Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-10-24
2002-07-23
Bell, Bruce F. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S277000, C204S278000
Reexamination Certificate
active
06423194
ABSTRACT:
TECHNICAL FIELD
This invention relates to a gas diffusion electrode suitable for use as an oxygen electrode of an ion-exchange membrane type sodium chloride electrolytic cell, etc. and a sodium chloride electrolytic cell using the electrode.
BACKGROUND ART
A cathode of a currently available ion-exchange type sodium chloride electrolytic cell is made of nickel and generates hydrogen in electrolysis. Replacement of this hydrogen-generating cathode with an oxygen cathode comprising a gas diffusion electrode requires an additional gas chamber, making three chambers in all. That is, the electrolytic cell comprises an ion-exchange membrane, a caustic soda aqueous solution (a liquid chamber), a gas diffusion electrode (an oxygen cathode), and a gas chamber in this order. These chambers are thin, desirably as thin as about 1 mm each. The desired thinness has imposed restrictions on the supply of gas and liquid, making it difficult to take measures against liquid and gas leakage.
The conventional sodium chloride electrolytic cell using the hydrogen-generating cathode can be supplied with caustic soda simply by attaching an inlet and an outlet to a catholyte chamber having a thickness of about 4 cm.
However, in the case of a sodium chloride electrolytic cell having an oxygen cathode, both the liquid chamber and the gas chamber must be constructed in the form of a layer as thin as several millimeters or less.
FIG. 23
is a cross section of an electrolytic cell using a conventional oxygen cathode. A flat gas diffusion electrode
1
is provided with a gas chamber
20
on one side (back side) thereof. The gas chamber
20
has a gas inlet
9
. On the front side of the gas diffusion electrode
1
is provided a cathode chamber
18
, which is sandwiched between the gas diffusion electrode
1
and an ion-exchange membrane
16
. A cathode chamber frame forming the perimeter of the cathode chamber
18
is sealed with gaskets
17
. An electrolytic solution inlet
19
is made through the cathode chamber frame.
That is, the cathode chamber
18
is formed by a metal frame
50
having a thickness of about 3 mm through which holes are pierced as an inlet and an outlet for an electrolyte, and a gasket
17
is inserted between the ion-exchange membrane
16
and the metal frame
50
and between the metal frame
50
and the gas diffusion electrode
1
. The cathode chamber
18
having such a structure, it is impossible to make the cathode chamber
18
as thin as is required of an oxygen cathode. A thicker cathode chamber
18
results in an greater loss of electricity due to an increased resistance of the liquid so that the voltage of the electrolytic cell cannot be reduced.
(1) It is desirable for practical use that the thickness of the liquid chamber be 1 mm or smaller. Further, the electrolytic cell including the above-mentioned structure is complicated in structure, requiring an increased number of gaskets. The more the number of sealing parts, the more the likelihood of gas or liquid leakage. It has therefore been demanded to develop an electrolytic cell that is less likely to leak gas and liquid.
(2) In the above-described electrolytic cell, even through the inlet and the outlet for the catholyte are made as small as about 1 mm in diameter, it is still difficult to decrease the thickness of the cathode chamber frame to 2 mm or less because the frame should be prevented from deformation due to packing pressure. On the other hand, it is preferred for the inlet and the outlet to have a larger diameter to avoid clogging. From this viewpoint, it is obviously preferred for the cathode chamber frame to have a large thickness. The gasket preferably has a thickness of about 1 mm. These restrictions had led to the difficulty in making the cathode chamber thinner than 3 mm. Under the present situation, therefore, there is a loss corresponding to a voltage increase of 100 mV or more due to the electrolytic solution resistance. In order to reduce the resistance loss, it is necessary to make the catholyte chamber as thin as possible.
(3) In the cathode chamber of the conventional electrolytic cell, a gas chamber is provided to use a gas diffusion electrode as mentioned above. The gas chamber is pressed by the surroundings in intimate contact therewith so as to prevent gas leakage. Since the back side of the gas diffusion electrode is not joined, if higher than the gas pressure, the gas diffusion electrode protrudes easily and sometimes breaks. Further, electricity has been collected from the perimeter of the gas diffusion electrode. Where the liquid pressure is higher than the gas pressure, a gas feed layer is brought into contact under pressure with a metallic porous body used as a gas chamber material, and electricity is collected via the metallic porous body as an conducting path.
(4) A cathode used in an existing ion-exchange membrane type sodium chloride electrolytic cell is usually made of nickel, etc., and a hydrogen generating reaction proceeds on the cathode.
It has been deemed desirable to replace the hydrogen-generating cathode of an electrolytic cell with an oxygen cathode of which power saving is expected. In order to displace the hydrogen-generating cathode with an oxygen cathode, it is necessary to remodel the hydrogen-generating cathode and to set up a gas chamber in addition.
Where the remodelling for introducing an oxygen cathode into a conventional electrolytic cell is conducted by attaching thereto a gas diffusion electrode and a gas chamber pan which directly becomes a gas chamber and making an inlet and an outlet for oxygen gas, such alterations hardly achieve high precision, meeting difficulty in sealing between an electrolytic solution and gas. Under the present situation, it is easier to make a cathode frame from the start, which is bad economy.
In order to make use of an existing electrolytic cell, a means has been demanded with which the existing electrolytic cell can be remodelled with no or, if any, minimum alternations.
DISCLOSURE OF THE INVENTION
(1) An object of the present invention is to provide a gas diffusion electrode attached to a metallic frame (metal-framed gas diffusion electrode) and a gas diffusion electrode and gas chamber which is based on the metal-framed gas diffusion electrode, with which a sodium chloride electrolytic cell little liable to leak liquid or gas can be construed; and a sodium chloride electrolytic cell using the same.
(2) An object of the present invention is to provide the above-described metal-framed gas diffusion electrode, wherein the surface of the gas diffusion electrode is brought closer to the ion-exchange membrane irrespective of the position of the metal frame thereby to make the cathode chamber sufficiently thin and to minimize the resistance loss due to the electrolytic solution resistance; a gas diffusion electrode and gas chamber which is based on this metal-framed gas diffusion electrode; and an ion-exchange membrane type sodium chloride electrolytic cell using the same.
(3) An object of the present invention is to provide a gas diffusion electrode which allows current collection directly from the back side thereof without using passage through a current collecting network inside the gas diffusion electrode as has been the case with the conventional element, of which the back side can be fixed at a number of points, which can be provided with gas passageways so that oxygen may sufficiently diffuse in the electrode, which enables current collection through a short distance to minimize a voltage loss, and which is not deformed and destroyed even if a difference between a liquid pressure and a gas pressure develops.
(4) In the state-of-the-art electrolytic cell in which the gas diffusion electrode is fixed to the electrolytic cell frame only at the periphery thereof, current is collected from the perimeter mainly through the current collecting network inside the gas diffusion electrode in the planar direction over a long distance. A structure has been demanded, such that a gas diffusion electrode does not protrude and break even if the gas pre
Bell Bruce F.
Furuya Nagakazu
Young & Thompson
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