Patent ID: 8106220
Filing Date: 2012-01-31
Classification: C07C,C07D

Abstract:
1. A process for preparing phthalic anhydride by catalytic gas phase oxidation of o-xylene, in which a gaseous mixture of o-xylene and an oxygenous gas is converted in a main reactor to a gaseous intermediate reaction product which comprises unconverted o-xylene, phthalic anhydride underoxidation products and phthalic anhydride, the heat of reaction which arises in the main reactor being removed at least partly by indirect cooling with a heat carrier medium, and the intermediate reaction product being introduced into a postreactor with a temperature which is lower than the lowest temperature of the heat carrier medium, wherein the concentration of unconverted o-xylene in the intermediate reaction product is at least 1% by weight, and the sum of the concentrations of phthalic anhydride underoxidation products in the intermediate reaction product is at least 0.5% by weight, based in each case on the total weight of the organic components in the intermediate reaction product, and wherein the concentration of o-tolylaldehyde in the intermediate reaction product is at least 0.25% by weight.