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.