Novel zeolite/carbon monolith adsorbents for efficient CH₄/N₂ separation

The Si/Al ratio in zeolite will be altered and the porous structure will be diluted by the traditional silica/aluminum-based binder in the granulation process. Here, a novel zeolite/activated carbon monolith (Z/AC) was prepared by adding coal-tar pitch in silicalite-1 (Si/Al greater than 400), where the pure silica characteristic is well maintained and the coal-tar pitch transforms to porous carbon with a uniform pore structure, in comparison, the aluminum-based bonded silicalite-1 pellet (ABSP) shows a much lower Si/Al ratio of 4.1. As a result, the Z/AC-600 monolith demonstrates a competitive CH₄ adsorption capacity of 23.45 cm³/g, outperforming silicalite-1 powder and ABSP pellet, and the CH₄/N₂ selectivity is higher than 4.0 at 298 K and 1 bar. The gas-mixture breakthrough experiments demonstrated that Z/AC-600 can effectively separate the CH₄/N₂ mixtures (20/80 and 50/50; v/v) with dynamic selectivity of 4.2 and 3.9, respectively. Pressure swing adsorption (PSA) simulations further indicate that, by one step enrichment, pristine 50% methane can be enriched to 80% with a recovery of 85%.