The Structubent: A Nanocomposite Solution to Compressed Natural Gas Storage

Compressed natural gas (CNG) is an attractive energy storage and transportation platform over liquefaction as it conserves the heat of vaporization of the fuel. However, the high pressure compression between 200 and 250 bar creates challenges in material design. Adequate reinforcement of the compression vessel at high pressure must yield a minimal hydrocarbon capacity to vessel weight ratio, which is unfavorable for those that are exclusively steel lined. Adsorption beds have been proposed for adsorbed natural gas (ANG) storage, but they are not ideal at present due to unfavorable weight to capacity ratios for common adsorbents and kinetic limitations upon discharge. In this work, we develop a model of a structural adsorbent, or structubent, as a reinforcing nanocomposite of the pressure vessel that offset their added volume using hydrocarbon adsorption capacity. Equations are presented that evaluate the stored methane capacity per vessel mass and volume in terms of nanocomposite properties under isothermal conditions. Furthermore, the ratios of mass- and volume-specific capacities of the structubent versus CNG and ANG systems are derived which act as criteria for feasibility. An analysis of common adsorbents and matrix materials are performed, showing the structubent concept to be favorable in intermediate pressure regimes around 10 MPa.