Electrode mounting assembly, cell, and method of use

Abstract

This invention provides an electrolytic cell and a method for using the same, which extend the lifespan of the carbon electrodes in the electrolytic cell. [Solution] An electrolytic cell and a method of using the same are provided. An electrode mounting assembly for an electrolytic cell, an electrolytic cell having one or more electrode mounting assemblies, and a method of using the same, comprising a carbon-containing electrode and one or more deformable mounting elements in direct or indirect contact with the carbon-containing electrode, wherein one or more deformable mounting elements deform during use at a stress less than the stress that would cause the carbon-containing electrode to break, in order to adapt to the elongation of the carbon-containing electrode.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims priority to U.S. Provisional Application No. 63 / 057561, filed on September 8, 2020, the entire contents of which are incorporated herein by reference for all purposes.

Background Art

[0002] The industrial production of fluorine element (F2) and related fluorinated gases, such as nitrogen trifluoride (NF3), is mainly carried out in electrolytic cells. In particular, for the production of fluorine gas, the anode of such cells is made of carbon. In order to function, the anode must be connected to a power supply so that current can flow between the cathode and the anode.

[0003] Making a reliable connection to the anode in a fluorine cell is difficult due to the very active chemical conditions found in such cells. The liquid electrolyte used in such cells is typically a molten salt mixture of potassium fluoride (KF) and hydrogen fluoride (HF). For the production of NF3, ammonium fluoride is used instead of, or in addition to, KF. This electrolyte results in very corrosive conditions that tend to attack the metal components of the anode connection device, combined with elevated operating temperatures and the anode potential applied to the anode. Further, for efficient and stable operation, the electrical resistance of the connection to the anode must start and remain low over the life of the anode. Deterioration of the electrical connection to the anode is known to cause anode failure, as well - described by Ring and Royston (Australian Atomic Energy Commission Report E281, 1973, ISBN 0 642 99601 6).

[0004] Numerous methods for attaching a carbon anode to an electrical source and / or other support element have been proposed in the prior art, including those disclosed in U.S. Patent No. 5,290,413 (circumferential metal sleeve around the top of the anode), U.S. Patent No. 3,041,266 (metal hanger bar with anode attached by several bolts), Japanese Patent No. 7,173,664 (threaded bolt inserted first through a metal bar and then into the carbon anode), U.S. Patent No. 5,688,384 (thread in the top of the carbon anode), Korean Patent No. 10-0286,717 (carbon anode held by bolts between two metal plates), Chinese Patent Application Publication No. 102,337,491 (clamp plate), U.S. Patent No. 8,349,164 (clamp plate), Zhao et al. (clamp plate), and U.S. Patent No. 6,210,549 (C-type anode hanger bar and threaded rod). [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Despite the many different mounting methods, carbon anodes will eventually break down during use in electrolysis after a certain period. The breakdown of the carbon anode renders the cell unusable, requiring the reconstruction of at least some part of the cell. Therefore, there is a need in this field to extend the lifespan of carbon electrodes in electrolytic cells. [Means for solving the problem]

[0006] The present invention provides an electrode mounting assembly and an electrolytic cell comprising the electrode mounting assembly, the electrode mounting assembly comprising a carbon-containing electrode and one or more deformable mounting elements in direct or indirect contact with the carbon-containing electrode, the one or more deformable mounting elements deform at a stress lower than the fracture strength of the carbon-containing electrode to adapt to the elongation of the carbon-containing electrode during use.

[0007] In one other embodiment, the present invention provides an electrolytic cell comprising one or more electrode mounting assemblies of the present invention, a container, an electrical distribution element, an electrolytic bath, and one or more reverse-charged electrodes.

[0008] In one yet another embodiment, the present invention provides a use or method of an electrolytic cell for producing a fluorine-containing material, comprising the step of introducing electrical energy into the electrolytic cell to cause a reaction in a carbon-containing electrode and one or more reverse-charged electrodes to produce a fluorine-containing material in the carbon-containing electrode.

[0009] The present invention provides the benefits of a cell and electrode mounting assemblies, which may be anode mounting assemblies that reduce the tendency of carbon electrodes (anodes) to fail, thereby extending the life of the electrodes, enabling longer cell operation, reducing maintenance costs by decreasing the frequency of cell rebuilding, and improving safety. Sometimes, a failed electrode (anode) can cause an electrical short circuit or electric arc within the cell, resulting in damage to many of the internal components of the cell. Furthermore, the present invention provides an electrode mounting assembly (anode mounting assembly) that has good electrical contact and resistance to corrosion. In addition, corrosion of electrical contacts to carbon electrodes can be reduced by keeping the connection points and metal components "dry," i.e., preferably on the surface of the liquid electrolyte. Cells made using the electrode mounting assemblies of the present invention can, in some cases, be used for more than 20% longer than conventional electrodes operated in equivalent cells under the same operating conditions. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of the electrolytic cell of the present invention. [Figure 2] This is a schematic diagram of one electrode mounting assembly of the present invention. [Figure 3] This is a schematic diagram of another electrode mounting assembly of the present invention. [Figure 4] This is a schematic diagram of another electrode mounting assembly of the present invention. [Figure 5] This is a schematic diagram of another electrode mounting assembly of the present invention. [Figure 6] This is a schematic diagram of another electrode mounting assembly of the present invention. [Modes for carrying out the invention]

[0011] Detailed description of the invention All patents and patent applications referenced in the background art or in this detailed description are incorporated herein by reference in their entirety.

[0012] Figure 1 is a simplified schematic diagram showing one embodiment of an electrolytic cell for the electrolytic synthesis of fluorine-containing materials having an electrode mounting assembly according to the present invention. Reference numeral 10 indicates an electrolytic cell for the electrolytic synthesis of fluorine-containing materials that uses a fluoride ion-containing molten salt electrolytic bath 12 in an electrolyte resistance container 19. The fluoride ion-containing molten salt electrolytic bath 12 may contain a mixed molten salt containing one or more fluoride salts and hydrogen fluoride (HF), such as KF-2HF, NH4-2HF, or a mixture of KF, NH4F and HF. Furthermore, the electrolytic cell comprises an anode 13 at least partially immersed in the molten salt electrolytic bath 12, a cathode 14, and a partition wall 15. Furthermore, the electrolytic cell comprises a current distribution element which may be a supply busbar 16, an optional rectifier, and a power supply source 17. Typically, the cathode 14 includes nickel, stainless steel, carbon steel, etc. Typically, the anode 13 includes a carbon-containing material. The electrode assembly of the present invention comprises at least one electrode, typically at least one anode, and a mounting assembly comprising one or more deformable elements, which may also be referred to as a deformable mounting assembly, embodiments of the mounting assembly are shown in detail in Figures 2-6. In addition, the electrolytic cell 10 of the present invention may further comprise means for maintaining temperature (not shown) and means for replenishing salts such as HF and / or NH3 consumed during the process of producing a fluorine-containing material which may be fluorine gas, nitrogen trifluoride, or other fluorinated gas. The present invention is understood to be usable for any carbon-containing electrode (although described herein as an anode) to produce any final product, typically a fluorine-containing material.

[0013] In the embodiment shown in Figure 1, when the electrolytic cell 10 is operating, electrical energy triggers a chemical reaction in the cell bath. The fluorine-containing material is produced at the anode 13. The partition wall 15 separates and retains the fluorine-containing gas from the hydrogen gas produced at the cathode 14. The hydrogen gas and the fluorine-containing gas are removed from the cell by a separation conduit (not shown) connected to a separation collection container (not shown).

[0014] Typically, the anode 13 used in an electrochemical fluorine generation cell is made of a carbon-containing material such as carbon or ungraphitized carbon, but carbon of varying degrees of graphitization, including fully graphitized carbon, can also be used. (Carbon-containing materials can be used to make cathodes in other electrolytic cells that benefit from the present invention; therefore, note that the present invention is not limited to anodes made of carbon-containing materials, and the terms carbon-containing electrode, carbon-containing anode, carbon electrode and carbon anode may be used interchangeably herein.) The carbon-containing material used to make the electrode may be low-permeability, high-permeability, monolithic, or composite in structure. In a composite structure, there may be an internal core of low-permeability carbon and an external shell or conductive diamond layer of high-permeability carbon. Alternatively, in a composite structure, the carbon-containing anode may comprise a carbon fiber material and one other form of carbon, such as isotropically pressed carbon powder or mesocarbon microbeads. The outer layer of the carbon electrode may be formed on, coated on, or attached to the inner core or an alternative carrier (UK Patent Application No. 2135335 (Marshall)), or otherwise assembled or fabricated (US Patent Nos. 3655535 (Ruehlen et al.), 3676324 (Mills), 3708416 (Ruehlen et al.) and 3720597 (Ashe et al.) and US Patent Application Publication No. 2008 / 0314759 (Furuta et al.)). Furthermore, carbon impregnated with a metal such as nickel or a salt such as lithium fluoride is also useful in the present invention. Furthermore, carbon electrodes coated with a thin layer of metal in the region where the anode is connected to or intersects with a power source for the anode are also useful in the present invention. The surface of the carbon may be rough, or it may be smoothly cut or polished. The surface may have features such as grooves and holes. Any carbon anode containing any useful type of carbon can be used as the carbon electrode in the electrode assembly of the present invention. Typically, carbon-containing electrodes used as anodes in electrolytic cells are molded lumps of compressed carbon, including in the form of coal or petroleum-derived coke, and a pitch binder.Typically, the formed anode is baked to increase density, harden, and carbonize the pitch. Blocks of isotropically pressed carbon powder can also be used, which can be directly molded into the final shape or machined from a larger block into the final shape. Generally, carbon anodes are rectangular in shape with a substantially flat or flat surface, but may have any shape such as a square, disc, or cylinder.

[0015] Through numerous investigations into the causes of anode failure, the inventors discovered a previously unrecognized mode of failure. They found that electrodes containing carbon-containing materials of the type used in electrolytic cells for fluorine and fluoride gas production undergo physical expansion during use. Generally, the degree of this expansion is small, less than 1% for many carbon materials under the conditions found inside electrolytic cells. However, this amount of expansion is sufficient to generate enough stress to break the carbon in many mounting designs. The amount of physical elongation is variable, but typically increases by approximately 0.1% to 2.0% in each dimension of the carbon electrode.

[0016] To demonstrate this characteristic, three samples of non-graphitized carbon (ABR grade manufactured by SGL Carbon (Wiesbaden, Germany)) were placed in a container and exposed to conditions similar to those in the gas phase headspace of a fluorine cell containing HF and F2 gases at 100°C. After several gas charges, the samples were removed, and it was found that their respective length dimensions increased by 0.27%, 1.42%, and 0.53% in size.

[0017] The inventors determined that carbon expansion is induced by the conditions observed inside the electrolytic cell during operation, and that this phenomenon causes excessive stress and fracture. The expansion of anodes containing carbon-containing material is greater than that of conventional kinetic elastic compression and elongation, which are subjected to pressure by all materials in contact with the carbon electrode, i.e., all mounting elements that are in direct or indirect contact with the electrode in the cell and support the electrode in the cell, and / or supply power to the electrode. Furthermore, they found that the expansion of the carbon anode is not reversible, in contrast to changes induced by other means such as thermal expansion. Once carbon undergoes expansion, it maintains its new, larger size even when the cell is stopped. Moreover, the inventors found that the expansion process is not self-limiting; rather, the carbon continues to elongate slowly over time. This effect prevents users from pre-elongating the carbon before mounting it in the electrolytic cell, as the carbon continues to elongate after it has been mounted and positioned for use in the electrolytic cell.

[0018] Devices that generate pressure contact (clamping force) hold the carbon anode in place and provide the typically very strong contact pressure necessary for good electrical connection. Mounting elements such as bolts, bands, and threaded rods are all used as structural elements and provide the pressured contact. Many structural materials are useful, including steel such as Ni-Cu alloy 400, copper, nickel, and nickel-copper alloys. Often, material selection in the prior art is based on corrosion resistance and the ability to withstand the mechanical stresses of assembly conditions. The inventors have found that the use of these types of high-strength materials causes anode fracture after a certain operating time because these materials are considerably stronger than the carbon anode and do not yield when the carbon expands. Typically, the carbon materials used to make electrodes in such cells exhibit brittle fracture behavior, i.e., they withstand only slight elastic deformation before failure by brittle fracture. The carbon material of the carbon anode exhibits no ductile deformation behavior at all, or very limited ductile deformation behavior, which further decreases as the electrode ages with use.

[0019] When attached with normal compressive forces applied to ensure a suitable physical and electrical connection between a carbon anode and one or more of those attachment elements, for example bolts, rods, bands, plates, hangers, clamping devices or combinations thereof made of steel, nickel or normally cold-rolled copper, with respect to a rigid high-strength attachment element, carbon can only stretch slightly before reaching the limit of its elastic deformation. Carbon breaks at the point of maximum stress induced by the attachment element, or near that point of maximum stress. The use of pressure distribution devices such as clamping plates does not prevent this mode of failure. This is because of the elongation of carbon at the boundary of one or more rigid attachment elements.

[0020] The inventors have determined that under normal assembly conditions, the distortion of metal bolts and plates in conventional attachment elements may be on the order of 10 microns, while the expansion of carbon, which is the subject of the present invention, may be 100 microns or more. As described elsewhere, the elongation of the carbon-containing material of the anode due to expansion when used in an electrolytic cell for producing a fluorine-containing material is greater than the expansion of normal attachment elements, and may be more than 1.5 times, more than 2 times, more than 5 times or more than 8 times greater than the expansion of normal attachment elements. Therefore, due to the difference in the scale of elongation between carbon and normal attachment elements, normal (rigid) attachment elements are unable to adapt to the elongation of carbon.

[0021] Typically, the fact that carbon-containing materials weaken over time with use exacerbates the problem of anode failure. The weakening may be the result of chemical decomposition or attack by the severe oxidation environment typically found in these cells, or internal stresses caused by expansion. As a result, after a period of use, often the carbon-containing material exhibits a lower compressive strength than when new. This decrease can be on the order of 50%. Therefore, avoiding the failure of carbon-containing materials depends on the ability to reduce the peak stress on the carbon-containing materials to a relatively low value.

[0022] Many carbon-containing materials used as anodes in electrolytic cells for the production of fluorine and other fluorinated gases have a compressive strength of about 8,000 to 15,000 pounds per square inch (psi) when new. After long-term use in an electrolytic cell, this value can be reduced by half due to the effects of chemical decomposition and expansion of the carbon. Thus, after a period of use, carbon breakage can occur even at stresses above about 6,000 psi.

[0023] The present invention provides a deformable attachment element, cell, and method that accommodate expansion of an anode including a carbon-containing material to prevent breakage of the anode, thereby extending the service life of the electrolytic cell. To achieve this, the deformable attachment element of the present invention reduces the peak stress on the carbon-containing material to a relatively low value.

[0024] Conventional components used to attach an anode by an attachment or clamping force, such as bolts, bands, or rods, are designed to operate within the elastic limit of the material. Greater stresses have required using higher-strength materials or attachment devices with larger cross-sections to reduce the stress in the attachment element. Typically, prior art attachment devices have focused on protecting the contact surface from corrosion and achieving low electrical resistance at the connection due to high contact stresses, using one or more attachment devices that result in high attachment or clamping pressures.

[0025] In contrast, the present invention offers the possibility of improving the mounting of carbon anodes in electrolytic cells by using one or more adaptable or yielding mounting elements to accommodate the physical expansion of carbon. Such one or more deformable mounting elements can be stretched through elastic or plastic deformation, preferably by about 0.1% to about 2% or about 0.1% to about 1% in length (and / or other dimensions), while limiting the maximum stress that can be applied to the carbon to less than the fracture strength of the carbon. Since carbon may weaken over time, the design should limit the peak stress on the carbon to less than 8000 psi, less than 7000 psi, more preferably less than 6000 psi, or even less than 5500 psi. The one or more deformable elements used in the electrode mounting assembly must be selected to provide sufficient displacement, typically suitable displacements being at least about 0.05 to about 10%, about 0.05 to about 5%, about 0.1 to about 3%, or about 0.1 to about 2% of the original dimensions of the carbon.

[0026] This can be achieved by using ductile, low-yield metals or reduced cross-sections in mounting elements (such as bolt shafts, rods, or bands) that transmit mounting forces, which may be clamping forces. The materials and cross-sections are selected together to ensure that the components reach their yield point and deform ductilely before they exert stresses on the carbon electrodes that exceed the fracture stress of carbon.

[0027] One embodiment of a ductile, low-yield metal is well-annealed copper, also known as O60 temper. This copper is any industrially pure grade, such as C11000 alloy. It is well known that copper metals work harden. Under normal conditions for machining copper parts, copper is supplied in a state referred to as "cold-rolled," instead of "1 / 8 hard" or H00 temper, with a minimum yield strength of 20,000 psi (137.9 MPa) at a 0.5% elongation. Harder grades, such as 1 / 4 hard or 1 / 2 hard, are also available. In contrast, well-annealed copper does not have a specific minimum yield strength at a 0.5% elongation, but typically its value is very low, less than about 10,000 psi (69 MPa), often less than about 6,500 psi (44.8 MPa). Typically, machined copper parts need to be annealed to obtain an O60 temper. Other metals that may be suitable, besides copper and copper alloys, include lead, gold, silver, tin, zinc, aluminum, brass, bronze, and various alloys of these metals.

[0028] As described above, the thickness of a metal element can be increased to increase its rigidity; therefore, it is possible to manufacture deformable mounting elements useful in the present invention by using stronger known metals, including steel, Monel, etc., and to reduce the thickness of the metal element to create a deformable mounting element. Because the harsh conditions in electrolytic cells often cause corrosion over time, if one or more deformable elements are used in a mounting assembly, it may be sufficient to simply reduce the thickness of some of the elements by using stronger metals, as is done in the prior art.

[0029] For example, in the embodiment shown in Figure 2, a 3 / 4-inch diameter 4100 series steel alloy metal bolt, commonly used for mounting anodes, is replaced with a bolt made of H00 copper, reducing the diameter to less than approximately 0.5 inches, allowing the bolt to plastically deform before the carbon anode fractures. Carbon steel bolts can also be used, but their diameter needs to be further reduced to less than 0.3 inches. The reduction in bolt shaft diameter should preferably be done without significantly altering the area in which the original bolt cap resides; that is, the bolt shaft must become thinner, but the cap should remain close in size, or otherwise the same size. The combination of size and material properties must be considered so that the deformable mounting element yields sufficiently at some point before the carbon fractures, taking into account all relevant stress concentrations brought about by the details of the mechanical mounting design. Therefore, any changes to the bolt shaft diameter must be made without altering the mounting area for the bolt head in carbon in this example, so as not to increase the stress on the carbon. Therefore, the need to consider these many different criteria, as well as factors such as current capacity for current transmission elements, requires considerable care to achieve all necessary requirements.

[0030] In an alternative embodiment, heat-annealed copper can be used to create deformable mounting elements, deformable regions, or deformable portions thereof. Heat-annealed copper such as ASTM O60 temper does not have a specific yield stress, but it is known to deform under stresses of approximately 10,000 psi (69 MPa) or less. For comparison, H00 temper copper has a yield stress of 20,000 psi (138 MPa), and the most common steels have a yield stress of 25,000 psi (172 MPa) or more.

[0031] As described above, several common metals for this application, such as cold-rolled H00 copper, steel, or copper-nickel alloy 400, can be used as deformable components, provided that care is taken to ensure that the material yields before carbon fracture occurs. Other metals or materials that can be used include lead, gold, silver, tin, zinc, aluminum, brass, and bronze. Conductive polymers such as graphite-filled polytetrafluoroethylene (PTFE) can also be used for current-transmitting components. Softer materials such as plastics and elastomers can be used for non-current-transmitting components, but they must have sufficient strength to support the required mechanical load and be chemically compatible with the environment in the cell. Preferably, the deformable mounting elements include metal. Preferably, the deformable mounting elements do not have, or substantially do not have, materials and elastomer elements that react, burn, or decompose due to the cell environment, or materials and elastomer elements that are otherwise incompatible with the cell environment. Preferably, the deformable mounting elements are conductive and provide conductivity higher than 300 S / m. In some designs, the deformable mounting elements are load-bearing.

[0032] Chinese Utility Model No. 204434734 discloses a flexible element between a carbon anode plate and a metal busbar. Such a flexible element is designed to seal the joint between these elements and prevent corrosion. The flexible element is described as a graphite gasket with a metal coating. Such a flexible element typically does not remain sufficiently compressible after the initial compression set during assembly and therefore does not satisfy the function required in the present invention.

[0033] When properly designed, elastomer components can be used as deformable elements or one of several deformable elements in an electrode assembly. The elastomer components must be chemically compatible with the cell environment or protected from it. Halogenated elastomers such as FKM (fluoroelastomer), FFKM (fluoroelastomer), chloroprene, and other similar materials can be used. Halogenated or non-halogenated polymers such as silicone rubber or any variety of hydrocarbon-based elastomers can be used if protected by encapsulation with a resistant material such as a fluoropolymer. The elastomer components must allow sufficient deformation of the carbon without introducing stress necessary to break the carbon after initial assembly. Therefore, the elastomer components do not need to be fully compressed during the initial assembly of the electrode assembly.

[0034] Useful deformable mounting elements in the electrode mounting assemblies of the present invention may include, in any combination, one or more of the following: springs, disc springs or spring washers, coil springs or other spring bolts, screws, posts, rods, shafts, threaded rods, bands, straps, bracing, crush washers, disc springs or spring washers, U-shaped or C-shaped hanger bars, C-shaped clamps, and elastomer pads, gaskets or washers. A single or any combination of deformable mounting elements may have suitable mechanical properties or their deformable parts and be designed to provide such deformation. A deformable mounting element may include a deformable part or region, i.e., a part of the element that contains a deformable material or is otherwise designed to deform to prevent electrode failure under pressure.

[0035] As described above, Figure 2 shows one embodiment of the present invention. Figure 2 shows an anode mounting assembly 20 of the present invention comprising one or more deformable mounting elements. As shown, the deformable mounting elements are a plurality of bolts designed to plastically yield at a stress low enough to prevent carbon fracture. The bolts may be made of a soft metal such as annealed copper, or a hard metal such as steel or nickel-copper alloy 400 having a reduced bolt cross-sectional area. Figure 2 shows a common copper metal hanger or busbar 16 supported by a metal rod 7 fixed to the busbar 16 by any suitable means. The rod 7 may extend through an opening at the top of an electrolytic cell (not shown) and can be used in combination with a tap nut (not shown) for securing the rod 7 to the top of the cell. The rod 7 can also be used to connect to a power source.

[0036] As shown in Figure 2, multiple carbon anodes 13 are fixed to a busbar 16. Each anode 13 has multiple holes that are drilled all the way through. Each of these holes is a counterbore, providing a shoulder or land for the head of a bolt 3. As shown, each bolt 3 has a slotted head and a shaft 21. Copper washers 4 are inserted under the head of each bolt 3 to protect the carbon anodes. As shown in the cropped portion of the figure, each bolt 3 is provided with threads that engage with internal threads in holes 6 in the busbar 16 in order to fix the anodes 13 to the busbar 16.

[0037] In this embodiment, each head of the bolt 3 is protected from corrosion by a carbon or elastomer plug 5. These plugs 5 may be slightly tapered to ensure a tight fit into a recessed hole, but may also be designed in accordance with the invention to allow for the elongation of a carbon-containing electrode.

[0038] Figure 3 shows another embodiment of an electrode assembly 20 having one or more deformable mounting elements. The electrode assembly 20 comprises a U-shaped or C-shaped hanger 36 having a bolt 33, such as a load-bearing bolt as shown in Figure 3. In a typical mechanical design, the bolt is selected so that the bolt shaft does not yield under the applied pressure. In the present invention, the mounting of the carbon anode 13 in the electrolytic cell can be improved by using a bolt 33 (and / or other element) that deforms by yielding, allowing the carbon to elongate without reaching a stress sufficient to break the carbon. The clamping force on the carbon is provided by compressing the U-shaped or C-shaped hanger 36 by the bolt 33. If the bolt is rigid, as the carbon expands during use, the clamping force increases until the stress on the carbon becomes high enough to break the carbon, which typically occurs at the lower edge 35 of the U-shaped or C-shaped hanger, where the shape of the edge results in a shear stress concentration point in the carbon-containing electrode in contact with the edge 35. To prevent this, deformable bolts 33, elastomer elements 37 and / or deformable C-shaped or U-shaped hangers can be used, or any combination of these deformable elements can be used. If elastomer elements 37 are used, they may be inserted between at least one surface of the U-shaped or C-shaped hanger and the carbon anode. Figure 3 shows a U-shaped or C-shaped hanger 36 having sides 32, 34 and a top 38 located between the sides 32 and 34 and connecting the sides 32 and 34. Figure 3 shows an elastomer element 37 between one side 32 of the U-shaped or C-shaped hanger and the anode 13. Alternatively, the elastomer element 37 may be located between any or both of the sides 32, 34 and the anode 13, and / or between one of the sides 32 or 34 and the top 38 of the hanger and the anode 13, or between both sides 32, 34 and the top 38 of the hanger and the anode 13.As the carbon stretches, the elastomer elements may compress, the bolt may stretch in length, and / or the hanger may deform, thereby preventing the stress on the carbon from increasing to the carbon's fracture point.

[0039] Figure 4 shows another embodiment of the deformable electrode assembly 20 of the present invention, comprising an elastomer component and / or a deformable bolt or post. As shown in Figure 4, a threaded bolt or post is mounted in the anode 13 through an anode support 46. Furthermore, Figure 4 includes an elastomer element 47 positioned between the anode 13 and the metal support 46. By positioning the elastomer element 47 between the anode 13 and the metal support 46, the elastomer element 47 deforms as the carbon anode expands. In the absence of the elastomer element 47, the expanding carbon anode would cause an increase in the clamping force between the anode and the busbar or support 46, which would typically cause the carbon anode 13 to break at the point of maximum stress where the bolt threads engage with the carbon anode. With the elastomer component present, as the carbon expands during use, the elastomer component is compressed, which prevents the clamping force from increasing sufficiently to break the carbon in the anode 13. In addition, or instead, the bolts and posts may be made of a soft metal such as annealed copper or another soft metal as described above, which is soft enough that it does not produce enough stress to plastically yield as the carbon expands and break the carbon.

[0040] In an alternative embodiment, posts or rods can be used to provide mechanical support and electrical contact within the carbon anode. Regardless of the number or position of posts or rods, the coaxial extension of carbon with respect to the posts exerts significant stress on the carbon in areas where the carbon and posts interlock, such as in areas where the posts are threaded. When the carbon expands during use, the stresses at these points cause the carbon to break. Therefore, when the expansion of an electrode containing carbon material comes into contact with posts or rods, deformable posts and rods should be used for mechanical support or electrical contact.

[0041] Figure 5 shows another embodiment of the electrode mounting assembly 20 of the present invention, comprising one or more deformable elements. In Figure 5, the electrode assembly 20 comprises a carbon-containing anode 13 on which a metal support 56 is positioned. The anode 13 and the metal support 56 are surrounded by an anode current carrier 53 comprising a metal sleeve 18 and a compression means 52. The anode 13, the metal support 56 and the metal sleeve 18 are circumferentially compressed together by the compression means 52. An optional anode probe 55 is shown descending into the anode 13 through a central opening in the metal support 56, and the anode probe 55 may be a covered thermocouple that measures temperature and voltage at the anode 13. Typically, a small hole 23 is drilled at the geometric center of the anode 13. In this embodiment, with respect to the design of the thermocouple, note that carbon extension around the hole is provided. The compression means 52 used to provide a compressive force between the current carrier 53 and the carbon anode 13 may be one or more bands, straps, or other bracing. Furthermore, a metal sleeve 18 may provide some compression around the carbon anode. The current carrier 53 provides a compressive force to hold the anode, resulting in electrical communication between the sleeve and the carbon anode. The bands or straps are deformable; that is, they are made using stronger metals or low-yield metals with suitable cross-sections, allowing the bands or straps to deform plastically as the carbon anode expands during use.

[0042] Figure 6 shows another embodiment of the electrode mounting assembly of the present invention, comprising deformable mounting elements. In this embodiment, at least one of the one or more deformable mounting elements comprises an element having a spring-like action. Examples of elements having a spring-like action include disc springs or spring washers, coil springs, or other springs known in the art. In addition, one or more C-clamps 68 having an opening smaller than the size of the carbon anode can be used as springs by utilizing the natural spring constant of the metal used to make the C-clamp 68 or the deformable portion of the C-clamp. If one or more springs 62 are used, as with the deformable mounting elements, the spring constant must be selected to achieve a force that does not impose sufficient stress on the carbon to cause fracture when the carbon stretches (typically about 0.1% to about 2% or more of its dimensions).

[0043] Figure 6 shows an electrode mounting assembly 20 having a spring 62 as at least one of the deformable mounting elements. Furthermore, the electrode mounting assembly includes a C-clamp element 68 supporting the anode 13. Both the C-clamp element 68 and the coil spring 62 function as deformable elements, designed to deform elastically to allow carbon elongation without generating stress sufficient to break the carbon. During use, the expansion of the carbon generates forces horizontally to the C-clamp and vertically to the metal element 66. The C-clamp 68 is deformable, elastically elongating outward from the anode to adapt to the elongation, while the spring 62 is compressed (deformed) to allow vertical elongation of the carbon. A mounting assembly with a rod 7 and a spring connector 63 is also shown. Elements 7, 68, 63, 62, and 66 may all be welded together or connected by bolts and nuts (not shown), and the electrode 13 may be held in a position opposite the metal support 66 by a metal channel piece 67 which is part of the C-clamp element 68. The metal channel piece 67 fits into a channel 61 which is machined or otherwise formed in the electrode 13 to receive it.

[0044] In some embodiments, elements of the anode mounting assembly that provide the mechanical clamping force used to hold the anode in place are deformable. Furthermore, if, for example, a bolt is inserted into the hole of the anode and the hole has a larger diameter than the bolt even after carbon elongation, the bolt must be designed to adapt to the elongation of the carbon anode by having a deformable shaft or cap.

[0045] When the deformable element is a bolt, it is preferable that the bolt is designed to allow the shaft or shank of the bolt to stretch. However, other parts of the bolt may also be designed to be deformable instead of, or in addition to, the shaft or shank. In some embodiments, the deformable mounting element is uniformly deformable over the entire length, width, and / or diameter of the mounting element. In other embodiments, the deformable mounting element may include a “deformable region” or a portion of the deformable element. For example, the deformable region of a bolt may be its shank, or a portion of the shank, for example, a portion of the shank that has a relatively narrow diameter and / or may contain a different material such as a different metal.

[0046] As can be seen below, by using the present invention, the lifespan of the electrode can be extended by more than 30% or more than 50%. [Examples]

[0047] The present invention is illustrated by example as follows: The cell mounting method described in detail in U.S. Patent No. 3041266 involves mounting each carbon anode using four bolts of high-strength alloy 4100 series steel. The carbon has a breaking strength of approximately 12,000 psi (82.7 MPa) when new, which gradually decreases to approximately 6,000 psi (41.4 MPa) during use as a result of chemical decomposition. The bolts have a shaft with a diameter of 0.75 inches (1.9 cm) and a cap diameter of 1.3 inches (3.3 cm). As described in U.S. Patent No. 3041266, the bolts are specified to be tightened to a torque of 120 ft-lbs (162.7 Nm), which, assuming a friction coefficient of 0.2, results in a compressive load of approximately 9,600 lbf (42.7 kN) from each bolt. The contact area with carbon is only below the bolt cap, and the equivalent stress on carbon is approximately 11,000 psi (75.8 MPa), which is close to the fracture point for carbon. The bolt has a yield stress of over 95,000 psi (655 MPa) and a width of 0.334 square inches (2.16 cm). 2) has a tensile stress area and therefore, it takes 31,700 lb to reach the yield point. f A force of 141 kN is required. At that force, the pressure on carbon is approximately 38,000 psi (262 MPa), which is considerably higher than the compressive strength of carbon. These bolts do not deform plastically before the carbon breaks. Nickel and nickel-copper alloys such as alloy 400 have similar strengths and yield the same results. The elastic elongation of the bolt at the carbon fracture point is only about 60 micrometers, while the elongation of carbon is over 150 micrometers. Therefore, carbon breaks during elongation.

[0048] If a bolt is made from conventional cold-rolled copper, it will have a yield strength of at least 20,000 psi (137.9 MPa). Using the same analysis as for steel, the bolt will exert a stress of approximately 7,650 psi (52.7 MPa) against carbon before yielding. As the anode ages and its compressive strength falls below this value, the anode will further fracture.

[0049] When using the present invention, the bolt in the example is replaced with a copper bolt of the same size that has been thoroughly heat-annealed after manufacturing. Well-annealed copper has a yield strength of only about 6500 psi (44.8 MPa). It yields by more than 1% before the stress against carbon reaches 5100 psi (35.2 MPa), and thus prevents carbon elongation from breaking the carbon.

[0050] Using well-annealed copper as a bolt material is not very common due to the material's low strength. This low strength prevents bolts made from it from being tightened to high torques. In the previous example, the annealed copper bolt could be tightened to a torque of only about 30 ft-lbs (40.7 Nm) before it began to deform. Such a bolt could never be used with the original assembly specification of 120 ft-lbs (162.7 Nm), but instead would need to be tightened to much lower torques of about 30 ft-lbs (40.7 Nm) or less, 28 ft-lbs (37.96 Nm) or less, or 25 ft-lbs (33.9 Nm) or less.

[0051] Similarly, the present invention can be applied to other types of connections. In the type of connection proposed in Japanese Patent No. 7173664, the threaded rod or bolt end portion inserted into the top of the carbon anode must be able to extend vertically along with the elongation of the anode. Failure to do so would result in the conductor being drawn out of the carbon or the brittle carbon fracturing at the connection point.

[0052] Here again, in order to balance the requirement of achieving the necessary elongation of 0.1% to 2% or more of the rod's current transmission capacity while keeping it lower than the fracture strength of carbon, it is preferable to use a soft conductor such as well-annealed copper. Alternatively, another deformable material containing a polymer such as PTFE combined with an AC current transmission path such as a flexible wire can achieve the same effect.

[0053] In prior art designs that utilize pressure plates to distribute bolt clamping force, such as those described in Korean Patent Publication No. 10-0286717, the problem of anode fracture is not prevented. While such plates effectively prevent the bolt from directly exerting high pressure on the carbon, they continue to maintain a high overall force across the region of the plate in contact with the carbon anode. The carbon directly beneath the plate is constrained, while the carbon outside the plate's region is not constrained and typically elongates. This uneven elongation of the carbon results in very large local stresses concentrated at the lower edge of the pressure plate, where the carbon body cracks.

[0054] The present invention can also be applied to designs incorporating such pressure plates. The expansion of the carbon must be accommodated without causing stress exceeding the compressive strength of the carbon, even locally at the edges of the pressure plate. To achieve this, the structural components that move the clamp load, described in U.S. Patent No. 8,349,164 as two large bolts, must be modified. Any of the aforementioned designs will work, including the use of spring-acting components such as coil springs, spring washers, or elastic gaskets between one or more sides of the clamp surface that are in direct or indirect contact with the carbon and the carbon-containing electrode, or the use of plastic deformation devices such as low-yield bolts or crush washers. However, the thickness and deformation characteristics of one or more deformable mounting elements must be large enough to accommodate the expansion of the carbon anode.

[0055] Comparative Example 1 A set of six electrolytic cells for producing elemental fluorine by electrolysis of an HF-based molten salt was constructed using an anode mounting design substantially similar to that described in U.S. Patent No. 3041266, but also incorporating a flexible element substantially similar to that described in Chinese Utility Model No. 204434734 by Zhu et al. The cells were assembled such that the hanger bars and anode bolt connection areas were suspended above the surface of the liquid electrolyte to reduce the rate of hanger bar corrosion. The cells were operated for a median life of only 83 days before operation stopped due to excessively high cell voltage. Upon opening the cells, it was found that approximately half of the anodes had failed in the bolted area due to anode expansion. Prior art cells of the same design with hanger bars submerged in liquid electrolyte to reduce expansion lasted approximately 250 days, but the hanger bars showed severe corrosion.

[0056] Comparative Example 2 An electrolytic cell for producing fluoride gas by electrolysis of an HF-based molten salt was constructed using 4100 series alloy steel bolts, utilizing an anode mounting design substantially similar to that described in U.S. Patent No. 9,528,191. The cell was operated for approximately six months before becoming inoperable due to the failure of multiple anodes near the bolt connection points.

[0057] Example 1 A set of bolts of the same size and shape as those used in Comparative Example 2 was manufactured according to ASTM B-187 specifications, using pure copper and alloy C11000. After manufacturing, the bolts were thoroughly heat-annealed to obtain a temperature of 060 (well-annealed). The bolts were inserted into an electrode mounting design substantially similar to that of U.S. Patent No. 9,528,191, and the bolts were measured for plastic deformation behavior by tightening them to progressively high torque values. The bolts had a yield strength of approximately 6500 psi (44.8 MPa) and achieved a plastic deformation strain of 1% when the stress on carbon reached 3200 psi (22.1 MPa).

[0058] An electrolytic cell identical to that of Comparative Example 2 was constructed using the aforementioned well-annealed copper bolts instead of steel bolts. The initial assembly torque for the copper bolts was 20 ft-lbs (27.1 Nm). This cell was operated in parallel with the cell of Comparative Example 2 under the same conditions. The cell withstood more than 30% longer without showing carbon anode failure.

[0059] Deformable mounting elements adapt to the expansion of electrodes made of carbon-containing materials, thereby extending the lifespan of those electrodes. For any design including rods, threads, threaded rods or posts partially or fully inserted into the carbon anode, or mounting elements that compress the carbon anode, carbon fracture can be delayed by using elements that deform under stresses lower than those required to fracture the carbon. In this way, assembly operation in an electrolytic cell increases and decreases the number of stoppages required for rebuilding or replacing the anode assembly.

[0060] The present invention is described for illustrative purposes only, not limitingly, and it is clear that it is applicable to fields other than those described.

Claims

1. An electrode mounting assembly for an electrolytic cell, comprising a carbon-containing electrode and one or more deformable mounting elements in direct or indirect contact with the carbon-containing electrode, wherein the one or more deformable mounting elements deform during use at a stress lower than the stress that would cause the carbon-containing electrode to break, thereby accommodating the elongation of the carbon-containing electrode.

2. The electrode mounting assembly according to claim 1, wherein the one or more deformable mounting elements never exert a stress exceeding 8,000 psi on any portion of the carbon-containing electrode.

3. The electrode mounting assembly according to claim 1 or 2, wherein the one or more deformable mounting elements never exert a stress exceeding 6,000 psi on any portion of the carbon-containing electrode.

4. The electrode mounting assembly according to any one of claims 1 to 3, wherein one or more deformable mounting elements deform under a pressure between 4,000 and 10,000 psi.

5. The electrode mounting assembly according to any one of claims 1 to 4, wherein one or more deformable mounting elements deform under a pressure between 4,000 and 8,000 psi.

6. The electrode mounting assembly according to any one of claims 1 to 5, wherein one or more of the deformable mounting elements include metal.

7. The electrode mounting assembly according to any one of claims 1 to 6, wherein no part of the electrode assembly is polymer-free.

8. The electrode mounting assembly according to any one of claims 1 to 7, wherein the one or more deformable mounting elements include a metal selected from well-annealed copper corresponding to ASTM O60 temper.

9. The electrode mounting assembly according to any one of claims 1 to 8, wherein the one or more deformable mounting elements include a carbon alloy C11000.

10. The electrode mounting assembly according to any one of claims 1 to 9, wherein the one or more deformable mounting elements have a yield strength of less than 10,000 psi with an elongation of 0.5%.

11. The electrode mounting assembly according to any one of claims 1 to 10, wherein the deformable mounting device includes one or more selected from compression bands, straps, screws, threaded bolts, rods, threaded rods, posts, or shafts.

12. The electrode mounting assembly according to any one of claims 1 to 11, wherein the deformable mounting device includes one or more selected from a spring, a coil spring, a bolt, a screw, a bracing, a crush washer, a U-shaped or C-shaped hanger bar, and a C-shaped clamp.

13. The electrode mounting assembly according to any one of claims 1 to 12, wherein the deformable mounting device includes one or more selected from disc spring washers, screw washers, crush washers, elastomer pads, gaskets, or washers.

14. The electrode mounting assembly according to any one of claims 1 to 13, wherein the deformable mounting element includes one or more bolts.

15. The electrode mounting assembly according to any one of claims 1 to 14, wherein the carbon-containing electrode comprises carbon selected from non-graphitized carbon, graphitized carbon, low-permeability carbon, high-permeability carbon, carbon fiber, pressurized carbon powder, mesocarbon microbeads, metal-impregnated carbon, carbon coated with a thin layer of metal, carbon diamond, coal, or petroleum-derived coke.

16. The electrode mounting assembly according to any one of claims 1 to 15, wherein the carbon-containing electrode has a monolithic structure or a composite structure.

17. The electrode mounting assembly according to any one of claims 1 to 16, wherein the carbon-containing electrode is a molded mass of compressed carbon and a pitch binder, including the form of coal or petroleum-derived coke, which has been baked, densified, hardened, and had its pitch carbonized.

18. The electrode mounting assembly according to any one of claims 1 to 17, wherein one or more deformable elements deform to accommodate an elongation of the carbon-containing electrode of about 0.1% to about 1.0% without exerting stress on the carbon-containing electrode beyond the fracture strength of the carbon-containing electrode.

19. The electrode mounting assembly according to any one of claims 1 to 18, wherein one or more of the deformable elements are elastically deformable.

20. The electrode mounting assembly according to any one of claims 1 to 19, wherein one or more of the deformable elements are plastically deformable.

21. The electrode mounting assembly according to any one of claims 1 to 20, wherein one or more of the deformable elements comprises well-annealed copper.

22. The electrode mounting assembly according to any one of claims 1 to 21, wherein the one or more deformable elements exert a stress of less than 8,000 psi on the carbon-containing electrode after a 0.5% elongation of the carbon-containing electrode.

23. The electrode mounting assembly according to any one of claims 1 to 22, wherein the one or more deformable elements exert a stress of less than 6,000 psi on the carbon-containing electrode after a 0.5% elongation of the carbon-containing electrode.

24. The electrode mounting assembly according to any one of claims 1 to 23, wherein the one or more deformable elements include well-annealed copper, cold-rolled copper, steel, copper-nickel alloy, lead, gold, silver, tin, zinc, aluminum, brass, bronze, and alloys thereof.

25. The electrode mounting assembly according to any one of claims 1 to 24, wherein one or more of the deformable elements comprises well-annealed copper.

26. The electrode mounting assembly according to any one of claims 1 to 25, wherein the one or more deformable elements include a halogenated elastomer, graphite-filled PTFE, or silicone rubber.

27. The electrode mounting assembly according to any one of claims 1 to 26, wherein one or more of the deformable elements include a material having conductivity greater than 300 S / m.

28. The electrode mounting assembly according to any one of claims 1 to 27, wherein one or more of the deformable elements are load-bearing.

29. The electrode mounting assembly according to any one of claims 1 to 28, wherein the one or more deformable elements include one or more metals.

30. The electrode mounting assembly according to any one of claims 1 to 29, wherein the one or more deformable elements comprises one or more bolts, the bolts being tightened to a torque of 30 ft-lbs (40.7 N-m) or less.

31. The electrode mounting assembly according to any one of claims 1 to 30, wherein the carbon-containing electrode is an anode.

32. An electrolytic cell comprising one or more electrode mounting assemblies according to any one of claims 1 to 31, a container, an electrical distribution element, an electrolytic bath, and one or more reverse-charged electrodes.

33. The electrolytic cell according to claim 32, wherein the carbon-containing electrode in the one or more electrode mounting assemblies is an anode.

34. The electrolytic cell according to claim 32 or 33, wherein the electrolytic cell produces a fluorine-containing material.

35. Use of an electrolytic cell according to any one of claims 32 to 34 for manufacturing a fluorine-containing material, the use comprising the step of introducing electrical energy into the electrolytic cell to cause a chemical reaction between the carbon-containing electrode and the one or more reverse-charged electrodes in the one or more electrode mounting assemblies.

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