A common relation for correlating pyrolysis yields of coals and oil shales

A sample of kerogen isolated from Huadian oil shale was studied using a combination of solid-state 13 C NMR, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), and X-ray diffraction (XRD) techniques to evaluate its structural characteristics. 13 C NMR results indicate that the carbon skeletal structure of this kerogen is mainly composed of a fairly high fraction of aliphatic carbon (86.1%), with a very low aromaticity (f a ) of 9.7%; methylene (CH 2 ) carbons dominate in all types of aliphatic carbons and the majority of them exist as many long straight chains but not saturated alicyclics. The average methylene carbon chain length (C n ) is between 12 and 24. There are only one fused aromatic ring (e.g., naphthalene) or two single aromatic rings (one benzene ring and one penta-heterocycle) per 100 carbon atoms. However, aromatic rings in this kerogen have a very high value of substitutive degree (δ = 0.42À0.75). Furthermore, XRD analysis suggests that most methylene straight chains and aromatic carbons can not form crystalline but amorphous structure and are linked to each other by various bridge bonds and methylene (CH 2 ) chains. FT-IR, XPS, and 13 C NMR results show that organic oxygen in the kerogen exists as mainly three types of oxygen functional groups. Both XPS and 13 C NMR results agree on the same ordering of their respective contents: CÀO and CÀOH groups are dominant, followed by OdCÀO, and CdO or OÀCÀO groups. The 13 C NMR results further suggest that more oxygen of CÀO and CÀOH groups is bound to aromatic carbons. XPS shows that over half the total amount of organic nitrogen in Huadian kerogen exists as aromatic heterocycles, which concludes pyrrolic nitrogen richest in total organic nitrogen, pyridinic, and protonated-pyridinic forms. A relatively high content of amino nitrogen over 30 mol % also is present in this kerogen, which is much higher than that of other same type kerogens. Organic sulfur is distributed in this kerogen as aromatic and aliphatic sulfur, sulfone, and sulfoxide in the order of the relative mole fraction.

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confidence: 93%

Evaluation of Structural Characteristics of Huadian Oil Shale Kerogen Using Direct Techniques (Solid-State ¹³C NMR, XPS, FT-IR, and XRD)

et al. 2011

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“…According to the van Krevelen diagram, kerogen can be classified into four types on the basis of their ratios of H/C and O/C. In the past 2 decades, much efforts have been devoted to study kerogen, focusing on the research of the molecular structure, − kerogen pyrolysis, − and natural oil generation. − The chemical structure features of kerogen are of great practical significance to understand the pyrolysis mechanism and guide the actual industrial processes.…”

Section: Introductionmentioning

confidence: 99%

Three-Dimensional Structure of a Huadian Oil Shale Kerogen Model: An Experimental and Theoretical Study

et al. 2015

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The molecular structural information on a kerogen isolated from Huadian oil shale was obtained using solid-state 13 C nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), and X-ray diffraction (XRD) techniques. Then, a series of Huadian kerogen isomers were constructed on the basis of these structural data. The possible carbon skeleton isomer and the substituted position effects of the aromatic ring, aliphatic ether bond, carboxylic acid, and carboxylic acid derivative as well as the quantity of tertiary and quaternary carbons on Huadian kerogen model stability have been systematically studied on the basis of density functional theory (DFT) calculations. For the carbon skeleton isomer, the calculated total energy decreases with the increasing number of the closed annular space (grid), which is constituted by connecting the aliphatic chain to the aromatic cluster or other aliphatic chain. DFT calculations show an about 16.8 kcal mol −1 decrease in total energy for every grid increase when the number of grids increases from 2 to 11. A significant break in the decrease of the total energy has been obtained for an isomer with 11 grids, which means that a proper number of grids (11 grids is appropriate in this paper) in carbon skeleton should be considered for building the chemical structure of Huadian kerogen. For the substituted position effects, aliphatic ether bonding to quaternary carbon, carboxylic acid attaching to secondary carbon, and carboxylic acid derivative bonding to quaternary carbon seem to give a lower energy structure than other connections. Besides, a high quantity of tertiary and quaternary carbons is conducive to a stable model for Huadian kerogen. The aromatic cluster dispersed distribution also makes a contribution to improve the stability of the model. According to these results, we proposed a relatively stable Huadian kerogen three-dimensional (3D) model. Moreover, this 3D model was testified reasonablely through the match between calculated and experimental 13 C NMR spectra.

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“…Miknis et al − performed NMR on several oil samples and residual carbons from oil shale retorts, showing differences between shales of different geological formations. Maciel et al reported that oil yields from oil shale correlated with aliphatic carbon content as measured by 13 C NMR spectroscopy, and a more general correlation was developed by Miknis and Conn . Solomon and Miknis developed a similar correlation of oil yield using aliphatic carbon content as measured by Fourier transform infrared (FTIR) spectroscopy on crushed oil shale pressed into KBr pellets.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Macromolecular Structure Elements from a Green River Oil Shale, II. Characterization of Pyrolysis Products by ¹³C NMR, GC/MS, and FTIR

et al. 2014

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This paper is Part II of a study of the chemical structural components of the organic matter of oil shale in the Green River formation. Three sections of a well-characterized oil shale core from the Utah Green River formation were demineralized, and the resulting kerogen was pyrolyzed at 10°C/min in nitrogen at atmospheric pressure at temperatures up to 525°C. The pyrolysis products (light gas, tar, and char) were analyzed using 13 C NMR, GC/MS, and (FTIR). Pyrolysis yields of 80% (daf basis) were achieved at these conditions, with 60% daf tar yield at the highest temperature. The solid-state NMR results indicate that the aromaticity of the kerogen char increased from 20% (at RT) to 80% during pyrolysis, with a corresponding decrease in the average aliphatic carbon chain length from 12 to less than 1. The average number of aromatic carbons per cluster increased from 12 to 20 in a narrow temperature window between 425 and 525°C, with an increase in the number of attachments per cluster from 6 to 8 in that same temperature window. Liquid-state NMR results of the condensed tars showed predominance of n-alkyl chains, with similar carbon aromaticities at each temperature. The alkyl chains were also observed in the GC/MS data. The light gases determined by FTIR were primarily CH 4 , CO, and CO 2 . The combination of gas, tar, and char yields and chemical structure analyses are valuable for modeling of oil shale processes based on chemical structure rather than based on empiricism.

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A common relation for correlating pyrolysis yields of coals and oil shales

Cited by 28 publications

References 15 publications

Evaluation of Structural Characteristics of Huadian Oil Shale Kerogen Using Direct Techniques (Solid-State ¹³C NMR, XPS, FT-IR, and XRD)

Evaluation of Structural Characteristics of Huadian Oil Shale Kerogen Using Direct Techniques (Solid-State ¹³C NMR, XPS, FT-IR, and XRD)

Three-Dimensional Structure of a Huadian Oil Shale Kerogen Model: An Experimental and Theoretical Study

Characterization of Macromolecular Structure Elements from a Green River Oil Shale, II. Characterization of Pyrolysis Products by ¹³C NMR, GC/MS, and FTIR

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A common relation for correlating pyrolysis yields of coals and oil shales

Cited by 28 publications

References 15 publications

Evaluation of Structural Characteristics of Huadian Oil Shale Kerogen Using Direct Techniques (Solid-State 13C NMR, XPS, FT-IR, and XRD)

Evaluation of Structural Characteristics of Huadian Oil Shale Kerogen Using Direct Techniques (Solid-State 13C NMR, XPS, FT-IR, and XRD)

Three-Dimensional Structure of a Huadian Oil Shale Kerogen Model: An Experimental and Theoretical Study

Characterization of Macromolecular Structure Elements from a Green River Oil Shale, II. Characterization of Pyrolysis Products by 13C NMR, GC/MS, and FTIR

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Evaluation of Structural Characteristics of Huadian Oil Shale Kerogen Using Direct Techniques (Solid-State ¹³C NMR, XPS, FT-IR, and XRD)

Evaluation of Structural Characteristics of Huadian Oil Shale Kerogen Using Direct Techniques (Solid-State ¹³C NMR, XPS, FT-IR, and XRD)

Characterization of Macromolecular Structure Elements from a Green River Oil Shale, II. Characterization of Pyrolysis Products by ¹³C NMR, GC/MS, and FTIR