抄録
The simultaneous optical resolution by cooling crystallization using seed crystals of different two size groups was examined. It was proved as a useful method of optical resolution by crystallization. In this study, DL-asparagine (Asn) was used as a model substance. Seeded cooling crystallization was performed with the L-Asn seeds of large size and the D-Asn seeds of small size. Both seeds were added enough over the critical seed loading ratio, which was determined for a given seed size by using a correlation proposed previously for non-chiral systems (Doki, et al. 2002). The product crystals obtained had bi-modal distribution without fines. The large crystals were L-Asn of 100% purity and the small crystals were D-Asn of 100% purity. These results suggested that nucleation was suppressed by the addition of seeds and the crystallization was dominated by the growth of seed crystals. The size difference between the L- and D-products was also controllable. The optical resolution was accomplished by subsequent mechanical classification of crystals after crystallization. The simultaneous optical resolution was also examined for the case of insufficient seeding. In this case, fines removal by a dissolving circuit attached to the crystallizer was effective for perfect optical resolution. Further, the phenomena were discussed quantitatively in detail.
