•Structural analyzes of coking and non-coking coal by WAXS, FTIR, and TG/DTG – DSC.•The results obtained show demineralization influence of functional groups of coals.•The structural parameters of ...coking and non-coking coals show a bimodal distribution.•Variation of aromaticity for non-coking coals is more than that of coking coals.•Carbon stacking structure of coking and non-coking coal has been identified.
Eight coking and non-coking coals have been studied by Wide Angle X-ray Scattering (WAXS), Fourier Transform Infrared Spectroscopy (FTIR), and TG/DTG (Thermogravimetry/Derivative Thermogravimetry) – DSC (Differential Scanning Calorimeter). The FTIR study shows that the demineralization treatment significantly influences –OH, aliphatic (–CH3, –CH2), aromatic (C=O), and aromatic nucleus (C=C) functional groups of the raw coals. The structural parameters like interlayer spacing (d002), crystallite size (Lc), lateral size (La), aromaticity (fa)XRD, and rank (I26/I20) are determined from WAXS. The WAXS results of demineralized coal show that d002 (range 3.75–3.51 Å) decreases, but (fa)XRD (range 0.69–0.88) increases with the increase of elemental carbon percentage (Cdaf) and rank of coals. The combustion and kinetic parameters of these coals have been evaluated by TG/DTG – DSC analysis. The ignition temperature (Ti), DTG Tpeak, DSC Tpeak, and burnout temperature (Tb) vary in the range of 338–410 °C, 475–551 °C, 490–555 °C, and 579–641 °C, respectively for demineralized coals however variations of these parameters for raw coals are 345–361 °C, 462–621 °C, 467–631 °C, and 560–675 °C, respectively. The TG/DTG – DSC and FTIR results show that demineralization influences the thermal behaviors and functional groups vis-à-vis structural moieties of coals.
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In this study, three high-ash Indian sub-bituminous coals of different thermal maturities from three different open cast mines of Raniganj basin, eastern India, were studied to understand their ...combustion and pyrolysis behavior. The combustion analyses were performed under three different heating rates (5°C, 10°C, and 15°C/min). From the thermograms of TG-DTG pyrolysis curves, it was observed that the overall pyrolysis reaction can be deduced into four different temperature regions with each region showing unique properties, and those regions are inherent moisture loss, prior to primary pyrolysis, primary pyrolysis, and secondary pyrolysis regions. The main pyrolysis reaction occurs in the primary pyrolysis region for all the samples but a significant devolatilization has also been seen for the early oil window mature noncoking coal in the secondary pyrolysis region. The kinetic parameters were also evaluated for both combustion and pyrolysis analysis. X-ray diffraction revealed that this sample consists of a significant amount of siderite and pyrite, and consequently showed distinct behavior. It was observed that the pyrolysis properties and kinetics were closely related to their complex mechanisms and reactions. Rock-Eval pyrolysis also confirmed the presence of siderite in the sample, which decomposed simultaneously with the organic-matter during pyrolysis.
The Rock-Eval pyrolysis-stage derived parameters such as free hydrocarbons (S1), heavier pyrolysis-hydrocarbons (S2), pyrolyzable carbon (PC) and pyrolysis Tmax (from S2 curve) have received ...considerable interest for source-rock screening and thermal maturity assessment. On the other hand, the Rock-Eval oxidation-stage S4CO2 curve, which gives the amount of residual carbon (RC), only recently has received some interest. While the pyrolysis-stage S2 temperature-peak (Tmax) is conventionally used as a maturity proxy, in this work we show that the temperature-peak of S4CO2 curve (S4Tmax) can also be used as a thermal maturity proxy for shales. For overmature and low-TOC shale samples, showing asymmetric S2 shape and concomitantly producing doubtful Tmax, the S4 curves showed symmetric nature and consequently the S4Tmax was observed to be a reliable thermal maturity estimate. While the S4Tmax clearly resolved immature and overmature shales, for the early mature and peak mature shales the S4Tmax showed overlapping values. S4Tmax of pre-pyrolyzed and pyrolyzed masses showed good positive correlation with differential scanning calorimetry temperature-peak (DSCTpeak), and consequently indicated its applicability as a thermal maturity proxy. When early mature pre-pyrolyzed samples were directly analyzed using the Rock-Eval oxidation stage, the S4 curves showed formation of two sub-peaks, and consequently the Tmax was observed to decrease. It is recommended that analysts and interpreters should thoroughly cross-check S2 curves before reporting data, and in case of asymmetric or unreliable S2 curves, the S4Tmax can be used as a maturity proxy.
•Importance of Rock-Eval oxidation stage.•S4Tpeak as a thermal maturity proxy for shales.•Critical monitoring of Rock-Eval S2 curves.
