U.S. patent application number 15/804632 was filed with the patent office on 2018-03-29 for catalysts for hydrocarbon reforming.
The applicant listed for this patent is LG Fuel Cell Systems, Inc.. Invention is credited to John R. Budge.
Application Number | 20180086636 15/804632 |
Document ID | / |
Family ID | 50382731 |
Filed Date | 2018-03-29 |
United States Patent
Application |
20180086636 |
Kind Code |
A1 |
Budge; John R. |
March 29, 2018 |
CATALYSTS FOR HYDROCARBON REFORMING
Abstract
In some examples, a method for treating a reforming catalyst,
the method comprising heating a catalyst metal used for reforming
hydrocarbon in a reducing gas mixture environment. The reducing gas
mixture comprises hydrogen and at least one sulfur-containing
compound. The at least one sulfur-containing compound includes one
or more of hydrogen sulfide, carbonyl sulfide, carbonyl disulfide
and organic sulfur-containing compounds such as thiophenes,
thiophanes, sulfides (RSH), disulfides (RS.sub.2R'), tri-sulfides
(RS.sub.3R') and mercaptans (RSR').
Inventors: |
Budge; John R.; (Beachwood,
OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG Fuel Cell Systems, Inc. |
North Canton |
OH |
US |
|
|
Family ID: |
50382731 |
Appl. No.: |
15/804632 |
Filed: |
November 6, 2017 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13837544 |
Mar 15, 2013 |
9809453 |
|
|
15804632 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01B 3/38 20130101; B01J
23/464 20130101; C01B 2203/066 20130101; Y02P 20/141 20151101; C01B
2203/1258 20130101; C01B 2203/0244 20130101; C01B 2203/1235
20130101; Y02E 60/50 20130101; Y02P 20/52 20151101; H01M 8/0618
20130101; B01J 37/20 20130101; C01B 2203/0238 20130101; B01J 23/74
20130101; H01M 2008/1293 20130101; C01B 3/40 20130101; B01J 23/96
20130101; C01B 2203/1052 20130101; B01J 23/40 20130101; C01B
2203/0233 20130101 |
International
Class: |
C01B 3/40 20060101
C01B003/40; B01J 23/46 20060101 B01J023/46; B01J 23/74 20060101
B01J023/74; B01J 37/20 20060101 B01J037/20; C01B 3/38 20060101
C01B003/38; H01M 8/0612 20060101 H01M008/0612 |
Claims
1. A method for treating a reforming catalyst, the method
comprising heating a catalyst metal used for reforming hydrocarbon
in a reducing gas mixture environment, wherein the reducing gas
mixture comprises hydrogen and at least one sulfur-containing
compound, wherein the at least one sulfur-containing compound
includes one or more of hydrogen sulfide, carbonyl sulfide,
carbonyl disulfide and organic sulfur-containing compounds such as
thiophenes, thiophanes, sulfides (RSH), disulfides (RS.sub.2R'),
tri-sulfides (RS.sub.3R') and mercaptans (RSR').
2. The method of claim 1, wherein the catalyst metal is treated
with a dose of sulfur during treatment such that catalyst
performance is stabilized without substantially negatively
impacting activity of the catalyst metal.
3. The method of claim 1, wherein the heating the catalyst metal
comprises heating the catalyst metal to a temperature between
approximately 350 to 1,200 degrees Celsius.
4. The method of claim 1, further comprising reforming hydrocarbons
via a reformer with the catalyst metal to produce hydrogen.
5. The method of claim 4, wherein reforming hydrocarbons comprises
steam reforming.
6. The method of claim 4, further comprising supplying the hydrogen
to the fuel side of a solid oxide fuel cell stack.
7. The method of claim 4, wherein the at least one sulfur compound
is periodically added to a feed stream of the reformer while
reforming the hydrocarbons.
8. The method of claim 7, wherein a frequency, amount, and duration
of the periodic addition of the sulfur compounds is selected such
that catalyst performance is stabilized without substantially
negatively impacting activity of the catalyst metal.
9. The method of claim 1, wherein the catalyst metal is supported
by a catalyst carrier.
10. The method of claim 1, wherein the catalyst metal comprises one
or more of Ni, Co, Rh, Ru, Pd, Pt and Co.
11. An article for reforming hydrocarbons, the article comprising a
catalyst metal for reforming hydrocarbons, wherein the catalyst
metal has been treated by heating the in a reducing gas mixture
environment, wherein the reducing gas mixture comprises hydrogen
and at least one sulfur-containing compound, wherein the at least
one sulfur-containing compound includes one or more of hydrogen
sulfide, carbonyl sulfide, carbonyl disulfide and organic
sulfur-containing compounds such as thiophenes, thiophanes,
sulfides (RSH), disulfides (RS.sub.2R'), tri-sulfides (RS.sub.3R')
and mercaptans (RSR').
12. The article of claim 11, wherein the catalyst metal has been
treated with a dose of sulfur during treatment such that catalyst
performance is stabilized without substantially negatively
impacting activity of the catalyst metal.
13. The article of claim 11, wherein, during treatment, the
catalyst metal is heated to a temperature between approximately 350
to 1,200 degrees Celsius.
14. The article of claim 11, further comprising a reformer for
reforming hydrocarbons, wherein the treated catalyst metal is used
by the reformer to produce hydrogen.
15. The article of claim 14, wherein reformer comprises a steam
reformer.
16. The article of claim 14, further comprising a solid oxide fuel
cell stack, wherein the hydrogen produced by the reformer is
supplied to the fuel side of the solid oxide fuel cell stack.
17. The article of claim 14, wherein the at least one sulfur
compound is periodically added to a feed stream of the reformer
while reforming the hydrocarbons.
18. The article of claim 17, wherein a frequency, amount, and
duration of the periodic addition of the sulfur compounds is
selected such that catalyst performance is stabilized without
substantially negatively impacting activity of the catalyst
metal.
19. The article of claim 11, wherein the catalyst metal is
supported by a catalyst carrier.
20. The article of claim 11, wherein the catalyst metal comprises
one or more of Ni, Co, Rh, Ru, Pd, Pt and Co.
Description
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/837,544, filed Mar. 15, 2013 by Budge. The
entire content of U.S. patent application Ser. No. 13/837,544 is
incorporated herein by reference.
TECHNICAL FIELD
[0002] The disclosure generally relates to hydrocarbon reforming,
such as, e.g., for use with solid oxide fuel cell systems.
BACKGROUND
[0003] Fuel cells and fuel cell systems, such as, e.g., solid oxide
fuel cell and solid oxide fuel cell systems remain an area of
interest. Some existing systems have various shortcomings,
drawbacks, and disadvantages relative to certain applications.
Accordingly, there remains a need for further contributions in this
area of technology.
SUMMARY
[0004] In some examples, the disclosure relates to catalyst metals
for use in the reformation of hydrocarbons, such as, e.g., for use
with steam reformers, to produce hydrogen. The catalyst may be
treated with a reducing gas comprising hydrogen and a sulfur
compound. The sulfur compound includes one or more of hydrogen
sulfide, carbonyl sulfide, carbonyl disulfide and organic
sulfur-containing compounds such as thiophenes, thiophanes,
sulfides (RSH), disulfides (RS.sub.2R'), tri-sulfides (RS.sub.3R')
and mercaptans (RSR'). By treating the catalyst with the proper
dose of sulfur, the catalyst performance may be stabilized while
not substantially negatively impacting catalyst activity. In some
examples, the treatment of catalyst metals may be performed in situ
during reformation via a reformer by periodically adding the
sulfur-containing compound to the reformer feed stream. The
hydrogen produced via the reformer employing the metal catalyst
metal may be fed to the fuel side of a solid oxide fuel stack.
[0005] In one example, the disclosure is directed to a method for
treating a reforming catalyst, the method comprising heating a
catalyst metal used for reforming hydrocarbon in a reducing gas
mixture environment, wherein the reducing gas mixture comprises
hydrogen and at least one sulfur-containing compound, wherein the
at least one sulfur-containing compound includes one or more of
hydrogen sulfide, carbonyl sulfide, carbonyl disulfide and organic
sulfur-containing compounds such as thiophenes, thiophanes,
sulfides (RSH), disulfides (RS.sub.2R'), tri-sulfides (RS.sub.3R')
and mercaptans (RSR').
[0006] In another example, the disclosure is directed to an article
for reforming hydrocarbons, the article comprising a catalyst metal
for reforming hydrocarbons, wherein the catalyst metal has been
treated by heating in a reducing gas mixture environment, wherein
the reducing gas mixture comprises hydrogen and at least one
sulfur-containing compound, wherein the at least one
sulfur-containing compound includes one or more of hydrogen
sulfide, carbonyl sulfide, carbonyl disulfide and organic
sulfur-containing compounds such as thiophenes, thiophanes,
sulfides (RSH), disulfides (RS.sub.2R'), tri-sulfides (RS.sub.3R')
and mercaptans (RSR').
[0007] The details of one or more embodiments of the disclosure are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the disclosure will be
apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0008] The description herein makes reference to the accompanying
drawings wherein like reference numerals refer to like parts
throughout the several views.
[0009] FIG. 1 is a schematic diagram illustrating an example fuel
cell system.
[0010] FIG. 2 is a schematic diagram illustrating an example fuel
cell stack.
[0011] FIG. 3 is a schematic diagram illustrating an example cross
section of a fuel cell stack.
[0012] FIG. 4 is a plot of an activity function Y versus
time-on-stream (TOS).
DETAILED DESCRIPTION
[0013] FIG. 1 is a schematic diagram illustrating an example fuel
cell system 50 in accordance with an embodiment of the present
disclosure. Fuel cell system 50 includes fuel cell stack 54 and
steam reformer 52. For ease of illustration, examples of the
disclosure are primarily described with regard to steam reformers
configured to produce hydrogen from the steam reformation of
hydrocarbons using examples of treated catalyst metals. However,
examples are not limited to steam reformation. Other examples may
include use of example treated catalysts through the process of dry
reforming of hydrocarbons, autothermal reforming of hydrocarbons,
and/or catalytic partial oxidation of hydrocarbons.
[0014] Steam reformer 52 may receive a gaseous feed stream
including one or more hydrocarbons. Example hydrocarbons fed to
reformer 52 may preferably include lighter hydrocarbons such as
methane, ethane, propane, butane and also Cs and heavier
hydrocarbons. The hydrocarbon feed reacts with steam at a high
temperature in the presence of catalyst metal 56. The reaction in
the steam reformer via reformer 52 produces, among others,
hydrogen. The reformed hydrogen may be fed from the steam reformer
to the fuel side of fuel cell stack 54, while air (or other
oxidant) is fed to the oxidant side of fuel cell stack 54. Fuel
cell stack 54 may produce electricity using the hydrogen fed to the
fuel side of the fuel cell stack.
[0015] As noted above, catalyst metal 56 may be treated with a
reducing gas comprising hydrogen and a sulfur compound. The sulfur
compound includes one or more of hydrogen sulfide, carbonyl
sulfide, carbonyl disulfide and organic sulfur-containing compounds
such as thiophenes, thiophanes, sulfides (RSH), disulfides
(RS.sub.2R'), tri-sulfides (RS.sub.3R') and mercaptans (RSR'). By
treating the catalyst with the proper dose of sulfur, the catalyst
performance may be stabilized while not substantially negatively
impacting catalyst activity. In some examples, the treatment of
catalyst metals may be performed in situ during reformation via a
reformer by periodically adding the sulfur-containing compound to
the reformer feed stream. The hydrogen produced via the reformer
employing the metal catalyst metal may be fed to the fuel side of a
solid oxide fuel stack. In this manner, resulting improvement in
catalyst durability may result in operational savings, e.g., due to
the longer maintenance interval for either changing out the
catalyst or replacing a reformer unit.
[0016] Steam reforming catalyst metal 56 may comprise one or more
catalytically active metals selected from the group Ni, Co, Rh, Ru,
Pd, Pt and Co. Catalyst metal 56 may be supported on a suitable
carrier. The amount of catalytically active metal 56 on the carrier
may vary over a wide range, but in some examples are present in
amounts ranging from about 0.1 to 40 wt %, such as, e.g., between
about 0.5 and 10 wt %. Suitable carriers for the catalyst 56
include refractory oxides such as silica, alumina, titania,
zirconia, tungsten oxides, and mixtures thereof. Mixed refractory
oxides comprising at least two cations may also be employed as
carrier materials for catalyst 56. Alumina oxides stabilized with
oxides such as baria, ceria, lanthana and magnesia may be preferred
carriers. The catalytically active metals may be deposited on the
carrier by any suitable techniques including those known in the
art. One suitable technique for depositing metals on the carrier is
by impregnation, which may comprises contacting the carrier
material with a solution of the catalytically active metal(s),
followed by drying and calcining the resulting material.
[0017] Steam reforming is endothermic and heat transfer is an
important consideration in the process design. In many steam
reforming applications it is often advantageous to coat the steam
reforming catalyst onto a metallic substrate in order to facilitate
heat transfer from an external heat source to the process stream. A
metal monolithic structure, for example, may be fabricated from a
heat and oxidation resistant metal such as stainless steel or the
like. FeCr alloy may be a preferred metal alloy for supporting
catalysts and forming monoliths. Monolith supports may be made from
such materials by placing a flat and a corrugated sheet one over
the other and rolling the stacked sheets into a tubular
configuration about an axis to the corrugations to provide a
cylindrical structure having a plurality of fine parallel gas flow
passages which may range typically from 200 to 1200 per square inch
of end face area of the tubular roll.
[0018] Other suitable metallic substrate forms may include metallic
foams and hot metal surfaces that are in direct contact with the
process stream. An example of the latter would be the metallic
heat-exchange surface of a heat exchanger. With a heat exchanger, a
catalyst supported on corrugated metal foil, metal mesh, metal wire
or porous metal foams may also be placed directly in the
heat-exchanger channels. The catalytic materials can be coated onto
the surface of the metallic substrate by techniques such as wash
coating that are well known in the art. Further, the bonding
between the catalyst wash-coat and the metal substrate may often be
improved by pre-treating and activating the metal surface.
[0019] In accordance with one or more examples of the disclosure,
while sulfur is considered in most instances to be a severe poison
for steam reforming catalysts (e.g., Ni), it has been surprisingly
found that the durability of steam reforming catalysts can be
significantly improved by treating the catalyst with a reducing gas
comprising hydrogen and one or more sulfur compounds selected from
the group: hydrogen sulfide, carbonyl sulfide, carbonyl disulfide
and organic sulfur-containing compounds such as thiophenes,
thiophanes, sulfides (RSH), disulfides (RS.sub.2R'), tri-sulfides
(RS.sub.3R') and mercaptans (RSR'). The sulfur dose (e.g., as
defined by the product of the concentration of sulfur in the
reducing treatment gas and the duration of the treatment) may vary
over wide ranges, but the sulfur dose should preferably be
sufficient to stabilize catalyst performance without greatly
impacting catalyst activity. Catalyst performance, as reflected in
the hydrocarbon conversion to reformed products, may degrade over
time, e.g., due to several deactivations mechanism that reduce
hydrocarbon conversion. The degradation mechanisms may include
sintering of catalyst metal particles, loss of catalyst surface
area and fouling. In some example, the techniques described herein
significantly reduce the decline in hydrocarbon conversion over
time without suppressing catalyst activity. This may be compared
with processes described in the art which reduce catalyst
deactivation but at the same time significantly reduce hydrocarbon
conversion. Further, in some examples, a higher sulfur
concentration in the reducing gas may reduce the treatment time.
The sulfur dosage (ppb-hours), defined as the product of the sulfur
level (in parts per billion) in the reducing gas and the exposure
time (hours), can be used as a measure of the degree of sulfur
treatment and resulting catalyst stabilization. Thus, comparable
degrees of catalyst stabilization can be achieved by either: a)
catalyst treatment with a higher feed sulfur level for a shorter
time period, or b) catalyst treatment with a lower feed sulfur for
a longer time period.
[0020] In accordance with examples of the disclosure, catalyst 56
may be treated with one or more sulfur compounds. While not wanting
to be bound by theory, it is believed that the sulfur treatments
result in metal sulfide formation close to the catalytically active
metal centers which inhibits catalyst deactivation. The treatment
of catalyst 56 as described herein may be carried out prior to
operating the reforming process, or alternatively may be carried
out in-situ (e.g., while the reforming process is in progress). In
the case of in-situ treatment, the sulfur-containing compound(s)
may be mixed in the hydrocarbon feed received by reformer 52. In
this case, hydrogen addition to the feed is optional, as hydrogen
is produced by the reforming reaction. In other examples, a
reducing gas mixture including hydrogen and sulfur-containing
compound(s) may be fed to reformer 52 via a separate feed line. The
sulfur-containing compound(s) may be fed to reformer 52 for
treatment of catalyst metal 56 on a substantially continuous or
periodic basis. In the case of periodic treatment, catalyst metal
56 may be re-treated by feeding sulfur-containing compound(s) to
reformer 52 if the rate of catalyst deactivation increases after
extended periods of operation. When the reforming process is used
with a fuel cell or other downstream process which has catalytic
components, it is preferable to adjust the sulfur level in the
reformer feed and the duration of treatment so as not to greatly
impact the activity of either the reforming catalyst, fuel cell or
other downstream processes.
[0021] In the case of pre-treatment, catalyst metal 56 may be
treated by heating catalyst metal 52, prior to catalyst 52 being
used for reforming hydrocarbon, in a reducing gas mixture
environment, e.g., within a reactor. The reducing gas mixture may
include hydrogen and at least one sulfur-containing compound, where
the at least one sulfur-containing compound includes one or more of
hydrogen sulfide, carbonyl sulfide, carbonyl disulfide and organic
sulfur-containing compounds such as thiophenes, thiophanes,
sulfides (RSH), disulfides (RS.sub.2R'), tri-sulfides (RS.sub.3R')
and mercaptans (RSR'). The pretreatment could be done in reformer
52 or in a separate vessel. Again, catalyst metal 56 may be
re-treated by feeding sulfur-containing compound(s) to reformer 52
if the rate of catalyst deactivation increases after extended
periods of operation.
[0022] As noted above, the dose of sulfur used for the treatment of
metal catalyst 56 may be sufficient to stabilize catalyst
performance without greatly impacting catalyst activity. The dose
may be a function of concentration of sulfur in the reducing gas
mixture as well as the duration of time that the reducing gas
mixture is fed to the catalyst. For cases in which the reducing gas
mixture is fed periodically to the catalyst, the frequency at which
the mixture is fed may also determine the dosage. The effectiveness
of the sulfur dosing may be dependent on the process conditions,
metal and required treatment frequency. The sulfur dosage per
treatment may range from about 100 to 50,000 ppb-h, and preferably
from about 500 to 5000 ppb-h.
[0023] In some examples, since sulfur is a severe poison for steam
reforming catalysts, the reducing gas mixture may preferably have a
total sulfur concentration in the range of approximately 0.005 to
approximately 10 parts per million volume (ppm-v), such as, e.g.,
approximately 0.02 to approximately 0.5 ppm-v. In some examples,
catalyst pretreatment may preferably be carried out at temperatures
of approximately 300 to approximately 1200 degrees Celsius,
pressures of approximately 1 to approximately 200 bar, and gas
hourly space velocities (GHSVs) of approximately 50 to
approximately 100,000 hour.sup.-1. For example, the catalyst
treatment may be carried out at approximately 600 to approximately
1,000 degrees Celsius, pressure of approximately 1 to approximately
10 bar, and GHSVs of approximately 100 to approximately 50,000
hr.sup.-1. Values other than those above are contemplated.
[0024] The steam reforming of hydrocarbons may be carried out via
reformer 52 with catalyst metals 56 treated according to the
techniques disclosed herein, e.g., at pressures of approximately 1
to approximately 50 bar, temperatures of approximately 500 to
approximately 1200 degrees Celsius, GHSVs of approximately 100 to
approximately 100,000 hr.sup.-1, and steam to carbon ratios of
approximately 0.5 to approximately 10. Values other than those
above are contemplated. As noted above, in addition to steam
reforming, other examples, such as, autothermal reforming, dry
reforming and catalytic partial oxidation processes may also be
carried out using catalysts treated according to the methods
described herein.
[0025] In some examples, catalyst metals, such as, e.g., Ni, may be
more susceptible to coke formation. In some examples, sulfur may be
added to the stream reforming process to reduce catalyst metal
coking. However, the relatively high levels of sulfur that may help
reduce coking can also results in a significant reduction of
catalyst activity. In accordance with one or more examples of the
disclosure, the relatively low amount of sulfur provided to treat
catalyst metal 56 may not result in a significant reduction of
catalyst activity. The sulfur pretreatment dosage may be adjusted
to give a reduction in hydrocarbon conversion that is less than 1%,
and preferably less than 0.5%.
[0026] FIG. 2 is a schematic diagram illustrating fuel cell stack
54 includes a plurality of electrochemical cells 12 (or "individual
fuel cells") formed on substrate 14. As described above, hydrogen
produce by reformer 52 may be fed to the fuel side of fuel cell
stack 54. Fuel cell stack 54 may then produce electricity using the
reformed hydrogen. However, the techniques for generating reformed
hydrogen using the treated catalyst metals described herein are not
limited to use with fuel cells. Rather, the reformed hydrogen
produced via the techniques described herein may be used for any
suitable purpose.
[0027] Electrochemical cells 12 are coupled together in series by
interconnects 16. Fuel cell system 10 is a segmented-in-series
arrangement deposited on a flat porous ceramic tube, although it
will be understood that the present disclosure is equally
applicable to segmented-in-series arrangements on other substrates,
such on a circular porous ceramic tube. In various embodiments,
fuel cell system 10 may be an integrated planar fuel cell system or
a tubular fuel cell system.
[0028] Each electrochemical cell 12 includes an oxidant side 18 and
a fuel side 20. The oxidant is generally air, but could also be
pure oxygen (O.sub.2) or other oxidants, e.g., including dilute air
for fuel cell systems having air recycle loops, and is supplied to
electrochemical cells 12 from oxidant side 18. Substrate 14 may be
porous, e.g., a porous ceramic material which is stable at fuel
cell operation conditions and chemically compatible with other fuel
cell materials. In other embodiments, substrate 14 may be a
surface-modified material, e.g., a porous ceramic material having a
coating or other surface modification, e.g., configured to prevent
or reduce interaction between electrochemical cell 12 layers and
substrate 14. A fuel, such as a reformed hydrocarbon fuel, e.g.,
synthesis gas, is supplied to electrochemical cells 12 from fuel
side 20 via channels (not shown) in porous substrate 14.
[0029] FIG. 3 is a schematic diagram illustrating an example cross
section of fuel cell stack 54. Fuel cell stack 54 may be formed of
a plurality of layers screen printed onto substrate 14. Fuel cell
stack 54 layers include an anode conductive layer 22, an anode
layer 24, an electrolyte layer 26, a cathode layer 28 and a cathode
conductive layer 30. In one form, electrolyte layer 26 may be a
single layer or may be formed of any number of sub-layers.
[0030] Interconnects 16 for solid oxide fuel cells (SOFC) are
preferably electrically conductive in order to transport electrons
from one electrochemical cell to another; mechanically and
chemically stable under both oxidizing and reducing environments
during fuel cell operation; and nonporous, in order to prevent
diffusion of the fuel and/or oxidant through the interconnect. If
the interconnect is porous, fuel may diffuse to the oxidant side
and burn, resulting in local hot spots that may result in a
reduction of fuel cell life, e.g., due to degradation of materials
and mechanical failure, as well as reduced efficiency of the fuel
cell system. Similarly, the oxidant may diffuse to the fuel side,
resulting in burning of the fuel. Severe interconnect leakage may
significantly reduce the fuel utilization and performance of the
fuel cell, or cause catastrophic failure of fuel cells or
stacks.
[0031] In each electrochemical cell 12, anode conductive layer 22
conducts free electrons away from anode 24 and conducts the
electrons to cathode conductive layer 30 via interconnect 16.
Cathode conductive layer 30 conducts the electrons to cathode
28.
[0032] Interconnect 16 is embedded in electrolyte layer 26, and is
electrically coupled to anode conductive layer 22, and extends in
direction 32 from anode conductive layer 22 through electrolyte
layer 26, then in direction 36 from one electrochemical cell 12 to
the next adjacent electrochemical cell 12, and then in direction 32
again toward cathode conductive layer 30, to which interconnect 16
is electrically coupled. In particular, at least a portion of
interconnect 16 is embedded within an extended portion of
electrolyte layer 26, wherein the extended portion of electrolyte
layer 26 is a portion of electrolyte layer 26 that extends beyond
anode 24 and cathode 28, e.g., in direction 32, and is not
sandwiched between anode 24 and cathode 28. Although not shown in
FIG. 3, in some examples, fuel cell system 10 may include one or
more chemical barrier layers between interconnect 16 and adjacent
components to reduce or prevent diffusion between the interconnect
and adjacent components, e.g., an anode and/or an anode conductor
film and/or cathode and/or cathode conductor film, may adversely
affect the performance of certain fuel cell systems.
EXAMPLES
[0033] A series of experiments were performed to evaluate one or
more aspects related to examples of the present disclosure.
Comparative Example
No Catalyst Pretreatment with Sulfur
[0034] A BASF supplied RM75 (Pt/Rh) catalyst coated on Alumchrome Y
that was not treated with sulfur according to the examples
described herein. The catalyst was aged for 2000 hours under the
following steam reforming conditions: 800 C, 4 Bara and feed gas
composition of 14.2% CH.sub.4, 9.3% CO, 18.1% C0.sub.2, 14.2%
H.sub.2, 39.6% H.sub.20 and 4.6% N2. The catalyst had a first-order
deactivation rate of 1.47.times.10.sup.-4 h.sup.-.
Example 1
Catalyst Treated with Sulfur
[0035] A BASF supplied RM75 (Pt/Rh) catalyst coated on Alumchrome Y
was aged under the following steam reforming conditions: 800 C, 4
Bara and feed gas composition of 14.2% CH4, 9.3% CO, 18.1% C02,
14.2% H2, 39.6% H20, 4.6% N2. Periodically, the feed stream was
spiked with sulfur. Table 1 summarizes the sulfur level and
duration of the sulfur spiking. The sulfur dose is defined as the
product of the feed sulfur level (ppb) and exposure time (h). The
periodic introduction of sulfur into the feed is detailed the
following table.
TABLE-US-00001 Treatment TOS Sulfur [S] Temp. Sulfur Dose No. (h)
Dopant (ppbv) (C.) (ppb-h) A 30 H.sub.2S/CH.sub.4 80 750 5120 B 885
H.sub.2S/CH.sub.4 80 800 1840 C 986 H.sub.2S/CH.sub.4 80 750 5120 D
1800 PNG 200 800 4800 E 2524 PNG 30 800 1980 F 3025 PNG 30 800 690
G 3167 PNG 30 800 630 H 3335 PNG 30 800 660 I 3505 PNG 30 800 660 J
3839 PNG 30 800 534 K 4012 PNG 40 800 534
[0036] The sulfur was introduced in the feed stream either as
H.sub.2S or the naturally occurring sulfur compounds present in the
available pipeline natural gas (PNG). It was found that introducing
sulfur in the feed stream reduced the catalyst deactivation rate by
at least 30%. FIG. 4 is a plot of an activity function Y versus
time-on-stream (TOS) comparing Example 1 and the Comparative
Example. It is expected that further adjustment of the frequency
and level of sulfur dosing will further reduce the observed rate of
catalyst deactivation.
[0037] The surfaces of both the treated and untreated catalyst were
analyzed and the catalysts showed no evidence of carbon build up on
the catalysts. Thus, coking does not appear to be significantly
contributing to catalyst deactivation. While not wanting to be
bound by theory, it is believed that maintaining a relatively low
level of catalyst sulfidation inhibits the sintering of the highly
dispersed metal crystallites that catalyze the steam reforming
reactions.
[0038] Various embodiments of the invention have been described.
These and other embodiments are within the scope of the following
claims.
* * * * *