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Applicability of the Langmuir Equation of State for Asphaltene Adsorption at the Oil–Water Interface: Coal-Derived, Petroleum, and Synthetic Asphaltenes
journal contribution
posted on 2015-12-17, 08:29 authored by Jayant
P. Rane, Sharli Zarkar, Vincent Pauchard, Oliver C. Mullins, Dane Christie, A. Ballard Andrews, Andrew E. Pomerantz, Sanjoy BanerjeeIn recent studies of asphaltenes
from the Norwegian continental
shelf at water–oil interfaces, adsorption from largely aliphatic
oils appeared to be governed at early times by molecular diffusion
and at later times by molecular random sequential adsorption. In addition,
the interfacial tension of asphaltenes at the oil–water interface
was a a unique function of interfacial coverage, and no apparent rearrangement
of asphaltenes at the interface was observed within an experimental
time frame of up to 12 h. Confirmation of this result was obtained
by showing that high frequency elasticity is a unique function of
asphaltene interfacial tension. Both interfacial tension versus coverage
and elasticity versus interfacial tension data have been successfully
captured by the Langmuir Equation of State (EoS), which also allows
estimates of the sizes of the asphaltene polyaromatic cores to be
made. The value obtained in experiments with asphaltenes from a Norwegian
crude oil is 0.32 nm2/molecule, which corresponds to an
average size of ∼6.2 ring polyaromatic core resting flat on
the oil–water interface, which is supported by estimates made
by other means. In the current study, we provide further investigation
of these findings. UG8 asphaltenes, which have been well-studied previously,
show interfacial behavior similar to the asphaltenes from the Norwegian
oil. Experiments with coal-derived asphaltenes, which are known to
have smaller cores, and model asphaltenes, with a larger cores, both
confirm the applicability of the Langmuir EoS to fit the interfacial
tension data and enable estimates of the polyaromatic core sizes from
tensiometric measurements.