Energy-saving electrolysis

A new process for making chlorine from hydrochloric acid could cut energy usage by 30%, according to German major Bayer. The company has installed two electrolysers based on the technology at its Brunsbüttel site, producing a total of 20 000tpa of chlorine.

The new process uses a technology based around an oxygen depolarising cathode (ODC). Generally, electrolysing hydrochloric acid produces chlorine and hydrogen, but the ODC introduces oxygen into the system, converting the hydrogen directly into water.

'In principle, we have incorporated a fuel cell into the process,' explains Fritz Gestermann, who leads Bayer's electrolysis process development. This allows the cell to operate at a much lower voltage at the same current density, considerably reducing energy usage.

Of course, this means that the process generates less carbon dioxide emissions, and also reduces the costs. But the system has other advantages. The OCD process makes pure chlorine which can be used directly without post-production cleaning steps, and the amount of chlorine produced can be altered easily.

Bayer developed the process, the first to use a purely metallic electrolysis cell with an ion exchanger membrane for HCl electrolysis, in cooperation with Uhdenora, a joint venture between Uhde and the Italo-American firm De Nora. The companies plan to license and market the process.