Rheological studies of Ratawi vacuum residue at 366 K

Ratawi vacuum residue is a typical bottom-of-the-barrel fraction from an asphaltenic sour crude oil, and previous work indicates that Ratawi asphaltenes are typical petroleum asphaltenes. The rheology of Ratawi vacuum residue is analysed in this work by employing theories given by Pal and Rhodes, Eilers, Campbell and Forgacs, and Grimson and Barker to describe the rheology of concentrated suspensions of solid particles. The excellent and self-consistent description provided by these theories shows that Ratawi asphaltenes are a distinct species in vacuum residue. Information about the macrostructure of asphaltenes in their natural environment, the crude oil or residue, is also obtained. Ratawi asphaltenes are solvated spheres of different sizes in the vacuum residue. Their solvated volume is two to three times the dry volume at 366 K. Direct interparticle interactions between solvated asphaltenic particles are weak at 366 K. These forces are repulsive, and account for the stability of Ratawi vacuum residue with respect to asphaltene precipitation. A method of employing the Grimson-Barker theory suggests that the Ratawi asphaltenes are charged. The solvation effect arises because polar molecules in the non-asphaltenic fraction surround the particles and screen the charge.