WO2001068947A1 - Electrolyte and diaphragm for fused salt electrolysis - Google Patents
Electrolyte and diaphragm for fused salt electrolysis Download PDFInfo
- Publication number
- WO2001068947A1 WO2001068947A1 PCT/US2000/007265 US0007265W WO0168947A1 WO 2001068947 A1 WO2001068947 A1 WO 2001068947A1 US 0007265 W US0007265 W US 0007265W WO 0168947 A1 WO0168947 A1 WO 0168947A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- diaphragm
- cell
- sodium
- electrolyte
- cathode
- Prior art date
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
- C25C7/005—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells of cells for the electrolysis of melts
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
- C25C3/02—Electrolytic production, recovery or refining of metals by electrolysis of melts of alkali or alkaline earth metals
Definitions
- This invention relates to an electrolytic cell for the electrolysis of fused alkali chloride salts to produce alkali metals such as sodium and lithium.
- Electrolytic cells for the electrolysis of fused alkali chloride salts are used widely in industry to produce alkali metals, such as sodium and lithium, that are difficult to reduce to a metallic state.
- alkali metals such as sodium and lithium
- a major cost for operating these cells is the cost of electric power. Since the early 1970's, the cost of electric power has increased sharply. Development of more energy-efficient electrolysis processes, therefore, has become increasingly important.
- the electrolytic recovery of sodium metal is commercially carried out via non-aqueous molten chloride salt electrolysis. While the discussion below concentrates on sodium manufacture, the features relating to cell design and mechanical operation also apply to manufacture of lithium and other alkali metals.
- the electrolyte typically used is a mixture of sodium chloride with other salts to lower the melt temperature.
- a cell operating temperature of about 600 degrees C is ordinarily employed.
- Ullmann lists a suitable mixture as 28 wt% NaCl, 25 wt% CaC12 and 47 t% BaC12.
- US Patent No. 2,850,442 discloses a mixture of about 26 wt% NaCl, 60 wt% SrC12, and 14 wt% BaC12. Adaev et al, Zh. Prikl. Khim.
- a modern Downs cell typically contains four graphite carbon rods that serve as anodes. Each anode is surrounded by a concentric steel cylinder that serves as a cathode. In operation, sodium is deposited on the inside surface of the steel cathodes and chlorine gas is liberated at the graphite anodes. Typically, in a cell with four pairs of electrodes, the chlorine is collected in four shafts from the anodes while the sodium is collected in a single compartment covering all four cathodes.
- a hydraulically permeable diaphragm is used to separate the cathode and anode compartments to prevent back-mixing and reaction of the sodium and chlorine. It typically is made of steel mesh, and has a relatively short life of about two months because it corrodes and plugs with debris. When the diaphragm develops any major holes, it must be replaced because the holes lead to back- mixing and reaction of the sodium and chlorine, in turn reducing current efficiency and energy efficiency. Replacement of the diaphragm is a labor- intensive and costly step.
- any new electrolyte composition must not increase the melting temperature of the mixture or the tendency of associated metal salts to precipitate out of solution, and must produce a sodium metal of acceptable purity.
- a new electrolyte composition also should improve the operability and "health" of the cell.
- the present invention provides an electrolytic cell for the production of chlorine and an alkali metal from a fused chloride electrolyte having at least one graphite rod anode, a concentric cylindrical cathode surrounding each anode, a rigid cylindrical diaphragm positioned between said anode and cathode, and insulated aligning means that engage the diaphragm and the anode or cathode to concentrically align said diaphragm as it is placed in position (i.e., the diaphragm is self-aligning).
- the aligning means are sets of insulating rollers, conveniently mounted on the outer surface of the diaphragm to engage the inner surface of the cathode as the diaphragm is inserted into position.
- the self-aligning diaphragm has a buoyancy chamber that causes the diaphragm assembly to float in the electrolyte.
- the self-aligning diaphragm mechanically locks into position by a locking mechanism mounted on top of the diaphragm that engages a sodium collector structure mounted above the cathode.
- the invention also provides the following electrolytic compositions for the production of chlorine and sodium:
- Figure 1A and IB are vertical and horizontal cross-sections, respectively, of a typical Downs cell having four sets of electrodes.
- Figure 2 illustrates one embodiment of the self-aligning diaphragm of this invention.
- Figure 3 illustrates a second embodiment of the self-aligning diaphragm of this invention.
- This invention provides several substantial improvements to the mechanical and electrolytic elements of an electrolytic cell for the production of molten alkali metal and gaseous chlorine by the electrolysis of fused chloride salts. While the mechanical and electrolytic improvements are discussed separately one or more of these improvements may be incorporated in a single design of an improved electrolysis cell. While the description is given in terms of electrolyzing sodium chloride, the mechanical improvements of the improved cell may also be used for the electrolysis of lithium and other alkali metals.
- Figures 1A and IB respectively, illustrate vertical and horizontal cross- sections of a typical Downs-type cell having four sets of electrodes.
- the cell has a cylindrical brick-lined, steel casing 1.
- Cylindrical graphite anodes 2 project upwardly through the bottom of the steel casing.
- the cathodes 3 are steel cylinders having two diametrically opposed steel arms 4 that project outside the cell casing to serve as electric terminals.
- Cylindrical steel screen mesh diaphragms 5 are suspended about midway in the annular space between the anodes and the cathodes.
- Annular collector ring 6 collects molten metal that rises in the fused electrolyte 7 from the cathodes.
- Outlet tube 8 carries the metal collected in the collector ring to the outside of the cell.
- Gas dome 9 carries gaseous anodic products formed by the electrolysis. Elements 5, 6, 8 and 9 are supported in the cell by means not shown, typically by rigid means such as conventional bolts, fasteners or welding.
- a steel-mesh screen currently is employed as a diaphragm to separate the cathode and anode compartments.
- the diaphragm prevents back-mixing and reaction of the cathodically produced alkali metal and anodically produced chlorine.
- the relatively short life of the diaphragm combined with the labor- intensive method of replacing and aligning them, is a major cost factor in the operation of the Downs cell.
- such diaphragms are of limited effectiveness, in part due to alignment deficiencies, with groups of cells typically only achieving overall current efficiencies in the range of 80% to 90%.
- the diaphragm designs of the current invention overcome these limitations of the prior art by providing a self-aligning diaphragm.
- self-aligning it is meant that the diaphragm aligns itself concentric with, and at a predetermined distance from, the cathode and anode as the diaphragm is inserted into place.
- Figure 2 illustrates one embodiment of the self-aligning diaphragm provided by this invention.
- the diaphragm K) is made of conventional screening or slotted materials such as disclosed in prior art, but has the following features that make it self-aligning. Instead of a rigid, bolted connection between the diaphragm and the sodium collector U .
- the diaphragm floats in the electrolyte and rests against the bottom of the sodium collector, separated from it electrically by a number of mechanically rugged electrical insulator supports 12, such as a modified spark plug, fastened at intervals around the top of the diaphragm. These insulator supports are so fastened that their bottoms will rest on the cathode 14 when the floating diaphragm is in its lowest position. Also fastened to the top of the diaphragm is a buoyancy chamber 3 , a hat-like device containing small bleed holes in the top. The volume of the buoyancy chamber is sized so that the diaphragm will rest against the sodium collector in normal operation, buoyed up by the upflowing chlorine gas collected in the chamber.
- This movable diaphragm has at least two sets of insulating roller-spacers 15, one near the bottom of the diaphragm and one set higher up on the diaphragm, to provide the self-aligning feature. Only the upper set is shown.
- the clearance between the roller-spacers and the cathode wall is sufficient to allow the diaphragm assembly to freely move up and down, but not so large as to allow mis-alignment that would unnecessary increase in the path for current flow, which would increase the cell voltage required for operation.
- the buoyancy chamber fills with chlorine gas evolved at the anode, the remaining amount of chlorine bypassing the buoyancy chamber and going to the collection system.
- the chlorine in the buoyancy chamber floats the entire diaphragm assembly upwards until the upper part of the insulator supports rests against the sodium collector.
- need for a bolted or rigid connection to the collector is avoided, eliminating the costly "pit" operation required for repair and replacement by the conventional design.
- chlorine evolution at the anode stops and the chlorine in the buoyancy chamber slowly escapes through the small bleed holes.
- the chamber gradually fills with molten electrolyte and loses its buoyancy, causing the diaphragm assembly to sink until the insulator supports rest on the top surface of the cathode.
- This up-and-down motion can be deliberately achieved by turning the cell current on and off.
- the up-and-down motion is very useful in breaking and shearing off calcium dendrites that often form during cell operation, causing partial shorts, arcing and loss of current efficiency.
- the sets of insulating roller-spacers keep the diaphragm centered and prevent it from shorting against the electrodes during this operation.
- Means other than insulated rollers may be employed to self-align the diaphragm, and the means may be mounted on the diaphragm, cathode, anode, or other structural element of the cell.
- FIG. 3 illustrates a second embodiment of the self-aligning diaphragm of this invention.
- the diaphragm 20 is made of conventional screening or slotted materials.
- the diaphragm has a metal piece 21 rigidly fastened to its top portion that contains a number of L-shaped slots, of which slot 22 is shown in side view. Fitted into each slot is a rod, of which rod 23 is shown in end view. These rods are rigidly fastened to the sodium collector, but are not fastened to the diaphragm.
- the slots and rods are positioned such that the diaphragm assembly can be inserted from below the sodium collector, with the vertical portion of each slot in line with each matching rod, then moved upward and rotated (as if screwing a glass jar onto its lid) to the end of the slot's travel.
- a small upward widening of the slot at its end locks the diaphragm in position within the cathode 24.
- the clearance between the widened slot locks and the rods is sufficient for a slight sidewards free movement of the diaphragm.
- this slightly moveable diaphragm In order for this slightly moveable diaphragm to be self-aligning, it has at least two sets of insulating roller-spacers 25, one near the bottom of the diaphragm and one set higher up on the diaphragm to provide the self-aligning feature of this design. Only the upper set is shown in this Figure.
- the clearance between the roller- spacers and the cathode wall is sufficient to allow the diaphragm to be rotated into position, but not so large as to allow mis-alignment that would unnecessary increase the path for current flow, which would increase cell voltage required for operation.
- Means other than insulated rollers may be employed to self-align the diaphragm, and the means may be mounted on the diaphragm, cathode, anode, or other structural element of the cell.
- the insulator supports and the insulating roller spacers for the above diaphragms can be made of any insulating materials which have adequate strength and mechanical properties at bath temperatures and are insoluble in the molten electrolyte, such as silicon nitride (S N ⁇ alumina (ALO 3 ) and other materials known to those skilled in the art.
- the axles on the rollers can be any rigid material which is suitable for the bath environment, preferably a metal such as steel.
- the electrolyte composition used in a sodium cell influences operability of the cell in several ways. Not only is the melting temperature of the overall composition important, but also the variation in melting temperature as the ratio of ingredient changes. Due to poor cell circulation, both electrolyte composition and temperature vary in different parts of the cell. Typically, the bottom of the cell is cooler than the rest, creating problems due to deposition of electrolyte ingredients and impurities. These depositions cause productivity and current efficiency of the cell to deteriorate, requiring the cell to be shut down for repair and/or replacement of the diaphragm. Other problems may occur, causing a phenomenon referred to in the trade as "smoking.” The smoothness of operation of a cell, while maintaining good productivity, is referred to as the "health" of the cell.
- cells with poor operability are referred to as “sick" cells.
- the electrolyte For the health of a cell, it is important that the electrolyte have a wide ratio of compositions that remain entirely molten over a wide range of temperatures.
- the ability of a substance to promote free movement of the fused electrolyte salts over a range of temperatures is referred to herein as its "fluxing" ability.
- the strongest effect on lowering melting temperature is between 0.2% to 10% LiCl addition.
- the rise in temperature between 20% and 40% LiCl indicates the presence of a eutectic within this composition range for this quaternary mixture.
- a range of 0.2 to 15 wt% addition of LiCl is preferred for reasons of economy, corresponding to a composition of about 20 to 40 wt% NaCl; 30 to 50 wt% BaCl 2 ; 15 to 30 wt% CaCl 2 ; and 0.2 to 13.0 wt% LiCl.
- the EMF gap increases from about 0.1 volts based on the standard EMFs between Na and Li at 600°C to about 0.2 volts. This is a big increase in the EMF gap, and means that at low LiCl concentrations the driving force is for Na deposition without Li deposition, a favorable result. Similar results were obtained for the strontium- based bath.
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electrolytic Production Of Metals (AREA)
- Secondary Cells (AREA)
- Manufacture And Refinement Of Metals (AREA)
Abstract
Description
Claims
Priority Applications (6)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE60013331T DE60013331T2 (en) | 2000-03-15 | 2000-03-15 | ELECTROLYTE AND DIAFRAGMA FOR MELT FLUOR ELECTROLYSIS |
MXPA02009013A MXPA02009013A (en) | 2000-03-15 | 2000-03-15 | Electrolyte and diaphragm for fused salt electrolysis. |
EP00915009A EP1272690B1 (en) | 2000-03-15 | 2000-03-15 | Electrolyte and diaphragm for fused salt electrolysis |
CA002398069A CA2398069A1 (en) | 2000-03-15 | 2000-03-15 | Electrolyte and diaphragm for used salt electrolysis |
JP2001567822A JP2003527487A (en) | 2000-03-15 | 2000-03-15 | Electrolyte and diaphragm for electrolysis of molten salt |
PCT/US2000/007265 WO2001068947A1 (en) | 2000-03-15 | 2000-03-15 | Electrolyte and diaphragm for fused salt electrolysis |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
PCT/US2000/007265 WO2001068947A1 (en) | 2000-03-15 | 2000-03-15 | Electrolyte and diaphragm for fused salt electrolysis |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2001068947A1 true WO2001068947A1 (en) | 2001-09-20 |
Family
ID=21741165
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US2000/007265 WO2001068947A1 (en) | 2000-03-15 | 2000-03-15 | Electrolyte and diaphragm for fused salt electrolysis |
Country Status (6)
Country | Link |
---|---|
EP (1) | EP1272690B1 (en) |
JP (1) | JP2003527487A (en) |
CA (1) | CA2398069A1 (en) |
DE (1) | DE60013331T2 (en) |
MX (1) | MXPA02009013A (en) |
WO (1) | WO2001068947A1 (en) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2009019250A (en) * | 2007-07-13 | 2009-01-29 | Osaka Titanium Technologies Co Ltd | Method and apparatus for producing metal |
Citations (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR1259880A (en) * | 1960-06-16 | 1961-04-28 | Solvay | Process for the production of sodium by electrolysis of molten salt baths |
DE1162575B (en) * | 1959-12-21 | 1964-02-06 | Ethyl Corp | Process for the production of pure sodium by fused salt electrolysis |
US3257297A (en) * | 1961-02-17 | 1966-06-21 | Ici Ltd | Production of sodium |
GB1151654A (en) * | 1966-04-08 | 1969-05-14 | Du Pont | Electrolytic Cells |
FR2066836A1 (en) * | 1969-09-03 | 1971-08-13 | Blinov Alexandr | |
WO1999005343A1 (en) * | 1997-07-25 | 1999-02-04 | E.I. Du Pont De Nemours And Company | Fused chloride salt electrolysis cell |
US6063247A (en) * | 1998-08-07 | 2000-05-16 | E.I. Du Pont De Nemours And Company | Modified electrolyte and diaphragm for fused salt electrolysis |
-
2000
- 2000-03-15 MX MXPA02009013A patent/MXPA02009013A/en active IP Right Grant
- 2000-03-15 JP JP2001567822A patent/JP2003527487A/en active Pending
- 2000-03-15 DE DE60013331T patent/DE60013331T2/en not_active Expired - Fee Related
- 2000-03-15 WO PCT/US2000/007265 patent/WO2001068947A1/en active IP Right Grant
- 2000-03-15 CA CA002398069A patent/CA2398069A1/en not_active Abandoned
- 2000-03-15 EP EP00915009A patent/EP1272690B1/en not_active Expired - Lifetime
Patent Citations (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE1162575B (en) * | 1959-12-21 | 1964-02-06 | Ethyl Corp | Process for the production of pure sodium by fused salt electrolysis |
FR1259880A (en) * | 1960-06-16 | 1961-04-28 | Solvay | Process for the production of sodium by electrolysis of molten salt baths |
US3257297A (en) * | 1961-02-17 | 1966-06-21 | Ici Ltd | Production of sodium |
GB1151654A (en) * | 1966-04-08 | 1969-05-14 | Du Pont | Electrolytic Cells |
FR2066836A1 (en) * | 1969-09-03 | 1971-08-13 | Blinov Alexandr | |
WO1999005343A1 (en) * | 1997-07-25 | 1999-02-04 | E.I. Du Pont De Nemours And Company | Fused chloride salt electrolysis cell |
US6063247A (en) * | 1998-08-07 | 2000-05-16 | E.I. Du Pont De Nemours And Company | Modified electrolyte and diaphragm for fused salt electrolysis |
Also Published As
Publication number | Publication date |
---|---|
DE60013331D1 (en) | 2004-09-30 |
EP1272690A1 (en) | 2003-01-08 |
MXPA02009013A (en) | 2003-04-25 |
EP1272690B1 (en) | 2004-08-25 |
JP2003527487A (en) | 2003-09-16 |
DE60013331T2 (en) | 2005-09-08 |
CA2398069A1 (en) | 2001-09-20 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US5024737A (en) | Process for producing a reactive metal-magnesium alloy | |
US5254232A (en) | Apparatus for the electrolytic production of metals | |
EP0638133B1 (en) | Anode-cathode arrangement for aluminum production cells | |
CA1043732A (en) | Electrochemical cell | |
US2760930A (en) | Electrolytic cell of the diaphragm type | |
RU2680039C1 (en) | Systems and methods for purifying aluminum | |
EP0998595B1 (en) | Fused chloride salt electrolysis cell | |
WO2006007863A1 (en) | Electrolysis apparatus with solid electrolyte electrodes | |
US3254010A (en) | Refining of silicon and germanium | |
US4737247A (en) | Inert anode stable cathode assembly | |
US6811676B2 (en) | Electrolytic cell for production of aluminum from alumina | |
US2919234A (en) | Electrolytic production of aluminum | |
US6063247A (en) | Modified electrolyte and diaphragm for fused salt electrolysis | |
US2848397A (en) | Electrolytic production of metallic titanium | |
WO2006046800A1 (en) | Method for manufacturing high purity indium and apparatus therefor | |
US4440610A (en) | Molten salt bath for electrolytic production of aluminum | |
EP1272690B1 (en) | Electrolyte and diaphragm for fused salt electrolysis | |
AU659247B2 (en) | Cell for the electrolysis of alumina preferably at low temperatures | |
US2507096A (en) | Process for the electrolytic refining or lead or lead alloys containing bismuth | |
US4108741A (en) | Process for production of aluminum | |
US4597839A (en) | Method and apparatus for production of a metal from metallic oxide ore | |
US4495037A (en) | Method for electrolytically obtaining magnesium metal | |
JP4557565B2 (en) | Electrolyzer | |
US4547272A (en) | Method and apparatus for production of a metal from metallic oxide ore using a composite anode | |
US2898276A (en) | Production of titanium |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
AK | Designated states |
Kind code of ref document: A1 Designated state(s): CA JP MX ZA |
|
AL | Designated countries for regional patents |
Kind code of ref document: A1 Designated state(s): AT BE CH CY DE DK ES FI FR GB GR IE IT LU MC NL PT SE |
|
121 | Ep: the epo has been informed by wipo that ep was designated in this application | ||
DFPE | Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101) | ||
WWE | Wipo information: entry into national phase |
Ref document number: 2398069 Country of ref document: CA |
|
WWE | Wipo information: entry into national phase |
Ref document number: 2000915009 Country of ref document: EP |
|
ENP | Entry into the national phase |
Ref country code: JP Ref document number: 2001 567822 Kind code of ref document: A Format of ref document f/p: F |
|
WWE | Wipo information: entry into national phase |
Ref document number: PA/a/2002/009013 Country of ref document: MX |
|
WWP | Wipo information: published in national office |
Ref document number: 2000915009 Country of ref document: EP |
|
WWG | Wipo information: grant in national office |
Ref document number: 2000915009 Country of ref document: EP |