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 (delta(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 delta(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 delta(crit) for unaged Brazilian asphaltenes equal to 16.80 MPa1/2, which shows that the validity of knt is wider and is less impacted by the solvents used. It was obtained delta(crit )= 17.28 +/- 0.11 MPa1/2 for NOA and delta(crit) = 16.79 +/- 0.10 MPa1/2 for NA. The Hansen solubility parameter calculated through the Flory-Huggins model corroborates the effect of aging, since the delta(NOA) is 33.47 MPa1/2 and delta(NA) is 32.67 MPa1/2. 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.