Confined tetrahydrofuran in a superabsorbent polymer for sustainable methane storage in clathrate hydrates

For developing a reusable hydrate-based gas storage system, the confined tetrahydrofuran (THF) solution in a superabsorbent polymer (SAP) was investigated. The high surface area of the swollen SAP could disperse the THF solution immediately initiating the nucleation and simultaneously accelerating the growth of THF-methane binary hydrate. This formation behavior was maintained over 20 cycles of the formation-dissociation of hydrates, indicating that the THF solution-absorbed SAP could be practically utilized in a non-stirred system. We defined the elapsed time (trapid,) for rapid hydrate growth, and evaluated it under various conditions over 20 cycles. As we vented and refilled methane gas per cycle to simulate the enclathration/regeneration process, the storage capacity of methane decreased slightly over multiple cycles due to the gradual loss of volatile THF. However, as the tuning phenomenon occurred with the loss of THF, the storage capacity reached a constant value. Through spectroscopic analyses of the hydrate formed in the twenty-first cycle, we confirmed that methane occupied 5(12)6(4) cages of the structure II (sII)-hydrate, thus retaining the overall same methane storage capacity. This work can contribute to applying clathrate hydrates to a sustainable gas storage system consisting of a thermodynamic promoter fixed in a reusable matrix.