Process for production of isobutene and propylene from hydrocarbon cuts containing four carbon atoms

A process for the conversion of an olefinic C.sub.4 cut to isobutene and propylene, the cut containing diolefins, butene-1, butene-2, isobutene and acetylenic impurities, characterized in that said process comprises the following successive steps:

• 1) selective hydrogenation of diolefins and acetylenic impurities and simultaneous isomerisation of butene-1 to butene-2, wherein hydrogenation and isomerization occur in the same zone, to obtain an effluent containing mainly butene-2 and isobutene, and containing practically no diolefins or acetylenic compounds;
• 2) separating the effluent of step 1, by distillation, an overhead cut containing mainly isobutene and butene-1 which was not converted during the first step, and a bottom cut containing essentially butene-2 and butane, at most 1% by weight of isobutene and at most 1% by weight of butene-1;
• 3) metathesis of the butene-2 in the bottom cut from the preceding step with ethylene, in the presence of a catalyst comprising at least one rhenium oxide deposited on a support, at a temperature in the range 0.degree. C. to 100.degree. C., and at a pressure which is at least equal to the vapour pressure of the reaction mixture at the reaction temperature, to obtain an effluent containing propylene, metathesis being followed by separation of the propylene.