Kerogen Chemistry 6. Involvement of Native Free Radicals in Kerogen Thermal Deoxygenation

and, John W. Larsen; Ashida, Ryuichi; Doetschman, David C.

doi:10.1021/ef0501288

Cited by 9 publications

(10 citation statements)

References 10 publications

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“…The radicals and other highly reactive products that are not able to find sites to react with remain in the kerogen. Similarly, it has been demonstrated experimentally 65,66 that demineralized kerogens contain uncoupled electrons at concentrations of 10 17 −10 19 cm −3 . The newly developed reaction sites (e.g., carbon radicals) can also satisfy their reactivity through covalent bond formation with hydrogen atoms present in the kerogen or with olefinic moieties formed by β scission.…”

Section: Energy and Fuelsmentioning

confidence: 59%

Reactive Molecular Dynamics Simulation of Kerogen Thermal Maturation and Cross-Linking Pathways

2017

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Molecular dynamics simulations were performed with a ReaxFF reactive force field to investigate bond breaking and bond formation mechanisms during the thermal maturation of three kerogens and potential cross-linking pathways toward the formation of three-dimensional (3D) quasi-infinite molecular networks (cross-linked kerogen macromolecules). Starting with small ensembles of high molecular mass models for immature type I Green River Shale kerogen (kerogen 1-I), top of the oil window type II kerogen (kerogen 2-L), and low maturity type III kerogen (kerogen 3-L), low molecular mass species including H2O, C2H4, and C3H6 were produced as the maturities of the remaining kerogens increased. Highly reactive fragments, which are not detected in pyrolysis experiments, were also produced. Further, the cross-linking mechanisms in the newly developed polymeric kerogen networks appear to be highly complex, and covalent C–S, C–O, and C–C bonds were the primary cross-links that structurally bond kerogen monomers together. The trends observed in the simulated thermochemical transformation of kerogen and the kerogen cross-linking pathways are consistent with theoretical and experimental studies reported in the scientific literature. Reactive force field molecular dynamics simulation provides a potentially valuable approach to the development of realistic three-dimensional models for kerogen molecular networks. However, the conversion of kerogen molecules into a 3D cross-linked molecular network was low (the density of the intermolecular cross-links was low).

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Section: Energy and Fuelsmentioning

confidence: 59%

Reactive Molecular Dynamics Simulation of Kerogen Thermal Maturation and Cross-Linking Pathways

2017

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“…The evolution of N g with kerogen maturation has been discussed extensively (Morishima and Matsubayash, 1978;Marchand and Conard, 1980;Aizenshtat et al, 1986;Seehra et al, 1986;Fowler et al, 1987;Bakr et al, 1991;McTavish, 2003;Larsen et al, 2005Larsen et al, , 2006Lewan et al, 2006). The different evolutions of N g with vitrinite reflectance between three kerogen types are shown in Figure 1.…”

Section: Resultsmentioning

confidence: 97%

“…Since then, many ESR studies have documented the structure, maturation and reactivity of carbonaceous materials, such as coal, petroleum and kerogen (Retcofsky et al, 1968;Durand et al, 1977;Marchand and Conard, 1980;Tissot and Welte, 1984;Larter, 1988;Bakr et al, 1991;Trudy et al, 1995; Diaz et al, 2000;Bandara et al, 2005;Dick et al, 2005;Walters et al, 2007;Pancost et al, 2008;Tiem et al, 2008). The structure of kerogen was investigated by ESR method and attempts to correlate ESR parameters of kerogen with its maturation have been reported (Pusey, 1973;Marchand and Conard, 1980;Bakr et al, 1988;McTavish, 2003;Larsen et al, 2005Larsen et al, , 2006Lewan et al, 2006;Sun et al, 2006). Free radical concentrations in kerogen increase with maturity.…”

Section: Introductionmentioning

confidence: 99%

Temperature and Time Effects on Free Radical Concentration in Organic Matter: Evidence from Laboratory Pyrolysis Experimental and Geological Samples

Qiu

et al. 2012

Energy Exploration & Exploitation

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The free radicals concentration (N g ) of organic matter evolves with the temperature, time, kerogen types and other factors for the individual kerogens. This paper focuses on the N g evolution of immature type I and II kerogens and a type III coal under the laboratory pyrolysis temperature and heating time. The experiments were carried out in a closed system pyrolysis at an isothermal reactor in the temperature range from 300 to 500°C over 30 to 480 minutes. A temperature time index (TTI) is applied and the TTI values were calculated in order to indicate the pyrolysis temperature and time at which the kerogen had experienced. Some equations were established to show the relationship between the TTI and N g of type I, II and III kerogens, based on the tested data from laboratory anhydrous pyrolysis experiments of three kerogen types and geological type I kerogen samples. However, the evolution of free radicals concentration with temperature and time shows some differentials between different types of kerogen samples. This paper also discusses the different TTI-N g relation of type I kerogen between laboratory pyrolysis experimental and geological samples, which are collected from core samples with depth interval of 1137 to 4090.6 m. The TTI-N g equation from pyrolysis experimental samples should be calibrated by the data from geological samples when the equation is to be extended to the geological timescales. As the free radical concentration in organic matter is strongly maturity dependent, the relationship between TTI-N g may prove to be a valuable method to study paleotemperature of sedimentary basins.Keywords: Free radicals, Vitrinite reflectance (R o ), Kerogen, Temperature Time Index (TTI), Thermal history, Pyrolysis experiment INTRODUCTIONFree radicals are units with an unpaired electron in organic matter. Kerogen, the portion of sedimentary organic matter not soluble in organic solvents, is believed to have analogous structures in which numerous aromatic rings form angularly conjunctive aromatic sheets, with substituents (such as paraffinic side chains) attached at the sheet margins (Tisssot and Welte, 1984). Thermal cracking of paraffinic chains from the kerogen molecules initially forms alkyl and kerogen free radicals (Wang and Chen, 1988). Smaller alkyl radicals are highly unstable and are thus rapidly quenched by hydrogen extracted from the surrounding environment. However, the larger kerogen free radical is stabilized by the extended aromatic system and can be stable through geological time. Although there have been various structure models for different types of kerogen at different level maturity, the main chemical structure of kerogen include the core structures and linkages. Kerogen is defined to be a complex geopolymer and a heterogeneous macromolecule comprised of randomly cross-linked core structures that may be aliphatic, naphthenic, aromatic and/or heteroatomic . The chemical structures of kerogen and the free radicals reactions have been studied widely (Siskin et al., 1995;Sun and P...

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“…The anhydrides will persist to higher temperatures and may be observable spectroscopically. We have previously observed them by using diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy. − If sufficient reactive radicals are present in the kerogen, then anhydride decomposition will be faster than in the absence of those radicals. In the extreme case, the anhydrides will react as soon as they are formed and their concentration will never get high enough for them to be observable.…”

Section: Resultsmentioning

confidence: 99%

“…We have recently published the observation that kerogens form anhydrides in an endothermic process when they are heated at temperatures below 200 °C . These anhydrides then decompose by a radical chain reaction initiated by attack of a kerogen radical on the anhydride carbonyl oxygen. , The products are CO and an ester. Thus, kerogens can decarboxylate at low temperatures in a two-step process (Scheme ) that yields a kerogen ester, water, and CO. Because this process proceeds through anhydride formation, it will not occur in water-wet systems.…”

Section: Introductionmentioning

confidence: 99%

Kerogen Chemistry 9. Removal of Kerogen Radicals and Their Role in Kerogen Anhydride Decomposition

et al. 2006

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By treatment with CrCl2, the radical populations of Kimmeridge and Bakken kerogens were significantly decreased. When both kerogens are mildly heated, anhydride formation at low temperatures can be detected by infrared spectroscopy only when radicals have been removed by CrCl2 treatment. The “native” kerogen radicals react with thermally formed carboxylic acid anhydrides to form esters and CO. Some of the observable kerogen radicals are persistent and reactive. The Acholla and Orr method for pyrite removal also reduces the radical population of these kerogens.

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Kerogen Chemistry 6. Involvement of Native Free Radicals in Kerogen Thermal Deoxygenation

Cited by 9 publications

References 10 publications

Reactive Molecular Dynamics Simulation of Kerogen Thermal Maturation and Cross-Linking Pathways

Reactive Molecular Dynamics Simulation of Kerogen Thermal Maturation and Cross-Linking Pathways

Temperature and Time Effects on Free Radical Concentration in Organic Matter: Evidence from Laboratory Pyrolysis Experimental and Geological Samples

Kerogen Chemistry 9. Removal of Kerogen Radicals and Their Role in Kerogen Anhydride Decomposition

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