PROCESS FOR PREPARING ISOBUTENE BY CLEAVING MTBE-CONTAINING MIXTURES

The invention relates to a process for production of isobutene from MTBE-containing mixtures which comprises the following steps a) cracking, in a reactor R, a mixture obtained from an MTBE-containing feedstock (1a) and/or an MTBE-containing stream (13, 5), delivering a stream (6) of reaction products consisting of isobutene, methanol, MTBE and also by-products, wherein these consist of a1) high boilers having a boiling range above 55°C at a pressure of 0.1 MPa; a2) medium boilers having a boiling range from 12 to 55°C at a pressure of 0.1 MPa; and a3) low boilers having a boiling range below 12°C at a pressure of 0.1 MPa; b) separation of stream (6) by distillation into a stream (7) which contains the product isobutene and low boilers and a stream (8) which contains MTBE, methanol, medium boilers and high boilers; c) separating the stream (8) by distillation obtaining an MTBE-containing stream (10, 12) and a methanol-containing high-boiler stream (9, 11); d) recirculating an MTBE-containing stream (10, 12, 13) to step a) of the process, wherein the medium-boilers are completely or partially separated off from the medium-boiler-rich streams (10, 12) upstream of step d).