Imaging the supersaturation in high-pressure systems for particle generation

The supersaturation which is the driving force for particle precipitation was quantified in situ for the injection of a solution into a supercritical antisolvent. Firstly, saturation mole fractions of the solute yttrium acetate were measured via elastic light scattering in the homogeneous ternary system, which is composed of the solute itself, the solvent dimethylsulfoxide and the antisolvent carbon dioxide. The saturation experiments were carried out at pressures of 8.5, 12 and 16 MPa and at a temperature of 313 K. Secondly, applying a Raman based optical measurement technique the actual solute mole fraction was imaged in situ during the injection of the solution (solute dissolved in solvent) into the antisolvent. The injection experiments were carried out at pressures of 12 and 16 MPa and at a temperature of 313 K. Finally, the ratio of the actual solute mole fractions and the saturation solute mole fractions, which were measured during the injection experiment and during the saturation experiment, respectively, quantifies the supersaturation. High supersaturation values are evidenced already close to the nozzle exit. For the first time, an optical method was developed to measure the supersaturation in situ in a dynamic process under high-pressure.