Innovative density measurement techniques for vacuum residues of crude oil and their fractions using toluene dilution

Abstract

The growing availability of vacuum residues has provoked the development of studies that may improve refining processes to increase capacity conversion. Therefore, conducting a detailed analysis on the trend of the physicochemical properties of representative fractions is necessary. In this work, a set of vacuum residues were fractionated using n-hexane as a supercritical fluid and the molecular distillation process. The results show that the increase in density, micro-carbon content and molecular weight in the extractable fractions is associated with their SARA compositional. As a result, density determination for these extractable fractions by standard methodologies, such as ASTM D70, has shown limitations for samples with densities higher than 1.0879 g/ml. To measure the density of vacuum residues and their fractions, a density dilution methodology was conducted, using toluene as a solvent. In this study, 87 fractions obtained from different vacuum residues and processed with n-hexane and molecular distillation were selected. The proposed dilution methodology allows measuring densities with repeatability and reproducibility values of 0.0031 and 0.0061 g/g/ml, respectively. The average boiling point (Tb50) of vacuum residues and their fractions was correlated with density and molecular weight, to estimate their quality. The correlations of density and average boiling point properties Tb50 exhibited R2 correlation coefficients of 0.9949 and 0.9908 with P values less than 0.0031. The values of these statistical parameters show that the developed correlations have a confidence level of 95%.