Preparation of acrolein, acrylic acid or a mixture thereof from propane

A process for preparing acrolein, acrylic acid or a mixture thereof from propane, in which

• A) in a first stage A, the propane is subjected to a partial heterogeneously catalyzed dehydrogenation in the gas phase to give propylene,
• B) the product gas mixture from stage A containing propylene and unreacted propane is used in a second stage B as feed to an oxidation reactor and in the oxidation reactor the propylene is subjected to a selective heterogeneously catalyzed gas-phase partial oxidation with molecular oxygen to give acrolein, acrylic acid or a mixture thereof as target product, with pure oxygen being used as oxygen source, and
• C) in a third stage C, the target product is separated from the product gas stream obtained from the partial oxidation of the propylene in stage B and at least the unreacted propane present in the product gas stream from stage B is recirculated to the dehydrogenation stage A,
• wherein, from among the constituents other than propane and propylene present in the product gas mixture from stage A, at least the hydrogen and the water vapor are separated from the product gas mixture before it is used as feed to the oxidation reactor of the second stage B.