GB720341A - Process for the recovery by distillation of the solvent used in the extraction of phenols from aqueous liquors - Google Patents

Abstract

<PICT:0720341/III/1> In a process for the recovery of a solvent from a mixture of the solvent, one or more phenols and water, such as is obtained in the extraction of a phenol from an aqueous solution with an organic solvent which is immiscible or only partially miscible with water, the mixture is preliminarily heated up to a temperature greater than the boiling point of the solvent/water azeotrope but lower than the boiling point of the phenol, and is submitted to fractional distillation in a column so that there passes overhead a vapour mixture containing water and solvent but none of the phenol, while an anhydrous mixture of phenol and solvent is obtained as bottoms. The bottoms are separated into phenol and solvent in a further fractionation stage. Liquors from the low-temperature carbonization of lignite are dephenolized with butyl acetate; and the extract, which is a mixture of phenols, butyl acetate and water, is collected in vessel 2. The extract is passed through pipe 4 to condenser 5, where it is preheated by the vapours issuing from column 9; and it is then passed through pipe 6 to evaporator 7, where it is raised to 130 DEG C. The mixture of vapour and liquid so obtained is passed through pipe 8 into bubble-cap column 9, the base of which is maintained at 175 DEG C. by external heater 11. A mixture of butyl acetate and water vapours, with only traces of phenols, leaves the head of the column through pipe 13 and is condensed in condenser 5. The condensate is passed through pipe 14 to cooler 15 and the cooled condensate flows through pipe 18 to separator 19, where butyl acetate and water separate. The water, which is withdrawn through outlet 20, contains a small quantity of butyl acetate and is passed to the column (not shown) in which the dephenolized liquor is stripped of solvent. Butyl acetate is in part withdrawn through outlet 21 and is returned to the extraction plant. Part of the butyl acetate is, however, returned as reflux to column 9 via pipe 22. A mixture containing 50 per cent. of phenols and 50 per cent. of butyl acetate is withdrawn from the base of column 9 and is passed through pipe 24 to column 25, which is packed with Raschig rings and is heated by external heater 26. The base of column 25 is maintained at 135 DEG C. and the absolute pressure in the column is maintained at 50-60 mm. Hg. by means of steam-jet pump 28, which is connected to the head of the column via condenser 30. The condensate from column 25, which contains 80 per cent. butyl acetate and 20 per cent. phenols, flows through barometric downpipe 31 and is mixed with the feed to column 9 in pipe 4. Phenol oil containing only 0.5 per cent. of butyl acetate is withdrawn via pipe 35 from the base of column 25, and is collected in tank 34.