Note: Descriptions are shown in the official language in which they were submitted.
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FUEL-CELL FUELS, METHODS, AND SYSTEMS
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of the filing dates of, and fully
incorporates by reference for all purposes, U.S. Patent Applications Serial
Nos.
60/127,465, filed March 31, 1999 (provisional), 60/161,659, filed October 21,
1999
(provisional), and 09/499,690, filed February 8, 2000 (regular).
TECHNICAL FIELD OF THE INVENTION
The present invention relates to fuel cells, and more particularly, to fuel-
cell
fuels, to methods of making such fuels, and to fuel-cell powered systems, for
example fuel cell systems powered by such fuels and light hydrocarbon
conversion systems powered at least in part by fuel cells employing such
fuels.
BACKGROUND OF THE INVENTION
Available technical literature indicates that fuels may be used in a fuel cell
indirectly or directly, that is, with or without preliminary treatment in a
fuel cell fuel
processor, e.g., a reformer, to liberate hydrogen from the fuel. In the former
case,
which presently appears to be of principal interest to researchers, the
processor
and fuel cell cooperate, for example they may be fluidly inter-connected, to
form a
fuel cell system in which hydrogen liberated from fuel in the processor is fed
to the
fuel cell and there converted to electricity. In the latter case, the fuel
cell system
includes a fuel cell and possibly other components, but does not include a
processor.
The present fuels of choice of the fuel cell industry are methanol, methane
and propane, although interest has also been shown in gasoline derived from
petroleum. Common forms of these fuels suffer from the hazards of, and/or the
expenses of avoiding, one or more serious problems. Among these are fuel cell
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catalyst-debilitating sulfur content, water solubility with ensuing
environmental
dangers, transportation and storage complications and unsuitability for
distribution
in existing distribution infrastructure. Continued interest in these fuels,
despite
their disadvantages, bears mute testimony to existence of an unfulfilled need
for
improved fuel cell fuels. The present invention is intended to address this
need.
SUMMARY OF THE INVENTION
In a first aspect, the present invention includes a fuel cell fuel that may
comprise or be composed substantially of synthetic products of Fischer-Tropsch
processing, including paraffinic and optionally iso-paraffinic hydrocarbons,
and
containing less than 0.001 weight percent sulfur.
In one embodiment of the foregoing aspect, the fuel cell fuel contains less
than 5 weight percent of aromatics.
In another embodiment of said aspect, the fuel cell fuel comprises tail gas
of substantially C5 or less.
In yet another embodiment of the above aspect, the fuel comprises liquids
boiling in the range of CS-C2o.
In still another embodiment of the first aspect, the fuel cell fuel comprises
more hydrogen than C4, preferably C5 and more preferably C6 hydrocarbon
species, or more hydrogen than gasoline derived from petroleum.
In a second aspect, the present invention includes a fuel cell fuel which
may comprise or be substantially composed of synthetic liquid, gaseous and/or
vaporous products, preferably predominantly by weight liquid products, of
Fischer-
Tropsch processing, which have optionally been hydroisomerized and/or
hydrocracked, including paraffinic and optionally iso-paraffinic hydrocarbons,
having up to about 18, up to about 20 or up to about 22 carbon atoms.
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In certain embodiments of either of the foregoing aspects, said fuel cell fuel
may contain less than 5 weight percent or less than 1 weight percent of
aromatics
In certain other embodiments of either of the foregoing aspects, said fuel
cell fuel may contain small or substantial amounts of alcohols, if any, small
or
substantial amounts of unsaturates other than aromatics, if any, negligible
amounts of S, and, preferably, only negligible amounts of N. In this context,
negligible means insufficient in amount to require removal for successful use
of
the fuel containing same as a fuel cell fuel.
As is known to those skilled in the art, products of Fischer-Tropsch
processing are products of methylene chain-propagating reactions of hydrogen
and/or light hydrocarbons with CO in the presence of a methylene chain
propagating catalyst(s), such as an iron, cobalt, rhenium or ruthenium
catalyst of
the types used in Fischer-Tropsch reactions, which are usually supported
catalysts and may include promoters. Preferably, the reactions are conducted
under non-shifting conditions, which are described in the Fischer-Tropsch
literature.
In the descriptions of the foregoing aspects and embodiments of the
invention and in the descriptions of other aspects and embodiments of the
invention which follow, indications that fuels or fuel components include
hydrocarbons or other compounds in a particular range of carbon numbers, such
as up to about C22 or in the range of about Coo to about C2o, are intended to
indicate, unless the context clearly indicates the contrary, that these
compounds
may be distributed substantially throughout the stated range or may represent
only a portion/portions of that range.
Fuels according to the invention may comprise or be composed
substantially of hydrocarbons in the C~ to C4 or C, to CS ranges. In many
embodiments, the fuels will be composed predominantly, on a weight basis, of
hydrocarbons in a range of at least about C4 or C5 and higher, e.g., in a
range of
about C5 to about C2o, in a range of about C5 to about CAB, and in the ranges
of
about C5 to about C9 and about Coo to about C2o.
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A preferred form of liquid fuel cell fuel according to either of the foregoing
aspects comprises a light Fischer-Tropsch liquid containing at least 77 wt.
normal and iso-paraffins, less than 20% wt. % olefins, less than 9 wt. %
alcohols,
less than 0.001 wt. % sulfur, and less than 5 wt. % aromatics.
The fuel, or portions of the fuel, may have been subjected to hydrogenation
and/or hydrocracking treatment.
For example, the invention contemplates fuels prepared by subjecting a
Fischer-Tropsch liquid product, which may include hydrocarbons in the range of
at
least about C4 or at least about C5, preferably up to about C2g, or higher, by
subjecting the hydrocarbons to hydrotreating and/or hydrocracking, and by
separating from the product of hydrotreating and/or hydrocracking a fuel or
fuel
component in a suitable boiling range, for example in the ranges of about Ca
or
about CS to about C2o, in the range of about C5 to about C,8, in the range of
about
C5 to about C9, in the ranges of about C1o to about C~e or about C2o, or any
other
useful range.
According to another aspect of the present invention, a Fischer-Tropsch
fuel cell fuel is formed as a blend of one or more alcohols (up to 9 wt. %)
and a
Fischer-Tropsch product. The alcohols may include methanol, ethanol, propanol,
and/or butanol which may be process alcohols, and/or may be from other
sources.
Or the fuel cell fuel may be a blend of Fischer-Tropsch product containing
from 70 to more than 99 wt. % normal and iso-paraffin, less than 20% wt.
olefins, less than 0.001 wt. % sulfur, less than 5% wt. % aromatics and up to
about 9 wt. %, based on the total weight of blend, of alcohol or alcohols
comprising at least one member of the group consisting of methanol, ethanol,
propanol and butanol.
In another embodiment of the second aspect of the invention, the fuel-cell
fuel may be a light Fischer-Tropsch liquid having: at least about 20, more
particularly at least about 50, preferably at least about 77 and more
preferably at
least about 95 wt. % of normal and/or iso-paraffins; less than about 70, more
particularly less than about 50, preferably less than about 35 and more
preferably
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less than about 20 wt. % olefins; less than 5 or less than 1 wt. % aromatics;
less
than 9, more particularly less than 5, preferably less than 1 and more
preferably
less than 0.1 wt. % alcohols; preferably less than 0.001, more preferably less
than
0.0005 and still more preferably less than 0.0001 wt. % sulfur; and preferably
less
than 0.050, more preferably less than 0.010, still more preferably less than
0.001
and yet more preferably less than 0.0005 wt. % nitrogen.
In yet another aspect, the fuel cell fuel may be composed predominantly,
on a weight basis, of material in the Cs-C22 range, and include material
boiling
above and below 700 degrees F. At least about 50% by weight of the material
boiling above 700 degrees F. has been subjected to treatment with hydrogen
under conditions sufficient to saturate at least a portion of any aromatics
and/or
other unsaturates that may have been present therein. Moreover, the fuel
comprises at least about 99, at least about 99.3 or at least about 99.5% by
weight
of normal- and/or iso- paraffins based on the total weight of hydrocarbons,
and
has less than about 500, or less than about 200, or less than about 100, or
less
than about 50, or substantially zero ppm of unsaturates, based on the total
weight
of said fuel. The latter also has a cetane number of at least about 70, at
least
about 74 or at least about 75, and contains less than about 1 ppm, less than
about 750 ppb, less than about 500 ppb or less than about 300 ppb each of S
and
N, based on the total weight of the fuel.
According to a preferred embodiment, the fuel hydrocarbon content is
composed predominantly, or substantially, or entirely of material prepared by
Fischer-Tropsch synthesis.
In still another embodiment, the hydrocarbon content of the fuel has an iso-
to normal- paraffin weight ratio in the range about 0.02:1 to about 20:1, or
in the
range of about 0.1:1 to about 15:1, or in the range of about 0.5:1 to about
12:1.
In other embodiments, (a) at least about 50% by weight of the material
boiling below 700 degrees F., or (b) substantially all of the material boiling
above
700 degrees F., or (c) substantially all of the material boiling below 700
degrees
F., or any combination thereof, has been subjected to treatment with hydrogen
under conditions sufficient to saturate at least a portion, a substantial
portion, or
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substantially all, of any aromatics and/or other unsaturates that may have
been
present therein.
In still another embodiment, the fuel is composed predominantly, or
substantially, or entirely of material prepared by Fischer-Tropsch synthesis,
and
substantially all of the material prepared by Fischer-Tropsch synthesis has
been
subjected to treatment with hydrogen under conditions sufficient to saturate
at
least a portion, a substantial portion, or substantially all, of any
unsaturates and/or
alcohols that may have been present therein.
In particularly preferred embodiments, the fuel contains less than about
200, less than about 100, less than about 50 or substantially zero ppm of C~2-
C2a
primary alcohol oxygenate, as oxygen, on a water free basis, based on the
total
weight of said fuel.
There are also embodiments of the invention in which the fuel has a flash
point, as measured by ASTM D-93 of at least about 80 degrees F., or at least
about 100 degrees F., or at least about 120 degrees F, or at least about 150
degrees F.
In other embodiments, the fuel has a flash point, as measured by ASTM D-
93, in the range of about 80 to about 150 degrees F., or in the range of about
90
to about 130 degrees F.
Another aspect of the invention is a method of manufacturing a fuel cell
fuel comprising: preparing a Fischer-Tropsch product; separating from the
Fischer-Tropsch product a light portion comprising material in the range of C5
to
C2o or C28 having at least 77 wt. % normal and iso-paraffins, less than 20 wt.
olefins, less than 9 wt. % alcohols, less than 0.001 wt. % sulfur, and less
than 5
wt. % aromatics.
The invention also includes certain improvements representing preferred
embodiments of the foregoing general method. In one such embodiment, the
step of separating comprises separating from the Fischer-Tropsch product a
light
Fischer-Tropsch liquid having less than 1 wt. % aromatics.
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Another embodiment of the method of manufacturing a fuel-cell fuel further
comprises the step of hydrogenating the light portion.
According to another embodiment of this method of manufacturing a fuel-
cell fuel, the separated light portion makes up the fuel cell fuel.
Yet another embodiment of this method further comprises: separating from
the Fischer-Tropsch product a heavy portion comprising material in the range
of
C2~+; hydrocracking the heavy portion to produce a hydrocrackate; and
separating
material in the range of C5 to C2o from the hydrocrackate.
In one optional way of performing the last-mentioned embodiment, the
material in the range of C5 to C2o separated from the hydrocrackate makes up
the
fuel cell fuel.
Another optional way of performing the method of manufacturing a fuel-cell
fuel and various embodiments thereof comprises the step of hydrogenating the
light product stream.
In other optional ways of performing the method of manufacturing a fuel-
cell fuel and various embodiments thereof, the hydrocrackate and the
hydrogenated light portion make up the fuel cell fuel.
According to a preferred embodiment of the foregoing method, the
separated light Fischer-Tropsch liquid comprises a fuel additive; and said
fuel
additive is added to a petroleum fuel feedstock to provide a product with less
than
about 0.05 wt. % sulfur and less than about 10 wt. % aromatics, and wherein
the
resultant product comprises the fuel-cell fuel.
Any of the above-described fuels may be used as the sole fuels or as
blends containing these fuels and one or more other fuel component(s), such as
alcohols or petroleum-based fuels, in fuel cell systems and in systems powered
by
fuel cells.
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Thus, yet another aspect of the invention comprises a fuel cell system, as
above described, containing any of the above-described fuels according to the
invention, whether as the sole fuel or as an additive to or blend with another
fuel
component(s).
Moreover, the invention includes fuel cell powered systems, such as aerial,
marine or land vehicles or homes or businesses containing appliances, i.e.,
heating or cooling units or other devices, that are electrically inter-
connected with
a fuel cell system containing a fuel according to the invention.
A specific example of a fuel cell powered system according to the invention
is a conversion system for converting light hydrocarbons into heavier
hydrocarbons. It includes: a synthesis gas subsystem for receiving light
hydrocarbons and, optionally, other synthesis gas forming reactants, such as
steam and/or oxygen-containing gas, and for developing a synthesis gas
therefrom; a synthesis subsystem fluidly coupled to the synthesis gas
subsystem
for receiving synthesis gas therefrom and producing heavier hydrocarbons
therefrom; a fuel cell processor fluidly coupled to the synthesis gas
subsystem for
receiving synthesis gas therefrom and preparing the synthesis gas for use in a
fuel cell as a hydrogen-containing gas; and a fuel cell coupled to the fuel-
cell
processor for receiving a hydrogen-containing gas therefrom and producing
electrical power. The electrical power may be fed to power-consuming devices,
such as lighting, heating and pumping or compressing facilities, within or
without
the hydrocarbon conversion system.
According to a preferred form of the specific example of the invention
described in the preceding paragraph, the synthesis subsystem is adapted to
produce heavier hydrocarbons and tail gas and the fuel cell processor is
adapted
to prepare the tail gas for use as a hydrogen-containing gas in the fuel cell
to
produce electrical power.
According to yet another aspect of the present invention, a conversion
system for converting light hydrocarbons into heavier hydrocarbons includes a
fuel
cell system for receiving light hydrocarbons and, optionally, other synthesis
gas
forming reactants, such as steam and/or oxygen-containing gas, for generating
a
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first synthesis gas and electrical power; and a synthesis unit coupled to the
fuel
cell for receiving a first synthesis gas therefrom and generating the heavier
hydrocarbons therefrom.
In a preferred embodiment, the conversion system of the foregoing aspect
further comprises a synthesis gas unit operable to produce a second synthesis
gas, the synthesis gas unit being fluidly coupled to the synthesis unit.
Another aspect of the invention is a method of operating a fuel cell to
produce electrical power. Thus, in one embodiment, the invention includes a
method which comprises the steps of: providing a fuel cell fuel that may
comprise
or may be composed substantially of synthetic products of Fischer-Tropsch
processing, including paraffinic and optionally iso-paraffinic hydrocarbons,
and
containing less than 0.001 weight percent of sulfur; and supplying the fuel
cell fuel
to the fuel cell to produce electrical energy therefrom.
In another embodiment of this aspect, the method of operating a fuel cell to
produce electrical power comprises the steps of: providing a fuel cell fuel
that may
comprise or be substantially composed of synthetic liquid, gaseous and/or
vaporous products, preferably predominantly by weight liquid products, of
Fischer-
Tropsch processing, which have optionally been hydroisomerized and/or
hydrocracked, including paraffinic and optionally iso-paraffinic hydrocarbons,
having up to about 18, up to about 20 or up to about 22 carbon atoms.
In another embodiment, the fuel cell operating method comprises the steps
of: providing a fuel cell fuel comprising a light Fischer-Tropsch liquid
having at
least 77 wt. % normal and iso-paraffins, less than 20 wt. % olefins, less than
9 wt.
alcohols, less than 0.001 wt. % sulfur, and less than 5 wt. % aromatics; and
supplying the fuel-cell fuel to the fuel cell to produce electrical energy
therefrom.
Any of the embodiments of these methods of operating a fuel cell may
further comprise the step of providing a fuel cell fuel containing less than 5
or less
than 1 weight percent of aromatics.
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Moreover, the foregoing methods of operating a fuel cell may include the
use of a fuel cell fuel which is a blend of said light Fischer-Tropsch liquid
containing from 70 to more than 99 wt. % normal and iso-paraffins, less than
20
wt. % olefins, less than 0.001 wt. % sulfur, less than 5 wt. % aromatics and
up to
about 9 wt. %, based on the total weight of blend, of alcohol or alcohols
comprising at least one member of the group consisting of methanol, ethanol,
propanol and butanol.
ADVANTAGES
Although all of the embodiments included within the scope of the invention
will not possess all of the following advantages, certain preferred
embodiments of
the invention will be found to exhibit one or more of these advantages.
The preferred fuel cell fuels based on Fischer-Tropsch liquids provide, on a
per unit fuel volume basis, high yields of hydrogen from a fuel cell fuel
processor.
It will be shown to what extent certain preferred embodiments of the Fischer-
Tropsch based fuel cell fuels can provide greater energy density than other
fuel
cell fuels, such as methane and methanol. It appears that the theoretical
hydrogen yield of C5-Cs F-T fuel cell fuel is approximately 90 % greater, by
volume, and approximately 110% greater, by mass, than that of methanol.
It appears that a fuel cell power generation station, or buses using synthetic
gasoline-range paraffin, could generate greater than 87% more energy from a
given volume of fuel than from the same fuel cell using methanol, based on non-
ideal conversion to H2 and CO. Vehicles using such a fuel could travel almost
twice as far as the same vehicle using methanol or methane.
Certain embodiments of the fuel-cell fuel can readily be handled in the
same fuel distribution systems used for distributing and dispensing internal
combustion engine fuels such as gasoline and diesel fuel. Thus, refueling
would
be no more complicated than fueling a car today, and would involve none of the
toxicity concerns of methanol
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With a fuel cell fuel from the Fischer-Tropsch process as described herein,
that contains substantially no sulfur, no or minimal aromatics, and only small
amounts of olefins and alcohol, many of the present complications of gasoline
reforming for fuel cells are eliminated. Fuel cell fuel processor systems no
longer
need to scrub sulfur, chorine, and metal from the processor gas stream. The
task
of removing sulfur from the hydrogen feed stream before it can damage the fuel
cell is all but eliminated. Implications of a clean, substantially sulfur-free
fuel cell
fuel with no or minimal aromatics are interesting.
F-T (Fischer-Tropsch)-alcohol fuel cell fuel blends in which paraffins are
replaced by alcohol(s) of equivalent or lesser carbon number have lower pour-
point temperatures than those of F-T neat. This is due to the presence of the
alcohol or alcohols in the blends. Thus, such blends may have lower start-up
temperatures in the presence of some catalysts. These blends also have a
hydrogen carrying capacity which is higher than that of pure alcohol or
alcohol fuel
cell fuel blends and proportional to the F-T component of the F-T-alcohol
blend
fuel cell fuel.
Another advantage is that the fuel-cell fuel can be made from feedstock
natural gas generally available worldwide.
Still another advantage is that including a fuel cell as an aspect of a
conversion system for converting light hydrocarbons to heavier hydrocarbons
can
result in improved system efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are illustrative and non-limiting, include
illustrations of embodiments of the invention and its advantages.
FIGURE 1 is a schematic diagram of a system for converting light
hydrocarbons into heavier hydrocarbons, including a fuel-cell fuel.
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FIGURE 2 is a bar chart, based on theoretical calculations, showing the
relative hydrogen yields of a number of species, including an embodiment of
the
present invention.
FIGURE 3 is a schematic diagram of a conversion system for converting
lighter hydrocarbons into heavier hydrocarbons according to the invention.
FIGURE 4 is a schematic diagram of another example of a conversion
system for converting lighter hydrocarbons into heavier hydrocarbons according
to
an aspect of the present invention.
FIGURE 5 is a schematic diagram of yet another conversion system for
converting lighter hydrocarbons into heavier hydrocarbons in which a fuel cell
is
used at least in part to produce synthesis gas.
FIGURE 6 is a schematic diagram of a system for hydrogenating a portion
of the F-T product stream.
FIGURE 7 is a schematic diagram of a system for hydrocracking all of the
F-T product.
DESCRIPTION OF VARIOUS AND PREFERRED EMBODIMENTS
For a more complete understanding of the present invention and
advantages thereof, reference is now made to the following description of
various
illustrative and non-limiting embodiments thereof, taken in conjunction with
the
accompanying drawings in which like reference numbers indicate like features.
A. Introduction to The Fischer-Tropsch Process
The Fischer-Tropsch reaction for converting synthesis gas, which is usually
primarily CO and Hz, has been characterized in some instances by the following
general reaction:
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2H2 + CO ~--~ H (- CH2 -)n H + H20
Catalyst
The hydrocarbon products derived from the Fischer-Tropsch reaction range from
some methane to high molecular weight paraffin waxes containing more than 50
carbon atoms (n = 1-50). Both normal- and iso- paraffins, including both
saturated and unsaturated hydrocarbons, and some aromatics and alcohols, may
be produced. In practice, the mole ratio of Hz and CO used to conduct the
reaction varies. It has been suggested that this ratio can vary from about 1:1
to
about 3:1 (HaJCO). The synthesis reaction is exothermic and temperature
sensitive whereby temperature control is required to maintain desired
hydrocarbon
product selectivity.
Numerous catalysts have been used in carrying out the Fischer-Tropsch
reaction, such as iron-, cobalt-, rhenium- or ruthenium- based catalysts.
Cobalt-
based catalysts, supported on an alumina or other suitable support, are
preferred
for use in the present invention.
Operating conditions that minimize formation of carbon dioxide byproducts
are preferred. Thus, non-shift Fischer-Tropsch reaction conditions are
preferred,
and these can be achieved by a variety of methods, including one or more of
the
following: operating at relatively low carbon monoxide partial pressures, that
is,
operating at hydrogen to carbon monoxide ratios of at least about 1.4:1 to
about
2.5:1, more particularly about 1.7 to about 2.5:1, more particularly at least
about
1.9:1 and still more particularly in the range of about 1.9:1 to about 2.3:1
for a
cobalt-based catalyst. Operating with ratios below 2:1 may be of assistance in
minimizing water deactivation of cobalt-based catalysts. Optimum ratios for
other
F-T catalysts may vary.
B. Synthesis Gas Production
Synthesis gas may be made from natural gas, gasified coal, and other
gaseous raw materials. Three basic methods have been most frequently
mentioned as useful for producing the synthesis gas ("syngas"), which is
substantially carbon monoxide and molecular hydrogen, utilized as feedstock in
the Fischer-Tropsch reaction. These include steam reforming, partial oxidation
or
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autothermal reforming. For example, see U.S. Patent 2,552,308. However, it has
been suggested that relatively low temperature plasma (high voltage ionization
field) treatment of light hydrocarbons, with or without some oxygen present,
is also
useful for making synthesis gas. An autothermal reformer utilizes steam with
O.C.G. (oxygen-containing gas), for example air, enriched air, or oxygen. The
autothermal reforming process can be carried out in a relatively inexpensive
refractory lined carbon steel vessel whereby a lower relative cost is
typically
involved.
The autothermal process results in lower hydrogen to carbon monoxide
ratio in the synthesis gas than does steam reforming alone. That is, the steam
reforming reaction with methane results in a ratio of about 3:1 or higher
while the
partial oxidation of methane results in a ratio of less than about 2:1. A good
ratio
for the hydrocarbon synthesis reaction carried out at low or medium pressure
over
a cobalt catalyst is about 2:1 or less, such as about 1.9. When the feed to
the
autothermal reforming process is a mixture of light shorter-chain hydrocarbons
such as a natural gas stream, some form of additional control may be required
if it
is desired to maintain the ratio of hydrogen to carbon monoxide in the
synthesis
gas at a ratio of about 2:1. For this reason steam and/or C02 may be added to
the synthesis gas reactor. See for example, United States Patents 4,883,170 to
Agee and 4,973,453 to Agee, which are both incorporated by reference herein
for
all purposes.
C. ILLUSTRATIVE CONVERSION SYSTEM FOR PRODUCING FUEL-CELL
FUELS
Referring now to FIGURE 1, an example of a Fischer-Tropsch system is
presented. Conversion system 110 is preferably a Fischer-Tropsch system for
converting lighter, shorter-chain hydrocarbons to heavier, longer-chain
hydrocarbons. System 110 has a synthesis gas system, in this case synthesis
gas subsystem 112, and a synthesis subsystem 116. The synthesis gas
subsystem 112 receives a plurality of feedstocks and produces synthesis gas,
which includes primarily hydrogen and carbon monoxide. The synthesis gas is
delivered to a synthesis subsystem 116 where heavier, longer-chain
hydrocarbons
are formed. As will be described further below, one or more of the plurality
of
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feedstocks may be enriched with respect to carbon through a stripper (or
contaminant removal) subsystem 114. The stripper subsystem 114 strips or helps
to remove contaminants from one or more byproduct water streams delivered to
it
from the synthesis gas subsystem 112 and/or the synthesis subsystem 116.
The plurality of feed streams to the synthesis gas subsystem 112 may
include an O.C.G., oxygen-containing gas, such as air or enriched air, which
is
shown delivered through conduit 118; steam, which is shown delivered through
conduit 120; a low-BTU residue, or tail gas, which is delivered through
conduit
122; and light hydrocarbons, which are shown delivered through conduits 123
and
124. The hydrocarbon feedstock delivered through conduits 123 and 124 is a
hydrocarbon feedstock that has been carbon enriched by stripper subsystem 114.
The synthesis gas prepared by synthesis gas subsystem 112 is delivered through
synthesis gas conduit 126 to synthesis subsystem 116.
Synthesis gas subsystem 112 may utilize a partial oxidation system, a
steam reformer, an autothermal reformer, or a plasma syngas generator, using
air, enriched air, oxygen, or other oxygen-containing gas or gases. By
"enriched
air," is meant air, the oxygen content of which has been increased to above
that of
standard air, i.e., above about 21 percent oxygen.
Synthesis subsystem 116 receives synthesis gas from subsystem 112 and
uses a reactor or reactors with a catalyst to produce heavier, longer-chain
hydrocarbons preferably using the Fischer-Tropsch reaction. Any suitable
Fischer-
Tropsch catalyst may be used. The catalysts include cobalt or iron as the
primary
catalysts, preferably supported cobalt, and more preferably supported cobalt
where the support may be silica, alumina, silica-alumina or Group IVB metal
oxides, e.g. titania. Promoters may also be employed, e.g. ruthenium, rhenium,
titanium, zirconium, hafnium. Whereas various catalysts can be used to convert
synthesis gas to Fischer-Tropsch liquids, supported cobalt catalysts are
preferred
in that they tend to produce primarily paraffinic product.
The synthesis subsystem 116 produces a heavy Fischer-Tropsch liquid and
light Fischer-Tropsch liquid that are separated. The heavy Fischer-Tropsch
liquid
is delivered into conduit 128 where it may go to storage or to be hydrocracked
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then go to stabilization or directly to storage. The light Fischer-Tropsch
liquid
(preferably about Ca to about Cza) is delivered into conduit 130, from where
it may
proceed to storage or on for other processing or use. The light Fischer-
Tropsch
liquid is essentially a flash product that has been flashed at temperature and
pressure such that the liquid contains a broad boiling range, about Ca to
about C2a
with a bell-curve type distribution. The light Fischer-Tropsch liquid will
substantially overlap the heavy Fischer-Tropsch liquid. At room temperature,
the
light Fischer-Tropsch liquid is a liquid and the heavy Fischer-Tropsch liquid
is a
solid.
A low BTU residual gas or tail gas (substantially C5 or less) is separated
from the light F-T liquid product stream and delivered into conduit 122. The
residual or tail gas delivered into conduit 122 may be returned to the
synthesis
gas subsystem 112, where it may be used as a fuel for a combustor of a
turbine,
as fuel for burners used within subsystem 112, or for other useful purposes.
Synthesis subsystem 116 also produces process condensate stream or byproduct
water that is delivered into conduit 132, which delivers the aqueous byproduct
to
stripper subsystem 114. Synthesis gas subsystem 112 also produces process
condensate stream or byproduct water, which is also carried to stripper
subsystem
114 by a conduit 134. The synthesis subsystem 116, which preferably includes a
Fischer-Tropsch reactor, produces aqueous byproducts. As noted earlier, the
synthesis gas subsystem 112, which includes an autothermal reformer, produces
aqueous byproducts that include contaminants such as ammonia and other
nitrogen species.
Before the aqueous byproduct streams from subsystems 112 and 116 may
be disposed of or utilized elsewhere in the process, contaminants should be
substantially removed or lowered to safe levels, and for this reason, a
stripper
subsystem 114 is included as an important aspect of the present invention. The
treated water from which the contaminants have been substantially removed by
stripper subsystem 114 is delivered to conduit 138. The process alcohols in
conduit 124 stripped from byproduct streams 132 and/or 138 may be separated
and blended with fuel-cell fuels produced from the product streams of 130
and/or
128, if desired. The process alcohols are produced during production of the F-
T
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liquids. For example, the product water from the F-T reactor may include
methanol and ethanol that can be captured and reintroduced to form a fuel-cell
fuel. Up to 9 wt. % alcohol is the preferred range.
From there the treated water may be delivered to other parts of system
110, such as for use as boiler feed water in a closed loop cooling system
associated with either a reactor in synthesis gas subsystem 112 or a reactor,
such
as the Fischer-Tropsch reactor, of synthesis subsystem 116. Other Fischer-
Tropsch systems may be used as well to produce the fuel-cell fuel described
herein; for example, the systems shown in U.S. Patent 5,733, 941 or U.S. Pat.
5,861,441, both of which are incorporated by reference for all purposes, might
be
used.
The light F-T liquid product delivered to conduit 130 may be further
separated as necessary to produce a product in the range of from about Ca or
C5
to about C,a or to about C2o or to about C22, or in the range of about C1o to
about
C2o or preferably in the range of about C5 to about C9, having the following
characteristics: at least 77 wt. % normal and iso-paraffins, less than 20 wt.
olefins, less than 9 wt. % alcohols, less than 0.001 wt. % sulfur, and less
than 10
wt. % aromatics (preferably less than 5 wt. % aromatics, and more preferably
still
less than 1 wt. % aromatics). As such, the product makes a good fuel-cell
fuel.
The fuel based on F-T light liquid product may be further hydroprocessed
(saturated with hydrogen) if desired. In addition, the heavy F-T product of
conduit
128 may be hydrocracked to a hydrocrackate in the range of from about Ca or C5
to about Ga or to about C2o or to about C22, or in the range of about Coo to
about
C2o or preferably in the range of about C5 to about C9, which is useful as
fuel cell
fuel. The hydrocracking may include hydrotreating to reduce or remove
unsaturation in the hydrocrackate.
What has been referred to as the fuel-cell fuel above may be used as an
additive or intermediate product to mix with conventional petroleum fuels,
such as
diesel , gasoline, jet fuels, etc., to arrive at a resultant fuel-cell fuel
that has less
than .05 wt. % sulfur and less than 10 wt. % aromatics. Other additives might
be
added as well.
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The following chart shows calculated theoretical hydrogen yields for
Fischer-Tropsch based fuels and other fuels processed in a fuel cell fuel
processor.
Fuel Formula H2 Yield (Max) COz
Yield
(Min.)
Ka/L K_g/kg__ Ka/L Ka~ka
Methanol CHsOH 0.125 0.159 1.08 1.38
Ethanol C2HsOH 0.159 0.204 1.47 1.87
Gasoline C7.3H14.8O0.10.224 0.321 2.16 3.09
F-T Fuel (one
embodiment) C~.olH~s.s 0.235 0.336 2.16 3.08
Kg/L = kg of H2 per Liter of fuel; kg/kg = kg of H2 per kg of fuel.
Compared to methanol, the F-T-based fuel can produce about 90 % more
hydrogen based on fuel volume and 111 % more hydrogen based on fuel weight,
after the water gas shift reaction in a fuel cell fuel processor.
The bar graph of Figure 2 illustrates comparative H2 yields achievable from
reforming the species indicated therein, assuming complete conversion of
equivalent volumes of those species to C02 and H2. These relative yields
assume
complete water gas shift reaction. That reaction is defined as n C + 2n H20 -~
n
C02 + 2n H2.
Other systems and fuel cell fuels are discussed further below.
D. FUEL CELL ENHANCED FISCHER-TROPSCH SYSTEM
While Fischer-Tropsch derived fuel affords significant advantages to fuel
cells, advantages may also be obtained in a Fischer-Tropsch system by
incorporating one or more fuel cells. Referring to FIGURE 3, a fuel cell
enhanced
conversion system 200 is presented. System 200 is in most respects a Fischer-
Tropsch conversion system similar to that shown in FIGURE 1, except a fuel
cell
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202 has been added to use a portion of the synthesis gas to generate
electricity
that may be used elsewhere in the plant such as to assist with compression.
Light hydrocarbons 204 are delivered to a synthesis gas subsystem 206,
which may be a partial oxidation system, steam reformer, autothermal reformer,
or
plasma type syngas generator. Steam 208, which may be used to adjust the
molar ratios of the syngas, and oxygen-containing gas 210 are also delivered
to
the synthesis gas subsystem 206. The synthesis gas subsystem 206 produces
synthesis gas 212 (substantially CO and molecular hydrogen) that is delivered
to
a synthesis subsystem 214, which is preferably a Fischer-Tropsch based system.
The synthesis subsystem 214 produces a heavy product 217 (e.g., C~4+,
but predominantly C~8+) that goes to storage 219, and a lighter product and
water
that are separated by separator 218. Water 220 can go for treatment and
heavier
products 222 (preferably C5-C~8) that are separated go to storage 224 or for
downstream processing. A light residual gas or tail gas 226 (preferably about
Ci-
C5) is delivered to the synthesis gas subsystem 206 for use as fuel in
addition to
the light hydrocarbons.
A portion of the synthesis gas is delivered to a fuel processor, e.g., water-
gas-shift-and-clean-up unit 216, which processes synthesis gas 212 to produce
hydrogen for use in the fuel cell 202. For example, unit 216 removes CO, which
is
a poison to some fuel cell catalysts. Some fuel cell designs perform the
processes
of unit 216 within the cell.
Fuel cell 202 produces electricity 228 that may be used to drive various
components in system 200 and may also be used external to system 200. For
example, it is frequently desirable to include an air compressor as part of
the
synthesis gas subsystem 206 as is suggested by reference numeral 230 (or as
part of a pretreatment unit) and the compressor may be powered altogether on
in
part by electricity 228 from the fuel cell 202.
FIGURE 4 presents another possible embodiment of a fuel cell enhanced
conversion system 300 that is analogous to that of FIGURE 3, except the fuel
cell
fuel processor unit 316 includes a reformer as well as water-gas-shift-and-
clean-
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up/fuel processor components, and utilizes tail gas 326 from the synthesis
subsystem 314. As suggested by conduit 321, unit 316 may also utilize product
water 320 for steam generation. Air is delivered through conduit 323.
Analogous
components have the same last two digits for the reference numerals, but
instead
of being in the 200s are in the 300s. The tail gas 326 is delivered to a fuel
cell
fuel processor (water-gas-shift-and-clean-up unit) and then delivered (as a
fuel
cell fuel of C02 and H2) to the fuel cell 302.
FIGURE 5 presents another embodiment of the present invention with a
fuel cell enhanced conversion system that is analogous to FIGURE 4 except that
the source of synthesis gas is also a source of electrical power in a Fischer-
Tropsch process. The analogous items have corresponding reference numerals.
As shown in this embodiment, a system 330 may have a fuel cell 332 as the
source of synthesis gas in a Fischer-Tropsch process.
Although the invention can be used with a wide variety of different types of
fuel cells, the fuel cell 332 of this embodiment is preferably an internally
reforming
fuel cell, such as a Solid Oxide Fuel Cell (SOFC), that supplies both power
and all
or a portion of the synthesis gas for system 330. Fuel 304, steam 308, and an
oxygen-containing gas 310 are supplied to the fuel cell 332 where it is
converted
to electrical power and synthesis gas. Water vapor, tail gas and/or other
fuel, and
if practical, C02 introduced into the SOFC is converted to H2, H20, CO and
C02.
Hydrogen concentration may be controlled by means of pressure swing
absorption or other method. COz may be removed for recycle or sequestration.
Under appropriate circumstances, a portion of the heat losses linked with the
electrochemical production of electrical energy can be used for the reforming
process; and the fuel cell stack can be cooled by the endothermic reforming
process. Other designs are possible.
The synthesis gas is delivered through conduit 312 to Fischer-Tropsch
synthesis unit 314. Power is delivered to power conduit 334 from where it may
go
to supply power for system 330 as suggested by 336 and/or for external power
as
suggested by 338.
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As one alternative, system 330 may further include a second source of
synthesis gas, such as synthesis gas unit 340 shown in dashed lines. Unit 340
may be, for example, an autothermal reformer (ATR) or a partial oxidation unit
(POX). If this alternative is used, the additional synthesis gas is delivered
through
conduit 342 to conduit 312.
5. ADDITIONAL ILLUSTRATIVE FUEL CELL FUEL SYSTEMS
The fuel cell fuel is preferably made through a Fischer-Tropsch system as
previously mentioned. Numerous embodiments are possible, and a couple of
additional systems are now presented. In one embodiment, substantially the
entire F-T light liquid product is hydrogenated to make a saturated stream
right
away. It can for example contain hydrocarbons in the range of from about Ca or
C5 to about C18 or to about C2o or to about C22. Alternatively, portions of
the light
liquid product may be hydrogenated. These can for example contain
hydrocarbons in the range of about C,o to about C2o or preferably in the range
of
about C5 to about C9. Preferably a C5 to C2o light liquid fraction, and
preferably a
CS- Coo portion, is used and preferably has at least 90 wt. % paraffin and
less than
10 wt. % alcohol and unsaturates. In another embodiment, the F-T product is
separated into light and heavy portions and the heavy portion is hydrocracked
and/or hydrotreated and blended with the light portion to produce the fuel
cell fuel.
Further, as described further below, the F-T product may be blended with
alcohols and/or other substances to produce the fuel cell fuel.
Referring now to FIGURE 6, a system 400 for producing a fuel cell fuel is
presented. System 400 receives synthesis gas, preferably a nitrogen-diluted
synthesis gas from a blown synthesis gas system using an oxygen-containing
gas,
through feed 402. Stream 402 is preferably a synthesis gas with Hz and CO in
mole ratios within the ranges described above. A diluent is present which
consists
of N2, and may further have traces of air-related gases and combustion
products.
The synthesis gas feed 402 is delivered to Fischer-Tropsch unit 404 that
contains
a Fischer-Tropsch (F-T) reactor at conditions known to those skilled in the
art
which will produce paraffinic F-T products.
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The light gaseous effluent of the F-T unit 404 is delivered as feed 406 to
cooling unit 408. Stream 406 will include gaseous F-T reactor effluent with
hydrocarbons synthesized from the synthesis gas in the range of C~ to C28 (or
greater) as well as unspent synthesis gas, water, and diluent. Unit 408 cools
and
removes water from the feed. The removed water is carried away as water
stream 410. Stream 410 will also include some alcohols that may be stripped
allowing the water to be used elsewhere if desired. The liquid product
separated
in unit 408 is delivered to flash drum 412 by feed 414. Feed 414 includes F-T
light oils that are preferably C4-C2s paraffins, olefins, and alcohols. The
gaseous
remains, or tailgas, of cooling unit 408 are discharged as stream 416 which
may
be used elsewhere in system 400 or may be used in the synthesis gas system or
a fuel cell system or other processes as a fuel. Stream 416 includes diluent,
Hz,
CO, CHa and some minor compounds.
The feed 414 is delivered to flash drum 412 and the flashed light product is
delivered as feed 418 to distillation unit 420. Feed 418 is the flashed light
product
(preferably at about 100 psig at 100-200 degrees Fahrenheit). The gaseous
effluent is delivered as discharge 422 for use as a fuel gas stream or for
other
processes.
The heavy F-T products from F-T unit 404 are delivered as feed 424 to
solids separation unit 426. Feed 424 is the F-T effluent preferably in the
range of
about C,4 to about Cso or greater. Solids filtration may or may not be
required. If
required, some solids will be rejected from the process or recycled. Removed
solids 428 may be recycled to unit 404. The product continues as stream 430 to
flash drum 432. Stream 430 is an F-T heavy product that is preferably about
C1a
to about Cso or higher paraffins. The gaseous product of drum 432 is delivered
as
stream 434 for inclusion with stream 414. The heavy product stream 436 is
delivered to distillation unit 420. Stream 434 is a flash vapor from the F-T
heavy
product that is preferably at about 115 psig and in the range of about 300 to
600
degrees Fahrenheit. Stream 436 is the flashed heavy product (preferably about
115 psig and 300-600 degrees Fahrenheit).
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Distillation unit 420 produces a plurality of cuts. The following discharge
streams are preferred from unit 420. Stream 438 is a C4 and below stream,
e.g.,
with Butane, etc. Stream 440 is the cut preferably containing a C5 to C2o fuel
cell
fuel. The fuel cell fuel preferably has at least about 77% wt. Paraffin
(normal
paraffin and iso-paraffin), less than 20 % wt. Olefins (predominately
terminal), less
than 9 % wt: Alcohols (predominately primary alcohols), less than 0.001 % wt.
Sulfur, and less than 5 % wt. Aromatics. Stream 444 is a C2~+ heavy stream; it
is
the heavy oil separated for further processing by wax finishing, fuels
hydrocracking, or lubricant isomerization. Steam is supplied as needed through
feed 446.
Referring now to FIGURE 7, a subsystem 500 may be used with system
400 of FIGURE 6 to process the C2~+ stream 444 from the distillation unit 420.
Within hydrocracker unit 502, the stream 444 is boosted to hydrocracker
operation
pressures and heated to hydrocracker operation temperatures before being
exposed to the hydrocracking and/or hydrotreating catalyst. A makeup hydrogen
stream 504 provides the necessary hydrogen for the hydrocracking reaction.
Stream 506 is the hydrogen purge. Process water is removed as shown by
stream 508. Preferred parameters for the reaction zone of unit 502 are as
follows: temperatures between 400-800 degrees Fahrenheit (catalyst average
temperature); pressure ranging between 300-1500 psig (total pressure); LHSV
ranging from 0.5 to 3.0 h-'; a gas to oil ratio of 1000-10000 SCF/Bbl; and
finally
with the hydro-treating and/or hydrocracking catalyst being a noble metal or
base
metal oxide on a zeolite-type support, which is a type known to those skilled
in the
art to which it pertains.
Reactor effluent is cooled and separated via flashing and then fed as light
hydrocrackate 510 and heavy hydrocrackate 512 to a distillation unit 520. Unit
520 preferably operates as a steam-stripped column at or near atmospheric
pressures. In one mode, two light products are produced from this distillation
column/unit 520. First, a light synthetic paraffin stream 522 that is
preferably at
least about C4 or about C5 to about C9. Second distillate stream 524 is
preferably
about Coo to about C2o and may be used as a fuel cell fuel or a fuel for gas
turbines or compression ignition engines. Steam is provided as needed at 528.
The light ends are removed at stream 530. The bottom stream 526 is recycled
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and has under-converted products that are combined with the feed 444 and
reprocessed. Recycle operations afford higher yields of middle distillates
products than a once through arrangement. In the event that a lighter product
slate is desired, the cut point between the synthetic distillate 524 and the
under-
converted oil of stream 526 can be reduced and reaction temperature increased
to yield a lighter product. Also the reaction temperature could be reduced,
cut
point increased, and a heavier distillate product 524 would result. Streams
522
and 524 are both suitable for use as fuel cell fuel separately or in
combination or
further in combination with stream 440 (FIG. 6).
As an alternative system to that described above (FIGURES 5 and 6), all of
the light or heavy F-T flash products of streams 418 and 436 (FIGURE 6) or the
C5 to C2o fuel cell fuel of stream 440 (FIGURE 6) can be taken to a
hydrocracker
unit 502 (FIGURE 7). Distillation unit 420 may or may not be used with this
process. This would be applicable if a completely saturated (with hydrogen)
fuel
cell fuel is desired. The operation would otherwise be analogous to that
described
in connection with FIGURE 7.
F. FUEL CELL FUELS MADE WITH BLENDS
The F-T fuel cell fuel described above may also be made as a blended
product. An F-T product may be blended with methanol, ethanol, propanol,
butanol, or blends of these alcohols or other fuel species. Also, a fuel cell
fuel
may be made by adding a F-T product to a conventional petroleum fuel
feedstock.
Conventional petroleum feed stocks includes gasolines with a Ca to C» boiling
range of napthenes, aromatics, paraffins, and olefins; heavy naptha or a
kerosene
(Ca to C,s), and #1 diesel.
With the blends, the alcohols may be "process alcohols", i.e., from an F-T
system as described above, or may be from another process. The preferred
blends include ethanol and/or methanol and may include a blend preferably
having greater than 10 wt. % and going up to as much as 95 wt. % of the fuel
cell
fuel. The blends help lower the fuel cloud point, pour points and fuel cell-
processor activation energy and this may have particular advantages in efforts
to
adapt fuel cells to make practical fuel cell-powered automobiles. Consider
that a
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lower activation temperature in the fuel cell processor may allow quicker
start
times for a fuel cell-powered car.
The ability of the blends to help lower the activation energy required in the
fuel cell processor may be seen by considering the following catalytic
reforming
temperatures of a experimental gas composition:
Fuel Species Activation Temperature
(Deg. Centigrade)
2-Pentene (Olefin) 670
Toulene (aromatic) 655
Iso-Octane (paraffin) 630
Ethanol (alcohol) 580
Methanol (alcohol) 450
The blend may be used as the primary fuel or as a startup fuel which can
be replaced after startup by a fuel requiring a higher catalyst temperature
for
partial oxidation.
With the above referenced ranges and suggestions, many possible
blended fuel cell fuels are possible. A few examples follow. A Fischer-Tropsch
fuel cell fuel made as a blend of process alcohols and a Fischer-Tropsch
product
with between >99 and 70% normal and iso-paraffin, less than 20 wt. % olefins,
less than 0.001 wt. % sulfur, and less than 5 wt. % aromatics. A Fischer-
Tropsch
fuel cell fuel made as a blend of methanol and a Fischer-Tropsch product
having
between >99 and 5% normal and iso-paraffin, less than 20 wt. % olefins, less
than
0.001 wt. % sulfur, and less than 5 wt. % aromatics. A Fischer-Tropsch fuel
cell
fuel made as a blend of ethanol and a Fischer-Tropsch product having between
>99 and 5% normal and iso-paraffin, less than 20 wt. % olefins, less than
0.001
wt. % sulfur, and less than 5 wt. % aromatics. A Fischer-Tropsch fuel cell
fuel
made as a blend of propanol and a Fischer-Tropsch product with between >99
and 5% normal and iso-paraffin, less than 20 wt. % olefins, less than 0.001
wt.
sulfur, and less than 5 wt. % aromatics. A Fischer-Tropsch fuel cell fuel made
as
a blend of butanol and a Fischer-Tropsch product having between >99 and 5%
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normal and iso-paraffin, less than 20 wt. % olefins, less than 0.001 wt. %
sulfur,
and less than 5 wt. % aromatics.
G. CONCLUSION
Although the present invention and its advantages have been described in
detail, it should be understood that various changes, substitutions and
alterations
can be made therein without departing from the spirit and scope of invention
as
defined by the appended claims. For example, components and systems shown
in one embodiment may be included in other embodiments.
26
