A process for preparing butadiene

The invention concerns a first process for preparing butadiene from n-butane comprising the steps of A) providing an n-butane-containing feed gas stream a; containing B) feeding the n-butane feed gas stream a into at least one first dehydrogenation zone and nonoxidative catalytic dehydrogenation of n-butane to obtain a product gas stream b comprising n-butane, 1-butene, 2-butene, butadiene, hydrogen, low-boiling secondary constituents and optionally water vapor; C) feeding the product gas stream b of the nonoxidative catalytic dehydrogenation and an oxygenous gas into at least one second dehydrogenation zone and oxidative dehydrogenation of 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 is obtained, which has a higher content of butadiene than the product gas stream b; D) removing hydrogen, the low-boiling secondary constituents and of water vapor to give a C E) separating the C F) if appropriate, partial or complete feeding of the substantially of butadiene ...