Mitigating nucleation delay in hydrate-based HNGB deblending using a transient agitation strategy with kinetic additives

Abstract

Hydrogen–natural gas blends (HNGB) offer a practical pathway for hydrogen transport via existing pipeline infrastructure; however, efficient separation is essential to recover high-purity CH4. This study investigates hydrate-based CH4 enrichment using sII thermodynamic promoters—1,3-dioxane (Dioxane), 1,3-dioxolane (DIOX), and tetrahydrofuran (THF)—in combination with L-Tryptophan (L-Tryp) as a kinetic additive. Phase equilibrium and structural characterization confirmed that while the promoters stabilized sII hydrates under milder conditions, the crystalline framework remained unaffected by L-Tryp. Raman and 13C solid-state NMR analyses further revealed the preferential encapsulation of CH4 within the small cages of the sII lattice. Crucially, a transient stirring strategy was implemented to optimize the balance between formation kinetics and energy efficiency. This approach effectively mitigated the stochastic nucleation delays typical of unstirred systems while achieving CH4 purities exceeding 98.6%, comparable to continuous stirring. Among the tested systems, the DIOX + L-Tryp formulation exhibited superior separation performance. These findings demonstrate that the synergy between dual promoters and a transient agitation strategy provides an energy-lean, scalable route for high-purity CH4 recovery from HNGB.