Investigation of generation mechanisms in nitrogenous compounds of shale oil using GC-NCD and theoretical calculations

The nitrogenous compounds in shale oil at various final pyrolysis temperatures were detected using gas chromatography-nitrogen chemiluminescence detection (GC-NCD). Thirty structural models of nitrogenous compounds were constructed using density functional theory and transition state theory calculations. To investigate the effects of different reaction mechanisms, forty reaction paths were designed around the models consisting of aliphatic amines, anilines, pyrroles, pyridines, indoles, and carbazoles. The results indicated that pyrroles, pyridines, and quinolines acted as intermediates during the processes for the formation of nitrogen-containing compounds. The contents of alkylindoles decreased while that of alkylcarbazoles increased, both following a consistent trend. Additionally, the presence of hydroxyl radicals and intramolecular hydrogen transfer significantly reduced the reaction energies of nitrogenous compounds during generation. Path23-1 begins with hydrogen radical transfer from the hydroxyl group attached to the carbon to the neighboring carbon, and forming a carbonyl group. This process breaks the delocalized π-bonds off the ring, with a reaction energy of 273.2 kJ/mol.