Activation of mixed sawdust and spirulina with or without a pre‑carbonization step: Probing roles of volatile-char interaction on evolution of pyrolytic products.

Volatile-char interaction has been well documented in co-pyrolysis of varied feedstocks, which might also exist in activation process and impact pore evolution of activated carbon (AC). This was investigated herein in activation of mixed sawdust and spirulina with K 2 C 2 O 4 at 800 °C in two scenarios: one-step direct activation or two-step activation with an intermediate pre‑carbonization. The results showed that volatile-char interaction via cross-polymerisation of the volatiles was more significant in the pre‑carbonization step, forming more biochar/bio-oil while less gases. However, volatile-char interaction was not that important in impacting product yields and evolution of pore structures of AC in activation. This was due to the dominance of gasification/cracking with presence of K 2 C 2 O 4 , minimizing the chances for volatile-char interaction. The in-situ DRIFTS characterization of the activation process showed that removal of oxygen-containing species like C O with K 2 C 2 O 4 was important for generating pore structures. Comparing with two-step activation, one-step activation of sawdust, spirulina and their mixture without pre‑carbonization all generated the ACs of more developed pore structures and showed higher environmental impact. The pre‑carbonization removed a significant portion of thermally unstable aliphatic structures, enhancing aromatic degree and creating difficulty for generating pores via gasification/cracking in subsequent activation. [Display omitted] • Volatile-char interaction in pre‑carbonization forms more biochar while less gases. • Dominance of gasification/cracking weakens volatile-char interaction on activation. • Abundant aliphatic structures develop more pores in direct activation of feedstock. • Pre‑carbonization enhance aromatic degree, negatively impacting pore development. • Activation with K 2 C 2 O 4 cracks O-containing species, suppressing aromatization. [ABSTRACT FROM AUTHOR]