Patent ID: 6740779
Filing Date: 2004-05-25
Classification: C07C

Abstract:
A process for the catalytic gas-phase oxidation of propene to acrylic acid, in which a reaction gas starting mixture which comprises propene, molecular oxygen and at least one inert gas and contains the molecular oxygen and the propene in a molar O2: C3H6 ratio of &gE;1 is passed, in a first reaction stage, using a propene loading of &gE;160 liter (S.T.P.) of propene/liter of fixed catalyst bed 1 per hour, under formation of acrolein and optionally acrylic acid as a byproduct, over a fixed catalyst bed 1 which is arranged in two spatially successive reaction zones A, B, the temperature of the reaction zone A being from 300 to 370Â° C. and the temperature of the reaction zone B beings from 305 to 380Â° C. and simultaneously at least 5Â° C. above the temperature of the reaction zone A wherein catalyst bed 1 comprises on active material catalyst bed 1 being at least one multimetal oxide containing at least the elements Mo, Fe and Bi, in such a way that the propene conversion in reaction zone A is from 40 to 80 mol % and the propene conversion during a single pass through the fixed catalyst bed 1 is &gE;90 mol % and the associated selectivity of the acrolein formation and of the acrylic acid byproduct formation together are &gE;90 mol %, and the resulting product gas mixture, which contains the molecular oxygen and the acrolein in a molar O2: C3H4O ratio of &gE;0.5, is passed, in a second reaction stage, over a fixed catalyst bed 2 which is arranged either in a single reaction zone C or in two spatially successive reaction zones D, E, the temperature of the reaction zone C being from 230 to 300Â° C. and the temperature of the reaction zone D being from 230 to 280Â° C. and the temperature of the reaction zone E being from 250 to 300Â° C. and simultaneously at least 5Â° C. above the temperature of the reaction zone D and the active material of catalyst bed 2 being at least one multimetal oxide containing at least the elements Mo and V, in such a way that the acrolein conversion during a single pass through the reaction zone C or the reaction zones D and E is &gE;90 mol % and the selectivity of the acrylic acid formation balanced over all reaction zones and based on propene converted is &gE;80 mol %, the sequence in which the reaction gas starting mixture flows through the reaction zones corresponding to the alphabetic sequence of the reaction zones, wherein both the fixed catalyst beds 1 and 2 and the reaction zones A, B and C or A, B, D and E are present in a single tube-bundle reactor comprising a plurality of catalyst tubes.