Enantioseparation of d,l-lactic acid by membrane techniques

The d,l-lactic acid resolution was studied in two types of membrane techniques, by supported liquid membrane and by solid chiral membrane, using polypropylene hollow fiber module of effective membrane area of 0.2 m2 and standard pore size of 0.1 μm (Microdyn Modulbau GMBH Wuppertal, Germany). In the latter case, the liquid membrane containing the chiral selector was evaporated from the membrane pores, thus, the selector was deposited as an amorphous, solid layer on the internal membrane surface. The enantioselective transport of d,l-lactic acid from the aqueous feed phase (lumen side) to the stripping bidistilled water (shell side) was facilitated by chiral selector: N-3,5-dinitrobenzoyl-l-alanine octylester. In a series of experiments, the selector dissolved in toluene was supported into the membrane pore as a liquid membrane. Then, alternately, toluene was totally removed and applied for enantioseparation. The liquid membrane system had no enantioselectivity while the solid, chiral membrane, obtained by drying the supported liquid membrane containing the chiral selector, had high selectivity with lower mass transfer rates. Evaluation of the components of the chiral versus achiral physico-chemical effects in the overall mass transport as well as the swelling behavior of the polypropylene fiber is given which have fundamental role in the membrane enantioseparation.