Fluid Phase Equilibria, 60 (1990) 261-271 Elsevier Science Publishers B.V., Amsterdam ON THE APPLICATION OF CUBIC EQUATIONS OF STATE TO SYNTHETIC HIGH-PRESSURE VLE MEASUREMENTS G. SOAVE Eniricerche SpA, 20097 San Donato Milanese (Italy) M. FERMEGLIA Istituto di Chimica Applicata e Industriale, Uniuersita'di Trieste, 34127 Trieste (Italy) (Received December 5, 1989; accepted in final form May 22,7990) ABSTRACT Soave, G. and Fermeglia, M., 1990. On the application of cubic equations of state to synthetic high-pressure VLE measurements. Fluid Phase Equilibria, 60: 261-217. A procedure is proposed for the accurate estimation of the compositions of vapour and liquid phases in an equilibrium cell from a knowledge of the weight and composition of the feed and the volume of the vapour phase. A cubic equation of state (van der Waals or Redlich-Kwong), modified according to Peneloux, is applied. The pure component parameters are determined from vapour pressure and liquid density values. A single binary constant is determined by imposing the value of the vapour phase volume within the cell. The accuracy of the calculated phase compositions is higher than or comparable to the values obtained by chromatographic analysis, with the advantage of a smaller experimental effort. INTRODUCTION Synthetic methods have been widely used for the experimental determina- tion of equilibrium phase compositions (Deiters and Schneider, 1986). Different apparatuses have been developed in the last few years (Fornari et al., 1990), showing a renewed interest in this experimental method. The basic idea of the method is that no sampling is necessary of either liquid or vapour phases; their compositions are calculated by a material balance, provided that the vapour volume is known and a reasonable model for the vapour phase is available. Consequently, the method is particularly suitable for measuring VLE data in those cases where sampling is the main source of inaccuracy, namely at elevated pressure, near the critical condi- tions and for complex multiphase systems. 0378-3812 /90/$03.50 o 1990 - Elsevier Science Publishers B.V. 261