Fractional crystallization by gas antisolvent technique: Theory and experiments

The efficacy of CO, as an antisolvent was studied experimentally for the precipitation of naphthalene and phenanthrene from their solutions in toluene at 298 and 310 K. Phenanthrene was salted out of solution at every condition investigated, whereas naphthalene was never segregated as a solid phase. These behaviors are explained by a model representing the composition of the phases and supersaturation of the solution as functions of pressure. Based on results from ternary systems experiments were performed with the quaternary system CO2-toluene-naphthalene-phenanthrene: starting from an equimolar solution of the two solids in toluene, phenanthrene with a purity higher than 98.5% can be collected in the precipitation cell, while naphthalene with about 13% of phenanthrene is recovered fi om the liquid phase after expansion. The simulation of the process was able to account for the experimental evidence. Although the solutes used do not have a practical application, a general method is outlined to exploit the possibility of using the supercritical antisolvent technique for separation.