Energy-Efficient Upgrading of Low-Concentration Coal Mine Methane by a Micro-Pressure Swing Adsorption

The utilization of low-concentration coal mine methane (LC-CMM) is hindered by safety risks and high costs associated with its low methane and significant oxygen content. This study presents an innovative micro-pressure swing adsorption (MPSA) process for the safe and economical enrichment of LC-CMM. Unlike conventional methods requiring high pressure or deep vacuum, the proposed MPSA process operates under mild conditions (adsorption pressure ≤125 kPa, desorption pressure ≥10 kPa) matching the output range of in-mine drainage systems. A commercial carbon molecular sieve was employed as the adsorbent to leverage kinetic selectivity for the challenging CH₄/O₂/N₂ separation. The effects of key parameters, including desorption pressure, inlet flow rate, adsorption pressure, feed concentration, bed volume ratio, and adsorption time, were systematically investigated. The results demonstrate that reducing the inlet flow rate enhances product purity, while a lower adsorption pressure is favorable when a larger buffer bed is used. An optimal adsorption time window of 120 seconds was identified to balance deoxygenation and methane recovery. Under optimized conditions (110 kPa adsorption, 25 kPa desorption, 150 mL/min flow rate, 6.7:1 volume ratio), the methane concentration was enriched from 4.5% to 10.9% with a recovery rate of 80.7% while maintaining high deoxygenation efficiency. This work validates the MPSA process as a technically viable and energy-efficient strategy for LC-CMM upgrading. It provides a practical pathway for mitigating methane emissions and recovering energy from a resource currently vented to the atmosphere, contributing to both environmental protection and sustainable resource use in the mining industry.