Porous Metal-Organic Frameworks: Promising Materials for Methane Storage

doi:10.1016/j.chempr.2016.09.009

Chem

Volume 1, Issue 4, 13 October 2016, Pages 557-580

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The Bigger Picture

Porous metal-organic frameworks (MOFs) have received extensive attention as an emerging class of adsorbents for methane storage. Although the MOF methane or natural gas fuel tank is already on board, methane storage capacities of MOFs under 65 bar and 298 K are still quite far from the new DOE targets, which certainly hampers further implementation of MOFs for such an important application. We speculate and further confirm that adjusting the storage temperature to 270 K (another feasible temperature) can notably improve methane storage capacities of MOFs at 65 bar. Our discovery of two unique MOFs with an extremely high deliverable capacity of ∼240 cm³ (STP) cm⁻³ and gravimetric capacity of ∼0.5 g/g will allow our industrial partners to fully explore the feasibility of MOFs for methane storage at 270 K. This review not only provides the updated status of MOFs for methane storage but also directs research endeavors to pursue better MOFs for practical applications.

Summary

Metal-organic frameworks (MOFs) are the most promising porous adsorbents for methane storage; however, the highest reported storage capacities of about 270 cm³ (STP) cm⁻³ at 298 K and 65 bar are still much lower than the new US Department of Energy (DOE) target of 350 cm³ (STP) cm⁻³. Furthermore, it is very difficult to reach the DOE targets for volumetric (350 cm³ [STP] cm⁻³) and gravimetric (0.5 g [CH₄]/g) storage capacities simultaneously for a single MOF. This review systematically evaluates and compares the methane storage capacities of reported MOFs at both 298 and 270 K. We found that slightly reducing the storage temperature to 270 K can significantly improve both the volumetric and gravimetric uptake. Our discoveries highlight that two unique MOFs, NU-111 and MOF-177 (which have high pore volumes of 2.09 and 1.89 cm³ g⁻¹, respectively), not only have very high gravimetric capacities of 0.5 and 0.43 g/g, respectively, but also exhibit the highest working capacities ever reported: 239 and 230 cm³ (STP) cm⁻³, respectively. In addition, a usable empirical equation for predicting methane storage capacities (at 270 K and 65 bar) and some engineering strategies for thermal management are discussed.

Graphical Abstract

Keywords

porous materials

metal-organic frameworks

methane storage

natural gas

gravimetric uptake

volumetric uptake

working capacity

empirical equation

thermal management

UN Sustainable Development Goals

SDG7: Affordable and clean energy