US2916425A

US2916425A - Apparatus for the electrolysis of alkali metal salts and process therefor

Info

Publication number: US2916425A
Application number: US738356A
Authority: US
Inventors: Fujioka Shogo; Yoshida Seiji; Terasawa Shotaro; Shiragami Osamu
Original assignee: Asahi Glass Co Ltd
Current assignee: AGC Inc
Priority date: 1957-06-01
Filing date: 1958-05-28
Publication date: 1959-12-08
Anticipated expiration: 1976-12-08
Also published as: DE1093337B; FR1208271A; GB852597A

Description

1959 SHOGO FUJIOKA ETAL 2,916,425 APPARATUS FOR THE ELECTROLYSIS of" ALKALI METAL SALTS AND PROCESS THEREFOR 2 Sheets-Sheet 1 Filed May 28, 1958 Dec. 8, 1959 SHOGO FUJIOKA ETAL APPARATUS FOR THE ELECTROLYSIS OF ALKALI METAL SALTS AND PROCESS THEREFOR 2 Sheets-Sheet 2 Filed May 28, 1958 United States Patent APPARATUS FOR THE ELECTROLYSIS OF ALKALI METAL SALTS AND PROCESS THEREFOR Shogo Fujioka and Seiji Yoshida, Osaka, Shotaro Terasawa, Amagasaki, and Osamu Shiragami, Toyonaka, all of Japan, assignors to Asahi Garasu Kabuslnki Kaisha, Tokyo, Japan, a corporation of Japan Application May 28, 1958, Serial No. 738,356 Claims priority, application Japan June 1, 1957 5 Claims. (Cl. 20468) The present invention relates to apparatus designed for the electrolysis of solution of alkali metal salts, especially alkaline chlorides such as sodium chloride and the like, with the aid of mercury electrode and process therefor.

It is an object of this invention to provide a remarkably improved electrolytic apparatus or electrolyser as compared with the conventional electrolytic apparatus.

It is possible according to the present invention to provide an electrolytic apparatus having various advantages, such as the required amount of mercury is extremely small and the electrolysis can be carried into effect at a high current density but low voltage, and the like, which result from the fact that mercury is forcedly caused to flow and spread in all directions on a revolving metallic disc in the form of a thin layer.

According to this invention, mercury is fed on a metallic disc rotatable in a horizontal position, said mercury being forcedly caused to flow in all directions in the form of thin layer on the said disc while flowing thereon due to the centrifugal force of the revolving metallic disc, while a solution of alkali metal salt is submitted to the electrolysis between said mercury layer as cathode and an anode arranged in opposite and above to said mercury layer. Therefore, there is an advantage that the necessary quantity of mercury in an electrolyser or electrolytic cell is remarkably small. In addition, because of mercury being caused to flow and widen in the form of uniform thin layer, not only the spacing between both cathode and anode can be made small, but also the electrolyte solution is caused to flow and widen with stirring at high velocity by the revolution of the metallic disc. Thus, gas such as chlorine gas evolved on the lower face of the anode can be quickly dispersed. Consequently, the rise of the electrolytic voltage will be low even when the electrolysis is carried out at a high current density. It is possible, therefore, to perform the electrolysis at a high current density and, accordingly, the current efficiency is increased.

Furthermore, according to this invention, the mercury is forcedly caused to flow over the rotating metallic disc and the flowing movement of the mercury is favorably effected with stirring as described above. Accordingly, the allowable limitation for calcium and magnesium salts which are contained in the electrolyte solution becomes wider, leading to a decrease in the refining cost on account of a simple refining step of the electrolyte. Moreover, as described above, the flowing movement of mercury is performed satisfactorily, with the result the surfacial concentration of mercury amalgam being low and being capable of operating at low voltage, and the increase of current density as well as the improvement in current efiiciency can be obtained. Furthermore, a further advantage of this invention resides in that the head of mercury in the electrolyser or electrolytic cell can be made remarkably low. Because of various advantageous features as set forth above, a small, but extremely high ice electrolytic capacity can be obtained in this invention, whereby the floor area of the electrolytic cell is small with low construction and equipment costs.

Other objects, features and advantages of the present invention will be apparent from the following descriptions given with reference to the accompanying drawings.

In order that the present invention may be more clearly understood and readily carried into effect, three examples of the embodiment of this invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a longitudinal sectional view of an embodiment of the electrolyser or electrolytic cell according to this invention;

Fig. 2 is a plan view thereof, partially broken away;

Fig. 3 shows diagrammatically a longitudinal sectional view of another embodiment of electrolyser of a type wherein the electrolyser as illustrated in Figs. 1 and 2 are heaped one above another; and

Fig. 4 is a longitudinal sectional view showing a further embodiment of an electrolyser according to this invention.

Referring to Figures 1 and 2, a circular opening or bore 2 is formed at the center of an iron disc 1 horizontally positioned. A vertical hollow shaft 3 is secured at the disc shaped base 4 of its bottom end to a peripheral edge of said circular opening 2 by a suitable manner, for instance, welding or bolting and the like. The said shaft 3 is supported by a bearing (not shown in the drawings) and revolved by an appropriate driving means, thereby said iron disc 1 being horizontally positioned and revolved at 20100 r.p.m., for instance. Further, the upper face of said iron disc 1 may be horizontally machined, or inclined somewhat towards the outer periphery, or the said face may also be made as a curved surface. Moreover, these faces are usually finished smooth, but if necessary, a groove may be formed, or iron wires or nets may be secured thereto by welding in order to increase the surface area, which is permitted in cases where no obstacles exist. All these features are included within the scope of the present invention.

The aforesaid iron disc 1 is formed with the bent portion 6 by downwardly bending the circumferential edge portion throughout the whole circumferential portion of said disc.

The anode 7 made of a well-known material such as a graphite and the like is arranged above and oppositely to said iron disc 1 at the desired spacing thereto. This anode 7 is arranged in opposition to and above said iron disc 1 at the required spacing to said disc as set forth above. The anode 7 whose section is shown in Fig. 1 is a graphite disc having approximately the same diameter as said iron disc 1, and can be made of a single block of graphite material, or formed from an assembly of suitable shaped graphite blocks.

The anode '7 is carried in an ascendable and descendable manner on a cover plate 9 of an iron electrolytic cell 3, which includes the above-mentioned iron disc 1 and the anode 7, in the well-known manner. The position of said anode '7 is designed to be adjustable in accordance with the abrasion of anode 7 on its lower end face. 10 represents an anode lead of said graphite anode 7. Moreover, the iron electrolyser 8 is formed in the cylindrical form and bottom portion 11 thereof is formed in the conical form. In the joining portion between the cylindrical and conical portions of the electrolyser body an amalgam trap 12 is provided along the entire inside periphery. The said amalgam trap 12 comprises an overflow wall (12 surrounding the entire periphery of the conical body in order to reserve the amalgam therein.

The bent portion 6 of flange of said iron disc 1 extends to such a position that said bent portion 6 is immersed in the amalgam retained in the said amalgam trap 12, thereby the cylindrical body of electrolyser and the conical bottom body 11 are sealed by the said amalgam. Thus, the electrolyser body is divided with said sealing into an amalgamating chamber 13 of the cylindrical body and an amalgam decomposition chamber 14 below.

Further, the cover plate 9 of the electrolyser 8 is respectively provided with one or more feed pipes 15 for an alkaline salt solution and outlet pipes 16 for generated gas. Moreover, a suitable number of outlet pipes 17 for a depleted alkali metal salt solution or an electrolysed waste solution is fitted around the cylindrical wall of the amalgamation chamber 13, i.e. the upper half cylindrical portion of electrolyser 8.

The upper cylindrical wall of electrolyser 8, i.e. side wall of amalgamation chamber 13 is lined on its inner surface with corrosion resistant and electrical insulating material such as polyethylene chloride trifluoride (not shown). In particular, said lining extends to the lower end of the amalgam trap 12, and on the lining portion of said trap a thin iron plate is preferably set.

The bottom portion of electrolyser 8, i.e. the portion following to the lower end of the amalgam trap is conical as described above, the bottom wall 11 sloping toward the middle, said middle portion being formed with a recess 17, and the said recess serves as a mercury reservoir. A mercury pump 18 is immersed at its bottom end in the mercury in said mercury reservoir 18 (refer to Fig. 1). The mercury pump 18 is rotated by means of the revolving shaft 19 arranged in the hollow revolving shaft 3 of the said iron disc 1 and secured at its bottom to a rotator 20 of said pump 18. Said mercury pump as represented in Fig. 1 is of an inverted truncated cone shape with its top being cut olf. Between the casing of said pump 18 and the outer surface of the inner rotator 20 is formed a narrow conical space. This rotator may also be provided with blades, if necessary. The mercury is sucked up along the said space with the revolution of the pump. The top face of said pump is previously positioned at substantially the same level as the upper face of the iron disc 1 or somewhat lower than the said upper face. Thus sucked-up mercury is supplied to the upper surface of the iron disc 1 through a small hole provided in the portion for connecting the iron disc 1 and the disc shaped base 4 of the hollow revolving shaft 3. The surface of bottom wall 11 of the amalgam decomposition chamber 14 is conveniently provided with a number of blocks of amalgam decomposing material 21 made of, for instance, a graphite or sintered material of iron and graphite. For instance, they are preferably arranged radially at the suitable spacing around the mercury reservoir as a center and secured on the bottom plate 11 with wire gauzes and the like. The amalgam overflowing from amalgam trap 12 flows down among said blocks of the amalgam decomposing material 21, in the course of which said amalgam is decomposed by amalgam decomposing water. An inlet pipe 22 for amalgam decomposing water and another outlet pipe 23 for discharging a caustic alkali produced by the decomposition of amalgam are respectively inserted from below through the bottom wall 11 of said amalgam decomposing chamber 14 and these

pipes

22 and 23 open respectively at a desired level in said chamber. From this pipe 22 is introduced the amalgam decomposing water and the amalgam is decomposed to produce caustic alkali. The formed caustic alkali is discharged from the outlet pipe 23 together with the resulting hydrogen gas. Thereafter, the hydrogen gas may be separated from the caustic alkali. The mercury produced by the decomposition of amalgam is sucked up from the mercury reservoir 18 by the mercury pump 18 as referred to above, and fed through the aforesaid small hole 5 again on the iron disc 1 and forcedly spread in all directions on the surface of the said disc in the form of thin layer under flowing thereon due to the centrifugal force of the revolving iron disc 1, and the electroyte solution introduced from inlet pipe 15 for alkali metal salt solution is electrolysed between the anode and the cathode of the thin mercury layer, the resulting amalgam collecting in the amalgam trap. 12. On the other hand, the electrolysed waste solution is discharged from the outlet pipe 17, and circulated again as is wellknown after alkali metal salt is dissolved therein. The connection between the present electrolyser and an electric source (not shown in the drawings) is performed in such a manner that the anode current is connected from the electric source to the anode lead and the cathode bus bar is connected with the bottom plate of the amalgam trap 12 and the cathode current is connected to the mercury flowing down on the iron disc 1, thus a circuit is created. Further, alkali metal salt solution may be, if necessary, supplied from the upper enlarged portion 24 of the hollow revolving shaft 3.

As shown in the plan view, Fig. 2, the amalgam trap 12 is formed with an amalgam butter box 25 by extending the end of said trap 12 in the tangential direction of the cylindrical portion of the electrolyser. Thus, amalgam butter or anodic disintegratings formed during the electrolysis collect in said box 25, the amalgam butter and the disintegratings being conveniently drawn out through the opening 26.

Fig. 3 illustrates, by way of example, an electrolyser of a. type, wherein an electrolyser or electrolytic cell as shown in Figs. 1 and 2 is superposed in three rows, and which differs from the electrolyser of Fig. 1 only in that without providing a mercury pump 18 as described above at the middle inside of each electrolyser in order to transmit the mercury consecutively from the upper cell to the next lower one, and from the lowest or the third cell the mercury is recycled to the first cell by means of a pump installed outside of the electrolysers.

Such an arrangement as set forth above is more effective in order to reduce the floor area of the electrolyser.

In Figure 3,

numerals

27, 28 and 29 are respectively iron discs, each of which is mounted on the revolving shaft 30 and revolves at the predetermined velocity.

31, 32 and 33 represent all anodes respectively. Mercury is first fed through inlet pipe 34 and supplied on the iron disc 27 in an amalgamation chamber 63 of the first row of the electrolyser 41 through a pipe 35 surrounding the outside of the revolving shaft 30. Then, the mercury is forcedly spread, under flowing on the iron disc in the form of a thin layer over the surface of the disc 27 through the centrifugal force due to the revolution of said disc 27, and the electrolysis is effected between the cathode of the thin mercury layer and the anode 31. Alkali metal salt solution to be electrolysed may be fed from the mercury inlet pipe together with the mercury, or an inlet pipe therefor may be separately provided. Amalgam thus produced is collected in the amalgam trap 36. This amalgam trap 36 has a similar construction as that described in connection with Figs. 1 and 2. The amalgam over-flown from the said amalgam trap flows down among a number of blocks of amalgam decomposition material 38 in the amalgam decomposition chamber 37, in the course of which said amalgam is decomposed by the amalgam decomposing water and collected in the mercury reservoir 39. In this mercury reservoir 39, there is provided a cover 40, the lower end of which is immersed in the mercury of said mercury reservoir, thereby the amalgam decomposition chamber 37 of electrolyser 41 of the first row as well as the amalgamation chamber 64 of electrolyser 42 are arranged to be sealed with the mercury of the said reservoir 39. The cover 40 for sealing may be mounted on the revolving shaft 30 or secured to the bottom wall of amalgam decomposition chamber 37. The mercury over-flows from the over-flowing wall 44 through the lower end of said cover 40 and flows down to the iron disc 28 of the second row. The electrolyser 42 of the second row has a similar construction as that of .electrolyser 41 of the first row, and the mercury becomes amalgam on the iron disc 28 and collected in amalgam trap 45, from which the amalgam over-flows in the amalgam decomposition chamber 43 and is decomposed by amalgam decomposing water under flowing among a number of blocks of amalgam decomposing material 46 and collected at a mercury reservoir 47. Mercury overfiown a over-flow wall 61 of said reservoir 47 is fed from here onto the iron disc 29 into an amalgamation chamber 62 of electrolyser 48 of the third row similarly as in the case with said mercury reservoir 39. Thus, mercury flows over the disc 29, collected in an amalgam trap 49 after having become amalgam further over-flows and then flows down among a number of blocksof amalgam decomposing material 59 in an amalgam decomposition chamber 52 of electrolyser 48 of the third row and is decomposed and then collected in the last mercury reservoir 51 of electrolyser 48 of the third row. The mercury collected here is recycled to the mercury feeding opening 34 by means of a mercury pump 53 through a feed pipe 54. Each of

amalgam decomposition chambers

37, 43 and 52 is respectively provided with

feed pipes

55, 56 and 57 for amalgam decomposing water and outlet pipes 58, S9 and 60 for caustic alkali produced in the electrolysis.

In the

amalgamation chambers

63, 64 and 62 of the first, second and third rows, there are respectively provided feed pipes for alkali metal salt solution and outlet pipes for electrolysed waste solution in a suitable manner although they are not shown in the drawings. The outlet pipes for discharging gas generated in the amalgamation chambers are also arranged respectively in suitable positions though they are not shown in the drawings. The

anode lead rods

66, 67 and 68 are connected with anode laterally of each respective electrolysers. In the cathode consisting of the thin mercury layer, a cathode current is fed to the mercury layer by connecting a cathode bus bar (not shown) with the amalgam trap.

A further another embodiment of this invention as shown in Fig. 4 will he explained.

The electrolyser illustrated in Fig. 4 has a further simple construction as compared with those illustrated in Figs. 1 and 2 may be regarded as one adapted as an independent unit from those types illustrated in Fig. 3. Namely, a mercury pump is arranged outside of the electrolyser in order to circulate the mercury outside the cell. Namely, the electrolyser body, as in the said Figs. 1 to 3, consists of a cylindrical portion 69 and a conical portion 70, the bottom portion thereof being made of iron, said cylindrical portion 69 constitutes an outside wall of an amalgamation chamber 71, and the said conical portion 70 constituting the bottom wall of an amalgam decomposition chamber 72. The cylindrical portion 69 of said electrolyser is lined on the inner face thereof with a corrosion resistant and electrical insulating material such as polyethylene chloride tri-fiuoride resin, and the like. Said lining is so extended that it may also line the inner face of amalgam trap and a thin iron plate is preferably set on the lining portion of the said trap as described hereinbefore. Like the cases with said Figs. 1 to 3, the iron disc 73 has its circumferential edge portion bent downward, said iron disc 73 being so positioned that the disc may constitute the bottom plate for the amalgamation chamber 71, said disc 73 being carried by the revolving shaft 74 secured to the lower face of the middle of said disc and simultaneously designed to be revolved by an appropriate driving means (not shown) through said revolving shaft 74. The surface of the iron disc 73 may also be inclined towards its periphery or may have a curved face similarly as in the case of the electrolyser illustrated in Figs. 1 and 2. In the middle portion of the surface of said iron disc 73 is formed a circular recess 75, and mercuryis designed feed pipe 76 is hung down from above through the cover plate 77 of the electrolyser and is opened with its bottom end at a position slightly apart from the surface of said recess 75. Inside the mercury feed pipe 76 is fitted an iron plate having a number of small perforations (not shown). The mercury which is fed to the recess 75 of the iron disc 73 is arranged advantageously to be supplied in the form of small drops after passing through said small perforations. Further, the cover plate 77 of electrolyser is fitted with a feed pipe 78 for alkali metal salt solution such as, for instance, sodium chloride solution, through which the alkali metal salt solution is fed to the amalgamation chamber 71. To the side wall 69 of the amalgamation chamber 71 is secured an outlet pipe 79 for an electrolysed waste solution, through .which the waste solution is drawn out after the electrolysis has been elfected. Thereafter, as is well-known, said solution is again circulated after alkali met-a1 salt has been dissolved therein. On the cover plate 77 of electrolyser an outlet pipe 80 for gas generated in the amalgamation chamber 71 is secured separately. Gas generated during the electrolysis at the anode, for instance, chlorine gas is drawn out therefrom. Beneath the peripheral edge of iron disc 73 there is provided an amalgam trap 81 along the entire circumference of the cylindrical body 69 of the electrolyser. This amalgam trap 81 is so constructed that amalgam may be reserved up to a certain predetermined level by means of an inner wall 82 having over-flow notches 93.

Further, a bent portion 83 of peripheral edge of the iron disc 73 and the wall 82 are so designed that the bottom end of said bent portion 83 may be immersed in amalgam of the amalgam trap 81. Thus, the amalgamation chamber 71 and amalgam decomposition chamber 72 of the present electrolyser are sealed with amalgam in the amalgam trap 81, thereby preventing the electrolyte solution of the amalgamation chamber 71 from flowing into the amalgam decomposition chamber 72. The anode 85 is made of well-known anode material, such as graphite as described in Fig. 1 and formed at its middle with a circular opening or bore 84, through which a mercury feed pipe 76 centrally extends. The size of said anode is such that its outer radius is substantially similar to that of the iron disc 73. This graphite anode is also provided with a graphite lead 86. In the accompanying drawings, though it is not shown, this anode 85 with graphite lead 86 is supported in a usual supporting manner, and simultaneously connected with the source of electric current in order to conduct the anode current therethrough. For the cathode current a cathode bus bar 94 is connected with the bottom plate of the amalgam trap 81, and the mercury is supplied from the mercury feed pipe 76 to the recess 75 of said revolving iron disc 73. The mercury thus supplied to the recess 75 is forcedly spread in all directions on said iron disc 73 in the form of a uniform thin layer under flowing thereon by the centrifugal force due to the revolution of said disc, while the electrolysis of alkali metal salt solution is effected between the anode and the cathode of the thin mercury layer and the mercury becomes amalgam and collects in the amalgam trap 81. Thus, the amalgam collected in the amalgam trap overflows from the over-flow notches 93 of the over-flow wall 82 and enters in the amalgam decomposition chamber 72 and flows down along the bottom Wall thereof. The amalgam decomposition chamber 72 is conical as referred to above and has an inclined bottom wall 70 sloping down toward the center. An inlet pipe 87 for amalgam decomposing water extends through the inclined bottom wall 70 of said amalgam decomposition chamber from below and opens to the interior of the amalgam decomposition chamber 72, and an outlet pipe 88 for produced caustic alkali solution is also secured to the inclined bottom wall 70 of said amalgam decomposition chamber. These two pipes 87 and 88 open respectively to appropriate levels inside the amalgam decomposition chamber 72. On the upper face of the said inclined bottom wall 70 are suitably disposed a number of blocks of amalgam decomposing materials 89. As the amalgam decomposing material, a well-known material, for instance, a graphite or sintered material of graphite and iron, and the like are used. These blocks of amalgam decomposing materials 89 are respectively held, for instance, by a fitting piece secured to the inclined bottom wall 70 of the amalgam decomposition chamber 72. The amalgam over-flown from the overflow notches 93 of the over-flow wall 82 of the amalgam trap 81 passes through among said blocks of the amalgam decomposing materials 89 and flows down toward the center of amalgam decomposition chamber 72, in the course of which the amalgam is decomposed by the amalgam decomposing water fed from the feeding pipe 87. Caustic alkali solution thus then formed is drawn out of the outlet pipe 88 together with generated hydrogen gas, and then said hydrogen gas is separated in a suitable manner. A mercury reservoir 90 is formed at the center of the bottom of the amalgam decomposition chamber 72, a merury outlet pipe 91 is connected to said mercury reservoir 90.

The mercury, which is obtained from the decomposition of the amalgam in the amalgam decomposition chamber 72, flows down said chamber and is collected first in the mercury reservoir 90 and discharged through the mercury outlet pipe 91 and then recycled to the amalgamation chamber by means of a pump (not shown). At the underside of said iron disc 73 are fitted any suitable number, for instance, a few stirring blades 92 in order to promote the decomposing action, two of which are shown in Fig. 4. Also in this electrolyser, though not shown, the amalgam trap extends tangentially to the cylindrical body 69 of the electrolyser to constitute an amalgam butter box similarly as in the case of the electrolyser shown in Figs. 1 and 2. The amalgam thus produced in the cell is arranged to collect in said amalgam butter box and to be drawn out by any convenient manner.

The number of revolutions of the iron disc in the electrolyser or electrolytic cell of the aforesaid embodiments varies depending on the diameter of the said disc and other conditions. In general, 20 to 100 r.p.m. are satisfactory. However, the optimum number of revolutions may be selected in each case. For instance, it has been found from the result of the experiments effected with respect to the electrolyser of the type illustrated in Fig. 4 that in the case where a mild steel disc having a diameter of 530 mm. and a thickness mm. is used and a recess having a diameter of 70 mm. and a depth of 3 mm. is formed at the center of the bottom wall wherein the mercury is fed at a rate of 3 litres per minute, and sodium chloride solution is electrolysed, a satisfactory result is obtained at around 20 to 100, preferably 40 to 60 revolutions per minute.

In the said experiment, the mercury running on the iron disc may run smoothly in the form of a thin layer of below 0.5 mm. Accordingly, the spacing between the anode and cathode may be extremely small. Furthermore, from the result of this experiment, it has been found that even a minimum spacing of 1.3 mm. permits satisfactory electrolysis. However, with a little allowance a practical operation was carried out at the spacing of 3 mm., with extremely favorable results. Because of the above possibility of small clearance, the electrolytical voltage can be made remarkably low. Consequently, the electrolysis can be effected at a high current density. Thereby, the current efficiency is remarkably increased.

The result of the electrolysis effected in the electrolyser having an iron disc of 530 mm. in diameter under the following conditions is, by way of example, shown as follows:

Current efflclency Voltage Current density (Amp/din!) (Volt) (percent) Further, when an impure sodium chloride solution containing 1 g./l. of CaO such as calcium salt and 500 mg./l. of MgO as magnesium salt was electrolysed similarly in the same electrolyser, a smooth operation could be continued without any obstructions. The hydrogen gas in the chlorine gas generated at the time was below 0.5%. In a 25,000 amp. electrolyser, the diameter of the iron disc may be 1800 mm. and the thickness may be 15 mm. In this instance, the total mercury amount throughout the amalgamation chamber, the amalgam decomposition chamber and other pipings was 250 kg. The floor area of the electrolyser was 9 m. for caustic soda 1 metric ton/day in a caustic soda electrolytic plant of 2000 metric tons/month. Both values were remarkably small as compared with those in the usual electrolyser.

The electrolyser or electrolytic cell according to the present invention is by no means restricted by the foregoing descriptions of the embodiments. For instance, the electrolyser may be provided with a suitable stirrer for the electrolyte of the amalgamation chamber. Moreover, the anode may be so constructed that it may be rotated in the same or reverse direction with the iron disc. On the other hand, the amalgam decomposition chamber is not limited to the type described in the foregoing embodiments, and the amalgam decomposition chamber as shown in Fig. 4 may be used merely as a passage for amalgam. It is also within the scope of the invention to permit the amalgam to be drawn out of the electrolytic cell and introduced into a separate amalgam decomposition cell, such as a vertical type amalgam decomposition cell, and then decomposed therein.

T-hese modifications are included within the scope of the present invention.

Furthermore, the following types of amalgam decomposition cells may also be used. Namely, the revolving iron discs as set forth hereinbefore may be used similarly for the decomposition of the amalgam. That is, an iron disc may be similarly revolved, on which amalgam is fed, and the amalgam may now be caused to widen on the disc under flowing thereon in the form of a thin layer due to its centrifugal force. An extremely good result can be obtained even when amalgam is decomposed while being fiown. As an amalgam decomposition cell wherein such an operation is carried out, an amalgam decomposition cell can be employed in which a revolving shaft is secured to one or more iron discs and a mercury feed pipe for feeding mercury on said iron discs; an inlet pipe for amalgam decomposing water; and an outlet pipe for discharging produced caustic alkali are respectively provided and a counter-electrode is disposed directly or somewhat apart from the said iron disc.

What we claim is:

1. Apparatus for the electrolysis of alkali metal salts, which comprises a metallic disc rotatable in a horizontal position, an anode arranged opposite the said metallic disc and thereabove, and a mercury feed pipe for feeding mercury to the central portion of said metallic disc, a cathode being formed of a thin layer of mercury which is fed on the revolving metallic disc and spread in all directions on said disc in the form of a thin layer while flowing thereon by the centrifugal force produced due to the rotation of said metallic disc.

2. Apparatus for the electrolysis of alkali metal salts, which comprises an electrolytic cell body consisting of a cylindrical upper half portion and a conical lower half portion, the upper half and the lower half of which cell body form respectively an electrolytic chamber and an amalgam decomposition chamber, a rotatable metallic disc so arranged as to constitute the bottom portion of said cylindrical electrolytic cell portion and having a downwardly bent portion along the circumferential edge, a mercury feed pipe disposed at the central portion of said rotatable metal disc, an amalgam trap provided along the entire inner periphery of the boundary portion between the said cylindrical upper portion the said conical lower portion of the electrolytic cell body, the bent portion of the aforesaid rotatable metal disc being dipped in the amalgam collected in said trap, whereby the upper cylindrical half portion and the lower conical half portion are sealed from each other, and a number of blocks of amalgam decomposing material arranged on a conical bottom wall of said lower half portion, whereby the amalgam over-flowing from said amalgam trap flows down along the inclined bottom wall of the said lower conical portion, in the course of which the amalgam is decomposed by means of amalgam decomposing water.

3. Apparatus for the electrolysis of alkali metal salts, wherein at least two of the electrolytic cell body as defined in claim 2 are superposed vertically and the amalgamation is carried into effect in the upper electrolytic cell portion, and then the decomposed mercury is transferred to the lower electrolytic cell portion through a mercury seal.

4. Apparatus for the electrolysis of alkali metal salts as claimed in claim 2, wherein a mercury pump is provided at the central portion of an electrolytic cell body, the lower end of said pump being dipped in a mercury reservoir provided at the center of the bottom of the conical amalgam decomposition chamber and the upper end thereof being positioned at substantially the same level as the face of a rotatable metallic disc, whereby the mercury is adapted to be sucked up by the operation of a pump, while the mercury obtained in the amalgam decomposition chamber is recycled to the rotatable metallic disc by a mercury pump disposed outside the electrolytic cell.

5. A process for the continuous electrolysis of alkali metal salts which comprises the steps of producing a horizontal, radially flowing thin film of mercury by centrifugal action, flowing a horizontal, radially flowing film of alkaline metal salt solution upon said film of mercury, energizing said film of mercury to function as a cathode, arranging an anode directly above said mercury film to effect the electrolysis during the radial flowing of said mercury and metal salt films, collecting the produced amalgam and contacting said amalgam with amalgam decomposing material and solutions decomposing said amalgam and recycling the mercury thus obtained to produce the aforementioned mercury film.

References Cited in the file of this patent UNITED STATES PATENTS 646,313 Rhodin Mar. 27, 1900 705,264 Mactear July 22, 1902 FOREIGN PATENTS 1,020,965 Germany Dec. 19, 1957

Claims

5. A PROCESS FOR THE CONTINUOUS ELECTROLYIS OF ALKALI METAL SALTS WHICH COMPRISES THE STEPS OF PRODUCING A HORIZTONTAL, RADICALLY FLOWING THIN FILM OF MERCURY BY CENTRIFUGAL ACTION, FLOWING A HORIZONTAWL, RADIALLY FLOWING FILM OF ALKALINE METAL SALT SOLUTION UPON SAID FILM OF MERCURY ENERGIZING SAID FILM OG MERCURY TO FUNCTION AS A CATHODE ARRANGING AN ANNODE DIRECTLY ABOVE SAID MERCURY FILM OF EFFECT THE ELECTROLYIS DURING THE RADICAL FLOWING OF SAID MERCURY AND METAL SALT FILMS, COLLECTING THE PRODUCED AMALGAM AND CONTACTING SAID AMALGAM WITH AMALGAM DECOMPOSING MATERIAL AND SOLUTIONS DECOMPOSING SAID AMALGAM AND RECYCLING THE MERCURY THUS OBTAINED TO PRODUCE THE AFOREMENTIONED MERCURY FILM.