Premium
On the interpretation of viscosity data of suspensions of asphaltene nano‐aggregates
Author(s) -
Pal Rajinder,
Vargas Francisco
Publication year - 2014
Publication title -
the canadian journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.404
H-Index - 67
eISSN - 1939-019X
pISSN - 0008-4034
DOI - 10.1002/cjce.21896
Subject(s) - asphaltene , viscosity , volume fraction , solvation , thermodynamics , relative viscosity , atomic packing factor , particle (ecology) , volume (thermodynamics) , chemistry , work (physics) , fraction (chemistry) , materials science , chromatography , organic chemistry , molecule , physics , crystallography , geology , oceanography
The viscous behaviour of suspensions of asphaltene nano‐aggregates is often described in terms of the Pal and Rhodes model (Pal, Rhodes, J. Rheol . 1989 , 33, 1021). The model assumes particles to be spherical in shape and takes into account the solvation or hydration of particles. However, the solvation coefficient estimated from the Pal and Rhodes model for asphaltene particles is generally too high to be realistic. Furthermore, the model does not consider the packing limitations (maximum packing volume fraction) of the asphaltene particles. A large body (14 sets) of the available viscosity data for asphaltene suspensions are reinterpreted in terms of the Krieger–Dougherty model. The data analysis indicates that asphaltene nano‐aggregates are non‐spherical disk‐shaped particles with low aspect ratio (ratio of particle thickness to particles diameter). The aspect ratio depends on the nature of the asphaltene/oil system. For a given system, it increases with the increase in the temperature. Interestingly, the maximum packing volume fraction ( φ m ) of asphaltene particles is found to be nearly constant ( φ m ≈ 0.37 ) , independent of the nature of the asphaltene/oil system and temperature. Also the values of φ m predicted from the viscosity data are in reasonable agreement with the values predicted from a percolation model. Based on the analysis carried out in this work, the following model is proposed for accurate estimation and correlation of the viscosity of asphaltene suspensions: η r = [1 − ( φ /0.37)] −0.37[ η ] , where η r is the relative viscosity, [ η ] is the intrinsic viscosity and φ is the volume fraction of asphaltene particles.