Diastereomeric
crystallization has been used to separate the racemic
mixture of enantiomers of 2-methylbutanoic acid. The enantiomers have
been converted into a pair of diastereomeric salts using optically
pure (R)-(+)-α-methylbenzylamine as a resolving
agent. The mixture obtained formed a solid solution in the crystalline
phase. The solution was further processed by multistage fractional
crystallization where diastereomeric excess of the target derivative
of (S)-(+)-2-methylbutanoic acid was generated in
the solid phase. The process was realized in cross-current and countercurrent
flow systems consisting of batch crystallizers. In both flow modes
all streams were properly synchronized to enable direct connection
of inlets and outlets of subsequent stages, i.e., without intermediate
adjusting of the composition and volume of the solid and liquid phases.
The flow sheets for both operation modes were determined by use of
an optimization routine accounting for yield and purity of the product
as the performance indicators. Additionally, a procedure for recycling
of the postreaction mother liquor has been proposed, which was based
on the synthesis of diastereomeric salts with pure (S)-(−)-α-methylbenzylamine.