The presented paper addresses the optimization of isothermal preferential crystallization for the separation of pure enantiomers from racemic mixtures. For the optimization, a rigorous process model is used. A sequence of stochastic and deterministic minimization algorithms is applied. The initial values of the mass of the racemate, the mass of the seeds, and the mean seed size are interesting parameters being optimized. The approach is illustrated by a case study for the amino acid L-/D-threonine. A promising cyclic operation mode is discussed. Although the results are not yet validated experimentally, the aim of this work is to increase the applicability of the process.