Patent ID: 8188310

Claim:
A process for the long-term operation of a heterogeneously catalyzed partial gas phase oxidation of an organic starting compound to an organic target compound, in which a reaction gas input mixture comprising the organic starting compound and molecular oxygen is first conducted through a freshly charged fixed catalyst bed which is installed into two spatially successive temperature zones A, B whose temperatures T A and T B are such that the difference ΔT BA between the temperature T B of the temperature zone B and the temperature T A of the temperature zone A and calculated with the higher of the two temperatures as the minuend is >0° C., with the proviso that the reaction gas input mixture flows through temperature zones A, B in the time sequence “first A” and “then B”, temperature zone A extending up to a conversion of the organic starting compound of C A =from 15 to 85 mol % and the conversion of the organic starting compound increasing in temperature zone B to a value C B of ≧90 mol %, and in which, with increasing operating time, in order to counteract the reduction in the quality of the fixed catalyst bed, the temperature of temperature zones A, B is then changed, wherein, with increasing operating time, the temperature of that temperature zone which initially had the lower temperature is increased and the difference ΔT BA between the temperatures of the two temperature zones is reduced, the difference being formed by the temperature of that temperature zone which initially had the higher temperature retaining its position as the minuend, wherein ΔT BA does not change its preceding sign for a minimum of 2 months operating time.