US1847435A - Electrolytic manufacture of chlorine - Google Patents

Description

March 1, 1932. F. s LOW 1,847,435

ELECTROLYTIC MANUFACTURE OF CHLORINE March 1, 1932. F, s Qw 1,847,435

ELECTROLYTIC MANUFACTURE OF CXLORINE bmw,

F1 RT@ Nv Patented Mar. l, 1932 UNITED STATES PATENT OFFICE FRANK S. LOW, OF IPLAINIIELD, NEW JERSEY, ASSIGNOR T 'WESTVCO CHLOBINE ,i PRODUCTS, INC., OF NEW YORK, N. Y., A CORPORATION 0F WEST 'VIRGINIA ELECTBOLYTIC MANUFACT'URE 0F CHLORINE Application iled January 27, 1930. Serial No. 423,782.

This invention relates to the electrolytic manufactureof chlorine; and it comprises a process wherein a body of hydrochloric acid solution is kept in cyclic flow, to,

through and away from an electrolytic cell wherein chlorine and hydrogen are produced and separately collected; thesaid body flowing successively into and through a cathode and an anodecompartmeiit of said cell, thence through degasifying means to remove free chlorine, thence through means for replenishing the HC1 content and back to the cell; and it also comprises certain assemblages of apparatus elements useful in said process; all as more fully hereinafter set forth and as claimed.

In a. process described in my copending application, Serial N o. 315,007, whereon the present invention is an improvement, a body of HCl solution is electrolyzed, forming hydrogen and chlorine. I have found it is advantageous to maintain the body in cyclic circulation to and through the cell, through chlorine removino means, through means for replenishing the lCl concentration and back to the cell. With a forced' flow from the cathode chamber to the anode chamber and through means removing free chlorine from the lliquid before it goes back to the cell,`

cathodes of copper and other metals have a longer life.

In the accompanying drawings, I have shown a specic embodiment of apparatus within the purview of my invention and capable of use in the performance of the described process. IIn this showing:

Fig. 1 shows, more or less diagrammatically, the assemblage as a whole;

Fig. 2 is a side elevation of the electrolytic cell, certain parts being broken away;

Fig. 3 is a transverse section of the cell of Fig. 2 on the line 3-3;

ig. 4 is a side sectional view of a blow box or chlorine eliminating unit; while Fig. 5 is a diagrammatic-plan view of the blow box showing the arrangement of the baiiies.

In Fig. 1, the electrolytic cell is designated generally as 1. From acid storagel tank 2 59 acid 'Hows to and through the cell, and thence chlorine.

through a blow box 3, where chlorine is rei moved from the solution by air bubbled therethrough; the air being introduced at the bottom of the blow box. Chlorine carried forward is absorbed at 4. From the y blow box the acid flows downward throu h a tower 5 meeting an upward flow of H l, which it absorbs, replenishing its acid content. Tater may be introduced at 6 to make up the evaporation losses of the system. From the bottom of tower 5, the reconstituted acid may be returned to acid storage by the pump 7. A small electric heater isshown at 8 which may be used to heat the acid just before it enters the cell.

The construction of the electrolytic cell is best shown in Figs. 2 and 3. The cell comprises a containing case or tank 9, which may bel of stoneware or acid proof composition, a cathode 10, a cathode cap 11, a diaphragm 12, anodes 13, and anode cap 14. The cathode is an elongated box-shaped structure open at the top and conveniently made of perforated sheet metal. The metal used may be copper, nickel, Monel metal or other metal having a fair resistance to the attack of chlorine-free hydrochloric acid. The top edges of the cathl nuts 16 hold the anodes in position, shoulder ing ca them lagainst the anode cap 14'.' `Electrinuts and these are connected to the positive busses 17. Electrical connection is made to the cathode through the copper rods 18 which extend through holes in the cathode cap 11,

and are supported in position by the cathode nuts 21. To the lower end of the copper rods are welded channel bars 19 which are in turn conductors are held between the anode A riveted to the inner sides of the cathode. Resting on the channel bars and surrounding the copper rod is placed a glass sleeve 20. This extends below the normal surface of the acid in the cell and protects the copper rod from corrosion. I have found that any portions of the cathode protruding into the gas space of the cell are rapidly corroded. Hence I provide for total immersion of the cathode proper and for protection for the copper rods.

18 inthe gas space. l

The anode and cathode caps can be made of stoneware, concrete or acid proof composition. The anode cap bears a peripheral flange which may rest in a recess in the top of the tank 1. Joints between the container and the anode cap and between the latter and the cathode cap are rendered gas 'tight by means of putty seals 22. The acid inlet' and the hydrogen and chlorine outlets are designated at 23, 24 and 25, respectively. An acid exit and a drain are provided at 26 and 27, respectively. Acid inlet 23 delivers into the cathode compartment at any desired level which may be near the top or bottom and acid exit 25 takes out from the anode compartment.

The construction of the chlorine eliminat-V ing device or blow box is best shown in Figs. 4 and 5. The box like structure 3 is partitioned by means of a porous diaphragm 28. This may be conveniently a ,Filtros plate or be of other acid proof, finely porous material. Air enters at 29 below this diaphragm and is forced through the acid which enters the unit at 30, Hows over the -diaphragm in a sinuous path between the baiiies 31, becoming thoroughly aerated in passing and finally leaves at 32. The air intermixed with chlorine liberated from the acid leaves at 33 and may be led through an absorption unit 4 (Fig. 1). In this hypochlorite may' be made. In operation, the flow of the acid through the cell from cathode to the anode compartment is adjusted at such a rate that diffusion of the dissolved chlorine from the tration. The minimum rate of flow to preanode compartment back through `the dia` phragm and into the cathode compartment 1s prevented. The iiow is also correlated to control the exit liquor at the desiredconcenvent the presence of chlorine in the'cathode compartment will vary with the dimensions of the cathode compartment, with the porosity of the diaphragm, etc. In a specilicexample, using a cathode having4 an external surface of approximately 20 square feet and e the best grade of twilled asbestos cloth a flow of 36 to`48 gallons per day was found sutiicient. This represents about 1.8 to 2.4:l gal lons per day, per square foot of diaphragm area.

lIf the strength of the acid isfdepleted too 'far in its passage through the cell the eiiiciency of the process is reduced due to the voltage rise. In a series of experiments it was found that the voltage required to give a constant current in the cell remained substantially constant as the exit acid concentration was gradually reduced from 30 to 20 per cent. At. lower concentrations the required voltage gradually increased; the rise becoming accelerated below concentrations of about 10 per cent. Exit acid concentrations of less than about vper cent result in inetticient operation of Vthe cell. I have found that the maximum and minimum concentrations, for suitable operation, of the entering and exit acids are about 25 per cent and 5 per cent, respectively, while the advantageous concentrations range between 20 and l0 per cent.

Control of temperature is an important factor in reduction of operating cost. Experiments conducted in laboratoryv cells, where variations through wide limits were possible, have shown a reduction in voltage of about 0.01 volt per degree between 20 and 40, a reduction of about 0.007 volt per degree between 40" and 50 and a reduction of about 0.005 volt per degree between 50 and 70 C. An increase in temperature of the electrolyte also reduces the solubility of the chlorine dissolved in the hydrochloric acid, causing a larger proportion to be liberated in the cell and less in the blow box. .Y

I have found that the Joule heat is suiii cient to maintain the temperature of the electrolyte within the cell between about 45 and 75 C. Considerable heat is also liberated in the solution of the HCl gas in the spent electrolyte. To supplement these sources of heat, however, I may provide a heating unit such as shown at 8 inFig. l. I consider the best operating temperature as within the range from 45 to 100 C. The acid boils at about 110 C., and at any temperature above 100 C. an inconveniently large amount of water va.-` porY is present in the evolved chlorine and hydrogen.

Most of the hydrogen generated in the cell is evolved at the outside of the cathode, between the diaphragm and the cathode and finds its way through the perforations into the cathode compartment.l

I have taken precautions to prevent attack of the copper while the apparatus is in use, but in standing idle some slight attack usually occurs. This, however, has some advantage since the dissolved copper is redeposited on the cathode as spongy copper. I have noticed that the presence of this spongy copper results in an appreciable lowering of the voltage of the cell and'therefore in someeconomy o power. I sometimes purposely coat the cathode vwith lspongy copper.` Roughening its surface by a sand-blast is also an advantageous expedient.

I nd that on the whole I obtain the best results bythe use of copper as a cathode. I

have found, for example, that a voltage of 2.5 between two graphite electrodes is lowered t0 about 2.1 volts when the graphite is replaced by a copper cathode. The resulting reduction in operating cost is highly important in contributing to the economic success of my process.

I have found that in the electrolysis of hydrochloric acid the anode current'density is more important than that at the cathode. This makes advisable the use of an interior cathode and peripherally disposed anodes as shown in my cell design.

While I have illustrated a tower for the acid absorption unit, thehydrochloric acid and solution passing in countercurrent flow, I have had considerable success with an absorption unit of similar design to my blow box, the hydrochloric acid gas being forced in below the Filtros plate and into the solution.

A material advantage of my process lies in the extremely high purity of the chlorine obtained, which will run 99.9 per cent Cl2 over long periods of operation, with O2 and CO2 entirely absent. Since there are no secondary reactions in the cell when the above described operating conditions are maintained the maintenance cost for the cell is very low.

vWhat I claim is:

1. In the process of claim 9, maintaining the electrolyte in the cell at a temperature between and 100 C.

2. In the process of claim 9, maintaining the HC1 concentration not below 5 per cent in the solution flowing out of the cell and not above per cent in the solution flowing into the cell.

3. In the process of claim 9, maintaining a concentration of about 20 per cent HCl in the solution flowing into the cell and about 1,0 per cent HC1 in outiowing liquid.

4. ln the process of claim 9, electrolyzing thel flowing liquid between graphite anodes and a copper cathode.

5. In apparatus for the manufacture of chlorine from a hydrochloric acid solution the combination of an electrolytic cell having an anode chamber and a cathode chamber, means for flowing HCl solution into the cathode chamber, means for flowing the HCl solution out of the anode chamber, means for dechlorinating removed solution, means outside the cell for replenishing the HCl content of the dechlorinated solution and means for returning the replenished solution to the cell; all in continuous flow.

6. In apparatus for the electrolysis of HC1 solution, a casing, a. central perforated` metal cathode, a porous diaphragm on said cathode, anodes between the cathode and the sides of the casing, means adapted to supplying replenishing HC1 solution near the cathode and means for removing depleted acid solution from a point near the anode.

7 In apparatus for the electrolysis of HC1 solution, a cell with a centrally' disposed cathode, a cathode cap resting on said cathode to form a cathode compartment therewith, anodes surrounding said cathode, an anode cap to form an anode compartment surrounding said cathode compartment, gas outlets from said cathode and anode compartments, a pervious diaphragm separating the anode and cathode compartments, an acid solution feed leading to the cathode compartment and an acid solution exit leading from the anode compartment.

8. In producing hydrogen and chlorine byA electrolysis of a solution of HCl the process which comprises establishing and maintaining a flow ot HCl solution through anelectrolytic cell having anode and cathode chambers, the iow being from the cathode chamber to the anode chamber and at a rate sufficiently rapid to ensure. that no substantial amount of chlorine reaches the cathode chamber to mingle with the hydrogen there evolved.

9."I`he process of producing chlorine and hydrogen which comprises electrolyzing a body of HCl solution to form gaseous chlorine and hydrogen in an electrolytic cell having an anode chamber and a cathode chamber, removing themchlorine gas from the anode chamber and sepalxrately removing the hydrogen gas fromtle' cathode chamber while flowing said body of HC1 solution in a closed circuit through the cathode` chamber, thence through the anode chamber, through dechlorinating means, through HCl replenishing means and back to the cathode chamber.

10. In the process of claim 9, flowing the I-ICl solution at a rate between 1.8 and 2.4 gallons per day per square foot of surface` area between the cathode and the anode chambers.

11. A process which comprises electrolyzing an aqueous solution of HC1 substantially free of other ingredients in an individual cell having an anode chamber anda cathode chamber separated by a pervious diaphragm, thereby producing substantially pure gaseous chlorine and hydrogen, removing partially depleted solution from the anode chamber, replenishing said depleted solution by dissolving HCI gas therein and returning the replenished solution to the cathode chamber.

In testimony whereof, I have hereunto affixed my signature.

FRANK S. LW.,

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