Removal of the local fence-like SiO2 in rice husk facilitates pore development in activation

As an indispensable fraction of majority biomass, inorganics might not be inert in activation, due to their potential interaction with volatiles/activators and steric hindrance created for accessing organics in inner structure by activator. This was verified herein by conducting the activation of rice husk (RH), with inherent silica leached partially or completely by KOH, with ZnCl 2 or K 2 C 2 O 4 as an activator at 550 or 800 °C. The results indicated that removal of SiO 2 promoted condensation reactions with ZnCl 2 while cracking reactions with K 2 C 2 O 4 , forming more activated carbon (AC) with ZnCl 2 (41.1 %) but less AC-K 2 C 2 O 4 on organic basis (26.8 %). This resulted from enhanced permeability and more sufficient contact of the activator to organics via eliminating steric hindrance. After removing SiO 2 , the specific surface area increased from 1348.8 to 1712.3 m 2 /g −1 with ZnCl 2 as an activator, while that with K 2 C 2 O 4 increased from 615.4 to 1121.6 m 2 /g −1 . Moreover, the degree of aromatization in activation also increased after removing SiO 2 , forming rigid aromatic skeleton preserving micropores formed (97.6 % versus 86.0 % with AC-RH-K 2 C 2 O 4 ). The in-situ IR characterization of activation process confirmed negative impacts of SiO 2 on aromatization process from segregation of organics, which further deterred development of pores.