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

4.2 Diaphragm cell plants
4.2.1 Abatement of asbestos emissions and discharges
Chapter 4
{This Section is proposed to be deleted completely. Rationale: The original chlor-alkali BREF
concluded that BAT for asbestos diaphragm cell plants is to convert to the membrane cell
technique or to use non-asbestos diaphragms. Since then, 6 asbestos diaphragm plants were
converted to membrane cell plants (see Section 4.2.3). In addition 3 plants were converted to
asbestos-free diaphragms and 1 plant plans to finalise this conversion by 2012 (see
Section 4.2.2). In 2011, only two plants remained which use asbestos diaphragms. These
developments indicate that the conversion of asbestos diaphragm cell plants to the membrane
cell technique or to asbestos-free diaphragms is technically and economically viable. Given that
techniques to avoid the use of asbestos are available, it is therefore not anymore necessary to
describe techniques which reduce asbestos emissions and asbestos waste generation.}
4.2.2 Asbestos-free diaphragms Application of non-asbestos
diaphragm material
{Please note that the paragraphs of the original text were reordered to be compatible with the
current standard 10-heading structure.}
Description
This technique consists in using asbestos-free diaphragms which are based on fluoropolymer
fibres and metal oxide fillers. A conversion to asbestos-free diaphragms may require new
equipment for the preparation of the diaphragms, for brine purification and for the protection of
the cathode against corrosion during shutdowns.
Technical description
Extensive worldwide research and development has been performed by industry to replace
asbestos in diaphragms by other materials. Around 1970, polytetrafluoroethylene (PTFE),
developed for astronautics, appeared on the market. With its superior characteristics regarding
stability against chlorine, caustic soda and other chemicals as well as its dimensional stability, it
was considered as ideal alternative for asbestos. Asbestos swells during operation in a
diaphragm cell and this increases the energy demand. PTFE does not show this swelling effect,
and therefore the energy demand would be lower. In addition, the high stability against chlorine
and caustic soda should result in a very long lifetime of the diaphragm. Due to these advantages
the hope was to develop an everlasting non-asbestos diaphragm with a low energy demand. A
lot of efforts were made for a couple of years but because of the inherent hydrophobic nature of
PTFE it is only possible to replace up to around 20 % of asbestos fibres by this material with
only small improvements in energy savings and extension of the diaphragm lifetime. This
so-called polymer modified asbestos (PMA) diaphragm is still in use in 2011. Research was also
done with some non-asbestos materials in combination with PTFE but no successful asbestos
replacement could be developed. For these reasons research and development activities were
rather limited for a certain time at the beginning of the 1980s [ 31, Euro Chlor 2010 ].
WORKING DRAFT IN PROGRESS
Laboratory tests using non-asbestos diaphragms began again in the mid-1980s, following the
increasing increased pressure to reduce the use and emissions of asbestos due to serious health
concerns. For the commercially available diaphragm cells, suitable alternatives have been
developed at industrial scale with the objective of bringing the new asbestos-free diaphragm
technique technology to the same commercial level as the polymer modified asbestos (PMA)
diaphragms. Some requirements on for the asbestos-free diaphragms are [ 31, Euro Chlor
2010 ]:
adaptability to different cell designs;
TB/EIPPCB/CAK_Draft_1 December 2011 171