Electrolytic cell especially for chloralkali electrolysis with a

Details Electrolytic cell especially for chloralkali electrolysis with a Electrolytic cell especially for chloralkali electrolysis with a

1979-11-02

1983-03-15

Valentine, Donald R.

Chemistry: electrical and wave energy

Apparatus

Electrolytic

204266, 204283, 204290R, 204291, 204292, 204294, 204295, 204296, C25B 900, C25B 1103, C25B 1108, C25B 1306

Patent

active

043766919

DESCRIPTION:

BRIEF SUMMARY
The energy cost is a heavy item in the calculus for electrolytically produced chlorine and alkali. An increasing cost for electrical energy will accentuate these circumstances further. Technical developments in the chlor-alkali field therefore has an objective to reduce the energy consumption in the electrolytic process. One possibility to reduce the cell voltage is to introduce air cathodes so as to eliminate the energy consuming hydrogen development in the cathode fingers. Hydrogen being developed in conventional electrolysers seldom finds a meaningful use at the chlor-alkali plants. Introduction of air cathodes will reduce the cell voltage with something between 0.5-1 volt depending on the current density, the temperature and the activity of the air electrode. This reduction of the cell voltage will evidently have very great importance for the economics of the chlor-alkali process.
The inventors have therefore shown a certain interest in this question and there are several designs of chlor-alkali cells with air cathodes described in the literature, see e.g. the U.S. Pat. No. 3,262,868.
Another more radical possibility is to introduce a bifunctional hydrogen electrode at the same time in order to adjust the production of chlorine and alkali to the market demand with the minimum sacrifice of electrical energy for every specific market profile for chlorine respectively alkali, see the U.S. Pat. No. 3,864,236.
A particularly advantageous design for air cathodes which are quite useful for bi-polar chlor-alkali cells is shown in the German Offenlegungsschrift No. 2627142. 1-41.
Chlorine and alkali are produced on a very large scale in all industrialized countries and the amount of capital which has been invested in these chlor-alkali plants is very large. The useful life of these plants is also quite long. It is not unusual that plants last 20-30 years and even longer. However, it is necessary to renovate the cells at frequent intervals, change anodes, put on new diaphragms etc. It has also been possible to develop existing cells towards better performance e.g. by the introduction of so-called dimensionally stable anodes instead of graphite anodes in mercury cells as well as in diaphragm cells. These different cell types are described e.g. in Kirk-Othmer "Encyclopedia of Chemical Technology", Second Edition, Volume 1, pp. 668-707, J. S. Sconce "Chlorine" ACS monograph No. 154, 1962, and e.g. the U.S. Pat. Nos. 3,124,520, 3,262,868 and other publications and patents. Pertinent information which is quite up to date from many point of views is found in the Proceedings from the Chlorine Bicentennial Symposium, ECS, 1974, and Hardie: "Electrolytic Manufacture of Chemicals from Salt" The Chlorine Institute 1975.
Work up to day to develop and introduce air cathodes in chlor-alkali electrolysis has been concerned with the task to develop a completely new electrolytic cell e.g. by means of bi-polar electrode designs. Much would be gained however if a design could be envisaged which would make it possible to introduce air cathodes in existing cells of diaphragm or membrane type with monopolar electrodes. Such air electrodes could then be used with existing electrolytic plants and thus immediately give very important global conservation of electrical energy. The operating costs for the chlor-alkali process would also be reduced considerably with such modification. It is fair to say that such an innovation would be even more important than the earlier introduction of dimensionally stable anodes.
One objective for the present invention is therefore to make possible conversion of existing chlor-alkali cells of diaphragm or membrane type with monopolar electrodes to air electrodes.
A second objective is to reduce the consumption of electrical energy for the electrolysis considerably due to the fact that also existing plants may be converted to air electrodes.
A third objective is to furnish a design which makes possible simple renovation of the air electrode on the same occasion as exchange of dimensionally stable anodes, m

REFERENCES:
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patent: 3616442 (1971-10-01), Cheng et al.
patent: 3809630 (1974-05-01), De Nora et al.
patent: 3864236 (1975-02-01), Lindstrom
patent: 4035255 (1977-07-01), Gritzner
patent: 4181776 (1980-01-01), Lindstrom
patent: 4191618 (1980-03-01), Coker et al.
patent: 4244793 (1981-01-01), Johnson et al.

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