Solid-Liquid Equilibrium in Mixtures of Pyrene and Long Chain Normal-Alkanes with Optimization of Larsen Equation Parameters

Thermodynamic properties of mixtures of polycyclic aromatic hydrocarbons and long chain normal-alkanes are important for understanding phase transformations of heavy petroleum fractions. In this study, a new method for optimization of parameters of modified UNIFAC model as proposed by Larsen was suggested and validated by comparing the calculated solubility and activity coefficients of a polycyclic aromatic hydrocarbons (pyrene) in long chain normal-alkanes(n-C18H38, n-C28H58, n-C30H62, n-C36H74, n-C50H102) with experimental data. Good agreement was observed between experimental data and model in diagrams of solid-liquid equilibrium temperature and activity coefficient of pyrene versus solubility of pyrene in long chain normal Alkanes. These results also were compared with another set of calculated results in literature and they were comparable or superior to the published results. Larsen model parameters were calculated by using values as reported by Larsen as initial guess. Then these values were optimized by a nonlinear optimization code for minimizing the error.