A process for preparing butadiene, comprising nonoxidatively dehydrogenating n-butane from a stream (a) in a first dehydrogenation zone to obtain stream (b) comprising 1-butene and 2-butene; oxidatively dehydrogenating the 1-butene and 2-butene of (b) in the presence of an oxygenous gas in a second dehydrogenation zone to obtain stream (c) comprising n-butane, butadiene, hydrogen, carbon dioxide, and steam; compressing and cooling (c) to obtain stream (d2) comprising n-butane, butadiene, hydrogen, carbon dioxide, and steam; extractively distilling (d2) into stream (e1) comprising butadiene and stream (e2) comprising n-butane, hydrogen, carbon dioxide, and steam; compressing and cooling (e2) to obtain stream (f1) comprising n-butane and water and stream (f2) comprising n-butane, hydrogen, and carbon dioxide; cooling (f2) to obtain stream (g1) comprising n-butane and stream (g2) comprising carbon dioxide and hydrogen; phase separating water from (f1) to obtain stream (h1) comprising n-butane; and recycling (h1) into the first dehydrogenation zone.