New approach to chlor-alkali process

[adityasalunkhe]

Los Alamos Laboratory researchers have found new approach to chlor-alkali electrolysis which is based on the substitution of oxygen-consuming cathodes in place of conventional hydrogen-evolving cathodes. This change has resulted in lower cell voltages and power savings of nearly one third. Researchers have demonstrated that oxygen-reducing cathodes can save about 0.9V out of the 3.1-3.3V required for the operation of membrane chlor-alkali process.

The overall chemical reaction for oxygen consuming chlor-alkali cells becomes
                       O₂ + 2H₂O + 4NaCl –> 4NaOH + 2Cl₂
The new reaction has lower energy requirements and also eliminates the hydrogen byproduct present in conventional cells which was of relatively low value.

The oxygen electrode is a "gas diffusion electrode". In such electrodes, the gaseous reactant diffuses through a thin liquid film to reach the catalyst site. This process must occur with minimal transport losses. And, a thin layer of the catalyst has to be applied in a highly optimized way to ensure effective catalyst utilization and high reaction rates.

The above two requirements must be fulfilled by the initial cathode composition and structure, and must also be maintained throughout long-term cell operation. This second requirement is particularly demanding in chlor-alkali cells because the oxygen cathode is highly susceptible to the possible extremes of "flooding" (by the alkaline solution in the cathode compartment), or excessive drying of the catalyst layer (resulting in loss of electrocatalytic activity).

[Vishwanath Dalvi]

Interesting.  So they burn the hydrogen to get a free energy advantage.  

I suspect (as you will see later when we get into hydrotreating) that H2 is more useful as H2 rather than as electricity.