Simulation of particle formation during the rapid expansion of supercritical solutions

Experimental and theoretical results for the rapid expansion of supercritic al solutions (RESS-process) are presented. Experiments were carried out wit h the solvents carbon dioxide (CO2) and trifluoromethane (CHF,) and the org anic solutes cholesterol, benzoic acid and griseofulvin. It is shown that f or each of these solutes it is possible to produce particles in the size ra nge of 200 nm which leads to improved dissolution. Furthermore, to demonstr ate the higher bioavailability of the micronized pharmaceutical griseofulvi n as of the original material, results of a dissolution experiment are show n. Besides the experiments the flow and particle formation and growth in th e expansion unit (inlet-capillary nozzle-supersonic free jet) of the RESS-p rocess is modelled numerically. The model to calculate the flow field consi sts of mass, momentum and energy balances as well as the extended generaliz ed Bender equation of state (egB-EoS). The flow is assumed to be steady, on e-dimensional, viscid and non-adiabatic. The general dynamic equation (GDE) is included to model the particulate phase. The results of the modelling s how that particle formation occurs in most of the cases mainly in the super sonic free jet and that the main mechanism for particle growth is coagulati on. Furthermore, it can be inferred from the high particle number concentra tion at the Mach disk that particle growth by coagulation continues in the subsonic part of the free jet (expansion chamber). Experimental results wit h variation of additional air supply to the expansion chamber are presented to confirm the theoretical results. (C) 2001 Elsevier Science Ltd. All rig hts reserved.