Process for recovering structurally unsaturated cyclic hydrocarbons from hydrocarbon oils by extractive distillation

摘要

Aromatic and unsaturated alicyclic hydrocarbons are separated from saturated hydrocarbons by submitting the mixture to extractive distillation using molten phthalic anhydride as solvent, whereby the saturated hydrocarbons (containing a small proportion of the anhydride) are obtained as "heads", and a mixture of the cyclic hydrocarbons and the bulk of the anhydride, is obtained at "bottoms". The process may be used for the separation of naphthalene from dodecane, decalin and other saturated hydrocarbons present in certain PICT:0673511/III/1 cracked petroleum oils such as "light cycle gas oil." The gas oil is introduced into the side of distilling-column 2 through line 1, and phthalic anhydride is introduced through inlet 9. The overhead vapours, which contain about 6 per cent of phthalic anhydride, are passed to condenser 5. Part of the condensate is returned to column 2 as reflux, and the remainder is cooled to 20 DEG C. in cooler 11, where phthalic anhydride crystallizes out. The crystal-slurry is passed to centrifuge 13 from which the separated paraffins are discharged through pipe 25. The last traces of phthalic anhydride may be removed from the paraffins by a wash with aqueous caustic alkali. The liquid from the base of column 2 is passed through pipe 14 to column 15. Aromatic and naphthenic hydrocarbons are withdrawn from the head of column 15, and phthalic anhydride is withdrawn from the base. The recovered anhydride is recirculated to column 2 through pipe 17, make-up being introduced through pipe 18.