Flash Pyrolysis Coupled to GC×GC-­TOFMS and GC­-high Resolution TOFMS for Characterization of Crude Oil and Petroleum Fractions

Significance of the Topic

Petroleum encompasses an extraordinarily complex mixture of organic compounds, and characterizing its heavy fractions and asphaltenes is essential for optimizing refining processes and evaluating feedstock quality.
Advanced analytical approaches combining thermal desorption, pyrolysis, and high-resolution mass spectrometry provide deeper insight into molecular composition, maturity, and environmental markers of crude oils.

Study Objectives and Overview

This work aimed to evaluate a flash pyrolysis probe coupled to two complementary GC-MS platforms – comprehensive two-dimensional GC with TOFMS and one-dimensional GC with high-resolution TOFMS – to achieve detailed characterization of crude oil and isolated asphaltene fractions.
The focus was on assessing isomer distributions of polycyclic aromatic hydrocarbons and sulfur analogs and correlating pyrolysis products to crude oil composition and origin.

Methodology and Instrumentation

Crude oil samples from multiple geographic origins underwent sequential thermal desorption at 350 °C and 500 °C, followed by pyrolysis at 800 °C using a quartz-tube pyroprobe.
Analytes were transferred via helium carrier gas to GC systems for separation and MS detection.

Used Instrumentation

• Flash pyrolysis probe model 5200 interfaced to an Agilent 7890A GC.
• Pegasus 4D GC×GC-TOFMS with dual-stage quad-jet thermal modulator (modulation period 4 s).
• Pegasus GC-HRT high-resolution TOFMS operated ≥25 000 resolving power.
• Columns: Rxi-5MS (30 m) for first-dimension separation, Rxi-17MS (1.25 m) for second-dimension, and Rxi-5MS (30 m) for one-dimensional GC.

Main Results and Discussion

Pyrolysis at elevated temperature revealed distinct profiles of light and heavy PAHs and PASHs in crude oils and asphaltene residues.
GC×GC-TOFMS provided high peak capacity and resolution of coeluting isomers, enabling detailed isomeric fingerprinting.
High-resolution TOFMS afforded accurate mass assignments for unequivocal chemical formula determination.
Comparative analysis indicated that asphaltene pyrolysis products closely resemble the residue left after 500 °C desorption, underscoring the heavy aromatic content of asphaltenes.

Benefits and Practical Applications

• Enhanced molecular-level understanding of crude oil fraction composition.
• Improved assessment of thermal maturity, biodegradation, and depositional environment markers based on isomer ratios.
• Support for feedstock evaluation in refining and environment forensics.

Future Trends and Opportunities

Integration of data-driven chemometric techniques with GC×GC and HRTOFMS data promises more robust source attribution and quality prediction.
Advances in pyrolysis probe automation and higher-resolution detectors may further increase throughput and analytical depth.
Expanding the approach to heavier bitumen and unconventional oil sources could broaden its industrial impact.

Conclusion

The dual GC×GC-TOFMS and GC-HRTOFMS workflow with flash pyrolysis effectively resolves complex aromatic distributions in crude oil and asphaltenes.
High peak capacity and mass accuracy are complementary for isomer separation and formula confirmation, paving the way for more comprehensive petroleum characterization.

References

• Chiaberge S.; Fiorani T.; Cesti P. Methyldibenzothiophene isomer ratio in crude oils: GC-MS/MS analysis. Fuel Processing Technology 92 (2011) 2196–2201.
• Sarmah M.K.; Borthakur A.; Dutta A. Pyrolysis of petroleum asphaltenes and maturity indicators. Bulletin of Materials Science 33 (2010) 509–515.