Preferential cage occupation of CH4 into clathrate hydrate for selective CH4 enrichment from hydrogen-natural gas blends

Hydrogen (H 2 ) energy, recognized as a viable alternative source for decarbonization, requires effective transport solutions. Blending hydrogen into natural gas pipelines , forming hydrogen-natural gas blends (HNGB), offers a promising bridging technology toward a low-carbon future. However, high-purity methane (CH 4 ) separation remains crucial for existing natural gas infrastructure. Thus, this study explores gas hydrates as a potential CH 4 enrichment media, with employing thermodynamic promoters, tetrahydrofuran (THF), 1,3-dioxolane (DIOX), and 1,3-dioxane (Dioxane), to alleviate thermodynamic formation conditions. Since promoters occupy large cages, promoters inevitably limit CH 4 occupancy. Hence, the tuning effect, which can allow CH 4 in empty large cages by adjusting promoter concentration, was proposed as a novel approach to enhance CH 4 selectivity. In this study, we adjusted promoter concentrations from 5.6 mol% to 4.0 mol% to investigate CH 4 selectivity via tuning effect from simulated HNGB, CH 4 (80%) + H 2 (20%) under conditions of 284.15 K and 7.0 MPa. Thermodynamic stability analysis revealed that THF exhibited the superior promotion effect. Synchrotron XRD confirmed that all promoters at varying concentrations formed sII hydrate. Furthermore, Raman and 13 C solid-state NMR analyses provided evidence of enhanced CH 4 occupancy in the sII-L, with DIOX (4.0 mol%) achieving a CH 4 purity of 99.30 mol% in the hydrate phase. These findings demonstrate that tuning effect can increase CH 4 selectivity within the hydrate phase, presenting a promising approach for CH 4 enrichment from HNGB. Therefore, we believe that our findings can provide valuable insights into potential hydrate-based separation technology, especially for CH 4 enrichment for future transition toward sustainable energy systems. • Selective CH 4 enrichment from HNGB was investigated via cage occupation behavior. • DIOX showed the highest CH 4 cage occupancy in sII-S than THF and Dioxane. • Tuned CH 4 in sII-L was observed in the DIOX (4.0 mol%) hydrate. • DIOX hydrate exhibited higher CH 4 selectivity in hydrate phase than THF and Dioxane. • 99.30% CH 4 purity in hydrate phase was achieved for DIOX (4.0 mol%) hydrate.