Molecular simulation of CO 2 /CH 4 self- and transport diffusion coefficients in coal

Zhao, Yongliang; Feng, Yanhui; Zhang, Xinxin

doi:10.1016/j.fuel.2015.10.035

Cited by 123 publications

(99 citation statements)

References 56 publications

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“…However, it is very challenging to quantitatively investigate the microscopic diffusion behavior of gas in coal, especially in the micropores. Systematic research on the diffusion process and mechanisms of CH 4 , CO 2 , and N 2 at different geometric scales in coal seams can both efficiently enhance both CBM production and the implementation of CO 2 capture, utilization, and sequestration (CCUS) [11,12].…”

Section: Introductionmentioning

confidence: 99%

“…The self-diffusion process is driven through the spontaneous thermal motion of micro-particles and follows Einstein's laws [21], which are independent of pressure and concentration gradients. Most scholars focus on the self-diffusion process and further obtain the diffusion coefficient through molecular simulations [12]. This diffusion coefficient, although at the microscale, can efficiently reflect the motion characteristics of the diffusion particles and is the basis for the macroscopic mass transport [22].…”

Section: Introductionmentioning

confidence: 99%

“…Charrière et al (2010) [23] estimated the CO 2 and CH 4 diffusion coefficients of 1.4 × 10 −12 m 2 /s and 0.41 × 10 −12 m 2 /s, respectively, based on the unique model combined with experimental adsorption data and calculated the activation energies of CO 2 and CH 4 as 18 kJ/mol and 34 kJ/mol, respectively. Zhao et al [12] (2016) researched the diffusion characteristics of CO 2 and CH 4 in micropores based on the Wiser bituminous coal model. The diffusion coefficients of CO 2 and CH 4 were calculated to be 8.13 × 10 −10 m 2 /s and 2.08 × 10 −10 m 2 /s, respectively.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Molecular Dynamics Simulation of Diffusion Behavior of CH4, CO2, and N2 in Mid-Rank Coal Vitrinite

Liu

Wang

2019

Energies

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The diffusion characteristics of CH4, CO2, and N2 in coal are important for the study of CO2-enhanced coalbed methane (CO2-ECBM) recovery, which has become the most potential method for carbon sequestration and natural gas recovery. However, quantitative research on the diffusion characteristics of CH4 and the invasive gases (CO2 and N2) in coal, especially those in micropores, still faces enormous challenges. In this paper, the self-, Maxwell’s, and transport diffusions of CO2, CH4, and N2 in mid-rank coal vitrinite (MRCV) macromolecules were simulated based on the molecular dynamics method. The effects of the gas concentration, temperature, and pressure on the diffusion coefficients were examined via the comparison of various ranks. The results indicated that the diffusion coefficients have the order of D(N2) > D(CO2) > D(CH4) in their saturated adsorption states. However, when MRCV adsorbed the same amounts of CH4, CO2, and N2, the self- and transport diffusion coefficients followed the order of DS(N2) > DS(CO2) > DS(CH4) and Dt(CO2) > Dt(N2) > Dt(CH4), respectively. Independent of the gas species, all these diffusion coefficients decreased with increasing gas concentration and increased with increasing temperature. In the saturated adsorption state, the diffusion activation energies of CH4, CO2, and N2 were ordered as CH4 (27.388 kJ/mol) > CO2 (11.832 kJ/mol) > N2 (10.396 kJ/mol), indicating that the diffusion processes of CO2 and N2 occur more easily than CH4. The increase of temperature was more conducive to the swelling equilibrium of coal. For the pressure dependence, the diffusion coefficients first increased until the peak pressure (3 MPa) and then decreased with increasing pressure. In contrast, the diffusion activation energy first decreased and then increased with increasing pressure, in which the peak pressure was also 3 MPa. The swelling rate changed more obviously in high-pressure conditions.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Molecular Dynamics Simulation of Diffusion Behavior of CH4, CO2, and N2 in Mid-Rank Coal Vitrinite

Liu

Wang

2019

Energies

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“…The results showed that the transport diffusion coefficient is larger than the corrected diffusion coefficient, and the corrected diffusion coefficient is larger than the self-diffusion coefficient. The three diffusion coefficients increased with temperature and the gas phase mole fraction increased gradually [46]. Meanwhile, scholars have researched the adsorption and diffusion of shale gas using molecular simulation methods.…”

Section: Introductionmentioning

confidence: 99%

Study on the Adsorption, Diffusion and Permeation Selectivity of Shale Gas in Organics

Wang

Liu

et al. 2017

Energies

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Abstract:As kerogen is the main organic component in shale, the adsorption capacity, diffusion and permeability of the gas in kerogen plays an important role in shale gas production. Based on the molecular model of type II kerogen, an organic nanoporous structure was established. The Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods were used to study the adsorption and diffusion capacity of mixed gas systems with different mole ratios of CO 2 and CH 4 in the foregoing nanoporous structure, and gas adsorption, isosteric heats of adsorption and self-diffusion coefficient were obtained. The selective permeation of gas components in the organic pores was further studied. The results show that CO 2 and CH 4 present physical adsorption in the organic nanopores. The adsorption capacity of CO 2 is larger than that of CH 4 in organic pores, but the self-diffusion coefficient of CH 4 in mixed gas is larger than that of CO 2 . Moreover, the self-diffusion coefficient in the horizontal direction is larger than that in the vertical direction. The mixed gas pressure and mole ratio have limited effects on the isosteric heat and the self-diffusion of CH 4 and CO 2 adsorption. Regarding the analysis of mixed gas selective permeation, it is concluded that the adsorption selectivity of CO 2 is larger than that of CH 4 in the organic nanopores. The larger the CO 2 /CH 4 mole ratio, the greater the adsorption and permeation selectivity of mixed gas in shale. The permeation process is mainly controlled by adsorption rather than diffusion. These results are expected to reveal the adsorption and diffusion mechanism of gas in shale organics, which has a great significance for further research.

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“…As the important cements and inorganic components of shale and coal seams, clay minerals interacting with CH 4 have been one of the research hotspots in the energy field (Zhang et al 2014;Zhao et al 2016). Kaolinite is the most common clay mineral with large specific surface area and complex pore structure (from micropore to mesopore), which makes kaolinite have strong adsorption capacity (Murray 1999) and.…”

Section: Introductionmentioning

confidence: 99%

Molecular dynamics simulations of CH4 diffusion in kaolinite: influence of water content

Zhang

Kang

et al. 2019

Int J Coal Sci Technol

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Understanding the interaction of CH 4 with kaolinite is significant for researchers in the fields of coalbed CH 4 and shale gas. The diffusion behaviors of CH 4 in kaolinite with water contents ranging from 0 to 5 wt% have been analyzed by molecular dynamics simulations. The results of the simulations indicate that CH 4 molecules can jump between adjacent holes in the kaolinite matrix. CH 4 diffusion coefficient was very low (3.28 9 10 -9 m 2 /s) and increased linearly with the increasing of water content. As the water content decreased, the value of radial distribution function first peak between CH 4 and oxygen was larger, meaning that with lower water content, the interaction energy between CH 4 and oxygen in kaolinite is stronger. The interaction between CH 4 and water is linearly positively correlated with water content, in contrast, the interaction energy between kaolinite and water as well as between kaolinite and CH 4 decreased linearly with increasing water content. On the other hand, the diffusion of CH 4 molecules adsorbed on the surfaces also can be accelerated by the fast diffusion of water molecules in the middle micropore of the kaolinite.

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Molecular simulation of CO 2 /CH 4 self- and transport diffusion coefficients in coal

Cited by 123 publications

References 56 publications

Molecular Dynamics Simulation of Diffusion Behavior of CH4, CO2, and N2 in Mid-Rank Coal Vitrinite

Molecular Dynamics Simulation of Diffusion Behavior of CH4, CO2, and N2 in Mid-Rank Coal Vitrinite

Study on the Adsorption, Diffusion and Permeation Selectivity of Shale Gas in Organics

Molecular dynamics simulations of CH4 diffusion in kaolinite: influence of water content

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