Preparation of propene

A process for preparing propene by

• a) reaction of a mixture containing 1-butene, 2-butene and isobutene to give a product mixture containing propene, 2-pentene and 2-methyl-2-butene 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,
• b) subsequent separation by distillation of the product mixture formed in a), into low boiling C2-3 hydrocarbons, intermediate C4 hydrocarbons and a mixture of 2-pentene and 2-methyl-2-butene or a mixture of 2-pentene, 2-methyl-2-butene and small amounts of higher boiling compounds,
• c) subsequent reaction of said mixture of 2-pentene and 2-methyl-2-butene or said mixture containing 2-pentene, 2-methyl-2-butene and small amounts of higher boiling compounds from b, with ethene to give a mixture containing propene, 1-butene and isobutene, or propene, 1-butene, isobutene and butanes, 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 an excess of ethene in not uncut,
• d) subsequent separation by distillation of the mixture formed in step c into low boiling C2-3 hydrocarbons, a mixture of 1-butene and isobutene or mixture of 1-butene, isobutene and butanes, and C≧5-hydrocarbons,
• e) subsequent return of the mixture of 1-butene and isobutene or mixture of 1-butene, isobutene and butanes resulting from step d) to step a).