(286a) A Continuous Crystallization Process to Separate Mixtures of Enantiomers Exploiting Two Coupled Fluidized Bed Crystallizers

Crystallization is one of the most effective ways to separate mixtures of enantiomers. So far, primarily batch processes are used. In particular, Preferential Crystallization (PC) has proven to be applicable in batch processes to crystallize selectively pure enantiomers from conglomerate forming racemic mixtures [1]. This contribution presents results of applying a fluidized bed crystallizer configuration for continuous PC of pure enantiomers from a racemic mother liquor [2]. To crystallize both enantiomers simultaneously two fluidized bed crystallizers are coupled via their liquid phases. Saturated racemic mother liquor is supplied from a feed tank with a specific flow rate into the bottom sections of the two double jacketed fluidized bed crystallizers. To initiate the crystallization process in both crystallizers seeds of the opposite enantiomers are added. The preferential growth of the seed crystals reduces the supersaturation in both vessels. In order to allow for continuous production of crystals with a defined size, the lower sections of both crystallizers are conical to offer the opportunity of classified product removal at a certain height. The depleted solutions leaving both crystallizers are returned into the feed tank. In this way always racemic solution is supplied to both crystallizers. Nuclei of the counter enantiomer and other small particles, which have a negative effect on the purity of the product, are taken out with the fluid phases at the tops of the two crystallizers and subsequently dissolved in the heated recycle lines. To assure that the process can be continued continuously, larger particles and formed agglomerates are withdrawn at the bottom, crushed and reinjected to provide permanently new seeds. As a proof of feasibility we will describe the set up developed [3] and present experimental results for the separation of the enantiomers of D/L-asparagine monohydrate [4]. The status of theoretically describing the process using detailed [5] and reduced models [6] will be discussed as well as challenges and opportunities for the separation of other chiral substances. The financial support of German Research Foundation (DFG) within the priority program "Dynamic simulation of interconnected solids processes DYNSIM-FP (SPP 1679)" is gratefully acknowledged.

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2. H.-H. Tung, E. L. Paul, M. Midler, J. A. McCauley, Crystallization of Organic Compounds: An Industrial Perspective, Wiley, Hoboken, New Jersey, 2009.

3. D.. Binev, H. Lorenz, A. Seidel-Morgenstern, Chemical Engineering Science 133, 2015, 116.

4. D. Binev, H. Lorenz, A. Seidel-Morgenstern, Crystal Growth & Design, 16, 2016, 1409.

5. K. Kerst, L. Medeiros de Souza, A. Bartz, A. Seidel-Morgenstern, G. Janiga, Computer Aided Chemical Engineering , 2015, 263.

6. M. Mangold, L. Feng, D. Khlopov, S, Palis, P. Benner, D. Binev., A. Seidel-Morgenstern, Journal of Computational and Applied Mathematics 289, 2015, 253.