Ultra-fine particles formation of C.I. Pigment Green 36 in different phase regions via a supercritical anti-solvent process

Ultra-fine particles of C.I. Pigment Green 36 were prepared using a continuous supercritical anti-solvent (SAS) apparatus employing quinoline as solvent and supercritical carbon dioxide as anti-solvent. A series of precipitation experiments were conducted at different temperatures, pressures, and flow rates of pigment solution. The vapor–liquid phase boundaries of carbon dioxide + quinoline mixtures were also measured with a volume-variable phase equilibrium analyzer at temperatures from 308.2 K to 328.2 K. Mapping the estimated composition of mixtures in a model CSTR (continuously stirred tank reactor) precipitator at the end of injection of pigment solution onto the phase diagram found that the morphology of prepared particles was mainly governed by the phase behavior of anti-solvent + solvent mixtures. Nano-particles were obtained as the precipitation loci were manipulated within either supercritical or superheated vapor region through the SAS process, whereas micro-metric aggregated ball-like particles were produced as the precipitation loci passed by the vapor–liquid coexistence region.