A fixed-bed Reactor with cocurrent downflow operating in downward bubble flow regime for hydrogenation of pyrolysis gasoline (PYGAS) has been simulated. In order to model the reactor, suitable thermodynamic, hydrodynamic and reaction models were solved simultaneously. A set of ten hydrogenation reaction kinetics was considered, taking into account a cut of hydrocarbons C-5-C-11. It was demonstrated the importance of how the choice of a specific thermodynamic model may, or not, improve the results obtained, and how this may affect the prediction of the system. The use of Soave-Redlich-Kwong equation of state with the mixing rule of Panagiotopoulo-Reid modified by SimSci is the recommendation made to represent the vapor-liquid-equilibrium, reporting 3.4% AARD (average absolute relative deviation) in the hydrogen solubility in PYGAS. The model predicts the steady state conditions and it is validated by comparing the results with actual plant data under the following operating conditions: T-inlet = 366 K, P-inlet = 5.03 MPa, and (<0.001) molar of styrene in the reactor effluent. From simulation results, it is compared the predictions of the model with actual plant data, finding a good agreement between both, and showing AARD of 0.8% in the temperature profile and 9% in the composition of reactor effluent between ours results and the plant data. (C) 2013 Elsevier B.V. All rights reserved.