Liquid–liquid extraction and air stripping in membrane contactor: application to aroma compounds recovery

This work focuses on a non-destructive process for recovering valuable aromatic fractions from odorous industry aqueous effluent. Non-dispersive extraction of ten selected aroma compound was carried out on very diluted model aqueous solutions, using membrane contactors, in two configurations: liquid–liquid and liquid–gas. Mass transfers from water to n-hexane, from water to miglyol (two solvents widely used in aromatic industry) and from water to air were studied using a cross-flow designed hollow fibre membrane contactor. The influence of physico-chemical properties of the aroma compounds and the influence of the solvent viscosity on mass transfer are discussed. Moreover, a resistance-in-series model has been applied and allowed to predict the mass transfer intensity in agreement with experimental values whatever the separation principle, liquid–liquid or liquid–gas.

Membrane contactors for aroma compounds extraction from an aqueous solution was performed using different stripping phase (organic phases and 10–1 gas phase). The controlling step of the mass transfer depends on the properties of aroma compounds, and on the stripping phase. For hydrophobic compounds or high volatile aroma compound (liquid–liquid partition coefficient >10 or gas– liquid partition coefficient ≥10–2) and low viscous stripping phase, the operation is limited by diffusion from the bulk aqueous feed phase to the membrane. Hence, it would be interesting to study other module configurations in order to improve hydrodynamic conditions in the feed phase. The air membrane stripping shows two main advantages compared with liquid–liquid membrane extraction: it provides a solvent free extract and a high selectivity of mass transfer.