Article pubs.acs.org/EF
Probing the Effect of Side-Chain Length on the Aggregation of a Model Asphaltene Using Molecular Dynamics Simulations Cuiying Jian, Tian Tang,* and Subir Bhattacharjee Department of Mechanical Engineering, University of Alberta, Edmonton, AB T6G 2G8, Canada S Supporting Information *
ABSTRACT: A series of molecular dynamics simulations were performed to investigate the effect of aliphatic side-chain length on the aggregation behavior of a model asphaltene in water. We found that the extent of aggregation has a nonmonotonic relationship with the side-chain length. Asphaltene molecules with very short or very long side chains can form dense aggregates, whereas those with intermediate chain lengths cannot. Through analysis of the kinetics and driving forces of the aggregation, the role of the side chains in affecting the aggregation behavior was elucidated. Long side chains hinder the formation of parallel stacking structures of the polyaromatic cores while also favoring aggregation through hydrophobic association. The simulation results reported here can be used to propose appropriate means to reduce the extent of aggregation of asphaltene in the presence of water.
1. INTRODUCTION Asphaltenes, which are the heaviest fraction of crude oil and are classified as a complex mixture of heavy organic molecules, have drawn great interest because of their serious effects on the processing of petroleum resources, from clogging pipelines to reducing oil recovery.1,2 Most of these problems can be attributed to the aggregation and precipitation behavior of asphaltenes,3,4 which have been widely observed in experimental studies. For example, vapor pressure osmometry,5,6 interfacial tension measurements,6 small-angle X-ray scattering,7 small-angle neutron scattering,5,8 calorimetric titration,9 photon correlation spectroscopy,10 and nuclear magnetic resonance spectroscopy11,12 have all shown the aggregation of asphaltenes. A wide range of experimental studies have been shown13 to be consistent with the Yen−Mullins model.14,15 According to this model,13 in organic solvents and at sufficient concentration, asphaltene molecules form nanaoaggregates with aggregation numbers of
