Point Source Capture of Methane Using Ionic Liquids in Packed Bed Absorbers/Strippers: Experimental and Modelling

Fugitive methane emissions from the mining industry, particularly so-called ventilation air methane (VAM) emissions, are considered among the largest sources of greenhouse gas (GHG) emissions. VAM emissions not only contribute to the global warming but also pose a significant hazard to mining safety due to the risk of accidental fires and explosions. This research presents a novel approach that investigates the capture of CH₄ in a controlled environment using 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide [BMIM][TF₂N] ionic liquid (IL), which is an environmentally friendly solvent. The experimental and modelling results confirm that CH₄ absorption in [BMIM][TF2N], in a packed column, can be a promising technique for capturing CH₄ from point sources, particularly the outlet streams of ventilation shafts in underground coal mines, which typically accounts for <1% v/v of the flow. This study assessed the effectiveness of CH₄ removal in a packed bed column by testing various factors such as absorption temperature, liquid and gas flow rates, flow pattern, packing size, desorption temperature, and desorption pressure. According to the optimisation results, the following parameters can be used to achieve a CH₄ removal efficiency of 23.8%: a gas flow rate of 0.1 L/min, a liquid flow rate of 0.5 L/min, a packing diameter of 6 mm, and absorption and desorption temperatures of 303 K and 403.15 K, respectively. Additionally, the experimental results indicated that ILs could concentrate CH₄ in the simulated VAM stream by approximately 4 fold. It is important to note that the efficiency of CH₄ removal was determined to be 3.5-fold higher compared to that of N₂. Consequently, even though the VAM stream primarily contains N₂, the IL used in the same stream shows a notably superior capacity for removing CH₄ compared to N₂. Furthermore, CH₄ absorption with [BMIM][TF₂N] is based on physical interactions, leading to reduced energy requirements for regeneration. These findings validate the method’s effectiveness in mitigating CH₄ emissions within the mining sector and enabling the concentration of VAM through a secure and energy-efficient procedure.