Theoretical modeling of molecular interactions of iron with asphaltenes from heavy crude oil

Systematic study on dynamic pyrolysis behaviors, products, and mechanisms of weathered petroleum-contaminated soil with Fe2O3

Weathered petroleum-contaminated soil (WPCS) with a high proportion of heavy hydrocarbons is difficult to remediate. Our previous research demonstrated that Fe₂O₃-assisted pyrolysis was a cost-effective technology for the remediation of WPCS. However, the pyrolysis behaviors, products, and mechanisms of the WPCS with Fe₂O₃ are still unclear. In this study, a combination of Thermogravimetric-Fourier transform infrared spectroscopy (TG-FTIR) and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) techniques were used to explore these pyrolysis characteristics. The thermal desorption/degradation of light and heavy hydrocarbons in the WPCS mainly occurred at 200-400 °C and 400-550 °C, respectively. The activation energy of thermal reaction of heavy hydrocarbons was decreased in the presence of Fe₂O₃ during the WPCS pyrolysis processes. In the process, the released inorganic gaseous products were mainly H₂O and CO₂, while the released organic gaseous compounds were primarily cycloalkanes, alkanes, acids/esters, alcohols, and aldehydes. Compared with the WPCS pyrolysis without Fe₂O₃, the yields of gaseous products released during the WPCS pyrolysis with Fe₂O₃ were reduced significantly, and some gaseous products were even not detected. This phenomenon was contributed by the following two reasons: 1) heavy hydrocarbons in the WPCS were more easily transformed into coke in the presence of Fe₂O₃ during pyrolysis; 2) some released gaseous products were reacted with Fe₂O₃ and fixed on the soil particles. Therefore, the WPCS pyrolysis with Fe₂O₃ can effectively reduce the burden of tail gas treatment. Criado method analysis results suggested that the reaction mechanism of heavy hydrocarbons during the WPCS pyrolysis with Fe₂O₃ was rendered as the synergic effects of diffusion, order-based, and random nucleation and growth reactions.

Hematite-facilitated pyrolysis: An innovative method for remediating soils contaminated with heavy hydrocarbons

As a recalcitrant fraction of petroleum, heavy hydrocarbons (including aromatics, resins, and asphaltenes) can remain in contaminated soils even after decades of weathering, thereby causing serious harm to the soil ecosystem and human health. Pyrolysis is a promising technique for remediating petroleum-contaminated soil. However, this technique still presents some drawbacks, such as high energy consumption and damage to soil properties. Therefore, an innovative method using hematite (Fe₂O₃) for the catalytic pyrolysis of weathered petroleum-contaminated soil was developed in this study. Compared with soil pyrolyzed without Fe₂O₃ at 400 °C for 30 min, the residual concentrations of aromatics, resins, and asphaltenes in soil pyrolyzed with 5.0% Fe₂O₃ were reduced by 67.8%, 52.3%, and 67.9%, respectively. After pyrolysis with 5.0% Fe₂O₃, the water-holding capacity of soil was considerably increased and the soil became darker and rougher. Scanning electron microscopy analysis showed that many small holes occurred on the surface of the pyrolytic soil. X-ray photoelectron spectrometer analysis showed that a thin layer of graphitic C was formed and deposited on the surface of the pyrolytic soil. We also observed that the wheat germination percentage and biomass yield in the soil pyrolyzed with 5.0% Fe₂O₃ were even higher than those in clean soil.