Are Empirical Models Based on the Response Surface Methodology Suitable for Biodiesel Production Optimization?

The response surface methodology (RSM) can constitute a useful tool for the optimization of biodiesel production when applied to establish the relationship between biodiesel yields and the remaining process operation variables. For this reason, in the present study, several kinetic models were fitted to three sets of experimental data available in the literature and compared to second-order empirical models traditionally used in RSM studies. The obtained results show the asymptotic increase of oil or free fatty acid (FFA) conversion (X A) with the increase of the reaction time, alcohol to oil/FFA molar ratio, and catalyst concentration, differently from the behavior predicted by most empirical models described in the literature and used to perform RSM studies. Particularly, when the reaction temperature is also varied, it is possible to observe experimental conditions where X A attains a maximum value as the result of the nonlinear structure of the kinetic models proposed in the present work. Therefore, these results clearly show that phenomenological models should be preferred during the optimization of biodiesel production and also used to perform RSM studies.