Characterization of Heavy Crude Oils, Their Fractions, and Hydrovisbroken Products by the Asphaltene Solubility Fraction Method
2012
Ovalles, César | Rogel, Estrella | Moir, Mike | Thomas, Lori | Pradhan, Ajit
An improved method for the separation of asphaltene solubility fractions is presented and has been proven useful for the characterization of heavy crude oils and their fractions. Mixtures of heptane, dichloromethane, and methanol are used to obtain four different and well-defined asphaltene fractions with increasing solubility parameter. A good correlation (0.95) is found between the solubility fraction method and the gravimetric asphaltenes for virgin materials. For processed samples, the correlation depends upon the type of conversion process chosen [fluidized catalytic cracking, thermal cracking, or hydroprocessing]. The characterization of asphaltenes by the asphaltene solubility fraction method for a heavy oil feed and its visbroken products indicated that the low solubility parameter asphaltenes are processed first (“easy-to-react”) and then the higher solubility parameter counterparts (“hard-to-process”). Preparative separations and characterization of Mexican vacuum residue asphaltenes and a thermally cracked residue were carried out using an automatic solvent extractor (ASE) apparatus and the same set of solvents as the solubility fraction method. The results indicated that the H/C ratio of the extracted asphaltene fractions decreased and the aromaticity increased with the solubility parameter of the solvent. However, small differences in the distributions of asphaltene fractions were observed and were attributed to the larger precipitant/sample ratio used in the asphaltene solubility fraction method (>50:1) compared to the ASE preparative separation (20:1).
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