Patent ID: 7592483

Claim:
A process for preparing acrolein or acrylic acid or a mixture thereof by heterogeneously catalyzed partial gas phase oxidation of propylene, in which a starting reaction gas mixture 2 which comprises the propylene and molecular oxygen reactants and inert molecular nitrogen and propane diluent gases and is conducted at elevated temperature through a fixed catalyst bed whose active composition is at least one multimetal oxide comprising the elements Mo, Fe and Bi, wherein starting reaction gas mixture 2 , based on its total volume, has the following contents: from 7 to 9% by volume of propylene, from 9.8 to 15.5% by volume of molecular oxygen, from 10.5 to 15.5% by volume of propane and from 40 to 60% by volume of molecular nitrogen, with the proviso that the molar ratio V 1 of propane present in starting reaction gas mixture 2 to propylene present in starting reaction gas mixture 2 is from 1.5 to 2.2, the molar ratio V 2 of molecular nitrogen present in starting reaction gas mixture 2 to molecular oxygen present in starting reaction gas mixture 2 is from 3.5 to 4.5 and the molar ratio V 3 of molecular oxygen present in starting reaction gas mixture 2 to propylene present in starting reaction gas mixture 2 is from 1.5 to 2.14.