Decoupling the role of lignin, cellulose/hemi-cellulose, and ash on ZnCl2-activated carbon pore structure†

Activated carbon (AC), generally synthesized from fossil fuels or biomass waste, is a crucial form of porous carbon used for the purification of gases and liquids. Its key performance metrics vary widely when produced from biomass because of the differing amounts of cellulose, hemicellulose, lignin, and mineral/ash content. In this study, we adapted the Aqueous Lignin Purification using Hot Agents (ALPHA) process, originally developed for purifying lignin-rich waste streams, to control the sugars (as cellulose/hemicellulose) and mineral/ash content of a given biomass. Biomass samples having a wide range of sugars (0.01–56 wt%) and mineral/ash compositions (0.01–7.1 wt%) were generated from a single, hybrid poplar cultivar and used to create AC using ZnCl₂-impregnation and low-temperature carbonization. Strong correlations were developed between the biomass sugars and mineral/ash composition and the AC surface area, pore size, and pore distribution, with the maximum surface area of 2500 m² g⁻¹ being obtained from the precursor with the highest level (56 wt%) of sugars. These findings may provide a path to predicting the properties of AC from biomasses encompassing a wide range of compositions, and furthermore, select AC precursors for target applications.