Chemical Technology April 2015

HDK ® pyrogenic silica – Creating products by closing loops 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.

W acker 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

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Chemical Technology • April 2015