CRYSTALLIZATION OF PHENANTHRENE FROM TOLUENE WITH CARBON-DIOXIDE BY THE GAS PROCESS

The crystallization of phenanthrene from toluene with carbon dioxide a s the antisolvent gas is described. In the GAS process, a pressurized gas is dissolved into a liquid solvent, where it causes a volumetric e xpansion and lowers the solubility of the solute. Theoretical models a ve presented for the liquid-phase expansion and the solubility as a fu nction of pressure and temperature. The Nyvlt theory for batch crystal lization is adapted to predict the pressure profile in the crystallize r needed to maintain a constant supersaturation and growth rate. Gener ation of seeds is accomplished via a pressure pulse at the saturation pressure. The average particle size of the phenanthrene could be varie d from 160 to 540 mu m. Creation of seeds doubles the particle size an d reduces the coefficient of variation significantly. The residual amo unt of toluene in the crystals without treatment is approximately 70 p pm. The particles are agglomerates of phenanthrene crystals.