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

6 EMERGING TECHNIQUES
6.1 Introduction
Chapter 6
Since the adoption of the first Chlor-alkali Manufacturing Industry BREF in 2001, some
techniques which were not described therein have in the meantime been successfully introduced
in several installations. This includes the catalytic reduction of chlorate with hydrogen (see
Section 4.3.6.4) and the removal of sulphate from the brine by nanofiltration (see
Section 4.3.6.2.2).
Two of the three emerging techniques described in the chlor-alkali BREF from 2001 were not
introduced on an industrial scale: the development of sophisticated membranes allowing the
direct production of caustic soda at the commercial concentration of 50 wt-% was abandoned in
approximately 2000 due to technical problems [ 49, Euro Chlor 2010 ]. In addition, the
manufacturer reported in 1999 that due to the cell voltage increase (lower conductivity of
50 wt-% NaOH compared to 32 wt-% NaOH, higher electrical resistance of the modified
membrane) the technique is economically only feasible if steam costs are comparatively high
and electricity costs are comparatively low and that therefore demand was too low for
commercialisation [ 50, Asahi Glass 1999 ]. The development of built-in precathode
diaphragms was also discontinued mainly because of the availability of commercially proven
asbestos-free diaphragms for standard electrolysers [ 49, Euro Chlor 2010 ]. Regarding the third
emerging technique, an industrial installation with a chlorine capacity of 20 kt/yr using
oxygen-depolarised cathodes is expected to be put into operation in 2011 (see Section 6.2).
Another emerging technique is the use of stationary fuel cells in chlor-alkali plants (see
Section 6.3).
A number of new promising techniques are being developed with energy savings as the main
driving force. Some of these new techniques for the membrane and diaphragm processes are
described below. Fundamental research programmes related to mercury technology are not
being developed since it is very unlikely that any new mercury plants will be built. The only
recent improvements in mercury cells concern the anode geometry with the aim of improving
gas release in order to decrease electrical energy usage and increase anode coating life.
In diaphragm technology, with the exception of non-asbestos technology referred to in section
4.3.2, improvements are minor and related to reducing power consumption in the cell. An
interesting example is a specific development of activated cathode technology, the pre-cathode
concept, which is presented in section 0.
Oxygen-depolarised cathodes in membrane cells have the potential to save around 500-600
kWh/tonne of chlorine produced and are now being tested at the industrial scale.
At least one supplier is developing a membrane that can produce high concentration (50%)
caustic soda and believes that it could be available at an acceptable cost within a few years.
WORKING DRAFT IN PROGRESS
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