MEMBRANE-BASED SOLVENT-EXTRACTION AND STRIPPING OF LACTATE IN HOLLOW-FIBER CONTACTORS

This work reports lactate extraction with Aliquat 336, an ion-exchange carrier, using membrane contactors with hydrophobic microporous membr anes. The overall mass-transfer coefficients were evaluated by either assuming a constant distribution coefficient or using the equilibrium equation. The mass-transfer coefficients calculated using the equilibr ium relationship between C-f and C-0, proved to be more rigorous, sin ce the variation of the distribution coefficient with solute concentra tion is accounted for throughout the extraction process. Assuming the resistance in series model, the membrane resistance was identified as the limiting step on the mass-transfer process. In order to increase t he membrane mass-transfer coefficient, it is necessary to increase the diffusion coefficient of the lactate-amine complex; this can be achie ved by reducing the viscosity of the organic phase either through a te mperature increase or reduction of the carrier concentration. Using a plate-and-frame module with a well-defined hydrodynamic characterizati on of both phases, the mass-transfer coefficients can be rigorously ev aluated; these were compared with the values obtained with hollow-fibr e modules. Simultaneous extraction and stripping of lactate was accomp lished using two hollow-fibre modules in series. This configuration as sures that saturation of the carrier does not occur, as it is permanen tly regenerated; furthermore, the carrier concentration can be reduced while still maintaining the mass-transfer rate, thus decreasing the a ssociated operating costs of the process.