Abstract
High hydrogen pressure pyrolysis (hydropyrolysis) was performed on samples of solvent extracted Kimmeridge Clay Formation source rock with a maturity equivalent to ca. 0.35% vitrinite reflectance. We describe the types and distributions of organic nitrogen compounds in the pyrolysis products (hydropyrolysates) using GC-MS. Compounds identified included alkyl-substituted indoles, carbazoles, benzocarbazoles, quinolines and benzoquinolines. The distributions of the isomers of methylcarbazoles, C2-alkylcarbazoles and benzocarbazoles in the hydropyrolysates were compared to a typical North Sea oil. The hydropyrolysates compared to the North Sea oil, showed increased contributions from alkylcarbazole isomers where the nitrogen group is exposed (no alkyl substituents adjacent to the nitrogen functionality) and appreciable levels of benzo[b]carbazole relative to benzo[a]- and benzo[c]carbazoles. Hydropyrolysis is found to be an ideal technique for liberating appreciable quantities of heterocyclic organic nitrogen compounds from geomacromolecules. The products released from the immature Kimmeridge Clay are thought to represent a potential source of nitrogen compounds in the bound phase (kerogen) able to contribute to the free bitumen phase during catagenesis.
Highlights
Hydropyrolysis refers to pyrolysis assisted by high hydrogen gas pressures (w10 MPa)
In an open-system, ®xed-bed reactor con®guration with an active catalyst dispersed in the sample, overall conversions are typically greater than 90% for petroleum source rocks with high selectivities to soluble tar products.[1,2]
Subsequent work has demonstrated the unique ability of the hydropyrolysis procedure to release higher yields of aliphatic biomarker hydrocarbons from immature kerogens in comparison with solvent extraction and conventional pyrolysis methods4±8 with excellent retention of product structural and stereochemical features
Summary
Hydropyrolysis refers to pyrolysis assisted by high hydrogen gas pressures (w10 MPa). The pyrroles and indoles are susceptible to alteration and occur only as minor constituents of petroleum[16,17] and may contribute to sediment formation in middle distillates and fuel oils.[18] The carbazoles and benzocarbazoles (benzo[a]- (IV), benzo[b]- (V) and benzo[c]carbazoles (IV)) have been extensively studied in source rocks and petroleum.19±21 The pyridinic forms of nitrogen compounds in petroleum and shale oils are commonly represented by pyridine (VII), quinoline (VIII) and benzoquinolines (IX, X, XI, XII).
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