PROCESS FOR THE SIMULTANEOUS MANUFACTURE OF PURE MTB AND A SUBSTANTIALLY ISOBUTENE-FREE MIXTURE OF C4-HYDROCARBONS

There is provided a process for the simultaneous manufacture of pure MTB (methyl tert.-butyl ether) and a substantially isobutene-free mixture of C4-hydrocarbons, by reacting isobutene contained in a mixture of C4-hydrocarbons with excess methanol in the liquid phase at elevated temperatures on strongly acid, macroporous, organic ion exchange resins, characterised by the following steps: (a) methanol and isobutene are reacted in a molar ratio of 2:1 to 5:1 at temperatures between 30 and 100.degree.C, (b) uncon-verted hydrocarbon products are then removed as a top product under a pressure of 2 to 10 bars from a first rectification column, (c) a bottom product from said first column is rectified in a second rectification column under normal pressure or under a slight excess pressure of up to 2 bars at the top of said second column, a bottom product from said second rectification column is recycled to step (a), if necessary after separating off a portion of the tert.-butanol formed and the C8-olefines, and (d) a top product or distillate from said second column is rectified in a third rectification column under a pressure of 5 to 30 bars, obtaining a top product or distillate which is recycled to step (c) and pure MTB is withdrawn from the bottom of said third column. Utilizing this process results in unconverted hydrocarbon products having an isobutene content of