In this paper, a concept to identify the adsorption isotherm of Simulated Moving Bed processes online during the operation is proposed. The influence of model parameters on the measurements is analyzed by a sensitivity analysis which enables to identify the set of parameters that can be estimated simultaneously. The parameters are estimated in real-time by a moving horizon state and parameter estimation scheme. Numerical simulations of validated models for separation problems with nonlinear isotherms of Langmuir type are presented. Furthermore, it is it shown that a structural plant/model mismatch in the void fraction can be compensated to a large extent by modifying the Henry coefficients of the adsorption isotherm such that the estimated model can be used in the context of online optimizing control. (C) 2010 Elsevier Ltd. All rights reserved.