Effect of dilution ratio on amount of asphaltenes separated from stock tank oil

We have investigated the effect of n-alkane dilution on the amount of asphaltene separated from stock tank oil. Asphaltenes were produced from three different oils by mixing each oil with varying amounts of n-alkanes, including n-pentane, n-hexane, and n-heptane. The n-alkane: oil ratio ranged from 1:1 to 1000:1. With increasing n-alkane:oil ratio, the amount of separated asphaltene initially increased, passed through a maximum, then decreased gradually with further dilution. The maximum occurred at an n-alkane:oil ratio of around 30:1 to 40:1 for n-hexane and n-heptane, and 80:1 for n-pentane. A two-component thermodynamic model based on Flory-Huggins theory was adapted to match the observed trend of produced asphaltene by assuming a polydisperse model of the asphaltene fraction.