Carbons Suitable for Medium Pressure (6.9 MPa) Methane Storage

Abstract

The storage and delivery of natural gas using adsorbent carbon monoliths at 3.4 MPa is only about 75% that of natural gas compressed to 21 MPa on an equal volume basis. One possible way to increase ambient temperature adsorbed natural gas (ANG) storage is to simply increase the storage pressure. However, this will only be beneficial if there is unfilled micropore capacity within the carbon adsorbent. Carbons that have been optimized for storage at 3.4 MPa may not have sufficient micropore capacity to give increased storage at 6.9 MPa. In the present work, carbons have been prepared which are considered to be more useful for storage at 6.9 MPa than at 3.4 MPa due to their having an increased micropore volume fraction per monolith or storage volume. Although the pore wall separation of these carbons may not be ideal for maximum adsorbate density, these carbons showed that more than 180 v/v can be delivered from 6.9 MPa. This value approaches that of delivery from compressed natural gas (CNG) and exceeds it if the rectangular external envelope is considered as the realistic volume of the storage vessel. The results obtained clearly show the diminishing returns for methane adsorption storage with pressure increase. An increase of only about 30% in storage capacity was achieved from a doubling of the storage pressure from 3.4 MPa to 6.9 MPa.