Method and system for isotopic lithium separation using molecular still

Abstract

A molecular distillation system and process for isotopic separation of lithium with a molecular still (1). The molecular still comprises at least one bottom plate (6) forming an evaporator and at least one top plate (8) forming a condenser. The molecular still (7) comprises at least one capillary member (10,11,12) for transporting molten lithium in the molecular still (1) by capillary effect of the at least one capillary member (10,11,12) and the process comprises transporting molten lithium along the bottom plate and / or along the top plate by flow of molten lithium driven by capillary action of at least one capillary member (10,11,12).

Description

[0001] METHOD AND SYSTEM FOR ISOTOPIC LITHIUM SEPARATION USING

[0002] MOLECULAR STILL

[0003] TECHNICAL FIELD

[0004] The disclosure relates to methods and systems for isotopic lithium separation of lithium-7 and lithium-6, in particular isotopic separation of lithium-7 and lithium-6 from naturally occurring lithium.

[0005] BACKGROUND

[0006] Naturally occurring lithium is a mixture of lithium-7 and lithium-6 in varying proportions due to the geological isotopic separation of the two, with the lithium-6 concentration varying roughly between 2% and 8%, with 5% being the norm.

[0007] Molten salt reactors utilizing lithium fluoride or chloride salts practically need to have highly enriched lithium-7 due to the large differences in the thermal capture neutron cross sections of lithium-6 and lithium-7, of 941 barn and 0.014 barn, respectively for thermal neutrons, and partly to minimize tritium production from neutron capture by lithium- 6.

[0008] Naturally occurring lithium has a thermal capture crosssection of roughly 65 barn, which is very high when compared to e.g. naturally occurring sodium, with a thermal capture cross-section of 0.5 barn, or naturally occurring potassium, with a thermal capture cross-section of 2 barn. For comparison 99.9% enriched lithium-7 (3N 7Li) has a thermal capture crosssection of 0.95 barn, 99.99% enriched lithium-7 (4N 7Li) has a thermal capture cross-section of 0.11 barn, and 99.999% enriched lithium-7 (5N 7Li) has a thermal capture crosssection of 0.02 barn. This means that 99.99% to 99.999% enriched lithium-7 (4-5N 7Li) is desired for the use of lithium in molten salt reactor salts.

[0009] Examples of lithium fluoride salt that can be used in molten salt reactor salts are7LiF-BeF2,7LiF-BeF2-UF4,7LiF-ThF4,7LiF-ThF4-UF4, and7LiF-ThF4-PuF3. Examples of lithium chloride salt that can be used in molten salt fast reactors are7LiCl- KCI-UCI3,7LiCl-UCl3,7LiCl-PuCl3,7LiCl-UCl3-PuC13.

[0010] Highly enriched lithium-7 is especially important for thermal molten salt breeder reactors, which have the potential to scale much faster than other nuclear technologies given a constrained supply of fissile fuel. For scaling thermal molten salt breeder reactors to meet global energy demand in the coming decades, an annual enrichment capacity of lithium-7 of several tens of thousands of metric tons would be needed, which is a major challenge for scaling this type of reactor.

[0011] When lithium-6 captures a thermal neutron there is a high probability that it leads to tritium production. The production of tritium from lithium-6 is considered a radionuclide release hazard for nuclear reactors, while it is the goal in some fusion reactor blankets. Thus, nuclear (fission) reactors utilizing lithium need enriched lithium-7 while fusion reactors need enriched lithium-6, and the isotopic separation of lithium can serve both industries synergistically.

[0012] Examples of fluoride salts that can be used in fusion reactor blanket salts are6LiF-BeF2 and6LiF-7LiF-BeF2 , where the beryllium also serves as a neutron multiplier, and examples of molten metal alloys that can be used in fusion reactor blankets are6Li,6Li-Pb, and6Li-Bi.

[0013] The predominant method for industrialized isotopic lithium separation is the COLEX process, which is a two-liquid-phase chemical exchange, between lithium hydroxide aqueous solution and a mercury-lithium amalgam, where lithium-6 has a slightly larger affinity for the mercury amalgam. The COLEX process involves large quantities of mercury and mercury compounds, which along with its high energy consumption makes the process unattractive for future isotopic lithium separation.

[0014] The COLEX process COLEX separation is a mercury-based chemical approach for isotopic separation of lithium-6 and lithium-7, with aqueous lithium hydroxide (LiOH) contacted with lithiummercury amalgam, exploiting greater affinity of lithium-7 than Lithium-6 for the element mercury. The COLEX separation process involves passing a counter-flow of an aqueous lithium hydroxide flow up and a lithium-mercury amalgam flows down through a series of exchange columns containing a cation exchange resin. Mercury drains the lithium-6 fraction preferentially, although lithium-7 primarily flows with the hydroxide. The amalgam is separated from the lithium (enriched with lithium-6) at the bottom of the column, and the mercury is recovered for subsequent use. The lithium-7 fraction is electrolyzed to release the lithium hydroxide solution at the top. The operating temperature, flow rate, and column length all affect the enrichment that can be achieved with this process .

[0015] Facilities at Oak Ridge, Tennessee using the COLEX process were operated between 1955 and 1963 to generate the current US stockpiles of 6Li and 7Li.

[0016] The COLEX process has several downsides, such as:

[0017] Toxicity of the large amounts of mercury involved.

[0018] Tendency of amalgams to decompose in aqueous solutions. Formation of dangerous mercury-containing waste High energy consumption.

[0019] Potentially disastrous environmental implications since a substantial amount of mercury is required (24 million pounds were used in the U.S. between 1955 and 1963) and many opportunities for leaks into the environment exist.

[0020] Many methods have been researched and developed for the isotopic separation of lithium, including two-liquid-phase chemical exchange, ion exchange resins, ion exchange membranes, laser absorption, thermal diffusion, electromigration, fractional crystallization, microalgal, and molecular distillation. While multiple of these methods have been shown to work, none of them has shown to be an economical replacement for the COLEX process.

[0021] Isotopic separation of lithium metal using molecular distillation has seen limited research, with only a handful of articles published in the late 1950s and early 1960s, and was ultimately abandoned.

[0022] One example of a publication of this period is "SOME EXPERIMENTS ON THE SEPARATION OF LITHIUM ISOTOPES BY MOLECULAR DISTILLATION" by D.B. TRAUGER, J. J. KEYES, Jr. , G.A. KUIPERS AND D.M. LANG, Oak Ridge Gaseous Diffusion Plant, Union Carbide Nuclear Company Oak Ridge, Tenn. , published in PROCEEDINGS OF THE SYMPOSIUM ON ISOTOPE SEPARATION, AMSTERDAM, 1957, describes a horizontal still for the isotopic separation of lithium using molecular distillation of lithium. This still relies on lithium evaporating under high vacuum on a horizontal plate with the condensate condensing just above on another place and the condensate running off by gravity back to the previous stage, while the remaining lithium at the bottom evaporator plate is allowed to flow forwards to the next stage. A series of baffle plates are employed to guide the flow of the molten lithium between stages, to guide the condensate back to the previous stage, and to provide a labyrinth flow within a single stage to increase the residence time of the molten lithium in a given stage. Building a horizontal still in this fashion requires high precision and high tolerance to keep the entire bottom of the still level reclined at a specific angle to guide the flow. Furthermore, the complexity of the still construction is moderate to high due to the many pieces that have to be assembled and welded leak-tight. Thus, it is desired to provide a horizontal still design and construction method that is less expensive and less complicated to produce, but still serves the same function of efficient molecular distillation of lithium for the purposes of lithium enrichment. The still described by Tauger has several millimeters of lithium hold-up throughout the evaporator to ensure that no single stage 'runs dry' and baffles in each stage to provide a labyrinth-like flow are required to slow the flow of the lithium through each stage and to ensure that zones of stagnant molten lithium do not arise within a single stage. Furthermore, with an angled condenser plate, the molten lithium condensate has the chance of dripping back down onto the evaporator stage, before being collected, requiring a angle of several degrees to guide the molten lithium condensate to the previous stage, this makes each stage thicker the larger the stages needs to be since the same angle is needed across the condenser of each stage. Larger distances between the evaporator and condenser equates to more collisions between the lithium vapor atoms or between the lithium vapor atoms and the remaining cover gas atmosphere still present even at high vacuum, and thus lower separation factor, thus a small distance between the condenser and evaporator is desired.

[0023] CN115193253 discloses a method and a device for separating isotopes 6Li and 7Li using molecular distillation. Based on the difference of the atomic mass of 6Li and 7Li, 6Li and 7 Li are separated by a thermal evaporation method. The method is characterized in that in a vacuum chamber, after natural metal lithium is heated and evaporated and lithium vapor is kept under a certain pressure and is subjected to heat balance, 6Li is mainly distributed at the upper part of the vacuum chamber, and 7Li is mainly distributed at the lower part of the vacuum chamber. The boundary of 6Li and 7Li vapor can be determined according to the content proportion of 6Li and 7Li in natural metal lithium, the temperature and the pressure. And a partition plate which can be inserted or withdrawn at any time as required is arranged at the vapor boundary of 6Li and 7Li. During heat balance, the partition plate is inserted, then 6Li and 7Li vapor f < n > is released into respective cooling containers to be cooled into solids, and a protective layer is added, so that separation of 6Li and 7Li is realized.

[0024] SUMMARY

[0025] It is an object to provide a method and system for isotopic lithium separation that overcomes or at least reduces the problems above.

[0026] The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description, and the figures .

[0027] According to a first aspect, there is provided a molecular distillation system for isotopic separation of lithium comprising a molecular still, the molecular still comprises at least one bottom plate forming an evaporator and at least one top plate forming a condenser, the molecular still comprises at least one capillary member for transporting molten lithium in the molecular still by capillary effect of the at least one capillary member.

[0028] By using a capillary member for flow the lithium metal processing medium can be made to flow within a stage and or between stages without the need for complex structures such as welded internal baffle plates or machined structure, allowing for much faster, simpler, and less expensive construction. Furthermore, by using the capillary flow to guide the lithium metal processing medium the horizontal molecular still becomes less sensitive to the dimensional tolerances of the still' s construction and installation making it easier to operate and making it easier to construct larger stills. Using capillary members to guide the flow also makes it easier to produce stages with small dimensions, when compared to construction using baffle plates where a lot of small precision welds or costly machining would be involved. This, combined with the large allowed dimensional tolerances, allows for large still constructions that can house a larger number of stages, making it possible to have 200 to 300 stages in a single still, allowing for high lithium-7 enrichment in a single still of moderate output, where multiple of these can be run in parallel to achieve a large yield as opposed to multiple still with large stage construction and high dimensional tolerance requirements with a higher yield but strung together in series to reach the desired number of stages, which is more complicated to operate due to the components and systems required to transport the lithium between stills.

[0029] Using capillary flow of capillary members, e.g. wicks, makes the lithium flow through the capillary member at an even flow rate and distributes the flow more evenly over the capillary members, negating the need for labyrinth-like flow path on the evaporator and at a sufficiently low speed to allow evaporation of the lithium within each stage and negating the need for an angled condenser plate to drain the condensate since the capillary flow will guide the condensate to the previous stage by gravity. Furthermore, the lithium hold-up throughout the evaporator only needs to be enough to wet the capillary member, but the capillary member can be made thin and will still be fully wetted because of the surface tension of the lithium ensuring even wetting. Thus, lithium hold-up in the still can be drastically reduced.

[0030] Additionally, neither the condenser nor evaporator capillary members (wicks) need an angle / tilt to guide the flow by gravity. Instead, the flow can be a combination of gravity- driven flow and capillary flow, this means that the condenser and evaporator stages can be placed much closer to each other, even with larger stage construction. Importantly this allows for a larger stage separation factor (often denominated alpha) since fewer lithium vapor collisions occur with other lithium vapor atoms or remaining cover gas atoms. This lowers the requirements on the necessary vacuum to be achieved to run the still, and if an inert cover gas is used like argon or helium, then a suitable vacuum can potentially be achieved with cheaper vacuum pump systems and shorter bake-out times.

[0031] Thus, the molecular distillation system according to the first aspect allows for faster, simpler, and less expensive construction with lower dimensional tolerance requirements while also allowing for simpler and cheaper operation.

[0032] According to a possible implementation form of the first aspect, the at least one capillary member is configured to transport molten lithium along the at least one bottom plate and / or along the at least one top plate by the capillary effect of the at least one capillary member.

[0033] According to a possible implementation form of the first aspect, the capillary member comprises one or more of: capillary flow lumens, capillary flow channels, porous material, web material .

[0034] According to a possible implementation form of the first aspect, the at least one capillary member extends along at least a portion of the at least one bottom plate and or extends along a portion of the at least one top plate.

[0035] According to a possible implementation form of the first aspect, the at least one bottom plate is a substantially horizontal plate.

[0036] According to a possible implementation form of the first aspect, the at least one top plate is a substantially horizontal plate.

[0037] According to a possible implementation form of the first aspect, the molecular still comprises two or more stages, wherein the at least one capillary member is configured to transport molten lithium within a stage and / or from one stage to a neighboring stage.

[0038] According to a possible implementation form of the first aspect, the at least one bottom plate extends along several stages, and / or wherein the at least one top plate extends along several stages.

[0039] According to a possible implementation form of the first aspect, the still comprises:

[0040] - a feed port for receiving the mixture of molten lithium,

[0041] - a first outlet port for enriched molten lithium-6, and

[0042] - a second outlet port for enriched molten lithium-7.

[0043] According to a possible implementation form of the first aspect, the at least one capillary member is associated with the bottom plate and configured to transport enriched molten lithium-7 toward the second outlet port.

[0044] According to a possible implementation form of the first aspect, the at least one capillary member is configured to transport enriched molten lithium-6 toward the first outlet port .

[0045] According to a possible implementation form of the first aspect, the system comprises plurality stages, each stage comprising at least one capillary member associated with the top plate for transporting enriched molten lithium-6 within the stage concerned and towards a next stage or towards the first outlet port.

[0046] According to a possible implementation form of the first aspect, at least one stage comprises at least one capillary member that is associated with the top plate and is configured for transporting enriched molten lithium-6 back to the start of the previous stage or towards the first outlet port. According to a possible implementation form of the first aspect, the system comprises one or more channels or conduits configured for transporting molten lithium by gravity.

[0047] According to a possible implementation form of the first aspect, the system comprises a housing forming an outer leak- tight barrier in which the top plate and bottom plate are disposed, the housing comprising an upper part for accommodating the top plate and a lower part for accommodating the bottom plate, wherein the upper part is connected to the lower part by an expansion joint or mechanism that allows for differential thermal expansion of the lower part relative to the upper part, the expansion joint or mechanism preferably comprising bellows.

[0048] According to a possible implementation form of the first aspect, the at least one capillary member is shaped like a pad.

[0049] According to a possible implementation form of the first aspect, the capillary member comprises wire screen, fine metal wire screen, sintered wire mesh, microporous sintered metal mesh sheet, sintered metal fiber felt, and / or carbon felt.

[0050] According to a possible implementation form of the first aspect, the capillary member comprises capillary channels, preferably the capillary channels are grooves arranged in a surface of the capillary member, preferably the capillary channels are formed in a surface of the top plate, in a surface of the bottom plate, and / or in a surface of the sides of plates or baffles spacing the top and bottom plates from touching while under vacuum, preferably the capillary channels in the sides of the baffle plates guiding the condensate lithium from one condenser stage to the start of the previous evaporator stage to produce a counterflow.

[0051] According to a possible implementation form of the first aspect, the at least one capillary member is attached to either the top plate or the bottom plate by welding, preferably spot welding or laser welding, by bonding, preferably brazing or sintering, or by mechanical attachment, preferably using one or more of clamps, brackets, holders, fasteners, joints, springs.

[0052] According to a possible implementation form of the first aspect, the top plate is configured to be operated at a temperature below the temperature at which the bottom plate (6) is operated and wherein the material of the top plate has a different coefficient of thermal expansion from the material of the bottom plate for obtaining identical or similar thermal expansion of the top-and bottom plate between non-operating temperature of the top- and bottom plates and the respective operating temperatures of the top-and bottom plates.

[0053] According to a second aspect, there is provided a molecular distillation process for isotopic separation of lithium in a molecular still comprising at least one bottom plate forming an evaporator and at least one top plate forming a condenser, the process comprising transporting molten lithium along the bottom plate and / or along the top plate by flow of molten lithium driven by capillary action of at least one capillary member .

[0054] According to a possible implementation form of the second aspect, the method comprises isotopically separating a feed stream of molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 into an enriched molten lithium-6 stream and an enriched molten lithium-7 stream by molecular distillation of the feed stream of molten lithium metal feed material, using the molecular still.

[0055] According to a possible implementation form of the second aspect, the method comprises operating the bottom plate at a higher temperature than operating the top plate to obtain a higher evaporation rate on the bottom plate than on the top plate thereby generating a net flow of molten lithium from the bottom plate to the top plate, preferably within each stage .

[0056] According to a possible implementation form of the second aspect, the method comprises operating the molecular still with a partial vacuum, preferably a high vacuum. expansion joint connecting a housing upper part to a housing lower part, preferably an expansion joint, comprising using the expansion joint as a vacuum suction conduit.

[0057] According to a possible implementation form of the second aspect, an expansion joint connecting a housing upper part to a housing lower part, preferably an expansion joint comprising bellows, serves as a vacuum suction conduit thereby allowing the molecular still to be brought to high vacuum quicker due to the shorter distance to a vacuum pump when going through the expansion joint.

[0058] In a possible implementation form of the first or second aspect, the molecular still is configured for one of: isotopic separation by molecular distillation of potassium-39 and potassium-41 as molten potassium metal (K) with a melting point of 64 °C and a boiling point of 756 °C, at atmospheric pressure, isotopic separation by cryogenic molecular distillation or cryogenic short path distillation of chlorine-35 and chlorine-37 as dichlorine (C12) with a melting point of -102°C and a boiling point of -34°C, at atmospheric pressure, preferably operating below -34°C, isotopic separation by cryogenic molecular distillation or cryogenic short path distillation of chlorine-35 and chlorine-37 as hydrogen chloride (HC1) with a melting point of -114°C and a boiling point of -85°C, at atmospheric pressure, preferably operating below -85 °C, isotopic separation by cryogenic molecular distillation or cryogenic short path distillation of carbon-14 from carbon-12 and carbon-13 as methane (CH4) or carbon monoxide (CO) , isotopic separation by cryogenic molecular distillation or cryogenic short path distillation of boron-11 and boron-12 as boron trifluoride (BF3) with a melting point of -127°C and a boiling point of -100°C, at atmospheric pressure, preferably operating below -100°C, isotopic separation by molecular distillation or short path distillation of hydrogen-1 and hydrogen-2 (deuterium) as hydrogen dioxide (H20) with a melting point of 0°C and 4°C and a boiling point of 100°C and 101°C, for water and heavy water respectively, at atmospheric pressure, preferably operating between 5 °C and 10°C, or isotopic separation by molecular distillation or short path distillation of hydrogen-2 (deuterium) and hydrogen-3 (tritium) as hydrogen dioxide (H20) with a melting point of 4°C and 9°C and a boiling point of 101°C and 102 °C, for heavy water and super heavy water respectively, at atmospheric pressure, preferably operating between 10°C and 15°C.

[0059] These and other aspects will be apparent from the example (s) and embodiment ( s ) described below.

[0060] BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In the following detailed portion of the present disclosure, the aspects, embodiments, and implementations will be explained in more detail with reference to the example embodiments shown in the drawings, in which:

[0062] Fig. 1 is a side-sectional view of a diagrammatic representation of an embodiment of a molecular still,

[0063] Fig. 2 is a top-sectional view of a diagrammatic representation of an upper portion of the molecular still of Fig. 1,

[0064] Fig. 3 is a top-sectional view of a diagrammatic representation of a lower portion of the molecular still of Fig. 1, Fig, 4 is a top-sectional view of a diagrammatic representation of an upper portion of the molecular still of Fig. 2 with a larger number of stages,

[0065] Fig. 5 is a top-sectional view of a diagrammatic representation of a lower portion of the molecular still of Fig. 4, and

[0066] Fig. 6 is a sectional view of a diagrammatic representation of an embodiment of a molecular still with a large number of stages .

[0067] DETAILED DESCRIPTION

[0068] Fig. 1 shows an embodiment of a molecular distillation system for isotopic separation of lithium comprising a molecular still 1 for isotopically separating lithium-6 and lithium-7 from a mixture thereof by molecular distillation.

[0069] The still 1 is configured for isotopically separating a feed stream of molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 into an enriched molten lithium-6 stream and an enriched molten lithium-7 stream. The feed stream of molten lithium metal feed material enters the still 1 through a feed port 2 on the lower side of the still 1. The enriched molten lithium-6 stream leaves the still 1 through a first outlet port 3 which is arranged in a lateral area of the still 1, e.g. as shown in a lateral side or in the bottom of the housing near a lateral side and an enriched molten lithium-7 stream leaves the still 1 through a second outlet port 4 which is arranged on an opposite lateral side of the still 1. The molecular still 1 may be described as a horizontal still since the main extent of the molecular still 1 is in a horizontal direction. The molecular still 1 may comprise a single stage or several stages in series. Fig. 1 shows a still 1 with three stages, the first stage is shown on the left side of Fig. 1, the third stage is shown on the right side of Fig. 1 and the second stage is between the first and second stage, i.e. the stages extend horizontally. The second stage is marked by an interrupted line forming a rounded rectangle.

[0070] Molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 is fed to the still 1 by a feed conduit (not shown) that leads to a feed port 2, preferably as a substantially constant stream, but this could also be an intermittent stream.

[0071] The molecular still 1 comprises a, preferably substantially horizontal, top plate 8 that forms a condenser that preferably extends horizontally along all of the stages of the still 1, although it is also possible to provide a separate top plate for a stage. The top plate 8 is arranged in an upper part of the molecular still 1, above a bottom plate 6 that forms an evaporator. The, preferably substantially horizontal, bottom plate 6 extends substantially horizontally along all of the stages of the still 1, although it is also possible to provide a separate bottom plate for a stage. The bottom plate 6 is arranged in the lower part of the still 1 vertically spaced from the top plate 8. The space between the top- and bottom plates 8, 6 is hollow and a vacuum, preferably a high vacuum is applied to this space during operation of the still 1. Spacer plates or baffles (not shown) may be placed between the top- and bottom plates 8, 6 to maintain a fixed spacing, to resist the large force from ambient atmosphere pressing on the top- and bottom plates 8, 6, and to ensure the top- and bottom plates 8, 6 do not deform or creep under the large forces. The vacuum is obtained by connection to an external vacuum pump (not shown) and the top- and bottom plates 8, 6 are received in a leak-tight housing to allow the creation of a high vacuum between the top- and bottom plates 8, 6. The outside of still 1 can be placed in air, inside of a containment with inert gas to minimize oxidation of the outside of the still or to allow for carbon felt insulation, which does not react with lithium metal but oxidizes in air, or in a vacuum chamber, allowing for the still 1 not to experience pressure differential forces. In case of leaks it is preferable to have inert gas or vacuum on the outside of the still 1 and a second barrier / containment to minimize the risk of fire or ingress of oxygen into the still 1.

[0072] A heat exchange medium is supplied to the molecular still 1, where it is utilized to heat the evaporator plate 6 to drive the isotopic separation process. The evaporator plate 6 is preferably heated to at least approximately 400°C, preferably to approximately 550°C.

[0073] High-temperature heat exchange medium is fed to a lower passage 5 in the still 1 extending substantially horizontally along the evaporator plate 6 for heating the molten lithium in the lower portion of the molecular still 1 and from there the heat exchange medium passes through a heat exchanger (not shown) where it exchanges heat with a cooling medium so that the temperature of the heat exchange medium is lowered before entering an upper passage 7 of the molecular still 1. The cool heat exchange medium in the upper passage 7 cools the top plate 8.

[0074] The high-temperature heat exchange medium enters the lower passage 5 through a first heat exchange medium inlet 15 that is arranged at or close to the free horizontal extremity of the first stage and exits the lower passage 5 through a first heat exchange medium outlet 16 which is arranged at or close to the free horizontal extremity of the last stage (in the present embodiment the free horizontal extremity of the third stage) . The cool heat exchange medium enters the upper passage 7 through a second heat exchange medium inlet 17 that is arranged at or near the free horizontal extremity of the last stage and exits the upper passage 7 through a second heat exchange medium outlet 18 that is arranged at or near the free horizontal extremity of the first stage.

[0075] Thus, the cooled heat exchange medium is fed to the upper passage 7 that extends horizontally along the top plate 8 of the still 1 with its condensing element (s) 130, and from there the heat exchange medium exits the molecular still 1 through the second heat exchange medium outlet 18, and from there the heat exchange medium is can be transported to a heat exchanger (not shown) that heats the heat exchange medium so that it can be circulated back to the lower passage 5.

[0076] The heat exchange medium is preferably circulated in a heat exchange loop (not shown) . Alternatively, electrical heating elements can be used to supply heat to the bottom plate 6 to drive the isotopic separation process and gas cooling can be circulated in the upper passage 7 to cool the condenser. Constant evaporator and condenser temperatures can be maintained by measuring the temperature of the bottom plate 6 (evaporator) and top plate 8 (condenser) , respectively, using thermocouples and adjusting the electric current supplied to the heaters and adjusting a blower speed circulating the cooling gas (heat exchange medium) , respectively, to maintain specified operating temperatures.

[0077] Alternatively, the bottom plate 6 (evaporator) can be cooled by passive means such as cooling fins (not shown) which transfer the heat to air which is driven by buoyancy or by radiative cooling to the surroundings.

[0078] Molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 is fed to the molecular still 1 by a feed conduit that leads to the feed port 2 at the lower portion of the molecular still 1, preferably as a substantially constant stream, but this could also be an intermittent stream. The lithium can be fed by e.g. gravity, siphon, thermosiphon, gas lift, mechanical pump. The molecular still 1 may comprise a plurality of horizontally distributed stages (three are shown as an example in this embodiment) but a molecular still 1 could constitute more than 100 stages.

[0079] After entering through the feed port 2, molten lithium is transported by a capillary member 12 in the molecular still 1. The capillary member 12 extends horizontally along or on the bottom plate 6 (preferably as a pad-shaped member) or is an integral part of the bottom plate 6, e.g. by the upper surface of the open plate forming the capillary member 12. The heat supplied by the hot heat exchange medium in the lower passage 5 is transferred to the bottom plate 6 and to the capillary member 12. A suitable temperature range for the bottom plate 6 and / or the capillary member 12 for evaporation of molten lithium is between 400°C and 700°C.

[0080] Evaporation of molten lithium from the one or more capillary members 12 or from molten lithium on the bottom plate 6 causes lithium to be removed from the capillary member and through the capillary effect of the capillary member molten lithium is transported to those areas of the capillary member 12 with the lowest content / concentration of molten lithium in the capillary member 12. The molecular still 1 is configured such that the capillary member 12 transports enriched lithium-7 towards the second outlet port 4.

[0081] One or more capillary members 10,11 are arranged in the upper portion of the molecular still 1. The one or more capillary members 10,11 are part of the top plate 8 or are in contact with the top plate 8 and extend in parallel with the top plate 8. In an embodiment, the one or more capillary members 10,11 are pad-shaped elements. In another embodiment, the one or more capillary members 10, 11 are an integral part of the top plate 8, e.g. by the one or more capillary members 10,11 being an integral part of the downwardly facing surface of the top plate 8. One or more capillary members 11 are arranged between the top plate 8 and the bottom plate 6 for transporting molten lithium from the end of a stage back to the start of a previous stage, or from the end of a stage to the first outlet 3. This capillary member 11 is angled / tilted downwards from the top plate 8 to a laterally displaced position on the bottom plate 6 of the previous stage or to the first outlet 3. In embodiment, this slanting capillary member 11 transports molten lithium by a combination of gravity and surface tension and or capillary effect. However, it should be understood that this slanting capillary member 11 may in fact not be a capillary member and instead be a member that is configured to transport molten lithium by gravity only.

[0082] The top plate 8 and / or the one or more capillary members 10, 11 are cooled by the cool heat exchange medium in the upper passage 7, for keeping the top plate 8 and / or the one or more capillary members 10,11 at a temperature that is suitable for compensation of the evaporated lithium. A suitable temperature range for the top plate 8 and / or the one or more capillary members 10,11 is 300 to 600 °C or generally known to 200 °C cooler than the bottom plate 6, preferably 100 °C cooler than the bottom plate 6, minimizing the evaporation of condensed lithium from the top plate without having large radiative and conductive heat losses.

[0083] The lithium that is evaporated in the lower part of the molecular still 1 condenses on the one or more capillary members 10,11, and / or on the top plate 8. The capillary members 10,11 are configured to transport enriched lithium-6 that has condensed thereon to a previous stage of the molecular still 1, or to the first outlet 3, together with the capillary members 11. Accordingly, the capillary members 10,11,12 are arranged such that lithium flow from one stage to the other is serial. While the lithium passing through the bottom of a stage some of the lithium will evaporate and condense on the top plate 8 / capillary member 10, 11 associated with that stage and condensed lithium is transported by the capillary member 11 to the bottom plate 8 of the previous stage or to the first outlet port 3. This drives the condensed lithium backward towards the first stage, while the condensed lithium transported to the bottom of the stages displaces molten lithium forwards assisted by the capillary effect of the capillary member 12. In this way counter flowing streams of lithium are provided where the condensed lithium which is lithium-6 rich flows backward through the stages to the first outlet port 3 and the remaining lithium which is lithium-7 rich flows forward through the stages towards the second outlet port 4. In this way, enriched lithium-6 is concentrated at the start of a stage and enriched lithium-7 is concentrated at the end of the stage. The evaporator and condenser patterns are overlaid in assembly, connecting each condenser stage with the previous evaporator stage.

[0084] The molecular still 1 comprises a housing forming an outer leak-tight barrier in which the top plate 8 and bottom plate 6 are accommodated. The housing comprises an upper part for accommodating the top plate 8 and a lower part for accommodating the bottom plate 6. The upper part is connected to the lower part by an expansion joint or mechanism 19 that allows for differential thermal expansion of the lower part relative to the upper part. The expansion joint or mechanism 19 preferably comprises bellows. The molecular still 1 can also have spacer plates or baffles, not shown, that maintain a fixed spacing of the bottom plate 6 and top plate 8 throughout the molecular still, and resisting collapsing or deformation from the potential forces exerted by potential differential pressure between the inside and outside of the molecular still 1. The spacer plates or baffles, not shown, can also be equipped with capillary members to e.g. guide the lithium from a condenser stage to a previous evaporator stage. Portions of the molecular still 1 not equipped with capillary members can have coatings not wetted by lithium or features to minimize or eliminate the flow or bypass of molten lithium where it could be undesirable, e.g. condensed lithium bypassing down the spacer plates or baffles, not shown, to the evaporator bellow, lowing the stage separation factor and thus the overall efficiency of the still.

[0085] In an embodiment, the expansion joint 19 is used as a vacuum suction conduit, allowing the molecular still 1 to be brought to high vacuum quicker due to a shorter distance to a vacuum pump when going through the bellow expansion joint 19.

[0086] Figs. 4 and 5 show another embodiment of the molecular stilll for isotopically separating lithium-6 and lithium-7 from a mixture thereof by molecular distillation. In this embodiment, structures, and features that are the same or similar to corresponding structures and features previously described or shown herein are denoted by the same reference numeral as previously used for simplicity. This embodiment is essentially the same as the first embodiment, except that the molecular still 1 according to this embodiment comprises five stages, and accordingly, there are four capillary members 10 and four capillary members 11 transporting the condensed lithium-6 rich lithium through the stages and through the molecular still 1 and towards the first outlet 3.

[0087] Fig. 6 shows another embodiment of the molecular stilll for isotopically separating lithium-6 and lithium-7 from a mixture thereof by molecular distillation. In this embodiment, structures, and features that are the same or similar to corresponding structures and features previously described or shown herein are denoted by the same reference numeral as previously used for simplicity. This embodiment is essentially the same as the first embodiment, except that the molecular still 1 according to this embodiment comprises sixty stages. However, it should be understood that the molecular still 1 may be constructed with a much larger number of stages, such as well over 100 stages. In Fig 6. the arrows between stages 20 indicate the main direction of the flow of molten lithium.

[0088] In an embodiment, the capillary member 10,11,12 comprises one or more of: capillary flow lumens, capillary flow channels, porous material, web material.

[0089] In an embodiment, not shown, the molecular still comprises one or more channels or conduits configured for transporting molten lithium by gravity, e.g. by slanting or sloping channels or conduits. In an embodiment, the capillary member 10, 11,12 comprises wire screen, fine metal wire screen, sintered wire mesh, microporous sintered metal mesh sheet, sintered metal fiber felt, and / or carbon felt.

[0090] In an embodiment, the capillary member 10, 11,12 comprises capillary channels. Preferably the capillary channels are grooves arranged in a surface of the capillary members 10,11,12 preferably the capillary channels are formed in a surface of the top plate 8, or in a surface of the bottom plate 6, and or in a surface of the spacer or baffle plates, not shown.

[0091] In an embodiment, capillary member 10,11,12 is attached to either the top plate 8 or the bottom plate 6 by welding, preferably spot welding or laser welding, by bonding, preferably brazing or sintering, or by mechanical attachment, preferably using one or more of clamps, brackets, holders, fasteners, joints, springs.

[0092] In another embodiment, the one or more capillary members 10,11 are oriented perpendicular to the top plate 8 for transporting molten lithium from the end of a stage back to the start of a previous stage, or from the end of a stage to the first outlet 3, as to optimize the surface area of capillary members 10,11. In another embodiment, the one or more capillary members 10,11 are made thin, e.g. in the form of braided wire strands, for transporting molten lithium from the end of a stage back to the start of a previous stage, or from the end of a stage to the first outlet 3, as to optimize the surface area of capillary members 10,11. In an embodiment, the top plate 8 is configured to be operated at a temperature below the temperature at which the bottom plate 6 is operated, and the material of the top plate 8 has a different coefficient of thermal expansion from the material of the bottom plate 6 for obtaining identical or similar thermal expansion of the top- and bottom plate 8, 6 between non-operating temperature (ambient temperature) of the top- and bottom plates 8, 6 and the respective operating temperatures of the top- and bottom plates 8, 6.

[0093] In an embodiment, the top plate 8, the bottom plate 6, and or the spacer or baffle plates, not shown, have a coating or other features to obstruct the flow of lithium in undesirable directions, e.g. to stop lithium from short circuiting between the evaporator and condenser capillary members for the same stage or from the condenser capillary member of one state to the neighboring condenser capillary members. An example of such a feature is to leave a small spacing between the capillary member or members of the top- or bottom plates 8, 6, as shown in the Figs. , such that only a smooth metal surface is presented to the molten lithium, making it difficult for the molten lithium to flow across by because of surface tension of molten lithium.

[0094] In an embodiment, the bottom plate 6 is operated at a higher temperature than the top plate 8 to obtain a higher evaporation rate on the bottom plate 6 than on the top plate 8 thereby generating a net flow of molten lithium from the bottom plate 6 to the top plate 8, preferably within each stage . In an embodiment, the molecular still 1 is operated with a partial vacuum, preferably a high vacuum.

[0095] In an embodiment, the molecular still 1 is configured for isotopic separation of media other than lithium, e.g. : isotopic separation by molecular distillation of potassium-39 and potassium-41 as molten potassium metal (K) with a melting point of 64°C and a boiling point of 756 °C, at atmospheric pressure, isotopic separation by cryogenic molecular distillation or cryogenic short path distillation of chlorine-35 and chlorine-37 as dichlorine (C12) with a melting point of -102°C and a boiling point of -34 °C, at atmospheric pressure, preferably operating below -34°C, isotopic separation by cryogenic molecular distillation or cryogenic short path distillation of chlorine-35 and chlorine-37 as hydrogen chloride (HC1) with a melting point of -114°C and a boiling point of -85°C, at atmospheric pressure, preferably operating below -85 °C, isotopic separation by cryogenic molecular distillation or cryogenic short path distillation of carbon- 14 from carbon-12 and carbon-13 as methane (CH4) or carbon monoxide (CO) , isotopic separation by cryogenic molecular distillation or cryogenic short path distillation of boron- 11 and boron-12 as boron trifluoride (BF3) with a melting point of -127°C and a boiling point of -100°C, at atmospheric pressure, preferably operating below -100°C, isotopic separation by molecular distillation or short path distillation of hydrogen-1 and hydrogen-2 (deuterium) as hydrogen dioxide (H2O) with a melting point of 0°C and 4°C and a boiling point of 100°C and 101°C, for water and heavy water respectively, at atmospheric pressure, preferably operating between 5°C and 10°C, or isotopic separation by molecular distillation or short path distillation of hydrogen-2 (deuterium) and hydrogen-3 (tritium) as hydrogen dioxide (H2O) with a melting point of 4°C and 9°C and a boiling point of 101°C and 102°C, for heavy water and super heavy water respectively, at atmospheric pressure, preferably operating between 10 °C and 15°C.

[0096] The various aspects and implementations have been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed sub ect-matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0097] The reference signs used in the claims shall not be construed as limiting the scope. Unless otherwise indicated, the drawings are intended to be read (e.g. , cross-hatching, arrangement of parts, proportion, degree, etc. ) together with the specification, and are to be considered a portion of the entire written description of this disclosure. As used in the description, the terms "horizontal", "vertical", "left", "right", "up" and "down", as well as adjectival and adverbial derivatives thereof simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms "inwardly" and "outwardly" generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.

Claims

CLAIMS1. A molecular distillation system for isotopic separation of lithium comprising a molecular still (1) , the molecular still comprises at least one bottom plate (6) forming an evaporator characterized by at least one top plate (8) forming a condenser, and by the molecular still (1) comprising at least one capillary member (10,11,12) configured for transporting molten lithium in the molecular still (1) by capillary effect of the at least one capillary member (10,11,12) .

2. The molecular distillation system of claim 1, wherein the at least one capillary member (10, 11,12) is configured to transport molten lithium along the at least one bottom plate (6) and / or along the at least one top plate (8) by capillary effect of the at least one capillary member.

3. The molecular distillation system of claim 1 or 2, wherein the capillary member (10,11,12) comprises one or more of: capillary flow lumens, capillary flow channels, porous material, web material .

4. The molecular distillation system of any one of claims 1 to 3, wherein the at least one capillary member (10,11, 12) extends along at least a portion of the at least one bottom plate (6) and / or extends along a portion of the at least one top plate ( 8 ) .

5. The molecular distillation system of any one of claims 1 to 4, wherein the at least one bottom plate (6) is a substantially horizontal plate.

6. The molecular distillation system of any one of claims 1 to 5, wherein the at least one top plate (8) is a substantially horizontal plate.

7. The molecular distillation system of any one of claims 1 to 6, wherein the molecular still (1) comprises two or more stages, wherein the at least one capillary member (10, 11,12) is configured to transport molten lithium within a stage and / or from one stage to a neighboring stage.

8. The molecular distillation system of claim 7, wherein the at least one bottom plate (6) extends along several stages, and / or wherein the at least one top plate (8) extends along several stages.

9. The molecular distillation system of any one of claims 1 to 8, wherein the molecular still (1) comprises:- a feed port (2) for receiving the mixture of molten lithium,- a first outlet port (3) for enriched molten lithium-6, and- a second outlet port (4) for enriched molten lithium-7.

10. The molecular distillation system of claim 9, wherein the at least one capillary member (12) is associated with the bottom plate (6) and configured to transport enriched molten lithium-7 towards the second outlet port (4) .

11. The molecular distillation system of claim 9 or 10, wherein the at least one capillary member (10,11,12) is configured to transport enriched molten lithium-6 towards the first outlet port (3) .

12. The molecular distillation system of any one of claims 1 to 11, comprising a plurality of stages, each stage comprising at least one capillary member (10) associated with the top plate (8) for transporting enriched molten lithium-6 within the stage concerned and towards a next stage or towards the first outlet port (3) .

13. The molecular distillation system of claim 12, wherein at least one stage comprises at least one capillary member (11) that is associated with the top plate (8) and is configured for transporting enriched molten lithium-6 back to the start of the previous stage or towards the first outlet port (3) .

14. The molecular distillation system of any one of claims 1 to 13, comprising one or more channels or conduits configured for transporting molten lithium by gravity.

15. The molecular distillation system of any one of claims 1 to 14, comprising a housing forming an outer leak-tight barrier in which the top plate (8) and bottom plate (6) are accommodated, the housing comprising an upper part for accommodating the top plate (8) and a lower part for accommodating the bottom plate (6) , wherein the upper part is connected to the lower part by an expansion joint or mechanism (19) that allows for differential thermal expansion of thelower part relative to the upper part, the expansion joint or mechanism (19) preferably comprising bellows.

16. The molecular distillation system of any one of claims 1 to 15, wherein the at least one capillary member (10, 11,12) is shaped like a pad.

17. The molecular distillation system of any one of claims 1 to 16, wherein the capillary member (10,11,12) comprises wire screen, fine metal wire screen, sintered wire mesh, microporous sintered metal mesh sheet, sintered metal fiber felt and / or carbon felt.

18. The molecular distillation system of any one of claims 1 to 17, wherein the capillary member (10,11,12) comprises capillary channels, preferably the capillary channels are grooves arranged in a surface of the capillary member (10,11, 12) , preferably the capillary channels are formed in a surface of the top plate (8) , in a surface of the bottom plate (6) , and / or in a surface of the sides of spacer or baffle plates, spacing the top- and bottom plates (8, 6) from touching one another while under vacuum, preferably the capillary channels in the sides of the baffle plates guiding the condensate lithium from one condenser stage to the start of the previous evaporator stage to produce a counterflow.

19. The molecular distillation system of any one of claims 1 to 18, wherein the at least one capillary member (10, 11,12) attached to either the top plate (8) or the bottom plate (6) by welding, preferably spot welding or laser welding, by bonding, preferably brazing or sintering, or by mechanicalattachment, preferably using one or more of clamps, brackets, holders, fasteners, joints, springs.

20. The molecular distillation system of any one of claims 1 to 19, wherein the top plate (8) is configured to be operated at a temperature below the temperature at which the bottom plate (6) is operated and wherein the material of the top plate (8) has a different coefficient of thermal expansion from the material of the bottom plate (6) for obtaining identical or similar thermal expansion of the top- and bottom plate (8, 6) between the non-operating temperature of the top- and bottom plates (8, 6) and the respective operating temperatures of the top- and bottom plates (8, 6) .

21. A molecular distillation process for isotopic separation of lithium in a molecular still (1) comprising at least one bottom plate (6) forming an evaporator and characterized by at least one top plate (8) forming a condenser, the process comprising transporting molten lithium along the bottom plate and / or along the top plate by flow of molten lithium driven by capillary action of at least one capillary member (10,11, 12) .

22. The molecular distillation process of claim 21, comprising isotopically separating a feed stream of molten lithium metal feed material containing the mixture of lithium-6 and lithium- 7 into an enriched molten lithium-6 stream and an enriched molten lithium-7 stream by molecular distillation of the feed stream of molten lithium metal feed material, using the molecular still (1) .

23. The molecular distillation process of claim 21 or 22, comprising operating the bottom plate (6) at a higher temperature than operating the top plate (8) to obtain a higher evaporation rate on the bottom plate (6) than on the top plate (8) thereby generating a net flow of molten lithium from the bottom plate (6) to the top plate (8) , preferably within each stage.

24. The molecular distillation process of any one of claims 21 to 23, comprising operating the molecular still (1) with a partial vacuum, preferably a high vacuum.

25. The molecular distillation process claim 24, wherein an expansion joint (19) connecting a housing upper part to a housing lower part, preferably an expansion joint, comprising using the expansion joint (19) as a vacuum suction conduit.

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