Supercritical fluid simulated moving bed chromatography II. Langmuir isotherm

The simulated moving bed (SMB) technology offers the possibility of scaling up single column, batch chromatographic separations to continuous operatio n. This has proved particularly effective for the separation of enantiomers , and has been applied in the liquid and gas phase, as well as using a supe rcritical fluid as eluent (SF-SMB). In the last case, the main performance improvements are due to the possibility of tuning the elution strength of t he mobile phase, by changing the pressure in the four sections of the SMB u nit. Thus a SF-SMB can be operated in two modes, i.e. the isocratic and the pressure gradient mode. In this research, design criteria for these two op erating modes have been developed, which can be applied to systems describe d by linear as well as nonlinear Langmuir adsorption isotherms. The role an d effect of an appropriate modifier in increasing solubility and reducing r etention times have been investigated. The results reported allow to identi fy the operating conditions, including the pressure levels and the modifier concentration, which lead to optimal separation performance in terms of pr oductivity and desorbent requirement. (C) 2001 Elsevier Science BN. All rig hts reserved.