GB768941A - Separation of phenols from aromatic iso-propyl compounds by distillation - Google Patents

Abstract

<PICT:0768941/III/1> A mixture containing a phenol and an isopropyl-substituted benzene or naphthalene, e.g. a mixture obtained by the decomposition of an organic hydroperoxide, is subjected to distillation in the presence of water using a fractionating column whereby an azeotrope of water and the isopropyl compound distils over; the vapours are condensed yielding a condensate which separates into a hydrocarbon layer and a water layer, part of the hydrocarbon layer and part or all of the water layer are returned to the column as reflux, and phenol, free from the isopropyl compound, is obtained as base product. The hydrocarbon obtained as distillate contains only a trace of phenol, and may be subjected to oxidation to make hydroperoxide. The distillation may be employed for the separation of phenol from cumene, of cresol from cymene, of pyrogallol from tri-isoproyl-benzene, and of naphthol from isopropyl-naphthalene. The distillation may be carried out under normal pressure, partial vacuum, or superatmospheric pressure. In an example, water ((75 parts) is added to a reaction mixture containing cumene (75 parts) and phenol (25 parts). The resulting mixture is subjected to discontinuous distillation at atmospheric pressure in an apparatus comprising a still, fractionating column, dephlegmator, condenser, and decanter. The cumene-water azeotrope passes over at a head temperature of 94 DEG -95 DEG C. A reflux ratio of 6:1 of the condensed cumene layer is employed. The water layer is returned in part to the column and in part to the still so that the ratio cumene:water is always at least 1:1. About 92 per cent of the cumene is recovered as distillate in this manner; and contains only 0.03 per cent of phenol. An intermediated fraction is next recovered, until the head temperature reaches 100 DEG C. without supplying water to the still; and finally the water remaining in the still is distilled off. The aqueous intermediate fraction which contains a small amount of cumene and 4.3 per cent phenol, is added to the next batch of reaction mixture to be distilled. The phenol obtained as still-residue is free from water and cumene. In another example, a mixture containing 1 part of phenol and 3 parts of cumene is introduced through tube 1 into the upper part 3 of a tray-type fractionating column. Simultaneously, water is introduced into the column at about the same level through tube 18, the ratio water:cumene of the feed being 3:4 by weight. The overhead vapours are taken off at a temperature of about 95 DEG C., and are conducted through tube 4 to mechanical compressor 5 where the pressure is increased by about 0.2-0.4 kg./cm2. The compressed vapours are condensed, at a temperature of at least 100 DEG C., in coil 6 disposed in trough 7 which receives the reflux flowing down the column; and the reflux liquid is partly vaporized by the heat of condensation of the compressed vapours. The excess reflux overflows through tube 8 to the top tray of the lower part 2 of the column. The sump 20 of the column is maintained at the boiling-point of phenol by means of reheater 22. Phenol, free from cumene, is discharged through tube 21. The condensate discharged from coil 6 is relieved from pressure in pot 9, and flows to separator 10. Cumene overflows from separator 10 to receiver 11. Part of the cumene is supplied by pump 12 to the head of the column as reflux, and the remainder is withdrawn from the system through tube 13. The water separated in separator 10 flows through tube 23 into receiver 14. From the latter, water is pumped through tube 16 to the head of the column in such an amount that the reflux contains water and cumene in the ratio of 3:4. Pump 17 supplies water to the column through tube 18. If, instead of a mechanical compressor, a steam jet compressor is used, water corresponding to the amount of power steam, will leave receiver 14 through tube 19. Specifications 595,406 and 626,095 [Group IV(b)] are referred to.