Soobhankar Pati

Solid oxide membrane technology for environmentally sound production of titanium

Abstract Despite its attractive properties, titanium is limited in use by its high price, due to the cost of smelting and processing the ore. The solid oxide membrane (SOM) process aims to consolidate most of the processing steps required for conventional titanium production into a single step, making it an energy efficient and cost effective method for producing CP billet and ingot and possibly also powders used to make titanium alloys. In the SOM process experiment, a steel crucible contains MgF2–CaF2–TiO2 flux; an inert metal/carbon rod serves as the cathode; an oxygen ion conducting yttrium stabilised zirconia (YSZ) membrane in the form of a one end closed tube contains either a liquid metal that acts as the anode or a liquid MgF2–CaF2 ionic flux that connects the YSZ membrane to an anode. During electrolysis, titanium ions are reduced at the cathode while the oxygen ions pass through the YSZ membrane and are oxidised at the anode by a reducing agent, hydrogen gas or carbon, forming steam or CO(g) respectively. To date, a suitable MgF2–CaF2–TiO2 flux has been selected and an optimum operating temperature has been determined. Several electrolysis experiments have been performed. As expected, lower valence deposits of titanium oxides have been witnessed at the cathode before depositing pure titanium. Continuing work will aim to extend the electrolysis time to pass enough charge to produce a significant amount (100 g) of titanium at the cathode.

Hydrogen Production Using Solid Oxide Membrane Electrolyzer with Solid Carbon Reductant in Liquid Metal Anode

A laboratory-scale solid oxide membrane (SOM) steam electrolyzer that can potentially utilize the energy value of coal or any hydrocarbon reductant to produce high purity hydrogen has been fabricated and evaluated. The SOM electrolyzer consists of an oxygen-ion-conducting yttria-stabilized zirconia (YSZ) electrolyte with a Ni-YSZ cermet cathode coated on one side and liquid tin anode on the other side. Hydrogen production using the SOM electrolyzer was successfully demonstrated between 900 and 1000{sup o}C by feeding a steam-rich gas to the Ni-YSZ cermet cathode and solid carbon reductant into the liquid tin anode. It was confirmed that the energy required for hydrogen production can be effectively lowered by feeding a solid carbon reductant in the liquid tin anode. A polarization model for the SOM electrolyzer was developed. The experimental data obtained under different operating conditions were curve fitted into the model to identify the various polarization losses. Based on the results of this study, work needed toward increasing the electrochemical performance of the SOM electrolyzer is discussed.

EFFICIENCY AND STABILITY OF SOLID OXIDE MEMBRANE ELECTROLYZERS FOR MAGNESIUM PRODUCTION

Solid oxide membrane (SOM) process has been successfully employed for the production of magnesium directly from its oxide. The process involves dissolving MgO in a fluoride based ionic flux and electrochemically pumping out the oxygen ions from the flux via an oxygen-ion-conducting SOM to the anode where they are oxidized, while reducing magnesium ions at the cathode. Understanding the long-term stability of the SOM in the flux is critical for the commercial success of this technology. In this study long term SOM stability is investigated under potentiostatic conditions. Additionally, study utilizes electrochemical techniques such as impedance spectroscopy and linear sweep voltammetry to investigate key concepts related to MgO dissociation and current efficiency. Results show that the dissociation potential of MgO is dependent on the partial pressures at which magnesium is generated and the membrane stability is likely related to the current efficiency.

Scaling‐Up Solid Oxide Membrane Electrolysis Technology for Magnesium Production

Metal Oxygen Separation Technologies, Inc. (MOxST) is actively developing Solid Oxide Membrane (SOM) electrolysis technology for production of magnesium directly from its oxide. The vital component of this technology is the oxygen ion-conducting solid zirconia electrolyte separating the molten flux (a mixture of salts and oxide) and the inert anode. The zirconia not only protects the anode from the flux but also prevents anode gas back-reaction, increasing the efficiency. This makes it possible to produce low-cost high-purity magnesium and high-purity oxygen as a byproduct with no direct greenhouse gas emissions. In this paper we discuss the design modifications made to address the scaling-up challenges, particularly for producing magnesium in liquid form. The key accomplishment to date is the successful development of a prototype capable of producing few kilograms of magnesium per day. We will also describe the prerequisite properties of an inert anode and suitable materials for the same.

Solid Oxide Membrane Electrolyzer Utilizing the Energy Value in Solid and Gaseous Reductant for Hydrogen Production

This paper describes a novel Solid Oxide Membrane (SOM) electrolyzer that can utilize the energy value in any carbon and hydrocarbon reductant to lower the energy requirement for hydrogen production from steam. The Solid Oxide Membrane (SOM) electrolyzer consists of a one-end closed oxygen-ion conducting yttria stabilized zirconia (YSZ) tube with Ni-YSZ cathode coated on the outside and liquid metal anode inside the tube. In the SOM electrolyzer steam is reduced at the cathode and the oxygen produced on the anodic side reacts with the reductant supplied in the liquid metal anode. In the present study the SOM electrolyzer is evaluated using solid carbon and humidified hydrogen as reductant.