Environmental Aspects of Using Metallic Organic Frameworks As Adsorbents in Natural Gas Storage Systems

Abstract

The use of natural gas (NG) for automotive industry has gained renewed interest due to its growing supplies in the United States, relatively low cost compared to gasoline and diesel fuels and reduced emissions of carbon and particulate per equivalent. Because of its relatively low energy density NG must be stored at high pressure, 3,600 psi service pressure in the United States, in order to achieve an energy density suitable for vehicular use. Compressed NG cylinders are available in four types. Type 1, all metal (steel or aluminum) are the most widely used CNG cylinders in the world. Type 2 cylinders are metal liner reinforced by composite wrap (glass or carbon fiber) around the middle. Metal liner reinforced by composite wrap around the entire tank constitutes Type 3. While Type 4 cylinders are made of plastic gas-tight liner reinforced by composite wrap around the entire tank. Utilization of CNG storage systems in light duty vehicles has limited market penetration because of the cost of the pressure vessel and its occupancy of cargo space. Adsorbents materials are becoming an attractive option to develop low pressure and conformable NG storage system. Adsorbed NG storage relies on physisorption, i.e. weak gas-solid interactions between the fuel and the adsorbent surface. While research into adsorbents has focused on assessing their storage capabilities there is, to our knowledge, no reported data on their compatibility with the storage vessel and components in NG environment. High surface area porous materials such as Activated Carbons and Metal Organic Frameworks (MOF) are considered as the most promising adsorbents. The Cu3(btc)2 MOF, copper benzene-1,3,5-tricarboxylate also known as HKUST-1, has been extensively studied for gas storage. Herein we report its compatibility in NG environment with the pressure vessel, more particularly with the metal liner. We show that not only the stability of the adsorbent but also the integrity of the metallic liner can be drastically affected.