U.S. patent application number 10/614865 was filed with the patent office on 2004-04-15 for electrochemicall cell.
This patent application is currently assigned to Bayer Aktiengesellschaft. Invention is credited to Bulan, Andreas, Gestermann, Fritz, Klesper, Walter, Malchow, Richard, Pinter, Hans-Dieter.
Application Number | 20040069621 10/614865 |
Document ID | / |
Family ID | 30469229 |
Filed Date | 2004-04-15 |
United States Patent
Application |
20040069621 |
Kind Code |
A1 |
Gestermann, Fritz ; et
al. |
April 15, 2004 |
Electrochemicall cell
Abstract
The present invention relates to an electrochemical cell
suitable for a membrane electrolysis process, comprising (i) at
least one anode compartment having a metal electrode, (ii) a
cathode compartment having a gas diffusion electrode (iii) and an
ion exchange membrane arranged between the anode compartment and
the cathode compartment. The metal electrode that functions as an
anode is capable of being dipped into an electrolyte during use and
is provided with one or more orifices for the passage of gas formed
during operation. The metal electrode can optionally be angled
and/or curved, and the orifices preferably have guide structures
that conduct the gas formed to a side of the metal electrode that
faces away from the cathode. The present invention also relates to
electrodes per se as well as methods for use of electrodes and
electrochemical cells.
Inventors: |
Gestermann, Fritz;
(Leverkusen, DE) ; Bulan, Andreas; (Langenfeld,
DE) ; Malchow, Richard; (Koln, DE) ; Pinter,
Hans-Dieter; (Wermelskirchen, DE) ; Klesper,
Walter; (Bergisch Gladbach, DE) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
SUITE 800
1990 M STREET NW
WASHINGTON
DC
20036-3425
US
|
Assignee: |
Bayer Aktiengesellschaft
|
Family ID: |
30469229 |
Appl. No.: |
10/614865 |
Filed: |
July 9, 2003 |
Current U.S.
Class: |
204/266 ;
204/284 |
Current CPC
Class: |
C25B 11/03 20130101 |
Class at
Publication: |
204/266 ;
204/284 |
International
Class: |
C25B 011/03; C25C
007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2002 |
DE |
10234806.5 |
Claims
What is claimed is:
1. An electrochemical cell suitable for use in a membrane
electrolysis process, comprising; at least one anode compartment
having a metal electrode capable of functioning as an anode; a
cathode compartment having a gas diffusion electrode capable of
functioning as a cathode and; an ion exchange membrane arranged
between said anode compartment and said cathode compartment,
wherein the metal electrode has at least one orifice for the
passage of the gas formed during operation and said metal electrode
optionally being angled and/or curved, and further wherein one or
more of the orifices are provided with a guide structure which is
capable of conducting gas formed to a side of the metal electrode
facing away from said cathode compartment.
2. An electrochemical cell according to claim 1, wherein the total
cross-sectional area of the orifices is in the range from 20% to
70% of the area which is formed by the height and width of the
metal electrode.
3. An electrochemical cell according to claim 1, wherein the metal
electrode has a corrugated, zigzag-shaped or rectangular cross
section.
4. An electrochemical cell according to claim 3, wherein the metal
electrode has a depth of at least 1 mm.
5. An electrochemical cell according, to claim 1, wherein the metal
electrode comprises two expanded metals adjacent to one another,
wherein one expanded metal faces the cathode compartment and is
more finely structured than a second expanded metal facing away
from the cathode compartment, the more finely structured expanded
metal being rolled flat and the second expanded metal being
arranged such that mesh webs thereof are inclined in a direction of
the cathode compartment and serve as said guide structures.
6. A metal electrode comprising: at least one orifice that is
provided with a guide, said guide being capable of conducting gas
away from said metal electrode.
7. An electrode as claimed in claim 6, wherein said metal electrode
is angled and/or curved.
8. An electrode according to claim 6, wherein the total
cross-sectional area of all orifices provided in said electrode is
in the range from 20% to 70% of the area which is formed by the
height and width of the metal electrode.
9. An electrode according to claim 6, wherein the metal electrode
has a corrugated, zigzag-shaped or rectangular cross section.
10. An electrode according to claim 6, wherein the metal electrode
has a depth of at least 1 mm.
11. An electrode according to claim 6, wherein the metal electrode
comprises two expanded metals adjacent to one another, wherein one
of said expanded metals is more finely structured than the second
expanded metal, the more finely structured expanded metal being
rolled flat and the second expanded metal being arranged such that
mesh webs thereof are inclined and serve as said guide.
12. An electrochemical cell comprising a metal electrode as claimed
in claim 6.
13. A method for conducting an electrolysis operation comprising
employing an electrode according to claim 6.
14. A method for conducting an electrolysis operation comprising
employing an electrochemical cell according to claim 12.
15. A method for conducting an electrolysis operation comprising
employing an electrochemical cell according to claim 1.
16. An electrochemical cell according to claim 12, comprising an
anode of a titanium-palladium alloy and a cathode based on
carbon.
17. A method for reducing the voltage required in the electrolysis
of aqueous solutions of hydrogen chloride comprising employing an
electrode according to claim 6.
18. A method for reducing the voltage required in the electrolysis
of aqueous solutions of hydrogen chloride comprising employing an
electrochemical cell according to claim 12.
19. A method for carrying out the electrolysis of an aqueous
solution of hydrogen chloride comprising employing an anode
comprising a combination of at least two expanded metals, one of
said expanded metals being more finely structured than the other of
said expanded metals.
20. A method according to claim 19, wherein said method permits use
of a voltage of less than 1.67 V when a current density of 5
kA/m.sup.2 is employed.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to an electrochemical cell which is
used in particular for the electrolysis of an aqueous solution of
hydrogen chloride by a membrane process with a gas diffusion
electrode functioning as the cathode.
[0003] 2. Description of Related Art
[0004] Aqueous solutions of hydrogen chloride, also referred to
below as hydrochloric acid, are obtained as a by-product in many
chemical processes, in particular, in processes in which organic
hydrocarbon compounds are oxidized with the aid of chlorine. Many
of these organic chlorine compounds are important intermediates for
industrial chemistry, for example, in the production of plastics.
The recovery of chlorine from these hydrochloric acids is of
economic interest since the residual chlorine can be used, for
example, to conduct further chlorinations. Chlorine from
hydrochloric acid can be recovered, for example, electrolytically,
that is, by electrolysis.
[0005] A process for the electrolysis of hydrochloric acid is
disclosed, for example, in U.S. Pat. No. 5,770,035, the content of
which is incorporated herein by reference. In a typical process, an
anode compartment with a suitable anode is employed that is made,
for example, of a substrate of a titanium-palladium alloy coated
with a mixed oxide of ruthenium, iridium and titanium. During use,
the anode compartment is filled with an aqueous solution of
hydrogen chloride. The chlorine formed at the anode escapes from
the anode compartment and is fed to a suitable treatment. The anode
compartment is generally separated from the cathode compartment by
a commercial cation exchange membrane. A gas diffusion electrode
rests on the cation exchange membrane on the cathode side. The gas
diffusion electrode in turn rests on a current distributor. Gas
diffusion electrodes are, for example, oxygen-consuming cathodes
(OCC). When an OCC is employed as a gas diffusion electrode, an
oxygen-containing gas or pure oxygen is usually passed into the
cathode compartment and the oxygen reacts at the OCC.
[0006] The electrochemical formation of gas at the electrode
adversely affects the electrolysis process. In addition to
potentially negative hydrostatic and hydrodynamic effects, the gas
bubbles that form result in an increased ohmic resistance in the
electrolyte. In order to counteract the influences of the gas
bubbles, DE-A 3 401 637 proposes an electrolysis process in an
electrochemical cell with a separated anode compartment and cathode
compartment, in which one or both electrodes have a passage, and an
electrolyte flows from top to bottom through one or both half-cells
so that the electrodes are wet. Thus, the electrolyte flows in a
direction opposite to the direction the electrochemically formed
gas is flowing. The resulting air bubbles burst at the phase
boundary between the descending electrolyte film and the adjacent
gas space.
SUMMARY OF THE INVENTION
[0007] An object of the present invention was to provide an
electrochemical cell for a membrane electrolysis process, which
cell has, as the anode, a metal electrode preferably having as
large an electrochemically active surface as possible, and orifices
that make it possible to conduct gas formed from the side facing
the cathode into a space located behind the metal electrode. In
particular, the electrochemical cell is suitable for use in the
electrolysis of an aqueous solution of hydrogen chloride, the
cathode used typically being a gas diffusion electrode. The anode
compartment is preferably completely filled with the hydrochloric
acid, the latter flowing through the anode compartment from bottom
to top.
[0008] These and other objects can be achieved, for example, by
providing one or more orifices of the metal electrode with a guide
structures which conduct the gas formed into the space behind the
metal electrode. At the same time, the metal electrode is
preferably angled and/or curved, with the result that its
electrochemically active area is increased. The present invention
is further directed to electrodes as well as to methods for their
use.
[0009] Additional objects, features and advantages of the invention
will be set forth in the description which follows, and in part,
will be obvious from the description, or may be learned by practice
of the invention. The objects, features and advantages of the
invention may be realized and obtained by means of the
instrumentalities and combination particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention is explained in more detail below with the aid
of preferred embodiments with reference to the attached
drawings.
[0011] FIG. 1 shows a diagram of a first preferred embodiment of
the electrode structure in perspective view
[0012] FIG. 2 shows a diagram of a second preferred embodiment of
the electrode structure in perspective view
[0013] FIG. 3 shows a diagram of a third preferred embodiment of
the electrode structure in perspective view
[0014] FIG. 4 shows a diagram of a fourth preferred embodiment of
the electrode structure in perspective view
[0015] FIG. 4a shows a section of the embodiment shown in FIG.
4
[0016] FIG. 5 shows a diagram of a fifth preferred embodiment of
the electrode structure in perspective view
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0017] The invention generally relates to an electrochemical cell
suitable for a membrane electrolysis process, comprising at least
one anode compartment having a metal electrode as the anode, a
cathode compartment having a gas diffusion electrode as the cathode
and an ion exchange membrane arranged between the anode compartment
and cathode compartment. The metal electrode is generally capable
of being dipped into an electrolyte and is provided with orifices
for the passage of the gas formed during operation and is further
optionally angled and/or curved, for example as shown in FIGS. 1-5.
The orifices are preferably provided with one or more guide
structures which are capable of conducting gas formed onto the side
of the metal electrode facing away from the cathode.
[0018] The orifices of the electrode can comprise slots or holes
and/or can optionally be formed by the meshes of an expanded metal.
In order to conduct the gas in a controlled manner into the space
behind the metal electrode, (also referred to herein as the "back
space"), the guide structures at the orifices are advantageously
inclined in the direction of the ion exchange membrane. Thus, the
gas that builds up at the surface of the metal electrode facing the
ion exchange membrane is conducted away from the surface and, on
ascending, is discharged from a narrow gap between the metal
electrode and the ion exchange membrane. This prevents the gas from
collecting in the narrow intermediate space and substantially
minimizes the likelihood of increased resistance in the
electrolyte.
[0019] In a preferred embodiment of the electrochemical cell
according to the invention, the orifices of the metal electrode
advantageously have a total cross-sectional area which is in the
range from 20% to 70% of the area which is formed by the height and
width of the metal electrode. In the case of a perpendicular
arrangement of the metal electrode in the electrochemical cell, the
length of the substantially perpendicularly arranged side of the
electrode is to be regarded as the "height" of the metal electrode,
while the length of that side of the electrode which is arranged
substantially parallel to the opposite electrode and horizontally
is to be regarded as the "width."
[0020] If the electrode substantially comprises a metal sheet, the
electrode is preferably not flat but rather, is advantageously
curved and/or corrugated. For such an electrode structure, a
corrugated, zigzag-shaped or rectangular cross section is
preferably chosen. In this way, the size of the electrochemically
active surface of the metal electrode is increased. In particular,
such an electrode structure is important for the electrolysis of
aqueous solutions of hydrogen chloride (hydrochloric acid) since,
owing to the relatively high conductivity of hydrochloric acid, an
electrochemical reaction is effected, even when there is a
relatively large distance between the electrode and the opposite
electrode. The electrochemically active surface of the metal
electrode is formed in particular by that surface of the metal
electrode facing the opposite electrode, in this case the cathode.
However, an electrochemical reaction also occurs at surfaces that
do not face the opposite electrode. This applies, for example, to
surfaces at right angles to the opposite electrode, such as, for
example, edges, or surfaces facing away from the opposite
electrode, such as, for example, the back of the metal electrode.
The "electrochemically active surface" is therefore to be
understood as meaning the proportion of the total surface area of
the metal electrode at which an electrochemical reaction takes
place. In some embodiments of the present invention, the ratio of
electrochemically active surface area to the surface area which is
formed by the height and width of the metal electrode is preferably
at least 1.2.
[0021] In a further preferred embodiment of the electrolysis cell,
the metal electrode preferably has a depth of at least 1 mm. The
depth is regarded as the side length of the metal electrode which
is arranged substantially perpendicular to the opposite electrode
and horizontally. In the case of a corrugated cross section of the
metal electrode, the depth preferably corresponds to twice the
amplitude of the wave. Expressed otherwise, the depth corresponds
to the difference between the minimum and maximum distance formed
by one of the edges of the electrode and of the ion exchange
membrane. The same preferably applies to the depth in the case of a
zigzag-shaped cross section of the electrode.
[0022] With a suitable mesh size, web thickness and web width, the
expanded metal, if employed, preferably also has the same desired
properties as the electrode structure, namely a large
electrochemically active surface which has depth, and orifices for
conducting away the gas. The mesh structure enables the gas to be
conducted away to the back of the metal electrode. In such a case,
the webs perform the function of the guide structure if the
expanded metal is arranged so that the webs are inclined in the
direction of the opposite electrode. It is also possible to use a
combination of two or more identical or different expanded metals
if at least one of the expanded metals is installed in the
electrochemical cell as a metal electrode, in particular as the
anode, in the manner described. The metal electrode is preferably
based on two adjacent expanded metals, the expanded metal facing
the opposite electrode preferably having a finer structure than the
expanded metal facing away from the opposite electrode. Moreover,
the more finely structured expanded metal is preferably rolled flat
while the webs of the more coarsely structured expanded metal
preferably serve as guide structures and is advantageously arranged
in such a way that the mesh webs are inclined in the direction of
the opposite electrode.
[0023] A typical cell according to the invention can be used in any
desired application and in particular for the electrolysis of
aqueous solutions of hydrogen chloride. The anode half-cell
generally has an inlet and an outlet for the electrolyte, which
flows from bottom to top through the half-cell and completely fills
it. The outlet of the electrolyte simultaneously typically serves
as an outlet for the gas formed. A suitable anode is, for example,
a noble metal-coated or noble metal-doped titanium electrode.
Suitable anodes include a titanium electrode or titanium alloy
electrode, in particular a titanium-palladium alloy electrode which
is provided with an acid-resistant, chlorine-evolving coating, for
example based on a ruthenium-titanium mixed oxide, or on an iridium
oxide or based on platinum. The anode half-cell is typically
separated from the cathode half-cell by an ion exchange membrane. A
gap is generally present between the anode and the ion exchange
membrane. In particular, a gas diffusion electrode which functions
as an oxygen-consuming cathode serves as the cathode. The gas
diffusion electrode rests both against the ion exchange membrane
and also against a current collector. If the gas diffusion
electrode is used as an oxygen-consuming cathode, oxygen or an
oxygen-containing gas can flow through the cathode compartment. It
is also conceivable to, influence the oxygen inside the cathode
compartment in its direction of flow using baffles or other similar
devices. The oxygen can be passed in from below via an inlet and
removed again at the top via an outlet. However, it is also
possible for the oxygen to flow from top to bottom or for there to
be lateral flow in the cathode compartment in any desired
direction, for example, from bottom left to top right and so on.
With respect to the reaction taking place, oxygen should preferably
be supplied in a superstoichiometric amount in order to achieve
advantageous results in some applications.
[0024] Gas diffusion electrodes which contain a catalyst of the
platinum group, preferably platinum or rhodium, are preferably
used. Gas diffusion electrodes from E-TEK (USA) which have 30% by
weight of platinum on active carbon with a noble metal coating of
1.2 mg of Pt/cm.sup.2 on the electrode may be mentioned as
exemplary suitable electrodes by way of example.
[0025] Suitable ion exchange membranes include, for example, those
comprising perfluoroethylene which contain sulpho groups as active
centres. For example, commercial membranes from DuPont can be used,
for example the membrane Nafion.RTM. 324. Single-layer membranes
having sulpho groups of identical equivalent weights on both sides
as well as membranes having sulpho groups with different equivalent
weights on both sides are suitable. Membranes having carboxyl
groups can also conceivably be used. Any desired ion exchange
membrane can be employed depending on the intended application.
[0026] The current distributor on the cathode side may comprise,
for example, expanded titanium metal or noble metal-coated
titanium. It is also possible to use alternative stable materials
as well as any other desired current distributor available to those
of skill in the art.
[0027] In the embodiment described below, the surface of a metal
electrode which faces an ion exchange membrane and hence the
opposite electrode is referred to as the "front", and accordingly
the surface facing away from the ion exchange membrane is referred
to as the "back". In a typical electrochemical cell according to
the present invention, the electrode is preferably not located on
the ion exchange membrane, but rather, a gap filled with
electrolyte is present between the anode and ion exchange membrane.
In such a case, the gap is preferably not separated from the
remaining space of the half-cell. The gap can advantageously be, as
a rule from about 1 to 3 mm. It is formed by virtue of the fact
that the anode compartment is preferably kept at a higher pressure
than the cathode compartment. Thus, the ion exchange membrane is
pressed onto the gas diffusion electrode and then in turn, onto a
current collector. It is preferable that the cell is arranged such
that a suitable electrolyte preferably can flow freely from bottom
to top through the half-cell. The space of the half-cell which is
adjacent to the back of the electrode is also referred to herein as
"back space".
[0028] In the embodiment shown in FIG. 1, the electrode includes
perpendicularly arranged metal lamellae 10 which are substantially
at right angles to the ion exchange membrane. Baffle plates 12
which are advantageously inclined in the direction of the ion
exchange membrane are present as guide structures in each case
between two adjacent lamellae. The baffle plates 12 aid ascending
gas being conducted from the front of the electrode, i.e. the side
facing the ion exchange membrane, backwards into the back space of
the electrochemical half-cell through the orifices 14. Contact of
the lamellae can be effected, for example, via current feeds 16.
The depth of the lamellae is preferably in the range from about 1
to 40 mm and the distance between two adjacent lamellae is
preferably in the range from about 1 to 10 mm.
[0029] In a further preferred embodiment (not shown here) which is
similar to the principle according to that shown in FIG. 1, the
perpendicularly arranged lamellae are at an angle of from 50 to
90.degree. to the ion exchange membrane.
[0030] In the embodiment shown in FIG. 2, the structure of the
electrode 20 and of the baffle plates corresponds substantially to
the embodiment shown in FIG. 1 (identical or different components
are therefore denoted by the same reference numerals). The
substantial difference is that the lamellae 20 are connected at
their edges facing away from the ion exchange membrane to a metal
sheet 28 which has, below the baffle plates 22, orifices 24 for
conducting away the gas. The metal sheet 28 mounted to the back of
the lamellae is thus substantially parallel to the ion exchange
membrane.
[0031] In an embodiment shown in FIG. 3, the metal electrode 30 is
based on a corrugated cross section. The orifices 34 are present in
the region of the wave summits facing away from the ion exchange
membrane. The guide structures 32 are preferably formed of metal
sheets which are substantially the shape of a half-wave and are
mounted above the orifices 34 and inclined in the direction of the
ion exchange membrane. Such an electrode structure can be produced
in a simple manner, for example, by punching substantially
triangular orifices 34 in the region of the wave summits from the
back of the electrode 30. The triangular orifices are preferably
not punched out completely, but the punched parts each remain
connected to the electrode in the region of the upper vertex of the
triangle, so that the punched parts can be bent as guide structures
32 in the direction of the ion exchange membrane and can be
arranged at an angle of inclination of preferably from 10 to
60.degree.. The guide structures 32 can optionally be welded at
their lateral edges to the electrode 30. Preferably, however,
orifices 34 are punched from the back of the electrode 30 in a
shape corresponding to the shape of the wave summit, since in this
way the guide structures 32 bent towards the front of the electrode
30 and inclined in the direction of the opposite electrode,
terminate with the electrode. An additional connection of the guide
structures 32 to the electrode 30 can therefore be eliminated. In
such a method of production, the area of the punched orifices 34
substantially determines the area of the guide structures 32. Those
punched metal parts of the electrode which function as guide
structures can also be reduced in size so that they project to a
lesser extent into the space between electrode and ion exchange
membrane. Preferably, the size of the orifices 34 is chosen so that
the area of the guide structures 32 is close to the same as, or is
exactly the same as the area of the wave summit. The depth of the
electrode, which is understood here as meaning the distance from
wave summit to wave valley, i.e. double the amplitude of a wave, is
preferably from 2 to 40 mm. The distance between two adjacent wave
summits or valleys, which would correspond to the wavelength, is
preferably from about 3 to 30 mm. In this embodiment, the gas
generally flows substantially in the direction marked with the
arrow 39.
[0032] A further embodiment (not shown here) is in principle an
electrode structure similar to that shown in FIG. 3, but the
electrode is based on a zigzag-shaped cross section. Analogously to
the method of production described above, this electrode structure
can be produced, for example, by punching out a triangular orifice
from behind in the region of the vertices facing away from the ion
exchange membrane.
[0033] The embodiment shown in FIG. 4 differs from that shown in
FIG. 3 once again only in the cross section on which the electrode
structure 40 is based. Here, it is a rectangular cross section, the
orifices 44 (FIG. 4a) being present on the longitudinal sides face
away from the ion exchange membrane. These are preferably arranged
substantially parallel to the ion exchange membrane. The guide
structures 42 conduct the gas into the back space of the half-cell,
preferably corresponding to the direction marked with the arrow 49
(FIG. 4a).
[0034] In a further preferred embodiment (FIG. 5), with a likewise
rectangular cross section of the electrode structure. 50, the
orifices 54 are arranged not on the rear longitudinal side, but
rather, on one of the transverse sides, i.e., on one of those sides
of the electrode which are perpendicular to the ion exchange
membrane. In this embodiment, the guide structures 52 are
accordingly not inclined in the direction of the ion exchange
membrane but instead, in the direction of the opposite transverse
side of the electrode. The gas flow from the front to the back of
the electrode is marked with the arrows 59.
[0035] An electrode structure having a large electrochemically
active surface and orifices with guide structures for conducting
the gas into the back space of the half-cell can also comprise
expanded metals if desired. Thus, a further preferred embodiment
includes at least two expanded metals adjacent to one another, the
expanded metal facing the ion exchange membrane particularly
preferably having a finer structure than the expanded metal facing
away from the ion exchange membrane. A more finely structured
expanded metal is characterized by a smaller mesh width and mesh
size and a smaller web width and web thickness than a more coarsely
structured expanded metal. Moreover, the more finely structured
expanded metal is preferably rolled flat and the more coarsely
structured expanded metal is not arranged arbitrarily, but rather,
is preferably arranged in such a way that the mesh webs perform the
function of guide structures. The meshes are preferably rhombic or
square and the webs of the coarser expanded metal facing away from
the ion exchange membrane are typically inclined in the direction
of the ion exchange membrane. The total area of the orifices, both
in the case of the more finely structured and in the case of the
more coarsely structured expanded metal, are preferably in the
range from 20 to 70% of the area which is given by the external
dimensions, i.e. the edge lengths, of the expanded metals. The
following parameters are used for characterizing the expanded
metals: the web thickness corresponds to the thickness of the metal
sheet used for the production of the expanded metal. The web width
results from the distance between two cuts parallel to one another
but offset. The mesh size characterizes the length of the cut, and
the mesh width characterizes the maximum distance between two
adjacent webs as a result of stretching deformation.
[0036] Surprisingly, it has been found that, in this preferred
embodiment of the invention, a lower operating voltage is employed
as compared with the operating voltage in electrolysis cells having
conventional electrode structures. This voltage effect is clearly
evident in the examples described below.
EXAMPLES
[0037] The electrolysis of an aqueous solution of hydrogen chloride
(hydrochloric acid) was carried out using a gas diffusion electrode
as an oxygen-consuming cathode. The concentration of the
hydrochloric acid was 13% by weight and its temperature on entry
into the anode half-cell was adjusted so that the temperature in
the discharge was 60.degree. C. The circulation volume flow of the
hydrochloric acid was adjusted so that the flow rate of the
hydrochloric acid in the anode half-cell was 0.3 cm/s. The material
of the anodes was a titanium-palladium alloy activated with a
ruthenium-titanium mixed oxide layer (DSA.RTM. coating). A cationic
membrane from DuPont, Nafion.RTM. 324 type was used between the
anode compartment and the cathode compartment. The cathode used was
a gas diffusion electrode from E-TEK (USA), which was based on
carbon and activated with rhodium sulphide. The gas diffusion
electrode was fastened to the current collector, and was formed of
an activated titanium-palladium expanded metal. The width of the
electrode was 730 mm and the height was 1200 mm. The minimum
distance between the anode and the cation exchange membrane was 3.5
mm.
Example 1
[0038] The anode used as a combination of two titanium expanded
metals adjacent to one another, a more finely structured expanded
metal being applied to a more coarsely structured expanded metal.
The more finely structured expanded metal had a mesh size of 4.2 mm
and a mesh width of 3.1 mm and a web width of 0.6 mm and a web
thickness of 0.4 mm. Accordingly, the total area of the orifices
was 53% of the area of the expanded metal. This expanded metal was
rolled flat to a thickness of 0.5 mm. The more coarsely structured
of the two expanded metals had a mesh size of 13.2 mm, a mesh width
of 6.3 mm, a web width of 2.4 mm and a web thickness of 3.5 mm.
Thus, the total area of the orifices was 24% of the area of the
expanded metal. The anode was installed in such a way that the
finer expanded metal which had been rolled flat faced the cation
exchange membrane.
[0039] The voltage was 1.59 V at a current density of 5
kA/m.sup.2.
Example 2 (comparative example)
[0040] The anode comprised a single coarsely structured expanded
metal having a mesh size of 6.2 mm, a mesh width of 3.6 mm and a
web width of 1.1 mm and a web thickness of 1 mm. The total area of
the orifices was accordingly 24% of the total area of the
anode.
[0041] The voltage was 1.67 V at a current density of 5 kA/m.sup.2
and was thus higher than in the electrolysis of a hydrochloric acid
solution under comparable conditions but with the special
combination of a more finely structured expanded metal which had
been rolled flat and faced the cathode and a more coarsely
structured expanded metal located behind.
[0042] According to certain embodiments of the present invention,
it is possible to conduct electrolysis of hydrogen chloride at
voltages less than 1.67 V at a current density of 5 kA/m.sup.2. The
voltage will also be reduced at other current densities.
[0043] Additional advantages, features and modifications will
readily occur to those skilled in the art. Therefore, the invention
in its broader aspects is not limited to the specific details and
representative devices, shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
[0044] All documents referred to herein are specifically
incorporated herein by reference in their entireties.
[0045] As used herein and in the following claims, articles such as
"the", "a" and "an" can connote the singular or plural.
[0046] The priority document, German Patent Application No. 102 34
806.5 filed Jul. 31, 2002 is incorporated herein by reference in
its entirety.
* * * * *