U.S. patent application number 10/493485 was filed with the patent office on 2004-12-09 for eletrochemical half-element.
Invention is credited to Bulan, Andreas, Gestermann, Fritz, Klesper, Walter, Pinter, Hans-Dieter.
Application Number | 20040245095 10/493485 |
Document ID | / |
Family ID | 7703438 |
Filed Date | 2004-12-09 |
United States Patent
Application |
20040245095 |
Kind Code |
A1 |
Pinter, Hans-Dieter ; et
al. |
December 9, 2004 |
Eletrochemical half-element
Abstract
An electrochemical half cell comprises a gas diffusion electrode
(22) that serves as an anode or cathode and separates an electrode
space from a gas space (2). In addition, a number of gas pockets
(2) are provided that are formed by the gas diffusion electrode
(22) and a rear wall (5). A gas connecting channel (1) that
connects two gas pockets to one another is provided through which
the gas flows via a gas supply connection (3) into the gas pocket
located thereabove. In order to be able to easily detach the
connection, the gas supply connection (3) is accessible from the
side of the gas diffusion electrode (22).
Inventors: |
Pinter, Hans-Dieter;
(Wermelkirchen, DE) ; Bulan, Andreas; (Langenfeld,
DE) ; Klesper, Walter; (Bergisch Gladbach, DE)
; Gestermann, Fritz; (Leverkusen, DE) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
SUITE 800
1990 M STREET NW
WASHINGTON
DC
20036-3425
US
|
Family ID: |
7703438 |
Appl. No.: |
10/493485 |
Filed: |
April 23, 2004 |
PCT Filed: |
October 14, 2002 |
PCT NO: |
PCT/EP02/11476 |
Current U.S.
Class: |
204/265 |
Current CPC
Class: |
C25B 15/08 20130101;
C25B 9/19 20210101 |
Class at
Publication: |
204/265 |
International
Class: |
C25B 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2001 |
DE |
101 52 274.6 |
Claims
1. An electrochemical half-element, in particular for the
electrolysis of aqueous solutions of alkali metal chloride,
comprising at least an electrode space for receiving electrolyte
having an electrolyte feed and an electrolyte discharge, a gas
space formed from a plurality of gas pockets for receiving gas,
each gas pocket having a back wall and a gas diffusion electrode as
cathode or anode which separates the gas space from the electrode
space, a connecting passage which connects two gas pockets to one
another and through which the gas which emerges from a lower gas
pocket via an outlet opening flows via a gas-feed connection into a
gas pocket above, wherein the gas-feed connection can be detached
from the side of the gas diffusion electrode.
2. The electrochemical half-element as claimed in claim 1, wherein
the gas-feed connection has a fixed part, which is connected to the
connecting passage, and a mating piece, which is connected to the
gas pocket, the fixed part and the mating piece being releasably
connected to one another.
3. The electrochemical half-element as claimed in claim 2, wherein
the mating piece has a through-opening extending from the back wall
to the gas diffusion electrode.
4. The electrochemical half-element as claimed in claim 3, wherein
the through-opening serves to receive a securing pin which is
connected to the fixed part.
5. The electrochemical half-element as claimed in claim 2, wherein
the fixed part and the mating piece have gas passages which are in
communication with one another.
6. The electrochemical half-element as claimed in claim 5, wherein
the fixed part and/or the mating piece has a compensation passage
for compensating for any offset between the gas passages.
7. The electrochemical half-element as claimed in claim 2, wherein
a baffle plate is arranged between the gas passages provided in the
mating piece and the gas diffusion electrode.
8. The electrochemical half-element as claimed in claim 1, wherein
the gas-feed connection is arranged centrally between two
longitudinal sides of the gas pocket, and outlet openings, which
can be opened or closed depending on the arrangement, are provided
in each case on the longitudinal sides.
9. An electrochemical half-element as claimed in claim 2, wherein
the fixed part is connected to a front wall of the connecting
passage.
10. An electrochemical half-element as claimed in claim 2, wherein
the melting piece is connected to a back wall of the gas
pocket.
11. The electrochemical half-element as claimed in claim 3, wherein
the fixed part and the mating piece have gas passages which are in
communication with one another.
12. The electrochemical half-element as claimed in claim 4, wherein
the fixed part and the mating piece have gas passages which are in
communication with one another.
13. The electrochemical half-element as claimed in claim 3, wherein
a baffle plate is arranged between the gas passages provided in the
mating piece and the gas diffusion electrode.
14. The electrochemical half-element as claimed in claim 4, wherein
a baffle plate is arranged between the gas passages provided in the
mating piece and the gas diffusion electrode.
15. The electrochemical half-element as claimed in claim 5, wherein
a baffle plate is arranged between the gas passages provided in the
mating piece and the gas diffusion electrode.
16. The electrochemical half-element as claimed in claim 2, wherein
the gas-feed connection is arranged centrally between two
longitudinal sides of the gas pocket, and outlet openings, which
can be opened or closed depending on the arrangement, are provided
in each case on the longitudinal sides.
17. The electrochemical half-element as claimed in claim 3, wherein
the gas-feed connection is arranged centrally between two
longitudinal sides of the gas pocket, and outlet openings, which
can be opened or closed depending on the arrangement, are provided
in each case on the longitudinal sides.
18. The electrochemical half-element as claimed in claim 4, wherein
the gas-feed connection is arranged centrally between two
longitudinal sides of the gas pocket, and outlet openings, which
can be opened or closed depending on the arrangement, are provided
in each case on the longitudinal sides.
19. The electrochemical half-element as claimed in claim 5, wherein
the gas-feed connection is arranged centrally between two
longitudinal sides of the gas pocket, and outlet openings, which
can be opened or closed depending on the arrangement, are provided
in each case on the longitudinal sides.
20. The electrochemical half-element as claimed in claim 7, wherein
the gas-feed connection is arranged centrally between two
longitudinal sides of the gas pocket, and outlet openings, which
can be opened or closed depending on the arrangement, are provided
in each case on the longitudinal sides.
Description
[0001] The invention relates to an electrochemical half-element
having a gas diffusion electrode, in particular for the
electrolysis of aqueous solutions of alkali metal chloride.
[0002] The use of gas diffusion electrodes in alkali metal chloride
electrolysis as consumable oxygen cathodes advantageously involves
pressure compensation between the height-dependent pressure of the
sodium hydroxide solution in front of the gas diffusion electrode
and the constant pressure of the oxygen behind the gas diffusion
electrode, in the form of gas pockets, as shown in EP-A-0 717 130.
In this context, it has proven advantageous for the gas to be
routed in such a way that active venting of the gas pockets is
ensured, as described in U.S. Pat. No. 6,165,332.
[0003] A further development of pressure compensation by means of
gas pockets is described in EP-A-0 946 791 and relates to removable
gas pockets. However, technical tests have revealed a number of
drawbacks, relating in particular to the following points:
[0004] The attachment of the oxygen supply at the rear by flanging
flexible hoses onto connection stubs on the rear side of the gas
pocket is highly laborious and difficult. The operation involves
attaching the oxygen supply to the rear side, remote from the gas
diffusion electrode, of the gas pocket. Furthermore, the presence
of projecting connection stubs on the gas pockets, which in
practice are over two meters long and approx. 30 cm wide, is a
nuisance and has in some cases led to mechanical damage. A further
drawback is the need, for design reasons, to keep in stock two
types of gas pockets, namely gas pockets whose gas inlet opening is
arranged on the right-hand side of the gas pocket and whose gas
outlet opening is arranged on the left-hand side of the gas pocket,
and gas pockets in which, conversely, the gas inlet opening is
arranged on the left-hand side and the gas outlet opening is
arranged on the right-hand side. Screwing on the gas pockets in the
manner described above has also proven laborious and in need of
improvement.
[0005] It is an object of the invention to provide a gas pocket
which is simple to exchange.
[0006] According to the invention, the object is achieved by the
features of claim 1.
[0007] The present invention relates to an electrochemical
half-cell with gas diffusion electrode as cathode or anode with
pressure-compensated gas supply via gas pockets, in such a manner
that the removable gas pockets, during all removal and installation
operations, are designed such that they can be operated from the
side of the gas diffusion electrode, and the mechanical and
electrical connection of the gas pockets to the frame-like
supporting structure or the like of the half-shell, supporting the
gas pockets, is preferably likewise effected by means of readily
releasable connections.
[0008] In the context of the present invention, the term half-shell
is to be understood as meaning the space which receives the
electrode space for receiving the electrolyte, the gas space,
formed from the gas pockets, for receiving gas and the connecting
passage which connects two gas pockets to one another in each case,
and which allows electrical contact to be made with the gas
diffusion electrodes. A frame-like supporting structure or the like
is provided in the half-shell for the purpose of attaching the gas
pockets.
[0009] According to the invention, the electrochemical half-cell
has a gas-feed connection which is arranged between a gas pocket
and a gas-connecting passage which connects two gas pockets to one
another, and can be detached from the side of the gas diffusion
electrode. For this purpose, it is preferable for a fixed part or a
distributor plate with screw head and sealing system to be arranged
as an element of the gas-feed connection at the gas-connecting
passage, in particular at a front wall of the gas-connecting
passage. The fixed part can be releasably connected to a mating
piece which is connected to the gas pocket, in particular to the
back wall of the gas pocket. The mating piece preferably has gas
inlet openings leading into the gas pocket, and the gas diffusion
electrode has an aperture which is gastight with respect to the gas
pocket. This forms a through-opening which extends from the back
wall of the gas pocket to the gas diffusion electrode. The fixed
part and the mating piece are designed in such a manner that the
connecting elements of one or both parts are accessible from the
gas diffusion electrode, i.e. from the front. This, by simple
release of the connection, allows the gas pocket to be exchanged
and/or removed. It may also be necessary for connecting elements in
the boundary region of the gas pocket, which are connected to a
support structure or the like of the half-element, to be released
for this purpose.
[0010] One advantage of the half-cell according to the invention is
that the gas pockets do not have any connection stubs. Instead, the
gas pockets are flat, easy-to-handle units.
[0011] The gas supply is preferably fitted halfway up one end of
the gas pocket. Gas outlet openings are provided at the other end
of the gas pocket, both at the bottom and at the top. This has the
advantage that only one type of gas pocket has to be constructed,
since, depending on whether the gas supply into the gas pocket
takes place to the right or to the left, the gas outlet openings at
the top are closed off and those at the bottom are opened or
fitted. Therefore, the gas outlet from the gas pocket is always at
the bottom, irrespective of how the gas pocket is fitted. The
gas-connecting passages may in this case be installed in the
half-shell as a fixed unit which is independent of the gas
pocket.
[0012] It has proven advantageous for the back wall of the gas
pocket to be provided with a dimension which projects on all sides
and for this projection to be connected to the support structure,
in order for the gas pockets to be installed in the half-cell, i.e.
for the gas pockets to be connected to the support structure, which
in EP-A-0 946 791 is effected releasably by screw connection or
clamping strips. The projections of the gas pockets on the
longitudinal sides are preferably used for this purpose, while the
projections on the narrow sides are bent up to the level of the
sealing surface of the half-shell and are pushed under the
seals.
[0013] If what are known as dimensionally stable gas diffusion
electrodes in accordance with DE-A 100 27 339 are used, their rigid
edge region which is not coated with catalyst material can be bent
downward in a Z shape onto the level of the gas pocket back wall
and at this level can be connected to the back wall of the gas
pocket. Accordingly, in this case the projection of the back wall
with the rigid edge region of the gas diffusion electrode resting
on it can be connected to the support structure for the purpose of
securing the gas pockets in the half-cell.
[0014] The gas pockets can in each case be connected to the support
structure of the half-shell using special self-centering screws or
using tensile rivets. The projections of adjacent gas pockets in
this case overlap one another. The seal with respect to the
electrolyte behind the gas pockets, which is required in order to
avoid bypass flows out of the electrolyte gap through which flow is
forced into the back space, can be achieved by an elastic seal and
a prestressed metal section, both with mating holes, being
introduced. This prestress allows continuous linear electrical
contact with the holding structure. Furthermore, the resistive
losses can be minimized here by the contact regions being coated
with applications of precious metal, e.g. of silver or gold.
[0015] Alternatively, the gas pocket could also be secured in the
half-shell by welding or soldering. A releasable connection which
offers the option of installing and removing an individual gas
pocket directly on site, i.e. in the chlorine factory, is
preferably selected, however. A gas pocket which can be handled
individually has the advantage, for example, that it is
considerably easier to fit a gas diffusion electrode, for example
when the gas diffusion electrode is being changed on account of
wear or damage or for quality assurance checking for any incorrect
penetration of gas through the gas diffusion electrode.
[0016] Nickel is preferably selected as the material for
constructing the gas pockets and the gas-connecting passage.
Alternatively, it would also be possible to use alkali-resistant,
eluate-free special steel compounds, such as for example Hastalloy.
The gas diffusion electrodes are substantially an electrochemically
active coating which contains a catalyst metal and/or a nonmetallic
compound of a metal which forms the catalyst, e.g. silver(I) oxide,
and a binder, e.g. a polymer, such as polytetrafluoroethylene
(PTFE), on an electrically conductive support, for example a metal
mesh, nonwoven or woven fabric. Furthermore, the support may be a
carbon mesh, a carbon nonwoven or a carbon woven fabric or a
corresponding mesh etc. made from other electrically conductive
materials.
[0017] The invention is explained in more detail below on the basis
of preferred embodiments and with reference to the appended
drawings, in which:
[0018] FIG. 1 shows a diagrammatic longitudinal section through a
gas pocket according to the invention,
[0019] FIG. 2 shows an excerpt from a diagrammatic cross section
through the gas pocket on line A-A' in FIG. 1,
[0020] FIG. 3 shows an excerpt from a diagrammatic cross section
through a further embodiment of the gas pocket,
[0021] FIG. 4 shows an enlarged view of the gas-feed connection as
illustrated in FIG. 2, and
[0022] FIG. 5 shows a diagrammatic cross section, corresponding to
FIG. 4, through a further embodiment of the gas-feed
connection.
[0023] The gas pocket according to the invention described below is
used in a cathode half-element during the electrolysis of an
aqueous solution of alkali metal chloride. The gas diffusion
electrode is in this case operated as an oxygen consumption
cathode.
[0024] A gas pocket 2 is provided with a detachable gas-feed
connection 3 which is arranged on one side of the gas pocket
symmetrically or centrally between the longitudinal sides 37, 38
(FIG. 1). Of the outlet openings 30 and 30', only those which lie
at the bottom are open. Gas pockets with a gas-feed connection
located on the left are thus of the same design as those with a
gas-feed connection located on the right. There is therefore only
one basic type of gas pockets, which are arranged above one another
with the gas-feed connection on the left or the right
alternately.
[0025] The gas-feed connection 3 comprises a fixed part 6 (FIGS. 2
and 4), which is connected to the front wall 4 of the
gas-connecting passage 1, and the mating piece 7, which is part of
the removable gas pocket 2. The gas-connecting passage 1 is used to
connect two gas pockets 2 located above one another. The gas which
emerges from the lower gas pocket flows through the gas-connecting
passage into the gas pocket above. For the gas supply, the bottom
gas pocket has a gas-feed connection stub, and a further connection
is provided for the gas discharge, and the gas can be discharged
together with the electrolyte via the gas discharge connection
stub. The gas pocket 2 is connected to the gas-connecting passage I
via a screw connection between fixed part 6 and mating piece 7
through the through-opening 19 in the mating piece 7 via a securing
pin, such as for example a threaded pin 15 and the nut 16 with
washer 17. The through-opening 19 extends from the back wall 5 to
the gas diffusion electrode 22 and is therefore accessible from the
front, i.e. from the side on which the gas diffusion electrode 22
is arranged. Simply loosening the nut 16 allows the gas-feed
connection 3 to be released and the gas pocket 2 can be removed
after the connection to a support structure 33, which in the
exemplary embodiment illustrated is configured as a riveted
connection 34 (FIG. 2), has been released. Gas is in this case
transported via the mating channels or gas passages 8 and 10 in the
fixed part 6 and in the mating piece 7, respectively, with a
compensation passage 9 serving to improve the gas transport in the
event of poorly aligned, for example offset, gas passages 8, 10.
Seals 13 and 14 outside and inside the through-openings in
corresponding seal seats 11 and 12 are responsible, in the
screwed-together state, for providing a seal with respect to the
electrolyte and therefore for avoiding uncontrolled loss of
gas.
[0026] A baffle plate, in particular a metal baffle sheet, 20
fitted to the edge 18 of the mating piece 7 associated with the gas
pocket 2 diverts the incoming gas into a direction of flow parallel
to the gas diffusion electrode 22 and thereby avoids unacceptably
high gas velocities at the rear side of the gas diffusion electrode
22.
[0027] The connection of the gas diffusion electrode 22 to the edge
18 can be effected either by means of a suitable weld (ultrasonic
or laser welding) or by soldering. Alternatively, it is possible to
select a screw connection 16' (FIG. 5) with a seal 25, which is
designed in such a way that the mating piece 7 and the fixed part
6, on the one hand, and the gas diffusion electrode 22 and the edge
18, on the other hand, are connected to one another fixedly, i.e.
in a gastight manner.
[0028] The gas pocket 2 itself is provided with a rim 21, the
height of which defines the distance between back wall 5 and gas
diffusion electrode 22. Back wall 5, rim 21 and gas diffusion
electrode 22 are preferably connected by ultrasonic or laser
welding, welding advantageously being carried out using an angle
plate 24 designed as an edge protector. This constitutes a gas
pocket electrode unit.
[0029] Alternatively, the gas pocket may also be formed from a
dimensionally stable gas diffusion electrode 36 (FIG. 3), whose
region 35 which is not coated with catalyst material in the edge
region is bent down in a Z shape onto the level of the gas pocket
back wall 5 and is connected to the back wall 5 of the gas pocket 2
at this level, for example by welding or soldering. If the flank of
the Z is selected to be less than 90.degree., the outlet openings
30 at the bottom are in any event at a lower level than the bottom
edge of the active zone of the gas diffusion electrode and thereby
ensure good removal of condensate without wetting the active zone.
In both cases, the way in which the releasable gas-feed connection
3 is fitted to the gas pocket electrode unit is identical.
[0030] The gas pockets are likewise secured to the securing rail 33
belonging to the cathode half-cell (FIG. 2) releasably by means of
a screw connection or riveted connection 34. To achieve
particularly good electrical contact between the two components and
at the same time to avoid a leaking flow of electrolyte between the
front side and the rear side of the gas pocket, a prestressed metal
profiled strip 31, which is perforated so as to match the
perforations in the gas pocket and securing rail, and a permanently
elastic seal 32 beneath it are pressed on via the screw
connection/riveted connection, thereby producing linear contact
between the securing points of the gas pocket electrode unit.
[0031] An advantage of all these variants is that the gas pocket
electrode units can be exchanged using components which have been
tested for leaktightness, the gas pocket electrode units forming
flat structures without projecting parts which are therefore easy
to handle. If the releasable connection of the gas pocket electrode
units is also selected, they can be exchanged in situ in the
installation.
* * * * *