Numerical analysis of the characteristic times controlling supercritical antisolvent micronization

Abstract

In this work jet break-up time and of dynamic surface tension vanishing are considered as mechanisms in competition during supercritical antisolvent precipitation and a mathematical model, based on these two characteristic phenomena, is presented.Jet break-up time has been evaluated solving continuity and conservation of momentum equations; on the other hand, dynamic surface tension vanishing time has been evaluated according to the time-evolution model proposed by Cahn and Hilliard. Phase equilibria have also been taken into account, considering the Peng and Robinson equation of state and the related mixing rules.Calculations have been applied to yttrium acetate (YAc) as model solute, dimethylsulphoxide (DMSO) as liquid solvent and carbon dioxide (CO2) as antisolvent.The cross-over times, between jet break-up dominated and dynamic surface tension vanishing dominated regions, have been calculated at different pressures for pure DMSO and at different YAc concentrations in the liquid solution; a good agreement with previous experimental results has been obtained. The numerical results also correctly describe the influence of solute concentration on the pressure at which cross-over between the two regions is obtained.The characteristic times for acetone (AC) have also been evaluated, to perform a comparison with DMSO; in this case, cross-over has been observed in proximity of the mixture critical point pressure of the binary system.