Thermodynamic analysis of thermally coupled distillation sequences

Thermodynamic efficiency calculations have been performed for the separation of ternary and quaternary mixtures of hydrocarbons in both conventional and thermally coupled distillation sequences. When ternary mixtures were considered, energy savings achieved in the thermally coupled distillation sequences were between 10 and 30% in comparison to the two conventional distillation sequences. Regarding thermodynamic efficiency, thermally coupled distillation sequences presented the highest values in almost all of the cases considered. When the analysis was extended to the separation of quaternary mixtures, the thermally coupled distillation sequences show acceptable energy savings and the thermodynamic efficiency of a thermally coupled distillation sequence linked to a side stripper and a side rectifier was better than that obtained in the conventional distillation sequence; however, for the thermally coupled distillation with prefractionator (Petlyuk-type column), the second law efficiency was low when compared to that of the conventional distillation sequence for the separation of a quaternary mixture with a low content of intermediate components.