Quantitative Analysis of Pore Structure and Its Impact on Methane Adsorption Capacity of Coal

• Published in: Natural resources research (New York, N.Y.) Vol. 30; no. 1; pp. 605 - 620
• Main Authors: Xu, Shipei, Hu, Erfeng, Li, Xingchun, Xu, Yu
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.02.2021; Springer Nature B.V
• Subjects: Adsorption; Carbon dioxide; Chemistry and Earth Sciences; Coal; Computer Science; Earth and Environmental Science; Earth Sciences; Fossil Fuels (incl. Carbon Capture); Fractal geometry; Fractal models; Fractals; Geography; Heterogeneity; Low pressure; Mathematical Modeling and Industrial Mathematics; Methane; Mineral Resources; Original Paper; Parameters; Physics; Pore size; Statistics for Engineering; Surface area; Surface chemistry; Sustainable Development; Grey relational analysis; Methane adsorption; Fractal dimension; Pore structure; Modified coal
• ISSN: 1520-7439; 1573-8981
• DOI: 10.1007/s11053-020-09723-2

Better understanding of the storage and transportation characteristics of methane in coal seams is important to further develop and utilize the methane resources in the coalbed. This study is devoted to investigating the relationship between methane adsorption performance and pore structure by analyzing twelve coal samples derived from the typical methane-rich coalbeds in China. To eliminate the influence of inorganic components such as ash in different coal samples, a specific fixed-bed reactor with internals was employed for the coal treatment. Based on N 2 /CO 2 adsorption analysis at low-pressure condition, the pores in coal were classified into three types in this study: ultra-micropore (pore width < 1 nm), micropore (1 nm < pore width < 2 nm) and mesopores (2 nm < pore width < 50 nm). According to the Langmuir equation, the Langmuir volume ( V L ) and Langmuir pressure ( P L ) were calculated to characterize the high-pressure adsorption of methane, and the influence of methane adsorption associated parameters was evaluated. The results indicate that N 2 -pore size distributions (1–50 nm) varied a lot among samples, suggesting the significant heterogeneity of pore structure among samples. Estimated by the FHH model, pore surface fractal dimension (D 1 ) and spatial geometry fractal dimension (D 2 ) were, respectively, ranging in 2.059–2.808 and 2.649–2.852, which indicated that the more irregular surface, namely more inhomogeneous pore structures, resulted in the more surface area and stronger adsorption capability. By grey relational analysis (GRA), the importance of the pore structure factors on methane adsorption was identified, as an order from the most important to the least: ultra-micropore volume (0.9085) > ultra-micropore surface area (0.8976) > fractal dimension D 1 (0.8862) > N 2 -BET surface area (0.7915) > micropore volume (0.5035) > micropore surface area (0.5006). This study shows the influence of parameters of pore structure on methane adsorption of coal and clarifies the order importance of these parameters by the GRA method.