Adsorption thermodynamic characteristics are an important part of the methane adsorption mechanism, and are useful for understanding the energy transmission mechanism of coalbed methane (CBM) migration in coal reservoirs. To study the effect of coal pore characteristics on methane adsorption heat, five different types of rank coals were used for low-pressure nitrogen, low-pressure carbon dioxide, and methane adsorption experiments. Pore structure and adsorption parameters, including maximum adsorption capacity and adsorption heat, were obtained for five coal samples, and their relationships were investigated. The results show that the low-pressure nitrogen adsorption method can measure pores within 1.7–300 nm, while the low-pressure carbon dioxide adsorption method can measure micropores within 0.38–1.14 nm. For the five coal samples, comprehensive pore structure parameters were obtained by combining the results of the low-pressure nitrogen and carbon dioxide adsorption experiments. The comprehensive results show that micropores contribute the most to the specific surface area of anthracite, lean coal, fat coal, and lignite, while mesopores contribute the most to the specific surface area of coking coal. Mesopores contribute the most to the pore volume of the five coal samples. The maximum adsorption capacity has a significant positive correlation with the specific surface area and pore volume of micropores less than 2 nm, indicating that methane is mainly adsorbed on the surface of micropores, and can also fill the micropores. The adsorption heat has a significant positive correlation with the specific surface area and pore volume of micropores within 0.38–0.76 nm, indicating that micropores in this range play a major role in determining the methane adsorption heat.

The adsorption mechanism of carbon dioxide, oxygen and nitrogen in coal is important for preventing and controlling coal spontaneous combustion and for understanding the technology of CO₂ storage in goaf. Adsorption amount and adsorption heat are key adsorption parameters that are required to understand the material and energy conversions during adsorption in coal. In this study, we studied the factors that influence the adsorption amounts and adsorption heat values of carbon dioxide, oxygen and nitrogen in coal by testing four different coal samples using conventional coal quality analysis, low-pressure nitrogen and carbon dioxide adsorption, Fourier transform infrared spectroscopy and three gas adsorption experiments at different temperatures. Then, we analyzed the relationships between the structural parameters of the coal samples and the adsorption amounts and the adsorption heat values of carbon dioxide, oxygen and nitrogen. The results show that the adsorption isotherms of carbon dioxide conform to the Langmuir equation, and the adsorption isotherms of oxygen and nitrogen conform to Henry’s law between 0 and 110 kPa. The adsorption amounts of carbon dioxide, oxygen and nitrogen decreased with an increase in temperature, and the change in the rate of the adsorption amount with temperature was determined by the adsorption heat. The results of the pore structure show that the pores of the coal samples are composed of mesopores and micropores; the micropores contribute to the main specific surface area. The micropore and mesopore structures are the main determinants of the adsorption amounts of carbon dioxide, oxygen and nitrogen in coal. The gas adsorption heat is affected by the pore structure and the chemical composition of coal. The adsorption heat of nitrogen correlates positively with the pore structure of the coal. The adsorption heat of oxygen correlates positively with the ash, elemental nitrogen, elemental sulfur and mineral contents of the coal. The adsorption heat of carbon dioxide correlates positively with the elemental sulfur content of the coal.

The CO₂ injection technology for replacing CH₄ to enhance coalbed methane (CBM) recovery (CO₂-ECBM) offers dual benefits, i.e., reducing CO₂ emissions through sequestration and increasing CBM recovery, thereby leading to economic gains. However, there is no clear consensus on how temperature and pressure affect the competitive adsorption characteristics of CO₂ and CH₄ mixed gases in coal. Therefore, the competitive adsorption behavior of CO₂ and CH₄ mixed gases at various pressures and temperatures were investigated using the breakthrough curve method. Anthracite was selected for the adsorption experiment conducted under three gas injection pressure levels (0.1 MPa, 0.5 MPa, and 1 MPa) and at three temperature levels (20 °C, 40 °C, and 60 °C). This study showed that, when the temperature remained constant and the pressure ranged from 0.1 to 1 MPa, the adsorption rates of CO₂ and CH₄ increased as pressure rose. Additionally, the selectivity coefficient for CO₂/CH₄ decreased with an increase in pressure, suggesting that higher pressures within this range are not conducive to the replacement efficiency of CH₄ by CO₂. As the temperature increased from 20 to 60 °C under constant pressure conditions, both the selectivity coefficients for CO₂/CH₄ and the adsorption rates of CO₂ and CH₄ exhibited a downward trend. These findings imply that, within this temperature range, a reduced temperature improves the ability of CO₂ to efficiently displace CH₄. Moreover, CO₂ exhibits a higher isosteric heat of adsorption compared to CH₄.

The permeability of more than 70% of coal seams in China is less than 1 mD, creating difficulties in recovering underground coal methane. Therefore, a new technology of high-temperature nitrogen (HTN₂) injection into the coal seam was proposed to improve the coal permeability and gas extraction rate. In this paper, the effects of the N₂ temperature, injection pressure and cycle number on the permeability of naturally fractured coking coal has been investigated. When HTN₂ was injected into coal samples, the results indicated that the permeability decreased over time in the beginning, suddenly increased to a large value, and was subsequently maintained in a relatively stable range. The maximum permeability ratio increased with the rise of the N₂ temperature and injection pressure. An analysis indicated that the increase of coal permeability was the result of the increase of the global coal strain caused by thermal expansion and the adsorption-induced expansion. The maximum permeability ratios in various cycles of multicycle N₂ injection into the coal sample were all greater than 1.0 while progressively declining. Obviously, the alternating stress was conducive to the further expansion of the coal fractures to increase the coal permeability. However, on the basis of the first period of expansion, re-expansion was difficult and required more energy. The effects of multicycle N₂ injection on coal permeability have been considerably improved when compared with N₂ injection with only one cycle. The research results are helpful for rapidly extracting methane and guaranteeing mine safety.

Xinjiang is an arid and semi-arid region where ecosystems are fragile, and monitoring how its ecology changes over time is critical for its sustainable development. In this study, a Remote Sensing Ecological Index (RSEI) was established for Xinjiang from 2000 to 2025. To understand temporal and spatial changes in ecological quality, we conducted spatial autocorrelation analysis, Theil–Sen median trend analysis, a Mann–Kendall trend test, and Hurst exponent analysis. We also used Geodetector to determine which factors affect the RSEI. The main results were as follows: (1) The RSEI in Xinjiang remained low, with a mean value between 0.285 and 0.336. Mountainous areas had higher values, basins had lower values, and spatial clustering was strong (Moran’s I index: 0.81–0.86). (2) H-H clusters expanded and then shrank, while L-L clusters grew after 2015. Areas with excellent ecological grades increased, but so did areas with poor grades, indicating that improvement and degradation both exist. (3) Most areas were stable, but 19.13% showed persistent degradation, indicating that these areas need more attention. (4) Land surface temperature (q = 0.624) and land cover (q = 0.576) were the main driving factors, and factor interactions showed enhanced effects. The results of this study could provide a scientific basis for ecosystem protection and restoration in Xinjiang.

The presence of water during coalbed methane development significantly affects gas adsorption and migration. However, the factors governing primary and secondary water vapor adsorption amounts and adsorption heats remain unclear. In this study, the chemical and pore structures of five coals with different ranks were characterized, and water vapor adsorption experiments were conducted at three temperatures. The variation patterns of water vapor adsorption and heat in coal were investigated, along with the factors influencing these parameters. More importantly, the factors affecting the primary and secondary adsorption amounts were examined, as well as the primary and secondary adsorption heats. The results indicate that the hydrophilic/hydrophobic properties of coal surfaces and the micropore fractal dimension are the primary factors influencing the amount of water vapor adsorption in coal. The oxygen-containing functional group structural parameter ‘C’ ranges from 0.22 to 0.55, and the micropore fractal dimension ranges from 2.26695 to 2.41057. The micropore fractal dimension exhibits the strongest influence on secondary adsorption (r = 0.90). The primary and secondary adsorption heats range from 30 to 73 kJ/mol and 34 to 47 kJ/mol, respectively. The initial adsorption heat of water vapor in coal exhibits a strong positive relationship with both the specific surface area (57.24–160.06 m²/g) and volume (0.0184–0.0515 cm³/g) of micropores, with r > 0.90.