Page 152 - Chiral Separation Techniques

130 5 Membranes in Chiral Separations

5.2.1.2 Supported Liquid Membranes

In supported liquid membranes, a chiral liquid is immobilized in the pores of a mem-
brane by capillary and interfacial tension forces. The immobilized film can keep
apart two miscible liquids that do not wet the porous membrane. Vaidya et al. [10]
reported the effects of membrane type (structure and wettability) on the stability of
solvents in the pores of the membrane. Examples of chiral separation by a supported
liquid membrane are extraction of chiral ammonium cations by a supported (micro-
porous polypropylene film) membrane [11] and the enantiomeric separation of pro-
pranolol (2) and bupranolol (3) by a nitrate membrane with a N-hexadecyl-L-
hydroxy proline carrier [12].

5.2.1.3 Bulk Liquid Membranes

In the classical set-up of bulk liquid membranes, the membrane phase is a well-
mixed bulk phase instead of an immobilized phase within a pore or film. The prin-
ciple comprises enantioselective extraction from the feed phase to the carrier phase,
and subsequently the carrier releases the enantiomer into the receiving phase. As for-
mation and dissociation of the chiral complex occur at different locations, suitable
conditions for absorption and desorption can be established. In order to allow for
effective mass transport between the different liquid phases involved, hollow fiber