(BAT) Reference Document for the Production of Chlor-alkali ...

Chapter 4
Driving force for implementation
The driving forces for implementation of this technique include:
reduction of costs related to energy consumption;
improvement of product quality (less oxygen in chlorine, less chlorate in caustic);
reduction of costs related to equipment and maintenance.
Example plants
Brine acidification is frequently applied in chlor-alkali plants.
Reference literature
[ 1, Ullmann's 2006 ], [ 34, Solvay 2010 ], [ 72, Nishio 2011 ]
4.3.6.4.3 Acidic reduction
Description
This technique consists in reducing chlorate to chlorine by using hydrochloric acid at
temperatures higher than 85 °C.
Technical description
Acidic chlorate reduction is typically used to treat a side stream of the depleted brine leaving the
cells (Figure 4.9) [ 1, Ullmann's 2006 ].
HCl
Acidic chlorate reduction
Figure 4.9: Flow diagram of acidic chlorate reduction
Depleted brine to resaturation
Brine dechlorination
Depleted brine from electrolysis
During the reaction, chlorate and chloride ions comproportionate (symproportionate) to
molecular chlorine which is removed under vacuum and can be recycled to the process [ 49,
Euro Chlor 2010 ]:
ClO3 - + 6 H + + 5 Cl - V 3 H2O + 3 Cl2
WORKING DRAFT IN PROGRESS
The reaction is typically carried out at temperatures higher than 85 °C and a pH value of 0 (HCl
concentration > 30 g/l). The reactor design needs to take into account the required residence
time of the reactants and the corrosive conditions (temperature, pH value, chlorine). Compared
to catalytic chlorate reduction (see Section 4.3.6.4.4), the technique is easier to implement and
to operate [ 34, Solvay 2010 ].
{Please TWG advise if this technique also reduces bromate levels.}
Achieved environmental benefits
The achieved environmental benefits of this technique include:
246 December 2011 TB/EIPPCB/CAK_Draft_1
HCl