A thermodynamic analysis based on the second law of thermodynamics has been applied to the separation of binary and ternary systems by continuous distillation. Previously developed analytical solution of groups (ASOG) group contribution methods were used for estimating phase equilibria and liquid-phase excess enthalpy and excess entropy. Thermodynamic efficiency of the distillation processes was studied as a function of reflux ratio. An incorporation of a heat recovery system was also tested. In the studied cases, a heat recovery system showed almost no effect on the thermodynamic efficiency of the processes. A maximum of the thermodynamic efficiency was observed at the minimum reflux ratio.