Optimization of the removal of lignin and silica from rice husks with alkaline peroxide

Rice husks surround rice grains, and are known to provide them with a protective lignocellulosic cover. This biomass has many potential uses, such as biofuel production. However, the high concentrations of lignin and silica limit its use, for example, they hinder fermentation reactions. In this study, both the delignification and silica removal from husks using a combination of hydrogen peroxide and sodium hydroxide has been investigated. Response surface methodology has been used to find the optimum conditions for maximizing lignin and silica removal, and solid yield. Three independent variables, namely, NaOH concentration, H₂O₂ concentration and reaction temperature were studied by using Box-Behnken design. The first optimization focused on maximum removal of impurity, and was found at 8% NaOH, 1% H₂O₂ and 20 °C. Under such conditions, 71.78% lignin removal, 88.47% silica removal and 50.89% solid yield were achieved. The second optimization emphasized the reduction of chemical costs, and was found at 5.29% NaOH, 1% H₂O₂ and 20 °C; resulting in 59.85% lignin removal, 75.13% ash removal and 59.21% solid yield.