Process of purifying aromatic hydrocarbons

摘要

A crude light oil is fractionated to obtain a fraction containing a desired aromatic hydro carbon, particularly benzol, toluol or xylol, which is washed with sulphuric acid, neutralized and fractionated to obtain the desired aromatic fraction containing not more than 5 per cent of impurities including paraffinic, naphthenic and sulphur compounds, and unsaturated hydrocarbons, this fraction is vaporized and passed over a dehydrogenating catalyst, e.g. oxides of Cr, Al or Fe, at 450-600 DEG C. for a time sufficient to dehydrogenate the impurities only, and the condensed product is acid-washed, neutralized, and distilled. The catalyst is periodically regenerated by burning off carbon with air or steam at not more than 600 DEG C. A nitration grade of benzol, prepared from a crude light oil by fractionation, acid-washing, neutralization and fractionation, and containing 1 per cent of impurities, is heated to 530 DEG C. and passed through a mixture of chromium and aluminium oxides kept at 530 DEG C., with a contact time of about 3 secs., the treated vapours being condensed, acid-washed, neutralized and distilled. The Specification as open to inspection under Sect. 91 comprises subjecting crude benzol or other aromatic hydrocarbon, without prior acid washing, to the dehydrogenation and subsequent treatment. This subject-matter does not appear in the Specification as accepted.