US2104679A - Method of operating electrolytic cells - Google Patents

Description

Jgnr4, 1938. E. SORENSEN METHOD OF OPERTING ELEgJTROLYTIC CELLS -3 Sheets-Sheet 1 Filed June 25, 1936 INVENTOR BY I ATTORNEYS Jan. 4, 193

- E. soR'ENsEN,

METHOD OF OPERATING ELECTROLYTIC CELLS Filed Jfine 2s, 1936 3 Shets-Shet 2 1 I IKIA I r 1 I 1 w w I I I II I I MHW MHHH INVENTOR ATTORNEYS Jan. 4, 1938.

E. SO RENSEN METHOD OF OPERATING ELECTROLYTIC CELLO Filed June 23, 1936,

. I INVENTOR 6 am 41144 ATTORNEYS Patented Jan. 4, 1938 I UNITED STATES PATENT. OFFICE MZETHOD OF OPERATING ELECTROLYTIC CELLS Einar Sorensen, Rumiord, Maine, assignor to Oxford Paper Company, a corporation of Maine Application June 23, 1936, Serial No. 86,725

. V lClaim. This invention relates to electrolytic cells for producing chlorine and sodium hydroxide from of the brine;

brine of the type disclosed in my prior Patent #1,613,966, issued January 11, 1927, and more palil'ticularly to the method of operating such a ce The cell disclosed in my priorpatent coinprises a casing having a longitudinal partition which divides the cell into adecomposingcompartment and an oxidizing compartment. Brine, to be treated, enters the decomposing compartment, the floor of which is covered with'a slowly moving layer of mercury which constitutes a cathode. Graphite plates 1 located above the mercury constitute the anode. Electric current passing between the graphite plates and the mercury liberates chlorine irom the brine and the mercury forms an amalgam with the sodium The amalgam flows out of the decomposing compartment into the oxidizing com- 1 partment where it passes-over notched graphite plates. Measured quantities of water are fed into the oxidizing compartment. By the action.

set upin the oxidizing compartment the amalga n is decomposed and the sodium reacts with the water to f rm sodium hydroxide solution.

The mercury t us freed of its sodium thenenters a pump chamber in which a rotary pump liits the mercury and returns it to the decomposing compartment.

In the operation of electrolytic cells of the kind described above hydrogen gas is liberated during the reaction that takes place in the oxidizing compartment, The hydrogen gas escaping from the cell entrains some of the caustic. This results in a small loss of caustic but a more serious consequence is that the caustic entrained by the escaping hydrogen contaminates the cell room atmosphere.

The object of this invention is to provide a" method of operating a cell of the general type described above that will prevent the entrainment of caustic by the escaping hydrogen gas.

This is accomplished by providing-a liquid seal for the oxidizing compartment by'maintaining on the body of caustic a floating layer of a liquid which will permit the hydrogen gas to escape through it but which will hold back any caustic which tries to escape with the hydrogen.

An electrolytic cell capable of being operated by my method is shown in the accompanying drawings, but it is tobe understood that the method is applicable to cellsdiifering very materially from the one illustrated. The particular cell shown'in the drawings is an improve ment on the cellshown in my priorlpatent above referred to and certain features not claimed herein are claimed in my co-pendlng applications, Serial No. 43,027, filed October 1, 1935, 'Serial NO. 81,344, filed May 23, 1936, Serial N0.

93,580, filed July 31, 1936 and Serial No. 97,884, iiled August 26, 1936.

In the drawings: V

Figure 1 is a plan view of the cell with the cover and the anode assembly of the decomposing compartment removed to expose to view the interior. construction of this compartment;

Fig. 2 is a longitudinal section through the deof Fig. 1. In this View the cover and the anode assembly are in place; I

Fig. 6 is a longitudinal section through the oxidizing compartment taken on the line 3--3 of Fig. 1; E

Fig. 4 isa detailed sectional view of one "end of the oxidizing compartment taken on the line 4-4 of Fig.1;

Fig. 5 is a sectional view similar to Fig. 4 taken 7 on the line 5-5 of Fig. 1; g

Fig. 6 is a'transverse section taken on the line 6-6 of Fi 1; p

composing compartment taken on the line 2--2 Fig. 7 is a transverse sectiontaken :Iust to the rear of the section of Fig. 6, i. e., on the line 1-4 of Fig. 1; i

Fig. 8 is a transverse section taken just to the rear of the section of Fig. 7, i. e., on the line 8-8 of Fi 1, and j Fig. 9 is a transverse section taken on the line 9-9 of Fig.1.

The cell illustrated in the drawings has an external metal casing l which is generally rectangular in shape as shown in Fig. 1. It is divided into two compartments by a longitudinal partition 2. One of these compartments, designated 3, is the decomposing compartment and the other one designated 4 is the oxidizing compartment. As best shown in Figs. 6 to 9, inclusive, that part of the metal casing which houses the oxidizing compartment projects .downwardly to a lower-level passage through the channels 45, 46 and-"and is discharged through the passage 9 into the ox-' idizing compartment. the mercury is indicated by the arrows in Fig. 1. The mercury'in the decomposing compartment io'rms the cathode of an electric circuit, the anode being graphite plates l0 supported with their lower faces just above the-surface oi the mercury. As the mercury passes through the The directionof flow of tion to maintain the desired depth of brine within the decomposing compartment.

In the oxidizing cell the mercury amalgam passes over the notched graphite plates l2. are fed into this scribed to maintain in this compartment a pre determined density and -to compensate for. the

water consumed in' the displacement action. The displacement'action which takes place in this cell frees the amalgam of its sodium and causes the sodium to unite with the water to form" sodium hydroxide solution. The sodium] hydroxide solution is withdrawn from the oxidizing compartment through a pipe I! (Figs. 1'

and 9) which discharges into the lower end of receptacle M. This receptacle has a vertical partition l5 dividing it into two compartments. The sodium hydroxide solution enters the bottom of the right hand compartment (as. viewed in'Fig. 1) and flowsover the upper edge of the partition It is then- IS into the left hand compartment. discharged through an outlet pipe I! in the bottom of the left hand compartment. In the right hand' compartmentthere may be located a hydrometer ll (Fig. 9) by which the density of the sodium hydroxide solution may be measured. The level of the sodium hydroxide solution in the oxidizing compartment is determined by the elevation of the upper edge of the partition l5.

Therefore, the level of the sodium hydroxide solution in the oxidizing compartment may be varied. if desired, by raising or lowering the receptacle i4 and thereby raising or lowering the elevation of the upper edge of the partition 15. This may be effected by providing the pipe II with a removable section I. which may be replaced by a longer or shorter section.

The mercury freed of its sodium passes into a pump well It. A rotary pump 20 lifts the mercury from the well and discharges it at a higher elevation where it flows into the passage 8 of the decomposing compartment thereby completing the cycle. The pump has a series of peripheral pockets 2| (Fig. 6) to which the mercury is admitted through peripheral openings 22. It is discharged from these pockets through openings 23 (Figs. 7. and 8) in the lateral wall of the pump. It is then caught in the manner herein: after to-be described and passed on to the decomposing compartment. The mercury pump is operated by' a sprocket wheel 24 connected by means of'a chain 25 (Fig. 6) to -a sprocket wheel 28 (Fig. 3) on a any suitable manner.

The water to be supplied to the oxidizing compartmentflrst enters a receptacle 28 through a pipe 20. A pipe Ill having an elbow 3| at its outer end, which forms a small bucket, is oscillated so that it dips down into the water in the receptacle 28 and then as the pipe rises the water flows through the pipe and is discharged from the inner end 32 of the pipe into another compartment 33 of-the receptacle 28. The pipe 30 is mounted on a horizontal shaft 34 to the outer end of which is connected an arm 85;. This arm is engaged and deflected by a projection 35 associated with the sprocket wheel 24 so. that every Fig. 1)- there is a drive shaft 21 driven in the compartment 88 the water passes through a pipe 811 directlyinto the pump well l9. The pump picks up both the mercury and the water and the manner in which the water and mercury are separated so that the water is delivered to oxidizing compartment and the mercury delivered to the decomposing compartment will be hereinafter described.

The anode plates II are rigidly fastened to, and suspended from, the cover 53 of the decomposing compartment and forms unit therewith. Each anode plate is rigidly secured to the cover 53 by a graphite lead '1 threaded at both ends. .The lower end of the lead I1 is screwed into the anode ll, as'shown at I! and the upper end of .the lead passes through an opening in the cover 53 and is clamped to the cover by a fibre nut 59. In the particular cell shown in the drawings there are three anode plates in each channel thus making nine all together. The three anode plates of each traverse row are electrically con- 7 bedded in the concrete floor of the decomposing compartment are a series of transversely extend ing metal bars or strips 83 (Figs. 1 and 2).

These are supplied with current by a bus bar 64. I

Bolt terminals a are screwed and welded to the transverse bars'fland extend through the metal container and are secured to the bus bar 64 by means of nuts 64b. Over each metal bar 63 the concrete floor is provided with.a series of holes Giby means of which the mercury makes contact 7 with the bar. The path of the current is therefore from the bus bar N to the bolts 41, to the transverse bars 63, then to the mercury cathode, through the brine to the graphite anodes Ill, then .through the leads 51 and connecting strips to the bus bars 62. After the mercury leaves the decomposing compartment and before it enters the oxidizing com partment it forms a seal and thereby prevents brine from passing from the decomposing compartment to the-oxidizing compartment. This seal is therefore called the brine seal" and is constructed as follows: At the right hand end of the oxidimng compartment l (as viewed in pit or well 10 molded in the concrete lining; In plan view this well is relatively narrow longitudinally of the cell and is relatively long transversely of the cell. The bottom of the well is tapered to form a V as shown at H in Fig. 9, the taper being ,in such a direction that the mercury passing from the decomposing compartment through the passage 0 will flow down one of the arms of the V'.

The well 10 forms one of the chambers ofthe brine seal,-the other chambeig'shown at 72, (Figs.

1 and 3) being a pit located in the floor of the ening 13 extending through the wall I4 that sep-.

arates the well 10 from the oxidizing compartment. It is obvious from this arrangement that a body of mercury will be maintained in the chambers 10 and 12 of the seal at a constant level. As the mercury is continuously fed into the well 10 it is ,continuously discharged from the pit 12 into the oxidizing compartment. The body of mercury maintained in this manner by the seal "3,104,070 chambers and "I2 prevents anybrine from'ening 13. The mercury thus passing into the well dizing compartment through the seal and may enwash water through the a This prevents brine from being the mercury as it passes into the oxidizing compartment thus maintaining purity of the sodium hydroxide solution produced in the oxidizing com- I0, down one side of the v-shaped bottom and partly up its other side has its velocity spent. entrained with Dartment. The well 10 also serves as a concentration point for any broken up or dispersed mercury as well as any precipitated graphite from the anodes. This concentrated material can be easily removed during operation of the cell which greatly lengthens the time of operation possible between wash-ups. It is important to concentrate and remove the dispersed or broken up mercury for otherwise it will pass into the oxitrain some of the brinej Furthermore, any dispersed mercury which finds its way into the oxidizing compartment will remain in suspension in the sodium hydroxide solution and pass oil. with it thereby causing a continuous loss of mercury. The outer wall of the well 10 has anormally closed pipe 15 extending through it which communicates with the interior of the well and affords a convenient outlet for the wash water during washups. Moreover, by discharging the I pipe 15 it is prevented from entering the oxidizing compartment.

In passing from the oxidizing compartment into the pump well, the mercury forms a second seal called the caustic seal because it prevents caustic from passing along with the mercury to the pump well. a This seal comprises a pit 71 molded in the concrete floor of the oxidizing compartment anda pit I8 molded in the concrete floor of the pump well (Figs. 3 and 5) Communication between these two pits is established by a passage 19 in the wall 80 which separates the oxidizing compartment. from the pump well. The body ofmercury maintained in the 'cham; bers and I8. at a constant level constitutes a seal similar to the one previously described. As the mercury is continuously fed into the compartment 11 it is continuously discharged from the compartment 18 into the well of the mercury pump but no caustic can pass into the pump well.

28 picks up the mercuryin the pump well and also the water which has been fed to the pump .well by the water bucket 3!, already described.

and 7), which conducts them to a third mercury seal called the water seal because it prevents the water from passing alongwith the mercury into the decomposing compartment. This seal is formed by pits 82 and 83 molded in the con-' crete and a connecting passage M which places the bottom of these pits in communication, (Figs. 1, 3, 4, 5, 6, and 7.). As the mercury is continui ovsly fed into the pit 62 it is continuously discharged over the edge 85 and then passes into the transverse passage B which conducts the mercury to the first channel 45' of the decomposing compartment. The water held back by the seal 82-83-84 and which floats on top of the mercury as it passes through back into the pump well.

As previously stated the rotary mercury pump oi the pit 33 (Fig. 6)

splash of the mercury as it is discharged from the pump 20. Splashing of the mercury at this Point would be harmful as it would cause break-- ing up or dispersing of the mercury or would also augment vaporization. Prevention of vaporization of the mercury is very important from a health standpoint. A spill plate 81 (Figs. 1 and 3) extends from the bottom of the trough ll to I a point closely adjacent the discharge outlets 23 of the pump to prevent .spill of the mercury The water in the trough ll (supplied by the oscillating bucket 31 to the pump well and delivered by the pump to the trough 8|) acts as a. cushion for the falling mercury. It also acts as a wash and a submerging cover for the mercury the water seal 8243-84.

As previously described the oscillating water bucket]! supplies a uniformand measured quantity of water to the oxidizingcompartment. As

during its travel to the water is first delivered to the pump well'it keeps the mercury in the pump well and-in the pockets of the pump covered with water and thereby prevents vaporization of the mercury and the consequentcontamination of the;room atmosphere.

In the oxidizlng compartment hydrogen gasp is liberated whenthe sodium is freed from the amalgam and reacts with the water to form sodium hydroxide solution; The hydrogen gas is v usually permitted to escape to the cell room atmosphere and in so doing entrains a small amount of caustic. In order toprevent entrainment of caustic by the liberated hydrogen gas I maintain on the body of caustic in the oxidizing compartment a; liquid seal shown at 16 in Fig. 3.

The liquid floats on the surface of the caustic and permits the hydrogen gas to bubble through it but holds back any caustic which would otherwisebe entrained by the escaping hydrogen gas.

Prevention of entrainment of caustic by the hydrogen gas which is liberated-to the cellv room atmosphere is ,an important consideration from a, health standpoint. It also decreases the loss of caustic.

It will be noted from the foregoing description tain' in the oxidizing compartment a body or caustic solution having suilicint depth to prevent the liquid floating on its surface from contactingnwith the mercury on the floor of the oxidizingcompartment. This is made clear in Fig. 3 of the drawings. the caustic in the oxidizing compartment can be adjusted'by varyingthe elevation of theupper edge of the partition I6 in the caustic discharge re ceptacle l6.

The liquid employed for the seal lighter thanthe caustic solution so that it will float upon it, and it should have suflicient fluidity to enable the hydrogen to escape through it. The material used for thellquid seal should preferably possess the following additional characteristics; inertness with respect to the caustic, immiscibility in'caustic andwater and inability to emulsify with either; a sumciently high boiling point to prevent excessive vaporization and freedom from metallic impurities which would otherwisacontaminate the caustic and the mercury. 'I have found that a hydrocarbon mineral As above stated the levelof 4 gimme.

and have mcceaeoil 18 Mutable for the. fully used such an oil having the following specincationsz Type or baae I claim:

The method of operating an eiectroiytic of the type which has n decomposing commit-'- mient and an oxidizin: comportment throulh which mercury may be circulated, which oomprises producin: and maintainin: lbod! 0! canstic solution in the oxidizin: compartment. and

maintaining on the surface of the caustic eolution a. layer'oi' hydrocarbonminenl oil which is inert with respect to the. amide and which has sumcient fluidity to permit :03 produced in the oxidizing compartment .0 escape through it tvhereby the entrainment oi cauatic by the eslocaning gas is prevented.

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