in this extraction step (hypothetical case with negligible external mass transfer
resistance), the fluid phase is in equilibrium with solid phase
throughout the extractor. The second period is controlled by the
solute diffusion from inner cells of vegetal structure and corresponds
to the diffusion from intact cells. In Xavier et al. (2011)
model, mass transfer properties of recovered oil were considered
constant throughout the process. The general equations considered
in this model are the mass balances per unit volume extraction bed
consist of equations for the solute in fluid and solid-phases
described by (eqs. 3.1 and 3.2)