Mass and heat transfer analysis of SAS: effects of thermodynamic states and flow rates on droplet size

Abstract

The supercritical antisolvent (SAS) process entails attainment of extremely high supersaturation in an atomized solution droplet by a very rapid increase in the antisolvent CO 2 mole fraction in it during its flight through a CO 2 continuum. In this work the droplet dynamics has been studied for a single droplet of CO 2–acetone solution falling in a flowing CO 2 environment in terms of variations in its concentration, temperature and size due to the two-way mass transfer of CO 2 and solvent. A model based on the SAS mechanism of simultaneous mass and heat transfer has been simulated to study the effects of the thermodynamic states and the individual flow rates of CO 2 and solution. The hydrodynamics of the droplet and the convective mass and heat transfer have been combined in the model to ascertain the individual number of moles of CO 2 and solvent transferred and their directions at any instant of time during the flight. The effects of process parameters have been analyzed for the initial droplet size of the solution. The swelling or shrinking of the droplet has been analyzed with time till the solvent is completely evaporated, in the pressure range of 71–350 bar, temperature range of 313–333 K, SC CO 2 flow rate of 0.1136–1.136 mol/s and the ratio of the volumetric flow rates of CO 2-to-solution in the range of 100–1000. The mole fraction of CO 2 attained inside the non-isothermal droplet has been analyzed with time, which is needed in the design of supersaturaton and nucleation kinetics in the SAS process.