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Abstract:
Crude oil fouling remains one of the biggest and until now unresolved problems in petroleum industry. Deposition of unwanted material during up- or downstream operation results in loss of thermal efficiency on the heat transfer equipment, catalyst poisoning, plugged pipelines or thermal instability. These in turn, can cause a series of operating difficulties, which might finally end with the units shut down. Since the incorporation of heavier crude oils (e.g. extra heavy oil, oil shale) into the market, the problem has become even more severe due to the increased content of heteroatoms (N, O, S), metals (e.g. V, Fe, Ni) and asphaltenes, which are thought to have a negative effect on the fouling phenomenon.
The main challenge regarding the formation of solid deposits is that the reaction mechanisms, let alone the compounds that are responsible for it, are poorly understood. The ability of gaining information on the details is limited, firstly, due to the complex nature of crude oil, which contains more than a million different chemical compounds and, secondly, due to the various reaction pathways (e.g. autoxidation, polymerization and thermal decomposition) involved in fouling.
During the course of this study, a procedure was designed to simulate fouling on a laboratory scale. For this, a reactor was developed that allows the simulation of an industrial reaction in the laboratory. Several parameters such as temperature, oxygen or the presence of water are studied with their effect on the fouling rate. After the successful simulation of fouling using a light crude oil fraction the resulting products were analyzed using ultrahigh resolution mass spectrometry. This method allows a view into the molecular details of such a complex phenomenon by its ability to unambiguously determine the elemental composition of any detected signal.
The behavior of different groups of compounds –based on their heteroatom content- has been studied in detail. According to the results obtained before and after the reactions, it was finally possible to suggest a potential mechanism for crude oil fouling. Using standard reference compounds for a simulated fouling experiment, the mechanism was verified by means of tandem mass spectrometry.
