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US 7,803,342 B2Granted
Process for recycling high-boiling compounds within an integrated chlorosilane system
AssigneeWacker Chemie AG
InventorsUwe Paetzold, Markus Niemetz
Life of this patent
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Abstract
Highly pure pyrogenic silica is produced in an integrated polycrystalline silicon production plant by separating offgas from polycrystalline silicon production into a high boiler fraction, vaporizing this fraction into a pyrogenic silica burner and reacting with air and/or oxygen and hydrogen to form pyrogenic silica.
Claims15
A process for preparing pyrogenic silica, comprising condensing the offgas from deposition of polycrystalline silicon from chlorosilane and hydrogen to form a condensed offgas fraction;
- fractionating the condensed offgas fraction in a distillation column, with a bottom fraction from the distillation column comprising a high boiler fraction containing 0.5-20% by weight of high-boiling chlorosilanes and 99.5-80% by weight of silicon tetrachloride, and evaporating at least a portion of the high boiler fraction to form a chlorosilane vapor, and feeding chlorosilane vapor thus obtained to a burner and reacting with air or oxygen and with hydrogen in a flame to give pyrogenic silica, and collecting the pyrogenic silica as a finely divided silica powder.
Dependencies are inferred from the claim text.