Monopolar and bipolar electrolyzer and electrodic structures the

Details Monopolar and bipolar electrolyzer and electrodic structures the Monopolar and bipolar electrolyzer and electrodic structures the

1986-10-17

1988-08-30

Valentine, Donald R.

Chemistry: electrical and wave energy

Apparatus

Electrolytic

204263, 204279, 204284, 204289, 204290R, 204290F, 204257, C25B 900, C25B 1103, C25B 1508

Patent

active

047675195

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention concerns monopolar and bipolar diaphragm or membrane electrolyzers, particularly electrolyzers comprising a multiplicity of electrolytic cells and more particularly the electrodic and current distributing structures thereof and electrodic structures thereof.


PRIOR ART

As it is well-known to the expert of the art, electrolyzers provided with separators (porous diaphragms or ion exchange membranes) positioned between the anodic and cathodic compartments comprise a series of intermediate electrodic structures electrically connected and positioned between two electrodic end structures. Each cell of the electrolyzer is delimited by walls, acting as current distributors and means for supporting the electrodes. The electrodes usually consist of expanded sheets, or perforated sheets or foraminous sheets, made of suitable materials, such as, for example, titanium for the anode and nickel or steel for the cathode.
Each intermediate electrodic structure is constituted by one of said walls and the relevant electrodes.
The electrodic structures are assembled in the so-called filter-press arrangement, being pressed together by suitable devices, e.g. tie-rods, jacks. Electrical connection is provided either in series or in parallel, taking into account the specific requirements and practical and economical considerations.
In the case the connection is in series, the electric current applied to the electrode end-structures gives rise to a bipolarity between the current distributing surfaces belonging to the same electrodic structure and therefore the electrode supported by one face is the anode of one cell whereas the electrode supported by the opposite face is the cathode of the adjacent cell.
In the case of parallel connection, current is fed by means of a series of electrical contacts connecting the busbars and each of the walls. Therefore, current flows longitudinally through the walls and then is fed to the electrodes by the supporting elements. When parallel connection is resorted to, the two electrodes supported by the same current conducting wall separating two adjacent cells have the same polarity (monopolar electrolyzers). In order to keep the current distribution in this type of electrolyzers as uniform as possible, it is necessary to minimize the ohmic drops inside the current distributing walls. As it is known, uneven current distribution causes an increased power consumption and shorter operating lifetime of the electrodes and membranes.
The larger the electrolyzers and thus the current distributing walls are, the more difficult results providing for an even current distribution: a material with a good electrical conductivity would be highly preferred for the construction of the current conducting walls. Most unfortunately, metals exhibiting a good electrical conductivity often do not resist under the corrosive electrolyzer environment. Therefore, metals are utilized which are substantially less conductive but are capable of undergoing the electrolyzer environment: for example, titanium is resorted to for the anodic structures and nickel for the cathodic ones. As a consequence, that fraction of the current distributing wall, which is more distant from the electrical connection to the bus-bar, is usually fed with substantially less current than the closer one.
A further problem occurs with the process for fabricating such electrolyzers, which involves several weldings of the electrodes to the supporting means, which are in turn welded to the current distributing walls.
U.S. Pat. No. 4,464,242 reduces this complexity of fabrication by obtaining the supporting means for the electrodes on both sides of a metal sheet through a stamping process. This metal sheet, which also acts as a current distributing wall, has to be made of a material resistant to corrosion and therefore, for the above reasons, the necessity of keeping the disuniformity of current distribution within certain limits leads to severe restrictions as regards the stamped sheet dimensions.
U.S. Pat. No. 4,48

REFERENCES:
patent: 3980545 (1976-09-01), Lachaux et al.
patent: 4402809 (1983-09-01), Dilmore
patent: 4440615 (1984-04-01), Perei
patent: 4464242 (1984-08-01), Boulton
patent: 4581114 (1986-04-01), Morris et al.

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