Differences in Macromolecular Structure Evolution during the Pyrolysis of Vitrinite and Inertinite Based on In Situ FTIR and XRD Measurements
Abstract
:1. Introduction
2. Samples Preparation and Methods
2.1. Samples Preparation
2.2. Experimental Process
2.2.1. In Situ FTIR Spectroscopy
2.2.2. In Situ XRD
3. Results and Analysis
3.1. Analysis of the In Situ FTIR Results
3.1.1. In Situ FTIR Spectrum Characteristics
Aromatic Structure Absorption Bands
Oxygen-Containing Functional Groups Absorption Band
Aliphatic Structure Absorption Bands
Hydroxyl Absorption Band
3.1.2. In Situ FTIR Structural Parameter Characteristics
Aromatic Structure
Aliphatic Structure
3.2. Analysis of In Situ XRD Results
3.2.1. In Situ XRD Pattern Characteristics
3.2.2. In Situ XRD Structural Parameters
4. Discussion
- (1)
- During pyrolysis, the macromolecular structures of vitrinite and inertinite change with increasing temperature. The DOC of vitrinite and inertinite increases, and the plane extensibility and the Lc increase continuously, indicating that both the vitrinite and inertinite of low–middle rank coals have an evolution trend of increasing degree of aromatization in the early stages of pyrolysis. The increase in aromatization is reflected mainly in the continuous expansion of the aromatic structural units. The differences in the structural evolution of vitrinite and inertinite are reflected mainly by the continuous decrease in the d002 peak of vitrinite with increasing temperature, in which the reduced value is 0.013 nm, but there is no obvious change in inertinite. Second, the I, DOC, La, and Lc of inertinite are always higher than those of vitrinite, indicating that the degree of inertinite aromatization is always higher than that of vitrinite.
- (2)
- The pyrolysis process of vitrinite and inertinite can be divided into three stages. Between 30 °C and 200 °C, the content of aromatic groups in vitrinite and inertinite shows no obvious change, while that of aliphatic groups increases slightly. The total amount of oxygen-containing functional groups decreases gradually. The content of C–O–C groups, aromatic C=O, and aromatic ring C=C has a small decrease in a relatively stable situation. The content of aliphatic CH2 and CH3 decreases significantly, and that of Ar–OH groups increases significantly (Figure 17). The content of O–H–π-H bonds increases greatly, and that of free O–H groups decreases greatly. There is no significant change in the I and DOC (Figure 13), which suggests that aliphatic and aromatic structures are enriched slightly at this stage. The enlargement of the aromatic structural system is not obvious in this stage, and the detachment of oxygen-containing functional groups and the enrichment of aliphatic hydrocarbons are the dominating chemical reactions [45].
5. Conclusions
- (1)
- During the pyrolysis process, both the inertinite and vitrinite show an increasing degree of aromatization. With increasing pyrolysis temperature, aromaticity (I), polycondensation degree of aromatic rings (DOC), average lateral sizes (La) of BSU, and stacking heights (Lc) of BSU in vitrinite and inertinite increase, but the aromatization level of inertinite has always been higher than that of vitrinite.
- (2)
- In the temperature range of 30–500 °C for the in situ FTIR spectroscopy, the macromolecular structure evolution of vitrinite and inertinite is divided into three stages: 30–200 °C, 200–300 °C, and 300–500 °C. At 30–200 °C, the detachment of oxygen-containing functional groups and the enrichment of aliphatic hydrocarbons occurs. The 200–300 °C stage is filled mainly by the synergistic effects of aliphatic and aromatic groups. The stage of 300–500 °C is dominated by the aromatization and condensation of macromolecules. The substituents of the aromatic system gradually detach, leading to an increase in I and DOC.
- (3)
- In the temperature range of 30–1000 °C by in situ XRD, the difference in macromolecular structure evolution between vitrinite and inertinite is manifested mainly by the arrangement of aromatic layers, which tends to be more and more ordered in vitrinite regular during the pyrolysis process, while there is no significant change in inertinite. However, the aromatic layers of inertinite are always more compact than that of vitrinite. In addition, the aliphatic side chains of inertinite are more stable than that of vitrinite during pyrolysis.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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No. | Density Interval (g/cm3) | Ro,max (%) | Macerals (%) | Notes | ||
---|---|---|---|---|---|---|
Vitrinite | Inertinite | Liptinite | ||||
1 | 1.3–1.35 | 0.698 | 90 | 8 | 2 | Vitrinite |
2 | 1.35–1.4 | 1.526 | 5 | 95 | 0 | Inertinite |
Wavenumber Range | Absorption Peak Assignment |
---|---|
3600–3700 | free OH bonds |
3500 | OH–π–H bonds |
3350–3400 | self-associated OH bonds |
3300 | OH–ether O hydrogen bonds |
3180–3240 | cyclic OH groups |
3200–3000 | the C–H stretching vibration of the aromatic nucleus |
2940–3000 | aliphatic CH3 asymmetric stretching vibration |
2940–2900 | aliphatic CH2 asymmetric stretching vibration |
2863 | aliphatic CH3 symmetric stretching vibration |
2848 | aliphatic CH2 symmetric stretching vibration |
1700 | the stretching vibration of aromatic C=O |
1650−1520 | the stretching vibration of the aromatic ring C=C |
1440−1360 | aliphatic CH3, and CH2 deformation vibration |
1340–1200 | Ar–OH |
1100 | aryl ether |
1039 | alkyl ether |
868 | aromatic nucleus (CH), one adjacent H deformation |
810 | aromatic nucleus (CH), three adjacent H deformation |
Maceral Category | Temperature (°C) | 2θ002 (°) | d002 (nm) | FWHM | Lc (nm) | 2θ100 (°) | La (nm) |
---|---|---|---|---|---|---|---|
Inertinite | 30 | 25.579 | 0.34796 | 6.841 | 1.191 | 43.104 | 1.093 |
200 | 26.052 | 0.34175 | 6.596 | 1.236 | 42.998 | 1.074 | |
400 | 25.594 | 0.34776 | 5.804 | 1.404 | 43.401 | 1.595 | |
600 | 25.354 | 0.35099 | 5.342 | 1.524 | 44.299 | 1.738 | |
800 | 25.573 | 0.34804 | 4.717 | 1.727 | 42.848 | 1.912 | |
1000 | 25.491 | 0.34915 | 3.552 | 2.293 | 42.955 | 2.720 | |
Vitrinite | 30 | 24.320 | 0.36567 | 8.014 | 1.014 | 42.959 | 1.094 |
200 | 24.805 | 0.35864 | 6.204 | 1.311 | 44.388 | 1.301 | |
400 | 24.919 | 0.35703 | 5.233 | 1.555 | 44.251 | 1.350 | |
600 | 24.983 | 0.35613 | 5.619 | 1.448 | 43.511 | 1.503 | |
800 | 25.104 | 0.35444 | 5.138 | 1.584 | 42.764 | 1.742 | |
1000 | 25.229 | 0.35271 | 4.338 | 1.877 | 44.968 | 2.757 |
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Zhao, M.; Wang, A.; Cao, D.; Wei, Y.; Ding, L. Differences in Macromolecular Structure Evolution during the Pyrolysis of Vitrinite and Inertinite Based on In Situ FTIR and XRD Measurements. Energies 2022, 15, 5334. https://doi.org/10.3390/en15155334
Zhao M, Wang A, Cao D, Wei Y, Ding L. Differences in Macromolecular Structure Evolution during the Pyrolysis of Vitrinite and Inertinite Based on In Situ FTIR and XRD Measurements. Energies. 2022; 15(15):5334. https://doi.org/10.3390/en15155334
Chicago/Turabian StyleZhao, Meng, Anmin Wang, Daiyong Cao, Yingchun Wei, and Liqi Ding. 2022. "Differences in Macromolecular Structure Evolution during the Pyrolysis of Vitrinite and Inertinite Based on In Situ FTIR and XRD Measurements" Energies 15, no. 15: 5334. https://doi.org/10.3390/en15155334