Page 295 - Chiral Separation Techniques

274 10 The Use of SMB for the Manufacture of Enantiopure Drug Substances: From …

Calculation of the SMB system: As the enantioselectivity is 1.5, we need
between 200 and 400 theoretical plates in the system with a working pressure of 10
bar. The system constraints are similar to those of the linear system, one has:

L = 1.43 m (8 columns of 18 cm length) u = 0.0064 m s –1

The column diameter is then determined using the mean flow rate in the SMB.

∅= ⋅ 4 Q mean = 016 m
.
π ⋅u
and Equation (21) gives the shift period: ∆T = 0.89 min.

Using simulation software (essentially solving the mass balance equation in the
transitory regime), one can show that the internal profiles of the products in the sys-
tem are given by the profiles presented in Figure 10.8. Samples are taken between
the column at half period.
C (g/L)
6
5

4

3

2
1

0

Eluent Extract Feed Raffinate
Figure 10.8. Internal profile (simulated) obtained for the separation under nonlinear condition.
According to the simulation of the process, the purity of the raffinate product was
98.0 % and the extract was slightly below 97.3 %. These results are quite close to
the target purity of 99 %. To verify these constraints, the operating conditions were
adjusted.

Two possible options allow the increase in purity of the recovered streams:
Increase the number of plates equivalent to the system (adjusting column length,
or fluid velocity).
Increase the shift periods between the different zones (change internal flow rates).