Process for the separation of C5 hydrocarbons present in streams prevalently containing C4 products used for the production of high-octane hydrocarbon compounds by the selective dimerization of isobutene

A process for continuously separating C5 hydrocarbons from a hydrocarbon stream comprising 0.5 to 20% by weight C5 hydrocarbons and a majority of C4 products, comprising:

• selectively dimerizing isobutene in one or more reaction steps in the presence of an oxygenated hydrocarbon stream comprising at least one linear alcohol, at least one tertiary branched alcohol and at least one alkyl ether, wherein the branched alcohol forms a C5/branched alcohol azeotrope mixture with the Cs hydrocarbons, wherein the oxygenated hydrocarbon stream is present in such a quantity as to have a molar ratio of (alcohols+alkyl ethers)/isobutene of greater than 0.01, and
• separating the C5/branched alcohol azeotrope mixture and an oxygenated stream comprising the at least one tertiary branched alcohol and the at least one alkyl ether from a dimerization product, and recycling the oxygenated stream to the one or more reaction steps,
• wherein the level of the linear alcohol, the tertiary branched alcohol and the alkyl ether remains constant during the selectively dimerizing isobutene,
• wherein the linear alcohol is methanol, the branched alcohol is TBA, and the alkyl ether is MTBE, and
• wherein the separating of the C5/branched alcohol azeotrope mixture and the oxygenated stream is carried out by one of the following steps:
• subjecting a dimerization effluent from the one or more reaction steps to a distillation column to produce a top stream comprising undimerized isobutene and the at least one linear alcohol and a bottom stream comprising the C5/branched alcohol azeotrope mixture, the at least one tertiary branched alcohol, the at least one alkyl ether, and the dimerization product, and then subjecting the bottom stream to one or more fractionation columns to produce (i) a stream comprising the C5/branched alcohol azeotrope mixture, (ii) the oxygenated stream comprising the at least one tertiary branched alcohol and the at least one alkyl ether, and (iii) a product stream comprising the dimerization product;
• subjecting a dimerization effluent from the one or more reaction steps to a distillation column to produce a top stream comprising undimerized isobutene and the at least one linear alcohol, a side stream comprising the C5/branched alcohol azeotrope mixture, and a bottom stream comprising the at least one tertiary branched alcohol, the at least one alkyl ether, and the dimerization product, and then subjecting the bottom cut to another fractionation column to obtain (i) the oxygenated stream comprising the at least one tertiary branched alcohol and the at least one alkyl ether and (ii) a product stream comprising the dimerization product;
• or
• subjecting a dimerization effluent from the one or more reaction steps to a distillation column to produce a top stream comprising undimerized isobutene and the at least one linear alcohol and the C5/branched alcohol azeotrope mixture and a bottom stream comprising the at least one tertiary branched alcohol, the at least one alkyl ether, and the dimerization product, subjecting the top steam to one or more separation columns to produce a stream comprising the C5/branched alcohol azeotrope mixture, and subjecting the bottom stream to another fractionation column to obtain to obtain (i) the oxygenated stream comprising the at least one tertiary branched alcohol and the at least one alkyl ether and (ii) a product stream comprising the dimerization product.