Hydrodynamic Shape and Size of Khafji Asphaltene in Benzene

Abstract

Three different semiaxes of Khafji asphaltene, assumed to be an ellipsoidal model, were calculated from the viscosity of a benzene solution of the asphaltene and from Harding's relationship between the axial ratio of an ellipsoid and the constant φ in Einstein's viscosity formula. The constant φ for carbon disulfide solution with fullerene showed that Einstein's formula was applicable to the benzene solution. The asphaltene consists of double layers with semiaxes of 31.9, 10.5, and 3.6 Å, leaving out consideration of solvation. The asphaltene, assumed to be solvated by one molecular layer of benzene, consists of triple or quadruple layers. The calculated semiaxes are significantly affected by the solvent thickness as follows: (1) Quadruple layers with the semiaxes a, b, and c of 18.7, 9.0, and 7.2 Å, respectively, at the solvent thickness of 3.2 Å (c only at 3.6 Å). (2) Triple layers with the semiaxes a of 18.3 to 15.0, b of 12.2 to 15.0, and c of 5.4 Å at the solvent thickness range of 3.0 to 3.18 Å. (3) Quadruple layers with the semiaxes a of 17.1 to 15.9, b of 9.8 to 10.5, and c of 7.2 Å at the range of 3.56 to 3.7 Å.