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 hydrocarbon mixtures the influence of the temperature dependency of the attractive parameter, alpha(T), in the Peng-Robinson equation of state is discussed. All systems studied contain methane at supercritical conditions and a heavy hydrocarbon, namely, decane, hexadecane, tetracosane, 1-phenyldodecane, phenanthrene, and 5-alpha-cholestane. The Peng-Robinson equation of state with the classical quadratic mixing rules is combined with eight different alpha functions. Next to the alpha functions taken from the literature also a correlation of alpha values optimized to IUPAC recommended fugacities of supercritical methane (T = 250-500 K) is applied. The superior performance of the proposed correlation is most evident when all interaction coefficients are set to zero. This is partly compensated by the use of interaction coefficients. Nevertheless, it is shown that also when k(ij) is optimized to vapor-liquid equilibrium (VLE) data or k(ij) and l(ij) are optimized to VLE and solid-liquid equilibrium (SLE) data, the proposed correlation still performs better than the other alpha functions.