Patent ID: 7687425
Filing Date: 2010-03-30
Classification: B01J,C07C

Abstract:
1. A catalyst system for preparing phthalic anhydride, which comprises four catalyst layers which are arranged above one another in a reaction tube and whose active composition comprises from 70 to 99% by weight of titanium dioxide in the anatase modification, wherein (i) in the uppermost layer the catalyst comprises from 7 to 10% by weight, based on the total catalyst, of active composition comprising from 6 to 11% by weight of V (ii) in the middle layers the catalyst comprises from 7 to 12% by weight, based on the total catalyst, of active composition comprising from 5 to 13% by weight of V (iii) in the bottom-most layer the catalyst comprises from 8 to 12% by weight, based on the total catalyst, of active composition comprising from 5 to 30% by weight of V with the proviso that the BET surface area of the titanium dioxide in the uppermost layer (i) is less than the BET surface area of the titanium dioxide in the middle layers (ii) and the BET surface area of the titanium dioxide in the bottom-most layer (iii) is greater than the BET surface area of the titanium dioxide in the middle layers, and wherein the titanium dioxide in the upper middle layer has a BET surface area of from 10 to 35 m