Investigation of interactions between oxygen-containing groups and water molecules on coal surfaces using density functional theory

Wang, Chengyong; Xing, Yaowen; Xia, Yangchao; Zhang, Rui; Wang, Shiwei; Shi, Kaiyi; Tan, Jinlong; Gui, Xiahui

doi:10.1016/j.fuel.2020.119556

Cited by 65 publications

(23 citation statements)

References 40 publications

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“…The coal–water interactions have a significant influence on coalbed methane (CBM) extraction, coal utilization, and the prediction of coal mine gas disasters. − In the CBM field, the inherent moisture of coal is considered to be an important factor that affects the interactions between coal and gas . The inherent moisture is mainly absorbed on the surface sites of coal pores due to the physical adsorption and the effects of oxygen-containing functional groups . Moreover, the existing oxygen-containing functional groups are preferentially occupied by the adsorbed water molecules .…”

Section: Introductionmentioning

confidence: 99%

“… 4 The inherent moisture is mainly absorbed on the surface sites of coal pores due to the physical adsorption and the effects of oxygen-containing functional groups. 5 Moreover, the existing oxygen-containing functional groups are preferentially occupied by the adsorbed water molecules. 6 Through long-term research, researchers have found that the existence of water can diminish gas (e.g., CH 4 , CO 2 ) adsorption, diffusion, and seepage capacities of coal.…”

Section: Introductionmentioning

confidence: 99%

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Experimental Study of the Pore Structure and Gas Desorption Characteristics of a Low-Rank Coal: Impact of Moisture

Chen

Zhang

et al. 2022

ACS Omega

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Coal–water interactions have a prominent impact on the prediction of coal mine gas disasters and coalbed methane extraction. The change of characteristics in the microscopic pores of coal caused by the existence of water is an important factor affecting the diffusion and migration of gas in coal. The low-pressure nitrogen adsorption experiments and gas desorption experiments of a low-rank coal with different equilibrium moisture contents were conducted. The results show that both the specific surface area and pore volume decrease significantly as the moisture content increases, and the micropores (pore diameter <10 nm) are most affected by the water adsorbed by coal. In particular, for a water-equilibrated coal sample at 98% relative humidity, micropores with pore sizes smaller than 4 nm as determined by the density functional theory model almost disappear, probably due to the blocking effects of water clusters and capillary water. In this case, micropores with a diameter less than 10 nm still contribute most of the specific surface area for gas adsorption in coal. Furthermore, the fractal dimensions at relative pressures of 0–0.5 (D 1) and 0.5–1 (D 2) calculated by the Frenkel–Halsey–Hill model indicate that when the moisture content is less than 4.74%, D 1 decreases rapidly, whereas D 2 shows a slight reduction as the moisture content increased. In contrast, when the moisture content exceeds 4.74%, further increases in the moisture content cause D 2 to decrease significantly, while there is nearly no change for D 1. The correlation analyses show that the ultimate desorption volume and initial desorption rate are closely related to the fractal dimension D 1, while the desorption constant (K t) mainly depends on the fractal dimension D 2. Therefore, the gas desorption performances of coal have a close association with the pore properties of coal under water-containing conditions, which indicate that the fluctuation in moisture content should be carefully considered in the evaluation of gas diffusion and migration performances of in situ coal seams.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental Study of the Pore Structure and Gas Desorption Characteristics of a Low-Rank Coal: Impact of Moisture

Chen

Zhang

et al. 2022

ACS Omega

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“…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 investigated the adsorption behavior of the binary component CH 4 :CO 2 (molar ratio of 1:1) using the grand canonical Monte Carlo (GCMC) method, and the results showed that the adsorption capacity for CO 2 was significantly greater than that for CH 4 at the same temperature and pressure, the competitive advantage was evident, and CO 2 injection could help effectively displace CH 4 . 26 Xu et al investigated the adsorption and desorption of CH 4 and CO 2 on a 4 × 4 carbon model using the DFT, and the results showed that CO 2 had a higher adsorption stability than CH 4 and that CO 2 injection could promote the desorption of CH 4.…”

Section: Introductionmentioning

confidence: 99%

“…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 . 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 . Xiang et al .…”

Section: Introductionmentioning

confidence: 99%

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

Zhao

Liu

2022

ACS Omega

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To investigate the adsorption mechanism of H 2 O, CO 2 , and CH 4 molecules on oxygen-containing functional groups (OFGs) in coal molecules, quantum chemical density functional theory (DFT) simulations were performed to study the partial density of states and Mulliken bond layout of H 2 O molecules bonded to different OFGs. The adsorption energy and Mulliken charge distribution of the H 2 O, CO 2 , and CH 4 molecules for each OFG were determined. The results showed that H 2 O molecules form 2, 1, 1, and 1 hydrogen bonds with −COOH, −OH, —C=O, and −O–R groups, respectively. Double hydrogen bonds connected the H 2 O molecules to −COOH with the smallest adsorption distances and highest Mulliken bond layout values, resulting in the strongest bonding between the H 2 O molecules and −COOH. The most stable configuration for the adsorption of these molecules by the −OH group was when the O–H bond in the OFG served as a hydrogen bond donor and the O atom in the H 2 O molecule served as a hydrogen bond acceptor. The order of the bonding strength between the OFGs and H 2 O molecules was Ph–COOH > Ph–OH > Ph—C=O > Ph–O–R. The adsorption energy calculation results showed that H 2 O molecules have a higher adsorption stability than CO 2 and CH 4 molecules. Compared with the −OH, —C=O, and −O–R groups, the −COOH group had a higher adsorption capacity for H 2 O, CO 2 , and CH 4 molecules. The adsorption stability of the CO 2 molecules for each OFG was higher than that of the CH 4 molecules. From the Mulliken charge layout, it was clear that after the adsorption of the H 2 O molecules onto the OFGs, the O atoms in the OFGs tend to gain electrons, while the H atoms involved in bonding with the H 2 O molecules tend to lose electrons. The formation of hydrogen bonds weakens the strength of the bonds in the H 2 O molecule and OFGs, and thus, the bond lengths were elongated.

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“…Water in coal can be divided into two types: inherent moisture in coal matrix and free water in cleat system (Pan et al 2010). The inherent moisture mainly exists in the absorbed state, which can occupy the surface sites of coal pores due to the physical adsorption and oxygen-containing functional group effects (Wang et al 2021). Moreover, the existing of oxygen-containing functional groups (e.g.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on Pore Structure and Gas Desorption Characteristics of a Low Rank Coal: Impact of Moisture

Yang

Chen

Tian

et al. 2021

Preprint

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Coal and gas outburst is one of the most serious disasters for underground coal mining. The water adsorbed on coal can leads to that the pore structure of moist coal is different from that of dry coal, thereby affecting methane desorption characteristics of coal for the outburst risk prediction. In this paper, the impact of moisture on pore structure and methane desorption performance were investigated. The analysis on low-temperature nitrogen gas adsorption tests show that the micropores (pore diameter < 10 nm) are most affected by the adsorbed water. In particular, for water-equilibrated coal sample at 98% relatively humidity, the micropores less than 4 nm analyzed by DFT pore size distributions almost disappear probably due to the blocking effect of the formed water clusters and capillary water. In this case, the micropores can still contributes most sites for gas adsorption. Furthermore, the fractal dimension at relative pressure of 0–0.5 (D1) and 0.5–1 (D2) calculated by the Frenkel-Halsey-Hill model indicates that, when moisture content is less than 4.74%, D1 decreases rapidly while D2 shows a slight change; whereas, further increases in moisture content results in that D2 decreases significantly and D1 remains at about 2.32. Further investigation shows that, below the equilibrium moisture content, the ultimate desorption volume (A) and initial desorption rate (V0) are closely related to D1, while the desorption constant (Kt) mainly depends on D2. Therefore, the adsorbed moisture has significant negative impact on methane desorption performances by affecting characteristics of coal’s pores.

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Investigation of interactions between oxygen-containing groups and water molecules on coal surfaces using density functional theory

Cited by 65 publications

References 40 publications

Experimental Study of the Pore Structure and Gas Desorption Characteristics of a Low-Rank Coal: Impact of Moisture

Experimental Study of the Pore Structure and Gas Desorption Characteristics of a Low-Rank Coal: Impact of Moisture

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

Experimental Study on Pore Structure and Gas Desorption Characteristics of a Low Rank Coal: Impact of Moisture

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Investigation of interactions between oxygen-containing groups and water molecules on coal surfaces using density functional theory

Cited by 65 publications

References 40 publications

Experimental Study of the Pore Structure and Gas Desorption Characteristics of a Low-Rank Coal: Impact of Moisture

Experimental Study of the Pore Structure and Gas Desorption Characteristics of a Low-Rank Coal: Impact of Moisture

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

Experimental Study on Pore Structure and Gas Desorption Characteristics of a Low Rank Coal: Impact of Moisture

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