Size and shape of a coal asphaltene studied by viscosity and diffusion coefficient measurements

Hydrodynamic properties, such as intrinsic viscosity and diffusivity, were measured to investigate the solution state characteristics of coal-derived materials in three organic solvents: toluene, pyridine, and N-methyl-2-pyrolidinone. A coal-derived asphaltene was prepared using coal liquefaction residue and was used as the solute. The translational diffusion coefficient of the coal-derived asphaltene was determined using the Taylor dispersion technique. The sphere equivalent hydrodynamic radius of the coal asphaltene was estimated to be 0.6–0.8 nm, depending on the solvent. The combined intrinsic viscosity and diffusion coefficient data suggest that the shape of coal asphaltene can be modeled as a prolate ellipsoid.