Alternative feedstock for the production of activated carbon with ZnCl2: Forestry residue biomass and waste wood

Abstract

In order to substitute fossil resources in activated carbon (AC) production, recent efforts have focused on the utilization of renewable raw materials. Regions with important wood industries offer two potentially underestimated resource types: forestry residue biomass (FRB) and waste wood (WW). Although these materials are widely available (approx. 130 mio. m³a^-1 FRB, approx. 50 mio. ta^-1 WW in the EU), they are mostly valorised through energy production, as they are high in ashes and may be contaminated with organics and heavy metals. In this study, both FRB and WW were treated via one-step pyrolysis for AC production. ZnCl₂ was applied as activating agent at pyrolysis temperatures varying from 400 to 600 °C and residence times between 1 and 3 h. Overall, 76 samples were prepared and characterized thoroughly via elemental analysis, N₂/CO₂ ad/-desorption, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and infrared spectroscopy (FTIR). The produced carbons showed specific surface areas of up to 1430 m²g⁻¹ and a pore size distribution with a micropore share of up to 80 %. The presence of oxygen-containing functional groups was confirmed via FTIR. Potential feedstock contamination can be mitigated, as minerals and heavy metals could be leached out (up to –99.15 %) by an additional wash step and organic contamination undergoes thermal cracking during pyrolysis. The presented study could be a next step in upcycling considerable waste streams from the wood sector through localised and non-fossil-based AC production.