Evaluation of Synthetic Conditions for H3PO4 Chemically Activated Rice Husk and Preparation of Honeycomb Monoliths

Abstract

Activated carbons in this work were prepared from rice husk by phosphoric acid activation followed by alkaline desilication. Pseudo-random selection of 16 rice husk samples was subjected to carbonization at the following conditions: 0.5 to 2 h of activation time, 300-600 ºС and Н3РО4/precursor (wt/wt) impregnation ratio of 0.5 to 2. Concentration of NaOH desilication solution varied from 0.5 to 2M. It was found that out of the four factors impregnation ratio is clearly the strongest and at the impregnation ratio of 2 for 1 h at 500 °C N2 BET-surface area reaches 1690 m2/g (SBET (Ar)=2492 m2/g) while pore volume becomes 1.95 cm3/g. Elemental analysis showed highest carbon content for this sample (87.96%). All samples have insignificant amount of Si and traces of metals, but considerable amount of phosphorus. Blocks of honeycomb structure prepared from Ca-montmorillonite and desilicated carbonized rice husk (impregnation ratio is 1.5, 1 h at 600 ºC) have BET-surface area obtained by thermal desorption of argon up to 856 m2/g.