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Modeling of the PGSS process by crystallization and atomization



A particles from gas-saturated solution (PGSS) process for the model system hydrogenated palm oil (HPO) with CO2 was implemented and particle information, including size, size distribution, and morphology, is reported. The PGSS process in a capillary nozzle is modeled to be in steady, one-dimensional, inviscid, and two-phase (CO2-rich phase and liquid HPO/CO2 phase) annular-mist flow. The Peng–Robinson equation of state is applied for the nonideality of the binary CO2/HPO and the fluid hydrodynamic equations of two phases are established to describe the system's pressure, temperature, velocity, and density along the nozzle. The aerosol dynamic equation for the crystallization of HPO in the CO2-rich phase is used to explain the HPO crystal formation and growth under supercooling and supersaturation. For the liquid HPO/CO2 phase, the atomization mechanism in terms of the interaction of the two phases gives HPO droplet information. The coupled model equations are numerically solved to obtain the HPO particle size and particle size distribution at the nozzle exit under several operating conditions. Different distribution modes are found, in agreement with the experimentally obtained particle spectra, an indication of the soundness of the model's particle formation mechanisms. Particles produced by atomization usually prevail over those formed from crystallization; yet, there exist special operating conditions under which the rapid expansion of supercritical solution (RESS) mechanism cannot be neglected and melt crystallization may be significant. The comparison between theoretical and experimental particle morphologies indicates that atomization may produce mainly spherical but relatively large particles; melt crystallization provides amorphous crystal particles, and the RESS process gives small and irregular crystals. © 2005 American Institute of Chemical Engineers AIChE J, 2005

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