Chemical Technology April 2015

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Chemical Technology • April 2015 24
HDK ® pyrogenic silica –
Creating products by closing
loops
Wacker has been producing pyrogenic silica
(brand name HDK®) for more than 45 years.
Production currently takes place at the com-
pany’s Burghausen and Nünchritz sites in Germany and
in Zhangjiagang in China. The main use of pyrogenic silica
is in the manufacture of silicones. Approximately half the
volume produced worldwide is used to reinforce silicone
elastomers and for the rheology control of silicone sealants.
Pyrogenic silica finds further application as a free flow
aid, anti-settling agent, high-performance insulating mate-
rial and rheology additive in a broad range of recipes and
application areas. It has become indispensable in many in-
dustrial production processes and is thus in great demand.
According to Wacker estimates, the market is growing by
three to six percent every year.
Alongside Evonik and Cabot, Munich-based Wacker is
among the world’s largest producers of pyrogenic silica. At
its German sites, byproducts and intermediates fromsiloxane
and polysilicon production typically serve as the raw materi-
als, thus contributing to value creation. Byproducts generated
during HDK® manufacture are also recycled or used in other
production processes. Such a high degree of material-flow in-
tegration creates the foundation for a sustainable integrated
production system that makes it possible to use rawmaterials
efficiently and economically, to recycle byproducts effectively
and, in large measure, to avoid waste.
Significant efficiency gains can be achieved through inte-
grated HDK® production, as demonstrated at the Nünchritz
site. Thanks to synergies and economies of scale, the
specific operating costs for HDK® production at Nünchritz
have improved over the years. Due to process enhance-
ments, energy demand has decreased, while production
volumes have increased on a continuous basis. These
productivity advances, which are continually promoted,
further strengthen the site’s competitiveness and are key
for the success of the product range.
Integrated HDK® production at the site also benefits
the manufacture of silicones. Silicone elastomers require
by Dr Robert Johnston, Director Business Team HDK®, Wacker Silicones, Wacker Chemie
AG, Germany
In chemical terms, pyrogenic silica consists
of very pure amorphous silicon dioxide.
Unlike precipitated silica, silica sol or silica
gel, pyrogenic silica is produced by the
reaction of chlorosilanes with hydrogen
and oxygen in an oxyhydrogen flame at
over 1 000 °C. In the flame, the primary
particles fuse into larger aggregates, with
typical diameters of around 100 to 500
nanometers. On cooling, flaky agglomerates
several micrometres in size, form.