Molecular simulation of thermodynamic properties of CH4 and CO2 adsorption under different moisture content and pore size conditions

Li, Ziwen; Bai, Yiming; H, Yu; Hu, Hongqing; Wang, Yinji

doi:10.1016/j.fuel.2023.127833

Cited by 11 publications

(6 citation statements)

References 41 publications

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“…The parameter used in the simulation software was fugacity, and the fugacity–pressure relationship was converted to approximate real data. The Soave–Redlich–Kwong (S–R–K) eq of state was introduced, , especially when equal proportions of CH 4 /CO 2 binary-components injection, the S–R–K eq can be used to control the injection of CH 4 /CO 2 into the coal body in equal proportions through the S–R–K equation as follows: p = R T V m − b − a α ( T ) V m ( V normalm + b ) where a = 0.45724 R 2 T c 2 p normalc , 0.25em b = 0.08664 R T c p normalc , V m is the molar volume of the gas; T is the temperature, K; T c is the critical temperature, K; P is the pressure, MPa; P c the critical pressure, MPa; and R is the gas constant, 8.314 J/(mol·K).…”

Section: Models and Methodsmentioning

confidence: 99%

“…The entropy of adsorption can measure the degree of chaos in the coal macromolecule adsorption gas system, when coal molecules adsorb CH 4 /CO 2 and undergo physical adsorption, the degree of freedom of activity of the gas molecules decreases, and therefore the system Δ S < 0. According to the fundamental law of thermodynamics, the entropy of adsorption, Δ S , can be expressed according to the Gibbs–Helmholtz equation: normalΔ S = ( Δ H − Δ G ) / T where Δ S is the adsorption entropy change, Δ H enthalpy change, and Δ G Gibbs free energy.…”

Section: Models and Methodsmentioning

confidence: 99%

“…Busch 32 pointed out that water adsorption is an important mechanism to control gas adsorption in coal. Li et al 33 found by molecular simulation that coal with 3% moisture content is favorable for CO 2 displacement of CH 4 . Coal with increasing pore size, the selectivity of CO 2 in competitive adsorption decreases, and CO 2 displacement of CH 4 becomes less and less effective.…”

Section: Introductionmentioning

confidence: 99%

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Molecular Simulation of Thermodynamic Properties of CH₄/CO₂ Adsorption by Coal Molecules at Different Temperatures and Moisture Contents under Variable Pressure Conditions

Jia,

Wu,

2023

ACS Omega

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In order to further elucidate the thermodynamic mechanism of CH 4 /CO 2 adsorption by coal molecules, the adsorption behavior of a molecular model of coal (C 206 H 128 O 36 N 2 ) at Wucaiwan, Zhundong was investigated by applying Materials Studio 2020 and Monte Carlo (GCMC) simulation methods, and the adsorption behavior of CH 4 and CO 2 was studied from the thermodynamic point of view under the conditions of different temperatures, pressures, and moisture contents. The results showed that at different temperatures or moisture contents, CH 4 molecules had a low-density scattering distribution and CO 2 molecules had a high-density polymerization distribution. Temperature and moisture content and adsorption constants a and b were negatively correlated. Under the same conditions, the relationship between single- and binary-component adsorption amounts was CO 2 > CH 4 and the relationship between heat of adsorption was CO 2 > CH 4 . When adsorption potential energy or entropy of adsorption was the same, the adsorption capacity was CO 2 > CH 4 . Temperatures and moisture contents were negatively correlated with the total adsorption capacity of CH 4 /CO 2 ; pressure was positively correlated with the total adsorption capacity of CH 4 /CO 2 . The effect of temperature on the equivalent heat of adsorption was greater than that of pressure at different temperatures, and the entropy of adsorption was positively correlated between temperature and CH 4 /CO 2 , while the amount of adsorption was negatively correlated with the entropy of adsorption. The effect of moisture content on the equivalent heat of adsorption was greater than that of pressure at different moisture contents, and the entropy of adsorption was negatively correlated between moisture content and amount of adsorption. The adsorption entropy of CH 4 /CO 2 was negatively correlated, and the adsorption amount was positively correlated to the adsorption entropy. At a temperature above 318 K or moisture content above 10%, the total CH 4 /CO 2 adsorption decreased significantly and the CO 2 adsorption decreased significantly. From a thermodynamic point of view, the presence of a large amount of H 2 O had a much greater effect on CO 2 than on CH 4 , and an increase in temperature or moisture content was unfavorable for CO 2 sequestration, CO 2 ...

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Section: Models and Methodsmentioning

confidence: 99%

Section: Models and Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Molecular Simulation of Thermodynamic Properties of CH₄/CO₂ Adsorption by Coal Molecules at Different Temperatures and Moisture Contents under Variable Pressure Conditions

Jia,

Wu,

2023

ACS Omega

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“…13 C NMR can be used to obtain the nuclear magnetic maps, types, and proportions of functional groups of DT coal samples and HW coal samples. , In this section, the macromolecular structure formulas of coal samples can be deduced from the nuclear magnetic maps obtained by experiments. Then, ACD laboratories, gNMR, and other software were used to repeatedly adjust and compare, − as shown in Figure , until the obtained wave crest morphology was consistent with the physical experimental structure.…”

Section: Numerical Simulationmentioning

confidence: 99%

Effect of Slickwater on Methane Adsorption in Coal: Experiment and Molecular Simulation

Li,

Wang,

Ning

et al. 2024

Energy Fuels

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Slickwater is generally applied in the domain of coalbed methane (CBM) stimulation. However, the residual slickwater after fracturing operations may adversely affect the production of CBM. In this paper, nuclear magnetic resonance (NMR) measurements are used to compare and analyze the differences of functional groups on the coal surface in different regions and provide the basis for the construction of molecular simulation models. Then, different concentrations of slickwater were made, and coal samples from different regions were soaked. Isothermal adsorption experiments and molecular simulations were applied to explore the effect of slickwater on methane adsorption properties of coal from different regions. The NMR results show that the amount of naphthalene functional groups in coal samples from Dongtan coal mine (DT) is more than that in coal samples from Houwenjialiang coal mine (HW), which has a stronger attraction to methane. The isothermal adsorption experiment results show that the methane adsorption capacity of the coal sample from HW is stronger than that of the coal sample from DT. When the concentration of slickwater is 0.5%, the methane adsorption capacity of DT increases to 3/2 of raw coal, and the methane adsorption capacity of HW declines to 1/3 of raw coal. The retention of slickwater will have different effects on coal samples in different areas. Comparing the experimental and simulation results, we can see that polyacrylamide can adsorb methane, thereby increasing the specific surface area of the local “slickwater–coal” system due to its porous coating structure, resulting in an increase in the methane adsorption capacity. The negative effect of slickwater on the methane adsorption properties is because slickwater changes the pore, resulting in the reduction of effective surface area and finally damages the adsorption amount of methane.

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“…Therefore, it may be more reasonable to analyze the adsorption of CH 4 /CO 2 from a microscopic molecular point of view [16][17][18][19]. Li et al researched the effect of coal rank and moisture on the competitive adsorption of CH 4 and CO 2 through molecular simulations [20][21][22][23]. Lu et al found that supercritical CO 2 can change the nature of coal's pore structures to affect the adsorption of CH 4 [24].…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulation of CH4 Displacement through Different Sequential Injections of CO2/N2

Bai,

Li,

et al. 2023

Sustainability

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As a clean energy source, coalbed methane (CBM) produces almost no exhaust gas after combustion, and its extraction and efficient utilization play a key role in supporting sustainable development. Therefore, molecular dynamics simulations were used to research the diffusion of CH4 in coal after injecting CO2/N2 in different sequences and to clarify the efficiency of CBM extraction under different injection sequences, so as to contribute to sustainable development. The results show that the adsorption amounts of CO2 and N2 in different injection sequences are obviously different. To narrow the gap between the two injection amounts, the injection pressure of N2 can be appropriately increased and that of CO2 can be reduced, or N2 can be injected preferentially instead of CO2. When CO2 is injected first, the interaction energy between CH4 and coal is stronger and increases slightly with displacement time as a whole. The interaction energy curve of the N2 injection decreases, and the displacement effect becomes worse and worse. From the diffusion and relative concentration distribution of CH4, it can be seen that the diffusion of CH4 molecules outside the grain cell is more obvious when N2 is injected first. In terms of the number of CH4 molecules diffusing outside the crystal cell, it is less when CO2 is injected first than when N2 is injected first. The average value of the velocity distribution of CH4 increases slightly when CO2 is injected first and decreases significantly when N2 is injected first, but the average value is overall higher for N2 injection first. From the difference in diffusion coefficients before and after the gas injection, it can be seen that the decrease in permeability due to the expansion of the coal matrix by CO2 is more obvious than the increase in permeability due to the contraction of the coal matrix by N2.

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Molecular simulation of thermodynamic properties of CH4 and CO2 adsorption under different moisture content and pore size conditions

Cited by 11 publications

References 41 publications

Molecular Simulation of Thermodynamic Properties of CH₄/CO₂ Adsorption by Coal Molecules at Different Temperatures and Moisture Contents under Variable Pressure Conditions

Molecular Simulation of Thermodynamic Properties of CH₄/CO₂ Adsorption by Coal Molecules at Different Temperatures and Moisture Contents under Variable Pressure Conditions

Effect of Slickwater on Methane Adsorption in Coal: Experiment and Molecular Simulation

Molecular Dynamics Simulation of CH4 Displacement through Different Sequential Injections of CO2/N2

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Molecular simulation of thermodynamic properties of CH4 and CO2 adsorption under different moisture content and pore size conditions

Cited by 11 publications

References 41 publications

Molecular Simulation of Thermodynamic Properties of CH4/CO2 Adsorption by Coal Molecules at Different Temperatures and Moisture Contents under Variable Pressure Conditions

Molecular Simulation of Thermodynamic Properties of CH4/CO2 Adsorption by Coal Molecules at Different Temperatures and Moisture Contents under Variable Pressure Conditions

Effect of Slickwater on Methane Adsorption in Coal: Experiment and Molecular Simulation

Molecular Dynamics Simulation of CH4 Displacement through Different Sequential Injections of CO2/N2

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Molecular Simulation of Thermodynamic Properties of CH₄/CO₂ Adsorption by Coal Molecules at Different Temperatures and Moisture Contents under Variable Pressure Conditions

Molecular Simulation of Thermodynamic Properties of CH₄/CO₂ Adsorption by Coal Molecules at Different Temperatures and Moisture Contents under Variable Pressure Conditions