EP1073780B1 - Electrolysis apparatus for producing halogen gases - Google Patents

Description

The invention relates to an electrolysis apparatus for production of halogen gases from aqueous alkali halide solution with several arranged side by side in a stack and in plate-like electrical contact Electrolysis cells, each a housing made of two half-shells made of electrically conductive material with outside Have contact strips on at least one rear wall of the housing, wherein the housing means for feeding the Electrolysis currents and electrolysis input materials and Devices for discharging the electrolysis current and the Electrolysis products and two essentially flat surfaces Has electrodes (anode and cathode), the Anode and the cathode with blind-like openings for a flow through the electrolysis input materials and Electrolysis products provided and by a partition from each other are separated and arranged parallel to each other and by means of metallic stiffeners with the respectively assigned one Rear wall of the housing electrically connected are.

The individual electrolytic cells are manufactured in such a way that the respective housing from two half shells each Interposition of the necessary facilities and the cathode and anode as well as the partition and by fixation the same assembled by means of metallic stiffeners and anode and housing or cathode and housing be attached to each other in an electrically conductive manner, then the plate-shaped electrolytic cells thus produced arranged next to each other in a stack in an electrically conductive manner and against each other in the stack for sustainable contact be tense.

The electrolysis current is fed to the cell stack on one outer cell of the stack, it passes through the cell stack in a direction substantially perpendicular to the central planes of the plate-shaped electrolysis cells and it is discharged at the other outer cell of the stack. In relation to the middle level, the electrolysis current reaches mean current density values of at least 4 kA / m ² .

Such an electrolysis apparatus is known from DE 196 41 125 A1 Applicant known. In this known electrolysis apparatus are the anode or the cathode with the respective rear wall the housing halves over vertical, web-like metallic Stiffeners connected. On the back of the anodes or Half of the cathode shell is a vertical contact strip for the electrical contact to the neighboring, same electrolysis cell attached. The current flows through the contact strip through the back wall into the vertical, web-like metallic stiffeners and of there it is distributed starting from the metallic contact points (Stiffening / anode) over the anode. After this the current passed through the partition (membrane) is, it is taken up by the cathode to over the vertical, web-like stiffeners in the rear wall flow to the cathode side and then back into the contact strip and from there to the next electrolytic cell enter. The connection of the current-carrying components is done by welding. In the welds the electrolysis current bundles to form peak current densities.

The vertical, web-like metallic stiffeners are designed as webs aligned with the contact strips, the side edges over the entire height of the rear wall and the anode or cathode on the rear wall and the anode or cathode.

The vertical bars divide the electrode back space within the respective housing half into individual electrolyte-carrying Segments. So it doesn't become a complete one uneven concentration distribution in the electrolyte comes along the depth of the respective housing half an inlet distributor is provided in each half of the housing, through which the electrolysis input substances into the individual, segments formed by the webs in the half-shells are feedable.

By means of an electrolyzer designed in this way gas generating electrolysis processes, such as Chlor-alkali electrolysis, hydrochloric acid electrolysis or alkaline water electrolysis performed. In chlor-alkali electrolysis aqueous alkali halide solutions, for example sodium and potassium chloride, in the electrolysis cell under the influence of electric current in a aqueous alkali lye, e.g. sodium or potassium lye, and in a halogen gas such as chlorine and hydrogen decomposed. In the water electrolysis water is decomposed and Hydrogen and oxygen are formed on the electrodes.

The spatial separation of the electrode spaces is done using the partition mentioned above, generally one Diaphragm or a so-called ion exchange membrane. The Diaphragm is made of a porous material that is related the media, temperatures and Pressing is chemically, thermally and mechanically stable. at the ion exchange membrane is generally perfluorinated hydrocarbons. These membranes are gas and almost liquid-tight, but leave an ion transport in the electric field too.

There is a special peculiarity of these electrolysis processes in the fact that the diaphragm or the ion exchange membrane pressed against at least one of the two electrodes becomes. This is necessary because it fixes the partition and is therefore largely mechanically unloaded. Frequently the partition may only be on one of the two electrodes only because this is the only way to ensure the longest possible service life all components (electrodes and partition) to achieve. When the partition is in direct contact with both In some cases, electrodes can cause a chemical reaction between the partition and the electrodes gases developed in the electrodes take place. So is one Distance between the membrane and the cathode in chlor-alkali electrolysis established, otherwise the electrocatalyst, or with inactive nickel cathodes, nickel from the Electrode is released. Another example is nickel oxide diaphragms, those in alkaline water electrolysis be used. If the distance to the hydrogen-evolving one is too small Electrode, the nickel oxide is reduced to nickel and thus conductive, which eventually leads to a short circuit leads.

The support of the membrane or diaphragm on at least an electrode causes it to be in gas evolving processes to a gas jam in the electrolyte interface between the electrode and the membrane or the diaphragm comes. Of these, even the ones mentioned at the beginning are Electrodes that are designed so that they are affected by the electrolysis input materials and the electrolysis products are flowable. Such electrodes are preferably included Provide perforations (perforated sheet, expanded metal, wattle or thin sheets with blind-like openings), so that despite their flat arrangement in the electrolysis cell those formed in the boundary layer during electrolysis Gases enter the back of the electrolytic cell more easily can.

Especially in those that are oriented downwards in the cell Edges or edges of the openings agglomerate the gas bubbles rising in the electrolyte and remain there the gussets between the adjacent partition (membrane) and the break through edges. These bubbles disturb electricity transport, i.e. the mass transport through the Partition because they block the membrane exchange surface and thus make it inaccessible, i.e. inactive.

In the case of an electrode design which was created by the applicant to reduce this gas build-up and which is described in German patent DE 44 15 146 C2, the electrodes are profiled, for example by providing them with grooves and holes. In this way, on the one hand, the gas can escape more easily and, on the other hand, fresh electrolyte can get into the electrolytically active boundary layer between the electrode and the membrane. When electrodes with a profile of this type are subjected to current densities above 4 kA / m ² , however, the gas evolution increases and the profiled electrode then reaches the limit of its gas dissipation capability.

In gas-developing electrolysis reactions, as occurs, for example, in the anodic chlorine evolution of chlor-alkali electrolysis or in the anodic oxygen evolution of alkaline water electrolysis, there is also a separation problem, ie the gas evolved does not separate from the electrolyte, which leads to foam formation. This problem leads to the fact that the current density distribution is inhomogeneous, in particular at current densities above 4 kA / m ² . On the one hand, this limits the lifespan of active cell components such as membranes, diaphragms and electrode activations. On the other hand, the electrolysers are also limited to approximately 4 kA / m ² with regard to the maximum current density. In addition, the foam formation leads to pressure fluctuations within the electrochemical cell, since the foam at least temporarily closes the cell outlet for the gas formed. The outlet is blown free again by a slight increase in pressure within the cell, which leads to the known effect of the surge flow and to the pressure fluctuations mentioned. This is disadvantageous for the operation of an electrolyzer.

Furthermore, the life span of membranes in particular influenced by the concentration distribution. The more homogeneous for example the salt concentration in the anode compartment Chlor-alkali electrolyser, the longer the lifespan the membrane. To ensure a homogeneous electrolyte distribution reach, either via externally arranged pumps generated additional circulation, or by installing one Baffles in the cell due to internal circulation of a density difference.

The object of the invention is to provide an electrolysis apparatus which can also be operated at current densities above 4 kA / m ² and, accordingly, increased gas generation in the boundary layer while maintaining long-term service life of the membrane and with low pulsation.

This task is done with an electrolysis machine at the beginning designated type solved according to the invention in that the blind-like openings of the anode and cathode against the horizontal are inclined.

By means of this design according to the invention, it has been found that the gas removal from the electrolyte boundary layer close to the membrane can be improved in such a way that current densities of 6 to 8 kA / m ² are achieved for the first time while maintaining a long service life of the membrane. Due to the inclination of the electrode rods relative to the horizontal, the gas bubbles that form roll along the lower edge of the electrode, collide with bubbles still adhering to the electrode edge and coalesce. This in turn leads to the gas bubbles being accelerated due to the increasing volume, ie the effect accelerates itself. At the same time, the gas volume in the electroactive zone decreases, as a result of which a lower cell voltage is achieved. A suction effect, which is caused by the movement of the glass bubbles along the edge of the electrode, ensures that the fresh electrolyte is sucked into the electroactive zone between the membrane or diaphragm and the electrode, which is a necessary prerequisite for long alkali life, for example in chlor-alkali electrolysis. In addition, there is a directional flow, since all gas bubbles are forced in one direction. As a result, the density of the electrolyte / gas mixture decreases on one side due to the increasing gas content, which leads to an internal circulation which is 10 to 100 times greater than when entering the electrolyte stream. Excellent homogenization of the electrolyte is thereby achieved.

It has been found to be particularly advantageous that the angle of inclination towards the blind-like openings the horizontal is between 7 ° and 10 °.

In a particularly preferred design, it is provided that that the bottom of each case is parallel arranged to the horizontal and the blind-like Breakthroughs of the anode and cathode against the bottom of the respective housing are arranged inclined. The electrolysis machine in itself is then compared to known electrolysis apparatus to modify only slightly, only the The anode and the cathode must be installed at an angle and on the edge be designed accordingly so that they are appropriate can be installed.

Alternatively, it can also be provided that the underside of the respective housing inclined to the horizontal is arranged. The individual housings must then face each other previously known housings are practically unchanged, they just have to be inclined to the horizontal can be built in, which automatically makes the blind-like Breakthroughs of cathode and anode in relation to the horizontal are inclined.

Fig. 1

einen Schnitt durch zwei nebeneinander angeordnete Elektrolysezellen eines Elektrolyseapparates,

Fig. 2

einen Ausschnitt aus Fig. 1 in perspektivischer Darstellung und in

Fig. 3

ebenfalls in perspektivischer Darstellung einen vergrößerten Ausschnitt aus Fig. 1.

The invention is explained below with reference to the drawing, for example. This shows in

Fig. 1

2 shows a section through two electrolysis cells of an electrolysis apparatus arranged side by side,

Fig. 2

a section of Fig. 1 in perspective and in

Fig. 3

also an enlarged detail from FIG. 1 in a perspective view.

A generally designated 1 electrolysis apparatus for Production of halogen gases from aqueous alkali halide solution has several, arranged side by side in a stack and plate-like in electrical contact Electrolysis cells 2, examples of which are shown in FIG. 1 two such electrolysis cells 2 arranged side by side are shown. Each of these electrolytic cells 2 has one Housing consisting of two half-shells 3, 4 with flange-like Edges are provided, between which by means of seals 5 a partition (membrane) 6 is clamped in each case. The clamping of the membrane 6 can, if necessary, also on others Way.

Over the entire depth of the rear walls 4A of the respective Electrolysis cell 2 are parallel to each other A plurality of contact strips 7 arranged through Welding or the like. On the outside of the rear wall in question 4A are attached or applied. This Contact strips 7 make electrical contact with the neighboring one Electrolysis cell 2, namely to the rear wall in question 3A forth, on which no separate contact strip is provided.

Within the respective housing 3, 4 are in each case to the Membrane 6 adjacent a flat anode 8 and planar cathode 9 is provided, the anode 8 or the cathode 9 each in alignment with the contact strips 7 arranged stiffeners are connected as webs 10 are formed. The webs 10 are preferred along its entire side edge 10A at the anode or Cathode 8, 9 attached in a metallically conductive manner. To feed of the electrolysis input materials and the removal of the electrolysis products to allow the webs 10 to taper starting from the side edges 10A across their width to to the adjacent side edge 10B and have a height there on, which corresponds to the height of the contact strips 7. she are accordingly with their two edges 10B over the entire height of the contact strip 7 on the contact strip 7 opposite rear of the rear wall 12A or 4A attached.

A suitable one is to supply the electrolysis products Device provided for the respective electrolysis cell 2, such a device is indicated by 11. Likewise is a device for every electrolysis cell Removal of the electrolysis products is provided, but this is not shown.

The electrodes (anode 8 and cathode 9) are designed such that they are the electrolysis input product or the output products 3 flow through or let flow through, for what the anode 8 and the cathode 9 are designed like blinds, i.e. each from individual blind-like electrode rods exist and exist between the blind-like openings are. This applies to both the anode 8 and Cathode 9, only one in FIGS. 2 and 3 Electrode 8, 9 is shown. There are the individual Electrode rods designated 8A and 9A, while the blind-like Breakthroughs are designated 8B and 9B. It is essential for the invention that these are blind-like Breakthroughs 8B, 9B inclined to the horizontal are arranged, preferably at an angle between 7 ° and 10 °. This angle is designated α in FIG. 2.

As can be seen from Figures 2 and 3, is the back room the electrodes 8 and 9 chambered by the vertical webs 10 (i.e. divided into several chambers). As it turns out has, this design leads to the fact that the forming glass bubbles due to the inclined arrangement of the electrode rods 8A, 9A on the lower edge of the anode 8 and the Roll cathode 9 along, then still on the electrode edge adhering bubbles meet and coalesce. This causes the gas bubbles to increase due to the Volume are accelerated, so that the effect itself accelerated. At the same time, this drops in the electroactive Zone located gas volume, resulting in a lower cell voltage is achieved. A suction effect caused by the movement of the glass bubbles along the edge of the electrode will ensure that fresh electrolyte in the electroactive Zone between membrane 6 or diaphragm and electrode 8, 9 is taken care of, for example, in chlor-alkali electrolysis a necessary requirement for a long Membrane life is. In addition, there is one directional flow since all glass bubbles in one direction be forced. This flow is through the arrows indicated in Fig. 2. This will decrease due to one side the increasing gas content the density of the electrolyte gas mixture, which leads to internal circulation, which compared to the incoming electrolyte current around the Factor 10 to 100 is larger. This will make an excellent one Homogenization of the electrolyte achieved.

The structure of the electrolysis apparatus is otherwise different not from known electrolysis devices. The sequence several plate-shaped electrolysis cells 2 happens in a framework, the so-called cell framework. The plate-shaped electrolytic cells 2 are between the hooked into the two upper longitudinal beams of the cell frame, that their plate plane is perpendicular to the side member axis stands. So that the plate-shaped electrolytic cells 2 you Transfer weight to the top flange of the side member can have them on the top edge of the plate on each Side of a cantilever-like holder. The holder extends horizontal in the direction of the plate level and protrudes the edges of the flanges. In the scaffolding the plate-shaped electrolytic cells are attached Lower edge of the cantilever-like holder on the upper flange on.

The plate-shaped electrolysis cells 2 hang comparatively like folders in a hanging file in the cell structure. in the The plate surfaces of the electrolysis cells stand in a cell frame in mechanical and electrical contact, as if they were be stacked. Electrolysers of this design are Called electrolysers in hanging stack type.

By lining up several electrolytic cells 2 in Hanging stack construction using known tensioning devices the electrolysis cells 2 via the contact strips 7 each with adjacent electrolytic cells in a stack electrically connected. From the contact strips 7 the current then flows through the half-shells over the webs 10 into the anode 8. After passing through the membrane 6 the current from the cathode 9 is taken up via the lands 10 to flow into the other half shell or the rear wall 3A and here in the contact strip 7 of the next cell convert. In this way the electrolysis current penetrates the entire electrolytic cell stack, whereby he initiated on one outer cell and on the other outer cell is derived.

The configuration is not shown in detail in the figures of the electrolytic cells 2 in the lower area the electrolyte inlet. The electrolyte entry can both selectively as well as with a so-called inlet distributor respectively. The inlet distributor is designed so that a tube is arranged in the element, which has openings. As a half-shell through the webs 10, which the connection between the rear walls 3A and 4A and the electrodes 8, 9 represent, segmented, one achieves one optimal concentration distribution when both half shells 3, 4 are equipped with an inlet distributor, whereby the length of the inlet distributor arranged in the half-shell corresponds to the width of the half-shell and each segment through at least one opening in the inlet manifold the respective electrolyte is supplied. The sum of the Cross-sectional area of the openings in the inlet manifold should smaller than or equal to the inner cross section of the distributor pipe his.

As can be seen from Fig. 1, the two half-shells 3, 4 provided with flanges in the flange area, which are screwed are. The cells constructed in this way become one Cell framework not shown either hung or posed. Hooking or placing in the cell structure takes place via not shown, located on the flanges Holding devices. The electrolysis apparatus 1 can consist of a single cell or preferably by stringing together of several electrolytic cells 2 in a hanging stack design. Are several single cells according to the hanging stack principle pressed together, the single cells be aligned plane-parallel before the jig is closed, otherwise the current transfer from one Single cell to the next not over all contact strips 7 can be done. Around the cells after hanging or setting to align in parallel in the cell structure it is necessary that the usually empty let the approximately 210 kg elements move easily. Around to fulfill this requirement are those not shown Mounts or located on the cell frame and cell frame Support surfaces with assigned coatings Mistake. Here are the ones located on the element flange frame Brackets with a plastic, e.g. PE, PP, PVC, PFA, FEP, E / TFE, PVIF or PTFE, relined while the Support surfaces on the cell frame also with one of these Plastic is coated. The plastic can only laid on or guided over a groove, glued on, welded on or be screwed on. The only essential thing is that the plastic pad is fixed. In that touching two plastic surfaces are those in the scaffolding Individual elements so easily movable that these without additional lifting or sliding device by hand in parallel can be aligned. When closing the tensioning device the elements lay down in the cell structure due to their easy to move across the entire rear wall flat on what is the prerequisite for an even Power distribution is. In addition, this is the Cell electrically isolated from the cell framework.

Of course, the invention is not limited to that in the drawings illustrated embodiments limited. Further Refinements are possible without the basic idea leave. So can to the inclination of the blind-like Breakthroughs 8B, 9B and the electrode rods 8A, 9A of the two Electrodes 8, 9 with respect to the horizontal, as shown, the respective electrode 8, 9 obliquely in the respective electrolytic cell 2 are installed. alternative but can also be provided that the entire electrolytic cell is arranged at an angle, such that the bottom the respective housing half-shell with respect to the horizontal is inclined, so that inevitably the blind-like openings 8A, 9B are arranged inclined are and that described in relation to Figures 2 and 3 Effect.

Claims (4)

1. Electrolysis apparatus for producing halogen gases out of aqueous alkali halide solution, with several plate-shaped electrolysis cells arranged in a stack next to one another and in electrical contact, which each have a housing of two half-shells of electrically conductive material with external contact strips on at least one housing rear wall, wherein the housing has devices for supplying the electrolysis current and the electrolysis input substances and devices for removing the electrolysis current and the electrolysis products, and in each case two essentially planar electrodes (anode and cathode), wherein the anode and the cathode are equipped with louvre-like apertures to allow a through-flow of the electrolysis input substances and the electrolysis products, and are separated from one another by means of a partition wall and are arranged parallel to one another, and are connected in an electrically conductive manner by means of metallic stiffeners to that rear wall of the housing that has been respectively allocated,
   characterised in that
   the louvre-like apertures (8B, 9B) of the anode (8) and cathode (9) are arranged so as to be inclined relative to the horizontal.
2. Electrolysis apparatus in accordance with claim 1,
   characterised in that the angle of inclination of the louvre-like apertures (8B, 9B) lie between 7° and 10° relative to the horizontal.
3. Electrolysis apparatus in accordance with claim 1 or 2,
   characterised in that the underside of the respective housing (3, 4) is arranged parallel to the horizontal and the louvre-like apertures
   characterised in that the underside of the respective housing (3, 4) is arranged parallel to the horizontal and the louvre-like apertures (8B, 9B) of the anode (8) and the cathode (9) are arranged inclined relative to the underside of the respective housing (3, 4).
4. Electrolysis apparatus in accordance with claim 1 or 2,
   characterised in that the underside of the respective housing (3, 4) is arranged inclined relative to the horizontal.

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