Improvements in and relating to the purification of hydrofluoric acid by distillation

摘要

Hydrofluoric acid is purified by distillation PICT:0872263/III/1 under reduced pressure from a thermoplastic vessel which is not attacked by the acid, e.g. polyethylene or p polytetrafluoroethylene, the vessel being enclosed in a second vessel maintained at the same pressure. The pressure is preferably such that the acid distils at below 50 DEG C. As shown, water 3 in a double-walled water bath 2 is heated electrically, thereby heating the glycerin bath 13. A polyethylene bottle 5 contains aqueous 35-40% hydrofluoric acid which boils at the lower pressure obtained by a water jet pump (not shown) attached to a vessel 35 filled with caustic potash. Vaporized acid is passed into a tube 7, condensed by a water-cooled condenser, and collected in a vessel 22 which, like the bottle 5, is situated in a second vessel 23. This second vessel is freely connected with the receiver 22 by a tube 28 which passes into a tube 29 of wider diameter, thus equalising pressures in the whole system. Tube 29 connects with a piece 36 at the head of a vessel 33 filled with soda lime. A safety bottle 16 is inserted between the piece 36 and tube 15 to collect any glycerin from the bath 13 which may foam over if the distillation process is disrupted.