KR102258315B1 - Process for recovering alkali metals and sulfur from alkali metal sulfides and polysulfides - Google Patents

Abstract

Alkali metal 126 and sulfur 128 may be recovered from alkali monosulfide and polysulfide 122 in an electrolytic process using an electrolytic cell 120 having an alkali ion conductive membrane. The anolyte solution includes an alkali monosulfide, an alkali polysulfide, or a mixture thereof and a solvent that dissolves elemental sulfur. The catholyte contains molten alkali metal. Applying an electric current oxidizes the sulfides and polysulfides in the anolyte compartment, causes alkali metal ions to pass through the alkali ion conductive membrane to the catholyte compartment, and reduces alkali metal ions in the catholyte compartment. Liquid sulfur can be separated and recovered from the anolyte solution. The electrolytic cell is operated at a temperature at which the formed alkali metal and sulfur melt.

Description

Method for recovering alkali metals and sulfur from alkali metal sulfides and polysulfides {PROCESS FOR RECOVERING ALKALI METALS AND SULFUR FROM ALKALI METAL SULFIDES AND POLYSULFIDES}

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 61/781,557, filed March 14, 2013, which is incorporated by reference. This application is a continuation in part of U.S. Application Serial No. 12/576,977, filed October 9, 2009, which claims the benefit of U.S. Provisional Patent Application Serial No. 61/103,973, filed October 9, 2008.

Government-only license

This invention was made with government support under Financial No. DE-FE0000408 awarded by the US Department of Energy. The government has certain rights in this invention.

Field of invention

FIELD OF THE INVENTION The present invention relates to a process for removing nitrogen, sulfur, and heavy metals from sulfur-, nitrogen-, and metal-containing shale oil, bitumen, heavy oil, or refinery streams. More particularly, the present invention relates to a method for recovering alkali metals from sulfides (mono- and polysulfides) of those metals. The present invention further relates to the removal and recovery of sulfur from alkali metal sulfides and polysulfides.

The demand for energy and the hydrocarbons from which such energy is derived continues to increase. However, hydrocarbon feedstocks used to provide this energy include those that are difficult to remove sulfur and metals that impede their use. Sulfur can cause air pollution and can contaminate catalysts designed to remove hydrocarbons and nitrogen oxides from automobile exhaust. Similarly, other metals contained in hydrocarbon streams can contaminate catalysts typically used for the removal of sulfur through standard and improved hydro-desulphurization processes, whereby hydrogen is used to decompose sulfur-containing organo-sulfur molecules. reacts under phosphorus conditions.

Extensive reserves of shale oil exist in the United States, increasingly serving to meet U.S. energy demand. More than one trillion barrels of reserves are buried 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 must be addressed in the future. A significant issue is the amount of sulfur and metal content contained in shale oil chemistry after retorting as well as treatment It treats relatively high levels of nitrogen.

Shale oil is characteristically high in nitrogen, sulfur, and heavy metals that make subsequent hydroprocessing difficult. America's Strategic Unconventional Fuels, Vol. III - Resource and Technology Profiles, p. According to 111-25, nitrogen is typically about 2% and sulfur is about 1% with some metals in shale oil. Heavy metals in shale oil pose a big problem for upgraders. Sulfur and nitrogen are typically removed via treatment with hydrogen at high temperature and pressure with a catalyst such as Co-Mo/Al ₂ O ₃ or Ni-Mo/Al ₂ O _{3 .} These catalysts are deactivated by metal masking the catalyst.

Another example of a source of hydrocarbon fuels for which removal of sulfur poses a problem is bitumen, which is present in sufficient quantities in Alberta, Canada, and heavy oil, such as in Venezuela. In order to remove enough sulfur from the bitumen to make it useful as an energy resource, excess hydrogen must be introduced under extreme conditions, which creates an inefficient and economically undesirable process.

Over the past few years, sodium has been recognized as effective in the treatment of high-sulfur petroleum oil distillates, crude, heavy oils, bitumen, and shale oils. Sodium can react with oils and their contaminants to dramatically reduce sulfur, nitrogen, and metal content through the formation of sodium sulfide compounds (sulfides, polysulfides and hydrosulfides). Examples of methods are described in US Pat. Nos. 3,785,965; 3,787,315; 3,788,978; 4,076,613; 5,695,632; 5,935,421; and 6,210,564.

Alkali metals such as sodium or lithium are reacted with the oil at about 350° C. and 300-2000 psi. For example 1-2 moles sodium and 1-1.5 moles hydrogen may be required per mole of sulfur according to the following initial reaction with an alkali metal:

R - S - R' + 2Na + H ₂ → RH + R'-H + Na ₂ S

R,R',R"-N + 3Na + 1.5H ₂ → RH + R'-H + R"-H + Na ₃ N

wherein R, R', R" represents an organic molecule or part of an organic ring.

The sodium sulfide and sodium nitride products of the reaction described above can be further reacted with hydrogen sulfide according to the following reaction:

Na ₂ S + H ₂ S → 2 NaHS (liquid at 375 °C)

Na ₃ N + 3H ₂ S → 3 NaHS + NH ₃

Nitrogen is vented and removed in the form of recoverable ammonia. Sulfur is removed in the form of alkali hydrosulfide, ie NaHS, which is separated for further processing. Heavy metals and organic phases can be separated by gravimetric separation techniques. The reaction is expressed using sodium but can be substituted with lithium.

Heavy metals contained in organometallic molecules such as complex porphyrins are reduced to a metallic state by alkali metals. Once the heavy metal has been reduced, it can be separated from the oil as it is no longer chemically bound to the organic structure. Also, when metals are removed from the porphyrin structure, nitrogen heteroatoms in the structure are exposed for further denitrification.

The following is a non-limiting description of the aforementioned process using alkali metals to treat petroleum organics. Liquid alkali metals are contacted with 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 occurs more readily without complete saturation of hydrogen with organics. Hydrogen is needed for the reaction to fill where heteroatoms and metals are removed to prevent coking and polymerization, but alternatively, gases other than hydrogen can be used to prevent polymerization. When 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, using steam or hydrogen sulfide to form a hydroxide phase if steam is used or a hydrosulfide phase if hydrogen sulfide is used. At the same time, it is assumed that the alkali nitrides react to form ammonia and more alkali hydroxides or hydrosulfides. Gravimetric separations such as centrifugation or filtering can separate organic, refined oils from the salt phase.

In conventional hydroprocessing, instead of forming _{Na 2} S for desulfurization or Na _{3 N for denitrification, H 2} S and NH ₃ are respectively formed. The reaction to form hydrogen sulfide and ammonia is thermodynamically much less favorable than the formation of sodium or lithium compounds, so the parent molecule must be stabilized to a greater extent for the desulfurization of the denitrification reaction to proceed. T. Kabe, A Ishihara, W. Qian, in Hydrodesulfurization and Hydrodenitrogenation , pp. 37, 110-112, Wiley-VCH, 1999, this destabilization occurs mainly after the benzo ring is saturated. To provide this saturation of the ring, more hydrogen is needed for the desulfurization and denitrification reactions and more severe conditions are needed to achieve the same level of sulfur and nitrogen removal as compared to removal with sodium or lithium. As mentioned above, desulfurization and denitrification using hydrogen without sodium or lithium is further complicated by masking of the catalyst surface from precipitating heavy metals and coke. Since sodium is in the liquid phase, it has better access to the sulfur, nitrogen and metals where it is desirable to react.

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). Bituminous or heavy oil will be considered synthetic crude oil (SCO) and may be transported through pipelines for further refining. Similarly, shale oil would have improved significantly after such treatment. Subsequent purification will be easier as the cumbersome metals have been removed.

While 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 as practical, cost-effective methods for regenerating alkali metals have not yet been proposed to date. Several researchers have proposed the regeneration of sodium using an electrolytic cell, which uses a sodium-ion-conducting beta-alumina membrane. However, beta-alumina is both expensive and fragile, and significant metal production does not utilize beta-alumina as a membrane separator. In addition, the cell utilizes a sulfur anode, which results in a high polarization of the cell which results in excessive specific energy requirements.

Metallic sodium is produced almost exclusively commercially in Downs-cells such as those described in US Pat. No. 1,501,756. Such cells electrolyze sodium chloride dissolved in a molten salt electrolyte to form molten sodium at the cathode and chlorine gas at the anode. The cell operates at a temperature close to 600° C., ie at a temperature compatible with the electrolyte used. Unlike sulfur anodes, chlorine anodes are used commercially both in molten salts, as in the co-production of sodium, and in brine solutions, as in the co-production of sodium hydroxide.

Another cell technology capable of reducing the electrolyte melting range and operation of an electrolyzer below 200° C. is disclosed by US Pat. No. 6,787,019 to Jacobson et al. and US Pat. No. 6,368,486 to Thompson et al. In such disclosure, a low temperature co-electrolyte is used as an alkali halide to form a low temperature molten electrolyte.

U.S. Patent No. 8,088,270 to Gordon discloses that when introduced into a cell with an alkali ion conductive membrane, it electrolyzes to form sulfur at the anode and alkali metal at the cathode and where a portion of the anolyte is removed from the cell so that the sulfur is completely precipitated. The use of a solvent that dissolves sulfur at cell operating temperature to form an anolyte that is allowed to cool until

It is an object of the present invention to provide a cost-effective and efficient process for the regeneration of alkali metals used in the desulfurization, denitrification, and demetallization of hydrocarbon streams. As described herein, the present invention can remove contaminants and isolate unwanted material products from desulfurization/denitrification/demetallization reactions, and then recover those materials for later use.

Another object of the present invention is to teach improvements in methods and apparatus for recovering alkali metals from alkali metal sulfides produced by sulfur removal and remediation methods.

Brief summary of the invention

The present invention provides a process for removing nitrogen, sulfur, and heavy metals from sulfur-, nitrogen-, and metal-containing shale oil, bitumen, heavy oil, or refinery streams. The present invention further provides an electrolytic method for regenerating alkali metals from sulfides, polysulfides, nitrides, and polynitrides of such metals. The present invention further provides an electrolytic method for removing sulfur from a polysulfide solution.

One non-limiting embodiment includes methods for electrochemically oxidizing alkali metal sulfides and polysulfides within the scope of the present invention. The method utilizes an electrolytic cell having an alkali ion conductive membrane configured to selectively transport alkali ions, the membrane separating an anolyte compartment composed of an anode and a catholyte compartment composed of a cathode. The anolyte solution is introduced into the anolyte compartment. The anolyte solution comprises an anolyte solvent that partially dissolves alkali metal sulfides and/or polysulfides and elemental sulfur and alkali metal sulfides and polysulfides. The catholyte solution is introduced into the catholyte compartment. The catholyte solution contains an alkali metal ion 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 an alkali metal. Applying an electric current to the electrolytic cell oxidizes the sulfide and/or polysulfide in the anolyte compartment to form higher levels of polysulfide and causes the high level polysulfide to oxidize to elemental sulfur. The current further causes alkali metal ions to be transferred from the anolyte compartment through the alkali ion conductive membrane to the catholyte compartment and reduces the alkali metal ions in the catholyte compartment to form elemental alkali metal.

Sulfur can be recovered in liquid form when the temperature exceeds the melting point of the sulfur and the sulfur content of the anolyte exceeds the solubility of the solvent. Most anolyte solvents have a lower specific gravity compared to sulfur, so liquid sulfur settles to the bottom. Such sedimentation may occur within a sedimentation zone within the cell where sulfur may be withdrawn through an outlet. Alternatively, a portion of the anolyte solution may be transferred to a sedimentation zone outside the cell where settling of sulfur may occur more effectively than within the cell.

The melting temperature of sulfur is around 115°C, so the cell works best above that temperature, i.e. above 120°C. At or above that temperature, the alkali metal also melts if the alkali metal is sodium. Operation near higher temperatures, such as in the range of 125-150°C, allows the sulfur to remain completely in the solution formed as is from polysulfide at the anode, and then the anolyte in the cell where the temperature can be 5-20°C cooler. or when flowing into the settling zone outside it, the reduced solubility of sulfur in the solvent causes the formation of a sulfur liquid phase having a higher specific gravity and settling from the anolyte. The anolyte then has a solubility that has the capacity to dissolve the formed sulfur as it is, when sulfur flows back towards the anode where sulfur is being formed through the electrochemical oxidation of the polysulfide, thereby preventing contamination and polarization at the anode or membrane. prevent from the surface.

Within the scope of the present invention in one non-limiting embodiment, there is provided a cell for electrolyzing an alkali metal sulfide or polysulfide wherein the cell operates at a temperature above the melting temperature of the alkali metal and wherein the cathode is between the anolyte compartment and the catholyte compartment. wholly or partially impregnated in a bath of molten alkali metal having a divider of The catholyte in this case essentially comprises a molten alkali metal but may also comprise a solvent and an alkali metal salt. The divider may be permeable to alkali metal cations and substantially impermeable to anions, solvents and dissolved sulfur. The divider includes, in part, an alkali metal conductive ceramic or glass ceramic. The divider may be conductive to alkali ions including lithium and sodium.

In another non-limiting embodiment, a cell for electrolyzing alkali metal polysulfide is provided with an anolyte compartment and a catholyte compartment and the anolyte solution comprises a polar solvent and dissolved alkali metal polysulfide. The anolyte solution contains a solvent that dissolves some elemental sulfur. The anolyte may include a solvent, at least one of which is N,N -dimethylaniline, quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene, cyclohexane, fluorobenzene, trifluorobenzene, toluene, Xylene, tetraethylene glycol dimethyl ether (tetraglyme), diglyme, isopropanol, ethyl propional, dimethyl carbonate, dimethoxy ether, dimethylpropyleneurea, formamide, methyl formamide, dimethyl formamide, acetamide, methyl acetate amide, dimethyl acetamide, triethylamine, diethyl acetamide, ethanol and ethyl acetate, propylene carbonate, ethylene carbonate, and diethyl carbonate.

In one non-limiting embodiment, a method for electrochemically oxidizing sulfides and polysulfides from an anolyte solution at an anode is disclosed wherein the anolyte solution partially comprises an anolyte solvent that dissolves some elemental sulfur. In the method, the anolyte solvent dissolving some elemental sulfur is one or more of: N,N -dimethylaniline, quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene, cyclohexane, fluorobenzene, tri Fluorobenzene, 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.

In another non-limiting embodiment, a cell for electrolyzing alkali metal monosulfide or polysulfide is provided with an anolyte compartment and a catholyte compartment wherein the anolyte solution comprises a polar solvent and dissolved alkali metal monosulfide or polysulfide. do. The anolyte solution contains a solvent that dissolves some elemental sulfur. The anolyte may include a solvent, at least one of which is N,N-dimethylaniline, quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene, cyclohexane, fluorobenzene, trifluorobenzene, toluene, Xylene, tetraethylene glycol dimethyl ether (tetraglyme), diglyme, isopropanol, ethyl propional, dimethyl carbonate, dimethoxy ether, dimethylpropyleneurea, formamide, methyl formamide, dimethyl formamide, acetamide, methyl acetamide amide, dimethyl acetamide, triethylamine, diethyl acetamide, ethanol and ethyl acetate, propylene carbonate, ethylene carbonate, and diethyl carbonate.

In one non-limiting embodiment, a method for electrochemically oxidizing monosulfide or polysulfide from an anolyte solution at an anode is disclosed wherein the anolyte solution partially comprises an anolyte solvent dissolving some elemental sulfur. . In the method, the anolyte solvent dissolving some elemental sulfur is one or more of: N,N -dimethylaniline, quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene, cyclohexane, fluorobenzene, tri Fluorobenzene, 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.

In one non-limiting embodiment, the anolyte solvent comprises about 60-100 volume % polar solvent and 0-40 volume % non-polar solvent. The mixing of different anolyte solvents can help optimize the solubility of elemental sulfur and the solubility of sulfides and polysulfides.

Another non-limiting embodiment is that a method for removal of dissolved elemental sulfur from a solvent/alkali metal polysulfide mixture causes cooling, reducing the solubility of sulfur in the solvent and forming a second liquid phase comprising elemental sulfur, the method comprising: and then separating the liquid sulfur from the liquid phase solvent mixture. Separation of liquid-phase sulfur from liquid-phase anolyte comprises one or more of the following: gravimetric, centrifugation. Alkali metal polysulfides are a class that includes sodium polysulfide and lithium polysulfide.

The present invention may provide certain advantages including, but not limited to:

Continuous or semi-continuous removal of alkali metals in liquid form from cells.

Continuous or semi-continuous removal of sulfur from a cell in liquid form.

Continuous or semi-continuous removal of high alkali metal polysulfides and dissolved sulfur from electrolytic cells, thereby reducing the polarization of the anode by sulfur.

The continuous or semi-continuous separation of sulfur from a stream containing a mixture of solvent, sulfur, and alkali metal polysulfide such that the solvent and alkali metal polysulfide can be substantially recovered and returned to the electrolytic process.

By operating the electrolytic cell at temperature and pressure, the electrolytic cell material of construction may include materials that are not resistant to high elevated temperatures.

References throughout this specification to features, advantages, or similar language do not imply that all features and advantages that may be realized with the invention are or should be in any single embodiment of the invention. Rather, language referring to features and advantages is understood to mean that a particular feature, advantage, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Accordingly, discussions of features and advantages, and similar language, may refer to all implementations, although not necessarily referring to the same implementation throughout this specification.

Moreover, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. Those skilled in the relevant art will recognize that the present invention may be practiced without one or more of the specific features or advantages of specific embodiments. In other instances, additional features and advantages may be recognized in some embodiments that may not be present in all embodiments of the invention.

These features and advantages of the invention will become more fully apparent from the following description and appended claims, or may be learned by practice of the invention as set forth below.

In order that the above-cited and other features and advantages of the invention may be readily understood, a more specific description of the invention briefly set forth above will be provided with reference to specific embodiments thereof, which are illustrated in the accompanying drawings. The invention will be described and illustrated with further specificity and detail through the use of the accompanying drawings, provided that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope:
1 depicts an overall process for removing nitrogen, sulfur, and heavy metals from sulfur-, nitrogen-, and metal-containing oil sources and regenerating alkali metals using alkali metals.
2a and 2b show a schematic process for converting alkali metal hydrosulfide to alkali metal polysulfide and recovering hydrogen sulfide.
3 shows a schematic cross-section of an electrolytic cell utilizing many features within the scope of the present invention.
4 shows a schematic diagram of several electrolytic cells operated in series to extract alkali metals and oxidize alkali metal sulfides to polysulfides and low polysulfides to high polysulfides and high polysulfides to sulfur.

BRIEF DESCRIPTION OF THE DRAWINGS This embodiment of the invention will be best understood by reference to the drawings, wherein like parts are designated by like numbers throughout. It will be readily understood that the components of the present invention may be prepared and designed in many different configurations, as generally described and illustrated in the drawings herein. Accordingly, the following more detailed description of embodiments of the method and battery of the present invention is not intended to limit the scope of the invention as claimed, as represented in Figures 1-4, but only the current embodiments of the invention. indicates.

The overall process is schematically shown in FIG. 1 of one non-limiting embodiment of using alkali metals to remove nitrogen, sulfur, and heavy metals from sulfur-, nitrogen-, and metal-containing oil sources and to regenerate alkali metals. In the method 100 of FIG. 1 , an oil source 102 , such as a high-sulfur petroleum oil distillate, crude, heavy oil, bitumen, or shale oil, is introduced into a reaction vessel 104 . Alkali metal (M) 106 , such as sodium or lithium, is also introduced into the reaction vessel, along with a large amount of hydrogen 108 . Alkali metals and hydrogen react with oils and their contaminants to dramatically reduce sulfur, nitrogen, and metal content through the formation of sodium sulfide compounds (sulfides, polysulfides and hydrosulfides) and sodium nitride compounds. Examples of methods are known in the art, and include, but are not limited to, U.S. Patent Nos. 3,785,965; 3,787,315; 3,788,978; 4,076,613; 5,695,632; 5,935,421; and 6,210,564.

Alkali metal (M) and hydrogen are reacted with oil at about 350° C. and 300-2000 psi according to the following initial reaction:

R - S - R' + 2M + H ₂ → RH + R'-H + M ₂ S

R,R',R"-N + 3M + 1.5H ₂ → RH + R'-H + R"-H + M ₃ N

wherein R, R', R" represents an organic molecule or part of an organic ring.

The sodium sulfide and sodium nitride products of the reaction described above can be further reacted with hydrogen sulfide 110 according to the following reaction:

M ₂ S + H ₂ S → 2 MHS (liquid at 375°C)

M ₃ N + 3H ₂ S → 3 MHS + NH ₃

Nitrogen is removed in the form of ammonia 112, which can be aerated and recovered. Sulfur is removed from the oil source in the form of alkali hydrosulfides (MHS), such as sodium hydrosulfide (NaHS) or lithium hydrosulfide (LiHS). The reaction product 113 is transferred to a separation vessel 114 . Within the separation vessel 114, the heavy metals 116 and the improved oil organic phase 118 may be separated by gravimetric separation techniques.

Alkali hydrosulfide (MHS) is isolated for further processing. The alkali hydrosulfide stream may be the primary source of alkali metal and sulfur from the process of the present invention. If alkali hydrosulfides are reacted with the medium for high polysulfides (ie M ₂ S _x ; 4≤x≤6) then hydrogen sulfide will be released and the resulting mixture contains additional alkali metals with a lower sulfur to alkali metal ratio and will have a sulfide content. Hydrogen sulfide 110 may be used upstream of the washing step where alkali sulfides and alkali nitrides and metals need to be initially removed from the treated oil.

A schematic representation of this method is shown in FIG. 2A . For example, in the case of sodium the following reaction may occur:

Na ₂ S _x + 2NaHS → H ₂ S + 2[Na ₂ S _(x+1)/2 ]

where x:y represents the average ratio of sodium to sulfur atoms in solution. In the process shown in Figure 2a, alkali polysulfides with high sulfur content are converted to alkali polysulfides with lower sulfur content.

Alternatively, instead of reacting the alkali metal hydrosulfide with the alkali metal polysulfide, the alkali metal hydrosulfide may be reacted with sulfur. A schematic representation of this method is shown in FIG. 2B . For example, in the case of sodium the following reaction may occur:

YS + 2NaHS → H ₂ S + Na ₂ S _(Y+1)

where Y is the molar amount of sulfur added to sodium hydrosulfide.

Alkali metal polysulfides can be further processed in electrolytic cells to remove and recover sulfur and to remove and recover alkali metals. One electrolytic cell 120 is shown in FIG. 1 . The electrolytic cell 120 contains an alkali polysulfide 122 . Under the influence of the source power 124 , alkali metal ions are reduced to form alkali metal (M) 126 , which can 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 method within the scope of the present invention is given in FIG. 3 . A more detailed discussion related to the recovery of sulfur 128 is given in FIG. 4 below.

The vessel in which the reaction depicted in FIGS. 2A and 2B takes place may be the anolyte compartment of the electrolytic cell 120 depicted in FIG. 1 , wherein the thickener 312 is used in FIG. 4 , or the resulting hydrogen sulfide gas 110 . Depicted in individual containers to aid in capture and retrieval. Alternatively, the sulfur produced in the method depicted in FIG. 1 may be used as input as depicted in FIG. 2B .

3 shows a schematic cross-sectional view of an electrolytic cell 300 utilizing many of the features within the scope of the present invention. The cell consists of a housing 310, which is typically an electrical insulator and is chemically resistant to solvents and sodium sulfide. A cationically conductive membrane 312 , in this case in the form of a tube, divides the catholyte compartment 314 and the anolyte compartment 316 . Cathode 324 is in the catholyte compartment. Cathode 324 may be configured to have a lead 326 through housing 310 or through housing 310 so that a connection may be made to the negative pole of a DC power supply (not shown). The anode 326 , shown in this case as a porous mesh-type electrode in the form of a cylinder, surrounding the membrane tube 312 is within the anolyte compartment 316 . Lead 328 runs through the housing so that a connection can be made to the positive pole of the DC power supply. The anolyte solution flows through the anolyte inlet 330 . The anolyte consists of a mixture of a solvent and an alkali metal sulfide. As the anolyte flows through the inlet 330 , the anolyte also flows out at the outlet 332 . In some cases the second liquid phase of molten sulfur may also flow out with the anolyte. The second outlet may be provided from the anolyte compartment at a lower position than the anolyte outlet 332 . The lower second outlet can be further used for removal of molten sulfur that has settled and accumulated at the bottom of the cell. The space between the cathode 324 and the film 312 is typically filled with molten alkali metal. As the cell operates, alkali metal ions pass through membrane 312 to form alkali metal in catholyte compartment 314 causing a flow of alkali metal through catholyte outlet 334 and at cathode 324 . is reduced

A cell can have multiple anodes, cathodes, and membranes. Within the cell, the anodes will all be parallel and the cathodes will all be parallel.

Referring to FIG. 3 , the electrolytic cell housing 310 is preferably an electrically insulating material such as most polymers. The material is also preferably chemically resistant to solvents. Particularly suitable are Kynar® polyvinylidene fluoride, or high density polyethylene (HDPE) as well as polytetrafluoroethylene (PTFE). The battery housing 310 may also be fabricated from non-insulating materials and non-chemically resistant materials, provided that the interior of the housing 310 is lined with such insulating and chemically resistant materials. Other suitable materials would be inorganic materials such as alumina, silica, alumino-silicate and other insulating refractory or ceramic materials.

The cation conductive membrane 312 is preferably substantially permeable to only cations and substantially impermeable to anions, polyanions, and dissolved sulfur. 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 suitable material for the divider is known as NaSICON, which has a relatively high ionic conductivity at room temperature. A typical NaSICON composition would be substantially Na _{1 + x} Zr ₂ Si _x P _{3 - x} O ₁₂ , where 0<x<3. Other NaSICON compositions are known in the art. Alternatively, if the metal to be recovered from the cell is lithium, then a particularly suitable material for the divider is lithium titanium having a composition _{substantially Li (1+x+4y)} Al _x Ti _(1-xy) (PO ₄ ) _{3 .} phosphate (LTP), where 0<x<0.4. Other suitable materials may come from the ionically conductive glass and glass ceramic families such as the general composition Li _1+x Al _x Ge _2-x PO ₄ . Other lithium conductive materials are known in the art. Membrane 312 prevents liquid in anolyte compartment 316 and catholyte compartment 314 from being transferred from one compartment to another but substantially only alkali ions (M ⁺ ), such as sodium ions or lithium ions, into the anolyte. It may have a portion of its thickness with negligible through porosity to allow transfer from compartment 316 to catholyte compartment 314 . The film may also be partially composed of alkali metal conductive glass-ceramics such as materials produced by Ohara Glass of Japan.

The anode 326 is located within the anolyte compartment 316 . It can be made of electrically conductive materials 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 the DC power supply. Anode 326 may be a mesh, monolithic structure or may be a monolith with features that allow passage of the anolyte through the anode structure. The anolyte solution is supplied to the anolyte compartment through an inlet 330 and passes out of the compartment through an outlet 332 . Electrolytic cell 300 may also be operated in a semi-continuous manner in which the anolyte compartment is supplied and partially withdrawn through the same passage.

The electronically conductive cathode 324 is in the form of a strip, band, rod, or mesh. 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 the catholyte compartment 314 and a portion outside the cell housing 310 for electrical contact. Alternatively, the lead 325 may extend from the cathode outside the cell housing 310 for electrical contact.

An alkali ionically conductive liquid, which may include a polar solvent, is in the catholyte compartment 314 . Non-limiting examples of suitable polar solvents are tetraethylene glycol dimethyl ether (tetraglyme), diglyme, dimethyl carbonate, dimethoxy ether, propylene carbonate, ethylene carbonate, diethyl carbonate, and the like. Suitable alkali metal salts such as chloride, bromide, iodide, perchlorate, hexafluorophosphate and the like are dissolved in a polar solvent to form such catholyte solution. Mainly the catholyte is a bath of molten alkali metal.

One non-limiting example of the operation of the electrolytic cell 300 is described as follows: An anolyte solution is supplied to the anolyte compartment 316 . Electrodes 324 and 326 are energized such that, depending on the composition, there is a potential between the anode 326 and the cathode greater than the decomposition voltage ranging between about 1.8V and about 2.5V. At the same time, alkali metal ions, such as sodium ions, are transferred to the catholyte compartment 314 through the membrane 312 , and the sodium ions are reduced to a metallic state within the catholyte compartment 314 where electrons are supplied through the cathode 324 . sulfides and polysulfides are oxidized at the anode 326 such that the low polysulfide anions become high polysulfide anions and/or elemental sulfur is formed in the anode. During the formation of sulfur it is dissolved in whole or in part into the anolyte solvent. Upon sulfur saturation or cooling, the sulfur may form a second liquid phase of such settles at the bottom of the anolyte compartment 316 of the electrolytic cell. The sulfur may be removed with the anolyte solution to settle in a vessel external to the cell, as shown in FIG. 3 , or it may be removed directly from the settling zone 336 via an optional sulfur outlet 338 .

The mode of operation may allow the anolyte of one electrolytic cell to flow to and from the second cell to the third cell, etc. and in each successive cell the ratio of sodium to sulfide decreases as the polysulfide form becomes higher. do. 4 shows alkali metal extraction and conversion of alkali metal sulfide to low alkali metal polysulfide, low alkali metal polysulfide to higher alkali metal polysulfide, and higher alkali metal polysulfide to high alkali metal polysulfide, and It is a non-limiting schematic diagram of four electrolytic cells 402, 404, 406, 408 operated in series to oxidize alkali metal polysulfide to sulfur. Electrolytic cells 402, 404, 406, and 408 can be operated such that only the final cell produces sulfur, but alkali metals are produced at all cathodes.

In a non-limiting example, an alkali metal monosulfide, such as sodium sulfide (Na ₂ S), may be introduced into the first electrolytic cell 402 . Under the influence of the DC power supply, sodium ions are transported from the anolyte compartment to the catholyte compartment and alkali ions are reduced to form alkali metals. Sulfides are low polysulfides, such as Na ₂ S ₄ . oxidized in the anolyte compartment to form. The low alkali metal polysulfide is transported to the anolyte compartment of the second electrolytic cell 404 . Under the influence of the DC power supply, sodium ions are transported from the anolyte compartment to the catholyte compartment and alkali ions are reduced to form alkali metals. Low polysulfides produce higher polysulfides, such as Na ₂ S ₆ . oxidized in the anolyte compartment to form. The higher alkali metal polysulfide is transported to the anolyte compartment of the third electrolytic cell 406 . Under the influence of the DC power supply, sodium ions are transported from the anolyte compartment to the catholyte compartment and alkali ions are reduced to form alkali metals. Higher polysulfides are oxidized in the anolyte compartment to form high polysulfides, such as Na ₂ S _{8 .} The high alkali metal polysulfide is transported to the anolyte compartment of the fourth electrolytic cell 408 . Under the influence of the DC power supply, sodium ions are transported from the anolyte compartment to the catholyte compartment and alkali ions are reduced to form alkali metals. High polysulfide is oxidized in the anolyte compartment to form sulfur, which is subsequently removed and recovered from the anolyte compartment.

It will be understood that the foregoing examples of different polysulfides are given as representative examples of the underlying principle that such higher polysulfides can be formed by a combination of oxidizing the polysulfide and removing sodium ions.

The multi-cell embodiment described with respect to FIG. 4 allows alkali metals and sulfur to be formed more energy efficiently compared to a single cell embodiment. The reason for energy efficiency is that less energy is required to oxidize the lower polysulfide compared to the higher polysulfide. The voltage required to oxidize polysulfide to sulfur is about 2.2 volts, while monosulfide and low polysulfide can be oxidized at lower voltages, such as 1.7 volts.

When the alkali metal is sodium, the following typical reaction may occur in electrolytic cell 300:

At the cathode:

Na ⁺ + e- → Na

At the anode:

1) Na ₂ S _x → Na ⁺ + e ^- + ½ Na ₂ S _(2x)

2) Na ₂ S _x → Na ⁺ + e ^- + ½ Na ₂ S _x + x/16 S ₈

where x ranges from 0 to about 8.

Most sodium is produced commercially from the electrolysis of sodium chloride in molten salt rather than sodium polysulfide, but the decomposition voltage and energy requirements are about half for polysulfide compared to chloride as shown in Table 1.

Table 1. Decomposition voltage and energy (watt-hour/mol) of sodium and lithium chloride and sulfide

The open circuit potential of the sodium/polysulfide cell is _{as low as 1.8 V when the lower polysulfide, Na 2} S _{3 ,} is decomposed, while the voltage rises with the rising sulfur content. Therefore, it may be desirable to operate a portion of the electrolysis using an anolyte having a lower sulfur content. In one embodiment, planar NaSICON or lithium titanium phosphate (LTP) membranes are used to regenerate sodium or lithium, respectively. NaSICON and LTP have good low temperature conductivity as shown in Table 2. Conductivity values for beta alumina were obtained from May. It was estimated from the 300°C conductivity and activation energy reported by G. May , J. Power Sources, 3, 1 (1978).

Table 2. Conductivity of NaSICON, LTP, Beta Alumina at 25°C and 120°C

It may be beneficial to operate two or more sets of cells, a non-limiting example of which is shown in FIG. 4 . Some cells will operate with lower order sulfides and polysulfides in the anolyte while another set of cells will operate with higher order polysulfides. In the latter, free sulfur will be a product that requires removal.

The following examples discussing one specific embodiment within the scope of the present invention are provided below. These embodiments are exemplary in nature and should not be construed as limiting the scope of the invention in any way.

The electrolytic flow cell ^{utilizes a 1" diameter NaSICON membrane with an active area of approximately 3.2 cm 2} . NaSICON is also sealed in a scaffold comprised of a non-conductive material that is resistant to the environment. One suitable scaffold material is alumina. Glass can be used as sealing material The flow path of electrolyte will be through the gap between electrode and membrane Anode (sulfur electrode) can be made of aluminum Cathode can be aluminum or stainless steel Bipolar electrode design It is within the scope of the present invention to construct a flow cell with a flow cell.The anolyte and catholyte solution will each have a reservoir and a pump.The anolyte reservoir will have a shaker.The whole system is temperature controlled with a maximum temperature of 150°C. It would also be desirable for the system to have a power supply capable of delivering at ^{5 VDC and up to 100 mA/cm 2 .}

To the extent possible, materials that are resistant to corrosion under the expected conditions will be selected for construction. The flow cell will be designed so that the gap between the electrode and the membrane can be varied.

In view of the foregoing, it will be appreciated that the disclosed invention includes one or more of the following advantages:

Continuous or semi-continuous removal of alkali metals in liquid form from cells.

Continuous or semi-continuous liquid removal of sulfur from a cell.

Continuous or semi-continuous removal of high alkali metal polysulfides and dissolved sulfur from electrolytic cells, thereby reducing the polarization of the anode by sulfur.

The continuous or semi-continuous separation of sulfur from a stream containing a mixture of solvent, sulfur, and alkali metal polysulfide such that the solvent and alkali metal polysulfide can be substantially recovered and returned to the electrolytic process.

By operating the electrolytic cell at temperature and pressure, the electrolytic cell material of construction may include materials that are not resistant to high elevated temperatures.

While specific embodiments of the present invention have been illustrated and described, numerous modifications can be made without significantly departing from the spirit of the invention, the scope of protection being limited only by the scope of the appended claims.

Claims (25)

A method for electrochemically oxidizing alkali metal monosulfides and polysulfides, comprising:
obtaining an electrolytic cell comprising an alkali ion conductive membrane configured to selectively transport alkali ions, wherein the membrane separates an anolyte compartment composed of an anode and a catholyte compartment composed of a cathode;
introducing into the anolyte compartment an anolyte solution comprising an alkali metal monosulfide, alkali metal polysulfide, or mixtures thereof, and an anolyte solvent that partially dissolves elemental sulfur;
introducing catholyte into the catholyte compartment, wherein the catholyte comprises molten alkali metal;
By applying an electric current to the electrolytic cell at an operating temperature:
i. oxidizing monosulfide or polysulfide in said anolyte compartment to form liquid elemental sulfur or higher levels of alkali metal polysulfide and alkali metal ions;
ii. causing the alkali metal ions to pass from the anolyte compartment through the alkali ion conductive membrane to the catholyte compartment;
iii. reducing the alkali metal ion in the catholyte compartment to form a liquid elemental alkali metal;
allowing liquid elemental sulfur to be saturated in the anolyte solution; and
separating liquid elemental sulfur from the anolyte to form a second liquid phase;
How to include. The method of claim 1 , wherein the liquid elemental sulfur is separated from the anolyte solution in a settling zone within the electrolytic cell. The method of claim 1 , wherein the liquid elemental sulfur is separated from the anolyte solution in a settling zone external to the cell. The method of claim 1 , wherein the separation of the liquid elemental sulfur from the anolyte solution comprises one or more of a separation technique selected from gravimetry, filtration, and centrifugation. The method of claim 1 , wherein the alkali ion conductive membrane is substantially impermeable to anions, the catholyte solvent, the anolyte solvent, and dissolved sulfur. The method of claim 1 , wherein the alkali ion conductive membrane partially comprises an alkali metal conductive ceramic or glass ceramic. The method according to claim 1, wherein the alkali ion conductive membrane comprises a solid MSICON (Metal Super Ion CONducting) material, and M is Na or Li. According to claim 1, wherein the anolyte solvent is N,N-dimethylaniline, quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene, cyclohexane, fluorobenzene, trifluorobenzene, 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 A method comprising at least one solvent selected from acetamide, triethylamine, diethyl acetamide, ethanol and ethyl acetate, propylene carbonate, ethylene carbonate, and diethyl carbonate. The method of claim 1 , wherein the anolyte solvent comprises 60-100% by volume polar solvent and 0-40% by volume apolar solvent. A method for electrochemically oxidizing alkali metal polysulfides and monosulfides, comprising:
obtaining a first electrolytic cell comprising a first alkali ion conductive membrane configured to selectively transport alkali ions, wherein the membrane comprises a first anolyte compartment composed of a first anode and a first catholyte compartment composed of a first cathode separating;
introducing a first anolyte solution comprising an alkali metal monosulfide, an alkali metal polysulfide, or mixtures thereof, and an anolyte solvent partially dissolving elemental sulfur into the first anolyte compartment;
introducing a first catholyte into the first catholyte compartment, the catholyte comprising molten alkali metal;
By applying a current to the electrolytic cell:
i. oxidizing monosulfide or polysulfide in said first anolyte compartment to form higher levels of polysulfide and alkali metal ions;
ii. causing the alkali metal ions to pass from the first anolyte compartment through the first alkali ion conductive membrane to the first catholyte compartment;
iii. reducing the alkali metal ion in the first catholyte compartment to form elemental alkali metal;
transporting an anolyte solution from the first electrolytic cell to a second electrolytic cell comprising a second alkali ion conductive membrane configured to selectively transport alkali ions, the membrane comprising a second anolyte compartment comprising a second anode; and separating a second catholyte compartment composed of a catholyte and a second catholyte;
By applying a current to the second electrolytic cell:
i. oxidizing higher levels of polysulfide in the second anolyte compartment to form liquid elemental sulfur and alkali metal ions;
ii. causing the alkali metal ions to transfer from the second anolyte compartment through the second alkali ion conductive membrane to the second catholyte compartment;
iii. reducing the alkali metal ions in the second catholyte compartment to form a liquid elemental alkali metal;
allowing liquid elemental sulfur to be saturated in the anolyte solution in the second electrolytic cell; and
separating liquid elemental sulfur from the anolyte to form a second liquid phase;
How to include. 11. The method of claim 10, wherein said liquid elemental sulfur is separated from said anolyte in a settling zone within said second electrolytic cell. 11. The method of claim 10, wherein said liquid elemental sulfur is separated from said anolyte in a settling zone external to said second electrolytic cell. 11. The method of claim 10, wherein the separation of the liquid elemental sulfur from the anolyte solution comprises one or more of a separation technique selected from gravimetry, filtration, and centrifugation. 11. The method of claim 10, wherein the first alkali ion conductive membrane and the second alkali ion conductive membrane are substantially impermeable to anions, the catholyte solvent, the anolyte solvent, and dissolved sulfur. 11. The method of claim 10, wherein the first alkali ion conductive membrane and the second alkali ion conductive membrane partially comprise an alkali metal conductive ceramic or glass ceramic. 11. The method of claim 10, wherein the first alkali ion conductive membrane and the second alkali ion conductive membrane comprise a solid MSICON (Metal Super Ion CONducting) material, and M is Na or Li. 11. The method of claim 10, wherein the anolyte solvent is N,N-dimethylaniline, quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene, cyclohexane, fluorobenzene, trifluorobenzene, 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 A method comprising at least one solvent selected from acetamide, triethylamine, diethyl acetamide, ethanol and ethyl acetate, propylene carbonate, ethylene carbonate, and diethyl carbonate. 11. The method of claim 10, wherein the anolyte solvent comprises 60-100 volume % polar solvent and 0-40 volume % apolar solvent. An electrolytic cell for oxidizing alkali metal monosulfide or alkali metal polysulfide, comprising:
composed of an anode; an anolyte solution comprising an alkali metal monosulfide, an alkali metal polysulfide, or mixtures thereof, and an anolyte solvent that partially dissolves elemental sulfur; an anolyte compartment further comprising an anolyte solution inlet and an anolyte solution outlet;
composed of a cathode; contains a catholyte comprising molten alkali metal; a catholyte compartment further comprising a catholyte outlet;
configured to selectively transport alkali ions; an alkali ion conductive membrane substantially impermeable to anions, the anolyte solvent, and dissolved sulfur;
is electrically coupled to the anode and the cathode,
oxidizing alkali metal monosulfide or polysulfide in said anolyte compartment to form liquid elemental sulfur and alkali metal ions;
causing the alkali metal ions to pass from the anolyte compartment through the alkali ion conductive membrane to the catholyte compartment;
a source of electrical potential configured to reduce the alkali metal ion in the catholyte compartment to form a liquid elemental alkali metal; and
an elemental sulfur precipitation zone in which the liquid elemental sulfur forms a second liquid phase and is separated from the anolyte solution; and
a sulfur outlet for removal of liquid elemental sulfur from the electrolytic cell disposed at a position lower than the anolyte solution outlet
An electrolytic cell comprising a. 20. The electrolytic cell of claim 19, wherein the alkali ion conductive membrane partially comprises an alkali metal conductive ceramic or glass ceramic. 20. The electrolytic cell of claim 19, wherein the alkali ion conductive membrane comprises a solid MSICON (Metal Super Ion CONducting) material, and M is Na or Li. 20. The method of claim 19, wherein the anolyte solvent is N,N-dimethylaniline, quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene, cyclohexane, fluorobenzene, trifluorobenzene, 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 An electrolytic cell comprising at least one solvent selected from acetamide, triethylamine, diethyl acetamide, ethanol and ethyl acetate, propylene carbonate, ethylene carbonate, and diethyl carbonate. 20. The electrolytic cell of claim 19, wherein the anolyte solvent comprises 60-100 volume % polar solvent and 0-40 volume % non-polar solvent. A plurality of coupled electrolytic cells comprising a first electrolytic cell according to claim 19 and a second electrolytic cell according to claim 19, wherein the anolyte solution inlet of the second electrolytic cell is the anolyte of the first electrolytic cell a plurality of coupled electrolytic cells connected to the solution outlet. A plurality of coupled electrolytic cells comprising a first electrolytic cell according to claim 19 , a second electrolytic cell according to claim 19 , a third electrolytic cell according to claim 19 , and a fourth electrolytic cell according to claim 19 . wherein the anolyte solution inlet of the fourth electrolytic cell is connected to the anolyte solution outlet of the third electrolytic cell, and the anolyte solution inlet of the third electrolytic cell is connected to the anolyte solution outlet of the second electrolytic cell, and the anolyte solution inlet of the second electrolytic cell is connected to the anolyte solution outlet of the first electrolytic cell.

Images