Oxygen-Depolarized Cathode (HCl-ODC) Technology 

The electrolyzer operates at an anode-side pressure of 200 mbar(g) to ensure optimal contact between the membrane, the oxygen-depolarized cathode (ODC), and the cathode current distributor. The hydrochloric acid feed to the electrolyzer is maintained at 14 wt.% and is automatically controlled in the anolyte tank by blending concentrated hydrochloric acid (37 wt.%) with depleted circulating acid. A small portion of the resulting 12.5 wt.% hydrochloric acid stream is recycled back to the absorption unit.

The anode chamber is supplied with 14 wt.% hydrochloric acid, where anodic oxidation takes place and chlorine is generated while hydrochloric acid is consumed. The produced chlorine is separated from the depleted 12.5 wt.% hydrochloric acid and collected in the chlorine header. The depleted acid is returned to the anolyte tank. In addition, part of the water as well as H⁺ and Cl⁻ ions are transported through the membrane to the cathode chamber.

The cathode chamber is fed with oxygen. At the ODC, oxygen is cathodically reduced and reacts with H⁺ ions transferred from the anode chamber, forming water. A small excess of oxygen at the cathode outlet is required to prevent hydrogen formation. The acidic condensate generated at the cathode can either be sent to wastewater treatment or recycled back to the anolyte system.

Due to the very high chlorine quality, the product can be fed directly to downstream consumers without the need for chlorine liquefaction or evaporation. In most cases, cooling and filtration of wet chlorine are sufficient. In addition, the chlorine can be dried and compressed for storage as liquid chlorine or returned to the consumer to close the chlorine recycle loop.