Page 288 - Chiral Separation Techniques
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10.4 Example of process design 267
The total number of plates (N) required can easily be obtained based on the
knowledge of the selectivity α = K /K : about 100 plates are required for large
B/A B A
selectivities (greater than 2) and abut 600 plates are required for small selectivities
(about 1.1–1.2). Typical values of 200–400 plates allow high purity with significant
productivity for intermediate selectivity.
10.3.2.3 Step C: Calculation of SMB
Using SMB flowrates simply derived from those of the TMB, the SMB behavior is
simulated according to the number of columns and equivalent number of plates per
column. The SMB raffinate, extract, and eluent flowrates are identical to those of the
TMB feed. The SMB recycling flowrate Q (zone I) is given by:
R
ε
Q = Q + ⋅ Q (20)
l
R
1 − ε
Moreover, the shift period is derived from:
∆T = (1 − V ⋅ ) ε col (21)
Q
where V is the volume of a single column.
col
All of the flow rates as well as the shift period are known. The remaining param-
eters to be determined are:
Number of columns: the number of columns and equivalent number of plates per
column are determined in order to obtain the expected purities and yield. For a
first estimation, choose total number of 8 columns, that is to say 2 columns per
zone, and use the number plates proposed in the TMB calculation.
Column length and diameter: these are set according to the minimum number
of plates required and the maximum acceptable pressure-drop, and calculated by
taking into account the constraints given by the Van Deemter and Darcy’s laws.
10.4 Example of process design
10.4.1 Manufacture of Enantiopure Drug Substances
In order to illustrate an example of process design for the manufacture of enantio-
pure drug substances on an industrial SMB system, consider manufacturing 10 ton/
year of an enantiopure drug. The racemic drug by definition is a 50:50 mixture of
each enantiomer (products A and B). The goal is to process enantiopure drug sub-
stances in order to obtain 99 % purity for both the extract and the raffinate.
