U.S. patent application number 13/286890 was filed with the patent office on 2012-03-01 for electrochemical cell for the production of synthesis gas using atmospheric air and water.
Invention is credited to Shekar Balagopal, S. Elangovan, John Howard Gordon, Joseph J. Hartvigsen, Michele Hollist, Ashok V. Joshi.
Application Number | 20120048730 13/286890 |
Document ID | / |
Family ID | 37772525 |
Filed Date | 2012-03-01 |
United States Patent
Application |
20120048730 |
Kind Code |
A1 |
Hartvigsen; Joseph J. ; et
al. |
March 1, 2012 |
ELECTROCHEMICAL CELL FOR THE PRODUCTION OF SYNTHESIS GAS USING
ATMOSPHERIC AIR AND WATER
Abstract
A method is provided for synthesizing synthesis gas from carbon
dioxide obtained from atmospheric air or other available carbon
dioxide source and water using a sodium-conducting electrochemical
cell. Synthesis gas is also produced by the coelectrolysis of
carbon dioxide and steam in a solid oxide fuel cell or solid oxide
electrolytic cell. The synthesis gas produced may then be further
processed and eventually converted into a liquid fuel suitable for
transportation or other applications.
Inventors: |
Hartvigsen; Joseph J.;
(Kaysville, UT) ; Joshi; Ashok V.; (Salt Lake
City, UT) ; Elangovan; S.; (South Jordan, UT)
; Balagopal; Shekar; (Sandy, UT) ; Gordon; John
Howard; (Salt Lake City, UT) ; Hollist; Michele;
(South Jordan, UT) |
Family ID: |
37772525 |
Appl. No.: |
13/286890 |
Filed: |
November 1, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11467524 |
Aug 25, 2006 |
8075746 |
|
|
13286890 |
|
|
|
|
60711252 |
Aug 25, 2005 |
|
|
|
Current U.S.
Class: |
204/256 ;
204/278 |
Current CPC
Class: |
H01M 2008/1293 20130101;
C25B 1/04 20130101; C25B 1/00 20130101; Y02E 60/50 20130101; C25B
1/02 20130101; C25B 9/77 20210101; Y02E 60/36 20130101 |
Class at
Publication: |
204/256 ;
204/278 |
International
Class: |
C25B 9/08 20060101
C25B009/08; C25B 1/02 20060101 C25B001/02; C25B 9/10 20060101
C25B009/10; C25B 9/18 20060101 C25B009/18 |
Claims
1. An electrochemical cell for producing synthesis gas comprising:
an anode chamber comprising an electrochemically active anode and a
source of water in which the water is decomposed according to the
following reaction: 1/2H2O.fwdarw.1/4O2+H++e-, wherein O2 is
collected and removed from the anode chamber and wherein the anode
chamber has a source of entry for Na2CO3 at a sufficient distance
away from the anode such that the Na2CO3 reacts with H+ in solution
according to the reaction: H++1/2Na2CO3.fwdarw.1/2CO2+1/2H2O+Na+,
and wherein CO2 is collected and removed at a location spaced apart
from the anode where O2 is collected and removed; a cathode chamber
comprising an electrochemically active cathode separated from the
anode chamber by a membrane which permits transport of Na+ ions,
wherein the cathode chamber has a source of water and Na+ ions, in
which the water is decomposed according to the following reaction:
Na++H2O+e-.fwdarw.NaOH+1/2H2, wherein H2 is collected and removed
from the cathode chamber and wherein NaOH is collected and removed
from the cathode chamber; and means for facilitating the reaction
of CO2 and H2 to form synthesis gas comprising CO and H2.
2. The electrochemical cell according to claim 1, wherein the
source of Na2CO3 comprises Na2CO3 obtained by reacting the NaOH
removed from the cathode with a source of CO2.
3. The electrochemical cell according to claim 2, wherein the
source of CO2 is atmospheric air.
4. The electrochemical cell according to claim 2, wherein the
source of CO2 is combustion gases.
5. The electrochemical cell according to claim 2, wherein the
source of CO2 is aerobic decomposition gases.
6. The electrochemical cell according to claim 1, wherein the means
for facilitating the reaction of CO2 and H2 to form synthesis gas
comprises a catalyst exposed to the mixture of CO2 and H2.
7. The electrochemical cell according to claim 6, wherein the
catalyst comprises a watergas shift catalyst.
8. The electrochemical cell according to claim 6, wherein the
catalyst comprises a Fischer-Tropsch catalyst.
9. The electrochemical cell according to claim 6, wherein the
mixture of CO2 and H2 is heated to enable a homogenous gas phase
equilibrium reaction.
10. The electrochemical cell according to claim 6, the means for
facilitating the reaction of CO2 and H2 to form synthesis gas
further comprises an oxygen ion conducting electrolysis cell to
cause electrolysis of CO2 to form CO, which is mixed with H2 to
produce synthesis gas.
11. The electrochemical cell according to claim 1, wherein the
electrochemical cell is embodied within a plurality of stacked
electrochemical cells separated by bipolar plates.
12. The electrochemical cell according to claim 1, wherein the
membrane which permits transport of Na+ ions comprises a sodium
super ionic conductor ceramic material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional application of, and claims priority to,
U.S. application Ser. No. 11/467,524 filed Aug. 25, 2006, which
claimed priority to U.S. Provisional Application No. 60/711,252
filed Aug. 25, 2005. Both of these applications are incorporated
herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates in general to methods for
producing synthesis gas from easily obtainable precursors, and more
particularly, to the generation of such synthesis gas from
atmospheric air and water.
BACKGROUND OF THE INVENTION
[0003] Users of fuels such as gasoline and diesel (in commercial
applications) and JP-8, F-76 and other similar fuels (in military
applications) have benefited from the existence of an extensive and
well-established infrastructure for their shipping, delivery to end
users, and use. The presence of this infrastructure has also
enabled technology development of liquid fuel-based systems for
uses ranging from automobiles to military aircraft. Within areas
well-served by this infrastructure, dependence upon such liquid
fuel-based systems is largely unquestioned.
[0004] In some applications, however, continued dependence on the
availability of such liquid fuel products is unwise. Such
applications include industrial or commercial applications in
primitive regions and military operations in remote locations away
from standard supply systems and sources. In applications such as
military logistics supporting extended naval missions, assuring the
availability of a steady and sufficient supply of liquid fuel
products may become critically important and very difficult. While
all-electric-powered ships and aircraft are planned, moves toward
these platforms are slow and their completion is still only
foreseen in the somewhat distant future. It is anticipated that a
transition away from liquid fuels will be simpler and more rapidly
adopted in larger apparatus such as aircraft carriers via the use
of on-board nuclear power plants than in smaller equipment such as
aircraft.
[0005] As a result, it is anticipated that reliance upon liquid
fuel-based systems will continue well into the foreseeable future.
It would thus be beneficial to provide new methods and systems for
generating liquid fuels using electricity and commonly-available
resources that could be employed on-location to reduce the
criticality of long supply chains. The availability of such a
process based on plentiful electricity and common resources could
speed conversion to all-electric power sources in some simpler
applications while retaining support for others in which electric
power-based systems are either difficult or impractical.
[0006] Such methods and systems are provided herein.
[0007] BRIEF SUMMARY OF THE INVENTION
[0008] The present invention is directed to processes, methods, and
systems for the production of synthesis gas for fuel production or
other applications. The processes, methods, and systems of the
present invention utilize commonly-available resources as inputs
and rely upon electricity to provide synthesis gas as an
output.
[0009] The present invention includes an electrochemical cell for
producing synthesis gas. In one embodiment within the scope of the
invention, the electrochemical cell includes an anode chamber
containing an electrochemically active anode. Water is decomposed
at the anode to produce oxygen and hydrogen ions. The oxygen is
preferably collected and removed from the anode chamber. A source
of sodium carbonate is provided which reacts with the hydrogen ions
and decomposes to form carbon dioxide, water, and sodium ions. The
carbon dioxide is preferably collected and removed.
[0010] In one embodiment, the anode chamber is divided by a
separator, permeable to hydrogen ions, to form an intermediate
chamber. The separator which permits transport of hydrogen ions may
be a microporous separator, a cation exchange membrane, a mesh or a
screen. In this embodiment, the sodium carbonate is added to the
intermediate chamber. The anode chamber need not be divided by a
separator, but a separator may facilitate collection and removal of
the oxygen and carbon dioxide gases. It may also eliminate the need
for later separation of carbon dioxide from oxygen.
[0011] The electrochemical cell includes a cathode chamber
containing an electrochemically active cathode separated from the
anode chamber, or intermediate chamber, by a membrane which permits
transport of Na.sup.+ ions. The membrane which permits transport of
Na.sup.+ ions is preferably a sodium super ionic conductor ceramic
material, a cation exchange membrane, or other similar
membrane.
[0012] Water is reduced in the cathode chamber to produce hydrogen
gas and hydroxyl ions. The hydroxyl ions combine with sodium ions
to form sodium hydroxide. The hydrogen gas is collected and removed
from the cathode chamber.
[0013] The system or process includes means for facilitating the
reaction of CO.sub.2 and H.sub.2 to form synthesis gas comprising
CO and additional H.sub.2. Such means may include a catalyst
exposed to the mixture of CO.sub.2 and H.sub.2. The catalyst may be
a watergas shift catalyst or a Fischer-Tropsch catalyst. The
mixture of CO.sub.2 and H.sub.2 may alternatively be heated to
enable a homogenous gas phase equilibrium reaction with CO and
H.sub.2O. The means for facilitating the reaction of CO.sub.2 and
H.sub.2 to form synthesis gas may include an oxygen ion conducting
electrolysis cell to cause electrolysis of CO.sub.2 to CO, which
with the H.sub.2 comprises synthesis gas.
[0014] In the foregoing embodiment, sodium hydroxide is preferably
removed from the cathode and reacted with a source of carbon
dioxide to form sodium carbonate which may replenish the sodium
carbonate decomposed in the anode chamber. The source of carbon
dioxide includes, but is not limited to atmospheric air, combustion
gases, and aerobic decomposition gases.
[0015] The electrochemical cell may be embodied within a plurality
of stacked electrochemical cells separated by bipolar plates. The
use of stacked electrochemical cells may enable the efficient
production of large quantities of synthesis gas.
[0016] The electrochemical cell may perform a process for producing
synthesis gas by decomposing water within an anode chamber
according to the following reaction: 1/2H.sub.2O.fwdarw.
1/40O.sub.2+H.sup.++e.sup.- and removing oxygen from the anode
chamber. Na.sub.2CO.sub.3 and H.sup.+ ions may react within anode
chamber according to the following reaction:
H.sup.++1/2Na.sub.2CO.sub.3.fwdarw.1/2CO.sub.2+1/2H.sub.2O+Na.sup.+.
This reaction preferably occurs at a location a distance away from
the anode but within the anode chamber. The process includes the
steps of removing CO.sub.2 from the anode chamber at a location
near where it is produced and transporting Na.sup.+ ions from the
anode chamber to a cathode chamber. Water decomposes within the
cathode chamber according to the following reaction:
Na.sup.++H.sub.2O+e.sup.-.fwdarw.NaOH+1/2H.sub.2. H.sub.2 is
collected and removed from the cathode chamber. The collected
CO.sub.2 and H.sub.2 react to form synthesis gas comprising CO and
H.sub.2. NaOH may be removed from the cathode chamber, reacted with
carbon dioxide to form Na.sub.2CO.sub.3, and transported to the
anode to replenish the Na.sub.2CO.sub.3 consumed in the reaction
with hydrogen ions.
[0017] Another embodiment within the scope of the invention
includes an electrochemical device for the coelectrolysis of carbon
dioxide and steam to produce synthesis gas. This electrochemical
device includes an oxygen ion conducting membrane, a cathode
attached to one surface of the oxygen ion conducting membrane and
an anode attached to an opposite surface of the oxygen ion
conducting membrane. The cathode is electrochemically active for
reduction of steam to form hydrogen and oxygen ions. The anode is
electrochemically active for recombination of oxygen ions into
oxygen molecules.
[0018] A source of steam and carbon dioxide may contact the cathode
under conditions which cause the following reactions to occur:
H.sub.2O+2e.sup.-.fwdarw.H.sub.2+O.sup.-2,
CO.sub.2+2e.sup.-.fwdarw.CO+O.sup.-2 and
CO.sub.2+H.sub.2.revreaction.CO+H.sub.2O. Synthesis gas comprising
CO and H.sub.2 is collected and recovered at the cathode, and
oxygen ions are conducted through the oxygen ion conducting
membrane to the anode where they are recombined to form O.sub.2,
which is collected and recovered.
[0019] The cathode preferably comprises a mixture of nickel oxide
and another oxide. In one embodiment, the cathode comprises a first
metal oxide and a solid solution of nickel oxide and a second metal
oxide selected from the group consisting of magnesium oxide, cobalt
oxide, copper oxide, and mixtures thereof. The second metal oxide
is preferably present in an amount from 1 to 50 mole % relative to
the nickel oxide. In one embodiment, the first metal oxide is
zirconia doped with one or more oxides selected from the group
consisting of yttrium oxide, ytterbium oxide, calcium oxide,
magnesium oxide, and scandium oxide. In another embodiment, the
first metal oxide is ceria doped with one or more oxides selected
from samarium oxide, gadolinium oxide, yttrium oxide, ytterbium
oxide, calcium oxide, magnesium oxide, and scandium oxide. In yet
another embodiment, the first metal oxide is lanthanum gallium
oxide doped with one or more elements selected from strontium,
magnesium, iron, and cobalt. The cathode preferably comprises a
surface dispersed catalyst selected from the group consisting of
Pr, Co, Ce, Eu, other rare earth elements and mixtures thereof.
[0020] The anode preferably comprises a mixture of perovskite and
an oxide. In one embodiment, the anode comprises a mixture of
perovskite and an anode oxide, wherein the perovskite is
(Pr.sub.1-xLa.sub.x),.sub.z-yA.sub.yBO.sub.3-.delta., where A is an
alkaline earth metal selected from Sr and Ca and mixtures thereof,
B is a transition metal selected from Mn, Co, Fe, and mixtures
thereof, with 0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.0.5,
0.8.ltoreq.z.ltoreq.1.1, .delta. is an oxygen non-stoichiometry
value, wherein the anode oxide is selected from zirconia doped with
one or more of yttrium oxide, ytterbium oxide, calcium oxide,
magnesium oxide, scandium oxide, and cerium oxide and ceria doped
with one or more of yttrium oxide, ytterbium oxide, calcium oxide,
magnesium oxide, scandium oxide, and zirconium oxide. One presently
preferred perovskite material is
Pr.sub.0.8Sr.sub.0.2MnO.sub.3-.delta.. The anode preferably
comprises a surface dispersed catalyst selected from the group
consisting of Pr, Co, Ce, Eu, other rare earth elements, Sr, Ca,
and mixtures thereof.
[0021] The source of carbon dioxide is preferably selected from
atmospheric air, combustion gases, or aerobic decomposition
gases.
[0022] Other advantages and aspects of the present invention will
become apparent upon reading the following description of the
drawings and detailed description of the invention. These and other
features and advantages of the present invention will become more
fully apparent from the following figures, description, and
appended claims, or may be learned by the practice of the invention
as set forth hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] In order that the manner in which the above-recited and
other features and advantages of the invention are obtained will be
readily understood, a more particular description of the invention
briefly described above will be rendered by reference to specific
embodiments thereof that are illustrated in the appended drawings.
Understanding that these drawings depict only typical embodiments
of the invention and are not therefore to be considered to be
limiting of its scope, the invention will be described and
explained with additional specificity and detail through the use of
the accompanying drawings in which:
[0024] FIG. 1 is a schematic view of a two-compartment
electrochemical cell for generating synthesis gas within the scope
of the present invention;
[0025] FIG. 2 is a schematic view of an electrochemical cell for
generating synthesis gas showing recycle of NaOH and regeneration
of NaCO.sub.3 and capture and separation of CO.sub.2;
[0026] FIG. 3 is a schematic view of an oxygen ion conducting
electrolysis cell useful in generating synthesis gas;
[0027] FIG. 4 is a schematic view of a three-compartment
electrochemical cell for generating synthesis gas within the scope
of the present invention;
[0028] FIG. 5 is a schematic view of a synthesis gas generating
system which produces synthesis gas from the coelectrolysis of
steam and carbon dioxide; and
[0029] FIG. 6 is a schematic view of another oxygen ion conducting
electrolysis cell useful in generating synthesis gas.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The presently preferred embodiments of the present invention
will be best understood by reference to the drawings, wherein like
parts are designated by like numerals throughout. It will be
readily understood that the components of the present invention, as
generally described and illustrated in the figures herein, could be
arranged and designed in a wide variety of different
configurations. Thus, the following more detailed description of
the embodiments of the processes, methods, and systems for the
production of synthesis gas for fuel or other applications of the
present invention, as represented in FIGS. 1 through 6, is not
intended to limit the scope of the invention, as claimed, but is
merely representative of presently preferred embodiments of the
invention.
[0031] In a first embodiment of the processes of the present
invention, a process is disclosed for producing synthesis gas, also
known as "syngas," comprising a mixture of CO and H.sub.2. This
process 10 is illustrated schematically in FIG. 1. The process 10
utilizes a two-compartment electrochemical cell 12. The
electrochemical cell includes an anode compartment or chamber 14
and a cathode compartment or chamber 16. A sodium-conducting
membrane 18 separates the anode chamber 14 from the cathode chamber
16. Suitable sodium-conducting membranes 18 include NaSICON (sodium
(Na) Super Ionic CONductor) ceramic materials, as well as other
ceramic and polymer cation exchange membranes known to persons
skilled in the art.
[0032] The anode chamber 14 includes an electrochemically active
anode 20 and a source of water in which the water (H.sub.2O) is
decomposed according to the following reaction:
1/2H.sub.2O.fwdarw.1/4O.sub.2+H.sup.++e.sup.- (1)
The O.sub.2 is collected and removed from the anode chamber 14.
[0033] In this process 10, sodium carbonate (Na.sub.2CO.sub.3) is
decomposed in the anode chamber 20 of the electrochemical cell 12
to produce carbon dioxide (CO.sub.2) according to the following
reaction:
H.sup.++1/2Na.sub.2CO.sub.3.fwdarw.1/2CO.sub.2+1/2H.sub.2O+Na.sup.+
(2)
The CO.sub.2 is collected and removed from the anode chamber 14.
Sodium ions are transferred across the sodium-conducting membrane
18. A source of sodium carbonate is provided sufficiently close to
the anode 14 so that the sodium carbonate reacts with H.sup.+ ions
in solution. It may be preferred to space the sodium carbonate a
sufficient distance away from the anode to facilitate separate
removal of the O.sub.2 produced at the anode 14 and the CO.sub.2
produced by the decomposition of sodium carbonate. Sodium carbonate
may be directly provided for use in the cell 12, or may
alternatively be readily obtained by the reaction of sodium
hydroxide with a carbon dioxide source according to the following
reaction:
NaOH+1/2CO.sub.2.fwdarw.1/2Na.sub.2CO.sub.3+1/2H.sub.2O (3)
Examples of typical carbon dioxide sources include, but are not
limited to, atmospheric air, combustion gases, or aerobic
decomposition gases. Aerobic decomposition gases include gases
naturally produced upon decomposition of various organic materials,
including waste materials.
[0034] The cathode chamber 16 includes an electrochemically active
cathode 22 and a source of water in which the water is reduced
according to the following reaction:
Na.sup.++H.sub.2O+e.sup.-.fwdarw.NaOH+1/2H.sub.2 (4)
The H.sub.2 is collected and removed from the cathode chamber. The
NaOH may optionally be collected and removed from the cathode
chamber, as shown by NaOH stream 24 in FIG. 2. As mentioned above,
sodium hydroxide may be reacted with a source of carbon dioxide 26
to form sodium carbonate which may be recycled to the anode chamber
as a sodium carbonate source 28, shown in FIG. 2.
[0035] By applying an electrical potential across the
two-compartment cell 12, water and sodium carbonate are decomposed
and produce a flow 30 of oxygen and a flow 32 of carbon dioxide.
The reduction of water at the cathode 22 generates hydroxyl ions
and a flow 34 of hydrogen gas. As the sodium ions migrate through
the membrane 18 from the anolyte side (anode chamber 14) of the
cell 12 to the catholyte side (cathode chamber 16), they will
combine with the hydroxyl ions produced by the reduction of water
to form sodium hydroxide solution as shown in reaction (4).
[0036] During operation of the electrochemical cell 12, oxygen and
carbon dioxide may be collected as separate gas flows 30, 32 or
they may be mixed gases 36, shown in FIG. 2. If mixed, the oxygen
is preferably separated from the carbon dioxide in a carbon dioxide
separator 38 so that the carbon dioxide may be used in subsequent
process steps. Carbon dioxide separation in carbon dioxide
separator 38 may be conducted using various processes known to
those of ordinary skill in the art. Such processes include, but are
not limited to, use of activated carbon or molecular sieves to
absorb CO.sub.2 from the gases removed from the cathode 14. Such
techniques often utilize multiple absorption beds which are rotated
such that those which are full are rotated out of the gas stream
and stripped prior to continued use. Other methods include
filtration of the gas stream 36 using a polymeric membrane
selectively permeable by either O.sub.2 or CO.sub.2, or using
CO.sub.2-absorbent fluids such as amine solutions presented to the
gas stream 36 as in a scrubber unit. Oxygen may be separated from
carbon dioxide by exposing the mixed CO.sub.2 and O.sub.2 gas
stream to an oxygen-conducting membrane such as yttria-stabilized
zirconia (or "YSZ") to extract the oxygen. Other methods of
separating CO.sub.2 and O.sub.2 are well known to those of ordinary
skill in the art and may be implemented within the scope of the
invention.
[0037] The cathode chamber 16 of this embodiment of the
electrochemical cell 12 contains water and sodium hydroxide as the
catholyte. In the cathode chamber 16, water is reduced in the
presence of sodium ions to release a flow of hydrogen gas 34 and
form sodium hydroxyide. Thus, the reactions conducted in the
electrochemical cell 12 may be represented as follows:
[0038] Anode [0039] H.sub.2O.fwdarw.1/2O.sub.2+2H.sup.++2e.sup.-
[0040] 2H.sup.++Na.sub.2CO.sub.3.fwdarw.CO.sub.2+H.sub.2O+2Na.sup.+
[0041]
Na.sub.2CO.sub.3(aq).fwdarw.CO.sub.2+1/2O.sub.2+2Na.sup.++2e.sup.-
(overall)
[0042] Cathode [0043]
2Na.sup.++2H.sub.2O+2e.sup.-.fwdarw.2NaOH+H.sub.2
[0044] Overall [0045]
Na.sub.2CO.sub.3+2H.sub.2O.fwdarw.2NaOH+CO.sub.2+H.sub.2+1/2O.sub.2
[0046] The CO.sub.2 flow 32 from the anode chamber 14 and the
H.sub.2 flow 34 from the cathode chamber 16 may be combined and
further processed to convert the CO.sub.2 into CO to form syngas
40. CO.sub.2 and H.sub.2 may react to form the components of the
syngas mixture 40 (CO+H.sub.2). Syngas may be obtained from
CO.sub.2 and H.sub.2 according to one or more of the following
reactions:
CO.sub.2+2e.sup.-.fwdarw.CO+O.sup.-2 (5)
CO.sub.2+H.sub.2.fwdarw.CO+H.sub.2O (6)
[0047] It should be noted that such syngas mixtures 40 may also
include amounts of CO.sub.2 and H.sub.2O. Means may be provided to
facilitate the reaction of CO.sub.2 and H.sub.2 to form synthesis
gas. Such means may include a catalytic reactor 42 in which a
suitable catalyst is exposed to the mixture of CO.sub.2 and
H.sub.2, as shown in FIG. 2 For example, the catalyst may be a
watergas shift catalyst, also known as a shift catalyst or reverse
shift catalyst. The catalyst may comprise a Fischer-Tropsch
catalyst. The CO.sub.2 and H.sub.2 gases may be heated to
facilitate a homogenous gas phase equilibrium reaction. Other means
to facilitate the reaction of CO.sub.2 and H.sub.2 to form
synthesis gas may comprise an oxygen ion conducting electrolysis
cell 44 to cause electrolysis of CO.sub.2 and form CO and O.sub.2.
The CO is collected, and with H.sub.2, forms synthesis gas.
[0048] A schematic representation of an oxygen ion conducting
electrolysis cell 44 is shown in FIG. 3. Cell 44 includes an oxygen
ion conducting membrane 46. A variety of materials may be used to
fabricate the oxygen ion conducting, including but not limited to,
yttria-stabilized zirconia ("YSZ"). The electrochemical device for
the electrolysis of carbon dioxide to product carbon monoxide may
also include a source of carbon dioxide in contact with a cathode
48. The cathode 48 is attached to a surface of the oxygen ion
conducting membrane 46 which is electrochemically active to reduce
carbon dioxide to form carbon monoxide and oxygen ions according to
reaction (5), above. CO is collected and recovered at the cathode
the oxygen ions are conducted through the oxygen ion conducting
membrane to the and anode 50. The anode 50 is attached to an
opposite surface of the oxygen ion conducting membrane 42 which is
electrochemically active for recombination of oxygen ions into
oxygen molecules, according to the following reaction:
O.sup.-2.fwdarw.1/2O.sub.2+2e.sup.- (7)
[0049] The cathode 48 and anode 50 should be sufficiently permeable
to allow diffusion of carbon dioxide, oxygen, or other gaseous
species that may react or be produced at the interface of the
oxygen ion conductor 46 and the cathode 48 and the interface of the
oxygen ion conductor 46 and the anode 50. By applying an electrical
potential across the oxygen ion conducting electrolysis cell 44,
carbon dioxide is reduced to form carbon monoxide and oxygen. It
produces a flow 52 of carbon monoxide and a flow 54 of oxygen. The
reduction of carbon dioxide at the cathode 48 generates oxygen ions
and the flow 52 of carbon monoxide. As the oxygen ions migrate
through the membrane 46 from the cathode 48 to the anode 50 they
will combine to form oxygen as shown in reaction (7), above.
[0050] The materials and configurations used for the cathode 48 and
anode 50 may be the same or similar to those used in connection
with the cathode and anode described below in connection with FIG.
6.
[0051] This syngas mixture 40 can be further processed to produce
liquid hydrocarbon fuel using any suitable process available in the
art. One such process commonly used to convert syngas 40 to liquid
fuel is the Fischer-Tropsch process, in which syngas 40 is reacted
in the presence of a catalyst (such as an iron or cobalt catalyst)
to produce liquid hydrocarbon fuels. Other suitable processes,
including variations on the Fischer-Tropsch process, are known to
those of ordinary skill in the art, and could be used with the
processes of the present invention. Here the term liquid
hydrocarbon fuel also includes lighter hydrocarbons such as
methane, ethane, propane, butane, etc. which may be vapors at
ambient conditions but which also may be liquefied under pressure
or cryogentic conditions. A typical Fischer-Tropsch process
produces a wide distribution of hydrocarbon chain length, all
having fuel value.
[0052] The processes and systems of the present invention further
allow for replenishment of the electrochemical cell 12 using
generally-readily-available materials. As mentioned above in
relation to FIG. 2, the NaOH generated in the cathode chamber 16
may be recycled in NaOH stream 24 and reacted with CO.sub.2 source
26, such as CO.sub.2 in atmospheric air, via a spontaneous reaction
(encouraged by heat) to generate the sodium carbonate. The
regenerated sodium carbonate or other sodium carbonate source 28
may replenish the sodium carbonate consumed in the anode chamber
14. Various systems for speeding this process are available and
known to one of ordinary skill in the art. This allows the anode
chamber 14 to be replenished. The cathode chamber 16, on the other
hand, may be replenished by adding water 56. Alternatively, the
sodium carbonate regeneration step may be skipped and the
electrochemical cell may be replenished by direct supply of sodium
carbonate. Thus, this embodiment of the processes of the present
invention only requires electric power, CO.sub.2 from a carbon
source or from atmospheric air, and water as the only inputs needed
to generate syngas.
[0053] In another embodiment within the scope of the present
invention, a three-compartment electrochemical cell 60 is provided.
Cell 60, shown in FIG. 4, is similar to cell 12, except that the
anode chamber 14 includes a separator 62 which allows transport of
H.sup.+ ions. Suitable separators may include a microporous
separator, cation exchange membrane, a mesh or a screen. In this
embodiment, the separator 62 defines an intermediate chamber 64
disposed between the separator 62 and the sodium-conducting
membrane 18. Water is decomposed at the anode 20 according to
reaction (1), above. Sodium carbonate is decomposed in the
intermediate chamber according to reaction (2), above. The
three-compartment electrochemical cell may facilitate collection,
separation and removal of the product gases, oxygen, carbon
dioxide, and hydrogen. A separate process for separating carbon
dioxide from oxygen may not be required. In addition, a plurality
of three-compartment electrochemical cells 60, separated by bipolar
plates, may be stacked or connected in a way to efficiently
generate large quantities of carbon dioxide and hydrogen for use in
producing synthesis gas.
[0054] In yet another embodiment of the methods of the present
invention, syngas 40 may be produced by the coelectrolysis of
carbon dioxide and steam. FIG. 5 includes a diagram of this process
100. In this process 100, a flow 102 of carbon dioxide is provided
from a carbon dioxide source 104, such as discussed above. The
carbon dioxide source may include a gas separator, discussed above,
to separate carbon dioxide from atmospheric air. The process 100
also includes a flow of steam 106 provided from a source of steam
108. The carbon dioxide flow 102 and steam flow 106 are sent to a
solid oxide electrolysis cell (SOEC) 110. Electricity 120 and any
required heat are provided to the cell 110 to drive the following
reactions:
CO.sub.2+2e.sup.-.fwdarw.CO+O.sup.-2 (5)
H.sub.2O+2e.sup.-.fwdarw.H.sub.2+O.sup.-2 (8)
O.sup.-2.fwdarw.1/2O.sub.2+2e.sup.- (7)
The following additional reaction may also occur in the SOEC
110:
CO.sub.2+H.sub.2.revreaction.CO+H.sub.2O (6)
The net equation of the SOEC is shown as follows:
H.sub.2O+CO.sub.2.fwdarw.H.sub.2+CO+O.sub.2 (9)
[0055] In the SOEC 110, oxygen is stripped from the incoming
CO.sub.2 102 and H.sub.2O 106 (as steam) by an oxygen
ion-conducting electrolysis cell 140, similar to the electrolysis
cell 44, discussed above and illustrated in FIG. 3. FIG. 6 shows
that electrolysis cell 140 includes an oxygen ion conducting
membrane 142. A variety of materials may be used to fabricate the
oxygen ion conducting, including but not limited to,
yttria-stabilized zirconia ("YSZ"). A cathode 144 is attached to a
surface of the oxygen ion conducting membrane 142 which is
electrochemically active to reduce carbon dioxide to form carbon
monoxide and oxygen ions according to reaction (5), above, and also
electrochemically active to reduce steam (water) to form hydrogen
gas and oxygen ions according to reaction (8), above. An anode 146
is attached to an opposite surface of the oxygen ion conducting
membrane 142 which is electrochemically active for recombination of
oxygen ions into oxygen molecules, according to reaction (7),
above.
[0056] The cathode 144 and anode 146 should be sufficiently
permeable to allow diffusion of carbon dioxide, steam, oxygen, or
other gaseous species that may react or be produced at the
interface of the oxygen ion conductor 142 and the cathode 144 and
the interface of the oxygen ion conductor 142 and the anode
146.
[0057] By applying an electrical potential across the oxygen ion
conducting electrolysis cell 140, carbon dioxide and water are
reduced to form carbon monoxide, hydrogen, and oxygen. It produces
a flow 150 of carbon monoxide, a flow 152 of hydrogen, and a flow
154 of oxygen. The reduction of carbon dioxide and steam at the
cathode 144 generates oxygen ions and the flow 150 of carbon
monoxide and flow 152 of hydrogen. As the oxygen ions migrate
through the membrane 142 from the cathode 144 to the anode 146 they
will combine to form oxygen as shown in reaction (7), above.
[0058] This syngas mixture 40 can be further processed to produce
liquid hydrocarbon fuel using any suitable process available in the
art.
[0059] The carbon dioxide and steam are reduced at the cathode side
144 of the oxygen-ion conducting membrane. Oxygen ions are
transported through the oxygen ion conducting membrane 142 and
evolved at the anode 146 as oxygen gas. The SOEC 110 provides an
outflow 122 of O.sub.2. As with the process 10 of the invention,
this process 100 results in an outflow 122 of O.sub.2 and a
separate stream of syngas 124 comprising CO, and H.sub.2. The
oxygen may be produced at high purity without any subsequent
separation required. As also discussed above, the syngas 124 may be
further processed to produce a liquid hydrocarbon fuel suitable for
use with current equipment using known methods.
[0060] The anode may be a mixture of perovskite and an oxide. In
one embodiment, the anode consists of a perovskite and an oxide
mixed in the volume ratio of oxide,
O.ltoreq.V.sub.oxide.ltoreq.70%. The anode perovskite may be
(Pr.sub.1-xLa.sub.x).sub.z-y A.sub.y B O.sub.3-.delta. where A is
an alkaline earth in particular Sr or Ca, and B is a transition
metal in particular Mn, Co and Fe and mixtures thereof, with
0.ltoreq.x.ltoreq.1.0, 0.ltoreq.y.ltoreq.0.5,
0.8.ltoreq.z.ltoreq.1.1. .delta. is the oxygen non-stoichiometry
determined by the crystalline chemistry and electro-neutrality
conditions. The anode oxide may be zirconia doped with one or more
of yttrium oxide, ytterbium oxide, calcium oxide, magnesium oxide,
scandium oxide, and cerium oxide. The anode oxide could also be
ceria doped with one or more of yttrium oxide, ytterbium oxide,
calcium oxide, and magnesium oxide, scandium oxide, and zirconium
oxide. In one embodiment, the oxide doping in zirconia and ceria
ranges from about 2 to about 15 mole %.
[0061] The cathode may be a mixture of nickel oxide and an oxide.
In one embodiment, the nickel oxide is a solid solution with
magnesium oxide. The cathode solid solution may contain between
about 1 to about 25 mole % magnesium oxide relative to the nickel
oxide. The nickel oxide in the solid solution is reduced to nickel
during cell operation. The oxide in the cathode may include one of
the group of zirconia, ceria, and mixtures thereof. The zirconia in
the cathode may be doped with one or more of yttrium oxide,
ytterbium oxide, calcium oxide, magnesium oxide, and scandium
oxide. Ceria in the cathode may be doped with one or more of
samarium oxide, gadolinium oxide, yttrium oxide, ytterbium oxide,
calcium oxide, magnesium oxide, and scandium oxide.
[0062] The anode and cathode may be infiltrated with a catalyst
material. The catalyst may be a surface dispersed catalyst selected
from one of the group of Pr, Co, Ce, Eu, other rare earth elements,
and combinations thereof. The catalyst in addition may contain one
or more of Sr and Ca. The catalyst may be infiltrated as a salt
soluble in water or an organic solvent. The catalyst may also be
infiltrated as oxide particles.
[0063] A source of steam and carbon dioxide in contact with the
cathode 144 under conditions which cause the following reactions to
occur: H.sub.2O+2e.sup.-.fwdarw.H.sub.2+O.sup.-2,
CO.sub.2+2e.sup.-.fwdarw.CO+O.sup.-2 and
CO.sub.2+H.sub.2.fwdarw.CO+H.sub.2O, wherein synthesis gas
comprising CO and H.sub.2 is collected and recovered at the cathode
and wherein oxygen ions are conducted through the oxygen ion
conducting membrane to the anode where they are recombined to form
O.sub.2, which is collected and recovered.
[0064] While specific embodiments of the present invention have
been illustrated and described, numerous modifications come to mind
without significantly departing from the spirit of the invention,
and are included within its scope.
* * * * *