Prediction of molecular-type analysis of petroleum fractions and coal liquids

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 correlatlons 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). The n-d-M method of Van Nes and Van Westen (1951) for estimating the percentage carbon as an aromatic, naphthenic, or paraffinic structure from measured values of density, refractive index, and molecular weight is based on limited and mainly saturated data. Riazi (1979) has shown that the method gives high errors in the prediction of the composition of petroleum fractions. Riazi and Daubert (1980) developed a set of correlations for molecular-type analysis which required viscosity, specific gravity, density, and refractive index as input parameters. The fractions were divided into light (M C 200) and heavy (M > 200) molecular weight ranges, and the correlations were in terms of the refractivity intercept (RI) and viscosity gravity relation (VG). These two characterizing parameters were defined as