Pyrolysis Kinetics And Reaction Mechanism Of Kerogen From Green River

The access to more energy is the major challenge of our time.A promising strategy to address this challenge is converting alternative hydrocarbon resources such as kerogen in oil shale to transportation fuels,which could be easily fitted into existing infrastructure.Kerogen,a sedimentary and insoluble macromolecular organic matter(OM),is by far the most abundant form of OM on Earth.On the other hand,it has a high hydrogen-to-carbon ratio with a potential to be superior to heavy oil or coal as a source of liquid fuel.Currently,the most common conversion technology of kerogen is by retorting processes to produce liquid fuels(i.e.,shale oil).Therefore,fundamentally understanding the pyrolysis kinetics and pyrolysis pathway of kerogen is of prime scientific and industrial importance to design a viable process for the kerogen decomposition to right oil.Considering that kerogen exists in a complicated heterogeneous mixture of organic components including bitumen linked to a mineral matrix usually containing carbonates,the thermochemical decomposition of kerogen is usually accompanied by that of bitumen and carbonates,leading to very complex thermal behaviors.Therefore,it is highly desirable to exclude the interference of bitumen and carbonates for understanding the intrinsic thermal behavior of kerogen.The objective of this work is to investigate the non-isothermal pyrolysis kinetics and pyrolysis pathway of kerogen prepared from Green River oil shale.Three commonly used model-fitting methods,i.e.,the Popescu method,master plots method and non-linear least squares analysis,were comparatively employed to discriminate the most probable kinetic model from the commonly used 15 reaction models based on four types of solid-state pyrolysis mechanisms.Moreover,the effect of pyrolysis temperature and time on the kerogen pyrolysis is investigated.The distribution and content of shale oil,as well as the surface chemical structure of char are analyzed to propose the plausible pyrolysis reaction pathway.(1)The Green River oil shale resource potential is evaluated by the TG analysis.Then,SEM/EDX,ICP and XRD are employed to investigate the elements and crystal phase of oil shale and kerogen,which is prepared through Soxhlet extraction with dichloromethane followed by decarbonation of the Green River oil shale.It is found that our prepared kerogen sample is bitumen-and carbonates-free,which would be used as the starting material for fundamental understanding of kerogen pyrolysis kinetics without the interferences from bitumen and carbonates.(2)The non-isothermal kerogen pyrolysis kinetics is studied.It is found that the non-linear least squares analysis except Popescu method and master plots method is identified as an effective method for the discrimination of the most probable kinetic model from the 15 reaction models.Two-stage reaction models are proposed to well describe the kerogen pyrolysis process,which demonstrates a wide applicability owing to their insensitivities on the heating rate and estimation methods of the activation energies.(3)The effects of pyrolysis temperature and time on shale oil yield from the prepared kerogen are investigated,and the optimum temperature and time can be obtained.Moreover,Py-GC/MS,Raman and FTIR are employed to analyze distribution/content of paraffins,olefins and aromatic hydrocarbons,as well chemical structures of resultant shale char at different pyrolysis time.Based on these analyses,plausible kerogen pyrolysis pathways are proposed that the kerogen is decomposed to the paraffin,olefin and aromatic hydrocarbon by cracking,and the shale char is mainly produced by the aromatic hydrocarbons dehydrogenation and free radical polymerization.