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

Abstract

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.

Evaluation of the porous structure of Huadian oil shale during pyrolysis using multiple approaches

“…The strongly aliphatic hydrocarbon stretching bands at 2920 cm À1 (v as CH 2 ) and 2850 cm À1 (v s CH 2 ) correlate with the kerogen in the sample [20,22]. A sharp peak appeared at about 720 cm À1 is attributed to the skeletal vibration of straight chains with more than four CH 2 groups, this is content with the conclusion from 13 C NMR reported by Tong [23]. The similar spectra of Sraw and S300, particularly at 2920 and 2850 cm À1 (Fig.…”

Structural Characterization of Typical Organic Species in Jincheng No. 15 Anthracite

“…45,46 As exhibited in Figure 2, the XPS C 1s spectrum of DMJ15A is separated into three peaks, corresponding to C−C or C−H, C−O− or C−OH, and >CO, respectively. The C− O− or C−OH groups may be present in aliphatic ethers or alkanols, while >CO groups may exist in esters and ketones, which is in accordance with the 13 C NMR analysis.…”

Insight into the structural features of Zhaotong lignite using multiple techniques

“…The assignments of different carbon types were referred to previous studies [8,[31][32][33]. The solid-state 13 C NMR spectra of coals can generally be divided into three main chemical regions: aliphatic carbons (0-90 ppm), aromatic carbons (90-170 ppm), and carbonyl carbons (170-220 ppm).…”