Methane storage capacities and pore textures of active carbons undergoing mechanical densification

Abstract

Chemically activated anthracites with pore textures optimised for methane storage were densified by mixing suitable granular fractions, and the prepared mixtures were submitted to increasingly high mechanical pressures (up to 220 kg cm −2). The effect of densification was investigated and discussed. It was shown that, while the apparent densities increase significantly, compressing of the adsorbent has no effect on the adsorption capacities. This was confirmed by the measurement of surface areas and micropore volumes using several probe molecules; the microporosity of the material undergoing compression was found to be generally unchanged, whatever the applied pressure and whatever the burn-off. Densification of the material decreases the amount of compressed gas within the storage vessel and, as a result, the global mass storage capacities were found to decrease with the compacting force. Consequently, it was shown that because the density and mass capacities vary in opposite directions, the volume storage capacity should not be extrapolated from measurements made on uncompacted material. An optimal compaction pressure close to 100 kg cm −2, corresponding to maxima of volume storage capacities of methane, was evidenced and found as 193 V/V stored and 163 V/V deliverable at 3.5 MPa and 20 °C.