Abstract: A feed mixture containing C.sub.4 -olefins to C.sub.7 -olefins is evaporated and mixed with steam in a weight ratio of H.sub.2 O:hydrocarbons in the range from 0.5:1 to 3:1. The steam containing feed mixture with an inlet temperature in the range from 380.degree. to 500.degree. C. is introduced into a reactor, which contains a bed of granular, form-selective zeolite catalyst. The zeolite is of the pentasil type and has an atomic ratio of Si:Al of 10:1 to 200:1. From the bed a product mixture is withdrawn whose temperature is 20.degree. to 80.degree. lower than the inlet temperature, and whose total content of propylene and butene isomers is at least 60 wt-% of the olefinic constituents of the feed mixture.

Abstract: The starting material is a vanadium-containing residue, which contains at least 5 weight percent carbon on an anhydrous basis. The residue is thermally treated in a furnace a) at temperatures from 400.degree. to 700.degree. C. under an oxidizing atmosphere and an O.sub.2 partial pressure of at least 10.sup.-4 bar, measured within the region which is occupied by the residue, and/or b) at temperatures from 500.degree. to 1300.degree. C. under an O.sub.2 partial pressure not in excess of 10.sup.-2 bar, measured within the region which is occupied by the residue. A solids mixture which contains at least 5 weight percent vanadium oxide is withdrawn from the furnace. A multiple-hearth furnace or a rotary kiln or a fluidized bed reactor containing a stationary or circulating fluidized bed may be used as a furnace for the thermal treatment.