GB542696A - Improvements in or relating to solvent extraction - Google Patents

Abstract

542,696. Recovering volatile liquids. BOOTH, W. E., COSWAY, R., and IMPERIAL CHEMICAL INDUSTRIES, Ltd. June 19, 1940, Nos. 10587, 12408 and 13957. [Class 32] In solvent extraction processes e.g. for degreasing metal articles in which the solvent is recovered by distillation from contaminated residues, an amount of water considerably less than that required for steam distillation of the solvent is added thereto and the mixture is heated indirectly to drive off a mixture of steam and solvent, the distillate is condensed, separated into aqueous and non-aqueous layers and the aqueous layer is returned to the still. When the solvent used is a chlorinated hydrocarbon e.g. trichlorethylene stabilised by a compound containing a basic nitrogen atom e.g. pyridine, triethylamine &c. a small quantity of non- volatile basic material, e.g. lime, is added to prevent de-stabilisation. A tank 1 having a sloping bottom 3 forming a solvent sump is heated by gases &c. supplied through line 2. Cooling coils 4 are provided to condense the vapours formed and the condensate is collected in an annular trough 5. The condensate flows from a receptacle 6 into a separator 7 which is provided with draw-offs 13, 14 by which the water according as it is heavier or lighter than the solvent, is returned to the still through pipe 15 and inlet 12 while the solvent is withdrawn through lines 8 or 10. The lines are provided with valves so that the vessel 1 may be used alternatively as a degreasing or solvent recovery apparatus. In modifications the separator is arranged inside the extraction tank and the trough 5 itself may be adapted to provide separation of the solvent and aqueous layers.