Tailoring Low-Cost Granular Activated Carbons Intended for CO₂ Adsorption

Physical adsorption on activated carbons has shown to be a very attractive methodology for CO₂ separation from flue gas streams and biogas. In this context, the goal of this work was to prepare granular activated carbons intended for CO₂ adsorption from an abundant and low-cost biomass residue (coconut shell) by using practical and cost-effective procedures. By the first time, parameters involved in chemical activation with dehydrating agents (H₃PO₄ or ZnCl₂) and/or physical activation with CO₂ were systematically screened in depth in order to obtain materials with improved performance for CO₂ adsorption on a volume basis. Compared with the commonly used mass basis, the data expressed on a volume basis are very important for industrial applications because they permit to estimate the efficiency of a fixed bed adsorption column. The work permitted to prepare granular activated carbons with a blend of relatively high gravimetric CO₂ uptake and bulk density, so that high volumetric CO₂ uptakes were attained. The highest values were 2.67 and 1.17 mmol/cm³ for CO₂ pressures of 1.0 and 0.15 bar, respectively. It is remarkable that the obtained results were similar to those reported by other authors for carbons chemically activated with KOH, the activation methodology that has been widely claimed as the one that produce ACs with the best performances for CO₂ adsorption, but which involves severe restrictions. Therefore, the present work can be considered a very important step in paving the way toward making CO₂ adsorption an each time more interesting technology to reduce the emissions of anthropogenic greenhouse gases.