Natural gas (NG) has long been considered as a preferable energy alternative to traditional fossil fuels due to its high hydrogen to carbon ratio and lower CO2 emissions. However, the low energy density of methane compared with traditional fossil fuels restrains its on-board applicability. A long-standing challenge has been to design storage systems that efficiently and safely store methane at a realistic volume and that allow it to be easily extracted at reasonable pressures and temperatures. In 2012, the US Department of Energy (DOE) set the ambitious volumetric storage target for adsorbed natural gas (ANG) to 263 cm3 (STP) cm−3 at room temperature and 65 bar, equivalent to the storage capacity of an empty tank at 250 bar – targets which, to this day, have not been met by any conformed material after packing. Here, we report the synthesis of a porous monolithic metal-organic framework (MOF), HKUST-1, based on a sol-gel process without requiring binders and/or high pressures. The mild conditions of the synthetic protocol and soft drying process lead to a dense monolithic structure. Small primary particles and only a mild drying process are necessary to allow the successful synthesis. The monolithic HKUST-1 was able to retain the characteristic structure and porosity of the powder while showing a three times higher density and therefore volumetric gas adsorption capacity. It showed an outstanding methane capacity of 259 cm3 (STP) cm−3 at 65 bar and room temperature, becoming the first conformed adsorbent, after successful densification and shaping, to achieve the volumetric DOE target (that is, 263 cm3 (STP) cm−3).2 This is the highest value reported to date for conformed shape porous solids and represents a greater than 50% improvement over any previously reported experimental value. From the mechanical point of view, it is striking to discover that the hardness of the monolithic HKUST-1 exceeds twice that of any conventional HKUST-1 material published to date. Finally, we have extended the synthesis of monolithic MOFs to multiple systems finding similar enhanced performance. We believe this work represents a significant step forward in the shaping and densification of MOFs, opening the gate towards their applicability in ANG and other real-world industrial applications where high volumetric adsorption capacities and resilient mechanical properties are critical.

Sol–gel monolithic metal-organic frameworks with enhanced adsorption properties

2019 Fall National Meeting

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