A New Empirical Model to Predict Methane Adsorption Amount of Anthracite Considering Temperature Effect

Abstract

Geo-temperature is a key geological parameter for coalbed methane (CBM) recovery. Especially for deep CBM, the impact of temperature on methane adsorption of coal should receive more emphasis. In this study, the methane adsorption performances of three anthracite coal samples from Shanxi Province, China, under different temperature and gas pressure conditions (20–60 °C, 1–10 MPa) are simulated based on the grand canonical Monte Carlo (GCMC) method. The results show that the Dubinin-Astakhov (DA) model has a higher applicability for characterizing CH4 adsorption than the Langmuir model and Dubinin–Radushkevich (DR) model, which can be attributed to the heterogeneous micropore surface of coal with great specific surface area, and the unfixed value of the structural heterogeneity parameter s. Further analysis indicates that the CH4 adsorption capacities of the studied coals are reduced by approximately 3.3 cm3/g for each 10 °C increase in temperature. This finding is mainly related to the great kinetic energy of gas molecules and the easier transformation of the adsorbed gas into free gas under high temperature conditions. Moreover, the net heat of CH4 adsorption in coal increases with temperature, because of the enhanced thermal movement of gas molecules. Furthermore, a new equation for the adsorbed gas amount of coal that considers temperature effect is established, where both the DA adsorption model and a negative power-type equation n = 0.011P –0.39 are introduced. Compared to the classical equation, the newly established model provides a better predication of the adsorbed gas amount of anthracite. This indirect calculation method is a good supplement to the field tests of the CBM content.

Coal and rock dynamic disasters: Advances of physical and numerical simulation in monitoring, early warning, and prevention

“…3.2.2 Analysis of the influence of temperature on initial adsorption amount of gas Wang et al (2016); ; (Chen et al, 1995); (Zhong et al, 2002); ; (Liu et al, 2012); (Cai et al, 2019); (Wang et al, 2022) and others found that the amount of gas adsorption gradually decreased with the increase of temperature. It is generally accepted that the adsorption amount decreases by 8% for a 1 °C temperature increase.…”

Estimation of Adsorption Isotherm for Deep Coalbed Methane: A Monolayer-Filling Model Based on Pore Fractal Dimension

“…37 Its expression is simple and exhibits good fitting effects for methane adsorption data, making it one of the most widely used models for describing methane adsorption behavior. 34,36 The L-F model, an improvement over the Langmuir model, represents a gas monolayer adsorption model that accounts for the surface heterogeneity of the adsorbent. 30,38 The BET model demonstrates good applicability in the adsorption on nonporous or mesoporous solid surfaces, describing multilayer adsorption of molecules on solid surfaces.…”

“…32,35 The D−A model is a semiempirical formula that establishes a functional relationship between adsorption potential and the volume of the adsorption layer, based on the pore filling theory. 34,39 Undoubtedly, these models have significantly contributed to the study of the adsorption behavior in coalbed methane. However, they still exhibit certain limitations in describing methane adsorption in deep coal.…”

“…Common adsorption isotherm models mainly include Langmuir, Langmuir–Freundlich (L-F), Brunauer–Emmett–Teller (BET), and Dubinin–Astahov (D-A) models. − The Langmuir model assumes noninteracting gas molecules adsorbing as a monolayer on an ideally homogeneous surface . Its expression is simple and exhibits good fitting effects for methane adsorption data, making it one of the most widely used models for describing methane adsorption behavior. , The L-F model, an improvement over the Langmuir model, represents a gas monolayer adsorption model that accounts for the surface heterogeneity of the adsorbent. , The BET model demonstrates good applicability in the adsorption on nonporous or mesoporous solid surfaces, describing multilayer adsorption of molecules on solid surfaces. , The D–A model is a semiempirical formula that establishes a functional relationship between adsorption potential and the volume of the adsorption layer, based on the pore filling theory. , Undoubtedly, these models have significantly contributed to the study of the adsorption behavior in coalbed methane. However, they still exhibit certain limitations in describing methane adsorption in deep coal.…”