Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1999-08-26
2000-12-26
Valentine, Donald R.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204265, 204266, 204277, 204278, C25B 900
Patent
active
061653322
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/EP97/02689, filed May 26, 1997.
The present invention relates to an electrochemical half cell comprising at least one electrode space for receiving an electrolyte, a gas space, and at least one gas diffusion electrode as anode or cathode and separating the gas space and electrode space, in which the gas space is subdivided into two or more superimposed or overlying gas pockets in which gas inflow and gas outflow takes place through separate openings and the pressure on the electrolyte side of the electrode, when compared with the pressure on the gas side of the electrode, is compensated by an opening in the gas pockets for the electrolyte.
The operation of electrochemical cells based on gas diffusion electrodes, for example for use as an oxygen consumption cathode in alkali halide electrolysis, is basically known and is described for example in U.S. Patent Specification 4,657,651.
The gas diffusion electrode is an open-pore membrane between the electrolyte and gas space, which has an electrically conducting layer with catalyst and is intended to enable an electrochemical reaction, for example reduction of oxygen, to take place at the triple-phase boundary between electrolyte, catalyst and reactant gas in the membrane. The boundary layer is generally held in the membrane by the surface tension of the electrolyte on the hydrophobic electrode material opposing the hydrostatic pressure of the electrolyte on the membrane. However, in this connection only a small pressure drop between the gas side and liquid side of the membrane is permissible. If the gas-side pressure is too high, the gas finally penetrates the membrane and interferes with the operation of the electrode in this region, and the electrolysis process is interrupted. If on the other hand the liquid pressure is too high, the triple-phase boundary is forced out from the region containing the catalyst in the membrane, which likewise interferes with the operation of the cathode and, if there is a further rise in pressure, causes liquid electrolyte to penetrate the gas space. With vertically arranged electrodes, as is necessary for example with membrane electrolysers, in order to be able to remove the desired product chlorine efficiently, this limits the structural height of the gas diffusion electrodes since otherwise at the top of the electrode gas will penetrate the cathode space and also at the bottom of the electrode electrolyte liquid will penetrate the gas space. The technically realisable structural height is therefore limited to ca. 20-30 cm, which is unattractive for conventional industrial membrane electrolysis units.
In order to solve the problem of pressure compensation, various arrangements have been proposed in the prior art.
According to U.S. Patent Specification 4,657,651, pressure compensation between the gas space and the electrolyte space on both sides of a gas diffusion cathode is achieved by subdividing the cathode into individual horizontal chambers that are individually charged with gas, the gas pressure being regulated by passing the outflowing gas stream in each case into vertical chambers in such a way that their depth corresponds to the height of the electrolyte over the respective chamber. The disadvantage of this arrangement is the complexity and cost of the equipment, which stands in the way of a technical implementation. Moreover, the pressure in each individual gas chamber has to be adjusted separately, through respective valves.
The still unpublished German patent application No. P 4 444 114.2 describes an electrochemical half cell with a gas diffusion electrode, in which pressure compensation between the gas space and the electrolyte space on both sides of a gas diffusion electrode is achieved by subdividing the gas space into two or more gas pockets superimposed in a cascade-like manner, which are separated from one another and are open at the bottom to the electrolyte so that the pressure in each gas pocket is in equilibrium, via the opening for the electrolyte, with the pressure of t
REFERENCES:
patent: 4657651 (1987-04-01), Wainerdi
patent: 5650058 (1997-07-01), Wenske et al.
patent: 5693202 (1997-12-01), Gestermann et al.
Patent Abstracts of Japan, vol. 095, No. 011, Dec. 26, 1995 & JP 07 220728 A (Tanaka Kikinzoku Kogyo KK; Others: 01), Aug. 18, 1995.
"Meeting Abstracts 96-1, Abstract No. 949, Spring Meeting May 5--Oct. 1996" of the Electrochemical Society.
Gestermann Fritz
Pinter Hans Dieter
Bayer Aktiengesellschaft
Valentine Donald R.
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