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Gas hydrates, specifically clathrate hydrates, have emerged as a potential separation medium for biogas containing methane (CH₄) and carbon dioxide (CO₂). However, the efficient separation of CH₄ and CO₂ remains challenging due to their similar cage occupation behavior within the hydrate structure. This study aimed to enhance CH₄ selectivity by modifying the hydrate lattice to exclude CO₂ from large cages and reduce the size of small cages through lattice engineering. To achieve this, tert-butyl alcohol (TBA) and trimethylene oxide (TMO) were employed as thermodynamic promoters, inducing strong and weak cage expansion, respectively. The results revealed that TMO hydrates, with their weak cage expansion, exhibited improved CH₄ selectivity compared to TBA hydrates, which displayed strong cage expansion due to the larger size of TBA. Multi-stage separation experiments demonstrated that TMO …