In several industrial fields, the
existence of chiral molecules
causes challenges when only one enantiomer is the desired active ingredient
in the final product. The separation of pairs of enantiomers can be
achieved with different techniques. Once these enantiomers crystallize
as conglomerates, preferential crystallization (PC) is a very attractive
alternative. So far, various batchwise operating strategies have been
developed and applied successfully. Very likely, however, it can be
more beneficial to use PC in a continuous manner, since continuous
processes can often outrun their batch counterpart in terms of productivity,
product quality, and process complexity. In this contribution, chiral
separation is investigated and performed in a continuous manner adapting
the concept of mixed-suspension mixed-product-removal (MSMPR) to the
requirements of preferential crystallization. Continuous PC could
be realized successfully in two different experimental setups involving
only one MSMPR crystallizer and two MSMPR crystallizers coupled via
an exchange of their liquid phases. For the model system d-/l-threonine/water, this first experimental demonstration
of the concept proves that the process can continuously separate enantiomers
with purities >99%. The agreement of the experimental results with
results of process simulation indicates the strength and usefulness
of a previously published mathematical model.
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