EP3688206B1 - Electrolysis device - Google Patents

Description

The present invention relates to an electrolysis device for the electrolytic treatment of liquids with an anode chamber and a cathode chamber, which are separated from one another by an ion exchange membrane, the chambers being equipped with an inlet opening and an outlet opening for the flowing electrolyte and each with an electrode, and the interior the anode chamber and / or the cathode chamber is subdivided by webs or ribs extending transversely to the electrodes, the webs or ribs being provided with holes or recesses at least in some areas.

For the electrolysis process to function properly in the interior of the electrode chambers, the electrolyte must be distributed as evenly as possible over the entire chamber height and width, which is why good mixing of the liquid in the two electrolysis chambers is desirable. In the case of chlor-alkali cells, this liquid mixing is particularly important in the anolyte chambers (anode chambers), since the ion exchange membranes only work optimally in a relatively narrow range of chloride concentration, temperature and pH value. It cannot be ruled out that, in areas of the anode chamber that are unfavorably located in terms of flow, stagnation of the anolyte may lead to chloride depletion, which can lead to local membrane damage.

In the anolyte chamber, the buoyancy effect of the chlorine gas causes a certain natural mixing in the vertical direction. The mean flow velocity in the anolyte chamber in the horizontal direction is low and therefore the natural mixing in the horizontal direction is also very low. In addition, the gas bubbles rising in the electrolyte tend to unite in the upper area to form a closed foam layer. This foam formation is greater, the greater the cell load and the higher the cell. Since the electrical resistance in the foam is greater than in the rest of the electrolyte, the current distribution over the membrane surface and thus the membrane load becomes uneven.

From the DE 42 24 492 C1 an electrolysis device is known with the features mentioned at the beginning, in which a better liquid mixing is sought in the two electrolysis chambers. In order to create a defined mixing flow in each anode and / or cathode chamber, at least one separating element in the form of a separating plate, which is surrounded by flow in some areas, is provided, which is equipped with flow guide webs. The gas bubbles formed on the electrodes are used as a kind of conveying aid, in that the distribution of the gas bubbles over the entire chamber space is prevented. An upward flow is generated due to the gas bubbles that arise only on one side of the separating plate in the area of the electrode. Since the separating element is designed so that it can be flushed around, there is a natural vertical circulation in the chambers.

In the EP 0 220 659 B1 an electrolytic device of the bipolar type is described, which contains a plurality of bipolar unit cells arranged in series, each cell is composed of an anode-side trough-shaped body and a cathode-side trough-shaped body, each comprising a hook-shaped flange, a frame wall and a partition wall, the anode and cathode are each welded to the partition wall via electrically conductive ribs (webs). Each of these conductive ribs is provided with spaced-apart holes over its entire height in order to enable the electrolyte and the electrolysis product to pass through the ribs.

In electrolysis devices of the type mentioned above, the membrane is usually very close to the electrodes. The ribs or webs running between the electrodes and in the transverse direction to them divide the interior of the electrolysis device into several compartments (also referred to as compartments). If massive ribs or webs are used, the membrane may not be supplied with sufficient brine which, if flat anodes are used, leads to the formation of blisters on the membrane.

If, on the other hand, webs are provided with recesses or holes over the entire height of the webs, as cited above EP 0 220 659 B1 is proposed, in order to achieve better longitudinal mixing in the entire cell chamber, this has the disadvantage that the desired mammoth pump effect is no longer given in the individual compartment of the cell chamber. The term "mammoth pump effect" is understood to mean the phenomenon described by Carl Immanuel Löscher that the liquid level can be raised by a certain amount by gas bubbles introduced into a liquid below the liquid level. This effect is used in the so-called mammoth pumps for pumping liquids. Since gas bubbles arise in the electrolyte during electrolysis, which then rise upwards in the liquid, the mammoth pump effect occurs here, by means of which vertical mixing of the electrolyte is achieved, which is to a certain extent desirable in an electrolysis device according to the invention.

From the DE 696 07 197 T2 For example, an electrode arrangement for an electrolyzer of the filter press type is known in which anode spacers and cathode spacers are used which extend in the transverse direction to the flat electrodes. A Z-shaped spacer is also referred to as an upper spacer, while U-shaped or C-shaped spacers are located below it. These Z-shaped or U-shaped spacers are, however, arranged horizontally in the electrolytic cell, that is to say they run transversely to the vertical direction of the electrolytic cell. The spacers have circular or oval perforations of different sizes. These perforations serve to mix the electrolyte vertically, the larger perforations being intended to improve the gas flow of the gas rising in the electrolyte. A subdivision of the electrolysis cell in the longitudinal direction, that is to say in the direction of the longitudinal extension of the spacers, is not provided here.

In the DE 199 54 247 A1 describes an electrolysis cell with a gas diffusion electrode, in which the cell is divided into several superimposed spaces by horizontally extending webs, so that the gas flows through the gas space in a meandering fashion from bottom to top and flows horizontally in the individual spaces. A further subdivision of the electrolytic cell by webs running vertically in the height direction is not provided here.

the U.S. 5,693,202 A also describes an electrochemical cell with an ion exchange membrane, in which a lower inlet opening and an upper outlet opening are provided. In the cell, horizontally extending connecting elements run transversely to the electrodes, which divide the cell into several superimposed chambers and in which a plurality of regularly arranged openings are provided, which allow gas to pass through in the vertical direction of the electrolytic cell. A vertical mixing of the electrolyte is provided, whereas a further subdivision of the cell by vertically extending webs cannot be seen.

Out DE 10 2004 014 969 A1 an electrolytic cell is known, the electrodes being attached to the half-shells by means of ribs. Flat strips are arranged between the ribs, which divide the electrolyte space into an ascending flow of gas / electrolyte and a descending degassed flow. The ribs are provided with openings that allow the electrolyte to mix crosswise. Depending on the arrangement of the flat or folded strips, these openings are free, completely covered or partially covered in the vertical direction, the ribs not having at least one lower area, seen in the vertical direction, in which the ribs are free of openings to maintain the mammoth pump effect.

The object of the present invention is to provide an electrolysis device with the features of the type mentioned at the outset, in which, on the one hand, there is sufficient mixing in the longitudinal direction, but at the same time the mammoth pump effect is maintained.

The solution to the aforementioned problem is provided by an electrolysis device of the type mentioned at the beginning with the features of claim 1.

For a better understanding of the present invention, the geometric relationships in an electrolysis cell of the type according to the invention are defined at this point. The electrolysis cell extends in three spatial directions that are orthogonal to one another. The spatial direction in which the electrolytic cell usually has its greatest extent is defined as the longitudinal direction. The flat electrodes extend in this longitudinal direction and in the height direction. The direction of the normal to the surface of the electrodes is referred to herein as the transverse direction. Gas bubbles rise in the electrolysis cell against gravity from bottom to top. This direction from bottom to top is referred to herein as the height direction.

The conventional mixing of the electrolyte in the vertical direction, which is also present in the prior art, is referred to in the present application as vertical mixing. This is to be distinguished from the thorough mixing of the electrolyte in the longitudinal direction of the electrolytic cell, for the purpose of which the vertical webs provided according to the invention have holes or recesses through which the electrolyte can flow. These webs thus run in the vertical direction of the electrolytic cell according to the above definition or essentially in the vertical direction, and they also extend in the transverse direction of the electrolytic cell, that is to say transversely to the flat electrodes. Thus, a subdivision of the electrolytic cell in its longitudinal direction into several compartments is created by these webs. The flow of the electrolyte through holes or recesses in these webs is thus essentially a flow in the longitudinal direction of the electrolytic cell and is also referred to herein as horizontal mixing.

The terms "below" or "above" used herein relate to the extent of the electrolytic cell in the vertical direction. In the context of the present invention, therefore, means that an “upper” area, viewed in the height direction of the electrolysis cell, is located higher up than a “lower” area.

According to the invention it is provided that the webs or ribs extend in the vertical direction of the electrolysis device and, viewed in the vertical direction, have at least one lower area in which they are free of holes or recesses, that is, no holes or recesses are provided there. Because the webs or ribs are solid in the lower area and have no holes or recesses, the unimpeded mammoth pump effect is guaranteed there. In the lower area, the gas bubbles formed during the electrolysis can thus rise upwards unhindered in the compartment of the electrolysis cell separated by the web. The vertical flow predominates in this lower area and there is no significant longitudinal mixing of the electrolysis medium. In contrast, according to the invention, there are holes or recesses in the upper region of the webs or ribs. In this upper area, the rising gas bubbles form a foam phase of the electrolysis medium and longitudinal mixing is therefore desirable here. This longitudinal mixing is achieved through the holes or recesses in the webs or ribs, which allow the electrolysis medium to flow into the adjacent compartment of the electrolysis cell.

The direction in which the electrodes extend is understood in the present application as the longitudinal direction of the electrolysis device. Thus, when it is mentioned herein that the webs or ribs extend transversely to the electrodes, this means that the webs or ribs extend essentially in the transverse direction of the electrolysis device and preferably approximately at right angles to the electrodes. As a rule, the two electrolysis chambers each have an approximately cuboidal interior space which receives the electrolyte. The webs or ribs thus run in the electrolysis cell essentially in the vertical direction and in the transverse direction in the sense of the above definitions. The one that is also provided for conventional electrolysis cells Vertical mixing corresponds to a flow of the electrolyte essentially parallel to the webs or ribs, that is to say to a flow in the vertical direction of the electrolytic cell in the individual compartments between two webs or ribs. In the case of the longitudinal mixing described in the present application, on the other hand, the electrolyte flows through the holes in a web in an essentially horizontal flow, so that the electrolyte flows through holes in a web from one compartment into an adjacent compartment. The longitudinal mixing thus takes place in an essentially horizontal flow direction which is basically oriented orthogonally to the vertical mixing in the height direction, that is to say orthogonally or at least transversely to the gas bubbles rising in the electrolyte.

The term "holes" as used herein does not imply any restriction to any particular outline shape. The holes can, for example, have a round, oval, oblong or angular outline. The term "recesses" used herein includes on the one hand through holes with any contour shape that are surrounded on all sides by the material of a web, as well as openings in the material that allow the electrolysis medium to pass through, but are not surrounded on all sides by the material of a web , that is, they can optionally also be open at one or more places on their circumference.

The design of the webs or ribs according to the invention thus advantageously combines two effects with one another. On the one hand, the mammoth pump effect is obtained in the lower area of the webs (which leads to cross-mixing) and, on the other hand, a longitudinal mixing is achieved in the upper area of the webs. This ensures optimal mixing of the inflow and brine transport to the anode over the entire cell height through the mammoth pump effect and at the same time an optimal brine transport to the anode over the cell width through the holes or recesses in the webs in the upper foam phase. This prevents damage to the membrane that would otherwise arise from its insufficient supply of NaCl, for example when chlor-alkali electrolysis is carried out in the electrolysis cell. If the membrane is insufficiently supplied with brine, the formation of blisters on the membrane is favored, which can be observed in particular when operating with permanently high current densities.

A preferred development of the object solution according to the invention provides that the webs or ribs have at least one upper area with holes or recesses, as seen in the height direction of the electrolysis cell. Longitudinal mixing is possible there through these holes or recesses in the upper area of the webs or ribs. A foam phase is formed there by the rising gas bubbles, in the area of which longitudinal mixing of the electrolyte is advantageous.

The lower region in which the webs or ribs have no holes or recesses preferably extends at least approximately over the lower half of the total height of the webs or ribs, in particular at least over the lower half of the total height of the webs or ribs.

The end of the lower range naturally depends on the individual conditions in the respective electrolysis cell. For example, it can be determined empirically up to which height of the webs the mammoth pump effect is desired and longitudinal mixing is to be prevented and at what level the foam phase begins. Tests have shown that it is generally advantageous to make at least approximately the lower half of the webs or ribs, in particular at least the lower half of the webs or ribs, solid, i.e. without holes or recesses. The area in which the holes begin can thus be determined in individual cases, for example, depending on the parameters of the electrolysis cell, the type of electrolyte used and the conditions under which electrolysis takes place, such as temperature, pH value, current density, etc. vary.

A preferred development of the invention provides that the lower area, in which the webs or ribs have no holes or recesses, extends at least approximately over the lower two thirds, in particular over the lower two thirds, of the entire height of the webs or ribs. In this possible variant, the area in which the webs or ribs are solid extends over the middle of the webs or ribs upwards, while only approximately in the upper third, especially in the upper third, where the foam phase is formed , Holes or recesses are provided.

According to a preferred development of the invention it is provided that the upper area in which the webs or ribs have holes or recesses extends at least approximately over the upper quarter, in particular over the upper quarter, of the entire height of the webs or ribs. In this possible variant, the area in which the webs or ribs are solid thus extends further upwards, while holes or recesses are provided at least approximately in the upper quarter, in particular in the upper quarter, where the foam phase is formed are.

Particularly preferably, the upper area in which the webs or ribs have holes or recesses extends at least approximately over the upper third of the total height of the webs or ribs, in particular at least over the upper third of the total height of the webs or ribs.

A preferred development of the invention provides that the webs or ribs have a plurality of holes or recesses spaced from one another by solid regions in the height direction of the webs or ribs in the at least one upper region.

Another preferred development of the device according to the invention provides that the webs or ribs in the at least one upper area have at least partially approximately round holes in outline. The shape of a keyhole is only mentioned as an example at this point. However, in principle, any other contour shapes for the holes or recesses are also conceivable. For example, holes or recesses with different outlines and in different sizes can also be provided, for example depending on how strong the effect is Longitudinal mixing is desired and how much volume of electrolyte per unit of time should flow through the holes or recesses into the adjacent compartment.

Another preferred development of the invention provides that the webs or ribs in the at least one upper area have a plurality of holes or recesses which are spaced differently from one another, viewed in the direction of the height of the webs or ribs. This offers a further possibility of varying the effect of mixing in the longitudinal direction by using holes or recesses of approximately the same size, but the distances between them vary over the height of the webs or ribs, so that with more densely arranged holes or recesses larger total areas of holes per unit area of the webs are given. A similar effect can of course also be achieved by using holes or recesses of different sizes. However, due to the width of the webs or ribs, for reasons of mechanical stability of the webs, there is an upper limit for the diameter or the width of the holes or recesses, so that in this case larger hole areas for longitudinal mixing can be achieved by arranging the holes at closer intervals can.

For example, the holes or recesses in the webs or ribs can be arranged in a first lower section of the upper region at smaller distances from one another than in a second section of the upper region that adjoins them upwards.

In the context of the present invention, it is advantageous if the holes or recesses have a certain minimum size in order to achieve the desired mixing effect. The free cross section of at least one hole or recess is therefore preferably at least about 10 mm ² , particularly preferably at least about 15 mm ² . The free cross-section of all holes or recesses is preferably at least about 300 mm ^{2 in} total and the individual holes have the aforementioned minimum cross-sections, this also depending on how many holes or recesses are provided in total and the distance between them.

The present invention also relates to a method for the electrolytic treatment of a flowable medium in an electrolysis device having the features of one of claims 1 to 10.

The method according to the invention preferably comprises a chlor-alkali electrolysis. Electrolysis devices of the type described herein are particularly suitable for chloralkali electrolysis. However, the electrolysis devices according to the invention can also be used for other electrolysis processes.

• Figur 1 eine schematisch vereinfachte Ansicht eines Querschnitts durch eine beispielhafte erfindungsgemäße Elektrolysevorrichtung gemäß einer ersten Ausführungsvariante;
• Figur 2 eine Ansicht einer beispielhaften erfindungsgemäßen Elektrolysevorrichtung;
• Figur 3 eine Schnittansicht in Längsrichtung der in Figur 2 dargestellten Elektrolysevorrichtung;
• Figur 4 eine Schnittansicht in Querrichtung der in Figur 2 dargestellten Elektrolysevorrichtung;
• Figur 5 eine Detailansicht eines einzelnen Stegs mit den Löchern für die Längsdurchmischung des Elektrolyten.

The present invention is explained in more detail below using an exemplary embodiment with reference to the accompanying drawings. It shows:

• Figure 1 a schematically simplified view of a cross section through an exemplary electrolysis device according to the invention according to a first embodiment variant;
• Figure 2 a view of an exemplary electrolysis device according to the invention;
• Figure 3 a sectional view in the longitudinal direction of the in Figure 2 illustrated electrolysis device;
• Figure 4 a sectional view in the transverse direction of the in Figure 2 illustrated electrolysis device;
• Figure 5 a detailed view of a single bar with the holes for the longitudinal mixing of the electrolyte.

In the following, with reference to the Figure 1 the basic structure of an electrolysis device of this type is explained in more detail. As a rule, an electrolytic cell 10 comprises a housing with two half-shells, namely a cathode half-shell 11 and an anode half-shell 12, which are each provided with flange-like edges at the top and bottom, between which a membrane 13 is clamped by means of seals. This membrane 13 forms a partition between the cathode half-shell 11 (corresponds to the cathode chamber or catholyte chamber) and anode half-shell 12 (corresponds to the anode chamber or anolyte chamber). In each case in the area of their flange-like edges, the cathode half-shell 11 and anode half-shell are connected to one another at the top and bottom by means of screws 14 aligned in the transverse direction to form an electrolytic cell 10. In the lower area in each of the two half-shells 11, 12 extends in the longitudinal direction of the electrolytic cell, an inlet manifold 15, 16 for electrolyte solution and used electrolyte is discharged from the electrolytic cell via an outlet pipe 17. The anode and cathode each extend flat in the vertical direction in the respective half-shell close to the membrane.

How to get in Figure 1 recognizes, there is an obliquely aligned baffle 18 in the upper area in the anode half-shell, so that on the side of this baffle 18 facing the anode, gas-laden liquid rises in the direction of the arrows and the less or no gas-laden liquid sinks on the back of the baffle. This results in a circulation of the anolyte in the lower area, which leads to vertical mixing. This circulation compensates for the differences in the concentration of electrolyte (e.g. NaCl) between the inlet and the liquid in the cell.

In the view of an electrolytic cell according to Figure 2 the two inlet manifolds 15, 16 for the two half-shells and the outlet pipes 17 each assigned to a half-shell can be seen in FIG Figure 2 the surrounding frame 19, in the area of which the flange-like edges of the two half-shells are screwed together.

In Figure 3 is the in Figure 2 The electrolytic cell shown is shown cut open in the longitudinal direction. It can be seen here that, in electrolysis cells of this type, the rear space of the two electrodes in both half-shells is divided into individual compartments by webs 20 running in an approximately vertical direction and in the transverse direction. These webs also serve to stiffen and support the cathode and anode. In the cross-sectional view according to Figure 4 one of these webs 20 can be clearly seen in the drawing on the left. It can be seen that the web 20 is provided with holes 24 in the upper area, via which the electrolyte is mixed longitudinally. More details regarding the training and the function of these webs 20 are shown below with reference to the individual part drawing Figure 5 explained in more detail.

The representation according to Figure 5 shows a single web 20, which is cut obliquely in its lower end area 21 and thus tapers continuously in width towards the lower end. Viewed in the direction of its height, this web 20 has in principle two differently designed areas, namely a lower area 22 and an upper area 23. The lower area 22 is solid, with no holes or recesses being provided in it. This lower region 22 extends in the exemplary embodiment according to FIG Figure 5 over a little more than the lower two thirds of the total height of the web 20. The upper region 23 of the web 20 adjoins the lower region 22 at the top, the web 20 being provided in this upper region 23 with holes 24 through which Electrolyte can pass through in the longitudinal direction of the electrolytic cell, so that longitudinal mixing of the electrolyte takes place in this upper region 23. There is a foam phase of the electrolyte due to the rising gas bubbles.

How to get in Figure 5 sees a number of several spaced apart holes 24 are provided. In the exemplary embodiment, five such holes 24 are shown by way of example. It can also be seen that the two lower holes 24 a at the level of the web 20 have a smaller distance from one another than the upper holes. The number of holes 24 and their respective spacings from one another can be varied virtually as desired within the scope of the present invention.

List of reference symbols

10

Electrolytic cell

11

Cathode half-shell

12th

Anode half-shell

13th

membrane

14th

Screws

15th

Inlet manifold

16

Inlet manifold

17th

Outlet pipe

18th

Baffle

19th

surrounding frame

20th

Bridges

21

lower end area, cut at an angle

22nd

lower area, massive

23

upper area, with holes

24

Holes

24 a

lower holes, with smaller spacing

Claims (13)

1. Electrolysis device for the electrolytic treatment of liquids, having an anode chamber and a cathode chamber which are separated from one another via an ion exchange membrane, wherein the chambers are provided with at least one inlet opening and one outlet opening for a flowing electrolyte and with at least in each case one electrode, and wherein the inner space of the anode chamber and/or of the cathode chamber are/is subdivided by webs (20) or ribs extending transversely with respect to the electrodes, wherein the webs or ribs are provided at least regionally with holes (24) or cutouts, characterized in that the webs (20) or ribs extend in the height direction of the electrolysis device and comprise, as viewed in the height direction, at least one lower region (22) in which the webs (20) or ribs are free of holes (24) or cutouts.
2. Electrolysis device according to Claim 1, characterized in that the webs (20) or ribs comprise, as viewed in the height direction of the electrolysis cell, at least one upper region (23) with holes (24) or cutouts.
3. Electrolysis device according to Claim 1 or 2, characterized in that the lower region (22), in which the webs (20) or ribs are free of holes (24) or cutouts, extends at least approximately over the lower half of the entire height of the webs (20) or ribs.
4. Electrolysis device according to one of Claims 1 to 3, characterized in that the lower region (22), in which the webs (20) or ribs comprise no holes (24) or cutouts, extends at least approximately over the lower two thirds of the entire height of the webs (20) or ribs.
5. Electrolysis device according to one of Claims 1 to 4, characterized in that the upper region (23), in which the webs (20) or ribs comprise holes (24) or cutouts, extends at least approximately over the upper quarter of the entire height of the webs (20) or ribs.
6. Electrolysis device according to one of Claims 1 to 5, characterized in that the upper region (23), in which the webs (20) or ribs comprise holes or cutouts, extends at least approximately over the upper third of the entire height of the webs (20) or ribs.
7. Electrolysis device according to one of Claims 2 to 6, characterized in that the webs (20) or ribs comprise, in the at least one upper region (23), multiple holes (24) or cutouts which are spaced apart from one another by solid regions in the height direction of the webs (20) or ribs.
8. Electrolysis device according to one of Claims 2 to 6, characterized in that the webs (20) or ribs at least partially have, in the at least one upper region (23), holes (24) which have an approximately circular contour.
9. Electrolysis device according to one of Claims 2 to 8, characterized in that the webs (20) or ribs comprise, in the at least one upper region (23), multiple holes (24, 24 a) or cutouts which, as viewed in the direction of the height of the webs (20) or ribs, have different spacings from one another.
10. Electrolysis device according to Claim 9, characterized in that the holes (24 a) or cutouts in the webs (20) or ribs, in a first lower section of the upper region (23), are arranged with smaller spacings from one another than in a second section of the upper region (23) adjoining towards the top.
11. Electrolysis device according to one of Claims 1 to 10, characterized in that the free cross section of at least one hole (24) or one cutout amounts to at least approximately 10 mm², particularly preferably at least approximately 15 mm².
12. Method for the electrolytic treatment of a flowable medium in an electrolysis device having the features of one of Claims 1 to 11.
13. Method according to Claim 12, characterized in that it comprises chlor-alkali electrolysis.

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