Flexible preparation of propene and hexene

A process for preparing propene and hexene from a raffinate II feed stream comprising olefinic C4-hydrocarbons, which comprises

• a) a metathesis reaction in which butenes present in the feed stream are reacted with ethene in the presence of a metathesis catalyst comprising at least one compound of a metal of transition groups VIb, VIIb or VIII of the Periodic Table of the Elements to give a mixture comprising ethene, propene, butenes, 2-pentene, 3-hexene and butanes, using, based on the butenes, from 0.05 to 0.6 molar equivalents of ethene,
• b) firstly fractionally distilling the product stream obtained in this way to give a low-boiling fraction A comprising C2-C3-olefins and a high-boiling fraction comprising C4-C6-olefins and butanes,
• c) subsequently feeding into a distillation column in the work-up sequence of a cracker or fractionally distilling the low boiling fraction A obtained from b) to give an ethene-containing fraction and a propene containing fraction, with the ethene-containing fraction being returned to the process step a) and the propene-containing fraction being discharged as product,
• d) subsequently fractionally distilling the high-boiling fraction obtained from b) to give a low-boiling fraction B comprising butenes and butanes, a pentene-containing intermediate-boiling fraction C and a hexene-containing high-boiling fraction D,
• e) where the fractions B and C are completely or partly returned to the process step a) and the fraction D is discharged as product.