Mass Transfer Modelling of Sclerocarya Birrea Kernels in Supercritical Carbon Dioxide

Abstract

Experimental data was obtained from literature for the supercritical fluid extraction (SFE) process of Sclerocarya birrera kernel oil in supercritical carbon dioxide (CO2). The external mass transfer, diffusion, and axial dispersion coefficients were determined from the experimental values as well as the Sherwood, Reynolds, and Schmidt dimensionless consortiums. The Reynolds number ranged between 8 to 15, indicating that natural convection occurred. The Sherwood and Schmidt numbers were between 2 to 3.4 and 1.6 to 4. Although the solubility of marula oil decreased with an increase in temperature, its effective diffusivity and external mass transfer coefficient increased. However, the external mass transfer coefficient, diffusion coefficient and axial dispersion coefficient decreased with an increase in pressure due to a decrease in binary diffusivity. Even though the density of the solvent increases with pressure, which results in an increase in the diffusivity of the solute in supercritical CO2, the coefficients however decrease. The amount of extract is also amplified by the increase in solvent power.