|A nano-sized crystalline cage that shows promise as a superior storage material for methane. Click to enlarge. Courtesy of Shengqian Ma, Miami University.|
Researchers have developed a new metal-organic framework (MOF) material with what they believe to be the highest methane storage capacity yet measured. Methane adsorption studies of the new material—PCN-14—at 290 K (16.9°C or 62°F) and 35 bar show an absolute methane-adsorption capacity of 230 v/v (standard temperature and pressure equivalent volume of methane per volume of the adsorbent material), 28% higher than the US Department of Energy (DOE) target (180 v/v) for on-board methane storage.
The PCN-14 compound, composed of clusters of nano-sized cages, has a high surface area of 2,176 m2/g and a pore volume of 0.87 cm3/g. Hong-Cai Zhou and colleagues describe the development of PCN-14 in an report in the 23 January edition of the Journal of the American Chemical Society.
The DOE has established a target for on-board methane storage at 180 v/v under 35 bar, near ambient temperature, with the energy density of adsorbed natural gas (ANG) being comparable to that of compressed natural gas (CNG) used in current practice.
A number of different types of porous materials have been evaluated for ANG storage, but until last year, no material had hit the 180 v/v target. In February 2007, researchers at the University of Missouri-Columbia (MU) and Midwest Research Institute (MRI) in Kansas City created carbon briquettes with complex nanopores capable of storing natural gas with 180 v/v. (Earlier post.)
Metal-organic frameworks (MOFs) are a relatively new class of nano-porous material that show promise for gaseous storage applications—hydrogen, methane, CO2, etc.—because of their tunable pore size and functionality. MOF compounds consist of metal-oxide clusters connected by organic linkers.
The researchers first developed an anthracene-based ultramicroporous MOF (PCN-13, PCN stands for Porous Coordination Network), but it had very limited methane uptake because of its confined pore size.
To enlarge the pore size and to continue our theme of building metal-organic frameworks containing nanoscopic coordination cages for gas storage, we have adopted a new ligand, 5,5'-(9,10-anthracenediyl)di-isophthalate (adip). Under solvothermal reaction conditions, the reaction between H4adip and Cu(NO3)2 gave rise to a porous MOF designated PCN-14.
The work was supported by the Department of Energy and the National Science Foundation.
Ma, S., Sun, D., Simmons, J.M., Collier, C.D., Yuan, D., and Zhou, H.-C. Metal-Organic Framework from an Anthracene Derivative Containing Nanoscopic Cages Exhibiting High Methane Uptake. J. Am. Chem. Soc., 130, 3, 1012 - 1016, 2008, 10.1021/ja0771639