Hydrate-based adsorption-hydration hybrid approach enhances methane storage in wet MIL-101(Cr)@AC under mild condition

Abstract

Hydrate-based adsorption and hydration natural gas (AHNG) technology was reported to achieve large methane storage density under mild conditions. In order to enhance methane uptake, a composite nano porous material of MIL-101(Cr)@AC was prepared through fluorine-free hydrothermal reaction, and methane adsorption isotherms for both dry and wet samples were measured under hydrate favorable conditions. Hydrate in-situ formation loaded by the composite material was also carried out, while hydrate kinetics was evaluated by Raman spectrum. It was found that MIL-101(Cr) remains cubic symmetric structure when activated carbon (AC) was doped, but its size decreases with the increase in AC doping amount, while the specific surface area and pore volume significantly increase, and this enhances methane adsorption that increases by 65.58%. More enhanced methane uptake was obtained when wet sample was applied due to adsorption and hydration synergy, wherein methane physical adsorption ability remains, while formed hydrate stores extra methane. The contribution of hydrate to methane uptake is up to 40%, so large methane storage density is anticipated, methane volumetric uptake is up to 179.3 V/V under a mild condition (9.3 MPa and 274.15 K), which increases by 38.03%. Compared with our recently reported ZIF-8@AC, methane storage capacity in this new material increases by 36.5% (Chem. Eng. J., 2023, 455, 140503). In addition, hydrate progressive growth with the increase in adsorption pressure was observed, the area ratio of hydrate large cages to small one finally approaches to the theoretical value of 3:1, suggesting approximately complete conversion of pre-adsorbed water.