DETERMINATION OF BINARY PARAMETERS OF AN EQUATION OF STATE FROM METHANOL PLUS N-ALKANE VAPOR-LIQUID-EQUILIBRIUM DATA ENSURING THERMODYNAMICSTABILITY OF THE CALCULATED LIQUID-PHASE

The false liquid-liquid splits that often occur when modelling polar-n onpolar binary mixtures can be avoided in most cases by either includi ng upper critical solution points (UCSPs) in the fit, or by using a co nstrained fit. Including UCSPs in the fit gives a better control of ho w the region of false liquid-liquid splits is shifted including a corr ect pressure dependence if UCSPs are known at more than one pressure. A constrained fit can only guarantee that the region of false liquid-l iquid splits is shifted away from the region of the experimental VLE d ata. When there are more than one parameter in the mixing rule, two co nstraints are needed to avoid oscillations in the numerical process. A voiding instability leads to a worse fit of the VLE data. The methods are illustrated on fits of five mixtures of methanol + n-alkane using the Patel-Teja EOS with association, and on predictions of one ternary mixture.