Beyond the Average Molecule Description of Asphaltenes: Hyphenated Gel Permeation Chromatography and Spectroscopic Analyses

Abstract

A combination of different techniques [gel permeation chromatography (GPC), nuclear magnetic resonance, elemental analysis, etc.] is usually employed to calculate average molecular features of asphaltenes, directly or through application of models. Such an average picture has intrinsic limitations, particularly concerning the distribution of aromatic rings in the molecular structures. To improve the description of asphaltenes beyond the “average molecule” concept, which is quite limiting in the case of products containing such a large distribution of species, a new approach is developed and applied to untreated and hydrotreated asphaltenes. The hydrotreating process was applied here as a tool for simplifying the pristine asphaltene molecules, breaking them into smaller structures, by not only elimination of the alkyl side chains but also transformation of the original building blocks. In this approach, the GPC elution was separated into 1 min fractions along the whole run and the fractions were further analyzed by ultraviolet–visible absorption and fluorescence spectroscopic tools. The combination of these techniques allows for the definition of the contribution of the aromatic cores and the alkyl chains to the molecular weight of asphaltenes during their evolution. In this way, the main structural building blocks of the pristine and hydrotreated asphaltenes were determined and some insights were obtained in the molecular weight evolution.