Process for flexible production of MTBE and isononanol comprising the steps of: a) providing a C4-hydrocarbon stream containing at least n-butenes (1-butene and 2-butene), n-butane and isobutane as a first input stream and distillatively separating at least a portion of the isobutane and at least a portion of the 1-butene from the first input stream, wherein the C4-hydrocarbon stream is a raffinate-II stream; b) using the isobutane separated from the first input stream and additional isobutane separated from a field butane stream or an FCC-C4 stream as a second input stream; c) sending the first input stream to an oligomerization in which the n-butenes are catalytically oligomerized to afford C8-olefins, separating the formed oligomers from the remaining oligomerizate (raw butane) containing at least n-butane and unconverted butenes, sending at least a portion of the raw butane to a hydrogenation and providing the hydrogenated raw butane as a third input stream; d) sending the C8-olefins formed in the oligomerization in step c) to a hydroformylation in which C8-olefins are catalytically reacted with synthesis gas to afford C9-aldehydes; e) sending the C9-aldehydes from the hydroformylation in step d) to a hydrogenation in which C9-aldehydes are catalytically converted into isononanol; f) sending the second and the third input stream to a dehydrogenation to obtain a dehydrogenation mixture containing at least n-butenes (1-butene and 2-butene), isobutene, butadiene, unconverted butane and unconverted isobutane and optionally separating the unconverted n-butane and/or isobutane from the dehydrogenation mixture; g) sending the dehydrogenation mixture from step f) to an MTBE or ETBE synthesis in which isobutene is catalytically reacted with methanol to afford MTBE or with ethanol to afford ETBE and separating the formed MTBE or ETBE from the remaining dehydrogenation mixture; h) sending the dehydrogenation mixture freed of MTBE or ETBE from step g) to a selective hydrogenation in which butadiene is selectively hydrogenated to afford butene, thus obtaining a hydrogenation mixture; i) sending the hydrogenation mixture from step g) to an oligomerization in which the n-butenes are catalytically oligomerized to afford C8-olefins, j) sending the C8-olefins formed in the oligomerization in step i) to a hydroformylation in which C8-olefins are catalytically reacted with synthesis gas to afford C9-aldehydes; k) sending the C9-aldehydes from the hydroformylation in step j) to a hydrogenation in which C9-aldehydes are catalytically converted into isononanol. a) providing a C4-hydrocarbon stream containing at least n-butenes (1-butene and 2-butene), n-butane and isobutane as a first input stream and distillatively separating at least a portion of the isobutane and at least a portion of the 1-butene from the first input stream, wherein the C4-hydrocarbon stream is a raffinate-II stream; b) using the isobutane separated from the first input stream and additional isobutane separated from a field butane stream or an FCC-C4 stream as a second input stream; c) sending the first input stream to an oligomerization in which the n-butenes are catalytically oligomerized to afford C8-olefins, separating the formed oligomers from the remaining oligomerizate (raw butane) containing at least n-butane and unconverted butenes, sending at least a portion of the raw butane to a hydrogenation and providing the hydrogenated raw butane as a third input stream; d) sending the C8-olefins formed in the oligomerization in step c) to a hydroformylation in which C8-olefins are catalytically reacted with synthesis gas to afford C9-aldehydes; e) sending the C9-aldehydes from the hydroformylation in step d) to a hydrogenation in which C9-aldehydes are catalytically converted into isononanol; f) sending the second and the third input stream to a dehydrogenation to obtain a dehydrogenation mixture containing at least n-butenes (1-butene and 2-butene), isobutene, butadiene, unconverted butane and unconverted isobutane and optionally separating the unconverted n-butane and/or isobutane from the dehydrogenation mixture; g) sending the dehydrogenation mixture from step f) to an MTBE or ETBE synthesis in which isobutene is catalytically reacted with methanol to afford MTBE or with ethanol to afford ETBE and separating the formed MTBE or ETBE from the remaining dehydrogenation mixture; h) sending the dehydrogenation mixture freed of MTBE or ETBE from step g) to a selective hydrogenation in which butadiene is selectively hydrogenated to afford butene, thus obtaining a hydrogenation mixture; i) sending the hydrogenation mixture from step g) to an oligomerization in which the n-butenes are catalytically oligomerized to afford C8-olefins, j) sending the C8-olefins formed in the oligomerization in step i) to a hydroformylation in which C8-olefins are catalytically reacted with synthesis gas to afford C9-aldehydes; k) sending the C9-aldehydes from the hydroformylation in step j) to a hydrogenation in which C9-aldehydes are catalytically converted into isononanol.