(737g) Resolution of Conglomerates Using Preferential Crystallization and Enzymatic Racemization

Producing pure enantiomers is of great interest to pharmaceutical and fine chemicals industries, since these molecules interact differently with living organisms. Preferential crystallization (PC) is an important resolution technique to purify enantiomers. Nonetheless the separation can only reach maximum 50% yield. The addition of racemization of the non-desired enantiomer increases the theoretical process yield to 100%. Free and immobilized enzymes are attractive catalysts for this recycling step coupled with chiral separation processes. In this contribution, the separation of a model conglomerate forming system was investigated experimentally and the results were evaluated using a shortcut mathematical model for the coupling of enzymatic racemization with PC.

The amino acid racemase used was overproduced in bacteria and purified using affinity chromatography. The kinetic properties of the enzyme were investigated in preliminary studies. Low enantiomeric excesses produced by PC generate low driving forces for the racemization. This causes severe requirements related to the enzyme dosage. The optimal immobilization conditions were established to enable reuse of the catalyst and its easy separation from the products. Besides performing systematic experiments, a simple consistent mathematical model was developed assuming a lumped crystallization mechanism. The effective growth rate and the racemase kinetics were used to simulate the process combination. The performance of the biocatalyst was evaluated for the proposed application based on the experimental and simulated results.