US1837177A - Electrolytic process and apparatus - Google Patents

Description

Dec.'15, 1931; ca. BAUM 7 1,837,177

ELECTROLYTIC PROCESS AND APPARATUS I Filed Jan. 5. 1927 s Sheets-Sheet 1 r. 1. fig 11 Jt'CT/O/VAT/I-A 7/7 INVENTOR.

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' ATTORNEW a. BALJM ELECTROLYTIC PROCESS AND "APPARATUS Filed Jan. s. 1927 3 Sheets-Sheet 2 n M M a M/ b a n mmmv T mm w Mm me F76; ZZZ:

INVENTOR. M 73W BY A TTORNEYSQ Dec. 15, 1931. G. BAUM ELEQTROLYTIFC PROCESS AND APPARATUS Filed Jan. 5, 7

ATTORNEYS.

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Patented Dec. 15, 1931 1 UNITED STATES PATENT OFFICE GUSTAV BAUM, OF WEISSENSTEINFON-THE-DRAU, AUSTRIA, ASSIGNOR TO THE NIAG- ABA ELECTRO CHEMICAL COMPANY, INC., 0]? NEW YORK, N. Y., A. CORPORATION 01' NEW YORK ELECTROLYTIC PROCESS D APPARATUS Application filed January 3, 1927, Serial No. 158,457, and in. 'Austria January 28, 1828.

This invention relates to the production of persulphuric acid and materials derived therefrom, such as persulphates and-hydrogen peroxide, by electrolysis, and has for 1ts object to-provide an improved process and electrolytic cell whereby these results can be accomplishedmore efliciently and cheaply than heretofore and with a minimum of expense of investment in the platinum requiredfor anodes. Persulphuric acid or the persulphates can be decomposed or hydrolyzed to give sulphuric acid, or sulphates, as the case may be, and hydrogen peroxide.

It has heretofore been proposed to electrolyze an aqueous solution of sulphuric acid in a cell having a platinum anode in the anolyte, and a lead cathode in the catholyte, the anolyte and thecatholyte being separated by a porous diaphragm. Such arrangements have not commercially successful for a number of reasons. Among these are excessive heat generated in the cell by internal resistance, decomposition of product and side reactions due to theheat generated, low current density, contamination of anolyte due prolongation of the time of electrolysis n the effort to increase the yield, polarlzatlon-of the anode, etc. It has been attempted to over come the objection of heating'by cooling the anode and the electrolyte, but these expedients have only been of sli ht benefit to the yield or to the efiiciency an have not reduced the expense of installation and of maintenance to such extent as to be of practical benefit.

I have discovered that a minimum internal resistance of a diaphragm cell of this type is not only necessary to reduce heating but is also of decided advantage in permitting higher current concentrations to be used, and that the higher the current concentration used, the greater the unit conversion'to persulphuric acid. I havefurther found that in order to avoid side reactions or decompo-' sition in a cell having high current concentration and minimum internal resistance, the amount of anolyte between the anode and the diaphragm must be asthin as possible in the form of a thin sheet or film, and that such heretofore to my knowledge been necessary to use re rigeration for this purpose in order to maintain the desired work! ing temperature at the desired high current concentratlon employed. Previous attempts at this electrolysis required electrolyte temperatures of below 10 C. to 15 C.

The above advantages are all realized in an electrolytic cell wherein the anolyte, diaphragm, catholyte and cathode are concentric,

with the anode at the center because thereby its entire surface is effectively utilized and its volume is at a minimum. The anolyte is preferably circulated lengthwise of the anode as a thin sheet in a narrow annular space between the anode and diaphragm. Inasmuch as platinum is today the preferable anode material, the total cost of platinum in a large plant becomes very-material, but by having a platinum anode at the center within the anolyte, or in a centrall located concentric anode chamber, the total investment for platinum is materially reduced. The lead cathode can conveniently be in theform of a coiled tube encircling the diaphragm, through which cooling water can be passed to maintain the desired catholyte temperature. The internal resistance of a cell constructed as above described is substantially less than that 'of any prior cell with which I am familiar,

This arran ement did not allow of rapid difluslon o the persulphuric acid from the anodes and decomposition and overheating resulted. I have overcome this by utilizing way I have obtained solutions containing u to or more of per-sulphuric acid wit high yields at a temperature of about 20 C. These remarkable results have, hitherto never been attained.

Inasmuch as a number of anodes and diaphragms as above described can be connected 1n parallel in one catholyte, it is within the broad sco of'this invention to connect sinle cellsm cascade or a plurality of units Eaving a single catholyte and multiple anode units in cascade. Besides the advantage realized in increase of overall concentration of er-sulphuric acid by cascadin of cells, I ave found that while the ano yte may be circulated from cell to cell, and the catholyte similarly circulated from cell to cell, a decided gain in yield is obtained if the anolyte fromthe last unit, after being treated to separate hydro en peroxide, is then passed through the cat olyte circulating system before being returned to the anolyte circulating s stem. Apparently the cathodic action on this regenerated sul' huric acid removes substances which are ot erwise deleterious in the anolyte. Make-up solutions of sulphuric acid may also be subjected to this cathodic treaten Y -In order to carry out my improved process I have constructed an electrolytic cell of novel features. This will be described with reference to the attached drawings. Fig. I is an external front view of the cell; Fig. II is a vertical cross-section of a cell along line AA of Fi I, showing the arrangement of parts- Fig. II shows'a cascade arrangement of cells for series operation in a continuous process; Fig. IV shows in detail the-method of anode insertion in the anode chamber; Fig.

. V shows a slotted porous disk and Fig. VI

shows one form of anode strip. The same numbers are used throughout to designate the same or similar portionsof each cell.

Referring to the drawings, 1 is the cell container, constructed of material resistant to the action of the electrolyte or lined with such material, such as lead or a resinous compound. The container is provided w1th an overflow 2, at or near the top. The container is shown as having a round cross section but may be square or oval. In the center of the container is a cylindrical diaphra 3 of thin porous material and closed at t e bottom; this may be of unglazed porcelain. The space 5 open at the top but sea between the diaphragm and the container wall forms the cathode chamber. The cathode chamber is made large enough to carry a lead coil 14 which serves as the cathode and also for carrying cooling water. An overflow 4 is provided near the top of the diaphragm cylinder above the container wall. Inside the diaphragm cylinder is a glass tube ed at the bottom having a glass tube 6 leading through the seal into the anode chamber at 7. An overflow 13 leads from near the top of the tube 5 over the 3 top of the diaphragm. The tube 5 is of such diameter that. a narrow annular space 8 of less than about 3 millimeters is formed be-' tween the tube and the diaphragm. This narrow space is the anode chamber. The glass tube 5 rests on a slotted porous disk 21 (Fig. V). v

The anode may be any suitable arrangement of non-attackable metal having the proper electrolytic characteristics, such as platinum, inserted in the anode chamber 8. I prefer to construct my anode as follows:

A lead ring 9 having a connector 10 is fitted over the tube 5 and rests on a shoulder 11 formed on the tube. On the circumference of the ring 9 I fasten several strips 12 of platand the, number of the strips may be varied to adjust the anode surface to an amount desired. The anode surface is adiusted so as to give an anode current density of less than 2 amperes and preferably about 0.6 to 0.8 amperes per square centimeter. I have found that very thin platinum strips maybe used; these are preferably reenforced by being riveted or clamped to a strip of other metal not attacked during the electrolysis. Thus I have found that an anode strip of tantalum andplatinum such as described in my U. S. P. 1477,09!) one form of which is shown in Fig. VI, gives satisfactory results even though the tantalum is in contact with 'the electrolyte. The strips are fastened to the lead anode ring by rivets, screws or by brazing or soldering.

The cathode is formed by the oil of lead tubing 14 arranged in the 'catho' e chamber. A lead connector 15 is fastened to the coils to act as the cathode lead. The lower end of the cathode coil is carried up and over the edge of the container as at 16 and connects with the cooling water sup ly 17 by a rubber or other non-conducting'tu e 18. The upper end 19 'of the cathode coil'is carried up and bent over so as to feed into a tube 20 inserted into the glass tube 5. Cooling ofthe anolyte can thus be effected. The cooling water enters from 17 passes into the coil 14 and,

some cases because of structural features it is preferable to cool the anolyte by a separate cooling water supply. In this case the cathode cooling water is run directly to the sewer and a separate cold water supply led to the tube 20 as shown in Fi III.

In operation the ano yte is fed into the central tube 6 and flows to-the bottom of the diaphragm cylinder and then rises in the anode chamber in contact with the anode and overflows through 4. The catholyte is fed into the cathode chamber and overflows through 2. The passage of the current between the electrodes oxidizes the sulphuric acid or the sulphates to per-sulphuric acid or to the corresponding persulphate as the case may be.

As noted above, the current concentration is a most important factor in this electrolysis. It is now seen that I can easily apply high current densities per unit of volume. For example, if the anode chamber has an average diameter of about 5.0 centimeters, a depth about 50 cm. and a thickness of 0.2-0.3 centimeter its volume will be about 0.18 to .23 liters. If 80 to 100 amperes are passed through there will be an anolyte current concentration of between 300-550 amperes per liter.

.This type of cell construction enables me to obtain very low internal diaphragm resistances. The diaphragm can be made very thin as it does not support weight nor is it exposed to unbalanced pressures. I

- can thus obtain voltage drops of less than 0.5 volts across a porous ceramic diaphragm; the value of this is seen when it is realized that in previous work on this problem diaphragm resistances have been such that voltage drops of 0.8 to 1 volt have occurred.

The rate of flow of the anolyte can of course vary within wide limits. I have found that a suitable rate in a cell of the above dimensions is' about 3.25 cc. /ampere/ minute. Thus if the cell iscarrying a current of 100 amperes the flow will be about 0.325 liters per minute. At the rates and current densities noted above and at about 20 C. I have obtained a solution containing over 1% persulphuric acid from one passage through the cell. This solution can be recirculated, in the anode chamber of this the tube 6 of the topmost cell, passes through the anode chamber and overflows through 4 1 into the anode feed tube 6 of the next cell; the cathol-yte is likewise fed into the topmost cell and overflows through 2 into the cathode chamber of the next cell. The voltage drop across each cell is from 4 to 8 volts. This allows a series of electrical connection of the cascade, giving for 20 cells a total voltage drop of about 80 to 160 volts. In order to best utilize the current supply several of these series cascades may be arranged in parallel electrically. In this last case it ode chamber containing one large lead cathode coil. These several anode units are connected together and then connected to the cathode of the preceding cell thus giving a series-parallel electrical connection. The

anolytes from each anode unit in such an arrangement flow from one anode unit into a corresponding anode unit in the next set while the catholyte flows from the one common cathode chamber to the next.

When the anolyte leaves the lowest cell of such a cascade it contains a high concentration of persulphuric acid; the persulphuric acid is now decomposed to give hydrogen peroxide and sulphuric acid. The recovered acid is then raised to the upper cell and preferably made the catholyte supply. After passing the last cathode chamber the acid is returned to the upper cell and then added to the anolyte supply. This anolyte supply is adjusted by fresh acid and pure water so that its specific gravity will is convenient to have a number of anode units uncludmg the diaphragm in one large cathbe preferably about 1.285 although other concentrations may be used.

The anode chambers of the cells of the dimensions given above in a bank of 20 would have a total volume of 3.6 to 4.6 liters. The electrolyte would then be subjected to anode action for a total period of about 10 to 15 minutes.

I have thus electrolyzed in a 17 cell bank of cells, as described above, a solution of sulphuric acid containing about 500 grams sulphuric acid per liter at a temperature of- 20 C. to 21 C. and an anolyte current concentration of 400 amperes per liter. The anode current density was about 0.8 amperes/ cm. A 30.8% solution of per-sulphuric acid was obtained with a current efliciency of 71.5%. I v

' Solutions of sulphates can also be employed. Thus, I have electrolyzed a solution containing 20% ammonium sulphate, 2% sulphuric acid and 7 70 K SO at a temperature of 35 C. in the above apparatus.

The per salts were obtained by cooling outside of the apparatus'and showed a current 'etliciency of 74%. .I have also obtained sat:

isfactory results but lower current efliciencies at as low as 300 amperes per liter.

The cell described above is most suitable for my process but I do not wish to be limited, to Its structure since the high current concentration, thin flowing sheets of electro-' lyte and other features may be attained in other structures equivalent to that described.

.Nor do I wish to be limited to the exact rates persulphuric acid or' per-salts can be ob-' tained by anodic action.

I What I claim is:

1. Process which comprises anodically treating an aqueous solution ofsulphuric acid to form persulphuric aci'd,'decomposing the persulphuric acid to form hydrogen peroxide and sulphuric acid, cathodically treating the recovered sulphuric acid, and then anodically treating said sulphuric acid to produce addi-' tional persulphuric acid.

,2. Process for the production of persulphuric acid in a diaphragm type of elec- Ztrolysis cell which comprises subjecting an aqueous solution of sulphuric acid toanodic actionin a thin flowing layer-in said cell at an anolyte current concentration of between 300 and 550 amperes per liter.

3. The rocess of producing persulphuric acid in a iaphragm type of electrolysis cell equi ped with a lead cathode and latinum ano e, comprising electrolyzing a so ution of sulphuric acid having a specific gravity of :about 1.285 in said cell,sa1delectrolysis being c rried out at an anolyte current concentr tion ofbetween 300 and 550 amperes per liter and with a volta drop of less than 0.5 volts through said dlaphragm,

4. A rocess for producing hydrogen per- .oxide w ich comprises subjecting a solution of sulphuric acid having a specific avity of about 1.285 to anodic action in an e ectrolytic cell having separate anode and cathode cham- Zbers separated by a thin porous diaphragm,

said electrolytic anode action being carried out at an anolyte current concentration of 300 to 550 amperes per liter and with a voltage drop of less than10.5 volts across said ;'diaphragm, continuing said anode action tillthe anolyte ersulphuric acid content isin excess of 25 o, decomposing said persulphuric acid tolhydrogen eroxide and returning the recovered sulphuric acid to the cathode cham- Tber of the cell .while in part replenishin the anolyte with solution drawn from the cat ode chamber.

- 5.' Process of producing persulphuric acid in a diaphragm type of electrolytic cell com prising electrolyzing a flowing layer of aque ous sulphuric acid solution of less than ap proximately 3 mm. thickness as the anolyte. 6. Process of producing persulphuric acid in a diaphragm type of electrolytic cell comprising electrolyzing a flowing layer of aqueous sulphuric acid solution of less thanapproximatel 3 mm. thickness as the anolyte, the flow 0' said layer being longitudinal of the anode. 7. Process of producing a high concentration persulphuric acid solution by the electrolysis of aqueous sulphuric acid solutions in diaphragm type electrolytic cells which comprises increasing the persulphuric acid concentration in such solution by successive increments by anodic action in a plurality. of successive cells wherein the sulphuric acid of'the anolyte is electrolyzed in flowing layers of less than approximately 3 mm. thickness at a current concentration of between 300 and 550 amperes per liter.

8. In a process for the production of persulphuric acid by the electrolysis of aqueous sulphuric acid solution the step which comprises subjecting said sul huric acid solution to cathodic action be ore passing it in contact with the anode for the production of said persulphuric acid.

9. The process of producing concentrated solutions of persulphuric ac1d com rising purifying an aqueous solution of su phuric acid by passage as catholyte through a cascade of cells and thereafter passing said sulphuric acid at a rapid rate as anolyte through the said or similar cascade thereby oxidizing said sulphuric acid to ersulphuric acid.

10. Process of pro ucing high concentration persulphuric acid solution by the electrolysis of aqueous sulphuric acid solutions in diaphragm type electrolytic cells which comprises increasing the persulphuric acid concentration in such solution by successive increments by anodic action in a plurality of successive cells wherein the sulphuric acid of the anolyte is electrolyzed in flowing layers of less than approximately 3 mm. thickness at a current concentration of between 300 and 550amperes per liter, the rate of flow of said layers being such as to remove from the anode surface the high concentration of persulphuric acid as fast as formed.

11. Process of producing a high concentration of persulphuric acid by the electrolysis of aqueous suphuric acid solution which comprises increasing the persulphuric acid concentration insaid solution by successive increments by anodic action at a current concentration of between 300 and 550 amperes per liter on-thin flowing layers Of Sflld solution in a plurality of successive cells.

Signed at Vienna, Austria, this 15th day of December, 1926.

' GUSTAV 1B AUM.

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