U.S. patent application number 16/754981 was filed with the patent office on 2020-09-17 for arrangement for the electrolysis of carbon dioxide.
This patent application is currently assigned to Siemens Aktiengesellschaft. The applicant listed for this patent is Siemens Aktiengesellschaft. Invention is credited to Philippe Jeanty, Erhard Magori, Remigiusz Pastusiak, Christian Scherer, Kerstin Wiesner-Fleischer.
Application Number | 20200291537 16/754981 |
Document ID | / |
Family ID | 1000004896533 |
Filed Date | 2020-09-17 |
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United States Patent
Application |
20200291537 |
Kind Code |
A1 |
Jeanty; Philippe ; et
al. |
September 17, 2020 |
ARRANGEMENT FOR THE ELECTROLYSIS OF CARBON DIOXIDE
Abstract
An arrangement for the electrolysis of carbon dioxide, includes:
an electrolytic cell having an anode and a cathode, wherein the
anode and cathode are connected to a voltage supply, wherein the
cathode is configured as a gas diffusion electrode to which a gas
compartment is attached on a first side and a cathode compartment
is attached on a second side; an electrolyte circuit connecting to
the electrolytic cell; and a gas supply for supplying carbon
dioxide-containing gas into the gas compartment, wherein one or
more channels are arranged in the gas compartment, wherein the
channels are at least partially in contact with the gas diffusion
electrode and are configured for transporting electrolyte fluid
passing through the gas diffusion electrode to a lateral region of
the gas compartment.
Inventors: |
Jeanty; Philippe; (Munchen,
DE) ; Magori; Erhard; (Feldkirchen, DE) ;
Pastusiak; Remigiusz; (Munchen, DE) ; Scherer;
Christian; (Unterschlei heim, DE) ;
Wiesner-Fleischer; Kerstin; (Hohenkirchen-Siegertsbrunn,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Siemens Aktiengesellschaft |
Munich |
|
DE |
|
|
Assignee: |
Siemens Aktiengesellschaft
Munich
DE
|
Family ID: |
1000004896533 |
Appl. No.: |
16/754981 |
Filed: |
October 15, 2018 |
PCT Filed: |
October 15, 2018 |
PCT NO: |
PCT/EP2018/078031 |
371 Date: |
April 9, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 3/04 20130101; C25B
15/08 20130101; C25B 9/08 20130101 |
International
Class: |
C25B 15/08 20060101
C25B015/08; C25B 9/08 20060101 C25B009/08; C25B 3/04 20060101
C25B003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 7, 2017 |
DE |
10 2017 219 766.8 |
Claims
1. An arrangement for carbon dioxide electrolysis, comprising an
electrolysis cell having an anode and a cathode, where anode and
cathode are connected by a power supply, where the cathode is
configured as a gas diffusion electrode adjoined on a first side by
a gas space and on a second side by a cathode space, an electrolyte
circuit adjoining the electrolysis cell, a gas feedfor supply of
carbon dioxide-containing gas to the gas space, characterized in
that there are one or more channels disposed in the gas space,
where the channels at least partly adjoin the gas diffusion
electrode and are configured for transport of electrolyte liquid
penetrating through the gas diffusion electrode to a side region of
the gas space.
2. The arrangement as claimed in claim 1, in which the channels
have an essentially linear configuration and an oblique arrangement
with an angle to the horizontal between 1.degree. and
30.degree..
3. The arrangement as claimed in claim 1, in which the distance
between the channels is between 3 cm and 10 cm.
4. The arrangement as claimed in claim 1, in which the channels are
connected by a common support structure, where the support
structure is spaced apart from the gas diffusion electrode.
5. The arrangement as claimed in claim 1, in which the support
structure has one or more support pins in mechanical contact with
the surface of the gas diffusion electrode.
6. The arrangement as claimed in claim 5, in which the support pins
have a diameter of less than 1 mm.
7. The arrangement as claimed in claim 1, in which at least some of
the support pins have vortexing elements arranged at a distance
from the surface of the gas diffusion electrode of at least 1 mm,
especially at least 2 mm.
8. The arrangement as claimed in claim 7, in which the vortexing
elements have a corrugated configuration.
9. The arrangement as claimed in claim 1, in which the support
structure, the support pins and/or the channels comprise a material
having low hydrophobicity, for example PE.
10. The arrangement as claimed in claim 1, having an electrically
conductive material for contacting the gas diffusion electrode.
11. The arrangement as claimed in claim 1, in which the support
structure and/or the channels comprise an electrically conductive
material for contacting the gas diffusion electrode.
12. The arrangement as claimed in claim 5, in which the support
pins comprise an electrically conductive material for contacting
the gas diffusion electrode.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2018/078031 filed 15 Oct. 2018, and claims
the benefit thereof. The International Application claims the
benefit of German Application No. DE 10 2017 219 766.8 filed 7 Nov.
2017. All of the applications are incorporated by reference herein
in their entirety.
FIELD OF INVENTION
[0002] The invention relates to an arrangement for carbon dioxide
electrolysis.
BACKGROUND OF INVENTION
[0003] The combustion of fossil fuels currently covers about 80% of
global energy demand. These combustion processes in 2011 emitted
around 34 000 million tonnes of carbon dioxide into the atmosphere
globally.
[0004] Discussion about the adverse effects of the greenhouse gas
CO2 on the climate has led to consideration of reutilization of
CO2. CO2 is a strongly bonded molecule and can therefore be reduced
back to usable products only with difficulty.
[0005] In nature, CO2 is converted to carbohydrates by
photosynthesis. This complex process can be reproduced on the
industrial scale only with great difficulty. One currently
technically feasible route is the electrochemical reduction of CO2.
The carbon dioxide is converted here with supply of electrical
energy to a product of higher energy value, for example CO, CH4,
C2H4 or C1-C4 alcohols. The electrical energy in turn
advantageously comes from renewable energy sources such as wind
power or photovoltaics.
[0006] For electrolysis of CO2, in general, metals are used as
catalysts. The type of metal affects the products of the
electrolysis. For example, CO2 is reduced virtually exclusively to
CO over Ag, Au, Zn and, to a limited degree, over Pd and Ga,
whereas a multitude of hydrocarbons are observed as reduction
products over copper. As well as pure metals, metal alloys are also
of interest, as are mixtures of metal and metal oxide having
cocatalytic activity, since these can increase selectivity for a
particular hydrocarbon.
[0007] In CO2 electrolysis, a gas diffusion electrode can be used
as cathode in a similar manner to that in chlor-alkali electrolysis
in order to establish a three-phase boundary between the liquid
electrolyte, the gaseous CO2 and the solid silver particles. This
is done using an electrolysis cell, as also known from fuel cell
technology, having two electrolyte chambers, wherein the
electrolyte chambers are separated by an ion exchange membrane.
[0008] The working electrode is a porous gas diffusion electrode
(GDE). It typically comprises a metal mesh, to which a mixture of
PTFE, activated carbon, a catalyst and further components has been
applied. It has a pore system into which the reactants penetrate
and react at the three-phase interfaces.
[0009] The counterelectrode is sheet metal coated, for example,
with platinum or a mixed iridium oxide. The GDE is in contact with
the electrolyte on one side. On the other side it is supplied with
CO2. The mode of function of a GDE is known, for example, from EP
297377 A2, EP 2444526 A2 and EP 2410079 A2.
[0010] For a continuous process, the electrolysis cell can be
operated in flow-by mode. In this mode, the reactant gas diffuses
into the pores of the GDE. The reaction in the pores of the GDE
forms OH.sup.- ions that cause a locally high pH. If the reactant
gas CO2 meets this alkaline liquid that additionally also contains
alkali metal cations, for example potassium, sparingly soluble
carbonates are formed, which precipitate out in salt form and block
the pores.
[0011] There are various ways of avoiding this, including the
utilization of the transpiration of the electrolyte through the
GDE. This clears the pores in situ, runs off downward on the gas
side of the GDE and is discharged from the cell at the base of the
cell together with the unconverted reactant gas and the product
gases.
[0012] In order to bring about good mixing of the gas in the gas
space and hence promote diffusion of the carbon dioxide into the
pores of the GDE, flow grids are used. These ensure vortexing and
crossmixing and hence promote the mass transfer of reactant and
product gases. Furthermore, the flow grids support the GDE, such
that it cannot bend.
[0013] Although this enables stable long-term operation (>1000
h) of the gas diffusion electrode in CO2 electrolysis, the high
liquid content in the gas space reduces the efficiency of the
process. Firstly, the liquid film on the GDE makes it difficult for
the reactant gases to diffuse into the pores of the GDE.
Furthermore, known flow grids in the form of grid structures or
knits make it difficult for the transpiration liquid to flow away
since it adheres to and accumulates in the flow grids.
SUMMARY OF INVENTION
[0014] It is an object of the present invention to specify an
improved arrangement for carbon dioxide electrolysis, by which
stable long-term operation is enabled with avoidance of the
disadvantages mentioned at the outset.
[0015] This object is achieved by an arrangement having the
features of the independent claim. The dependent claims relate to
advantageous configurations of the arrangement.
[0016] The arrangement of the invention for carbon dioxide
electrolysis comprises an electrolysis cell having an anode and a
cathode, where anode and cathode are connected by a power supply,
where the cathode is configured as a gas diffusion electrode
adjoined on a first side by a gas space and on a second side by a
cathode space. The arrangement for carbon dioxide electrolysis
further comprises an electrolyte circuit adjoining the electrolysis
cell and a gas feed for supply of carbon dioxide-containing gas to
the gas space. Finally, the arrangement for carbon dioxide
electrolysis comprises one or more channels in the gas space, where
the channels at least partly adjoin the gas diffusion electrode and
are configured for transport of electrolyte liquid penetrating
through the gas diffusion electrode to a side region of the gas
space.
[0017] The channels advantageously bring about removal of
electrolyte that penetrates through the cathode as transpiration
liquid and wets the surface of the gas diffusion electrode. If the
electrolyte layer on the surface of the gas diffusion electrode is
thick enough, the electrolyte begins to run off. The channels guide
the electrolyte away to the side and hence reduce the thickness of
the electrolyte layer in the region beneath a respective channel.
This creates better access for the carbon dioxide to the surface of
the gas diffusion electrode and hence enables an improvement in
electrolysis efficiency.
[0018] Furthermore, the channels, by virtue of their position and
arrangement, also ensure flow resistance for the carbon dioxide
flowing across the surface of the gas diffusion electrode. This
interrupts the laminar flow of the gas and generates vortices. This
likewise brings about better utilization of the carbon dioxide
present in the gas.
[0019] Advantageous configurations of the arrangement of the
invention for carbon dioxide electrolysis are apparent from the
dependent claims. The embodiment according to the independent claim
can be combined here with the features of one of the dependent
claims or else with those from multiple dependent claims.
Accordingly, the following features may additionally be provided
for the arrangement: [0020] The channels may have an essentially
linear configuration and an oblique arrangement with an angle to
the horizontal between 1.degree. and 30.degree., especially between
1.degree. and 10.degree.. [0021] According to the basic length of
the vertical extent of the gas diffusion electrode, a channel may
be present, where the basic length is between 3 cm and 10 cm. In
other words, the distance between the channels is between 3 cm and
10 cm. [0022] The channels are advantageously connected by a common
support structure, where the support structure is spaced apart from
the gas diffusion electrode. This enables anchoring and mechanical
integrity for the channels independently of the cathode since the
channels are retained by the support structure. However, the
support structure does not prevent the access of gas to the surface
of the gas diffusion electrode. [0023] The support structure has
one or more support pins in mechanical contact with the surface of
the gas diffusion electrode. This enables better mechanical
strength for the support structure. [0024] The support pins
advantageously have a diameter of less than 1 mm. This achieves the
effect that the surface coverage of the gas diffusion electrode by
the support pins is small and hence the support pins have only a
minor influence on the electrolysis. [0025] It is particularly
advantageous when at least some of the support pins have vortexing
elements arranged at a distance from the surface of the gas
diffusion electrode of at least 1 mm, especially at least 2 mm. As
a result, the gas stream that otherwise flows across the surface of
the gas diffusion electrode in a largely laminar manner experiences
vortexing, which distinctly improves the access of the carbon
dioxide to the cathode. At the same time, the distance from the
surface of the cathode ensures that electrolyte does not collect on
the surface of the vortexing elements and hence is prevented from
running off. The vortexing elements may have a corrugated
configuration, for example. [0026] The support structure, the
support pins and/or the channels advantageously comprise a material
having low hydrophobicity, for example PE. This material
advantageously constitutes the surface of the individual elements,
for example as a coating. Alternatively, it is possible for the
support structure, the support pins and/or the channels to be
largely or entirely made from the material. As a result, the liquid
is distributed more easily over the material surface and the runoff
of the liquid is facilitated. [0027] The support structure, the
support pins and/or the channels may also have an electrically
conductive material for contacting the gas diffusion electrode. In
the case of the connection of multiple cells to form what is called
a stack, it is possible in this way, via the flow grid formed from
support structure, support pins, vortexing elements and channels,
to electrically connect a cell unit to the next cell unit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] An advantageous, but in no way limiting, working example of
the invention will now be elucidated in detail with reference to
the figures of the drawing. The features are shown here in
schematic form. The figures show:
[0029] FIG. 1 an electrolysis system for CO2 electrolysis and
[0030] FIGS. 2 and 3 a side view and a top view of a flow grid.
DETAILED DESCRIPTION OF INVENTION
[0031] The structure of an electrolysis cell 11 shown in schematic
form in FIG. 1 is typically suitable for undertaking carbon dioxide
electrolysis. This embodiment of the electrolysis cell 11 comprises
at least one anode 13 with an adjacent anode space 12, and a
cathode 15 and an adjacent cathode space 14. Anode space 12 and
cathode space 14 are separated from one another by a membrane 21.
The membrane 21 is typically manufactured from a PTFE-based
material. According to the electrolyte solution used, another
conceivable structure is one without a membrane 21, in which case
pH adjustment extends beyond that by the membrane 21.
[0032] Anode 13 and cathode 15 are electrically connected by a
power supply 22, which is controlled by the control unit 23. The
control unit 23 may apply a protective voltage or an operating
voltage to the electrodes 13, 15, i.e. the anode 13 and the cathode
15. The anode space 12 of the electrolysis cell 11 shown is
equipped with an electrolyte inlet. The anode space 12 depicted
likewise comprises an outlet for electrolyte and, for example,
oxygen O.sub.2 or another gaseous by-product which is formed at the
anode 13 in carbon dioxide electrolysis. The cathode space 14
likewise in each case has at least one product and electrolyte
outlet. It is possible here for the overall electrolysis product to
be composed of a multitude of electrolysis products.
[0033] The electrolysis cell 11 is also executed in a three-chamber
structure in which the carbon dioxide CO.sub.2 is introduced into
the cathode space 14 via the cathode 15 in the form of a gas
diffusion electrode. Gas diffusion electrodes enable contacting of
a solid catalyst, a liquid electrolyte and a gaseous electrolysis
reactant with one another. For this purpose, for example, the
catalyst may be porous and may assume the electrode function, or a
porous electrode assumes the catalyst function. The pore system of
the electrode is such that the liquid and gaseous phases can
equally penetrate into the pore system and may be present
simultaneously therein or at its electrically accessible surface.
One example of a gas diffusion electrode is an oxygen-depolarized
electrode which is used in chlor-alkali electrolysis.
[0034] For configuration as a gas diffusion electrode, the cathode
15 in this example comprises a metal mesh to which a mixture of
PTFE, activated carbon and a catalyst has been applied. For
introduction of the carbon dioxide CO2 into the catholyte circuit,
the electrolysis cell 11 comprises a carbon dioxide inlet 24 into
the gas space 16. The carbon dioxide in the gas space 16 reaches
the cathode 15, where it can penetrate into the porous structure of
the cathode 15 and hence react.
[0035] In addition, the arrangement 10 comprises an electrolyte
circuit 20 by means of which the anode space 12 and the cathode
space 14 are supplied with a liquid electrolyte, for example K2SO4,
KHCO3, KOH, Cs2SO4, and the electrolyte is returned to a reservoir
19. The electrolyte is circulated in the electrolyte circuit 20 by
means of an electrolyte pump 18.
[0036] The gas space 16 in the present example comprises an outlet
25 disposed in the base region. The outlet 25 is configured as an
opening of sufficient cross section such that both electrolyte that
passes through the cathode 15 and carbon dioxide and product gases
can pass through the outlet into the connected tube. The outlet 25
leads to an overflow vessel 26. The liquid electrolyte is collected
and accumulates in the overflow vessel 26. Carbon dioxide and
product gases coming from the gas space 16 are separated from the
electrolyte and accumulate above it.
[0037] From a point at the upper end of the overflow vessel 26, a
further pipe 28 leads to a pump 27, a membrane pump in this working
example, and further to the gas feed 17. The pump 27 may also be a
piston pump, reciprocating pump, extruder pump or gear pump. Part
of the gas feed 17, the gas space 16, the pipe 28 and the overflow
vessel 26 together with its connection to the outlet 25 thus
collectively form a circuit. By means of the pump 27, the carbon
dioxide and product gases present are guided from the overflow
vessel 26 back into the gas feed and hence the gas is partly
circulated. The volume flow rate of the pump 27 here is distinctly
higher than the volume flow rate of new carbon dioxide. As yet
unconsumed reactant gas is thus advantageously guided once more
past the cathode 15 and has one or more further opportunities to be
reduced. Product gases are likewise partly circulated here. The
repeated guiding of the carbon dioxide past the cathode 15
increases the efficiency of the conversion.
[0038] There is a further connection from the overflow vessel 26
that leads back to the electrolyte circuit 20. This connection
begins with an outlet 29 disposed on a side wall of the overflow
vessel 26, advantageously close to the base, but not in the base.
The outlet 29 is connected to a throttle 30 in the form of a
vertical pipe section having a length of 90 cm, for example. The
diameter of this pipe section is much greater than that of the
feeds to the throttle 30. The feed has, for example, an internal
diameter of 4 mm; the pipe section has an internal diameter of 20
mm. The throttle 30 is connected to the electrolyte circuit 20 on
the outlet side, i.e. at the upper end of the pipe section.
[0039] In the course of operation, the throttle 30 establishes and
maintains a pressure differential between the electrolyte circuit
20 connected at the upper end and hence also the cathode space 14
on the one hand, and the overflow vessel 26 and the gas space 16 on
the other hand. This pressure differential is between 10 and 100
hPa, meaning that the gas space 16 remains at only a slightly
elevated pressure relative to the cathode space 14.
[0040] When the electrolysis is started, in spite of the slightly
elevated pressure on the gas side, i.e. in the gas space 16,
electrolyte is "pumped" out of the catholyte space 14 through the
gas diffusion electrode, i.e. the cathode 15, in the direction of
gas space 16 on account of the electrical potential applied at the
cathode 15. Droplets arise at the surface of the cathode 15 on the
side of the gas space 16, which coalesce and collect in shape in
the lower region of the cathode 15.
[0041] The OH.sup.- ions passing through the cathode 15 do cause
salt formation together with the carbon dioxide and the alkali
metal cations from the electrolyte, but the pressure differential
at the cathode 15 is so small that sufficient liquid is purged
through the cathode 15 and brings the salt formed into solution,
washes it away permanently and transports it out of the gas space
16 into the overflow vessel 26. A further pressure rise that would
lead to crystallization of the salt formed is prevented by the
throttle 30.
[0042] A flow grid 40 is disposed on the gas diffusion electrode.
This flow grid 40 is arranged such that the gas flow between the
carbon dioxide inlet 24 and the outlet 25 is between the surface of
the gas diffusion electrode and a support structure 41 of the flow
grid 40. The specific construction of the flow grid 40 is shown in
FIG. 2 and FIG. 3.
[0043] FIG. 2 shows an enlarged side view of the flow grid 40. The
flow grid 40 adjoins the cathode 15 by the right-hand side in FIG.
2. FIG. 3 shows a top view of the flow grid 40 from the side of the
cathode 15.
[0044] The flow grid 40 comprises a support structure composed of
struts or plates that mechanically connects the further elements.
The flow grid 40 is concluded on the outside by an essentially
rectangular frame 46 that permits gas access and gas exit only at
orifices 47 and 48. In the region of the orifices 47, 48, the flow
grid 40 has parallel ridges 50 aligned in gas flow direction and
one or more baffles 49 to shape the gas flow.
[0045] In a middle region of the flow grid 40 is disposed a
multitude of support pins 42. The support pins 42 serve to increase
the mechanical strength of the flow grid and bring about a fixed
minimum distance of the support structure 41 from the surface of
the gas diffusion electrode. In the present example, 8 horizontal
rows of 9 and 10 support pins 42 in alternation are present. The
support pins 42 have a distance from one another of about 6 mm. In
other executions of the flow grid 40, therefore, it is also
possible for more support pins 42 or fewer support pins 42 to be
present, according to the size of the flow grid 40. The distance
between the support pins 42 is advantageously between 3 mm and 12
mm. The support pins should cover not more than 10% of the area of
the gas diffusion electrode, the coverage advantageously being less
than 5%.
[0046] At a distance from the surface of the cathode 15 of 1.5 mm,
or in another example of 2.5 mm, a vortexing element 43 is disposed
on each of the support pins 42. The vortexing elements 43 in the
present example are in the form of a flat, essentially rectangular
piece of material, but one that has been bent to form a
corrugation. The vortexing elements 43 are arranged essentially
transverse to the main flow direction of the gas. By virtue of
their shape and the remaining flow regions between the vortexing
elements 43, the gas flow is made turbulent to a considerable
degree, i.e. laminar flow past the gas diffusion electrode is
eliminated.
[0047] Likewise in the middle region of the flow grid 40, the flow
grid 40 also has two channels 44. The channels 44 are secured to
multiple support pins 42 in each case and arranged such that they
adjoin the surface of the gas diffusion electrode. They are
arranged at a small angle from the horizontal of 10.degree., for
example, i.e. are not entirely horizontal. By virtue of their
arrangement on the surface of the cathode 15, they take up
transpiration liquid, i.e. electrolyte passing through the cathode
15, that runs off downward at the surface of the cathode 15, and
transport the liquid to the side by virtue of their inclination. At
the side of the flow grid 40, the channels 44 in the frame 41
conclude in a runoff channel 45 that allows the liquid to run off
downward to the orifice 48. This achieves the effect that the
transpiration liquid wets the surface of the cathode 15 to a lesser
degree and hence the entry of gas into the pores of the gas
diffusion electrode is hindered to a lesser degree.
[0048] Just as in the case of the support pins 42, the number of
channels 44 depends on the total size of the flow grid 40 and hence
on the size of the cathode 15. The channels are advantageously
arranged at a distance from one another of between 3 cm and 10
cm.
[0049] In the present example, the flow grid 40 has been
manufactured from polyethylene to a significant degree. In other
execution variants, it is possible to choose other materials,
advantageously having low hydrophobicity. The flow grid 40 may be
manufactured wholly or essentially from the material, or the
material is applied as a surface coating. By virtue of the low
hydrophobicity, the contact angle between the flow grid 40 and the
material is minimized, such that the liquid is distributed over the
material surface and the best possible runoff is assured.
* * * * *