Novel Reaction Scheme for the Selective Oxidation of o- Xylene to Phthalic Anhydride

The oxidation of o-xylene to phthalic anhydride is one of the important industrial processes based on selective oxidation reactions. For the last 50 years vanadia titania catalysts have been used in this process. The reaction parameters like temperature range of operation, reactor inlet pressure, contact time, etc. slightly changed during this continuous process optimization. However, the fundamental understanding of the byproduct formation is still an open task. By using a sample port pilot plant, a detailed investigation was conducted for the first time of the by-product formation at different operation conditions. Several hitherto unknown intermediates could unambiguously be identified. The combination of process conditions and by-product formation enables the discussion of a new improved reaction scheme for the catalytic oxidation of o-xylene.