Continuous chromatographic separation through simulated moving beds under linear and nonlinear conditions

Simulated Moving Bed (SMB) technology is receiving more and more attention as a convenient technique for the production scale continuous chromatographic separation of fine chemicals. Thanks to the efficient simulated countercurrent contact between the stationary and the fluid phase, SMB units can operate under high productivity overload conditions. These lead to nonlinear competitive adsorption behavior, which has to be accounted for when designing and optimising new SMB separations. The so called 'Triangle Theory', which is briefly revised here, provides explicit criteria for the choice of the operating conditions of SMB units to achieve the prescribed separation of a mixture characterized by Langmuir, modified Langmuir and bi-langmuir isotherms. In all these cases, the effect of increasing nonlinearity of the separation, due to increased feed concentration can be predicted. in this paper, the use of this approach for the design of linear and nonlinear SMBs is considered, with reference to examples reported previously. Alternative strategies have been proposed in the literature, which are based on the use of safety factors for linear systems and on an adaptation of this for nonlinear ones. In the cases considered, which involve experimental data for a linear system and numerical experiments for a nonlinear Langmuir system, it is shown that 'Triangle Theory' allows attainment of a better understanding of and a deeper insight into the behavior of SMB units. (C) 1998 Elsevier Science B.V. All rights reserved.