Phenomenological modeling of Acutodesmus obliquus microalgae in situ transesterification

The aim of this study was to establish a phenomenological model capable of describing the mass transfer and kinetic effects of the in situ transesterification of Acutodesmus obliquus microalgae dry biomass. This model was developed considering the following: homogeneous cell volume and composition; cells agglomerate forming clusters during in situ reaction; the cluster is considered to be formed of internal and external regions; the species concentration in the cluster is described considering multicomponent Langmuir isotherm model; the fatty acids diffusion inside clusters is described by Fick's Law; mass transfer of the fatty acids between external solid and bulk phases is governed by convection; and reaction occurs homogenously in the bulk phase. Results show that the proposed model fits the experimental data and adequately describes the reaction kinetics and mass transfers between bulk and external solid phases as well as from internal to external solid phases. It was verified that ester production is higher in the initial period of reaction due to the greater availability of lipids, tending to achieve a maximum over time. The mass transfer coefficients values suggest that the alcohol moves towards the solid phase more hardly than the fatty acids are extracted to the bulk phase. Moreover, the Langmuir constants show that the alcohol has higher adsorption strength in the biomass than the esters.