Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Gas – vapor – or critical fluid
Reexamination Certificate
1999-07-09
2001-05-29
Gorgos, Kathryn (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Gas, vapor, or critical fluid
C205S496000
Reexamination Certificate
active
06238547
ABSTRACT:
This invention relates to a process of reacting a gas or gas mixture in the presence of an ion-conducting liquid in an electrochemical cell comprising at least two electrodes, namely at least one anode and at least one cathode, where between the cathode and the anode an electric d.c. voltage is acting, which has been applied from the outside, and a direct current flows through the ion-conducting liquid.
Such process is described in the German Patent 195 04 920. The electrochemical cell contains an aqueous ammonium sulfide solution, which virtually completely covers the electrode surfaces. Gas containing free oxygen gets in contact with the solution through a gas diffusion cathode, so that ammonium polysulfide is formed as product. In this connection it should be noted that the liquid level in the cell cannot be chosen arbitrarily, as otherwise a disturbing leakage may occur. Furthermore, the current-voltage characteristic of the cell is unfavorably influenced by a high liquid level.
It is the object underlying the invention to perform the electrochemical reaction of gases with liquids also in the presence of catalysts in an inexpensive way with a high consumption, safely and also at a high pressure. In accordance with the invention this is achieved in the above-mentioned process in that in the lower portion of the cell a sump of the ion-conducting liquid is provided, into which the electrodes are immersed, that at least 20% of the entire surface of at least one of the electrodes are disposed outside the sump in an upper portion through which flows the gas or gas mixture, and that the upper portion is sprinkled or sprayed with the ion-conducting liquid, and the electrode surface is at least partly wetted while the gas or gas mixture flows along the electrode surfaces. In this way, different gases and liquids can be reacted. Usually, the gas or gas mixture is oxidized or reduced in the process.
All or at least part of the electrodes are disposed vertically in the sump of the ion-conducting liquid, and this sump ensures the flow of current between the electrodes. In most cases, 20-95% of the entire surface of at least one of the electrodes will be disposed above the sump. It is also possible that either the anode or the cathode is completely covered by the liquid of the sump. The electrodes may not only have a plate-shaped or a cylindrical design, but one electrode may also be designed as current-conducting bed or stacked packing of current-conducting elements contacting each other. Such bed or packing may additionally be coated with a catalyst.
Between the anode and the cathode of the cell a d.c. voltage is applied from the outside, which may be chosen in a wide range. The voltage between adjacent anodes and cathodes may lie in the range between 0.01 and 100 V, usually these voltages lie in the range from 0.1 to 10 V.
A large part of the entire electrode surface is disposed outside the liquid sump and is sprayed or sprinkled by the liquid serving as electrolyte. At the same time, the gas conducted into the cell gets in contact with the surfaces of the electrodes, which are disposed outside the sump. In this connection it is not important in what direction the gas flows. The gas may first of all be introduced into the liquid sump in the lower portion of the cell and flow upwards, or the gas is introduced into the upper portion of the cell, without conducting it through the sump, to the sprayed or sprinkled electrodes. With the gas, one component for the reaction to be performed in the cell, for instance oxygen or hydrogen, can be supplied. As gas, there can thus be introduced air, O
2
, H
2
S, NH
3
, SO
2
, SO
3
, or a synthesis gas mixture (CO+H
2
) or also mixtures of these gases into the cell.
The ion-conducting liquid contained in the cell, which also serves as electrolyte, will usually be an organic or inorganic solution or a melt.
The electrodes may consist of different materials, and they may be formed for instance from metal alloys, mixed oxides or be carbonaceous. When the electrode material itself has no catalytic effect, a catalyst may for instance be applied as coating on an electrically conductive substrate. In this way, both cathodes and anodes may be especially designed for different reactions. It is also possible that the electrodes are consumed during the reaction and act as what is called sacrificial electrodes. When high-carbon electrodes are employed, it may be expedient to make their surface hydrophobic, which is accomplished in a known manner by partly covering the surface with polytetrafluoroethylene.
When it is desired to subdivide the cell into a plurality of reaction chambers with partial exchange of liquid, this can be achieved by means of a diaphragm or also a plurality of diaphragms, which are porous and liquid-permeable in a manner known per se. A further possibility for the subdivision is to use ion-selective membranes, which are likewise known per se.
The desired product of the reaction in the cell may be contained in the liquid withdrawn from the cell or in the exhaust gas withdrawn or both in the exhaust gas and in the liquid. The separation and concentration of the product is then effected in a manner known per se.
The control of the desired reaction or reactions is effected for instance by varying the supply of gas and/or liquid and also by the flow of current in the cell and the electric voltage applied from the outside. Furthermore, the redox potential in the electrolyte sump can be measured and be used as control variable.
Embodiments of the process will be explained with reference to the drawing, wherein:
FIG. 1
shows a first variant of the electrochemical cell in a schematic representation,
FIG. 2
shows a second variant of the cell,
FIG. 3
shows a third variant of the cell,
FIG. 4
shows a horizontal section along line IV—IV of
FIG. 3
,
FIG. 5
shows the horizontal section through a cell similar to
FIG. 3
,
FIG. 6
shows a cell with bipolar electrodes, and
FIG. 7
shows a cell with a gas diffusion electrode.
REFERENCES:
patent: 3996118 (1976-12-01), Sanders
patent: 5104497 (1992-04-01), Tetzlaff et al.
patent: 5480515 (1996-01-01), Gallien
patent: 5840174 (1998-11-01), Lehmann et al.
patent: 6071401 (2000-06-01), Engel et al.
Anastasijevic Nikola
Laibach Stefan
Werner Dietrich
Dubno Herbert
Feely Michael J
Gorgos Kathryn
Metallgesellschaft Aktiengesellschaft
Myers Jonathan
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