Renewable activated carbon from wood-based gasification char: A comprehensive study on physical activation

Abstract

Wood gasification produces gasification char (GC), a carbonaceous by-product with limited sustainable valorisation strategies. The physical activation of wood-based GC as a precursor has received insufficient attention, likely due to the inherent challenges associated with the precursor, namely its soft skeleton, high degree of graphitisation, ash content, and reduced porosity. This study investigates methods to enhance the porosity and adsorption properties of renewable activated carbon (AC) derived from GC while maximising yield using a Design of Experiments approach. Yield-oriented porosity optimisation revealed that mild H₂O activation ($⩽$750 °C, $⩾$20 min) was the most effective, followed by CO₂ activation at 817 °C and 16.2 min. The AC with the highest overall porosity was produced by sequential activation, leveraging the high surface area obtained from H₂O activation (812 m²/g) and the high micropore fraction from CO₂ activation (49.3 vol%). In micropollutant adsorption assays, this AC (maximum adsorption capacity $q_{\max }$ for metoprolol: $89.9\mathrm{mg}/g$) partially outperformed commercial AC ($89.1\mathrm{mg}/g$). We found that the utilisation of GC for AC production represents a fundamentally distinct starting point when compared to previously employed precursors, as evidenced by significantly reduced activation times and temperatures. This study provides valuable insights for the efficient conversion of GC into high-value AC, a pathway of significant interest for industrial applications.