Mass transfer of solids in supercritical CO2

An experimental technique has been developed to determine mass transfer parameters in processes using supercritical fluids, in the present study supercritical CO₂ (scCO₂) was used. Mass transfer rates of the dissolution of a rod consisting of stearic acid in scCO₂ were studied as a model system. A new experimental approach was employed for measuring mass transfer coefficients under well-controlled conditions of 150–350 bar, 40–50 °C, and 30–70 g/min flow rates. In obtaining diffusivities, reliability was maintained by means of the Stokes-Einstein relation, while inconsistency in published available solubility data resulted in uncertainty in interpreting results. Therefore, additional research is required to arrive at reliable data on the solubility of stearic acid in scCO₂. Despite this, the dissolution behaviour could be well correlated by a Sherwood-Reynolds-Schmidt relation of the form Sℎ = c₁Re^0.62Sc^1/3 where c₁ varies from 0.24 to 0.87 depending on the used solubility model. The findings provide an experimental technique for the determination and characterization of mass transfer in systems with supercritical fluids and more specifically scCO₂. Also, there is a need for more accurate solubility data to optimize correlation parameters and improve process design in supercritical fluid extraction technologies.