U.S. patent application number 11/484224 was filed with the patent office on 2006-12-21 for desulfurization system and method for desulfurizing a fuel stream.
This patent application is currently assigned to SUD-CHEMIE INC.. Invention is credited to Mike McKinney, R. Steve Spivey, Eric Jamie Weston.
Application Number | 20060283780 11/484224 |
Document ID | / |
Family ID | 37605705 |
Filed Date | 2006-12-21 |
United States Patent
Application |
20060283780 |
Kind Code |
A1 |
Spivey; R. Steve ; et
al. |
December 21, 2006 |
Desulfurization system and method for desulfurizing a fuel
stream
Abstract
A method for producing a substantially desulfurized hydrocarbon
fuel stream at temperatures less than 100.degree. C. including
providing a nondesulfurized fuel cell hydrocarbon fuel stream and
passing the fuel stream through a sequential sulfur adsorbent
system containing calcium exchanged zeolite, hydrated alumina and a
selective sulfur adsorbent placed in sequence to produce a
substantially desulfurized hydrocarbon fuel stream.
Inventors: |
Spivey; R. Steve;
(Louisville, KY) ; Weston; Eric Jamie;
(Shepherdsville, KY) ; McKinney; Mike;
(Louisville, KY) |
Correspondence
Address: |
Scott R. Cox
Ste. 2100
500 W. Jefferson St.
Louisville
KY
40202
US
|
Assignee: |
SUD-CHEMIE INC.,
LOUISVILLE
KY
|
Family ID: |
37605705 |
Appl. No.: |
11/484224 |
Filed: |
July 11, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11207154 |
Aug 18, 2005 |
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11484224 |
Jul 11, 2006 |
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10932177 |
Sep 1, 2004 |
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11207154 |
Aug 18, 2005 |
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Current U.S.
Class: |
208/213 ;
210/252 |
Current CPC
Class: |
B01J 20/0237 20130101;
B01J 20/0244 20130101; C10G 53/08 20130101; B01J 2220/42 20130101;
B01D 53/04 20130101; C10G 25/003 20130101; B01J 20/06 20130101;
B01D 2256/245 20130101; B01J 20/28057 20130101; B01J 20/08
20130101; B01J 20/20 20130101; B01D 2259/4145 20130101; B01J
20/0222 20130101; B01J 20/0229 20130101; B01D 2257/30 20130101;
B01D 2257/304 20130101; B01D 2253/1124 20130101; B01D 53/02
20130101; B01D 2253/108 20130101; B01J 20/186 20130101; B01J
20/28052 20130101; C10G 25/05 20130101; B01D 2257/306 20130101;
B01D 2257/308 20130101; B01J 20/2803 20130101 |
Class at
Publication: |
208/213 ;
210/252 |
International
Class: |
C10G 45/04 20060101
C10G045/04 |
Claims
1. A process for desulfurization of a hydrocarbon feed stream
comprising providing a hydrocarbon feed stream, which is
contaminated with sulfur compounds, including carbonyl sulfide,
passing the sulfur contaminated feed stream through a sequential
sulfur adsorbent system comprising in sequence zeolite, hydrated
alumina, and a selective sulfur adsorbent to produce a hydrocarbon
feed stream which has been substantially desulfurized.
2. The process of claim 1, where the zeolite comprises a calcium
exchanged zeolite X or LSX.
3. The process of claim 2, wherein the calcium exchanged zeolite X
or LSX is exchanged with calcium ions at least about 50%.
4. The process of claim 3, wherein the calcium exchanged zeolite X
or LSX is further exchanged with metal ions selected from the group
consisting of zinc, cadmium, cobalt, nickel, copper, iron,
manganese, silver, gold, scandium, lithium and combinations
thereof.
5. The process of claim 1, wherein the Si:Al ratio of the zeolite
is from about 1.0 to about 1.25.
6. The process of claim 1, wherein the composition of the hydrated
alumina is selected from boehmite, pseudo-boehmite and
gibbsite.
7. The process of claim 1, wherein the composition of the hydrated
alumina is selected from Al(OH).sub.3 and AlO(OH).
8. The process of claim 1, wherein the selective sulfur absorbent
comprises zinc oxide, copper oxide and a binder.
9. The process of claim 1, wherein the selective sulfur absorbent
comprises copper oxide and one or more manganese compounds.
10. The process of claim 1, wherein the selective sulfur absorbent
comprises one or more manganese compounds and an iron compound.
11. The process of claim 1, wherein the temperature of the
sequential sulfur adsorbent system, as the feed stream passes
therethough, is from ambient to about 100.degree. C.
12. The process of claim 1, wherein the temperature of the
sequential sulfur adsorbent system, as the feed stream passes
therethough, is from ambient to about 60.degree. C.
13. The process of claim 1, wherein the feed stream contacts the
zeolite prior to contacting either the hydrated alumina or the
selective sulfur absorbent.
14. The process of claim 1, wherein the feed stream contacts the
zeolite prior to contacting the hydrated alumina and contacts the
selective sulfur adsorbent after contacting the hydrated
alumina.
15. A process for desulfurization of a hydrocarbon fuel cell feed
stream comprising providing a hydrocarbon feed stream to a fuel
cell processing train, wherein the feed stream is contaminated with
sulfur compounds, including carbonyl sulfide, passing the sulfur
contaminated feed stream through a sequential sulfur adsorbent
system comprising, in sequence, calcium-exchanged zeolite, hydrated
alumina and a selective sulfur adsorbent to produce a hydrocarbon
feed stream which has been substantially desulfurized, and
delivering the substantially desulfurized hydrocarbon feed stream
to remaining components of the fuel cell processing train.
16. The process of claim 15, wherein the temperature of the
sequential sulfur adsorbent system as the feed stream passes
therethough is from ambient to about 100.degree. C.
17. A process for the desulfurization of a hydrocarbon fuel cell
feed stream comprising providing the hydrocarbon feed stream to a
fuel cell processing train, wherein the feed stream is contaminated
with sulfur compounds, including one or more compounds selected
from the group consisting of carbonyl sulfide, hydrogen sulfide,
tetra hydro thiophene, dimethyl sulfide, mercaptans, disulfides,
thiophenes, sulfoxides, other organic sulfides, and higher
molecular weight organic sulfur compounds and combinations thereof,
passing the sulfur contaminated feed stream through a sequential
sulfur adsorbent system comprising, in sequence, calcium exchange
zeolite X or LSX, hydrated alumina, selected from the group
consisting of boehmite, pseudo-boehmite and gibbsite and mixtures
thereof, and a selective sulfur adsorbent selected from the group
consisting of a blend of components selected from a) copper oxide,
a manganese compound and a binder; b) copper oxide, a zinc compound
and a binder, and c) a manganese compound, an iron compound and a
support to produce a hydrocarbon feed stream which has been
substantially desulfurized, and delivering the substantially
desulfurized hydrocarbon feed stream to remaining components of the
fuel cell processing train.
18. The process of claim 17, wherein the temperature of the
sequential sulfur adsorbent system as the feed stream passes
therethrough is from ambient to about 100.degree. C.
19. The process of claim 17, wherein the pressure of the sulfur
contaminated feed stream as it passes through the sequential sulfur
adsorbent system is from about 1 bar to about 18 bar.
20. A sequential adsorbent system for use in a fuel cell processing
train comprising in sequence calcium exchanged zeolite, hydrated
alumina and a selective sulfur adsorbent, wherein the calcium
exchanged zeolite comprises calcium exchanged zeolite X or LSX ion
exchanged to at least 50% of the available metal ions with calcium
ions; wherein the hydrated alumina is selected from the group
consisting of gibbsite, boehmite, pseudo-boehmite and mixtures
thereof; and wherein the selective sulfur adsorbent comprises from
about 60 to about 80% by weight of one or more manganese compounds
selected from the group consisting of MnO.sub.2, Mn.sub.2O.sub.3,
Mn.sub.3O.sub.4 and Mn(OH).sub.4 and mixtures thereof, from about
15 to about 40% by weight of copper oxide, and a binder.
21. A sequential adsorbent system for use in a fuel cell processing
train comprising in sequence calcium exchanged zeolite, wherein the
calcium exchanged zeolite comprises calcium exchanged zeolite X or
LSX, ion exchanged to at least 50% of the available metal ions with
calcium ions; hydrated alumina selected from the group consisting
of gibbsite, boehmite, pseudo-boehmite and mixtures thereof, and a
selective sulfur adsorbent comprising from about 15 to about 40
copper oxide, from about 5 to about 15 of a zinc compound and at
least about 40% alumina.
22. A sequential adsorbent system for use in a fuel cell processing
train comprising in sequence calcium exchanged zeolite X or LSX,
ion exchanged to at least 50% of the available metal ions with
calcium cations; hydrated alumina selected from the group
consisting of gibbsite, boehmite, pseudo-boehmite and mixtures
thereof, and a selective sulfur adsorbent comprising from about 20
to about 40% of a manganese compound or compounds selected from the
group consisting of MnO.sub.2, Mn.sub.2O.sub.3, Mn.sub.3O.sub.4,
Mn(OH).sub.4 and mixtures thereof, from about 40 to about 80% of
iron oxide, and a support.
Description
CROSS REFERENCED TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part application based
on application Ser. No. 11/207,154, filed on Aug. 18, 2005, which
is a continuation-in-part application based on application Ser. No.
10/923,177, which was filed on Sep. 1, 2004.
BACKGROUND OF INVENTION
[0002] The present invention relates to a novel method for
producing a substantially desulfurized hydrocarbon fuel stream,
particularly for hydrogen generation, and more particularly for use
within a fuel cell processing train, by passing a nondesulfurized
hydrocarbon fuel stream, particularly natural gas, propane or
liquefied petroleum gas (LPG), through a sequential sulfur
adsorbent system at temperatures less than 100.degree. C., wherein
the sequential sulfur adsorbent system contains in sequence a
zeolite sulfur adsorbent, a hydrated alumina adsorbent, and a
selective sulfur adsorbent. The present invention further relates
to a process for producing hydrogen within a fuel cell processing
train from a substantially desulfurized hydrocarbon fuel stream,
particularly desulfurized natural gas, propane or LPG, wherein the
hydrocarbon fuel stream is desulfurized using the above-described
sequential sulfur adsorbent system. The present invention further
includes the desulfurization system described above utilized for
hydrogen generation, particularly within a fuel cell processing
train, which system desulfurizes hydrocarbon fuel streams,
particularly comprising natural gas, propane or LPG, at
temperatures as low as ambient temperature, even when the level of
water or other hydrolyzing agents within that fuel stream is less
than 500 ppm.
[0003] For hydrogen generation, particularly for use in a
conventional low temperature fuel cell processing train, such as a
proton exchange membrane (PEM) fuel cell, which is suitable for use
in a stationary application or in a vehicle, such as an automobile,
the hydrocarbon fuel stream can be derived from a number of
conventional fuel sources with the preferred fuel sources including
natural gas, propane and LPG. In a conventional hydrogen generation
system, particularly a fuel cell processing train, the hydrocarbon
fuel stream is passed over and/or through a desulfurization system
to be desulfurized. The desulfurized hydrocarbon fuel stream for
such fuel cell processing train then flows into a reformer wherein
the fuel stream is converted into a hydrogen-rich fuel stream. From
the reformer the fuel stream passes through one or more heat
exchangers to a shift converter where the amount of CO in the fuel
stream is reduced. From the shift converter the fuel stream again
passes through various heat exchangers and then through a selective
oxidizer or selective methanizer having one or more catalyst beds,
after which the hydrogen rich fuel stream flows to the fuel cell
stack where it is utilized to generate electricity.
[0004] Raw fuels, in gaseous or liquid phase, particularly natural
gas, propane and LPG, are useful as a fuel source for hydrogen
generation, particularly for fuel cell processing trains.
Unfortunately, virtually all raw fuels of this type contain
relatively high levels, up to as high as 1,000 ppm or so, but
typically in the range of 20 to 500 ppm, of various naturally
occurring sulfur compounds, such as, but not limited to, carbonyl
sulfide, hydrogen sulfide, thiophenes, such as tetra hydro
thiophene, dimethyl sulfide, various mercaptans, disulfides,
sulfoxides, other organic sulfides, higher molecular weight organic
sulfur compounds, and combinations thereof. In addition, because
hydrocarbon fuel streams, particularly natural gas, propane and
LPG, may have different sources of origin, the quantity and
composition of the sulfur compounds that may be present in the fuel
streams can vary substantially. Further, these fuel stream sources
generally contain low quantities of water and other hydrolyzing
agents, generally at a level that may be as low as 500 ppm or
lower.
[0005] The presence of sulfur-containing compounds, particularly
carbonyl sulfide, in a hydrocarbon fuel stream can be very damaging
to components of the fuel cell processing train, including the fuel
cell stack itself, and such compounds must therefore be
substantially removed. If not substantially removed, the sulfur
compounds may shorten the life expectancy of the components of the
fuel cell processing train.
[0006] An especially efficient desulfurization system is necessary
for use in such fuel cell processing trains as they generally only
contain a single desulfurization system. Further, desulfurization
systems for such uses must have high capacity, as they may need to
be in use for an extended period of time before replacement.
[0007] Several processes, conventionally termed "desulfurization,"
have been employed for the removal of sulfur from gas and liquid
fuel streams for hydrogen generation. Adsorption of
sulfur-contaminated compounds from these hydrocarbon streams using
a "physical" sulfur adsorbent is the most common method for removal
of sulfur compounds from such hydrocarbon fuel streams because of
their relatively low capital and operational costs. (For purposes
of this specification, the terms "adsorption" and "absorption" as
well as "adsorbents" and "absorbents" each have the same, all
inclusive meaning.) While physical adsorbents are useful, they can
desorb the sulfur compounds from the adsorbent under certain
operating conditions. In addition, there are often limits on the
quantity of sulfur compounds which can be adsorbed by such physical
sulfur adsorbents.
[0008] An additional type of adsorbent that has been useful as a
desulfurization agent is a "chemical" sulfur adsorbent. However,
chemical desulfurization normally requires the desulfurization
system to be heated to temperatures of 150.degree. C. to
400.degree. C. before the nondesulfurized hydrocarbon fuel streams
can be effectively desulfurized by the chemical adsorbent
desulfurization system. In addition, other operational problems may
occur when such chemical desulfurization processes are
utilized.
[0009] While many different desulfurization processes have been
suggested for hydrocarbon fuel streams, there is still a need for
improved processes for desulfurization to achieve enhanced
adsorption of sulfur components, especially carbonyl sulfide, over
an extended range of sulfur concentrations, especially at
relatively low operating temperatures and pressures, and for
extended periods of time. In addition, these improved processes for
desulfurization must be able to achieve enhanced adsorption of
sulfur compounds even when the quantity of water or other
hydrolyzing agents in the feed stream is low, i.e. less than 500
ppm. Further, there is a need for improved desulfurization system
to adsorb substantial quantities of a wide range of sulfur
compounds, including particularly hydrogen sulfide, carbonyl
sulfide, tetra hydro thiophene, dimethyl sulfide, various
mercaptans, disulfides, sulfoxides, other organic sulfides, various
higher molecular weight sulfur-containing compounds and
combinations thereof, especially carbonyl sulfide without addition
of hydrolyzing agents. Further, it is important that these improved
desulfurization systems absorb this broad range of sulfur compounds
effectively for an extended period of time to delay "breakthrough"
of sulfur compounds as long as possible. "Breakthrough" occurs when
the amount of any sulfur compound remaining in the feed stream
after desulfurization is above a predetermined level. Typical
"breakthrough" levels for sulfur compounds occur at less than 1
ppm. Breakthrough by virtually any of the sulfur compounds present
in the hydrocarbon fuel stream is disadvantageous as substantially
all sulfur compounds can cause damage to components of a hydrogen
generation system, particularly for a fuel cell processing train.
Further, some sulfur compounds, particularly carbonyl sulfide, are
quite difficult to remove from such fuel streams, especially
without the addition of hydrolyzing agents.
[0010] In addition, some prior art adsorbents, while effective as
adsorbents for some sulfur compounds, can synthesize the production
of sulfur compounds even as they are removing some of the naturally
occurring sulfur compounds that are present in the hydrocarbon fuel
stream. (These newly produced sulfur compounds are referred to
herein as "synthesized sulfur compounds.") It is important that the
desulfurization system avoid the production of synthesized sulfur
compounds to the greatest extent possible and for the longest
period of time possible.
[0011] The foregoing description of preferred embodiments of the
invention provides processes, systems and products that address
some or all of the issues discussed above.
SUMMARY OF INVENTION
[0012] One of the inventions disclosed is a process for supplying a
substantially desulfurized hydrocarbon fuel stream, particularly
for hydrogen generation, and most particularly for use in a fuel
cell processing train, comprising providing a nondesulfurized
hydrocarbon fuel stream, preparing a desulfurization system
comprising a sequential sulfur adsorbent system comprising, in
sequence, a calcium exchanged zeolite sulfur adsorbent, a hydrated
alumina adsorbent, and a selective sulfur adsorbent, and passing
the nondesulfurized hydrocarbon fuel stream through or over the
desulfurization system at a temperature optimally less than about
100.degree. C. to produce a substantially desulfurized hydrocarbon
fuel stream with desulfurization levels as low as about 50 ppb or
so. Preferably, this level of desulfurization is accomplished even
when the level of water and other hydrolyzing agents that are
present in the feed stream are less than 500 ppm. One feature of
one embodiment of this invention is that effective sulfur removal,
particularly for the removal of carbonyl sulfide, can be achieved
without the addition of conventional hydrolyzing agents to the feed
stream. The composition and choice of the selective sulfur
adsorbent within the desulfurization system depends on the
composition of the sulfur compounds which are present in that fuel
stream and the extent of sulfur removal and time before
breakthrough occurs that are required.
[0013] Another of the inventions is a process for generating
hydrogen for use in a fuel cell processing train by use of a
substantially desulfurized hydrocarbon fuel stream comprising
preparing a fuel cell processing train containing the
desulfurization system described above, passing a nondesulfurized
hydrocarbon fuel cell fuel stream through the desulfurization
system at a temperature, preferably less than about 100.degree. C.,
and introducing the substantially desulfurized hydrocarbon fuel
stream to the remaining components of the fuel cell processing
train.
[0014] Another of the inventions is a desulfurization system,
particularly for hydrogen generation and most particularly for use
in a fuel cell processing train, comprising an inlet for receiving
a nondesulfurized hydrocarbon fuel stream, particularly natural
gas, propane and/or LPG, the sequential adsorbent system described
above, and an outlet for passing a substantially desulfurized
hydrocarbon fuel stream downstream to the remaining components of
the hydrogen generation system.
[0015] A further invention is a sequential sulfur adsorbent system,
particularly for hydrogen generation and most particularly for use
in a fuel cell processing train, comprising, in sequence, a calcium
exchanged zeolite, a hydrated alumina adsorbent, and a selective
sulfur adsorbent. The choice of the specific selective sulfur
adsorbent that is used within the sequential sulfur adsorbent
system depends upon the composition and quantity of the sulfur
compounds that are present in the hydrocarbon fuel stream and the
level of sulfur removal and time for breakthrough that are
required. One particularly preferred selective sulfur adsorbent
comprises one or more manganese compounds, copper oxide and a
binder. A further alternative preferred selective sulfur adsorbent
comprises copper oxide, zinc oxide and alumina. An additional
alternative preferred selective sulfur adsorbent comprises one or
more manganese compounds, iron oxide and a high surface area
carrier, particularly alumina.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1 is a graph showing a comparison of the performance of
two sequential adsorbent systems of Example 1 and Example 2 for the
removal of carbonyl sulfide from a synthetic natural gas feed
stream.
[0017] FIG. 2 comprises the performance of the desulfurization
systems of Example 1 and Example 2 for the removal of carbonyl
sulfide from a fuel stream.
DISCLOSURE OF A PREFERRED EMBODIMENT OF THE INVENTION
[0018] The invention includes, but is not limited to, a method for
supplying a substantially desulfurized hydrocarbon fuel stream,
particularly for a hydrogen generation system and most particularly
for a fuel cell processing train. Raw fuel, for use in such
hydrogen generation systems, particularly a fuel cell processing
train, such as natural gas, propane and LPG, must be desulfurized
prior to use because such fuel streams contain relatively high
levels of sulfur compounds, such as, but not limited to, hydrogen
sulfide, carbonyl sulfide, thiophenes, such as tetra hydro
thiophene, dimethyl sulfide, mercaptans (including ethyl, methyl,
propyl and tertiary butyl mercaptan), other sulfides, various
higher molecular weight organic sulfur compounds and combinations
thereof. In addition, some sulfur compounds, particularly carbonyl
sulfide can be quite difficult to remove from such raw fuel. These
sulfur compounds can damage components of the hydrogen generation
system and the fuel cell processing train. While numerous
combinations and quantities of these sulfur compounds may be
present in the fuel stream, in some situations the sulfur compounds
present in the fuel stream may be limited to only one or two of
such sulfur compounds. Such raw fuels, particularly natural gas,
generally contain limited amounts of water and other common
hydrolyzing agents, such as ethanol or methane, generally 500 ppm
or less. It is one feature of this invention that effective removal
of sulfur compounds, particularly carbonyl sulfide, can be achieved
without the addition of a hydrolyzing agent, such as water, ethanol
or methanol to the fuel stream.
[0019] Where the raw fuel stream comprises natural gas, which is in
a gaseous state at operating temperatures below 100.degree. C.,
particularly below 60.degree. C., the level of sulfur compounds,
such as carbonyl sulfide, hydrogen sulfide, tetra hydro thiophene,
dimethyl sulfide, mercaptans, other organic sulfur compounds, and
combinations thereof may be as high as 100 ppm or so. The presence
of such high levels of sulfur compounds, if not removed, results in
the poisoning of components of the fuel cell processing train and
may foul the fuel cell stack itself. Substantially complete removal
of all of the sulfur compounds is necessary as the presence of even
modest quantities of even a single sulfur compound can damage
components of the fuel cell processing train.
[0020] While the desulfurization system of one embodiment of the
invention can be utilized for a number of different hydrogen
generation processes, one particularly preferred utilization is
within a fuel cell processing train. For purposes of this
specification while the use of this desulfurization system with all
hydrogen generation systems is included, one preferred embodiment
is the use of this system within a fuel cell processing train.
[0021] The inventors have surprisingly discovered that substantial
desulfurization of a hydrocarbon fuel stream down to levels as low
as 50 ppb or so can be achieved when a sequential sulfur adsorbent
system is used for desulfurization which comprises, in sequence, a
zeolite adsorbent, particularly a calcium exchanged zeolite, more
particularly a calcium exchanged zeolite X or LSX, a hydrated
alumina, and a selective sulfur adsorbent. In a preferred
embodiment the sequence of use of the components in the
desulfurization system is first the zeolite adsorbent, then the
hydrated alumina, and finally the selective sulfur adsorbent. The
composition of the components of the sequential sulfur adsorbent
system can be modified depending on the composition and quantity of
the sulfur compounds that are present in the hydrocarbon feed
stream, the extent of removal of sulfur that is required and the
time that is required before breakthrough occurs.
[0022] While not a preferred embodiment, it is possible to achieve
effective sulfur removal from a feed stream where two or more of
the components of the desulfurization system are partially or
completely blended together before placement in the desulfurization
system. For example, some portion or all of the hydrated alumina
may be blended with either or both of the calcium exchanged zeolite
and the selective sulfur adsorbent. It is preferred, however, to
separate the three components from each other even though minimal
blending may occur at the border between two components when those
components are placed together in a desulfurization system, for
example, when the components are introduced in layers without any
physical separation therebetween.
[0023] The selective sulfur adsorbent(s) of the invention may be
selected from a wide variety of adsorbents. As used herein a
"selective sulfur adsorbent" is a material that preferentially
absorbs at least one of the sulfur compounds that are commonly
present in hydrocarbon fuel cell fuel streams, particularly natural
gas, propane or LPG, such as hydrogen sulfide, carbonyl sulfide,
tetra hydro thiophene, dimethyl sulfide, mercaptans, particularly
ethyl, methyl, propyl, and tertiary butyl mercaptans and
combinations thereof, particularly carbonyl sulfide, at a
temperature below about 100.degree. C., particularly below
60.degree. C., and at pressures of about 1 bar to 18 bar. These
fuel streams also commonly contain less than 500 ppm of water and
other hydrolyzing agents, such as ethanol and methanol. Because of
the choice of the components of the sequential bed, it is not
necessary to add a hydrolyzing agent to the feed stream, to
hydrolyze one or more of the sulfur compounds contained therein,
particularly COS, before they are removed therefrom.
[0024] Each selective sulfur adsorbent selectively adsorbs one or
more of the sulfur compounds that are commonly present in the
hydrocarbon fuel cell fuel stream, preferably natural gas. However,
each of these adsorbents may be less or more effective than other
of the selective sulfur adsorbents for the adsorption of particular
sulfur compounds or combinations of these compounds. Further,
problems can be created in the feed stream when some of the
selective sulfur adsorbents are used, as these selective sulfur
adsorbents can synthesize existing sulfur compounds into different,
higher molecular weight sulfur compounds that are not removable
from the fuel stream by the particular selective sulfur adsorbent
that is utilized.
[0025] It has been surprisingly discovered that a desulfurization
system can be substantially enhanced by utilizing a zeolite
adsorbent, particularly a calcium exchanged zeolite, and more
particularly a calcium exchanged zeolite X or LSX, and a hydrated
alumina adsorbent in sequence before the selective sulfur
adsorbent. In particular, the combination of a selective sulfur
adsorbents with the calcium exchanged zeolite adsorbent and
hydrated alumina adsorbent in sequence performs surprisingly better
than any of the individual selective sulfur adsorbents, the
hydrated alumina adsorbent or the calcium exchanged zeolite, when
used individually, or even the selective sulfur adsorbent utilized
with the calcium exchanged zeolite, without also using the hydrated
alumina adsorbent. The preferred choice and arrangement of the
selective sulfur adsorbent(s), the hydrated alumina adsorbent, and
the zeolite within the sequential sulfur adsorbent system also
reduces the likelihood of the production of synthesized sulfur
compounds that are sometimes created when a selective sulfur
adsorbent is used with or without the calcium exchanged zeolite in
a desulfurization system.
[0026] It has been further surprisingly discovered that the removal
of various combinations of sulfur compounds can be enhanced by the
specific arrangement and choice of the adsorbents in the sequential
sulfur adsorbent system. For the removal of various sulfur
compounds, it is preferable to place the calcium exchanged zeolite
in the sequential sulfur adsorbent system prior to both the
hydrated alumina adsorbent and the selective sulfur adsorbent. In a
more preferred embodiment the sequence of the components of the
sulfur adsorbent system is first the calcium exchanged zeolite,
followed by the hydrated alumina and finally the selective sulfur
adsorbent.
[0027] Sulfur adsorption by this system is further enhanced because
some sulfur compounds, which may be synthesized to larger and more
difficult to remove sulfur compounds by a particular selective
sulfur adsorbent, are removed from the feed stream by the zeolite
adsorbent, particularly the calcium-exchanged zeolite adsorbent
and/or the hydrated alumina adsorbent when used in a sequential
combination, prior to synthesis by the selective sulfur
adsorbent.
[0028] Useful selective sulfur adsorbents are selected from a group
of adsorbents including, but not limited to, an adsorbent
comprising substantially manganese compounds; an adsorbent which
includes manganese compounds, copper oxide and a binder; an
adsorbent which includes manganese compounds, iron oxide and a
support, particularly alumina, most particularly a hydrated
alumina; an adsorbent which includes zinc oxide and a carrier,
particularly alumina; an adsorbent which includes activated carbon
with copper oxide; an adsorbent which includes a zinc oxide/copper
oxide blend, preferably containing small quantities of carbon and
alumina; an adsorbent which includes copper oxide with alumina; an
adsorbent which includes a copper oxide/zinc oxide blend mixed with
alumina, preferably a hydrated alumina; an adsorbent which includes
nickel on silica or alumina and various known selective sulfur
adsorbents which include copper and zinc. Various quantities of the
individual components of each of these selective sulfur adsorbents
can be utilized and the quantity of the individual components can
be modified to enhance the adsorption capacity of the overall
desulfurization system, depending on the particular sulfur
compounds that are present in the hydrocarbon fuel cell fuel stream
and the quantity thereof.
[0029] In one preferred embodiment, the selective sulfur adsorbent
includes one or more manganese compounds blended with iron oxide on
a support, such as alumina, silica, silica-alumina, titania, and
other inorganic refractory oxides. The preferred quantity of the
support comprises from about 5 to about 25% by weight, preferably
from about 5 to about 20% by weight, and most preferably from about
5 to about 15% by weight of the total weight of this selective
sulfur adsorbent. One primary function of the support material is
to provide a large and accessible surface area for deposition of
the active metal compounds.
[0030] The metal compounds which are deposited on or incorporated
within the support of this selective sulfur adsorbent, other than
the one or more manganese compound(s), include iron oxide. In a
preferred embodiment the iron oxide and manganese compound(s)
together comprise at least about 60% by weight, preferably at least
about 70% by weight and most preferably about 80% to about 90% of
this selective sulfur adsorbent, by weight.
[0031] In a preferred embodiment the quantity of iron oxide present
in this selective sulfur adsorbent exceeds the quantity of the
manganese compound(s). It is preferred that the ratio of the iron
oxide to the manganese compound(s) by weight, should be at least
about 1:1 and preferably from about 1:1 to about 6:1. The preferred
loading of iron oxide on the support is in the range of about 40
weight percent to about 80 weight percent and, more preferably from
about 50 to about 70 weight percent of the total weight of the
selective sulfur adsorbent. Various forms of iron oxide may be
used, such as FeO and Fe.sub.2O.sub.3 and mixtures thereof.
[0032] The one or more manganese compound(s) comprise from about 15
weight percent to about 40 weight percent, preferably from about 20
weight percent to about 40 weight percent of the total weight of
the selective sulfur adsorbent. Various forms of manganese
compounds can be used including MnO.sub.2, Mn.sub.2O.sub.3,
Mn.sub.3O.sub.4 and Mn(OH).sub.4 and mixtures thereof.
[0033] A promoter or promoters may also be added to this selective
sulfur adsorbent, preferably an alkali or alkaline earth metal
oxide, promoter and more preferably calcium oxide, in quantities
from about 5 to about 15% by weight. While calcium oxide is the
preferred promoter, alkali or other alkaline earth metal oxide
promoters, such as magnesium oxide, may also, or alternatively, be
utilized in combination with the calcium oxide.
[0034] The iron oxide/manganese compound(s) selective sulfur
adsorbent according to the present invention may be prepared by
coprecipitation, decomposition, impregnation or mechanical mixing.
Preferably, this selective sulfur adsorbent is produced by
coprecipitation or decomposition. The method chosen should
guarantee that there has been an intensive blending of the
components of the selective sulfur adsorbent.
[0035] The pore volume of the iron oxide/manganese compound(s)
adsorbent produced by those procedures determined by mercury
porosimetry is preferably from about 0.3 cc/g to about 0.6 cc/g. In
addition, this selective sulfur adsorbent preferably has a
compacted bulk density of about 0.4 to about 1.1 g/cc. Once the
material is in its preliminary product form, it can be further
processed to form the final selective sulfur adsorbent by
pelletizing or extrusion. This selective sulfur adsorbent
preferably is formed into moldings, especially in the form of
spheres or pellets, preferably ranging in size from about 0.1 cm to
about 1 cm in diameter. The materials for this selective sulfur
adsorbent are preferably chosen to achieve a surface area of at
least about 100 m.sup.2/g and more preferably from about 100
m.sup.2/g to about 300 m.sup.2/g.
[0036] This iron oxide/manganese compound(s) selective sulfur
adsorbent when used alone has shown especially good sulfur
adsorption when the sulfur compounds contained in a fuel cell fuel
stream comprise hydrogen sulfide, carbonyl sulfide (COS), tertiary
butyl mercaptan (TBM) and ethyl mercaptan (EM). This selective
sulfur adsorbent, when utilized with the calcium-exchanged zeolite
adsorbent and the hydrated alumina adsorbent, has shown enhanced
utility for adsorption of sulfur compounds that are commonly
present in a fuel cell fuel stream including COS, tetra hydro
thiophene (THT) and dimethyl sulfide (DMS), especially when the
zeolite is placed in a adsorption system in sequence before the
hydrated alumina adsorbent followed by the iron oxide/manganese
compound(s) adsorbent in the sequential sulfur adsorbent
system.
[0037] An additional preferred selective sulfur adsorbent that can
be utilized with the zeolite adsorbent and the hydrated alumina
adsorbent in the sequential sulfur adsorbent system includes one or
more manganese compound(s), copper oxide and small quantities of a
binder. The manganese compound(s) of this selective sulfur
adsorbent may be utilized in any of the forms previously described
for the manganese compound of the selective sulfur adsorbent
described above. The manganese compound(s) of this selective sulfur
adsorbent comprise from about 50 to about 80% and preferably from
about 60 to about 75% of this selective sulfur adsorbent, by
weight. The copper oxide comprises from about 15 to about 40% and
preferably from about 15 to about 30%, by weight, of this selective
sulfur adsorbent. The binder comprises from about 5 to 20%, by
weight, of this selective sulfur adsorbent. In a preferred
embodiment the binder may be selected from a wide variety of clays
including bentonite, diatomaceous earth, attapulgite, kaolin,
sepiolite, illite and mixtures thereof. More preferably, the binder
comprises bentonite clay. Promoters may be added to this selective
sulfur adsorbent to enhance its operating characteristics. This
adsorbent is prepared by conventional procedures. The materials for
this selective sulfur adsorbent are chosen so that the surface area
of this manganese compound(s)/copper oxide with binder ranges from
about 100 to about 300 m.sup.2/g, preferably from about 200 to
about 300 m.sup.2/g.
[0038] This manganese compound(s)/copper oxide/binder selective
sulfur adsorbent when used alone has shown great utility for the
adsorption of hydrogen sulfide, carbonyl sulfide, tertiary butyl
mercaptan, ethyl mercaptan and mixtures thereof. In addition, this
manganese compound(s)/copper oxide/binder selective sulfur
adsorbent, when utilized in sequence after the zeolite adsorbent
and the hydrated alumina in the sequential sulfur adsorbent system,
has shown significant adsorption for sulfur compounds contained in
hydrocarbon fuel cell feed streams of the same type as those
described above where the selective sulfur adsorbent composition
comprises iron oxide, manganese compound(s) and small quantities of
a support. This selective sulfur adsorbent has shown particular
utility when it is necessary to reduce the level of carbonyl
sulfide in the feed stream to extremely low levels, as low as 50
ppb or so, especially without the addition of any hydrolyzing agent
to the feed stream.
[0039] An additional selective sulfur adsorbent, that can be
utilized with the zeolite adsorbent and the hydrated alumina
adsorbent in the sequential adsorbent system, comprises copper
oxide, zinc oxide and alumina, preferably a hydrated alumina. The
quantity of copper oxide present is from about 15 to about 25%, the
quantity of the zinc oxide is from about 5 to about 15%, and the
quantity of the alumina is from about 65 to about 85%, by weight.
The adsorbent is prepared by conventional procedures. The materials
for this selective sulfur adsorbent are chosen so that its surface
area is from about 100 to about 300 m.sup.2/g, preferably from
about 150 to 300 m.sup.2/g. This selective sulfur adsorbent
catalyst is prepared by conventional procedures.
[0040] This selective sulfur adsorbent when used alone is
particularly useful for the adsorption of hydrogen sulfide,
carbonyl sulfide, tertiary butyl mercaptan, ethyl mercaptan, and
mixtures thereof. This selective adsorbent has shown particular
utility for the adsorption of carbonyl sulfide for extended periods
of time before "breakthrough" occurs, especially without the
addition of any hydrolyzing agent to the feed stream.
[0041] An additional selective sulfur adsorbent that can be
utilized with the zeolite adsorbent and the hydrated alumina
adsorbent in the sequential sulfur adsorbent system in place of, or
in addition to, the above described selective sulfur adsorbents
comprises zinc oxide alone or in combination with a carrier. While
alumina is the preferred carrier, other carriers with similar
performance characteristics can be utilized. In a preferred
embodiment, the zinc oxide comprises at least about 60%, preferably
from about 60 to about 95%, and more preferably from about 70 to
about 90%, by weight, of the selective sulfur adsorbent with the
remaining portion preferably comprising alumina. Additives may be
added to this selective sulfur adsorbent to enhance its capacity to
absorb sulfur compounds or other performance characteristics. The
surface area of this selective sulfur adsorbent ranges from 5 to
about 75 m.sup.2/g and preferably from about 10 to about 50
m.sup.2/g. This zinc oxide/alumina selective sulfur adsorbent is
prepared by conventional procedures.
[0042] The zinc oxide alumina selective sulfur adsorbent when used
alone as a sulfur adsorbent has shown good sulfur adsorption when
the sulfur compounds contained within the fuel cell fuel stream
comprise hydrogen sulfide and ethyl mercaptan and mixtures
thereof.
[0043] Another selective sulfur adsorbent that can be utilized with
the zeolite adsorbent and the hydrated alumina adsorbent in the
sequential sulfur adsorbent system is comprised of activated carbon
containing small quantities of copper oxide. In a preferred
embodiment the activated carbon comprises from about 80 to about
95%, preferably 85 to 95%, by weight, of this selective sulfur
adsorbent with the remaining portion comprising copper oxide.
Additives may be added to the composition to enhance its
performance. The activated carbon/copper oxide selective sulfur
adsorbent is prepared by conventional procedures. The surface area
of the composition ranges from about 300 to about 1000 m.sup.2/g,
with the preferred surface area being from about 500 m.sup.2/g to
about 1000 m.sup.2/g. This selective sulfur adsorbent is prepared
by conventional procedures.
[0044] This activated carbon with copper oxide selective sulfur
adsorbent when used alone has shown great utility for the
adsorption of tetra hydro thiophene, tertiary butyl mercaptan,
ethyl mercaptan and mixtures thereof.
[0045] Another useful selective sulfur adsorbent that can be
utilized with the zeolite adsorbent and the hydrated alumina
adsorbent in a sequential sulfur adsorbent system comprises copper
oxide and zinc oxide with alumina, preferably with small quantities
of carbon. In a preferred embodiment the copper oxide comprises
from about 50 to about 65% and more preferably from about 50 to
about 60% of the selective sulfur adsorbent, by weight. The zinc
oxide comprises from about 20 to about 35% of the selective sulfur
adsorbent and the alumina comprises from about 5 to about 20%,
preferably from about 10 to 20% of the selective sulfur adsorbent,
by weight. The quantity of the carbon, if used, should be less than
10%, preferably from about 1 to about 10%, by weight. The surface
area of this selective sulfur adsorbent containing copper oxide,
zinc oxide, alumina, and preferably small quantities of carbon, is
from about 100 to about 300 m.sup.2/g and preferably from about 100
to about 200 m.sup.2/g. The process for the preparation of this
selective sulfur adsorbent is conventional.
[0046] This copper oxide/zinc oxide/alumina, preferably with small
quantities of carbon, selective sulfur adsorbent when used alone is
especially useful for the adsorption of hydrogen sulfide, tertiary
butyl mercaptan, ethyl mercaptan, carbonyl sulfide and mixtures
thereof.
[0047] An additional selective sulfur adsorbent that can be
utilized with the zeolite adsorbent and the hydrated alumina
adsorbent in the sequential sulfur adsorbent system, comprises
manganese compound(s), used alone, which may be utilized in a
number of forms including MnO.sub.2, Mn.sub.2O.sub.3,
Mn.sub.3O.sub.4 and Mn(OH).sub.4 or mixtures thereof. The surface
area of the manganese compound(s) range from about 100 to about 300
m.sup.2/g, and preferably from about 200 to about 300 m.sup.2/g.
Additional materials may be combined with the manganese compound(s)
including calcium, silver and magnesium to promote the performance
of the manganese compound(s). Conventional methods are utilized for
the formation of this selective sulfur adsorbent.
[0048] The manganese compound(s) selective sulfur adsorbent when
used alone has shown great utility for the adsorption of hydrogen
sulfide, tertiary butyl mercaptan, ethyl mercaptan and mixtures
thereof.
[0049] An additional selective sulfur adsorbent, that can be
utilized with the zeolite adsorbent and the hydrated alumina
adsorbent in the sequential sulfur adsorbent system, comprises
copper oxide with alumina, wherein the quantity of the copper oxide
is from about 5 to about 25%, preferably from about 10 to about
20%, by weight, and the quantity of the alumina is from about 75 to
about 95%, preferably from about 80 to about 90%, by weight. The
surface area of this selective sulfur adsorbent is from about 100
to about 300 m.sup.2/g and preferably from about 150 to about 300
m.sup.2/g. This selective sulfur adsorbent is prepared by
conventional procedures.
[0050] This selective sulfur adsorbent when used alone has shown
particularly usefulness for the adsorption of hydrogen sulfide,
carbonyl sulfide, tertiary butyl mercaptan, ethyl mercaptan and
mixtures thereof.
[0051] The preferred sequence of use of the adsorbents in the
desulfurization system is the zeolite adsorbent placed prior to the
hydrated alumina adsorbent and followed by the selective sulfur
adsorbent. The preferred ratio of the zeolite adsorbent to the
combination of the hydrated alumina adsorbent and selective sulfur
adsorbent is from about 1:3 to 3:1 and preferably 1:2 to about 2:1
and most preferably in the range from about 1:1, by volume.
[0052] The inventors have discovered that while a number of
selective sulfur adsorbents may be utilized with the combination of
the calcium exchange zeolite and the hydrated alumina to remove
sulfur compounds from a feed stream, the preferred selective sulfur
adsorbents, especially when carbonyl sulfide is present,
particularly for hydrogen generation, comprise: a) one or more
manganese compounds blended with copper oxide on small quantities
of a binder, b) copper oxide, zinc oxide and alumina, preferably a
hydrated alumina, and c) one or more manganese compounds, iron
oxide and a support.
[0053] The inventors have surprisingly discovered that while
several types of ion exchanged zeolites may be useful as the
zeolite adsorbent for this sequential sulfur adsorbent system, the
preferred ion exchanged zeolite is a calcium exchanged zeolite.
While a number of calcium exchanged zeolites are known, including
calcium exchanged zeolite A, zeolite X, zeolite Y, zeolite ZSM-5,
zeolite Beta, synthetic mordenite and blends thereof, the preferred
calcium exchanged zeolite for this desulfurization system is a
calcium exchanged zeolite X. A particularly preferred calcium
exchanged zeolite X is a calcium exchanged, low silica zeolite X,
known as "LSX", or calcium exchanged low silica faujasite, known as
"LSF". Zeolite X generally has a Si:Al equivalent ratio of about
1.0 to about 1.25. In one example, a conventional, non-calcium
exchanged precursor synthesized LSF has the following anhydrous
chemical composition: 2.0 SiO.sub.2:Al.sub.2O.sub.3:0.73
Na.sub.2O:0.27K.sub.2O, although the ratio between sodium and
potassium cations can vary, sometime significantly, depending upon
the process of manufacture of the LSF.
[0054] In one embodiment of the invention, a substantial percentage
of the cations of the zeolite X are preferably ion exchanged with
calcium ions using conventional ion exchange procedures, such as by
treatment of the zeolite X with calcium salts, such as, but not
limited to, calcium chloride. Several methods can be used for the
ion exchange procedure with ion exchange preferably occurring after
the zeolite adsorbent has been formed into its preferred final
form, such as a bead or an extrudate. The zeolite X is ion
exchanged to a level of at least about 50%, preferably at least
60%, more preferably at least 70%, and most preferably 85 to 95% of
the exchangeable metal ions. The remaining ions may be sodium
and/or potassium ions. (For reference purposes the term "calcium
exchanged zeolite X" means a zeolite X containing at least about
50% calcium cations.) The calcium exchanged zeolite X of one
embodiment of the invention generally contains some sodium or
potassium ions in addition to the calcium ions after the calcium
ion exchange. However, a portion, up to substantially all of these
sodium/potassium ions, can be ion exchanged with other cations to
enhance or modify the performance characteristics of the calcium
exchanged zeolite X, especially for sulfur adsorption. For example,
the additional cations that may be ion exchanged onto the zeolite X
to enhance its performance include zinc, cadmium, cobalt, nickel,
copper, iron, manganese, silver, gold, scandium, lithium and
combinations thereof. The percentage of ion exchange of these
additional metal ions can range from as little as about 1% up to
about 40% or so, depending upon the level of calcium exchange of
the zeolite X. The particular metal ions that are ion exchanged
onto the calcium exchanged zeolite depend on the particular sulfur
compounds which are intended to be removed from the fuel cell fuel
stream by the sequential sulfur adsorbent system of the
invention.
[0055] The calcium exchanged zeolite, when utilized as a sulfur
adsorbent, has shown significant capability for the adsorption of
various sulfur materials, particularly tetra hydro thiophene (THT),
di-methyl sulfide (DMS), tertiary butyl mercaptan (TBM) and ethyl
mercaptan (EM).
[0056] The alumina component of the invention comprises
substantially a hydrated alumina. For purposes of this invention
the terms "alumina hydrate" or "hydrated alumina" comprise aluminum
hydroxides that commonly have the formula Al(OH).sub.3 or AlO(OH).
The crystalline forms of these hydrated aluminas are trihydroxides
and include gibbsite, bayerite and nordstrandite. Hydrated alumina
also includes aluminum oxide-hydroxides such as boehmite,
pseudo-boehmite, and diaspore. The preferred forms of hydrated
alumina for the alumina component of various forms of the invention
include boehmite, pseudo-boehmite and gibbsite. The percentage of
the alumina, which comprises hydrated alumina of the type described
above, is greater than 60%, preferably greater than 80%, and most
preferably it approaches 100%.
[0057] While non-activated hydrated aluminas are the preferred form
of hydrated alumina for the desulfurization system, "activated"
hydrated aluminas may also have utility for some sulfur removal
applications. For purposes of this invention, "activation" of a
hydrated alumina requires impregnation of a hydrated alumina with
one or more alkali metal or alkaline earth metal ions, preferably
in an amount from about 0.01 to about 10 wt. %, wherein the wt. %
is measured as a percentage weight of the impregnated alkali metal
or alkaline earth metal to the total weight of the alkali
metal/alkaline earth metal and aluminum in the composition.
Activated hydrated alumina is generally activated by impregnation
with alkali metal ions, most preferably sodium or potassium ions.
Activated hydrated alumina of this type is prepared by methods
recognized in the art, such as those disclosed, for example, in
U.S. Pat. Nos. 3,058,800 and 4,835,338, both of which patents are
incorporated herein by reference.
[0058] It has been surprisingly discovered that the capability of
the selective sulfur adsorbents described above, when used
individually, the hydrated alumina described above, and the calcium
exchanged zeolite, when used individually, can be enhanced
dramatically by the sequential use of the calcium exchanged zeolite
X and the hydrated alumina when placed prior to the selective
sulfur adsorbents in the flow of the feed stream to form the
sequential sulfur adsorbent system for the desulfurization of a
hydrocarbon fuel cell feed stream. The use of this combination of
calcium exchanged zeolite, hydrated alumina and selective sulfur
adsorbent placed in sequence, permits the adsorption of a broader
range of sulfur containing compounds than has been conventionally
been adsorbed using any of the components alone. For example, it
has been surprisingly discovered that by the use of calcium
exchanged zeolite X, hydrated alumina, and selective sulfur
adsorbents placed in sequence, enhanced sulfur adsorption of a
broad range of sulfur compounds, including carbonyl sulfide,
hydrogen sulfide, tetra hydro thiophene, dimethyl sulfide, and
various mercaptans, including ethyl, methyl, propyl, and tertiary
butyl mercaptan and combinations thereof, is possible. This
combination of materials when used in this sequence has shown
particular utility for the removal of carbonyl sulfide from the
feed stream, even when the level of conventional hydrolysis agents,
such as water, ethanol, and methanol, in the feed stream is low,
i.e. less than about 500 ppm. Efficient removal occurs even without
the addition of conventional hydrolysis agents. In addition,
especially efficient removal of carbonyl sulfide to levels as low
as 50 ppb has been achieved when the selective sulfur adsorbent
comprises one or more manganese compounds, copper oxide and small
quantities of a binder, as previously discussed.
[0059] It has also been surprisingly discovered that the
breakthrough time for sulfur compounds commonly present in a
hydrocarbon fuel system can be extended by the use of the calcium
exchanged zeolite X, hydrated alumina and selective sulfur
adsorbent placed in sequence in the feed stream in the preferred
order of the components. This breakthrough time is enhanced over a
desulfurization system containing only the calcium exchanged
zeolite and the selective sulfur adsorbent when used in
combination. This extension of breakthrough time is particularly
apparent when the selective sulfur adsorbent comprises copper
oxide, zinc oxide and alumina, as previously discussed.
[0060] It has also been surprisingly discovered that by placement
of the calcium exchanged zeolite X prior to the hydrated alumina,
which is then followed by the selective sulfur adsorbent in the
sequential sulfur adsorption system, the likelihood of the
production of synthesized sulfur compounds is substantially
reduced.
[0061] The inventors have also surprisingly discovered that the
sequential sulfur adsorbent system as described herein can be
utilized at temperatures lower than normally utilized for
conventional sulfur adsorption systems. While conventional chemical
sulfur adsorbents require temperatures for the feed stream of at
least about 150.degree. C. to about 400.degree. C., embodiments of
the sequential sulfur adsorbent system can be utilized effectively
to adsorb the sulfur contaminants at temperatures below 100.degree.
C. Such embodiments can be especially effective for removal of some
sulfur compounds at temperatures from ambient temperature to
100.degree. C., particularly from ambient to 60.degree. C.
[0062] In addition, when the sequential sulfur adsorbent system as
described is used, the pressure on the feed stream can be reduced
to a range from about 1 bar to about 18 bar, preferably from about
1.7 bar to about 7 bar. These pressure ranges are lower than
normally are utilized for the adsorption of sulfur compounds in a
conventional fuel cell processing train.
[0063] In addition, when the sequential sulfur adsorbent system as
described herein is used, the applicants have surprisingly
discovered that it is not necessary that there be a conventional
hydrolysis agent, such as water, ethanol, or methanol in the feed
stream to enhance sulfur removal. In previous sulfur adsorbent
systems, especially those used for the removal of carbonyl sulfide,
it was necessary that a hydrolyzing agent, either be present in the
feed stream or be added to the feed stream in significant
quantities. The inventors have surprisingly discovered that
efficient and effective sulfur removal, especially for the removal
of carbonyl sulfide, can occur when the sequential sulfur adsorbent
system of the invention is utilized, even when the quantity of
water or other hydrolyzing agents in the feed stream is less than
500 ppm. In fact, the absence of water or other hydrolyzing agents
from the feed stream in amounts greater than 500 ppm is a preferred
composition for a feed stream utilizing the sequential sulfur
adsorbent system of the invention to reduce the likelihood that the
calcium exchanged zeolite absorbs excessive levels of water or
other hydrolyzing agents.
[0064] The inventors have also surprisingly discovered a method for
supplying a substantially desulfurized hydrocarbon fuel stream to a
fuel cell processor using the sequential sulfur adsorbent system
described herein. In this process a sulfur contaminated hydrocarbon
fuel stream is passed over or through the sequential sulfur
adsorbent system of a fuel cell processor at a temperature from
about ambient to about 100.degree. C., preferably less than
60.degree. C., and more preferably at ambient temperatures. By
passing a hydrocarbon fuel stream comprising, for example, natural
gas, propane or LPG, containing sulfur components at levels up to
500 ppm, a substantial reduction in the quantity of those sulfur
compounds, preferably down to a level of less than about 50 ppb,
can be achieved. It has also been surprisingly discovered that this
reduction in sulfur occurs even when the level of water or other
hydrolyzing agents in the fuel stream is less than 500 ppm.
Utilization of feed streams with this low level of water or other
hydrolyzing agents is a preferred embodiment.
[0065] The inventors have also discovered that the above-described
sequential sulfur adsorbent system of the invention can be used in
a desulfurizer, particularly for use in a fuel cell processing
train. This desulfurizer includes an inlet for receiving the
nondesulfurized hydrocarbon fuel stream, such as natural gas,
propane or LPG, the sequential sulfur adsorbent system, as
described herein, which is placed in a location to desulfurize the
hydrocarbon fuel stream, and an outlet where the desulfurized
hydrocarbon fuel stream is passed down stream for further
processing. For example, the desulfurized hydrocarbon fuel stream
can be passed through the fuel cell processing train to the fuel
cell stack for the production of electricity.
[0066] The inventors have also surprisingly discovered that this
method for supplying a substantially desulfurized hydrocarbon fuel
stream is more advantageous than methods using conventional
desulfurization systems as it permits desulfurization of a broader
range of sulfur compounds, increases the sulfur compound
breakthrough time for the system, reduces the production of
synthesized sulfur compounds, reduces the required temperature of
and pressure on the feed stream, does not require the presence of
substantial quantities of water or other hydrolyzing agents in the
feed stream, and permits the choice of different selective sulfur
adsorbents to be used in the sequential sulfur adsorbent system
depending on the sulfur compounds that are present in the
particular feed stream. The compositions and methods of the
processes also permit the production of a substantially
desulfurized hydrocarbon fuel stream containing levels of sulfur
below those achievable with conventional desulfurizing
processes.
[0067] The inventors have also discovered that the sequential
sulfur adsorbent system as described herein can be used in fuel
cell processors for a longer period of time than conventional
adsorbents and still achieve high levels of sulfur absorbency.
[0068] The inventors have also discovered that the sequential
sulfur adsorbent system as described herein is also not subject to
desorption of the adsorbed sulfur compounds when the conditions
surrounding the sulfur adsorbent system change, as often occurs
with some conventional sulfur adsorbents.
EXAMPLES
[0069] The following examples are intended to be illustrative of
one embodiment of the invention and to teach one of ordinary skill
in the art to make and use this embodiment. These examples are not
intended to limit the invention in any way.
[0070] In order to illustrate the operation of one embodiment of
the invention, the inventors have compared the performance of a
first sulfur adsorbent system containing, in sequence, a
calcium-exchanged zeolite X followed by a particular selective
sulfur adsorbent with a second sulfur adsorbent system containing
the same calcium-exchanged zeolite X and selective sulfur adsorbent
to which has been added hydrated alumina. In the two component
system, the volume of the adsorbents (10 ccs) consists of fifty
percent (50%) of each component with the calcium-exchanged zeolite
X placed in the system prior to the selective sulfur adsorbent. In
the three component system, the same overall volume of the
adsorbents (10 ccs) consists of fifty percent (50%) by volume of
the calcium-exchanged zeolite X followed by twenty-five percent
(25%) by volume of the hydrated alumina, and twenty five (25%) by
volume of the selective sulfur adsorbent.
[0071] In each example, a synthetic natural gas feed stream is
utilized comprising 93% methane, 3% ethane, 2% propane, 0.2%
butane, 1% carbon dioxide and 0.75% nitrogen. Also included in this
synthetic natural gas is 10 ppm (as sulfur) of carbonyl sulfide.
This synthetic natural gas is passed through an artificial reactor
containing the two or three component sulfur adsorbent systems. The
zeolite adsorbent is in the form of 2 mm spheres. The selective
sulfur adsorbent is a 1.18 mm.times.0.85 mm mesh particulate,
typically produced by grinding 1.6 mm extrudates. The hydrated
alumina is in the form of 3.2 mm extrudates ground into 1.18
mm.times.0.85 mm mesh particles. The various components are sized
and loaded into the reactor and the synthetic natural gas feed
stream is passed through the reactor. The temperature of the feed
stream is maintained at 38.degree. C. with a space velocity of 3000
hr.sup.-1 at a pressure of 2 bar. "Breakthrough" for this test
occurs when an amount greater than 1 ppm of sulfur in the form of
carbonyl sulfide is observed in the natural gas feed stream after
passage through the adsorbent systems.
[0072] To determine the gas phase sulfur level of the feed stream,
analysis is performed using an Agilent 6890 gas chromatograph
attached to an Antek 7090 sulfur analyzer. The gas chromatograph
utilizes a 60 m.times.320 micron DB-1 capillary column for sulfur
compound separation. The Antek 7090 utilizes a sulfur
chemiluminescense detector (SCD) for sulfur detection. The
operational detection limit for the system is approximately 50 ppb
(mole). The test unit is controlled by automation software.
Example 1
[0073] The synthetic natural gas containing carbonyl sulfide is
passed through a reactor containing, in sequence, calcium-exchanged
zeolite X and the selective sulfur adsorbent. The zeolite X has an
Si:Al equivalent ratio of 1.17 and a calcium exchange of 70% with
the remaining metal ions comprising sodium and/or potassium. The
selective sulfur adsorbent comprises 70% by weight manganese
compounds, 21% copper oxide comprising Cuo and 9% silica. The
temperature of the reactor is maintained at 38.degree. C. and the
pressure is maintained at about 2 bar. The sulfur adsorbency of the
two component system is shown on FIG. 1, and shows breakthrough
occurring at 136 hours. The percent S in the form of COS that is
removed by this system is listed in FIG. 2.
Example 2
[0074] A further test is run wherein the calcium exchanged zeolite
and selective sulfur adsorbent of Example 1 are used in combination
with a hydrated alumina in the reactor. The hydrated alumina is
commercial pseudoboehmite. The hydrated alumina is placed in
sequence in the system after the calcium-exchanged zeolite X and
before the selective sulfur adsorbent. Fifty percent of the
components by volume is composed of the zeolite X and 25% is
composed of each of the selective sulfur adsorbent and the hydrated
alumina. A total of 10 ccs of the components is used. The operating
conditions and the composition of the feed stream are the same as
for Example 1. The percent S in the form of COS that was removed by
the system is listed in FIG. 2. When the feed stream is passed
through the reactor, breakthrough does not occur until 204 hours,
as shown in FIG. 1. In addition, as shown in FIG. 2, a higher
percentage of sulfur is removed from the feed stream by
breakthrough utilizing the three component system than occurs with
the two component system.
[0075] As is clear from these examples, the combination of the
calcium exchanged zeolite with the hydrated alumina adsorbent
followed by the selective sulfur adsorbent increases the time of
sulfur breakthrough and extends the lifetime of the sequential
sulfur adsorbent system.
[0076] As many changes and variations in the disclosed embodiments
may be made without departing from the inventive concept, the
invention is not intended to be limited by this description.
* * * * *