U.S. patent application number 10/076670 was filed with the patent office on 2002-08-08 for method for desulfurizing gasoline or diesel fuel for use in an internal combustion engine.
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 | 20020104781 10/076670 |
Document ID | / |
Family ID | 24037417 |
Filed Date | 2002-08-08 |
United States Patent
Application |
20020104781 |
Kind Code |
A1 |
Lesieur, Roger R. ; et
al. |
August 8, 2002 |
Method for desulfurizing gasoline or diesel fuel for use in an
internal combustion engine
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
an internal combustion engine in a mobile environment, such as an
automobile, bus, truck, boat, or the like, or in a stationary
environment. The fuel stock 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 nickel
reactant 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 desulfurized organic
remnants continue through the remainder of the fuel processing
system. 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 apparatus
and 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, CA) ; 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: |
24037417 |
Appl. No.: |
10/076670 |
Filed: |
February 19, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10076670 |
Feb 19, 2002 |
|
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09512035 |
Feb 24, 2000 |
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Current U.S.
Class: |
208/208R ;
208/244 |
Current CPC
Class: |
C10G 29/04 20130101 |
Class at
Publication: |
208/208.00R ;
208/244 |
International
Class: |
C10G 017/00 |
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 an internal
combustion engine, 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 the oxygenate is selected from the
group consisting of water, MTBE, ethanol, methanol, and mixtures
thereof.
4. The method of claim 1 wherein said hydrocarbon fuel is
gasoline.
5. The method of claim 1 wherein said hydrocarbon fuel is diesel
fuel.
6. A method for desulfurizing a gasoline or diesel 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 an
internal combustion engine, 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 or diesel 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.
7. The method of claim 5 wherein the oxygenate is selected from the
group consisting or water, alcohol, ether, and mixtures
thereof.
8. The method of claim 7 wherein the oxygenate is selected from the
group consisting of water, MTBE, ethanol, methanol, and mixtures
thereof.
9. A method for desulfurizing a gasoline or diesel fuel stream so
as to convert the fuel stream into a low sulfur content fuel, which
low sulfur content fuel is suitable for use in an internal
combustion engine, 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 or diesel 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 a continuous fuel stream at an exit end of said nickel
reactant station which continuous fuel stream contains on average
no more than about 0.05 ppm sulfur.
10. A method for desulfurizing a gasoline or diesel fuel stream so
as to convert the fuel stream into a low sulfur content fuel, which
low sulfur content fuel is suitable for use in an internal
combustion engine, 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 or diesel 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 fuel stream at an
exit end of said nickel reactant station which continuous fuel
stream contains no more than about 0.05 ppm sulfur.
11. A method for desulfurizing a gasoline or diesel fuel stream so
as to convert the fuel stream into a low sulfur content fuel, which
low sulfur content fuel is suitable for use in an internal
combustion engine, 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 or diesel fuel stream which contains an oxygenate into
said nickel reactant desulfurization station, said oxygenate being
present in said fuel stream in an amount which is effective to
provide a low sulfur content fuel stream at an exit end of said
nickel catalyst station which low sulfur content 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 fuel stream
being formed so long as said nickel reactant continues to convert
the oxygenate.
12. A method for desulfurizing a liquid gasoline or diesel fuel
stream so as to convert the fuel stream into a low sulfur content
fuel, which low sulfur content fuel is suitable for use in an
internal combustion engine, said method comprising the steps of: a)
providing a nickel reactant desulfurization station which is
operative to convert All 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 or diesel fuel
stream which contains an oxygenate into said nickel reactant
desulfurization station, said oxygenate being present in said fuel
stream in an amount which is effective to provide a low sulfur
content fuel stream at an exit end of said nickel reactant station
which low sulfur content 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 fuel stream being
formed so long as said nickel reactant continues to convert the
oxygenate.
13. A method for desulfurizing a liquid gasoline or diesel fuel
stream so as to convert the fuel stream into a low sulfur content
fuel, which low sulfur content fuel is suitable for use in an
internal combustion engine, 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 or diesel 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 fuel stream at an exit
end of said nickel reactant station, which low sulfur content 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 fuel stream being
formed so long as said nickel reactant continues to consume the
oxygenate.
14. The method of claim 13 wherein the water in said mixture is the
sole oxygenate in said mixture.
15. The method of claim 13 wherein the oxygenate includes an
alcohol present in said fuel stream.
16. The method of claim 15 wherein the alcohol is selected from the
group consisting of methanol, ethanol, propanol, and mixtures
thereof.
17. The method of claim 13 wherein said oxygenate is an ether.
18. The method of claim 17 wherein said oxygenate is MTBE.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method and system for
desulfurizing gasoline, diesel fuel or like hydrocarbon fuels so as
to reduce the sulfur content of the fuel and render the fuel more
desirable for use in a mobile vehicular internal combustion engine.
More particularly, the desulfurizing method and system of this
invention are operable to reduce the amount of organic sulfur
compounds found in gasoline to levels which will not cause undue
corrosion to engine and exhaust components. Another advantage to
use of the sulfur-depleted gasoline fuel is the increased
efficiency and useful life of the catalytic converters used to
scrub IC engine exhaust. The method of this invention involves the
use of a nickel reactant bed which has an extended useful life
cycle due to the presence of oxygenates such as alcohols, water, or
other compounds in the fuel stream.
BACKGROUND OF THE INVENTION
[0002] Gasoline, diesel fuel, and like hydrocarbon fuels are useful
as a fuel for internal combustion engines, despite the existence of
relatively high levels of naturally-occurring complex organic
sulfur compounds in the gasoline or diesel fuel. The sulfur
compounds are undesirable since they are known to cause corrosion
damage components of the internal combustion engine system, such as
engine cylinder walls and exhaust system walls when the fuel is
combusted. As noted above, catalytic converter perfomance is also
adversely effected. The sulfur compounds in the aforesaid fuels are
also undesirable since they are converted to sulfur dioxide
(SO.sub.2) when the fuel is combusted. It is well known that
SO.sub.2 and SO.sub.3, when exhausted into the atmosphere will
cause "acid rain" due to its subsequent conversion to
H.sub.2SO.sub.3 and H.sub.2SO.sub.4 in the ambient atmosphere. The
former problem of engine damage has not been addressed in any
fashion, other than by attempting to reduce the amount of sulfur in
the gasoline or diesel fuel during the refining process. This
solution also helps ameliorate the exhaust problem, but the
acceptable amount of sulfur compounds in gasoline or diesel fuel is
not consistent from state-to-state. At the present time, California
has the most stringent requirements for fuel sulfur content, which
is about 30 ppm sulfur in the fuel. Even with this low
concentration of sulfur in the fuel, engine damage and decreased
catalytic converter perfomance can still result.
[0003] 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.
[0004] It would be highly desirable from an environmental
standpoint to be able to power vehicles, such as an automobile with
a low sulfur fuel, such as a low sulfur gasoline or diesel fuel. 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. The
desulfurized fuel can be used 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 reactant 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. Previously filed U.S. patent applications Nos.
09/104,254, filed Jun. 24, 1998; and 09/221,429, filed Dec. 28,
1998 generally 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.
[0005] We have discovered that desulfurization of a gasoline or
diesel fuel which uses a nickel catalytic adsorbent bed cannot be
performed over a significantly extended period of time, unless the
fuel includes an oxygenate compound in appropriate proportions, a
small amount of added water, preferably in the form of steam, or a
small amount of added hydrogen. Various oxygenates which could
suffice for the desulfurization process include MTBE, ethanol or
other alcohols, ethers, or the like.
DISCLOSURE OF THE INVENTION
[0006] 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.
[0007] Gasoline, for example, is a hydrocarbon mixture of
paraffins, naphthenes, 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.
[0008] 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)- , ethanol, or water vapor for example,
will 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, water vapor, or the like.
[0009] 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. F.
[0010] 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
molecules, rather than desorbing intact, decompose to evolve
hydrogen, leaving the surface covered by partially dehydrogenated
fragments, 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
reactant from adsorbing sulfur after a relatively short period of
time.
[0011] 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 .pi. 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 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.
[0012] 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 hydrocarbons 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] 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;
[0014] 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;
[0015] 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;
[0016] 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;
[0017] 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;
[0018] 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;
[0019] FIG. 7 is a graph of the operating temperatures of the
system described in FIG. 6 over the same period of time; and
[0020] FIG. 8 is a schematic view of an embodiment of the gasoline
desulfurizer system of this invention, which desulfurizes gasoline
on board a vehicle whose engine is powered by the desulfurized
gasoline.
SPECIFIC MODES FOR CARRYING OUT THE INVENTION
[0021] 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.
[0022] 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 eminently suitable for fueling an
internal combustion engine. It will be understood that, "sulfur
breakthrough" is defined by our requirements as occurring when a
sustained post-reactant bed sulfur content of greater than about
0.05 ppm is present in the desulfurized gasoline. 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.
[0023] 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 fuel exiting the nickel reactant bed
was about 11% by volume which is the same concentration of MTBE in
the gasoline 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.
[0024] 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.
[0025] 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.
[0026] At this stage, we conclude that the presence of oxygenates
in the gasoline or other fuel maintains the desulfurization
activity of the nickel reactant by significantly suppressing the
carbon deposition (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 other oxygenated organic molecules, are
strongly adsorbed on the Ni surface due to their high dipole moment
where they decompose to isobutylene and methanol. The adsorbed
oxygenate decomposes because the nickel reactant is very active and
the C--O bond is easily broken. 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
[0027] A nickel reactant promotes the formation of methanol, a
byproduct of MTBE decomposition, or ethanol disproportionation
reaction. When methanol is decomposed, the following reactions
occur:
4CH.sub.3->3CH.sub.4+CO.sub.2+2H.sub.2O (1)
4CH.sub.3->2CH.sub.4+2CO.sub.2+4H.sub.2 (2)
[0028] For ethanol, the same reactions should produce ethane
instead of methane. The presence of water vapor or hydrogen
suppresses 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.
[0029] 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 paraffins. 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.
[0030] 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
[0031] 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 Desulfurization After
Desulfurization Paraffins 64.6% 64.50% Olefins 3.7% 3.65%
Naphthenes 2.89% 2.82% Aromatics 28.8% 29.00% Sulfur 30.9 ppm 1.00
ppm
[0032] 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.
[0033] 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
internal combustion engine 14 where it is combusted.
[0034] 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, has been shown to provide the same quantity of water and
hydrogen as is produced from the use of MTBE.
[0035] As a result, the MTBE could be eliminated from the gas
stream when a vaporized water stream is utilized. Minimal amounts
of water oxygenate can be 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. The operating temperature
range of 325.degree. F.-450.degree. F. for liquid fuels, and
250.degree. F.-450.degree. F. for gaseous fuels available in
performance of this invention, both of which are below the
temperature range suggested in the prior art for the performance of
the prior art hydrodesulfurization processes.
[0036] It will be readily appreciated that the inclusion of an
effective amount of an oxygenate, or water in a sulfur-containing
fuel, such as gasoline, will allow sulfur to be removed from the
fuel to the extent necessary to provide a low sulfur content fuel,
i.e., less than about 0.05 ppm sulfur, for fueling an internal
combustion engine. The sulfur compounds are removed from the raw
fuel by means of a nickel reactant bed through which the fuel flows
prior to entering the internal combustion engine. The oxygenate
addition also serves to control carbon deposition on the nickel
reactant bed thereby extending the nickel reactant bed's useful
life and enhancing the sulfur removal capabilities of the nickel
reactant bed. The desulfurization process can be performed inside
of the vehicle, in the service station fuel pumping apparatus, or
at the fuel refinery.
[0037] 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.
* * * * *