No abstract

In this work, we use a molecular based equation of state, the Soft-SAFT equation, to predict complete Joule−Thomson inversion curves for carbon dioxide and the n-alkane series, including heavy n-alkanes up to octatetracontane (n-C48H98). Comparisons with available experimental and correlation data, for carbon dioxide and the lighter n-alkanes, show good quantitative agreement. We observe a strong dependence of the inversion curve on the set of molecular parameters used in the calculations, especially near the inversion point and in the high-temperature region. The equation is able to predict the general trend of inversion curves even for extreme conditions, with reduced pressure, P r = P/P c, values up to 40, and reduced temperatures, T r = T/T c, of almost 5.

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The shape of the Joule-Thomson inversion curve of a fluid at high temperatures is shown to be directly related to its second and third virial coefficients. Experimental values and empirical correlations of the third virial coefficient of carbon dioxide are used to resolve a previously observed conflict between inversion curves obtained from different equations of state for this fluid. In particular, third virial coefficients predicted from the Pitzer-Sterner equation of state are shown to be in error, resulting therefore in an incorrect inversion curve.