Engineering aspects and a fundamental study of adsorbed natural gas on activated carbon were conducted to evaluate this material as an adsorbent to lower tank pressure in vehicles fueled with natural gas.
Engineering considerations for ANG were compared with direct storage of methane as compressed natural gas (CNG). In an ANG storage vessel, about one-third of the methane is stored as free gas and two-thirds as ANG. At 20 MPa (3000 psig), ANG and CNG vessels store the same amount of methane per unit vessel; below 20 Mpa (3000 psig), ANG stores more. The heat released during filling of ANG tanks is low enough to be easily manageable.
The super high surface area (3000m2/g) of Amoco PX-21 provided high expectation for storing natural gas as an alternative fuel for future automobile use. However, the low bulk density (0.26 g/cc) of the powder activated carbon is at a disadvantage for the delivery of gas on the volume bases. A technique of producing high density (0.45 g/cc) monolith carbon was developed resulting in an adsorbency capacity of 124 v/v (Volume of delivered gas per unit volume of adsorbent).
The structure of Amoco carbon was found to be vastly different than the conventional carbon produced by steam activation. Solid state NMR (Nuclear Magnetic Resonance) electron microscope, and Parallel Electron Energy-Loss Spectra indicates that Amoco carbon is highly aromatic but has no resemblance to a graphitic structure.