Method for producing methacrolein from isobutane

A process for preparing methacrolein from isobutane by

• A) subjecting the isobutane in a reaction zone A to a partial selective heterogeneously catalyzed dehydrogenation in the gas phase to form a product gas mixture A which comprises isobutene and unconverted isobutane,
• B) passing the isobutane- and isobutene-containing product gas mixture A into a reaction zone B and subjecting the isobutene in the reaction zone B to a selective heterogeneously catalyzed partial oxidation in the gas phase using molecular oxygen to form a methacrolein-containing product gas mixture B and
• C) using the methacrolein contained in the product gas mixture B either for preparing methacrylic acid or for another purpose and either recycling at least unconverted isobutane contained in the product gas mixture B into reaction zone A or using it for another purpose,
• which comprises feeding the molecular oxygen required in reaction zone B to reaction zone B accompanied by molecular nitrogen in a molar ratio of molecular oxygen to molecular nitrogen of from 1:1 to 1:10.