Some Preliminary Results on a Physico-Chemical Characterization of a Hassi Messaoud Petroleum Asphaltene Y. Bouhadda, † D. Bendedouch, † E. Sheu,* ,‡ and A. Krallafa † Laboratoire de Physico-Chimie et de Modelisation, Institut de Chimie Universite ´ d’Oran (Es-Senia), Oran 31000, Algeria, and Vanton Research Laboratory, #7 Olde Creek Place, Lafayette, California 94549 Received October 6, 1999. Revised Manuscript Received January 26, 2000 Viscosimetry, tensiometry, and X-ray diffraction have been employed to determine physico- chemical and structural properties of an Algerian asphaltene in solution. A new viscosity analysis scheme was adopted to extract information about the shape of the asphaltene aggregates, the solvation, and the inter-aggregate interactions. The average molecular weight (MW) was deduced by combining the surface tension and viscosity studies. The average MW of this asphaltene appears to be small in comparison with those measured by vapor pressure osmometry (VPO) but comparable with the recent results from mass spectroscopy, atomic force microscopy, and fluorescent spectroscopy. X-ray measurements show that asphaltene molecules aggregate, even in the neat phase, and an average aggregate is composed of 4-5 aromatic sheets. The viscosity study suggests that asphaltenes in toluene solutions behave in accordance with a spherical micellar model containing aggregated asphaltene molecules with a substantial amount of solvation. Introduction In the past two decades, petroleum asphaltenes have been extensively studied because of their impact on the oil industry. In addition to changing the physical properties, such as density and viscosity of crude oils, it is also responsible for several technical problems commonly encountered during production, recovery, pipeline transportation, and even in refining. 1-8 These problems usually arise from phase separation and/or precipitation of asphaltene, which likely result from its strong self-association propensity. Asphaltene is conventionally defined as the fraction of crude insoluble in low-boiling n-paraffin solvents but soluble in toluene under certain conditions. 8 It is a class of material with varieties of molecular structures, rather than a substance with a well-defined molecular struc- ture. The first hypothetical colloidal structure of as- phaltene dispersions was proposed by Saal and Pfeiffer in the 1940s. 9 Since then, many molecular models have been proposed to describe their physicochemical proper- ties. Among them, the commonly accepted one was proposed by Dickie and Yen. 10-11 They described an asphaltene “particle” as a superposition of many aro- matic sheets containing heteroatoms attached with aliphatic chains. Metals such as iron, vanadium, and nickel under porphyrinic structures are often present as the heteroatoms. 12-13 Other than the molecular structures, the solution behavior appears to be crucial and likely responsible for many practical problems. To reveal microscopically the structural behavior and their relevance to industrial practices, many techniques have been applied to char- acterize these complex molecules, 14-19 as well as their physical and chemical properties in solutions. Through these studies, it gradually becomes clear that the impact of asphaltenes heavily depends on their molecular weight and self-association propensity. It is thus neces- * Corresponding author. † Institut de Chimie Universite ´ d’Oran (Es-Senia). ‡ Vanton Research Laboratory. (1) See, for examples, the chapters in AsphaltenesFundamentals and Applications; Sheu, E. Y.; Mullins, O. C., Eds.; Plenum Press: New York, 1995. (2) See, for examples, the chapters in Structures and Dynamics of Asphaltenes; Mullins, O. C., Sheu, E. Y., Eds.; Plenum Press: New York, 1998. (3) Speight, G. The Chemistry and Technology of Petroleum; Marcel Dekker: New York, 1980. (4) Speight, J. G. Fuel Science and Technology Handbook; Marcel Dekker, New York, 1993; pp 1190. (5) Yen, T. F. In The Future of Heavy Crude and Tar Sands; Meyer, R. F., Steele, C. T., Eds.; McGraw-Hill: New York, 1980; pp 174-179. (6) Hassket, C. E.; Tartera, M. J. Pet. Technol. 1965, April, 387- 391. (7) Tuttle, R. N. J. Pet. Technol. 1983, June, 1192-1196. (8) Aczel, T.; Williams, R. B.; Chamberlain, N. F. Chemistry of Asphaltenes, Advances in Chemistry Series 195; Bunger, J. W., Li, N. C., Eds.; American Chemical Society: Washington, DC, 1981; p 237. (9) Pfeiffer, J. P.; Saal, R. N. J. J. Phys. Chem. 1940, 44, 139. (10) Dickie, J. P.; Yen, T. F. Anal. Chem. 1982, 39 (14), 1487-1852. (11) Erdman, J. G.; Pollak, S. S.; Yen, T. F. Anal. Chem. 1961, 33, 1587-1594. (12) Pearson, C. D.; Green, J. B. Energy Fuels 1993, 7, 338. (13) Freedman, D. A.; Saint Martin, D. C.; Boreham, C. J. Energy Fuels 1993, 7, 194. (14) Brown, J. K.; Ladner, W. L. Fuel 1960, 36, 79. (15) Maekawa, Y.; Yoshida, T.; Yoshida, Y. Fuel 1979, 58, 864. (16) Barron, P. F.; Bendall, M. R.; Armstrong, R. J.; Athkins, A. R. Fuel 1984, 63, 1276. (17) Cookson, D. J.; Smith, B. E. Fuel 1987, 1, 11. (18) Overfield, R. E.; Sheu, E. Y.; Sinha, S. K.; Liang, K. S. Fuel Sci. Technol. Int. 1989, 7, 611. (19) Ravey, J. V.; Decouret, G.; Espinat, D. Fuel 1988, 67, 1560. 845 Energy & Fuels 2000, 14, 845-853 10.1021/ef9902092 CCC: $19.00 © 2000 American Chemical Society Published on Web 05/06/2000