Combined preparation of at least butene and octene from ethene

A process for the combined preparation of at least butene and octene from ethene, the process comprising:

• a) providing an inert solvent;
• b) mixing ethene having a purity of more than 99.9% and said inert solvent to provide a first feed mixture comprising said inert solvent and ethene dissolved therein;
• c) in a first synthesis, oligomerizing at least a portion of the ethene present in the first feed mixture in the presence of a first heterogeneous catalyst to obtain a first reaction mixture comprising said inert solvent, butenes, hexenes and octenes;
• d) working-up of the first reaction mixture and/or a stream based thereon into a low boiler fraction comprising the inert solvent, at least one C4-fraction comprising butenes, a C6-fraction comprising hexenes, a C8-fraction comprising octenes and into a C8+-fraction comprising hydrocarbons having more than eight carbon atoms;
• e) recycling at least a portion of the low boiler fraction to the first feed mixture;
• f) mixing hexene and ethene to provide a second feed mixture comprising ethene dissolved in the hexene wherein hexene is provided using at least a portion of the C6-fraction;
• g) in a second synthesis, reacting at least a portion of the ethene present in the second feed mixture with at least a portion of the hexene present in the second feed mixture in the presence of a second heterogeneous catalyst to obtain a second reaction mixture comprising at least octene, wherein the second synthesis is spatially separated from the first synthesis;
• and
• h) feeding the second reaction mixture to the working-up of said first reaction mixture;
• wherein said inert solvent has a boiling point or boiling range below any butene formed in said first synthesis;
• a solid is used as the first heterogenous catalyst and/or the second heterogenous catalyst which comprises at least two components,
• wherein a first component comprises at least one element selected from the group consisting of Ni, Cr, Fe, and Ti, which is present in a metallic and/or oxidic and/or hydridic form, and
• wherein a second component comprises at least one metal oxide selected from the group consisting of Al2O3, SiO2, TiO2, and ZrO2 and mixtures thereof.