Practical separation performance evaluation of coal mine methane upgrading with carbon molecular sieves

Abstract Upgrading coal mine methane (CMM) with adsorption method is an effective way to enhance the energy utilizing efficiency and reduce greenhouse gas emissions. In this work, adsorption equilibrium and kinetics of CH 4 , N 2 and O 2 , as typical components in CMM, on three carbon molecular sieves (CMSs) and the corresponding separation performances were studied. The equilibrium and kinetic selectivity were obtained from adsorption isotherms fitted with the Langmuir model and uptake curves fitted with the micropore-diffusion model, respectively. O 2 with the highest diffusion time constant among three gases suggests the advantage of CMS-based kinetic separation in deoxygenation of CMM and the critical role that N 2 /CH 4 kinetic separation plays in CH 4 enrichment. CMS-1 with the highest microporosity has the largest adsorption capacities, and CMS-3 with a proper average pore size has the greatest N 2 /CH 4 kinetic selectivity. The actual separation performances shown by CH 4 /N 2 /O 2 breakthrough curves according to the principle for practical CMM upgrading processes exhibit the order of CMS-1 > CMS-3 > CMS-2 which is inconsistent with that of the conventional N 2 /CH 4 selectivity highly due to the underestimation of effects of N 2 equilibrium adsorption relative to N 2 kinetic selection without covering specific adsorption range corresponding to practical working capacity region. A modified selectivity with consideration of actual N 2 amount adsorbed was therefore developed, showing the correct performance order and the potential to be used as a practical adsorbent selection parameter. An advanced CMS materials design with proper existence of microporosity would benefit practical CMM upgrading in terms of reaching an optimal balance between adsorption equilibrium and kinetics.