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US 5,476,916 AGranted
Process for preparing polydimethylsiloxanes
AssigneeWacker Chemie AG
InventorsBernd Pachaly, Gerhard Nagy, Wolfgang Jacques, Robert Christa
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Abstract
The present invention describes a process wherein dimethyldichlorosilane is reacted, in a first step, with water present in hydrochloric acid to give a crude hydrolysate comprising cyclic and linear, chlorine-containing polydimethylsiloxanes and gaseous hydrogen chloride and, in a second step, the crude hydrolysate is treated with steam to reduce the chlorine content and form hydrochloric acid, with the hydrochloric acid formed in the second step being used in the first step.
Claims6
A process for the hydrolysis of dimethyldichlorosilane to form polydimethylsiloxanes, comprising:
- a) hydrolyzing dimethyldichlorosilane with aqueous hydrochloric acid containing an amount of water less than the stoichiometric amount calculated on the basis of hydrolyzable chlorine in said dimethyldichlorosilane to form a hydrolysate comprising cyclic polydimethylsiloxanes and chlorine-containing linear polydimethylsiloxanes;
- b) separating gaseous hydrogen chloride generated during said hydrolysis from said hydrolysate to form a crude polydimethylsiloxane hydrolysate;
- c) treating said crude polydimethylsiloxane hydrolysate with steam to reduce the chlorine content of chlorine-containing linear polydimethylsiloxanes contained in said crude polydimethylsiloxane hydrolysate and form hydrochloric acid;
- d) recycling the hydrochloric acid from step c) to a further hydrolysis of dimethyldichlorosilane as defined in step a);
- wherein the amount of water supplied as steam in step c) is such that the hydrochloric acid recycled in step d) contains a deficiency of water with respect to dimethyldichlorosilane in step a).
2 more elements
Dependencies are inferred from the claim text.