Theoretical Approach to the Stability of Visbroken Residues

A theoretical method to calculate solubility parameter distributions was used to study the main factors that affect the stability of residues and products of their visbreaking with respect to asphaltene deposition. With this method it was possible to analyze the changes observed on the solubility parameter distributions of asphaltenes due to visbreaking. The results obtained showed a decrease in easily soluble asphaltenes, while there is an increase in difficult-to-dissolve asphaltenes during processing. To evaluate the instability, a compatibility index between asphaltenes and resins/or aromatics is proposed using the theoretical solubility profiles. By use of this index, it was possible to identify the factors involved in instability and to establish their relative importance for each sample. Among all the factors studied, the characteristics of the asphaltene fraction seem to be the main one. For the group of fractions examined, it was found that the average solubility parameter calculated was directly proportional to the H/C atomic ratio.