Solubility of asphaltenes samples in polar and apolar synthetic mixtures: experimental and modeling

This work presents a study of the solubility parameter at the onset of asphaltenes precipitation ( δ_crit ) in synthetic mixtures. Therefore, a total of nine solvents were used and two samples of asphaltenes, a “new” asphaltene (NA) and a naturally oxidized asphaltene (NOA) extracted eight years before. NOA mixtures showed greater δ_crit values when compared to mixtures using the same asphaltene in previous studies, indicating an oxidation effect on this asphaltene. It was concluded that there is a tendency towards a universal δ_crit for unaged Brazilian asphaltenes equal to 16.80 MPa^1/2 , which shows that the validity of δ_crit is wider and is less impacted by the solvents used. It was obtained δ_crit = 17.28 ± 0.11 MPa^1/2 for NOA and δ_crit = 16.79 ± 0.10 MPa^1/2 for NA. The Hansen solubility parameter calculated through the Flory–Huggins model corroborates the effect of aging, since the δ_NOA is 33.47 MPa^1/2 and δ_NA is 32.67 MPa^1/2 . The contribution of polar interactions is higher for NOA, which reinforces the expectation of sample oxidation. The study of the fugacity ratio indicates a straightforward application of the model to other asphaltenic systems by changing only its solubility parameter.