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A new vapor pressure model containing one parameter is presented. The vapor pressure curves of all hydrocarbons that may contain heteroatoms merge together at a common point. Thus, the vapor pressure curve can be predicted using one known data point. If no data are available, the characteristic parameter can be obtained using structural information about the component. Since vapor pressure curves end in their critical points, the equation allows internally consistent prediction of critical pressure from known critical temperature, or vice versa, and for predicting the acentric factor. For calculating the heat of vaporization at any temperature using the Clapeyron equation, knowledge of the nonideal behavior of a component along the vapor pressure curve is needed. The equations presented for this purpose show excellent agreement for all components for which experimental data have been found.

The main objective of this article is to provide a model for predicting critical properties of heavy and nonboiling hydrocarbon fractions. For this purpose, the methods available today are discussed. The procedures for application to complex mixtures are of empirical nature, and most of them are limited to distillates.The detailed information required for application of group contribution methods is usually not available for complex heavy mixtures. A new procedure is presented which takes up the concept of group contributions. The critical properties are predicted on the basis of the molecular weight and the double-bond equivalent (DBE). Since the DBE can be calculated from molecular weight and elemental composition, even nonboiling fractions can be characterized. The exactness of the model depends on the available analytical information.

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