COLLOIDAL FORCES IN WATER-IN-DILUTED-BITUMEN EMULSIONS

摘要

In the oil sands industry, undesirable water-in-diluted-bitumen emulsions are often formed during the bitumen recovery process where water is used to liberate bitumen from sand grains. Most of the water is separated from the diluted-bitumen except for a small percentage (about 1-2 %) that remains in diluted bitumen as micron sized droplets. The stability of such water-in-diluted-bitumen emulsions depends, among other things, on the thin film of diluted-bitumen between two approaching water droplets. The properties of such films, including the colloidal forces acting within the film, can be studied using a modification of the Thin Liquid Film-Pressure Balance Technique. In this technique, a single microscopic thin film of diluted bitumen is formed within an aqueous environment. The model water/diluted-bitumen/water film is very similar to the films formed between two approaching water droplets within an emulsion. Microinterferometry is used to measure various parameters of this model film, such as film thickness, film drainage rate, and disjoining pressure-thickness isotherms. A key finding of this study has been obtained from measurements of the disjoining pressure-thickness isotherms. The isotherms provide information about the colloidal forces acting within the film (and the emulsion) and the structure of the molecules at the diluted-bitumen/water interface. Results indicate that a phase-like transition occurs at the diluted-bitumen/water interface as the ratio of solvent to bitumen is increased. This phase transition is clearly related to the stability of the water/diluted-bitumen/water films. The current study also focused on the contribution of heptane-precipitated asphaltenes to the colloidal forces acting within the film.