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

Chapter 4
Example plants
High-performance membranes are generally used by membrane cell chlor-alkali plants.
Reference literature
[ 3, Euro Chlor 2011 ], [ 22, Uhde 2009 ], [ 26, Euro Chlor 2010 ], [ 63, Euro Chlor 2010 ],
[ 136, Asahi Kasei 2008 ], [ 188, DuPont 2006 ], [ 189, Nitini 2011 ], [ 203, Eckerscham 2011 ],
[ 204, Asahi Glass 2011 ]
4.3.2.3.4 High-performance electrodes and coatings
Description
This technique consists in using electrodes and coatings with improved gas release (low bubble
overpotential), small gap between the electrodes (diaphragm cell technique: Q 3 mm; membrane
cell technique: Q 0.1 mm) and low electrode overpotentials.
Technical description
As in the development of high-performance membranes, manufacturers are continuously
improving the performance of electrodes and coatings. Factors which are taken into account for
the electrode structure include current distribution, gas release, ability to maintain structural
tolerances, electrical resistance and the practicability of recoating. Coatings are optimised in
terms of mechanical and (electro-)chemical robustness as well as low overpotentials
[ 21, Kirk-Othmer 1995 ].
In the case of the diaphragm cell technique, the use of the expandable anode (see Section 2.3.2)
allows for the creation of a controlled 3-mm gap between the electrodes, thereby reducing
energy consumption [ 21, Kirk-Othmer 1995 ]. Coatings used for anodes and cathodes are
described in Section 2.3.2.
{Please TWG provide more information on the replacement of older anodes by the expandable
anode: performance (reduction of cell voltage and energy consumption), technical
considerations for retrofitting and economics.}
In the case of the membrane cell technique, the most important aspects of the electrode
structures are the need to support the membrane and the gas release to the back of the electrode
surface. The latter aims at reducing the electrical resistance caused by gas bubbles
[ 1, Ullmann's 2006 ].
{Please TWG provide information on the development of electrode coatings in membrane cells.}
Achieved environmental benefits
The achieved environmental benefit of this technique is a reduction of energy consumption.
Environmental performance and operational data
The anode coatings of diaphragm cells have a lifetime of more than twelve years and production
of chlorine exceeds 240 t Cl2/m 2 [ 1, Ullmann's 2006 ].
WORKING DRAFT IN PROGRESS
The typical lifetimes of anode and cathode coatings of membrane cells exceed eight years [ 22,
Uhde 2009 ] [ 134, INEOS 2011 ].
The conversion to asbestos-free diaphragms at Arkema also involved the replacement of anodes
and cathodes by expandable anodes and better performing cathodes resulting in an overall
reduction of electricity consumption for electrolysis of 3 – 4 % (see Section 4.2.2) [ 31, Euro
Chlor 2010 ]. The replacement of anodes in diaphragm cells by expandable anodes typically
leads to electricity savings of Q 50 AC kWh/t Cl2 produced [ 3, Euro Chlor 2011 ].
{Please TWG provide information on the performance of electrode coatings in membrane cells.}
202 December 2011 TB/EIPPCB/CAK_Draft_1