Three-Dimensional Structure of a Huadian Oil Shale Kerogen Model

Article pubs.acs.org/EF

Three-Dimensional Structure of a Huadian Oil Shale Kerogen Model: An Experimental and Theoretical Study Xiao-Hui Guan, Yao Liu, Di Wang, Qing Wang, Ming-Shu Chi, Shuang Liu, and Chun-Guang Liu* College of Chemical Engineering, Northeast Dianli University, Jilin, Jilin 132012, People’s Republic of China S Supporting Information *

ABSTRACT: 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 13C NMR spectra. et al.71 proposed a 2D model of kerogen for the Green River oil shale with a chemical formula of C645H1017N19O17S4. The data of the model by Siskin et al. were mainly obtained by NMR and mass spectroscopy of materials isolated under mild conditions. 13 C NMR quantified the specific carbon-containing functional groups, and mass spectrometry analyzed the gas evolution and species during kerogen pyrolysis. This model was also compared to the results of NMR, X-ray photoemission spectroscopy (XPS), and sulfur X-ray absorption near edge structure (XANES). Later, Lille et al.11 evaluated the chemical structure of Estonian kukersite kerogen using a simulation of 13 C magic angle spinning (MAS) NMR spectra. In comparison to the 2D model, a three-dimensional (3D) structural model not only defines the structural information but also provides a new way to determine the pyrolysis reaction mechanism and active sites as well as predict the reaction trend.73−75 Orendt et al.76 recently developed a 3D structural model of Green River kerogen based on the 2D structure of Siskin et al. using a combination of quantum chemistry and molecular dynamic calculations. In their work, the molecular dynamics were employed to achieve the initial monomer conformations. Then, a simulated annealing procedure was repeatedly employed to obtain the lowest energy monomer conformations. The minimum energy structure was further

1. INTRODUCTION Oil shale is an important potential energy source, consisting of an inorganic mineral matrix containing organic matter. The organic matter is generally divided into two fractions: bitumen and kerogen. Kerogen is insoluble in normal organic solvents and believed to be the source material for oil and gas that formed during the oil shale thermal process.1−5 The composition of kerogen depends upon the organic matter origin, the conditions of preservation of organic matter during sedimentation, and the thermal maturation. 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,6−27 kerogen pyrolysis,28−50 and natural oil generation.51−80 The chemical structure features of kerogen are of great practical significance to understand the pyrolysis mechanism and guide the actual industrial processes. Development of a two-dimensional (2D) model of kerogen provides a reasonable starting point for understanding the chemical structure of oil shale.65−72 According to the structural information obtained from elemental analysis, electron microscopy, 13C nuclear magnetic resonance (NMR), thermogravimetry, functional analysis, and pyrolysis, Behar and Vandenbroucke66 proposed the models for kerogens of type I, type II, and type III at different evolution stages (beginning of diagenesis, beginning of catagenesis, and end of catagenesis) with the molecular weight of about 25 000, respectively. Siskin © 2015 American Chemical Society

Received: December 23, 2014 Revised: June 18, 2015 Published: June 18, 2015 4122

DOI: 10.1021/ef502759q Energy Fuels 2015, 29, 4122−4136

Article

Energy & Fuels

ular systems. It should be stressed that the DFT method turned out to be insufficient for describing the weak intra- or intermolecular interactions, but it is the most accurate method that can be used on large molecules at an affordable computational cost. During the past few years, our group did research in the combustion characteristics and physicochemical properties of oil shales, combustion and co-combustion characteristics of semi-coke, etc.83−99 Semi-coke mentioned here refers to the solid waste left after oil shale retorting, which contains phenols, polycyclic aromatic hydrocarbons (PAHs), and oil products.100,101 However, few studies were focused on the chemical structure of kerogen in oil shale. Therefore, the aim of this paper is (i) to obtain the detailed structural information on Huadian kerogen through a variety of experimental methods, (ii) and on the basis of these experimental data, a series of Huadian kerogen 3D isomer models have been constructed to consider the carbon skeleton isomerization, the substituted position effects of the aromatic ring, aliphatic ether bond, carboxylic acid, and carboxylic acid derivative, and the quantity of tertiary and quaternary carbons on model stability using DFT calculations. Research in this paper probably provides a scientific guide to build and find the kerogen 3D model. Although the constructed kerogen model in this paper is not the lowest energy conformation among infinite kerogen geometric isomers, it is still valuable for building the model of kerogen. What we emphasize is that, during the process of building a model of kerogen, the carbon skeleton isomerization, substituted position effects, and quantity of tertiary and quaternary carbons should be taken into reasonable considerations. For most of the cases in the current, these factors were not considered or inadequately described in building a 3D model of kerogen.

optimized at the restricted Hartree−Fock (HF) level of the quantum chemical theory using the minimal STO-3G basis sets. On the basis of optimized geometries of the 3D structure, NMR was calculated using density functional theory (DFT) PBE1PBE exchange correlation functional and 4-31G basis sets. This work provided a general methodology to develop a 3D model based on a known 2D model of kerogen. Li and coworkers77 has defined the lowest energy conformation of the Huadian kerogen molecular structure using a simulated annealing procedure. Structural parameters of the lowest energy conformation were further analyzed. On the basis of the above molecular dynamics simulation methods, they proposed the possible reaction sites and pyrolysis process of kerogen. For the 3D molecular simulation, the interaction between kerogen and other molecular units coming from the organic matter of oil shale should also be considered. In general, the organic matter mainly composes of kerogen (the most abundant), asphaltenes, resins, hydrocarbons, and other fluids (such as carbon dioxide, water, and nitrogen). Galliero et al.78 constructed a 3D molecular model of organic matter presenting a type II oil shale in the middle of the oil generation window using molecular dynamics simulations (NPT molecular dynamics and force fields). Their results provide a lot of valuable information at the molecular levels, such as the fluid distribution within the organic matter, pore size distributions, isothermal compressibility, and dynamic of the fluids within the kerogen matrix. Very recently, a molecular dynamic simulation79 has been applied to a representative set of kerogen for the purpose of obtaining quantitative predictions of volumetric properties, which also take into account the interaction among them. The density results are well in agreement with the welldocumented trends of kerogen density with thermal maturity and organic type. As mentioned above, both Orendt and Li adopted a simulated annealing algorithm to seek the lowest energy conformation of kerogen. However, the simulated annealing algorithm80 is based on a given 2D model with fixed connections and structural characteristics to obtain a more compact and superior conformation than the initial model. That is, molecular dynamic simulation considers the conformational isomer rather than the geometric isomer. The kerogen model has numerous geometric isomers. Only considering one connection case to seek the lowest conformation is not convincing and sufficient. Besides, it is impracticable to endlessly optimize all possible geometric isomers for a largesized kerogen molecule because of limitations in computational resources.80−82 Thus, it is valuable to explore the relationship between isomer stability and molecular geometries of kerogen. The HF method provided a reasonable starting point to probe the chemical structure for macromolecular systems but failed to consider the electron correlation effects, which is important for calculating structure and energies of a molecule. To overcome the weakness in electron correlation effects, coupled cluster, configuration interaction, and perturbation theory have been developed. However, they are not suitable for macromolecular systems because of the high computational cost. In contrast, the DFT method has been proven to be efficient in evaluation of the physicochemical property for a wide range of compounds with a large size because of proper consideration of electron correlation and moderate computational cost. Currently, DFT is a widespread acceptance method for understanding physicochemical properties of macromolec-

2. EXPERIMENTAL SECTION 2.1. Sample Preparation. The oil shale sample used in this paper was obtained from Huadian mine located in Jilin, China. Large oil shale blocks were first crushed and sieved to 0.2 mm to obtain the experimental oil shale sample. Bitumen was extracted from the shale using chloroform. Then, the oil shale sample was demineralized by a four-step extraction procedure using HCl−HF−HNO3−HCl. The demineralization effect has been checked using the X-ray diffraction (XRD) technique (see below). The results of elemental analysis of Huadian kerogen are shown in Table 1. According to the atomic H/C and O/C ratios,51,102 Huadian kerogen belongs to type I, although the atomic H/C and O/C ratios of our kerogen differ from other Huadian kerogen reported in previous studies.23,77 This may be due to the fact that the reported sample preparation process did not remove asphaltenes. The various structure of kerogen obtained in the same mine but different sedimentary layers

Table 1. Elemental Analysis of Huadian Kerogen (wt %, Dry and Ash-Free Basis) C H O N Sta H/Cb O/Cb N/Cb S/Cb a

4123

71.73 8.885 11.033 1.29 2.257 1.486 0.115 0.189 0.012

Total sulfur. bAtomic ratio. DOI: 10.1021/ef502759q Energy Fuels 2015, 29, 4122−4136

Article

Energy & Fuels

Figure 1. Structural formula of 12 geometric isomers of Huadian kerogen 2D models. The black solid circle area represents a grid. These geometric isomers with the same molecular formula of C235H365O25N3S3 were used as the starting point for the 3D models developed in this work. The detailed structural information is shown in Table S1 of the Supporting Information. may also account for the difference, which indirectly reflects the complexity and diversity of the structure of kerogen. In addition, the sum of five elemental analysis results is 95.195% rather than 100%, which is attributed to the interaction of the kerogen structure with the inorganic matrix, resulting in kerogen binding tightly to the mineral matter73 and the complete isolation of kerogen from oil shales remaining difficult.103−105 2.2. Structural Characterization. Solid-state 13C NMR spectroscopic measurement for Huadian kerogen was performed with a Bruker AVANCE III 400 MHz NMR spectrometer, operating at

100.63 MHz at room temperature. The kerogen sample was packed into a 5 mm diameter zirconia rotor and spun at 5 kHz. A contact time of 2 ms and recycle delay time of 6 s were used in the crosspolarization (CP) experiments. To quantify the relative proportion of different carbon types in this kerogen, curve fitting of the 13C NMR spectra were conducted using a NMR peak-fitting program. Fourier transform infrared (FTIR) analysis for the Huadian kerogen sample was carried out on a VERTEX 70/70 V FTIR spectrometer. The kerogen sample (1 mg) was further ground to powder with a size of about 200 mesh and mixed with KBr (500 mg). The sample presser 4124


Article

Energy & Fuels

Table 2. Two-Dimensional Models of 19 Isomers of Structure S10 (Representative Aliphatic Ether Bond Position, T1−T4, Representative Carboxylic Acid Position, T5−T7; Representative Carboxylic Acid Derivative Position, T8−T11; Representative Quantity of Tertiary and Quaternary Carbons, T12−T17; and Representative Aromatic Cluster Position, T18−T19)

4125


Article

Energy & Fuels Table 2. continued

4126


Article

Energy & Fuels Table 2. continued

was used to press the resulting mixtures to discs of 10 mm diameter at 10 MPa for 5 min. FTIR spectra for the sample were obtained at 2 cm−1 resolution and collected in the 4000−400 cm−1 wavenumber range. The XPS experiment for this kerogen was measured on Thermo Scientific ESCALAB 250Xi XPS with monochromatic Al Kα radiation, running at a 15 kV voltage and 10 mA current. To obtain the fraction of various functional groups containing O, N, or S heteroatom, the carbon 1s (C 1s), nitrogen 1s (N 1s), and sulfur 2p (S 2p) spectra obtained from the XPS experiment for this kerogen were fitted.18 The XRD spectra of the Huadian kerogen sample was generated on a Bruker D8 VENTURE X-ray single-crystal diffraction equipped with a Cu tube operating at 40 kV and 30 mA. The scan range (2θ) was from 5° to 90°. 2.3. Computational Model and Details. We first chose C235H365O25N3S3 as the total molecular formula of Huadian kerogen, which belongs to the same order of magnitude with Green River oil shale kerogen106 (molecular formula of C235H397O13N3S5) and the kerogen of Li and co-workers 77 (molecular formula of C243H407N3O25S2). On the basis of our experimental characterization data, we constructed 12 2D models (S1−S12) of the Huadian kerogen with the number of “grids” ranging from 2 to 13 to examine the relationship between the structural stability of the model and the number of grids (see Figure 1). The concept of “grid” represents a closed annular space constituted by connecting the aliphatic chain to the aromatic cluster or other aliphatic chain. Three representative heterocycles (pyrrole, pyridine, and thiophene) and six aromatic rings were selected as the construction center. On average, each aromatic ring consists of one oxy-aromatic carbon, two protonated carbons, two branched aromatic carbons, and one bridgehead carbon. Then, these aromatization units were attached to the aliphatic chain, and the functional groups were also placed in the appropriate position. The most stable structure among S1−S12 was then chosen as the starting point to construct 19 2D isomers models (T1−T19; see Table 2) to explain 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 model

stability. For T1−T4, aliphatic ether bonds were attached to primary carbons (T1), secondary carbons (T2), tertiary carbons (T3), and quaternary carbons (T4). For T5−T7, all carboxyl carbons were presented in the form of carboxylic acid and were located next to the secondary carbons (T5), tertiary carbons (T6), and quaternary carbons (T7). For T8−T11, all carboxyl carbons existed as the carboxylic acid derivative and were attached to the primary carbons (T8), secondary carbons (T9), tertiary carbons (T10), and quaternary carbons (T11). T5−T11 were also employed to consider the substituted position effects of carboxyl carbon in this work. For T12−T17, the quantity of tertiary and quaternary carbons ranges from 15 to 20; they were used to explore whether the quantity of tertiary and quaternary carbons have an impact on the stability of the kerogen model. For T18, all aromatic clusters were located at the end position of aliphatic chains, while for T19, the aromatic clusters were on the aliphatic chain and closer to each other. Both T18 and T19 were constructed to investigate the substituted position effects of aromatic clusters. All molecular geometries were fully optimized and characterized as minima of the potential energy surface by calculating the harmonic vibrational frequencies at the B3LYP107−111/STO-3G112 level. Then, the energies of these optimized structures were further refined by single-point calculation at the B3LYP level using the 3-21g basis set. To check the reliability of our DFT calculations, the energy of isomers S1−S12 were further refined by single-point calculation at the B3LYP/ 6-31g(d) level on the basis of the optimized geometries (see the Supporting Information). The Berny analytical gradient optimization routines were used for all optimized calculations. The requested convergence on the density matrix was 10−8 atomic units; the threshold value of maximum displacement was 0.0018 Å; and that of maximum force was 0.000 45 Hartree/Bohr. To verify the accuracy of our DFT calculations, the lowest energy conformation (Huadian kerogen 3D model) was used in the simulation of the NMR spectra. NMR calculations were performed at the B3LYP level using the 3-21g basis set, and the calculated chemical shielding values were converted to chemical shifts on the tetramethylsilane scale using the shielding calculation of methane at the same level of theory. All DFT 4127


Article

Energy & Fuels

Figure 2. (a) Solid-state 13C CP/MAS NMR spectra and (b) its fitting curve of Huadian kerogen.

Table 3. Chemical Shift Values and Mole Percent of Different Structural Carbons in Solid-State 13C NMR Spectra of Huadian Kerogen

calculations were carried out using the Gaussian 09 software113 packages.

than that of the aliphatic band, and almost no signal was observed in the carbonyl carbon region (170−220 ppm). According to the information on the fitting curve (shown in Figure 2b), more details about the structural features of aliphatic carbon can be obtained (shown in Tables 3 and 4). The results show that there are 65 methylene carbons and about 5 alkyl branched aromatic carbons per 100 carbon atoms. The average methylene carbon chain length is 10−16. There are about 7 methine (CH) carbons or quaternary carbons in total per 100 carbons. Approximately 4 aliphatic carbons bonded to oxygen per 100 carbons may exist as aliphatic ethers or alcohols. Besides, Huadian kerogen has a very low aromaticity (fa) of 16.15%, This indicates that there are about 16 aromatic carbons per 100 carbon atoms. According to the results listed in Table 3 and the substituted degree of aromatic rings (δ) in Table 4, each aromatic ring consists of about one oxy-aromatic carbon, two protonated carbons, two

3. RESULTS AND DISCUSSION 3.1. Huadian Kerogen Structural Features. 3.1.1. 13C NMR Spectra Analysis. The CP/MAS 13C NMR specta (illustrated in Figure 2a) are dominated by the aliphatic band (0−90 ppm), which indicates that aliphatic carbons compose the carbon skeletal structure of Huadian kerogen. The main peak centered at 31 ppm implies that methylene (CH2) carbons dominate in all types of aliphatic carbons and the majority of them exists as many long straight chains but not saturated alicyclics. The small sharp peak around 15 ppm confirms the small quantity of methyl. The weak resonance signals appear in the region between 50 and 90 ppm, arising from various aliphatic alcohols and ethers. In stark contrast, the signal intensity of the aromatic band (100−170 ppm) is rather weaker 4128


Article

Energy & Fuels Table 4. Structural Parameters Obtained from the Experiment and Constructed Structure structural parameter aromaticity (%) ratio of aliphatic carbon (%) average methylene chain length branched degree of aliphatic chain (%) substitutive degree of aromatic ring ratio of hydrogen and carbon fraction of oil-prone carbon (%) fraction of gas-prone carbon (%)

symbol

experiment

Table 5. XPS Results for Forms of Organic Oxygen, Nitrogen, and Sulfur model

fa fal Cn BI

16.15 82.19 10−16 8.5

17.0 81.3 13 7.85−10.5

δ H/C fo fg

0.62−0.72 1.49 68.10 14.09

0.71 1.55 67.65 13.65

elemental peaks C 1s

N 1s

S 2p

branched aromatic carbons, and one bridgehead carbon. The bridgehead aromatic carbons can be used to estimate an average aromatic cluster size.114 On average, only one bridgehead carbon is present on each of the aromatic rings, indicating that the average aromatic cluster size (carbon atoms per cluster) is about 10 for Huadian kerogen. The parameter σ + 112 means that the average number of attachments on each aromatic cluster is about 4 for Huadian kerogen. However, both the average aromatic cluster size and σ + 1 value cannot reflect the distribution of cluster sizes, just average estimates. Besides, the quantities of carboxyl and carbonyl carbons are very low, with approximately 1−2 carboxyl or carbonyl carbons per 100 carbon atoms, and dominated by carboxyl carbons. It is well-known that kerogens from different regions have different oil and gas potentials because of the various chemical structures. To evaluate the oil and gas potentials of Huadian kerogen, the fraction of oil-prone carbon ( fo) and fraction of gas-prone carbon ( fg) were calculated using the data of 13C NMR according to the method reported by Qin et al.115 The results of fo (68.10%) and fg (14.09%) indicated that Huadian kerogen has a high oil potential and a relatively low gas potential, belonging to the typical type I kerogen. 3.1.2. XPS Spectra Analysis. The XPS technique can be qualitative and quantitative analyses of oxygen, nitrogen, and sulfur functional groups.105 The XPS C 1s spectra were fitted with four peaks at 284.529, 286.196, 287.471, and 289.035 eV, corresponding to the following groups: aliphatic and aromatic carbon, C−O and C−OH (alcohol, phenol, and ether), O C−O (carboxyl), and OC (carbonyl). The analytical results are listed in Table 4. According to the quantitative data obtained from XPS, there are about 8 OH or 4 C−O−C, 2 OC−O, or OC per 100 carbon atoms. The data about nitrogen forms listed in Table 5 show that the richest organic nitrogen-containing functional group in Huadian kerogen is the pyrrolic unit, followed by amine and pyridine. Besides the above several nitrogen species, Huadian kerogen also contains a certain quantity of nitrogen oxides. This indicates that most nitrogen oxides survive from demineralization because they are either in hindered structures or not completely reacted in the demineralization process. It is doubtless that 163.854, 165.480, 166.780, and 167.998 eV are assigned to FeS2, aliphatic sulfur and aromatic sulfur, sulfoxide, and sulfone, respectively. The results for sulfur show that most sulfur is present in different organic forms, except a rather small quantity of pyrite in Huadian kerogen. The dominant organic sulfur phases are sulfoxide, followed by a certain amount of aliphatic and aromatic sulfur. It is worth mentioning that sulfoxides do not appear in untreated coal sample,116,117 while are widely present in kerogens,118,119

a

functionalities aliphatic and aromatic carbon C−O and C−OH OC−O OC pyrrolic pyridine amino nitrogen oxides pyrite C−S sulfoxide sulfone

fwhma (eV)

binding energy (eV)

relative area (%)

0.275

284.529

88.44

0.902 1.128 0.662 1.798 0.659 1.065 1.450 0.531 0.558 1.510 0.520

286.196 287.471 289.035 400.668 397.479 399.245 403.624 163.854 165.480 166.780 167.998

8.06 2.42 1.08 40.94 15.82 22.64 20.60 16.29 21.94 53.88 7.89

fwhm = full width at half maximum.

suggesting that the sulfoxides in kerogen are most likely from the possible artifacts in kerogen isolation. It has been proven that, under oxidation conditions, sulfides initially present in fresh coals can convert to the oxidized form, especially sulfones and sulfoxides.120 If the same situation occurs in kerogen, the origin of the sulfoxides in kerogen is most likely due to the oxidation of HNO3 during the extraction procedure and it is present in kerogen in the form of organic sulfur. 3.1.3. FTIR Analysis. The infrared spectra of the Huadian kerogen are shown in Figure 3. Two peaks around 2930 and

Figure 3. FTIR spectra of Huadian kerogen.

2850 cm−1 arising from the asymmetrical and symmetrical alkyl CH2 stretching vibrations have the strongest signal in spectra, which is in good agreement with the rather strong resonance signal around 31 ppm observed in 13C NMR spectra, showing that CH2 has an absolute advantage in quantity. The sharp peak appearing at about 720 cm−1 proves the presence of the skeletal vibration of straight chains with more than four CH2 groups. The strong absorption peak at about 1710 cm−1 indicates the presence of a carbonyl group, although with less content. CC stretching contributes to the relatively broader peak at 1630 cm−1 and shows that kerogen contains a certain amount of olefins and aromatic rings. The weak peaks between 1395 and 4129


Article

Energy & Fuels 1365 cm−1 are due to the symmetric bending vibration of CH3. It is suggested that the quantity of CH3 groups is rather less in Huadian kerogen. The peak at 1200−1290 cm−1 proves the presence of ethers and alcohols, and the signal around 3500 cm−1 is mainly attributed to OH stretching of phenols and carboxylic acids. 3.1.4. XRD Spectra Analysis. The XRD spectra of Huadian oil shale and kerogen are shown in Figure 4. The dominant

3.2. Model Stability. A total of 12 2D models (S1−S12) of the Huadian kerogen with the number of grids ranging from 2 to 13 are shown in Figure 1. They were used to discuss the stability characteristics of carbon skeleton isomers of Huadian kerogen. Table 3 summarizes the experimental and theoretical structural parameters of Huadian kerogen. The match between experimental and theoretical values strongly suggests that the constructed models can represent the real Huadian kerogen structure within acceptable levels. It is worth mentioning that, with the increase of the number of grids in the model, the degree of cross-linking of the macromolecular structure was enhanced. This eventually leads to the quantity of methine and quaternary carbon beyond our NMR-measured quantity; therefore, we only discuss the isomer containing up to 13 grids in this work. The total energy distribution obtained at B3LYP/3-21g levels of S1−S12 is shown in Figure 5a (detailed structure information on S1−S12 is presented in Table S1 of the Supporting Information, and calculated energy is presented in Table S2 of the Supporting Information). As seen from Figure 5, the total energy distribution between structures S1 and S10 shows a significant downward trend with the number of grids increasing from 2 to 11. Specifically, each additional grid, the total energy of the model decreases about 16.8 kcal mol−1. When the number of grids is over 11 (starting from structure S10), the curve begins to climb and the total energy of the model shows a rising trend, which means that S10 is not only the inflection of the curve but also the most stable structure among all 12 3D models studied here. Therefore, 11 is the proper number of grids in the carbon skeleton of Huadian kerogen for the consideration of model stability. To discuss the reproducibility of the kerogen model with 11 grids corresponding to the lowest energy conformation, the energy of isomers S1−S12 were further refined by single-point calculation at the B3LYP/6-31g(d) level on the basis of the optimized geometries. Their energy distribution is shown in Figure S1 of the Supporting Information. The curve presents a similar changing trend with the curve at the B3LYP/3-21g level, which further explains that the isomer with 11 grids corresponds to the lowest energy conformation. That is, 11 grids are necessary and sufficient to build an optimal kerogen model in this paper. It is well-known that the kerogen molecule contains several long alkane groups. The dihedral torsion angles among them would change at different temperatures and, thus, will affect their geometries and energies. In the present paper, the

Figure 4. XRD spectra of Huadian oil shale and kerogen. I/S, illite and smectite mixed layer; K, kaolinite; M, muscovite; Q, quartz; C, calcite; Z, zeolite; and P, pyrite.

mineral phases identified in the Huadian original oil shale are quartz and calcite while also containing small amounts of other minerals, including muscovite, kaolinite, zeolite, pyrite, illite, and smectite mixed layers. After the demineralization process, one broad hump and several small sharp peaks are observed from the XRD spectra of Huadian kerogen as well as several small sharp peaks coming from pyrite, which is not decomposed by demineralization. The formation of the broad hump at about 20° = 2θ is mainly attributed to both alkanes and naphthenes. One characteristic peak at 28° =2θ named the 002 peak represents the existence of aromatic structures. Two peaks at 43° and 73° = 2θ with a considerably weak intensity named 010 and 011 peaks, respectively, come from aromatic carbon diffraction. All of these imply that Huadian kerogen is mainly composed of aliphatic methylene.

Figure 5. (a) Energy distribution of 12 3D models of Huadian kerogen at the B3LYP/3-21g level. (b) Energy gap distribution of 12 3D models of Huadian kerogen at the B3LYP/3-21g level. 4130


Article

Energy & Fuels

Figure 6. Area I, substituted position effects of aliphatic ether bonds on model stability; area II, substituted position effects of carboxylic acid on model stability; area III, substituted position effects of the carboxylic acid derivative on model stability; area IV, quantity of tertiary and quaternary carbons on model stability; and area V, effects of aromatic cluster position on model stability.

Figure 7. Final 3D model (T4) of Huadian kerogen. In the (a) front view, (b) side view, and (c) top view, oxygen atoms are shown in red, nitrogen atoms are shown in pink, sulfur atoms are shown in claybank, carbon atoms are shown in yellow, and hydrogen atoms are shown in light blue.

temperature effects on molecular geometries were not considered because of the limitation of DFT-optimized calculations. However, these data obtained from DFT calculations at the same level are still instructive for discussing geometric isomerization. The energy gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) can sometimes be used to estimate the chemical reactivity of a molecule. When the band gap is wider, the structure is more stable. As shown in Figure 5b, the largest energy HOMO−LUMO gap is assigned to structure S7 (with 8 grids, ΔEHOMO−LUMO = 3.242 ev). Then the energy gap decreases and reaches a basically flat stage between structures S9 and S11 (ΔEHOMO−LUMO = 3.155−3.159 ev). Overall, structure S10 has a low reactivity, although its energy gap is 0.087 ev less than S7. On the basis of the above analysis, S10 was viewed as the most stable structure among 12 3D models and selected as the starting point to build 19 isomers (T1−

T19) to discuss the substituted position effects on model stability. To explain the substituted position effects of the aromatic ring, aliphatic ether bond, carboxylic acid, and carboxylic acid derivative as well as the effect of quantity of tertiary and quaternary carbons on model stability, the most stable structure S10 was chosen as the starting point to construct 19 2D isomer models (see Figure 2). The total energy distribution obtained at the B3LYP/3-21g level of T1−T19 is shown in Figure 6 (detailed structure information on T1−T12 is presented in Table S1 of the Supporting Information, and calculated energy is presented in Table S3 of the Supporting Information). Figure 6 (area I) shows the substituted position effects of aliphatic ether bonds. For structures T1, T2, T3, and T4, whose aliphatic ether bonds attach to primary, secondary, tertiary, and quaternary carbons, respectively, the curve between them presents a significant downward trend, which implies that, under the same chemical environment, the model with aliphatic 4131


Article

Energy & Fuels

Figure 8. Comparison between (a) calculated 13C NMR spectra and (b) experimental solid-state 13C NMR spectra of Huadian kerogen.

3.3. Evaluation of the Huadian Kerogen 3D Model. Because structure T4 is the most stable species among all of the isomers of Huadian kerogen, T4 was viewed as the final Huadian kerogen 3D model and the further discussion will be based on T4 in this paper. Figure 7 displays the geometries of the final Huadian kerogen 3D model (T4). It can be seen that the Huadian kerogen 3D model presents an excellent compact spatial structure and has very little polycyclic aromatic structure. Most of the aromatic units are separated by various bridge bonds and/or many CH2 long chains, almost without being coplanar in space. The degree of cross-linking of the 3D model is high, which leads to the space macromolecular network structure of Huadian kerogen. To explore reasonability of the proposed Huadian kerogen 3D model, the 13C NMR spectra to this Huadian kerogen 3D model have been calculated at B3LYP/3-21g levels (see Figure 8). According to the calculated 13C NMR spectra, the ratio of aliphatic carbon and aromatic carbon is calculated to be 81.39 and 17.98%, with each of them comparable to the experimental values of 82.19 and 16.15%, respectively. The fraction of carbonyl carbon in calculated 13C NMR spectra is 0.63%, which is 1.66% in experimental 13C NMR spectra. Overall, the spectra obtained from the 3D model and experimental 13C NMR spectra are very similar, with only slight differences in the carboxyl carbon and carbonyl carbon chemical shift regions. This is not unexpected; the significant peak cannot be clearly observed in experimental spectra because of the very small amount of carboxyl and carbonyl carbon presented in Huadian kerogen. For the calculated spectra, because of restrictions by the size of the model, these peaks can not be found in higher chemical shifts (170−220 ppm). The agreement between calculated and experimental spectra is quite good in terms of line shape for both aliphatic and aromatic regions as well as in the relative intensities. These studies further confirm that the final 3D model (T4) can represent the features of Huadian kerogen and demonstrate the feasibility of extending the 2D model into a 3D model.

ethers bonding to quaternary carbons tends to be more stable than others. The correlation between the stability of the model and the present status of carboxyl carbons is presented in Figure 6 (areas II and III). For one case, where carboxyl carbons present as carboxylic acid, the total energy of the model increases in the following order: secondary (T5) < quaternary (T7) < tertiary (T6). This means that carboxyl carbons attaching to secondary carbons can lead to a lower energy structure. For another case, where carboxyl carbons exist as the carboxylic acid derivative, the order of total energy can be concluded as follows: primary (T8) > secondary (T9) > tertiary (T10) > quaternary (T11). In contrast with carboxylic acid, the results show that the carboxylic acid derivative bonding to quaternary carbon contributes to a more stable model. The quantity of tertiary and quaternary carbons is also taken into account. Figure 6 (area IV) presents the total energy changing trend between T12 and T17 (S10 is also considered) with the quantity of tertiary and quaternary carbons increasing from 15 to 21. For T12, T13, and T14, the quantity of tertiary and quaternary carbons is 15, 16, and 17, respectively, and their total energy is significantly higher than other structures. While for T15, T16, T17, and S10 (the quantity of tertiary and quaternary carbon is 18, 19, 20, and 21, respectively), the total energy is obviously lower with no apparent difference between them, which indicates that a higher quantity of tertiary and quaternary carbons is conducive to a stable model and 18−21 is the ideal quantity for tertiary and quaternary carbons in this work. To discuss the effects of aromatic cluster position, all aromatic clusters are located at the end position of aliphatic chains in model T18 and lie on the aliphatic chain and close to each other in model T19. S10 is also taken into consideration here. As shown in Figure 6 (area V), structure S10 has the lowest energy between them, whose aromatic clusters are evenly distributed in the spatial structure of macromolecules and located within the grid, which shows that, for the consideration of model stability, aromatic clusters should have a dispersed distribution in the structure. 4132


Energy & Fuels

■

4. CONCLUSION In the present paper, the chemical structure of Huadian kerogen was investigated using solid-state 13C NMR, XPS, FTIR, XRD techniques, and DFT calculations. The possible carbon skeleton isomer and substituted position effects of the aromatic ring, aliphatic ether bond, carboxyl carbons, etc. of the Huadian kerogen molecule have been systematically considered. According to these results, a relatively stable Huadian kerogen 3D model was proposed. From the research, we can draw the following conclusions: (i) Aliphatic carbons (82.19%) compose the carbon skeletal structure of Huadian kerogen, and methylene carbons dominate in all types of carbon. Although Huadian kerogen has a very low aromaticity of 16.15%, the substitutive degree of aromatic ring is relatively high (0.62− 0.72). Organic oxygens mainly exist as C−O, C−OH, OC− O, and CO. The richest organic nitrogen-containing functional group in Huadian kerogen is pyrrolic, followed by amine and pyridinic. Organic sulfurs are distributed as sulfoxide, aromatic, and aliphatic sulfur. (ii) DFT calculation on carbon skeleton isomers shows that the calculated total energy decreases with the number of grids, specifically about a 16.8 kcal mol−1 decrease in total energy for every grid increase when the number of grids increases from 2 to 11. However, the total energy of the model is no longer declining and starts to climb when the number of grids is over 11, which means that 11 grids are appropriate in this paper for building the chemical structure of Huadian kerogen. (iii) 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. An aromatic cluster dispersed distribution also makes a contribution to improve the stability of the model. (iv) The Huadian kerogen 3D model was tested reasonably through the match between the calculated and experimental 13C NMR spectra, which indicates that the model with a molecular formula in the magnitude of C235H365O25N3S3 can represent the structural features of Huadian kerogen.

■ ■

REFERENCES

(1) Miknis, F. P.; Smith, J. W. An NMR survey of United States oil shales. Org. Geochem. 1984, 5, 193−201. (2) Brandt, A. R. Converting oil shale to liquid fuels with the Alberta Taciuk Processor: Energy inputs and greenhouse gas emissions. Energy Fuels 2009, 23, 6253−6258. (3) Han, S. B.; Zhang, J. C.; Li, Y. X.; Horsfield, B.; Tang, X.; Jiang, W. L.; Chen, Q. Evaluation of Lower Cambrian shale in northern Guizhou province, south China: Implications for shale gas potential. Energy Fuels 2013, 27, 2933−2941. (4) Ballice, L. Effect of demineralization on yield and composition of the volatile products evolved from temperature-programmed pyrolysis of Beypazari (Turkey) oil shale. Fuel Process. Technol. 2005, 86, 673− 690. (5) Al-Harahsheh, A.; Al-Harahsheh, M.; Al-Otoom, A.; Allawzi, M. Effect of demineralization of El-lajjun Jordanian oil shale on oil yield. Fuel Process. Technol. 2009, 90, 818−824. (6) Engel, M. H.; Macko, S. A. A review of macromolecular organic compounds that comprise living organisms and their role in kerogen, coal, and petroleum formation. Organic Geochemistry: Principles and Applications; Springer: New York, 1993; p 62. (7) Miknis, F. P.; Szeverenyi, N. M.; Maciel, G. E. Characterization of the residual carbon in retorted oil shale by solid-state 13C NMR. Fuel 1982, 61, 341−345. (8) Solomon, P. R.; Miknis, F. P. Use of Fourier transform infrared spectroscopy for determining oil shale properties. Fuel 1980, 59, 893− 896. (9) Kolodziejski, W.; Klinowski, J. Kinetics of cross-polarization in solid-state NMR: A guide for chemists. Chem. Rev. 2002, 102, 613− 628. (10) Trewhella, M. J.; Poplett, L. J. F.; Grint, A. Structure of Green River oil shale kerogen: Determination using solid state 13C NMR spectroscopy. Fuel 1986, 65, 541−546. (11) Lille, Ü .; Heinmaa, I.; Pehk, T. Molecular model of Estonian kukersite kerogen evaluated by 13C MAS NMR spectra. Fuel 2003, 82, 799−804. (12) Solum, M. S.; Mayne, C. L.; Orendt, A. M.; Pugmire, R. J.; Adams, J.; Fletcher, T. H. Characterization of macromolecular structure elements from a Green River oil shale, I. Extracts. Energy Fuels 2014, 28, 453−465. (13) Mao, J. D.; Fang, X. W.; Lan, Y. Q.; Schimmelmann, A.; Mastalerz, M.; Xu, L.; Schmidt-Rohr, K. Chemical and nanometerscale structure of kerogen and its change during thermal maturation investigated by advanced solid-state 13C NMR spectroscopy. Geochim. Cosmochim. Acta 2010, 74, 2110−2127. (14) Boucher, R. J.; Standen, G.; Eglinton, G. Molecular characterization of kerogens by mild selective chemical degradation ruthenium tetroxide oxidation. Fuel 1991, 70, 695−702. (15) Petsch, S. T.; Smernik, R. J.; Eglinton, T. I.; Oades, J. M. A solid state 13C NMR study of kerogen degradation during black shale weathering. Geochim. Cosmochim. Acta 2001, 65, 1867−1882. (16) Resing, H. A.; Garroway, A. N.; Hazlett, R. N. Determination of aromatic hydrocarbon fraction in oil shale by 13C NMR with magic angle spinning. Fuel 1978, 57, 450−454. (17) Miknis, F. P.; Smith, J. W.; Maughan, E. K.; Maciel, G. E. 13C NMR measurements of the genetic potentials of oil shales. Geochim. Cosmochim. Acta 1982, 46, 977−984. (18) Miknis, F. P.; Maciel, G. E.; Bartuska, V. J. Cross polarization magic-angle spinning 13C NMR spectra of oil shales. Org. Geochem. 1979, 1, 169−176. (19) Miknis, F. P.; Lindner, A. W.; John Gannon, A.; Davis, M. F.; Maciel, G. E. Solid state 13C NMR studies of selected oil shales from Queensland, Australia. Org. Geochem. 1984, 7, 239−248. (20) Vandenbroucke, M.; Largeau, C. Kerogen origin, evolution and structure. Org. Geochem. 2007, 38, 719−838. (21) McCollum, J. D.; Wolff, W. F. Chemical beneficiation of shale kerogen. Energy Fuels 1990, 4, 11−14. (22) Kelemen, S. R.; Afeworki, M.; Gorbaty, M. L.; Sansone, M.; Kwiatek, P. J.; Walters, C. C.; Freund, H.; Siskin, M.; Bence, A. E.;

ASSOCIATED CONTENT

S Supporting Information *

Detailed structural information, calculated total energy configurational isomers, and xyz Cartesian coordinates Huadian kerogen (PDF). The Supporting Information available free of charge on the ACS Publications website DOI: 10.1021/ef502759q.

Article

of of is at

AUTHOR INFORMATION

Corresponding Author

*Telephone/Fax: 86-0432-64606919. E-mail: liucg407@163. com and/or [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (51276034 and 21373043) and the Chinese Postdoctoral Science Foundation (2013M540261). 4133


Article

Energy & Fuels Curry, D. J.; Solum, M.; Pugmire, R. J.; Vandenbroucke, M.; Leblond, M.; Behar, F. Direct characterization of kerogen by X-ray and solidstate 13C nuclear magnetic resonance methods. Energy Fuels 2007, 21, 1548−1561. (23) Tong, J. H.; Han, X. X.; Wang, S.; Jiang, X. M. Evaluation of structural characteristics of Huadian oil shale kerogen using direct techniques (solid-state 13C NMR, XPS, FT-IR, and XRD). Energy Fuels 2011, 25, 4006−4013. (24) Fletcher, T. H.; Gillis, R.; Adams, J.; Hall, T.; Mayne, C. L.; Solum, M. S.; Pugmire, R. J. Characterization of macromolecular structure elements from a Green River oil shale, II. Characterization of pyrolysis products by 13C NMR, GC/MS, and FTIR. Energy Fuels 2014, 28, 2959−2970. (25) Bunger, J. W.; Russell, C. P.; Cogswell, D. E. Molecular composition of shale oil. Oil Shale 2010, 5, 103−113. (26) Salmon, E.; Behar, F.; Hatcher, P. G. Molecular characterization of type I kerogen from the Green River formation using advanced NMR techniques in combination with electrospray ionization/ ultrahigh resolution mass spectrometry. Org. Geochem. 2011, 42, 301−315. (27) Crawford, P. M.; Killen, J. C. New challenges and directions in oil shale development technologies. Oil Shale 2010, 2, 21−60. (28) Burnham, A. K.; Braun, R. L.; Gregg, H. R. Comparison of methods for measuring kerogen pyrolysis rates and fitting kinetic parameters. Energy Fuels 1987, 1, 452−458. (29) Aboulkas, A.; Makayssi, T.; Bilali, L.; El harfi, K.; Nadifiyine, M.; Benchanaa, M. Co-pyrolysis of oil shale and plastics influence of pyrolysis parameters on the product yields. Fuel Process. Technol. 2012, 96, 209−213. (30) Al-Harahsheh, M.; Al-Ayed, O.; Robinson, J.; Kingman, S.; AlHarahsheh, A.; Tarawneh, K.; Saeid, A.; Barranco, R. Effect of demineralization and heating rate on the pyrolysis kinetics of Jordanian oil shales. Fuel Process. Technol. 2011, 92, 1805−1811. (31) Williams, P. T.; Ahmad, N. Investigation of oil-shale pyrolysis processing conditions using thermogravimetric. Appl. Energy 2000, 66, 113−133. (32) Braun, R. L.; Rothman, A. J. Oil-shale pyrolysis: Kinetics and mechanism of oil production. Fuel 1975, 54, 129−131. (33) Bai, F. T.; Sun, Y. H.; Liu, Y. M.; Li, Q.; Guo, M. Y. Thermal and kinetic characteristics of pyrolysis and combustion of three oil shales. Energy Convers. Manage. 2015, 97, 374−381. (34) Williams, P. F. V. Thermogravimetry and decomposition kinetics of British Kimmeridge Clay oil shale. Fuel 1985, 64, 540−545. (35) Hagaman, E. W.; Cronauer, D. C.; Schell, F. M. Oil-shale analysis by CP/MAS−13C NMR spectroscopy. Fuel 1984, 63, 915− 919. (36) Miknis, F. P.; Turner, T. F.; Berdan, G. L.; Conn, P. J. Formation of soluble products from thermal decomposition of Colorado and Kentucky oil shales. Energy Fuels 1987, 1, 477−483. (37) Netzel, D. A.; Miknis, F. P. NMR study of U.S. eastern and western shale oils produced by pyrolysis and hydropyrolysis. Fuel 1982, 61, 1101−1109. (38) Miknis, F. P.; Conn, P. J. A common relation for correlating pyrolysis yields of coals and oil shales. Fuel 1986, 65, 248−250. (39) van Krevelen, D. W. Coal Typology Physics Chemistry Constitution, 2nd ed.; Elsevier: Amsterdam, Netherlands, 1993. (40) Burnham, A. K. On solar thermal processing and retorting of oil shale. Energy 1989, 14, 667−674. (41) Burnham, A. K.; Happe, J. A. On the mechanism of kerogen pyrolysis. Fuel 1984, 63, 1353−1356. (42) Hillier, J. L.; Fletcher, T. H. Pyrolysis kinetics of a Green River oil shale using a pressurized TGA. Energy Fuels 2011, 25, 232−239. (43) Hillier, J. L.; Fletcher, T. H.; Solum, M. S.; Pugmire, R. J. Characterization of pyrolysis products from a Colorado Green River oil shale by 13C NMR, XPS, GC/MS, and FTIR. Ind. Eng. Chem. Res. 2013, 52, 15522−15532. (44) Tiwari, P.; Deo, M.; Lin, C. L.; Miller, J. D. Characterization of oil shale pore structure before and after pyrolysis by using X-ray micro CT. Fuel 2013, 107, 547−554.

(45) Tiwari, P.; Deo, M. Detailed kinetic analysis of oil shale pyrolysis TGA data. AIChE J. 2012, 58, 505−515. (46) Tiwari, P.; Deo, M. Compositional and kinetic analysis of oil shale pyrolysis using TGA−MS. Fuel 2012, 94, 333−341. (47) Huss, E. B.; Burnham, A. K. Gas evolution during pyrolysis of various Colorado oil shales. Fuel 1982, 61, 1188−1196. (48) Han, X. X.; Kolaots, I.; Jiang, X. M.; Suuberg, E. M. Review of oil shale semicoke and its combustion utilization. Fuel 2014, 126, 143−161. (49) Huizinga, B. J.; Aizenshtat, Z. A.; Peters, K. E. Programmed pyrolysis−gas chromatography of artificially matured Green River kerogen. Energy Fuels 1988, 2, 74−81. (50) Reynolds, J. G.; Crawford, R. W.; Burnham, A. K. Analysis of oil shale and petroleum source rock pyrolysis by triple quadrupole mass spectrometry: Comparisons of gas evolution at the heating rate of 10 °C/min. Energy Fuels 1991, 5, 507−523. (51) Tissot, B. P.; Welte, D. H. Petroleum Formation and Occurrence, 2nd ed.; Springer-Verlag: Berlin, Germany, 1984; p 700. (52) McIver, R. D. Composition of kerogenClue to its role in the origin of petroleum. Proceedings of the 7th World Petroleum Congress; Mexico City, Mexico, April 2−9, 1967; Vol. 1, pp 25−36. (53) Brandt, A. R. Converting oil shale to liquid fuels: Energy inputs and greenhouse gas emissions of the shell in situ conversion process. Environ. Sci. Technol. 2008, 42, 7489−7495. (54) Wang, S.; Jiang, X. M.; Han, X. X.; Tong, J. H. Effect of retorting temperature on product yield and characteristics of non-condensable gases and shale oil obtained by retorting Huadian oil shales. Fuel Process. Technol. 2014, 121, 9−15. (55) Jaber, J. O.; Probert, S. D.; Williams, P. T. Evaluation of oil yield from Jordanian oil shales. Energy 1999, 24, 761−781. (56) Behar, F.; Kressmann, S.; Rudkiewicz, J. L.; Vandenbroucke, M. Experimental simulation in a confined system and kinetic modelling of kerogen and oil cracking. Org. Geochem. 1992, 19, 173−189. (57) Han, X. X.; Liu, Q. Q.; Jiang, X. M. Heat transfer characteristic of oil shale particle during the retorting. Int. J. Heat Mass Transfer 2015, 84, 578−583. (58) Pepper, A. S.; Corvit, P. J. Simple kinetic models of petroleum formation. Part I: Oil and gas generation from kerogen. Mar. Pet. Geol. 1995, 12, 291−319. (59) Maciel, G. E.; Bartuska, V. J.; Miknis, F. P. Correlation between oil yields of oil shales and 13C nuclear magnetic resonance spectrum. Fuel 1978, 57, 505−506. (60) Maciel, G. E.; Bartuska, V. J.; Miknis, F. P. Improvement in correlation between oil yields of oil shales and 13C NMR spectra. Fuel 1979, 58, 155−156. (61) Campbell, J. H.; Koskinas, G. H.; Stout, N. D. Kinetics of oil generation from Colorado oil shale. Fuel 1978, 57, 372−376. (62) Braun, R. L.; Burnham, A. K.; Reynolds, J. G. Oil and gas evolution kinetics for oil shale and petroleum source rocks determined from pyrolysis−TQMS data at two heating rates. Energy Fuels 1992, 6, 468−474. (63) Tissot, B.; Deroo, G.; Hood, A. Geochemical study of the Uinta Basin: Formation of petroleum from the Green River formation. Geochim. Cosmochim. Acta 1978, 42, 1469−1485. (64) Burnham, A. K. Chemistry and kinetics of oil shale retorting. Oil Shale 2010, 6, 115−134. (65) Kidena, K.; Murata, S.; Nomura, M. A newly proposed view on coal molecular structure integrating two concepts: Two phase and uniphase models. Fuel Process. Technol. 2008, 89, 424−433. (66) Behar, F.; Vandenbroucke, M. Chemical modeling of kerogens. Org. Geochem. 1987, 11, 15−24. (67) Aboulkas, A.; Harfi, K. E. Effects of acid treatments on Moroccan Tarfaya oil shale and pyrolysis of oil shale and their kerogen. J. Fuel Chem. Technol. 2009, 37, 659−667. (68) Li, D. D.; Greenfield, M. L. Chemical compositions of improved model asphalt systems for molecular simulations. Fuel 2014, 115, 347−356. (69) Diallo, M. S.; Cagin, T.; Faulon, J. L.; Goddard, W. A. Thermodynamic properties of asphaltenes: A predictive approach 4134


Article

Energy & Fuels based on computer assisted structure elucidation and atomistic simulations. In Asphaltenes and Asphalts, 2. Developments in Petroleum Science; Yen, T. F., Chilingarian, G. V., Eds.; Elsevier Science, Ltd.: Los Angeles, CA, 2000; Vol. 2, Chapter 5, pp 103−127. (70) Monin, J. C.; Durand, B.; Vandenbroucke, M.; Huc, A. Y. Experimental simulation of the natural transformation of kerogen. Phys. Chem. Earth 1980, 12, 517−530. (71) Siskin, M.; Scouten, C. G.; Rose, K. D.; Aczel, D.; Colgrove, S. G.; Pabst, R. E. Detailed structural characterization of the organic material in Rundle Ramsay crossing and Green River oil shales. In Composition, Geochemistry and Conversion of Oil Shales; Snape, C., Ed.; Kluwer Academic Publishers: Norwell, MA, 1995; p 143. (72) Faulon, J. L.; Vandenbroucke, M.; Drappier, J. M.; Behar, F.; Romero, M. 3D chemical model for geological macromolecules. Org. Geochem. 1990, 6, 981−993. (73) Vandergrift, G. F.; Winans, R. E.; Scott, R. G.; Horwitz, E. P. Quantitative study of the carboxylic acids in Green River oil shale bitumen. Fuel 1980, 59, 627−633. (74) Jeong, K. M.; Kobylinski, T. P. Organic−mineral matter interactions in Green River oil shale. Prepr. Pap.Am. Chem. Soc., Div. Fuel Chem. 1983, 28, 493−512. (75) Brons, G.; Siskin, M.; Botto, R. I.; Guven, N. Quantitative mineral distribution in Green River and Rundle oil shales. Energy Fuels 1989, 3, 85−88. (76) Orendt, A. M.; Pimienta, I. S. O.; Badu, S. R.; Solum, M. S.; Pugmire, R. J.; Facelli, J. C.; Locke, D. R.; Chapman, K. W.; Chupas, P. J.; Winans, R. E. Three-dimensional structure of the Siskin Green River oil shale kerogen model: A comparison between calculated and observed properties. Energy Fuels 2013, 27, 702−710. (77) Ru, X.; Cheng, Z. Q.; Song, L. H.; Wang, H. Y.; Li, J. F. Experimental and computational studies on the average molecular structure of Chinese Huadian oil shale kerogen. J. Mol. Struct. 2012, 1030, 10−18. (78) Collell, J.; Ungerer, P.; Galliero, G.; Yiannourakou, M.; Montel, F.; Pujol, M. Molecular simulation of bulk organic matter in type II shales in the middle of the oil formation window. Energy Fuels 2014, 28, 7457−7466. (79) Ungerer, P.; Collell, J.; Yiannourakou, M. Molecular modeling of the volumetric and thermodynamic properties of kerogen: Influence of organic type and maturity. Energy Fuels 2015, 29, 91−105. (80) Curtis, M. A. Optimization by simulated annealing theory and chemometric applications. J. Chem. Educ. 1994, 71, 775. (81) Heller, E. J. Guided Gaussian wave packets. Acc. Chem. Res. 2006, 39, 127−134. (82) Dupuis, M.; Watts, J. D.; Villar, H. O.; Hurst, G. J. B. The general atomic and molecular electronic structure system hondo: Version 7.0. Comput. Phys. Commun. 1989, 52, 415−425. (83) Wang, Q.; Zhao, W. Z.; Liu, H. P.; Jia, C. X.; Li, S. H. Interactions and kinetic analysis of oil shale semi-coke with cornstalk during co-combustion. Appl. Energy 2011, 88, 2080−2087. (84) Wang, Q.; Yang, B. W.; Bai, J. R. Rate constant computation on some chlorination reactions of Hg in combustion flue gas. Energy Procedia 2012, 14, 66−72. (85) Bai, J. R.; Wang, Q.; Wei, Y. Z.; Liu, T. Geochemical occurrences of rare earth elements in oil shale from Huadian. J. Fuel Chem. Technol. 2011, 39, 489−494. (86) Qing, H.; Yang, K.; Sun, B. Z.; Wang, Q.; Xu, C. H.; Qi, Y. Q. Experimental study on spouted bed hydrodynamics for oil shale semicoke. Energy Procedia 2012, 17, 1740−1746. (87) Zhang, J.; Kong, L. W.; Bai, J. R.; Wang, Q. Pyrolysis characteristics of oil shale of six density sections. Energy Procedia 2012, 17, 196−201. (88) Sun, B. Z.; Lei, S.; Huang, Z. R.; Wang, Q.; Li, S. H. Analysis on temperature character of CFB bench when cocombustion of oil shale and its semi-coke. Energy Procedia 2012, 17, 1513−1519. (89) Zhang, L. D.; Zhang, X.; Li, S. H.; Wang, Q. Comprehensive utilization of oil shale and prospect analysis. Energy Procedia 2012, 17, 39−43.

(90) Bai, J. R.; Wang, Q.; Jiao, G. J. Study on the pore structure of oil shale during low temperature pyrolysis. Energy Procedia 2012, 17, 1689−1696. (91) Qin, H.; Hao, Z. J.; Wang, Q.; Bai, J. R. Sulfur release from oil shale in retort. Energy Procedia 2012, 17, 1747−1753. (92) Wang, Q.; Kong, L. W.; Bai, J. R.; Gu, Z. Y. The pyrolysis characteristics and pore structure of oil shale of different densities. Energy Procedia 2012, 17, 876−883. (93) Zhang, L. D.; Zhang, X.; Li, S. H.; Wang, Q. Experimental research on mixing and motion with discontinuous feed for oil shale particle groups in rotary kiln. Energy Procedia 2012, 17, 44−48. (94) Wang, Q.; Gu, Z. Y.; Bai, J. R.; Liu, J.; Liu, H. P. Comparative study of the characteristics of oil shale with hot air drying and microwave drying. Energy Procedia 2012, 17, 884−891. (95) Wang, Q.; Xiao, J. B.; Liu, H. P. CFD simulation of hydrodynamics on the dense zone on a 65 t/h oilshale-fired high− low bed CFB boiler. Powder Technol. 2013, 249, 339−352. (96) Wang, Q.; Feng, J. T.; Sun, B. Z.; Qi, Y. Q.; Chen, D. F.; Luo, J. L. Numerical simulation research on gas-solid two phase flow in oil shale circulating fluidized bed. Energy Procedia 2012, 17, 851−860. (97) Wang, Q.; Xu, H.; Liu, H. P.; Jia, C. X.; Zhao, W. Z. Cocombustion performance of oil shale semi-coke with corn stalk. Energy Procedia 2012, 17, 861−868. (98) Wang, Q.; Wang, H. G.; Sun, B. Z.; Bai, J. R.; Guan, X. H. Interactions between oil shale and its semi-coke during co-combustion. Fuel 2009, 88, 1520−1529. (99) Wang, Q.; Luo, J. L.; Xu, C. H.; Chen, D. F.; Sun, B. Z.; Feng, J. T. Numerical simulation of the gas−particle flow behavior in oil shale semi-coke spouted bed. Energy Procedia 2012, 17, 892−900. (100) Raave, H.; Kuldkepp, P.; Leedu, E.; Merivee, A. Recultivation substance and composts produced from semi-coke: The effect on soil characteristics, the yield of field crops and the environment. Oil Shale 2004, 21, 59−73. (101) Pae, T.; Luud, A.; Sepp, M. Artificial mountains in North-East Estonia: Monumental dumps of ash and semi-coke. Oil Shale 2005, 22, 333−344. (102) Ulrike, W. Z. Thermal maturity of type II kerogen from the New Albany shale assessed by 13C CP/MAS NMR. Solid State Nucl. Magn. Reson. 2005, 27, 140−148. (103) Gupta, R.; Gidaspow, D.; Wasan, D. T. Electrostatic beneficiation of eastern oil shales. Chem. Eng. Commun. 1991, 108, 49. (104) Ibrahimov, R. A.; Bissada, K. K. (A dry) Comparative analysis and geological significance of kerogen isolated using open-system (palynological) versus chemically and volumetrically conservative closed-system methods. Org. Geochem. 2010, 41, 800. (105) Siskin, M.; Brons, G.; Payack, J. F., Jr. Disruption of kerogen− mineral interactions in oil shales. Energy Fuels 1987, 1, 248−252. (106) Mith, O. A.; Icby, L. W. Preparation of organic concentrate from Green River oil shale. Anal. Chem. 1960, 32, 1718−1719. (107) Becke, A. D. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648−5652. (108) Lee, C.; Yang, W.; Parr, R. G. Development of the ColleSalvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 1988, 37, 785−789. (109) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Results obtained with the correlation energy density functionals of Becke and Lee, Yang and Parr. Chem. Phys. Lett. 1989, 157, 200−206. (110) Rogel, E.; Carbognani, L. Density estimation of asphaltenes using molecular dynamics simulations. Energy Fuels 2003, 17, 378− 386. (111) Kryachko, E. S.; Ludeña, E. V. Density functional theory: Foundations reviewed. Phys. Rep. 2014, 544, 123−239. (112) Hehre, W. J.; Stewart, R. F.; Pople, J. A. Self-consistent molecular orbital methods I. Use of Gaussian expansions of Slater type atomic orbitals. J. Chem. Phys. 1969, 51, 2657. (113) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; 4135


Article

Energy & Fuels Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09; Gaussian, Inc., Wallingford, CT, 2009. (114) Solum, M. S.; Pugmire, R. J.; Grant, D. M. 13C solid-state NMR of Argonne Premium coals. Energy Fuels 1989, 3, 187−193. (115) Qin, K. Z.; Chen, D. Y.; Li, Z. G. A new method to estimate the oil and gas potentials of coals and kerogens by solid state 13C NMR spectroscopy. Org. Geochem. 1991, 17, 865−872. (116) George, G. N.; Gorbaty, M. L.; Kelemen, S. R.; Sansone, M. Direct determination and quantification of sulfur forms in coals from the Argonne premium sample program. Energy Fuels 1991, 5, 93−97. (117) Huffman, G. P.; Mitra, S.; Huggins, F. E.; Shah, N.; Vaidya, S.; Lu, F. L. Quantitative analysis of all major forms of sulfur in coal by Xray absorption fine structure spectroscopy. Energy Fuels 1991, 5, 574− 581. (118) Wiltfong, R.; Mitra-Kirtley, S.; Mullins, O. C.; Andrews, B.; Fujisawa, G.; Larsen, J. W. Sulfur speciation in different kerogens by XANES spectroscopy. Energy Fuels 2005, 19, 1971−1976. (119) Riboulleau, A.; Derenne, S.; Sarret, G.; Largeau, C.; Baudin, F.; Connan, J. Pyrolytic and spectroscopic study of a sulphur-rich kerogen from the “Kashpir oil shales” (Upper Jurassic, Russian platform). J. Org. Geochem. 2000, 31, 1641−1661. (120) Gorbaty, M. L.; Kelemen, S. R.; George, G. N. Characterization and Chemistry of Organically Bound Sulfur during Coal Conversion. Exxon Research & Engineering Co.: Annandale, NJ, 1990; pp 961− 964.

4136


Three-Dimensional Structure of a Huadian Oil Shale Kerogen Model

Recommend Documents