The invention relates to a process for obtaining isobutene from an isobutene containing C4-
hydrocarbon mixture (1) in a
plant comprising an etherification unit (3), a first
distillation unit (5), an
ether cleavage unit (10) and a second
distillation unit (12), the process comprising: (a) contacting the C4-
hydrocarbon mixture (1) with a
primary alcohol (2) and reacting the mixture with the
primary alcohol in the presence of an acidic catalyst to form the corresponding
alkyl tert-butyl
ether in the etherification unit (3); (b) distilling the reaction mixture (4) from the etherification unit (3) in the first
distillation unit (5), a C4-
hydrocarbon raffinate being withdrawn as the overhead product (6), and the
alkyl tert-butyl
ether being withdrawn as the bottom product (7); (c) vaporizing the bottom product from the first distillation unit (5) in an
evaporator (8) obtaining a vapor
stream (9); (d) reacting the vapor
stream (9) of step (c) in the presence of an acidic catalyst obtaining isobutene and the
primary alcohol as reaction products in the ether cleavage unit (10); (e) distilling the reaction mixture (11) from the ether cleavage unit (10) in the second distillation unit (12), isobutene being withdrawn as the overhead product (13), the primary
alcohol and diisobutene being withdrawn as the bottom product (14) and being recycled to the etherification unit (3); wherein a purge
stream (15) containing high boiling components with a normal
boiling point higher than that of the
alkyl tert-butyl ether is withdrawn from the
evaporator (8) in step (c).