Comprehensive characterization of chemical structures in heavy crude oil asphaltenes by using liquid chromatography and ultrahigh-resolution mass spectrometry

Crude oil is known as the main global energy source, however the reserves are limited. As the remaining valuable light oils are diminishing, alternative solutions such as upgrading of high boiling conventional and uncon ventional oil sources such as tar sands and oil shales have to be exploited for replacement to overcome the worlds emerging energy needs. These alternative sources co ntain a high amount of heteroatoms (e.g. N, O, S) and are of high viscosity causing difficulties to the environment and on industrial sites during oil transportation and production. Most of the problems are associated with asphaltenes which are the heaviest fraction of crude oil. Asphaltenes are considered to be responsible for clogging pipelines and wellbores, creating deposits. A thorough understanding of the chemical and physical attributes of asphaltenes is essential to contribute to optimization, improvements and new technological developments in up-to-date refining processes. The extreme complexity of crude oil consisting of probably more than one million different chemical compounds leads to a broad range of properties in terms of polarity, molecular weights and molecular architecture. In order to receive a more clear and comprehensive picture of structural details, different approaches, meaning combinations of advanced analytical techniques, need to be involved. Mass spectrometry with ultrahigh resolution and mass accuracy provide s information on a molecular level. One of the main objectives of this study is the structural elucidation of individual compounds in very complex oil mixtures using MS/MS measurements as the method of choice. Unfortunately, isolation of small mass windows leads to a large number of different compounds that would participate in the f ragmentation process leading to MS/MS spectra that are extremely difficult to interpret. Therefore, prior simplification is required to reduce the different types of species within the selected mass window subjected to fragmentation. Application of two different chromatographic separation methods, each focusing on different attributes of the compounds, is beneficial prior to mass spectrometric analysis. The separation methods applied here are size exclusion chromatography (separation according to molecular size) and argentation chromatography (separation according to unsaturation and heteroatom content). The combination of these separation methods makes it possible to apply collision activated dissociation methods to study structural details and suggest a theory of asphaltene structures and its formation