The recovery of bitumen from the Alberta oil sands depends critically on the coalescence of the dispersed oil drops. When suspended in water, the surfaces of the bitumen drops are negatively charged. According to DLVO theory, the resulting diffuse layer repulsion is sufficiently strong to prevent any coalescence of the droplets. From experience, however, it is known that the oil droplets do coalesce, although randomly. Further, the probability of coalescence is seen to increase sharply with increasing drop size. The underlying mechanism of the process appears therefore not to be deterministic; it may, however, be understood through a probabilistic approach. In this presentation, we propose a model of heterogeneous surfaces which considers the bitumen-water interface to be randomly charged. The DLVO theory, according to this model, remains sound - but only on the microscopic scale. With this new approach, we are able to successfully predict the coalescence probabilities in variety of experimental conditions. This research work suggests that the bitumen-water interface is composed of patchy domains with a characteristic size of about 0.6 micrometer.
Payman Esmaeili is doing his PhD in Chemical Engineering under the supervision of Dr Tony Yeung. |
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