Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis
Patent
1998-05-11
2000-06-20
Valentine, Donald R.
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
204253, 204267, 204294, C25B 300, C25B 900, C25B 1112, C25B 1300
Patent
active
060774142
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a novel stacked plate cell and to a process for the electrolysis of substances.
Electrolysis cells are employed in modem chemistry in a variety of forms for a multiplicity of tasks. An overview on the construction possibilit ies of electrolysis cells is found, for example, in D. Pletcher, F. Walsh, Industrial Electrochemistry, 2nd Edition, 1990, London, pp. 60ff.
A frequently used form of electrolysis cells is the stacked plate cell. A simple arrangement thereof is the capillary gap cell. The electrodes and corresponding separating elements are frequently arranged here like a filter press. In this type of cell, several electrode plates are arranged parallel to one another and separated by separating media such as spacers or diaphragms. The intermediate spaces are filled with one or more electrolyte phases. An undivided cell usually comprises only one electrolyte phase; a divided cell has two or more such phases. As a rule, the phases adjacent to the electrodes are liquid. However, solid electrolytes such as ion exchange membranes can also be employed as electrolyte phases. If the electrode in this case is directly applied to the ion exchange membrane, e.g. in the form of an electrocatalytic and finely porous layer, additional contacts are necessary which, on the one hand, must be designed as current collectors and, on the other hand, as substance transport promoters. The individual electrodes can be connected in parallel (monopolar) or serially (bipolar). In the context of the invention, cells having bipolar connection of the stacked electrodes are exclusively considered.
In order to achieve as high a substance conversion as possible in electrolysis cells, according to general knowledge the electrolyte should be passed over the electrodes in such a way that optimum substance transport is achieved. In the case of liquid electrolytes, it is frequently proposed to allow the electrolyte liquid to flow parallel to the electrodes.
The space-time yield and the selectivity of the electrolysis also depend, in addition to the flow over the electrodes, on the electrode materials used. These affect the service life, size and weight of the cell considerably.
In known stacked plate cells, the electrodes are as a rule designed as solid plates, for example graphite disks. Electrodes of this type have various disadvantages which result from the solidity of the material, for example the decreased surface area compared with a porous material and the decreased substance conversion, higher weight and greater space requirement accompanying it.
It is thus an object of the present invention to provide a stacked plate cell having increased space-time yield, high selectivity, low weight and space requirement, which is as simple as possible to produce and to operate. A further object of the invention is the provision of electrolysis processes having a high space-time yield and a high selectivity.
We have found that these objects are achieved by the stacked plate cell described in the claims and the processes described.
In the context of the invention, a stacked plate cell having serially (bipolar) connected stacked electrodes is provided, at least one stacked electrode consisting of a graphite felt plate, a carbon felt plate, a web having a carbon-covered starting material contact surface or a porous solid having a carbon-covered starting material contact surface or comprising such a material.
Felts suitable for use in the context of the present invention are commercially available. Both graphite felts and carbon felts can be employed here, both types of felt differing, especially, by the structure of the carbon. Instead of or in addition to the felts described, other porous materials can also be used whose contact surfaces with the starting material are completely or largely covered with carbon. Contact surfaces are in this case those external and internal surfaces with which the starting material to be electrolyzed comes into contact during the electrolysis reaction. These materials can in this cas
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Hannebaum Heinz
Putter Hermann
BASF - Aktiengesellschaft
Valentine Donald R.
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