Page 159 - Chiral Separation Techniques

5.2 Chiral Membranes 137

Fig. 5-7. Cascade configuration for the
separation of a racemic mixture into a top
and bottom concentration of X[N] and
X[1], respectively [55].

found, a large number of stages is required, leading to a substantial membrane area.
The possibility to make membranes of opposite chirality, e.g. by using the MIP tech-
nique, allows for the use of membranes of alternating chirality. According to the
analysis described above, the required membrane surface area can then effectively
be lowered by approximately 25 %. Generally, it can be concluded that the large
number of (independent) stages required, resulting from low selectivities, in combi-
nation with low permeabilities leading to a large membrane area, are currently pro-
hibitive for application of enantioselective membranes on an industrial scale. Obvi-
ously, there is a need for increased selectivities at higher permeabilities, which
clearly will not be an easy task to perform.

Fig. 5-8. McCabe–Thiele diagram for α<1. The curved line is the selectivity curve.