DE1467215A1 - Process for the electrolysis of alkali chlorides using the mercury process and an electrolysis cell for this process - Google Patents

Description

• MÖNCHEN 27 Dr.-Ing. HANS RUSCHKE ρ »» »» «* st ™ *, a

Pat AnMmIl Anular IBERLlN 33 Dipl.-Ing. HEINZ AGULAR

Augu.t.-Viktoria-Str.Be «6 PATENTANWÄLTE

Μ. * ».». »« «· Ϊ25Γ« βΪΓ

Telephone: Mil / "» ™ ^ l B »* l <oote:

Postal checking account; I A · D / Z | O Dresdner Bank

Berlin Weet 74 94 Munich Bank account: Dep.-K »s * e LeopoldetraBe Bank f. Commerce and Indtwtri · Account 69 BIS Deposit box 82 Telegram address:

Tepi'itz «straBe 42 Quadrature Manchen

Account 32 7608 Telegram address:

Quadrature Berlin A 792

Asahi Easei Kogyo Kabushiki Kaisha, Osaka. Japan

Process for the electrolysis of alkali chlorides by the mercury process and electrolysis cell for This method

The invention relates to a process for the electrolysis of alkali chlorides using the mercury process and an electrolytic cell that can be used for this method. The invention particularly relates to such a method in which electrolysis is carried out at a high current density using an anode made of titanium plated with platinum, as well as an electrolytic cell for this purpose

In the electrolysis of alkali chlorides by the mercury process, it was common practice to use a graphite anode and to choose the current density as high as it was economically possible with regard to the voltage to be used, in order to reduce the production costs in this way. Usually, however, the working current density is 35 - 50 Amp./dm ² ,

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at most about 100 amps / dm. A higher current density has never been used because in electrolysis at a high current density of

over 100 Amp./dm with a graphite anode an increased heat development, an increase in the voltage, a break of the plates and other ^ aids due to the poor conductivity of the graphite anode are due. Furthermore, when working at high current densities, there is a risk of explosions as a result a mixture of the chlorine gas with hydrogen gas, the as a result of the drop in hydrogen overvoltage generated by the broken pieces of the panels has been caused. Furthermore, the chlorine gas is contaminated with the carbon dioxide produced and finally, the economy due to the reduction in current efficiency degraded. For these reasons, there have hitherto been extremely difficult to use electrolysis a graphite anode at such a high current density of over 100 Amp./dm.

To avoid these disadvantages, platinum-titanium anodes are used has been introduced. Such an anode has high corrosion resistance, machinability, electrical conductivity, mechanical strength and oxygen overvoltage. Since this electrode neither with

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the formed gas reacts and leaves fragments disfigured by breaking the plates, it does not form hydrogen gas. By using such an electrode, the chlorine gas is therefore kept in a highly pure state, the risk of explosion is reduced and the current density is kept at a remarkably high level. These and other advantages of the new electrode, however, more than offset by the high cost of titanium%

and platinum materials and the difficulty of platinum plating titanium plates. Beyond that there is no noticeable difference in the electrolysis voltage between the platinum, titanium and graphite anodes, provided that the the same structure and procedure can be applied. As a result of these disadvantages, the new electrode has not been produced on an economical scale.

The subject of the present invention is a process for the electrolysis of alkali salts by the mercury process, in which to work at .3 \ eneT

Current density up to 300 A / dm and with a voltage of not more than 4.5 volts and with an electrode gap of less than 3.5 mm for immersion of the anode end below the mercury level, an anode consisting of titanium plated with platinum is used.

The electrolytic cell for carrying out the method according to the invention is characterized in that

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a salt water gas separation chamber attached to the amalgation chamber and one at its lower part with an opening for peeling off of the mercury provided queek silver deposition chamber adjoin that in the upper parts the Partition walls of the three chambers with the exception of the border area between the amalgation chamber and the mercury separation chamber for overflow of salt water and foam openings or with their lower ends attached to the bottom of the cell Partition walls are arranged that the chambers with a cover consisting of one piece or common are covered separately with several lids and that the overflow of salt water and foam from the amalgation into the salt water gas separation chamber by means of a Device, such as a turbine stirrer or a a spraying of the electrolyte surface with salt water or gas jets enabling device promoted will.

The electrolytic cell has an anode arrangement, which consists of individual grooves or bores consists of thin platinum-plated titanium plates that are parallel to each other and either perpendicular or combined with a certain inclination to the cathode surface or combined with electrically conductive parts into one piece are.

Is the electrolysis with a graphite anode one

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carried out in the usual type, they grow on the electrode surface The gas bubbles formed gradually increase to a diameter of about 0.5 - 1 mm and then begin to form move further as a result of the flow of the liquid as well as its own buoyancy. While moving along The vesicles continue to grow on the electrode surface to a diameter of about 2 - 3 mm and sometimes even 6 - 8 mm. Finally, the bubbles rise upwards and are released from the cell through channels or gas outlets discharged.

In the mercury process, the anode is usually placed horizontally, and therefore it collects the gas on the flat part - if there is one - of the electrode surface, whereby the Electrolysis process is interrupted on this part. To overcome this difficulty, have been done so far Numerous attempts have been made to determine the processes for making the panels and for carrying out the To improve electrolysis. However, with all of these improvements, the application of a current density within a range below 100 amp./dm collected. Working at a high current density of

over 100 amp./dm was due to various difficulties not recommended.

At a high current density of over 100 Amp./dm 909808/0879

the gas bubbles formed have a small size and a large total volume, and the amount of the bubbles generated is larger than the amount of the bubbles escaping from the surface of the electrolyte. As a result, the difficulty arises of causing the gas bubbles on the surface to burst - a problem which has not existed with the low current density of less than 100 amps / dm used up to now. At the interface of the electrolyte and the gas phase in the amalgamation chamber, therefore, a layer of accumulated gas bubbles is formed, with the result of an increase in the electrolysis voltage. When the electrolysis is performed, for example in a conventional electrolytic cell at a current density of over 180 Amp./dm, the entire space is taken out of the bottom of the electrode from an accumulated layer of gas bubbles, and the Amalga- \ mierungskammer filled with the foam, whereby a sharp increase in the electrolytic voltage is caused.

The vesicles not only isolate the one to be electrolyzed Area of effective electrolysis, but also cut off the supply of salt water to the Electrode surface. This appearance of the vesicle accumulation occurs in a conventional electrolysis cell in which, as described above, a graphite anode at a

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Current density of no more than about 100 amperes / dm used will, not on. The removal of the salt water has therefore usually been carried out in such a way that it from the amalgamation chamber to the salt water separation chamber was peeled off in the end box to prevent it from spreading through on the queek silver surface floating broken graphite pieces secondary formed hydrogen gas mixed with the chlorine gas. f

However, with the application of a higher current density, this stage calls for the drawing of the diluted salt water from the soil the amalgamation chamber accelerates the accumulation of the vesicles and reduces the effective The electrolysis surface of the anode, which causes a deterioration in the electrolysis conditions, as already described above. Therefore, if you want electrolysis at a high current density of over 100 Amp./

dm with high yield are not only

Improvements to the usual devices for defoaming the electrode surface as well as with regard to the construction of the electrode structure are necessary, but it is still essential to develop a defoaming process with the aid of which the foam layer formed on the surface of the electrolyte in the amalgamation chamber can be removed so that the effective electrolysis area can be kept as large as possible.
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An anode plate of the usual type is provided with channels or holes which have the defoaming effect and increase the effective electrolysis area, which helps to keep the working voltage low at low current density. When used at high However, current density, such an anode plate has many disadvantages. As the total amount of on the anode surface The bubbles formed are larger than the amount of bubbles released into the gas space on the electrolyte surface the foam layer soon expands to the underside as well the anode off. Furthermore, a plate of the usual type has such a large thickness that the formed Bubbles remain on the plate for a long time, with the result that the foam takes up the effective surface on the Prevents electrolysis, causing the voltage to rise. Furthermore, the great thickness makes the plate in practice a correspondingly large average Inter-pole spacing required, which leads to disadvantages in terms of the effective use of the electrical Energy leads.

On the other hand, a platinum-titanium anode - as described above - has numerous features that make it Make anode material suitable for use at high current density. For practical use, however, it is advisable that the anode considering the fact that

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the bubbles formed at high current density are small and have a large total volume, narrow inter-channel spacings and that its plate thickness is as small as it is in view of the current capacity of the plate is only possible at all, whereby the foam formed can be directed directly into an area where it does not cover the effective electrolysis area and does not interrupt the electrolysis. The individual anode plates th should be made thinner and the number of plates increased in relation to the effective electrolytic area to make a certain cathode area as large as possible. Furthermore, the thickness (height) of the Plates should be as small as possible in order to reduce the true mean inter-pole spacing to a minimum *

One way to lower the electrolytic voltage is to shorten the interpolation distance and the Reduce the resistance voltage of the electrolyte. In the electrolysis of alkali salts, however, the Diffusion of the chlorine gas generated on the anode and its charging caused a secondary reaction, whereby in turn, a reduction in the current yield is brought about. For this reason one is generally to the Believes that the interpole distance for reasons of economy are between 3.5 and 3.8 mm must.

According to the invention, as a result of with

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Tests carried out on platinum-titanium anodes found that the electrolysis even with an interpole distance of less than 3.5 mm and sometimes even with immersion of the anode end can be carried below the mercury level if the current density is increased. There was no short circuit but, on the contrary, a decrease in voltage, and the current yield was

* high. These discoveries eventually led to the development of a process in which electrolysis was carried out in quite advantageously at a very high current density of 300 amp. / cm and a voltage of no more than 4 »5 volts and at which one is surprising high current yield of $ 99 is achieved.

In the method according to the invention, the electrolysis is characteristically at a high Current density performed using a platinum-titanium anode instead of a conventional graphite electrode, in that the gas bubbles together with the only a relatively low salt concentration Salt water can be removed from the amalgamation chamber immediately after electrolysis, and by using a Inter-pole spacing of less than 3.5 mm or sometimes even with the anode end submerged under the Mercury level is worked.

The removal of the vesicles is by force

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At guide through. Suction, by overflowing, with help caused by defoaming stirrers described below or with the aid of a salt water * or chlorine gas jet. The addition of defoaming agents or the application heat is also useful for this purpose.

The anode arrangement used according to the invention consists of a thin TitanplatYnmaterial, which in narrow strips have been cut and combined to form a panel arrangement, the individual panels of which are in stand perpendicular or inclined with respect to the cathode and which is integrally connected to a conductive part which has been made from a good conductor.

The invention will be further explained with reference to the accompanying drawings.

Pig. Figure 1 is a perspective view, partly in section, of one to be used in accordance with the invention Anode arrangement.

FIGS. 2 and 3 show other embodiments of the anode assembly of FIG. 1 to be used according to the invention Outside.

Fig. 4 is an external view of a further embodiment of the anode assembly, Figs. 4a, 4b, 4c and FIG. 4d depicts Dell cross-sections parallel to the electrically conductive part (3), the various embodiments of the panels show.

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The Pig. 5, 6 and 7 illustrate an apparatus suitable for carrying out the method according to the invention.

Pig. Figure 5 is a cross-section through an electrolytic cell fitted with overflow devices for removal the gas bubbles are provided.

Pig. 5a eats a perspective, partially in Cross-sectional view of the electrolytic cell of Fig. 5, and Pig. Figure 5b is a plan view the Pig electrolytic cell. 5.

Pig. Figure 6a is a perspective view of the Pig electrolytic cell. 6, and Pig. 6b is a perspective view of the turbine stirrer (15) shown in FIG. 6 Electrolytic cell.

The plate arrangement of the anode material used in accordance with the invention can be of many different types Make combinations such as parallel, concentric, spiral, lattice, radial and other combined Arrangements. The one in Pig. 1 shown lattice-like arrangement, an embodiment of the invention of conductive particles (1), (2), (3), (4) and (5) and plates (6) and (7).

The conductive parts (1), (4) and (5) are made of thin titanium plates. To the bottom of the part (1) a plate (6) is welded on. Inside the part (1) the titanium plates are tight with a steel or aluminum link associated with good conductivity, and continue to do so

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This is an elongated conductor (3) in close connection. The titanium sheet (5) of the elongated conductor (3) is welded at the bottom to the titanium plates (4), so that the conductors (2) and (3) are not directly exposed to the electrolyte, and the conductors (1) are in close, electrically conductive connection to the conductor (2).

The plates welded to the conductive parts

(6) and (7) are mutually exclusive either by combining "

by suitable design or by welding together united on the upper sides. When using a high current density, an anode assembly with a single or multiple conductive parts of the type described are provided. It is also possible to use the parts (1), (b) and (7) to be manufactured in one piece by casting. One can also just use a combination of (1) and (b) manufacture.

Fig. 2 explains an inventive anode (

Order which is formed spirally, while in Fig. 3 an anode arrangement according to the invention of the parallel type is shown. In these figures and in Fig. 1, like reference numerals designate like parts.

4 illustrates further embodiments of the anodes according to the invention. The anodes consist of one conductive part (3) and titanium plates (2), which bind with platinum (1) plated. The titanium plates have the ones in the

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Mg. 4a, 4b, 4c and 4d and are in one appropriate distance from each other connected to the lower surface (4) of the electrically conductive part (3). According to the invention, the anode consists of thin plates which, in a combination, are either perpendicular or are arranged with a certain inclination to the cathode surface. Bas total volume of the vesicles that

™ remain on the plate surface, is therefore limited, and satisfactory defoaming is achieved. By tightly combining the thin, strip-like Sufficient current capacity is achieved, though, with sheet metal parts with connecting construction panels the thickness (height) of the plates has been reduced, causing the gas bubbles formed to immediately return to the rear of the plates are urged so that they do not isolate the effective electrolytic area of the plates. The lower

} right or inclined arrangement of the plates with respect to the flow of salt water also has advantages in that it increases the effective electrolytic area and the stream of salt water can only flow in one direction from the bottom near the top can.' In this way, the current yield is not influenced by a shortened inter-pole distance.

In the following, the method according to the invention and the apparatus according to the invention are referred to in FIG

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the drawings explained. In Pig. 5 is shown an electrolytic cell with overflow deviceYlJur removal the gas bubbles are provided. First is through a suction pipe (2) saturated salt water into the middle part of the bottom section of an amalgamation chamber (1) introduced. The salt water then gets there in the space between the cathode (5) and the

Anode (6) where it is electrolyzed. The salt water %

(through the gaps, then rises together with the developed uniorgasr between the plates and arrives directly at the electrolyte surface on the back of the plates.The bubbles of the chlorine gas formed are then together with the salt water in the area indicated by an arrow (14) Direction, namely by the natural overflow of the salt water through V-shaped channels cut into an overflow wall (8). In this way, the overflow passes from the amalgamation B chamber (1) into a separation chamber (10), which is attached to the The amalgamation chamber is located at the periphery and in which the salt water is separated from the chlorine gas. The bubbles that fall into the separation chamber burst here and are completely separated into gas and salt water. The salt water, which after the electrolysis process has only a relatively low salt concentration has, is via a discharge pipe (9)

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deducted, but in the separation chamber a certain Fluid levels are maintained. The chlorine gas is drawn off via a discharge pipe (11) and into a Chlorine treatment prevention conducted.

Fig. 6 shows an electrolytic cell in which with the help of a defoaming stirrer, the destruction the gas bladders are used, a forcible overflow discharge from the amalgamation chamber. In the same way as the overflow method described above the salt water is electrolyzed and runs together with the gas bubbles through a partition wall (β) in the direction indicated by an arrow (14). There is also a to accelerate the overrun Turbine stirrer (15) provided with the help of a rotating device (16) is rotated from the outside of the cell, bringing the salt water together with the formed Gas bubbles is discharged from the amalgamation chamber. It is also possible to use the turbine stirrer (15) and the rotating device (16) by arranged on the outside of the mercury collection tubes (2) and (3) You enb it to replace chicklings pipes that are in the amount of Trennwaniung (8) are provided with a plurality of horizontally arranged nozzles, from which a large amount Salt water or Ohlorgas is squeezed out in order to prevent the overflow of the inside out

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To accelerate material from the amalgam fluid chamber forcibly.

As shown in Figs. 4 and 5, the mercury is fed through a mercury feed tube (3) to a position above the cathode plate (5), from there flows towards the periphery of the cathode plate (5), being turned into amalgam , overflows and flows through a discharge opening (12) (

into an amalgam separation chamber (13) and is finally out of the cell through a mercury outlet (7) discharged.

7 shows a further embodiment of the electrolytic cell according to the invention, which is provided with a suction device for removing the gas bubbles is. This apparatus is above that in the amalgam! A suction tube with several openings is arranged in the anode plates located in the chamber, and the layer of gas bubbles formed above the plates is removed together with the salt water from the cell, which is used for electrolysis and has a reduced salt content aspirated with the help of a pump or some other suction device. In Fig. 7, the electrolytic cell has a flat, horizontal floor over which the mercury (2), which forms the cathode, flows. Opposite to the cathode is inside the amalgam chamber (1)

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an anode (3) arranged. That through an opening (4) concentrated salt water supplied is electrolyzed in the space between electrodes (2) and (3). The sodium formed combines with the mercury to form sodium amalgam, which is extracted from the amalgamation chamber (1) is deducted. The small chlorine gas bubbles generated on the anode surface rise duroh the spaces between the individual anode plates immediately to the rear of the anode. The gas bubbles and the salt water, reduced in its salt concentration by the electrolysis, is removed from the amalgamation chamber suctioned through a suction opening (5)> which is provided above the anode with the aid of a suction pump (6). The discharged mixture is then in a gas-liquid separation device (7) separated into chlorine and diluted salt water. The Chlorgae is about a Gas outlet (8) and the salt water via a liquid outlet (9) discharged.

In the method according to the invention, the saturated salt water introduced into the amalgamation chamber is used Electrolyzed between the plates then rises along with a large amount of the small vesicles formed through the gaps between the plates immediately on the back of the plates and becomes echludlioh aua the amalgam! erujig8kanuner discharged. In this way

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a growth of the foam chi ent is prevented, and a filling of the space between the anode plates with foam and an interruption of the electrolysis these places does not take place. A decrease in the current yield can therefore be prevented even if when the inter-pole distance is reduced to a minimum. This is likely due to that most of the salt water introduced into the amalgamation chamber is unidirectional from the bottom flows upwards, and in particular that the salt water electrolyzed on the anode surface after at the top, and not in the opposite direction to the cathode, flows and is immediately discharged from the amalgamation chamber will.

With the aid of the method according to the invention, the electrolysis can be carried out in the normal way even if the electrode plates are immersed below the mercury surface, ie even if the inter-pole spacing is practically reduced to a value of zero or a negative value. The reason for this is that when the electrolysis is carried out at a very high current density, the gas surfaces formed have a small size and a very large total volume, so that the anode end immersed in the mercury is separated by a gap between the pressed down mercury surface and the surface

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gaseous phase consisting of small vesicles is cushioned, and that the salt water is adequately renewed as it moves upwards the bubble is sucked in. In this embodiment, no short circuit occurs, so that the inter-pole spacing can be shortened in an ideal way. To this

In a way, not only a reduction in voltage is achieved, but there can also be a decrease in the withstand voltage of the electrolyte from any current loss can be achieved, bringing the voltage closer to the theoretical decomposition voltage can be. In addition, the use of a platinum-titanium anode according to the invention, which in contrast is wear-resistant compared to the usual electrodes, a simplification of the inter-pole adjustment devices achieved and enables the interpole pole

'stood easily and comfortably shortened to a minimum can be.

Since the anode assembly is exposed to a high current density, the small gas bubbles formed come easily detached from the electrode surface, and the Increasing the piling speed of the salt water per unit area accelerates the piling speed of the liquid and the rate of ascent of the Gas puffing, which improves de-foamability

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will. This allows the panels with reduced gaps and arranged in a combination of an increased number of plates. Therefore, despite a reduction in the thickness or height of the individual plates, the effective electrolysis area can be increased. Furthermore the thin plates can shorten the true mean interpolation distance and the grass vesicles formed cause them to immediately move towards the ™ Moving the back of the plates, which prevents the foam from isolating the electrolysis surface will.

As described above, it allows the amalgamation chamber to be modified using a platinum-plated titanium anode according to the invention that the electrolysis with a high current density can be carried out. Furthermore, according to the invention, the salt water is caused to move in a single direction from ( the lower side to flow to the upper side. In particular, this will decrease near the end of the electrolysis diluted · causes salt water to flow in a direction opposite to that of the cathode. Farther According to the invention, the inter-pole distance is as short as made possible. These arrangements have made it possible to reduce the current efficiency with an inter-pole spacing of less than 3.5 mm, which is common practice

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has caused great difficulties, and have finally led to the unique electrolysis process of the invention, according to which the electrolysis at the high current density of 300 Amp./dm and an electrolysis voltage of 4.5 volts with a current efficiency of
99 i ° can be carried out.

The advantages achieved by the electrolysis process according to the invention in terms of improvement
the power per electrolysis unit, the reduction
the construction costs as well as in many other respects are noteworthy.

Example 1

In the following table, the use of an electrolytic cell according to the invention (Pig. 3) » which are provided with a suction device for de-foaming was compared with those obtained using an electrolytic cell of the usual type. (Electrodes of the type shown in FIG. 1 were used in both vessels).

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Current density Method according to the invention 200 2
Amp./dm Usual
procedure 5.2 ρ
(Amp./dm) 100 2
Amp./dm 4.0 300 ρ ¹⁸ ° 2
Amp./dm amp./dm 80 ElektroIyBe-
cell chip
voltage (volts) 3.4 80 4.6 97 electrolysis
cell temperature
temperature C 80 97.0 80 0.16 Current yield
W) 97.0 0.16 98.4 310 Amalgam consensus
tration (#) 0.15 310 0.16 250 Salzv / aeser-Ein
wash concentrate
tion (g / l) 310 250 310 0.5 Salt water
wash concentrate
tion (g / l) 250 0.5 250 Zwisohenpol-
distance (mm) 0.5 0.5

Example 2

The following table compares the results of the electrolysis (A) carried out with the anode body according to the invention with those obtained in

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an electrolysis with a graphite anode similar to the Japanese one Patent Specification 279 365 (B) were achieved.

50 100 A. 300 B. Current density
(Amp./dm) 3.2 3.3 200 4.5 50 Electrolytic cell
lens tension
(Volt) 80 80 3.9 80 4.48 Electrolytic cell
lentemperature
( ⁰ O) 95 97.3 80 99.2 75 Current efficiency
00 0.16 0.16 98.0 0.16 94 Amalgam concentrate
tration (#) 310 310 0.16 310 0.12 Saltwater a
let concentrate
on (g / l) 250 250 310 250 310 Saltwater off
let concentrate
on (g / l) +0.5 ± 0 250 -0.5 250 Interpole
stand (mm) -0.5 4th

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Claims (3)

H67215 patent claims: 1. Process for the electrolysis of alkali salts according to the mercury process, characterized in that for working at a current density of up to 300 A / dm. and with a voltage of not more than 4 »5 volts and with an electrode spacing of less than 3.5 mm for submerging the anode end under the mercury level, an anode consisting of platinum plated Titanium, is used. 2. Electrolysis cell for carrying out the method according to claim 1, characterized in that the amalgation chamber is adjoined by a salt water-gas separation chamber and a mercury separation chamber provided at its lower part with an opening for removing the mercury, that in the upper parts the separating walls of the three Chambers with the exception of the border area amalgation chamber / mercury separation chamber for overflow of salt water and foam openings or partition walls attached to the bottom of the cell with their lower ends are arranged so that the chambers are sealed off together with a cover consisting of one piece or with several covers separately and that the overflow of salt water and foam from the amalgation into the salt water Gae separation chamber means 909808/0879 Unbriayen (Art. 7 $ I Abs. 2 Nr. 1 Satt 3 of the amendment of the 4. 9. T467215 a device such as a turbine stirrer or a spraying of the electrolyte surface with salt water or Gas jets enabling facility is promoted. 3. electrolytic cell naoh claim 2, characterized in that the anode arrangement consists of individual, with grooves or holes provided thin platinum-plated titanium plates, which are parallel to each other and either perpendicular or combined with a certain inclination to the cathode surface or with electrically conductive ones Parts are united into one piece. 90980 8/0879