In our previous study, ethylcellulose (EC), an effective, nontoxic, and biodegradable natural polymer, was found effective in dewatering water-in-diluted bitumen emulsions. In this study, the demulsification mechanism of water-in-diluted bitumen emulsions by EC is investigated. In situ experiments using a micropipet apparatus provided direct evidence on both flocculation and coalescence of water droplets in diluted bitumen by EC. The addition of EC was found to decrease naphtha-diluted bitumen-water interfacial tension significantly. At the molecular level, AFM imaging revealed disruption of the continuous interfacial films formed from surface-active components of bitumen by EC. Our study clearly indicates that the demulsification by EC is through both flocculation and coalescence of water droplets, attained by competitive adsorption of EC at the oil-water interface and disruption of the original protective interfacial films formed from the surface-active components of bitumen.
The need for alkaline conditions in oil sands processing is, in part, to produce natural surfactants from bitumen. Previous studies have shown that the produced surfactants are primarily carboxylic salts of naphthenic acids with the possibility of sulfonic salts as well. The role of these natural surfactants, particularly those in the naphthenate class, is to provide a physicochemical basis for several subprocesses in bitumen extraction. In this study, it was found that the content of indigenous naphthenic acids in bitumen can destabilize, to some extent, the water-in-oil emulsion by lowering the interfacial tension, reducing the rigidity and promoting the coalescence of water droplets.
Role of bitumen components in stabilization of water-in-diluted oil emulsions was studied using the micropipette technique. Naturally occurring components of bitumen, asphaltenes and maltenes were separated (by precipitating asphaltenes with n-pentane) to investigate their influence on the properties of water drop surfaces in Heptol (a mixture of heptane and toluene at a 4:1 volume ratio). The Heptol-water interfacial tension decreased with increasing adsorption of surface active components from both asphaltenes and maltenes. Rigidity of emulsified water droplet surfaces was observed in the presence of asphaltenes dissolved in Heptol. The observed surface crumpling is attributed to the irreversible adsorption of asphaltenes on the emulsified water droplet in Heptol. Further, the results of droplet interaction experiments indicated that the stability of the water-in-diluted oil emulsions was mainly due to the presence of asphaltenes dissolved in Heptol. However, it was observed that the presence of maltenes can also contribute to the emulsion stability even without welldefined skin formation on the emulsified water droplet surfaces.
Obstacle avoidance systems for autonomous driving vehicles have significant effects on driving safety. The performance of an obstacle avoidance system is affected by the obstacle avoidance path planning approach. To design an obstacle avoidance path planning method, firstly, by analyzing the obstacle avoidance behavior of a human driver, a safety model of obstacle avoidance is constructed. Then, based on the safety model, the artificial potential field method is improved and the repulsive field range of obstacles are rebuilt. Finally, based on the improved artificial potential field, a collision-free path for autonomous driving vehicles is generated. To verify the performance of the proposed algorithm, co-simulation and real vehicle tests are carried out. Results show that the generated path satisfies the constraints of roads, dynamics, and kinematics. The real time performance, effectiveness, and feasibility of the proposed path planning approach for obstacle avoidance scenarios are also verified.
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