Published March 2001
The economics of chloralkali production has been continuously improved over the years through development of new improved cationic exchange membranes and improved activated electrodes. This results in reduction of cell voltage below 3 volts, and increase of current density up to 50-60 A/dm2 while maintaining current efficiency at greater than 95% in the production of pure chlorine and 35 wt% caustic soda.
In recent announcements, both Asahi Chemical (Asahi Kasei) and Asahi Glass report the development new improved electrolytic cells, which require less than 3 volts of cell voltage for salt electrolysis. The power consumption was reported at 2,300 kWh/t of chlorine for an electrolytic cell operated at a current density up to 60 A/dm2. Separately, Chlorine Engineers (a sub-sidiary of Mitsui & Co.) has also developed an electrolytic cell, "BiTAC," that requires reduced power consumption at a current density of 50 A/dm2 and a cell voltage of less than 3 volts. Also reported is the direct production of 50 wt% caustic soda.
This Review presents a technoeconomic evaluation of the current development of technology. We conclude that the current technology for operating an electrolytic cell at a current density of 50 A/dm2 provides the best economics for the membrane process. As to the membrane process for direct production of 50 wt% caustic soda solution from electrolytic cells, our evaluation indicates that it is not economically compatible at the present stage. There is a need for further improvement in membrane and cathode in order either to reduce the cell voltage or to increase the current density.