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Fossil Fuels
Probing the Effect of Salt on Asphaltene Aggregation in Aqueous Solutions Using Molecular Dynamics Simulations Xiaoyu Sun, Cuiying Jian, Yingkai He, Hongbo Zeng, and Tian Tang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01191 • Publication Date (Web): 29 Jun 2018 Downloaded from http://pubs.acs.org on June 29, 2018
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Energy & Fuels
Probing the Effect of Salt on Asphaltene Aggregation in Aqueous Solutions Using Molecular Dynamics Simulations Xiaoyu Sun†, Cuiying Jian‡, Yingkai He‡, Hongbo Zeng*,†, Tian Tang*,‡ †
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB T6G
2V4, Canada ‡
Department of Mechanical Engineering, University of Alberta, Edmonton, AB T6G 2V4,
Canada * Corresponding author: E-mail:
[email protected] (H.Z.); Phone: +1-780-492-1044; E-mail:
[email protected] (T.T.); Phone: +1-780-492-5467.
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ABSTRACT The presence of salts in different processes of oil production has attracted wide attention because of its effects on asphaltene aggregation, stability and interactions of emulsions, etc. In this work, molecular dynamics simulations were employed to study the effect of salts on aggregation of model asphaltenes. Four types of polyaromatic compounds possessing key structural features of continental-type asphaltenes were dispersed into NaCl solutions of different concentrations. These models have the same polyaromatic core but different lengths for the side chains. In the two models with relatively long side chains, the hydrophobic association among side chains is the main driving force for aggregation. The effect of salt on aggregation is therefore closely tied to its influence on the hydrophobic interaction: the salt ions promote the hydrophobic interaction at low salt concentration while suppressing it at high salt concentration. For the model with intermediate side chain length, the hydrophobic interaction between side chains becomes less dominant, and the salt has mutual influences on the core-core, chain-chain and core-chain interactions. For the model with the shortest side chains, although the core-core and core-chain interactions are more important, the side chains still play a role in aggregation when the salt is present. Our results provide new insights into the fundamental understanding of the influence of salts on the aggregation and interaction behaviors of polyaromatic compounds in aqueous environment.
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Energy & Fuels
1. INTRODUCTION Asphaltenes are the heaviest components in crude oil.1 Their aggregation and interfacial activities pose serious problems during oil production, such as changing the wettability of oil reservoir, choking the pore throats, and stabilizing the interface between water and oil.2,3,12,4–11 Spontaneous aggregation of asphaltenes is mostly studied in toluene, in which asphaltenes are by definition soluble. It was observed that above the critical nanoaggregate concentration (CNAC), on the order of 100 mg/L, nanoaggregates are formed each containing a small number of molecules (
