Solid Oxide Membrane Electrolysis Process for Aluminum Production: Experiment and Modeling

Abstract

This paper reports a solid oxide membrane (SOM) electrolysis process using an LSM (La 0.8 Sr 0.2 MnO 3-δ )-Inconel inert anode current collector and liquid silver anode for production of aluminum and oxygen from aluminum oxide dissolved in a pre-selected molten oxy-fluoride flux containing Ca, Mg, Al and Y at 1473K (1200 • C). The electrochemical behavior of the SOM cell was characterized by various electrochemical techniques including electrochemical impedance spectroscopy, potentiodynamic scan and potentiostatic electrolysis. Based on the electrochemical measurement results, an equivalent circuit model of the SOM electrolysis process is presented. A polarization model for aluminum and oxygen production was developed and the polarization losses in the cell were analyzed according to the equivalent circuit. Based on the polarization model analysis, potential approaches to improve the cell performance are also discussed. The aluminum produced and the yttria stabilized zirconia (YSZ) membrane were characterized with scanning electron microscope and energy-dispersive X-ray spectroscopy after the electrolysis. Aluminum is the third most abundant element in the earth's crust, and the most abundant metallic element. It is an essential material in modern manufacturing. It is known for its low density, high strength, corrosion resistance, good recyclability and high electrical and thermal conductivities. Aluminum is also often alloyed with other elements such as magnesium, silicon, tin and zinc in order to improve its properties. Aluminum and its alloys have a wide range of applications making them the second most used industrial metal for the past fifty years. Global aluminum production has been growing at a rate of 5% annually for the past five years.1 Demand for aluminum will continue to grow, mainly due to its increasing use in the transportation sector as a light-weight structural material.The aluminum smelting process was invented in 1886 by Charles Martin Hall and Paul L.T. Héroult (i.e. the Hall-Héroult process). It involves electrolysis of cryolite-alumina melt and even to this day the process used has fundamentally remained the same. The average energy intensity of the process is 14.29 kWh/(kg Al), 2 while its theoretical minimum energy requirement is 5.99 kWh/(kg Al).3 The process is energy-intensive and has low energy efficiency. The use of graphite anode, the electricity input, and the anode effect of the process result in an average of 6.9 kg of equivalent CO 2 emission per kg of Al produced.3 The market potential of aluminum and the environmental impact of the current aluminum production process justify research and development of alternative electrolytic processes for aluminum production that can both reduce the cost and eliminate adverse environmental impacts.Solid oxide membrane (SOM) electrolysis is a novel metals extraction technique that is being developed for the production of several energy-intensive metals, semiconductors or alloys, such as Mg, Ti, Ta, Yb, Si, CeNi 5 and Ti-Fe alloy. [4][5][6][7]...

Stereolithographic Additive Manufacturing of Zirconia Electrodes with Dendritic Patterns for Aluminum Smelting

“…Recently, YSZ electrodes have been used in the molten salt electrolysis of aluminum smelting [7]. Metal anodes of mesh tubes coated with fine YSZ layers can attract oxygen ions in molten alumina, reducing the melting point by cryolite addition.…”

Applicability of the Electrochemical Oxygen Sensor for In-Situ Evaluation of MgO Solubility in the MgF2–LiF Molten Salt Electrolysis System

“…The solid oxide membrane (SOM) process is considered an environmentally friendly metal extraction technique with high energy efficiency and low capital costs [13]. Owing to its simplicity and energy efficiency, SOM is often utilized for the extraction of high-purity magnesium, silicon, titanium, tantalum, and aluminum [12][13][14][15][16][17][18]. In the SOM process, the liquid-metal anode is separated from a molten fluoride bath containing dissolved target metal oxide by the oxygen-ion-conducting material: yttria-stabilized zirconia (YSZ).…”

Chlorine Production by HCl Oxidation in a Molten Chloride Salt Catalyst

“…Molten halide salts have been used as catalysts in a number of chemical processes, , and the unit operations and system management are well understood. Molten salt catalysts have been used in extraction of ores, metal production, − catalytic coal gasification, Wacker oxidation of ethylene, diesel soot catalytic oxidation, and oxidative dehydrogenation of alkanes. ,, …”