Upgrading of butadiene and crude C4 stream -: Connections with shortages in isobutene and propylene.

The evolution of the outlets for C-4 cuts from ethylene plants shows quite contradictory results. On one hand, European and Asiatic petrochemists are more constrained to recycle this type of effluent, which contains butadiene and isobutene, to the steam cracker. Likewise, the demand for isobutene for MTBE1 production is such that it has to be produced by the dehydrogenation of isobutane. This situation is effectively caused by the surplus of butadiene, a by-product of ethylene, and for which the demand is not increasing as fast as the demand for ethylene. To improve cracking performances during the recycling of the C4 cut, butadiene is more and more selectively hydrogenated. Under these conditions, rather than cracking it, the new processes could make it possible to better upgrade it. Indeed, after selective hydrogenation, most of the cut can be transformed into MTBE by implementing the new n-butene isomerisation process into isobutene. Another upgrading scheme consists in transforming isobutene into MTBE and n-butenes into propylene by metathesis with ethylene. In a context in which its price has dropped sharply, butadiene should find new applications by its conversion into high-value added products.