Recovery of sulfur aroma compounds using membrane-based solvent extraction

This work focuses on a non-destructive process for recovering valuable aromatic fractions from the food industry's odorous wastewaters. Non-dispersive solvent extraction of three sulfur aroma compounds, dimethyldisulfide, dimethyltrisulfide and S-methyl thiobutanoate, was carried out from very diluted aqueous solutions representing real effluent. The mass transfer from water to n-hexane was studied using a cross-flow designed hollow fiber membrane contactor. A preliminary study showed high affinity of solutes for n-hexane, with constant partition coefficients at infinite dilution between water and hexane in a 90-560 range. The influence of tube and shell side hydrodynamics on mass transfer was studied, with the aqueous phase on the tube side, and the organic phase on the shell side. The diffusion of solutes from the bulk aqueous phase to the aqueous-organic interface controlled the separation and contributed, under the conditions tested, to more than 97% of the overall mass transfer resistance. A resistance-in-series model overestimated overall mass transfer coefficients. The main explanation is the inaccuracy of the Leveque correlation used at low Reynolds numbers. The choice of a correlation for predicting mass transfers in the solvent phase did not affect the estimation, since the corresponding mass transfer resistance was negligible. Mass transfer fluxes obtained experimentally by membrane-based solvent extraction were greater for the three aroma compounds than those obtained by pervaporation. (C) 2001 Elsevier Science B.V. All rights reserved.