非表示:
キーワード:
-
要旨:
Organic molecules which are interesting for the pharmaceutical, food and agricultural industry often are chiral. The well known fact is that usually only one of the enantiomers shows the desired properties [1, 2]. In recent years, besides the most commonly used classical resolution via formation of diastereomers, direct crystallization methods have become increasingly important. An attractive process is enantioselective preferential crystallization [3, 4]. In a batch crystallizer conglomerate forming systems tend to reach an equilibrium state in solution in which the liquid phase will have racemic composition and the solid phase will consist of a mixture of crystals of both enantiomers. However, before approaching this state, it is possible to preferentially produce just one of the enantiomers after seeding with homochiral crystals. Perfectly mixed batch crystallizers, typically used for preferential crystallization, can be described mathematically in a simplified manner using a dynamic, one dimensional model which includes experimentally determined kinetic parameters. As a model the threonine-H2O system [4, 5] has been taken into consideration. Based on the simplified approach a more attractive and effective operation mode using two batch crystallizers coupled via liquid phase [6] has been studied (see Fig. 1). In each vessel one of both enantiomers is seeded and grows subsequently. An exchange of the crystal free liquid phases between the crystallizers leads to an increase of driving forces and process productivity. The influence of important process variables like enantiomeric excess, initial seed size distribution, exchange flow rate between crystallizers, and temperature has been analyzed theoretically. As an example the influence of mass of seeds on the productivity and product quality is shown in Fig. 2. It is obvious that by increasing the mass of seeds added to each vessel smaller particles can be achieved. This phenomenon may be explained due to higher nucleation rates at the beginning of the process which restricts the growth of seeded crystals. Nevertheless, such a performance of the process can lead to higher total mass of the final product and obviously to higher process productivity. Theoretical studies have shown that optimal process variables are forced by desired product properties. Parallel to the theoretical analysis, an experimental validation of this process is currently performed and results will be also given in this presentation.
[1] Collins, A.N., Sheldrake, G.N., Crosby, J. (1994): Chirality in Industry: The Commercial Manufacture and Applications of Optically Active Compounds, John Wiley & Sons
[2] Collins, A.N., Sheldrake, G.N., Crosby, J. (1997): Chirality in Industry II: Developments in the Manufacture and Applications of Optically Active Compounds, John Wiley & Sons
[3] Jacques, J.; Collet, A.; Wilen, S.H. (1994): Enantiomers, racemates and resolutions, Krieger, Malabar
[4] Elsner, M.P., Fernández Menéndez, D., Alonso Muslera, E., Seidel-Morgenstern, A. (2005): Experimental study and simplified mathematical description of preferential crystallization, Chirality 17 (S1), S183-S195
[5] Lorenz, H., Perlberg, A., Sapoundjiev, D., Elsner, M.P., Seidel-Morgenstern, A., (2006) Crystalization of enantiomers, Chemical Engineering and Processing, Chem. Eng. and Proc., doi, 10.1016/ j. cep. 2005.11.013
[6] Ziomek, G., Elsner, M.P. Seidel-Morgenstern, A., Analysis and optimization of different configurations for preferential crystallization, AIChE Annual Meeting Cincinnati 2006.
