A type of carbon molecular sieve (CMS-3KT) was used as the adsorbent for the CH4 enrichment of a methane/oxygen/nitrogen (CH4/O2/N2) mixture using micro-positive pressure vacuum pressure swing adsorption (∼120 kPa). The adsorption isotherms of individual CH4, O2, and N2 on CMS-3KT were studied and fitted. The results indicated the important influence of the adsorbent surface heterogeneity on the adsorption equilibrium process. In addition, the interaction of adsorbent-adsorbate in this process was studied from the measured adsorption heat. The adsorption uptake curves were fitted linearly with a classical micropore model for evaluating the kinetics-based separation possibility of CH4/O2/N2, and the corresponding diffusion time constants of CH4, O2, and N2 were calculated. Based on the results of adsorption equilibrium and kinetics, breakthrough experiments were employed to explore the upper limit value of methane concentration in feed gas such that methane can be enriched feasibly but difficultly. The breakthrough experiments were performed on the CH4/O2/N2 mixture with CH4 concentration ranging from 1 to 30%. Regarding industrial application, the O2 removal and CH4 enrichment performance of ultra-low-concentration methane (CH4 < 5%) were evaluated according to the results of the breakthrough experiment. The results indicated that the proposed method was promising for enriching O2-containing ultra-low-concentration CBM.
© 2021 The Authors. Published by American Chemical Society.