Determination of solubility of asphaltenes in aromatic solvents

Abstract

Asphaltenes precipitated from curde oil during production, transportation, and the processing process cause serious problems in the petroleum industry. This study focused on determining of solubility of the asphltenes precipitated from eight different crude oils (NM1, NM5, Mesa, Cold Lake, Co1-2, CHA, BRB and Villano Creek) in the mixtures of aromatic/alkane solvents. The effect of temperature on the solubility of NM1 and NM5 asphaltenes and the effect of aging of the crude oil with nitrogen, oxygen and air on the solubility of Cold Lake asphaltene were also investigated. Asphaltene obtained from a stable crude, NM5, had higher solubility values in the aromatic/heptane solvents than the unstable crude, NM1. Moreover, both asphaltenes dissolved better in 1-methyl naphthalene, than in toluene or decalin. Higher temperature resulted in greater solubility of the asphaltenes in aromatic/heptane solvents. Hovever, for small percentages of toluene, 1-methyl naphthalene and decalin in heptane, temperature had no significant effect on the solubility of asphaltenes. On the other hand, temperature had a great effect on the solubility of asphaltenes at high percentages of toluene, 1-methyl naphthalene, and decalin in heptane. Unaged asphaltenes from the Cold Lake reservoir had a slightly greater solubility than asphaltenes aged with nitrogen, oxygen and air. However, there was no significant difference in the dolubility of asphaltenes aged with oxygen and with air in the toluene/heptane solvent. The predicted asphaltene molecular weight could be obtained from the solubility data. The higher the polar freaction of asphltenes, the higher was the predicted molecular weight of asphaltenes.