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A generalized empirical correlation has been proposed to predict physical properties of pure hydrocarbons and undefined petroleum fractions. Properties such as critical temperature (Tc), critical pressure (Pc), critical volume (Vc), molecular weight (M), normal boiling point (Tb), specific gravity (£>), refractive index (n), carbon-to-hydrogen weight ratio (CH), and heat of vaporization ( ) may be predicted from any pair of available characterizing parameters (Tb, S), (Tb, ), (Tb, CH), ( , S), ( , ), (M, CH), (vlt S), ( I), or (v1, CH) as input parameters. Proposed correlations are generally superior or at least equivalent to the existing correlations and are applicable in the molecular weight range 70-300 and normal boiling point range 80-650 °F.

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A simple and generalized correlation in terms of viscosity and molar density is proposed to estimate diffusion coefficients for hydrocarbon systems. The correlation can be used for both gases and liquids up to a pressure of about 400 bar (6000 psia). It has been shown that the proposed method may also be used to estimate effective diffusion coefficients in multicomponent systems with a reasonable degree of accuracy. Although the proposed correlation is based on experimental data in hydrocarbon systems, preliminary evaluations have shown that it is also satisfactory for nonhydrocarbon systems as well. The proposed equation predicts diffusion coefficients in gases with an absolute average deviation of 8% and in liquid systems with an absolute average deviation of 15%. The input parameters for the correlation are molecular weight, critical properties, and acentric factor of components in the system; mixture molar density; low-pressure gas viscosity; and actual viscosity. The last three properties may be predicted from appropriate correlations.

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Different sets of correlations for prediction of composition of petroleum fractions and coal liquids in terms of readily available parameters are proposed. Paraffinic, naphthenic, and aromatic portions of olefin-free fractions can be predicted from the knowledge of either specific gravity, refractive index, and viscosity or molecular weight, refractive index, and carbon to hydrogen weight ratio. The proposed correlations may be used for fractions with molecular weights of 70-600. For coal liquids or highly aromatic fractions, correlations in terms of molecular weight, refractive index, and density are proposed to predict monoaromatic and polyaromatic portions of the fraction. These correlations are applicable to fractions with molecular weights up to 250.Petroleum fractions are mixtures of different hydrocarbons from different homologous groups. When the pseudocompound method is used for prediction of thermophysical properties of undefined petroleum fractions (Huang and Daubert 1974;Riazi, 1979), knowledge of the paraffin, olefin, naphthene, and aromatic content of the fraction is necessary. However, most petroleum fractions for which data on their composition are available are free from olefins, and most coal liquids are highly aromatic (80-90% aromatic).