Exploration of critical moisture content of coal based on CH4, N2, and CO2 adsorption experiments

Xiaotong  Lu; Hongmin  Yang; Liwei  Chen; Danhui  Wang

doi:10.6180/jase.202607_30.024

Exploration of critical moisture content of coal based on CH4, N2, and CO2 adsorption experiments

Xiaotong Lu¹This email address is being protected from spambots. You need JavaScript enabled to view it., Hongmin Yang^1,2,3This email address is being protected from spambots. You need JavaScript enabled to view it., Liwei Chen^1,2,3, and Danhui Wang¹

¹College of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo 454003, China

²State Collaborative Innovation Center of Coal Work Safety and Clean-efficiency Utilization, Jiaozuo 454003, China

³Engineer Research Center of Minister of Education for Coal Mine Disaster Prevention and Emergency Relief, Jiaozuo 454003, China

Received: August 14, 2025
Accepted: October 28, 2025
Publication Date: December 28, 2025

Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

Download Citation: ||https://doi.org/10.6180/jase.202607_30.024

Two types of experiments were designed to systematically analyze the mechanisms regulating gas adsorption by the wet phase state of the coal body and the critical moisture. Water vapor adsorption experiments at variable relative humidity (0-97% RH ) were used to characterize the moisture state transitions. These were combined with isothermal adsorption experiments at 25^◦C and gas injection displacement experiments to determine the adsorption characteristics of single-component gases and post-injection displacement gases. The experimental data show that when the moisture content reaches the phase transition threshold (critical moisture content = 4.50% ), the pore water undergoes the transition from an adsorbed to a free state; the inhibitory effect of moisture content on gas adsorption diminishes with the increase of moisture content, and the rate of change in gas adsorption capacity ∆Q approaches zero near the critical moisture content. The critical moisture content values measured for the CH₄/N₂/CO₂ system converge within the range of 4.50−4.95%. Following gas injection replacement, the total gas adsorption change ∆Q_mix approaches zero at the critical moisture content, consistent with the single-component system. This confirms the universality of critical moisture content determination for gases, where N₂ and CO₂ can serve as substitutes.

Keywords: water vapor adsorption, moisture state of coal, critical moisture content, gas isothermal adsorption

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