Structurally Tailoring Cage-like MOFs via Methyl Functionalization for Enhanced Methane Purification Performance

Abstract

Light hydrocarbon contaminants in raw natural gas considerably compromise methane purity and energy utilization efficiency. The highly similar physicochemical properties of light hydrocarbons also create substantial obstacles for the high-efficiency purification of methane. Metal–organic frameworks (MOFs) show great potential in gas separation, yet the mutual restriction between adsorption capacity and selectivity limits their practical industrial utilization. Herein, a methyl-functionalized cage-like MOF (Co-tpt-btb-(CH3)3) was successfully synthesized via a ligand functionalization strategy for precise modulation of the pore microenvironment. Through methyl modification, polyhedral cage cavities undergo uniform contraction and surface active sites are rationally optimized, which markedly enhances host–guest interactions between the MOF framework and C2H6/C3H8. Co-tpt-btb-(CH3)3 delivers prominent saturated adsorption amounts of 4.96 and 7.23 mmol·g–1 for C2H6 and C3H8, respectively, while presenting extremely low CH4 adsorption loading of only 0.49 mmol·g–1 at 298 K and 100 kPa. Dynamic breakthrough testing confirms that Co-tpt-btb-(CH3)3 can effectively discriminate ternary natural gas compositions (C3H8/C2H6/CH4, 5/10/85, v/v/v) for high-efficiency gas separation, producing high-purity CH4 (purity > 99.9%). Theoretical density functional theory simulations reveal that the synergistic multiple interactions, including C–H···O, C–H···N, and C–H···π, endow C2H6 and C3H8 with significantly enhanced adsorption energy. Moreover, the good chemical stability of Co-tpt-btb-(CH3)3 endows great application potential as a high-efficiency adsorbent for CH4 purification.