Adsorbed natural gas (ANG) storage and delivery at room temperature requires high surface area adsorbents that have a constant adsorption enthalpy near 15-20 kJ mol<sup>-1</sup>. Zeolite-templated carbons (ZTCs) have a very high specific surface area (~3800 m<sup>2</sup>/g) and have a homogeneous pore size of optimal size for methane storage (~1.2 nm), and little or no void volume excluded from adsorption. Carbonaceous adsorbents like ZTCs typically have lower but more constant adsorption enthalpies than metal-organic frameworks (MOFs), which have been reported to exhibit the highest theoretical volumetric methane uptake to date. In this work, we explore whether the constant enthalpy of adsorption of ZTCs can be retained in compressed pellets. Powder adsorbents are challenging to pack efficiently, and rarely approach the theoretical single crystal limit in terms of methane stored. However, our results show that optimized samples of hot-pressed ZTCs can exhibit total methane uptake matching that of an ideal monolith, and are among the highest deliverable methane uptakes ever reported at room temperature. The role of pelletization conditions on packing efficiency and pore modification, and the resulting methane uptake characteristics will be presented. The compaction process leads to a 1-2 kJ/mol increased adsorption enthalpy over ZTC powder due to micropore alterations from pressurization. This work lends crucial insights into the effective design of metal-free carbonaceous adsorbents for ANG energy storage applications.

Optimizing methane storage in pelletized zeolite-templated carbons

ACS Spring 2022

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