Cracking Products of Oleic Acid and Olive Oil

Importance of the Topic

Vegetable oils, including olive oil, offer a renewable alternative to conventional diesel fuel but suffer from high viscosity that can impair engine performance. Thermal cracking, or controlled pyrolysis, reduces molecular weight and viscosity by breaking long-chain triglycerides and fatty acids into lighter hydrocarbons. Understanding the specific cracking products of common feedstocks such as oleic acid and olive oil is essential for optimizing bio-fuel properties and process conditions.

Objectives and Overview

This study employs microscale pyrolysis coupled with gas chromatography-mass spectrometry (GC/MS) to characterize the low-molecular-weight products generated from supermarket olive oil and its principal monounsaturated fatty acid, oleic acid. The goals are to compare product distributions, identify major hydrocarbon classes, and assess the influence of oleic acid on overall oil cracking behavior.

Methodology and Instrumentation

Each sample (olive oil or pure oleic acid) was loaded into a quartz tube and pyrolyzed at 750 °C for 15 s using a platinum coil pyroprobe. Volatile and semi-volatile cracking products were swept into an Agilent 6890/5975 GC/MS system. Key conditions included a 30 m phenyl column, helium carrier gas with a 50:1 split ratio, an injector at 300 °C, an oven program from 40 °C to 300 °C at 8 °C/min, and MS detection over m/z 25–550.

Main Results and Discussion

Pyrograms revealed a prominent late-eluting peak around 30 min for oleic acid, attributed to uncracked acid desorbing. Despite its single double bond and relative thermal stability, oleic acid yielded a variety of products. Identified compounds with library match ≥80% included benzene and toluene (aromatics), along with long-chain alkenes, alkanes, and alkynes. Notably, octane appeared in both samples, likely formed by cleavage adjacent to the C=C bond of oleic acid. Olive oil showed a similar product profile, reflecting its high oleic acid content.

Benefits and Practical Applications

• Provides detailed speciation of pyrolysis fragments to guide reactor optimization.
• Helps tailor fuel properties by targeting specific hydrocarbon chain lengths.
• Offers a rapid microscale screening method for feedstock evaluation.

Future Trends and Opportunities

Advances may include integration with real-time MS techniques for instantaneous product analysis, development of improved spectral libraries for better identification of novel pyrolysis fragments, exploration of catalysts to steer cracking toward desired fuel fractions, and scaling microscale findings to pilot- and industrial-scale pyrolysis processes.

Conclusion

Microscale pyrolysis–GC/MS effectively characterizes the thermal cracking products of olive oil and oleic acid, revealing key hydrocarbon classes and pathways such as octane formation. These insights support the development of optimized bio-fuel production strategies by linking feedstock composition to final fuel quality.

Reference

D. G. Lima et al., Diesel-like fuel obtained by pyrolysis of vegetable oils, Journal of Analytical and Applied Pyrolysis 71 (2004) 987–996.