A kinetic study of the photocatalytic degradation of 4-chlorophenol employing titanium dioxide is presented. Experiments were carried out in a cylindrical slurry reactor irradiated by UV lamps. The aromatic reaction intermediates were identified and quantified. Intrinsic expressions to represent the kinetics of 4-chlorophenol and the main intermediates, 4-chlorocatechol and hydroquinone, were derived from a proposed reaction scheme. These expressions include explicitly the effect of photon absorption on the reaction rate. The modeling of the radiation field in the reactor was accomplished by solving the radiative transfer equation with the discrete ordinate method. Experimental runs were performed by varying the catalyst concentration, the incident radiation, and the reactor length. The parameters of the kinetic model were estimated from the experiments by applying a non-linear regression procedure. Good agreement was obtained between model predictions and experimental data, with a root mean square error of 14.4%. (C) 2008 Elsevier B.V. All rights reserved.