Crossover SAFT equation of state: Application for normal alkanes

In this paper we develop a crossover modification of the statistical associ ating fluid theory (SAFT) equation of state for macromolecular chain fluids which incorporates the scaling laws asymptotically close to the critical p oint and. is transformed into the original classical SAFT equation of state far away from the critical point. A comparison is made with experimental d ata for pure methane, ethane, n-hexane, n-decane, and n-eicosane in the one - and two-phase regions. We also present comparisons with experimental sing le-phase data for n-triacontane and n-tetracontane. We show that, over a wi de range of states, the crossover SAFT model yields a much better represent ation of the thermodynamic properties of pure fluids than the original SAFT equation of state, The crossover SAFT equation of state reproduces the sat urated pressure data in the entire temperature range from the triple point to the critical temperature with an average absolute deviation (AAD) of abo ut 3.8%, the saturated liquid densities with an AAD of about 1.5%, and the saturated vapor densities with an AAD of about 3.4%. In the one-phase regio n, the crossover SAFT equation represents the experimental values of pressu re in the critical region with an AAD of about 2.9% in the region bounded b y 0.05 rho(c) less than or equal to rho less than or equal to 2.5 rho(c) an d T-c less than or equal to T less than or equal to 2T(c), and the liquid d ensity data with an AAD of about 3% at the pressures up to P = 2000 bar. Fo r the n-alkanes CmH2m+2 with the molecular weight M-w > 142 (m > 10), the c rossover SAFT model contains no adjustable parameters and can be used for t he pure prediction of the fluid thermodynamic surface.