Volatiles from pyrolysis of wet or dry tomato leaves make a drastic difference in activation of sawdust-derived biochar

Pyrolysis of biomass generates abundance of steam in volatiles, which might be used for activation of biochar to produce activated carbon for recovering the heat carried by steam and for making full use of steam. Hence, the volatiles from pyrolysis of dry and wet tomato leaves in an upper bed at 500 °C on activation of sawdust-derived biochar in the lower-bed at 700 and 800 °C were investigated. The results showed that the volatiles from the pyrolysis of dry tomato leaves reacted with the sawdust-derived biochar via polymerization/condensation reactions, forming substantial amount of carbonaceous deposit. This reduced specific surface area of the lower-bed biochar from 308 to 0.8 m2 g−1, as solid deposits from the volatile-char interaction filled majority of the pores. In converse, the abundance of water generated from pyrolysis of wet leaves facilitated gasification of the carbonaceous deposit and created more micropores. The overall specific surface area also increased to 361 m2 g−1 at 800 °C, owing to dominance of gasification but not volatile-char interactions. This rendered the biochar with higher capability for adsorption of phenol. The volatile-char interactions made the biochar oxygen-rich, more hydrophilic but thermally more stable via forming ether bridge bonds connecting benzene rings in skeleton of biochar.