CO₂ capture by novel hierarchical activated ordered micro-mesoporous carbons derived from low value coal tar products

Activated ordered mesoporous carbon (AOMC) sorbents for CO₂ capture have been synthesized, characterized and evaluated. They were obtained using low-value products from the distillation of coal tar and following a hard templating method to achieve an ordered mesoporous structure. Both physical and chemical activation processes were applied. It was observed that neither physical nor chemical activation affected the mesopore structure of the samples. Regarding the CO₂ capture, the best chemical AOMC was the one activated at 850 °C with a KOH:carbon ratio of 4:1 (2.48 mmol/g AOMC), whilst the best physical activated one was obtained upon activation during 48 h with a burn-off degree of 48% and dissolving the template afterwards (2.38 mmol/g AOMC). In the present case the ordered mesoporous structure was thought to facilitate CO₂ diffusion into the micropores of the porous carbons. The best samples were tested for CO₂ capture at different operational conditions, considering capture temperatures up to 150 °C and CO₂ partial pressures between 5 and 90% (balance N₂). Their performance was also tested over six adsorption-desorption cycles, and it was determined that the working capacity remained constant and the mesoporous structure was not modified.