A unified method is developed for the designing preparative chromatographic processes of various types. The method allows, for example, generalizing the established triangle theory of counter-current simulated moving bed technique for other single and multi-column chromatographic schemes including (1) classical batch chromatography, (2) mixed-recycle steady state recycling chromatography, (3) cross-current chromatography, and (4) mixed-recycle cross-current recycling chromatography. The approach allows direct prediction of the range of feasible dimensionless operating parameters that lead to complete separation of a binary feed mixture. By using the equilibrium theory of chromatography, explicit design equations are derived for systems that follow linear or competitive Langmuir isotherm model. It is shown that under ideal conditions the boundaries of the dimensionless operating parameters are identical for all studied process concepts, except for the upper limit of a parameter that is related to the regeneration of the fluid phase in the case of Langmuir isotherm. The practical relevance of the unified design method is demonstrated with numerical simulations, It is shown that even under non-ideal conditions the counter-current SMB can be designed with good accuracy based on a single pulse injection to a batch Column, especially for relatively low purity requirements. (C) 2014 Elsevier Ltd. All rights reserved.