Electrode connection assembly, electrolytic cell, and method of use

Abstract

An electrode connection assembly for an electrolytic cell and an electrolytic cell having one or more electrode connection assemblies, and methods of using the same, are provided. The electrode connection assembly includes a carbon-containing electrode and one or more deformable connection elements in direct or indirect contact with the carbon-containing electrode, wherein the one or more deformable connection elements deform at a stress lower than a stress that causes the carbon-containing electrode to fracture to accommodate expansion of the carbon-containing electrode during use.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Application No. 63 / 057,561, filed September 8, 2020, the entire contents of which are incorporated herein by reference for all permissible purposes. Background Art

[0003] The industrial production of elemental fluorine (F2) and related fluorinated gases, such as nitrogen trifluoride (NF3), is primarily carried out in electrolytic cells. For the production of fluorine gas in particular, the anodes of such electrolytic cells are made of carbon. To function, the anode must be connected to a power source so that current can flow between the cathode and the anode.

[0004] Reliably connecting to the anode in a fluorine electrolysis cell is challenging because there are very highly corrosive chemical conditions in such an electrolysis cell. The liquid electrolyte used in such an electrolysis cell is typically a molten salt mixture of potassium fluoride (KF) and hydrogen fluoride (HF). In order to produce NF3, ammonium fluoride is used instead of KF or in addition to KF. This electrolyte, combined with the elevated operating temperature and the anode potential applied to the anode, produces highly corrosive conditions that tend to corrode the metal parts of the anode connection device. In addition, for efficient and stable operation, the resistance of the anode connection must be low during the entire life of the anode. It is known that any deterioration of the electrical connection to the anode will lead to anode destruction, as fully described by Ring and Royston (Australian Atomic Energy Commission Report E281, 1973, ISBN 0642 996016).

[0005] Many methods of connecting carbon anodes to a power source and / or other supporting members have been proposed in the prior art, including in US 5290413 (circumferential metal sleeve around the top of the anode), US3041266A (metal hanger with anodes connected by several bolts), JP7173664A (threaded bolts first passed through a metal rod and then inserted into the carbon anode), US5688384 (screws on the top of the carbon anode), KR100286717 B1 (carbon anode held between two metal plates by bolts), CN102337491A (clamp), US8349164 (clamp), Zhao et al. (clamp), US6210549 (C-shaped anode hanger and threaded rod).

[0006] Despite many different connection methods, carbon anodes can break down after a period of use in electrolysis. This breakage can render the electrolytic cell unusable and require rebuilding at least some portion of the electrolytic cell. Therefore, there is a need in the art for extending the life of carbon electrodes in electrolytic cells. Summary of the Invention

[0007] The present invention provides an electrode connection assembly and an electrolytic cell including the electrode connection assembly, wherein the electrode connection assembly includes a carbon-containing electrode and one or more deformable connection elements in direct or indirect contact with the carbon-containing electrode, wherein the one or more deformable connection elements deform under a stress lower than the breaking strength of the carbon-containing electrode to accommodate the expansion of the carbon-containing electrode during use.

[0008] In another embodiment, the present invention provides an electrolytic cell comprising one or more electrode connection assemblies of the present invention, a container, a current distribution member, an electrolytic cell, and one or more oppositely charged electrodes.

[0009] In yet another embodiment, the present invention provides a method or use of an electrolytic cell for producing a fluorine-containing material, comprising the step of introducing electrical energy into the electrolytic cell to induce a chemical reaction at the carbon-containing electrode and the one or more oppositely charged electrodes to produce a fluorine-containing material at the carbon-containing electrode.

[0010] The present invention provides benefits of an electrolytic cell and an electrode connection assembly, which may be an anode connection assembly that reduces the tendency of the carbon electrode (anode) to crack, thereby extending the life of the electrode, which enables longer electrolytic cell operation, reduces maintenance costs by reducing the frequency of rebuilding the electrolytic cell, and improves safety. A cracked electrode (anode) can sometimes cause an electrical short circuit inside the electrolytic cell or cause arc discharge, resulting in damage to many internal components of the electrolytic cell. The present invention also provides an electrode connection assembly (anode connection assembly) with good electrical contact and corrosion resistance. By keeping the connection points and metal parts "dry", i.e., preferably above the surface of the liquid electrolyte, corrosion of the electrical connection to the carbon electrode can also be reduced. In some cases, under the same operating conditions, the service life of the electrolytic cell manufactured using the electrode connection assembly of the present invention is 20% longer than that of conventional electrodes operated in a comparable electrolytic cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic diagram of an electrolytic cell of the present invention.

[0012] Figure 2 Schematic diagram of an electrode connection assembly of the present invention.

[0013] Figure 3 is a schematic diagram of another electrode connection assembly of the present invention.

[0014] Figure 4 is a schematic diagram of another electrode connection assembly of the present invention.

[0015] Figure 5 is a schematic diagram of another electrode connection assembly of the present invention.

[0016] Figure 6 is a schematic diagram of another electrode connection assembly of the present invention. DETAILED DESCRIPTION

[0017] All patents and patent applications mentioned in the Background or anywhere in this specification are incorporated herein by reference in their entirety.

[0018] Figure 1 1 is a simple schematic diagram showing an embodiment of an electrolytic cell for electrolytic synthesis of fluorine-containing materials having an electrode connection assembly according to the present invention. Reference numeral 10 represents an electrolytic cell for electrolytic synthesis of fluorine-containing materials, which uses a molten salt electrolytic cell 12 containing fluoride ions in an electrolyte-resistant container 19. The molten salt electrolytic cell 12 containing fluoride ions may include 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, etc. The electrolytic cell also includes an anode 13, a cathode 14 and a partition wall 15, which are at least partially immersed in the molten salt electrolytic cell 12. The electrolytic cell also includes a current distribution member, which may be a feed bus 16, an optional rectifier and a power supply 17. The cathode 14 typically contains nickel, stainless steel, carbon steel, etc. The anode 13 typically contains a carbonaceous material. The electrode assembly of the present invention includes at least one electrode (typically at least one anode) and a connection assembly (including one or more deformable elements), which may also be referred to as a deformable connection assembly, an embodiment of which will be described in detail in the following. Figure 2-6 The electrolytic cell 10 of the present invention may further include a device for maintaining temperature (not shown) and a device for replenishing salts (not shown), such as HF and / or NH3, consumed in the process of producing the fluorine-containing material, which may be fluorine gas, nitrogen trifluoride, or other fluorinated gases. It should be understood that the present invention can be used with any carbon-containing electrode (although it may be described herein as an anode) to produce any end product, although typically a fluorine-containing material.

[0019] exist Figure 1 In the illustrated embodiment, when electrolytic cell 10 is in operation, electrical energy causes a chemical reaction in the electrolytic cell. Fluorine-containing material is formed at anode 13. Dividing wall 15 keeps the fluorine-containing gas separate from the hydrogen gas formed at cathode 14. The hydrogen and fluorine-containing gases are released from the electrolytic cell via separate conduits (not shown) connected to separate collection containers (not shown).

[0020] The anode 13 used in the electrochemical fluorine production electrolytic cell is typically made of a carbonaceous material, such as carbon or ungraphitized carbon, although carbon with different degrees of graphitization, including fully graphitized carbon, can be used. (Note that carbonaceous materials can be used to make cathodes in other electrolytic cells that will benefit from the present invention; the present invention is therefore not limited to anodes made of carbonaceous materials, and therefore the terms carbonaceous electrode, carbonaceous anode and carbon electrode and carbon anode are used interchangeably herein). The carbonaceous material used to make the electrode can be a monolithic structure or a composite structure of low permeability or high permeability. In the composite structure, there can be a core of low permeability carbon and a shell of high permeability carbon or a conductive diamond layer. Alternatively, in the composite structure, the carbonaceous anode can comprise a carbon fiber material and another form of carbon, such as isostatically pressed carbon powder or mesophase carbon microbeads. The outer layer of the carbon electrode may be formed, coated or connected to the inner core or alternative support (see UK Patent Application 2 135 335A (Marshall)) or otherwise assembled or manufactured (see U.S. Patent Nos. 3,655,535 (Ruehlen et al.), 3,676,324 (Mills), 3,708,416 (Ruehlen et al.) and 3,720,597 (Ashe et al.) and US 2008 / 0314759 (Furuta et al.)). Also useful in the present invention are carbons that have been impregnated with metals such as nickel or with salts such as lithium fluoride. Carbon electrodes coated with a thin layer of metal in the area where the anode meets or connects to the power supply for the anode may also be used in the present invention. The surface of the carbon may be rough or may be cut or polished to be smooth. The surface may also contain features such as grooves or holes. Any carbon anode comprising any useful type of carbon may be used as the carbon electrode in the electrode assembly of the present invention. Typically, the carbonaceous electrode used as an anode in an electrolytic cell is typically a shaped block of compressed carbon, which contains a form of coal or petroleum-derived coke and a pitch binder. The formed anode is typically baked to densify, harden, and carbonize the pitch. Isostatically pressed carbon powder blocks can also be used, which can be directly formed into the final shape or machined into the final shape from a larger block. Carbon anodes are typically rectangular in shape with approximately flat or flat surfaces, but they can have any shape, such as square, disc, or cylindrical.

[0021] Through extensive research into the causes of anodic fracture, the inventors discovered an unrecognized failure mode. They discovered that electrodes containing carbonaceous materials of the type used in electrolytic cells for fluorine and fluorinated gas production experience physical swelling during use. The extent of this swelling is typically small, less than 1% for most carbons under the conditions found within electrolytic cells. However, in most connection designs, this amount of swelling is sufficient to generate sufficient stress to fracture the carbon. The amount of physical expansion can vary, but typically ranges from an increase of about 0.1% to about 2.0% in each dimension of the carbon electrode.

[0022] To demonstrate this feature, three samples of ungraphitized carbon (grade "ABR" manufactured by SGL Carbon, Wiesbaden, Germany) were placed in a container and exposed to conditions similar to the gaseous headspace of a fluorine electrolysis cell containing HF and F2 gases at 100° C. After several gassing cycles, the samples were removed and found to have increased in size by 0.27%, 1.42%, and 0.53% in each length dimension.

[0023] Because the swelling of the carbon is caused by the conditions that exist inside the electrolytic cell during operation, the inventors determined that this phenomenon leads to excessive stress and cracking. The swelling of an anode comprising carbonaceous materials is large compared to the classical mechanical elastic compression and extension experienced by all materials in pressurized contact with the carbon electrode (i.e., all connected elements that directly or indirectly contact the electrode in the electrolytic cell and support the electrode and / or provide power to the electrode). It was also discovered that, in contrast to changes caused by other means (such as thermal expansion), the swelling of a carbon anode is not reversible. Once the carbon undergoes swelling, it maintains this new larger size even when the electrolytic cell is shut down. In addition, the inventors discovered that the swelling process is not self-limiting. Instead, the carbon will continue to expand slowly over time. This effect prevents users from pre-expanding the carbon before installing it in the electrolytic cell because the carbon will continue to expand once installed and put into use in the electrolytic cell.

[0024] The means for producing the pressurized contact (clamping force) that holds the carbon anode in place and provides the contact pressure required for a good electrical connection are typically very strong. Connecting elements such as bolts, straps, and threaded rods are all used as structural members to provide pressurized contact. A variety of construction materials are useful, including steel, copper, nickel, and nickel-copper alloys, such as Ni-Cu alloy 400. The selection of materials in the prior art is often 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 leads to anode failure after a certain operating period because these materials are much stronger than carbon anodes and do not yield when the carbon swells. The carbon materials commonly used to make electrodes in such electrolytic cells have a brittle failure mode, that is, they tolerate a small amount of elastic deformation before failing by brittle fracture. The carbon materials of carbon anodes do not exhibit any or only very limited ductile deformation properties, which also decreases as the electrode ages in use.

[0025] When connected to rigid, high-strength connecting elements, such as steel, nickel, or conventional cold-rolled copper bolts, rods, straps, plates, hangers, or clamps, or combinations thereof, the carbon can expand only slightly before reaching its elastic deformation limit under conventional compressive forces applied to ensure adequate physical and electrical connection between the carbon anode and one or more of these connecting elements. The result is that the carbon ruptures at or near the point of maximum stress caused by the connecting element. The use of pressure distribution devices (such as clamps) cannot prevent this failure mode because the root cause is the expansion of the carbon within the confines of the rigid connecting element or elements.

[0026] The inventors determined that under normal assembly conditions, the deflection of the metal bolts and plates in conventional connecting elements can be on the order of 10 microns, while the expansion of the carbon, the subject of the present invention, can be 100 microns or greater. In other words, when used in an electrolytic cell to produce a fluorine-containing material, the expansion of the carbon-containing material of the anode due to swelling is greater than the expansion of conventional connecting elements, and can be greater than 1.5 times, greater than 2 times, greater than 5 times, or greater than 8 times the expansion of conventional connecting elements. Therefore, the difference in expansion scale between carbon and conventional connecting elements results in the inability of conventional (rigid) connecting elements to accommodate carbon expansion.

[0027] Exacerbating the problem of anode cracking is the fact that carbonaceous materials typically weaken over time. This weakening can be the result of chemical degradation, attack by the harsh oxidizing environment typically found in these electrolytic cells, or internal stresses caused by swelling. Consequently, after a period of use, carbonaceous materials typically exhibit a compressive strength lower than that of new material. This reduction can be as much as 50%. Therefore, avoiding cracking of carbonaceous materials relies on the ability to reduce peak stresses on the carbonaceous material to relatively low values.

[0028] Most carbonaceous materials used as anodes in electrolytic cells for producing fluorine and other fluorinated gases have a compressive strength of about 8,000 to 15,000 pounds per square inch (psi) when new. This value can drop by as much as half after extended use in electrolytic cells due to chemical degradation and swelling of the carbon. Consequently, stresses above about 6,000 psi can cause the carbon to crack after a period of use.

[0029] The present invention provides a deformable connecting element, an electrolytic cell, and a method that prevents anode rupture by accommodating the swelling of an anode comprising a carbonaceous material, thereby extending the service life of the electrolytic cell. To achieve this, the deformable connecting element of the present invention reduces the peak stress on the carbonaceous material to a relatively low value.

[0030] Conventional components used to connect anodes via connecting or clamping forces, such as bolts, straps, or rods, are designed to operate within the elastic limits of the material. Higher stresses dictate the use of higher-strength materials or connecting devices with larger cross-sections to reduce stress in the connected elements. Traditionally, prior art connecting devices have used one or more connecting devices to generate high connecting or clamping pressures, focusing on protecting the contact surfaces from corrosion and achieving low electrical resistance in the joint through high contact stress.

[0031] In contrast, the present invention provides a method for improving the connection of carbon anodes in electrolytic cells by using one or more compliant or yielding connecting elements to accommodate the physical swelling of the carbon. Such one or more deformable connecting elements can expand by 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 applied to the carbon to less than the carbon's fracture strength. Since carbon may weaken over time, the design should limit the peak stress on the carbon to less than 8,000 psi, or less than 7,000 psi, and more preferably less than 6,000 psi, or even less than 5,500 psi. The one or more deformable elements used in the electrode connection assembly must be selected to provide sufficient displacement, which is typically at least between about 0.05% to about 10% of the original carbon dimensions, or about 0.05% to about 5%, or about 0.1% to about 3%, or about 0.1% to about 2%.

[0032] This can be achieved by using ductile, low-yield metals or reduced cross-sections in the connecting elements that transmit the connecting force (which can be a clamping force), such as bolts, shafts, rods or straps. The material and cross-section must be selected together to ensure that the component reaches its yield point and can deform in a ductile manner before a stress higher than the carbon fracture stress is applied to the carbon electrode.

[0033] One embodiment of a ductile, low yield metal is fully annealed copper, also known as the O60 temper. The copper is any commercially pure grade, such as alloy C11000. It is well known that copper metal can be work-hardened. In the conventional state for machining copper parts, copper is provided in the so-called "cold rolled" state, otherwise known as "1 / 8 hard" or H00 temper, and has a minimum yield strength of 20,000 psi (137.9 MPa) at 0.5% elongation. Harder forms, such as 1 / 4 hard or 1 / 2 hard, are also available. In contrast, fully annealed copper has no specified minimum yield strength at 0.5% elongation, but this value is generally very low, less than about 10,000 psi (69 MPa) and often about 6,500 psi (44.8 MPa). Machined copper parts must generally be annealed to achieve the O60 temper. In addition to copper and its alloys, other metals that may be suitable include lead, gold, silver, tin, zinc, aluminum, brass, bronze, and various alloys of these metals.

[0034] As mentioned above, the thickness of the metal element can be increased to improve its rigidity; therefore, in order to use higher strength known metals (including steel, Monel, etc.) to make the deformable connecting element useful in the present invention, it is possible to reduce the thickness of the metal element to allow the deformable connecting element to be produced. Because the harsh conditions in the electrolytic cell often lead to corrosion over time, if more than one deformable element is used in the connecting assembly, it is possible to use stronger metals used in the prior art and perhaps only reduce the thickness of some of the elements.

[0035] For example, in Figure 2 In the illustrated embodiment, derived from US Pat. No. 3,041,266, the ¾-inch diameter 4100 series steel alloy metal bolts typically used for the anode connection are replaced with bolts made of H00 copper and reduced in diameter to less than approximately 0.5 inches to allow plastic deformation of the bolts to occur before the carbon anode ruptures. Carbon steel bolts can also be used, but the diameter must be further reduced to less than 0.3 inches in diameter. The reduction in bolt shaft diameter should preferably be performed without significantly altering the original nut seat area; that is, the shank must be thinner, but the nut should remain approximately the same (if not the same) size. Considering all relevant stress concentrations arising from the details of the mechanical connection design, a combination of dimensions and material properties must be considered to ensure that the deformable connection element fully yields at a point before the carbon ruptures. Therefore, in this example, the change in shank diameter must also occur without changing the projected area of ​​the bolt head on the carbon, lest stresses on the carbon increase. Therefore, these many different criteria, along with factors such as the ampacity of the current-carrying member, need to be carefully considered to achieve all necessary requirements.

[0036] In an alternative embodiment, thermally annealed copper can be used to fabricate the deformable connecting element or its deformable region or portion. Thermally annealed copper, such as ASTM O60 temper, does not have a standard yield stress, but has been found to deform at stresses of about 10,000 psi (69 MPa) or less. For comparison, H00 tempered copper has a yield stress of 20,000 psi (138 MPa), and most common steels have a yield stress of 25,000 psi (172 MPa) or more.

[0037] As mentioned above, some common metals used for this purpose, such as cold-rolled H00 copper, steel, or copper-nickel alloy 400, can be used as deformable components, but only careful design is required to ensure that the material yields before the carbon breaks. 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-carrying components. Soft materials such as plastics and elastomers can be used for non-current-carrying components, although they still must have sufficient strength to withstand the required mechanical loads and be chemically compatible with the environment in the electrolytic cell. Preferably, the deformable connecting element comprises metal. Preferably, the deformable connecting element does not contain or is substantially free of elastomeric elements and materials that react, burn, degrade, or are otherwise incompatible with the electrolytic cell environment. Preferably, the deformable connecting element is electrically conductive and provides an electrical conductivity greater than 300 S / m. In some designs, the deformable connecting element is load-bearing.

[0038] CN204434734U discloses a flexible member between a carbon anode plate and a metal busbar. This flexible member is designed to seal the joint between these components to prevent corrosion. The flexible member is typically a graphite gasket with a metal coating. Such flexible members do not achieve the desired function of the present invention because they typically do not retain sufficient compressibility after the initial compression set during assembly.

[0039] The elastomeric component can be used as a deformable element, or if properly designed, can be used as one of several deformable elements in an electrode assembly. The elastomeric component must be chemically compatible with or provide protection for the electrolytic cell environment. Halogenated elastomers such as FKM (fluoroelastomer), FFKM (fluoroelastomer), chloroprene and other similar materials can be used. If protected by encapsulation with a resistant material (such as a fluoropolymer), halogenated or non-halogenated polymers such as silicone rubber or any of a variety of hydrocarbon-based elastomers can be used. The elastomeric component must allow the carbon to fully deform after initial assembly without generating the stress required to rupture the carbon. Therefore, the elastomeric component cannot be fully compressed during the initial assembly of the electrode assembly.

[0040] Useful deformable connecting elements that can be used in the electrode connection assembly of the present invention can include one or more of the following in any combination: springs, conical or spring washers, coil springs or other spring bolts, screws, posts, rods, shafts, threaded rods, bands, strips, struts, squeeze washers, conical or spring washers, U-shaped or C-shaped hangers, C-shaped clamps and elastic pads, liners or washers. The deformable connecting elements, alone or in any combination, are designed to have appropriate mechanical properties or deformable portions thereof to provide for their deformation. The deformable connecting elements may include deformable portions or regions, i.e., portions of the element that include a deformable material or are otherwise designed to deform under pressure to prevent electrode rupture.

[0041] As discussed above, Figure 2 One embodiment of the present invention is shown. Figure 2 An anode connection assembly 20 of the present invention is shown that includes one or more deformable connection elements. As shown, the deformable connection elements are a plurality of bolts that are designed to plastically yield at sufficiently low stresses to prevent carbon cracking. The bolts can be constructed of a soft metal such as annealed copper, or they can be a hard metal such as steel or nickel copper alloy 400, but with a reduced cross-sectional area. Figure 2 A common copper metal hanger or busbar 16 is shown supported by a metal rod 7 secured to the busbar 16 by any suitable means. The rod 7 can extend through an opening (not shown) in the top of the electrolytic cell and can be used in combination with a tap nut (not shown) for securing the rod 7 to the top of the electrolytic cell. The rod 7 can also be used to connect to a power source.

[0042] like Figure 2 As shown, a plurality of carbon anodes 13 are secured to a busbar 16. Each anode 13 has a plurality of holes drilled completely therethrough. Each of these holes is countersunk to provide a shoulder or platform for the head of a bolt 3. As shown, each bolt 3 has a slotted head and a shank 21. A copper washer 4 is inserted under the head of each bolt 3 to protect the carbon anode. Each bolt 3 is provided with threads that engage the internal threads of a hole 6 in the busbar 16, thereby securing the anode 13 to the busbar 16, as shown in the cutaway portion of the figure.

[0043] In this embodiment, the head of each 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 in the recessed holes, but are also designed in accordance with the invention to allow for expansion of the carbon containing electrode.

[0044] Figure 3 Another embodiment of an electrode assembly 20 including one or more deformable connecting elements is shown. The electrode assembly 20 includes a bolt 33 (e.g., Figure 3A U-shaped or C-shaped hanger 36 (shown as a load-bearing bolt) is provided. In conventional mechanical designs, bolts are selected so that the screw does not yield under applied stress. In the present invention, the connection of the carbon anode 13 in the electrolytic cell can be improved by using bolts 33 (and / or other elements) that deform by yielding, thereby allowing the carbon to expand without reaching sufficient stress to rupture the carbon. The clamping force on the carbon is generated by compressing the U-shaped or C-shaped hanger 36 with the bolts 33. If the bolts are rigid, as the carbon swells during use, the clamping force increases until the stress on the carbon is high enough to rupture the carbon. This typically occurs at the lower edge 35 of the U-shaped or C-shaped hanger, where the geometry of the edge creates a shear stress concentration point in the carbon-containing electrode in contact with the edge 35. To prevent this, a deformable bolt 33 and / or an elastomeric element 37 and / or a deformable C-shaped or U-shaped hanger can be used, or any combination of these deformable elements can be used. If an elastomeric element 37 is used, it can be inserted between at least one surface of the U-shaped or C-shaped hanger and the carbon anode. Figure 3 A U-shaped or C-shaped hanger 36 is shown including side portions 32 , 34 and a top portion 38 located between and connecting the side portions 32 and 34 . Figure 3 An elastomeric element 37 is shown between one side 32 of the anode U-shaped or C-shaped hanger and the anode 13. Alternatively, the elastomeric element 37 may be located between either or both of the sides 32, 34S and the anode 13, and / or between one side 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 36 and the anode 13, as long as it is arranged to allow current to enter the electrode through the hanger or other current supply (not shown). As the carbon expands, the elastomeric element is compressed, and / or the length of the bolt can expand and / or the hanger can deflect, thereby preventing the stress on the carbon from increasing to the point of carbon rupture.

[0045] Figure 4 Another embodiment of a deformable electrode assembly 20 of the present invention is shown, which includes an elastomeric member and / or a deformable bolt or post. Figure 4 As shown, threaded bolts or posts are attached through anode support 46 and into anode 13 . Figure 4Also included is an elastomeric element 47 positioned between the anode 13 and the metal support 46. By positioning the elastomeric element 47 between the anode 13 and the metal support 46, the elastomeric element 47 will deform as the carbon anode swells. In the absence of the elastomeric element 47, swelling of the carbon anode would result in an increase in the clamping force between the anode and the busbar or support 46, thereby causing rupture of the carbon anode 13 at the highest stress point, typically where the bolt threads engage the carbon anode. In the presence of the elastomeric component, as the carbon swells during use, the elastomeric component is compressed, thereby preventing the clamping force from increasing sufficiently to rupture the carbon of the anode 13. Additionally or alternatively, the bolts and posts may be made of a soft metal, such as annealed copper, or another soft metal as described above, which plastically yields as the carbon swells and does not generate sufficient stress to rupture the carbon.

[0046] In an alternative embodiment, posts or rods can be used to provide internal mechanical support and electrical contact to the carbon anode. Regardless of the number or location of the posts or rods, the expansion of the carbon in a direction coaxial with the posts exerts significant stress on the carbon in the areas where the carbon and posts are joined (e.g., where the posts are threaded). As the carbon swells during use, the stresses generated at these points cause the carbon to crack. Therefore, if swelling of an electrode containing carbonaceous material contacts the posts or rods, deformable posts and rods should be used, regardless of whether they are used for mechanical support or electrical contact.

[0047] Figure 5 Another embodiment of the electrode connection assembly 20 of the present invention including one or more deformable elements is shown. Figure 5 In FIG, electrode assembly 20 includes a carbonaceous anode 13 topped with a metal support 56. Anode 13 and metal support 56 are surrounded by an anode current carrier 53 comprising a metal sleeve 18 and a compression device 52. Anode 13, metal support 56, and metal sleeve 18 are circumferentially compressed together by compression device 52.

[0048] An optional anode probe 55 is shown lowered into the anode 13 through an opening in the center of the metal support 56 and can be a sheathed thermocouple that measures the temperature and voltage in the anode 13. Typically, a small hole 23 is drilled in the geometric center of the anode 13. In this embodiment, care is taken in the thermocouple design to provide for expansion of the carbon around the hole. The compression device 52 for providing compression between the carrier fluid 53 and the carbon anode 13 can be one or more bands, strips or other struts. The metal sleeve 18 can also provide some compression around the carbon anode. The carrier fluid 53 provides compression to hold the anode and create electrical communication between the sleeve and the carbon anode. The bands or strips are deformable, that is, they are made of a low yield metal or a stronger metal with an appropriate cross-section to allow them to plastically deform as the carbon anode swells during use.

[0049] Figure 6 Another embodiment of the electrode connection assembly of the present invention including a deformable connection element is shown. In this embodiment, at least one of the deformable connection elements includes an element having a spring-like action. Examples of elements having a spring-like action include conical washers or spring washers, coil springs, or other spring types known in the art. In addition, one or more C-clamps 68 having an opening smaller than the size of the carbon anode can also be used as springs, 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 deformable connection elements alone or in combination with other connection elements, the spring constant must be selected to obtain a force that does not generate sufficient stress on the carbon to cause rupture when the carbon expands (typically expanding in size by about 0.1% to about 2% or more).

[0050] Figure 6 An electrode connection assembly 20 is shown having a spring 62 as at least one deformable connection element. The electrode connection assembly also includes a C-shaped clamping member 68 that supports the anode 13. Both the C-shaped clamping member 68 and the coil spring 62 serve as deformable elements and are designed to elastically deform to allow carbon expansion without generating sufficient stress to damage the carbon. In use, the carbon swells and generates forces horizontally on the C-shaped clamp and vertically on the metal element 66. The C-shaped clamp 68 is deformable and elastically expands outward from the anode to accommodate the expansion, while the spring 62 is compressed (deformed) to allow vertical expansion of the carbon. The connection assembly is shown as having a rod 7 and a spring connector 63. Elements 7, 68, 63, 62, and 66 can all be welded together or connected via bolts and nuts (not shown), and the electrode 13 can be held in place against the metal support 66 by a metal channel 67 that is part of the C-shaped clamping member 68. The metal channel 67 fits into a channel 61 machined or otherwise formed in the electrode 13 to receive it.

[0051] In some embodiments, the elements of the anode connection assembly that generate the mechanical clamping force used to hold the anode in place are deformable. For example, if a bolt is inserted into a hole in the anode such that, even after carbon expansion, the hole has a diameter wider than the bolt, the bolt must still be designed to accommodate the expansion of the carbon anode by having a deformable rod or cap.

[0052] When the deformable element is a bolt, it is preferred that the bolt be designed to allow the screw or shank to expand. However, other parts of the bolt may also be designed to deform instead of or in addition to the screw or shank. For some embodiments, the deformable connection element will deform equally across the entire length and / or width and / or diameter of the connection element. In other embodiments, the deformable connection element may include a "deformation zone" or only a portion of the element that is deformable. For example, the deformation zone of the bolt may be its shank or only a portion of the shank, wherein, for example, the diameter of the shank may be narrower and / or may include a different material, such as a different metal.

[0053] As will be seen below, by using the present invention, the life of the electrodes can be extended by more than 30%, or more than 50%.

[0054] Example

[0055] The present invention is illustrated by the following examples. The electrolytic cell connection method described in detail in US3041266 uses four high-strength alloy 4100 series steel bolts to connect each carbon anode. When new, carbon has a fracture strength of about 12,000psi (82.7MPa), which slowly decreases to about 6000psi (41.4MPa) due to chemical degradation during use. The bolt has a rod of 0.75 inch (1.9cm) diameter and a cap of 1.3 inches (3.3cm) diameter. As described in US3041266, the bolt is specified to be tightened to a torque of 120ft-lbs (162.7Nm), which produces a compressive load of about 9600lbf (42.7kN) from each bolt, thereby presenting a friction coefficient of 0.2. The contact area with the carbon is only the area under the bolt cap, so that the equivalent stress on the carbon is about 11,000psi (75.8MPa), close to the breaking point of the carbon. The bolts have a yield stress greater than 95,000 psi (655 MPa) and a 0.334 square inch (2.16 cm 2 ) tensile stress area, thus each requires 31,700 lbf (141 kN) to reach the yield point. At this force, the pressure on the carbon is almost 38,000 psi (262 MPa), which is far higher than the compressive strength of carbon. These bolts do not plastically deform before the carbon breaks. Nickel and nickel-copper alloys (such as Alloy 400) have similar strengths and would produce the same results. The elastic expansion of the bolt at the breaking point of carbon is only about 60 microns, while carbon expands over 150 microns. Therefore, the carbon breaks when it expands.

[0056] If the bolt is made of conventional cold-rolled copper, it will have a yield stress of at least 20,000 psi (137.9 MPa). Using the same analysis as for steel, the bolt exerts a stress of about 7650 psi (52.7 MPa) on the carbon before yielding. Once the anode ages and the compressive strength drops below this value, the anode still cracks.

[0057] Using the present invention, the bolt in this example is replaced with a copper bolt of the same size that is fully heat annealed after manufacture. Fully annealed copper has a yield stress of only about 6,500 psi (44.8 MPa). It will yield by more than 1% before the stress on the carbon reaches 5100 psi (35.2 MPa), thus preventing the expansion of the carbon from causing it to crack.

[0058] The use of fully annealed copper as a bolt material is highly unusual 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 only be tightened to about 30 ft-lbs (40.7 Nm) of torque before it began to deform. Such a bolt would never have been used with the original component specification of 120 ft-lbs (162.7 Nm), but would have needed to be tightened to much lower values ​​of no more than about 30 ft-lbs (40.7 Nm), or no more than 28 ft-lbs (37.96 Nm), or no more than 25 ft-lbs (33.9 Nm).

[0059] The present invention can also be applied to other types of connections. In a connection of the type proposed in JP7173664A, the portion of the threaded rod or bolt end inserted into the top of the carbon anode must be able to extend vertically as the anode expands. Failure to do so will result in the conductor being pulled out of the carbon or the brittle carbon fracturing at the connection point.

[0060] The use of a soft conductor (such as fully annealed copper) is also preferred in order to balance the current carrying capacity of the rod with the need to achieve the required expansion of 0.1% to 2% or more while maintaining a fracture strength below that of carbon. Alternatively, another deformable material including a polymer (such as PTFE) combined with an alternate current carrying path (such as a flexible wire) will achieve the same effect.

[0061] Prior art designs that utilize pressure plates to distribute the bolt's clamping force, such as those described in KR100286717B1, do not prevent the problem of anode cracking. While such plates successfully prevent the bolts from exerting high pressure directly on the carbon, they continue to maintain high overall forces in the area where the plate contacts the carbon anode. The carbon directly below the plate is restrained, while the carbon outside the area of ​​the plate is not restrained and expands normally. This uneven expansion of the carbon results in very high localized stresses concentrated at the lower edge of the pressure plate, where the bulk of the carbon can crack.

[0062] The present invention can be equally applied to such designs of integrated pressure plates. The expansion of the carbon must be accommodated without generating stresses that exceed the compressive strength of the carbon, even locally at the edges of the pressure plate. In order to achieve this, the structural components that carry the clamping loads must be modified, which are described in US8349164 as two large bolts. Any of the above designs function, including the use of spring-action components such as coil springs, spring washers or elastic washers between the carbon and one or more sides of the clamping surface that is in direct or indirect contact with the carbon-containing electrode, or the use of plastic deformation devices such as low-yield bolts or squeeze washers. However, it is required that the thickness and deformation characteristics of the one or more deformable connecting elements are large enough to accommodate the swelling of the carbon anode.

[0063] Comparative Example 1.

[0064] A set of six electrolytic cells were assembled for the production of elemental fluorine by electrolysis of HF-based molten salts, the cells utilizing an anode connection design substantially similar to that described in US 3041266A, but also including a flexible member substantially similar to that described in CN204434734U to Zhu et al., but with the hanger rod and anode bolting area elevated above the surface of the liquid electrolyte to reduce the corrosion rate of the hanger rod. The cells operated for a median life of only 83 days before being shut down due to excessive cell voltage. Upon opening the cells, approximately half of the anodes were found to have cracked at the bolting area due to anode swelling. A prior art electrolytic cell with the same design of hanger rod immersed in the liquid electrolyte to reduce swelling lasted approximately 250 days, although corrosion of the hanger rod was severe.

[0065] Comparative Example 2.

[0066] An electrolytic cell for producing fluorinated gases by electrolyzing HF-based molten salts was constructed using 4100 series alloy steel bolts using an anode connection design substantially similar to that described in US 9528191. The cell operated for almost 6 months before failing due to multiple anode cracks near the bolting points.

[0067] Example 1.

[0068] A set of bolts identical in size and shape to those used in Comparative Example 2 were manufactured from pure copper alloy C1100 to ASTM B-187 specifications. The bolts were fully heat annealed after manufacture to achieve an O60 (fully annealed) temper. The plastic deformation behavior of the bolts was measured by inserting them into an electrode connection design substantially similar to that of US Pat. No. 9,528,191 and tightening them to progressively higher torque values. The bolts had a yield strength of approximately 6,500 psi (44.8 MPa), and a 1% plastic deformation strain was achieved when the stress on the carbon reached 3,200 psi (22.1 MPa).

[0069] An electrolytic cell identical to that in Comparative Example 2 was constructed using the fully annealed copper bolts just described in place of the steel bolts. The initial assembly torque for the copper bolts was 20 ft-lbs (27.1 Nm). This electrolytic cell was operated in parallel with the electrolytic cell in Comparative Example 2 under the same conditions. The electrolytic cell lasted over 30% longer without any signs of carbon anode cracking.

[0070] Deformable connecting elements accommodate the swelling of electrodes made from carbonaceous materials, thereby extending the life of those electrodes. For any design involving connecting elements (including rods, screws, threaded rods, or posts that are partially or completely inserted into or compress the carbon anode), the carbon fracture can be delayed by using elements that deform at stresses lower than those required to fracture the carbon. In this way, the operation of the assembly in the electrolytic cell will be increased and the number of shutdowns required to rebuild or replace the anode assembly will be reduced.

[0071] The present invention has been described by way of illustration and not limitation, and it will be apparent that the invention has applicability in fields other than those described.

Claims

1. An electrode connection assembly for an electrolytic cell, comprising a carbon-containing electrode and one or more deformable connection elements in direct or indirect contact with the carbon-containing electrode, wherein the one or more deformable connection elements deform under a stress lower than a stress that would cause the carbon-containing electrode to fracture to accommodate expansion of the carbon-containing electrode during use, characterized in that The deformable connecting element comprises fully annealed copper.

2. The electrode connection assembly of claim 1, wherein the one or more deformable connection elements do not exert a stress exceeding 8,000 psi on any portion of the carbon-containing electrode at any time.

3. The electrode connection assembly of claim 1 or 2, wherein the one or more deformable connection elements do not exert a stress exceeding 6,000 psi on any portion of the carbon-containing electrode at any time.

4. The electrode connection assembly of claim 1 or 2, wherein the one or more deformable connection elements deform under a pressure between 4,000 and 10,000 psi of stress.

5. The electrode connection assembly of claim 1 or 2, wherein the one or more deformable connection elements deform under a pressure between 4,000 and 8,000 psi of stress.

6. The electrode connection assembly according to claim 1 or 2, wherein no portion of the electrode connection assembly comprises a polymer.

7. The electrode connection assembly of claim 1 or 2, wherein the fully annealed copper has mechanical properties conforming to ASTM O60 temper.

8. The electrode connection assembly of claim 1 or 2, wherein the one or more deformable connection elements comprise copper alloy C11000.

9. The electrode connection assembly of claim 1 or 2, wherein the one or more deformable connection elements have a yield strength of less than 10,000 psi at 0.5% extension.

10. The electrode connection assembly of claim 1 or 2, wherein the deformable connection element comprises one or more selected from a compression band, a strap, a screw, a bolt, a rod, a threaded rod, a post, or a shaft.

11. The electrode connection assembly according to claim 1 or 2, wherein the deformable connection element comprises one or more selected from a spring, a coil spring, a bolt, a screw, a strut, a squeeze washer, a U-shaped or C-shaped hanger, and a C-shaped clamp.

12. The electrode connection assembly according to claim 1 or 2, wherein the deformable connection element comprises one or more selected from a conical washer, a spring washer, a squeeze washer, an elastic pad, a gasket or a washer.

13. The electrode connection assembly of claim 1 or 2, wherein the deformable connection element comprises one or more bolts.

14. The electrode connection assembly of claim 1 or 2, wherein the carbon-containing electrode comprises carbon selected from the group consisting of non-graphitized carbon, graphitized carbon, low permeability carbon, high permeability carbon, carbon fiber, pressed carbon powder, mesocarbon microbeads, metal-impregnated carbon, metal-thin-layer-coated carbon, carbon diamond, coal- or petroleum-derived coke.

15. The electrode connection assembly according to claim 1 or 2, wherein the carbon-containing electrode is a monolithic structure or a composite structure.

16. The electrode connection assembly of claim 1 or 2, wherein the carbonaceous electrode is a shaped block of compressed carbon comprising a form of coal or petroleum derived coke and a pitch binder, which is baked to densify, harden and carbonize the pitch.

17. An electrode connection assembly as described in claim 1 or 2, wherein the one or more deformable elements deform to accommodate an expansion of the carbon-containing electrode of 0.1% to 1.0%, and the one or more deformable elements do not impose a stress on the carbon-containing electrode that exceeds the breaking strength of the carbon-containing electrode.

18. The electrode connection assembly of claim 1 or 2, wherein the one or more deformable elements deform elastically.

19. The electrode connection assembly of claim 1 or 2, wherein the one or more deformable elements are plastically deformed.

20. The electrode connection assembly of claims 1 or 2, wherein the one or more deformable elements exert a stress on the carbon-containing electrode of less than 8,000 psi after 0.5% expansion of the carbon-containing electrode.

21. The electrode connection assembly of claim 1 or 2, wherein the one or more deformable elements exert a stress on the carbon-containing electrode of less than 6,000 psi after 0.5% expansion of the carbon-containing electrode.

22. The electrode connection assembly of claim 1 or 2, wherein the one or more deformable elements comprise cold-rolled copper, steel, copper-nickel alloy, lead, gold, silver, tin, zinc, aluminum, brass, bronze, and alloys thereof.

23. The electrode connection assembly of claim 1 or 2, wherein the one or more deformable elements further comprise a halogenated elastomer, graphite-filled PTFE, or silicone rubber.

24. An electrode connection assembly as described in claim 1 or 2, wherein the one or more deformable elements comprise a material having an electrical conductivity greater than 300 S / m.

25. An electrode connection assembly as claimed in claim 1 or 2, wherein the one or more deformable elements are load-bearing.

26. The electrode connection assembly of claims 1 or 2, wherein the one or more deformable elements comprise one or more bolts, wherein the bolts are tightened to a torque of no greater than 30 ft-lbs (40.7 Nm).

27. The electrode connection assembly of claim 1 or 2, wherein the carbon-containing electrode is an anode.

28. An electrolytic cell comprising one or more electrode connection assemblies according to any one of the preceding claims, a container, a power distribution member, an electrolytic cell and one or more oppositely charged electrodes.

29. The electrolytic cell of claim 28, wherein the carbon-containing electrode in the one or more electrode connection assemblies is an anode.

30. The electrolytic cell of claim 28 or 29, wherein the electrolytic cell produces fluorine-containing material.

31. Use of the electrolytic cell according to any one of claims 28 to 30 for producing a fluorine-containing material, comprising the following steps: Electrical energy is introduced into the electrolytic cell to induce a chemical reaction at the carbon-containing electrode and the one or more oppositely charged electrodes in the one or more electrode connection assemblies.

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