METHOD FOR PRODUCING PHTHALIC ANHYDRIDE

摘要

The invention relates to a method for producing phthalic anhydride during which the catalytic gas phase oxidation of o-xylol and/or naphthalene is carried out over at least three layers of catalysts of increasing activity, whereby only the last layer of the catalyst system contains phosphorous, and the last layer contains at least 10% by weight of vanadium (expressed as V2O5) with regard to the active mass of the catalyst and has a ratio of vanadium (expressed as V2O5) to phosphorous of greater than 35.