Quantum Chemical Calculation of the Effects of H₂O on Oxygen Functional Groups during Coal Spontaneous Combustion

Abstract

The effects of H2O on the low-temperature oxidation characteristics of coal have always been one of the keys in the research of coal spontaneous combustion, but most studies rely on experiments for macroscopic derivation, and theoretical researches at the microlevel are rarely mentioned. In this paper, phenylacetaldehyde, phenylethyl alcohol, phenylacetic acid, and ethylbenzene hydroperoxide were used as modeling compounds of coal molecules containing aldehyde (−CHO), alcohol hydroxyl (−OH), carboxyl (−COOH), and peroxide (−C–O–OH). The surface electrostatic potential (ESP), electron density of atoms in molecules (AIM), and reduced density gradient (RDG) of coal molecules were calculated by density functional theory (DFT), and the thermokinetic parameters of low-temperature oxidation of coal molecules with or without H2O were analyzed. The results show that the extreme positive and negative ESPs are located at the H and O atoms of oxygen functional groups (OFGs), respectively, which are the active sites for H2O adsorption. The AIM and RDG show that the phenylacetaldehyde···H2O complexes have two kinds of adsorption configurations with two and three hydrogen bonds, and that the phenylethyl alcohol···H2O complexes also have two kinds of adsorption configurations with one and three hydrogen bonds, and that both phenylacetic acid···H2O and ethylbenzene hydroperoxide···H2O only have one adsorption configuration, forming two and three hydrogen bonds, respectively. According to electron density ρ­(r) and potential energy density V(r), the adsorption strength of H2O by four kinds of oxygen functional groups is ranked as −C–O–OH > −COOH > −OH > −CHO. The thermokinetic parameters show that H2O can increase the activation energy (ΔE) of the oxidation reactions of phenylacetaldehyde and phenylethyl alcohol, which can inhibit the reaction and decrease the activation energy (ΔE) of the oxidation reaction of phenylacetic acid and ethylbenzene hydroperoxide, which can promote the reactions.

Experimental and Quantum Chemical Study on the Inhibition Characteristics of Glutathione to Coal Oxidation at Low Temperature

“…From previously published studies, the ESP of the red region of the molecular structure is positive, and the darker the color is, the more likely it is that the nucleophilic reactions occur; while the ESP in the blue region is negative, and the darker the color is, the more likely it is that the electrophilic reactions occur . Statistically, the reactive site and its ESP value of each molecule are shown in Table , and it can be seen that the ESP near the H37 atom of the GSH molecule is extremely large, which can readily provide electrons to react with the reactive groups and is a nucleophilic reagent.…”

“…In addition, the selection of inhibitors is poorly targeted, the identification of determinant reactive groups is missing, and there is a significant lack of research correlating the inhibiting effects with the chemical structures change in the coal. Wang, Qi, and Zhu et al − established and refined the chain reaction model of COLT, and the results demonstrated that alkyl radicals, alkoxy radicals, hydroxyl radicals, and peroxyl radicals are the main reactive substances. Accordingly, the search for an inhibitor that could inert them is a top priority of current research.…”

Density Functional Calculation of H2O/CO2/CH4 for Oxygen-Containing Functional Groups in Coal Molecules

“…investigated the adsorption strength of different oxygen-containing functional groups (OFGs) for H 2 O molecules using the DFT, and based on the analysis of the electron density and potential energy density, the order of the capacity of four different OFGs to adsorb H 2 O molecules was found to be Ph–C–O–OH > Ph–COOH > Ph–OH > Ph–CHO. 24 Wang et al studied the interaction between H 2 O molecules and OFGs using the quantum chemical DFT and concluded that the order of influence of the H 2 O molecules on the adsorption stability of the OFGs was carboxyl group > phenolic hydroxyl group > aldehyde group > ether and that the OFGs could improve the wettability on the surface of coal molecules. 25 Xiang et al .…”

Study of Butylated Hydroxytoluene Inhibiting the Coal Oxidation at Low Temperature: Combining Experiments and Quantum Chemical Calculations

“…The low-grade coal is about 190 billion tons, accounting for 41.18% of the total coal reserves. 3 − 6 Coal spontaneous combustion is a common disaster phenomenon in the process of coal mining, storage, and utilization. Coal spontaneous combustion will produce toxic and harmful gases such as CO, CO 2 , SO 2 , and NO.…”

“…At present, the coal is still the main production energy and raw material in the world, accounting for 30% of the world’s energy consumption, while Asia’s coal consumption accounts for about 75% of the world. , China is rich in coal resources, accounting for more than 67.5% of disposable energy, but the quality is poor. The low-grade coal is about 190 billion tons, accounting for 41.18% of the total coal reserves. − Coal spontaneous combustion is a common disaster phenomenon in the process of coal mining, storage, and utilization. Coal spontaneous combustion will produce toxic and harmful gases such as CO, CO 2 , SO 2 , and NO.…”