Porous Metal-Organic Frameworks: Promising Materials for Methane Storage

Metal-organic frameworks (MOFs) are the most promising porous adsorbents for methane storage; however, the highest reported storage capacities of about 270 cm(3) (STP) cm(-3) at 298 K and 65 bar are still much lower than the new US Department of Energy (DOE) target of 350 cm(3) (STP) cm(-3). Furthermore, it is very difficult to reach the DOE targets for volumetric (350 cm(3) [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 cm(3) 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 cm(3) (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.