U.S. patent application number 10/076669 was filed with the patent office on 2003-03-13 for method for desulfurizing gasoline or diesel fuel for use in a fuel cell power plant.
Invention is credited to Boedeker, Laurence R., Dardas, Zissis A., Huang, He, Lesieur, Roger R., Sangiovanni, Joseph J., Spadaccini, Louis J., Sun, Jian, Tang, Xia, Teeling, Christopher.
Application Number | 20030047490 10/076669 |
Document ID | / |
Family ID | 23867800 |
Filed Date | 2003-03-13 |
United States Patent
Application |
20030047490 |
Kind Code |
A1 |
Lesieur, Roger R. ; et
al. |
March 13, 2003 |
Method for desulfurizing gasoline or diesel fuel for use in a fuel
cell power plant
Abstract
A fuel processing method is operable to remove substantially all
of the sulfur present in an undiluted oxygenated hydrocarbon fuel
stock supply which contains an oxygenate and which is used to power
a fuel cell power plant in a mobile environment, such as an
automobile, bus, truck, boat, or the like, or in a stationary
environment. The power plant hydrogen fuel source can be gasoline,
diesel fuel, or other like fuels which contain relatively high
levels of organic sulfur compounds such as mercaptans, sulfides,
disulfides, and the like. The undiluted hydrocarbon fuel supply is
passed through a desulfurizer bed wherein essentially all of the
sulfur in the organic sulfur compounds reacts with the nickel
reactant, and is converted to nickel sulfide, while the now
desulfurized hydrocarbon fuel supply continues through the
remainder of the fuel processing system. The method does not
require the addition of steam or a hydrogen source to the fuel
stream prior to the desulfurizing step. The method can be used to
desulfurize either a liquid or a gaseous fuel stream, which
contains an oxygenate such as MTBE, ethanol, methanol, or the like.
The inclusion of the oxygenate serves to extend the useful life of
the desulfurization method.
Inventors: |
Lesieur, Roger R.; (Enfield,
CT) ; Teeling, Christopher; (Enfield, CT) ;
Sangiovanni, Joseph J.; (West Suffield, CT) ;
Boedeker, Laurence R.; (W. Simsbury, CT) ; Dardas,
Zissis A.; (Worcester, MA) ; Huang, He;
(Glastonbury, CT) ; Sun, Jian; (Simsbury, CT)
; Tang, Xia; (West Hartford, CT) ; Spadaccini,
Louis J.; (Manchester, CT) |
Correspondence
Address: |
William W. Jones
Patent Counsel
6 Juniper Lane
Madison
CT
06443
US
|
Family ID: |
23867800 |
Appl. No.: |
10/076669 |
Filed: |
February 19, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10076669 |
Feb 19, 2002 |
|
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09470483 |
Dec 22, 1999 |
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6454935 |
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Current U.S.
Class: |
208/208R ;
208/244 |
Current CPC
Class: |
C10G 29/04 20130101;
H01M 8/0662 20130101; Y02E 60/50 20130101; H01M 8/0675
20130101 |
Class at
Publication: |
208/208.00R ;
208/244 |
International
Class: |
C10G 029/00 |
Claims
What is claimed is:
1. A method for desulfurizing a hydrocarbon fuel stream so as to
convert the hydrocarbon fuel stream into a low sulfur content fuel,
which low sulfur content fuel is suitable for use in a fuel
processing section in a fuel cell power plant, said method
comprising the steps of: a) providing a nickel reactant
desulfurization station which is operative to convert sulfur
contained in organic sulfur compounds contained in the fuel stream
to nickel sulfide; b) introducing a hydrocarbon fuel stream which
contains an oxygenate into said nickel reactant desulfurization
station; and c) said oxygenate being present in said fuel stream in
an amount which is effective to provide an effluent fuel stream at
an exit end of said nickel reactant station which effluent fuel
stream contains no more than about 0.05 ppm sulfur.
2. The method of claim 1 wherein the oxygenate is selected from the
group consisting of water, alcohol, ether, and mixtures
thereof.
3. The method of claim 2 wherein said oxygenate is present in
amounts operable to provide an operating life for the method which
is at least about three times the operating life of a
desulfurinzing method which does not include an oxygenate in the
fuel stream.
4. The method of claim 2 wherein the oxygenate is selected from the
group consisting of water, MTBE, ethanol, methanol, and mixtures
thereof.
5. A method for desulfurizing a gasoline fuel stream so as to
convert the gasoline fuel stream into a low sulfur content fuel,
which low sulfur content fuel is suitable for use in a fuel
processing section in a fuel cell power plant, said method
comprising the steps of: a) providing a nickel reactant
desulfurization station which is operative to convert sulfur
contained in organic sulfur compounds contained in the fuel stream
to nickel sulfide; b) introducing a gasoline fuel stream which
contains an oxygenate into said nickel reactant desulfurization
station; and c) said oxygenate being present in said gasoline fuel
stream in an amount which is effective to provide an effluent
gasoline fuel stream at an exit end of said nickel reactant station
which effluent gasoline fuel stream contains no more than about
0.05 ppm sulfur.
6. The method of claim 5 wherein the oxygenate is selected from the
group consisting or water, alcohol, ether, and mixtures
thereof.
7. The method of claim 6 wherein the oxygenate is selected from the
group consisting of water, MTBE, ethanol, methanol, and mixtures
thereof.
8. A method for desulfurizing a gasoline fuel stream so as to
convert the gasoline fuel stream into a low sulfur content fuel,
which low sulfur content fuel is suitable for use in a fuel
processing section of a fuel cell power plant, said method
comprising the steps of: a) providing a nickel reactant
desulfurization station which is operative to convert sulfur
contained in organic sulfur compounds contained in the fuel stream
to nickel sulfide; b) introducing a gasoline fuel stream which
contains an oxygenate into said nickel reactant desulfurization
station; and c) said oxygenate being present in said gasoline fuel
stream in an amount which is effective to provide a continuous
gasoline fuel stream at an exit end of said nickel reactant station
which continuous gasoline fuel stream contains on average no more
than about 0.05 ppm sulfur.
9. A method for desulfurizing a gasoline fuel stream so as to
convert the gasoline fuel stream into a low sulfur content fuel,
which low sulfur content fuel is suitable for use in a fuel
processing section in a fuel cell power plant, said method
comprising the steps of: a) providing a nickel reactant
desulfurization station which is operative to convert sulfur
contained in organic sulfur compounds contained in the fuel stream
to nickel sulfide; b) introducing a gasoline fuel stream which
contains an oxygenate into said nickel reactant desulfurization
station; and c) said oxygenate being converted to isobutylene and
methanol by said nickel catalyst in amounts which are effective to
inhibit carbon deposition in said nickel catalyst station and
provide a continuous gasoline fuel stream at an exit end of said
nickel reactant station which continuous gasoline fuel stream
contains no more than about 0.05 ppm sulfur.
10. A method for desulfurizing a gasoline fuel stream so as to
convert the gasoline fuel stream into a low sulfur content fuel,
which low sulfur content fuel is suitable for use in a fuel
processing section in a fuel cell power plant, said method
comprising the steps of: a) providing a nickel reactant
desulfurization station which is operative to convert sulfur
contained in organic sulfur compounds contained in the fuel stream
to nickel sulfide; b) introducing a gasoline fuel stream which
contains an oxygenate into said nickel reactant desulfurization
station, said oxygenate being present in said gasoline fuel stream
in an amount which is effective to provide a low sulfur content
gasoline fuel stream at an exit end of said nickel catalyst station
which low sulfur content gasoline fuel stream contains no more than
about 0.05 ppm sulfur; and c) said oxygenate being converted to
isobutylene and methanol by said nickel reactant during said
desulfurizing step, said low sulfur content gasoline fuel stream
being formed so long as said nickel reactant continues to convert
the oxygenate.
11. A method for desulfurizing a liquid gasoline fuel stream so as
to convert the gasoline fuel stream into a low sulfur content fuel,
which low sulfur content fuel is suitable for use in a fuel
processing section in a fuel cell power plant, said method
comprising the steps of: a) providing a nickel reactant
desulfurization station which is operative to convert sulfur
contained in organic sulfur compounds contained in the fuel stream
to nickel sulfide; b) maintaining said nickel reactant
desulfurization station at a temperature in the range of about
300.degree. F. to about 450.degree. F.; c) introducing a liquid
gasoline fuel stream which contains an oxygenate into said nickel
reactant desulfurization station, said oxygenate being present in
said gasoline fuel stream in an amount which is effective to
provide a low sulfur content gasoline fuel stream at an exit end of
said nickel reactant station which low sulfur content gasoline fuel
stream contains no more than about 0.05 ppm sulfur; and d) said
oxygenate being converted to isobutylene and methanol by said
nickel reactant during said desulfurizing step, said low sulfur
content gasoline fuel stream being formed so long as said nickel
reactant continues to convert the oxygenate.
12. A method for desulfurizing a liquid gasoline fuel stream so as
to convert the gasoline fuel stream into a low sulfur content fuel,
which low sulfur content fuel is suitable for use in a fuel
processing section in a fuel cell power plant, said method
comprising the steps of: a) providing a nickel reactant
desulfurization station which is operative to convert sulfur
contained in organic sulfur compounds contained in the fuel stream
to nickel sulfide; b) maintaining said nickel reactant
desulfurization station at a temperature in the range of about
300.degree. F. to about 450.degree. F.; c) introducing a mixture of
about 2% to about 5% water and a liquid gasoline fuel stream, which
mixture contains an oxygenate, into said nickel reactant
desulfurization station, said oxygenate being present in said
mixture in an amount which is effective to provide a low sulfur
content gasoline fuel stream at an exit end of said nickel reactant
station, which low sulfur content gasoline fuel stream contains no
more than about 0.05 ppm sulfur; and d) said oxygenate being
consumed by said nickel reactant during said desulfurizing step,
said low sulfur content gasoline fuel stream being formed so long
as said nickel reactant continues to consume the oxygenate.
13. The method of claim 12 wherein the water in said mixture is
derived by recirculating a portion of a selective oxidizer output
back to an inlet to said nickel reactant station.
14. The method of claim 12 wherein the water in said mixture is the
sole oxygenate in said mixture.
15. The method of claim 12 wherein the oxygenate includes an
alcohol present in said gasoline fuel stream.
16. The method of claim 14 wherein the alcohol is selected from the
group consisting of methanol, ethanol, propanol, and mixtures
thereof.
17. The method of claim 12 wherein said oxygenate is an ether.
18. The method of claim 16 wherein said oxygenate is MTBE.
19. The method of claim 12 wherein said recirculated portion of the
selective oxidizer output is between 1% and 10% of the total
selective oxidizer output.
20. A method for desulfurizing a liquid gasoline fuel stream so as
to convert the gasoline fuel stream into a low sulfur content fuel,
which low sulfur content fuel is suitable for use in a fuel
processing section in a fuel cell power plant, said method
comprising the steps of: a) providing a nickel reactant
desulfurization station which is operative to convert sulfur
contained in organic sulfur compounds contained in the fuel stream
to nickel sulfide; b) maintaining said nickel reactant
desulfurization station at a temperature in the range of about
300.degree. F. to about 450.degree. F.; and c) introducing a
mixture of a fuel cell selective oxidizer output recycle, which
recycle contains hydrogen and water; and a liquid gasoline fuel,
into said nickel reactant desulfurization station, said selective
oxidizer output recycle being present in an amount which is
effective to provide a low sulfur content gasoline fuel stream at
an exit end of said nickel reactant station, which low sulfur
content gasoline fuel stream contains no more than about 0.05 ppm
sulfur.
21. The method of claim 20 wherein said selective oxidizer recycle
comprises about 1% to about 10% of total selective oxidizer
output.
22. A method for desulfurizing a gaseous fuel stream so as to
convert the gaseous fuel stream into a low sulfur content fuel,
which low sulfur content fuel is suitable for use in a fuel
processing section in a fuel cell power plant, said method
comprising the steps of: a) providing a nickel reactant
desulfurization station which is operative to convert sulfur
contained in organic sulfur compounds contained in the fuel stream
to nickel sulfide; b) introducing a gaseous fuel stream which
contains a fuel cell selective oxidizer recycle mixture of hydrogen
and water into said nickel reactant desulfurization station; and c)
said selective oxidizer recycle mixture being present in said
gaseous fuel stream in an amount which is effective to provide an
effluent gaseous fuel stream at an exit end of said nickel reactant
station which effluent gaseous fuel stream contains no more than
about 0.05 ppm sulfur.
23. The method of claim 21 wherein the gaseous fuel is selected
from the group consisting of methane, ethane, propane and
butane.
24. The method of claim 21 wherein the desulfurization station
operates in a temperature range of about 250.degree. F. to about
450.degree. F.
25. The method of claim 21 wherein said recirculated portion of the
selective oxidizer output is between 1% and 10% of the total
selective oxidizer output.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for desulfurizing
gasoline, diesel fuel or like hydrocarbon fuel streams so as to
render the fuel more suitable for use in a mobile vehicular fuel
cell power plant assembly. More particularly, the desulfurizing
method of this invention is operable to remove organic sulfur
compounds found in gasoline to levels which will not poison the
catalysts in the fuel processing section of the fuel cell power
plant assembly. The method of this invention involves the use of a
nickel reactant bed which has an extended useful life cycle due to
the inclusion of oxygenates in the fuel stream in appropriate
amounts.
BACKGROUND OF THE INVENTION
[0002] Gasoline, diesel fuel, and like hydrocarbon fuels have not
been useful as a process fuel source suitable for conversion to a
hydrogen rich stream for small mobile fuel cell power plants due to
the existence of relatively high levels of naturally-occurring
complex organic sulfur compounds. Hydrogen generation in the
presence of sulfur results in a poisoning effect on all of the
catalysts used in the hydrogen generation system in a fuel cell
power plant. Conventional fuel processing systems used with
stationary fuel cell power plants include a thermal steam reformer,
such as that described in U.S. Pat. No. 5,516,344. In such a fuel
processing system, sulfur is removed by conventional
hydrodesulfurization techniques which typically rely on a certain
level of recycle as a source of hydrogen for the process. The
recycle hydrogen combines with the organic sulfur compounds to form
hydrogen sulfide within a catalytic bed. The hydrogen sulfide is
then removed using a zinc oxide bed to form zinc sulfide. The
general hydrodesulfurization process is disclosed in detail in U.S.
Pat. No. 5,292,428. While this system is effective for use in large
stationary applications, it does not readily lend itself to mobile
transportation applications because of system size, cost and
complexity. Additionally, the gas being treated must use process
recycle in order to provide hydrogen in the gas stream, as noted
above.
[0003] Other fuel processing systems, such as a conventional
autothermal reformer, which use a higher operating temperature than
conventional thermal steam reformers, can produce a hydrogen-rich
gas in the presence of the foresaid complex organic sulfur
compounds without prior desulfurization. When using an autothermal
reformer to process raw fuels which contain complex organic sulfur
compounds, the result is a loss of autothermal reformer catalyst
effectiveness and the requirement of reformer temperatures that are
200.degree. F.-500.degree. F. higher than are required with a fuel
having less than 0.05 ppm sulfur. Additionally, a decrease in
useful catalyst life of the remainder of the fuel processing system
occurs with the higher sulfur content fuels. The organic sulfur
compounds are converted to hydrogen sulfide as part of the
reforming process. The hydrogen sulfide can then be removed using a
solid absorbent scrubber, such as an iron or zinc oxide bed to form
iron or zinc sulfide. The aforesaid solid scrubber systems are
limited, due to thermodynamic considerations, as to their ability
to lower sulfur concentrations to non-catalyst degrading levels in
the fuel processing components which are located downstream of the
reformer, such as in the shift converter, or the like.
[0004] Alternatively, the hydrogen sulfide can be removed from the
gas stream by passing the gas stream through a liquid scrubber,
such as sodium hydroxide, potassium hydroxide, or amines. Liquid
scrubbers are large and heavy, and are therefore useful principally
only in stationary fuel cell power plants. From the aforesaid, it
is apparent that current methods for dealing with the presence of
complex organic sulfur compounds in a raw fuel stream for use in a
fuel cell power plant require increasing fuel processing system
complexity, volume and weight, and are therefore not suitable for
use in mobile transportation systems.
[0005] An article published in connection with the 21st Annual
Power Sources Conference proceedings of May 16-18, 1967, pages
21-26, entitled "Sulfur Removal for Hydrocarbon-Air Systems", and
authored by H. J. Setzer et al, relates to the use of fuel cell
power plants for a wide variety of military applications. The
article describes the use of high nickel content hydrogenation
nickel reactant to remove sulfur from a military fuel called JP-4,
which is a jet engine fuel, and is similar to kerosene, so as to
render the fuel useful as a hydrogen source for a fuel cell power
plant. The systems described in the article operate at relatively
high temperatures in the range of 600.degree. F. to 700.degree. F.
The article also indicates that the system tested was unable to
desulfurize the raw fuel alone, without the addition of water or
hydrogen, due to reactor carbon plugging. The carbon plugging
occurred because the tendency for carbon formation greatly
increases in the temperature range between about 550.degree. F. and
about 750.degree. F. A system operating in the 600.degree. F. to
700.degree. F. range would be very susceptible to carbon plugging,
as was found to be the case in the system described in the article.
The addition of either hydrogen or steam reduces the carbon
formation tendency by supporting the formation of gaseous carbon
compounds thereby limiting carbon deposits which cause the plugging
problem.
[0006] It would be highly desirable from an environmental
standpoint to be able to power electrically driven vehicles, such
as an automobile, for example, by means of fuel cell-generated
electricity; and to be able to use a fuel such as gasoline, diesel
fuel, naphtha, lighter hydrocarbon fuels such as butane, propane,
natural gas, or like fuel stocks, as the fuel consumed by the
vehicular fuel cell power plant in the production of electricity.
In order to provide such a vehicular power source, the amount of
sulfur in the processed fuel gas would have to be reduced to and
maintained at less than about 0.05 parts per million.
[0007] The desulfurized processed fuel stream can be used to power
a fuel cell power plant in a mobile environment or as a fuel for an
internal combustion engine. The fuel being processed can be
gasoline or diesel fuel, or some other fuel which contains
relatively high levels of organic sulfur compounds such as
thiophenes, mercaptans, sulfides, disulfides, and the like. The
fuel stream is passed through a nickel desulfurizer bed wherein
essentially all of the sulfur in the organic sulfur compounds
reacts with the nickel reactant and is converted to nickel sulfide
leaving a desulfurized hydrocarbon fuel stream which continues
through the remainder of the fuel processing system. Previously
filed U.S. patent applications Ser. No. 09/104,254, filed Jun. 24,
1998; and Ser. No. 09/221,429, filed Dec. 28, 1998 describe systems
for use in desulfurizing a gasoline or diesel fuel stream for use
in a mobile fuel cell vehicular power plant; and in an internal
combustion engine, respectively.
[0008] We have discovered that desulfurization of a gasoline or
diesel fuel stream which uses a nickel catalytic adsorbant bed
cannot be performed over a significantly extended period of time
unless the fuel stream includes an oxygenate compound in
appropriate proportions. Various oxygenates could suffice for the
desulfurization process including MTBE, ethanol or other alcohols,
ethers, or the like.
DISCLOSURE OF THE INVENTION
[0009] This invention relates to an improved method for processing
a gasoline, diesel, or other hydrocarbon fuel stream over an
extended period of time, which method is operable to remove
substantially all of the sulfur present in the fuel stream.
[0010] Gasoline, for example, is a hydrocarbon mixture of
paraffins, napthenes, olefins and aromatics, whose olefinic content
is between 1% and 15%, and aromatics between 20% and 40%, with
total sulfur in the range of about 20 ppm to about 1,000 ppm. The
national average for the United States is 350 ppm sulfur. The
legally mandated average for the State of California is 30 ppm
sulfur. As used in this application, the phrase "California
Certified Gasoline" refers to a gasoline which has between 30 and
40 ppm sulfur content, and which contains about 11% by volume MTBE
at the present time. California Certified Gasoline is used by new
car manufacturers to establish compliance with California emissions
certification requirements.
[0011] We have discovered that the presence of oxygenates in the
gasoline, like MTBE (methyl-tertiary-butyl ether, i.e.,
(CH.sub.3).sub.3COCH.sub.3)- , or ethanol, for example, prevent
rapid deactivation of the nickel catalytic adsorption of organic
sulfur compounds from the fuel stream. Ethanol could be an
appropriate solution to this problem since it is non-toxic, is not
a carcinogen, and is relatively inexpensive and readily available
in large supplies as a byproduct of the agriculture industry.
Methanol, which would also extend the desulfurizer bed life, is not
preferred since it is toxic; while MTBE is likewise not preferred
since it is thought to be a carcinogenic compound, and may be
banned in certain areas of the United States in the near future by
new environmental regulations. Preferred oxygenates are non-toxic
and non-carcinogenic oxygen donor compounds, such as ethanol or the
like.
[0012] The effectiveness of a nickel adsorbent reactant to adsorb
organic sulfur compounds from gasoline depends on the relative
coverage of the active reactant sites by adsorption of all the
various constituents of gasoline. In other words, the catalytic
desulfurization process depends on the amount of competitive
adsorption of the various constituents of gasoline. From the
adsorption theory, it is known that the relative amount of
adsorbate on an adsorbent surface depends primarily on the
adsorption strength produced by attractive forces between the
adsorbate and adsorbent molecules; secondarily on the concentration
of the adsorbate in the gasoline, and temperature. Coverage of a
reactant surface by an adsorbate increases with increasing
attractive forces; higher fuel concentration; and lower
temperatures. Relative to gasoline, Somorjai (introduction to
Surface Chemistry and Catalysis, pp, 60-74) provides some relevant
information on the adsorption of hydrocarbons on transition metal
surfaces, such as nickel. Saturated hydrocarbons only physically
adsorb onto the nickel reactant surface at temperatures which are
less than 100.degree. F., therefore paraffins, and most likely
napthenes, won't compete with sulfur compounds for adsorption sites
on the nickel reactant at temperatures above 250.degree. F. and
300.degree..degree.F. On the other hand, unsaturated hydrocarbons,
such as aromatics and olefins, adsorb largely irreversibly on
transition metal surfaces even at room temperature. When an
unsaturated hydrocarbon such as an aromatic or an olefin adsorbs on
a transition metal surface, and the surface is heated, the adsorbed
molecule rather than desorbing intact, decomposes to evolve
hydrogen, leaving the surface covered by the partially
dehydrogenated fragment, i.,e., tar or coke precursors. We have
discovered that, at 350.degree. F., unsaturated hydrocarbons are
nearly completely dehydrogenated, and the dehydrogenated tar
fragments form multiple carbon atom-to-nickel reactant surface
bonds. This explains why aromatics and olefins in gasoline, in the
absence of oxygenated compounds in appropriate concentrations, will
deactivate the nickel nickel reactant from adsorbing sulfur after a
relatively short period of time.
[0013] In general, the adsorption strength of a compound depends on
the dipole moment, or polarity, of the molecule. A higher dipole
moment indicates that the compound is more polar and is more likely
to adsorb on a reactant surface. Aromatics are an exception to this
rule because their molecular structure includes a n ring of
electron forces that produces a cloud of induced attractive forces
with adjacent surfaces. Based on the dipole moments of
hydrocarbons, allowing for the rr ring in aromatics, the order of
adsorption strength (highest to lowest) is: nitrogenated
hydrocarbons>oxygenated
hydrocarbons>aromatics>olefins>hydroc- arbons containing
sulfur>saturated hydrocarbons. Since the adsorption strength of
the oxygenated hydrocarbons (such as ethanol, methanol, MTBE, or
the like) is greater than that for aromatics and olefins,
oxygenated hydrocarbons, or other oxygen donor compounds, if
present in the gasoline or diesel fuel stream being desulfurized,
will provide greater coverage of the nickel reactant sites than do
the aromatics and olefins in the gasoline. Thus, the oxygenated
hydrocarbons can reduce the adsorption of aromatics and olefins on
the nickel reactant bed. Although saturated hydrocarbons (paraffins
and cycloparaffins) would not be expected to be adsorbed on the
desulfurization nickel reactant to a significant extent, oxygenated
hydrocarbons will also prevent them from adsorbing onto the nickel
reactant.
[0014] We have also discovered that the adsorbed oxygenated
hydrocarbons do not inhibit the sulfur compounds from being
adsorbed on the nickel reactant. The oxygenated hydrocarbons and
the sulfur compounds are both quite polar and therefore they are
miscible, which allows the sulfur compounds to dissolve into and
diffuse through the adsorbed layer of oxygenated hydrocarbon to the
active nickel metal reactant sites. Thus, the oxygenated
hydrocarbons provide a "shield" which inhibits the carbon-forming
hydrocarbons from contacting the nickel reactant sites while
allowing the sulfur compounds to contact and react with the active
nickel metal reactant sites.
[0015] Further non-essential but enabling information relating to
this invention will become readily apparent to one skilled in the
art from the following detailed description of a preferred
embodiment of the invention when taken in conjunction with the
accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a graph of the result of a short (seven hour)
desulfurizer bed test run with three different modified
formulations of California Certified Gasoline showing the sulfur
level in parts per million (ppm) at the reactant bed exit for the
various gasoline formulations, versus the test run operating time
in hours;
[0017] FIG. 2 is a graph of the results of a longer desulfurizer
bed test run (about four hundred eighty five hours) with unmodified
California Certified Gasoline showing the sulfur level in the
gasoline in ppm at the nickel reactant bed exit, versus the
operating time in hours;
[0018] FIG. 3 is a graph of the results of the same desulfurizer
bed test run shown in FIG. 2, but showing the oxygenate level in
the gasoline, in percent by weight, at the reactant bed exit,
versus the test run operating time in hours;
[0019] FIG. 4 is a graph of the result of a desulfurizer bed test
run with a commercially available gasoline showing the sulfur level
in ppm at the nickel reactant bed exit versus the operating time of
the desulfurizer in hours;
[0020] FIG. 5 is a graph of the result of several different
duration desulfurizer bed test runs using different modified
formulations of California Certified Gasoline, one with, and one
without oxygenates, and showing the carbon level (in percent by
weight) which was deposited on the reactant in each successive
section of the desulfurizer at the end of the test runs;
[0021] FIG. 6 is a graph of the sulfur content of the exit stream
of a desulfurized gasoline fuel stream over a period of time at
varied operating temperatures, when a small amount of water is
present, and when no water is present, in the fuel stream; and
[0022] FIG. 7 is a graph of the operating temperatures of the
system described in FIG. 6 over the same period of time; and
[0023] FIG. 8 is a schematic view of an embodiment of the gasoline
desulfurizer system of this invention, which desulfurizes gasoline
on board a vehicle powered by a fuel cell power plant.
SPECIFIC MODES FOR CARRYING OUT THE INVENTION
[0024] Referring now to the drawings, FIG. 1 is a graph of the
results of relatively short desulfurizer test runs using various
formulations of California Certified Gasoline, which graph shows
the sulfur level in ppm for the various formulations at the
reactant bed exit, versus the operating time of the test runs in
hours. In these short term (seven hour) test runs, sulfur was added
to all of the California Certified Gasoline formulations, so that
the gasoline contained 240 ppm of sulfur. One of the gasoline
formulations contained 11% MTBE by volume, which is an oxygenate
and which is presently a conventional component of California
Certified Gasoline; another of the formulations contained 10%
ethanol by volume, which is also an oxygenate; and the third
formulation contained essentially no oxygenate. In each of the test
runs, the gasoline was run through a nickel reactant bed so as to
attempt to remove sulfur from the gasoline. The trace line A shows
the sulfur content of the gasoline formulation which did not
contain an oxygenate. The sulfur content was measured at the exit
end of the desulfurizer reactant bed. Trace A clearly shows that
the oxygenate-free gasoline formulation had a steadily rising
sulfur content at the desulfurizer exit during the duration of the
test despite being run through the desulfurizer reactant bed
indicating deactivation of the desulfurization reactant. Trace B
shows the sulfur content of the gasoline formulation which
contained MTBE. Trace C shows the sulfur content of the gasoline
formulation which contained ethanol. This graph shows a major
improvement and a decrease in sulfur at the reactant bed exit, when
an MTBE or ethanol oxygenate is contained in the gasoline. This
graph shows that the oxygenate component of the gasoline prolongs
the ability of the reactant bed to remove sulfur from the
gasoline.
[0025] FIG. 2 is a graph of the results of a longer desulfurizer
test run using California Certified Gasoline which contained about
30 ppm sulfur and about 11% MTBE by volume. The test was run until
sulfur breakthrough occurred. The goal of the desulfurizer is to
maintain the sulfur content of the gasoline below about 0.05 ppm so
that the gasoline will be suitable for processing for use in a
mobile fuel cell power plant. Therefore, "sulfur breakthrough" is
defined by our requirements as occurring when a sustained
post-reactant bed sulfur content of greater than about 0.05 ppm in
the gasoline is present. The trace D shows the sulfur level in ppm
at the exit of the reactant bed versus the operating time in hours
and shows that the desulfurizer operated successfully for about 400
hours with consistent sulfur levels in the nickel reactant bed exit
stream of below 0.05 ppm. In this test run, the long term benefit
of using an oxygenate in the fuel to minimize sulfur penetration
through the desulfurizer device is demonstrated.
[0026] FIG. 3 is a graph of the results of the same longer term
desulfurizer test run shown in FIG. 2, but showing the oxygenate
level by percent weight at the nickel reactant bed exit versus the
operating time in hours. From this figure, it will be noted that
when the nickel reactant bed can no longer decompose the oxygenate,
the nickel reactant loses its ability to remove organic sulfur
compounds. It is noted from trace E in FIG. 3 that at about 400
hours, the MTBE content of the gas stream exiting the nickel
reactant bed was about 11% by volume which is the same
concentration of MTBE in the gasoline stream entering the nickel
reactant bed. Note that early in the test run, the nickel reactant
bed is more capable of decomposing the MTBE, but this ability
gradually declines as the test run continues. This inability to
decompose the oxygenate results in an increase in the sulfur
content at the nickel reactant bed exit, as shown in FIG. 2.
[0027] FIG. 4 is a graph of the results of another longer term
desulfurizer test run using a gasoline which had about a 90 ppm
sulfur content and which contained about 11% MTBE by volume. Trace
F shows that the sulfur level at the nickel reactant bed exit
remained below 0.05 ppm for about 125-135 hours, after which sulfur
breakthrough occurred. In this test run, the long term benefit of
using oxygenates in the fuel to minimize sulfur getting through the
desulfurizing bed is also demonstrated.
[0028] FIG. 5 is a graph showing the results of two desulfurizer
test runs using two different formulations of California Certified
Gasoline, one containing an oxygenate (MTBE, 11% by volume), and
the other containing no oxygenate. This graph shows the carbon
level by percent weight deposited in each successive section of the
desulfurizer nickel reactant bed. In this figure, the post test
carbon content for successive sections of the desulfurizers was
measured and is shown for two tests that were run for different
time periods, both of which were run until sulfur breakthrough
occurred. Trace H shows the results of the test run for the
gasoline formulation that contained no oxygenate. This test was run
for 60 hours at which point in time, sulfur breakthrough occurred.
Trace G shows the results of the test run for the gasoline
formulation that contained MTBE. This test was run for 485 hours at
which point in time, sulfur breakthrough occurred. It was noted
that the presence or absence of the oxygenate in the gasoline being
processed did not effect the carbon build up profile on the nickel
reactant bed, but it did increase the time period which is needed
to reach the sulfur breakthrough point in terms of carbon
deposition. In each test, the degree of carbon build up on the
nickel reactant at the sulfur breakthrough point in each section of
the desulfurizer is almost exactly the same. This figure
demonstrates that "sulfur breakthrough" is a function of the extent
of carbon deposition on the nickel reactant bed, and is not a
function of the extent of sulfur removal by the nickel reactant
bed. This figure also demonstrates that the addition of oxygenates
to the gasoline retards carbon deposition on the nickel reactant
bed, and thus enables extended sulfur removal from the fuel stream
by the nickel reactant bed.
[0029] At this stage, we conclude that the presence of oxygenates
in the gasoline maintains the desulfurization activity of the
nickel reactant by significantly suppressing the carbon content
(coke deposits and strongly adsorbed species), and by keeping the
nickel reactant active sites clean and available for
desulfurization of the S-containing organic molecules. As was
mentioned before, this could be achieved by an in situ formation of
hydrogen and/or water vapor due to the MTBE decomposition process
(chemical reaction effect). Therefore, we propose that MTBE, and
for the same reason any oxygenated organic molecule, is strongly
adsorbed on the nickel surface due to its high dipole moment where
it decomposes to isobutylene and methanol. The adsorbed oxygenate
decomposes because the nickel reactant is very active and the C--O
bond can easily break. In general, the order in the required energy
to break a C--X bond is:
C--O<C--S<C--N<C--C<C--H
[0030] A nickel catalyst promotes the formation of methanol, a
byproduct of MTBE decomposition, or ethanol disproportionation
reaction. When methanol is decomposed, the following reactions
occur:
4CH.sub.3OH.fwdarw.3CH.sub.4+CO.sub.2+2H.sub.2O (1)
4CH.sub.3OH.fwdarw.2CH.sub.4+2CO.sub.2+4H.sub.2 (2)
[0031] For ethanol, the same reactions should produce ethane
instead of methane. The presence of water vapor or hydrogen is well
known to suppress carbon formation, especially at elevated
temperatures. The hydrogen produced on the nickel reactant bed by
equation (2) will hydrogenate carbon precursors emanating from the
desulfurized organic sulfur components, and from the
adsorbed/decomposed olefins and aromatics in the gasoline, through
reaction with hydrogen emanating from the desulfurized fuel gas
(Ely-Rideal mechanism) or through hydrogen spill over.
Hydrogenation of carbon precursors from sulfur compounds, olefins
and aromatics could occur entirely on the nickel reactant surfaces
from spill over of hydrogen generated by decomposition of the MTBE
without initiating hydrogen exchange with the fuel gas stream.
"Spill over" is the surface migration of hydrogen atoms from the
nickel reactant site(s) that produce the hydrogen in equation (2)
to the site(s) that adsorb the olefins and aromatics.
[0032] The formation of hydrogen is demonstrated in Table 1
(below), which shows the decrease in olefin level during the
desulfurization process for the same commercially available
gasoline containing MTBE shown in FIG. 4. Apparently, the hydrogen
provided by decomposition of MTBE serves to hydrogenate the olefins
thereby forming saturated parafins. It is apparent from Table 1
that the decomposition of MTBE not only generates hydrogen, but
also catalyzes the dehydrogenation of naphthenes to generate
aromatics and more hydrogen.
[0033] Table 1 is a "PONA" (which is an acronym for paraffins,
olefins, naphthene, and aromatics) analysis of the changes in PONA
compounds which are found in the gasoline described in FIG. 4, both
before and after desulfurization; and also of the change in the
sulfur content of the gasoline.
1TABLE 1 Hydrocarbon Type Before Desulfurization After
Desulfurization Paraffins 38.8% 41.1% Olefins 14.9% 12.6%
Naphthenes 9.6% 5.8% Aromatics 36.7% 40.6% Sulfur 90 ppm <0.05
ppm
[0034] Table 2 shows that, without MTBE, there is essentially no
change in the "PONA" percentages in a low sulfur content,
commercially available gasoline which is passed through the
desulfurization nickel reactant bed. Also, Table 2 demonstrates
that the sulfur content of the low sulfur content gasoline still
contains an unacceptably high content of sulfur after the
desulfurization step.
2TABLE 2 Hydrocarbon Type Before Desutfurization After
Desulfurization Paraffins 64.6% 64.5% Olefins 3.7% 3.65% Naphthenes
2.89% 2.82% Aromatics 28.8% 29% Sulfur 30.9 ppm 1.0 ppm
[0035] Desulfurization of a gasoline fuel sample containing about
30 ppm sulfur was carried out at a temperature of 375.degree. F.
FIG. 6 shows the exit stream desulfurization history of this low
sulfur gasoline fuel sample. The desulfurization test run shown in
FIG. 6 was run at a temperature of 375.degree. F., except for the
time period between 73 and 120 hours. During that time period, the
reaction temperature was lowered to 350.degree. F., as shown in
FIG. 7. At the 375.degree. F. operating temperature, the fuel
stream exiting the desulfurizer nickel reactant bed contained about
1% to about 2% water condensate which was derived from the MTBE. At
the operating temperature of 350.degree. F., the exiting fuel
stream did not contain any obvious water condensate. This fact
confirms the formation of water, and coextant superior
desulfurization results obtained when water is present in the fuel
stream. It is noted from FIG. 6, that after the operating
temperature is lowered to 350.degree. F., and the water condensate
in the fuel stream disappears, the sulfur level in the exiting fuel
stream begins to rise, and then, sometime after the operating
temperature is increased, and the water condensate reappears in the
fuel stream, the sulfur level in the exiting fuel stream
subsides.
[0036] FIG. 8 shows an embodiment of the desulfurization system of
this invention wherein the desulfurizing bed 8 is positioned
onboard a vehicle 2. The system includes a fuel line 3 from the
vehicle gas tank to a pump 4 which pumps the fuel through a line 6
to the desulfurizer bed 8. The bed 8 is heated to operating
temperatures by an electric heater 10. The desulfurized gasoline
passes from the desulfurizing bed 8 through a line 12 to the fuel
cell power plant 14 where the desulfurized fuel is further
processed and converted to electricity for powering the vehicle
2.
[0037] We have determined that the oxygenate not only protects the
nickel reactant metal surface with an oxygenate "shield", it also
produces hydrogen and water which enables the metal surface to
remain free of excessive carbon deposits for longer periods of time
than if no oxygenate were present. The addition of very small
quantities of water in the fuel stream at the desulfurizer bed
inlet, or the recirculation of a 1% to 10%, by volume, fraction of
the fuel stream emanating from a downstream selective oxidizer
outlet back to the desulfurizer bed inlet, would provide the same
quantity of water and hydrogen as can be produced from the
MTBE.
[0038] As a result, the MTBE could be eliminated from the gas
stream when a fuel cell recycle stream is utilized. Minimal amounts
of water can be injected, either by itself, or when recycle is
employed, contrary to the teachings of aforementioned Setzer et al
article which was published in the 21 st Annual Power Sources
conference proceedings, which article requires the use of three
pounds of water for one pound of fuel in order to reform the fuel
gas stream.
[0039] By contrast, utilization of selective oxidizer exhaust will
provide only 2%-5% water for introduction into the desulfurizer
bed, which would provide sufficient hydrogen to hydrogenate the
adsorbed olefins and prevent the fouling of the metal nickel
reactant surface with carbonaceous deposits. The operating range of
300.degree. F.-450.degree. F. for liquid fuels, and 250.degree.
F.-450.degree. F. for gaseous fuels, both of which are below the
temperature range suggested in the prior art for the performance of
a hydrodesulfurization process are available in performance of this
invention.
[0040] It will be readily appreciated that the addition of an
effective amount of an oxygenate, or water, or a fuel cell fuel
processing recycle stream which contains water and hydrogen, to a
sulfur-containing fuel, will allow the sulfur to be removed from
the fuel to the extent necessary for use of the fuel as a hydrogen
source for a mobile fuel cell power plant without poisoning the
fuel cell power plant nickel reactant beds with sulfur. The sulfur
compounds are removed from the fuel by means of a nickel reactant
bed through which the fuel flows prior to entering the fuel cell
power plant's fuel processing section. The oxygenate,
hydrogen-containing recycle, or water (steam) addition, also serves
to control carbon deposition on the nickel reactant bed thereby
extending its useful life and enhancing the sulfur removal
capabilities of the nickel reactant bed.
[0041] Since many changes and variations of the disclosed
embodiment of the invention may be made without departing from the
inventive concept, it is not intended to limit the invention
otherwise than as required by the appended claims.
* * * * *