(163b) The Relationship Between Contact Pressure and Coalescence Time for Water-in-Bitumen Emulsions

After the froth treatment section in the processing of oil sands from Alberta, the product â?? diluted bitumen, still contains about 2 to 3 wt% of water¹. The salts in the residual water have strong implications for bitumen upgradation, including the possibility of corrosion of equipment and poisoning of catalysts, both of which lead to significant downtimes. In the past, coalescence has been evaluated as a strategy to combine the small water droplets with themselves or with bigger water droplets to produce larger drops that can be separated by inclined settling and centrifugation. Unfortunately, these studies have indicated that these water-in-bitumen emulsions are extremely difficult to break^1,2, and ascribe this difficulty to the presence of asphaltenes at the oil-water interface. A review of these studies revealed that there were at least two key deficiencies in these studies. First, very few of these studies were performed under industrially relevant conditions in terms of the weight percent of bitumen and the aromaticity of the diluent. Second, we believe that the contact times and contact forces were not sufficiently high to allow coalescence.

In this work, we have performed experiments with dueling, Hele-Shaw, water drops at the end of micropipettes within a microchannel, contacting them at controlled times and contact pressures. Our modified experimental setup allows us to study the coalescence of water drops in bitumen concentrations between 33 and 67 wt% (a solvent to bitumen ratio ranging between 0.5 to 2, which is close to the industrial operating range). Our investigations show that unlike prior studies, water drops in bitumen do coalesce, but only if the right combination of contact time and contact pressure are provided. The greater the contact pressure, the shorter the coalescence time. At a given contact pressure, the coalescence time increases as the weight percent of bitumen increases, but decreases as the pH of water is increased from 8.3 to 9.9. Empirical correlations are developed for the contact time as a function of the contact pressure for each combination of bitumen concentration and pH. These correlations are used to generate maps of drop radius vs. strain rate, outlining the parameter regimes in which coalescence should be expected in sheared emulsions. The regime of drop radius vs. strain rate for coalescence expands with pH, as expected, but also expands as the bitumen concentration is increased, which is counterintuitive. These aspects will be explained in detail in the presentation.

References

1. F. Rao and Q. Liu, â??Froth Treatment in Athabasca Oil Sands Bitumen Recovery Process: A Reviewâ?, Energy Fuels 27, 7199â??7207 (2013).

2. P. Tchoukov, F. Yang, Z. Xu, T. Dabros, J. Czarnecki, and J. SjoÌ?blom, "Role of Asphaltenes in Stabilizing Thin Liquid Emulsion Filmsâ? , Langmuir 30, 3024â??3033 (2014).