Despite its complexity, reactive extrusion is continuously developing for the production of new and performing materials. Due to the strong coupling between flow, rheology and chemistry, optimizing this process for a given reaction remains a difficult task. Moreover, the scale-up from the laboratory to the production scale is another crucial question, which cannot be solved by conventional techniques. In this paper, we show how the use of numerical modeling limy help answer these complex questions by providing realistic solutions, rapidly and without excessive costs. The example of a transesterification reaction was chosen because this reaction has been carefully characterized in previous studies. The reaction kinetics and the kinetic constants are well known and the modeling of this reactive extrusion process has proved to be realistic and accurate.