Pore Structure Characterization of Different Rank Coals Using N₂ and CO₂ Adsorption and Its Effect on CH₄ Adsorption Capacity: A Case in Panguan Syncline, Western Guizhou, China

Abstract

To determine the pore structure characteristics of different coal ranks in Panguan syncline, both N 2 adsorption− desorption (LP-N 2 GA) and CO 2 adsorption (LP-CO 2 GA) were carried out with the goal of revealing the differentiation evolution of total pore volume (TPV), specific surface area (SSA), pore size distribution (PSD), and pore shape of 14 coal samples, and the influences of SSA to adsorption capability at different sizes (supermicroporous < 2 nm, micropore: 2−10 nm, transition pore: 10−100 nm) were further discussed. Density functional theory (DFT) is used for the determination of pore structure parameters to ensure its accuracy. Results show that the pore shape in the Panguan area is mostly the semi-open pores with poor connectivity (e.g., wedge-shaped, cylindrical, and slit-shaped pores with one closed side). Only a small amount of the pores is in open shapes (e.g., slit-shaped pores or cylindrical pores with two ends open). For most of the coal samples, the PSDs of pores tested by LP-N 2 GA appear to be multimodal, and the N 2 -TPV is mainly from the contribution of the transition pore (73.69−95.21%), followed by the micropore. The PSDs of supermicroporous (tested by LP-CO2GA) appear to be bimodal, with two peak values present at 0.52−0.61 nm and 0.82−0.87 nm, respectively, and a bigger pore volume distribution interval corresponds to a higher specific surface area. The N 2 -SSA (pore diameter ranges from 2 to 100 nm) mainly comes from the contribution of the pores 2−3 nm in diameter, and a bigger N 2 -TPV means a higher N 2 -SSA. The CO 2 -SSA (pore diameter ranges from 0.489 to 1.083 nm) which has a better positive linear correlation with Langmuir volume is related to CO 2 -TPV and the distribution frequency of pore volume at different pore sizes, and the contribution rate of CO 2 -SSA to the total SSA (CO 2 -SSA + N 2 -SSA) reaches 99%, indicating that supermicroporous has a significant effect on the coal adsorption capacity. With the increase of the vitrinite reflectance (R o,ran , 0.83 → 2.27%), the N 2 -SSA increase gradually, and its increase tendency presents to be a half-reversed "U" shape in the whole, while the CO 2 -SSA presents an extremely significant linear increase tendency. Accordingly, the Langmuir volume (2.61 → 21.26 m 3 /t) also displays a linear growth tendency with the increasing vitrinite reflectance. The results of this study will provide guidance to the CBM development in the Panguan area.

A comparative study of the nanopore structure characteristics of coals and Longmaxi shales in China

“…The adsorption capacity of porous media is mainly controlled by the SSA . As two special porous media, both coal and shale should meet this law.…”

“…However, the adsorbed gas content in shale only accounts for 30%‐60% of the total gas content, with a saturated adsorption capacity that is usually in the 2‐4 m 3 /t range . (c) Both are dual‐pore media consisting of matrix pore and fracture . The occurrence of free and adsorbed gases is controlled by the pore size, and gas transport is controlled by the fractures .…”

“…Similar experimental methods are used in the pore structure characterization of coal and shale gas reservoirs, which primarily consist of fluid injection and noninvasive imaging methods. The fluid injection method includes low‐pressure nitrogen gas adsorption (LP‐N 2 GA), low‐pressure carbon dioxide gas adsorption (LP‐CO 2 GA), high‐pressure mercury injection (HPMI), and low‐field nuclear magnetic resonance (LF‐NMR) . The noninvasive imaging method includes micro‐ and nano‐CT, scanning electron microscope (SEM), focused ion beam scanning electron microscope (FIB‐SEM), and small‐angle neutron scattering (SANS) .…”

Electrospun Nanofibers Embedding ZnO/Ag2CO3/Ag2O Heterojunction Photocatalyst with Enhanced Photocatalytic Activity

“…Meanwhile, P1, P2, P3, and P4 demonstrated a Type IV curve with a H3-type hysteresis loop and with mesoporous materials characterization [59]. Other than that, the abrupt increment in the N 2 uptake at high relative pressures (P/P 0 > 0.9) described the presence of macropores [60]. The outcome established that the embedded heterojunction photocatalyst displayed the hierarchical macro-and mesoporous structure.…”

Adsorption Mechanism and Kinetic Characterization of Bituminous Coal under High Temperatures and Pressures in the Linxing‐Shenfu Area

“…The pore diameter tested by CO 2 adsorption is 0.489 -1.083 nm, and the pore size is classified as supermicroporous (Chen et al, 2017). As shown in Table 3, the total pore volume tested by CO 2 (CO 2 TVP) of the 6 coal samples is 0.00882-0.01652 cm 3 /g, with an average value of 0.0133 cm 3 /g.…”