Molecular Mechanism of Oil Shale Pyrolysis in Nitrogen and Hydrogen Atmospheres

This paper describes the changes in carbon functionality that occur during the pyrolysis and hydropyrolysis of Colorado oil shale. This paper is different from earlier work in that characterization of shale and products is combined with highly mass-balanced reactions to allow a mechanistic discussion of the role of functionalities in the generation of oil during shale pyrolysis. We identify some important factors in maximizing the conversion of kerogen to oil. Colorado oil shale was pyrolyzed under conditions of slow heatup (6°C/min) and short gas residence times (2-4 sec) in a nitrogen or hydrogen atmosphere at 2600 kPa. Product characterization was by elemental analysis, GC (gas), and NMR (solid & liquid). The aliphatic portion of the shale either cracks to give oil and gas or aromatizes to give aromatics in the oil or spent shale. There is an 80% increase in aromatic carbon during pyrolysis. The aromatic portion of the kerogen either cracks to give oil or ends up in the spent shale. Mineral carbonates, rather than organic functionalities, are the source of most of the CO 2 . Hydrogen is effective at inhibiting the reactions which lead to aromatization and formation of residual carbon. Molecular hydrogen in the system also reduces carbonates to methane and water.