U.S. patent application number 15/279926 was filed with the patent office on 2017-09-28 for process for recovering alkali metals and sulfur from alkali metal sulfides and polysulfides.
The applicant listed for this patent is Ceramatec, Inc.. Invention is credited to John Howard Gordon.
Application Number | 20170275771 15/279926 |
Document ID | / |
Family ID | 51164351 |
Filed Date | 2017-09-28 |
United States Patent
Application |
20170275771 |
Kind Code |
A9 |
Gordon; John Howard |
September 28, 2017 |
PROCESS FOR RECOVERING ALKALI METALS AND SULFUR FROM ALKALI METAL
SULFIDES AND POLYSULFIDES
Abstract
Alkali metals and sulfur may be recovered from alkali
monosulfide and polysulfides in an electrolytic process that
utilizes an electrolytic cell having an alkali ion conductive
membrane. An anolyte includes an alkali monosulfide, an alkali
polysulfide, or a mixture thereof and a solvent that dissolves
elemental sulfur. A catholyte includes molten alkali metal.
Applying an electric current oxidizes sulfide and polysulfide in
the anolyte compartment, causes alkali metal ions to pass through
the alkali ion conductive membrane to the catholyte compartment,
and reduces the alkali metal ions in the catholyte compartment.
Liquid sulfur separates from the anolyte and may be recovered. The
electrolytic cell is operated at a temperature where the formed
alkali metal and sulfur are molten.
Inventors: |
Gordon; John Howard; (Salt
Lake City, UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ceramatec, Inc. |
Salt Lake City |
UT |
US |
|
|
Prior
Publication: |
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Document Identifier |
Publication Date |
|
US 20170016128 A1 |
January 19, 2017 |
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|
Family ID: |
51164351 |
Appl. No.: |
15/279926 |
Filed: |
September 29, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14210891 |
Mar 14, 2014 |
9475998 |
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15279926 |
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12576977 |
Oct 9, 2009 |
8728295 |
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14210891 |
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61781557 |
Mar 14, 2013 |
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61103973 |
Oct 9, 2008 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01B 17/22 20130101;
C25C 7/06 20130101; C25C 3/02 20130101; C25C 1/02 20130101; C01B
17/34 20130101; C10G 32/02 20130101; C10G 2300/202 20130101; C25B
1/00 20130101 |
International
Class: |
C25C 1/02 20060101
C25C001/02; C25C 3/02 20060101 C25C003/02; C10G 32/02 20060101
C10G032/02; C25B 1/00 20060101 C25B001/00; C01B 17/22 20060101
C01B017/22; C01B 17/34 20060101 C01B017/34 |
Goverment Interests
GOVERNMENT LICENSE RIGHTS
[0002] This invention was made with government support under Award
No. DE-FE0000408 awarded by the United States Department of Energy.
The government has certain rights in the invention.
Claims
1. A process for oxidizing an alkali metal monosulfide or alkali
metal polysulfide comprising: obtaining an electrolytic cell
comprising an alkali ion conductive membrane configured to
selectively transport alkali ions, the membrane separating an
anolyte compartment configured with an anode and a catholyte
compartment configured with a cathode; introducing into the anolyte
compartment an anolyte comprising an alkali metal monosulfide, an
alkali metal polysulfide, or a mixture thereof and an anolyte
solvent that partially dissolves elemental sulfur; introducing into
the catholyte compartment a catholyte wherein the catholyte
comprises at least one of a molten alkali metal and a solvent;
applying an electric current to the electrolytic cell at an
operating temperature thereby: i. oxidizing the alkali metal
monosulfide or polysulfide in the anolyte compartment to form
liquid elemental sulfur and alkali metal ions; ii. causing the
alkali metal ions to pass through the alkali ion conductive
membrane from the anolyte compartment to the catholyte compartment;
and iii. reducing the alkali metal ions in the catholyte
compartment to form liquid elemental alkali metal; allowing liquid
elemental sulfur to become saturated in the anolyte and to form a
second liquid phase.
2. The process according to claim 1 where the liquid elemental
sulfur separates from the anolyte in a settling zone that is within
the electrolytic cell.
3. The process according to claim 1 where the liquid elemental
sulfur separates from the anolyte in a settling zone that is
external to the cell.
4. The process according to claim 1 where the separation of liquid
elemental sulfur from the anolyte includes one or more of the
separation techniques selected from gravimetric, filtration, and
centrifugation.
5. The process according to claim 1, wherein the alkali ion
conductive membrane is substantially impermeable to anions, the
catholyte solvent, the anolyte solvent, and dissolved sulfur.
6. The process according to claim 1, wherein the alkali ion
conductive membrane comprises in part an alkali metal conductive
ceramic or glass ceramic.
7. The process according to claim 1, wherein the alkali ion
conductive membrane comprises a solid MSICON (Metal Super Ion
CONducting) material, where M is Na or Li.
8. The process according to claim 1, wherein the anolyte solvent
comprises one or more solvents selected from N,N-dimethylaniline,
quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene,
cyclohexane, fluorobenzene, thrifluorobenzene, toluene, xylene,
tetraethylene glycol dimethyl ether (tetraglyme), diglyme,
isopropanol, ethyl propional, dimethyl carbonate, dimethoxy ether,
dimethylpropyleneurea, formamide, methyl formamide, dimethyl
formamide, acetamide, methyl acetamide, dimethyl acetamide,
triethylamine, diethyl acetamide, ethanol and ethyl acetate,
propylene carbonate, ethylene carbonate, and diethyl carbonate.
9. The process according to claim 1, wherein the anolyte solvent
comprises from about 60-100 vol. % polar solvent and 0-40 vol. %
apolar solvent.
10. A process for oxidizing an alkali metal monosulfide or alkali
metal polysulfide comprising: obtaining a first electrolytic cell
comprising an alkali ion conductive membrane configured to
selectively transport alkali ions, the membrane separating an
anolyte compartment configured with an anode and a catholyte
compartment configured with a cathode; introducing into the anolyte
compartment an anolyte comprising an alkali metal monosulfide, an
alkali metal polysulfide, or a mixture thereof and an anolyte
solvent that partially dissolves elemental sulfur; introducing into
the catholyte compartment a catholyte, wherein the catholyte
comprises at least one of a molten alkali metal and a solvent;
applying an electric current to the electrolytic cell thereby: i.
oxidizing the alkali metal sulfide or polysulfide in the anolyte
compartment to form a higher level polysulfide and alkali ions; ii.
causing the alkali metal ions to pass through the alkali ion
conductive membrane from the anolyte compartment to the catholyte
compartment; and iii. reducing the alkali metal ions in the
catholyte compartment to form elemental alkali metal; transporting
anolyte from the first electrolytic cell to a second electrolytic
cell comprising an alkali ion conductive membrane configured to
selectively transport alkali ions, the membrane separating an
anolyte compartment configured with an anode and a catholyte
compartment configured with a cathode and a catholyte; applying an
electric current to the second electrolytic cell thereby: i.
oxidizing polysulfide in the anolyte compartment to form liquid
elemental sulfur and alkali metal ions; ii. causing the alkali
metal ions to pass through the alkali ion conductive membrane from
the anolyte compartment to the catholyte compartment; and iii.
reducing the alkali metal ions in the catholyte compartment to form
liquid elemental alkali metal; allowing liquid elemental sulfur to
become saturated in the anolyte and to form a second liquid
phase.
11. The process according to claim 10 where the liquid elemental
sulfur separates from the anolyte in a settling zone that is within
the electrolytic cell.
12. The process according to claim 10 where the liquid elemental
sulfur separates from the anolyte in a settling zone that is
external to the cell.
13. The process according to claim 10 where the separation of
liquid elemental sulfur from the anolyte includes one or more of
the separation techniques selected from gravimetric, filtration,
and centrifugation.
14. The process according to claim 10, wherein the alkali ion
conductive membrane is substantially impermeable to anions, the
catholyte solvent, the anolyte solvent, and dissolved sulfur.
15. The process according to claim 10, wherein the alkali ion
conductive membrane comprises in part an alkali metal conductive
ceramic or glass ceramic.
16. The process according to claim 10, wherein the alkali ion
conductive membrane comprises a solid MSICON (Metal Super Ion
CONducting) material, where M is Na or Li.
17. The process according to claim 10, wherein the anolyte solvent
comprises one or more solvents selected from N,N-dimethylaniline,
quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene,
cyclohexane, fluorobenzene, thrifluorobenzene, toluene, xylene,
tetraethylene glycol dimethyl ether (tetraglyme), diglyme,
isopropanol, ethyl propional, dimethyl carbonate, dimethoxy ether,
dimethylpropyleneurea, formamide, methyl formamide, dimethyl
formamide, acetamide, methyl acetamide, dimethyl acetamide,
triethylamine, diethyl acetamide, ethanol and ethyl acetate,
propylene carbonate, ethylene carbonate, and diethyl carbonate.
18. The process according to claim 10, wherein the anolyte solvent
comprises from about 60-100 vol. % polar solvent and 0-40 vol. %
apolar solvent.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of, and claims priority to,
U.S. patent application Ser. No. 14/210,891 (the "'891
Application"), filed Mar. 14, 2014, which application claims the
benefit of U.S. Provisional Patent Application No. 61/781,557,
filed Mar. 14, 2013. The '891 Application is also a
continuation-in-part of U.S. application Ser. No. 12/576,977, filed
Oct. 9, 2009, which has issued as U.S. Pat. No. 8,728,295 and which
claims the benefit of U.S. Provisional Patent Application No.
61/103,973, filed Oct. 9, 2008. These applications are incorporated
by reference.
FIELD OF THE INVENTION
[0003] The present invention relates to a process for removing
nitrogen, sulfur, and heavy metals from sulfur-, nitrogen-, and
metal-bearing shale oil, bitumen, heavy oil, or refinery streams.
More particularly, the invention relates to a method of
regenerating alkali metals from sulfides (mono- and polysulfides)
of those metals. The invention further relates to the removal and
recovery of sulfur from alkali metal sulfides and polysulfides.
BACKGROUND OF THE INVENTION
[0004] The demand for energy and the hydrocarbons from which that
energy is derived is continually rising. The hydrocarbon raw
materials used to provide this energy, however, contain difficult
to remove sulfur and metals that hinder their usage. Sulfur can
cause air pollution, and can poison catalysts designed to remove
hydrocarbons and nitrogen oxide from motor vehicle exhaust.
Similarly, other metals contained in the hydrocarbon stream can
poison catalysts typically utilized for removal of sulfur through
standard and improved hydro-desulfurization processes whereby
hydrogen reacts under extreme conditions to break down the sulfur
bearing organo-sulfur molecules.
[0005] Extensive reserves of shale oil exist in the U.S. that will
increasingly play a role in meeting U.S. energy needs. Over 1
trillion barrels reserves lay in a relatively small area known as
the Green River Formation located in Colorado, Utah, and Wyoming.
As the price of crude oil rises, the resource becomes more
attractive but technical issues remain to be solved. A key issue is
addressing the relatively high level of nitrogen contained in the
shale oil chemistry after retorting as well as addressing sulfur
and metals content.
[0006] Shale oil characteristically is high in nitrogen, sulfur,
and heavy metals which makes subsequent hydrotreating difficult.
According to America's Strategic Unconventional Fuels, Vol.
III--Resource and Technology Profiles, p. 111-25, nitrogen is
typically around 2% and sulfur around 1% along with some metals in
shale oil. Heavy metals contained in shale oil pose a large problem
to upgraders. Sulfur and nitrogen typically are removed through
treating with hydrogen at elevated temperature and pressure over
catalysts such as Co--Mo/Al.sub.2O.sub.3 or Ni--Mo/Al.sub.2O.sub.3.
These catalysts are deactivated as the metals mask the
catalysts.
[0007] Another example of a source of hydrocarbon fuel where the
removal of sulfur poses a problem is in bitumen existing in ample
quantities in Alberta, Canada and heavy oils such as in Venezuela.
In order to remove sufficient sulfur from the bitumen for it to be
useful as an energy resource, excessive hydrogen must be introduced
under extreme conditions, which creates an inefficient and
economically undesirable process.
[0008] Over the last several years, sodium has been recognized as
being effective for the treatment of high-sulfur petroleum oil
distillate, crude, heavy oil, bitumen, and shale oil. Sodium is
capable of reacting with the oil and its contaminants to
dramatically reduce the sulfur, nitrogen, and metal content through
the formation of sodium sulfide compounds (sulfide, polysulfide and
hydrosulfide). Examples of the processes can be seen in U.S. Pat.
Nos. 3,785,965; 3,787,315; 3,788,978; 4,076,613; 5,695,632;
5,935,421; and 6,210,564.
[0009] An alkali metal such as sodium or lithium is reacted with
the oil at about 350.degree. C. and 300-2000 psi. For example 1-2
moles sodium and 1-1.5 moles hydrogen may be needed per mole sulfur
according to the following initial reaction with the alkali
metal:
R--S--R'+2Na+H.sub.2.fwdarw.R--H+R'--H+Na.sub.2S
R,R',R''--N+3Na+1.5H.sub.2.fwdarw.R--H+R'--H+R''--H+Na.sub.3N
[0010] Where R, R', R'' represent portions of organic molecules or
organic rings.
[0011] The sodium sulfide and sodium nitride products of the
foregoing reactions may be further reacted with hydrogen sulfide
according to the following reactions:
Na.sub.2S+H.sub.2S.fwdarw.2NaHS(liquid at 375.degree. C.)
Na.sub.3N+3H.sub.2S.fwdarw.3NaHS+NH.sub.3
[0012] The nitrogen is removed in the form of ammonia which may be
vented and recovered. The sulfur is removed in the form of an
alkali hydrosulfide, NaHS, which is separated for further
processing. The heavy metals and organic phase may be separated by
gravimetric separation techniques. The above reactions are
expressed using sodium but may be substituted with lithium.
[0013] Heavy metals contained in organometallic molecules such as
complex porphyrins are reduced to the metallic state by the alkali
metal. Once the heavy metals have been reduced, they can be
separated from the oil because they no longer are chemically bonded
to the organic structure. In addition, once the metals are removed
from the porphyrin structure, the nitrogen heteroatoms in the
structure are exposed for further denitrogenation.
[0014] The following is a non-limiting description of the foregoing
process of using alkali metals to treat the petroleum organics.
Liquid phase alkali metal is brought into contact with the organic
molecules containing heteroatoms and metals in the presence of
hydrogen. The free energy of reaction with sulfur and nitrogen and
metals is stronger with alkali metals than with hydrogen so the
reaction more readily occurs without full saturation of the
organics with hydrogen. Hydrogen is needed in the reaction to fill
in the where heteroatoms and metals are removed to prevent coking
and polymerization, but alternatively, gases other than hydrogen
may be used for preventing polymerization. Once the alkali metal
compounds are formed and heavy metals are reduced to the metallic
state, it is necessary to separate them. This is accomplished by a
washing step, either with steam or with hydrogen sulfide to form a
hydroxide phase if steam is utilized or a hydrosulfide phase if
hydrogen sulfide is used. At the same time alkali nitride is
presumed to react to form ammonia and more alkali hydroxide or
hydrosulfide. A gravimetric separation such as centrifugation or
filtering can separate the organic, upgraded oil, from the salt
phase.
[0015] In conventional hydrotreating, instead of forming Na.sub.2S
to desulfurize, or forming Na.sub.3N to denitrogenate, H.sub.2S and
NH.sub.3 are formed respectively. The reaction to form hydrogen
sulfide and ammonia is much less favorable thermodynamically than
the formation of the sodium or lithium compounds so the parent
molecules must be destabilized to a greater degree for the
desulfurization of denitrogenation reaction to proceed. According
to T. Kabe, A Ishihara, W. Qian, in Hydrodesulfurization and
Hydrodenitrogenation, pp. 37, 110-112, Wiley-VCH, 1999, this
destabilization occurs after the benzo rings are mostly saturated.
To provide this saturation of the rings, more hydrogen is required
for the desulfurization and denitrogenation reactions and more
severe conditions are required to achieve the same levels of sulfur
and nitrogen removal compared to removal with sodium or lithium. As
mentioned above, desulfurizing or denitrogenating using hydrogen
without sodium or lithium is further complicated with the masking
of catalyst surfaces from precipitating heavy metals and coke.
Since the sodium is in the liquid phase, it can more easily access
the sulfur, nitrogen and metals where reaction is desirable.
[0016] Once the alkali metal sulfide has been separated from the
oil, sulfur and metals are substantially removed, and nitrogen is
moderately removed. Also, both viscosity and density are reduced
(API gravity is increased). Bitumen or heavy oil would be
considered synthetic crude oil (SCO) and can be shipped via
pipeline for further refining. Similarly, shale oil will have been
considerably upgraded after such processing. Subsequent refining
will be easier since the troublesome metals have been removed.
[0017] Although the effectiveness of the use of alkali metals such
as sodium in the removal of sulfur has been demonstrated, the
process is not commercially practiced because a practical,
cost-effective method to regenerate the alkali metal has not yet
heretofore been proposed. Several researchers have proposed the
regeneration of sodium using an electrolytic cell, which uses a
sodium-ion-conductive beta-alumina membrane. Beta-alumina, however,
is both expensive and fragile, and no significant metal production
utilizes beta-alumina as a membrane separator. Further, the cell
utilizes a sulfur anode, which results in high polarization of the
cell causing excessive specific energy requirements.
[0018] Metallic sodium is commercially produced almost exclusively
in a Downs-cell such as the cell described in U.S. Pat. No.
1,501,756. Such cells electrolyze sodium chloride that is dissolved
in a molten salt electrolyte to form molten sodium at the cathode
and chlorine gas at the anode. The cells operate at a temperature
near 600.degree. C., a temperature compatible with the electrolyte
used. Unlike the sulfur anode, the chlorine anode is utilized
commercially both with molten salts as in the co-production of
sodium and with saline solution as in the co-production of sodium
hydroxide.
[0019] Another cell technology that is capable of reducing
electrolyte melting range and operation of the electrolyzer to less
than 200.degree. C. has been disclosed by Jacobsen et al. in U.S.
Pat. No. 6,787,019 and Thompson et al. in U.S. Pat. No. 6,368,486.
In those disclosures, low temperature co-electrolyte is utilized
with the alkali halide to form a low temperature melting
electrolyte.
[0020] Gordon in U.S. Pat. No. 8,088,270 teaches the utilization of
solvents which dissolve sulfur at a cell operating temperature and
dissolving sodium polysulfide in such solvents to form an anolyte
which when introduced into a cell with an alkali ion conductive
membrane are electrolyzed to form sulfur at the anode and alkali
metal at the cathode and where a portion of the anolyte is removed
from the cell, allowed to cool until the sulfur precipitates
out.
[0021] It is an object of the present invention to provide a
cost-effective and efficient method for the regeneration of alkali
metals used in the desulfurization, denitrogenation, and
demetallation of hydrocarbon streams. As will be described herein,
the present invention is able to remove contaminants and separate
out unwanted material products from
desulfurization/denitrogenation/demetallation reactions, and then
recover those materials for later use.
[0022] Another objective of the present invention is to teach
improvements in the process and device for recovering alkali metal
from alkali metal sulfide generated by the sulfur removal and
upgrading process.
BRIEF SUMMARY OF THE INVENTION
[0023] The present invention provides a process for removing
nitrogen, sulfur, and heavy metals from sulfur-, nitrogen-, and
metal-bearing shale oil, bitumen, heavy oil, or refinery streams.
The present invention further provides an electrolytic process of
regenerating alkali metals from sulfides, polysulfides, nitrides,
and polynitrides of those metals. The present invention further
provides an electrolytic process of removing sulfur from a
polysulfide solution.
[0024] One non-limiting embodiment within the scope of the
invention includes a process for oxidizing alkali metal sulfides
and polysulfides electrochemically. The process utilizes an
electrolytic cell having an alkali ion conductive membrane
configured to selectively transport alkali ions, the membrane
separating an anolyte compartment configured with an anode and a
catholyte compartment configured with a cathode. An anolyte is
introduced into the anolyte compartment. The anolyte includes an
alkali metal sulfide and/or polysulfide and an anolyte solvent that
partially dissolves elemental sulfur and alkali metal sulfide and
polysulfide. A catholyte is introduced into the catholyte
compartment. The catholyte includes alkali metal ions and a
catholyte solvent. The catholyte solvent may include one of many
non-aqueous solvents such as tetraethylene glycol dimethyl ether
(tetraglyme), diglyme, dimethyl carbonate, dimethoxy ether,
propylene carbonate, ethylene carbonate, diethyl carbonate. The
catholyte may also include an alkali metal salt such as an iodide
or chloride of the alkali metal. Applying an electric current to
the electrolytic cell oxidizes sulfide and/or polysulfide in the
anolyte compartment to form higher level polysulfide and causes
high level polysulfide to oxidize to elemental sulfur. The electric
current further causes alkali metal ions to pass through the alkali
ion conductive membrane from the anolyte compartment to the
catholyte compartment, and reduces the alkali metal ions in the
catholyte compartment to form elemental alkali metal.
[0025] Sulfur may be recovered in the liquid form when the
temperature exceeds the melting point of sulfur and the sulfur
content of the anolyte exceeds the solubility of the solvent. Most
of the anolyte solvents have lower specific gravity compared to
sulfur so the liquid sulfur settles to the bottom. This settling
may occur within a settling zone in the cell where the sulfur may
be drained through an outlet. Alternatively a portion of the
anolyte may be transferred to a settling zone out of the cell where
settling of sulfur may occur more effectively than in a cell.
[0026] The melting temperature of sulfur is near 115.degree. C. so
the cell is best operated above that temperature, above 120.degree.
C. At that temperature or above, the alkali metal is also molten if
the alkali metal is sodium. Operation near a higher temperature,
such as in the 125-150.degree. C. range, allows the sulfur to fully
remain in solution as it is formed from the polysulfide at the
anode, then when the anolyte flows to a settling zone, within or
external to the cell where the temperature may be 5-20.degree. C.
cooler, the declining solubility of the sulfur in the solvent
results in a sulfur liquid phase forming which is has higher
specific gravity and settles from the anolyte. Then when the
anolyte flows back toward the anodes where sulfur is forming
through electrochemical oxidation of polysulfide, the anolyte has
solubility has the capacity to dissolve the sulfur as it is formed,
preventing fouling and polarization at the anodes or at membrane
surfaces.
[0027] In one non-limiting embodiment within the scope of the
invention, a cell for electrolyzing an alkali metal sulfide or
polysulfide is provided where the cell operates at a temperature
above the melting temperature of the alkali metal and where the
cathode is wholly or partially immersed in a bath of the molten
alkali metal with a divider between an anolyte compartment and a
catholyte compartment. In this case the catholyte essentially
comprises molten alkali metal but may also include solvent and
alkali metal salt. The divider may be permeable to alkali metal
cations and substantially impermeable to anions, solvent and
dissolved sulfur. The divider comprises in part an alkali metal
conductive ceramic or glass ceramic. The divider may be conductive
to alkali ions which include lithium and sodium.
[0028] In another non-limiting embodiment, a cell for electrolyzing
an alkali metal polysulfide is provided with an anolyte compartment
and a catholyte compartment where the anolyte comprises a polar
solvent and dissolved alkali metal polysulfide. The anolyte
comprises a solvent that dissolves to some extent elemental sulfur.
The anolyte may comprise a solvent where one or more of the
solvents includes: N,N-dimethylaniline, quinoline, tetrahydrofuran,
2-methyl tetrahydrofuran, benzene, cyclohexane, fluorobenzene,
thrifluorobenzene, toluene, xylene, tetraethylene glycol dimethyl
ether (tetraglyme), diglyme, isopropanol, ethyl propional, dimethyl
carbonate, dimethoxy ether, dimethylpropyleneurea, formamide,
methyl formamide, dimethyl formamide, acetamide, methyl acetamide,
dimethyl acetamide, triethylamine, diethyl acetamide, ethanol and
ethyl acetate, propylene carbonate, ethylene carbonate, and diethyl
carbonate.
[0029] In one non-limiting embodiment, a method for oxidizing
sulfides and polysulfides electrochemically from an anolyte at an
anode is disclosed where the anolyte comprises in part an anolyte
solvent that dissolves to some extent elemental sulfur. In the
method, the anolyte solvent that dissolves to some extent elemental
sulfur is one or more of the following: N,N-dimethylaniline,
quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene,
cyclohexane, fluorobenzene, thrifluorobenzene, toluene, xylene,
tetraethylene glycol dimethyl ether (tetraglyme), diglyme,
isopropanol, ethyl propional, dimethyl carbonate, dimethoxy ether,
dimethylpropyleneurea, formamide, methyl formamide, dimethyl
formamide, acetamide, methyl acetamide, dimethyl acetamide,
triethylamine, diethyl acetamide, ethanol and ethyl acetate,
propylene carbonate, ethylene carbonate, and diethyl carbonate.
[0030] In another non-limiting embodiment, a cell for electrolyzing
an alkali metal monosulfide or a polysulfide is provided with an
anolyte compartment and a catholyte compartment where the anolyte
comprises a polar solvent and dissolved alkali metal monosulfide or
a polysulfide. The anolyte comprises a solvent that dissolves to
some extent elemental sulfur. The anolyte may comprise a solvent
where one or more of the solvents includes: N,N-dimethylaniline,
quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene,
cyclohexane, fluorobenzene, thrifluorobenzene, toluene, xylene,
tetraethylene glycol dimethyl ether (tetraglyme), diglyme,
isopropanol, ethyl propional, dimethyl carbonate, dimethoxy ether,
dimethylpropyleneurea, formamide, methyl formamide, dimethyl
formamide, acetamide, methyl acetamide, dimethyl acetamide,
triethylamine, diethyl acetamide, ethanol and ethyl acetate,
propylene carbonate, ethylene carbonate, and diethyl carbonate.
[0031] In one non-limiting embodiment, a method for oxidizing
monosulfide or polysulfides electrochemically from an anolyte at an
anode is disclosed where the anolyte comprises in part an anolyte
solvent that dissolves to some extent elemental sulfur. In the
method, the anolyte solvent that dissolves to some extent elemental
sulfur is one or more of the following: N,N-dimethylaniline,
quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene,
cyclohexane, fluorobenzene, thrifluorobenzene, toluene, xylene,
tetraethylene glycol dimethyl ether (tetraglyme), diglyme,
isopropanol, ethyl propional, dimethyl carbonate, dimethoxy ether,
dimethylpropyleneurea, formamide, methyl formamide, dimethyl
formamide, acetamide, methyl acetamide, dimethyl acetamide,
triethylamine, diethyl acetamide, ethanol and ethyl acetate,
propylene carbonate, ethylene carbonate, and diethyl carbonate.
[0032] In one non-limiting embodiment, the anolyte solvent
comprises from about 60-100 vol. % polar solvent and 0-40 vol. %
apolar solvent. A blend of different anolyte solvents may help
optimize the solubility of elemental sulfur and the solubility of
sulfide and polysulfide.
[0033] Another non-limiting embodiment discloses a method for
removal of dissolved elemental sulfur from a solvent/alkali metal
polysulfide mixture includes cooling, reducing the solubility of
sulfur in the solvent and causing a second liquid phase to form
comprising elemental sulfur, and then separating the liquid phase
sulfur from the liquid phase solvent mixture. The separation of
liquid phase sulfur from liquid phase anolyte includes one or more
of the following: gravimetric, centrifugation. The alkali metal
polysulfide is of the class including sodium polysulfide and
lithium polysulfide.
[0034] The present invention may provide certain advantages,
including but not limited to the following:
[0035] Removing an alkali metal continuously or semi-continuously
in liquid form from the cell.
[0036] Removing sulfur continuously or semi-continuously in liquid
form from the cell.
[0037] Removing high alkali metal polysulfides and dissolved sulfur
continuously or semi-continuously from the electrolytic cell,
thereby reducing polarization of the anode by sulfur.
[0038] Separating sulfur continuously or semi-continuously from a
stream containing a mixture of solvent, sulfur, and alkali metal
polysulfides such that the solvent and alkali metal polysulfides
are substantially recovered such that they can be returned back to
an electrolytic process.
[0039] Operating the electrolytic cells at temperatures and
pressures, so that the electrolytic cell materials of construction
can include materials which would not tolerate high elevated
temperature.
[0040] Reference throughout this specification to features,
advantages, or similar language does not imply that all of the
features and advantages that may be realized with the present
invention should be or are in any single embodiment of the
invention. Rather, language referring to the features and
advantages is understood to mean that a specific feature,
advantage, or characteristic described in connection with an
embodiment is included in at least one embodiment of the present
invention. Thus, discussion of the features and advantages, and
similar language, throughout this specification may, but do not
necessarily, refer to the same embodiment, but may refer to every
embodiment.
[0041] Furthermore, the described features, advantages, and
characteristics of the invention may be combined in any suitable
manner in one or more embodiments. One skilled in the relevant art
will recognize that the invention may be practiced without one or
more of the specific features or advantages of a particular
embodiment. In other instances, additional features and advantages
may be recognized in certain embodiments that may not be present in
all embodiments of the invention.
[0042] These features and advantages of the present invention will
become more fully apparent from the following description and
appended claims, or may be learned by the practice of the invention
as set forth hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0043] In order that the manner in which the above-recited and
other features and advantages of the invention are obtained will be
readily understood, a more particular description of the invention
briefly described above will be rendered by reference to specific
embodiments thereof that are illustrated in the appended drawings.
Understanding that these drawings depict only typical embodiments
of the invention and are not therefore to be considered to be
limiting of its scope, the invention will be described and
explained with additional specificity and detail through the use of
the accompanying drawings in which:
[0044] FIG. 1 shows an overall process for removing nitrogen,
sulfur, and heavy metals from sulfur-, nitrogen-, and metal-bearing
oil sources using an alkali metal and for regenerating the alkali
metal.
[0045] FIGS. 2A and 2B show schematic processes for converting
alkali metal hydrosulfide to alkali metal polysulfide and
recovering hydrogen sulfide.
[0046] FIG. 3 shows a schematic cross-section of an electrolytic
cell which utilizes many of the features within the scope of the
invention.
[0047] FIG. 4 shows a schematic of several electrolytic cells
operated in series to extract alkali metal and oxidize alkali metal
sulfide to polysulfide and low polysulfide to high polysulfide and
high polysulfide to sulfur.
DETAILED DESCRIPTION OF THE INVENTION
[0048] The present embodiments of the present invention will be
best understood by reference to the drawings, wherein like parts
are designated by like numerals throughout. It will be readily
understood that the components of the present invention, as
generally described and illustrated in the figures herein, could be
arranged and designed in a wide variety of different
configurations. Thus, the following more detailed description of
the embodiments of the methods and cells of the present invention,
as represented in FIGS. 1 through 4, is not intended to limit the
scope of the invention, as claimed, but is merely representative of
present embodiments of the invention.
[0049] The overall process is shown schematically in FIG. 1 of one
non-limiting embodiment for removing nitrogen, sulfur, and heavy
metals from sulfur-, nitrogen-, and metal-bearing oil sources using
an alkali metal and for regenerating the alkali metal. In the
process 100 of FIG. 1, an oil source 102, such as high-sulfur
petroleum oil distillate, crude, heavy oil, bitumen, or shale oil,
is introduced into a reaction vessel 104. An alkali metal (M) 106,
such as sodium or lithium, is also introduced into the reaction
vessel, together with a quantity of hydrogen 108. The alkali metal
and hydrogen react with the oil and its contaminants to
dramatically reduce the sulfur, nitrogen, and metal content through
the formation of sodium sulfide compounds (sulfide, polysulfide and
hydrosulfide) and sodium nitride compounds. Examples of the
processes are known in the art, including but not limited to, U.S.
Pat. Nos. 3,785,965; 3,787,315; 3,788,978; 4,076,613; 5,695,632;
5,935,421; and 6,210,564.
[0050] The alkali metal (M) and hydrogen react with the oil at
about 350.degree. C. and 300-2000 psi according to the following
initial reactions:
R--S--R'+2M+H.sub.2.fwdarw.R--H+R'--H+M.sub.2S
R,R',R''--N+3M+1.5H.sub.2.fwdarw.R--H+R'--H+R''--H+M.sub.3N
[0051] Where R, R', R'' represent portions of organic molecules or
organic rings.
[0052] The sodium sulfide and sodium nitride products of the
foregoing reactions may be further reacted with hydrogen sulfide
110 according to the following reactions:
M.sub.2S+H.sub.2S.fwdarw.2MHS(liquid at 375.degree. C.)
M.sub.3N+3H.sub.2S.fwdarw.3MHS+NH.sub.3
[0053] The nitrogen is removed in the form of ammonia 112, which
may be vented and recovered. The sulfur is removed from the oil
source in the form of an alkali hydrosulfide (MHS), such as sodium
hydrosulfide (NaHS) or lithium hydrosulfide (LiHS). The reaction
products 113, are transferred to a separation vessel 114. Within
the separation vessel 114, the heavy metals 118 and upgraded oil
organic phase 116 may be separated by gravimetric separation
techniques.
[0054] The alkali hydrosulfide (MHS) is separated for further
processing. The alkali hydrosulfide stream may be the primary
source of alkali metal and sulfur from the process of the present
invention. When the alkali hydrosulfide is reacted with a medium to
high polysulfide (i.e. M.sub.2S.sub.x; 4.ltoreq.x.ltoreq.6) then
hydrogen sulfide will be released and the resulting mixture will
have additional alkali metal and sulfide content where the sulfur
to alkali metal ratio is lower. The hydrogen sulfide 110 can be
used in the washing step upstream where alkali sulfide and alkali
nitride and metals need to be removed from the initially treated
oil.
[0055] A schematic representation of this process is shown in FIG.
2A. For example, in the case of sodium the following reaction may
occur:
Na.sub.2S.sub.x+2NaHS.fwdarw.H.sub.2S+.sup.2[Na.sub.2S.sub.(x+1)/2]
[0056] Where x:y represent the average ratio of sodium to sulfur
atoms in the solution. In the process shown in FIG. 2A, an alkali
polysulfide with high sulfur content is converted to an alkali
polysulfide with a lower sulfur content.
[0057] Alternatively, rather than reacting the alkali metal
hydrosulfide with an alkali metal polysulfide, the alkali metal
hydrosulfide can be reacted with sulfur. A schematic representation
of this process is shown in FIG. 2B. For example, in the case of
sodium the following reaction may occur:
YS+2NaHS.fwdarw.H.sub.2S+Na.sub.2S.sub.(Y+1)
[0058] Where Y is a molar amount of sulfur added to the sodium
hydrosulfide.
[0059] The alkali metal polysulfide may be further processed in an
electrolytic cell to remove and recover sulfur and to remove and
recover the alkali metal. One electrolytic cell 120 is shown in
FIG. 1. The electrolytic cell 120 receives alkali polysulfide 122.
Under the influence of a source electric power 124, alkali metal
ions are reduced to form the alkali metal (M) 126, which may be
recovered and used as a source of alkali metal 106. Sulfur 128 is
also recovered from the process of the electrolytic cell 120. A
detailed discussion of one possible electrolytic cell that may be
used in the process within the scope of the present invention is
given with respect to FIG. 3. A more detailed discussion relating
to the recovery of sulfur 128 is given with respect to FIG. 4,
below.
[0060] The vessel where the reaction depicted in FIGS. 2A and 2B
occurs could be the anolyte compartment of the electrolytic cell
120 depicted in FIG. 1, the thickener 312 depicted in FIG. 4, or in
a separate vessel conducive to capturing and recovering the
hydrogen sulfide gas 110 generated. Alternatively, sulfur generated
in the process depicted in FIG. 1 could be used as an input as
depicted in FIG. 2B.
[0061] FIG. 3 shows a schematic sectional view of an electrolytic
cell 300 which utilizes many of the features within the scope of
the invention. The cell is comprised of a housing 310, which
typically is an electrical insulator and which is chemically
resistant to solvents and sodium sulfide. A cation conductive
membrane 312, in this case in the form of a tube, divides the
catholyte compartment 314 from the anolyte compartment 316. Within
the catholyte compartment is a cathode 324. The cathode 324 may be
configured to penetrate the housing 310 or have a lead 325 that
penetrates the housing 310 so that a connection may be made to
negative pole of a DC electrical power supply (not shown). Within
the anolyte compartment 316 is an anode 326 which in this case is
shown as a porous mesh type electrode in a cylindrical form which
encircles the membrane tube 312. A lead 328 penetrates the housing
so that a connection may be made with a positive pole of the DC
power supply. An anolyte flows through an anolyte inlet 330. The
anolyte is comprised of a mixture of solvents and alkali metal
sulfides. As anolyte flows in through the inlet 330 anolyte also
flows out of the outlet 332. In some cases a second liquid phase of
molten sulfur may also exit with the anolyte. A second outlet may
be provided from the anolyte compartment at a location lower than
the anolyte outlet 332. The second, lower outlet may be used more
for removal of molten sulfur that has settled and accumulated at
the cell bottom. The space between the cathode 324 and the membrane
312 is generally filled with molten alkali metal. As the cell
operates, alkali metal ions pass through the membrane 312 and
reduce at the cathode 324 to form alkali metal in the catholyte
compartment 314 resulting in a flow of alkali metal through the
catholyte outlet 334.
[0062] A cell may have multiple anodes, cathodes, and membranes.
Within a cell the anodes all would be in parallel and the cathodes
all in parallel.
[0063] Referring to FIG. 3, electrolytic cell housing 310 is
preferably an electrically insulative material such as most
polymers. The material also is preferably chemically resistant to
solvents. Polytetrafluoroethylene (PTFE) is particularly suitable,
as well as Kynar.RTM. polyvinylidene fluoride, or high density
polyethylene (HDPE). The cell housing 310 may also be fabricated
from a non insulative material and non-chemically resistant
materials, provided the interior of the housing 310 is lined with
such an insulative and chemically resistant material. Other
suitable materials would be inorganic materials such as alumina,
silica, alumino-silicate and other insulative refractory or ceramic
materials.
[0064] The cation conductive membrane 312 preferably is
substantially permeable only to cations and substantially
impermeable to anions, polyanions, and dissolved sulfur. The
membrane 312 may be fabricated in part from an alkali metal ion
conductive material. If the metal to be recovered by the cell is
sodium, a particularly well suited material for the divider is
known as NaSICON which has relatively high ionic conductivity at
room temperature. A typical NaSICON composition substantially would
be Na.sub.1+xZr.sub.2Si.sub.xP.sub.3-xO.sub.12 where 0<x<3.
Other NaSICON compositions are known in the art. Alternatively, if
the metal to be recovered in the cell is lithium, then a
particularly well suited material for the divider would be lithium
titanium phosphate (LTP) with a composition that is substantially,
Li.sub.(1+x+4y)Al.sub.xTi.sub.(1-x-y)(PO.sub.4).sub.3 where
0<x<0.4, 0<y<0.2. Other suitable materials may be from
the ionically conductive glass and glass ceramic families such as
the general composition Li.sub.1+xAl.sub.xGe.sub.2-xPO.sub.4. Other
lithium conductive materials are known in the art. The membrane 312
may have a portion of its thickness which has negligible through
porosity such that liquids in the anolyte compartment 316 and
catholyte compartment 314 cannot pass from one compartment to the
other but substantially only alkali ions (M.sup.+), such as sodium
ions or lithium ions, can pass from the anolyte compartment 316 to
the catholyte compartment 314. The membrane may also be comprised
in part by an alkali metal conductive glass-ceramic such as the
materials produced by Ohara Glass of Japan.
[0065] The anode 326 is located within the anolyte compartment 316.
It may be fabricated from an electrically conductive material such
as stainless steel, nickel, iron, iron alloys, nickel alloys, and
other anode materials known in the art. The anode 326 is connected
to the positive terminal of a direct current power supply. The
anode 326 may be a mesh, monolithic structure or may be a monolith
with features to allow passage of anolyte through the anode
structure. Anolyte is fed into the anolyte compartment through an
inlet 330 and passes out of the compartment through and outlet 332.
The electrolytic cell 300 can also be operated in a semi-continuous
fashion where the anolyte compartment is fed and partially drained
through the same passage.
[0066] The electronically conductive cathode 324 is in the form of
a strip, band, rod, or mesh. The cathode 324 may be comprised of
most electronic conductors such as steel, iron, copper, or
graphite. A portion of the cathode may be disposed within the
catholyte compartment 314 and a portion outside the catholyte
compartment 314 and cell housing 310 for electrical contact.
Alternatively, a lead 325 may extend from the cathode outside the
cell housing 310 for electrical contact.
[0067] Within the catholyte compartment 314 is an alkali ion
conductive liquid which may include a polar solvent. Non-limiting
examples of suitable polar solvents are as tetraethylene glycol
dimethyl ether (tetraglyme), diglyme, dimethyl carbonate, dimethoxy
ether, propylene carbonate, ethylene carbonate, diethyl carbonate
and such. An appropriate alkali metal salt, such as a chloride,
bromide, iodide, perchlorate, hexafluorophosphate or such, is
dissolved in the polar solvent to form that catholyte. Most often
the catholyte is a bath of molten alkali metal.
[0068] One non-limiting example of the operation of the
electrolytic cell 300 is described as follows: Anolyte is fed into
the anolyte compartment 316. The electrodes 324, 326 are energized
such that there is an electrical potential between the anode 326
and the cathode 324 that is greater than the decomposition voltage
which ranges between about 1.8V and about 2.5V depending on the
composition. Concurrently, alkali metal ions, such as sodium ions,
pass through the membrane 312 into the catholyte compartment 314,
sodium ions are reduced to the metallic state within the catholyte
compartment 314 with electrons supplied through the cathode 324,
and sulfide and polysulfide is oxidized at the anode 326 such that
low polysulfide anions become high polysulfide anions and/or
elemental sulfur forms at the anode. While sulfur is formed it is
dissolved into the anolyte solvent in entirety or in part. On
sulfur saturation or upon cooling, sulfur may form a second liquid
phase of that settles to the bottom of the anolyte compartment 316
of the electrolytic cell. The sulfur may be removed with the
anolyte to settle in a vessel outside of the cell or it may be
directly removed from a settling zone 336 via an optional sulfur
outlet 338, as shown in FIG. 3.
[0069] A mode of operation may be to have the anolyte of one
electrolytic cell flow into a second cell and from a second cell
into a third cell, and so forth where in each successive cell the
ratio of sodium to sulfide decreases as the polysulfide forms
become of higher order. FIG. 4 is non-limiting schematic of four
electrolytic cells, 402, 404, 406, 408 operated in series to
extract alkali metal and oxidize alkali metal sulfide to low alkali
metal polysulfide, to oxidize low alkali metal polysulfide to
higher alkali metal polysulfide, and to oxidize higher alkali metal
polysulfide to high alkali metal polysulfide, and to oxidize high
alkali metal polysulfide to sulfur. The electrolytic cells 402,
404, 406, and 408 may be operated such that only in the final cell
is sulfur produced but where alkali metal is produced at the
cathode of all of them.
[0070] In a non-limiting example, an alkali metal monosulfide, such
as sodium sulfide (Na.sub.2S) may be introduced into the first
electrolytic cell 402. Under the influence of a DC power supply,
sodium ions are transported from the anolyte compartment to the
catholyte compartment where the alkali ions are reduced to form
alkali metal. Sulfide is oxidized in the anolyte compartment to
form a low polysulfide, such as Na.sub.2S.sub.4. The low alkali
metal polysulfide is transported to the anolyte compartment of a
second electrolytic cell 404. Under the influence of a DC power
supply, sodium ions are transported from the anolyte compartment to
the catholyte compartment where the alkali ions are reduced to form
alkali metal. The low polysulfide is oxidized in the anolyte
compartment to form a higher polysulfide, such as Na.sub.2S.sub.6.
The higher alkali metal polysulfide is transported to the anolyte
compartment of a third electrolytic cell 406. Under the influence
of a DC power supply, sodium ions are transported from the anolyte
compartment to the catholyte compartment where the alkali ions are
reduced to form alkali metal. The higher polysulfide is oxidized in
the anolyte compartment to form a high polysulfide, such as
Na.sub.2S.sub.8. The high alkali metal polysulfide is transported
to the anolyte compartment of a fourth electrolytic cell 408. Under
the influence of a DC power supply, sodium ions are transported
from the anolyte compartment to the catholyte compartment where the
alkali ions are reduced to form alkali metal. High polysulfide is
oxidized in the anolyte compartment to form sulfur, which is
subsequently removed from the anolyte compartment and
recovered.
[0071] It will be understood that the foregoing examples of
different polysulfides are given as representative examples of the
underlying principle that that higher order polysulfides may be
formed by and the combination of oxidizing the polysulfide and
removing sodium ions.
[0072] The multi-cell embodiment described in relation to FIG. 4
enables alkali metal and sulfur to be formed more energy
efficiently compared to a single cell embodiment. The reason for
the energy efficiency is because it requires less energy to oxidize
lower polysulfides compared to higher polysulfides. The voltage
required to oxidize polysulfides to sulfur is about 2.2 volts,
whereas monosulfide and low polysulfide may be oxidized at a lower
voltage, such as 1.7 volts.
[0073] In the case of the alkali metal being sodium, the following
typical reactions may occur in the electrolytic cell 300:
[0074] At the Cathode:
Na.sup.++e-.fwdarw.Na
[0075] At the Anode:
Na.sub.2S.sub.x.fwdarw.Na.sup.++e.sup.-+1/2Na.sub.2S.sub.(2x)
1)
Na.sub.2S.sub.x.fwdarw.Na.sup.++e.sup.-+1/2Na.sub.2S.sub.x+x/16S.sub.8
2)
[0076] Where x ranges from 0 to about 8.
[0077] Most sodium is produced commercially from electrolysis of
sodium chloride in molten salt rather than sodium polysulfide, but
the decomposition voltage and energy requirement is about half for
polysulfide compared to chloride as shown in Table 1.
TABLE-US-00001 TABLE 1 Decomposition voltage and energy
(watt-hour/mole) of sodium and lithium chlorides and sulfides NaCl
Na.sub.2S LiCl Li.sub.2S V 4.0 <2.1 4.2 2.3 Wh/mole 107 <56
114 60
[0078] The open circuit potential of a sodium/polysulfide cell is
as low as 1.8V when a lower polysulfide, Na.sub.2S.sub.3 is
decomposed, while the voltage rises with rising sulfur content.
Thus, it may be desirable to operate a portion of the electrolysis
using anolyte with lower sulfur content. In one embodiment, a
planar NaSICON or Lithium Titanium Phosphate (LTP) membrane is used
to regenerate sodium or lithium, respectively. NaSICON and LTP have
good low temperature conductivity as shown in Table 2. The
conductivity values for beta alumina were estimated from the
300.degree. C. conductivity and activation energy reported by May.
G. May, J. Power Sources, 3, 1 (1978).
TABLE-US-00002 TABLE 2 Conductivities of NaSICON, LTP, Beta alumina
at 25.degree. C., 120.degree. C. Conductivity mS/cm Temperature
.degree. C. NaSICON LTP Beta alumina (est) 25 0.9 0.9 0.7 120 6.2
1.5 7.9
[0079] It may be beneficial to operate 2 or more sets of cells, a
non-limiting example of which is shown in FIG. 4. Some cells would
operate with lower order sulfide and polysulfides in the anolyte
while another set of cells operate with higher order polysulfide.
In the latter, free sulfur would become a product requiring
removal.
[0080] The following example is provided below which discusses one
specific embodiment within the scope of the invention. This
embodiment is exemplary in nature and should not be construed to
limit the scope of the invention in any way.
[0081] An electrolytic flow cell utilizes a 1'' diameter NaSICON
membrane with approximately 3.2 cm.sup.2 active area. The NaSICON
is sealed to a scaffold comprised of a non-conductive material that
is also tolerant of the environment. One suitable scaffold material
is alumina. Glass may be used as the seal material. The flow path
of electrolytes will be through a gap between electrodes and the
membrane. The anode (sulfur electrode) may be comprised of
aluminum. The cathode may be either aluminum or stainless steel. It
is within the scope of the invention to configure the flow cell
with a bipolar electrodes design. Anolytes and catholytes will each
have a reservoir and pump. The anolyte reservoir will have an
agitator. The entire system will preferably have temperature
control with a maximum temperature of 150.degree. C. and also be
configured to be bathed in a dry cover gas. The system preferably
will also have a power supply capable of delivering to 5 VDC and up
to 100 mA/cm.sup.2.
[0082] As much as possible, materials will be selected for
construction that are corrosion resistant with the expected
conditions. The flow cell will be designed such that the gap
between electrodes and membrane can be varied.
[0083] In view of the foregoing, it will be appreciated that the
disclosed invention includes one or more of the following
advantages:
[0084] Removing an alkali metal continuously or semi-continuously
in liquid form from the cell.
[0085] Removing sulfur continuously or semi-continuously in liquid
form from the cell.
[0086] Removing high alkali metal polysulfides and dissolved sulfur
continuously or semi-continuously from the electrolytic cell,
thereby reducing polarization of the anode by sulfur.
[0087] Separating sulfur continuously or semi-continuously from a
stream containing a mixture of solvent, sulfur, and alkali metal
polysulfides such that the solvent and alkali metal polysulfides
are substantially recovered such that they can be returned back to
an electrolytic process.
[0088] Operating the electrolytic cells at temperatures and
pressures, so that the electrolytic cell materials of construction
can include materials which would not tolerate high elevated
temperature.
[0089] While specific embodiments of the present invention have
been illustrated and described, numerous modifications come to mind
without significantly departing from the spirit of the invention,
and the scope of protection is only limited by the scope of the
accompanying claims.
* * * * *