Mass transfer enhancement in supercritical fluid extraction by acoustic waves

A computational fluid dynamics model of extraction of a solute (caffeine) from a porous solid matrix (coffee beans) using a supercritical solvent (carbon dioxide) is developed. Supercritical fluid extraction of a solute from a solid matrix is a slow process even when solute free solvent is circulated. The use of acoustic waves represents a potential efficient way of enhancing mass transfer processes. The effect of acoustically excited flows on supercritical fluid extraction from a porous solid matrix is investigated. The mathematical model considers diffusion-controlled regime in the porous solid matrix and convective-diffusive transport in the bulk fluid. Henryʹs law is used to describe the equilibrium states of the solid and the fluid phases. Accurate representation of the thermo-physical properties of supercritical solvent is considered by using the NIST Standard Reference Database 12. The conservation equations for mass, momentum, energy and species are numerically solved using implicit finite volume method. The effect of process parameters, such as initial state (pressure and temperature) of solvent and acoustic waves on the yield of solute extraction is also investigated numerically.