Optimal operation of simulated moving-bed units for non-linear chromatographic separations - II. Bi-Langmuir isotherm

Several important theoretical results have been previously obtained to predict the behaviour of continuous chromatographic separation units in the case of Langmuirian type of isotherms. Concerning separation of binary mixtures in a non-adsorbable carrier with SMB units, stoichiometric and non-stoichiometric Langmuir and modified Langmuir have been considered in the frame of equilibrium theory. For these isotherms explicit constraints on the operating parameters have been found to achieve complete separation (M. Mazzotti, G. Storti, M. Morbidelli, J. Chromatogr. A 769 (1997) 3; M. Mazzotti, G. Storti, M. Morbidelli, AIChE J, 42 (1996) 2784; M. Mazzotti, M. Pedeferri, M. Morbidelli, in: Chiral Europe '96 Symposium, Spring Innovations Limited, Stockport, UK, 1996); the design of the SMB unit was then reduced to the analysis of the so-called region of complete separation for the operating parameters. In this paper, the same result is presented for the bi-Langmuir case, which can avoid the constant selectivity limit of the Langmuir isotherms. Langmuir and bi-langmuir isotherms fitting the same set of data taken from the literature were then used here to show the difference in the prediction of the region of complete separation. Finally an analysis of non-linearity effects on performance parameters is presented as a useful criterion for optimization of the separation performances. (C) 1998 Elsevier Science B.V.