Patent ID: 7435860

Claim:
A process for preparing butadiene from n-butane, comprising the steps of A) providing a feed gas stream (a) comprising n-butane; B) feeding said feed gas stream (a) into at least one first dehydrogenation zone and nonoxidatively, catalytically dehydrogenating n-butane to obtain a gas stream (b) comprising n-butane, 1-butene, 2-butene, butadiene, and hydrogen, and optionally comprising carbon dioxide and/or steam; C) feeding said gas stream (b) and an oxygenous gas into at least one second dehydrogenation zone and oxidatively dehydrogenating 1-butene and 2-butene to obtain a gas stream (c) comprising n-butane, butadiene, hydrogen, carbon dioxide, and steam; D) compressing in at least one first compression stage and cooling said gas stream (c) to obtain at least one condensate stream (d 1 ) comprising water, and a gas stream (d 2 ) comprising n-butane, butadiene, hydrogen, carbon dioxide, and steam; E) separating said gas stream (d 2 ) by extractive distillation into a product stream (e 1 ) consisting substantially of butadiene, and a stream (e 2 ) comprising n-butane, hydrogen, carbon dioxide, and steam, F) compressing in at least one further compression stage and cooling said gas stream (e 2 ) to obtain at least one condensate stream (f 1 ) comprising n-butane and water, and a gas stream (f 2 ) comprising n-butane, hydrogen, and carbon dioxide, G) cooling said gas stream (f 2 ) to obtain a condensate stream (g 1 ) comprising n-butane, and an offgas stream (g 2 ) comprising carbon dioxide and hydrogen, and H) removing water from said at least one condensate stream (f 1 ), and optionally from said condensate stream (g 1 ), by phase separation to obtain at least one recycle stream (h 1 ) comprising n-butane, and at least one wastewater stream (h 2 ), and recycling said at least one recycle stream (h 1 ) into said first dehydrogenation zone.