Settling of Asphaltene Aggregates in n-Alkane Diluted Bitumen

The settling rate of asphaltene aggregates is a key design parameter for partial deasphalting processes and yet few data and models are available for these systems. The settling rates of asphaltene aggregates were measured in two Western Canadian bitumens diluted with n-heptane or n-pentane at 21°C and atmospheric pressure. The density and viscosity of the mixtures, the size distributions of the aggregates, and the fractal dimensions of the aggregates were also measured. The asphaltene aggregates settled as a zone; that is, all aggregates settled at the same rate. The settling rates increased with increasing n-alkane content, reached a maximum at approximately 75 wt% n-alkane and then decreased at higher dilutions. The maximum settling rate corresponded to the maximum aggregate diameter and fractal dimension. The maximum settling rate in n-pentane diluted bitumen was two orders of magnitude greater than in the same bitumen diluted with n-heptane. The difference was attributed to the lower density and visc...