Crystallization is one of the oldest and the most significant unit operations, which is extensively used in chemical industries In addition to conventional methods which have been used to generate supersaturation, such as cooling and evaporation, antisolvent addition including the introduction of liquids, dense gases or supercritical fluids, has been an alternative method in this area. In this technique second solvent which is known as antisolvent or precipitant, is added to the solution, causing the reduction of solute solubility in the primary solution, hence resulting in supersaturation generation. In this study, the antisolvent crystallization system containing phenanthrene as the solute, toluene as the primary solvent and supercritical CO2 as the antisolvent was considered. At first by the application of experimental data in references, an empirical correlation was obtained to calculate the solubility of phenanthrene in CO2-toluene system, which resulted in a correlation for the phenanthrene solubility and supersaturation rate with pressure (anti-solvent injection). Afterwards, the kinetic modeling of supercritical antisolvent crystallization process using Population Balance Equation method was fulfilled. Population balance models which describe the particle kinetics of primary and secondary nucleation as well as growth in supercritical and gas antisolvent crystallization (GAS) processes are rather complicated, and have often integro-partial differential form. In this paper a powerful numerical algorithm which is a combination of the Lax-Wendroff and Crank-Nicholson methods applied to solve the population balance model. The Algorithm simulations were performed by the changes in the main SAS process operating parameters, i.e., the anti-solvent addition rate by changing the system pressure and supersaturation. The simulations were performed at a process emperature of 40◦C, while the pressure was varied between 0.34-5.63 Mpa. Using supersaturation for the calculation of the nucleation and the crystal growth rates crystal size distribution were determined by the numerical solution to the Population Balance Equation implementing Discretization technique.

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