Thermal stability characterization of n-alkanes from determination of produced aromatics

The thermal stability of n-nonane and n-undecane, as the model endothermic hydrocarbon fuels, was evaluated by determining the content change of produced aromatics during the thermal cracking process. The 1H nuclear magnetic resonance spectroscopy (1H NMR), along with the high-performance liquid chromatography (HPLC) and the gas chromatography/mass spectrometry (GC/MS) analyses, is mainly considered to follow the formation of aromatics in the liquid cracking residues of the n-alkanes. The results of the aromatic contents obtained from these three analytical methods show satisfactory agreements. The 1H NMR method also gives the olefin content and the branching index of the liquid residues. The changes of the aromatics, olefins and branching index against the temperature directly reflect the thermal stability of the n-alkanes. Based on the results from 1H NMR, HPLC and GC/MS, a scheme of the formation of aromatics from the thermal cracking of n-alkanes is discussed.