The main purpose of this study is the optimization of the operating mode for cryogenic distillation columns that provide an isotopic enrichment in stable isotopes. The analysis is based on an experimental cycle for C-13 enrichment by CO cryogenic distillation conducted in semi-batch mode in the column of the National Institute for Research and Development of Isotopic and Molecular Technologies. The experimental run is reproduced closely using the simulation software ProSim-BatchColumn, applied for the first time to this type of separations. It is, then, used to investigate the dynamics of the process and the effect of the feed flowrate on the separation to be achieved. As a result, an optimized cycle is proposed, which allows reaching the desired specifications in around one-third the time. The obtained results are interesting and can be applied to all the mixtures where heavy components have a higher commercial value than the light ones. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.