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.

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 separating the liquid elemental sulfur from the anolyte 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 a first alkali ion conductive membrane configured to selectively transport alkali ions, the membrane separating a first anolyte compartment configured with a first anode and a first catholyte compartment configured with a first cathode; introducing into the first anolyte compartment a first 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 first catholyte compartment a first catholyte, wherein the catholyte comprises at least one of a molten alkali metal and a solvent; applying an electric current to the first electrolytic cell thereby: i. oxidizing the alkali metal sulfide or polysulfide in the first anolyte compartment to form a higher level polysulfide and alkali ions; ii. causing the alkali metal ions to pass through the first alkali ion conductive membrane from the first anolyte compartment to the first catholyte compartment; and iii. reducing the alkali metal ions in the first catholyte compartment to form elemental alkali metal; transporting anolyte 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 separating a second anolyte compartment configured with a second anode and a second catholyte compartment configured with a cathode and a second catholyte; applying an electric current to the second electrolytic cell thereby: i. oxidizing polysulfide in the second 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 second anolyte compartment to the second catholyte compartment; and iii. reducing the alkali metal ions in the second catholyte compartment to form liquid elemental alkali metal; allowing liquid elemental sulfur to become saturated in the anolyte in the second electrolytic cell; and separating the liquid elemental sulfur from the anolyte 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 second 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 second electrolytic 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 first alkali ion conductive membrane and the second 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 first alkali ion conductive membrane and the second alkali ion conductive membrane comprises in part an alkali metal conductive ceramic or glass ceramic.

16. The process according to claim 10, wherein the first alkali ion conductive membrane and the second 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

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) 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:

(2) 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.

(3) FIGS. 2A and 2B show schematic processes for converting alkali metal hydrosulfide to alkali metal polysulfide and recovering hydrogen sulfide.

(4) FIG. 3 shows a schematic cross-section of an electrolytic cell which utilizes many of the features within the scope of the invention.

(5) 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

(6) 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.

(7) 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.

(8) The alkali metal (M) and hydrogen react with the oil at about 350 C. and 300-2000 psi according to the following initial reactions:
RSR+2M+H.sub.2.fwdarw.RH+RH+M.sub.2S
R,R,RN+3M+1.5H.sub.2.fwdarw.RH+RH+RH+M.sub.3N

(9) Where R, R, R represent portions of organic molecules or organic rings.

(10) 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 C.)
M.sub.3N+3H.sub.2S.fwdarw.3MHS+NH.sub.3

(11) 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.

(12) 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; 4x6) 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.

(13) 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]

(14) 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.

(15) 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)

(16) Where Y is a molar amount of sulfur added to the sodium hydrosulfide.

(17) 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.

(18) 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.

(19) 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.

(20) 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.

(21) 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 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.

(22) 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.3xO.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.(1xy)(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.2xPO.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.

(23) 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.

(24) 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.

(25) 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.

(26) 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.

(27) 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.

(28) 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.

(29) 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.

(30) 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.

(31) In the case of the alkali metal being sodium, the following typical reactions may occur in the electrolytic cell 300:

(32) At the Cathode:
Na.sup.++e.fwdarw.Na

(33) At the Anode:
Na.sub.2S.sub.x.fwdarw.Na.sup.++e.sup.+Na.sub.2S.sub.(2x)1)
Na.sub.2S.sub.x.fwdarw.Na.sup.++e.sup.+Na.sub.2S.sub.x+x/16S.sub.82)

(34) Where x ranges from 0 to about 8.

(35) 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.

(36) 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

(37) 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 C. conductivity and activation energy reported by May. G. May, J. Power Sources, 3, 1 (1978).

(38) TABLE-US-00002 TABLE 2 Conductivities of NaSICON, LTP, Beta alumina at 25 C., 120 C. Conductivity mS/cm Temperature C. NaSICON LTP Beta alumina (est) 25 0.9 0.9 0.7 120 6.2 1.5 7.9

(39) 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.

(40) 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.

(41) 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 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.

(42) 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.

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

(44) Removing an alkali metal continuously or semi-continuously in liquid form from the cell.

(45) Removing sulfur continuously or semi-continuously in liquid form from the cell.

(46) Removing high alkali metal polysulfides and dissolved sulfur continuously or semi-continuously from the electrolytic cell, thereby reducing polarization of the anode by sulfur.

(47) 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.

(48) 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.

(49) 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.