Electrolysis device

Abstract

The invention relates to an electrolysis device, comprising at least one horizontal electrolytic cell with a housing (6) and an anode (8) that has a membrane or a diaphragm (18), and a cathode (9) that has a gas diffusion electrode (17). The device further comprises supply (21) and discharge (23) means for gas (3) which lead to or away from the gas chamber (22) of the cathode (9), and supply (16; 19) and discharge (16; 20) means for electrolytes (1) which lead to or away from the first electrolytic chamber (4) and to or away from the second electrolytic chamber (5). The anode (8) and the membrane or the diaphragm (18) have at least one respective opening for the supply (19) of electrolytes (1) to the second electrolytic chamber (5), and at least one one further opening for the discharge (20) of electrolytes from the second electrolytic chamber.

Description

[0001] The present invention relates to an electrolysis device that has at least one horizontal electrolytic cell that has a housing and an anode with a membrane or diaphragm, and a cathode with a gas-diffusion electrode, as well as means for supplying and discharging gas into or out of the gas chamber of the cathode, and well as means for supplying and discharging electrolytes into or out of a first electrolytic chamber, and into or out of a second electrolytic chamber, the electrolytic chambers being separated from one another by the membrane or diaphragm.

[0002] An electrolysis device of this kind is described in EP-A-182 144. In this, the electrolyte is supplied and discharged by way of openings disposed on the edge between the electrodes. Because of this, the cross sectional area of the openings is restricted by the dimensions of the electrodes and the distance between them. Since the spacing between the electrodes amounts to only a few millimeters, the cross sectional area that is available for supplying and discharging the electrolyte is relatively small. For this reason, such electrolysis devices are suitable only for electrolytic cells that are connected electrolytically in parallel, since only small quantities of electrolyte pass through these.

[0003] In the case of cells that are electrolytically connected in series, as is described, for example, in EP-B-0 865 516, the quantity of electrolyte that passes through them is greater, in keeping with the number of cells, and unacceptable pressure losses can be caused at the openings because of high electrolyte speeds. This is particularly so if an electrode is coated with a porous gas-diffusion electrode. An hydraulic pressure acts on the gas-diffusion electrode as a function of the pressure losses at the openings, and this can result in flooding of the electrode if the gas pressure on the other side of the electrode is not great enough. It is true that—generally speaking—gas-diffusion electrodes are hydrophobic since they contain a considerable quantity of Teflon that binds the carbon, so that they can in part be loaded with water columns greater than 500 mm without the water penetrating into the cells. However, practice has shown that this is not the case in an electrolysis device since, when current is flowing and ions are present, the surface will be wetted even at pressures below 40 mm of water column. In the same way that hydraulic pressure increases as the length of pipe line through which there is a flow increases, so the pressure acting on the gas-diffusion electrode increases with the increasing number of cells connected electrolytically in series. This results in the highest pressure being found in the first cell, and the lowest pressure being found in the last cell. In such a case, flooding of the gas-diffusion electrode can only be prevented by maintaining a specific gas pressure in each individual cell.

[0004] In order to permit operation of the cells in a manner that is less costly and thus more economical, and with only one gas pressure, a cascade flow has to be generated, i.e., the electrolyte passes in overflow from the outlet pipe of one cell into the inlet pipe of the next cell. At the overflow point, which corresponds to an adjustable-height overflow as described in EP-B-0 865 516, the hydraulic pressure falls off so that the pressure is equal in each cell. In the case of cells with vertical electrodes, this can be achieved by the lengths of the inlet and outlet pipes, which correspond to the hydraulic pressures. In contrast to this, this is not possible in the case of horizontal electrodes, such as those described in EP-A-01 82 114 and in EP-B-0 856 516. In the present case, the permissible variation of the acceptable hydraulic pressure is determined by the installed height of the cell. As a rule, this amounts to a few centimeters in order to save both space and materials. For this reason, one possibility for generating only appropriately low hydraulic pressures lies in the structural enlargement of the inlet and outlet openings. This can be achieved in that the inlet and the outlet openings are not arranged between the electrodes, but rather adjacent to the electrodes, as proposed in EP-A-0 168 600, EP -A-0 330 849 and EP-B-0 865 516. The cross sectional areas of the openings is then no longer limited by the amount of space between the electrodes, but can be matched to the increased quantities of electrolyte by the appropriate layout of the frame geometry in the case of electrolytically series connection. However, one disadvantage with such an arrangement of the openings is the additional requirement for a sealing frame that joins the membrane of the diaphragm to the frame so that it is gas-tight and liquid-tight, in order that the quantities in the individual chambers are prevented from mixing. Since it is located between the electrodes, such a frame also means that the distance between the electrodes and will be increased by the thickness of the frame. This causes the voltage drop in the electrolytes to increase and increases energy consumption.

[0005] Increasing the spacing can be avoided if the membrane or diaphragm or—as is proposed in U.S. Pat. No. 4 436 608—even the gas diffusion electrode is bent round at the sides. However, this entails the danger that too great a shear force will act at the corners of the frame, so that the membrane or diaphragm will no longer be tight because it has been damaged.

[0006] For this reason, it is the objective of the present invention to describe an electrolysis device of the kind referred to in the introduction hereto, in which the above cited problems associated with the prior art have been resolved, and in particular to describe an electrolysis device of this kind which is of simple construction and can be operated economically.

[0007] According to the present invention, this problem has been solved, for example, in that the anode as well as the membrane or the diaphragm each have at least one opening for supplying electrolytes to the second electrolytic chamber, and at least one additional opening for discharging electrolytes from the second electrolytic chamber.

[0008] In this respect, it is particularly advantageous if the membrane or the diaphragm be clamped so as to be gas and liquid tight in the area of the electrolyte supply opening and the electrolyte discharge opening in a sealing frame, the thickness of which does not exceed the thickness of the anode, and on the sealing frames and the seals that lie on the anodes. Such an arrangement entails the advantage that the spacing between the electrodes is not affected by this clamping and the shear forces acting on the membrane or the diaphragm are minimized.

[0009] Most of today's electrolysis cells are manufactured from metal because, providing appropriate alloys are used, it is possible to ensure long-term resistance to chemical and mechanical stresses at very high temperatures. Disadvantages of metal structures are the materials and production costs, which are mostly very high and which, as a rule, include costly welding operations. This is particularly the case with cells that use different materials for the anodes and cathodes, for example chlorine-alkali membrane cells, in which the anode is of a titanium-palladium alloy that is coated with ruthenium oxide, and the cathode is of nickel. Such cells basically comprise an anode and a cathode bath with the particular electrodes. In the case of electrical series connection, the individual baths are welded together, e.g., through explosive plated, bipolar rails. Ideally, the cells are welded together by way of such rails using a laser, when the welding range or the temperature zone can be so arranged spatially that any mixing of the different alloys involved, and thus corrosion, can be prevented. It is simpler to manufacture an electrolytic cell if the anode and the cathode are of identical material, as is the case, for example, with a cell for producing hydrogen peroxide in alkaline solution using a gas-diffusion cathode. In this case, nickel can be used as the material. In order to obtain a bipolar cell, the electrodes are simply connected to one another electrically through connectors or the cell walls themselves. In this cell, it is important that when a diaphragm is used at the anode there be a gas tight partition between the anode and the cathode—as is described in EP-B-0 865 516—so that the gas pressure, which is meant to prevent flooding of the gas-diffusion cathode by the catholyte, does not act on the anolytes. In contrast to a membrane, a diaphragm is liquid permeable, so that pressure that acts on the anolytes also acts on the catholytes. Without a partition, the pressure differential would act on the gas-diffusion cathode and cause flooding. However, installation of such a partition requires a considerable outlay from the standpoint of manufacturing technology, since the requirement for gas-tight sealing does not permit the use of spot welding, so that the partition must be welded to the connectors and the cell walls by continuous welds. In most cases, however, this leads to warping, since the thinnest possible material is selected for reasons of economy, and the welding heat is not dissipated effectively. As is the case with chlorine-alkali membrane electrolysis, laser welding is recommended because the temperature zone can be determined very precisely. However, because of costly set up, long preparation times, and the great demands made on its quality, laser welding is very cost intensive.

[0010] In order to avoid these production and material costs that result from using two metal baths, as in EP-0-A 182 114, for example, a further development of the inventive concept proposes that the housing of the electrolysis cell be formed from two plastic panels, between which the electrolysis chambers and the gas chamber are delimited by the use of frame-like seals.

[0011] At the same time, when a plurality of electrolytic cells are arranged one above the other, the middle plastic panel(s) forms or form the bottom of the upper electrolysis cell and the cover of the electrolysis cell that is located below.

[0012] The electrolysis supply and discharge channels for the second electrolyte chamber can be incorporated in these plastic panels in a simple manner, in particular, by being milled into them. The same applies to the electrolyte supply and discharge channels for the first electrolyte chamber.

[0013] PP, PVC, and post-chlorinated PVC can be used as the plastic. These plastics are resistant to a number of chemicals, even at temperatures of up to approximately 80° C. The plastic panels can be fitted with seals so that the necessary electrolyte and gas chambers are left between the electrodes and a plastic panel without incurring any major expense. Thus, it is possible to dispense with a material-intensive version with two baths, and without welding a partition into place.

[0014] In the case of electrolysis operations other than that used for the electrolysis of peroxide, it is preferred that the plastic panels be of materials that differ from one another since the anolyte and the catholyte consist of different compounds. Since the anolyte and the catholyte are routed across the identical plastic panel, these can more usefully consist of two different plastics.

[0015] In the case of a plurality of electrolysis cells, the electrolyte discharge channels of the upper electrolysis cell can in each instance be electrically connected to the electrolyte supply channels of the electrolysis cell located below so as to permit a flow, by way of external connecting lines.

[0016] If plastic panels are used as a housing, it is not possible to supply current to the electrodes by way of the housing wall since these are then non-conductive. A conventional electrical connection by way of connectors that are located in the electrolyte area should also be avoided, since these would have to be additionally sealed against the plastic panel. It would also be necessary to mill passages into the plastic panel, a procedure that would degrade the rigidity of the panel.

[0017] Accordingly, the present invention proposes that the anode and the cathode be routed out through the seals that delimit the electrolyte chambers and the gas chamber to the outside, and that they be fitted with their electrical connectors or connections from the anode to the cathode outside the chamber.

[0018] The electrical connectors or connections can also be located within the plastic panel, and edge recesses or openings can be provided for this purpose; they can also be arranged externally. The rigidity of the plastic panel will not be degraded in this case.

[0019] The materials used for the electrical connectors and connections can be selected as desired since these connectors and connections are no longer exposed to the chemical and thermal stresses generated by the electrolytes. For this reason, it is possible to use highly conductive copper, for example, which is not normally used at this location because of its poor chemical and thermal resistance. This leads to a favourable reduction of the cost entailed for the number and the dimensions of the electrical connectors and connections, to which must be added the corresponding conductor rails to which the electrical connections are made.

[0020] Particularly easy assembly is ensured if the connectors and/or connections to the anodes and the cathodes are made by way of clamping elements. Cost-intensive welding is then no longer necessary.

[0021] When gas diffusion electrolysis is used, a major role is also played by the gas requirement. This must be many times the stoichiometric requirement for the reactions taking place in gas diffusion electrolysis, so that no losses of efficiency result. In most cases, the oxygen in a gas diffusion cathode is converted with the hydrogen that is generated at the cathode during the production of energy. As a rule, for reasons of economy, air is used in place of oxygen. Since, as is known, air contains only 21% oxygen, correspondingly larger quantities of it must be introduced into the electrolysis cell. This requires supply and discharge lines that are of appropriately large cross-section, which means that the thickness of the cell frame must be increased; this is undesirable. Any reduction of the cross section with a simultaneous increase in the number of lines must in most instances be precluded for reasons of economy.

[0022] According to another proposal made by the present invention, for this reason a gas supply channel and a gas removal channel pass through the plastic panels that define the electrolysis cell(s) and optionally the anodes and the cathodes, from above to below, whilst sealing the electrolyte chambers, and in a flow connection with the particular gas chamber. The cross section of the supply and removal openings can thus be determined regardless of the thickness of the panel. To this end, there are openings with identical dimensions in the individual plastic panels and, optionally, in the electrodes, and these are aligned with each other in order that the gas, for example the air, is distributed within the cell stack with the least possible loss of pressure and in a manner that is favorable from the energy standpoint. The openings are so laid out that the required cross-section is available and so that sufficient material is left over for the flow of current. Because the air flows downward from above, any electrolyte that passes through the gas diffusion electrode by way of minor leaks can be removed. A further advantage of the possibility for converting large quantities of gas is the increased absorption of the evaporative heat that is generated at the gas diffusion electrode, so that internal cooling takes place and this then replaces external cooling and eliminates the costs that would be incurred for a heat exchanger.

[0023] Thus, according to the present invention it is possible to construct electrolysis devices for use in gas diffusion electrolysis, and to do so in a simple and economical manner. No costly welding operations are needed. The individual parts can be assembled directly at the intended site of operation, which means that the costs associated with intermediate assembly are eliminated and transportation costs can be reduced. The combination of different materials for the electrodes and plastics means that cells for various electrolysis processes can be assembled in a cost-effective, modular system

[0024] Additional objectives, features, advantages, and possible applications for the present invention are set out in the following description of the embodiments, on the basis of the drawings appended hereto. Either alone or in any combination, all of the features that the described or illustrated herein constitute the object of the present invention, regardless of their combination in the individual claims or their references.

[0025] The drawing show the following:

[0026] FIG. 1: A diagrammatic representation of an the electrolysis device according to the present invention, which is assembled from four electrolysis cells;

[0027] FIG. 2: An enlarged view showing a section of a pair of electrodes in the area of an electrolyte supply opening or an electrolyte discharge opening;

[0028] FIG. 3: a plan view of a sealing frame as is used in FIG. 2.

[0029] The electrolysis device shown in FIG. 1 has four horizontal electrolysis cells that are stacked one above the other, and a housing 6 that is formed from plastic panels 6′, 6″, the uppermost plastic panel 6′ forming a cover and the lowest plastic panel 6″ forming a bottom for the uppermost or lowest electrolysis cell, respectively, whereas the middle plastic panel 6″ simultaneously forms the bottom of the electrolysis cell that is located above it and the cover for the electrolysis cell that is located beneath it.

[0030] Each electrolysis cell has an anode 8 with a membrane or a diaphragm 18, and a cathode 9 with a gas-diffusion electrode 17, a first electrolyte chamber 4 being formed by the seals 11, 12, 13 as an anode chamber and a second electrolyte chamber 5 being formed as a cathode chamber, with a gas chamber 22 being formed on the outside of the cathode 9.

[0031] Electrolyte 1 is routed by way of an electrolysis supply channel 19′ in the upper most plastic panel 6′ to an opening 19 in the anode 8 and to the associated membrane or to the associated diaphragm 18 and thus to the second electrolyte chamber 5. Electrolyte is removed from the second electrolytic chamber 3 through an electrolyte removal opening 20 into an electrolyte removal channel 20′ which analogously to the electrolyte supply channel 19′ is milled into the first uppermost plastic panel 6′ and runs from the second electrolyte chamber 5 first vertically and then horizontally. Corresponding channels and openings also provided in the remaining plastic panels, and anodes and membranes or diaphragms. In the same way that the electrolyte 1 is routed through a side supply opening 26 to the outer edge of the uppermost plastic panel 6′, the electrolyte 1 flows from the electrolyte removal channel 20′ laterally to the outside and into a connecting line 20 to the second plastic panel 6″, which defines the uppermost electrolysis cell as the bottom and then into an electrolyte feed channel which corresponds to the supply channel 19′ of the uppermost plastic panel 6′, or until the electrolyte is discharged from the side of the next to last plastic panel 6″ through an outlet tube 25. Gas, for example, oxygen or air, is routed downwards into a gas supply channel 21 that passes through all of the plastic panel 6′, 6″ of the housing 6 that is sealed off from the electrolyte chambers 4, 5 so as to be both gas and liquid tight, although there is a flow connection to the corresponding gas chamber 22 of the particular electrolysis cell.

[0032] Below, the gas supply channel 21 opens out in the lowest gas chamber. On the opposite side of the stack of electrolysis cells, a vertical gas removal channel 23 extends from the first gas chamber 22 as far as a lower outlet opening in the lowest plastic panel 6′.

[0033] In the middle of the plastic panel 6′, 6″ there is in each instance an electrolyte supply or electrolyte discharge opening 16 of the first electrolysis chamber 4 (anode chamber) and the associated electrolyte supply and electrolyte discharge channels 16′. The corresponding channels 16′ can also be milled into the plastic panel 6′, 6″ in the same way as the channels 19′, 20′, as well as the gas passage openings which are aligned with each other and located in the edge area of the particular plastic panel 6′, 6″ and form the vertical gas channels 21, 23.

[0034] FIG. 1 also shows that the electrodes 8, 9 are routed out at the side through the seals that define the electrolyte chambers 4, 5 and the gas chamber 22 and are in this way traversed by the vertical gas channels 21, 23.

[0035] In the outermost edge area, the plastic panels 6′, 6″ are provided with edge recesses 24 that are aligned with each other. Within these, on both sides, both above and below, there are electrical connectors 8 (above) and the cathode 9 (below) that are connected to the contact rails 2; in the middle plastic panel 6″ there are electrical connections 7′ between the cathode 9 and the anode 8 of the electrolysis cells that follow one another.

[0036] The contact rails 2 as well as the connectors 7 and the connections 7′ can be of a material, such as copper, that possesses good current-conducting properties. The connectors 7 and the connections 7′ can also be secured to the anode 8 and the cathode 9 through clamping elements (not shown herein).

[0037] FIG. 2 shows how sealing is effected in the area of and in electrolyte supply opening 19 and in an electrolyte discharge opening 20. Whereas the gas diffusion electrode coating 17 on the cathode is continuous as far as the edge area of the cathode 9, where it is covered by a sealing element 12; in the area of the openings 19, 20 the membrane or the diaphragm 18 is angled upward so as to lie on a sealing frame 15, which is no thicker than the anode 8. The sealing frame 15 is accommodated in a large cutout 27 in the anode 8, and internally it defines the openings 19, 20. Above the angled area of the membrane or of the diaphragm 18 there is a sealing element 14 above the anode 8. In the vicinity of the openings 19, 20 the membrane or diaphragm 18 is clamped by the edge that faces the openings 19, 20 between sealing frames 15 and sealing element 14 so as to be gas tight and liquid tight.

[0038] FIG. 3 shows that the sealing frame 50, which is shown in FIG. 2 in vertical cross-section on the line II-II is narrow and its short sides are curved and thus enclose the openings 19, 20. 1 Reference Numbers  1 Electrolyte  2 Contact rails (of copper)  3 Gas, e.g., O2 or air  4 First electrolyte chamber (anode)  5 Second electrolyte chamber (cathode)  6 Housing  6′, 6″ Plastic panels  7′, 7″ Electrical connectors or connections  8 Anode, cross hatched area covered by membrane or diaphragm  9 Cathode, cross hatched area covered by gas-diffusion electrode 10 Connecting line 11, 12 Sealing element 13, 14 Sealing element 15 Sealing frame 16 Electrolyte supply and discharge opening of first electrolyte chamber (anode chamber) 16′ Electrolyte supply and discharge channel of first electrolyte chamber (anode chamber) 17 Gas-diffusion electrode 18 Membrane or diaphragm 19 Electrolyte supply opening of the second electrolyte chamber (cathode chamber) 19′ Electrolyte supply channel of the second electrolyte chamber (cathode chamber) 20 Electrolyte discharge opening of the second electrolyte chamber (cathode chamber) 20′ Electrolyte discharge channel of the second electrolyte chamber (cathode chamber) 21 Gas supply channel 22 Gas chamber 23 Gas discharge channel 24 Edge cutout 25 Outlet pipe 26 Supply pipe 27 Cutout

Claims

1. Electrolysis device with at least one horizontal electrolysis cell, with a housing (6), the anode of which has a membrane or diaphragm (18) and the cathode of which has a gas-diffusion electrode (17), with means to supply (21) and discharge (23) gas (3) into or out of the gas chamber (22) of the cathode (9), respectively, as well as means to supply (16, 19) and discharge (16, 20) electrolytes (1) into or out of a first electrolyte chamber (4), and into or out of a second electrolyte chamber (5), characterized in that the anode (8) as well as the membrane or diaphragm (18) each have at least one opening for supplying electrolyte (1) to the second electrolyte chamber (6) and at least one additional opening for discharging (20) electrolytes (1) from the second electrolyte chamber (5).

2. Electrolysis device as defined in claim 1, characterized in that in the area of an electrolyte supply opening (19) and of an electrolyte discharge opening (20), the membrane or diaphragm (18) is clamped by a sealing frame (15), the thickness of which does not exceed the thickness of the anode (8), as well as at the seals (14) that are close to the frame (15) and the seals, so as to be gas and liquid tight.

3. Electrolysis device as defined in claim 1 or claim 2, characterized in that the housing (6) of the electrolysis cell is formed from two plastic panels (6, 6′, 6″) between which the electrolyte chambers (4, 5) are restricted by the use of frame-like seals (11 to 13)

4. Electrolysis device as defined in claim 3, characterized in that the plastic panels (6′, 6″) consist of materials that differ from each other.

5. Electrolysis device as defined in claim 3 or claim 4, characterized that a plastic panel (6″) consists of two different materials.

6. Electrolysis device as defined in one of the claims 1 to 5, characterized in that when a plurality of electrolyte cells are arranged one above the other, the middle plastic panel (s) (6′, 6″) form(s) the bottom of the upper electrolyte cell and the cover of the electrolyte cell that is located below.

7. Electrolysis device as defined in one of the claims 1 to 6, characterized in that electrolyte supply (19′) and) discharge channels (20′) of the second electrolyte chamber (5) are incorporated, in particular milled, into the plastic panels (6′, 6″).

8. Electrolysis device as defined in one of the claims 1 to 7, characterized in that electrolyte supply and discharge channels (16′) of the first electrolyte chamber (4) are incorporated, in particular milled, into the plastic panels (6′, 6″).

9. Electrolysis device as defined in one of the claims 1 to 8, characterized in that when a plurality of electrolysis cells are arranged one above the other, electrolyte discharge channels (16′, 20′) of the upper electrolysis cell are in a flow connection with the electrolyte supply channels (16′, 19′) of the electrolysis cell located below, by way of external connection lines (10).

10. Electrolysis device as defined in one of the claims 1 to 9, characterized in that the anode (8) and the cathode (9) are routed to the exterior through the frame-like seals (11 to 14) that define the electrolyte chambers (4, 5) and the gas chamber (2) to the outside, and outside the chambers (4, 5; 22) are provided with electrical connectors (7) or connections (7′) to each other.

11. Electrolysis device as defined in one of the preceding claims, characterized in that the electrical connectors (7) are connected to upper and lower contact rails (2) that are, for example, of copper.

12. Electrolysis device as defined in one of the preceding claims, characterized in that the connectors (7) and/or the connections (7′) are accommodated in edge cutouts'(24) of the plastic panels (6′, 6″).

13. Electrolysis device as defined in one of the claims 1 to 12, characterized in that the connectors (7) and/or the connections (7′) are pressed tightly against the anode (8) and the cathode (9) by way of clamping elements.

14. Electrolysis device as defined in one of the preceding claims, characterized in that a gas supply channel (21) and a gas discharge channel (23) pass through the plastic panels (6′, 6″) and optionally the anode (8) and the cathode (9) whilst being sealed off against the electrolyte chambers (4, 5), in a flow connection with the particular gas chamber (22), downwards from above.