The photolytic behavior of diluted bitumen in simulated seawater by exposed to the natural sunlight

- Diluted bitumen experienced similar photolytic trends but decreased removal efficiencies compared to light crude oil.
- Aromatics were most photosensitive, followed by n-alkanes, then biomarkers.
- Summer exposure led to higher photolysis than winter.
- The differences of PAHs structure did not significantly affect their photolytic rates.

Two diluted bitumen, Cold Lake Blend (CLB), Accessed Western Blend (AWB), and Alberta Sweet Mixed Blend #5 crude oil (ASMB#5), were spiked into 3.3% NaCl aqueous solution, then exposed to natural sunlight for 90 days in the winter and summer in the Northern Hemisphere (Ottawa, Canada). The effects of temperature and solar intensity on the photolytic behavior of diluted bitumen were evaluated. Simultaneously, the photolytic similarities and differences between diluted bitumen and crude oil were compared. It was found that, in all test oils, the decrease of all total petroleum hydrocarbons followed a pseudo-first-order reaction kinetic with the exposure time regardless of seasons. Aromatic fractions had the highest apparent rate constants. Similarly, the chemical fingerprinting analysis of test oils demonstrated that polycyclic aromatic hydrocarbons (PAHs) and their alkylated homologues (APAHs) were the most photosensitive compounds among the identified targets, followed by n-alkanes, then terpanes, and steranes. The photolytic efficiencies of the target petroleum hydrocarbons in ASMB#5 were generally higher than the two diluted bitumen. Photolysis of APAHs occurred faster in summer than in winter; however, APAHs with different number of rings and degree of alkylation did not have obvious photolytic differences. These phenomena suggest that the photolytic similarities between dilbits and conventional crude oil depend on their similar chemical structure of petroleum hydrocarbons; their differences depend on the specific oil properties. The accumulated solar irradiation intensity and temperature are the main factors contributing to their photolytic differences for winter and summer exposed oils.

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