Response of oxidized asphaltene aggregations in presence of rejuvenators and characteristics of molecular assembly behavior

Abstract

In this work, a high quantum level of density functional theory (DFT-D) approach and fourier transform infrared spectrum (FTIR) at a micro-level were used to understand one phenomenon: the specific molecular mechanisms responsible for the deagglomeration effect of 10 kinds of representative molecules of bio- and petroleum-based rejuvenators on asphaltene aggregations found in the aged asphalt. The DFT results indicated that the action site of rejuvenators in sulfoxide group (S = O) position was bound stronger than those in carbonyl (C = O) and pyridine nitrogen. Compared with petroleum-based rejuvenators, bio-rejuvenators were responsible for significant contribution to the deagglomeration process when they were adequately inserted into the oxidized asphaltene dimer. Especially, 2-methoxyphenol (phenolic compounds) showed significantly higher efficiency than either of them. The deagglomeration behavior was mainly attributed to a new interaction (hydrogen-bonds of O-H··O/N-H··O and dispersion-attraction) of a series of competing factors between the rejuvenators and the asphaltenes. This polarized the charge distribution throughout the aromatic region of the asphaltene dimer and built up a multi-centered electron density (such as a three-center four-electron H-bond), thus destroying eventual interactions between asphaltene stacks and reducing the extent of clustering of asphaltene units that were intensified during oxidative aging. The FTIR data painted a preliminary picture of the hybrid rejuvenator-asphaltene as aromatic cores with shorter aliphatic side chains and more carbonyl and hydroxyl side groups, and showed the absence of chemical bonding interaction between the rejuvenators and asphaltene nanoclusters.