Patent ID: 6933407

Claim:
A process for preparing methacrylic acid from isobutane comprising A) subjecting isobutane in a reaction zone A to a partial heterogeneously catalyzed dehydrogenation in the gas phase to form a product mixture A which comprises isobutene and unconverted isobutane, B) charging a reaction zone B with the product gas mixture A and subjecting the isobutene in reaction zone B to a heterogeneously catalyzed partial oxidation in the gas phase with molecular oxygen to form a product gas mixture B comprising methacrolein, wherein the molar conversion of isobutene is ≧95 mol% and C) charging a reaction zone C with the product gas mixture B without prior removal of components contained therein and subjecting the methacrolein in a reaction zone C to a heterogeneously catalyzed partial oxidation with molecular oxygen in the gas phase to form a product gas mixture C comprising methacrylic acid, wherein at least 80 mol% of the components other than isobutane and isobutene in the product gas mixture A are removed before the charging to reaction zone B, and wherein the molecular oxygen is introduced to reaction zone B as a mixture with molecular nitrogen in a molar ratio Rof molecular oxygen to molecular nitrogen of from 1:1 to 1:10.