Hypothetical Thermodynamic Properties: Vapor Pressures and Vaporization Enthalpies of the Even n-Alkanes from C78 to C92 at T=298.15 K by Correlation-Gas Chromatography

The temperature dependence of gas chromatographic retention times of hexaheptacontane to dononacontane is reported. These data are used with a summary of earlier work to evaluate and compare the vaporization enthalpies and vapor pressures of the n-alkanes from T = (298.15 to 540) K for heneicosane to dononacontane. The vapor pressure and vaporization enthalpy results obtained are compared with estimated data from Morgan's "PERT2" extended corresponding states principle (CSP) which uses n-alkane input parameters based on the works of Kudchadker.and Zwolinski and of Tsu. The results are also compared with a model previously developed from empirical. data which predicts that vaporization enthalpies measured at the boiling temperatures should approach a maximum value and then asymptotically approach zero as the chain length approaches infinity. Some curvature in the enthalpy of transfer from the gas chromatographic column to the gas phase, expected to show the same dependence on size, is indeed observed as the number of carbon atoms exceeds 60. The vapor pressure equations generated from the gas chromatographic results are used to predict boiling temperatures. A comparison of these temperatures with those obtained by extrapolation of an empirical fit of experimental boiling temperatures to a hyperbolic function is remarkably good.