A process for starting up a plant for removing isobutene from an isobutene-containing C4-hydrocarbon mixture, the plant comprising an etherification unit containing moist acidic ion exchange resin, a first distillation unit, an ether cleavage unit, and a second distillation unit, the process comprising (a) filling the etherification unit with isobutanol; (b) filling the first distillation unit with C4-hydrocarbon and/or isobutanol, and operating the first distillation unit with total reflux; (c) filling the second distillation unit with C4-hydrocarbon and/or isobutanol, and operating the second distillation unit with total reflux; (d) withdrawing a bottom product of the second distillation unit, removing water from the bottom product and directing the bottom product to the etherification unit; (e) directing a discharge of the etherification unit to the first distillation unit; (f) directing a bottom product of the first distillation unit to the second distillation unit while bypassing the ether cleavage unit; (g) after the bottom product of the second distillation unit is essentially free of water, providing a flow of isobutene-containing C4-hydrocarbon mixture into the etherification unit and reacting the isobutene-containing C4-hydrocarbon mixture with isobutanol to form a mixture of IBTBE and unconverted hydrocarbons; (h) directing the mixture of IBTBE, unconverted hydrocarbons and unreacted isobutanol from the etherification unit to the first distillation unit and distilling the mixture to obtain a top product comprising the unconverted hydrocarbons, and a bottom product comprising IBTBE and unreacted isobutanol; (i) after IBTBE in the bottom product of the first distillation unit has reached a predetermined concentration, directing the bottom product of the first distillation unit to the ether cleavage unit to decompose the IBTBE to obtain isobutene and isobutanol; (j) directing the mixture of isobutene and isobutanol produced in step (i) to the second distillation unit and distilling the mixture of isobutene and isobutanol to obtain a top product comprising isobutene, and a bottom product comprising isobutanol and; (k) recycling the bottom product obtained in step (j) at least partially to the etherification unit. (a) filling the etherification unit with isobutanol; (b) filling the first distillation unit with C4-hydrocarbon and/or isobutanol, and operating the first distillation unit with total reflux; (c) filling the second distillation unit with C4-hydrocarbon and/or isobutanol, and operating the second distillation unit with total reflux; (d) withdrawing a bottom product of the second distillation unit, removing water from the bottom product and directing the bottom product to the etherification unit; (e) directing a discharge of the etherification unit to the first distillation unit; (f) directing a bottom product of the first distillation unit to the second distillation unit while bypassing the ether cleavage unit; (g) after the bottom product of the second distillation unit is essentially free of water, providing a flow of isobutene-containing C4-hydrocarbon mixture into the etherification unit and reacting the isobutene-containing C4-hydrocarbon mixture with isobutanol to form a mixture of IBTBE and unconverted hydrocarbons; (h) directing the mixture of IBTBE, unconverted hydrocarbons and unreacted isobutanol from the etherification unit to the first distillation unit and distilling the mixture to obtain a top product comprising the unconverted hydrocarbons, and a bottom product comprising IBTBE and unreacted isobutanol; (i) after IBTBE in the bottom product of the first distillation unit has reached a predetermined concentration, directing the bottom product of the first distillation unit to the ether cleavage unit to decompose the IBTBE to obtain isobutene and isobutanol; (j) directing the mixture of isobutene and isobutanol produced in step (i) to the second distillation unit and distilling the mixture of isobutene and isobutanol to obtain a top product comprising isobutene, and a bottom product comprising isobutanol and; (k) recycling the bottom product obtained in step (j) at least partially to the etherification unit.