Activated carbon monoliths for gas storage at room temperature

Abstract

Porous materials are interesting candidates for gas storage in different applications. The present study analyses at room temperature the high pressure storage of H₂, CH₄ and CO₂ in a number of porous carbons (eight monoliths and two powdered activated carbons). The samples cover a wide range of porosities and densities (monoliths having high porosity with moderate density or moderate porosity with high density) with the aim to discuss the relative importance that the sample surface area has on the volumetric storage capacity, in relation to the importance of the density of the material. Our results show that the gravimetric storage capacities of the three studied gases are controlled by the textural properties of the adsorbent, whereas the volumetric storage capacities are mainly controlled by the adsorbent density. High volumetric excess adsorption capacity values (for example, H₂: 10 g l⁻¹; CH₄: 110 g l⁻¹ and CO₂: 440 g l⁻¹) correspond to monoliths having high densities, despite their moderately developed porosities. This paper also compares these results with those obtained similarly (same gases and same experimental conditions) using the highest known surface area material (MOF-210). In summary, our volumetric results, obtained with commercially available ATMI monoliths and their CO₂ activation, are, to the best of our knowledge, amongst the highest that have been reported; higher than the high surface area samples of the M3M monolith prepared from Maxsorb (S_BET: 2610 m² g⁻¹) or MOF-210 (S_BET: 6240 m² g⁻¹). Although a variety of MOFs have been reported to exceed our results, oftentimes these values are overestimated due to the fact that the volumetric capacity of MOFs was calculated using crystal density rather than experimentally measured density.