A kinetic expression to represent the photocatalytic degradation of 4-chlorophenol (4-CP) has been derived in a small, well-stirred, slurry reactor. Based on a plausible reaction sequence, the obtained mathematical representation describes with good accuracy the decomposition of 4-CP as well as the evolution of the most important reaction intermediates. This information is used to actionate a very different reactor in size, shape and operating conditions. The adopted approach consists in the precise modeling of the laboratory reactor to estimate intrinsic kinetic parameters. Afterward, the reaction kinetics obtained in the small reactor is used to model a bench scale reactor, without employing any adjustable parameters. Simulation results are in good agreement with the experimental data obtained in the larger reactor. This approach points to the development of a full scale-up procedure employing exclusively laboratory reactor information. (c) 2007 Elsevier B.V. All rights reserved.