U.S. patent application number 12/288565 was filed with the patent office on 2009-06-25 for electrochemical treatment of heavy oil streams followed by caustic extraction or thermal treatment.
Invention is credited to Mark A. Greaney, Frank C. Wang, Kun Wang.
Application Number | 20090159503 12/288565 |
Document ID | / |
Family ID | 40787340 |
Filed Date | 2009-06-25 |
United States Patent
Application |
20090159503 |
Kind Code |
A1 |
Greaney; Mark A. ; et
al. |
June 25, 2009 |
Electrochemical treatment of heavy oil streams followed by caustic
extraction or thermal treatment
Abstract
This invention relates to the electrochemical conversion of
dibenzothiophene type molecules of petroleum feedstreams to
mercaptans that can then be removed, in one embodiment, by caustic
extraction. In another embodiment, the mercaptans can be thermally
decomposed, removing sulfur as hydrogen sulfide. The conversion of
dibenzothiophenes to mercaptans is performed by electrochemical
means without the required addition of hydrogen and in the
substantial absence of water.
Inventors: |
Greaney; Mark A.; (Upper
Black Eddy, PA) ; Wang; Kun; (Bridgewater, NJ)
; Wang; Frank C.; (Annandale, NJ) |
Correspondence
Address: |
ExxonMobil Research and Engineering Company
P.O. Box 900
Annandale
NJ
08801-0900
US
|
Family ID: |
40787340 |
Appl. No.: |
12/288565 |
Filed: |
October 21, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61008413 |
Dec 20, 2007 |
|
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Current U.S.
Class: |
208/228 |
Current CPC
Class: |
C10G 32/02 20130101;
C10G 53/12 20130101 |
Class at
Publication: |
208/228 |
International
Class: |
C10G 19/00 20060101
C10G019/00 |
Claims
1. A process for removing sulfur from a sulfur-containing petroleum
feedstream having at least a portion of its sulfur in the form of
hindered dibenzothiophene compounds, comprising: a) passing a
sulfur-containing petroleum feedstream to an electrochemical cell;
b) subjecting said feedstream to an effective voltage and current
that will result in the conversion of at least a portion of said
hindered dibenzothiophene compounds to mercaptan compounds; c)
passing the electrochemically treated petroleum feedstream
containing said mercaptans compounds to a caustic treatment zone
wherein it is contacted with an aqueous caustic solution wherein
mercaptan-containing compounds are extracted by the aqueous caustic
solution; and d) collecting a reduced-sulfur petroleum product
stream from the caustic treatment zone; wherein the reduced-sulfur
petroleum product stream has a lower sulfur content by wt % than
the sulfur-containing petroleum feedstream.
2. The process of claim 1, wherein the sulfur-containing petroleum
feedstream is comprised of a bitumen.
3. The process of claim 2, wherein the electrochemical cell is run
at about 4 volts to about 500 volts and a current density of about
10 to about 1000 mA/cm.sup.2.
4. The process of claim 3, wherein the aqueous caustic solution is
a sodium hydroxide solution.
5. The process of claim 4, wherein the sulfur-containing petroleum
feedstream is comprised of a bitumen.
6. The process of claim 1, wherein the sulfur-containing petroleum
feedstream is a distillate boiling range hydrocarbon stream and an
effective amount of an electrolyte is mixed with the mixture of
water and distillate boiling range hydrocarbon stream.
7. The process of claim 6, wherein the distillate boiling range
hydrocarbon stream is a low sulfur automotive diesel oil.
8. The process of claim 6, wherein the electrolyte is an organic
electrolyte.
9. The process of claim 8, wherein the organic electrolyte is
selected from quaternary carbyl- and hydrocarbyl-onium salts.
10. The process of claim 8, wherein the organic electrolyte is
comprised of an organic soluble salt selected from the group
consisting of 1-butyl-1-methylpyrrolidinium
tris(pentafluoroethyl)trifluoro phosphate, 1-butyl-1-methyl
pyrrolidinium trifluoro-methyl sulfonated,
trihexyltetradecylphosphonium
tris(pentafluoroethyl)trifluorophosphate and
ethyl-dimethylpropyl-ammonium
bis(trifluoro-methylsulfonyl)imide.
11. The process of claim 8, wherein the electrolyte is an inorganic
electrolyte selected from the group consisting of sodium hydroxide,
potassium hydroxide and sodium phosphates.
12. The process of claim 6, wherein the electrochemical cell is run
at about 4 volts to about 500 volts and a current density of about
10 to about 1000 mA/cm.sup.2.
13. The process of claim 12, wherein the aqueous caustic solution
is a sodium hydroxide solution.
14. The process of claim 12, at least a portion of the mercaptan
compounds are alkylated biphenyl mercaptan compounds.
15. A process for removing sulfur from a sulfur-containing
petroleum feedstream having at least a portion of its sulfur in the
form of hindered dibenzothiophene compounds, which method
comprising: a) passing a sulfur-containing petroleum feedstream to
an electrochemical cell; b) subjecting said feedstream to an
effective voltage and current that will result in the conversion of
at least a portion of said hindered dibenzothiophene compounds to
mercaptan compounds; c) passing the electrochemically treated
petroleum feedstream containing mercaptan compounds to a thermal
decomposition zone wherein at least a portion of the mercaptans are
decomposed to hydrogen sulfide at temperatures from about
302.degree. F. to about 932.degree. F. (150.degree. C. to
500.degree. C.); and d) collecting a reduced-sulfur petroleum
product stream from the thermal decomposition zone; wherein the
reduced-sulfur petroleum product stream has a lower sulfur content
by wt % than the sulfur-containing petroleum feedstream.
16. The process of claim 15, wherein the sulfur-containing
petroleum feedstream is comprised of a bitumen.
17. The process of claim 16, wherein the electrochemical cell is
run at about 4 volts to about 500 volts and a current density of
about 10 to about 1000 mA/cm.sup.2.
18. The process of claim 17, wherein the thermal decomposition
temperature is from about 482.degree. F. to about 932.degree. F.
(250.degree. C. to 500.degree. C.).
19. The process of claim 18, wherein the sulfur-containing
petroleum feedstream is comprised of a bitumen.
20. The process of claim 15, wherein the sulfur-containing
petroleum feedstream is a distillate boiling range hydrocarbon
stream and an effective amount of an electrolyte is mixed with the
mixture of water and distillate boiling range hydrocarbon
stream.
21. The process of claim 20, wherein the distillate boiling range
hydrocarbon stream is a low sulfur automotive diesel oil.
22. The process of claim 20, wherein the electrolyte is an organic
electrolyte.
23. The process of claim 22, wherein the organic electrolyte is
selected from quaternary carbyl- and hydrocarbyl-onium salts.
24. The process of claim 22, wherein the organic electrolyte is
selected from the organic soluble salt is selected from the group
consisting of 1-butyl-1-methylpyrrolidinium
tris(pentafluoroethyl)trifluoro phosphate, 1-butyl-1-methyl
pyrrolidinium trifluoro-methyl sulfonated,
trihexyltetradecylphosphonium
tris(pentafluoroethyl)trifluorophosphate and
ethyl-dimethylpropyl-ammonium
bis(trifluoro-methylsulfonyl)imide.
25. The process of claim 20, wherein the electrolyte is an
inorganic electrolyte selected from the group consisting of sodium
hydroxide, potassium hydroxide and sodium phosphates.
26. The process of claim 20, wherein the electrolyte is an organic
electrolyte selected from quaternary carbyl- and hydrocarbyl-onium
salts.
27. The process of claim 20, wherein the electrochemical cell is
run at about 4 volts to about 500 volts and a current density of
about 10 to about 1000 mA/cm.sup.2.
28. The process of claim 27, at least a portion of the mercaptan
compounds are alkylated biphenyl mercaptan compounds.
29. The process of claim 27, wherein the thermal decomposition
temperature is from about 482.degree. F. to about 932.degree. F.
(250.degree. C. to 500.degree. C.).
Description
[0001] This Application claims the benefit of U.S. Provisional
Application No. 61/008,413 filed Dec. 20, 2007.
FIELD OF THE INVENTION
[0002] This invention relates to the electrochemical conversion of
dibenzothiophene type molecules of petroleum feedstreams to
mercaptans that can then be removed, in one embodiment, by caustic
extraction. In another embodiment, the mercaptans can be thermally
decomposed, removing sulfur as hydrogen sulfide. The conversion of
dibenzothiophenes to mercaptans is performed by electrochemical
means without the required addition of hydrogen and in the
substantial absence of water.
BACKGROUND OF THE INVENTION
[0003] The sulfur content of petroleum products is continuing to be
regulated to lower and lower levels throughout the world. Sulfur
specifications in motor gasoline ("mogas") and on-road diesel have
been most recently reduced and future specifications will further
lower the allowable sulfur content of off-road diesel and heating
oils. Sulfur is currently removed from petroleum feedstreams by
various processes depending on the nature of the feedstream.
Processes such as coking, distillation, and alkali metal
dispersions are primarily used to remove sulfur from heavy
feedstreams, such as bitumens which are complex mixtures and
typically contain hydrocarbons, heteroatoms, and metals, with
carbon chains in excess of about 2,000 carbon atoms. For lighter
petroleum feedstreams, such as distillates, catalytic
hydrodesulfurization is typically used. The sulfur species in such
feedstreams span a range of molecular types including sulfides,
thiols, thiophenes, benzothiophenes to dibenzothiophenes in order
of decreasing hydrodesulfurization (HDS) reactivity. The most
difficult to remove sulfur is found in sterically hindered
dibenzothiophene molecules such as diethyl dibenzothiophene. The
space velocity, temperature and hydrogen pressures of catalytic HDS
units are determined primarily by the slow reaction kinetics of
these relatively minor components of the feed. These are the
molecules that are typically left in the product after conventional
low-pressure hydrotreating. Further removing these molecules often
requires higher hydrogen pressure and higher temperature ("deep
desulfurization") which leads to higher hydrogen consumption and
shorter catalyst run lengths which are costly results. Therefore,
it is desirable to have alternative processes that are capable of
removing these refractory sulfur molecules without incurring more
severe reaction conditions for catalytic hydrotreating, which can
result in significant capital and energy savings.
SUMMARY OF THE INVENTION
[0004] In accordance with a preferred embodiment of the present
invention there is provided a process for removing sulfur from
petroleum feedstreams containing sulfur in the form of hindered
dibenzothiophene compounds, comprising:
[0005] a) passing a sulfur-containing petroleum feedstream to an
electrochemical cell;
[0006] b) subjecting said feedstream to an effective voltage and
current that will result in the conversion of at least a portion of
said hindered dibenzothiophene compounds to mercaptan
compounds;
[0007] c) passing the electrochemically treated petroleum
feedstream containing said mercaptans compounds to a caustic
treatment zone wherein it is contacted with an aqueous caustic
solution wherein mercaptan-containing compounds are extracted by
the aqueous caustic solution; and
[0008] d) collecting a reduced-sulfur petroleum product stream from
the caustic treatment zone;
[0009] wherein the reduced-sulfur petroleum product stream has a
lower sulfur content by wt % than the sulfur-containing petroleum
feedstream.
[0010] In a preferred embodiment, the sulfur-containing petroleum
feedstream is comprised of a bitumen.
[0011] In another preferred embodiment, the feedstream is a
distillate boiling range hydrocarbon stream and an effective amount
of an electrolyte is mixed with the distillate boiling range stream
to be treated.
[0012] Also in accordance with another preferred embodiment of the
present invention is a process for removing sulfur from petroleum
feedstreams containing sulfur in the form of hindered
dibenzothiophene compounds, comprising:
[0013] a) passing a sulfur-containing petroleum feedstream to an
electrochemical cell;
[0014] b) subjecting said feedstream to an effective voltage and
current that will result in the conversion of at least a portion of
said hindered dibenzothiophene compounds to mercaptan
compounds;
[0015] c) passing the electrochemically treated petroleum
feedstream containing mercaptan compounds to a thermal
decomposition zone wherein at least a portion of the mercaptans are
decomposed to hydrogen sulfide at temperatures from about
302.degree. F. to about 932.degree. F. (150.degree. C. to
500.degree. C.); and
[0016] d) collecting a reduced-sulfur petroleum product stream from
the thermal decomposition zone;
[0017] wherein the reduced-sulfur petroleum product stream has a
lower sulfur content by wt % than the sulfur-containing petroleum
feedstream.
[0018] In a preferred embodiment, the sulfur-containing petroleum
feedstream is comprised of a bitumen.
[0019] In another preferred embodiment, the feedstream is a
distillate boiling range stream and an effective amount of an
electrolyte is mixed with the distillate boiling range stream to be
treated.
BRIEF DESCRIPTION OF THE FIGURES
[0020] FIG. 1 hereof is a plot of conductivity versus temperature
for various petroleum residues and crudes.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Feedstreams suitable for use in the present invention range
from heavy oil feedstreams, such as bitumens to those boiling in
the distillate range. In a preferred embodiment the heavy oil
feedstream contains at least about 10 wt. %, preferably at least
about 25 wt. % of material boiling above about 1050.degree. F.
(565.degree. C.), both at atmospheric pressure (0 psig). Such
streams include bitumens, heavy oils, whole or topped crude oils
and residua. The bitumen can be whole, topped or froth-treated
bitumen. Non-limiting examples of distillate boiling range streams
that are suitable for use herein include diesel fuels, jet fuels,
heating oils, kerosenes, and lubes. Such streams typically have a
boiling range from about 302.degree. F. (150.degree. C.) to about
1112.degree. F. (600.degree. C.), preferably from about 662.degree.
F. (350.degree. C.) to about 1022.degree. F. (550.degree. C.).
Other preferred streams are those typically known as Low Sulfur
Automotive Diesel Oil ("LSADO"). LSADO will typically have a
boiling range of about 350.degree. F. (176.degree. C.) to about
550.degree. F. (287.degree. C.) and contain from about 200 wppm
sulfur to about 2 wppm sulfur, preferably from about 100 wppm
sulfur to about 10 wppm sulfur. The process embodiments of the
present invention electrochemically treat a sulfur-containing
petroleum feedstream resulting in a reduced-sulfur petroleum
product stream which has a lower sulfur concentration by wt % than
the sulfur-containing petroleum feedstream.
[0022] A major of the sulfur contained in heavy oils and
distillates are in the form of hindered dibenzothiophene molecules.
Although such molecules are difficult to remove by conventional
hydrodesulfurization processes without using severe conditions,
such as high temperatures and pressures, such molecules are
converted by the practice of the present invention to sulfur
species that are more easily removed by conventional non-catalytic
processes. For example, the electrochemical step of the present
invention converts the hindered dibenzothiophene ("DBT") molecules,
which are substantially refractory to conventional
hydrodesulfurization, to hydrogenated naphthenobenzothiophene
mercaptan molecules that are more readily extracted with use of
caustic solution or by thermal decomposition. This capability can
significantly debottleneck existing distillate hydrotreating
process units by converting the slowest to convert molecules
(hindered dibenzothiophenes) into much more readily extractable
mercaptan species, preferably alkylated biphenyl mercaptan
species.
[0023] The process of the present invention does not require the
addition of an electrolyte when heavy oil is the feedstream, but
rather, relies on the intrinsic conductivity of the heavy oil at
elevated temperatures. It will be understood that the term "heavy
oil" and "heavy oil feedstream" as used herein includes both
bitumen and other heavy oil feedstreams, such as crude oils,
atmospheric resids, and vacuum resids. This process is preferably
utilized to upgrade bitumens and/or crude oils that have an API
gravity of less than about 15. The inventors hereof have undertaken
studies to determine the electrochemical conductivity of crudes and
residues at temperatures up to about 572.degree. F. (300.degree.
C.) and have demonstrated an exponential increase in electrical
conductivity with temperature as illustrated in FIG. 1 hereof. It
is believed that the electrical conductivity in crudes and residues
is primarily carried by electron-hopping in the .pi.-orbitals of
aromatic and heterocyclic molecules. Experimental support for this
is illustrated by the simple equation, shown in FIG. 1 hereof, that
can be used to calculate the conductivity of various cuts of a
crude using only its temperature dependent viscosity and its
Conradson carbon content. The molecules that contribute to
Concarbon are primarily the large multi-ring aromatic and
heterocyclic components.
[0024] A 4 mA/cm.sup.2 electrical current density at 662.degree. F.
(350.degree. C.) with an applied voltage of 150 volts and a
cathode-to-anode gap of 1 mm was measured for an American crude
oil. Though this is lower than would be utilized in preferred
commercial embodiments of the present invention, the linear
velocity for this measurement was lower than the preferred velocity
ranges by about three orders of magnitude: 0.1 cm/s vs. 100 cm/s.
Using a 0.8 exponent for the impact of increased flow velocity on
current density at an electrode, it is estimated that the current
density would increase to about 159 mA/cm.sup.2 at a linear
velocity of about 100 cm/s. This suggests that more commercially
attractive current densities achieved at higher applied voltages.
Narrower gap electrode designs or fluidized bed electrode systems
could also be used to lower the required applied voltage.
[0025] Unlike bitumen, performing controlled potential electrolysis
on a non-conductive fluid such as a LSADO, or other petroleum
distillate streams, requires the introduction of an effective
amount of an electrolyte, such as a conductive salt. There is an
insufficient concentration of large multi-ring aromatic and
heterocyclic molecules in distillate boiling range feedstreams to
produce sufficient intrinsic conductivity without the use of an
electrolyte. The direct addition of a conductive salt to the
distillate feedstream can be difficult for several reasons. The
term "effective amount of electrolyte" as used herein means at
least than amount needed to produce conductivity between the anode
and the cathode of the electrochemical cell. Typically this amount
will be from about 0.5 wt. % to about 50 wt. %, preferably from
about 0.5 wt. % to about 10 wt. %, of added electrolytic material
based on the total weight of the feed plus the electrolyte. Once
dissolved in the oil, most salts are difficult to remove after
electrolysis. Incomplete salt removal is unacceptable due to
product specifications, negative impact on further catalytic
processing, potential corrosivity and equipment fouling. Even salts
that are soluble in a low dielectric medium are often poorly
ionized and therefore unacceptable high concentrations are required
to achieve suitable conductivities. In addition, such salts are
typically very expensive. However, recent advances in the field of
ionic liquids have resulted in new organic soluble salts having
melting points lower than about 212.degree. F. (100.degree. C.)
that can be used in the present invention. They can be recovered by
solvent washing the petroleum stream after electrolysis.
Non-limiting examples of such salts include:
1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluoro
phosphate, 1-butyl-1-methyl pyrrolidinium trifluoro-methyl
sulfonated, trihexyltetradecylphosphonium
tris(pentafluoroethyl)trifluorophosphate and
ethyl-dimethylpropyl-ammonium
bis(trifluoro-methylsulfonyl)imide.
[0026] An alternate solution to the low conductivity problem of
distillate boiling range feedstreams to produce a two phase system.
Rather than adding an electrolyte to the feedstream, the feedstream
can be dispersed in a conductive, immiscible, non-aqueous
electrolyte. Such a two-phase system of oil dispersed in a
continuous conductive phase provides a suitable electrolysis
medium. The continuous conductive phase provides the sufficient
conductivity between the cathode and anode of an electrochemical
cell to maintain a constant electrode potential. Turbulent flow
through the electrochemical cell brings droplets of the feedstream
in contact with the cathode, at which point electrons are
transferred from the electrode to sulfur containing species on the
droplet surface.
[0027] After reaction, the immiscible electrolyte from the treated
feedstream is separated by any suitable conventional means
resulting in a reduced sulfur product stream. The immiscible
electrolyte can be recycled. The electrolyte in the immiscible
electrolysis medium is preferably an electrolyte that dissolves, or
dissociates, in the solvent to produce electrically conducting
ions, but that does not undergo a redox reaction in the range of
the applied potentials used. Suitable organic electrolytes for use
in the present invention, other than those previously mentioned,
include quaternary carbyl- and hydrocarbyl-onium salts, e.g.,
alkylammonium hydroxides. Non-limiting examples of inorganic
electrolytes include, e.g., NaOH, KOH and sodium phosphates, and
mixtures thereof. Non-limiting examples of onium ions that can be
used in the practice of the present invention include mono- and
bis-phosphonium, sulfonium and ammonium, preferably ammonium.
Preferred carbyl and hydrocarbyl moieties are alkyl carbyl and
hydrocarbyl moieties. Suitable quaternary alkyl ammonium ions
include tetrabuytyl ammonium, and tetrabutyl ammonium toluene
sulfonate. Optionally, additives known in the art to enhance
performance of the electrodes can also be used. Non-limiting
examples of such additives suitable for use herein include
surfactants, detergents, emulsifying agents and anodic depolarizing
agents. Basic electrolytes are most preferred. The concentration of
salt in the electrolysis medium should be sufficient to generate an
electrically conducting solution in the presence of the feedstream.
Typically, a concentration of about 1 to about 50 wt % conductive
phase, preferably about 5 to about 25 wt % based on the overall
weight of the oil/water/electrolyte mixture is suitable. It is
preferred that petroleum stream immiscible solvents be chosen, such
as dimethyl sulfoxide, dimethylformamide or acetonitrile.
[0028] Dispersions are preferred for ease of separation following
electrolysis. However, more stable oil-in-solvent emulsions can
also be used. Following electrolytic treatment, the resulting
substantially stable emulsion can be broken by the addition of heat
and/or a de-emulsifying agent.
[0029] The electrochemical cell used in the practice of the present
invention may be divided or undivided. Such systems include stirred
batch or flow through reactors. The foregoing may be purchased
commercially or made using technology known in the art. Suitable
electrodes known in the art may be used. Included as suitable
electrodes are three-dimensional electrodes, such as carbon or
metallic foams. The optimal electrode design would depend upon
normal electrochemical engineering considerations and could include
divided and undivided plate and frame cells, bipolar stacks,
fluidized bed electrodes and porous three dimensional electrode
designs; see Electrode Processes and Electrochemical Engineering by
Fumio Hine (Plenum Press, New York 1985). While direct current is
typically used, electrode performance may be enhanced using
alternating current or other voltage/current waveforms. The gap
between electrode surfaces will preferably be about 1 to about 50
mm, more preferably from about 1 to about 25 mm, and the linear
velocity in the electrochemical cell will be in the range of about
1 to about 500 cm/s, more preferably in the range of about 50 to
about 200 cm/s.
[0030] The applied cell voltage, that is, the total voltage
difference between the cathode and anode will vary depending upon
the cell design and electrolytes used. What is critical, however,
is that the cathode be polarized sufficiently to achieve electron
transfer to the dibenzothiophene molecules, which occurs at
reduction potentials more negative than -2.3 Volts versus a
standard calomel electrode. Normal electrochemical practices can be
used to ensure that the cell is operated under these conditions. In
preferred embodiments, the voltage across the electrochemical cell
will be about 4 to about 500 volts, preferably from about 100 to
about 200 volts, with a resulting current density of about 10
mA/cm.sup.2 to about 1000 mA/cm.sup.2, preferably from about 100
mA/cm.sup.2 to about 500 mA/cm.sup.2.
[0031] At least a portion of the hindered dibenzothiophene
compounds in the feedstream are converted to the corresponding
alkylated biphenyl mercaptan compounds in the electrochemical cell.
The mercaptans containing treated feedstream is passed to a caustic
wash step wherein it is contacted with an aqueous caustic solution
for extraction of the mercaptan species. Any suitable caustic wash
technology can be used in the practice of the present invention.
The most preferred caustic wash would be an aqueous solution of
sodium hydroxide having a strength from about 0.5 M to about 5 M
and mixing the mercaptan-containing stream with air and the caustic
solution to remove the mercaptan species in the caustic solution.
Non-limiting examples of caustic extraction processes that can be
used in the practice of the present invention include the UOP.RTM.
MEROX.RTM. process and the Merichem.RTM. THIOLEX.RTM. and
EXOMER.RTM. processes. The MEROX.RTM. Process was announced to the
industry in 1959. The Oil & Gas J. 57(44), 73-8 (1959) contains
a discussion of the MEROX.RTM. Process. In the MEROX.RTM. oxidation
process, mercaptan compounds are extracted from the feed and then
oxidized by air in the caustic phase in the presence of the
MEROX.RTM. catalyst, which is typically an iron group chelate
(cobalt phthalocyanine) to form disulfides which are then
redissolved in the hydrocarbon phase, leaving the process as
disulfides in the hydrocarbon product. The disulfides, which are
not soluble in the caustic solution, can be separated and recycled
for mercaptan extraction. The treated stream is usually sent to a
water wash in order to reduce the sodium content.
[0032] All of these processes take advantage of the acidity of the
mercaptan species. By contacting a petroleum stream that contains
acidic mercaptan species with an aqueous base solution, the
mercaptans are de-protonated, converted to salts and are now more
soluble in the aqueous stream and thus can be extracted nearly
quantitatively from the petroleum stream. Such an extraction is
ineffective with the original, non-acidic dibenzothiophenic sulfur
species. The desulfurized petroleum stream is then separated from
the resulting mercaptide containing caustic solution. The caustic
solution can then be regenerated and the mercaptides isolated in a
variety of conventional ways depending on the process design. Such
mercaptan extractions are widely used in the petroleum refining
industry and it is likely that every refinery has at least one such
unit. The extracted mercaptans can be readily oxidized to
disulfides, separated from the caustic stream, and recycled for
more mercaptan extraction. The hindered dibenzothiophene ("DBT")
species which are removed from the feedstream are converted to a
relatively small substantially pure stream of disulfides that can
be disposed of via combustion. They can also be fed to a coking
unit for thermal decomposition. Being able to target hindered DBT
molecules can also enable the disposition of Light Catalytic Cycle
Oil ("LCCO"), which is rich in DBTs, to distillate
hydrotreaters.
[0033] In a second embodiment of the present invention, following,
or simultaneous with the electrochemical conversion of the
dibenzothiophenic species to mercaptans, a thermal decomposition
reaction of the mercaptans is performed to decompose them with loss
of hydrogen sulfide from the mercaptan molecule. This thermal
decomposition can be performed at temperatures from about
302.degree. F. to about 932.degree. F. (150.degree. C. to
500.degree. C.), preferably from about 482.degree. F. to about
932.degree. F. (250.degree. C. to 500.degree. C.) and at ambient to
autogenous pressure. Subsequent removal of this hydrogen sulfide
from the petroleum stream will produce a reduced sulfur product
stream that is lower is sulfur content by wt % than the
sulfur-containing petroleum feedstream treated by the current
process.
[0034] The present invention will be better understood with
reference to the following examples which are presented for
illustrative purposes and are not to be taken as limiting the
invention in anyway.
[0035] The following three examples were performed using a 300-cc
autoclave (Parr Instruments, Moline, Ill.) was modified to allow
two insulating glands (Conax, Buffalo, N.Y.) to feed through the
autoclave head. Two cylindrical stainless steel (316) mesh
electrodes are connected to the Conax glands, where the power
supply (GW Laboratory DC Power Supply, Model GPR-1810HD) is
connected to the other end. The autoclave body is fitted with a
glass insert, a thermal-couple and a stirring rod. The autoclave
can be charged with desired gas under pressure and run either in a
batch- or a flow-through mode.
EXAMPLE 1
Electrochemical Treatment of DBT Under N.sub.2 in Dimethyl
Sulfoxide Solvent with Tetrabutylammonium Hexaflouorphosphate
Electrolyte
[0036] To the glass insert was added 1.0 g dibenzothiophene
("DBT"), 3.87 g tetrabutylammonium hexafluorophosphate
(TBAPF.sub.6), and 100 milliliter ("ml") anhydrous dimethyl
sulfoxide (DMSO, Aldrich). After the content was dissolved, the
glass insert was loaded into the autoclave body, the autoclave head
assembled and pressure tested. The autoclave was charged with 70
psig of N.sub.2 and heated to 212.degree. F. (100.degree. C.) with
stirring (300 rpm). A voltage of 5 Volts was applied and the
current was 0.8 Amp. The current gradually decreased with time and
after two hours, the run was stopped. The autoclave was opened and
the content acidified with 10% HCl (50 ml). The acidified solution
was then diluted with 100 ml of de-ionized ("DI") water, extracted
with ether (50 ml.times.3). The ether layer was separated and dried
over anhydrous Na.sub.2SO.sub.4, and ether was allowed to evaporate
under a stream of N.sub.2. The isolated dry products were analyzed
by GC-MS. A conversion of 12% was found for DBT and the products
are as the following.
##STR00001##
[0037] This example shows that the electrochemical reduction of DBT
under N.sub.2 resulted in: 12% DBT conversion after 2 h at
212.degree. F. GC-MS revealed that the products consisted of 35%
2-phenyl benzenethiol, 8% tetrahydro-DBT, and 57% of a species with
a mass of 214. The assignment of this peak as 2-phenyl benzenethiol
was done by comparing with an authentic sample. The mass 214
species was tentatively assigned as 2-phenyl benzenethiol with two
methyl groups added. Addition of methyl groups to DBT indicates
that decomposition of solvent DMSO occurred since it is the only
source of methyl groups in this system. No desulfurization product
biphenyl was observed in this run.
COMPARATIVE EXAMPLE A
Electrochemical Treatment of DBT Under Hydrogen in Dimethyl
Sulfoxide Solvent with Tetrabutylammonium Hexaflouorphosphate
Electrolyte
[0038] To the glass insert was added 0.5 g dibenzothiophene
("DBT"), 3.87 g tetrabutylammonium hexafluorophosphate
(TBAPF.sub.6), and 100 ml anhydrous dimethyl sulfoxide (DMSO,
Aldrich). After the content was dissolved, the glass insert was
loaded into the autoclave body, the autoclave head assembled and
pressure tested. The autoclave was charged with 300 psig of H.sub.2
and heated to 257.degree. F. (125.degree. C.) with stirring (300
rpm). A voltage of 4.5 Volts was applied and the current was 1.0
Amp. The current gradually decreased with time and after three and
half (3.5) hours, the run was stopped. The autoclave was opened and
the content acidified with 10% HCI (50 ml). The acidified solution
was then diluted with 100 ml of DI water, extracted with ether (50
ml.times.3). The ether layer was separated and dried over anhydrous
Na.sub.2SO.sub.4, and ether was allowed to evaporate under a stream
of N.sub.2. The isolated dry products were analyzed by GC-MS. A
conversion of 16.5% was found for DBT and the products are as the
following.
##STR00002##
COMPARATIVE EXAMPLE B
Electrochemical Treatment of DEDBT Under Hydrogen in Dimethyl
Sulfoxide Solvent with Tetrabutylammonium Hexaflouorphosphate
Electrolyte
[0039] To the glass insert was added 1.0 g 4,6-diethyl
dibenzothiophene ("DEDBT"), 3.87 g tetrabutylammonium
hexafluorophosphate (TBAPF.sub.6), and 100 ml anhydrous dimethyl
sulfoxide (DMSO, Aldrich). After the content is dissolved, the
glass insert was loaded into the autoclave body, the autoclave head
assembled and pressure tested. The autoclave was charged with 200
psig of H.sub.2 and heated to 100.degree. C. with stirring (300
rpm). A voltage of 7 Volts was applied and the current was 1.0 Amp.
The current gradually decreased with time and after two and half
(2.5) hours, the run was stopped. The autoclave was opened and the
content acidified with 10% HCl (50 ml). The acidified solution was
then diluted with 100 ml of DI water, extracted with ether (50
ml.times.3). The ether layer was separated and dried over anhydrous
Na.sub.2SO.sub.4, and ether was allowed to evaporate under a stream
of N.sub.2. The isolated dry products were analyzed by GC-MS. A
conversion of 16% was found for DEDBT and the products are as the
following.
##STR00003##
[0040] Similarly, desulfurization was also observed for sterically
hindered Diethyl Dibenzothiophene (DEDBT) under H.sub.2. A
conversion of 16% of the DEDBT was observed and the products
contained 53% desulfurized compounds, 46% dihydro-DEDBT and a trace
amount of tetrahydro-DEDBT. Solvent decomposition also occurs in
this case. Although electrochemical desulfurization of DBT and
hindered DBT has been achieved under H.sub.2 in the 212.degree. F.
to 257.degree. F. (100.degree. C. to 125.degree. C.) temperature
range, the conversion is still quite low. Increased conversions
were attempted by extending the run time by operating within this
temperature range or by running at higher temperature of about
392.degree. F. (200.degree. C.) to about 482.degree. F.
(250.degree. C.).
[0041] The first example illustrates that DBT's can be readily
converted into alkylated biphenyl mercaptans electrochemically
without the addition of hydrogen or water. The mercaptans can be
removed by caustic extraction. For example, standard MEROX.RTM.
caustic treatment could be used to remove these molecules from the
electro-treated LSADO producing ultra-low sulfur distillate without
the need for additional hydrotreatment. Due to the low
concentration of these molecules in the LSADO, the power
consumption should be minimal. The comparative examples demonstrate
that, electrochemical reduction in the presence of hydrogen leads
to production of hydrogenated naphtheno dibenzothiophenes and not
biphenyl mercaptans. These species are not caustic extractable. By
limiting the availability of hydrogen sources by eliminating the
hydrogen or water content, the products of the electrolysis can be
controlled. The chemistry of conversion to biphenyl mercaptans and
subsequent extraction processes are as follows:
##STR00004##
EXAMPLE 2
Thermal Decomposition of 2-Phenylthiophenol in Tetralin at
400.degree. C.
[0042] A volume of 1.5 ml of a tetralin solution containing 0.1 M
of 2-phenylthiopheol was placed into 3 ml stainless-steel mini-bomb
inside a dry-box. The mini-bomb was heated at 400.degree. C. in an
oven for a certain period of time and the content analyzed by
GC/MS. Results in Table 1 below indicate desulfurization of
2-phenylthiophenol, giving biphenyl as the major product.
EXAMPLE 3
Thermal Decomposition of 2-Phenylthiophenol in Tetralin at
375.degree. C.
[0043] A volume of 1.5 ml of a tetralin solution containing 0.1 M
of 2-phenylthiopheol was placed into 3 ml stainless-steel mini-bomb
inside a dry-box. The mini-bomb was heated at 375.degree. C. in an
oven for a certain period of time and the content analyzed by
GC/MS. Results in Table 1 below indicate desulfurization of
2-phenylthiophenol, giving biphenyl as the major product.
EXAMPLE 4
Thermal Decomposition of 2-Phenylthiophenol in Tetralin at
350.degree. C.
[0044] A volume of 1.5 ml of a tetralin solution containing 0.1 M
of 2-phenylthiopheol was placed into 3 ml stainless-steel mini-bomb
inside a dry-box. The mini-bomb was heated at 350.degree. C. in an
oven for a certain period of time and the content analyzed by
GC/MS. Results in Table 1 below indicate desulfurization of
2-phenylthiophenol, giving biphenyl as the major product. Based on
the thermal decomposition rates at various temperatures, the
activation energy for 2-phenylthiophenol thermal decomposition was
determined to be .about.29.2 kcal/mol.
EXAMPLE 5
Thermal Decomposition of Phenyl Disulfide in Tetralin at
300.degree. C.
[0045] A volume of 1.5 ml of a tetralin solution containing 0.1 M
of phenyl disulfide (PhS--SPh) was placed into 3 ml stainless-steel
mini-bomb inside a dry-box. The mini-bomb was heated at 572.degree.
F. (300.degree. C.) in an oven for 4h and the content analyzed by
GC/MS. All disulfide is converted into thiophenol. By analogy,
biphenyl disulfide (Ph-Ph-S--S-Ph-Ph) can be converted into
2-phenylthiophenol, which can be desulfurized at higher temperature
as shown in Examples 2 through 4 herein. Equation 5 illustrates the
thermal conversion of 2-phenylthiophenol to biphenyl and hydrogen
sulfide.
##STR00005##
TABLE-US-00001 TABLE 1 Thermal Decomposition of 2-Phenylthiophenol
(0.1 M) in Tetralin Temp. (.degree. C.) Time (h) ##STR00006##
##STR00007## ##STR00008## ##STR00009## 400 0 100% 0 0 0 2 22.1%
60.4% 4% 12.5% 4 29.3% 53% 4.7% 12% 375 1 83.6% 11.9% 1.3% 3.1% 3
59.7% 31% 3.8% 5.4% 350 1 95.1% 3.6% 1.3% 4 72.6% 17.4% 5.7%
4.3%
[0046] As Examples 2 through 5 clearly demonstrate, the biphenyl
mercaptan can be desulfurized by thermal treatment. This reaction
could occur simultaneously with electrochemical processing if
conducted at sufficiently elevated temperatures or may require a
separate thermal soak step.
* * * * *