U.S. patent application number 14/810048 was filed with the patent office on 2016-03-03 for stabilization of jet fuel.
This patent application is currently assigned to ExxonMobil Research and Engineering Company. The applicant listed for this patent is Heather A. ELSEN, Mark A. GREANEY, Anthony S. MENNITO, Kuangnan QIAN, Richard J. QUANN. Invention is credited to Heather A. ELSEN, Mark A. GREANEY, Anthony S. MENNITO, Kuangnan QIAN, Richard J. QUANN.
Application Number | 20160060545 14/810048 |
Document ID | / |
Family ID | 55401768 |
Filed Date | 2016-03-03 |
United States Patent
Application |
20160060545 |
Kind Code |
A1 |
GREANEY; Mark A. ; et
al. |
March 3, 2016 |
STABILIZATION OF JET FUEL
Abstract
The stability of distillate type jet fuels is improved by
cathodic hydrogenation in an electrolytic cell with a proton
permeable membrane separating cathode and anode compartments; a
source of hydrogen is oxidized in the anode compartment to form
protons which permeate the membrane to effect a cathodic reduction
of the nitrogenous components of the fuel in the cathode
compartment.
Inventors: |
GREANEY; Mark A.; (Upper
Black Eddy, PA) ; QUANN; Richard J.; (Moorestown,
NJ) ; ELSEN; Heather A.; (Bethlehem, PA) ;
QIAN; Kuangnan; (Skillman, NJ) ; MENNITO; Anthony
S.; (Flemington, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GREANEY; Mark A.
QUANN; Richard J.
ELSEN; Heather A.
QIAN; Kuangnan
MENNITO; Anthony S. |
Upper Black Eddy
Moorestown
Bethlehem
Skillman
Flemington |
PA
NJ
PA
NJ
NJ |
US
US
US
US
US |
|
|
Assignee: |
ExxonMobil Research and Engineering
Company
Annandale
NJ
|
Family ID: |
55401768 |
Appl. No.: |
14/810048 |
Filed: |
July 27, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62042363 |
Aug 27, 2014 |
|
|
|
Current U.S.
Class: |
205/703 |
Current CPC
Class: |
C10G 49/18 20130101;
C10G 2300/1048 20130101; C10G 32/02 20130101; C10G 2300/202
20130101; C10G 49/06 20130101; C10G 49/007 20130101; C10L 2270/04
20130101; C10L 2200/043 20130101; C10L 2290/38 20130101 |
International
Class: |
C10G 32/02 20060101
C10G032/02; C10G 29/00 20060101 C10G029/00; C10L 1/04 20060101
C10L001/04; C10G 31/06 20060101 C10G031/06 |
Claims
1. A method for the denitrogenation of a distillate boiling range
jet fuel which comprises cathodically hydrogenating nitrogenous
components of the fuel in a cathode compartment of a divided
electrolytic cell having a proton permeable membrane separating the
cathode compartment from an anode compartment in which a source of
hydrogen is anodically oxidized to form protons.
2. A method according to claim 1 in which the proton permeable
membrane comprises a membrane electrode assembly comprising a
having a catalytic anode surface and a catalytic cathode surface on
opposing surfaces of the membrane.
3. A method according to claim 1 in which the proton permeable
membrane comprises an ionomer.
4. A method according to claim 1 in which the proton permeable
membrane comprises sulfonated poly(tetrafluoroethylene).
5. A method according to claim 2 in which the catalytic anode
surface comprises a noble metal.
6. A method according to claim 5 in which the catalytic anode
surface comprises platinum or palladium.
7. A method according to claim 2 in which the catalytic cathode
surface comprises a an electrically conductive catalytic material
having hydrogenation activity.
8. A method according to claim 7 in which the catalytic cathode
surface comprises a finely divided Raney-type metal.
9. A method according to claim 7 in which the catalytic cathode
surface comprises a noble metal.
10. A method according to claim 7 in which the catalytic cathode
surface comprises platinum or palladium.
11. A method according to claim 1 which is carried out at a
temperature of not more than 80.degree. C.
12. A method according to claim 1 in which the distillate boiling
range jet fuel comprises a kerosene having an initial boiling point
of not less than 150.degree. C. and an endpoint not more than
300.degree. C. (ASTM D86).
13. A method according to claim 1 in which nitrogenous components
of the fuel are hydrogenated to form ammonia which is released from
the treated fuel in a liquid/gas separator.
14. A method according to claim 13 in the ammonia is released from
the treated fuel by stripping with inert gas.
15. A method according to claim 13 in the ammonia is released from
the treated fuel by increasing the temperature of the treated
fuel.
16. A method according to claim 1 in which the hydrogen source
comprises hydrogen gas.
17. A method according to claim 1 in which the hydrogen source
comprises water.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 62/042,363 filed Aug. 27, 2014, herein
incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to a method for stabilization of
distillate type jet fuel.
BACKGROUND OF THE INVENTION
[0003] The stability of distillate type jet fuel, either during
storage or during use, has always been a significant technical
challenge and is becoming more of an issue recently with increasing
volumes of cracked stock entering the jet pool. Nitrogen compounds
are known to be deleterious to the stability of hydrocarbon fuels
by promoting the formation of highly intractable sediment or sludge
under storage conditions and during thermal stress. Frankenfeld et
al, demonstrated that "the rate of sediment formation was dependent
on the presence of nitrogen compounds . . . The initial reaction
rate was approximately first order in nitrogen concentration . . .
. and appears to involve a free-radical oxidative self-condensation
of the nitrogen compound." (Ind. Eng. Chem. Prod. Res. Dev. 1983,
22, 608-614). This is still the consensus view of the issue today,
although the increased use of cracked stocks in the jet pool has
added olefinic materials as another contributor to jet fuel
instability. Therefore, nitrogen removal is a key element of
improving the stability of kerosene jet fuels.
[0004] The conventional and standard approach to stabilizing jet
fuel is to use catalytic hydrodenitrogenation to achieve this goal.
Catalytic processes require ever more severe conditions (equipment,
temperatures, pressure, residence time, hydrogen consumption) to
achieve ever lower levels of nitrogen in the final product. More
severe conditions generally translates into higher processing costs
and a more costly product.
[0005] Alternative desulfurization processes have received
considerable attention, including electrochemical process such as
those reviewed by Lam in Fuel Processing Technology 98 (2012),
30-38. Among those techniques are the variant electrochemical
processes in which hydrogen generated in an electrolytic cell is
used to reduce the sulfur compounds to inorganic form (H.sub.2S)
which can then be removed from the hydrocarbons. Examples of such
desulfurization methods are described by Greaney in US2007/0108101;
US 2009/0159427; 2009/0159500; US2009/0159501 and US 2009/0159503.
Exploitation of the intrinsic electrical conductivity at elevated
temperatures in the range of about 200 to 400.degree. C. in the
electrochemical desulfurization methods described by Greaney
dispenses with the use of liquid electrolytes but does require the
use of the high temperatures which restrict the material choices in
the processing equipment.
[0006] While conventional hydrotreating processes effect
denitrogenation along with desulfurization little attention has
been given to the problem of improving jet fuel stability by the
removal of the nitrogenous compounds.
SUMMARY OF THE INVENTION
[0007] An electrochemical approach can be used to improve the
stability of distillate type jet fuels by denitrogenation under
mild conditions (e.g. 60.degree. C., atmospheric pressure)
utilizing a polymer electrolyte membrane fuel cell, hydrogen gas or
water and electricity. There are several advantages to this
approach. First, this process can achieve equivalent results at
milder conditions and could be used as a "polishing" step after
standard hydrotreating. This could thereby reduce the severity
required in the hydrogenative step. This could reduce process costs
for example, by reducing hydrogen consumption and extending
catalyst life by operation at lower temperatures. Fuel cells could
also be distributed to fuel storage facilities and used locally to
stabilize fuel, once it is delivered and ensure that it remains
stable over time. These fuel cells are commercially available and
are designed for ease of installation for distributed power
generation.
[0008] According to the present invention, the distillate jet fuel
is denitrogenated by cathodically hydrogenating the fuel in a
electrolytic cell analogous to a proton exchange membrane (PEM)
fuel cell in which a proton permeable membrane separates the anode
and cathode compartments. A source of hydrogen is oxidized to form
protons in the anode compartment which permeate the membrane to
effect a cathodic reduction of the nitrogenous components of the
fuel in the cathode compartment.
[0009] The electrolytic cell in which the denitrogenation is
carried out is a divided cell in which a proton permeable membrane
separates the anode and cathode compartments. A source of hydrogen
is oxidized in the anode compartment to form protons which permeate
through the membrane to the cathode side through which the jet fuel
is passed. The electrolytic denitrogenation is carried out by
cathodic reduction of the nitrogen species to ammonia which takes
place in the cathode compartment of the cell. The ammonia is
released from the treated fuel in a liquid/gas separator with
separation being enhanced by stripping with inert gas or by
increase of temperature.
DRAWINGS
[0010] The single FIGURE of the accompanying drawings is a
simplified sectional diagram of a divided cell electrolysis cell
useful for jet fuel denitrogenation.
DETAILED DESCRIPTION
Jet Fuel
[0011] The present invention is applicable to the treatment of
distillate (kerosene type) jet fuels such as Jet-A, Jet A-1, JP-5
and JP-8. These fuels typically have an initial boiling point of
not less than 150.degree. C. and an endpoint not more than
300.degree. C. (ASTM D86). Flashpoint is not less than 38.degree.
C. (ASTM D56 or D3828) and freeze point not more than -40.degree.
C. (-47.degree. C. for Jet A-1 and JP-8). Smoke point (ASTM D1322)
not less than 25 mm of smoke point or not less than 18 mm if
naphthalenes are not more than 3 vol. pct (ASTM D1840). The sulfur
specification is a maximum of 0.3 wt. pct; nitrogen is not
specified but, as noted above, is important to stability. Thermal
stability (JFTOT, ASTM D3241) is defined as a pressure drop less
than 25 mm Hg and deposits less than 3.
Denitrogenation
[0012] The major nitrogen component of distillates, such as jet
fuels, are molecules which are difficult to remove by conventional
hydroprocessing methods without using severe conditions, such as
high temperatures and hydrogen pressures, these molecules are
however, converted by the practice of the present invention to
ammonia which can be readily removed. Nitrogen species such as
alkylbenzo derivatives of pyridine and pyrrole.are removed together
with mixed heterocyclic species containing one nitrogen (pyridinic,
quinolinic) with one sulfur (thiophenic) or oxygen (hydroxyl) atoms
as well; there is also the added possibility for saturation of
olefinic species which may be present. The electrolytic
denitrogenation is carried out by the cathodic reduction of the
nitrogen species to ammonia in a cell analogous to a proton
exchange membrane (PEM) fuel cell. In the cell, a source of
hydrogen is oxidized in the anode compartment to form protons which
permeate through the membrane electrode assembly (MEA) which
divides the cell to the cathode side through which the jet fuel is
passed. The anode reaction can be represented as:
H.sub.2.fwdarw.2H.sup.++2e.sup.-
[0013] The reduction of the nitrogen species in the jet fuel takes
place in the reaction at the cathode side which may be represented
simplistically as:
2R--N--H+6H.sup.++6e.sup.-.fwdarw.2R--H+2NH.sub.3
Proton Exchange Electrolytic Cell
[0014] A much simplified diagrammatic section of a proton exchange
electrolytic cell suitable for carrying out the present
denitrogenation reaction is shown in the FIGURE. The electrolytic
cell 1 contains and anode compartment 2 and a cathode compartment 3
separated by a membrane electrode assembly composed of
catalytically-active, electrically-conductive anode 4, a
catalytically-active electrically-conductive cathode 6 which form
the faces of a permeable membrane 6 in the two respective
compartments. Anode 4 and cathode 3 are connected to a source of dc
current 7 to provide power to the two electrodes during operation.
The anode compartment is provided with an inlet 10 for the hydrogen
source and an outlet 11 for excess not consumed in the reaction.
The cathode compartment is similarly fitted with an inlet 12 for
the fuel and an outlet 13 for fuel containing the denitrogenated
species. The anode and cathode compartments are constructed to be
narrow so that they each constitute a flow passage for the
respective process fluid (hydrogen source or jet fuel) which
optimizes contact of the fluid with the respective electrode.
[0015] The hydrogen source may suitably be hydrogen gas or water.
Other hydrogen sources susceptible to electrolytic oxidation may
also be used, for example, methanol. If hydrogen itself is used,
the effluent from the anode compartment will be excess hydrogen
which can be recycled to the inlet; it is not, however, necessary
to maintain a high flow regime using hydrogen since essentially all
the hydrogen is consumed in the anode reaction and transported to
the cathode where the reduction reactions are effected. If water is
used, the effluent will contain oxygen formed in the cathodic
oxidation which can be separated from the water in a simple
gas/liquid separator before recycling the water, if desired.
[0016] The anode and cathode of the membrane electrode assembly are
separated by a thin, proton-conducting membrane with the respective
electrode materials attached directly to its opposing surfaces.
Suitable anodes include graphite, platinum, platinum-coated
titanium, or ruthenium oxide titanium oxide-coated titanium (the
so-called dimensionally stable anode materials). The electrolytic
cathode is an electrically conductive catalytic material having
hydrogenation activity. Suitable materials comprises a finely
divided metal such as Raney-type metals (e.g., nickel, cobalt,
copper, molybdenum), Raney alloys (e.g., nickel-molybdenum and
nickel-cobalt), and high surface area precious (noble) metals
(e.g., platinum black, ruthenium black, and palladium black as well
as palladium-loaded carbon powder).
[0017] The cathode can have several configurations. The cathode can
consist of a finely divided catalyst powder layered in a bed about
100-300 microns thick (although thicker beds have no deleterious
effects on the hydrogenation reaction). The bed is prepared by
allowing the catalyst particles to gravity-settle (coat) onto a
flat sheet current collector. The particles in the bed must contact
one another for the applied current to pass from one particle to
another. The cathode can consist of a mixture of catalyst particles
and an inert binder such as polytetrafluoroethylene (PTFE) rolled
into a flat sheet and affixed to the surface of the membrane.
[0018] The membrane comprises a proton exchange membrane which
permits permeation of the protons while inhibiting passage of the
gases, liquids and the electrons generated in the anode reaction. A
proton exchange membrane (PEM) is a semipermeable membrane
generally made from ionomers and designed to conduct protons while
being impermeable to gases such as oxygen or hydrogen. PEMs can be
made from either pure polymer membranes or from composite membranes
where other materials are embedded in a polymer matrix. One of the
most common and commercially available PEM materials is the
fluoropolymer (PFSA) Nafion.RTM. from DuPont. Nafion is an ionomer
with a perfluorinated backbone and pendant sulfonate groups in the
H.sup.+ form produced by incorporating perfluorovinyl ether
moieties terminated with sulfonate groups onto a
tetrafluoroethylene backbone. Nafion polymers are noted for their
excellent thermal and mechanical stability, making them highly
suitable for use in electrolysis cells although their preferred
range of operating temperatures is typically less than 100.degree.
C. and for best functioning, less than 80.degree. C. e.g. 75 or
60.degree. C. Nafion polymers will tend to dehydrate (thus losing
proton conductivity) when temperature is significantly above
.about.80.degree. C. but versions capable of operation at higher
temperatures can be made by incorporating silica and zirconium
phosphate into the polymers to increase the working temperature to
above 100.degree. C. Nafion polymers can be extrusion cast into
thin membranes, e.g. from about 125 to 250 microns, to form
membrane assemblies. Other ionomers also exist, however, which are
useful for proton exchange membranes and which can be used at
higher temperatures. Other ionomer materials with potential for
higher temperature operation include sulfonated
polyetheretherketones, sulfonated polysulfones, polybenzimidazoles,
diaminobenzidines and polybenzimidazole/poly(tetrafluoro ethylene)
composites. The membrane exchange assembly is suitably made by
connecting or depositing the electrode material on both sides of
the membrane. If elevated pressures are contemplated, a structural
reinforcement may be provided with the use of a permeable support
material which may be pressed onto the membrane.
[0019] The process is preferably carried out at normal atmospheric
pressures and a temperatures of about 25 to about 75.degree. C.,
e.g., 60.degree. C. Elevated pressures are not required but may be
used (e.g. 50-100 kPag) provided the mechanical integrity of the
MEA is preserved in the reactor. Mildly elevated pressures may have
a beneficial effect by helping to maintain a high hydrogen
concentration on the cathode surface, promoting permeation through
the membrane assemble to affect the hydrodenitrogenation.
EXAMPLE
[0020] A 500 ml sample of kerosene (API gravity=43.degree., boiling
range=110-290.degree. C. (about 228-550.degree. F.), freeze
pt=-46.degree. C.) was circulated through the cathodic side of a
polymer electrolyte membrane fuel cell. The fuel cell is a
commercially available product from Scribner Associates, of
Southern Pines, N.C., consisting of two carbon blocks with
serpentine flow channels designed for a 5.times.5 cm active area of
catalyst. The membrane electrode assembly was purchased from
Lynntech, Inc of College Station, Tex. and consisted of a
Nafion.RTM. 117 polymer electrolyte membrane with a 2.5 mg/cm.sup.2
anode catalyst layer of platinum black and a 2 mg/cm.sup.2 cathode
catalyst layer of palladium black. The catalyst layers were first
deposited on Toray Paper TGP-H-060 gas diffusion material before
being hot pressed to the Nafion. The kerosene was circulated at a
flow rate of 50 cm.sup.3/min while simultaneously passing hydrogen
gas at atmospheric pressure through the anodic side of the membrane
electrode assembly at a flow rate of 100 cm.sup.3/min. The cell
temperature was maintained at 70-75.degree. C. throughout the run
of two hours. A constant current of 1 amp was applied to the cell
during the run. The nitrogen content was found to be reduced from
an initial concentration of 22 wppm down to a 1 wppm level after
two hours of treatment.
[0021] As a control experiment, the procedure was repeated
identically, except no power was applied to the fuel cell. In this
instance, the nitrogen level dropped to 13 wppm, which we attribute
to adsorption of the surface active nitrogen species on the carbon
support of the MEA.
[0022] The storage stability of the untreated and electrochemically
treated kerosenes were tested by storing two 100 ml samples of each
in closed glass containers, in the dark, at ambient temperatures
for two years. At the end of this test, the untreated kerosene had
darkened to a yellow orange color and contained solid matter. The
treated kerosene remained a straw color and did not have any
sediment visible to the eye. To quantify the solids, both solutions
were filtered through Whatman.TM. 47 mm diameter glass microfiber
filters. The filters were dried in a vacuum oven at 100.degree. C.
until constant weight was achieved. The untreated kerosene produced
the equivalent of 500 mg/L of dry solids, whereas the treated
kerosene only produced 40 mg/L. To compare the discoloration,
visible light absorbance at 400 nm was measured for each. The
untreated kerosene had an absorbance of 0.40 absorbance units,
whereas the treated sample had an absorbance of 0.11 absorbance
units.
[0023] Close inspection of the fuel by Electrospray Ionization
(ESI) Mass Spectrometry (KQ and AM) provided further insight into
the types of nitrogen species present in the fuel sample and the
changes in composition that occurred during the control experiment
without power and the proof-of-principle experiment with power. It
was found that not only are nitrogen species removed, but also
mixed heterocyclic species containing one nitrogen (pyridinic,
quinolinic) with one sulfur (thiophenic) or oxygen (hydroxyl)
atoms.
* * * * *