Preparation of isobutene by dissociation of MTBE

A process for preparing isobutene, the process comprising:

• (a) reacting at least one hydrocarbon mixture comprising isobutene with at least one alcohol stream comprising methanol, over at least one acidic ion exchanger to give a first stream comprising methyl tert-butyl ether and tert-butanol;
• (b) separating the first stream by distillation to obtain a second stream comprising methyl tert-butyl ether and tert-butanol;
• (c) dissociating the second stream in the gas phase over a heterogeneous catalyst to give a third stream comprising isobutene, methanol, methyl tert-butyl ether, water and tert-butanol;
• (d) separating the third stream by distillation to give a fourth stream comprising more than 50% by mass of the amounts of methanol, tert-butanol, methyl tert-butyl ether and water present in the third stream and a fifth stream comprising isobutene;
• (e) separating the water from the fourth stream to less than 1% by mass by distillation to give a sixth stream comprising methanol, tert-butanol and methyl tert-butyl ether;
• and
• (f) totally or partially recirculating the sixth stream to the reacting (a) with the at least one hydrocarbon mixture.