Applications for CO ₂ ‐Activated Carbon Monoliths: I. Gas Storage

Carbon monoliths with high densities are studied as adsorbents for the storage of H ₂ , CH ₄ , and CO ₂ at ambient temperature and high pressures. The starting monolith A3 (produced by ATMI Co.) was activated under a CO ₂ flow at 1073 K, applying different activation times up to 48 h. Micropore volumes and apparent surface areas were deduced from N ₂ and CO ₂ adsorption isotherms at 77 K and 273 K, respectively. CO ₂ and CH ₄ isotherms were measured up to 3 MPa and H ₂ up to 20 MPa. The BET surface area of the starting monolith (941 m ² /g) could be significantly increased up to 1586 m ² /g, and the developed porosity is almost exclusively comprised of micropores <1 nm. Total storage amounts take into account the compressed gas in the void space of the material, in addition to the adsorbed gas. Remarkably, high total storage amounts are reached for CO ₂ (482 g/L), CH ₄ (123 g/L), and H ₂ (18 g/L). These values are much higher than for other sorbents with similar surface areas, due to the high density of the starting monolith and of the activated ones, for which the density decreases only slightly (from 1.0 g/cm ³ to 0.8 g /cm ³ upon CO ₂ activation). The findings reveal the suitability of high density activated carbon monoliths for gas storage application. Thus, the amounts of stored gas can be increased by more than a 70 % in the case of H ₂ at 20 MPa, almost 5.5 times in the case of CH ₄ at 3 MPa, and more than 7.5 times in the case of CO ₂ at 3 MPa when adsorbents are used for gas storage under the investigated conditions rather than simple compression. Furthermore, the obtained results have been recently confirmed by a scale‐up study in which 2.64 kg of high density monolith adsorbent was filled a tank cylinder of 2.5 L (Carbon, 76, 2014, 123).