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AssigneeAllied Chemical Corporation
InventorsKrishnamurthy Nagasubramanian, Frederick P. Chlanda, Kang-Jen Liu
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An improved process is described for converting aqueous fluosilicic acid waste product into anhydrous hydrogen fluoride and finely divided silica in which aqueous fluosilicic acid is pyrolyzed to produce silica and a dilute aqueous solution of hydrogen fluoride and fluosilic acid. The resulting dilute solution is subjected to electrodialysis, thereby obtaining a hydrogen fluoride concentration greater than that which characterizes the boiling point ridge which divides the phase diagram of the system hydrogen fluoride/fluosilicic acid/water, i.e. HF/H.sub.2 SiF.sub.6 /H.sub.2 O, into two regions. Anhydrous hydrogen fluoride is recovered from the resulting composition by distillation.
In a process for converting aqueous fluosilicic acid to anhydrous hydrogen fluoride and finely divided silica comprising pyrolyzing aqueous fluosilicic acid to form finely divided silica and a dilute aqueous solution of hydrogen fluoride and fluosilicic acid and thereafter distilling out hydrogen fluoride, the improvement which comprises subjecting the dilute solution to electrodialysis, thereby obtaining a hydrogen fluoride concentration greater than that which characterizes the boiling point ridge which divides the phase diagram of the system hydrogen fluoride/fluosilicic acid/water into two regions, and recovering anhydrous hydrogen fluoride from the resulting composition by distillation.
A process for recovering anhydrous hydrogen fluoride from liquid HF/H.sub.2 SiF.sub.6 /H.sub.2 O systems which comprises the steps of:
Dependencies are inferred from the claim text.