(12) Patent Application Publication (10) Pub. No.: US 2013/0319876A1 Hsieh (43) Pub

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US 201303 19876A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2013/0319876A1 Hsieh (43) Pub. Date: Dec. 5, 2013

(54) MERCURY-FREE FUSIBLE ALLOY FOR Publication Classification ELECTROLYZING SALTS (51) Int. Cl. (75) Inventor: Peter Yaw-Ming Hsieh, Arcadia, CA f f 30.8 (US) C25B I5/08 (2006.01) C25B 9/18 (2006.01) (52) U.S. Cl. (73) Assignee: United States Government, as USPC ...... 205/516; 204/267; 205/510 represented by the Secretary of the Navy, Arlington, VA (US) (57) ABSTRACT An apparatus and method is provided for the production of alkali metals and caustic Solutions. The apparatus and method (21) Appl. No.: 13/373,751 do not require the use of toxic liquid mercury-Sodium amal gam electrodes. The apparatus and methods utilizeabismuth indium-tin eutectic alloy as a Substitute for the mercury elec (22) Filed: Nov. 23, 2011 trode used in a conventional Castner-Kellner apparatus.

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MERCURY-FREE FUSIBLE ALLOY FOR P. Surmann and H. Zeyat, “Voltammetric analysis using a ELECTROLYZING SALTS self-renewable non-mercury electrode'. Anal. Bioanal. Chem. (2005) 383 (6): 1009-1013 reports that liquidgalinstan STATEMENT OF GOVERNMENT INTEREST electrodes are similar to mercury electrodes in terms of hydrogen overpotential, simplicity of Surface renewal, and 0001. The invention described was made in the perfor good electrochemical behavior without the danger posed by mance of official duties by one or more employees of the mercury toxicity. Department of the Navy, and thus, the invention herein may 0009. The use of liquid gallium and gallium alloys as a be manufactured, used or licensed by or for the Government mercury substitute was considered for a number of different of the United States of America for governmental purposes applications, ranging from electrical and mechanical sensors without the payment of any royalties thereon or therefor. to electrical contact lubrication, as taught in U.S. Pat. Nos. 5,478,978 and 5,792.236 to Taylor et al. Mercury-free ther BACKGROUND OF THE INVENTION mometers using galinstan have recently been brought to mar 0002 (1) Field of the Invention ket as indicated in U.S. Pat. No. 6,019,509 to Speckbrocket 0003. The invention relates to methods and apparatus for al. the production of alkali metals and caustic Solutions and, 0010 Alloys containing bismuth, indium, and tin has been more particularly, to a mercury-free Castner-Kellner process proposed for use as a cadmium-free heat transfer medium and and apparatus. sealing material, as taught by U.S. Pat. No. 2,649.366 to 0004 (2) Description of the Prior Art Smith et al. and U.S. Pat. No. 4,214,903 to Murabayashi et al. 0005 Electrolysis of salt solutions is widely used in the U.S. Pat. Nos. 4,738,858 and 5,168,020 to Jow describe the chemical industry to produce alkali metals and caustic Solu use of a rechargeable Sodium alloy anode, the constituents of tions. The Castner-Kellner process has been used for over a which may contain lead, antimony, selenium, mercury, and century to produce high-purity caustic soda by utilizing a cadmium in addition to bismuth and tin. The presence of these mercury electrode to separate the brine feedstock from the toxic metals in the electrode alloy may contaminate the elec product. However, the use of mercury is undesirable today trolyte solution via leaching during cell operation. due to the metals toxicity. Typically, mercury ions can be found in the caustic Soda solution and spent brine, which are SUMMARY OF THE INVENTION the products of the Castner-Kellner process. Additional fil 0011. There is consequently a need for an apparatus and tration is necessary to remove mercury from the final product method for producing alkali metals and caustic solutions that and unreacted brine. The cost of monitoring and reducing does not require the use of mercury or other toxic heavy mercury levels in electrolyte Solutions to safe levels poses an metals. economical constraint on the use of mercury cathodes in 0012. According to one aspect of various exemplary industry. embodiments, an electrolysis cell comprises a first cell type 0006 Electrochemical reduction of cations at a liquid adapted to contain a first electrolyte Solution; a second cell metal cathode surface can result in the diffusion of the type, separated from the first cell, the second cell type adapted reduced metal into the electrode, thereby changing the alloy to contain a second electrolyte Solution; an alloy electrode composition. For mercury-based cathodes, the process is disposed at a bottom of and electrically interconnecting the known as amalgamation. The alloy can be less reactive than first cell, and the second cell, the alloy electrode being mer the reduced metal in water, thereby preventing back and side cury-free; walls separating the first cell from the second cell, reactions from taking place. Mercury cathodes were widely the wall intersecting the alloy electrode but not bisecting the used in the chlor-alkali industry to produce sodium hydroxide alloy electrode; a first cell type anode disposed in the first cell; (caustic soda) via the Castner-Kellner process, as taught in and a second cell type cathode disposed in the second cell. U.S. Pat. No. 452,030 to Castner. The use of liquid metal 0013. According to another aspect of various exemplary cathodes can be advantageous compared with Solid cathodes embodiments, a method for the production of caustic soda when ease of Surface alloying and transport of dissolved comprises applying electrical current to an anode disposed in metallic element are important to the electrochemical pro a first electrolysis cell containing an alkali metal halide solu CCSS, tion; applying electrical current to a cathode disposed in a 0007. The chlor-alkali industry has largely abandoned the second electrolysis cell containing water; and interconnect use of mercury cathodes and the Castner-Kellner process in ing the alkali metal halide solution of the first electrolysis cell favor of asbestos diaphragm and selective ion-exchange with the water contained in the second electrolysis cell with a membrane cells. Both rely on the selective diffusion of non-toxic mercury-free alloy electrode. Sodium ions through the separatory barrier. Diaphragm cells 0014. According to a further aspect of various exemplary are capable of producing 11% sodium hydroxide (NaOH), embodiments, an electrolysis system comprises a first cell with up to 15% salt. Membrane cells produce 35% sodium adapted to contain a first electrolysis Solution of an alkali hydroxide. In comparison, mercury cells can produce from metal halide; a first cell anode adapted to deliver electrical 50% to 70% sodium hydroxide with very little salt present in current to the first electrolysis solution; a second cell adapted the product. The reduction of sodium to its metallic state and to contain a second electrolysis solution; a second cell cath amalgamation with mercury effectively blocks anion trans ode adapted to deliver electrical current to the second elec port during the separation process, resulting in a high purity trolysis solution; and an alloy electrode adapted to electri product with low salt content. cally interconnect the first electrolysis solution and the 0008 Galinstan, a eutectic alloy containing gallium (Ga), second electrolysis solution, the alloy electrode formed from indium (In), and tin(Sn), has been tested as a replacement for a bismuth-indium-tinternary alloy. mercury (Hg) in electrochemical analysis. The eutectic alloy 0015 The above and other features of the inventions melts at -19°C. and is liquid at room temperature. A paper by exemplary embodiments, including various novel details of US 2013/03 19876 A1 Dec. 5, 2013

construction and combinations of parts, will now be more typically an iron (Fe) cathode, may be disposed in the elec particularly described with reference to the accompanying trolyte solution 22. Abismuth-indium-tin alloy, typically the drawings and pointed out in the claims. It will be understood eutectic alloy described above, may be used along the bottom that the particular assembly embodying the invention is of the electrolysis cell 10 to form an alloy electrode 26. shown by way of illustration only and not as a limitation of the 0024. The alloy electrode 26 may be disposed along a invention. The principles and features of this invention may shared bottom of both cells of the cell types 14, 16. This may be employed in various and numerous embodiments without be achieved by having the walls 12 separating the cells inter departing from the scope of the invention. sect or dip below the level of the electrolytes, but still allow the alloy electrode 26 to flow beneath them by not bisecting BRIEF DESCRIPTION OF THE DRAWINGS the alloy electrode 26. An electric current may be applied to the anode 20 and the cathode 24 to begin the electrolysis 0016 Reference is made to the accompanying drawings in process. which is shown an illustrative embodiment of the invention, 0025 A rocking mechanism may be provided to agitate from which its novel features and advantages will be appar the electrolysis cell 10. The rocking mechanism may include ent, wherein corresponding reference characters indicate cor a fulcrum 28 and a rotating eccentric 30 under the electrolysis responding parts throughout the several views of the drawings cell 10, as is known in the art. and wherein: 0026. Upon initial operation, alkali metal ions from the 0017 FIGS. 1 and 2 are cross-sectional views of an elec electrolyte solution 18 are reduced electrochemically and trolysis apparatus according to two exemplary embodiments alloys with the bismuth-indium-tin electrode 26. Continued of the present invention. operation cause the alkali metal concentration to reach an equilibrium value. The alkali-metal enriched alloy functions DETAILED DESCRIPTION OF EXEMPLARY to transport alkali metal ions from the salt solution to the EMBODIMENTS caustic Solution through paired oxidation reduction reactions 0018. The following detailed description is of the best at the electrolyte solution 18, 22-alloy electrode 26 interfaces. currently contemplated modes of carrying out exemplary (0027. The electrolyte solution 18 of the first cell type 14 embodiments of the invention. The description is not to be may carry out the following reactions. The reaction at the taken in a limiting sense, but is made merely for the purpose electrolyte solution 18 anode 20 interface, with sodium of illustrating the general principles of the invention: the chloride as the alkali metal halide, is: scope of the invention is best defined by the appended claims. 0019 Broadly, the current invention provides apparatus and methods for the production of alkali metals and caustic 0028. The chlorine gas that results from (i) may be vented Solutions without the use of toxic liquid mercury-Sodium at the top of the first cell type 14 where in may be collected as amalgam electrodes. The current invention may utilize a bis a by-product. The reaction at the electrolyte solution 18 al muth-indium-tin eutectic alloy as a replacement for the mer loy electrode 26 interface is: cury electrode used in a conventional Castner-Kellner appa 2Na+2e->2Na. (ii) ratuS. 0020 Bismuth, tin and indium forms an eutectic alloy, 0029. In the second cell type 16, the reaction at the elec with a composition (by mass) of 32.5% bismuth (Bi), 51.0% trolyte solution 22 alloy electrode 26 interface is: indium (In), and 16.5% tin(Sn), which melts at 60.5°C. The 2Na (alloy)->2Na+2e. (iii) constituent elements are nontoxic and are safe to handle with 0030 The reaction at the electrolyte solution 22 anode out protective safety equipment. The alloy may be prepared 24 interface is: by melting commercially pure bismuth, indium and tin in an oven or furnace at 300° C. for one hour. Heating under 2H2O+2e->2OH +H. (iv) vacuum oran inert gas atmosphere will reduce the quantity of 0031. The net effect is that the concentration of alkali dross formed at the surface of the crucible, but any dross metal halide (sodium chloride, for example) in the right cell present may be skimmed off during pouring and casting. (first cell type 14) decreases, and the concentration of the 0021. The melting point and resistivity of the ternary bis caustic solution (sodium hydroxide) in the left cell (second muth-indium-tinalloy may be adjusted by changing the quan cell type 16) increases. As the process continues, some tity of bismuth, indium and tin used during initial fabrication. sodium hydroxide solution may be withdrawn from the sec For example, an alloy may be formed from about 10-60% ond cell type 16 as output product and replaced with water. bismuth, about 20-80% indium, and about 5-50% tin (by Sodium chloride may be added to the first cell type 14 to mass). Other compositions may be contemplated within the replace sodium chloride that has been electrolyzed. scope of the current invention as defined by the appended 0032 For sodium and the production of caustic soda (e.g., claims. NaOH), the equilibrium concentration is about 1% by weight 0022 Referring now to FIG. 1, an electrolysis cell 10 may (about 6% Molar concentration). It is possible to prepare the be divided into two cells separated by a wall 12, typically slate alloy by direct incorporation of sodium metal in its initial or rubber coated steel. The first cell type 14 may use an manufacture to avoid the need for charging during initial electrolyte solution 18 of an alkali metal halide, typically operation. sodium chloride (NaCl). An anode 20, typically a graphite or 0033. The apparatus and methods provided in various titanium electrode, may be disposed in the electrolyte Solu exemplary embodiments may be used not only for the pro tion 18 in the first cell types 14. duction of caustic soda and alkali metals, but also as a means 0023 The second cell type 16 may use an electrolyte solu of electrochemical desalination of sea water (or brackish tion 22 of a caustic soda, typically sodium hydroxide water) using a non-toxic metal alloy as the ion transport (NaOH), or may use water (H2O). A metallic cathode 24, medium. The apparatus and methods described by these US 2013/03 19876 A1 Dec. 5, 2013 embodiments may also be applied to the commercial produc a barrier physically separating the first electrolyte Solution tion of hydrogen and chlorine gases. from the second electrolyte solution; and 0034. In some embodiments of the current invention, the a eutectic electrode contacting the first and second electro electrolysis cell may be used, in “reverse', as a fuel cell. An lyte solutions, the eutectic electrode excluding mercury open-cell potential of 2.1 V was observed in the circuit after free and comprising an alloy of bismuth, indium and tin, external power was disconnected. Other low melting-point and electrically interconnecting the first cell and the metals, such as gallium (Ga), and alloys (containing bismuth, second cell. indium, tin or gallium) may also be used to form amalgams 2. The electrolysis cell assembly of claim 1, wherein the for alkali metal transport in the methods and apparatus of the first electrolyte salt solution is contains an alkali-metal-halide current invention. salt. 0035. The following Table shows the change in alloy com 3. The electrolysis cell assembly of claim 2, wherein the position by the use of various exemplary embodiments in an alkali-metal-halide salt is sodium chloride. electrolytic cell with the nontoxic alloy electrode. Aqueous 4. The electrolysis cell assembly of claim 2, wherein the alkali metal solutions were electrolyzed by applying potential alkalai-metal-halide Salt is potassium chloride. of 10V across the working and counter electrodes for 90 5. The electrolysis cell assembly of claim 1, wherein the minutes. The difference between the initial and final compo second electrolyte caustic soda solution becomes a sodium sition of the electrode alloy demonstrates the formation of hydroxide solution during operation of the electrolysis cell alkali metals and diffusion into the body of the electrode. assembly. These metals include aluminum (Al), Sodium (Na), potas 6. The electrolysis cell assembly of claim 1, wherein the second electrolyte caustic soda solution becomes a potassium sium (K), bismuth (Bi), indium (In), and tin (Sn). hydroxide solution during operation of the electrolysis cell assembly. TABLE 7. The electrolysis cell assembly of claim 1, wherein the Change in alloy composition after salt electrolysis anode comprises graphite. 8. The electrolysis cell assembly of claim 1, wherein anode Final alloy Final alloy Initial alloy composition composition comprises titanium. composition (NaCl) (KCl) 9. (canceled) 10. The electrolysis cell assembly of claim 1, wherein the Al O.92 0.12 1.12 O.10 Na O.O3O41 1.13 - 0.21 eutectic alloy has a bismuth:indium:tin ratio of 32.5:51.0: K 1.60 O.28 16.5 by mass. B 33.6S 1.50 29.87 0.60 31.390.44 11. (canceled) In 53.521.54 52.11 - 0.61 S1.OS O.47 12. (canceled) Sn 12.81 - 1.34 15.97 O.S2 1483 - 0.40 13. (canceled) 14. (canceled) 0036 While the above description focuses on the alloy 15. (canceled) electrode and use in water-based oraqueous electrolytic cells, 16. (canceled) the current invention may be applied to other electrolyte 17. (canceled) systems. For example, various embodiments may be applied 18. An electrolysis system comprising: to molten-salt and organic electrolytic cells. a first cell containing a first electrolysis salt solution of an 0037 FIG. 2 shows a similar electrolysis cell 40, contain alkali-metal and a halogen; ing a pair of first cell types 14 that flank the second cell type a first cell anode for receiving electrical current from the 16, both first cell types 14 having corresponding anodes 20 first electrolysis salt solution; disposed therein. It will be understood that many additional a second cell adapted to contain a second electrolysis caus changes in the details, materials, steps and arrangement of tic Soda solution; parts, which have been herein described and illustrated in a second cell cathode for delivering electrical current to the order to explain the nature of the invention, may be made by second electrolysis caustic soda solution; and those skilled in the art within the principle and scope of the a eutectic electrode electrically interconnecting the first invention as expressed in the appended claims. electrolysis salt Solution and the second electrolysis 0038. The foregoing description of the preferred embodi caustic Soda solution, the eutectic electrode formed from ments of the invention has been presented for purposes of a bismuth-indium-tinternary alloy. illustration and description only. It is neither intended to be 19. The electrolysis system of claim 18, wherein the alkali exhaustive nor to limit the invention to the precise form dis metal and the halogen constitute a salt of sodium chloride. closed; and obviously many modifications and variations are 20. The electrolysis system of claim 18, further comprising possible in light of the above teaching. Such modifications a wall separating the first cell from the second cell, wherein and variations that may be apparent to a person skilled in the the eutectic electrode is disposed along a bottom Surface of art are intended to be included within the scope of this inven the first and second cells and the wall intersects, without tion as defined by the accompanying claims. bisecting, the eutectic electrode. 1. An electrolysis cell assembly comprising: 21. The electrolysis system of claim 18, wherein the alloy a first cell chamber containing a first electrolyte salt solu electrode contains bismuth, indium and tin in a ratio of 32.5: tion and an anode: 51:16.5 by mass. a second cell chamber containing a second electrolyte 22. (canceled) caustic soda solution and a cathode: