Improved methane storage capacities by sorption on wet active carbons

The possibility of storing large amounts of natural gas within wet active carbons is examined. The sorption isotherms of methane at 2 degreesC and up to 8 MPa are built for four carbonaceous materials. Three of them originate from the same precursor (coconut shell), are physically activated at various burn-offs and are mainly microporous. The fourth material is a highly mesoporous chemically activated pinewood carbon. These adsorbents are wetted with a constant weight ratio water/carbon close to 1. The resulting isotherms all exhibit a marked step occurring near the expected formation pressure of methane hydrates, thus supporting their occurrence within the porous materials. The amount of gas stored at the highest pressures investigated then ranges from 6 to 17 moll kg of wet adsorbent (i.e., corresponding to 10-36 mol/kg of dry carbon), depending on the material. The results are discussed on the basis of the known pore texture of each adsorbent, and stoichiometrics of the formed hydrates are calculated. Considerations about adsorption/desorption kinetics and metastability are also developed. (C) 2004 Elsevier Ltd. All rights reserved.