Published September 2015
Industrial chlorine production is conducted using electrochemical cells. An aqueous solution of sodium chloride feeds the cell, producing chlorine vapor at the anode, and a dilute caustic soda solution at the cathode. Small quantities of hydrogen and sodium carbonate are also produced. The concentration of the dilute caustic soda solution is increased to 50% (in order to satisfy sales specifications) in a separate multistage flash or vacuum evaporation system. Early electrochemical cells used mercury for the electrochemical separation. Due to mercury’s toxicity, these systems have largely been replaced by diaphragm cells, and more recently, by membrane cells.
In Germany, Bayer has recently (2013) demonstrated the use of an oxygen depolarization cathode (ODC) membrane on the cathode side of the cell, which suppresses the formation of hydrogen gas, reducing electricity consumption up to a claimed 30%. The best membrane cell systems consume approximately 2500 kWh of electricity per metric ton of chlorine produced. This ODC technology was developed jointly by Bayer and the De Nora subsidiary of Uhde, which is owned by Thyssen-Krupp. INEOS also claims to be developing a similar oxygen depolarization cathode membrane for chlorine production.
In this PEP review, we develop the process engineering inputs for a Class-3 process design, and use the design outputs to prepare a corresponding production cost estimate for making chlorine using Bayer ODC technology. We then compare these new economics to our understanding of the best conventional membrane cell economics available for license.