Efficient separation of CH₄/N₂ mixtures is important for the upgrading and utilization of coalbed methane, because the high N₂ content in raw gas markedly lowers its calorific value and restricts its direct use as a fuel or chemical feedstock. Adsorptive separation under mild conditions is considered a promising alternative to energy-intensive cryogenic distillation; however, the development of adsorbents that combine competitive CH₄/N₂ separation performance with scalable, low-cost, and green synthesis remains challenging. Herein, we report a layered manganese-based coordination polymer, Mn-DHBQ, as a promising adsorbent for CH₄/N₂ separation. Mn-DHBQ was synthesized from manganese acetate tetrahydrate and 2,5-dihydroxy-p-benzoquinone in pure water at room temperature using inexpensive and commercially available precursors. Structurally, Mn-DHBQ is composed of one-dimensional coordination chains that are further stacked through intermolecular hydrogen bonding to form a quasi-three-dimensional supramolecular microporous network. Powder X-ray diffraction confirmed the phase purity and crystallinity of the as-synthesized material, while N₂ sorption at 77 K gave a BET surface area of 428.7 m²•g⁻¹. Gas adsorption measurements showed that Mn-DHBQ adsorbs CH₄ much more strongly than N₂. At 298 K and 0.1 MPa, the CH₄ uptake reaches 1.10 mmol•g⁻¹, whereas the N₂ uptake is only 0.27 mmol•g⁻¹. The corresponding IAST CH₄/N₂ (V/V, 50/50) selectivity is 5.82 at 298 K. Virial analysis further revealed a higher isosteric heat of adsorption for CH₄ (28.85 kJ•mol⁻¹) than for N₂ (10.59 kJ•mol⁻¹), indicating a substantially stronger affinity of the framework toward CH₄. Dynamic breakthrough experiments using an equimolar CH₄/N₂ mixture at 298 K and 0.1 MPa demonstrated clear separation behavior, with N₂ eluting rapidly and CH₄ breaking through at 10.2 min•g⁻¹; the dynamic CH₄ uptake reached 0.46 mmol•g⁻¹, close to the equilibrium uptake at the corresponding partial pressure. In a single adsorption-desorption cycle, the CH₄ concentration could be enriched to above 98.9%, and stable separation performance was maintained over three cycles. Importantly, Mn-DHBQ was further synthesized on a 1000-fold larger scale in water within 8 h, affording about 0.21 kg product with a space-time yield of 63 kg•m⁻³•d⁻¹. The scaled-up sample retained comparable crystallinity, porosity, morphology, and CH₄/N₂ breakthrough performance to the mg-scale material. These results indicate that Mn-DHBQ is a promising and practically relevant adsorbent for CH₄ enrichment and coalbed methane upgrading.

Key words: metal-organic frameworks, coordination polymer, CH₄/N₂ separation, scale-up synthesis