A competitive approach for the production of activated carbons from lignocellulosic biomass

Lignocellulosic biomass-derived activated biochars (ABCs) are effective solid adsorbents for removing various contaminants from both aqueous and gaseous effluents. Typically, the lignocellulosic biomass precursor undergoes a two-step process involving pyrolysis followed by thermochemical activation to produce adsorbents with high surface areas and appropriate pore size distribution. The pore structures, surface functional groups, and elemental composition of ABCs are influenced by the biomass precursor, conversion technology, operational conditions, and activation process. These factors have been extensively studied and summarized in various research papers and review articles. The current objective is to scale up the production of these solid adsorbents to an industrial level. This study evaluates the feasibility of producing ABCs through a single-stage (1S) simultaneous pyrolysis and chemical activation process compared to the traditional two-step (2S) thermochemical process. The results from both methods were compared considering two aspects: firstly, the performance of the generated ABCs as adsorbent, and secondly, the process efficiency considering energy, chemicals and carrier gas consumptions, downtime, and residence time. The produced carbons were characterized (proximate analysis, chemical groups (FTIR), microscopic structure (SEM), morphology, textural properties (specific surface area, micropore volume and average pore width, by N2 adsorption–desorption experiments). The performance of 1S and 2S ABCs for methylene blue (MB) adsorption was compared to define a competitive route for scaling up to industrial production. Results indicated that 1S and 2S ABCs were comparable in terms of physicochemical properties and adsorption capacity. The study demonstrates that ABCs produced from apple tree pruning via 1S process were even more effective as those from the traditional 2S method in removing MB dye, while being significantly more energy- and time-efficient. The 1S route achieved nearly 100% dye removal, consumed ~ 24% less energy, used ~ 60% less gas, and reduced processing time by ~ 18%, making it a promising approach for sustainable large-scale production.