Sustainable synthesis of activated porous carbon from lignin for enhanced CO2 capture: a comparative study of physicochemical activation routes†

A sustainable and readily available material, lignin protobind 2400, was upcycled to activated porous carbon (APC) compatible with post-combustion CO₂ capture. The effectiveness of the novel two-step physicochemical activation using KOH + CO₂ and ZnCl₂ + CO₂ was compared with that of the respective physical (only CO₂) and chemical activation (only KOH or ZnCl₂). The effect of carbonization conditions (N₂ or CO₂ purging) on the resulting APC properties and CO₂ adsorption performance was studied. The maximum BET surface area of 1480 m² g⁻¹ and the best CO₂ adsorption capacity of 5.68, 3.66, and 2.67 mmol g⁻¹ were observed at 0, 25, and 40 °C/1 bar, respectively. From the precursor to the final product, the APC yield falls within the range of 14.5–40.8 wt%. The APC derived from lignin exhibited better CO₂/N₂ selectivity. The isosteric heat of adsorption for all the APCs remained below 40 kJ mol⁻¹, which suggested a lower energy requirement during the regeneration. The excellent reusability with fluctuations of only 0.51% in the amount of CO₂ adsorbed over ten consecutive adsorption/desorption cycles highlights the APC's outstanding recyclability.