Eco-friendly synthesis of selective CO2 sorbents for post-combustion capture: The key role of basicity

Selective CO2 sorbents were successfully synthesized through carbonisation and physical (CO2) activation of oak wood. ACs thus synthesized along with a commercial carbon (GAC) included for comparison purposes were tested for CO2 capture. Under pure CO2 and 35 °C, although having much lower surface areas (highest SBET = 627 m2/g), oak wood-derived carbons exhibited similar uptakes as those achieved by the commercial AC (SBET = 1231 m2/g). On the other hand, upon changing to post-combustion conditions (ca. 53 °C, 15 % CO2/85 % N2), oak wood-based sorbents exhibited as large as (OW250PA) or even greater (OW800PA) sorption capacity than the commercial AC. The higher selectivity shown by oak wood derivatives was associated with their substantial amount of Ca-based inorganic fraction (up to nearly 12 wt. % for OW800PA), evidently related to their outstanding basicity (up to 93 % for OW800PA). Conversely, commercial AC is characterized by a negligible inorganic content (less than 1 wt. %) and lower basicity (ca. 67 %). Accordingly, it was proved that under post-combustion conditions the contribution of a more favoured (basic) surface chemistry outweighs the texture effect. Basic functionalities ensured stronger interactions with the carbon dioxide molecule, therefore implying a more selective sorption at lower gas concentration. Moreover, sorbents selectivity toward CO2 was obtained exploiting the advantageous properties (basicity) of the raw precursor rather than applying expensive and environmentally unsustainable chemical treatments.