Activated carbons synthesized from unaltered and pelletized biomass wastes for bio-tar adsorption in different phases

The activated carbons were synthesized from rice husk (RH) and rice husk pellet (RHP) by the two-step pyrolysis (carbonization followed by KOH activation). Based on their textural properties, the activated carbons were comparatively studied for sorption of phenol (tar model compound) in different phases. The surface area (S-BET) and pore volumes of RH and RHP chars could be significantly improved with increasing the amount of KOH. Particularly, the RH char-3 showed a highest S-BET (1818.45 m(2)/g) with a higher micro-porosity (93.3%), so the KOH activation of RH char favored the development of microporous structures. Compared with the RH char-3, the RHP char-3 with relatively low S-BET (1320 m2/g) showed a meso-microporous structure along with a lower micro-porosity (69.2%), contributing to a higher breakthrough adsorption capacity (740 mg/g) of gaseous phenol. Generally, the adsorption capacity of phenol in the gas phase was higher than that in the liquid phase. RHP favored to form the hierarchical porous carbon enhancing the phenol molecules transportation via the outer layer and then the phenol molecules uptake by the adsorption sites on the inner layer. Also, the appropriate moisture in biochar benefited for adsorption, while the excessive water formed the liquid film, controlling the molecules transport. (C) 2019 Elsevier Ltd. All rights reserved.