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The thermokinetics and gaseous products of Jurassic coals collected from northern Shaanxi, China at four different heating rates were determined via thermogravimetry-Fourier transform infrared spectroscopy experiments. The results showed that the trends of thermogravimetric pyrolysis and oxidation curves were divided into three stages and five stages, respectively, and presented the same variations. As the heating rate increased, their curves moved the high temperature. In addition, the characteristic temperatures indicated that the coal samples had a relatively significant spontaneous combustion tendency. In the stage of water evaporation and gas desorption, the rates of formation of CO and CO2 went up promptly, and gaseous water produced during the oxidation reaction began to increase, but its generation rate was lower than that in the stage of oxygen absorption and mass increase. The apparent activation energy (Ea) showed a characteristic jump with increasing temperature, and the optimal mechanism function was chosen by integration and differentiation. Moreover, the relationship between Ea and lnA was linear, which indicated that there was a kinetic compensation effect.

Spontaneous combustion of coal has become an important disaster that threatens the safety of coal mines. FeS2 is the main component of pyrite, which is suspected to be a major contributor to coal spontaneous combustion (CSC). So, it has important significance to FeS2 on the characteristics of coal oxidation for prevention and treatment. This study used coal samples mixed with different proportions of FeS2 (2.0 mass%, 4.0 mass%, and 6.0 mass% mass percentage) were tested to investigate the characteristics of spontaneous combustion, as compared with the fresh sample. The CO and CO2 production rates, critical temperature, and dry cracking temperature during oxidation were analyzed. The temperature-programmed experiments was conducted to simulate low-temperature oxidation processes realistically. In-situ infrared spectroscopy was used to appraise the evolution of low-temperature (

Coal spontaneous combustion (CSC) has become a safety topic and has been widely debated. This study investigated the inhibiting effect on CSC by using a series of novel ionic liquids (ILs) as chemical inhibitors. The microstructure and thermokinetic characters were observed and evaluated by Fourier transform infrared spectroscopy and synchronous thermal analyser. The results indicated that ILs could destroy reactive groups on relatively active coal surfaces, such as OH, aliphatic C H, and O-containing groups. However, as aromatic CH is the main chain of coal molecule, damaging it is difficult. Different anions and cations found in ILs exhibited different abilities for destroying the groups on the surface of coal molecules. The damage was caused by the properties of anions and cations by affecting the chain length, number of chains of the anion and cations, and electronegativity strength. The changes in microstructure increased the physical adsorption capacity of inhibitive coal samples during low-temperature oxidation, which changed the characteristic temperature points. In stages of water evaporation and desorption mass loss (stage 2) and the thermal decomposition (stage 3), the apparent activation energy of coal samples increased. The kinetic characteristics of the obstructed coal sample were predicted using the Flynn–Wall–Ozawa method. The development ability was delayed and the risk level was reduced of CSC in stages 2 and 3. Therefore, ILs should be utilised at relatively low-temperatures (

To investigate the effects of ionic liquids (ILs) on the oxidative combustion characteristics of coal, the oxidation characteristics of ILs on coal, such as characteristic temperature, thermal mass loss rate, and oxidation kinetics characteristic parameters, were determined. The results the [BMIm][I]-treated coal samples increased cracking temperature (T1), maximum oxidization mass gain (T2), ignition temperature (T3), burnout temperature (T4), minimum thermal rate (Ta), maximum thermal energy (Tb), and maximum thermal rate (Tc) by 33.2, 29.3, 20.7, 42.8, 11.4, 23.0, and 27.9 °C, respectively. The increase mass ratio of coal samples treated with ILs increased and decreased at the water evaporation and thermal decomposition stages, respectively. The apparent activation energy (Ea) of coal samples treated with ILs increased, and the mechanism function also changed accordingly. These showed that the ILs improved the thermal stability of the coal samples in the stages of absorbing oxygen and increased mass, and the loss of combustion. The ILs caused damage to the molecular structure of the coal and ultimately effected changes in the combustion performance. In addition, the [BMIm][BF4] hardly weakens the inhibitory effectiveness of the coal sample over time; coal spontaneous combustion could be effectively inhibited.

The effects of ionic liquids (ILs) on the macrostructures and characteristic parameters of coal samples during low-temperature oxidation (30.0–200.0 °C) were investigated. The Fourier transform infrared (FTIR) spectroscopy results clearly illustrated that the destruction of functional groups in the coal molecular structure was prominent, and that the benzene rings in the coal molecular structure were barely affected. Therefore, it can be inferred that ILs played a primary role in the destruction of functional groups in the side chain of the coal molecular structure; thus, the aromatic ring was barely affected. Moreover, the inhibition of the functional group at high temperatures by the ILs was also barely effective. The analysis results of the temperature-programmed testing system indicated that the CO concentration and the production rate of CO by coal samples treated with the ILs presented decreasing trends. This result was in sound agreement with the FTIR results for the quantity of carbonyl groups in oxidation stage. The oxygen consumption rate of the sample treated with the ILs gradually decreased beyond the cracking temperature. Moreover, the difference between the thermal release intensity of coal samples treated with the ILs and that of raw coal gradually increased beyond the critical temperature. The inhibiting effect of [Bmim][BF4] appeared to be greater than that of other ILs, and [Bmim][I] and [Emim][BF4] exerted a slight influence on the low-temperature oxidation process of coal samples. Therefore, we conducted a comprehensive comparison of the inhibiting effect of four ILs on bituminous coal during low-temperature oxidation and found that the ILs can be listed in the following order on the basis of their inhibiting effect: [Bmim][BF4] > [Bmim][NO3] > [Emim][BF4] > [Bmim][I].

This study examined the combustion characteristics and kinetics of coal samples treated with imidazole-based ionic liquids (ILs), namely, [Emim][BF4], [Bmim][BF4], [Bmim][NO3], and [Bmim][I], under oxidation. The oxidation of the coal samples was investigated using thermogravimetry (TG) at heating rates of 4.0, 6.0, 8.0, and 10.0 °C·min−1. The results for the IL-treated samples revealed that the composite index S (representing the ignition, combustion, and burnout properties) decreased and Hf (representing the rate and intensity of the combustion process) increased with high correlation coefficients. The characteristic temperatures of the maximum oxidization mass gain (T2), ignition point (T3), maximum mass loss rate (T4), and burnout point (T5) increased by 13.1 ± 0.5, 9.2 ± 0.5, 21.5 ± 0.5, and 35.9 ± 0.5 °C, respectively. At T3 and the maximum mass loss rate, the release of CO and CO2 was further altered, suggesting that the C O functional groups were damaged or oxidized. The results of the Ozawa-Flynn-Wall kinetic equation used to determine the apparent activation energy (Ea) of coal samples revealed that the Ea of the treated samples increased. The reaction rate constant characterizes the effect of Ea and pre-exponential factors (A), and the results showed that ILs can weaken the reaction process at low temperatures (

To study the effect of ionic liquids (ILs) of the microstructure on the surface of the coal, four ILs ([Emim][BF4], [Bmim][BF4], [Bmim][NO3], and [Bmim][I]) were selected to treat the coal samples. Fourier transform infrared spectroscopy and synchronous thermal analyzer were employed to conduct the experimental tests. Active functional groups were analyzed when the ILs contained the same anion or cation. The results indicated that the quantity of the hydrocarbyls and the oxygen-containing functional groups for the coal sample treated by [Emim][BF4] was significantly less than the three coal samples by other ILs treated, in which the maximum area ratio of the hydrocarbons and the oxygen-containing functional groups was 0.553 and 1.159, respectively. However, ILs had lesser destructive effects on the aromatic hydrocarbons. The ILs containing [Emim]+ shared stronger destructibility to the coal’s micro-active structure than that containing [Bmim]+. The highest impact was the hydrocarbyl of the coal. While including the same [Bmim]+, the extent of destruction to the hydrocarbyls and the oxygen-containing functional groups of coal was varied in descending order as [NO3]− > [I]− > [BF4]−. The aliphatic hydrocarbons were destroyed by the anion of ILs following the order: [I]− > [BF4]− > [NO3]−. During the low-temperature oxidation stage, the apparent activation energy increased, whereas the reactivity of coal samples by ILs treated decreased in the order: [Bmim][NO3]

To investigate the effect of coal metamorphism on the probability of coal spontaneous combustion (CSC), five types of coal sample were subjected to a temperature-programmed testing system. The gas indicators and limiting parameters of CSC were analysed and the characteristics of different ranks of coal were observed during low-temperature oxidation. The CO production rate of each coal sample was positively correlated with temperature and the CO production rate of low-ranked coal was greater than that of high-ranked coal. The CO/O2 and CO productivity trends were the same. Analysis of the change in the alkene ratio revealed that the oxidation reaction became more intense if the coal temperature exceeded the dry cracking temperature. The oxygen consumption rate of each coal sample was positively correlated with temperature, low-ranked coal samples exhibiting higher oxygen consumption rates. Graham’s fire coefficient can be used as an auxiliary gas indicator to judge CSC tendency. Analysis of the limiting parameters of CSC revealed that the low limiting oxygen volume fraction and the minimal thickness of residual coal of high-rank samples were higher, whereas maximal air leakage intensity was lower. This paper further demonstrated differences in CSC tendency depending on the coal rank. These findings clarified certain factors affecting CSC, which may aid in preventing CSC in the future.

The chemical structure and morphological of lignite treated with four imidazole ionic liquids (ILs), namely [BMIM][BF4], [BMIM][NO3], [BMIM][I], and [EMIM][BF4], was characterized through scanning electron microscopy and X-ray diffraction. Furthermore, the exothermic properties of the oxidation process at low temperatures ( [BMIM][NO3]-tc > [BMIM][I]-tc > [EMIM][BF4]-tc > [BMIM][BF4]-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.