The heterogeneous catalysis of lactic acid (88 wt %) esterification with ethanol in the presence of Amberlyst 15-wet was studied for catalyst loading of 1.2-3.9 wt %, initial molar ratio of reactants of 1.1-2.8, and temperature from 50 to 90 degrees C. In this work a methodology based on the UNIQUAC model was developed to determine the thermodynamic equilibrium constant since in the literature there is inconsistency concerning the temperature dependence of the thermodynamic equilibrium constant. A simplified Langmuir-Hinshelwood kinetic model was used to predict the experimental data. The proposed rate law is r = k(c)(aE(th)a(La) - a(EL)a(w)/K)/(1 + K(Eth)a(Eth) + K(w)a(w))(2); the kinetic parameters are the preexponential factor, k(c,0) = 2.70 x 10(7) mol.g(-1).min(-1), and the activation energy, E-a = 49.98 kJ/mol. The equilibrium reaction constant is K = 19.35 exp(-515.13/T (K)) with reaction enthalpy 4.28 kJ/mol. The model reasonably predicts the kinetic experimental data, and it will be very useful to apply to the design and optimization of industrial hybrid reactive separation processes.