Mass transfer in hollow fiber membrane contactor extraction using compressed solvents

Ethanol and acetone were extracted from aqueous feed streams (10 wt.% solute) at ambient temperature using compressed propane (34.5 bar) and CO2 (69 bar) in a polypropylene hollow fiber membrane contactor (HFC). Overall mass transfer coefficients were determined and related to tubeside, membrane, and shellside mass transfer by varying the aqueous velocity (0.6–11.8 cm/s) and molar solvent to feed ratio (1 to 3) in countercurrent flow. The overall mass transfer coefficient for ethanol and acetone extraction with compressed propane ranged from 3.8×10−4 to 1.1×10−2 and 1.1×10−4 to 1.7×10−3 cm/s, respectively. For compressed CO2, the overall mass transfer coefficient ranged from 5.1×10−4 to 1.4×10−3 cm/s for ethanol extraction and 4.1×10−4 to 9.5×10−4 cm/s for acetone extraction. Experimentally determined shellside mass transfer coefficients were compared to values predicted by existing correlations for HFC extraction with non-pressurized solvents. Enhanced HFC mass transfer is observed with compressed solvents relative to both conventional liquid HFC extraction and to column extraction with compressed CO2. Our results demonstrate the applicability of compressed hydrocarbons to HFC-based processes, and the ability to analyze compressed solvent-based extraction using conventional HFC techniques.