Membrane contactors for the extraction process with subcritical carbon dioxide or propane: Simulation of the influence of operating parameters

This work focuses on the modelling of solvent extraction processes carried out in a hollow fiber membrane contactor (HFC). A mass transfer model with resistances in series has been adapted to deal with a solvent in subcritical conditions. Three kinds of applications have been chosen to test its validity: extraction of acetone from an aqueous solution by subcritical carbon dioxide or propane in a single fiber module, and extraction of caffeine by subcritical carbon dioxide in a three-fiber module. Modifications in membrane characteristics and operating parameters have been investigated in order to estimate optima conditions. Simulations were carried out considering a partition coefficient between the aqueous and extracting solvents greater or smaller than one. In the first case the predominant transfer resistance is placed in the aqueous boundary layer. Simulations show that membrane parameters do not greatly affect the extraction efficiency in this case (only 2% of increase of the extraction efficiency for an increase of inner diameter of the fiber from 250 to 800 μm). In the second case, like for acetone/propane and caffeine/carbon dioxide cases, the resistances in the membrane and in the solvent boundary layer cannot be neglected. In this case, membrane properties have a great effect upon the extraction efficiency (multiplied by 2.7 and 5.5, respectively for acetone/propane and caffeine/carbon dioxide while the porosity to tortuosity ratio ranges from 0.05 to 0.4).