The surface tension of heavy oil and its temperature dependence were measured by the pendant drop method under atmospheric pressure in the temperature range of 30 to 250 °C. The surface tension was determined by fitting the numerical solution of the Young-Laplace equation to the image of a droplet hanging at the tip of a 1/16" stainless steel tube. The distillates and residues fractionated by vacuum distillation of atmospheric residue and bitumen were used as samples. The surface tensions of all samples decreased linearly with temperature. The fractionation of samples by column chromatography revealed that the samples, which were poor in saturates and rich in aromatics, had higher surface tension. In addition, a model on the basis of the principle of corresponding states was used to predict the surface tension of heavy oil. It was demonstrated that the model was capable of predicting the surface tension of the distillates with good accuracy, but it was insufficient to predict the surface tension of residue.
In this work, a new method of predicting the surface tension of heavy oils and its temperature dependence was developed. The surface tensions of five fractions and residue fractionated by the vacuum distillation of atmospheric residue (AR), and AR itself were predicted, based on a detailed composition and molecular structure analysis, i.e., "petroleomics". In this method, the chemical compositions and molecular structures of compounds included in the fractions and residue were identified by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and then the critical pressure, critical temperature and boiling point of each compound were calculated by the group contribution method. Next, using the calculated properties, the surface tension of each compound was predicted by the principle of corresponding states. Finally, a mixing rule, in which the surface tension of mixtures was expressed as a linear function of mole fraction of each compound, was used to predict the surface tensions of the five fractions and residue of AR and AR itself. By comparing the predicted and experimental values of the surface tensions and their temperature dependence, it was found that the present method is useful for predicting the surface tension of heavy oils.
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