A study of radiation-induced ring opening, ring enlargement and ring closure in petroleum hydrocarbons: evidence from EPR, FT-IR and UV spectroscopy.

Petroleum hydrocarbons were treated with nanostructured Na-bentonite and exposed to Co-60 γ-radiation under vacuum to evaluate the combined effect of irradiation and mineral surface interactions on crude-oil transformation. Untreated crude oil (C0), bentonite-treated oil (C1), irradiated oil (C2), and irradiated oil containing Na-bentonite (C3) were compared using gas chromatography, FT-IR, UV-vis, EPR and thermal analysis. The combined treatment produced the most pronounced changes in the chromatographic distribution of the crude oil. In particular, the low-retention-time fraction increased from 18.2 ± 2.1% for untreated oil to 44.6 ± 3.1% for the combined irradiation/bentonite system at 550 kGy. FT-IR and UVvis spectra revealed changes in the aliphatic, unsaturated and aromatic/conjugated hydrocarbon regions, while EPR confirmed the formation of persistent paramagnetic centres after irradiation. Thermal analysis also showed treatment-dependent changes in the physicochemical behaviour of the oil. These findings indicate that γ-irradiation in the presence of Na-bentonite promotes hydrocarbon conversion through a set of competing reactions, including bond cleavage, hydrogen transfer, isomerization and cyclization. Ring opening, ring enlargement and ring closure are proposed as plausible pathways for the observed collective changes. Although individual intermediates were not directly identified, the results demonstrate that the irradiation-bentonite combination can modify petroleum fractions and may be useful for radiation-assisted petroleum processing.