US20160108532A1

US20160108532A1 - Method and apparatus for liquid metal electrode connection in production or refining of metals

Info

Publication number: US20160108532A1
Application number: US14/886,725
Authority: US
Inventors: Adam Clayton Powell, IV; Matthew EARLAM; Robert Steve TUCKER; Alton TABEREAUX; Gregory Hardie
Original assignee: Infinium Inc
Current assignee: Infinium Inc
Priority date: 2014-10-17
Filing date: 2015-10-19
Publication date: 2016-04-21
Also published as: WO2016061577A1

Abstract

In some aspects, the invention relates to apparatuses and methods for connecting a liquid first metal cathode to a current source of an electrolytic cell comprising a conduit having a first and second end, liquid first metal disposed at the first end of the conduit, a solid first metal disposed at the second end of the conduit, and a solid conductor portion in electrical contact with the solid first metal.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. provisional patent application Ser. No. 62/065,405, filed Oct. 17, 2014, entitled “Aluminum Cathode Current Collector for Aluminum Molten Salt Electrolysis”, the disclosure of which is hereby incorporated by reference in its entirety for all purposes.
All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. The patent and scientific literature referred to herein establishes knowledge that is available to those skilled in the art. The issued patents, applications, and other publications that are cited herein are hereby incorporated by reference to the same extent as if each was specifically and individually indicated to be incorporated by reference. In the case of inconsistencies, the present disclosure will prevail.

GOVERNMENT SUPPORT

This invention was made with government support under Contract No. DE-AR0000412 awarded by the United States Department of Energy. The government has certain rights in the invention.

FIELD OF THE INVENTION

The invention relates to apparatuses and methods for production of metals via molten salt electrolysis.

BACKGROUND OF THE INVENTION

The Hall-Heroult cell revolutionized aluminum production in 1886 (U.S. Pat. No. 400,664; herein incorporated by reference in its entirety) by reducing aluminum oxide dissolved in a molten salt electrolyte, with a consumable carbon anode that reacts with the oxygen to form carbon dioxide. However, the Hall-Heroult molten salt electrolysis remains limited in cost and energy efficiency for several reasons. The Hall-Heroult process electrical energy efficiency is below 55% (“U.S. Energy Requirements for Aluminum Production,” U.S. Department of Energy, EERE Report, February 2007; herein incorporated by reference in its entirety), and generates about 0.9 kg CO₂-equivalent (CO₂e) direct greenhouse gas (GHG) emissions per kg of aluminum produced, leaving much room for improvement. Moreover, production of carbon anodes adds considerable energy use and expense. The industry has spent the past 125 years trying new innovations. Production of the required carbon anode is costly, as well as carbon- and energy-intensive. The liquid aluminum product on the bottom of the cell acts as the cathode, and a cell floor made of extruded graphite blocks connects the liquid aluminum to steel cathode current collector bars (U.S. Pat. No. 2,378,142; herein incorporated by reference in its entirety). This cathode arrangement works well when the molten salt electrolyte is less dense than the liquid aluminum product, such that there is a large graphite area and low current density through the graphite. In contrast, if the molten salt electrolyte is more dense than the liquid aluminum product, the aluminum floats to the top of the cell. In a conventional cell, this is problematic because it would be difficult to connect the carbon anode to the bath without either shorting it to the floating aluminum or creating a large distance between the floating aluminum cathode and broad carbon anode in the bath below it.
The aluminum industry has tried various approaches to non-consumable inert anodes to avoid the high cost of carbon anodes. Approaches have included cermets, generally of doped nickel ferrites with base/noble metal alloys, transition metals which form conducting surface oxides, composites which combine these two, aluminum bronzes generally with copper, and porous graphite with fuel gas flow to the outer surface. See, e.g., U.S. Pat. Nos. 4,397,729; 4,960,494; 5,254,232; 5,865,980; 6,030,518; 6,113,758; 6,126,799; 6,217,739; 6,248,227; 6,284,562; 6,322,969; 6,372,009; 6,372,119; 6,416,649; 6,423,195; 6,423,204; 6,521,115; 6,758,991; 6,821,312; 6,878,247; 7,033,469; 7,235,161; 7,431,812; 7,507,322; and 8,366,891; and Sankar Namboothiri, Mark P. Taylor, John J. J. Chen, Margaret M. Hyland and Mark Cooksey, “Aluminum production options with a focus on the use of a hydrogen anode: a review,” Asia-Pacific Journal of Chemical Engineering 2(5):442-447 (2007); each herein incorporated by reference in its entirety.
Use of a solid electrolyte barrier, such as stabilized zirconia, between the molten salt and anode presents an effective barrier between the metal produced at the cathode and oxidizing gases produced at the anode (see, e.g., U.S. Pat. Nos. 3,562,135; 4,108,743; 5,942,097; 5,976,345; 6,187,168; and 6,299,742; each herein incorporated by reference in its entirety). This prevents back-reaction between aluminum product and anode gas such as CO₂, enables the use of a sealed cell creating an inert or reducing environment, and optionally, a enables floating liquid aluminum product pad (see, e.g., U.S. Provisional Patent Application 62/011,652, filed Jun. 13, 2014 and International Patent Application Publication WO 2015/006331; each herein incorporated by reference in its entirety). Other benefits of the solid electrolyte include: enabling new classes of inert anodes or the use of natural gas reductant, eliminating carbon anode costs and contaminants, reducing or eliminating direct greenhouse gas emissions, clean anode emissions and no perfluorocarbon generation, reducing thermal losses by using an insulated steel vessel, simplified feeding, stabilizing the cell during oxide depletion due to lower zirconia resistance at high temperature, and vertical electrodes leading to much higher productivity per unit cell footprint. The floating aluminum pad can further simplify metal collection, enable use of sintered oxide fines in some cases, reduce contamination due to broken solid electrolyte tubes and release of anode material, and increase magnetic field for improved magneto-hydrodynamic stirring (MHD) (see, e.g., U.S. Provisional Patent Application 62/011,652 filed Jun. 13, 2014 and International Patent Application Publication WO 2015/006331; each herein incorporated by reference in its entirety).
Development of the solid oxide membrane (SOM) electrolysis process has provided an alternative method for refinement of metal oxides (see, e.g, U.S. Pat. Nos. 5,976,345, and 6,299,742; each herein incorporated by reference in its entirety). The process as applied to metal production consists of a metal cathode, a molten salt electrolyte bath that dissolves the metal oxide that is in electrical contact with the cathode, a solid electrolyte oxygen ion conducting membrane (SOM) typically consisting of zirconia stabilized by yttria (YSZ) or other low valence oxide-stabilized zirconia, for example, magnesia- or calcia-stabilized zirconia (MSZ or CSZ, respectively) in ion-conducting contact with the molten salt bath, an anode in ion-conducting contact with the SOM, and a power source for establishing a potential between the cathode and anode. Metal cations are reduced to metal at the cathode, and oxygen ions migrate through the membrane to the anode where they are oxidized to produce oxygen gas or other oxides. The SOM blocks back-reaction between anode and cathode products. It also blocks ion cycling, which is the tendency for subvalent cations to be re-oxidized at the anode, by removing the electronic connection between the anode and the metal ion containing molten salt because the SOM conducts only oxide ions, not electrons (see, U.S. Pat. Nos. 5,976,345, and 6,299,742; each herein incorporated by reference in its entirety); however the process runs at high temperatures, typically 1000-1300° C. in order to maintain high ionic conductivity of the SOM.
The SOM electrolysis can proceed with high- or low-density electrolytes, and in some embodiments combines several desired characteristics of metal oxide reduction technology including, for example, 1) low-cost, low-toxicity metal oxide feedstock to avoid costs of producing, dehydrating and handling toxic metal chlorides; 2) insulated molten salt containment to reduce heat loss from the frozen sidewall; 3) separation between anode gas and molten salt for reduced emission of HF contaminated gases and heat recovery from the voluminous anode gas; 4) low anode-cathode distance for low resistance and excess heat production; 5) scale-down ability to mini-mills and on-site sale of liquid metal to customers; 6) ability to retrofit existing metal smelters; 7) use of clean, inexpensive fuel (e.g., natural gas) with high energy content and half the CHG emissions of expensive carbon anodes, optionally with uncontaminated carbon dioxide capture for sequestration or sale as a by-product; and/or 8) optional oxygen-producing inert anode without contamination of the oxygen by-product by HF, fluorine or other toxic gases. Moreover, anodes that switch between fueled and inert operation can take advantage of fluctuating electricity costs due to intermittent renewable energy sources or low demand periods (such as overnight).
In addition, advantages particular to primary production of metal, e.g., aluminum, include, e.g., eliminating carbon anode costs, clean emissions with no anode effect from SOM selectivity, anode flexibility and energy efficiency, reduction of thermal loss, simpler metal collection, simplified feeding and improved electrode geometry.
Anode Flexibility and Energy Efficiency.
The zirconia solid electrolyte tubes can accommodate either liquid silver or perovskite inert anodes that produce pure oxygen by-product or fueled (e.g., natural gas) anodes emitting only water and carbon dioxide. Hot swapping anode assemblies are also contemplated, as is exchanging current collectors while leaving zirconia tubes in place to change between inert and fueled (e.g., natural gas) operation for GHG and cost savings.
Reducing Thermal Loss.
The molten salt (cryolite) bath used in the Hall-Heroult cell requires a “frozen sidewall” of cryolite for containment since it dissolves all refractory oxides and accelerates oxidation of most metals. This frozen sidewall withdraws an enormous amount of thermal energy from the process, which increases energy consumption dramatically. With SOM technology, oxygen originates inside the SOM tube(s), and the bath produces little to no gas. Thus, a metal container can contain the salts without a frozen side wall, there is no oxidant (e.g., oxygen, carbon dioxide or water) outside of the tube(s) that would oxidize the metal container, and anode gas originates in the SOM and does not pick up corrosive volatiles (e.g., HF) so it is easy to seal and inert the container using very little inert gas, e.g., argon or nitrogen, preventing oxidation of a metal container. Such a configuration permits advantageous operation in a sealed, e.g., welded, steel vessel surrounded by thermal insulation, eliminating much of the thermal losses.
In designs such as those of U.S. Provisional Patent Application 62/011,652 and International Patent Application Publication WO 2015/006331, a floating liquid aluminum cathode would require connection through the top of the cell, as side connection would lead to very high current density and overpotential through a graphite side-wall. Likewise for an aluminum pad below the bath, in a cell with higher than traditional productivity and current per unit cell footprint, a traditional carbon block cathode would have very high current density and overpotential. High overpotential reduces cell energy efficiency. If connecting through the top, cathode bus connections must be interspersed with anode bus connections in a complex top plate.
One approach to connecting to a floating pad is to use vertical graphite connectors. The Hoopes cell (U.S. Pat. No. 1,534,320; herein incorporated by reference in its entirety) employs graphite connectors and is in widespread use for production of high-purity aluminum. While possible to operate at high current density, the Hoopes cell requires very high voltage and energy consumption in part due to the high overpotential in these conductors.
Thus, there remains a need for a high-conductivity metal connection to a metal pad that results in low overpotential and increased energy efficiency. There also remains a need for a less complex top plate and manifold.
The present invention provides a high-conductivity metal connection to the floating or submerged aluminum pad, resulting in low overpotential and energy usage, and a less complex top plate and manifold.

BRIEF SUMMARY OF THE INVENTION

In one aspect, an apparatus is provided comprising: (a) a conduit having a first end and a second end; (b) a liquid first metal disposed at the first end of the conduit and within the conduit; (c) a solid first metal disposed at the second end of the conduit and within the conduit; (d) a solid conductor portion in electrical contact with the solid first metal; and (e) a cooling mechanism disposed at the second end of the conduit; wherein at least a portion of the liquid first metal and the solid first metal are in electrical contact, and the solid conductor disposed to provide electrical contact between the solid first metal and an electrical source outside the conduit.
In some embodiments, the conduit does not dissolve into the first metal more than about 5% by weight. In some embodiments, the conduit comprises carbon, silicon carbide, titanium diboride, boron nitride, silicon nitride, aluminum nitride, aluminum oxide or an aluminum-bearing compound with an element that does not dissolve into the first metal.
In some embodiments, the apparatus further comprises a conduit sheath disposed around at least a portion of the conduit.
In some embodiments, the cooling mechanism comprises a jacket disposed around a portion of the conduit, wherein the jacket has an inlet and an outlet.
In some embodiments, air, gas, and/or a cooling liquid are disposed within at least a portion of the jacket.
In some embodiments, the solid conductor comprises the first metal.
In some embodiments, the apparatus further comprises a first container configured to contain at least a portion of the liquid first metal.
In some embodiments, the first container comprises a well, tube or ledge extending from a second container.
In some embodiments, the apparatus further comprises a vacuum port disposed along at least a portion of the conduit.
In some embodiments, at least a portion of the conduit and solid conductor portion comprise a mould for extraction of the solid first metal.
In some embodiments, the apparatus further comprises a second container for holding a molten electrolyte, the second container having an interior surface; an anode in ion-conducting contact with the molten electrolyte; and a power source for generating an electric potential between the anode and the liquid first metal.
In some embodiments, during generation of the electric potential, the first metal is recovered from an oxide of the first metal dissolved in the molten electrolyte and the first metal collects on the floor of the second container.
In some embodiments, during generation of the electric potential, the first metal is recovered from an oxide of the first metal dissolved in the molten electrolyte and the first metal collects on a top surface of the molten electrolyte when the electrolyte is disposed in the second container.
In some embodiments, a portion of a side wall of the second container defines a first passage between the interior of the second container and the first container.
In some embodiments, the first metal comprises aluminum, magnesium, lithium, beryllium, silicon, strontium, potassium, sodium, barium, scandium, titanium, silicon or calcium. In some embodiments, the first metal comprises aluminum or magnesium. In some embodiments, the first metal comprises aluminum.
In another aspect, an apparatus is provided comprising a conduit having a first end and a second end; a first container disposed at the second end of the conduit, and configured to contain at least a portion of a liquid first metal within the conduit and a liquid second metal within the conduit, the liquid second metal having higher density than the liquid first metal; and a solid conductor portion in electrical contact with the second liquid metal; wherein the solid conductor is disposed to provide electrical contact between the second liquid metal and an electrical source outside the conduit.
In some embodiments, the apparatus further comprises a second container disposed at the first end of the conduit, and configured to hold a molten electrolyte, the second container having an interior surface; a cooling mechanism disposed around at least a portion of the first container; an anode disposed in ion-conducting contact with the molten electrolyte; and a power source for generating an electric potential between the anode and the first liquid metal; wherein the conduit comprises a ledge extending from the interior of the second container to the first container.
In some embodiments, the apparatus further comprises a solid conductor portion in electrical contact with the liquid second metal, and wherein at least a portion of the liquid first metal and the liquid second metal are in electrical contact, the liquid second metal disposed to provide electrical contact between the liquid first metal and an electrical source outside the conduit.
In some embodiments, the conduit does not dissolve into the first metal more than about 5% by weight. In some embodiments, the conduit comprises carbon, silicon carbide, titanium diboride, boron nitride, aluminum nitride, silicon nitride, aluminum oxide or an aluminum-bearing compound with an element that does not dissolve into the first metal more than about 5% by weight.
In some embodiments, the liquid second metal does not dissolve into the first metal more than about 5% by weight.
In another aspect, a method for electrically connecting a liquid first metal cathode to a current source of an electrolytic cell is provided comprising: providing a conduit having a first end and a second end; providing a liquid first metal disposed at the first end of the conduit and within the conduit; providing a solid first metal disposed at the second end of the conduit and within the conduit; providing a solid conductor portion in electrical contact with the solid first metal; and providing a cooling mechanism disposed at the second end of the conduit; wherein at least a portion of the liquid first metal and the solid first metal are in electrical contact, and the solid conductor provides electrical contact between the solid first metal and an electrical source outside the conduit.
In some embodiments, the conduit does not dissolve into the first metal more than about 5% by weight.
In some embodiments, the conduit comprises carbon, silicon carbide, titanium diboride, boron nitride, silicon nitride, aluminum nitride, aluminum oxide or an aluminum-bearing compound with an element that does not dissolve into the first metal more than about 5% by weight.
In some embodiments, the methods further comprise providing a conduit sheath disposed around at least a portion of the conduit.
In some embodiments, the cooling mechanism comprises air, gas, and/or a cooling liquid.
In some embodiments, the solid conductor comprises the first metal.
In some embodiments, the methods further comprise providing a first container configured to contain at least a portion of the liquid first metal.
In some embodiments, the first container comprises a well, tube, or ledge extending from a second container.
In some embodiments, at least a portion of the liquid first metal is drawn into the conduit via vacuum.
In some embodiments, the methods further comprise providing a second container holding a molten electrolyte, the second container having an interior surface; and providing a power source for generating an electric potential between the anode and the cathode.
In some embodiments, during generation of the electric potential, the first metal collects on the floor of the second container.
In some embodiments, during generation of the electric potential, the first metal collects on a top surface of the molten electrolyte when the electrolyte is disposed in the second container.
In some embodiments, a temperature gradient develops along the first metal and extends to form the electrical contact with the solid metal portion of the current collector.
In some embodiments, the temperature gradient exists between the operating temperature of the cell and the melting point of the first metal disposed in the conduit.
In another aspect, a method for electrically connecting a liquid first metal cathode to a current source of an electrolytic cell is provided comprising: providing a conduit having a first end and a second end; providing the liquid first metal disposed at the first end of the conduit and within the conduit; providing a first container disposed at the second end of the conduit, the first container containing at least a portion of a liquid first metal and a liquid second metal, the liquid second metal having higher density than the liquid first metal; and providing a solid conductor portion in electrical contact with the liquid second metal; wherein at least a portion of the liquid first metal and the liquid second metal are in electrical contact, and the solid conductor provides electrical contact between the liquid second metal and an electrical source outside the conduit.
In some embodiments, the conduit does not dissolve into the first metal more than about 5% by weight.
In some embodiments, the conduit comprises carbon, titanium diboride, silicon carbide, boron nitride, silicon nitride, aluminum nitride, aluminum oxide or an aluminum-bearing compound with an element that does not dissolve into the first metal more than about 5% by weight.
In some embodiments, the method further comprises providing a conduit sheath disposed around at least a portion of the conduit.
In some embodiments, the first container comprises a well, tube, or ledge extending from a second container.
In some embodiments, at least a portion of the liquid first metal is drawn into the conduit via vacuum.
In some embodiments, the method further comprises providing a second container holding a molten electrolyte, the second container having an interior surface; and providing a power source for generating an electric potential between the anode and the cathode.
In some embodiments, during generation of the electric potential, the first metal collects on a top surface of the molten electrolyte when the electrolyte is disposed in the second container.
In some embodiments, the temperature gradient exists between the operating temperature of the cell and the melting point of the first metal disposed in the conduit.
In some embodiments, the liquid first metal is drawn from the second container toward the liquid second metal.
In some embodiments, the liner comprises carbon, boron nitride, titanium diboride, SiC, Si₃N₄, aluminum nitride, or fused alumina. In some embodiments, the liner comprises titanium diboride, boron nitride, Si₃N₄, or fused alumina. In some embodiments, the liner comprises boron nitride, Si₃N₄, or fused alumina. In some embodiments, the liner comprises titanium diboride. In some embodiments, the liner comprises boron nitride. In some embodiments, the liner comprises Si₃N₄. In some embodiments, the liner comprises fused alumina.
In some embodiments, a portion of a side wall of the second container defines a first passage between the interior of the second container and the first container.
In some embodiments, a sheath is disposed around at least a portion of the solid oxygen ion-conducting membrane, the sheath extending from a level below the first metal-molten electrolyte interface to a level above the top surface of the first metal, and the sheath preventing contact between the first metal being recovered and the solid oxygen ion-conducting membrane. In some embodiments, the sheath comprises boron nitride, Si₃N₄, aluminum nitride, or fused alumina. In some embodiments, the sheath comprises Si₃N₄, or fused alumina. In some embodiments, the sheath comprises boron nitride or Si₃N₄. In some embodiments, the sheath comprises boron nitride. In some embodiments, the sheath comprises Si₃N₄. In some embodiments, the sheath comprises fused alumina.
In some embodiments, the solid oxygen ion-conducting membrane and sheath define an annular space between the membrane and sheath, the apparatus further comprising a gas inlet in communication with the annular space. In some embodiments, the solid oxygen ion-conducting membrane and sheath define an annular space between the membrane and sheath, the method further comprising providing a gas in the annular space.
In some embodiments, the first metal comprises aluminum, magnesium, lithium, beryllium, silicon, strontium, potassium, sodium, barium, scandium, titanium, silicon or calcium. In some embodiments, the first metal comprises aluminum, magnesium, lithium, beryllium, silicon, strontium, potassium, or calcium. In some embodiments, the first metal comprises aluminum or magnesium. In some embodiments, the first metal comprises aluminum. In some embodiments, the first metal comprises magnesium.
In some embodiments, the solid conductor comprises the first metal.
In some embodiments, a tapping well is provided on the first container.
In some embodiments, at least a portion of the second container is thermally insulated.
In some embodiments, the first container comprises a well, tube or ledge extending from the second container. In some embodiments, the first container comprises a tube or ledge extending from the second container. In some embodiments, the first container comprises a well or ledge extending from the second container. In some embodiments, the first container comprises a well or tube extending from the second container. In some embodiments, the first container comprises a well extending from the second container. In some embodiments, the first container comprises a tube extending from the second container. In some embodiments, the first container comprises a ledge extending from the second container.
In some embodiments, a liquid second metal is disposed in the first container, the liquid second metal having low miscibility in the liquid first metal. In some embodiments, liquid first metal is drawn from the second container toward the liquid second metal.
In some embodiments, at least a portion of the first metal collects as a liquid on a top surface of the molten electrolyte and extends through the conduit to the first container.
In some embodiments, a conduit sheath is disposed around at least a portion of the conduit. In some embodiments, the conduit sheath comprises steel.
In some embodiments, a temperature gradient develops along the first metal and extends to form the electrical contact with the solid metal portion. In some embodiments, a temperature gradient exists between the operating temperature of the cell and the melting point of the first metal disposed in the conduit.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are illustrative only and are not intended to be limiting.

FIG. 1. An illustrative embodiment of an electrolytic cell configuration and method according to an embodiment of the invention.

FIG. 2. An illustrative embodiment of an electrolytic cell configuration and method according to an embodiment of the invention.

FIG. 3. An illustrative embodiment of an electrolytic cell configuration and method according to an embodiment of the invention.

FIG. 4. An illustrative embodiment of an electrolytic cell configuration and method according to an embodiment of the invention.

FIG. 5. An illustrative embodiment of an electrolytic cell configuration and method according to an embodiment of the invention.

FIG. 6. An illustrative embodiment of an electrolytic cell configuration and method according to an embodiment of the invention.

FIG. 7. Shows voltage and current vs. time according to an illustrative embodiment of the invention.

FIG. 8. Shows voltage and current vs. time according to an illustrative embodiment of the invention.

FIG. 9. Shows voltage and current in a ramp from 0 to 2.0 V, according to an illustrative embodiment of the invention.

FIG. 10. Calculated temperature distribution for a 0.8 m long aluminum lead with a 100 A/cm²current density.

FIG. 11. Calculated energy loss through the current collector vs. length for current density 20-100 A/cm².

DETAILED DESCRIPTION

As used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the content clearly dictates otherwise.
The term “about” is used herein to mean approximately, in the region of, roughly, or around. When the term “about” is used in conjunction with a numerical range, it modifies that range by extending the boundaries above and below the numerical values set forth. The term “about” is used herein to modify a numerical value above and below the stated value by a variance of 20%.
The present invention provides designs and methods for a conduit that enables a solid metal to maintain electrical contact with a liquid metal to form a current collector. In some embodiments, the current collector comprises a non-carbon metallic electrical connection to a floating or submerged liquid metal pad in an metal reduction cell. In some embodiments, the non-carbon metallic electrical connection exhibits high-conductivity.
In one aspect, an apparatus is provided comprising: (a) a conduit having a first end and a second end; (b) a conduit sheath disposed around at least a portion of the conduit; (c) a liquid first metal disposed at the first end of the conduit; (d) a solid first metal disposed at the second end of the conduit; (e) a solid conductor portion in electrical contact with the solid first metal; and (f) a cooling mechanism disposed at the second end of the conduit; wherein at least a portion of the liquid first metal and the solid first metal are in electrical contact, and the solid conductor disposed to provide electrical contact connects between the solid first metal and an electrical source outside the conduit.
In some embodiments, the apparatus further comprises: a second container for holding a molten electrolyte, the second container having an interior surface; a liner disposed along at least a portion of the interior surface of the second container; a solid oxygen ion-conducting membrane disposed to be in ion-conducting contact with the electrolyte when the molten electrolyte is disposed in the second container; an anode in ion-conducting contact with the solid oxygen ion-conducting membrane, the solid oxygen ion-conducting membrane disposed between the anode and the molten electrolyte; and a power source for generating an electric potential between the anode and the liquid first metal.
In another aspect, an apparatus is provided comprising: (a) a conduit having a first end and a second end; (b) a first container disposed at the second end of the conduit, and configured to contain at least a portion of a liquid first metal and a liquid second metal, the liquid second metal having higher density than the liquid first metal; (c) a second container disposed at the second end of the conduit, and configured to hold a molten electrolyte, the second container having an interior surface; (d) a solid conductor portion in electrical contact with the liquid first metal; (e) a cooling mechanism disposed around at least a portion of the first container; (f) a liner disposed along at least a portion of the interior surface of the second container; (g) an anode disposed in electrical contact with the molten electrolyte; and (h) a power source for generating an electric potential between the anode and the first liquid metal; wherein the conduit comprises a ledge extending from the interior of the second container to the first container, and wherein the solid conductor is disposed to provide electrical contact between the solid first metal and an electrical source outside the conduit.
In another aspect, an apparatus is provided comprising: (a) a conduit having a first end and a second end; (b) a liquid first metal disposed at the first end of the conduit; and (c) a first container disposed at the second end of the conduit, the first container configured to contain at least a portion of the first liquid metal and a liquid second metal, the liquid second metal having higher density than the first liquid metal; wherein at least a portion of the liquid first metal and the liquid second metal are in electrical contact, the liquid second metal disposed to provide electrical contact between the liquid first metal and an electrical source outside the conduit.
In another aspect, a method for electrically connecting a liquid first metal cathode to a current source of an electrolytic cell is provided, comprising: (a) providing a conduit having a first end and a second end; (b) providing a conduit sheath disposed around at least a portion of the conduit; (c) providing a liquid first metal disposed at the first end of the conduit; (d) providing a solid first metal disposed at the second end of the conduit; (e) providing a solid conductor portion in electrical contact with the solid first metal; and (f) providing a cooling mechanism disposed at the second end of the conduit; wherein at least a portion of the liquid first metal and the solid first metal are in electrical contact, and the solid conductor provides electrical contact between the solid first metal and an electrical source outside the conduit.
In some embodiments, the method further comprises; (g) providing a second container holding a molten electrolyte, the second container having an interior surface; (h) providing a liner disposed along at least a portion of the interior surface of the second container; (i) providing a solid oxygen ion-conducting membrane disposed in ion-conducting contact with the molten electrolyte; and (j) a power source for generating an electric potential between the anode and the cathode.
In another aspect, a method for electrically connecting a liquid first metal cathode to a current source of an electrolytic cell is provided, comprising: (a) providing a conduit having a first end and a second end; (b) providing the liquid first metal disposed at the first end of the conduit; (c) providing a first container disposed at the second end of the conduit, the first container containing at least a portion of a liquid first metal and a liquid second metal, the liquid second metal having higher density than the liquid first metal; (d) providing a solid conductor portion in electrical contact with the solid first metal; and (e) providing a cooling mechanism disposed at the second end of the conduit; wherein at least a portion of the liquid first metal and the liquid second metal are in electrical contact, and the solid conductor provides electrical contact between the solid first metal and an electrical source outside the conduit.
In some embodiments, the method further comprises; (f) providing a second container holding a molten electrolyte, the second container having an interior surface; (g) providing a liner disposed along at least a portion of the interior surface of the second container; (h) providing a solid oxygen ion-conducting membrane disposed in ion-conducting contact with the molten electrolyte; and (i) a power source for generating an electric potential between the anode and the cathode.
In some embodiments, the conduit does not dissolve into the first metal. In some embodiments, the conduit comprises graphitic carbon, silicon carbide, boron nitride, aluminum oxide or an aluminum-bearing compound with an element that does not dissolve into the first metal. In some embodiments, a vacuum port is disposed along at least a portion of the conduit. In some embodiments, at least a portion of the liquid first metal is drawn into the conduit via vacuum.
In some embodiments, at least a portion of the conduit and solid conductor portion comprise a mould for extraction of the solid first metal.
In some embodiments, the apparatus and/or methods further comprise a first container configured to contain at least a portion of the liquid first metal. In some embodiments, the first container comprises a well, tube or ledge extending from a second container.
In some embodiments, the apparatus and/or methods further comprise a cooling mechanism. In some embodiments, the cooling mechanism comprises air, gas, and/or a cooling liquid. In some embodiments, the cooling mechanism comprises an inert gas, and/or a cooling liquid. In some embodiments, the cooling mechanism comprises an inert gas. In some embodiments, the cooling mechanism comprises a cooling liquid. In some embodiments, the cooling liquid comprises oil.
In some embodiments, the apparatus and/or methods further comprise a cathode conductor, at least a portion of which is disposed in electrical contact with the molten electrolyte. In some embodiments, the apparatus and/or methods further comprise a cathode conductor, at least a portion of which is disposed in electrical contact with the molten electrolyte and the liquid first metal.
In some embodiments, the interior surface of the second container includes a floor and the floor comprises carbon.
In some embodiments, the liner extends from the floor upward along the interior surface of the second container to a level that prevents contact between the liquid first metal and the interior surface of the second container.
In some embodiments, during generation of the electric potential, the first metal is recovered from an oxide of the first metal dissolved in the molten electrolyte and the first metal collects on the floor of the second container.
In some embodiments, the liner extends from a first level below the first metal-molten electrolyte interface to a second level above the first metal-molten electrolyte interface, and the liner prevents contact between the first metal-molten electrolyte interface and the interior surface of the second container.
In some embodiments, during generation of the electric potential, the first metal is recovered from an oxide of the first metal dissolved in the molten electrolyte, the first metal collects on the floor of the second container, and the liner extends to a level that prevents contact between the first metal-molten electrolyte interface and the interior surface of the second container.
In some embodiments, the solid conductor comprises the first metal.
In some embodiments, the second container comprises steel. In some embodiments, the second container is electrically isolated from the cathode.
In some embodiments, at least a portion of the metal floats on the molten electrolyte. In some embodiments, during generation of the electric potential at least a portion of the metal collects on the floor of the second container.
In some embodiments, during generation of the electric potential, the first metal is recovered from an oxide of the first metal dissolved in the molten electrolyte, the first metal collects on the floor of the second container.
In some embodiments, during generation of the electric potential, the first metal is recovered from an oxide of the first metal dissolved in the molten electrolyte and the first metal collects on a top surface of the molten electrolyte when the electrolyte is disposed in the second container, the liner extends from a first level below the first metal-molten electrolyte interface to a second level above the first metal-molten electrolyte interface, and the liner prevents contact between the first metal-molten electrolyte interface and the interior surface of the second container.
In some embodiments, the liner comprises carbon, boron nitride, titanium diboride, SiC, Si₃N₄, or fused alumina. In some embodiments, the liner comprises titanium diboride, boron nitride, Si₃N₄, or fused alumina. In some embodiments, the liner comprises boron nitride, Si₃N₄, or fused alumina. In some embodiments, the liner comprises titanium diboride. In some embodiments, the liner comprises boron nitride. In some embodiments, the liner comprises Si₃N₄. In some embodiments, the liner comprises fused alumina.
In some embodiments, a portion of a side wall of the second container defines a first passage between the interior of the second container and the first container.
In some embodiments, a sheath is disposed around at least a portion of the solid oxygen ion-conducting membrane, the sheath extending from a level below the first metal-molten electrolyte interface to a level above the top surface of the first metal, and the sheath preventing contact between the first metal being recovered and the solid oxygen ion-conducting membrane. In some embodiments, the sheath comprises boron nitride, Si₃N₄, or fused alumina. In some embodiments, the sheath comprises Si₃N₄, or fused alumina. In some embodiments, the sheath comprises boron nitride or Si₃N₄. In some embodiments, the sheath comprises fused alumina. In some embodiments, the sheath comprises boron nitride. In some embodiments, the sheath comprises Si₃N₄.
In some embodiments, the solid oxygen ion-conducting membrane and sheath define an annular space between the membrane and sheath, the apparatus further comprising a gas inlet in communication with the annular space. In some embodiments, the solid oxygen ion-conducting membrane and sheath define an annular space between the membrane and sheath, the method further comprising providing a gas in the annular space.
In some embodiments, the first metal comprises aluminum, magnesium, lithium, beryllium, silicon, strontium, potassium, or calcium. In some embodiments, the first metal comprises aluminum or magnesium. In some embodiments, the first metal comprises aluminum. In some embodiments, the first metal comprises magnesium.
In some embodiments, the solid conductor comprises the first metal.
In some embodiments, a tapping well is provided on the first container.
In some embodiments, at least a portion of the second container is thermally insulated.
In some embodiments, the first container comprises a well, tube or ledge extending from the second container. In some embodiments, the first container comprises a tube or ledge extending from the second container. In some embodiments, the first container comprises a well or ledge extending from the second container. In some embodiments, the first container comprises a well or tube extending from the second container. In some embodiments, the first container comprises a well extending from the second container. In some embodiments, the first container comprises a tube extending from the second container. In some embodiments, the first container comprises a ledge extending from the second container.
In some embodiments, a liquid second metal is disposed in the first container, the liquid second metal having low miscibility in the liquid first metal. In some embodiments, liquid first metal is drawn from the second container toward the liquid second metal.
In some embodiments, at least a portion of the first metal collects as a liquid on a top surface of the molten electrolyte and extends through the conduit to the first container.
In some embodiments, a conduit sheath is disposed around at least a portion of the conduit. In some embodiments, the conduit sheath comprises steel.
In some embodiments, a temperature gradient develops along the first metal and extends to form the electrical contact with the solid metal portion. In some embodiments, a temperature gradient exists between the operating temperature of the cell and the melting point of the first metal disposed in the conduit.
In one aspect, an apparatus is provided comprising: (a) a conduit having a first end and a second end; (b) optionally, a conduit sheath disposed around at least a portion of the conduit; (c) a liquid first metal disposed at the first end of the conduit; (d) a solid first metal disposed at the second end of the conduit; (e) a solid conductor portion in electrical contact with the solid first metal; and (f) a cooling mechanism disposed at the second end of the conduit; wherein at least a portion of the liquid first metal and the solid first metal are in electrical contact, and the solid conductor disposed to provide electrical contact connects between the solid first metal and an electrical source outside the conduit.
In some embodiments, the apparatus further comprises: a second container for holding a molten electrolyte, the second container having an interior surface; a liner disposed along at least a portion of the interior surface of the second container; a solid oxygen ion-conducting membrane disposed to be in ion-conducting contact with the electrolyte when the molten electrolyte is disposed in the second container; an anode in ion-conducting contact with the solid oxygen ion-conducting membrane, the solid oxygen ion-conducting membrane disposed between the anode and the molten electrolyte; and a power source for generating an electric potential between the anode and the liquid first metal.
In another aspect, an apparatus is provided comprising: (a) a conduit having a first end and a second end; (b) a first container disposed at the second end of the conduit, and configured to contain at least a portion of a liquid first metal and a liquid second metal, the liquid second metal having higher density than the liquid first metal; (c) a second container disposed at the second end of the conduit, and configured to hold a molten electrolyte, the second container having an interior surface; (d) optionally, a solid conductor portion in electrical contact with the liquid first metal; (e) a cooling mechanism disposed around at least a portion of the first container; (f) a liner disposed along at least a portion of the interior surface of the second container; (g) an anode disposed in electrical contact with the molten electrolyte; and (h) a power source for generating an electric potential between the anode and the first liquid metal; wherein the conduit comprises a ledge extending from the interior of the second container to the first container, and wherein the solid conductor is disposed to provide electrical contact between the solid first metal and an electrical source outside the conduit.
In another aspect, an apparatus is provided comprising: (a) a conduit having a first end and a second end; (b) a liquid first metal disposed at the first end of the conduit; and (c) a first container disposed at the second end of the conduit, the first container configured to contain at least a portion of the first liquid metal and a liquid second metal, the liquid second metal having higher density than the first liquid metal; wherein at least a portion of the liquid first metal and the liquid second metal are in electrical contact, the liquid second metal disposed to provide electrical contact between the liquid first metal and an electrical source outside the conduit.
In another aspect, a method for electrically connecting a liquid first metal cathode to a current source of an electrolytic cell is provided, comprising: (a) providing a conduit having a first end and a second end; (b) providing a conduit sheath disposed around at least a portion of the conduit; (c) providing a liquid first metal disposed at the first end of the conduit; (d) providing a solid first metal disposed at the second end of the conduit; (e) providing a solid conductor portion in electrical contact with the solid first metal; and (f) providing a cooling mechanism disposed at the second end of the conduit; wherein at least a portion of the liquid first metal and the solid first metal are in electrical contact, and the solid conductor provides electrical contact between the solid first metal and an electrical source outside the conduit.
In some embodiments, the methods further comprise; providing a second container holding a molten electrolyte, the second container having an interior surface; providing a liner disposed along at least a portion of the interior surface of the second container; providing a solid oxygen ion-conducting membrane disposed in ion-conducting contact with the molten electrolyte; and providing a power source for generating an electric potential between the anode and the cathode.
In another aspect, a method for electrically connecting a liquid first metal cathode to a current source of an electrolytic cell is provided, comprising: (a) providing a conduit having a first end and a second end; (b) providing the liquid first metal disposed at the first end of the conduit; (c) providing a first container disposed at the second end of the conduit, the first container containing at least a portion of a liquid first metal and a liquid second metal, the liquid second metal having higher density than the liquid first metal; (d) providing a solid conductor portion in electrical contact with the solid first metal; and (e) providing a cooling mechanism disposed at the second end of the conduit; wherein at least a portion of the liquid first metal and the liquid second metal are in electrical contact, and the solid conductor provides electrical contact between the solid first metal and an electrical source outside the conduit.
In some embodiments, the methods further comprise; providing a second container holding a molten electrolyte, the second container having an interior surface; providing a liner disposed along at least a portion of the interior surface of the second container; providing a solid oxygen ion-conducting membrane disposed in ion-conducting contact with the molten electrolyte; and providing a power source for generating an electric potential between the anode and the cathode.
One illustrative embodiment is an aluminum connection from the liquid first metal pad all the way to an external cathode bus near the environment temperature. Because the typical cell operating temperature at 950° C. is hundreds of degrees above the aluminum melting point at 660° C., this aluminum connection will be liquid on the end of the aluminum pad in the cell, and solid on the end of the cathode bus connection.
The liquid first metal can be contained in a conduit comprising materials with low solubility in the liquid metal (e.g, wherein the liquid metal is aluminum), such as but not limited to carbon, e.g. graphitic carbon, or silicon carbide, or boron nitride, or aluminum oxide, or other aluminum-bearing compounds with elements having low solubility in aluminum. Any of these materials can be used as dense solids, powders, or coatings. The conduit allows the first metal (e.g., aluminum) to maintain conductivity, and advantageously does not react appreciably with and/or does not dissolve into the first metal. Thus, in some embodiments the conduit comprises materials with low solubility in the liquid first metal. In some embodiments the conduit does not dissolve into the liquid first metal. In some embodiments the conduit does not dissolve into the liquid first metal more than about 5% by weight. In some embodiments the conduit does not dissolve into the liquid first metal more than about 4% by weight. In some embodiments the conduit does not dissolve into the liquid first metal more than about 3% by weight. In some embodiments the conduit does not dissolve into the liquid first metal more than about 2% by weight. In some embodiments the conduit does not dissolve into the liquid first metal more than about 1% by weight. In some embodiments the conduit does not dissolve into the liquid first metal more than about 0.5% by weight. In some embodiments the conduit comprises materials with low solubility in aluminum. In some embodiments the conduit comprises carbon, silicon carbide, boron nitride, aluminum oxide, or aluminum-bearing compounds comprising elements having low solubility in the liquid first metal. In some embodiments the conduit comprises carbon, silicon carbide, boron nitride, aluminum oxide, or aluminum-bearing compounds comprising elements having low solubility in aluminum. In some embodiments the conduit comprises carbon, silicon carbide, boron nitride, or aluminum oxide. In some embodiments the conduit comprises carbon, silicon carbide, or boron nitride. In some embodiments the conduit comprises silicon carbide, boron nitride, aluminum oxide, aluminum nitride, or aluminum-bearing compounds comprising elements having low solubility in the liquid first metal. In some embodiments the conduit comprises silicon carbide, boron nitride, or aluminum oxide. In some embodiments the conduit comprises boron nitride, or aluminum oxide. In some embodiments the conduit comprises carbon. In some embodiments the conduit comprises graphitic carbon. In some embodiments the conduit comprises silicon carbide. In some embodiments the conduit comprises boron nitride. In some embodiments the conduit comprises aluminum oxide. In some embodiments the conduit comprises aluminum-bearing compounds comprising elements having low solubility in aluminum.
Because these conduit materials are relatively brittle, it is advantageous to provide a conduit sheath, e.g. a strong steel sheath, around at least a portion of the conduit, both for mechanical support to minimize stresses on the conduit, and also to limit the amount of metal that can flow out of the conduit in the event of breach of the conduit. The conduit sheath advantageously is strong at operating temperature of the cell and resistant to heat and air. In some embodiments, the conduit sheath improves mechanical robustness and/or corrosion resistance. The conduit sheath may be comprised of materials other than steel, such as titanium or its alloys, nickel or its alloys, or other materials with melting point above about 1400° C. and creep strength above about 1 MPa throughout the device temperature range. Thus, in some embodiments, the conduit sheath comprises materials with a melting point above about 1400° C. and creep strength above about 1 MPa throughout the device temperature range. In some embodiments, the conduit sheath comprises steel, titanium, alloys of titanium, nickel, or alloys of nickel. In some embodiments, the conduit sheath comprises steel, titanium, or nickel. In some embodiments, the conduit sheath comprises steel. In some embodiments, the conduit sheath comprises titanium. In some embodiments, the conduit sheath comprises nickel.
A schematic embodiment is shown in FIG. 1, with the current collector using aluminum as an exemplary first liquid metal. FIG. 1 shows an exemplary current collector and electrolytic cell configuration with high-density salt and floating aluminum pad, with a liquid aluminum ledge and an insulated solid aluminum plate or rod current collector. An anode (100) is shown in contact with a solid oxygen ion-conducting electrolyte (105). The molten salt (110) is contained within a second container that is thermally insulated (115) and further contains at least one cathode conductor (120) and a seal pot (125) on the side. A gas inlet (130) for inert gas, e.g., argon, is disposed between the annulus of the SOM and an insulating sheath (135). Metal oxide, e.g., alumina, is fed into the container and reduced to liquid aluminum metal (140), which settles on top of the molten electrolyte, and can be removed via a tap on the side of the container. A liner (145) is disposed along the interior surface of the second container, and extends from a first level below the liquid aluminum-molten electrolyte interface to a second level above the liquid aluminum-molten electrolyte interface, and prevents contact between the liquid aluminum-molten electrolyte interface and the interior surface of the second container. Oxygen ions migrate from the molten salt (110) through the solid electrolyte (105) to the liquid metal anode (100), where they form dissolved oxygen atoms. The oxygen atoms diffuse through the liquid metal anode to the gas phase where they form oxygen gas that evolves from the anode (See, e.g., U.S. Pat. No. 8,658,007; herein incorporated by reference in its entirety). The current collector comprises liquid aluminum, a first container (150) (e.g., a ledge in this embodiment), and the solid first metal (155) and a conduit (160). The first container (150) (e.g., horizontal tube and/or ledge) contains liquid aluminum and extends from the molten electrolyte bath with a temperature gradient between the cell temperature and aluminum melting point. Thus, a cooling gradient is provided along the tube and/or ledge. The solid first metal (155) comprising aluminum plates or shafts connects at the end of the tube and/or ledge away from the bath and anode. The solid aluminum connects directly to the external cathode bus. A conduit (160) is disposed around at least a portion of the current collector, which maintains conductivity of the aluminum. Optional embodiments further provide a steel sheath disposed around at least a portion of the conduit and/or a high-conductive metal (e.g., solid conductor portion) at the environment end of the current collector.
Another schematic embodiment is shown in FIG. 2. FIG. 2 shows an exemplary electrolytic cell configuration with high-density salt and floating aluminum pad, with an insulating current collector tube or conduit drawing liquid aluminum into contact with solid aluminum. An anode (200) is shown in contact with a solid oxygen ion-conducting electrolyte (205). The molten salt (210) is contained within a second container that is thermally insulated (215) and further contains at least one cathode conductor (220) and a seal pot (225) on the side. A gas inlet (230) for inert gas, e.g., argon, is disposed between the annulus of the SOM and an insulating sheath (235). Metal oxide, e.g., alumina, is fed into the container and reduced to liquid aluminum metal (240), which settles on top of the molten electrolyte, and can be removed via a tap on the side of the second container. A liner (245) is disposed along the interior surface of the second container, and extends from a first level below the liquid aluminum-molten electrolyte interface to a second level above the liquid aluminum-molten electrolyte interface, and prevents contact between the liquid aluminum-molten electrolyte interface and the interior surface of the second container. Oxygen ions migrate from the molten salt (210) through the solid electrolyte (205) to the liquid metal anode (200), where they form dissolved oxygen atoms. The oxygen atoms diffuse through the liquid metal anode to the gas phase where they form oxygen gas that evolves from the anode (See, e.g., U.S. Pat. No. 8,658,007; herein incorporated by reference in its entirety). In this embodiment, the current collector comprising a conduit (260) (e.g., vertical tube) draws liquid aluminum upward from the cell toward a solid conductor. The solid first metal (255) comprising solid aluminum plates or shafts connects at the aluminum conductor portion of the conduit away from the bath and anode. In this embodiment, the solid conductor portion is also the solid first metal. The solid aluminum connects directly to the external cathode bus. The conduit (260) is disposed around at least a portion of the liquid first metal (240), which maintains conductivity of the aluminum. Optional embodiments further provide a steel sheath disposed around at least a portion of the conduit and/or a high-conductive metal at the environment end of the current collector.
Both of the arrangements in FIGS. 1 and 2 also apply to a cell with low-density bath and submerged liquid metal pad, in which case the conduit and, optionally, a conduit sheath would have an end submerged into the liquid metal pad below the bath.
It can be advantageous in some embodiments to include a second high-melting conductive material at the environment end of the solid conductor portion, e.g, copper, tungsten, molybdenum, silver or nickel. With such a connector present, if a strong process transient event heats the conductor rapidly and melts the solid conductor, e.g., aluminum, the second conductor will remain solid and maintain a connection to the liquid first metal, e.g., aluminum, avoiding an open connection. In some embodiments, that material is copper or nickel. In some embodiments, that material is copper. In some embodiments, that material is nickel.
Similarly, it can be advantageous to prime the second container with an amount of the liquid first metal portion prior to generating electric potential, such that the liquid first metal portion floats on or submerges in the molten salt depending on the relative densities of the liquid first metal and the molten salt.
Further embodiments provide a liquid first metal, e.g. aluminum, connection from the pad to a liquid second metal that is saturated with the first metal that itself has low solubility in the liquid first metal, e.g. tin, bismuth, or lead. In some embodiments, the liquid second metal comprises tin, bismuth or lead. In some embodiments, the liquid second metal comprises tin. In some embodiments, the liquid second metal comprises bismuth. In some embodiments, the liquid second metal comprises lead. At least a portion of the liquid first metal and liquid second metal are contained in a first container comprising a liner with low solubility in both metals, such as but not limited to carbon, e.g. graphitic carbon, or silicon carbide, or boron nitride, or aluminum oxide, or other aluminum-bearing compounds with elements having low solubility in liquid first metal and the liquid second metal. Any of these materials can be used as dense solids, powders, or coatings. Bismuth and lead have the advantage of minimal interaction with steel, so a break in the carbon, boron nitride, alumina, etc. would not dissolve and puncture steel the way tin would. The liquid second metal has low miscibility with the liquid first metal, e.g, aluminum, and, optionally is more dense than the liquid first metal, e.g., aluminum. The denser second metal is at a lower temperature than the liquid first metal near it, thus liquid first metal above the denser second metal is stratified (colder second-metal-saturated higher-density liquid first metal is on the bottom) and resists convection, minimizing transport of the second metal through the liquid first metal and into the first metal product. Cathode bus connection to the liquid second metal is via a solid conductor portion, e.g., immiscible solid metal, such as a steel connection to bismuth or lead, or carbon connection to tin. Such embodiments have the advantage of eliminating melt interface instability during constant current operation; however aluminum product contamination by the liquid second metal may occur.
An exemplary schematic for other embodiments is shown in FIG. 3. FIG. 3 shows an exemplary electrolytic cell configuration with high-density salt and floating liquid first metal, e.g., aluminum, pad, with a current collector configured as a liquid aluminum ledge with a liquid second metal pool. An anode (300) is shown in contact with a solid oxygen ion-conducting electrolyte (305). The molten salt (310) is contained within a second container that is thermally insulated (315) and further contains at least one cathode conductor (320) and a seal pot (325) on the side. A gas inlet (330) for inert gas, e.g., argon, is disposed between the annulus of the SOM and an insulating sheath (335). Metal oxide, e.g., alumina, is fed into the container and reduced to liquid aluminum metal (340), which settles on top of the molten electrolyte, and can be removed via a tap on the side of the container. A liner (345) is disposed along the interior surface of the second container, and extends from a first level below the liquid aluminum-molten electrolyte interface to a second level above the liquid aluminum-molten electrolyte interface, and prevents contact between the liquid aluminum-molten electrolyte interface and the interior surface of the second container. Oxygen ions migrate from the molten salt (310) through the solid electrolyte (305) to the liquid metal anode (300), where they form dissolved oxygen atoms. The oxygen atoms diffuse through the liquid metal anode to the gas phase where they form oxygen gas that evolves from the anode (See, e.g., U.S. Pat. No. 8,658,007; herein incorporated by reference in its entirety). In this embodiment, the current collector comprising a conduit (360) (e.g., horizontal tube and/or ledge) contains liquid aluminum (340) and extends from the molten electrolyte bath with a temperature gradient between the cell temperature to the first container (350), which contains the cooler second metal (365) in a pool below the ledge.
Another exemplary schematic for such embodiments is shown in FIG. 4. FIG. 4 shows an exemplary electrolytic cell configuration with high-density salt and floating liquid first metal, e.g., aluminum, pad, with a metal current collector configured as an insulating current collector bridge tube to a liquid second metal pool. An anode (400) is shown in contact with a solid oxygen ion-conducting electrolyte (405). The molten salt (410) is contained within a second container that is thermally insulated (415) and further contains at least one cathode conductor (420) and a seal pot (425) on the side. A gas inlet (430) for inert gas, e.g., argon, is disposed between the annulus of the SOM and an insulating sheath (435). Metal oxide, e.g., alumina, is fed into the container and reduced to liquid aluminum metal (440), which settles on top of the molten electrolyte, and can be removed via a tap on the side of the container. A liner (445) is disposed along the interior surface of the second container, and extends from a first level below the liquid aluminum-molten electrolyte interface to a second level above the liquid aluminum-molten electrolyte interface, and prevents contact between the liquid aluminum-molten electrolyte interface and the interior surface of the second container. Oxygen ions migrate from the molten salt (410) through the solid electrolyte (405) to the liquid metal anode (400), where they form dissolved oxygen atoms. The oxygen atoms diffuse through the liquid metal anode to the gas phase where they form oxygen gas that evolves from the anode (See, e.g., U.S. Pat. No. 8,658,007; herein incorporated by reference in its entirety). In this embodiment, a conduit (460) draws liquid aluminum from the cell toward a first container (450) containing an external pool of liquid second metal (465). The aluminum can be drawn upward into the bridge tube by pulling a partial vacuum in it, e.g, from a vacuum port (470) at the top of the bridge.
Another exemplary schematic is shown in FIG. 5. FIG. 5 shows an exemplary electrolytic cell configuration with low-density salt and submerged liquid first metal pad with an insulating current collector tube or conduit drawing liquid aluminum into contact with solid first metal. An anode (500) is shown in contact with molten salt (510) with a submerged first metal (540). A liner (545) is disposed along the bottom of the second container. In this embodiment, the current collector comprising a conduit (560) (e.g., vertical tube) draws liquid first metal upward from the cell. The conduit configured with a cooling jacket, such that cooling fluid, e.g., heat transfer oil, can flow into (590) and through the jacket and exit (575), thereby inducing a cooling effect on the first metal. A hydraulically driven oscillating liquid cooled mould (580) extracts the solid first metal (555) from the conduit via a continuous process to maintain metal inventory. The mould oscillates vertically and a billet cut off saw (585) is used to remove the solid first metal.
In embodiments such as shown in FIG. 5, a continuous tapping technique that does not require first metal accumulation or change in first metal level is achieved. Thus, the device enables a continuous tapping and ingot casting as well as an electrical contact. The solid first metal is vertically extracted from a pool of first metal through an oscillating, liquid cooled vertical mould. The solid billet is continuously removed from the first metal pool in the cell via an oscillating, liquid cooled mould to maintain metal inventory. Mould cooling utilizes, e.g, heat transfer oil to avoid the risks associated with water and aluminum. The mould cooling method is not limited to heat transfer oil, but can also be performed via active liquid or gas cooling (e.g., via circulation through the conduit), or via exposure of the second container to an environment such that the first metal cools and solidifies. Exemplary exposure includes to temperatures less than the operating temperature of the cell. The mould oscillates vertically and slowly creeps upward at the required rate via hydraulic actuators and clamps. At the required interval it resets to a lower position. The billet comprising solid first metal is cut off at an appropriate interval, advantageously by a dedicated vehicle servicing many cells. Oscillation is optional, and prevents and/or minimizes sticking of the first metal to the second container. The upper portion of the solid first metal is clamped. The clamp is oscillating and moving upward slowly to withdraw the solid first metal out of the second container, then releases the solid first metal and re-clamps at a lower section. The lower portion of the clamp remains fixed.
When the device is used as metal caster, the metal will be extracted at a rate dependent on the production of the cell and the billet diameter, and can be calculated by those of ordinary skill in the art via, e.g., volumetric calculations. In some embodiments, to keep the conduit from sticking to the solid metal being extracted from the cell, it is advantageous that the conduit, where the freeze line occurs, is in motion as it continuously sticks for a short distance (both moving in same direction in the cycle), and then is broken by the opposite/shearing motion.
Another embodiment is to provide a tap to remove the solid first metal from the cell.
Also contemplated is a busbar electrical connection to the mould and clamp applying this tapping/casting approach. The forced cooling of the mould would facilitate more flexibility on conductor current density and voltage drop and, advantageously, be more robust to process excursions.
In some embodiments, the flexible busbar is connected to the top and bottom of the mould sleeves to facilitate current connection and avoid voltage potentials between the two, which may cause over heating if there is a sub-optimal contact. It is advantageous not to use the hydraulic cylinders to carry current. Thus, the cylinders are constructed with insulated connections to ensure no current path, even at 10× normal voltage or above.
In some embodiments, the mould operates at a low oscillation frequency—of the order of a couple of Hertz or slower. Length of the freeze zone that attaches is between about 5 mm and 15 mm. In some embodiments, the solid first metal has a surface freeze thickness (or length) that can be easily broken by the sleeve motion. Thus, in some embodiments the diameter of the solid first metal is about 1 cm to about 40 cm. In some embodiments, the diameter of the solid first metal is about 3 cm to about 30 cm. In some embodiments, the diameter of the solid first metal is about 5 cm to about 30 cm. In some embodiments, the diameter of the solid first metal is about 10 cm to about 30 cm. In some embodiments, the diameter of the solid first metal is about 15 cm to about 30 cm. In some embodiments, the diameter of the solid first metal is about 3 cm to about 25 cm. In some embodiments, the diameter of the solid first metal is about 5 cm to about 25 cm. In some embodiments, the diameter of the solid first metal is about 10 cm to about 25 cm. In some embodiments, the diameter of the solid first metal is about 15 cm to about 30 cm. In some embodiments, the diameter of the solid first metal is about 20 cm to about 30 cm.
In some embodiments, the mould caster operates with a sinusoidal frequency, and it is advantageous to match the metal billet extraction velocity on the upstroke followed by a fast-shock shear on the down stroke to achieve shorter disconnection and improve electrical contact. Hydraulic activation would provide such flexibility, as would mechanical analogs. Thus, the caster can operate via variable frequency and amplitudes.
In some embodiments, the apparatus and/or method can be applied to a Hoopes cell (U.S. Pat. No. 1,534,320; herein incorporated by reference in its entirety) with an additional liquid layer of first metal/copper mix (e.g., Al/Cu mix) beneath the molten salt. The current collector will be in contact with the floating liquid metal above the molten salt, but would not extend to the liquid layer of first metal/copper mix. The Hoopes Cell, or Hoopes Process, named for its inventor William Hoopes, is a three-layer liquid metal electrorefining cell for aluminum metal. To create a dense molten metal anode at the bottom of the cell, impure aluminum feed metal is poured into the dense alloy via an underflow wire and mixes with a denser metal such as aluminum-copper alloy. The molten salt bath in the middle layer typically comprises a fluoride of aluminum and barium. The top layer is where the purified aluminum accumulates and acts as the cell cathode.
On application of a DC electric current across the cell, aluminum metal from the aluminum-copper alloy anode on the bottom oxidizes to become aluminum cations at the interface between the lower liquid metal anode and the molten salt bath in the middle layer, and aluminum cations in the bath reduce at its interface with the upper liquid cathode to form pure aluminum metal in the top layer. More electronegative elements than aluminum, such as the copper alloyed with it, iron, silicon, and many other contaminants remain behind in the impure liquid anode. Less electronegative elements, such as magnesium, oxidize with the aluminum to form cations in the molten salt bath, but those cations do not reduce to metal at the cathode. Thus the aluminum product is much purer than the feedstock.
The anode connection on the bottom of the cell, connecting to the aluminum-copper anode, consists of a series of rectangular graphite blocks forming a large flat conductive electrode similar to the cathode connection at the bottom of a Hall-Héroult cell. The cathode connection on the top of the cell, connecting to the high-purity liquid aluminum product layer, consists of graphite electrodes with current densities of 2-20 A/cm². At such high current density, the voltage drop across those graphite electrodes is often as high as one volt, contributing about 3 kWh/kg to the energy consumption per unit aluminum product. The remainder of the cell, including the resistance in the molten salt bath, anode assembly and busbars, contributes about 1.3-2.0 V to the energy consumption, i.e. 4-6 kWh/kg, so the resistance of the graphite cathode connectors represents 30-40% of the total energy consumption of the cell.
The present invention would operate at a voltage drop of about 0.15-0.2 V in the current collector, at current density of 20-100 A/cm². This would significantly reduce the energy consumption of the cell as a whole, and also allow all of the current to pass through a reduced number of smaller diameter current collectors.
In some embodiments, the current collector tube is bent such that gas bubbles, if present, will accumulate at top and can be removed via suction, e.g., from a vacuum port at the top of the tube.
Various cooling techniques are contemplated and may be used within the scope of the invention. For example, active liquid and/or gas cooling (e.g., via circulation through the jacket on the outside of the conduit), or via exposure of the second container to an environment such that the first metal cools and solidifies. Exemplary environments include temperatures less than the operating temperature of the cell, such as an environment that is not insulated or insulated to a lesser extent than that of the second container, thus cooling the first liquid metal to a temperature at which it solidifies.
The cathode conductor is advantageously stable at the bath/metal interface, e.g., between the cathode conductor, liquid first metal, and molten salt). The cathode conductor material is advantageously compatible with liquid metal and molten salt and has high electronic conductivity. In some embodiments, the cathode conductor comprises TiB₂, ZrB₂or composites of TiB₂/graphite. In some embodiments, the cathode conductor comprises TiB₂or ZrB₂. In some embodiments, the cathode conductor comprises TiB₂or composites of TiB₂/graphite. In some embodiments, the cathode conductor comprises TiB₂. In some embodiments, the cathode conductor comprises ZrB₂. In some embodiments, the cathode conductor comprises composites of TiB₂/graphite.
In embodiments wherein the liquid aluminum is submerged beneath the molten salt, the liquid aluminum product rests on a carbon floor to prevent it from contacting the steel of the second container. At the liquid aluminum-molten salt interface level, a liner material prevents aluminum reaction with the steel vessel, and also salt catalysis of aluminum carbide (Al₄C₃) formation. Because the interface level rises and falls with production and withdrawal of liquid aluminum, the liner extends vertically over the full extent of the rising and falling of the interface. In some embodiments, it is advantageous that the liner extend over the entire vertical interior surface of the vessel.
The liner can be one of several materials stable in contact with steel, not soluble in liquid metal, and either not soluble or slow-dissolving in the molten salt bath. Exemplary materials include stabilized zirconia, such as yttria-stabilized zirconia similar to that used in the zirconia tubes, or low-cost calcia-stabilized zirconia; oxide materials such as alumina, e.g. fuse-cast alumina; other compounds such as boron nitride, cerium oxide, TiB₂, SiC, and/or Si₃N₄
The liner materials can be applied by several methods including: insertion of plates, tiles, or bricks; or thermal spray to create an adhering layer of material on the steel and carbon. The liners need not create a perfect seal between the steel vessel and liquid metal or molten salt bath. The inert environment makes the steel vessel stable in the molten salt, and the liner need only slow down metal-steel interaction kinetics sufficiently to prevent liquid first metal from breaking out of the second container, e.g., steel vessel, and to prevent steel from contaminating the liquid first metal beyond the product composition specification.
In some embodiments, the floating liquid first metal configuration uses a dam, tube, or similar partition to create an opening through the floating liquid metal and permit direct feeding of first metal oxide into the molten salt bath. This constraint material preferably has minimal reaction with the first metal and molten salt, such that zirconia, TiB₂, boron nitride, or similar materials will have long lifetime in this function.
In some embodiments, larger metal oxide (e.g., alumina) pellets are fed into the liquid first metal (e.g., aluminum), when the metal oxide has higher density than liquid first metal, such that as long as surface tension does not support the metal oxide, it will sink through the liquid first metal into the salt and dissolve therein.
Floating metal configurations enable simplified tapping using a separate chamber, or seal pot, holding liquid first metal, which is lined with carbon, boron nitride, TiB₂or similar material not soluble in the metal. An opening in the vessel can allow liquid first metal to flow out of the vessel and into the seal pot.
In some embodiments, the floating liquid first metal configuration adds greater flexibility in metal oxide feed morphology: pellets of sintered metal oxide fines which fall to the bottom slowly dissolve in the molten salt, where in the other configurations or the conventional Hall-Héroult cell they would sink through the liquid first metal and accumulate as sludge; less contamination of metal product if a zirconia tube breaks and releases the liquid metal anode, which will likely have higher density than the salt bath as the main candidates are silver, copper and tin; and opportunity for simplified tapping using the liquid metal seal pot with top tapping.
A sealed second container, e.g. steel, can be used to produce liquid first metal and is enabled by creation of a non-oxidizing environment such as a reducing or inert environment. The sealed container prevents ingress of air and/or gas that would react with the liquid first metal or corrode the interior of the container. The non-oxidizing environment prevents or minimizes oxidation of the steel container catalyzed by the molten electrolyte. The non-oxidizing environment exists because oxygen containing components (oxygen gas, carbon dioxide or water vapor) are positioned on the inside of the zirconia tube, and the applied electrical potential drives oxygen into the zirconia tube from the molten salt outside of it. Such configurations enable insulation to reduce thermal energy loss and/or allow the process to run at high salt superheat (above its melting point), which avoids the complication of crust management in conventional systems. Thus, feeding first metal oxide is simplified because there is no crust to break in order to mix the metal oxide into the molten electrolyte. Embodiments where liquid first metal is disposed on top of the molten electrolyte salt are also enabled by the non-oxidizing environment, as the non-oxidizing environment prevents oxidation of the floating metal.
A non-oxidizing environment can be established by any number of ways including, e.g., providing an inert gas and, optionally, electrochemically pumping oxygen by establishing an anode-cathode potential, or by bubbling inert gas below the molten electrolyte and/or the liquid first metal. Bubbling inert gas below the molten electrolyte and/or liquid first metal may further advantageously provide mixing to assist the metal oxide reach the oxide-ion conducting membrane.
The inert gas may comprise a noble gas, e.g., argon, or nitrogen. Other inert gases include SF₆and CF₄. In some embodiments, the inert gas comprises a noble gas or nitrogen. In some embodiments, the inert gas comprises argon or nitrogen. In some embodiments, the inert gas comprises argon. In some embodiments, the inert gas comprises nitrogen.
Dry scrubbing the inert gas is also an optional process. Thus, any HF present (e.g., in the inert gas or otherwise) can be absorbed by the metal oxide, e.g., alumina, and converted to metal fluoride (e.g., aluminum trifluoride) and water. In some embodiments, an inert gas exit bleed is controlled and carries HF to the metal oxide to form metal fluoride. By feeding the resulting metal fluoride back into the molten electrolyte, such embodiments preserve fluoride contents in the system. Metal oxide particles known to avoid sludge problems can also be used for the scrubbing process.
In some embodiments wherein liquid first metal is disposed on top of the molten electrolyte salt, a side tapping well is added on the first container. The well enables removal of metal from the apparatus. In some embodiments wherein liquid metal is disposed on top of the molten electrolyte salt, a partition or dam is provided to separate the metal from a portion of the top surface of the molten salt electrolyte, such that the metal oxide can be fed directly into the salt.
The first metal produced is not limited to aluminum. In some embodiments, the first metal is any metal that has a density less than the molten salt electrolyte at the operating temperature of the cell. Thus, in some embodiments, the first metal will float on top of the electrolyte. In some embodiments, the first metal comprises aluminum, magnesium, lithium, beryllium, silicon, strontium, potassium, sodium, barium, scandium, titanium, silicon or calcium. In some embodiments, the first metal comprises aluminum, magnesium, lithium, beryllium, silicon, strontium, potassium or calcium. In some embodiments, the first metal comprises aluminum, lithium, beryllium, silicon, strontium, or potassium. In some embodiments, the first metal comprises aluminum, lithium, beryllium, strontium, or potassium. In some embodiments, the first metal comprises aluminum, lithium, strontium, or potassium. In some embodiments, the first metal comprises aluminum, magnesium, lithium, beryllium, silicon, potassium or calcium. In some embodiments, the first metal comprises aluminum, magnesium, lithium, silicon, potassium or calcium. In some embodiments, the first metal comprises aluminum, magnesium, silicon, potassium or calcium. In some embodiments, the first metal comprises aluminum or magnesium. In some embodiments, the first metal comprises magnesium. In some embodiments, the first metal comprises aluminum. It is understood that the metal oxide comprises an oxide of the metal to be produced.
In some embodiments, the solid electrolyte comprises zirconia doped with yttria, calcia, magnesia, scandia, other rare earth oxide, or other additives that stabilize its cubic phase and enhance its conductivity; or ceria doped with oxides to increase its ion, e.g oxygen, conductivity; or any other oxygen ion-conducting solid electrolyte. In some embodiments, the solid electrolyte comprises zirconia doped with yttria, calcia, magnesia, scandia, or other rare earth oxide; or ceria doped with oxides to increase its oxygen ion conductivity. In some embodiments, the solid electrolyte comprises zirconia doped with yttria, calcia, magnesia, scandia, or other rare earth oxide. In some embodiments, the solid electrolyte comprises zirconia doped with yttria, calcia, magnesia, or scandia. In some embodiments, the solid electrolyte comprises ceria doped with oxides.
The molten electrolyte composition may be comprised of several components. Preferred molten electrolyte systems are selected based on several criteria:
Cation oxide free energy. All salt cation species ideally have oxide free energies of formation more negative than that of the metal, such that the process does not reduce spectator cations along with the product. Representative cation species include magnesium, sodium, cerium, lanthanum, calcium, strontium, barium, lithium, potassium and ytterbium. Thus, in some embodiments, the molten electrolyte comprises cations of magnesium, sodium, cerium, lanthanum, calcium, strontium, barium, lithium, potassium or ytterbium. In some embodiments, the molten electrolyte comprises cations of magnesium, sodium, cerium, and lanthanum.
Low volatility. Preferably the salt exhibits very low vapor pressure and evaporation rate in the process temperature range. Combining thermo-gravimetric analysis (TGA) with differential scanning calorimetry (DSC) or differential thermal analysis (DTA) experiments can efficiently evaluate the salt for this criterion. In some embodiments, fluoride salts are advantageous over chlorides. The volatility of lithium fluoride makes it less advantageous.
Low melting point. A preferred range of about 900-1200° C. provides balance between energy efficiency and material flexibility at low temperature, and good oxide ion conductivity in stabilized zirconia at high temperature. The salt must be liquid at the operating temperature.
High ionic conductivity supports high current density without significant transport limitation. By way of example, a salt with low ionic conductivity inhibits mass transfer to the zirconia and the cathode; at the zirconia oxygen ions are depleted in the boundary layer, reducing the current, and at the cathode the target metal ions are depleted in the boundary layer, leading to reduction and co-deposition of salt cations, reducing purity.
Low viscosity. Viscosity inhibits mass transport to electrodes. Salts with high fluoride/oxide ratio have had sufficiently high ionic conductivity and low viscosity to support up to about 2 A/cm²anode and cathode current density.
Target oxide solubility. The salt must dissolve the metal oxide to at least about 3-5 wt % in order to achieve preferred ionic current densities. DSC or DTA experiments at various compositions can efficiently characterize oxide solubility.
Low metal solubility and electronic conductivity. If the salt is a good electronic conductor, then it effectively becomes an extended cathode and can reduce the zirconia. This is impacted in part by solubility of the reduced metal in the salt, e.g. calcium metal is soluble in many salts. Methods for reducing metal solubility inline are also contemplated (See, e.g., U.S. Patent Publication No. 2013/0152734; herein incorporated by reference in its entirety).
Zirconia, ceria or other solid electrolyte material stability. Salt corrosion of the solid electrolyte is preferably very slow. Ideally, the salt preferably satisfies two criteria: salt optical basicity and yttria (or other stabilizing oxide) chemical potential are both close to those values in the solid electrolyte. To evaluate stability, solid electrolyte material is immersed in the salt at the process temperature for several hundred hours, then sectioned and characterized.
Fluoride salts are particularly preferred as they offer advantageous combinations of properties due to their low volatility and viscosity, high oxide solubility and ionic conductivity, and low basicity.
Preferred molten salts comprise LiF, NaF, CaF₂, MgF₂, SrF₂, and AlF₃. These have melting points around 700° C. with relatively low vapor pressure. The optimal molten salt will have maximum metal oxide solubility and minimum metal solubility.
It can be advantageous to have multiple current collectors attached to a cell, such that failure of one or more does not result in disconnection and open circuit. By way of example, if the apparatus is running with a single current collector in a constant current circuit and a disturbance occurs such that some of the solid conductor portion of the current collector is melted, the resistance is increased and more electrical energy flows and causes additional melting, which eventually results in disconnection.
In the case of multiple current collectors, if the apparatus is running at about constant current and a disturbance occurs such that some of the solid conductor portion is melted, the resistance is increased and more electrical energy flows through the other current collectors. However, it is about stable at constant voltage operation, e.g., about 1 volt. By way of example, if a cell is running at constant current with 10 aluminum connectors going into the cell, and one of the connectors fails or melts such that resistance in that connector increases, the overall current would increase by about 11% in the remaining connectors. Re-freezing would reduce resistance in the formerly melted current collector and bring it back to an equilibrium state. If the connectors are all connected to a common bus outside the cell, the interface is advantageously stabilized.
Advantageously, the apparatus is configured such that current density×lead length is about constant. In some embodiments, current density×length is between about 4×10⁵A/m and 7×10⁶A/m. In some embodiments, current density×length is between about 5×10⁵A/m and 5×10⁶A/m. In some embodiments, current density×length is between about 8×10⁵A/m and 3×10⁶A/m. In some embodiments, current density×length is between about 8×10⁵A/m and 1×10⁶A/m. In some embodiments, current density×length is about 9×10⁵A/m.
Advantageously, the apparatus is configured such that aluminum current density is about 10⁶A/m²(about 100 A/cm²). In some embodiments, current density is about 10⁶A/m²and length of the aluminum lead is about 1 m. In some embodiments, current density is about 10⁶A/m²and length of the aluminum lead is about 0.85 m.
Advantageously, the apparatus is configured such that energy loss through the current collector is about 0.3V to about 1.8V. In some embodiments, energy loss through the current collector is about 0.3V to about 1.3V. In some embodiments, energy loss through the current collector is about 0.4V to about 1.8V. In some embodiments, energy loss through the current collector is about 0.4V to about 1.3V. In some embodiments, energy loss through the current collector is about 0.5V to about 0.8V. In some embodiments, energy loss through the current collector is about 0.5V to about 1.8V. In some embodiments, energy loss through the current collector is about 0.5V to about 1.3V. In some embodiments, energy loss through the current collector is about 0.5V to about 0.8V.
As previously mentioned herein, the configurations and methods also apply to a cell with low-density bath and submerged aluminum pad. By way of example, a sealed steel cell creates a controlled environment which can be made inert by injecting argon, helium, nitrogen, or other gas. This prevents rapid steel corrosion by molten salt catalysis of steel oxidation. It also prevents molten salt catalysis of TiB₂corrosion, enabling that cathode material to protrude upward out of the salt.
In some embodiments, the injection site for the inert gas is submerged in the bath, in order to create gas lift stirring and promote oxide circulation, thus minimizing and/or preventing localized oxide depletion.
The steel vessel further creates opportunities for thermal manipulation. For example one can apply heating (including fuel-fired heaters) directly to the steel during start-up or accidental cooling due to power failure. If the cell gets too hot, removal of insulation or blowing cooling fluid through insulation can help to cool it. This can potentially reduce or eliminate thermal runaway problems during a voltage/temperature increase event caused by alumina depletion.
It will be recognized that one or more features of any embodiments disclosed herein may be combined and/or rearranged within the scope of the invention to produce further embodiments that are also within the scope of the invention.
Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are also intended to be within the scope of the present invention.

Examples

The examples provided below facilitate a more complete understanding of the invention. The following examples illustrate exemplary modes of making and practicing the invention. However, the scope of the invention is not limited to specific embodiments disclosed in such examples, which are illustrative only, since alternative methods can be utilized to obtain similar results.
Experimental Design and Procedure
FIG. 6 shows a schematic of an exemplary current collector experiment. Two isomolded graphite tubes (660) with dimensions 2.54 cm OD 0.95 cm ID 61 cm length act as vertical conduits for the liquid-solid aluminum leads. Both are immersed into a 1 kg pool of liquid aluminum (640) in a 10 cm ID graphite crucible (690). Each graphite tube has an inner volume of 43 cm³, and can hold about 90-110 g of liquid (640) and solid (655) aluminum. The remaining 780-820 g liquid aluminum in the crucible will have a depth of 4-4.5 cm.
Two 4.13 cm OD alumina tubes (691) act as electrical insulators between the graphite tubes and apparatus, and as thermal insulators between those tubes and the environment. Additional magnesiosilicate blanket insulation (692) packs the annulus between the alumina and graphite tubes, minimizing lateral temperature difference in the graphite. The alumina tubes and graphite tubes pass through openings in the top plate of the retort, which is purged with argon gas. The tops of the graphite tubes have fittings (693) which seal to coaxial 0.63 cm diameter copper rods (694), which descend from the top into the graphite tubes to connect with the aluminum. The apparatus is further configured with a furnace tube lid (695), radiation baffles (696), a furnace tube (697), and furnace heating elements (690).
At this experiment's liquid aluminum temperature of 850° C. (1123 K) and environment temperature of 25° C. so ΔT=825° C., the relationship
$\begin{matrix} Δ V = \frac{P + Q}{I} = 2 \sqrt{L_{ei} T Δ T} & (Eq . 1) \end{matrix}$
estimates minimum total energy loss per unit charge at about 0.30 V. About half of that is electrical resistance and half thermal loss through the aluminum. 1-D FEA of the cathode potential and temperature distributions from a 1000° C. crucible shows that actual optimal voltage is 5-10% above the theoretical estimate. Thus, operating each lead at 0.15-17 V, for a total of 0.30-0.33 V in the circuit, should come close to that optimum.
At 61 cm length, optimal current density is around 150 A/cm². Current in the aluminum core with cross section area 0.71 cm²will be about 106 A. Using u=10⁵S/m, current in the graphite tubes with cross section 4.35 cm²—over six times that of the aluminum—would be about 70 A. This conductivity value is approximately that of room temperature graphite conductivity, so actual conductivity and resulting current will be lower.
Experimental Procedure
1. Purge the apparatus with argon for at least an hour, until oxygen partial pressure is below 10⁻³atm. The purge should reach up into the tubes, so one can act as inlet and the other exhaust, or both exhaust with a separate inlet.
2. Heat the crucible until the liquid aluminum temperature reaches 850° C. All components are very thermally robust, so the furnace can heat up quickly.
3. Lower the graphite tubes into the liquid aluminum in the graphite crucible, hitting the bottom and backing out approximately 2 cm.
4. Attach leads to the graphite tubes, and ramp voltage from 0 to 0.4 V at 0.001 V/sec (over ˜7 minutes). Current should rise linearly from 0 to about 50-60 A.
5. Hold voltage at 0.4 V, 0.3 V, 0.2 V and 0.1 V to allow current to stabilize, and measure change in current over time.
6. Use thermocouples in each of the graphite tubes to measure temperature vs. height every 10 cm. Case is exercised so as not to submerge the thermocouple in the aluminum pool, as this would dissolve its end. Temperature distribution should be about the same in both tubes.
7. On one graphite tube, connect the vacuum source to the fitting at the top, without opening the valve to allow vacuum connection.
8. Attach one lead to a copper rod, and quickly lower it to where its bottom end is about 20 cm below the top of the graphite tube.
9. Quickly open the vacuum source to the tube fitting, which should raise the liquid aluminum upward, connecting with the copper. The top of the copper rod should quickly heat up.
10. Repeat steps 4-5 with one lead on the copper rod of step 8. Current should rise to about 30% higher during the ramp than it did in step 5, and may decline slightly over time at 0.3 V due to aluminum melting in the tube.
11. Repeat steps 7-9 for the second graphite tube.
12. Repeat steps 4-5 with both leads on the copper rods. Current should rise to about 100 A during the ramp, and may decline slightly over time at 0.3 V due to aluminum melting in the second tube.
13. Turn off the power supply and furnace, and allow the apparatus to cool to room temperature.
Experimental Results
FIG. 7 shows the voltage and current vs. time during steps 4-5 in the above procedure. Measured current is lower than predicted, due to poor electrical connection to the graphite tubes, and incomplete melting and consolidation of the aluminum in the bottom of the crucible. That said, current and voltage are roughly linearly related as predicted.
FIG. 8 shows the voltage and current vs. time during a second set of experiments. First voltage was increased to 4 V, resulting in about 150 A current across the graphite (voltage curve tracking above the current curve for about the first 0.4 hr). Second, voltage was reduced to 0.4 V. While connected to the graphite holding at total system voltage of 0.4 V, at about 0.4 hours into the experiment, steps 7-9 were performed on one current collector, causing liquid aluminum to flow upward into it and partially solidify from the top. This increased the current from 14.5 A to a steady state value of 19.9 A (voltage curve tracking below the current curve from about 0.4 hr to about 1.7 hr). At about 0.7 hours, steps 7-9 were performed on the second current collector, causing liquid aluminum to flow upward into it and partially solidify from the top. This increased the current to 25.6 A, about twice the original current. Thus about as much current flowed through the aluminum as through the graphite, despite having only about one-sixth the cross section area. This demonstrated the very high current density in this liquid-solid aluminum current collector with a graphite conduit. A subsequent increase in voltage to 2.9 V caused current to reach 184 A, indicating about one half the prior resistance. This also demonstrated the ability of this device to carry current at about 100 A/cm²in the aluminum core.
FIG. 9 shows the voltage and current in a ramp from 0 to 2.0 V, resulting in current increase to a maximum of 165 A, again demonstrating very low resistance and high current density. Voltage curve in FIG. 9 tracks above the current curve from about 0.015 hr to about 0.145 hr.
Optimal Connection Geometry
The Wiedemann-Franz law indicates that a good electrical conductor is a good thermal conductor. There is an optimum balance between electrical and thermal resistance of the current collector to minimize the sum of electrical resistance creating heat, and thermal resistance preventing excess heat loss from the cell. The resistivity of aluminum varies widely over the temperature range from the environment, e.g, 20° C. where it is ρ=2.65×10⁻⁸Ω-m to 927° C. where it is 2.89×10⁻⁷Ω-m (J. Phys. Chem. Ref Data 13(4):1132 (1984); herein incorporated by reference in its entirety). Since for a material with constant properties, ΔV=ρJL (J is current density, L is lead length), this bounds the product JL to be between about 6×10⁵and 7×10⁶A/m. Typical maximum industrial aluminum bus bar current density is around 10⁶A/m²(i.e. 100 A/cm²); using this current density would result in optimal aluminum lead length on the order of 1 m.
Optimal geometry with a second metal, whether a high-melting connector such as copper or nickel or a low-melting metal such as tin, bismuth or lead, depends on its composition and temperature distribution.
1-D Finite Difference Model
A 1-D Finite Difference model of electrical and thermal conduction in the liquid and solid current collector helps to quantify the trade-off between electrical and thermal losses. This analysis assumes constant cross-section area of the liquid and solid aluminum ledge or conduit, uniform current density J throughout it, and uniform temperature in any cross-section. It neglects effects of convection and radiation, assumes a single flat liquid-solid interface, and assumes that the outside of the conduit is perfectly insulated. The latter assumption is a design goal for the conduit, as it is most effective at retaining energy when thermal loss from its sides is as low as possible.
This model takes into account temperature-dependent electrical and thermal conductivity of solid and liquid aluminum (J. Phys. Chem. Ref Data 13(4) (1984); herein incorporated by reference in its entirety), and calculates the location of the melt interface. It sets constant-temperature Dirichlet boundary conditions: 1000° C. at the liquid pad end (x=0) and 200° C. at the environment end (x=L). It has 20 intervals along the length of the current collector.
FIG. 10 shows the calculated temperature-distance relationship along the aluminum for J=100 A/cm²and L=0.8 m. Its curvature is high above the 660° C. melting point and low below it because the liquid exhibits both higher resistivity and generation of heat, and lower thermal conductivity, than the solid. The slope at the environment end ∂T/∂× times thermal conductivity k gives the total energy loss per unit cross-section area of the conductor q. Total thermal energy loss per unit metal product is proportional to q/J, which has units of volts.
FIG. 11 shows the calculated total energy loss q/J as a function of total current collector length L for several values of current density J. It indicates that minimum total energy loss is approximately 0.34 V (1.0 kWh/kg) for values of J from 40 to 100 A/cm². In addition, the product of current density times optimal length at that current density is roughly constant at approximately 90 m·A/cm², i.e. 9×10⁵A/m.
For this reason, an aluminum solid/liquid current collector operating at 100 A/cm²should be approximately 0.85 m long. It loses approximately 16% more energy if it is 30% shorter, and 7% more energy if it is 30% longer, than this optimal length.
As will be apparent to one of ordinary skill in the art from a reading of this disclosure, further embodiments of the present invention can be presented in forms other than those specifically disclosed above. The particular embodiments described above are, therefore, to be considered as illustrative and not restrictive. Those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific embodiments described herein. Although the invention has been described and illustrated in the foregoing illustrative embodiments, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the details of implementation of the invention can be made without departing from the spirit and scope of the invention, which is limited only by the claims that follow. Features of the disclosed embodiments can be combined and rearranged in various ways within the scope and spirit of the invention. The scope of the invention is as set forth in the appended claims and equivalents thereof, rather than being limited to the examples contained in the foregoing description.

Claims

What is claimed is:

1. An apparatus comprising:

(a) a conduit having a first end and a second end;

(b) a liquid first metal disposed at the first end of the conduit and within the conduit;

(c) a solid first metal disposed at the second end of the conduit and within the conduit;

(d) a solid conductor portion in electrical contact with the solid first metal; and

(e) a cooling mechanism disposed at the second end of the conduit;

wherein at least a portion of the liquid first metal and the solid first metal are in electrical contact, the solid conductor disposed to provide electrical contact between the solid first metal and an electrical source outside the conduit.

2. The apparatus of claim 1, wherein the conduit does not dissolve into the first metal more than about 5% by weight.

3. The apparatus of claim 2, wherein the conduit comprises carbon, silicon carbide, titanium diboride, boron nitride, silicon nitride, aluminum nitride, aluminum oxide or an aluminum-bearing compound with an element that does not dissolve into the first metal.

4. The apparatus of claim 1, further comprising a conduit sheath disposed around at least a portion of the conduit.

5. The apparatus of claim 1, wherein the cooling mechanism comprises a jacket disposed around a portion of the conduit, wherein the jacket has an inlet and an outlet.

6. The apparatus of claim 5, wherein air, gas, and/or a cooling liquid are disposed within at least a portion of the jacket.

7. The apparatus of claim 1, wherein the solid conductor comprises the first metal.

8. The apparatus of claim 1, further comprising a first container configured to contain at least a portion of the liquid first metal.

9. The apparatus of claim 8, wherein the first container comprises a well, tube or ledge extending from a second container.

10. The apparatus of claim 1, further comprising a vacuum port disposed along at least a portion of the conduit.

11. The apparatus of claim 1, wherein at least a portion of the conduit and solid conductor portion comprise a mould for extraction of the solid first metal.

12. The apparatus of claim 1, further comprising:

(f) a second container for holding a molten electrolyte, the second container having an interior surface;

(g) an anode in ion-conducting contact with the molten electrolyte; and

(h) a power source for generating an electric potential between the anode and the liquid first metal.

13. The apparatus of claim 12, wherein, during generation of the electric potential, the first metal is recovered from an oxide of the first metal dissolved in the molten electrolyte and the first metal collects on the floor of the second container.

14. The apparatus of claim 12, wherein, during generation of the electric potential, the first metal is recovered from an oxide of the first metal dissolved in the molten electrolyte and the first metal collects on a top surface of the molten electrolyte when the electrolyte is disposed in the second container.

15. The apparatus of claim 12, wherein a portion of a side wall of the second container defines a first passage between the interior of the second container and the first container.

16. The apparatus of claim 1, wherein the first metal comprises aluminum, magnesium, lithium, beryllium, silicon, strontium, potassium, sodium, barium, scandium, titanium, silicon or calcium.

17. The apparatus of claim 16, wherein the first metal comprises aluminum or magnesium.

18. The apparatus of claim 17, wherein the first metal comprises aluminum.

19. An apparatus comprising:

(a) a conduit having a first end and a second end;

(b) a first container disposed at the second end of the conduit, and configured to contain at least a portion of a liquid first metal within the conduit and a liquid second metal within the conduit, the liquid second metal having higher density than the liquid first metal; and

(c) a solid conductor portion in electrical contact with the second liquid metal;

wherein the solid conductor is disposed to provide electrical contact between the second liquid metal and an electrical source outside the conduit.

20. The apparatus of claim 19, further comprising:

(d) a second container disposed at the first end of the conduit, and configured to hold a molten electrolyte, the second container having an interior surface;

(e) a cooling mechanism disposed around at least a portion of the first container;

(f) an anode disposed in ion-conducting contact with the molten electrolyte; and

(g) a power source for generating an electric potential between the anode and the first liquid metal;

wherein the conduit comprises a ledge extending from the interior of the second container to the first container.

21. The apparatus of claim 19, further comprising a solid conductor portion in electrical contact with the liquid second metal, and wherein at least a portion of the liquid first metal and the liquid second metal are in electrical contact, the liquid second metal disposed to provide electrical contact between the liquid first metal and an electrical source outside the conduit.

22. The apparatus of claim 19, wherein the conduit does not dissolve into the first metal more than about 5% by weight.

23. The apparatus of claim 22, wherein the conduit comprises carbon, silicon carbide, titanium diboride, boron nitride, aluminum nitride, silicon nitride, aluminum oxide or an aluminum-bearing compound with an element that does not dissolve into the first metal more than about 5% by weight.

24. The apparatus of claim 23, wherein the liquid second metal does not dissolve into the first metal more than about 5% by weight.

25. A method for electrically connecting a liquid first metal cathode to a current source of an electrolytic cell comprising:

(a) providing a conduit having a first end and a second end;

(b) providing a liquid first metal disposed at the first end of the conduit and within the conduit;

(c) providing a solid first metal disposed at the second end of the conduit and within the conduit;

(d) providing a solid conductor portion in electrical contact with the solid first metal; and

(e) providing a cooling mechanism disposed at the second end of the conduit;

wherein at least a portion of the liquid first metal and the solid first metal are in electrical contact, and the solid conductor provides electrical contact between the solid first metal and an electrical source outside the conduit.

26. The method of claim 25, wherein the conduit does not dissolve into the first metal more than about 5% by weight.

27. The method of claim 26, wherein the conduit comprises carbon, silicon carbide, titanium diboride, boron nitride, silicon nitride, aluminum nitride, aluminum oxide or an aluminum-bearing compound with an element that does not dissolve into the first metal more than about 5% by weight.

28. The method of claim 25, further comprising providing a conduit sheath disposed around at least a portion of the conduit.

29. The method of claim 25, wherein the cooling mechanism comprises air, gas, and/or a cooling liquid.

30. The method of claim 25, wherein the solid conductor comprises the first metal.

31. The method of claim 25, further comprising providing a first container configured to contain at least a portion of the liquid first metal.

32. The method of claim 31, wherein the first container comprises a well, tube, or ledge extending from a second container.

33. The method of claim 25, wherein at least a portion of the liquid first metal is drawn into the conduit via vacuum.

34. The method of claim 25, further comprising:

(f) providing a second container holding a molten electrolyte, the second container having an interior surface; and

(g) providing a power source for generating an electric potential between the anode and the cathode.

35. The method of claim 34, wherein, during generation of the electric potential, the first metal collects on the floor of the second container.

36. The method of claim 34, wherein, during generation of the electric potential, the first metal collects on a top surface of the molten electrolyte when the electrolyte is disposed in the second container.

37. The method of claim 25, wherein a temperature gradient develops along the first metal and extends to form the electrical contact with the solid metal portion of the current collector.

38. The method of claim 37, wherein the temperature gradient exists between the operating temperature of the cell and the melting point of the first metal disposed in the conduit.

39. The method of claim 25, wherein the first metal comprises aluminum, magnesium, lithium, beryllium, silicon, strontium, potassium, sodium, barium, scandium, titanium, silicon or calcium.

40. The method of claim 39, wherein the first metal comprises aluminum or magnesium.

41. The method of claim 40, wherein the first metal comprises aluminum.

42. A method for electrically connecting a liquid first metal cathode to a current source of an electrolytic cell comprising:

(a) providing a conduit having a first end and a second end;

(b) providing the liquid first metal disposed at the first end of the conduit and within the conduit;

(c) providing a first container disposed at the second end of the conduit, the first container containing at least a portion of a liquid first metal and a liquid second metal, the liquid second metal having higher density than the liquid first metal; and

(d) providing a solid conductor portion in electrical contact with the liquid second metal;

wherein at least a portion of the liquid first metal and the liquid second metal are in electrical contact, and the solid conductor provides electrical contact between the liquid second metal and an electrical source outside the conduit.

43. The method of claim 42, wherein the conduit does not dissolve into the first metal more than about 5% by weight.

44. The method of claim 43, wherein the conduit comprises carbon, titanium diboride, silicon carbide, boron nitride, silicon nitride, aluminum nitride, aluminum oxide or an aluminum-bearing compound with an element that does not dissolve into the first metal more than about 5% by weight.

45. The method of claim 42, further comprising providing a conduit sheath disposed around at least a portion of the conduit.

46. The method of claim 42, wherein the first container comprises a well, tube, or ledge extending from a second container.

47. The method of claim 42, wherein at least a portion of the liquid first metal is drawn into the conduit via vacuum.

48. The method of claim 42, further comprising:

(e) providing a second container holding a molten electrolyte, the second container having an interior surface; and

(f) providing a power source for generating an electric potential between the anode and the cathode.

49. The method of claim 48, wherein, during generation of the electric potential, the first metal collects on a top surface of the molten electrolyte when the electrolyte is disposed in the second container.

50. The method of claim 42, wherein the temperature gradient exists between the operating temperature of the cell and the melting point of the first metal disposed in the conduit.

51. The method of claim 48, wherein the liquid first metal is drawn from the second container toward the liquid second metal.

52. The method of claim 42, wherein the first metal comprises aluminum, magnesium, lithium, beryllium, silicon, strontium, potassium, sodium, barium, scandium, titanium, silicon or calcium.

53. The method of claim 52, wherein the first metal comprises aluminum or magnesium.

54. The method of claim 53, wherein the first metal comprises aluminum.