The CryoCell® CO2 separation process has been developed with a clear understanding of the vapour-liquid-solid thermodynamic equilibrium (VLSE) of the CO2-light hydrocarbon system. State-of-the-art commercial process simulators (such as Aspen HYSYS®) are programmed to handle vapour-liquid equilibrium (VLE) and do not have VLSE flash calculation capabilities. Proprietary multiphase flash prediction software such as STFlash®, developed by Shell Research and Technology Centre, can be used for predicting solid CO2 formation, post isenthalpic expansion temperatures and phase compositions for given CO2 – natural gas mixtures at various conditions.Although STFlash® served as a critical tool in understanding the VLSE process – it is not a process simulator.