Preparation of C5-/C6-olefins

A process for preparing C5-/C6-olefins and propene from steam cracker or refinery C4 streams, comprising the substeps

• (1) removal of butadiene and acetylenic compounds by, optionally, extracting butadiene with a butadiene-selective solvent and subsequently or alternatively selectively hydrogenating butadienes and acetylenic impurities present in the residual steam cracker or refinery C4 streams to give a reaction product comprising n-butenes and isobutene and essentially no butadienes and acetylenic compounds,
• (2) removing isobutene by either oligomerization or polymerization, or by reacting the reaction product from the preceding stage with an alcohol in the presence of an acid catalyst to give an ether, and separating off the ether and the alcohol either simultaneously with or after the etherification to give a reaction product comprising n-butenes and optionally oxygen-containing impurities, where the ether formed is discharged or redissociated to obtain pure isobutene and the etherification step can be followed by a distillation step for separating off isobutene, where, optionally, C3-, i-C4- and C5-hydrocarbons, introduced in a FCC fraction, are removed by distillation of the ether,
• (3) optionally removing the oxygen-containing impurities from the raffinate II stream from step (2) by treating the raffinate II stream with adsorber materials,
• (4) carrying out a metathesis reaction of the raffinate II stream from step (3) in the presence of a metathesis catalyst comprising at least one compound of a metal of transition group VIb, VIIb or VIII of the Periodic Table of the Elements so as to convert the 1-butane, 2-butene and isobutene present in the raffinate II stream into a mixture of C2-C6-olefins and butanes,
• (5) firstly fractionating the product stream of step (4) by distillation to give a low boiler fraction A comprising C2-C4-olefins and butanes or C2-C3-olefins, which is discharged, and a high boiler fraction comprising C4-C6-olefins and butanes,
• (6) subsequently fractionating the high boiler fraction from step (5) by distillation to give a low boiler fraction B comprising butenes and butanes, an intermediate boiler fraction C comprising pentene and methylbutene and a high boiler fraction D comprising hexene and methylpentene,
• (7) where all or part of the fractions B and/or C are recirculated to the process step 4) and the fraction D is discharged as product.