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Itis widely recognized by experts that the computer-based designof chemical processes depends strongly on the correlated thermodynamicand transport properties, and the effect of property uncertaintiesshould be incorporated into the design. The most significant sourceof property uncertainties on process design is from the correlationsof phase equilibrium. Many approaches have been proposed, but uncertaintyanalysis is not a routine component of today’s industrial practice,mainly because education and awareness is lacking, and the proposedmethods are difficult to apply. The purpose of this paper is to reporta new approach to uncertainty analysis that is intuitively appealingand easy to apply in process simulation. The proposed approach focuseson activity coefficients and is based upon the simplification that,for the purpose of perturbation, the liquid mixture can be treatedas a set of pseudobinaries described by the Margules equation. Theresulting perturbation in the activity coefficient of component igoes to zero when its mole fraction approaches unity,and also is relatively small when its estimated activity coefficientis close to unity (i.e., near-ideal systems are likely to be modeledmore accurately than highly nonideal systems). In practice, the proposeduncertainty analysis is performed by varying a single parameter foreach component in the mixture. The utility of the proposed uncertaintymethod is demonstrated by application to two problems: (1) a propylene–propanesuperfractionator for which small changes in correlated relative volatilitieshave a large effect on the design of the distillation column, and(2) a dehexanizer column that separates a mixture containing manyclose-boiling components. It is demonstrated that the proposed analysisprovides quantitative insight into the effect of property uncertaintiesand helps to quantify the safety factors that need to be imposed uponthe design. While the proposed method is applied to activity-coefficientmodels, the same idea is applicable to other models such as equationsof state. [ABSTRACT FROM AUTHOR]