GB978706A - Improvements in or relating to the manufacture of pure benzene - Google Patents

Abstract

Benzene having a solidification point of 5.4 DEG C. or above is obtained from a hydrocarbon mixture also containing naphthenes, e.g. cyclohexane and methylcyclohexane, and possibly n-heptane by (1) distilling at normal or reduced pressure to separate a fore-runnings containing benzene-cyclohexane azeotrope and additional quantities of benzene; (2) subjecting the fore-runnings from step 1 to catalytic reforming to increase the benzene content and adding the reformate to the feed to step (1), and (3) distilling the bottoms from step (1) at superatmospheric pressure, e.g. 2-20 atmospheres to recover pure benzene overhead and as bottoms methylcyclohexane, n-heptane and higher boiling aromatics. If desired, toluene may be recovered from the bottoms from step (3) by a 2-stage distillation, the first at normal or reduced pressure to remove fore-runnings which may also be reformed and the second at increased pressure to obtain pure toluene overhead. The feed may be a pressure refined coke oven benzene, or a benzene cut from a catalytic reformate (in which case the benzene fore-runnings are reformed in the main reactor) or from a pyrolysis gasoline. If sulphur compounds are present in the hydrocarbons or hydrogen, reforming is effected over a sulphur-resistant catalyst, e.g. cobalt molybdate. In the absence of sulphur, platinum may be used.