Robust Kinetic Modelling of Heterogeneously Catalyzed Free Fatty Acids Esterification in (Monophasic Liquid)/Solid Packed-Bed Reactor: Rival Model Discrimination

Abstract

Biofuels are key products for the sustainability of the world energy consumption in the next years. Biodiesel in particular is a non-toxic, biodegradable, environmentally friendly alternative diesel fuel. Nowadays, the main problem for the commercialization of biodiesel is its final cost, that is strongly dependent (about 85 % of the total) by the feedstock used. A possible way to lower the biodiesel production costs is using raw oils, which contain a higher amount of Free Fatty Acids (FFA) that should be eliminated before the transesterification reaction to avoid soaps formation. In this work the regression of kinetic parameters of heterogeneously catalyzed esterification with a packed-bed reactor was made. Robust techniques for kinetic parameters estimation and simultaneous discrimination of rival models were adopted and combined with a dedicated differential-algebraic equation (DAE) model that characterizes the system. The main kinetic parameters were regressed using kinetic models other than literature models in considering the activity (UNIQUAC model was used to calculate the activity coefficients) of the components instead of the concentration because the oil/methanol/water/FAME system is highly non ideal. The kinetic parameters were obtained using equilibrated resins, i.e. using the catalyst after having let it to adsorb reactants and products at the operative conditions. The regressed parameters allow to represent the system in a wide range of operating conditions with a little residual error.