Chemistry Reference
In-Depth Information
INTRINSICALLY
ENANTISELECTIVE MEMBRANE
(Chiral separation)
ENANTIOCATALYTIC
MEMBRANE REACTOR
(Kinetic resolution)
ORGANIC PHASE
AQUEOUS PHASE
ORGANIC PHASE
AQUEOUS PHASE
(
R,S
)-RCOOR
1
(
R,S
)-RCOOR
1
E
N
Z
Y
M
E
E
N
Z
Y
M
E
E
N
Z
Y
M
E
E
N
Z
Y
M
E
E
N
Z
Y
M
E
E
N
Z
Y
M
E
Enzyme
H
2
O
(R)-RCOOR
1
(R)-RCOOR
1
(S)-RCOOR
1
(S)-RCOOR
1
(S)-RCOOH
(S)-RCOOH
(S)-RCOOR
1
(S)-RCOOR
1
(S)-RCOOH
(S)-RCOOH
+
R
1
OH
+
+
R
1
OH
+
(R)-RCOOR
1
(R)-RCOOR
1
Enantioselective
membrane
Enantiocatalytic
membrane
Figure 12.3 Schematic configuration of membrane technologies used to produce enantiomers.
two different compartments. The biocatalyst (lipase) is heterogenized on polyacrilonitrile
(PAN) hollow-fibre membranes through entrapment. The reactant is fed into the solvent,
while the product is extracted into the water from the other side of the membrane.
An improvement on the multiphase membrane reactor system using heterogenized lipase
for enantiomer separation is the emulsion enzyme membrane reactor. In this system the
organic water interface at the membrane level is obtained by immobilizing an oil-in-water
emulsion produced through membrane emulsification on the biocatalytic membrane. In this
way, each poreworks as amicroreactor containing immobilized enzyme [58]. By this process
the selectivity and productivity of the biocatalytic system are significantly improved.
A further improvement was developed by Giorno et al. [59], in which enantioselective
particles were produced through a membrane emulsification process. In these particles, oil-
in-water emulsions were stabilized using lipase heterogenized at the interface between the
oil and water. The biocatalyst in the original application had the action of both the emulsion
stabilizer and the enantioselective catalyst.
Other examples of membrane bioreactors used for enantiomer separation are given in
Table 12.13.
As previously described, the other method for enantiomer separation is based on a physical
stereoselectivity by an enantioselective membrane. In order to carry out optical resolution,
the membrane must contain a chiral environment in its structure. The production of a
polymeric membrane with intrinsic enantioselective properties can be prepared for by using
chiral polymers [1] or by chiral modification of achiral porous membranes using chiral
selectorsofnatural (proteins, oligosaccarides, polysaccarides, antibiotics, etc.), semisynthetic
(modified oligosaccarides, modified polysaccarides, polysaccaharide sulfates, etc.) or syn-
thetic (helical synthetic polymers, etc.) origin [70]. Some examples of recent and innovative
works on the development of enantioselective membranes are given in Table 12.14.
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