This paper is focused on using molecular simulation as a tool to guide the choice of desorbent for the separation propane/propylene by simulated moving bed (SMB) processes. Equilibrium adsorption isotherms of n-butane and neopentane on zeolite 13X and adsorption equilibria of binary mixtures of each one of these adsorbates with propane and with propylene were obtained by molecular simulation, in a predictive screening of an adequate desorbent for the separation of propane/propylene by the SMB technology. Comparisons of experimental isotherms with grand canonical Monte Carlo simulations in zeolite 13X showed that the results of n-butane are in excellent agreement with reported simulations and experimental data. The carbon cation interactions for the quaternary carbon atom of neopentane were established and validated through determination of adsorption properties of binary mixtures of neopentane with propane and with propylene. The lack of experimental data of neopentane adsorption motivated the present study, providing the opportunity to predict the single adsorption isotherms over a temperature range from 273 to 423 K and pressures up to 150 kPa. From the simulated isotherms of neopentane in 13X zeolite, the isosteric heat of adsorption of 39.19 kJ/mol was calculated by using the Clausius-Clapeyron equation, in close agreement with the published value of 41.7 kJ/mol. Additionally, the simulation results of the binary mixtures with propane and with propylene showed that neopentane and propane have similar affinities to the adsorbent, which indicates a less favorable desorption effect for neopentane, compared with that of n-butane.