Evaluation of different methodologies to determine the n-paraffin distribution of petroleum fractions

Abstract

Petroleum fractions are complex mixtures composed of a large number of components, which makes impossible to obtain their detailed composition and difficult to apply conventional thermodynamic equations to carry out phase equilibrium calculations. Consequently, alternative approaches as the pseudo-component or the continuous thermodynamic methods are used to describe the composition of petroleum mixtures, required as input information for the thermodynamic models.The purpose of this work is to evaluate the capabilities of different experimental techniques to calculate the n-paraffin distribution of petroleum mixtures. A number of petroleum cuts of a paraffinic crude oil were selected and analyzed by High Temperature Gas Chromatography (HTGC), obtaining their n-paraffin distribution by direct integration of the chromatograms. In addition, the n-paraffin distribution was determined from the simulated distillation curves (SDA). Each distillation curve was fitted to a continuous model to obtain the distribution of boiling temperature for each mixture and thereafter, the boiling temperature distribution was converted into composition. Finally, both the n-paraffin distribution and the average molecular weight of the mixture were obtained. Differential Scanning Calorimetry (DSC) was also used in this work to obtain the wax appearance temperature (WAT) and the n-paraffin distribution. The comparison of the n-paraffin distributions obtained by the different techniques shows a reasonable agreement, despite their different approaches.