Sustainable and Regenerable Alkali Metal-Containing Carbons Derived from Seaweed for CO2 Post-Combustion Capture

Alkali-based CO2 sorbents were prepared from a novel material (i.e., Laminaria hyperborea). The use of this feedstock, naturally containing alkali metals, enabled a simple, green and low-cost route to be pursued. In particular, raw macroalgae was pyrolyzed at 800 °C. The resulting biochar was activated with either CO2 or KOH. KOH–activated carbon (AC) had the largest surface area and attained the highest CO2 uptake at 35 °C and 1 bar. In contrast, despite much lower porosity, the seaweed-derived char and its CO2-activated counterpart outweighed the CO2 sorption performance of KOH–AC and commercial carbon under simulated post-combustion conditions (53 °C and 0.15 bar). This was ascribed to the greater basicity of char and CO2–AC due to the presence of alkali metal-based functionalities (i.e., MgO) within their structure. These were responsible for a sorption of CO2 at lower partial pressure and higher temperature. In particular, the CO2–AC exhibited fast sorption kinetics, facile regeneration and good durability over 10 working cycles. Results presented in the current article will be of help for enhancing the design of sustainable alkali metal-containing CO2 captors.