of chlorine from the cell. A plug 39 closes the mouth of the cylinder I6, which extends above the cover.

Theoperation of the device described above is as follows: In the normal operation of the electrolytic cell chlorine gas, spent brine solution, and mercury containing metallic sodium pass from the brine chamber I into the unit. Spent brine and chlorine pass out together through overflow outlet I9. Normally the fiow of brine through the cell may be such as to provide a liquid level on the order of of an inch higher than the edge of the outlet. Mercury containing metallic sodium passes into the depression I3 and thence in the direction of the arrows in Fig. 1 into the reservoir I4. The flow of mercury continues in a counterclockwise direction over the surface of the pool of mercury in reservoir I4 thus forcing any foreign material floating on the surface of the mercury toward the depression 29. The mercury settles in reservoir I4 and rises between walls '23 and 24 until it overflows wall 24 and is conveyed by conduit 26 into distributing depression 21, whence it flows into the graphite groovesconstituting the regenerator floor and gives up its metallic sodium content towater flowing countercurrent to the mercury in this chamber. The resulting aqueous sodium hydroxide solution together with hydrogen generated by reaction of water and sodium passes out through overflow outlet conduit 28. I

Since conduit 26 and cylinder I6 are in direct Qilioiid ommunication with the gas space of the regenera'tor, the mercury during its passage through thissection of the apparatus is protected by an atmosphere of hydrogen. At all other times it is coveredeither by brine or by regenerating liquid.

, The flow of fluids through the unit continues as described during the normal operation of the cell. Depending upon the construction of the cell the accumulation of foreign material on the surface of mercury in reservoir :4 may be more or less rapid and it may be desirable to remove this materi'al at intervals of anywhere from a few hours to a week. In order to effect removal of this foreign material, valve 22V is opened for 30 to 90 seconds; Since the normal brine level is in" the neighborhood of 4 to 6 inches above the mouthfof' outlet pipe 22, a sufficient head of brine exists to provide a relatively high velocity flow of brine out through the outlet pipe. In view of the disposition of ceiling IS the flow of brine to the outlet pipe is confined to the space between the surface of the mercury on floor it and in reservoir M and this ceiling. Thus the brine follows essentially the same pathas normally pursued by the mercury. The combined flow of'brine and mercury overthis path causes any foreign material to be swept along with the flow of liquids toward outlet 22. The mercury also tends to flow toward this outlet, but the step 2| serves as a stop for the mercury and accordingly relatively little mercury finds its way to outlet 22. Accumulations of relatively less dense material on the surface of the mercury, however, climbthis step when propelled along by the fiow of brine and therefore pass out of the unit. When the brine flowing out through outlet 2-2 becomes clean, valve 22V is closed and the cell continues its normal operation.

Usually it is desirable to secure sufiicient volume of flow to provide more than the normal flow of brine during this skimming operation. A rate of flow between 1000 and 2000 liters per hour during skimming operations has been found satisfactory; A one-inchoutlet 22 and a 3-inch outlet i91are satisfactory for cells involving a normal brine flow of ZOO-to 800 liters per hour.

Analternative structure is shown in Fig. 8; The view in Fig. 8' corresponds in some measure to the viewin Fig. 6. This embodiment has a sloped floor [2a, a mercury reservoir Ma, which, as in the structure of'Figs. 1 to 7, acts as a seal between the brine chamber and the regenerator chamber, an observation cylinder lfia, a cover plate 3a, which, as in the structure of Figs. 1 to '7, forms a ceiling at least coextensive in area with the surface of the mercury in reservoir Ida, a brine overflow and chlorine outlet I911, a sloped depression 221a, an outlet conduit 22a, and a mercury conduit 26a; as will be seen from Fig. 8, ceiling Ito co-operates with the side walls of reservoir I do to form a constricted passageway over the surface of the mercury in reservoir I la. An aperture provided with plug 22p may be provided in ceiling lBa.

The operation of this alternative embodiment is essentially the same as that of the embodiment illustrated in Figs. 1 to 7 except that the normal flow of brine from the cell is through conduit 22a and thence to conduit I9a, which may be located entirely outside the unit.

With an appropriate flow of brine through the cell, accumulations of foreign material are continuously removed during the operation of the cell and collect at the bottom of conduit 22a, from which they may be removed through a drain 3| whenever desired. In; case the desired flow of brine issuch that mercury may be carried-into conduit 22a to an undesirably great degree, plug up may be removed fromceiling Ito and returned tdits closed position only when it is desired-to skim deposits from the mercury. Since the raising of plug 22p permits brine to flow directly over ceiling 18a into conduit 22a, the raising of plug 22preduces the velocity of brine over the-surface of the mercuryin reservoir Ma and in the-depression 20a so that it has little or no tendency to carry mercury with it into conduit 22a.

In Fig. 9 a second alternative embodiment is illustrated, like parts being designated. by like numeralswith-the letter I) appended. Thus depression 20b and plate I812 cooperate to provide a constricted passage for brine leading to outlet conduit 22b; plate l8b, as in the structure of Figs. lto 7, forms a ceiling at least co-exten sive'in area with the surface of the mercury in reservoir Mb, which reservoir, as in Figs. 1 to 7, forms a seal between the brine chamber and the regenerator chamber. Within outlet 22b anopenended pipesection 32 is adapted to be shifted vertica-lly from the normal elevated position to a lower-position indicated by dotted lines. In its normal position its open upper end is in approximate alignment with the top of a weir 3-3. When pipe 32' is in such a position, chlorine gas and brine will flow out over the weir and into pipe 32' thence down through conduit 22b to collecting chamber 34" and finally outthrough common conduit I92). If the pipe 32 is lowered substantially, for example, to the position shown by broken lines, normal brine flowis through the aforementioned constricted passage, then between Weir 33 and pipe 32 and finally down pipe 32 and out as before. Chlorine gas escapes by the route previously outlined. In order to remove foreign material from the surface of the mercury in reservoir I 411, pipe section 32 is depressed thus altering the brine head differential at the two ends of the constricted passage and accelerating brine flow through the constricted passage. Foreign material is thus swept into collecting chamber 34, from which it may be withdrawn as desired. B'y constructing chamber 34 of glass, the progress of the cleaning may be readily observed. It should be noted that conduit 22d of Fig. 8 serves as a collector in a manner similar to vessel 34 and maybe enlarged to assure more satisfactory settling and also may be made of glass for facilitating observation.

We claim:

1. In a mercury cathode electrolytic cell comprising a brine chamber and a regenerator chamber at different levels, the combination including means for conducting mercury between said chambers including amercury seal structure in which is disposed a pool of mercury, a ceiling above the mercury in said seal, said ceiling being at least coextensive in area With the mercury in said seal and defining with the upper surface of the mercury a constricted passageway terminating in an outlet from the seal structure, and means in said outlet which, when actuated, causes electrolyte from one of said chambers to flow through said passageway to said outlet so as to sweep foreign material from the surface of the mercury. I

2. In a mercury cathode electrolytic cell comprising a brine chamber and a regenerator chamber at a lower level than said brine chamber, the combination including means for conducting mercury from the brine chamber to the regenerator chamber including a mercury seal, a low ceiling over the mercury in said seal and disposed below the level of the brine in the brine chamber, said ceiling being at least co-extensive in area with the surface of the mercury in said seal and defining with said surface a constricted passageway terminating in an outlet from the seal structure, and means in said outlet which, when actuated, causes brine to flow through said constricted passageway to flush foreign material from the surface of the mercury.

3. In a mercury cathode electrolytic cell comprising a brine chamber and a regenerator chamber at a lower level than the brine chamber, the combination comprising means for conducting mercury from the brine chamber to the regenerator chamber including a mercury seal structure in which is disposed a pool of mercury, a low ceiling over said pool and disposed below the level of the brine in the brine chamber, said ceiling being at least co-extensive in area with the surface of the pool of mercury and defining with said surface a constricted passageway communicating at one end with the brine chamber and terminating at the other end in a conduit leading ofif from the space above the pool of mercury at a point slightly above the level of the mercury therein, a sloped floor rising gradually from below the normal level of mercury in the pool to said conduit and -means in said outlet which, whenv actuated, causes brine "to flow from said brine chamber through said passageway to sweep accumulations of foreign material from the surface of the mercury.

4. In a mercury cathode electrolytic cell comprising a brine chamber and a regenerator chamber at a lower level than the brine chamber, the combination including an overflow outlet for brine from the brine chamber disposed so as to maintain a substantially constant brine level in said brine chamber during normal operation of the cell, means for conducting mercury from the brine chamber to the regenerator chamber including a seal structure in which is disposed a pool of mercury, a low'ceiling over the surface of said pool and disposed below the level of the brine in the brine chamber, said ceiling being at least co -extensive in area with the surface of said pool and deflning'with said surface a constricted passageway communicating at one end with the brine chamber and terminating at the other end in a valved conduit leading from the space between the ceiling and mercury surface at a point slightly above the level of the mercury therein,

and a sloped floor rising gradually from the normal level of the mercury in 'said pool to said conduit, whereby, upon opening the valve, flow of brine is diverted from said overflow outlet to the constricted passageway to flush foreign material from the surface of the mercury.

5. In a mercury cathode electrolytic cell comprising a brine chamber and a regenerator chamber at a lower level than the brine chamber, the combination including a weir disposed near the outlet end of said brine chamber, an adjustable overflow outlet disposed behind said weir, said outlet, during normal operation of the cell, being maintained at a level at least as high as that of the upper edge of the weir so that brine flows from the brine chamber over the weir and through said outlet, means for conducting mercury from the brine chamber to the regenerator chamber including a mercury seal structure in which is disposed a pool of mercury, a low ceiling over the surface of the mercury in said pool and below the level of the brine in the brine chamber, said ceiling being at least coextensive in area with the surface of the mercury in said pool and defining with said surface a constricted passageway communicating at one end with the brine chamber and terminating at said overflow outlet, and means for lowering the level of said overflow outlet below the level of the upper edge of the weir, whereby brine is caused to flow through said constricted passageway to said outlet and thereby flush foreign material from the surface of the mercury in the seal structure.

ROY A. HORST. EUGENE B. PORT.

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

14,135 British 1902