US2094384A - Electrolysis apparatus and process - Google Patents

Description

c. w. TUCKER ET AL ELECTROLYSIS APPARATUS AND PROCESS Filed Nov. 12,1934

' INVENTORS Carl w Tucker Karl 'F. Paul ATTbRNEY Sept. 28, 1937.

Patented Sept. 28, 1937 ctco'rnotrsrs APPARATUS AND raoocss' Carl W. Tucker and Karl F. Paul, Niagara Falls,

1 N; Y., assignors to E. I.

du Pont de Nemours & Company, Wilmington, Del., a corporation oi.

Delaware Application November 12, 1934, Serial No. 752,636

17 Claims.

This invention relates to an electrolysis cell construction and the process of electrolysis carried out in that electrolysis cell. More specifically our invention relates to the preparation of persulfuric 5 acid and, persulfates, and materials derived there-,

from, such as hydrogen peroxide, by electrolysis. More particularly the invention disclosed in this application is concerned with an improved construction for an electrolysis cell designed particularly for the preparation of the products above enumerated whereby these compounds may be produced more efficiently and more cheaply than heretofore possible.

One of the objects of fore the development of an electrolysis cell and an electrolysis process for the preparation of persulfuric acid and persulfates electrolytically which will operate at a higher electrical efliciency than is usual with the electrolysis cells now in ordinary commercial usage. Another object of our invention resides in so arranging the diflerent elements comprising our electrolysis cell that mechanical and/or chemical losses now incident a to the production of persulfuric acid and persulfates by electrolysis may be reduced to a substantial degree. Still another and more specific object of our invention resides in preventing loss of the liquid containing persulfuric acid or a persulfate, which has been prepared by electrolysis, as a result of diffusion losses through'the porous diaphragm which is usually an element of such electrolysis cells and separates the chamber containing the anode liquid or anolyte fromthe chamber containing the cathode liquid or catholyte. These and other objects of our invention, which will be obvious from the ensuing description, result in an improved electrolysis cell and an improved method of producing persulfuric acid, persulfates, and other similar chemicals by electrolytic action. The novel process resulting from the employment in electrochemical manufacturing of our novel electrolysis cell prepares the desired percompounds at higher electrical, chemical and mechanical efficiencies than are attainable in present day commercial operations.

Persulfuric acid is now commercially prepared by the electrolysis of an aqueoussolution of sulfuric acid in an electrolysis cell having a platinum anode immersed in the anolyte (or liquid surrounding the anode) and a lead cathode in the catholyte (or liquid surrounding the cathode). When it is desired to prepare a persulfate salt electrolytically the same type of cell is utilized employing in lieu of the sulfuric acid usually an alkali metal sulfate or an acidulated solution of this invention is there a lower cell in the ammonium sulfate. These cells contain a porous diaphragm which divides the space within the cell into two chambers, one containing the anolyte and the other containing the catholyte. It has beencustomary to form the porous diaphragm as a cylinder closed at the bottom, the space within the cylinder containing the anolyte and the anode assembly. The space external to the porous diaphragm contains the catholyte and the cathode,

which may be made of lead bent in the form of a coiled tube which encircles the porous diaphragm. This lead tube ordinarily functions both as cathode and as a means through which the cooling water may be circulated for the purpose of cooling the catholyte.

Since it has not been possible in economical operation to produce persulfuric acid or persul fates in high concentrations in asingle cell wherein the electrolysis is carried out in a large volume of liquid, it is now customary in commercial practice to arrange a number of electrolysis cells in a cascade arrangement. Ordinarily such cells are arranged in banks each bank comprising an assembly of many anodes and anolyte liquors surrounded by a single catholyte and cathode as-' sembly. Accordingly both the anolyte and the catholyte are permitted to flow trom one cell of the cascade arrangement after electrolysis into cascade arrangement where the liquids are again subjected to electrolysis thereby increasing the total overallconcentration of persulfuric acid or persulfate in the anolyte. The concentration of persulfuric acid or persulfate is built up in the anolyte and it is this liquor in which we are interested because of its subsequent distillation and hydrolysis to yield vapors of hydrogen peroxide.

By thus circulating the cathode and anode liquids and permitting them to flow from cell to cell down through the bank, the cells being arranged in cascade, it has been possible to obtain ultimately in the final cell of the bank a liquid 'rich enough in persulfuric acid or persulfate to permit economical subsequent treatment to yield hydrogen peroxide. Ordinarily it is the aim that the anolyte in the final cell of the cascade arrangement shall have its persulfuric acid or perbuilt up as a result of the successive electrolyses so that the concentration of percompound therein amounts to 20% or higher. It is to be understood that while both the anolyte and catholyte liquids are circulated it is the anolyte which is of value in. the preparation of hydrogen peroxide although if the cell disclosed in this application should be utilized in the electrolysis of other solutions it is conceivable that the catholyte might be the valuable material.

Electrolysis cells as at.present employed are disclosed in the Baum Patent Nos. 1,837,177 and 1,937,621. As disclosed in these patents, the anolyte is circulated as previously described, as is the catholyte. The cathode consists of a coiled lead tube which surrounds the porous separating diaphragm and has the double function of acting as a cooling coil as well as an electrical element of the cell. It will be evident from the drawing forming a part of the patents previously referred to, illustrating the. electrolysis cell to which the patents relate, that it is necessary for the anolyte or liquid in the anode chamber to be at a higher level than the catholyte since in the construction of this cell the anolyte is carried by an overflow pipe over into the next succeeding cell of the cascade arrangement at a liquid level which is higher than the liquid level in the cathode chamber. Mere inspection of the drawings of Patents 1,837,177 and 1,937,621 will make this evident as the overflow pipe, illustrated by the numeral 4 in those patents, is at a higher level than is ever attainable by the liquid within the cell container and surrounding the coiled lead cathode l4. Thus, to state this fact another way,

it has been customary for the porous diaphragm containing the anolyte to project out of the catholyte. Therefore, in order for the anolyte liquid to flow over into the next succeeding cell it is essential in the cell illustrated in the patents referred to that the level of the anolyte within the porous diaphragm be higher than that of the catholyte in the cathode chamber.

The reason for this has been generally that of constructional expediency. Obviously it is easier to carry the overflow or discharge tube for the anolyte over the top of the cathode chamber rather than carry it through the catholyte and cell wall. One important reason for this is that the cell walls are. ordinarily constructed in commercial practice of glass or ceramic materials which do not readily lend themselves to the piercing of apertures and the joining of metallic or non-metallic portions. Still another reason is that the anode assembly and overflow tube for the anolyte should be free to have some slight movement relative to the rest of the cell, as, for example, movement occasioned by vibration. Should the glass anolyte discharge tubes be securely held, as by passing through an aperture in the cell container wall, it would be broken ofi in practice should the anode assembly move even slightly with respect to the rest of the cell.

The necessity for operating so that the level of the anolyte is higher than the level of the catholyte has resulted in serious disadvantages.

-There is a tendency for the anolyte to difiuse through the porous diaphragm intothe catholyte, due to the pressure diiference resulting from the difference in level between the two liquids. The persulfuric acid or persulfate in the anolyte which has diffused through the porous diaphragm is decomposed when it comes in contact with the cathode thereby resulting in a distinct loss in difference in level between anolyte and catholyte ,is approximately the same in all cells regardless of their position in the cascade arrangement, the loss of persulfuric acid or persulfate will obviously increase proportionally with the concentration of the chemical in the electrolyte. As a result the anolyte flowing from cell to cell down the bank its persalt concentration increasing in its course, the loss'of persulfuric acid or persulfate is appreciably greater at the bottom of each bank of cells than at the top of each bank. While the volume loss through difiusion is constant, obviously that liquid lost at the lower cells contains a greater amount of the desired percompound.

In order to avoid diffusion of the anolyte through the porous diaphragm into the catholyte with its resulting loss in persulfuric acid or persulfate, we have improved the construction of the conventional electrolysis cell for this type of electrolysis as shown in Patents 1,837,177 and 1,937,621 thereby raising the level of the cathode liquid or catholyte so that it is approximately at the same level as the anolyte. This results in an improved electrolysis cell and in an improved process of operation in which all losses of product due to diffusion through the porous diaphragms are practically eliminated. While especially useful in the preparation of persulfuric acid and persulfates electrolytically, our process is of course adaptable for use in the manufacture of other chemical compounds by electrolysis. Accordingly with the improved process in mind, changes have been made in the conventional cell construction for the purpose of developing an improved electrolysis cell which changes are shown on the appended drawing wherein:

Fig. I is a plan view on the line AA of Figs. II and III showing the electrolysis cell assembly. The porous diaphragms are shown but the anodes and other elements within the porous diaphragm constituting the anode assembly have been omitted in each case. In one case the upper lip portion of the cathode box, described below, has been cut away to show the method by which the overflow tube for the anolyte is secured thereto.

Fig. II is a view partly in section and partly in elevation taken on the line B-B of Fig. I.

Fig. III is a view partly in section and partly in elevation taken on the line C-C of Fig. I.

In all these views none of the constructon of the anodes or anode assembly within the porous diaphragm has been shown because these features are not necessary to a complete understanding of our invention. In Figs. II and III, however, that portion of the anode assembly projecting out of the porous diaphragms has been illustrated. The anodes and conducting members leading thereto may be constructed as shown in the two patents previously referred to.

Referring to the drawing, the numeral 3 represents the cell container which is constructed of material resistant to the action of the electrolyte or is lined with such a material. Thus lead or a resinous compound is suitable since these materials are acid resistant. The container has inserted therein a number of cylindrical porous diaphragms 4 of which six are shown. These porous diaphragms are spaced throughout the length of the cell container in line as shown in Fig. I. Surrounding the porous diaphragms and running parallel with the inner wall of the cell container is a coiled tube 5 which may be of lead or of some other acid-resistant metallic material. This tube functions both asthe cathode and as a means ject.

' access;

The porous diaphra'gms- 4, which are closed at the bottom, rest on porcelain blocks 6 which support them from the bottom of cell. From each porous diaphragm at the upper end thereof, ex-

tending over the top of the cell container ll, is a discharge spout l which carries the anolyte liquid 7 overflows flange l3 and then flows to outlet conduit 8.

Completely surroundin the coiled tube cathode both at the sides and the bottomthereof and extending the full length of the electrolysis cell, is a cathode box 9 which may be formed of lead or some other acid-resistant conducting material. This box, which may be built of sheet material functions together with the coiled tube to serve as the cathode of the electrolysis cell.' The lead or other material of this cathode boxis continued across the top of the cell above the coiled tube electrode and the top of the cathode box is pierced by a number of openings for various purposes as will hereinafter beapparent. It is evident that the electrolysis cell comprises a number of anodes of which six are illustrated and but one cathode which functionsfor all the anodes.

If desired, the cell container may be omitted and the outside of the cell formed by the lead cathode box 9. However, this is generally unsatisfactory as the problem of suitably insulating the cathode boxes of adjacent cells becomes difiicult to solve. We have found it best to place the cathode box within an insulating cell container as shown.

I At each porous diaphragm there are openings in the top surface ill of the cathode box through which the diaphragms and anode assemblies pro- At each opening an edge or lip portion l l is turned downwardly into the cell close up against and surrounding the porous diaphragm fora purpose which will be explained subsequently. Along the outside of all the diaphragms the lead box is formed withan upstanding lip orflange portion 33 which is bent outwardly into a series of lip portions i l at which each anolyte overflow spout projects outwardly. These lip portions M are shaped to allow the tubes l to extend through the cathode box assembly. The overflow tubes or pipes may be cemented to the cathode box as shown at l5 and are thereby securely retained in place. As shown at l2 the upstanding lip or flange portion l3 of the cathode box is bent outwardly at one portion to form a sort of enlarged receiving spout through which the catholyte of the next higher cell in the cascade arrangement flows into the cell after leaving the catholyte outlet pipe 8 of the next higher cell. in Figs. IIand III,-the elevation of the central part of the lip portions It is lower than that of the remaining portions of upstanding flange it,

this is not so in the case of the enlarged receiving spout l2. The edge "or top portion of the metal forming spout i2 is at the same level as the remaining portions of the upstanding lip or flange portions l3.

If desired, the anolyte discharge tubes or spouts i may merely be positioned in the lip portions It and not securely held thereto by the cement it;

In this case the space between the lip portion and the tube should be regulated so that any While as shown catholyte liquid which may travel up between flanges ii and anode assemblies 4 will be prevented from flowing down the outside of the dis-' charge spout l by surface tension. This may be a preferable way of preventing seepage of liquid down the outside of the discharge tube as we have found that some cements tend to aid the flow of catholyte out through the space between lip M-and tube 7.

At one end of the electrolytic cell in the top portion ii! of the cathode box are provided a series of openings l6, 18, Hand 20 as shown. Opening. it is surrounded by a cylindrical sleeve 2| which constitutes a discharge outlet for the escape of hydrogen evolved as a result of the electrolysis in the catholyte. Openings i8 and i9 constitute respectivelylnletsand outlets for'the I catholyte cooling water which circulates through the coiled cathode 5. Opening 20 provides a thermometer well wherein a thermometer may be placed for the purpose of observing the temperature of the catholyte. mentioned that the anolyte overflow discharge tubes l are provided 'with small gas escape tubes H which permit any gases evolved in the anolyte to escape to the external atmosphere as the anolyte is carried over to the next lower cell in the cascade series.

In operation the liquid surrounding the cathode or the catholyte is maintained at a higher level than previously usual at those portions of the electrolytic cell surrounding the porous diaphragms. This is'accomplished by means of the elevating lips or flanges 53 attached to the cathode box 9. It is evident that the level/of the catholyte at each porous diaphragm may be as high as the top of the cell container 3 since the flanges l3 permit the catholyte to reach this level. Obviously then, the catholyte level is very close to a the level of the anolyte which latter level is determined by the level of the discharge tubes 1. The cathode liquid can therefore fill up the space at those portions of the cell surrounding each porous diaphragm between the upstanding flange l3 and the wall of the cell container. 3, thus in- At this time it may be suring practical identity of level between the anolyte and catholyte.

The depending flange or edge portions ll surrounding each porous diaphragm and inserted into the catholyte within the cathode box prevent any hydrogen evolved within the catholyte from escaping around the porous diaphragms. Any hydrogen-set free by electrolysis is thus confined within the cathode box and is allowed to escape through the discharge opening Hi. It may be mentioned that hydrogen is not electrically evolved in the space between the anode assembly and the depending portions it as the active portion of each anode (not shown) is below the level of the flanges, as illustrated in the drawings of 'the patents previously referred to. .A; small amount of hydrogen may escape thru the space between flange ill and the anode assembly d of each anode, but this amount is, in general, very small.

It may be mentioned that the catholyte in addition to filling up the space Within the cathode box also fills up the annular chamber between the cathode box it and the cell container 3. When the catholyte of the next higher cell is permitted to flow through discharge spout 8 over into the receiving spout l2 the catholyte obviously flows down into the interior of .the cathode box through the narrow inlet space between the depending flanges H and porous diaphragm d. If desired assembly which trated at 28, 29 may be placed in the top surface In of the cathode box for the purpose of permitting the catholyte liquid to get down within the cathode box. Or, if desired, the receiving spout I! may lead directly down into the interior of the cathode box. The apertures 28, 29 may be omitted if desired. 'If it is desired to provide narrow annular space between flange. I I and diaphragml. Of course it is to be understood that even without extending catholyte'spout 8 in this manner a certain amount of catholyte circulation occurs in any case.

Figs. II and III show that portion of the anode projects out of the porous diaphragms. f These parts comprise principally the anolyte tube Zlwhich carries the anolyte from the next higher cell in the cascade arrangement into the anode chamber within the cylindrical glass member 26. Surrounding the cylindrical glass member is metallic ring 23 to which are attached tantalum strips 22 which extend down within the porous diaphragm to platinum anodes '(not shown). Obviously the glass cylinder 26 provides a chamber through which cooling water .may be circulated for the purpose of cooling the anolyte.

Attached to the coiled cathode and serving as a plurality of conducting members through which the electrical connections are made to the cell, is a series of metallic strips which should be formed of a metal which is resistant to the action of the catholyte. Thesestrips are shown in Fig. I and are indicated by the numeral 25. On the drawing the electrical connection for the positive pole is indicated by a mark, whereas the conductors electrically connected marked by a sign.

One advantage-obtained by our novel expedient of maintaining the level of the anolyte and catholyte liquors substantially identical is that flawed ,or imperfect diaphragms can be used without large losses occurring. In practice many diaphragms. have small or them, especially after they have been in use for some time. By maintaining the levels of the two liquids substantially identical, we have made the surprising observation that intermingling of the two liquids does not occur through these apertures, as the positive pressure due to difference in level is no longer available to force one liquid into theother. This is a marked advantage of our construction and permits a considerable saving in the cost of maintaining the diaphragms, always an appreciable item in the cost of cell operation. 1

It will be appreciated that our improved cell may be useful for the manufacture of other sub stances or for other uses and accordingly we do not wish to be limited to details of construction or operation except as necessitated by the appended claims.

Therefore in the appended claims wherever we may refer to sulfuric acid solutions we mean to include therein not only aqueous solutions of sulfuric acid alone but tain various addition from whichpersulfuric also solutions which conagents, stabilizers, etc., acid or persalts can be to the cathode are I minute apertures in 2,094,384 an additional aperture or apertures such as illusobtained by anodic action. By an electrolysis cell is meant a cell in which electrical power is converted into chemical action as for the manufacture of desired chemical compounds.

We claim:

1. An electrolysis cell, including an anode and a cathode, said cell comprising in combination, a cell container, anolyte and catholyte liquids positioned within said cell container, and means secured to said cathode to maintain said anolyte and said catholyte liquids at approximately the same level.

2. An electrolysis cell including an anode and cathode, said cathode being formed as a coiled lead tube, said cell comprising in combination a cell container, anolyte and catholyte liquids positioned within said cell container, and means secured to and forming a. part of said cathode for maintaining said anolyte and catholyte liquids at approximately the same level.

3. An electrolysis cell including an anode and a cathode, said cathode comprising a coiled lead tube, said cell comprising in combination a cell container, anolyte and catholyte liquids positioned within said cell container, a lead box positioned below the level of said anolyte surrounding said coiled lead tube'cathode, and elevating flanges attached to the upper portion of said lead box to maintain said anolyte and catholyte liquids at approximately the same level.

4. An electrolysis cell formed with an anode, and a cathode in the form of a coiled lead tube, said cell comprising in combination a cell container, anolyte and catholyte liquids positioned within said cell container, a porous diaphragm surrounding an anode of said cell, a lead box positioned below the level of said anolyte surrounding said coiled tube cathode-and forming therewiththe cathode of said cell, an elevating flange secured to said lead box for the purpose of maintaining said catholyte at approximately the level of said anolyte liquid at those portions of the cell adjacent the porous diaphragm.

5. An electrolysis cell formed with an anode,

and a cathode in the form of a coiled tube, said ing an anode of said electrolysis cell, a discharge tube for carrying anolyte liquid out of the electrolysis cell, a lead box positioned below the level of said anolyte surrounding said coiled lead tube cathode and forming therewith the cathode of said cell, an elevating flange adjacent the portions of said porous diaphragm and forming part of said lead box for the purpose of maintaining said catholyte liquid at approximately the same level as said anolyte liquid at those portions of the cell adjacent the porous diaphragm, said elevating flange being bent outwardly into a lipped portion at one portion thereof to provide a means through which said discharge tube may extend for the purpose of carrying the anolyte over the upper portion of the cell container.

6. An electrolysis cell formed with a plurality of anodes and a cathode, said anodes being positioned within a plurality of porous cylinders, and said cathode comprising, in part, a coiled lead tube, said electrolysis cell comprising in combination, a cell container, anolyte and catholyte liquids positioned within said container and kept separate by said porous diaphragms, a plurality of anolyte discharge tubes, a lead box surrounding said coiled tube cathode and functioning therewith as the cathode of said electrolysis cell,

trolysis cell adjacent said lead box being provided with elevating flanges, for the purpose of maintaining the catholyte at alevel approximately equal to that of the anolyte at those portions of said eleceach of said porous diaphragms, said elevating flange being shaped at portions adjacent "to each of said diaphragms so as to permit said anolyte discharge tubes to carry said anolyte over the top of said cell container, and depending flanges closely adjacent to and surrounding each of said'porous diaphragms for the purpose of preventing the escape of any gasv which may be formed within said catholyte around said porous diaphragms. v

7. An electrolysis cell in which the catholyte and anolyte liquids are circulated which comprises, in combination, an anode, a coiled tube cathode, conducting means sm'rounding said coiled cathode tube and providing a chamber within which the catholyte is contained, a porous diaphragm positioned within said conducting means and surrounding said anode, the anolyte liquid being positioned within said diaphragm, means attached to said conducting means for maintaining said catholyte at approximately the level of said anolyte at those portions of said electrolysis cell adjacent to said porous diaphragm, and means adjacent the porous diaphragm for preventing the escape of gases developed within said catholyte at those portions'of said cell adjacent said diaphragm.

8. In an electrolysis cell including an anode and a cathode of the type in which the anolyte and the catholyte liquids are separated by a po-' rous diaphragm, means adjacent to said porous diaphragm for elevating the level of said catholyte so that it is substantially at the same level as said anolyte, said means being secured to and forming a part of the cathode of said cell.

9. An electrolysis cell comprising a cathode, a plurality of anodes, a plurality of porous diaphragms surrounding said anodes, a catholyte liquid adjacent to said cathode, a plurality of anolyte liquids positioned within said porous diaphragms and separated from said catholyte thereby, means for removing said anolyte from each of said porous diaphragms, and means adjacent to each of said porous diaphragms for elevating the level of said catholyte to approximately the level I of said anolytes which is determined in each case by the level of said anolyte outlet means.

10. An electrolysis cell comprising a plurality of anodes, a plurality of porous diaphragms surrounding said anodes, a-catholyte liquid, a plurality of anolyte liquids positioned within said porous diaphragms and separated from said catholyte thereby, a cathode positioned below the level of said anolyte liquid, means for removin said anolyte from within each of said porous diaphragms, and means adjacent toeach of said porous diaphragms for elevating the level of said catholyte to approximately the level of said anolyte, said level being determined by the level of said anolyte outlet means, said elevating means including an elevating flange secured to and forming a part of said cathode.

11. An electrolysis cell which comprises an anode and a cathode, a cell container, anolyte and catholyte liquids positioned container, a porous diaphragm surrounding said anode, said anolyte extending above the level of the major portion of said catholyte, and means for maintaining said anolyte and said catholyte liquids at approximately the same level at that portion of the cell adjacent said porous diaphragm.

12. In a two-liquid electrolysis cell including an anolyte and a catholyte, the combination which comprises a cathode positioned below the level of said anolyte liquid, an anode, a porous diaphragm separating said catholyte liquid from said anolyte liquidand means comprising an elevating flange attached to and forming a part of said cathode for maintaining said catholyte and anolyte liquids at substantially the same level at that portion of said cell adjacent'said porous diaphragm. I

13. A process for preparing persulfuric acid or persulfates by electrolysis which comprises treating a solution of sulfuric acid or a sulfate successively in atplurality of electrolysis cells arranged in cascade arrangement, said electrolysis cells being provided with porous diaphragms arranged to separate said electrolyte into a catholyte and anolytes positioned interiorly of said catholyte, circulating said catholyte and anolyte liquids from cell to cell in said cascade arrangement and maintaining said catholyte and said anolytes at substantially the same level in each of said electrolysis cells of said cascade arrangement throughout the entire electrolysis.

i l/An electrolysis cell including anolyte and catholyte liquids, an anode and a cathode, said anode extending substantially above the level of the major portion of said catholyte liquid, and means for maintaining said anolyte and catholyte liquids at approximately the same level only at that portion of said cell adjacent said anode.

15. An electrolysis cell which comprises anolyte and catholyte liquids, an anode, a cathode positioned substantially below the level of the upper portion of said anode and means cooperating with said cathode for maintaining said anolyte and catholyte liquids at approximately the same level only at that portion of said cell adjacent said anode.

16. An electrolysis cell including an anode and a cathode, a. cell container, anolyte and catholyte liquids within said cell container, the major portion of said catholyte liquid being positioned within said cell container below the upper level of said anolyte,and means cooperating with said cathode for maintaining said anolyte and said catholyte liquids at approximately the same level at that portion of said cell adjacent said anode.

, 1'7; An electrolysis cell including an anode and a cathode, anolyte and catholyte liquids, said anolyte liquid being positioned so as to have a level higher than the level of the major portion of said catholyte liquid, and means for maintaining said anolyte and catholyte liquids at approximately the same level at that portion of said cell adja cent said anode.

CARL W. TUCKER. KARL F. PAUL. I

within said cell

Images