7. Conclusions

Separation of a non-ideal A-B mixture usually requires the addition of a carrier E to the feed (azeotropic distillation) or continuously (extractive distillation). In order to increase the driving force of the separation, the selectivity of the carrier must be as far away from 1 as possible. It is evaluated by the ratio of the activity coefficients or relative volatilities of A and B at infinite dilution in E, ${\gamma }_A^{\infty }/{\gamma }_B^{\infty }$ or preferably ${\alpha }_{AE}^{\infty }/{\alpha }_{BE}^{\infty }$...