Chemistry: electrical and wave energy – Processes and products
Patent
1994-02-18
1996-01-02
Valentine, Donald R.
Chemistry: electrical and wave energy
Processes and products
204270, 204284, 204290R, 204293, B01D 5940, C25B 100, C25B 300
Patent
active
054805155
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an electrolysis cell for gas-developing or gas-consuming electrolytic processes as well as to a method for operating the electrolysis cell.
BACKGROUND OF THE INVENTION
An electrode consisting of several very thin foil-like elements with parallel arrangement is described in DD-PS 285 125 and WO 91/00379 A1. Between the adjoining elements of one electrode there is a narrow gap which causes the capillary effect.
Very thin fine-structured electrodes of this kind have a high degree of efficiency. On one side the surface involved in the reaction is very large while on the other side the capillary forces ensure an intensive electrolyte exchange and the discharge of the gas formed cross-wise through the electrode into the degasification chamber each side of the reaction surface. This degasification chamber must be several millimeters deep depending on the structural height of the electrolysis cell and thus takes up space in the order of magnitude of the electrode itself.
It is not possible to dispense with the degasification chamber while retaining the capillary conditions which are advantageous, per se, between the electrode elements because the electrode elements which are structured substantially across the electrode plane do not allow hardly any vertical material transport. DD-PS 285 127 and DD-PS 285 128 describe electrode elements with different profiles, They serve to maintain the capillary gaps through simple positioning of adjoining electrode elements and also to provide their electrical contact.
However even when using unprofiled electrode elements and a vertically permeable capillary gap electrode it would not be possible to dispense with the degasification chamber. The gas bubbles cannot rise unhindered in the capillary gaps, They would coagulate into large bubbles which take up the entire width of the electrode and then "blow out" the electrolyte from the electrode.
DD-PS 285 122 discloses an electrolysis cell which without using a membrane which separates the anode from the cathode chamber ensures separation of the gases thus formed. To do this the electrodes which are made from thin foil-like elements with capillary spacing are sealed sufficiently well from the cell wall enclosing same. The distance between the electrodes must correspond to at least three times the bubble release diameter, Furthermore in the upper cell area a partition is provided which prevents the gases formed in the anode and cathode chambers from mixing in the upper electrolyte-free chamber.
FR 22 44 836 shows an electrolysis cell with an electrode made of several parallel oblong parts wherein the adjoining parts should have a distance in the range of 1.5 to 10 mm, Thus even with an electrode spacing of 6 mm maximum and a current density of 2 kA/m.sup.2 the electrolyte is reliably prevented from being blown out from the reaction chamber. However there is the drawback that even with a retarded foam formation the gas bubbles remain for a long time in the reaction chamber between the electrodes whereby the electrical conducting capacity of the electrolyte is noticeably reduced.
An electrode of porous materials is described in FR-PS 2 308 701. It consists of a self-supporting compound of two porous layers wherein the surface of the electrode on the reaction side is connected to an insulating fireproof oxide layer whose pore radii have at the most a tenth of the pore radii of the electrode material. The oxide layer is hydrophillic and is permeated by the electrolyte.
The gas formed by the electrode in the large pores cannot readily pass into the smaller pores of the oxide layer so that the gas emerges at the back of the electrode. Furthermore it is proposed to provide the back of the electrode with a hydrophobic gas-permeable layer in order to allow the gas to enter directly into a degasification chamber, separate from the electrolyte.
This electrode does indeed avoid any gas bubble loading of the electrolyte between the anode and cathode, but this advantage is at least partly given
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