Study of Solvent−Bitumen−Water Rag Layers

Abstract

A major operational issue in the crude oil industry is the formation of intermediate rag layers, (primarily water-in-oil emulsions) in oil−water separation processes that limit the amount and quality of recoverable oil. In this study, the formation of rag layers is evaluated as a function of solvent−bitumen−water ratios, solvent aromaticity, and temperature, with various imaging techniques. Using these techniques, it is possible to obtain an estimate of the amount of oil, water, and asphalthenes in the rag layer and excess phases. On the basis of these material balances, it was observed that when bitumen is diluted with a more paraffinic (poor) solvent, such as Heptol 80/20 (80% heptane and 20% toluene), the asphaltenes in solution tend to adsorb/segregate at exposed oil−water interfaces, impacting the extent of rag layer formation. Diluting similar systems with a more aromatic solvent (Heptol 50/50) reduces the surface activity of the asphaltenes, and the stability of rag layers, as evidenced by lower asphaltene and oil losses to the rag layer. Furthermore, it was observed that increasing the temperature of the system minimizes rag layer formation and the fraction of oil lost to the rag layer. The better separation at high temperature could be explained by the lower viscosity of the oil, which results in improved oil drainage from the rag layer.

Problematic Stabilizing Films in Petroleum Emulsions: Shear Rheological Response of Viscoelastic Asphaltene Films and the Effect on Drop Coalescence

“…In the worst case the presence of this densely packed layer can completely stop the oil-water separation process. 6,15 The rheological study of interfacial asphaltene films by harmonic volume oscillations of a pendant drop has shown that the dilatational elasticity dominates the interfacial microstructure with only a small viscous contribution. 16,17,18 Such rheological characteristic has been observed over a wide range of asphaltene concentrations and extensive aging time, with emulsion stability at equivalent asphaltene concentrations being qualitatively linked to rheological properties of the interfacial film.…”

Role of Caustic Addition in Bitumen–Clay Interactions

“…13 The attached clays to the bitumen surface can also cause problems in bitumen froth treatment by forming a rag layer. [14][15][16] The mechanism for bitumen slime coating has recently been studied in detail by Masliyah et al using atomic force microscopy (AFM) and zeta potential distribution measurement. 12,[17][18][19][20][21][22][23] While oil sands ores are a complex mixture of clays including kaolinite, illite, chlorite, montmorillonite, not all the clays cause slime coating.…”

Understanding Mechanisms of Asphaltene Adsorption from Organic Solvent on Mica

“…[14][15][16][17][18][19][20] In oil production, the formation of a complex multiphase dispersion layer in the middle of oil-water separation vessel, known as rag layers, is frequently encountered. 21,22 The rag layers are extremely stable multiemulsions with the stabilizing species identified as surfactants, asphaltenes and inorganic fine particles. The inorganic fine particles are predominantly iron-containing solids that readily associate with organic compounds such as asphaltenes to form biwettable solids which preferentially stabilize w/o emulsions.…”