Intermolecular potential combining rules utilizing corresponding states correlations for pure substances having nonspherical molecules

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Virginia Polytechnic Institute and State University


Second virial coefficient data for many pure substances with both spherical and nonspherical molecules are used to determine the characteristic parameters of two different three-parameter potential functions. Parameters for the rectangular well potential function and a new function, called the r⁻⁶ potential, are calculated from the data by means of a nonlinear, least squares curve fitting technique. Correlations are given for the potential parameters of each substance in terms of its critical temperature, critical volume, and acentric factor. The accuracy of these correlations is near to that of the Pitzer and Curl equations.

The three-parameter correlations for pure substances are used in a new set of combining rules for calculating interaction potential parameters of mixtures, The new combining rules obtained represent empirical correlations of potential parameters calculated from interaction second virial coefficient data for mixtures. The potential parameters calculated from the new rules are compared with those obtained from the data as well as those calculated from other combining rules now being used. The combining rules presented in this work give much improved results for mixtures involving substances with nonspherical molecules.