FEASIBILITY OF SEPARATIONS FOR DISTILLATION OF NONIDEAL TERNARY MIXTURES

The product compositions in single-feed distillation columns can be sp ecified only in certain regions of the composition space, which depend only on the pressure, feed, and vapor-liquid equilibrium for the mixt ure. In nonideal mixtures, even without azeotropes, the regions may al low unusual product distributions. For example, the distillate in a '' direct split '' is composed primarily of the lightest component. Intui tion and experience with relatively ideal mixtures suggest that the ne xt most plentiful component is the intermediate boiler. In nonideal mi xtures, however, with or without azeotropes, the next most plentiful c omponent may be the highest-boiling species with only trace amounts of the intermediate boiler. For azeotropic mixtures, distillation bounda ries may give rise to additional restrictions on the product compositi ons. We describe how simple distillation boundaries deform into contin uous distillation boundaries and, in a limited number of cases, how th e simple distillation boundaries can be crossed in continuous columns for certain ranges of the design variables. Unfortunately, such design s may be quite sensitive to model uncertainties or to disturbances in the parameters.