Abstract: In the removal of pure aromatics from aromatic-containing hydrocarbon mixtures by liquid-phase extraction or extractive distillation using a selective solvent, the specific cost of separation can be reduced at the same yield of aromatics or the yield of aromatics can be increased at the same specific cost of separation if the liquid-phase extraction or the extractive distillation is carried out in the presence of a reactive solid. At the same time, substantially aromatic-free raffinates are obtained.

Abstract: n-Alkenes can be converted catalytically into isoalkenes, when a mixture containing at least one n-alkene and hydrogen is brought into contact at a temperature of 400.degree. to 600.degree. C. and a residence time of 0.2 to 20 seconds with an Al.sub.2 O.sub.3 or SiO.sub.2 catalyst which is specifically activated and is promoted with halogen compounds of elements of the third to fifth main groups and second to eighth sub-groups of the periodic system and/or hydrohalic acids. The specific activation comprises calcining, before the promotion process, an aluminum hydroxide or aluminum oxide hydrate or a silica gel having a content of volatile ammonium salts to give Al.sub.2 O.sub.3 or SiO.sub.2, with expulsion of these volatile ammonium salts. For the conversion of the n-alkenes, the catalyst can be employed in a fixed or a mobilized catalyst bed.