Lignin derivatives are obtained in low levels of production by using catalytic processes in batch operations. Considering the availability of vegetable biomass with high lignin content it is processing to be economically feasible, should be conducted through continuous processes. In this way, the objective of this paper is to provide predictions for the aromatic aldehyde production from the aqueous alkaline lignin processed by wet oxidation in a three-phase fluidized bed reactor. A heterogeneous steady-state model was formulated to describe the continuous, isothermal operations of lignin oxidation associating hydrodynamic phenomena, mass transfer, and chemical reaction. The reactor operation was simulated considering a feed with 0.21 mmol/L of oxygen and 0.30 g/L of lignin at 393K and 20bar, presenting stationary profiles of the reagents and products. The mathematical model studied represented a stationary behavior and was solved by the finite difference methods in a code in FORTRAN 95.