IMPROVED MODELING OF THE PHASE-BEHAVIOR OF ASYMMETRIC HYDROCARBON MIXTURES WITH THE PENG-ROBINSON EQUATION OF STATE USING A DIFFERENT TEMPERATURE DEPENDENCY OF THE PARAMETER A

In this paper, for phase equilibrium calculations in asymmetric hydroc arbon mixtures the influence of the temperature dependency of the attr active parameter, alpha(T), in the Peng-Robinson equation of state is discussed. All systems studied contain methane at supercritical condit ions and a heavy hydrocarbon, namely, decane, hexadecane, tetracosane, 1-phenyldodecane, phenanthrene, and 5-alpha-cholestane. The Peng-Robi nson equation of state with the classical quadratic mixing rules is co mbined with eight different alpha functions. Next to the alpha functio ns taken from the literature also a correlation of alpha values optimi zed to IUPAC recommended fugacities of supercritical methane (T = 250- 500 K) is applied. The superior performance of the proposed correlatio n is most evident when all interaction coefficients are set to zero. T his is partly compensated by the use of interaction coefficients. Neve rtheless, it is shown that also when k(ij) is optimized to vapor-liqui d equilibrium (VLE) data or k(ij) and l(ij) are optimized to VLE and s olid-liquid equilibrium (SLE) data, the proposed correlation still per forms better than the other alpha functions.