U.S. patent application number 10/734236 was filed with the patent office on 2004-07-01 for method for desulfurizing gasoline or diesel fuel for use in a fuel cell power plant.
Invention is credited to Cocolicchio, Brian A., Lesieur, Roger R., Vincitore, Antonio M..
Application Number | 20040124125 10/734236 |
Document ID | / |
Family ID | 24622562 |
Filed Date | 2004-07-01 |
United States Patent
Application |
20040124125 |
Kind Code |
A1 |
Lesieur, Roger R. ; et
al. |
July 1, 2004 |
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 hydrocarbon fuel stock supply
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, thiophenes 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 now desulfurized
hydrocarbon fuel supply continues through the remainder of the fuel
processing system. The method involves adding hydrogen to the fuel
stream prior to the desulfurizing step. The method can be used to
desulfurize either a liquid or a gaseous fuel stream. The addition
of hydrogen serves to extend the useful life of the nickel
reactant. The hydrogen can be derived from source of pure hydrogen
gas, a recycle gas stream, or can be derived from an electrolysis
cell which breaks down water produced in the fuel cell into its
hydrogen and oxygen components. The hydrogen when added to the fuel
stock serves to prevent or minimize carbon formation on the nickel
reactant bed, thereby extending the useful life of the reactant
bed, since carbon deposits tend to block active sites in the
reactant bed.
Inventors: |
Lesieur, Roger R.; (Enfield,
CT) ; Cocolicchio, Brian A.; (Danbury, CT) ;
Vincitore, Antonio M.; (Manchester, CT) |
Correspondence
Address: |
William W. Jones
Patent Counsel
6 Juniper Lan
Madison
CT
06443
US
|
Family ID: |
24622562 |
Appl. No.: |
10/734236 |
Filed: |
December 15, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10734236 |
Dec 15, 2003 |
|
|
|
09653858 |
Sep 1, 2000 |
|
|
|
6726836 |
|
|
|
|
Current U.S.
Class: |
208/217 ;
208/209; 208/213 |
Current CPC
Class: |
Y02E 60/50 20130101;
H01M 8/0662 20130101; C10G 45/06 20130101 |
Class at
Publication: |
208/217 ;
208/209; 208/213 |
International
Class: |
C10G 045/00 |
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 in the fuel stream to nickel
sulfide; b) introducing a hydrocarbon fuel stream which contains a
molecular hydrogen (H2) additive into said nickel reactant
desulfurization station; and c) said H2 additive being present in
said fuel stream in an amount which is effective to suppress carbon
deposition on said nickel reactant and 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 H.sub.2 additive is derived
from a container of H2 in the fuel processing section of the fuel
cell power plant.
3. The method of claim 1 wherein said H.sub.2 additive is derived
from recycled reformed fuel gas from a selective oxidzer in the
fuel processing section of the fuel cell power plant.
4. The method of claim 1 wherein said H.sub.2 additive is derived
from an electrolysis cell in the fuel processing section of the
fuel cell power plant which converts water to H.sub.2 and
O.sub.2.
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 a hydrogen (H.sub.2) additive into said nickel reactant
desulfurization station; and c) said H2 additive 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. A system 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 a fuel
processing section in a fuel cell power plant, said system
comprising: a) 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) means for
introducing a gasoline or diesel fuel stream into said nickel
reactant desulfurization station; and c) a supply of a hydrogen
(H.sub.2) additive and means connecting said H.sub.2 additive
supply to said fuel stream, said H.sub.2 additive 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 system of claim 6 wherein said supply of H.sub.2 additive is
derived from recycled gas from a fuel cell power plant selective
oxidizer.
8. The system of claim 6 wherein said supply of H.sub.2 additive is
derived from a container of H.sub.2.
9. The system of claim 6 wherein said supply of H.sub.2 additive is
derived from a hydride bed.
10. The system of claim 6 wherein said supply of H.sub.2 additive
is derived from a water electrolysis cell.
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 addition of hydrogen to the fuel stream in appropriate
amounts.
BACKGROUND OF THE INVENTION
[0002] Gasoline, diesel fuel, and similar 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. Not only is the hydrodesulfurization process more
complicated because it is a two step process, but to be effective
in desulfurizing heavier fuels containing thiophenic sulfur
compounds, it must operate at elevated pressures, usually greater
than about 150 psig.
[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 21 st 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] Commonly owned co-pending U.S. patent application Ser. No.
09/470,483, filed Dec. 22, 1999 describes a system and method for
desulfurizing gasoline and/or diesel fuel by passing the fuel
through a nickel reactant bed wherein a major portion of the sulfur
in the fuel is converted to nickel sulfide. The fuel stream
contains an oxygenate such as ethanol, methanol or MTBE which acts
to extend the useful like of the nickel reactant bed by suppressing
carbon formation on the reactant bed. The use of such oxygenates
has been found to increase the capacity of the nickel reactant bed
to convert sulfur in organic sulfur compounds in the fuel to nickel
sulfide by about five hundred percent. The operating conditions of
the system and method described in the above-noted patent
application are suitable for use in mobile applications of fuel
cell power plants, such as those usable in powering vehicles. One
problem incurred by using MTBE is that the MTBE itself decomposes
to an unsaturated hydrocarbon so it adds to the total potential
carbon deposited onto the nickel. Carbon formation tends to poison
the reactant by blocking pores and active sites of the nickel
reactant.
[0007] 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.
[0008] 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.
[0009] We have discovered that the capacity of a nickel reactant
bed for desulfurizing a gasoline or diesel fuel stream can be
extended through the addition of hydrogen to the fuel stream in
appropriate proportions without the need to include oxygenates in
the fuel stream. The addition of hydrogen to the fuel stream
essentially doubles the useful life of the nickel reactant bed over
and above the procedure which utilizes the inclusion of oxygenates
in the fuel stream.
DISCLOSURE OF THE INVENTION
[0010] 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.
[0011] 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. California Certified Gasoline is used by new
car manufacturers to establish compliance with California emissions
certification requirements.
[0012] We have discovered that the addition of hydrogen (H.sub.2)
to the gasoline or diesel fuel stream extends the effective life of
the nickel reactant sulfur-adsorption bed. The added hydrogen
supresses carbon deposition on the nickel reactant bed, which
carbon deposition would otherwise occupy and cover active
sulfur-adsorption sites in the nickel bed, and could thereby
shorten the effective life of the nickel reactant bed.
[0013] The effectiveness of a nickel adsorbent reactant to strip
sulfur from organic sulfur compounds contained in gasoline or
diesel fuel depends on the maintenance of as many active
sulfur-adsorption sites in the reactant bed for the longest
possible time. In other words, the desulfurization process depends
on the amount of competitive adsorption sites of the various
sulfur-containing constituents of gasoline or diesel fuel. 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
naphthenes, won't compete with sulfur compounds for adsorption
sites on the nickel reactant at temperatures above 250.degree. F.
and 300.degree. F.
[0014] 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., some unsaturated hydrocarbons
are dehydrogenated, and the dehydrogenated tar fragments form
multiple carbon atom-to-nickel reactant surface bonds. This
explains why aromatics and olefins in gasoline or diesel fuel, in
the absence of H.sub.2 in appropriate concentrations, will
deactivate the nickel reactant from adsorbing sulfur after a
relatively short period of time.
[0015] 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 .pi. 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. The presence of hydrogen in the
gasoline or diesel fuel being scrubbed results in hydrogenation of
the dehydrogenated byproducts of the desulfurized organic compounds
which are adsorbed onto the reactant surface, which frees the
byproducts from the nickel reactant adsorption sites. Thus,
hydrogenation can reduce the adsorption of desulfurized aromatic
and olefin byproducts 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, hydrogenation of olefins and aromatics will
also prevent them from adsorbing onto the nickel reactant.
[0016] We have also discovered that the hydrogenated hydrocarbons
do not inhibit the sulfur compounds from being adsorbed on the
nickel reactant because they do not adsorb onto the nickel reactant
surface at temperatures in the range of about 200.degree. F. to
about 500.degree. F. The sulfur compounds are quite polar and
therefore contact and react with the active nickel metal reactant
sites.
[0017] 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
[0018] FIG. 1 is a schematic drawing of a system which is formed in
accordance with this invention for desulfurizing a gasoline or
diesel fuel stream so that the latter may serve as a source of
hydrogen for powering an fuel cell power plant used to supply
energy for operating a vehicle;
[0019] FIG. 2 is a graph showing sulfur exit levels versus total
operation time comparing recycle hydrogen from the selective
oxidizer with an MTBE additive but no hydrogen additive; and with
neither MTBE nor hydrogen additive;
[0020] FIG. 3 is a graph comparing the catalyst loading with sulfur
and the sulfur exit level results noted when desulfurizing
California premium blend gasoline with MTBE and with hydrogen
recycle from a selective oxidizer in the system; and
[0021] FIG. 4 is graph showing carbon deposition on a nickel
reactant bed as a function of the length of the reactant bed.
SPECIFIC MODES FOR CARRYING OUT THE INVENTION
[0022] Referring now to the drawings, FIG. 1 is a schematic view of
a desulfurizing system which can be used onboard a vehicle to
provide hydrogen to a fuel cell power plant that is used to produce
electricity to operate the vehicle. The fuel being desulfurized can
be gasoline or diesel fuel, or some other fuel which is normally
available to operate an internal combustion engine. It will be
noted that all of the components of the system are disposed onboard
the vehicle in question. The system is denoted generally by the
numeral 2 and includes a fuel supply tank 4 and a line 6 which
leads from the fuel tank 4 to a nickel reactant desulfurizer bed 8.
The desulfurizer bed 8 may be heated to operating temperatures by a
battery 1 connected to the desulfurizer bed 8 by cables 12. The
desulfurizer bed 8 will preferably be run at temperatures which
will vaporize the fuel stream entering the desulfurizer bed 8. The
desulfurized fuel passes through a line 14 to a reformer 16, which
is preferably an autothermal reformer. The hydrogen-enriched
reformed fuel passes through a line 18, through a first heat
exchanger 20 and thence through a line 22 into a second heat
exchanger 24. The heat exchangers 20 and 24 serve to lower the
temperature of the reformed fuel stream while raising the
temperature of the fuel, steam and air entering the reformer. The
reformed fuel stream then passes through a line 26 and thence
through a water gas shift converter 27 before it enters a selective
oxidizer 28 where CO in the fuel stream is oxidized to CO.sub.2,
before the H.sub.2 enriched gas stream is fed to the fuel cell
anode. The treated fuel stream exits the selective oxidizer 28 via
line 32 and ultimately enters the fuel cell power plant 55. A
hydrogen recycle line 30 connects the selective oxidizer 28 and the
line 6 so that a controlled amount of hydrogen can be removed from
the selective oxidizer 28 and recycled back into the fuel stream in
the line 6. The hydrogen recycle line 30 could also be connected to
the desulfurizer bed 8 if so desired. The purpose of the recycle
line 30 is to add a controlled amount of hydrogen (H.sub.2) to the
fuel stream as it enters the desulfurizer bed 8. The amount of
hydrogen fed into the bed 8 can be controlled by means of a pump or
an ejector (not shown). An ejector is a device which is used to
draw a secondary fluid into a primary fluid stream with no moving
parts, such as a Venturi tube assembly.
[0023] The H.sub.2 additive can also be derived from a source of
H.sub.2 34 that can take the form of a hydrogen tank; a hydride
bed; or an electrolysis cell which breaks down water from the fuel
cell 55, or from some other source, into H.sub.2 and O.sub.2. When
water from the fuel cell is used, the water will be delivered to
the H.sub.2 source 34 by means of a line 36. H.sub.2 from the
H.sub.2 source 34 is delivered to the line 6 via a line 38. As
noted above, the addition of H.sub.2 to the fuel stream results in
hydrogenation of adsorbed unsaturated hydrocarbons which will then
desorb from the nickel reactant so as not to inhibit the sulfur
compounds from being adsorbed on the nickel reactant.
[0024] FIG. 2 is a graph of the results of short term desulfurizer
test runs which compares the effectiveness of hydrogen and MTBE as
desulfurizing gasoline with an gasoline which had no additives at
all. It will be noted that the hydrogen additive resulted in a
lower desulfurizer exit stream sulfur level for a longer time than
the MTBE, and for a much longer time than when no additive was
added to the gasoline. In the samples used in this test run, the
additive-free gasoline and the hydrogen additive samples contained
twenty one ppm sulfur at the desulfurizer inlet, and the sample to
which MTBE was added contained twenty five ppm sulfur at the
desulfurizer inlet. The amount of MTBE in the gasoline was 11% by
weight, and the amount of hydrogen added to the gasoline was 160
ml/min, which is equivalent to about 0.7% of the hydrogen exiting
from the selective oxidizer. The temperature was 350.degree. F. and
the space velocity was twenty six pounds of fuel per hour per pound
of reactant.
[0025] FIG. 3 is a graph which compares the catalyst loading of
sulfur and exit levels of sulfur in a vaporized gasoline stream of
California special blend gasoline, one of which gasoline streams
included a hydrogen (H.sub.2) additive, and the other of which
included an MTBE additive, but no H.sub.2 additive. The solid line
trace on the graph indicates the desulfurizer bed catalyst loading
with sulfur and exit sulfur level of the fuel stream which was
provided with an H.sub.2 additive, and the broken line indicates
the same data when the gasoline was provided with MTBE. The sulfur
loading of the catalyst bed in each instance is also shown in FIG.
3. It will be noted that the sulfur levels at the exit end of the
desulfurizing bed 8 in ppm rise faster when MTBE is used than when
H.sub.2 is used as an additive. It is also noted that the ability
of the nickel reactant to absorb sulfur increases when H.sub.2 is
used as an additive, as compared to MTBE. The amount of hydrogen
added was 13 mole percent, the temperature of the tests was
375.degree. F. and the space velocity was two pounds of fuel per
hour per pound of reactant. The amount of hydrogen used in this
test equaled about 1% of the hydrogen exiting the selective
oxidizer, and was added to the gasoline stream by means of a
simulated recyce stream from the selective oxidizer. The MTBE was
present in an amount of 11% by weight.
[0026] FIG. 4 is a graph showing carbon deposition on the nickel
reactant as a function of the length of the reactant bed shown in
percentages of the total reactant bed length. The solid line
indicates the extent of carbon deposition from a gasoline fuel
which included MTBE but no hydrogen additive. The broken line
indicates the extent of carbon deposition from a gasoline which
included a hydrogen additive, but no MTBE. It can be seen that when
11% MTBE was added to the gasoline, more carbon was deposited on
the nickel reactant bed in two hundred eighteen hours than was
deposited on the reactant bed when 13 mole % of hydrogen was added
to the gasoline after four hundred fifty hours. The addition of
hydrogen to the gasoline being desulfurized enabled the nickel
reactant surface to remain available for sulfur reaction for a much
longer period of time, thus allowing a much higher sulfur loading
on the reactant bed to be achieved.
[0027] We conclude that the presence of hydrogen 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. It will be readily appreciated that
the addition of an effective amount of H.sub.2 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 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 hydrogen serves to
control carbon deposition on the nickel reactant bed thereby
extending the useful life of the reactant bed and enhancing the
sulfur removal capabilities of the nickel reactant bed.
[0028] 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.
* * * * *