This paper presents results of a modelling study on the separation of ethane/ethylene mixture by selective adsorption on zeolite 13X in a simulated moving bed (SMB) unit. Propane and n-butane are evaluated as desorbent candidates. The study encompasses molecular simulation calculations for determination of adsorption parameters, whose results will then be used in a mathematical model for evaluating the performance of an SMB unit. This work is entirely done in silico, by using available force field parameters for the molecular simulations part and reliable mathematical models for the SMB part. Experimental data are solely used for comparison with the molecular simulation results, which are subsequently expanded to calculate adsorption properties for separating the mixtures, without further experimental work. The separation regions of an SMB unit operating with zeolite 13X for ethane/ethylene separation, using propane and n-butane as desorbents, were obtained by simulation at 110 kPa and at four different temperatures: 298, 323, 348 and 373 K. For each desorbent, an operating point was selected, and the size of the required unit was presented for the complete separation of the two components of the mixture.