Modelling and experimental evaluation of reaction kinetics in reactive extraction for chiral separation of amines, amino acids and amino-alcohols

This paper reports on determination of the intrinsic reaction kinetics in reactive extraction of chiral compounds. It is important to know the mass transfer rates and reaction kinetics separately for a reliable scale-up. A kinetic model is developed to interpret the experimental data from the selected model reactor, the modified Lewis cell. The two-phase homogeneous reaction model was selected over the interfacial reaction model, because physical partitioning is considerable in all systems studied. It was shown by simulations and by theoretical considerations that conventional regime analysis fails for reactive extraction in a number of regimes, because the conditions of an irreversible reaction and a negligible resistance to mass transfer in the non-reactive phase are generally not fulfilled in reactive extraction. Furthermore, it follows from the simulations that enhancement of mass transfer by reaction may be partly invisible. Finally, it becomes clear that only the fraction of the species that is in the fight 'extractable' form should be used in the calculations. As the conventional regime analysis cannot be applied to determine the reaction kinetics in the chiral systems, first the mass transfer rate was measured during physical extraction to determine the location of the main resistance to mass transfer. Then the enhancement of mass transfer was measured during reactive extraction. By model simulation, it was determined how much enhancement of mass transfer should be observable. In this way, it was concluded that the reaction kinetics of the azophenolic crown ether system are between fast and instantaneous, and the reaction kinetics of the Cu(II)-N-dodecyl-L-hydroxyproline system are between slow and fast. The Lewis cell is not the most suitable model contactor to determine reaction kinetics in reactive extraction systems. (c) 2006 Elsevier Ltd. All rights reserved.