Water sorption on coal: effects of oxygen-containing function groups and pore structure

Abstract

Coal-water interactions have profound influences on gas extraction from coal and coal utilization. Experimental measurements on three coals using X-ray photoelectron spectroscopy (XPS), low-temperature nitrogen adsorption and dynamic water vapor sorption (DVS) were conducted. A mechanism-based isotherm model was proposed to estimate the water vapor uptake at various relative humidities, which is well validated with the DVS data. The validated isotherm model of sorption was further used to derive the isosteric heat of water vapor sorption. The specific surface area of coal pores is not the determining parameter that controls water vapor sorption at least during the primary adsorption stage. Oxidation degree dominates the primary adsorption, and which togethering with the cumulative pore volume determine the secondary adsorption. Higher temperature has limited effects on primary adsorption process.The isosteric heat of water adsorption decreases as water vapor uptake increases, which is found to be close to the latent heat of bulk water condensation at higher relative humidity. The results confirmed that the primary adsorption is controlled by the stronger bonding energy while the interaction energy between water molecules during secondary adsorption stage is relatively weak. However, the thermodynamics of coal-water interactions are complicated since the internal bonding interactions within the coal are disrupted at the same time as new bonding interactions take place within water molecules. Coal has a shrinkage/swelling colloidal structure with moisture loss/gain and it may exhibit collapse behavior with some collapses irreversible as a function of relative humidity, which further plays a significant role in determining moisture retention.

Methane Adsorption and Desorption on a Deep Shale Matrix under Simulative Reservoir Temperature and Pressure

“…The maximum pattern found in GSE adsorption isotherms is broadly reported in high-pressure CH 4 adsorption on the shale matrix, ,, which is due to the fact that the increasing rate in the bulk phase density of CH 4 is higher than that in the adsorption phase density with the elevated equilibrium pressure. Moreover, the increase in the operating adsorption temperature from 313.15 to 353.15 K could provide the additional energy required by the previously adsorbed CH 4 molecules to evaporate from the shale sample, thus decreasing the GSE adsorption amount of CH 4 . To better address the temperature dependence of CH 4 adsorption on the shale sample, the Ono–Kondo lattice model with a superior prediction capability for the reservoir fluid adsorption equilibrium behavior was adopted in this study. , Particularly, this model is a nonlinear equation typically describing the density profile of successive layers of adsorbate molecules.…”

“…Volumetric and gravimetric methods have long been employed for measuring CH 4 adsorption data of various shale samples under simulative reservoir conditions. − In accordance with the experimental CH 4 adsorption isotherms, adsorption equilibrium models are always adopted to provide key parameters of physical adsorption of CH 4 on the shale matrix such as the saturation capacity and isosteric adsorption heat. The microcosmic mechanism accounting for a specific physical adsorption system mainly comprises surface coverage and micropore filling. − Accordingly, many types of adsorption equilibrium models, for instance, the Langmuir model, the Sips model, the Brunauer–Emmett–Teller (BET) model, the Guggenheim–Anderson-de Boer (GAB) model, the Frenkel–Halsely–Hill (FHH) model, and the Ono–Kondo lattice model conform to the former mechanism.…”

Effect of H2O on the Transformation of Sulfur during Demineralized Coal Pyrolysis: Molecular Dynamics Simulation Using ReaxFF

“…The oxygen-containing functional groups include carboxyl, carbonyl, hydroxyl, methoxy, and etheroxy, and also contain a pyridine ring. The sulfur-containing macromolecule M3 (C 202 H 118 O 35 N 2 S 6 , see Figure ) constructed by Liu was selected. M3 contains four typical organic sulfur: thiophenol, disulfide, thiophene, and sulfone.…”

Permeability Enhancement Technology for Soft and Low-Permeability Coal Seams Combined with Hydraulic Perforation and Hydraulic Fracturing

“…The coal and gas outburst dynamics are the result of the combined effects of ground stress, gas pressure, and coal mechanical properties [1][2][3][4][5][6]; it always threatens the safety of underground production as a serious mine disaster [7][8][9][10][11][12]. In some soft outburst coal seams with low permeability in China, the coal seam has suffered from strong structural compression deformation due to the influence of multistage geological structure, and its primary structure has been damaged seriously, and the coal body strength and coal seam permeability are low [13][14][15][16][17].…”