Patent ID: 7435848

Claim:
A method for the continuous preparation of an alicyclic carboxylic acid or an ester thereof comprising catalytically hydrogenating an aromatic carboxylic acid, an ester thereof, an anhydride thereof, or a mixture of two or more of these, with a hydrogen-comprising gas in the presence of at least one solid catalyst disposed in a fixed bed, wherein the hydrogenation is carried out in at least three series-connected hydrogenation units; wherein at least the first two series-connected hydrogenation units of the at least three series-connected hydrogenation units are operated in loop operating mode; wherein the at least the first two series-connected hydrogenation unites operating in loop operating mode operate with different residence times, and wherein the residence time in one of the at least first two series-connected hydrogenation units operating in loop operating mode is less than the residence time in a directly following hydrogenation unit operating in loop operating mode.