Patent ID: 7482500

Claim:
A process for preparing butadiene from n-butane comprising: A) providing a feed gas stream a comprising n-butane; B) feeding the feed gas stream a comprising n-butane into at least one first dehydrogenation zone and nonoxidatively catalytically dehydrogenating n-butane to obtain a product gas stream b comprising n-butane, 1-butene, 2-butene, butadiene, hydrogen, low-boiling secondary constituents and optionally steam; C) feeding the product gas stream b of the nonoxidative catalytic dehydrogenation and an oxygenous gas into at least one second dehydrogenation zone and oxidatively dehydrogenating 1-butene and 2-butene to obtain a product gas stream c comprising n-butane, 2-butene, butadiene, hydrogen, low-boiling secondary constituents and steam, said product gas stream c having a higher content of butadiene than the product gas stream b; D) removing hydrogen, the low-boiling secondary constituents and steam to obtain a C 4 product gas stream d substantially consisting of n-butane, 2-butene and butadiene; E) separating the C 4 product gas stream d into a recycle stream el consisting substantially of n-butane and 2-butene and a stream e2 consisting substantially of butadiene by extractively distilling and recycling the stream el into the first dehydrogenation zone; F) optionally, feeding some or all of the stream e2 consisting substantially of butadiene into a selective hydrogenation zone and selectively hydrogenating butadiene to 1- and/or 2-butene to obtain a stream f comprising 1 -butene and 2-butene; G) optionally, when F is carried out, feeding the stream f comprising 1-butene and 2-butene into a distillation zone and removing a product of value stream g1 consisting substantially of 1-butene to leave a stream g2 comprising 2-butene; H) optionally, when F and G are carried out, recycling the stream g2 comprising 2-butene into the first dehydrogenation zone.