EFFECT OF SOLVENT DEASPHALTING PROCESS ON THE PROPERTIES OF DEASPHALTED OIL AND ASPHALTENES FROM BITUMEN

Abstract

Asphaltenes are a solubility class of bitumen known to have undesirable properties. As asphaltenes are insoluble in paraffinic solvents, they can be separated from bitumen by adding a solvent such as n-pentane or n-heptane to produce better quality deasphalted oil (DAO). This process is called Solvent Deasphalting (SDA). Several methods of SDA are reported in literature. The solvent, solvent to bitumen (S/B) ratio, precipitation time, temperature and pressure affect the yield and properties of asphaltenes. The objective of this work is to study the effect of solvent, S/B ratio and precipitation time in the SDA process on the properties of asphaltenes and DAO. Characterization of asphaltenes and DAO produced at different conditions of the SDA process could help in predicting how the SDA process affects the thermal cracking process and downstream processes. Experiments were performed using Canadian oil sands bitumen from Athabasca region. n-pentane, n-hexane and n-heptane were used as solvents at S/B ratios 3:1, 4:1, 5:1 and 40:1 (ml/g), and the effect of changing precipitation time from the most commonly used 24h, to longer time (330h), was also studied. All the experiments were performed at room temperature and atmospheric pressure. The solvent and S/B ratio were found to affect the yield and the following characteristics of asphaltenes and DAO: hydrogen to carbon ratio, heteroatoms (N, S), metal content (Ni, V), distillation curve, micro carbon residue, free radical content, liquefying point and refractive index. The separation selectivity and extractability of components from bitumen into asphaltenes and DAO respectively, change with solvent and S/B ratio in the SDA process. These process variables also impact the thermal cracking behavior of asphaltenes and DAO. The change in precipitation time from 24h to 330h in the SDA process did not significantly affect the boiling point distribution and micro carbon residue of asphaltenes and DAO. This work could be extended to the temperatures and pressures used in the industrial process of solvent deasphalting, and to a wider range of solvents with different structural aspects.