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Abstract

Oil spills occur regularly, negatively affect the environment and have high economic costs. For efficient remediation and assessment of consequences of the spills, knowledge of oil weathering processes is required. One of the crucial weathering processes is photooxidation. It has been reported earlier that in some oils a solid phase is formed as a result of irradiation. This process has not been studied yet using modern analytical techniques.
In this thesis photooxidation of a light crude oil fraction and a model compound (octylbenzene) was studied. The samples were irradiated by visible and UV light in presence and absence of water and TiO₂. In addition, an accelerated heating experiment was performed, in which samples were heated to 60°C. All the samples were analyzed by ultra-high-resolution mass spectrometry using APPI ionization. To study the structure of the resulting compounds, MSⁿ experiments were undertaken.
In the irradiated samples a precipitate forms with highly oxygenated species up to O₁₇. In the water phase oxygenated species up to O₁₁ are seen. Analysis of the DBE and carbon count of the samples shows the formation of higher molecular weight compounds with two distinct DBE trends. One of them, which is seen in control too, can be attributed to the elevated temperature. TiO₂ prevents the formation of the precipitate and of the heaviest compounds in the irradiated samples, eventually fully degrading it. The irradiation products, as a rule, have a large condensed aromatic core with short alkyl chains attached. The oxygenation happens on both the alkyl chains and the core. The irradiation of the model compound produces highly oxygenated dimers and trimers. The oxygen is introduced at various locations in the molecule. Some of the reactions may form a single fused aromatic core from simpler aromatic precursors. That highlights the complexity of photochemical reactions.
The formation of an insoluble precipitate from light oil indicates that the creation of tarry residues may be a result of (photo)chemical transformations of the oil components and not only physical processes. TiO₂ exhibits a potential of use for oil spill remediation, being environmentally friendly and cheap.