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    Problematic Stabilizing Films in Petroleum Emulsions: Shear Rheological Response of Viscoelastic Asphaltene Films and the Effect on Drop Coalescence

    Year: 2014

    Journal: Langmuir, 2014, 30 (23), pp 6730–6738, 20141006

    Authors: David Harbottle †, Qian Chen ‡, Krishna Moorthy †,Louxiang Wang †, Shengming Xu ‡, Qingxia Liu †,Johan Sjoblom §, and Zhenghe Xu †‡

    Last authors: Zhenghe Xu

    Organizations: † Department of Chemical and Materials Engineering,University of Alberta, Edmonton, Alberta Canada T6G 2V4 ‡ Institute of Nuclear and New Energy Technology,Tsinghua University, Beijing, P. R. China 1000084 § Ugelstad Laboratory, Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway

    Country: Canada, China, Norway

    Adsorption of asphaltenes at the water–oil interface contributes to the stability of petroleum emulsions by forming a networked film that can hinder drop–drop coalescence. The interfacial microstructure can either be liquid-like or solid-like, depending on (i) initial bulk concentration of asphaltenes, (ii) interfacial aging time, and (iii) solvent aromaticity. Two techniques—interfacial shear rheology and integrated thin film drainage apparatus—provided equivalent interface aging conditions, enabling direct correlation of the interfacial rheology and droplet stability. The shear rheological properties of the asphaltene film were found to be critical to the stability of contacting drops. With a viscous dominant interfacial microstructure, the coalescence time for two drops in intimate contact was rapid, on the order of seconds. However, as the elastic contribution develops and the film microstructure begins to be dominated by elasticity, the two drops in contact do not coalescence. Such step-change transition in coalescence is thought to be related to the high shear yield stress (∼104 Pa), which is a function of the film shear yield point and the film thickness (as measured by quartz crystal microbalance), and the increased elastic stiffness of the film that prevents mobility and rupture of the asphaltene film, which when in a solid-like state provides an energy barrier against drop coalescence.