In the previous paper

a new plate-to-plate method was successfully used by the proper selection of iterative variables for performance prediction of ideal systems. In the present paper

similar method is used for calculating extractive distillation processes. The mole fraction of solvent in the bottom product XEB

as well as mole fraction ratios of components to be seperated on various plates vijs are selected as iteractive variables. An outer loop iteration and an inner loop iteration are involved in. The outer loop iteration is for the solvent. The mole fraction of solvent is calculated from the bottom upward and is matched at the top; XEB is then relaxed with the match tolerance. The inner loop iteration is for the components to be seperated. The subsequent set of vijs is calculated using the program proposed in the previous paper with ralative volatilities αijs obtained from the stagewise calculation. The inner loop iteration is carried out with fixed αijs and much less computer time is needed. The outer-loop consists of a single strong loop together with a number of comparatively insignificant ones. Therefore

this multivariable system is transferred into a single variable like system as mentioned in the previous paper.