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

eduction of chlorate emissions;
reduction of salt consumption;
reduction of chloride emissions due to reduced brine purge volumes.
Chapter 4
Environmental performance and operational data
At the Solvin plant in Lillo-Antwerp (Belgium), a chlorate reduction efficiency of 60 – 70 % is
achieved after treating the depleted brine at 85 °C with hydrochloric acid at a concentration of
30 g/l, a flow rate of 10 m 3 /h and a residence time of 1 h. Residual chlorate levels range
between 1 – 2 g/l [ 34, Solvay 2010 ].
Cross-media effects
Some raw materials and energy are consumed for the construction of the reactor. During
operation, steam and hydrochloric acid are consumed for the reaction. In addition, significant
amounts of sodium hydroxide are required for the neutralisation of the reactor effluent which is
necessary for the primary brine treatment. To reduce this consumption of sodium hydroxide, the
treated brine leaving the reactor is sent to the dechlorination unit in order to reuse a maximum
of the HCl excess (Figure 4.9) [ 34, Solvay 2010 ].
Chlorine dioxide may be formed in a side reaction and require an additional treatment of the
gaseous reactor effluent [ 34, Solvay 2010 ]:
5 ClO3 - + 6 H + + Cl - V 6 ClO2 + 3 H2O
Technical considerations relevant to applicability
Generally, there are no technical restrictions to the applicability of this technique. Diaphragm
plants do not recirculate the brine and therefore do not use acidic chlorate reduction. Any
chlorate produced during electrolysis leaves the process with the caustic liquor.
Economics
{Please TWG provide information.}
Driving force for implementation
The driving forces for implementation of this technique include:
improvement of product quality (less chlorate in caustic);
reduction of costs related to equipment and maintenance;
environmental legislation.
Example plants
Acidic chlorate reduction is used by many membrane cell chlor-alkali plants. Example plants
include:
Solvin in Antwerp-Lillo, chlorine capacity 180 kt/yr.
Reference literature
[ 1, Ullmann's 2006 ], [ 34, Solvay 2010 ], [ 49, Euro Chlor 2010 ]
WORKING DRAFT IN PROGRESS
4.3.6.4.4 Catalytic reduction
Description
This technique consists in reducing chlorate to chloride and bromate to bromide in a pressurised
trickle-bed reactor by using hydrogen and a rhodium catalyst in a three-phase reaction.
Technical description
Similar to acidic chlorate reduction (see Section 4.3.6.4.3), catalytic chlorate reduction is
typically used to treat a side stream of the depleted brine leaving the cells. Chlorate is reduced to
TB/EIPPCB/CAK_Draft_1 December 2011 247