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 From the bed a product mixture is withdrawn whose temperature is 20.degree.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: A process for producing styrene by the dehydrogenation of ethyl benzene whereby the ethyl benzene in a mixture with steam is introduced into a tubular reactor, the tubes of which are heated by molten salts. The structural parameters of this process are the tube diameter which should be 20 to 35 millimeters, the temperature of the molten salts which should be 580.degree. to 660.degree. C. and at most 20.degree. C. higher than the reaction temperature at the catalyst and the weight ratio of steam to ethyl benzene of the feed stock which should be 0.5 to 1. The process saves energy and increases efficiency by reducing the steam consumption.