MXPA98002862A - Semicelda electroquim - Google Patents

Abstract

The present invention relates to an electrochemical half cell (1) with a gas diffusion electrode (7) as an odode cathode, wherein the gas chamber (6) is divided in particular into two or more gas receptacles (6a, 6b, 6c) arranged one on top of the other, the electrode chamber (2) of the half cell (1) is divided into compartments (2a, 2b, 2c) which, for the passage of the electrolyte (23), are connected to each other in the form of waterfall via conduits (17), (18), (1

Description

ELECTROQUÍMICA SEMICELDA DESCRIPTION OF THE INVENTION The invention relates to an electrochemical half cell with a gas diffusion electrode as a cathode or anode, wherein the electrode chamber of the half cell is divided into transverse compartments optionally upwards which, for the passage of the electrolyte, are connected to each other in the form of cascade via conduits and wherein the gas chamber is divided in particular into two or more gas receptacles arranged one on top of the other. The operation of electrochemical cells based on gas diffusion electrodes, for example to be used as an oxygen-consuming cathode in the alkali halide electrolysis, is basically known and is described for example in U.S. Patent No. 4,657,651. Gas diffusion electrode is an open pore structure between the electrolyte and the gas chamber having an electrically conductive coating with a catalyst and allowing an electrochemical reaction, for example oxygen reduction, to take place in the three-phase limit of the electrolyte, the catalyst and the reactive gas in the electrode structure. The boundary layer is REF: 27086 generally maintained in the structure by the surface tension of the electrolyte on the hydrophobic electrode material against the hydrostatic pressure of the electrolyte on the electrode structure. However, only a small pressure drop between the gas side and the liquid side of the structure acting as a diaphragm is allowed. If the pressure on the gas side is too high, the gas finally bursts through the diaphragm, the electrode interrupts its function in this region and the electrolytic process is interrupted. If, on the other hand, the liquid pressure is too high, the three-phase limit is displaced from the region of the diaphragm containing the catalyst, likewise it interrupts the function of the cathode and in the case of an additional increase in pressure, this leads to an irruption of the liquid through the electrolyte into the gas chamber. In the case of a vertical electrode array, as required for example in diaphragm electrolysis to allow a favorable discharge of the target chlorine product, this leads to a limitation of the total height of the gas diffusion electrodes as in other circumstances where the gas from the upper part penetrates into the cathode chamber of the electrode and where the electrolytic liquid from the bottom penetrates into the gas chamber. The technologically obtainable total height therefore remains limited to approximately 20-30 cm, which is unattractive for commercial diaphragm electrolysers. To overcome the problem of pressure compensation, several arrangements have been proposed in the prior art. According to US Patent No. 4 657 651, a pressure compensation is achieved between the gas chamber and the electrolyte chamber on both sides of a gas diffusion cathode in which the cathode is divided into individual horizontal chambers. which are fed individually with gas, the pressure of the gas is regulated in each case by precipitating the flow of exhaust gas through the vertical chambers, since the depth of the vertical chambers corresponds to the level of the electrolyte in the respective chamber. One disadvantage is the high operating costs in terms of the devices, which impede commercial realization. The pressure in each individual gas chamber must in fact be adjusted separately via the respective valves. German Patent DE 4 444 114 C2 discloses an electrochemical half cell with a gas diffusion electrode wherein the pressure compensation between the gas chamber and the electrolyte chamber on both sides of a gas diffusion electrode is achieved since the Gas chamber is divided into two or more gas receptacles placed cascaded one on top of the other, the gas receptacles are separated from each other and are open at the bottom towards the electrolyte, so that the opening towards the electrolyte causes the pressure in each gas receptacle to be in equilibrium with the pressure of the electrolyte liquid column in the corresponding part of the electrode chamber arranged upstream of the gas diffusion electrode, and wherein a possible supply and discharge of gas takes place via the openings towards the electrolyte. However, the electrolytic cell constructions have a number of technical disadvantages. In particular, in the case of electrolytic cells having a relatively large overall height, it is necessary to prevent hydrostatic pressure on the lower part of the gas diffusion electrode. Another disadvantage of the half-cell construction according to DE 4 444 144 is that possible gas bubbles entering with the electrolyte accumulate in the region of the electrolyte space upstream of the gas diffusion electrode during the operation of the cell and they can interrupt the operation of the cell. It was also necessary to avoid the disadvantage of being unable to regulate the gas pressure independently of the structural properties of the cell defined initially, which exists for example in the case of DE 4 444 144. In addition, the gas pressure must be capable of being adjusted during operation independently of the electrolyte pressure and optionally changed in relation to an electrolyte pressure that is also independent of the height of the cell. The object of the invention, which starts from the technique described above, is to make available an electrochemical half cell based on a gas diffusion electrode that allows pressure compensation between the gas side and the electrolyte side of the electrode of gas diffusion, but which does not possess the disadvantages mentioned above of the known cell structures. In particular the new cell structure is to facilitate as much as possible the construction of the half cell. The object is achieved according to the invention, by means of an electrochemical half cell based on a gas diffusion electrode as a cathode or anode, wherein the electrode chamber of the half cell is divided into compartments which, for the passage of the electrolyte , are connected to each other in the form of cascade via conduits. The invention relates to an electrochemical half cell consisting of an electrode chamber for the accommodation of an electrolyte, a gas chamber, and at least one gas diffusion electrode which separates the gas chamber and the electrode chamber and serves As a cathode or anode, the gas chamber is optionally divided in particular into two or more gas receptacles arranged one above the other, characterized in that the chamber of the electrode is divided into compartments which, for the passage of the electrolyte, are connected to each other in cascade form via conduits, the electrode chambers are each transverse in particular in the upward direction. In particular in the region of the base of the compartment, the compartments have inlet openings for the electrolyte which provide passage of the electrolyte through the respective compartment in the upward direction. Particularly preferably, the openings are arranged in the base of the compartment distributed on the base of the compartment. The electrolyte inlet tube towards the electrochemical half cell is preferably arranged in the uppermost compartment of the half cell, so that the electrolyte flows through the series of interconnected compartments beginning with the uppermost compartment. The gas chamber of the half cell preferably divided into a plurality of gas receptacles arranged one above the other and corresponding in particular number to the number of compartments. The invention also relates to an electrochemical half cell consisting of an electrode chamber for the accommodation of an electrolyte., a gas chamber and at least one gas diffusion electrode, which separates the gas chamber and the electrode chamber and serves as a cathode or anode, the gas chamber is divided into two or more gas receptacles arranged one on top of the other. another, characterized for adjusting a pressure difference corresponding to the pressure upstream of the gas diffusion electrode, the gas receptacles are connected to each other via stepped throttling orifices and the gas inlet priority is arranged in the receptacle of the gas. lower gas. In a preferred variant, the division of the gas chamber of the electrochemical half cell towards the gas receptacles is also coupled with the design of the half cell according to the invention comprising the division of the electrode chamber into compartments. In the electrochemical half cell according to the invention comprising compartments placed one above the other in the electrolyte space and comprising a gas displacement chamber, the compartments are fed consecutively according to the principle of overflow and in each case traversed in upward direction, so that a hydrostatic pressure created in the respective compartment is still limited only according to the height of the respective electrolyte column. In the case of the half-cell comprising an electrolyte inlet in the region of the base of the compartment, the upward flow prevents the suspension of possible gas bubbles introduced into the electrolyte column. The pressure conditions in the individual stages placed one above the other are fundamentally the same, thus allowing any desired technical structural height without having to withstand greater pressure on the lower part of the gas diffusion electrode in the upper part. The reaction gas, for example oxygen, can therefore be supplied on the other side of the inlet of the gas diffusion electrodes to the cascade stages via a single gas chamber, which can be divided into individual gas receptacles interconnected on the gas side. The pressure difference between the gas and the electrolyte can be selected here freely. As a result, the cathode chamber can be made extremely flat. It is conceivable, for example, to make the total thickness of the cell approximately 2/3 of the thickness of the known electrolytic half cells. An electrolyser comprising a plurality of diaphragm cells can then be equipped with 1/3 more elements and, taking into account a reduction in the operating voltage of 1/3, can be operated at the same total voltage as the conventional diaphragm electrolyzer . The operation mode of the electrochemical half cell with pressure compensation via the gas receptacles injected by stepped throttle elements will be described as follows. In the design comprising a displacement electrode chamber the reaction gas is fed through the gas receptacles arranged in cascade form on one another and connected only via staggered throttling elements (eg stepped throttling orifices), which they begin with the lowest gas receptacle, so that the gas pressure that occurs in each case as a result of the stepped throttling and decreases in the upward direction corresponds to approximately the corresponding electrolyte pressure upstream of the steering electrode Of gas. Also in this variant the electrode flows in an upward direction to prevent suspension in the electrode chamber of any gas bubbles fed at random. The preliminary pressure of the reaction gas corresponds approximately to the pressure at which the electrolyte is fed into the cell at the bottom and is, optionally, easily adjustable here by precipitation or by means of an air receiver in each case in association with the electrolyte. The supply of current to the gas diffusion electrode can take place in accordance with the basically known arrangements. A supply arrangement of current is preferred via the gas diffusion electrode mounting device, which is again connected in a low conical shape via the back side of the electrolytic cell to an external current source, and an additional metallic grid structure is applied to the mounting device, grid structure which is connected to the diffusion electrode of gas on the gas side or the electrolyte side depending on the pressure difference between the electrolyte side and the gas side and provides short current paths. In the case of a gas diffusion electrode with integrated metal grid, this is optionally possible to be distributed with the metal grid structure separated on the mounting device, if the diffusion electrode holder in the direction of the gas chamber It is secured by another simple contact device. The power supply can also preferably take place via a low conical connection to the rear side of the half cell.

An advantageous embodiment of the half cell according to the invention is characterized in that the total structure of the electrode is designed to be removed from the half cell, for example, an electrolytic half cell. The half cell according to the invention can be used basically in all electrochemical processes in which the gas diffusion electrode is operated in direct contact with a liquid electrolyte. The examples of use of the half cell according to the invention are the following: Electrolysis of sodium dichromate where, for example, an anode that consumes hydrogen is used; here the production of hydrogen at the cathode can be replaced by the reduction of oxygen at a cathode that consumes oxygen. Production of hydrogen peroxide via the reduction of oxygen at a gas diffusion cathode. Application in alkaline fuel cells used for example to enrich soda lye where it is possible to use semicells according to the invention connected as an anode for the conversion of hydrogen and half-cells connected as a cathode for the reduction of oxygen. The use of the half cell according to the invention is basically possible for conventional commercially available diaphragm electrolysers for the electrolysis of the alkali halide solution to be converted for the energy saving operation for example with oxygen-consuming cathodes. This also applies in particular to cell types with a vertical flange structure or internal vertical or horizontal structure flanges. All types known primarily of gas diffusion electrodes can be used in the half cell according to the invention, for example types having integrated metal support or current distributing gratings or electrodes constructed on carbon slabs or other conductive structures. In the following the invention will be explained in detail by way of example with reference to the figures without particularly limiting the invention.

In the Figures: Figure 1 is a longitudinal section along line AA 'of Figure 2a through a half cell according to the invention in the form of an oxygen-consuming cathode, seen in the direction of the rear side of the surface of the diffusion electrode.

Figure 2a is a cross section through the half cell according to Figure 1 along the line B-B 'of Figure 1. Figure 2b is a diagram explaining the difference in pressure on the diffusion electrode. Figure 3 shows an elongated detail of a part of the half-cell according to the invention shown in Figure 1. Figure 4 is a longitudinal section through a variation of the half-cell comprising stepped throttling orifices between the gas receptacles.

Examples Example 1 An electrochemical half cell 1 connected as an oxygen-consuming cathode is illustrated in Figures 1, 2a and 3 and operates as follows: The electrolyte 23 enters the half-cell 1, in particular the conduit 17, through the electrolyte inlet tube 12. The electrolyte 23 flows on and through the horizontal distributor 5c via the orifices 21c towards the compartment 2c of the chamber of the electrode 2 and ascends uniformly in the compartment 2c. The electrolyte 23 is sent from the compartment 2c through the opening 22c (see Figure 2a) to the horizontal collector 4c and is discharged with the overflow principle through the conduit 18 connected to the distributor 5b. In the same way the electrolyte 23 in each case flows on and through the conduits 19 and 20, the distributors 5a and 5b with the outlet openings 21a and 21b, the compartments 2a and 2b, the outlet openings 22a and 22b and the openings. upper manifolds 4a and 4b until finally the electrolyte is sent from the half cell via the conduit 20 through the outlet tube of the electrolyte 13. The reaction gas, for example oxygen, enters the gas chamber 6 via the tube 14. The channels carrying gas 16a and 16b provide a uniform gas supply connected to the gas chamber 6. The excess reaction gas, together with the possible condensates, is sent from the half cell 1 via the gas outlet pipe 15. The divider rod 3a and 3b between the collectors and the distributors and the support elements 10a and 10b between the segments separate them hydraulically between yes. The support elements 10a and 10b and the elements of the flange lia and 11b on one side define the chamber space of the electrode 2 between the ion exchange diaphragm 9 and the gas diffusion cathode 7 and press the latter against the channels of the distributor of the collector, whereby the gas diffusion cathode 7 is sealed from it and at the same time placed in electrical contact. The sum of the cross sections of the outlet openings 21a to 21c is smaller in terms of the total cross-sectional area of the distributor channels 5a to 5c to ensure a uniform flow of the electrolyte 23 into the compartments 2a to 2c. On the other hand, the outlet openings 22a to 22c in the collectors must be large enough to prevent the suspension of possible gas bubbles entering before these openings. The supply of electrolyte 23 to the half cell, optionally in place via the inlet tube at an appropriate geometric level or by a forced through flow. In particular in the latter case it is possible to reduce the number or cross section of the openings 21c towards the upper chamber to avoid the creation of a dangerous pressure on the gas diffusion electrode in the upper compartment 2c and in the other cascades. For this reason it may be advantageous to increase the number or cross-section of the compartment-to-compartment openings, beginning with the compartment 2c. If gas bubbles have entered the catalytic space, they coagulate first in the upper manifold and in the case of a sufficiently high flow rate enter down through the channel 4c, feed into the next compartment 2b and finally discharge via the last compartment. Alternatively, in the case of the concepts employing a low flow rate, each manifold 4a to 4c may be provided with ventilation means (not shown here) leading to the gas chamber in a corresponding manner. In this case the pressure of the reaction gas must be adapted to the hydraulic pressure in the region of the manifolds while in the case of the dynamic variant the oxygen pressure can be freely selected within the tolerances of the gas diffusion electrode. Figure 2b shows the distribution of the pressure differences on the individual segments of the half cell. Here it is essential that, due to the free discharge via the channels, the absolute pressure depends on the level of the respective segments.

Example 2 Figure 4 illustrates the principles of the cascade-like pressure break in the example of a half-cell comprising five gas receptacles 6a to 6e arranged one above the other. The reaction gas enters the chamber 6a through the tube 14 at a preliminary pressure of 1560 mm wc (wc - water column) and is sent from the chamber 6a through the stepped throttle 40 produced by the consumed amount of 0.12 mVh , then enters the chamber 6b with a lower pressure of 313 mm wc and is issued from the chamber 6b through the stepped throttle 41 reduced by the consumed amount of 0.12 mVh, etc., until the excess gas 0.4 mVh is issued from the chamber 6e through the stepped choke 44. In this embodiment of the invention the electrode chamber 2 is passed through and the electrolyte supply takes place through the feed tubes 12 from the bottom in accordance with Figure 4. Flow outward at the top (not shown here) passes through a corresponding collector according to Figure 4. In the case of a cell that has a height of 1.2 m, a vent of 0.8 my 5 segments, for soda lye at 32% an increase in hydrostatic pressure of 312 mm wc occurs in each stage, pressure increases which must be compensated. With an energy density of 3 kA / m2, the net consumption of oxygen amounts at 0.6 mVh that is, 0.12 mVh per segment. With an amount fed of 1 mVh the stepped throttling orifices directed upwards have the following diameter: Stepped throttle 44 outlet gas canister 6e 2.3 mm Stepped throttle 53 outlet gas canister 6d 2.1 mm Stepped throttle 42 outlet gas canister 6c 1.9 mm Stepped throttle 41 outlet gas can 6b 1.7 mm Stepped throttle 40 gas canister output 6a 1.5 mm The level at which the soda lye is discharged corresponds to the level of the upper edge of the cell.

It is noted that in relation to this date, the best method known by the applicant to bring to practice the aforementioned invention, is the conventional for the manufacture of the objects to which it refers. Having described the invention as above, property is claimed as contained in the following:

Claims (8)

1. An electrochemical half cell comprising an electrode chamber for accommodating an electrolyte, a gas chamber, and at least one gas diffusion electrode which separates the gas chamber and the electrode chamber and serves as a cathode or anode, characterized because the electrode chamber is divided into compartments which, for the passage of the electrolyte, are connected to each other in the form of a cascade via conduits.

2. The electrochemical half cell according to claim 1, characterized in that the electrolyte flows upwards in the compartments of the electrode chamber.

3. The electrochemical half cell according to claim 1 2, characterized in that the compartments have inlet openings for the electrolyte, openings which are arranged in the region of the base of the respective compartment.

4. The electrochemical half cell according to claims 1 to 3, characterized in that the compartments have exit openings for the electrolyte, the openings are arranged in the region of the upper part of the compartment and their total area is greater than that of the inlet openings .

5. The electrochemical half cell according to claims 1 to 4, characterized in that the electrolyte inlet tube in the half cell is arranged in the uppermost compartment.

6. The electrochemical half cell according to claims 1 to 5, characterized in that the gas chamber is divided into a plurality of gas receptacles which are arranged one on top of the other and corresponding in particular number to the number of compartments, the receptacles of Gases are connected to each other on the gas side without having direct contact with the electrolyte.

7. The electrochemical half cell according to claims 1 to 6, characterized in that the gas pressure in the gas chamber, in particular the gas receptacles, is adjustable independently of the electrolytic pressure without affecting the pressure compensation.

8. The electrochemical half cell, in particular according to claim 1, comprising an electrode chamber for the electrolyte accommodation, a gas chamber and at least one gas diffusion electrode separating the gas chamber and the electrode chamber and serving as a cathode or anode, wherein the gas chamber is divided into two or more gas receptacles arranged one above the other, characterized in that the adjustment of the pressure difference corresponds to the pressure upstream of the gas diffusion electrode, The gas receptacles are connected to each other via the stepped choke holes and the gas supply pipe is arranged in the lowermost gas receptacle.