GB1499066A - Process for isolating anthraquinone - Google Patents

Abstract

1499066 Separation of anthraquinone BAYER AG 16 July 1976 [19 July 1975] 29721/76 Heading C2C Anthraquinone is separated from a mixture containing at least one part by weight of phthalic anhydride per part by weight of anthraquinone (particularly a mixture obtained from the oxidation of naphthalene) by feeding the mixture to a first distillation column which is operated under reduced pressure (usually 100-900 millibars) to obtain a top product comprising the phthalic anhydride and any impurities which have lower boiling points than anthraquinone, and a sump product; feeding the sump product to a vaporizer from which anthraquinone is obtained in vapour form, any impurities in the sump product having higher boiling points than anthraquinone being discharged ; and feeding the anthraquinone vapour into a second distillation column from which virtually pure anthraquinone is obtained as a top product. Some of the phthalic anhydride from the top of the first column may be recycled to the feed mixture to increase the proportion of phthalic anhydride therein, the remainder being isolated, and a part of the anthraquinone from the second column may be recycled to the first column. The feed product for the first column may itself be fed to a vaporizer, from the sump of which high-boiling by-products together with part of the anthraquinone and small amounts of phthalic anhydride may be taken off and optionally worked up separately, the vapours formed being introduced into the first column, particularly into the middle region thereof. The vaporizer (or vaporizers) may be of the falling film, thin-film or circulation type, and the columns may be sieve tray, bubble cap tray or packed columns.