Phase behavior of the ternary system carbon dioxide + toluene + asphaltene

The effect of carbon dioxide on the phase behavior of a model oil and, in particular, on asphaltene precipitation has been studied in this work. A mixture of toluene and asphaltene with a constant asphaltene mass fraction of 0.0034 on a CO2-free basis was chosen as the model oil. The asphaltene was extracted from a crude oil. The phase transitions from liquid–vapor to liquid and from solid–liquid–vapor to liquid–vapor were determined in the temperature range from 295 K to 365 K and in a pressure range from atmospheric pressure to 7 MPa with the so-called synthetic method. Thereby, different amounts of carbon dioxide were added to the model oil. It was found that the temperature and the CO2 concentration affect the stability of the asphaltene containing model oil solution. If the CO2 concentration is higher than 10 mass%, precipitation of asphaltene occurs.