U.S. patent application number 16/641753 was filed with the patent office on 2020-08-20 for electrolyser arrangement.
This patent application is currently assigned to Siemens Aktiengesellschaft. The applicant listed for this patent is Siemens Aktiengesellschaft. Invention is credited to Marc Hanebuth, Katharina Meltzer, Gunter Schmid, Dan Taroata.
Application Number | 20200263311 16/641753 |
Document ID | 20200263311 / US20200263311 |
Family ID | 1000004826390 |
Filed Date | 2020-08-20 |
Patent Application | download [pdf] |
United States Patent
Application |
20200263311 |
Kind Code |
A1 |
Hanebuth; Marc ; et
al. |
August 20, 2020 |
ELECTROLYSER ARRANGEMENT
Abstract
An electrolyser arrangement with at least one electrolytic cell,
having two electrodes, namely an anode and a cathode, each of the
two electrodes being in contact with an electrode compartment for
filling with a liquid electrolyte, the two electrode compartments
being separated by a membrane and a conveying device being
provided, one for each of the two electrodes, for conveying the
electrolyte in each case in a circuit, a cathode circuit and an
anode circuit, through the electrode compartment via at least one
collection vessel per circuit and back into the electrode chamber.
A device is provided outside the electrolytic cell, for conveying
an auxiliary volume flow between the cathode circuit and the anode
circuit.
Inventors: |
Hanebuth; Marc; (Nurnberg,
DE) ; Schmid; Gunter; (Hemhofen, DE) ;
Meltzer; Katharina; (Erlangen, DE) ; Taroata;
Dan; (Erlangen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Siemens Aktiengesellschaft |
Munich |
|
DE |
|
|
Assignee: |
Siemens Aktiengesellschaft
Munich
DE
|
Family ID: |
1000004826390 |
Appl. No.: |
16/641753 |
Filed: |
September 13, 2018 |
PCT Filed: |
September 13, 2018 |
PCT NO: |
PCT/EP2018/074697 |
371 Date: |
February 25, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 15/08 20130101;
C25B 3/04 20130101; C25B 9/10 20130101; C25B 1/10 20130101 |
International
Class: |
C25B 15/08 20060101
C25B015/08; C25B 9/10 20060101 C25B009/10; C25B 1/10 20060101
C25B001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 2017 |
DE |
10 2017 216 710.6 |
Claims
1. An electrolyzer arrangement having comprising: at least one
electrolysis cell comprising two electrodes, namely an anode and a
cathode, wherein each of the two electrodes is in contact with an
electrode space for filling with a liquid electrolyte, wherein the
two electrode spaces are separated by a membrane, a conveyor
apparatus for each of the two electrodes for conveying the
electrolyte through the electrode space in a respective circuit,
comprising a cathode circuit and an anode circuit, and an apparatus
outside the electrolysis cell for conveying a secondary volume flow
between the cathode circuit and the anode circuit.
2. The electrolyzer arrangement as claimed in claim 1, wherein the
cathode circuit and the anode circuit each have a collecting
container.
3. The electrolyzer arrangement as claimed in claim 2, wherein a
first secondary volume flow takes place between a first collecting
container and the second collecting container.
4. The electrolyzer arrangement as claimed in claim 1, further
comprising: a second conveyor apparatus for producing a second
secondary volume flow between the two circuits, which takes place
in the opposite direction from the first secondary volume flow.
5. The electrolyzer arrangement as claimed in claim 4, wherein the
second conveyor apparatus for producing the second secondary volume
flow is configured in the form of a membrane module.
6. The electrolyzer arrangement as claimed in claim 5, wherein both
the cathode circuit and the anode circuit pass through the membrane
module.
7. The electrolyzer arrangement as claimed in claim 4, further
comprising: a pump apparatus between the collecting containers in
order to bring about the second secondary volume flow.
8. The electrolyzer arrangement as claimed in claim 2, further
comprising: an overflow or a pump apparatus between the two
collecting containers in order to bring about the first partial
volume flow.
9. The electrolyzer arrangement as claimed in claim 1, wherein the
membrane between the electrode spaces is a cation permeable
membrane.
10. The electrolyzer arrangement as claimed in claim 8, wherein the
secondary volume flow takes place from the cathode circuit to the
anode circuit.
11. The electrolyzer arrangement as claimed in claim 1, further
comprising: a vapor deposition container in the cathode circuit
and/or in the anode circuit and there is provision for a connecting
line from one of the vapor deposition containers to an educt supply
apparatus.
12. A method for operating an electrolyzer having at least one
electrolysis cell that in turn has two electrodes, comprising an
anode and a cathode, wherein each electrode has an electrode space
through which a liquid electrolyte having a conducting salt
dissolved therein is conveyed in a respective conveyor circuit
namely in a cathode circuit and an anode circuit, in a respective
primary volume flow and wherein the two electrode spaces and hence
the electrolyte contained therein are separated by a membrane, the
method comprising: conveying the electrolyte from one circuit to a
second circuit in a secondary volume flow.
13. The method as claimed in claim 12, wherein the secondary volume
flow is at least 0.01 and at most 10% of the larger of the two
primary volume flows.
14. The method as claimed in claim 13, wherein the secondary volume
flow is at least 0.1 and at most 1% of the larger of the two
primary volume flows.
15. The method as claimed in claim 12, further comprising: a
collecting container in each of the two circuits; wherein the
electrolyte in the secondary volume flow is conveyed from a first
collecting container to a second collecting container.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2018/074697 filed 13 Sep. 2018, and claims
the benefit thereof. The International Application claims the
benefit of German Application No. DE 10 2017 216 710.6 filed 21
Sep. 2017. All of the applications are incorporated by reference
herein in their entirety.
FIELD OF INVENTION
[0002] The invention relates to an electrolyzer arrangement and to
a method for operating an electrolyzer.
BACKGROUND OF INVENTION
[0003] Major changes can be observed on the energy market at
present. The use of fossil fuels is being reduced as far as
possible as part of an energy turnaround, since they cause a large
share of carbon dioxide emissions. At the same time, high outputs
of renewable energies are available, but not always at the desired
location and at the desired time. One technical challenge is to
produce products of value from carbon dioxide, CO.sub.2, using
excess energies that arise in particular when renewable energies
are supplied at increased levels in the network. One approach is to
produce gaseous products of value, such as e.g. carbon monoxide, CO
or ethylene, C.sub.2H.sub.4, by means of electrochemical reduction
of carbon dioxide. These reactions are performed inside what are
known as CO.sub.2 electrolyzers, for example.
[0004] A typical design of CO.sub.2 electrolyzers is based on
aqueous electrolytes, which contain a conducting salt, that is to
say a salt that is dissolved in the electrolyte and is electrically
active. The CO.sub.2 electrolyzers are dealt with in this instance
in exemplary fashion for all electrolysis apparatuses that have a
liquid electrolyte. A cation permeable membrane is used to keep the
anode space and the cathode space separate from one another. This
prevents a gaseous substance of value formed at the cathode from
being able to get to the anode side. However, it also prevents a
gas formed on the anode side, typically oxygen, from getting to the
cathode side. Reciprocal mixing of the two gases is thus avoided.
This is necessary in order to prevent dangerous operating states,
e.g. as a result of the formation of explosive gas mixtures.
However, there are other reasons to avoid mixing of the gases. By
way of example, depending on the application, there are demands on
gas purities of the product gas. By way of example, CO used in
anerobic gas fermentation can contain only traces of oxygen.
[0005] Although the membranes used are practically impermeable to
gases, they need to be permeable to ionic charge carriers. When a
conducting salt is used, one frequent occurrence, however, is that
the cations of the conducting salt, e.g. potassium, are transported
into the foreground, i.e. the potassium cation diffuses through the
membrane from the anode side to the cathode side. This in turn
results in a difference in the concentration of cations between the
electrolytes on the anode side and the cathode side.
[0006] By and large, it can be stated that a crossing of cations,
with the exception of protons, leads to many disadvantages. It is
thus desirable for the composition of anolyte, that is to say the
electrolyte on the anode side, and catholyte to be kept as
identical as possible. Along with the aforementioned crossing of
the cations, water gets through the membrane, which leads to a
thinning of the catholyte, that is to say the electrolyte on the
cathode side, while the anolyte is concentrated. This effect makes
keeping the composition of the anolyte and the catholyte equal as
desired difficult.
[0007] It is known from the prior art that the two electrolytes can
be mixed with one another in a common storage container, so that
the equalization of the concentration of both ions and water is
assured after passage through the electrolyzer. Since there are
always gas impurities in the individual electrolyte liquids,
however, said impurities resulting from the electrolysis and
substantially consisting of the product gas or hydrogen and oxygen,
this joint concentration equalization also holds certain risks.
Additionally, a frequently required product purity is made
difficult by a contamination of the product with hydrogen or with
oxygen.
SUMMARY OF INVENTION
[0008] The object of the invention is to provide an electrolyzer
arrangement and a method for operating an electrolyzer arrangement
that are suitable for ensuring a necessary equalization of
concentrations between an anolyte and a catholyte in the
electrolyzer and at the same time for reducing gas
contaminations.
[0009] The object is achieved by means of an electrolyzer having
the features of patent claim 1 and by a method for operating the
electrolyzer having the features of patent claim 12.
[0010] The inventive electrolyzer as claimed in patent claim 1
comprises at least one electrolysis cell that in turn comprises two
electrodes, namely an anode and a cathode. Each of the two
electrodes is connected to what is known as an electrode space. The
electrode space is suitable for being filled with a liquid
electrolyte. The two electrode spaces are separated from one
another by a membrane, the two electrodes comprising a conveyor
apparatus for conveying the electrolyte in a respective circuit, a
cathode circuit and an anode circuit. The invention is
distinguished in that there is provision outside the electrolysis
cell for a conveyor apparatus for conveying a secondary volume flow
between the cathode circuit and the anode circuit.
[0011] The advantage of the invention described is that a secondary
volume flow allows an equalization of cations and anions between
the two circuits to take place. Further, it is also possible for a
larger volume of water to be equalized without this resulting in
substantial volumes of product gases, such as hydrogen or oxygen,
being shifted between the individual circuits, so that excessive
contaminations or reactive mixtures are avoided. The terms anode
circuit and cathode circuit are each understood to mean an
apparatus, in particular a pipeline apparatus, in particular having
a pump apparatus, that is suitable for having an applicable
electrolyte circulated or recirculated in it.
[0012] In one embodiment of the invention, there is provision for a
respective collecting container for each of the two circuits. This
has a process-engineering advantage, as care is taken to ensure
that there is always sufficient electrolyte available for the two
electrolyte circuits.
[0013] In one configuration of the invention, the collecting
container is divided into at least two subcontainers, wherein a
first subcontainer is connected to the cathode circuit and a second
subcontainer is connected to the anode circuit and the secondary
volume flow takes place between the first subcontainer and the
second subcontainer. Equalization of the electrolytes, that is to
say the anolyte and the catholyte, outside the electrolysis cell in
two separate containers by means of a defined secondary volume
flow, for example by a pipeline having a specific flow rate
controllable by a pump, is particularly expedient because the
electrolyte is collected in this subcontainer and the volume flow
can easily be regulated.
[0014] In a further advantageous embodiment of the invention, there
is provision for a second conveyor apparatus for producing a second
secondary volume flow between the two circuits. This takes place in
the opposite direction from the first secondary volume flow. This
can be expedient if the first secondary volume flow routes for
example water and cations from a first to a second subcontainer and
equalization of anions can take place in the second secondary
volume flow.
[0015] In one embodiment of the invention, the conveyor apparatus
between the two circuits for producing the second secondary volume
flow is configured in the form of a membrane module.
[0016] In this case, it is expedient for the membrane module to be
both part of the cathode circuit and part of the anode circuit.
There is likewise a membrane arranged in the membrane module, as
between the two electrode spaces, said membrane being available as
an exchange area for the dissolved ions. These are cations and
anions.
[0017] The membrane between the electrode spaces is advantageously
a cation permeable membrane. In contrast to a porous membrane, this
is suitable for keeping gases from the individual electrode spaces,
which arise there during the electrolysis, separate from one
another. However, this also results in cations, such as for example
potassium, which is part of the conducting salt, migrating through
the membrane. This in turn necessitates increased equalization of
concentrations between the catholyte and the anolyte outside the
electrolysis cell. When a cation permeable membrane is used, the
secondary volume flow advantageously takes place from the cathode
circuit to the anode circuit.
[0018] A further part of the invention is a method having the
features of patent claim 12, which is suitable for operating an
electrolyzer arrangement. In this case, the electrolyzer
arrangement has an electrolysis cell that in turn has two
electrodes, namely an anode and a cathode. The electrodes each have
an electrode space through which a liquid electrolyte having a
conducting salt dissolved therein is conveyed in a respective
circuit, namely a cathode circuit and an anode circuit. In this
case, the electrode spaces and hence also the electrolytes
contained therein are separated by a membrane. The invention is
distinguished in that the electrolyte is conveyed from one circuit
to the second circuit in a secondary volume flow.
[0019] The method has the same advantages as have already been
discussed in regard to the electrolysis arrangement. The secondary
volume flow described both achieves equalization of the
concentration of ions, anions and cations and also returns water,
which can be in excess in one circuit, to the other circuit without
at the same time producing too strong a mixing of product gases,
such as oxygen and hydrogen or else carbon monoxide, in a common
collecting container.
[0020] In one particular embodiment of the invention, the secondary
volume flow is designed such that it has at least 0.01%, no more
than 10%, advantageously between 0.1% and 1%, of the larger of the
two primary volume flows, that is to say of either the volume flow
of the cathode circuit or of the anode circuit. In this case, it
should be noted that the term secondary volume flow is understood
to mean a flow of molecules and ions, both in regard to the method
and in regard to the electrolyzer arrangement. The secondary volume
flow can take place in applicable pipelines, hoses or else
channels, in the form of a flow of the electrolyte, in particular
water-based with conducting salt contained therein and the
applicable ions. On the other hand, it can also take place in the
form of a diffusion through a membrane. Hence, the term conveyor
apparatus for a secondary volume flow is understood to mean any
apparatus suitable for providing the cited flow of molecules and
ions. This firstly includes an appropriate pump, in particular, but
also an appropriate line, or channel, that produces the secondary
volume flow on the basis of pressure differences or gravity.
Further, the term conveyor apparatus also includes a membrane that
causes ions to be transferred and returned from one circuit to the
other circuit.
[0021] Further, it is expedient for there to be provision for a
vapor deposition container in the cathode circuit and/or in the
anode circuit and for there to be provision for a connecting line
from at least one of the vapor deposition containers to an educt
supply apparatus. This allows anode gas and/or cathode gas, which
can in turn be an educt gas for process reasons, to be supplied to
the actual electrolysis process again. This has a positive
influence on the economical viability of the process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Further embodiments and further features of the invention
emerge from the drawings. These are not a limitation for the
invention, since they merely describe advantageous embodiments. In
the drawings:
[0023] FIG. 1 shows an electrolyzer arrangement having a secondary
volume flow between the anode circuit and the cathode circuit,
[0024] FIG. 2 shows an electrolyzer arrangement as in FIG. 1 having
additional deposition containers,
[0025] FIG. 3 shows an electrolyzer arrangement having two options
for depicting apparatuses for a secondary volume flow having two
collecting containers,
[0026] FIG. 4 shows an electrolyzer arrangement having two options
for depicting apparatuses for a secondary volume flow,
[0027] FIG. 5 shows a schematic depiction of an electrolyzer
arrangement, wherein two collecting containers are in the
foreground, and
[0028] FIG. 6 shows a membrane module.
DETAILED DESCRIPTION OF INVENTION
[0029] FIG. 1 schematically depicts an electrolyzer arrangement 2
that has an electrolysis cell 4 in which an electrolyte 5 is
arranged. The electrolysis cell 4 has two electrodes, a cathode 7,
which in this case is configured in the form of a gas permeable
electrode, and an anode 6. The two electrodes, namely the anode 6
and the cathode 7, each adjoin an electrode space, a distinction
being drawn between an electrode space 8 for the anode 6 and an
electrode space 9 for the cathode 7. The two electrode spaces 8, 9
are separated from one another by a membrane 10. The electrode
spaces contain the electrolyte 5, which, depending on where it is
in the electrolysis cell 4, is referred to as anolyte 38, if it is
in the electrode space 8 of the anode 6, and which is referred to
as catholyte 40 if it is in the electrode space 9 of the cathode
7.
[0030] The electrolyte 5 or 38 and 40 is not in the electrode
spaces 8 and 9 in a stationary manner, but rather is in a circuit
14, 15. To this end, there is provision for conveyor apparatuses 12
and 13, which each provide the applicable volume flow of
electrolyte 5 or 38 and 40 for an anode circuit 14 or a cathode
circuit 15. This involves the electrolyte 5 being moved along the
respective circuit 14 (anode circuit) and 15 (cathode circuit). If
the cathode circuit 15 is now considered in exemplary fashion, the
catholyte 40 is pumped through the conveyor apparatus 13 from the
electrode space 9 of the cathode 7 via the line provided with the
reference sign 15.
[0031] Further, there exists in the electrolyzer arrangement an
educt feed 42 that introduces an educt, for example carbon dioxide,
into the electrolysis cell 4, and a product outlet 44. During the
electrolysis, which involves electric current being applied to the
cathode 7 and to the anode 6, the carbon dioxide is reduced in this
example to carbon monoxide, which leaves the electrolysis cell 4
again via the product outlet 44. During this electrolysis, both
protons and the cations of a conducting salt dissolved in the
electrolyte 5, for example potassium, migrate through the membrane
10, which is in the form of a cation permeable membrane in this
embodiment. This results in the anolyte 38 and the catholyte 40
having different concentrations of cations, in particular cations
of the conducting salt, as electrolysis activity increases. This
can be tolerated up to a certain degree of approximately 2%
difference, the economic viability and profitability of the
electrolysis process no longer being ensured upward of a specific
concentration difference. For this reason, it is expedient to
perform a constant exchange between the anolyte 38 and the
catholyte 40. In accordance with the prior art, in an extremely
simple form, a single collecting container is used that is part of
both the circuit 14, the anode circuit, and the cathode circuit 15.
In a common collecting container, which is not depicted here, good
equalization of concentrations and complete mixing of the
electrolyte 5 enriched or depleted in the electrolysis cell take
place. However, product gases, in particular hydrogen in the
cathode circuit 15 and oxygen from the anode circuit 14, are also
transferred in this common collecting container, which is not
depicted here. This can lead to an explosive mixture; additionally,
product gases, such as carbon monoxide, which are likewise present
in the common collecting container in small amounts, are
contaminated by the gases oxygen and hydrogen.
[0032] To solve this problem, there is provision for a secondary
volume flow 20 to take place, which takes place via a secondary
volume flow apparatus 18. The secondary volume flow results in an
exchange of concentrations taking place between the anode circuit
and the cathode circuit, and vice-versa. The direction in which the
secondary volume flow occurs is dependent on the respective process
control. The secondary volume flow is advantageously no more than
10% of the electrolyte volume flows in the cathode circuit 15 or in
the anode circuit 14. At minimum, the secondary volume flow is
0.01% of the electrolyte volume flow; in particular, the range that
covers the secondary volume flow 20 is between 0.1% an 1% of the
electrolyte volume flows. If the two electrolyte volume flows are
of different magnitude, then the larger of the two electrolyte
volume flows is used as reference for the secondary volume
flow.
[0033] It is expedient in this instance for the pH value of the
anolyte to be between 4 and 5 and for the pH value of the catholyte
to be between 7 and 9 in steady-state operation.
[0034] FIG. 2 provides an analogous configuration of the apparatus
shown in FIG. 1, there being provision in both the cathode circuit
15 and the anode circuit 14 for a respective deposition container
53, 55 in which respective gaseous constituents of the electrolyte
can be removed. In the case of the deposition container 53, for
example deposited carbon dioxide can be supplied to the educt
supply apparatus 42 again.
[0035] In FIG. 3, there is provision for the cathode circuit 15 to
have a collecting container 23 in which the catholyte 40 is
conveyed and for the anode circuit 14 to have a collecting
container 22 into which the anolyte 38 is put. The two collecting
containers 23 and 22 are fundamentally separate from one another,
and they likewise have, but in a different embodiment, an apparatus
18 that is used to produce a secondary volume flow 20. This
apparatus 18 is depicted highly schematically in FIG. 3; it can be
configured in the form of an overflow channel, for example, that
allows a small amount to get from one container to the other
collecting container by means of a defined gradient or a defined
slope. It is also possible for an appropriate pipeline, not
depicted here, or an appropriate hose to cause a secondary volume
flow 20 between the containers 22 and 23, said flow being brought
about by gravity or else by a pressure difference, for example.
[0036] FIG. 5 depicts an apparatus 18 for producing the secondary
volume flow 20, said apparatus being provided in the form of
pipelines that incorporate a pump 30. In this case, as shown in
FIG. 5, it can also be expedient, in order to ensure equalization
of concentrations between the anolyte 38 and the catholyte 40 in
regard to the anions, for there to be provision for a second
secondary volume flow 26 produced by a second conveyor apparatus
24, for example in the pump apparatus 30 shown in FIG. 5. In this
case, it is also expedient for the two subcontainers 22, 23 to
contain stirring apparatuses 27 that ensure uniform mixing of the
electrolyte 38, 40 in the respective containers 22 and 23. It goes
without saying that it is likewise possible to achieve good mixing
inside the subcontainers without active stirring apparatuses, e.g.
by means of a suitable flow guide.
[0037] If the membrane 10 used is a cation permeable membrane, a
particularly large number of cations from the conducting salt
migrate from the anode side, that is to say from the anolyte 38
that is in the electrode space 8 of the anode 6, through the
membrane 10 to the electrode space 9 of the cathode 7. Together
with the cations, water, what is known as drag water, also migrates
through the membrane, so that equalization in particular from the
cathode circuit 15 to the anode circuit 14 is necessary. In this
case, when a cation permeable membrane is used, the first secondary
volume flow from the cation circuit 15 to the anode circuit 14
therefore takes place. This advantageously takes place between the
collecting container 23 of the cathode circuit 15 and the
collecting container 22 of the anode circuit 14, specifically in
the direction described. The second secondary volume flow is then
used to equalize anions that ensue between the container 22 and the
container 23 via the second secondary volume flow 26.
[0038] A further option for producing a secondary volume flow
exists in the form of a membrane module 28 in which a membrane 29
is arranged (cf. FIGS. 3 and 4). Both the cathode circuit 15 and
the anode circuit 14 pass through this membrane module 28 as shown
in FIG. 3. In this case, the membrane module 28 has not only the
membrane 29 but also two module chambers, a first module chamber 46
through which the anode circuit 14 runs and a second module chamber
47 through which the cathode circuit 15 goes. The module chamber 47
therefore contains the catholyte 40 and the module chamber 46
contains the anolyte 38. The membrane 29 in this case provides an
exchange area for the dissolved ions in the electrolytes 38 and 40,
specifically for cations and for anions. Porous membranes that are
as thin as possible are particularly well suited to this task.
These introduce a relatively low transport resistance, which means
that comparatively small membrane areas are adequate. The transport
in porous membranes (permeation) is caused by two different
mechanisms, an externally enforced transport through pores, that is
to say a purely convected transport, or a transport on the basis of
diffusion of a dissolved component. The transport mechanism for the
ions through the porous membrane corresponds to the diffusion,
which takes place without energy consumption. What is known as the
drag water can also be pushed through the membrane by convection,
in principle, by applying a small differential pressure.
[0039] The necessary size of the porous membrane 29 can be
ascertained by means of the maximum material flow rate of cations
to be expected inside the electrolysis cell by at the same time
stipulating a maximum tolerable concentration difference between
the anolyte 38 and the catholyte 40 (for example 0.2 mol/l). With
the aid of known passage coefficients, it is possible to estimate
that when thin porous membranes 29 are used, the membrane module 28
can be configured to be distinctly smaller than the area provided
therefor in the electrolysis cell 4 or the membrane 10 stretched
therein. The entire membrane area of the membrane 29 is smaller
than the entire electrolysis cell area of the membrane 10, but is
at least one hundredth of the membrane area of the membrane 10. A
ratio of from 1:20 between the membrane 29 and the membrane 10 to
1:5 between the membrane 29 and the membrane 10 is particularly
advantageous.
[0040] The porous membrane 29 also allows water to be transported,
in principle, by virtue of a lower differential pressure prevailing
inside the membrane module 28. Said pressure is advantageously less
than 100 mbar.
[0041] The entire arrangement described allows intermixing of the
gases produced during the carbon dioxide electrolysis of the
electrolysis cell 4 to be avoided, as a result of which complex
conditioning of the electrolyte 5 or of the gases produced is
dispensed with. By way of example, the catholyte 40 therefore
contains no oxygen that contaminates the catholyte product gas.
Additionally, neither product gas (for example carbon monoxide,
methane or hydrogen) nor educt gas such as carbon dioxide is lost
via the anolyte 38 in practice.
[0042] Use of two separate electrolysis circuits, namely the anode
circuit 14 and the cathode circuit 15, cannot prevent a certain
amount of drifting apart by the compositions and hence also by the
pH values of the anolyte 38 and the catholyte 40. In addition, drag
water from the anolyte 38 gets into the catholyte 40. Conventional
conditioning would have a high level of associated energy
expenditure, e.g. as a result of thermal degassing or vacuum
degassing. Alternatively, the process can also have an additive
added that chemically binds unwanted gases. The use of an additive
has associated costs, however. In addition, it is not foreseeable
to what extent possible additives influence the electrochemical
process. The catalytic removal of undesirable gases likewise has a
high level of associated energy expenditure. The arrangement
described therefore shows a simple technical solution to ensure
appropriate equalization of ions and water between the anode
circuit 14 and the cathode circuit 15.
* * * * *