Patent ID: 8618336

Claim:
A process for the long-term operation of a heterogeneously catalyzed partial gas phase oxidation of propene to acrolein, comprising conducting a reaction gas input mixture which comprises propene, molecular oxygen and at least one inert gas through a fixed catalyst bed whose active material is at least one multimetal oxide comprising the elements Mo, Fe and Bi, with the proviso that: the reaction gas input mixture comprises the molecular oxygen and the propene in a molar O 2 :C 3 H 6 ratio of â‰§1, the fixed catalyst bed is arranged in two spatially successive temperature zones A, B, both the temperature T A of temperature zone A and the temperature T B of temperature zone B are a temperature in the temperature range from 280 to 420Â° C., the reaction gas input mixture flows through temperature zones A, B in the time sequence â€œfirst Aâ€ and â€œthen Bâ€, temperature zone A extending up to a conversion C A of the propene present in the reaction gas input mixture in the range from 45 to 85 mol %, and the conversion of the propene increasing in temperature zone B to a value C B of â‰§90 mol %, in a single pass of the reaction gas input mixture through the overall fixed catalyst bed, the selectivity of acrolein formation, based on propene converted, is â‰§80 mol %, the space velocity of propene present in the reaction gas input mixture on the fixed catalyst bed is â‰§140 l (STP) of propene/l of fixed catalyst bedÂ·h, the temperatures T A and T B on completion of fresh charging of the fixed catalyst bed are such that the difference Î”T BA =T B âˆ’T A >0Â° C., then, with increasing operating time, in order to counteract the reduction in the quality of the fixed catalyst bed, at least one of the two temperatures T A , T B is increased, wherein the increasing of the at least one of the two temperatures T A , T B is undertaken such that the difference Î”T BA =T B âˆ’T A increases with increasing operating time.