Probing the Effect of Salt on Asphaltene Aggregation in Aqueous

Jun 29, 2018 - Abstract | PDF w/ Links | Hi-Res PDF · Effect of CO2 on the Interfacial and Transport Properties of Water/Binary and Asphaltenic Oils: ...
1 downloads 0 Views 952KB Size
Subscriber access provided by UNIVERSITY OF TOLEDO LIBRARIES

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

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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.

ACS Paragon Plus Environment

1

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 30

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.

ACS Paragon Plus Environment

2

Page 3 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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 (