Settling Rates of Asphaltenes and Solids from Diluted Bitumen

Abstract

One method to remove fine solids from bitumen prior to transportation is to add a paraffinic solvent to precipitate asphaltenes, which flocculate with the fine solids and enhance the settling rate. The process conditions, solvent type, and ratio of solvent to bitumen must be optimized to achieve practical settling rates while minimizing solvent and bitumen losses. A settling model was developed that requires the size distribution, density, and fractal dimension of the flocculated asphaltene/solids, and the density and viscosity of the fluid as inputs. Settling rates were measured using visual and sampling methods for three diluted bitumen mixtures: n-pentane/WC-B-A3, n-heptane/WC-B-A3 and n-heptane/WC-B-B2. The floc size distributions were measured using micrography and the Focused Beam Reflectance Method. Densities and viscosities were calculated from the component properties. The fractal dimension was determined from sediment volumes. The settling model predicted the settling rates to within 15%, except near the onset of precipitation.