U.S. patent application number 17/711281 was filed with the patent office on 2022-07-21 for systems and methods for variable pressure electrochemical carbon dioxide reduction.
The applicant listed for this patent is Air Company Holdings, Inc.. Invention is credited to Stafford W. Sheehan.
Application Number | 20220228275 17/711281 |
Document ID | / |
Family ID | |
Filed Date | 2022-07-21 |
United States Patent
Application |
20220228275 |
Kind Code |
A1 |
Sheehan; Stafford W. |
July 21, 2022 |
SYSTEMS AND METHODS FOR VARIABLE PRESSURE ELECTROCHEMICAL CARBON
DIOXIDE REDUCTION
Abstract
Electrochemical devices, such as membrane electrode assemblies
and electrochemical reactors, are described herein, as well as and
methods for the conversion of reactants such as carbon dioxide to
value-added products such as ethanol. In certain aspects, the
membrane electrode assemblies are configured to allow for
distributed pressure along the cathodic side of a membrane
electrode assembly is described. The pressure vessel acts as a
cathode chamber, both for the feed of reactant carbon dioxide as
well as collection of products. The designs described herein
improves the safety of high pressure electrochemical carbon dioxide
reduction and allows for varied pressures to be used, in order to
optimize reaction conditions. Configurations optimized for
producing preferred products, such as ethanol, are also
described.
Inventors: |
Sheehan; Stafford W.;
(Tiverton, RI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Air Company Holdings, Inc. |
Brooklyn |
NY |
US |
|
|
Appl. No.: |
17/711281 |
Filed: |
April 1, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16383373 |
Apr 12, 2019 |
11293107 |
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17711281 |
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PCT/US2017/056589 |
Oct 13, 2017 |
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16383373 |
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62468676 |
Mar 8, 2017 |
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62433828 |
Dec 14, 2016 |
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62408172 |
Oct 14, 2016 |
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International
Class: |
C25B 3/25 20060101
C25B003/25; C12G 3/04 20060101 C12G003/04; C25B 15/08 20060101
C25B015/08; C12G 3/00 20060101 C12G003/00; C25B 9/00 20060101
C25B009/00; C25B 9/77 20060101 C25B009/77 |
Claims
1. An electrochemical cell, comprising: an electrode assembly
comprising; an anode endplate; a cathode endplate; and a polymer
electrolyte membrane having a cathodic side and an anodic side
disposed between the anode endplate and the cathode endplate; and a
fluid surrounding the electrode assembly: wherein the cathodic side
of the polymer electrolyte membrane is in open fluid communication
with the fluid surrounding the electrode assembly.
2. The electrochemical cell of claim 1, further comprising a
cathode catalyst disposed on the cathodic side of the polymer
electrolyte membrane.
3. (canceled)
4. (canceled)
5. An electrochemical reactor, comprising: a pressure vessel; and
an electrode stack comprising one or more electrochemical cells
according to claim 1.
6. The electrochemical reactor of claim 5, wherein the cathodic
side of the polymer electrolyte membrane is open to the atmosphere
of the pressure vessel.
7. The electrochemical reactor of claim 5, wherein the electrode
stack is completely contained within the pressure vessel.
8. The electrochemical reactor of claim 5, wherein the pressure
vessel comprises a reactant input fitting and a product output
fitting.
9-15. (canceled)
16. The electrochemical cell of claim 1, wherein the fluid
surrounding the electrode assembly is a catholyte comprising
CO.sub.2.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of International Patent
Application No. PCT/US2017/056589, filed Oct. 13, 2017, which
claims the benefit of U.S. Provisional Patent Application No.
62/408,172, filed Oct. 14, 2016, U.S. Provisional Patent
Application No. 62/433,828, filed Dec. 14, 2016, and U.S.
Provisional Patent Application No. 62/468,676, filed Mar. 8, 2017,
the contents of each of which are fully incorporated by reference
herein in their entireties.
BACKGROUND OF THE INVENTION
[0002] Plants use photosynthesis to convert carbon dioxide, water,
and solar energy into chemical energy by creating sugars and other
complex hydrocarbons. This effectively stores the energy in
absorbed photons from the sun in the chemical bonds of a
carbon-based compound. This process has been supporting the Earth's
ecosystem and balancing carbon dioxide concentration in our
atmosphere for billions of years, and humans use this process to
grow crops for food and chemical production.
[0003] In the last century, human beings have harnessed byproducts
of photosynthesis, such as fossil fuels, to provide the energy
required for modern life. Since the industrial revolution, human
activity has released millions of tons of carbon dioxide into the
Earth's atmosphere. To counteract these emissions, researchers have
been attempting to find processes that can sequester carbon dioxide
into the chemical bonds of carbon-based compounds. However, methods
of efficiently transforming carbon dioxide into useful chemicals
are still needed.
SUMMARY OF THE INVENTION
[0004] In certain aspects, the present disclosure provides an
electrode assembly comprising an anode endplate; a cathode
endplate; a polymer electrolyte membrane having a cathodic side and
an anodic side disposed between the anode endplate and the cathode
endplate; and a cathode catalyst disposed on the cathodic side of
the polymer electrolyte membrane; wherein the cathode endplate is
configured to allow the cathodic side of the polymer electrolyte
membrane to be in fluid communication with a fluid surrounding the
electrode assembly
[0005] In certain aspects, the present disclosure provides an
electrochemical reactor, comprising a pressure vessel; an electrode
stack comprising one or more electrode assemblies; wherein the
cathodic side of the polymer electrolyte membrane is open to the
atmosphere of the pressure vessel.
[0006] In certain aspects, the present disclosure provides a method
for electrochemical reduction of carbon dioxide using an electrode
assembly or an electrochemical reactor comprising an electrode
assemble, comprising supplying a catholyte comprising CO.sub.2 to
the cathodic side of the polymer electrolyte membrane; supplying an
anolyte comprising water to the anodic side of the polymer
electrolyte membrane; and applying a voltage between the anode
endplate and the cathode endplate, thereby reducing the CO.sub.2 to
a CO.sub.2 reduction product. In certain embodiments, the reduction
product comprises ethanol.
[0007] In certain aspects, the present disclosure provides a method
for producing an alcoholic beverage, comprising mixing ethanol
produced by the above methods with a beverage ingredient.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 shows a simplified flow diagram for the case of flue
gas emissions from a coal-fired power plant in a CO.sub.2 reduction
process. First, flue gas is purified to remove soot and potential
catalyst poisons or membrane fouling agents. It is then fed into
the cathode chamber of an electrochemical system, where it is
combined with protons supplied via the water oxidation half
reaction and electrons from a DC power source to form the
products.
[0009] FIG. 2 shows one embodiment of an exemplary electrochemical
system of the present disclosure, which includes an MEA stack with
cathodes open to the pressure vessel and an anode feed that is not
open to the pressure vessel. Carbon dioxide under high pressure is
flowed into the cathode chamber, and may be moistened to assist
membrane hydration and product formation at the MEAs. Variable
temperature at the stacks (due to overpotential heat loss) and at
the bottom of the pressure vessel allow for product collection.
[0010] FIG. 3 shows the internal configuration of an individual MEA
in an electrolyzer stack or electrolysis unit, showing individual
components and how the feed reactants (water from the anode feed
and moistened carbon dioxide from the cathode feed) can be
transported to the anode and cathode gas diffusion layers and
electrodes of the membrane electrode assembly by directed flow. The
flow field patterns may be any pattern that maximizes contact
between the anolyte (water) or catholyte (carbon dioxide) and the
membrane electrode assembly and allows for transportation of
products (oxygen gas, ethanol, and other byproducts) out of the
system, such as a serpentine pattern or a parallel pattern.
[0011] FIG. 4 shows the internal configuration of an electrolysis
unit in which the cathode side of the membrane is open to the
atmosphere of the pressure vessel. The channels in the cathode
endplate are open to allow CO.sub.2 to reach the membrane by
diffusion, or by flowing through the channels at a very low
pressure drop, as could be caused by a low-power fan.
[0012] FIG. 5 shows an external view of an exemplary reactor that
uses high pressure carbon dioxide as a reactant to produce
ethanol.
[0013] FIG. 6 shows an external view of the lid of an exemplary
reactor, where the reactants carbon dioxide and water are fed in
and positive and negative terminals for the cathode and anode are
provided for connection with a DC power source.
[0014] FIG. 7 shows a view of the inside of an exemplary reactor,
which contains an electrolysis unit having the internal
configuration depicted in FIG. 4 and an outlet through with ethanol
product can be collected.
[0015] FIG. 8 shows the peripheral systems around the reactor that
support the high pressures on either side of the membrane. Carbon
dioxide is fed directly into the system, while water is
recirculated in an external loop to ensure consistent pressure
across the anode flow plate.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present disclosure provides apparatus and methods for
reducing carbon dioxide to carbon dioxide reduction products. In
general form, the reaction that takes place is:
xCO.sub.2+yH.sub.2O.fwdarw.Products+zO.sub.2
Where x, y, z are stoichiometric coefficients and are dependent on
the products being made by the carbon dioxide reduction reaction.
Common products of this reaction include, but are not limited to,
CO, HCO.sub.2H, HCHO, CH.sub.3OH, CH.sub.4, CH.sub.3CH.sub.2OH,
CH.sub.3CH.sub.3.
[0017] Electrocatalytic carbon dioxide reduction operates using
electricity as the energy source to drive the reduction of carbon
dioxide at a cathode, coupled with an anodic half-reaction that
provides electrons and protons required to reduce carbon dioxide.
The oxidative process at the anode is typically water oxidation,
similar to what takes place in plants, and can rapidly liberate
four protons and four electrons per molecule of oxygen generated.
The oxidative half-reaction is not limited to this, however, and
can include carbon-hydrogen bond oxidation reactions which provide
protons and electrons with a lower energy requirement than water
oxidation.
[0018] Electrocatalytic carbon dioxide reduction has the advantage
of being tunable in both its rate and selectivity, by changing the
electrocatalyst present, reaction conditions, or by varying
electrode potentials. Key among these advantages is the potential
to identify process parameters that deliver selectivity for various
desired organic compounds, such as ethanol. High selectivity for a
desired compound allows for synthetic purity and targeted
generation of a value-added product as is required for economic
deployment of this technology. Furthermore, flexibility in the
choice of electrolyte and proton source can be used to minimize the
overall consumption of chemicals. Lastly, electricity used to drive
this process can be obtained from renewable resources that do not
generate additional carbon dioxide, allowing for a truly
carbon-negative solution to our increasing carbon dioxide
emissions.
[0019] With electrocatalytic carbon dioxide reduction, carbon
dioxide effluent streams can be used as a feedstock for the
generation of value-added chemicals which reduces their impact on
the Earth's atmosphere. One major source of anthropogenic carbon
dioxide is flue gas effluent from coal and natural gas power
plants. Flue gas is not solely carbon dioxide and in many cases is
between 5% and 50% carbon dioxide or more, depending on the
process. It furthermore consists of combustion byproducts including
nitrous oxide and soot. It is generated on massive scales at power
plants, therefore it is desirable for a carbon dioxide reduction
device that can both operate at high selectivity for carbon dioxide
and at high rates of reaction. To date, the only electrocatalytic
carbon dioxide systems that have been able to operate at these
rates operate under high pressure. Therefore, there is a need for
new architectures of high pressure carbon dioxide reduction systems
that are scalable and able to operate under varied pressures so
that the optimum conditions can be found and achieved on industrial
scales for certain catalyst materials.
[0020] To circumvent the use of fermentation processes for ethanol,
we can use electrolyzers. In these systems, ethanol can be
generated from carbon dioxide, water and electricity. This allows
for a concentration and purity of ethanol is much larger than is
accessible to yeast organism in the final product. It also allows
for direct, single-step generation of ethanol from carbon dioxide,
rather than requiring the two-step process wherein plants sequester
carbon dioxide to form sugars, then the sugars are fermented to
form ethanol.
[0021] Membrane Electrode Assembly
[0022] In certain aspects, the present disclosure provides membrane
electrode assemblies (MEAs) useful for reducing carbon dioxide and
selectively producing desired reduction products. An MEA as a whole
has an anodic side and a cathodic side, and comprises an anode
diffusion layer; a cathode diffusion layer; and a polymer
electrolyte membrane (PEM) disposed between the anode diffusion
layer and the cathode diffusion layer. When the MEA is in use, the
anodic side of the MEA will be in contact with the anolyte, for
instance water; and the cathodic side of the MEA will be in contact
with the catholyte, for instance CO.sub.2.
[0023] The MEA comprises a polymer electrolyte membrane (PEM),
which has a first, or anodic, side and a second, or cathodic side.
The PEM used in the MEA may be any PEM known in the art for use in
conducting ionic species, such as protons. In some embodiments, the
PEM is a is cationic ion-exchange membrane, such as
perfluorosulfonic acid membrane such as Nafion.RTM.; a
perfluorocarboxylic acid membrane such as Flemion.RTM.. In some
embodiments, the PEM is an anionic ion-exchange membrane, such as
an imidazolium-functionalized styrene polymer such as
Sustainion.TM. (Kutz et al. (2016), Sustainion.TM. Imidazolium
Functionalized Polymers for CO.sub.2 Electrolysis. Energy Technol.
doi:10.1002/ente.201600636); or a sulfonated styrene divinyl
benzene copolymer such as Selemion.RTM..
[0024] The PEM may have a reactant-accessible surface area of 1
cm.sup.2, 25 cm.sup.2, 50 cm.sup.2, 100 cm.sup.2, 2,500 cm.sup.2,
10,000 cm.sup.2, and above.
[0025] Catalysts may be disposed on either side of the PEM, or on
both sides. An anode catalyst may be disposed on the anodic side of
the PEM. A cathode catalyst may be disposed on the cathodic side of
the PEM. Many catalysts are known in the art, and catalysts
suitable for the aims of the present disclosure are described
herein. Catalysts may be applied to the PEM by methods known in the
art, some of which are described herein.
[0026] A gas diffusion electrode (GDE) or gas diffusion layer (GDL)
may be disposed on either side of the PEM, or on both sides. Such
layers are known in the art to promote mass transport and electron
transport to the catalyst, to help maintain similar partial
pressures across the membrane, and to help prevent fouling of the
membrane. Exemplary GDEs are described in U.S. Pat. Nos. 5,618,392
and 6,821,661. In some embodiments, a GDE may also function as a
catalyst or co-catalyst. When a catalyst is disposed directly on
the membrane, a catalyst-free GDL may be used. The GDL or GDE may
comprise a conductive carbon-based material, such as carbon wool.
The GDE may have a thickness of between 0.25 mm to 1.0 mm, for
example 0.254 mm or 1.5 mm.
[0027] In some embodiments, the PEM is a part of a five-layer MEA,
comprising a cathode catalyst, a cathode GDE or GDL, the PEM, an
anode GDE or GDL, and an anode catalyst.
[0028] Electrochemical Cells
[0029] In some embodiments, the present disclosure provides
electrochemical cells useful for reducing carbon dioxide and
selectively producing desired reduction products, comprising an
MEA, a cathode endplate, and an anode endplate. The endplates of
the electrochemical cell are configured to transfer charge and
provide reactant access to the MEA. The cathode endplate is
configured to provide catholyte to the cathodic side of the MEA.
The anode endplate is configured to provide anolyte to the anodic
side of the MEA. The endplates may comprise carbon, a metal or
metals such as copper or titanium, or any other suitable
materials.
[0030] Reactants may be provided by directed flow along the
membrane, or by allowing open channels between the exterior of the
MEA and the membrane. When the reactant is provided by directed
flow, the flow pattern may be any suitable flow pattern, for
instance parallel, serpentine, or labyrinthine, and the endplate
preferably comprises access points for reactant to be supplied at a
sufficient pressure to flow through the directed flow channels.
Directed flow systems generally involve a pressure drop along the
direction of the flow, which ensures a sufficient velocity of
reactant across the membrane.
[0031] When the reactant is provided by open channels in the
endplate, the endplate is configured such that the MEA is in direct
fluid communication with the atmosphere surrounding the MEA. In
such a configuration, the channels in the endplate are preferably
wide enough to allow diffusion or flow through the channels and
across the membrane without an appreciable pressure drop or
pressure variation, and to allow for collection of liquid products.
This is advantageous, because many electrochemical reactions
involving gaseous species (such as CO.sub.2) are pressure
sensitive, in that the Faradaic efficiency or the selectivity of
the reaction for one product or another depends in large part on
the pressure at the location where the reaction is taking place.
Providing a pressure-sensitive reactant to the membrane at a
constant, or approximately constant, pressure across the entire
membrane allows the operating pressures for those reactants to be
tuned to optimize reaction conditions. When the endplate is open so
that the atmosphere surrounding the electrochemical cell can access
the MEA, reactants can be provided to the membrane by diffusion, or
by slow, non-directed circulation as would be provided by a fan or
by convection. In some embodiments, waste heat generated by the
operation of the MEA may provide the convection. By contrast,
directed flow systems operate with pressure drops along the flow
field that can cause inconsistent selectivity for reduction
products between the start of the flow field and the end of the
flow field.
[0032] The channels may also be configured to allow for collection
of liquid products. Mass transport is easier when the endplate is
open to the atmosphere surrounding the electrochemical cell. In
some embodiments, the channels of the endplate are of non-uniform
depth, i.e., their floors are angled. This allows a liquid CO.sub.2
reduction product to drip off of the endplate to a collection pool
below the electrochemical cell. In some embodiments, the channels
can be configured with a constant (linear) angle. Additionally, or
alternatively, the channels can be configured with an undulating
pattern of local peaks and troughs to provide a plurality of
dripping locations for collection of the CO.sub.2 reduction
product. The channel geometry can be consistent throughout an
entire stack, or varied as desired. For example, a gradient of
channel density can be employed in which channels at the bottom of
a given stack are formed wider than channels at the top of the
stack.
[0033] In preferred embodiments, the electrochemical cell is
configured such that the catholyte, such as CO.sub.2, can be
provided to the cathodic side of the MEA without appreciable
pressure variation across the MEA, i.e., at constant or
approximately constant pressure (i.e., substantially uniform
pressure) across the MEA. Preferably, the cathode endplate
comprises channels that place the cathodic side of the membrane in
open fluid communication with the atmosphere surrounding the MEA,
such as the atmosphere in a pressure vessel. The channels may have
varied aspect ratios. The channels may be parallel, may be a
circular design, or may form a grid pattern. In some embodiments,
the channels run straight across the endplate, and are present at a
cross-sectional density of at least 1 channel per cm, preferably
2-3 channels per cm. In some embodiments, the channels have a width
of 0.1-1 cm, preferably about 0.2 cm. In some embodiments, the
channels have an aspect ratio of 0.1-10, preferably 0.5. In some
embodiments, there are at least 5 channels per endplate, at least 8
channels per endplate, or at least 10 channels per endplate. In
some embodiments, the channels are tapered.
[0034] Open-channel endplates as described herein also allow
electrochemical cells to be stacked more easily. For instance, the
electrochemical cells described herein can be put into stacks with
bipolar plates connecting individual MEAs, rather than using many
monopolar plates. In such a configuration, one bipolar plate may
simultaneously serve as the cathode endplate for one
electrochemical cell and the anode endplate for the next
electrochemical cell. Monopolar plates may also be used with the
MEAs described herein.
[0035] In some embodiments, the electrochemical cell further
comprises high-pressure gaskets disposed between the MEA and the
cathode and/or anode endplates. Depending on the materials
comprising the membrane and the endplates, such gaskets may be
necessary to allow the desired pressure variations between the two
sides of the MEA, or to contain a directed flow reactant on one
side or the other of the MEA. The gaskets can be formed as discrete
members spaced between adjacent components, or integrally coupled
to an end of a component (e.g. MEA or endplate). In some
embodiments the membranes can be formed as a mask having a boundary
defining an opening or window which overlies the MEA, with the
boundary portion coinciding with the perimeter of the endplates, as
shown in FIG. 4. Furthermore, the gaskets ensure that appropriate
contact is made between the flow plates and the MEA for efficient
current flow.
[0036] The electrochemical cells, MEAs, and PEMs of the present
disclosure are able to withstand pressure differences between
anolyte and catholyte of up to 50 psi, 100 psi, or 250 psi,
preferably 500 psi, 750 psi, or 1000 psi. Many electrochemical
reactions involving gaseous species (such as CO.sub.2) are known to
be pressure sensitive, in that the Faradaic efficiency or the
selectivity of the reaction for one product or another depends on
the pressure. The tolerance of the MEA to pressure differences
between anolyte and catholyte allow the operating pressures for
those reactants to be selected independently to optimize reaction
conditions.
[0037] The electrochemical reactions performed at the MEA in
operation are two individual half-reactions. An exemplary anolyte
is water. Water may be oxidized at the anode to form oxygen gas,
protons, and electrons. The oxygen gas is released as a byproduct,
the protons travel through the PEM portion of the MEA, and the
electrons travel through an external circuit where a voltage is
applied to increase the energy of the electrons. An exemplary
catholyte is CO.sub.2. CO.sub.2 is reduced at the cathode and (when
water is the anolyte) combines with protons generated by the water
to form CO.sub.2 reduction products. Other catholytes and anolytes
may be used with the MEAs of the present invention to produce
different products.
[0038] In order to drive the electrochemical reactions described
herein, electrical contact must be made between each side of the
MEA and a voltage source. In some embodiments, contact will be made
between the MEA and the external circuit by a conductive flow
plate. In some cases, the flow plate is an endplate that then
contacts with a current collector. When electrons travel from the
MEA anode into the flow plate, then to the anodic current
collector, they are fed into the external circuit, which includes a
voltage source, and can then be utilized for the thermodynamically
uphill reduction of carbon dioxide to a product, such as ethanol,
by being fed into the cathodic current collector, traversing the
cathodic endplate, and being fed into the cathode catalyst on the
opposite side of the MEA.
[0039] In some embodiments, the endplate used in an MEA will be a
bipolar plate that also serves as the opposite endplate for a
different MEA. Thus, the same physical component may serve as the
cathode endplate of one electrochemical cell and the anode endplate
of an adjacent electrochemical cell. An individual MEA and its
adjacent flow plates, are denoted as an "electrochemical cell" or
"electrolyzer cell". The MEAs may thus be combined into stacks.
[0040] Reactor Configuration
[0041] In certain aspects, the present disclosure provides
electrochemical reactors comprising one or more electrochemical
cells (the MEAs and their associated flow plates) as described
herein. In some embodiments, the reactor comprises a pressure
vessel, and the one or more MEAs are disposed within the pressure
vessel. In some embodiments, the pressure vessel is able to
withstand variable pressures up to 10 psi, 100 psi, 500 psi, 1000
psi, 1500 psi, 2000, psi, 3000 psi, and higher. The entirety of the
MEA stack, including the flow plates, MEAs, and required gaskets to
maintain separation of fluids (gases, liquids, or supercritical
fluids) under high pressure, sits inside the pressure vessel. The
reaction may be run at any pressure suitable for the desired
reaction. For instance, the fluid within the pressure vessel may be
gaseous, liquid, or supercritical.
[0042] In some embodiments, the reactor comprises one or more
stacks of MEAs, which may be connected to each other by bipolar
plates as described herein.
[0043] In some embodiments, the reactor comprises heating or
cooling elements, or is otherwise configured to regulate the
temperature inside the reactor.
[0044] In some embodiments, the reactor comprises components to
facilitate mass transport and/or product collection. In some
embodiments, the reactor comprises a circulating fan to aid in
circulation of a reactant throughout the reactor body and to the
MEA(s). In some embodiments, the reactor comprises a product
collection vessel. The vessel may be a component that is separate
from, but fastened to, the inside of the reactor. Alternatively,
the vessel may be integrally formed into the body of the reactor,
for instance as a depression or bowl in the bottom of the
reactor.
[0045] In some embodiments, the reactor is configured to allow the
pressure to be adjusted or tuned to optimize the production of
preferred products. In order to do so, as described above with
respect to the MEAs, when the reactor is configured for CO.sub.2
reduction, the cathode endplates are preferably configured to allow
the atmosphere within the pressure vessel of the reactor to be in
fluid communication with the cathodic side of the PEMs. This is in
contrast to a configuration for directed flow, such as a serpentine
flow pattern that requires a gas be fed through discrete and
dedicated conduits. Having the cathode endplates open to the
pressure vessel atmosphere allows for equalization of pressure
across the cathode side of the MEA, as well as collection of
certain liquid-phase products in the cathode chamber. Water can be
fed into the anode side at similarly high pressures, or at a lower
pressure, as long as the MEA is able to withstand the pressure
difference.
[0046] In some embodiments, the reactor is configured to allow a
catholyte, such as a catholyte comprising CO.sub.2, to be fed in
during operation. For example, the reactor may comprise fittings
for catholyte input and catholyte output.
[0047] In some embodiments, the reactor is configured to allow an
anolyte, such as a catholyte comprising water, to be fed in during
operation. For example, the reactor may comprise fittings for
anolyte input and anolyte output.
[0048] In some embodiments, the reactor is configured to allow a
product, such as ethanol, to be removed during operation. For
example, the reactor may comprise a fitting, such as a spigot that
allows products to be collected during reactor operation, i.e.,
without stopping the electrochemical reaction or appreciably
lowering the pressure within the reactor.
[0049] In some embodiments, the reactor comprises a high-pressure
water recirculation system, or a fitting adapted to connect to a
high-pressure water circulation system. Such a high-pressure water
circulation system may be used with the reactor in addition to a
carbon dioxide feed. The water loop allows better control and
uniformity of pressure across the anode flow plate.
[0050] One advantage of electrolyzing carbon dioxide and water into
products using the reactors of the present disclosure is that the
pressure in the cathode chamber can be easily varied using a
compressor or other external pressure control system, which can
allow the operator to adjust the rate of reaction and/or the
selectivity of the reaction. Since the anode is supplied with
water, which possesses a density much higher than that of gaseous
carbon dioxide at standard pressure, the proton-generating water
oxidation reaction is not rate-limiting. By varying the carbon
dioxide pressure, and thereby its chemical state from gas, to
liquid, and to supercritical fluid in a safe and distributed manner
using the cathode chamber design reaction rates and conditions can
easily be improved.
[0051] Product Selectivity
[0052] In some embodiments, the product of carbon dioxide reduction
reaction may be ethanol, methanol, propanol, methane, ethane,
propane, formic acid, ethylene glycol, acetic acid, ethylene,
butanol, butane, and long-chain hydrocarbons such as octanol,
decanol, and cyclooctane. In some embodiments, the product of
carbon dioxide reduction is ethanol. Use of an appropriate cathode
catalyst enables selectivity for ethanol and reduced production of
the byproducts.
[0053] If a catalyst is employed at the anode or cathode, the
identity of the catalyst will affect the selectivity of the
reaction that takes place.
[0054] In some embodiments, a cathodic catalyst is disposed on the
PEM or within a GDE that is disposed on the PEM. The cathodic
catalyst may comprise a copper-containing catalyst, such as copper
metal or copper oxide nanoparticles/nanostructures, a
ruthenium-containing catalyst, a rhenium-containing catalyst, an
iron-containing catalyst, a manganese-containing catalyst, or any
mixture of transition metals with the above. In some embodiments,
the cathode catalyst comprises a metal oxide, and in others, the
cathode catalyst comprises a molecular species. In some
embodiments, the catalyst comprises a transition metal compound,
such as a first-row transition metal oxide. In some embodiments,
the cathode catalyst comprises a rhenium rhodium, or
ruthenium-containing compound. In some embodiments, the catalyst
comprises copper oxide or a mixed metal oxide comprising copper
oxide. In some embodiments, the cathodic catalyst further comprises
an ionomer. In some embodiments, the cathodic catalyst further
comprises binders.
[0055] In some embodiments, an anodic catalyst is disposed on the
PEM or within a GDE that is disposed on the PEM. In some
embodiments, the anode catalyst comprises iridium oxide, platinum,
or an iridium-containing compound. In some embodiments, the anode
catalyst comprises a transition metal or transition metal oxide,
such as iridium oxide, platinum metal, ruthenium oxide, iridium
ruthenium oxide, iridium-based molecular species, iron oxide,
nickel oxide, or cobalt oxide. In some embodiments, the anode
catalyst comprises nanoparticles comprising a transition metal or
transition metal oxide, such as iridium oxide, platinum metal,
ruthenium oxide, iridium ruthenium oxide, iridium-based molecular
species, iron oxide, nickel oxide, or cobalt oxide. In some
embodiments, the anodic catalyst further comprises an ionomer. In
some embodiments, the anodic catalyst further comprises
binders.
[0056] In some embodiments, a catalyst (either anodic or cathodic)
is supported using a scaffold comprised of carbon, antimony-doped
tin oxide, or tin-doped indium oxide.
[0057] The composition of the endplate can also affect the
selectivity of the reaction that takes place. The endplates used in
the MEAs of the present disclosure may be made of any materials
that can withstand the conditions in the reactor, including the
pressure differences, the charge transport, and the operating
temperature. In some embodiments, an endplate comprises carbon,
such as graphite. In some embodiments, an endplate comprises metal,
such as copper. In some embodiments, copper endplates or
copper-coated endplates (such as copper-plated titanium) may be
used to promote the production of ethanol.
[0058] Feed Carbon Dioxide
[0059] In preferred embodiments, the catholyte comprises CO.sub.2.
Carbon dioxide comes in varied concentrations, between atmospheric
(0.04%) and high purity carbon dioxide (99.99%). The present
disclosure provides electrochemical reactors that can convert
carbon dioxide streams that are at least 0.04%, 1%, 5%, 10%, 20%,
40%, 60%, 80%, 90%, 95%, 98%, 99% or higher carbon dioxide on a
per-volume basis. Although the concentration can vary
significantly, it is the partial pressure of CO.sub.2 that
primarily controls the selectivity and rate of the electrochemical
reduction reaction.
[0060] The source of the CO.sub.2 may be effluent from coal and
natural gas fired power plants. Such effluent typically comes in
the form of flue gas, which is a mixture of carbon dioxide, carbon
monoxide, and other combustion products, produced on the scale of
tons to thousands of tons per day. This requires a system that is
able to operate using large volumes. In some embodiments of this
invention, the carbon dioxide flue gas is purified or scrubbed of
some of its more harmful contaminants or membrane fouling agents
(such as fine particulates, e.g. soot) prior to being introduced to
the electrochemical system. The resulting carbon dioxide stream may
possess a lower percentage of aerosol particles, before being
compressed to high pressure and introduced to the cathode chamber.
A flow chart depicting an example of this process is shown in FIG.
1.
[0061] In some embodiments of this invention, the feed carbon
dioxide containing stream is compressed prior to introduction to
the cathode chamber and electrolysis system. In others, it is
liquefied using a thermal process. The present disclosure provides
reactors and systems that can be configured for compatibility with
atmospheric pressure gaseous carbon dioxide, high pressure gaseous
carbon dioxide, high pressure liquid carbon dioxide, or all three.
The variable pressure nature of these systems allow gaseous carbon
dioxide, liquid carbon dioxide, liquefied flue gas, or any gaseous
or liquid phase of a carbon-containing feed stream to be utilized.
Furthermore, it is an object of the invention to feed this
carbon-containing stream at variable pressures into a pressure
vessel that also serves as a cathode chamber and houses the
electrolyzer stacks, as shown in FIG. 2. In some embodiments, the
pressure of the feed carbon dioxide may be 10 psi, 100 psi, 500
psi, 1000 psi, 1500 psi, 2000, psi, or 3000 psi. In some
embodiments, the pressure of the feed carbon dioxide may be 10-3000
psi, 100-3000 psi, 500-3000 psi, 1000-3000 psi, 1500-3000 psi,
2000-3000, psi, or about 3000 psi.
[0062] In some embodiments, the feed carbon dioxide is moistened or
otherwise mixed with water prior to introduction into the
electrochemical reactor.
[0063] Methods for Producing Carbon Dioxide Reduction Products
[0064] In certain aspects, the present disclosure provides methods
for producing CO.sub.2 reduction products using the MEAs and/or
electrochemical reactors described here, comprising supplying a
catholyte comprising CO.sub.2 to the cathodic side of the polymer
electrolyte membrane; supplying an anolyte comprising water to the
anodic side of the polymer electrolyte membrane; and applying a
voltage between the anode endplate and the cathode endplate,
thereby reducing the CO.sub.2 to a CO.sub.2 reduction product which
varies depending on the pressure, temperature, and voltage applied
in the system.
[0065] Apparatus and Methods for Producing Ethanol
[0066] In certain aspects, the present disclosure provides
apparatus for producing ethanol as a CO.sub.2 reduction product,
such as MEAs and electrochemical reactors. The overall reaction
that occurs is the reduction of carbon dioxide to ethanol and
oxidation of water to form oxygen.
[0067] This is shown in the reaction scheme below.
2CO.sub.2+3H.sub.2O.fwdarw.CH.sub.3CH.sub.2OH+O.sub.2
[0068] In electrochemical systems that are used for alcoholic
beverage production, the major product of the carbon dioxide
reduction reaction is ethanol. Common minor products of this
reaction include, CO, HCO.sub.2H, HCHO, CH.sub.3OH, CH.sub.4,
CH.sub.3CH.sub.3.
[0069] In certain embodiments, the faradaic efficiency of the
reduction reaction to form ethanol may be at least 20%, 40%, 60%,
80%, 90%, 95%, 98%, 99%, 99.5%, 99.9%, or higher with the presence
of a suitable catalyst.
[0070] Preferred cathodic catalysts for the production of ethanol
comprise copper oxide. In some preferred embodiments, the cathodic
catalyst comprises copper oxide, copper oxide on a tin oxide
support, or copper oxide nanoparticles.
[0071] Preferred cathodic endplates for the production of ethanol
comprise a carbon allotrope or metal, even more preferably
titanium, graphite, or copper. In some preferred embodiments, the
cathodic endplate comprises 50%, 75%, 90%, or 99% copper or
comprises a 92% titanium coated with copper.
[0072] Preferred pressure vessels and other apparatus for the
production of ethanol can sustain cathodic pressures of at least
50, 100, 250, 500, 750, 1000, or 1500 psi.
[0073] In certain aspects, the present disclosure provides methods
for producing ethanol by electrochemical reduction of CO.sub.2
using the MEAs and/or electrochemical reactors described here,
comprising supplying a catholyte comprising CO.sub.2 to the
cathodic side of the polymer electrolyte membrane; supplying an
anolyte comprising water to the anodic side of the polymer
electrolyte membrane; and applying a voltage between the anode
endplate and the cathode endplate, thereby reducing the CO.sub.2 to
a CO.sub.2 reduction product.
[0074] In certain embodiments, ethanol produced by the methods of
the present disclosure is used for the production of alcoholic
beverages containing ethanol. In most cases, ethanol or an ethanol
and water mixture will be generated by the reactor. This resulting
product may go through further purification or dilution to produce
ethanol that is suitable for human consumption, and may then be
mixed with another beverage ingredient, such as either water or an
aqueous mixture of flavorings, to produce an alcoholic beverage
that is at least 1%, 5%, 10%, 20%, 40%, 60%, 80%, 90%, 95%, 98%,
99% or higher alcohol content by volume.
EXEMPLIFICATION
[0075] The invention now being generally described, it will be more
readily understood by reference to the following examples, which
are included merely for purposes of illustration of certain aspects
and embodiments of the present invention, and are not intended to
limit the invention.
Example 1: Selectivity of Various Catalysts
[0076] A Nafion-based MEA was prepared with various metal oxide or
molecular cathode layer catalysts layered on top of it. For each
catalyst tested, an MEA stack was placed into a pressure vessel and
sandwiched between either a graphite or copper cathode flow plate
and a platinum-coated titanium anode flow plate. CO.sub.2 was
introduced into the reactor at pressures between 1000 and 1500 psi,
and voltages were applied across the cell from a DC power source.
The results of the reactions are listed in Table 1, where
bpy=2,2'-bipyridine, and sb=surface bound to an antimony-doped tin
oxide conductive support.
TABLE-US-00001 TABLE 1 Reaction Conditions for Various Catalysts
Primary Voltage Current product Catalyst Lifetime (2-cell) Density
(% yield) Re(bpy)(CO).sub.3(sb) <1 hour 2.0 91 mA/cm.sup.2 Not
Detectable Copper Oxide 7+ days 2.1 786 mA/cm.sup.2 Ethanol (7%)
CuMn Mixed 7+ days 2.5 1.01 A/cm.sup.2 Formic Acid Oxide (71%) CuFe
Mixed 34 hours 2.1 402 mA/cm.sup.2 Methanol (3%) Oxide
Example 2: Production of Ethanol Using Various Catalysts
[0077] Various Copper-based catalysts were tested for their
capacity to catalyze the reduction of CO.sub.2 to ethanol in a
Nafion-based or Selemion-based MEA. For each tested catalyst, an
MEA stack was placed into a pressure vessel sandwiched between a
copper cathode flow plate and a platinum-coated titanium anode flow
plate. CO.sub.2 was introduced into the reactor at a pressure of
approximately 1000 psi, and voltages were applied across the cell
from a DC power source. The results are presented in Table 2, where
the first two entries used a Nafion-based membrane and the last
used a Selemion-based membrane.
TABLE-US-00002 Primary Voltage Current product Catalyst Lifetime
(2-cell) Density (% yield) Copper oxide 7+ days 2.1 786 mA/cm.sup.2
Ethanol (7%) Copper oxide 5 days 2.1 572 mA/cm.sup.2 Ethanol (3%)
on tin oxide support Copper oxide 7+ days 2.0 415 mA/cm.sup.2
Ethanol (45%) nanoparticles
INCORPORATION BY REFERENCE
[0078] All publications and patents mentioned herein are hereby
incorporated by reference in their entirety as if each individual
publication or patent was specifically and individually indicated
to be incorporated by reference. In case of conflict, the present
application, including any definitions herein, will control.
EQUIVALENTS
[0079] Those skilled in the art will recognize, or be able to
ascertain using no more than routine experimentation, numerous
equivalents to the compounds and methods of use thereof described
herein. Such equivalents are considered to be within the scope of
this invention and are covered by the following claims. Those
skilled in the art will also recognize that all combinations of
embodiments described herein are within the scope of the
invention.
* * * * *