Modelling of high-pressure phase equilibria using the Sako-Wu-Prausnitz equation of state - I. Pure-components and heavy n-alkane solutions

A cubic equation of state (EOS) proposed by Sake, Wu and Prausnitz (SWP) [T . Sako, A.H. Wu, J.M. Prausnitz, J. Appl. Polym. Sci. 38 (1989) 1839-1858.] is used to correlate phase equilibria in systems containing small and larg e molecules. Two pure-component parameters are fitted to vapour pressures ( volatile molecules) and to liquid density data (non-volatile molecules and polymers), respectively. New pure-component parameters for nitrogen and a s eries of 1-alkenes are reported. The parameter estimation procedure for pol ymers and polymer-like substances such as heavy n-alkanes is refined. For t his purpose, the repulsion parameter b is refitted to describe the correct slope of the PV-isotherms. This was found to be necessary to improve the ph ase-equilibrium calculations of binary polymer systems. Binary systems of e thylene with heavy alkanes or alkenes and one ternary system (ethylene/eico sane/tetracontane) are investigated. It is shown that one temperature-indep endent binary interaction parameter is sufficient to describe the phase equ ilibrium in these binary systems. The accuracy of the correlation in system s containing a heavy alkane is comparable or better than the results obtain ed from the Peng-Robinson (PR) EOS. (C) 1999 Elsevier Science B.V. All righ ts reserved.