The dynamic behaviour of the semicontinuous operation was simulated assuming the system composed of six components (CO2 – EEC14:0 – EEC16:0 – EEC18:0 – EE-EPA – EE-DHA) and assuming equilibrium conditions between the liquid and the vapour phases. The mass decrease of oil components inside the extractor was calculated from the balance differential equation:

where Fout is the outlet mass flow rate, yi represents the mass fraction in the outlet stream and Ni stands for the mass of component i inside the extractor. Ni is given by:

where Li and Vi stands for the mass of component i in the liquid and the vapour phase respectively. Since it was assumed the perfect mixing of the vapour phase inside the extractor, the composition of this phase is equal to that one in the outlet stream. Vapour mass fractions were linked to the liquid mass fraction from the equilibrium condition:

Furthermore, the condition about the extractor fixed volume was imposed:

Fugacity coefficients and specific volumes were calculated by means of PREOS with van der

Waals mixing rules for the parameters am and bm. In the mixing rules it was assumed:

Therefore, two binary interaction parameters (kij and hij) were included in the mixing rules. Pure component parameters (ai and bi) were calculated from critical properties and acentric factors. Critical values of fatty acids ethyl esters were estimated by a group contribution method [5] while acentric factors were calculated.

Since it was also necessary to estimate normal boiling temperatures of FAEE, because no experimental data are available for most of them, a new group contribution method was adopted. These data are reported in Table 20. On the contrary, binary parameters of interaction between ethyl ester i and ethyl ester j were neglected because these components show similar thermodynamic behaviour.

Table 20: Normal boiling point temperatures, critical properties and acentric factors used in the

modellization.