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Coal spontaneous combustion (CSC) characteristics were identified by their different types of coal. In this study, the samples of lignite, non-caking coal, lean coal, and anthracite were chosen to investigate the variations of gaseous products and main active groups during the low-temperature oxidation. The law of indicator gases was obtained by temperature-programmed experiment, and active groups of four coal samples had specific and different probabilities of spontaneous combustion via Fourier transform infrared spectrometer (FTIR). The relationship between the indicator gases at different stages and the main functional groups of coal were explored by Grey correlation analysis. The results indicated that the characteristic temperatures of water evaporation and gases desorption period of four types of coal showed the similar variation with those in thermal storage stage (Stage 1). Moreover, temperature ranges (TRs) in Stage 1 of lignite, non-caking coal, lean coal, and anthracite were 20–60, 20–60, 20–60, and 20–80°C, respectively; TRs in Stage 2 were 60–100, 60–140, 60–120, and 80–200°C, respectively; TRs in Stage 3 were 100–180, 140–180, 120–180, and 200–240°C, respectively. Based on the correlation analysis, the hydroxyl, carboxyl, and methylene had a sound temperature correlation with indicator gases emission. Eventually, the prediction system for CSC during the low-temperature oxidation was revealed. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion (CSC) is a global, long-standing thermal hazard in coal mining that causes serious environmental damage, particularly in developing countries. Ionic liquids (ILs) are environmentally friendly, green, economical, and a new type of fire-preventing material that inhibits coal oxidation and alleviates thermal production. In this study, 1-butyl-3-methyl imidazole tetrafluoroborate ([BMIM][BF4]) and 1-butyl-3-methyl imidazole ([BMIM][I]) at various mass ratios (0.0, 0.5, 2.0, 5.0, and 10.0 mass%) were used to treat three types of coal (lignite, 1/3 coking coal, and anthracite) for CSC. The combustion-mass loss and thermal release rate of ILs treated relative to untreated coal samples were investigated using a synchronous thermal analyzer, and the optimal addition mass ratio of ILs was predicted. Not only do ILs have the most efficient inhibiting effect, but they also consider the economic benefit. Per thermogravimetric-differential scanning calorimetry, for the content of 5.0 mass% [BMIM][BF4], the inhibiting effect is favorable for universal applications. In addition, coal samples treated with 5.0 mass% [BMIM][BF4] were subjected to programmed-temperature heating experiment testing. The oxygen consumption rate, inhibiting effect, as well as apparent activation energy, were determined. The inhibiting effect at 120.0–150.0 °C was the most obvious, which provided the basis of the application for CSC prevention. [ABSTRACT FROM AUTHOR]

The chemical structure and morphological of lignite treated with four imidazole ionic liquids (ILs), namely [BMIM][BF 4 , [BMIM][NO 3 , [BMIM][I], and [EMIM][BF 4 , was characterized through scanning electron microscopy and X-ray diffraction. Furthermore, the exothermic properties of the oxidation process at low temperatures (<200.0 °C) were investigated using a C80 microcalorimeter. The results revealed that the IL partially dissolved minerals and side chains of surface molecules in lignite, resulting in reduction of the unit stacking degree, ductility, and number of effective piles, which ultimately led to a lower coalification degree of the treated coal sample. The initial exothermic temperature of the treated coal sample increased and that more thermal energy was absorbed and less thermal energy was released in the endothermic and exothermic phases, respectively, as a result of the destruction of the molecular structure of coal by IL. The exotherm and the exothermic heat release rates from treated coal samples were consistent and in the following order: IL-untc > [BMIM][NO 3 -tc > [BMIM][I]-tc > [EMIM][BF 4 -tc > [BMIM][BF 4 -tc. The IL destroys the chemical structure of the coal, resulting in a decrease in the activity of the coal, which is manifested by an increase in apparent activation energy. • A new initial temperature characterization method was established. • The external morphology and structure of coal have changed due to ILs. • ILs have a prominent effect of reducing on the exothermic properties. • The oxidation activity of coal could be feasibly inert by ILs. [ABSTRACT FROM AUTHOR]

To contain coal fires, three green antioxidants of plant extract which cover resveratrol (Res), tea polyphenols (TP), and β -carotene (β -car) are investigated in this paper, and their inhibitory effects on surface groups and structure are revealed. X-ray diffraction test tells that antioxidants exert a slight augment of d 100 and L c and are able to destroy the unstable side chains to some extent. Though coal samples are affected by antioxidants, minimal differences of aromatic structure have been proved. Fourier-transform infrared spectroscopy technique is employed and a new concept of influence sensitivity value is introduced. The results indicate that antioxidants and addition amounts have an impact on various groups, and the majority of groups tend to be inhibited within 3 wt% addition. Further, the optimal inhibitory concentration of Res, TP, and β -car is 1 wt%, 3 wt%, and 1 wt%, respectively. Combined with gaseous indexes, CO 2 emissions of Res and TP exhibit a wave variation under 100 °C, and exponential growths of others occurred twice is acquired. Antioxidants can bring out the decline of apparent activation energy (E a), and TP worked most brilliantly and it increases E a by 7.503 kJ/mol. In summary, the order of inhibitory effect is TP > Res > β -car. • Antioxidants have a slight effect on microcrystalline structure. • A new definition is introduced to explain the groups' variation. • The best inhibitory effect of antioxidants is addition of 1 wt% or 3 wt%. • Inhibitory effect contains a complex action of physics and chemistry probably. [ABSTRACT FROM AUTHOR]