Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
  • C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous

Definitions

• the invention relates to an electrochemical cell which is used in particular for the electrolysis of an aqueous solution of hydrogen chloride by the membrane method with a gas diffusion electrode as the cathode.
• Aqueous solutions of hydrogen chloride hereinafter also referred to as hydrochloric acid, are a by-product of many chemical processes. This includes
• Chlorine from hydrochloric acids can be recovered electrolytically, for example.
• a method for the electrolysis of hydrochloric acid is known, for example, from US Pat. No. 5,770,035.
• Ruthenium, iridium and titanium coated is filled with the aqueous solution of hydrogen chloride.
• the chlorine formed on the anode escapes from the anode compartment and is fed to a suitable treatment.
• the anode compartment is from a cathode compartment through a commercially available cation exchange membrane
• Gas diffusion electrodes are, for example, oxygen consumable cathodes (SVK).
• SVK oxygen consumable cathodes
• an oxygen-containing gas or cleaner is usually introduced into the cathode compartment
• Cathode space proposed, in which one or both electrodes are broken and an electrolyte flows from top to bottom through one or both half cells in such a way that the electrodes are wetted.
• the electrolyte flows against the electrochemically formed and rising gas.
• the resulting gas bubbles finally burst at the phase boundary between the falling electrolyte film and the adjacent gas space.
• the object of the present invention is to provide an electrochemical cell for the membrane electrolysis process, which has as the anode a metal electrode with the largest possible electrochemically active surface and openings which make it possible for the gas formed from the side facing the cathode as the counter electrode lead into the space of the half cell behind the metal electrode.
• the electrochemical cell is to be used for the electrolysis of an aqueous solution of hydrogen chloride, a gas diffusion electrode being used as the cathode.
• the anode compartment is completely filled with hydrochloric acid, which flows from bottom to top through the anode compartment.
• the metal electrode is angled and / or curved, which increases its electrochemically active area.
• the invention accordingly relates to an electrochemical cell for the membrane electrolysis process, comprising at least one anode compartment with a
• Metal electrode as an anode, a cathode compartment with a gas diffusion electrode as Cathode and one between anode compartment and.
• Ion exchange membrane arranged in the cathode space, the metal electrode being immersed in an electrolyte and having openings for the passage of the gas formed during operation and possibly being angled and / or curved.
• the openings in this case have 5 conductive structures which discharge the gas formed to the side of the metal electrode facing away from the cathode.
• the openings of the electrode can not only be slots or holes, but can also be formed by the mesh of an expanded metal.
• the guide structures at the openings are inclined in the direction of the ion exchange membrane.
• the gas, which is increasingly formed on the surface of the metal electrode facing the ion exchange membrane, is thus conducted away from the surface and as it rises from the narrow gap
• the openings of the metal electrode have a total cross-sectional area which is in the range from 20 ° to 70% of the area which is formed by the height and width of the metal electrode.
• the length of the essentially vertically arranged side of the electrode is to be regarded as the height of the metal electrode and the length of the side of the electrode which is essentially parallel to the counterelectrode and horizontally arranged as the width.
• the electrode consists essentially of a metal sheet
• the electrode is preferably not flat, but curved and / or corrugated.
• a wavy, zigzag or rectangular cross section is preferably selected.
• the electrochemically active surface of the metal electrode is particularly important for the electrolysis of aqueous solutions of hydrogen chloride (hydrochloric acid), since due to the higher conductivity of the hydrochloric acid, an electrochemical reaction can be observed even with a greater distance between the electrode and the counter electrode.
• the electrochemically active surface of the metal electrode is formed in particular by the surface of the metal electrode pointing in the direction of the counter electrode, here the cathode.
• the electrochemical reaction can also be observed on surfaces which are not facing the counter electrode.
• the electrochemically active surface is understood to mean the proportion of the total surface of the metal electrode on which an electrochemical reaction takes place.
• the ratio of the electrochemically active area to the area which is determined by the height and width of the
• Metal electrode is formed, at least 1.2.
• the metal electrode has a depth of at least 1 mm.
• the side length of the metal electrode which is essentially perpendicular to
• the depth corresponds to twice the amplitude of the wave.
• the depth corresponds to the difference between the minimum and maximum distance formed by one of the edges of the electrode and the ion exchange membrane. The same applies to the depth in the case of a zigzag-shaped cross section of the electrode.
• expanded metals also have the desired properties of the electrode structure, namely a large electrochemically active surface that extends in depth, and openings for them
• the meshes allow the gas to be discharged onto the Back of the metal electrode, the webs taking over the function of the conductive structure, provided the expanded metal is arranged so that the webs are inclined in the direction of the counter electrode.
• a combination of two or more identical or different expanded metals is also possible if at least one of the expanded metals is inserted into the electrochemical cell in the manner described
• Metal electrode especially as an anode, is installed.
• the metal electrode is preferably based on two adjacent expanded metals, the expanded metal pointing towards the counter electrode being further structured than the expanded metal facing away from the counter electrode, the finely structured expanded metal also being flat-rolled and the webs of the coarsely structured expanded metal serving as guide structures, in that the expanded metal is so is arranged that the mesh webs are inclined in the direction of the counter electrode.
• the cell according to the invention is used in particular for the electrolysis of aqueous solutions of hydrogen chloride.
• the anode half-cell has an inlet and an outlet for the electrolyte, which flows through the half-cell from bottom to top and fills it completely.
• the outlet for the electrolyte also serves as an outlet for the gas formed.
• a suitable anode is e.g. a noble metal coated or noble metal doped titanium electrode. This also includes an electrode made of titanium or a titanium alloy, in particular a titanium-palladium
• Alloy which is provided with an acid-resistant, chlorine-developing coating for example based on a ruthenium-titanium mixed oxide, an iridium oxide or based on platinum.
• the anode half cell is separated from the cathode half cell by an ion exchange membrane. There is a gap between the anode and the ion exchange membrane.
• a gas diffusion electrode which functions as an oxygen consumption cathode, is used in particular as the cathode.
• the • gas diffusion electrode rests on the one hand on the ion exchange membrane and on the other hand on a current collector. If the gas diffusion electrode is used as an oxygen consumable cathode, oxygen or the oxygen-containing gas can flow through the cathode compartment.
• oxygen should be offered over-stoichiometrically with regard to the reaction taking place.
• Gas diffusion electrodes are preferably used which contain a platinum group catalyst, preferably platinum or rhodium. Gas diffusion electrodes from E-TEK (USA), which contain 30% by weight of platinum, may be mentioned as examples
• Suitable ion exchange membranes are, for example, those of perfluoroethylene which contain sulfonic acid groups as active centers.
• commercially available membranes from DuPont can be used, such as the National® 324 membrane.
• Both single-layer membranes which have sulfonic acid groups with the same equivalent weights on both sides and membranes which have sulfonic acid groups with different equivalent weights on both sides are suitable.
• Membranes with carboxyl groups are also conceivable.
• the cathode-side power distributor can consist, for example, of titanium expanded metal or titanium coated with noble metal.
• Fig. 1 is a schematic of a first preferred embodiment of the electrode structure in a perspective view
• FIG. 2 shows a diagram of a second preferred embodiment of the electrode structure in a perspective view
• Fig. 3 is a schematic of a third preferred embodiment of the electrode structure in a perspective view
• Fig. 4 is a schematic of a fourth preferred embodiment of the electrode structure in perspective
• FIG. 4a shows a detail from the embodiment shown in FIG. 4
• FIG. 5 shows a diagram of a fifth preferred embodiment of the electrode structure in perspective
• the surface of the metal electrode which faces the ion exchange membrane and thus the counterelectrode is referred to as the front side and accordingly the surface facing away from the ion exchange membrane as the rear side of the electrochemical cell according to the invention does not lie on the ion exchange membrane, but between Anode and ion exchange membrane are located with
• Electrolyte filled gap where the gap is not separated from the rest of the half cell space.
• the gap is usually 1 to 3 mm. It arises from the fact that the anode compartment is kept at a higher pressure than the cathode compartment. This presses the ion exchange membrane onto the gas diffusion electrode, which in turn is pressed onto the current collector.
• the electrolyte flows freely from below up through the entire half cell.
• the space of the half cell, which adjoins the rear of the electrode, is also referred to below as the rear space.
• the electrode consists of vertically arranged metal lamellae 10 which are at a substantially right angle to the ion exchange membrane.
• baffles 12 inclined in the direction of the ion exchange membrane between two adjacent lamellae, with the aid of which the rising gas from the front, i.e. the side facing the ion exchange membrane, the electrode is directed rearward into the rear space of the electrochemical half cell through the openings 14.
• Cloning of the lamellas is carried out using Sfrorn feeders 16.
• the depth of the lamellas is in the range of 1 to 40 mm and the distance between two adjacent lamellae is in the range of 1 to 10 mm.
• the vertically arranged fins are at an angle to the ion exchange membrane, which is from 50 to 90 °.
• the structure corresponds to the electrode
• the fins 20 are connected at their edges facing away from the ion exchange membrane to a plate 28 which has openings 24 below the baffles 22 for the discharge of the gas.
• the sheet 28 attached to the rear of the fins is thus essentially parallel to the ion exchange membrane.
• the metal electrode 30 is based on a wave-shaped cross section.
• the openings 34 are in the
• the leading Structures 32 consist of metal sheets, which essentially have the shape of a half-wave and are attached at an angle above the openings 34 in the direction of the ion exchange membrane.
• Such an electrode structure can be produced in a simple manner, for example, by punching essentially triangular openings 34 in the region of the wave crests from the rear of the electrode 30. The triangular openings are not completely punched out, but the punched-out parts remain connected to the electrode in the area of the upper triangle tip, so that the punched-out parts can be bent as guide structures 32 in the direction of the ion exchange membrane and can be arranged at an angle of inclination of 10 to 60 ° ,
• the lead structures consist of metal sheets, which essentially have the shape of a half-wave and are attached at an angle above the openings 34 in the direction of the ion exchange membrane.
• openings 34 are preferably punched from the rear of the electrode 30 in a shape which corresponds to the shape of the wave crests, since the conductive structures 32 which are bent toward the front of the electrode 30 and inclined in the direction of the counterelectrode terminate with the electrode. An additional connection of the conductive structures 32 to the electrode 30 can therefore be omitted.
• the area of the punched out openings 34 essentially determines the area of the guide structures 32.
• the punched out metal parts of the electrode which act as guide structures can also be reduced in size so that they do not protrude as far into the space between the electrode and the ion exchange membrane.
• the size of the openings 34 is preferably selected such that the area of the guide structures 32 corresponds exactly to the area of a wave crest.
• the depth of the electrode with which the distance from wave crest to wave trough, ie twice the amplitude of a wave, is understood here, is from 2 to 40 mm. The distance between two adjacent wave crests or wave valleys, what the
• Corresponding wavelength is from 3 to 30 mm.
• the gas flows essentially in the direction marked by the arrows 39.
• this electrode structure can be produced by punching out a triangular opening from behind in the area of the tips facing away from the ion exchange membrane.
• FIG. 4 differs from that shown in FIG. 3 only in the cross section on which the electrode structure 40 is based.
• This is a rectangular cross-section, the openings 44 (FIG. 4a) being located on the longitudinal lines facing away from the ion exchange membrane. These are arranged essentially parallel to the ion exchange membrane.
• the guide structures 42 discharge the gas into the rear space of the half-cell in accordance with the direction marked with the arrow 49 (FIG. 4a).
• the openings 54 are also arranged on a rectangular cross section of the electrode structure 50 not on the rear long sides, but on one of the transverse sides, i.e. on one of the sides of the electrode perpendicular to the ion exchange membrane. Accordingly, the guide structures 52 in this embodiment are not inclined in the direction of the ion exchange membrane, but in the direction of the opposite transverse side of the electrode. The flow of the gas from the front to the back of the electrode is marked with arrows 59.
• Expanded metals also offer an electrode structure with a large electrochemically active surface and openings with conductive structures for the discharge of the gas into the rear space of the half cell. So there is another preferred one
• a finely structured expanded metal is characterized by a smaller mesh width and mesh width as well as a smaller web width and web thickness. It is also preferred the finely structured expanded metal is rolled flat and the coarser structured expanded metal is not arranged in any way, but in such a way that the mesh webs take on the function of lead structures.
• the meshes are preferably diamond-shaped or square, and the webs of the coarser expanded metal facing away from the ion exchange membrane are inclined in the direction of the ion exchange membrane.
• the total area of the openings in both the finely structured and the coarsely structured expanded metal is in the range from 20 to 70% of the area which is given by the outer dimensions, ie the edge lengths, of the expanded metal.
• the following parameters are used to identify the expanded metals:
• the web thickness corresponds to the thickness used to manufacture the expanded metal
• the web width results from the distance between two parallel but offset cuts.
• the mesh size identifies the length of the cut, the mesh width of the maximum distance between two adjacent webs that is created by stretching deformation.
• hydrolysis of an aqueous solution of hydrogen chloride was carried out using a gas diffusion electrode as the oxygen consumable cathode.
• concentration of hydrochloric acid was 13% by weight and its temperature when it entered the
• Anode half cell was set so that the temperature in the outlet was 60 ° C.
• the pumped volume flow of the hydrochloric acid was adjusted so that the speed of the hydrochloric acid in the anode half cell was 0.3 cm / s.
• the material of the anodes consisted of a titanium-palladium alloy, which was activated with a ruthenium-titanium mixed oxide layer (DSA ® coating).
• Expanded metal existed.
• the width of the electrode was 730 mm, the height was 1200 mm.
• the minimum distance between the anode and the cation exchange membrane was 3.5 mm.
• a combination of two adjacent titanium plug-in metals was used as the anode, a finely structured expanded metal being applied to a coarser structured expanded metal.
• the finely structured expanded metal had a mesh size of 4.2 mm and a mesh width of 3.1 mm as well as a web width of 0.6 mm and a web thickness of 0.4 mm. Accordingly, the total area of the openings is 53% of the area of the expanded metal.
• This expanded metal was flat rolled to a thickness of 0.5 mm.
• the coarser structured of the two expanded metals had a mesh size of 13.2 mm, a mesh width of 6.3 mm, a web width of 2.4 mm and a web thickness of 3.5 mm. The total area of the openings was thus 24% of the area of the expanded metal.
• the anode was installed in such a way that the flat-rolled, finer expanded metal faced the cation exchange membrane.
• the voltage was 1.59 V at a current density of 5 kA / m 2
• the anode consisted of a single, roughly structured expanded metal with a mesh size of 6.2 mm, a mesh width of 3.6 mm and a web width of 1.1 mm and a web thickness of 1 mm.
• the total area of the openings was 24% of the total area of the anode.
• the voltage was 1.67 V at a current density of 5 kA / m 2 and was therefore greater than when electrolysis of a hydrochloric acid solution under comparable conditions, but with the special combination of a finely structured, flat-rolled expanded metal facing the cathode was, and a coarser structured expanded metal behind it.

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• Chemical & Material Sciences (AREA)
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• Chemical Kinetics & Catalysis (AREA)
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• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
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• 2002
  • 2002-07-31 DE DE10234806A patent/DE10234806A1/de not_active Withdrawn
• 2003
  • 2003-07-09 US US10/614,865 patent/US20040069621A1/en not_active Abandoned
  • 2003-07-18 PL PL03374671A patent/PL374671A1/xx not_active Application Discontinuation
  • 2003-07-18 JP JP2004525240A patent/JP2005534806A/ja active Pending
  • 2003-07-18 EP EP03766213A patent/EP1527211A1/de not_active Withdrawn
  • 2003-07-18 WO PCT/EP2003/007823 patent/WO2004013379A1/de not_active Application Discontinuation
  • 2003-07-18 CN CNA038182076A patent/CN1671889A/zh active Pending
  • 2003-07-18 KR KR1020057001610A patent/KR20050028050A/ko not_active Application Discontinuation
  • 2003-07-18 BR BR0305706-2A patent/BR0305706A/pt not_active Application Discontinuation
  • 2003-07-18 AU AU2003250100A patent/AU2003250100A1/en not_active Abandoned
  • 2003-07-30 TW TW092120735A patent/TW200409396A/zh unknown

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