PROCESS FOR PREPARING ACROLEIN, ACRYLIC ACID OR MIXTURES THEREOF FROM PROPANE

Prodn. of acrolein (I) and/or acrylic acid (II) from C3H8 involves (A) gas phase partial dehydrogenation of C3H8 to C3H6, using heterogeneous catalyst; (B) using the prod. gas mixt. of C3H6 and unreacted C3H8 for charging an oxidn. reactor, in which C3H6 is converted to (I) and/or (II) by gas phase selective partial oxidn. with pure O2 using heterogeneous catalyst; and (C) separating the prod. from the prod. gas stream and recycling at least the unreacted C3H8 from stage (B) to stage (A). The novelty is that, before entering stage (B), constituents other than C3H8 and C3H6, at least H2 and steam, are removed from the prod. gas mixt. from stage (A). Pref. all constituents except C3H8 and C3H6 are removed after stage (A). Stage (B) is carried out in 2 consecutive reactors charged with multi-metal oxide catalysts, the first of Mo-Bi-Fe and the second of Mo-V. The prod. gas mixt. from the first oxidn. reactor is passed directly into the second; and the vol. ratio of organic cpd. for partial oxidn. (C3H6 or (II)) to O2 is 1:(1-3) in both reactors.